Acute elevations in free fatty acids (FFAs) stimulate insulin secretion, but prolonged lipid exposure impairs ␤-cell function in both in vitro studies and in vivo animal studies. In humans data are limited to short-term (<48 h) lipid infusion studies and have led to conflicting results. We examined insulin secretion and action during a 4-day lipid infusion in healthy normal glucose tolerant subjects with (FH؉ group, n ‫؍‬ 13) and without (control subjects, n ‫؍‬ 8) a family history of type 2 diabetes. Volunteers were admitted twice to the clinical research center and received, in random order, a lipid or saline infusion. On days 1 and 2, insulin and C-peptide concentration were measured as part of a metabolic profile after standardized mixed meals. Insulin secretion in response to glucose was assessed with a ؉125 mg/dl hyperglycemic clamp on day 3. On day 4, glucose turnover was measured with a euglycemic insulin clamp with [3-3 H]glucose. Day-long plasma FFA concentrations with lipid infusion were increased within the physiological range, to levels seen in type 2 diabetes (ϳ500 -800 mol/l). Lipid infusion had strikingly opposite effects on insulin secretion in the two groups. After mixed meals, day-long plasma C-peptide levels increased with lipid infusion in control subjects but decreased in the FH؉ group (؉28 vs. ؊30%, respectively, P < 0.01). During the hyperglycemic clamp, lipid infusion enhanced the insulin secretion rate (ISR) in control subjects but decreased it in the FH؉ group (first phase: ؉75 vs. ؊60%, P < 0.001; second phase: ؉25 vs. ؊35%, P < 0.04). When the ISR was adjusted for insulin resistance (ISR Rd ‫؍‬ ISR ، [1/R d ], where R d is the rate of insulin-stimulated glucose disposal), the inadequate ␤-cell response in the FH؉ group was even more evident. Although ISR Rd was not different between the two groups before lipid infusion, in the FH؉ group, lipid infusion reduced first-and second-phase ISR Rd to 25 and 42% of that in control subjects, respectively (both P < 0.001 vs. control subjects). Lipid infusion in the FH؉ group (but not in control subjects) also caused severe hepatic insulin resistance with an increase in basal endogenous glucose production (EGP), despite an elevation in fasting insulin levels, and impaired suppression of EGP to insulin. In summary, in individuals who are genetically predisposed to type 2 diabetes, a sustained physiological increase in plasma FFA impairs insulin secretion in response to mixed meals and to intravenous glucose, suggesting that in subjects at high risk of developing type 2 diabetes, ␤-cell lipotoxicity may play an important role in the progression from normal glucose tolerance to overt hyperglycemia.

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 ⅐min) 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/kg⅐min, P < 0.005) and reduced EGP (0.23 ؎ 0.04 to 0.05 ؎ 0.02 mg/kg⅐min, 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 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. (J Clin Endocrinol Metab 89: 200 -206, 2004)

The effect of pioglitazone on splanchnic glucose uptake (SGU), endogenous glucose production (EGP), and hepatic fat content was studied in 14 type 2 diabetic patients (age 50 ؎ 2 years, BMI 29.4 ؎ 1.1 kg/m 2 , HbA 1c 7.8 ؎ 0.4%). Hepatic fat content (magnetic resonance spectroscopy) and SGU (oral glucose load-insulin clamp technique) were quantitated before and after pioglitazone (45 mg/day) therapy for 16 weeks. Subjects received a 7-h euglycemic insulin (100 mU ⅐ m ؊2 ⅐ min ؊1 ) clamp, and a 75-g oral glucose load was ingested 3 h after starting the insulin clamp. Following glucose ingestion, the steady-state glucose infusion rate during the insulin clamp was decreased appropriately to maintain euglycemia. SGU was calculated by subtracting the integrated decrease in glucose infusion rate during the 4 h after glucose ingestion from the ingested glucose load. 3-[ 3 H]glucose was infused during the initial 3 h of the insulin clamp to determine rates of EGP and glucose disappearance (R d ). Pioglitazone reduced fasting plasma glucose (10.0 ؎ 0.7 to 7.5 ؎ 0.6 mmol/l, P < 0.001) and HbA 1c (7.8 ؎ 0.4 to 6.7 ؎ 0.3%, P < 0.001) despite increased body weight (83 ؎ 3 to 86 ؎ 3 kg, P < 0.001). During the 3-h insulin clamp period before glucose ingestion, pioglitazone improved R d (6.9 ؎ 0.5 vs. 5.2 ؎ 0.5 mg ⅐ kg ؊1 ⅐ min ؊1 , P < 0.001) and insulinmediated suppression of EGP (0.21 ؎ 0.04 to 0.06 ؎ 0.02 mg ⅐ kg ؊1 ⅐ min ؊1 , P < 0.01). Following pioglitazone treatment, hepatic fat content decreased from 19.6 ؎ 3.6 to 10.4 ؎ 2.1%, (P < 0.005), and SGU increased from 33.0 ؎ 2.8 to 46.2 ؎ 5.1% (P < 0.005). Pioglitazone treatment in type 2 diabetes 1) decreases hepatic fat content and improves insulin-mediated suppression of EGP and 2) augments splanchnic and peripheral tissue glucose uptake. Improved splanchnic/peripheral glucose uptake and enhanced suppression of EGP contribute to the improvement in glycemic control in patients with type 2 diabetes. Diabetes 52:1364 -1370, 2003 T he splanchnic tissues play a pivotal role in the maintenance of normal glucose homeostasis (1). Hyperglycemia, plasma free fatty acid (FFA) concentration, and route of glucose administration all exert independent effects on splanchnic glucose uptake (SGU). When glucose is administered intravenously, the resultant hyperglycemia enhances SGU in proportion to the increase in plasma glucose concentration such that the splanchnic glucose clearance remains unchanged (2,3). This mass-action effect of hyperglycemia to augment SGU is dependent upon maintained portal insulin levels (2-5,8). Insulin per se does not increase SGU (2,5). Studies by DeFronzo and colleagues (3,5) in humans and by Cherrington and colleagues (6,7) in dogs have shown that the gastrointestinal/portal route of glucose administration has a specific enhancing effect on SGU. Thus, following glucose ingestion, the fractional, as well as absolute rate of glucose uptake by the splanchnic tissues is significantly greater than the combined effects of hyperinsulinemia plus hyperglycemia created...

The association between elevated plasma free fatty acid (FFA) concentrations and insulin resistance is well known. Although the cause and effect relationship between FFAs and insulin resistance is complex, plasma FFA is negatively correlated with the expression of peroxisome proliferator activated receptor-␥ cofactor-1 (PGC-1) and nuclear encoded mitochondrial genes. To test whether this association is causal, we infused a triglyceride emulsion (or saline as control) into healthy subjects to increase plasma FFA for 48 h followed by muscle biopsies, microarray analysis, quantitative real time PCR, and immunoblots. Lipid infusion increased plasma FFA concentration from 0.48 ؎ 0.02 to 1.73 ؎ 0.43 mM and decreased insulin-stimulated glucose disposal from 8.82 ؎ 0.69 to 6.67 ؎ 0.66 mg/kg⅐min, both with p < 0.05. PGC-1 mRNA, along with mRNAs for a number of nuclear encoded mitochondrial genes, were reduced by lipid infusion (p < 0.05). Microarray analysis also revealed that lipid infusion caused a significant overexpression of extracellular matrix genes and connective tissue growth factor. Quantitative reverse transcription PCR showed that the mRNA expression of collagens and multiple extracellular matrix genes was higher after the lipid infusion (p < 0.05). Immunoblot analysis revealed that lipid infusion also increased the expression of collagens and the connective tissue growth factor protein. These data suggest that an experimental increase in FFAs decreases the expression of PGC-1 and nuclear encoded mitochondrial genes and also increases the expression of extracellular matrix genes in a manner reminiscent of inflammation.

Dapa attenuated the activation of the inflammasome, fibrosis, and deterioration of LVEF in BTBR mice. The anti-inflammatory, anti-fibrotic effects are likely SGLT2- and glucose-lowering-independent, as they were replicated in the in vitro model. The effects on remodeling were augmented when Saxa was added to Dapa. Yet, adding Saxa to Dapa did not result in a greater effect on myocardial fibrosis and collagen levels.

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.

Aims/hypothesis. The recent discovery of two adiponectin receptors (AdipoR1 and AdipoR2) will improve our understanding of the molecular mechanisms underlying the insulin-sensitising effect of adiponectin. The aim of this study was to determine for the first time whether skeletal muscle AdipoR1 and/or AdipoR2 gene expression levels are associated with insulin resistance. Methods. Using RT-PCR and northern analysis we measured AdipoR1 and AdipoR2 gene expression in skeletal muscle from healthy Mexican Americans with normal glucose tolerance who had (n=8) or did not have (n=10) a family history of Type 2 diabetes. Results. Gene expression profiling indicated that the AdipoR1 and AdipoR2 isoforms are highly expressed in human skeletal muscle, unlike in mice where AdipoR2 expression was highest in the liver, and AdipoR1 was highest in skeletal muscle. In the study subjects, the expression levels of AdipoR1 (p=0.004) and AdipoR2 (p=0.04), as well as plasma adiponectin concentration (p=0.03) were lower in people with a family history of Type 2 diabetes than in those with no family history of the disease. Importantly, the expression levels of both receptors correlated positively with insulin sensitivity (r=0. 64, p=0.004 and r=0.47, p=0.048 respectively). Conclusions/interpretation. Collectively, these data indicate that both isoforms of the adiponectin receptor play a role in the insulin-sensitising effect of adiponectin.

ABSTRACT.