Vitamin status and intake as primary determinants of homocysteinemia in an elderly population

Consequences of hyperhomocyst(e)inemia on vascular function in atherosclerotic monkeys

Moderate elevation of plasma homocyst(e)ine is associated with increased risk for atherosclerotic vascular disease. In a previous study, we observed impaired vascular function in nonatherosclerotic monkeys with moderate hyperhomocyst(e)inemia. In this study, we tested the hypothesis that dietary intervention to lower plasma homocyst(e)ine corrects vascular dysfunction in atherosclerotic monkeys. Cynomolgus monkeys were fed an atherogenic diet that produces both hypercholesterolemia and moderate hyperhomocyst(e)inemia. After 17 months, the atherogenic diet was supplemented with B vitamins (5 mg folic acid, 400 micrograms vitamin B-12, and 20 mg vitamin B-6 daily) for 6 months. Total plasma homocyst(e)ine decreased from 12.8 +/- 2.8 to 3.5 +/- 0.3 mumol/L (n = 9; mean +/- SE; P < .01) after vitamins were added to the diet, but plasma cholesterol remained elevated (522 +/- 63 versus 514 +/- 41 mg/dL; P > .05). In response to intra-arterial infusion of collagen, blood flow to the leg decreased by 30 +/- 3% and 38 +/- 5%, respectively, before and after vitamin supplementation (P > .05). In vivo responses of resistance vessels to endothelium-dependent vasodilators (acetylcholine or ADP) were impaired at baseline and did not improve after vitamin supplementation. In carotid artery studied ex vivo, relaxation to low doses of acetylcholine improved after vitamin supplementation, but maximal relaxation remained impaired. Ex vivo thrombomodulin anticoagulant activity was threefold higher in monkeys fed the atherogenic diet (with or without B vitamins) than in normal monkeys (P < .05). We conclude that normalization of plasma homocyst(e)ine is insufficient to restore normal vascular function in atherosclerotic monkeys with persistent hypercholesterolemia and that atherosclerosis, with or without hyperhomocyst(e)inemia, is associated with elevated thrombomodulin activity.

A mutation in the methylenetetrahydrofolate reductase gene is not associated with increased risk for coronary artery disease or myocardial infarction

OBJECTIVES

We sought to determine whether the C677T transition in the methylenetetrahydrofolate reductase (MTHFR) gene is associated with increased risk for coronary artery disease (CAD) or myocardial infarction (MI).

BACKGROUND

Elevated plasma homocysteine has been identified as a risk factor for coronary atherosclerosis. Homocysteinemia may result from deficient MTHFR activity. A thermolabile form of MTHFR, associated with a C677T genetic transition, shows reduced activity and may be a risk factor for CAD.

METHODS

Blood was withdrawn from patients undergoing coronary angiography, and DNA was extracted by a phenol-chloroform method. Genotyping was done by polymerase chain reaction (PCR) amplification of a 198-base pair segment of the MTHFR gene that brackets nucleotide 677. The amplicon was digested with the HinfI restriction enzyme. Products were visualized after electrophoresis in 1.5% agarose with ethidium bromide.

RESULTS

Among 200 patients with a diagnosis of MI, the polymorphic allelic frequency was 33.3%, compared with 32.1% among 554 control subjects (p = 0.68); homozygosity was present in 11.5% of patients and 10.6% of control subjects (p = 0.74, odds ratio [OR] 1.09, 95% confidence interval [CI] 0.63 to 1.82). Among 510 patients with severe CAD (>60% stenosis), allelic frequency was 32.0%, compared with 34.8% for 168 subjects without CAD (<10% stenosis, p = 0.33); 11.2% of patients with CAD compared with 13.1% of control subjects were homozygous (p = 0.50, OR 0.83, 95% CI 0.5 to 1.40).

CONCLUSIONS

Patients with angiographic evidence of CAD or clinical MI do not show an increased frequency of the C677T transition in the MTHFR gene. Our findings do not support this polymorphism as a risk factor for CAD or MI in a predominantly white, well nourished population of unrestricted age.

High prevalence of hyperhomocysteinemia and asymptomatic vascular disease in siblings of young patients with vascular disease and hyperhomocysteinemia

Hyperhomocysteinemia (HHC) is associated with an increased risk of atherosclerotic vascular disease and may be inherited. Fasting and postmethionine HHC are independent risk factors that overlap to a limited extent. To study the familial occurrence of HHC, we investigated the prevalence of HHC (both fasting and after methionine) among 450 siblings of 167 consecutive young patients with vascular disease and postmethionine HHC. Furthermore, all subjects with postmethionine HHC (n = 125) were invited for noninvasive vascular testing; 101 (80.8%) agreed. Of those with a normal postmethionine plasma level (n = 325), we randomly selected 73 subjects for further studies; 53 agreed (72.6%). Thus, a total of 154 siblings underwent ultrasonography of the carotid arteries, measurement of ankle-brachial pressure indices at rest and after a treadmill exercise test, and exercise electrocardiographic stress testing. We observed HHC after methionine, fasting, or both, in 27.8% (95% CI, 23.7 to 31.9), 11.1% (CI, 8.2 to 14.0) and 8.7% (CI, 6.1 to 11.3) of the siblings. Abnormal peripheral, coronary, or carotid artery tests were observed in 35.7% (CI, 28.1 to 43.3), 7.1% (CI, 3.0 to 11.2), and 7.1% (CI, 3.0 to 11.2). Univariate and multivariate analyses revealed weak evidence of a relationship with homocysteine levels. In conclusion, we found a high prevalence of HHC and asymptomatic vascular disease in siblings of young patients with vascular (mainly peripheral arterial) disease and HHC. Our data raise the possibility that homocysteine does not play a major role in the early, asymptomatic phases of vascular disease, at least among siblings of young patients with vascular disease.

Elevated fasting total plasma homocysteine levels and cardiovascular disease outcomes in maintenance dialysis patients. A prospective study

There is an excess prevalence of hyperhomocysteinemia in dialysis-dependent end-stage renal disease (ESRD) patients. Cross-sectional studies of the relationship between elevated total homocysteine (tHcy) levels and prevalent cardiovascular disease (CVD) in this patient population suffer from severe methodologic limitations. No prospective investigations examining the association between tHcy levels and the subsequent development of arteriosclerotic CVD outcomes among maintenance dialysis patients have been reported. To assess whether elevated plasma tHcy is an independent risk factor for incident CVD in dialysis-dependent ESRD patients, we studied 73 maintenance peritoneal dialysis or hemodialysis patients who received a baseline examination between March and December 1994, with follow-up through April 1, 1996. We determined the incidence of nonfatal and fatal CVD events, which included all validated coronary heart disease, cerebrovascular disease, and abdominal aortic/lower-extremity arterial disease outcomes. After a median follow-up of 17.0 months, 16 individuals experienced at least one arteriosclerotic CVD event. Cox proportional-hazards regression analyses, unadjusted and individually adjusted for creatinine, albumin, and total cholesterol levels, total/HDL cholesterol ratio, dialysis adequacy/residual renal function, baseline CVD, and the established CVD risk factors (ie, age, sex, smoking, hypertension, diabetes/glucose intolerance, and dyslipidemia) revealed that tHcy levels in the upper quartile (> or = 27.0 mumol/L) versus the lower three quartiles (< 27.0 mumol/L) were associated with relative risk estimates (hazards ratios, with 95% confidence intervals for the occurrence of (pooled) nonfatal and fatal CVD ranging from 3.0 to 4.4; 95% confidence intervals (1.1-8.1) to (1.6-12.2). We conclude that the markedly elevated fasting tHcy levels found in dialysis-dependent ESRD patients may contribute independently to their excess incidence of fatal and nonfatal CVD outcomes.

Thermolabile methylenetetrahydrofolate reductase in coronary artery disease

BACKGROUND

Hyperhomocysteinemia, an independent and graded risk factor for coronary artery disease (CAD), may result from both environmental and hereditary factors. Methylenetetrahydrofolate reductase (MTHFR) catalyzes the conversion of methylenetetrahydrofolate to methyltetrahydrofolate, the methyl donor in the remethylation of homocysteine to methionine. A 677C-->T mutation in the MTHFR gene has been associated with elevated homocysteine concentrations in homozygous (+/+) individuals.

METHODS AND RESULTS

We assessed the frequency of this common mutation in 735 CAD patients from the Regression Growth Evaluation Statin Study (REGRESS), a lipid-lowering coronary-regression trial, and in 1250 population-based control subjects. Furthermore, the association between the mutation and serum homocysteine concentrations was studied. The frequency of the homozygous (+/+) mutation was 9.5% among patients versus 8.5% among control subjects, resulting in an odds ratio of 1.21 (95% confidence interval [CI], 0.87 to 1.68), relative to the (-/-) genotype. Homocysteine concentrations were significantly elevated in both (+/+) and (+/-) individuals compared with (-/-) individuals (median homocysteine levels, 15.4, 13.4, and 12.6 micromol/L, for (+/+), (+/-), and (-/-) individuals, respectively). For a summary estimation of the risk of the (+/+) genotype for CAD, we performed a meta-analysis on 8 different case-control studies on thermolabile MTHFR in CAD. In the meta-analysis, the homozygous (+/+) genotype was present in 299 of 2476 patients (12.1%) and in 257 (10.4%) of 2481 control subjects, resulting in a significant odds ratio of 1.22 (95% CI, 1.01 to 1.47) relative to the (-/-) genotype.

CONCLUSIONS

Both the homozygous (+/+) and heterozygous (+/-) genotype result in elevated homocysteine concentrations. From our meta-analysis, we conclude that the homozygous (+/+) genotype is a modest but significant risk factor for CAD.

Inhibition of growth and p21ras methylation in vascular endothelial cells by homocysteine but not cysteine

Although hyperhomocysteinemia has been recognized recently as a prevalent risk factor for myocardial infarction and stroke, the mechanisms by which it accelerates arteriosclerosis have not been elucidated, mostly because the biological effects of homocysteine can only be demonstrated at very high concentrations and can be mimicked by cysteine, which indicates a lack of specificity. We found that 10-50 microM of homocysteine (a range that overlaps levels observed clinically) but not cysteine inhibited DNA synthesis in vascular endothelial cells (VEC) and arrested their growth at the G1 phase of the cell cycle. Homocysteine in this same range had no effect on the growth of vascular smooth muscle cells (VSMC) or fibroblasts. Homocysteine decreased carboxyl methylation of p21(ras) (a G1 regulator whose activity is regulated by prenylation and methylation in addition to GTP-GDP exchange) by 50% in VEC but not VSMC, a difference that may be explained by the ability of homocysteine to dramatically increase levels of S-adenosylhomocysteine, a potent inhibitor of methyltransferase, in VEC but not VSMC. Moreover, homocysteine-induced hypomethylation in VEC was associated with a 66% reduction in membrane-associated p21(ras) and a 67% reduction in extracellular signal-regulated kinase 1/2, which is a member of the mitogen-activated protein (MAP) kinase family. Because the MAP kinases have been implicated in cell growth, the p21(ras)-MAP kinase pathway may represent one of the mechanisms that mediates homocysteine's effect on VEC growth. VEC damage is a hallmark of arteriosclerosis. Homocysteine-induced inhibition of VEC growth may play an important role in this disease process.

Folic acid deficiency enhances oral contraceptive-induced platelet hyperactivity

In previous studies conducted in female rats and in women, oral contraceptives (OC) were found to induce a platelet hyperactivity that was related to an oxidative stress. Because cases of megaloblastic anemia have been reported to occur in women taking OC, these treatments are suspected of depleting folate stores. In the study presented herein, which was conducted in rats, we sought to determine the influence of dietary folic acid deficiency (FD) on the thrombogenicity of OC. Animals were fed for 6 weeks with either a folic acid-deficient diet (250 micrograms/kg folic acid) or a control diet (750 micrograms/kg). One-half of the animals in each group were treated with OC (ethinyl estradiol plus lynestrenol). FD and OC individually potentiated platelet aggregation in response to thrombin and ADP and the release and metabolism of arachidonic acid, in particular, the biosynthesis of thromboxane. These platelet activities were further enhanced in animals given both the folic acid-deficient diet and the OC treatment. In addition, FD enhanced the pro-oxidant state in OC-treated rats characterized by (1) a fall in platelet and plasma n-3 fatty acids, (2) an increase in plasma lipid peroxidation products such as conjugated dienes, lipid peroxides, and thiobarbituric reactive substances, (3) a rise in ex vivo erythrocyte susceptibility to free radicals. Moreover, we found that OC treatment led to a reduction of plasma and erythrocyte folate concentrations associated with a moderate hyperhomocysteinemia. Under our experimental conditions, we did not find significant synergistic effects between OC and FD. We propose that, although the untoward effects associated with the OC treatment may not primarily be dependent on FD, the folic acid deficiency magnified OC-induced oxidative stress, which resulted in platelet hyperactivity by elevating the pro-oxidant homocysteine plasma concentration. Despite the limitations of this animal model, the data of the present study suggest that in addition to cigarette smoking, inadequate folic acid intake might predispose those taking OC to vascular thrombosis.

Excess prevalence of fasting and postmethionine-loading hyperhomocysteinemia in stable renal transplant recipients

Hyperhomocysteinemia, either fasting or after methionine loading, may contribute to the increased incidence of cardiovascular disease events experienced by renal transplant recipients. Limited data are available on fasting homocysteine (Hcy) levels, and none on postmethionine-loading Hcy levels, in these patients. We assessed the prevalence and potential determinants of fasting and postmethionine-loading hyperhomocysteinemia in 29 stable renal transplant recipients and 58 age- and sex-matched, population-based controls free of renal disease with serum creatinine levels of 1.5 mg/dL or less. Total (t) plasma Hcy was determined fasting and 2 hours after methionine loading, along with fasting determinations of the B-vitamin cofactors/substrates for Hcy metabolism, ie, pyridoxal 5'-phosphate, B-12, and folate and serum creatinine. Geometric mean fasting (18.1 versus 9.8 microM, P < .001) and postmethionine-loading increase (22.0 versus 15.2, P = .001) in tHcy levels were significantly greater in the renal transplant recipients, as were the prevalence odds (with 95% confidence intervals) for fasting [14.8 (3.4-64.7)], postmethionine loading [6.9 (1.5-32.8)], combined fasting and postmethionine-loading [18.0 (2.3-142.1)] hyperhomocysteinemia, and inadequate circulating folate [4.2 (1.1-16.5)] or pyridoxal 5'-phosphate [3.2 (0.9-11.0) status. Correlation analyses suggested important potential relationships between creatinine and both fasting (+0.64, P < .001) and postmethionine-load increase (+0.38, P = .045) in tHcy, folate and fasting (-0.41, P = .025) tHcy, and pyridoxal 5'-phosphate and postmethionine-loading increase (-0.33, P = .091) in tHcy. We conclude that there is an excess prevalence of fasting and postmethionine-loading hyperhomocysteinemia in stable renal transplant recipients. Renal function is related to both fasting and postmethionine loading-hyperhomocysteinemia, inadequate folate status is associated with fasting hyperhomocysteinemia, and inadequate vitamin B-6 status may be related to postmethionine-loading hyperhomocysteinemia in this patient population.

The use of dietary supplements in the elderly: current issues and recommendations

Research on dietary intake in the elderly shows evidence of both adequate and inadequate nutrient consumption from food. More recent studies have documented inadequate mineral intake from food and confirmed the overall decline in nutrient intake from food as people age. Food is incontrovertibly the best vehicle for nutrient consumption. However, some authorities have found reason to recommend a daily multivitamin-mineral for the elderly as a reasonable way to assure adequate micronutrient intake. There appears to be no reason to recommend complete liquid supplements or modular macronutrient supplements to the active free-living elderly population.

The French paradox unmasked: the role of folate

The French paradox relates to the paradoxical association of a diet high in saturated fat and cholesterol with low coronary heart disease mortality and is contrary to the 'lipid hypothesis'. France and other regions with low heart disease mortality have a high consumption of fruit and vegetables. Epidemiologic studies show fruit and vegetable consumption is inversely related to coronary heart disease mortality, but recent intervention studies do not support the theory that protection is due to antioxidant vitamins. Fruit and vegetables, however, are rich sources of folate. Folate lowers plasma homocysteine levels. Even mild to moderate elevation in plasma homocysteine level is a strong risk factor for arteriosclerosis of the coronary, cerebral, and peripheral arteries. This should explain not only the French paradox but also why known risk factors may explain as little as 25% of the risk for coronary heart disease.

Homocyst(e)ine and risk of cardiovascular disease in the Multiple Risk Factor Intervention Trial

A nested case-control study was undertaken involving men participating in the Multiple Risk Factor Intervention Trial (MRFIT). Serum samples from 712 men, stored for up to 20 years, were analyzed for homocyst(e)ine. Cases involved nonfatal myocardial infarctions (MIs), identified through the active phase of the study, which ended on February 28, 1982, and deaths due to coronary heart disease (CHD), monitored through 1990. The nonfatal MIs occurred within 7 years of sample collection, whereas the majority of CHD deaths occurred more than 11 years after sample collection. Mean homocyst(e)ine concentrations were in the expected range and did not differ significantly between case patients and control subjects: MI cases, 12.6 mumol/L; MI controls, 13.1 mumol/L; CHD death cases, 12.8 mumol/L; and CHD controls, 12.7 mumol/L. Odds ratios versus quartile 1 for CHD deaths and MIs combined were as follows: quartile 2, 1.03; quartile 3, 0.84; and quartile 4, 0.92. Thus, in this prospective study, no association of homocyst(e)ine concentration with heart disease was detected. Homocyst(e)ine levels were weakly associated with the acute-phase protein (C-reactive protein). These results are discussed with respect to the suggestion that homocyst(e)ine is an independent risk factor for heart disease.

Homocysteine as a risk factor for vascular disease. Enhanced collagen production and accumulation by smooth muscle cells

An increased plasma homocysteine level is an independent risk factor for vascular disease. However, the pathological mechanisms by which homocysteine promotes atherosclerosis are not yet clearly defined. Arterial smooth muscle cells cultured in the presence of homocysteine grew to a higher density and produced and accumulated collagen at levels significantly above control values. Homocysteine concentrations as low as 50 mumol/L significantly increased both cell density and collagen production. Cell density increased by as much as 43% in homocysteine-treated cultures. Homocysteine increased collagen production in a dose-dependent manner. Smooth muscle cells treated with homocysteine at concentrations observed in patients with hyperhomocysteinemia had collagen synthesis rates as high as 214% of control values. Likewise, collagen accumulation in the cell layer was nearly doubled in homocysteine-treated cultures. Addition of aquacobalamin to homocysteine-treated cultures controlled the increase in smooth muscle cell proliferation and collagen production. These results indicate a cellular mechanism for the atherogenicity of homocysteine and provide insight into a potential preventive treatment.

Association between plasma total homocysteine and parental history of cardiovascular disease in children with familial hypercholesterolemia

BACKGROUND

Recently, we reported a relation between plasma total homocysteine (tHcy) in children and cardiovascular disease (CVD) in their male relatives, suggesting that tHcy may partly explain the increased risk related to a family history of CVD. Because individuals with familial hyperlipidemias have an exceptionally high risk of premature CVD, we explored the relationship between tHcy and parental history of CVD in children with familial hypercholesterolemia (FH).

METHODS AND RESULTS

Study subjects were 91 boys and 64 girls (age range, 7 to 17 years) with FH who were treated with a standard lipid-lowering diet at a tertiary care lipid clinic. We conducted a cross-sectional analysis of demographics, the diet, tHcy level, presence of the C677T mutation in the methylenetetrahydrofolate reductase gene (a common genetic cause of elevated tHcy) in children, and the prevalence of parental CVD. tHcy increased after puberty and was inversely related to parental educational level. Intakes of folate, vitamin C, and fruits and vegetables were inversely associated with tHcy, as were serum folate and vitamin B12 (Spearman's rho, -0.2 to 0.4; P<.05). tHcy was increased in children whose parent with FH had experienced CVD compared with children without parental CVD (median [interquartile range], 6.6 [5.3, 8.0] micromol/L versus 5.6 [4.7, 6.8] micromol/L; P=.01). This difference remained significant in multivariate regression analysis. Homozygosity for the C677T mutation was associated with a higher tHcy level and tended to be more frequent in the group with than in the group without a parental history of CVD (18% versus 8%; P=.07).

CONCLUSIONS

These findings suggest that a moderately elevated tHcy level may partly account for the contribution of the family history to risk of CVD in FH. Dietary recommendations for FH should include nutrients that affect homocysteine metabolism.

High homocysteine levels are independently related to isolated systolic hypertension in older adults

BACKGROUND

The association between homocysteine and isolated systolic hypertension in older adults was evaluated using a case-control design, and the relationship between homocysteine and clinical or subclinical atherosclerosis was explored.

METHODS AND RESULTS

Cases were 179 adults > or = 60 years with a systolic blood pressure of > or = 160 mm Hg and diastolic blood pressure < 90 mm Hg. One hundred seventy-one control subjects had the same criteria except systolic blood pressures were < 160 mm Hg. All had normal creatinine levels. Homocysteine levels were performed on fasting blood samples that had been stored at -70 degrees C. Atherosclerosis was defined as either a history of clinical disease, an internal carotid stenosis of > or = 40% by duplex scan, or an ankle/arm pressure ratio of < 0.9. The median homocysteine value was 11.5 micromol/L for cases and 9.9 for control subjects (P<.001). After control for potential confounders, homocysteine remained significantly associated with systolic hypertension (P=.019). For the hypertensive group, there was no apparent association between level of homocysteine and prevalence of atherosclerosis. However, among the normotensive group, the prevalence of atherosclerosis went from 22% in the lowest quintile of homocysteine values to 53% in the fifth quintile, with an odds ratio of 4.1 (fifth quintile in comparison to the first, P<.05). After adjustment for age, sex, systolic blood pressure, cholesterol, and smoking, this odds ratio increased to 6.4 (P<.01).

CONCLUSIONS

Elevated levels of homocysteine may be related to the cause of isolated systolic hypertension in some individuals. In normotensive older adults, homocysteine appears to be an independent risk factor for atherosclerosis.

Role of homocysteine in age-related vascular and non-vascular diseases

Homocysteine (Hcy) may represent a metabolic link in the pathogenesis of atherosclerotic vascular diseases and old-age dementias. Hyperhomocysteinemia is an independent risk factor for coronary artery disease and peripheral vascular disease, and is also associated with cerebrovascular disease; specifically, the risk of extracranial carotid atherosclerosis significantly increases in relation to Hcy levels. Hcy is a reliable marker of vitamin B12 deficiency, a common condition in the elderly which is known to induce neurological deficits including cognitive impairment; a high prevalence of folate deficiency has been reported in psychogeriatric patients suffering from depression and dementia. Both these vitamins occupy a key position in the remethylation and synthesis of S-adenosylmethionine (SAMe), a major methyl donor in CNS; therefore, deficiencies in either of these vitamins lead to a decrease in SAMe and increase in Hcy, which can be critical in the aging brain. Another pathogenetic mechanism linking high Hcy levels to reduced cognitive performances in the elderly might be represented by excitotoxicity, since hyperhomocysteinemia may lead to an excessive production of homocysteic acid and cysteine sulphinic acid, which act as endogenous agonists of NMDA receptors. Considering the reasonably high prevalence in the general population of a genetic predisposition to a thermolabile form of the enzyme 5,10-methylenetetrahydrofolate reductase (MTHFR), hyperhomocysteinemia can be seen as the result of multiple genetic and environmental factors leading to vascular and/or neurodegenerative disorders where age-related involutive phenomena represent a common pathogenetic ground. Systematic studies in different psychogeriatric conditions monitoring Hcy levels and clinical features before and after vitamin supplementation are therefore highly recommended.

Homocysteine, oxidative stress, and vascular disease

First recognized in patients with rare inborn errors of metabolism, the association of elevated plasma homocysteine concentrations with atherosclerosis and thrombosis now seems relevant to the general population as well. The mechanism of injury appears to involve oxidative damage to endothelial cells. Vitamin supplementation can normalize homocysteine levels and may lower the incidence of atherothrombotic vascular disease.

Assessment of homocysteine status

Plasma total homocysteine (tHcy) determination is used in the diagnosis of homocystinuria, in cobalamin and folate deficiency and in cardiovascular risk assessment. However, determination of tHcy includes many pitfalls which complicate the assessment of homocysteine status. In the present article, we review basic knowledge for a rational use of plasma tHcy in diagnostic as well as scientific work. The subjects dealt with are procedures for sample handling and processing, the principles of tHcy analyses, and genetic and acquired determinants of the plasma tHcy concentration.

The role of vitamins in the pathogenesis and treatment of hyperhomocyst(e)inaemia

The relation between vitamin nutritional status and circulating plasma homocyst(e)ine concentrations is reviewed. Several studies have shown that plasma concentrations of folate, vitamin B12 and pyridoxal 5'-phosphate are inversely associated with plasma total homocyst(e)ine concentrations. Of the three vitamins mentioned above, folate is the most powerful homocyst(e)ine lowering agent and a daily supplement of 0.65 mg/day is sufficient to normalize moderate hyperhomocyst(e)inaemia in most individuals with normal renal function. In patients with severe renal failure, high doses of folate are required to treat hyperhomocyst(e)inaemia. Folic acid is ineffective in reducing plasma total homocyst(e)ine concentrations in patients with a vitamin B12 deficiency. Vitamin B6 supplementation has no effect on fasting plasma total homocyst(e)ine concentrations, but attenuates the post-methionine load plasma homocyst(e)ine peak. At least one report has shown that some individuals appear to be unable to maintain plasma total homocyst(e)ine concentrations in the normal reference range by a dietary intake of folic acid only. Long-term vitamin supplementation may be indicated in these individuals. However, the clinical benefit of vitamin supplementation has not yet been demonstrated and controlled trials are urgently required.

New views on the RDAs for older adults

The oldest age category in the 1989 edition of the Recommended Dietary Allowances (RDAs) is 51 years and above. Future committees on dietary reference intakes will likely define recommendations for age categories older than this. Instead of extrapolations from data derived from experiments on younger people, future RDAs should be derived directly from experiments on older people. Further, scientists are now interested in the amount of the nutrient that it takes to prevent chronic diseases from occurring rather than to prevent deficiencies, and this will likely influence RDA numbers. A review of past and current data suggests that the current RDAs for the elderly are too low for riboflavin, vitamin B-6, folic acid, vitamin B-12, vitamin D, and calcium, and are probably too high for vitamin A.

Plasma total homocysteine, B vitamins, and risk of coronary atherosclerosis

Epidemiological research has shown that elevated plasma total homocysteine (tHcy) is a risk factor for atherosclerotic disease. In the present case-control study, we investigated whether fasting or postmethionine-loading tHcy was a stronger predictor of risk of severe coronary atherosclerosis. Furthermore, we studied levels of B vitamins, which are involved in homocysteine metabolism. Subjects were recruited from men and women, aged 25 to 65 years, who underwent coronary angiography between June 1992 and June 1994 in a hospital in Rotterdam, The Netherlands. Cases (n=131) were defined as those with > or =90% occlusion in one and > or =40% occlusion in a second coronary artery, while control subjects (n=88) had <50% occlusion in only one coronary vessel. In addition, a population-based control group free from clinical cardiovascular disease (n=101) was studied. Coronary patients were studied at least 2.5 months after angiography or other acute illness, such as myocardial infarction. After adjusting for age and sex differences between the groups, cases had 9% (P=.01) higher geometric mean fasting and 7% (P=.04) higher geometric mean postload tHcy than the combined control groups. Despite higher levels of tHcy for cases, their geometric mean levels of red cell folate and pyridoxal 5'-phosphate were higher than for control subjects, whereas plasma vitamin B12 was only slightly lower in cases. The frequency distribution of tHcy values in cases was slightly shifted toward the right, across the entire range, compared with the distribution in the combined control group. This was somewhat more obvious for fasting than postload tHcy levels. The odds ratio (OR) for severe coronary atherosclerosis (case status) for each 1 SD increase in fasting tHcy (5 micromol/L) was 1.3 (95% confidence interval [CI], 1.0-1.6), similar to the OR for each 1 SD increase (12 micromol/L) in postmethionine-loading tHcy (1.3 [95 CI, 1.0-1.7]), after adjustment for sex, age, and other potential confounders. Furthermore, there was a significant linear trend of increasing fasting tHcy with increasing number of occluded arteries (P=.01), correcting for sex, age, and other potential confounders. Our data show a positive association between plasma tHcy and risk of severe coronary atherosclerosis, of similar strength for fasting and postload tHcy levels. The data suggest that the association exists over a wide range of tHcy levels, without a clear cutoff point below which there is no increased risk.

Interrelation of hyperhomocyst(e)inemia, factor V Leiden, and risk of future venous thromboembolism

BACKGROUND

Because patients with rare familial homocystinuria who also carry factor V Leiden have an increased incidence of venous thromboembolism (VTE), we hypothesized an interrelation of moderate hyperhomocyst(e)inemia, factor V Leiden, and risk of VTE in the general population.

METHODS AND RESULTS

In a large prospective cohort, we determined total homocysteine level and factor V Leiden mutation in baseline blood samples from 145 initially healthy men who subsequently developed VTE and among 646 men who remained free of vascular disease during a 10-year follow-up period. Hyperhomocyst(e)inemia was defined as a total homocysteine level above the 95th percentile (17.25 mumol/L). Compared with men with normal total homocysteine levels, those with hyperhomocyst(e)inemia had no increase in risk of any VTE but were at increased risk of idiopathic VTE (relative risk [RR] = 3.4, P = .002). Compared with men without Leiden mutation, those with mutation were at increased risk of developing any VTE (RR = 2.3, P = .005) as well as idiopathic VTE (RR = 3.6, P = .0002). Compared with men with neither abnormality, those affected by both disorders had a 10-fold increase in risk of any VTE (RR = 9.65, P = .009) and a 20-fold increase in risk of idiopathic VTE (RR = 21.8, P = .0004).

CONCLUSIONS

Apparently healthy men with coexistent hyperhomocyst(e)inemia and Leiden mutation are at substantially increased risk of developing future VTEs, particularly those events considered idiopathic. In these data, the risk of VTE among doubly affected individuals was far greater than the sum of the individual risks associated with either abnormality alone.

Abnormal homocysteine metabolism in rheumatoid arthritis

OBJECTIVE

To assess total homocysteine (tHcy) metabolism in patients with rheumatoid arthritis (RA).

METHODS

Assessments were performed to determine the fasting levels of tHcy and the increase in tHcy in response to methionine (Met) challenge in blood samples from 28 patients with RA and 20 healthy age-matched control subjects.

RESULTS

Fasting levels of tHcy were 33% higher in the RA patients than in the control subjects (mean +/- SD 11.7 +/- 1.5 nmoles/ml versus 8.8 +/- 1.1 nmoles/ml; P < 0.01). Four hours after Met challenge, the increase in plasma tHcy levels (delta tHcy) was higher in the RA patients (20.9 +/- 10.4 nmoles/ml) than in the control subjects (15.5 +/- 1.6 nmoles/ml) (P < 0.02). In a subgroup analysis, the delta tHcy in patients taking methotrexate (12.9 +/- 2.2 nmoles/ml) did not differ from that in the control group, while the delta tHcy in patients not taking methotrexate (25.3 +/- 1.7 nmoles/ml) was significantly higher (P < 0.0001).

CONCLUSION

Elevated tHcy levels occur commonly in patients with RA, and may explain some of the increased cardiovascular mortality seen in such patients. Studies of the prevalence and mechanism of hyperhomocysteinemia in RA are warranted.

Folate deficiency causes uracil misincorporation into human DNA and chromosome breakage: implications for cancer and neuronal damage

Folate deficiency causes massive incorporation of uracil into human DNA (4 million per cell) and chromosome breaks. The likely mechanism is the deficient methylation of dUMP to dTMP and subsequent incorporation of uracil into DNA by DNA polymerase. During repair of uracil in DNA, transient nicks are formed; two opposing nicks could lead to chromosome breaks. Both high DNA uracil levels and elevated micronucleus frequency (a measure of chromosome breaks) are reversed by folate administration. A significant proportion of the U.S. population has low folate levels, in the range associated with elevated uracil misincorporation and chromosome breaks. Such breaks could contribute to the increased risk of cancer and cognitive defects associated with folate deficiency in humans.

Hyperhomocyst(e)inemia is associated with impaired endothelium-dependent vasodilation in humans

BACKGROUND

Hyperhomocyst(e)inemia is a risk factor for atherosclerosis and is prevalent in the elderly. The objective of this study was to determine whether hyperhomocyst(e)inemia is associated with impaired endothelium-dependent vasodilation in humans.

METHODS AND RESULTS

High-resolution vascular ultrasonography was used to study endothelium-dependent and -independent vasodilation in a nonatherosclerotic peripheral conduit artery of 26 elderly hyperhomocyst(e)inemic subjects and 15 age- and sex-matched subjects with normal homocysteine levels. Flow-mediated, endothelium-dependent (nitric oxide-mediated) vasodilation was assessed by measuring the percent change in brachial artery diameter during reactive hyperemia. Endothelium-independent vasodilation was assessed after the administration of 0.4 mg sublingual nitroglycerin. Endothelium-dependent vasodilation was significantly impaired in the hyperhomocyst(e)inemic subjects compared with control subjects (3.7 +/- 0.6% versus 8.1 +/- 1.2%; P = .004), whereas endothelium-independent vasodilation was not different between the two groups (10.1 +/- 1.6% versus 9.3 +/- 1.5%; P = NS). In a linear regression analysis with serum homocysteine concentration, folic acid, age, sex, cholesterol (serum total, LDL, or HDL cholesterol), mean arterial blood pressure, use of antihypertensive medication, and baseline brachial artery diameter included as covariates, serum homocysteine concentration emerged as the only significant predictor of flow-mediated vasodilation.

CONCLUSIONS

These data indicate that hyperhomocyst(e)inemia is associated with impaired endothelium-dependent vasodilation in humans and suggest that the bioavailability of nitric oxide is decreased in hyperhomocyst(e)inemic humans.

Correlation of a common mutation in the methylenetetrahydrofolate reductase gene with plasma homocysteine in patients with premature coronary artery disease

Mild hyperhomocysteinemia, a risk factor for occlusive arterial disease, can be caused by disruptions of homocysteine metabolism. Methylenetetrahydrofolate reductase (MTHFR) catalyzes the synthesis of 5-methyltetrahydrofolate, the methyl donor for homocysteine remethylation to methionine. A common mutation in MTHFR, an alanine-to-valine substitution, may contribute to mild hyperhomocysteinemia in coronary artery disease (CAD). To test this hypothesis, we studied 152 patients with CAD by mutation analysis, MTHFR enzymatic assays, and measurements of plasma homocysteine and several vitamins. The MTHFR mutation was associated with reduced enzymatic activity and increased enzyme thermo-lability in these patients. The difference in the prevalence of the homozygous mutant genotype between the CAD patients (14%) and an unmatched group of healthy subjects (10%) was not significant. However, individuals with the homozygous mutant genotype had higher plasma homocysteine, particularly when plasma folate was below the median value. This genetic-environmental interaction is proposed to be a risk factor for CAD.

Nonlipoprotein risk factors for coronary heart disease: evaluation and management

Appropriate prevention and management of coronary heart disease (CHD) requires an integrated approach to the reduction of risk factors. These principally include reduction of elevated lipids, control of blood pressure, and cessation of smoking. In addition, appropriate exercise, diet, and weight reduction (where necessary) are also important. Control of diabetes and stress management may also be helpful. Aspirin therapy is appropriate for all patients with known CHD and selected patients without CHD who have several risk factors, including nonmodifiable risk factors such as age, a positive family history, and male gender.

Folate nutrition and older adults: challenges and opportunities

Folate fortification of bread and grains has been directed to prevent neural tube birth defects. Research has also challenged previous concepts of folate nutritional status and suggested that folate may play a role in reducing the risk of vascular disease. Although folate status of many elderly people is adequate according to traditional, hematologic criteria, some elderly persons have elevated blood concentrations of the metabolite homocysteine, which indicates subclinical deficiency of folate or vitamin B-12. Higher homocysteine concentrations, even within the normal range, are associated with increased risk of vascular disease. Elderly people with better folate and vitamin B-12 status have lower homocysteine concentrations and may have lower risk for vascular disease. Although the new folate fortification rules provide the benefit of increasing folate in the food supply, they could be a risk for the elderly because excess folate intake can mask vitamin B-12 deficiency, thereby delaying diagnosis. Elderly people have a higher prevalence of vitamin B-12 deficiency as a result of absorption problems. Those deficient in vitamin B-12 should be treated to prevent irreversible neurologic damage. Modern approaches to screening the elderly include using higher cutoff points for serum vitamin B-12 and obtaining blood concentrations of the metabolite methylmalonic acid, which is elevated in deficiency of vitamin B-12 but not folate. To examine current folate intake and food sources, food frequency questionnaires were administered to 308 elderly volunteers aged 65 to 94 years. Mean (+/-standard error) folate intake from food was 299.6+/-5.8 microg/day. Supplements (median dose=400 microg/day) were consumed by 47% of participants. Only 3.2% of the sample had total folate intake greater than 1,000 microg/day, the recommended upper limit, and these were taking high-dose folate supplements (> or = 800 microg/day). Breakfast cereals provided 25.6% of folate intake; vegetables, 23.2%; fruit, 20.8%; refined breads/grains, 6.7%; dark bread, 5.0%; legumes/nuts, 5.9%; dairy products, 5.8%; meat/poultry/fish/eggs, 5.1%; other, 1.9%. Mean folate intake would increase 16.5% if enriched bread and grains were fortified. Such fortification could help some persons to lower serum homocysteine concentration and vascular disease risk. Dietitians should be aware of modern protocols for screening the elderly for vitamin B-12 deficiency.

Short-term and long-term variability of plasma homocysteine measurement

Within-person and methodological variability of a given analyte are important elements in determining whether an individual has altered concentrations of that analyte. We report the short-term (1 month) within-person, between-person, and methodological variability of plasma homocysteine in 20 healthy participants from whom samples were drawn weekly for 4 weeks. The short-term between-person variance was high, whereas within-person and methodological variances were relatively very low, giving a high reliability coefficient (R) for homocysteine (R = 0.94). The long-term (30 months) reliability coefficient was 0.65, but was greatly influenced by an outlier (R = 0.82 with the outlier excluded). The data suggest that an individual’s plasma homocysteine concentration is relatively constant over at least 1 month, and a single measurement characterizes the average concentration reasonably well.

Are dietary factors involved in DNA methylation associated with colon cancer?

Disturbances in DNA methylation have been hypothesized as being involved in carcinogenesis. It has been proposed that dietary factors such as folate, alcohol, and methionine may be associated with colon cancer because of their involvement in DNA methylation processes. Data from a large retrospective population-based case-control study of incident colon cancer were used to evaluate whether intake of alcohol and other dietary factors involved in DNA methylation are associated with colon cancer. Dietary data were obtained using a detailed diet history questionnaire. We did not observe strong independent associations between folate, vitamin B6, vitamin B12, methionine, or alcohol and risk of colon cancer after adjusting for body size, physical activity, cigarette smoking patterns, energy intake, and dietary intake of fiber and calcium. However, when assessing the associations between colon cancer and a composite dietary profile based on alcohol intake, methionine, folate, vitamin B12, and vitamin B6, we observed a trend of increasing risk as one moved from a low- to a high-risk group. This trend was modest and most marked in those diagnosed at a younger age [odds ratio (OR) for men = 1.3, 95% confidence interval (CI) = 0.9-1.9; OR for women = 1.6, 95% CI = 1.0-2.6]. We observed that associations with this high-risk dietary profile were greater among those who took aspirin or nonsteroidal anti-inflammatory drugs on a regular basis and were younger at the time of diagnosis (men OR = 1.7, 95% CI = 1.0-3.2; women OR = 2.2, 95% CI = 1.0-4.8) and for distal tumors (men OR = 1.4, 95% CI = 0.9-2.3; women OR = 2.0, 95% CI = 1.0-3.8). Findings from this study provide only limited support for previously reported associations between dietary factors involved in DNA methylation and risk of colon cancer.

Common mutation in methylenetetrahydrofolate reductase. Correlation with homocysteine metabolism and late-onset vascular disease

BACKGROUND

Increased homocysteine levels are a risk factor for atherosclerosis and its sequelae. A common genetic mutation in methylenetetrahydrofolate reductase (MTHFR), an enzyme required for efficient homocysteine metabolism, creates a thermolabile enzyme with reduced activity. We determined the prevalence of this mutation in many subjects with and without vascular disease and related it to homocysteine and folate levels.

METHODS AND RESULTS

DNA from 247 older subjects with vascular disease and 594 healthy subjects without vascular disease (in three different control groups) was screened for the MTHFR 677 C-to-T mutation. Within each group, 9% to 17% of the subjects were homozygous for this mutation, and the mutant allele frequency was 31% to 39%. The genotype distributions, homozygote frequencies, and allele frequencies did not differ significantly between the study groups. In the vascular disease subjects, despite significantly lower folate levels in MTHFR homozygotes, there was no significant difference in homocysteine levels among the MTHFR genotype groups. The negative slope of the regression line relating homocysteine and folate was significantly steeper for those with a homozygous MTHFR mutation compared with those without this mutation.

CONCLUSIONS

Although the thermolabile MTHFR mutation is very common, it does not appear to be a significant genetic risk factor for typical late-onset vascular disease. Because MTHFR homozygotes have increased homocysteine with low folate levels, this mutation may contribute to early-onset or familial vascular disease. The genotype dependence of the folate-homocysteine correlation further suggests that homozygotes for this mutation may have both an exaggerated hyperhomocysteinemic response to folic acid depletion and a better response to folic acid therapy.

Methylenetetrahydrofolate reductase polymorphism, plasma folate, homocysteine, and risk of myocardial infarction in US physicians

BACKGROUND

Hyperhomocysteinemia appears to be an independent risk factor for coronary disease. Elevated levels of plasma total homocysteine (tHCY) can result from genetic or nutrient-related disturbances in the transsulfuration or remethylation pathways for homocysteine metabolism. The enzyme 5,10-methylenetetrahydrofolate reductase (MTHFR) catalyzes the reduction of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, the predominant circulatory form of folate, which serves as a methyl donor for remethylation of homocysteine to methionine. A common mutation in MTHFR recently has been identified.

METHODS AND RESULTS

We assessed the polymorphism in MTHFR, plasma tHCY, and folate using baseline blood levels among 293 Physicians' Health Study participants who developed myocardial infarction (MI) during up to 8 years of follow-up and 290 control subjects. The frequency of the three genotypes was (-/-) (homozygous normal), 47%; (+/-) (heterozygous), 41%; and (+/+) (homozygous mutant), 12%, with a similar distribution among both MI case patients and control subjects. Compared with those with genotype (-/-), the relative risk (RR) of MI among those with (+/-) was 1.1 (95% CI, 0.8 to 1.5), and it was 0.8 (0.5 to 1.4) for the (+/+) genotype; none of these RRs were statistically significant. However, those with genotype (+/+) had an increased mean tHCY level (mean +/- SEM, 12.6 +/- 0.5 nmol/ mL), compared with those with genotype (-/-) (10.6 +/- 0.3) (P < .01). This difference was most marked among men with low folate levels (the lowest quartile distribution of the control subjects): those with genotype (+/+) had tHCY levels of 16.0 +/- 1.1 nmol/mL, compared with 12.3 +/- 0.6 nmol/mL (P < .001) for genotype (-/-).

CONCLUSIONS

In this population, MTHFR polymorphism was associated with higher homocysteine levels but not with risk of MI. A gene-environment interaction might increase the risk by elevating tHCY, especially when folate intake is low.

Determinants and vitamin responsiveness of intermediate hyperhomocysteinemia (> or = 40 micromol/liter). The Hordaland Homocysteine Study

From 1992-93, we screened 18,043 subjects, aged 40-67 yr, and found 67 cases (0.4%) with total plasma homocysteine (tHcy) > or = 40 micromol/liter. Compared to 329 controls, the cases had lower plasma folate and cobalamin levels, lower intake of vitamin supplements, consumed more coffee, and were more frequently smokers. Homozygosity for the C677T mutation in the methylenetetrahydrofolate reductase gene was observed in 73.1% of the cases and 10.2% of the controls. Only seven cases with cobalamin deficiency and one with homocystinuria received specific therapeutic instructions. 2 yr after the screening, 58 subjects were reinvestigated. 41 still had tHcy > 20 micromol/liter, and in 37 of these, intervention with low dose folic acid (0.2 mg/d) was started. Notably, 34 of 37 (92%) had homozygosity for the C677T mutation. Plasma tHcy was reduced in all but two after 7 wk, and became normal within 7 mo in 21 of 37 subjects. Most of the remaining subjects obtained a normal tHcy level with 5 mg/d of folic acid. We conclude that most subjects with hyperhomocysteinemia > or = 40 micromol/liter in the general population have the C677T mutation combined with low folate status. Daily supplement of low dose folic acid will reduce and often normalize their tHcy level.

Plasma homocysteine as a risk factor for atherothrombotic events in systemic lupus erythematosus

BACKGROUND

The aim of this study was to assess whether plasma homocysteine is a risk factor for stroke and other thrombotic events in patients with systemic lupus erythematosus (SLE)--a condition known to be associated with premature atherothrombotic complications.

METHODS

In this prospective study, we investigated the association between homocysteine and risk of stroke and thrombotic events in 337 SLE patients in the Hopkins Lupus Cohort Study, with follow-up of 1619 person-years (mean 4.8 [SD 1.7] years). Each patient had four follow-up assessments per year to obtain information about established risk factors for thrombosis and coronary artery disease. The prospectively defined endpoints were occurrence of stroke and arterial or venous thrombotic events between 1987 and 1995. Blood samples were taken at study entry from fasting patients. Plasma homocysteine, folate, vitamin B12, and pyridoxal 5'-phosphate (PLP) concentrations were measured. Raised homocysteine concentrations were defined as more than 14.1 mumol/L.

FINDINGS

93% of the study population were women, 54% African American, and 45% white. The mean age of participants was 34.9 (SD 11.7) years. During follow-up there were 29 cases of stroke and 31 arterial thrombotic events. Raised homocysteine concentrations were found in 51 (15%) SLE patients. The log-transformed total homocysteine concentrations correlated with serum folate (r = 0.31, p = 0.0001). In univariate analyses, raised homocysteine concentrations were significantly associated with stroke (odds ratio 2.24 [95% CI 1.22-4.13], p = 0.01) and arterial thrombotic events (3.74 [1.96-7.13], p = 0.0001). After adjustment for established risk factors, total plasma homocysteine concentrations remained an independent risk factor for stroke (2.44 [1.04-5.75], p = 0.04) and arterial thromboses (3.49 [0.97-12.54], p = 0.05).

INTERPRETATION

Homocysteine is a potentially modifiable, independent risk factor for stroke and thrombotic events in patients with SLE.

Are different reference intervals for methylmalonic acid and total homocysteine necessary in elderly people?

To determine whether age-adjusted reference intervals for methymalonic acid (MMA) and total homocysteine (tHcy) are necessary, data from 2 previous studies were used. First, the reference intervals for serum vitamin B12, folate, methylmalonic acid and total homocysteine were determined in 2 reference sample groups: 99 healthy adults and 64 selected healthy elderly subjects living at home. Secondly, health-related reference limits were estimated in 143 elderly subjects after supplementing the nutritional status with a combination of vitamin B12, vitamin B6 and folate during a 3-wk period. In the latter group, the adjusted reference intervals for MMA (46-288 nmol/L) as well as for tHcy (5-13.6 mumol/L) are different with considerably lower upper reference limits than that estimated with the original reference values (72-476 nmol/L for MMA; 6.8-21 mumol/L for tHcy) in the elderly subjects. Our data suggest that the MMA and tHcy levels increase with age. Moreover, the upper reference limit for MMA and tHcy, conventionally defined as the mean +2 SD in healthy elderly reference sample group without supplementing the nutritional status, might result in falsely high values due to a high prevalence of an inadequate vitamin B12, vitamin B6 and folate status.

Homocystinuria: what about mild hyperhomocysteinaemia?

Hyperhomocysteinaemia is associated with an increased risk of atherosclerotic vascular disease and thromboembolism, in both men and women. A variety of conditions can lead to elevated homocysteine levels, but the relation between high levels and vascular disease is present regardless of the underlying cause. Pooled data from a large number of studies demonstrate that mild hyperhomocysteinaemia after a standard methionine load is present in 21% of young patients with coronary artery disease, in 24% of patients with cerebrovascular disease, and in 32% of patients with peripheral vascular disease. From such data an odds ratio of 13.0 (95% confidence interval 5.9 to 28.1), as an estimate of the relative risk of vascular disease at a young age, can be calculated in subjects with an abnormal response to methionine loading. Furthermore, mild hyperhomo-cysteinaemia can lead to a two- or three-fold increase in the risk of recurrent venous thrombosis. Elevated homocysteine levels can be reduced to normal in virtually all cases by simple and safe treatment with vitamin B6, folic acid, and betaine, each of which is involved in methionine metabolism. A clinically beneficial effect of such an intervention, currently under investigation, would make large-scale screening for this risk factor mandatory.