The Lack of Funding for Chronic Kidney Disease Research is Not an Outlier

In this commentary, scientists note the paucity of funding for chronic kidney disease research, given the widespread suffering and death caused by this presently incurable condition. This and many other areas of medicine are seen as solved problems by the powers that be simply because there is some form of treatment, even palliative treatment, in widespread use. That the treatment does little and many people die doesn't appear to motivate those who could fund progress. There is no sense of urgency and little sense of need. We might make the same comments in the case of atherosclerosis, a condition many consider to be adequately treated and under control, due to the existence of statins and similar drugs that lower LDL cholesterol in the bloodstream, despite the fact that these treatments only somewhat reduce mortality, and that atherosclerosis still kills 27% of our species at the present time. We could indeed make much the same argument for many other primarily age-related conditions.

The uptake of the current concept of chronic kidney disease (CKD) by the public, physicians and health authorities is low. Physicians still mix up CKD with chronic kidney insufficiency or kidney failure. In a recent manuscript, only 23% of participants in a cohort of persons with CKD had been diagnosed by their physicians as having CKD while 29% has a diagnosis of cancer and 82% had a diagnosis of hypertension. For the wider public and health authorities, CKD evokes kidney replacement therapy (KRT). In Spain, the prevalence of KRT is 0.13%.

A prevalent view is that for those in whom kidneys fail, the problem is "solved" by dialysis or kidney transplantation. However, the main burden of CKD is accelerated aging and all-cause and cardiovascular premature death. CKD is the most prevalent risk factor for lethal COVID-19 and the factor that most increases the risk of death in COVID-19, after old age. Moreover, men and women undergoing KRT still have an annual mortality which is 10-100-fold higher than similar age peers, and life expectancy is shortened by around 40 years for young persons on dialysis and by 15 years for young persons with a functioning kidney graft. CKD is expected to become the fifth global cause of death by 2040 and the second cause of death in Spain before the end of the century, a time when 1 in 4 Spaniards will have CKD.

However, by 2022, CKD will become the only top-15 global predicted cause of death that is not supported by a dedicated well-funded CIBER network research structure in Spain. Leading Spanish kidney researchers aim to prevent the dire predictions for the global 2040 burden of CKD from becoming true. However, only the highest level of research funding through the CIBER will allow to adequately address the issue before it is too late.

Link: https://doi.org/10.1016/j.nefro.2021.09.004

Heart Rate Variability, Aging, and Cardiovascular Fitness

Heart rate variability is an increasingly popular measure of cardiovascular health. Heart rate variability is known to decline with age, but to what degree is this a reflection of processes of cardiovascular aging versus the loss of physical fitness that is a feature of old age in our present, overly sedentary societies? This remains an open question, and an important one, given the range of evidence for exercise programs, and thus increased physical fitness, to be as effective as many medical interventions when it comes to improving cardiovascular health and reducing mortality in later life. Yes, aging causes an inevitable decline in physical condition, but living a sedentary lifestyle certainly speeds up that process.

Fluctuation analysis in intervals between heartbeats provides important indices related to autonomic modulation of heart rate variability (HRV). These indices are considered predictors of morbidity and mortality as they are frequently altered in patients with chronic degenerative diseases, especially in those with cardiovascular and metabolic diseases. Similarly, a reduction in HRV is common with aging. In all cases, cardiovascular fitness is often reduced to below the predicted values.

In turn, increases in cardiovascular fitness through regular physical exercise, especially aerobic exercise, represent an important therapeutic tool capable of promoting positive adjustments in cardiac autonomic modulation. These adjustments are characterized by reduced sympathetic modulatory influence and/or increased vagal modulatory influence on the heart, increasing the HRV. Therefore, several methodological tools have been used to assess the degree of impairment of autonomic modulation and the therapeutic effects of physical exercise.

In summary, there is a close relationship between cardiovascular fitness and HRV. This relationship was more evident in patients with cardiovascular and metabolic diseases and in aging, especially in those whose cardiovascular fitness and HRV were below the predicted values for age and sex. The challenge is to develop techniques and interpretation of increasingly accurate data, as well as standardizing the application of these techniques.

Link: https://doi.org/10.2147/VHRM.S279322

Senolytic Treatment Minimizes the Contribution of Excess Fat Tissue to Insulin Resistance in Mice

Senescent cells accumulate with age throughout the body, and contribute directly to the onset and progression of a wide range of age-related conditions. While never present in large numbers in comparison to normal somatic cells, senescent cells are metabolically active, secreting signals that provoke chronic inflammation, altered cell behavior, and numerous forms of tissue dysfunction. Senolytic therapies selectively target senescent cells for destruction, most by forcing these errant cells into the programmed cell death process of apoptosis. Senescent cells are primed to self-destruct, and suppressing anti-apoptosis mechanisms for a time can push them over the edge while leaving normal cells largely unaffected.

In recent years, researchers have shown that many of the detrimental effects of excess visceral fat tissue are mediated by the presence of senescent cells in that fat tissue. This isn't just age-related: excess visceral fat generates senescent cells even in youth, but it does become worse with age. Thus eliminating senescent cells on a periodic basis via the use of senolytic therapies may allow for some decoupling of excess visceral fat from poor health and accelerated aging. One of the more prominent consequences of gaining too much fat tissue is the onset of type 2 diabetes, a condition that can be reversed even at a comparatively late stage by low-calorie diets leading to weight loss. Senescent cells appear to play an important role here, causing the death and dysfunction of islet cells in the pancreas, cells that are necessary for the correct function of insulin metabolism.

Researchers here demonstrate that eliminating senescent cells in fat tissue causes a sizable improvement in the manifestations of type 2 diabetes in mice. This isn't the first time that results of this sort have been produced by the scientific community, and the data here can be added to that from similar studies conducted in last few years. Since most of these studies used the readily available senolytic treatment of dasatinib and quercetin, presently in human trials for other conditions, it is perhaps surprising to see little movement towards off-label use in humans, given the considerable size of the diabetic patient community.

Deleting Dysfunctional Cells Alleviates Diabetes

The cells in your body are constantly renewing themselves, with older cells aging and dying as new ones are being born. But sometimes that process goes awry. Occasionally damaged cells linger. Called senescent cells, they hang around, acting as a bad influence on other cells nearby. Their bad influence changes how the neighboring cells handle sugars or proteins and so causes metabolic problems. Type 2 diabetes is the most common metabolic disease in the US. Most people with diabetes have insulin resistance, which is associated with obesity, lack of exercise, and poor diet. But it also has a lot to do with senescent cells in people's body fat, according to new findings. And clearing away those senescent cells seems to stop diabetic behavior in obese mice.

Alleviating the negative effects of fat on metabolism was a dramatic result, the researchers said. If a therapy worked that well in humans, it would be a game-changing treatment for diabetes. Researchers tested the efficacy of a combination of experimental drugs, dasatinib and quercetin. Dasatinib and quercetin had already been shown to extend lifespan and good health in aged mice. In this study, they found these drugs can kill senescent cells from cultures of human fat tissue. The tissue was donated by individuals with obesity who were known to have metabolic troubles. Without treatment, the human fat tissues induced metabolic problems in immune-deficient mice. After treatment with dasatinib and quercetin, the harmful effects of the fat tissue were almost eliminated.

Targeting p21Cip1 highly expressing cells in adipose tissue alleviates insulin resistance in obesity

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 plus quercetin, eliminates p21high cells in human fat ex vivo and mitigates insulin resistance following xenotransplantation into immunodeficient mice. Our findings lay the foundation for pursuing the targeting of p21high cells as a new therapy to alleviate insulin resistance.

Oral Bacteria and Age-Related Airway Inflammation

Researchers have in the past proposed links between oral bacteria and chronic inflammation, particularly in the heart and brain, proposing that bacterial toxins and bacteria themselves enter the bloodstream via damaged gums. This undoubtedly happens, but supporting data is mixed when it comes to the question of whether or not this has a meaningful effect size in comparison to other inflammatory mechanisms and contributions to age-related disease. Here, a different route for bacteria is proposed: passage into the airways and lungs, a possibly explanation as why gum disease and respiratory mortality are correlated in older patients.

The global population is aging, and elderly people have a higher incidence of lower airway diseases owing to decline in swallowing function, airway ciliary motility, and overall immunity associated with aging. Furthermore, lower airway diseases in the elderly tend to have a high mortality rate. Their prevention is important for extending healthy life expectancy and improving the quality of life of each individual.

In recent years, the relationship between chronic periodontitis and oral bacteria, especially the periodontopathic ones, and respiratory diseases (e.g., pneumonia, chronic obstructive pulmonary disease, and influenza) has become clear. In addition, the association of several periodontal pathogens with the onset and aggravation of coronavirus disease 2019 (COVID-19) is also being reported. The oral cavity is the entry point for bacteria and viruses to enter the body, and it is also the entrance to the lower airway, including the bronchi and lungs, in which inflammation occurs during lower airway diseases. Therefore, if aspiration of oral bacteria has an adverse effect on lower airway diseases, it is not difficult to imagine such an effect.

In support of these findings, oral health management has shown to reduce deaths from pneumonia and prevent influenza in nursing homes and inpatient wards. This has led to clinical and multidisciplinary cooperation between physicians and dentists, among others. However, to date, the mechanisms by which chronic periodontitis and oral bacteria contribute to lower airway diseases have not been well understood. Clarifying these mechanisms will lead to a theoretical basis for answering the question, "Why is oral health management effective in preventing lower airway diseases?"

Link: https://doi.org/10.1016/j.jdsr.2021.10.003

Tongue Exercise Does Not Help with the Age-Related Decline of Tongue Muscle Function in Rats

Exercise in the form of strength training creates such broad changes in metabolism and produces such diverse benefits to health that it is interesting to see a specific example in which it doesn't help at all. That is possibly a path to better understanding which of the results of exercise are important, versus which are not, when it comes to functional improvement of specific tissues in later life. Many of the benefit of exercise are likely secondary effects produced by changes in skeletal muscle metabolism and myokine signaling on other parts of the body. Those effects will be largely absent in a study such as this, where only one small set of muscles are trained.

Exercise-based treatment approaches for dysphagia may improve swallow function in part by inducing adaptive changes to muscles involved in swallowing. We have previously shown that both aging and progressive resistance tongue exercise, in a rat model, can induce biological changes in the genioglossus (GG); a muscle that elevates and protrudes the tongue. However, the impacts of progressive resistance tongue exercise on the retrusive muscles (styloglossus, SG; hyoglossus, HG) of the tongue are unknown. The purpose of this study was to examine the impact of a progressive resistance tongue exercise regimen on the retrusive tongue musculature in the context of aging. Given that aging alters retrusive tongue muscles to more slowly contracting fiber types, we hypothesized that these biological changes may be mitigated by tongue exercise.

Hyoglossus (HG) and styloglossus (SG) muscles of male rats were assayed in age groups of young (9 months old, n = 24), middle-aged (24 months old, n = 23), and old (32 months old, n = 26), after receiving an 8-week period of either progressive resistance protrusive tongue exercise, or sham exercise conditions. Following exercise, HG and SG tongue muscle contractile properties were assessed in vivo. HG and SG muscles were then isolated and assayed to determine myosin heavy chain isoform (MyHC) composition.

Both retrusive tongue muscle contractile properties and MyHC profiles of the HG and SG muscles were significantly impacted by age, but were not significantly impacted by tongue exercise. Old rats had significantly longer retrusive tongue contraction times and longer decay times than young rats. Additionally, HG and SG muscles showed significant MyHC profile changes with age, in that old groups had slower MyHC profiles as compared to young groups. However, the exercise condition did not induce significant effects in any of the biological outcome measures.

Link: https://doi.org/10.3389/fphys.2021.740876

Like Elephants, Long-Lived Galapagos Tortoises Exhibit Duplication of Genes Related to Longevity and Cancer Suppression

Genes determine species longevity, though within a species, and particularly within our species, the estimated involvement of genetic variants in individual life expectancy is becoming ever smaller as ever more data accumulates. Nonetheless, researchers are very interested in the comparative biology of aging, the question of why long-lived species are long-lived in comparison to their closest relatives. Which of the many evolved differences tend to produce a longer life span?

A longer species life span necessarily requires a lower incidence of cancer. Cancer is a numbers game: a larger body size means that there are more cells that can suffer mutation and become cancerous; a longer life allows more time for those cells to suffer mutation and become cancerous. Thus in larger and longer-lived species there must be mechanisms that either (a) lower the rate at which cancerous mutations can occur, or (b) increase the efficiency of cancer suppression mechanisms. These mechanisms are layered, ranging from those inside cells that provoke self-destruction when damage is identified, to the ability of the immune system to detect and destroy cancerous cells.

Elephants are both large and long-lived, and yet have a lower risk of cancer than is the case for our species. In recent years, researchers identified that elephants have many duplicated copies of the TP53 cancer suppression gene. The protein p53 produced from this gene is involved in DNA repair, as well as induction of cellular senescence and programmed cell death in response to DNA damage. It is thus an important part of cellular responses to potentially cancerous mutations. In today's open access paper, researchers report on their discovery of similar duplications in genes related to longevity and cancer suppression in long-lived Galapagos tortoises, indicating that this sort of evolutionary change is probably commonplace in longer-lived species.

It is interesting to consider that continually upregulating TP53 expression in short-lived mammals such as mice does improve cancer suppression, but also shortens life span, via mechanisms that likely include a reduction in stem cell activity and increase in the burden of cellular senescence. Too much vigilance has its costs. Researchers have worked around this issue, in mice at least, via forms of intermittent upregulation that only operate when TP53 is called upon, or via combining p53 upregulation with telomerase upregulation.

Concurrent evolution of anti-aging gene duplications and cellular phenotypes in long-lived turtles

A recurring theme in lifespan and aging regulation is the critical role played by processes that promote cellular protection and maintenance, including the ability of cells to recycle materials, repair damage, and remove waste. Senescent cells, whose numbers greatly increase with age, exhibit declines in these processes, and are also associated with pro-inflammatory phenotypes that are linked to age-related diseases. At the same time, apoptosis, which is the programmed destruction of unfit or damaged cells, is reduced in older individuals. This decline in cell performance in combination with a decreased ability to remove poor-performing cells is central to the aging process. Similarly, cancer can arise from cumulative genotoxic and cytotoxic stress, and apoptosis also plays a primary role in cancer resistance by removing potentially cancerous cells. Thus, if cancer-suppressing mechanisms are similar across species, then larger, longer-lived organisms should be at greater risk of cancer than smaller, shorter-lived ones. While this correlation exists within species, for example, cancer incidence increases with increasing adult height for most cancer types in humans and overall body mass in dogs, there is no such correlation between species - an observation often referred to as "Peto's paradox".

The molecular and cellular mechanisms underlying the evolution of large bodies and long lifespans have been explored in mammals such as elephants, whales, bats, and naked mole rats, but are less well studied in other vertebrates. Reptiles are an excellent system in which to study the evolution of body size and longevity because diverse lineages have repeatedly evolved large body sizes and long lifespans. Turtles, in particular, have lower rates of neoplasia than snakes and lizards, are especially long-lived, and are "slower aging" than other reptiles. Most notably, Galapagos giant tortoises (C. niger) and Aldabra giant tortoises (Aldabrachelys gigantea) can live over 150 years (3-5 times longer than their closest relatives) and weigh over 200 kg (50-100 times heavier than their closest relatives). Galapagos giant tortoises also appear to have evolved a suite of cellular traits that may contribute to their longevity, such as a slower rate of telomere shortening and extended cellular lifespans compared to mammals.

Here, we explore the evolution of body size and lifespan in turtles by integrating several approaches: (1) phylogenetic comparative analysis of body size, lifespan, and intrinsic cancer risk in turtles; (2) gene duplication analysis of aging and cancer-related genes across available turtle genomes; (3) cell-based assays of apoptosis and necrosis in multiple turtle species varying in body size and lifespan. We show that species with remarkably long lifespans, such as Galapagos giant tortoises, also evolved reduced cancer risk. We also confirm that the Galapagos giant and desert tortoise genomes encode numerous duplicated genes with tumor suppressor and anti-aging functions. Our comparative genomic analysis further suggests that cells from large, long-lived species may respond differently to cytotoxic stress, including endoplasmic reticulum (ER) stress and oxidative stress. The combined genomic and cellular results suggest that at least some turtle lineages evolved large bodies and long lifespans, in part, by increasing the copy number of tumor suppressors and other anti-aging genes and undergoing changes in cellular phenotypes associated with cellular stress.

Macrophages Essential to Limb Regeneration in the Axolotl Emerge from the Liver

Regeneration from injury is an intricate dance between stem cells, somatic cells, senescent cells, and immune cells. In particular, research into the biochemistry of species such the axolotl that can regenerate limbs and organs has identified the innate immune cells known as macrophages as essential to the process. Specific differences in macrophage behavior between more regenerative species such as the axolotl and less regenerative species such as our own are still under exploration. Here, researchers uncover a greater level of complexity in axolotl regeneration, in that only some macrophages are important to scar-free regeneration, and these cells originate in the liver rather than the bone marrow.

In 2013 it was discovered that a type of white blood cell called a macrophage is essential to limb regeneration in the axolotl. Without macrophages, which are part of the immune system, regeneration did not take place. Instead of regenerating a limb, the axolotl formed a scar at the site of the injury, which acted as a barrier to regeneration, just as it would in a mammal such as a mouse or human. Now, in a new study, researchers have identified the origin of pro-regenerative macrophages in the axolotl as the liver. By providing science with a place to look for pro-regenerative macrophages in humans - the liver, rather than the bone marrow, which is the source of most human macrophages - the finding paves the way for regenerative medicine therapies in humans.

Although the prospect of regrowing a human limb may be unrealistic in the short term due to its complexity, regenerative medicine therapies could potentially be employed in the shorter term in the treatment of the many diseases in which scarring plays a pathological role, including heart, lung and kidney disease. "If axolotls can regenerate by having a single cell type as their guardian, then maybe we can achieve scar-free healing in humans by populating our bodies with an equivalent guardian cell type, which would open up the opportunity for regeneration."

Although it remains to be seen if achieving scar-free healing in mammals will allow regeneration to proceed, researchers believe that may be the case. Because mammals already possess the machinery for regeneration - young mice can regenerate, as can human newborns - mammalian regeneration may simply be a matter of removing the barrier posed by scarring. "In axolotls, macrophages act as a brake on fibrosis, or scarring. Humans may possess macrophages that are doing their hardest to repair the damage, but are being held back. If we can engineer human macrophages to promote scar-free healing, we might be able to achieve a huge improvement in repair with just a little tweak. We have the luxury in the salamander of being able to work out which macrophage functions are essential to scar suppression and regeneration, gene by gene if we have to. If we can find out what that is, then maybe we can get that interaction happening in mammals."

Link: https://mdibl.org/press-release/mdi-biological-laboratory-scientist-advances-prospect-of-regeneration-in-humans/

Evidence that Metformin Does Not Interfere in the Beneficial Response to Exercise

There have been suggested that metformin, a at best weak calorie restriction mimetic, can suppress some of the beneficial metabolic response to exercise. Metformin is in general a poor choice in comparison to mTOR inhibitors when it comes to animal evidence for an ability to modestly slow the progression of aging. The primary human evidence for metformin to be useful, and why it attracted interest in the first place, comes from a large study of diabetic patients, and the gain in life expectancy was not large. Researchers here provide evidence against any suppression by metformin of beneficial mechanisms resulting from exercise, but I can't say that this does much to make metformin an attractive option. At the end of the day, small effect sizes are just not worth chasing, given the many other lines of research and development that offer greater promise.

Metformin and exercise both improve glycemic control, but in vitro studies have indicated that an interaction between metformin and exercise occurs in skeletal muscle, suggesting a blunting effect of metformin on exercise training adaptations. Two studies (a double-blind, parallel-group, randomized clinical trial conducted in 29 glucose-intolerant individuals and a double-blind, cross-over trial conducted in 15 healthy lean males) were included in this paper. In both studies, the effect of acute exercise with or without metformin treatment on different skeletal muscle variables, previously suggested to be involved in a pharmaco-physiological interaction between metformin and exercise, was assessed. Furthermore, in the parallel-group trial, the effect of 12 weeks of exercise training was assessed.

Skeletal muscle biopsies were obtained before and after acute exercise and 12 weeks of exercise training, and mitochondrial respiration, oxidative stress, and AMPK activation was determined. Metformin did not significantly affect the effects of acute exercise or exercise training on mitochondrial respiration, oxidative stress or AMPK activation, indicating that the response to acute exercise and exercise training adaptations in skeletal muscle is not affected by metformin treatment. Further studies are needed to investigate whether an interaction between metformin and exercise is present in other tissues, e.g. the gut.

Link: https://doi.org/10.1139/apnm-2021-0194

AMPK Activator O304 as an Exercise Mimetic Drug

Most of the work aimed at treating aging as a medical condition is focused on stress response upregulation, finding ways to trigger some of the regulatory pathways and mechanisms involved in beneficial cellular reactions to the mild stresses of exercise, reduced calorie intake, hypoxia, heat, cold, and so forth. Improved cell behavior leads to improved tissue function, which in turn slows the progression of degenerative aging. Many of these pathways converge on autophagy, and evidence from the study of calorie restriction suggests that improved autophagy is the largest contributing factor.

Autophagy is the name given to a collection of cellular maintenance processes that remove unwanted or damaged structures and proteins, ensuring that they are broken down in a lysosome and the raw materials returned to the cell for reuse. Autophagy becomes less effective with age, and researchers have in recent years identified a range of age-related defects in the various component parts of the autophagic process. Tracing these issues back to root causes is, as for most of the changes observed in cells in aged tissues, quite challenging and very much a work in progress.

Stress response upregulation is much more effective at extending life span in short-lived species than it is in long-lived species. Calorie restriction can increase life span by 40% in mice, but certainly doesn't do that in humans. Stress response upregulation as a strategy for the development of therapies does not seem likely to greatly improve the healthy human life span to a much greater degree than is already possible via lifestyle changes. So it is disappointing that so much of present efforts are directed towards this part of the field. Results in mice should not be taken as indicative of the benefits that these same treatments might achieve in longer-lived species such as our own.

AMPK activator O304 improves metabolic and cardiac function, and exercise capacity in aged mice

Metabolic function, cardiac capacity, and vascular flexibility decline progressively with age, which in combination reduce work capacity, mobility, and quality of life. Type 2 diabetes (T2D) and cardiovascular diseases (CVDs) incidence increase with age and are current global epidemics representing major challenges to health care systems. Regular exercise not only increases work/exercise capacity but also counteracts the development of numerous age-related diseases, including several forms of metabolic and CVDs, thus promoting healthy aging. However, aged individuals are frequently unable to engage in regular exercise/physical activity. Thus, there is a large need to develop pharmacological treatments that can increase exercise/work capacity to counteract metabolic dysfunction and improve cardiac and vascular function and thereby promote healthy aging and increase quality of life in the aging population.

Insulin resistance and associated hyperinsulinemia are predictors of age-related diseases such as T2D and CVD. Increased activity of AMP-activated protein kinase (AMPK), a key energy sensor that is activated in response to low energy and glucose levels following exercise, enhances insulin-dependent and insulin-independent skeletal glucose uptake, thus improving glucose homeostasis and insulin resistance. AMPK activity declines however with age. Thus, AMPK has emerged as a potential important link between, and mediator of, numerous positive effects of exercise including protection against age-related diseases.

We previously showed that pan-AMPK activator O304 stimulates AMPK activity and glucose uptake in both skeletal muscle and heart of diet-induced obese (DIO) mice in vivo. In DIO mice, O304 mitigated hyperglycemia, hyperinsulinemia, insulin resistance, and obesity, and in a transgenic type 2 diabetic mouse model, O304 reversed established diabetes. O304 also significantly increased stroke volume, end-diastolic volume, and reduced heart rate in DIO mice, mimicking the cardiac effects of exercise. Thus, AMPK activator O304 efficiently ameliorated obesity-provoked insulin resistance, diabetes, and cardiovascular dysfunction in obese mice. O304 is currently in clinical development, and in a short proof-of-concept phase IIa clinical trial in T2D patients O304 reduced fasting plasma glucose levels and insulin resistance, i.e., HOMA-IR, and increased microvascular perfusion in the calf muscle and reduced blood pressure.

Here we show that the pan-AMPK activator O304, which is well tolerated in humans, prevented and reverted age-associated hyperinsulinemia and insulin resistance, and improved cardiac function and exercise capacity in aged mice. These results provide preclinical evidence that O304 mimics the beneficial effects of exercise. Thus, as an exercise mimetic in clinical development, AMPK activator O304 holds great potential to mitigate metabolic dysfunction, and to improve cardiac function and exercise capacity, and hence quality of life in aged individuals.

In Type 2 Diabetes, Arterial Stiffening Causes Increased Structural Damage to the Brain

Researchers here mine patient data in order to demonstrate that type 2 diabetes combines with the age-related stiffening of blood vessels to produce greater structural damage in the brain, leading to a more rapid cognitive decline. This correlation between stiffening and damage was not observed in non-diabetic patients. This is an interesting result, as a reasonable view of the consequence of blood vessel stiffening with age is that it will produce increased blood pressure and consequence pressure damage to delicate tissues regardless of other factors. The authors conclude that the most likely explanation is that diabetes makes this process significantly worse, and thus more easily identified in patient data.

Cerebrovascular dysfunction has been proposed as a possible mechanism underlying cognitive impairment in the context of type 2 diabetes mellitus (DM). Although magnetic resonance imaging (MRI) evidence of cerebrovascular disease, such as white matter hyperintensities (WMH), is often observed in DM, the vascular dynamics underlying this pathology remain unclear. Thus, we assessed the independent and combined effects of DM status and different vascular hemodynamic measures (i.e., systolic, diastolic, and mean arterial blood pressure and pulse pressure index [PPi]) on WMH burden in cognitively unimpaired (CU) older adults and those with mild cognitive impairment (MCI).

559 older adults (mean age: 72.4 years) from the Alzheimer's Disease Neuroimaging Initiative were categorized into those with diabetes (DM+; CU = 43, MCI = 34) or without diabetes (DM-; CU = 279; MCI = 203). Participants underwent BP assessment, from which all vascular hemodynamic measures were derived. The presence of DM, but not PPi values, was independently associated with greater WMH burden overall after adjusting for covariates. Higher PPi values predicted greater WMH burden in the DM group only. No significant interactions were observed in the CU group.

Results indicate that higher PPi values are positively associated with WMH burden in diabetic older adults with MCI, but not their non-diabetic or CU counterparts. Our findings suggest that arterial stiffening and reduced vascular compliance may have a role in development of cerebrovascular pathology within the context of DM in individuals at risk for future cognitive decline. Given the specificity of these findings to MCI, future exploration of the sensitivity of earlier brain markers of vascular insufficiency (i.e., prior to macrostructural white matter changes) to the effects of DM and arterial stiffness/reduced vascular compliance in CU individuals is warranted.

Link: https://doi.org/10.3389/fnagi.2021.716638

Modulation of the Aged Gut Microbiome to Benefit Health is a Field in its Infancy

Research of the past decade makes it clear that it is plausible and possible to alter the aged gut microbiome in ways that will reduce chronic inflammation and improve long-term health. This goal has been achieved in animal models via a range of different means, including flagellin immunization and fecal microbiota transplantation. In short-lived species, healthy life spans can be extended by restoring a more youthful gut microbiome, and in our own species, the detrimental changes that take place in gut microbiome populations are increasingly well catalogued. The next step has yet to be taken in earnest, however: to roll out human trials of the known ways to beneficially alter the gut microbiome.

Changes in the intestinal microflora with aging are related to the pathogenesis of age-related chronic diseases. Dietary intervention, exercise, and drug therapy are currently the most studied anti-aging measures and can improve the intestinal microbial imbalance caused by aging and promote a healthier intestinal environment to achieve anti-aging effects. In addition, gut microbiota modification represents a promising intervention for anti-aging and aging-related diseases, such as the use of probiotics, prebiotics, and synbiotics.

Studies suggest that modifying the gut microbiota of the elderly population by the intake of functional food as probiotics, prebiotics, or synbiotics may be an effective strategy to counteract natural aging. At the same time, these functional products may be suitable, affordable, and economical to most elderly people. However, their effects on health are complex, depending on individual populations and the duration of treatments. Evidence of probiotic, prebiotic and synbiotic use in elderly people is in its infancy compared with other measures.

Despite much research on these interventions, there are no firm conclusions about the benefits for human health. The reasons may be as follows: (1) Most of the relevant studies have been conducted in laboratory and animal models. These findings do not necessarily apply to humans directly. (2) Most clinical trials with humans are short-term and insufficient to understand long-term health effects. (3) Humans are quite different from each other in terms of sex, size, age, genetics, environment, lifestyle, and other factors. An anti-aging intervention that was found to help one person might not have the same effect on another. (4) Although many probiotics have proven strong safety profiles, we should still be careful to monitor their potential risks in different populations in the development of new probiotics.

Therefore, future research needs to focus on addressing these issues to better understand the safety and efficacy of these anti-aging measures in humans. In addition, although much hope and investment are currently focused on drug development, the application of anti-aging drugs in humans still has a long way to go. It is important to note that sensible habits may be more effective at extending healthspan than taking a medication. This means eating healthy foods, exercising, drinking alcohol in moderation or not at all, not smoking, getting adequate sleep, and maintaining an active lifestyle.

Link: https://doi.org/10.1080/19490976.2021.1994835

Present Calorie Restriction Mimetics are a Poor Substitute for the Practice of Calorie Restriction

The portion of the medical research and development community that is focused on aging spends most of its time and funding on classes of treatment that cannot outperform good lifestyle choices when it comes to improving health and slowing degenerative aging. Why is this? If billions and decades are to be expended on building a pipeline from fundamental research through to clinical trials, why is the goal only an incremental benefit to health, smaller than that produced by regular exercise, intermittent fasting, or the practice of calorie restriction? Why such a lack of ambition, given the many possible projects that could achieve far more?

The small patient advocacy community focused on the treatment of aging as a medical condition spent long years convincing scientific and industry groups that it is both possible and desirable to extend the healthy human life span. The result of that work is, it appears, largely the initiation of projects that simply don't matter in the bigger picture, that won't meaningfully change the shape of later life, that won't greatly extend healthy human life spans.

Today's research materials are a reminder that the lion's share of effort and investment in the longevity industry is devoted to treatments and potential treatments that upregulate cellular stress responses, such as autophagy, to recreate a thin fraction of the natural metabolic outcomes of exercise, fasting, hypoxia, or calorie restriction. It remains the case that far too little attention is given to work that can in principle produce rejuvenation, by repairing the molecular damage that is the underlying cause of aging. Yes, senolytic therapies to clear senescent cells have made the leap, but senolytics see a fraction of the interest given to calorie restriction mimetics.

This is an important topic for continued patient advocacy. It is clearly not enough to convince the institutions of the world to work towards the treatment of aging; that is an important and ongoing battle, but it is only a first step. We must also advocate for a focus on the right sort of research programs, those that are in principle capable of producing sizable gains in health and life span, versus those that are not. If another two decades slip away with nothing to show for it but the clinical approval of varieties of mTOR inhibitor and other calorie restriction mimetic small molecule drugs, then a great opportunity to improve the human condition and save countless lives will have been squandered.

Diet trumps drugs for anti ageing and good metabolic health

A study comparing the impact of diet versus drugs on the inner workings of our cells has found nutrition has a much stronger impact. The pre-clinical study suggests the makeup of our diet could be more powerful than drugs in keeping conditions like diabetes, stroke, and heart disease at bay. Conducted in mice, the research showed nutrition (including overall calories and macronutrient balance) had a greater impact on ageing and metabolic health than three drugs commonly used to treat diabetes and slow down ageing: metformin, resveratrol, and rapamycin.

The research builds on the team's pioneering work in mice and humans demonstrating the protective role of diet and specific combinations of proteins, fats, and carbohydrates against ageing, obesity, heart disease, immune dysfunction, and risk of metabolic diseases, such as type 2 diabetes. Drugs can also target the same biochemical pathways as nutrients. There has been a huge effort to discover drugs aimed at improving metabolic health and ageing without requiring a change in diet. "We discovered dietary composition had a far more powerful effect than drugs, which largely dampened responses to diet rather than reshaped them."

Nutritional reprogramming of mouse liver proteome is dampened by metformin, resveratrol, and rapamycin

Nutrient sensing pathways influence metabolic health and aging, offering the possibility that diet might be used therapeutically, alone or with drugs targeting these pathways. We used the Geometric Framework for Nutrition to study interactive and comparative effects of diet and drugs on the hepatic proteome in mice across 40 dietary treatments differing in macronutrient ratios, energy density, and drug treatment (metformin, rapamycin, resveratrol). There was a strong negative correlation between dietary energy and the spliceosome and a strong positive correlation between dietary protein and mitochondria, generating oxidative stress at high protein intake. Metformin, rapamycin, and resveratrol had lesser effects than and dampened responses to diet. Rapamycin and metformin reduced mitochondrial responses to dietary protein while the effects of carbohydrates and fat were downregulated by resveratrol. Dietary composition has a powerful impact on the hepatic proteome, not just on metabolic pathways but fundamental processes such as mitochondrial function and RNA splicing.

A Narrow Window for Exercise to Improve Neurogenesis via Growth Hormone in Aged Mice

There is mixed evidence for exercise to improve neurogenesis and cognitive function in very old mice. Researchers here suggest that this is because the duration of an exercise program matters greatly, and there is a comparatively narrow window of time in which the result is a net gain in function. This may be an example of the frailty of old age: mild stresses such as exercise that are robustly beneficial in younger individuals become more of a balancing act between cost and benefit in age-damaged individuals. The results are interesting, and will likely guide further explorations of the effects of exercise in very old human patients. That said, it isn't clear that the findings are in any way informative as to the dose-response curve for the effects of exercise on neurogenesis and cognitive function in old humans.

Hippocampal function is critical for spatial and contextual learning, and its decline with age contributes to cognitive impairment. Exercise can improve hippocampal function, however, the amount of exercise and mechanisms mediating improvement remain largely unknown. Here, we show exercise reverses learning deficits in aged (24 months) female mice but only when it occurs for a specific duration, 5 weeks, with longer or shorter periods proving ineffective.

While others have reported that a 5-week period of daily voluntary exercise results in the improvement of hippocampal cognitive function in aged mice, surprisingly, our results reveal that if we extended this period of exercise, there was abrogation of cognitive improvement. The discovery of a "sweet spot" of exercise duration critical for both neurogenic activation and improved spatial learning may help explain previous conflicting reports of the efficacy of exercise in improving cognitive improvement in aged mice.

A spike in the levels of growth hormone (GH) and a corresponding increase in neurogenesis during this sweet spot mediate this effect because blocking GH receptor with a competitive antagonist or depleting newborn neurons abrogates the exercise-induced cognitive improvement. Moreover, raising GH levels with GH-releasing hormone agonist improved cognition in nonrunners. We show that GH stimulates neural precursors directly, indicating the link between raised GH and neurogenesis is the basis for the substantially improved learning in aged animals.

Link: https://doi.org/10.1016/j.isci.2021.103275

Heterochronic Parabiosis Reduces Epigenetic Age in Mice

Heterochronic parabiosis is the surgical linking of the circulatory systems of an old individual and young individual, usually mice. The older mouse shows signs of rejuvenation, while the younger mouse shows signs of accelerated aging. There is a robust ongoing process of debate and discovery regarding the mechanisms by which these effects are mediated. At present it appears that a dilution of harmful factors in old blood is likely to account for most of the outcome, but there is evidence for beneficial factors in young blood to be involved. In the study here, researchers show that epigenetic and transcriptomic measures of age are reduced in old mice following heterochronic parabiosis, and that this effect persists for at least a few months following the end of the intervention.

Heterochronic parabiosis (HPB) is known for its functional rejuvenation effects across several mouse tissues. However, its impact on the biological age of organisms and their long-term health remains unknown. Here, we performed extended (3-month) HPB, followed by a 2-month detachment period of anastomosed pairs. Old detached mice exhibited improved physiological parameters and lived longer than control isochronic mice. HPB drastically reduced the biological age of blood and liver based on epigenetic analyses across several clock models on two independent platforms; remarkably, this rejuvenation effect persisted even after 2 months of detachment.

Transcriptomic and epigenomic profiles of anastomosed mice showed an intermediate phenotype between old and young, suggesting a comprehensive multi-omic rejuvenation effect. In addition, old HPB mice showed transcriptome changes opposite to aging, but akin to several lifespan-extending interventions. Altogether, we reveal that long-term HPB can decrease the biological age of mice, in part through long-lasting epigenetic and transcriptome remodeling, culminating in the extension of lifespan and healthspan.

Link: https://doi.org/10.1101/2021.11.11.468258

Considering Mechanistic Links Between Vascular Calcification and Osteoporosis

With advancing age, regulatory pathways involved in bone remodeling are activated inappropriately in smooth muscle cells of blood vessel walls and cardiac tissue. The result is calcification of tissue, making it inflexible, and disrupting the normal elasticity. That leads to hypertension and other, worse cardiovascular issues. Inflammatory signaling and the presence of senescent cells appear to be involved in causing this process, but firmly proven chains of cause and effect are yet to be established, as is the case for all too much of the panoply of dysfunctions that arise in the progression of degenerative aging.

Separately, the mechanisms of bone remodeling are disrupted in bone tissue itself, giving rise to an imbalance between deposition on the part of osteoblast cells and resorption on the part of osteoclast cells. The density and resilience of bone decreases over time, leading to osteoporosis. In today's review materials, researchers discuss the regulatory mechanisms involved in both osteoporosis and vascular calcification, noting that while incidence of these conditions are correlated with one another to some degree, it remains unclear as to whether one condition is driving the other, or whether they develop independently from shared root causes, such as the age-related increase in chronic inflammation.

Are vascular calcification and bone loss linked disorders of aging?

A recent review paper elucidates the numerous pathophysiological mechanisms shared by vascular calcification and bone loss, identifying the following key associations. Firstly, vascular calcification is an active process of calcium and phosphate precipitation that involves the transition of the vascular smooth muscle cells (VSMCs) into osteoblast-like cells. Secondly, among the molecules involved in this process, parathyroid hormone (PTH) plays a key role, acting through several mechanisms which include the regulation of the RANK/RANKL/OPG system and the Wnt/ß-catenin pathway, the main pathways for bone resorption and bone formation, respectively. Thirdly, some microRNAs have been implicated as common regulators of bone metabolism, vascular calcification, left ventricle hypertrophy and myocardial fibrosis.

The increase or decrease in tissue and/or serum levels of PTH, the RANK/RANKL/OPG system and the Wnt/bcatenin pathways, calcium, phosphate, FGF23, among the most studied factors, may play a pathogenic role but can also be used as markers of bone and cardiovascular diseases. However, levels of some serum markers should be interpreted with caution, as the correlation between hormone levels and tissue levels needs to be better investigated.

Pathophysiology of Vascular Calcification and Bone Loss: Linked Disorders of Ageing?

This review shows that vascular calcification and bone loss that often coexist in ageing individuals, share numerous pathophysiological mechanisms. In this context, PTH, the RANK/RANKL/OPG system and the Wnt/ß-catenin pathway are the most studied factors. High PTH thus increases bone resorption and bone loss, but also triggers mechanisms that favour vascular calcification involving the RANK/RANKL/OPG and Wnt/ß-catenin pathways. Furthermore, other closely related factors such as calcium, phosphate, FGF23, Klotho, vitamin D and other regulatory factors that regulate PTH render these interactions extremely complex. The presence of low or high PTH levels, and consequently of low or high bone turnover, facilitate the process of deposition of hydroxyapatite in the wall of the vessels, leading to progression of vascular calcification when present for prolonged periods. The process eventually becomes severe, potentially increasing vascular molecular signals in order to reduce "bone deposition in the vessels", which in turn could favour the reduction of normal bone formation. Thus, in the presence of severe vascular calcification, a vicious circle may be established, further reducing bone mass.

The increase or decrease in tissue and/or serum levels of any these factors may play a pathogenic role in both bone loss and vascular calcification, and may be potentially promisingly used as a marker of bone and cardiovascular disease. However, caution should be exerted in the interpretation of these markers. For instance, whereas higher serum levels of sclerostin have been associated with vascular calcification and poor outcomes, this may not necessarily be due to a cause and effect relationship, but to a potential overproduction of sclerostin as a protective factor against vascular calcification. Similarly, serum sclerostin levels have been positively, and not negatively, associated with higher bone mass.

Although the pathogenesis and progression of vascular calcification and bone loss shares several common factors and pathways, it remains a "chicken-and-egg" situation, where it difficult to stablish cause and effect as to whether bone loss is driving vascular calcification or vice-versa, or whether there is a higher level of dysregulation generated by the ageing process that impacts on both tissues simultaneously, using common mechanisms.