Homocysteine: an emergent cardiovascular risk factor?

Involvements of Hyperhomocysteinemia in Neurological Disorders

Homocysteine (HCY), a physiological amino acid formed when proteins break down, leads to a pathological condition called hyperhomocysteinemia (HHCY), when it is over a definite limit. It is well known that an increase in HCY levels in blood, can contribute to arterial damage and several cardiovascular disease, but the knowledge about the relationship between HCY and brain disorders is very poor. Recent studies demonstrated that an alteration in HCY metabolism or a deficiency in folate or vitamin B12 can cause altered methylation and/or redox potentials, that leads to a modification on calcium influx in cells, or into an accumulation in amyloid and/or tau protein involving a cascade of events that culminate in apoptosis, and, in the worst conditions, neuronal death. The present review will thus summarize how much is known about the possible role of HHCY in neurodegenerative disease.

Homocysteine pre-treatment increases redox capacity in both endothelial and tumor cells

OBJECTIVE

We studied the modulatory effects of homocysteine pre-treatment on the disulfide reduction capacity of tumor and endothelial cells.

METHODS

Human MDA-MB-231 breast carcinoma and bovine aorta endothelial cells were pre-treated for 1-24 hours with 0.5-5 mM homocysteine or homocysteine thiolactone. After washing to eliminate any rest of homocysteine or homocysteine thiolactone, cell redox capacity was determined by using a method for measuring disulfide reduction.

RESULTS

Homocysteine pre-treatments for 1-4 hours at a concentration of 0.5-5 mM increase the disulfide reduction capacity of both tumor and endothelial cells. This effect cannot be fully mimicked by either cysteine or homocysteine thiolactone pre-treatments of tumor cells.

DISCUSSION

Taken together, our data suggest that homocysteine can behave as an anti-oxidant agent by increasing the anti-oxidant capacity of tumor and endothelial cells.

Relationship between High Serum Cystatin C Levels and the Risk of Gestational Diabetes Mellitus

Aims

Serum cystatin C (CysC) has recently been shown to be associated with the incidence of type 2 diabetes mellitus (T2DM) and progression to the pre-diabetic state. The aim of this study was to explore the relationship between serum CysC and the risk of gestational diabetes mellitus (GDM) in Chinese pregnant women.

Methods

This cross-sectional study consisted of 400 pregnant women including111 with GDM and 289 with normal glucose tolerance at 24–28 weeks of gestation. The subjects were further divided into four groups according to the CysC quartiles, and their clinical characteristics were compared. The serum CysC concentration was measured using immunoturbidimetry and the degree of insulin resistance was assessed by the homeostasis model assessment of insulin resistance (HOMA-IR).

Results

Serum CysC levels were significantly higher in pregnant women with GDM than in the healthy pregnant women[1.0(0.8–1.8) vs 0.7(0.6–1.0), P<0.01). The Spearman’s correlation analysis showed that serum CysC was positively associated with HOMA-IR(r = 0.118, P<0.05) and the occurrence of GDM(r = 0.348, P<0.01). The pregnant women were divided into quartiles according to their serum CysC concentrations. Compared to the first quartile, pregnant women in Q2 (OR, 2.441; P = 0.025), Q3 (OR, 3.383; P = 0.001) and Q4 (OR, 5.516; P<0.001) had higher risk of GDM after adjusted for age, BMI, HbA1c and HOMA-IR. Further, with a rise in the serum CysC, there was an increasing trend in the HOMA-IR levels (P<0.05). A binary logistic regression analysis after adjusting for other confounding variables revealed a significant and independent association between serum CysC and GDM [OR = 14.269; 95% confidence interval, 4.977–40.908, P<0.01].The receiver operating characteristic curve analysis revealed that the optimal cutoff point for serum CysC to indicate GDM was 0.95mg/L.

Conclusions

Serum CysC is significantly and independently associated with insulin resistance and GDM. It may be a helpful biomarker to identify the risk of GDM in Chinese pregnant women.

Erythrocyte glutathione transferase activity: a possible early biomarker for blood toxicity in uremic diabetic patients

Erythrocyte glutathione transferase (e-GST) displays increased activity in patients with renal damage and positive correlation with homocysteine (Hcy) in patients under maintenance hemodialysis. Here, we determined e-GST, Hcy, and erythrocyte catalase (e-CAT) in 328 patients affected by type 2 diabetes mellitus (T2DM), 61 diabetic non-nephropathic patients and 267 affected by diabetes and by chronic kidney disease (CKD) under conservative therapy subdivided into four stages according to K-DOQI lines. e-GST activity was significantly higher in all T2DM patients compared to the control group (7.90 ± 0.26 vs. 5.6 ± 0.4 U/g(Hb)), and we observed an enhanced activity in all subgroups of CKD diabetic patients. No significant correlation or increase has been found for e-CAT in all patients tested. Mean Hcy in diabetic patients is higher than that in healthy subjects (33.42 ± 1.23 vs. 13.6 ± 0.8 μM), and Hcy increases in relation to the CKD stage. As expected, a significant correlation was found between e-GST and Hcy levels. These findings suggest that e-GST hyperactivity is not caused directly by diabetes but by its consequent renal damage. e-GST, as well as Hcy, may represent an early biomarker of renal failure.

Hemin/G-quadruplex-catalyzed aerobic oxidation of thiols to disulfides: application of the process for the development of sensors and aptasensors and for probing acetylcholine esterase activity

This study describes the novel hemin/G-quadruplex DNAzyme-catalyzed aerobic oxidation of thiols to disulfides and the respective mechanism. The mechanism of the reaction involves the DNAzyme-catalyzed oxidation of thiols to disulfides and the thiol-mediated autocatalytic generation of H2O2 from oxygen. The coupling of a concomitant H2O2-mediated hemin/G-quadruplex-catalyzed oxidation of Amplex Red to the fluorescent resorufin as a transduction module provides a fluorescent signal for probing the catalyzed oxidation of the thiol to disulfides and for probing sensing processes that yield the hemin/G-quadruplex as a functional label. Accordingly, a versatile sensing method for analyzing thiols (L-cysteine, glutathione) using the H2O2-mediated DNAzyme-catalyzed oxidation of Amplex Red to the resorufin was developed. Also, the L-cysteine and Amplex Red system was implemented as an auxiliary fluorescent transduction module for probing recognition events that form the catalytic hemin/G-quadruplex structures. This is exemplified with the development of thrombin aptasensor. The thrombin/thrombin binding aptamer recognition complex binds hemin, and the resulting catalytic complex activates the auxiliary transduction module, involving the aerobic oxidation of l-cysteine and the concomitant formation of the fluorescent resorufin. Finally, the hemin/G-quadruplex DNAzyme/Amplex Red system was used to follow the activity of acetylcholine esterase, AChE, and to probe its inhibition. The AChE-catalyzed hydrolysis of acetylthiocholine to the thiol-functionalized thiocholine enabled the probing of the enzymatic activity of AChE through the hemin/G-quadruplex-catalyzed aerobic oxidation of thiocholine to the respective disulfide and the concomitant generation of the fluorescent resorufin product.

Thiol reactive probes and chemosensors

Thiols are important molecules in the environment and in biological processes. Cysteine (Cys), homocysteine (Hcy), glutathione (GSH) and hydrogen sulfide (H₂S) play critical roles in a variety of physiological and pathological processes. The selective detection of thiols using reaction-based probes and sensors is very important in basic research and in disease diagnosis. This review focuses on the design of fluorescent and colorimetric probes and sensors for thiol detection. Thiol detection methods include probes and labeling agents based on nucleophilic addition and substitution, Michael addition, disulfide bond or Se-N bond cleavage, metal-sulfur interactions and more. Probes for H₂S are based on nucleophilic cyclization, reduction and metal sulfide formation. Thiol probe and chemosensor design strategies and mechanism of action are discussed in this review.

Value and level of plasma homocysteine in patients with angina pectoris undergoing coronary angiographic study

This study tested whether the plasma level of total homocysteine (tHcy) was predictive of obstructive coronary artery disease (CAD) and clinical outcome in patients undergoing coronary angiographic (CAG) study. From September 2002 to October 2004, 1,305 consecutive patients with angina pectoris undergoing CAG study were consecutively enrolled. Blood samples were prospectively collected to assess the plasma level of tHcy from each patient before catheterization. Of these 1305 patients, 676 (51.8%) had multivessel disease (group 1), 367 (28.1%) had single-vessel disease (group 2), and 262 (20.1%) had normal coronary artery or insignificant coronary artery disease (group 3). The plasma level of tHcy was notably higher in group 1 than in groups 2 and 3 (11.6 ± 4.4 versus 10.9 ± 4.0 versus 10.4 ± 3.8, P < 0.001). Univariate binary logistic regression analysis demonstrated that the plasma tHcy level was strongly associated with multiple-vessel disease (MVD) (defined as ≥ 2 vessel disease) (P < 0.001). Multivariate binary logistic regression analysis showed that tHcy level, fasting blood sugar, diabetes mellitus, and age were significantly and independently predictive of MVD (all P < 0.03). Univariate Cox regression analysis demonstrated that tHcy level was predictive of long-term mortality (P = 0.042). However, the tHcy level was not an independent predictor of long-term mortality on multivariate Cox regression analysis (P > 0.05). The results of our study support the hypothesis that tHcy level is an independent predictor of MVD in patients with chest pain undergoing CAG study. Conversely, our study did not support the tHcy level as an independent predictor of long-term mortality in this clinical setting.

Regulatory cross-talk of mouse liver polyamine and methionine metabolic pathways: a systemic approach to its physiopathological consequences

Both polyamines and methionine derivatives are nitrogen compounds directly related to the regulation of gene expression. In silico predictions and experimental evidence suggest a cross-talk between polyamine and methionine metabolism in mammalian tissues. Since liver is the major organ that controls nitrogen metabolism of the whole organism, it is the best tissue to further test this hypothesis in vivo. In this work, we studied the effects of the chronic administration of a methionine-supplemented diet (0.5% Met in drinking water for 5 months) on the liver of mice (designated as MET-mice). Metabolic and proteomic approaches were performed and the data obtained were subjected to biocomputational analysis. Results showed that a supplemental methionine intake can indeed regulate biogenic amine metabolism in an in vivo model by multiple mechanisms including metabolic regulation and specific gene demethylation. Furthermore, putative systemic effects were investigated by molecular and cellular biology methods. Among other results, altered expression levels of multiple inflammation and cell proliferation/death balance markers were found and macrophage activation was observed. Overall, the results presented here will be of interest across a variety of biomedical disciplines, including nutrition, orphan diseases, immunology and oncology.

Effect of lipopenic and hypotensive treatment on homocysteine levels in type 2 diabetics

AIM

Evaluate the effect of lipopenic and hypotensive treatment on homocysteine levels.

METHODS

We recruited 145 type 2 diabetics and 130 control subjects. Thirty-seven diabetics had no complications, 54 had microvascular complications and 54 had macrovascular complications. We determined the parameters homocysteine of lipid, vitamin B12, triglycerides, and folates for all subjects. Associated treatments used one or more of the following drugs, statin, fibrate, angiotensin-converting enzyme inhibitor and beta-blockers.

RESULTS

Hyperhomocysteinemia was present in 35.6% of patients. Diabetics had elevated serum levels of triglycerides (P < 0.001), homocysteine (P < 0.01), folates (P < 0.01) and vitamin B12 (P < 0.001). A strong association was found between type 2 diabetes and hyperhomocysteinemia (P < 0.001). Diabetics with associated treatment had elevated homocysteine, vitamin B12 and folate levels when compared to diabetes-free controls. For diabetics with macrovascular complications, we found significant differences in homocysteine (P = 0.010) and folate (P = 0.014) between those taking associated drugs and those who did not. For diabetics with microvascular complications, a significant difference was found in folate only (P = 0.012).

CONCLUSION

Drugs used for hypertension and hyperlipidemia may have an effect on homocysteine levels, for this reason the interaction between drug action and homocysteine levels should be taken into consideration.

Changes in Atrium and Thoracic Aorta Reactivity to Adenosinergic and Adrenergic Agonists in Experimental Hyperhomocysteinemia

We prepared diet-induced hyperhomocysteinemia (hHcy) in adult male Wistar rats and investigated the effects of hHcy on the adenosinergic and adrenergic responses in vitro and in vivo. The responsiveness of right atria from hHcy rats to the negative chronotropic effects of adenosine (Ado) was found to be significantly greater in hHcy rats than in controls. The pD2 value and maximum effect of Ado were significantly increased in 12-week hHcy right atria when compared with those from age-matched controls. The vasodilatory effect of Ado on rat thoracic aorta was also increased in hHcy rats. In the presence of dipyridamole, an Ado uptake inhibitor, the negative chronotropic and vasodilatory effects of Ado were significantly potentiated in the hHcy rats much more than in the control rats. In anesthetized rats, Ado and dipyridamole, given as a rapid bolus into the femoral artery, led to reduction in mean blood pressure and heart rate. This effect was significantly pronounced in hHcy rats when compared with control animals. Otherwise, hHcy atria were found to have increased responsiveness to the positive chronotropic response to isoproterenol, an beta-adrenoceptor agonist. However, there were no significant differences between two groups in the vasoconstrictor effects to phenylephrine, an alpha-adrenoceptor agonist. On the basis of these results, we concluded that hHcy rats were significantly more sensitive to the negative chronotropic and vasorelaxant effects of Ado, possibly because of accelerated cellular Ado uptake and/or a change in Ado receptor-G protein system. This change may be related with the increased responsiveness to beta-adrenergic agonists in hHcy rats, and might contribute to the harmful cardiac effects of hHcy.

Impact of Elevated Plasma Total Homocysteine Concentration on Coronary Atherosclerosis in Chinese Patients With Acute Myocardial Infarction Undergoing Primary Coronary Intervention

Elevated plasma total homocysteine (tHcy) has been considered to be a new risk factor for coronary atherosclerotic disease. However, the association has not been proven indisputably, and the strength of the relationship and the interaction of plasma tHcy with other conventional risk factors remain uncertain in the clinical setting of acute myocardial infarction (AMI). The aim of this study was to investigate whether an elevated plasma level of tHcy is an independent predictor of the late stage of coronary atherosclerotic lesions in Chinese patients with AMI, who are undergoing primary percutaneous coronary intervention (PCI). Plasma levels of tHcy were prospectively measured in 178 consecutive patients with ST-segment elevated AMI undergoing primary PCI. The plasma level of tHcy was also measured in 30 control subjects with normal coronary angiographic findings. The plasma level of tHcy was significantly higher in the patients with AMI than in control subjects (10.5 +/- 3.3 micromol/L versus 8.3 +/- 2.4 micromol/L, P = 0.0004). Multiple stepwise logistic regression analysis of the baseline characteristics demonstrated that smoking (P = 0.004) and creatinine level (P < 0.0001) were independent predictors of an elevated plasma level of tHcy. Moreover, an increased plasma level of tHcy (P = 0.003), female gender (P = 0.008), diabetes mellitus (P = 0.020), and the presence of previous myocardial infarction (P = 0.003) were independent predictors of the late stage of multivessel diffuse atherosclerosis (defined by > or = 2 epicardial vessels with moderate or severe diffuse atherosclerosis). In conclusion, this investigation supports the hypothesis that a raised homocysteine concentration is a strong risk factor for the late stage of diffuse coronary atherosclerosis in Chinese patients with AMI undergoing primary PCI. This result therefore raises the prospect of the need for major therapeutic research in Chinese patients.

Plasma homocysteine in polycystic ovary syndrome: does it correlate with insulin resistance and ethnicity?

BACKGROUND

Polycystic ovary syndrome (PCOS) is associated with insulin resistance and premature coronary artery disease (CAD). Hyperhomocysteinaemia is a recognized risk factor for atherosclerosis, particularly among migrant South Asians, and has recently been shown to be correlated positively with the degree of insulin resistance/hyperinsulinaemia.

OBJECTIVES

To compare total plasma homocysteine (Hcy) in PCOS with controls from ethnic groups at high and low risk of insulin resistance.

METHODS

Case control study of three ethnic groups, Sri Lankans (SL), British Asians (BA) and white Europeans (C), with and without PCOS at specialist centres in Sri Lanka and Yorkshire, UK. Fasting total plasma Hcy concentration was analysed by fluorescence polarization immunoassay and examined for any correlation with age, body mass index (BMI), central obesity, fasting insulin and insulin sensitivity [calculated by the Quantitative Insulin Sensitivity Check Index (QUICKI) method], lipids and testosterone in each ethnic group.

RESULTS

Eighty SL with PCOS and 45 controls, 47 BA with PCOS and 11 controls, and 40 C with PCOS and 22 controls were studied. Both Asian groups with PCOS were younger than affected Europeans (P = 0.008). Sri Lankans with PCOS had significantly lower BMI values than other affected groups: mean +/- SEM (SL) 26.3 +/- 0.95; (BA) 30.59 +/- 7.54; (C) 32.1 +/- 5.95 kg/m2 (P = 0.006). However, waist : hip ratios (WHR) of Sri Lankans with PCOS were similar to others: mean +/- SEM (SL) 0.97 +/- 0.01 (BA) 1.04 +/- 0.02 (C) 0.92 +/- 0.01, P = 0.33. Mean plasma Hcy was significantly higher in all PCOS groups than in their ethnically matched controls (Student's t-test): (SL) 10.2 +/- 1.9 vs 9.0 +/- 3.8, P = 0.01; (BA) 7.9 +/- 1.9 vs 6.8 +/- 2.5, P < 0.0001; (C) 8.3 +/- 2.3 vs 6.8 +/- 1.5, P = 0.0007 micromol/l. Sri Lankans with PCOS had significantly greater Hcy concentrations than British Asians and Europeans with PCOS [P = 0.001; single-factor analysis of variance (anova)] and also significantly greater fasting insulin concentrations [(SL) 242.9 +/- 38.9; (BA) 89.4 +/- 8.9; (C) 48.6 +/- 4.8 pmol/l (P = 0.0003)] and significantly lower QUICKI [(SL) 0.308 +/- 0.004; (BA) 0.335 +/- 0.005; (C) 0.375 +/- 0.002 (P = 0.0007)]. Fasting plasma Hcy correlated best with fasting insulin (r = 0.56, P = 0.0001) and QUICKI (r =-0.53, P < 0.0001) in Sri Lankans with PCOS. Hcy in PCOS subjects from all three ethnic groups correlated significantly with fasting insulin following adjustment for age, BMI and WHR (r = 0.45, P = 0.0001), but this was not evident in the controls (r =-0.32, P = 0.1).

CONCLUSIONS

Elevation of fasting plasma homocysteine in PCOS varies with ethnicity and correlates significantly with fasting insulin. High homocysteine in young Sri Lankans with PCOS has major implications for their long-term risk for atherosclerosis.

An in vitro evaluation of the effects of homocysteine thiolactone on key steps of angiogenesis and tumor invasion

Homocysteine thiolactone is a highly reactive homocysteine derivative that can react easily with proteins. Protein homocysteinylation has been suggested as a possible mechanism underlying the pathological consequences of impaired homocysteine metabolism. Homocysteine inhibits key steps of angiogenesis and tumor invasion. It can be hypothesized that homocysteine thiolactone could mimic the described anti-angiogenic and anti-invasive effects of homocysteine. Therefore, we studied the effects of homocysteine thiolactone on different key steps of angiogenesis and tumor invasion, using model endothelial and tumor cell lines. This study demonstrates that homocysteine thiolactone, in high contrast to homocysteine, is not an anti-angiogenic compound. Furthermore, our results suggest that homocysteine thiolactone could behave as a pro-angiogenic compound.

Comparative effects of atorvastatin, simvastatin, and fenofibrate on serum homocysteine levels in patients with primary hyperlipidemia

Hyperhomocysteinemia is regarded as an independent risk factor for cardiovascular disease. Lipid-lowering agents, such as fibrates, can modify homocysteine levels. However, less is known about the effect of statin therapy on homocysteine. The authors compared the effects of atorvastatin (40 mg/day), simvastatin (40 mg/day), and micronized fenofibrate (200 mg/day) on the serum concentrations of total homocysteine, vitamin B12, and folic acid in patients with primary hyperlipidemia. A total of 128 patients with primary hyperlipidemia (total cholesterol > 240 mg/dL and triglycerides < 350 mg/dL) were assigned to atorvastatin, simvastatin, or fenofibrate. Serum lipid and metabolic parameters were measured at baseline and at 6 and 12 weeks of treatment. Homocysteine correlated positively with serum creatinine and uric acid levels and inversely with serum folic acid levels. All treatment modalities reduced total, low-density lipoprotein (LDL) cholesterol, and triglyceride concentrations. High-density lipoprotein (HDL) cholesterol levels significantly increased only in the fenofibrate-treated patients (47.9 +/- 12.5 vs. 50.7 +/- 12.6 vs. 51.2 +/- 12.8 mg/dL, p < 0.01). Atorvastatin and fenofibrate treatment resulted in a significant reduction of serum uric acid levels (5.3 +/- 1.6 vs. 4.9 +/- 1.4 vs. 4.8 +/- 1.4 mg/dL, p < 0.0001 for atorvastatin; 5.6 +/- 1.6 vs. 4.3 +/- 1.4 vs. 4.4 +/- 1.4 mg/dL, p < 0.0001 for fenofibrate). Homocysteine levels were significantly increased only by fenofibrate (10.3 +/- 3.3 vs. 14.1 +/- 3.8 vs. 14.2 +/- 3.6 microU/L, p < 0.001) but did not change from baseline following statin treatment. Neither statins nor fenofibrate had any effect on serum vitamin B12 and folic acid levels. In contrast to fenofibrate, therapeutic dosages of atorvastatin and simvastatin have a neutral effect on serum homocysteine levels, which is in favor of their "cardioprotective" properties.

Homocysteine is a potent inhibitor of human tumor cell gelatinases

Extracellular matrix-degrading gelatinases are mainly involved in tumor invasion and metastasis. Previous experimental data from our group and others suggested that homocysteine could have a potential modulatory role on the proteolytic balance at the extracellular matrix. Therefore, we studied the effects of homocysteine on extracellular matrix-degrading proteases using model human tumor cell lines and a combination of in vitro fluorogenic assay and zymographic techniques. Homocysteine is shown to be the thiol compound with the most potent inhibitory activity on matrix metalloproteinase 9. Zymographies reveal that matrix metalloproteinase 2 is, at least, as sensitive to inhibition by homocysteine as matrix metalloproteinase 9 is. This study opens new ways to the potential pharmacological use of thiol compounds.

Determination of homocysteine in human plasma by micellar electrokinetic chromatography and in-capillary detection reaction with 2,2'-dipyridyl disulfide

We present a new method for homocysteine quantitation in human plasma based on in-capillary reaction of homocysteine with 2,2'-dipyridyl disulfide. Homocysteine is in this so-called thiol-exchange reaction quantitatively transformed in mixed disulfide concomitantly with formation of an equimolar amount of 2-thiopyridone that is further separated by micellar electrokinetic chromatography and determined specifically at 343 nm. The concentration of homocysteine is thus estimated indirectly from the result of 2-thiopyridone determination. The linear detection range for concentration versus peak area for the assay was from 0.03-3 mM (correlation coefficient 0.994) with a detection limit of 6 microM and a limit of quantitation 20 microM. The inter-day reproducibility of the peak area and the migration time were 1.37% and 0.05%, respectively. The method is simple, relatively rapid and can be easily automated. Moreover the common capillary electrophoresis apparatus with a UV detector can be used to distinguish between normal and pathological hyperhomocysteinemia plasma samples.

Development and evaluation of an isotope dilution LC/MS method for the determination of total homocysteine in human plasma

Elevated plasma homocysteine has been identified as a strong and independent risk factor for cardiovascular diseases, and recently, it has been associated with the development of dementia in older adults. Selected ion-monitoring isotope-dilution LC/MS (electrospray) has been developed and evaluated as a reference method for the accurate determination of total homocysteine in human plasma. Homocysteine is quantitatively isolated from plasma via the use of anion-exchange resins and then detected and quantified in stabilized plasma extracts with selected ion-monitoring LC/MS. This method is shown to be highly comparable to LC/MS/MS determinations in terms of its analytical accuracy and precision, yet this alternative measurement approach does not necessitate the enhanced instrumentation or added expense required of tandem MS/MS determinations. LC/MS detection of homocysteine was linear (standard error of the estimate for the regression line was 0.0323) over 3 orders of magnitude, and the calculated limits of detection and quantification were 0.06 micromol/L (0.12 ng on column) and 0.6 micromol/L (1.2 ng on column), respectively. Independent calibration curves showed excellent linearity (r2 > or = 0.996) between 0 and 25 micromol/L homocysteine over a 3-day period. The accuracy and precision of total homocysteine measurements for patient samples and quality control pools using LC/MS were compared to total homocysteine measurements using LC/MS/MS, GC/MS, FPIA, and LC-FD. LC/MS performed well in relation to the other homocysteine methods in terms of its capability to accurately quantify plasma homocysteine over the normal range (5-15 micromol/L).

Homocysteine inhibits the proliferation and invasive potential of HT-1080 human fibrosarcoma cells

The impairment of homocysteine metabolism has been related to several disorders and diseases. Recently, homocysteine has been shown to inhibit key steps of angiogenesis, including endothelial cell proliferation, invasion, and remodeling of the extracellular matrix. Since these are also key steps in tumor invasion and metastasis, it can be hypothesized that homocysteine can also interfere in these processes. Therefore, we studied the effects of homocysteine on tumor proliferation and invasion, as well as on urokinase, a key extracellular matrix-degrading protease, using a model human tumor cell line. This study demonstrates that, in fact, homocysteine inhibits HT-1080 proliferation and invasion, and is a potent inhibitor of tumor cell urokinase expression.

Hyperhomocysteinemia: An emerging risk factor for cardiovascular disease

There is considerable epidemiological evidence, which confirms the importance of plasma homocysteine as a powerful predictor of future risk of coronary heart disease and other complications of atherosclerosis. Treatment of hyperhomocysteinemia varies with the underlying cause. However, an inexpensive vitamin supplementation with folic acid, vitamin B12 and vitamin B 6 is generally effective in reducing homocysteine concentrations. Several randomised, controlled trials evaluating the effects of folic acid based supplements on homocysteine concentrations have been conducted over the last decade. In most patients, folic acid alone, and in combination of vitamin B12 and B6, has been shown to reduce homocysteine concentrations within four to six weeks after the initiation of therapy (34).However, no study has yet demonstrated that lowering of homocysteine by vitamin supplementation decreases the cardiovascular morbidity or mortality. Avoidance of excessive meat intake and increased consumption of fresh vegetables and fruits is a dietary measure, which has many health benefits, including a potential to reduce elevated homocysteine levels. The other reasonable approach is to determine levels of fasting homocysteine in high risk patients and it may be advisable to increase their intake of vitamin fortified foods and/or to suggest the daily use of supplemental vitamins. Several large scale randomised trials like Heart Outcomes Prevention Evaluation (HOPE-2) Study, Mcmaster University, Canada, Study of the Effectiveness of Additional Reductions in Cholesterol and Homocysteine (SERCH), Clinical Trial Service Unit, Oxford, U.K, Cambridge Heart Antioxidant Study (CHAOS-2) University of Cambridge, U.K, Bergen Vitamin Study, University of Bergen Norway, Women's Antioxidant and Cardiovascular Disease Study (WACS) Harvard Medical School, U.S.A, Prevention with a combined inhibitor and folate in Coronary Heart Disease (PACIFIC) study, University of Sydney, Australia, and many others are ongoing to assess the effect of homocysteine-lowering by vitamin supplementation on risk of vascular disease.

Effect of hyperhomocysteinemia on plasma or tissue adenosine levels and renal function

BACKGROUND

Hyperhomocysteinemia (hHcys) is considered an independent risk factor of cardiovascular diseases. Recent studies in our laboratory have shown that hHcys produced glomerular dysfunction and sclerosis independently of hypertension. However, the mechanism mediating these pathogenic effects of homocysteine (Hcys) is poorly understood. Because Hcys and adenosine (Ado) are simultaneously produced via hydrolysis of S-adenosylhomocysteine (SAH), we hypothesized that hHcys may produce its pathogenic effects by decrease in plasma or tissue Ado concentrations.

METHODS AND RESULTS

L-Hcys (1.5 micromol/min per kilogram) was infused intravenously for 60 minutes to produce acute hHcys in Sprague-Dawley rats. Plasma Hcys levels increased from 6.7+/-0.4 to 14.7+/-0.5 micromol/L, but Ado decreased from 141.7+/-15.1 to 52.4+/-6.8 nmol/L in these rats with acute hHcys. This hHcys-induced reduction of Ado was also observed in the kidney dialysate. In rats with chronic hHcys, plasma Ado levels were also significantly decreased. By kinetic analysis of the enzyme activities, decrease in renal Ado levels in hHcys was shown to be associated with inhibition of SAH hydrolase but not 5'-nucleotidase. Functionally, intravenous infusion of Hcys was found to decrease renal blood flow, glomerular filtration rate, and sodium and water excretion, which could be blocked by the Ado receptor antagonist 8-SPT.

CONCLUSIONS

These results strongly suggest that hHcys decreases plasma and tissue Ado concentrations associated with inhibition of SAH hydrolase. Decrease in plasma and tissue Ado may be an important mechanism mediating the pathogenic effects of Hcys.

Hyperhomocysteinemia and impaired vasomotor function in type 2 diabetes mellitus

BACKGROUND

Hyperhomocysteinemia has been shown to adversely affect vascular function. The aim of this study was to determine whether hyperhomocysteinemia was independently associated with changes in endothelium-dependent and -independent vasomotor functions in patients with type 2 diabetes mellitus.

MATERIALS AND METHODS

Fasting homocysteine (tHcy) was measured in 123 patients with type 2 diabetes and in 61 nondiabetic controls. Endothelium-dependent and -independent vasodilation was measured using high-resolution vascular ultrasound.

RESULTS

Plasma tHcy concentration was increased in the diabetic patients (11.1 +/- 3.7 micromol L(-1) vs. 9.8 +/- 2.9, P < 0.05). The prevalence of hyperhomocysteinemia (defined as tHcy > 15 micromol L(-1)) was higher in the diabetic patients (P < 0.05). Within group comparisons showed that both the abnormalities in endothelium-dependent and -independent vasodilation were significantly more severe in diabetic patients with tHcy 10-15 (P < 0.05) and tHcy > 15 micromol L(-1) (P < 0.05) than in those patients with tHcy < 10 micromol L(-1). When compared with nondiabetic controls matched for tHcy levels, impairment of endothelium-dependent and -independent vasodilation were already evident, even in patients with normal tHcy levels (P < 0.01). Despite significant univariate relationships between tHcy and endothelium-dependent (r = -0.24, P < 0.01) and -independent vasodilation (r = -0.33, P < 0.01) in patients with diabetes, only the relationship between tHcy and endothelium-independent vasodilation remained significant after adjusting for other cardiovascular risk factors in multiple regression analysis.

CONCLUSIONS

Impairment of endothelium-dependent and -independent vasodilation was already present in diabetic patients with normal tHcy levels, and these abnormalities became more severe with increasing tHcy levels. Only the association between tHcy and endothelium-independent vasodilation was free of other cardiovascular risk factors.

Anti-angiogenic effects of homocysteine on cultured endothelial cells

High levels of homocysteine induce a sustained injury on arterial endothelial cells which accelerates the development of thrombosis and atherosclerosis. Some of the described effects of homocysteine on endothelial cells are features shared with an anti-angiogenic response. Therefore, we studied the effects of homocysteine on key steps of angiogenesis using bovine aorta endothelial cells as a model. Homocysteine decreased proliferation and induced differentiation. Furthermore, 5 mM homocysteine produced strong inhibitions of matrix metalloproteinase-2 and urokinase, two proteolytic activities that play a key role in extracellular matrix re-modeling, and decreased migration and invasion, other two key steps of angiogenesis. This study demonstrates that homocysteine can inhibit several steps of the angiogenic process.

Roles of homocysteine in cell metabolism: old and new functions

Mild hyperhomocysteinemia has been suggested as a new, independent risk factor for cardiovascular disease. This fact has produced a new, increased interest in the study of homocysteine metabolism and its relation to pathogenesis. This emergent area of biomedical research is reviewed here, stressing the biochemical and metabolic basis of the pathogenicity of increased levels of homocysteine.