Reacciones de N-homocisteinilación asociadas a hiperhomocisteinemia / N-homocysteinylation reactions related to hyperhomocysteinemia / Reações de N-homocisteinilação associadas a hiper-homocisteinemia

Numerosas evidencias clínicas avalan la asociación entre concentración plasmática elevada de homocisteína (hiperhomocisteinemia) y las enfermedades vasculares oclusivas, tales como la aterosclerosis y la trombosis. La homocisteína reducida (Hcy) y su éster cíclico homocisteína-tiolactona (HTL) serían los principales responsables de los efectos nocivos asociados a la hiperhomocisteinemia. Tanto la Hcy como la HTL pueden interactuar espontáneamente con proteínas, a través de reacciones de S y N-homocisteinilación, respectivamente. Ambos procesos provocan alteraciones proteicas post-traduccionales, e inducen cambios estructurales y funcionales a nivel molecular. En los últimos años ha cobrado interés el conocimiento acerca de la HTL y las consecuencias de concentraciones elevadas de este metabolito sobre la salud humana. En las reacciones de N-homocisteinilación, el grupo carbonilo de la HTL se une al grupo ε-amino de los residuos lisina de las proteínas, con lo que se generan grupos sulfhidrilo libres, susceptibles de participar en reacciones redox. Las proteínas N-homocisteiniladas pueden sufrir plegamiento incorrecto de la molécula y daño oxidativo, y en consecuencia se inducen efectos citotóxicos e inmunogénicos. Se ha establecido que la conversión metabólica de la Hcy en HTL y la N-homocisteinilación de proteínas es uno de los mecanismos involucrados en el desarrollo de patologías asociadas con la hiperhomocisteinemia, tales como las enfermedades cardiovasculares y neurodegenerativas.

Increased plasma homocysteine levels (hyperhomocysteinemia) are associated with occlusive vascular diseases, such as atherosclerosis and thrombosis. Reduced homocysteine (Hcy) and its cyclic ester, homocysteine thiolactone (HTL) would be involved in the detrimental effects associated to hyperhomocysteinemia. These two species, Hcy and HTL can spontaneously react with proteins, through S and N-homocysteinylation process, respectively. Both reactions produce post-translational protein changes, impairing structural and functional features. In recent years, interest has been developed in HTL and its effects on human health. N-homocysteinylation is the reaction between the carboxyl group of HTL and ε-amino group of lysine residues, rendering free sulfhydryl groups able to participate in redox reactions. N-homocysteinylated proteins are prone to misfolding and oxidative damage, inducing cytotoxic and immunogenic effects. Metabolic conversion of Hcy to HTL as well as protein N-homocysteinylation is one of the mechanisms underlying the development of pathologies associated to hyperhomocysteinemia, such as cardiovascular and neurodegenerative diseases.

Numerosas evidências clínicas garantem a associação entre concentração plasmática elevada de homocisteína (hiper-homocisteinemia) e as doenças vasculares oclusivas, tais como a aterosclerose e a trombose. A homocisteína reduzida (Hcy) e seu éster cíclico homocisteína tiolactona (HTL) seriam os principais responsáveis pelos efeitos nocivos associados à hiper-homocisteinemia. Tanto a Hcy quanto a HTL podem interagir espontaneamente com proteínas, através de reações de S e N-homocisteinilação, respectivamente. Ambos os processos provocam alterações proteicas pós-traducionais, induzindo alterações estruturais e funcionais em nível molecular. Nos últimos anos, cobrou interesse o conhecimento acerca da HTL e as consequências de concentrações elevadas deste metabólito sobre a saúde humana. Nas reações de N-homocisteinilação, o grupo carbonila da HTL se une ao grupo ε-amino dos resíduos lisina das proteínas, gerando grupos sulfidrila livres, suscetíveis de participar em reações redox. As proteínas N-homocisteiniladas podem sofrer dobramento incorreto da molécula e dano oxidativo, induzindo efeitos citotóxicos e imunogênicos. Estabeleceu-se que a conversão metabólica da Hcy em HTL e a N-homocisteinilação de proteínas é um dos mecanismos envolvidos no desenvolvimento de patologias associadas com a hiper-homocisteinemia, tais como as doenças cardiovasculares e neurodegenerativas.

Homocysteine & its metabolite homocysteine-thiolactone & deficiency of copper in patients with age related macular degeneration - A pilot study.

Background & objectives: Age related macular degeneration (ARMD) is a leading cause of blindness, particularly in persons above 60 yr of age. Homocysteine is implicated in many ocular diseases including ARMD. This study was undertaken to assess the status and relationship between plasma homocysteine, homocysteine - thiolactone, homocysteinylated protein and copper levels in patients with ARMD. Methods: A total of 16 patients with ARMD and 16 age-matched controls were recruited for the study. Plasma glutathione, homocysteine, homocysteine - thiolactone and extent of homocysteine conjugation with proteins, copper and thiobarbituric acid reactive substances were measured. Results: Homocysteine levels were elevated with increase in homocysteine-thiolactone, thiobarbituric acid reactive substances and a decrease of glutathione. The levels of homocysteinylated protein were elevated in ARMD. The elevated homocysteine, homocysteine-thiolactone correlated with the decrease in copper level. Interpretation & conclusions: Elevated homocysteine and its metabolite homocysteine-thiolactone and decreased levels of copper may play an important role in the pathogenesis of ARMD.

Study of the relationship between plasma homocysteine thiolactone concentrations and type 2 diabetic macrovascular complications / 中国实用内科杂志

Objective To investigate the role of homocysteine(Hcy)and homocysteine thiolactone(HcyT)in the development of macrovascular complications in patients with type 2 DM.Methods A total of 160 subjects were recruited in this study:40 healthy controls,120 with type 2 DM.Plasma Hcy levels were measured by Polarization Immunoassay(FPIA),and HcyT concentrations were monitored using high-performance liquid chromatography(HPLC)on a reversephase C18 column with ultraviolet detection.Plasma folic acid and Vitamin B12 levels were measured with radioimmunoassay method.Results Plasma Hcy and HcyT concentrations in type 2 DM patients were significantly higher than healthy controls[Hcy:9.28(7.51～11.82)?mol/L vs 5.64(5.17～8.00)?mol/L,P

Effects of antioxidants on homocysteine thiolactone-induced apoptosis in human umbilical vein endothelial cells / 老年心脏病学杂志（英文版）

Background and objectives Hyperhomocysteinemia is an independent risk factor for cardiovascular disease. Homocysteine thiolactone (HcyT), one of the homocysteine metabolites in vivo, is toxic both in vivo and in vitro. The aim of this study was to investigate the effect of HcyT on apoptotic damage in human umbilical vein endothelial cells (HUVECs) and the role of antioxidants in the reduction of HcyT-induced apoptosis. Methods HUVECs were cultured in DMEM supplemented with 20% heat inactivated fetal bovine serum cell cultures were maintained in a humidified 5% CO2 atmosphere at 37 ℃. Cytotoxicity was determined by MTT assay,which consists of hypodiploid cells with propidium iodide labeling and intracellular reactive oxygen species levels using 2',7'-dichlorofluorescein diacetate as the probe by flow cytometry. Results HcyT (250-2000μM) induced HUVECs apoptosis in a time- and concentration-dependent manner. Reactive oxygen species levels rose in response to increasing HcyT concentrations at 24-h incubation.The reduction of cell apoptosis by N-acetylcysteine, vitamin E, or pyrrolidine dithiocarbamate, occurred simultaneously with a significant decrease in intracellular reactive oxygen species levels. Conclusion HcyT exerts its cytotoxic effects on endothelial cells through an apoptotic mechanism involving cellular reactive oxygen species production. The capacity of N-acetylcysteine, vitamin E, and pyrrolidine dithiocarbamate to scavenge HcyT-induced cellular reactive oxygen species correlates well with their efficiency to protect against HcyT-promoted apoptotic damage. The protective effect of pyrrolidine dithiocarbamate on cell apoptosis indicates HcyT-generated hydrogen peroxide may provoke cell apoptosis via activating nuclear factor-kappa binding protein.