MANCOZEB EXPOSURE RESULTS IN OXIDATIVE STRESS AND DISRUPTION OF MITOCHONDRIAL COMPLEXES III & IV IN TRANSFORMED HUMAN COLON CELLS

The ethylene bisdithiocarbamate pesticides, a subclass of the dithiocarbamate pesticides, are broad spectrum organometallic fungicides used on a variety of crops. The fungicide Mancozeb is comprised of an ethylene bisdithiocarbamate backbone complexed to the metals manganese and zinc. Ingestion of food containing pesticide residue and occupational exposure are common routes of Mancozeb exposure. Previous work demonstrated that Mancozeb exposure to HT-29 colon cancer cells resulted in cytotoxicity, apoptosis, and disruption of mitochondrial complex I, II, and V activity. The current study investigated the effect of Mancozeb exposure on mitochondrial complex III and IV activity and oxidative stress parameters in the HT-29 cell line. Kinetic assays were used to evaluate and compare the effect of Mancozeb exposure on the activity of complexes III and IV. Complex III showed a significant decrease in activity at 60 µM and 100 µM Mancozeb. Activity of complex IV showed significant decreases at 60 µM, 100 µM, and 140 µM Mancozeb. Further mitochondrial disruption was seen in transmission electron micrographs that showed severe mitochondrial distortions at 100 µM Mancozeb. Significant loss of mitochondrial membrane potential (60 µM, 100 µM, and 140 µM Mancozeb) measured with use of a fluorescent mitochondrial potential dye, further confirmed mitochondrial disruption and induction of apoptosis. Scanning electron micrographs demonstrated cellular blebbing at concentrations of 80-140 µM Mancozeb. Quantification of cell blebbing from SEM micrographs revealed a significant increase in the mean percentage of blebbed cells at 100 µM Mancozeb. Oxidative stress parameters were measured to determine the role in mitochondrial dysfunction following Mancozeb exposure. Cellular reactive oxygen species, mitochondrial superoxide, and superoxide dismutase 2 levels were all significantly increased at concentrations of 100 µM and 140 µM Mancozeb. The antioxidant capacity of the cells was significantly decreased at 100 µM and 140 µM Mancozeb. Antioxidant pre-treatment and co-treatment with butylated hydroxy toluene and MitoQ failed to increase cell viability of cells exposed to 100 µM Mancozeb. The results indicate that the underlying mechanism of Mancozeb toxicity that contributes to mitochondrial dysfunction is oxidative stress in HT-29 cells