First‐pass disappearance of cysteine in healthy adolescents

Abstract

Cysteine (Cys), a dispensable amino acid serves as a precursor for some important substrates, such as glutathione and taurine. There are no data on Cys first‐pass disappearance in healthy children receiving cysteine by oral (PO) or intravenous (IV) route. We studied 10 healthy adolescents (age 15.8±1.8 y; wt 56.1±8.4 kg), receiving a 2‐day dietary period providing adequate energy and protein intakes. On day 3, subjects received a dual, primed, 6h, continuous tracer infusion of L‐13C‐ and L‐2H2‐Cys by the IV and PO routes randomly, while consuming small isocaloric and isonitrogenous meals every 30 min. The following day the route of tracer administration was reversed. The first‐pass disappearance of 13C‐ and 2H2‐Cys labels was 40.9±9.2% and 45.4±7.6 %, respectively, and there's no tracer effect (P = 0.11). Cys was oxidized to a greater extent by the PO route in contrast to the IV route (28 vs. 19%; P < 0.01). True Cys flux determined by plasma ApoB‐100 enrichment was significantly higher when the tracer was given IV (P < 0.001), suggesting that the splanchnic region is a major site of whole body cysteine utilization during the fed state. NIH DK‐62363, T32 HD‐007445, Ajinomoto 3‐ARP; USDA/ARS 25337387