Programmed cell death by interaction of ochratoxin A with other nephrotoxins

We determined the effects of co-exposure of OTA and other (potentially) nephrotoxic substances on renal tubule cells (IHKE, from the proximal tubule; MDCK-C7 cells, representing principal cells of the collecting duct) by measuring the activation of caspase-3, an enzyme with key roles in the process of programmed cell death or apoptosis.Substances used in combination with OTA included: cadmium, a known nephrotoxin with apoptotic effects, cisplatin (anticancer drug, also a known nephrotoxin), cyclosporin A (an immunosuppresive agent), H2O2 (generated during oxidative cell stress), amphotericin B (antifungal agent), and fumonisin B1. Because of the great number of possible combinations, a method based on the 96-well format was developed which allowed a fast and cost-efficient succesive measurement of caspase-3 activity and protein content in one well as well as necrotic effects in parallel.We found that cells responded differently to the various combinations: for example, 1 µM OTA combined with 100 µM cisplatin had an antagonizing effect on caspase-3 activation in IHKE cells but potentiating effects in MDCK-C7. DNA ladder formation confirmed the results. Necrotic effects were very small and additive. We conclude that the co-exposure of renal cells to OTA with other substances can enhance or reduce the apoptotic potential of one substance alone depending on the substance and on the cell line investigated. A "harmless" substance can thus convert to a potent cell toxic substance when combined with OTA or other mycotoxins.These first findings show the necessity to further investigate the combined effects of OTA or other mycotoxins with other substances or of mycotoxins with each other.