Vitamin E Protects DNA from Oxidative Damage in Human Hepatocellular Carcinoma Cell Lines

Expression of multiple drug resistant (MDR) phenotype and over-expression of P-glycoprotein (P-gp) in the human hepatocellular carcinoma (HCC) cell clone P1(0.5), derived from the PLC/PRF/5 cell line (P5), are associated with strong resistance to oxidative stress and a significant (?p<0.01) increase in intracellular vitamin E content as compared with the parental cell line. This study evaluates the role of vitamin E in conferring resistance to drugs and oxidative stress in P1(0.5) cells. Parental drug-sensitive cells, P5, were incubated in α-tocopherol succinate (α-TS, 5?μM for 24?h) enriched medium to increase intracellular vitamin E content to levels comparable to those observed in P1(0.5) cells at basal conditions. Susceptibility to lipid peroxidation and oxidative DNA damage were assessed by measuring the concentration of thiobarbituric-reactive substances (TBARS) and 8-hydroxy-2′-deoxyguanosine (8-OHdG) at basal and after experimental conditions. Cell capacity to form colonies and resistance to doxorubicin were also studied. P5 cells, treated with α-TS, became resistant to ADP-Fe³⁺ and to ionizing radiation-induced lipid peroxidation as P1(0.5) cells. Exposure to ADP-Fe³⁺ or ionizing radiation increased TBARS and the 8-OHdG content in the P5 cells, while vitamin E enrichment abolished these effects. Irradiation doses at 5?cGy increased TBARS and 8-OHdG. They also inhibited cell capacity to form colonies in the untreated P5 cells. Incubation with α-TS fully reverted this effect and significantly (p<0.01) reduced the inhibitory effect of cell proliferation induced by irradiation doses at >500?cGy. Resistance to doxorubicin was not affected by α-TS. These observations demonstrate the role of vitamin E in conferring protection from lipid peroxidation, ionizing radiation and oxidative DNA damage on the human HCC cell line. They also rule out any role of P-gp over-expression as being responsible for these observations in cells with MDR phenotype expression.