The role of calcium in apoptosis induced by 7β‐hydroxycholesterol and cholesterol‐5β,6β‐epoxide

Journal of Biochemical and Molecular Toxicology - Tập 23 Số 5 - Trang 324-332 - 2009
Sinéad Lordan1, Nora M. O’Brien1, John J. Mackrill2
1Department of Food and Nutritional Sciences University College, Cork, Republic of Ireland
2Department of Physiology, University College Cork, Republic of Ireland

Tóm tắt

AbstractOxysterols, such as 7β‐hydroxy‐cholesterol (7β‐OH) and cholesterol‐5β,6β‐epoxide (β‐epoxide), may have a central role in promoting atherogenesis. This is thought to be predominantly due to their ability to induce apoptosis in cells of the vascular wall and in monocytes/macrophages. Although there has been extensive research regarding the mechanisms through which oxysterols induce apoptosis, much remains to be clarified. Given that experimental evidence has long associated alterations of calcium (Ca2+) homeostasis to apoptotic cell death, the aim of the present study was to determine the influence of intracellular Ca2+ changes on apoptosis induced by 7β‐OH and β‐epoxide. Ca2+ responses in differentiated U937 cells were assessed by epifluorescence video microscopy, using the ratiometric dye fura‐2. Over 15‐min exposure of differentiated U937 cells to 30 μM of 7β‐OH induced a slow but significant rise in fura‐2 ratio. The Ca2+ channel blocker nifedipine and the chelating agent EGTA blocked the increase in cytoplasmic Ca2+. Moreover, dihydropyridine (DHP) binding sites identified with BODIPY‐FLX‐DHP were blocked following pretreatment with nifedipine, indicating that the influx of Ca2+ occurred through L‐type channels. However, following long‐term incubation with 7β‐OH, elevated levels of cytoplasmic Ca2+ were not maintained and nifedipine did not provide protection against apoptotic cell death. Our results indicate that the increase in Ca2+ may be an initial trigger of 7β‐OH–induced apoptosis, but following chronic exposure to the oxysterol, the influence of Ca2+ on apoptotic cell death appears to be less significant. In contrast, Ca2+ did not appear to be involved in β‐epoxide–induced apoptosis. © 2009 Wiley Periodicals, Inc. J Biochem Mol Toxicol 23:324–332, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20295

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Journal of Biochemical and Molecular Toxicology

Tập 23 Số 5

324-332

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