Cadmium-induced apoptotic death of human retinal pigment epithelial cells is mediated by MAPK pathway.

Cadmium (Cd), released from cigarette smoke and metal industrial activities, is known to accumulate in human body organs including retina and is particularly higher in retinal tissues of age-related macular degeneration (AMD) eyes compared to non-AMD eyes. We have determined the cytotoxic effects of Cd on human retinal pigment epithelial (RPE) cells. Upon Cd treatment, there was a dose- and time-dependent decline in ARPE-19 cell viability as well as early apoptotic changes such as altered mitochondrial membrane potential (MMP) and Cytochrome C release in cytosol. Depletion of GSH by buthionine-[S,R]-sulfoximine (BSO) resulted in increased Cd toxicity in ARPE-19 cells. Cadmium also caused reactive oxygen species (ROS) generation and activation of mitogen-activated protein kinases (MAPKs) pathway including c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase 1/2 (Erk1/2), and p38 in ARPE-19 cells. Antioxidants such as N-acetylcysteine (NAC) significantly reduced Cd-induced toxicity. These results indicate that elevated ROS-induced activation of the MAPK signaling pathway could be associated with Cd-induced RPE cell apoptosis, one of the major contributing factors in AMD. The toxic effects of Cd on ARPE-19 cells indicate that environmental heavy metals such as Cd could be important potential factors in RPE cells death associated retinal diseases particularly related to smoking.

Oxidative stress-induced up-regulation of the chloride channel and Na+/Ca2+ exchanger during cataractogenesis in diabetic rats.

We have determined the abundance of the chloride channel, ClC-3, and Na(+)/Ca(2+) exchanger proteins in isolated rat lens cortex fiber cells by immunofluorescence method using polyclonal anti-ClC-3 antibodies and monoclonal antibodies against the canine cardiac Na(+)/Ca(2+) exchanger protein. These proteins were also quantified in the lens cortex of streptozotocin-injected rats by Western blots. Also, mRNA for ClC-3 was determined by Northern blot analysis. The isolated rat lens cortical fibers expressed basal levels of ClC-3 and Na(+)/Ca(2+) exchanger proteins. As compared to controls, the ClC-3 protein in the lens cortex of diabetic rats (blood glucose>400 mg%) increased by 2.5-fold in 7 days and 4.5-fold in 14 days. However, the ClC-3 protein decreased to near-normal values in 40 days. The changes in ClC-3 mRNA closely followed the protein levels. Similarly, as compared to controls, on Day 7, the Na(+)/Ca(2+) exchanger protein in the diabetic rat lens cortex increased by 3.5-fold and on Day14 by 5.5-fold. Subsequently, it decreased to control levels on Day 40. Treatment with the antioxidant, Trolox (2 mg/kg body weight), prevented the initial increase in ClC-3 and Na(+)/Ca(2+) exchanger proteins. The up-regulation of ClC-3 and Na(+)/Ca(2+) exchanger proteins during the early stages of diabetes and its prevention by antioxidants suggests that the proteins regulating ion transport may have a pathophysiological role in the development of diabetic cataracts.

Cadmium-induced induction of cell death in human lens epithelial cells: implications to smoking associated cataractogenesis.

Cadmium is reported to accumulate in human eye tissues suggesting its implication in diverse ocular pathology. Using an in vitro cell culture model we investigated the effects of cadmium on human lens epithelial cells (HLECs) (HLE-B3). We observed cadmium-induced dose- as well as time-dependent decline in HLECs viability which was exacerbated significantly upon reduction of intracellular glutathione levels by buthionine sulfoximine (BSO). There was a dose-dependent significant increase in lactate dehydrogenase (LDH) release from HLECs suggesting cadmium-induced alteration of membrane integrity as well as necrotic cell death. The decline in cell viability was also due to apoptosis of the HLECs as determined by quantifying % apoptotic cells as well as PARP cleavage. Moreover, release of apoptosis inducing factor (AIF) into the cytosol was also detected. Cadmium was also observed to increase oxidative stress, lipid peroxidation and activation of MAPK pathway in HLECs. Antioxidants like N-acetylcysteine (NAC) and alpha-Tocopherol significantly prevented cadmium-induced toxicity in HLECs. Our findings suggest that cadmium-induced elevated oxidative stress as well as activation of MAPK signaling cascade eventually led to cell death of HLECs through apoptosis as well as necrosis. The loss of HLECs by cadmium could possibly explain its implication in cataract development particularly associated with smoking.