title: Melatonin induces apoptosis through a caspase-dependent but reactive oxygen species-independent mechanism in human leukemia Molt-3 cells.
abstract: Melatonin is a naturally occurring indoleamine synthesized in the pineal gland that exhibits an extensive repertoire of biological activities. An increasing number of studies indicate that melatonin protects normal cells, while it reducing cancer cell proliferation. In this study, we investigated the effect of melatonin on the growth of the human leukemia cells and found that it efficiently reduced the number of cells in a concentration- and time-dependent manner. Thus, incubation with the indoleamine increased the percentage of cells with a hypodiploid DNA content, augmented the number of annexin V-positive cells, and also provoked ultrastructural changes that are features of apoptotic cell death. Evaluation of caspases revealed that caspase-3, caspase-6, caspase-7, and caspase-9, but not caspase-8 and caspase-2, were quickly activated (3-6 hr). The increase in the activity of these proteases was associated with up-regulation of the pro-apoptotic factor Bax and also with the release of cytochrome c from mitochondria. Pretreatment of the cells with the general caspase inhibitor z-VAD-fmk, reduced melatonin-induced apoptosis, but it did not block cell death suggesting that melatonin activates an alternative cell death modality in the absence of caspase activity. Thus, the activation of caspases was preceded by a fast (<30 min) increase in reactive oxygen species (ROS). Rotenone and antimycin A reduced the levels of ROS stimulated by melatonin, indicating that the complex I and the complex III of the mitochondrial electron transport chain are important sources of these chemical species. However, the role of ROS in melatonin-induced cell death remains elusive because anti-oxidants that were shown to decrease ROS levels (glutathione, N-acetyl-l-cysteine and Trolox) were unable to abrogate melatonin-induced cell death.
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Fisiología, Genética e Inmunología, Facultad de Ciencias de la Salud, Universidad de Las Palmas de Gran Canaria, Las Palmas de Gran Canaria, Spain.
authors.forename: Juan
authors.initials: J
authors.lastname: Perdomo
authors.forename: Javier
authors.initials: J
authors.lastname: Cabrera
authors.forename: Francisco
authors.initials: F
authors.lastname: Estévez
authors.forename: Juan
authors.initials: J
authors.lastname: Loro
authors.forename: Russel J
authors.initials: RJ
authors.lastname: Reiter
authors.forename: José
authors.initials: J
authors.lastname: Quintana
mesh_terms: D000975:Antioxidants / Q000494:pharmacology / Q000627:therapeutic use*; D017209:Apoptosis / Q000187:drug effects*; D053453:Caspase 9 / Q000502:physiology*; D045744:Cell Line, Tumor; D045304:Cytochromes c / Q000378:metabolism; D004353:Drug Evaluation, Preclinical; D006801:Humans; D007938:Leukemia / Q000188:drug therapy*; D008550:Melatonin / Q000494:pharmacology / Q000627:therapeutic use*; D017382:Reactive Oxygen Species / Q000378:metabolism*; D051028:bcl-2-Associated X Protein / Q000378:metabolism
chemical_list: D000975:Antioxidants; D017382:Reactive Oxygen Species; D051028:bcl-2-Associated X Protein; D045304:Cytochromes c; D053453:Caspase 9; D008550:Melatonin
keywords: Molt-3; ROS; anti-oxidants; caspases; cell proliferation; melatonin