Endothelial membrane potential regulates production of both nitric oxide and superoxide--a fundamental determinant of vascular health

Pathomechanisms of Prenatally Programmed Adult Diseases

Based on epidemiological observations Barker et al. put forward the hypothesis/concept that an adverse intrauterine environment (involving an insufficient nutrient supply, chronic hypoxia, stress, and toxic substances) is an important risk factor for the development of chronic diseases later in life. The fetus responds to the unfavorable environment with adaptive reactions, which ensure survival in the short run, but at the expense of initiating pathological processes leading to adult diseases. In this review, the major mechanisms (including telomere dysfunction, epigenetic modifications, and cardiovascular-renal-endocrine-metabolic reactions) will be outlined, with a particular emphasis on the role of oxidative stress in the fetal origin of adult diseases.

Tissue Sodium Accumulation: Pathophysiology and Clinical Implications

Excessive sodium intake has been well established as a risk factor for the development and progression of cardiovascular and renal diseases. Its adverse effects are achieved by renal sodium retention and related volume expansion and by inducing low-grade inflammation and oxidative stress (OS) in the target tissues. This review presents the recent concept of nonosmotic sodium storage in the skin interstitium, the subsequent dissociation of sodium and volume homeostasis, and the cellular response to the increased tissue sodium concentration. Furthermore, data are shown on the sodium barrier and buffering potential of the endothelial glycocalyx that may protect the functional integrity of the endothelium when it is challenged by an increased sodium load. Finally, examples will be given of the involvement of oxygen free radicals (OFR) in sodium-induced tissue damage, and some clinical entities will be mentioned that are causally associated with sodium/volume retention and OS.

Postulating the major environmental condition resulting in the expression of essential hypertension and its associated cardiovascular diseases: Dietary imprudence in daily selection of foods in respect of their potassium and sodium content resulting in oxidative stress-induced dysfunction of the vascular endothelium, vascular smooth muscle, and perivascular tissues

We hypothesize that the major environmental determinant of the expression of essential hypertension in America and other Westernized countries is dietary imprudence in respect of the consumption of daily combinations of foods containing suboptimal amounts of potassium and blood pressure-lowering phytochemicals, and supraphysiological amounts of sodium. We offer as premise that Americans on average consume suboptimal amounts of potassium and blood pressure-lowering phytochemicals, and physiologically excessive amounts of sodium, and that such dietary imprudence leads to essential hypertension through oxidative stress-induced vascular endothelial and smooth muscle dysfunction. Such dysfunctions restrict nitric oxide bioavailability, impairing endothelial cell-mediated relaxation of the underlying vascular smooth muscle, initiating and maintaining inappropriately increased peripheral and renal vascular resistance. The biochemical steps from oxidative stress to vascular endothelial dysfunction and its pernicious cardiovascular consequences are well established and generally accepted. The unique aspect of our hypothesis resides in the contention that Americans' habitual consumption of foods resulting in suboptimal dietary intake of potassium and supraphysiological intake of sodium result in oxidative stress, the degree of which, we suggest, will correlate with the degree of deviation of potassium and sodium intake from optimal. Because suboptimal intakes of potassium reflect suboptimal intakes of fruits and vegetables, associated contributors to oxidative stress include suboptimal intakes of magnesium, nitrate, polyphenols, carotenoids, and other phytochemical antioxidants for which fruits and vegetables contain abundant amounts. Currently Americans consume potassium-to-sodium in molar ratios of less than or close to 1.0 and the Institute of Medicine (IOM) recommends a molar ratio of 1.2. Ancestral diets to which we are physiologically adapted range from molar ratios of 5.0 to 10.0 or higher. Accordingly, we suggest that the average American is usually afflicted with oxidative stress-induced vascular endothelial dysfunction, and therefore the standards for normal blood pressure and pre-hypertension often reflect a degree of clinically significant hypertension. In this article, we provide support for those contentions, and indicate the findings that the hypothesis predicts.

NADPH Oxidase Activity in Cerebral Arterioles Is a Key Mediator of Cerebral Small Vessel Disease-Implications for Prevention

Cerebral small vessel disease (SVD), a common feature of brain aging, is characterized by lacunar infarcts, microbleeds, leukoaraiosis, and a leaky blood-brain barrier. Functionally, it is associated with cognitive decline, dementia, depression, gait abnormalities, and increased risk for stroke. Cerebral arterioles in this syndrome tend to hypertrophy and lose their capacity for adaptive vasodilation. Rodent studies strongly suggest that activation of Nox2-dependent NADPH oxidase activity is a crucial driver of these structural and functional derangements of cerebral arterioles, in part owing to impairment of endothelial nitric oxide synthase (eNOS) activity. This oxidative stress may also contribute to the breakdown of the blood-brain barrier seen in SVD. Hypertension, aging, metabolic syndrome, smoking, hyperglycemia, and elevated homocysteine may promote activation of NADPH oxidase in cerebral arterioles. Inhibition of NADPH oxidase with phycocyanobilin from spirulina, as well as high-dose statin therapy, may have potential for prevention and control of SVD, and high-potassium diets merit study in this regard. Measures which support effective eNOS activity in other ways-exercise training, supplemental citrulline, certain dietary flavonoids (as in cocoa and green tea), and capsaicin, may also improve the function of cerebral arterioles. Asian epidemiology suggests that increased protein intakes may decrease risk for SVD; conceivably, arginine and/or cysteine-which boosts tissue glutathione synthesis, and can be administered as N-acetylcysteine-mediate this benefit. Ameliorating the risk factors for SVD-including hypertension, metabolic syndrome, hyperglycemia, smoking, and elevated homocysteine-also may help to prevent and control this syndrome, although few clinical trials have addressed this issue to date.

Marinobufagenin and cyclic strain may activate endothelial NADPH oxidase, contributing to the adverse impact of salty diets on vascular and cerebral health

Limited but provocative ecologic epidemiology suggests that dietary salt may play a central role in the genesis of not only of stroke, but also dementia, including Alzheimer's disease. Impairment of nitric oxide bioactivity in the cerebral microvasculature is a likely mediator of this effect. Salted diets evoke increased adrenal secretion of the natriuretic steroid marinobufagenin (MBG), which promotes natriuresis via inhibition of renal tubular Na+/K+-ATPase; this effect is notably robust in salt-sensitive rodent strains in which other compensatory natriuretic mechanisms are subnormally efficient. MBG-mediated inhibition of sodium pumps in vascular smooth muscle likely plays a role in the hypertension induced by salty diets in these rodents. However, salt sensitivity in humans is associated with increased vascular mortality and ventricular hypertrophy independent of blood pressure; this suggests that MBG may be pathogenic via mechanisms unrelated to blood pressure control. Indeed, recent evidence indicates that MBG, via interaction with alpha1 isoforms of the sodium pump, can activate various intracellular signaling pathways at physiological concentrations too low to notably inhibit pump activity. An overview of current evidence suggests the hypothesis that MBG - as well as the cyclic strain induced by hypertension per se - may induce endothelial oxidative stress by activating NADPH oxidase. If so, this could rationalize the increase in vascular and systemic oxidative stress observed in salt-sensitive rodents fed salty diets, or in rodents infused with MBG; moreover, if this effect is a particularly prominent determinant of oxidative stress in cerebrovascular endothelium, it might help to explain the virtual absence of stroke and dementia in low-salt societies. As a corollary of this hypothesis, it can be predicted that spirulina-derived phycobilins, which appear to mimic the physiological role of bilirubin as an inhibitor of NAPDH oxidase complexes, may have potential for ameliorating the adverse health impacts of MBG and of salty diets. Potassium-rich diets are also likely to be protective in this regard, as they should suppress MBG production via their natriuretic impact, while their stimulatory effect on sodium pump activity may exert a hyperpolarizing effect on plasma membranes that suppresses NADPH oxidase activity.

The emerging chondrocyte channelome

Chondrocytes are the resident cells of articular cartilage and are responsible for synthesizing a range of collagenous and non-collagenous extracellular matrix macromolecules. Whilst chondrocytes exist at low densities in the tissue (1-10% of the total tissue volume in mature cartilage) they are extremely active cells and are capable of responding to a range of mechanical and biochemical stimuli. These responses are necessary for the maintenance of viable cartilage and may be compromised in inflammatory diseases such as arthritis. Although chondrocytes are non-excitable cells their plasma membrane contains a rich complement of ion channels. This diverse channelome appears to be as complex as one might expect to find in excitable cells although, in the case of chondrocytes, their functions are far less well understood. The ion channels so far identified in chondrocytes include potassium channels (K(ATP), BK, K(v), and SK), sodium channels (epithelial sodium channels, voltage activated sodium channels), transient receptor potential calcium or non-selective cation channels and chloride channels. In this review we describe this emerging channelome and discuss the possible functions of a range of chondrocyte ion channels.

GPR55-dependent and -independent ion signalling in response to lysophosphatidylinositol in endothelial cells

BACKGROUND AND PURPOSE

The glycerol-based lysophospholipid lysophosphatidylinositol (LPI) is an endogenous agonist of the G-protein-coupled receptor 55 (GPR55) exhibiting cannabinoid receptor-like properties in endothelial cells. To estimate the contribution of GPR55 to the physiological effects of LPI, the GPR55-dependent and -independent electrical responses in this cell type were investigated.

EXPERIMENTAL APPROACH

Applying small interference RNA-mediated knock-down and transient overexpression, GPR55-dependent and -independent effects of LPI on cytosolic free Ca(2+) concentration, membrane potential and transmembrane ion currents were studied in EA.hy296 cells.

KEY RESULTS

In a GPR55-dependent, GDPbetaS and U73122-sensitive manner, LPI induced rapid and transient intracellular Ca(2+) release that was associated with activation of charybdotoxin-sensitive, large conductance, Ca(2+)-activated, K(+) channels (BK(Ca)) and temporary membrane hyperpolarization. Following these initial electrical reactions, LPI elicited GPR55-independent long-lasting Na(+) loading and a non-selective inward current causing sustained membrane depolarization that depended on extracellular Ca(2+) and Na(+) and was partially inhibited by Ni(2+) and La(3+). This inward current was due to the activation of a voltage-independent non-selective cation current. The Ni(2+) and La(3+)-insensitive depolarization with LPI was prevented by inhibition of the Na/K-ATPase by ouabain.

CONCLUSIONS AND IMPLICATIONS

LPI elicited a biphasic response in endothelial cells of which the immediate Ca(2+) signalling depends on GPR55 while the subsequent depolarization is due to Na(+) loading via non-selective cation channels and an inhibition of the Na/K-ATPase. Thus, LPI is a potent signalling molecule that affects endothelial functions by modulating several cellular electrical responses that are only partially linked to GPR55.

The hyperpolarizing impact of glycine on endothelial cells may be anti-atherogenic

Studies to date indicate that endothelial cells express glycine-activated chloride channels, which promote hyperpolarization of the endothelial plasma membrane. If such channels are expressed by endothelial cells lining conduit arteries, glycine is likely to have anti-atherogenic activity. This reflects the fact that endothelial hyperpolarization promotes calcium influx, activating the endothelial isoform of nitric oxide synthase, while also down-regulating the activity of the membrane-bound NADPH oxidase, chief endothelial source of superoxide. Since macrophages express glycine-activated chloride channels that suppress production of oxidants and cytokines, glycine may also oppose atherogenesis by influencing intimal macrophage function. In rats, supplemental glycine exerts anti-inflammatory and anti-angiogenic effects attributed to chloride channel activation. Administration of large daily doses of glycine would appear to be practical and safe, and has already been shown to inhibit protein glycation in human diabetics.

Scavenging of peroxynitrite-derived radicals by flavonoids may support endothelial NO synthase activity, contributing to the vascular protection associated with high fruit and vegetable intakes

Ample intakes of fruit and vegetables have been linked epidemiologically with reduced risk for coronary disease, stroke, hypertension, obesity, many types of cancer, chronic pulmonary disease, osteoporosis, and various ocular disorders. The favorable impact of diets rich in fruit and vegetables on coronary risk has been confirmed in meta-analyses, and is thought to be largely attributable to the folk acid and potassium supplied by these foods. Although high intakes of vitamin C appear to confer some cardiovascular protection, the amounts supplied by typical diets may be too low to be of much benefit in this regard. High flavonoid intakes emerge as protective in some epidemiological studies, albeit the dose-response pattern observed is often L-shaped - seemingly more consistent with low intakes being harmful, than with high intakes being protective. Nonetheless, flavonoids have shown anti-atherogenic activity in rodent models, and both clinical and rodent supplementation studies with foods and food extracts rich in flavonoids demonstrate improvements in endothelium-dependent vasodilation traceable to increased endothelial nitric oxide synthesis. However, flavonoids do not appear to increase the expression of endothelial NO synthase, nor do they modify endothelial superoxide production. A likely explanation is that, even in nanomolar concentrations achievable in vivo, flavonoids can act as efficient scavengers of peroxynitrite-derived radicals, thereby protecting the cofactor tetrahydrobiopterin, crucial for NO synthase activity. Studies with cultured endothelial cells should be useful for evaluating this possibility. It would also be appropriate to assess the effects of flavonoids on prostacylin synthetase activity, on endothelial catabolism of asymmetric dimethylarginine, and on signaling mechanisms that activate NO synthase. Since peroxynitrite can induce mutagenic damage to DNA, it is conceivable that scavenging of peroxynitrite-derived radicals contributes to the reduction in mutagenesis associated with high intakes of fruits and vegetables. Carotenoids also have the potential to prevent peroxynitrite-mediated damage, although, as contrasted with flavonoids, there is comparatively little evidence that these compounds are anti-atherogenic or beneficial for endothelial function; a recent meta-analysis of epidemiological studies suggests that high lutein intakes may modestly reduce coronary risk.

Toward prevention of Alzheimers disease--potential nutraceutical strategies for suppressing the production of amyloid beta peptides

Alzheimers disease (AD) can be viewed as a vicious cycle in which excess production and deposition of amyloid beta (Abeta) peptides promote microglial activation, and the resultant production of inflammatory mediators further boosts Abeta production while inducing death and dysfunction of neurons. Abeta production is mediated by beta- and gamma-secretase activities; it is prevented by alpha-secretase activity, and insulin-degrading enzyme (IDE) catabolizes Abeta. High cellular cholesterol content increases Abeta synthesis by boosting beta-secretase activity; inhibition of cholesterol syntheses and/or stimulation of cholesterol export thus diminishes Abeta production. PPARgamma activity decreases Abeta production by promoting harmless catabolism of amyloid precursor protein while blocking the up-regulatory impact of cytokines on beta-secretase expression. Nitric oxide produced by the healthy cerebral microvasculature can suppress Abeta production by boosting expression of alpha-secretase while suppressing that of beta-secretase; conversely, cerebral ischemia provokes increased APP expression. Good insulin sensitivity and efficient brain insulin function protect by inhibiting gamma-secretase activity and increasing expression of IDE. The DHA provided by fish oil diminishes cerebral Abeta deposition in rodent AD models, for unclear reasons. Various measures which oppose microglial activation can inhibit up-regulation of beta-secretase and gamma-secretase by oxidants and cytokines, respectively. These considerations suggest that a number of nutraceutical or lifestyle measures may have potential for preventing or slowing AD: policosanol; 9-cis-beta-carotene; isomerized hops extract; DHA; measures which promote efficient endothelial NO generation, such as low-salt/potassium-rich diets, exercise training, high-dose folate, and flavanol-rich cocoa; chromium picolinate and cinnamon extract as aids for insulin sensitivity; and various agents which can oppose microglial activation, including vitamin D, genistein, and sesamin. The impact of these measures on Abeta production in rodent models of AD should be evaluated, with the intent of defining practical strategies for AD prevention.

Multifocal angiostatic therapy: an update

Multifocal angiostatic therapy (MAT) is a strategy that seeks to impede cancer-induced angiogenesis by addressing multiple targets that regulate the angiogenic capacity of a cancer and/or the angiogenic responsiveness of endothelial cells, using measures that are preferentially, but not exclusively, nutraceutical. A prototype of such a regimen has been proposed previously, composed of green tea polyphenols, fish oil, selenium, and high-dose glycine, complementing a low-fat vegan diet, exercise training, and the copper-sequestering drug tetrathiomolybdate (TM). A review of more recent evidence suggests additional agents that could appropriately be included in this regimen and clarifies to some extent the mechanisms of action of its constituents. Diindolylmethane, a widely available crucifera-derived nutraceutical, has inhibited cancer growth in several mouse xenograft models; this effect may be largely attributable to an angiostatic action, as concentrations as low as 5 to 10 muM inhibit proliferation, migration, and tube-forming capacity of human endothelial cells in vitro, and a parenteral dose of 5 mg/kg markedly impairs matrigel angiogenesis in mice. Silymarin/silbinin, which has slowed the growth of human xenografts in a number of studies, suppresses the proliferation, migration, and tube-forming capacity of endothelial cells and inhibits vascular endothelial growth factor (VEGF) secretion by a range of human cancer cell lines, in concentrations that should be clinically feasible. The angiostatic activity of orally administered green tea now appears likely to reflect inhibition of the kinase activity of VEGFR-2. Glycine's angiostatic activity may be attributable to a hyperpolarizing effect on endothelial cells that decreases the activity of NADPH oxidase, now known to promote tyrosine kinase signaling in endothelial cells. The ability of TM to suppress cancer cell production of a range of angiogenic factors results at least in part from a down regulation of NF-kappaB activation. Dual-purpose molecular targets, whose inhibition could be expected to decrease the aggressiveness and chemoresistance of cancer cells while simultaneously impeding angiogenesis, include NF-kappaB, cox-2, c-Src, Stat3, and hsp90; drugs that can address these targets are now in development, and salicylates are notable for the fact that they can simultaneously inhibit NF-kappaB and cox-2. The potential complementary of the components of MAT should be assessed in nude mouse xenograft models.

Rationale for a novel nutraceutical complex 'K-water': potassium taurine bicarbonate (PTB)

Potassium taurine bicarbonate (PTB), an equimolar blend of potassium bicarbonate and taurine, provides a convenient and feasible means of delivering physiologically significant doses of potassium, taurine, and organic base when dissolved in water ("K-water"). This brief essay reviews the versatile and complementary health benefits that likely would accrue in individuals making regular use of K-water; in particular, an adequate intake of PTB could be expected to aid blood pressure control, lessen risk for atherosclerosis and its thromboembolic complications (particularly stroke), promote maintenance of bone density, help to prevent calcium renal stones, and possibly reduce risk for weight gain and diabetes.

Should we restrict chloride rather than sodium?

Low-salt diets have potential for prevention and treatment of hypertension, and may also reduce risk for stroke, left ventricular hypertrophy, osteoporosis, renal stones, asthma, cataract, gastric pathology, and possibly even senile dementia. Nonetheless, the fact that salt restriction evokes certain counter-regulatory metabolic responses-- increased production of renin and angiotensin II, as well as increased sympathetic activity--that are potentially inimical to vascular health, has suggested to some observers that salt restriction might not be of unalloyed benefit, and might in fact be contraindicated in some "salt-resistant" subjects. Current epidemiology indicates that lower-salt diets tend to reduce coronary risk quite markedly in obese subjects, whereas the impact of such diets on leaner subjects (who are less likely to be salt sensitive) is equivocal--seemingly consistent with the possibility that salt restriction can exert countervailing effects on vascular health. There is considerable evidence that sodium chloride, rather than sodium per se, is responsible for the known adverse effects of dietary salt. Other non-halide sodium salts, such as sodium citrate or bicarbonate, do not raise plasma volume, increase blood pressure, boost urinary calcium loss, or promote stroke in stroke-prone rats. Nonetheless, these compounds have been shown to blunt the impact of salt restriction on renin, angiotensin II, and sympathetic activity in humans. This may rationalize limited clinical evidence that organic sodium salts can decrease blood pressure in salt-restricted hypertensives. Furthermore, organic sodium salts have an alkalinizing metabolic impact favorable to bone health. These considerations suggest that restricting dietary salt to the extent feasible, while encouraging consumption of organic sodium salts in mineral waters, soft drinks, or other nutraceuticals--preferably in conjunction with organic potassium salts and taurine--may represent a superior strategy for controlling blood pressure, promoting vascular health, and preserving bone density. Further clinical studies should determine whether a moderately salt-restricted diet supplemented with organic sodium salts has a better and more uniform impact on hypertension than salt restriction alone, while rodent studies should examine the comparative impact of these regimens on rodents prone to vascular disease.

Marinobufagenin may mediate the impact of salty diets on left ventricular hypertrophy by disrupting the protective function of coronary microvascular endothelium

Individuals who eat salty diets and who are "salt-sensitive" tend to have increased left ventricular mass, independent of blood pressure; this phenomenon awaits an explanation. It is clear that local up-regulation of angiotensin II (AngII) production and activity play a key role in the induction of left ventricular hypertrophy (LVH). Recent evidence suggests that a healthy coronary microvascular endothelium opposes this effect by serving as a paracrine source of nitric oxide (NO), a natural antagonist of AngII activity, and that up-regulation of this mechanism can account for the protective role of bradykinin with respect to LVH. The coronary microvasculature also possesses NAD(P)H oxidase activity that can generate superoxide, inimical to the bioactivity of endothelial NO. There is now good reason to believe that the triterpenoid marinobufagenin (MBG), a selective inhibitor of the alpha-1 isoform of the sodium pump, mediates the impact of salty diets on blood pressure; production of MBG by the adrenal cortex is boosted when salt-sensitive animals are fed salty diets. It is hypothesized that coronary microvascular endothelium expresses the alpha-1 isoform of the sodium pump, and that MBG thus can target this endothelium. If that is the case, MBG would be expected to decrease membrane potential in these cells; as a consequence, superoxide production would be up-regulated, NO synthase activity would be down-regulated, and myocardial NO bioactivity would thus be suppressed. This would offer a satisfying explanation for the impact of salt and salt-sensitivity on risk for LVH. If expression of the alpha-1 isoform of the sodium pump is a more general property of vascular endothelium, MBG may suppress NO bioactivity in other regions of the vascular tree, thereby contributing to other adverse effects elicited by salty diets: reduced arterial compliance, medial hypertrophy, impaired endothelium-dependent vasodilation, hypertensive/diabetic glomerulopathy, increased risk for stroke, and hypertension.

Differential membrane potential and ion current responses to different types of shear stress in vascular endothelial cells

Vascular endothelial cells (ECs) distinguish among and respond differently to different types of fluid mechanical shear stress. Elucidating the mechanisms governing this differential responsiveness is the key to understanding why early atherosclerotic lesions localize preferentially in arterial regions exposed to low and/or oscillatory flow. An early and very rapid endothelial response to flow is the activation of flow-sensitive K+ and Cl− channels that respectively hyperpolarize and depolarize the cell membrane and regulate several important endothelial responses to flow. We have used whole cell current- and voltage-clamp techniques to demonstrate that flow-sensitive hyperpolarizing and depolarizing currents respond differently to different types of shear stress in cultured bovine aortic ECs. A steady shear stress level of 10 dyn/cm2 activated both currents leading to rapid membrane hyperpolarization that was subsequently reversed to depolarization. In contrast, a steady shear stress of 1 dyn/cm2 only activated the hyperpolarizing current. A purely oscillatory shear stress of 0 ± 10 dyn/cm2 with an oscillation frequency of either 1 or 0.2 Hz activated the hyperpolarizing current but only minimally the depolarizing current, whereas a 5-Hz oscillation activated neither current. These results demonstrate for the first time that flow-activated ion currents exhibit different sensitivities to shear stress magnitude and oscillation frequency. We propose that flow-sensitive ion channels constitute components of an integrated mechanosensing system that, through the aggregate effect of ion channel activation on cell membrane potential, enables ECs to distinguish among different types of flow.

Marinobufagenin may mediate the impact of salty diets on left ventricular hypertrophy by disrupting the protective function of coronary microvascular endothelium

Individuals who eat salty diets and who are "salt-sensitive" tend to have increased left ventricular mass, independent of blood pressure; this phenomenon awaits an explanation. It is clear that local up-regulation of angiotensin II (AngII) production and activity play a key role in the induction of left ventricular hypertrophy (LVH). Recent evidence suggests that a healthy coronary microvascular endothelium opposes this effect by serving as a paracrine source of nitric oxide (NO), a natural antagonist of AngII activity, and that up-regulation of this mechanism can account for the protective role of bradykinin with respect to LVH. The coronary microvasculature also possesses NAD(P)H oxidase activity that can generate superoxide, inimical to the bioactivity of endothelial NO. There is now good reason to believe that the triterpenoid marinobufagenin (MBG), a selective inhibitor of the alpha-1 isoform of the sodium pump, mediates the impact of salty diets on blood pressure;production of MBG by the adrenal cortex is boosted when salt-sensitive animals are fed salty diets. It is hypothesized that coronary microvascular endothelium expresses the alpha-1 isoform of the sodium pump, and that MBG thus can target this endothelium. If that is the case, MBG would be expected to decrease membrane potential in these cells;as a consequence, superoxide production would be up-regulated, NO synthase activity would be down-regulated, and myocardial NO bioactivity would thus be suppressed. This would offer a satisfying explanation for the impact of salt and salt-sensitivity on risk for LVH. If expression of the alpha-1 isoform of the sodium pump is a more general property of vascular endothelium, MBG may suppress NO bioactivity in other regions of the vascular tree, thereby contributing to other adverse effects elicited by salty diets: reduced arterial compliance, medial hypertrophy, impaired endothelium-dependent vasodilation, hypertensive/diabetic glomerulopathy, increased risk for stroke, and hypertension.

Pathogenesis of spontaneous cervico-cerebral artery dissection. A hypothesis and a review of the literature

The pathogenesis of spontaneous cervico-cerebral artery dissection remains speculative due to the rarity of histopathological observations, which often correspond to late stage lesions. Transposition of theoretic data from experimental models, study of pathologies with morphological lesions of the same type, and review of some clinical cases, suggest a sequence for the pathological events leading to arterial dissection. Arterial dysplasia, aneurysms and dissections could all result from vascular remodeling in response to endothelial injury. It induces morphologic changes of the internal elastic lamina, smooth muscle cell proliferation, various matrix abnormalities involving the fibrillary components or their enzymatic regulation, arterial wall neoangiogenesis and dissection. Endothelial dysfunction could so play a key role in the imbalance between arterial degenerative and reparative processes and the initiation of cervico-cerebral artery dissection.

Coping with endothelial superoxide: potential complementarity of arginine and high-dose folate

Superoxide overproduction is a prominent mediator of the endothelial dysfunction associated with a range of vascular disorders, acting in a number of complementary ways to inhibit effective endothelial nitric oxide (NO) activity. The ability of superoxide to quench NO is well known, but oxidants derived from superoxide also appear to inhibit dimethylarginine dimethylaminohydrolase (DDAH) and to oxidize tetrahydrobiopterin (THBP). The former effect boosts the level of methylated arginines that act as potent competitive inhibitors of NO synthase, whereas the latter effect decreases the ability of this enzyme to generate NO, while converting it to a form that readily generates superoxide. The adverse impact of DDAH deficiency on NO production can be offset with supplemental arginine. Although supplementation with THBP has the potential to compensate for the rapid oxidative destruction of this compound, and maintaining optimal vitamin C nutrition may protect or restore the endothelial THBP pool to a limited extent, the most practical way to optimize NO synthase activity in the context of THBP deficit may be administration of high-dose folic acid. The primary circulating metabolite of folate, 5-methyltetrahydrofolate (5MTHF), is structurally analogous to THBP, and appears to normalize the activity of NO synthase in THBP-depleted endothelial cells, either because it "pinch hits" for the absent THBP, or interacts allosterically with NO synthase in some other way to promote the proper function of this enzyme. This observation may rationalize recent clinical studies showing a favorable effect of oral folic acid (5-10 mg daily) on dysfunctional endothelium, independent of any concurrent modulation of homocysteine levels. A recent study reports that, whereas either arginine or THBP alone have only a modest impact on dysfunctional aortic endothelium derived from hypercholesterolemic mice, the combination of the two produces a complete normalization of endothelial function. In aggregate, these considerations suggest that joint administration of arginine and high-dose folate may represent a fruitful approach to preventing and treating vascular disorders - albeit the underlying overproduction of superoxide should also be addressed by ameliorating relevant vascular risk factors.

Vascular endothelium is the organ chiefly responsible for the catabolism of plasma asymmetric dimethylarginine – an explanation for the elevation of plasma ADMA in disorders characterized by endothelial dysfunction

Plasma levels of asymmetric dimethylarginine (ADMA), an endogenously produced competitive inhibitor of nitric oxide synthase (NOS), have been found to be elevated in a large number of disorders characterized by endothelial dysfunction; this remarkable phenomenon has yet to receive a plausible explanation. ADMA arises by proteolysis of methylated proteins throughout the body; the majority of this ADMA is catabolized by the enzyme dimethylarginine dimethylaminohydrolase (DDAH), found in many tissues, including those that express NOS. Since the production of ADMA can be considered constitutive, and little intact ADMA emerges in the urine, impaired catabolism is most likely responsible for elevations of plasma ADMA. The association of elevated ADMA with endotheliopathy is readily explained if we assume that vascular endothelium is the organ chiefly responsible for the catabolism of plasma ADMA--a view that is credible owing to the privileged access of endothelium to plasma, the capacity of endothelium for active transport of arginine (and methylated arginines), and the ample DDAH activity of healthy endothelial cells--and further assume that endothelial dysfunction is often attended by a loss of DDAH activity and/or an impairment of arginine transport, reducing the efficiency of ADMA catabolism. Indeed, there is recent evidence that DDAH is inhibited by endothelial oxidative stress, a typical feature of endotheliopathy; there is also some reason to suspect that arginine transport may be less efficient in dysfunctional endothelium. From this perspective, increased plasma ADMA is not the primary cause of the endothelial dysfunction in various disorders, but rather its effect--though the rise in ADMA can then exacerbate this dysfunction by inhibiting endothelial NOS. Supplemental arginine should be of some clinical benefit in disorders characterized by elevated ADMA, since it can offset that adverse impact of ADMA on NOS activity, and possibly exert other beneficial effects on endothelium--but it cannot be expected to reverse the primary cause of the endothelial dysfunction. Whether or not ADMA plays an important pathogenic role, it seems likely to emerge as a potent risk factor for adverse vascular events, since it may be viewed as a barometer of endothelial health.

IGF-I activity may be a key determinant of stroke risk--a cautionary lesson for vegans

IGF-I acts on vascular endothelium to activate nitric oxide synthase, thereby promoting vascular health; there is reason to believe that this protection is especially crucial to the cerebral vasculature, helping to ward off thrombotic strokes. IGF-I may also promote the structural integrity of cerebral arteries, thereby offering protection from hemorrhagic stroke. These considerations may help to explain why tallness is associated with low stroke risk, whereas growth hormone deficiency increases stroke risk--and why age-adjusted stroke mortality has been exceptionally high in rural Asians eating quasi-vegan diets, but has been declining steadily in Asia as diets have become progressively higher in animal products. There is good reason to suspect that low-fat vegan diets tend to down-regulate systemic IGF-I activity; this effect would be expected to increase stroke risk in vegans. Furthermore, epidemiology suggests that low serum cholesterol, and possibly also a low dietary intake of saturated fat--both characteristic of those adopting low-fat vegan diets--may also increase stroke risk. Vegans are thus well advised to adopt practical countermeasures to minimize stroke risk--the most definitive of which may be salt restriction. A high potassium intake, aerobic exercise training, whole grains, moderate alcohol consumption, low-dose aspirin, statin or policosanol therapy, green tea, and supplementation with fish oil, taurine, arginine, and B vitamins--as well as pharmacotherapy of hypertension if warranted--are other practical measures for lowering stroke risk. Although low-fat vegan diets may markedly reduce risk for coronary disease, diabetes, and many common types of cancer, an increased risk for stroke may represent an 'Achilles heel'. Nonetheless, vegans have the potential to achieve a truly exceptional 'healthspan' if they face this problem forthrightly by restricting salt intake and taking other practical measures that promote cerebrovascular health.

Insulin's stimulation of endothelial superoxide generation may reflect up-regulation of isoprenyl transferase activity that promotes rac translocation

Recent research demonstrates that statin drugs exert a number of favorable effects on endothelial function, independent of lipid modulation, that appear to be mediated by a partial inhibition of prenylation reactions. Statin-induced suppression of PKC-evoked superoxide production may be attributable to an inhibition of rac prenylation and thus translocation that impedes activation of the membrane-bound NAD(P)H oxidase. Conversely, it is now known that hyperinsulinemia up-regulates prenylation reactions by boosting the activities of isoprenyl transferases. In light of new evidence that hyperinsulinemia stimulates endothelial superoxide production via NAD(P)H oxidase, it is tempting to conclude that up-regulation of rac prenylation is at least partially responsible for this phenomenon. In patients afflicted with insulin resistance syndrome, this adverse impact of hyperinsulinemia may be exacerbated by an excessive free fatty acid flux that activates endothelial PKC - another stimulant of the NAD(P)H oxidase - while impeding insulin-mediated activation of nitric oxide synthase. The resulting imbalance of endothelial nitric oxide and superoxide production may be responsible for much of the excess vascular risk associated with this syndrome.

Up-regulation of endothelial nitric oxide activity as a central strategy for prevention of ischemic stroke - just say NO to stroke!

Nitric oxide (NO) produced by the endothelium of cerebral arterioles is an important mediator of endothelium-dependent vasodilation (EDV), and also helps to prevent thrombosis and vascular remodeling. A number of risk factors for ischemic stroke are associated with impaired EDV, and this defect is usually at least partially attributable to a decrease in the production and/or stability of NO. These risk factors include hypertension, high-sodium diets, homocysteine, diabetes, visceral obesity, and aging. Conversely, many measures which may provide protection from ischemic stroke - such as ample dietary intakes of potassium, arginine, fish oil, and selenium - can have a favorable impact on EDV. Protection afforded by exercise training, estrogen replacement, statin drugs, green tea polyphenols, and cruciferous vegetables may reflect increased expression of the endothelial NO synthase. IGF-I activity stimulates endothelial NO production, and conceivably is a mediator of the protection associated with higher-protein diets in Japanese epidemiology and in hypertensive rats. These considerations prompt the conclusion that modulation of NO availability is a crucial determinant of risk for ischemic stroke. Multifactorial strategies for promoting effective cerebrovascular NO activity, complemented by measures that stabilize platelets and moderate blood viscosity, should minimize risk for ischemic stroke and help maintain vigorous cerebral perfusion into ripe old age. The possibility that such measures will also diminish risk for Alzheimer's disease, and slow the normal age-related decline in mental acuity, merits consideration. A limited amount of ecologic epidemiology suggests that both stroke and senile dementia may be extremely rare in cultures still consuming traditional unsalted whole-food diets. Other lines of evidence suggest that promotion of endothelial NO activity may decrease risk for age-related macular degeneration.