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 inhibitory capacity of different antioxidants on UV- and drug-induced apoptosis in the human leukemic cell line, HL-60. We found that the oxygen radical scavenger, BHA, the radioprotector cysteamine and the metal chelators, pyrrolidinedithiocarbamate (PDTC), diethyldithiocarbamate (DEDTC), and dimethyldithiocarbamate (DMDTC), were able to significantly 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 capable 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 elucidate the working mechanism of PDTC, we have looked at the effect of PDTC on DNA fragmentation in isolated nuclei, under conditions that promote activation of endogenous endonuclease involved in apoptosis. In contrast to ZnCl2, a potent inhibitor of endonuclease activity, PDTC was 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 serve as potent inhibitors of apoptosis induced by a wide variety of stimuli.