DNA damage in human fibroblasts exposed to fumonisin B sub(1)

Fumonisins are mycotoxins produced by several Fusarium species (Fusarium verticilloides and F. proliferatum) that infest corn and other cereals. Fumonisin B sub(1) (FB sub(1)), structurally resembling sphingoid bases, is an inhibitor of ceramide synthetase, a key enzyme involved in de novo sphingolipid biosynthesis and in the reacylation of free sphingoid bases derived from sphingolipid turnover. This inhibitory effect leads to accumulation of free sphinganine and sphingosine and subsequent induction of cell death. However, the downstream effectors activated by these sphingolipids in the cell death-signalling pathway are little known. The aim of this study was to evaluate, in FB sub(1)-exposed human fibroblasts, the involvement of oxygen free radicals and of some other biochemical pathways, caspase-3 activity, poly(ADP-ribose)polymerase (PARP) cleavage and DNA damage evaluated by comet assay. Our results indicate that FB sub(1) treatment (48, 72 h and 10, 50, 100 mu M) does not affect cellular viability. Conversely, after 72 h of treatment, FB sub(1) (50 and 100 mu M) induced DNA damage, an enhancement of caspase-3-activity and cleavage of PARP compared to controls. In addition, FB sub(1) increased the expression of HSP70 in a concentration and time-dependent manner. Our results indicate that DNA damage of apoptotic type in human fibroblasts is caused by exposure to FB sub(1) at high concentrations and for a prolonged time and that the genotoxic potential of FB sub(1) has probably been underestimated and should be reconsidered.