title: Cadmium-induced apoptosis in murine macrophages is antagonized by antioxidants and caspase inhibitors.
abstract: Cadmium is a toxic heavy metal that accumulates in the environment and is commonly found in cigarette smoke and industrial effluents. This study was designed to determine the role of reactive oxygen species (ROS) generation, and its antagonism by antioxidants, in cadmium-mediated cell signaling and apoptosis in murine macrophage cultures. Cadmium-generated ROS production was observed in J774A.1 cells at 6 h, reverting to control levels at 16 and 24 h. The ROS production was concentration related between 20 and 500 microM cadmium. Activation of caspase-3 was observed at 8 h and DNA fragmentation at 16 h in the presence of 20 microM cadmium, suggesting that caspase-3 activation is a prior step to DNA fragmentation in cadmium-induced apoptosis. Inhibitors of caspase-3, -8, -9, and a general caspase inhibitor suppressed cadmium-induced caspase-3 activation and apoptosis indicating the importance of caspase-3 in cadmium-induced toxicity in these cells. Protection against the oxidative stress with N-acetylcysteine (NAC) and silymarin (an antioxidant flavonoid) blocked cadmium-induced apoptosis. Pretreatment of cells with NAC and silymarin prevented cadmium-induced cell injury, including growth arrest, mitochondrial impairment, and necrosis, and reduced the cadmium-elevated intracellular calcium ([Ca2+]i), suggesting that the oxidative stress is a source of increased [Ca2+]i. NAC inhibited cadmium-induced activation of mitogen-activated protein kinases, the c-Jun NH2-terminal protein kinase (JNK) and extracellular signal-regulated kinase (ERK). However, silymarin provided only a partial protection for JNK activation, and only at the low concentration did it inhibit cadmium-induced ERK activation. Inhibition of caspase-3 protected oxidative stress produced by cadmium, suggesting that the activation of caspase-3 also contributes to generation of reactive oxygen species (ROS). Results emphasized the role of ROS, Ca2+ and mitogen-activated protein kinases in cadmium-induced cytotoxicity in murine macrophages.
authors.affiliation: Program in Toxicology, Department of Physiology and Pharmacology, College of Veterinary Medicine, The University of Georgia, Athens, Georgia 30602-7389, USA.
authors.forename: Jiyoung
authors.initials: J
authors.lastname: Kim
authors.forename: Raghubir P
authors.initials: RP
authors.lastname: Sharma
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D002104:Cadmium / Q000633:toxicity*; D053148:Caspase 3; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D002460:Cell Line; D004785:Environmental Pollutants / Q000633:toxicity*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008264:Macrophages / Q000187:drug effects*; D051379:Mice; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects*; D017382:Reactive Oxygen Species
chemical_list: D000975:Antioxidants; D061945:Caspase Inhibitors; D004785:Environmental Pollutants; D004791:Enzyme Inhibitors; D017382:Reactive Oxygen Species; D002104:Cadmium; D020929:Mitogen-Activated Protein Kinase Kinases; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020169:Caspases