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Reduced citrulline production in sepsis is related to diminished de novo arginine and nitric oxide production^1,2,3

¹ From the Center for Translational Research in Aging & Longevity, Donald W. Reynolds Institute on Aging, University of Arkansas for Medical Sciences, Little Rock, AR (YCL and NEPD), and the Departments of Surgery and Intensive Care, Maastricht University Hospital, Maastricht University, Maastricht, Netherlands (YCL, MP, GR, and NEPD)

² Supported by internal funds from Maastricht University.

³ Reprints not available. Address correspondence to NEP Deutz, Center for Translational Research in Aging & Longevity, Room 3.121, Donald W. Reynolds Institute on Aging, University of Arkansas for Medical Sciences, 4301 West Markham Street, Slot 807, Little Rock, AR 72205. E-mail: nep.deutz{at}ctral.org.

ABSTRACT

Background: L-Arginine is an important precursor of nitric oxide (NO) and protein synthesis. Arginine is produced in the body (mainly kidney) by de novo production from citrulline and by protein breakdown. Arginine availability appears to be limited in sepsis.

Objective: The objective was to compare arginine and citrulline metabolism in septic patients and nonseptic control patients in an intensive care unit (ICU) and in healthy control subjects.

Design: Ten patients with septic shock, 7 critically ill control patients, and 16 healthy elderly subjects were studied. Metabolism was measured by using a primed continuous (2 h) stable-isotope infusion protocol. NO production was calculated as the conversion rate of arginine to citrulline; de novo arginine production was calculated as the conversion rate of citrulline to arginine. Arterial blood (arterialized venous blood in healthy subjects) was collected for the measurement of amino acid enrichment and concentrations. Data are reported as means ± SDs.

Results: Whole-body citrulline production was significantly lower in septic patients (4.5 ± 2.1 µmol · kg^–1 · h^–1) than in ICU control patients (10.1 ± 2.9 µmol · kg^–1 · h^–1; P < 0.01) and in healthy control subjects (13.7 ± 4.1 µmol · kg^–1 · h^–1; P < 0.001). Accordingly, de novo arginine production was lower in patients with sepsis (3.3 ± 3.7 µmol · kg^–1 · h^–1) than in healthy controls (11.9 ± 6.6 µmol · kg^–1 · h^–1; P < 0.01) and tended to be lower in septic patients than in ICU control patients (10.9 ± 9.4 µmol · kg^–1 · h^–1; P = 0.05). NO production was lower in septic patients than in healthy control subjects (P < 0.01), whereas a larger part of arginine was converted to urea in sepsis.

Conclusions: Citrulline production is severely low in patients with sepsis and is related to diminished de novo arginine and NO production. These metabolic alterations contribute to reduced citrulline and arginine availability, and these findings warrant further studies of therapeutic nutritional interventions to restore arginine metabolism in sepsis.

Received for publication December 16, 2007. Accepted for publication September 16, 2008.

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