INHIBITION OF APOPTOSIS BY ANTIOXIDANTS IN THE HUMAN HL-60 LEUKEMIA-CELL LINE

Cell death via apoptosis is an important event involved in a number of immunological processes. Recently, apoptosis has been associated with oxidative stress in a number of cell systems. Here we assessed the in hibitory capacity of different antioxidants on UV- and drug-induced ap optosis in the human leukemic cell line, HL-60. We found that the oxyg en radical scavenger, BHA, the radioprotector cysteamine and the metal chelators, pyrrolidinedithiocarbamate (PDTC), diethyldithiocarbamate (DEDTC), and dimethyldithiocarbamate (DMDTC), were able to significant ly inhibit nuclear fragmentation and reduce the formation of apoptotic bodies in UV-irradiated human leukemic cells. Both BHA and PDTC were found to reduce DNA fragmentation as assessed by in situ DNA nick-end labelling and quantification thereof using fluorescence flow cytometry . In addition to inhibiting UV-induced apoptosis, PDTC was also capabl e of reducing the amount of apoptosis induced by a range of cytotoxic drugs, such as actinomycin-D, camptothecin, etoposide, and melphalan, whereas BHA and cysteamine were not as effective in these cases after more than four hours in culture when compared to PDTC. To further eluc idate the working mechanism of PDTC, we have looked at the effect of P DTC on DNA fragmentation in isolated nuclei, under conditions that pro mote activation of endogenous endonuclease involved in apoptosis. In c ontrast to ZnCl2, a potent inhibitor of endonuclease activity, PDTC wa s unable to inhibit DNA-ladder formation in this assay. Taken together , these results indicate that oxygen radicals may have a central role to play in the induction of apoptosis and that dithiocarbamates can se rve as potent inhibitors of apoptosis induced by a wide variety of sti muli.