Tissue Carnitine Deficiency due to Dietary Lysine Deficiency: Triglyceride Accumulation and Concomitant Impairment in Fatty Acid Oxidation

Abstract

Since the essential amino acid lysine is a precursor of carnitine, the effects of a cereal diet unsupplemented or supplemented with limiting amino acids or carnitine, on carnitine and lipid levels in tissues and fatty acid oxidation in heart of rats were examined. Male weanling rats were fed either a diet providing approximately 5% protein from wheat or 16% protein from casein for a period of 10 weeks. The wheat diet severely impaired growth and diminished carnitine levels in plasma and skeletal muscle, but not heart, or liver. Oxidation of [1-¹⁴C]palmitate by the 600 × g supernatant fraction of heart homogenate was also markedly impaired in the wheat diet fed rats and could not be fully restored by the addition of carnitine to the incubation mixture. Triglyceride content of heart, skeletal muscle and liver and total lipids in liver were markedly elevated in these rats. Supplementation of wheat diet with 0.2% carnitine produced significant increase in plasma, muscle and liver carnitine levels, restored fatty acid oxidation and reduced the triglyceride load of the tissues, without affecting growth. Supplementation of wheat diet with lysine and threonine at 0.2% level (keeping the food intake the same as the unsupplemented group), improved growth, muscle carnitine levels and palmitate oxidation, and diminished the triglyceride level of tissues. Food restriction per se, raised palmitate oxidation by heart. Data suggest that carnitine is an essential nutrient, and its supply has to be ensured either through adequate intake of precursor amino acids lysine and methionine or through preformed carnitine.