Effects of apocynin and natural antioxidant from spinach on inducible nitric oxide synthase and cyclooxygenase-2 induction in lipopolysaccharide-induced hepatic injury in rat

The immunoreactivity of inducible nitric oxide synthase, and cyclooxygenase -2 was compared among groups of male Wistar rats comprising those injected with lipopolysaccharide following pretreatment with either natural antioxid ant from spinach or the antioxidant apocynin, with lipopolysaccharide witho ut pretreatment with antioxidants, with each of the two antioxidants alone, and untreated controls. The grade of staining of both inducible nitric oxi de synthase and cyclooxygenase-2 increased with the severity of the inflamm atory reaction in the lipopolysaccharide-treated animals, compared to the a ntioxidant-treated groups. Interpretation of the results of the immunostain ed tissues indicated that pretreatment with either antioxidant significantl y (P<0.05) attenuated the lipopolysaccharide-stimulated inducible nitric ox ide synthase induction. Analysis of the cycloxygenase-2-stained liver sampl es indicated that the pretreatment with the natural antioxidant NAO signifi cantly (P<0.05) attenuated lipopolysaccharide-stimulated cycloxygenase-2 in duction; whereas, in animals pretreated with apocynin, there was a trend of reduction in the cyclooxygenase-2 expression, but not statistically signif icant (P>0.05). The negative nitrotyrosine immunoreactivity of the lipopoly saccharide-related hepatic lesions may indicate that there was relatively l ow interaction between superoxide anions and nitric oxide to form peroxynit rite or that the expression levels of the nitrotyrosine were below the limi t of detection. In all treatment groups a positive correlation (P<0.05, r=0 .86) found between the inducible nitric oxide synthase and cyclooxygenase-2 scores suggests a strong relationship between these two parameters. The re sults indicate the possible therapeutic efficacy of NAO and apocynin in the prevention of liver damage related to clinical endotoxemia known to be ass ociated with oxidative stress.