Elevated Plasma Total Homocysteine Research Articles

Homocysteine—a treatable risk factor for allograft vascular disease after heart transplantation?

Growing evidence suggests that elevated total plasma homocysteine (tHCY) levels are associated with cardiac allograft vasculopathy following heart transplantation. To assess the effect of folic acid supplementation on tHCY levels, we performed a prospective study in a cohort of 69 patients (7.0 ± 3.2 years after heart transplantation; mean age, 55.0 ± 9.6 years; 61 male) treated with 5 mg folic acid/day ( n = 34) vs no medication ( n = 35). Therapy with folic acid resulted in significantly decreased tHCY levels, from 22.6 ± 9.6 μmol/liter to 17.3 ± 5.5 μmol/liter ( p = 0.001) within 3 months, whereas values in the control group remained unchanged. We conclude that folic acid supplementation (5 mg per day) provides a simple and effective measure to lower elevated tHCY levels in heart transplant recipients.

Association between B vitamin intake and plasma homocysteine concentration in the general Dutch population aged 20–65 y

An elevated plasma total homocysteine (tHcy) concentration is associated with an increased risk of cardiovascular diseases. Folate, riboflavin, vitamin B-6, and vitamin B-12 are essential in homocysteine metabolism. The objective was to describe the association between dietary intakes of folate, riboflavin, vitamin B-6, and vitamin B-12 and the nonfasting plasma tHcy concentration. A random sample of 2435 men and women aged 20-65 y from a population-based Dutch cohort examined in 1993-1996 was analyzed cross-sectionally. Univariately, intakes of all B vitamins were inversely related to the plasma tHcy concentration. In multivariate models, only folate intake remained inversely associated with the plasma tHcy concentration. Mean plasma tHcy concentrations (adjusted for intakes of riboflavin, vitamin B-6, vitamin B-12, and methionine and for age, smoking, and alcohol consumption) in men with low (first quintile: 161 microg/d) and high (fifth quintile: 254 microg/d) folate intakes were 15.4 and 13.2 micromol/L, respectively; in women, plasma tHcy concentrations were 13.7 and 12.4 micromol/L at folate intakes of 160 and 262 microg/d, respectively. In men, the difference in the mean plasma tHcy concentration between men with low and high folate intakes was greater in smokers than in nonsmokers (2.8 compared with 1.6 micromol/L) and greater in nondrinkers than in drinkers of >2 alcoholic drinks/d (3.5 compared with 1.4 micromol/L). In women, the association between folate intake and plasma tHcy was not modified by smoking or alcohol consumption. In this Dutch population, folate was the only B vitamin independently inversely associated with the plasma tHcy concentration. Changing dietary habits may substantially influence the plasma tHcy concentration in the general population.

Plasma total cysteine as a risk factor for vascular disease: The European Concerted Action Project.

Elevated plasma total homocysteine (tHcy) is a risk factor for cardiovascular disease. Although cysteine is structurally similar and metabolically linked to tHcy, its relation to the risk of cardiovascular disease has received little attention. We studied the relation between plasma total cysteine (tCys) levels and the risk of vascular disease in the coronary, cerebral, and peripheral vessels. This case-control study included 750 patients with vascular disease and 800 age- and sex-matched control subjects recruited from 19 centers in 9 European countries. Conventional risk factors for cardiovascular disease were recorded. In addition, plasma levels of tCys, tHcy, folate, B(6), B(12), and creatinine were measured. Overall, a U-shaped relationship was observed between tCys and risk of vascular disease. With the middle range of 250 to 275 micromol/L tCys used as the reference category, the adjusted risk of vascular disease at low (</=225 micromol/L) tCys levels was 2.1 (95% CI 1.2 to 3.6), and the risk at high (>300 micromol/L) tCys levels was 1.6 (95% CI 1.1 to 2.3). Different shapes of the dose-response relationship were seen for the 3 vascular disease categories. The relation with peripheral vascular and cerebrovascular disease was U-shaped, whereas a weak positive relation was observed with coronary heart disease. Our data show a significant U-shaped relationship between tCys and cardiovascular disease after adjustment for tHcy, creatinine, and other cardiovascular disease risk factors.

Associations of homocysteine, C-reactive protein and cardiovascular disease in patients with renal disease.

In the past year, evidence from epidemiological studies in patients with renal disease has confirmed associations between both elevated plasma total homocysteine concentrations and the inflammatory marker C-reactive protein with an increased risk of arteriosclerotic vascular disease. However, it remains to be determined whether lowering total homocysteine or reducing inflammation will prevent 'hard' clinical outcome events such as stroke, myocardial infarction, and vascular death. Randomized trials of homocysteine lowering are currently ongoing and should further clarify the nature of the observed association between elevated total homocysteine and cardiovascular risk in patients with or without renal disease, and whether it is causal and modifiable. There are currently no known therapeutic interventions that specifically lower C-reactive protein levels in individuals or the prevalence of elevated C-reactive protein in the population but randomized trials of anti-inflammatory therapy (e.g. using selective cyclo-oxygenase-2 inhibitors) aimed at preventing cardiovascular disease are currently being planned.

Is the Heat Labile Variant of Methylene Tetrahydrofolate Reductase (MTHFR-HL) Associated with Elevated Plasma Total Homocysteine (tHcy) and Premature Coronary Artery Disease (CAD)?

P18 Patients with premature CAD (onset ≤55 in males, ≤65 in females) generally have higher tHcy while MTHFR-HL has been inconsistently associated with CAD. To address this issue we determined MTHFR genotype (HL vs wild type = WT), and measured tHcy, plasma folate, vitamins B12 and B6, and standard risk factors in 224 (74% male, mean age 56.0 ± 6.0) patients with premature, familial CAD (cases) and in 146 controls (56% male, mean age 48.7 ± 6.5). As expected, tHcy was significantly higher in cases (p &lt; 0.0001) and in subjects with low folate (&lt;16 nmol/L, p &lt;0.0001). Furthermore, there was a significant interaction between case status, MTHFR-HL homozygosity (HL/HL), and low folate as shown in the figure (shown are least-square means ± 95% CI; p = 0.0072 for interaction term; “other” refers to WT/WT and WT/HL genotypes). However, the frequency of MTHFR-HL homozygosity was not different in cases (10.71%) versus controls (10.96%), nor was there an excess of risk associated with having both HL/HL and low folate though numbers were small (4.9% of cases versus 4.1% of controls). Thus, the MTHFR-HL variant may contribute to high tHcy in premature CAD cases with low folate status, but a direct effect of MTHFR-HL on CAD risk appears to be unlikely, at least in populations with sufficient folate intake. Figure 1.

Effective treatment of hyperhomocysteinemia in heart transplant recipients with and without renal failure

Background: Elevated total plasma homocysteine (tHcy) levels have been associated with vascular disease and higher mortality in patients with coronary artery disease. Graft coronary disease is a major cause of mortality in long-term survivors of heart transplantation, and hyperhomocysteinemia may be one of its causes. The objectives of our study were to establish the effectiveness of a 3 stage homocysteine-lowering algorithm in a group of 84 heart transplant (HTx) patients and to evaluate the effect of renal function on the response to homocysteine-lowering therapy. Methods Prospective treatment of 84 Htx patients (64 male; mean age, 48 ± 13 years) with tHcy > 75th percentile consisted of a 3-stage treatment algorithm: Stage 1, folic acid (FA) 2 mg + vitamin (vit) B 12 500 mcg daily; Stage 2, addition of vit B 6 100 mg daily; Stage 3, increase FA to 15 mg daily. Serum creatinine (Cr) and tHcy levels were measured before treatment and 21 ± 19 weeks after each stage of treatment. Results All 3 stages of treatment significantly lowered mean tHcy from 22.4 ± 16.3 (mean ± SD) μmol/liter to 16.3 ± 6.7 μmol/liter ( p < 0.00001), from 17.6 ± 6.1 μmol/liter to 15.2 ± 5.3 μmol/liter ( p < 0.0001), and from 16.8 ± 5.2 μmol/liter to 15.6 ± 5.3 μmol/liter ( p < 0.05), respectively. The average reduction from baseline was 38%. Creatinine levels did not change significantly during the study period. Total plasma homocysteine levels decreased below the 75th percentile in 55% of patients, with Cr levels significantly lower in this group of patients (126 ± 36 μmol/liter vs 182 ± 65 μmol/liter, p < 0.00001). However, we found no significant relationship between % change in tHcy and baseline Cr. Conclusions In a group of 84 heart transplant patients with tHcy levels >75th percentile, treatment with FA and vit B 6 and B 12 according to a 3-stage algorithm resulted in statistically significant declines in mean tHcy levels. Overall, tHcy levels decreased 38%, with target tHcy levels <75th percentile achieved in 55% of the patients. The % change in tHcy was not related to Cr. Further studies are needed to correlate treatment of hyperhomocysteinemia with clinical endpoints, such as the time to development of transplant vasculopathy and long-term survival, and to define the most appropriate targets for therapy.

Homocysteine and stroke.

During the past year epidemiological studies have linked elevated plasma total homocysteine concentrations with an increased risk of ischaemic stroke because of arterial disease. Laboratory studies have further explored the mitogenic effects of total homocysteine on vascular smooth muscle, and cytotoxic and thrombophilic effects on vascular endothelium. Also, a clinical trial has shown that lowering total homocysteine by means of multivitamin therapy decreases the rate of abnormal exercise electrocardiography tests. However, it remains to be determined whether lowering total homocysteine prevents hard clinical outcome events, such as stroke and other serious vascular events. An alternative explanation for the observed association between elevated total homocysteine and stroke is a confounding effect of factors associated with hyperhomocysteinaemia (e.g. cigarette smoking, renal impairment, an atherogenic diet, cystine deficiency, folate deficiency) or perhaps even the acute vascular events themselves, whereby the tissue damage temporarily increases total homocysteine levels. The results of ongoing clinical trials in stroke patients to determine the impact of multivitamin therapy on recurrent stroke and other serious vascular events are awaited.

Elevated plasma homocysteine levels in centenarians are not associated with cognitive impairment

Background: Previous reports have shown elevated plasma total homocysteine (tHcy) levels in elderly person with impaired cognition. Objective: To study the association between cognitive status and plasma tHcy levels in centenarians. Design: Cross-sectional survey. Setting: Centenarians living in two northern Italian provinces. Participants: Thirteen cognitively normal centenarians, ten cognitively impaired not-demented centenarians, and 34 demented centenarians with a clinical diagnosis of Alzheimer's disease (AD). Measurements: Blood levels of homocysteine's biological determinants vitamin B12, folate, and vitamin B6. Results. Elevated plasma tHcy levels (>17 μmol/l) were common in the general population (77% of normal centenarians, 100% of cognitively impaired not-demented centenarians, 82% of AD centenarians). Demented centenarians had the lowest folate serum levels. Low or borderline vitamin B12 serum levels (<221 pmol/l) and low vitamin B6 plasma levels (<11.7 nmol/l) were found in 33 and 66% of all centenarians independently of cognitive status. Among demented centenarians only plasma tHcy correlated inversely with both serum vitamin B12 and folate. No significant difference was found for plasma tHcy levels among the three diagnostic groups, even after adjusting for B vitamin levels. Conclusions: Hyperhomocysteinemia is very common among centenarians, probably due to vitamin deficiencies, but does not seem to be associated with cognitive impairment.

Homocysteine-Lowering Effect of 500 μg Folic Acid Every Other Day versus 250 μg/Day

Background/Aims: Elevated plasma total homocysteine (tHcy) concentrations are a risk factor for neural tube defects and vascular diseases. Supplementation with folic acid decreases tHcy. We investigated whether supplementation with 500 µg folic acid every other day is as effective in lowering tHcy as 250 µg folic acid each day. Methods: In a 4-week intervention study, 22 healthy young women (18–40 years old) took either 500 µg folic acid every other day (500-µg/2d group) or 250 µg folic acid each day (250-µg/d group). Fasting blood was collected on days 0 and 28. Results: Plasma folate concentrations increased by 11.4 nmol/l (6.8–15.9) in the 250-µg/d group and by 9.1 nmol/l (95% Cl 1.9–16.3) in the 500-µg/2d group. These increases were not significantly different from each other. THcy concentrations decreased by 1.52 µmol/l (95% Cl –2.09 to –0.95; p < 0.001) in the 250-µg/d group and by 0.88 µmol/l (–1.53 to –0.23; p < 0.05) in the 500-µg/2d group. The difference in decrease between the 250-µg/d group and the 500-µg/2d group was 0.64 µmol/l (p = 0.11). Conclusion: Although not conclusive, this study suggests that supplying subjects with folic acid each day decreases tHcy more effectively than a double dose every other day.

Methylenetetrahydrofolate reductase mutation (677C → T) negatively influences plasma homocysteine response to marginal folate intake in elderly women

Individuals who are homozygous for the methylenetetrahydrofolate reductase (MTHFR) 677C → T mutation have depressed serum folate (SF) and elevated plasma total homocysteine (tHcy) concentrations, which may affect folate requirements and increase the risk for coronary artery disease. A controlled metabolic study (14 weeks) using a depletion/repletion protocol was performed in women (aged 60 to 85 years, N = 33) to provide age-specific data on the effects of the MTHFR mutation on SF and tHcy status. Subjects consumed a moderately folate-deplete diet (118 μg/d) for 7 weeks, followed by 7 weeks of folate repletion with 200 or 415 μg/d provided as two different treatments. Following folate depletion, the mean SF concentration was lower for homozygous (P = .017) versus heterozygous subjects. Homozygotes for the 677C → T mutation showed a higher (P = .015) percent increase in plasma tHcy (44%) than heterozygous (20%) or normal (15%) subjects. At week 7, the mean plasma tHcy concentration was higher in homozygous subjects (12.5 ± 5.3 μmol/L, mean ± SD) versus the heterozygous (10.8 ± 3.8 μmol/L, P = .008) or normal (11.3 ± 2.7 μmol/L, P = .001) genotype groups. Following folate repletion, plasma tHcy concentrations were not different between genotype groups, despite a higher (P < .016) SF concentration in subjects with the homozygous genotype. These data suggest that older women who are homozygous for the MTHFR 677C → T mutation may be at risk for greater elevations in plasma tHcy in response to moderately low folate intake as compared with individuals with the normal or heterozygous genotypes. Copyright © 2000 by W.B. Saunders Company

Betaine Supplementation and Plasma Homocysteine in Healthy Volunteers

Elevated plasma total homocysteine concentrations are considered a risk factor for giving birth to a child with a neural tube defect1-2 and for cardiovascular disease.3 Epidemiological studies suggest that elevated homocysteine concentrations are an independent and graded risk factor for vascular disease, with no apparent threshold.3-6 Therefore, it appears that a decrease in plasma total homocysteine concentration in the lower range is still relevant. Homocysteine can be transsulfurated to cysteine using vitamin B6 as a cofactor. It can also be remethylated to methionine. This reaction either uses 5-methyltetrahydrofolate as a substrate in a vitamin B12–dependent reaction or it uses betaine. In humans, the folate-dependent remethylation takes place in all cells, whereas the betaine-dependent remethylation reaction is mainly confined to the liver.7 Supplementation with folic acid has been shown to decrease total plasma homocysteine concentrations in healthy volunteers

The controversy over homocysteine and cardiovascular risk

Elevated plasma total homocysteine (tHcy) is a risk factor for occlusive cardiovascular disease (CVD). This concept is based on the observations of premature vascular disease in patients with homocystinuria, the relation between tHcy and both clinical CVD as well as preclinical atherosclerotic disease, the relation between tHcy in children and CVD in their parents or relatives, and reduction in CVD or surrogate endpoints after tHcy-lowering intervention with B vitamins. Plausible mechanisms include the in vivo interference with nitric oxide-dependent reactive vasodilatation. Some observations have raised questions about tHcy as a risk factor. 1) Some prospective studies showed a weak relation or no relation between tHcy and CVD. 2) Several traditional risk factors are associated with tHcy and may confound the relation between tHcy and CVD. 3) tHcy is related to renal function, and hyperhomocysteinemia may reflect early nephrosclerosis. 4) The C677T transition of the methylenetetrahydrofolate reductase gene causes a moderate increase in tHcy but no or only minor increased CVD risk. However, the strength of some of these arguments can be questioned because there is increasing evidence that tHcy is a proximate risk factor provoking the acute event, it strongly interacts with traditional risk factors, and it may predict CVD or death in patients with chronic renal failure. Furthermore, the studies of the C677T polymorphism lack statistical power, and the TT genotype may even modulate CVD risk independently of homocysteine. Thus, only placebo-controlled intervention studies with tHcy-lowering B vitamins and clinical endpoints can provide additional valid arguments for the debate over whether tHcy is a causal CVD risk factor.

Plasma total homocysteine levels in postmenopausal women with unstable coronary artery disease

An elevated plasma total homocysteine (tHcy) level is considered a risk factor for coronary artery disease (CAD), but the relationship between plasma tHcy and well-defined CAD in women is still unclear. Plasma tHcy concentrations and the covariates serum folate, vitamin B12, and creatinine were analysed in 157 angiographically examined postmenopausal women with unstable CAD and in 101 healthy controls. At coronary angiography, 16% had normal vessels and 84% had coronary atherosclerosis. Mean plasma tHcy concentration (μmol/l, 95% confidence interval) did not differ in patients compared to controls (13.1 (12.3–13.8) vs. 12.5 (11.6–13.5)) or in patients with or without coronary atherosclerosis (13.3 (12.4–14.1) vs. 12.0 (10.8–13.2)). A trend to an increasing plasma tHcy with increasing degree of coronary atherosclerosis was attenuated after adjustment for age and the previous mentioned covariates. Odds ratio for the risk of coronary artery disease and coronary atherosclerosis in hyperhomocysteinemic patients (≥90th percentile in controls) was approximately 3. However, the confidence interval included unity in half of the groups and the significance was therefore difficult to judge. Receiver operating characteristics showed age to be the only variable with a significant discriminatory ability regarding the presence of coronary atherosclerosis (area 0.77). Mild hyperhomocysteinemia seems not to be related to the risk of unstable CAD in postmenopausal women. The trend towards higher plasma tHcy with increasing degree of coronary atherosclerosis may be a marker of the disease. In future studies adjustment for age and the other three covariates should be considered.

Plasma homocysteine and its association with carotid intimal-medial wall thickness and prevalent coronary heart disease: NHLBI Family Heart Study

Mildly elevated plasma total homocysteine (tHcy) levels have been associated with increased risk of coronary heart disease (CHD). Carotid artery intimal-medial wall thickening is a predictor of cardiovascular disease and has been previously shown to be positively associated with plasma tHcy in studies of asymptomatic subjects. In the current study we examined 1467 subjects with regard to their fasting plasma tHcy levels and intimal-medial wall thickness as measured by B-mode ultrasound and early onset CHD. The results showed that there is a significant positive association between plasma tHcy levels and carotid-artery wall thickness in participants 55 years or older even after the tHcy levels are adjusted for age, smoking and anti-hypertensive medication. The direction and magnitude of the relationship is similar although the result was not statistically significant in younger participants (<55 years). Early onset CHD at any age was not significantly different across the tHcy quintiles. The lack of an association of tHcy and CHD in the presence of a positive association with intimal-medial wall thickening may be a reflection of increased statistical power of quantitative versus qualitative traits. We conclude that the present finding of a positive association between tHcy and intimal-medial wall thickness strengthens the in vitro finding of the stimulating effect of homocysteine on vascular smooth muscle cell growth. Vascular smooth muscle cell proliferation may be an important mechanism through which mildly elevated plasma tHcy promotes atherosclerosis.

Dietary strategies for lowering homocysteine concentrations

Elevated plasma total homocysteine (tHcy) concentrations are associated with increased risk of vascular disease, and there is a strong inverse association between dietary and blood folate and blood tHcy concentrations. Increased folate consumption may lower the risk of tHcy-mediated cardiovascular disease. The objective was to determine the most appropriate means of increasing dietary folate to reduce plasma tHcy. Sixty-five free-living subjects aged 36-71 y with tHcy concentrations >/=9 micromol/L participated in a randomized, controlled trial to compare 3 approaches for increasing dietary folate to approximately 600 microg/d: folic acid supplementation, consumption of folic acid-fortified breakfast cereals, and increased consumption of folate-rich foods. An intake of 437 microg folic acid/d from supplements resulted in a 27-nmol/L increase in serum folate and a 21% reduction in tHcy, relative to the change in a control group. In subjects who consumed folic acid-fortified breakfast cereal, folate intake increased by an average of 298 microg, serum folate increased by 21 nmol/L, and tHcy concentrations decreased by 24%. Increased intakes of folate-rich foods resulted in a 418-microg increase in dietary folate, a 7-nmol/L increase in serum folate, and a 9% reduction in tHcy concentrations. The decrease in tHcy was negatively correlated (r = -0.66) with the increase in serum folate. Daily consumption of folic acid-fortified breakfast cereals and the use of folic acid supplements appear to be the most effective means of reducing tHcy concentrations. The reduction in tHcy was significantly negatively correlated with the increase in serum folate, which may be a useful marker for measuring dietary change.

Impaired glucose tolerance (IGT) is not associated with disturbed homocysteine metabolism.

Elevated plasma total homocysteine (tHcy) has been suggested to be an additional risk factor for cardiovascular disease in subjects with impaired glucose tolerance (IGT) and Type 2 diabetes (T2D). In order to investigate whether an insulin resistant/chronic hyperinsulinemic situation in male diabetic and prediabetic subjects directly influences the tHcy metabolism, fasting tHcy and post-methionine load tHcy plasma levels (PML-tHcy) were determined in 15 men with IGT, 13 men with newly diagnosed T2D, and 16 normoglycemic controls (NGT). Fasting tHcy (IGT, 13.1 +/- 4.6; T2D, 12.8 +/- 4.0; NGT, 10.7 +/- 4.4 micromol/L) and PML-tHcy (IGT, 46.5 +/-17.39; T2D, 41.1 +/- 6.8; NGT, 38.0 +/- 9.7 micromol/L) showed no differences between the groups. Fasting tHcy and PML-tHcy correlated with fasting proinsulin (r = 0.395, p < 0.05; r = 0.386, p< 0.05) and creatinine (r = 0.489, p < 0.01; r = 0.339, p < 0.05), resp. Multiple regression analysis showed only a relationship between fasting tHcy and creatinine. No relationships have been found between fasting tHcy and PML-tHcy, resp., and indicators of an insulin resistant state, e.g., insulin and proinsulin, as well as serum cobalamin and folate concentrations. In conclusion, our data suggest that the degree of glucose intolerance has no direct impact on the metabolism of homocysteine. However, tHcy levels tend to be elevated with the development of nephropathy, indicating an association between tHcy and renal function in these subjects.

Polymorphisms in the CBS Gene Associated with Decreased Risk of Coronary Artery Disease and Increased Responsiveness to Total Homocysteine Lowering by Folic Acid

Elevated total plasma homocysteine (tHcy) is an established risk factor for the development of vascular disease and neural tube defects. Total homocysteine levels can be lowered by folic acid supplements but individual response is highly variable. In this case–control study, involving 142 coronary artery disease (CAD) patients and 102 controls, we have typed six genetic polymorphisms in three homocysteine metabolizing genes and examined their relationship to the incidence of CAD, tHcy levels, and lowering of tHcy levels in response to folic acid supplementation. We found that two single nucleotide polymorphisms in the cystathionine beta synthase (CBS) gene, 699C → T and 1080T → C, are associated with decreased risk of CAD and increased responsiveness to the tHcy lowering effects of folic acid. Individuals homozygous for 699T were significantly underrepresented in CAD patients as compared to controls (4.9% vs 17.3%, P = 0.0015), as were individuals homozygous for the 1080C (29.6% vs 44.2%, P = 0.018). Additionally, 699T and 1080C homozygous individuals were the most responsive to folate supplementation. 699T homozygotes lowered tHcy levels 13.6% on average, compared to 4.8% lowering in 699C homozygotes (P = 0.009), while 1080C homozygotes lowered 12.9% compared to just 2.7% for 1080T homozygotes (P = 0.005). The two polymorphisms in CBS are third codon changes and would not be predicted to affect the underlying protein. However, there is strong linkage disequilibrium between these two positions, suggesting that they may also be linked to other as yet unidentified polymorphisms within the CBS gene. These observations suggest that specific CBS alleles are a risk factor for the development of vascular disease and that genetic information could be predictive of individual response to folic acid supplementation.

Homocysteine concentrations and methionine loading in patients on antiepileptic drugs.

A few reports have shown elevated fasting total plasma homocysteine (tHcy) in patients taking antiepileptic drugs (AEDs). In this study we determined the influence of AEDs on plasma tHcy levels prior to and following methionine loading. Thirty-four patients on different AEDs and 34 matched controls were recruited. Blood samples were drawn prior to and 6 h post-methionine loading (6h-PML). The patients on AEDs inducing the cytochrome P450 (carbamazepine, phenytoin, phenobarbital, primidone), had higher fasting and 6h-PML plasma tHcy concentrations than the controls (P = 0.01 and P<0.001). Patients on AED inhibiting the cytochrome P450 (valproate [VPA]), had lower 6h-PML p-tHcy concentrations than controls (P = 0.01). Our data indicate that not only fasting but also 6h-PML tHcy levels should be determined in order to identify hyperhomocysteinemia among patients on AEDs. Inducer AEDs seem to have an opposite effect than the inhibitor VPA on plasma tHcy, erythrocyte folate and serum folate levels.

Polygenic influence on plasma homocysteine: association of two prevalent mutations, the 844ins68 of cystathionine β-synthase and A 2756G of methionine synthase, with lowered plasma homocysteine levels

A moderately elevated plasma total homocysteine (tHcy), whether measured during fasting or post-methionine load (PML), is increasingly being recognized as a risk factor for coronary artery diseases (CAD). However, etiologies for moderately elevated plasma tHcy, particularly with regard to the role of genetic influence on plasma tHcy levels, are still not well understood. In the current investigation, we studied 1025 individuals with respect to the effect of the 68-bp insertion (844ins68 variant) of the cystathionine β-synthase (CBS) gene, the A 2756G transition of the B 12-dependent methionine synthase (MS) gene and the C 677T transition of the methylenetetrahydrofolate reductase (MTHFR) gene on fasting and 4 h PML tHcy. Of these individuals, 153 (14.9%) were heterozygous for the 68-bp insertion, 329 (32.1%) were heterozygous for the G 2756 allele and 122 (11.9%) were homozygous for the C 677T transition. Individuals heterozygous for the insertion had significantly lower PML increase in tHcy concentrations, while individuals homozygous for the A 2756G transition had significantly lower fasting tHcy levels. A 2-way ANOVA showed that there was no interaction between the 844ins68 and the A 2756G transition for either fasting tHcy or PML increase in tHcy, confirming the fact that the effect of these two genotypes on plasma tHcy levels are additive. The effects are opposite but additive with the C 677T genotype of the MTHFR gene. In conclusion, we document evidence of polygenic regulation of plasma tHcy. Overall, >50% of all individuals in this study carried polymorphic traits, which predisposed them to either higher or lower plasma tHcy concentrations, thus providing new evidence of the importance of genetic influences as determinants of tHcy levels.

Elevated plasma homocysteine elicits an increase in antioxidant enzyme activity

Elevated plasma homocysteine is considered to be a risk factor for cardiovascular disease. The mechanisms for this effect are not fully understood but there is some evidence for a role for reactive oxygen species (ROS). This study was conducted to explore the effects of elevated plasma total homocysteine (tHcy) concentration on activity of antioxidant enzymes in the circulation. The study group consisted of 10 patients with inherited defects of homocysteine metabolism, from whom 41 blood samples were collected over a period of six months. Blood samples were also collected from 13 of their obligate heterozygous parents. For data analysis samples were classified as those with plasma tHcy < 20 μM or ≥ 20 μM. The activity of erythrocyte superoxide dismutase (SOD) and plasma glutathione peroxidase (GSHPx) was elevated in samples with plasma tHcy > 20 μM. Moreover, a significant correlation was demonstrated between plasma GSHPx activity, plasma glutathione peroxidase protein and plasma tHcy. In vitro studies confirmed that this observation was not due to a simple chemical enhancement of enzyme activity. Homocysteine protected GSHPx from loss of activity following incubation at 37°C. A similar effect was seen with another thiol-containing amino acid, cysteine. Results suggest that elevated plasma tHcy represents an oxidative stress, resulting in an adaptive increase in activity of antioxidant enzymes in the circulation.