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.

Zinc Supplementation Protects against Cadmium Accumulation and Cytotoxicity in Madin-Darby Bovine Kidney Cells

“…In line with previous observations in other species [23], [24], Cd 2+ triggered MDBK apoptotic cell death in a time- and dose-dependent manner. This was associated with a Cd 2+ -induced increase in ROS accumulation in these cells, and mitochondrial depolarization.…”

Circulating Monocytes in HIV-1-Infected Viremic Subjects Exhibit an Antiapoptosis Gene Signature and Virus- and Host-Mediated Apoptosis Resistance

“…After incubation in the presence or absence of 20 μ M CdCl 2 (Sigma-Aldrich, catalog no. 202908), an established apoptosis inducer (27–35), for 20 h, or with 100 ng/ml FasL (Sigma-Aldrich, catalog no. F0427) for 6 h, a million cells were stained with surface Abs purchased from BD Biosciences (CD14 for monocytes), Lineage cocktail (anti-CD56, catalog no.…”

Activation of liver X receptors inhibits cadmium-induced apoptosis of human renal proximal tubular cells

“…Cadmium induces renal proximal tubular cell death through generation of oxidative stress which depletes endogenous radical scavengers. Increasing ROS damages a variety of transport proteins, such as Na + /K + -ATPase (Thevenod and Friedmann, 1999;Filipic et al, 2006;Kim and Sharma, 2006). Although LXR activation was previously associated with anti-inflammation and antioxidant (Gong et al, 2009), its role in protection of cell death induced by cadmium has not been documented.…”

“…Evidence shows low concentration of CdCl 2 (20 mM) induced cell death in renal porcine proximal tubular cells (LLC-PK1) via the apoptosis pathway (Yokouchi et al, 2008) whereas cell necrosis is found with high concentration of CdCl 2 (>50 mM) (Lee et al, 2007). Oxidative stress is suggested as the mechanism responsible for cadmium toxicity (Filipic et al, 2006;Kim and Sharma, 2006). Moreover, evidences indicate cadmium increases intracellular reactive oxygen species (ROS) levels by depleting cellular glutathione (GSH) (Shaikh et al, 1999;Lopez et al, 2006) as well as by disturbing antioxidant enzymes, such as increasing superoxide dismutase (SOD) (Lopez et al, 2006), increasing quinone oxydoreductase 1 (NQO1) (Elbekai and El-Kadi, 2008), and decreasing catalase (CAT) (Casalino et al, 2002).…”