title: Toxic effects of mildly elevated homocysteine concentrations in neuronal-like cells.
abstract: Epidemiological and experimental evidence indicated that hyperhomocysteinemia is associated with neurodegeneration. However, homocysteine neurotoxic effects have been so far investigated mostly by employing homocysteine concentrations (≥100 µM) much higher than homocysteine mean plasma levels (20 µM) observed in patients with neurodegenerative disorders. While evaluating the effects of a prolonged exposure to ~20 µM homocysteine in neuronal-like differentiated SH-SY5Y cells, we observed a 35% loss of cell viability and a four-fold increase in reactive oxygen species levels in cells incubated with homocysteine for five days compared with controls. Moreover, homocysteine increased by 30% and around two-fold, respectively, the Comet-positive cell number and DNA damage indexes (tail length, T-DNA, olive tail moment) compared with controls. Cell response to homocysteine-induced DNA damage involved the up-regulation of Bax and, at a greater extent, Bcl-2, but not caspase-3, in association with a p53-independent increase of p21 levels; concomitantly, also p16 levels were increased. When looking at time-dependent changes in cyclin expression, we found that a significant up-regulation of cyclins D1, A1, E1, but not B1, concomitant with p21 down-regulation, occurred in cells incubated with homocysteine for three days. However, in line with the observed increase of p21 and p16 levels, a five days incubation with homocysteine induced cyclin down-regulation accompanied by a strong reduction of phosphorylated pRB amounts. These results suggest that, when prolonged, the exposure of neuronal-like cells to mildly elevated homocysteine concentrations triggers oxidative and genotoxic stress involving an early induction of cyclins, that is late repressed by G1-S check-point regulators.
authors.affiliation: Department of Biomedical Sciences and Morphofunctional Imaging, Polyclinic University of Messina, Via C. Valeria, 98125, Messina, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Currò
authors.forename: A
authors.initials: A
authors.lastname: Gugliandolo
authors.forename: C
authors.initials: C
authors.lastname: Gangemi
authors.forename: R
authors.initials: R
authors.lastname: Risitano
authors.forename: R
authors.initials: R
authors.lastname: Ientile
authors.forename: D
authors.initials: D
authors.lastname: Caccamo
mesh_terms: D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects* / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D006710:Homocysteine / Q000633:toxicity*; D006801:Humans; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis
chemical_list: D012333:RNA, Messenger; D006710:Homocysteine