POSSIBLE DUAL ROLE OF NITRIC-OXIDE IN OXIDATIVE STRESS INJURY - A STUDY IN PERFUSED HEPATOCYTES

Nitric oxide (NO) is a multifunctional messenger in many vertebrates. In the liver, NO was found to play an important but controversial role in injury produced by toxins or sepsis. The purpose of the present in vestigation was to further characterize the role of NO in hepatocyte o xidative injury. A cellular system formed of immobilized and perfused rat hepatocytes was used to test the ability of the latter to produce endogenous NO after lipopolysaccharide administration in vivo (LPS, 20 mg/kg i.p.) and how hepatocyte functionality competence is modified a ccording to NO level. This cellular system also was used to delineate a relationship between exogenously delivered NO to the perfusion mediu m as produced by the NO donor, sodium nitroprusside (2.0 and 0.2 mM), and any alteration in the degree of injury as evoked by anoxia/reoxyge nation or cumene hydroperoxide (1.0 mM and 0.2 mM). Rat hepatocytes we re immobilized in low-gelling agarose and perfused with Williams E med ium. Endogenous or exogenous NO was evaluated by measuring the end pro ducts of NO (NO2- + NO3-) in the perfusion medium. Functional integrit y of hepatocytes was evaluated from lactate dehydrogenase (LD) leakage , urea synthesis in the perfusion medium and lipid peroxides (LP) form ation. Normal, anoxia/reoxygenation or cumene hydroperoxide injured he patocytes did not exhibit measurable NO while LPS-treated hepatocytes produced NO. Apparently, within the present experimental conditions, i t seems that there was an inverse relation between the rate of NO prod uced after LPS administration and the rate of lipid peroxides formed i n the hepatocytes. Low concentration of sodium nitroprusside (as NO do nor) significantly decreased LD leakage, increased the rate of urea sy nthesis and increased trypan blue exclusion by hepatocytes in anoxia/r eoxygenation or cumene hydroperoxide injured (0.2 mM) cells. Lipid per oxides were decreased by NO in cumene hydroperoxide injured hepatocyte s. The present data suggest that NO endogenously produced, or exogenou sly delivered, has an ameliorative role in mild oxidative liver injury models, but not in severe cases and that inside hepatocytes, there is a very delicate balance between the rate of NO production and its con sumption. The disturbance in this balance may be responsible for injur y due to the formation of more toxic oxygen species. (C) 1998 Publishe d by Elsevier Science Ltd on behalf of the International Society for I mmunopharmacology.