Hyperhomocysteinemia and Endothelial Dysfunction.
TL;DR: Six mechanisms have been suggested explaining HHcy-induced endothelial dysfunction and the goal of this review is to elaborate these mechanisms and to discuss biological and molecular events related to HHCy-induced ED.
Abstract: Hyperhomocysteinemia (HHcy) is a significant and independent risk factor for cardiovascular diseases. Endothelial dysfunction (ED) is the earliest indicator of atherosclerosis and vascular diseases. We and others have shown that HHcy induced ED in human and in animal models of HHcy induced by either high-methionine load or genetic deficiency. Six mechanisms have been suggested explaining HHcy-induced ED. These include 1) nitric oxide inhibition, 2) prostanoids regulation, 3) endothelium-derived hyperpolarizing factors suppression, 4) angiotensin II receptor-1 activation, 5) endothelin-1 induction, and 6) oxidative stress. The goal of this review is to elaborate these mechanisms and to discuss biological and molecular events related to HHcy-induced ED.
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TL;DR: This review discussed and in particular emphasis the potential cellular pathways and the biological processes involved that lead to homocysteine-induced endothelial dysfunction, in particular in the impaired endothelial dependent dilatation aspect.
Abstract: This review discussed and in particular emphasis the potential cellular pathways and the biological processes involved that lead to homocysteine-induced endothelial dysfunction, in particular in the impaired endothelial dependent dilatation aspect. Hyperhomocysteinemia is an independent cardiovascular risk factor that has been associated with atherosclerotic vascular diseases and ischemic heart attacks. The potential mechanisms by which elevated plasma homocysteine level leads to reduction in nitric oxide bioavailability include the disruptive uncoupling of nitric oxide synthase activity and quenching of nitric oxide by oxidative stress, the enzymatic inhibition by asymmetric dimethylarginine, endoplasmic reticulum stress with eventual endothelial cell apoptosis, and chronic inflammation/prothrombotic conditions. Homocysteine-induced endothelial dysfunction presumably affecting the bioavailability of the potent vasodilator 'nitric oxide', and such dysfunction can easily be monitor by flow-mediated dilation method using ultrasound. Understanding the mechanisms by which plasma homocysteine alter endothelial nitric oxide production is therefore essential in the comprehension of homocysteine-induced impairment of endothelial dependent dilatation, and its association of cardiovascular risk and its pathophysiology.
262 citations
TL;DR: This review examines the main molecular factors involved in both endothelial function and dysfunction, and the evidence linking endothelial dysfunction with cerebral SVD, and gives an overview of clinical studies that have investigated the possible association between endothelial circulating biomarkers and SVD-related brain changes.
Abstract: The term cerebral small vessel disease (SVD) refers to a group of pathologic processes with various etiologies that affect small arteries, arterioles, venules, and capillaries of the brain. Magnetic resonance imaging (MRI) correlates of SVD are lacunes, recent small subcortical infarcts, white-matter hyperintensities, enlarged perivascular spaces, microbleeds, and brain atrophy. Endothelial dysfunction is thought to have a role in the mechanisms leading to SVD-related brain changes, and the study of endothelial dysfunction has been proposed as an important step for a better comprehension of cerebral SVD. Among available methods to assess endothelial function in vivo, measurement of molecules of endothelial origin in peripheral blood is currently receiving selective attention. These molecules include products of endothelial cells that change when the endothelium is activated, as well as molecules that reflect endothelial damage and repair. This review examines the main molecular factors involved in both endothelial function and dysfunction, and the evidence linking endothelial dysfunction with cerebral SVD, and gives an overview of clinical studies that have investigated the possible association between endothelial circulating biomarkers and SVD-related brain changes.
195 citations
TL;DR: Experimental and clinical studies have demonstrated that a variety of currently used or investigational drugs, such as angiotensin-converting enzyme inhibitors, ang Elliotensin AT1 receptors blockers, angiotENSin-(1-7), antioxidants, beta-blockers, calcium channel blockers, endothelial NO synthase enhancers, phosphodiesterase 5 inhibitors, sphingosine-1-phosphate and statins, exert endothelial protective effects.
Abstract: The endothelium exerts multiple actions involving regulation of vascular permeability and tone, coagulation and fibrinolysis, inflammatory and immunological reactions and cell growth. Alterations of one or more such actions may cause vascular endothelial dysfunction. Different risk factors such as hypercholesterolemia, homocystinemia, hyperglycemia, hypertension, smoking, inflammation, and aging contribute to the development of endothelial dysfunction. Mechanisms underlying endothelial dysfunction are multiple, including impaired endothelium-derived vasodilators, enhanced endothelium-derived vasoconstrictors, over production of reactive oxygen species and reactive nitrogen species, activation of inflammatory and immune reactions, and imbalance of coagulation and fibrinolysis. Endothelial dysfunction occurs in many cardiovascular diseases, which involves different mechanisms, depending on specific risk factors affecting the disease. Among these mechanisms, a reduction in nitric oxide (NO) bioavailability plays a central role in the development of endothelial dysfunction because NO exerts diverse physiological actions, including vasodilation, anti-inflammation, antiplatelet, antiproliferation and antimigration. Experimental and clinical studies have demonstrated that a variety of currently used or investigational drugs, such as angiotensin-converting enzyme inhibitors, angiotensin AT1 receptors blockers, angiotensin-(1-7), antioxidants, beta-blockers, calcium channel blockers, endothelial NO synthase enhancers, phosphodiesterase 5 inhibitors, sphingosine-1-phosphate and statins, exert endothelial protective effects. Due to the difference in mechanisms of action, these drugs need to be used according to specific mechanisms underlying endothelial dysfunction of the disease.
162 citations
TL;DR: It is suggested that anti-inflammatory/immunosuppressive cytokines serve as novel therapeutic targets for inhibiting endothelial dysfunction, vascular inflammation and cardio- and cerebro-vascular diseases.
Abstract: Endothelial dysfunction is a pathological status of the vascular system, which can be broadly defined as an imbalance between endothelium-dependent vasoconstriction and vasodilation. Endothelial dysfunction is a key event in the progression of many pathological processes including atherosclerosis, type II diabetes and hypertension. Previous reports have demonstrated that pro-inflammatory/immunoeffector cytokines significantly promote endothelial dysfunction while numerous novel anti-inflammatory/immunosuppressive cytokines have recently been identified such as interleukin (IL)-35. However, the effects of anti-inflammatory cytokines on endothelial dysfunction have received much less attention. In this analytical review, we focus on the recent progress attained in characterizing the direct and indirect effects of anti-inflammatory/immunosuppressive cytokines in the inhibition of endothelial dysfunction. Our analyses are not only limited to the importance of endothelial dysfunction in cardiovascular disease progression, but also expand into the molecular mechanisms and pathways underlying the inhibition of endothelial dysfunction by anti-inflammatory/immunosuppressive cytokines. Our review suggests that anti-inflammatory/immunosuppressive cytokines serve as novel therapeutic targets for inhibiting endothelial dysfunction, vascular inflammation and cardio- and cerebro-vascular diseases.
110 citations
Cites background from "Hyperhomocysteinemia and Endothelia..."
...Not limited to coronary artery endothelium, endothelium generally are capable of producing vasodilators such as NO, prostacyclin (PGI2), and endothelium-derived hyperpolarizing factor (EDHF) as well as vasoconstrictors such as endothelin-1 (ET-1), angiotensin II (Ang II), and free radicals [2,41] that maintain the physiologically balanced vascular tone....
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TL;DR: A comprehensive understanding of Cu speciation and a development of selective modulation of Cu coordination to Cu-binding molecules to avoid Cu-Hcy complex formation would effectively improve the condition of cardiovascular disease.
109 citations
Cites background from "Hyperhomocysteinemia and Endothelia..."
...manifested by decreased bioavailability of endothelium-derived NO (Cheng et al., 2009)....
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...Hcy has been shown to alter NO metabolism, mainly manifested by decreased bioavailability of endothelium-derived NO (Cheng et al., 2009)....
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...Studies in cultured endothelial cells have shown that Hcy decreases NO bioavailability, which is correlated with impairment of NOmediated relaxation in hyperhomocysteinemia in animal models (Cheng et al., 2009)....
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...mediated relaxation in hyperhomocysteinemia in animal models (Cheng et al., 2009)....
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References
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TL;DR: Higher folic acid intake by reducing tHcy levels promises to prevent arteriosclerotic vascular disease and under different assumptions, 13,500 to 50,000 CAD deaths annually could be avoided.
Abstract: Objective. —To determine the risk of elevated total homocysteine (tHcy) levels for arteriosclerotic vascular disease, estimate the reduction of tHcy by folic acid, and calculate the potential reduction of coronary artery disease (CAD) mortality by increasing folic acid intake. Data Sources. —MEDLINE search for meta-analysis of 27 studies relating homocysteine to arteriosclerotic vascular disease and 11 studies of folic acid effects on tHcy levels. Study Selection and Data Extraction. —Studies dealing with CAD, cerebrovascular disease, and peripheral arterial vascular disease were selected. Three prospective and six population-based case-control studies were considered of high quality. Five cross-sectional and 13 other case-control studies were also included. Causality of tHcy's role in the pathogenesis of vascular disease was inferred because of consistency across studies by different investigators using different methods in different populations. Data Synthesis. —Elevations in tHcy were considered an independent graded risk factor for arteriosclerotic vascular diseases. The odds ratio (OR) for CAD of a 5-μmol/L tHcy increment is 1.6(95% confidence interval [Cl], 1.4 to 1.7) for men and 1.8 (95% Cl, 1.3 to 1.9) for women. A total of 10% of the population's CAD risk appears attributable to tHcy. The OR for cerebrovascular disease (5-μmol/L tHcy increment) is 1.5 (95% Cl, 1.3 to 1.9). Peripheral arterial disease also showed a strong association. Increased folic acid intake (approximately 200 μg/d) reduces tHcy levels by approximately 4 μmol/L. Assuming that lower tHcy levels decrease CAD mortality, we calculated the effect of (1) increased dietary folate, (2) supplementation by tablets, and (3) grain fortification. Under different assumptions, 13 500 to 50 000 CAD deaths annually could be avoided; fortification of food had the largest impact. Conclusions. —A 5-μmol/L tHcy increment elevates CAD risk by as much as cholesterol increases of 0.5 mmol/L (20 mg/dL). Higher folic acid intake by reducing tHcy levels promises to prevent arteriosclerotic vascular disease. Clinical trials are urgently needed. Concerns about masking cobalamin deficiency by folic acid could be lessened by adding 1 mg of cobalamin to folic acid supplements. ( JAMA . 1995;274:1049-1057)
3,722 citations
"Hyperhomocysteinemia and Endothelia..." refers background in this paper
...Since then, abundant retrospective and prospective observational studies have shown a relation between plasma total homocysteine (tHcy) level and coronary artery disease, peripheral artery disease, stroke, or venous thrombosis [4,5]....
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...8-fold [4]....
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Journal Article•
TL;DR: Since the enzymatic abnormalities in both disorders share certain metabolic consequences, the conclusion has been reached that an elevated concentration of homocysteine, homocystine, or a derivative of hornocysteines is the common factor leading to arterial damage.
Abstract: NDiviDuAI with homocystinuria 12 have been found to lack normal activity of the enzyme cystathionine synthetase.3 In many of the patients progressive arterial disease develops in ildhood, frequently resulting in death from thrombosis in a vital organ45 In addition, congenital dislocation of the lenses, mental retardation, and skeletal abnormalitieseg, osteoporosis, arachnodactyly, and pectus excavatum or pectus carinatum-usually are foundL5' The vascular changes and other abnormalities encoumtered in homocystinuria have been attributed either to the metabolic effects of the elevated tissue concentrations of methionine, homocysteine, or homocystine, or to the metabolic consequences of decreased tissue concentrations of cystathionine found in the disease.7 In a child dying with homocystinuria, cystathioninuria, and methyl malonic aciduria, secondary to an abnormality of cobalamin (B12 ) metabolism, arterial lesions have been discovered that resemble in a striking way many of those found in cystathionine synthetase deficiency. The vascular findigs i this patient will be presented and compared with those in a patient with cystathionine synthetase deficiency. Since the enzymatic abnormalities in both disorders share certain metabolic consequences, the conclusion has been reached that an elevated concentration of homocysteine, homocystine, or a derivative of hornocysteine is the common factor leading to arterial damage. The possible role of elevated concentrations of homocysteine or its derivatives in the pathogenesis of arteriosclerosis in individls free of known enzyme deficiencies will be discussed and interpreted with particular reference to the findings in experimentally produced arteriosclerosis.
1,860 citations
"Hyperhomocysteinemia and Endothelia..." refers background in this paper
...McCully suggested that HHcy are causally related to cardiovascular diseases (CVD) in 1969 [2]....
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TL;DR: These results suggest that the normal endothelium modulates the potential, adverse effects of homocysteine by releasing EDRF and forming the adduct S-NO-homocysteines, a potent antiplatelet agent and vasodilator.
Abstract: Elevated levels of homocysteine are associated with an increased risk of atherosclerosis and thrombosis. The reactivity of the sulfhydryl group of homocysteine has been implicated in molecular mechanisms underlying this increased risk. There is also increasingly compelling evidence that thiols react in the presence of nitric oxide (NO) and endothelium-derived relaxing factor (EDRF) to form S-nitrosothiols, compounds with potent vasodilatory and antiplatelet effects. We, therefore, hypothesized that S-nitrosation of homocysteine would confer these beneficial bioactivities to the thiol, and at the same time attenuate its pathogenicity. We found that prolonged (> 3 h) exposure of endothelial cells to homocysteine results in impaired EDRF responses. By contrast, brief (15 min) exposure of endothelial cells, stimulated to secrete EDRF, to homocysteine results in the formation of S-NO-homocysteine, a potent antiplatelet agent and vasodilator. In contrast to homocysteine, S-NO-homocysteine does not support H2O2 generation and does not undergo conversion to homocysteine thiolactone, reaction products believed to contribute to endothelial toxicity. These results suggest that the normal endothelium modulates the potential, adverse effects of homocysteine by releasing EDRF and forming the adduct S-NO-homocysteine. The adverse vascular properties of homocysteine may result from an inability to sustain S-NO formation owing to a progressive imbalance between the production of NO by progressively dysfunctional endothelial cells and the levels of homocysteine.
857 citations
"Hyperhomocysteinemia and Endothelia..." refers background in this paper
...Exposure of ECs to Hcy led to the formation of S-nitrosohomocysteine, decreasing the bioactivity of NO [24]....
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TL;DR: Several mechanisms have been proposed to link this pivotal step to the subsequent smooth muscle hyperpolarization and the main concepts are considered in detail in this review.
845 citations
"Hyperhomocysteinemia and Endothelia..." refers background in this paper
...Epoxyeicosatrienoic acid likely has a regulatory role in this pathway [35]....
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TL;DR: Homocysteine post-translationally inhibits DDAH enzyme activity, causing ADMA to accumulate and inhibit nitric oxide synthesis, which may explain the known effect of homocysteines to impair endothelium-mediated nitricoxide–dependent vasodilatation.
Abstract: Background—Hyperhomocysteinemia is a putative risk factor for cardiovascular disease, which also impairs endothelium-dependent vasodilatation. A number of other risk factors for cardiovascular disease may exert their adverse vascular effects in part by elevating plasma levels of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase. Accordingly, we determined if homocysteine could increase ADMA levels. Methods and Results—When endothelial or nonvascular cells were exposed to DL-homocysteine or to its precursor L-methionine, ADMA concentration in the cell culture medium increased in a dose- and time-dependent fashion. This effect was associated with the reduced activity of dimethylarginine dimethylaminohydrolase (DDAH), the enzyme that degrades ADMA. Furthermore, homocysteine-induced accumulation of ADMA was associated with reduced nitric oxide synthesis by endothelial cells and segments of pig aorta. The antioxidant pyrrollidine dithiocarbamate preserved DDAH activity and reduced ADMA accumulation. Moreover, homocysteine dose-dependently reduced the activity of recombinant human DDAH in a cell free system, an effect that was due to a direct interaction between homocysteine and DDAH. Conclusion—Homocysteine post-translationally inhibits DDAH enzyme activity, causing ADMA to accumulate and inhibit nitric oxide synthesis. This may explain the known effect of homocysteine to impair endothelium-mediated nitric oxide– dependent vasodilatation. (Circulation. 2001;104:2569-2575.)
674 citations