Induction of heme-oxygenase 1 inhibits endothelial cell activation by endotoxin and oxidant stress.
BACKGROUND
Increased oxidant stress has been implicated in a number of disease states, including systemic inflammation caused by ischemia/reperfusion injury or sepsis. We have demonstrated previously that oxidants enhance the proinflammatory response to endotoxin (lipopolysaccharide), although antioxidants inhibit this response. Heme-oxygenase 1 (HO-1) is an inducible, cytoprotective enzyme, which is up-regulated under conditions of oxidant stress. We hypothesized that the induction of HO-1 protein would attenuate the proinflammatory response of endothelial cells to lipopolysaccharide and oxidant stress.


METHODS
Human umbilical vein endothelial cells were pretreated with hemin (100 micromol/L) for 5 hours, and the induction of HO-1 was confirmed by Western blot. After hemin exposure, cells were treated for 1 hour with either diamide, buthione sulfoximine, xanthine oxidase, or glucose oxidase to induce oxidant stress or lipopolysaccharide to induce an inflammatory response. Interleukin 8 (IL-8) and prostaglandin I(2) (PGI(2)) production were measured by enzyme-linked immunosorbent assay; p38 kinase, p42/44 extracellular regulated kinase, and c-jun N terminal kinase activation were measured by Western blot.


RESULTS
HO-1 protein was increased 3-fold by exposure to hemin under all conditions. IL-8 production in response to lipopolysaccharide and xanthine oxidase was inhibited significantly by hemin exposure, although PGI(2) production was not affected. The up-regulation of HO-1 protein levels resulted in the inhibition of the lipopolysaccharide- and oxidant-induced activation of all 3 mitogen-activated protein kinases: p38 kinase, p42/44 extracellular regulated kinase, and c-jun N terminal kinase.


CONCLUSIONS
The induction of HO-1 by hemin results in inhibition of the proinflammatory response of endothelial cells, as evidenced by the inhibition of IL-8 production without affecting PGI(2) production. All 3 mitogen-activated protein kinase signaling cascades are affected, which suggests that the mechanism of this effect may be proximal in the cell signaling process.
Bulger
Eileen M
EM
Department of Surgery, University of Washington, Seattle, WA, USA.
Garcia
Iris
I
Maier
Ronald V
RV
D002478:Cells, Cultured; D016207:Cytokines / Q000096:biosynthesis; D004730:Endothelium, Vascular / Q000187:drug effects* / Q000502:physiology*; D004789:Enzyme Activation / Q000502:physiology; D004790:Enzyme Induction; D006419:Heme Oxygenase (Decyclizing) / Q000378:metabolism*; D051547:Heme Oxygenase-1; D006427:Hemin / Q000494:pharmacology; D006801:Humans; D016209:Interleukin-8 / Q000096:biosynthesis; D048031:JNK Mitogen-Activated Protein Kinases; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008565:Membrane Proteins; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D018384:Oxidative Stress / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects; D014969:Xanthine Oxidase / Q000494:pharmacology; D048051:p38 Mitogen-Activated Protein Kinases
D016207:Cytokines; D016209:Interleukin-8; D008070:Lipopolysaccharides; D008565:Membrane Proteins; D006427:Hemin; C496541:HMOX1 protein, human; D006419:Heme Oxygenase (Decyclizing); D051547:Heme Oxygenase-1; D014969:Xanthine Oxidase; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases