Population variation and genetics of plasma homocyst(e)ine level

Prevalence and clinical demography of hyperhomocysteinemia in Han Chinese patients with schizophrenia

Previous studies have shown that high homocysteine worsens the occurrence, symptoms, and prognosis of patients with schizophrenia. The purpose of this study was to evaluate the prevalence, clinical correlation, and demographic characteristics of hyperhomocysteinemia in Han Chinese schizophrenia patients. In this study, we enrolled 330 schizophrenia patients and 190 healthy controls. Positive and Negative Syndrome Scale (PANSS) was used to evaluate the psychiatric symptoms of patients with schizophrenia. The plasma homocysteine level was measured by the enzyme cycle method and the concentration of homocysteine > 15 μmol/L was defined as hyperhomocysteinemia. The prevalence of hyperhomocysteinemia in Han Chinese schizophrenia patients and healthy controls was 55.05% and 26.98%, respectively. Schizophrenia patients with hyperhomocysteinemia had more male proportion, older age, higher smoking rate, lower HDL level, higher PANSS total score, and higher negative factor than those patients without hyperhomocysteinemia. Binary logical regression result showed that gender and age were the independent risk factors of hyperhomocysteinemia. Han Chinese patients with schizophrenia had high prevalence hyperhomocysteinemia than healthy controls, and elderly male patients have a higher risk of hyperhomocysteinemia. This study was registered in the China Clinical Trial Registration Center (chiCTR 1800017044).

Plasma Homocysteine is Associated with Retinopathy in Type 1 Diabetic Patients in the Absence of Nephropathy

INTRODUCTION

Previous cross-sectional studies suggested that plasma total homocysteine (tHcy) is associated with retinopathy in patients with type 1 diabetes (T1DM) only in cases of impaired renal function. The objective of this study was to examine whether there is an independent relationship between tHcy and retinopathy in normoalbuminuric T1DM patients with normal estimated glomerular filtration rate (eGFR).

METHODS

The study included 163 normoalbuminuric patients with T1DM and normal renal function (eGFR >60 ≤ 125 ml min(-1) 1.73 m(-2)). Urinary albumin excretion rate (UAE) was measured from at least two 24 h urine samples. Photodocumented retinopathy status was made according to the EURODIAB protocol. tHcy level was measured with the chemiluminescent immunoassay.

RESULTS

Retinopathy was present in 48% of normoalbuminuric patients. Patients with retinopathy were older (49 vs 42 years, p = 0.001), had higher systolic blood pressure (130 vs 120 mmHg, p = 0.001), triglycerides (0.89 vs 0.77 mmol/L, p = 0.01), tHcy (9.8 vs 9.1 µmol/L, p = 0.04), and lower eGFR (100 vs 106 ml min(-1) 1.73 m(-2), p = 0.03). In multivariate logistic regression analysis, after adjustment for variables that reached statistical significance in the univariate analysis, only tHcy was significantly associated with a risk of retinopathy in our subjects (p = 0.02), with odds ratios of 1.02 to 1.43.

CONCLUSION

These data suggest that tHcy is independently associated with retinopathy in normoalbuminuric T1DM with normal eGFR. The mechanisms relating tHcy and retinopathy in T1DM are not clear. Prospectives studies are needed to confirm whether higher tHcy in normoalbuminuric T1DM patients has predictive value for development of retinopathy.

Elevated homocysteine level in siblings of patients with schizophrenia

Increased homocysteine plasma levels were reported in patients with schizophrenia and Levine et al. (2002) suggested that such increase characterizes mainly males. In the following study we examined whether such increased levels also characterize male siblings of schizophrenia patients. Forty-four pairs of schizophrenia patients and their corresponding healthy male siblings were recruited and sampled for homocysteine. We also had age-matched controls for each of the sibling. The median homocysteine plasma level for patients was 13.0 µMol/L and 11.7 µMol/L for their male siblings compared with a median of 10.9 µMol/L for the siblings' controls. There was no significant difference between homocysteine plasma level in patients and their siblings. Significant difference was found for homocysteine plasma level between the siblings' group and their matched controls. A partial correlation of Ln plasma homocysteine level between patients and their siblings was found to be close to a zero correlation of -0.089, p=0.57 for the whole study group and -0.15, p=0.38 in the male-male patient-sibling pairs. Our results show that elevated homocysteine plasma level may characterize schizophrenia patients' male siblings, a finding that seems to agree with previous studies suggesting elevated homocysteine level as a risk factor for developing schizophrenia.

Clinical Use and Pathogenetic Basis of Laboratory Tests for the Evaluation of Primary Arterial Hypertension

This review focuses on the laboratory biochemical tests that are useful in the diagnostic approach to the hypertensive patient. A "minimal" diagnostic laboratory work-up, including a small number of tests that are simple and relatively inexpensive, is first described. Because these tests provide basic information on the presence of major cardiovascular (CV) risk factors and target organ damage, and might give some clues to the presence of a secondary form of hypertension (HT), they should be performed on all patients presenting with HT. Other tests that are aimed at assessing the overall CV risk, a major determinant of prognosis that dictates the therapeutic strategy in the individual HT patient, are then discussed. They allow identification of major CV risk factors and associated clinical conditions which, if present, lead to a substantial change of therapeutic strategy. The role of C-reactive protein as a marker of atherosclerosis and its predictive value for CV events are also discussed. Finally, a section is devoted to tests that are currently confined to research purposes, such as markers of endothelial function including endothelin-1, homocysteine and genetic analysis.

Effects of estrogen and estrogen-progestogen therapy on homocysteine levels and their correlation with carotid vascular resistance

OBJECTIVE

To evaluate the correlation between homocysteine levels and carotid vascular resistance in menopausal women submitted to estrogen and estrogen-progestogen therapy.

METHODS

Eighty-six women with a mean age of 52 years were enrolled in a prospective, randomized, double-blind, 6-month study. Patients were allocated to use one of three oral therapies: placebo (n = 26), micronized estradiol 2 mg/day (n = 30) or micronized estradiol 2 mg/day plus norethisterone acetate 1 mg/day (n = 30). Evaluation of homocysteine levels and Doppler sonography of the common carotid artery, used to calculate pulsatility index (PI), were carried out prior to initiating therapy and at the end of the study. The correlation between these two parameters was evaluated using Pearson's coefficient of correlation.

RESULTS

There was a significant reduction in homocysteine levels in the groups treated with estrogen alone or estrogen combined with norethisterone. PI was significantly lower only in users of estrogen alone; however, no significant correlation was found between homocysteine measurements and PI.

CONCLUSION

No significant correlation was found between homocysteine levels and carotid vascular resistance following hormone therapy.

Investigating the Genetic Determinants of Cardiovascular Disease Using Candidate Genes and Meta-analysis of Association Studies

Coronary artery disease (CAD) has a polygenic basis, and identification of CAD susceptibility genes has the potential to aid the development of new treatments and enhance prediction of disease risk. Thus far, the strategy has firstly been to choose "candidate" genes coding for important "rate-limiting" proteins in the homeostatic systems involved in maintaining cardiovascular health; secondly to identify common variants in these candidate genes; thirdly to carry out genotyping and statistical analysis using genetic association studies; and finally to test the functional effects of the identified variants in vitro and in vivo. However, lack of reproducibility of genetic association studies has led to uncertainty about the nature and number of genes involved. In part this is because many of the studies conducted have not been adequately powered to detect small risk effects, or to permit adequate exploration of gene-gene or gene-environment interactions in a robust manner. Spurious positive and negative associations due to type I and type II statistical errors are likely to co-exist with real associations in the published literature. By utilising all available data to increase statistical power, meta-analysis of genetic association studies is increasingly being used to identify genotypic risk with a greater degree of precision. Though potentially powerful, this approach may be prone to publication bias. Therefore, very large genetic association studies will also be required to identify risk genes for CAD. This review lays out the framework for the candidate gene approach for CAD and illustrates this with published results from a UK prospective study of 3000 middle-aged men.

In vitro effect of homocysteine on nucleotide hydrolysis by blood serum from adult rats

During the past few years, elevated blood levels of homocysteine (Hcy) have been linked to increased risk of premature coronary artery disease, stroke and thromboembolism. These processes can be also related to the ratio adenine nucleotide/adenosine, since extracellularly these nucleotides are associated with modulation of processes such as platelet aggregation, vasodilatation and coronary flow. Furthermore, there are some studies that suggest a relationship between Hcy and plasma adenosine concentrations. The sequential hydrolysis of ATP to adenosine by soluble nucleotidases constitutes one of the systems for rapid inactivation of circulating adenine nucleotides. Thus, the main objective of this study was to evaluate if Hcy can participate in the modulation of the extracellular adenine nucleotide hydrolysis by rat blood serum. Our results showed that Hcy, at final concentrations of 5.0 mM, inhibits in vitro ATP, ADP and AMP hydrolysis by 26, 21 and 16%, respectively. Also Hcy, at final concentrations of 8.0mM, inhibited the in vitro hydrolysis of ATP, ADP and AMP by 46, 44 and 44%, respectively. Kinetic analysis showed that the inhibitions of the three adenine nucleotide hydrolyses in the presence of Hcy, by serum of adult rats, is of the uncompetitive type. The IC50 calculated from the results obtained were 6.52+/-1.75 mM (n = 4), 5.18 +/- 0.64 mM (n = 3) and 5.16 +/- 1.22 mM (n = 3) for ATP, ADP and AMP hydrolysis, respectively.

Homocysteine levels--before and after methionine loading--in 51 Dutch families

Elevated levels of homocysteine are a risk factor for vascular disease, thrombosis, neural tube defects and dementia. The 677C>T polymorphism in the methylenetetrahydrofolate reductase (MTHFR) gene appears to be the most important single determinant of plasma homocysteine concentration. In the current study, we estimated heritability and fit a series of models of inheritance for both fasting and postmethionine-load homocysteine levels in the HOFAM-study (HOmocysteine in FAMilies study), which included 306 participants from 51 pedigrees, ascertained through a hyperhomocysteinemic proband. The crude heritability was 21.6% for fasting and 67.5% for postloading homocysteine. After adjustment for MTHFR 677C>T genotype, heritability dropped to 5.2 and 63.9%, respectively. Segregation analysis revealed that a nongenetic model with equal transmission was the best fitting and most parsimonious model for fasting homocysteine levels, while a two-distribution, Mendelian model with residual familial correlation was best for postmethionine-load homocysteine levels. This study shows that postload homocysteine levels have a stronger genetic determination than do fasting homocysteine levels. The heritability of postload homocysteine levels were not strongly affected by adjustment for MTHFR 677C>T genotype, in contrast to fasting homocysteine levels. Further studies are needed to identify the genes responsible for the inheritance of postload homocysteine levels.

Intranasal 17β-estradiol treatment and Vitamin B12, folate and homocysteine in menopause

OBJECTIVE

This study assessed the effect of intranasal administration of 17beta-estradiol (Aerodiol) on plasma levels of homocysteine, Vitamin B12 and folate in postmenopausal women.

METHODS

In all, 26 symptomatic postmenopausal women who had undergone hysterectomy and oophorectomy at least 12 months previously participated in this 6-month randomized prospective clinical study. Menopause was determined by serum FSH level >30 microIU/ml and serum estradiol concentration <30 pg/ml. Intranasal 17beta-estradiol treatment was given once daily at a standard daily dose of 300 microg to 16 women, and 10 did not receive any treatment.

RESULTS

In the group receiving intranasal 17beta-estradiol, mean (+/-S.D.) plasma homocysteine level decreased significantly from pre-treatment values (from 16.68+/-4.33 to 14.15+/-1.18 nmol/ml, p=0.029) and the mean folate level increased (from 4.11+/-0.80 to 5.64+/-1.87 ng/ml, p=0.012). Vitamin B12 levels showed a tendency towards increasing. In the treated group, significant negative correlations were observed between homocysteine and folate values (r=-0.586, p=0.017) and between homocysteine and Vitamin B12 values (r=-0.672, p=0.004). No significant changes were observed in the untreated group.

CONCLUSION

The reduction in plasma homocysteine levels observed after 6 months' treatment with intranasal 17beta-estradiol may reflect an alteration in folate and Vitamin B12 homeostasis.

Homocysteine levels in A/J and C57BL/6J mice: genetic, diet, gender, and parental effects

Increased levels of homocysteine in the blood have been associated with various birth defects and adult diseases. However, the extent to which genetic factors control homocysteine levels in healthy individuals is unclear. Laboratory mice are valuable models for dissecting the genetic and environmental controls of total homocysteine (tHcy) levels. We assessed the inheritance of tHcy levels in two inbred strains, A/J and C57BL/6J (B6), under controlled physiological conditions and assessed the relative importance of genetic, diet, gender, and parental effects. Diet affected mean tHcy levels, whereas gender affected both the mean and variance of tHcy levels. Moreover, gender of the parents influenced mean tHcy levels in reciprocal F1 hybrids, suggesting maternal effects. Finally, gene-diet interactions affected heritability of mean tHcy levels. These studies showed that each of these factors contributes to tHcy levels and provided important clues to understanding homocysteine homeostasis in humans.

Plasma total homocysteine in Mexican rural and urban women fed typical model diets

OBJECTIVE

The purpose of the present work was to determine the fasting plasma total homocysteine (tHcy) levels and the time-course response of tHcy concentrations after the consumption of urban and rural Mexican model diets in two groups of Mexican women from urban and rural areas.

METHODS

Thirty-three adult women (age range = 18-49 y) were studied. Fifteen women were from a rural community in the state of Mexico. The other 18 were from cities and consumed diets that regularly included an important amount of animal foods. The study was designed as a two-period crossover study in which subjects consumed the model urban or rural diet in a 2-wk interval. Seven milliliters of venous blood was drawn before ingestion of experimental diets (basal) to measure total cholesterol, high-density lipoprotein cholesterol, triacylglycerol, tHcy, folate, vitamin B12, and methionine. Blood samples were then obtained 30, 60, 90, 180, and 240 min after the beginning of meal consumption.

RESULTS

The rural and urban groups showed similar concentrations of tHcy 4 h after meal consumption and after fasting. However, the urban and rural groups had higher methionine plasma concentrations after the urban diet than after the rural diet. In contrast, there was no significant difference in methionine plasma levels between the rural and urban groups with each diet. Those women with low tHcy concentrations maintained those values over the study period, and those with high tHcy concentrations maintained those values. There was no significant difference in tHcy concentrations due to consumption of the two diets (P = 0.31) or the interaction between population and diet (P = 0.84). However, there was a significant difference in the concentration of tHcy between the rural (8.73 +/- 0.17 microM/L) and the urban (9.27 +/- 0.13 microM/L) populations (P = 0.01). In both groups, average tHcy concentration was in the normal range. In both populations, the nutrition status for folate and vitamin B12 was adequate, although plasma folate concentration was significantly lower in the rural population than in the urban population (P < 0.01). Plasma vitamin B12 concentrations were similar in both groups. No subject had low plasma vitamin B12.

CONCLUSIONS

Plasma tHcy concentrations in rural and urban Mexican women were within the range considered adequate; however, urban women showed significant higher concentrations than did rural women independently of the consumed diet and the plasma methionine concentration. These results indicated that there is no short-term variation in plasma tHcy due to the consumption of rural or urban diets.

A twin study of C-Reactive Protein compared to other risk factors for coronary heart disease

Coronary heart disease (CHD) tends to cluster in families, and several established risk factors for the disease are to some extent inherited. Inflammation plays a key role in the development of atherosclerosis and CHD. A low-grade inflammation may be detected by highly sensitive C-Reactive Protein (CRP) determination, which is strongly associated to CHD. In order to uncover any role of genetics in low-grade inflammation, we measured CRP in healthy monozygotic twins. The within-pair correlation coefficient of CRP was 0.40, suggesting an important genetic contribution to the control of CRP level. CRP correlated significantly to other CHD risk factors like body mass index (BMI), systolic blood pressure, diastolic blood pressure, plasma fibrinogen, serum high-density lipoprotein cholesterol, plasma homocysteine, and serum triglycerides. Of these variables, BMI was most significantly associated to CRP in a linear multiple regression analysis. We conclude that CRP level (reflecting a low-grade inflammation) exhibits a moderate, but significant degree of heritability. The association between CRP and BMI, which has a larger degree of heritability, could partly explain the heritability of serum CRP level.

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.

Plasmatic homocysteine concentration and its relationship with complications associated to diabetes mellitus

BACKGROUND AND METHODS

In the search for new factors of cardiovascular risk associated to diabetes mellitus (DM), special attention has been paid in recent years to hyperhomocysteinaemia. Therefore, we have established the concentration of homocysteine (Hcy) and other biochemical parameters in the plasma of a group of 57 type 1 and 32 type 2 diabetic patients and 54 control subjects and studied whether plasmatic homocysteinaemia was related to macroangiopathy, nephropathy, retinopathy and neuropathy. Because of significant differences for plasma Hcy values between men and women in the control group, we distinguished between both groups throughout the study.

RESULTS

Patients with DM had higher Hcy than control subjects (11.7+/-5.4 vs. 10.1+/-2.4 micromol/l, p<0.05). Fasting hyperhomocysteinaemia was considered as the mean of the plasma Hcy for control subjects+2 SD (14.9 micromol/l in total group, 15.6 micromol/l in males and 13.9 micromol/l in females). In the studied groups with complications, we found significant differences between normohomocysteinaemic type 1 diabetic patients and those considered hyperhomocysteinaemic by us. On the other hand, patients having type 1 DM and complications had higher plasmatic Hcy concentration than those with no complications.

CONCLUSIONS

We have found a relationship between high Hcy levels and prevalence of macroangiopathy, retinopathy and nephropathy in the type 1 diabetic patients, which was not been observed in the type 2 diabetic patients of our study. As a result, we consider plasmatic Hcy a complication-risk indicator in type 1 DM, and we recommend its use together with already established biochemical parameters in the control of the evolution of the disease.

Effect of long-term hormone replacement therapy on plasma homocysteine in postmenopausal women: a randomized controlled study

OBJECTIVE

The purpose of this study was to investigate the long-term effect of hormone replacement therapy on total homocysteine and to study whether there was any difference in effect between opposed and unopposed hormone replacement therapy or whether the methylenetetrahydrofolate reductase C677T polymorphism was associated with the effect of hormone replacement therapy on total homocysteine.

STUDY DESIGN

Two hundred nine healthy postmenopausal women were randomized to hormone replacement therapy (n = 103) or no substitution (n = 106) 5 to 7 years earlier.

RESULTS

Women who received hormone replacement therapy had significantly lower total homocysteine concentrations than women in the control group; median total homocysteine values were 8.6 micromol/L and 9.7 micromol/L, respectively, in a per-protocol analysis (P =.02). The effect was comparable in all methylenetetrahydrofolate reductase genotypes, and no difference between unopposed and opposed hormone replacement therapy could be demonstrated. Similar results were obtained when an intention-to-treat analysis was performed.

CONCLUSION

Long-term hormone replacement therapy results in lower total homocysteine concentrations in all methylenetetrahydrofolate reductase genotypes without demonstrable difference in effect between unopposed and opposed hormone replacement therapy.

Homocysteine and cardiovascular disease: current evidence and future prospects

Hyperhomocysteinemia is an independent risk factor for cardiovascular disease. Despite the well-known effectiveness of vitamin supplementation in reducing homocysteine levels, it is not known whether lowering of homocysteine levels is associated with a reduction in cardiovascular morbidity and mortality. The aim of this review is to discuss the epidemiologic evidence about the relation between homocysteine and cardiovascular disease, the pathophysiologic mechanisms responsible for the deleterious vascular and hemostatic effects of homocysteine, and studies of the potential benefits of homocysteine-lowering therapy.

Serum homocysteine concentration is related to diabetes mellitus, but not to coronary heart disease, in Saudi Arabians

INTRODUCTION

Plasma homocysteine (HCYS) concentration is believed to be an independent risk factor for atherosclerosis.

METHODS

HCYS was measured in a cohort of 584 Saudi Arabians participating in a national screening study of coronary heart disease (CHD) risk factors. A total of 173 subjects (114 men and 59 women) had clinical CHD, of whom 82 (47.4%) had type 2 diabetes mellitus (56 men and 26 women). A further 127 subjects (60 men and 67 women) also had type 2 diabetes mellitus but no CHD. A total of 284 individuals (120 men and 164 women) were recruited as healthy controls, and had no previous history of CHD or diabetes. Serum HCYS was measured by high-performance liquid chromatography (HPLC) with electrochemical detection.

RESULTS

Univariate analysis showed HCYS concentrations were significantly lower in those with diabetes mellitus (DM) than in controls, for both men [8.7 (4.2-18.6) vs. 10.5 (4.5-20.5) mmol/l, median (5th-95th percentiles, p = 0.009] and women [6.3 (3.3-24.0) vs. 8.1 (4.0-17.9) mmol/l, p = 0.049]. Stepwise multivariate regression analysis indicated a relationship between HCYS concentration and age, sex and the presence of DM, but not with CHD.

CONCLUSIONS

In the Saudi Arabian population, serum HCYS is not a risk factor for CHD, but is lower in patients with DM.

Effect of smoking on serum concentrations of total homocysteine and B vitamins in mid-pregnancy

There are conflicting findings in the literature on the effect of smoking on total homocysteine (tHcy) concentrations in non-pregnant subjects. We evaluated the effect of smoking on serum concentrations of tHcy, folate, vitamin B-12 pyridoxal 5'-phosphate (PLP, a coenzyme form of vitamin B-6) in 196 women at 18 and 30 weeks' gestation. The smokers were defined as those who self-reported cigarette smoking and had serum concentrations of thiocyanate, a biomaker of smoking, in the highest quartiles of the population. Mid-pregnancy serum tHcy concentrations were not significantly different between smokers and non-smokers. Folate, vitamin B-12 and PLP concentrations were generally lower in smokers than non-smokers. In smokers, tHcy concentrations had significant negative correlations with folate at both time points. The multiple regression analyses indicated that serum folate concentration was the most significant factor associated with tHcy concentrations among smokers, whereas thiocyanate concentrations showed no such effect. We conclude that serum tHcy concentrations were most strongly associated with the nutritional status of folate among the B vitamins tested during mid-pregnancy in our subjects. We suggest that it is essential to consider the nutritional status of folate, vitamin B-12 and vitamin B-6 in evaluating the effect of smoking on homocysteine metabolism.

Effect of long-term depletion of plasma methionine on the growth and survival of human brain tumor xenografts in athymic mice

Depletion of plasma methionine is expected to inhibit or reverse growth of methionine-dependent tumors; however, modulation of methionine and other sulfur amino acids is not a trivial task in experimental animals. L-Methioninase from Pseudomonas putida at 1,000 U/kg causes acute reduction of plasma methionine by 80% in mice, but recovery occurs within 14 hours. Restriction of dietary choline and replacement of dietary methionine with homocystine results in 50% chronic reduction of plasma methionine. A > 70% reduction can be accomplished with a diet deficient in methionine, homocystine, and choline, but ultimately this diet is lethal. Plasma methionine can be lowered to a steady state of < 5 microM in mice with a combination of dietary restriction of methionine, homocysteine, and choline and synchronous treatments with intraperitoneal injections of 1,000 U/kg L-methioninase and 25-50 mg/kg homocystine, each administered at 12-hour intervals. Modulation of plasma methionine by this means causes no weight loss or pathologies in liver or pancreas, and it does not markedly alter levels of cysteine, homocysteine, or glutathione in plasma or in hepatic tissue. When this procedure is applied to athymic mice bearing human medulloblastoma (Daoy) tumors subcutaneously, tumor growth is inhibited. Methionine deprivation arrests mitosis by blocking the cell cycle in G2 and induces apoptosis. Tumor stasis was achieved in 100% of treated animals within 4 days of treatment, and regression was seen in one-third of animals after a 10-day period. These data strongly support the use of methionine-depleting regimens for tumor treatments.

Increased plasma homocysteine after menopause

Besides genetic defects in the enzymes involved in homocysteine metabolism and nutritional deficiencies in vitamin cofactors, sex steroid hormones may modulate plasma homocysteine levels. The post-menopausal state has been found to be associated with higher plasma homocysteine levels, but data are inconsistent and studies published so far did not adjust for age, which is an important confounding factor in studying the effect of menopause. In the present study total plasma homocysteine levels were measured in a meticulously selected population in which the contrast in estrogen status between pre- and postmenopausal women of the same age was maximized. The study comprised 93 premenopausal and 93 postmenopausal women of similar age (range 43-55 years). Women were selected from respondents to a mailed questionnaire on menopause, which was sent to all women aged 40-60 years in the Dutch town of Zoetermeer (n = 12675). Postmenopausal women who were at least three years after menopause or whose menses had stopped naturally before age 48 were age-matched with premenopausal women with regular menses and without menopausal complaints. Plasma homocysteine levels in the fasting state were related to menopausal status; the age-adjusted geometric mean was 10.7 micromol/l in premenopausal and 11.5 micromol/l in postmenopausal women (difference of 7%, 95% confidence interval 0.3-14%, P = 0.04). Additional adjustment for plasma creatinine, body mass index, smoking habit (yes, no) and alcohol intake did not influence this difference. The results of this population-based study indicate that plasma homocysteine is affected by menopause.

The effect of estrogen replacement therapy on total plasma homocysteine in healthy postmenopausal women

OBJECTIVE

To clarify the effect of estrogen on total plasma homocysteine concentration and on the concentration of vitamins required for homocysteine metabolism (folate, vitamin B12, and vitamin B6).

METHODS AND RESULTS

We measured total fasting plasma homocysteine in 16 healthy postmenopausal women before and 6 hours after a methionine load (100 mg/kg); fasting concentrations of folate, vitamin B12, vitamin B6, total cholesterol, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol were also determined. After 6 months of estrogen replacement therapy with estradiol, 2 mg daily, and 1 cycle of quarterly methoxyprogesterone acetate, 5 mg daily administered on the 91st through 100th days, measurements were repeated. There was no significant change in mean +/- SD fasting homocysteine concentration (8.8+/-2.5 vs 8.5+/-2.0 micromol/L; P=.30); homocysteine concentrations after methionine load increased from 38.8+/-12.3 to 51.1+/-12.5 micromol/L (P=.01). During this time period, no significant changes occurred in the concentrations of folate (11.7+/-4.4 vs 9.8+/-4.1 nmol/L; P=.06), vitamin B12 (394+/-182 vs 411+/-155 pmol/L; P=.40), or vitamin B6 (pyridoxal phosphate) (26+/-21 vs 36+/-25 nmol/L; P=.15). The mean +/- SD concentration of low-density cholesterol declined 20% (from 147+/-32 to 118+/-37 mg/dL) and high-density lipoprotein increased 16% (from 40+/-13 to 46+/-19 mg/dL) during the study period.

CONCLUSIONS

Six months of estrogen replacement therapy did not lower fasting plasma total homocysteine concentrations and raised homocysteine concentrations following a methionine load. Lipid profiles improved significantly during the study period. A reduction in homocysteine concentrations is not likely to contribute to the reduction in cardiovascular events seen with estrogen replacement therapy.

Total homocysteine and cardiovascular disease

Recent data have shown that an elevated plasma level of the amino acid homocysteine (Hcy) is a common, independent, easily modifiable and possibly causal risk factor for cardiovascular disease (CVD) which may be of equal importance to hypercholesterolemia, hypertension and smoking. This paper reviews the biochemical, clinical, epidemiological and experimental data underlying this conclusion and is critically questioning whether elevated tHcy is a causal factor.

Homocysteine and cardiovascular disease

An elevated level of total homocysteine (tHcy) in blood, denoted hyperhomocysteinemia, is emerging as a prevalent and strong risk factor for atherosclerotic vascular disease in the coronary, cerebral, and peripheral vessels, and for arterial and venous thromboembolism. The basis for these conclusions is data from about 80 clinical and epidemiological studies including more than 10,000 patients. Elevated tHcy confers a graded risk with no threshold, is independent of but may enhance the effect of the conventional risk factors, and seems to be a particularly strong predictor of cardiovascular mortality. Hyperhomocysteinemia is attributed to commonly occurring genetic and acquired factors including deficiencies of folate and vitamin B12. Supplementation with B-vitamins, in particular with folic acid, is an efficient, safe, and inexpensive means to reduce an elevated tHcy level. Studies are now in progress to establish whether such therapy will reduce cardiovascular risk.

Prevalence of familial mild hyperhomocysteinemia

Previous studies have shown that elevated basal homocysteine levels are correlated among family members of patients with coronary vascular disease and juvenile venous thrombosis. This suggests the possibility of the presence of inherited basal mild hyperhomocysteinemia (mHH). We studied homocysteine levels, fasting as well as after methionine load, among 96 family members of 21 post-load hyperhomocysteinemic vascular index patients, i.e. 6 parents, 27 offspring, 38 siblings, 19 uncles and aunts and 6 cousins. In 15 out of 21 screened families post-load mHH was established in at least one family member. Fasting and post-load mHH was observed in 19 out of 89 (21%) screened family members (fasting homocysteine levels not measured in seven family members), and 31 out of 96 screened family members (32%), respectively. In 40% of all family members, post-load mHH was not accompanied by fasting mHH. We conclude that both fasting and post-load mHH seems to be inherited in the majority of hyperhomocysteinemic vascular patients.

Role of blood pressure, uric acid, and hemorheological parameters on plasma homocyst(e)ine concentration

Elevated concentration of plasma homocyst(e)ine is an independent risk factor for clinical atherosclerosis. In this study, the concentration of plasma homocyst(e)ine in men who lacked a history of atherosclerotic disease was correlated with hemodynamic, rheological and biochemical parameters. Hypertensive subjects had higher concentrations of plasma homocyst(e)ine than normotensive subjects. Positive correlations were found between concentrations of plasma homocyst(e)ine and several risk factors, but some of these correlations disappeared when they were adjusted for other variables. However, multivariate analyses demonstrated that systolic blood pressure, plasma uric acid, and hematocrit were predictors of concentrations of plasma homocyst(e)ine, after adjusting for certain risk factors. The possible significance of these interrelationships in atherogenesis require further study.

Homocyst(e)ine and arterial occlusive diseases

Homocysteine is a thiol-containing amino acid resulting from demethylation of methionine. The free and protein-bound forms of the amino acid and derived disulfides are called homocyst(e)ine [H(e)]. Multiple studies have shown elevated H(e) levels in patients with coronary, cerebrovascular, or peripheral arterial diseases; this association is frequent and independent of most other risk factors for atherosclerosis. In the 1993 Frontiers in Medicine Symposium investigators discussed the genetic, physiological, nutritional, and pharmacological mechanisms involved in the regulation of plasma H(e), the association of H(e) with arterial occlusive diseases, and the relationships of H(e) with nitric oxide and haemostasis. High plasma H(e) levels usually can be reversed with vitamin supplements. Whether vitamin supplements will affect the evolution of arterial occlusive diseases needs to be established in prospective, placebo-controlled, randomized, clinical trials.

Homocysteine and cysteine: determinants of plasma levels in middle-aged and elderly subjects

OBJECTIVES

Hyperhomocysteinaemia is an independent risk factor for cardiovascular disease. We explored possible determinants of plasma homocysteine and cysteine concentrations amongst middle-aged and elderly subjects.

DESIGN AND SUBJECTS

Of 501 35-95-year-old randomly selected residents of Lund and Malmö, Sweden, 244 (49%; 131 men, 113 women) were investigated.

RESULTS

Total plasma homocysteine concentrations were higher in men than in women (mean +/- SD: 13.9 +/- 4.1 and 12.3 +/- 4.1 mumol L-1; P < 0.001), increased markedly with age (Spearman's rho = 0.488; P < 0.001), and were correlated (P < 0.001) to concentrations of blood folate, serum vitamin B12, and serum creatine (rho = -0.366, -0.338, and 0.463). Users of multivitamins had lower homocysteine levels than nonusers [10.5 +/- 3.3 mumol L-1 (n = 31) and 13.5 +/- 4.2 mumol L-1 (n = 213), respectively; P < 0.001]. Total plasma cysteine concentrations also increased significantly with age and increasing serum creatinine, but were unrelated to gender, blood folate, serum vitamin B12 and use of multivitamins.

CONCLUSIONS

Age, gender, folate, serum vitamin B12, serum creatinine and multivitamin usage are all important determinants of the plasma homocysteine concentration, whereas only age and serum creatinine are determinants of the plasma cysteine concentration. The age-related increase in homocysteine and cysteine may be linked to the age-related impairment of renal function, whereas the sex difference in plasma homocysteine may be because of the fact that more homocysteine is formed in men than in women in conjunction with creatine-creatinine synthesis.

Hormone replacement therapy may reduce high serum homocysteine in postmenopausal women

In a prospective study we investigated the possible changes in fasting serum total homocysteine concentrations during continuous micronized 17 beta-oestradiol, 2 mg daily, in combination with cyclic dydrogesterone, 10 mg daily during the first 14 days of each 28 day cycle, in 21 healthy non-hysterectomized postmenopausal women. During the first six cycles mean serum homocysteine decreased by 10.9% (P = 0.013), after which no further significant changes were found during the 2 years of treatment. A 16.9% decrease (P = 0.017; n = 8) was found in women with high homocysteine concentrations, while in women with low homocysteine concentrations (n = 13) no significant changes were observed. The observed decrease in high homocysteine concentrations in postmenopausal women may in part contribute to the decreased risk of developing cardiovascular disease during hormone replacement therapy.

Homocysteine increases as folate decreases in plasma of healthy men during short-term dietary folate and methyl group restriction

Ten healthy adult men were fed a diet low in folate and exogenous methyl groups to study the effects on folate requirement and status. The men were housed in a metabolic unit for the entire 108-d study. After a 9-d base-line period (P1), the men were fed an amino acid-defined soybean product diet for 45 d, which provided 25 micrograms/d of folate for 30 d (P2) and (with a folate supplement) 99 micrograms/d for 15 d (P3). During P2 and P3, the low methionine and choline diet was supplemented with methionine for half the subjects to vary the dietary methyl group intake. The periods were then repeated over the next 54 d (P4-P6), with a cross-over of methionine intakes in P5 and P6. Restricting dietary methyl group intake did not increase the dietary folate requirement. Plasma total homocysteine rose during folate depletion and correlated inversely with plasma folate; however, the response of homocysteine to changes in folate intake varied among individuals from very strong to absent. The results support previous suggestions that increased plasma homocysteine concentrations provide a marker of functional folate deficiency, and further indicate that individuals may differ greatly in their susceptibility to hyperhomocysteinemia due to low folate intakes. Judged by the lack of normalization of high homocysteine concentrations during folate repletion, the current folate RDA for adult men may not provide the expected margin of protection.