Effect of oral citrulline supplementation on whole body protein metabolism in adult patients with short bowel syndrome: A pilot, randomized, double-blind, cross-over study.

BACKGROUND & AIMS: As citrulline is produced by small intestine, plasma citrulline concentration is decreased and may become essential in patients with short bowel syndrome (SBS). In a rat model of SBS, citrulline supplementation enhanced muscle protein synthesis. The aim of the study was to determine whether citrulline impacts whole body protein metabolism in patients with SBS. METHODS: Nine adults with non-malignant SBS (residual small bowel 90 ± 48 cm; mean ± SD) who were in near-normal nutritional status without any artificial nutrition, were recruited long after surgery. They received 7-day oral supplementation with citrulline (0.18 g/kg/day), or an iso-nitrogenous placebo in a randomized, double-blind, cross-over design with a 13-day wash-out between regimens, and an intravenous 5-h infusion of L-[1-13C]-leucine in the postabsorptive state to assess protein metabolism after each regimen. RESULTS: Plasma citrulline concentration rose 17-fold (25 ± 9 vs. 384 ± 95 µmol/L) and plasma arginine 3-fold after oral citrulline supplementation (both p < 4 × 10-6). Supplementation did not alter leucine appearance rate (97 ± 5 vs. 97 ± 5 µmol kg-1.h-1; p = 0.88), leucine oxidation (14 ± 1 vs. 12 ± 1 µmol kg-1.h-1; p = 0.22), or non-oxidative leucine disposal (NOLD), an index of whole-body protein synthesis (83 ± 4 vs. 85 ± 5 µmol kg-1.h-1; p = 0.36), nor insulin or IGF-1 plasma concentrations. In each of the 3 patients with baseline citrulline<20 µmol/L, citrulline supplementation increased NOLD. Among the 7 patients with plasma citrulline <30 µmol/L, the effect of supplementation on NOLD correlated inversely (r2 = 0.81) with baseline plasma citrulline concentration. CONCLUSION: 1) Oral citrulline supplementation enhances citrulline and arginine bioavailability in SBS patients. 2) Oral citrulline supplementation does not have any anabolic effect on whole body protein metabolism in patients with SBS in good nutritional status, in the late phase of intestinal adaptation, and with near-normal baseline citrulline homeostasis. 3) Whether oral citrulline would impact whole body protein anabolism in severely malnourished SBS patients in the early adaptive period, and with baseline plasma citrulline below 20 µmol/L, warrants further study. Registered under ClinicalTrials.gov Identifier no. NCT01386034.

Oral citrulline does not affect whole body protein metabolism in healthy human volunteers: results of a prospective, randomized, double-blind, cross-over study.

BACKGROUND & AIMS: Citrulline increases protein synthesis during refeeding in rodents with short bowel syndrome, aging and malnutrition, and improves nitrogen balance in fed healthy humans. The aim of the current study therefore was to determine whether citrulline had affected protein metabolism in healthy volunteers. METHODS: In a randomized, double-blind, cross-over study, 12 healthy adults received a 5-h intravenous infusion of L-[1-(13)C]-leucine in the post-absorptive state, after a 7-day oral supplementation with 0.18 g/kg/day citrulline, or an iso-nitrogenous placebo. Treatment order was randomized, treatment periods were separated by 13-day wash out. Leucine appearance rate (Ra) was determined from plasma [1-(13)C]-keto-iso-caproate enrichment and leucine oxidation from expired (13)CO(2), and nitrogen balance was estimated from 6-h urinary urea excretion. RESULTS: Compared with placebo, oral citrulline supplementation increased plasma citrulline, arginine and ornithine concentrations, but failed to affect albumin, transthyretin, free insulin and insulin-like growth factor (IGF)-1 plasma concentrations, urinary nitrate excretion, or nitrogen balance. Citrulline supplementation did not alter leucine Ra, leucine oxidation, nor whole-body protein synthesis. CONCLUSION: In healthy, well nourished volunteers, oral citrulline increases plasma citrulline and arginine availability but does not affect whole-body protein kinetics in the post-absorptive state.