Low insulin-like growth factor-1 level predicts survival in humans with exceptional longevity

Potential Anti-Aging Substances Derived from Seaweeds

Aging is a major risk factor for many chronic diseases, such as cancer, cardiovascular disease, and diabetes. The exact mechanisms underlying the aging process are not fully elucidated. However, a growing body of evidence suggests that several pathways, such as sirtuin, AMP-activated protein kinase, insulin-like growth factor, autophagy, and nuclear factor erythroid 2-related factor 2 play critical roles in regulating aging. Furthermore, genetic or dietary interventions of these pathways can extend lifespan by delaying the aging process. Seaweeds are a food source rich in many nutrients, including fibers, polyunsaturated fatty acids, vitamins, minerals, and other bioactive compounds. The health benefits of seaweeds include, but are not limited to, antioxidant, anti-inflammatory, and anti-obese activities. Interestingly, a body of studies shows that some seaweed-derived extracts or isolated compounds, can modulate these aging-regulating pathways or even extend lifespans of various animal models. However, few such studies have been conducted on higher animals or even humans. In this review, we focused on potential anti-aging bioactive substances in seaweeds that have been studied in cells and animals mainly based on their anti-aging cellular and molecular mechanisms.

Pregnancy as a model for aging

The process of aging can be defined as the sum accumulation of damages and changes in metabolism during the life of an organism, due to both genetic predisposition and stochastic damage. During the gestational period and following parturition, similar damage can be seen due to the strenuous effect on the maternal body, exhibited on both the physiological and cellular level. In this review, we will focus on the similar physiological and cellular characteristics exhibited during pregnancy and aging, including induction of and response to oxidative stress, inflammation, and degradation of telomeres. We will evaluate any similar processes between aging and pregnancy by comparing common biomarkers, pathologies, and genetic and epigenetic effects, to establish the pregnant body as a model for aging. This review will approach the connection both in respect to current theories on aging as a byproduct of natural selection, and regarding unrelated biochemical similarities between the two, drawing on existing studies and models in humans and other species where relevant alike. Furthermore, we will show the response of the pregnant body to these changes, and through that illuminate unique areas of potential study to advance our knowledge of the maladies relating to aging and pregnancy, and an avenue for solutions.

Genetics of extreme human longevity to guide drug discovery for healthy ageing

Ageing is the greatest risk factor for most common chronic human diseases, and it therefore is a logical target for developing interventions to prevent, mitigate or reverse multiple age-related morbidities. Over the past two decades, genetic and pharmacologic interventions targeting conserved pathways of growth and metabolism have consistently led to substantial extension of the lifespan and healthspan in model organisms as diverse as nematodes, flies and mice. Recent genetic analysis of long-lived individuals is revealing common and rare variants enriched in these same conserved pathways that significantly correlate with longevity. In this Perspective, we summarize recent insights into the genetics of extreme human longevity and propose the use of this rare phenotype to identify genetic variants as molecular targets for gaining insight into the physiology of healthy ageing and the development of new therapies to extend the human healthspan.

IGF-1R Inhibitor Ameliorates Neuroinflammation in an Alzheimer's Disease Transgenic Mouse Model

Aging is a major risk factor for Alzheimer's disease (AD). Insulin-like growth factor-1 receptor (IGF-1R) regulates general aging and lifespan. However, the contribution of IGF-1 to age-related AD pathology and progression is highly controversial. Based on our previous work, AβPP/PS1 double transgenic mice, which express human mutant amyloid precursor protein (APP) and presenilin-1 (PS-1), demonstrated a decrease in brain IGF-1 levels when they were crossed with IGF-1 deficient Ames dwarf mice (df/df). Subsequently, a reduction in gliosis, amyloid-β (Aβ) plaque deposition, and Aβ_1-40/42 concentrations were observed in this mouse model. This supported the hypothesis that IGF-1 may contribute to the progression of the disease. To assess the role of IGF-1 in AD, 9-10-month-old male littermate control wild type and AβPP/PS1 mice were randomly divided into two treatment groups including control vehicle (DMSO) and picropodophyllin (PPP), a selective, competitive, and reversible IGF-1R inhibitor. The brain penetrant inhibitor was given ip. at 1 mg/kg/day. Mice were sacrificed after 7 days of daily injection and the brains, spleens, and livers were collected to quantify histologic and biochemical changes. The PPP-treated AβPP/PS1 mice demonstrated attenuated insoluble Aβ_1-40/42. Additionally, an attenuation in microgliosis and protein p-tyrosine levels was observed due to drug treatment in the hippocampus. Our data suggest IGF-1R signaling is associated with disease progression in this mouse model. More importantly, modulation of the brain IGF-1R signaling pathway, even at mid-life, was enough to attenuate aspects of the disease phenotype. This suggests that small molecule therapy targeting the IGF-1R pathway may be viable for late-stage disease treatment.

The mitochondrial derived peptide humanin is a regulator of lifespan and healthspan

Humanin is a member of a new family of peptides that are encoded by short open reading frames within the mitochondrial genome. It is conserved in animals and is both neuroprotective and cytoprotective. Here we report that in C. elegans the overexpression of humanin is sufficient to increase lifespan, dependent on daf-16/Foxo. Humanin transgenic mice have many phenotypes that overlap with the worm phenotypes and, similar to exogenous humanin treatment, have increased protection against toxic insults. Treating middle-aged mice twice weekly with the potent humanin analogue HNG, humanin improves metabolic healthspan parameters and reduces inflammatory markers. In multiple species, humanin levels generally decline with age, but here we show that levels are surprisingly stable in the naked mole-rat, a model of negligible senescence. Furthermore, in children of centenarians, who are more likely to become centenarians themselves, circulating humanin levels are much greater than age-matched control subjects. Further linking humanin to healthspan, we observe that humanin levels are decreased in human diseases such as Alzheimer's disease and MELAS (Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like episodes). Together, these studies are the first to demonstrate that humanin is linked to improved healthspan and increased lifespan.

Insulin-like Growth Factor-1 and IGF Binding Proteins Predict All-Cause Mortality and Morbidity in Older Adults

While the growth hormone/insulin-like growth factor-1 (GH/IGF-1) pathway plays essential roles in growth and development, diminished signaling via this pathway in model organisms extends lifespan and health-span. In humans, circulating IGF-1 and IGF-binding proteins 3 and 1 (IGFBP-3 and 1), surrogate measures of GH/IGF-1 system activity, have not been consistently associated with morbidity and mortality. In a prospective cohort of independently-living older adults (n = 840, mean age 76.1 ± 6.8 years, 54.5% female, median follow-up 6.9 years), we evaluated the age- and sex-adjusted hazards for all-cause mortality and incident age-related diseases, including cardiovascular disease, diabetes, cancer, and multiple-domain cognitive impairment (MDCI), as predicted by baseline total serum IGF-1, IGF-1/IGFBP-3 molar ratio, IGFBP-3, and IGFBP-1 levels. All-cause mortality was positively associated with IGF-1/IGFBP-3 molar ratio (HR 1.28, 95% CI 1.05–1.57) and negatively with IGFBP-3 (HR 0.82, 95% CI 0.680–0.998). High serum IGF-1 predicted greater risk for MDCI (HR 1.56, 95% CI 1.08–2.26) and composite incident morbidity (HR 1.242, 95% CI 1.004–1.538), whereas high IGFBP-1 predicted lower risk for diabetes (HR 0.50, 95% CI 0.29–0.88). In conclusion, higher IGF-1 levels and bioavailability predicted mortality and morbidity risk, supporting the hypothesis that diminished GH/IGF-1 signaling may contribute to human longevity and health-span.

Insulin-like growth factor 1 signaling in motor neuron and polyglutamine diseases: From molecular pathogenesis to therapeutic perspectives

The pleiotropic peptide insulin-like growth factor 1 (IGF-I) regulates human body homeostasis and cell growth. IGF-I activates two major signaling pathways, namely phosphoinositide-3-kinase (PI3K)/protein kinase B (PKB/Akt) and Ras/extracellular signal-regulated kinase (ERK), which contribute to brain development, metabolism and function as well as to neuronal maintenance and survival. In this review, we discuss the general and tissue-specific effects of the IGF-I pathways. In addition, we present a comprehensive overview examining the role of IGF-I in neurodegenerative diseases, such as spinal and muscular atrophy, amyotrophic lateral sclerosis, and polyglutamine diseases. In each disease, we analyze the disturbances of the IGF-I pathway, the modification of the disease protein by IGF-I signaling, and the therapeutic strategies based on the use of IGF-I developed to date. Lastly, we highlight present and future considerations in the use of IGF-I for the treatment of these disorders.

Female Specific Association of Low Insulin-Like Growth Factor 1 (IGF1) Levels with Increased Risk of Premature Mortality in Renal Transplant Recipients

Associations between insulin-like growth factor 1 (IGF1) and mortality have been reported to be female specific in mice and in human nonagenarians. Intervention in the growth hormone (GH)-IGF1 axis may particularly benefit patients with high risk of losing muscle mass, including renal transplant recipients (RTR). We investigated whether a potential association of circulating IGF1 with all-cause mortality in stable RTR could be female specific and mediated by variation in muscle mass. To this end, plasma IGF1 levels were measured in 277 female and 343 male RTR by mass spectrometry, and their association with mortality was assessed by Cox regression. During a median follow-up time of 5.4 years, 56 female and 77 male RTR died. In females, IGF1 was inversely associated with risk (hazard ratio (HR) per 1-unit increment in log2-transformed (doubling of) IGF1 levels, 95% confidence interval (CI)) of mortality (0.40, 0.24-0.65; p < 0.001), independent of age and the estimated Glomerular filtration rate (eGFR). In equivalent analyses, no significant association was observed for males (0.85, 0.56-1.29; p = 0.44), for which it should be noted that in males, age was negatively and strongly associated with IGF1 levels. The association for females remained materially unchanged upon adjustment for potential confounders and was furthermore found to be mediated for 39% by 24 h urinary creatinine excretion. In conclusion, low IGF1 levels associate with an increased risk of all-cause mortality in female RTR, which may link to conditions of low muscle mass that are known to be associated with poor outcomes in transplantation patients. For males, the strongly negative association of age with IGF1 levels may explain why low IGF1 levels were not found to be associated with an increased risk of all-cause mortality.

The influence of vitamin D supplementation on IGF-1 levels in humans: A systematic review and meta-analysis

BACKGROUND

Inconsistencies exist with regard to influence of vitamin D supplementation on IGF-1 levels. The inconsistencies could be attributed to several factors, such as dosage and duration of intervention, among others. To address these inconsistencies, this study was conducted to determine the impact of vitamin D supplementation on IGF-1 levels through a systematic review and meta-analysis of randomized controlled trials (RCTs).

METHODS

A comprehensive systematic search was carried out in PubMed/MEDLINE, Web of Science, SCOPUS and Embase for RCTs that investigated the impact of vitamin D intake on circulating IGF-1 levels from inception until June 2019. Weighted mean difference (WMD) with the 95 % CI were applied for estimating combined effect size. Subgroup analysis was performed to specify the source of heterogeneity among studies.

RESULTS

Pooled results from eight studies demonstrated an overall non-significant increase in IGF-1 following vitamin D supplementation (WMD: 4 ng/ml, 95 % CI: -4 to 11). However, a significant degree of heterogeneity among studies was observed (I² = 66 %). The subgroup analyses showed that vitamin D dosage of ≤1000 IU/day (WMD: 10 ng/ml) significantly increased IGF-1 compared to the vitamin D dosage of <1000 IU/day (WMD: -1 ng/ml). Moreover, intervention duration ≤12 weeks (WMD: 11 ng/ml) significantly increased IGF-1 compared to intervention duration <12 weeks (WMD: -3 ng/ml). In the epidemiological cohort study, participants under 60 years of age with a higher dietary vitamin D intake had significantly higher IGF-1 levels when compared to those with lower dietary vitamin D intake in second categories.

CONCLUSION

The main results indicate a non-significant increase in IGF-1 following vitamin D supplementation. Additionally, vitamin D dosages of <1000 IU/day and intervention durations of <12 weeks significantly raised IGF-1 levels.

Mechanisms of Calorie Restriction: A Review of Genes Required for the Life-Extending and Tumor-Inhibiting Effects of Calorie Restriction

This review focuses on mechanisms of calorie restriction (CR), particularly the growth hormone (GH)/insulin-like growth factor-1 (IGF-1) axis as an evolutionary conserved signal that regulates aging and lifespan, underlying the effects of CR in mammals. Topics include (1) the relation of the GH-IGF-1 signal with chronic low-level inflammation as one of the possible causative factors of aging, that is, inflammaging, (2) the isoform specificity of the forkhead box protein O (FoxO) transcription factors in CR-mediated regulation of cancer and lifespan, (3) the role for FoxO1 in the tumor-inhibiting effect of CR, (4) pleiotropic roles for FoxO1 in the regulation of disorders, and (5) sirtuin (Sirt) as a molecule upstream of FoxO. From the evolutionary view, the necessity of neuropeptide Y (Npy) for the effects of CR and the pleiotropic roles for Npy in life stages are also emphasized. Genes for mediating the effects of CR and regulating aging are context-dependent, particularly depending on nutritional states.

Autophagy in Cardiovascular Aging

Cardiovascular diseases are the most prominent maladies in aging societies. Indeed, aging promotes the structural and functional declines of both the heart and the blood circulation system. In this review, we revise the contribution of known longevity pathways to cardiovascular health and delineate the possibilities to interfere with them. In particular, we evaluate autophagy, the intracellular catabolic recycling system associated with life- and health-span extension. We present genetic models, pharmacological interventions, and dietary strategies that block, reduce, or enhance autophagy upon age-related cardiovascular deterioration. Caloric restriction or caloric restriction mimetics like metformin, spermidine, and rapamycin (all of which trigger autophagy) are among the most promising cardioprotective interventions during aging. We conclude that autophagy is a fundamental process to ensure cardiac and vascular health during aging and outline its putative therapeutic importance.

Mitochondria in the signaling pathways that control longevity and health span

Genetic and pharmacological intervention studies have identified evolutionarily conserved and functionally interconnected networks of cellular energy homeostasis, nutrient-sensing, and genome damage response signaling pathways, as prominent regulators of longevity and health span in various species. Mitochondria are the primary sites of ATP production and are key players in several other important cellular processes. Mitochondrial dysfunction diminishes tissue and organ functional performance and is a commonly considered feature of the aging process. Here we review the evidence that through reciprocal and multilevel functional interactions, mitochondria are implicated in the lifespan modulation function of these pathways, which altogether constitute a highly dynamic and complex system that controls the aging process. An important characteristic of these pathways is their extensive crosstalk and apparent malleability to modification by non-invasive pharmacological, dietary, and lifestyle interventions, with promising effects on lifespan and health span in animal models and potentially also in humans.

Therapeutic Targeting of the IGF Axis

The insulin like growth factor (IGF) axis plays a fundamental role in normal growth and development, and when deregulated makes an important contribution to disease. Here, we review the functions mediated by ligand-induced IGF axis activation, and discuss the evidence for the involvement of IGF signaling in the pathogenesis of cancer, endocrine disorders including acromegaly, diabetes and thyroid eye disease, skin diseases such as acne and psoriasis, and the frailty that accompanies aging. We discuss the use of IGF axis inhibitors, focusing on the different approaches that have been taken to develop effective and tolerable ways to block this important signaling pathway. We outline the advantages and disadvantages of each approach, and discuss progress in evaluating these agents, including factors that contributed to the failure of many of these novel therapeutics in early phase cancer trials. Finally, we summarize grounds for cautious optimism for ongoing and future studies of IGF blockade in cancer and non-malignant disorders including thyroid eye disease and aging.

Central IGF-1 protects against features of cognitive and sensorimotor decline with aging in male mice

Disruptions in growth hormone/insulin-like growth factor-1 (GH/IGF-1) signaling have been linked to improved longevity in mice and humans. Nevertheless, while IGF-1 levels are associated with increased cancer risk, they have been paradoxically implicated with protection from other age-related conditions, particularly in the brain, suggesting that strategies aimed at selectively increasing central IGF-1 action may have favorable effects on aging. To test this hypothesis, we generated inducible, brain-specific (TRE-IGF-1 × Camk2a-tTA) IGF-1 (bIGF-1) overexpression mice and studied effects on healthspan. Doxycycline was removed from the diet at 12 weeks old to permit post-development brain IGF-1 overexpression, and animals were monitored up to 24 months. Brain IGF-1 levels were increased approximately twofold in bIGF-1 mice, along with greater brain weights, volume, and myelin density (P < 0.05). Age-related changes in rotarod performance, exercise capacity, depressive-like behavior, and hippocampal gliosis were all attenuated specifically in bIGF-1 male mice (P < 0.05). However, chronic brain IGF-1 failed to prevent declines in cognitive function or neurovascular coupling. Therefore, we performed a short-term intranasal (IN) treatment of either IGF-1 or saline in 24-month-old male C57BL/6 mice and found that IN IGF-1 treatment tended to reduce depressive (P = 0.09) and anxiety-like behavior (P = 0.08) and improve motor coordination (P = 0.07) and unlike transgenic mice improved motor learning (P < 0.05) and visuospatial and working memory (P < 0.05). These data highlight important sex differences in how brain IGF-1 action impacts healthspan and suggest that translational approaches that target IGF-1 centrally can restore cognitive function, a possibility that should be explored as a strategy to combat age-related cognitive decline.

The impact of dietary protein intake on longevity and metabolic health

Lifespan and metabolic health are influenced by dietary nutrients. Recent studies show that a reduced protein intake or low-protein/high-carbohydrate diet plays a critical role in longevity/metabolic health. Additionally, specific amino acids (AAs), including methionine or branched-chain AAs (BCAAs), are associated with the regulation of lifespan/ageing and metabolism through multiple mechanisms. Therefore, methionine or BCAAs restriction may lead to the benefits on longevity/metabolic health. Moreover, epidemiological studies show that a high intake of animal protein, particularly red meat, which contains high levels of methionine and BCAAs, may be related to the promotion of age-related diseases. Therefore, a low animal protein diet, particularly a diet low in red meat, may provide health benefits. However, malnutrition, including sarcopenia/frailty due to inadequate protein intake, is harmful to longevity/metabolic health. Therefore, further study is necessary to elucidate the specific restriction levels of individual AAs that are most effective for longevity/metabolic health in humans.

Growth Hormone Deficiency: Health and Longevity

The important role of GH in the control of mammalian longevity was first deduced from extended longevity of mice with genetic GH deficiency (GHD) or GH resistance. Mice with isolated GHD (IGHD) due to GHRH or GHRH receptor mutations, combined deficiency of GH, prolactin, and TSH, or global deletion of GH receptors live longer than do their normal siblings. They also exhibit multiple features of delayed and/or slower aging, accompanied by extension of healthspan. The unexpected, remarkable longevity benefit of severe endocrine defects in these animals presumably represents evolutionarily conserved trade-offs among aging, growth, maturation, fecundity, and the underlying anabolic processes. Importantly, the negative association of GH signaling with longevity extends to other mammalian species, apparently including humans. Data obtained in humans with IGHD type 1B, owing to a mutation of the GHRH receptor gene, in the Itabaianinha County, Brazil, provide a unique opportunity to study the impact of severe reduction in GH signaling on age-related characteristics, health, and functionality. Individuals with IGHD are characterized by proportional short stature, doll facies, high-pitched voices, and central obesity. They have delayed puberty but are fertile and generally healthy. Moreover, these IGHD individuals are partially protected from cancer and some of the common effects of aging and can attain extreme longevity, 103 years of age in one case. We think that low, but detectable, residual GH secretion combined with life-long reduction of circulating IGF-1 and with some tissue levels of IGF-1 and/or IGF-2 preserved may account for the normal longevity and apparent extension of healthspan in these individuals.

Rates of erythropoiesis in mammals and their relationship with lifespan and hematopoietic stem cells aging

Investigations on possible links between hematological parameters and longevity are nearly absent. We tested the hypothesis that a fast rate of erythropoiesis, causing an earlier aging of the hematopoietic stem cells pool, contributes to a shorter lifespan. With this aim, we employed a new quantity, daily produced red blood cells per gram of body mass, as a measure of mass-specific rate of erythropoiesis. We found that among mammals rate of erythropoiesis and maximum lifespan are significantly correlated, independently from mass residuals. This seems to be confirmed also by intra-species comparisons and, although with limited data, by the significant correlation of rate of erythropoiesis and rate of telomere shortening in leukocytes (a proxy for hematopoietic stem cell telomere shortening). In our view, this may give a link of causality between rate of erythropoiesis and maximum lifespan. Further studies could test a similar hypothesis also for other kinds of stem cells.

Autophagy and cardiac aging

Cardiovascular disease (CVD) is the leading cause of death and the prevalence of CVD dramatically increases with age. Cardiac aging is associated with hypertrophy, fibrosis, inflammation, and decreased contractility. Autophagy, a bulk degradation/recycling system, is essential to maintain cellular homeostasis. Cardiac autophagy is decreased with age, and misfolded proteins and dysfunctional mitochondria are accumulated in the aging heart. Inhibition of autophagy leads to exacerbated cardiac aging, while stimulation of autophagy improves cardiac function and also increases lifespan in many organisms. Thus autophagy represents a potential therapeutic target for aging-related cardiac dysfunction. This review discusses recent progress in our understanding of the role and regulation of autophagy in the aging heart.

Revisiting the Role of Insulin-Like Growth Factor-I Receptor Stimulating Activity and the Apolipoprotein E in Alzheimer's Disease

Background: Alterations in insulin-like growth factor I (IGF-I) signaling have been associated with dementia and Alzheimer's disease (AD). Studies on the association between IGF-I levels and dementia risk have been inconclusive. We reported earlier that higher levels of IGF-I receptor stimulating activity are associated with a higher prevalence and incidence of dementia. Objective: In the present study, we test the robustness of the association between IGF-I receptor stimulating activity and dementia by extending the follow-up period to 16 years and investigate possible effect modification by apolipoprotein E (ApoE). Methods: At baseline, circulating IGF-I receptor stimulating activity was determined by the IGF-I kinase receptor activation (KIRA) assay in 1,014 elderly from the Rotterdam Study. Dementia was assessed from baseline (1997-1999) to follow-up in January 2015. Associations of IGF-I receptor stimulating activity and incident dementia were assessed with Cox proportional hazards models. Results: During 10,752 person-years of follow-up, 174 people developed dementia. In the extended follow-up we no longer observed a dose-response relationship between IGF-I receptor stimulating activity and risk of dementia [adjusted odds ratio 1.11; 95% confidence interval (CI) 0.97-1.28]. Interestingly, we found evidence of an interaction between ApoE-ε4 and tertiles of IGF-I receptor stimulating activity. IGF-I receptor stimulating activity in the median and top tertiles was related to increased dementia incidence in hetero- and homozygotes of the ApoE-ε4 allele, but did not show any association with dementia risk in people without the ApoE-ε4 allele (adjusted odds ratio medium vs. low IGF-I receptor stimulating activity in ApoE-ε4 carriers: 1.45; 95% CI 1.00-2.12). These findings suggest a threshold effect in ApoE-ε4 carriers. In line with the hypothesis that downregulation of IGF-I signaling is associated with increased dementia risk, ApoE-ε4 homozygotes without prevalent dementia displayed lower levels of IGF-I receptor stimulating activity than heterozygotes and non-carriers. Conclusion: The findings shed new light on the association between IGF-I signaling and the neuropathology of dementia and ask for replication in other cohorts, using measures of IGF-I receptor stimulating activity rather than total serum levels as putative markers of dementia risk.

Targeting growth hormone function: strategies and therapeutic applications

Human growth hormone (GH) is a classical pituitary endocrine hormone that is essential for normal postnatal growth and has pleiotropic effects across multiple physiological systems. GH is also expressed in extrapituitary tissues and has localized autocrine/paracrine effects at these sites. In adults, hypersecretion of GH causes acromegaly, and strategies that block the release of GH or that inhibit GH receptor (GHR) activation are the primary forms of medical therapy for this disease. Overproduction of GH has also been linked to cancer and the microvascular complications that are associated with diabetes. However, studies to investigate the therapeutic potential of GHR antagonism in these diseases have been limited, most likely due to difficulty in accessing therapeutic tools to study the pharmacology of the receptor in vivo. This review will discuss current and emerging strategies for antagonizing GH function and the potential disease indications.

Emerging therapies are offering an expanded toolkit for combatting the effects of human growth hormone overproduction. Human growth hormone (GH) is a major driver of postnatal growth; however, systemic or localized overproduction is implicated in the aberrant growth disease acromegaly, cancer, and diabetes. In this review, researchers led by Jo Perry, from the University of Auckland, New Zealand, discuss strategies that either inhibit GH production, block its systemic receptor, or interrupt its downstream signaling pathways. The only licensed GH receptor blocker is pegvisomant, but therapies are in development that include long-acting protein and antibody-based blockers, and nucleotide complexes that degrade GHR production have also shown promise. Studies investigating GHR antagonism are limited, partly due to difficulty in accessing therapeutic tools which block GHR function, but overcoming these obstacles may yield advances in alleviating chronic disease.

Impact of Growth Hormone-Related Mutations on Mammalian Aging

Mutations of a single gene can lead to a major increase in longevity in organisms ranging from yeast and worms to insects and mammals. Discovering these mutations (sometimes referred to as “longevity genes”) led to identification of evolutionarily conserved molecular, cellular, and organismal mechanisms of aging. Studies in mice provided evidence for the important role of growth hormone (GH) signaling in mammalian aging. Mice with mutations or gene deletions leading to GH deficiency or GH resistance have reduced body size and delayed maturation, but are healthier and more resistant to stress, age slower, and live longer than their normal (wild type) siblings. Mutations of the same genes in people can provide remarkable protection from age-related disease, but have no consistent impact on lifespan. Ongoing research indicates that genetic defects in GH signaling are linked to extension of healthspan and lifespan via a variety of interlocking mechanism, including improvements in genome and stem cell maintenance, stress resistance, glucose homeostasis, and thermogenesis, along with reductions in the mechanistic target of rapamycin (mTOR) C1 complex signaling and in chronic low grade inflammation.

Developmental programming of aging trajectory

There is accumulating evidence that aging phenotype and longevity may be developmentally programmed. Main mechanisms linking developmental conditions to later-life health outcomes include persistent changes in epigenetic regulation, (re)programming of major endocrine axes such as growth hormone/insulin-like growth factor axis and hypothalamic-pituitary-adrenal axis and also early-life immune maturation. Recently, evidence has also been generated on the role of telomere biology in developmental programming of aging trajectory. In addition, persisting changes of intestinal microbiota appears to be crucially involved in these processes. In this review, experimental and epidemiological evidence on the role of early-life conditions in programming of aging phenotypes are presented and mechanisms potentially underlying these associations are discussed.

The aging heart

As the elderly segment of the world population increases, it is critical to understand the changes in cardiac structure and function during the normal aging process. In this review, we outline the key molecular pathways and cellular processes that underlie the phenotypic changes in the heart and vasculature that accompany aging. Reduced autophagy, increased mitochondrial oxidative stress, telomere attrition, altered signaling in insulin-like growth factor, growth differentiation factor 11, and 5'- AMP-activated protein kinase pathways are among the key molecular mechanisms underlying cardiac aging. Aging promotes structural and functional changes in the atria, ventricles, valves, myocardium, pericardium, the cardiac conduction system, and the vasculature. We highlight the factors known to accelerate and attenuate the intrinsic aging of the heart and vessels in addition to potential preventive and therapeutic avenues. A greater understanding of the processes involved in cardiac aging may facilitate our ability to mitigate the escalating burden of CVD in older individuals and promote healthy cardiac aging.

40 YEARS of IGF1: IGF1: the Jekyll and Hyde of the aging brain

The insulin-like growth factor 1 (IGF1) signaling pathway has emerged as a major regulator of the aging process, from rodents to humans. However, given the pleiotropic actions of IGF1, its role in the aging brain remains complex and controversial. While IGF1 is clearly essential for normal development of the central nervous system, conflicting evidence has emerged from preclinical and human studies regarding its relationship to cognitive function, as well as cerebrovascular and neurodegenerative disorders. This review delves into the current state of the evidence examining the role of IGF1 in the aging brain, encompassing preclinical and clinical studies. A broad examination of the data indicates that IGF1 may indeed play opposing roles in the aging brain, depending on the underlying pathology and context. Some evidence suggests that in the setting of neurodegenerative diseases that manifest with abnormal protein deposition in the brain, such as Alzheimer's disease, reducing IGF1 signaling may serve a protective role by slowing disease progression and augmenting clearance of pathologic proteins to maintain cellular homeostasis. In contrast, inducing IGF1 deficiency has also been implicated in dysregulated function of cognition and the neurovascular system, suggesting that some IGF1 signaling may be necessary for normal brain function. Furthermore, states of acute neuronal injury, which necessitate growth, repair and survival signals to persevere, typically demonstrate salutary effects of IGF1 in that context. Appreciating the dual, at times opposing 'Dr Jekyll' and 'Mr Hyde' characteristics of IGF1 in the aging brain, will bring us closer to understanding its impact and devising more targeted IGF1-related interventions.

Late-life targeting of the IGF-1 receptor improves healthspan and lifespan in female mice

Diminished growth factor signaling improves longevity in laboratory models, while a reduction in the somatotropic axis is favorably linked to human aging and longevity. Given the conserved role of this pathway on lifespan, therapeutic strategies, such as insulin-like growth factor-1 receptor (IGF-1R) monoclonal antibodies (mAb), represent a promising translational tool to target human aging. To this end, we performed a preclinical study in 18-mo-old male and female mice treated with vehicle or an IGF-1R mAb (L2-Cmu, Amgen Inc), and determined effects on aging outcomes. Here we show that L2-Cmu preferentially improves female healthspan and increases median lifespan by 9% (P = 0.03) in females, along with a reduction in neoplasms and inflammation (P ≤ 0.05). Thus, consistent with other models, targeting IGF-1R signaling appears to be most beneficial to females. Importantly, these effects could be achieved at advanced ages, suggesting that IGF-1R mAbs could represent a promising therapeutic candidate to delay aging.

The association between peripheral total IGF-1, IGFBP-3, and IGF-1/IGFBP-3 and functional and cognitive outcomes in the Mayo Clinic Study of Aging

Levels of insulin-like growth factor (IGF)-1, IGF-binding protein (IGFBP)-3, and their ratio in the blood may be useful for monitoring those at risk of cognitive and functional decline. However, the association between IGF measures and functional and cognitive outcomes has been mixed, and the associations may vary by sex. The present study investigated the cross-sectional, sex-specific associations between serum measures total IGF-1, IGFBP-3, and the IGF-1/IGFBP-3 ratio, gait speed, and cognition in 1320 cognitively unimpaired participants aged 50-95 years enrolled in the Mayo Clinic Study of Aging. We used multivariable linear regression models to determine the association between IGF measures and gait speed or cognitive test performance by sex. IGF measures were not associated with cognitive or functional performance among men. Among women, higher levels of log total IGF-1 and IGFBP-3 were associated with better performance in attention, visuospatial, and global cognitive domains, independent of the gait speed. These findings suggest that among women, IGF measures are associated with cognition, and these associations are independent of function.

Growth Hormone and Aging: Updated Review

Role of growth hormone (GH) in mammalian aging is actively explored in clinical, epidemiological, and experimental studies. The age-related decline in GH levels is variously interpreted as a symptom of neuroendocrine aging, as one of causes of altered body composition and other unwelcome symptoms of aging, or as a mechanism of natural protection from cancer and other chronic diseases. Absence of GH signals due to mutations affecting anterior pituitary development, GH secretion, or GH receptors produces an impressive extension of longevity in laboratory mice. Extension of healthspan in these animals and analysis of survival curves suggest that in the absence of GH, aging is slowed down or delayed. The corresponding endocrine syndromes in the human have no consistent impact on longevity, but are associated with remarkable protection from age-related disease. Moreover, survival to extremely old age has been associated with reduced somatotropic (GH and insulin-like growth factor-1) signaling in women and men. In both humans and mice, elevation of GH levels into the supranormal (pathological) range is associated with increased disease risks and reduced life expectancy likely representing acceleration of aging. The widely advertised potential of GH as an anti-aging agent attracted much interest. However, results obtained thus far have been disappointing with few documented benefits and many troublesome side effects. Possible utility of GH in the treatment of sarcopenia and frailty remains to be explored.

MECHANISMS IN ENDOCRINOLOGY: Lessons from growth hormone receptor gene-disrupted mice: are there benefits of endocrine defects?

Growth hormone (GH) is produced primarily by anterior pituitary somatotroph cells. Numerous acute human (h) GH treatment and long-term follow-up studies and extensive use of animal models of GH action have shaped the body of GH research over the past 70 years. Work on the GH receptor (R)-knockout (GHRKO) mice and results of studies on GH-resistant Laron Syndrome (LS) patients have helped define many physiological actions of GH including those dealing with metabolism, obesity, cancer, diabetes, cognition and aging/longevity. In this review, we have discussed several issues dealing with these biological effects of GH and attempt to answer the question of whether decreased GH action may be beneficial.

Birth weight predicts aging trajectory: A hypothesis

Increasing evidence suggests that risk for age-related disease and longevity can be programmed early in life. In human populations, convincing evidence has been accumulated indicating that intrauterine growth restriction (IUGR) resulting in low birth weight (<2.5 kg) followed by postnatal catch-up growth is associated with various aspects of metabolic syndrome, type 2 diabetes and cardiovascular disease in adulthood. Fetal macrosomia (birth weight > 4.5 kg), by contrast, is associated with high risk of non-diabetic obesity and cancers in later life. Developmental modification of epigenetic patterns is considered to be a central mechanism in determining such developmentally programmed phenotypes. Growth hormone/insulin-like growth factor (GH/IGF) axis is likely a key driver of these processes. In this review, evidence is discussed that suggests that different aging trajectories can be realized depending on developmentally programmed life-course dynamics of IGF-1. In this hypothetical scenario, IUGR-induced deficit of IGF-1 causes "diabetic" aging trajectory associated with various metabolic disorders in adulthood, while fetal macrosomia-induced excessive levels of IGF-1 lead to "cancerous" aging trajectory. If the above reasoning is correct, then both low and high birth weights are predictors of short life expectancy, while the normal birth weight is a predictor of "normal" aging and maximum longevity.

Leukocyte count, systemic inflammation, and health status in older adults: a narrative review

Epidemiological and clinical studies suggest that elevated leukocyte count within the normal range can predict cardiovascular and total mortality in older adults. These findings are remarkable because this simple and common laboratory test is included in routine medical check-ups. It is well known that chronic systemic inflammation (inflammaging) is one of the hallmarks of aging and an important component of obesity-associated insulin resistance that can lead to type 2 diabetes and other health problems in both overweight individuals and elderly people. To understand the molecular mechanisms linking increased systemic inflammation with aging-associated diseases and elevated leukocyte counts in the elderly is to unravel the multiplicity of molecular factors and mechanisms involved in chronic low-grade systemic inflammation, the gradual accumulation of random molecular damage, age-related diseases, and the process of leukopoiesis. There are several possible mechanisms through which chronic low-grade systemic inflammation is associated with both higher leukocyte count and a greater risk of aging-associated conditions in older adults. For example, the IL-6 centric model predicts that this biomediator is involved in chronic systemic inflammation and leukopoiesis, thereby suggesting that elevated leukocyte count is a signal of poor health in older adults. Alternatively, an increase in neutrophil and monocyte counts can be a direct cause of cardiovascular events in the elderly. Interestingly, some authors assert that the predictive ability of elevated leukocyte counts with regard to cardiovascular and allcause mortality among older adults surpass the predictive value of total cholesterol. This review reports the recent findings on the links between elevated but normal leukocyte counts and the increased risks of all-cause, cardiovascular, and cancer mortality. The possible molecular mechanisms linking higher but normal leukocyte counts with increased risk of aging-associated diseases in the elderly are discussed here.

Prolonged Growth Hormone/Insulin/Insulin-like Growth Factor Nutrient Response Signaling Pathway as a Silent Killer of Stem Cells and a Culprit in Aging

The dream of slowing down the aging process has always inspired mankind. Since stem cells are responsible for tissue and organ rejuvenation, it is logical that we should search for encoded mechanisms affecting life span in these cells. However, in adult life the hierarchy within the stem cell compartment is still not very well defined, and evidence has accumulated that adult tissues contain rare stem cells that possess a broad trans-germ layer differentiation potential. These most-primitive stem cells-those endowed with pluripotent or multipotent differentiation ability and that give rise to other cells more restricted in differentiation, known as tissue-committed stem cells (TCSCs) - are of particular interest. In this review we present the concept supported by accumulating evidence that a population of so-called very small embryonic-like stem cells (VSELs) residing in adult tissues positively impacts the overall survival of mammals, including humans. These unique cells are prevented in vertebrates from premature depletion by decreased sensitivity to growth hormone (GH), insulin (INS), and insulin-like growth factor (IGF) signaling, due to epigenetic changes in paternally imprinted genes that regulate their resistance to these factors. In this context, we can envision nutrient response GH/INS/IGF signaling pathway as a lethal factor for these most primitive stem cells and an important culprit in aging.

Insulin-like Growth Factor 1 (IGF-1) as a marker of cognitive decline in normal ageing: A review

Insulin-like Growth Factor 1 (IGF-1) and its signaling pathway play a primary role in normal growth and ageing, however serum IGF-1 is known to reduce with advancing age. Recent findings suggest IGF-1 is essential for neurogenesis in the adult brain, and this reduction of IGF-1 with ageing may contribute to age-related cognitive decline. Experimental studies have shown manipulation of the GH/GF-1 axis can slow rates of cognitive decline in animals, making IGF-1 a potential biomarker of cognition, and/or its signaling pathway a possible therapeutic target to prevent or slow age-related cognitive decline. A systematic literature review and qualitative narrative summary of current evidence for IGF-1 as a biomarker of cognitive decline in the ageing brain was undertaken. Results indicate IGF-1 concentrations do not confer additional diagnostic information for those with cognitive decline, and routine clinical measurement of IGF-1 is not currently justified. In cases of established cognitive impairment, it remains unclear whether increasing circulating or brain IGF-1 may reverse or slow down the rate of further decline. Advances in neuroimaging, genetics, neuroscience and the availability of large well characterized biobanks will facilitate research exploring the role of IGF-1 in both normal ageing and age-related cognitive decline.

Nutrient Sensing, Signaling and Ageing: The Role of IGF-1 and mTOR in Ageing and Age-Related Disease

Nutrient signaling through insulin/IGF-1 was the first pathway demonstrated to regulate ageing and age-related disease in model organisms. Pharmacological or dietary interventions targeting nutrient signaling pathways have been shown to robustly attenuate ageing in many organisms. Caloric restriction, the most widely studied longevity promoting intervention, works through multiple nutrient signaling pathways, while inhibition of mTOR through treatment with rapamycin reproducibly delays ageing and disease through specific inhibition of the mTOR complexes. Although the benefits of reduced insulin/IGF-1 in lifespan and health are well documented in model organisms, defining the precise role of the IGF-1 in human ageing and age-related disease has proven more difficult. Association studies provide some insight but also reveal paradoxes. Low serum IGF-1 predicts longevity, but IGF-1 decreases with age and IGF-1 therapy benefits some of age-related pathologies. Circulating IGF-1 has been associated both positively and negatively with risk of age-related diseases in humans, and in some cases both activation and inhibition of IGF-1 signaling have provided benefit in animal models of the same diseases. Interventions designed modulate the nutrient sensing signaling pathways positively or negatively are already available for clinical use, highlighting the need for a clear understanding of the role of nutrient signaling in ageing and age-related disease. This chapter examines data from model organisms and human genetic association studies, with a special emphasis on IGF-1 and mTOR, and discusses potential models for resolving the paradoxes surrounding IGF-1 data.

The role of dietary patterns and exceptional parental longevity in healthy aging

BACKGROUND

Individuals with exceptional longevity and their offspring manifest a lower prevalence of age-related diseases than families without longevity. However, the contribution of dietary habits to protection from disease has not been systematically assessed in families with exceptional longevity.

OBJECTIVE

The aim of this study is to compare dietary patterns between individuals with parental longevity and individals without parental longevity.

METHODS

Dietary intake was evaluated using the Block Brief Food Frequency Questionnaire in 234 community dwelling Ashkenazi Jewish adults aged 65 years and older who were participants of the LonGenity study, which enrolls the offspring of parents with exceptional longevity (OPEL) and offspring of parents with usual survival (OPUS).

RESULTS

OPEL constituted 38% of the subjects. The two groups had similar daily intake of total calories (1119 vs. 1218 kcal, p = 0.83), grams of cholesterol (141 g vs. 143 g, p = 0.19), and grams of sodium (1324 g vs.1475 g, p = 0.45), in OPEL vs. OPUS respectively. There were also no significant differences in the intake of other macronutrients, micronutrients, nutritional supplements and consumption of various food groups between OPEL and OPUS after adjustment for age and sex.

DISCUSSION

A healthy diet is associated with a lower risk of several chronic diseases. Our study revealed that dietary intake did not differ between OPEL and OPUS; thus, pointing to the role of longevity genes in protecting from disease among individuals with familial longevity.

CONCLUSION

The offspring of long-lived parents do not differ in their dietary patterns compared to individuals without parental longevity.

Neurotrophic and Neuroregenerative Effects of GH/IGF1

Introduction. Human neurodegenerative diseases increase progressively with age and present a high social and economic burden. Growth hormone (GH) and insulin-like growth factor-1 (IGF-1) are both growth factors exerting trophic effects on neuronal regeneration in the central nervous system (CNS) and peripheral nervous system (PNS). GH and IGF-1 stimulate protein synthesis in neurons, glia, oligodendrocytes, and Schwann cells, and favor neuronal survival, inhibiting apoptosis. This study aims to evaluate the effect of GH and IGF-1 on neurons, and their possible therapeutic clinical applications on neuron regeneration in human subjects. Methods. In the literature, we searched the clinical trials and followed up studies in humans, which have evaluated the effect of GH/IGF-1 on CNS and PNS. The following keywords have been used: “GH/IGF-1” associated with “neuroregeneration”, “amyotrophic lateral sclerosis”, “Alzheimer disease”, “Parkinson’s disease”, “brain”, and “neuron”. Results. Of the retrieved articles, we found nine articles about the effect of GH in healthy patients who suffered from traumatic brain injury (TBI), and six studies (four using IGF-1 and two GH therapy) in patients with amyotrophic lateral sclerosis (ALS). The administration of GH in patients after TBI showed a significantly positive recovery of brain and mental function. Treatment with GH and IGF-1 therapy in ALS produced contradictory results. Conclusions. Although strong findings have shown the positive effects of GH/IGF-1 administration on neuroregeneration in animal models, a very limited number of clinical studies have been conducted in humans. GH/IGF-1 therapy had different effects in patients with TBI, evidencing a high recovery of neurons and clinical outcome, while in ALS patients, the results are contradictory. More complex clinical protocols are necessary to evaluate the effect of GH/IGF-1 efficacy in neurodegenerative diseases. It seems evident that GH and IGF-1 therapy favors the optimal recovery of neurons when a consistent residual activity is still present. Furthermore, the effect of GH/IGF-1 could be mediated by, or be overlapped with that of other hormones, such as estradiol and testosterone.

Lower circulating insulin-like growth factor-I is associated with better cognition in females with exceptional longevity without compromise to muscle mass and function

Mutations that reduce somatotropic signaling result in improved lifespan and health-span in model organisms and humans. However, whether reduced circulating insulin-like growth factor-I (IGF-I) level is detrimental to cognitive and muscle function in older adults remains understudied. A cross-sectional analysis was performed in Ashkenazi Jews with exceptional longevity (age ≥95 years). Cognition was assessed using the Mini-Mental State Examination and muscle function with the chair rise test, grip-strength, and gait speed. Muscle mass was estimated using the skeletal muscle index. Serum IGF-I was measured with liquid chromatography mass spectrometry. In gender stratified age-adjusted logistic regression analysis, females with IGF-I levels in the first tertile had lower odds of being cognitively impaired compared to females with IGF-I levels within the upper two tertiles, OR (95% CI) 0.39 (0.19-0.82). The result remained significant after adjustment for multiple parameters. No significant association was identified in males between IGF-I and cognition. No relationship was found between IGF-I tertiles and muscle function and muscle mass in females or males. Lower circulating IGF-I is associated with better cognitive function in females with exceptional longevity, with no detriment to skeletal muscle mass and function.

Cellular lifespan and senescence: a complex balance between multiple cellular pathways

The study of cellular senescence and proliferative lifespan is becoming increasingly important because of the promises of autologous cell therapy, the need for model systems for tissue disease and the implication of senescent cell phenotypes in organismal disease states such as sarcopenia, diabetes and various cancers, among others. Here, we explain the concepts of proliferative cellular lifespan and cellular senescence, and we present factors that have been shown to mediate cellular lifespan positively or negatively. We review much recent literature and present potential molecular mechanisms by which lifespan mediation occurs, drawing from the fields of telomere biology, metabolism, NAD(+) and sirtuin biology, growth factor signaling and oxygen and antioxidants. We conclude that cellular lifespan and senescence are complex concepts that are governed by multiple independent and interdependent pathways, and that greater understanding of these pathways, their interactions and their convergence upon specific cellular phenotypes may lead to viable therapies for tissue regeneration and treatment of age-related pathologies, which are caused by or exacerbated by senescent cells in vivo.

Somatic growth, aging, and longevity

Although larger species of animals typically live longer than smaller species, the relationship of body size to longevity within a species is generally opposite. The longevity advantage of smaller individuals can be considerable and is best documented in laboratory mice and in domestic dogs. Importantly, it appears to apply broadly, including humans. It is not known whether theses associations represent causal links between various developmental and physiological mechanisms affecting growth and/or aging. However, variations in growth hormone (GH) signaling are likely involved because GH is a key stimulator of somatic growth, and apparently also exerts various “pro-aging” effects. Mechanisms linking GH, somatic growth, adult body size, aging, and lifespan likely involve target of rapamycin (TOR), particularly one of its signaling complexes, mTORC1, as well as various adjustments in mitochondrial function, energy metabolism, thermogenesis, inflammation, and insulin signaling. Somatic growth, aging, and longevity are also influenced by a variety of hormonal and nutritional signals, and much work will be needed to answer the question of why smaller individuals may be likely to live longer.

β-Hydroxybutyrate: A Signaling Metabolite

Various mechanisms in the mammalian body provide resilience against food deprivation and dietary stress. The ketone body β-hydroxybutyrate (BHB) is synthesized in the liver from fatty acids and represents an essential carrier of energy from the liver to peripheral tissues when the supply of glucose is too low for the body's energetic needs, such as during periods of prolonged exercise, starvation, or absence of dietary carbohydrates. In addition to its activity as an energetic metabolite, BHB is increasingly understood to have cellular signaling functions. These signaling functions of BHB broadly link the outside environment to epigenetic gene regulation and cellular function, and their actions may be relevant to a variety of human diseases as well as human aging.

Aging: Molecular Pathways and Implications on the Cardiovascular System

The world's population over 60 years is growing rapidly, reaching 22% of the global population in the next decades. Despite the increase in global longevity, individual healthspan needs to follow this growth. Several diseases have their prevalence increased by age, such as cardiovascular diseases, the leading cause of morbidity and mortality worldwide. Understanding the aging biology mechanisms is fundamental to the pursuit of cardiovascular health. In this way, aging is characterized by a gradual decline in physiological functions, involving the increased number in senescent cells into the body. Several pathways lead to senescence, including oxidative stress and persistent inflammation, as well as energy failure such as mitochondrial dysfunction and deregulated autophagy, being ROS, AMPK, SIRTs, mTOR, IGF-1, and p53 key regulators of the metabolic control, connecting aging to the pathways which drive towards diseases. In addition, senescence can be induced by cellular replication, which resulted from telomere shortening. Taken together, it is possible to draw a common pathway unifying aging to cardiovascular diseases, and the central point of this process, senescence, can be the target for new therapies, which may result in the healthspan matching the lifespan.

Predictive value of multiple cytokines and chemokines for mortality in an admixed population: 15-year follow-up of the Bambui-Epigen (Brazil) cohort study of aging

Inflammation, particularly elevated IL-6 serum levels, has been associated with increased mortality risk, mostly in Caucasians. The influence of genetic ethno-racial background on this association is unknown. We examined associations between baseline serum levels of Interleukin-6 (IL-6) and other cytokines (IL1-2, TNF, IL-10, and IL1β) and chemokines (CCL2, CCL5, CXCL8, CXCL9 and CXCL10) with 15-year mortality in 1,191 admixed Brazilians aged 60years and over. Elevated IL6 level (but not other biomarkers) was associated with increased risk of deaths with fully adjusted hazard ratios of 1.51 (95% CI=1.15, 1.97), 1.54 (95% CI=1.20, 1.96) and 1.79 (95% CI=1.40, 2.29) for the 2nd, 3rd and the highest quartiles, respectively. Genomic African and Native American proportions did not modify the association (p>0.05). The discriminatory ability to predict death of a model based on IL-6 alone was similar as that of a comprehensive morbidity score (C statistics=0.59 and 0.60, respectively). The abilities of IL-6 and the morbidity score models to predict death remained stable for very long term after the baseline measurement. Our results indicate that genome-based African and Native American ancestries have no impact on the prognostic value of IL-6 for mortality.

THE ENDOCRINOLOGY OF AGING: A KEY TO LONGEVITY "GREAT EXPECTATIONS"

ABBREVIATIONS

AMP = adenosine monophosphate CETP = cholesteryl ester transfer protein FOXO = Forkhead box O GH = growth hormone HDL = high-density lipoprotein IGF-1 = insulin-like growth factor 1 LDL = low-density lipoprotein miRNA = microRNA mTOR = mammalian target of rapamycin SIRT = sirtuin T4 = thyroxine TSH = thyroid-stimulating hormone "The Moving Finger writes; and, having writ, Moves on: nor all thy Piety nor Wit Shall lure it back to cancel half a Line, Nor all thy Tears wash out a Word of it." Omar Khayyam ( 1 ).