Rosiglitazone Improves Insulin Resistance Mediated by 10,12 Conjugated Linoleic Acid in a Male Mouse Model of Metabolic Syndrome

Abstract

Trans-10, cis-12 conjugated linoleic acid (10,12 CLA) is a dietary fatty acid that promotes weight loss and disproportionate fat loss. Obese mice fed a high-fat, high-sucrose (HFHS) diet containing 10,12 CLA are resistant to weight gain and contain markedly reduced subcutaneous fat and adiponectin, with a concurrent lack of improvement in insulin sensitivity despite significant weight loss. Taken together, 10,12 CLA promotes a phenotype resembling peroxisome proliferator-activated receptor (PPAR)γ antagonism. Because thiazolidinediones such as rosiglitazone (Rosi) are used clinically to improve insulin sensitivity by activating PPARγ, with particular efficacy in subcutaneous white adipose tissue, we hypothesized that Rosi would improve glucose metabolism in mice losing weight with 10,12 CLA. Obese low-density lipoprotein receptor-deficient mice were fed a HFHS control diet, or supplemented with 1% 10,12 CLA with or without Rosi (10 mg/kg) for 8 weeks. Body composition, glucose and insulin tolerance tests, tissue gene expression, and plasma lipid analyses were performed. Mice consuming 10,12 CLA with Rosi lost weight and body fat compared with control groups, but with a healthier redistribution of body fat toward more subcutaneous adipose tissue than with 10,12 CLA alone. Further, Rosi improved 10,12 CLA-mediated insulin resistance parameters and increased plasma and subcutaneous adipose tissue adiponectin levels without adverse effects on plasma or hepatic lipids. We conclude that cotreatment of mice with 10,12 CLA and Rosi promotes fat loss with a healthier fat distribution that leads to improved insulin sensitivity, suggesting that the combination treatment strategy of 10,12 CLA with Rosi could have therapeutic potential for obesity treatment.

Figure 1.

Rosi restores 10,12 CLA-blunted Pparg gene expression and improves PPARγ nuclear translocation. 3T3-L1 differentiated adipocytes were treated with FAFA (control) or 10,12 CLA, ^+/− 1 nM Rosi. Gene expression of (a) Pparg, (c) Adipoq, and (d) Cpt1a measured using quantitative real-time polymerase chain reaction. (b) Nuclear PPARγ protein was quantified by enzyme-linked immunosorbent assay, normalized to total nuclear protein. *P < 0.05 from control; #P < 0.05 from 10,12 CLA. Data presented are mean ± standard error of the mean from three independent experiments performed in triplicate.

Figure 2.

Animal study design. Ldlr^−/− male mice were fed a HFHS diet for 14 weeks and then switched to one of four test diets for an additional 8 weeks. Rosi groups included a 2-week lead-in prior to test diets. The dose of 10,12 CLA was 1% weight-to-weight ratio, and the Rosi dose was 10 mg/kg. Measurements were obtained as indicated. n = 8 to 12 mice per group.

Figure 3.

Rosi attenuates 10,12 CLA-induced subcutaneous fat loss. (a) Body weights measured weekly. (b) Food intake measured after 1 and 5 weeks on indicated diets (15 and 19 weeks of HFHS feeding, respectively). (c) Body composition performed at baseline (B; 9 weeks of HFHS feeding), and again after 2 and 5 weeks on the indicated diets and presented as % body fat (left) and lean body mass (right). (d) Excised fat pads weighed at euthanasia. R, Rosi lead-in. n = 8 to 12 mice per group, presented as mean ± standard error of the mean. *P < 0.05 from HFHS control; #P < 0.05 from 10,12 CLA.

Figure 4.

Rosi improves glucose metabolism. (a–c) Mice were subjected to an IPGTT at baseline (B; after 10 weeks of HFHS feeding) and again after 6 weeks on indicated diets. (a) Plasma insulin measured at the 30-minute time point during the IPGTT. (b) IPGTT. (c) Area under the curve (AUC) from IPGTT. (d) Intraperitoneal insulin tolerance testing performed at baseline (11 weeks of HFHS feeding) and again after 7 weeks on indicated diets. (e) Fasting blood glucose and (f) plasma insulin levels measured at baseline (12 weeks of HFHS feeding), and again after 3 and 8 weeks on indicated diets. n = 8 to 12 mice per group, presented as mean ± standard error of the mean. *P < 0.05 from HFHS control; **P < 0.05 from baseline; #P < 0.05 from 10,12 CLA.

Figure 5.

Adipogenic gene expression is restored by Rosi, without altering FAO. Gene expressions of (a) Pparg, (b) Adipoq, (c) solute carrier family 2 member 4, (d) Dgat1, (e) Pparg, (f) Cpt1b, (i) Saa3, and (j) Mac2 were quantified from EWAT, MWAT, RWAT, and IWAT at euthanasia, presented normalized to EWAT HFHS controls. (g) Fasting plasma NEFA and (h) plasma adiponectin quantified at baseline (B; after 12 weeks of HFHS feeding), and again after 3 and 8 weeks on indicated diets. n = 8 to 12 mice per group, presented as mean ± standard error of the mean. *P < 0.05 from HFHS control; $P < 0.05 from EWAT; #P < 0.05 from 10,12 CLA.

Figure 6.

Rosi has little effect on plasma or liver lipids in combination with 10,12 CLA, but improves 10,12 CLA-mediated systemic inflammation. Fasting (a) plasma cholesterol and (b) triglycerides (TGs) quantified at baseline (B; after 12 weeks of HFHS feeding), and again after 3 and 8 weeks on indicated diets. (c) Lipoprotein profiles obtained by fast-phase liquid chromatography of pooled fasted plasma samples taken after 8 weeks on indicated diets. (d) Liver weight determined at euthanasia. (e) Liver cholesterol (chol) and (f) TGs quantified. (g) Hepatic gene expression of Saa2 quantified after 8 weeks on diets. Plasma (h) SAA and (i) IL-6 quantified at baseline (after 12 weeks of HFHS feeding) and again after 3 and 8 weeks on indicated diets. n = 8 to 12 mice per group, presented as mean ± standard error of the mean. *P < 0.05 from HFHS control; #P < 0.05 from 10,12 CLA. VLDL, very-low-density lipoprotein; HDL, high-density lipoprotein.