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

Hyperhomocysteinemia in Adult Patients: A Treatable Metabolic Condition

Hyperhomocysteinemia (HHcy) is recognized as an independent risk factor for various significant medical conditions, yet controversy persists around its assessment and management. The diagnosis of disorders afffecting homocysteine (Hcy) metabolism faces delays due to insufficient awareness of its clinical presentation and unique biochemical characteristics. In cases of arterial or venous thrombotic vascular events, particularly with other comorbidities, it is crucial to consider moderate to severe HHcy. A nutritional approach to HHcy management involves implementing dietary strategies and targeted supplementation, emphasizing key nutrients like vitamin B6, B12, and folate that are crucial for Hcy conversion. Adequate intake of these vitamins, along with betaine supplementation, supports Hcy remethylation. Lifestyle modifications, such as smoking cessation and regular physical activity, complement the nutritional approach to enhance Hcy metabolism. For individuals with HHcy, maintaining a plasma Hcy concentration below 50 μmol/L consistently is vital to lowering the risk of vascular events. Collaboration with healthcare professionals and dietitians is essential for developing personalized dietary plans addressing the specific needs and underlying health conditions. This integrated approach aims to optimize metabolic processes and reduce the associated health risks.

Role of Serum Homocysteine and Outcome in Patients With Traumatic Brain Injury

Background

There have been indications of a correlation between serum homocysteine (Hcy) levels and poor patient outcomes in traumatic brain injury (TBI). Thus, we aimed to explore the role of serum Hcy in influencing the outcome post TBI.

Methods

A case-control study was conducted at Liaquat University of Medical and Health Sciences (LUMHS) between January 15, 2022 and July 1, 2022. All patients between the ages of 18 and 75 years who presented with TBI, irrespective of severity, were included in the study. All patients with neurological disorders and infections, including but not limited to cerebral tuberculosis, Alzheimer's disease, epilepsy, brain cancer, Parkinson's, and stroke, were excluded from the study. For comparison, healthy controls with similar demographics were enrolled in the study. All patients and controls underwent biochemical evaluation of serum Hcy and neurological assessment at presentation. In addition, all sociodemographic and clinical parameters, including the Glasgow Outcome Score (GOS), were collected in a predefined pro forma.

Results

A total of 175 patients were included who had experienced TBIs, along with an equal number of healthy controls. The most common etiology was road traffic accidents in 82 (46.9%) patients. The mean Glasgow Coma Score (GCS) at presentation was 5.78 ± 1.72. The mean Hcy levels were 31.4 ± 7.97 µmol/L in TBI patients and 11.12 ± 5.87 µmol/L in the control healthy patients (p=0.001). It was found that the severity of hyperhomocysteinemia (HHcy) was significantly related to the worst outcome possible, i.e., death (p=0.001).

Conclusion

The study concluded that patients who had suffered from a TBI had significantly higher serum Hcy levels. Furthermore, the study highlighted that the patients with the worst outcomes had more severe hyperhomocysteinemia (HHcy) than those with better outcomes. Moreover, patients with low GOS scores were more likely to have HHcy.

Consumption of Cashew (Anacardium occidentale L.) Nuts Counteracts Oxidative Stress and Tissue Inflammation in Mild Hyperhomocysteinemia in Rats

Hyperhomocysteinemia (HHcy) is a methionine metabolism problem that causes a variety of inflammatory illnesses. Oxidative stress is among the processes thought to be involved in the pathophysiology of the damage produced by HHcy. HHcy is likely to involve the dysfunction of several organs, such as the kidney, liver, or gut, which are currently poorly understood. Nuts are regarded as an important part of a balanced diet since they include protein, good fatty acids, and critical nutrients. The aim of this work was to evaluate the anti-inflammatory and antioxidant effects of cashew nuts in HHcy induced by oral methionine administration for 30 days, and to examine the possible pathways involved. In HHcy rats, cashew nuts (100 mg/kg orally, daily) were able to counteract clinical biochemical changes, oxidative and nitrosative stress, reduced antioxidant enzyme levels, lipid peroxidation, proinflammatory cytokine release, histological tissue injuries, and apoptosis in the kidney, colon, and liver, possibly by the modulation of the antioxidant nuclear factor erythroid 2-related factor 2 NRF-2 and inflammatory nuclear factor NF-kB pathways. Thus, the results suggest that the consumption of cashew nuts may be beneficial for the treatment of inflammatory conditions associated with HHcy.

Subacute combined degeneration of the spinal cord concurrent with acute pulmonary embolism: a case report

A 58-year-old male vegetarian presented with progressive numbness and weakness in the lower extremities. Laboratory examinations showed reduced vitamin B12 level with megaloblastic anaemia. Spinal magnetic resonance imaging (MRI) revealed hyperintensity within the posterior and lateral columns on T2-weighted imaging. The diagnosis of subacute combined degeneration (SCD) of the spinal cord was established. Unexpectedly, the patient developed transitory syncope on the second day after hospitalization. The diagnostic computed tomography pulmonary angiography (CTPA) confirmed multiple small pulmonary emboli. An isolated significantly elevated level of homocysteine (117.1 µmol/l) was documented when screening for hypercoagulable markers. Except for a long-term vegetarian diet, no other risk factors for hyperhomocysteinaemia (such as a family history of homocysteinuria) was found. The severity of the hyperhomocysteinaemia found in this current patient was unusual for patients with an insufficient intake of vitamin B12. In SCD patients, elevated homocysteine may increase the risk of thrombosis, which may exacerbate existing problems. Knowing the risk factors should help physicians choose appropriate diagnostic and therapeutic strategies.

Homocysteine inhibits angiogenesis through cytoskeleton remodeling

Homocysteine (Hcy) is an intermediate non-diet amino acid connecting methionine and folate cycles. Elevated total Hcy level in blood, denoted as hyperhomocysteinemia, has emerged as a prevalent and strong risk factor for multiple diseases including atherosclerotic vascular disease in coronary, cerebral, and peripheral vessels. Its detrimental effect on vascular system implies the potential application as an inhibitor of angiogenesis. However, the detailed mechanism is unveiled. Inhibitory effect of Hcy was assessed on vascular endothelial growth factor (VEGF) induced cell proliferation and migration with endothelial cell (EC) culture system. Its effect on angiogenesis was further examined in vitro and in vivo After Hcy treatment, key angiogenic factors were measured by RT-qPCR. Cellular skeletal structure was also evaluated by actin stress fiber staining. VEGF-induced human umbilical vein EC (HUVEC) proliferation and migration were dramatically down-regulated by Hcy in a dose-responsive manner. Hcy treatment significantly inhibited the VEGF-induced angiogenesis in vitro by tube formation assay and chick chorioallantoic membrane (CAM) vessel formation in vivo Key angiogenic factors like VEGFR1/2 and angiopoietin (Ang)1/2 were substantially reduced by Hcy in HUVEC- and VEGF-induced actin stress fiber cytoskeletal structure was abolished. We demonstrated that Hcy could inhibit angiogenesis by targetting key angiogenic factor and disruption of actin cytoskeleton which is crucial for cell migration.

Allicin improves carotid artery intima-media thickness in coronary artery disease patients with hyperhomocysteinemia

Homocysteine (Hcy) is an important and independent risk factor for atherosclerotic diseases, such as coronary artery disease and ischemic cerebrovascular disease. Increased carotid artery intima-media thickness (IMT) is a non-invasive marker of systemic atherosclerosis. Allicin treatment may decrease serum Hcy levels and improve impaired endothelial function in rats with hyperhomocysteinemia (HHcy). The present study hypothesized that allicin has an anti-atherosclerotic effect in coronary heart disease and tested the effects of allicin treatment on carotid artery IMT and plasma Hcy levels in coronary heart disease patients with HHcy. Sixty-two coronary heart disease patients with HHcy were randomly divided into an allicin group and a control group. All patients underwent diagnostic assessment, plasma Hcy assay, blood lipid measurement and B-mode ultrasound of the carotid artery prior to and after treatment. Plasma Hcy levels were determined by high-performance liquid chromatography and fluorescence detection. Carotid artery IMT was calculated using an automated algorithm based on a validated edge-detection technique. After 12 weeks, significant decreases in carotid artery IMT, plasma Hcy levels, total cholesterol and triglycerides were observed in the allicin group (all P<0.05), and the decreases in the allicin group were significantly greater than those in the control group (all P<0.01). These findings suggested that reducing plasma Hcy levels may be useful for preventing the generation and development of atherosclerosis in patients with coronary heart disease. Allicin was able to decrease Hcy levels, total cholesterol and triglycerides as well as carotid artery IMT.

Disturbed nitric oxide and homocysteine production are involved in the increased risk of cardiovascular diseases in the F1 offspring of maternal obesity and malnutrition

PURPOSE

The present study aimed to evaluate the changes in levels of different independent risk factors for vascular diseases in the rat offspring of maternal obesity and malnutrition as maternal health disturbances are thought to have direct consequences on the offspring health. The effect of postnatal diet on the offspring was also assessed.

METHODS

Three groups of female Wistar rats were used (control, obese and malnourished). After the pregnancy and delivery, the offspring were weaned to control diet or high-caloric (HCD) diet and followed up for 30 weeks. Every 5 weeks postnatal, 20 pups (10 males and 10 females) of each subgroup were sacrificed after overnight fasting, the blood sample was obtained, and the rats were dissected out to obtain heart muscle. The following parameters were assessed; lipid profile, NEFA, homocysteine (Hcy), nitric oxide end product (NOx) and myocardial triglyceride content.

RESULTS

Maternal obesity and malnutrition caused significant elevation in the body weight, triglycerides, NEFA, Hcy and NOx in the F1 offspring especially those maintained under HCD. Also, the male offspring showed more prominent changes than female offspring.

CONCLUSIONS

Maternal malnutrition and obesity may increase the risk of the development of cardiovascular diseases in the offspring, especially the male ones.

Melatonin's role as a co-adjuvant treatment in colonic diseases: A review

Melatonin is produced in the pineal gland as well as many other organs, including the enterochromaffin cells of the digestive mucosa. Melatonin is a powerful antioxidant that resists oxidative stress due to its capacity to directly scavenge reactive species, to modulate the antioxidant defense system by increasing the activities of antioxidant enzymes, and to stimulate the innate immune response through its direct and indirect actions. In addition, the dysregulation of the circadian system is observed to be related with alterations in colonic motility and cell disruptions due to the modifications of clock genes expression. In the gastrointestinal tract, the activities of melatonin are mediated by melatonin receptors (MT2), serotonin (5-HT), and cholecystokinin B (CCK2) receptors and via receptor-independent processes. The levels of melatonin in the gastrointestinal tract exceed by 10-100 times the blood concentrations. Also, there is an estimated 400 times more melatonin in the gut than in the pineal gland. Gut melatonin secretion is suggested to be influenced by the food intake. Low dose melatonin treatment accelerates intestinal transit time whereas high doses may decrease gut motility. Melatonin has been studied as a co-adjuvant treatment in several gastrointestinal diseases including irritable bowel syndrome (IBS), constipation-predominant IBS (IBS-C), diarrhea-predominant IBS (IBS-D), Crohn's disease, ulcerative colitis, and necrotizing enterocolitis. The purpose of this review is to provide information regarding the potential benefits of melatonin as a co-adjuvant treatment in gastrointestinal diseases, especially IBS, Crohn's disease, ulcerative colitis, and necrotizing enterocolitis.

Vein graft disease in a knockout mouse model of hyperhomocysteinaemia

A major reason for vein graft failure after coronary artery bypass grafting is neointimal hyperplasia and thrombosis. Elevated serum levels of homocysteine (Hcy) are associated with higher incidence of cardiovascular disease, but homocysteine levels also tend to increase during the first weeks or months after cardiac surgery. To investigate this further, C57BL/6J mice (WT) and cystathionine-beta-synthase heterozygous knockout mice (CBS+/-), a mouse model for hyperhomocysteinaemia, underwent interposition of the vena cava of donor mice into the carotid artery of recipient mice. Two experimental groups were examined: 20 mice of each group underwent bypass surgery (group 1: WT donor and WT recipient; group 2: CBS+/- donor and CBS+/- recipient). After 4 weeks, the veins were harvested, dehydrated, paraffin-embedded, stained and analysed by histomorphology and immunohistochemistry. Additionally, serum Hcy levels in CBS knockout animals and in WT animals before and after bypass surgery were measured. At 4 weeks postoperatively, group 2 mice showed a higher percentage of thrombosis compared to controls, a threefold increase in neointima formation, higher general vascularization, a lower percentage of elastic fibres with shortage and fragmentation in the neointima, a lower percentage of acid mucopolysaccharides in the neointima and a more intense fibrosis in the neointima and media. In conclusion, hyperhomocysteinaemic cystathionine-beta-synthase knockout mice can play an important role in the study of mechanisms of vein graft failure. But further in vitro and in vivo studies are necessary to answer the question whether or not homocysteine itself or a related metabolic factor is the key aetiologic agent for accelerated vein graft disease.

ADMA and hyperhomocysteinemia

Hyperhomocysteinemia is a risk factor for cardiovascular disease and stroke. Like many other cardiovascular risk factors, hyperhomocysteinemia produces endothelial dysfunction due to impaired bioavailability of endothelium-derived nitric oxide (NO). The molecular mechanisms responsible for decreased NO bioavailabil ity in hyperhomocysteinemia are incompletely understood, but emerging evidence suggests that asymmetric dimethylarginine (ADMA), an endogenous inhibitor of NO synthase, may be a key mediator. Homocysteine is produced during the synthesis of ADMA and can alter ADMA metabolism by inhibiting dimethylarginine dimethy laminohydrolase (DDAH). Several animal and clinical studies have demonstrated a strong association between plasma total homocysteine, plasma ADMA, and endothelial dysfunction. These observations suggest a model in which elevation of ADMA may be a unifying mechanism for endothelial dysfunction during hyper homocysteinemia. The recent development of transgenic mice with altered ADMA metabolism should provide further mechanistic insights into the role of ADMA in hyperhomocysteinemia.

Homocysteine-induced apoptosis in endothelial cells coincides with nuclear NOX2 and peri-nuclear NOX4 activity

Apoptosis of endothelial cells related to homocysteine (Hcy) has been reported in several studies. In this study, we evaluated whether reactive oxygen species (ROS)-producing signaling pathways contribute to Hcy-induced apoptosis induction, with specific emphasis on NADPH oxidases. Human umbilical vein endothelial cells were incubated with 0.01–2.5 mM Hcy. We determined the effect of Hcy on caspase-3 activity, annexin V positivity, intracellular NOX1, NOX2, NOX4, and p47^phox expression and localization, nuclear nitrotyrosine accumulation, and mitochondrial membrane potential (ΔΨ_m). Hcy induced caspase-3 activity and apoptosis; this effect was concentration dependent and maximal after 6-h exposure to 2.5 mM Hcy. It was accompanied by a significant increase in ΔΨ_m. Cysteine was inactive on these parameters excluding a reactive thiol group effect. Hcy induced an increase in cellular NOX2, p47^phox, and NOX4, but not that of NOX1. 3D digital imaging microscopy followed by image deconvolution analysis showed nuclear accumulation of NOX2 and p47^phox in endothelial cells exposed to Hcy, but not in control cells, which coincided with accumulation of nuclear nitrotyrosine residues. Furthermore, Hcy enhanced peri-nuclear localization of NOX4 coinciding with accumulation of peri-nuclear nitrotyrosine residues, a reflection of local ROS production. p47^phox was also increased in the peri-nuclear region. The Hcy-induced increase in caspase-3 activity was prevented by DPI and apocynin, suggesting involvement of NOX activity. The data presented in this article reveal accumulation of nuclear NOX2 and peri-nuclear NOX4 accumulation as potential source of ROS production in Hcy-induced apoptosis in endothelial cells.

Methylenetetrahydrofolate reductase C677T and A1298C polymorphisms and variations of homocysteine concentrations in patients with Behcet's disease

BACKGROUND

Behcet's disease (BD) is a chronic, relapsing, multi-systemic inflammatory disorder of unknown causes. This disease is mainly characterized by mucocutaneous, ocular, vascular, and central nervous system manifestations. The aim of this study is to investigate the associations between C677T and A1298C polymorphisms in the methylenetetrahydrofolate reductase (MTHFR) gene and the plasma homocysteine (Hcy), folate, and B12 levels in a relatively large cohort of Tunisian patients with BD.

METHODS

The study included 142 patients with BD and 172 healthy controls. The C677T and A1298C polymorphisms were genotyped using PCR-RFLP. Serum Hcy level was determined using a fluorescence polarization immunoassay. Serum folate and vitamin B12 levels were measured by electrochemiluminescence immunoassay.

RESULTS

Genotype and allele frequencies of the two studied MTHFR polymorphisms did not show any significant differences among BD patients compared to controls. Patient carriers of the 677TT variant and the 677T allele displayed significantly higher Hcy concentration. Moreover, no significant association was found between neither A1298C polymorphism nor the C allele and Hcy, folate, and B12 levels. In multivariate analyses, we reported that 677T allele, male gender, and creatinine level were independent risk factors for hyperhomocysteinemia (HHC).

CONCLUSIONS

In the present study, we report the absence of any significant differences between genotype and allele frequencies for both studied polymorphisms among BD patients compared to healthy controls. Besides, we showed that the T allele of MTHFR C677T polymorphism influenced the Hcy level which is an independent risk factor for HHC in Tunisian BD patients.

Effect of L-homocysteine on endothelial cell-cell junctions following F-actin stabilization through tropomyosin-1 overexpression

Since the identification of actin in non‑muscle cells, it has been suggested that the regulation of the mechanical behaviors of the actin cytoskeleton regulates cellular shape changes and the generation of forces during cell migration and division. The maintenance of cell shape and polarity are important in the formation of cell-cell junctions. The aim of the present study was to determine the effect of L‑homocysteine thiolactone hydrochloride on EA.hy926 endothelial cells in the context of the maintenance cell-cell junctions through the stabilization of filamentous actin cytoskeleton (F‑actin). The actin filaments were stabilized by the overexpression of tropomyosin-1, which has the ability to stabilize actin filaments in muscle and non-muscle cells. The stabilization of F-actin induced a significant decrease in the percentage of late apoptotic and necrotic cells following treatment with L-homocysteine. Moreover, the migratory potential of the endothelial cells was greater in the cells overexpressing tropomyosin-1 treated with L-homocysteine. Additionally, our results indicated that the stabilization of F-actin in the EA.hy926 cells significantly increased the expression of junctional β‑catenin, as compared to the cells not overexpressing tropomyosin‑1. Similarly, the fluorescence intensity of junctional α-catenin was also increased in the cells with stabilized F‑actin cytoskeleton. However, this increase was only slightly higher than that observed in the EA.hy926 cells not overexpressing tropomyosin-1. Furthermore, the analysis of Zonula occludens (ZO)‑1 relative fluorescence demonstrated a statistically significant decrease in the cell-cell junction areas among the cells with stabilized F-actin cytoskeleton in comparison to the cells not overexpressing tropomyosin-1. Our results indicate that the stabilization of F-actin does not affect the migratory potential of cells, and consequently protects the EA.hy926 cells against the L-homocysteine-induced decrease in cell mobility. Moreover, it is suggested that α‑catenin may participate in the suppression of actin polymerization in the area of cell-cell junctions. It can be hypothesized that the stabilization of F-actin strengthens endothelial adherens and tight junctions by increasing the number of cell-cell junctions due to the amplification of β-catenin and the ZO‑1 fluorescence signal. However, ZO-1 stabilizes the endothelial barrier function through the stabilization of F-actin and F-actin itself stabilizes the localization of ZO-1.

Aged garlic extract restores nitric oxide bioavailability in cultured human endothelial cells even under conditions of homocysteine elevation

ETHNOPHARMACOLOGICAL RELEVANCE

Supplementation with aged garlic extract (AGE) has been shown to restore impaired endothelium-dependent vasodilator response in subjects with acutely elevated plasma homocysteine (Hcy) levels after an oral methionine load and in patients with chronic coronary artery disease. Moreover, AGE has been shown to inhibit the progression of coronary calcifications in patients with coronary artery disease. The molecular mechanisms, by which AGE preserves endothelial function is unknown. Our objective was to explore whether AGE preserves endothelial nitric oxide (NO) output even under conditions of elevated Hcy levels by preventing oxidative inactivation of the NO synthase cofactor tetrahydrobiopterin.

MATERIAL AND METHODS

Endothelial (EA.hy 926) cells were incubated with hypoxanthine, aminopterin, thymidine and methionine (HAT/MET) to increase cellular Hcy levels, and with and without AGE. Agonist stimulated NO output was measured using the fluorescent probe DAF-2, and cellular thiol levels (Hcy, cysteine, reduced and oxidized glutathione) and cellular tetrahydrobiopterin levels were measured by high performance liquid chromatography.

RESULTS

HAT/MET incubation resulted in significantly increased cellular Hcy levels, unaffected by coincubation with AGE. Elevated Hcy went along with significantly decreased NO output (to 34.4 ± 4.4% of control) and levels of tetrahydrobiopterin (from 4.67 ± 2.17 to 2.17 ± 0.97 pmol/mg). Incubation with AGE (5mg/mL) in HAT/MET-treated cells prevented the declines in NO output and tetrahydrobiopterin levels. AGE increased cellular levels of cysteine and total glutathione, and prevented glutathione and tetrahydrobiopterin oxidation induced by elevated Hcy.

CONCLUSION

Incubation with AGE preserved normal NO output from endothelial cells even under conditions of elevated Hcy levels by increasing cellular thiol antioxidant and prevention of tetrahydrobiopterin oxidation. This suggests that AGE might be useful in the prevention of endothelial dysfunction.

Combined methylmalonic acidemia and homocystinuria, cblC type. II. Complications, pathophysiology, and outcomes

Combined methylmalonic acidemia and homocystinuria, cblC type, is stated to be the most common inborn error of intracellular cobalamin metabolism. The disorder can display a wide spectrum of clinical manifestations, spanning the prenatal period through late adulthood. While increased homocysteine concentrations and impaired methyl group metabolism may contribute to disease-related complications, the characteristic macular and retinal degeneration seen in many affected patients appears to be unique to cblC disease. The early detection of cblC disease by newborn screening mandates a careful assessment of therapeutic approaches and provides a new opportunity to improve the outcome of affected patients. The following article reviews the current knowledge on the complications, pathophysiology, and outcome of cblC disease in an effort to better guide clinical practice and future therapeutic trials.

Chronic mild hyperhomocysteinemia alters ectonucleotidase activities and gene expression of ecto-5'-nucleotidase/CD73 in rat lymphocytes

Since mild hyperhomocysteinemia is a risk factor for cardiovascular and cerebral diseases and extracellular nucleotides/nucleosides, which are controlled by the enzymatic action of ectonucleotidases, can induce an immune response, in the present study, we investigated the effect of chronic mild hyperhomocysteinemia on ectonucleotidase activities and expression in lymphocytes from mesenteric lymph nodes and serum of adult rats. For the chronic chemically induced mild hyperhomocysteinemia, Hcy (0.03 μmol/g of body weight) or saline (control) were administered subcutaneously from the 30th to the 60th day of life. Results showed that homocysteine significantly decreased ATP, ADP, and AMP hydrolysis in lymphocytes of adult rats. E-NTPDases transcriptions were not affected, while the ecto-5'-nucleotidase transcription was significantly decreased in mesenteric lymph nodes of hyperhomocysteinemic rats. ATP, ADP, and AMP hydrolysis were not affected by homocysteine in rat serum. Our findings suggest that Hcy in levels similar to considered risk factor to development of vascular diseases modulates the ectonucleotidases, which could lead to a pro-inflammatory status.

Homocysteine-induced cardiomyocyte apoptosis and plasma membrane flip-flop are independent of S-adenosylhomocysteine: a crucial role for nuclear p47(phox)

We previously found that homocysteine (Hcy) induced plasma membrane flip-flop, apoptosis, and necrosis in cardiomyocytes. Inactivation of flippase by Hcy induced membrane flip-flop, while apoptosis was induced via a NOX2-dependent mechanism. It has been suggested that S-adenosylhomocysteine (SAH) is the main causative factor in hyperhomocysteinemia (HHC)-induced pathogenesis of cardiovascular disease. Therefore, we evaluated whether the observed cytotoxic effect of Hcy in cardiomyocytes is SAH dependent. Rat cardiomyoblasts (H9c2 cells) were treated under different conditions: (1) non-treated control (1.5 nM intracellular SAH with 2.8 μM extracellular L -Hcy), (2) incubation with 50 μM adenosine-2,3-dialdehyde (ADA resulting in 83.5 nM intracellular SAH, and 1.6 μM extracellular L -Hcy), (3) incubation with 2.5 mM D, L -Hcy (resulting in 68 nM intracellular SAH and 1513 μM extracellular L -Hcy) with or without 10 μM reactive oxygen species (ROS)-inhibitor apocynin, and (4) incubation with 100 nM, 10 μM, and 100 μM SAH. We then determined the effect on annexin V/propodium iodide positivity, flippase activity, caspase-3 activity, intracellular NOX2 and p47(phox) expression and localization, and nuclear ROS production. In contrast to Hcy, ADA did not induce apoptosis, necrosis, or membrane flip-flop. Remarkably, both ADA and Hcy induced a significant increase in nuclear NOX2 expression. However, in contrast to ADA, Hcy additionally induced nuclear p47(phox) expression, increased nuclear ROS production, and inactivated flippase. Incubation with SAH did not have an effect on cell viability, nor on flippase activity, nor on nuclear NOX2-, p47phox expression or nuclear ROS production. HHC-induced membrane flip-flop and apoptosis in cardiomyocytes is due to increased Hcy levels and not primarily related to increased intracellular SAH, which plays a crucial role in nuclear p47(phox) translocation and subsequent ROS production.

Cellular hypomethylation is associated with impaired nitric oxide production by cultured human endothelial cells

Hyperhomocysteinemia (HHcy) is a risk factor for vascular disease, but the underlying mechanisms remain incompletely defined. Reduced bioavailability of nitric oxide (NO) is a principal manifestation of underlying endothelial dysfunction, which is an initial event in vascular disease. Inhibition of cellular methylation reactions by S-adenosylhomocysteine (AdoHcy), which accumulates during HHcy, has been suggested to contribute to vascular dysfunction. However, thus far, the effect of intracellular AdoHcy accumulation on NO bioavailability has not yet been fully substantiated by experimental evidence. The present study was carried out to evaluate whether disturbances in cellular methylation status affect NO production by cultured human endothelial cells. Here, we show that a hypomethylating environment, induced by the accumulation of AdoHcy, impairs NO production. Consistent with this finding, we observed decreased eNOS expression and activity, but, by contrast, enhanced NOS3 transcription. Taken together, our data support the existence of regulatory post-transcriptional mechanisms modulated by cellular methylation potential leading to impaired NO production by cultured human endothelial cells. As such, our conclusions may have implications for the HHcy-mediated reductions in NO bioavailability and endothelial dysfunction.

Homocysteine enhances transmigration of rat monocytes through a brain capillary endothelial cell monolayer via ICAM-1

Increased homocysteine (Hcy) levels contribute to a variety of cardiovascular and cerebrovascular diseases including stroke and Alzheimer's disease. Recent data has shown that elevated levels of Hcy can lead to the blood-brain barrier (BBB) dysfunction and activation. However, the mechanism for Hcy-mediated dysfunction remains unclear. The aim of this study is to characterize the effects of moderate Hcy administration in rat brain capillary endothelial cells (BCECs), which serve as a simple model to study blood-brain barrier (BBB) functions. This present study shows that addition of 20 microM Hcy for 6 days did not significantly affect BCEC survival, as measured by acridine orange staining, propidium iodide staining, and nitrite content. However, addition of 20 microM Hcy for 6 days did elevate lactate dehydrogenase (LDH) activity released into the supernatant of BCECs, as well as significantly enhance the transmigration of monocytes across the BCEC in a time-dependent manner. In addition, TNFalpha levels in BCEC were also elevated by Hcy, whereas inflammatory markers MIP3alpha and RANTES were significantly reduced. Finally, this study also shows that intercellular adhesion molecule-1 (ICAM-1) expression is significantly enhanced by 20 microM Hcy treatment compared to control conditions. These results suggest that moderate levels of homocysteine can affect proinflammatory patterns expressed by BCECs ultimately leading to BBB activation and dysfunction through enhanced monocyte transmigration and ICAM-1 expression.

Redox Pioneer: Professor Joseph Loscalzo

Dr. Joseph Loscalzo (M.D., 1978; Ph.D., 1977) is recognized here as a Redox Pioneer because he has published two articles in the field of antioxidant/redox biology that have been cited more than 1,000 times and 22 articles that have been cited more than 100 times. Dr. Loscalzo is known for his seminal contributions to our understanding of the vascular biology of nitric oxide. His initial discovery that the antiplatelet effects of organic nitrates are potentiated by thiols through a mechanism that involved metabolism to S-nitrosothiols was followed by the demonstration that S-nitrosothiols are formed endogenously through S-transnitrosation, stabilize nitric oxide, and facilitate the transport and transfer of nitric oxide between and within cells of the vessel wall. These properties led to the development of S-nitrosothiol-containing pharmacotherapies to treat disease states characterized by nitric oxide deficiency. Dr. Loscalzo's other scientific contributions include identifying the vascular functional consequences of genetic deficiencies of antioxidant enzymes that decrease nitric oxide bioavailability, collectively termed the "oxidative enzymopathies," and demonstrating the role of mitochondria in modulating the disulfide subproteome, and in redox signaling in hypoxia. He has received numerous awards and honors for his scientific contributions, including election to the Institute of Medicine of the National Academy of Sciences.

Homocysteine-mediated thrombosis and angiostasis in vascular pathobiology

The mechanisms by which homocysteine contributes to atherothrombosis are complex and their in vivo relevance uncertain. In this issue of the JCI, Jacovina and colleagues report a unique in vivo mechanism by which homocysteine may contribute to vascular disease (see the related article beginning on page 3384). This group had previously reported that homocysteine impairs endothelial cell surface plasminogen activation by posttranslationally modifying annexin A2, the coreceptor for plasminogen and tissue plasminogen activator. They now show that an annexin A2-deficient mouse rendered hyperhomocysteinemic by dietary means has impaired fibrinolysis, perivascular fibrin persistence, and attenuated angiogenesis (angiostasis). Potential mechanisms by which homocysteine-dependent changes in endothelial phenotype link thrombosis to angiostasis are reviewed and their relationship to homocysteine-dependent vascular disease considered.

Matrix imbalance by inducing expression of metalloproteinase and oxidative stress in cochlea of hyperhomocysteinemic mice

Clinical study reports hearing loss in patients with low folic acid (FA) and elevated homocysteine (Hcy). We hypothesize that elevated Hcy induces imbalance in matrix turnover and oxidative stress in cochlea. Cystathione beta-synthase heterozygous knockout mice were used as model for hyperhomocysteinemia. Matrix remodeling induced by Hcy resulted from elevated MMP-2, -9, and -14. MMP-2 and -9 showed elevated gelatinase activity in CBS (+/-) cochlea. Tissue inhibitors of matrix metalloproteinase were significantly lower in CBS (+/-) cochlea. The expression analyses for MMPs and TIMPs were equally represented at protein and mRNA levels. Cochlea of CBS mice showed following structural changes; (1) detachment of tectorial membrane lying on hair cells (2) thinner s. vascularis (3) large fibroblast in spiral ligament. Hcy induced higher protein nitrotyrosination and cytosolic NADPHoxidase subunit p22(phox) in cochlea. It is thus suggested that Hcy induced matrix imbalance, structural changes and oxidative stress in cochlea.

Homocysteine and lipids: S-adenosyl methionine as a key intermediate

An association between hyperlipidemia and hyperhomocysteinemia (HHCY) has been suggested. This link is clinically important in management of vascular risk factors especially in elderly people and patients with metabolic syndrome. Higher plasma homocysteine (Hcy) was associated with lower high-density lipoprotein (HDL)-cholesterol level. Moreover, HHCY was associated with disturbed plasma lipids or fatty liver. It seems that hypomethylation associated with HHCY is responsible for lipid accumulation in tissues. Decreased methyl group will decrease the synthesis of phosphatidylcholine, a major phospholipid required for very low-density lipoprotein (VLDL) assembly and homeostasis. The effect of Hcy on HDL-cholesterol is probably related to inhibiting enzymes or molecules participating in HDL-particle assembly.

Homocysteine effects on cellular glutathione peroxidase (GPx-1) activity under in vitro conditions

Hyperhomocysteinemia is associated with a lot of diseases including cardiovascular diseases and neural tube defect, but it has not been clarified exactly which mechanism is responsible for occurence disease. Here, homocysteine (Hcy) and cysteine (Cys), which are thiol containing amino acids, were examined for their effect on glutathione peroxidase (GPx) activity. It was observed that the GPx-1 activity was inhibited under severe hyperhomocysteinemia (50-500 microM Hcy) conditions, especially at low glutathione concentrations but that cysteine increased GPx-1 activity at low glutathione concentrations and inhibition clearly appeared at 500 microM Cys concentration.

Intraperitoneal Administration of Methylene Blue Attenuates Oxidative Stress, Increases Peritoneal Fibrinolysis, and Inhibits Intraabdominal Adhesion Formation

BACKGROUND

Mounting evidence indicates that postoperative oxidative stress may be linked to decreased fibrinolytic activity and, subsequently, the development of intraabdominal adhesions. The goal of this study was to determine if methylene blue, a highly redox active dye that has been shown to inhibit adhesion formation (1) acts as an antioxidant in the postoperative peritoneum, and (2) subsequently affects fibrinolytic activity.

MATERIALS AND METHODS

Intraabdominal adhesions were surgically induced in rats receiving methylene blue (30 mg/kg) or vehicle (sterile water) intraperitoneally at surgery. At 24 h and 7 d following surgery, adhesion formation, oxidative stress, and peritoneal fibrinolytic activity were assessed.

RESULTS

Methylene blue did not affect adhesion formation at 24 h, but did induce a >50% regression in adhesions after 7 d (P < 0.05). Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and myeloperoxidase (MPO) activities, and 8-isoprostane and thiobarbituric acid-reactive substances were all significantly increased in peritoneal tissue samples (P < 0.05) by 24 h following surgery. Methylene blue inhibited NADPH oxidase by 98% and MPO activity by 78% in the 24 h tissue samples, and blunted the corresponding surgery-induced increases in tissue lipid and protein oxidation. Furthermore, methylene blue significantly increased (P < 0.05) fibrinolytic activity in peritoneal fluid at 24 h.

CONCLUSIONS

Methylene blue acts as an antioxidant in this experimental system and may reduce intraabdominal adhesion formation by enhancing peritoneal fibrinolytic activity following surgery.

Vascular oxidant stress and inflammation in hyperhomocysteinemia

Elevated plasma levels of homocysteine are a metabolic risk factor for atherosclerotic vascular disease, as shown in numerous clinical studies that linked elevated homocysteine levels to de novo and recurrent cardiovascular events. High levels of homocysteine promote oxidant stress in vascular cells and tissue because of the formation of reactive oxygen species (ROS), which have been strongly implicated in the development of atherosclerosis. In particular, ROS have been shown to cause endothelial injury, dysfunction, and activation. Elevated homocysteine stimulates proinflammatory pathways in vascular cells, resulting in leukocyte recruitment to the vessel wall, mediated by the expression of adhesion molecules on endothelial cells and circulating monocytes and neutrophils, in the infiltration of leukocytes into the arterial wall mediated by increased secretion of chemokines, and in the differentiation of monocytes into cholesterol-scavenging macrophages. Furthermore, it stimulates the proliferation of vascular smooth muscle cells followed by the production of extracellular matrix. Many of these events involve redox-sensitive signaling events, which are promoted by elevated homocysteine, and result in the formation of atherosclerotic lesions. In this article, we review current knowledge about the role of homocysteine on oxidant stress-mediated vascular inflammation during the development of atherosclerosis.

Homocysteine and glutathione peroxidase-1

Mildly elevated homocysteine levels (Hcy) increase the risk for atherothrombotic vascular disease in the coronary, cerebrovascular, and peripheral arterial circulations. The molecular mechanisms responsible for decreased bioavailability of endothelium-derived nitric oxide (NO) by Hcy involve an increase of vascular oxidant stress and inhibition of important antioxidant capacity. Glutathione peroxidase-1 (GPx-1), a selenocysteine-containing antioxidant enzyme, may be a key target of Hcy's deleterious actions, and several experimental and clinical studies have demonstrated a complex relationship between plasma total homocysteine (tHcy), GPx-1, and endothelial dysfunction. Hcy may promote endothelial dysfunction, in part by decreasing GPx-1 expression; however, there is evidence to suggest that overexpression of GPx-1 can compensate for these effects. This review summarizes the current knowledge of the metabolism of Hcy, the effects of hyperhomocysteinemia observed in in vitro and in vivo models that lead to endothelial dysfunction and the possible mechanisms for these actions, and the role of GPx-1 in the pathogenesis of Hcy-induced cardiovascular disease (CVD).

Methylenetetrahydrofolate reductase C677T mutation and nonalcoholic fatty liver disease

A mutation in the methylenetetrahydrofolate reductase (MTHFR) gene is known as one of the causes of hyperhomocyteinemia. The oxidation products of homocysteine can initiate lipid peroxidation, which has a central role in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). We aimed to assess the possible role of the MTHFR C677T mutation in the progression of simple steatosis to an advanced form of NAFLD. Thirty-four patients with NAFLD diagnosed by histologic analysis and 282 healthy controls were included in the study. The discrimination of nonalcoholic steatohepatitis (NASH) from another NAFLD was made by NAFLD activity score (NAS), and a NAS>or=5 was considered NASH. Patients with either NASH or nonalcoholic fatty liver (NAFL) and controls were evaluated for frequency of the MTHFR C677T mutation. The frequency of the MTHFR C677T mutation was 53.5% (CT, 44.7%; TT, 8.9%) in controls and 41.5% (CT, 37.7%; TT, 3.8%) in patients (odds ratio [OR], 0.62; 95% confidence interval [CI], 0.34-1.12). There was no statistical difference in the frequency of this genotype between patients with NAFL and those with NASH (36% [CT, 28%; TT, 8%] vs 46.4% [CT, 46.4; TT, 0%]; OR, 0.65; 95% CI, 0.22-1.96). According to this study, the MTHFR C677T mutation does not seem to be a risk factor for the progression of NAFL to NASH.

Hyperhomocysteinaemia induced by dietary folate restriction causes kidney oxidative stress in rats

Diet is the most common cause of mild hyperhomocysteinaemia (HHcy), which occurs in approximately 5–7 % of the general population. Since HHcy causes endothelial damage by oxidative stress in different organs, the present study was designed to examine whether HHcy might be involved in renal oxidative stress. Twenty-five male Wistar rats were randomly divided into two groups: one (n13) was fedad libituma folate-free diet (FF) and the other (n12) was fed the same diet supplemented with folic acid (control, CO). After 8 weeks the animals were killed and kidneys removed. Malondialdehyde (MDA), superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities were measured in plasma and kidney homogenates. Renal tissue sections were analysed by indirect immunostaining with the primary antibody against oxidatively modified LDL receptor (LOX-1). A marked HHcy was confirmed in the FF group. As compared with CO animals, MDA levels in plasma and kidney homogenate were significantly higher in FF rats (P<0·05). Similarly, renal GPx and SOD activities were significantly higher in the FF group (P<0·001). No differences were found in LOX-1 immunohistochemical expression, which in the two groups was displayed in tubular cells. The present study provides evidence that HHcy does produce renal oxidative stress mediated by lipid peroxidation, and that the increased kidney MDA displayed by FF animals may enhance kidney antioxidant activity and thereby attenuate both kidney damage and expression of LOX-1.

Effects of soy isoflavones and phytate on homocysteine, C-reactive protein, and iron status in postmenopausal women

BACKGROUND

Soy protein or its components may protect against the atherosclerotic cardiovascular disease (CVD) risk factors total homocysteine (tHcy), C-reactive protein (CRP), and excess body iron, which generally increase with menopause.

OBJECTIVE

The primary objective of this study was to determine the independent effect of the soy protein components isoflavones and phytate on CVD risk factors in postmenopausal women. The secondary objective was to identify factors [blood lipids, oxidative stress indexes, serum ferritin, plasma folate, plasma vitamin B-12, and body mass index (BMI)] contributing to tHcy and CRP concentrations.

DESIGN

In a double-blind, 6-wk study, 55 postmenopausal women aged 47-72 y were randomly assigned to 1 of 4 soy protein (40 g/d) isolate treatments: native phytate and native isoflavone (n = 14), native phytate and low isoflavone (n = 13), low phytate and native isoflavone (n = 14), or low phytate and low isoflavone (n = 14). We measured iron indexes, tHcy, CRP, and BMI.

RESULTS

Soy protein with native phytate significantly reduced tHcy (P = 0.017), transferrin saturation (P = 0.027), and ferritin (P = 0.029), whereas soy protein with native isoflavones had no effect on any variables. At baseline, BMI was highly correlated with tHcy (r = 0.39, P = 0.003) and CRP (r = 0.55, P < 0.0001), whereas HDL cholesterol was correlated with CRP (r = -0.30, P = 0.02). Multiple regression analysis showed that LDL cholesterol and BMI contributed significantly (R2= 19.9%, P = 0.003) to the overall variance in tHcy.

CONCLUSION

Consuming phytate-rich foods and maintaining a healthy weight may reduce atherosclerotic CVD risk factors in postmenopausal women.

ADMA and hyperhomocysteinemia

Hyperhomocysteinemia is a risk factor for cardiovascular disease and stroke. Like many other cardiovascular risk factors, hyperhomocysteinemia produces endothelial dysfunction due to impaired bioavailability of endothelium-derived nitric oxide (NO). The molecular mechanisms responsible for decreased NO bioavailability in hyperhomocysteinemia are incompletely understood, but emerging evidence suggests that asymmetric dimethylarginine (ADMA), an endogenous inhibitor of NO synthase, may be a key mediator. Homocysteine is produced during the synthesis of ADMA and can alter ADMA metabolism by inhibiting dimethylarginine dimethylaminohydrolase (DDAH). Several animal and clinical studies have demonstrated a strong association between plasma total homocysteine, plasma ADMA, and endothelial dysfunction. These observations suggest a model in which elevation of ADMA may be a unifying mechanism for endothelial dysfunction during hyperhomocysteinemia. The recent development of transgenic mice with altered ADMA metabolism should provide further mechanistic insights into the role of ADMA in hyperhomocysteinemia.

Homocysteinylation of low-density lipoproteins (LDL) from subjects with Type 1 diabetes: effect on oxidative damage of human endothelial cells

BACKGROUND

Homocysteine (Hcy) is an independent risk factor for cardiovascular disease (CVD). Individuals with Type 1 and Type 2 diabetes are more susceptible to the effects of homocysteine than non-diabetic subjects. The interaction between homocysteine-thiolactone (Hcy-thiolactone), a reactive product of Hcy, and low-density lipoproteins (LDL) induces the formation of homocystamide-LDL adducts (Hcy-LDL) and it has been suggested that homocysteinylation could increase atherogenicity of lipoproteins.

AIM

The aim of the study was to compare the effect of in vitro homocysteinylation of LDL isolated from healthy control subjects (C-LDL) and from Type 1 diabetic patients (DM-LDL) and to investigate the effect of homocysteinylated LDL (Hcy-C-LDL and Hcy-DM-LDL) on peroxynitrite production of endothelial cells.

METHODS

The in vitro homocysteinylation of LDL isolated from control (n = 12) and DM subjects (n = 12) was carried out by incubating lipoproteins with Hcy-thiolactone. The reaction was verified by quantifying the increase in sulphydryl groups (-SH groups) in Hcy-LDL with respect to control LDL. Control and homocysteinylated LDL were incubated with human aortic endothelial cells (HAEC) in culture. Peroxynitrite production in cells treated in different experimental conditions was assayed by a fluorimetric method.

RESULTS

The increase in -SH groups after incubation with homocysteine was greater in LDL from diabetic subjects compared with LDL from control subjects (P < 0.001). In addition, peroxynitrite production from HAEC incubated with Hcy-LDL from diabetic patients was greater than after incubation with Hcy-LDL from control subjects and untreated LDL from diabetic patients (P < 0.001).

CONCLUSIONS

These results show that LDL from diabetic patients is more susceptible to in vitro homocysteinylation than LDL from non-diabetic individuals and demonstrate that the compositional changes in Hcy-LDL from diabetic subjects have cytotoxic effects on human endothelial cells.

Effect of maternal exposure to homocystine on sodium valproate-induced neural tube defects in the mouse embryos

BACKGROUND

Neural tube defects (NTD) are mainly of multifactorial origin. Maternal treatment with valproic acid (VPA) during pregnancy induces NTD in susceptible fetuses. Elevated levels of homocysteine are observed in pregnancies with NTD. The mechanism by which homocysteine might cause NTD is unknown.

AIM OF THE STUDY

The aim of this study was to determine if homocystine would augment VPA-induced exencephaly in an experimental model.

METHODS

Groups of mice were injected (IP) on gestational day 8 (GD) with a single dose of 75 mg/kg of L: -Homocystine (HC) or a proportionate volume of saline, followed by a single dose of 600 mg/kg of VPA or an equal volume of saline. In a second experiment, mice were treated with a daily dose of 75 mg/kg of HC or an equal volume of saline (IP) from GD 5 and continued through GD 10. These animals had a single exposure to 600 mg/kg of VPA or saline (IP) on GD 8. All animals were killed by cervical dislocation on GD 18. Plasma homocysteine, folate and vitamin B12 were determined on GD 8 and GD 10 from single and multiple dose groups of mice, respectively, from additional experiments.

RESULTS

The VPA and HC+VPA induced significantly higher rates of embryonic resorption and intrauterine growth retardation (IUGR) than HC or saline alone. HC + VPA groups had significantly more numerous fetuses with severe IUGR than HC alone or VPA alone groups. Both single and multiple doses of HC augmented VPA-induced reduction in fetal body weight. Successive doses of HC did not augment the rate of IUGR more significantly than a single dose of HC. Incidence of exencephaly was significantly enhanced in the HC + VPA groups compared to that in the HC or VPA alone groups. HC alone was not teratogenic. Plasma homocysteine levels increased several fold both in HC and HC + VPA groups and the increase was not particularly more marked in multiple dose groups than in the single dose groups. VPA did not elevate homocysteine concentration. Both FA and vitamin B12 concentrations were reduced by VPA, HC and HC + VPA, but HC and VPA when combined did not produce an additive effect on vitamin levels.

CONCLUSION

These data indicate that HC and VPA interact in neurulation stage embryos, affect fundamental processes of closure of the neural tube and lead to enhanced incidence of NTD.

Stereospecific and Redox-Sensitive Increase in Monocyte Adhesion to Endothelial Cells by Homocysteine

Objective— Previous studies have shown that elevated homocysteine (Hcy) levels promote the development of atherosclerotic lesions in atherosclerosis-prone animal models. There is evidence that oxidant stress contributes to Hcy’s deleterious effects on the vasculature. The accumulation and adhesion of monocytes to the vascular endothelium is a critical event in the development of atherosclerosis. We investigated the effects of Hcy on the interaction between human endothelial cells (EC) (EC line EA.hy 926 and primary human umbilical vein EC [HUVEC]) and the monocytic cell line THP-1, and the impact of vascular oxidant stress and redox-sensitive signaling pathways on these events.

Methods and Results— L-Hcy, but not D-Hcy, increases the production of reactive oxygen species inside EC, enhances nuclear factor(NF)-κB activation, and stimulates intercellular adhesion molecule-1 (ICAM-1) RNA transcription and cell surface expression. This leads to a time- and dose-dependent increase in monocyte adhesion to ECs. Pretreatment of ECs with superoxide scavengers (MnTBAP and Tiron) or with an inhibitor of NF-κB activation abolished Hcy-induced monocyte adhesion, ICAM-1 expression, and nuclear translocation of NF-κB.

Conclusions— These findings suggest that reactive oxygen species produced under hyperhomocysteinemic conditions may induce a proinflammatory situation in the vessel wall that initiates and promotes atherosclerotic lesion development.

Homocysteine-induced endothelin-1 release is dependent on hyperglycaemia and reactive oxygen species production in bovine aortic endothelial cells

BACKGROUND

Elevated plasma homocysteine (Hcy) is a risk factor for coronary disease. The objective of this study was to investigate whether Hcy either alone or in high glucose conditions induces endothelin-1 (ET-1) synthesis via the production of reactive oxygen species (ROS).

METHODS

Bovine aortic endothelial cells were grown in high (25 mmol/l) and low (5 mmol/l) glucose medium.

RESULTS

In high glucose, Hcy caused a time-dependent increase in ET-1 release, which was greatest with 50 micromol/l Hcy at 24 h (p < 0.01). This effect was not seen in low glucose conditions. In high glucose and 50 micromol/l Hcy, ET-1 mRNA levels were maximal after 1 h (p < 0.05). Tissue factor mRNA levels were raised at 4 h (p < 0.05) and functional activity was raised at 6 h (p < 0.01). Intracellular ROS production was increased by 50 micromol/l Hcy after 24 h (p < 0.05) but only in high glucose. To investigate the role of mitochondrial metabolism in ROS production, cells were incubated with thenoyltrifluoroacetone (inhibitor of complex II) or carbonyl cyanide m-chlorophenylhydrazone (uncoupler of oxidative phosphorylation). Both compounds abolished the Hcy-induced increase in ROS production and ET-1 release. There was an alteration in intracellular glutathione (GSH) levels with Hcy treatment with more oxidised GSH present.

CONCLUSION

The combined metabolic burden of Hcy and high glucose stimulates ET-1 synthesis in bovine aortic endothelial cells via a mechanism dependent on the production of mitochondrial ROS, but may not be generalisable to all types of endothelial cells.

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.

Elevated levels of homocysteine compromise blood-brain barrier integrity in mice

Elevated levels of plasma homocysteine (Hcy) correlate with increased risk of cardiovascular and Alzheimer diseases. We studied the effect of elevated Hcy on the blood-brain barrier (BBB) to explore the possibility of a vascular link between the 2 diseases. On a hyperhomocysteinemic diet, cystathionine beta-synthase (Cbs)-heterozygous mice develop hyperhomocysteinemia. Intravital microscopy analysis of the mesenteric venules showed that leukocyte rolling velocity was markedly decreased and numbers of adherent cells were increased in the mutant mice. This was due at least in part to increased expression of P-selectin. BBB permeability was measured by Evans blue dye permeation and was found to be 25% greater in the Cbs(+/-) cortex compared with wild-type controls. Our study suggests an important toxic effect of elevated Hcy on brain microvessels and implicates Hcy in the disruption of the BBB.

Hyperhomocyst(e)inemia impairs angiogenesis in a murine model of limb ischemia

Hyperhomocyst(e)inemia (HH) is an established independent risk factor for coronary, cerebral and peripheral vascular diseases. Recent studies have indicated that certain cardiovascular risk factors, including diabetes and hypercholesterolemia, impair expression of vascular endothelial growth factor (VEGF) and endogenous angiogenesis. In this study, we investigate the impact of moderate HH on angiogenesis and VEGF pathway in a mouse model of hindlimb ischemia. Upon induction of unilateral hindlimb ischemia, endogenous angiogenesis, expression of VEGF, and phosphorylation of the VEGF receptor Flk-1 were evaluated in mice heterozygous for a deletion of the cystathionine beta-synthase gene (CBS) and compared with those observed in CBS+/+ mice. CBS+/- mice exhibit moderate HH, as demonstrated by measuring plasma total homocyst(e)ine (tHcy) levels, which were significantly higher in these animals compared with CBS+/+ mice (4.77 +/- 0.82 vs 2.10 +/- 0.28, p < 0.01). Twenty-eight days after induction of ischemia, hindlimb blood flow was significantly reduced in CBS+/- mice compared with CBS+/+ animals (0.49 +/- 0.03, n = 12 vs 0.71 +/- 0.09, n = 10; p < 0.05). In addition, there was a significant negative correlation between plasma homocyst(e)ine levels and the laser Doppler perfusion ratio in CBS+/- mice (p = 0.0087, r = -0.7171). While VEGF expression and Flk-1 phosphorylation were not impaired in the ischemic muscles of CBS+/- mice, phosphorylation of the endothelial cell survival factor Akt was significantly inhibited by homocyst(e)ine in a dose-dependent manner in human umbilical vein endothelial cell (HUVECs) in vitro. In conclusion, our findings demonstrate that endogenous angiogenesis is inversely related to plasma levels of homocyst(e)ine in genetically engineered, heterozygous mice with moderate HH. This impairment, however, is not dependent on reduced expression of VEGF or impaired phosphorylation of its receptor Flk-1. In contrast, our data suggest that impaired Akt phosphorylation mediates the impairment of angiogenesis associated with HH.

The high atherosclerotic risk among epileptics: the atheroprotective role of multivitamins

Neurologists have little concern about the high atherosclerotic risk among epileptics. Recent evidences mount that chronic epilepsy and prolonged use of antiepileptic drugs (AEDs) are associated with multiple risk factors that are critically implicated in pathobiology and dysfunction of the vessel wall through complex molecular mechanisms that promote atherogenesis. This review is concerned with three metabolic alterations, which are attributed as major risk factors for atherosclerosis among epileptics: altered metabolism of a) homocysteine (Hcy), b) lipids and lipoproteins, and c) uric acid. Most conventional AEDs reduce folic acid levels, thereby raising Hcy levels. Hyperhomosysteinemia is recently believed to induce endothelial dysfunction and promote atherosclerosis through complex oxidative and excitatory neurotoxic molecular mechanisms. However, Hcy itself is a convulsing substance with increased seizure recurrence and intractability to antiepileptic medications. AEDs can disturb lipid metabolism with resultant hypercholestrolemia and dyslipidemia, common recognized risks for atherosclerosis. Altered uric acid metabolism is common among epileptics. Uric acid has been implicated in endothelial cell damage and decreased endothelial nitric oxide bioavailability. In the presence of atherosclerotic milieu, uric acid interacts with other substrate toxicities and increased reactive oxygen species, accelerating atherosclerosis. The above information forms the rationale for future routine screening and correction of such metabolic alterations in epileptics. A convincing argument now develops that routine polyvitamin supplementation (folic acid, vitamin B12, vitamin B6, vitamin C, vitamin E, and beta-carotene) becomes increasingly important for women and men receiving AEDs at all ages. The atheroprotective effect of multivitamins is through their antioxidant and anti-inflammatory effects together with their lipid and Hcy lowering effects.

Mechanisms of homocysteine-induced atherothrombosis

Elevation of plasma homocysteine level is a risk factor for cardiovascular disease, stroke, and venous thromboembolism. It is still uncertain, however, whether hyperhomocysteinemia is a causative factor or a marker of vascular disease. The strongest evidence that homocysteine plays a causal role in atherothrombosis has been provided by studies using animal models. In the past decade, considerable progress in defining the vascular effects of hyperhomocysteinemia was achieved through the use of genetic and dietary approaches to induce hyperhomocysteinemia in experimental animals. A key vascular phenotype observed in hyperhomocysteinemic animals is endothelial dysfunction, manifested by decreased bioavailability of endothelium-derived nitric oxide. Impairment of endothelial function may be mediated by either accelerated oxidative inactivation of nitric oxide or inhibition of nitric oxide production caused by the endogenous nitric oxide synthase inhibitor, asymmetric dimethylarginine. Hyperhomocysteinemia also increases susceptibility to arterial thrombosis and accelerates the development of atherosclerosis in susceptible models such as the apolipoprotein E-deficient mouse. Mechanisms of atherothrombosis may include homocysteine-induced thiolation or acylation of plasma or endothelial proteins and endoplasmic reticulum stress, which activates signal transduction pathways leading to inflammation and apoptosis.

von Willebrand factor multimer composition is modified following oral methionine load in women with thrombosis, but not in healthy women

Hyperhomocysteinemia is associated with an increased risk of venous and arterial thrombosis, probably by inducing endothelial damage. Von Willebrand factor (VWF) is an endothelial marker protein. It is a plasma multimeric molecule that plays a thrombophilic role. Our purpose was to investigate VWF changes in patients with thrombosis following oral methionine load. We evaluated homocysteine levels and VWF parameters (plasma levels, activity, proteolysis fragments, and multimer composition) before and after methionine load in 42 women with venous or arterial thrombosis and in 36 healthy women. Methionine load induced mild hyperhomocysteinemia in 10 patients and two controls. No changes in VWF levels and activity were observed, but an increased amount of VWF proteolysis fragments was found post-load in patients and controls. VWF multimer composition was unaffected in controls, while a decrease of the largest VWF multimers was found in women with thrombosis. Homocysteine levels inversely correlated with the amount of the largest multimers in hyperhomocysteinemic patients. Large VWF molecules were probably released from endothelial cells following load, and rapidly cleaved by the specific VWF-cleaving protease. VWF proteolysis was enhanced in mild hyperhomocysteinemic patients, thus leading to downregulation of VWF size to smaller multimers.

Coffee consumption and human health--beneficial or detrimental?--Mechanisms for effects of coffee consumption on different risk factors for cardiovascular disease and type 2 diabetes mellitus

Coffee is probably the most frequently ingested beverage worldwide. Especially Scandinavia has a high prevalence of coffee-drinkers, and they traditionally make their coffee by boiling ground coffee beans and water. Because of its consumption in most countries in the world, it is interesting, from both a public and a scientific perspective, to discuss its potential benefits or adverse aspects in relation to especially two main health problems, namely cardiovascular disease and type 2 diabetes mellitus. Epidemiological studies suggest that consumption of boiled coffee is associated with elevated risk for cardiovascular disease. This is mainly due to the two diterpenes identified in the lipid fraction of coffee grounds, cafestol and kahweol. These compounds promote increased plasma concentration of cholesterol in humans. Coffee is also a rich source of many other ingredients that may contribute to its biological activity, like heterocyclic compounds that exhibit strong antioxidant activity. Based on the literature reviewed, it is apparent that moderate daily filtered, coffee intake is not associated with any adverse effects on cardiovascular outcome. On the contrary, the data shows that coffee has a significant antioxidant activity, and may have an inverse association with the risk of type 2 diabetes mellitus.

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.

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.

No evidence for oxidative stress as a mechanism of action of hyperhomocysteinemia in humans

Oxidative stress has been suggested as one of the physiopathologic conditions underlying the association of total plasma homocysteine (p-tHcy) with cardiovascular disease (CVD), but this hypothesis has not been validated in human epidemiological studies. We measured plasma and erythrocyte antioxidant enzymes glutathione peroxidase (GPx) and superoxide dismutase (SOD), along with serum lipid-soluble antioxidants alpha-tocopherol, beta-carotene, lycopene and retinol, in a sample of 123 healthy elderly subjects (54 men, 69 women). Plasma malondialdehyde (p-MDA) was determined as a marker of lipid peroxidation, and p-tHcy was quantified by HPLC. No significant differences were found for p-MDA, GPx or SOD activities or serum antioxidant concentrations, in subjects with elevated p-tHcy (> or =15 micromol/l) as compared to those with lower plasma homocysteine. Hyperhomocysteinemia did not lead to increased risk of having the highest p-MDA values, in either sex. We found no evidence that p-tHcy was associated with lipid peroxidation in this elderly human sample. Our results do not support the view that hyperhomocysteinemia would induce an adaptive response of antioxidant systems, either. More epidemiologic and clinical research is needed to clarify whether homocysteine promotes atherosclerosis by means of an oxidative stress mechanism.

Similar rhythms of seasonal conceptions in neural tube defects and schizophrenia: A hypothesis of oxidant stress and the photoperiod

BACKGROUND

Numerous studies have found that people with schizophrenia tend to be born most often in late winter and least often in late summer. The same rhythm appears in the birth of children with neural tube defects (NTDs). In the northern hemisphere, both disorders thus show a conception peak in May-June and a trough around November-December. The senior author found the same May-June conception peak among left-handed American baseball players and the opposite effect (a November-December peak) among extreme right-handed players. A similar rhythm appeared with respect to characteristics related to artistic as opposed to scientific modes of thought.

DISCUSSION

Schizophrenia has been proposed to involve a deficit in the establishment of lateral asymmetry, as does left-handedness. The artist-scientist dichotomy is also believed to involve cerebral dominance. Thus, the similarity of seasonal variation in month of conception between NTDs, schizophrenia, left-handedness, and artistic intuition suggests that these four conditions may share some factor affecting the cellular processes involved in both neural tube closure and asymmetry development during the early-fourth week, neural-fold stages of embryogenesis. We propose that maternal oxidant stress, which can rise with exposure to intense solar radiation, may interfere with both neural tube closure and asymmetry development. The June and December extremes of sunlight would thus explain the peak times of the seasonal fluctuations. Moreover, regardless of mechanisms, the parallel between the two conception rhythms suggests that the same periconceptional folate regimens found effective in preventing NTDs may also lower the risk of schizophrenia. This paper reviews some of the clinical and experimental evidence supporting this hypothesis.

Homocysteine induces oxidative stress by uncoupling of NO synthase activity through reduction of tetrahydrobiopterin

Hyperhomocysteinemia is a risk factor for cardiovascular diseases that induces endothelial dysfunction. Here, we examine the participation of endothelial NO synthase (eNOS) in the homocysteine-induced alterations of NO/O(2)(-) balance in endothelial cells from human umbilical cord vein. When cells were treated for 24 h, homocysteine dose-dependently inhibited thrombin-activated NO release without altering eNOS phosphorylation and independently of the endogenous NOS inhibitor, asymmetric dimethylarginine. The inhibitory effect of homocysteine on NO release was associated with increased production of reactive nitrogen and oxygen species (RNS/ROS) independent of extracellular superoxide anion (O(2)(-)) and was suppressed by the NOS inhibitor L-NAME. In unstimulated cells, L-NAME markedly decreased RNS/ROS formation and the ethidium red fluorescence induced by homocysteine. This eNOS-dependent O(2)(-) synthesis was associated with reduced intracellular levels of both total biopterins (-45%) and tetrahydrobiopterin (-80%) and increased release of 7,8-dihydrobiopterin and biopterin in the extracellular medium (+40%). In addition, homocysteine suppressed the activating effect of sepiapterin on NO release, but not that of ascorbate. The results show that the oxidative stress and inhibition of NO release induced by homocysteine depend on eNOS uncoupling due to reduction of intracellular tetrahydrobiopterin availability.