High-fat diet induces skeletal muscle oxidative stress in a fiber type-dependent manner in rats

This study investigated the effects of high-fat (HF) diet on parameters of oxidative stress among muscles with distinct fiber type composition and oxidative capacities. To accomplish that, male Wistar rats were fed either a low-fat standard chow (SC) or a HF diet for 8 weeks. Soleus, extensor digitorum longus (EDL), and epitrochlearis muscles were collected and mitochondrial H₂O₂ (mtH₂O₂) emission, palmitate oxidation, and gene expression and antioxidant system were measured. Chronic HF feeding enhanced fat oxidation in oxidative and glycolytic muscles. It also caused a significant reduction in mtH₂O₂ emission in the EDL muscle, although a tendency towards a reduction was also found in the soleus and epitrochlearis muscles. In the epitrochlearis, HF diet increased mRNA expression of the NADPH oxidase complex; however, this muscle also showed an increase in the expression of antioxidant proteins, suggesting a higher capacity to generate and buffer ROS. The soleus muscle, despite being highly oxidative, elicited H₂O₂ emission rates equivalent to only 20% and 35% of the values obtained for EDL and epitrochlearis muscles, respectively. Furthermore, the Epi muscle with the lowest oxidative capacity was the second highest in H₂O₂ emission. In conclusion, it appears that intrinsic differences related to the distribution of type I and type II fibers, rather than oxidative capacity, drove the activity of the anti- and pro-oxidant systems and determine ROS production in different skeletal muscles. This also suggests that the impact of potentially deleterious effects of ROS production on skeletal muscle metabolism/function under lipotoxic conditions is fiber type-specific.

Antilipolytic and antilipogenic effects of the CPT-1b inhibitor oxfenicine in the white adipose tissue of rats

Oxfenicine is a carnitine-palmitoyl transferase 1b (CPT-1b)-specific inhibitor that has been shown to improve whole body insulin sensitivity while suppressing fatty acid (FA) oxidation and increasing circulating FA. Because the white adipose tissue (WAT) is an organ that stores and releases FAs, this study investigated whether oxfenicine-induced inhibition of FA oxidation affected adiposity and WAT metabolism in rats fed either low (LF) or high-fat (HF) diets. Following 8 wk of dietary intervention, male Sprague-Dawley rats were given a daily intraperitoneal injection of oxfenicine (150 mg/kg body wt) or vehicle (PBS) for 3 wk. Oxfenicine treatment reduced whole body fat oxidation, body weight, and adiposity, and improved insulin sensitivity in HF-fed rats. All of these effects occurred without alterations in food intake, energy expenditure, and ambulatory activity. In vivo oxfenicine treatment reduced FA oxidation and lipolysis in subcutaneous inguinal (SC Ing) adipocytes, whereas glucose incorporation into lipids (lipogenesis) was significantly reduced in both SC Ing and epididymal (Epid) adipocytes. In summary, our results show that oxfenicine-induced inhibition of CPT-1b markedly affects WAT metabolism, leading to reduced adiposity through a mechanism that involves reduced lipogenesis in the SC Ing and Epid fat depots of rats.