title: Differential cellular regulation of the mitochondrial permeability transition in an in vitro model of 1,3-dinitrobenzene-induced encephalopathy.
abstract: Exposure to 1,3-dinitrobenzene (DNB) is associated with neuropathologic changes in specific brainstem nuclei, mediated by oxidative stress and mitochondrial dysfunction. The expression of Bcl-2-family proteins as a function of sensitivity to 1, 3-dinitrobenzene (DNB)-induced mitochondrial permeability transition (MPT) was examined in C6 glioma and SY5Y neuroblastoma cells. Neuroblastoma cells were 10-fold more sensitive than glioma cells to DNB-induced decreases in mitochondrial reducing potential, measured by reduction of the tetrazolium compound, 3-[4, 5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT). The IC(50) values for DNB-related inhibition of MTT reduction were 107+/-25 microM in SY5Y cells and 1047+/-101 microM in C6 cells. Levels of reactive oxygen species (ROS) were increased in both SY5Y and C6 cells following DNB exposure by 4.6- and 6.0-fold above control, respectively. DNB caused abrupt depolarization of mitochondria in both neuroblastoma and glioma cells that was inhibited by trifluoperazine. The first order rate constants for mitochondrial depolarization were: C6, k=0.31+/-0.02 min(-1); SY5Y, k=0.14+/-0.01 min(-1). Onset of MPT occurred at 10-fold lower concentration of DNB in SY5Y cells than in C6 cells. The antioxidants, deferoxamine and alpha-tocopherol, effectively prevented DNB-induced MPT in C6 and SY5Y cells, suggesting involvement of ROS in the initiation of MPT. Exposure to DNB resulted in decreased cellular ATP content in SY5Y cells and efflux of mitochondrial calcium in both SY5Y and C6 cells, concurrent with onset of MPT. The expression of Bcl-2, Bcl-X(L), and Bax was evaluated in both cell types by Western blot analysis. C6 glioma cells strongly expressed Bcl-X(L) and only weakly expressed Bcl-2 and Bax, whereas SY5Y neuroblastoma cells expressed lower levels of Bcl-X(L) and higher levels of both Bcl-2 and Bax. Collectively, these results suggest that higher constitutive expression of Bcl-X(L), rather than Bcl-2, correlates with resistance to DNB-induced MPT in SY5Y and C6 cells and that differential regulation of the permeability transition pore may underlie the cell-specific neurotoxicity of DNB.
authors.affiliation: Toxicology Program, Department of Environmental Health Sciences, University of Michigan, 1420 Washington Heights, Ann Arbor, MI 48109-2029, USA.
authors.forename: R B
authors.initials: RB
authors.lastname: Tjalkens
authors.forename: M M
authors.initials: MM
authors.lastname: Ewing
authors.forename: M A
authors.initials: MA
authors.lastname: Philbert
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000975:Antioxidants / Q000494:pharmacology; D001927:Brain Diseases / Q000139:chemically induced* / Q000473:pathology / Q000503:physiopathology*; D002118:Calcium / Q000378:metabolism; D003676:Deferoxamine / Q000494:pharmacology; D004136:Dinitrobenzenes / Q000494:pharmacology; D004594:Electrophysiology; D005910:Glioma / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D006801:Humans; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D009447:Neuroblastoma / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D010084:Oxidation-Reduction / Q000187:drug effects; D010539:Permeability; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D013778:Tetrazolium Salts / Q000378:metabolism; D013844:Thiazoles / Q000378:metabolism; D014268:Trifluoperazine / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014810:Vitamin E / Q000494:pharmacology; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein
chemical_list: D000975:Antioxidants; C494826:BAX protein, human; C494811:BCL2L1 protein, human; D004136:Dinitrobenzenes; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D017382:Reactive Oxygen Species; D013778:Tetrazolium Salts; D013844:Thiazoles; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D014810:Vitamin E; D014268:Trifluoperazine; D000255:Adenosine Triphosphate; C017906:3-dinitrobenzene; C022616:thiazolyl blue; D003676:Deferoxamine; D002118:Calcium