N-acetylcysteine augments the cellular redox changes and cytotoxic activity of internalized mycobacterium bovis in human bladder cancer cells

Abstract

Purpose: We determined whether changes in cellular reactive oxygen species correlated with mycobacteria internalization and bladder cancer cell death.

Materials and methods: Reactive oxygen species and thiols in RT112 and MGH bladder cancer cells were determined using the fluorescence probes 5-(and 6)-carboxy-2', 7' dichlorodihydrofluorescein diacetate and monobromobimane. Superoxide and nitrite production were measured using bis-N-methylarcridinium nitrate and Griess reagents. Cytotoxicity was determined by the release of 14C-thymidine from cells with 14C labeled DNA.

Results: MGH cells that internalize bacillus Calmette-Guerin (BCG) had decreased cellular reactive oxygen species and thiols, although superoxide and nitric oxide production increased. RT112 cells, which do not internalize BCG, did not show a decrease in reactive oxygen species after incubation with BCG. Blocking BCG uptake in MGH cells abrogated reactive oxygen species reduction, confirming that the changes in reactive oxygen species were internalization dependent events. Treating cells with BCG and the antioxidant N-acetylcysteine caused a greater reduction in reactive oxygen species, and induced earlier and greater cytotoxicity in MGH but not in RT112 cells.

Conclusions: The induction of bladder cancer cell killing by BCG parallels the ability of cells to internalize BCG, which in turn indicates that the susceptibility of tumor cells to the cytotoxic effects of BCG may be related to changes in cellular levels of reactive oxygen species and thiols. Supplementation with an antioxidant could enhance the antitumor effect of BCG.