Fenofibrate inhibits adipocyte hypertrophy and insulin resistance by activating adipose PPARalpha in high fat diet-induced obese mice

Abstract

Peroxisome proliferator-activated receptor alpha (PPARalpha) activation in rodents is thought to improve insulin sensitivity by decreasing ectopic lipids in non-adipose tissues. Fenofibrate, a lipid-modifying agent that acts as a PPARalpha agonist, may prevent adipocyte hypertrophy and insulin resistance by increasing intracellular lipolysis from adipose tissue. Consistent with this hypothesis, fenofibrate decreased visceral fat mass and adipocyte size in high fat diet-fed obese mice, and concomitantly increased the expression of PPARalpha target genes involved in fatty acid beta-oxidation in both epididymal adipose tissue and differentiated 3T3-L1 adipocytes. However, mRNA levels of adipose marker genes, such as leptin and TNFalpha, were decreased in epididymal adipose tissue by fenofibrate treatment. Fenofibrate not only reduced circulating levels of free fatty acids and triglycerides, but also normalized hyperinsulinemia and hyperglycemia in obese mice. Blood glucose levels of fenofibrate-treated mice were significantly reduced during intraperitoneal glucose tolerance test compared with obese controls. These results suggest that fenofibrate-induced fatty acid beta-oxidation in visceral adipose tissue may be one of the major factors leading to decreased adipocyte size and improved insulin sensitivity.

Figure 1

Body weight and adipose tissue mass after fenofibrate treatment. Adult male mice received a low fat, high fat, or fenofibrate-supplemented (FF; 0.05% w/w) high fat diet for seven weeks. All values are expressed as the mean ± SD. (A) Body weights at the end of the treatment period are significantly different when comparing the high fat group to the low fat or high fat plus FF (P < 0.05) groups. (B) Total and visceral adipose tissues were measured at the end of the study. ^*P < 0.05 compared with low fat group, ^**P < 0.05 compared with high fat group.

Figure 2

Histology of epididymal white adipose tissue. Adult male mice received a low fat, high fat, or fenofibrate-supplemented (FF; 0.05% w/w) high fat diet for seven weeks. (A) Representative hematoxylin and eosin-stained sections (5 µm thick) of epididymal adipose tissue. Adipocyte size from high fat plus FF groups was smaller than that from high fat groups. The size (B) and number (C) of adipocytes in a fixed area (1,000,000 µm²) were measured. All values are expressed as the mean ± SD. ^*P < 0.05 compared with low fat group, ^**P < 0.05 compared with high fat group.

Figure 3

The mRNA expression levels of PPARα target genes in visceral adipose tissue of obese mice. (A) The relative mRNA expression of PPARα target enzymes was measured in obese mice after fenofibrate treatment. RNA was extracted from epididymal adipose tissue, and mRNA levels of PPARα target enzymes and β-actin were measured as described in the Methods. All values are expressed as the mean ± SD of R.D.U. (relative density units) using β-actin as a reference. ^*P < 0.05 compared with high fat group. (B) Representative PCR bands from one of three independent experiments are shown. ACOX, acyl-CoA oxidase; HD, enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase; MCAD, medium chain acyl-CoA dehydrogenase.

Figure 4

The mRNA expression levels of PPARα target genes in differentiated 3T3-L1 adipocytes. (A) The relative mRNA expression of PPARα target enzymes was measured in differentiated 3T3-L1 adipocytes after Wy14,643 (Wy) treatment. RNA was extracted from differentiated 3T3-L1 adipocytes, and mRNA levels of PPARα target enzymes and β-actin were measured as described in Methods. All values are expressed as the mean ± SD of R.D.U. (relative density units) using β-actin as a reference. ^*P < 0.05 compared with control group. (B) Representative PCR bands from one of three independent experiments are shown. ACOX, acyl-CoA oxidase; HD, enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase; MCAD, medium chain acyl-CoA dehydrogenase.

Figure 5

The mRNA expression levels of adipocyte marker genes in visceral adipose tissue of obese mice. (A) Adult male mice received a high fat diet or fenofibrate-supplemented (FF; 0.05% w/w) high fat diet for seven weeks. RNA was extracted from epididymal adipose tissue and mRNA levels of leptin, TNFα, and β-actin were measured as described in the Methods. All values are expressed as the mean ± SD of R.D.U. (relative density units) using β-actin as a reference. (B) Representative PCR bands from one of three independent experiments are shown. ^*P < 0.05 compared with high fat group.

Figure 6

Changes in blood glucose levels during intraperitoneal glucose tolerance test. Adult male mice received a high fat diet or fenofibrate-supplemented (FF; 0.05% w/w) high fat diet for seven weeks. After a twelve-hour fast, mice intraperitoneally received glucose (2 g/kg body weight). All values are expressed as the mean ± SD. ^*P < 0.05 compared with high fat group.