Enhanced in vivo lipid peroxidation at elevated plasma total homocysteine levels

Evaluation of cardiovascular risk factors and related clinical markers in healthy young Japanese adults

BACKGROUND

Since atherosclerosis is a slowly progressive process at a young age, effective preventive measures should be taken early in life to prevent future events associated with cardiovascular disease.

METHODS

The study population comprised 132 young Japanese adults (mean age 21.4 years, range 18-31 years). We screened plasma total homocysteine and serum folate levels and evaluated mean carotid intima-media thickness and cardio-ankle vascular index.

RESULTS

Multiple regression analysis after adjustment for age and sex revealed that only folate levels were significantly correlated with plasma total homocysteine levels (beta=-0.37, p=0.028). Carotid intima-media thickness adjusted for age and sex and compared between quintiles of total homocysteine levels was significantly increased in the highest quintile compared with other quintiles. Cardio-ankle vascular index increased with age in both women and men, but no additional determinants were identified in young adults.

CONCLUSION

Serum folate is an independent determinant of plasma total homocysteine levels, and mild hyperhomocysteinemia may represent a risk factor for increased carotid intima-media thickness, even in young adults. Comprehensive health education from the early period of life, including the suggestion of appropriate dietary measures, is important for effective prevention of future atherosclerosis.

Pyridoxamine analogues scavenge lipid-derived gamma-ketoaldehydes and protect against H2O2-mediated cytotoxicity

Isoketals and levuglandins are highly reactive gamma-ketoaldehydes formed by oxygenation of arachidonic acid in settings of oxidative injury and cyclooxygenase activation, respectively. These compounds rapidly adduct to proteins via lysyl residues, which can alter protein structure/function. We examined whether pyridoxamine, which has been shown to scavenge alpha-ketoaldehydes formed by carbohydrate or lipid peroxidation, could also effectively protect proteins from the more reactive gamma-ketoaldehydes. Pyridoxamine prevented adduction of ovalbumin and also prevented inhibition of RNase A and glutathione reductase activity by the synthetic gamma-ketoaldehyde, 15-E2-isoketal. We identified the major products of the reaction of pyridoxamine with the 15-E2-isoketal, including a stable lactam adduct. Two lipophilic analogues of pyridoxamine, salicylamine and 5'-O-pentylpyridoxamine, also formed lactam adducts when reacted with 15-E2-isoketal. When we oxidized arachidonic acid in the presence of pyridoxamine or its analogues, pyridoxamine-isoketal adducts were found in significantly greater abundance than the pyridoxamine-N-acyl adducts formed by alpha-ketoaldehyde scavenging. Therefore, pyridoxamine and its analogues appear to preferentially scavenge gamma-ketoaldehydes. Both pyridoxamine and its lipophilic analogues inhibited the formation of lysyl-levuglandin adducts in platelets activated ex vivo with arachidonic acid. The two lipophilic pyridoxamine analogues provided significant protection against H2O2-mediated cytotoxicity in HepG2 cells. These results demonstrate the utility of pyridoxamine and lipophilic pyridoxamine analogues to assess the potential contributions of isoketals and levuglandins in oxidant injury and inflammation and suggest their potential utility as pharmaceutical agents in these conditions.

Measures of Oxidative Stress

Development of in vivo markers of oxidative stress that are sensitive, specific, reliable, and accurate in reflecting underlying atherosclerotic disease states and prediction of cardiovascular risk and clinical events will be invaluable in the future in clinical medicine. Oxidized low-density lipoprotein (OxLDL) and isoprostanes are emerging plasma biomarkers that hold promise for cardiovascular risk prediction. This article describes the pathophysiology of OxLDL and isoprostanes as potential biomarkers, the rationale behind development of methods to measure OxLDL and isoprostanes, and a detailed description of current methodologies, including advantages and disadvantages of available assays. Clinical investigations consisting of epidemiological, case-control, and prospective studies are reviewed to elucidate the role of these biomarkers in reflecting pathophysiology and risk prediction.

Modified Low-Density Lipoproteins and High-Density Lipoproteins

It has long been known that the oxidative state of the various plasma lipoproteins modulates platelet aggregability, thereby contributing to atherogenesis. Low-density lipoprotein (LDL), occurring in vivo both in the native and oxidised forms, interacts directly with platelets, by binding to specific receptors. While the identity of the receptors for native LDL and some subfractions of high-density lipoproteins (HDL) remains disputed, apoE-containing HDL(2) binds to LRP8. The nature of these interactions as well as the distinction between candidate receptor proteins was elucidated using covalently modified apolipoproteins, which pointed to the participation of apolipoproteins in high affinity binding. However, the platelet effects initiated by binding of native lipoproteins remain controversial. Some of this ambiguity can be traced to the fact that native LDL inevitably undergoes substantial oxidisation upon modification, including by radiolabelling. The platelet-activating effects provoked by oxidised LDL are irrefutable, but many details remain unknown. The role of CD36 in platelet binding by oxidised LDL is well established, although additional receptors may exist. Much less is known about the interaction of oxidised HDL with platelets, since platelet activation was observed in some, but not all studies. Various frequently applied in vitro oxidation methods produce modified lipoprotein species that may not be relevant in vivo. Based on the reported modifications obtained by in vitro oxidation of LDL, early investigations focused mainly on the formation and the eventual effects of oxidised lipids. More recently, alterations to lipoproteins performed using hypochloric acid and myeloperoxidase redirected the attention to the role of modified apoproteins in triggering platelet responses.

Homocysteine enhances bone resorption by stimulation of osteoclast formation and activity through increased intracellular ROS generation

Hyperhomocystinemia is a modifiable risk factor for osteoporosis and fracture. Physiologic concentrations of Hcy directly activate osteoclast formation and activity through stimulation of p38 MAPK and integrin beta3. The effects of Hcy were mediated by generation of intracellular ROS.

INTRODUCTION

Hyperhomocysteinemia is a modifiable risk factor for osteoporosis and its related bone fractures. It has been reported that bone resorption and turnover rate were increased in hyperhomocystinemia. Using mouse bone marrow cells, we examined the direct effects of homocysteine (Hcy) on osteoclast formation and activity.

MATERIALS AND METHODS

Osteoclast formation was determined by TRACP staining and TRACP activity. Intracellular reactive oxygen species (ROS) generation was measured using a fluorescent probe, dichlorodihydrofluorescein diacetate. Intracellular signaling cascades of p38 mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and NF-kappaB were measured by Western blotting. Integrin beta3 mRNA levels were measured by RT-PCR. Actin ring formation and bone resorption assays were also performed.

RESULTS

Physiologic concentrations of Hcy upregulated TRACP+ multinucleated cells and TRACP activity, stimulated actin ring formation, and increased the number of nuclei per cell and the level of expression of integrin beta3 mRNA. In addition, Hcy increased bone resorption and stimulated p38 MAPK activity and intracellular reactive oxygen species (ROS) generation. All of these Hcy-induced changes were blocked by pretreatment with the antioxidant, N-acetyl cysteine.

CONCLUSIONS

Hcy directly activates osteoclast formation and activity through increased generation of intracellular ROS. These findings suggest that, in individuals with mild to moderate hyperhomocystinemia, increased bone resorption by osteoclasts may contribute to osteoporosis and that an antioxidant may attenuate bone loss in these individuals.

F2-isoprostanes as markers of oxidative stress in vivo: an overview

The isoprostanes are a unique series of prostaglandin-like compounds formed in vivo via a non-enzymatic mechanism involving the free radical-initiated peroxidation of arachidonic acid. This article summarizes selected aspects regarding current knowledge of these compounds and their value as markers of oxidative injury. Novel aspects related to the biochemistry of isoprostane formation are discussed and methods by which these compounds can be analysed and quantified are summarized. A considerable portion of this article examines the utility of F(2)-isoprostanes as markers of oxidant injury in vivo. Numerous studies carried out over the past decade have shown that these compounds are extremely accurate measures of lipid peroxidation and have illuminated the role of oxidant injury in a number of human diseases including atherosclerosis, Alzheimer's disease and pulmonary disorders.

Aspirin resistance: mechanisms and clinical implications

Acetylsalicylic acid (aspirin) has been shown to irreversibly interfere with platelet function, an effect that is associated with a reduction in morbid and mortal arterial thrombotic events in multiple clinical studies. This clinical benefit appears to be attenuated by resistance to the antiplatelet effects of aspirin in up to 35% of patients. The mechanisms for aspirin resistance are multifactorial and include noncompliance with aspirin therapy, diabetes mellitus, cell-cell and drug-drug interactions, genetic polymorphisms, and coronary artery disease. It has not been determined what the best laboratory procedure is to screen for aspirin resistance. Those individuals at high risk for aspirin resistance might best be treated with an additional oral antiplatelet drug (eg, clopidogrel) to achieve maximal protection against arterial thrombotic events.

Effect of alpha-tocopherol supplementation on plasma homocysteine and oxidative stress in highly trained athletes before and after exhaustive exercise

The interrelationship between physical exercise, antioxidant supplementation, oxidative stress and plasma levels of homocysteine (Hcy) has not been adequately examined. The purpose of this study was to examine the effect of 2 months of vitamin E supplementation (800 IU/day alpha-tocopherol) (E) or placebo (P) in 38 triathletes on plasma Hcy concentrations, antioxidant potential and oxidative stress. It was hypothesized that vitamin E supplementation would reduce plasma Hcy and oxidative stress markers compared to placebo. Blood samples were collected 1 day prior to the race, immediately postrace and 1.5 h postrace. Plasma alpha-tocopherol was 75% higher (P<.001) in E versus P prerace (24.1+/-1.1 and 13.8+/-1.1 micromol/L, respectively), and this group difference was maintained throughout the race. Cortisol was significantly increased in both E and P (P<.001), but there was no difference in the pattern of change. There were no significant time, group or interaction effects on plasma Hcy concentrations between E and P. Plasma F(2)-isoprostanes increased 181% versus 97% during the race in E versus P, and lipid hydroperoxides were significantly elevated (P=.009) 1.5 h postrace in E versus P. Plasma antioxidant potential was significantly higher 1.5 h postrace in E versus P (P=.039). This study indicates that prolonged large doses of alpha-tocopherol supplementation did not affect plasma Hcy concentrations and exhibited pro-oxidant characteristics in highly trained athletes during exhaustive exercise.

Plasma total homocysteine and gallstone in middle-aged Japanese men

BACKGROUND

We wished to determine whether selected coronary risk factors correlated with the presence of gallstone (GS) in middle-aged Japanese men.

METHODS

We carried out a cross-sectional study of 974 male Self-Defense officials. The odds ratio of a 1-SD increment in levels of coronary risk factors for the presence of GS was calculated in a logistic regression analysis.

RESULTS

Nine subjects had undergone cholecystectomy. Gallstone was detected in 39 subjects and not in 926 subjects. The presence of GS was associated with total homocysteine (tHcy), but not with total cholesterol, triglyceride, gamma-glutamyl transferase, glucose, or folate. The odds ratio of a 2.8-micromol/l increase (1 SD) in tHcy levels for the presence of GS was 1.34 (95% confidence interval [CI], 1.05-1.69; P = 0.017), and the ratio was 1.33 (95% CI, 1.04-1.70; P = 0.025) after being adjusted for lifestyle factors, including cigarette smoking, vegetable intake, physical activity, and abstention from alcohol.

CONCLUSIONS

Plasma tHcy, but not the other coronary risk factors, correlated with the presence of GS in middle-aged Japanese men. This association may partly explain the reported high prevalence rate of coronary heart disease in subjects with GS.

Plasma homocysteine and markers for oxidative stress and inflammation in patients with coronary artery disease--a prospective randomized study of vitamin supplementation

BACKGROUND

Elevated plasma levels of total homocysteine (tHcy) are associated with an increased risk of developing occlusive vascular diseases. To better illustrate the relationship between plasma tHcy concentration, oxidative stress, and inflammation in patients with coronary artery disease (CAD), we measured plasma 8-isoprostane-prostaglandin F 2 (Iso-P), plasma malondialdehyde (MDA), and several markers of inflammation. We also aimed to demonstrate the effects of vitamin supplementation on these markers.

METHODS

A total of 93 patients with ischemic heart disease were investigated. Of these, 34 had plasma tHcy < or =8 micromol/L, while 59 had plasma tHcy > or = 15.0 micromol/L. The 59 patients were randomized to open therapy with folic acid, 5 mg, pyridoxine, 40 mg, and cyancobalamin, 1 mg once daily for 3 months (n = 29) or to no vitamin treatment (n = 30). Blood samples were obtained from both groups before randomization and 3 months later. A sample was also obtained from the remaining 34 patients.

RESULTS

Plasma Iso-P, serum amyloid A (S-AA), and plasma intercellular adhesion molecule-1 (ICAM-1) concentrations were higher in patients with high plasma tHcy levels than in patients with low to normal tHcy levels. Plasma levels of P-, L-, E-selectins, MDA, C-reactive protein (CRP), and orosomucoid did not differ between the groups. Vitamin therapy reduced plasma tHcy from 17.4 (15.3/20.1) to 9.2 (8.3/10.3) micromol/L (25th and 75th percentiles in parentheses) (p<0.0001). Plasma levels of Iso-P remained unchanged and, of all inflammatory markers, only the S-AA concentrations were slightly reduced by the vitamin treatment, from 5.3 (2.2/7.0) ng/L at baseline to 4.6 (2.1/6.9) ng/L (p<0.05) after 3 months of vitamin supplementation.

CONCLUSION

Patients with CAD and high plasma tHcy levels had elevated plasma levels of Iso-P. The increase remained unaffected by plasma tHcy-lowering therapy, suggesting that homocysteine per se does not cause increased lipid peroxidation. Levels of plasma ICAM-1 and S-AA were increased in patients with high plasma tHcy, suggesting an association between homocysteinemia and low-grade inflammation.

Reduced in vivo oxidative stress following 5-methyltetrahydrofolate supplementation in patients with early-onset thrombosis and 677TT methylenetetrahydrofolate reductase genotype

The protective role of folate in vascular disease has been related to antioxidant effects. In 45 patients with previous early-onset (at age <50 years) thrombotic episodes and the 677TT methylenetetrahydrofolate reductase genotype, we evaluated the effects of a 28 d-course (15 mg/d) of 5-methyltetrahydrofolate (MTHF) on homocysteine metabolism and on in vivo generation of 8-iso-prostaglandin F2alpha (8-iso-PGF2alpha), a reliable marker of oxidative stress. At baseline, patients' fasting total homocysteine (tHcy) was 11.5 micromol/l (geometric mean) and urinary excretion of 8-iso-PGF2alpha was 304 pg/mg creatinine, with the highest metabolite levels in the lowest quartile of plasma folate distribution (P < 0.05). After 5-MTHF supplementation, plasma folate levels increased approximately 13-fold (P < 0.0001 versus baseline); tHcy levels (6.7 micromol/l, P < 0.0001) and urinary 8-iso-PGF2alpha (254 pg/mg creatinine, P < 0.001) were both significantly lowered, their reduction being proportional to baseline values (r = 0.98 and r = 0.77, respectively) and maximal in patients with the lowest pre-supplementation folate levels (P < 0.05). The effects on folate (P < 0.0001) and tHcy (P = 0.0004) persisted for at least up to 2 months after withdrawing 5-MTHF. In parallel with long-lasting tHcy-lowering effects, a short-course 5-MTHF supplementation reduces in vivo formation of 8-iso-PGF2alpha in this population, supporting the antioxidant protective effects of folate in vascular disease.

Ascorbate is particularly effective against LDL oxidation in the presence of iron(III) and homocysteine/cystine at acidic pH

Metal-catalyzed LDL oxidation is enhanced by the presence of homocysteine. In this study, the effectiveness of ascorbic acid against low-density lipoprotein (LDL) oxidation by iron(III) and copper(II) in the presence of homocysteine and the main plasma disulfide cystine was investigated. Relative to the degree of LDL oxidation reached in the absence of antioxidants, ascorbic acid was particularly effective against iron-catalyzed LDL oxidation at pH 6.0. This can be explained from its stability under acidic conditions and is likely to be important in ischemia, in inflammation and exhausting exercise. At pH 7.4, an ascorbic acid concentration at least as high as the concentration of homocysteine might be necessary to efficiently inhibit LDL oxidation by iron(III) and copper(II) in the presence of homocysteine and cystine. Histidine increased the efficiency of ascorbic acid as an antioxidant against copper-mediated oxidation in this system. The capacity of homocysteine to regenerate ascorbic acid from dehydroascorbic acid appeared to play a minor role in inhibition of ascorbic acid oxidation by copper as compared to copper chelation by homocysteine.

Beta blocker effects on plasma homocysteine levels in patients with hypertension

Recent studies have shown that hyperhomocysteinemia might play a role in the pathogenesis of hypertension. The effects of antihypertensive agents on plasma homocysteine levels have not been tested extensively. We investigated the effects of beta-blocker therapy on homocysteine levels in patients with hypertension. In the study, 120 patients with newly diagnosed hypertension were enrolled. All patients received metoprolol succinate 100 mg/day initially. If blood pressure was above normal on the 15th day of follow-up, the metoprolol dosage was doubled. Before initiation of the antihypertensive medication and after the fourth month of treatment, homocysteine levels were measured. Of the 120 patients enrolled, 39 could not complete the study. Homocysteine levels decreased significantly by the end of the fourth month when compared with basal values (13.5+/-4.5 micromol/l versus 12.4+/-4.9 micromol/l; P = 0.001). There was no relation between homocysteine level and blood pressure control. There was a significant decrease in homocysteine levels in the women treated in this study (P = 0.001); however, this effect was absent in men (P = 0.185). We demonstrate that metoprolol succinate treatment significantly decreases plasma homocysteine levels in patients with hypertension, especially in women.

Cystathionine beta synthase deficiency promotes oxidative stress, fibrosis, and steatosis in mice liver

BACKGROUND & AIMS

Cystathionine beta-synthase (CBS) deficiency causes severe hyperhomocysteinemia, which confers diverse clinical manifestations, notably liver disease. To investigate this aspect of hyperhomocysteinemia, we performed a thorough investigation of liver pathology in CBS-deficient mice, a murine model of severe hyperhomocysteinemia.

METHODS

The degree of liver injury and inflammation was assessed by histologic examination, by measurements of products of lipid peroxidation, and by formation of carbonyl groups on protein as a measure for the occurrence of protein oxidation. Analysis of profibrogenic, proinflammatory factors and cell apoptosis was performed by Western blots, real-time quantitative reverse-transcription polymerase chain reaction, caspase-3 activity, DNA laddering, and TUNEL assay.

RESULTS

Histologic evaluation of liver specimens of 8- to 32-week-old CBS-deficient mice showed that CBS-deficient mice develop inflammation, fibrosis, and hepatic steatosis, concomitant with an enhanced expression of tissue inhibitor of metalloproteinase-1, alpha-smooth muscle actin, pro(alpha)1 collagen type I, transforming growth factor-beta1, and proinflammatory cytokines. Moreover, even if the proapoptotic protein Bax was dominantly expressed and Bcl-2 was down-regulated, caspase-3 was not activated, DNA laddering was not detected, and number of positive TUNEL cells was not increased in liver of CBS-deficient mice compared with wild-type mice.

CONCLUSIONS

The results show that hyperhomocysteinemia in liver of CBS-deficient mice promotes oxidative stress, which may cause mitochondrial damage in association with activation of hepatic stellate cells, leading to liver injury. The absence of caspase-3 activation, DNA fragmentation, and TUNEL-positive cells shows that protective signals may counteract apoptotic signals in liver of CBS-deficient mice.

Urinary 8-epi-PGF2α and its endogenous β-oxidation products (2,3-dinor and 2,3-dinor-5,6-dihydro) as biomarkers of total body oxidative stress

Although measurements of plasma F2-isoprostanes are established markers of oxidative stress, their quantification only reflects acute non-enzymatic lipid peroxidation. In this study, a new approach is described for the rapid isolation and measurement of urinary 8-epi-PGF2alpha and its endogenous beta-oxidation metabolites (2,3-dinor-8-epi-PGF2alpha and 2,3-dinor-5,6-dihydro-PGF2alpha) for use as index of total body oxidative stress. Isoprostanes were partitioned with ethyl acetate and subsequently purified by chromatography on an aminopropyl (NH2) and silica (Si) cartridge. Final analysis of F2-isoprostanes as trimethylsilyl-ester/pentafluorobenzyl ester derivatives was carried out by stable isotope dilution mass spectrometry. Overall recovery of F2-isoprostanes was 80+/-4%. Inter- and intra-assay coefficients of variation were 5% and 7%, respectively. In a group of healthy humans, the mean excretion rates expressed as nmol/mmol creatinine for 2,3-dinor-8-epi-PGF2alpha, 2,3-dinor-5,6-dihydro-8-epi-PGF2alpha, and 8-epi-PGF2alpha were 5.43+/-1.93, 2.16+/-0.71, and 0.36+/-0.16, respectively. Correlations were obtained between 8-epi-PGF2alpha and 2,3-dinor-8-epi-PGF2alpha or 2,3-dinor-5,6-dihydro-8-epi-PGF2alpha (r=0.998 and r=0.937, respectively). A strong relationship was also seen between 2,3-dinor-8-epi-PGF2 and 2,3-dinor-5,6-dihydro-8-epi-PGF2alpha (r=0.949). The new technique allows for high sample throughput and avoids the need for HPLC and/or other expensive equipment required for the initial sample preparation. Simultaneous analysis of urinary 8-epi-PGF2alpha and its metabolites should provide unique tool in clinical trials exploring the role of oxidant injury in human disease.

Homocysteine and redox signaling

Homocysteine is a thiol-containing amino acid that has gained notoriety because its elevation in the plasma is correlated with complex and multifactorial diseases, including cardiovascular diseases, neurodegenerative diseases, and neural tube defects. Homocysteine is redox-active, and its toxic effects have been frequently attributed to direct or indirect perturbation of redox homeostasis. Although the literature on the pathophysiology of elevated homocysteine is rather extensive, a very wide range of concentrations of this amino acid has been used in these studies ranging from normal to pathophysiological to unphysiological. It is clear that homocysteine induces varied responses that are specific to cell type and that cells, depending on their origin, display a wide range of sensitivity to homocysteine. In this review, we focus on the redox signaling pathways that have been connected to homocysteine in vascular (endothelial and smooth muscle) cells and in neuronal cells. We also discuss redox regulation of the key enzymes involved in homocysteine clearance: methionine synthase, betaine-homocysteine methyltranferase, and cystathionine beta-synthase.

Mild hyperhomocysteinemia promotes renal hemodynamic dysfunction without histopathologic changes in adult rats

BACKGROUND

Hyperhomocysteinemia is able to promote glomerular damage and generate tubulointerstitial lesions. These findings were reported in rats with unilateral nephrectomy or in weanling rats with normal function, two experimental models that are exposed to other concomitant vascular risk factors. The aim of this work is to study whether mild hyperhomocisteinemia per se can induce renal histopathologic changes in adults rats with normal renal function at either 10 or 44 weeks of hyperhomocysteinemia.

METHODS

Two months old male Wistar rats (N= 52) were randomly allocated to either a normal control (N= 26) or hyperhomocysteinemic (N= 26) group. Control and hyperhomocysteinemic groups had free access to either tap water or homocysteine thiolactone 50 mg/kg/day, during 10 or 44 weeks. Plasma homocysteine levels were determined by a high-performance liquid chromatography (HPLC) method. Glomerular filtration rate (GFR) and renal plasma flow (RPF) were calculated from inulin and sodium para-aminohippurate (PAH) clearance determinations. Structural renal changes were investigated in kidneys fixed by perfusion. Histopathologic and morphometric analysis were carried out by standard methods.

RESULTS

Plasma total homocysteine levels were 53% (10 weeks) and 56% (44 weeks) higher in hyperhomocysteinemic group compared to the control group. GFR and RPF were significantly lower in hyperhomocysteinemic than in control group. The histopathologic and morphometric studies did not show any differences between the control and hyperhomocysteinemic rats at 10 or 44 weeks.

CONCLUSION

The present results show that mild hyperhomocysteinemia is able to induce renal functional and biochemical alterations in male adult rats that are not associated with renal histopathologic changes.

High levels of homocysteine inhibit lysyl oxidase (LOX) and downregulate LOX expression in vascular endothelial cells

BACKGROUND

Hyperhomocysteinemia, an independent risk factor for cardiovascular disease and atherothrombosis, alters endothelial function through a mechanism not fully understood. Downregulation of lysyl oxidase (LOX), an enzyme involved in extracellular matrix maturation, impairs the endothelial barrier function and could be involved in homocysteine (HC)-induced endothelial dysfunction.

OBJECTIVE

The aim of this study was to analyze the effect of HC on LOX regulation in vascular endothelial cells.

RESULTS

HC at pathophysiological concentrations (35 microM) inhibited LOX activity in porcine aortic endothelial cells. Homocysteine thiolactone and related molecules containing sulfhydryl groups (cysteine), but not methionine or homocystine (non-containing thiol-group) inhibited LOX. In addition, the blockade of HC-sulfhydryl group by N-ethylmaleimide abrogated HC-induced LOX downregulation. This process was triggered by oxidative stress since superoxide dismutase and vitamin C reverted LOX inhibition caused by HC. On the contrary, the effect was not mediated through the induction of endoplasmic reticulum stress. Finally, higher doses of HC (200 microM), common in severe hyperhomocysteinemia, decreased LOX mRNA levels ( approximately 2-fold) and LOX promoter activity in transient transfection experiments.

CONCLUSIONS

These findings suggest that LOX inhibition contributes to the endothelial dysfunction associated with hyperhomocysteinemia. This effect was dependent on a mechanism involving both an inhibition of LOX activity and a reduction of LOX expression.

Generation of free radical by interaction of iron with thiols in human plasma and its possible significance

It has been reported that iron can generate reactive oxygen species (ROS) with thiols. In this study, we examined the interaction of iron with thiols in plasma and the generation of ROS. In human plasma, unlike with Fe(3+), treatment with Fe(2+) increased lucigenin-enhanced chemiluminescence in a concentration-dependent manner, and this was inhibited by superoxide dismutase. Boiling of plasma did not affect chemiluminescence generation induced by Fe(2+). Thiol depletion in plasma by pretreatment with N-ethylmaleimide (NEM) decreased chemiluminescence significantly. Consistent with these findings, albumin, the major thiol contributor in plasma, also generated ROS with Fe(2+). Treatment with Fe(2+) resulted in significant reduction of oxygen radical absorbance capacity (ORAC value) in plasma followed by an increase in low-density lipoprotein (LDL) oxidation. These results suggest that generation of ROS by nonenzymatic reaction of Fe(2+) with plasma thiols could lead to reduction of total antioxidant capacity in plasma, thereby enhancing susceptibility of plasma LDL to oxidation under iron overload conditions.

Fluvastatin Ameliorates the Hyperhomocysteinemia-Induced Endothelial Dysfunction-The Antioxidative Properties of Fluvastatin-

BACKGROUND

Hyperhomocysteinemia induces vascular endothelial dysfunction, contributing to a predisposition to the onset and/or progression of atherosclerosis. The major mechanism suggested for the adverse effect of homocysteine on vascular function seems to involve oxidative stress. Thus, we hypothesized that the administration of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor fluvastatin, which is experimentally demonstrated to have antioxidative properties as one of its pleiotropic effects, is a useful strategy for eliminating the detrimental events induced by hyperhomocysteinemia.

METHODS AND RESULTS

In diet-induced hyperhomocysteinemic rats, we estimated oxidative stress and assessed endothelium-dependent vasodilatation. Hyperhomocysteinemia induced significant increases in urinary 8-isoprostaglandin F2alpha-III excretion and vascular superoxide generation, and impaired endothelium-dependent vasodilatation. Additional oral administration of the antioxidant fluvastatin or vitamin E, which normalized increased oxidative stress induced by hyperhomocysteinemia, ameliorated endothelial dysfunction.

CONCLUSIONS

Hyperhomocysteinemia, even mild to moderate, induces endothelial dysfunction through its oxidative effect. The antioxidant fluvastatin was able to cancel out the oxidative stress induced by hyperhomocysteinemia and ameliorate endothelial dysfunction. Clinical use of fluvastatin might be a potent strategy for eliminating the detrimental events induced by hyperhomocysteinemia as well as hyperlipidemia. In addition to lowering homocysteine by means of folate supplementation, administration of the antioxidants is expected to be a potentially effective anti-homocysteine therapy.

Factors regulating isoprostane formation in vivo

Discovery of the F2-isoprostanes, a group of prostaglandin F2-like compounds biosynthesized from arachidonic acid nonenzymatically, has uncovered a new and novel facet of free radical biology. Some of these compounds are bioactive and thus may mediate adverse effects associated with oxidant stress. F2-Isoprostanes have also been shown to be reliable biomarkers of lipid peroxidation. Factors influencing their formation and metabolism have been studied to some extent, although much remains to be determined. The purpose of this review is to summarize our current knowledge of conditions that modulate endogenous generation of these compounds. Isoprostanes have a wide daily variation in secretion in humans. Although normal levels can be defined, these compounds are found in increased concentrations in various pathophysiological states, including ischemia-reperfusion injury, atherosclerosis, and diabetes, and in experimental conditions of oxidative stress and inflammation. Alterations in isoprostane biosynthesis, secretion, and excretion in normal physiology and in pathophysiological states are due to the various types of endogenous and exogenous regulatory mechanisms that control the availability of precursors required for isoprostane synthesis, such as dietary and tissue arachidonic acid content, oxygen concentration, and the generation of various free radical species. Selected aspects of issues related to isoprostane formation and metabolism in vivo will be examined herein.

The response of muscle interstitial F2-isoprostane (8-ISO-PGF2alpha) during dynamic muscle contractions in humans

8-Iso-prostaglandin F2alpha (8-iso-PGF2alpha) is a characteristic F2-isoprostane which is produced in humans via a free radical-catalysed lipid peroxidation mechanism of arachidonic acid, independent of the cycloxygenase pathway. The measurement of the plasma levels of 8-iso-PGF2alpha was shown to be the most reliable biochemical index of oxidant stress status in the human body. However, there is no reference in literature of local muscle interstitial 8-iso-PGF2alpha production during dynamic muscle contractions. The aim of the present study was to evaluate the response of 8-iso-PGF2alpha during intensive exercise with a cycle ergometer. Two microdialysis probes with CMA-60 microdialysis catheters were inserted into the vastus lateralis muscle of the right leg of six healthy male volunteers. After insertion, these microdialysis probes were attached to a perfusion pump that perfused ringer acetate solution at a rate of 0.3 microl/min. The dialysate fluid samples were collected: (a) during a 30 min rest period and (b) during a 30 min period of dynamic exercise with a cycle ergometer at 150 Watts. Our measurements showed that the levels of 8-iso-PGF2alpha in the interstitial fluid (IF) of the vastus lateralis muscle increase significantly during exercise (from 113.5 +/- 30.2 to 329.9 +/- 69.8 pg/ml, P = 0.05). In conclusion, dynamic muscle exercise produces a local increase of the IF levels of 8-iso-PGF2alpha due to local peroxidation injury of the contractive muscle. The microdialysis method is widely applied, easily repeated and it could contribute in evaluating the local lipid muscle peroxidation during intensive exercise.

Supplementation with cactus pear (Opuntia ficus-indica) fruit decreases oxidative stress in healthy humans: a comparative study with vitamin C

BACKGROUND

Cactus pear (Opuntia ficus-indica) fruit contains vitamin C and characteristic betalain pigments, the radical-scavenging properties and antioxidant activities of which have been shown in vitro.

OBJECTIVE

We investigated the effects of short-term supplementation with cactus pear fruit compared with vitamin C alone on total-body oxidative status in healthy humans.

DESIGN

In a randomized, crossover, double-treatment study, 18 healthy volunteers received either 250 g fresh fruit pulp or 75 mg vitamin C twice daily for 2 wk, with a 6-wk washout period between the treatments. Before (baseline) and after each treatment, 8-epi-prostaglandin F(2alpha) (8-epi-PGF(2alpha)) and malondialdehyde in plasma, the ratio of reduced to oxidized glutathione (GSH:GSSG) in erythrocytes, and lipid hydroperoxides in LDL were measured as biomarkers of oxidative stress; plasma Trolox-equivalent antioxidant activity (TEAC) and vitamins A, E, and C were evaluated as indexes of antioxidant status.

RESULTS

Both treatments caused comparable increases compared with baseline in plasma concentrations of vitamin E and vitamin C (P < 0.05); vitamin A and TEAC did not change significantly. After supplementation with cactus pear fruit, 8-epi-PGF(2)alpha and malondialdehyde decreased by approximately 30% and 75%, respectively; GSH:GSSG shifted toward a higher value (P < 0.05); and LDL hydroperoxides were reduced by almost one-half. Supplementation with vitamin C did not significantly affect any marker of oxidative stress.

CONCLUSIONS

Consumption of cactus pear fruit positively affects the body's redox balance, decreases oxidative damage to lipids, and improves antioxidant status in healthy humans. Supplementation with vitamin C at a comparable dosage enhances overall antioxidant defense but does not significantly affect body oxidative stress. Components of cactus pear fruit other than antioxidant vitamins may play a role in the observed effects.

Stability of Measurements of Biomarkers of Oxidative Stress in Blood Over 36 Hours

Oxidative stress is hypothesized to play an important role in a variety of chronic diseases, but the short-term and long-term stability of measurements of biomarkers related to oxidative stress remains unclear. The objective of this study was to evaluate the stability of measurements of malondialdehyde (MDA), F2-isoprostanes, and fluorescent oxidation products in blood stored on ice within 36 hours until processing. Whole blood samples from six healthy women were processed at 0, 24, and 36 hours after being stored on ice. MDA was measured by the thiobarbituric acid–reactive substances assay with high-pressure liquid chromatography. F2-isoprostanes were measured by gas chromatography/mass spectrometry. The fluorescent oxidation products were measured by spectrofluorometry. Measurements of fluorescent oxidation products were very stable up to 36 hours. Intraclass correlation coefficients (ICC) were &gt;0.95 for each time interval (0 to 24 and 0 to 36 hours). Measurements of MDA were the least stable. The median increased significantly from 0 to 24 hours and from 0 to 36 hours. The ICC for MDA for each time interval (0 to 24 and 0 to 36 hours) was &lt;0.1. Finally, the median of F2-isoprostane measurements at each time point also increased significantly. ICCs were 0.45 for 0 to 24 hours and 0.09 for 0 to 36 hours. We conclude that measurements of fluorescent oxidation products in blood remain stable for up to 36 hours and may be used in large prospective epidemiologic studies of chronic diseases.

Hyperhomocysteinemia in healthy young men and elderly men with normal serum folate concentration is not associated with poor vascular reactivity or oxidative stress

The mechanism by which homocysteine (Hcy) causes endothelial dysfunction is probably mediated by oxidative stress. The aim of this study was to evaluate the effect of oxidative stress on endothelial function in young and elderly hyperhomocysteinemic (HHcy) men. A total of 35 HHcy (Hcy > 15 micro mol/L), young (n = 15; 20-40 y) and elderly men (n = 20; > 65 y) and 33 normohomocysteinemic (NHcy; controls) young (n = 14) and elderly (n = 19) men (Hcy < 13 micro mol/L), without classic cardiovascular risk factors were recruited. Serum Hcy, folate, and vitamin B-12, whole-blood glutathione, plasma total antioxidants status, TBARS, and 8-F(2alpha) isoprostanes were determined. Noninvasive ultrasound measurements of endothelium-dependent (EDVR) and -independent dilatation (EIVR) were performed. EDVR, EIVR, and markers of oxidative stress did not differ among the groups. Folate concentrations were higher in elderly than in young men (P < 0.001), independent of Hcy concentrations. Vitamin B-12 concentrations were lower in HHcy than in NHcy elderly men (P < 0.045). EDVR was correlated with folate concentrations in young men (r = 0.40, P = 0.04) and negatively with BMI in elderly men (r = -0.52, P = 0.002). In the present study, HHcy with normal serum folate concentrations was not associated with poor EDVR or oxidative stress in healthy young and elderly men.

8-isoprostane increases scavenger receptor A and matrix metalloproteinase activity in THP-1 macrophages, resulting in long-lived foam cells

BACKGROUND

Oxidative stress is a key factor in atherogenesis, in which it is closely associated with the inflammation and formation of bioactive lipids. Although 8-isoprostane is regarded as a reliable marker of oxidative stress in vivo, the pathogenic role of this F(2)-isoprostane in atherogenesis is far from clear. Based on the important role of foam cells in the initiation and progression of atherosclerosis we hereby examined the ability of 8-isoprostane to modulate oxidized (ox)LDL-induced foam cell formation and the function of these cells, particularly focusing on the effect on matrix degradation.

METHODS AND RESULTS

8-isoprostane (10 micro M) augmented the oxLDL-induced (20 micro g mL(-1)) lipid accumulation of THP-1 macrophages evaluated by Oil-Red-O staining and lipid mass quantification (colourimetric assay). Additionally, 8-isoprostane induced the expression of the scavenger receptor A type 1 (MSR-1) [mRNA and protein level], assessed by RT-PCR and Western blotting, respectively. Moreover, 8-isoprostane counteracted the oxLDL-induced apoptosis of these cells, involving both mitochondrial-protective and caspase-suppressive mechanisms. Along with these changes, 8-isoprostane increased the oxLDL-induced gene expression of matrix metalloproteinase (MMP)-9 and its endogenous inhibitor [i.e. tissue inhibitor of MMP (TIMP)-1] accompanied by enhanced total MMP activity.

CONCLUSIONS

We show that 8-isoprostane increases foam cell formation at least partly by enhancing MSR-1 expression and by inhibiting apoptosis of these cells, inducing long-lived foam cells with enhanced matrix degrading capacity. Our findings further support a role for 8-isoprostane not only as a marker of oxidative stress in patients with atherosclerotic disorders, but also as a mediator in atherogenesis and plaque destabilization.

F2-isoprostanes as indices of lipid peroxidation in inflammatory diseases

Isoprostanes are a new class of lipids, isomers of conventional enzymatically derived prostaglandins, which are produced in vivo primarily by a free radical-catalyzed peroxidation of polyunsaturated fatty acids. F2-isoprostanes, isomers of the enzyme-derived prostaglandin F2alpha, are the most studied species. Because of their mechanisms of formation, specific structural features that distinguish them from other free radical-generated products and chemical stability, they provide a reliable index of the oxidative component of several diseases in vivo. Consistent data suggest that formation of F2-isoprostanes is indeed altered in a variety of clinical settings associated with inflammation and oxidant stress. Moreover, measurement of F2-isoprostanes might provide a sensitive biochemical basis of dose-selection in studies of natural and synthetic antioxidants.

Copper-mediated LDL oxidation by homocysteine and related compounds depends largely on copper ligation

Oxidation of low-density lipoprotein (LDL) is thought to be a major factor in the pathophysiology of atherosclerosis. Elevated plasma homocysteine is an accepted risk factor for atherosclerosis, and may act through LDL oxidation, although this is controversial. In this study, homocysteine at physiological concentrations is shown to act as a pro-oxidant for three stages of copper-mediated LDL oxidation (initiation, conjugated diene formation and aldehyde formation), whereas at high concentration, it acts as an antioxidant. The affinity for copper of homocysteine and related copper ligands homocysteine, cystathionine and djenkolate was measured, showing that at high concentrations (100 microM) under our assay conditions, they bind essentially all of the copper present. This is used to rationalise the behaviour of these ligands, which stimulate LDL oxidation at low concentration but generally inhibit it at high concentration. Albumin strongly reduced the effect of homocystine on lag time for LDL oxidation, suggesting that the effects of homocystine are due to copper binding. In contrast, copper binding does not fully explain the pro-oxidant behaviour of low concentrations of homocysteine towards LDL, which appears in part at least to be due to stimulation of free radical production. The likely role of homocysteine in LDL oxidation in vivo is discussed in the light of these results.

Homocysteine and essential hypertension

The authors examine the available clinical and experimental data supporting the view that homocysteine, an alternative risk factor of cardiovascular disease, may play a role in the pathogenesis of essential hypertension. The mechanism of this disease has not been elucidated, but it may be related to impairment of vascular endothelial and smooth muscle cell function. Therefore, the occurrence of endothelial dysfunction could contribute to alterations of the endothelium-dependent vasomotor regulation. Elevated homocysteinemia diminishes the vasodilation by nitric oxide, increases oxidative stress, stimulates the proliferation of vascular smooth muscle cells, and alters the elastic properties of the vascular wall. Thus, homocysteine contributes to elevate the blood pressure. Also it is known that elevated plasma levels of homocysteine could lead to oxidant injury to the endothelium. The correction of elevated homocysteinemia by administration of vitamins B12 and B6 plus folic acid, could be a useful adjuvant therapy of hypertension. However, further controlled randomized trials are necessary to establish the efficacy and tolerability of these potentially therapeutic agents.

Acute hyperhomocysteinemia induces a reduction in arterial distensibility and compliance

OBJECTIVE

The aim of the study was to evaluate the effects of acute hyperhomocysteinemia on distensibility and compliance of large peripheral arteries. Isoprostanes generation and antioxidant vitamins were used to assess the role of oxidative stress.

DESIGN

A cross-over, double-blind study on distensibility (DC: distensibility coefficient) and compliance (CC: cross-sectional compliance) of common femoral and brachial arteries was performed in 12 healthy young male volunteers by means of a wall track system before and 4 h after a single oral methionine (100 mg/kg) or placebo administration. The effects of methionine load were investigated also after oral administration of vitamin C (1g/day) and vitamin E (800 mg/day) for 8 consecutive days.

RESULTS

Oral methionine induced a significant increase in plasmatic levels of homocysteine. Distensibility and compliance of brachial and femoral arteries were significantly reduced after methionine load in comparison to placebo. This acute impairment of arterial wall mechanical properties was associated to endothelial dysfunction, since altered flow-dependent vasodilatation (P < 0.05 versus placebo) was observed in the same arterial districts. A significant increase in urinary 8-iso-prostaglandin F2alpha was observed after methionine. Pretreatment with vitamins C and E prevented the effects of methionine on femoral and brachial arteries as well as on urinary 8-iso-prostaglandin F2alpha excretion.

CONCLUSIONS

Hyperhomocysteinemia seems responsible for altered arterial wall elasticity and for endothelial dysfunction. A pivotal role can be attributed to oxidative stress.

Implications of oxidative stress and homocysteine in the pathophysiology of essential hypertension

The present review examines the clinical and experimental data to support the view that homocysteine and oxidative stress, two alternative risk factors of vascular disease, may play a role in the pathogenesis of primary or essential hypertension. Although the precise mechanism of this disease has not been elucidated, it may be related to impairment of vascular endothelial and smooth muscle cell function. Thus, the occurrence of endothelial dysfunction could contribute to alterations of the endothelium-dependent vasomotor regulation. Hyperhomocysteinemia limits the bioavailability of nitric oxide, increases oxidative stress, stimulates the proliferation of vascular smooth muscle cells, and alters the elastic properties of the vascular wall. The link between oxidative stress and hyperhomocysteinemia is also biologically plausible, because homocysteine promotes oxidant injury to the endothelium. Cumulated evidence suggests that the diminution of oxidative stress with antioxidants or the correction of hyperhomocysteinemia with vitamins-B plus folic acid, could be useful as an adjuvant therapy for essential hypertension. Further studies involving long-term trials could help to assess the tolerability and efficacy of the use of these therapeutic agents.

Isoketals: highly reactive γ-ketoaldehydes formed from the H2-isoprostane pathway

Oxidation of arachidonic acid leads to the formation of highly reactive gamma-ketoaldehydes now termed isoketals. Isoketals react with proteins at a rate that far exceeds other well studied products of lipid peroxidation such as 4-hydroxynonenal and demonstrate a remarkable proclivity to crosslink these proteins. For these reasons, isoketals have the potential to significantly alter protein function and contribute to disease processes. This article reviews the chemistry of isoketal formation, of their adduction to proteins, and of their proclivity to crosslink proteins, as well as their effects on protein function, and their potential role in diseases associated with oxidative injury.

L-Homocysteine and L-homocystine stereospecifically induce endothelial nitric oxide synthase-dependent lipid peroxidation in endothelial cells

Atherothrombotic cardiovascular disease associated with hyperhomocysteinemia has been proposed to result, at least in part, from increased vascular oxidative stress. Here we characterize one mechanism by which homocyteine may induce a vascular cell type-specific oxidative stress. Our results show that L-homocysteine at micromolar levels stereospecifically increases lipid peroxidation in cultured endothelial cells, but not in vascular smooth muscle cells or when medium is incubated in the absence of cells. Consistent with these observations, homocysteine also increases the formation of intracellular reactive oxygen species. The pro-oxidant effect of homocysteine can be fully replicated by an equivalent concentration of homocystine (i.e., an oxidized form of homocysteine), but not with cysteine or glutathione. Homocyst(e)ine-dependent lipid peroxidation is independent of H(2)O(2) and alterations in glutathione peroxidase activity, but dependent on superoxide. Mechanistically, the pro-oxidant effect of homocysteine appears to involve endothelial nitric oxide synthase (eNOS), as it is blocked by the eNOS inhibitor L-N(G)-nitroarginine methyl ester. Thus, homocyst(e)ine actively promotes oxidative stress in endothelial cells via an eNOS-dependent mechanism.

Oxidative stress-induced dysregulation of arteriolar wall shear stress and blood pressure in hyperhomocysteinemia is prevented by chronic vitamin C treatment

We aimed to test the hypothesis that an enhanced level of reactive oxygen species (ROS) is primarily responsible for the impairment of nitric oxide (NO)-mediated regulation of arteriolar wall shear stress (WSS) in hyperhomocysteinemia (HHcy). Thus flow/WSS-induced dilations of pressurized gracilis muscle arterioles (basal diameter: approximately 170 microm) isolated from control (serum Hcy: 6 +/- 1 microM), methionine diet-induced HHcy rats (4 wk, serum Hcy: 30 +/- 6 microM), and HHcy rats treated with vitamin C, a known antioxidant (4 wk, 150 mg. kg body wt-1.day-1; serum Hcy: 32 +/- 10 microM), were investigated. In vessels of HHcy rats, increases in intraluminal flow/WSS-induced dilations were converted to constrictions. Constrictions were unaffected by inhibition of NO synthesis by N omega-nitro-L-arginine methyl ester (L-NAME). Vitamin C treatment of HHcy rats reversed the WSS-induced arteriolar constrictions to L-NAME-sensitive dilations but did not affect control responses. Similar changes in responses were obtained for the calcium ionophore A-23187. In addition, diastolic and mean arterial blood pressure and serum 8-isoprostane levels (a marker of in vivo oxidative stress) were significantly elevated in rats with HHcy, changes that were normalized by vitamin C treatment. Taken together, our data show that in chronic HHcy long-term vitamin C treatment, by decreasing oxidative stress in vivo, enhanced NO bioavailability, restored the regulation of shear stress in arterioles, and normalized systemic blood pressure. Thus our study provides evidence that oxidative stress is an important in vivo mechanism that is primarily responsible for the development of endothelial dysregulation of WSS in HHcy.

The effects of tobacco smoke on the homocysteine level--a risk factor of atherosclerosis

Homocysteine may promote atherogenesis and thrombogenesis. There is evidence from case - control and cross-sectional cohort studies that there is a positive association between plasma homocysteine levels and coronary artery disease, cerebrovascular disease and peripheral vascular disease. There is also some evidence that certain life-style factors such as cigarette smoking may affect homocysteine levels. In this work is presented a review of recent opinion about the influence of tobacco smoking on homocysteine levels.

Hyperhomocysteinemia accelerates atherosclerosis in cystathionine beta-synthase and apolipoprotein E double knock-out mice with and without dietary perturbation

Although hyperhomocysteinemia is an independent risk factor for cardiovascular disease, a direct role for homocysteine (Hcy) in this disease remains to be shown. Whereas diet-induced hyperhomocysteinemia promotes atherosclerosis in animal models, the effects of Hcy on atherogenesis in the absence of dietary perturbations is not known. We have generated double knock-out mice with targeted deletions of the genes for apolipoprotein E (apoE) and cystathionine beta-synthase (CBS), which converts Hcy to cystathionine. ApoE(-/-)/CBS(-/-) mice developed aortic lesions even in the absence of dietary manipulation; lesion area and lesion cholesteryl ester (CE) and triglyceride (TG) contents increased with animal age and plasma Hcy levels. Plasma total cholesterol was significantly increased, whereas high density lipoprotein (HDL) cholesterol and TG concentrations of apoE(-/-)/CBS(-/-) mice were decreased. Cholesterol esterification and activities of enzymes catalyzing CE or TG formation in the vessel wall and in peritoneal macrophages were not changed by hyperhomocysteinemia. However, uptake of human acetyl-LDL, but not native low density lipoprotein (LDL), by mouse peritoneal macrophages was higher in the presence of hyperhomocysteinemia. These results suggest that isolated hyperhomocysteinemia is atherogenic and alters hepatic and macrophage lipoprotein metabolism, in part, by enhancing uptake of modified LDL.

Ramatroban, a TP receptor antagonist, improves vascular responses to acetylcholine in hypercholesterolemic rabbits in vivo

Recent studies show that 8-iso-prostaglandin F(2alpha), a member of F(2)-isoprostane family, acts as a vasoconstrictor via TP receptor activation; and its local release may contribute to an abnormal vasomotor tone associated with hypercholesterolemia. The purpose of this study was to examine whether ramatroban, a TP receptor antagonist, improves abnormal vascular reactivity in vivo in hypercholesterolemic rabbits. The plasma 8-iso-prostaglandin F(2alpha) levels in hypercholesterolemic groups were significantly higher than those in normal groups. The treatment by ramatroban reversed the attenuation of the vascular response to acetylcholine in hypercholesterolemic groups. However, L-N(G)-nitroarginine methyl ester, a nitric oxide synthase inhibitor, did not inhibit the protective effects of ramatroban. Attenuation of the vascular response to acetylcholine in hypercholesterolemic rabbits was significantly enhanced by 8-iso-prostaglandin F(2alpha). Attenuation of the vascular response to acetylcholine by a cholesterol-rich diet and 8-iso-prostaglandin F(2alpha) was canceled by ramatroban. These findings suggest that ramatroban improves the vascular response in vivo to acetylcholine in hypercholesterolemic rabbits by blocking the action of 8-iso-prostaglandin F(2alpha).

Changes in markers of vascular injury in response to transient hyperhomocysteinemia

The purpose of this study was to test whether transient increases in homocysteine would promote changes in markers of endothelial injury, cellular fibronectin (cFN), and soluble vascular cell adhesion molecule 1 (sVCAM-1). Homocysteine, cFN, and sVCAM-1 concentrations increased significantly in response to a methionine load by 6 hours in human subjects. However, no correlation was observed between homocysteine and cFN or sVCAM-1. To directly test whether homocysteine can injure endothelial cells, human umbilical vein endothelial cells (HUVEC) were incubated with increasing concentrations of homocysteine, plasma, or serum from hyperhomocysteinemic mice or from the methionine-loaded test subjects. cFN release was increased from endothelial cells cultured with plasma (but not serum) of hyperhomocysteinemic transgenic mice or from methionine-loaded human subjects. These data suggest that very high homocysteine concentrations can promote endothelial injury; however, this effect is likely mediated by secondary effects that include a factor(s) present in plasma that affects endothelial cells.

Vitamin C protects low-density lipoprotein from homocysteine-mediated oxidation

Homocysteine, an atherogenic amino acid, promotes iron-dependent oxidation of low-density lipoprotein (LDL). We investigated whether vitamin C, a physiological antioxidant, could protect LDL from homocysteine-mediated oxidation. LDL (0.2 mg of protein/ml) was incubated at 37 degrees C with homocysteine (1000 microM) and ferric iron (10-100 microM) in either the absence (control) or presence of vitamin C (5-250 microM). Under these conditions, vitamin C protected LDL from oxidation as evidenced by an increased lag time preceding lipid diene formation (> or = 5 vs. 2.5 h for control), decreased thiobarbituric acid-reactive substances accumulation (< or = 19 +/- 1 nmol/mg when vitamin C > or = 10 microM vs. 32 +/- 3 nmol/mg for control, p <.01), and decreased lipoprotein anodic electrophoretic mobility. Near-maximal protection was observed at vitamin C concentrations similar to those in human blood (50-100 microM); also, some protection was observed even at low concentrations (5-10 microM). This effect resulted neither from altered iron redox chemistry nor enhanced recycling of vitamin E in LDL. Instead, similar to previous reports for copper-dependent LDL oxidation, we found that vitamin C protected LDL from homocysteine-mediated oxidation through covalent lipoprotein modification involving dehydroascorbic acid. Protection of LDL from homocysteine-mediated oxidation by vitamin C may have implications for the prevention of cardiovascular disease.

Hyperhomocysteinemia and oxidative stress during dialysis treatment

BACKGROUND/AIMS

The concomitant presence of hyperhomocysteinemia and oxidative stress may represent a determinant factor for the occurrence of vascular alterations and cardiac diseases, the main cause of death among dialysis patients. The aim was to analyze the occurrence of hyperhomocysteinemia and oxidative stress and their possible relationship in dialysis patients.

METHODS

Antioxidant substances, homocysteine, folate, and vitamin B12 were determined in blood from 32 patients on hemodialysis (HD), 21 patients on peritoneal dialysis (PD), and 12 healthy individuals.

RESULTS

Different degrees of hyperhomocysteinemia were observed in all HD patients and in 95% of the PD patients (45.30 +/- 24.89 microM in HD and 35.50 +/- 26.53 microM in PD). Oxidative stress defined as an imbalance between oxidant and antioxidant forces was observed in all dialysis patients, but was more intense in HD individuals. In this group, lipoperoxidation and protein oxidation were associated with lower concentrations of antioxidants such as erythrocyte vitamin E and vitamin C.

CONCLUSIONS

Hyperhomocysteinemia and oxidative stress occur in both types of dialysis treatment, possibly contributing to the establishment of complications in these patients.

Reduction in plasma total homocysteine through increasing folate intake in healthy individuals is not associated with changes in measures of antioxidant activity or oxidant damage

BACKGROUND

Various mechanisms have been proposed to explain the association between plasma total homocysteine (tHcy) and risk of cardiovascular disease, including oxidative activity of homocysteine.

OBJECTIVE

To explore the putative role of reactive oxygen species in the association between plasma tHcy and risk of cardiovascular disease in healthy individuals.

DESIGN

A double-blind, placebo-controlled crossover intervention to increase folate intake through diet (increased consumption of folate-rich foods) and supplement (400 micro g folic acid) was carried out in 126 healthy men and women. Measurements were made of antioxidant activity in red blood cells and plasma, and products of oxidant damage in plasma.

RESULTS

Diet and supplement-based interventions led to an increase in measures of folate status and a reduction in plasma tHcy. This was not associated with any significant change in measures of antioxidant activity (plasma and red blood cell glutathione peroxidase activity and red blood cell superoxide dismutase activity) or oxidant damage (plasma malondialdehyde), although an improvement in plasma total antioxidant capacity just failed to reach significance.

CONCLUSIONS

In healthy individuals lowering plasma tHcy does not have any functional implications regarding oxidative damage.

Anticardiolipin antibody titre and plasma homocysteine level independently predict intima media thickness of carotid arteries in subjects with idiopathic antiphospholipid antibodies

This study evaluated whether IgG anticardiolipin antibody (aCL) titre and traditional risk factors for atherosclerosis bore any relationship to the intima media thickness (IMT) of carotid arteries of patients with idiopathic antiphospholipid antibodies (aPL). IMT was assessed by high-resolution sonography at the common carotid, carotid bifurcation and internal carotid in 42 (13 male, 29 female, mean age 31+/-10 years) aPL subjects, 29 with primary thrombotic antiphospholipid syndrome and 13 with persistence of aPL in the absence of any underlying disorder. In the same subjects the following were measured: plasma fibrinogen (FNG), von Willebrand factor (vWF), plasminogen activator inhibitor (PAI), homocysteine (HC), total cholesterol (CHO), triglycerides (TG), high density and low density lipoprotein (HDL and LDL), platelet numbers and aCL of IgG and IgM isotype. IMT of the internal carotid was greater in males than females (0.48+/-0.03 vs 0.39+/-0.01 mm, P=0.02). IMT of the carotid bifurcation was greater in thrombotic than nonthrombotic subjects (0.50+/-0.02 vs 0.42+/-0.02 mm, P=0.04). By simple regression, IMT of the common carotids correlated with age (P< 0.0001) IgG aCL titre (P=0.001), FNG (P=0.006), LDL (0.01), CHO (0.02) and PAI (P=0.02). IMT of the carotid bifurcation correlated with age (P=0.002), IgG aCL titre (P=0.0002), FNG (P=0.0001), HC (P=0.009), CHO (P=0.02), vWF (P=0.01) and number of thrombotic events (P=0.03). IMT of the internal carotids correlated with age (P=0.002), IgG aCL titre (P=0.0001), FNG (P=0.0008), PAI (P=0.002) and HC (P=0.01). By stepwise multiple regression analysis, IgG aCL titre independently predicted IMT at all carotid segments examined (P always <0.005). In addition, plasma FNG and HC also resulted independent predictors of IMT at the carotid bifurcation (P=0.001 and P<0.0001, respectively) and internal carotid (P=0.03 and P<0.0001, respectively). These data strongly support an atherogenic role for IgG aCL in patients with aPL. Measurement of plasma HC and FNG may help define aPL subjects at higher vascular risk who may require lowering of HC and FNG by vitamin and/or pharmacologic intervention.

Folate Improves Endothelial Function in Patients with Coronary Heart Disease

Elevated plasma homocysteine is associated with increased cardiovascular risk but it remains unproven that the effect is directly causal. Folate and homocysteine metabolism are closely linked such that administration of folic acid in doses ranging from 0.2-10 mg/day lowers plasma total homocysteine (tHcy) by up to 25%. Folic acid has been widely advocated as a therapy which may reduce cardiovascular risk, but the clinical benefit remains as yet unproven and the choice of dose remains unclear. The effect of folic acid on endothelial function has been investigated in patients with proven coronary heart disease (CHD) by measuring flow-mediated dilatation (FMD) in the brachial artery. Oral folic acid (5 mg/day) markedly enhances endothelial function (FMD) and lowers homocysteine. Studies of the acute effects of folic acid have shown that this improvement occurs within the first 2-4 hours following the first dose, at which times there was no significant reduction in plasma tHcy. Administration of 5-methyltetrahydrofolate directly into the brachial artery markedly enhances FMD, an effect that is blocked by monomethyl arginine (LNMMA), suggesting that the effects of folate are mediated by nitric oxide. This Review summarises studies which show that pharmacological doses of folate markedly enhance endothelial function in patients with CHD. The discordance with changes in plasma homocysteine suggests that these effects may occur by mechanisms distinct from homocysteine lowering.

Plasma homocysteine levels and late outcome after coronary angioplasty

OBJECTIVES

The aim of this study was to evaluate a possible relationship between homocysteine levels on admission and late outcome after successful percutaneous coronary intervention (PCI).

BACKGROUND

Increasing evidence suggests that mild to moderate elevation of total plasma homocysteine is a graded and potentially modifiable risk factor for cardiovascular disease and death that appears to be largely independent of other traditional risk factors.

METHODS

A total of 549 patients were included after successful PCI of at least one coronary stenosis (> or =50%). End points were cardiac death, nonfatal myocardial infarction (MI), target lesion revascularization (TLR), and a composite of major adverse cardiac events (MACE). The relationship between homocysteine levels and study endpoints was assessed.

RESULTS

After a median (+/- SD) follow-up of 58 +/- 20 weeks, 6 patients died of cardiac death, 14 were diagnosed with a new MI, and 71 underwent repeat TLR. A graded relationship between homocysteine levels (quartiles) and freedom from MACE was found (p = 0.01). Homocysteine levels (+/- SD) were associated with cardiac death (14.9 +/- 1.7 micromol/l vs. 9.6 +/- 4.3 micromol/l, p < 0.005), TLR (10.7 +/- 4.4 micromol/l vs. 9.5 +/- 4.3 micromol/l, p < 0.05), and overall MACE (11.0 +/- 4.4 micromol/l vs. 9.4 +/- 4.3 micromol/l, p < 0.005). These findings remained unchanged after adjustment for potential confounders.

CONCLUSIONS

Plasma homocysteine is an independent predictor of mortality, nonfatal MI, TLR, and overall adverse late outcome after successful coronary angioplasty.

Effects of pinealectomy on the levels and the circadian rhythm of plasma homocysteine in rats

Hyperhomocysteinemia is an independent cardiovascular risk factor. There are several factors including aging that contribute to the development of hyperhomocysteinemia. Nevertheless, the exact mechanisms causing this condition are still debated. We hypothesize that the age-related decrease in melatonin levels may be consequential in hyperhomocysteinemia. Recently, we found that plasma homocysteine (Hcy) levels are increased in pinealectomized (PINX) rats and melatonin reverses this increase. The aim of the present study was to determine if there is a circadian rhythm of plasma Hcy in rats and to examine the effect of pinealectomy on this cycle. Plasma Hcy levels demonstrated a 24-hr rhythm with a peak at 02:00 hr and a nadir at 14:00 hr in both control and PINX rats. Pinealectomy did not change the phase of the rhythm or the nocturnal elevation of plasma Hcy, but it did significantly increase mean plasma Hcy levels compared with those in controls and in rats that were sham pinealectomized (sPINX) (P < 0.05). Melatonin decreases plasma Hcy levels while causing an increase in total glutathione (tGSH). In conclusion, we speculate that decreasing levels of melatonin during aging lead to hyperhomocysteinemia and a decrease in tGSH and the latter may be one of the factors causing hyperhomocysteinemia in the elderly population.

Homocysteine impairs coronary microvascular dilator function in humans

OBJECTIVES

We sought to use positron emission tomography (PET) to test the hypothesis that hyperhomocysteinemia adversely effects coronary microvascular dilator function.

BACKGROUND

Hyperhomocysteinemia is associated with abnormal endothelium-dependent vasodilation in peripheral human arteries. However, its effect on the coronary circulation is not known.

METHODS

Eighteen healthy humans, age 24 to 56 years, were enrolled in a double-blind, crossover trial. Basal and adenosine-stimulated myocardial blood flow (MBF) was determined by PET: after ingestion of placebo and after methionine-induced hyperhomocysteinemia. Further, brachial ultrasonography was used to assess flow-mediated vasodilation. Additionally, to assess the role of nitric oxide (NO) in adenosine-mediated vasodilation, the MBF response to adenosine was measured in the presence and absence of the NO synthase antagonist NG-monomethyl-l-arginine (l-NMMA) (0.3 mg/kg/min intravenously).

RESULTS

Hyperhomocysteinemia resulted in a reduction in the MBF dose-response curve to adenosine (p < 0.05). This was most apparent with low dose adenosine, where MBF augmentation was significantly blunted during hyperhomocysteinemia (1.06 +/- 1.00 ml/min/g vs. 0.58 +/- 0.78 ml/min/g, placebo vs. methionine, p < 0.05). Similarly, flow-mediated brachial artery vasodilation was impaired during hyperhomocysteinemia (4.4 +/- 2.6% vs. 2.6 +/- 2.3%, placebo vs. methionine, p < 0.05). In a separate series of experiments, MBF during adenosine was reduced in the presence of l-NMMA (p < 0.05 analysis of variance). This was most apparent at the low dose of adenosine, where MBF response to adenosine was blunted in the presence of l-NMMA (2.08 +/- 1.34 ml/min/g vs. 1.48 +/- 1.32 ml/min/g, placebo vs. l-NMMA, p < 0.05).

CONCLUSION

The data, therefore, support the hypothesis that acute hyperhomocysteinemia impairs microvascular dilation in the human coronary circulation as a result of reduced NO bioavailability.

Endothelial dysfunction and atherothrombosis in mild hyperhomocysteinemia

Mildly elevated plasma homocysteine levels are an independent risk factor for atherothrombotic vascular disease in the coronary, cerebrovascular, and peripheral arterial circulation. Endothelial dysfunction as manifested by impaired endothelium-dependent regulation of vascular tone and blood flow, by increased recruitment and adhesion of circulating inflammatory cells to the endothelium, and by a loss of endothelial cell antithrombotic function contributes to the vascular disorders linked to hyperhomocysteinemia. Increased vascular oxidant stress through imbalanced thiol redox status and inhibition of important antioxidant enzymes by homocysteine results in decreased bioavailability of the endothelium-derived signaling molecule nitric oxide via oxidative inactivation. This plays a central role in the molecular mechanisms underlying the effects of homocysteine on endothelial function. Supplementation of folic acid and vitamin B12 has been demonstrated to be efficient in lowering mildly elevated plasma homocysteine levels and in reversing homocysteine-induced impairment of endothelium-dependent vasoreactivity. Results from ongoing intervention trials will determine whether homocysteine-lowering therapies contribute to the prevention and reduction of atherothrombotic vascular disease and may thereby provide support for the causal relationship between hyperhomocysteinemia and atherothrombosis.