title: Cytotoxic effects of cadmium and zinc co-exposure in PC12 cells and the underlying mechanism.
abstract: Cadmium (Cd2+) is a well studied inducer of cellular necrosis and apoptosis. Zinc (Zn2+) is known to inhibit apoptosis induced by toxicants including Cd2+both in vitro and in vivo. The mechanism of Zn2+-mediated protection from Cd2+-induced cytotoxicity is not established. In this study, we aimed to understand the effects of Zn2+on Cd2+-induced cytotoxicity and apoptosis using PC12 cells. Cell viability and DNA fragmentation assays in PC12 cells exposed to Cd2+and/or Zn2+revealed that Cd2+(5 and 10 μmol/L) alone induced significant cell death, and co-exposure to Zn2+(5, 10, and 100 μmol/L) for 48 h had a protective effect. Assessment of intracellular free sulfhydryl levels and lactate dehydrogenase activity suggested that Cd2+(10 μmol/L) induced oxidative stress and disrupted cell membrane integrity. Addition of Zn2+(10 and 100 μmol/L) reduced Cd2+-mediated cytotoxicity. Changes in expression of the apoptotic factors Bax, Bcl-2, Bcl-x, and cytochrome c were measured via western blot and expression of caspase 9 was detected via reverse transcriptase polymerase chain reaction. Western blots showed that Zn2+(10 and 100 μmol/L) suppressed Cd2+-induced apoptosis (10 μmol/L) by reducing cytochrome c release into the cytosol, and downregulating the proapoptotic protein, Bax. In addition, expression of caspase 9 was lower in Cd2+(5 μmol/L)-treated PC12 cells when co-treated with Zn2+(2 and 5 μmol/L). These findings suggest that the effective inhibition of Cd2+-induced apoptosis in PC12 cells by Zn2+might be due to suppression of mitochondrial apoptosis pathway and inhibition of Cd2+-induced production of reactive oxygen species.
authors.affiliation: Graduate School of Environmental Science, Hokkaido University, Japan; Department of Environmental Sciences, Jahangirnagar University, Bangladesh.
authors.forename: Md Mostafizur
authors.initials: MM
authors.lastname: Rahman
authors.affiliation: Graduate School of Environmental Science, Hokkaido University, Japan.
authors.forename: Junki
authors.initials: J
authors.lastname: Ukiana
authors.affiliation: Graduate School of Environmental Science, Hokkaido University, Japan.
authors.forename: Rachael
authors.initials: R
authors.lastname: Uson-Lopez
authors.affiliation: Faculty of Health Sciences, Hokkaido University, Japan; Faculty of Environmental Earth Science, Hokkaido University, Japan.
authors.forename: Md Tajuddin
authors.initials: MT
authors.lastname: Sikder
authors.affiliation: Faculty of Health Sciences, Hokkaido University, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Saito
authors.affiliation: Graduate School of Environmental Science, Hokkaido University, Japan; Faculty of Environmental Earth Science, Hokkaido University, Japan. Electronic address: kura@ees.hokudai.ac.jp.
authors.forename: Masaaki
authors.initials: M
authors.lastname: Kurasaki
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D002104:Cadmium / Q000633:toxicity*; D053453:Caspase 9 / Q000378:metabolism; D045304:Cytochromes c / Q000378:metabolism; D053938:DNA Fragmentation / Q000187:drug effects; D015536:Down-Regulation / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects; D016716:PC12 Cells; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism; D015032:Zinc / Q000633:toxicity*; D051028:bcl-2-Associated X Protein / Q000378:metabolism; D051020:bcl-X Protein
chemical_list: D019253:Proto-Oncogene Proteins c-bcl-2; D017382:Reactive Oxygen Species; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D002104:Cadmium; D045304:Cytochromes c; D053453:Caspase 9; D015032:Zinc
keywords: Apoptosis; Caspase 9; Cytochrome c; DNA; Glutathione; Heavy metals