Mangiferin protects human peripheral blood lymphocytes against γ-radiation–induced DNA strand breaks: a fluorescence analysis of DNA unwinding assay

Ionizing radiations induce free radicals that lead to a cascade of events causing damage to cellular DNA. It is generally accepted that cell death induced by ionizing irradiation is due to DNA double-strand breaks. Therefore, agents that can neutralize free radicals may be able to reduce DNA damage effectively and protect cell death. Effect of 0, 5, 10, 20, 50, or 100 μg/mL mangiferin, a glucosylxanthone present in mango (Mangifera indica), has been studied in human peripheral blood lymphocytes (HPBLs) exposed to 3 Gy γ-radiation by fluorescence analysis of DNA unwinding assay. This assay detects DNA single- and double-strand breaks and alkali-labile sites by their effect on the rate of DNA denaturation in alkali, which was monitored by the fluorescence intensity of an intercalating dye, Hoechst 33258 (bisbenzimide). Estimation of DNA damage by fluorescence analysis of DNA unwinding assay showed that mangiferin as such did not have adverse effect on DNA damage, and it reduced the radiation-induced DNA damage in a concentration-dependent manner. In addition, a maximum undamaged double-stranded DNA was observed for 50 μg/mL of mangiferin. Therefore, further experiments were carried out using this concentration, wherein lymphocytes were exposed to 0, 1, 2, 3, or 4 Gy γ-radiation 30 minutes after mangiferin treatment. Irradiation of HPBLs caused a radiation dose-dependent increase in the DNA strand breaks and a reduction in the undamaged double-stranded DNA, whereas treatment of lymphocytes with 50 μg/mL mangiferin before irradiation significantly reduced DNA strand breaks and subsequently enhanced the undamaged double-stranded DNA at 4 hours posttreatment, indicating repair of radiation-induced DNA strand breaks. Mangiferin treatment restored the undamaged double-stranded DNA to almost normal level after 1 Gy irradiation, whereas it was 50% for 4 Gy at 4 hours postirradiation. Our observations suggest that mangiferin reduces initial DNA damage and enhances DNA repair in the HPBLs exposed to 1 to 4 Gy γ-radiation and could serve as a protector against the radiation-induced DNA damage during planned and unplanned radiation exposures.