Apoptosis and oxidative stress induced by ochratoxin A in rat kidney
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Ochratoxin A (OTA) is a widespread mycotoxin produced by several species of fungi. OTA induces a tubular-interstitial nephropathy in humans and in animals. It has been implicated as one of the aetiological agents involved in the development of endemic nephropathy. OTA-induced oxidative stress and apoptosis may play key roles in the development of chronic tubulointerstitial nephritis connected to the long-term exposure to this food contaminant. We studied the effects of low doses of OTA on kidney cells. Wistar rats were treated with 120 μg OTA/kg bodyweight daily, for 10, 30 or 60 days. Toxin concentration in kidney was proportional to the time of exposure, and amounted to 547.2, 752.5 and 930.3 ng OTA/g kidney tissue after 10, 30 and 60 days, respectively. OTA treatment caused an increased number of cells undergoing apoptosis in both proximal and distal epithelial kidney cells. The apoptotic cells were visualised using the TUNEL assay and staining with haematoxylin and eosin in situ. The number of apoptotic cells in rats treated for 10, 30 and 60 days increased by 5-, 6.4- and 12.7-fold, respectively, compared with the control cells. However, DNA electrophoresis did not show characteristic fragmentation (DNA laddering). The oxidative stress was evident via increased malondialdehyde formation. The concentration of lipid peroxides showed an increase (36%), but the activity of superoxide dismutase decreased (26%) in 60-day treated rats. In spite of the observed biochemical and morphological changes in the kidney cells, renal functional status was preserved to the end of experiment. This study demonstrates that a combination of morphologic and biochemical markers can be used to monitor early cell death in OTA-induced renal injury. We have shown that the exposure to the relatively low OTA concentrations has activated apoptotic processes and oxidative damage in kidney cells.