Serum folate and risk for ischemic stroke. First National Health and Nutrition Examination Survey epidemiologic follow-up study

The protective mechanism of folic acid on hyperhomocysteinemia-related arterial injury in spontaneously hypertensive rats: Folic acid against arterial inflammation

BACKGROUND

Hypertension associated with hyperhomocysteinemia (HHcy) is correlated with a high risk of vascular diseases. Studies found that folic acid (FA) supplementation can reduce the risk of cardiovascular and cerebrovascular events. The aim of the present study was to explore the potential mechanisms of FA attenuating HHcy-related arterial injury in spontaneously hypertensive rats (SHRs).

METHODS

24 SHRs were randomized into the control group, the HHcy group, and the HHcy + FA group (8 per group). The SHRs in the HHcy group and the HHcy + FA group were given DL-Hcy intraperitoneally to mimic hypertension associated with HHcy. The SHRs in the HHcy + FA group were given FA by gavage to mimic an FA-fortified diet. The histopathology and immunohistochemistry of rat aorta and carotid artery were analyzed, and the relative expression levels of immune/inflammation and oxidative stress molecules in arterial tissue were detected by quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot.

RESULTS

FA significantly reduced the expression levels of nuclear factor-κ-gene binding (NF-κB) p65/Rela and interleukin-6 (IL-6) in rat arterial tissues, as well as the levels of plasma HHcy and serum malondialdehyde (MDA) in hypertension associated with HHcy rats (p < 0.05). At the same time, FA significantly increased the serum superoxide dismutase (SOD) level in hypertension associated with HHcy rats, and even the SOD level of the HHcy + FA group was higher than that of the control group (p < 0.05). However, HHcy induced the opposite results of the above indicators in SHRs compared with the control group (p < 0.05).

CONCLUSIONS

The arterial protection mechanisms of FA are related to reducing the concentration of HHcy to eliminate the tissue toxicity of HHcy, inhibiting NF-κBp65/Rela/IL-6 pathway molecules to regulate inflammatory response, and promoting the potential anti-oxidative stress pathway molecules to reduce oxidative stress level.

Predicting Risk of Stroke From Lab Tests Using Machine Learning Algorithms: Development and Evaluation of Prediction Models

Background

Stroke, a cerebrovascular disease, is one of the major causes of death. It causes significant health and financial burdens for both patients and health care systems. One of the important risk factors for stroke is health-related behavior, which is becoming an increasingly important focus of prevention. Many machine learning models have been built to predict the risk of stroke or to automatically diagnose stroke, using predictors such as lifestyle factors or radiological imaging. However, there have been no models built using data from lab tests.

Objective

The aim of this study was to apply computational methods using machine learning techniques to predict stroke from lab test data.

Methods

We used the National Health and Nutrition Examination Survey data sets with three different data selection methods (ie, without data resampling, with data imputation, and with data resampling) to develop predictive models. We used four machine learning classifiers and six performance measures to evaluate the performance of the models.

Results

We found that accurate and sensitive machine learning models can be created to predict stroke from lab test data. Our results show that the data resampling approach performed the best compared to the other two data selection techniques. Prediction with the random forest algorithm, which was the best algorithm tested, achieved an accuracy, sensitivity, specificity, positive predictive value, negative predictive value, and area under the curve of 0.96, 0.97, 0.96, 0.75, 0.99, and 0.97, respectively, when all of the attributes were used.

Conclusions

The predictive model, built using data from lab tests, was easy to use and had high accuracy. In future studies, we aim to use data that reflect different types of stroke and to explore the data to build a prediction model for each type.

Interaction of serum vitamin B12 and folate with MTHFR genotypes on risk of ischemic stroke

OBJECTIVE

We evaluated the interaction of serum folate and vitamin B₁₂ with methylenetetrahydrofolate reductase (MTHFR) C677T genotypes on the risk of first ischemic stroke and on the efficacy of folic acid treatment in prevention of first ischemic stroke.

METHODS

A total of 20,702 hypertensive adults were randomized to a double-blind treatment of daily enalapril 10 mg and folic acid 0.8 mg or enalapril 10 mg alone. Participants were followed up every 3 months.

RESULTS

Median values of folate and B₁₂ concentrations at baseline were 8.1 ng/mL and 280.2 pmol/L, respectively. Over a median of 4.5 years, among those not receiving folic acid, participants with baseline serum B₁₂ or serum folate above the median had a significantly lower risk of first ischemic stroke (hazard ratio [HR], 0.74; 95% confidence interval [CI], 0.57-0.96), especially in those with MTHFR 677 CC genotype (wild-type) (HR, 0.49; 95% CI, 0.31-0.78). Folic acid treatment significantly reduced the risk of first ischemic stroke in participants with both folate and B₁₂ below the median (2.3% in enalapril-folic acid group vs 3.6% in enalapril-only group; HR, 0.62; 95% CI, 0.46-0.86), particularly in MTHFR 677 CC carriers (1.6% vs 4.9%; HR, 0.24; 95% CI, 0.11-0.55). However, TT homozygotes responded better with both folate and B₁₂ levels above the median (HR, 0.28; 95% CI, 0.10-0.75).

CONCLUSIONS

The risk of first ischemic stroke was significantly higher in hypertensive patients with low levels of both folate and B₁₂. Effect of folic acid treatment was greatest in patients with low folate and B₁₂ with the CC genotype, and with high folate and B₁₂ with the TT genotype.

Reproductive Senescence and Ischemic Stroke Remodel the Gut Microbiome and Modulate the Effects of Estrogen Treatment in Female Rats

Our previous work has shown that reproductively senescent (or middle-aged; 10-12-month-old) Sprague-Dawley female rats, that are naturally estrogen-deficient, have worse stroke outcomes as compared to normally estrous-cycling adult (5-6-month-old) females. Paradoxically, estrogen replacement to this middle-aged group exacerbates stroke outcomes, while it is neuroprotective in adult females. Recent studies reveal an important role for the gut microbiome and gut metabolites in cardiovascular health, including stroke outcomes. To determine whether gut dysbiosis underlies stroke severity in reproductive senescent females, and underlies the anomalous effects of estrogen on stroke, we compared the gut microbiota and gut metabolites pre and post stroke in (a) gonadally intact adult and middle-aged females, (b) in ovariectomized and estrogen-treated (OVX+E) adult and OVX+E middle-aged females, and (c) in middle-aged OVX+E females after fecal microbiome transfer. Our data show significant gut dysbiosis in reproductive senescent females at baseline and after stroke as indicated by an elevated ratio of the major phyla, Firmicutes/Bacteroidetes (F:B), reduced alpha diversity, and significant shifts in beta diversity as compared with adult females. Specific bacterial families were also altered as a result of reproductive aging, as well as gut metabolites, including elevated serum endotoxin levels and decreased short-chain fatty acids (SCFAs), with a concomitant increase in IL-17A, indicating that reproductive senescence significantly affects gut communities under pathologic conditions. Despite the differences in gonadally intact adult and middle-aged females, estrogen-treated ovariectomized (OVX+E) females of either age group displayed no differences in the major phyla, but there was increased abundance in specific bacterial taxa, including Prevotella and Lactobacillus. The SCFA butyrate was significantly reduced at baseline in the middle-aged OVX+E females, while circulating endotoxin LPS were elevated in this group after stroke, suggesting that gut metabolites were differently affected by estrogen treatment in the two age groups. A fecal transfer from adult OVX+E females to middle-aged OVX+E females significantly reduced infarct volume, improved behavioral recovery and transiently reduced IL-17A expression. These data provide the first evidence that microbial gut communities and metabolites are altered by reproductive senescence in female rats at baseline and after stroke, and suggest that estrogen may impact stroke recovery differently in adult and reproductive senescent females due to an age-specific effect on gut microbiota and metabolites.

Mendelian randomisation study of the associations of vitamin B12 and folate genetic risk scores with blood pressure and fasting serum lipid levels in three Danish population-based studies

BACKGROUND/OBJECTIVES

The aim was to examine the association of genetic risk scores (GRSs) of vitamin B12 and folate-associated variants with blood pressure and lipids.

SUBJECTS/METHODS

The study included 12 532 adults from three population-based studies (Inter99, Health2006 and Dan-MONICA10) conducted in Denmark. GRSs were calculated by summarising the number of vitamin B12 and folate increasing alleles. Weighted GRSs were calculated as the sum of weights for each allele corresponding to genetic effects sizes.

RESULTS

GRSs for serum vitamin B12 and folate were associated with serum vitamin B12 and folate, respectively. The β coefficients (95% confidence interval (CI), P-value) for regression of log-transformed serum B12/folate on the weighted GRSs were 0.57 (0.54, 0.61), P<0.001 and 0.85 (0.70, 1.01), P<0.01. No associations were observed between the vitamin B12 GRSs and any of the blood pressure and lipid-related outcomes in the combined analyses. Increasing number of folate increasing alleles was associated with increased high-density lipoprotein (HDL) cholesterol concentrations (β coefficient (95% CI, P-value) for regression of log-transformed HDL on the weighted GRSs, 0.081 (0.015, 0.148), P=0.017), but not with blood pressure, triglyceride, and low-density lipoprotein and total cholesterol levels.

CONCLUSIONS

GRSs were not associated with blood pressure and lipid levels, except for an association between the GRS for folate and HDL cholesterol. Further studies are needed to determine whether a causal association between folate and HDL cholesterol exists.

Association of reduced folate carrier-1 (RFC-1) polymorphisms with ischemic stroke and silent brain infarction

Stroke is the second leading cause of death in the world and in South Korea. Ischemic stroke and silent brain infarction (SBI) are complex, multifactorial diseases influenced by multiple genetic and environmental factors. Moderately elevated plasma homocysteine levels are a major risk factor for vascular diseases, including stroke and SBI. Folate and vitamin B12 are important regulators of homocysteine metabolism. Reduced folate carrier (RFC), a bidirectional anion exchanger, mediates folate delivery to a variety of cells. We selected three known RFC-1 polymorphisms (-43C>T, 80A>G, 696T>C) and investigated their relationship to cerebral infarction in the Korean population. We used the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method to analyze associations between the three RFC-1 polymorphisms, disease status, and folate and homocysteine levels in 584 ischemic stroke patients, 353 SBI patients, and 505 control subjects. The frequencies of the RFC-1 -43TT, 80GG, and 696CC genotypes differed significantly between the stroke and control groups. The RFC-1 80A>G substitution was also associated with small artery occlusion and SBI. In a gene-environment analysis, the RFC-1 -43C>T, 80A>G, and 696T>C polymorphisms in the ischemic stroke group had combined effects with all environmental factors. In summary, we found that the RFC-1 -43C>T, 80A>G, and 696T>C polymorphisms may be risk factors for ischemic stroke.

The role of homocysteine-lowering B-vitamins in the primary prevention of cardiovascular disease

Cardiovascular disease (CVD) is the leading cause of mortality in the Western world. The effort of research should aim at the primary prevention of CVD. Alongside statin therapy, which is maintained to be an effective method of CVD prevention, there are alternative methods such as vitamin B substitution therapy with folic acid (FA), and vitamins B12 and B6 . B-vitamins may inhibit atherogenesis by decreasing the plasma level of homocysteine (Hcy)-a suspected etiological factor for atherosclerosis-and by other mechanisms, primarily through their antioxidant properties. Although Hcy-lowering vitamin trials have failed to demonstrate beneficial effects of B-vitamins in the prevention of CVD, a meta-analysis and stratification of a number of large vitamin trials have suggested their effectiveness in cardiovascular prevention (CVP) in some aspects. Furthermore, interpretation of the results from these large vitamin trials has been troubled by statin/aspirin therapy, which was applied along with the vitamin substitution, and FA fortification, both of which obscured the separate effects of vitamins in CVP. Recent research results have accentuated a new approach to vitamin therapy for CVP. Studies undertaken with the aim of primary prevention have shown that vitamin B substitution may be effective in the primary prevention of CVD and may also be an option in the secondary prevention of disease if statin therapy is accompanied by serious adverse effects. Further investigations are needed to determine the validity of vitamin substitution therapy before its introduction in the protocol of CVD prevention.

Plasma homocysteine, dietary B vitamins, betaine, and choline and risk of peripheral artery disease

OBJECTIVE

Few studies have examined the roles of homocysteine and related nutrients in the development of peripheral artery disease (PAD). We examined the associations between plasma homocysteine, dietary B vitamins, betaine, choline, and supplemental folic acid use and incidence of PAD.

METHODS

We used two cohort studies of 72,348 women in the Nurses' Health Study (NHS, 1990-2010) and 44,504 men in the Health Professionals Follow-up Study (HPFS, 1986-2010). We measured plasma homocysteine in nested matched case-control studies of clinically recognized PAD within both cohorts, including 143 PAD cases and 424 controls within the NHS (1990-2010) and 143 PAD cases and 428 controls within the HPFS (1994-2008). We examined the association between diet and risk of incident PAD in the cohorts using a food frequency questionnaire and 790 cases of PAD over 3.1 million person-years of follow-up.

RESULTS

Higher homocysteine levels were positively associated with risk of PAD in men (adjusted IRR 2.17; 95% CI, 1.08-4.38 for tertile 3 vs. 1). There was no evidence of an association in women (adjusted IRR 1.14; 95% CI, 0.61-2.12). Similarly, higher folate intake, including supplements, was inversely associated with risk of PAD in men (adjusted HR 0.90; 95% CI, 0.82-0.98 for each 250 μg increase) but not women (HR 1.01, 95% CI, 0.88-1.15). Intakes of the other B vitamins, betaine, and choline were not consistently associated with risk of PAD in men or women.

CONCLUSION

Homocysteine levels were positively associated and dietary folate intake was inversely associated with risk of PAD in men but not in women.

The potential role of homocysteine mediated DNA methylation and associated epigenetic changes in abdominal aortic aneurysm formation

Previous studies have suggested that homocysteine (Hcy) has wide-ranging biological effects, including accelerating atherosclerosis, impairing post injury endothelial repair and function, deregulating lipid metabolism and inducing thrombosis. However, the biochemical basis by which hyperhomocysteinemia (HHcy) contributes to cardiovascular diseases (CVDs) remains largely unknown. Several case-control studies have reported an association between HHcy and the presence of abdominal aortic aneurysms (AAA) and there are supportive data from animal models. Genotypic data concerning the association between variants of genes involved in the methionine cycle and AAA are conflicting probably due to problems such as reverse causality and confounding. The multifactorial nature of AAA suggests the involvement of additional epigenetic factors in disease formation. Elevated Hcy levels have been previously linked to altered DNA methylation levels in various diseases. Folate or vitamin B12 based methods of lowering Hcy have had disappointingly limited effects in reducing CVD events. One possible reason for the limited efficacy of such therapy is that they have failed to reverse epigenetic changes induced by HHcy. It is possible that individuals with HHcy have an "Hcy memory effect" due to epigenetic alterations which continue to promote progression of cardiovascular complications even after Hcy levels are lowered. It is possible that deleterious effect of prior, extended exposure to elevated Hcy concentrations have long-lasting effects on target organs and genes, hence underestimating the benefit of Hcy lowering therapies in CVD patients. Therapies targeting the epigenetic machinery as well as lowering circulating Hcy concentrations may have a more efficacious effect in reducing the incidence of cardiovascular complications.

Epigenetics in Parkinson's and Alzheimer's diseases

Neurodegenerative disorders, such as Parkinson's and Alzheimer's disease, are highly complex, due to their multifactorial origin, not only depending on genetic but also on environmental factors. Several genetic risk factors have already been associated with both the diseases, however, the precise way through which the environment contributes to neurodegeneration is still unclear.Recently, epigenetic mechanisms, such as DNA methylation, chromatin remodeling or miRNAs, which may induce alterations in genes expression, have started to be implicated in both AD and PD. Epigenetic modulation is present since pre-natal stages and throughout lifetime, and depends on lifestyle conditions and environmental exposures, and consequently could represent the missing link between risk factors and the development of sporadic disorders. This chapter will discusses the role of epigenetics in AD and PD.

Folate intake and incidence of hypertension among American young adults: a 20-y follow-up study

BACKGROUND

Laboratory studies suggest that folate intake may decrease blood pressure (BP) through increasing nitric oxide synthesis in endothelial cells and/or reducing plasma homocysteine concentrations. However, human studies, particularly longitudinal data, are limited.

OBJECTIVE

Our objective was to investigate whether dietary folate intake is associated with the 20-y incidence of hypertension.

DESIGN

We prospectively followed 4400 men and women (African Americans and whites aged 18-30 y) without hypertension at baseline (1985) in the Coronary Artery Risk Development in Young Adults study 6 times, in 1987, 1990, 1992, 1995, 2000, and 2005. Diet was assessed by dietary-history questionnaire at baseline and in 1992 and 2005. Incident hypertension was defined as the first occurrence at any follow-up examination of systolic BP ≥ 140 mm Hg, diastolic BP ≥ 90 mm Hg, or use of antihypertensive medication.

RESULTS

A total of 989 incident cases were identified during the 20-y follow-up. After adjustment for potential confounders, participants in the highest quintile of total folate intake had a significantly lower incidence of hypertension (HR: 0.48; 95% CI: 0.38, 0.62; P-trend < 0.01) than did those in the lowest quintile. The multivariable HRs for the same comparison were 0.33 (95% CI: 0.22, 0.51; P-trend < 0.01) in whites and 0.54 (95% CI: 0.40, 0.75; P-trend < 0.01) in African Americans (P-interaction = 0.047). The inverse associations were confirmed in a subset of the cohort (n = 1445) with serum folate measured at baseline and in 1992 and 2000.

CONCLUSIONS

Higher folate intake in young adulthood was longitudinally associated with a lower incidence of hypertension later in life. This inverse association was more pronounced in whites. Additional studies are warranted to establish the causal inference.

Association between adherence to folic acid supplements and serum folate, and plasma homocysteine among hemodialysis patients

OBJECTIVE

To examine the relationship between adherence to prescribed folic acid supplements and folic acid intake, serum folate and plasma homocysteine in hemodialysis patients. The effects of change in adherence patterns from enrollment to 1 year later on changes in these same measures were also assessed.

DESIGN

Secondary data analysis.

PARTICIPANTS

Eighty-six hemodialysis patients who participated in the Hemodialysis (HEMO) Study's Homocysteine ancillary study.

MAIN OUTCOME MEASURES

Folic acid supplement intake, serum folate, and plasma homocysteine.

RESULTS

Eighty-eight percent of patients at enrollment and 91% 1 year later were adherent to prescribed folic acid supplements. Nonadherers had lower intakes of folic acid at both enrollment and 1 year later and lower serum folate levels at enrollment. Percent change was significantly different between the 3 adherence change groups for folic acid intake (P = .001) and plasma homocysteine (P < .001) from enrollment to 1 year later. The nonadherent group at enrollment had the lowest intakes and serum folate levels, and the highest plasma homocysteine levels. When they became adherent 1 year later, they had the greatest change in folic acid intake (5,461%; P = .03), coupled with a 69% increase in serum folate (P = .04) and a 29% decrease in plasma homocysteine (P = .03).

CONCLUSIONS

Hemodialysis patients who were nonadherent to folic acid supplement prescriptions had low folic acid intakes, low serum folates, and high homocysteine levels. When their adherence improved, folic acid intakes rose, serum folates increased, and plasma homocysteine levels decreased, although mild hyperhomocysteinemia persisted.

Characterization of uptake of folates by rat and human blood-brain barrier endothelial cells

This study aimed to characterize (3)H-folic acid ((3)H-FA) and (14)C-methyltetrahydrofolic acid ((14)C-MTHF) uptake by rat (RBE4) and human (hCMEC/D3) blood-brain barrier (BBB) endothelial cell lines. Uptake of (3)H-FA and (14)C-MTHF by RBE4 cells was time dependent and linear for the first 2 min of incubation; uptake by hCMEC/D3 cells showed a less marked time-dependency and a greater experimental variability. So, further experiments were performed in RBE4 cells only. Uptake of (3)H-FA was stimulated at acidic and alkaline pH, Na(+) dependent, stimulated when F(-) substituted for Cl(-), energy independent, inhibited by premetrexed, stimulated by cytochalasin D, and unaffected by MTHF, DIDS, SITS, methotrexate, monensin, and FA. Uptake of (14)C-MTHF was found to be pH-, Na(+)-, Cl(-)- and energy independent, inhibited by premetrexed and methotrexate, stimulated by cytochalasin D, and unaffected by FA, DIDS, SITS, monensin, and MTHF. RT-PCR analysis showed mRNA expression of reduced folate transporter (RFC), but neither of FRalpha nor of proton-coupled folate transporter (PCFT) in RBE4 cells, and mRNA expression of RFC and PCFT, but not of FRalpha, in hCMEC/D3 cells. In conclusion, both human and rat BBB endothelial cells show little capacity for (3)H-FA and (14)C-MTHF apical uptake. Hence, these cell lines do not appear to be a good model to study the transport of folates at the BBB.

Folic acid deficiency increases delayed neuronal death, DNA damage, platelet endothelial cell adhesion molecule-1 immunoreactivity, and gliosis in the hippocampus after transient cerebral ischemia

Folic acid deficiency increases stroke risk. In the present study, we examined whether folic acid deficiency enhances neuronal damage and gliosis via oxidative stress in the gerbil hippocampus after transient forebrain ischemia. Animals were exposed to a folic acid-deficient diet (FAD) for 3 months and then subjected to occlusion of both common carotid arteries for 5 min. Exposure to an FAD increased plasma homocysteine levels by five- to eightfold compared with those of animals fed with a control diet (CD). In CD-treated animals, most neurons were dead in the hippocampal CA1 region 4 days after ischemia/reperfusion, whereas, in FAD-treated animals, this occurred 3 days after ischemia/reperfusion. Immunostaining for 8-hydroxy-2'-deoxyguanosine (8-OHdG) was performed to examine DNA damage in CA1 neurons in both groups after ischemia, and it was found that 8-OHdG immunoreactivity in both FAD and CD groups peaked at 12 hr after reperfusion, although the immunoreactivity in the FAD group was much greater than that in the CD group. Platelet endothelial cell adhesion molecule-1 (PECAM-1; a final mediator of neutrophil transendothelial migration) immunoreactivity in both groups increased with time after ischemia/reperfusion: Its immunoreactivity in the FAD group was much higher than that in the CD group 3 days after ischemia/reperfusion. In addition, reactive gliosis in the ischemic CA1 region increased with time after ischemia in both groups, but astrocytosis and microgliosis in the FAD group were more severe than in the CD group at all times after ischemia. Our results suggest that folic acid deficiency enhances neuronal damage induced by ischemia.

Mechanisms and potential therapeutic targets for folic acid in cardiovascular disease

Folic acid (FA) is a member of the B-vitamin family with cardiovascular roles in homocysteine regulation and endothelial nitric oxide synthase (eNOS) activity. Its interaction with eNOS is thought to be due to the enhancement of tetrahydrobiopterin bioavailability, helping maintain eNOS in its coupled state to favor the generation of nitric oxide rather than oxygen free radicals. FA also plays a role in the prevention of several cardiac and noncardiac malformations, has potent direct antioxidant and antithrombotic effects, and can interfere with the production of the endothelial-derived hyperpolarizing factor. These multiple mechanisms of action have led to studies regarding the therapeutic potential of FA in cardiovascular disease. To date, studies have demonstrated that FA ameliorates endothelial dysfunction and nitrate tolerance and can improve pathological features of atherosclerosis. These effects appear to be homocysteine independent but rather related to their role in eNOS function. Given the growing evidence that nitric oxide synthase uncoupling plays a major role in many cardiovascular disorders, the potential of exogenous FA as an inexpensive and safe oral therapy is intriguing and is stimulating ongoing investigations.

Characterization of folate uptake by choroid plexus epithelial cells in a rat primary culture model

Reduced derivatives of folic acid (folates) play a critical role in the development, function and repair of the CNS. However, the molecular systems regulating folate uptake and homeostasis in the central nervous system remain incompletely defined. Choroid plexus epithelial cells express high levels of folate receptor alpha (FRalpha) suggesting that the choroid plays an important role in CNS folate trafficking and maintenance of CSF folate levels. We have characterized 5-methyltetrahydrofolate (5-MTHF) uptake and metabolism by primary rat choroid plexus epithelial cells in vitro. Two distinct processes are apparent; one that is FRalpha dependent and one that is independent of the receptor. FRalpha binds 5-MTHF with high affinity and facilitates efficient uptake of 5-MTHF at low extracellular folate concentrations; a lower affinity FRalpha independent system accounts for increased folate uptake at higher concentrations. Cellular metabolism of 5-MTHF depends on the route of folate entry into the cell. 5-MTHF taken up via a non-FRalpha -mediated process is rapidly metabolized to folylpolyglutamates, whereas 5-MTHF that accumulates via FRalpha remains non-metabolized, supporting the hypothesis that FRalpha may be part of a pathway for transcellular movement of the vitamin. The proton-coupled folate transporter, proton-coupled folate transporter (PCFT), mRNA was also shown to be expressed in choroid plexus epithelial cells. This is consistent with the role we have proposed for proton-coupled folate transporter in FRalpha-mediated transport as the mechanism of export of folates from the endocytic compartment containing FRalpha.

Folate and vitamin B12 levels in levodopa-treated Parkinson's disease patients: their relationship to clinical manifestations, mood and cognition

We tested the hypothesis that mood, clinical manifestations and cognitive impairment of levodopa-treated Parkinson's disease (PD) patients are associated with vitamin B12 and folate deficiency. To this end, we performed this cross-sectional study by measuring serum folate and vitamin B12 blood levels in 111 consecutive PD patients. Levodopa-treated PD patients showed significantly lower serum levels of folate and vitamin B12 than neurological controls, while depressed patients had significantly lower serum folate levels as compared to non-depressed. Cognitively impaired PD patients exhibited significantly lower serum vitamin B12 levels as compared to cognitively non-impaired. In conclusion, lower folate levels were associated with depression, while lower vitamin B12 levels were associated with cognitive impairment. The effects of vitamin supplementation merit further attention and investigation.

Serum homocysteine, folate and risk of stroke: Kuopio Ischaemic Heart Disease Risk Factor (KIHD) Study

BACKGROUND

Homocysteine and folate have been suggested to have opposite effects on the risk of stroke, although the results are controversial.

DESIGN AND METHODS

The purpose of this study was to assess the effects of serum total homocysteine (tHcy) and serum folate levels on the risk of stroke in a prospective cohort study. The subjects were 1015 men aged 46-64 years and free of prior stroke, examined in 1991-1993 in the Kuopio Ischaemic Heart Disease Risk Factor (KIHD) Study.

RESULTS

At baseline the mean serum tHcy concentration was 10.9 micromol/l (SD 3.4). During an average follow-up time of 9.6 years, 49 men experienced a stroke, of which 34 were ischaemic. In Cox proportional hazards models, men in the highest tHcy third had a risk factor-adjusted hazard rate ratio (RR) of 2.77 [95% confidence interval (CI): 1.23-6.24] for any stroke and 2.61 (95% CI: 1.02-6.71) for ischaemic stroke, compared with men in the lowest third. The mean baseline serum folate concentration was 10.4 nmol/l (SD 4.1). Men in the highest third of serum folate (>11.2 nmol/l) had an adjusted RR for any stroke of 0.35 (95% CI: 0.14-0.87) and for ischaemic stroke of 0.40 (95% CI: 0.15-1.09), compared with men in the lowest third.

CONCLUSION

Elevated serum tHcy is associated with increased risk of all strokes and ischaemic strokes in middle-aged eastern Finnish men free of prior stroke. On the other hand, high serum folate concentration may protect against stroke.

Homocysteine and carotid intima-media thickness: a critical appraisal of the evidence

This review examines the relationship between hyperhomocysteinemia, a risk factor for vascular disease, and carotid intima-media thickness (CIMT), a valid marker of generalized atherosclerosis and future vascular disease risk. The relationship between two important determinants of hyperhomocysteinemia in the general population-folate status and the 677C --> T methylenetetrahydrofolate reductase (MTHFR) polymorphism-and CIMT is also covered.

METHODS

We searched literature databases for articles examining homocysteine and CIMT published before September 2003.

RESULTS

We identified 54 studies. Observational studies generally failed to demonstrate a relationship between homocysteine and CIMT in homocystinuric, uremic, hypercholesterolemic or non-insulin-dependent diabetes mellitus patients or in subjects with insulin insensitivity. Weak associations, but usually only in certain sub-populations were found in vascular disease patients and in population-based studies. B vitamins reduce the progression of CIMT in renal transplant recipients and vascular disease patients as demonstrated by two trials. The majority of studies demonstrated increased CIMT in individuals with the MTHFR 677TT genotype. Folate status showed no relation to CIMT.

DISCUSSION

In non-patient populations, hyperhomocysteinemia is weakly associated with CIMT. The association of the 677 C--> T MTHFR polymorphism with CIMT further supports this finding. Lastly, folate levels may need to reach a critically low status before an association can be found between folate and CIMT. Larger trials in various population types are needed to determine whether folate alone or in combination with Vitamins B6 and B12 will slow down or even reverse atherosclerotic progression.

Folate, homocysteine, endothelial function and cardiovascular disease

Evidence reported from numerous clinical studies over the past decade has revealed an association between increased plasma total homocysteine (tHcy) concentrations and cardiovascular disease (CVD). In addition, epidemiological studies have identified an inverse association between blood folate concentrations, folate intake and cardiovascular endpoints, that are independent of homocysteine. Folic acid supplementation can lower plasma tHcy concentrations safely and inexpensively. Furthermore, folic acid can reverse endothelial dysfunction observed in patients with CVD. This reversal in endothelial dysfunction with folic acid has been shown to be independent of plasma tHcy lowering, suggesting that folate has pleiotropic effects on the vasculature other than homocysteine lowering. In vitro evidence demonstrates that 5-methyltetrahydrofolate (5MeTHF) the main circulating metabolite of folate, can increase nitric oxide production and can directly scavenge superoxide radicals. The potential beneficial role of folic acid supplements on vascular disease are currently being tested in randomized placebo controlled studies.

Serum Vitamin B12 and Folic Acid Levels in Acute Cerebral Atherothrombotic Infarction

Hyperhomocysteinemia is an independent risk factor for atherothrombotic cerebral stroke. Vitamin B12 and folic acid are important determinants of homocysteine metabolism. We aimed to evaluate the relationship, if present, between vitamin B12 and folic acid levels and acute cerebral stroke in this study. Blood aliquots drawn within 24 hours after the stroke from hospitalized patients (n=66) with the diagnosis of acute ischemic cerebrovascular episode and also blood samples from 38 healthy controls without any vascular risk factor were analyzed. With a competitive, chemoluminescence assay, serum levels of vitamin B12 and folic acid were measured in blood samples taken within 24 hours after the stroke. The differences and correlations were tested using frequency test, student-t test and multivariate analysis. Mean serum vitamin B12 levels were significantly lower in the patients than in the control subjects, 245.40 (S.D.: 72.9) and 343.2 (S.D.: 113.0) pg/ml respectively (p=0.0001). This difference was independent from other risk factors. Likewise, mean serum folic acid levels were lower in the patients than in the control subjects, 4.62 (S.D.: 1.94) and 5.97 (S.D.: 1.19) ng/ml, respectively (p=0.003). Mean serum levels of vitamin B12 and folate at the convalescence phase were 253.05 (S.D.: 68.78) pg/ml and 4.48 (S.D.: 2.08) ng/ml, respectively; the values obtained at the acute phase were not significantly different from the values obtained at the convalescence phase. We conclude that low vitamin B12 and folic acid concentrations are associated with an increased risk of stroke, and the relationship for vitamin B12 is independent from the other known modifiable stroke risk factors. For understanding the effects of B12 and folate in stroke patients, more detailed follow-up studies with long period are needed.

Combined acetaldehyde and nicotine exposure depresses cardiac contraction in ventricular myocytes: prevention by folic acid

Chronic alcoholism can progress to alcoholic cardiomyopathy characterized by ventricular dilation and impaired ventricular contractility. Nicotine abuse continues to remain a serious risk factor for cardiovascular diseases. However, little is know regarding the combined effects. This study was designed to examine the role of short-term combined exposure of the main alcohol metabolite acetaldehyde (ACA) and nicotine on cardiac contractile function in adult rat ventricular myocytes, and if folate exposure attenuates the effect of ACA/nicotine. Mechanical and intracellular Ca2+ properties were evaluated by an IonOptix SoftEdge system. Short-term (4-6 h) culture of myocytes with ACA (10 microM), nicotine (100 microM), or combination of the two in sealed vials with silicone septa depressed maximal velocity of shortening/relengthening, without affecting duration of shortening/relengthening and intracellular Ca2+ handling. Interestingly, the toxin-induced defects on myocyte mechanical properties were ablated with cotreatment of folate (100 microM), an essential vitamin required for DNA synthesis and repair. Collectively, these data provided evidence that ACA and nicotine, either alone or in combination, directly depressed cardiomyocyte mechanical function possibly through mechanisms related to DNA damage.

Risk factors for cryptogenic ischaemic stroke

This case-control study was designed to identify risk factors for cryptogenic brain infarction. We assessed the frequency of prothrombotic states, homocysteine, lipoprotein (a) [Lp(a)] and other lipids and the apolipoprotein E phenotype together with conventional risk factors in 46 patients (19 women and 27 men) with cryptogenic brain infarction aged from 15 to 60 years and in 104 community-based controls. Multivariate odds ratios (ORs) for risk factors and 95% CIs were calculated by logistic regression. Hypertension (OR 4.5; 95% CI, 1.5-13.2; P = 0.006), current smoking (OR 2.9; 95% CI, 1.2-6.8; P = 0.012), low HDL cholesterol (HDL-C) (OR 5.4; 95% CI, 1.1-25.5; P = 0.035) and high clotting factor VIII activity (OR 3.6; 95% CI, 1.1-12.2; P = 0.041) were variables associated with cryptogenic brain infarction. These risk factors were not equally frequent in women and men. Low HDL-C and high factor VIII activity in the women, and hypertension, current smoking and a low level of plasma folate in the men were risk factors for cryptogenic stroke. Several of the observed risk factors for cryptogenic brain infarction were lifestyle-associated, which emphasizes the role of health education in addition to pharmacological treatment in the prevention of stroke.

Homocysteine and occlusive arterial disease

BACKGROUND

An increased plasma level of homocysteine has been proposed as an independent risk factor for atherosclerosis; this review examines the evidence.

METHODS

A Medline search was undertaken for English language articles on homocysteine and vascular disease. Further papers were identified by cross-referencing from the reference lists of relevant major articles.

RESULTS

Although much interest has been generated about homocysteine and atherosclerotic disease, contradictory data exist regarding its role in disease progression. There is insufficient current evidence to regard increased homocysteine level as a causative factor in atherosclerotic disease.

CONCLUSION

It is not known whether lowering plasma homocysteine concentration will reduce cardiovascular risk in the long term. Until such data become available, there is no evidence for the widespread use of folic acid therapy to reduce cardiovascular disease risk.

Is folate a promising agent in the prevention and treatment of cardiovascular disease in patients with renal failure?

Management of the conventional cardiovascular risk factors is insufficient to prevent the dramatic increase in atherosclerotic cardiovascular morbidity and mortality in patients with renal failure. Folate recently received attention as a potential alternative treatment option to decrease the excess cardiovascular risk in the uremic population. Folate administration is the principal treatment modality for hyperhomocysteinemia. Hyperhomocysteinemia is prevalent in more than 85% of patients with end-stage renal disease (ESRD) and is independently associated with increased odds for atherosclerotic cardiovascular disease. Several attempts have been made to normalize homocysteine levels in uremic patients with folate-based vitamin regimens. Although supraphysiologic doses of folic acid afford greater reductions in homocysteine levels than standard doses, the response to treatment is generally only partial and the large majority of ESRD patients have residual hyperhomocysteinemia. Several defects in folate metabolism have been described in uremia, which may explain the relative folate resistance in patients with renal failure, but their clinical relevance remains uncertain. It appears unlikely that the hyperhomocysteinemia in ESRD can be cured solely with folic acid supplements, since folate does not affect the prolonged plasma elimination of homocysteine, which is the primary defect in homocysteine metabolism in uremia. Folate restores endothelial dysfunction, associated with hyperlipidemia, diabetes and hyperhomocysteinemia. The beneficial effect appears to be independent of its homocysteine-lowering capacity and is possibly related to an improved bioavailability of nitric oxide. However, folate has failed to improve endothelial dysfunction in uremic patients. In the ESRD population, multiple metabolic and hemodynamic abnormalities adversely affect endothelial function. In addition, irreversible structural vascular disease already may be present. Folate should, therefore, probably be an integral part of an "endothelial protective regimen," consisting of lipid-lowering agents, antihypertensives and antioxidant vitamins and started very early in patients with renal failure. Before large-scale folate administration can be recommended, effects on hard endpoints of cardiovascular disease need to be demonstrated in randomized trials. Such trials are currently underway in patients with normal renal function at high risk for cardiovascular disease, and one trial has recently been initiated in stable renal transplant recipients.

Assessment of nutritional folate status and selected vitamin status of women of childbearing age

OBJECTIVE

The aim of the study was to investigate folate and other selected vitamin status (ascorbic acid, tocopherol, retinol, vitamin B12), haematological indices and total homocysteine concentration of serum in women of childbearing age.

DESIGN

A cross-sectional study.

SETTING

Warsaw.

SUBJECTS

Healthy women aged 18-30 y (n=78) not pregnant presently or previously, and not taking drugs.

RESULTS

Haemoglobin and haematocrit values according to WHO criteria for 18 to 30-y-old women were normal. The optimal levels of serum tocopherol, >1.29 mg/dl (>29.9 micromol/l) to preventing civilization diseases, were found in 5.5% and serum retinol >71.6 mcg/dl (>2.5 micromol/l) in 6.4% of all studied persons. The analysis of serum folate concentration showed high-risk deficiency,<3 ng/ml (<6.8 nmol/l), in 6.4%, moderate and low risk together (7.0-14.9 nmol/l) in 61.6% and optimal folate levels (>14.9 nmol/l) in 32.0% of the studied group. Folate body stores were insufficient in almost all women. There was no high or moderate deficiency risk of vitamin B12 or ascorbic acid. None of the women under study had serum total homocysteine (tHcy) concentration >15 micromol/l, indicating hyperhomocysteinaemia. Serum total homocysteine concentrations in the range of 5-15 micromol/l were found in 71.8%, and serum tHcy >10 micromol/l in 7.7% of the studied group of women.

SPONSORSHIP

The study was sponsored by the Polish Committee for Scientific Research.

Impaired homocysteine metabolism and atherothrombotic disease

Based on recent retrospective, prospective, and experimental studies, mild to moderate elevation of fasting or postmethionine-load plasma homocysteine is accepted as an independent risk factor for cardiovascular disease and thrombosis in both men and women. Hyperhomocysteinemia results from an inhibition of the remethylation pathway or from an inhibition or a saturation of the transsulfuration pathway of homocysteine metabolism. The involvement of a high dietary intake of methionine-rich animal proteins has not yet been investigated and cannot be ruled out. However, folate deficiency, either associated or not associated with the thermolabile mutation of the N(5,10)-methylenetetrahydrofolate reductase, and vitamin B(6) deficiency, perhaps associated with cystathionine beta-synthase defects or with methionine excess, are believed to be major determinants of the increased risk of cardiovascular disease related to hyperhomocysteinemia. Recent experimental studies have suggested that moderately elevated homocysteine levels are a causal risk factor for atherothrombotic disease because they affect both the vascular wall structure and the blood coagulation system. The oxidant stress that results from impaired homocysteine metabolism, which modifies the intracellular redox status, might play a central role in the molecular mechanisms underlying moderate hyperhomocysteinemia-mediated vascular disorders. Because folate supplementation can efficiently reduce plasma homocysteine levels, both in the fasting state and after methionine loading, results from further prospective cohort studies and from on-going interventional trials will determine whether homocysteine-lowering therapies can contribute to the prevention and reduction of cardiovascular risk. Additionally, these studies will provide unequivocal arguments for the independent and causal relationship between hyperhomocysteinemia and atherothrombotic disease.

Association of folate intake and serum homocysteine in elderly persons according to vitamin supplementation and alcohol use

BACKGROUND

The serum total homocysteine concentration (tHcy), an indicator of folate status and a possible risk factor for vascular disease, is elevated with impaired renal function and poor vitamin B-12 status, which are common in the elderly.

OBJECTIVE

Our objective was to determine the association between tHcy, folate intake, alcohol consumption, and other lifestyle factors in elderly persons.

DESIGN

This cross-sectional study used linear regression to model changes in tHcy. Subjects were 278 men and women aged 66-94 y studied in 1993.

RESULTS

Total folate intake was negatively associated with tHcy in models adjusted for age, sex, serum creatinine, and serum albumin. We found an interaction between food folate intake and supplement use. Food folate intake had an inverse dose-response relation with tHcy that was limited to nonusers of supplements. Predicted tHcy was 1.5 micromol/L lower in users of supplements containing folate and vitamin B-12 than in nonusers and was independent of food folate intake. We found a positive dose-response relation of coffee and tea intake with tHcy, a positive association for alcohol intake of > or = 60 drinks/mo compared with low intake, and an interaction of alcohol use with folate intake and supplement use. Compared with alcohol users, nonusers had higher predicted tHcy and a lower inverse dose-response relation of food folate intake with tHcy.

CONCLUSIONS

The inverse association between folate intake and tHcy was strongest among nonusers of supplements and among alcohol drinkers. Identifying modifiable factors related to tHcy, a possible risk factor for vascular disease, is especially important in elderly persons.

The role of folic acid in the prevention of cardiovascular disease

Coronary heart disease is the leading cause of death in the developed world. Current surgical and pharmacological interventions are essentially palliative and interest in preventive strategies, particularly through nutrition and avoidance of tobacco has increased in recent years. Basic scientific, clinical and epidemiological evidence indicates a positive association between the plasma level of the amino acid homocysteine and vascular disease. Homocysteine levels are inversely related to both intake and plasma levels of folate. Less strong evidence indicates an inverse relationship between folate intake and coronary heart disease risk. It is likely that current estimates of dietary folate requirements are lower than optimal. Folic acid supplementation reliably reduces homocysteine levels, and may also modify endothelial function independent of this effect on homocysteine. Such treatment is cheap and appears to be essentially free of risk. However, until present randomised control trials are complete, it will not be known definitively whether or not increasing folate intake reduces cardiovascular risk.

Homocysteine elicits a DNA damage response in neurons that promotes apoptosis and hypersensitivity to excitotoxicity

Elevated plasma levels of the sulfur-containing amino acid homocysteine increase the risk for atherosclerosis, stroke, and possibly Alzheimer's disease, but the underlying mechanisms are unknown. We now report that homocysteine induces apoptosis in rat hippocampal neurons. DNA strand breaks and associated activation of poly-ADP-ribose polymerase (PARP) and NAD depletion occur rapidly after exposure to homocysteine and precede mitochondrial dysfunction, oxidative stress, and caspase activation. The PARP inhibitor 3-aminobenzamide (3AB) protects neurons against homocysteine-induced NAD depletion, loss of mitochondrial transmembrane potential, and cell death, demonstrating a requirement for PARP activation and/or NAD depletion in homocysteine-induced apoptosis. Caspase inhibition accelerates the loss of mitochondrial potential and shifts the mode of cell death to necrosis; inhibition of PARP with 3AB attenuates this effect of caspase inhibition. Homocysteine markedly increases the vulnerability of hippocampal neurons to excitotoxic and oxidative injury in cell culture and in vivo, suggesting a mechanism by which homocysteine may contribute to the pathogenesis of neurodegenerative disorders.

Homocysteine and cardiovascular disease: cause or effect?

Both markedly and mildly elevated circulating homocysteine concentrations are associated with increased risk of vascular occlusion. Here we review possible mechanisms that mediate these effects. Inborn errors of homocysteine metabolism result in markedly elevated plasma homocysteine (200-300 micromol/L) and thromboembolic (mainly venous) disease: treatment to lower but not to normalize these concentrations prevents vascular events. Mild homocysteine elevation (>15 micromol/L) occurs in approximately 20-30% of patients with atherosclerotic disease. Usually, this is easily normalized with oral folate and ongoing trials are assessing the effect of folate treatment on outcomes. Although there is evidence of endothelial dysfunction with both markedly and mildly elevated homocysteine concentrations, the elevated homocysteine concentration in atherosclerotic patients is also associated with most standard vascular risk factors, and importantly, with early decline in renal function, which is common in atherosclerosis. Decline in renal function alone causes elevated plasma homocysteine (and cysteine). These observations suggest that mild hyperhomocysteinemia could often be an effect rather than a cause of atherosclerotic disease. Data on the common C677T methylenetetrahydrofolate reductase polymorphism supports this, in that, although homozygosity is a frequent cause of mild hyperhomocysteinemia when plasma folate is below median population concentrations, it appears not to increase cardiovascular risk. Indeed, there is recent evidence suggesting an acute antioxidant effect of folic acid independent of its effect on homocysteine concentrations. This antioxidant mechanism may oppose an oxidant effect of homocysteine and be relevant to treatment of patients with vascular disease, especially those with chronic renal insufficiency. Such patients have moderately elevated plasma homocysteine and greatly increased cardiovascular risk that is largely unexplained.

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.

Nutritional factors in stroke

Observational studies support the role of modifying lifestyle-related risk factors such as diet, physical activity and alcohol use in stroke prevention. For example, increased Na intake is associated with hypertension, and reduction in salt consumption may significantly lower blood pressure and may reduce stroke mortality. Moderately elevated homocysteine levels may be associated with stroke and are associated with deficiency of dietary intake of folate, vitamin B6 and vitamin B12. Consumption of a diet rich in fruits, vegetables, folate, K, Ca, Mg, dietary fibre, fish and milk may protect against stroke. Regular physical activity may also protect against stroke through its role in controlling various risk factors such as hypertension, diabetes mellitus and obesity. The role of fat intake as a risk factor for stroke remains uncertain, whereas the association between stroke and cholesterol has more convincingly been demonstrated by the recent intervention trials using statins. There is also evidence that a low serum albumin may be causally linked to stroke risk and outcome and that a significant number of stroke patients are undernourished on admission and their nutritional status deteriorates further whilst in hospital. Undernutrition is associated with increasing morbidity and mortality and nutritional supplements may have some beneficial effect on some outcome measures.

Clinical relevance of hyperhomocysteinaemia in atherothrombotic disease

High fasting plasma homocysteine levels (> 12 to 15 mumol/L) are commonly encountered in clinical practice and are associated with increased risk of atherothrombotic disease. Treatment with folic acid (1 to 5 mg/day) is inexpensive and effective in normalising plasma homocysteine levels. High plasma homocysteine levels after methionine loading (> 40 to 50 mumol/L) are also common and can be treated with pyridoxine-based regimens (50 to 250 mg/day). As compared with fasting plasma homocysteine levels, the association between high postmethionine loading plasma homocysteine levels and atherothrombotic disease has been less extensively studied. There is reasonable, but not clearly definitive, evidence that high plasma homocysteine levels are causally related to atherothrombotic disease. Results of randomised trials of homocysteine-lowering treatment with clinical end-points will be available in 4 to 6 years. At present, a reasonable policy for the practising clinician would be to consider homocysteine-lowering treatment in individuals at very high risk of atherothrombotic disease, such as patients with clinically manifest atherothrombotic disease with onset before 55 years of age, patients with end stage renal disease, and healthy subjects with a strong family history of early-onset atherothrombotic disease. Such a policy should be reassessed as the results of randomised trials become available.

Whole blood folate, homocysteine in serum, and risk of first acute myocardial infarction

High level of total homocysteine (tHcy) is a risk factor for coronary artery disease (CAD), but the mechanism is not known. The serum concentration of tHcy, total cholesterol, high density lipoprotein cholesterol (HDL-C), and apolipoprotein A-I (apo A-I) and the concentration of folate in whole blood were measured in 107 patients with first acute myocardial infarction (MI) and 103 controls. The level of whole blood folate was lower and that of tHcy higher in cases than in controls. An increase of 50 nmol/l whole blood folate was associated with an OR for MI of 0.75, and an increase of 5 micromol/l tHcy with an OR for MI of 1.57. Correlations were observed between the levels of whole blood folate and tHcy and between whole blood folate and alcohol intake, and in MI cases, between tHcy, HDL-C, and apo A-I as well as between HDL-C and alcohol intake. The number of cigarette smokers was higher among cases than controls. In smokers, the level of tHcy was higher and that of whole blood folate lower than in non-smokers. After adjustment for smoking, the whole blood folate and tHcy-associated risks of MI became non-significant. We conclude that smoking may affect folate status and tHcy level adversely. The risk of MI in smokers may at least partly be attributed to hyperhomocysteinemia or low folate.

Homocyst(e)ine and cardiovascular disease: a critical review of the epidemiologic evidence

PURPOSE

To review epidemiologic studies on the association between homocyst(e)ine level and risk for cardiovascular disease and the potential benefits of homocysteine-decreasing therapies.

DATA SOURCES

Computerized and manual searches of the literature on total homocysteine levels and cardiovascular disease.

STUDY SELECTION

Prospective studies and major retrospective epidemiologic studies evaluating the association between homocyst(e)ine levels and cardiovascular disease and the association between blood levels or dietary intake of folate, vitamin B6, and vitamin B12 and cardiovascular disease.

DATA EXTRACTION

Relevant data on patient population, plasma homocyst(e)ine levels, duration of follow-up, and main results were extracted from studies that met the inclusion criteria.

DATA SYNTHESIS

The designs and results of studies included in this review are summarized. A formal meta-analysis was not performed because the studies were heterogeneous in method and design.

CONCLUSIONS

Results of epidemiologic studies suggest that moderately elevated plasma or serum homocyst(e)ine levels are prevalent in the general population and are associated with an increased risk for cardiovascular disease, independent of classic cardiovascular risk factors. Simple, inexpensive, nontoxic therapy with folic acid, vitamin B6, and vitamin B12 reduces plasma homocyst(e)ine levels. Although the association between homocyst(e)ine levels and cardiovascular disease is generally strong and biologically plausible, the data from the prospective studies are less consistent. In addition, epidemiologic observations of an association between hyperhomocyst(e)inemia and cardiovascular risk do not prove the existence of a causal relation. Therefore, the effectiveness of folate, vitamin B6, and vitamin B12 in reducing cardiovascular morbidity and mortality requires rigorous testing in randomized clinical trials. Several such trials are under way; their results may greatly affect cardiovascular morbidity and mortality, given the simplicity and low cost of vitamin therapy.

Low-dose folic acid supplementation decreases plasma homocysteine concentrations: a randomized trial

BACKGROUND

An elevated plasma total homocysteine concentration is a risk factor for cardiovascular disease and neural tube defects. A high daily intake of supplemental folic acid is known to decrease total homocysteine concentrations.

OBJECTIVE

We studied the effect of low-dose folic acid administration (250 or 500 (microgram/d) for 4 wk on plasma total homocysteine concentrations and folate status. We also investigated whether total homocysteine concentrations and blood folate concentrations returned to baseline after an 8-wk washout period.

DESIGN

In this placebo-controlled study, 144 healthy women aged 18-40 y received 500 microgram folic acid/d, 500 microgram folic acid every second day (250 microgram/d), or a placebo tablet with their habitual diet (mean dietary folate intake: 280 microgram/d).

RESULTS

Administration of 250 and 500 microgram folic acid/d for 4 wk significantly increased folate concentrations in plasma (P < 0.001) and red blood cells (P < 0.01). Total homocysteine concentrations decreased significantly (P < 0.001) in women (n = 50) who took 250 microgram folic acid/d [mean (+/-SEM) deviation from baseline: - 11.4 +/- 198%] and in women (n = 45) who took 500 microgram folic acid/d (-21.8 + 1.49%). Eight weeks after the end of the intervention period (week 12), plasma total homocysteine concentrations in the folic acid-supplemented groups had not returned to baseline (week 0).

CONCLUSIONS

Doses of folic acid as low as 250 microgram/d, on average, in addition to usual dietary intakes of folate significantly decreased plasma total homocysteine concentrations in healthy, young women. An 8-wk washout period was not sufficient for blood folate and plasma total homocysteine concentrations to return to baseline concentrations.

Serum folate and risk for coronary heart disease: results from a cohort of US adults

PURPOSE

To assess the role of serum folate in the risk for coronary heart disease in a national cohort of US adults.

METHODS

Data from the First National Health and Nutrition Examination Survey Epidemiologic Follow-up Study (N = 1921) were used to determine whether a low serum folate concentration was associated with an increased risk for incident coronary heart disease (N = 284). The Cox proportional hazards model adjusted for age, sex, race, education, serum cholesterol, systolic blood pressure, body mass index, cigarette smoking, and alcohol consumption.

RESULTS

The association between folate and risk for coronary heart disease differed by age group (p = 0.03). Among persons aged 35-55 years, the relative risk for heart disease was 2.4 (95% confidence interval (CI), 1.1-5.2) for persons in the lowest quartile (< or = 9.9 nmol/L) when compared with those in the highest quartile (> or = 21.8 nmol/L). However, among persons > or = 55 years the relative risk was 0.5 (95% CI, 0.3-0.8) for comparisons of the lowest versus highest quartiles.

CONCLUSIONS

If the age differences in the risk for heart disease are confirmed, randomized clinical trials assessing the role of folic acid for the prevention of heart disease may need to include young adults in order to demonstrate benefits related to folate supplementation.

Folate deficiencies and cardiovascular pathologies

Although folates are widely distributed in foods, folate deficiencies may be more frequent than expected because their true availability may be impaired due to their lability under various food cooking and processing conditions. Folate deficiency is frequently observed in elderly people, smokers, alcoholics and oral contraceptive users. It is also associated with the mutation leading to the thermolabile variant of N5,10-methylenetetrahydrofolate reductase which is observed in about 10% of the population. In addition to the essential role of the intracellular pool of polyglutamates in de novo biosynthesis of deoxyribonucleotides which allow cell growth and division, the reduced and methylated form of folate, N5-methyltetrahydrofolate, is required for the remethylation of homocysteine to methionine. By inhibiting this remethylation pathway, folate deficiency induces homocysteine efflux into the circulation. Many studies have shown a negative correlation between plasma folate, particularly N5-methyltetrahydrofolate, and circulating homocysteine levels. In addition, folate deficiency is a major cause of hyperhomocysteinemia which is fully recognised as an independent risk factor for atherothrombosis. Epidemiological and recent experimental studies have demonstrated that folate deficiency might increase the risk of cardiovascular disease by increasing circulating homocysteine levels. Thus, the clinical efficiency of folate supplementation, especially N5-methyltetrahydrofolate, in reducing homocysteine-dependent cardiovascular risk should be evaluated.