Modulation of radiation-induced cytotoxicity in U 87 cells by RH-3 (a preparation of Hippophae rhamnoides)

Hippophae rhamnoides L. has been widely exploited for medicinal purposes and an extract of its whole berries coded as RH-3 has been found to render radioprotection. Effect of pre-irradiation treatment of up to 10 microg/ml RH-3 was studied in U 87 cells using MTT assay. This study aims at unraveling the mechanism of action of RH-3 in amelioration of radiation-induced cytotoxicity in vitro.

Most effective doses selected were studied further for the elucidation of radiomodifying properties of RH-3, especially with respect to early and late events of apoptosis.

RH-3 at concentrations of 7.5 and 10 microg/ml (-15 min) were found most effective in protecting against 2 Gy induced cytotoxicity in terms of MTT reducing ability in U 87 cells. RH-3 was observed to mitigate radiation-induced cellular and mitochondrial free radicals. Mitochondrial membrane potential depletion (studied up to 12 h) was prevented by RH-3 pre-irradiation administration. It could also restore the level of antiapoptotic protein Bcl-2 at 24 and 48 h comparable to the control value. RH-3 also prevented radiation-induced increase in mitochondrial mass at 48 and 72 h post-treatment and the values were comparable to that of control cells. Annexin-V-FITC assay at 12 and 24 h time intervals indicated significant protection against radiation-induced apoptosis by RH-3 pre-irradiation treatment.

Our findings showed that probably RH-3 acts as an antioxidant preventing cellular and mitochondrial free radical generation that could contribute to its ability to inhibit radiation-induced apoptosis and cytotoxicity.