The PPARα Agonists Fenofibrate and CP-778875 Cause Increased β-Oxidation, Leading to Oxidative Injury in Skeletal and Cardiac Muscle in the Rat

Weak peroxisome proliferator-activated receptor (PPAR) alpha agonists (fibrates) are used to treat dyslipidemia. This study compared the effects of the potent and selective PPAR alpha agonist CP-778875 on peroxisomal beta-oxidation and cardiac and/or skeletal muscle injury with those of the weak PPAR alpha agonist fenofibrate. We hypothesized that these muscle effects are mediated through the PPAR alpha receptor, leading to increased beta-oxidation and consequent oxidative stress. CP-778875 (5 or 500 mg/kg) and fenofibrate (600 or 2,000 -> 1,200 mg/kg, dose lowered because of intolerance) were administered to rats for six weeks. Standard end points, serum troponin I, heart and skeletal muscle beta-oxidation of palmitoyl-CoA, and acyl co-oxidase (AOX) mRNA were assessed. Both compounds dose-dependently increased the incidence and/or severity of cardiomyocyte degeneration and necrosis, heart weight, troponin I, and skeletal muscle degeneration. Mean heart beta-oxidation (3.4- to 5.1-fold control) and AOX mRNA (2.4- to 3.2-fold control) were increased with CP-778875 500 mg/kg and both doses of fenofibrate. beta-Oxidation of skeletal muscle was not affected by either compound; however, a significant increase in AOX mRNA (1.6- to 2.1-fold control) was observed with CP-778875 500 mg/kg and both doses of fenofibrate. Taken together, these findings were consistent with PPAR alpha agonism and support the link between increased cardiac and skeletal muscle beta-oxidation and resultant muscle injury in the rat.