Relationship between glucose tolerance and glucose-stimulated insulin response in 65-year-olds

β-Cell function during a high-fat meal in young versus old adults: role of exercise

The acute effect of exercise on β-cell function during a high-fat meal (HFM) in young adults (YA) versus old adults (OA) is unclear. In this randomized crossover trial, YA (n = 5 M/7 F, 23.3 ± 3.9 yr) and OA (n = 8 M/4 F, 67.7 ± 6.0 yr) underwent a 180-min HFM (12 kcal/kg body wt; 57% fat, 37% CHO) after a rest or exercise [∼65% heart rate peak (HRpeak)] condition ∼12 h earlier. After an overnight fast, plasma lipids, glucose, insulin, and free fatty acid (FFA) were determined to estimate peripheral, or skeletal muscle, insulin sensitivity (Matsuda index) as well as hepatic [homeostatic model assessment of insulin resistance (HOMA-IR)] and adipose insulin resistance (adipose-IR). β-Cell function was derived from C-peptide and defined as early-phase (0-30 min) and total-phase (0-180 min) disposition index [DI, glucose-stimulated insulin secretion (GSIS) adjusted for insulin sensitivity/resistance]. Hepatic insulin extraction (HIE), body composition [dual-energy X-ray absorptiometry (DXA)], and peak oxygen consumption (V̇o2peak) were also assessed. OA had higher total cholesterol (TC), LDL, HIE, and DI across organs as well as lower adipose-IR (all, P < 0.05) and V̇o2peak (P = 0.056) despite similar body composition and glucose tolerance. Exercise lowered early-phase TC and LDL in OA versus YA (P < 0.05). However, C-peptide area under the curve (AUC), total phase GSIS, and adipose-IR were reduced postexercise in YA versus OA (P < 0.05). Skeletal muscle DI increased in YA and OA after exercise (P < 0.05), whereas adipose DI tended to decline in OA (P = 0.06 and P = 0.08). Exercise-induced skeletal muscle insulin sensitivity (r = -0.44, P = 0.02) and total-phase DI (r = -0.65, P = 0.005) correlated with reduced glucose AUC180min. Together, exercise improved skeletal muscle insulin sensitivity/DI in relation to glucose tolerance in YA and OA, but only raised adipose-IR and reduced adipose-DI in OA.NEW & NOTEWORTHY High-fat diets may induce β-cell dysfunction. This study compared how young and older adults responded to a high-fat meal with regard to β-cell function and whether exercise comparably impacted glucose regulation. Older adults secreted more insulin during the high-fat meal than younger adults. Although exercise increased β-cell function adjusted for skeletal muscle insulin sensitivity in relation to glucose tolerance, it raised adipose insulin resistance and reduced pancreatic β-cell function relative to adipose tissue in older adults. Additional work is needed to discern nutrient-exercise interactions across age to mitigate chronic disease risk.

Persistence of improved glucose homeostasis in Gclm null mice with age and cadmium treatment

Antioxidant signaling/communication is among the most important cellular defense and survival pathways, and the importance of redox signaling and homeostasis in aging has been well-documented. Intracellular levels of glutathione (GSH), a very important endogenous antioxidant, both govern and are governed by the Nrf2 pathway through expression of genes involved in its biosynthesis, including the subunits of the rate-limiting enzyme (glutamate cysteine ligase, GCL) in GSH production, GCLC and GCLM. Mice homozygous null for the Gclm gene are severely deficient in GSH compared to wild-type controls, expressing approximately 10% of normal GSH levels. To compensate for GSH deficiency, Gclm null mice have upregulated redox-regulated genes, and, surprisingly, are less susceptible to certain types of oxidative damage. Furthermore, young Gclm null mice display an interesting lean phenotype, resistance to high fat diet-induced diabetes and obesity, improved insulin and glucose tolerance, and decreased expression of genes involved in lipogenesis. However, the persistence of this phenotype has not been investigated into old age, which is important in light of studies which suggest aging attenuates antioxidant signaling, particularly in response to exogenous stimuli. In this work, we addressed whether aging compromises the favorable phenotype of increased antioxidant activity and improved glucose homeostasis observed in younger Gclm null mice. We present data showing that under basal conditions and in response to cadmium exposure (2 mg/kg, dosed once via intraperitoneal injection), the phenotype previously described in young (<6 months) Gclm null mice persists into old age (24+ months). We also provide evidence that transcriptional activation of the Nrf2, AMPK, and PPARγ pathways underlie the favorable metabolic phenotype observed previously in young Gclm null mice.

Insulin and aging

Aging is characterized by a progressive loss of physiological function leading to increase in the vulnerability to death. This deterioration process occurs in all living organisms and is the primary risk factor for pathological conditions including obesity, type 2 diabetes mellitus, Alzheimer's disease and cardiovascular diseases. Most of the age-related diseases have been associated with impairment of action of an important hormone, namely insulin. It is well-known that this hormone is a critical mediator of metabolism, growth, proliferation and differentiation. Insulin action depends on two processes that determine its circulating levels, insulin secretion and clearance, and insulin sensitivity in its target tissues. Aging has deleterious effects on these three mechanisms, impairing insulin action, thereby increasing the risk for diseases and death. Thus, improving insulin action may be an important strategy to have a healthier and longer life.

The roles of first phase, second phase insulin secretion, insulin resistance, and glucose effectiveness of having prediabetes in nonobese old Chinese women

It has been established that prediabetes can causes significant comorbidities, particularly in the elderly. The deterioration of glucose metabolism are generally considered to be results of the impairment of the 4 factors: first, second insulin secretion (FPIS, SPIS, respectively), glucose effectiveness (GE), and insulin resistance. In this study, we enrolled older women to investigate their relationships with prediabetes.Five thousand four hundred eighty-two nonobese, nondiabetic women were included. They were divided into normal glucose tolerance and prediabetes groups. Receiver operating characteristic curve was performed to investigate the effects on whether to have prediabetes for each factors. Two models were built: Model 1: FPIS + SPIS, and Model 2: model 1 + GE. The area under the receiver operating characteristic (aROC) curve was used to determine the predictive power of these models.The aROC curve of GE was significantly higher than the diagonal line followed by SPIS and FPIS accordingly. The aROC curve of Model 1 (0.611) was not different from GE. However, Model 2 improved significantly up to 0.663. Based on this model, an equation was built (-0.003 × GE - 212.6 × SPIS - 17.9 × insulin resistance + 4.8). If the calculated value is equal or higher than 0 (≥0), then the subject has higher chance to have prediabetes (sensitivity = 0.607, specificity = 0.635).Among the 4 factors, GE is the most important contributor for prediabetes in older women. By building a model composed of FPIS, SPIS, and GE, the aROC curve increased significantly. The equation built from this model could predict prediabetes precisely.

The historical context and scientific legacy of John O. Holloszy

John O. Holloszy, as perhaps the world's preeminent exercise biochemist/physiologist, published >400 papers over his 50+ year career, and they have been cited >41,000 times. In 1965 Holloszy showed for the first time that exercise training in rodents resulted in a doubling of skeletal muscle mitochondria, ushering in a very active era of skeletal muscle plasticity research. He subsequently went on to describe the consequences of and the mechanisms underlying these adaptations. Holloszy was first to show that muscle contractions increase muscle glucose transport independent of insulin, and he studied the mechanisms underlying this response throughout his career. He published important papers assessing the impact of training on glucose and insulin metabolism in healthy and diseased humans. Holloszy was at the forefront of rodent studies of caloric restriction and longevity in the 1980s, following these studies with important cross-sectional and longitudinal caloric restriction studies in humans. Holloszy was influential in the discipline of cardiovascular physiology, showing that older healthy and diseased populations could still elicit beneficial cardiovascular adaptations with exercise training. Holloszy and his group made important contributions to exercise physiology on the effects of training on numerous metabolic, hormonal, and cardiovascular adaptations. Holloszy's outstanding productivity was made possible by his mentoring of ~100 postdoctoral fellows and substantial NIH grant funding over his entire career. Many of these fellows have also played critical roles in the exercise physiology/biochemistry discipline. Thus it is clear that exercise biochemistry and physiology will be influenced by John Holloszy for numerous years to come.

Older Subjects With β-Cell Dysfunction Have an Accentuated Incretin Release

OBJECTIVE

Insulin secretion (IS) declines with age, which increases the risk of impaired glucose tolerance (IGT) and type 2 diabetes mellitus (T2DM) in older adults. IS is regulated by the incretin hormones glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP). Here we tested the hypotheses that incretin release is lower in older adults and that this decline is associated with β-cell dysfunction.

RESEARCH DESIGN

A total of 40 young (25 ± 3 years) and 53 older (74 ± 7 years) lean nondiabetic subjects underwent a 2-hour oral glucose tolerance test (OGTT). Based on the OGTT, subjects were divided into three groups: young subjects with normal glucose tolerance (Y-NGT; n = 40), older subjects with normal glucose tolerance (O-NGT; n = 32), and older subjects with IGT (O-IGT; n = 21).

MAIN OUTCOME MEASURES

Plasma insulin, C-peptide, GLP-1, and GIP concentrations were measured every 15 to 30 minutes. We quantitated insulin sensitivity (Matsuda index) and insulin secretory rate (ISR) by deconvolution of C-peptide with the calculation of β-cell glucose sensitivity.

RESULTS

Matsuda index, early phase ISR (0 to 30 minutes), and parameters of β-cell function were lower in O-IGT than in Y-NGT subjects but not in O-NGT subjects. GLP-1 concentrations were elevated in both older groups [GLP-1 area under the curve (AUC)0-120 was 2.8 ± 0.1 in Y-NGT, 3.8 ± 0.5 in O-NGT, and 3.7 ± 0.4 nmol/L∙120 minutes in O-IGT subjects; P < 0.05], whereas GIP secretion was higher in O-NGT than in Y-NGT subjects (GIP AUC0-120 was 4.7 ± 0.3 in Y-NGT, 6.0 ± 0.4 in O-NGT, and 4.8 ± 0.3 nmol/L∙120 minutes in O-IGT subjects; P < 0.05).

CONCLUSIONS

Aging is associated with an exaggerated GLP-1 secretory response. However, it was not sufficient to increase insulin first-phase release in O-IGT and overcome insulin resistance.

Increase of Calcium Sensing Receptor Expression Is Related to Compensatory Insulin Secretion during Aging in Mice

Type 2 diabetes is caused by both insulin resistance and relative insulin deficiency. To investigate age-related changes in glucose metabolism and development of type 2 diabetes, we compared glucose homeostasis in different groups of C57BL/6J mice ranging in age from 4 months to 20 months (4, 8, 12, 16 and 20 months). Interestingly, we observed that non-fasting glucose levels were not significantly changed, but glucose tolerance gradually increased by 20 months of age, whereas insulin sensitivity declined with age. We found that the size of islets and glucose-stimulated insulin secretion increased with aging. However, mRNA expression of pancreatic and duodenal homeobox 1 and granuphilin was decreased in islets of older mice compared with that of 4-month-old mice. Serum calcium (Ca²⁺) levels were significantly decreased at 12, 20 and 28 months of age compared with 4 months and calcium sensing receptor (CaSR) mRNA expression in the islets significantly increased with age. An extracellular calcium depletion agent upregulated CaSR mRNA expression and consequently enhanced insulin secretion in INS-1 cells and mouse islets. In conclusion, we suggest that decreased Ca²⁺ levels and increased CaSR expression might be involved in increased insulin secretion to compensate for insulin resistance in aged mice.

Long noncoding RNAs in diseases of aging

Aging is a process during which progressive deteriorating of cells, tissues, and organs over time lead to loss of function, disease, and death. Towards the goal of extending human health span, there is escalating interest in understanding the mechanisms that govern aging-associated pathologies. Adequate regulation of expression of coding and noncoding genes is critical for maintaining organism homeostasis and preventing disease processes. Long noncoding RNAs (lncRNAs) are increasingly recognized as key regulators of gene expression at all levels--transcriptional, post-transcriptional and post-translational. In this review, we discuss our emerging understanding of lncRNAs implicated in aging illnesses. We focus on diseases arising from age-driven impairment in energy metabolism (obesity, diabetes), the declining capacity to respond homeostatically to proliferative and damaging stimuli (cancer, immune dysfunction), and neurodegeneration. We identify the lncRNAs involved in these ailments and discuss the rising interest in lncRNAs as diagnostic and therapeutic targets to ameliorate age-associated pathologies and prolong health. This article is part of a Special Issue entitled: Clues to long noncoding RNA taxonomy1, edited by Dr. Tetsuro Hirose and Dr. Shinichi Nakagawa.

Insulin, aging, and the brain: mechanisms and implications

There is now an impressive body of literature implicating insulin and insulin signaling in successful aging and longevity. New information from in vivo and in vitro studies concerning insulin and insulin receptors has extended our understanding of the physiological role of insulin in the brain. However, the relevance of these to aging and longevity remains to be elucidated. Here, we review advances in our understanding of the physiological role of insulin in the brain, how insulin gets into the brain, and its relevance to aging and longevity. Furthermore, we examine possible future therapeutic applications and implications of insulin in the context of available models of delayed and accelerated aging.

Short-term exercise reduces markers of hepatocyte apoptosis in nonalcoholic fatty liver disease

Increased hepatocyte apoptosis is a hallmark of nonalcoholic fatty liver disease (NAFLD) and contributes to the profibrogenic state responsible for the progression to nonalcoholic steatohepatitis (NASH). Strategies aimed at reducing apoptosis may result in better outcomes for individuals with NAFLD. We therefore examined the effect of a short-term exercise program on markers of apoptosis-plasma cytokeratin 18 (CK18) fragments, alanine aminotransferase (ALT), aspartate aminotransferase (AST), soluble Fas (sFas), and sFas ligand (sFasL)-in 13 obese individuals with NAFLD [body mass index 35.2 ± 1.2 kg/m(2), >5% intrahepatic lipid (IHL) assessed by (1)H-MR spectroscopy]. Exercise consisted of treadmill walking for 60 min/day on 7 consecutive days at ∼85% of maximal heart rate. Additionally, subjects underwent an oral glucose tolerance test and a maximal oxygen consumption (Vo(2max)) test before and after the exercise intervention. The Matsuda index was used to assess insulin sensitivity. We observed significant decreases in CK18 fragments (558.4 ± 106.8 vs. 323.4 ± 72.5 U/l, P < 0.01) and ALT (30.2 ± 5.1 vs. 24.3 ± 4.8 U/l, P < 0.05), and an increase in whole body fat oxidation (49.3 ± 6.1 vs. 69.4 ± 7.1 mg/min, P < 0.05), while decreases in circulating sFasL approached statistical significance (66.5 ± 6.0 vs. 63.0 ± 5.7 pg/ml, P = 0.06), as did the relationship between percent change in circulating CK18 fragments and ALT (r = 0.55, P = 0.05). We also observed a significant correlation between changes in fat oxidation and circulating sFasL (rho = -0.65, P < 0.05). There was no change in IHL following the intervention (18.2 ± 2.5 vs. 17.5 ± 2.1%, NS). We conclude that short-term exercise reduces a circulatory marker of hepatocyte apoptosis in obese individuals with NAFLD and propose that changes in the proapoptotic environment may be mediated through improved insulin sensitivity and increased oxidative capacity.

Type 2 diabetes and the aging pancreatic beta cell

The incidence of and susceptibility to Type 2 diabetes increases with age, but the underlying mechanism(s) within beta cells that contribute to this increased susceptibility have not been fully elucidated. Here we review how aging affects the proliferative and regenerative capacity of beta cells and how this impacts beta cell mass. In addition we review changes that occur in beta cell function with age. Although we focus on the different rodent models that have provided insight into the characteristics of the aging beta cell, the limited knowledge from non-rodent models is also reviewed. Further studies are needed in order to identify potential beta cell targets for preventing or slowing the progression of diabetes that occurs with age.

Effect of a 2-h hyperglycemic-hyperinsulinemic glucose clamp to promote glucose storage on endurance exercise performance

Carbohydrate stores within muscle are considered essential as a fuel for prolonged endurance exercise, and regimes for enhancing such stores have proved successful in aiding performance. This study explored the effects of a hyperglycaemic-hyperinsulinemic clamp performed 18 h previously on subsequent prolonged endurance performance in cycling. Seven male subjects, accustomed to prolonged endurance cycling, performed 90 min of cycling at ~65% VO(2max) followed by a 16-km time trial 18 h after a 2-h hyperglycemic-hyperinsulinemic clamp (HCC). Hyperglycemia (10 mM) with insulin infused at 300 mU/m(2)/min over a 2-h period resulted in a total glucose uptake of 275 g (assessed by the area under the curve) of which glucose storage accounted for about 73% (i.e. 198 g). Patterns of substrate oxidation during 90-min exercise at 65% VO(2max) were not altered by HCC. Blood glucose and plasma insulin concentrations were higher during exercise after HCC compared with control (p < 0.05) while plasma NEFA was similar. Exercise performance was improved by 49 s and power output was 10-11% higher during the time trial (p < 0.05) after HCC. These data suggest that carbohydrate loading 18 h previously by means of a 2-h HCC improves cycling performance by 3.3% without any change in pattern of substrate oxidation.

Retinol-binding protein 4 (RBP4) protein expression is increased in omental adipose tissue of severely obese patients

Visceral fat has been linked to insulin resistance and type 2 diabetes mellitus (T2DM); and emerging data links RBP4 gene expression in adipose tissue with insulin resistance. In this study, we examined RBP4 protein expression in omental adipose tissue obtained from 24 severely obese patients undergoing bariatric surgery, and 10 lean controls (4 males/6 females, BMI = 23.2 +/- 1.5 kg/m(2)) undergoing elective abdominal surgeries. Twelve of the obese patients had T2DM (2 males/10 females, BMI: 44.7 +/- 1.5 kg/m(2)) and 12 had normal glucose tolerance (NGT: 4 males/8 females, BMI: 47.6 +/- 1.9 kg/m(2)). Adipose RBP4, glucose transport protein-4 (GLUT4), and p85 protein expression were determined by western blot. Blood samples from the bariatric patients were analyzed for serum RBP4, total cholesterol, triglycerides, and glucose. Adipose RBP4 protein expression (NGT: 11.0 +/- 0.6; T2DM: 11.8 +/- 0.7; lean: 8.7 +/- 0.8 arbitrary units) was significantly increased in both NGT (P = 0.03) and T2DM (P = 0.005), compared to lean controls. GLUT4 protein was decreased in both NGT (P = 0.02) and T2DM (P = 0.03), and p85 expression was increased in T2DM subjects, compared to NGT (P = 0.03) and lean controls (P = 0.003). Regression analysis showed a strong correlation between adipose RBP4 protein and BMI for all subjects, as well as between adipose RBP4 and fasting glucose levels in T2DM subjects (r = 0.76, P = 0.004). Further, in T2DM, serum RBP4 was correlated with p85 expression (r = 0.68, P = 0.01), and adipose RBP4 protein trended toward an association with p85 protein (r = 0.55, P = 0.06). These data suggest that RBP4 may regulate adiposity, and p85 expression in obese-T2DM, thus providing a link to impaired insulin signaling and diabetes in severely obese patients.

The glucose-dependent insulinotropic polypeptide and glucose-stimulated insulin response to exercise training and diet in obesity

Aging and obesity are characterized by decreased beta-cell sensitivity and defects in the potentiation of nutrient-stimulated insulin secretion by GIP. Exercise and diet are known to improve glucose metabolism and the pancreatic insulin response to glucose, and this effect may be mediated through the incretin effect of GIP. The purpose of this study was to assess the effects of a 12-wk exercise training intervention (5 days/wk, 60 min/day, 75% Vo(2 max)) combined with a eucaloric (EX, n = 10) or hypocaloric (EX-HYPO, pre: 1,945 +/- 190, post: 1,269 +/- 70, kcal/day; n = 9) diet on the GIP response to glucose in older (66.8 +/- 1.5 yr), obese (34.4 +/- 1.7 kg/m(2)) adults with impaired glucose tolerance. In addition to GIP, plasma PYY(3-36), insulin, and glucose responses were measured during a 3-h, 75-g oral glucose tolerance test. Both interventions led to a significant improvement in Vo(2 max) (P < 0.05). Weight loss (kg) was significant in both groups but was greater after EX-HYPO (-8.3 +/- 1.1 vs. -2.8 +/- 0.5, P = 0.002). The glucose-stimulated insulin response was reduced after EX-HYPO (P = 0.02), as was the glucose-stimulated GIP response (P < 0.05). Furthermore, after the intervention, changes in insulin (DeltaI(0-30)/DeltaG(0-30)) and GIP (Delta(0-30)) secretion were correlated (r = 0.69, P = 0.05). The PYY(3-36) (Delta(0-30)) response to glucose was increased after both interventions (P < 0.05). We conclude that 1) a combination of caloric restriction and exercise reduces the GIP response to ingested glucose, 2) GIP may mediate the attenuated glucose-stimulated insulin response after exercise/diet interventions, and 3) the increased PYY(3-36) response represents an improved capacity to regulate satiety and potentially body weight in older, obese, insulin-resistant adults.

Decreased visfatin after exercise training correlates with improved glucose tolerance

Nampt/pre-B-cell colony-enhancing factor/visfatin (visfatin) release from adipocytes has recently been suggested to be nutrient responsive and linked to systemic nicotinamide adenine dinucleotide biosynthesis and regulation of pancreatic beta-cell function.

PURPOSE

We hypothesized that if visfatin does play a role in the insulin response, then the exercise training-induced reduction in insulin response to an oral glucose load would correlate with reduced plasma visfatin.

METHODS

Sixteen obese men and women (age = 65 +/- 1 yr, body mass index = 33.4 +/- 1.5 kg x m(-2)) volunteered to participate in a 12-wk supervised exercise program (5 d x wk(-1), 60 min x d(-1) at 85% of HRmax). Visceral (VAT) and subcutaneous adipose tissue (SAT) were measured by computed tomographic scans. A 2-h 75-g oral glucose tolerance test was performed to determine the effect of exercise training on the insulin response to a glucose load. Fasting plasma visfatin was measured by enzyme-linked immunosorbent assay.

RESULTS

Exercise training resulted in an increase in (.)VO2max (21.1 +/- 0.9 vs 24.2 +/- 1.1 mL x kg(-1) x min(-1), P < 0.001), a decrease in body weight (96.4 +/- 4.1 vs 92.4 +/- 3.7 kg, P < 0.001), VAT (191 +/- 16 vs 144 +/- 16 cm, P < 0.001), and SAT (369 +/- 34 vs 309 +/- 41 cm, P < 0.02). Area under the glucose (450 +/- 31 vs 392 +/- 33 mmol x L(-1) x 2 h(-1), P < 0.01) and insulin (45,767 +/- 6142 vs 35,277 +/- 4997 pmol x L(-1) x 2 h(-1), P < 0.003) response curves were decreased after training. After intervention, plasma visfatin levels were significantly reduced (16.9 +/- 2.2 vs 14.5 +/- 1.8 ng x mL(-1), P < 0.05), and the change in visfatin was associated with the corresponding change in insulin (r = 0.56, P < 0.05) and glucose AUC (r = 0.53, P < 0.05).

CONCLUSION

The exercise-induced reduction of plasma visfatin is most likely the result of weight loss and body composition changes. The potential regulatory role of visfatin in mediating the pancreatic insulin response to oral glucose requires further investigation.

Assessment of Age-Related Changes in Abdominal Organ Structure and Function With Computed Tomography and Positron Emission Tomography

With the size of the aged population in the United States expected to grow considerably during the next several decades, the number of imaging studies performed on such aged individuals will similarly increase. Thus, it is important to understand normal age-related changes in the structural and functional imaging appearance of the abdominal organs. We therefore present preliminary data and a review of the literature relevant to structural and functional changes in the abdominal organs of children and older adults. In a retrospective study of both adult and pediatric populations, we used computed tomography (CT), positron emission tomography (PET), and PET/CT imaging to investigate age-associated changes in size, attenuation, and metabolic function of the abdominal organs. Organs of interest include the liver, spleen, pancreas, kidneys, adrenal glands, stomach, small bowel, colon, and rectum. Although volumes of adult liver, spleen, pancreas, and kidneys do not change significantly with age, adult left and right adrenal gland volumes do significantly increase with age (r = 0.2823, P = 0.0334, and r = 0.3676, P = 0.0049, respectively). Also, the attenuation of adult liver (r = -0.2122, P = 0.0412), spleen (r = -0.4508, P < 0.0001), pancreas (r = -0.5124, P = 0.0007), and left and right adrenal gland (r = -0.5835, P < 0.0001 and r = -0.6135, P < 0.0001, respectively) decrease significantly with increasing age. Every organ studied in the pediatric population demonstrates a positive association between organ volume and age. Significant age-related changes in organ function are noted in the adult liver and small bowel, with the liver demonstrating a positive association between metabolic activity and age (r = 0.4434, P = 0.0029) and the small bowel showing an inverse association between mean small bowel standardize uptake value and age (r = -0.2435, P = 0.0174). Also, the maximum overall small bowel and colon metabolic activity in children increases with age (r = 0.6478, P = 0.0008). None of the other organs studied (ie, spleen, pancreas, adrenal glands, stomach, colon, rectum) demonstrate significant changes in metabolism with advancing age. The metabolic volumetric product (calculated as the product of organ volume and mean organ SUV) of the liver and spleen does not change significantly with age. In conclusion, various abdominal organs demonstrate differential changes in volume, attenuation, and/or metabolism with increasing age in pediatric and adult populations.

Change in pancreatic B-cell function (HOMA-B) varies in different populations with similar genetic backgrounds but different environments

OBJECTIVE

To determine whether pancreatic B-cell function varies in different populations with similar genetic backgrounds but different environments.

RESEARCH DESIGN/METHODS

We compared a specific migrant Gujarati community in the UK (n = 205) with people still resident in the same villages of origin in Gujarat, India (n = 246). Pancreatic B-cell function (HOMA-B) was determined and the influence of age, migration and other factors was explored.

RESULTS

As anticipated, there was an age-related decline in log(HOMA-B) in both groups. However, the age-related fall in log(HOMA-B) was more pronounced in the UK than in Gujarat (normalized beta-0.29 vs. -0.14, P for difference = 0.03). The decline of HOMA-B with age persisted after adjustment for body mass index (UK beta = -0.31; Gujarat beta = -0.16, P = 0.015, P < 0.001). There was no significant change in insulin sensitivity (HOMA-S) with age at either site, although insulin sensitivity was lower in the UK. Fasting non-estrified fatty acid (NEFA) levels rose with age in the UK but not in Gujarat (P = 0.003 for difference in gradients). In multiple linear regression analysis, lower log(HOMA-B) was independently associated with higher fasting log(NEFA) levels; normalized beta = -0.24, P < 0.001, age; beta = -0.16, P = 0.005, higher log(insulin-like growth factor binding protein-1); beta = -0.19, P = 0.007 and lower body mass index; beta = 0.26, P = 0.001. This model accounted for 25% of the variability in HOMA-B.

CONCLUSIONS

HOMA-B as a measure of B-cell function declines more rapidly with age in the migrant UK group than in Gujarat. This may be a direct consequence of chronically higher NEFA exposure in the UK group.

Diabetes mellitus in the elderly: insulin resistance and/or impaired insulin secretion?

Elderly people are more glucose intolerant and insulin resistant than young individuals, and many of them will develop type 2 diabetes. It remains, however, controversial whether this decrease in function is due to an inevitable consequence of "biological aging" or due to environmental or lifestyle variables. Indeed, increased adiposity/altered fat distribution, decreased fat free mass/abnormal muscle composition, poor dietary habits and physical inactivity all contribute to reduce insulin sensitivity. Insulin resistance in elderly people appears to predominate in skeletal muscle, whereas hepatic glucose output seems to be almost unaffected. Several abnormalities in islet beta-cell and insulin secretion were also pointed out in elderly people such as increased amyloid deposition and decreased amylin secretion, impaired insulin secretion pulsatility, decreased insulin sensitivity of pancreatic beta-cells to insulinotropic gut hormones and diminished insulin response to non-glucose stimuli such as arginine. Controversial results were reported concerning the effects of aging on absolute insulin secretion in response to oral or intravenous glucose. However, insulin secretion appears to decrease with age, with significantly diminished beta-cell sensitivity and acute insulin response to glucose, provided it is analyzed relative to concomitant decreased insulin sensitivity. Thus, there is an interplay between decreased insulin secretion and increased insulin resistance that largely explains the abnormal glucose metabolism seen in elderly. Weight loss, especially reduction of abdominal adiposity, and increased physical activity may contribute to improve insulin sensitivity and glucose tolerance, and prevent the development of type 2 diabetes in elderly people.

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.

Decrease in glucose-stimulated insulin secretion with aging is independent of insulin action

While the incidence of diabetes increases with age, a decrease in beta-cell function independent of age-related insulin resistance has not been conclusively determined. We studied insulin secretion (by hyperglycemic clamp) in 3-, 9-, and 20-month-old chronically catheterized, awake, Sprague Dawley (SD) rats (n = 78). Insulin action was modulated in a group of old rats by caloric restriction (CR) or by surgical removal of visceral fat (VF-). During the first 2 h of the clamp (11 mmol/l glucose), insulin secretion and insulin resistance (S(i hyper clamp)) demonstrated the characteristic hyperbolic relationship. However, after hyperglycemia for an additional 2 h, the ability to maintain insulin secretion, commensurate with the degree of insulin resistance, was decreased in all aging rats (P < 0.05). Increasing plasma glucose levels to 18 mmol/l glucose, after clamp at 11 mmol/l, increased insulin secretion by approximately threefold in young rats, but failed to induce similar magnitude of response in the aging rats ( approximately 50%). However, elevation of plasma free fatty acid (FFA) levels by twofold (by intralipid infusion during 11 mmol/l glucose clamp) resulted in a robust, approximate twofold response in both young and old rats. Thus, prolonged stimulation by hyperglycemia unveiled a functional defect in insulin secretion with aging. This age-related defect is independent of insulin action and is specific to glucose and not FFAs. We suggest that prolonged hyperglycemic stimulation can be a tool to identify functional defects in insulin secretion, particularly in the context of the hyperbolic relationship with insulin action, in elderly subjects or those at risk for type 2 diabetes.

Glucose clearance is delayed after hyperglycemia in healthy elderly men

Delayed glucose clearance after hyperglycemia may contribute to insulin resistance. Rates of glucose and insulin decay were measured after 3 h of sustained hyperglycemia (10 mmol/L) in 8 healthy older men (66 +/- 2 y) and were compared with those of 8 younger men (22 +/- 1 y). Fractional glucose clearance rates were calculated by regression analysis. Insulin decay was estimated from insulin levels through 30 min postinfusion. Abdominal adiposity was estimated from waist-to-hip ratios. Body weight and basal plasma glucose, insulin and C-peptide concentrations did not differ between groups. Fat mass, abdominal adiposity, fasting serum triglycerides and total cholesterol, although normal, were higher (P < 0.05) in the older group. The elderly group experienced lower glucose clearance rates (1.9 +/- 0.2 vs. 2.9 +/- 0.1%/min, P < 0.002) and higher plasma insulin after hyperglycemia (P < 0.03). Glucose and insulin decay correlated with glucose infusion rates (r = 0.88, P < 0.0002 and r = 0.51, P < 0.05). Delayed glucose clearance was associated with greater abdominal adiposity (r = -0.56, P < 0.03), higher serum triglycerides (r = -0.73, P < 0.003) and elevated serum cholesterol (r = -0.56, P < 0.04). In conclusion, modest increases in abdominal adiposity and circulating lipids are associated with abnormal glucose clearance in clinically healthy older men; this may be a precursor to the development of insulin resistance and related complications that arise from prolonged postprandial hyperglycemia.

Mechanisms of the age-associated deterioration in glucose tolerance: contribution of alterations in insulin secretion, action, and clearance

Glucose tolerance decreases with age. For determining the cause of this decrease, 67 elderly and 21 young (70.1 +/- 0.7 vs. 23.7 +/- 0.8 years) participants ingested a mixed meal and received an intravenous injection of glucose. Fasting glucose and the glycemic response above basal were higher in the elderly than in the young participants after either meal ingestion (P < 0.001) or glucose injection (P < 0.01). Insulin action (Si), measured with the meal and intravenous glucose tolerance test models, was highly correlated (r = 0.72; P < 0.001) and lower (P <or= 0.002) in the elderly than in the young participants. However, when adjusted for differences in percentage body fat and visceral fat, Si no longer differed between groups. When considered in light of the degree of insulin resistance, all indexes of insulin secretion were lower (P < 0.01) in the elderly participants, indicating impaired beta-cell function. Hepatic insulin clearance was increased (P < 0.002), whereas total insulin clearance was decreased (P < 0.002) in the elderly subjects. Multivariate analysis (r = 0.70; P < 0.001) indicated that indexes of insulin action (Si) and secretion (Phi(total)) but not age, peak oxygen uptake, fasting glucose, degree of fatness, or hepatic insulin clearance predicted the postprandial glycemic response. We conclude that the deterioration in glucose tolerance that occurs in healthy elderly subjects is due to a decrease in both insulin secretion and action with the severity of the defect in insulin action being explained by the degree of fatness rather than age per se.

Impaired substrate oxidation in healthy elderly men after eccentric exercise

The metabolic response to eccentric exercise in healthy older adults is unknown. Therefore, substrate metabolism was examined in the basal state and after sustained hyperglycemia (180 min, 10 mM) in eight healthy, sedentary older [66 +/- 2 yr; body mass index (BMI) of 25.5 +/- 1.2 kg/m] and nine younger (23 +/- 1 yr; BMI of 23.6 +/- 1.7 kg/m) men, under control conditions and 48 h after eccentric exercise. Indirect calorimetry was performed to evaluate carbohydrate and lipid oxidation (C(ox) and L(ox), respectively). Eccentric exercise caused muscle soreness and increased plasma creatine kinase in both groups of men (P < 0.02). Although a similar level of hyperglycemia was maintained in the two groups, glucose infusion rates were lower (P < 0.001) in the older men. Compared with basal levels, hyperglycemia stimulated an increase in C(ox) and a decrease in L(ox) during the control and exercise trials in the younger group (P < 0.03), but only during the control trial in the older subjects (P < 0.007). C(ox) was unchanged after eccentric exercise in the younger men [4.00 +/- 0.30 vs. 3.54 +/- 0.44 mg x kg fat-free mass (FFM)(-1) x min(-1); exercise vs. control] but was suppressed by 20% in the older group (3.37 +/- 0.37 vs. 4.21 +/- 0.23 mg x kg FFM(-1) x min(-1); P < 0.04). Moreover, L(ox) was reduced by 38% in the younger subjects (0.47 +/- 0.09 vs. 0.76 +/- 0.10 mg x kg FFM(-1) x min(-1); P< 0.03) but was augmented by 89% in the older group (0.68 +/- 0.11 vs. 0.36 +/- 0.08 mg x kg FFM(-1) x min(-1); P < 0.04). In addition, hyperglycemia-stimulated C(ox), L(ox), and respiratory exchange ratio responses to eccentric exercise were related to abdominal adiposity (r = -0.57, P < 0.04, r = 0.68, P < 0.02 and r = -0.60, P < 0.02, respectively). Despite normal glucose tolerance and the absence of obesity per se, older men experience a reduction in carbohydrate oxidation in response to hyperglycemia after eccentric exercise.

Aging and insulin secretion

Glucose tolerance progressively declines with age, and there is a high prevalence of type 2 diabetes and postchallenge hyperglycemia in the older population. Age-related glucose intolerance in humans is often accompanied by insulin resistance, but circulating insulin levels are similar to those of younger people. Under some conditions of hyperglycemic challenge, insulin levels are lower in older people, suggesting beta-cell dysfunction. When insulin sensitivity is controlled for, insulin secretory defects have been consistently demonstrated in aging humans. In addition, beta-cell sensitivity to incretin hormones may be decreased with advancing age. Impaired beta-cell compensation to age-related insulin resistance may predispose older people to develop postchallenge hyperglycemia and type 2 diabetes. An improved understanding of the metabolic alterations associated with aging is essential for the development of preventive and therapeutic interventions in this population at high risk for glucose intolerance.

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.

Age-related increase in haemoglobin A1c and fasting plasma glucose is accompanied by a decrease in beta cell function without change in insulin sensitivity: evidence from a cross-sectional study of hospital personnel

AIMS

To examine the influence of age on glucose homeostasis in a population of healthy, non-diabetic hospital personnel.

METHODS

One hundred and twenty female and 71 male non-diabetic individuals (fasting plasma glucose < 7.0 mmol/l) were fasted overnight prior to blood sampling. Glycated haemoglobin (HbA1c), fasting plasma glucose (FPG) and fasting plasma insulin (FPI) were measured using a BioRad Diamat automated HPLC, a Hitachi 747 analyser and a sensitive in-house radioimmunoassay, respectively. Mathematical modelling of the fasting glucose and insulin pairs (homeostasis model assessment (HOMA)) generated indices of pancreatic beta cell function, HOMA-B and tissue insulin sensitivity HOMA-S.

RESULTS

Spearman rank correlation analysis showed that in the whole group there was a significant negative correlation between age and HOMA-B (rs = -0.218, P = 0.0022) and a significant positive correlation between age and both HbA1c (rs = 0.307, P = 0.0001) and FPG (rs = 0.26, P = 0.0003). There was no correlation between age and either FPI (rs = -0.08, P = 0.266) or HOMA-S (rs = 0.024, P = 0.75). Analysis by gender showed the above associations to be present in the females (rs = -0.243, P = 0.0076; rs = 0.304, P = 0.0007; rs = 0.32, P = 0.0004 for age vs. HOMA-B, HbA1c, and FPG, respectively). Again there was no correlation of age with FPI or insulin sensitivity. In the males there was a significant correlation of HbA1c with age (rs = 0.35, P = 0.002), but no significant correlation of age with any of the other parameters.

CONCLUSIONS

Glycaemic control deteriorates with age in healthy, non-diabetic individuals. Age-related rises in FPG and haemoglobin A1c result from a small but steady decline in pancreatic beta cell function.

Relationships among age, proinsulin conversion, and beta-cell function in nondiabetic humans

The aim of the present study was to examine the relationships among beta-cell function, proinsulin conversion to insulin, and age. We studied insulin and proinsulin secretion in nondiabetic subjects during an oral glucose tolerance test (OGTT) using published indexes of beta-cell function (n = 379, age 16--68 years) and a modified hyperglycemic clamp (10 mmol/l, additional glucagon-like peptide [GLP-1] infusion, final arginine bolus; n = 50, age 19--68 years). Proinsulin conversion to insulin was assessed using proinsulin/insulin (PI/I) ratios immediately after an acute stimulus (OGTT, 30 min; hyperglycemic clamp, 2.5-5.0 min after glucose and arginine). There was a negative correlation between age and beta-cell function (adjusted for insulin sensitivity, BMI, and fasting glucose) in the OGTT (r = -0.21, P < 0.001) and first phase of the hyperglycemic clamp (r = -0.30, P = 0.03), but not second phase (r = -0.08, P = 0.6) or arginine-induced insulin secretion (r = 0.06, P = 0.7). There was a positive correlation between age and the PI/I ratio in the OGTT (r = 0.24, P < 0.001). Analogously, there was also a positive correlation between age and the PI/I ratio during first phase (r = 0.37, P = 0.009) and arginine stimulation (r = 0.33, P = 0.01) of the hyperglycemic clamp. First-phase insulin secretion of the hyperglycemic clamp was inversely correlated with the PI/I ratio (r = -0.60, P < 0.001). Interestingly, adjusting first-phase secretion rate for the PI/I ratio abolished the linear relationship with age (r = -0.06, P = 0.7). In conclusion, aging is associated with deteriorating beta-cell function and deteriorating proinsulin conversion to insulin. The age effect on insulin secretion appears to be attributable at least in part to an impairment of proinsulin conversion to insulin.

Human aging is associated with altered TNF-alpha production during hyperglycemia and hyperinsulinemia

Changes in tumor necrosis factor-alpha (TNF-alpha) may provide a mechanism to explain impaired glucose metabolism with advancing age. Hyperglycemic clamps (180 min, 10 mM) were performed on seven older [67 +/- 2 yr; body mass index (BMI) 24.7 +/- 1.0 kg/m(2)] and seven younger (22 +/- 1 yr; BMI 21.8 +/- 1.3 kg/m(2)) healthy sedentary males with normal glucose tolerance. TNF-alpha production at basal and at the end of 180 min of hyperglycemia and hyperinsulinemia was measured ex vivo from lipopolysaccharide-stimulated (1 ng/ml) peripheral blood mononuclear cells. Plasma glucose, insulin, and C-peptide levels were similar in both groups at basal and during the last 30 min of the hyperglycemic clamp. Glucose infusion rates were lower (P < 0.004) in the older group compared with the young, indicating decreased insulin action among the older subjects. Basal TNF-alpha secretion was similar in older and younger subjects. TNF-alpha was suppressed (P < 0.02) in the younger group (230 +/- 46 vs. 126 +/- 49 pg/ml; basal vs. clamp) but not in the older group (153 +/- 37 vs. 182 +/- 42 pg/ml), with significant group differences in response (P < 0.05). A significant correlation was observed between the level of suppression in TNF-alpha production and insulin action (Kendall's rank, tau = 0.40, P < 0.05). Furthermore, the TNF-alpha response during the clamp was related to fat mass (r = 0.88, P < 0.001) and abdominal fat (r = 0.81, P < 0.003). In conclusion, these findings suggest a possible mechanism by which TNF-alpha may modulate glucose metabolism in younger people. Aging and modest increases in adiposity prevent the "normal" suppression of TNF-alpha production after a sustained postprandial-like hyperglycemic-hyperinsulinemic stimulus, which may contribute in part to the decline in insulin sensitivity in older men.

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.

Age-associated decline in gamma-glutamylcysteine synthetase gene expression in rats

Although glutathione (GSH) concentration has been reported to diminish with age, the mechanism underlying such age-associated decline in the GSH content is not well understood. In this study, we compared the gene expression of both subunits of gamma-glutamylcysteine synthetase (GCS), the rate-limiting enzyme in de novo GSH synthesis, in young, adult, and old Fisher 344 rats. It was found that GCS activity was significantly decreased with increased age in liver, kidney, lung, and red blood cells (RBC). Parallel with the decreased enzyme activity, the protein and mRNA contents of both GCS subunits also changed inversely with age in liver, kidney, and lung, implying a decreased GCS gene expression during aging. Such a reduced GCS gene expression was accompanied by a decline in total GSH content without any change in cysteine concentration. Furthermore, the decreased GCS gene expression in old rats was not associated with a decline in the plasma insulin or cortisol level. This study showed, for the first time, that the expression of both GCS subunit genes was decreased in some organs of old rats, which would result in a reduced rate of GSH biosynthesis. Such decline in GSH synthetic capacity may underlie the observed decrease in GSH content during aging.

Age-related differences in the pancreatic beta-cell response to hyperglycemia after eccentric exercise

Eccentric exercise (ECC) causes muscle damage, insulin resistance, and increased pancreatic beta-cell secretion in young individuals. However, the effects of age on the pancreatic beta-cell response to glucose after ECC are unknown. Hyperglycemic clamps (180 min, 10.0 mM) were performed on eight young (age 22 +/- 1 yr) and eight older (age 66 +/- 2 yr) healthy sedentary males without exercise (CONT) and 48 h after ECC. ECC increased (P < 0.02) muscle soreness ratings and plasma creatine kinase concentrations in both groups. Insulin and C-peptide secretions were similar between young and older subjects during CONT clamps. ECC increased (P < 0.05) first-phase (0-10 min) C-peptide area under the curve in young (4.2 +/- 0.4 vs. 3.7 +/- 0.6 nM . min; ECC vs. CONT, respectively) but not in older subjects (3.2 +/- 0.7 vs. 3.5 +/- 0.7 nM . min; ECC vs. CONT), with significant group differences (P < 0.02). Indeed, ECC repressed (P < 0.05) first-phase peak C-peptide concentrations in older subjects (0. 93 +/- 0.16 vs. 1.12 +/- 0.11 nM; ECC vs. CONT). Moreover, first-phase C-peptide-to-insulin molar ratios suggest age-related differences (P < 0.05) in insulin/C-peptide clearance after ECC. Furthermore, the observed C-peptide response after ECC was related to abdominal adiposity [r = -0.62, P < 0.02, and r = -0.66, P < 0. 006, for first and second (10-180 min) phases, respectively]. In conclusion, older individuals did not exhibit the compensatory increase in beta-cell secretion observed among young individuals after ECC. Thus, with increasing age, the pancreatic beta-cell may be less responsive to the physiological stress associated with ECC.