Effect of hydroxycamptothecin combined with etoposide on apoptosis of human Tenon capsule fibroblast and its mechanism

Abstract

Background Previous study showed that both hydroxycamptothecin (HCPT) and etoposide (VP-16) can induce the apoptosis of human Tenon capsule fibroblasts (HTFs).However,whether the combination of HCPT with VP-16 enhance the efficacy of drugs is unknown.Olbjeetive This study was to investigate the synergistic effect and its mechanism of HCPT combined with VP-16 on apoptosis of HTFs.Methods Human Tenon capsule tissue was obtained from the eye bank of Jiangsu Province People's Hospital.HTFs were cultured in vitro using explant method and identified by immunofluorescence with vimentin.The fourth generation of cells were incubated in 96-well plate,and different concentrations of HCPT (1,5,10,50,100 mg/L),VP-16 (0.6,2.5,5.0,25.0,50.0 mg/L) and HCPT+VP-16 (2:1,final concentrations 0.80,3.75,7.50,37.50,75.00 mg/L) were added for 24 hours.The inhibiting rate of drugs to HTFs growth was detected using CCK-8 kit.The HTFs were divided into blank control group,HCPT (50 ng/L) treated group,VP-16 (25 mg/L) treated group and HCPT+ VP-16 (37.5 mg/L) treated group,and the apoptosis rates of HTFs in various groups were assayed by flow cytometry.The expressions of caspase-3,cleaved caspase-3,bax,bcl-2,JNK,p-JNK,Akt,p-Akt in the cells were detected by Western blot assay.Results Cultured cells grew well with the polygon shape and positive response for vimentin.The inhibiting rate was elevated with the increase of drug dosage 24 hours after addition of drugs (HCPT:F=41.34,P=0.00 ; VP-16:F =62.60,P =0.00 ; HCPT+VP-16:F =46.77,P =0.00).The half maximal inhibitory concentrations (IC50) of HCPT,VP-16,HCPT+VP-16 were 80.99,27.93,19.81 mg/L,respectively,and the combined index (CI) of HCPT with VP-16 was 0.399,showing a stronger synergistic action.The apoptotic rates of HTFs were (4.87±0.78) ％,(11.20± 1.94)％,(12.67±1.51)％ and (19.77±2.01)％ in the blank control group,HCPT treated group,VP-16 treated group and HCPT+VP-16 treated group,respectively,with a significant difference among them (F=18.23,P ＜ 0.01),and the apoptotic rate was significantly raised in the HCPT + VP-16 treated group,HCPT treated group and VP-16 treated group compared with the blank control group (q'=15.67,16.32,26.88,all at P＜0.01).Compared with the blank control group,the grey scale values of cleaved caspase-3,bax,p-JNK in the cells of HCPT+VP-16 treated group,HCPT treated group and VP-16 treated group were significantly increased (all at P＜0.01),and those in the HCPT+VP-16 treated group significant ascent in comparison with the HCPT treated group and VP-16 treated group (all at P＜0.01).However,the changes of caspase-3,JNK and Akt expression were insignificant.The grey scale values of bcl-2 and p-Akt in the HTFs of the HCPT,VP-16 and HCPT+VP-16 treated groups were significantly lower than those of the blank control group,with a dominant reducing in the HCPT+VP-16 treated group (all at P＜0.01).Conclusions HCPT and VP-16 induce the apoptosis of HTFs in vitro at a dose-dependent manner.The combination of HCPT with VP-16 has a stronger synergistic efficacy.The up-regulation of p-JNK and bax as well as the down-regulation of p-Akt and bcl-2 in HTFs are involved in the coaction of HCPT and VP-16. Key words: Hydroxycamptothecin; Etoposide; Human Tenon capsule fibroblast; Apoptosis; Synergistic effect; Cell culture/in vitro