The cytotoxic effects of fumonisin B1 in human kidney cells and the ability of allicin to ameliorate these effects.
Mahlalela, Nomalungelo Nothando Felicity.
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Fumonisin B1 (FB1) is a widespread contaminant of crops and is produced as a secondary metabolite of fungi. It has been found to disrupt sphingolipid metabolism, cause epigenetic modifications and induce cellular toxicity that can manifest through oxidative stress and apoptosis. Although implicated in animal toxicity including kidney cancer in rats, FB1 effects in the human kidney have not been explored. Allicin is a biological component of garlic that has been widely studied for its health benefits including its anti-cancer and antioxidant properties. This study evaluated allicin as a possible therapeutic measure for FB1-induced cytotoxicity in Hek293 cells. Both FB1 and allicin decreased cellular viability (MTT assay) in a dose-dependent manner and generated IC50 values of 215 μM and 3.905 μM respectively. Three 24 h treatments (FB1, allicin and combined FB1+allicin) were compared to untreated cells for induction of apoptosis and oxidative stress. Luminometry was used to determine cytotoxicity (lactate dehydrogenase assay), caspase activity and mitochondrial toxicity (apoptosis), and quantify intracellular ROS (iROS) and glutathione (GSH) (oxidative stress). Free radical production was estimated by the TBARS and NOS assays respectively, while DNA damage was evaluated using the comet assay. Western blotting confirmed the expression of various antioxidant and apoptotic proteins, and superoxide dismutase 2 (SOD2) transcripts were quantified using qPCR. ATP concentration was increased for all treatments, but mitochondrial toxicity was increased in the allicin treatment. While lipid peroxidation decreased, luminometry results indicate that iROS was increased and was accompanied by a corresponding decrease in SOD2 and catalase protein expression. Depletion of GSH was consistent with increased GPx1, HSP70 and Nrf2 protein expression suggesting the presence of oxidative stress. SOD2 transcripts were only increased in the allicin treatment. Apoptosis was initiated as indicated by increased caspases 8 and 9, and pro-apoptotic Bax protein expression, but caspase 3/7 was not activated for the FB1 treatment. However, DNA fragmentation and cPARP were increased for all treatments suggesting that apoptosis was executed. Overall, FB1 and allicin individually and combined induced oxidative stress by increasing ROS and decreasing antioxidants. Apoptosis was also induced, although in a caspase independent manner in the FB1 treatment. Overall, allicin did not ameliorate the effects of FB1 in Hek293 cells.