played a critical role in protecting the liver from oxida-An iron-mediated oxidative stress caused by an intive stress. (HEPATOLOGY 1997;25:122-127.) crease of the intracellular pool of low molecular weight complex of iron (LMWC) can be observed with iron overloading or ethanol metabolism. The aim of this study
The formation of nitric oxide (NO) by different liver cell was to determine whether nitric oxide (NO) behaved as a types, including Kupffer cells and hepatocytes, during endopro-oxidant or an antioxidant in such an iron-mediated toxemia and inflammation is now well established. Also, it oxidative stress in rat hepatocytes. The cells were set up has been reported in patients with chronic liver diseases. 5 in primary cultures and incubated with lipopolysaccha-Given its main role in detoxification, the liver is exposed ride (LPS) and g-interferon (IFN) for 18 hours to induce particularly to many sources of oxidative stress such as drugs NO synthase and to trigger NO production. Then 20 and toxins (halothane, bleomycine, carbon tetrachloride, iron, mmol/L iron or 50 mmol/L ethanol were added. Oxidative adriamycin, acetaminophen, ethanol, etc.). 6,7 Small quanti- stress was evaluated by measuring lipoperoxidation usties of highly toxic reactive oxygen intermediates are proing two markers: malondialdehyde (MDA) and conjuduced continuously that the cells can usually eliminate by gated dienes. Simultaneously, NO production was folnonenzymatic and enzymatic mechanisms. However, many lowed by the quantitation of nitrites in the culture xenobiotics and metals can increase dramatically formation medium, dinitrosyl iron complexes (DNICs) and mononiof reactive oxygen intermediates leading to oxidation of liptrosyl iron complexes (MNICs) in intact hepatocytes. ids, proteins, and nucleic acids.
DNIC and MNIC, evaluated by electron paramagnetic
In the liver, the effect of NO on oxidative stress seems to resonance (EPR), corresponded to NO bound to ironbe complex and paradoxical because both pro-oxidant and containing molecules and to free NO, respectively. In antioxidant properties have been reported. In vitro, as an cultures preincubated with LPS and IFN before iron or antioxidant, NO could ''scavenge'' superoxide anion by removethanol addition, a net decrease of lipid peroxidation ing it through the rapid formation of peroxynitrite (if the induced by either NO, iron, or ethanol was noted. Moresubsequent degradation products are nontoxic). 9-11 NO could over, an elevation of iron-bound NO and a decrease of act also as an antioxidant by scavenging lipid radicals 10, free NO were observed in these cultures compared with or by forming inactive complexes with low-molecular-weight the cultures incubated with only LPS and IFN. These complex of iron (LMWC iron). 14 LMWC iron consists of iron data support the idea that there is a relationship bespecies that are not contained in high-molecular-weight moltween the changes of NO pool and the inhibition of oxiecules such as ferritin, mitochondrial ferroproteins. These dative stress. In addition, using N G -monomethyl-L-argispecies can trigger oxidative stress by catalyzing formation nine (L-NMMA), a NO synthase inhibitor, NO was shown of a highly reactive free radical, the hydroxyl radical. As a to be involved in the inhibition of oxidative stress inpro-oxidant, NO could lead to secondary formation of highly duced by iron or ethanol. Addition of the chelator of oxidizing molecules. NO and superoxide anion react to form LMWC iron, deferiprone, was followed by the inhibition a peroxynitrite anion that can be protonated rapidly to yield of the increase of iron-bound NO and the reincrease of two other oxidizing molecules, i.e., hydroxyl radical-like and lipid peroxidation extent, which was as high as in culnitrogen dioxide. 9,15 Peroxynitrite is capable of oxidizing liptures incubated only with LPS and IFN. Thus LMWC ids, 16 desoxyribose, 17 a-tocopherol, 18 aminoacids, and proiron appeared to be involved also in the inhibition of teins. Moreover, NO may combine with hydrogen peroxide oxidative stress induced by NO. All the results favor the to form singlet oxygen. Additionally, NO may increase hyconclusion that NO acts as an antioxidant in iron-medidroxyl radical production via a release of LMWC iron from ated oxidative stress in rat hepatocytes. NO reacted with ferritin. In vivo, hepatic NO production also led to opposite LMWC iron to form inactive iron complexes unable to effects on the oxidative stress. Inhibition of NO production induce oxidative stress in rat hepatocytes. Thus NO has been reported to result in enhanced formation of superoxide anion in the perfused liver 22 and during endotoxemia; nitric oxide can prevent hepatic damage induced by free radi-Abbreviations: NO, nitric oxide; LMWC iron, low-molecular-weight complex of iron; LPS, cals. By contrast, NO has been described also as being lipopolysaccharide; IFN, g-interferon; L-NMMA, N G -monomethyl-L-arginine; DETC, diethcapable of triggering toxicity via peroxynitrite formation durylthiocarbamate; MDA, malondialdehyde; DNIC, dinitrosyl iron complex; EPR, electron paramagnetic resonance; MNIC, monitrosyl iron complex.