Adiposity, anthropometric measures, and plasma insulin levels of rhesus monkeys

In order to characterize spontaneous adult-onset obesity in a non-human primate model, we have studied a group of twenty-four obese and non-obese male rhesus monkeys (Macaca mulatta). The monkeys, ranging in age from 12 to 27 years, were defined as obese on the basis of tritiated water estimates of body fat content exceeding 25 percent of body weight. Although the obese and non-obese monkeys had similar crown-rump lengths, they differed significantly not only in body weight (17.0 +/- 3.2 vs 11.7 +/- 1.8 kg, X +/- s.d., P less than 0.001), and average body fat content (37.8 +/- 6.6 vs 13.2 +/- 5.4 percent, P less than 0.001) but also in midgirth circumferences (57.5 +/- 8.4 vs 34.8 +/- 6.2 cm, P less than 0.001) and abdominal (but not triceps or scapular) skinfold thicknesses (22.74 +/- 5.8 vs 9.82 +/- 1.82 mm, P less than 0.001), thus, indicating the predominantly abdominal distribution of the fat mass. A new Obesity Index Rh, for rhesus monkeys, defined as body weight divided by the square of the crown-rump length, was developed as an adaptation of obesity indices used for humans and rats. The high correlation of the Obesity Index Rh with percent body fat and its relative independence of height make possible future identification of obese rhesus monkeys on the basis of anthropometric measurements. There were slight, but not significant, differences between the obese and the non-obese groups in lean body mass (10.9 +/- 2.8 vs 8.8 +/- 1.8 kg) and in fasting plasma glucose levels (87.1 +/- 31.8 vs 63.2 +/- 7.5 mg/dl). Obese monkeys had significantly larger average fat cell sizes (1.29 +/- 0.54 vs 0.61 +/- 0.29 microgram lipid/cell, P less than 0.05) and significantly greater fat cell numbers (6.1 X 10(9) vs 2.2 X 10(9), P less than 0.01). Fat cell numbers were better correlated with body weight and total body fat parameters than fat cell size, while fat cell size was more closely associated with the log of fasting plasma insulin levels than was fat cell number. The similarities to studies in humans indicate the importance of the spontaneously obese adult rhesus monkey as an animal model in the study of obesity.     

肥胖青少年血清瘦素、胰岛素和胰岛素原水平的变化

目的　检测肥胖青少年血清瘦素、胰岛素、胰岛素原水平的变化 ,探讨青少年肥胖与代谢综合征的关系。方法　从年龄 14～ 16岁的 2 2 17例学生中筛选出体重指数 (BMI)≥ 2 5kg/m2 的肥胖学生 (肥胖组 ) 198例 ,BMI在 18 5～ 2 3 0kg/m2 之间的体重正常学生 (正常组 ) 78例 ,用放射免疫方法测定血清瘦素、胰岛素和胰岛素原水平 ,同时测定血糖及血脂水平 ,比较两组间差异。结果　血清瘦素水平女生明显高于同龄男生 [(18 5 3± 1 4 1) μg/L比 (6 33± 1 79) μg/L]。肥胖组血清瘦素、胰岛素和胰岛素原水平均高于同龄体重正常者 [分别为 (19 94± 1 91) μg/L比 (11 2 7± 2 0 4 ) μg/L ,(15 34± 1 6 6 ) μIU/L比 (13 17± 1 4 3) μIU/L ,(16 19± 1 6 4 )pmol/L比 (11 79± 1 70 )pmol/L ],血糖、甘油三酯 (TG)和高密度脂蛋白胆固醇 (HDL C)水平虽然在正常范围内 ,但肥胖者血糖和TG水平高于同龄体重正常者 [分别为 (4 6 3± 0 5 0 )mmol/L比 (4 13± 0 33)mmol/L ,(1 2 0± 0 5 6 )mmol/L比 (0 90±0 32 )mmol/L],HDL C水平低于同龄体重正常者 [(1 14± 0 2 4 )mmol/L比 (1 38± 0 2 6 )mmol/L]。结论　肥胖青少年可能存在瘦素抵抗、胰岛素抵抗及潜在的糖代谢和脂代谢异常等代谢综合征改变 ,     

Elevated plasma levels of alpha-melanocyte stimulating hormone (alpha-MSH) are correlated with insulin resistance in obese men

OBJECTIVE: The role of alpha-melanocyte stimulating hormone (MSH) in obesity has been well-documented. However, circulating alpha-MSH concentrations in obese men and their relationship with clinical indicators of obesity and glucose metabolism have not as yet been evaluated. METHODS: We measured the plasma concentrations of alpha-MSH in 15 obese and 15 non-obese male subjects. The relationship of the plasma concentrations of alpha-MSH with body mass index (BMI), body fat mass (measured by bioelectric impedance), body fat distribution (measured by computed tomography), insulin levels, insulin resistance (assessed by the glucose infusion rate (GIR) during an euglycemic hyperinsulinemic clamp study) and with the serum concentrations of leptin and TNF-alpha were also evaluated. RESULTS: In obese men, the plasma alpha-MSH concentrations were significantly increased compared with those in non-obese men (P< 0.02). The plasma levels of alpha-MSH were positively correlated with BMI (r= 0.560, P< 0.05), fasting insulin levels (r=0.528, P< 0.05) and with visceral fat area (r=0.716, P<0.01), but negatively correlated with GIR (r= -0.625, P< 0.02) in obese male subjects. There were significant correlations between plasma concentrations of alpha-MSH and visceral fat area (r=0.631, P< 0.02), and GIR (r = -0.549, P< 0.05) in non-obese male subjects. Circulating concentrations of alpha-MSH were not significantly correlated with the serum concentrations of leptin and TNF-alpha in both obese and non-obese men. CONCLUSION: Circulating concentrations of alpha-MSH are significantly increased and correlated with insulin resistance in obese men.     

Elevated plasma levels of oxytocin in obese subjects before and after gastric banding

Impaired glucose tolerance and hyperinsulinaemia are common features of obesity. Since oxytocin has been shown to influence glucose metabolism and insulin secretion, the objective of the present study was to investigate whether the plasma level of oxytocin is elevated in obese subjects and if so, whether it is affected by weight reduction following gastric banding. Repeated blood samples were collected in connection with ingestion of a liquid test meal from subjects weighing about 130 kg. Normal weight subjects were tested likewise. Further tests were performed on obese subjects 6 months after operation with gastric banding and a subsequent weight reduction of about 30 kg. Plasma levels of oxytocin were measured by radioimmunoassay. It was found that plasma levels of oxytocin were 4-fold higher in the obese subjects when compared to the control subjects. Analysis with high performance liquid chromatography demonstrated that the oxytocin-like material, as determined by radioimmunoassay, in extracted plasma from one obese subject coeluted with synthetic oxytocin standard. Ingestion of a test meal did not seem to influence oxytocin levels. The mean oxytocin level was equally elevated in male and female obese subjects. Following operation oxytocin levels decreased significantly, but were still significantly higher than in the control subjects. The mechanism behind the hyperoxytocinaemia and possible consequence of it remain obscure.     

Elevated blood pressure in obese children: influence of gender, age, weight and serum insulin levels

Prepubescent and early pubescent obese children (n = 114, mean percent IBW = 165, mean age 7.3 years) were studied to determine the relationship of weight (WT), percent of ideal body weight (percent IBW), gender, and insulin (I) to systolic (SBP) and diastolic (DBP) blood pressure. Subjects were assessed for weight, height, percent IBW, systolic and diastolic blood pressure, and Tanner stage; subjects with Tanner stage greater than 3 were excluded. Multiple regression revealed that body weight accounted for the greatest variance in SBP (adj. R2 = 0.34, P less than 0.05), followed by the age. For DBP, weight also accounted for the greatest variance (adj. R2 = 0.16, P less than 0.05) followed by gender. A subgroup (n = 50) was evaluated for oral glucose tolerance. Subjects ingested 1.75 g glucose (GLU)/kg weight and had blood samples drawn at 0, 30, 60, 90, 120 and 180 min. Pearson correlations showed SBP correlated significantly to I at 0 (r = 0.44) and the total integrated area for insulin (r = 0.45); however, adjusting SBP for age by using z-score transformations negated all correlations between SBP and insulin. GLU at 0 and the total integrated area were not significantly correlated to SBP or DBP in absolute or age-adjusted terms. These data on prepubescent, nondiabetic, obese children suggest an association between insulin and elevations in SBP, but not DBP, that is largely due to a mutual association between age and weight. Also, insulin resistance as reflected in GLU response was not related to SBP or DBP.     

Adipose tissue glycogen synthase activation by in vivo insulin in spontaneously insulin-resistant and Type 2 (non-insulin-dependent) diabetic rhesus monkeys

Summary In skeletal muscle, a defect in the covalent activation of glycogen synthase by insulin has been identified in insulin resistance and in Type 2 (non-insulin-dependent) diabetes mellitus, but a similar defect in insulin action at the adipose tissue has not been demonstrated. We sought to determine whether this defect in insulin action in muscle was also present in the same pathway in adipose tissue. We examined the effect of in vivo insulin on adipose tissue glycogen synthase and phosphorylase activity in normal (n=11), hyperinsulinaemic (n=8), and impaired glucose tolerant and Type 2 diabetic (n=8) rhesus monkeys. Adipose tissue samples were obtained before and during a euglycaemic hyperinsulinaemic clamp. Glycogen synthase fractional velocity, independent and total activities were significantly higher in the insulin-stimulated samples compared to the basal samples in the normal group (p<0.05, respectively). In the hyperinsulinaemic group, however, insulin had no effect on glycogen synthase fractional velocity or independent activity, but did increase the total activity of glycogen synthase and phosphorylase (p<0.05, respectively). Furthermore, both the basal and the insulin-stimulated total activities of these two enzymes were significantly greater in the hyperinsulinaemic group as compared to both the normal and the diabetic groups (p<0.05, respectively). In the diabetic group, insulin was without effect on glycogen synthase fractional velocity, independent activity or total activity. We conclude that the covalent activation of adipose tissue glycogen synthase by insulin is absent in both obese hyperinsulinaemic and in spontaneously diabetic monkeys.     

Elevated plasma adiponectin concentrations in patients with liver cirrhosis correlate with plasma insulin levels

Abstract: Background: Adiponectin is a hormone secreted by adipocytes and has anti‐diabetic and anti‐atherogenic properties. Hypoadiponectinemia is associated with insulin‐resistant diabetes and liver dysfunction. The aim of this study was to determine plasma adiponectin and insulin levels in patients with liver cirrhosis. Methods: Adiponectin and insulin levels were determined in 38 patients with cirrhosis and 30 healthy controls, and were correlated with various clinical and biochemical parameters. Patients included 21 with Child A, eight Child B, and nine with Child C liver cirrhosis. Results: Log adiponectin and insulin levels were significantly elevated in patients with cirrhosis compared with the control. In liver cirrhosis, the level of adiponectin increased proportionately with the Child's classification score. In control subjects, plasma adiponectin correlated inversely with insulin levels. In contrast, plasma adiponectin correlated positively with insulin levels in patients with liver cirrhosis. Plasma adiponectin levels did not correlate with age, sex, body mass index, total bilirubin, aspartate aminotransferase, and fasting blood sugar levels in both groups, while alanine aminotransferase correlated negatively with adiponectin in control subjects as reported previously. Conclusion: Our results of high plasma adiponectin in patients with liver cirrhosis could reflect an imbalance between its production by adipocytes and metabolism in the liver.     

IGF-1 levels link estimated glomerular filtration rate to insulin resistance in obesity: A study in obese, but metabolically healthy, subjects and obese, insulin-resistant subjects

Background and Aims

Metabolically healthy but obese (MHO) subjects have a favourable cardio-metabolic risk profile, but whether they are also at lower risk for kidney dysfunction is still questionable.

Methods and Results

A total of 106 MHO, 122 normal-weight and 212 insulin-resistant obese (IRO) subjects were stratified on the basis of their insulin sensitivity and body mass index (BMI). The CKD-EPI equation was used to estimate glomerular filtration rate (eGFR) and ISI index was used to estimate insulin sensitivity.eGFR was significantly lower in IRO as compared to MHO subjects after adjusting for age, gender and BMI (P = 0.008). In a logistic regression model adjusted for age, gender and BMI, IRO subjects showed an increased risk of having eGFR in the lowest quartile (odds ratio (OR) 1.91, 95% confidence interval (CI) 1.01-3.58; P = 0.04) as compared with MHO subjects. This association was maintained when waist, lean body mass, blood pressure, HDL cholesterol, triglyceride, fasting glucose and insulin levels were additionally included into the model (OR 2.49, 95%CI 1.17-5.27; P = 0.01), but its independence was not retained with further inclusion of insulin-like growth factor-1 (IGF-1) levels (OR 2.16, 95%CI 0.93-5.04; P = 0.07) No differences in eGFR were observed between non-obese and MHO individuals.

Conclusions

These results indicate that heterogeneity in obese phenotypes may account for conflicting evidence regarding the significance of obesity as a risk factor for chronic kidney disease. Our findings suggest that obesity is associated with lower kidney function only when insulin sensitivity is reduced, and that plasma IGF-1 is likely to be an important mechanism linking the IRO phenotype with reduced eGFR.     

Increased in vivo phosphorylation of insulin receptor at serine 994 in the liver of obese insulin-resistant Zucker rats

Serine phosphorylation of the insulin receptor (IR) has been proposed to exert an inhibitory influence on its tyrosine kinase activity. Previous works using site-directed mutagenesis suggested that serine 994 of the IR (IR Ser 994) might be part of an inhibitory domain of the receptor. In this study we examined whether this residue is subjected to phosphorylation in vivo. We used a site-phosphospecific antibody to determine the extent of phosphorylation of IR Ser 994 in insulin target tissues from two animal models of insulin resistance with different IR kinase (IRK) activity: obese (fa/fa) Zucker rats and transgenic mice overexpressing bovine growth hormone (PEPCK-bGH mice).Phosphorylation at IR Ser 994 was markedly increased in liver of obese rats. This alteration appeared to be tissue-selective since no phosphorylation on Ser 994 was detected in IRs isolated from skeletal muscle of these animals. On the other hand, the phosphorylation level of IR Ser 994 was very low in liver of PEPCK-bGH mice and did not differ from that of the control group. We have also demonstrated that protein kinase (PK) C isoforms alpha, betaI and zeta are able to promote the in vitro phosphorylation of the IR on Ser 994. Differential findings in these two models of insulin resistance might thus reflect increased PKC activity resulting from increased lipid availability in obese Zucker rats. Our results suggest that Ser 994 is a novel in vivo IR phosphorylation site that might be involved in the regulation of the IRK in some states of insulin resistance.     

Elevated fibrinogen fragment levels in uremic plasma inhibit platelet function and expression of glycoprotein IIb-IIIa

Hemostatic dysfunction is frequently noted in uremia, but the mechanisms responsible for it are poorly understood and are assumed to be multifactorial. Preliminary findings from our laboratory suggest that elevated levels of circulating fibrinogen fragments (FF) might contribute to the hemostatic defect in uremic patients. Defibrinated plasma obtained from chronic hemodialysis (HD) patients as well as normal subjects were examined by SDS-PAGE and immunoblotting and quantified by an immunoassay. In addition, endogenous FF isolated from normal and uremic plasma using affinity chromatography were examined by flow cytometry for their effect on glycoprotein (GP) IIb-IIIa receptor expression and tested for their ability to inhibit platelet aggregation. The mean FF concentration in uremic plasma (1.14 +/- 0.85 mg/ml) was noted to be eight times greater than in normal plasma (0.15 +/- 0.01 mg/ml) (P < 0.05). Moreover, the mean FF level decreased by 48.25% following HD (from 1.14 +/- 0.85 mg/ml to 0.59 +/- 0.33 mg/ml; P < 0.05). SDS-PAGE and immunoblotting experiments showed that the decrease was observed in both medium-sized (20-60 kDa) as well as large (>100 kDa) FF. Further, FF isolated from uremic plasma inhibited platelet aggregation by (46.8 +/- 18.1)% (P < 0.05) and the GP IIb-IIIa receptor expression by (28.0 +/- 7.6)% (P < 0.05 vs. control). The results show that (1) FF levels are elevated in uremic plasma, (2) HD results in significant decrease in FF and (3) endogenous FF inhibit platelet function, presumably via competitive binding to the fibrinogen receptor GP IIb-IIIa. The decrease in plasma levels of FF > 100 kDa following HD suggests that adsorption to the dialysis membrane contributes to their removal.     

Dietary caloric restriction prevents the age-related decline in plasma melatonin levels of rhesus monkeys.

Rhesus monkeys exhibit an age-associated decrease in peak plasma melatonin levels analogous to that reported for humans. This decrease is essentially abolished in monkeys subjected to a 30% reduction in caloric intake over a 12-yr period. The caloric restriction (CR) effect does not seem to be a reversal, but rather a long-term prevention, of the age-related decline in hormone concentrations. The age effect does not seem to be due to a phase shift in the peak of melatonin secretions, as has been observed in some populations of aged humans. It is also extremely unlikely that the CR effect simply reflects a phase shift, since old monkeys on the diet have nocturnal melatonin levels equal to or greater than adult fully fed controls. Thus, if peak times (approximately 0200 h) were actually shifted, maximal levels in old CR monkeys would be even higher. These findings, coupled with previous observations in humans, suggest that peak plasma melatonin levels may represent a possible candidate "biomarker of aging" in primates. Moreover, this index of age-associated physiological decrement seems to be inhibited by dietary CR.     

Comparison of biosynthetic human insulin and purified pork insulin. Studies in insulin-resistant obese patients using the insulin suppression test

An insulin suppression test performed in random order with either biosynthetic human insulin or purified pork insulin was used to compare biological activity of these two insulins in obese patients suffering from varying degrees of glucose intolerance. Blood glucose curve, steady-state blood glucose levels, insulin sensitivity indices and steady-state plasma insulin levels were identical during the two sets of tests. Furthermore endogenous insulin and glucagon secretion were similarly suppressed. The insulin suppression test is a simple and rapid procedure to compare the biological activity of fast-acting insulins. Our results confirm the insulin-resistance in obesity and clearly show that biosynthetic human and porcine insulins have similar biological potency.     

Contribution of postprandial insulin and glucose to glucose disposal in normal and insulin-resistant obese subjects

We recently found that postprandial hyperinsulinemia does not compensate for the insulin resistance of obese subjects and proposed that postprandial hyperglycemia might be more important in promoting glucose disposal via the mass action effect of glucose. To test this idea we perform oral glucose tolerance tests (OGTT) in six lean and eight obese subjects, measuring glucose and insulin levels. Afterward two insulin infusion studies were performed. During infusion study I, insulin was infused in a dynamic square wave fashion to mimic the individual post-OGTT insulin levels at content euglycemic glucose levels. During study II, glucose and insulin infusions were varied to mimic post-OGTT levels in each subject. Overall glucose turnover was measured isotopically by infusion of [3-3H] glucose. During the OGTT the obese subjects exhibited significantly higher insulin (P less than 0.005) and glucose levels (P less than 0.002). Insulin-stimulated glucose disposal rates and total incremental glucose disposal (IGD) over 4 h during study I at euglycemia were significantly lower in obese compared to lean subjects (area under the curve, 824 +/- 166 vs. 1222 +/- 161 mmol/L.m2; P less than 0.01) despite higher post-OGTT insulin levels in obese subjects. When insulin plus glucose levels were matched to the individual OGTT levels, IGD was not significantly different between obese and control subjects (1712 +/- 253 vs. 1617 +/- 444 mmol/L.m2; P = NS). A significant inverse correlation (r = -0.73; P less than 0.05) existed between the degree of glucose intolerance (OGTT) and the decrease in IGD during the phasic hyperinsulinemic euglycemic study (infusion study I). These data suggest that with increasing insulin resistance, hyperinsulinemia is less effective in compensating for this decrease in insulin action, and hyperglycemia becomes more important in augmenting overall glucose disposal values.     

Insulin resistance and impaired insulin secretion in prenatally androgenized male rhesus monkeys

Polycystic ovary syndrome (PCOS) is a familial disease. Affected males harbor some of the metabolic deficits seen in affected females. The prenatally androgenized (PA) female rhesus monkey, an animal model for PCOS, manifests glucoregulatory and reproductive abnormalities similar to those seen in PCOS women. The purpose of this study was to determine whether exposure of fetal male rhesus monkeys to testosterone excess would induce glucoregulatory and reproductive deficits. Seven adult PA males and seven matched controls underwent somatometric measurements, sex steroid analysis, and a frequently sampled i.v. glucose tolerance test. Body measurements were similar in the two groups, although arm circumference was greater in control compared with PA males (P < 0.01). There were no differences in neonatal weight or serum levels of sex steroids between the two male groups. Measures of insulin sensitivity and pancreatic beta-cell compensation (disposition index) were clearly diminished in PA compared with control males [insulin sensitivity: PA, mean 0.8 (95% confidence interval, 0.11, 5.82); controls, 3.06 (1.51, 6.19) x 10(-4)/min/microU/ml; P < 0.05; disposition index: PA, 226.38 (69.54, 383.22); controls, 509.21/min (306.52, 711.89); P < 0.02]. PA males do not exhibit elevated androgens during adulthood, suggesting that insulin resistance and impaired pancreatic beta-cell function may result from fetal reprogramming of key metabolic tissues.