Improved methodology to assay carnitine and levels of free and total carnitine in human plasma.

Carnitine, once known as vitamin Bt, is intrinsic to human tissue and is biochemically established as being acylated with fatty acids by Acyl-CoA to give Acyl-carnitines which then are transported to the inner mitochondrial membrane by a translocase. Carnitine is of increasing clinical interest and importance, and endomyocardial deficiencies of carnitine have been reported for patients in heart failure. Consequently, a reproducible and accurate analysis of human tissue specimens for levels of free carnitine and Acyl-carnitine to guide and to support continuing clinical studies of disease states is needed. We have devised an analytical method which utilizes 5,5'-dithiobis-2-nitro-benzoate and demonstrated recovery, reproducibility and precision. Hydrolysis of a specimen at 90 degrees C for 15 min, and control of pH below 6.0 are critical steps. The mean levels of free carnitine and total carnitine in 17 ordinary subjects were 50.6 +/- 9.7 nmol./ml and 62.6 +/- 11.7 nmol./ml. respectively.