CALCIUM CHELATOR QUIN-2 PREVENTS CROCIDOLITE-INDUCED DNA STRAND BREAKAGE IN HUMAN WHITE BLOOD-CELLS

Exposure of human white blood cells to UICC crocidolite asbestos in vi tro resulted in the formation of DNA strand breakage in a dose-depende nt manner up to a fibre concentration of 100 mu g/ml. Subsequent incub ations with the iron chelator desferrioxamine or the intracellular Ca2 + chelator Quin-2 prevented DNA strand break formation above control i ncubations. Addition of aurintricarboxylic acid, an endonuclease inhib itor, similarly abolished crocidolite-induced DNA strand breaks in the se cells. These results suggest that crocidolite-derived hydroxyl radi cals do not directly induce DNA strand breakage in mammalian white blo od cells. In order to assess Ca2+ mobilisation from intracellular stor es in control and crocidolite-treated cells, the fullness of these sto res was measured by treating with thapsigargin, a specific inhibitor o f the endoplasmic reticulum Ca2+-ATPase. On addition of thapsigargin t o fura-2AM-loaded cells treated with crocidolite we demonstrated that the endoplasmic reticulum stores had been depleted as no further Ca2was released, unlike control cells. We suggest that strand breakage is caused by a complex set of events involving oxygen free radicals that may disturb intracellular Ca2+ homoeostasis and the breaks are produc ed by secondary reactions, involving Ca2+-mediated enzymes.