Activation of AMP-activated protein kinase (AMPK) by exercise induces several cellular processes in muscle. Exercise activation of AMPK is unaffected in lean (BMI ϳ25 kg/m 2 ) subjects with type 2 diabetes. However, most type 2 diabetic subjects are obese (BMI >30 kg/m 2 ), and exercise stimulation of AMPK is blunted in obese rodents. We examined whether obese type 2 diabetic subjects have impaired exercise stimulation of AMPK, at different signaling levels, spanning from the upstream kinase, LKB1, to the putative AMPK targets, AS160 and peroxisome proliferator-activated receptor coactivator (PGC)-1␣, involved in glucose transport regulation and mitochondrial biogenesis, respectively. Twelve type 2 diabetic, eight obese, and eight lean subjects exercised on a cycle ergometer for 40 min. Muscle biopsies were done before, during, and after exercise. Subjects underwent this protocol on two occasions, at low (50% VO 2max ) and moderate (70% VO 2max ) intensities, with a 4 -6 week interval. Exercise had no effect on LKB1 activity. Exercise had a time-and intensity-dependent effect to increase AMPK activity and AS160 phosphorylation. Obese and type 2 diabetic subjects had attenuated exercise-stimulated AMPK activity and AS160 phosphorylation. Type 2 diabetic subjects had reduced basal PGC-1 gene expression but normal exercise-induced increases in PGC-1 expression. Our findings suggest that obese type 2 diabetic subjects may need to exercise at higher intensity to stimulate the AMPK-AS160 axis to the same level as lean subjects. Diabetes 56:836 -848, 2007

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.

We examined the relationship between peripheral/hepatic insulin sensitivity and abdominal superficial/deep subcutaneous fat (SSF/DSF) and intra-abdominal visceral fat (VF) in patients with type 2 diabetes mellitus (T2DM). Sixty-two T2DM patients (36 males and 26 females, age = 55 +/- 3 yr, body mass index = 30 +/- 1 kg/m2) underwent a two-step euglycemic insulin clamp (40 and 160 mU. m(-2). min(-1)) with [3-3H]glucose. SSF, DSF, and VF areas were quantitated with magnetic resonance imaging at the L(4-5) level. Basal endogenous glucose production (EGP), hepatic insulin resistance index (basal EGP x FPI), and total glucose disposal (TGD) during the first and second insulin clamp steps were similar in male and female subjects. VF (159 +/- 9 vs. 143 +/- 9 cm2) and DSF (199 +/- 14 vs. 200 +/- 15 cm(2)) were not different in male and female subjects. SSF (104 +/- 8 vs. 223 +/- 15 cm2) was greater (P < 0.0001) in female vs. male subjects despite similar body mass index (31 +/- 1 vs. 30 +/- 1 kg/m2) and total body fat mass (31 +/- 2 vs. 33 +/- 2 kg). In male T2DM, TGD during the first insulin clamp step (1st TGD) correlated inversely with VF (r = -0.45, P < 0.01), DSF (r = -0.46, P < 0.01), and SSF (r = -0.39, P < 0.05). In males, VF (r = 0.37, P < 0.05), DSF (r = 0.49, P < 0.01), and SSF (r = 0.33, P < 0.05) were correlated positively with hepatic insulin resistance. In females, the first TGD (r = -0.45, P < 0.05) and hepatic insulin resistance (r = 0.49, P < 0.05) correlated with VF but not with DSF, SSF, or total subcutaneous fat area. We conclude that visceral adiposity is associated with both peripheral and hepatic insulin resistance, independent of gender, in T2DM. In male but not female T2DM, deep subcutaneous adipose tissue also is associated with peripheral and hepatic insulin resistance.

Aims/hypothesis The molecular mechanisms by which thiazolidinediones improve insulin sensitivity in type 2 diabetes are not fully understood. We hypothesised that pioglitazone would activate the adenosine 5′-monophosphate-activated protein kinase (AMPK) pathway and increase the expression of genes involved in adiponectin signalling, NEFA oxidation and mitochondrial function in human skeletal muscle. Methods A randomised, double-blind, parallel study was performed in 26 drug-naive type 2 diabetes patients treated with: (1) pioglitazone (n=14) or (2) aggressive nutritional therapy (n=12) to reduce HbA1c to levels observed in the pioglitazone-treated group. Participants were assigned randomly to treatment using a table of random numbers. Before and after 6 months, patients reported to the Clinical Research Center of the Texas Diabetes Institute for a vastus lateralis muscle biopsy followed by a 180 min euglycaemic–hyperinsulinaemic (80 mU m−2 min−1) clamp. Results All patients in the pioglitazone (n=14) or nutritional therapy (n=12) group were included in the analysis. Pioglitazone significantly increased plasma adiponectin concentration by 79% and reduced fasting plasma NEFA by 35% (both p<0.01). Following pioglitazone, insulin-stimulated glucose disposal increased by 30% (p<0.01), and muscle AMPK and acetyl-CoA carboxylase (ACC) phosphorylation increased by 38% and 53%, respectively (p<0.05). Pioglitazone increased mRNA levels for adiponectin receptor 1 and 2 genes (ADIPOR1, ADIPOR2), peroxisome proliferator-activated receptor gamma, coactivator 1 gene (PPARGC1) and multiple genes involved in mitochondrial function and fat oxidation. Despite a similar reduction in HbA1c and similar improvement in insulin sensitivity with nutritional therapy, there were no significant changes in muscle AMPK and ACC phosphorylation, or the expression of ADIPOR1, ADIPOR2, PPARGC1 and genes involved in mitochondrial function and fat oxidation. No adverse (or unexpected) effects or side effects were reported from the study. Conclusions/interpretations Pioglitazone increases plasma adiponectin levels, stimulates muscle AMPK signalling and increases the expression of genes involved in adiponectin signalling, mitochondrial function and fat oxidation. These changes may represent an important cellular mechanism by which thiazolidinediones improve skeletal muscle insulin sensitivity.