Influence of hyperhomocysteinemia on the cellular redox state--impact on homocysteine-induced endothelial dysfunction.

Hyperhomocysteinemia is an independent risk factor for the development of atherosclerosis. An increasing body of evidence has implicated oxidative stress as being contributory to homocysteine's deleterious effects on the vasculature. Elevated levels of homocysteine may lead to increased generation of superoxide by a biochemical mechanism involving nitric oxide synthase, and, to a lesser extent, by an increase in the chemical oxidation of homocysteine and other aminothiols in the circulation. The resultant increase in superoxide levels is further amplified by homocysteine-dependent alterations in the function of cellular antioxidant enzymes such as cellular glutathione peroxidase or extracellular superoxide dismutase. One direct clinical consequence of elevated vascular superoxide levels is the inactivation of the vasorelaxant messenger nitric oxide, leading to endothelial dysfunction. Scavenging of superoxide anion by either superoxide dismutase or 4,5-dihydroxybenzene 1,3-disulfonate (Tiron) reverses endothelial dysfunction in hyperhomocysteinemic animal models and in isolated aortic rings incubated with homocysteine. Similarly, homocysteine-induced endothelial dysfunction is also reversed by increasing the concentration of the endogenous antioxidant glutathione or overexpressing cellular glutathione peroxidase in animal models of mild hyperhomocysteinemia. Taken together, these findings strongly suggest that the adverse vascular effects of homocysteine are at least partly mediated by oxidative inactivation of nitric oxide.     

Interactions of homocysteine, nitric oxide, folate and radicals in the progressively damaged endothelium.

The endothelium exerts fundamental control over vascular tone, and injury to the endothelium followed by dysfunction is an early key event preceding manifestation of vessel pathology. Both elevated plasma homocysteine and low folate status have been identified as major and independent risk factors for atherosclerosis and have stirred an enormous and still increasing interest. The damaging effects of hyperhomocysteinemia on endothelial function are, at least in part, reversible through folate supplementation. Because of the inverse relationship between plasma folate and homocysteine levels, however, it is difficult to discriminate between their respective effects. Endothelial dysfunction refers mainly to reduced bioavailability of nitric oxide (NO), which is involved in homocysteinemediated vascular damage. Accumulating evidence further suggests that radical oxygen species are fundamentally involved in hyperhomocysteinemia. NO production is determined by cofactors such as tetrahydrobiopterin, which is oxidized and depleted in conditions of oxidant stress by peroxynitrite. Deficiency of tetrahydrofolate contributes to uncoupling, turning the NO synthase into a superoxide radical-producing enzyme. It appears that progression of vascular disease is likely to determine the multiple interactions between homocysteine, NO, oxygen radicals and folate. Folate has only recently been found to exert direct anti-oxidative effects and contribute to restoration of impaired NO metabolism. Understanding of the complex interactions between homocysteine, radicals, NO and folate offers promising perspectives in the individual treatment of vascular disease. Thus, preventive and therapeutic strategies may require a more distinct approach and better discrimination of target groups for greatest possible efficacy.     

DACH-LIGA homocystein (german, austrian and swiss homocysteine society): consensus paper on the rational clinical use of homocysteine, folic acid and B-vitamins in cardiovascular and thrombotic diseases: guidelines and recommendations.

About half of all deaths are due to cardiovascular disease and its complications. The economic burden on society and the healthcare system from cardiovascular disability, complications, and treatments is huge and getting larger in the rapidly aging populations of developed countries. As conventional risk factors fail to account for part of the cases, homocysteine, a "new" risk factor, is being viewed with mounting interest. Homocysteine is a sulfur-containing intermediate product in the normal metabolism of methionine, an essential amino acid. Folic acid, vitamin B12, and vitamin B6 deficiencies and reduced enzyme activities inhibit the breakdown of homocysteine, thus increasing the intracellular homocysteine concentration. Numerous retrospective and prospective studies have consistently found an independent relationship between mild hyperhomocysteinemia and cardiovascular disease or all-cause mortality. Starting at a plasma homocysteine concentration of approximately 10 micromol/l, the risk increase follows a linear dose-response relationship with no specific threshold level. Hyperhomocysteinemia as an independent risk factor for cardiovascular disease is thought to be responsible for about 10% of total risk. Elevated plasma homocysteine levels (>12 micromol/l; moderate hyperhomocysteinemia) are considered cytotoxic and are found in 5 to 10% of the general population and in up to 40% of patients with vascular disease. Additional risk factors (smoking, arterial hypertension, diabetes, and hyperlipidemia) may additively or, by interacting with homocysteine, synergistically (and hence over-proportionally) increase overall risk. Hyperhomocysteinemia is associated with alterations in vascular morphology, loss of endothelial anti-thrombotic function, and induction of a procoagulant environment. Most known forms of damage or injury are due to homocysteine-mediated oxidative stress. Especially when acting as direct or indirect antagonists of cofactors and enzyme activities, numerous agents, drugs, diseases, and lifestyle factors have an impact on homocysteine metabolism. Folic acid deficiency is considered the most common cause of hyperhomocysteinemia. An adequate intake of at least 400 microg of folate per day is difficult to maintain even with a balanced diet, and high-risk groups often find it impossible to meet these folate requirements. Based on the available evidence, there is an increasing call for the diagnosis and treatment of elevated homocysteine levels in high-risk individuals in general and patients with manifest vascular disease in particular. Subjects of both populations should first have a baseline homocysteine assay. Except where manifestations are already present, intervention, if any, should be guided by the severity of hyperhomocysteinemia. Consistent with other working parties and consensus groups, we recommend a target plasma homocysteine level of <10 micromol/l. Based on various calculation models, reduction of elevated plasma homocysteine concentrations may theoretically prevent up to 25% of cardiovascular events. Supplementation is inexpensive, potentially effective, and devoid of adverse effects and, therefore, has an exceptionally favorable benefit/risk ratio. The results of ongoing randomized controlled intervention trials must be available before screening for, and treatment of, hyperhomocysteinemia can be recommended for the apparently healthy general population.     

冠心病患者同型半胱氨酸水平变化与血管内皮功能的关系

目的:探讨血浆同型半胱氨酸水平变化对冠心病患病的意义以及与内皮素、一氧化氮的相关性。方法:分别测定115例冠心病患者和52例正常对照组血浆同型半胱氨酸及血脂各参数、内皮素、一氧化氮水平,并进行比较。结果:冠心病组的同型半胱氨酸、内皮素水平均明显高于对照组(P<0.01),而一氧化氮低于对照组(P<0.01)。结论:半胱氨酸与冠心病具有密切联系,高同型半胱氨酸是同型半胱氨酸患者的一个新的危险因素,检测血浆同型半胱氨酸对预防和诊治冠心病具有一定临床价值。     

Folate,homocysteine, endothelial function and cardiovascular disease. What is the link?

Elevated plasma homocysteine concentrations are associated with an increased risk of cardiovascular disease, but the relationship has not been proven to be causal. Folate is the strongest nutritional and pharmacological determinant of plasma homocysteine concentrations, which also interact with the genetic variation in methylenetetrahydrofolate reductase (MTHFR). Endothelial dysfunction due to reduced nitric oxide bioavailability is an early feature of vascular pathology. This can be assessed noninvasively by measurement of flow-mediated dilatation. Human studies on folic acid, homocysteine and endothelial function are reported. It is proposed that folic acid in high doses may have beneficial effects on endothelial function, which are independent of homocysteine lowering.     

Rapid analysis of total plasma homocysteine by tandem mass spectrometry

Elevated plasma homocysteine levels may be an independent risk factor for premature vascular disease. Early detection and population screening are warranted to recognise hyperhomocysteinemia and initiate homocysteine lowering therapy. Current methods for homocysteine analysis are time consuming, labor intensive and/or expensive. We developed a sensitive and fast method for homocysteine analysis based on tandem mass spectrometry that avoids the need for derivatization and preanalytical chromatography.     

Hyperhomocysteinemia and cardiovascular risk in postmenopausal women: the role of folate supplementation.

In the postmenopausal period, cardiovascular diseases are a frequent chronic condition leading to high risk of myocardial infarction and death. Recently hyperhomocysteinemia and even mildly elevated plasma concentrations of homocysteine have been recognized as independent risk factors for vascular damage predisposing to arteriosclerosis. Elevated plasma levels of homocysteine induce vascular endothelial damage and are frequently associated with low folate levels. In this review we evaluate literature data on some aspects related to menopause and homocysteine metabolism. In particular, we show the effect of folic acid supplementation on homocysteine concentrations and on homocysteine-related thiols, such as cysteine and cysteine-glycine, as well as the relationship with glucose, insulin, and lipidic metabolism in postmenopausal women. We also analyze the influence of folate supplementation on endothelial function, by brachial artery flow-mediated dilatation (endothelium-dependent) and nitroglycerine-induced dilatation (endothelium-independent) before and after a methionine load. Folate administration in postmenopausal women is able to reduce high plasma homocysteine levels and to modify impaired endothelial function induced by hyperhomocysteinemia.     

Homocysteine and asymmetric dimethylarginine (ADMA): biochemically linked but differently related to vascular disease in chronic kidney disease.

Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, is formed by methylation of arginine residues in proteins and released after proteolysis. In this reaction, S-adenosylmethionine is methyldonor and S-adenosylhomocysteine the demethylated product. ADMA and homocysteine are thus biochemically linked. Both plasma homocysteine and ADMA concentrations are increased in patients with renal dysfunction, probably as a result of an impairment in their metabolic, but not urinary, clearance. Hyperhomocysteinemia has been associated with an increased risk of cardiovascular disease in end-stage renal disease, especially in patients without malnutrition and inflammation. Also, plasma ADMA levels have been associated with cardiovascular disease in renal failure patients. Both homocysteine and ADMA are thought to mediate their adverse vascular effects by impairing endothelial, nitric oxide-dependent function resulting in decreased vasodilatation, increased smooth muscle cell proliferation, platelet dysfunction and increased monocyte adhesion. At the same time, it has been shown that the correlation between plasma ADMA and homocysteine is weak and that, in renal patients, the association of plasma ADMA carotid intima-media thickness, cardiovascular events and overall mortality is independent of homocysteine. This indicates that the negative vascular effects of ADMA and homocysteine have a different etiology. Treatment with folic acid substantially lowers homocysteine, but not ADMA concentration. So far, homocysteine-lowering therapy has not been very successful in decreasing cardiovascular disease. In patients with renal failure, ADMA reduction may be an interesting new goal in the prevention of cardiovascular disease.     

Hyperhomocysteinemia and the risk of restenosis after coronary artery stenting: fact or fiction?

The incidence of restenosis after coronary artery stent placement is approximately 38%. An interesting view has been stipulated: that hyperhomocysteinemia may be partly responsible for in-stent restenosis. Epidemiologic evidence exists that is persuasive in suggesting that individuals with occlusive vascular disease have a higher blood homocysteine concentration than control subjects. Thus, elevated plasma levels of homocysteine have been implicated as a risk factor for coronary artery disease. The composition of the current clinical knowledge on the question of whether hyperhomocysteinemia is a significant factor for restenosis of coronary artery stents consists of several trials with different approaches, objectives and outcomes. However, the current studies that have been published in the peer-reviewed medical literature have not reached a consensus as to whether an elevated plasma level of homocysteine is an independent risk factor responsible for restenosis following stent implantation. Our current knowledge as to the place of plasma homocysteine levels in the development of in-stent restenosis seems incomplete, and in the realm of homocysteine and restenosis of stents, there are plenty of questions that still remain to be answered.     

Hyperhomocysteinemia and the risk of restenosis after coronary artery stenting: fact or fiction?

The incidence of restenosis after coronary artery stent placement is approximately 38%. An interesting view has been stipulated: that hyperhomocysteinemia may be partly responsible for in-stent restenosis. Epidemiologic evidence exists that is persuasive in suggesting that individuals with occlusive vascular disease have a higher blood homocysteine concentration than control subjects. Thus, elevated plasma levels of homocysteine have been implicated as a risk factor for coronary artery disease. The composition of the current clinical knowledge on the question of whether hyperhomocysteinemia is a significant factor for restenosis of coronary artery stents consists of several trials with different approaches, objectives and outcomes. However, the current studies that have been published in the peer-reviewed medical literature have not reached a consensus as to whether an elevated plasma level of homocysteine is an independent risk factor responsible for restenosis following stent implantation. Our current knowledge as to the place of plasma homocysteine levels in the development of in-stent restenosis seems incomplete, and in the realm of homocysteine and restenosis of stents, there are plenty of questions that still remain to be answered.     

Homocysteine and diabetic macroangiopathy

Moderate hyperhomocysteinemia is one of risk factors for arteriosclerotic disease. In diabetic patients, hyperhomocysteinemia is an independent risk factor for macroangiopathy and mortality. Homocysteinemia is also associated with diabetic microangiopathy, silent stroke, and cognitive impairment. However, excluding those with nephropathy or microangiopathy, plasma homocysteine is lower in diabetic patients than non-diabetic controls. Oral treatment with folic acid, vitamin B12 and B6 reduces plasma homocysteine concentration about by 30%. The vitamin treatment for reduction of hyperhomocysteinemia improves endothelial dysfunction and retards carotid atherosclerosis. Few randomized control trials have showed a positive effect of the vitamin treatment on prevention from stroke and ischemic heart disease. Further prospective intervention studies are necessary to address the issue whether lowering homocysteine does prevent the development and progression of diabetic macroangiopathy.     

Hyperhomocysteinemia as a risk factor for venous thrombosis.

Classical homocystinuria is associated with arterial vascular diseases and venous thrombosis. In the last decade, several studies have been published indicating that even mild hyperhomocysteinemia is a risk factor for venous thrombosis. The 677C-->T mutation in the methylenetetrahydrofolate reductase (MTHFR) gene is an important cause of mild hyperhomocysteinemia, but this polymorphism does not seem to be a risk factor for venous thrombosis. Studies on the interaction between hyperhomocysteinemia and other thrombotic risk factors are conflicting. Little is known about the pathophysiology of venous thrombosis in hyperhomocysteinemia. Several mechanisms proposed for vascular disease may be applied to venous thrombosis as well. However, up to now there is no satisfying model which might explain a thrombophilic state at plasma homocysteine concentrations in the range of mild hyperhomocysteinemia. The results of a first clinical intervention study are expected in 2002. As the results are pending, clinicians could perform homocysteine measurements in patients with venous thrombosis if screening for thrombophilia is indicated. Vitamin supplementation could be prescribed if homocysteine levels are elevated. However, the patient should be informed about the uncertainty of the benefits of vitamin supplementation.     

急性脑梗死患者血浆同型半脘氨酸水平及其与改良急性卒中治疗低分子肝素试验病因分型的关系

目的探讨急性脑梗死患者血浆中同型半胱氨酸（Hcy）的水平变化及其与改良急性卒中治疗低分子肝素试验（TOAST）病因分型间的关系,为脑梗死的防治提供依据。方法采用回顾性分析,选择2012年4月-2013年4月收治的急性脑梗死患者120例为脑梗死组;按照2007年韩国改良TOAST病因分型分为5种不同的亚型,即动脉粥样硬化血栓形成型（AT）48例（40．0％）、小动脉疾病型（SAD）36例（30．0％）、心源性栓塞型（CE）14例（11．7％）、其他原因卒中型（SOD）2例（1．6％）、不明原因卒中型（SUD）20例（16．7％）。同时选择同期健康体检者60例为对照组,检测各组的血浆Hcy水平,分析改良TOAST各亚型与Hcy水平的关系。结果脑梗死组患者血浆Hcy水平高于对照组（P〈0．01）;脑梗死改良TOAST各亚型中SOD因例数少未作分析,其他各型中AT、SAD、CE、SUD组血浆Hcy水平均高于对照组（P〈0．05）,AT组Hcy水平与SAD组相比差异无统计学意义（P〉0．05）;AT组高于SUD组与CE组,差异有统计学意义（P〈0．05）。结论脑梗死与高Hcy血症有关,各亚型的血浆Hcy水平均增高并随TOAST亚型的不同而变化,AT、SAD亚型水平最高,提示高Hcy血症可能通过致动脉粥样硬化和对血管内皮细胞损伤引起脑梗死。     

Serum homocysteine is weakly associated with von Willebrand factor and soluble vascular cell adhesion molecule 1, but not with C-reactive protein in type 2 diabetic and non-diabetic subjects - The Hoorn Study

BACKGROUND: Hyperhomocysteinaemia may constitute an independent risk factor for cardiovascular disease, but it is still unclear by which pathophysiological mechanisms homocysteine (tHcy) may promote atherothrombosis. The aim of this study was firstly to examine whether tHcy is associated with endothelial dysfunction, increased adherence of leukocytes, and/or chronic low-grade inflammation, as estimated from plasma levels of von Willebrand factor (vWf), soluble vascular cell adhesion molecule 1 (sVCAM-1) and C-reactive protein (CRP), respectively. Secondly we investigated whether the presence of type 2 diabetes modifies these associations. MATERIALS AND METHODS: Six hundred and ten subjects of a general population of middle-aged and elderly subjects, 170 of whom had type 2 diabetes, participated in this cross-sectional study. Linear regression analyses were used to study whether tHcy was associated with vWf, sVCAM-1 and CRP, and whether the presence of diabetes modified these associations. RESULTS: After adjustment for confounders, tHcy was significantly but weakly associated with vWf (beta = 0.15, P = 0.05) and sVCAM-1 (beta = 0.082, P = 0.04). tHcy was not significantly associated with CRP (beta = 0.02, P = 0.91). The presence of diabetes did not significantly modify these associations. CONCLUSIONS: This study provides evidence that tHcy is, at most, weakly associated with endothelial dysfunction as estimated from plasma vWf, and with leukocyte adhesion as estimated from plasma sVCAM-1. tHcy was not significantly associated with chronic low-grade inflammation as estimated from plasma CRP. Our data thus suggest that the link between tHcy and atherothrombosis cannot be explained by associations of tHcy with vWf, sVCAM-1 or CRP.     

Assessment of homocysteine, neopterin and nitric oxide levels in Beh?et's disease.

BACKGROUND: Beh?et's disease is a multisystemic immunoinflammatory disease with a wide variety of clinical manifestations, whereas recurrent aphthous stomatitis is a local oral disease. The aim of this study was to examine the distribution of homocysteine levels in patients with active Beh?et's disease, possible association of homocysteine with nitric oxide and neopterin levels, and to characterize the differences between patients with Beh?et's disease and those with recurrent aphthous stomatitis in terms of these parameters compared with healthy controls. METHODS: A total of 23 patients with active Beh?et's disease, 25 patients with recurrent aphthous stomatitis as positive controls, and 21 healthy subjects were included in this study. Serum homocysteine and neopterin levels were measured flourimetrically by HPLC. Serum nitric oxide production was assayed by measuring total nitrite levels with Griess reagent. RESULTS: Significantly higher homocysteine (12.9+/-3.3 micromol/L) and lower nitric oxide (41.5+/-10.9 micromol/L) and neopterin (6.4+/-1.0 nmol/L) levels were observed in patients with Beh?et's disease compared with healthy controls (10.7+/-2.0 micromol/L, 49.7+/-16.2 micromol/L, 8.7+/-2.2 nmol/L, respectively) (p<0.03 for neopterin, p<0.04 for homocysteine and nitric oxide). However, homocysteine, nitric oxide, biopterin and neopterin levels and the neopterin/biopterin ratio for recurrent aphthous stomatitis patients were not significantly different compared to healthy controls. A significant positive correlation was observed between serum homocysteine and serum neopterin/biopterin ratio in patients with Beh?et's disease (r=0.975, p<0.005). CONCLUSIONS: In contrast to recurrent aphthous stomatitis, there is a higher prevalence of hyperhomocysteinemia in Behcet's disease. Homocysteine may have deleterious effects on the pathology of Behcet's disease by decreasing nitric oxide levels and interfering with the immune system.     

Association between homocysteine, vitamin B(6) concentrations and inflammation.

During the last years, a growing body of evidence has been accumulated on the role of hyperhomocysteinemia in the occurrence of coronary artery disease and other arterial occlusive diseases. The mechanism by which high circulating homocysteine concentrations are a risk factor for atherothrombosis is incompletely understood. The present review is aimed to evaluate the role of inflammation in influencing homocysteine (Hcy) and vitamin B(6) concentrations. Results of a large population-based study have suggested that inflammatory markers are the major determinants of Hcy and vitamin B(6) concentrations. This association, independent of the leading factor, may explain, at least in part, why subjects with high concentrations of Hcy and low concentrations of vitamin B(6) have a high risk of developing cardiovascular diseases.     

Homocysteine--relevant for atherogenesis?

Numerous studies report strong associations between hyperhomocysteinemia and premature atherosclerotic vascular disease. Causes of hyperhomocysteinemia are hereditary heterozygous or, in very rare cases, homozygous defects, and quite frequently a lack of the coenzymes B6 and B12 and the cosubstrate folate. Lifestyle factors, age, sex, acute and chronic illness, vitamin deficiency and certain drugs may elevate homocysteine concentrations. Vitamin B supplementation, especially folic acid, is an effective treatment of hyperhomocysteinemia. Clinical trials are required to confirm the potential benefit of lowering homocysteine in regard of the development and progression of atherosclerotic vascular disease. The relevance of hyperhomocysteinemia as a risk factor for atherosclerosis, in contrast to the classical triad of risk factors, namely hypercholesterolemia, smoking and hypertension, is still unknown. Furthermore, a lack of standardized analytical methods for the determination of both homocysteine and blood folate renders the evaluation of studies and clinical data difficult. Therefore, at present, diagnosis and treatment is only recommended in high-risk patients (strong family history of premature atherosclerosis or arterial occlusive disease, especially in the absence of other risk factors, as well as in members of their families) with hyperhomocysteinemia.     

急性心肌梗死患者血清血管内皮生长因子与一氧化氮检测的意义

目的:检测急性心肌梗死患者血清血管内皮生长因子和一氧化氮水平,探讨血管内皮生长因子和一氧化氮在急性心肌梗死发病中的作用。方法:选择冠心病患者60例,其中稳定型心绞痛30例,急性心肌梗死30例,健康人30例为对照组,均于入院第1 d抽取空腹静脉血测定血清血管内皮生长因子及一氧化氮的水平。结果:冠心病患者血清中血管内皮生长因子含量明显高于正常对照组(P<0.01);急性心肌梗死组血清中血管内皮生长因子含量明显高于稳定型心绞痛组和正常对照组(P<0.01);冠心病患者血清中一氧化氮含量低于正常对照组(P<0.01),急性心肌梗死患者血清中血管内皮生长因子含量低于稳定型心绞痛组和正常对照组(P<0.01)。结论:冠心病患者血清中血管内皮生长因子含量高而一氧化氮含量低,提示动脉发生粥样硬化的过程中,血管内皮生长因子与一氧化氮相互调节的作用可能发生障碍,血管内皮生长因子与一氧化氮调节失衡可能与动脉粥样硬化发生、发展有关。     

Homocysteine in cerebrovascular disease: an independent risk factor for subcortical vascular encephalopathy.

Hyperhomocysteinemia is a risk factor for obstructive large-vessel disease. Here, we studied plasma concentrations of homocysteine and vitamins in patients suffering from subcortical vascular encephalopathy (SVE), a cerebral small-vessel disease leading to dementia. These results were compared to the homocysteine and vitamin plasma concentrations from patients with cerebral large vessel disease and healthy control subjects. Plasma concentrations of homocysteine, vascular risk factors and vitamin status (B6, B12, folate) were determined in 82 patients with subcortical vascular encephalopathy, in 144 patients with cerebral large-vessel disease and in 102 control subjects. Patients with SVE, but not those with cerebral large-vessel disease, exhibited pathologically increased homocysteine concentrations in comparison with control subjects without cerebrovascular disease. Patients with SVE also showed lower vitamin B6 values in comparison to subjects without cerebrovascular disease. Logistic regression analysis showed that homocysteine is associated with the highest risk for SVE (odds ratio 5.7; CI 2.5-12.9) in comparison to other vascular risk factors such as hypertension, age and smoking. These observations indicate that hyperhomocysteinemia is a strong independent risk factor for SVE.     

Hyperhomocysteinemia, endothelial nitric oxide synthase polymorphism, and risk of coronary artery disease

BACKGROUND: Hyperhomocysteinemia is an independent, graded risk factor for coronary artery disease (CAD). The G894T variant of endothelial nitric oxide synthase (eNOS) was postulated to be associated with hyperhomocysteinemia and could influence individual susceptibility to CAD. The aims of this study were to investigate (a) the relationship of the eNOS G894T polymorphism with the presence and the severity of CAD and (b) the possible relationship between hyperhomocysteinemia and the eNOS G894T variant for the risk of CAD severity in a Tunisian population. METHODS: We used PCR with restriction fragment length polymorphism analysis to detect the G894T variant of the eNOS gene in 100 patients with CAD and 120 healthy controls. The severity of CAD was expressed by the number of affected vessels. Total plasma homocysteine concentrations were determined by direct chemiluminescence assay. RESULTS: The frequencies of the eNOS GG, GT, and TT genotypes in the CAD group were significantly different from those in the control group (45%, 44%, and 11% vs 60%, 35.8% and 4.2%, respectively; P = 0.035). There was no association between the eNOS G894T genotype frequencies and the number of stenosed vessels (P = 0.149). In the CAD group, the coexistence of the 894 GT or TT genotypes and hyperhomocysteinemia led to an increased risk of CAD severity. CONCLUSION: The G894T polymorphism of the eNOS gene is associated with the presence of CAD, and in conjunction with hyperhomocysteinemia, increased the risk of CAD severity in a Tunisian population.