Tumor and non-tumor tissues differential oxidative stress response to supplemental DHA and chemotherapy in rats

Abstract

Developing approaches that will increase the selectivity of anticancer drugs remains a challenge. Docosahexaenoic acid (DHA) has the potential to increase tumor sensitivity to chemotherapy with no sensitization of normal tissues. This study was aimed at exploring the mechanism involved in this differential sensitization with a focus on oxidative stress, one of the main determinants involved in DHA enhancement of anthracycline-based chemotherapy. In a previously validated model of chemically induced mammary tumors in rats where supplemental DHA sensitized tumors to epirubicin, DHA level, lipid hydroperoxides (LPO), total antioxidant activity, glutathione peroxidase (GPx), and superoxide dismutase (SOD) activities were measured in tumors, intestine, liver, and heart in rats treated with DHA+epirubicin and in control rats (palm oil, no chemotherapy). At baseline, the level of LPO was similar in tumors, liver, heart, and small intestine. The proportion of DHA was higher in non-tumor tissues compared to tumors (liver or heart, p < 0.0001; intestine, p = 0.01). DHA and epirubicin induced a significant increase in LPO in tumors (p = 0.03), but no increase was detected in liver, heart, or intestine. The difference in LPO production between these tissues was associated with differences in their antioxidant defenses. In tumors, the adjustment of GPx activity was possible but limited, and no adjustment of their total antioxidant and SOD activities was observed compared to other tissues. Supplementing DHA during an anthracycline-based chemotherapy induced a selective increase of LPO in tumors. This selectivity might result from a differential handling of oxidative stress between tumor and non-tumor tissues.