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

Regulation of fatty acid uptake and metabolism in L6 skeletal muscle cells by resistin

Resistin has been proposed as a potential link between obesity and insulin resistance. It is also well established that altered metabolism of fatty acids by skeletal muscle can lead to insulin resistance and lipotoxicity. However, little is known about the effect of resistin on long chain fatty acid uptake and metabolism in skeletal muscle. Here we show that treating rat skeletal muscle cells with recombinant resistin (50 nM, 24 h) decreased uptake of palmitate. This correlated with reduced cell surface CD36 content and lower expression of FATP1, but no change in FATP4 or CD36 expression. We also found that resistin decreased fatty acid oxidation by measuring 14CO2 production from [1-14C] oleate and an increase in intracellular lipid accumulation was detected in response to resistin. Decreased AMPK and ACC phosphorylation were observed in response to resistin while expression of ACC and AMPK isoforms was unaltered. Resistin mediated these effects without altering cell viability. In summary, our results demonstrate that chronic incubation of skeletal muscle cells with resistin decreased fatty acid uptake and metabolism via a mechanism involving decreased cell surface CD36 content, FATP1 expression and a decrease in phosphorylation of AMPK and ACC.

Increased serum resistin in adults with prader-willi syndrome is related to obesity and not to insulin resistance

CONTEXT

Determinants of insulin resistance in Prader-Willi syndrome (PWS) are not completely understood. The discovery of several adipokines with relevant effects on insulin resistance and cardiovascular complications of metabolic syndrome offered new tools of investigation of insulin resistance in PWS.

OBJECTIVE

The purpose of this study was to measure serum resistin and mRNA in adipose tissue of patients with PWS, those with simple obesity, and healthy controls and correlate resistin levels with anthropometric and biochemical features.

DESIGN

Twenty-eight adult PWS patients, 29 obese patients, and 25 healthy controls were studied. Anthropometric variables were measured and fasting serum and plasma were collected for measurement of resistin, adiponectin, leptin, lipid profile, glucose, and insulin.

RESULTS

Serum resistin and resistin mRNA expression in adipose tissue was significantly higher in PWS patients, compared with both healthy lean controls and obese patients. Moreover, on regression analysis resistin was significantly correlated with body mass index, whereas no significant association was found between resistin and homeostasis model assessment index. A weak association between resistin and adiponectin was found in the PWS group only. However, on multivariate analysis only the correlation between resistin and body mass index remained significant.

CONCLUSIONS

These results support a link between circulating resistin and obesity in humans but do not support a role for resistin in human insulin resistance.

Effects of the PPARgamma agonist pioglitazone on lipoprotein metabolism in patients with type 2 diabetes mellitus

Elevated plasma levels of VLDL triglycerides (TGs) are characteristic of patients with type 2 diabetes mellitus (T2DM) and are associated with increased production rates (PRs) of VLDL TGs and apoB. Lipoprotein lipase-mediated (LPL-mediated) lipolysis of VLDL TGs may also be reduced in T2DM if the level of LPL is decreased and/or the level of plasma apoC-III, an inhibitor of LPL-mediated lipolysis, is increased. We studied the effects of pioglitazone (Pio), a PPARgamma agonist that improves insulin sensitivity, on lipoprotein metabolism in patients with T2DM. Pio treatment reduced TG levels by increasing the fractional clearance rate (FCR) of VLDL TGs from the circulation, without changing direct removal of VLDL particles. This indicated increased lipolysis of VLDL TGs during Pio treatment, a mechanism supported by our finding of increased plasma LPL mass and decreased levels of plasma apoC-III. Lower apoC-III levels were due to reduced apoC-III PRs. We saw no effects of Pio on the PR of either VLDL TG or VLDL apoB. Thus, Pio, a PPARgamma agonist, reduced VLDL TG levels by increasing LPL mass and inhibiting apoC-III PR. These 2 changes were associated with an increased FCR of VLDL TGs, almost certainly due to increased LPL-mediated lipolysis.

The effects of rosiglitazone and metformin on the plasma concentrations of resistin in patients with type 2 diabetes mellitus

Resistin is a protein secreted from adipose tissue that is thought to play a role in insulin sensitivity. We examined the effects of rosiglitazone and metformin on the plasma resistin levels in individuals with type 2 diabetes mellitus. Patients with type 2 diabetes mellitus who showed poor glycemic control with glimepiride (4 mg/d) were randomized to rosiglitazone (4 mg/d) and metformin (500 mg bid) treatment groups. All subjects continued glimepiride treatment as well. The plasma concentrations of resistin were measured at baseline and at 6 months of treatment for both groups. The anthropometric parameters, fasting plasma glucose, HbA1c, total cholesterol, triglyceride, high-density lipoprotein cholesterol, free fatty acids, and adiponectin concentrations were also measured. After 6 months of treatment, the reduction in plasma glucose levels was similar between the 2 groups. There were no significant changes in the lipid profiles of either group during the study period. The plasma resistin levels decreased in the rosiglitazone group (2.49 +/- 1.93 vs 1.95 +/- 1.59 ng/ml; P < .05) but increased in the metformin group (2.61 +/- 1.69 vs 5.13 +/- 2.81 ng/ml; P < .05). The plasma adiponectin concentrations were increased in the rosiglitazone group (2.91 +/- 1.46 vs 4.23 +/- 1.77 microg/ml; P < .05) but were unchanged in the metformin group. In summary, rosiglitazone treatment decreased the plasma resistin levels whereas metformin treatment increased them in patients with type 2 diabetes mellitus showing poor glycemic control with sulfonylurea therapy. These results suggest that the observed changes in plasma resistin levels are not the consequences of improved insulin resistance, nor are they consequences of glycemic control. Considering the potential role of resistin in insulin resistance, decrease in resistin levels may contribute to improving insulin action with rosiglitazone treatment.

Resistin is an inflammatory marker of atherosclerosis in humans

BACKGROUND

Resistin, a plasma protein, induces insulin resistance in rodents. Recent reports suggest that circulating levels of resistin are elevated in obese and insulin-resistant rodents and humans. Whereas rodent resistin is made in adipocytes, macrophages are a major source of human resistin. Given the convergence of adipocyte and macrophage function, resistin may provide unique insight into links between obesity, inflammation, and atherosclerosis in humans.

METHODS AND RESULTS

We examined whether plasma resistin levels were associated with metabolic and inflammatory markers, as well as with coronary artery calcification (CAC), a quantitative index of atherosclerosis, in 879 asymptomatic subjects in the Study of Inherited Risk of Coronary Atherosclerosis. Resistin levels were positively associated with levels of inflammatory markers, including soluble tumor necrosis factor-alpha receptor-2 (P<0.001), interleukin-6 (P=0.04), and lipoprotein-associated phospholipase A2 (P=0.002), but not measures of insulin resistance in multivariable analysis. Resistin levels also were associated (odds ratio and 95% confidence interval in ordinal regression) with increasing CAC after adjustment for age, sex, and established risk factors (OR, 1.23 [CI, 1.03 to 1.52], P=0.03) and further control for metabolic syndrome and plasma C-reactive protein (CRP) levels (OR, 1.25 [CI, 1.04 to 1.50], P=0.01). In subjects with metabolic syndrome, resistin levels further predicted CAC, whereas CRP levels did not.

CONCLUSIONS

Plasma resistin levels are correlated with markers of inflammation and are predictive of coronary atherosclerosis in humans, independent of CRP. Resistin may represent a novel link between metabolic signals, inflammation, and atherosclerosis. Further studies are needed to define the relationship of resistin to clinical cardiovascular disease.

An inflammatory cascade leading to hyperresistinemia in humans

BACKGROUND

Obesity, the most common cause of insulin resistance, is increasingly recognized as a low-grade inflammatory state. Adipocyte-derived resistin is a circulating protein implicated in insulin resistance in rodents, but the role of human resistin is uncertain because it is produced largely by macrophages.

METHODS AND FINDINGS

The effect of endotoxin and cytokines on resistin gene and protein expression was studied in human primary blood monocytes differentiated into macrophages and in healthy human participants. Inflammatory endotoxin induced resistin in primary human macrophages via a cascade involving the secretion of inflammatory cytokines that circulate at increased levels in individuals with obesity. Induction of resistin was attenuated by drugs with dual insulin-sensitizing and anti-inflammatory properties that converge on NF-kappaB. In human study participants, experimental endotoxemia, which produces an insulin-resistant state, causes a dramatic rise in circulating resistin levels. Moreover, in patients with type 2 diabetes, serum resistin levels are correlated with levels of soluble tumor necrosis factor alpha receptor, an inflammatory marker linked to obesity, insulin resistance, and atherosclerosis.

CONCLUSIONS

Inflammation is a hyperresistinemic state in humans, and cytokine induction of resistin may contribute to insulin resistance in endotoxemia, obesity, and other inflammatory states.