The Genotoxicity of Nitroprusside as a Nitrosonium Cation Donor

Abstract

The genotoxicity of sodium nitroprusside on human MCF-7 mammary gland adenocarcinoma cells was studied using the neutral comet method and the contribution of the nitrosonium ion (NO+) to the genotoxicity of sodium nitroprusside was determined. Genotoxicity was assessed by the yield of double-stranded DNA breaks after incubation of a cell culture with the agent for 1.5 hours. The genotoxicity of NO+ in sodium nitroprusside was determined after the procedure of reducing sodium nitroprusside using sodium dithionite, which converts nitroprusside from an NO+ donor to an NO only donor. It has been shown that sodium nitroprusside induces double-stranded DNA breaks in MCF-7 cells after 1.5 hours. This ability does not depend on the stage of the cell cycle: the proportions of damaged cells in the G0/G1 and G2/M+S stages are 29 ± 7 and 27 ± 6%, respectively. As a result of 90-minute incubation with 100 μM of sodium nitroprusside the proportion of cells that were severely damaged in the form of double-stranded DNA breaks is 25–30%, which is close to the proportion of nonviable cells according to the results of the MTT test at 24 and 48 hours of incubation (22 ± 4%). Sodium dithionite, by removing the toxic effect of NO+, protected MCF-7 cells from the genotoxic effects of nitroprusside, which indicates the involvement of NO+ in the formation of double-strand breaks. The mechanisms of double-stranded DNA fragmentation in cells under the action of nitroprusside are discussed.