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senolytics directory


“Orally-active, Clinically-translatable Senolytics Restore Α-Klotho in Mice and Humans”, Zhu et al 2022

“Orally-active, clinically-translatable senolytics restore α-Klotho in mice and humans”⁠, Yi Zhu, Larissa G. P. Langhi Prata, Erin O. Wissler Gerdes, Jair Machado Espindola Netto, Tamar Pirtskhalava et al (2022-03-13; similar):

Background: α-Klotho is a geroprotective protein that can attenuate or alleviate deleterious changes with ageing and disease. Declines in α-Klotho play a role in the pathophysiology of multiple diseases and age-related phenotypes. Pre-clinical evidence suggests that boosting α-Klotho holds therapeutic potential. However, readily clinically-translatable, practical strategies for increasing α-Klotho are not at hand. Here, we report that orally-active, clinically-translatable senolytics can increase α-Klotho in mice and humans.

Methods: We examined α-Klotho expression in 3 different human primary cell types co-cultured with conditioned medium (CM) from senescent or non-senescent cells with or without neutralizing antibodies. We assessed α-Klotho expression in aged, obese, and senescent cell-transplanted mice treated with vehicle or senolytics. We assayed urinary α-Klotho in patients with idiopathic pulmonary fibrosis (IPF) who were treated with the senolytic drug combination, Dasatinib plus Quercetin (D+Q).

Findings: We found exposure to the senescent cell secretome reduces α-Klotho in multiple non-senescent human cell types. This was partially prevented by neutralizing antibodies against the senescence-associated secretory phenotype (SASP) factors, activin A and Interleukin 1α (IL-1α). Consistent with senescent cells’ being a cause of decreased α-Klotho, transplanting senescent cells into younger mice reduced brain and urine α-Klotho. Selectively removing senescent cells genetically or pharmacologically increased α-Klotho in urine, kidney, and brain of mice with increased senescent cell burden, including naturally-aged, diet-induced obese (DIO), or senescent cell-transplanted mice. D+Q increased α-Klotho in urine of patients with IPF, a disease linked to cellular senescence.

Interpretation: Senescent cells cause reduced α-Klotho, partially due to their production of activin A and IL-1α. Targeting senescent cells boosts α-Klotho in mice and humans. Thus, clearing senescent cells restores α-Klotho, potentially opening a novel, translationally-feasible avenue for developing orally-active small molecule, α-Klotho-enhancing clinical interventions. Furthermore, urinary α-Klotho may prove to be an useful test for following treatments in senolytic clinical trials.

[Keywords: cellular senescence, α-Klotho, senolytics]

“Restoration of Hippocampal Neural Precursor Function by Ablation of Senescent Cells in the Aging Stem Cell Niche”, Fatt et al 2022

“Restoration of hippocampal neural precursor function by ablation of senescent cells in the aging stem cell niche”⁠, Michael P. Fatt, Lina M. Tran, Gisella Vetere, Freda D. Miller, Paul W. Frankland, David R. Kaplan (2022-01-20; similar):

  • Senescent neural precursor cells accumulate in the hippocampus with age
  • Senescent precursor accumulation is coincident with declining adult neurogenesis
  • Ablating senescent precursors increases precursor proliferation and neurogenesis
  • Ablating senescent precursors improves hippocampus-dependent spatial memory

Senescent cells are responsible, in part, for tissue decline during aging. Here, we focused on CNS neural precursor cells (NPCs) to ask if this is because senescent cells in stem cell niches impair precursor-mediated tissue maintenance.

We demonstrate an aging-dependent accumulation of senescent cells, largely senescent NPCs, within the hippocampal stem cell niche coincident with declining adult neurogenesis. Pharmacological ablation of senescent cells via acute systemic administration of the senolytic drug ABT-263 (Navitoclax) caused a rapid increase in NPC proliferation and neurogenesis. Genetic ablation of senescent cells similarly activated hippocampal NPCs.

This acute burst of neurogenesis had long-term effects in middle-aged mice. One month post-ABT-263, adult-born hippocampal neuron numbers increased and hippocampus-dependent spatial memory was enhanced.

These data support a model where senescent niche cells negatively influence neighboring non-senescent NPCs during aging, and ablation of these senescent cells partially restores neurogenesis and hippocampus-dependent cognition.

[Keywords: neural stem cells, senescence, aging, neurogenesis, ABT-263, senolytic, hippocampus, spatial memory, senescence-associated secretory phenotype]

“Combination of Dasatinib and Quercetin Improves Cognitive Abilities in Aged Male Wistar Rats, Alleviates Inflammation and Changes Hippocampal Synaptic Plasticity and Histone H3 Methylation Profile”, Krzystyniak et al 2022

“Combination of dasatinib and quercetin improves cognitive abilities in aged male Wistar rats, alleviates inflammation and changes hippocampal synaptic plasticity and histone H3 methylation profile”⁠, Adam Krzystyniak, Malgorzata Wesierska, Gregory Petrazzo, Agnieszka Gadecka, Magdalena Dudkowska, Anna Bielak-Zmijewska et al (2022-01-18; similar):

Aging is associated with cognitive decline and accumulation of senescent cells in various tissues and organs. Senolytic agents such as dasatinib and quercetin (D+Q) in combination have been shown to target senescent cells and ameliorate symptoms of aging-related disorders in mouse models. However, the mechanisms by which senolytics improve cognitive impairments have not been fully elucidated particularly in species other than mice.

To study the effect of senolytics on aging-related multifactorial cognitive dysfunctions we tested the spatial memory of male Wistar rats in an active allothetic place avoidance task.

Here we report that 8 weeks treatment with D+Q alleviated learning deficits and memory impairment observed in aged animals. Furthermore, treatment with D+Q resulted in a reduction of the peripheral inflammation measured by the levels of serum inflammatory mediators (including members of senescent cell secretome) in aged rats. Statistically-significant improvements in cognitive abilities observed in aged rats upon treatment with D+Q were associated with changes in the dendritic spine morphology of the apical dendritic tree from the hippocampal CA1 neurons and changes in the level of histone H3 trimethylation at lysine 9 and 27 in the hippocampus⁠. The beneficial effects of D+Q on learning and memory in aged rats were long-lasting and persisted at least 5 weeks after the cessation of the drugs administration.

Our results expand and provide new insights to the existing knowledge associated with effects of senolytics on alleviating age-related associated cognitive dysfunctions.

“Results of a 5-Year n-of-1 Growth Hormone Releasing Hormone Gene Therapy Experiment”, Hanley et al 2021

2021-hanley.pdf: “Results of a 5-Year n-of-1 Growth Hormone Releasing Hormone Gene Therapy Experiment”⁠, Brian P. Hanley, Keith Brewer, George Church (2021-12-16; ):

Here presented for the first time are results showing persistence over a 5+ year period in a human [Brian P. Hanley] who had a hormone gene therapy administered to muscle.

This growth hormone releasing hormone (somatocrinin/​somatoliberin/​GHRH) therapy was administered in 2 doses, a year apart, with a mean after the second dose of 195 ng/​mL (13 × normal, σ = 143, σM = 34, max = 495, min = 53). This level of GHRH therapy appears to be safe for the subject, although there were some adverse events.

Insulin-like growth factor 1 levels were little affected, nor were the growth hormone test results, showing no indications of acromegaly for the hormone homologue used.

Heart rate declined 8 to 13 bpm, persistent over 5 years. Testosterone rose by 52% (σ = 22%, σM = 6%). The high-density lipoprotein/​low-density lipoprotein ratio dropped from 3.61 to mean 2.81 (σ = 0.26, σM = 0.057, max = 3.3, min = 2.5), and triglycerides declined from 196 mg/​dL to mean 94.4 mg/​dL (σ = 21.9, σM = 5.0, min = 59, max = 133, min = 59). White blood cell counts increased, however, the baseline was not strong. CD4 and CD8 mean increased by 11.7% (σ = 11.6%, σM = 3.3%, max = 30.7%, min = −9.6%) and 12.0% (σ = 10.5%, σM = 3.0%, max = 29.1%, min = −6.7%), respectively. Ancillary observations comprise an early period of euphoria, and a dramatic improvement in visual correction after the first dose, spherical correction from baseline (L/​R) −2.25/​−2.75 to −0.25/​−0.5. Over the next 5 years, correction drifted back to −1.25/​−1.75. Horvath PhenoAge epigenetic clock was cut 44.1% post-treatment. At completion, epigenetic age was −6 years (−9.3%), and telomere age was +7 months (+0.9%).

[Keywords: GHRH, GRF, GHRF, growth hormone releasing hormone, somatocrinin, somatoliberin, somatorelin⁠, self-experimentation, n-of-1]

…Sans anesthetic, electroporation elicited the remark, “On a POW that would be a war crime.” Available literature greatly understated sensations.

Euphoria: The subject reported being euphoric after the first inoculation, a feeling of “more intense reality” with joyful/​blissful body feelings. One adviser to the study was quite concerned, being of the opinion that euphoria was probably signaling pathology, and so, it was logged as a mild grade 1 adverse event. The subject did not think it was pathological, nor adverse.

Results: Subjective first-person overview

A self-experiment provides for more than an objective observation of the experiment. The subjective experience can also inform us, allowing observations that could be missed. This experiment generated a number of such, and a third person will be dispensed with for this section.

The first inoculation was traumatic, causing strong activation of the quadriceps, and an electrical shock sensation. Inoculation sites on both legs felt “hit with a hammer.” Modifications made the second inoculation go smoothly. This is ascribed to 2 things. Without tetany of muscle cells near the electroporation site, there was no trauma to the muscle from that cause. Also, chilling prevented tissue heating.

I was surprised (because I believed that this dose would be too low to be perceptible) that in the first half-hour, I felt a tingling sensation that I had never experienced. I speculate that this was due to rapid stimulation of gonadotropin release, and the rise in testosterone level fits this idea. The first inoculations were primarily intended as a live test of the protocol. Low dose was serendipitous, as I well may have canceled the experiment and removed the site if the euphoria had continued to increase.

Over the first several days I felt better and better—my legs and whole body felt lively when going cycling, and I wondered if this could plausibly be a placebo effect. This liveliness then went over the edge into euphoria that was so strong I did not care enough to bother putting my foot down as I fell over on my bicycle due to moving too slowly. I think this suggests that GHRH, through receptors in the central nervous system, has an upregulating effect on a range of neurotransmitter receptors in the receptorome.

A curious effect on muscles occurred in the first week that I suspect is connected to later developments. During arm weight work, a sensation occurred as if minuscule spots at or near the attachments of upper body muscles were popping. This slight stinging sensation was so distributed, and so tiny for each of the countless locations, that it didn’t bother me enough to stop. Later, I had old soft tissue injuries recur, a second lumbar disc herniation, then a new shoulder injury. This shoulder injury occurred on a relatively light body weight rep after a maximal weight effort competing with young men in their mid-20s. The injury was not a full tear.

However, there was an unusual event that suggests something more. I had a motorcycle accident at 18, which left me with a gouge in my right kneecap and a lump of collagen/​scar ~0.6 cm thick × 1 cm × 2.5 cm. This lump spontaneously came loose and slipped down under my skin. It was absorbed in a 3-week period.

The first hypothesis about these injuries is that higher exercise tolerance drove my body beyond its current limits. The second hypothesis is based on speculating what saturation levels of this hormone might do to a senescent cell. It may be that senescent cells respond and create weaker tissue, or undergo apoptosis in doing so. A third hypothesis is that there may be an expression level of GHRH that corresponds to childhood, perhaps very young childhood, and triggers some neotenous cell growth pattern.

Because of concerns about further soft tissue effects, in July of 2019, I decided on a course of senolytics (dasatinib 400mg and quercetin 4g per day for 5 days) repeated 2 months later. Since then, there have been no new events. A cycling crash (over 20MPH) shortly after the second course of senolytics resulted in a mild concussion, and no other injuries, despite hitting so hard, that immediately afterward I was sure I had multiple broken bones. I have had cycling accidents in the past, breaking both wrists, a collarbone, etc. This crash was like having an accident in my 20s. As I sprinted to avoid a speeding car, I put too much focus on the car that stopped half-way across the intersection with squealing tires, and caught a pedal on the pillar in the middle of the bike path entrance.

The mental effects were pleasant after the first inoculation and largely so after the second. However, the second inoculation also included disturbing effects. My physiological responses to the world around me changed completely. This isn’t a mental thing, it’s in the body, what the Japanese call the hara. It became apparent that my identity foundation is integral with this. I talked with a psychiatrist, and did meditative exercises intentionally embracing and accepting who I was now. This was difficult, including what most would call nightmares. My unconscious operated like a child’s, piecing metaphors together to understand what I had done. I didn’t feel afraid, I felt unmoored, wondering why I felt no fear. This was probably a dose effect.

An effect I didn’t expect and still remains is that I feel I felt rejuvenated after doing leg work. This isn’t a minor effect. I consistently go in tired and by the end of my workout feel like doing it again. This begins to dissipate 2–3 hours later, and I suspect it is a direct effect of GHRH production triggered by use of the affected muscles. This also signals that upregulation of the myosin gene happens within 20–30 minutes of heavy exercise stimulation.

Sleep improved dramatically, becoming like a teens sleep for a couple of months after first inoculation. This faded, in part, probably from stress, but overall sleep improved. Since 2 months after second inoculation I wake up so hungry I cannot sleep. Eating a sizeable (800–1,000 calories) meal before bed can sometimes get me through 6 hours. However, I should note that my normal exercise schedule is 6–7 days a week, 1–2.5 hours per weekday session and up to 5 hours on weekends.

The GHRH graph shows impressive expression for more than 5 years, the first finding of such long-term expression. After 5 and ½ years, this level of long-term expression does appear to be reasonably safe.

“Deletion of SA Β-Gal+ Cells Using Senolytics Improves Muscle Regeneration in Old Mice”, Dungan et al 2021

“Deletion of SA β-Gal+ cells using senolytics improves muscle regeneration in old mice”⁠, Cory M. Dungan, Kevin A. Murach, Christopher J. Zdunek, Zuo Jian Tang, Georgia L. VonLehmden, Camille R. Brightwell et al (2021-12-13; ; similar):

Systemic deletion of senescent cells leads to robust improvements in cognitive, cardiovascular, and whole-body metabolism, but their role in tissue reparative processes is incompletely understood. We hypothesized that senolytic drugs would enhance regeneration in aged skeletal muscle.

Young (3 months) and old (20 months) male C57Bl/​6J mice were administered the senolytics dasatinib (5 mg/​kg) and quercetin (50 mg/​kg) or vehicle bi-weekly for 4 months. Tibialis anterior (TA) was then injected with 1.2% BaCl2 or PBS 7-days or 28-days prior to euthanization.

Senescence-associated β-Galactosidase positive (SA β-Gal+) cell abundance was low in muscle from both young and old mice and increased similarly 7 days following injury in both age groups, with no effect of D+Q. Most SA β-Gal+ cells were also CD11b+ in young and old mice 7-days and 14-days following injury, suggesting they are infiltrating immune cells. By 14 days, SA β-Gal+/​CD11b+ cells from old mice expressed senescence genes, whereas those from young mice expressed higher levels of genes characteristic of anti-inflammatory macrophages. SA β-Gal+ cells remained elevated in old compared to young mice 28 days following injury, which were reduced by D+Q only in the old mice. In D+Q-treated old mice, muscle regenerated following injury to a greater extent compared to vehicle-treated old mice, having larger fiber cross-sectional area after 28 days. Conversely, D+Q blunted regeneration in young mice. In vitro experiments suggested D+Q directly improve myogenic progenitor cell proliferation.

Enhanced physical function and improved muscle regeneration demonstrate that senolytics have beneficial effects only in old mice.

“A New Gene Set Identifies Senescent Cells and Predicts Senescence-Associated Pathways Across Tissues”, Saul et al 2021

“A New Gene Set Identifies Senescent Cells and Predicts Senescence-Associated Pathways Across Tissues”⁠, Dominik Saul, Robyn Laura Kosinsky, Elizabeth J. Atkinson, Madison L. Doolittle, Xu Zhang, Nathan K. LeBrasseur et al (2021-12-11; similar):

Although cellular senescence is increasingly recognized as driving multiple age-related co-morbidities through the senescence-associated secretory phenotype (SASP), in vivo senescent cell identification, particularly in bulk or single cell RNA-sequencing (scRNA-seq) data remains challenging. Here, we generated a novel gene set (SenMayo) and first validated its enrichment in bone biopsies from two aged human cohorts. SenMayo also identified senescent cells in aged murine brain tissue, demonstrating applicability across tissues and species.

For direct validation, we demonstrated significant reductions in SenMayo in bone following genetic clearance of senescent cells in mice, with similar findings in adipose tissue from humans in a pilot study of pharmacological senescent cell clearance. In direct comparisons, SenMayo outperformed all six existing senescence/​SASP gene sets in identifying senescent cells across tissues and in demonstrating responses to senescent cell clearance.

We next used SenMayo to identify senescent hematopoietic or mesenchymal cells at the single cell level from publicly available human and murine bone marrow/​bone scRNA-seq data and identified monocytic and osteolineage cells, respectively, as showing the highest levels of senescence/​SASP genes. Using pseudotime and cellular communication patterns, we found senescent hematopoietic and mesenchymal cells communicated with other cells through common pathways, including the Macrophage Migration Inhibitory Factor (MIF) pathway, which has been implicated not only in inflammation but also in immune evasion, an important property of senescent cells.

Thus, SenMayo identifies senescent cells across tissues and species with high fidelity. Moreover, using this senescence panel, we were able to characterize senescent cells at the single cell level and identify key intercellular signaling pathways associated with these cells, which may be particularly useful for evolving efforts to map senescent cells (eg. SenNet). In addition, SenMayo represents a potentially clinically applicable panel for monitoring senescent cell burden with aging and other conditions as well as in studies of senolytic drugs.

“Senolytic Vaccination Improves Normal and Pathological Age-related Phenotypes and Increases Lifespan in Progeroid Mice”, Suda et al 2021

2021-suda.pdf: “Senolytic vaccination improves normal and pathological age-related phenotypes and increases lifespan in progeroid mice”⁠, Masayoshi Suda, Ippei Shimizu, Goro Katsuumi, Yohko Yoshida, Yuka Hayashi, Ryutaro Ikegami, Naomi Matsumoto et al (2021-12-10; similar):

Elimination of senescent cells (senolysis) was recently reported to improve normal and pathological changes associated with aging in mice1⁠,2. However, most senolytic agents inhibit antiapoptotic pathways3, raising the possibility of off-target effects in normal tissues. Identification of alternative senolytic approaches is therefore warranted.

Here we identify glycoprotein nonmetastatic melanoma protein B (GPNMB) as a molecular target for senolytic therapy. Analysis of transcriptome data from senescent vascular endothelial cells revealed that GPNMB was a molecule with a transmembrane domain that was enriched in senescent cells (seno-antigen). GPNMB expression was upregulated in vascular endothelial cells and/​or leukocytes of patients and mice with atherosclerosis⁠.

Genetic ablation of Gpnmb-positive cells attenuated senescence in adipose tissue and improved systemic metabolic abnormalities in mice fed a high-fat diet, and reduced atherosclerotic burden in apolipoprotein E knockout mice on a high-fat diet. We then immunized mice against Gpnmb and found a reduction in Gpnmb-positive cells. Senolytic vaccination also improved normal and pathological phenotypes associated with aging, and extended the male lifespan of progeroid mice⁠.

Our results suggest that vaccination targeting seno-antigens could be a potential strategy for new senolytic therapies.

Figure 4: Gpnmb vaccination decreases tissue senescence and alleviates normal and pathological age-related phenotypes: d, Lifespan of Zmpste24 KO mice treated with Gpnmb vaccine (‘Gpnmb vac’) or control vaccine (‘Cont vac’) at 10 weeks of age (Cont vac, n = 19 for male mice and n = 18 for female mice.)

…To investigate the effect of vaccination on normal aging, we administered Gpnmb vaccine to middle-aged mice (50 weeks old) and examined their performance in the open field test before vaccination and 20 weeks after vaccination (70 weeks old). In the control group, both total movements and the average speed of movement decreased with age, but these age-associated changes were statistically-significantly ameliorated by Gpnmb vaccination (Figure 4c). To investigate the effects of Gpnmb vaccine on the lifespan, we vaccinated Zmpste24 KO mice (a model of Hutchinson-Gilford progeria syndrome) at 10 weeks of age and evaluated their survival. In the control group, all of the mice died by 30 weeks of age. In contrast, mice, especially male mice, administered Gpnmb vaccine showed a better survival rate, even when the vaccine was administered at 10 weeks of age (Figure 4d). Likewise, administration of Gpnmb vaccine statistically-significantly extended the median lifespan of Zmpste24 KO mice, especially male mice, compared with mice treated with control vaccine (male and female mice, 21.1 ± 0.85 weeks versus 25.3 ± 1.10 weeks (p < 0.01); male mice, 21.7 ± 1.27 weeks versus 27.1 ± 1.53 weeks).

“The Flavonoid Procyanidin C1 Has Senotherapeutic Activity and Increases Lifespan in Mice”, Xu et al 2021

“The flavonoid procyanidin C1 has senotherapeutic activity and increases lifespan in mice”⁠, Qixia Xu, Qiang Fu, Zi Li, Hanxin Liu, Ying Wang, Xu Lin, Ruikun He, Xuguang Zhang, Zhenyu Ju, Judith Campisi et al (2021-12-06; similar):

Ageing-associated functional decline of organs and increased risk for age-related chronic pathologies is driven in part by the accumulation of senescent cells, which develop the senescence-associated secretory phenotype (SASP).

Here we show that procyanidin C1 (PCC1), a polyphenolic component of grape seed extract (GSE), increases the healthspan and lifespan of mice through its action on senescent cells. By screening a library of natural products, we find that GSE, and PCC1 as one of its active components, have specific effects on senescent cells.

At low concentrations, PCC1 appears to inhibit SASP formation, whereas it selectively kills senescent cells at higher concentrations, possibly by promoting production of reactive oxygen species and mitochondrial dysfunction. In rodent models, PCC1 depletes senescent cells in a treatment-damaged tumour microenvironment and enhances therapeutic efficacy when co-administered with chemotherapy. Intermittent administration of PCC1 to either irradiated, senescent cell-implanted or naturally aged old mice alleviates physical dysfunction and prolongs survival.

We identify PCC1 as a natural senotherapeutic agent with in vivo activity and high potential for further development as a clinical intervention to delay, alleviate or prevent age-related pathologies.

…To establish the potential of senescent cell elimination to extend the remaining lifespan of WT mice, we performed PCC1 treatment beginning at a very old age (Figure 8k). Mice receiving PCC1 administration (once every 2 weeks or biweekly) starting at 24–27 months of age (roughly equivalent to an age of 75–90 years in humans) had a 64.2% longer median post-treatment lifespan (or 9.4% longer overall lifespan) and lower mortality hazard (65.0%, p < 0.0001) than the vehicle-treated group (Figure 8l, Figure 8m). These data indicate that PCC1 can substantially decrease the risk of age-associated mortality in old mice.

“Targeting p21Cip1 Highly Expressing Cells in Adipose Tissue Alleviates Insulin Resistance in Obesity”, Wang et al 2021

2021-wang.pdf: “Targeting p21Cip1 highly expressing cells in adipose tissue alleviates insulin resistance in obesity”⁠, Lichao Wang, Binsheng Wang, Nathan S. Gasek, Yueying Zhou, Rachel L. Cohn, Dominique E. Martin, Wulin Zuo et al (2021-11-22; similar):

  • p21high cells, distinct from p16high cells, accumulate in fat with obesity
  • Intermittent p21high cell clearance both prevents and alleviates insulin resistance
  • Exclusive inactivation of NF-κB in p21high cells improves insulin sensitivity
  • A senolytic reduces p21high cells in human fat and alleviates its metabolic harm in vivo

Insulin resistance is a pathological state often associated with obesity, representing a major risk factor for type 2 diabetes⁠. Limited mechanism-based strategies exist to alleviate insulin resistance.

Here, using single-cell transcriptomics, we identify a small, critically important, but previously unexamined cell population, p21Cip1 highly expressing (p21high) cells, which accumulate in adipose tissue with obesity.

By leveraging a p21-Cre mouse model, we demonstrate that intermittent clearance of p21high cells can both prevent and alleviate insulin resistance in obese mice. Exclusive inactivation of the NF-κB pathway within p21high cells, without killing them, attenuates insulin resistance. Moreover, fat transplantation experiments establish that p21high cells within fat are sufficient to cause insulin resistance in vivo. Importantly, a senolytic cocktail, dasatinib+quercetin⁠, eliminates p21high cells in human fat ex vivo and mitigates insulin resistance following xenotransplantation into immuno-deficient mice.

Our findings lay the foundation for pursuing the targeting of p21high cells as a new therapy to alleviate insulin resistance.

[Keywords: Cellular senescence⁠, diabetes, senolytics, fat transplantation, NF-κB, xenograft]

“Sexual Dimorphic Responses of C57BL/6 Mice to Fisetin or Dasatinib and Quercetin Cocktail Oral Treatment”, Fang et al 2021

“Sexual dimorphic responses of C57BL/6 mice to Fisetin or Dasatinib and Quercetin cocktail oral treatment”⁠, Yimin Fang, David Medina, Robert Stockwell, Sam McFadden, Kathleen Quinn, Mackenzie R. Peck, Andrzej Bartke et al (2021-11-08; similar):

Senolytic treatment in aged mice clears senescent cell burden leading to functional improvements. We hypothesized that administering senotherapeutics in young adulthood of mice would slow physiological markers of aging through mid-life. C57BL/​6 mice were treated monthly with either Fisetin or a Dasatinib (D) plus Quercetin (Q) cocktail from 4–13 months of age. Fisetin treated male mice had reduced senescence-associated secretory phenotype (SASP), enhanced glucose and energy metabolism, improved cognitive performance, and increased hippocampal expression of adiponectin 1 receptor and glucose transporter 4. D+Q treated females had increased SASP expression along with accumulation of white adipose tissue, reduced energy metabolism, and cognitive performance. Senotherapeutics in young adulthood, has beneficial, negligible, or detrimental effects in mice dependent upon sex and treatment.

“A Collective Analysis of Lifespan-extending Compounds in Diverse Model Organisms, and of Species Whose Lifespan Can Be Extended the Most by the Application of Compounds”, Berkel & Cacan 2021

2021-berkel.pdf: “A collective analysis of lifespan-extending compounds in diverse model organisms, and of species whose lifespan can be extended the most by the application of compounds”⁠, Caglar Berkel, Ercan Cacan (2021-10-21; ; similar):

Research on aging and lifespan-extending compounds has been carried out using diverse model organisms, including yeast, worms, flies and mice. Many studies reported the identification of novel lifespan-extending compounds in different species, some of which may have the potential to translate to the clinic. However, studies collectively and comparatively analyzing all the data available in these studies are highly limited.

Here, by using data from the DrugAge database, we first identified top compounds in terms of their effects on percent change in average lifespan of diverse organisms, collectively (n = 1,728).

We found that, when data from all organisms studied were combined for each compound, aspirin resulted in the highest percent increase in average lifespan (52.01%), followed by minocycline (27.30%), N-acetyl cysteine (17.93%), nordihydroguaiaretic acid (17.65%) and rapamycin (15.66%), in average. We showed that minocycline led to the highest percent increase in average lifespan among other compounds, in both Drosophila melanogaster (28.09%) and Caenorhabditis elegans (26.67%), followed by curcumin (11.29%) and gluconic acid (5.51%) for D. melanogaster and by metformin (26.56%), resveratrol (15.82%) and quercetin (9.58%) for C. elegans.

Moreover, we found that top 5 species whose lifespan can be extended the most by compounds with lifespan-extending properties are Philodina acuticornis⁠, Acheta domesticus⁠, Aeolosoma viride⁠, Mytilina brevispina and Saccharomyces cerevisiae (211.80%, 76%, 70.26%, 55.18% and 45.71% in average, respectively).

This study provides novel insights on lifespan extension in model organisms, and highlights the importance of databases with high quality content curated by researchers from multiple resources, in aging research.

Figure 1: Top compounds in terms of their effects on average lifespan change in diverse organisms collectively. Percent change in average lifespan of organisms treated with longevity-extending compounds, when data from all organisms studied were combined for each compound. Top plot: Compounds were ordered as the compound which caused the highest percent increase in average lifespan in all organisms combined, given at the top of the plot. Data points for each species were given a different color. Yellow vertical line indicates no change (0%) in average lifespan. Vertical lines in boxplots indicates the median value. Legend shows the color code for each species. Bottom plot: Distribution of the percent change in average lifespan for each drug, when data from all organisms studied were combined per compound. Yellow vertical line indicates no change (0%) in average lifespan. Values in red at the end of x-axis for every y-value indicate mean percent change in average lifespan for each compound. Compounds were ordered as the compound which caused the highest percent increase in average lifespan (aspirin, 52.01%) in all organisms combined, given at the top of plot. Legend shows the color scale indicating percent change in average lifespan.

“The Metabolic Roots of Senescence: Mechanisms and Opportunities for Intervention”, Wiley & Campisi 2021

“The metabolic roots of senescence: mechanisms and opportunities for intervention”⁠, Christopher D. Wiley, Judith Campisi (2021-10-18; similar):

Cellular senescence entails a permanent proliferative arrest, coupled to multiple phenotypic changes. Among these changes is the release of numerous biologically active molecules collectively known as the senescence-associated secretory phenotype, or SASP. A growing body of literature indicates that both senescence and the SASP are sensitive to cellular and organismal metabolic states, which in turn can drive phenotypes associated with metabolic dysfunction.

Here, we review the current literature linking senescence and metabolism, with an eye toward findings at the cellular level, including both metabolic inducers of senescence and alterations in cellular metabolism associated with senescence.

Additionally, we consider how interventions that target either metabolism or senescent cells might influence each other and mitigate some of the pro-aging effects of cellular senescence.

We conclude that the most effective interventions will likely break a degenerative feedback cycle by which cellular senescence promotes metabolic diseases, which in turn promote senescence.

“Strategies for Targeting Senescent Cells in Human Disease”, Gasek et al 2021

“Strategies for targeting senescent cells in human disease”⁠, Nathan S. Gasek, George A. Kuchel, James L. Kirkland, Ming Xu (2021-10-07; similar):

Cellular senescence represents a distinct cell fate characterized by replicative arrest in response to a host of extrinsic and intrinsic stresses. Senescence facilitates programming during development and wound healing, while limiting tumorigenesis. However, pathologic accumulation of senescent cells is implicated in a range of diseases and age-associated morbidities across organ systems. Senescent cells produce distinct paracrine and endocrine signals, causing local tissue dysfunction and exerting deleterious systemic effects.

Senescent cell removal by apoptosis-inducing senolytic agents or therapies that inhibit the senescence-associated secretory phenotype have demonstrated benefit in both preclinical and clinical models of geriatric decline and chronic diseases, suggesting that senescent cells represent a pharmacologic target for alleviating effects of fundamental aging processes. However, senescent cell populations are heterogeneous in form, function and tissue distribution, and even differ among species, possibly explaining issues of bench-to-bedside translation in current clinical trials.

Here we review features of senescent cells and strategies for targeting them, including immunologic approaches, as well as key intracellular signaling pathways. Additionally, we survey current senolytic therapies in human trials.

Collectively, there is demand for research to develop targeted senotherapeutics that address the needs of the aging and chronically ill.

“Modulation of Fracture Healing by the Transient Accumulation of Senescent Cells”, Saul et al 2021

“Modulation of fracture healing by the transient accumulation of senescent cells”⁠, Dominik Saul, David G. Monroe, Jennifer L. Rowsey, Robyn Laura Kosinsky, Stephanie J. Vos, Madison L. Doolittle et al (2021-10-07; similar):

Senescent cells have detrimental effects across tissues with aging but may have beneficial effects on tissue repair, specifically on skin wound healing. However, the potential role of senescent cells in fracture healing has not been defined.

Here, we performed an in silico analysis of public mRNAseq data and found that senescence and senescence-associated secretory phenotype (SASP) markers increased during fracture healing. We next directly established that the expression of senescence biomarkers increased markedly during murine fracture healing. We also identified cells in the fracture callus that displayed hallmarks of senescence, including distension of satellite heterochromatin and telomeric DNA damage; the specific identity of these cells, however, requires further characterization.

Then, using a genetic mouse model (Cdkn2aLUC) containing a Cdkn2aInk4a-driven luciferase reporter, we demonstrated transient in vivo senescent cell accumulation during callus formation. Finally, we intermittently treated young adult mice following fracture with drugs that selectively eliminate senescent cells (‘senolytics’, Dasatinib plus Quercetin), and showed that this regimen both decreased senescence and SASP markers in the fracture callus and statistically-significantly accelerated the time course of fracture healing.

Our findings thus demonstrate that senescent cells accumulate transiently in the murine fracture callus and, in contrast to the skin, their clearance does not impair but rather improves fracture healing.

“Fisetin for COVID-19 in Skilled Nursing Facilities: Senolytic Trials in the COVID Era”, Verdoorn et al 2021

“Fisetin for COVID-19 in skilled nursing facilities: Senolytic trials in the COVID era”⁠, Brandon P. Verdoorn, Tamara K. Evans, Gregory J. Hanson, Yi Zhu, Larissa G. P. Langhi Prata, Robert J. Pignolo et al (2021-08-10; similar):

The burden of senescent cells (SnCs), which do not divide but are metabolically active and resistant to death by apoptosis⁠, is increased in older adults and those with chronic diseases.

These individuals are also at the greatest risk for morbidity and mortality from SARS-CoV-2 infection. SARS-CoV-2 complications include cytokine storm and multi-organ failure mediated by the same factors as often produced by SnCs through their senescence-associated secretory phenotype (SASP). The SASP can be amplified by infection-related pathogen-associated molecular profile factors.

Senolytic agents, such as Fisetin⁠, selectively eliminate SnCs and delay, prevent, or alleviate multiple disorders in aged experimental animals and animal models of human chronic diseases, including obesity, diabetes, and respiratory diseases. Senolytics are now in clinical trials for multiple conditions linked to SnCs, including frailty; obesity/​diabetes; osteoporosis; and cardiovascular, kidney, and lung diseases, which are also risk factors for SARS-CoV-2 morbidity and mortality. A clinical trial is underway to test if senolytics decrease SARS-CoV-2 progression and morbidity in hospitalized older adults.

We describe here a National Institutes of Health-funded, multicenter, placebo-controlled clinical trial of Fisetin for older adult skilled nursing facility (SNF) residents who have been, or become, SARS-CoV-2 rtPCR-positive, including the rationale for targeting fundamental aging mechanisms in such patients. We consider logistic challenges of conducting trials in long-term care settings in the SARS-CoV-2 era, including restricted access, consent procedures, methods for obtaining biospecimens and clinical data, staffing, investigational product administration issues, and potential solutions for these challenges.

We propose developing a national network of SNFs engaged in interventional clinical trials.

“Senolytics and the Compression of Late-life Mortality”, Kowald & Kirkwood 2021

“Senolytics and the compression of late-life mortality”⁠, Axel Kowald, Thomas B. L Kirkwood (2021-04-26; similar):

Senescent cells play an important role in mammalian ageing and in the etiology of age-related diseases. Treatment of mice with senolytics—drugs that selectively remove senescent cells—causes an extension of median lifespan but has little effect on maximum lifespan. Postponement of some mortality to later ages, without a corresponding increase in maximum mortality, can be termed ‘compression of mortality’. When we fit the standard Gompertz mortality model to the survival data following senolytic treatment, we find an increase in the slope parameter, commonly described as the ‘actuarial ageing rate’. These observations raise important questions about the actions of senolytic treatments and their effects on health and survival, which are not yet sufficiently understood.

To explore how the survival data from senolytics experiments might be explained, we combine recent exploration of the evolutionary basis of cellular senescence with theoretical consideration of the molecular processes that might be involved. We perform numerical simulations of senescent cell accumulation and senolytic treatment in an ageing population. The simulations suggest that while senolytics diminish the burden of senescent cells, they may also impair the general repair capacity of the organism, leading to a faster accumulation post-treatment of new senescent cells. Our results suggest a framework to address the benefits and possible side effects of senolytic therapies, with the potential to aid the design of optimal treatment regimens.

“Procyanidin C1 Is a Natural Agent With Senolytic Activity against Aging and Age-related Diseases”, Xu et al 2021

“Procyanidin C1 is a natural agent with senolytic activity against aging and age-related diseases”⁠, Qixia Xu, Qiang Fu, Zi Li, Hanxin Liu, Ying Wang, Xu Lin, Ruikun He, Xuguang Zhang, Judith Campisi, James L. Kirkland et al (2021-04-14; similar):

Aging causes functional decline of multiple organs and increases the risk of age-related pathologies. In advanced lives, accumulation of senescent cells, which develop the senescence-associated secretory phenotype (SASP), promotes chronic inflammation and causes diverse conditions. Here we report the frontline outcome of screening a natural product library with human primary stromal cells as an experimental model. Multiple candidate compounds were assayed, and grape seed extract (GSE) was selected for further investigation due to its leading capacity in targeting senescent cells.

We found procyanidin C1 (PCC1), a polyphenolic component, plays a critical role in mediating the antiaging effects of GSE. PCC1 blocks the SASP expression when used at low concentrations. Importantly, it selectively kills senescent cells upon application at higher concentrations, mainly by enhancing production of reactive oxygen species (ROS) and disturbing mitochondrial membrane potential, processes accompanied by upregulation of Bcl-2 family pro-apoptotic factors Puma and Noxa in senescent cells.

PCC1 depletes senescent cells in treatment-damaged tumor microenvironment (TME) and enhances therapeutic efficacy when combined with chemotherapy in preclinical assays. Intermittent administration of PCC1 to both senescent cell-implanted mice and naturally aged animals alleviated physical dysfunction and prolonged post-treatment survival, thus providing substantial benefits in late life stage. Together, our study identifies PCC1 as a distinct natural senolytic agent, which may be exploited to delay aging and control age-related pathologies in future medicine.

“Oxylipin Biosynthesis Reinforces Cellular Senescence and Allows Detection of Senolysis”, Wiley et al 2021

2021-wiley.pdf: “Oxylipin biosynthesis reinforces cellular senescence and allows detection of senolysis”⁠, Christopher D. Wiley, Rishi Sharma, Sonnet S. Davis, Jose Alberto Lopez-Dominguez, Kylie P. Mitchell et al (2021-04-02; similar):

Senolytics—transgenic, and pharmacological interventions that selectively kill senescent cells—are currently in clinical trials aiming to treat age-related degenerative pathologies. Here, Wiley et al discover that senescent cells produce multiple signaling lipids known as oxylipins⁠. One oxylipin, dihomo-15d-PGJ2, promotes features of senescence by activating RAS and is released from cells during senolysis, serving as the first biomarker of the process in culture and in vivo.

  • Senescent cells make several oxylipins, dihomo-prostaglandins, and leukotrienes
  • Dihomo-15d-PGJ2 is intracellular during senescence and released during senolysis
  • Dihomo-15d-PGJ2 activates RAS, promoting senescence and the SASP
  • Positive feedback between prostaglandins, RAS, and p53 maintains senescence

Cellular senescence is a stress or damage response that causes a permanent proliferative arrest and secretion of numerous factors with potent biological activities. This senescence-associated secretory phenotype (SASP) has been characterized largely for secreted proteins that participate in embryogenesis, wound healing, inflammation, and many age-related pathologies. By contrast, lipid components of the SASP are understudied.

We show that senescent cells activate the biosynthesis of several oxylipins that promote segments of the SASP and reinforce the proliferative arrest. Notably, senescent cells synthesize and accumulate an unstudied intracellular prostaglandin, 1a,1b-dihomo-15-deoxy-delta-12,14-prostaglandin J2. Released 15-deoxy-delta-12,14-prostaglandin J2 is a biomarker of senolysis in culture and in vivo. This and other prostaglandin D2-related lipids promote the senescence arrest and SASP by activating RAS signaling.

These data identify an important aspect of cellular senescence and a method to detect senolysis.

[Keywords: cellular senescence, senescence, aging, lipids, metabolomics, eicosanoid, SASP, prostaglandin, dihomo-prostaglandin, biomarker, mass spectrometry, 15d-PGJ2, oxylipin, RAS]

[A universal biomarker measurable in blood for senolytics: “This biomarker is an unique signaling lipid metabolite, normally exclusively intracellular, but is released when senescent cells are forced to die.”]

“Whole-body Senescent Cell Clearance Alleviates Age-related Brain Inflammation and Cognitive Impairment in Mice”, Ogrodnik et al 2021

“Whole-body senescent cell clearance alleviates age-related brain inflammation and cognitive impairment in mice”⁠, Mikolaj Ogrodnik, Shane A. Evans, Edward Fielder, Stella Victorelli, Patrick Kruger, Hanna Salmonowicz et al (2021-01-20; similar):

Cellular senescence is characterized by an irreversible cell cycle arrest and a pro-inflammatory senescence-associated secretory phenotype (SASP), which is a major contributor to aging and age-related diseases. Clearance of senescent cells has been shown to improve brain function in mouse models of neurodegenerative diseases. However, it is still unknown whether senescent cell clearance alleviates cognitive dysfunction during the aging process.

To investigate this, we first conducted single-nuclei and single-cell RNA-seq in the hippocampus from young and aged mice. We observed an age-dependent increase in p16Ink4a senescent cells, which was more pronounced in microglia and oligodendrocyte progenitor cells and characterized by a SASP.

We then aged INK-ATTAC mice, in which p16Ink4a-positive senescent cells can be genetically eliminated upon treatment with the drug AP20187 and treated them either with AP20187 or with the senolytic cocktail Dasatinib and Quercetin⁠. We observed that both strategies resulted in a decrease in p16Ink4a exclusively in the microglial population, resulting in reduced microglial activation and reduced expression of SASP factors. Importantly, both approaches statistically-significantly improved cognitive function in aged mice.

Our data provide proof-of-concept for senolytic interventions’ being a potential therapeutic avenue for alleviating age-associated cognitive impairment.

“The Quest to Slow Ageing through Drug Discovery”, Partridge et al 2020

2020-partridge.pdf: “The quest to slow ageing through drug discovery”⁠, Linda Partridge, Matias Fuentealba, Brian K. Kennedy (2020-05-28; backlinks; similar):

Although death is inevitable, individuals have long sought to alter the course of the ageing process. Indeed, ageing has proved to be modifiable; by intervening in biological systems, such as nutrient sensing, cellular senescence, the systemic environment and the gut microbiome, phenotypes of ageing can be slowed sufficiently to mitigate age-related functional decline. These interventions can also delay the onset of many disabling, chronic diseases, including cancer, cardiovascular disease and neurodegeneration, in animal models. Here, we examine the most promising interventions to slow ageing and group them into two tiers based on the robustness of the preclinical, and some clinical, results, in which the top tier includes rapamycin, senolytics, metformin, acarbose, spermidine, NAD⁺ enhancers and lithium. We then focus on the potential of the interventions and the feasibility of conducting clinical trials with these agents, with the overall aim of maintaining health for longer before the end of life.

“Senolytic Drugs: from Discovery to Translation”, Kirkland & Tchkonia 2020

“Senolytic drugs: from discovery to translation”⁠, J L. Kirkland, T. Tchkonia (2020; backlinks; similar):

Senolytics are a class of drugs that selectively clear senescent cells (SC). The first senolytic drugs Dasatinib, Quercetin, Fisetin and Navitoclax were discovered using a hypothesis-driven approach. SC accumulate with ageing and at causal sites of multiple chronic disorders, including diseases accounting for the bulk of morbidity, mortality and health expenditures. The most deleterious SC are resistant to apoptosis and have up-regulation of anti-apoptotic pathways which defend SC against their own inflammatory senescence-associated secretory phenotype (SASP), allowing them to survive, despite killing neighbouring cells. Senolytics transiently disable these SCAPs, causing apoptosis of those SC with a tissue-destructive SASP. Because SC take weeks to re-accumulate, senolytics can be administered intermittently—a ‘hit-and-run’ approach.

In preclinical models, senolytics delay, prevent or alleviate frailty, cancers and cardiovascular, neuropsychiatric, liver, kidney, musculoskeletal, lung, eye, haematological, metabolic and skin disorders as well as complications of organ transplantation, radiation and cancer treatment. As anticipated for agents targeting the fundamental ageing mechanisms that are ‘root cause’ contributors to multiple disorders, potential uses of senolytics are protean, potentially alleviating over 40 conditions in preclinical studies, opening a new route for treating age-related dysfunction and diseases.

Early pilot trials of senolytics suggest they decrease senescent cells, reduce inflammation and alleviate frailty in humans. Clinical trials for diabetes, idiopathic pulmonary fibrosis, Alzheimer’s disease, COVID-19, osteoarthritis, osteoporosis, eye diseases and bone marrow transplant and childhood cancer survivors are underway or beginning. Until such studies are done, it is too early for senolytics to be used outside of clinical trials.

“A Look Back at 2019: Progress Towards the Treatment of Aging As a Medical Condition”, Reason 2019

“A Look Back at 2019: Progress Towards the Treatment of Aging as a Medical Condition”⁠, Reason (2019-12-31; ; similar):

[Aging research over the past year, 2019. Categories include: The State of Funding, Conferences and Community, Clinical Development, Cellular Senescence, Mitochondria in Aging, Nuclear DNA Damage, Cross-Links, Neurodegeneration, Upregulation of Cell Maintenance, In Vivo Cell Reprogramming, Parabiosis⁠, The Gut Microbiome in Aging, Biomarkers of Aging, Cancer, The Genetics of Longevity, Regenerative Medicine, Odds and Ends, Short Articles, and In Conclusion.]

As has been the case for a few years now, progress towards the implementation of rejuvenation therapies is accelerating dramatically, ever faster with each passing year. While far from everyone is convinced that near term progress in addressing human aging is plausible, it is undeniable that we are far further ahead than even a few years ago. Even the public at large is beginning to catch on. While more foresightful individuals of past generations could do little more than predict a future of rejuvenation and extended healthy lives, we are in a position to make it happen.

“Senolytics Decrease Senescent Cells in Humans: Preliminary Report from a Clinical Trial of Dasatinib plus Quercetin in Individuals With Diabetic Kidney Disease”, Hickson et al 2019

“Senolytics decrease senescent cells in humans: Preliminary report from a clinical trial of Dasatinib plus Quercetin in individuals with diabetic kidney disease”⁠, LaTonya J. Hickson, Larissa G.P. Langhi Prata, Shane A. Bobart, Tamara K. Evans, Nino Giorgadze, Shahrukh K. Hashmi et al (2019-09-18; similar):

Background: Senescent cells, which can release factors that cause inflammation and dysfunction, the senescence-associated secretory phenotype (SASP), accumulate with ageing and at etiological sites in multiple chronic diseases. Senolytics, including the combination of Dasatinib and Quercetin (D + Q), selectively eliminate senescent cells by transiently disabling pro-survival networks that defend them against their own apoptotic environment. In the first clinical trial of senolytics, D + Q improved physical function in patients with idiopathic pulmonary fibrosis (IPF), a fatal senescence-associated disease, but to date, no peer-reviewed study has directly demonstrated that senolytics decrease senescent cells in humans.

Methods: In an open label Phase 1 pilot study, we administered 3 days of oral D 100 mg and Q 1000 mg to subjects with diabetic kidney disease (n = 9; 68·7 ± 3·1 years old; 2 female; BMI:33·9 ± 2·3 kg/​m2; eGFR:27·0 ± 2·1 mL/​min/​1·73m2). Adipose tissue, skin biopsies, and blood were collected before and 11 days after completing senolytic treatment. Senescent cell and macrophage/​Langerhans cell markers and circulating SASP factors were assayed.

Findings: D + Q reduced adipose tissue senescent cell burden within 11 days, with decreases in p16INK4A-and p21CIP1-expressing cells, cells with senescence-associated β-galactosidase activity, and adipocyte progenitors with limited replicative potential. Adipose tissue macrophages, which are attracted, anchored, and activated by senescent cells, and crown-like structures were decreased. Skin epidermal p16INK4A+ and p21CIP1+ cells were reduced, as were circulating SASP factors, including IL-1α, IL-6, and MMPs-9 and −12.

Interpretation: “Hit-and-run” treatment with senolytics, which in the case of D + Q have elimination half-lives <11 h, statistically-significantly decreases senescent cell burden in humans.

Funding: NIH and Foundations. Identifier: NCT02848131. Senescence, Frailty, and Mesenchymal Stem Cell Functionality in Chronic Kidney Disease: Effect of Senolytic Agents.

[Keywords: senolytics, cellular senescence, dasatinib, quercetin, diabetic kidney disease, senescence-associated secretory phenotype (SASP)]

Evidence before this study: Senescent cells accumulate in tissues with ageing and at etiological sites in multiple chronic diseases, including adipose tissue in diabetes. Senescent cells can release products that cause inflammation and death of non-senescent cells, the senescence-associated secretory phenotype (SASP). Intermittent administration of the senolytic drug combination, Dasatinib plus Quercetin (D + Q), which transiently disables the pro-survival pathways that defend senescent cells against their own apoptotic environment, selectively eliminates senescent cells from mouse and human cell cultures, ageing mice, mice with insulin resistance and many other chronic disorders, and freshly-isolated adipose tissue explants from obese, diabetic human subjects. In the first clinical trial of senolytics, D + Q alleviated physical dysfunction in patients with idiopathic pulmonary fibrosis (IPF), a progressive, fatal, cellular senescence-associated disease. In another clinical trial, prolonged D administration to patients with systemic sclerosis appeared to reduce the SASP and other senescence markers in skin biopsies. To date, no peer-reviewed clinical trial report has directly demonstrated that administering senolytics decreases senescent cells.

Added value of this study: Here, in an open-label Phase 1 pilot study, we show for the first time that senolytic drugs decrease senescent cell abundance in humans. A 3-day oral course of D + Q in subjects with diabetic kidney disease (DKD) reduced adipose tissue senescent cell burden 11 days later, as indicated by decreases in cells with markers of senescence: p16INK4A-and p21CIP1-expressing cells, cells with senescence-associated β-galactosidase (SAβgal) activity, and adipocyte progenitors with limited replicative potential. Consistent with decreased overall senescent cell burden in humans treated with senolytics, skin epidermal p16INK4A-expressing and p21CIP1-expressing cells were also reduced, as were key SASP factors, including interleukin (IL)-1α, IL-6, and MMPs 9 & 12, in blood. Thus, “hit-and-run” treatment with senolytic agents, which in the case of D + Q have elimination half-lives of <11 h, is sufficient to decrease senescent cell burden in humans. Thereafter, senescent cell burden remains low for days to weeks, consistent with the >2 weeks it takes for new senescent cells to develop (at least in cell culture).

Implications of all the available evidence: Interventions targeting fundamental ageing processes such as cellular senescence could delay, prevent, or alleviate multiple age-related diseases and disorders as a group, instead of one-at-a-time, as per the Geroscience Hypothesis. Increasingly in mice, this hypothesis appears to be true. Combined with the first clinical trial of senolytic agents showing that D + Q improves physical function in patients with IPF published earlier this year in this journal, our current article showing that D + Q actually decreases senescent cell burden in humans is consistent with the possibility that the Geroscience Hypothesis may also hold true for humans. If clinical trials over the next few years support and extend our findings to show that these agents can alleviate additional age-related and cellular-senescence-related disorders and diseases (beyond IPF) and reduce senescent cell burden (beyond adipose tissue and skin and as reflected by decreased SASP factors in blood), senolytics might become an entirely new path for alleviating currently untreatable chronic diseases and enhancing human healthspan.

“Metformin and Aging: A Review”, Glossmann & Lutz 2019

“Metformin and Aging: A Review”⁠, Hartmut H. Glossmann, O. M. Lutz (2019-09-13; ; backlinks; similar):

Metformin is sometimes proposed to be an “anti-aging” drug, based on preclinical experiments with lower-order organisms and numerous retrospective data on beneficial health outcomes for type 2 diabetics. Large prospective, placebo-controlled trials are planned, in pilot stage or running, to find a new use (or indication) for an aging population. As one of the metformin trials has “frailty” as its endpoint, similar to a trial with a plant-derived senolytic, the latter class of novel anti-aging drugs is briefly discussed. Concerns exist not only for vitamin B12 and B6 deficiencies, but also about whether there are adverse effects of metformin on individuals who try to remain healthy by maintaining cardiovascular fitness via exercise.

Conclusions, Recommendations, and Perspectives: The rationale for the ongoing or planned metformin trials is almost exclusively based on observations (associations) of potential benefits in a diabetic (or prediabetic) population. Its efficacy even in an at-risk cohort of aged people has not yet been proven. Metformin is associated with a higher risk of vitamin B12 and vitamin B6 deficiency, which may result in an increased risk of cognitive dysfunction98. Supplementation is strongly recommended to metformin users.

Of greater concern are the results of small trials in which the effects of metformin on metabolic responses to exercise or on cardiorespiratory fitness were tested. In a placebo-controlled, double-blind, crossover trial with healthy young subjects, metformin caused a small but statistically-significant decline in maximal aerobic capacity99. A double-blind, placebo-controlled landmark trial with older adults with one risk factor for T2D investigated the effects of metformin and 12 weeks of aerobic exercise 100. Contrary to expectations—namely, that the effects of exercise and the drug would be additive–“metformin attenuated the increase in whole-body insulin sensitivity and abrogated the exercise-mediated increase in skeletal muscle mitochondrial respiration.” The results of the (repurposing) MASTERS trial (NCT02308228; Metformin to Augment Strength Training Effective Response in Seniors)100 will be instructive. MASTERS is testing the hypothesis that older individuals’ long-term treatment with metformin augments the effects of resistance exercise, especially in the “nonresponder” aging population.

“Senolytic Treatment Targets Aberrant P21-expression to Restore Liver Regeneration in Adult Mice”, Ritschka et al 2019

“Senolytic treatment targets aberrant p21-expression to restore liver regeneration in adult mice”⁠, Birgit Ritschka, Tania Knauer-Meyer, Alba Mas, Jean-Luc Plassat, Daniel Sampaio Gonçalves, Hugues Jacobs et al (2019-09-05; similar):

Young mammals possess a limited regenerative capacity in tissues such as the liver, heart and limbs, but which is quickly lost upon maturation or transition to adulthood. Chronic cellular senescence is a known mediator of decreased tissue function in aging and disease. Here we investigated whether senescence plays a role in the progressive loss of liver regenerative capacity that develops in young adult mice. We find that following partial hepatectomy, the senescence markers p21, p16Ink4a and p19Arf become dynamically expressed at an age when regenerative capacity decreases. In addition, we demonstrate that treatment with a senescence-inhibiting drug improves regenerative capacity, through targeting of aberrant p21 expression. Surprisingly, we also find that the senescence marker p16Ink4a is expressed in a different cell-population to p21, and is unaffected by senescence targeting. This work suggests that senescence may initially develop as a heterogeneous cellular response, and that treatment with senolytic drugs may aid in promoting organ regeneration.

“Galactose-modified Duocarmycin Prodrugs As Senolytics”, Guerrero et al 2019

“Galactose-modified duocarmycin prodrugs as senolytics”⁠, Ana Guerrero, Romain Guiho, Nicolás Herranz, Anthony Uren, Dominic J. Withers, Juan Pedro Martínez-Barbera et al (2019-08-24; similar):

Senescence is a stable growth arrest that impairs the replication of damaged, old or preneoplastic cells, therefore contributing to tissue homeostasis. Senescent cells accumulate during ageing and are associated with diseases, such as cancer, fibrosis and many age-related pathologies. Recent evidence suggests that the selective elimination of senescent cells can be effective on the treatment of many of these senescence-associated diseases. A universal characteristic of senescent cells is that they display elevated activity of the lysosomal β-galactosidase this has been exploited as a marker for senescence (senescence-associated β-galactosidase activity). Consequently, we hypothesised that galactose-modified cytotoxic prodrugs will be preferentially processed by senescent cells, resulting in their selective killing. Here, we show that different galactose-modified duocarmycin (GMD) derivatives preferentially kill senescent cells. GMD prodrugs induce selective apoptosis of senescent cells in a lysosomal β-galactosidase (GLB1)-dependent manner. GMD prodrugs can eliminate a broad range of senescent cells in culture, and treatment with a GMD prodrug enhances the elimination of bystander senescent cells that accumulate upon whole body irradiation or doxorubicin treatment of mice. Moreover, taking advantage of a mouse model of human adamantinomatous craniopharyngioma (ACP), we show that treatment with a GMD pro-drug result selectively reduced the number of β-catenin-positive preneoplastic senescent cells, what could have therapeutic implications. In summary, the above results show that galactose-modified duocarmycin prodrugs behave as senolytics, suggesting that they could be used to treat a wide range of senescence-related pathologies.

“Senolytics Improve Physical Function and Increase Lifespan in Old Age”, Xu et al 2018

2018-xu.pdf: “Senolytics improve physical function and increase lifespan in old age”⁠, Ming Xu, Tamar Pirtskhalava, Joshua N. Farr, Bettina M. Weigand, Allyson K. Palmer, Megan M. Weivoda et al (2018-01-01; backlinks)

“Investigation of Quercetin and Hyperoside As Senolytics in Adult Human Endothelial Cells”, Hwang et al 2017

“Investigation of quercetin and hyperoside as senolytics in adult human endothelial cells”⁠, HyunTae V. Hwang, Darlene Thuy Tran, Michelle Nicole Rebuffatti, Chin-Shang Li, Anne A. Knowlton (2017-12-13; similar):

Quercetin has been reported to act as a senolytic by selectively removing senescent endothelial cells, and thus it would seem quercetin could revolutionize the field of gerontology. However, given quercetin’s narrow therapeutic index reported in work done with human umbilical vein endothelial cells (HUVECs), we hypothesized that quercetin is not innocuous for non-senescent adult human vascular endothelial cells at concentrations that have been reported to be safe for proliferating HUVECs. Furthermore, we investigated quercetin 3-D-galactoside (Q3G; hyperoside), an inactive quercetin derivative that needs to be cleaved by beta-galactosidase overexpressed in senescent cells to release quercetin, as a potential safer senolytic. We compared the effectiveness of quercetin and Q3G in primary human coronary artery endothelial cells (HCAEC), which are adult microvascular cells. We found that quercetin caused cell death in non-senescent endothelial cells at a concentration that has been reported to selectively remove senescent cells, and that Q3G was not cytotoxic to either young or senescent cells. Thus, in primary adult human endothelial cells, quercetin and Q3G are not senolytics. Earlier work reporting positive results was done with HUVECs, and given their origin and the disparate findings from the current study, these may not be the best cells for evaluating potential senolytics in clinically relevant endothelial cells.

New and noteworthy:

Previously, quercetin has been reported to be a senolytic, a drug that selectively removes senescent cells, in HUVECs. However, we found neither quercetin nor Q3G was effective as a senolytic for adult human endothelial cells.

“Targeting Cellular Senescence Prevents Age-related Bone Loss in Mice”, Farr et al 2017

“Targeting cellular senescence prevents age-related bone loss in mice”⁠, Joshua N. Farr, Ming Xu, Megan M. Weivoda, David G. Monroe, Daniel G. Fraser, Jennifer L. Onken, Brittany A. Negley et al (2017; similar):

Aging is associated with increased cellular senescence, which is hypothesized to drive the eventual development of multiple comorbidities. Here we investigate a role for senescent cells in age-related bone loss through multiple approaches. In particular, we used either genetic (ie. the INK-ATTAC ‘suicide’ transgene encoding an inducible caspase 8 expressed specifically in senescent cells) or pharmacological (ie. ‘senolytic’ compounds) means to eliminate senescent cells. We also inhibited the production of the proinflammatory secretome of senescent cells using a JAK inhibitor (JAKi). In aged (20- to 22-month-old) mice with established bone loss, activation of the INK-ATTAC caspase 8 in senescent cells or treatment with senolytics or the JAKi for 2–4 months resulted in higher bone mass and strength and better bone microarchitecture than in vehicle-treated mice. The beneficial effects of targeting senescent cells were due to lower bone resorption with either maintained (trabecular) or higher (cortical) bone formation as compared to vehicle-treated mice. In vitro studies demonstrated that senescent-cell conditioned medium impaired osteoblast mineralization and enhanced osteoclast-progenitor survival, leading to increased osteoclastogenesis. Collectively, these data establish a causal role for senescent cells in bone loss with aging, and demonstrate that targeting these cells has both anti-resorptive and anabolic effects on bone. Given that eliminating senescent cells and/​or inhibiting their proinflammatory secretome also improves cardiovascular function, enhances insulin sensitivity, and reduces frailty, targeting this fundamental mechanism to prevent age-related bone loss suggests a novel treatment strategy not only for osteoporosis, but also for multiple age-related comorbidities.

“The Clinical Potential of Senolytic Drugs”, Kirkland et al 2017

“The Clinical Potential of Senolytic Drugs”⁠, James L. Kirkland, Tamara Tchkonia, Yi Zhu, Laura J. Niedernhofer, Paul D. Robbins (2017; similar):

Senolytic drugs are agents that selectively induce apoptosis of senescent cells. These cells accumulate in many tissues with aging and at sites of pathology in multiple chronic diseases. In studies in animals, targeting senescent cells using genetic or pharmacological approaches delays, prevents, or alleviates multiple age-related phenotypes, chronic diseases, geriatric syndromes, and loss of physiological resilience. Among the chronic conditions successfully treated by depleting senescent cells in preclinical studies are frailty, cardiac dysfunction, vascular hyporeactivity and calcification, diabetes mellitus, liver steatosis, osteoporosis, vertebral disk degeneration, pulmonary fibrosis, and radiation-induced damage.

Senolytic agents are being tested in proof-of-concept clinical trials. To do so, new clinical trial paradigms for testing senolytics and other agents that target fundamental aging mechanisms are being developed, because use of long-term endpoints such as lifespan or healthspan is not feasible. These strategies include testing effects on multimorbidity, accelerated aging-like conditions, diseases with localized accumulation of senescent cells, potentially fatal diseases associated with senescent cell accumulation, age-related loss of physiological resilience, and frailty.

If senolytics or other interventions that target fundamental aging processes prove to be effective and safe in clinical trials, they could transform geriatric medicine by enabling prevention or treatment of multiple diseases and functional deficits in parallel, instead of one at a time.

“Naturally Occurring P16(Ink4a)-positive Cells Shorten Healthy Lifespan”, Baker et al 2016

“Naturally occurring p16(Ink4a)-positive cells shorten healthy lifespan”⁠, Darren J. Baker, Bennett G. Childs, Matej Durik, Melinde E. Wijers, Cynthia J. Sieben, Jian Zhong, Rachel A. Saltness et al (2016; backlinks; similar):

Cellular senescence, a stress-induced irreversible growth arrest often characterized by expression of p16(Ink4a) (encoded by the Ink4a/​Arf locus, also known as Cdkn2a) and a distinctive secretory phenotype, prevents the proliferation of preneoplastic cells and has beneficial roles in tissue remodelling during embryogenesis and wound healing. Senescent cells accumulate in various tissues and organs over time, and have been speculated to have a role in ageing. To explore the physiological relevance and consequences of naturally occurring senescent cells, here we use a previously established transgene, INK-ATTAC, to induce apoptosis in p16(Ink4a)-expressing cells of wild-type mice by injection of AP20187 twice a week starting at one year of age. We show that compared to vehicle alone, AP20187 treatment extended median lifespan in both male and female mice of two distinct genetic backgrounds. The clearance of p16(Ink4a)-positive cells delayed tumorigenesis and attenuated age-related deterioration of several organs without apparent side effects, including kidney, heart and fat, where clearance preserved the functionality of glomeruli, cardio-protective KATP channels and adipocytes, respectively. Thus, p16(Ink4a)-positive cells that accumulate during adulthood negatively influence lifespan and promote age-dependent changes in several organs, and their therapeutic removal may be an attractive approach to extend healthy lifespan.

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Cellular senescence