The effect of homocysteine on DNA synthesis in cultured human vascular smooth muscle

Epigallocatechin gallate protects against homocysteine-induced vascular smooth muscle cell proliferation

Epigallocatechin gallate (EGCG), a bioactive ingredient of green tea, plays a protective role in the cardiovascular system. Homocysteine (Hcy) is a major risk factor for chronic kidney disease and cardiovascular disease. The present study aimed to investigate the role of EGCG in Hcy-induced proliferation of vascular smooth muscle cells (VSMCs) and its underlying mechanism. We also explored the roles of rennin-angiotensin system (RAS), extracellular signal-regulated kinases (ERK1/2), and p38 mitogen-activated protein kinase (p38 MAPK) in this process. Human aortic smooth muscle cells (HASMCs) were treated with different drugs for different periods. The proliferation rate of HASMCs was detected using the CCK-8 and BrdU labeling assays. The Western blot assay was used to determine the expression levels of angiotensin II type 1 receptor (AT-1R), ERK1/2, and p38 MAPK. Compared with the control group, the HASMCs treated with Hcy at different doses (100, 200, 500, and 1000 µM) showed significantly increased proliferation. Hcy increased the expression of AT-1R, whereas EGCG decreased the protein expression of AT-1R. Furthermore, we found that Hcy-induced expression of p-ERK1/2 and p-p38MAPK was dependent on AT-1R. Compared with Hcy (500 µM)-treated cells, EGCG (20 µM)-treated cells showed decreased proliferation as well as expression of AT-1R, p-ERK1/2, and p-p38MAPK. In addition, HASMC proliferation was suppressed by the addition of an AT-1R blocker (olmesartan), an ERK1/2 inhibitor (PD98059), and a p38MAPK inhibitor (SB202190). EGCG can inhibit AT-1R and affect ERK1/2 and p38MAPK signaling pathways, resulting in the decrease of VSMC proliferation induced by Hcy.

Joint effect of maternal plasma homocysteine and prepregnancy obesity on child blood pressure: a prospective birth cohort study

BACKGROUND/OBJECTIVES

Elevated homocysteine (Hcy) is a known cardiovascular risk factor. However, its role in intergenerational cardiometabolic risk is unknown. We hypothesized that maternal elevated Hcy can act alone or in combination with maternal prepregnancy obesity to increase child systolic blood pressure (SBP).

METHODS

This study included 1279 mother-child pairs who were enrolled at birth and followed prospectively up to age 9 years from 2003 to 2014 at the Boston Medical Center. Child SBP percentile was calculated according to US reference data and elevated SBP was defined as SBP⩾75th percentile.

RESULTS

A U-shaped relationship between maternal Hcy and her child SBP was observed. The risk for child elevated SBP was higher among those in the lowest quartile (Q1, odds ratio (OR): 1.27; 95% confidence interval (CI): 0.94-1.72), and highest quartile (Q4, OR: 1.34; 95% CI: 1.00-1.81) as compared with those in quartiles 2 and 3. The highest risk of child elevated SBP was found among children born to obese mothers with Hcy in Q4 (OR: 2.22; 95%CI: 1.35-3.64), compared with children of non-obese mothers with Hcy in Q2-Q3. This association was independent from maternal folate and vitamin B12 status, and was not mediated by gestational age or size at birth.

CONCLUSIONS

In this prospective birth cohort, we observed a U-shaped association between maternal Hcy levels and child elevated SBP. Maternal high Hcy (Q4) and prepregnancy obesity jointly increased the risk of child elevated SBP by more than two-fold.

Dichotomous effects of isomeric secondary amines containing an aromatic nitrile and nitro group on human aortic smooth muscle cells via inhibition of cystathionine-γ-lyase

Excessive proliferation of vascular smooth muscle cells (SMC) is an important contributor to the progression of atherosclerosis. Inhibition of proliferation can be achieved by endogenously produced and exogenously supplied nitrogen monoxide, commonly known as nitric oxide (NO). We report herein the dichotomous effects of two isomeric families of secondary amines, precursors to the N-nitrosated NO-donors, on HASMC proliferation. The syntheses of these two families were carried out using two equivalents of homologous, aliphatic monoamines and 2,6-difluoro-3-nitrobenzonitrile (2,6-DFNBN, O family) or 2,4-difluoro-5-nitrobenzonitrile (2,4-DFNBN, P family). The secondary amines belonging to the P family inhibited HASMC proliferation at all concentrations, whereas the O family induced HASMC proliferation at low concentrations, and exhibited inhibitory properties at high concentrations. A probable explanation of these behaviors is proposed herein. l-homocysteine (HCY) is known to induce HASMC proliferation at low concentrations (<1 mM) and inhibit HASMC proliferation at higher concentrations (>2.5 mM). Our findings suggest that these two families of amines inhibit cystathionine-γ-lyase (CSE) to varying extents, which directly results in altered levels of intracellular HCY and consequent changes in HASMC proliferation.

C-Reactive Protein and Inflammatory Cytokines during Percutaneous Coronary Intervention

BACKGROUND

C-reactive protein (CRP) is significantly associated with cardiovascular diseases; however, whether CRP plays a causal role in coronary artery disease has yet to be determined. In addition, the relationship between CRP, atherosclerosis, and inflammation remains controversial.

METHODS AND RESULTS

Serum interleukin (IL)-6, IL-1β, and CRP levels were determined in 160 patients at time points around percutaneous coronary intervention (PCI) with drug-eluting stent implantation. The levels were found to be at peak at 24 h post-PCI and gradually declined to the level before PCI at day 30 post-PCI. These inflammation markers around PCI have no statistical difference in the different postdilation pressures (≤14, 14-18, and ≥18 atm) and stent number (1 and ≥2 stents) groups. Treatment of cultured human vascular smooth muscle cells (VSMCs) with a combination of IL-6 and IL-1β at concentrations associated with PCI did not result in any significant change in the CRP mRNA levels. The IL-6-augmented CRP expression in human internal mammary arteries (IMAs) stretched with a mechanical strength of 3 g was blocked by the nuclear factor-κB (NF-κB) peptide inhibitor SN50 and not by the inactive SN50 analog SN50M. IL-6 treatment increased NF-κB activity in human IMAs stretched with 3 g, and this effect was further blocked by stretch-activated channel (SAC) inhibitors (streptomycin or GdCl3) and SN50.

CONCLUSIONS

The current study provides evidence that increased serum IL-6, IL-1β, and CRP levels around PCI are not different between different postdilation pressure and stent number groups. The combination of IL-6 and IL-1β at concentrations associated with PCI cannot induce CRP expression in human VSMCs, but they can augment mechanical strain-induced CRP synthesis via the SAC-NF-κB pathway in human IMAs.

miR-125b targets DNMT3b and mediates p53 DNA methylation involving in the vascular smooth muscle cells proliferation induced by homocysteine

MicroRNAs (miRNAs) are short non-coding RNA and play crucial roles in a wide array of biological processes, including cell proliferation, differentiation and apoptosis. Our previous studies found that homocysteine(Hcy) can stimulate the proliferation of vascular smooth muscle cells (VSMCs), however, the underlying mechanisms were not fully elucidated. Here, we found proliferation of VSMCs induced by Hcy was of correspondence to the miR-125b expression reduced both in vitro and in the ApoE knockout mice, the hypermethylation of p53, its decreased expression, and DNA (cytosine-5)-methyltransferase 3b (DNMT3b) up-regulated. And, we found DNMT3b is a target of miR-125b, which was verified by the Dual-Luciferase reporter assay and western blotting. Besides, the siRNA interference for DNMT3b significantly decreased the methylation level of p53, which unveiled the causative role of DNMT3b in p53 hypermethylation. miR-125b transfection further confirmed its regulative roles on p53 gene methylation status and the VSMCs proliferation. Our data suggested that a miR-125b-DNMT3b-p53 signal pathway may exist in the VSMCs proliferation induced by Hcy.

Biphasic dose responses in biology, toxicology and medicine: accounting for their generalizability and quantitative features

The most common quantitative feature of the hormetic-biphasic dose response is its modest stimulatory response which at maximum is only 30-60% greater than control values, an observation that is consistently independent of biological model, level of organization (i.e., cell, organ or individual), endpoint measured, chemical/physical agent studied, or mechanism. This quantitative feature suggests an underlying "upstream" mechanism common across biological systems, therefore basic and general. Hormetic dose response relationships represent an estimate of the peak performance of integrative biological processes that are allometrically based. Hormetic responses reflect both direct stimulatory or overcompensation responses to damage induced by relatively low doses of chemical or physical agents. The integration of the hormetic dose response within an allometric framework provides, for the first time, an explanation for both the generality and the quantitative features of the hormetic dose response.

Folate transporter expression decreases in the human placenta throughout pregnancy and in pre-eclampsia

The transport of folate across the placenta involves a number of different receptors including folate receptor-alpha (FR-α), reduced folate carrier (RFC) and proton coupled folate transporter (PCFT). In addition there are a number of ATP-dependent transporters which have also recently been shown to be involved in folate transport; these include ABCB1, ABCC2 and BCRP (ABCG2). The aim of the current study was to characterise the placental mRNA and protein expression of these folate transporters throughout gestation and also to see if expression is altered in pre-eclampsia. Placental tissue was collected from women undergoing termination of pregnancy (TOP) and from women undergoing elective Caesarean section. To investigate mRNA expression quantitative real time PCR was used with gene specific oligonucleotide primers to FR-α, RFC, PCFT, ABCB1, ABCC2, BCRP and the reference gene YWHAZ. Protein expression was also characterised using immunohistochemistry of paraffin embedded placental tissue. Both protein and mRNA expression of all transporters examined decreased as the gestation progressed. Expression of FR-α and PCFT mRNA and protein were decreased in pre-eclampsia compared with normal term pregnancy. The higher levels of expression of FR-α, RFC, PCFT, ABCB1, ABCC2 and BCRP in early pregnancy indicate that these transporters may have an important role in the establishment and development of the placenta, with expression reducing in preparation for parturition. Reductions in FR-α and PCFT in pre-eclampsia may be a mechanism involved in the pathogenesis of pre-eclampsia by limiting placental folate uptake resulting in reduced levels of angiogenesis, cell proliferation and antioxidant protection.

Homocysteine induces oxidative-nitrative stress in heart of rats: prevention by folic acid

Hyperhomocysteinemia is a risk factor for cardiovascular disease, stroke, and thrombosis; however, the mechanisms by which homocysteine triggers these dysfunctions are not fully understood. In the present study, we investigated the effect of chronic hyperhomocysteinemia on some parameters of oxidative stress, namely thiobarbituric acid reactive substances, an index of lipid peroxidation, 2',7'-dichlorofluorescein (H(2)DCF) oxidation, activities of antioxidant enzymes named superoxide dismutase and catalase, as well as nitrite levels in heart of young rats. We also evaluated the effect of folic acid on biochemical alterations elicited by hyperhomocysteinemia. Wistar rats received daily subcutaneous injection of homocysteine (0.3-0.6 μmol/g body weight) and/or folic acid (0.011 μmol/g body weight) from their 6th to the 28th day of life. Controls and treated rats were killed 1 h and/or 12 h after the last injection. Results showed that chronic homocysteine administration increases lipid peroxidation and reactive species production and decreases enzymatic antioxidant defenses and nitrite levels in the heart of young rats killed 1 h, but not 12 h after the last injection of homocysteine. Folic acid concurrent administration prevented homocysteine effects probable by its antioxidant properties. Our data indicate that oxidative stress is elicited by chronic hyperhomocystenemia, a mechanism that may contribute, at least in part, to the cardiovascular alterations characteristic of hyperhomocysteinemic patients. If confirmed in human beings, our results could propose that the supplementation of folic acid can be used as an adjuvant therapy in cardiovascular alterations caused by homocysteine.

Ozone acting on human blood yields a hormetic dose-response relationship

The aim of this paper is to analyze why ozone can be medically useful when it dissolves in blood or in other biological fluids. In reviewing a number of clinical studies performed in Peripheral Arterial Diseases (PAD) during the last decades, it has been possible to confirm the long-held view that the inverted U-shaped curve, typical of the hormesis concept, is suitable to represent the therapeutic activity exerted by the so-called ozonated autohemotherapy. The quantitative and qualitative aspects of human blood ozonation have been also critically reviewed in regard to the biological, therapeutic and safety of ozone. It is hoped that this gas, although toxic for the pulmonary system during prolonged inhalation, will be soon recognized as a useful agent in oxidative-stress related diseases, joining other medical gases recently thought to be of therapeutic importance. Finally, the elucidation of the mechanisms of action of ozone as well as the obtained results in PAD may encourage clinical scientists to evaluate ozone therapy in vascular diseases in comparison to the current therapies.

Hormesis provides a generalized quantitative estimate of biological plasticity

Phenotypic plasticity represents an environmentally-based change in an organism's observable properties. Since biological plasticity is a fundamental adaptive feature, it has been extensively assessed with respect to its quantitative features and genetic foundations, especially within an ecological evolutionary framework. Toxicological investigations on the dose-response continuum (i.e., very broad dose range) that include documented evidence of the hormetic dose response zone (i.e., responses to doses below the toxicological threshold) can be employed to provide a quantitative estimate of phenotypic plasticity. The low dose hormetic stimulation is an adaptive response that reflects an environmentally-induced altered phenotype and provides a quantitative estimate of biological plasticity. Analysis of nearly 8,000 dose responses within the hormesis database indicates that quantitative features of phenotypic plasticity are highly generalizable, being independent of biological model, endpoint measured and chemical/physical stress inducing agent. The magnitude of phenotype changes indicative of plasticity is modest with maximum responses typically being approximately 30-60% greater than control values. The present findings provide the first quantitative estimates of biological plasticity and its capacity for generalization. Summary This article provides the first quantitative estimate of biological plasticity that may be generalized across plant, microbial, animal systems, and across all levels of biological organization. The quantitative features of plasticity are described by the hormesis dose response model. These findings have important biological, biomedical and evolutionary implications.

Oxidative stress elevated DNA damage and homocysteine level in normal pregnant women in a segment of Pakistani population

Maternal oxidative stress during pregnancy may impair fetal growth and help in the development of diseases in adulthood. The aim of current study was to assess total oxidation status (TOS), related parameters and their relationship to DNA damage (%) and homocysteine level in normal pregnant women in low-income participants. In a cross-sectional study healthy women were grouped as normal, while age matched nulliparous and singleton pregnancies were included for first, second and third trimester groups. TOS (P<0.01), melanodialdehyde (MDA) (P<0.001), aspartate aminotransferase (AST) (P<0.01), triiodothyronine (T3) (P<0.01), thyroxine (T4) (P<0.01), and homocysteine (P<0.001), in pregnant women were significantly higher as compared to normal healthy women. While serum total proteins (P<0.01), albumin (P<0.01) and total antioxidant status (TAS) (P<0.001) decreased significantly as compared to normal healthy women. Women in third trimester showed a significantly high level of body temperature (P<0.01), triglyceride (P<0.01), LDL-cholesterol (P<0.05), AST (P<0.01), T3 (P<0.01), homocysteine (P<0.001), TOS (P<0.01) and MDA (P<0.001) but a lower concentration of serum proteins, albumin and TAS at the end of the pregnancy. Pearson correlation indicated a positive relationship of homocysteine with triglycerides (P<0.027), TOS (P<0.01), MDA (P<0.035) and had a negative relationship with total protein (P<0.026). DNA damage was strongly related with T3 (P<0.008), TOS (P<0.02), MDA (P<0.037) and MBI (P<0.048) profiles of pregnant women. These changes were considered normal for pregnant women having optimum blood pressure and normal child birth. Hormonal influences and hemodilution may contribute towards the observed changes in this study.

Elevated plasma homocysteine levels in chronic periodontitis: a hospital-based case-control study

BACKGROUND

Plasma homocysteine (Hcy), a novel risk factor for cardiovascular disease, has been found to be increased in inflammatory diseases, such as rheumatoid arthritis. Our study investigates the association between chronic periodontitis and plasma Hcy.

METHODS

This case-control study involves 85 age- and sex-matched subjects with chronic periodontitis and 91 healthy controls. Patients were grouped into moderate and severe periodontitis. Plaque index, calculus component of simplified oral hygiene index, and modified gingival index were recorded. Body mass index, fasting blood sugar, total cholesterol, triglycerides, high-density lipoprotein, low-density lipoprotein, very-low-density lipoprotein, and plasma Hcy were also assessed.

RESULTS

Case and control groups had similar levels of fasting blood sugar, lipid profile, and body mass index. The mean plasma Hcy was found to be 19.22 ± 8.27 and 10.27 ± 2.50 μmol/L for cases and controls, respectively. A significant elevation in plasma Hcy levels was observed in cases (P <0.05). No significant differences were observed in plasma Hcy levels between moderate and severe chronic periodontitis (P = 0.722).

CONCLUSIONS

Elevated levels of plasma Hcy were observed in patients with chronic periodontitis. Future research should be directed on the effect of periodontal therapy on plasma Hcy levels.

Levels of circulating homocysteine, vitamin B6, vitamin B12, and folate in different types of open-angle glaucoma

OBJECTIVE

To compare the levels of plasma homocysteine (Hcy), vitamin B6 (vit-B6), serum vitamin B12 (vit-B12), and folate in healthy individuals and in patients with normal tension glaucoma (NTG), pseudoexfoliative glaucoma (PXG), or primary open-angle glaucoma (POAG).

STUDY DESIGN

A prospective controlled trial.

PARTICIPANTS AND METHODS

Forty healthy subjects, 48 patients with NTG, 38 patients with PXG, and 34 patients with POAG were included in the study. Those who used vitamin supplements or medications affecting Hcy and vitamin levels were excluded from the study. The levels of Hcy and vit-B6 were measured by High Performance Liquid Chromatography (HPLC). The levels of serum vit-B12 and folic acid were measured by competitive chemiluminescent enzyme immunoassay (CEI). One-way analysis if variance (ANOVA), analysis of covariance (ANCOVA), and the Tukey honestly significant difference test were used for statistical analysis.

RESULTS

The mean Hcy level of the PXG group was 15.46+/-9.27 micromol/L which was significantly higher (P=0.03) than that of the control group. There were no statistical differences in serum vit-B12 and folate levels among control subjects and NTG, PXG and POAG groups (P>0.05). It was found that the mean plasma vit-B6 level was significantly higher in subjects with NTG (P=0.03) and POAG (P=0.025) versus controls. Mean vit-B6 levels in NTG and POAG were 30.50+/-11.29 microg/L and 30+/-12.15 microg/L, respectively.

CONCLUSIONS

The plasma level of Hcy was found to be increased only in PXG patients and the plasma levels of vit-B6 were found to increase in the NTG and POAG sample groups. Using homocysteine and vit-B6 levels as the determinants of hyperhomocysteinemia still needs further research.

Effects of Homocysteine and Ginsenoside Rb1 on Endothelial Proliferation and Superoxide Anion Production

BACKGROUND

Homocysteine (Hcy) is an independent risk factor for cardiovascular disease by its multiple effects on vascular cells and throbmosis factors, which may be involved in oxidative stress mechansims. Ginsenoside Rb1, a constituent of ginseng, bears various beneficial effects on the cardiovascular system. In the present study, we investigated the effect of Hcy on endothelial proliferation and a protective effect of ginsenoside Rb1 on the action of Hcy.

METHODS

We initially incubated a mouse lymph node endothelial cell line (SVEC4-10) with increasing concentrations of Hcy or for different time periods and then assessed cell proliferation by using [(3)H]-thymidine incorporation. We then incubated SVEC4-10 cells with Hcy (50 microM) for 24 h with or without Rb1 (10 microM) to examine its inhibitory effect on the proliferation. These experiments were repeated in human umbilical vein endothelial cells (HUVECs). To explore the underlying molecular mechanisms, we measured superoxide anion, a reactive oxygen species (ROS), by using dihydroethidium (DHE) staining.

RESULTS

SVEC4-10 cells treated with Hcy (50, 100, and 200 microM) for 24 h significantly reduced cell proliferation by 43%, 42%, and 40%, respectively, as compared with control cells (P < 0.01). SVEC4-10 cells treated with Hcy (50 microM) for 12 and 24 h showed a significant reduction of cell proliferation (P < 0.05). In HUVECs, Hcy (50 microM) significantly reduced cell proliferation by 55% as compared with control cells (P < 0.05). In the presence of Rb1, Hcy-induced inhibition of cell proliferation was effectively blocked in both SVEC4-10 and HUVECs. Furthermore, Hcy (50 microM) significantly increased superoxide anion production by 23% in SVEC4-10 as compared with control cells (P < 0.05). However, in the presence of Rb1, Hcy increased superoxide anion production by only 8%, showing that RB1 almost completely blocked the effect of Hcy.

CONCLUSION

Hcy significantly inhibits endothelial proliferation with increased production of superoxide anion, which is effectively blocked by ginsenoside Rb1. This study provides some new aspects of Hcy-induced endothelial dysfunction, and suggests a potential role of Rb1 to block Hcy action, which may have clinical applications.

Homocysteine promotes p38-dependent chemotaxis in bovine aortic smooth muscle cells

OBJECTIVE

Increased levels of homocysteine in the blood are a risk factor for atherosclerosis. The purpose of this study was to examine the effects of homocysteine on smooth muscle cell (SMC) migration and to determine whether p38 was involved in this process.

METHODS

The effect of 0.5 to 2.0 mmol/L d , l -homocysteine as a chemoattractant for SMCs was assayed with a modified Boyden chamber. To determine the functional role of p38 in SMC chemotaxis induced by d , l -homocysteine, we treated SMCs with a p38 inhibitor, SB203580, before the assay.

RESULTS

The number of migrated cells was increased 7.0 +/- 1.2-fold (n = 15; P < .001) by 2.0 mmol/L d , l -homocysteine. SB203580 partially prevented the migration of SMCs toward homocysteine. Preconditioning SMCs with 2.0 mmol/L d , l -homocysteine significantly enhanced chemotaxis toward 10% fetal bovine serum compared with nonconditioned control SMCs (28.9 +/- 3.3-fold vs 15.6 +/- 2.8-fold; P < .05). There was a fourfold p38 activation after exposure of SMCs to 2.0 mmol/L d , l -homocysteine by immunoblot.

CONCLUSIONS

These results suggest that homocysteine not only is a chemoattractant for SMC but can also enhance SMC chemotactic potential. The mechanism of these effects may involve p38 activation.

CLINICAL RELEVANCE

This study demonstrates that homocysteine can promote chemotaxis of SMCs through a p38-dependent pathway. To our knowledge, this is the first report that homocysteine may influence SMC chemotaxis. It may be an important mechanism for homocysteine-induced atherogenesis, because the migration of SMCs from the media is believed to play a critical role in progressive intimal thickening. Although homocysteine promotes atherogenesis and thrombosis by a variety of mechanisms, the effects of homocysteine on SMC proliferation and migration might be critical elements that may have potential therapeutic implications, because selective blockade of the p38 pathway is feasible.

Homocysteine as a risk factor for coronary heart diseases and its association with inflammatory biomarkers, lipids and dietary factors

The causal relation of total Homocysteine (tHcy) to coronary heart diseases (CHD) is unclear. In vitro studies suggest a proinflammatory effect. Among 32,826 women from the Nurses' Health Study who provided blood samples in 1989-1990, 237 CHD events were documented during 8 years of follow-up. The cases (1:2) were matched to controls on age, smoking, and month of blood draw. Plasma tHcy was inversely associated with blood levels of folate (partial r = -0.3, P < 0.0001) and B1(2) (r = -0.2, P < 0.0001) and with dietary intake of folate (r = -0.1, P < 0.01) and B(2) vitamin (r = -0.1, P = 0.01). tHcy was positively associated with soluble tumor necrosis receptor (sTNF-R) 1 and 2 (partial r = 0.2, P < 0.0001). In a multivariate model adjusted for age, smoking, BMI, parental history, hypertension, diabetes, postmenopausal hormone use, physical activity and alcohol intake, the relative risk of CHD between the extreme quartiles of tHcy was 1.66 (95% CI; 1.05-2.64, P trend = 0.02). The association was not appreciably attenuated after further adjustments for sTNF-R1, sTNF-R2, CRP, or Total Cholesterol:/HDL-c ratio. tHcy is an independent risk predictor of CHD and modestly associated with TNF-receptors. However, the inflammatory biomarkers measured could not explain its role in CHD.

Increased plasma homocysteine concentrations accelerate cardiac allograft vasculopathy

BACKGROUND

A toxic and pro-oxidative effect of homocysteine on the coronary endothelium may accelerate cardiac allograft vascular disease (CAVD). In this study, we evaluated the influence of hyperhomocysteinemia on the course of CAVD.

METHODS

We investigated plasma homocysteine (tHCY) concentrations in 183 consecutive heart transplant recipients (158 men and 25 women, mean aged 53.1 +/- 10.0 years, at 6.7 +/- 3.2 years after transplantation) to evaluate the course of CAVD. We used serial coronary angiography to assess coronary status and graded the severity of CAVD based on the extent of luminal obstruction in the main coronary arteries (graded as 1-4). We defined progression as increased focal stenosis of >/=30% or as detection of a new coronary lesion after a mean observation period of 2.8 +/- 1.0 years. A multivariate analysis (backward logistic regression) was performed that included potential risk factors for CAVD. We excluded patients undergoing dialysis.

RESULTS

Initially, tHCY concentrations were increased in the entire cohort (mean, 18.6 +/- 7.6 mumol/liter) and ranged from 6.6 to 46.9 mumol/liter. A total of 105 patients (57.0%) had CAVD at first angiography, and progression was detected in 52 transplant recipients (28.0%). Patients with progressive CAVD had significantly greater tHCY concentrations (21.6 +/- 6.2 mumol/liter) at baseline investigation compared with patients who had stable courses (17.4 +/- 7.7 mumol/liter; p < 0.001). These results were independent of parameters such as sex, age, dyslipoproteinemia, cyclosporine blood concentrations, and indication for transplantation.

CONCLUSIONS

Progression of CAVD is strongly associated with increased tHCY concentrations. The intervals between routine surveillance angiography should be shortened in patients with hyperhomocysteinemia, and routine medical treatment to decrease homocysteine concentrations should be considered.

High dietary methionine plus cholesterol exacerbates atherosclerosis formation in the left main coronary artery of rabbits

Although mild hyperhomocysteinemia is a risk factor for cardiovascular events and mortality, there is no evidence to suggest that mild hyperhomocysteinemia stimulates coronary artery atherosclerosis formation.

OBJECTIVE

To compare the development of coronary artery atherosclerosis in rabbits following the induction of hyperhomocysteinemia and hypercholesterolemia through diet, and whether the combination of these risk factors exacerbated atherosclerosis formation.

METHODS

New Zealand White rabbits were fed for 12 weeks either a control diet, a 1% methionine diet (Meth), a 0.5% cholesterol diet (Chol) or the combination of the two diets (MethChol). Using volumetric stereological techniques, we quantitated the volume of intima, media and lumen of the left main coronary artery (LMCA).

RESULTS

Atherosclerosis was present in the Chol group, and increased in the MethChol group. There was no atherosclerosis in the control or Meth groups.

CONCLUSIONS

These results underscore the difference in the atherogenicity of hypercholesterolemia alone and mild hyperhomocysteinemia alone. Thus, we suggest that isolated mild hyperhomocysteinemia is not a risk factor for the initiation of coronary artery atherosclerosis formation over a short period of time, but may act in conjunction with other risk factors to further increase plaque formation.

Homocysteine and cardiovascular disease: biological mechanisms, observational epidemiology, and the need for randomized trials

Basic research indicates that homocysteine causes endothelial dysfunction and damage, accelerates thrombin formation, inhibits native thrombolysis, promotes lipid peroxidation through free radical formation, and induces vascular smooth muscle proliferation and monocyte chemotaxis. Most, but not all, observational epidemiological studies indicate that individuals with higher homocysteine levels have increased risks of cardiovascular disease. The magnitude ranges from approximately 20% in prospective studies to approximately 80% in retrospective case-control studies. In all observational epidemiological studies, however, the amount of uncontrolled and uncontrollable confounding is as large as the postulated small to moderate effect size. Thus, the totality of evidence should include randomized trials of sufficient sample size and duration with clinical end points. Folic acid reduces levels of homocysteine, but at present, despite several plausible biological mechanisms and a large body of observational epidemiological data, it is unclear whether supplementation will reduce risks of cardiovascular disease. It is also unclear whether any benefit of folic acid is attributable to lowering homocysteine levels. The current evidence is necessary, but not sufficient to judge causality. Such judgments await the availability of data from large-scale randomized trials. The availability of such data would permit rational clinical decision-making for individual patients and policy decisions for the health of the general public.

Total plasma homocysteine and primary open-angle glaucoma

PURPOSE

To evaluate total plasma homocysteine (tHcy) levels in patients diagnosed with primary open-angle glaucoma (POAG) and normal subjects.

DESIGN

Case-control study.

METHODS

This study involved 55 POAG patients, 16 patients with secondary open-angle glaucoma or angle-closure glaucoma (non-POAG group), and 39 control healthy subjects undergoing ocular surgery. All glaucoma patients had characteristic glaucomatous optic disk damage and visual field loss. Fasting tHcy concentrations of all study participants were determined using high-performance liquid chromatography. Analysis of variance was used to compare homocysteine levels among the three diagnostic groups, and multivariate analysis was conducted to assess the associations between tHcy and diagnostic group, age, gender, smoking status, systemic hypertension, hyperlipidemia, and cardiovascular or cerebrovascular disease.

RESULTS

Mean +/- standard deviation of tHcy levels in POAG individuals, non-POAG patients and control subjects was 14.90 +/- 6.45 micromol/l, 14.30 +/- 4.35 micromol/l, and 14.81 +/- 4.56 micromol/l, respectively (P =.93; ANOVA). No statistically significant difference was found in the proportion of patients with abnormal tHcy levels among the three diagnostic groups. In multivariate analysis, only age and positive smoking status were significantly correlated with total plasma homocysteine levels.

CONCLUSION

No significant difference was found in plasma homocysteine levels among POAG patients and normal control individuals.

Menopause, the Cardiovascular Risk Factor Homocysteine, and the Effects of Treatment

Since the identification of homocysteine (Hcy) as a risk factor for cardiovascular disease, it has been the subject of much research. As with other cardiovascular risk factors, a gender difference exists for Hcy. Plasma levels are lower in women of reproductive age than in men and postmenopausal women. This has led to the hypothesis that the increased risk of cardiovascular disease documented in postmenopausal women may be related to the increase in Hcy levels. Factors affecting total plasma levels of Hcy include genetic factors, nutritional factors, and lifestyle. Many studies appear to support the ability of estrogen replacement therapy to significantly lower both basal levels of Hcy and levels following methionine loading. A mean reduction of 10-15% in Hcy levels after 6 months of hormone therapy has been reported. Similarly, raloxifene and tamoxifen and low-dose folic acid administration induce reductions in plasma Hcy levels of the same degree observed for hormone therapy. The reduction occurs after a few months of therapy and is sustained, suggesting the potential for cardioprotective effects. Although there is a positive effect of estrogen therapy and hormone therapy on Hcy levels, recent studies do not recommend the use of estrogen or hormone replacement therapy for the primary or secondary prevention of cardiovascular disease. Further research is therefore needed to identify strategies to maximize the efficacy of hormone replacement therapy, while minimizing the risks.

The Women's Antioxidant Cardiovascular Study: Design and Baseline Characteristics of Participants

BACKGROUND

The evidence for a potential benefit of antioxidant vitamins and folic acid in cardiovascular disease (CVD) prevention is derived from laboratory, clinical, and observational epidemiological studies but remains inconclusive. Large-scale randomized trials with clinical end points are necessary to minimize confounding and provide unbiased estimates of the balance of benefits and risks, yet data from such trials are scarce, especially among women.

METHODS

The Women's Antioxidant Cardiovascular Study (WACS) is a randomized, double-blind, placebo-controlled trial testing whether antioxidant vitamins and a folic acid/vitamin B(6)/vitamin B(12) combination prevent future cardiovascular events among women with preexisting CVD or >or=3 CVD risk factors. This paper describes the design of the trial and baseline characteristics of participants, evaluates the success of randomization, and addresses the generalizability of future findings.

RESULTS

In a factorial design, 8171 U.S. female health professionals aged >or=40 years were randomized to vitamin E, vitamin C, beta-carotene, or placebos. Of these women, 5442 were also subsequently randomized to folic acid/vitamin B(6)/vitamin B(12) or placebo. The randomization was successful, as evidenced by similar distributions of baseline demographic, health, and behavioral characteristics across treatment groups. The clinical profile of participants was similar to that observed in another large trial of women with CVD.

CONCLUSIONS

The similar distribution of known potential confounders across treatment groups provides reassurance that unmeasured or unknown potential confounders are also equally distributed. Although a definitive conclusion regarding generalizability requires additional trials in diverse populations, there is little biological basis for supposing that the benefit-risk balance differs in other high-risk women.

Homocysteine and cardiovascular disease in renal disease. Review Article

Elevated homocysteine (hyperhomocysteinaemia) in renal patients is a major concern for physicians. Although cause and effect between homocysteine and cardiovascular disease (CVD) has not been established in either the general population or renal patients, there is much evidence that this relationship does exist. Purported mechanisms that may explain this effect include increases in endothelial injury, smooth muscle cell proliferation, low-density lipoprotein oxidation and changes in haemostatic balance. Renal patients have a much greater incidence of hyperhomocysteinaemia and this may be explained by decreases in either the renal or extrarenal metabolism of the compound. We conclude that data from long-term placebo-controlled trials are urgently required to determine whether hyperhomocysteinaemia in renal patients is a cause of CVD events and requires therapeutic targeting.

Homocysteine induces trophoblast cell death with apoptotic features

Hyperhomocysteinemia has been suggested as a possible risk factor in women suffering from habitual abortions, placental abruption or infarcts, preeclampsia, and/or intrauterine growth retardation. However, little is known about the pathogenic mechanisms underlying the action of homocysteine. The present study investigated the in vitro ability of homocysteine to affect trophoblast gonadotropin secretion and to induce cell death. In primary human trophoblast cells, homocysteine treatment (20 micromol/L) resulted in cellular flattening and enlargement, extension of pseudopodia, and cellular vacuolization. Cellular detachment, apoptosis, and necrosis were favored. With in situ nick end labeling, we investigated DNA degradation, and we used M30 CytoDEATH to selectively stain the cytoplasm of apoptotic cells. Cytochrome c release from mitochondria to the cytosol and DNA cleavage in agarose gel have been investigated. Homocysteine, but not cysteine, induced trophoblast apoptosis and significantly reduced human chorionic gonadotropin secretion. These findings suggest that trophoblast cell death might represent a pathogenic mechanism by which homocysteine may cause pregnancy complications related to placental diseases.

S-Adenosylhomocysteine Enhances Hydrogen Peroxide-Induced DNA Damage by Inhibition of DNA Repair in Two Cell Lines

It has been proposed that hyperhomocysteinemia may exert its pathogenic effects largely through metabolic accumulation of S-adenosylhomocysteine (SAH), a strong noncompetitive inhibitor of most methyltransferases. Here, we investigated the effects of SAH on H(2)O(2)-induced cellular DNA damage in comparison with the effects of homocysteine (Hcy) in a mouse endothelial cell line and a human intestinal cell line. Cells were preincubated for 2 h with H(2)O(2) (20 microM) followed by incubation with SAH or Hcy for 3 h. DNA strand breakage was determined using comet assay and DNA repair capacity determined using the same assay over time at 1, 2, and 3 h during SAH incubation. In both types of cells, SAH at 0.25-2 microM strongly and dose dependently enhanced H(2)O(2)-dependent DNA damage and inhibited DNA repair, whereas Hcy had a much weaker effect. SAH markedly increased uracil misincorporation, and this effect was also much stronger than that of Hcy. Taken together, our results show that SAH potentiates H(2)O(2)-induced DNA damage in cell cultures through impaired DNA repair capability and suggest that such effects are related to uracil misincorporation. Although the in vivo relevance of our findings is unclear, the biological significance of SAH-mediated detrimental effect, secondary to elevated intracellular Hcy, is an interesting area awaiting further exploration.

The maturing of hormesis as a credible dose-response model

Hormesis is a dose-response phenomenon that has received little recognition, credibility and acceptance as evidenced by its absence from major toxicological/risk assessment texts, governmental regulatory dose-response modeling for risk assessment, and non-visibility in major professional toxicological society national meetings. This paper traces the historical evolution of the hormetic dose-response hypothesis, why this model is not only credible but also more common than the widely accepted threshold model in direct comparative evaluation, and how the toxicological community made a critical error in rejecting hormesis, a rejection sustained over 70 years.

A novel homocysteine-responsive gene, smap8, modulates mitogenesis in rat vascular smooth muscle cells

We isolated the cDNA of a gene, designated smooth muscle-associated protein 8 (smap8), during a search for new genes expressed in human aortic smooth muscle cells. The full-length smap8 cDNA is 3241 bp long and contains an open reading frame of 1113 bp encoding an approximately 45 kDa soluble protein identical to NDRG4 protein. Smap8 mRNA was expressed predominantly in the brain and heart, and moderately in vascular smooth muscle cells. Expression of smap8 mRNA was induced within 3-12 h by treatment with 10 mm homocysteine in rat aortic smooth muscle cells (A10 cells). Expression of exogenous smap8 markedly reduced both the proliferation and migration rates of rat A10 cells, however, PDGF-induced proliferation was significantly enhanced in smap8-expressed cells compared with mock-transfected cells. To ascertain the involvement of smap8 in mitogenesis, we tested the effects of stimulation of smap8, MEK1/2 or ERK1/2, which is known as a proliferation relating intermediate, by various growth factors and cytokines. PDGF was the most prominent in promoting phosphorylation of the smap8 protein. PDGF-dependent phosphorylation of smap8 was induced prior to ERK1/2 activation, and was repressed by staurosporine, a general inhibitor of serine/threonine kinases. Furthermore, activation of both MEK1/2 and ERK1/2 was markedly enhanced in these cells. Smap8 might therefore regulate the potentiation of ERK1/2 signalling induced by PDGF treatment. Our results imply that smap8 is involved in the regulation of mitogenic signalling in vascular smooth muscle cells, possibly in response to a homocysteine-induced injury.

Plasma total cysteine, pregnancy complications, and adverse pregnancy outcomes: the Hordaland Homocysteine Study

BACKGROUND

Total homocysteine (tHcy) is associated with pregnancy complications and adverse pregnancy outcomes. The associations of plasma total cysteine (tCys) with such outcomes have not been investigated in large populations.

OBJECTIVE

We investigated the association between plasma tCys and pregnancy complications, congenital malformations, and other adverse pregnancy outcomes.

DESIGN

The plasma tCys concentrations of 5883 women aged 40-42 y that were measured in 1992-1993 during a cardiovascular health screening were compared with the outcomes and complications of 14492 pregnancies in the same women that were registered in the Medical Birth Registry of Norway from 1967 to 1996.

RESULTS

After adjustment for parity, mother's age, tHcy, total cholesterol, body mass index, smoking, and coffee drinking, high plasma tCys concentrations (above the 95th percentile) were associated with significantly higher risks of preeclampsia [n = 342; odds ratio (OR): 1.6; 95% CI: 1.1, 2.4; P = 0.03], premature delivery (n = 774; OR: 1.8; 95% CI: 1.3, 2.5; P = 0.001), and very low birth weight (n = 175; OR: 2.0; 95% CI: 1.1, 3.9; P = 0.03) than were lower plasma tCys concentrations. tCys was not associated with the risk of placental abruption. High tCys concentrations showed a weak association with congenital malformations and stillbirths with birth weight <1500 g. The associations were independent of the tHcy concentrations.

CONCLUSION

High tCys concentrations were associated with risks of preeclampsia, premature delivery, and low birth weight.

Homocysteine and occlusive arterial disease

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Role of abnormal methionine metabolism in alcoholic liver injury

Methionine catabolism occurs mostly in the liver through the formation of S-adenosylmethionine (SAM) in a reaction catalyzed by methionine adenosyltransferase (MAT). S-adenosylmethionine is the principal biologic methyl donor, a precursor for polyamines, and in liver, it is also a precursor for reduced glutathione (GSH). Liver-specific and non-liver-specific MAT are products of two different genes, MAT1A and MAT2A, respectively. Mature liver expresses MAT1A, whereas MAT2A is expressed in extrahepatic tissues and induced during liver growth and de-differentiation. The type of MAT expressed by the cell affects the steady-state SAM level, DNA methylation, and growth rate. This has been demonstrated further by using the MAT1A knockout mouse model in which hepatic SAM and GSH levels decrease, the liver becomes larger and more susceptible to injury, and steatohepatitis develops spontaneously. Altered methionine metabolism in alcoholic liver disease results in decreased transmethylation and transsulfuration, changes that may play important pathogenic roles. Major changes include a relative switch in MAT expression; decreased hepatic SAM, GSH, and DNA methylation levels; decreased homocysteine metabolism; and hyperhomocysteinemia. Consequences of hepatic DNA hypomethylation include increased expression of c-myc and DNA strand break accumulation. One possible consequence of hyperhomocysteinemia is increased fibrogenesis. Abnormal methionine metabolism may also occur in Kupffer cells, which express both forms of MAT. If SAM levels also decrease in these cells, this may contribute to the induction of tumor necrosis factor (TNF) expression and release. In summary, altered hepatic methionine metabolism can have serious consequences that affect not only hepatocytes, but also hepatic stellate and Kupffer cells. These changes can lead to impaired antioxidant defense, altered gene expression, promotion of fibrogenesis, and even hepatocarcinogenesis.

Differential effects of homocysteine on porcine endothelial and vascular smooth muscle cells

High concentrations of homocysteine damage endothelial cells and lower concentrations increase vascular smooth muscle cell (VSMC) growth. This study investigated the effects of various concentrations of homocysteine on endothelial cells (VECs) and VSMCs in terms of cell survival, proliferation, and function. VECs and VSMCs from porcine thoracic aorta were studied. These cells were exposed to homocysteine in concentrations of 20 microM, 400 microM, and 1 mM every 8 h for 24 h, and its effect on cell survival, proliferation, and function were studied using methylthiazoletetrazolium assay, [3H]-thymidine incorporation test, and 6-keto-prostaglandin F1alpha enzyme-linked immunosorbent assay for VECs, and platelet-derived growth factor (PDGF) enzyme-linked immunosorbent assay for VSMCs, respectively. In VECs, 20 microM of homocysteine reduced the viable cell count to 95 +/- 31%, 400 microM reduced it to 89 +/- 35%, 1,000 microM reduced it to *58 +/- 29% (control = 100 +/- 30%, n = 18, *p < 0.05). In VSMCs, 20 microM of homocysteine slightly increased the viable cell count to 106 +/- 30%, but there was no statistical significance; 400 microM of homocysteine reduced the viable cell count to *74 +/- 29%, 1,000 microM to *50 +/- 24% (control = 100 +/- 28%, n = 18, *p < 0.05). In VECs, 20 microM of homocysteine reduced [3H]-thymidine uptake by 98 +/- 14%, 400 microM reduced it by *82 +/- 17%, 1,000 microM reduced it by *66 +/- 17% (control = 100 +/- 12, n = 6, *p < 0.05), respectively. But in VSMCs, 20 microM of homocysteine significantly increased [3H]-thymidine uptake (*131 +/- 16%), and thereafter, homocysteine decreased VSMCs [3H]-thymidine uptake, 400 microM by *24 +/- 7%, 1,000 microM by *29 +/- 10% (control = 100 +/- 16, n = 6, *p < 0.05), respectively. Homocysteine decreased VEC prostacyclin secretion in a dose-dependent manner, 20 microM by 105 +/- 0.65 pg/100 microl, 400 microM by *100 +/- 2.37 pg/100 microl, 1,000 microM by *93 +/- 2.54 pg/100 microl (control = 107 +/- 1.26 pg/100 microl, n = 6, *p = 0.007). In VSMCs, 20 microM of homocysteine slightly increased PDGF secretion by 62.2 +/- 20.7 pg/100 microl, but there was little statistical significance (p = 0.13); 400 microM of homocysteine reduced PDGF secretion by *28.9 +/- 10.7 pg/100 microl, and 1,000 microM reduced it by *21.3 +/- 4.7 pg/100 microl (control = 54.5 +/- 9.3 pg/100 microl, n = 6, *p < 0.05). High concentrations of homocysteine damaged both VECs and VSMCs with respect to cell survival, proliferation, and function. By increasing exposure to homocysteine, it was shown that physiologic high concentrations of homocysteine enhanced VSMC proliferation.

Homocysteine in myointimal hyperplasia

INTRODUCTION

homocysteine, a sulphur-containing non-essential amino acid, appears to play a role in the pathophysiology of atherosclerosis. However, its role in myointimal hyperplasia, the cause of almost 30% of failures of interventional therapeutic procedures, is much less clear.

METHODS

a review of the published scientific data concerning the role of homocysteine in myointimal hyperplasia was performed using MEDLINE and other on-line databases. Evidence was sought from cell culture experiments, animal models and clinical studies.

RESULTS

several clinical studies have recently been published linking plasma homocysteine levels to restenosis in coronary and peripheral arterial disease. However, several contradictory studies also exist making the role of homocysteine unclear. There are currently no published randomised trials. Cell culture and animal model experiments have elucidated several potential mechanisms by which may stimulate myointimal hyperplasia. Possible mechanisms include endothelial cell activation with the enhanced release of inflammatory cytokines and growth factors and a direct effect on vascular smooth muscle cell migration and proliferation.

CONCLUSIONS

further studies are required before the true role of homocysteine in the pathogenesis of myointimal hyperplasia can be clearly evaluated. If evidence does confirm a role, the ease with which homocysteine levels can be normalised makes it an attractive alternative therapeutic target for intervention.

Homocyst(e)ine and coronary heart disease: pharmacoeconomic support for interventions to lower hyperhomocyst(e)inaemia

Homocyst(e)ine, a sulphur-containing amino acid, is an intermediate formed during the metabolism of the essential amino acid methionine. Biological and epidemiological evidence suggest that elevated plasma levels of homocyst(e)ine are a risk factor for atherosclerosis and coronary heart disease (CHD). In the general US population, hyperhomocyst(e)inaemia is common and most often due to mild nutritional deficiencies in the B vitamins (folic acid, vitamin B(12) and vitamin B(6)). While high homocyst(e)ine levels can be effectively lowered using folic acid and other B vitamins, it is unknown whether such vitamin therapy will lead to clinical benefits. Given that strategies for homocyst(e)ine-lowering are safe and inexpensive, however, even small reductions in CHD risk will be highly cost effective. Thus, it may be prudent for patients to ensure an adequate daily intake of dietary folic acid and other B vitamins and for physicians to screen high-risk adults such as those with established CHD as we await definitive results from ongoing clinical trials.

Decreased rate of coronary restenosis after lowering of plasma homocysteine levels

BACKGROUND

We have previously demonstrated an association between elevated total plasma homocysteine levels and restenosis after percutaneous coronary angioplasty. We designed this study to evaluate the effect of lowering plasma homocysteine levels on restenosis after coronary angioplasty.

METHODS

A combination of folic acid (1 mg), vitamin B12 (400 microg), and pyridoxine (10 mg)--referred to as folate treatment--or placebo was administered to 205 patients (mean [+/-SD] age, 61+/-11 years) for six months after successful coronary angioplasty in a prospective, double-blind, randomized trial. The primary end point was restenosis within six months as assessed by quantitative coronary angiography. The secondary end point was a composite of major adverse cardiac events.

RESULTS

Base-tine characteristics and initial angiographic results after coronary angioplasty were similar in the two study groups. Folate treatment significantly lowered plasma homocysteine levels from 11.1+/-4.3 to 7.2+/-2.4 micromol per liter (P<0.001). At follow-up, the minimal luminal diameter was significantly larger in the group assigned to folate treatment (1.72+/-0.76 vs. 1.45+/-0.88 mm, P=0.02), and the degree of stenosis was less severe (39.9+/-20.3 vs. 48.2+/-28.3 percent, P=0.01). The rate of restenosis was significantly lower in patients assigned to folate treatment (19.6 vs. 37.6 percent, P=0.01), as was the need for revascularization of the target lesion (10.8 vs. 22.3 percent, P=0.047).

CONCLUSIONS

Treatment with a combination of folic acid, vitamin B12, and pyridoxine significantly reduces homocysteine levels and decreases the rate of restenosis and the need for revascularization of the target lesion after coronary angioplasty. This inexpensive treatment, which has minimal side effects, should be considered as adjunctive therapy for patients undergoing coronary angioplasty.

Plasma homocysteine, methylenetetrahydrofolate reductase mutation and carotid damage in elderly healthy women

Plasma homocysteine (Hcy) is an independent vascular risk factor. Its remethylation to methionine is regulated by the activity of the enzyme 5,10-methylene tetrahydrofolate reductase (MTHFR). A C-to-T substitution at nucleotide 677 of the MTHFR gene is frequently associated to hyperhomocysteinemia. In this study, we evaluated the relationship among MTHFR C677T polymorphism, Hcy and some ultrasonographic parameters at the level of carotid arteries in 120 elderly women with normal ECG, normal blood pressure values, total cholesterol <250 mg/dl, normal glucose tolerance, normal albumin excretion rate. In all subjects, we measured Hcy by HPLC, MTHFR mutation by polymerase chain reaction followed by HinfI digestion and intima-media thickness (IMT), peak velocity of the systolic flow (SP(V)), end-diastolic velocity (ED(V)) and resistance and pulsatility indexes of intracranial circulation (RI and PI) by ultrasound imaging. Twenty-eight women were homozygotes for the wild type allele (Ala/Ala), 72 were heterozygotes (Ala/Val) and 20 were homozygotes for the mutation (Val/Val). Groups were comparable for age, blood pressure values and plasma lipid levels. Hcy was higher in Val/Val group; moreover, after adjustment for confounding factors, Val/Val had significantly greater IMT and ED(V) (P<0.001 and P<0.05, respectively). Logistic analysis revealed that Val/Val genotype was the strongest risk factor for IMT (OR 30.8, 95% CI 2.82-335.6). Our results show that, in elderly healthy women, Val/Val homozygosity for C677T mutation in MTHFR gene could identify subjects at risk for asymptomatic carotid atherosclerotic impairment.

Serum homocysteine does not associate with uncomplicated coronary heart disease

BACKGROUND

Elevated serum homocysteine concentrations have been related to coronary heart disease. However, the association has not indisputably been proven, and the mechanisms by which homocysteine may be atherogenic have only partially been elucidated. The objective of the present study was to investigate whether serum homocysteine is associated with angina pectoris and myocardial infarction.

METHODS

We compared serum homocysteine concentrations in subjects with clinical evidence of angina pectoris or history of myocardial infarction to age-matched controls. The study included 248 males, who participated in a large cross-sectional risk factor survey carried out in five geographic areas in Finland.

RESULTS

Serum homocysteine concentration was significantly higher in subjects with a history of myocardial infarction compared to controls (15.3 micromol L-1 and 13.9 micromol L-1 respectively, P = 0.037). In a logistic regression model including several cardiovascular risk factors, serum homocysteine was significantly associated with myocardial infarction (95% CI 1.0157-1.2990, P = 0.027). Serum homocysteine concentrations did not differ between subjects with angina pectoris and age-matched controls (13.9 micromol L-1 and 14.2 micromol L-1 respectively).

CONCLUSIONS

Our results suggest that elevated serum homocysteine is associated with myocardial infarction but not with uncomplicated coronary heart disease.

Hormesis: U-shaped dose responses and their centrality in toxicology

The fundamental nature of the dose response is neither linear or threshold, but rather U-shaped. When studies are properly designed to evaluate biological activity below the traditional toxicological threshold, low-dose stimulatory responses are observed with high frequency and display specific quantitative features. With a few exceptions, the low-dose stimulatory response is usually not more than twofold greater than the control response, with a stimulatory zone that is more variable, ranging from less than tenfold to more than several orders of magnitude of the dose. Considerable mechanistic evidence indicates that hormetic effects represent overcompensation in response to disruptions in homeostasis that are mediated by agonist concentration gradients with different affinities for stimulatory and inhibitory regulatory pathways.

Current concepts in the pathogenesis of alcoholic liver injury

Alcoholic liver disease (ALD) develops as a consequence of priming and sensitizing mechanisms rendered by cross-interactions of primary mechanistic factors and secondary risk factors. This concept, albeit not novel, is becoming widely accepted by the field, and more research is directed toward identifying and characterizing the interfaces of the cross-interactions to help understand individual predisposition to the disease. Another pivotal development is the beginning of cell type-specific research to elucidate specific contributions not only of hepatocytes, but also of hepatic macrophages, liver-associated lymphocytes, sinusoidal endothelial cells, and hepatic stellate cells to sensitizing and priming mechanisms. In particular, the critical role of hepatic macrophages has been highlighted and the priming mechanisms concerning this paracrine effect have been proposed. Glutathione depletion in hepatocyte mitochondria is considered the most important sensitizing mechanism. One of the contributing factors is decreased methionine metabolism. Remaining key questions include how altered methionine metabolism contribute to the pathogenesis of ALD; how cross-talk among nonparenchymal liver cells or between nonparenchymal cells and hepatocytes leads to ALD; how dysfunctional mitochondria determine the type of cell death in ALD; and what secondary factors are critical for the development of advanced ALD such as alcoholic hepatitis and cirrhosis.

Comparative methodologic study of NFkappaB activation in cultured endothelial cells

The transcriptional regulatory protein nuclear factor kappaB (NFkappaB) participates in the control of gene expression of many modulators of the inflammatory and immune responses. Various activators trigger NFkappaB release and nuclear translocation after phosphorylation and proteolytic degradation of IkappaB. This study evaluated the abilities of fluorescence and confocal microscopies, laser scanning cytometry (LSC), electrophoretic mobility-shift assay (EMSA), and Western blotting to detect NFkappaB activation in endothelial cells (ECs) and to investigate the role of homocysteine (Hcy) in NFkappaB activation. ECs were treated with interleukin-1B (10 ng/mL) or Hcy thiolactone (1 and 5 mmol/L) as NFkappaB activators. Hcy, a thiol-containing amino acid, has been shown to directly damage ECs in vitro. Experimental evidence suggests that the atherogenic propensity associated with hyperhomocysteinemia results from EC dysfunction. When ECs were pretreated with an inhibitor (pyrrolidine dithiocarbamate, 100 micromol/L) or with staurosporine (5 microL/mL), no NFkappaB activation was observed. NFkappaB activation in ECs could be detected with all five techniques, clearly showing NFkappaB translocation from the cytoplasm to the nuclei. Confocal microscopy was more sensitive and less subjective than immunofluorescence microscopy. LSC was even more sensitive, specific, and reproducible. EMSA, the reference method, has the disadvantages of being radioactive, expensive, and time consuming. Western blot analysis detected the NFkappaB p50 subunit implicated in NFkappaB activation. The techniques usually used to detect NFkappaB activation in ECs are immunofluorescence microscopy and confocal microscopy, LSC, EMSA, and Western blot analysis, but none of them is ready for routine use.

Homocysteine, B vitamins, and coronary artery disease

This article discusses the metabolism of homocysteine, factors affecting its plasma level, and the evidence for its role in the pathogenesis of vascular disease. The treatment of hyperhomocysteinemia and its possible impact on vascular disease prevention and progression are described also.

Effects of homocysteine on smooth muscle cell proliferation in both cell culture and artery perfusion culture models

BACKGROUND

Hyperhomocysteinemia is associated with increased risk for vascular disease. However, the pathogenic mechanisms of homocysteine are largely unknown. We evaluated the effects of homocysteine on smooth muscle cell (SMC) and endothelial cell proliferation in cell culture and on SMC proliferation of balloon angioplasty-injured arteries in a perfusion culture model.

METHODS

Human and pig SMCs and endothelial cells were cultured with variable amounts of homocysteine for 72 h and the total cells were counted using a hemocytometer. Fresh pig carotid arteries were harvested from a local slaughterhouse and cultured in a newly designed artery perfusion culture system. Five groups of arteries (six per group) were cultured for 48 h under different conditions: normal control, balloon angioplasty injury alone, and injury with three different doses of homocysteine. Vessel viability was evaluated. SMC proliferation was assayed by bromodeoxyuridine (BrdU) DNA labeling.

RESULTS

At concentrations equivalent to those in human hyperhomocysteinemia, homocysteine significantly stimulated both cultured human and pig SMC proliferation with a dose-dependent effect, while it inhibited cultured endothelial cell growth. Perfusion-cultured pig carotid arteries remained contractile in response to norepinephrine and relaxant to nitroglycerine, and viable cells were also isolated from the cultured arteries. SMC proliferation (BrdU index) showed significant differences among the groups. SMC proliferation was stimulated by vascular injury and further enhanced by homocysteine in a dose-dependent manner. The proliferative response occurred strongly on the luminal side of the vessel wall, with the effects tapering toward the adventitia.

CONCLUSIONS

Homocysteine had a mitogenic effect on vascular SMCs and a cytotoxic effect on endothelial cells. This differential effect of homocysteine on vascular cells may represent a pathogenic mechanism of vascular lesion formation in patients with hyperhomocysteinemia.

Folic acid inhibits homocysteine-induced proliferation of human arterial smooth muscle cells

PURPOSE

An elevated plasma homocysteine level has been identified as an independent risk factor for atherosclerosis. Whether this represents a marker for vascular disease or a direct effect on the vasculature remains unclear. Because vascular smooth muscle cells (VSMCs) play an integral role in the atherosclerotic process, we studied the effect of homocysteine on human infragenicular VSMC proliferation and the role of folic acid in reversing the homocysteine effect.

METHODS

Human infragenicular VSMCs harvested from amputation specimens were studied. Various cell groups were exposed to physiologic (6.25 micromol/L and 12.5 micromol/L) and pathologic (25 micromol/L to 500 micromol/L) concentrations of homocysteine. Similar groups were simultaneously exposed to 20 nmol/L of folic acid. Cell counts and DNA synthesis, as reflected by [methyl-(3)H]-thymidine incorporation, were performed at 6 days and 24 hours, respectively. Additional groups were exposed to various combinations of folic acid (20 nmol/L), vitamin B(6) (145 nmol/L), and vitamin B(12) (0.45 nmol/L) in the presence of homocysteine (25, 50, and 250 micromol/L).

RESULTS

Homocysteine resulted in a dose-dependent increase in DNA synthesis and cell proliferation. Cell counts increased significantly at homocysteine concentrations ranging from 25 micromol/L to 500 micromol/L (P <.05), with a maximal increase of 98% at 500 micromol/L of homocysteine. The addition of 20 nmol/L folic acid resulted in significant inhibition of cell proliferation at all homocysteine concentrations studied (P <.001). Maximal inhibition of 70% occurred in the cells exposed to 50 micromol/L of homocysteine. The increases in [methyl-(3)H]-thymidine incorporation ranged from 36% at 6 micromol/L homocysteine to a maximum of 247% at 500 micromol/L homocysteine. All increases were statistically significant (P <.05). The addition of 20 nmol/L folic acid resulted in significant inhibition of DNA synthesis (P <.002). Vitamins B(6) and B(12) did not demonstrate significant antiproliferative properties.

CONCLUSION

A possible role of homocysteine in the formation of atherosclerotic lesions is through a direct proliferative effect on VSMCs in a dose-dependent fashion. Folic acid intake at levels available in dietary supplements may prove protective in hyperhomocysteinemia-induced atherosclerosis. Vitamins B(6) and B(12) alone do not appear to exhibit a substantial inhibitory effect in the setting of elevated homocysteine levels.

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.