Biochemical and molecular basis of thimerosal-induced apoptosis in T cells: a major role of mitochondrial pathway.
The major source of thimerosal (ethyl mercury thiosalicylate) exposure is childhood vaccines. It is believed that the children are exposed to significant accumulative dosage of thimerosal during the first 2 years of life via immunization. Because of health-related concerns for exposure to mercury, we examined the effects of thimerosal on the biochemical and molecular steps of mitochondrial pathway of apoptosis in Jurkat T cells. Thimerosal and not thiosalcylic acid (non-mercury component of thimerosal), in a concentration-dependent manner, induced apoptosis in T cells as determined by TUNEL and propidium iodide assays, suggesting a role of mercury in T cell apoptosis. Apoptosis was associated with depolarization of mitochondrial membrane, release of cytochrome c and apoptosis inducing factor (AIF) from the mitochondria, and activation of caspase-9 and caspase-3, but not of caspase-8. In addition, thimerosal in a concentration-dependent manner inhibited the expression of XIAP, cIAP-1 but did not influence cIAP-2 expression. Furthermore, thimerosal enhanced intracellular reactive oxygen species and reduced intracellular glutathione (GSH). Finally, exogenous glutathione protected T cells from thimerosal-induced apoptosis by upregulation of XIAP and cIAP1 and by inhibiting activation of both caspase-9 and caspase-3. These data suggest that thimerosal induces apoptosis in T cells via mitochondrial pathway by inducing oxidative stress and depletion of GSH.
Cellular and Molecular Immunology Laboratories, Division of Basic and Clinical Immunology, University of California, Irvine 92697, USA.
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Makani
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Gollapudi
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Yel
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Chiplunkar
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Gupta
D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D051033:Apoptosis Inducing Factor; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D003574:Cytochrome c Group / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D005420:Flavoproteins / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D019169:Jurkat Cells; D008564:Membrane Potentials / Q000187:drug effects; D008565:Membrane Proteins / Q000378:metabolism; D008928:Mitochondria / Q000187:drug effects* / Q000378:metabolism*; D018384:Oxidative Stress / Q000187:drug effects; D011310:Preservatives, Pharmaceutical / Q000633:toxicity; D011506:Proteins / Q000037:antagonists & inhibitors; D017382:Reactive Oxygen Species / Q000378:metabolism; D012459:Salicylates / Q000633:toxicity; D013438:Sulfhydryl Compounds; D013601:T-Lymphocytes / Q000166:cytology* / Q000187:drug effects* / Q000378:metabolism; D013849:Thimerosal / Q000633:toxicity*; D051636:X-Linked Inhibitor of Apoptosis Protein
C494829:AIFM1 protein, human; D051033:Apoptosis Inducing Factor; D003574:Cytochrome c Group; D005420:Flavoproteins; D008565:Membrane Proteins; D011310:Preservatives, Pharmaceutical; D011506:Proteins; D017382:Reactive Oxygen Species; D012459:Salicylates; D013438:Sulfhydryl Compounds; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; D013849:Thimerosal; C441201:thiosalicylic acid; C505407:CASP3 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases; D005978:Glutathione