Structural changes of fibrinogen molecule mediated by the N-homocysteinylation reaction.

Homocysteine and its cyclic ester homocysteine thiolactone (HTL) have been involved in the detrimental consequences associated to hyperhomocysteinemia, an independent risk factor for vascular diseases. HTL reacts with protein lysine residues in a process named N-homocysteinylation. The aim of our study was to evaluate the in vitro effects of HTL on the fibrinogen through electrophoretic methods. Fibrinogen was incubated with HTL at different molar ratios and structural changes of the protein were assessed by polyacrylamide gel electrophoresis (PAGE), capillary zone electrophoresis (CZE) and capillary isoelectric focusing (CIEF). Ellman´s reaction, CZE and proton nuclear magnetic resonance (1H NMR) were used to evaluate HTL hydrolyisis. On denaturing PAGE numerous bands were observed, being the three lower bands identical to those obtained by treatment with 2-mercaptoethanol. This effect was also detected by CZE. The results show a reducing action of HTL on the fibrinogen molecule, probably attributed to the sulfhydryl groups generated by N-homocysteinylation and/or by the ones present in the homocysteine molecule yielded by HTL hydrolysis. In order to distinguish between these two options, HTL stability was evaluated at different pH and incubation times. The results showed minimum HTL hydrolysis in our experimental conditions. We postulate that the reducing effect observed would be mainly associated to the new sulfhydryl groups generated by the N-homocysteinylation process. Moreover, a displacement of the HTL-treated fibrinogen isoforms towards more acidic pH values was detected. The structural changes of N-homocysteinylated fibrinogen could be involved in the pathological consequences of hyperhomocysteinemia.

Impact of homocysteine-thiolactone on plasma fibrin networks.

Epidemiologic studies have shown that hyperhomocysteinemia is an independent risk factor for vascular disease. Homocysteine (Hcy) circulates as different species, mostly protein bound, and approximately 1% as its reduced form and the cyclic thioester homocysteine-thiolactone (HTL). Despite the level of plasma thiolactone being markedly low, detrimental effects are related to its high reactivity. HTL reacts with proteins by acylation of free basic amino groups; in particular, the epsilon-amino group of lysine residues forms adducts and induces structural and functional changes in plasma proteins. In order to assess the effects of HTL on plasma fibrin networks, a pool of normal plasma incubated with HTL (100, 500 and 1,000 µmol/L, respectively) was evaluated by global coagulation tests and fibrin formation kinetic assays, and the resulting fibrin was observed by scanning electron microscopy. HTL significantly prolonged global coagulation tests in a concentration-dependent manner with respect to control, and increases were up to 14.5%. Fibrin formation kinetic parameters displayed statistically significant differences between HTL-treated plasma and control in a concentration-dependent way, showing higher lag phase and lower maximum reaction velocity and final network optical density. Electron microscopy analysis of HTL plasma networks revealed a compact architecture, with more branches and shorter fibers than control. We can conclude that HTL induced a slower coagulation process, rendering more tightly packed fibrin clots. Since these features of the networks have been related to impaired fibrinolysis, the N-homocysteinylation reactions would be involved in the prothrombotic effects associated to hyperhomocysteinemia.

Extraction-free protocol combining proteinase K and heat inactivation for detection of SARS-CoV-2 by RT-qPCR.

Real-time reverse transcription PCR (RT-qPCR) is the gold-standard technique for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) detection in nasopharyngeal swabs specimens. The analysis by RT-qPCR usually requires a previous extraction step to obtain the purified viral RNA. Unfortunately, RNA extraction constitutes a bottleneck for early detection in many countries since it is expensive, time-consuming and depends on the availability of commercial kits. Here, we describe an extraction-free protocol for SARS-CoV-2 detection by RT-qPCR from nasopharyngeal swab clinical samples in saline solution. The method includes a treatment with proteinase K followed by heat inactivation (PK+HID method). We demonstrate that PK+HID improves the RT-qPCR performance in comparison to the heat-inactivation procedure. Moreover, we show that this extraction-free protocol can be combined with a variety of multiplexing RT-qPCR kits. The method combined with a multiplexing detection kit targeting N and ORF1ab viral genes showed a sensitivity of 0.99 and a specificity of 0.99 from the analysis of 106 positive and 106 negative clinical samples. In conclusion, PK+HID is a robust, fast and inexpensive procedure for extraction-free RT-qPCR determinations of SARS-CoV-2. The National Administration of Drugs, Foods and Medical Devices of Argentina has recently authorized the use of this method.

Active Surveillance of Asymptomatic, Presymptomatic, and Oligosymptomatic SARS-CoV-2-Infected Individuals in Communities Inhabiting Closed or Semi-closed Institutions.

Background: The high COVID-19 dissemination rate demands active surveillance to identify asymptomatic, presymptomatic, and oligosymptomatic (APO) SARS-CoV-2-infected individuals. This is of special importance in communities inhabiting closed or semi-closed institutions such as residential care homes, prisons, neuropsychiatric hospitals, etc., where risk people are in close contact. Thus, a pooling approach-where samples are mixed and tested as single pools-is an attractive strategy to rapidly detect APO-infected in these epidemiological scenarios. Materials and Methods: This study was done at different pandemic periods between May 28 and August 31 2020 in 153 closed or semi-closed institutions in the Province of Buenos Aires (Argentina). We setup pooling strategy in two stages: first a pool-testing followed by selective individual-testing according to pool results. Samples included in negative pools were presumed as negative, while samples from positive pools were re-tested individually for positives identification. Results: Sensitivity in 5-sample or 10-sample pools was adequate since only 2 Ct values were increased with regard to single tests on average. Concordance between 5-sample or 10-sample pools and individual-testing was 100% in the Ct ≤ 36. We tested 4,936 APO clinical samples in 822 pools, requiring 86-50% fewer tests in low-to-moderate prevalence settings compared to individual testing. Conclusions: By this strategy we detected three COVID-19 outbreaks at early stages in these institutions, helping to their containment and increasing the likelihood of saving lives in such places where risk groups are concentrated.

The C677T thermolabile variant of methylene tetrahydrofolate reductase on homocysteine, folate and vitamin B12 in a hemodialysis center.

Homocysteine is a risk factor for cardiovascular disease. Mutations in a key enzyme in homocysteine metabolism, methylenetetrahydrofolate reductase, may contribute to hyperhomocysteinemia and alter folate and cobalamin levels. After starting hemodialysis, 10 mg oral folate daily and 500 micrograms intravenous methylcobalamin once weekly were prescribed to 27 hemodialysis patients (time on hemodialysis > or = 12 months) and two groups were defined: Group A normal; Group B heterozygous. Initial, third and twelfth month measurements of homocysteine, serum folate and vitamin B12 levels were collected and analyzed. Heterozygous state of methylenetetrahydrofolate reductase prevalence was 48% and homozygozity 4%. Hyperhomocysteinemia was present in both groups. Cobalamin final levels were significantly lower in Group B compared to Group A. Homocysteine, serum folate and cobalamin levels at third and twelfth month were significantly different from baseline levels but non-different between them in both groups. In Group B, vitamin B12 at third month was significantly higher than initial, but final measurements were not different from baseline determinations. In conclusion, the heterozygous prevalence of the enzyme in hemodialysis patients is similar to that reported in the general population; hyperhomocysteinemia is frequent in hemodialysis patients and final levels in heterozygous patients are significantly higher than in normal patients. Cobalamin levels are lower in the heterozygous group. After one year of treatment, homocysteine tends to increase, suggesting a secondary resistance phenomenon to vitamin supplementation in heterozygous patients.

Characterization of N-homocysteinylated albumin adducts.

Increased plasma homocysteine levels are considered an important risk factor for vascular disease. Homocysteine, an intermediate compound in methionine metabolism, is an amino acid that includes a thiol group, and circulates as different species. One of them, Homocysteine thiolactone (HTL) forms adducts through irreversible reactions with epsilon-NH2 groups of lysine residues. These processes can alter the structure and biological function of diverse proteins that may be involved in the detrimental effects of homocysteine. Particularly, in this work we evaluated HTL-mediated molecular changes in human serum albumin (HSA) through electrophoretic techniques. Albumin and HTL were incubated (37 °C, 6 h) at HSA:HTL molar ratios of 1:25, 1:50 and 1:100. Polyacrylamid gel electrophoresis showed that electrophoretic mobility was increased in the treated HSA respect to control, in an HTL-concentration-dependent manner. That anodic shift of the treated samples was also observed in crossed immunoelectrophoresis profiles. As expected, a decrease in the isoelectric point of the homocysteinylated albumin (pI 4.7) in comparison to that of control (pI 4.8) was shown by the isoelectric focusing technique. Moreover, the electropherogram acquired by capillary zone electrophoresis indicated that migration times and full width at half height were enhanced with the rise of HTL concentration. We propose that the in vitro structural changes of albumin described in the present work would be involved in the harmful effects of the N-homocysteinylation process.

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.

The C677T thermolabile variant of methylene tetrahydrofolate reductase on homocysteine, folate and vitamin B12 in a hemodialysis center

Homocysteine is a risk factor for cardiovascular disease. Mutations in a key enzyme in homocysteine metabolism, methylenetetrahydrofolate reductase, may contribute to hyperhomocysteinemia and alter folate and cobalamin levels. After starting hemodialysis, 10 mg oral folate daily and 500 micrograms intravenous methylcobalamin once weekly were prescribed to 27 hemodialysis patients (time on hemodialysis > or = 12 months) and two groups were defined: Group A normal; Group B heterozygous. Initial, third and twelfth month measurements of homocysteine, serum folate and vitamin B12 levels were collected and analyzed. Heterozygous state of methylenetetrahydrofolate reductase prevalence was 48

. Hyperhomocysteinemia was present in both groups. Cobalamin final levels were significantly lower in Group B compared to Group A. Homocysteine, serum folate and cobalamin levels at third and twelfth month were significantly different from baseline levels but non-different between them in both groups. In Group B, vitamin B12 at third month was significantly higher than initial, but final measurements were not different from baseline determinations. In conclusion, the heterozygous prevalence of the enzyme in hemodialysis patients is similar to that reported in the general population; hyperhomocysteinemia is frequent in hemodialysis patients and final levels in heterozygous patients are significantly higher than in normal patients. Cobalamin levels are lower in the heterozygous group. After one year of treatment, homocysteine tends to increase, suggesting a secondary resistance phenomenon to vitamin supplementation in heterozygous patients.