Arginase activity in endothelial cells: inhibition by g
-hydroxyarginine during high-output nitric oxide production.
Buga, Georgette M., Rajan Singh, Shehla Pervin, Norma E. Rogers, Debra
A. Schmitz, Christopher P. Jenkinson, Stephen D. Cederbaum, and Louis
J. Ignarro.
Departments of Molecular Pharmacology, Psychiatry, Pediatrics and
Obstetrics & Gynecology, UCLA School of Medicine, Center for the
Health Sciences, Los Angeles, California 90095
APStracts 3:0252H, 1996.
Rat aortic endothelial cells were found to contain both constitutive
and lipopolysaccharide (LPS)-inducible arginase activity. Studies
were performed to determine whether induction of nitric oxide
synthase (NOS) by LPS and cytokines is accompanied by sufficient
arginase induction to render arginine concentrations rate-limiting
for high-output NO production. Unactivated cells contained abundant
arginase activity accompanied by continuous urea formation. LPS
induced the formation of both inducible NOS (iNOS) and arginase, and
this was accompanied by increased production of NO, citrulline and
urea. Immunoprecipitation experiments revealed the constitutive
presence of arginase-I in both unactivated and LPS-activated cells,
and arginase-II induction by LPS. Arginase-I and iNOS were verified
by reverse transcriptase-polymerase chain reaction. The induction of
large amounts of iNOS by LPS plus several cytokines resulted in the
production of large quantities of NO, citrulline and NG
-hydroxyarginine (NOHA) but urea production was markedly diminished.
Decreased urea production was attributed to increased formation of
NOHA, the precursor to NO and citrulline, and a potent inhibitor of
arginase-I activity with a Ki of 10-12 [mu]M. Inhibition of iNOS
activity by NG-methylarginine decreased NO and NOHA production and
increased urea production. This study reveals for the first time that
substantial arginase activity is present constitutively in rat aortic
endothelial cells, a different isoform of arginase is induced by LPS,
and intracellular arginase activity can be markedly inhibited during
cytokine induction of iNOS because of formation of NOHA. The
inhibition of arginase activity that occurs by NOHA during marked
iNOS induction may be a mechanism to ensure sufficient arginine
availability for high-output production of NO.
Received 29 February 1996; accepted in final form 15 May 1996.
APS Manuscript Number H202-6.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 28 June 96