Age and Sex Dependency of Carnitine Concentration in Human Serum and Skeletal Muscle

Abstract

Carnitine plays an essential role in fatty acid metabolism. It can be synthesized in the liver, but additional intestinal resorption is necessary (1). Carnitine mediates the transport of activated acyl residues via the carnitine palmityl transferase system into mitochondria for β-oxidation (2). Whereas primary carnitine deficiency is attributable to mutations in OCTN2 [a carnitine transporter of plasma membranes (3)], several other conditions can cause secondary deficiency (4). The leading symptom of either primary or secondary carnitine deficiency is weakness of skeletal muscles. In addition to these pathologic conditions in some animal models, a physiologic decline of carnitine concentration with aging has been reported (5)(6). In addition to increasing muscular carnitine concentrations (6), oral treatment with l-carnitine or its acetyl ester has also been shown to restore many of physiologic impairments that accompany aging (7)(8)(9)(10). These data indicate the important role of carnitine in the aging process, at least in mice and rats. For human skeletal muscle, confusing results exist with respect to the age dependency of carnitine content: Whereas Costell et al. (5) found a “drastic” age-dependent decrease of carnitine in human skeletal muscle and Gonzalez-Crespo et al. (11) detected reduced free carnitine concentrations in elderly patients undergoing hip surgery, an age-dependent decrease in carnitine concentration could not be confirmed by Starling et al. (12). The answer to the question of whether carnitine in human muscle is also age dependent is hampered by the different populations investigated and the different methods used. No reliable data exist concerning the sex dependency of a possible age-dependent variation. The present study seeks to clarify whether carnitine concentrations in human skeletal muscle and serum depend on age and sex. The physiologic relevance is discussed. Analysis of carnitine in serum was performed in samples from healthy …