Submitted on January 26, 2008
Accepted on August 8, 2008
Reduced citrulline availability by OTC-deficiency in mice is related to reduced nitric oxide production
Yvette Charlotte Luiking1, Marcella M Hallemeesch2, W.J. de Jonge3, Wouter H. Lamers4, and Nicolaas E. Deutz1*
1 Center for Translational Research in Aging & Longevity, University of Arkansas for Medical Sciences, Little Rock, Arkansas, United States
2 Department of Surgery, Maastricht University, Maastricht, Netherlands
3 Department of Gastroenterology, Academic Medical Centre, Amsterdam, Netherlands
4 Department of Anatomy & Embryology, Maastricht University, Amsterdam, Netherlands
* To whom correspondence should be addressed. E-mail: nep.deutz{at}ctral.org.
The amino acid arginine is the sole precursor for nitric oxide (NO) synthesis. We recently demonstrated that an acute reduction of circulating arginine does not compromise basal or lipopolysaccharide (LPS)-inducible NO production in mice. In the present study, we investigated the importance of citrulline availability in ornithine transcarbamoylase-deficient spfash (OTCD) mice on NO production, using stable isotope techniques and C57BL6/J (wild-type) mice controls.
Plasma amino acids and tracer-tracee ratios were measured by LC-MS. NO production was measured as the in vivo conversion of L-[guanidino -15N2]arginine to L-[guanidine-15N]citrulline; de novo arginine production as conversion of L-[ureido-13C-5,5-2H2]citrulline to L-[guanidino -13C-5,5-2H2]arginine. Protein metabolism was measured using L-[ring-2H5]phenylalanine and L-[ring-2H2]tyrosine.
OTC deficiency caused a reduction of systemic citrulline concentration and production to 30-50% (P<0.001), reduced de novo arginine production (P<0.05), reduced whole-body NO production to 50% (P<0.005) and increased net protein breakdown by a factor 2-4 (P<0.001). NO production was 2-fold higher in female than in male OTCD mice, in agreement with the X-linked location of the OTC gene. In response to LPS treatment (10 mg/kg i.p.), circulating arginine increased in all groups (P<0.001), and NO production was no longer affected by the OTC deficiency due to increased net protein breakdown as a source for arginine.
Our study shows that reduced citrulline availability is related to reduced basal NO production via reduced de novo arginine production. Under basal conditions this is probably c-NOS mediated NO production. When sufficient arginine is available after LPS stimulated net protein breakdown, NO production is unaffected by OTC deficiency.
