Age-specific effects of short- and long-term caloric restriction on the expression of adiponectin and adiponectin receptors: influence of intensity of food restriction

A systematic review and meta-analysis of environmental contaminant exposure impacts on weight loss and glucose regulation during calorie-restricted diets in preclinical studies: Persistent organic pollutants may impede glycemic control

Epidemiological evidence links chemical exposure with type 2 diabetes (T2DM) risk and prevalence. Chemical exposure may therefore also limit success of weight loss or restoration of glycemic control during calorie restricted diets. Few human studies examine this hypothesis. This systematic review and clustered meta-analysis examines preclinical evidence that exposure to anthropogenic environmental contaminants impedes weight loss and resumption of glycemic control during calorie restriction. Of five eligible papers from 212 unique citations, four used C57BL/6 mice and one used Sprague Dawley rats. In four the animals received high fat diets to induce obesity and impaired glycemic control. All examined persistent organic pollutants (POPs). Polychlorinated biphenyl (PCB) 77 exposure did not affect final mass (standardised mean difference (SMD) = -0.35 [-1.09, 0.39]; n = 5 (experiments); n = 3 (papers)), or response to insulin in insulin tolerance tests (SMD = -1.54 [-3.25, 0.16] n = 3 (experiments); n = 2 (papers)), but impaired glucose control in glucose tolerance tests (SMD = -1.30 [-1.96, -0.63]; n = 6 (experiments); n = 3 (papers)). The impaired glycemic control following perfluoro-octane sulphonic acid (PFOS) exposure and enhanced mass loss following dichlorodiphenyltrichloroethane (DDT) exposure have not been replicated. Animal studies thus suggest some chemical groups, especially PCB and PFOS, could impair glucose control management during calorie restriction, similar to conclusions from limited existing clinical studies. We discuss the research that is urgently required to inform weight management services that are now the mainstay prevention initiative for T2DM.

AMPK Activation Is Indispensable for the Protective Effects of Caloric Restriction on Left Ventricular Function in Postinfarct Myocardium

Background: Caloric restriction (CR) extends lifespan in many species, including mammals. CR is cardioprotective in senescent myocardium by correcting pre-existing mitochondrial dysfunction and apoptotic activation. Furthermore, it confers cardioprotection against acute ischemia-reperfusion injury. Here, we investigated the role of AMP-activated protein kinase (AMPK) in mediating the cardioprotective CR effects in failing, postinfarct myocardium. Methods: Ligation of the left coronary artery or sham operation was performed in rats and mice. Four weeks after surgery, left ventricular (LV) function was analyzed by echocardiography, and animals were assigned to different feeding groups (control diet or 40% CR, 8 weeks) as matched pairs. The role of AMPK was investigated with an AMPK inhibitor in rats or the use of alpha 2 AMPK knock-out mice. Results: CR resulted in a significant improvement in LV function, compared to postinfarct animals receiving control diet in both species. The improvement in LV function was accompanied by a reduction in serum BNP, decrease in LV proapoptotic activation, and increase in mitochondrial biogenesis in the LV. Inhibition or loss of AMPK prevented most of these changes. Conclusions: The failing, postischemic heart is protected from progressive loss of LV systolic function by CR. AMPK activation is indispensable for these protective effects.

Obesity-induced cognitive impairment in older adults: a microvascular perspective

Over two-thirds of individuals aged 65 and older are obese or overweight in the United States. Epidemiological data show an association between the degree of adiposity and cognitive dysfunction in the elderly. In this review, the pathophysiological roles of microvascular mechanisms, including impaired endothelial function and neurovascular coupling responses, microvascular rarefaction, and blood-brain barrier disruption in the genesis of cognitive impairment in geriatric obesity are considered. The potential contribution of adipose-derived factors and fundamental cellular and molecular mechanisms of senescence to exacerbated obesity-induced cerebromicrovascular impairment and cognitive decline in aging are discussed.

CTRP9 Mediates Protective Effects in Cardiomyocytes via AMPK- and Adiponectin Receptor-Mediated Induction of Anti-Oxidant Response

The C1q/tumor necrosis factor-alpha-related protein 9 (CTRP9) has been reported to exert cardioprotective effects, but its role in the right ventricle (RV) remains unclear. To investigate the role of CTRP9 in RV hypertrophy and failure, we performed pulmonary artery banding in weanling rats to induce compensatory RV hypertrophy seven weeks after surgery and RV failure 22 weeks after surgery. CTRP9 expression, signal transduction and mechanisms involved in protective CTRP9 effects were analyzed in rat and human RV tissue and cardiac cells. We demonstrate that CTRP9 was induced during compensatory RV hypertrophy but almost lost at the stage of RV failure. RV but not left ventricular (LV) cardiomyocytes or RV endothelial cells demonstrated increased intracellular reactive oxygen species (ROS) and apoptosis activation at this stage. Exogenous CTRP9 induced AMP-activated protein kinase (AMPK)-dependent transcriptional activation of the anti-oxidant thioredoxin-1 (Trx1) and superoxide dismutase-2 (SOD2) and reduced phenylephrine-induced ROS. Combined knockdown of adiponectin receptor-1 (AdipoR1) and AdipoR2 or knockdown of calreticulin attenuated CTRP9-mediated anti-oxidant effects. Immunoprecipitation showed an interaction of AdipoR1 with AdipoR2 and the co-receptor T-cadherin, but no direct interaction with calreticulin. Thus, CTRP9 mediates cardioprotective effects through inhibition of ROS production induced by pro-hypertrophic agents via AMPK-mediated activation of anti-oxidant enzymes.

Age-dependent effects of caloric restriction on mTOR and ubiquitin-proteasome pathways in skeletal muscles

In skeletal muscles, calorie restriction (CR) preserves muscle mass in middle-aged rats but not younger rats. The underlying mechanisms for this age-specific response are unknown. Skeletal muscle mass depends on several factors, with protein synthesis and degradation playing major roles. Therefore, the purpose of this study was to investigate whether CR affects younger and older animals differently on mTOR signaling and ubiquitin-proteasome pathway (UPP). Four-, 8-, and 16-month-old rats, with or without 40% CR for a duration of 14 weeks, were sacrificed after an overnight fasting. Total protein content and the phosphorylation level of AKT, mTOR, S6K, and 4EBP1 and protein content of key markers in the UPP (FOXO3a, atrogin, MuRF1, ubiquitinated proteins, proteasome subunits alpha 7 and beta 5) were determined. Unlike younger rats, CR decreased the content of phosphorylated mTOR, S6K, phosphorylated S6K, FOXO3a, and ubiquitinated proteins in middle-aged rats. In conclusion, CR-induced reduction of content/ phosphorylation levels of key proteins in mTOR signaling and the UPP occurred in the middle-aged rats but not younger rats. The age-dependent effects of CR on mTOR signaling and the UPP indirectly explained the age-related effects of CR on muscle mass of animals.

Mechanisms of Vascular Aging

Aging of the vasculature plays a central role in morbidity and mortality of older people. To develop novel treatments for amelioration of unsuccessful vascular aging and prevention of age-related vascular pathologies, it is essential to understand the cellular and functional changes that occur in the vasculature during aging. In this review, the pathophysiological roles of fundamental cellular and molecular mechanisms of aging, including oxidative stress, mitochondrial dysfunction, impaired resistance to molecular stressors, chronic low-grade inflammation, genomic instability, cellular senescence, epigenetic alterations, loss of protein homeostasis, deregulated nutrient sensing, and stem cell dysfunction in the vascular system are considered in terms of their contribution to the pathogenesis of both microvascular and macrovascular diseases associated with old age. The importance of progeronic and antigeronic circulating factors in relation to development of vascular aging phenotypes are discussed. Finally, future directions and opportunities to develop novel interventions to prevent/delay age-related vascular pathologies by targeting fundamental cellular and molecular aging processes are presented.

Effect of food restriction on energy budget in warm-acclimated striped hamsters

The capacity of small mammals to sustain periods of food shortage largely depends on the adaptive regulation of energy budget in response to the decrease in food supply. In addition to food availability, ambient temperature (Ta) is an important factor affecting the rates of both energy intake and expenditure. To examine the effect of Ta on energy strategy and the capacity to sustain food shortage, striped hamsters were exposed to a warm condition (30°C) and were then restricted to 70% of ad libitum food intake. Body mass, energy intake and expenditure and physiological markers indicative of thermogenesis were measured. Warm exposure had no effect on body mass and digestibility, but decreased energy intake, basal metabolic rate and maximum nonshivering thermogenesis. The mitochondria protein content, cytochrome c oxidase activity and uncoupling protein 1 level of brown adipose tissue were significantly lower in hamsters at 30°C than at 21°C. Food restriction induced a significant decrease in body mass, but the decreased body mass was attenuated at 30°C relative to 21°C. This suggests that striped hamsters could not compensate for the limited food supply by decreasing daily energy expenditure at 21°C, whereas they could at 30°C. The significant reductions in the rates of metabolism and thermogenesis in warm-acclimated hamsters increase the capacity to cope with food shortage. Although, it remains uncertain whether this response represents some generalized evolutionary adaptation, the Ta-dependent adjustment in the capacity to survive food restriction may reflect that warm acclimation plays an important role in adaptive regulation of both physiology and behavior in response to the variations of food availability.

Impact of caloric restriction on myocardial ischaemia/reperfusion injury and new therapeutic options to mimic its effects

Caloric restriction (CR) is the most reliable intervention to extend lifespan and prevent age-related disorders in various species from yeast to rodents. Short- and long-term CR confers cardio protection against ischaemia/reperfusion injury in young and even in aged rodents. A few human trials suggest that CR has the potential to mediate improvement of cardiac or vascular function and induce retardation of cardiac senescence also in humans. The underlying mechanisms are diverse and have not yet been clearly defined. Among the known mediators for the benefits of CR are NO, the AMP-activated PK, sirtuins and adiponectin. Mitochondria, which play a central role in such complex processes within the cell as apoptosis, ATP-production or oxidative stress, are centrally involved in many aspects of CR-induced protection against ischaemic injury. Here, we discuss the relevant literature regarding the protection against myocardial ischaemia/reperfusion injury conferred by CR. Furthermore, we will discuss drug targets to mimic CR and the possible role of calorie restriction in preserving cardiovascular function in humans.

Central adiponectin acutely improves glucose tolerance in male mice

Adiponectin, an adipocyte-derived hormone, regulates glucose and lipid metabolism. It is also antiinflammatory. During obesity, adiponectin levels and sensitivity are reduced. Whereas the action of adiponectin in the periphery is well established the neuroendocrine role of adiponectin is largely unknown. To address this we analyzed the expression of adiponectin and the 2 adiponectin receptors (AdipoR1 and AdipoR2) in response to fasting and to diet-induced and genetic obesity. We also investigated the acute impact of adiponectin on central regulation of glucose homeostasis. Adiponectin (1 μg) was injected intracerebroventricularly (ICV), and glucose tolerance tests were performed in dietary and genetic obese mice. Finally, the influence of ICV adiponectin administration on central signaling cascades regulating glucose homeostasis and on markers of hypothalamic inflammation was assessed. Gene expression of adiponectin was down-regulated whereas AdipoR1 was up-regulated in the arcuate nucleus of fasted mice. High-fat (HF) feeding increased AdipoR1 and AdipoR2 gene expression in this region. In mice on a HF diet and in leptin-deficient mice acute ICV adiponectin improved glucose tolerance 60 minutes after injection, whereas normoglycemia in control mice was unaffected. ICV adiponectin increased pAKT, decreased phospho-AMP-activated protein kinase, and did not change phospho-signal transducer and activator of transcription 3 immunoreactivity. In HF-fed mice, ICV adiponectin reversed parameters of hypothalamic inflammation and insulin resistance as determined by the number of phospho-glycogen synthase kinase 3 β(Ser9) and phospho-c-Jun N-terminal kinase (Thr183/Tyr185) immunoreactive cells in the arcuate nucleus and ventromedial hypothalamus. This study demonstrates that the insulin-sensitizing properties of adiponectin are at least partially based on a neuroendocrine mechanism that involves centrally synthesized adiponectin.

Increased bile acids in enterohepatic circulation by short-term calorie restriction in male mice

Previous studies showed glucose and insulin signaling can regulate bile acid (BA) metabolism during fasting or feeding. However, limited knowledge is available on the effect of calorie restriction (CR), a well-known anti-aging intervention, on BA homeostasis. To address this, the present study utilized a "dose-response" model of CR, where male C57BL/6 mice were fed 0, 15, 30, or 40% CR diets for one month, followed by BA profiling in various compartments of the enterohepatic circulation by UPLC-MS/MS technique. This study showed that 40% CR increased the BA pool size (162%) as well as total BAs in serum, gallbladder, and small intestinal contents. In addition, CR "dose-dependently" increased the concentrations of tauro-cholic acid (TCA) and many secondary BAs (produced by intestinal bacteria) in serum, such as tauro-deoxycholic acid (TDCA), DCA, lithocholic acid, ω-muricholic acid (ωMCA), and hyodeoxycholic acid. Notably, 40% CR increased TDCA by over 1000% (serum, liver, and gallbladder). Interestingly, 40% CR increased the proportion of 12α-hydroxylated BAs (CA and DCA), which correlated with improved glucose tolerance and lipid parameters. The CR-induced increase in BAs correlated with increased expression of BA-synthetic (Cyp7a1) and conjugating enzymes (BAL), and the ileal BA-binding protein (Ibabp). These results suggest that CR increases BAs in male mice possibly through orchestrated increases in BA synthesis and conjugation in liver as well as intracellular transport in ileum.

Obesity induces signs of premature cardiac aging in younger patients: the role of mitochondria

OBJECTIVES

The purpose of the present study was to investigate the influence of obesity on cardiac aging.

BACKGROUND

Obesity is associated with an increased incidence of left ventricular hypertrophy, diastolic dysfunction, heart failure, and atherosclerosis.

METHODS

Sixty male cardiac surgery patients were included in the study according to body mass index (18.5 to 25 kg/m²: normal weight; 30 to 35 kg/m²: obese) and age (<55 years: young; >70 years: old) and divided into 4 groups of 15 patients each. Right atrial cardiomyocytes were analyzed for mitochondrial function, markers of apoptosis, cardiac load or metabolism, and oxidative stress parameters. The metabolic state was further characterized in fasting blood samples.

RESULTS

Obesity resulted in disturbed mitochondrial biogenesis and function (respiratory chain complex I) in the cardiomyocytes of young and old patients. Disturbed mitochondrial function was associated with signs of increased oxidative stress (protein carbonyl content, 8-hydroxy-2'-deoxyguanosine) as well as telomere shortening by up to 30%. Cardiomyocytes from older (obese and normal-weight) and young obese patients demonstrated higher levels of load-induced markers (atrial natriuretic peptide and brain natriuretic peptide) and proapoptotic activation with increased Bax and Bcl-xS expression, cytochrome C release, and caspase 3/9 activation. Disturbances in glucose metabolism and adipocytokine release were detectable in old (obese and normal-weight) and young obese patients. However, only minor deteriorations in most parameters were observed in obese subjects older than 70 years of age compared with normal-weight, age-matched patients.

CONCLUSIONS

These data indicate that obesity results in premature cardiac aging in younger patients, which may contribute to an increased risk for heart failure.

Effect of chronic and intermittent calorie restriction on serum adiponectin and leptin and mammary tumorigenesis

The effect of chronic (CCR) and intermittent (ICR) caloric restriction on serum adiponectin and leptin levels was investigated in relation to mammary tumorigenesis. 10-wks old MMTV-TGF-α female mice were assigned to ad libitum fed (AL; AIN-93M diet), ICR (3-week 50% caloric restriction, AIN-93M-mod diet, 2× protein, fat, vitamins, and minerals followed by 3-wks 100% AL consumption of AIN-93M), and CCR (calorie and nutrient intake matched for each 6-wks ICR cycle, ∼ 75% of AL) groups. Mice were sacrificed at 79 (end of restriction) or 82 (end of refeeding) wks of age. Serum was obtained in cycles 1, 3, 5, 8, 11, and terminal. Mammary tumor incidence was 71.0%, 35.4%, and 9.1% for AL, CCR, and ICR mice, respectively. Serum adiponectin levels were similar among groups with no impact of either CCR or ICR. Serum leptin level rose in AL mice with increasing age but was significantly reduced by long-term CCR and ICR. The ICR protocol was also associated with an elevated adiponectin/leptin ratio. In addition, ICR-restricted mice had increased mammary tissue AdipoR1 expression and decreased leptin and ObRb expression compared with AL mice. Mammary fat pads from tumor-free ICR-mice had higher adiponectin expression than AL and CCR mice whereas all tumor-bearing mice had weak adiponectin signal in mammary fat pad. Although we did not show an association of either adiponectin or leptin with individual mice in relation to mammary tumorigenesis, we did find that reduced serum leptin and elevated adiponectin/leptin ratio were associated with the protective effect of intermittent calorie restriction.

Cardiovascular protection afforded by caloric restriction: essential role of nitric oxide synthase

Caloric restriction is an established intervention, of which anti-aging effects are scientifically proven. It has pleiotropic effects on the cardiovascular system: vascular protection, improvement of myocardial ischemic tolerance and retardation of cardiac senescence. First, increasing evidence from both experimental and clinical studies supports the concept that "a man is as old as his arteries". Caloric restriction could prevent the progression of atherosclerosis and vascular aging through direct and indirect mechanisms. Second, the hearts of senescent animals are more susceptible to ischemia than those of young animals. We demonstrated that short-term and prolonged caloric restriction confers cardioprotection against ischemia/reperfusion injury in young and aged rodents. Furthermore, we showed that the increase in circulating adiponectin levels and subsequent activation of adenosine monophosphate-activated protein kinase are necessary for the cardioprotection afforded by short-term caloric restriction. In contrast, the mechanisms by which prolonged caloric restriction confers cardioprotection seem more complicated. Adiponectin, nitric oxide synthase and sirtuin may form a network of cardiovascular protection during caloric restriction. Recently, by using genetically engineered mice, we found that, in addition to endothelial nitric oxide synthase, neuronal nitric oxide synthase plays an essential role in the development of cardioprotection afforded by prolonged caloric restriction. Third, long-term caloric restriction has cardiac-specific effects that attenuate the age-associated impairment seen in left ventricular diastolic function. It is possible that long-term caloric restriction partially retards cardiac senescence by attenuating oxidative damage in the aged heart. Overall, we strongly believe that caloric restriction could reduce morbidity and mortality of cardiovascular events in humans.

Commonly adopted caloric restriction protocols often involve malnutrition

Undernutrition without malnutrition is an intervention that enhances laboratory animal life span, and is widely studied to uncover factors limiting longevity. In a search of the literature over a course of four years, we found that most protocols currently adopted as caloric restriction do not meet micronutrient standards set by the National Research Council for laboratory rats and mice. We provide evidence that the most commonly adopted caloric restriction protocol, a 40% restriction of the AIN-93 diet without vitamin or mineral supplementation, leads to malnutrition in both mice and rats. Furthermore, others and we find that every other day feeding, another dietary intervention often referred to as caloric restriction, does not limit the total amount of calories consumed. Altogether, we propose that the term "caloric restriction" should be used specifically to describe diets that decrease calorie intake but not micronutrient availability, and that protocols adopted should be described in detail in order to allow for comparisons and better understanding of the effects of these diets.

Caloric restriction delays cardiac ageing in rats: role of mitochondria

AIMS

We tested whether long-term caloric restriction (CR) corrects pre-existing manifestations of cardiac ageing in rats.

METHODS AND RESULTS

The age-specific effects of CR (-40%, 6 months) on mortality, left ventricular (LV) function, mitochondrial function, oxidative damage, and apoptosis were analysed in young (6 + 6 months) and senescent rats (24 + 6 months). CR in senescent rats significantly reduced mortality. LV and cardiomyocyte hypertrophy were reduced together with the mRNA expression and plasma concentrations of overload indicators BNP/ANP. Mitochondrial function was improved, resulting in lower oxidative damage and apoptotic activation. In particular, the pro-apoptotic Bcl-xS/Bcl-xL isoform pattern, mitochondrial translocation of Bax, release of cytochrome C into cytosol, and caspase-9 activation were reduced in comparison to age-matched rats on the control diet. However, CR resulted only in minor changes in young rats. Serum obtained from old control or CR rats was used for in vitro experiments. H9C2 cardiomyoblasts and adult rat ventricular cardiomyocytes preconditioned with CR serum demonstrated a low Bcl-xS/Bcl-xL ratio. H9C2 cells were resistant against H(2)O(2)-mediated loss of mitochondrial membrane potential, apoptosis activation, and reduced cell viability. Thus, beneficial effects of CR are mediated through circulating factors and can be mimicked with CR serum. However, this protection critically depended on a high Bcl-xL protein expression as seen after siRNA-mediated Bcl-xL knockdown.

CONCLUSION

CR is cardioprotective in senescent myocardium by correcting pre-existing mitochondrial dysfunction and apoptotic activation and by preventing deterioration in LV function. Therefore, interventions that mimic these effects of CR may represent an additional therapeutic option for the aged or failing heart.

Mechanisms of vascular aging: new perspectives

This review focuses on molecular, cellular, and functional changes that occur in the vasculature during aging; explores the links between mitochondrial oxidative stress, inflammation, and development of vascular disease in the elderly patients; and provides a landscape of molecular mechanisms involved in cellular oxidative stress resistance, which could be targeted for the prevention or amelioration of unsuccessful vascular aging. Practical interventions for prevention of age-associated vascular dysfunction and disease in old age are considered here based on emerging knowledge of the effects of anti-inflammatory treatments, regular exercise, dietary interventions, and caloric restriction mimetics.

Mechanisms linking obesity, chronic kidney disease, and fatty liver disease: the roles of fetuin-A, adiponectin, and AMPK

Obesity is a risk factor for chronic kidney disease (CKD) and nonalcoholic fatty liver disease (NAFLD). Recent studies identify mechanisms common to both diseases linked through an interorgan communication orchestrated by fetuin-A and adiponectin. In liver and kidney, the energy sensor 5'-AMP activated protein kinase (AMPK) is pivotal to directing podocytes and hepatocytes to compensatory and potentially deleterious pathways, leading to inflammatory and profibrotic cascades culminating in end-organ damage. Regulation of these early upstream pathways may provide new therapeutic targets for these increasingly common sequelae of obesity.

Loss of cardioprotection with ageing

Not only the prevalence, but also the mortality due to ischaemic cardiovascular disease is higher in older than in young humans, and the demographic shift towards an ageing population will further increase the prevalence of age-related cardiovascular disease. In order to develop strategies aimed to limit reversible and irreversible myocardial damage in older patients, there is a need to better understand age-induced alterations in protein expression and cell signalling. Cardioprotective phenomena such as ischaemic and pharmacological pre and postconditioning attenuate ischaemia/reperfusion injury in young hearts. Whether or not pre and postconditioning are still effective in aged organs, animals, or patients, i.e. under conditions where such cardioprotection is most relevant, is still a matter of debate; most studies suggest a loss of protection in aged hearts. The present review discusses changes in protein expression and cell signalling important to ischaemia/reperfusion injury with myocardial ageing. The efficacy of cardioprotective manoeuvres, e.g. ischaemic pre and postconditioning in aged organs and animals will be discussed, and the development of strategies aimed to antagonize the age-induced loss of protection will be addressed.