| Endomorphins(EMs), endogenousμ-opioid receptor agonists, have been reported that can react with ROS, acting as free radical scavengers. The study mainly aims to the properties of in vivo antioxidants of EMs and the characters of their in vitro oxidative metabolites.1) The antioxidative capacity of endomorphin 1 (EM1), an endogenousμ-opioid receptor agonist, has been demonstrated by in vivo assays. The present study reported the effect of EM1 on hepatic damage induced by cadmium chloride (Cd(II)) in adult male mouse. Mouse were given intraperitoneally (i.p.) a single dose of Cd(II) (1 mg/kg body weight per day) and the animals were co-administrated with a dose of EM1 (50μM/kg body weight per day) for 6 days. Since hepatic damage induced by Cd(II) is related to oxidative stress, lipid peroxidation (LPO), protein carbonyl (PCO), superoxide dismutase (SOD), catalase (CAT) and reduced glutathione (GSH) were evaluated. The parameter indicating tissue damage such as liver histopathology was also determined. In addition, the concentrations of Cd and zinc (Zn) in the liver were analyzed. The intoxication of Cd(II) lead to the enhanced production of LPO and PCO, treatment with EM1 can effectively ameliorate the increase of LPO and PCO compared to the Cd(II) group. The increased activities of CAT, SOD and the elevated GSH induced by Cd(II) may relate to an adaptive-response to the oxidative damage, the effect of EM1 can restore the elevated antioxidant defense. Our results suggested that the structure features and the ability of chelating metal of EM1 may play a major role in the antioxidant effect of EM1 in vivo and opioid receptors may be involved in the protection of hepatic damage induced by Cd(II).2) It is well-known that Cd(II)-induced cardiac damage is mediated by oxidative pressure. The antioxidative capacity of EM1 and endomorphin 2 (EM2), endogenousμ-opioid receptor agonists, have been demonstrated by in vivo assays. The present study revealed the effecst of EM1 and EM2 on cardiac damage induced by cadmium chloride (Cd(II)) in adult male rats. Rats were given intraperitoneally (i.p.) a single dose of Cd(II) (2 mg/kg body weight per day) and the animals were co-administrated with a dose of EM1 (5μM/kg body weight per day) and a dose of EM2 (50μM/kg body weight per day) for 5 days. Lipid peroxidation (LPO), protein carbonyl (PCO), superoxide dismutase (SOD), catalase (CAT) and reduced glutathione (GSH) were evaluated. The parameter indicating tissue damage such as cardiac histopathology was also determined. Since cardiac damage induced by Cd(II) is related to the increase of blood pressure, mainly by the means of inhibiting the NO release of endothelial cell, the interaction of the concentrations of NO and the blood pressure and heart rate of anaesthetic rats have been studied. It ie revealed that EM1 and EM2 can ameliorate the change of blood pressure and increase the NO concentration. Exploring of the detailed mechanism of Cd-induced cadiac damage has been underway in our lab. 3) Endomorphin 1 (EM1), an endogenousμ-opioid receptor agonist, acts as a free radical scavenger in vitro and an antioxidant in vivo. The modification of EM1 by ROS and the properties of the oxidative metabolites (OMs) attracted our attention. In vitro assays were performed via reversed-phase high-performance liquid chromatography (RP-HPLC), spectrophotometry measurements, electron paramagnetic resonance (EPR) and amino acid analysis, Schmorl's reaction to define the formation of melanin-like compounds transformed from EM1, collectively named EM1-melanin and by solubility assay, radioligand-binding assay, NADH oxidation, superoxide anion scavenging assay to study some physical and chemical properties of EM1-melanin. Possible pathways of the formation of EM1-melanin were proposed.
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