Effect of pioglitazone on circulating adipocytokine levels and insulin sensitivity in type 2 diabetic patients

We examined the effect of pioglitazone (PIO) on circulating adipocytokine levels to elucidate the mechanisms by which thiazolidinediones improve insulin resistance in type 2 diabetes mellitus (T2DM). Twenty-three subjects with T2DM (age 54 +/- 2 yr, body mass index 29 +/- 1 kg/m(2)) were randomly assigned to receive placebo (n = 11) or PIO, 45 mg/d (n = 12), for 4 months. Before and after treatment, subjects received a 75-g oral glucose tolerance test (OGTT); euglycemic insulin clamp (40 mU/m(2).min) with 3-(3)H-glucose; determination of fat mass ((3)H(2)O); and measurement of fasting glucose, free fatty acids (FFAs), leptin, adiponectin, and TNFalpha concentrations. After 4 months of PIO, fasting plasma glucose concentration (Delta = -2.7 mol/liter), mean plasma glucose during OGTT (Delta = -3.8 mol/liter), and hemoglobin A(1c) (Delta = 1.7%) decreased (P < 0.05 vs. placebo) without change in fasting or post-OGTT plasma insulin levels. Fasting FFAs (Delta = 168 micromol/liter) and TNFalpha (Delta = 0.7 pg/ml) concentrations decreased (P < 0.05 vs. placebo), whereas adiponectin (Delta = 8.7 microg/ml) increased (P < 0.01 vs. placebo). Despite the increase in body fat mass (Delta = 3.4 kg) after PIO, plasma leptin concentration did not change significantly. No changes in plasma glucose, FFAs, or adipocytokine levels were observed in placebo-treated subjects. During the insulin clamp, endogenous (hepatic) glucose production decreased (Delta = -2.67 micromol/fat-free mass.min, P < 0.05 vs. placebo), whereas metabolic clearance rate of glucose (MCR) increased (Delta = 0.58 ml/fat-free mass.min, P < 0.05 vs. placebo) after PIO. In all subjects, before and after PIO, the decrease in plasma FFA concentration was correlated with the changes in both endogenous (hepatic) glucose production (r = 0.47, P < 0.05) and MCR (r = -0.41, P < 0.05), whereas the increase in plasma adiponectin concentration was correlated with the change in endogenous (hepatic) glucose production (r = -0.70, P < 0.01) and MCR (r = 0.49, P < 0.05). These results suggest that the direct effects of PIO on adipose tissue to decrease plasma FFA levels and increase plasma adiponectin contribute to the improvements in hepatic and peripheral insulin sensitivity and glucose tolerance in patients with T2DM.     

Increased activity of membrane glycoprotein PC-1 in the fibroblasts from non-insulin-dependent diabetes mellitus patients with insulin resistance.

Although most of patients with non-insulin-dependent diabetes mellitus (NIDDM) have insulin resistance, it is unknown whether a molecule might interfere with insulin action. Membrane glycoprotein PC-1 (plasma cell antigen-1), which inhibits insulin receptor tyrosine kinase activity, was isolated from fibroblasts of NIDDM patients. Because PC-1 content in skeletal muscle and adipose tissue correlated with whole body insulin sensitivity, PC-1 might play a role in insulin resistance. In order to know whether PC-1 activity of fibroblasts is also elevated in Japanese NIDDM patients, and whether PC-1 activity correlates with the parameters of insulin resistance in vivo or not, we measured PC-1 activity of cultured fibroblasts from 17 patients with NIDDM and seven healthy controls. PC-1 activity of the NIDDM patients was 85.2 +/- 33.1 nmol/mg per min (mean +/- S.D.), and was higher than that of healthy controls (42.6 +/- 12.7 nmol/mg per min, P = 0.0002). Insulin sensitivity was measured in 11 of 17 NIDDM patients by the artificial pancreas. PC-1 activity of the patients with insulin resistance (glucose infusion rate < 3.0 mg/kg per min, n = 7) was elevated to 99.9 +/- 31.9 nmol/mg per min, while that of the other patients (n = 4) was 55.3 +/- 7.5 nmol/mg per min (P = 0.003). In conclusion, glycoprotein PC-1 activity of dermal fibroblasts is correlated with insulin resistance in patients with NIDDM.     

The Q121 PC-1 variant and obesity have additive and independent effects in causing insulin resistance.

PC-1 is a membrane glycoprotein that impairs insulin receptor function. Its K121Q polymorphism is a genetic determinant of insulin resistance. We investigated whether the PC-1 gene modulates insulin sensitivity independently of weight status (i.e. both in nonobese and obese individuals). Nondiabetic subjects [164 males, 267 females; age, 37 +/- 0.6 yr, mean +/- SEM; body mass index (BMI), 32.7 +/- 0.5 kg/m(2)], who were subdivided into 220 nonobese (BMI < or = 29.9) and 211 obese, were studied. Although subjects were nondiabetic by selection criteria, plasma insulin concentrations during oral glucose tolerance test were higher (P < 0.05) in Q allele-carrying subjects (K121Q or Q121Q genotypes), compared with K121K individuals, in both the nonobese and obese groups. Insulin sensitivity, measured by euglycemic clamp in a representative subgroup of 131 of 431 randomly selected subjects, progressively decreased (P < 0.001) from nonobese K121K [n = 61; glucose disposal (M) = 34.9 +/- 1.1 micromol/kg/min] to nonobese Q (n = 21; M = 29.9 +/- 2.0), obese K121K (n = 31, M = 18.5 +/- 1.2), and obese Q (n = 18, M = 15.5 +/- 1.2) carriers. The K121Q polymorphism was correlated with insulin sensitivity independently (P < 0.05) of BMI, gender, age, and waist circumference. In conclusion, the Q121 PC-1 variant and obesity have independent and additive effects in causing insulin resistance.     

Decreased plasma adiponectin concentrations are closely related to hepatic fat content and hepatic insulin resistance in pioglitazone-treated type 2 diabetic patients

The effect of pioglitazone (PIO) on plasma adiponectin concentration, endogenous glucose production (EGP), and hepatic fat content (HFC) was studied in 11 type 2 diabetic patients (age, 52 +/- 2 yr; body mass index, 29.6 +/- 1.1 kg/m(2); HbA(1c), 7.8 +/- 0.4%). HFC (magnetic resonance spectroscopy) and basal plasma adiponectin concentration were quantitated before and after PIO (45 mg/d) for 16 wk. Subjects received a 3-h euglycemic insulin (100 mU/m(2).min) clamp combined with 3-[(3)H] glucose infusion to determine rates of EGP and tissue glucose disappearance (Rd) before and after PIO. PIO reduced fasting plasma glucose (10.0 +/- 0.7 to 7.2 +/- 0.6 mmol/liter, P < 0.01) and HbA(1c) (7.8 +/- 0.4 to 6.5 +/- 0.3%, P < 0.01) despite increased body weight (83.0 +/- 3.0 to 86.4 +/- 3.0 kg, P < 0.01). PIO improved Rd (6.6 +/- 0.6 vs. 5.2 +/- 0.5 mg/kg.min, P < 0.005) and reduced EGP (0.23 +/- 0.04 to 0.05 +/- 0.02 mg/kg.min, P < 0.01) during the 3-h insulin clamp. After PIO treatment, HFC decreased from 21.3 +/- 4.2 to 11.0 +/- 2.4% (P < 0.01), and plasma adiponectin increased from 7 +/- 1 to 21 +/- 2 micro g/ml (P < 0.0001). Plasma adiponectin concentration correlated negatively with HFC (r = -0.60, P < 0.05) and EGP (r = -0.80, P < 0.004) and positively with Rd before (r = 0.68, P < 0.02) pioglitazone treatment; similar correlations were observed between plasma adiponectin levels and HFC (r = -0.65, P < 0.03) and Rd after (r = 0.70, P = 0.01) pioglitazone treatment. EGP was almost completely suppressed after pioglitazone treatment; taken collectively, plasma adiponectin concentration, before and after pioglitazone treatment, still correlated negatively with EGP during the insulin clamp (r = -0.65, P < 0.001). In conclusion, PIO treatment in type 2 diabetes causes a 3-fold increase in plasma adiponectin concentration. The increase in plasma adiponectin is strongly associated with a decrease in hepatic fat content and improvements in hepatic and peripheral insulin sensitivity. The increase in plasma adiponectin concentration after thiazolidinedione therapy may play an important role in reversing the abnormality in hepatic fat mobilization and the hepatic/muscle insulin resistance in patients with type 2 diabetes.     

Effect of pioglitazone on abdominal fat distribution and insulin sensitivity in type 2 diabetic patients

We examined the effect of pioglitazone on abdominal fat distribution to elucidate the mechanisms via which pioglitazone improves insulin resistance in patients with type 2 diabetes mellitus. Thirteen type 2 diabetic patients (nine men and four women; age, 52 +/- 3 yr; body mass index, 29.0 +/- 1.1 kg/m(2)), who were being treated with a stable dose of sulfonylurea (n = 7) or with diet alone (n = 6), received pioglitazone (45 mg/d) for 16 wk. Before and after pioglitazone treatment, subjects underwent a 75-g oral glucose tolerance test (OGTT) and two-step euglycemic insulin clamp (insulin infusion rates, 40 and 160 mU/m(2).min) with [(3)H]glucose. Abdominal fat distribution was evaluated using magnetic resonance imaging at L4-5. After 16 wk of pioglitazone treatment, fasting plasma glucose (179 +/- 10 to 140 +/- 10 mg/dl; P < 0.01), mean plasma glucose during OGTT (295 +/- 13 to 233 +/- 14 mg/dl; P < 0.01), and hemoglobin A(1c) (8.6 +/- 0.4% to 7.2 +/- 0.5%; P < 0.01) decreased without a change in fasting or post-OGTT insulin levels. Fasting plasma FFA (674 +/- 38 to 569 +/- 31 microEq/liter; P < 0.05) and mean plasma FFA (539 +/- 20 to 396 +/- 29 microEq/liter; P < 0.01) during OGTT decreased after pioglitazone. In the postabsorptive state, hepatic insulin resistance [basal endogenous glucose production (EGP) x basal plasma insulin concentration] decreased from 41 +/- 7 to 25 +/- 3 mg/kg fat-free mass (FFM).min x microU/ml; P < 0.05) and suppression of EGP during the first insulin clamp step (1.1 +/- 0.1 to 0.6 +/- 0.2 mg/kg FFM.min; P < 0.05) improved after pioglitazone treatment. The total body glucose MCR during the first and second insulin clamp steps increased after pioglitazone treatment [first MCR, 3.5 +/- 0.5 to 4.4 +/- 0.4 ml/kg FFM.min (P < 0.05); second MCR, 8.7 +/- 1.0 to 11.3 +/- 1.1 ml/kg FFM(.)min (P < 0.01)]. The improvement in hepatic and peripheral tissue insulin sensitivity occurred despite increases in body weight (82 +/- 4 to 85 +/- 4 kg; P < 0.05) and fat mass (27 +/- 2 to 30 +/- 3 kg; P < 0.05). After pioglitazone treatment, sc fat area at L4-5 (301 +/- 44 to 342 +/- 44 cm(2); P < 0.01) increased, whereas visceral fat area at L4-5 (144 +/- 13 to 131 +/- 16 cm(2); P < 0.05) and the ratio of visceral to sc fat (0.59 +/- 0.08 to 0.44 +/- 0.06; P < 0.01) decreased. In the postabsorptive state hepatic insulin resistance (basal EGP x basal immunoreactive insulin) correlated positively with visceral fat area (r = 0.55; P < 0.01). The glucose MCRs during the first (r = -0.45; P < 0.05) and second (r = -0.44; P < 0.05) insulin clamp steps were negatively correlated with the visceral fat area. These results demonstrate that a shift of fat distribution from visceral to sc adipose depots after pioglitazone treatment is associated with improvements in hepatic and peripheral tissue sensitivity to insulin.     

Disruption of the pulsatile and entropic modes of insulin release during an unvarying glucose stimulus in elderly individuals.

Insulin is secreted in a pulsatile fashion with measurable orderliness (low entropy). Aging is characterized by alterations in pulsatile insulin release in the fasting state. We undertook the current studies to determine whether disruptions in pulsatile insulin release in response to sustained glucose infusion also accompany the age-related changes in carbohydrate metabolism. Healthy young (n = 10; body mass index, 23 +/- 1 kg/m2; age, 23 +/- 1 yr) and old (n = 10; body mass index, 24 +/- 1 kg/m2; age, 80 +/- 2 yr) volunteers underwent a 600-min hyperglycemic glucose clamp. During the entire 600 min, insulin was sampled every 10 min, and insulin release was evaluated by Cluster analysis. From 240-360 min, insulin was sampled every 1 min, and secretory pulse analysis was conducted using a multiparameter deconvolution technique. During the 1-min sampling interval, basal insulin secretion (P < 0.01), insulin production rate (P < 0.01), pulsatile mean and integrated insulin concentration (P < 0.01), insulin secretory burst mass (P < 0.01), and burst amplitude (P < 0.05) were reduced in the elderly. In addition, interpulse interval was increased in the aged (P < 0.05). In the 600-min studies, interpulse interval was greater in the aged (P < 0.01) and burst number (P < 0.01), basal concentration (P < 0.01), and burst increment (P < 0.05) were less. Approximate entropy, a measure of irregularity of insulin release, was increased in the aged, signifying the loss of orderliness of insulin secretion (P < 0.05). We conclude that in response to a sustained (10-h) glucose infusion, normal aging is characterized by a reduction in mass and amplitude of rapid insulin pulses and a decrease in the frequency, amplitude, and regularity of ultradian pulses. Whether these changes in insulin pulsatility contribute directly to the age-related changes in carbohydrate metabolism will require further clinical studies.     

Post-heparin lipolytic enzyme activities, sex hormones and sex hormone-binding globulin (SHBG) in men and women: The HERITAGE Family Study

We tested the hypothesis that androgen, estrogen, and sex hormone-binding globulin (SHBG) levels would be significantly related to post-heparin hepatic lipase (HL) and lipoprotein lipase (LPL) activities in a sample of Caucasian men (n = 233) and women (n = 235) aged 17-64 years from the HERITAGE Family Study. Body composition (hydrostatic weighing), abdominal adipose tissue distribution (computed tomography), plasma lipid-lipoprotein and hormone levels, and post-heparin lipases activities were measured. HL activity was significantly higher in males, whereas LPL activity was higher in women (P < 0.005). In women only, HL activity was positively associated with body fat mass (r = 0.17, P < 0.05) and intra-abdominal adipose tissue area (r = 0.18, P < 0.05). Significant associations were also found between fasting insulin and LPL activity (r = -0.16, P < 0.05 and r = -0.18, P < 0.005) as well as HL activity (r = 0.22, P < 0.005, and r = 0.27, P < 0.0001) in men and women, respectively. A positive association between total testosterone and HL activity was noted in men (r = 0.13, P = 0.05). In women, plasma SHBG levels were negatively associated with HL activity (r = -0.48, P < 0.0001), and statistical adjustment for body fat mass, visceral adipose tissue area, and fasting insulin did not attenuate this correlation. In multivariate analyses with models including adiposity variables and measurements of the hormonal profile, insulin, and testosterone levels were both independent positive predictors of HL activity in men. In women, hormone use was a significant positive predictor, and SHBG level a strong negative predictor of HL activity, independent of plasma estradiol and testosterone concentrations. Fasting insulin was the only significant predictor of LPL activity in men (negative association), whereas menstrual status, fasting insulin (negative associations), and plasma SHBG levels (positive association) were all independent predictors of LPL activity in women. These results suggest that the postulated sensitivity of lipolytic enzymes to androgens and estrogens is reflected by a strong negative association between SHBG levels and HL, and a lower magnitude positive association of this hormonal parameter to LPL activity in women. These associations appear to be independent from concomitant variation in total adiposity or body fat distribution.     

Elevated plasma cell membrane glycoprotein levels and diminished insulin receptor autophosphorylation in obese, insulin-resistant rhesus monkeys

In obese humans, insulin resistance is accompanied by elevated levels of plasma cell membrane glycoprotein (PC-1) and decreased insulin receptor (IR) tyrosine kinase activity in skeletal muscle. PC-1 overexpression inhibits IR tyrosine kinase and possibly other downstream signaling events. The rhesus monkey in captivity is susceptible to obesity with concomitant insulin resistance. In the present study we analyzed obese (n = 10, 29.4% +/- 1.2% body fat) and non-obese (n = 12, 19.4% +/- 1.9% body fat) rhesus monkeys. Glucose clearance during an euglycemic hyperinsulinemic (400 mU/m(2) body surface area/min) clamp was lower for the obese group (non-obese, 9.7 +/- 0.9; obese, 3.2 +/- 0.7 mg/kg fat-free mass [FFM]/min; P <.01). We performed vastus lateralis muscle biopsies prior to and during the clamp. We measured PC-1 levels in these muscle samples to determine whether PC-1 content is elevated in this primate model of insulin resistance. PC-1 levels were determined by assay of phosphodiesterase activity and specific PC-1 enzyme-linked immunosorbent assay (ELISA). In the obese group, both PC-1 content and activity were 2-fold higher than in the non-obese group (P <.05). In order to investigate the ability of insulin to stimulate IR signaling in vivo in these 2 groups of monkeys, we then measured tyrosine autophosphorylation of the IR by specific ELISA. The increase in IR autophosphorylation in the non-obese group was twice that of the obese group (fold increase over basal: non-obese, 3.7 +/- 0.3; obese, 1.9 +/- 0.6; P <.05). We conclude that insulin resistance secondary to obesity in rhesus monkeys is associated with increased levels of PC-1 and decreased IR signaling capacity in skeletal muscle.     

Plasma homocysteine concentrations in healthy volunteers are not related to differences in insulin-mediated glucose disposal.

This study was initiated to test the hypothesis that plasma homocysteine concentrations are increased in insulin resistant individuals. For this purpose, the relationship between insulin resistance, as assessed by the steady-state plasma glucose (SSPG) concentration during the insulin suppression test, and fasting plasma homocysteine concentration was defined in 55 healthy volunteers. The results indicated that homocysteine concentrations did not vary as a function of SSPG concentrations (r = 0.02, P = 0.88). Furthermore, mean (+/- S.E.M.) plasma homocysteine concentrations were similar (8.2+/-0.4 vs. 8.7+/-0.7 micromol/l) in individuals classified as being either insulin sensitive (SSPG <100 mg/dl) or insulin resistant (SSPG >180 mg/dl). On the other hand, SSPG concentration was significantly correlated with fasting plasma insulin (r = 0.58, P<0.001), triglycerides (r = 0.34, P<0.05), and HDL-cholesterol (r = -0.36, P = 0.04) concentrations. These data strongly suggest that the increased risk of atherosclerosis associated with increased plasma homocysteine concentrations is unrelated to insulin resistance and/or the metabolic abnormalities associated with it.     

Lipoprotein lipase (LPL) mass in preheparin serum reflects insulin sensitivity

Lipoprotein lipase (LPL) is one of the enzymes regulated by insulin and its plasma activity reflects insulin sensitivity. Although intravenous heparin injection is required to measure LPL activity, we can detect LPL mass in preheparin serum (Pr-LPL mass) by immunoassay. In this study, we examined whether Pr-LPL mass reflects insulin sensitivity. We measured Pr-LPL mass, insulin sensitivity (Si), and acute insulin release in response to a glucose bolus (AIRg) in subjects with normal glucose tolerance (NGT; n = 23), impaired glucose tolerance (IGT; n = 10), and Type II diabetes mellitus (DM; n = 48). Si and AIRg were determined by minimal model analysis. We also compared Pr-LPL mass with the homeostasis model assessment of insulin resistance (HOMA-R) and the urinary excretion of C-peptide (urine CPR). We found that Pr-LPL mass correlated significantly with Si ( r = 0.354, P < 0.01) in all the subjects. This correlation was still significant in the NGT group (P < 0.472, P < 0.05), DM group (r = 0.311, P < 0.01), and DM group with a fasting plasma glucose >150 mg/dl ( n = 20, r = 0.459. P < 0.05). Moreover, Pr-LPL mass correlated negatively with HOMA-R (r = -0.272. P < 0.05) and fasting IRI (r = -0.256, P < 0.05). By contrast, Pr-LPL mass was not correlated with either urine CPR or logAIRg that reflect the ability to secrete insulin. In conclusion, Pr-LPL mass reflects insulin sensitivity. We speculate that Pr-LPL mass might be used to assess insulin sensitivity not only in the general population but also in advanced diabetic patients.     

Relation of abdominal obesity to hyperinsulinemia and high blood pressure in men.

The relationships between body fatness, adipose tissue distribution, plasma glucose, insulin levels, lipoprotein levels, and resting blood pressure were studied in 81 men aged 36.0 +/- 3.3 years (mean +/- s.d.) (body mass index (BMI): 27.4 +/- 3.8 kg/m2, percentage body fat: 26.4 +/- 6.6%). Systolic and diastolic blood pressures (BP) were significantly associated with the BMI (r = 0.31, r = 0.33, P < 0.01), the waist circumference (r = 0.33, r = 0.27; P < 0.01) as well as with adipose tissue areas measured by computerized tomography (CT) (0.27 < or = r < or = 0.36, P < 0.01). Furthermore, the relative accumulation of subcutaneous abdominal fat, as estimated by the ratio of abdominal to femoral adipose tissue areas measured by CT, was positively correlated with systolic and diastolic BP (P < 0.01). Fasting plasma insulin level (r = 0.30, P < 0.01) as well as the insulin area measured during an oral glucose tolerance test (0.34 < or = r < or = 0.37, P < 0.01) were significantly correlated with blood pressure. Systolic and diastolic BP were significantly associated with HDL2-cholesterol (C) as well as with the HDL2-C/HDL3-C ratio (-0.24 < or = r < or = -0.34), whereas triglycerides (r = 0.23) and the HDL-C/C ratio (r = -0.23) were significantly correlated with diastolic BP only (P < 0.05). Multivariate analysis indicated that the insulin area was the most important variable associated with blood pressure and that this association was independent of total body fatness and regional adipose tissue distribution. Plasma insulin levels explained 14% and 11% of the variance observed in the systolic and diastolic blood pressures respectively. These results suggest that most of the association between abdominal obesity and high blood pressure is mediated by the hyperinsulinemia and/or the related insulin resistant state.     

Genetic polymorphism PC-1 K121Q and ethnic susceptibility to insulin resistance

Genetic susceptibility may be responsible for high prevalence of insulin resistance in Asian Indians. This study was carried out in samples of local Asian Indians and Caucasians to determine whether plasma cell membrane glycoprotein (PC)-1 K121Q and insulin receptor substrate-1 (IRS-1) G972A polymorphisms contribute significantly to susceptibility to insulin resistance in Asian Indians. The frequency of carrying at least one copy of the PC-1 121Q variant in Asian Indians was significantly higher than that in Caucasians (P = 0.01), but the frequency was similar for IRS-1 972A (6% and 7%). A significantly higher insulin area under the curve during oral glucose tolerance testing (P < 0.0001) and lower insulin sensitivity during hyperinsulinemic-euglycemic clamps (P = 0.04) were found in Asian Indians with PC-1 121Q variant compared with Asian Indians with wild-type PC-1 and with Caucasians with or without the polymorphism. IRS-1 972A was not associated with any change in insulin sensitivity. We conclude that the PC-1 K121Q polymorphism associates with primary insulin resistance in migrant Asian Indians. A relatively high frequency of this polymorphism thus may be one factor contributing to insulin resistance susceptibility in Asian Indians. This finding indicates the need for expanded studies on the association between PC-1 K121Q and insulin resistance in a representative sample of the Asian Indian population.     

Plasma resistin concentration, hepatic fat content, and hepatic and peripheral insulin resistance in pioglitazone-treated type II diabetic patients

OBJECTIVES: To study the effect of pioglitazone (PIO) on plasma resistin concentration, endogenous glucose production (EGP), and hepatic fat content (HFC) in patients with type II diabetes (T2DM). SUBJECTS: A total of 13 T2DM patients (age=51+/-2 y, BMI=29.7+/-1.1 kg/m(2), HbA(1c)=8.0+/-0.5%). METHODS: HFC (magnetic resonance spectroscopy) and basal plasma resistin concentration were quantitated before and after PIO treatment (45 mg/day) for 16 weeks. Subjects received a 3 h euglycemic insulin (100 mU/m(2)/min) clamp with 3-[(3)H] glucose to determine rates of EGP and tissue glucose disappearance (Rd) before and after PIO. RESULTS: PIO reduced fasting plasma glucose (10.3+/-0.7 to 7.6+/-0.6 mmol/l, P<0.001) and HbA(1c) (8.0+/-0.4 to 6.8+/-0.3%, P<0.001) despite increased body weight (83.2+/-3.4 to 86.3+/-3.4 kg, P<0.001). PIO improved Rd (4.9+/-0.4 to 6.6+/-0.5 mg/kg/min, P<0.005) and reduced EGP (0.22+/-0.04 to 0.06+/-0.02 mg/kg/min, P<0.01) during the insulin clamp. Following PIO, HFC decreased from 21.1+/-3.5 to 11.2+/-2.1% (P<0.005), and plasma resistin decreased from 5.3+/-0.6 to 3.5+/-0.3 ng/ml (P<0.01). Plasma resistin concentration correlated positively with HFC before (r=0.58, P<0.05) and after (r=0.55, P<0.05) PIO treatment. Taken collectively, plasma resistin concentration, before and after PIO treatment, correlated positively with hepatic fat content (r=0.66, P<0.001) and EGP during the insulin clamp (r=0.41, P<0.05). However, the plasma resistin concentration did not correlate with whole body glucose disposal (Rd) during the insulin clamp either before (r=-0.18, P=NS) or after (r=-0.13, P=NS) PIO treatment. CONCLUSIONS: PIO treatment in T2DM causes a significant decrease in plasma resistin concentration. The decrease in plasma resistin is positively correlated with the decrease in hepatic fat content and improvement in hepatic insulin sensitivity.     

Serum corticosteroid-binding globulin concentration and insulin resistance syndrome: a population study

It has been suggested that a low grade inflammatory state could predispose for developing insulin resistance and contribute to the development of obesity and type 2 diabetes. Corticosteroid-binding globulin (CBG), the main plasma protein transport for cortisol, has been shown to be negatively regulated by insulin and IL-6, at least in vitro, suggesting that insulin resistance and inflammation may both contribute to decreasing CBG levels. In the present study we measured CBG concentrations in a human healthy population and investigated the relationships of CBG with anthropometric and biochemical markers for inflammation and/or insulin resistance. The data showed that the mean serum CBG level was significantly lower in males (n = 151) than in females (n = 113; 32.5 +/- 9.1 vs. 39.2 +/- 13.9 mg/liter; P < 0.0001). In both sexes serum CBG levels were correlated negatively with age (r = -0.12; P = 0.04), body mass index (r = -0.31; P < 0.0001), waist to hip ratio (WHR; r = -0.39; P < 0.0001), systolic (r = -0.15; P < 0.01) and diastolic (r = -0.15; P = 0.01) blood pressures, and HOMA, an index of insulin resistance (r = -0.12; P = 0.04). In addition, the CBG concentration was negatively associated with serum IL-6 concentrations (r = -0.23; P = 0.017) and with the soluble fraction of TNFalpha receptors, soluble TNF receptor 1 (sTNFR1; r = -0.35; P < 0.0001), and sTNFR2 (r = -0.56; P < 0.0001) in women. A stepwise regression analysis using CBG as an independent variable showed that sex (P < 0.00001), body mass index (P = 0.0002), and HOMA (P = 0.0005), but not systolic blood pressure, diastolic blood pressure, IL-6, sTNFR1, or sTNFR2, constituted significant independent factors that explained 21% of the CBG variance (14%, 2%, and 5%, respectively). In a subsample of 120 men and 68 women, fasting serum free cortisol (calculated as the ratio fasting cortisol/CBG) was significantly associated with WHR (r = 0.24; P = 0.001), systolic (r = 0.18; P = 0.01) and diastolic (r = 0.19; P = 0.007) blood pressures, and HOMA value (r = 0.20; P = 0.005), but not with BMI or age. BMI (P < 0.0001), free cortisol (P = 0.003), and CBG (P = 0.009), but not WHR and age, contributed to 20%, 6%, and 8%, respectively, of HOMA variance in women in a multiple regression analysis. In this model only BMI (P < 0.0001) independently contributed to HOMA variance in men. These findings support the hypothesis that the CBG level is an interesting indicator for both insulin resistance and low grade inflammation. Whether the decrease in CBG levels is genetic by nature or directly associated to increased insulin and/or IL-6 merits further investigation. Nevertheless, because CBG has been shown to be expressed by the adipose tissue, decreased CBG could create locally increased cortisol disposal, with no change in circulating cortisol, and facilitate fat accumulation, insulin resistance, and type 2 diabetes.     

Leptin responses to insulin administration in children with short stature

Abstract The aim of the study was to investigate the effect of standard insulin tolerance test on plasma leptin levels in children with idiopathic short stature (ISS) and in children with growth hormone deficiency (GHD). Furthermore, plasma leptin levels were analyzed with regard to age, body mass index (BMI), and plasma levels of human growth hormone and of insulin-like growth factor-1 (IGF-1). Sixty-three patients with a height below the third percentile, an age of 10.24 +/- 0.40 years and a BMI standard deviation score (SDS) of -0.78 +/- 0.13 (weight SDS -0.07 +/- 0.12; height SDS -2.39 +/- 0.10) were investigated (mean +/- SD). Based on responses to insulin tolerance test, the patients were classified as ISS (n = 49) or GHD (n = 14). Plasma leptin levels were significantly lower in all patients 60 minutes ( P < .001) and 120 minutes ( P < .001) after insulin administration. This effect was independent of GHD, and no difference in leptin decrease was found when comparing patients with ISS to those with GHD. A correlation was found when comparing plasma leptin levels of all patients to BMI SDS (r = 0.43; P < .001) and plasma IGF-1 levels (r = 0.31; P < .01). Furthermore, positive correlation was found when BMI SDS was compared to IGF-1 (r = 0.25; P < .05). In summary, we found that insulin administration in children with short stature decreases plasma leptin levels, equally in those with and without GHD.     

Continuous subcutaneous insulin infusion therapy decreases insulin resistance in type 1 diabetes

The influence of continuous sc insulin infusion therapy for 6 weeks on sensitivity to insulin (euglycemic clamp technique) and hepatic glucose production (3-[3H]glucose technique) was measured in 10 type 1 diabetic patients whose mean duration of diabetes was 8 yr. Mean diurnal blood glucose fell from 8.5 +/- 0.8 (SEM) mmol/liter to 6.0 +/- 0.6 mmol/liter (P less than 0.05) and glycosylated hemoglobin from 10.5 +/- 0.4% to 8.7 +/- 0.3%. Insulin requirements declined by 23% from 47 +/- 4 U/day prepump to 36 +/- 2 U/day after 6 weeks of pump therapy (P less than 0.01). During the insulin clamp, plasma insulin was maintained at approximately 90 mU/liter and plasma glucose at approximately 5.0 mmol/liter in all studies. The rate of glucose metabolism in diabetic patients during conventional therapy (4.65 +/- 0.41 mg/kg X min) was 35% lower than in normal subjects (7.20 +/- 0.42 mg/kg X min, n = 14, P less than 0.001). After 6 weeks of pump therapy, total glucose uptake increased by 27% to 5.90 +/- 0.60 mg/kg X min, P less than 0.05 vs. prepump). This was still 18% lower than in the normal subjects (P less than 0.05). Basal hepatic glucose production in the diabetic patients during conventional therapy (3.07 +/- 0.14 mg/kg X min) was 70% higher than in the normal subjects (1.79 +/- 0.07 mg/kg X min, n = 7, P less than 0.001). After 6 weeks of pump therapy, hepatic glucose production fell to 2.48 +/- 0.19 mg/kg X min (P less than 0.05), which was still 40% higher than in the normal subjects (P less than 0.01). Basal hepatic glucose production was directly related to the fasting plasma glucose level (r = 0.67, P less than 0.001) and inversely proportional to fasting insulin concentration (r = -0.48, P less than 0.05) in the diabetic patients. Specific tracer insulin binding to erythrocytes in the diabetic patients (19.4 +/- 1.5%) was comparable to that in the normal subjects (19.6 +/- 1.2%) and remained unchanged during pump therapy. Thus the improved metabolic control resulting from pump therapy is associated with enhancement in sensitivity to insulin, and reduction in basal hepatic glucose production.     

Circulating tumor necrosis factor alpha concentrations are higher in abdominal versus peripheral obesity.

Fat tissue is a significant source of endogenous tumor necrosis factor alpha (TNFalpha), the pluripotent cytokine that plays an important role as a mediator of the peripheral insulin resistance found in obesity. The majority of evidence for this role of TNFalpha is from studies in animal models of obesity. To explore further the role of TNFalpha in the pathogenesis of obesity-related insulin resistance in humans, we compared plasma levels of TNFalpha and the other main endocrine cytokine, interleukin-6 ([IL-6] both measured by enzyme-linked immunosorbent assay), in 26 obese women (body mass index [BMI] > 30 kg/m2) and 13 female controls (BMI < 26 kg/m2) without a history of recent or active infection. Glucose and insulin levels were measured at 0, 1, and 2 hours after a 75-g oral glucose load. There was no significant difference in plasma TNFalpha or IL-6 levels between obese and non-obese subjects overall (2.10 +/- 0.19 v 1.65 +/- 0.18 pg/mL and 2.06 +/- 0.29 v 1.50 +/- 0.17 pg/mL, respectively). However, TNFalpha levels were significantly elevated in obese subjects with a 2-hour glucose level more than 140 mg/dL (n = 8) compared with the other obese subjects (n = 18) and the non-obese controls (2.88 +/- 0.46 v 1.75 +/- 0.10 and 1.65 +/- 0.18 pg/mL, respectively, P < .01). Furthermore, the TNFalpha level correlated significantly with the waist to hip ratio ([WHR] r = .53, P < .01) and fasting and post-oral glucose tolerance test (OGTT) insulin levels (r = .47, P < .02), but not with the BMI, and was higher in obese women with a WHR more than 0.90 (n = 14) in comparison to those with a WHR less than 0.90 (n = 12, 2.47 +/- 0.29 v 1.66 +/- 0.18 pg/mL, respectively, P < .03). The corresponding plasma leptin level was significantly higher in obese women versus the control group (41.6 +/- 2.5 v22.3 +/- 2.9 ng/mL, P < .001) and was related to the BMI (r = .60, P < .01) but not to TNFalpha or the WHR. There were no significant differences in the corresponding IL-6 concentration between groups, and IL-6 did not correlate with TNFalpha, leptin, BMI, WHR, or insulin levels. In conclusion, circulating TNFalpha levels are higher in abdominal obesity compared with peripheral obesity, and may contribute to the insulin resistance that more commonly complicates the former pattern of fat distribution.     

Sustained reduction in plasma free fatty acid concentration improves insulin action without altering plasma adipocytokine levels in subjects with strong family history of type 2 diabetes

To investigate the effect of a sustained (7-d) decrease in plasma free fatty acid (FFA) concentration in individuals genetically predisposed to develop type 2 diabetes mellitus (T2DM), we studied the effect of acipimox, a potent inhibitor of lipolysis, on insulin action and adipocytokine concentrations in eight normal glucose-tolerant subjects (aged 40 +/- 4 yr, body mass index 26.5 +/- 0.8 kg/m(2)) with at least two first-degree relatives with T2DM. Subjects received an oral glucose tolerance test (OGTT) and 120 min euglycemic insulin clamp (80 mU/m(2).min) with 3-[(3)H] glucose to quantitate rates of insulin-mediated whole-body glucose disposal (Rd) and endogenous (primarily hepatic) glucose production (EGP) before and after acipimox, 250 mg every 6 h for 7 d. Acipimox significantly reduced fasting plasma FFA (515 +/- 64 to 285 +/- 58 microm, P < 0.05) and mean plasma FFA during the OGTT (263 +/- 32 to 151 +/- 25 microm, P < 0.05); insulin-mediated suppression of plasma FFA concentration during the insulin clamp also was enhanced (162 +/- 18 to 120 +/- 15 microm, P < 0.10). Following acipimox, fasting plasma glucose (5.1 +/- 0.1 vs. 5.2 +/- 0.1 mm) did not change, whereas mean plasma glucose during the OGTT decreased (7.6 +/- 0.5 to 6.9 +/- 0.5 mm, P < 0.01) without change in mean plasma insulin concentration (402 +/- 90 to 444 +/- 102 pmol/liter). After acipimox Rd increased from 5.6 +/- 0.5 to 6.8 +/- 0.5 mg/kg.min (P < 0.01) due to an increase in insulin-stimulated nonoxidative glucose disposal (2.5 +/- 0.4 to 3.5 +/- 0.4 mg/kg.min, P < 0.05). The increment in Rd correlated closely with the decrement in fasting plasma FFA concentration (r = -0.80, P < 0.02). Basal EGP did not change after acipimox (1.9 +/- 0.1 vs. 2.0 +/- 0.1 mg/kg.min), but insulin-mediated suppression of EGP improved (0.22 +/- 0.09 to 0.01 +/- 0.01 mg/kg.min, P < 0.05). EGP during the insulin clamp correlated positively with the fasting plasma FFA concentration (r = 0.49, P = 0.06) and the mean plasma FFA concentration during the insulin clamp (r = 0.52, P < 0.05). Plasma adiponectin (7.1 +/- 1.0 to 7.2 +/- 1.1 microg/ml), resistin (4.0 +/- 0.3 to 3.8 +/- 0.3 ng/ml), IL-6 (1.4 +/- 0.3 to 1.6 +/- 0.4 pg/ml), and TNFalpha (2.3 +/- 0.3 to 2.4 +/- 0.3 pg/ml) did not change after acipimox treatment.We concluded that sustained reduction in plasma FFA concentration in subjects with a strong family history of T2DM increases peripheral (muscle) and hepatic insulin sensitivity without increasing adiponectin levels or altering the secretion of other adipocytokines by the adipocyte. These results suggest that lipotoxicity already is well established in individuals who are genetically predisposed to develop T2DM and that drugs that cause a sustained reduction in the elevated plasma FFA concentration may represent an effective modality for the prevention of T2DM in high-risk, genetically predisposed, normal glucose-tolerant individuals despite the lack of an effect on adipocytokine concentrations.     

Increased plasma concentration of macrophage migration inhibitory factor (MIF) and MIF mRNA in mononuclear cells in the obese and the suppressive action of metformin

The objective of the study was to determine whether plasma migration inhibitor factor (MIF) concentration and mononuclear cell (MNC) mRNA are elevated in obesity and whether treatment with metformin reduces plasma MIF concentration. Forty obese subjects [body mass index (BMI), 37.5 +/- 4.9 kg/m(2)] and 40 nonobese healthy subjects (BMI, 22.6 +/- 3.4 kg/m(2)) had their plasma MIF, glucose, insulin, free fatty acids (FFAs) and C-reactive protein (CRP) concentrations measured. Sixteen obese patients and 16 nonobese healthy subjects had RNA prepared from MNCs. Eight obese subjects with normal glucose concentration were treated with metformin 1 g (Glucophage XR; 1000 mg twice daily) twice daily for 6 wk. Eight obese subjects were used as controls. Plasma concentration of glucose, insulin, FFAs, and MIF was measured by appropriate assays. mRNA for MIF was measured by real-time PCR. Forty obese subjects had a fasting concentration of MIF of 2.8 +/- 2.0 ng/ml, whereas 40 nonobese subjects had a fasting MIF concentration of 1.2 +/- 0.6 ng/ml (P < 0.001). Plasma MIF concentrations were significantly related to BMI (r = 0.52; P < 0.001). mRNA for MIF was correlated to plasma FFAs (r = 0.40; P < 0.05) and plasma CRP (r = 0.42; P < 0.05) concentrations. Eight obese subjects had their fasting blood samples taken before and after taking a slow-release preparation of metformin at 1, 2, 4, and 6 wk. The mean plasma concentration fell from 2.3 +/- 1.4 to 1.6 +/- 1.2 ng/ml at 6 wk (P < 0.05). Obese subjects not on treatment with metformin showed no change. During the period of treatment with metformin, the body weight did not change and the plasma concentration of glucose, insulin, and FFAs did not alter. We conclude that: 1) plasma MIF concentrations and MIF mRNA expression in the MNCs are elevated in the obese, consistent with a proinflammatory state in obesity; 2) these increases in MIF are related to BMI, FFA concentrations, and CRP; 3) metformin suppresses plasma MIF concentrations in the obese, suggestive of an antiinflammatory effect of this drug; and 4) this action of metformin may contribute to a potential antiatherogenic effect, which may have implications for the reduced cardiovascular mortality observed with metformin therapy in type 2 diabetes mellitus.     

Deconvolution analysis of rapid insulin pulses before and after six weeks of continuous subcutaneous administration of glucagon-like peptide-1 in elderly patients with type 2 diabetes

CONTEXT: Insulin is secreted in a pulsatile fashion with measurable orderliness (low entropy). Normal aging and diabetes in middle-aged patients is characterized by alterations in pulsatile insulin release. OBJECTIVES: We undertook the current studies to determine whether disruptions in pulsatile insulin release also accompany diabetes in the elderly. DESIGN: Two studies were performed. In the first study, insulin values were sampled every minute for 1 h under fasting conditions. In the second study, subjects underwent a 2-h hyperglycemic glucose clamp (glucose 5.4 mm above basal). From 60-120 min, insulin was sampled every 1 min. Secretory pulse analysis was conducted using a multiparameter deconvolution technique. SETTING: The study was conducted in a general clinical research center and during outpatient visits. PATIENTS: Volunteers were healthy young [n = 10; body mass index (BMI), 23 +/- 1 kg/m2; age, 23 +/- 1 yr] and elderly (n = 10; BMI, 24 +/- 1 kg/m2; age, 78 +/- 2 yr) volunteers and elderly patients with diabetes (n = 8; BMI, 28 +/- 1 kg/m2; age, 73 +/- 2 yr). Intervention: Five of the older patients with type 2 diabetes (BMI, 29 +/- 1 kg/m2; age, 72 +/- 2 yr) were treated with continuous sc glucagon-like peptide-1 (GLP-1) (7-36) amide infusion for 6 wk, and a second 2-h hyperglycemic clamp was performed. MAIN OUTCOME MEASURES: Insulin burst mass, pulsatile insulin secretion, and entropy were measured. RESULTS: Under fasting conditions, elderly patients with diabetes had a reduction in insulin burst mass (P < 0.05) that was similar to normal elderly. During hyperglycemia, elderly patients with diabetes had an even greater impairment in insulin burst mass (P < 0.05) and basal (P < 0.05) and pulsatile insulin secretion (P < 0.05) than normal elderly. Approximate entropy, a measure of irregularity of insulin release, was increased to a greater extent in older diabetes patients than normal elderly, signifying loss of orderliness of insulin secretion (P < 0.05). In response to treatment with GLP-1, insulin burst mass (P < 0.05) and pulsatile insulin secretion (P < 0.05) improved significantly in elderly patients with diabetes. CONCLUSIONS: We conclude that alterations in pulsatile insulin release can be improved in elderly patients with diabetes by the administration of sc GLP-1.