Estimating protein turnover with a [N-15,C-13]leucine tracer: a study using simulated data

We explore the use of [N-15,C-13]leucine tracer to estimate whole-body frac tional rates of a fast-turning-over protein pool employing synthetic data. The kinetics of [N-15,C-13]leucine tracer are simplified compared with thos e of traditional leucine tracers and benefit from irreversible transaminati on to [C-13]alpha-ketoisocaproaic acid (KIC) resulting in a simplified mode l structure. A three-compartment model of [N-15,C-13]leucine kinetics was p roposed and evaluated using data generated by a Reference Model (based on a model by Cobelli et al.). The results suggest that fractional turnover rat es of a fast-turning-over protein pool can be estimated with low but accept able precision during a six-hour constant intravenous infusion of [N-15,C-1 3]leucine with frequent sampling of plasma tracer-to-tracee ratio (TTR) of [N-15,C-13]leucine. We conclude that [N-15,C-13]leucine may be useful for t he measurement of protein kinetics and its full potential should be explore d in clinical studies with compartmental data analysis. (C) 1999 Academic P ress.