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This Article Full Text Full Text (PDF) All Versions of this Article: 297/4/G840    most recent 90716.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Miki, K. Articles by Delude, R. L. PubMed PubMed Citation Articles by Miki, K. Articles by Delude, R. L.

INFLAMMATION/IMMUNITY/MEDIATORS

Extracellular activation of arginase-1 decreases enterocyte inducible nitric oxide synthase activity during systemic inflammation

¹Departments of Critical Care Medicine, and ²Pathology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania

Submitted December 22, 2008 ; accepted in final form August 20, 2009

Liver dysfunction secondary to severe inflammation is associated with the release of enzymes normally sequestered within hepatocytes. The purpose of these studies was to test the hypothesis that these enzymes are released, at least in part, to modulate potentially deleterious inflammatory processes in distant tissues like the gut. Human Caco-2_BBe enterocyte-like cells were exposed to cytomix (IFN-, TNF-, and IL-1β) in the absence or presence of human liver cytosol (LC). Nitric oxide (NO^•) and inducible nitric oxide synthase (iNOS) protein production were measured by the Griess assay and Western analysis, respectively. Cytomix induced the expression of iNOS and release of NO^•. LC protein (400 µg/ml) added to the basal compartment but not apical compartment completely blocked the release of NO^• but only slightly decreased the magnitude of iNOS protein induction. Ultrafiltration and ultracentrifugation studies demonstrated that microsome-associated arginase-1 activity was the iNOS-suppressing activity in LC. Liver arginase required activation by a <10-kDa factor that was present in supernatants of cytomix-stimulated cells. The selective iNOS inhibitor L-N⁶-(1-iminoethyl)-lysine·2HCl prevented production of this factor. The biotin switch assay detected increased S-nitrosylation of arginase-1 after incubation with supernatants from immunostimulated Caco-2 cells. Serum from endotoxemic mice contained significantly greater arginase activity compared with serum from control mice. Furthermore, the ratio of mucosal monomeric to dimeric iNOS increased in endotoxemic mice compared with controls. Thus reciprocal activation of arginase-1 and modulation of mucosal iNOS activity may be protective because it would be expected to decrease NO^•-dependent intestinal barrier dysfunction on that basis.

shock; systemic inflammatory response syndrome; liver damage