[Cysteine in parenteral nutrition: comparative study of N-acetyl-cysteine and N,N-diacetylcystine in the rat model].

In this study the question of whether N-N-diacetylcystine (DAC), which is more stable than N-acetylcysteine (AcCYS), may provide a useful cysteine source for parenteral nutrition was investigated. In in vitro studies the release of cysteine from DAC was measured. The Michaelis, constant and maximum velocity were compared with the corresponding results for AcCYS. In in vivo studies 3 groups of growing rats were maintained entirely by parenteral nutrition low in methionine for 15 days. Group I (n = 4) received a solution containing AcCYS, and group II (n = 6) was supplied with a corresponding amount of DAC. In the solution given to group III (n = 6) the CYS derivative was replaced by an isonitrogeneous amount of glycine. Utilization of the respective CYS derivatives was judged from weight gain, nitrogen balance, plasma amino acid pattern, and urinary excretion of free amino acids. The results from both the in vitro and in vivo studies indicate that DAC is not a suitable substitute for AcCYS in parenteral nutrition.