Study on glycyrrhizin in reducing neuronal damage by inhibiting high mobility group protein 1 in immature rats with epilepsy

Abstract

Objective To study the effect of glycyrrhizin(GL) on the gene expression of high mobility group protein 1(HMGB1) in hippocampus and serum.To evaluate the effect on the expression of neuron-specific nuclear-binding protein(Neu-N) in the hippocampus CA1, CA3 regions in the chronic stage of an immature rat epilepsy model. Methods Fifty-two 21 day-old SD rats were randomly divided into control group, model group Ⅰ and model groupⅡ according to the random table method.Model group Ⅰ was induced epilepsy by kainic acid(KA), and the model group Ⅱ was pretreated with GL by intraperitoneal injection at 30 min before KA injection.According to the different observation time points, each group was divided into 4 subgroups: 3 h, 12 h, 24 h and 7 d. Model groupⅡ was divided into 3 subgroups: 10 mg/kg, 50 mg/kg, 100 mg/kg, according to the different doses of GL.There were 3 animals in each subgroup.Score was performed according to the Racine score, and quantitative real-time polymerase chain reaction and Western blot were applied to detect the mRNA and protein expression of HMGB1 in the acute phase.Enzyme-linked immunosorbent assay(ELISA) was applied to measure the expression of HMGB1 in blood; immunohistochemical was applied to measure the expression of Neu-N in hippocampus in the chronic phase(7 d). Results Compared with model group Ⅰ, seizure onset time was obviously prolonged in model group Ⅱ [(24.08±1.98) min vs.(33.39±2.66) min], and the difference was statistically significant (t=9.231, P 0.05). The expression of HMGB1 in the serum also significantly increased, especially at 12 h(H=6.897, P<0.05). At the time of 12 h after KA injection, the gene expression of HMGB1 in the hippocampus was significantly decreased in model group Ⅱ compared with model group Ⅰ(H=10.721, P<0.05)(especially in the 100 mg/kg model group). Also, the expression of HMGB1 in the scrum was obviously decreased(H=6.967, P<0.05)(especially in the 100 mg/kg model group). At the time of 7 d after KA injection, hippocampal neuron loss in model group Ⅰwas significantly reduced compared with control group(P<0.05), and hippocampal neuron loss in model group Ⅱ was evidently decreased compared with model group Ⅰ(P<0.05), (especially in the 100 mg/kg model group in CA1, 50 mg/kg model group in CA3). Conclusions In the immature rat temporal lobe epilepsy model, GL may have neuroprotective by inhibiting the synthesis and release of HMGB1, inhibiting inflammation further to restrain the loss of neurons in the chronic phase. Key words: Glycyrrhizin; Kainic acid; Epilepsy; Immature rat; High mobility group protein 1; Neuronal injury