Effect of age and diet on insulin secretion and insulin action in the rat

Short-term physical exercise controls age-related hyperinsulinemia and improves hepatic metabolism in aged rodents

PURPOSE

Aging is associated with changes in glucose homeostasis related to both decreased insulin secretion and/or impaired insulin action, contributing to the high prevalence of type 2 diabetes (T2D) in the elderly population. Additionally, studies are showing that chronically high levels of circulating insulin can also lead to insulin resistance. In contrast, physical exercise has been a strategy used to improve insulin sensitivity and metabolic health. However, the molecular alterations resulting from the effects of physical exercise in the liver on age-related hyperinsulinemia conditions are not yet fully established. This study aimed to investigate the effects of 7 days of aerobic exercise on hepatic metabolism in aged hyperinsulinemic rats (i.e., Wistar and F344) and in Slc2a4^+/- mice (hyperglycemic and hyperinsulinemic mice).

RESULTS

Both aged models showed alterations in insulin and glucose tolerance, which were associated with essential changes in hepatic fat metabolism (lipogenesis, gluconeogenesis, and inflammation). In contrast, 7 days of physical exercise was efficient in improving whole-body glucose and insulin sensitivity, and hepatic metabolism. The Slc2a4^+/- mice presented significant metabolic impairments (insulin resistance and hepatic fat accumulation) that were improved by short-term exercise training. In this scenario, high circulating insulin may be an important contributor to age-related insulin resistance and hepatic disarrangements in some specific conditions.

CONCLUSION

In conclusion, our data demonstrated that short-term aerobic exercise was able to control mechanisms related to hepatic fat accumulation and insulin sensitivity in aged rodents. These effects could contribute to late-life metabolic health and prevent the development/progression of age-related T2D.

IL-1beta promotes the age-associated decline of beta cell function

Aging is the prime risk factor for the development of type 2 diabetes. We investigated the role of the interleukin-1 (IL-1) system on insulin secretion in aged mice. During aging, expression of the protective IL-1 receptor antagonist decreased in islets, whereas IL-1beta gene expression increased specifically in the CD45 + islet immune cell fraction. One-year-old mice with a whole-body knockout of IL-1beta had higher insulin secretion in vivo and in isolated islets, along with enhanced proliferation marker Ki67 and elevated size and number of islets. Myeloid cell-specific IL-1beta knockout preserved glucose-stimulated insulin secretion during aging, whereas it declined in control mice. Isolated islets from aged myeloIL-1beta ko mice secreted more insulin along with increased expression of Ins2, Kir6.2, and of the cell-cycle gene E2f1. IL-1beta treatment of isolated islets reduced E2f1, Ins2, and Kir6.2 expression in beta cells. We conclude that IL-1beta contributes the age-associated decline of beta cell function.

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Islets from aged mice have increased IL-1beta and decreased IL-1Ra expression

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Islet immune cells are the source of increased IL-1beta expression during aging

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Myeloid-cell-specific IL-1beta knockout preserves insulin secretion in aged mice

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IL-1beta targets genes regulating insulin secretion and proliferation during aging

Overview of age-related changes in psychomotor and cognitive functions in a prosimian primate, the gray mouse lemur (Microcebus murinus): Recent advances in risk factors and antiaging interventions

Aging is not homogeneous in humans and the determinants leading to differences between subjects are not fully understood. Impaired glucose homeostasis is a major risk factor for cognitive decline in middle-aged humans, pointing at the existence of early markers of unhealthy aging. The gray mouse lemur (Microcebus murinus), a small lemuriform Malagasy primate, shows relatively slow aging with decreased psychomotor capacities at middle-age (around 5-year old). In some cases (∼10%), it spontaneously leads to pathological aging. In this case, some age-related deficits, such as severe cognitive decline, brain atrophy, amyloidosis, and glucoregulatory imbalance are congruent with what is observed in humans. In the present review, we inventory the changes occurring in psychomotor and cognitive functions during healthy and pathological aging in mouse lemur. It includes a summary of the cerebral, metabolic, and cellular alterations that occur during aging and their relation to cognitive decline. As nutrition is one of the major nonpharmacological antiaging strategies with major potential effects on cognitive performances, we also discuss its role in brain functions and cognitive decline in this species. We show that the overall approach of aging studies in the gray mouse lemur offers promising ways of investigation for understanding, prevention, and treatments of pathological aging in humans.

Effects of food restriction and/or aerobic exercise on the GLUT4 in type 2 diabetic male rats

Background

The aim of present study was to compare the effects of negative energy balance with food restriction and/or aerobic exercise on the glucose, insulin, and GLUT4 levels in diabetic male rats.

Methods

Fifty-six 10-week old male Wistar rats were randomly assigned to seven groups: a non-diabetic (ND) group and six diabetic groups. After an infusion of type 2 diabetes, the diabetic groups were given labels as well, namely diabetic control (DC) group, exercise (Ex) group, food restriction with standard diet (FRSD) group, food restriction with low-carbohydrate diet (FRLCD) group, food restriction with standard diet combination in exercise (FRSDE) group, and food restriction with low-carbohydrate diet combination in exercise (FRLCDE) group. Further, to induce caloric restriction (CR), food intake was reduced by 20% and given to food restriction consists of both of (FRSD and FRLCD). Hundred percent food consumption for the Ex group was fixed, but instead, 20% of their energy intake in exercise was calculated, and time of daily exercise was determined. Finally, a combination of reduced food intake (10%) and exercise (10%) was applied in each group FRSDE and FRLCDE for 8 weeks.

Results

The results showed that type 2 diabetes inductions had reduced glucose, insulin, and GLUT4 gene expression compared to the ND group (P = 0.001). However, there were significant differences in GLUT4 gene expression between groups after 8 weeks of intervention (P = 0.001). A post hoc least significant difference test show that compared to DC group, GLUT4 gene expression level of Ex, FRSDE, and FRLCDE groups was significantly increased 47% (P = 0.004), 60% (P = 0.001), and 65% (P = 0.001), respectively after 8 week of intervention, but it was not significant or with any other diabetic groups (P > 0.05). Moreover, glucose levels were significantly higher in the FRLCDE, FRLCD, FRSD, FRSDE, Ex groups compared with the DC group in the same period (P = 0.0.01).

Conclusions

It was concluded that FRSD and FRLCD combination in regular exercise was elevated of GLUT4 gene expression in type 2 diabetes. These results may help to develop new methods for the treatment of obesity and type 2 diabetes mellitus.

Characterization of glucose-stimulated insulin release protocols in african green monkeys (Chlorocebus aethiops)

Background

Management of diabetes remains a major health and economic challenge, demanding test systems in which to develop new therapies. These studies assessed different methodologies for determining glucose tolerance in green monkeys.

Methods

Twenty‐eight African green monkeys between 4 and 24 years old underwent single or repeat intravenous glucose tolerance testing (IVGTT), oral glucose tolerance testing (OGTT), and/or graded glucose infusion testing.

Results

Geriatric monkeys exhibited glucose intolerance with impaired glucose‐stimulated insulin secretion following IVGTT. Repeat IVGTT and OGTT assessments were inconsistent. Monkeys with low glucose‐stimulated insulin secretion after graded glucose infusion exhibited elevated blood glucose levels.

Conclusion

IVGTT and graded glucose infusion protocols revealed differences in glucose tolerance among green monkeys at single time points, including age‐dependent differences suggestive of shifts in pancreatic beta‐cell functional capacity, but care should be applied to study design and the interpretation of data in the setting of longitudinal studies.

Calorie restriction prevents diet-induced insulin resistance independently of PGC-1-driven mitochondrial biogenesis in white adipose tissue

Calorie restriction (CR) exerts remarkable, beneficial effects on glucose homeostasis by mechanisms that are not fully understood. Given the relevance of white adipose tissue (WAT) in glucose homeostasis, we aimed at identifying the main cellular processes regulated in WAT in response to CR in a pathologic context of obesity. For this, a gene-expression profiling study was first conducted in mice fed ad libitum or subjected to 40% CR. We found that the gene network related to mitochondria was the most highly upregulated in WAT by CR. To study the role that increased mitochondrial biogenesis plays on glucose homeostasis following CR, we generated a mouse model devoid of the coactivators peroxisome proliferator-activated receptor γ coactivator 1 (PGC-1)α and PGC-1β specifically in adipocytes. Our results show that mice lacking PGC-1s in adipocytes are unable to increase mitochondrial biogenesis in WAT upon CR. Despite a blunted induction of mitochondrial biogenesis in response to calorie deprivation, mice lacking adipose PGC-1s still respond to CR by improving their glucose homeostasis. Our study demonstrates that PGC-1 coactivators are major regulators of CR-induced mitochondrial biogenesis in WAT and that increased mitochondrial biogenesis and oxidative function in adipose tissue are not required for the improvement of glucose homeostasis mediated by CR.-Pardo, R., Vilà, M., Cervela, L., de Marco, M., Gama-Pérez, P., González-Franquesa, A., Statuto, L., Vilallonga, R., Simó, R., Garcia-Roves, P. M., Villena, J. A. Calorie restriction prevents diet-induced insulin resistance independently of PGC-1-driven mitochondrial biogenesis in white adipose tissue.

Glucose-Induced Transcriptional Hysteresis: Role in Obesity, Metabolic Memory, Diabetes, and Aging

During differentiation transient, inducers produce permanent changes in gene expression. A similar phenomenon, transcriptional hysteresis, produced by transient or prolonged exposure to glucose, leads to cumulative, persistent, and largely irreversible effects on glucose-regulated gene expression, and may drive key aspects of metabolic memory, obesity, diabetes, and aging, and explain the protective effects of dietary restriction during aging. The most relevant effects of glucose-induced transcriptional hysteresis are the persistent effects of elevated glucose on genes that control glucose metabolism itself. A key observation is that, as with the lac operon, glucose induces genes that promote glycolysis and inhibits gene expression of alternative metabolic pathways including the pentose pathway, beta oxidation, and the TCA cycle. A similar pattern of metabolic gene expression is observed during aging, suggesting that cumulative exposure to glucose during aging produces this metabolic shift. Conversely, dietary restriction, which increases lifespan and delays age-related impairments, produces the opposite metabolic profile, leading to a shift away from glycolysis and toward the use of alternative substrates, including lipid and ketone metabolisms. The effect of glucose on gene expression leads to a positive feedback loop that leads to metastable persistent expression of genes that promote glycolysis and inhibit alternative pathways, a phenomenon first observed in the regulation of the lac operon. On the other hand, this pattern of gene expression can also be inhibited by activation of peroxisome proliferator activating receptor transcription factors that promote beta oxidation and inhibit metabolism of glucose-derived carbon bonds in the TCA cycle. Several pathological consequences may arise from glucose-induced transcriptional hysteresis. First, elevated glucose induces glycolytic genes in pancreatic beta cells, which induces a semi-stable persistent increase in insulin secretion, which could drive obesity and insulin resistance, and also due to glucose toxicity could eventually lead to beta-cell decompensation and diabetes. Diabetic complications persist even after complete normalization of glucose, a phenomenon known as metabolic memory. This too can be explained by persistent bistable expression of glucose-induced glycolytic genes.

A comprehensive review of the health perspectives of resveratrol

Many natural products present in our diet, including flavonoids, can prevent the progression of cancer and other diseases. Resveratrol, a natural polyphenol present in various fruits and vegetables, plays an important role as a therapeutic and chemopreventive agent used in the treatment of various illnesses. It exhibits effects against different types of cancer through different pathways. It additionally exerts antidiabetic, anti-inflammatory, and anti-oxidant effects in a variety of cell types. Furthermore, the cardiovascular protective capacities of resveratrol are associated with multiple molecular targets and may lead to the development of novel therapeutic strategies for atherosclerosis, ischemia/reperfusion, metabolic syndrome, and heart failure. Accordingly, this article presents an overview of recent developments in the use of resveratrol for the prevention and treatment of different diseases along with various mechanisms. In addition, the present review summarizes the most recent literature pertaining to resveratrol as a chemotherapeutic agent against multiple diseases and provides an assessment of the potential of this natural compound as a complementary or alternative medicine.

Targeting glucose metabolism for healthy aging

Advancing age is the greatest single risk factor for numerous chronic diseases. Thus, the ability to target the aging process can facilitate improved healthspan and potentially lifespan. Lack of adequate glucoregulatory control remains a recurrent theme accompanying aging and chronic disease, while numerous longevity interventions result in maintenance of glucoregulatory control. In this review, we propose targeting glucose metabolism to enhance regulatory control as a means to ameliorate the aging process. We highlight that calorie restriction improves glucoregulatory control and extends both lifespan and healthspan in model organisms, but we also indicate more practical interventions (i.e., calorie restriction mimetics) are desirable for clinical application in humans. Of the calorie restriction mimetics being investigated, we focus on the type 2 diabetes drug acarbose, an α-glucosidase inhibitor that when taken with a meal, results in reduced enzymatic degradation and absorption of glucose from complex carbohydrates. We discuss alternatives to acarbose that yield similar physiologic effects and describe dietary sources (e.g., sweet potatoes, legumes, and berries) of bioactive compounds with α-glucosidase inhibitory activity. We indicate future research should include exploration of how non-caloric compounds like α-glucosidase inhibitors modify macronutrient metabolism prior to disease onset, which may guide nutritional/lifestyle interventions to support health and reduce age-related disease risk.

Uteroplacental insufficiency leads to hypertension, but not glucose intolerance or impaired skeletal muscle mitochondrial biogenesis, in 12-month-old rats

Growth restriction impacts on offspring development and increases their risk of disease in adulthood which is exacerbated with “second hits.” The aim of this study was to investigate if blood pressure, glucose tolerance, and skeletal muscle mitochondrial biogenesis were altered in 12-month-old male and female offspring with prenatal or postnatal growth restriction. Bilateral uterine vessel ligation induced uteroplacental insufficiency and growth restriction in offspring (Restricted). A sham surgery was also performed during pregnancy (Control) and some litters from sham mothers had their litter size reduced (Reduced litter), which restricted postnatal growth. Growth-restricted females only developed hypertension at 12 months, which was not observed in males. In Restricted females only homeostasis model assessment for insulin resistance was decreased, indicating enhanced hepatic insulin sensitivity, which was not observed in males. Plasma leptin was increased only in the Reduced males at 12 months compared to Control and Restricted males, which was not observed in females. Compared to Controls, leptin, ghrelin, and adiponectin were unaltered in the Restricted males and females, suggesting that at 12 months of age the reduction in body weight in the Restricted offspring is not a consequence of circulating adipokines. Skeletal muscle PGC-1α levels were unaltered in 12-month-old male and female rats, which indicate improvements in lean muscle mass by 12 months of age. In summary, sex strongly impacts the cardiometabolic effects of growth restriction in 12-month-old rats and it is females who are at particular risk of developing long-term hypertension following growth restriction.

Insulin secretion and signaling in response to dietary restriction and subsequent re-alimentation in cattle

The objectives of this study were to examine systemic insulin response to a glucose tolerance test (GTT) and transcript abundance of genes of the insulin signaling pathway in skeletal muscle, during both dietary restriction and re-alimentation-induced compensatory growth. Holstein Friesian bulls were blocked to one of two groups: 1) restricted feed allowance for 125 days (period 1) (RES, n = 15) followed by ad libitum feeding for 55 days (period 2) or 2) ad libitum access to feed throughout (periods 1 and 2) (ADLIB, n = 15). On days 90 and 36 of periods 1 and 2, respectively, a GTT was performed. M. longissimus dorsi biopsies were harvested from all bulls on days 120 and 15 of periods 1 and 2, respectively, and RNA-Seq analysis was performed. RES displayed a lower growth rate during period 1 (RES: 0.6 kg/day, ADLIB: 1.9 kg/day; P < 0.001), subsequently gaining more during re-alimentation (RES: 2.5 kg/day, ADLIB: 1.4 kg/day; P < 0.001). Systemic insulin response to glucose administration was lower in RES in period 1 (P < 0.001) with no difference observed during period 2. The insulin signaling pathway in M. longissimus dorsi was enriched (P < 0.05) in response to dietary restriction but not during re-alimentation (P > 0.05). Genes differentially expressed in the insulin signaling pathway suggested a greater sensitivity to insulin in skeletal muscle, with pleiotropic effects of insulin signaling interrupted during dietary restriction. Collectively, these results indicate increased sensitivity to glucose clearance and skeletal muscle insulin signaling during dietary restriction; however, no overall role for insulin was apparent in expressing compensatory growth.

Hippocampal calcium dysregulation at the nexus of diabetes and brain aging

Recently it has become clear that conditions of insulin resistance/metabolic syndrome, obesity and diabetes, are linked with moderate cognitive impairment in normal aging and elevated risk of Alzheimer's disease. It appears that a common feature of these conditions is impaired insulin signaling, affecting the brain as well as peripheral target tissues. A number of studies have documented that insulin directly affects brain processes and that reduced insulin signaling results in impaired learning and memory. Several studies have also shown that diabetes induces Ca(2+) dysregulation in neurons. Because brain aging is associated with substantial Ca(2+) dyshomeostasis, it has been proposed that impaired insulin signaling exacerbates or accelerates aging-related Ca(2+) dyshomeostasis. However, there have been few studies examining insulin interactions with Ca(2+) regulation in aging animals. We have been testing predictions of the Ca(2+) dysregulation/diabetes/brain aging hypothesis and have found that insulin and insulin-sensitizers (thiazolidinediones) target several hippocampal Ca(2+)-related processes affected by aging. The drugs appear able to reduce the age-dependent increase in Ca(2+) transients and the Ca(2+) -sensitive afterhyperpolarization. Thus, while additional testing is needed, the results to date are consistent with the view that strategies that enhance insulin signaling can counteract the effect of aging on Ca(2+) dysregulation.

Effect of high-fat diet on metabolic indices, cognition, and neuronal physiology in aging F344 rats

The prevalence of obesity and type 2 diabetes increases with age. Despite this, few studies have examined these conditions simultaneously in aged animals, and fewer studies have measured the impact of these conditions on brain function. Using an established animal model of brain aging (F344 rats), we investigated whether a high-fat diet (HFD) exacerbates cognitive decline and the hippocampal calcium-dependent afterhyperpolarization (a marker of age-dependent calcium dysregulation). Young and mid-aged animals were maintained on control or HFD for 4.5 months, and peripheral metabolic variables, cognitive function, and electrophysiological responses to insulin in the hippocampus were measured. HFD increased lipid accumulation in the periphery, although overt diabetes did not develop, nor were spatial learning and memory altered. Hippocampal adiponectin levels were reduced in aging animals but were unaffected by HFD. For the first time, however, we show that the AHP is sensitive to insulin, and that this sensitivity is reduced by HFD. Interestingly, although peripheral glucose regulation was relatively insensitive to HFD, the brain appeared to show greater sensitivity to HFD in F344 rats.

Utilizing calorie restriction to evaluate the role of sirtuins in healthspan and lifespan of mice

Calorie restriction is the most powerful method currently known to delay aging-associated disease and extend lifespan. Use of this technique in combination with genetic models has led to identification of key metabolic regulators of lifespan. Limiting energy availability by restricting caloric intake leads to redistribution of energy expenditure and storage. The signaling required for these metabolic changes is mediated in part by the sirtuins at both the posttranslational and transcriptional levels, and consequently, sirtuins are recognized as instigating factors in the regulation of lifespan. This family of class III protein deacetylases is responsible for directing energy regulation based on NAD(+) availability. However, there are many effectors of NAD(+) availability, and hence sirtuin action, that should be considered when performing experiments using calorie restriction. The methods outlined in this chapter are intended to provide a guide to help the aging community to use and interpret experimental calorie restriction properly. The importance of healthspan and the use of repeated measures to assess metabolic health during lifespan experiments are strongly emphasized.

Effect of pregnancy for females born small on later life metabolic disease risk

There is a strong inverse relationship between a females own birth weight and her subsequent risk for gestational diabetes with increased risk of developing diabetes later in life. We have shown that growth restricted females develop loss of glucose tolerance during late pregnancy with normal pancreatic function. The aim of this study was to determine whether growth restricted females develop long-term impairment of metabolic control after an adverse pregnancy adaptation. Uteroplacental insufficiency was induced by bilateral uterine vessel ligation (Restricted) or sham surgery (Control) in late pregnancy (E18) in F0 female rats. F1 Control and Restricted female offspring were mated with normal males and allowed to deliver (termed Ex-Pregnant). Age-matched Control and Restricted Virgins were also studied and glucose tolerance and insulin secretion were determined. Pancreatic morphology and hepatic glycogen and triacylglycerol content were quantified respectively. Restricted females were born lighter than Control and remained lighter at all time points studied (p<0.05). Glucose tolerance, first phase insulin secretion and liver glycogen and triacylglycerol content were not different across groups, with no changes in β-cell mass. Second phase insulin secretion was reduced in Restricted Virgins (-34%, p<0.05) compared to Control Virgins, suggestive of enhanced peripheral insulin sensitivity but this was lost after pregnancy. Growth restriction was associated with enhanced basal hepatic insulin sensitivity, which may provide compensatory benefits to prevent adverse metabolic outcomes often associated with being born small. A prior pregnancy was associated with reduced hepatic insulin sensitivity with effects more pronounced in Controls than Restricted. Our data suggests that pregnancy ameliorates the enhanced peripheral insulin sensitivity in growth restricted females and has deleterious effects for hepatic insulin sensitivity, regardless of maternal birth weight.

Effects of chronic calorie restriction or dietary resveratrol supplementation on insulin sensitivity markers in a primate, Microcebus murinus

The prevalence of diabetes and hyperinsulinemia increases with age, inducing metabolic failure and limiting lifespan. Calorie restriction (CR) without malnutrition delays the aging process, but its long-term application to humans seems difficult. Resveratrol (RSV), a dietary polyphenol, appears to be a promising CR mimetic that can be easily administered in humans. In this work, we hypothesized that both CR and RSV impact insulin sensitivity in a non-human primate compared to standard-fed control (CTL) animals. Four- to five-year-old male grey mouse lemurs (Microcebus murinus) were assigned to three dietary groups: a CTL group, a CR group receiving 30% fewer calories than the CTL and a RSV group receiving the CTL diet supplemented with RSV (200 mg·day(-1)·kg(-1)). Insulin sensitivity and glycemia were assessed using an oral glucose tolerance test (OGTT) and the homeostasis model assessment of insulin resistance (HOMA-IR index) evaluation after 21 or 33 months of chronic treatment. Resting metabolic rate was also measured to assess the potential relationships between this energy expenditure parameter and insulin sensitivity markers. No differences were found after a 21-month period of treatment, except for lower glucose levels 30 min after glucose loading in CR animals. After 33 months, CR and RSV decreased glycemia after the oral glucose loading without decreasing fasting blood insulin. A general effect of treatment was observed on the HOMA-IR index, with an 81% reduction in CR animals and 53% in RSV animals after 33 months of treatment compared to CTL. Chronic CR and dietary supplementation with RSV affected insulin sensitivity by improving the glucose tolerance of animals without disturbing their baseline insulin secretion. These results suggest that both CR and RSV have beneficial effects on metabolic alterations, although these effects are different in amplitude between the two anti-aging treatments and potentially rely on different metabolic changes.

Age-related impairment in insulin release: the essential role of β(2)-adrenergic receptor

In this study, we investigated the significance of β(2)-adrenergic receptor (β(2)AR) in age-related impaired insulin secretion and glucose homeostasis. We characterized the metabolic phenotype of β(2)AR-null C57Bl/6N mice (β(2)AR(-/-)) by performing in vivo and ex vivo experiments. In vitro assays in cultured INS-1E β-cells were carried out in order to clarify the mechanism by which β(2)AR deficiency affects glucose metabolism. Adult β(2)AR(-/-) mice featured glucose intolerance, and pancreatic islets isolated from these animals displayed impaired glucose-induced insulin release, accompanied by reduced expression of peroxisome proliferator-activated receptor (PPAR)γ, pancreatic duodenal homeobox-1 (PDX-1), and GLUT2. Adenovirus-mediated gene transfer of human β(2)AR rescued these defects. Consistent effects were evoked in vitro both upon β(2)AR knockdown and pharmacologic treatment. Interestingly, with aging, wild-type (β(2)AR(+/+)) littermates developed impaired insulin secretion and glucose tolerance. Moreover, islets from 20-month-old β(2)AR(+/+) mice exhibited reduced density of β(2)AR compared with those from younger animals, paralleled by decreased levels of PPARγ, PDX-1, and GLUT2. Overexpression of β(2)AR in aged mice rescued glucose intolerance and insulin release both in vivo and ex vivo, restoring PPARγ/PDX-1/GLUT2 levels. Our data indicate that reduced β(2)AR expression contributes to the age-related decline of glucose tolerance in mice.

Effects of insulin on Na and K transporters in the rat CCD

We tested the effects of insulin (2 nM, 30-60 min) on principal cells of isolated split-open rat cortical collecting ducts (CCD) using whole-cell current measurements. Insulin addition to the superfusate of the tubules enhanced Na pump (ouabain-sensitive) current from 18 ± 3 to 31 ± 3 pA/cell in control and from 74 ± 9 to 126 ± 11 pA/cell in high K-fed animals. It also more than doubled ROMK (tertiapin-Q-sensitive) K(+) currents in control CCD from 320 ± 40 to 700 ± 80 pA/cell, although it did not affect this current in tubules from K-loaded rats. Insulin did not induce the appearance of amiloride-sensitive Na(+) current in control animals, while in high K-fed animals the currents were similar in the presence (140 ± 30) and the absence (180 ± 70 pA/cell) of insulin. Intraperitoneal injection of insulin plus hypertonic dextrose decreased Na excretion, as previously reported. However, injection of dextrose alone, or the nonmetabolized sugar mannose, had similar effects, suggesting that they were largely the result of vascular volume depletion rather than specific actions of the hormone. In summary, we find no evidence for acute upregulation of the epithelial Na channel (ENaC) by physiological concentrations of insulin in the mammalian CCD. However, the hormone does activate both the Na/K pump and apical K(+) channels and could, under some conditions, enhance renal K(+) secretion.

Preliminary Study of the Clinical Hypoglycemic Effects of Allium cepa (Red Onion) in Type 1 and Type 2 Diabetic Patients

BACKGROUND

Diabetes mellitus is a heterogeneous group of disorders characterized by abnormalities of carbohydrate, protein and lipid metabolism. Type 1 diabetes mellitus is an autoimmune disease caused by destruction of pancreatic beta cells and characterized by defect in insulin secretion while type 2 diabetes mellitus results from abnormalities in insulin secretion and/or insulin action or both.

OBJECTIVES

The present study was conducted to investigate the clinical hypoglycemic effects of Allium cepa in type 1 and type 2 diabetic patients.

RESULTS

In assessment of hypoglycaemic activity of Allium cepa in type 1 and type 2 diabetic patients, ingestion of crude Allium cepa (100 g) caused a considerable reduction in fasting blood glucose levels by about 89 mg/dl in relation to insulin (145 mg/dl) in type 1 diabetic patients and it reduced fasting blood glucose levels by 40 mg/dl, compared to glibenclamide (81 mg/dl) in type 2 diabetic patients, 4 hours later. The same dose of crude Allium cepa produced a significant reduction in the induced hyperglycemia (GTT) by about 120 mg/dl compared to water (77 mg/dl) and insulin (153 mg/dl) in type 1 diabetic patients and considerably reduced GTT by 159 mg/dl in relation to water (55 mg/dl) and glibenclamide (114 mg/dl) in type 2 diabetic patients, after 4 hours.

CONCLUSION

It was evident that, crude Allium cepa produced hypoglycemic effects, thus it could be used as a dietary supplement in management of type 1 and/or type 2 diabetes mellitus.

Type 2 diabetes: an expanded view of pathophysiology and therapy

Type 2 diabetes mellitus is a complicated metabolic disease affecting millions of individuals worldwide. The medications used to manage the disease are based on different pharmacologic approaches, including decreasing hepatic gluconeogenesis, stimulating pancreatic insulin production, slowing polysaccharide digestion, and increasing insulin sensitivity in muscle, liver, and fat to lower blood glucose. Incretin-based therapies, including glucagon-like peptide-1 (GLP-1) receptor agonists, mimic the effects of native GLP-1, while dipeptidyl peptidase-4 inhibitors increase circulating concentrations of endogenous GLP-1. This review focuses on means by which primary care physicians might evaluate the utility of pharmacologic agents based on their relation to the pathogenesis of type 2 diabetes. In general, patients with type 2 diabetes should be treated to their lowest targeted glycemic goals as soon as they are diagnosed, for as long as possible, as safely as possible, and as rationally as possible.

Calorie restriction initiated at a young age activates the Akt/PKC zeta/lambda-Glut4 pathway in rat white adipose tissue in an insulin-independent manner

Calorie restriction (CR) may exert an anti-aging effect through a metabolic adaptation to limited energy intake. The present study investigated the effect of CR on insulin signaling in response to glucose load in the epididymal adipose tissue of male F344 rats at 7 and 22 months of age. Young and middle-aged rats were fed ad libitum (AL) or 30% CR diets for 4 months, underwent glucose tolerance tests and were sacrificed 15 min after an intraperitoneal glucose or saline injection to evaluate glucose-stimulated insulin response and subsequent activation of insulin signaling molecules in the adipose tissue. In the 7- and 22- month AL groups, glucose administration increased serum insulin levels and also increased phosphorylated (p) levels of the insulin receptor (IR), v-akt murine thymoma viral oncogene homolog (Akt), protein kinase C (PKC) zeta/lambda and the membrane fraction of glucose transporter 4 (mGlut4). In contrast, in the 7-month CR group, p-Akt, p-PKC zeta/lambda and mGlut4 levels were upregulated without glucose stimulation; the glucose load augmented the p-IR level but there was no additional activation of the downstream molecules. In the 22-month CR group, these unexpected findings were not observed. In summary, basal levels of insulin signaling molecules such as p-Akt, p-PKC zeta/lambda, and mGlut4 were significantly increased with a low insulin response in the 7-month CR group. The present results suggest the presence of an age-specific insulin-independent mechanism that is induced by CR to regulate energy metabolism in white adipose tissue.

Dietary palatinose and oleic acid ameliorate disorders of glucose and lipid metabolism in Zucker fatty rats

Excessive dietary intake of carbohydrates and fats has been linked to the development of obesity. However, the mechanism by which these dietary factors interact to bring about metabolic changes has not been elucidated. We examined the combined effects of different types of dietary carbohydrates and fats on the etiology of obesity and its complications in the Zucker fatty (fa/fa) rat, a model of obesity. Specifically, these rats were fed an isocaloric diet containing various combinations of carbohydrates [palatinose (P), an insulin-sparing sucrose analogue, and sucrose (S)] and fatty acids [oleic acid (O) and linoleic acid (L)]. After 8 wk, palatinose feeding (PO and PL) led to significant reductions in visceral fat mass, adipocyte cell size, hyperglycemia, and hyperlipidemia compared with sucrose feeding (SO and SL); pancreatic islet hypertrophy was also prevented by palatinose feeding. Linoleic-acid-fed rats (PL and SL) exhibited reduced insulin-immunoreactive staining of the pancreatic islets, enhanced macrophage infiltration in adipose tissue, and an elevated plasma tumor necrosis factor-alpha concentration when compared with oleic-acid-fed rats (PO and SO). Furthermore, sucrose and linoleic acid synergistically increased the expression of genes involved in hepatic gluconeogenesis and lipogenesis [sterol regulatory-element binding protein (SREBP)-1c and SREBP-2]. In conclusion, a diet containing palatinose and oleic acid may prevent diet-induced metabolic abnormalities. The combination of palatinose and oleic acid holds promise for a new approach to preventing and treating obesity and its complications.

SIRT4 inhibits glutamate dehydrogenase and opposes the effects of calorie restriction in pancreatic beta cells

Sir2 is an NAD-dependent deacetylase that connects metabolism with longevity in yeast, flies, and worms. Mammals have seven Sir2 homologs (SIRT1-7). We show that SIRT4 is a mitochondrial enzyme that uses NAD to ADP-ribosylate and downregulate glutamate dehydrogenase (GDH) activity. GDH is known to promote the metabolism of glutamate and glutamine, generating ATP, which promotes insulin secretion. Loss of SIRT4 in insulinoma cells activates GDH, thereby upregulating amino acid-stimulated insulin secretion. A similar effect is observed in pancreatic beta cells from mice deficient in SIRT4 or on the dietary regimen of calorie restriction (CR). Furthermore, GDH from SIRT4-deficient or CR mice is insensitive to phosphodiesterase, an enzyme that cleaves ADP-ribose, suggesting the absence of ADP-ribosylation. These results indicate that SIRT4 functions in beta cell mitochondria to repress the activity of GDH by ADP-ribosylation, thereby downregulating insulin secretion in response to amino acids, effects that are alleviated during CR.

Are insulin resistance, impaired fasting glucose and impaired glucose tolerance all equally strongly related to age?

BACKGROUND

Insulin resistance (IR) has been considered an underlying cause of impaired glucose tolerance (IGT) and impaired fasting glucose (IFG). Whether IR increases with age has been debated. We investigated the age-associated deterioration in the homeostasis model assessment (HOMA) of IR and in glucose metabolism.

METHODS

Ten (nine including women) European studies contributed data on 6314 men and 6393 women aged 30-88 years. The cohort- and sex-specific top 25% of HOMA of IR in non-diabetic subjects was used to define HOMA-IR.

RESULTS

Compared with subjects aged 50-59 years, the cohort- and body mass index-adjusted odds ratio (95% confidence interval) for HOMA-IR was 0.83 (0.64, 1.08), 0.87 (0.74, 1.03), 1.20 (1.02, 1.42) and 1.45 (1.10, 1.92) in men and 0.84 (0.62, 1.14), 0.91 (0.77, 1.09), 1.38 (1.19, 1.62) and 1.71 (1.35, 2.17) in women, respectively, aged 30-39, 40-49, 60-69 and > or = 70 years (P < 0.0001 for trend test). The same increasing trend was also observed for IFG. In contrast, the corresponding odds ratios for IGT increased linearly and more strongly with age, being 0.37 (0.22, 0.63), 0.67 (0.52, 0.87), 1.55 (1.24, 1.92) and 2.96 (2.13, 4.13) in men and 0.51 (0.31, 0.85), 0.66 (0.52, 0.86), 1.92 (1.57, 2.35) and 3.85 (2.89, 5.12) in women, respectively.

CONCLUSIONS

Age is more strongly associated with IGT than with HOMA-IR or IFG in non-diabetic European populations.

Relationship between protein O-linked glycosylation and insulin-stimulated glucose transport in rat skeletal muscle following calorie restriction or exposure to O-(2-acetamido-2-deoxy-d-glucopyranosylidene)amino-N-phenylcarbamate

AIMS AND BACKGROUND

Protein O-linked glycosylation is regulated in vivo by the concentration of hexosamine substrates. Calorie restriction (60% of ad libitum intake) for 20 days causes decreased UDP-N-acetylhexosamine levels and increased insulin-mediated glucose transport in rat skeletal muscle. Conversely, prolonged incubation (19 h) of muscle with O-(2-acetamido-2-deoxy-D-glucopyranosylidene)amino-N-phenyl-carbamate (PUGNAc; an inhibitor of N-acetyl-beta-D-glucosaminidase) is characterized by increased O-linked glycosylation and insulin resistance. We aimed to determine the calorie restriction effect on O-linked glycosylation and characterize the temporal relationship between PUGNAc-induced O-linked glycosylation and insulin resistance.

HYPOTHESIS

A calorie restriction protocol characterized by decreased muscle hexosamine levels will result in a global reduction in O-linked glycosylated proteins in muscle, and PUGNAc-induced insulin resistance will coincide with increased O-linked glycosylation.

METHODS

Plantaris muscle and liver from rats (ad libitum or calorie restricted) were analysed for O-linked glycosylation using two antibodies against different O-linked N-acetylglucosamine epitopes. Also, rat epitrochlearis muscles were incubated for 8.5 h +/- 100 mum PUGNAc prior to measurement of [(3)H]-3-O-methylglucose transport and O-linked glycosylation.

RESULTS

Calorie restriction did not alter protein O-linked glycosylated levels in muscle or liver. Incubation with PUGNAc for 8.5 h resulted in increased in O-linked glycosylation but unaltered basal or insulin-stimulated glucose transport.

CONCLUSIONS

The delay between O-linked glycosylation and insulin resistance in muscle incubated with PUGNAc suggests an indirect, relatively slow mechanism for insulin resistance. The effect of calorie restriction on insulin action in muscle is unlikely to be the direct result of a global change in protein O-linked glycosylation.

Metabolic adaptations to fasting and chronic caloric restriction in heart, muscle, and liver do not include changes in AMPK activity

Activation of adenosine monophosphate-activated protein kinase (AMPK) plays a central role in allowing cells to adapt to nutrient deprivation in vitro. This link between AMPK activity and nutritional status has raised the possibility that AMPK plays a role in the metabolic adaptation to acute and chronic nutritional stress. However, the effects of nutritional stress on AMPK activity in vivo have not been systematically evaluated. To address this, we measured the effects of 24 h of fasting and 4 mo of caloric restriction (CR) on AMPK alpha 1 and -alpha 2 activities in heart, skeletal muscle, and liver in mice. Although fasting caused the expected changes in body weight, plasma leptin, and free fatty acids, it did not increase AMPK activity in heart or skeletal muscle and only increased liver AMPK activity by approximately 20% (P = 0.10). Likewise, CR caused the expected changes in body weight, plasma leptin, and free fatty acids but did not alter AMPK activity in any of the three tissues. Although CR did not alter liver AMPK activity, it dramatically decreased the amount of phosphorylated acetyl-CoA carboxylase, and this was found to be due to decreased protein expression. Plasma leptin, a putative activator of AMPK, varied eightfold across the four groups of mice in the absence of changes in AMPK activity in any tissue. We conclude that, although the metabolic adaptations to fasting and CR include changes in plasma leptin concentration and phosphorylated acetyl-CoA carboxylase, these effects occur without changes in AMPK activity.

Adding fat calories to meals after exercise does not alter glucose tolerance

A single session of exercise increases insulin sensitivity for hours and even days, and dietary carbohydrate ingested after exercise alters the magnitude and duration of this effect. Although increasing systemic fatty acid availability is associated with insulin resistance, it is uncertain whether increasing dietary fat availability after exercise alters the exercise-induced increase in insulin sensitivity. The purpose of this study was to determine whether adding fat calories to meals after exercise alters glucose tolerance the next day. Seven healthy men cycled 90 min at 66 ± 2% peak oxygen uptake followed by a maximum of five high-intensity intervals. During the hours after exercise, subjects ingested three meals containing either low-fat (5% energy from fat) or high-fat (45% energy from fat) foods (Low-Fat and High-Fat groups, respectively). Each diet contained the same amount of carbohydrate and protein. An oral glucose tolerance test was performed the next morning. Muscle glycogen and intramuscular triglyceride (IMTG) concentrations were measured in muscle biopsy samples obtained immediately before exercise and the next morning. The day after exercise, muscle glycogen concentration was identical in High-Fat and Low-Fat (393 ± 70 and 379 ± 38 mmol/kg dry wt). At the same time, IMTG concentration was ∼20% greater during High-Fat compared with Low-Fat (42.5 ± 3.4 and 36.3 ± 3.3 mmol/kg dry wt; P < 0.05). Despite the addition of ∼165 g of fat to meals after exercise (∼1,500 kcal) and a resultant elevation in IMTG concentration, glucose tolerance was identical in High-Fat and Low-Fat (composite index: 8.7 ± 1.0 and 8.4 ± 1.0). In summary, as long as meals ingested in the hours after exercise contain the same carbohydrate content, the addition of ∼1,500 kcal from fat to these meals did not alter muscle glycogen resynthesis or glucose tolerance the next day.

Brief calorie restriction increases Akt2 phosphorylation in insulin-stimulated rat skeletal muscle

Skeletal muscle insulin sensitivity improves with short-term reduction in calorie intake. The goal of this study was to evaluate changes in the abundance and phosphorylation of Akt1 and Akt2 as potential mechanisms for enhanced insulin action after 20 days of moderate calorie restriction [CR; 60% of ad libitum (AL) intake] in rat skeletal muscle. We also assessed changes in the abundance of SH2 domain-containing inositol phosphatase (SHIP2), a negative regulator of insulin signaling. Fisher 344 x Brown Norway rats were assigned to an AL control group or a CR treatment group for 20 days. Epitrochlearis muscles were dissected and incubated with or without insulin (500 microU/ml). Total Akt serine and threonine phosphorylation was significantly increased by 32 (P < 0.01) and 30% (P < 0.005) in insulin-stimulated muscles from CR vs. AL. Despite an increase in total Akt phosphorylation, there was no difference in Akt1 serine or Akt1 threonine phosphorylation between CR and AL insulin-treated muscles. However, there was a 30% decrease (P < 0.05) in Akt1 abundance for CR vs. AL. In contrast, there was no change in Akt2 protein abundance, and there was a 94% increase (P < 0.05) in Akt2 serine phosphorylation and an increase of 75% (P < 0.05) in Akt2 threonine phosphorylation of insulin-stimulated CR muscles compared with AL. There was no diet effect on SHIP2 abundance in skeletal muscle. These results suggest that, with brief CR, enhanced Akt2 phosphorylation may play a role in increasing insulin sensitivity in rat skeletal muscles.

Improved glucose tolerance with lifetime diet restriction favorably affects disease and survival in dogs

Labrador retrievers (42 of original 48) were used to assess the effects of lifetime diet restriction on glucose tolerance at ages 9-12 y. Restricted-fed (RF) dogs were fed 75% of the same diet consumed by control-fed (CF) pair-mates. An intravenous glucose tolerance test was done annually (maximal stimulation, nonsteady-state). Diet treatment, age, and interactions were fixed effects. Statistical procedures used included mixed-model, repeated-measures ANOVA; least-squares means; Tukey's multiple comparison; paired t tests; and Spearman rank correlations. Glucose k-value and half-life, and insulin sensitivity (total, and 9, 10, 11 y, and per lean mass) were higher (P < 0.05) in RF than in CF dogs. Late-phase insulin release [area under the curve (AUC) 30-120 min] was less (P < 0.05) in RF than in CR dogs. Early-phase insulin release (AUC 0-5 min), y 12 insulin sensitivity and insulinogenic index did not differ between RF and CF dogs. Insulin peak, delta and total AUC increased (P < 0.05) with age, whereas the glucose k-value and glucose half-life were not affected by age. Insulin sensitivity was negatively, and insulin AUC 30-120 min, peak and delta glucose were positively correlated with body weight, body condition score, fat mass, percentage of fat and abdominal fat/total tissue. Higher insulinogenic indices tended (P = 0.053) to be associated with greater median survival and dogs with higher insulin sensitivity were at lower (P < 0.05) risk of dying or receiving chronic disease treatment. Time to first osteoarthritis treatment or death was greater with lower basal glucose and higher insulin sensitivity (P < 0.05), but diet restriction explained most of this relationship's variation. Glucose disposal efficiency and insulin response were associated with increased quality and length of life in diet-restricted dogs.

Adaptogenic activity of a novel withanolide-free aqueous fraction from the roots of Withania somnifera Dun. (Part II)

In the Indian traditional system of medicine Withania somnifera Dun. is widely regarded as the Indian Ginseng. A new withanolide-free hydrosoluble fraction was isolated from the roots of Withania somnifera Dun. and was evaluated for putative antistress activity against a battery of tests to delineate the activity of this fraction. The latter fraction exhibited significant antistress activity in a dose-related manner (Singh et al., 2001) and was further studied against chemical and physical induced stress in rats and mice. The extract of Withania somnifera root (a commercial preparation available locally) was also used to compare the results. A preliminary acute toxicity study in mice showed a good margin of safety with a high therapeutic index.

Physiologic determinants of the anorexia of aging: insights from animal studies

The anorexia of aging is a syndrome characterized by unexplained losses in food intake and body weight that occur near the end of life. Proposed etiologies cover a wide range of biological and psychological conditions. The observation of this phenomenon in older laboratory animals suggests that physiological changes play a significant causal role. Research on the neurochemical control of energy balance has received much attention in recent years, and age-related alterations in the neuropeptidergic effectors of food intake have been implicated in the anorexia of aging. This review provides an update on putative mechanisms underlying this dysregulation of feeding during advanced age.

The effects of ad libitum overfeeding and moderate and marked dietary restriction on age-related spontaneous pancreatic islet pathology in Sprague-Dawley rats

This study compared the effects of ad libitum (AL) overfeeding and moderate or marked dietary restriction (DR) on aged-related degenerative and proliferative changes of the endocrine pancreas in Sprague-Dawley (SD) rats. SD rats were fed Purina Certified Rodent Diet AL (group 1), DR at 72-79% of AL (group 2), DR at 68-72% of AL (group 3) or DR at 47-48% of AL (group 4) for 106 weeks. Interim necropsies were performed at 13, 26, and 53 weeks, after a 7-day 5-bromo-2-deoxyuridine (BrdU)-filled minipump implantation. Before each necropsy, glucose and serum insulin levels were measured. In addition to the routine histopathologic examination performed in both sexes, determination of 9 pancreatic islet stereologic parameters was done in males at 13, 26, and 53 weeks. In AL-fed rats, early changes in the islet morphology occurred, which resulted in a high incidence of islet fibrosis, focal hyperplasias and adenomas by two years. DR was dose-proportionally associated with decreased glucose and serum insulin levels, and delayed the onset, and decreased the incidence and severity of islet fibrosis and hyperplasia. Results of the stereology supported the histopathologic and clinical chemistry findings. It demonstrated that, compared to AL-fed rats, DR-fed rats had smaller pancreas, smaller pancreatic islets, smaller insulin secreting cell volumes, a lower degree of islet fibrosis and a lower islet cell BrdU labeling index, which correlated with a lower incidence of islet adenoma and carcinoma at study termination. Moderate and marked degrees of DR delayed the onset and severity of islet hyperplasia and fibrosis in a temporal- and dose-related manner. In contrast to marked DR, which dramatically prevented these changes, moderate DR delayed but not prevented onset of islet tumors. These findings support the concept that moderate DR results in a better-controlled animal model with a lower incidence or delayed onset of chronic spontaneous endocrine diseases in the rat bioassay.

Beta cell function declines with age in glucose tolerant Caucasians

OBJECTIVE

As type 2 diabetes results from an imbalance between insulin sensitivity and beta cell function, either or both may worsen with age. However, existing data are controversial on the effect of ageing on both insulin sensitivity and beta cell function.

SUBJECTS AND DESIGN

We enrolled 149 healthy, glucose tolerant and normotensive Caucasians (age 35 +/- 1 years, body mass index 26.07 +/- 0.44 kg/m2, waist-hip ratio 0.842 +/- 0.009 cm/cm, mean +/- standard error). A cross-sectional study was designed to examine the impact of age on insulin sensitivity and beta cell function. Their beta cell function (percentage B [%B]) and insulin sensitivity (percentage S [%S]) were estimated using the homeostasis model assessment.

RESULTS

Simple regression analysis revealed that %B declined with age (P = 0.008) while no relation was found between %S and age (P = 0.769). A stepwise regression analysis revealed that body mass index and diastolic blood pressure explained 14.7% of variation in %S, while age, waist-hip ratio, gender, and systolic blood pressure had no influence on %S. Age, body mass index and diastolic blood pressure together accounted for 21.7% of variation in %B, with age being an independent variable.

CONCLUSIONS

In the present study, we showed that beta cell function declined with age at a rate of about 1% per year. In contrast, insulin sensitivity was not affected by ageing. Our observations suggest that the age-related decline in glucose tolerance is primarily related to the loss of beta-cell function.

Accumulation of advanced glycation endproducts in aging male Fischer 344 rats during long-term feeding of various dietary carbohydrates

The observation of accelerated collagen glycation in association with enhanced progression of many age-associated diseases in hyperglycemic subjects has led researchers to propose a role of glycation in the aging process. Although short-term studies in healthy animals suggest that feeding a diet high in fructose may increase serum glucose concentrations and increase glycemic stress, the effects of a long-term feeding, i.e., life span, are unknown. This study was designed to evaluate the long-term effects of dietary carbohydrates on serum and tissue markers of glycemic stress. Three-month-old male Fischer 344 rats were given free access to or restricted to 60% caloric intake of one of five isocaloric diets that contained as their carbohydrate source either cornstarch, glucose, sucrose, fructose or equimolar amounts of fructose and glucose. Rats were killed at 9-, 18- or 26-mo of age. Glycated hemoglobin, serum glucose and fructosamine levels were measured as markers of serum glycemic stress. Collagen-associated fluorescence and pentosidine concentrations were measured in skin, aortic, tracheal and tail tendon collagen as markers of advanced glycation endproducts (AGE). The source of dietary carbohydrate had little effect on markers of glycemic stress and the accumulation of AGE. Restricting the amount of calories consumed resulted in lower serum glucose concentrations, glycated hemoglobin levels and pentosidine concentrations in tail tendon collagen. Our data suggest that the rate of collagen glycation is tissue-specific. These results suggest that long-term feeding of specific dietary carbohydrates does not alter serum glucose concentrations or the rate of collagen glycation. Rather, age-related accumulation of AGE is more closely related to caloric intake.

Lower calorie intake enhances muscle insulin action and reduces hexosamine levels

Previous studies have demonstrated enhanced insulin sensitivity in calorie-restricted [CR, fed 60% ad libitum (AL) one time daily] compared with AL-fed rats. To evaluate the effects of reduced food intake, independent of temporal differences in consumption, we studied AL (unlimited food access)-fed and CR (fed one time daily) rats along with groups temporally matched for feeding [fed 3 meals (M) daily]: MAL and MCR, eating 100 and 60% of AL intake, respectively. Insulin-stimulated glucose transport by isolated muscle was increased in MCR and CR vs. AL and MAL; there was no significant difference for MCR vs. CR or MAL vs. AL. Intramuscular triglyceride concentration, which is inversely related to insulin sensitivity in some conditions, did not differ among groups. Muscle concentration of UDP-N-acetylhexosamines [end products of the hexosamine biosynthetic pathway (HBP)] was lower in MCR vs. MAL despite unaltered glutamine-fructose-6-phosphate aminotransferase activity (rate-limiting enzyme for HBP). These results indicate that the CR-induced increase in insulin-stimulated glucose transport in muscle is attributable to an altered amount, not timing, of food intake and is independent of lower triglyceride concentration. They further suggest that enhanced insulin action might involve changes in HBP.

Short-term calorie restriction improves disease-related markers in older male rhesus monkeys (Macaca mulatta)

Calorie restriction (CR) is widely known for its effects on life span, physiological aging and age-related disease in laboratory rats and mice. Emerging data from CR studies in rhesus monkeys suggest that this nutritional intervention paradigm may also have beneficial effects in long-lived mammals. Studies from our laboratory and others have suggested that young- or adult-onset CR might have beneficial effects on cardiovascular disease and diabetes. For example, long-term CR reduced body fat and serum triglycerides, and increased a subfraction of HDL cholesterol associated with decreased cardiovascular disease risk. These studies suggested that long-term CR begun in young or adult animals might have important effects on markers relevant to age-related disease. Few studies have examined the effects of CR initiated in older animals (rodents or monkeys), and the temporal nature of some potentially beneficial effects of CR is unknown. The present study examined several markers related to diabetes and cardiovascular disease in thirteen older adult (> 18 year) non-obese (body fat < 22%), male rhesus monkeys during a short-term CR paradigm. Specifically, we collected these data at baseline (ad libitum feeding), 10, 20, and 30% CR, and at 6 and 12 months on 30% CR. Fasting and peak insulin were significantly reduced as were the acute and second-phase insulin responses. CR also marginally reduced triglycerides (50% reduction), but had no effect on total serum cholesterol or blood pressure. Interestingly, the observed glucoregulatory changes emerged prior to any evidence of a change in body composition suggesting that certain effects of CR may not be wholly dependent on changes in body composition in older monkeys.

Age-dependent inability of the endocrine pancreas to adapt to pregnancy: a long-term consequence of perinatal malnutrition in the rat

We have recently shown that maternal food restriction during late pregnancy decreased beta-cell mass in the offspring at birth. Prolonged maternal malnutrition until weaning led to irreversible decrease of beta-cell mass in the adult male progeny. During pregnancy, the maternal endocrine pancreas demonstrates an acute and reversible increase in beta-cell mass. The aim of this work was to investigate whether perinatal malnutrition could have long-lasting effects on glucose homeostasis and the adaptation of the endocrine pancreas to a subsequent pregnancy. This study was conducted on 4- and 8-month-old female rats malnourished during their perinatal life and on age-matched control animals. Oral glucose tolerance tests (OGTT), pancreatic insulin content, and islet mass quantitation after dithizone staining were performed on the same animals. Four-month-old nonpregnant previously malnourished animals showed normal glucose tolerance but a significant decrease in insulin secretion during OGTT. These animals were, however, still able to adapt pancreatic insulin contents and doubled their islet mass in late gestation. At 8 months of age, insulin content before pregnancy was reduced to half that of controls. Moreover, it did not show the characteristic increase during gestation that could still be observed in pregnant control females. In those control animals, the islet mass increased regularly until late gestation (14.1+/-1.8 mg at day 20.5, vs. 9.8+/-1.2 mg, nonpregnant), whereas in previously malnourished animals the islet mass remained throughout pregnancy similar to the nonpregnant values (8.5+/-1.4 mg at day 20.5 vs. 8.9+/-3.6 mg, nonpregnant). In conclusion, early malnutrition has dramatic consequences on the capacity of the endocrine pancreas to meet the increased insulin demand during pregnancy and aging.

Effect of calorie restriction on in vivo glucose metabolism by individual tissues in rats

We evaluated the effects of 8 mo of calorie restriction [CR: 60% of ad libitum (AL) food intake] on glucose uptake by 14 tissues in unanesthetized, adult (12 mo) F344xBN rats. Glucose metabolism was assessed by the 2-[3H]deoxyglucose tracer technique at 1500 or 2100. Despite an approximately 60% decline in insulinemia with CR, plasma 2-[3H]deoxyglucose clearance for CR was greater than for AL at both times. A small, CR-related decrease in glucose metabolic index (R'g) occurred only at 1500 in the spleen and heart, and this decrease was reversed at 2100. In some tissues (cerebellum, lung, kidney, soleus, and diaphragm), R'g was unaffected by diet, regardless of time. In the other tissues (brown fat, 3 white fat pads, epitrochlearis, plantaris, and gastrocnemius), R'g was higher or tended to be higher for CR vs. AL at one or both times. These findings indicate that 8 mo of CR did not cause a continuous reduction in in vivo glucose uptake by any tissue studied, and, in several insulin-sensitive tissues, glucose uptake was at times greater for CR vs. AL rats.

Calorie restriction increases cell surface GLUT-4 in insulin-stimulated skeletal muscle

Reduced calorie intake [calorie restriction (CR); 60% of ad libitum (AL)] leads to enhanced glucose transport without altering total GLUT-4 glucose transporter abundance in skeletal muscle. Therefore, we tested the hypothesis that CR (20 days) alters the subcellular distribution of GLUT-4. Cell surface GLUT-4 content was higher in insulin-stimulated epitrochlearis muscles from CR vs. AL rats. The magnitude of this increase was similar to the CR-induced increase in glucose transport, and GLUT-4 activity (glucose transport rate divided by cell surface GLUT-4) was unaffected by diet. The CR effect was specific to the insulin-mediated pathway, as evidenced by the observations that basal glucose transport and cell surface GLUT-4 content, as well as hypoxia-stimulated glucose transport, were unchanged by diet. CR did not alter insulin's stimulation of insulin receptor substrate (IRS)-1-associated phosphatidylinositol 3-kinase (PI3K) activity. Muscle abundance of IRS-2 and p85 subunit of PI3K were unaltered by diet, but IRS-1 content was lower in CR vs. AL. These data demonstrate that, despite IRS-1-PI3K activity similar to AL, CR specifically increases insulin's activation of glucose transport by enhancing the steady-state proportion of GLUT-4 residing on the cell surface.

Effect of extracellular palmitate on 2-deoxy-d-glucose uptake in muscle from Ad libitum fed and calorie restricted rats

We studied the effect of a high physiologic concentration of palmitate (1mM) on in vitro 2-deoxy-D-glucose (2DG) uptake by flexor digitorum brevis (FDB) muscle from ad libitum fed rats (AL) and rats fed 60% of ad libitum intake (CR) for 20 days. CR did not alter muscle 2DG uptake in the absence of insulin, but relative to AL, CR significantly (p<0.01) increased 2DG uptake in the presence of 20,000 microU/ml insulin. This effect of CR persisted in the presence of 1mM palmitate. The presence of 1mM palmitate significantly (p<0.01) impaired 2DG glucose uptake, both in the presence and absence of insulin, to the same extent in AL and CR muscle, despite an 18% decrease in FABPpm expression with CR. Thus, although CR profoundly affects insulin-mediated muscle glucose uptake, it does not alter the ability of extracellular fatty acid to modulate glucose utilization by skeletal muscle.

Comparison of the effects of 20 days and 15 months of calorie restriction on male Fischer 344 rats

The aim of this study was to compare, in 19-month-old male Fischer 344 rats, the influence of brief (20 days) and prolonged (approximately 15 months) calorie restriction (CR; consuming approximately 60% of ad libitum, AL, intake) on circulating levels of glucose, insulin, C-peptide, and free fatty acids (FFA); age-matched AL rats were also studied. In the prolonged CR group, there was an approximately 85% decline in fat pad masses (epididymal and retroperitoneal) compared to AL and brief CR rats (these latter groups did not differ significantly). Compared to AL levels, glucose was 15% lower with prolonged CR (p < 0.05) while the brief CR values tended to be lower (10%) than AL; the CR groups did not differ significantly. Plasma FFA levels were significantly (p < 0.05) greater (85-106%) in the brief CR group compared to each of the other groups. Plasma insulin concentrations for the CR groups were lower (p < 0.05; approximately 50-60%) than AL levels. Plasma concentrations of C-peptide (an indicator of insulin secretion) were also lower for each CR group vs AL levels, and a high correlation was found between plasma insulin and C-peptide concentrations (r2 = 0.90; p < 0.001). The C-peptide/insulin ratios for the CR groups were similar, and the value of each CR group exceeded that for the AL rats. These results demonstrate that: the CR-induced reduction in plasma insulin is attributable in large part to reduced insulin secretion; these decreases in insulin secretion and concentration are essentially undiminished when brief CR is initiated rather late in life, and the reductions are independent of substantial reductions in body fat.