Fight Aging! provides a weekly digest of news and commentary for thousands of subscribers interested in the latest longevity science: progress towards the medical control of aging in order to prevent age-related frailty, suffering, and disease, as well as improvements in the present understanding of what works and what doesn't work when it comes to extending healthy life. Expect to see summaries of recent advances in medical research, news from the scientific community, advocacy and fundraising initiatives to help speed work on the repair and reversal of aging, links to online resources, and much more.
This content is published under the Creative Commons Attribution 4.0 International License. You are encouraged to republish and rewrite it in any way you see fit, the only requirements being that you provide attribution and a link to Fight Aging!
To subscribe or unsubscribe please visit: https://www.fightaging.org/newsletter/
- Evidence for Herpesvirus Infection to be a Significant Cause of Alzheimer's Disease
- Oisin Biotechnologies Produces Impressive Mouse Life Span Data from an Ongoing Study of Senescent Cell Clearance
- Hematopoietic Cells are Impacted by Cellular Senescence in Old Humans
- Thoughts on the Ending Age-Related Diseases Conference
- The Restrictive Political Anarchy of Off-Label Use is Why it Matters Whether or Not Aging is an Accepted FDA Indication
- Juvenescence Announces a Small Molecule Senolytics Joint Venture with Antoxerene
- A First Pass at a Signature of Aging Based on Blood Plasma Proteins
- Trial of mTORC1 Inhibition Improves Immune Function in Older Individuals
- MD2 Blockade to Prevent TLR4 Signaling Reverses Fibrosis in Mice
- Vinculin Upregulation Improves Cardiovascular Health and Extends Life in Flies
- Reviewing Waste Clearance in the Brain via the Glymphatic System
- An Interview with Peter de Keizer of Cleara Biotech
- Physical Activity Correlates with a Reduced Impact of Aging in Later Life
- A Drug Delivery System that Preferentially Targets Senescent Cells
- Enoxacin Modestly Extends Life in Nematodes via Mitochondrial Hormesis
Evidence for Herpesvirus Infection to be a Significant Cause of Alzheimer's Disease
A few recent papers have, collectively, added evidence for persistent viral infection to be a significant contributing cause of Alzheimer's disease. A number of viruses in the herpesvirus family are prevalent in the population but cause few obvious symptoms, such as HSV-1 and cytomegalovirus (CMV). Some of these, particularly CMV, are already under suspicion as being the cause of long-term dysfunction in the immune system. Viral infection is an attractive way to explain why only some of the people who exhibit all of the known risk factors for Alzheimer's disease actually go on to develop the full clinical manifestation of the condition. The proportion of the population with latent infection is high, but not too high: other candidate differentiating factors are a lot less convincing because either the population size is too small, or near everyone has it.
How can viral infections contribute to the development of Alzheimer's disease? The amyloid cascade hypothesis tells us that, in the first early stages of Alzheimer's disease, amyloid-β accumulates in the brain, producing only comparatively minor symptoms of degeneration. In later life, this accumulation reaches a critical point that causes tau protein to alter and form solid neurofibrillary tangles in significant amounts. It is this tau aggregation that causes the lion's share of the damage in the later stages of the condition - though a high enough level of amyloid-β can still be harmful in and of itself. Infection is important because amyloid generation is an innate immune mechanism that evolved to respond to viral infection. Thus infection speeds up the production and aggregation of amyloid-β in the brain, pushing things ever closer to the tipping point into pathology.
Herpes Viruses and Senile Dementia: First Population Evidence for a Causal Link
Authors have recently reported that infection with a different herpes virus, herpes simplex virus type 1 (HSV1), leads to a similarly increased risk of later developing senile dementia (SD). Further, when the authors looked at patients treated aggressively with antiherpetic medications at the time, the relative risk of SD was reduced by a factor of 10. It should be stressed that no investigations were made on subjects already suffering from SD, and that those treated were the few rare cases severely affected by HSV. Nonetheless, antiherpetic medication prevented later SD development in 90% of their study group. These articles provide the first population evidence for a causal link between herpes virus infection and senile dementia.
Multiscale Analysis of Independent Alzheimer's Cohorts Finds Disruption of Molecular, Genetic, and Clinical Networks by Human Herpesvirus
Investigators have long suspected that pathogenic microbes might contribute to the onset and progression of Alzheimer's disease (AD) although definitive evidence has not been presented. Whether such findings represent a causal contribution, or reflect opportunistic passengers of neurodegeneration, is also difficult to resolve. We constructed multiscale networks of the AD-associated virome, integrating genomic, transcriptomic, proteomic, and histopathological data across four brain regions from human post-mortem tissue. We observed increased human herpesvirus 6A (HHV-6A) and human herpesvirus 7 (HHV-7) from subjects with AD compared with controls. These results were replicated in two additional, independent and geographically dispersed cohorts. We observed regulatory relationships linking viral abundance and modulators of APP metabolism.
Alzheimer's Disease-Associated β-Amyloid Is Rapidly Seeded by Herpesviridae to Protect against Brain Infection
Amyloid-β peptide (Aβ) fibrilization and deposition as β-amyloid are hallmarks of Alzheimer's disease (AD) pathology. We recently reported Aβ is an innate immune protein that protects against fungal and bacterial infections. Fibrilization pathways mediate Aβ antimicrobial activities. Thus, infection can seed and dramatically accelerate β-amyloid deposition. Here, we show Aβ oligomers bind herpesvirus surface glycoproteins, accelerating β-amyloid deposition and leading to protective viral entrapment activity in mouse and human neural cell culture infection models against neurotropic herpes simplex virus 1 (HSV1) and human herpesvirus 6A and B. Herpesviridae are linked to AD, but it has been unclear how viruses may induce β-amyloidosis in brain. These data support the notion that Aβ might play a protective role in central nervous system innate immunity, and suggest an AD etiological mechanism in which herpesviridae infection may directly promote Aβ amyloidosis.
Oisin Biotechnologies Produces Impressive Mouse Life Span Data from an Ongoing Study of Senescent Cell Clearance
Oisin Biotechnologies is the company working on what is, to my eyes, the best of the best when it comes to the current crop of senolytic technologies, approaches capable of selectively destroying senescent cells in old tissues. Adding senescent cells to young mice has been shown to produce pathologies of aging, and removal of senescent cells can reverse those pathologies, and also extend life span. It is a very robust and reliable approach, with these observations repeated by numerous different groups using numerous different methodologies of senescent cell destruction.
Most of the current senolytic development programs focus on small molecules, peptides, and the like. These are expensive to adjust, and will be tissue specific in ways that are probably challenging and expensive to alter, where such alteration is possible at all. In comparison, Oisin Biotechnologies builds their treatments atop a programmable suicide gene therapy; they can kill cells based on the presence of any arbitrary protein expressed within those cells. Right now the company is focused on p53 and p16, as these are noteworthy markers of cancerous and senescent cells. As further investigation of cellular senescence improves the understanding of senescent biochemistry, Oisin staff could quickly adapt their approach to target any other potential signal of senescence - or of any other type of cell that is best destroyed rather than left alone. Adaptability is a very valuable characteristic.
The Oisin Biotechnologies staff are currently more than six months in to a long-term mouse life span study, using cohorts in which the gene therapy is deployed against either p16, p53, or both p16 and p53, plus a control group injected with phosphate buffered saline (PBS). The study commenced more than six months ago with mice that were at the time two years (104 weeks) old. When running a life span study, there is a lot to be said for starting with mice that are already old; it saves a lot of time and effort. The mice were randomly put into one of the four treatment groups, and then dosed once a month. As it turns out, the mice in which both p16 and p53 expressing cells are destroyed are doing very well indeed so far, in comparison to their peers. This is quite impressive data, even given the fact that the trial is nowhere near done yet.
The image of study data presented in this post is taken from the Oisin Biotechnologies PDF that accompanies a presentation given at the recent ICSA meeting in Montreal. We should certainly hope to see more of this sort of thing in the years ahead as senolytic technologies improve.
Hematopoietic Cells are Impacted by Cellular Senescence in Old Humans
Hematopoietic stem and progenitor cell populations are responsible for generating immune cells. Their decline is one of the causes of immune failure with age, as the pace at which new immune cells are created falters. There are other equally important issues in immune aging, such as the atrophy of the thymus, where T cells of the adaptive immune system mature, and the accumulation of malfunctioning immune cells in older individuals, but we'll put those to one side for this discussion.
Stem cell decline with aging is a complicated business with many contributing causes, and the relative importance of those causes seems to differ between populations and tissues. Few stem cell populations are very well studied when it comes to asking why exactly it is that they decline in activity with age. Those that are, such as muscle, hematopoietic, and neural populations all seem to be quite different. Muscle stem cells decline in activity but, given the right signals, appear quite ready to go back to work with minimal signs that they are greatly impacted by damage. Hematopoietic stem cells do appear to be more damage-limited, however.
In this open access paper, the authors look at the detrimental impact of cellular senescence on hematopoietic cells, and thus on the immune cells that they produce. Cellular senescence is a reaction to damage or excessive replication; senescent cells cease to replicate, and most such cells self-destruct or are destroyed by the immune system. Some linger, however, and the harmful, inflammatory mix of signals that they generate are implicated as a cause of degenerative aging. Studies in mice show that removing senescent cells improves health and extends life span. There are also populations of cells that show some of the markers and behaviors of senescence, but have yet to be definitively classified as senescent - nothing is simple when it comes to cellular biology. This pseudo-senescence or maybe-senesence may be the case here; more research will determine whether or not this is the case.
Elderly human hematopoietic progenitor cells express cellular senescence markers and are more susceptible to pyroptosis
Aging is associated with an increased prevalence of multiple comorbidities, including infectious and malignant diseases. Many of these disorders are thought to stem from old-age-related immune decline. Increasing efforts to characterize the immune system of elderly people in recent years have revealed that most immunocompetent cell compartments present profound quantitative as well as qualitative impairments. The cause of these impairments can vary, and is often related to the exhaustion of the cells or their functions over time in inflammatory settings.
The majority of mature blood cell compartments need, therefore, to be continuously replenished or replaced, which is the role of hematopoietic progenitor cells (HPCs) and, ultimately, hematopoietic stem cells (HSCs). While the self-renewal and differentiation potential of stem cells, along with their blood cell reconstitution capacity, have long been considered as infinite, increasing evidence indicates that this is not the case. Under conditions of stress, HSCs eventually exhibit several functional defects, including a diminished regenerative and self-renewal potential. Loss of stem cell activity is therefore a likely mechanism of impairment common to many mature cell types, thus representing a central cause of immune-competence decline.
Most studies on HSC aging have been carried out in mouse models, and have highlighted extrinsic and intrinsic factors affecting the function of HSCs. A recent study reveals that loss of autophagy in most HSCs from aged mice causes an activated metabolic state, which is associated with accelerated myeloid differentiation, and impairs HSC self-renewal activity and regenerative potential. In humans, much less information is available on the aged HSCs, due to the limited and challenging access to bone marrow samples of elderly humans, the niche of HSCs. Reduced transplantation success in patients receiving HSCs isolated from older (45 years and above) donor bone marrows indicates that human HSC regenerative capacity also declines with aging.
We performed here a comprehensive study of blood HPCs, as an alternative to bone marrow HSCs, to overcome the constraint of sample availability from elderly adults. Based on phenotypic analyses, in vitro T lymphocyte differentiation assays, and gene expression profiling of circulating HPCs from aged subjects, we demonstrate impaired lymphopoiesis and active cell cycling of HPCs with aging, and provide insights into their functional impairments. Our findings reveal that, while mobilized, elderly HPCs present evidence of cellular senescence and increased cell death by pyroptosis. Reduced telomere length and telomerase activity in old HPCs may affect the properties of their progeny, such as mature T lymphocytes. This pre-senescent profile is characteristic of the multiple intrinsic and extrinsic factors affecting HPCs in elderly individuals and represents a major obstacle in terms of immune reconstitution and efficacy with advanced age.
Thoughts on the Ending Age-Related Diseases Conference
I made the pilgrimage to storied Manhattan last week for the first conference organized by the Life Extension Advocacy Foundation (LEAF), titled Ending Age-Related Diseases. It was well organized, all in all a very professional effort. Congratulations are due to the volunteers who set it all up and kept everything moving smoothly. The attendees were a mix of researchers, entrepreneurs, advocates, interested members of the public, and investors of various stripes - a good mix, one that in the present excitable market environment provoked a great deal of useful networking.
The presentations were recorded and will start to appear online as the LEAF volunteers process them. You should make a point of taking a look when they turn up, particularly the view from the investor side of the house. Investors who are personally interested in the success of a field are very different beasts from the run of the mill individual who mechanically seeks returns. They usually have an interesting perspective on the real world challenges inherent in turning a promising technology into a therapy, and that was the case here. The Fight Aging! audience is perhaps more familiar with the science, and so may find considerations of the business side of the house novel and interesting.
While attending the conference, I had a chance to meet in person a sizable number of people who I have only talked to via email over the past decade or more. I apologize to the apparently equally sizable number of people I didn't have the chance to talk to during the breaks between presentations. Keith Comito of LEAF announced that the organization will be making this a yearly event, so I will endeavor to do better next year. Hopefully at that time I will have more interesting things to say about progress towards rejuvenation therapies at Repair Biotechnologies, and the state of the industry as a whole.
As I see things, this sort of mix of participants is very much needed in order to keep progress underway in our rejuvenation research community. We need a regular stirring up of the everyday patient advocates, the entrepreneurs and employees who build therapies, the scientists who discover new opportunities, and the investors who fund those tasks. Communication and building bridges are hard tasks, and there is ever a tendency to form camps and forget how to travel between them. There is a vast chasm between academia and commercial medical development, and all too many promising foundations for therapy fall in and are never seen again.
Is this because scientists are not doing enough to reach out to entrepreneurs and investors? Is it because there are too few entrepreneurs? That the universities make it too hard to license technologies developed in academia, discouraging investment across the field? That investors and their funds are sitting around waiting to be handed opportunities in a nice, neat package, rather than doing more legwork? I'm inclined to put more blame on the investor community simply because they have the resources to do better and more interesting things. They could work more systematically when it comes to reaching back into the research community to pick up promising work and assemble companies to develop it. Doing so in a robust, organized way will help all parties.
While at the conference, I buttonholed a number of people to espouse what we shall call the Dasatinib Empire concept. At this point in time, I think there is more than sufficient evidence to consider that dasatinib and quercetin in combination is most likely a useful, cheap senolytic treatment - a legitimate rejuvenation therapy that partially clears out the senescent cells that cause age-related disease and dysfunction. A single dose is in the 100 to 200 range, less if one shops cleverly, and one treatment every few years is likely close to the optimal dosage. Human trials, such as that ongoing at Betterhumans, will prove the benefits over the next few years, but it looks very compelling even right now. Dasatinib has side-effects that are very well categorized thanks to the past fifteen years of studies as a cancer therapeutic, and they appear neither onerous nor life-threatening in the senolytic scenario of a single dose once every few years, rather than the sustained dosing of cancer treatment.
Given this, and that dasatinib is a generic pharmaceutical, out of patent protection, why can't someone build a serious non-profit or for-profit effort to deliver dasatinib and quercetin at scale to the tens of millions of older people who would benefit significantly from it? An initiative could finalize the human data currently in progress, and then it would be as much a matter of delivering information as delivering pharmaceuticals: anyone can set forth and obtain dasatinib if they only know how to do it. Doing this at scale would probably entail driving a very large truck through the loophole of off-label use of a generic drug, working to help as many older people as possible, as rapidly as possible, and then weaponizing favorable public opinion to fend off the inevitable attention of the FDA. Indeed, this could be a path to change the regulatory landscape, to force regulators to accept the treatment of aging as a fait accompli. I'd say this is a better, more aggressive, more plausible way to do it than the slow approach of trying to change the FDA from within.
It is the case that FDA officials, as a rule, are strongly opposed to the prospect of widespread off-label use, meaning the physician-ordered use of a treatment for something other than the purposes the FDA has approved. They see their role as protecting the population, and off-label use, while completely legal, is viewed as an end-run around their shield. However, and as I have argued in the past, the FDA is too much of a barrier, too strongly opposed to any and all risk, too unwilling to grant patients any choice in their own lives. The cost of that barrier is higher than the benefit. Why should so many millions of people suffer when the evidence strongly suggests that their suffering could be alleviated to some degree at low cost and little risk? Shouldn't it be their choice?
Manhattan is a wealthy enclave. There are any number of individuals resident in that small section of New York real estate with the wealth, connections, and acumen to make something like the Dasatinib Empire a reality, were they to turn their attention to it for the years it would require. At some point it will become obvious to even those who have not watched the development of our longevity science community that the benefits of early senolytics are large, the costs are low, and there is thus much that might be accomplished in the world by joining up these dots. So I'll keep mentioning this to people. Sooner or later it will happen.
The Restrictive Political Anarchy of Off-Label Use is Why it Matters Whether or Not Aging is an Accepted FDA Indication
Over at the Life Extension Advocacy Foundation (LEAF), an argument is made that we shouldn't be overly concerned about the current unwillingness of the FDA and similar regulatory bodies to recognize the treatment of aging and its causes as a valid indication. What is an indication? The outcome of the present overly burdensome regulatory process is formal approval of the use of a specific medical technology for a specific defined condition or set of symptoms. That condition or set of symptoms is known as an indication. Aging is not currently in the list of recognized conditions. The argument made by LEAF is that there are defined paths for rejuvenation therapies to be approved as treatments for specific age-related diseases. Thus treatments can be developed in principle, and from there the concept of off-label use applies.
Not classing aging as a disease is not a major problem
Aging is a variety of distinct processes, damages, and errors; therefore, simply treating aging in clinical terms is not a viable endpoint. For a clinical trial to be conducted, it requires a verifiable indication, and aging is too general for the FDA and EMA to classify it as a disease. However, the majority of damage repair therapies, if not all, could be developed as therapies for diseases with accepted indications and verifiable endpoints, which should satisfy bodies such as the FDA and EMA. Therefore, whether regulatory agencies perceive aging as a disease or not is of no consequence to the development of rejuvenation biotechnologies that address the aging processes.
Even though classifying aging as a disease is unnecessary, significant reform in the regulatory system is still needed in order to encourage investors and companies to put the time and money into researching and developing rejuvenation therapies. One area in need of reform is the establishment of aging biomarkers, which indicate the repair or removal of age-related damage, as acceptable endpoints for rejuvenation therapies. Studies that use these biomarkers would also need to include long-term follow-up studies to ascertain the effects of a therapy over a longer period of time. Another area where regulatory bodies have struggled is keeping up with the rapid march of technology and medicine. Technologies such as gene therapies have struggled to gain traction due to an antiquated regulatory framework struggling to cope with them. Thankfully, this is also being acknowledged.
Aging not being classified as a disease by the FDA, EMA, etc. is not a major issue; the real need is for policy changes that make developing drugs and therapies that target the aging processes easier and more financially viable. It is good that changes are being made to current frameworks and that progress will almost certainly continue in these areas. Meanwhile, we can continue to support the development of repair-based approaches to aging knowing that such therapies, if they work, will be approved even in the current regulatory landscape.
The counterargument to this proposition is that off-label use at scale is not a given - it is by no means certain that a rejuvenation therapy can be approved for, say, arthritis patients, and then the floodgates immediately open for everyone and anyone to use it for any plausibly connected medical condition. Yes, off-label use, as written into law, says that physicians can prescribe approved therapies for unapproved uses. It is estimated that 20% of medical usage in the US is off-label, but this is something that has arisen slowly and organically over time. There are few good analogues in recent medical history for anything as broadly effective as a rejuvenation therapy, something that can beneficially treat hundreds of named conditions.
Why is this a problem? FDA staff see themselves as the shield that stands between unrestricted use of therapies and the public at large. They are opposed to widespread off-label use, as they see this as an end-run around their shield. This is the justification for preventing patient choice - the usual authoritarian assumption that people have no agency and are not qualified to make their own decisions or order their own affairs. When potential therapies and potential indications are first put in front of the FDA, minimizing the likelihood for off-label use is a topic that will come up. If you, for example, propose to treat only a fraction of the population of patients who have a specific condition, based on some biomarker that might be used to segregate the patient population into smaller groups than is presently the case, then the fact that this will tend to lead to significant off-label use in the rest of the patient population is one of the reasons why such designs can be rejected.
When off-label use rises to a significant level in some other way, the FDA may step in. But this is not a given. There are no hard and fast rules here. It is a political anarchy: FDA bureaucrats want to shut down that off-label use and force more clinical trials on their own terms, one named disease at a time, but there is always too much to do in any given day. On the other side of this are developers, patient advocates, and public opinion. People involved in providing therapies when the FDA has decided that they want to step in risk prosecution, fines, and jail time for their principles if the FDA decides to take a hard line. This is the case whether or not it is accepted by the letter of the law to offer these technologies off-label: the FDA will squeeze the manufacturers and the distributors, not the physicians. Fighting this sort of intervention may will be ruinously expensive, a long-running legal battle with a government agency with far greater resources than any of the other players in the space.
The bottom line is that when senolytics or other early rejuvenation therapies are narrowly approved for specific age-related conditions, that will likely roll right into a sizable battle over off-label use. It seems inevitable that people will try - and why shouldn't they? Does the law serve humanity, or does humanity serve the law? Should we all lie down and die because FDA staff are prissy about their rules? Because of the incentives and the parties involved, it just isn't the case that approval for the first few age-related diseases will immediately enable widespread use, unless the political and public opinion battle immediately goes very poorly for the FDA. Sadly, I don't see why it would: the leadership at the FDA has successfully shut down or held back numerous other avenues for off-label delivery of beneficial treatments over the past decades, over the objections of many well-supported advocacy organizations and the voices of suffering patients.
Juvenescence Announces a Small Molecule Senolytics Joint Venture with Antoxerene
The Ichor Therapeutics contingent present at the Ending Age-Related Diseases conference in New York last week were quite pleased that the timing worked out to allow them to announce during the conference a 10 million investment from Juvenescence into a joint venture with their portfolio company Antoxerene. Antoxerene started as a protein biotechnology infrastructure company, but the staff are now turning that infrastructure to the discovery and development of senolytic compounds, those capable of selective destruction of senescent cells. Antoxerene joins a number of existing companies working on various approaches to this goal: this diversity bodes well for our future health and wellbeing, given that senescent cells are thought to be one of the root causes of aging.
As regular readers will recall, the Juvenescence principals intend their fund to be a sizable and long term player in the commercialization of longevity science. They are quite vocal, and their published materials and comments to date suggest that they are supportive of the SENS model of rejuvenation based on damage repair - which of course has included and advocated senescent cell clearance since day one, long prior to the present growth of interest in this line of research. It is a pity that it took so long for senolytic research to become widely appreciated; from a purely technical viewpoint, meaningful progress could have been made, albeit at much greater cost, twenty years ago or more.
Antoxerene, Inc., a portfolio company of Ichor Therapeutics, Inc., focused on small molecule drug discovery for pathways of aging, announced today the launch of a joint venture with Juvenescence Limited. The joint venture, called FoxBio, Inc., will develop Antoxerene's collection of small molecules that target senescent cells. Juvenescence will provide the initiative 10 million in equity financing and drug development expertise.
"There has been a lot of interest surrounding the therapeutic applications of senolytic drugs - compounds that clear toxic senescent cells - particularly with respect to age-associated disease. As molecular pathways unique to senescent cells have begun to be identified, we can now develop drugs to target these pathways. We are eager to work with the Juvenescence team, whose experience in drug development, technical depth, and visionary leadership will help us to deliver on the immense potential of this field."
CEO of Juvenescence Dr. Bailey said, "this is one of the main focuses of Juvenescence - to modify aging through the clearance of senescent cells. FoxBio plays to both companies' strengths, which is why we are excited about working with the Antoxerene team. We are fascinated with the Antoxerene platform and its ability to discover intriguing compounds in the area of senescence. This is a great fit with Juvenescence's track record in drug development, so FoxBio is a very exciting new company in the area of longevity."
A First Pass at a Signature of Aging Based on Blood Plasma Proteins
Approaches to producing a biomarker of aging based on assessing levels of many proteins in the blood, and how those levels change with aging, are under development by a number of research groups. This paper should be considered a demonstration of methodology only, as a great deal of further work would be required to show that the relationships discovered here also apply across broader human populations. Still, it seems likely that proteomic analogies to the epigenetic clocks developed in recent years do in fact exist.
The challenge with all of these biomarkers and potential biomarkers is to connect them to the underlying causes of aging. If the end result of a test is just a number that represents how far removed one is from the average result across the population at a given age, then what action should be taken when that result shows a higher rather than lower physiological age? Presently there is no good answer to that question, and therein lies the problem.
Despite its importance for health, most epidemiological research considers aging merely as a confounder, a nuance dimension to be accounted for and then discarded, under the assumption that aging is unavoidable and unchangeable. This view is now changed. As the intrinsic biological mechanism of aging is slowly revealed, there is hope that interventions that slow aging and prevent or delay the onset of chronic disease and functional impairments can be discovered.
A critical goal in the field of aging biomarkers is to identify molecular changes that show robust patterns of change with normal aging, with the assumption that departures from this "signature" pattern provide not only information regarding future risk of pathology and functional decline but also clues on compensatory mechanisms by which our organism counteracts the effects of aging. Such a signature could be used both to identify individuals in the trajectory of accelerated aging and to track the effectiveness of interventions designed to slowdown biological aging.
The "epigenetic clock," a biomarker index that combines weighted information of a subset of DNA methylation sites raised great interest because it is strongly associated with chronological age and predicts multiple health outcomes, including cardiovascular disease, cancer, and mortality. These findings suggest that aging is associated with stereotyped and reproducible molecular changes that can potentially be used to identify individuals who are aging faster or slower than the average population. However, the underpinnings of these molecular changes have not been fully elucidated, at least in part because the effect of methylation on DNA function remains unclear.
A promising alternative to current methods may be to construct a similar aging biomarker clock based on circulating proteins. Proteins are attractive because they directly affect phenotypes and provide direct information on biological pathways that can be involved in many of the physiological and pathological manifestations of aging. We conducted proteomic analyses that measured 1,301 proteins in 240 adults aged 22-93 years, free of major chronic diseases, cognitive, and functional impairment. The goal was to identify proteins associated with chronological age avoiding as much as possible the effect of clinically detectable disease, examine their association with several clinical characteristics, and further compare our results to previous proteomic profile analyses that used the same technology.
We found 197 proteins were positively associated, and 20 proteins were negatively associated with age. The functional pathways enriched in the 217 age-associated proteins included blood coagulation, chemokine and inflammatory pathways, axon guidance, peptidase activity, and apoptosis. We created a proteomic signature of age based on relative concentrations of 76 proteins that highly correlated with chronological age. However, the generalizability of our findings needs replication in an independent cohort.
Trial of mTORC1 Inhibition Improves Immune Function in Older Individuals
Inhibitors of mechanistic target of rapamycin (mTOR) are arguably the most reliable of the current crop of compounds that slow aging by targeting stress response mechanisms, improving cellular health and resilience to some degree. The observed gain in life span in mice and lower species is likely to be much larger than the outcome achieved in longer-lived species such as our own, as that is unfortunately just the way things work for this class of approach to aging. Short-lived species evolved to have far greater plasticity of longevity in response to environmental circumstances.
The health benefits in old humans that can be obtained using mTOR inhibitors may well still be broad and sizable in comparison to most currently available medical technology for the treatment of age-related disease, but this is as much a suggestion that present technologies are not all that good, as it is a reflection of the utility of mTOR inhibitors. It seems likely that they won't hold a candle to approaches that are based on repair of underlying damage, such as those of the SENS portfolio.
The core challenge in developing therapies based on inhibition of mTOR is that mTOR forms two complexes, mTORC1 and mTORC2. These complexes have quite different roles in our cellular biochemistry; the unwanted side-effects of rapamycin stem from its inhibition of both complexes. Ideally, inhibiting mTORC1 but not mTORC2 is the way to go, but it has taken some years for drug candidates capable of this feat to be identified and progress through a development program. Here, one of these programs reports success in a human trial that targeted immune function in older individuals - and if you like the sound of the results here, just imagine how much more could be achieved through actually repairing the causes of immune failure with aging.
resTORbio today announced newly published data from a Phase 2a clinical trial demonstrating that target of rapamycin complex 1 (TORC1) inhibitor treatment improved immune function and decreased incidence of all infections, including respiratory tract infections (RTIs), in people aged 65 years and older. RTIs in particular are a significant health risk for the elderly with life-threatening consequences and few treatment options.
"Inhibition of TORC1 has extended both lifespan and healthspan in multiple pre-clinical species. The results of this Phase 2a trial raise the possibility that TORC1 inhibition also has health benefits in older humans. In the Phase 2a trial, TORC1 inhibitor treatment was associated with a clinically meaningful reduction in the incidence of infections in people aged 65 years and older and an enhancement in the function of the aging immune system as assessed by influenza vaccination response and antiviral gene expression. The results need to be validated in additional clinical trials, but may have broad implications for the treatment of diseases of aging that we are actively investigating with our TORC1 inhibitor program."
The data for this publication were gathered in a randomized, double-blinded, placebo-controlled Phase 2a study of 264 elderly volunteers at least 65 years of age without unstable medical conditions. Subjects were treated for 6 weeks with study drug and after a 2-week drug-free interval, were given a seasonal influenza vaccine. The incidence of infections was assessed for one year after initiation of study drug treatment. In the RTB101 monotherapy and RTB101+everolimus combination treatment arms, statistically significant and clinically meaningful reductions in the annual rate of infections of 33% and 38%, respectively, compared to placebo, were observed.
MD2 Blockade to Prevent TLR4 Signaling Reverses Fibrosis in Mice
Researchers appear to have found a novel way to sabotage fibrosis, the condition in which regenerative processes run awry with age and cells begin building scar-like structures that disrupt normal tissue function. The approach involves blocking TLR4 signaling. Fibrosis is a feature of the decline of many organs; liver, lung, kidney, heart, and so forth. If it can be turned off comparatively simply, that would produce noteworthy gains for the health of older individuals, even when the underlying causes of regenerative disarray are not addressed. The question is always whether or not there is a good way to interfere without also altering other important cellular processes, of course.
An interesting broader context for this TLR4 signaling inhibition is the growing evidence that suggests senescent cells to be a significant contributing cause of fibrosis. Senescent cells secrete a great many disruptive, inflammatory signal molecules, and that changes the behavior of surrounding cells, usually for the worse when that signaling persists for a long time. It may or may not be the case that senescent cells directly cause increased TLR4 signaling, but it is worthy of note that TLR4 deficient mice exhibit a reduced level of cellular senescence than their peers. There are some dots yet to be joined here.
Fibrosis, the hallmark of systemic sclerosis (SSc), is characterized by excessive production and persistent accumulation of collagens and other extracellular matrix (ECM) molecules in skin, lungs, and other internal organs. The process underlies a large number of fibrotic diseases that, in aggregate, account for a considerable proportion of deaths worldwide. With no effective therapy to date, fibrosis therefore represents a significant unmet global health need.
TLRs and related pattern-recognition receptors represent the first line of host defense against microbial pathogens. Cell surface receptors such as TLR4 and endosomal receptors such as TLR3 recognize extrinsic pathogen-associated molecule patterns (PAMPs) such as LPS and virus-derived nucleic acids. Significantly, TLRs also recognize damage-associated molecule patterns (DAMPs) that arise endogenously during various forms of noninfectious tissue injury. Regulated PAMP sensing by TLR4 has a unique requirement of myeloid differentiation 2 (MD2), an accessory receptor that interacts with TLR4 to form the signaling-competent receptor. The requirement for MD2 as an accessory pattern-recognition receptor for PAMPs appears to be unique for TLR4.
We recently demonstrated that particular DAMPs are markedly upregulated in fibrotic skin and lungs in patients with SSc and largely colocalize with TLR4-expressing myofibroblasts. In mice, genetic ablation of either of two DAMPs prominently associated with SSc resulted in markedly attenuated skin and lung fibrosis and enhanced fibrosis resolution, suggesting a fundamental pathogenic role for DAMP-TLR4 signaling in driving persistent organ fibrosis.
We developed a small molecule that selectively blocks MD2, which is uniquely required for TLR4 signaling. Targeting MD2/TLR4 abrogated inducible and constitutive myofibroblast transformation and matrix remodeling in fibroblast monolayers, as well as in 3-D scleroderma skin equivalents and human skin explants. Moreover, the selective TLR4 inhibitor prevented organ fibrosis in several preclinical disease models and mouse strains, and it reversed preexisting fibrosis.
Vinculin Upregulation Improves Cardiovascular Health and Extends Life in Flies
Researchers here report on a single gene alteration in fruit flies, increased levels of vinculin, that improves cardiovascular function in later life and increases life span. Effect sizes in flies are much larger than those in humans, where is is possible to directly compare interventions. Short-lived species have evolved to exhibit a far greater plasticity of longevity in response to environmental and genetic changes, at least in those methodologies tested to date. It remains to be seen as to whether the initial hypothesis on the important mechanisms linking vinculin levels to improved health turn out to be correct. Vinculin is involved in common cellular processes that in turn influence many aspects of tissue function. This is frequently the case in studies of slowed aging - finding out exactly how and why it works is a long and arduous process.
Our cells tend to lose their shape as we grow older, contributing to many of the effects we experience as aging. This poses particular problems for the heart, where aging can disrupt the protein network within muscle cells that move blood around the body. Researchers discovered that maintaining high levels of the protein vinculin - which sticks heart muscle cells to one another - confers health benefits to fruit flies. Their work shows that fruit flies bred to produce 50 percent more vinculin enjoyed better cardiovascular health and lived a third of their average life span longer.
Vinculin works at the intercalated disks that glue together heart muscle cells, called cardiomyocytes. As we age, cardiomyocytes make less vinculin. Vinculin organizes the heart's contractile proteins, so as vinculin levels fall our heartbeats become disorganized and less efficient. By breeding flies with complementary genes, researchers created a genetic switch that turned on extra copies of the vinculin-coding gene. To ensure that only cardiomyocytes were producing the protein, the group used the same activation machinery as a heart development gene called Tinman.
While typical fruit flies live for roughly six weeks, flies that made more vinculin survived up to nine weeks. Additionally, flies with a vinculin boost were more active and able to climb the walls of their enclosures, a test of fruit fly athletic ability. Researchers were surprised how much improving cardiac function also helped the flies maintain a healthier metabolism. To measure this improvement, researchers fed the flies a special form of glucose and detected how the flies modified and used the sugar. Flies with more vinculin broke down more glucose than their counterparts. The team concluded higher vinculin levels in the flies' hearts enabled other organs to efficiently get the nutrients they needed in the breakdown process.
Reviewing Waste Clearance in the Brain via the Glymphatic System
Clearance of metabolic waste from the brain via fluid drainage pathways is becoming an important topic in the context of age-related neurodegeneration, as is noted by the authors of this open access review paper. There is good evidence to suggest that drainage of cerebrospinal fluid is a significant path for the removal of wastes, such as the protein aggregates associated with dementia, and that the relevant fluid channels atrophy and fail with age. That decline may well be an important contribution to the development of neurodegenerative disease in later life, and the first efforts to do something about it are now underway. Restoring drainage is the goal of Leucadia Therapeutics, for example, a company that will probably be joined by similar initiatives in the years ahead.
Waste removal from the central nervous system is essential for maintaining brain homeostasis across the lifespan. Two interconnected, dynamic networks were recently uncovered, which may provide new information concerning the conundrum of how the brain manages waste removal in the absence of authentic lymphatic vessels (LVs). The glymphatic system serves as the brain's "front end" waste drainage pathway that includes a perivascular network for cerebrospinal fluid (CSF) transport, which is connected to a downstream authentic lymphatic network associated with the meninges, cranial nerves, and large vessels exiting the skull. The anatomical and functional components of the two systems are complex, and the processes by which they physically interconnect are only partly understood.
The first pioneering studies documented that soluble amyloid beta (Aβ) protein and tau oligomers - metabolic waste products whose buildup is associated with Alzheimer's disease (AD) - were transported from the interstitial fluid (ISF) space and out of the brain via the glymphatic system. This information was followed by another hallmark study reporting that slow wave sleep enhanced glymphatic Aβ clearance from brain when compared to wakefulness. Collectively, this information was met with excitement in the neuroscience and clinical communities because maintaining efficient brain waste drainage across the lifespan - possibly by preserving normal sleep architecture - emerged as a novel therapeutic target for preventing cognitive dysfunction and decline.
The idea of maximizing brain "waste drainage" as a new preventive or therapeutic target for neurodegenerative disease states was further strengthened by animal studies providing evidence of declining glymphatic transport efficiency in healthy aging, AD models, traumatic brain injury, cerebral hemorrhage, and stroke. Considering the novelty of the glymphatic system concept, along with the rapidly emerging literature associating key physiological processes (e.g., vascular pulsatility, and sleep) with glymphatic transport function and waste solute outflow from brain, we decided it was timely to review this information cohesively. Hence, the goal of this mini-review is to provide a broad overview of the current data, controversies, and gaps in knowledge of the glymphatic system and waste drainage from the brain, while addressing potential consequences of aging as well as critically reviewing evidence for its existence in the human brain.
An Interview with Peter de Keizer of Cleara Biotech
The Life Extension Advocacy Foundation volunteers recently published a long and interesting interview with Peter de Keizer, the researcher who led development of the FOXO4-p53 approach to selective destruction of senescent cells. As senescence cells cause aging and age-related disease, there is considerable interest in developing means to remove them, and thus produce rejuvenation. The FOXO4-DRI used in de Keizer's study is probably the best of the current crop of senolytic compounds, as while the degree to which it kills senescent cells is broadly similar to the others, the evidence to date suggests that it produces insignificant side-effects; its method of action is much more localized to senescent cells. A company, Cleara Biotech, has been funded to develop this research into a commercial therapy.
It doesn't seem like as many people in Europe talk about aging as in the U.S. Is being in Europe instead of the U.S. better or worse for your research?
As usual, the U.S. innovates, China imitates, and Europe hesitates. I returned to Europe for personal reasons, but I have been talking to American investors who want to explore Europe a bit more, and there are possibilities. People here do acknowledge aging as a problem, and the Undoing Aging conference in Berlin was a success. The downside with Silicon Valley is that there are big budgets and a great spirit, but we also need a style of research, which is, in every city, a little bit different. In Europe, the focus is very much molecular. I would like to combine the great vision and budget of Silicon Valley with European quality and maybe a bit of skepticism. We never publish anything unless we are really convinced. In that sense, I like Europe because people are interested in aging here; you just have to talk to the right people, and many people are skeptical. When I talk to scientists about what we do, they also get excited.
Are the regulations regarding trials more stringent than in the U.S.?
Yes, that's true, especially for animal work. There's a lot of societal pressure not to do animal work. We have to deal with these hurdles, but there's good money in science here, certainly in Western Europe, and we can make do quite well. This is generalizing, but we tend to talk less and do more.
Would you say that a potential side effect of the drug, if not used at the proper dose, could be excessive lysis?
The honest answer is "We don't know." I've seen in mice that you can go too far; if you look at the cell data, it's tenfold more potent against senescent cells. That sounds like a lot, but if you want to treat relatively healthy people with this, if one in ten cells that will be destroyed is basically a healthy cell, I find it very risky. So, you need to have a perfect dose or a perfect range.
With mice, we could scale it and we could say if it's too much or not, but for humans, it's more difficult. What we're doing now is trying to optimize this to make it tenfold more selective. This is version 4, and the published paper is on version 3; the first two were generated in the US in 2012, and they were not so effective. The first step was very short and had a very poor solubility, the second step lasted much longer, and the third peptide we made in D-amino acid is the one we published now. Now, we're making the fourth one because we know where the critical amino acids and the non-important and important ones are in the interaction domain of the two proteins, FOXO4 and p53. We plan on giving number 4 to a team of drug development experts to get it to a hundredfold selectivity, and then it should be much safer for use.
How long would you say it's going to be for this safe version four to be optimal?
That's the fun part. It took me ten years to come to this third version because in academia, we always have 20 other things that are also interesting. Now, we actually teamed up with a company, Cleara, that we founded just recently. The team has 20 people, with 10 structural experts, and they're going crazy on this. Every week, we have a meeting at which they have made some more progress, and it is super fast. We gave ourselves four months for a library screen on the first version, and then it's another ten rounds of optimizations. Once we have a lead candidate, we will start doing all the things that academia never wants to look at, like a liver update and all the stuff that scientists aren't interested in but is important to have. I want to do ten rounds of that, and it's three weeks per round, then we'll know roughly where the weak spots are in our current version, and we can go back and add heavy metal toxicity, etc. We gave ourselves a year for optimization, but I hope sooner.
How well does this treatment compare to other treatment options, such as fasting?
With fasting, you don't kill, you just delay the secretions from senescent cells. It's like rapamycin and aspirin; it just blocks the secretion profile. Fasting offers a transient benefit for sure, but a week later, you eat again, and they're just there again. It's just making them dormant. We have not seen evidence that senescent cells are removed by fasting, in mice or in cells.
Have you looked at other senolytics?
We tried a lot, and the BCL inhibitors look the most promising. What we saw when comparing them to FOXO4-DRI is that they are toxic at low levels and should not be given to healthy people. That's the downside of these drugs. In vitro, if you do low-level navitoclax on healthy cells, you get 10, 20 percent cell death. That's relatively stable. That's a decrease in viability because you're affecting some cells that are apparently sensitive to BCL inhibition. We did not see that with FOXO4, and that's what's reported in our paper. As for quercetin and dasatinib, I'm absolutely not a fan of those. We've tried a couple of experiments; we've never seen a good result.
How often do you think people would need senolytic treatments, will they be for older or younger people?
In mice, over a year; we did it once a month. It seemed to be enough, and I think we can actually reduce that frequency. But, I still have to do the experiment. If we do it once in a while, once every three months, once every half a year in mice, it might actually be sufficient. I don't think they accumulate that fast. Maybe later in life, you'll do it a bit faster. Early in life, there's really no reason to do it so often. It's like a car. If it's only a couple of years old, you don't go to the mechanic as often.
Physical Activity Correlates with a Reduced Impact of Aging in Later Life
The open access study noted here is one of many to show that greater levels of physical activity correlate well with a reduced risk of age-related disease. It isn't possibly to reliably live to extreme old age on the back of a good exercise program, but that physical activity does reliably improve the odds of experiencing better rather than worse health in later life. Even small benefits can be worth chasing when they cost little and are reliably obtained, so long as that pursuit doesn't distract from far more important initiatives. Exercise is beneficial, but it is no substitute for the rejuvenation therapies presently under development.
Successful aging has been defined as not suffering from chronic diseases, having optimal social engagement and mental health, and a lack of physical disability. Numerous studies have found that physical activity decreases the risk of many chronic diseases and increases longevity. However, the association between physical activity and successful aging has shown heterogeneity across studies. Some studies have shown either a lack of or a weak independent association between physical activity and successful aging; however, other cohort studies as well as systematic reviews have shown that higher levels of physical activity was associated with aging successfully.
Therefore, in our cohort study of 1,584 adults aged 49+ years at baseline we aimed to investigate whether total physical activity is independently associated with successful aging, which was defined as not experiencing disability and chronic disease (coronary artery disease, stroke, diabetes, cancer), having good mental health and functional independence, and reporting optimal physical, respiratory, and cognitive function during 10 years of follow-up. Participants provided information on the performance of moderate or vigorous activities and walking exercise and this was used to determine total metabolic equivalents (METs) minutes of activity per week.
Of the cohort, 249 (15.7%) participants had aged successfully 10 years later. Older adults in the highest level of total physical activity (more than 5000 MET minutes/week; n = 71) compared to those in the lowest level of total physical activity (less than 1000 MET minutes/week; n = 934) had 2-fold greater odds of aging successfully than normal aging. Our finding of a positive association between physical activity levels and successful aging is in agreement with the existing literature showing that physical activity might be an important parameter in enabling people to age successfully. Moreover, a systematic review found that the effect sizes for the association of successful or healthy aging with high levels of physical activity ranged from 1.27 to 3.09, which is in line with our observed estimate.
A Drug Delivery System that Preferentially Targets Senescent Cells
Senescent cells are thought to be one of the root causes of aging, and there is a sizable amount of evidence to back this view. The approach of removing senescent cells in order to turn back aspects of aging and extend life has been quite comprehensively demonstrated in mice, and a growing number of companies are now developing therapies for human medicine. In that context, this paper outlines what seems a promising line of work, a delivery system that is claimed to preferentially target senescent cells based on their distinctive biochemistry. The question, as is always the case, is the degree to which the delivery system prefers senescent cells in practice.
Present senolytics, therapies capable of destroying senescent cells, kill senescence cells versus normal cells at a ratio somewhere in the range of 3:1 to 12:1. The compounds that destroy more non-senescent cells tend to be those with worse side effects, for all the obvious reasons. These compounds and their side effects set a low bar, and they can certainly be improved upon. A reliable, selective delivery method should make it that much easier for the development community to engineer significant improvement.
Upon persistent damage or during aging, senescent cells accumulate, probably due to an inefficient clearance by immune cells, and this accumulation may lead to chronic inflammation and fibrosis. Indeed, evidence in mice indicates that the accumulation of senescent cells actively contributes to multiple diseases and aging. In this regard, genetic ablation of senescent cells delays and ameliorates some aging-associated diseases, reverts long-term degenerative processes associated with chemotherapy, and extends longevity. Importantly, senescent cells present vulnerabilities to particular small molecule inhibitors, known as "senolytics", that trigger apoptosis preferentially in senescent cells. These pharmacological treatments reduce the number of senescent cells in vivo and show therapeutic activity against senescence-associated diseases and aging.
Senescent cells in vitro are characterized by high levels of lysosomal β-galactosidase activity, known as senescence-associated β-galactosidase. In addition to β-galactosidase, senescent cells present high levels of most tested lysosomal hydrolases. Indeed, senescent cells show a remarkable accumulation of lysosomes, together with abnormal endosomal traffic and autophagy. Interestingly, damaged or diseased tissues generally contain cells that are positive for SAβGal, while normal healthy tissues are negative for this marker.
Here, we have explored the possibility of using lysosomal β-galactosidase as a vulnerable trait of senescent cells that can be exploited to deliver tracers or drugs preferentially to diseased tissues with high content of senescent cells. Our approach is based on the encapsulation of diagnostic or therapeutic agents with β(1,4)-galacto-oligosaccharides and their delivery to lysosomes via endocytosis. In a model of chemotherapy-induced senescence, encapsulated cytotoxic drugs target senescent tumor cells. Moreover, in a model of pulmonary fibrosis in mice, encapsulated cytotoxics target senescent cells, reducing collagen deposition and restoring pulmonary function. Finally, encapsulation reduces the toxic side effects of the cytotoxic drugs. Drug delivery into senescent cells opens new diagnostic and therapeutic applications for senescence-associated disorders.
Enoxacin Modestly Extends Life in Nematodes via Mitochondrial Hormesis
Many methods demonstrated to slow aging in short-lived species, such as the nematode worm Caenorhabditis elegans, involve hormesis. This is the induction of mild cellular stress and damage, through heat, or lack of nutrients, or raised levels of oxidative molecules generated by mitochondria, that leads to an enhanced cellular maintenance response. The net result is a gain in health and tissue function. The open access paper here discusses some of the known hormetic mechanisms in nematodes, those involving alterations in mitochondrial function, and illustrates one of many methods of triggering mitochondrial hormesis in that species. The degree to which longevity is enhanced in this case is not large at all when considering the plasticity of life span in nematodes; life spans in this species have been extended by a factor of ten by some research groups. Sadly, we know that these approaches have nowhere near the same outcome in mammals.
Alterations in microRNA (miRNA) processing have been previously linked to aging. Here we used the small molecule enoxacin to pharmacologically interfere with miRNA biogenesis and study how it affects aging in C. elegans. Enoxacin extended worm lifespan and promoted survival under normal and oxidative stress conditions. Enoxacin-induced longevity required the transcription factor SKN-1/Nrf2 and was blunted by the antioxidant N-acetyl-cysteine, suggesting a prooxidant-mediated mitohormetic response. The longevity effects of enoxacin were also dependent on the miRNA pathway, consistent with changes in miRNA expression elicited by the drug. Among these differentially expressed miRNAs, the widely conserved miR-34-5p was found to play an important role in enoxacin-mediated longevity.
And how does miR-34-5p down-regulation affect lifespan? Mir-34 has been previously associated with lifespan and the onset of age-related diseases in model organisms, but the directionality and the mechanisms underlying its effects have been a matter of debate. A previous study demonstrated that mir-34 loss-of-function significantly extends lifespan through activation of autophagy, but other studies did not see an effect on survival or even found the opposite. Here we show that both enoxacin and mir-34 loss-of-function extend lifespan via a mechanism that requires a prooxidative effect. Different types of food (e.g., dead bacteria here versus live bacteria in the previous studies) and slightly different experimental conditions could have created different thresholds of sensitivity to prooxidant agents or a different redox balance which in turn could explain the apparent discrepancies in reports associating mir-34 with longevity.
Sub-lethal levels of mitochondrial reactive oxygen species (ROS) are usually associated with beneficial effects and lifespan extension, while elevated ROS can be toxic - a phenomenon often referred to as mitohormesis. Mitochondrial ROS requires the transcription factor SKN-1/Nrf2 to increase lifespan and confer their beneficial effects, and so does enoxacin. Together, these results indicate that enoxacin promotes non-toxic levels of ROS through inhibition of miR-34-5p, which in turn activates stress response pathways mediated by SKN-1 and autophagy. In addition to its beneficial outcomes, there is a toxic effect caused by enoxacin treatment. Consistent with this notion, enoxacin-mediated miR-34-5p inhibition confers a lesser lifespan extension than deletion of the mir-34 gene.