Hemoglobin affects lipid peroxidation and prostaglandin E2 formation in rat corticocerebral tissues in vitro

Variations of lipid peroxidation and arachidonic acid (AA) metabolism products were found when experimental subarachnoid hemorrhage or ischemia and reperfusion were performed in an animal brain model. In a previous study, we showed that hemoglobin (Hb) produces prostaglandins when incubated in AA. To elucidate how Hb affects lipid peroxidation and AA metabolism in the CNS, we measured lipid hydroperoxides (LOOH), PGE2 and thiobarbituric acid reactant substances (TBARS) in corticocerebral homogenates and slices of rats (normal rats) after incubation with different concentrations (10(-9) to 10(-5) M) of Hb. In addition, brain cortices of indomethacin-treated (40 mg/Kg) rats (IN-treated rat) were incubated in the presence of 10(-5) M indomethacin (IN) to exclude the interference of prostaglandin enzyme synthetase. Hb was able to affect LOOH, PGE2, and TBARS production in both normal and IN-treated rat brain cortex homogenates and slices. In all cases, we found an increase in prostaglandin when 10(-8) M Hb was used, whereas no effect was noticed with 10(-9) M. On the other hand, with higher Hb concentrations (10(-6)-10(-5) M), the LOOH and PGE2 values did not reach statistical significance, and TBARS significantly increased. In all cases, when 10(-4) M scavenger or metal-chelating compounds were added to an incubation mixture with 10(-8) M Hb, PGE2 formation was inhibited, whereas no variation occurred when 10(-4) M IN was further added to IN-treated rat corticocerebral homogenate or slices. We hypothesize that in in vivo experimental neuropathologies, Hb must attain the 10(-8) M concentration in the reaction cellular microenvironment to stimulate PGE2 production, and that an evaluable part of this PGE2 production may be directly ascribable to the iron-heme oxy-redoxy activity of Hb.