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

We explore the use of [N-15,C-13]leucine tracer to estimate whole-body fractional rates of a fast-turning-over protein pool employing synthetic data. The kinetics of [N-15,C-13]leucine tracer are simplified compared with those of traditional leucine tracers and benefit from irreversible transamination to [C-13]alpha-ketoisocaproaic acid (KIC) resulting in a simplified model structure. A three-compartment model of [N-15,C-13]leucine kinetics was proposed and evaluated using data generated by a Reference Model (based on a model by Cobelli et al.). The results suggest that fractional turnover rates of a fast-turning-over protein pool can be estimated with low but acceptable precision during a six-hour constant intravenous infusion of [N-15,C-13]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 the measurement of protein kinetics and its full potential should be explored in clinical studies with compartmental data analysis. (C) 1999 Academic Press.