Protein-bound homocyst(e)ine. A possible risk factor for coronary artery disease

Association between elevated homocysteine levels and obstructive sleep apnea hypopnea syndrome: a systematic review and updated meta-analysis

Objective

This study aimed to distinguish between healthy controls and patients with OSAHS regarding homocysteine (HCY) levels and investigate how individuals with OSAHS respond to continuous positive airway pressure ventilation (CPAP) in terms of serum and plasma HCY levels.

Methods

To ascertain published articles about OSAHS, an exhaustive search was performed across medical databases, encompassing PubMed, Web of Science, EMBASE, CNKI, and Cochrane Library, until January 2, 2024. This study reviewed the literature regarding HCY levels in individuals with OSAHS and control groups, HCY levels under pre- and post-CPAP treatment, the Pearson/Spearman correlation coefficients between HCY levels and apnea-hypopnea index (AHI), and the hazard ratio (HR) of HCY levels concerning the occurrence of major adverse cerebrocardiovascular events (MACCEs) in patients with OSAHS. Meta-analyses were performed using weighted mean difference (WMD), correlation coefficients, and HR as effect variables. The statistical analysis was conducted using the R 4.1.2 and STATA 11.0 software packages.

Results

In total, 33 articles were selected for the final analysis. The OSAHS group exhibited significantly higher serum/plasma HCY levels than the control group (WMD = 4.25 μmol/L, 95% CI: 2.60-5.91, P< 0.001), particularly among individuals with moderate and severe OSAHS. Additionally, subgroup analysis using mean age, ethnicity, mean body mass index, and study design type unveiled significantly elevated levels of HCY in the serum/plasma of the OSAHS group compared to the control group. CPAP treatment can significantly decrease serum/plasma HCY levels in patients with OSAHS. Moreover, elevated HCY levels in individuals with OSAHS could be one of the risk factors for MACCEs (adjusted HR = 1.68, 95% CI = 1.10-2.58, P = 0.017). AHI scores show a positive correlation with serum/plasma HCY levels.

Conclusion

Patients with OSAHS had elevated serum/plasma HCY levels compared to healthy controls; however, CPAP therapy dramatically decreased HCY levels in patients with OSAHS. In patients with OSAHS, elevated HCY levels were linked with an increased risk of MACCEs, and HCY was positively connected with AHI values. HCY levels may serve as a useful clinical indicator for determining the severity and efficacy of OSAHS treatments.

Systematic review registration

https://www.crd.york.ac.uk/prospero/, identifier CRD42024498806.

Neurodegenerative Disease: Roles for Sex, Hormones, and Oxidative Stress

Neurodegenerative diseases cause severe impairments in cognitive and motor function. With an increasing aging population and the onset of these diseases between 50 and 70 years, the consequences are bound to be devastating. While age and longevity are the main risk factors for neurodegenerative diseases, sex is also an important risk factor. The characteristic of sex is multifaceted, encompassing sex chromosome complement, sex hormones (estrogens and androgens), and sex hormone receptors. Sex hormone receptors can induce various signaling cascades, ranging from genomic transcription to intracellular signaling pathways that are dependent on the health of the cell. Oxidative stress, associated with aging, can impact the health of the cell. Sex hormones can be neuroprotective under low oxidative stress conditions but not in high oxidative stress conditions. An understudied sex hormone receptor that can induce activation of oxidative stress signaling is the membrane androgen receptor (mAR). mAR can mediate nicotinamide adenine dinucleotide-phosphate (NADPH) oxidase (NOX)-generated oxidative stress that is associated with several neurodegenerative diseases, such as Alzheimer disease. Further complicating this is that aging can alter sex hormone signaling. Prior to menopause, women experience more estrogens than androgens. During menopause, this sex hormone profile switches in women due to the dramatic ovarian loss of 17β-estradiol with maintained ovarian androgen (testosterone, androstenedione) production. Indeed, aging men have higher estrogens than aging women due to aromatization of androgens to estrogens. Therefore, higher activation of mAR-NOX signaling could occur in menopausal women compared with aged men, mediating the observed sex differences. Understanding of these signaling cascades could provide therapeutic targets for neurodegenerative diseases.

Cardiovascular manifestations of intermediate and major hyperhomocysteinemia due to vitamin B12 and folate deficiency and/or inherited disorders of one-carbon metabolism: a 3.5-year retrospective cross-sectional study of consecutive patients

BACKGROUND

The association of moderate hyperhomocysteinemia (HHcy) (15-30 μmol/L) with cardiovascular diseases (CVD) has been challenged by the lack of benefit of vitamin supplementation to lowering homocysteine. Consequently, the results of interventional studies have confused the debate regarding the management of patients with intermediate/severe HHcy.

OBJECTIVE

We sought to evaluate the association of intermediate (30-100 μmol/L) and severe (>100 μmol/L) HHcy related to vitamin deficiencies and/or inherited disorders with CVD outcomes.

METHODS

We performed a retrospective cross-sectional study on consecutive patients who underwent a homocysteine assay in a French University Regional Hospital Center. Patients with CVD outcomes were assessed for vitamin B12, folate, Hcy, methylmalonic acid, and next-generation clinical exome sequencing.

RESULTS

We evaluated 165 patients hospitalized for thromboembolic and other cardiovascular (CV) manifestations among 1006 patients consecutively recruited. Among them, 84% (138/165) had Hcy >30 μmol/L, 27% Hcy >50 μmol/L (44/165) and 3% Hcy >100 μmol/L (5/165). HHcy was related to vitamin B12 and/or folate deficiency in 55% (87/165), mutations in one or more genes of one-carbon and/or vitamin B12 metabolisms in 11% (19/165), and severe renal failure in 15% (21/141) of the studied patients. HHcy was the single vascular risk retrieved in almost 9% (15/165) of patients. Sixty % (101/165) of patients received a supplementation to treat HHcy, with a significant decrease in median Hcy from 41 to 17 µmol/L (IQR: 33.6-60.4 compared with 12.1-28). No recurrence of thromboembolic manifestations was observed after supplementation and antithrombotic treatment of patients who had HHcy as a single risk, after ∼4 y of follow-up.

CONCLUSION

The high frequency of intermediate/severe HHcy differs from the frequent moderate HHcy reported in previous observational studies of patients with pre-existing CVD. Our study points out the importance of diagnosing and treating nutritional deficiencies and inherited disorders to reverse intermediate/severe HHcy associated with CVD outcomes.

The Different Relationship between Homocysteine and Uric Acid Levels with Respect to the MTHFR C677T Polymorphism According to Gender in Patients with Cognitive Impairment

In an elderly population with cognitive impairment, we investigated the association between serum uric acid (sUA) and serum homocysteine (sHcy), known risk factors for cerebrovascular disease. We also investigated the potential effect of the C677T polymorphism in the gene encoding methylenetetrahydrofolate reductase (MTHFR) to the sUA level in different dementia types. Participants underwent a battery of tests including measurements of sUA, sHcy, folic acid, and vitamin B12 as well as genotyping of the MTHFR locus. Data from 861 subjects (597 females to 264 males) were retrospectively analyzed. Subjects with hyperhomocysteinemia had lower serum folic acid and vitamin B12 and higher sUA than those with normal sHcy. sUA was significantly associated with serum creatinine, HbA1c, and sHcy regardless of gender. The TT genotype was found to be associated with hyperhomocysteinemia in both genders (p = 0.001). The levels of hyperlipidemia, sHcy, and sUA differed according to dementia subtypes. High sUA were associated with hyperhomocystenemia in TT genotype only in dementia with vascular lesion. This study reveals that sUA is positively associated with sHcy. We speculate that the two markers synergistically increase cerebrovascular burden and suggested that dietary intervention for sUA and sHcy would be helpful for cognitive decline with vascular lesion.

Hydrolysis of homocysteine thiolactone results in the formation of Protein-Cys-S-S-homocysteinylation

An increased level of homocysteine, a reactive thiol amino acid, is associated with several complex disorders and is an independent risk factor for cardiovascular disease. A majority (>80%) of circulating homocysteine is protein bound. Homocysteine exclusively binds to protein cysteine residues via thiol disulfide exchange reaction, the mechanism of which has been reported. In contrast, homocysteine thiolactone, the cyclic thioester of homocysteine, is believed to exclusively bind to the primary amine group of lysine residue leading to N-homocysteinylation of proteins and hence studies on binding of homocysteine thiolactone to proteins thus far have only focused on N-homocysteinylation. Although it is known that homocysteine thiolactone can hydrolyze to homocysteine at physiological pH, surprisingly the extent of S-homocysteinylation during the exposure of homocysteine thiolactone with proteins has never been looked into. In this study, we clearly show that the hydrolysis of homocysteine thiolactone is pH dependent, and at physiological pH, 1 mM homocysteine thiolactone is hydrolysed to ~0.71 mM homocysteine within 24 h. Using albumin, we also show that incubation of HTL with albumin leads to a greater proportion of S-homocysteinylation (0.41 mol/mol of albumin) than N-homocysteinylation (0.14 mol/mol of albumin). S-homocysteinylation at Cys³⁴ of HSA on treatment with homocysteine thiolactone was confirmed using LC-MS. Further, contrary to earlier reports, our results indicate that there is no cross talk between the cysteine attached to Cys³⁴ of albumin and homocysteine attached to lysine residues.

Sex-related differences in oxidative stress and neurodegeneration

Oxidative stress has been implicated in a number of neurodegenerative diseases spanning various fields of research. Reactive oxygen species can be beneficial or harmful, depending on their concentration. High levels of reactive oxygen species can lead to oxidative stress, which is an imbalance between free radicals and antioxidants. Increased oxidative stress can result in cell loss. Interestingly, sex differences have been observed in oxidative stress generation, which may underlie sex differences observed in neurodegenerative disorders. An enhanced knowledge of the role of sex hormones on oxidative stress signaling and cell loss can yield valuable information, leading to sex-based mechanistic approaches to neurodegeneration.

Hyperhomocysteinemia and Venous Thrombosis

Deep vein thrombosis (DVT) leads to venous ulcers in later life. Venous ulcers are the majority of chronic lower extremity wounds. Recent evidence suggests that hyperhomocysteinemia is an independent risk factor for venous thrombosis. Other evidence suggests that dietary supplementation with folic acids and vitamins helps to change hyper-homocysteinemia. This may be the key to wound management in the future.

Assessment of a possible link between hyperhomocysteinemia and hyperuricemia

BACKGROUND/AIM

Hyperhomocysteinemia and hyperuricemia are both considered risk factors for coronary artery disease. However, the relationship between the 2 has not yet been thoroughly investigated. This study aimed to evaluate this relationship more closely.

MATERIAL AND METHODS

This study is a retrospective cross-sectional analysis of data from a screening center in Israel assessing 16,477 subjects, within an age range of 20 to 80 years.

RESULTS

The mean age of the study sample was 46 years, and 68% were males. Hyperuricemia was found in 24.9% and 14.6% of subjects with elevated and normal homocysteine serum levels, respectively (P < 0.001). A positive association was found between homocysteine serum levels and uric acid serum levels. Compared with subjects with normal homocysteine serum levels, those with hyperhomocysteinemia had an odds ratio (OR) for hyperuricemia of 1.7 (95% confidence interval [CI], 1.5-1.9) and 1.6 (95% CI, 1.1-2.5) for males and females, respectively. After multivariate adjustment for age, hypertension, body mass index, estimated glomerular filtration rate, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and thiazide use, the association remained significant in males (OR, 1.5; 95% CI, 1.3-1.7; P < 0.001) but not in females (OR, 0.9; 95% CI, 0.6-1.6; P = 0.82).

CONCLUSIONS

This large cohort showed a significant association between hyperhomocysteinemia and hyperuricemia. Sex differences were observed. This study suggests that accelerated atherosclerosis may be a consequence of the combined effect of these 2 factors.

Elevated Plasma Homocysteine Concentration in Opium-Addicted Individuals

BACKGROUND

Although the triggering role of both opium use and elevated plasma homocysteine level for progressing atherosclerosis and, therefore, appearing coronary heart disease has been clearly determined, no study are available with respect to the relation between these to risk profiles. In the present study and for the first time, we hypothesized that the opium addiction can be potentially correlated with elevated homocysteine concentration.

METHODS

217 persons (103 opium-addicted and 114 non-addicted) were randomly selected from the Kerman Coronary Artery Disease Risk Study (KERCADRS), Iran, as a population-based, epidemiological prospective study. In all participants, an enzyme immunoassay kit was used to measure homocysteine in serum samples.

FINDINGS

The serum level of homocysteine was significantly higher in the opium-addicted ones compared to non-addicted individuals (11.49 ± 7.45 vs. 8.02 ± 3.87 μmol/l) (P < 0.001). In this regard, 21.3% of the opium users and only 3.2% of the non-users had homocysteine concentration > 15 μmol/l (P < 0.001). On the other hand, individuals addicted to opiates exhibited significantly elevated odds of having homocysteine level higher than 15 [odds ratio (OR) = 8.244, 95% confidence interval (CI) = 3.117-21.806]. Multivariable linear regression model showed that the opium addiction could strongly predict elevated homocysteine level in the study individuals [beta = 3.524, standard error (SE) = 0.852] (P < 0.001).

CONCLUSION

Opium consumption can be strongly accompanied with the elevation of plasma homocysteine concentration, and thus opium addiction can exhibit elevated odds of having hyperhomocysteinemia.

No association between MTHFR C677T and serum uric acid levels among Japanese with ABCG2 126QQ and SLC22A12 258WW

Several genome-wide association studies (GWAS) have revealed that single nucleotide polymorphisms (SNPs) of ABCG2 and SLC22A12 were strongly associated with serum uric acid (SUA), but those of methylene tetrahydrofolate reductase (MTHFR) were not. However, there were several studies indicating the association with MTHFR C677T polymorphism. This study examined the association with the polymorphism, taking into account the genotypes of ABCG2 Q126X and SLC22A12 W258X. Subjects were 5,028 health checkup examinees of Seirei Preventive Health Care Center (3,416 males and 1,612 females) aged 35 to 69 years, who participated in the Japan Multi-Institutional Collaborative Cohort Study (J-MICC Study). Hyperuricemia was defined as SUA equal to 7 mg/dL or over. The genotype frequency was 35.9% for CC, 48.1% for CT, and 16.0% for TT, being in Hardy-Weinberg equilibrium (p=0.90). Among 4,425 participants with ABCG2 126QQ and SLC22A12 258WW who were not under medication for hyperuricemia, the mean SUA was 5.6 mg/dL, 5.6 mg/dL, and 5.7 mg/dL, respectively. When 114 participants with ABCG2 126QQ and SLC22A12 258WW under medication for hyperuricemia were included in hyperuricemia cases, the sex-age adjusted odds ratio (OR) of hyperuricemia was not significant; OR=1.00 (95% confidence interval, 0.89-1.24) for CT genotype and OR=0.98 (0.84-1.32) for TT genotype, relative to CC genotype. The present study indicated no association between SUA and MTHFR C677T genotype, after the influences of ABCG2 Q126X and SLC22A12 W258X were removed.

Homocysteine as a risk factor for cardiovascular disease

Homocysteine is an amino acid that appears to damage the vascular endothelium and promote thrombosis. The most frequent causes of hyperhomocyst(e)inemia are the inherited defect of the enzyme cystathinonine B-synthase and nutritional deficiency of vitamin B(12) or folate. Hyperhomocyst(e)inemia is associated, perhaps causally, with atherosclerotic vascular disease. Interactions with risk factors such as cigarette smoking, hyperlipidemia, and hypertension are possible, but not yet defined. Dietary supplementation with vitamin B(12), folate, and other substances can reduce homocysteine levels. Such simple measures may reduce the risk of vascular disease in hyperhomocyst(e)inemic subjects.

The Effects of Muscle Mass on Homocyst(e)ine Levels in Plasma and Urine

The present study was designed to examine the relationship between homocyst(e)ine (H[e]) levels and muscle mass. Two experimental groups each of 24 Caucasian males, one consisting of higher-muscle mass subjects (HMM) and the other of lower-muscle mass subjects (LMM) participated in this study. Muscle mass was estimated from 24-hour urine collections of creatinine (Crt). Muscle mass was 40.3 ± 15.9 kg in HMM and 37.2 ± 11.4 kg in LMM (P= 0.002). Mean plasma H(e) levels in HMM were 10.29 ± 2.9 nmol/mL, and in LMM were 10.02 ± 2.4 nmol/L (Not significant, [NS]). Urinary H(e) levels (UH[e]) were 9.95 ± 4.3 nmol/mL and 9.22 ± 2.9 nmol/mL for HMM and LMM, respectively (NS). Plasma H(e) levels correlated well with UH(e) (HMM: r= 0.58, P= 0.009; LMM: r= 0.66, P= 0.004). Muscle mass and was not correlated to either plasma H(e) or UH(e). However, in HMM trends were identified for body mass to be correlated with UH(e) (r= 0.39, P= 0.10) and UCrt (r= 0.41, P= 0.08). Surprisingly, in HMM plasma and UCrt were only weakly correlated (r= 0.44, P= 0.06). Our results do not support a causal relationship between the amount of muscle mass and H(e) levels in plasma or urine.

Association of the C677T MTHFR Polymorphism With Homocysteine, Ox-LDL Levels, and Thiolactonase Activities in the Severity of Coronary Syndrome

Coronary artery diseases (CAD) are influenced by multiple genes of modest effect as the methylenetetrahydrofolate reductase (MTHFR) C677T gene polymorphism, related to MTHFR activity and total plasma homocysteine (tHcy) concentration. This study was designed to evaluate tHcy, oxidized low-density lipoprotein (LDL) (ox-LDL), high-sensibility C-reactive protein (Hs CRP) levels, and homocysteine thiolactonase (HTase) activities as new risk factors for CAD and to investigate an association between MTHFR polymorphism tHcy concentrations and coronary syndrome severity. Our results showed significantly higher levels of tHcy and ox-LDL in patients associated with lower HTase activities. These levels increased proportionally to disease severity. Total plasma Hcy levels were negatively correlated to HTase activities in patients where the TT genotype was significantly more frequent. In a multivariate analysis, tHcy level was the only independent factor affecting the coronary syndrome severity. High tHcy levels are associated with coronary syndrome severity and may be explained either by the elevated prevalence of TT genotype or by the diminished HTase activities.

Novel markers of peripheral arterial disease

Peripheral arterial disease (PAD), a relatively common manifestation of atherosclerotic vascular disease, is associated with significant morbidity and mortality. Although conventional risk factors contribute to the onset and progression of PAD, the role of 'novel' biomarkers in pathways of inflammation, thrombosis, lipoprotein metabolism, and oxidative stress in determining susceptibility to PAD is being increasingly recognized. Validation of novel risk factors for PAD may allow earlier detection, an improved understanding of disease etiology and progression, and the development of new therapies. In this review, we discuss available evidence for associations between novel circulating markers and several aspects of PAD including disease susceptibility, progression, functional limitation, and adverse outcomes.

Kinetics of albumin homocysteinylation measured with matrix-assisted laser/desorption ionization mass spectrometry versus with a radioactive tracer

Homocysteinylation is a post-translational protein modification which involves homocysteine-thiolactone and may be responsible for many pathophysiological changes secondary to hyperhomocysteinemia. Therefore, methods to measure protein homocysteinylation in intact biological samples are required. We tested whether matrix assisted-laser/desorption ionization mass spectrometry (MALDI-MS) can detect time- and dose-dependent changes in in vitro homocysteine-thiolactone binding to human serum albumin. We have compared this method with a 35S-thiolactone radioactive binding assay. Incubations with and without dithiothreitol allowed measurement of the amide-linked and disulfide-linked thiolactone-protein adducts, respectively. A good correspondence in time- and dose-dependent protein-thiolactone formation was observed between the two methods. A maximum of 9 to 12 thiolactone residues were bound to each albumin molecule. The 35S-thiolactone bound albumin tightly, particularly at the lowest concentrations, with approximately 70% of the binding amide-linked. Although the results of the two methods were rather similar, the radioactive method appears to be more sensitive than the MALDI-MS technique.

Association of homocysteine thiolactonase activity and PON1 polymorphisms with the severity of acute coronary syndrome

INTRODUCTION

Excess of total homocysteine (tHcy) and decrease of thiolactonase activities (HTase) have been proposed as risk factors for coronary artery diseases (CAD).

OBJECTIVES

We evaluated the relationship of tHcy and HTase with paraoxonase 1 (PON1) gene polymorphism according to CAD severity.

DESIGN AND METHODS

118 healthy volunteers and 91 CAD patients were compared.

RESULTS

Serum levels of tHcy and oxidized LDL (ox-LDL) increased significantly by 26% and 48% in CAD patients and were associated with significantly lower levels of HDL cholesterol (p=0.02) and 42% of decrease in HTase activities (p<0.05). In these patients the HTase activity was negatively associated with tHcy and Hs CRP levels (r=-0.622, p=0.00 and r=-0.355, p=0.007 respectively) but positively associated with apoB and triglyceride levels (r=0.35, p=0.042 and r=0.308, p=0.003 respectively). HTase activity decreased inversely to the number of affected vessels and according to PON1 polymorphism. PON1 Q192R RR and PON1 L55M MM genotypes were associated with higher HTase activities. Only PON1 L55M (MM) genotype frequency was significantly higher in CAD patients than in controls (P<0.05), while its frequency was similar between the two subgroups according to CAD severity. In a multivariate analysis, tHcy levels were the only independent factor affecting the severity of cardiovascular disease (p=0.029).

CONCLUSIONS

High tHcy levels are associated with the severity of cardiovascular disease and may be partly explained by the diminished HTase activities in these patients.

Relationship of asymmetric dimethylarginine with flow-mediated dilatation in subjects with newly detected severe hypercholesterolemia

BACKGROUND

Little is know about the relationship between asymmetric dimethylarginine (ADMA) and percent flow-mediated dilatation (%FMD) in subjects with severe hypercholesterolemia (HH).

AIM

The aim of the present study was the evaluation of the relationship of ADMA to %FMD, as well as to lipid parameters and other markers of endothelial dysfunction in newly detected subjects with severe HH.

METHODS

One hundred and twenty asymptomatic patients with severe, newly detected HH and 100 controls were evaluated. The plasma level of ADMA was tested by ELISA and total homocysteine (tHcy) - through fluid chromatographic analysis. The %FMD was evaluated by the diameter of brachial artery with 7.5 MHz transducer of HP SONOS 5500.

RESULTS

Significant difference was found between patients and controls, (P<0.05) regarding lipid total cholesterol, triglycerides, high-density lipoprotein, low-dencity lipoprotein, atherogenic indices) and non-lipid markers (ADMA, sICAM-1, sVCAM-1), as well as the endothelium dependent %FMD in contrast to flow independent vasodilation. (P>0.05) No significant difference was found between the groups with respect to tHcy, P-selectine and E-selectine. (P>0.05) A strong negative correlation was found between %FMD and ADMA. (r(xy) = -0.895; P<0.001), Apolipoprotein-B (r(xy )= -0.687; P<0.0001, tHcy (r(xy) = -0.560; P<0.001) and Apolipoprotein index -B/A1 (r(xy) = -0.518; P<0.001). The subsequent linear and multiple regression analysis selected ADMA as the most significant factor in relation to %FMD.

CONCLUSION

It is concluded that ADMA is the basic modulator of %FMD among all tested atherogenic risk biomarkers in in newly detected subjects with severe HH.

Relationship between metabolic syndrome categorized by newly recommended by International Diabetes Federation criteria with plasma homocysteine concentration

Plasma total homocysteine (tHcy) is an independent risk factor for cardiovascular disease and increased tHcy levels have been reported to be a novel risk factor of atherosclerotic disease. The aim of this study was to assess the association of the metabolic syndrome components with plasma (tHcy) level. Total 722 participants (284 men, 438 women) from the medical checkup program were enrolled in this study. The clinical characteristics and biochemical parameters of the subjects were assessed and the tHcy levels were compared according to the components of metabolic syndrome diagnosed by Adult Treatment Panel (ATP) III guideline and International Diabetes Federation (IDF) criteria. Among the components, groups with larger waist circumference and higher fasting blood glucose levels showed significantly higher tHcy level than the counterparts. Although statistically insignificant, mean concentrations of tHcy was higher in subjects with metabolic syndrome defined by both criteria. In multiple regression analysis, age, sex and systolic blood pressure were the independent determinants of tHcy level. In conclusion, tHcy level was not associated with metabolic syndrome defined by either criteria in Korean subjects.

Molecular targeting of proteins by L-homocysteine: mechanistic implications for vascular disease

Hyperhomocysteinemia is an independent risk factor for cardiovascular disease, complications of pregnancy, cognitive impairment, and osteoporosis. That elevated homocysteine leads to vascular dysfunction may be the linking factor between these apparently unrelated pathologies. Although a growing body of evidence suggests that homocysteine plays a causal role in atherogenesis, specific mechanisms to explain the underlying pathogenesis have remained elusive. This review focuses on chemistry unique to the homocysteine molecule to explain its inherent cytotoxicity. Thus, the high pKa of the sulfhydryl group (pKa, 10.0) of homocysteine underlies its ability to form stable disulfide bonds with protein cysteine residues, and in the process, alters or impairs the function of the protein. Studies in this laboratory have identified albumin, fibronectin, transthyretin, and metallothionein as targets for homocysteinylation. In the case of albumin, the mechanism of targeting has been elucidated. Homocysteinylation of the cysteine residues of fibronectin impairs its ability to bind to fibrin. Homocysteinylation of the cysteine residues of metallothionein disrupts zinc binding by the protein and abrogates inherent superoxide dismutase activity. Thus, S-homocysteinylation of protein cysteine residues may explain mechanistically the cytotoxicity of elevated L-homocysteine.

Are heterocygotes for classical homocystinuria at risk of vitamin B12 and folic acid deficiency?

OBJECTIVES/DESIGN

Comparative cross-sectional study to assess homocysteine and vitamin status in carriers of CBS gene mutations.

METHOD

Subjects included 34 parents (13 males, 21 females, age 27-59 years) of 30 patients with classical homocystinuria due to homozygous cystathionine beta-synthase deficiency. Control subjects were matched for gender and age (13 males, 21 females, age 25-59 years). All subjects were of Qatari origin, had normal liver and renal function tests and had not taken drugs or vitamin supplements prior to the study. The concentrations of homocysteine, folic acid and vitamins B6 and B12 in blood were determined after an overnight fast.

RESULTS

Heterozygous carriers had significantly increased fasting levels of homocysteine compared to controls (9.1 vs. 8.1 micromol/l, P=0.012). Both folic acid (328 vs. 478 pmol/l, P=0.002) and vitamin B12 concentrations (232 vs. 287 pmol/l, P=0.013) were reduced whilst there was no significant difference in vitamin B6 levels between the two groups (5.8 vs. 6.44 microg/l).

CONCLUSIONS

Increased homocysteine concentrations in CBS gene mutation carriers are associated with reduced concentrations of folic acid and vitamin B12 in blood. In view of the adverse effects of mild hyperhomocysteinemia, routine testing of vitamin status in parents of homocystinuria patients may be warranted. The causal relationship and pathophysiological consequences are uncertain; it is likely that CBS gene mutation carriers need higher doses of dietary vitamins.

The association of homocysteine and related factors to brachial artery diameter and flow-mediated dilation

Brachial artery flow-mediated dilation (BAFMD) has been proposed as a measurement of the degree and severity of cardiovascular disease. The purpose of this study was to (1) evaluate the associations between BAFMD and homocysteine, folate, vitamin B(12), vitamin B(6); (2) examine the influence of 5,10-methylenetetrahydrofolate reductase (MTHFR) genotypes on homocysteine levels and BAFMD; and (3) evaluate the effect of homocysteine on the baseline diameter of the vessel vs BAFMD. A total of 174 healthy research subjects were examined for BAFMD, homocysteine, folate, vitamin B(12), vitamin B(6), and MTHFR genotype, nucleotide 677 C-->T. The data indicated a significant inverse correlation between homocysteine and BAFMD (r = -0.1763, P = .02). There was a significant difference in BAFMD between MTHFR genotype groups (P = .01) (T/T vs C/C, P = .042; C/C vs C/T, P = .13; T/T vs C/T, P = .003). Homocysteine was significantly associated with the baseline brachial artery diameter (r = 0.1878, P = .013). The data confirmed a significant inverse correlation between baseline diameter and BAFMD (r = -0.3321, P = .0001). Regression analysis indicated that the MTHFR genotype, homocysteine, and age were significant predictors of BAFMD (P = .0001, r(2) = 0.118). When the baseline brachial diameter was incorporated into the model, the effect of homocysteine on BAFMD disappeared. The present data indicate an association between homocysteine and BAFMD and reduced BAFMD in individuals with the MTHFR nucleotide 677 T/T genotype, despite similar blood values for folate and homocysteine. Finally, the data suggest that the effect of homocysteine on vascular reactivity is in part a consequence of its influence on baseline brachial artery diameter.

High prevalence of hyperhomocysteinemia in Chinese adults is associated with low folate, vitamin B-12, and vitamin B-6 status

Elevated plasma total homocysteine (tHcy) concentrations are associated with lower folate, vitamin B-12, and vitamin B-6 status and are considered an independent risk factor for cardiovascular disease in developed countries, but data in developing countries are limited. We conducted a cross-sectional study to explore tHcy status and its association with plasma B vitamin status in 2471 Chinese men and women aged 35 to 64 y, living in the urban and rural areas of the northern and the southern regions of China. Blood samples were also collected in 2 seasons (spring and fall). The geometric mean plasma tHcy concentration was significantly higher in the north (adjusted geometric mean, 95% CI; 13.0 micromol/L, 12.6-13.3) than in the south (9.1, 8.9-9.4) after controlling for gender, area (urban and rural), age, and season (spring and fall). Twenty-eight percent of northerners and 7% of southerners had plasma tHcy concentrations>or=16.0 micromol/L, a level used to define hyperhomocysteinemia. Within each region, men had higher plasma tHcy concentrations than women (16.1 vs. 10.6 micromol/L in the north, and 10.7 vs. 7.9 micromol/L in the south) and 40% of the northern men had hyperhomocysteinemia. Generally, individuals living in the urban areas had 30% (95% CI, 1.0-1.6) greater odds of having high tHcy levels (>or=16 micromol/L) than those living in the rural areas. Low plasma concentrations of folate, vitamins B-12 and B-6, older age, being male, and living in urban areas were all independently associated with elevated tHcy, with low folate as the strongest determinant.

Hyperhomocysteinaemia is associated with the rate of abdominal aortic aneurysm expansion

OBJECTIVES

Previous literature has suggested an association between AAA and the presence of elevated plasma homocysteine levels (HCY). Homocysteine can stimulate elastolysis in the arterial media via activation of elastase and matrix metalloproteinases. No evidence in the literature exists correlating aneurysm expansion and HCY. The study objective is to identify whether the rate of AAA expansion is related to HCY.

METHODS

108 patients undergoing surveillance for AAA were identified at our vascular surgical unit. AAA size and growth rate were assessed by serial ultrasonographic measurements. Fasting total HCY levels were measured using fluorescence polarisation immunoassays. Demographic details and atherosclerotic risk factors were noted all AAA patients. A multivariate analysis was performed for growth rate vs. HCY, hypertension and hypercholesterolaemia. The correlation between AAA growth rate, AAA size and HCY levels were calculated.

RESULTS

60% of patients with AAA had some degree of hyperhomocysteinaemia (> 15 micromol/l). Multivariate analysis showed HCY to be the only significant factor affecting AAA growth rate. A positive correlation was demonstrated between HCY levels and AAA growth rate using a linear regression model (R=0.28, p=0.003). Median growth rate among patients with hyperHCY was double that of patients with normal HCY (0.5 mm/month vs. 0.25 mm/month, p=0.003). A growth rate of > 10 mm/year was seen in 25% of hyper HCY patients and in only 2% of patients with normal HCY. In addition patients with hyper HCY and larger AAAs (> 4 cm) had a growth rate twice as fast as patients with hyper HCY and AAAs < 4 cm.

CONCLUSIONS

A correlation between HCY and growth rate exists, although this is weak due to the multifactorial aetiology of AAAs. HyperHCY patients have faster expansion rates than patients with normal HCY, with significant numbers demonstrating rapid expansion (> 10 mm/year) and therefore an increased risk of rupture.

Homocysteine, folate, and vitamins B6 and B12 blood levels in relation to cognitive performance: the Maine-Syracuse study

OBJECTIVE

Our objective was to examine associations among plasma homocysteine concentrations (tHcy), the tHcy-cofactors (folate, vitamins B6 and B12), and multiple domains of cognitive performance, with statistical adjustment for possible confounds, including cardiovascular disease risk factors (CVD-RF) and cardiovascular disease (CVD).

METHODS

Subjects were 812 participants (58% women) of the Maine-Syracuse study who were free of dementia and stroke. Employing a cross-sectional design and multiple regression analyses, fasting concentrations of tHcy and its vitamin cofactors (folate, B6, and B12) were related to multiple domains of cognitive performance.

RESULTS

With adjustment for age, education, gender, ethnicity, and the vitamins, tHcy was inversely associated with visual-spatial organization, working memory, scanning-tracking, and abstract reasoning. The same results were found with adjustment for age, education, gender, ethnicity, CVD-RF, and CVD. Vitamin cofactors were positively related to cognitive performance, but with adjustment for CVD-RF and CVD, only vitamin B6 was related to multiple cognitive domains.

CONCLUSIONS

The inverse association of tHcy with multiple domains of cognitive functioning is not necessarily dependent on vitamin levels, vitamin deficiency, prevalent CVD risk factors, and manifest CVD. Serum folate, serum B12, and plasma B6 vitamin concentrations are positively associated with cognitive performance. Investigation of other possible mechanisms (e.g., tHcy neurotoxicity) mediating tHcy associations with cognitive performance is important, as are clinical trials examining the efficacy of folate, vitamin B6, and vitamin B12 for maintenance of cognitive functioning.

Homocysteine metabolism, hyperhomocysteinaemia and vascular disease: an overview

Hyperhomocysteinaemia has been regarded as a new modifiable risk factor for atherosclerosis and vascular disease. Homocysteine is a branch-point intermediate of methionine metabolism, which can be further metabolised via two alternative pathways: degraded irreversibly through the transsulphuration pathway or remethylated to methionine by the remethylation pathway. Both pathways are B-vitamin-dependent. Plasma homocysteine concentrations are determined by nongenetic and genetic factors. The metabolism of homocysteine, the role of B vitamins and the contribution of nongenetic and genetic determinants of homocysteine concentrations are reviewed. The mechanisms whereby homocysteine causes endothelial damage and vascular disease are not fully understood. Recently, a link has been postulated between homocysteine, or its intermediates, and an alterated DNA methylation pattern. The involvement of epigenetic mechanisms in the context of homocysteine and atherosclerosis, due to inhibition of transmethylation reactions, is briefly overviewed.

Relationship between plasma S-adenosylhomocysteine concentration and glomerular filtration rate in children

S-Adenosylhomocysteine (SAH) is the metabolic precursor of all the homocysteine (Hcy) produced in the body. It is formed by the enzyme SAH hydrolase in a reversible reaction. In a previous study we have shown that plasma SAH is a more sensitive indicator of the risk for cardiovascular disease, and in a second study involving patients with renal disease, we also showed that it is a more sensitive indicator of renal insufficiency than plasma Hcy. However, in the latter study, the patients with renal disease were older and had a variety of other diseases such as diabetes and primary hypertension, which are associated with vascular disease and which could reduce renal function by involvement of the kidneys. Our objective was to rule out these complicating factors as the cause of the elevated SAH in renal disease and determine whether renal insufficiency alone was the cause of the elevated SAH. We therefore measured SAH, Hcy, folate, and vitamin B12 in 23 patients between the ages of 1 and 18 years with a wide range of renal function, but who had none of these complicating factors. Glomerular filtration rate (GFR) was calculated using serum creatinine according to the Schwartz formula. None of the children were deficient in folate or vitamin B12. After adjusting for age, folate, and vitamin B12, there was a modest and insignificant decrease of 0.033 micromol/L of Hcy associated with an increase of 1 mL/min of GFR (95% confidence interval, -0.066 to 0.0002). However, there was a strong and statistically significant association between log(SAH) and log(GFR): P < .0005, R2 = 0.76. This result suggests that plasma SAH rather than Hcy is the metabolite primarily affected in renal disease. We suggest that plasma Hcy elevations that have been linked to vascular disease may be due to elevated SAH resulting from renal insufficiency.

Molecular targeting by homocysteine: a mechanism for vascular pathogenesis

Hyperhomocysteinemia is an independent risk factor for cardiovascular disease. Although there is a growing body of evidence that homocysteine plays a causal role in atherogenesis, specific mechanisms to explain the underlying pathology have remained elusive. This review focuses on chemistry unique to the homocysteine molecule to explain its inherent cytotoxicity. Thus, the high pKa of the sulfhydryl group (pKa=10.0) of homocysteine underlies its ability to form stable disulfide bonds with protein cysteine residues, and in the process, alters or impairs the function of the protein. Albumin, fibronectin, transthyretin, annexin II, and factor V have now been identified as molecular targets for homocysteine, and in the case of albumin, the mechanism of targeting has been elucidated.

Workgroup report: Biomonitoring study design, interpretation, and communication--lessons learned and path forward

Human biomonitoring investigations have provided data on a wide array of chemicals in blood and urine and in other tissues and fluids such as hair and human milk. These data have prompted questions such as a) What is the relationship between levels of environmental chemicals in humans and external exposures? b) What is the baseline or "background" level against which individual levels should be compared? and c) How can internal levels be used to draw conclusions about individual and/or population health? An interdisciplinary panel was convened for a 1-day workshop in November 2004 with the charge of focusing on three specific aspects of biomonitoring: characteristics of scientifically robust biomonitoring studies, interpretation of human biomonitoring data for potential risks to human health, and communication of results, uncertainties, and limitations of biomonitoring studies. In this report we describe the recommendations of the panel.

Plasma homocysteine levels and the left ventricular systolic function in coronary artery disease patients

BACKGROUND

Numerous studies have shown a relationship between hyperhomocysteinemia, atherothrombosis and cardiovascular mortality. However, an association between hyperhomocysteinemia and the extent of coronary artery disease (CAD) remains controversial whereas its relationship with left ventricular systolic function has not been established.

METHODS

One hundred and fifty-seven patients with angiographically defined CAD were included. The relationships between hyperhomocysteinemia, severity of CAD and left ventricular systolic function were studied. Left ventricular systolic function was determined primarily by ventriculography. The severity of CAD was determined through coronary angiography using the Gensini score and the number of vessels with > or = 50% stenosis.

RESULTS

The mean fasting plasma homocysteine level was 13.4 mumol/l+/-0.5 SE. Elevated levels of homocysteine correlated significantly with increased severity of CAD both by the Gensini scores (r-value = 0.344, P < 0.0005) and the total number of diseased vessels (r-value = 0.387, P < 0.0005). The patients with hyperhomocysteinemia were found to have significantly reduced left ventricular ejection fraction (r-value = -0.382, P < 0.0005). A multivariate regression analysis revealed homocysteine level to be an independent predictor of left ventricular systolic function. In addition, adjusted analysis revealed hyperhomocysteinemia to be associated with global left ventricular dysfunction.

CONCLUSION

In patients with CAD, homocysteine levels correlate independently with left ventricular systolic function. The mechanism of this association between homocysteine and left ventricular systolic function is unknown but may be due to a direct effect of homocysteine on myocardial function separate from its effects on coronary atherosclerosis.

The effect of estradiol valerate and dienogest combination on serum homocysteine levels in postmenopausal women: a clinical trial

Several studies have verified that hormone replacement therapy (HRT) has protective effects on postmenopausal women's cardiovascular condition. However, highly significant recent studies have reported that women treated with HRT have more cardiovascular events than untreated women. An elevated homocysteine level is one important risk factor for cardiovascular disease (CVD). As a good indicator of CVD risk, we examined the changes in plasma homocysteine levels of postmenopausal women treated with HRT. In our study, we administered estradiol valerate (2 mg) and dionegest (2 mg) to 34 postmenopausal women recruited randomly from our menopause clinic, and measured plasma homocysteine levels of patients at baseline and after 3 and 6 months of therapy. The changes in plasma homocysteine levels of treated patients were not statistically significant (p = 0.241). Our results indicate that 6 months of estradiol valerate and dionegest therapy does not change homocysteine levels in postmenopausal women.

Conditional risk factors for atherosclerosis

Although most patients who experience a coronary heart disease (CHD) event have one or more of the conventional risk factors for atherosclerosis, so do many people who have not yet experienced such an event. Therefore, predictive models based on conventional risk factors have a lower than desired accuracy, providing a stimulus to search for new tools to refine CHD risk prediction. In particular, there is intense interest in evaluating circulating biomarkers related to the atherosclerotic process that might add to our ability to better predict CHD risk. One such group of biomarkers was termed conditional risk factors in an American Heart Association/American College of Cardiology statement in 1999. The conditional risk factors include homocysteine, fibrinogen, lipoprotein(a), low-density lipoprotein particle size, and C-reactive protein. This review updates the conditional risk factors. The main focus is on the potential utility of these risk factors, which are currently available to clinicians, in the prediction of CHD risk in asymptomatic persons. The putative mechanisms of risk, available assays, evidence for association with CHD, and the clinical implications thereof are discussed for each of the risk factors.

Homocysteine and B vitamins

Homocysteine (tHcy) is an intermediate sulfur-containing amino acid which acts as a methyl group donor for methionine metabolism. Increased serum concentrations (=hyperhomocysteinemia, >10 micromol/l) have been associated with an increased cardiovascular risk. Homocystinuria, an infrequent genetic disease usually due to lack of cystathione beta-synthase, has been found with severely elevated serum homocysteine values (>150 micromol/l). Functional gene polymorphisms of key enzymes (e.g., N5,N10-methylene-tetrahydrofolate reductase) and dietary B-vitamin deficiencies in the elderly are, however, frequent in the 'Western' population. Hyperhomocysteinemia has been associated with other vascular effects such as atherothrombosis and endothelial dysfunction due to its auto-oxidative potential, thereby increasing the production of reactive oxygen species. Other effects may involve neurodegenerative diseases such as Alzheimer or dementia praecox of the elderly. Therapeutic interventions lowering tHcy may therefore offer novel tools for the prevention and treatment of atherosclerosis. B-vitamin supplementation (folic acid=vitamin B9, vitamin B6 and vitamin B12) is an efficient and safe tHcy-lowering therapy, decreases tHcy by 30%-50% and has been shown to lower cardiovascular morbidity and mortality. Furthermore, folic acid supplementation has been shown to reduce or even almost eliminate neurotubular birth defects (spina bifida) and to markedly decrease the rate of megaloblastic anemia. Thus, fortification of flour with folic acid in the USA was advocated several years ago in order to prevent these entities.

The C677 mutation in methylene tetrahydrofolate reductase gene: correlation with uric acid and cardiovascular risk factors in elderly Korean men

The C677T mutation in the methylene tetrahydrofolate reductase (MTHFR) gene results in elevated homocysteine levels and, presumably, in increased cardiovascular risk. Moreover, elevated homocysteine levels are reportedly associated with high serum uric acid levels. We evaluated the MTHFR genotype and a panel of biochemical, hematological variables, and lifestyle characteristics in 327 elderly Korean men (age range 40-81 yr; mean, 51.87). This study shows that mutation of the MTHFR gene may be a risk for hyperuricemia. The mean uric acid levels for the C/C, C/T and T/T genotypes were 5.54, 5.91 and 6.33 mg/dL, respectively (p=0.000). The T/T genotype was significantly more frequent in subjects with high uric acid levels (p=0.003). Thus, this mutation of the MTHFR gene is implied by the study results to be a risk factor of hyperuricemia in elderly Korean men. However, the relationship between the MTHFR mutation and uric acid metabolism remains unclear. Therefore, further studies are necessary to explain the associated between the MTHFR mutation and elevated uric acid levels, and to examine potential relationships between it and conventional cardiovascular risk factors.

Homocysteine and lipoprotein levels following resistance training in older adults

This investigation examined the effect of 6 months of high- or low-intensity resistance exercise on serum homocysteine and lipoprotein (a) levels in adults aged 60-80 years. Forty-three men and women completed the study protocol. Subjects were randomly assigned to a control (n=10), low-intensity (LEX, n=18), or high-intensity (HEX, n=15) group. Subjects performed 6 months of resistance training at either 50% of their one-repetition maximum for 13 repetitions (LEX) or 80% of one-repetition maximum for eight repetitions (HEX) 3 times per week for 24 weeks. The load was increased by 5% when their rating of perceived exertion dropped below 18. One-repetition maximum; serum homocysteine; lipoprotein (a); total and high-density lipoprotein cholesterol; and dietary intake of vitamins B12, B6, and folic acid were measured pre- and poststudy. Upper and lower body strength significantly (p<0.05) increased for the LEX and HEX groups. Serum homocysteine decreased 5.30% and 5.34% for the LEX and HEX groups, respectively (p<0.05), but increased 6.1% for the control group. A significant increase in lipoprotein (a) levels was noted in the control and LEX groups from pre- to poststudy. No significant differences were noted either pre- or poststudy for total and high-density lipoprotein cholesterol or any dietary variables. These data indicate that significant reductions in serum levels of homocysteine in the elderly can be derived from resistance exercise training.

Association between plasma homocysteine levels and coronary artery disease: a population-based study in northern Greece

OBJECTIVE

Elevated plasma total homocysteine (tHcy) levels constitute a risk factor for coronary artery disease (CAD). We prospectively examined the association of fasting tHcy levels in patients in Northern Greece who had established CAD.

PATIENTS AND METHODS

Plasma fasting tHcy levels were measured in 42 patients with angiographically documented CAD and compared to 42 age-, sex-, BMI- and smoking habit-matched control subjects. We also determined the plasma vitamin B(12), folic acid and lipoprotein levels in all patients and controls. Conventional risk factors for CAD were also estimated.

RESULTS

In a univariate analysis, tHcy (micromol/l) levels were higher in patients compared to controls almost reaching statistical significance (13 (7-41) vs 11.3 (4-39); p= 0.07). Multivariate analysis of conventional risk factors showed that tHcy levels were not an independent risk factor for CAD. However, tHcy levels were significantly higher in patients with a previous history of myocardial infarction compared to patients without such a history and to controls (15 (8.8-29) vs 11.7 (7-41); p = 0.007 and 15 (8.8-29) vs 11.3 (4-39); p = 0.002, respectively). Hyperhomocysteinaemia (> 15 micromol/l) was detected in 35.7% of patients and 11.9% of controls (p < 0.05).

CONCLUSIONS

In Northern Greece, plasma tHcy levels may not be an independent risk factor for CAD in patients with angiographically documented CAD. However, patients with CAD have a trend towards higher tHcy levels. Additionally, plasma tHcy levels may be associated with the development of myocardial infarction.

Elevated plasma homocysteine as risk factor for peripheral arterial disease--what is the evidence?

There is abundant evidence that elevated plasma homocysteine (HC) is independently associated with presence of atherosclerotic disease. There is credible evidence from a number of prospective studies that elevated HC is independently associated with progression of atherosclerotic disease. All studies to date agree that vitamin therapy, primarily folate, results in reliable decreases in HC, without recognized toxicity or side effects. Two small, randomized clinical trials have demonstrated clinically relevant benefit from folate treatment, which reduced HC in patients, compared to placebo. The results of multiple large scale clinical trials will be available within 2 to 5 years, and these have sufficient power to determine whether vitamin therapy intended to lower plasma HC will be established as the first effective therapy for atherosclerosis that does not involve expensive medication with toxic side effects and/or difficult changes in habits or lifestyle.

Relevance of different apolipoprotein content in binding of homocysteine to plasma lipoproteins

BACKGROUND AND AIMS

In plasma the atherogenic thiol homocysteine (Hcy) circulates either free or bound to proteins (Pb-Hcy). The present study sets out to evaluate the lipoprotein-Hcy (LP-Hcy) binding in vivo and the possible influence of different apolipoprotein content in this binding, being lipoprotein oxidation a possible mechanism of Hcy-induced damage.

METHODS AND RESULTS

In 34 healthy subjects we assayed fasting plasma lipoprotein and correspondent apolipoprotein (apo A-I, apo A-II, apo C-II, apo C-III, apo B, apo(a) and apo E content, and Hcy bound to different plasma protein fractions; moreover ten subjects underwent an oral methionine load in order to evaluate possible "dynamic" modifications of Pb-Hcy and LP-Hcy after induction of hyperhomocysteinemia. Pb-Hcy (mean values 9.22 +/- 1.7 mumol/L) represented about 78% of total plasma Hcy (mean values 11.8 +/- 1.8 mumol/L). Pb-Hcy distribution between the different fractions was as follows (mumol/L): VLDL = 0.25 +/- 0.08 (2.7%); LDL = 0.88 +/- 0.22 (9.5%); HDL = 1.40 +/- 0.36 (15.2%); fractions with density greater than 1.21 g/mL (Lipoprotein-Free Protein Fraction, LPDS) = 6.7 +/- 1.2 (72.6%). Hcy/protein ratios (nmol/mg of protein) in each protein fraction were: VLDL = 0.32 +/- 0.19, LDL = 0.43 +/- 0.37, HDL = 0.26 +/- 0.18, LPDS < 0.1, thus suggesting a higher binding capacity for Hcy by VLDL and LDL. These data were confirmed by the higher increase in Hcy content in LDL and VLDL (76 and 90%, respectively vs 36% and 3.1% for HDL and LPDS fractions) after hyperhomocysteinemia. Lp-Hcy binding significantly correlated with the apo B content of VLDL and LDL and Apo A-I content of HDL.

CONCLUSIONS

An important fraction of plasma Hcy circulates bound to LP (about 27% of Pb-Hcy); VLDL and LDL show the highest binding capacity for Hcy, probably due to their content in Apo B, a possible high capacity binding site for Hcy.

Homocysteine and risk of coronary artery disease: Folate is the important determinant of plasma homocysteine concentration

OBJECTIVES

The purposes of this study were to study the effects of folate and vitamins B6 and B12 on plasma homocysteine concentration and to estimate the risks for coronary artery disease (CAD) according to quartiles of plasma homocysteine concentration.

METHODS

The study was designed as a case-reference observational study. Case subjects (CAD group, n = 60) were identified by cardiac catheterization to have at least 70% stenosis of one major coronary artery; otherwise, patients were considered for a reference group (n = 60). Risk factors of cardiovascular disease were recorded, including age, sex, blood lipid profile, hypertension, smoking habits, and drinking habits. Plasma homocysteine, folate, pyridoxal 5'-phosphate, and vitamin B12 were measured.

RESULTS

CAD subjects had significantly higher mean plasma homocysteine concentrations than did the reference subjects (13.9 +/- 4.9 versus 9.1 +/- 3.3 micromol/L). There were no significant differences between groups with regard to the three B vitamins; however, mean serum folate concentrations for subjects in the highest two quartiles of plasma homocysteine concentration (10.8-13.8 and >/=13.9 micromol/L) were significantly lower than those for subjects in the lowest two quartiles (</=8.0 and 8.1-10.7 micromol/L). Plasma homocysteine was strongly inversely associated with serum folate in the CAD (beta= -0.166, P < 0.05), reference (beta= -0.178, P < 0.001), and pooled (beta = -0.190, P < 0.001) groups. Age, sex, other confounding factors, and B-vitamin-adjusted odds ratios were significantly increased in the highest quartile of homocysteine concentration (odds ration, 5.54; 95% confidence interval, 0.38-81.41). The elevation of 1 ng/mL in serum folate concentration was found to decrease plasma homocysteine by 0.166 micromol/L.

CONCLUSIONS

Serum folate, but not vitamin B6 or B12, was a strong predictor of plasma homocysteine; while all subjects had adequate B-vitamin status. Folate should be considered as a routine supplementation for individuals who have risk factors for CAD, even for individuals with adequate folate status.

Homocysteine and hemostatic disorder as a risk factor for myocardial infarction at a young age

INTRODUCTION

Hyperhomocysteinemia is a coronary risk factor, but its pathophysiologic mechanism remains unclear.

MATERIALS AND METHODS

The importance of hyperhomocysteinemia in the pathogenesis of early myocardial infarction, was determined in case-control study of 127 men with a first early myocardial infarction <or=45 years and 150 age-matched male controls. We measured plasma concentrations of homocysteine, fibrinogen, antithrombin, tissue factor, tissue factor pathway inhibitor, tissue plasminogen activator, plasminogen activator inhibitor-I, plasminogen, alpha(2)-antiplasmin, lipoprotein(a), protein C, protein S, factor VII, and activated factor VII.

RESULTS

Homocysteine concentrations were higher in patients with early myocardial infarction than in controls (11.2+/-5.3 and 8.3+/-5.0 micromol/l, respectively, P<0.001). Hyperhomocysteinemia was associated with early myocardial infarction (odds ratio=2.22, P<0.001) by multivariate logistic regression analysis. Tissue factor, antithrombin, plasminogen, tissue plasminogen activator, plasminogen activator inhibitor-I, lipoprotein(a), diabetes, and smoking also had associations. In a stepwise logistic regression analysis, hyperhomocysteinemia was the strongest predictor of early myocardial infarction (R(2)=0.19, P<0.001). Hyperhomocysteinemia also had positive correlations with tissue factor (rho=0.26, P=0.009), tissue factor pathway inhibitor (rho=0.23, P=0.020), and tissue plasminogen activator (rho=0.25, P=0.011) in patients with early myocardial infarction, but not in controls.

CONCLUSIONS

Hyperhomocysteinemia is an independent risk factor for early myocardial infarction, and is associated with a hypercoagulable state mediated by the extrinsic coagulation cascade.

[Hyperhomocysteinemia: an independent risk factor or a simple marker of vascular disease? 2. Epidemiological data]

Elevated plasma total homocysteine (tHcy) is considered as a risk factor for occlusive cardiovascular disease (CVD). This concept is based on the observations of premature vascular disease in patients with homocystinuria and on the association between tHcy and increased risk of CVD in prospective studies. However, some observations have raised questions about tHcy as a risk factor. First, low risk population based prospective studies tend to indicate a weak association or no association between tHcy and CVD. Second, several traditional risk factors for CVD are associated with tHcy and may confound the relation between tHcy and CVD. Third, the C667T transition of the methylenetetrahydrofolate reductase causes a moderate increase in tHcy but no or only minor increased CVD risk. Thus, only placebo-controlled intervention studies with tHcy-lowering B-vitamins and clinical endpoints can provide additional valid arguments for the debate over whether tHcy is a causal CVD risk factor.

Plasma homocysteine levels in Indian patients with essential hypertension and their siblings

BACKGROUND

An association between plasma homocysteine and essential hypertension and their non-hypertensive siblings is controversial.

METHODS AND RESULTS

Plasma homocysteine levels were measured in subjects with essential hypertension (n = 50), their normotensive siblings (n = 50) and normotensive controls (n = 50). All the subjects were non-diabetic, had no past history of myocardial infarction, stroke or peripheral vascular disease and had normal renal functions. The mean homocysteine values were 18.96 +/- 8.08 micromol/L in patients, 14.84 +/- 5.55 micromol/L in siblings and 10.50 +/- 4.92 micromol/L in controls. Plasma homocysteine level were found to be significantly higher in patients with hypertension (p < 0.0001) and their normotensive siblings (p < 0.0001) when compared to controls. Also patients with hypertension had their higher plasma homocysteine levels compared to their siblings (p < 0.0036).

CONCLUSION

Plasma homocysteine levels are significantly elevated in Indian patients with essential hypertension and their normotensive siblings. Thus, plasma homocysteine may serve as a marker for the development of essential hypertension.

Effects of estrogen and psychological stress on plasma homocysteine levels

OBJECTIVE

To investigate the effects of estrogen (E) and psychological stress on plasma total homocysteine levels in relation to menopausal status.

DESIGN

Double-blind, randomized, placebo-controlled study.

SETTING

The General Clinical Research Center of a university hospital.

PATIENT(S)

Thirty-six postmenopausal women and 26 premenopausal women. Both samples were healthy nonsmokers.

INTERVENTION(S)

Both premenopausal and postmenopausal women were subjected to a 6-minute psychological stressor. Postmenopausal women were randomized to one of three treatment arms: 2 mg of E2 or 2 mg of E2 + 5 mg of medroxyprogesterone acetate (MPA), or a placebo, all of which were given orally for 3 months. The psychological stressor was readministered after the 3-month regimen.

MAIN OUTCOME MEASURE(S)

Plasma total homocysteine levels were measured before and after the psychological stressor on one occasion for premenopausal women and before and after hormone replacement or placebo for postmenopausal women.

RESULT(S)

There were no significant differences in homocysteine levels between premenopausal (7.2 +/- 1.7 micromol/L; mean +/- SD) and postmenopausal women (7.9 +/- 2.06; mean +/- SD). There was no effect of stress or hormone replacement on homocysteine levels.

CONCLUSION(S)

Psychological stress, menopausal status, and oral hormone replacement therapy (HRT) do not affect plasma total homocysteine levels in women with normal basal homocysteine levels.

Homocysteine levels and C677T polymorphism of methylenetetrahydrofolate reductase in women with polycystic ovary syndrome

The aim of this study was to investigate the homocysteine (Hcy) levels and the C677T polymorphism of 5,10-methylenetetrahydrofolate reductase (MTHFR), a crucial factor of the Hcy metabolism in young women with polycystic ovary syndrome (PCOS). Seventy young women with PCOS and another 70 healthy women with low folate intake were enrolled. Cases and controls were matched for age, body mass index, and allele frequency. Hcy, vitamin B(12), and folate levels were measured, and a genetic analysis of 5,10-MTHFR at nucleotide 677 was performed in all subjects. No difference in mean Hcy levels was observed between PCOS women in comparison to the control group. Considering the different MTHFR polymorphism, no significant difference was found in serum Hcy levels between subjects with PCOS and controls showing CC (10.4 +/- 3.1 vs. 9.7 +/- 2.9 micromol/liter +/- SD) and CT genotypes (10.9 +/- 3.8 vs. 11.0 +/- 3.2 micromol/liter +/- SD). In subjects with a TT homozygous state, a significant (P < 0.05) difference was observed between PCOS and control women (11.5 +/- 3.9 vs. 22.0 +/- 7.8 micromol/liter +/- SD). In conclusion, our data show that in PCOS women, the serum Hcy levels are normal, and the C677T polymorphism of MTHFR does not influence the Hcy levels like in controls.

Plasma homocysteine in subjects with familial combined hyperlipidemia

Familial combined hyperlipidemia (FCH) is characterised by hypercholesterolemia and/or hypertriglyceridemia and associated with an increased risk of cardiovascular disease (CVD). The plasma lipid and lipoprotein levels in subjects with FCH are relatively moderately elevated and do not fully explain the increased risk of CVD. Hyperhomocysteinemia is a disorder of methionine metabolism and also a well-known independent risk factor for CVD. We investigated whether subjects with FCH have higher plasma homocysteine concentrations than controls, and whether homocysteine contributes to the increased risk of CVD in FCH. Furthermore we evaluated whether parameters of lipid and lipoprotein metabolism and/or insulin resistance are associated with the homocysteine level. In total 667 subjects, including 161 subjects with FCH, 109 spouses who referenced as control group and 397 normolipidemic relatives were studied. FCH was defined by the presence of plasma total cholesterol and/or triglyceride levels above the 90th percentile adjusted for age and gender. The mean homocysteine concentration of the FCH group did not significantly differ from the control group. The risk for CVD due to hyperhomocysteinemia in subjects with FCH was not higher than in subjects without FCH. No associations were observed between plasma homocysteine concentration and plasma lipid and lipoprotein levels, including small dense low density lipoprotein, nor between homocysteine concentration and insulin resistance.

Association of plasma homocysteine concentration with atherosclerotic carotid plaques and lacunar infarction

BACKGROUND AND PURPOSE

Higher plasma total homocysteine (tHcy) levels have been associated with carotid atherosclerosis and cerebral infarction in whites. However, data regarding such associations are limited for Asians. This study examined associations between tHcy levels and severity of carotid atherosclerosis in Japanese subjects. Additionally, because lacunar infarction is the most prevalent type of ischemic stroke in Japan, we also investigated its associations with tHcy levels.

METHODS

The subjects were 152 Japanese patients (age, 66.2+/-11.0 years) at our hospital. Using ultrasound, we evaluated severity of carotid atherosclerosis by plaque score, which is defined by the sum of all plaque (intima-media thickness > or =1.1 mm) height in bilateral carotid arteries. In 112 of 152 patients, the existence of lacunar infarction was evaluated on brain MRI scans.

RESULTS

A moderate linear association was found between tHcy levels and plaque score (r=0.48, P<0.0001). Moreover, tHcy level was associated with plaque score (beta=0.26, P<0.001) independently of traditional atherosclerotic risk factors. In logistic regression analyses, each 1-micromol/L-higher tHcy level was associated with a 1.37-fold-higher [95% confidence interval (CI), 1.19 to 1.58] likelihood for lacunar infarction, increasing the likelihood by 1.22-fold (95% CI, 1.04 to 1.43) independently of traditional atherosclerotic risk factors.

CONCLUSIONS

Higher tHcy levels appear to have associations with increased severity of carotid atherosclerotic plaques and prevalent lacunar infarction in the Japanese. Larger prospective studies are necessary to establish whether higher tHcy levels serve as a harbinger for insidious carotid and cerebrovascular diseases.

Homocysteine and the stage of atherosclerotic disease: a study in patients suffering from clinically silent and clinically manifest atherosclerotic disease

BACKGROUND

Elevated serum levels of homocysteine are considered a risk factor for cardiovascular disease. It has been suggested that homocysteine is a late stage predictor of adverse cardiovascular events, which might explain reported controversies in literature. The objective of the present study was to study the relationship between homocysteine levels and the stage of atherosclerotic disease.

METHODS

In a cross-sectional study we compared the prevalence of hyperhomocysteinemia in high risk patients without silent or clinically overt atherosclerosis (group I, n = 196) with two patient groups: patients with clinically manifest atherosclerosis in the past or asymptomatic atherosclerosis (group II, n = 364) and patients who currently suffer from a clinically relevant manifestation of ischemic cardiovascular disease (group III, n = 967). In addition, we related homocysteine levels with a cumulative index of atherosclerotic disease (SMART-score).

RESULTS

Homocysteine levels (micromol L(-1)) for the different groups were 13.5 +/- 8.9 (group I), 13.7 +/- 8.2 (group II) and 14.7 +/- 7.7 (group III). After adjustment for age, body mass index, creatinine levels and current use of vitamins, no significant differences in the prevalence of hyperhomocysteinemia were observed, compared with the reference category. Linear regression analysis revealed a significant relationship between Smart score and homocysteine levels that remained after adjustment for potential confounders (Beta = 0.36 (0.14-0.59), P = 0.001).

CONCLUSION

If homocysteine levels are associated with the presence and indicators of atherosclerotic plaque burden, then this relationship is apparently not affected by the stage of atherosclerotic disease.