title: Mercury-induced apoptosis and necrosis in murine macrophages: role of calcium-induced reactive oxygen species and p38 mitogen-activated protein kinase signaling.
abstract: The current study characterizes the mechanism by which mercury, a toxic metal, induces death in murine macrophages. The cytotoxic EC(50) of mercury ranged from 62.7 to 81.1 microM by various assays in J774A.1 cultures; accordingly, we employed 70 microM of mercuric chloride in most experiments. Mercury-induced intracellular calcium modulated reactive oxygen species (ROS) production, which resulted in both cell apoptosis and necrosis indicated by annexin V binding and caspase-3 activity, and propidium-iodide binding. Calcium antagonists abolished ROS production. Mercury stimulated p38 mitogen-activated protein kinase (MAPK) and additively stimulated lipopolysaccharide-activated p38. Mercury-activated p38 was decreased by pretreatment of cells with antioxidants, N-acetylcysteine (NAC) and silymarin, indicating that mercury-induced ROS were involved in p38 activation. Mercury increased the expression of tumor necrosis factor alpha (TNFalpha); antioxidants and a specific p38 inhibitor decreased this effect. Pretreatment with antioxidants, p38 inhibitor, and anti-TNFalpha antibody decreased mercury-induced necrosis; however, anti-TNFalpha antibody did not decrease mercury-induced apoptosis. Results suggest that mercury-induced macrophage death is a mix of apoptosis and necrosis employing different pathways. P38-mediated caspase activation regulates mercury-induced apoptosis and p38-mediated TNFalpha regulates necrosis in these cells. Calcium regulates ROS production and mercury-induced ROS modulate downstream p38 that regulates both apoptosis and necrosis.
authors.affiliation: Interdisciplinary Program in Toxicology, Department of Physiology and Pharmacology, College of Veterinary Medicine, The University of Georgia, Athens, GA 30602-7389, USA.
authors.forename: Sang Hyun
authors.initials: SH
authors.lastname: Kim
authors.forename: Raghubir P
authors.initials: RP
authors.lastname: Sharma
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D002118:Calcium / Q000378:metabolism*; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D004789:Enzyme Activation; D008264:Macrophages / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D008627:Mercuric Chloride / Q000633:toxicity*; D051379:Mice; D008807:Mice, Inbred BALB C; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009336:Necrosis; D017382:Reactive Oxygen Species / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D048051:p38 Mitogen-Activated Protein Kinases
chemical_list: D017382:Reactive Oxygen Species; D008627:Mercuric Chloride; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D002118:Calcium