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

Miki K, Kumar A, Yang R, Killeen ME, Delude RL. Extracellular activation of arginase-1 decreases enterocyte inducible nitric oxide synthase activity during systemic inflammation. Am J Physiol Gastrointest Liver Physiol 297: G840-G848, 2009. First published August 27, 2009; doi: 10.1152/ajpgi.90716.2008.-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-gamma, TNF-alpha, and IL-1 beta) in the absence or presence of human liver cytosol (LC). Nitric oxide (NO center dot) 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 center dot. LC protein (400 mu g/ml) added to the basal compartment but not apical compartment completely blocked the release of NO center dot 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-N-6-(1-iminoethyl)-lysine center dot 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 center dot-dependent intestinal barrier dysfunction on that basis.