Involvement of N-acetylcysteine-sensitive pathways in ricin-induced apoptotic cell death in U937 cells.
We have found that the antioxidant N-acetylcysteine (NAC) strongly inhibited ricin-induced apoptotic cell death in U937 cells (human myeloid leukemia), as judged by cytotoxicity, nuclear morphological change, and DNA fragmentation. Consistent with these observations, a significant depletion of cellular glutathione was observed in ricin-treated cells, and NAC prevented the decrease in cellular glutathione. On the other hand, among the caspase inhibitors tested, Z-Asp-CH2-DCB, which inhibited ricin cytotoxicity, also suppressed ricin-mediated glutathione depletion, while NAC did not affect the generation of caspase-3 like activity in ricin-treated cells. These results suggest that glutathione loss takes place downstream from caspase activation during the ricin-induced apoptotic process. Treatment with a specific inhibitor of glutathione biosynthesis, buthionine sulfoximine (BSO) failed to induce apoptosis, and had no effect on the overall extent of ricin-induced apoptosis, even though the glutathione level was decreased to less than 5% of the control level. However, NAC still protected against ricin-induced apoptosis in the BSO-treated cells. We conclude that glutathione loss is one of several apoptotic changes caused by ricin, but is not a sufficient factor for the progress of apoptosis. NAC may prevent ricin-induced apoptosis through maintaining an intracellular reducing condition by acting as a thiol supplier.
Oda
T
T
Division of Biochemistry, Faculty of Fisheries, Nagasaki University, Japan. t-oda@net.nagasaki-u.ac.jp
Iwaoka
J
J
Komatsu
N
N
Muramatsu
T
T
D000111:Acetylcysteine / Q000378:metabolism / Q000494:pharmacology*; D000975:Antioxidants / Q000378:metabolism / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D019328:Buthionine Sulfoximine / Q000494:pharmacology; D053148:Caspase 3; D061945:Caspase Inhibitors; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D053938:DNA Fragmentation / Q000187:drug effects / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004587:Electrophoresis, Agar Gel; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016166:Free Radical Scavengers / Q000378:metabolism / Q000494:pharmacology*; D005978:Glutathione / Q000494:pharmacology / Q000502:physiology; D006801:Humans; D008856:Microscopy, Fluorescence; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012276:Ricin / Q000378:metabolism*; D020298:U937 Cells
D000975:Antioxidants; D061945:Caspase Inhibitors; D004791:Enzyme Inhibitors; D016166:Free Radical Scavengers; D011500:Protein Synthesis Inhibitors; D019328:Buthionine Sulfoximine; D012276:Ricin; C505407:CASP3 protein, human; D053148:Caspase 3; D005978:Glutathione; D000111:Acetylcysteine