Methionine kinetics and first pass disappearance in healthy adolescents

Abstract

Methionine, an indispensable amino acid serves as precursor for important substrates. There are no data on methionine first‐pass disappearance (SU) and whole body kinetics in healthy children receiving methionine by the oral or intravenous route. We studied four healthy adolescents, (age 15.0±1.2 y; wt 51.9±6.3 kg) receiving a 2 day dietary period providing adequate energy and protein intakes. On day 3 the subjects received a dual, primed, 8h, continuous tracer infusion of L‐[13C]‐ and L‐[2H3]‐methyl methionine by the intravenous and enteral routes respectively, while consuming small isocaloric and isonitrogenous meals every 30 min. On the next day the route of tracer administration was reversed. HCY/Meth ratios were 0.89 and 0.66 respectively for the oral and IV tracers, while the SU of 13C‐ and 2H3‐methionine labels were 29±0.13% and 31±0.13 % respectively. Methionine transmethylation (TM), remethylation (RM) and transulfuration (TS) were 33±10, 14±5 and 18±6, and 23±3, 11±2 and 11±4 µmol/kg/h respectively, for the oral and IV tracer routes using HCY enrichment as precursor; and 29±19, 13±5 and 16±5 and 15±4, 8±2 and 7±4 µmol/kg/h respectively, for the oral and IV tracer routes when methionine enrichment was used. In this preliminary data, methionine SU in healthy adolescents was between 29‐31% and about 50% of methionine plasma flux was utilized for TM when the tracer was given by the oral route, while 22 and 28% were utilized for TS and RM respectively. Hence, the intestinal tract is a major site of whole body methionine TM. NIH DK‐62363, T32 HD‐007445, Ajinomoto 3‐ARP; USDA/ARS 25337387