Ginsenoside Rg1 suppressed inflammation and neuron apoptosis by activating PPARγ/HO-1 in hippocampus in rat model of cerebral ischemia-reperfusion injury

Generally accepted, inflammation and neuron apoptosis are two characterized pathological features of cerebral ischemia-reperfusion (IR) injury. Ginsenoside Rg1 was reported showing distinct neuroprotective effect in cerebral IR injury but the underlying mechanisms are still unclear. PPAR gamma/Heme oxygenase-1 (HO-1) signaling was proved effective in suppressing both apoptosis and inflammation. This study was aimed to investigate whether PPAR gamma/HO-1 signaling was involved in cerebral IR injury and ginsenoside Rg1's neuroprotective effect in cerebral IR injury. Cerebral IR injury was induced by middle cerebral artery occlusion in rats. The PPAR gamma agonist rosiglitazone (ROZ) and the HO-1 inhibitor zinc protoporphyrin-IX (ZnPP) and ginsenoside Rg1 at various concentrations were used to treat the modeled rats. Neurological deficits, apoptosis and inflammation in hippocampus were evaluated. Furthermore, HO-1 enzymatic activity, expression levels of apoptosis-related and inflammation-related proteins, concentrations of inflammatory cytokines were also determined. The results showed that PPAR gamma activation by ROZ significantly attenuated neurological deficits, apoptosis and inflammation in hippocampus in cerebral IR rats. However, the neuroprotective effect of ROZ was then impaired by HO-1 inhibitor ZnPP. This effect was evidenced by changes of expression levels of PPAR gamma, bcl-2, cleaved caspase-3, cleaved caspase-9, IL-1 beta, TNF-alpha, HMGB1, and RAGE in hippocampus of modeled animals. Ginsenoside Rg1 showed similar effect to ROZ in activating PPAR gamma/HO-1 in protecting against apoptosis and inflammation but also impaired by ZnPP administration. In conclusion, PPAR gamma/HO-1 signaling was critical in mediating apoptosis and inflammation, which was also the therapeutic target of ginsenoside Rg1 in cerebral IR injury.