Hypohomocysteinemia may increases the risk of dementia and Alzheimer's disease: A nationwide population-based prospective cohort study.

BACKGROUND: Hyperhomocysteinemia has been repeatedly found to increase the risk of dementia. However, the effects of hypohomocysteinemia on the risk of dementia have been barely investigated. If hypohomocysteinemia, like hyperhomocysteinemia, increases the risk of dementia, misuse or overuse of homocysteine-lowing agents such as vitamin supplements may increase the risk of dementia. AIMS: To investigate whether hypohomocysteinemia, like hyperhomocysteinemia, could increase the risk of dementia and Alzheimer's disease (AD) in a large population-based cohort of older adults. METHODS: This prospective cohort study followed 2655 randomly sampled, community-dwelling, non-demented individuals aged 60 years or older from 2010 to 2018. We measured baseline serum total homocysteine (tHcy) levels and examined the effect of serum tHcy on the risks of dementia and AD using Cox proportional hazards models. RESULTS: During the follow-up period (mean = 5.4 years, SD = 0.9), dementia and AD developed in 85 and 64 participants, respectively. Not only the participants with high serum tHcy (≥10.6 µmol/L) but also those with low serum tHcy (≤8.9 µmol/L) were 4-5 times more likely to develop dementia and AD compared to those with serum tHcy levels between 9.0 and 10.5 µmol/L. With the increase in serum tHcy concentration, the use of vitamin supplements decreased, and 41.2% of the participants with low serum tHcy (≤8.9 µmol/L) were taking vitamin supplements. CONCLUSIONS: Not only hyperhomocysteinemia but also hypohomocysteinemia considerably increased the risk of dementia and AD in older adults. The risk of dementia that results from overuse or misuse of vitamin supplements should be acknowledged and homocysteine-lowering health policies should be tailored to consider dementia risks that are associated with hypohomocysteinemia.

Homocysteine, Pyridoxine, Folate and Vitamin B12 Levels in Children with Attention Deficit Hyperactivity Disorder.

BACKGROUND: In our study, we aimed to evaluate the serum homocysteine levels, pyridoxine, folate and vitamin B12 levels in children with attention deficit hyperactivity disorders (ADHD). SUBJECTS AND METHODS: This study included 30 newly diagnosed drug-naive children with ADHD (23 males and 7 female, mean age 9.3±1.8 years) and 30 sex-and age matched healthy controls. The diagnosis of ADHD was made according to DSM-V criteria. Children and adolescents were administered the Schedule for Affective Disorders and Schizophrenia for School Aged Children, Present and Lifetime Version, the Conners' Parent Rating Scale-Revised, Long Form, the Conners' Teacher Rating Scale and the Wechsler Intelligence Scale for Children Revised (WISC-R) for all participants. Homocysteine, pyridoxine, folate and vitamin B12 levels were measured with enzyme-linked immunosorbent assay. RESULTS: Homocysteine, pyridoxine, folate and vitamin B12 levels were significantly lower in children with ADHD compared with their controls (p<0.05). A positive significant correlation was observed between the all WISC-R scores and vitamin B12 level in patients (r=0.408, p=0.025). CONCLUSIONS: The results obtained in this study showed that reduced homocysteine, pyridoxine, folate and vitamin B12 levels could be a risk factor in the etiology of ADHD.

Folic acid deficiency induces premature hearing loss through mechanisms involving cochlear oxidative stress and impairment of homocysteine metabolism.

Nutritional imbalance is emerging as a causative factor of hearing loss. Epidemiologic studies have linked hearing loss to elevated plasma total homocysteine (tHcy) and folate deficiency, and have shown that folate supplementation lowers tHcy levels potentially ameliorating age-related hearing loss. The purpose of this study was to address the impact of folate deficiency on hearing loss and to examine the underlying mechanisms. For this purpose, 2-mo-old C57BL/6J mice (Animalia Chordata Mus musculus) were randomly divided into 2 groups (n = 65 each) that were fed folate-deficient (FD) or standard diets for 8 wk. HPLC analysis demonstrated a 7-fold decline in serum folate and a 3-fold increase in tHcy levels. FD mice exhibited severe hearing loss measured by auditory brainstem recordings and TUNEL-positive-apoptotic cochlear cells. RT-quantitative PCR and Western blotting showed reduced levels of enzymes catalyzing homocysteine (Hcy) production and recycling, together with a 30% increase in protein homocysteinylation. Redox stress was demonstrated by decreased expression of catalase, glutathione peroxidase 4, and glutathione synthetase genes, increased levels of manganese superoxide dismutase, and NADPH oxidase-complex adaptor cytochrome b-245, α-polypeptide (p22phox) proteins, and elevated concentrations of glutathione species. Altogether, our findings demonstrate, for the first time, that the relationship between hyperhomocysteinemia induced by folate deficiency and premature hearing loss involves impairment of cochlear Hcy metabolism and associated oxidative stress.

Estudio prospectivo de cinco años de los niveles de homocisteinemia y riesgo cardiovascular en pacientes de una unidad de hemodiálisis / A prospective study of five years about homocysteinemia levels and cardiovascular risk in patients in a hemodialysis unit

La enfermedad cardiovascular es compleja y multifactorial. Uno de los marcadores conocido como factor de riesgo vascular independiente es la homocisteína; el aumento en 5 µmol/l por encima del rango normal equivale, en riesgo vascular, a un aumento de 20 mg/ dl por encima del colesterol normal. En la población general niveles ligeramente elevados de homocisteína (>15µmol/l), se asocian al incremento de la mortalidad y de los eventos cardiovasculares. Este factor también está presente en pacientes renales, siendo sus niveles 3-4 veces superiores a la población en general. Los mecanismos por los que la homocisteína está elevada en la insuficiencia renal no están claros, ya que su excreción renal sólo representa el 1% de su eliminación; si embargo, si está comprobado que la utilización de membranas de diálisis de alto flujo, diálisis lenta nocturna, o hemodiafiltración on-line diarias reducen significativamente los niveles de este aminoácido. Tal vez estos tratamientos, al conseguir una mayor reducción de los niveles de homocisteína, puedan reducir la morbimortalidad cardiovascular renal y, por ello, es aconsejable medir los niveles de homocisteína anualmente en los pacientes renales. Nos planteamos conocer el riesgo vascular de nuestros pacientes renales a lo largo de cinco años, según valores de homocisteína y determinar su relación con modalidad y tiempo en tratamiento, edad, sexo y grupo étnico. Realizamos un estudio observacional prospectivo en pacientes de una unidad renal durante cinco años. Recogimos datos sobre: edad, sexo, grupo étnico, modalidad de tratamiento (hemodiafiltración versus hemodiálisis), tiempo en tratamiento y valores de homocisteína. Estudiamos 115 pacientes, de edad media 59 años, 68 hombres y 47 mujeres; 107 pacientes caucásicos mediterráneo, 4 caucásicos norteafricano y 4 negroide. El 54,8% llevaba menos de 4 años en tratamiento renal. Un 63% estaba en hemodiálisis, 27% en hemodiafiltración alterna y 10% en diaria. El valor medio de homocisteína en varones fue de 23.47 µmol/l y en mujeres 24.29 µmol/l. Los valores de homocisteína en el tercer y cuarto año de estudio según el grupo cultural fueron en pacientes negroides 51,50 y 69,35 µmol/l respectivamente, con significación estadística. En la población general el riesgo cardiovascular se asocia a la edad y el sexo sin embargo, los niveles de homocisteína versus estas variables en nuestra población renal a estudio no se ven modificados. Otras diferencias vienen marcadas por el grupo étnico: menores en raza negra y asiáticos que en personas de raza blanca, mientras que los latinoamericanos tenían concentraciones intermedias. Estas afirmaciones no coinciden con los resultados de nuestro estudio, ya que el grupo caucásico mediterráneo (la mayoría de nuestros pacientes) que presenta valores intermedios con riesgo moderado y el grupo de etnia negroide valores más elevados incluso de riesgo elevado. Concluimos que nuestros pacientes presentaban un nivel moderado de riesgo vascular. Al enfrentar homocisteína con sexo, edad, modalidad y tiempo de tratamiento sustitutivo no encontramos relación estadística significativa. Sin embargo, el grupo étnico si presentaba variaciones significativas siendo el grupo negroide el de mayor riesgo vascular con niveles más elevados en los tres últimos años del estudio (AU)

Cardiovascular disease is complex and multifactorial. One of the markers known as independent vascular risk factor is homocysteine. In relation to vascular risk, the increase of 5 mmol/l above the normal range, corresponds to an increase of 20 mg/dl above normal cholesterol. In the general population, slightly elevated homocysteine levels (> 15µmol/l), are associated with increased mortality and cardiovascular events. Also, this factor is present in renal patients, at 3-times higher levels than the general population. Mechanisms by which homocysteine is elevated in renal failure are unclear, since renal excretion represents only 1% of its elimination. However, it has been shown that the use daily of membranes of high flux dialysis, slow nocturnal home dialysis, or on-line hemodiafiltration, significantly reduce these amino acid levels. These treatments could achieve a greater reduction in homocysteine levels and reduce the cardiovascular renal morbid-mortality, therefore, it is advisable to measure homocysteine levels in renal patients annually. The aim was to study the vascular risk in our renal patients in a study of five years, according to the homocysteine levels and determine their relationship with modality and time of treatment, age, sex and ethnicity. A prospective observational study of five year was carried out in our dialysis unit. Data about age, sex, ethnicity, type of treatment (hemodiafiltration versus hemodialysis), duration of treatment and homocysteine levels were collected. 115 patients (68 men and 47 women) with a mean age of 59 years were studied. 107 patients were Mediterranean Caucasians, 4 North African Caucasian and 4 African blacks. 54.8% had less than four years in renal treatment. 63% were on hemodialysis, 27% patients were in alternating hemodiafiltration, and 10% in daily hemodialysis. The mean level of homocysteine in males was 23.47 mmol/l, and in women of 24.29 mmol/l. According to the cultural group, homocysteine levels in the third and fourth year of study, were significant in African black patients, with levels of 51.50 and 69.35 mol/l respectively. In the general population, cardiovascular risk is associated with age and sex. However, homocysteine levels versus these variables in our renal study population are not modified. Other differences are marked by ethnic group: lower in blacks and Asians than in Caucasians, while Latin American had intermediate concentrations. This information do not coincide with our findings, because the Caucasian Mediterranean group (most of our patients) had intermediate values at moderate risk and the African black group had higher values, even of the high risk. We conclude that our patients had a moderate level of vascular risk. When relating homocysteine with sex, age, mode and time of replacement therapy no statistical significant relationship was found. However, ethnicity if present significant variations being the African black the group with higher vascular risk with higher levels in the last three years of the study (AU)

[Disturbances of folic acid and homocysteine metabolism in alcohol abuse]. / Zaburzenia metabolizmu kwasu foliowego i homocysteiny w warunkach naduzywania alkoholu.

Chronic alcohol abuse leads to malnutrition, and thus to the deficiency of many nutrients, including vitamins and trace elements. Most often comes to the deficiency of all vitamins, however because the clinical implications, the most important is folic acid (vitamin B9) deficiency. Biochemical effect of folate deficiency is elevated homocysteine concentration in the blood, named "cholesterol of XXI. century". In the paper, the folate and homocysteine metabolism in alcohol abuse was discussed. Mechanisms of alcohol action on folate homeostasis in the human body have been indicated. Chronic alcohol consumption leads to deficiency of this vitamin due to their dietary inadequacy, intestinal malabsorption, decreased hepatic uptake and increased body excretion, mainly via urine. The decreased concentration of serum folic acid may occur in 80% of alcoholics. The cause of elevated concentrations of homocysteine in the serum of alcohol abusers is also a deficiency of vitamins involved such as vitamin B12 and pyridoxal phosphate. Disturbance of folic acid and homocysteine metabolism in alcohol abusers can lead to serious clinical consequences. Folic acid deficiency leads inter alia to macrocytic and megaloblastic anemia and neurological disorders. Megaloblastic anemia occurs in about half of alcohol abusers with chronic liver diseases. In turn, high level of homocysteine in blood is associated with an inreased risk of cardiovascular diseases. Hyperhomocysteinemia is an independent risk factor that favors the occurrence of acute coronary syndromes in patients with coronary heart disease.

Extrahepatic portal vein thrombosis in children and adolescents: Influence of genetic thrombophilic disorders.

AIM: to explore the prevalence of local and genetic thrombophilic disorders as risk factors for portal vein thrombosis (PVT) in our series, the largest ever published in pediatric literature. METHODS: we conducted a case-control study enrolling 31 children with PVT and 26 age-matched controls. All were screened for thrombophilia, including genetic disorders, protein C, protein S and homocysteine deficiencies. All coagulation parameters were studied at least 3 mo after the diagnosis of portal vein obstruction. RESULTS: in our study we showed that most pediatric patients with PVT have local prothrombotic risk factors, which are probably the most important factors leading to PVT. However, there is a clear association between the presence of prothrombotic disorders and PVT, suggesting that these increase the risk of thrombosis in patients with local factors such as perinatal umbilical vein catheterization or sepsis. CONCLUSION: patients with PVT should be screened for inherited prothrombotic disorders regardless of a history of an obvious local risk factor.

Tratamento dietético da hiper-homocisteinemia na doença arterial periférica: [revisão] / Dietary treatment of hyperhomocysteinemia in peripheral arterial disease: [review]

A homocisteína está envolvida na gênese da aterosclerose e, assim, é considerada um importante e prevalente fator de risco na doença arterial periférica. O estado nutricional vitamínico deficiente, em especial do folato, é a principal causa de hiper-homocisteinemia nesses casos. Embora ainda não haja consenso sobre a dose exata e a forma de utilização do folato em suplementos e sobre adequação alimentar ou fortificação de cereais para o tratamento da hiper-homocisteinemia, diversos estudos realizados em pacientes com doença vascular periférica mostraram que o folato, isoladamente, pode reduzir as concentrações de homocisteína, bem como a concentração de alguns marcadores biológicos do processo de aterosclerose...

Homocysteine plays a role in the genesis of atherosclerosis and, thus, it is considered an important and prevalent risk factor for peripheral arterial disease. Impaired vitamin nutritional status, especially regarding folate, may be mainly attributed to hyperhomocysteinemia. Although there is still no consensus as to the exact dose and method of use of folate in supplements, dietary adjustment or cereal fortification for the treatment of hyperhomocysteinemia, several studies conducted in patients with peripheral vascular disease have shown that isolated folate may reduce homocysteine levels, as well as the levels of some biological markers in the atherosclerotic process...

The metabolic syndrome is not associated with homocysteinemia: the Persian Gulf Healthy Heart Study.

BACKGROUND: It is uncertain whether homocysteine and the metabolic syndrome or its components are related in the general population, as studies investigating the association between homocysteine levels and insulin resistance have shown conflicting results. METHODS: In an ancillary study to the Persian Gulf Healthy Heart Study, a cohort study of Iranian men and women aged >or=25 yr, a random sample of 1754 subjects were evaluated for the association of plasma homocysteine levels and the metabolic syndrome using National Cholesterol Education Program (NCEP)-Adult Treatment Panel (ATP)-III criteria. Total homocysteine levels and high sensitivity C-reactive protein (CRP) were determined by enzyme-linked immunosorbent assays. RESULTS: Subjects with lower HDL-cholesterol and higher blood pressure showed significantly higher homocysteine levels (p=0.001 and p<0.0001; respectively). There was no significant difference in serum levels of homocysteine between subjects with and without the metabolic syndrome. In multiple logistic regression analysis, the metabolic syndrome did not show a significant association with serum homocysteine levels after adjusting for sex, age, smoking, fruit and vegetable intake pattern, body mass index, and physical inactivity. Concurrent elevated CRP levels and the metabolic syndrome also did not show a significant association with serum homocysteine levels after adjusting for sex, age, and lifestyle cardiovascular risk factors. CONCLUSIONS: There was no association between the metabolic syndrome using NCEP-ATPIII criteria and homocysteinemia in this study. These data refute the hypothesis that homocysteine levels are influenced by the metabolic syndrome, at least in general healthy population.

[Does diet affect our mood? The significance of folic acid and homocysteine]. / Czy dieta ma wplyw na nasz nastrój? Znaczenie kwasu foliowego i homocysteiny.

UNLABELLED: In recent years, there has been growing interest in the association between national diet and the possibility of developing various mental disorders, as well as between deficiency of such vitamins as, e.g. folic acid, vitamin B12, B6, and others (e.g., omega-3 fatty acids), elevated serum homocysteine level and the functioning of human brain as well as the occurrence of such disorders as dementia, central nervous system vascular disorders and depression. THE AIM OF THE STUDY: was to present the current state of knowledge about the role of folic acid and homocysteine in the human organism as well as the significance of vitamin deficiency, mainly folic acid and hyperhomocysteinemy for the occurrence of mood disorders. METHOD: The authors conducted the search of the Internet database Medline (www.pubmed.com) using as key words: depression, mood, homocysteine, vitamin deficiencies: folic acid, B6 and 812 and time descriptors: 1990-2007. RESULTS: In depression, folate, vitamins B12 and B6, as well as unsaturated omega-3 fatty acids deficiency affects the biochemical processes in the CNS, as folic acid and vitamin B12, participate in the metabolism of S-adenosylmethionine (SAM), a donator of methyl groups, which play a decisive role in the functioning of the nervous system; they are, among others, active in the formation of neurotransmitters (e.g. serotonin), phospholipids that are a component of neuronal myelin sheaths, and cell receptors. The deficiency of the vitamins in question results in hyperhomocysteinemia (the research shows that approximately 45-55% of patients with depression develop significantly elevated serum homocysteine), which causes a decrease in SAM, followed by impaired methylation and, consequently, impaired metabolism of neurotransmitters, phospholipids, myelin, and receptors. Hyperhomocysteinemia also leads to activation of NMDA receptors, lesions in vascular endothelium, and oxidative stress. All this effects neurotoxicity and promotes the development of various disorders, including depression. Vitamins B12 and B6, folic acid and omega-3 fatty acids supplementation is thus important in patients suffering from their deficiency; national diet as a significant factor in prevention of numerous CNS disorders, including depression, is also worth consideration.

B-vitamin and homocysteine status determines ovarian response to gonadotropin treatment in sheep.

Maternal B-vitamin status and homocysteinemia can affect fertility and pregnancy establishment, although the direct effects on ovarian follicle and oocyte development are not known. We report on the effects of restricting the supply of vitamin B(12) and methionine from the diet of mature female sheep on ovarian folliculogenesis following follicle-stimulating hormone (FSH) stimulation. The study was split into three batches and involved 76 animals. Surprisingly, the number of growing, estrogen-active antral follicles following FSH treatment was enhanced (P = 0.005) following this dietary intervention. This increase occurred even in the presence of modest live-weight loss (batch 1 only) and depressed plasma insulin concentrations, suggesting a breakdown in the regulation of follicular responsiveness to FSH. This dietary intervention also increased plasma homocysteine concentrations. Physiological concentrations of homocysteine increased granulosa cell proliferation (P < 0.001), estradiol production (P = 0.05), and FSHR transcript expression (P = 0.017) during culture. Transcript levels for growth differentiation factor 9 and bone morphogenetic protein 15 in oocytes from treated ewes were increased (P < 0.05) in the first two batches. Furthermore, regression of BMP receptor 2 (BMPR2) transcript expression and diet on follicle number revealed a significant interaction (P = 0.01); BMPR2 transcript expression was associated with follicle number only in vitamin B(12)/methionine-restricted animals. Because FSHR transcript expression also was positively (P = 0.007) related to follicle number, the effects of diet may have arisen through enhanced FSH and BMP signaling. Although this remains to be confirmed, the data support an intraovarian impact of vitamin B(12)/methionine-deficient diets.

Regulation of extracellular signal-regulated kinase by homocysteine in hippocampus.

In several neurological disorders including hyperhomocysteinemia, homocysteine (Hcy) accumulates in the brain, and acts as a potent neurotoxin. However, the molecular mechanisms induced by increased levels of Hcy in brain are not well understood. Here we show an activation of the extracellular signal-regulated kinases (ERK1 and ERK2) and the downstream nuclear targets Elk-1 and calcium/cAMP response element binding protein, in the hippocampus of cystathionine beta synthase deficient mice, a murine model of hyperhomocysteinemia. An ex vivo model of hippocampal slices allowed us to reproduce Hcy -induced ERK activation and to unravel the mechanisms responsible of this activation. Of interest, N-methyl-d-aspartate (NMDA), non-NMDA and metabotropic glutamate receptor antagonists all blocked Hcy -induced ERK activation. Moreover, the ERK activation was blocked in the presence of Na+-channel blocker tetrodotoxin, indicating the existence of a trans-synaptic activity in ERK activation by Hcy in hippocampal slices. The effects of Hcy on ERK cascade activation were also dependent on calcium influx, CaMK-II, PKC as well as PKA activation. Thus, altogether these data support a role of Hcy on ERK activation, via complex mechanisms, starting with a control of glutamate release, which in turn activates ionotropic and metabotropic receptor subtypes and produces increases in intracellular calcium levels.

Vitamin C or Vitamin B6 supplementation prevent the oxidative stress and decrease of prostacyclin generation in homocysteinemic rats.

We hypothesize that homocysteinemia causes oxidative stress, decreases the aortic ability to generate prostacyclin and that antioxidants have a protective role. Four groups of eight rats each were fed for 8 weeks the control diet (group A), control diet with folic acid omitted and excess methionine (Me) added to drinking water (group B), diet B + 500 mg/kg of Vitamin C (group C) or diet B + 60 mg/kg Vitamin B6 (group D). The three groups of rats fed folic acid deficient (FD) diets (groups B, C and D) were homocysteinemic as indicated by the significant increase in their serum homocysteine (HC) concentration. Rats fed diet B had oxidative stress as indicated by an increase in serum thiobarbituric acid reactive substances (TBARS) and advanced oxidation protein products (AOPP) and urinary isoprostanes and had a decreased ability of their aortas to generate prostacyclin. Homocysteinemic rats fed a FD diet + Vitamin C (group C) or Vitamin B6 (group D) also had high levels of serum homocysteine but the oxidative stress markers and the ability of their aortas to generate prostacyclin returned to normal. This indicates that the homocysteinemic effect is through an oxidative mechanism and that Vitamin C as a free radical scavenger prevents these effects. Serum Vitamin C and liver glutathione concentrations significantly increased in rats fed excess Vitamin B6 compared to the control or FD rats. This may explain why Vitamin B6 has an antioxidative effect.

Enfermedad cardiovascular en pacientes con trasplante renal / No disponible

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Folate and homocysteine metabolism in neural plasticity and neurodegenerative disorders.

Folate is a cofactor in one-carbon metabolism, during which it promotes the remethylation of homocysteine -- a cytotoxic sulfur-containing amino acid that can induce DNA strand breakage, oxidative stress and apoptosis. Dietary folate is required for normal development of the nervous system, playing important roles regulating neurogenesis and programmed cell death. Recent epidemiological and experimental studies have linked folate deficiency and resultant increased homocysteine levels with several neurodegenerative conditions, including stroke, Alzheimer's disease and Parkinson's disease. Moreover, genetic and clinical data suggest roles for folate and homocysteine in the pathogenesis of psychiatric disorders. A better understanding of the roles of folate and homocysteine in neuronal homeostasis throughout life is revealing novel approaches for preventing and treating neurological disorders.

Effect of methylenetetrahydrofolate reductase 677C-->T polymorphism on toxicity and homocysteine plasma level after chronic methotrexate treatment of ovarian cancer patients.

MTHFR is a critical enzyme that regulates the metabolism of folate and methionine, both of which are important factors in DNA methylation and synthesis. Subjects with the 677C-->T variant have impaired remethylation of Hcy to methionine that could determine hyperhomocysteinemia. Remethylation of Hcy into methionine and DNA methylation are also affected by MTX treatment. Thus, a combined effect between MTX and reduced activity of the MTHFR 677C-->T polymorphism could occur, leading to toxicity. In a clinical trial, 43 ovarian cancer patients were treated with low doses of MTX. During MTX therapy, 12 patients (27.9%) developed G3/4 WHO toxicity. In these 12 patients, we observed 6 G3/4 thrombocytopenias, 1 G3 neutropenia, 1 G3 anemia, 9 G3 mucositis cases and 1 G4 mucositis case. A significant association was observed between toxicity and TT MTHFR 677 genotype (p < 0.0001). G3/4 toxicity occurred in 10 of 13 (77%), 1 of 17 (6%) and 1 of 13 (8%) patients with the TT, CT and CC MTHFR genotypes, respectively. According to the logistic regression model, patients with the TT genotype had a relative risk of 42.0 (95% CI 4.2-418.6) of developing G3/4 toxicity compared to patients with the CC and CT genotypes. Patients with the TT genotype had Hcy plasma levels after MTX therapy significantly (p = 0.0001) higher than basal levels (mean +/- SD = 16.71 +/- 4.72 vs. 12.48 +/- 3.57 micromol/l); moreover, they also had higher Hcy plasma levels after MTX than patients with other MTHFR 677 genotypes (CC mean +/- SD = 9.87 +/- 3.61 micromol/l and CT mean +/- SD = 11.48 +/- 3.13 micromol/l). Finally, significant associations were observed between G3/4 WHO toxicity and higher Hcy plasma levels after MTX treatment (p = 0.0004). In conclusion, our data suggest that the TT MTHFR 677 genotype is associated with marked MTX-induced hyperhomocysteinemia and could represent a pharmacogenetic marker for toxicity after chronic treatment with low doses of MTX.

Plasma homocysteine is regulated by phospholipid methylation.

Mild hyperhomocysteinemia is an independent risk factor for cardiovascular disease. Homocysteine, a non-protein amino acid, is formed from S-adenosylhomocysteine and partially secreted into plasma. A potential source for homocysteine is methylation of the lipid phosphatidylethanolamine to phosphatidylcholine by phosphatidylethanolamine N-methyltransferase in the liver. We show that mice that lack phosphatidylethanolamine N-methyltransferase have plasma levels of homocysteine that are approximately 50% of those in wild-type mice. Hepatocytes isolated from methyltransferase-deficient mice secrete approximately 50% less homocysteine. Rat hepatoma cells transfected with phosphatidylethanolamine N-methyltransferase secrete more homocysteine than wild-type cells. Thus, phosphatidylethanolamine N-methyltransferase is an important source of plasma homocysteine and a potential therapeutic target for hyperhomocysteinemia.

Metabolic response of normal and malignant tissue to acute and chronic methionine stress in athymic mice bearing human glial tumor xenografts.

Chronic methionine (MET) stress, defined as depletion of plasma MET to levels below 5 microM, can be induced in animals with withdrawal of dietary MET, homocysteine (HCYS), and choline (CHOL) plus periodic administration of recombinant L-methionine-alpha-deamino-gamma-lyase (rMETase) and rescue homocystine (HCYSS), given i.p. every 8 and 24 h, respectively. This study describes the effect of this MET depleting regimen (METdr) on normal and malignant tissue using athymic mice bearing human glial tumor xenografts. A 7-day METdr in athymic mice bearing SWB40 and U87 anaplastic astrocytoma xenografts reduced tumor MET to 30% of their baseline values. Although this reduction halted tumor growth, it did not induce the expected complete inhibition of mitosis or a rapid and extensive necrosis. In contrast, SWB77 and D-54 xenografts (glioblastomas) showed marked regression, widespread necrosis, and complete loss of mitotic activity when they were subjected to METdr. Levels of MET in SWB77 and D-54 did not respond to METdr as readily as those in SWB40 and U87 and remained relatively high as the tumor responded to treatment and regressed. High steady states of MET along with the absence of HCYS in high-grade gliomas indicates that transmethylation reactions may be inhibited in such tumors under modest methionine stress conditions. On the basis of these results, it is postulated that METdr in its present formulation is more effective against high-grade, more aggressive gliomas, which are resistant to chemotherapy, than against the more differentiated astrocytic tumors. This may be due to the higher requirements of high-grade gliomas for MET to maintain a state of active proliferation. Further studies are needed to identify the source of MET in glial tumors under METdr and to develop more effective regimens to deplete tumor MET, which might result in a complete and sustained regression of high-grade gliomas.

Methylenetetrahydrofolate reductase genotype, vitamin B12, and folate influence plasma homocysteine in hemodialysis patients.

Hyperhomocysteinemia, a well-recognized cardiovascular risk factor, is frequent in hemodialysis (HD) patients. A common polymorphism in the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene, C-->T substitution at nucleotide 677, is associated with homocysteine (Hcy) level elevation. We examined whether three factors involved in the methionine cycle could influence plasma Hcy concentrations in HD patients: MTHFR polymorphism; vitamin B12, an essential cofactor; and folate, the substrate. In a cross-sectional study, serum vitamin B12, folate, and plasma Hcy were measured and MTHFR genotyping was performed in 534 HD patients. Effects of MTHFR genotypes, vitamin B12, and folate on plasma Hcy levels were examined in 450 HD patients not administered vitamin B12 or folate. To examine the effect of vitamin B12 on plasma Hcy concentrations, we compared plasma Hcy concentrations in HD patients with and without vitamin B12 supplementation. To examine whether functional vitamin B12 deficiency exists even in HD patients with normal vitamin B12 concentrations, 15 HD patients (serum vitamin B12 concentrations, 250 to 2,100 pg/mL) were treated with vitamin B12 (mecobalamin, 1.5 mg/d) for 8 weeks. Serum concentrations of methylmalonic acid (MMA) and vitamin B12 were measured. Hcy levels were higher and folate levels were lower in patients with the TT and CT genotypes compared with patients with the CC genotype. Analysis of covariance to determine independent predictors of high Hcy levels identified low serum vitamin B12 and folate levels and high albumin (Alb) levels in CC-genotype patients, low folate levels and high Alb levels in CT-genotype patients, and low folate levels in TT-genotype patients. Plasma Hcy levels were lower in CC- and CT-genotype patients with vitamin B12 supplementation than in those without supplementation. Vitamin B12 supplementation for 8 weeks significantly reduced MMA concentrations in HD patients with normal serum vitamin B12 concentrations. These results indicate that MTHFR genotype influences the correlation of Hcy level with vitamin B12 and folate levels in HD patients. Functional vitamin B12 deficiency may exist, even in HD patients with normal vitamin B12 concentrations. The efficacy of vitamin B12 and folate supplementation on plasma Hcy levels may depend on MTHFR genotype.