Homocysteine inhibits endothelial progenitor cells proliferation via DNMT1-mediated hypomethylation of Cyclin A.

Endothelial progenitor cells (EPCs) contribute to neovasculogenesis and reendothelialization of damaged blood vessels to maintain the endothelium. Dysfunction of EPCs is implicated in the pathogenesis of vascular injury induced by homocysteine (Hcy). We aimed to investigate the role of Cyclin A in Hcy-induced EPCs dysfunction and explore its molecular mechanism. In this study, by treatment of EPCs with Hcy, we found that the expression of Cyclin A mRNA and protein were significantly downregulated in a dose-dependent manner. Knockdown of Cyclin A prominently reduced proliferation of EPCs, while over-expression of Cyclin A significantly promoted the cell proliferation, suggesting that Hcy inhibits EPCs proliferation through downregulation of Cyclin A expression. In addition, epigenetic study also demonstrated that Hcy induces DNA hypomethylation of the Cyclin A promoter in EPCs through downregulated expression of DNMT1. Moreover, we found that Hcy treatment of EPCs leads to increased SAM, SAH and MeCP2, while the ratio of SAM/SAH and MBD expression decrease. In summary, our results indicate that Hcy inhibits Cyclin A expression through hypomethylation of Cyclin A and thereby suppress EPCs proliferation. These findings demonstrate a novel mechanism of DNA methylation mediated by DNMT1 in prevention of Hcy associated cardiovascular disease.

[The effect of miR-124 on homocysteine-induced atherosclerosis via promoter region DNA methylation in ApoE(-/-) mice].

The aim of the present study is to explore the role of miR-124 and its promoter region DNA methylation in homocysteine (Hcy)-induced atherosclerosis. ApoE(-/-) mice were fed with hypermethionine diet for 16 weeks to duplicate hyperhomocysteinemia model. Meanwhile, a normal control group (C57BL/6J mice fed with normal diet, N-control) and a model control group (ApoE(-/-) mice fed with normal diet, A-control) were set. The degree of atherosclerosis was observed by HE and oil red O staining. Automatic biochemical analyzer was used to detect the serum levels of Hcy. Foam cell model was duplicated and oil red O staining was used to confirm whether the model was successfully established. And foam cells were stimulated with 0, 50, 100, 200, 500 µmol/L Hcy and 50 µmol/L Hcy + 10 µmol/L AZC respectively. Real-time quantitative PCR (RT-qPCR) was used to detect the expressions of miR-124 in mice aorta and foam cells; Nested landing methylation specific PCR (nMS-PCR) was used to detect the levels of miR-124 promoter DNA methylation in mice aorta and foam cells. Meanwhile, the effects of DNA methylation inhibitor AZC on miR-124 expression were observed at the cellular level. The effect of miR-124 promoter DNA methylation status on lipid accumulation in foam cells was observed by oil red O staining. The results showed that compared with model control group, the serum levels of Hcy in high methionine group were significantly increased (P < 0.01) and developed aortic atherosclerotic plaque, the expression of miR-124 was markedly decreased (P < 0.01), while the levels of miR-124 promoter DNA methylation were significantly increased (P < 0.01). Given different levels of Hcy, the expression of miR-124 in foam cells was decreased, while the levels of miR-124 promoter DNA methylation were increased in a dose-dependent manner (P < 0.05, P < 0.01). AZC reversed the results of mentioned indices as above markedly (P < 0.05). Downregulation of miR-124 may play a role in Hcy-induced atherosclerosis and its promoter DNA methylation status may be an important mechanism in this process.

[Effect of oxymatrine on JAK2/STAT3 signaling in renal tissues of rats with septic shock].

OBJECTIVE: To explore the effect of oxymatrine (OMT) on JAK2/STAT3 signaling in renal tissues of rats with septic shock. METHOD: The cecal ligation and puncture (CLP) was adopted to establish the rat septic shock model. Fifty-six male SD rats were randomly divided into 7 groups: the sham operation group, the model (CLP) group, CLP + OMT high, middle, low-dose (52, 26, 13 mg x kg(-1), vena caudalis bolus) groups and the positive control (CLP + dexamethasone, 10 mg x kg(-1)) group. The pathological changes in renal tissues were examined with lightmicroscope. BUN content was determined by urine enzymatic method. Expressions of tumournecrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) mRNA in renal tissues were determined by RT-PCR. Expression of JAK2 and STAT3 in renal tissues determined by Western blot. Changes in tumournecrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) contents in renal tissue were determined by radioimmunoassay. RESULT: OMT of different doses could inhibit the JAK2 and STAT3 activation in renal tissues (P<0.05), and decrease the protein expression of JAK2, STAT3, TNF-alpha and IL-1beta mRNA (P<0.05). Besides, it could reduce TNF-alpha and IL-1beta contents in renal tissue homogenate (P<0.05), serum BUN content (P<0.05), and improve such lesions as tissue hyperemia, edema and inflammatory cell infiltration, with identical results in medium and high-dose OMT groups, and the positive control group. CONCLUSION: OMT can inhibit JAK2/STAT3 signaling activity to reduce the expression of proin-flammatory factors (TNF-alpha, IL-1beta) and treat the renal injury in rats with septic shock.

[Involvement of p38 MAPK pathway in GLP-1-induced inhibition of apoptosis in human umbilical vein endothelial cells].

The aim of the present study was to investigate the effect of glucagon-like peptide-1 (GLP-1) on palmitate-induced apoptosis of human umbilical vein endothelial cells (HUVECs) and the underlying mechanism. HUVECs were cultured in vitro, and then treated by palmitate to induce apoptosis. Meanwhile, GLP-1 was added to explore its effect. After 24 h of the treatments, Caspase-3 activity and DNA fragmentation were measured using ELISA kits. Phospho-p38 mitogen-activated protein kinase (p-p38 MAPK) expression was detected by Western blot. The results showed that incubating HUVECs with 0.125 mmol/L GLP-1 increased Caspase-3 activity and DNA fragmentation. GLP-1 significantly inhibited palmitate-induced increases of Caspase-3 activity and DNA fragmentation in a concentration-dependent manner. Moreover, GLP-1 inhibited the up-regulation of p-p38 MAPK expression induced by palmitate in HUVECs. These results suggest GLP-1 protects HUVECs against lipo-apoptosis, and this effect may be mediated through inhibiting p38 MAPK pathway.

Hyperhomocysteinemia induces injury in olfactory bulb neurons by downregulating Hes1 and Hes5 expression.

Hyperhomocysteinemia has been shown to be associated with neurodegenerative diseases; however, lesions or histological changes and mechanisms underlying homocysteine-induced injury in olfactory bulb neurons remain unclear. In this study, hyperhomocysteinemia was induced in apolipoprotein E-deficient mice with 1.7% methionine. Pathological changes in the olfactory bulb were observed through hematoxylin-eosin and Pischingert staining. Cell apoptosis in the olfactory bulb was determined through terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) staining. Transmission electron microscopy revealed an abnormal ultrastructure of neurons. Furthermore, immunoreactivity and expression of the hairy enhancer of the split 1 (Hes1) and Hes5 were measured using immunohistochemistry, immunofluorescence, and western blot assay. Our results revealed no significant structural abnormality in the olfactory bulb of hyperhomocysteinemic mice. However, the number of TUNEL-positive cells increased in the olfactory bulb, lipofuscin and vacuolization were visible in mitochondria, and the expression of Hes1 and Hes5 decreased. These findings confirm that hyperhomocysteinemia induces injury in olfactory bulb neurons by downregulating Hes1 and Hes5 expression.

WITHDRAWN: Mechanism of extracellular­superoxide dismutase DNA methylation in a hyperhomocysteinemia­induced atherosclerosis in a mouse model.

Ahead of Print article withdrawn by publisher.

Homocysteine-induced proliferation of vascular smooth muscle cells occurs via PTEN hypermethylation and is mitigated by Resveratrol.

Vascular smooth muscle cell (VSMC) proliferation is a primary pathological event in the development of atherosclerosis (AS), and the presence of homocysteine (Hcy) acts as an independent risk factor for AS. However, the underlying mechanisms remain to be elucidated. Phosphatase and tensin homologue on chromosome 10 (PTEN), is endogenously expressed in VSMCs and induces multiple signaling networks involved in cell proliferation, survival and inflammation, however, the specific role of PTEN is still unknown. The present study detected the proliferation ratio of VSMCs following treatment with Hcy and Resveratrol (RSV). In the 100 µM Hcy group, the proliferation ratio increased, and treatment with RSV decreased the proliferation ratio induced by Hcy. Reverse transcription­quantitative polymerase chain reaction and western blotting were used to analyze PTEN expression, RSV treatment was associated with decreased PTEN expression levels in VSMCs. PTEN levels were decreased in Hcy treated cells, and the proliferation ratio of VSMCs were increased following treated with Hcy. To study the mechanism of regulation of PTEN by Hcy, the present study detected PTEN methylation levels in VSMCs, and PTEN DNA methylation levels were demonstrated to be increased in the 100 µM Hcy group, whereas treatment with RSV decreased the methylation status. DNA methyltransferase 1 is important role in the regulation of PTEN methylation. Overall, Hcy impacts the methylation status of PTEN, which is involved in cell proliferation, and induces the proliferation of VSMCs. This effect is alleviated by treatment with RSV, which exhibits an antagonistic mechanism against Hcy.

Dysfunction of endothelial NO system originated from homocysteine-induced aberrant methylation pattern in promoter region of DDAH2 gene.

BACKGROUND: Hyperhomocysteinemia (HHcy)-mediated dysfunction of endothelial NO system is an important mechanism for atherosclerotic pathogenesis. Dimethylarginine dimethylaminohydrolase (DDAH) is the key enzyme for degrading asymmetric dimethylarginine (ADMA), which is an endogenous inhibitor of endothelial nitric oxide (NO) synthase (eNOS). This study was designed to investigate whether the dysfunction of endothelial NO system originates from HHcy-mediated aberrant methylation modification in promotor region of DDAH2 gene. METHODS: Human umbilical vein endothelial cells (HUVECs) were cultured to the third generation and treated with homocysteine (Hcy) at different concentrations (0, 10, 30, 100, and 300 micromol/L) for 72 hours. The methylation pattern in promoter region CpG island of DDAH2 gene was analyzed by nested methylation-specific PCR (nMSP). The mRNA expression of eNOS gene and DDAH2 gene was detected by semi-quantitative RT-PCR. The activity of DDAH2 and eNOS in cells, and the concentrations of ADMA and NO in culture medium were assayed respectively. RESULTS: Mild increased concentration of Hcy (10 and 30 micromol/L) induced hypomethylation, while high concentration of Hcy (100 and 300 micromol/L) induced hypermethylation in the promoter CpG island of DDAH2 gene. The mRNA expression of DDAH2 increased in mild enhanced concentration of Hcy, and decreased in high concentration of Hcy correspondingly. The inhibition of DDAH2 activity, the increase of ADMA concentration, the reduction of eNOS activity and the decrease of NO production were all consistently relevant to the alteration of Hcy concentration. CONCLUSION: The increased concentration of Hcy induced aberrant methylation pattern in promotor region of DDAH2 gene and the successive alterations in DDAH/ADMA/NOS/NO pathway, which showed highly relevant and dose-effect relationship. The results suggested that the dysfunction of endothelial NO system induced by HHcy could be partially originated from Hcy-mediated aberrant methylation in DDAH2 gene.

[Effect of decreased GSH on sensitivity of breast cancer cells to ADM].

OBJECTIVE: Glutathione(GSH) maintains an optimum cellular redox potential. Elevated levels of GSH render some types of cancer cells resistant against anti-cancer drugs. The aim of this study was to determine the effect of a thiol-depleting agent, diethylmaleate (DEM), on the sensitivity of human breast cancer cells to ADM. METHODS: The ADM-resistant human breast cancer MCF-7/ADM cell lines and ADM-sensitive MCF-7/S cell lines were treated by thiol-depleting agent DEM for 3 h respectively. The changes of sensitivity to ADM were then measured by MTT assay. The intracellular GSH contents were examined by fluorescent-spectrophotometry and the correlation between the changes of sensitivity to ADM and the intracellular GSH content was analyzed. RESULTS: Treatment of MCF-7/ADM and MCF-7/S cells by 0.1 micromol/L DEM for 3 h decreased 37.4% and 29.7% of the intracellular GSH content respectively (P < 0.01). ADM also decreased intracellular GSH content in a ADM-concentration-dependent manner. The combined use of DEM and ADM depleted the intracellular GSH content in both cells significantly more than the sum of single use of ADM and DEM alone. The sensitivity of both cells to ADM increased with the decline of intracellular GSH content. CONCLUSION: The depletion effect of DEM on the intracellular GSH could be enhanced by ADM and such depletion may be involved in the changes of the sensitivity of MCF/7 cells to ADM.

[Effects of peroxisome proliferators activated receptors on caveolin-1 expression in foam cells].

OBJECTIVE: To study the effect of peroxisome proliferators activated receptors (PPAR) alpha, gamma ligand on ATP-binding cassette transporter A1 (ABCA1) and caveolin-1 expressions and cholesterol, ox-LDL contents in human monocyte derived foam cells. METHOD: Malondialdehyde (MDA) was measured by TBARS method, ox-LDL detected by ELISA method, cholesterol measured by fluorescence spectrophotometric method, ABCA1, caveolin-1 mRNA and protein expressions determined by RT-PCR and Western blot, in human monocytes, foam cells [human monocyte-derived macrophage induced by myristate acetate (PMA) further treated with 50 mg/L ox-LDL for 24 h], foam cells plus 10 micromol/L pioglitazone for 48 h, foam cells plus 5 micromol/L clofibrate for 48 h. RESULT: The intracellular total cholesterol (TC), free cholesterol (FC), cholesteryl ester (CE), ox-LDL and lipid peroxide were significantly increased and the membrane expressions of ABCA1, caveolin-1 were down-regulated in foam cells compared to monocytes (all P < 0.05) and these changes were significantly attenuated by cotreatment with PPARalpha, gamma ligand. CONCLUSION: The anti-atherosclerosis effects of PPARalpha, gamma ligand are related to reducing cholesterol contents and up-regulating ABCA1, caveolin-1 expressions in foam cells.

[Experimental study of anti-atherosclerosis potency by lycium seed oil and its possible mechanism].

OBJECTIVE: To study the effect of anti-atherosclerosis of Lycium Seed Oil (Lso) and its possible mechanism. METHODS: The rabbit atherosclerosis model was established by high fat diet, and the TC, TG, LDL-C, HDL-C levels in plasma were examined dynamically. The SOD, GSH-PX, T-AOC activities and the MDA levels in serum were monitored after 8 week's high fat diet. Aorta samples were observed for atherosclerotic extent, and NF-kappaB, TNF-alpha were assessed by immuno-histochemical method. The lovastatin was set up as a positive control. RESULTS: contents of HDL-C obviously increased in Plasma of low and high dosage groups and TC, TG, LDL-C levels significantly decreased compared with control group. The SOD, GSH-PX, T-AOC activities up-regulated while the NF-kappaB, MDA and NF-alpha levels decreased in Lycium Seed Oil groups compared with control group. Aortic atherosclerotic extent and area in low dosage and high dosage LSO groups were absolutely smaller than that in high fat diet group. The anti-atherosclerosis potency of Lycium Seed Oil was similar with that of lovastatin. CONCLUSION: Lycium Seed Oil has potent anti-atherosclerosis effects and its anti-atherosclerosis potency was similar with The lovastatin. The possible mechanism involve the decreasing of plasma lipids, anti-peroxidation, inhibiting the activation of NF-kappaB and down-regulating the inflammation cytokines of TNF-alpha.

Aberrant promoter methylation of multiple genes in VSMC proliferation induced by Hcy.

Vascular smooth muscle cell (VSMC) proliferation is a primary pathological event in atherosclerosis (AS), and homocysteine (Hcy) is an independent risk factor for AS. However, the underlying mechanisms are still lagging. Studies have used the combination of methylation of promoters of multiple genes to diagnose tumors, thus the aim of the current study was to investigate the role of methylation status of several genes in VSMCs treated with Hcy. CpG islands were identified in the promoters of platelet­derived growth factor (PDGF), p53, phosphatase and tensin homologue on chromosome 10 (PTEN) and mitofusin 2 (MFN2). Hypomethylation was observed to occur in the promoter region of PDGF, hypermethylation in p53, PTEN and MFN2, and hypomethylation in two global methylation indicators, aluminium (Alu) and long interspersed nucleotide element­1 (Line­1). This was accompanied by an increase in the expression of PDGF, and reductions of p53, PTEN and MFN2, both in mRNA and protein levels. An elevation of S­adenosylmethionine (SAM) and a reduction of S­adenosylhomocysteine (SAH) and the SAM/SAH ratio were also identified. In conclusion, Hcy impacted methylation the of AS­associated genes and global methylation status that mediate the cell proliferation, which may be a character of VSMCs treated with Hcy. The data provided evidence for mechanisms of VSMCs proliferation in AS induced by Hcy and may provide a new perspective for AS induced by Hcy.

Homocysteine­induced oxidative stress through TLR4/NF­κB/DNMT1­mediated LOX­1 DNA methylation in endothelial cells.

Atherosclerosis (AS) is a progressive disease of multifactorial origin, which occurs in response to endothelial injury. Increased homocysteine (Hcy) is considered a major cause of endothelial dysfunction, oxidative stress and DNA methylation; however, the mechanisms remain to be fully elucidated. The aim of the present study was to investigate whether Hcy causes injury to endothelial cells (ECs) by the effect of lectin­like oxidized­low density lipoprotein receptor­1 (LOX­1) DNA methylation through toll­like receptor 4(TLR4)/nuclear factor (NF)­κB/DNA methyltransferase (DNMT)1. The ECs were treated with different concentrations of Hcy, and it was found that Hcy promoted the expression of TLR4, leading to EC injury. The effect of oxidative stress was analyzed by measuring superoxide dismutase, malondialdehyde and hydrogen peroxide in the ECs. In addition, the association between NF­κB and DNMT1 was examined by treatment of the ECs with pyrrolidine dithiocarbamate (PDTC). The results suggested that Hcy induced LOX­1 DNA hypomethyaltion to promote the expression levels of LOX­1. Taken together, Hcy injured the ECs through the effect of methylation and trans­sulfuration metabolism of LOX­1 through TLR4/NF­κB/DNMT1. Following injury to the ECs, lipids, particularly ox­LDL, accumulated in the sub­endothelial layer to promote the formation of AS.

A regulatory circuit involving miR-143 and DNMT3a mediates vascular smooth muscle cell proliferation induced by homocysteine.

Accumulating evidence has suggested that homocysteine (Hcy) is an independent risk factor for atherosclerosis (AS). Hcy can promote vascular smooth muscle cell (VSMC) proliferation, which is pivotal in the pathogenesis and progression of AS. The aim of the present study was to investigate the epigenetic regulatory mechanism of microRNA (miR)­143­mediated VSMCs proliferation induced by Hcy. The results of a 3­(4,5­dimethylthiazol­2­yl)­2,5­diphe­nyltetrazolium bromide assay revealed that VSMC proliferation was increased by 1.39­fold following treatment with 100 mM Hcy, compared with the control group. The levels of miR­143 were markedly downregulated in the Hcy group, compared with the control group, as determined using reverse transcription­quantitative polymerase chain reaction analysis. In addition, the level of miR­143 methylation was increased markedly in the VSMCs treated with Hcy, compared with the control, and was reduced following transfection with DNA methyltransferase (DNMT)3a small interfering RNA, determined using methylation­specific­PCR. The activities of DNMT3a luciferase were also altered accordingly in VSMCs transfected with pre­miR­143 and miR­143 inhibitor, respectively. In addition, the expression of miR­143 was observed to be inversely correlated with the mRNA and protein expression of DNMT3 in the VSMCs. Taken together, these findings suggest that DNMT3a is a direct target of miR­143, and that the upregulation of DNMT3 is responsible for the hypermethylation of miR­143 in Hcy-induced VSMC proliferation.

[Corrigendum] Integration of gene expression and DNA methylation profiles provides a molecular subtype for risk assessment in atherosclerosis.

After the publication of the article, the authors noted that they had made an error regarding the order of one of their names. For Professor Zheng Yu, the given name is Yu and the family name is Zheng, therefore he should be listed as Professor Yu Zheng in the author list and as the corresponding author. [the original article was published in the Molecular Medicine Reports 13: 4791-4799, 2016; DOI: 10.3892/mmr.2016.5120].

Integration of gene expression and DNA methylation profiles provides a molecular subtype for risk assessment in atherosclerosis.

The aim of the present study was to identify an effective method for detecting early­phase atherosclerosis (AS), as well as to provide useful DNA methylation profiles to serve as biomarkers for the detection of AS. A total of 300 individuals (150 AS patients and 150 healthy subjects) were recruited for peripheral blood DNA methylation analyses at 12 gene promoter loci using nested methylation­specific polymerase chain reaction in a test set. Based on the test set, the promoter methylation of TIMP metallopeptidase inhibitor 1 (TIMP1), ATP binding cassette subfamily A member 1 (ABCA1), and acetyl-CoA acetyltransferase 1 (ACAT1) were determined to be candidate biomarkers; demonstrating the highest sensitivity (88%) and specificity (90%). The biomarkers that were candidates for early AS detection were validated in an independent validation set (n=100). In the validation set, the combination of TIMP1, ABCA1 and ACAT1 methylation achieved sensitivity, specificity and coincidence rate values of 88, 70 and 79%, respectively. In the current pilot study, the patterns of DNA methylation of AS­associated genes were observed to be significantly altered in the peripheral blood of AS patients. Thus, the AS-specific methylation of the three­gene panel (TIMP1, ABCA1, and ACAT1) may serve as a valuable biomarker for the early detection of AS.

High-methionine diets accelerate atherosclerosis by HHcy-mediated FABP4 gene demethylation pathway via DNMT1 in ApoE(-/-) mice.

Homocysteine (Hcy) is an independent risk factor for atherosclerosis, but the underlying molecular mechanisms are not known. We investigated the effects of Hcy on fatty acid-binding protein 4 (FABP4), and tested our hypothesis that Hcy-induced atherosclerosis is mediated by increased FABP4 expression and decreased methylation. The FABP4 expression and DNA methylation was assessed in the aorta of ApoE(-/-) mice fed high-methionine diet for 20weeks. Over-expression of FABP4 enhanced accumulation of total cholesterol and cholesterol ester in foam cells. The up-regulation of DNA methyltransferase 1 (DNMT1) promoted the methylation process and decreased FABP4 expression. These data suggest that FABP4 plays a key role in Hcy-mediated disturbance of lipid metabolism and that DNMT1 may be a novel therapeutic target in Hcy-related atherosclerosis.

Aberrant DNA methylation of the PDGF gene in homocysteine­mediated VSMC proliferation and its underlying mechanism.

It is well established that homocysteine (Hcy) is an independent risk factor for atherosclerosis (AS), which is characterized by vascular smooth muscle cell (VSMC) proliferation. However, the molecular mechanism underlying AS in VSMCs is yet to be elucidated. The aim of this study was to investigate the potential involvement of aberrant DNA methylation of the platelet­derived growth factor (PDGF) gene in Hcy­mediated VSMC proliferation and its underlying mechanism. Cultured human VSMCs were treated with varying concentrations of Hcy. VSMC proliferation, PDGF mRNA and protein expression and PDGF promoter demethylation showed a dose­dependent increase with Hcy concentration, suggesting an association among them. Cell cycle analysis revealed a decreased proportion of VSMCs in G0/G1 and an increased proportion in S phase, indicating that VSMC proliferation was increased under Hcy treatment. Furthermore, S­adenosylhomocysteine (SAH) levels were observed to increase and those of S­adenosylmethionine (SAM) were observed to decrease. The consequent decrease in the ratio of SAM/SAH may partially explain the hypomethylation of PDGF with Hcy treatment. Folate treatment exhibited an antagonistic effect against Hcy­induced VSMC proliferation, aberrant PDGF methylation and PDGF expression. These data suggest that Hcy may stimulate VSMC proliferation through the PDGF signaling pathway by affecting the epigenetic regulation of PDGF through the demethylation of its promoter region. These findings may provide novel insight into the molecular association between aberrant PDGF gene demethylation and the proliferation of VSMCs in Hcy­associated AS.

[The pathogenic mechanism of homocysteine -induced endothelial nitric oxide synthase dysfunction and the antagonistic effects by folic acid].

To investigate the pathogenic mechanism of homocysteine-induced endothelial nitric oxide synthase dysfunction and the antagonistic effects by folic acid (FA). Human umbilical vein endothelial cells (HUVEC)were cultured to the third generation. Then HUVEC were cultured with Hcy at different concentrations (0,10,30,100 and 300 micromol/L),with or without FA(100 micromol/L)for 72 hours. The mRNA and protein levels of endothelial nitric oxide synthase (eNOS) were analyzed by RT-PCR and immunohistochemistry respectively. Asymmetric dimethylarginine (ADMA)was measured by reversed-phase high performance liquid chromatography. The dimethylarginine dimethylaminohydrolase(DDAH), activity of eNOS and the production of NO were analyzed simulta- neously. After HUVEC were exposed to Hcy at different concentrations for 72 hours, the level of eNOS mRNA and the content of eNOS protein, the eNOS activity, and the production of nitric oxide (NO) were all significantly and dose-dependently reduced compared with the control group (P< 0.05). The activity of DDAH has a parallel decrease and the ADMA concentration showed a cor- responding increase. The addition of folic acid (100 micromol/L)resulted in partial antagonistic effects against the injury of Hcy on NOS system of endothelial cells, the eNOS protein level and eNOS activity, and NO production increased,and so does the DDAH activity,and the ADMA concentration reduced. But the FA didn't influence the eNOS mRNA expression. The pathogenic mechanism of homocysteine-induced eNOS dysfunction may involve two levels,the level of eNOS protein and eNOS activity,and the level of the expression of eNOS gene. The injury on the level of eNOS protein and eNOS activity may go through the DDAH-ADMA pathway. Folic acid can exert partial protective roles against the Hcy in the level of eNOS protein and eNOS activity,but without impact on the expression of eNOS gene.