NADPH-dependent lipid peroxidation capacity in unfixed tissue sections: characterization of the pro-oxidizing conditions and optimization of the histochemical detection

Summary Factors which influence the iron-stimulated lipid peroxidation in rat liver have been studied by incubating unfixed cryostat sections with a pro-oxidant system and using an optimized histochemical detection method for lipid peroxidation products with 3-hydroxy-2-naphthoic acid hydrazide and Fast Blue B. We used a method that was slightly different from the one described previously. The final reaction product was exclusively localized in the cytoplasm of liver parenchymal cells with a homogeneous distribution within the liver lobule. The absorbance maximum, as measured cytophotometrically, was found to be 550 nm. Maximum lipid peroxidation was observed when the pro-oxidant system contained 0.2 mm NADPH, 1 mm ADP and 15 μm FeCl₂. Some reaction product was found when NADPH was omitted. Iron concentrations higher than 180 μm prevented the formation of lipid peroxidation products in certain areas of the sections, whereas ADP concentrations higher than 1 mm inhibited the reaction in the whole section. A pH dependency was also observed, with the highest lipid peroxidation at pH 7.2. Optimum lipid peroxidation was induced by incubating for 30 min at 37°C with the pro-oxidant system. A linear relationship was found between the thickness of the sections (up to 20 μm) and the amount of lipid peroxidation products. The addition of scavengers of O2- (superoxide dismutase), hydrogen peroxide (catalase) and OH · (mannitol) to the first step medium did not affect the amount of final reaction product. These findings appear to confirm the hypothesis proposed for events occurring in isolated microsomes, leading to the formation of hydroperoxides and ultimately lipid peroxidation-derived carbonyls. The present method is a useful tool for studying the capacity of lipid peroxidation in tissues under different (patho)physiological conditions.