Leucine metabolism in cirrhotic patients with hepatic encephalopathy

The purpose of this study was to determine whether increased oxidation of or protein synthesis requiring leucine occurs in cirrhotic patients. Five control subjects and four subjects with cirrhosis were equilibrated on a baseline diet (0.6 g protein per kg ideal body weight [IBW]) with sufficient nonprotein calories to preclude negative nitrogen balance. An additional four patients were equilibrated on the same type of diet with a higher protein level (0.75 g per kg IBW). Control subjects and the patients were then studied during continuous infusion of L-[15N, 1-13C] leucine in the fasted state and, in the fed state, with a Propac diet which had the same distribution of energy nutrients as the baseline diets. Plasma levels of L-[15N, 1-13C], L-[1-13C] and L-[15N] leucine were measured during isotopic steady state by gas chromatography-mass spectrometry and fractional excretion of 13CO2 in breath samples were analyzed by isotopic ratio mass spectrometry. During the fasted and fed states leucine metabolism was measured to quantitate rates of nitrogen flux (Q/sub N/), carbon flux (Q/sub c/) and oxidation to carbon dioxide and water (C). From these measured values, proteins breakdown (B), protein synthesis (S), deamination (X0) and reamination (X/sub N/) were calculated. The results showed that protein synthesis and leucine metabolism were identical in controls and patients when both were fed a diet with 0.6 g protein/kg IBW and maintenance level of nonprotein calories. The data also showed that leucine metabolism can be quantitatively and reproducibly measured in subjects with cirrhosis