Ginkgo biloba extract attenuates cisplatin-induced renal interstitial fibrosis by inhibiting the activation of renal fibroblasts through down-regulating the HIF-1α/STAT3/IL-6 pathway in renal tubular epithelial cells

Background: Activation of renal fibroblasts into myofibroblasts plays an important role in promoting renal interstitial fibrosis (RIF). Ginkgo biloba extract (EGb) can alleviate RIF induced by cisplatin (CDDP). Purpose: To elucidate the effect of EGb treatment on cisplatin-induced RIF and reveal its potential mechanism. Methods: The two main active components in EGb were determined by high-performance liquid chromatography (HPLC) analysis. Rats were induced by CDDP and then treated with EGb, 2ME2 (HIF-1 alpha inhibitor) or amifostine. After HK-2 cells and HIF-1 alpha siRNA HK-2 cells were treated with CDDP, EGb or amifostine, the conditioned medium from each group was cultured with NRK-49F cells. The renal function of rats was detected. The renal damage and fibrosis were evaluated by H&E and Masson trichrome staining. The IL-6 content in the cell medium was detected by ELISA. The expression levels of indicators related to renal fibrosis and signaling pathway were examined by western blotting and qRT-PCR. Results: HPLC analysis showed that the contents of quercetin and kaempferol in EGb were 36.0 mu g/ml and 45.7 mu g/ml, respectively. In vivo, EGb and 2ME2 alleviated renal damage and fibrosis, as well as significantly decreased the levels of alpha-SMA, HIF-1 alpha, STAT3 and IL-6 in rat tissues induced by CDDP. In vitro, the levels of HIF-1 alpha, STAT3 and IL-6 were significantly increased in HK-2 cells and HIF-1 alpha siRNA HK-2 cells induced by CDDP. Notably, HIF-1a siRNA significantly decreased the levels of HIF-1 alpha, STAT3 and IL-6 in HK-2 cells, as well as the IL-6 level in medium from HK-2 cells. Additionally, the alpha-SMA level in NRK-49F cells was significantly increased after being cultured with conditioned medium from HK-2 cells or HIF-1 alpha siRNA HK-2 cells exposed to CDDP. Furthermore, exogenous IL-6 increased the alpha-SMA level in NRK-49F cells. Importantly, the expression levels of the above-mentioned indicators were significantly decreased after the HK-2 cells and HIF-1 alpha siRNA HK-2 cells were treated with EGb. Conclusion: This study revealed that EGb improves CDDP-induced RIF, and the mechanism may be related to its inhibition of the renal fibroblast activation by down-regulating the HIF-1 alpha/STAT3/IL-6 pathway in renal tubular epithelial cells.