Effects on insulin secretion and insulin action of a 48-h reduction of plasma free fatty acids with acipimox in nondiabetic subjects genetically predisposed to type 2 diabetes

Elevated plasma FFA cause beta-cell lipotoxicity and impair insulin secretion in nondiabetic subjects predisposed to type 2 diabetes mellitus [T2DM; i.e., with a strong family history of T2DM (FH+)] but not in nondiabetic subjects without a family history of T2DM. To determine whether lowering plasma FFA with acipimox, an antilipolytic nicotinic acid derivative, may enhance insulin secretion, nine FH+ volunteers were admitted twice and received in random order either acipimox or placebo (double-blind) for 48 h. Plasma glucose/insulin/C-peptide concentrations were measured from 0800 to 2400. On day 3, insulin secretion rates (ISRs) were assessed during a +125 mg/dl hyperglycemic clamp. Acipimox reduced 48-h plasma FFA by 36% (P < 0.001) and increased the plasma C-peptide relative to the plasma glucose concentration or DeltaC-peptide/Deltaglucose AUC (+177%, P = 0.02), an index of improved beta-cell function. Acipimox improved insulin sensitivity (M/I) 26.1 +/- 5% (P < 0.04). First- (+19 +/- 6%, P = 0.1) and second-phase (+31 +/- 6%, P = 0.05) ISRs during the hyperglycemic clamp also improved. This was particularly evident when examined relative to the prevailing insulin resistance [1/(M/I)], as both first- and second-phase ISR markedly increased by 29 +/- 7 (P < 0.05) and 41 +/- 8% (P = 0.02). There was an inverse correlation between fasting FFA and first-phase ISR (r2 = 0.31, P < 0.02) and acute (2-4 min) glucose-induced insulin release after acipimox (r2 =0.52, P < 0.04). In this proof-of-concept study in FH+ individuals predisposed to T2DM, a 48-h reduction of plasma FFA improves day-long meal and glucose-stimulated insulin secretion. These results provide additional evidence for the important role that plasma FFA play regarding insulin secretion in FH+ subjects predisposed to T2DM.     

Fasting for 72 h increases intramyocellular lipid content in nondiabetic,physically fit men

The purpose of this study was to determine changes in intramyocellular lipid (IMCL) content in the vastus lateralis of nondiabetic, physically fit males over 72 h of fasting. Six men, mean age 35 yr (range 23-55 yr), body mass index 23.7 kg/m2 (21.2-27.4 kg/m2), undertook a water-only fast for 84 h. Vastus lateralis IMCL content was determined using proton magnetic resonance spectroscopy after 12 and 84 h of fasting. Venous blood was sampled at 12-h intervals throughout the fast. IMCL-(CH2)n/water and IMCL-(CH2)n/total creatine ratios increased from 0.00623 +/- 0.00065 to 0.0142 +/- 0.0015 (P = 0.002) and 6.82 +/- 0.87 to 14.96 +/- 1.73 (P = 0.001), respectively. Plasma free fatty acid (FFA), serum triglyceride, and whole blood 3-hydroxybutyrate concentrations increased (P < 0.001, <0.05, <0.03, respectively), whereas plasma glucose and serum insulin concentrations decreased (both P < 0.001) during fasting. In conclusion, 72-h water-only fasting produces a large increase in plasma FFA concentration, a drop in serum insulin concentration, and accumulation of IMCL in the vastus lateralis muscle of nondiabetic, physically fit men.     

Obestatin, acylated and total ghrelin concentrations in the perinatal rat pancreas

BACKGROUND: Ghrelin and obestatin are encoded by the preproghrelin gene and originate from posttranslational processing of the preproghrelin peptide. The fetal rat pancreas contains acylated and desacylated ghrelin peptides, as well as growth hormone secretagogue receptor -1a mRNA. Acylated ghrelin inhibits insulin secretion. We investigated the plasma and tissue ontogeny of ghrelin and obestatin in the rat. METHODS: We measured obestatin and acylated and total ghrelin concentrations in plasma, pancreas and stomach from rat fetuses (F20) and neonates at postnatal day (PN) 1, 6, 12 and 21). RESULTS: Overall, obestatin concentrations were markedly lower than total ghrelin concentrations. In plasma, total ghrelin concentrations decreased abruptly after birth (p < 0.05), contrasting with a 3 times increase in the concentration of acylated ghrelin between F20 and PN1 (p < 0.05). In pancreas, total ghrelin and obestatin concentrations decreased progressively from PN1 to PN21 but acylated ghrelin concentrations increased 6-7 times from F20 (18 [6] pg/ml) to PN6 (122 [59] pg/ml). The percent of acylated ghrelin increased from 1.8 (0.6) at F20 to 39.7 (13.0) % of total ghrelin immunoreactivity at PN12 (p < 0.05). There were significant positive correlations between postnatal obestatin, acylated or total ghrelin and insulin concentrations in the pancreas (all p < 0.02, r(2) > 0.21) and between postnatal total ghrelin and obestatin (in pancreas, r(2) = 0.37) or acylated ghrelin (in stomach, r(2) = 0.27) (p < 0.001). CONCLUSION: Ghrelin and obestatin are present in the perinatal pancreas where they could potentially affect insulin secretion.     

The relationship between fasting hyperglycemia and insulin secretion in subjects with normal or impaired glucose tolerance

To assess the relationship between the fasting plasma glucose (FPG) concentration and insulin secretion in normal glucose tolerance (NGT) and impaired glucose tolerance (IGT) subjects, 531 nondiabetic subjects with NGT (n = 293) and IGT (n = 238; 310 Japanese and 232 Mexican Americans) received an oral glucose tolerance test (OGTT) with measurement of plasma glucose, insulin, and C-peptide every 30 min. The insulin secretion rate was determined by plasma C-peptide deconvolution. Insulin sensitivity (Matsuda index) was measured from plasma insulin and glucose concentrations. The insulin secretion/insulin resistance (IS/IR) or disposition index was calculated as DeltaISR/DeltaG / IR. As FPG increased in NGT subjects, the IS/IR index declined exponentially over the range of FPG from 70 to 125 mg/dl. The relationship between the IS/IR index and FPG was best fit with the equation: 28.8 exp(-0.036 FPG). For every 28 mg/dl increase in FPG, the IS/IR index declined by 63%. A similar relationship between IS/IR index and FPG was observed in IGT. However, the decay constant was lower than in NGT. The IS/IR index for early-phase insulin secretion (0-30 min) was correlated with the increase in FPG in both NGT and IGT (r = -0.43, P < 0.0001 and r = -0.20, P = 0.001, respectively). However, the correlation between late-phase insulin secretion (60-120 min) and FPG was not significant. In conclusion, small increments in FPG, within the "normal" range, are associated with a marked decline in glucose-stimulated insulin secretion and the decrease in insulin secretion with increasing FPG is greater in subjects with NGT than IGT and primarily is due to a decline in early-phase insulin secretion.     

Constant intravenous ghrelin infusion in healthy young men: clinical pharmacokinetics and metabolic effects

Ghrelin levels fluctuate rapidly and dynamically with surges before meal times and postprandial troughs, and ghrelin increases appetite and food intake. Circulating ghrelin correlates negatively with body mass index (BMI), but obese individuals have a reduced postprandial decrease in ghrelin levels. Whether this reflects changes in secretion or clearance of ghrelin is uncertain. We therefore studied the pharmacokinetics of ghrelin in relation to anthropometric and biochemical measures. We also studied the effects of ghrelin on hormones and metabolites. In fasting humans, we used a constant infusion rate of ghrelin lasting 180 min at 5 pmol.kg body wt(-1).min(-1) in a randomized, double-blind, placebo-controlled crossover study. Serum ghrelin (s-ghrelin; total levels) was distributed and eliminated according to a two-compartment model. s-Ghrelin initial half-life was 24 +/- 2 min and terminal half-life 146 +/- 36 min, respectively. Mean residence time (MRT) of ghrelin was 93 +/- 16 min. MRT correlated positively with both BMI (r = 0.51, P < 0.001) and high-density cholesterol (HDL) levels (r = 0.75, P < 0.001). Serum insulin levels remained constant during ghrelin infusion, whereas plasma glucose increased 0.3 +/- 0.1 mmol/l (P < 0.01) and free fatty acid levels more than doubled (to 1.03 +/- 0.08 mmol/l, P < 0.001), translating into a significant reduction of insulin sensitivity (P < 0.001). In conclusion, 1) we describe novel pharmacokinetics of ghrelin that are useful when tailoring ghrelin infusion rates in clinical experiments, 2) BMI and HDL correlate positively with MRT of infused ghrelin, and 3) supraphysiological ghrelin levels impair insulin sensitivity.     

Insulin secretion in lipodystrophic HIV-infected patients is associated with high levels of nonglucose secretagogues and insulin resistance of beta-cells

We examined whether plasma concentrations of nonglucose insulin secretagogues are associated with prehepatic insulin secretion rates (ISR) in nondiabetic, insulin-resistant, human immunodeficiency virus (HIV)-infected, lipodystrophic patients (LIPO). Additionally, the negative feedback of insulin on ISR was evaluated. ISR were estimated by deconvolution of plasma C-peptide concentrations during fasting (basal) and during the last 30 min of a 120-min euglycemic insulin clamp (40 mU.m(-2).min(-1)). Eighteen normoglycemic LIPO were compared with 25 normoglycemic HIV-infected patients without lipodystrophy (controls). Thirty minutes before start of the clamp, a bolus of glucose was injected intravenously to stimulate endogenous insulin secretion. Insulin sensitivity index (SiRd) was estimated from glucose tracer analysis. LIPO displayed increased basal ISR (69%), clamp ISR (114%), basal insulin (130%), and clamp insulin (32%), all P < or = 0.001, whereas SiRd was decreased (57%, P < 0.001). In LIPO, ISRbasal correlated significantly with basal insulin, alanine, and glucagon (all r > 0.65, P < 0.01), but not with glucose. In control subjects, ISR(basal) correlated significantly with insulin, glucagon, and glucose (all r > 0.41, P < 0.05), but not with alanine. In LIPO, ISRclamp correlated significantly with clamp free fatty acids (FFA), alanine, triglyceride, and glucagon (all r > 0.51, P < 0.05). In control subjects, ISRclamp correlated with clamp triglyceride (r = 0.45, P < 0.05). Paradoxically, in LIPO, ISRclamp correlated positively with clamp insulin (r = 0.68, P < 0.01), which suggests an absent negative feedback of insulin on ISR. Our data support evidence that lipodystrophic, nondiabetic, HIV-infected patients exhibit increased ISR, which can be partially explained by an impaired negative feedback of insulin on beta-cells and an increased stimulation of ISR by FFA, alanine, triglyceride, and glucagon.     

Comparison of local and systemic effects of insulin on myocardial glucose extraction in ischemic heart disease

Physiological increases in circulating insulin level significantly increase myocardial glucose uptake in vivo. To what extent this represents a direct insulin action on the heart or results indirectly from reduction in circulating concentrations of free fatty acids (FFA) is uncertain. To examine this, we measured myocardial glucose, lactate, and FFA extraction in 10 fasting men (ages 49-76 yr) with stable coronary artery disease during sequential intracoronary (10 mU/min, coronary plasma insulin = 140 +/- 20 microU/ml) and intravenous (100 mU/min, systemic plasma insulin = 168 +/- 26 microU/ml) insulin infusion. Basally, hearts extracted 2 +/- 2% of arterial glucose and extracted 27 +/- 6% of FFA. Coronary insulin infusion increased glucose extraction to 5 +/- 3% (P < 0.01 vs. basal) without changing plasma FFA or heart FFA extraction. Conversion to intravenous infusion lowered plasma FFA by approximately 50% and heart FFA extraction by approximately 75%, increasing heart glucose extraction still further to 8 +/- 3% (P < 0. 01 vs. intracoronary). This suggests the increase in myocardial glucose extraction observed in response to an increment in systemic insulin concentration is mediated equally by a reduction in circulating FFA and by direct insulin action on the heart itself. Coronary insulin infusion increased myocardial lactate extraction as well (from 20 +/- 10% to 29 +/- 9%, P < 0.05), suggesting the local action may include stimulation of a metabolic step distal to glucose transport and glycolysis.     

Changes of plasma obestatin, ghrelin and NPY in anorexia and bulimia nervosa patients before and after a high-carbohydrate breakfast

Peptides ghrelin, obestatin and neuropeptide Y (NPY) play an important role in regulation of energy homeostasis, the imbalance of which is associated with eating disorders anorexia (AN) and bulimia nervosa (BN). The changes in ghrelin, obestatin and NPY plasma levels were investigated in AN and BN patients after administration of a high-carbohydrate breakfast (1604 kJ). Eight AN women (aged 25.4+/-1.9, BMI: 15.8+/-0.5), thirteen BN women (aged 22.0+/-1.05, BMI: 20.1+/-0.41) and eleven healthy women (aged 25.1+/-1.16, BMI: 20.9+/-0.40) were recruited for the study. We demonstrated increased fasting ghrelin in AN, but not in BN patients, while fasting obestatin and NPY were increased in both AN and BN patients compared to the controls. Administration of high-carbohydrate breakfast induced a similar relative decrease in ghrelin and obestatin plasma levels in all groups, while NPY remained increased in postprandial period in both patient groups. Ghrelin/obestatin ratio was lower in AN and BN compared to the controls. In conclusions, increased plasma levels of fasting NPY and its unchanged levels after breakfast indicate that NPY is an important marker of eating disorders AN and BN. Different fasting ghrelin and obestatin levels in AN and BN could demonstrate their diverse functions in appetite and eating suppression.     

Thiazolidinediones upregulate impaired fatty acid uptake in skeletal muscle of type 2 diabetic subjects

We examined the regulation of free fatty acid (FFA, palmitate) uptake into skeletal muscle cells of nondiabetic and type 2 diabetic subjects. Palmitate uptake included a protein-mediated component that was inhibited by phloretin. The protein-mediated component of uptake in muscle cells from type 2 diabetic subjects (78 +/- 13 nmol. mg protein-1. min-1) was reduced compared with that in nondiabetic muscle (150 +/- 17, P < 0.01). Acute insulin exposure caused a modest (16 +/- 5%, P < 0.025) but significant increase in protein-mediated uptake in nondiabetic muscle. There was no significant insulin effect in diabetic muscle (+19 +/- 19%, P = not significant). Chronic (4 day) treatment with a series of thiazolidinediones, troglitazone (Tgz), rosiglitazone (Rgz), and pioglitazone (Pio) increased FFA uptake. Only the phloretin-inhibitable component was increased by treatment, which normalized this activity in diabetic muscle cells. Under the same conditions, FFA oxidation was also increased by thiazolidinedione treatment. Increases in FFA uptake and oxidation were associated with upregulation of fatty acid translocase (FAT/CD36) expression. FAT/CD36 protein was increased by Tgz (90 +/- 22% over control), Rgz (146 +/- 42%), and Pio (111 +/- 37%, P < 0.05 for all 3) treatment. Tgz treatment had no effect on fatty acid transporter protein-1 and membrane-associated plasmalemmal fatty acid-binding protein mRNA expression. We conclude that FFA uptake into cultured muscle cells is, in part, protein mediated and acutely insulin responsive. The basal activity of FFA uptake is impaired in type 2 diabetes. In addition, chronic thiazolidinedione treatment increased FFA uptake and oxidation into cultured human skeletal muscle cells in concert with upregulation of FAT/CD36 expression. Increased FFA uptake and oxidation may contribute to lower circulating FFA levels and reduced insulin resistance in skeletal muscle of individuals with type 2 diabetes following thiazolidinedione treatment.     

Race differences in the association of oxidative stress with insulin sensitivity in African- and European-American women

Excessive metabolism of glucose and/or fatty acids may impair insulin signaling by increasing oxidative stress. The objective of this study was to examine the association between insulin sensitivity and protein carbonyls, a systemic marker of oxidative stress, in healthy, nondiabetic women, and to determine if the relationship differed with race. Subjects were 25 African-Americans (AA, BMI 28.4 ± 6.2 kg/m(2), range 18.8-42.6 kg/m(2); age 33.1 ± 13.5 years, range 18-58 years) and 28 European-Americans (EA, BMI 26.2 ± 5.9 kg/m(2), range 18.7-48.4 kg/m(2); age 31.6 ± 12.4 years, range 19-58 years). Insulin sensitivity was determined using an intravenous glucose tolerance test incorporating [6,6-(2)H(2)]-glucose, and a two-compartment mathematical model. Multiple linear regression results indicated that insulin sensitivity was inversely associated with protein carbonyls in AA (standardized regression coefficient -0.47, P < 0.05) but not EA (0.01, P = 0.945), after adjusting for %body fat. In contrast, %body fat was significantly and positively associated with insulin sensitivity in EA (-0.54, P < 0.01) but not AA (-0.24, P = 0.196). Protein carbonyls were associated with free fatty acids (FFA) in AA (r = 0.58, P < 0.01) but not EA (r = -0.11, P = 0.59). When subjects were divided based on median levels of fasting glucose and FFA, those with higher glucose/FFA concentrations had a significantly greater concentration of circulating protein carbonyls compared to those with lower glucose/FFA concentrations (P < 0.05). These results suggest that oxidative stress independently contributes to insulin sensitivity among AA women. Further, this association in AA may be mediated by circulating FFA and/or glucose.     

Effect of moderate incremental exercise, performed in fed and fasted state on cardio-respiratory variables and leptin and ghrelin concentrations in young healthy men.

BACKGROUND: Although hormonal responses to exercise performed in fed state are well documented, far less in known about the effect of a single exercise bout, performed after overnight fasting, on cardio-respiratory responses and hormones secretion. It has been reported that recently discovered hormones as leptin and ghrelin may affect cardiovascular responses at rest. However, their effect on the cardiovascular responses to exercise is unknown. AIMS: This study was designed to determine the effect of overnight fasting on cardio- respiratory responses during moderate incremental exercise. We have hypothesised that fasting / exercise induced changes in plasma leptin / ghrelin concentrations may influence cardiovascular response. MATERIAL AND METHODS: Eight healthy non-smoking men (means +/- SE.: age 23.0 +/- 0.5 years; body mass 71.9 +/- 1.5 kg; height 179.1 +/- 0.8 cm; BMI 22.42 +/- 0.49 kg x m(-2) with VO2max of 3.71 +/- 0.10 l x min(-1)) volunteered for this study. The subjects performed twice an incremental exercise test, with the increase of power output by 30 W every 3 minutes. Tests were performed in a random order: once in the feed state--cycling until exhaustion and second, about one week later, after overnight fasting--cycling until reaching 150 W. RESULTS: In the present study we have compared the results obtained during incremental exercise performed only up to 150 W (59 +/- 2 % of VO2max) both in fed and fasted state. Heart rate measured during exercise at each power output, performed in fasted state was by about 10 bt x min(-1) (p = 0.02) lower then in fed subjects. Respiratory quotient and plasma lactate concentration in fasted state were also significantly (p<0.001) lower than in the fed state. Pre-exercise plasma leptin and ghrelin concentrations were not significantly different in fed and fasted state. Exercise induced increase in hGH was not accompanied by a significant changes in the studied gut hormones such as ghrelin, leptin, and insulin, except for plasma gastrin concentration, which was significantly (p = 0.008) lower in fasting subjects at the power output of 150 W. Plasma [IL-6] at rest before exercise performed in fasted state was significantly (p = 0.03) elevated in relation to the fed state. This was accompanied by significantly higher (p = 0.047) plasma noradrenaline concentration. Plasma IL-6 concentration at rest in fed subjects was negatively correlated with plasma ghrelin concentration (r = -0.73, p < 0.05) and positively correlated with plasma insulin concentration (r = 0.78, p < 0.05). Significant negative correlation (r = -0.90; p < 0.05) was found between plasma insulin and ghrelin concentration at rest in fed subjects. CONCLUSIONS: We have concluded that plasma leptin and ghrelin concentrations have no significant effect on the fasting-induced attenuation of heart rate during exercise. We have postulated that this effect is caused by increased plasma norepinephrine concentration, leading to the increase in systemic vascular resistance and baroreceptor mediated vagal stimulation. Moreover we believe, that the fasting-induced significant increase in plasma IL-6 concentration at rest, accompanied by higher plasma norepinephrine concentration and lower RQ, belongs to the physiological responses, maintaining energy homeostasis in the fasting state.     

Abdominal adipose tissue cytokine gene expression: relationship to obesity and metabolic risk factors

Adipose tissue is a major source of inflammatory and thrombotic cytokines. This study investigated the relationship of abdominal subcutaneous adipose tissue cytokine gene expression to body composition, fat distribution, and metabolic risk during obesity. We determined body composition, abdominal fat distribution, plasma lipids, and abdominal subcutaneous fat gene expression of leptin, TNF-alpha, IL-6, PAI-1, and adiponectin in 20 obese, middle-aged women (BMI, 32.7 +/- 0.8 kg/m2; age, 57 +/- 1 yr). A subset of these women without diabetes (n = 15) also underwent an OGTT. In all women, visceral fat volume was negatively related to leptin (r = -0.46, P < 0.05) and tended to be negatively related to adiponectin (r = -0.38, P = 0.09) gene expression. Among the nondiabetic women, fasting insulin (r = 0.69, P < 0.01), 2-h insulin (r = 0.56, P < 0.05), and HOMA index (r = 0.59, P < 0.05) correlated positively with TNF-alpha gene expression; fasting insulin (r = 0.54, P < 0.05) was positively related to, and 2-h insulin (r = 0.49, P = 0.06) tended to be positively related to, IL-6 gene expression; and glucose area (r = -0.56, P < 0.05) was negatively related to, and insulin area (r = -0.49, P = 0.06) tended to be negatively related to, adiponectin gene expression. Also, adiponectin gene expression was significantly lower in women with vs. without the metabolic syndrome (adiponectin-beta-actin ratio, 2.26 +/- 0.46 vs. 3.31 +/- 0.33, P < 0.05). We conclude that abdominal subcutaneous adipose tissue expression of inflammatory cytokines is a potential mechanism linking obesity with its metabolic comorbidities.     

Acute insulin infusion decreases plasma ghrelin levels in uncomplicated obesity

BACKGROUND: Plasma ghrelin levels have been shown to decrease after insulin infusion in lean subjects. Nevertheless, the mechanism of the suggested inhibitory effect of insulin on ghrelin is still unclear and no data about the effect of acute insulin infusion on plasma ghrelin concentration in obese subjects are available. OBJECTIVE: We sight to evaluate plasma ghrelin concentration during an hyperinsulinemic euglycemic clamp in uncomplicated obese subjects. METHODS: 35 uncomplicated obese subjects, body mass index (BMI) 43.3+/-10.1 kg/m(2), 33 women and 2 men, mean age 34.9+/-10, with a history of excess fat of at least 10 years underwent euglycemic hyperinsulinemic clamp. Blood samples for ghrelin were performed at baseline and steady state of euglycemic insulin clamp. RESULTS: Ghrelin concentrations decreased over time to 10.6+/-15% (range 2-39%) of baseline, from a mean of 205.53+/-93.79 pg/ml to 179.03+/-70.43 pg/ml during the clamp (95% CI, 10.69 to 36.44, P<0.01). In a univariate linear regression analysis baseline plasma ghrelin levels were inversely correlated to BMI (r=-0.564, P=0.04). A linear positive trend between whole body glucose utilization (M(FFMkg) index) and ghrelin reduction during the clamp was found (chi(2) 3.05, p=0.05). CONCLUSIONS: Our data seem to suggest that hyperinsulinemia during a euglycemic clamp is able to suppress plasma ghrelin concentrations in uncomplicated obesity. This effect appears to be positively related to insulin sensitivity.     

Dietary monounsaturated fat in early life regulates IGFBP2: implications for fat mass accretion and insulin sensitivity

The aim of this study was to investigate effects of dietary supplementation with fat or sugar on body composition (BC) and insulin sensitivity (IS) in maturing pigs. Fifty newborn pigs randomized to a control diet or 18% saturated fat (SF), 18% monounsaturated fat (MUF), 18% mixed fat (MF), or 50% sucrose (SUC), from 1 to 16 weeks of age. Outcomes included weight gain, BC (dual energy X-ray absorptiometry, DXA), IS (fasting insulin and hyperinsulinaemic-euglycaemic clamps), fasting Non-Esterified Fatty Acid (NEFA) concentrations, and mRNA expression of genes involved in lipogenesis and IS in skeletal muscle (SM), subcutaneous (SAT), and visceral adipose tissue (VAT). In vitro studies examined direct effects of fatty acids on insulin-like growth factor-binding protein 2 (IGFBP2) mRNA in C2C12 myotubes. While SUC-fed pigs gained most weight (due to larger quantities consumed; P < 0.01), those fed fat-enriched diets exhibited more weight gain per unit energy intake (P < 0.001). Total (P = 0.03) and visceral (P = 0.04) adiposity were greatest in MUF-fed pigs. Whole-body IS was decreased in those fed fat (P = 0.04), with fasting insulin increased in MUF-fed pigs (P = 0.03). SM IGFBP2 mRNA was increased in MUF-fed pigs (P = 0.009) and, in all animals, SM IGFBP2 mRNA correlated with total (P = 0.007) and visceral (P = 0.001) fat, fasting insulin (r = 0.321; P = 0.03) and change in NEFA concentrations (r = 0.285; P = 0.047). Furthermore, exposure of in vitro cultured myotubes to MUF, but not SF, reduced IGFBP2 mRNA suggesting a converse direct effect. In conclusion, diets high in fat, but not sugar, promote visceral adiposity and insulin resistance in maturing pigs, with evidence that fatty acids have direct and indirect effects on IGFBP2 mRNA expression in muscle.     

A study of the metabolism of apolipoprotein B100 in relation to insulin resistance in African American males.

The purpose of this study was to determine the relationship between insulin resistance and apoB100 metabolism in African American males. Fifteen subjects, 33 +/- 7.6 years old, were divided into two groups, insulin-resistant (IR) or insulin-sensitive (IS), based on the sum of the plasma insulin concentrations during an oral glucose tolerance test. The IR group (n = 8) differed significantly from the IS group (n = 7) with respect to body mass index (BMI) (30.1 vs 23.1 kg/m2; P = 0.0003), fasting triglycerides, (118 vs 54 mg/dl, P = 0. 013), and total plasma apolipoprotein B100 (80 vs 59 mg/dl, P = 0.014). Significantly elevated apoB100 levels in the IR group were seen in very low density lipoprotein (VLDL) (5.1 vs 3.4 mg/dl, P = 0.045) and intermediate density lipoprotein (IDL) (18 vs 12 mg/dl, P = 0.017) but not in low density lipoprotein (LDL) (57 vs 46 mg/dl, P = 0.19). Total cholesterol, high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), apolipoprotein A-I, and blood pressure were not significantly different between the two groups. There was a high correlation between the sum of insulins during the oral glucose tolerance test and the BMI (rho = 0.88, P = 0.0001). In five IR and five IS subjects, apoB100 kinetics were determined in the fasting state using a bolus dose of deuteroleucine and multicompartmental modeling. IR subjects had significantly lower fractional catabolic rates (FCR) in the larger VLDL1 (-70%), the smaller VLDL2 (-71%), and the IDL (-53%) fractions. No significant differences in production rates were observed for any lipoprotein class. There was a significant correlation between the sum of insulins and the FCR of the apoB100 of VLDL1 (rho = -0.65, P = 0.05) and of IDL (rho = -0.85, P = 0.004). The correlation coefficient of the sum of insulins and the FCR of VLDL2 was -0.61 with P = 0.067. We conclude that in this population of African American males, IR is correlated with a decreased FCR of apoB100 in VLDL and IDL and elevated plasma levels of apoB and triglycerides (TG). These changes might be explained by decreased clearance of the TG-rich lipoproteins. We postulate that this may reflect decreased lipoprotein and/or hepatic lipase activity related to insulin resistance and its association with obesity.     

Effect of liver fat on insulin clearance

A fatty liver is associated with fasting hyperinsulinemia, which could reflect either impaired insulin clearance or hepatic insulin action. We determined the effect of liver fat on insulin clearance and hepatic insulin sensitivity in 80 nondiabetic subjects [age 43 +/- 1 yr, body mass index (BMI) 26.3 +/- 0.5 kg/m(2)]. Insulin clearance and hepatic insulin resistance were measured by the euglycemic hyperinsulinemic (insulin infusion rate 0.3 mU.kg(-1).min(-1) for 240 min) clamp technique combined with the infusion of [3-(3)H]glucose and liver fat by proton magnetic resonance spectroscopy. During hyperinsulinemia, both serum insulin concentrations and increments above basal remained approximately 40% higher (P < 0.0001) in the high (15.0 +/- 1.5%) compared with the low (1.8 +/- 0.2%) liver fat group, independent of age, sex, and BMI. Insulin clearance (ml.kg fat free mass(-1).min(-1)) was inversely related to liver fat content (r = -0.52, P < 0.0001), independent of age, sex, and BMI (r = -0.37, P = 0.001). The variation in insulin clearance due to that in liver fat (range 0-41%) explained on the average 27% of the variation in fasting serum (fS)-insulin concentrations. The contribution of impaired insulin clearance to fS-insulin concentrations increased as a function of liver fat. This implies that indirect indexes of insulin sensitivity, such as homeostatic model assessment, overestimate insulin resistance in subjects with high liver fat content. Liver fat content correlated significantly with fS-insulin concentrations adjusted for insulin clearance (r = 0.43, P < 0.0001) and with directly measured hepatic insulin sensitivity (r = -0.40, P = 0.0002). We conclude that increased liver fat is associated with both impaired insulin clearance and hepatic insulin resistance. Hepatic insulin sensitivity associates with liver fat content, independent of insulin clearance.     

Energy expenditure, insulin, and VLDL-triglyceride production in humans

Hypertriglyceridemia is considered a cardiovascular risk factor in diabetic and nondiabetic subjects. In this study, we aimed to determine potential regulators of very low density lipoprotein-triglyceride (TG) production. VLDL-TG kinetics were measured in 13 men and 12 women [body mass index [mean (range)]: 24.8 (20.2-35.6) kg/m(2)]. VLDL-TG production was assessed from the plasma decay of a bolus injection of ex vivo labeled VLDL particles ([1-(14)C]triolein-VLDL-TG). Similar VLDL-TG production (micromol/min) was found in men and women. VLDL-TG production was not significantly correlated with palmitate flux ([9,10-(3)H]palmitate) (r = 0.09, P = 0.67) or palmitate concentration (r = -0.29, P = 0.2) but was correlated significantly with fasting insulin concentration (r = 0.46, P < 0.05) and resting energy expenditure (REE) (r = 0.45, P < 0.05). The latter correlation improved when adjusted for sex. The best multivariate model with VLDL-TG production as the dependent variable and REE, body composition, hormones, and substrate levels as independent variables included fasting insulin (P = 0.02) and REE (P = 0.02) (r(2) = 0.32, P < 0.001). We conclude that VLDL kinetics are similar in men and women and that REE and plasma insulin are significant independent predictors of VLDL-TG production. FFA availability and body fat distribution are unrelated to VLDL production. We suggest that REE plays a greater role in VLDL-TG production than previously anticipated. REE and insulin should be taken into account when VLDL-TG production comparisons between groups are made.     

The effect of weight reduction on plasma concentrations of ghrelin and insulin-like growth factor 1 in obese women

Introduction: The aim of the present study was to examine how weight loss treatment modulates plasma concentrations of ghrelin and insulin-like growth factor 1 (IGF-1) in obese women and to determine whether there is any association with possible changes in plasma concentrations of these hormones after weight loss. Material and methods: The study group consisted of 22 obese women without additional disease (age 40.6 +/- 12.9 years; BMI 37.2 +/- 4.6 kg/m(2)). All subjects participated in a 3-month weight reduction program. The measurements were performed at baseline and after weight loss. Plasma concentration of ghrelin and IGF-1 were measured by enzyme - linked immunosorbent assay (ELISA) kit. Serum concentrations of insulin were measured by radioimmunoassay (RIA). Body composition was determined by bioelectrical impedance analysis using a Bodystat analyser. Results: The mean weight loss was 9.3 +/- 4.1 kg (9.7 +/- 4.3%). Following weight loss, plasma ghrelin and IGF-1 concentrations increased significantly (63.5 +/- 13.0 vs. 72.8 +/- 15.1 pg/ml; p < 0.01; 126.9 +/- 67.0 vs. 170.5 +/- 83.3 ng/ml p < 0.01, respectively) and serum insulin concentrations decreased significantly (17.5 +/- 8.5 vs. 14.8 +/- 10.4 mIU/ml p< 0.05). We observed a significant positive correlation between the increase of ghrelin and decrease of body fat percentage after weight loss (r = 0.44, p = 0.03). There are no correlations between change of ghrelin and IGF-1concentrations and between changes of insulin and IGF 1 concentrations. Conclusion: Plasma concentrations of ghrelin and IGF-1 increased after weight loss. However, it seems there is no association between serum concentrations of ghrelin and IGF-1 in obese women.     

Simultaneous decrease of plasma obestatin and ghrelin levels after a high-carbohydrate breakfast in healthy women

Ghrelin is a gut peptide produced mainly by stomach, well known to induce appetite stimulatory actions. Obestatin, a recently identified peptide derived from preproghrelin, was initially described to antagonize stimulatory effect of ghrelin on food intake. The postprandial response of obestatin and its relationship with ghrelin in humans remains unknown. We therefore investigated the postprandial response of obestatin and total ghrelin, acyl and desacyl ghrelin and neuropeptide Y (NPY) to a high-carbohydrate breakfast (1 604 kJ) in eight healthy women (age: 24.2+/-0.82 years; BMI 21.6+/-0.61 kg/m(2)). Blood samples were collected before the meal, and 30, 60, 90, 120 and 150 min after the breakfast consumption. Postprandial plasma obestatin concentrations significantly decreased compared with preprandial levels as well as total ghrelin concentrations and reached the lowest values 90 and 120 min after the meal consumption, respectively (p<0.05). Plasma acyl and desacyl ghrelin concentrations decreased after the breakfast and reached lowest values in 30 and 60 min, respectively (p<0.05). Plasma NPY concentrations were lower than preprandial levels 90 and 150 min after consuming breakfast (p<0.05). In conclusion, we demonstrated in healthy young women that plasma obestatin concentrations decrease similarly to ghrelin after a high-carbohydrate breakfast.     

Proghrelin-derived peptides influence the secretion of insulin, glucagon, pancreatic polypeptide and somatostatin: a study on isolated islets from mouse and rat pancreas

Proghrelin, the precursor of the orexigenic and adipogenic peptide hormone ghrelin, is synthetized in endocrine (A-like) cells in the gastric mucosa. During its cellular processing, proghrelin gives rise to the 28-amino acid peptide desacyl ghrelin, which after octanoylation becomes active acyl ghrelin, and to the 23-amino acid peptide obestatin, claimed to be a physiological opponent of acyl ghrelin. This study examines the effects of the proghrelin products, alone and in combinations, on the secretion of insulin, glucagon, pancreatic polypeptide (PP) and somatostatin from isolated islets of mice and rats. Surprisingly, acyl ghrelin and obestatin had almost identical effects in that they stimulated the secretion of glucagon and inhibited that of PP and somatostatin from both mouse and rat islets. Obestatin inhibited insulin secretion more effectively than acyl ghrelin. In mouse islets, acyl ghrelin inhibited insulin secretion at low doses and stimulated at high. In rat islets, acyl ghrelin inhibited insulin secretion in a dose-dependent manner but the IC(50) for the acyl ghrelin-induced inhibition of insulin release was 7.5 x 10(-8) M, while the EC(50) and IC(50) values, with respect to stimulation of glucagon release and to inhibition of PP and somatostatin release, were in the 3 x 10(-12)-15 x 10(-12) M range. The corresponding EC(50) and IC(50) values for obestatin ranged from 5 x 10(-12) to 20 x 10(-12) M. Desacyl ghrelin per se did not affect islet hormone secretion. However, at a ten times higher concentration than acyl ghrelin (corresponding to the ratio of the two peptides in circulation), desacyl ghrelin abolished the effects of acyl ghrelin but not those of obestatin. Acyl ghrelin and obestatin affected the secretion of glucagon, PP and somatostatin at physiologically relevant concentrations; with obestatin this was the case also for insulin secretion. The combination of obestatin, acyl ghrelin and desacyl ghrelin in concentrations and proportions similar to those found in plasma resulted in effects that were indistinguishable from those induced by obestatin alone. From the data it seems that the effects of endogenous, circulating acyl ghrelin may be overshadowed by obestatin or blunted by desacyl ghrelin.