The primary carnitine deficiency syndromes are potentially fatal afflictions of children and adults. The exact etiologies of these syndromes are not known. Previous studies in this laboratory ruled out a defect in carnitine biosynthesis from Epsilon-trimethyl (TML) or abnormal degradation of carnitine in primary systemic carnitine deficiency (SCD). We identified a renal carnitine leak in SCD patients, but our studies showed that this defect could not fully account for clinical features of the syndrome. Primary SCD may be caused by defective methylation of lysine (the first step in carnitine biosynthesis), by defective transport of carnitine into tissues or by altered regulation of carnitine concentration gradients within tissues. Primary muscle (myopathic) carnitine deficiency (MCD) is thought to be due to defective transport of carnitine into tissues. We propose to quantitate TML (free and protein-bound) in muscle, plasma and urine of SCD patients and normal subjects, to determine the availability of this substrate for carnitine biosynthesis and hence as a measure of lysine methylation in these subjects. Also, using dietary manipulation with TML we will test the hypothesis that the rate of carnitine biosynthesis in rats is determined by the availability of TML. Studies of carnitine transport across rat skeletal muscle sarcolemma and renal brush border membranes (BBM) are designed to develop a better understanding of basic mechanisms of carnitine transport and retention in tissues, and their regulation. These studies will include kinetics and specificity and hormonal effects on carnitine transport across renal BBM, binding of carnitine to solubilized protein preparations from sarcolemma and BBM, and studies of kinetics and hormonal influences on carnitine metabolism in the isolated, perfused rat hindquarter. Finally, we will measure carnitine-acylcarnitine translocase activity in isolated mitochondria from normal subjects and a patient with an atypical form of SCD who is suspected of having a deficiency of this transport activity.
| Lehman, L J; Olson, A L; Rebouche, C J (1987) Measurement of epsilon-N-trimethyllysine in human blood plasma and urine. Anal Biochem 162:137-42 |
| Rebouche, C J; Lehman, L J; Olson, L (1986) epsilon-N-trimethyllysine availability regulates the rate of carnitine biosynthesis in the growing rat. J Nutr 116:751-9 |
