In vivo effects of hemin and nitric oxide donors on parameters of heme metabolism in rat liver and serum

Abstract

In vivo effects of hemin chloride (15 mg/kg body weight) and donors of nitrogen monoxide (NO) – sodium nitroprusside (SNP, 1 mg/kg) and substrate of NO-synthase L-arginine (L-Arg, 600 mg/kg) on the activity of key enzymes of heme synthesis (5-aminolevulinate synthase, ALAS) and heme degradation (heme oxygenase, HO), on the free heme level in liver and on the content of heme in blood serum of rats were studied. NO donors were administered alone or 30 min before hemin chloride injection. The level of free heme in liver was estimated by the ratio of holoenzyme and total tryptophan 2,3-dioxygenase (TDO) activities. Two hours after hemin chloride administration a significant increase in the level of heme-containing products and lipid peroxidation products (TBARS) was found in blood serum. These changes were accompanied by decrease in ALAS activity and by increase in holoenzyme activity and heme saturation of TDO, which was the result of free heme accumulation in liver. 24 hrs after administration of hemin chloride the content of heme in serum returned to normal level, while level of TBARS remained elevated. 24 hrs after hemin action a significant increase in the activities of HO and ALAS was observed in liver, while the degree of TDO heme saturation decreased, indicating the prevalence of heme degradation over its synthesis. Both NO donors did not affect the accumulation of heme in serum and liver first hours after hemin action. However, the specific features of SNP and L-Arg effects on the key enzyme of heme synthesis in liver and the TBARS level in serum were revealed. L-Arg, unlike SNP, prevented the accumulation of TBARS in serum, but did not prevent a decrease in ALAS activity 2 hrs after hemin chloride injection. The treatment by SNP itself caused an increase in TBARS level in serum, an increase in TDO activity and a decrease in ALAS activity in liver 2 hrs after action. Heme content in serum positively correlated with holoenzyme activity and heme saturation of TDO in liver. The pretreatment with NO donors did not affect the increase in HO activity, however, it blocked the induction of ALAS, a decrease in holoenzyme activity and heme saturation of TDO 24 hrs after the administration of hemin chloride. Thus, both SNP and Arg prevented a decrease in free heme level in liver, which might be due to heme nitrosylation in the presence of NO donors and, as a result, its slower degradation in the heme oxygenase reaction.