A Study On The Anti-cyanide Effect Of 4-DMAP And The Mechanism Of Its Increased Efficiency In Methemoglobin Formation Under Hypoxia Condition

Cyanide, a rapid-acting neurotoxic compound, has been used in the modern battle as one of chemical weapons. Cyanide inhibits various enzymes of the biological system, the most important being cytochrome oxidase in brain where there is induction of potential lethal cytotoxic hypoxia. 4-(N, N-dimethyl)-aminophenol (4-DMAP), an effective methemoglobin forming agent, is widely used for therapy of acute cyanide poisoning at the present time. However, methemoglobinemia may be induced if 4-DMAP of high concentrations is injected to patients of cyanide poisoning. Unfortunately, pharmacologic parameters of 4-DMAP under plateau have not been reported. Till now, whether the efficiency of 4-DMAP in methemoglobin forming would be altered with the changing environments or physiological conditions and whether the standard treatment strategy is suit for cyanide poisoning patients under plateau.To improve survival rate of cyanide poisoning patients under plateau, erythrocytes and rabbits treated with hypoxia respectively were employed to characterize the effect of 4-DMAP in ferrihemoglobin (MHb) formation. At the same time, reduced glutathione in blood (GSH), plasma malondialdehyde (MDA), erythrocyte superoxide dismutase (SOD), glutathione peroxidase (GPx) and NADH-cytochrome b5 reductase (b5R) activities were measured and b5R gene expression was checked by RT-PCR. The main results are as following:①LD50 of sodium cyanide in mice was 5.22 mg/kg under hypoxia condition, remarkable lower than normal oxygen condition (7.71 mg/kg). For the sodium cyanide poisoning hypoxic-mice, the highest rate (70% ~ 80%) appeared in 15 mg/kg 4-DMAP treated group, not the 25 mg/kg treated group which was the suitest dosage (90% survivering) for poisoning mice under normal oxygen condition. ②Hypoxia enhanced the effect of 4-DMAP in MHb formation. When erythrocytes under hypoxic oxygen condition for 6,10,14,18 and 22 h , the ability of MHb formatiom induced by 4-DMAP increased 51.4%,41.1%,37.4%,32.6% and 36.5% compared to with control group, respectively. The similar result was observed in whole animal model, the figures were 59.2%,154.7%,171.7% and 133.8% in 1,3,5 and 7 days hypoxia-treated rabbits. ③GSH and b5R were the impotant factors which affected 4-DMAP efficiency in MHb formation, MHb concentration increased significantly under treatement with inhibitor of GSH synthesize or b5R activity. ④Hypoxia altered physiological and biochemical characters, suppressed b5R gene expression, decreased b5R activity, reduced GSH concentration and declined antioxidant capacity. ⑤The increased efficiency of 4-DMAP in MHb formation in hypoxic model was caused by lower GSH concentration and b5R activity. At the initial stages of hypoxia, the major reason of increased effect of 4-DMAP was GSH concentration decrease, while during period of hypoxia treatment b5R activity gradually became dominant factor.These results strongly suggest that hypoxia alter physiological and biochemical characters, i.e. suppressed b5R gene expression, decreased b5R activity, reduced GSH concentration and declined antioxidant capacity, and lead to the increased ability of MHb formation induced by 4-DMAP.