Extracellular activation of arginase-1 decreases enterocyte inducible nitric oxide synthase activity during systemic inflammation.
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-1beta) 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 microg/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-N(6)-(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.
Miki
Keita
K
Departments of Critical Care Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA.
Kumar
Abhai
A
Yang
Runkuan
R
Killeen
Meaghan E
ME
Delude
Russell L
RL
D000818:Animals; D001119:Arginase / Q000378:metabolism*; D015153:Blotting, Western; D018938:Caco-2 Cells; D004195:Disease Models, Animal; D015536:Down-Regulation; D020895:Enterocytes / Q000187:drug effects / Q000201:enzymology* / Q000276:immunology; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007249:Inflammation / Q000139:chemically induced / Q000201:enzymology* / Q000276:immunology; D018836:Inflammation Mediators / Q000378:metabolism; D007371:Interferon-gamma / Q000378:metabolism; D053583:Interleukin-1beta / Q000378:metabolism; D008070:Lipopolysaccharides; D008099:Liver / Q000201:enzymology* / Q000276:immunology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009569:Nitric Oxide / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II / Q000037:antagonists & inhibitors / Q000378:metabolism*; D055503:Protein Multimerization; D011499:Protein Processing, Post-Translational; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
D004791:Enzyme Inhibitors; D018836:Inflammation Mediators; D053583:Interleukin-1beta; D008070:Lipopolysaccharides; D014409:Tumor Necrosis Factor-alpha; D009569:Nitric Oxide; D007371:Interferon-gamma; C496319:NOS2 protein, human; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse; C544448:Arg1 protein, mouse; D001119:Arginase