title: Clonidine Induces Apoptosis of Human Corneal Epithelial Cells through Death Receptors-Mediated, Mitochondria-Dependent Signaling Pathway.
abstract: Clonidine, an α2-adrenoreceptor agonist, is an anti-glaucoma drug clinically used in many developing countries, and its abuse might damage the cornea and impair human vision. However, its cytotoxicity and precise mechanisms need to be elucidated. Herein, we investigated the cytotoxicity of clonidine and its underlying mechanisms, using an in vitro model of human corneal epithelial (HCEP) cells and an in vivo model of cat corneas, respectively. HCEP cells were treated with various doses of clonidine for 1-28 h, resulting in abnormal morphology, decline of cell viability and G1 phase arrest in a time- and/or dose-dependent manner. Moreover, clonidine treatment induced elevation of plasma membrane permeability, phosphatidylserine externalization, DNA fragmentation, and apoptotic body formation in HCEP cells. Furthermore, we found that clonidine treatment resulted in activated caspase-2, -3, -8, and -9, disruption of the mitochondrial transmembrane potential, downregulation of Bcl-2, and upregulation of Bad, cytoplasmic cytochrome c and apoptosis inducing factor, suggesting that clonidine-induced apoptosis is triggered through Fas/TNFR1 death receptors and Bcl-2 family proteins-mediated mitochondria-dependent pathways. Finally, our in vivo results displayed that 0.25% clonidine could induce DNA fragmentation of cat corneal epithelial cells. In summary, our findings suggest that clonidine above 1/32 of its clinical therapeutic dosage is cytotoxic to corneal epithelial cells by inducing cell apoptosis both in vitro and in vivo, and its pro-apoptotic effect on HCEP cells is triggered by a Fas/TNFR1 death receptors-mediated, mitochondria-dependent signaling pathway.
authors.affiliation: Laboratory for Corneal Tissue Engineering, College of Marine Life Sciences, Ocean University of China, Qingdao, Shandong Province 266003, P.R. China.
authors.forename: Dan
authors.initials: D
authors.lastname: Fan
authors.affiliation: Laboratory for Corneal Tissue Engineering, College of Marine Life Sciences, Ocean University of China, Qingdao, Shandong Province 266003, P.R. China.
authors.forename: Ting-Jun
authors.initials: TJ
authors.lastname: Fan
mesh_terms: D058647:Adrenergic alpha-2 Receptor Agonists / Q000008:administration & dosage / Q000009:adverse effects*; D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D020169:Caspases / Q000737:chemistry / Q000378:metabolism; D002415:Cats; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism / Q000473:pathology / Q000648:ultrastructure; D002463:Cell Membrane Permeability / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D003000:Clonidine / Q000008:administration & dosage / Q000009:adverse effects*; D053938:DNA Fragmentation / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D019573:Epithelium, Corneal / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D016193:G1 Phase / Q000187:drug effects; D006801:Humans; D008297:Male; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D046529:Microscopy, Electron, Transmission; D047888:Receptors, Tumor Necrosis Factor, Type I / Q000819:agonists* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D019014:fas Receptor / Q000378:metabolism*
chemical_list: D058647:Adrenergic alpha-2 Receptor Agonists; C491901:FAS protein, human; D047888:Receptors, Tumor Necrosis Factor, Type I; C506235:TNFRSF1A protein, human; D019014:fas Receptor; D020169:Caspases; D003000:Clonidine
keywords: apoptosis; cat corneal epithelial cells; clonidine; cytotoxicity; human corneal epithelial cells; mitochondria-dependent signaling pathway.