Investigation of relationship between reduced, oxidized, and protein-bound homocysteine and vascular endothelial function in healthy human subjects

Impact of homocysteine on acute ischemic stroke severity: possible role of aminothiols redox status

BACKGROUND

Acute ischemic stroke (AIS) is one of the most common cerebrovascular diseases which accompanied by a disruption of aminothiols homeostasis. To explore the relationship of aminothiols with neurologic impairment severity, we investigated four aminothiols, homocysteine (Hcy), cysteine (Cys), cysteinylglycine (CG) and glutathione (GSH) in plasma and its influence on ischemic stroke severity in AIS patients.

METHODS

A total of 150 clinical samples from AIS patients were selected for our study. The concentrations of free reduced Hcy (Hcy), own oxidized Hcy (HHcy), free reduced Cys (Cys), own oxidized Cys (cysteine, Cyss), free reduced CG (CG) and free reduced GSH (GSH) were measured by our previously developed hollow fiber centrifugal ultrafiltration (HFCF-UF) method coupled with high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The concentration ratio of Hcy to HHcy (Hcy/HHcy), Cys to Cyss (Cys/Cyss) were also calculated. The neurologic impairment severity of AIS was evaluated using National Institutes of Health Stroke Scale (NIHSS). The Spearman correlation coefficient and logistic regression analysis was used to estimate and perform the correlation between Hcy, HHcy, Cys, Cyss, CG, GSH, Hcy/HHcy, Cys/Cyss and total Hcy with NIHSS score.

RESULTS

The reduced Hcy and Hcy/HHcy was both negatively correlated with NIHSS score in AIS patients with P = 0.008, r=-0.215 and P = 0.002, r=-0.249, respectively. There was no significant correlation of Cys, CG, GSH, HHcy, Cyss, Cys/Cyss and total Hcy with NIHSS score in AIS patients with P value > 0.05.

CONCLUSIONS

The reduced Hcy and Hcy/HHcy, not total Hcy concentration should be used to evaluate neurologic impairment severity of AIS patient.

Paracetamol toxicity in classic homocystinuria: Effect of N-acetylcysteine on total homocysteine

Classical homocystinuria (HCU) is caused by cystathionine β-synthase deficiency leading to impaired homocysteine transsulfuration and accumulation of homocysteine and methionine. Patients present with a wide spectrum of manifestations including ocular, skeletal, neuropsychiatric, and vascular manifestations. We report a 48-year-old female with pyridoxine-unresponsive HCU treated with betaine, cyanocobalamin, and folate. Her diet was non-restricted due to intolerance of low-methionine diet. She was admitted to hospital following a fall, with multiple fractures and subsequently developed acute liver failure with encephalopathy. Shock, sepsis, and liver ischaemia/thrombosis were excluded. In the context of glutathione depletion expected in HCU, hepatic dysfunction was presumed to be due to iatrogenic paracetamol toxicity, despite paracetamol intake at conventional therapeutic dose, with role of hypermethioninemia as a contributing factor being uncertain. Betaine was discontinued on hospital admission. N-Acetylcysteine (NAC) infusion was initiated. Plasma total homocysteine (tHcy) was 3.4 μmol/L 9 days following initiation of NAC treatment with a markedly elevated plasma methionine of 1278 μmol/L. tHcy concentration returned to pre-admission baseline after NAC was discontinued. Recovery following this episode was slow with a prolonged cholestatic phase and gradual improvement in jaundice and coagulopathy. We recommend that paracetamol should be administered cautiously in HCU patients due to underlying glutathione depletion and risk of toxicity even at therapeutic doses. NAC is clearly effective in lowering tHcy in classical HCU in the short-term however further research is required to assess clinical efficacy and use as a potential therapy in classical HCU.

Nicotinamide riboside supplementation is not associated with altered methylation homeostasis in Parkinson's disease

Replenishing nicotinamide adenine dinucleotide (NAD) via supplementation of nicotinamide riboside (NR) has been shown to confer neuroprotective effects in models of aging and neurodegenerative diseases, including Parkinson's disease (PD). Although generally considered safe, concerns have been raised that NR supplementation could impact methylation dependent reactions, including DNA methylation, because of increased production and methylation dependent breakdown of nicotinamide (NAM). We investigated the effect of NR supplementation on DNA methylation in a double blinded, placebo-controlled trial of 29 human subjects with PD, in blood cells and muscle tissue. Our results show that NR had no impact on DNA methylation homeostasis, including individuals with common pathogenic mutations in the MTHFR gene known to affect one-carbon metabolism. Pathway and methylation variance analyses indicate that there might be minor regulatory responses to NR. We conclude that short-term therapy with high-dose NR for up to 30 days has no deleterious impact on methylation homeostasis.

Does Risk of Hyperhomocysteinemia Depend on Thiol-Disulfide Exchange Reactions of Albumin and Homocysteine?

Significance: Increased plasma concentrations of total homocysteine (tHcy; mild-moderate hyperhomocysteinemia: 15-50 μM tHcy) are considered an independent risk factor for the onset/progression of various diseases, but it is not known about how the increase in tHcy causes pathological conditions. Recent Advances: Reduced homocysteine (HSH ∼1% of tHcy) is presumed to be toxic, unlike homocystine (∼9%) and mixed disulfide between homocysteine and albumin (HSS-ALB; homocysteine [Hcy]-albumin mixed disulfide, ∼90%). This and other notions make it difficult to explain the pathogenicity of Hcy because: (i) lowering tHcy does not improve pathological outcomes; (ii) damage due to HSH usually emerges at supraphysiological doses; and (iii) it is not known why tiny increments in plasma concentrations of HSH can be pathological. Critical Issues: Albumin may have a role in Hcy toxicity, because HSS-ALB could release toxic HSH via thiol-disulfide (SH/SS) exchange reactions in cells. Similarly, thiol-disulfide exchange processes of reduced albumin (albumin with free SH group of Cys34 [HS-ALB]) or N-homocysteinylated albumin are plausible alternatives for initiating Hcy pathological events. Adverse effects of albumin and other data reviewed here suggest the hypothesis of a role of albumin in Hcy toxicity. Future Directions: HSS-ALB might be involved in disruption of the antioxidant/oxidant balance in critical tissues (brain, liver, kidney). Since homocysteine-albumin mixed disulfide is a possible intermediate of thiol-disulfide exchange reactions, we suggest that homocysteinylated albumin could be a new pathological factor, and that studies on the redox role of albumin and mixed disulfide production via thiol-disulfide exchange reactions could offer new therapeutic insights for reducing Hcy toxicity.

Review on Headache Related to Dietary Supplements

PURPOSE OF REVIEW

The lifetime prevalence of headaches is 96%. Approximately 11% of the adult population worldwide has a migraine headache. Migraine is a complex disorder that is more than a simple headache. So far, many underlying mechanisms, i.e. inflammatory, vascular, neurogenic have been hypothesized. In recent years evidences proposed that an energy deficit due to changes in mitochondrial function contributes to migraine pathophysiology as an upstream disorder. Recent insights suggested that the coexistence of sensory-stimuli surplus and energy-reserve shortage activate the trigeminovascular system. Some nutrients are considered as essential elements in mitochondrial bioenergetics and some others are known as natural immuno-modulatory components. Also, evidence showed their beneficial effect in headache prophylaxis and treatment. In present study, we aimed to review the available data in this field.

RECENT FINDINGS

Vitamin B group, magnesium, and Coenzyme Q10 (CoQ10) are well-known for their function in mitochondrial energy metabolism. On the other hand, studies support their beneficial role in controlling migraine headache symptoms. For instance, daily intake of 400-milligram riboflavin for 3 months resulted in more than 50% reduction in migraine attacks in more than half of the consumers. According to recent evidence, vitamin D and Omega-3 which are considered as famous immune-modulatory compounds are also reported to be effective in migraine prophylaxis. For example, every 22% reduction in migraine headache occurrence was reported for every 5 ng/ml rise in serum vitamin D. Supplementation with vitamin B group, CoQ10, magnesium, vitamin D and Omega-3 could be considered as an effective, less costly strategy in headache/migraine prophylaxis.

A simple and accurate HFCF-UF method for the analysis of homocysteine, cysteine, cysteinyl-glycine, and glutathione in human blood

The presence of reduced aminothiols, including homocysteine (Hcy), cysteine (Cys), cysteinyl-glycine (CG), and glutathione (GSH), is significantly increased in the pathological state. However, there have been no reports on the relationship between reduced aminothiols (Hcy, Cys, CG, and GSH) and different genders, ages, and drug combinations in human blood. The accurate quantification of these reduced thiols in biological fluids is important for monitoring some special pathological conditions of humans. However, the published methods typically not only require cumbersome and technically challenging processing procedures to ensure reliable measurements, but are also laborious and time-consuming, which may disturb the initial physiological balance and lead to inaccurate results. We developed a hollow fiber centrifugal ultrafiltration (HFCF-UF) method for sample preparation coupled with a high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method and used it to determine four reduced aminothiols (Hcy, Cys, CG, and GSH) in human blood for the first time. A total of 96 clinical patients were enrolled in our study. The influence of different genders, ages, and drug combinations on the levels of four reduced thiols in human blood was also discussed by SPSS 24.0. The sample preparation was simplified to a single 5 min centrifugation step in a sealed system that did not disturb the physiological environment. The validation parameters for the methodological results were excellent. The procedure was successfully applied to monitoring the concentrations of four reduced aminothiols (Hcy, Cys, CG, and GSH) in 96 clinical blood samples. There were no significant differences in Hcy, Cys, CG, or GSH for the different genders, ages, or combinations with methotrexate or vancomycin (P > 0.05). However, there was a significant increase in Hcy concentration in patients treated with valproic acid who were diagnosed with epilepsy (p=0.0007). It is advisable to measure reduced Hcy level in patients taking valproic acid. The developed HFCF-UF method was simple and accurate. It can be easily applied in clinical research to evaluate oxidative stress in further study.

Disturbance of thiol/disulfide aminothiols homeostasis in patients with acute ischemic stroke stroke: Preliminary findings

OBJECTIVES

To determine the disruption of low-molecular-weight aminothiols (LMWTs: cysteine, cysteinylglycine, homocysteine, and glutathione) homeostasis in blood plasma during the acute and early subacute stages after ischemic stroke.

PATIENTS AND METHODS

We admitted 41 patients with primary large-artery atherosclerosis and cardioembolic stroke in the carotid arteries within the first 6-24 h from the moment of neurologic symptoms development. We included 31 patients with chronic cerebral ischemia in the control group. Total LMWT levels and their reduced forms were measured in blood plasma on the 1st, 3rd, 7th, and 15th days after stroke.

RESULTS

Our study demonstrated a decrease of cysteine and cysteinylglycine reduced forms and an increase of total glutathione and cysteine levels. There were no differences in LMWT levels among stroke subtypes (large-artery atherosclerosis and cardioembolic stroke). The decrease (or increase) in GSH and Hcy redox status on the 3^rd day after stroke was associated with severe neurological deficit. Total Hcy (1^st day), Cys (3^rd day) and CG(7^th day) levels were associated with the size of cerebral infarction area. Logistic regression analysis indicated that reduced homocysteine, total cysteinylglycine levels, and cysteine redox status at admission were predictive factors for ischemic stroke occurrence with a probability of 86.2% (p < 0.001).

CONCLUSIONS

LMWTs may indicate the severity of neurological deficit and the size of the cerebral infarct, and their complex determination can be of diagnostic importance both at an early stage of ischemic stroke development and during its monitoring.

Plasma Free Homocysteine Levels in Children with Idiopathic Nephrotic Syndrome

Altered metabolism of homocysteine in children with idiopathic nephrotic syndrome leads to raised plasma-free homocysteine levels. Elevated free homocysteine causes endothelial cell dysfunction and promotes early atherosclerosis and glomerulosclerosis. In this analytical study with a longitudinal follow-up, 29 children with first episode of nephrotic syndrome (FENS) aged 1–16 years along with 30 age andgender-matched healthy controls were enrolled. Plasma-free homocysteine was measured using high-performance liquid chromatography (HPLC). Other variables were measured using standard biochemical methods. The primary outcome measure was plasma-free homocysteine level in children with FENS and in controls. The secondary outcome measure was to observe the levels of plasma-free homocysteine in children with FENS at 12 weeks in remission and in steroid resistant states. Plasma-free homocysteine levels were significantly elevated in children with FENS at disease onset [Median (IQR) 2.170 (1.54–2.71); N = 29; P < 0.001], at 12 weeks of steroid-induced remission [Median (IQR) 1.946 (1.53–2.71); N = 22; P < 0.001], and in steroid-resistant states [Median (IQR) 2.262 (1.53–2.74); N = 7; P < 0.001] compared to controls. The levels did not decrease significantly at 12 weeks of steroid-induced remission compared to onset of nephrotic syndrome. Plasma-free homocysteine levels correlated positively with serum total cholesterol (P = 0.005; r = 0.362) and negatively with serum albumin (P = 0.032; r = 0.281). Plasma-free homocysteine levels are raised in children with FENS posing a risk of endothelial dysfunction which persists at least in short term. Long-term effects of raised plasma-free homocysteine needs to be studied.

Homocysteine Modification in Protein Structure/Function and Human Disease

Epidemiological studies established that elevated homocysteine, an important intermediate in folate, vitamin B₁₂, and one carbon metabolism, is associated with poor health, including heart and brain diseases. Earlier studies show that patients with severe hyperhomocysteinemia, first identified in the 1960s, exhibit neurological and cardiovascular abnormalities and premature death due to vascular complications. Although homocysteine is considered to be a nonprotein amino acid, studies over the past 2 decades have led to discoveries of protein-related homocysteine metabolism and mechanisms by which homocysteine can become a component of proteins. Homocysteine-containing proteins lose their biological function and acquire cytotoxic, proinflammatory, proatherothrombotic, and proneuropathic properties, which can account for the various disease phenotypes associated with hyperhomocysteinemia. This review describes mechanisms by which hyperhomocysteinemia affects cellular proteostasis, provides a comprehensive account of the biological chemistry of homocysteine-containing proteins, and discusses pathophysiological consequences and clinical implications of their formation.

Homocysteine causes vascular endothelial dysfunction by disrupting endoplasmic reticulum redox homeostasis

Endothelial dysfunction induced by hyperhomocysteinemia (HHcy) plays a critical role in vascular pathology. However, little is known about the role of endoplasmic reticulum (ER) redox homeostasis in HHcy-induced endothelial dysfunction. Here, we show that Hcy induces ER oxidoreductin-1α (Ero1α) expression with ER stress and inflammation in human umbilical vein endothelial cells and in the arteries of HHcy mice. Hcy upregulates Ero1α expression by promoting binding of hypoxia-inducible factor 1α to the ERO1A promoter. Notably, Hcy rather than other thiol agents markedly increases the GSH/GSSG ratio in the ER, therefore allosterically activating Ero1α to produce H₂O₂ and trigger ER oxidative stress. By contrast, the antioxidant pathway mediated by ER glutathione peroxidase 7 (GPx7) is downregulated in HHcy mice. Ero1α knockdown and GPx7 overexpression protect the endothelium from HHcy-induced ER oxidative stress and inflammation. Our work suggests that targeting ER redox homeostasis could be used as an intervention for HHcy-related vascular diseases.

Plasma Cystathionine and Risk of Incident Stroke in Patients With Suspected Stable Angina Pectoris

Background Cystathionine is an intermediate product in the transsulfuration pathway and formed during the B6-dependent conversion of methionine to cysteine. Elevated plasma cystathionine has been related to atherosclerosis, which is a major etiological factor for ischemic stroke. However, the role of cystathionine in stroke development is unknown. Therefore, we prospectively assessed the association of circulating levels of cystathionine with risk of total and ischemic stroke. Methods and Results Two-thousand thirty-six patients (64% men; median age, 62 years) undergoing coronary angiography for suspected stable angina pectoris were included. Stroke cases were identified by linkage to the CVDNOR (Cardiovascular Disease in Norway) project. Hazard ratios with confidence intervals (95% confidence interval) were estimated by using Cox-regression analyses. During 7.3 years of median follow-up, 124 (6.1%) incident strokes were ascertained, which comprised 100 cases of ischemic stroke. There was a positive association of plasma cystathionine with risk of total stroke and ischemic stroke. Comparing the fourth versus the first cystathionine quartiles, age- and sex-adjusted hazard ratios (95% confidence interval) were 2.11 (1.19-3.75) and 2.56 (1.31-4.99) for total and ischemic stroke, respectively. Additional adjustment for major stroke risk factors only slightly attenuated the associations, which tended to be stronger in patients without previous or existing atrial fibrillation at baseline (hazard ratio [95% confidence interval], 2.43 [1.27-4.65] and 2.88 [1.39-5.98] for total and ischemic stroke, respectively). Conclusions In patients with suspected stable angina pectoris, plasma cystathionine was independently related to increased risk of total stroke and, in particular, ischemic stroke. Clinical Trial Registration URL : http://www.clinicaltrials.gov . Unique identifier: NCT 00354081.

Plasma cystathionine and risk of acute myocardial infarction among patients with coronary heart disease: Results from two independent cohorts

BACKGROUND

Cystathionine is a thio-ether and a metabolite formed from homocysteine during transsulfuration. Elevated plasma cystathionine levels are reported in patients with cardiovascular disease; however prospective relationships with acute myocardial infarction (AMI) are unknown. We investigated associations between plasma cystathionine and AMI among patients with suspected and/or verified coronary heart disease (CHD).

METHODS

Subjects from two independent cohort studies, the Western Norway Coronary Angiography Cohort (WECAC) (3033 patients with stable angina pectoris; 263 events within 4.8 years of median follow-up) and the Norwegian Vitamin Trial (NORVIT) (3670 patients with AMI; 683 events within 3.2 years of median follow-up) were included.

RESULTS

In both cohorts, plasma cystathionine was associated with several traditional CHD risk factors (P < 0.001). Comparing the cystathionine quartile 4 to 1, age and gender adjusted hazard ratios (95% confidence intervals) for AMI were 2.08 (1.43-3.03) and 1.41 (1.12-1.76) in WECAC and NORVIT, respectively. Additional adjustment for traditional risk factors slightly attenuated the risk estimates, which were generally stronger in both cohorts among non-smokers, patients with higher age, and lower BMI or PLP status (P-interaction ≤ 0.04). Risk associations also tended to be stronger in patients not treated with B-vitamins. Additionally, in a subset of 80 WECAC patients, plasma cystathionine associated strongly negatively with glutathione, an important antioxidant and positively with lanthionine, a marker of H₂S production (P < 0.001).

CONCLUSIONS

Plasma cystathionine is associated with increased risk of AMI among patients with either suspected or verified coronary heart disease, and is possibly related to altered redox homeostasis.

Nailfold capillary morphology in exfoliation syndrome

PurposeThe purpose of the study was to investigate nailfold microvascular morphology in exfoliation syndrome with or without glaucoma (XFS/XFG) compared with primary open-angle glaucoma (POAG) and control subjects using nailfold capillary videomicroscopy.Patients and methodsWe used a JH-1004 capillaroscope to perform nailfold capillary videomicroscopy on the fourth and fifth digit of the non-dominant hand. We enrolled 56 XFS/XFG patients, 87 POAG patients, and 75 control subjects. Masked observers graded the videos for hemorrhages, avascular zones ≥200 microns (μm), and degree of microvascular tortuosity on a four-point subjective scale. Multivariable odds ratios, 95% confidence intervals and P-for trends for assessing the relation between morphological changes and POAG or XFS/XFG were obtained from logistic regression analyses. We also assessed this relation with XFS/XFG compared with POAG in multivariable models.ResultsAfter adjusting for multiple covariates, nailfold hemorrhages, avascular zones ≥200 μm, and higher degree of vascular tortuosity were more common in XFS/XFG vs controls (P-for trend ≤0.0001) and in POAG vs controls (P-for trend ≤0.01). For each 100 capillaries, the number of hemorrhages was similar (P-for trend=0.91) between XFS/XFG and POAG patients; however, there were more avascular zones per 100 capillaries with borderline significance (P-for trend=0.04) in the XFS/XFG group. XFS/XFG patients had more tortuosity than POAG patients; specifically, having a tortuosity score ≥1.5 was associated with a 4.4-fold increased odds of XFS/XFG (95% confidence interval: 1.5-13.3) relative to a tortuosity score <1.0 (P-for trend=0.005).ConclusionA high degree of nailfold capillary tortuosity is a distinct non-ocular feature associated with XFS/XFG compared with either POAG or controls.

Effect of multi-nutrient insufficiency on markers of one carbon metabolism in young women: response to a methionine load

BACKGROUND/OBJECTIVES

Multi-nutrient insufficiencies as a consequence of nutritional and economic factors are common in India and other developing countries. We have examined the impact of multi-nutrient insufficiency on markers of one carbon (1C) metabolism in the blood, and response to a methionine load in clinically healthy young women.

SUBJECTS/METHODS

Young women from Pune, India (n=10) and Cleveland, USA (n=13) were studied. Blood samples were obtained in the basal state and following an oral methionine load (50 mg/kg of body weight in orange juice). Plasma concentrations of vitamin B12, folate and B6 were measured in the basal state. The effect of methionine load on the levels of methionine, total homocysteine, cysteine, glutathione and amino acids was examined.

RESULTS

Indian women were significantly shorter and lighter compared with the American women and had lower plasma concentration of vitamins B12, folate and B6, essential amino acids and glutathione, but higher concentration of total homocysteine. The homocysteine response to methionine load was higher in Indian women. The plasma concentrations of glycine and serine increased in the Indian women after methionine (in juice) load. A significant negative correlation between plasma B6 and homocysteine (r= -0.70), and plasma folate and glycine and serine levels were observed in the Indian group (P<0.05) but not in the American group.

CONCLUSIONS

Multi-nutrient insufficiency in the Indian women caused unique changes in markers of whole body protein and 1C metabolism. These data would be useful in developing nutrient intervention strategies.

Determination of reduced homocysteine in human serum by elemental labelling and liquid chromatography with ICP-MS and ESI-MS detection

Analytical methods allowing sensitive determination of reduced homocysteine (rHcy), one of the so-called biothiols, in human serum is a topic of growing interest due to its close relation to several human disorders, mainly cardiovascular diseases. Although most widely used analytical strategies to determine total Hcy involve derivatization by means of fluorescent labels, this work proposes the use of ebselen, a Se-containing labelling agent to derivatize the reactive sulfhydryl group of the Hcy molecule in its "free" reduced form, which is more likely to play different roles in disease pathogenesis. Optimization of the derivatization and separation conditions by high-performance liquid chromatography (HPLC) to isolate the excess of derivatizing reagent is carried out here using UV/VIS detection. Further, the study of the Se labelling reaction by electrospray ionization tandem mass spectrometry (ESI-MS/MS) provides a stoichiometry of the derivative of 1:1. The main advantage of using ebselen as a labelling agent is the presence of the Se atom in the molecule that allows the use of inductively coupled plasma mass spectrometry (ICP-MS) as a sensitive and selective Se detector. The coupling of HPLC with ICP-MS provided excellent features for the determination of Se-derivatized rHcy (detection limit of 9.6 nM) in real samples. Quantification was accomplished by using post-column isotope dilution (ID) of Se in serum samples, after precipitation of the main serum proteins. Quantitative results for "free" rHcy turned out to be around 0.18-0.22 μM in serum samples from healthy individuals that could be directly analyzed without sample preconcentration.

Redox-based selective fluorometric detection of homocysteine

Homocysteine, an important biomarker, could be selectively quantified with a redox-sensitive fluorescent probe.

Heart rate affects endothelial function in essential hypertension

Increased heart rate (HR) is a risk factor for cardiovascular morbidity and mortality in the general population and in some clinical conditions. Endothelial dysfunction is an adverse prognostic factor for cardiovascular events. The aim of the study was to evaluate the effect of HR on central hemodynamic parameters and endothelial function in hypertension. We evaluated forearm blood flow (FBF) response to intra-arterial infusion of acetylcholine (ACh) and sodium nitroprusside (SNP) in 30 patients with HR ≤60 min(-1) and 30 with HR ≥80 min(-1). The FBF was measured by strain-gauge plethysmography. Transesophageal atrial pacing was used to increase the HR. Radial artery applanation tonometry and pulse wave analysis were used to derive central aortic pressures and correlate hemodynamic indices. The FBF response to ACh is lower in hypertensives with HR ≤60 min(-1) than in those with HR ≥80 min(-1) (10.6 ± 4.2 vs. 13.6 ± 5.1 ml × 100 ml(-1) of tissue × min(-1), P < 0.001). Vascular resistance decreases to 9.3 ± 2.8 U in patients with lower HR versus 7.2 ± 2.1 U in those with higher HR (P = 0.002). The FBF response to SNP is similar in both groups. Central systolic and pulse pressure are higher in bradycardic patients than in those with HR ≥80 min(-1) (140 ± 8 vs. 131 ± 8 mmHg, P = 0.0001 and 49 ± 10 vs. 39 ± 11 mmHg, P = 0.0001). All central hemodynamic parameters decrease during incremental atrial pacing. Augmentation index is the strongest predictor of endothelial dysfunction at multivariate analysis. These findings demonstrate that low HR affects endothelium-dependent vasodilation in hypertension. Increased central aortic pressure and hemodynamic correlates seem to be the underlying mechanisms by which bradycardia interferes with endothelium-dependent reactivity.

Inhibition of ATP-induced calcium influx by homocysteine in human umbilical vein endothelial cells

Mechanisms involved in the association between hyperhomocysteinemia and vascular occlusive diseases remain unclear. Homocysteine (Hcy) may disturb calcium (Ca(2+) ) cytosolic regulation in endothelial cells, a process that can directly affect the synthesis of vasoactive substances, such as nitric oxide (NO). We have investigated the effect of acute and chronic incubation with high concentrations of Hcy (100 and 500 μmol/L) on the changes in the intracellular Ca(2+) concentration ([Ca(2+) ]i ) induced by ATP, using primary cultures of human umbilical vein endothelial cells (HUVEC). The changes in [Ca(2+) ]i , expressed as ΔFt /Fb , were measured using the microspectrofluorimetric technique with Fluo-3 as Ca(2+) indicator. HUVEC acutely exposed to Hcy did not produce significant effects on any of the parameters studied. However, chronic exposition (24 h) caused a significant decrease in the speed of store-mediated Ca(2+) entry, expressed as (ΔFt /Fb )/t (s(-1) ). Exposure of HUVEC to 100 and 500 µmol/L Hcy gave significantly lower values (0.019 ± 0.002 s(-1) , n = 5 and 0.021 ± 0.004 s(-1) , n = 6, respectively) compared to the controls (0.046 ± 0.004 s(-1) , n = 8, P < 0.003). This was detected only when the sustained phase of the ATP-induced [Ca(+2) ]i increase was isolated. These results demonstrate that high concentrations of Hcy can affect the mechanisms involved in [Ca(2+) ]i regulation of HUVEC, and that alteration occurs specifically in the sustained phase, which has been directly associated with NO synthesis.

Extracellular transsulfuration generates hydrogen sulfide from homocysteine and protects endothelium from redox stress

Homocysteine, a cardiovascular and neurocognitive disease risk factor, is converted to hydrogen sulfide, a cardiovascular and neuronal protectant, through the transsulfuration pathway. Given the damaging effects of free homocysteine in the blood and the importance of blood homocysteine concentration as a prognosticator of disease, we tested the hypotheses that the blood itself regulates homocysteine-hydrogen sulfide metabolism through transsulfuration and that transsulfuration capacity and hydrogen sulfide availability protect the endothelium from redox stress. Here we show that the transsulfuration enzymes, cystathionine β-synthase and cystathionine γ-lyase, are secreted by microvascular endothelial cells and hepatocytes, circulate as members of the plasma proteome, and actively produce hydrogen sulfide from homocysteine in human blood. We further demonstrate that extracellular transsulfuration regulates cell function when the endothelium is challenged with homocysteine and that hydrogen sulfide protects the endothelium from serum starvation and from hypoxia-reoxygenation injury. These novel findings uncover a unique set of opportunities to explore innovative clinical diagnostics and therapeutic strategies in the approach to homocysteine-related conditions such as atherosclerosis, thrombosis, and dementia.

Prognostic value of free plasma homocysteine levels in patients hospitalized with acute coronary syndrome

Elevated total plasma homocysteine is an established risk factor for cardiovascular disease. Experimental evidence suggests that non-protein-bound free homocysteine is particularly hazardous to the vascular endothelium. This study evaluates the predictive role of free plasma homocysteine levels on cardiovascular endpoints in patients with acute coronary syndrome (ACS). In a cohort of 379 hospitalized patients with a diagnosis of myocardial infarction or unstable angina pectoris, total and free plasma homocysteine levels were measured by high performance liquid chromatography. The patients were followed for a median 2.7 years. The primary endpoint was a composite of cardiovascular death, myocardial infarction and stroke during follow-up. Stepwise Cox regression was used for multivariate analysis. Primary outcome events occurred in 82 patients (22%) with a median time to event of 6 months. The unadjusted hazard ratio for a free homocysteine level >4.11 micromol/L was 2.16 (95% confidence intervals [CI] 1.36 to 3.42) compared with the 4 lower quintiles. After adjusting for the covariates the hazard ratio was 2.25 (95% CI 1.41 to 3.58, p = 0.01). Compared with the lower 4 quintiles, patients with a total homocysteine level >22.4 micromol/L had a 2.09-fold higher risk (95% CI 1.31 to 3.35) for an event during follow-up. Adjusted for age, discharge diagnosis, serum creatinine, history of atherothrombotic events, and diabetes mellitus, the adjusted hazard ratio was 1.37 (95% CI 0.83 to 2.25, p = 0.22). In conclusion, plasma free homocysteine levels >4.11 micromol/L are a significant and independent risk factor for recurrent cardiovascular events in patients hospitalized for ACS, although total plasma homocysteine levels have no predictive value.

The molecular basis of homocysteine thiolactone-mediated vascular disease

Accumulating evidence suggests that a metabolite of homocysteine (Hcy), the thioester Hcy-thiolactone, plays an important role in atherogenesis and thrombosis. Hcy-thiolactone levels are elevated in hyperhomocysteinemic humans and mice. The thioester chemistry of Hcy-thiolactone underlies its ability to form isopeptide bonds with protein lysine residues, which impairs or alters the protein's function. Protein targets for the modification by Hcy-thiolactone in human blood include fibrinogen, low-density lipoprotein, and high-density lipoprotein. Protein N-homocysteinylation leads to pathophysiological responses, including increased susceptibility to thrombogenesis caused by N-Hcy-fibrinogen, and an autoimmune response elicited by N-Hcy-proteins. Chronic activation of these responses in hyperhomocysteinemia over many years could lead to vascular disease. This article reviews recent evidence supporting the hypothesis that Hcy-thiolactone contributes to pathophysiological effects of Hcy on the vascular system.

Tyrosine depletion alters cortical and limbic blood flow but does not modulate spatial working memory performance or task-related blood flow in humans

Dopamine appears critical in regulating spatial working memory (SWM) within the PFC of non-human primates; however findings in humans are less clear. Recent studies of the effects of global depletion of dopamine via acute tyrosine/phenylalanine depletion (TPD) on SWM task performance have yielded inconsistent results, which may be partly related to task differences. These previous studies do not address whether TPD can directly impair PFC functioning. The current study investigated the effects of TPD on (1) regional cerebral blood flow (rCBF) during a SWM n-back task using H(2) (15)O Positron Emission Tomography (PET), and (2) behavioural performance on three different SWM tasks. Ten healthy males were scanned twice: once following a placebo (balanced) amino acid mixture and once following an equivalent mixture deficient in tyrosine/phenylalanine (TPD condition). Participants completed two additional delayed-response tasks to examine whether differences in response demands influenced TPD effects on performance. TPD resulted in widespread increases in rCBF, with maximum increases in the region of the parahippocampal gyrus bilaterally, left inferior frontal gyrus, and the putamen. TPD related rCBF reductions were observed in the medial frontal gyrus bilaterally, right inferior temporal gyrus and the pons. Despite widespread changes in blood flow following TPD, no specific effects on SWM neural networks or task performance were observed. The use of three different SWM tasks suggests that task differences are unlikely to account for the lack of effects observed. These findings question the capacity of TPD to consistently modulate dopamine function and SWM neural networks in humans.

Administration of minor polar compound-enriched extra virgin olive oil decreases platelet aggregation and the plasma concentration of reduced homocysteine in rats

We investigated the effect of extra virgin olive oil (EVOO) on platelet aggregation and plasma concentrations of homocysteine (Hcy) redox forms in rats in relation to the minor polar compound (MPC) concentration of EVOO. We used 3 olive oil samples with similar fatty acid but different MPC concentrations: refined olive oil (RF) with traces of MPC (control oil), native EVOO with low MPC concentration (LC), and EVOO with high MPC concentration (HC) enriching LC with its own MPC. Oil samples were administered to rats by gavage (1.25 mL/kg body weight) using 2 experimental designs: acute (24-h food deprivation and killed 1 h after EVOO administration) and subacute (12-d treatment, a daily dose of oil for 12 d, and killed after 24 h of food deprivation). Platelet aggregation was induced by ADP (ex vivo tests) and a reduction in platelet reactivity occurred in cells from rats given LC in the subacute study and in cells from rats administered HC in both studies as indicated by an increase in the agonist half maximal effective concentration. HC inhibited platelet aggregation induced by low ADP doses (reversible aggregation) in cells of rats in both the acute and subacute studies, whereas LC had this effect only in the subacute experiment. Moreover, in rats administered HC in both experiments, the plasma concentration of free reduced Hcy (rHcy) was lower and Hcy bound to protein by disulfide bonds (bHcy) was greater than in RF-treated rats. bHcy was also greater in rats given LC than in RF-treated rats in the subacute experiment. Plasma free-oxidized Hcy was greater in rats given LC and HC than in those administered RF only in the subacute experiment. In conclusion, these results show that MPC in EVOO inhibit platelet aggregation and reduce the plasma rHcy concentration, effects that may be associated with cardiovascular protection.

Lowering homocysteine decreases levels and expression of VEGF(165) and endostatin

BACKGROUND

Homocysteine, vascular endothelial growth factor (VEGF), and endostatin have been implicated in angiogenesis and in the development and progression of atherothrombotic vascular disease. We sought to determine whether homocysteine modulates plasma levels of VEGF and endostatin and their expression in leukocytes in patients with peripheral arterial disease (PAD) or diabetes mellitus (DM).

MATERIALS AND METHODS

Ten patients with PAD and 15 patients with type 2 DM were evaluated before and 6 wk after oral administration of folic acid and B vitamins. Evaluation included measurements of plasma levels of homocysteine, VEGF, and endostatin by enzyme-linked immunosorbent assay and the expression of VEGF and endostatin mRNAs in leukocytes using RT-PCR. The measurements were compared with baseline findings in 12 healthy subjects.

RESULTS

Basal homocysteine (P < 0.001) and VEGF (P < 0.01) levels were elevated in all patients versus healthy subjects. Basal endostatin levels were lower in patients with PAD but were higher in patients with DM compared with healthy subjects (P < 0.001). In patients with PAD or DM, folic acid and B vitamins administration resulted in significant reduction (P < 0.001) of plasma levels of homocysteine (20.9% and 26.2%), VEGF (29.7% and 40.4%) and endostatin (9.4% and 5.7%), respectively. Moreover, VEGF and endostatin mRNA expression in leukocytes was down-regulated in all patients after B vitamins and folate treatment.

CONCLUSION

These findings demonstrate that lowering of homocysteine with B vitamins and folic acid resulted in substantial reduction of plasma levels of VEGF but minimal reduction of endostatin and in down-regulation of their expression in leukocytes in patients with PAD or DM.

Acute Hyperhomocysteinemia Induces Microvascular and Macrovascular Endothelial Dysfunction

BACKGROUND

Hyperhomocysteinemia (Hhcy) has been shown to induce endothelial dysfunction due to a decrease in bioavailable nitric oxide (NO) by increased vascular oxidant stress. This can be detected as an impairment of endothelium-dependent vasodilation in conductance arteries, like brachial or coronary arteries. The effect of Hhcy on endothelial function (EF) in small resistance vessels that critically determine organ perfusion, however, has not been studied systematically in humans. Therefore, we simultaneously determined macro- and microvascular EF in 11 healthy subjects before and during acute Hhcy induced by an oral methionine challenge.

METHODS

Macrovascular EF was determined by measuring endothelium-dependent flow-mediated vasodilation of the brachial artery by vascular ultrasound and microvascular EF by measuring skin perfusion during iontophoresis of acetylcholine using laser Doppler fluxmetry.

RESULTS

Oral methionine significantly increased homocysteine levels by about 5.1-fold. Acute Hhcy leads to a significant decrease in flow-mediated vasodilation of the brachial artery from 8.1 +/- 0.5% to 3.6 +/- 0.6% and to a significant decrease in the ratio of acetylcholine-stimulated vs. baseline laser Doppler flow in the forearm skin (from 9.2 +/- 1.0- to 7.8 +/- 1.3-fold).

CONCLUSIONS

Acute Hhcy impairs macro- as well as microvascular (EF) in humans.

Prospective, randomized trial of metformin and vitamins for the reduction of plasma homocysteine in insulin-resistant polycystic ovary syndrome

One hundred and two women with insulin-resistant polycystic ovary syndrome were randomized to treatment with a vitamin B preparation, metformin, or both, in conjunction with standard infertility treatment. Plasma homocysteine levels were significantly reduced by both B vitamins and metformin, but to a greater degree by B vitamins, and higher pregnancy rates were associated with vitamin B treatment.

Progressive glycosylation of albumin and its effect on the binding of homocysteine may be a key step in the pathogenesis of vascular damage in diabetes mellitus

The majority of diabetes research to date has rightly focussed on the direct effects of hyperglycaemia on tissues and a number of theories relating to the pathogenesis of vascular disease have been proposed. This research is important as until methods are found to achieve glycaemic control in all diabetic patients, prophylactic interventions to prevent vasculopathy will be required. One of the major blood proteins, human albumin is known to be covalently modified by extended incubation with glucose, leading to an impairment of ligand binding. One of the important ligands bound by albumin is homocysteine. There is increasing and compelling clinical, experimental and epidemiological evidence that homocysteine, and in particular the free unbound fraction, is vasculotoxic. If homocysteine binding to albumin is impaired by increasing glycosylation of albumin then either drugs which reduce homocysteine levels (pyridoxine, folic acid and cobalamin) or inhibit glycosylation (aminoguanidines) may be of benefit in the prevention of vascular damage in diabetic patients.

Acute effect of folic acid, betaine, and serine supplements on flow-mediated dilation after methionine loading: a randomized trial

OBJECTIVES

We investigated whether reducing post-methionine homocysteine concentrations via various treatments other than folic acid affects vascular function, as measured through flow-mediated dilation (FMD) of the brachial artery. High fasting and post-methionine homocysteine concentrations are associated with cardiovascular disease risk, but homocysteine might be a surrogate marker for low folate status.

DESIGN

This was a randomized, placebo-controlled, double-blind, crossover study.

SETTING

The study took place at Wageningen University in Wageningen in the Netherlands.

PARTICIPANTS

Participants were 39 apparently healthy men and women, aged 50-70 y.

INTERVENTIONS

Participants ingested 10 mg of folic acid, 3 g of betaine, 5 g of serine, and placebo together with an oral methionine load. Each supplement was tested on two different days.

OUTCOME MEASURES

On each of the eight treatment days, plasma homocysteine concentrations and FMD were measured before (t = 0 h, fasting) and 6 h (t = 6 h) after methionine loading.

RESULTS

The mean (+/- SD) fasting homocysteine concentrations averaged over the eight test days were 9.6 +/- 2.1 micromol/l. Mean fasting FMD was 3.1 +/- 2.4 FMD%. A methionine load with placebo increased homocysteine concentrations by 17.2 +/- 9.3 micromol/l at 6 h after loading, similar to the increase following methionine loading with folic acid. A methionine load together with betaine and with serine increased homocysteine by 10.4 +/- 2.8 micromol/l (p < 0.001 relative to placebo) and by 12.1 +/- 8.2 micromol/l (p < 0.001 relative to placebo), respectively. Methionine loading with placebo did not affect FMD, and neither did methionine loading with folic acid, betaine, or serine; differences relative to placebo were +0.7 FMD% (95%CI, -0.6; 1.9), +0.2 FMD% (-1.0; 1.3), and +0.3 FMD% (-0.8; 1.4), respectively.

CONCLUSIONS

Experimentally induced acute changes in homocysteine concentrations did not affect FMD in healthy volunteers. This implies that potential adverse effects of high homocysteine concentrations on the cardiovascular system are not mediated through vascular function. However, homocysteine or folate may affect cardiovascular disease risk through other mechanisms.

Iron sucrose augments homocysteine-induced endothelial dysfunction in normal subjects

Intravenous iron is commonly used in conjunction with erythropoietic agents to treat anemia in patients with chronic kidney disease. Iron has been proposed to promote oxidative stress and endothelial dysfunction in vascular tissues. We studied the acute effects of intravenous iron sucrose on homocysteine-induced endothelial dysfunction in the brachial artery of normal human subjects. In all, 40 healthy subjects received intravenous iron sucrose 100 mg or placebo over 30 min immediately before ingestion of 100 mg/kg of oral methionine in a double-blind, randomized study. Flow- and nitroglycerin-mediated dilation in the brachial artery, serum markers of iron stores, and homocysteine and nitrotyrosine levels were measured before and after study drug administration. Intravenous iron significantly increased transferrin saturation and non-transferrin-bound iron (NTBI) when compared with placebo. Flow-mediated dilation significantly decreased from baseline 1 h after administration of iron sucrose when compared with placebo (from 6.66+/-0.47 to 1.93+/-0.35% after iron sucrose vs from 6.00+/-0.40 to 5.61+/-0.46% after placebo, P<0.001), but did not differ between groups at 4 h (1.10+/-0.39 vs 1.33+/-0.51%). Nitroglycerin-mediated vasodilation, and homocysteine and 3-nitrotyrosine levels did not differ after administration of iron sucrose and placebo. Intravenous administration of iron sucrose in the setting of transient hyperhomocysteinemia induced by methionine ingestion significantly increased transferrin saturation and plasma levels of NTBI and significantly attenuated flow-mediated dilation in the brachial artery when compared with placebo. This potential mechanistic link between intravenous iron and endothelial dysfunction warrants further study of cardiovascular effects of intravenous iron in anemic chronic kidney disease populations.

Plasma Reduced Homocysteine and Other Aminothiol Concentrations in Patients With CKD

BACKGROUND

Hyperhomocysteinemia, a risk factor for cardiovascular disease, is present in the majority of patients with chronic kidney disease (CKD). Several studies indicated that the moiety of homocysteine (Hcy) with an unbound -SH group (reduced Hcy [rHcy]) is the atherogenic molecule. This study is designed to examine the relation between different forms of Hcy and other aminothiols in hemodialysis (HD) patients, peritoneal dialysis (PD) patients, and nondialyzed patients with CKD.

METHODS

rHcy, free Hcy (fHcy), and total Hcy (tHcy), as well as different forms of cysteine, cysteinyl-glycine, and glutathione, were studied by using a high-performance liquid chromatography technique in 19 HD patients, 12 PD patients, 47 patients with CKD, and 15 control subjects.

RESULTS

In PD patients, tHcy levels were 2.8 times greater compared with controls, and in HD patients and those with CKD, 2.1 and 1.9 times greater, respectively. Mean rHcy/tHcy ratios were significantly greater in both HD (P < 0.05) and PD patients (P < 0.01), but did not differ in patients with CKD compared with controls. The decrease in rHcy levels during 1 HD treatment was smaller than that in tHcy and fHcy levels, and rHcy/tHcy ratio increased (before HD, 1.25% +/- 0.44%; after HD, 1.44% +/- 0.66%; P < 0.05).

CONCLUSION

Levels of rHcy and other aminothiols are markedly increased in patients with impaired renal function. In dialysis patients, rHcy/tHcy ratio is markedly elevated and shows greater variability than in patients with CKD and controls. We conclude that because rHcy is believed to induce endothelial dysfunction and may be part of the accelerated atherogenic process in patients with CKD, plasma rHcy level could be a more relevant marker of cardiovascular disease risk than tHcy level.

Pathophysiological basis for the prophylaxis of preeclampsia through early supplementation with antioxidant vitamins

Preeclampsia (PE) is a multisystem disorder that remains a major cause of maternal and foetal morbidity and death. To date, no treatment has been found that prevents the development of the disease. Endothelial dysfunction is considered to underlie its clinical manifestations, such as maternal hypertension, proteinuria, and edema; however, the precise biochemical pathways involved remain unclear. A current hypothesis invokes the occurrence of oxidative stress as pathogenically important, as suggested by the fact that in PE, the placental and circulating levels of lipid peroxidation products (F2-isoprostanes and malondialdehyde [MDA]) are increased and endothelial cells are activated. A potential mechanism for endothelial dysfunction may occur via nuclear transcription factor kappa B (NF-kappaB) activation by oxidative stress. Alternatively, the idea that the antiangiogenic placental soluble fms-like tyrosine kinase 1 factor (sFlt1) is involved in the pathogenesis of this disease is just emerging; however, other pathophysiological events seem to precede its increased production. This review is focused on evidence providing a pathophysiological basis for the beneficial effect of early antioxidant therapy in the prevention of PE, mainly supported by the biological effects of vitamins C and E.

Relationship between S-adenosylmethionine, S-adenosylhomocysteine, asymmetric dimethylarginine, and endothelial function in healthy human subjects during experimental hyper- and hypohomocysteinemia

Experimental hyperhomocysteinemia after an oral methionine or homocysteine load is associated with impaired nitric oxide-dependent vasodilatation in healthy human beings. However, it remains unproven that this effect is mediated by elevations in plasma homocysteine. There is evidence that an increase in plasma homocysteine may increase the formation of asymmetric dimethylarginine (ADMA), an inhibitor of nitric oxide synthase. The methyl groups within ADMA are derived from the conversion of S -adenosylmethionine to S -adenosylhomocysteine intermediates in the methionine/homocysteine pathway. No previous study has assessed the role of methylation status, its impact on ADMA formation, and their association with endothelial function in healthy human beings. In a randomized, placebo-controlled, crossover study, 10 healthy subjects (mean age, 29.1 +/- 3.9 years) were administered an oral dose of methionine (0.1 g/kg), l -homocysteine (0.01 g/kg), N-acetylcysteine (NAC) (0.1 g/kg), or placebo. Endothelial function as assessed by flow-mediated dilatation (FMD) of the brachial artery was impaired after both the methionine and homocysteine load compared with placebo at 4 hours (36 +/- 15, 67 +/- 23 vs 219 +/- 26 microm, respectively, P < .001). N-Acetylcysteine had no effect on flow-mediated dilatation. Plasma total homocysteine was significantly elevated at 4 hours after methionine (23.1 +/- 6.2) and homocysteine (41.5 +/- 8.9) loading, but significantly reduced after NAC 2.4 +/- 0.6 vs 7.1 +/- 2.1 micromol/L in the placebo (P < .001). Plasma S-adenosylmethionine/S-adenosylhomocysteine ratio was significantly (P < .001) increased at 4 hours after methionine (10.9 +/- 0.7) compared with homocysteine (5.4 +/- 0.4), NAC (5.0 +/- 0.3), and placebo (6.0 +/- 0.5). Plasma ADMA concentrations were not altered by any intervention. Our results suggest that endothelial dysfunction due to methionine or homocysteine loading is not associated with an increase in plasma ADMA or a disruption in methylation status.

Interaction between vascular dysfunction and cardiac mass increases the risk of cardiovascular outcomes in essential hypertension

AIMS

To investigate the additive prognostic impact of both forearm endothelial dysfunction and left ventricular mass (LVM) for future cardiovascular events.

METHODS AND RESULTS

We enrolled 324 Caucasian, never treated, hypertensive outpatients. Endothelial function, by intra-arterial infusion of acetylcholine (ACh), and echocardiographic LVM were investigated. Patients were divided into tertiles on the basis of their increase in ACh-stimulated forearm blood flow (FBF) and LVM indexed by body surface area (LVMI). Cardiovascular events assessed were: fatal and non-fatal myocardial infarction, fatal and non-fatal stroke, transient cerebral ischaemic attack, unstable angina, coronary revascularization procedures, and symptomatic aorto-iliac occlusive disease. During a mean follow-up of 45.2+/-23.6 months, there were 47 new cardiovascular events (3.8 events/100 patient-years). The event rate was 6.8, 2.8, and 1.6% in the tertiles of ACh-stimulated FBF (log-rank test, P=0.0009), and 1.4, 3.4, and 6.6% in the tertiles of LVMI (log-rank test, P=0.0002), respectively. Besides, a significant interaction was documented between FBF and LVMI. In fact, the cardiovascular risk increases up to 11.4% in patients with low FBF and high LVMI.

CONCLUSION

For the first time, we demonstrate that the co-existence of LVH and endothelial dysfunction in hypertensive patients increases significantly the risk of subsequent cardiovascular events.

Various forms of homocysteine and oxidative status in the plasma of ischemic-stroke patients as compared to healthy controls

OBJECTIVES

We compared various forms of plasma homocysteine (Hcy) including total Hcy (tHcy), free reduced Hcy (reHcy), free oxidized Hcy (oxHcy) and reHcy plus oxHcy between patients with acute/subacute-ischemic stroke and healthy controls. We also investigated whether the patients have increased oxidative stress.

DESIGN AND METHODS

Using an in-tube derivatization method, we measured plasma levels of tHcy, reHcy and oxHcy in 55 ischemic-stroke patients (14 females and 41 males, median age 64) and 52 age-matched healthy subjects (15 females and 37 males, median age 60). We also measured plasma malondialdehyde (MDA, as lipid peroxidation marker) and oxygen-radical absorbance capacity (ORAC, as total antioxidant activity).

RESULTS

The plasma levels of reHcy and reHcy plus oxHcy and the ratio of reHcy to oxHcy were significantly higher in the patients than in the age-matched controls, whereas tHcy and oxHcy levels were not significantly different. The patients had a significantly higher level of MDA but a lower value of ORAC than that of controls. A significantly positive correlation was found in the levels of reHcy vs. MDA (r = 0.19, P < 0.03), whereas significant negative correlations were found for reHcy vs. ORAC (r = -0.30, P < 0.001) and free Hcy vs. ORAC (r = -0.30, P < 0.001).

CONCLUSIONS

reHcy and reHcy plus oxHcy Hcy, rather than tHcy, are significantly elevated in patients with acute/subacute ischemic stroke. The elevated reHcy along with elevated MDA level and lowered ORAC value in the plasma of the stroke patients indicates an imbalance of antioxidant-prooxidant status in acute ischemic stroke.

Effect of immunosuppressive agents on long-term survival of renal transplant recipients: focus on the cardiovascular risk

In the control of acute rejection, attention is being focused more and more on the long-term adverse effects of the immunosuppressive agents used. Since cardiovascular disease is the main cause of death in renal transplant recipients, optimal control of cardiovascular risk factors is essential in the long-term management of these patients. Unfortunately, several commonly used immunosuppressive drugs interfere with the cardiovascular system. In this review, the cardiovascular adverse effects of the immunosuppressive agents currently used for maintenance immunosuppression are thoroughly discussed. Optimising immunosuppression means finding a balance between efficacy and safety. Corticosteroids induce endothelial dysfunction, hypertension, hyperlipidaemia and diabetes mellitus, and impair fibrinolysis. The use of corticosteroids in transplant recipients is undesirable, not only because of their cardiovascular effects, but also because they induce such adverse effects as osteoporosis, obesity, and atrophy of the skin and vessel wall. Calcineurin inhibitors are the most powerful agents for maintenance immunosuppression. The calcineurin inhibitor ciclosporin (cyclosporine) not only induces these same adverse effects as corticosteroids but is also nephrotoxic. Tacrolimus has a more favourable cardiovascular risk profile than ciclosporin and is also less nephrotoxic. It has little or no effect on blood pressure and serum lipids; however, its diabetogenic effect is more prominent in the period immediately following transplantation, although at maintenance dosages, the diabetogenic effect appears to be comparable to that of ciclosporin. The diabetogenic effect of tacrolimus can be managed by reducing the dose of tacrolimus and early corticosteroid withdrawal. The effect of tacrolimus on endothelial function has not been completely elucidated. The proliferation inhibitors azathioprine and mycophenolate mofetil (MMF) have little effect on the cardiovascular system. Yet, indirectly, by inducing anaemia, they may lead to left ventricular hypertrophy. MMF is an attractive alternative to azathioprine because of its higher potency and possibly lower risk of malignancies. Sirolimus also induces anaemia, but may be promising because of its antiproliferative features. Whether the hyperlipidaemia induced by sirolimus counteracts its beneficial effects is, as yet, unknown. It may be combined with MMF, however, initial attempts resulted in severe mouth ulcers.

Assessment of flow-mediated vasodilatation (FMD) of the brachial artery: effects of technical aspects of the FMD measurement on the FMD response

AIMS

The ability to assess endothelial function non-invasively with B-mode ultrasound has lead to its widespread application in a variety of studies. However, the absolute values obtained using this approach vary considerably across studies. We studied whether technical aspects of the methodology can explain the wide variety in absolute values across studies.

METHODS AND RESULTS

A literature search was performed to identify published reports on flow-mediated vasodilatation (FMD) of the brachial artery published between 1992 and 2001. Information on type of equipment (wall track/B-mode), location of the measurement (antecubital fossa/upper arm), occlusion site (lower/upper arm), occlusion duration (min), and occlusion pressure was extracted. Patient characteristics were also extracted. For the healthy populations, mean FMD varied from 0.20 to 19.2%; for the coronary heart disease (CHD) patients FMD varied from -1.3 to 14%; for subjects with diabetes mellitus FMD varied from 0.75 to 12%. Compared with occlusion at the upper arm, lower arm occlusion was related to decreased FMD (mean difference in FMD -2.47%; 95% CI 0.55-4.39). An occlusion duration of > or =4.5 min was related to an increased FMD compared with an occlusion time of < or =4 min (mean difference 1.30%; 95% CI 0.35-2.46). These findings were adjusted for other technical aspects of the methodology and for differences in risk factors between populations.

CONCLUSION

Mean FMD differs widely between studies. There is a great overlap between populations (healthy, CHD, diabetics). Our findings suggest that the technical aspects of the measurements, the location, and the duration of the occlusion may explain some of these differences, whereas type of equipment, location of the measurement, and occlusion pressure do not.

Effects of homocysteine on apoptosis-related proteins and anti-oxidant systems in isolated human lymphocytes

Homocysteine (Hcy) is a nonprotein-forming sulphur amino acid that plays an important role in remethylation and trans-sulphuration processes. In recent years, it has been suggested that increased levels of plasma Hcy may play a role in the pathogenesis of various diseases, particularly at the cardiovascular level. The pathogenic mechanism of hyperhomocysteinemia, however, has not been clarified. Because oxygen radicals can be generated by the auto-oxidation of this amino acid, it has been suggested that Hcy may cause cellular damage through oxidative mechanisms, ultimately leading to apoptotic cell death. In this study, we sought to investigate the effects of Hcy on oxidative damage and antioxidant agent levels, as well as on apoptosis-related proteins and apoptosis occurrence in human cells. For this purpose, we measured levels of Bcl-2, caspase-3 and caspase-9 activity, Cu/Zn superoxide dismutase, reduced glutathione, lipid peroxidation [malondialdehyde and 4-hydroxy-2 (E)-nonenal concentrations], apoptotic single-stranded DNA and nuclear changes in human isolated lymphocytes exposed to increasing concentrations of Hcy. Incubation with Hcy did not induce significant changes in any of these biomarkers. Therefore, our results do not support the existence of a direct link between increased levels of Hcy and the occurrence of a pro-apoptotic state mediated by enhanced oxidative stress.

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.

Cross-talk between Cys34 and Lysine Residues in Human Serum Albumin Revealed by N-Homocysteinylation

Protein N-homocysteinylation involves a post-translational modification by homocysteine (Hcy)-thiolactone. In humans, about 70% of circulating Hcy is N-linked to blood proteins, mostly to hemoglobin and albumin. It was unclear what protein site(s) were prone to Hcy attachment and how N-linked Hcy affected protein function. Here we show that Lys(525) is a predominant site of N-homocysteinylation in human serum albumin in vitro and in vivo. We also show that the reactivity of albumin lysine residues, including Lys(525), is affected by the status of Cys(34). The disulfide forms of circulating albumin, albumin-Cys(34)-S-S-Cys and albumin-Cys(34)-S-S-Hcy, are N-homocysteinylated faster than albumin-Cys(34)-SH. Although N-homocysteinylations of albumin-Cys(34)-SH and albumin-Cys(34)-S-S-Cys yield different primary products, subsequent thiol-disulfide exchange reactions result in the formation of a single product, N-(Hcy-S-S-Cys)-albumin-Cys(34)-SH. We also show that N-homocysteinylation affects the susceptibility of albumin to oxidation and proteolysis. The data suggest that a disulfide at Cys(34) of albumin promotes conversion of N-(Hcy-SH)-albumin-Cys(34)-SH to a proteolytically sensitive form N-(Hcy-S-S-Cys)-albumin-Cys(34)-SH, which would facilitate clearance of the N-homocysteinylated form of mercaptoalbumin.

Influence of hyperhomocysteinemia on the cellular redox state--impact on homocysteine-induced endothelial dysfunction

Hyperhomocysteinemia is an independent risk factor for the development of atherosclerosis. An increasing body of evidence has implicated oxidative stress as being contributory to homocysteine's deleterious effects on the vasculature. Elevated levels of homocysteine may lead to increased generation of superoxide by a biochemical mechanism involving nitric oxide synthase, and, to a lesser extent, by an increase in the chemical oxidation of homocysteine and other aminothiols in the circulation. The resultant increase in superoxide levels is further amplified by homocysteine-dependent alterations in the function of cellular antioxidant enzymes such as cellular glutathione peroxidase or extracellular superoxide dismutase. One direct clinical consequence of elevated vascular superoxide levels is the inactivation of the vasorelaxant messenger nitric oxide, leading to endothelial dysfunction. Scavenging of superoxide anion by either superoxide dismutase or 4,5-dihydroxybenzene 1,3-disulfonate (Tiron) reverses endothelial dysfunction in hyperhomocysteinemic animal models and in isolated aortic rings incubated with homocysteine. Similarly, homocysteine-induced endothelial dysfunction is also reversed by increasing the concentration of the endogenous antioxidant glutathione or overexpressing cellular glutathione peroxidase in animal models of mild hyperhomocysteinemia. Taken together, these findings strongly suggest that the adverse vascular effects of homocysteine are at least partly mediated by oxidative inactivation of nitric oxide.