Role of glutathione in dimethylarsinic acid-induced apoptosis.
Inorganic arsenicals are clearly toxicants and carcinogens in humans. In mammals, including humans, inorganic arsenicals often undergo methylation, forming compounds such as dimethylarsinic acid (DMAs(V)). Recent evidence indicates that DMAs(V) is a complete carcinogen in rodents although evidence for inorganic arsenicals as carcinogens in rodents remains equivocal. Thus, we studied the molecular mechanisms of in vitro cytolethality of DMAs(V) using a rat liver epithelial cell line (TRL 1215). DMAs(V) selectively induced apoptosis in TRL 1215 cells; its LC(50) value after 48 h exposure was 4.5 mM. The addition of a glutathione synthase inhibitor, L-buthionine-[S,R]-sulfoximine (BSO), actually decreased DMAs(V)-induced apoptosis. DMAs(V) exposure temporarily decreased cellular reduced glutathione (GSH) levels and enhanced cellular glutathione S-transferase (GST) activity from 6 h after the exposure when the cells were still alive. Also, DMAs(V) exposure activated cellular caspase 3 activity with a peak at 18 h after the exposure when apoptosis began, and BSO treatment completely inhibited this enzyme activity. The additions of inhibitors of caspase 3, caspase 8, and caspase 9 significantly reduced DMAs(V)-induced apoptosis. Taken together, these data indicate that cellular GSH was required for DMAs(V)-induced apoptosis to occur, and activation of cellular caspases after conjugation of DMAs(V) with cellular GSH appears to be of mechanistic significance. Further research will be required to determine the role of intracellular GSH and methylation in the toxicity of arsenicals in chronic arsenic poisoning or in cases where arsenicals are used as chemotherapeutics.
Laboratory of Environmental Chemistry, School of Life Science, Tokyo University of Pharmacy and Life Science, Hachioji, Tokyo 192-0392, Japan. sakurai@ls.toyaku.ac.jp
Teruaki
T
Sakurai
Masayuki
M
Ochiai
Chikara
C
Kojima
Takami
T
Ohta
Masumi H
MH
Sakurai
Naoko O
NO
Takada
Wei
W
Qu
Michael P
MP
Waalkes
Kitao
K
Fujiwara
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D019328:Buthionine Sulfoximine / Q000494:pharmacology*; D002101:Cacodylic Acid / Q000378:metabolism / Q000633:toxicity*; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005982:Glutathione Transferase / Q000378:metabolism; D006540:Herbicides / Q000378:metabolism / Q000633:toxicity*; D006801:Humans; D008099:Liver / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344
D061945:Caspase Inhibitors; D004791:Enzyme Inhibitors; D006540:Herbicides; D019328:Buthionine Sulfoximine; D002101:Cacodylic Acid; D005982:Glutathione Transferase; D020169:Caspases