Effect of zinc protoporphyrin on carbon monoxide/heme oxygenase-1 system in rats subjected to recurrent febrile convulsion

Abstract

Background Studies on febrile convulsion (FC)-caused brain injury are disputed in many aspects. How FC cause nervous system injury in the developmental period and what are the characteristics of these pathological injury are unknown. The current studies have demonstrated that heme oxygenase-1 (HO-1) exerts effects on brain injury mainly by catalyzing hemoglobin to produce degradation products, and HO-1 not only has neuroprotective effects, but also has neurotoxic effects during the FC-caused brain injury. Study on the effect of zinc protoporphyrin (ZnPP) on brain injury is still in the stage of animal experiment. Objective To observe the effects of ZnPP on carbon monoxide (CO)/HO-1 system of rats subjected to FC, and to analyze the action pathway of ZnPP in brain protective effect. Design A randomized controlled animal experiment. Setting Department of Pediatrics, First Hospital Affiliated to Jiamusi University. Materials Sixty-five Wistar rats, of either gender, were involved in this study. They were randomized into normal control group( n = 14, 37 °C water bath) and febrile treatment group ( n = 51, 44.5 °C hot water bath). Febrile treatment group was sub-divided into febrile non-convulsion group (FNC group, n = 16) and FC group ( n = 35). FC group was further sub-divided into simple convulsion group ( n = 20) and ZnPP treatment group ( n = 15). HO-1 mRNA in situ hybridization kit was provided by Boster Bioengineering Co., Ltd. ZnPP(dark brown powder) was the product of Jingmei Bioengineering Company. Methods This study was carried out in the postgraduate laboratory of Jiamusi University between January 2004 and January 2007. Rats in the febrile treatment group were placed in the 44.5 °C hot water bath box. If rats did not convulse in the water within 5 minutes, they were taken out, namely FNC group ( n = 16), and those, which were convulsed within 5 minutes, were taken out immediately when they presented such a phenomenon, namely FC group ( n = 35). Convulsion induction was conducted once every other day, totally 10 times. Rats were euthanized for analysis at 24 hours after the last induction. Rats in the control group were placed in the 37 °C water. Rats in the ZnPP treatment group were intraperitoneally injected with ZnPP at 45 μmol/kg before FC attack. Rats in the simple convulsion group were only induced to be convulsed but not administrated. Main outcome measures CO level in the brain tissue homogenate and plasma of rats in each group was detected with a spectrophotometer. HO-1 mRNA expression in the hippocampal CA1 region, CA3 region and dentate gyrus of rats was observed by in situ hybridization technique. Results Sixty-five Wistar rats were involved in the study. Two rats died respectively due to drowning and convulsion in the FC group. One rat died due to convulsion drowning in the ZnPP treatment group. ▪ Plasma CO concentration of control group and ZnPP treatment group was significantly lower than that of the FC group ( P < 0.01), and was significantly higher in the ZnPP treatment group than in the FNC group ( P < 0.05). ▪ CO level in the brain tissue homogenate was significantly lower in the control group and ZnPP treatment group than in the FC group ( P < 0.01), and was very significantly higher in the ZnPP treatment group than in the control group ( P < 0.01). ▪ HO-1 mRNA expressions in the neuron of hippocampal CA1 region, CA3 region and dentate gyrus of the control group were the lowerest, and those in the FC group were the highest. HO-1 mRNA expression in the neuron of dentate gyrus in the FC group was significantly higher than that in the ZnPP treatment group ( P < 0.01), and those in the FNC group and control group was significantly lower than that in the ZnPP treatment group ( P < 0.01). Conclusion FC can cause brain injury. Over-expression of HO-1 mRNA and the increase of CO are involved in the patho-physiological process of FC. ZnPP can inhibit HO-1mRNA activity and decrease CO level, which is one of pathways for protecting brain.