Teresa B. Domagala

Pathogenesis of vascular disease in hyperhomocysteinaemia

Elevated plasma homocysteine is an independent risk factor for atherosclerosis and thrombosis. The exact mechanism by which homocysteine exerts its atherothrombotic action is still unclear. Accumulating evidence suggests that hyperhomocysteinaemia leads to endothelial injury and dysfunction, mediated by free radicals generated during the oxidation of homocysteine. Homocysteine also stimulates the proliferation of vascular smooth-muscle cells and inhibits the growth of vascular endothelial cells. Elevated homocysteine levels may also promote thrombosis by increased generation of thrombin. Other possible mechanisms for homocysteine-mediated atherogenesis include: The altered methylation of DNA and altered regulatory proteins associated with cell membrane, decreased bioavailability of nitric oxide, increased elastolysis and collagen accumulation, overstimulation of N-methyl-D-aspartate receptors and excessive adhesion of monocytes and neutrophils to endothelium. Understanding the mechanisms in vivo by which hyperhomocysteinaemia is associated with vascular disease may provide new approaches to prevention and treatment of atherothrombosis. ∗∗∗J Cardiovasc Risk 5:239-247

Early antithrombotic and anti-inflammatory effects of simvastatin versus fenofibrate in patients with hypercholesterolemia

The aim of the study was to determine whether a short-term treatment with simvastatin or fenofibrate may result in beneficial anti-inflammatory and antithrombotic effects in patients with high risk of coronary artery disease. In a randomized, double-blind study, we compared markers of inflammation, thrombin formation and platelet activation in patients with LDL cholesterol >130 mg/dl assigned to receive simvastatin (40 mg/d; n=20) or micronised fenofibrate (160 mg/d; n=22) for 28 days. Simvastatin, but not fenofibrate, lowered C-reactive protein (CRP) by 32% on day 3 (p<0.001), while both drugs reduced CRP significantly on day 28. Interleukin-6, soluble CD40 ligand, and monocyte chemoattractant protein-1 levels decreased significantly (by 20 to 50%) in both treatment groups on days 3 and 28. Soluble cell adhesion molecules remained unchanged in both groups. Simvastatin and fenofibrate significantly lowered plasma concentrations of thrombin-antithrombin complexes on days 3 and 28, but not platelet beta-thromboglobulin (betaTG) levels. Soluble P-selectin was lowered only in the simvastatin group. The total amount of thrombin generated at the site of microvascular injury also declined (by about 30%) as early as after 3 days of fenofibrate or simvastatin therapy, whereas beta TG release was reduced only in the simvastatin group on days 3 and 28. All the effects were independent of the changes in lipid profiles. Our results suggest that statins and fibrates can exert antithrombotic and anti-inflammatory effects as early as after 3 days of therapy. However, in contrast to statins, fibrates have no influence on platelet function within one month of therapy.

Treatment of Hyperhomocysteinemia with Folic Acid and Vitamins B12 and B6 Attenuates Thrombin Generation

The effect of homocysteine-lowering treatment on thrombin generation was investigated in 17 subjects with hyperhomocysteinemia (aged 22-60 years), 11 of whom had symptomatic atherosclerotic vascular disease. All subjects had fasting total homocysteine levels above 16 micromol/L. The formation of thrombin was assessed by measuring thrombin-antithrombin III complexes and prothrombin fragment 1+2 in peripheral venous blood and in the bleeding time blood collected at 30-second intervals from skin incisions on a forearm. All the tests were performed before and after an 8-week treatment with folic acid p.o. 5 mg/day, vitamin B6 p.o. 300 mg/day, and vitamin B12 i.m. 1000 microg given on a weekly basis. Following the 8-week therapy, the median plasma homocysteine concentration became significantly reduced from 20 to 10 micromol/L, while plasma levels of fibrinogen, prothrombin, and antithrombin III as well as activity of protein C, S, and factor VII showed no changes. Vitamin treatment was associated with a significant fall in thrombin-antithrombin III complexes and prothrombin fragment 1+2 concentrations in peripheral venous blood. Bleeding time became prolonged by about 60 seconds. At sites of hemostatic plug formation, plasma concentrations of both thrombin markers significantly decreased. Compared with pretreatment values, significantly less thrombin was produced during the first 3 minutes of bleeding after homocysteine-lowering therapy. In subjects with hyperhomocysteinemia a reduction of plasma fasting homocysteine concentration by folic acid and vitamins B12 and B6 administration is associated with attenuation of thrombin generation both in peripheral blood and at sites of hemostatic plug formation.

Hyperhomocysteinemia following oral methionine load is associated with increased lipid peroxidation.

Over the last years, homocysteine has been recognized as an independent risk factor for atherosclerotic vascular disease (1). The known reasons for an increased level of plasma homocysteine are genetic defects of cystathionine β-synthase (2) and methylenetetrahydrofolate reductase (3). An important role in development of hyperhomocysteinemia is also played by deficiency of folic acid, vitamins B 6 and B 12 (4). Hyperhomocysteinemia is defined when plasma homocysteine concentration exceeds l6μmol/l (5). In clinical setting it is useful not only to assess homocysteine level in fasting blood samples, but also to measure it after methionine loading test (6). The mechanism through which hyperhomocysteinemia promotes development of atherosclerosis are not clear. Homocysteine is toxic to vascular endothelium (7), it promotes thrombosis (8) and potentiates the oxidation of low density lipoprotein (LDL) in vitro (9). It has been suggested lately that oxidation of LDL may be one of the main factors involved in initial development of atherosclerotic lesions (10). The aim of our study was to assess the relationship between hyperhomocysteinemia and lipid peroxidation in vivo. The experimental model was the oral methionine loading test.

Nitric Oxide Production and Endothelium-Dependent Vasorelaxation Ameliorated by N1-Methylnicotinamide in Human Blood Vessels

N 1-methylnicotinamide (MNA+) has until recently been thought to be a biologically inactive product of nicotinamide metabolism in the pyridine nucleotides pathway. However, the latest observations imply that MNA+ may exert antithrombotic and anti-inflammatory effects through direct action on the endothelium. We examined both in vivo and in vitro whether the compound might induce vasorelaxation in human blood vessels through the improvement of nitric oxide (NO) bioavailability and a reduction of oxidative stress mediated by endothelial NO synthase (eNOS) function. MNA+ treatment (100 mg/m2 orally) in healthy normocholesterolemic and hypercholesterolemic subjects increased the l-arginine (l-NMMA)-inhibitable flow-mediated dilation (FMD) of brachial artery responses that also positively correlated with MNA+ plasma concentrations (r=0.73 for normocholesterolemics and r=0.78 for hypercholesterolemics; P<0.0001). MNA+ increased FMD at the same concentration range at which it enhanced NO release from cultured human endothelial cells after stimulation with either the receptor-dependent (acetylcholine) or the receptor-independent endothelial NO synthase agonists (calcium ionophore A23187). MNA+ restored the endothelial NO synthase agonist-stimulated NO release after the exposure of the cells to oxidized low-density lipoprotein. This effect was also associated with the normalization of the [NO]/[superoxide] balance in the endothelial cells. Taken together, the increased NO bioavailability in the endothelium contributes to the vasorelaxating properties of MNA+. Targeting eNOS with MNA+ might be therapeutically relevant for functional disorders of the endothelium, such as hypercholesterolemia and atherosclerosis.

The Relationship of Metabolic Syndrome with Stress, Coronary Heart Disease and Pulmonary Function - An Occupational Cohort-Based Study

Background and Aims Higher levels of stress impact the prevalence of metabolic syndrome (MetS) and coronary heart disease. The association between MetS, impaired pulmonary function and low level of physical activity is still pending assessment in the subjects exposed to stress. The study aimed to examine whether higher levels of stress might be related to MetS and the plaque presence, as well as whether MetS might affect pulmonary function. Design and Methods The study embraced 235 police officers (mean age 40.97 years) from the south of Poland. The anthropometrics and biochemical variables were measured; MetS was diagnosed using the International Diabetes Federation criteria. Computed tomography coronary angiography of coronary arteries, exercise ECG, measurements of brachial flow-mediated dilation, and carotid artery intima-media thickness were completed. In order to measure the self-perception of stress, 10-item Perceived Stress Scale (PSS-10) was applied. Pulmonary function and physical activity levels were also addressed. Multivariate logistic regression analyses were applied to determine the relationships between: 1/ incidence of coronary plaque and MetS per se, MetS components and the number of classical cardiovascular risk factors, 2/ perceived stress and MetS, 3/ MetS and pulmonary function parameters. Results Coronary artery atherosclerosis was less associated with MetS (OR = 2.62, 95%CI 1.24–5.52; p = 0.011) than with a co-existence of classical cardiovascular risk factors (OR = 5.67, 95% CI 1.07–29.85, p = 0.03; for 3 risk factors and OR = 9.05; 95% CI 1.24–66.23, p = 0.02; for 6 risk factors, respectively). Perceived stress increased MetS prevalence (OR = 1.07, 95% CI 1.03–1.13; p = 0.03), and impacted coronary plaque prevalence (OR = 1.05, 95% CI 1.001–1.10; p = 0.04). Leisure-time physical activity reduced the chances of developing MetS (OR = 0.98 95% CI 0.96–0.99; p = 0.02). MetS subjects had significantly lower values of certain pulmonary function parameters. Conclusions Exposure to job-specific stress among police officers increased the prevalence of MetS and impacted coronary plaque presence. MetS subjects had worse pulmonary function parameters. Early-stage, comprehensive therapeutic intervention may reduce overall risk of cardiovascular events and prevent pulmonary function impairment in this specific occupational population.

Relationship between changes in selected thrombotic and inflammatory factors, echocardiographic parameters and the incidence of venous thrombosis after pacemaker implantation based on our own observations.

Introduction Thrombosis (VTh) is a rare dangerous complication of pacemaker implantation (PM). The aim of the study was to determine the dynamics of change in selected thrombotic and inflammatory factors after PM. Material and methods The study involved 81 patients (30 female, mean age: 71.1 years) with PM, divided into two groups. Group A (71 patients) consisted of patients without VTh, whereas group B (10 patients) comprised the patients with VTh. A transthoracic echocardiogram (TTE) and a venous ultrasound (VU) examination were performed. The levels of D-dimers, fibrinogen, tissue factor (TF), factor VII, plasminogen activator inhibitor-1 (PAI-1), interleukin-6 (IL-6) and high-sensitivity C-reactive protein (hsCRP) were determined in the venous blood. After PM, the TTE and VU examinations were repeated at 6 and 12 months, and blood analyses were performed within 7 days after PM, and subsequently at 6 and 12 months. Results In 10 patients of group B, symptomatic VTh occurred at a mean time of 13.06 months after PM. Initially, the levels of IL-6, hsCRP, D-dimers, fibrinogen, TF, VII factor and PAI-1 were considerably higher in group B than in group A. In all patients the levels of these factors kept on increasing for up to 7 days after the procedure. In group A they subsequently decreased, whereas in group B they continued to rise. Conclusions Increased levels of inflammatory and thrombotic factors were observed in patients with VTh before and after PM. The factors of highest risk of VTh occurrence were D-dimers, fibrinogen and TF.

Thrombin formation in platelet-rich plasma after oral methionine loading: preliminary report.

Homocysteine, an intermediate of methionine metabolism, has been found to be an independent risk factor for thromboembolism [1]. Various mechanisms have been proposed to explain possible homocysteine-induced thrombogenicity, including endothelial damage, enhanced lipid peroxidation, impaired activity of the anticoagulant protein C system and increased expression of tissue factor [1–5]. Relevance of these findings in vivo remains controversial. Much less is known on the effects of homocysteine on platelet function [6]. In patients with homocystinuria, homocysteine might increase thromboxane A2 production [7] and stimulate platelet aggregation [8], though the effect of homocysteine on platelet survival is less evident [6]. Oxidative stress might lead to homocysteine oxidation, enhanced platelet activation and increased prothrombotic potential in hyperhomocysteinemia [9]. Methionine loading test is recognized as a method to induce a transient acute hyperhomocysteinemia and helps to identify individuals with abnormal methionine metabolism [10,11]. It remains to be determined whether in mild hyperhomocysteinemia platelet-mediated prothrombotic effects might be of importance. The aim of the study was to evaluate potential alterations in thrombin formation in platelet-rich plasma after oral methionine loading in healthy subjects. 2. Materials and methods