Homocysteine augments cytokine-induced chemokine expression in human vascular smooth muscle cells: implications for atherogenesis

Atherogenic Effect of Homocysteine, a Biomarker of Inflammation and Its Treatment

Hyperhomocysteinemia (HHcy) is an independent risk factor for atherosclerosis. Ischemic stroke and heart disease, coronary heart disease, and cardiovascular disease are events resulting from long-lasting and silent atherosclerosis. This paper deals with the synthesis of homocysteine (Hcy), causes of HHcy, mechanism of HHcy-induced atherosclerosis, and treatment of HHcy. Synthesis and metabolism of Hcy involves demethylation, transmethylation, and transsulfuration, and these processes require vitamin B 6 and vitamin B 12 folic acid (vitamin B 9 ). Causes of HHcy include deficiency of vitamins B 6 , B 9 , and B 12 , genetic defects, use of smokeless tobacco, cigarette smoking, alcohol consumption, diabetes, rheumatoid arthritis, low thyroid hormone, consumption of caffeine, folic acid antagonist, cholesterol-lowering drugs (niacin), folic acid antagonist (phenytoin), prolonged use of proton pump inhibitors, metformin, and hypertension. HHcy-induced atherosclerosis may be mediated through oxidative stress, decreased availability of nitric oxide (NO), increased expression of monocyte chemoattractant protein-1, smooth muscle cell proliferation, increased thrombogenicity, and induction of arterial connective tissue. HHcy increases the generation of atherogenic biomolecules such as nuclear factor-kappa B, proinflammatory cytokines (IL-1β, IL-6, and IL-8), cell adhesion molecules (intercellular adhesion molecule-1, vascular cell adhesion molecule-1, and E-selection), growth factors (IGF-1 and TGF-β), and monocyte colony-stimulating factor which lead to the development of atherosclerosis. NO which is protective against the development of atherosclerosis is reduced by HHcy. Therapy with folic acid, vitamin B 6 , and vitamin B 12 lowers the levels of Hcy, with folic acid being the most effective. Dietary sources of folic acid, vitamin B 6 , vitamin B 12 , omega-3 fatty acid, and green coffee extract reduce Hcy. Abstaining from drinking coffee and alcohol, and smoking also reduces blood levels of Hcy. In conclusion, HHcy induces atherosclerosis by generating atherogenic biomolecules, and treatment of atherosclerosis-induced diseases may be by reducing the levels of Hcy.

Hyperhomocysteinemia prevalence among patients with venous thromboembolism

AIMS

The objectives of this study were to determine the plasma homocysteine (Hcy) levels and the prevalence of Hyperhomocysteinemia (HHC) in a group of Tunisian patients with deep vein thrombosis (DVT) by comparing it with healthy controls.

METHODS

it was an observational case-control study including patients hospitalized for the management of unprovoked DVT. For each subject, a routine biochemical assay was conducted, including plasma homocysteine measurement and determination of vitamin B12 and B9 levels, as these vitamins are essential for assessing hyperhomocysteinemia in DVT patients due to their role in regulating homocysteine.

RESULTS

We observed an increased mean plasma Hcy level compared to controls and the prevalence of Hyperhomocysteinemia 61.7% against 4% in the control subjects. The risk of developing DVT with HHC is 3.54.

CONCLUSION

Our study found that homocysteine levels were higher in patients with DVT than in controls.

Homocysteine and IgA nephropathy: observational and Mendelian randomization analyses

BACKGROUND

High levels of plasma homocysteine occur almost uniformly in patients with end-stage renal disease (ESRD). IgA nephropathy (IgAN) is the most common form of primary glomerulonephritis and a common cause of ESRD in young adults. Here, we aimed to detect whether homocysteine was elevated and associated with clinical-pathologic manifestations of IgAN patients and tested its causal effects using a two-sample Mendelian randomization (MR) approach.

METHODS

For observational analysis, 108 IgAN patients, 30 lupus nephritis (LN) patients, 50 minimal change disease (MCD) patients, and 206 healthy controls were recruited from April 2014 to April 2015. Their plasma homocysteine was measured and clinical-pathologic manifestations were collected from medical records. For MR analysis, we further included 1686 IgAN patients. The missense variant methylenetetrahydrofolate reductase C677T (rs1801133) was selected as an instrument, which was genotyped by TaqMan allele discrimination assays.

RESULTS

Majority of IgAN patients (93.52%, 101/108) showed elevated levels of plasma homocysteine (>10 μmol/L). Plasma homocysteine in IgAN patients was significantly higher than that in MCD patients (median: 18.32 vs. 11.15 μmol/L, Z = -5.29, P < 0.01) and in healthy controls (median: 18.32 vs. 10.00 μmol/L, Z = -8.76, P < 0.01), but comparable with those in LN patients (median: 18.32 L vs. 14.50 μmol/L, Z = -1.32, P = 0.19). Significant differences were observed in sub-groups of IgAN patients according to quartiles of plasma homocysteine for male ratio (22.22% vs. 51.85% vs. 70.37% vs. 70.37%, χ = 14.29, P < 0.01), serum creatinine (median: 77.00 vs. 100.00 vs. 129.00 vs. 150.00 μmol/L, χ = 34.06, P < 0.01), estimated glomerular filtration rate (median: 100.52 vs. 74.23 vs. 52.68 vs. 42.67 mL·min·1.73 m, χ = 21.75, P < 0.01), systolic blood pressure (median: 120.00 vs. 120.00 vs. 125.00 vs. 130.00 mmHg, χ = 2.97, P = 0.05), diastolic blood pressure (median 80.00 vs. 75.00 vs. 80.00 vs. 81.00 mmHg, χ = 11.47, P < 0.01), and pathologic tubular atrophy and interstitial fibrosis (T) (T0/T1/T2: 62.96%/33.33%/3.70% vs. 29.63%/40.74%/29.63% vs. 24.00%/48.00%/28.00% vs. 14.81%/37.04%/48.15%, χ = 17.66, P < 0.01). The coefficient of each rs1801133-T allele on homocysteine levels after controlling age and sex was 7.12 (P < 0.01). MR estimates showed causal positive effects of homocysteine on serum creatine (β = 0.76, P = 0.02), systolic blood pressure (β = 0.26, P = 0.02), diastolic blood pressure (β = 0.20, P = 0.01), and pathologic T lesion (β = 0.01, P = 0.01) in IgAN.

CONCLUSIONS

By observational and MR analyses, consistent results were observed for associations of plasma homocysteine with serum creatinine, blood pressures, and pathologic T lesion in IgAN patients.

Homocysteine levels are independently associated with damage accrual in systemic lupus erythematosus patients from a Latin-American cohort

OBJECTIVE

To determine the impact of homocysteine levels on damage accrual in systemic lupus erythematosus (SLE) patients.

METHODS

This longitudinal study was conducted in consecutive patients seen every 6 months at our Rheumatology Department since 2012. Patients with available homocysteine levels and who had at least one subsequent visit were included. Univariable and multivariable Cox regression models were done to determine if homocysteine levels were predictive of damage accrual as per the SLICC Damage Index (SDI). The multivariable model was adjusted for pertinent variables (age at diagnosis, gender, socioeconomic status, disease duration, disease activity (SLEDAI), Framingham score, antimalarial and immunosuppressive drug use, average daily dose, and exposure time to prednisone (PDN)).

RESULTS

One hundred forty-five patients were included; their mean (SD) age at diagnosis was 43.70 (12.09) years, 136 (93.8%) were female, and nearly all were Mestizo. At baseline, disease duration was 7.55 (6.73) years; patients were followed for 3.54 (1.27) years. The SLEDAI was 5.60 (4.34), and the SDI 0.97 (1.35). The average daily PDN dose was 7.30 (5.78) mg/day and the time of PDN exposure was 7.36 (6.73) years. Mean homocysteine levels were 10.07 (3.71) μmol/L. The highest tertile of homocysteine levels predicted new damage accrual in the univariable and multivariable models [HR 1.78 (95% CI, 1.042-3.039); p = 0.035 and HR 2.045 (95% CI, 1.077-3.883); p = 0.029, respectively]. Increased levels (> 15 μmol/L) were found in 12 (8.3%) patients; 75 (51.7%) patients increased ≥ 1 SDI point.

CONCLUSION

In SLE patients, homocysteine levels predicted damage accrual independently of other well-known risk factors for such occurrence.

High levels of homocysteine downregulate apolipoprotein E expression via nuclear factor kappa B

AIM: To investigate the effect of high homocysteine (Hcy) levels on apolipoprotein E (apoE) expression and the signaling pathways involved in this gene regulation.

METHODS: Reverse transcriptase polymerase chain reaction (RT-PCR) and Western blot were used to assess apoE expression in cells treated with various concentrations (50-500 μmol/L) of Hcy. Calcium phosphate-transient transfections were performed in HEK-293 and RAW 264.7 cells to evaluate the effect of Hcy on apoE regulatory elements [promoter and distal multienhancer 2 (ME2)]. To this aim, plasmids containing the proximal apoE promoter [(-500/+73)apoE construct] alone or in the presence of ME2 [ME2/(-500/+73)apoE construct] to drive the expression of the reporter luciferase gene were used. Co-transfection experiments were carried out to investigate the downstream effectors of Hcy-mediated regulation of apoE promoter by using specific inhibitors or a dominant negative form of IKβ. In other co-transfections, the luciferase reporter was under the control of synthetic promoters containing multiple specific binding sites for nuclear factor kappa B (NF-κB), activator protein-1 (AP-1) or nuclear factor of activated T cells (NFAT). Chromatin immunoprecipitation (ChIP) assay was accomplished to detect the binding of NF-κB p65 subunit to the apoE promoter in HEK-293 treated with 500 μmol/L Hcy. As control, cells were incubated with similar concentration of cysteine. NF-κB p65 proteins bound to DNA were immunoprecipitated with anti-p65 antibodies and DNA was identified by PCR using primers amplifying the region -100/+4 of the apoE gene.

RESULTS: RT-PCR revealed that high levels of Hcy (250-750 μmol/L) induced a 2-3 fold decrease in apoE mRNA levels in HEK-293 cells, while apoE gene expression was not significantly affected by treatment with lower concentrations of Hcy (100 μmol/L). Immunoblotting data provided additional evidence for the negative role of Hcy in apoE expression. Hcy decreased apoE promoter activity, in the presence or absence of ME2, in a dose dependent manner, in both RAW 264.7 and HEK-293 cells, as revealed by transient transfection experiments. The downstream effectors of the signaling pathways of Hcy were also investigated. The inhibitory effect of Hcy on the apoE promoter activity was counteracted by MAPK/ERK kinase 1/2 (MEK1/2) inhibitor U0126, suggesting that MEK1/2 is involved in the downregulation of apoE promoter activity by Hcy. Our data demonstrated that Hcy-induced inhibition of apoE took place through activation of NF-κB. Moreover, we demonstrated that Hcy activated a synthetic promoter containing three NF-κB binding sites, but did not affect promoters containing AP-1 or NFAT binding sites. ChIP experiments revealed that NF-κB p65 subunit is recruited to the apoE promoter following Hcy treatment of cells.

CONCLUSION: Hcy-induced stress negatively modulates apoE expression via MEK1/2 and NF-κB activation. The decreased apoE expression in peripheral tissues may aggravate atherosclerosis, neurodegenerative diseases and renal dysfunctions.

Elevated fibrinogen and lowered homocysteine-vitamin determinants and their association with left atrial thrombus in patients with rheumatic mitral stenosis

Mitral stenosis (MS) causes stagnation of blood flow, leading to thrombus formation in the left atrium (LA), which may lead to systemic thrombo-embolic complications and stroke. We compared the alterations in echocardiographic and procoagulant parameters in patients with severe rheumatic MS with and without LA thrombus. The study was a cross-sectional study of patients with rheumatic MS, being evaluated for percutaneous mitral commisurotomy. Group 1 patients comprised of patients with rheumatic MS with LA thrombus (n=35) and Group 2 patients had rheumatic MS without LA thrombus (n = 45). Platelet aggregability, fibrinogen, homocysteine, vitamin B12 and folate; mitral valve area (MVA), mean mitral gradient and pulmonary artery pressure (PAP) were assessed in all study subjects. Significant increase in fibrinogen, homocysteine and platelet aggregation and fall in homocysteine-associated determinants were seen in Group 1, as compared with Group 2. Raised fibrinogen, lowered homocysteine-vitamin determinants and lowered mitral valve area were associated independently, with presence of LA thrombus in rheumatic MS. In this study, fibrinogen, vitamin B12 and folate were independently associated with the occurrence of thrombus in patients with rheumatic MS. Hence, our results suggest that increase in procoagulant mechanisms contribute to increased risk of thrombosis in the left atrium in patients with rheumatic MS.

The potential physiological crosstalk and interrelationship between two sovereign endogenous amines, melatonin and homocysteine

The antioxidant melatonin and the non-proteinogenic excitotoxic amino acid homocysteine (Hcy) are very distinct but related reciprocally to each other in their mode of action. The elevated Hcy level has been implicated in several disease pathologies ranging from cardio- and cerebro-vascular diseases to neurodegeneration owing largely to its free radical generating potency. Interestingly, melatonin administration potentially normalizes the elevated Hcy level, thereby protecting the cells from the undesired Hcy-induced excitotoxicity and cell death. However, the exact mechanism and between them remain obscure. Through literature survey we have found an indistinct but a vital link between melatonin and Hcy i.e., the existence of reciprocal regulation between them, and this aspect has been thoroughly described herein. In this review, we focus on all the possibilities of co-regulation of melatonin and Hcy at the level of their production and metabolism both in basal and in pathological conditions, and appraised the potential of melatonin in ameliorating homocysteinemia-induced cellular stresses. Also, we have summarized the differential mode of action of melatonin and Hcy on health and disease states.

Biomarkers of occupational exposure to air pollution, inflammation and oxidative damage in taxi drivers

Exposure to environmental pollutants has been recognised as a risk factor for cardiovascular events. 1-hydroxypyrene (1-OHP) is a biomarker of exposure to polycyclic aromatic hydrocarbons (PAHs) from traffic-related air pollution. Experimental studies indicate that PAH exposure could be associated with inflammation and atherogenesis. Thus, the purpose of this study was to evaluate whether the biomarker of PAH exposure is associated with biomarkers of inflammation and oxidative stress and if these effects modulate the risk of developing cardiovascular diseases in workers exposed to air pollution. This study included 60 subjects, comprising 39 taxi drivers and 21 non-occupationally exposed persons. Environmental PM2.5 and benzo[a]pyrene (BaP) levels, in addition to biomarkers of exposure and oxidative damage, were determined. Inflammatory cytokines (IL-1β, IL-6, IL-10, TNF-α, IFN-γ and hs-CRP) and serum levels of oxidised LDL (ox-LDL), auto-antibodies (ox-LDL-Ab) and homocysteine (Hcy) were also evaluated. PM2.5 and BaP exhibited averages of 12.4±6.9 μg m(-3) and 1.0±0.6 ng m(-3), respectively. Urinary 1-OHP levels were increased in taxi drivers compared to the non-occupationally exposed subjects (p<0.05) and were positively correlated with pro-inflammatory cytokines and negatively correlated with antioxidants. Furthermore, taxi drivers had elevated pro-inflammatory cytokines, biomarkers of oxidative damage, and ox-LDL, ox-LDL-Ab and Hcy levels, although antioxidant enzymes were decreased compared to the non-occupationally exposed subjects (p<0.05). In summary, our findings indicate that taxi drivers showed major exposure to pollutants, such as PAHs, in relation to non-occupationally exposed subjects. This finding was associated with higher inflammatory biomarkers and Hcy, which represent important predictors for cardiovascular events. These data suggest a contribution of PAHs to cardiovascular diseases upon occupational exposure.

Ethanol promotes rat aortic vascular smooth muscle cell proliferation via increase of homocysteine and oxidized-low-density lipoprotein

BACKGROUND

Increased levels of homocysteine and oxidized low-density lipoprotein (Ox-LDL) are considered independent risk factors for atherosclerosis. However, no previous study has examined the effects of ethanol-induced increase of homocysteine and Ox-LD on aortic vascular smooth muscle cell (VSMC) proliferation. The aim of the present study was to investigate the relationship between ethanol consumption, increase in homocysteine, Ox-LDL, and aortic VSMC proliferation in rats.

METHODS AND RESULTS

To address this issue, 24 male Wistar rats were randomly divided into three groups: control, sham, and ethanol-treated. Homocysteine, Ox-LDL, lipid profile, and aortic VSMC proliferation were assessed after 42 days. The results revealed a concurrent, significant increase in homocysteine and Ox-LDL levels, lipid profile levels, and aortic VSMC proliferation in the ethanol-treated group compared with the control and sham groups.

CONCLUSION

Based on these results, we conclude that ethanol apparently exerts aortic VSMC proliferation through increase in homocysteine and Ox-LDL-mediated oxidative stress, which in turn trigger proatherogenic changes in the aortic wall.

Increased expression of tumor necrosis factor-alpha in the rat hippocampus after acute homocysteine administration

Background and Purpose:

This paper evaluated the effect of acute homocysteine administration on inflammatory cytokine tumor necrosis factor-alpha (TNF-α) expression and neuronal apoptosis in the rat hippocampus and investigated the effects of vitamin C treatment on homocysteine-induced inflammation and neuronal death.

Methods:

Subjects were three-week-old, male Sprague-Dawley rats. Rats for the control group, we injected saline solution into the rats’ abdominal cavities for one week. Rats in the second group received 1 injection of homocysteine (11 mmol/kg) into their abdominal cavities after 1 week of saline solution administration. For the third group, we injected the rats with vitamin C (100 mg/kg) for a week, followed by 1 injection of homocysteine. The hippocampi were stained with an anti-TNF-α antibody, and apoptosis was evaluated using the TUNEL staining method.

Results:

The homocysteine-injected rats had strong TNF-α expression in every hippocampal region. Vitamin C significantly reduced TNF-α expression in the hippocampus’s CA1 region. Acute homocysteine administration did not cause apoptosis in the hippocampus.

Conclusions:

The pro-inflammatory cytokine TNF-α may mediate elevated homocysteine levels’ contributions to inflammatory reactions, and vitamin C has some protective effect on inflammatory reactions in the CA1 hippocampal region.

Stroke: roles of B vitamins, homocysteine and antioxidants

In the present review concerning stroke, we evaluate the roles of B vitamins, homocysteine and antioxidant vitamins. Stroke is a leading cause of death in developed countries. However, current therapeutic strategies for stroke have been largely unsuccessful. Several studies have reported important benefits on reducing the risk of stroke and improving the post-stroke-associated functional declines in patients who ate foods rich in micronutrients, including B vitamins and antioxidant vitamins E and C. Folic acid, vitamin B6and vitamin B12are all cofactors in homocysteine metabolism. Growing interest has been paid to hyperhomocysteinaemia as a risk factor for CVD. Hyperhomocysteinaemia has been linked to inadequate intake of vitamins, particularly to B-group vitamins and therefore may be amenable to nutritional intervention. Hence, poor dietary intake of folate, vitamin B6and vitamin B12are associated with increased risk of stroke. Elevated consumption of fruits and vegetables appears to protect against stroke. Antioxidant nutrients have important roles in cell function and have been implicated in processes associated with ageing, including vascular, inflammatory and neurological damage. Plasma vitamin E and C concentrations may serve as a biological marker of lifestyle or other factors associated with reduced stroke risk and may be useful in identifying those at high risk of stroke. After reviewing the observational and intervention studies, there is an incomplete understanding of mechanisms and some conflicting findings; therefore the available evidence is insufficient to recommend the routine use of B vitamins, vitamin E and vitamin C for the prevention of stroke. A better understanding of mechanisms, along with well-designed controlled clinical trials will allow further progress in this area.

Homocysteine and inflammation as main determinants of oxidative stress in the elderly

Oxidative stress is commonly observed in the elderly and could be involved in age-related diseases. However, the determinants of superoxide anion overproduction are not clearly understood. Superoxide anion production was evaluated using a lucigenin-based chemiluminescence method in 478 elderly subjects (304 women, 174 men; 79.5+/-7.1 years). Homocysteine (HCy) metabolism (homocysteinemia, vitamin B12, plasma, and erythrocyte folates), inflammation (CRP, fibrinogen, alpha-1 acid glycoprotein), lipid parameters (total cholesterol, triglycerides, HDL and LDL cholesterol), and nutritional parameters (albumin, transthyretin) were determined. The results show that HCy levels (p<0.001) and superoxide anion production (p=0.04) increase with aging, but CRP does not. Highest HCy (>20 microM) (OR 1.83 (1.09-3.07), p=0.02) and CRP over 5 mg/L (adjusted OR 2.01 (1.15-3.51), p=0.01) are the main determinants in superoxide anion production in the elderly. These clinical data are confirmed in an in vitro study using THP-1 monocyte-like cells. Incubation with HCy thiolactone (HTL) (0-200 microM) and LPS (0-20 ng/ml) dramatically enhances NADPH oxidase expression and activation. Moreover, a synergic action was evidenced for low concentrations of HTL (20 microM) and LPS (5 ng). Taken together, the clinical data and in vitro experiments support the hypothesis that moderate homocysteinemia and low-grade inflammation synergically enhance NADPH oxidase activity in the elderly.

Homocysteine stimulates monocyte chemoattractant protein-1 expression in mesangial cells via NF-kappaB activation

Hyperhomocysteinemia is regarded as an independent risk factor for cardiovascular disorders. Although renal dysfunction or failure is one of the important factors causing hyperhomocysteinemia, the role of homocysteine (Hcy) in the development of glomerulosclerosis is largely unknown. One of the key events in the pathogenesis of glomerulosclerosis is the infiltration of circulating monocytes into affected glomeruli. The objective of the present study was to investigate the effect of Hcy on the expression of monocyte chemoattractant protein-1 (MCP-1) in kidney mesangial cells and the mechanisms involved. Levels of MCP-1 and mRNA were significantly elevated in Hcy-treated rat mesangial cells. This increase was associated with activation of NF-kappaB as a result of increased phosphorylation of the inhibitor protein IkappaBalpha. Monocyte chemotactic activity in these cells was also enhanced. In addition, there was a significant elevation of superoxide anion produced by Hcy-treated cells, which preceded the increased phosphorylation of IkappaBalpha. Addition of superoxide dismutase or NF-kappaB inhibitors to the culture medium abolished Hcy-induced NF-kappaB activation and MCP-1 expression. Taken together, these results indicate that Hcy induced MCP-1 expression in mesangial cells. Such a process was mediated by oxidative stress and NF-kappaB activation. This may further aggravate renal function in patients with hyperhomocysteinemia.

Hyperhomocysteinemia, inflammation and autoimmunity

Hyperhomocysteinemia is independently associated with the development of coronary, cerebral and peripheral vascular disease and deep-vein thrombosis in the general population. The evidence that cardiovascular involvement is particularly frequent and advanced in patients affected with several autoimmune diseases (AD), in which hyperhomocysteinemia represent a common finding, led to an intensive investigation on homocysteine (Hcy) as a putative risk factor for the development of cardiovascular disease in such subjects. Indeed, recent data intriguingly expanded the spectrum of the possible pathogenetic implications for hyperhomocysteinemia in the course of AD. In fact, a bi-directional link seems to connect Hcy and the immuno-inflammatory activation characterizing AD, in which immuno-inflammatory activation may contribute to Hcy increase, and Hcy, in its turn, may act as a pro-inflammatory and immuno-stimulating molecule putatively cooperating to the injury of the disease-specific target organs, at least in rheumatoid arthritis and inflammatory bowel disease. Moreover, Hcy may be also a trigger of autoimmune reactions through its capability to bind and structurally modify specific proteins, then resulting in neoantigens formation potentially relevant either in the onset of specific AD and in the progression of the associated cardiovascular damage. More investigation is necessary to fully define the clinical relevance of such phenomena.

Effects of heparin on the production of homocysteine-induced extracellular matrix metalloproteinase-2 in cultured rat vascular smooth muscle cells

OBJECTIVE

To study the effects of heparin on the production of homocysteine-induced extracellular matrix metalloproteinase-2 (MMP-2) in cultured rat vascular smooth muscle cells.

METHODS

The effects of different homocysteine levels (0 micromol/L to 1000 micromol/L) on MMP-2 production and the effects of different heparin concentrations (0 microg/mL to 100 microg/mL) on homocysteine-induced MMP-2 in cultured rat vascular smooth muscle cells were examined using gelatin zymography and Western blotting. The changes in MMP-2 were further compared with various treatments for 24 h, 48 h and 72 h.

RESULTS

Homocysteine (50 micromol/L to 1000 micromol/L) increased the production of MMP-2 significantly in a dose-dependent manner. Increased production of MMP-2 induced by homocysteine was reduced by the extracellular addition of heparin in a dose-dependent manner. Production of MMP-2 with various treatment regimens for 72 h was greater than for 24 h and 48 h.

CONCLUSIONS

Extracellular addition of heparin decreased homocysteine-induced MMP-2 secretion. Data suggest a mechanism by which hyperhomocysteinemia is involved in the pathogenesis of coronary artery disease and demonstrate a beneficial effect of heparin on these conditions.

Alpha1D-adrenoceptor-induced relaxation on rat carotid artery is impaired during the endothelial dysfunction evoked in the early stages of hyperhomocysteinemia

Hyperhomocysteinemia is a known risk factor for cardiovascular diseases, but the underlying mechanisms of this pathology are complex. We aimed to evaluate the effect of hyperhomocysteinemia in vasorelaxations induced by alpha(1D)-adrenoceptor agonists. Vascular reactivity of rat carotid artery to the alpha-adrenoceptor agonist, phenylephrine, was enhanced in hyperhomocysteinemia. Mechanical removal of endothelium did not modify the carotid responsiveness to phenylephrine, compared to control. Phenylephrine induces endothelium-dependent relaxation, in the presence of 5-methyl urapidil (alpha(1A)-adrenoceptor antagonist). We hypothesised that endothelial-relaxant alpha(1)-adrenoceptors are impaired by hyperhomocysteinemia. Incubation with prazosin (selective alpha(1)-adrenoceptor antagonist) or BMY7378 (8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4,5]decane-7, 9-dione dihydrochloride) (selective alpha(1D)-adrenoceptor antagonist), similarly inhibited phenylephrine-induced relaxations in both control and hyperhomocysteinemic carotids. Immunohistochemistry showed enhanced immunoreactivity for eNOS and iNOS in hyperhomocysteinemic rats. In carotid arteries from hyperhomocysteinemic rats there was a decrease in superoxide dismutase activity and enhanced superoxide anion production. We conclude that alpha(1D)-adrenoceptors mediate endothelium-dependent relaxation triggered by phenylephrine in rat carotid artery and affect the final tone. Furthermore, the enhanced phenylephrine-induced contraction in carotid artery due to hyperhomocysteinemia is endothelium-dependent and involves a loss of the inhibitory effect of relaxant alpha(1D)-adrenoceptors by reducing NO biodisponibility.

Association of plasma homocysteine with serum interleukin-6 and C-peptide levels in patients with type 2 diabetes

Hyperhomocysteinemia is an independent risk factor for atherosclerotic disease. Because serum markers of inflammation and the metabolic syndrome are also associated with atherosclerotic disease and insulin resistance, we investigated whether plasma homocysteine (Hcy) levels were associated with serum markers of inflammation and factors of metabolic syndrome in 223 elderly patients with type 2 diabetes mellitus. The levels of plasma Hcy and serum interleukin-6 (IL-6), high-sensitivity C-reactive protein, and C-peptide were measured. The C677T mutation of methylenetetrahydrofolate reductase (MTHFR) gene was detected using the polymerase chain reaction-restriction fragment length polymorphism method. The number of abnormal metabolic factors (presence of diabetes, blood pressure > or =130/85 mm Hg, triglycerides > or =150 mg/dL, high-density lipoprotein cholesterol <35 mg/dL (men) or <39 mg/dL (women), or body mass index >25 kg/m 2 ) was assessed. Elevated plasma Hcy levels correlated significantly with serum IL-6 ( r = 0.25, P < .001), C-peptide ( r = 0.22, P < .01), and the number of abnormal metabolic factors ( r = 0.20, P < .01), but not with C-reactive protein. Multiple linear regression analysis revealed that log-transformed IL-6, serum C-peptide, vitamin B12 , and creatinine were significant determinants of plasma Hcy levels. The correlation between Hcy and IL-6 levels was strongest in those with TT genotype of C677T MTHFR among 3 genotypes. The association between plasma Hcy and serum IL-6 levels supports the hypothesis that the activation of innate immunity is involved in the pathogenesis of arteriosclerosis in patients with diabetes mellitus who are homozygous for the TT genotype of C677T MTHFR.

Negative association between circulating total homocysteine and proinflammatory chemokines MCP-1 and RANTES in prepubertal lean, but not in obese, children

This study investigated in prepubertal obese children (POC), compared with prepubertal lean children (PLC), a possible relation among plasma total homocysteine (tHcy)-an independent risk factor for future atherosclerosis-and MCP-1 and RANTES, two circulating chemokines inducing leukocyte transendothelial migration (TEM), implicated in the initial stages of the inflammatory part of the atherosclerotic process. Seventy-two POC were evaluated for circulating tHcy, MCP-1, and RANTES, and compared with 42 healthy PLC. The mean adjusted (for age, sex as well as log10total insulin, vitB12, folate, total cholesterol, HDL cholesterol, log10triglycerides, and log10glucose levels) differences in tHcy, MCP-1, and RANTES levels between PLC and POC were all significant [1.16 nmol/mL (P = 0.03), 26.6 pg/mL (P = 0.02), and 52.9 pg/mL (P = 0.03), respectively]. In PLC, but not in POC, tHcy levels were negatively associated with both circulating MCP-1 (B = -1.68, P = 0.007) and RANTES (B = -1.16, P = 0.01) after adjusting for age, sex, BMI, as well as log10total insulin, vitB12, folate, total cholesterol, HDL cholesterol, log10triglycerides, and log10glucose levels. In conclusion, in POC there is a lack, in contrast to PLC, of a possibly autoregulatory, negative association of elevated tHcy levels to increased MCP-1 and RANTES levels. This could contribute to future, homocysteine-induced atherosclerosis.

Inflammation meets oxidation: NF-kappaB as a mediator of initial lesion development in atherosclerosis

Transcription factor nuclear factor-kappaB (NF-kappaB) and its target genes are involved in the pathogenesis of atherosclerosis, in addition to many other diseases. Monocyte recruitment into subendothelial space is primarily mediated by NF-kappaB-dependent gene expression, and this event is a crucial milestone, because it is nearly impossible to reverse the progression of the lesion after this point. Recent advances in our understanding of atherosclerosis as a disease of childhood enforces the necessity of developing novel approaches for prevention and treatment. Here, the authors address NF-kappaB as a major therapeutic target, especially for preventive measures, in the light of two main hypotheses of atherosclerosis: oxidation and inflammation.

Plasma homocysteine and inflammation in elderly patients with cardiovascular disease and dementia

Increased levels of plasma total homocysteine (tHcy) may play a role in both cardiovascular diseases (CVD) and old-age dementias via enhancement of vascular inflammation. However, the association between plasma tHcy and serum C-reactive protein (sCRP), taken as a marker of low-grade inflammation, is still uncertain. We investigated this association in normal aging, CVD, and dementia, and examined whether it was modified by the presence of two major comorbid diseases of older age: chronic obstructive pulmonary disease (CPOD) and peptic ulcer (PU). Six hundred-twenty-seven individuals aged > or = 65 yr (74+/-7 yr) were selected for this study: 373 healthy controls; 160 patients with CVD but no evidence of comorbid diseases (CVD+/comorbidity-); 46 patients with CVD and concurrent CPOD and/or PU (CVD+/comorbidity+); and 48 patients with dementia. A positive association between plasma tHcy and serum CRP, independent of several confounders (socio-demographic status, known tHcy and sCRP determinants, inflammation markers, traditional vascular risk factors), was found for CVD+/comorbidity+ (p=0.001; not affected by dementia type) and dementia (p=0.001; not affected by dementia type), but not for CVD+/comorbidity- and controls. The results suggest that the association between plasma tHcy and sCRP is more an aspecific reflection of poor health than a specific correlate of vascular inflammation.

Nitric oxide modulates MCP-1 expression in endothelial cells: implications for the pathogenesis of pulmonary granulomatous vasculitis

Monocyte chemoattractant protein-1 (MCP-1) is a pivotal mediator of angiocentric granuloma formation in glucan-induced pulmonary granulomatous vasculitis. Based on the rationale that mononuclear phagocytes retrieved from granulomas are rich sources of nitric oxide (NO) and that the recruitment of mononuclear phagocytes into lesions abates as granuloma formation slows, we tested the hypothesis that MCP-1 gene expression is regulated by a NO-sensitive mechanism. Preexposure of endothelial cell (EC) monolayers to NO donor compounds markedly reduced cytokine-induced MCP-1 expression and cytosolic-to-nuclear translocation of nuclear factor-kappa B (NF-kappaB), reversed fluctuations in endothelial reduced glutathione (GSH) pools but did not affect cGMP concentrations. The lungs of mice bearing targeted disruptions of the inducible nitric oxide synthase (iNOS) gene exhibited significantly higher concentrations of MCP-1 following glucan infusion than did those of wild-type mice. Cumulatively, these data suggest that NO suppresses MCP-1 expression by blunting the redox changes associated with cytokine-induced EC activation.

Increased superoxide production in coronary arteries in hyperhomocysteinemia: role of tumor necrosis factor-alpha, NAD(P)H oxidase, and inducible nitric oxide synthase

OBJECTIVE

In coronary arteries, hyperhomocysteinemia (HHcy, a known risk factor for coronary heart disease) impairs flow-induced dilations, which can be reversed by superoxide dismutase (SOD). To evidence increased O2*- generation and elucidate its source, we characterized changes in activity (lucigenin chemiluminescence, hydroethidine staining) and expression of arterial pro- and antioxidant systems (Western blotting, immunohistochemistry, cDNA microarray, reverse-transcription polymerase chain reaction) in the coronary arteries of rats by using methionine diet-induced HHcy.

METHODS AND RESULTS

The increased generation of O2*- by HHcy coronary arteries was inhibited by SOD, diphenyleneiodonium, apocynin, and apocynin plus amino guanidine but was unaffected by allopurinol and rotenone. Also, diphenyleneiodonium-sensitive NADPH-driven O2*- generation was increased in HHcy vessels. In HHcy arteries expression of the smooth muscle-confined NAD(P)H oxidase subunit nox1 and that of iNOS was increased. Expression of p67phox, p22phox, and p47phox subunits and that of endothelial nitric oxide synthase, Cu,Zn-SOD, Mn-SOD, extracellular SOD (mRNA), and xanthine oxidase was unchanged. Microarray analysis showed increased expression of tumor necrosis factor (TNF)-alpha (confirmed by reverse-transcription polymerase chain reaction, Western blotting, and immunohistochemistry) that was localized in smooth muscle. In vitro incubation (18 hours) of HHcy arteries with anti-TNF-alpha antibody decreased O2*- production, whereas incubation of control vessels with TNF-alpha increased O2*- generation and nox1 expression.

CONCLUSIONS

In coronary arteries, HHcy increases TNF-alpha expression, which enhances oxidative stress through upregulating a nox1-based NAD(P)H oxidase and inducible nitric oxide synthase. Thus, TNF-alpha induces a proinflammatory vascular phenotype in HHcy that potentially contributes to the development of coronary atherosclerosis.

Plasma homocysteine is regulated by phospholipid methylation

Mild hyperhomocysteinemia is an independent risk factor for cardiovascular disease. Homocysteine, a non-protein amino acid, is formed from S-adenosylhomocysteine and partially secreted into plasma. A potential source for homocysteine is methylation of the lipid phosphatidylethanolamine to phosphatidylcholine by phosphatidylethanolamine N-methyltransferase in the liver. We show that mice that lack phosphatidylethanolamine N-methyltransferase have plasma levels of homocysteine that are approximately 50% of those in wild-type mice. Hepatocytes isolated from methyltransferase-deficient mice secrete approximately 50% less homocysteine. Rat hepatoma cells transfected with phosphatidylethanolamine N-methyltransferase secrete more homocysteine than wild-type cells. Thus, phosphatidylethanolamine N-methyltransferase is an important source of plasma homocysteine and a potential therapeutic target for hyperhomocysteinemia.

Homocysteine decreases endothelin-1 expression by interfering with the AP-1 signaling pathway

The increased cardiovascular risk associated with hyperhomocysteinemia has been linked to homocysteine-induced endothelial cell (EC) dysfunction. Endothelin-1 is a vasoactive peptide, synthesized mainly by vascular ECs. We have previously shown that homocysteine decreases endothelin-1 biosynthesis. Here we addressed the molecular mechanism of endothelin-1 regulation by homocysteine. Experiments with the transcription inhibitor actinomycin D indicated that the decrease in preproendothelin-1 mRNA content in homocysteine-treated cells did not result from transcript destabilization. Transient transfection assays demonstrated that homocysteine downregulated endothelin-1 at the transcriptional level by decreasing preproendothelin-1 promoter activity. Mutation of the activator protein-1 (AP-1) site of the promoter eliminated the repression induced by homocysteine. Western blot analysis showed that the homocysteine-induced decrease in promoter activity was not associated with reduced expression of the AP-1 components c-Fos and c-Jun. The inhibitory action of homocysteine on preproendothelin-1 mRNA expression was not prevented by cycloheximide. Electrophoretic mobility shift assays demonstrated that homocysteine reduced the binding activity of ECs nuclear extracts to an AP-1 consensus site. These results indicate that homocysteine downregulates endothelin-1 synthesis by inhibiting AP-1 activity, and that the AP-1 signaling pathway may be of major importance in homocysteine-induced endothelial dysfunction.