Objective: To study the possible anti-apoptotic mechanism of ginsenoside Rg1 on the apoptosis of hippocampal neuron after cerebral ischemia/reperfusion (I/R) injury rats.
Methods: Totally 120 healthy male adult SD rats were randomly divided into the cerebral I/R model group (the model group), the low dose ginsenoside Rg1 group (10 mg/kg), the middle dose ginsenoside Rg1 group (20 mg/kg), the high dose ginsenoside Rg1 group (40 mg/kg), and the sham-operation group, 18 in each group. Rats received medication by peritoneal injection. Equal volume of normal saline was peritoneally injected to rats in the sham-operation group and the model group, once daily, for 7 successive days. The cerebral I/R injury model was prepared by 2-h middle cerebral artery occlusion (MCAO) followed by 24-h reperfusion. Rats in the sham-operation group received the same surgical procedure without the carotid arteries occluded. The neurofunction was assessed using Longa EZ method. The injury of hippocampal pyramidal cells was observed by Nissel staining and TUNEL assay. The nerve cell apoptosis rate was calculated. The protein expression levels of extracellular signal-regulated kinase 1/2 (ERK1/2), phosphorylated extracellular signal-regulated kinase 1/2 (p-ERK1/2), c-Jun N-terminal kinases (JNK), and phosphorylated c-Jun N-terminal kinase (p-JNK) were detected using Western blot.
Results: Compared with the sham-operation group, the score of neurofunction, the apoptosis rate, the expression levels of p-JNK and p-ERK1/2 increased, the survived number of pyramidal cells decreased in the model group (P < 0.05, P < 0.01). Compared with the model group, the score of neurofunction and the apoptosis rate decreased in each ginsenoside Rg1 group (P < 0.05, P < 0.01). The survived number of pyramidal cells increased in the high and middle dose ginsenoside Rg1 groups, the expression of p-JNK in the hippocampal CA1 region decreased, and the expression level of p-ERK1/2 increased (P < 0.05, P < 0.01). Compared with the low dose ginsenoside Rg1 group, the score of neurofunction, the apoptosis rate, the p-JNK protein expression decreased, the survived number of pyramidal cells increased, the expression of p-ERK1/2 increased in the high and middle dose ginsenoside Rg1 groups (P < 0.05, P < 0.01). Three to four layers of pyramidal cells were arranged tightly and compactly in the hippocampal CA1 region of the sham - operation group. The nucleus was big and round under high power lens, with 1 -2 kernel. After cerebral I/R injury, the hippocampal nerve cells were severely injured. Normal structure was lost in the CA1 region, with disarranged cell line and reduced cell amount. Partial neurons were shrunken, and the kernel was condensed and darkenedly stained. They were in triangular, long strip, fusiform, or irregular shape. The staining of nucleus was clustered and the kernel was not clear. Ginsenoside Rg1 (20 and 40 mg/kg) could improve the morphology of ischemic nerve cells, reduce their loss. Of them, stronger effects were shown in the high dose ginsenoside Rg1 group than in the middle dose ginsenoside Rg1 group. The JNK protein band was divided into two subzones, JNK1 (46 kD) and JNK2 (54 kD). ERK protein band was also divided into two subzones, ERK1 (44 kD) and ERK2 (42 kD).
Conclusion: The protective effect of ginsenoside Rg1 on cerebral I/R injury was correlated with inhibiting the apoptosis of hippocampal neurons, regulating the expression levels of p-ERK1/2 and p-JNK.