Long-term dietary effects on substrate selection and muscle fiber type in very-long-chain acyl-CoA dehydrogenase deficient (VLCAD−/−) mice

Abstract

Dietary fat restriction and increased carbohydrate intake are part of treatment in very-long-chain acyl-CoA dehydrogenase (VLCAD)-deficiency, the most common defect of long-chain fatty acid oxidation. The long-term impact of these interventions is unknown. We characterized here the effects of a fat-reduced, carbohydrate-enriched diet and an increased fat intake on energy metabolism in a mouse model of VLCAD-deficiency.Wild-type and VLCAD−/− mice were fed one year either with a normal (5.1%), a high fat (10.6%) or a low-fat, carbohydrate-enriched (2.6%) diet. Dietary effects on genes involved in lipogenesis, energy homeostasis and substrate selection were quantified by real-time-PCR. Acylcarnitines as sign of impaired energy production were determined in dried blood spots and tissues. White skeletal muscle was analyzed for muscle fiber type as well as for glycogen and triglyceride content.Both dietary modifications induced enhanced triacylglyceride accumulation in skeletal muscle and inhibition of glucose oxidation. This was accompanied by an up-regulation of genes coding for oxidative muscle fiber type I and a marked accumulation of acylcarnitines, especially prominent in the heart (164±2.8 in VLCAD−/− vs. 82.3±2.1 in WT μmol/mg) under a low-fat, carbohydrate-enriched diet.We demonstrate here that both dietary interventions with respect to the fat content of the diet reverse endogenous compensatory mechanisms in muscle that have evolved in VLCAD−/− mice resulting in pronounced energy deficiency. In particular, the low-fat carbohydrate-enriched diet was not effective in the long term. Further experiments are necessary to define the optimal energy provision for fatty acid oxidation defects.