Leptin signaling and aging: insight from caloric restriction

Caloric restriction in female reproduction: is it beneficial or detrimental?

Caloric restriction (CR), an energy-restricted intervention with undernutrition instead of malnutrition, is widely known to prolong lifespan and protect against the age-related deteriorations. Recently it is found that CR significantly affects female reproduction via hypothalamic (corticotropin releasing hormone, neuropeptide Y, agouti-related peptide) and peripheral (leptin, ghrelin, insulin, insulin-like growth factor) mediators, which can regulate the energy homeostasis. Although CR reduces the fertility in female mammals, it exerts positive effects like preserving reproductive capacity. In this review, we aim to discuss the comprehensive effects of CR on the central hypothalamus-pituitary-gonad axis and peripheral ovary and uterus. In addition, we emphasize the influence of CR during pregnancy and highlight the relationship between CR and reproductive-associated diseases. Fully understanding and analyzing the effects of CR on the female reproduction could provide better strategies for the management and prevention of female reproductive dysfunctions.

Multi-Omic Biological Age Estimation and Its Correlation With Wellness and Disease Phenotypes: A Longitudinal Study of 3,558 Individuals

Biological age (BA), derived from molecular and physiological measurements, has been proposed to better predict mortality and disease than chronological age (CA). In the present study, a computed estimate of BA was investigated longitudinally in 3,558 individuals using deep phenotyping, which encompassed a broad range of biological processes. The Klemera-Doubal algorithm was applied to longitudinal data consisting of genetic, clinical laboratory, metabolomic, and proteomic assays from individuals undergoing a wellness program. BA was elevated relative to CA in the presence of chronic diseases. We observed a significantly lower rate of change than the expected ~1 year/year (to which the estimation algorithm was constrained) in BA for individuals participating in a wellness program. This observation suggests that BA is modifiable and suggests that a lower BA relative to CA may be a sign of healthy aging. Measures of metabolic health, inflammation, and toxin bioaccumulation were strong predictors of BA. BA estimation from deep phenotyping was seen to change in the direction expected for both positive and negative health conditions. We believe BA represents a general and interpretable "metric for wellness" that may aid in monitoring aging over time.

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.

The effect of different levels of dietary restriction on glucose homeostasis and metabolic memory

Over the past 50 years, dietary restriction (DR) has been shown to extend the life span of a wide variety of organisms. A hallmark feature of DR is improved glucose homeostasis resulting in increased glucose tolerance and insulin sensitivity of animals ranging from rodents to humans. In this study, we demonstrate the early effects of varying levels of DR on glucose tolerance. Within 10 days of 40% DR, glucose tolerance was significantly improved and by 120 days; 10 and 20% DR also showed enhanced glucose tolerance. All three levels of DR showed reduced adiposity, increased expression of genes involved in fat turnover, and a reduction in the expression for markers of inflammation. Studies have shown that mice fed a DR diet retained metabolic memory in terms of improved glucose tolerance even after DR is discontinued. We show that 40% DR not only has an early effect on glucose tolerance but also maintained it after DR was discontinued for 2 months. Therefore, improvement in glucose tolerance is brought about by all three levels of DR but the metabolic memory is not dose responsive.

The effects of graded levels of calorie restriction: II. Impact of short term calorie and protein restriction on circulating hormone levels, glucose homeostasis and oxidative stress in male C57BL/6 mice

Limiting food intake attenuates many of the deleterious effects of aging, impacting upon healthspan and leading to an increased lifespan. Whether it is the overall restriction of calories (calorie restriction: CR) or the incidental reduction in macronutrients such as protein (protein restriction: PR) that mediate these effects is unclear. The impact of 3 month CR or PR, (10 to 40%), on C57BL/6 mice was compared to controls fed ad libitum. Reductions in circulating leptin, tumor necrosis factor-α and insulin-like growth factor-1 (IGF-1) were relative to the level of CR and individually associated with morphological changes but remained unchanged following PR. Glucose tolerance and insulin sensitivity were improved following CR but not affected by PR. There was no indication that CR had an effect on oxidative damage, however CR lowered antioxidant activity. No biomarkers of oxidative stress were altered by PR. CR significantly reduced levels of major urinary proteins suggesting lowered investment in reproduction. Results here support the idea that reduced adipokine levels, improved insulin/IGF-1 signaling and reduced reproductive investment play important roles in the beneficial effects of CR while, in the short-term, attenuation of oxidative damage is not applicable. None of the positive effects were replicated with PR.

Obese mice on a high-fat alternate-day fasting regimen lose weight and improve glucose tolerance

Alternate-day fasting (ADF) causes body weight (BW) loss in humans and rodents. However, it is not clear that ADF while maintaining a high-fat (HF) diet results in weight loss and the accompanying improvement in control of circulating glucose. We tested the hypotheses that a high-fat ADF protocol in obese mice would result in (i) BW loss, (ii) improved glucose control, (iii) fluctuating phenotypes on 'fasted' days when compared to 'fed' days and (iv) induction of torpor on 'fasted days'. We evaluated the physiological effects of ADF in diet-induced obese mice for BW, heart rate (HR), body temperature (T_b ), glucose tolerance, insulin responsiveness, blood parameters (leptin, insulin, free fatty acids) and hepatic gene expression. Diet-induced obese male C57BL/6J mice lost one-third of their pre-diet BW while on an ADF diet for 10 weeks consisting of HF food. The ADF protocol improved glucose tolerance and insulin sensitivity, although mice on a fast day were less glucose tolerant than the same mice on a fed day. ADF mice on a fast day had low circulating insulin, but had an enhanced response to an insulin-assisted glucose tolerance test, suggesting the impaired glucose tolerance may be a result of insufficient insulin production. On fed days, ADF mice were the warmest, had a high HR and displayed hepatic gene expression and circulating leptin that closely mimicked that of mice fed an ad lib HF diet. ADF mice never entered torpor as assessed by HR and T_b . However, on fast days, they were the coolest, had the slowest HR, and displayed hepatic gene expression and circulating leptin that closely mimicked that of Chow-Fed mice. Collectively, the ADF regimen with a HF diet in obese mice results in weight loss, improved blood glucose control, and daily fluctuations in selected physiological and biochemical parameters in the mouse.

The effects of graded levels of calorie restriction: VI. Impact of short-term graded calorie restriction on transcriptomic responses of the hypothalamic hunger and circadian signaling pathways

Food intake and circadian rhythms are regulated by hypothalamic neuropeptides and circulating hormones, which could mediate the anti-ageing effect of calorie restriction (CR). We tested whether these two signaling pathways mediate CR by quantifying hypothalamic transcripts of male C57BL/6 mice exposed to graded levels of CR (10 % to 40 %) for 3 months. We found that the graded CR manipulation resulted in upregulation of core circadian rhythm genes, which correlated negatively with circulating levels of leptin, insulin-like growth factor 1 (IGF-1), insulin, and tumor necrosis factor alpha (TNF-α). In addition, key components in the hunger signaling pathway were expressed in a manner reflecting elevated hunger at greater levels of restriction, and which also correlated negatively with circulating levels of insulin, TNF-α, leptin and IGF-1. Lastly, phenotypes, such as food anticipatory activity and body temperature, were associated with expression levels of both hunger genes and core clock genes. Our results suggest modulation of the hunger and circadian signaling pathways in response to altered levels of circulating hormones, that are themselves downstream of morphological changes resulting from CR treatment, may be important elements in the response to CR, driving some of the key phenotypic outcomes.

The Association of Serum Leptin with Mortality in Older Adults

Objective

Elevated levels of serum leptin are associated with increased adiposity and production of pro-inflammatory cytokines. Both cytokines and body adiposity have been shown to predict cardiovascular events and mortality. The primary objective of the present study is to explore the associations between serum leptin and all-cause mortality and mortality from cardiovascular disease (CVD) over a span of 10 years, controlling for body adiposity and proinflammatory cytokines.

Methods

The Health, Aging and Body Composition (Health ABC) study is a prospective cohort of 3,075 older adults aged 70 to 79 years. This analysis includes 2,919 men and women with complete serum leptin and vital status data. Data on all-cause mortality and incident cardiovascular events (including Coronary Heart Disease and Congestive Heart Failure) were collected over 10 years of follow-up (mean 8.4 years).

Results

Women with leptin in quartile 2 and 3 were at lower risk of all-cause mortality, and those with leptin in quartile 2 were at lower risk of mortality from CVD as compared to women with lowest leptin values when adjusted for age, race, site, years of education, alcohol use, smoking, and physical activity. When these associations were additionally adjusted for body fat, C-reactive protein and pro-inflammatory cytokines, women with leptin values in quartile 3 were at lower risk of all-cause mortality and women with leptin in quartile 2 and 3 were at lower risk of mortality from CVD than women with lowest leptin values. These associations were not significant among men after adjusting for body fat and cytokines.

Conclusions

The present study suggests that moderately elevated concentrations of serum leptin are independently associated with lower risk of all-cause mortality and CVD-related mortality among older women. Among men, serum leptin is not associated with reduced risk of all-cause and CVD mortality after controlling for body fat and cytokines.

Exercise training and calorie restriction influence the metabolic parameters in ovariectomized female rats

The estrogen deficiency after menopause leads to overweight or obesity, and physical exercise is one of the important modulators of this body weight gain. Female Wistar rats underwent ovariectomy surgery (OVX) or sham operation (SO). OVX and SO groups were randomized into new groups based on the voluntary physical activity (with or without running) and the type of diet for 12 weeks. Rats were fed standard chow (CTRL), high triglyceride diet (HT), or restricted diet (CR). The metabolic syndrome was assessed by measuring the body weight gain, the glucose sensitivity, and the levels of insulin, triglyceride, leptin, and aspartate aminotransferase transaminase (AST) and alanine aminotransferase (ALT). The exercise training combined with the CR resulted in improvements in the glucose tolerance and the insulin sensitivity. Plasma TG, AST, and ALT levels were significantly higher in OVX rats fed with HT but these high values were suppressed by exercise and CR. Compared to SO animals, estrogen deprivation with HT caused a significant increase in leptin level. Our data provide evidence that CR combined with voluntary physical exercise can be a very effective strategy to prevent the development of a metabolic syndrome induced by high calorie diet.

Melatonin regulates aging and neurodegeneration through energy metabolism, epigenetics, autophagy and circadian rhythm pathways

Brain aging is linked to certain types of neurodegenerative diseases and identifying new therapeutic targets has become critical. Melatonin, a pineal hormone, associates with molecules and signaling pathways that sense and influence energy metabolism, autophagy, and circadian rhythms, including insulin-like growth factor 1 (IGF-1), Forkhead box O (FoxOs), sirtuins and mammalian target of rapamycin (mTOR) signaling pathways. This review summarizes the current understanding of how melatonin, together with molecular, cellular and systemic energy metabolisms, regulates epigenetic processes in the neurons. This information will lead to a greater understanding of molecular epigenetic aging of the brain and anti-aging mechanisms to increase lifespan under healthy conditions.

Plasma adipokines and risk of hepatocellular carcinoma in chronic hepatitis B virus-infected carriers: a prospective study in taiwan

BACKGROUND

Obesity is considered a risk factor for hepatocellular carcinoma (HCC). The relationship between adipocytokine and HCC in hepatitis B virus (HBV) carriers remains unclear. We prospectively investigated the association of adiponectin, leptin, and visfatin levels with HCC.

METHODS

We conducted a nested case-control study in a community-based cohort with 187 incident HCC and 374 HCC-free HBV carriers. Unconditional logistic regression was conducted to estimate the ORs and 95% confidence intervals (CI).

RESULTS

Adiponectin, but not leptin and visfatin, levels were associated with an increased risk of HCC after adjustment for other metabolic factors and HBV-related factors. The risk was increased [OR = 0.51; 95% CI, 0.12-2.11; OR = 4.88 (1.46-16.3); OR = 3.79 (1.10-13.0); OR = 4.13 (1.13-15.1) with each additional quintiles, respectively] with a significant dose-response trend (P(trend) = 0.003). HCC risk associated with higher adiponectin level was higher in HBV carriers with ultrasonographic fatty liver, genotype C infection, higher viral load, and with elevated alanine aminotransferase. Longitudinally, participants with higher adiponectin were less likely to achieve surface antigen of hepatitis B virus (HBsAg) seroclearance and more likely to have persistently higher HBV DNA. Eventually, they were more likely to develop liver cirrhosis [OR = 1.65 (0.62-4.39); OR = 3.85 (1.47-10.1); OR = 2.56 (0.96-6.84); OR = 3.76 (1.33-10.7) for the second, third, fourth, and fifth quintiles, respectively; P(trend) = 0.017] before HCC.

CONCLUSIONS

Elevated adiponectin levels were independently associated with an increased risk of HCC.

IMPACT

Adiponectin may play different roles in the virus-induced and metabolic-related liver diseases, but the underlying mechanism remains unknown.

Age versus nutritional state in the development of central leptin resistance

Leptin, a catabolic adiposity signal acts in the hypothalamus via suppressing food intake and inducing hypermetabolism. Age and obesity are accompanied by leptin resistance. The present study aimed to clarify which components of the catabolic leptin effects are influenced most strongly by aging and which ones by nutritional state-induced alterations in body composition. In our biotelemetric study the effects of a 7-day intracerebroventricular leptin infusion on various parameters of energy balance (food intake, body weight, oxygen consumption, heart rate and body temperature) were analyzed in male Wistar rats of different age-groups (from 3 to 24 months) and nutritional states (normally fed, diet-induced obese and calorie-restricted). Leptin resistance of older animals affected hypermetabolic actions, whereas leptin induced anorexia in all age-groups. Weight reducing effect of leptin diminished in middle-aged and aging animals to become significant again in the oldest group. In diet-induced obese rats leptin-induced hypermetabolism of the young rats and hypermetabolism plus anorexia of the aging ones were suppressed. Calorie-restriction reduced body weight and fat mass to a similar extent in all age-groups. It strongly enhanced leptin-induced hypermetabolism at all ages and prevented the manifestation of anorexigenic actions of leptin with the exception of the oldest group. This latter finding suggests an unexpected increase of responsiveness to anorexigenic leptin actions in old rats. Accordingly, anorexia and hypermetabolism change in disparate ways with aging. Nutritional state predominantly influences hypermetabolic leptin actions. Resistance to both hypermetabolic and anorexigenic actions were promoted by obesity, while calorie-restriction enhanced responsiveness to leptin, especially in old rats.

Lifelong caloric restriction prevents age-induced oxidative stress in the sympathoadrenal system of Fischer 344 x Brown Norway rats

Aging is associated with oxidative damage and an imbalance in redox signaling in a variety of tissues, yet little is known about the extent of age-induced oxidative stress in the sympathoadrenal system. Lifelong caloric restriction has been shown to lower levels of oxidative stress and slow the aging process. Therefore, the aims of this study were twofold: (1) to investigate the effect of aging on oxidative stress in the adrenal medulla and hypothalamus and (2) determine if lifelong 40% caloric restriction (CR) reverses the adverse effects of age-induced oxidative stress in the sympathetic adrenomedullary system. Adult (18months) and very old (38months) male Fischer 344 x Brown Norway rats were divided into ad libitum or 40% CR groups and parameters of oxidative stress were analyzed in the adrenal medulla and the hypothalamus. A significant age-dependent increase in lipid peroxidation (+20%, P<0.05) and tyrosine nitration (+111%, P<0.001) were observed in the adrenal medulla while age resulted in a reduction in the protein expression of key antioxidant enzymes, CuZnSOD (-27%, P<0.01) and catalase (-27%, P<0.05) in the hypothalamus. Lifelong CR completely prevented the age-induced increase in lipid peroxidation in the adrenal medulla and restored the age-related decline in antioxidant enzymes in the hypothalamus. These data indicate that aging results in a significant increase in oxidative stress in the sympathoadrenal system. Importantly, lifelong CR restored the age-related changes in oxidative stress in the adrenal medulla and hypothalamus. Caloric restriction could be a potential non-pharmacological intervention to prevent increased oxidative stress in the sympathetic adrenomedullary system with age.

Relationship between plasma ghrelin, insulin, leptin, interleukin 6, adiponectin, testosterone and longevity in the Baltimore Longitudinal Study of Aging

BACKGROUND AND AIMS

Caloric restriction (CR) is the most robust and reproducible intervention for slowing aging, and maintaining health and vitality in animals. Previous studies found that CR is associated with changes in specific biomarkers in monkeys that were also associated with reduced risk of mortality in healthy men. In this study we examine the association between other potential biomarkers related to CR and extended lifespan in healthy humans.

METHODS

Based on the Baltimore Longitudinal Study of Aging, "long-lived" participants who survived to at least 90 years of age (n=41, cases) were compared with "short-lived" participants who died between 72-76 years of age (n=31, controls) in the nested case control study. Circulating levels of ghrelin, insulin, leptin, interleukin 6, adiponectin and testosterone were measured from samples collected between the ages 58 to 70 years. Baseline differences between groups were examined with t-test or Wilcoxon test, and mixed effects general linear model was used for a logistic model to differentiate the two groups with multiple measurements on some subjects.

RESULTS

At the time of biomarkers evaluation (58-70 yrs), none of the single biomarker levels was significantly different between the two groups. However, after combining information from multiple biomarkers by adding the z-transformed values, the global score differentiated the long- and short-lived participants (p=0.05).

CONCLUSIONS

In their sixties, long-lived and short-lived individuals do not differ in biomarkers that have been associated with CR in animals. However, difference between the groups was only obtained when multiple biomarker dysregulation was considered.

Caloric restriction and antiaging effects

Caloric restriction (CR) is widely used to study aging processes. It is a simple and highly reproducible method for delaying the aging process, preventing the onset of aging-related diseases and extending average or maximum lifespan. However, the mechanism underlying these effects of CR is still not clear. CR can inhibit growth, reduce body size and maintain a low body temperature. At the same time, there is a measurable decrease in the volume of adipose tissue, hyperglycemia and hyperinsulinemia, accompanied by modifications of lipid and energy metabolism and increased resistance to endogenous and extraneous stress. The metabolic changes induced by dietary restriction, the inhibition of fat deposition in nonadipose tissue and the effects on signal transduction are considered the most likely candidates for mechanisms underlying the effects of CR.

Adipose-immune interactions during obesity and caloric restriction: reciprocal mechanisms regulating immunity and health span

Increasing evidence suggests a tight coupling of metabolic and immune systems. This cross-talk mediated by neuroendocrine peptides as well as numerous cytokines and chemokines is believed to be responsible for integrating energy balance to immune function. These neuroendocrine-immune interactions are heightened during the state of chronic positive energy balance, as seen during obesity, and negative energy balance caused by caloric restriction (CR). Emerging evidence suggests that obesity may be associated with an immunodeficient state and chronic inflammation, which contribute to an increased risk of premature death. The direct interactions between expanded leukocyte populations within the adipose tissue during obesity and an increased number of adipocytes within an aging lymphoid microenvironment may constitute an important adaptive or pathological response as a result of change in energy balance. In stark contrast to obesity, CR causes negative energy balance and robustly prolongs a healthy lifespan in all of the species studied to date. Therefore, the endogenous neuroendocrine-metabolic sensors elevated or suppressed as a result of changes in energy balance may offer an important mechanism in understanding the antiaging and potential immune-enhancing nature of CR. Ghrelin, one such sensor of negative energy balance, is reduced during obesity and increased by CR. Ghrelin also regulates immune function by reducing proinflammatory cytokines and promotes thymopoiesis during aging and thus, may be a new CR mimetic target. The identification of immune effects and molecular pathways used by such orexigenic metabolic factors could offer potentially novel approaches to enhance immunity and increase healthy lifespan.

Serum leptin level and cognition in the elderly: Findings from the Health ABC Study

Leptin is a peptide hormone secreted by adipocytes. It has been shown to modulate production and clearance of amyloid beta (Abeta) in rodent models. We sought to determine if serum leptin was associated with cognitive decline in the elderly. We studied 2871 well-functioning elders, aged 70-79, who were enrolled in a prospective study. Serum leptin concentrations were measured at baseline and analyzed by mean+/-1S.D. Clinically significantly cognitive decline over 4 years was defined as > or =5-point drop on the Modified Mini Mental State Exam (3MS). Compared to those in the lower leptin groups, elders in the high leptin group had less cognitive decline, 20.5% versus 24.7% (OR=0.79; 95% CI 0.61-1.02, p=0.07). After adjustment for demographic and clinical variables, including body mass index and total percent body fat, those in the high leptin group had significantly less likelihood of cognitive decline, OR=0.66 (95% CI 0.48-0.91). We conclude that in elderly individuals, higher serum leptin appears to protect against cognitive decline, independent of comorbidites and body fat.

Control of energy balance in relation to energy intake and energy expenditure in animals and man: an ecological perspective

In this paper, we consider the control of energy balance in animals and man. We argue that patterns of mammalian feeding have evolved to control energy balance in uncertain environments. It is, therefore, expected that, under sedentary conditions in which the diet is rich in nutrients and abundantly available, animals and man will overeat. This suggests that no physiological defects are needed to induce overweight and ultimately obesity in man. Several considerations arise from these observations. The time period over which energy balance is controlled is far longer than allowed by most experiments. Physiological models of energy balance control often treat excess energy intake as a defect of regulation; ecological models view the same behaviour as part of normal energy balance control in environments where resources are uncertain. We apply these considerations to common patterns of human and animal feeding. We believe that the ecological perspective gives a more accurate explanation for the functionality of excess fat and the need to defend nutrient balance and avoid gross imbalances, as well as explaining hyperphagia in the face of plenty. By emphasising the common features of energy balance control in different mammalian species, the importance of changes in behaviour to accommodate changes in the environment becomes apparent. This also opens up possibilities for the control of body weight and the treatment of obesity in man.

Effect of leptin on hypothalamic gene expression in calorie-restricted rats

Diminished leptin signaling to the arcuate nucleus of hypothalamus (ARH) may induce calorie restriction (CR)-specific neuroendocrine and metabolic adaptation, which is potentially relevant to the effect of CR. The present study investigated whether restoration of leptin signaling to the ARH could reverse CR-induced alterations in neuropeptide gene expression in rats. Male F344 rats, fed ad libitum or a 30% CR diet from 6 weeks of age, received leptin or vehicle intracerebroventricularly for 14 days via osmotic mini-pumps implanted in the subcutis at 34 weeks of age. The messenger RNA levels were quantified by real-time reverse transcription-polymerase chain reaction using total RNA extracted from microdissected tissues containing the ARH. The results indicated that leptin administration reversed the upregulated expression of neuropeptide Y and agouti-related protein genes in CR rats, suggesting the possibility of a role for the leptin-ARH pathway in the effect of CR.

Hyperleptinemia as a risk factor for high blood pressure in the elderly

CONTEXT

Studies have demonstrated that high serum leptin levels are associated with aging. However, we do not know whether hyperleptinemia is a relevant risk factor for high blood pressure (HBP) in the elderly.

OBJECTIVE

To determine the relationship between hyperleptinemia and HBP in the elderly.

DESIGN

A comparative cross-sectional study was carried out in a convenience sample of 70 healthy elderly persons comprising 46 women (mean age, 67 +/- 5.8 years) and 24 men (mean age, 73 +/- 7.5 years), and a group of 91 elderly persons with HBP, comprising 62 women (mean age, 67 +/- 8.2 years) and 29 men (mean age, 70 +/- 0.3 years). We measured serum leptin levels through the radioimmunoassay method.

RESULTS

The elderly subjects with HBP had significantly higher leptin levels than the healthy elderly subjects (P = .02). Furthermore, in female elderly subjects we observed a statistically significant correlation between systolic blood pressure and leptin (r = 0.37, P = .003), as well as systolic blood pressure and age (r = 0.29, P = .02), but not with diastolic blood pressure. In male elderly subjects, there was no correlation between leptin and systolic blood pressure or leptin and diastolic blood pressure. However, hyperleptinemia as risk factor for HBP was nearly 5 times higher in men than in women (men, odds ratio = 18.0, 95% confidence interval 3.2-100.9, P < .001 vs women, odds ratio = 3.33, 95% confidence interval 1.4-7.4, P = .003).

CONCLUSIONS

Our data suggest that hyperleptinemia was a significant risk factor for HBP elderly individuals, mainly in men.

Intracellular signalling pathways activated by leptin

Leptin is a versatile 16 kDa peptide hormone, with a tertiary structure resembling that of members of the long-chain helical cytokine family. It is mainly produced by adipocytes in proportion to fat size stores, and was originally thought to act only as a satiety factor. However, the ubiquitous distribution of OB-R leptin receptors in almost all tissues underlies the pleiotropism of leptin. OB-Rs belong to the class I cytokine receptor family, which is known to act through JAKs (Janus kinases) and STATs (signal transducers and activators of transcription). The OB-R gene is alternatively spliced to produce at least five isoforms. The full-length isoform, OB-Rb, contains intracellular motifs required for activation of the JAK/STAT signal transduction pathway, and is considered to be the functional receptor. Considerable evidence for systemic effects of leptin on body mass control, reproduction, angiogenesis, immunity, wound healing, bone remodelling and cardiovascular function, as well as on specific metabolic pathways, indicates that leptin operates both directly and indirectly to orchestrate complex pathophysiological processes. Consistent with leptin's pleiotropic role, its participation in and crosstalk with some of the main signalling pathways, including those involving insulin receptor substrates, phosphoinositide 3-kinase, protein kinase B, protein kinase C, extracellular-signal-regulated kinase, mitogen-activated protein kinases, phosphodiesterase, phospholipase C and nitric oxide, has been observed. The impact of leptin on several equally relevant signalling pathways extends also to Rho family GTPases in relation to the actin cytoskeleton, production of reactive oxygen species, stimulation of prostaglandins, binding to diacylglycerol kinase and catecholamine secretion, among others.

Effects of calorie restriction on reproductive and adrenal systems in Japanese quail: Are responses similar to mammals, particularly primates?

The benefits of calorie restriction (CR) have been established across a variety of vertebrate and invertebrate species. Although the effects of CR on lifespan in birds have not been examined, it is clear that CR has beneficial effects on reproductive, metabolic, and physiological function in adult poultry. We examined the effects of CR in Japanese quail, a rapidly maturing avian model, on reproductive endocrine and neuroendocrine systems. Male Japanese quail were pair fed at 0% ad libitum (AL), 20%, or 40% CR of AL, recorded for juveniles (3-7 weeks of age) or adults (12-16 weeks of age). Juvenile males on CR matured more slowly, and both juvenile and adult males had reduced plasma luteinizing hormone (LH) with CR. Adults on 40% CR showed evidence of stress, with increased plasma corticosterone and reduced testes weight and circulating androgens. In a separate study, pituitary gland response was tested in juvenile and adult castrated males that had been on the same CR treatments. All birds responded to gonadotropin releasing hormone (GnRH) challenge, with LH release. However, the 40% CR juvenile and adult birds had quantitatively lower responses, suggesting central inhibition of the reproductive axis. This hypothesis was tested by measurement of sexual behavior and catecholamines known to stimulate GnRH in hypothalamic regions that modulate these responses. Results showed reduced norepinephrine in key hypothalamic regions and reduced dopamine in posterior hypothalamus. These data support the hypothesis that CR affects reproductive function, with evidence for effects in the central nervous system. These data are discussed and compared to data collected in mammals, especially the rhesus monkey, on the effects of timing and degree of CR on reproductive and stress responses.

Energy restriction and aging

PURPOSE OF REVIEW

The focus of this review is on current research involving long-term calorie restriction and the resulting changes observed in possible biomarkers of aging. Special emphasis will be given to the basic and clinical science studies which are currently investigating the effects of controlled, high-quality energy-restricted diets on both biomarkers of longevity and on the development of chronic diseases related to age and obesity in humans.

RECENT FINDINGS

Prolonged calorie restriction has been shown to extend both the median and maximal lifespan in a variety of lower species such as yeast, worms, fish, rats, and mice. Mechanisms of this lifespan extension via calorie restriction are not fully elucidated, but possibly involve significant alterations in energy metabolism, oxidative damage, insulin sensitivity, and functional changes in both the neuroendocrine and sympathetic nervous systems. Ongoing studies of prolonged energy restriction in humans are now making it possible to analyze changes in these aging biomarkers to unravel some of the mechanisms of its antiaging phenomenon.

SUMMARY

With the incremental expansion of research endeavors in the area of energy or calorie restriction, data on the effects of calorie restriction in animal models and humans are becoming more accessible. Detailed analyses from controlled human trials involving long-term calorie restriction will allow investigators to link observed alterations in body composition down to changes in molecular pathways and gene expression, with their possible effects on the biomarkers of aging.

Reproductive Switch and Aging: The Case of Leptin Change in Dietary Restriction

We have proposed that normal food intake is geared toward optimizing the internal milieu for reproduction, despite some components of this milieu being detrimental to health. In dietary restriction, the animal is prevented from eating enough to attain or maintain reproductive capacity and this particular milieu does not materialize. Life extension occurs as a by-product. This idea provides a framework for exploring biomolecular changes in dietary restriction and their relevance to aging. Leptin is a case in point: here, a decrease in leptin level in dietary restriction is explored in the light of leptin's role in the complex signaling system of reproductive switch.

Adipose tissue energy metabolism: altered gene expression profile of mice subjected to long-term caloric restriction

We investigated the influences of short-term and lifespan-prolonging long-term caloric restriction (LCR) on gene expression in white adipose tissue (WAT). Over 11,000 genes were examined using high-density oligonucleotide microarrays in four groups of 10- to 11-month-old male C57Bl6 mice that were either fasted for 18 h before death (F), subjected to short-term caloric restriction for 23 days (SCR), or LCR for 9 months and compared with nonfasted control (CO) mice. Only a few transcripts of F and SCR were differentially expressed compared with CO mice. In contrast, 345 transcripts of 6,266 genes found to be expressed in WAT were altered significantly by LCR. The expression of several genes encoding proteins involved in energy metabolism was increased by LCR. Further, many of the shifts in gene expression after LCR are known to occur during adipocyte differentiation. Selected LCR-associated alterations of gene expression were supported by quantitative reverse transcriptase-polymerase chain reaction, histology, and histochemical examinations. Our data provide new insights on the metabolic state associated with aging retardation by LCR.

Anti-aging effects of caloric restriction: Involvement of neuroendocrine adaptation by peripheral signaling

Many hormonal signals from peripheral tissues contribute to the regulation of energy homeostasis and food intake. These regulators including leptin, insulin, and ghrelin, modulate the orexigenic and anorexigenic neuropeptide expression in hypothalamic nuclei. The anti-aging effects of caloric restriction have been explained from an evolutional viewpoint of the adaptive response of the neuroendocrine and metabolic response systems to maximize survival during periods of food shortage. In organisms, excess energy is stored in adipose tissues as a triglyceride preparation for such survival situations. Adipose tissue has recently been recognized as an endocrine organ, and leptin, as secreted by adipocyte, seems to be an especially important factor for the adaptive response to fasting and neuroendocrine alterations under caloric restriction. In this review, we discuss the potential involvement of neuroendocrine modulators in longevity and the anti-aging effects of caloric restriction.

Molecular-based therapeutic approaches in treatment of anorexia of aging and cancer cachexia

Loss of appetite, or anorexia, has profound implications for older persons, altering social interactions, reducing quality of life, and leading to weight loss with grave health consequences. Two conditions associated with anorexia considered in this article are the multidetermined anorexia of aging and the wasting syndrome termed cachexia induced by cancer. Nutritional interventions may have some benefit in the former, but are of limited value in the latter. Emerging studies at the molecular level relating to appetite regulation and energy balance may offer new approaches to arrest progressive weight loss in the anorexia of aging and cancer cachexia.

Aging is a deprivation syndrome driven by a germ-soma conflict

Evolution through natural selection can be described as driven by a perpetual conflict of individuals competing for limited resources. Recently, I postulated that the shortage of resources godfathered the evolutionary achievements of the differentiation-apoptosis programming [Rev. Neurosci. 12 (2001) 217]. Unicellular deprivation-induced differentiation into germ cell-like spores can be regarded as the archaic reproduction events which were fueled by the remains of the fratricided cells of the apoptotic fruiting body. Evidence has been accumulated suggesting that conserved through the ages as the evolutionary legacy of the germ-soma conflict, the somatic loss of immortality during the ontogenetic segregation of primordial germ cells recapitulates the archaic fate of the fruiting body. In this heritage, somatic death is a germ cell-triggered event and has been established as evolutionary-fixed default state following asymmetric reproduction in a world of finite resources. Aging, on the other hand, is the stress resistance-dependent phenotype of the somatic resilience that counteracts the germ cell-inflicted death pathway. Thus, aging is a survival response and, in contrast to current beliefs, is antagonistically linked to death that is not imposed by group selection but enforced upon the soma by the selfish genes of the "enemy within". Environmental conditions shape the trade-off solutions as compromise between the conflicting germ-soma interests. Mechanistically, the neuroendocrine system, particularly those components that control energy balance, reproduction and stress responses, orchestrate these events. The reproductive phase is a self-limited process that moulds onset and progress of senescence with germ cell-dependent factors, e.g. gonadal hormones. These degenerate the regulatory pacemakers of the pineal-hypothalamic-pituitary network and its peripheral, e.g. thymic, gonadal and adrenal targets thereby eroding the trophic milieu. The ensuing cellular metabolic stress engenders adaptive adjustments of the glucose-fatty acid cycle, responses that are adequate and thus fitness-boosting under fuel shortage (e.g. during caloric restriction) but become detrimental under fuel abundance. In a Janus-faced capacity, the cellular stress response apparatus expresses both tolerogenic and mutagenic features of the social and asocial deprivation responses [Rev. Neurosci. 12 (2001) 217]. Mediated by the derangement of the energy-Ca(2+)-redox homeostatic triangle, a mosaic of dedifferentiation/apoptosis and mutagenic responses actuates the gradual exhaustion of functional reserves and eventually results in a multitude of aging-related diseases. This scenario reconciles programmed and stochastic features of aging and resolves the major inconsistencies of current theories by linking ultimate and proximate causes of aging. Reproduction, differentiation, apoptosis, stress response and metabolism are merged into a coherent regulatory network that stages aging as a naturally selected, germ cell-triggered and reproductive phase-modulated deprivation response.