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.     

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.     

Marinobufagenin may mediate the adverse impact of salty diets on renal calcium retention by impairing the efficiency of renal tubular sodium-calcium exchange

For reasons yet to be clarified, salt loading and plasma volume expansion decrease renal calcium retention; consequently, high-salt diets are thought to increase risk for osteoporosis and renal stones. These measures also can evoke increased adrenal production of the natriuretic factor marinobufagenin (MBG), recently implicated in the genesis of essential hypertension. MBG achieves natriuresis via potent selective inhibition of the alpha-1-type sodium pump, expressed throughout the nephron. In as much as renal calcium retention is largely dependent on efficient activity of calcium-sodium exchangers situated in the basolateral membranes of tubular epithelium, it is evident that an increased intracellular sodium concentration consequent to sodium pump inhibition could blunt the activity of these exchangers. Thus, it is postulated that MBG mediates the impact of salt loading on renal calcium retention.     

Suppression of oxidative stress in the endothelium and vascular wall.

There is growing evidence that oxidative stress, meaning an excessive production of reactive oxygen and nitrogen species, underlies many forms of cardiovascular disease. The major source of oxidative stress in the artery wall is an NADPH oxidase. This enzyme complex in vascular cells, including endothelium, differs from that in phagocytic leucocytes in both biochemical structure and functions. The crucial flavin-containing catalytic subunits Nox1 and Nox4 are not present in leucocytes, but are highly expressed in vascular cells and upregulated in vascular remodeling, such as that found in hypertension and atherosclerosis. This offers the opportunity to develop "vascular specific" NADPH oxidase inhibitors that do not compromise the essential physiological signaling and phagocytic function carried out by reactive oxygen and nitrogen molecules. Although many conventional antioxidants fail to significantly affect outcomes in cardiovascular disease, targeted inhibitors of NADPH oxidase that block the source of oxidative stress in the vasculature are more likely to prevent the deterioration of vascular function that leads to stroke and heart attack.     

Mechanisms of H2O2-induced oxidative stress in endothelial cells exposed to physiologic shear stress

Hydrogen peroxide (H2O2) is produced by inflammatory and vascular cells and induces oxidative stress, which may contribute to vascular disease and endothelial cell dysfunction. In smooth muscle cells, H2O2 induces production of O2 by activating NADPH oxidase. However, the mechanisms whereby H2O2 induces oxidative stress in endothelial cells are not well understood, although O2 may play a role. Recent studies have documented increased O2 in endothelial cells exposed to H2O2 via uncoupled nitric oxide synthase (NOS) and NADPH oxidase under static conditions. To assess responses to H2O2 in porcine aortic endothelial cells (PAEC) under shearing conditions, a constant flow rate of 24. 4 ml/min was applied to produce physiologically relevant shear stress (8. 2 dynes/cm). Here we demonstrate that treatment with 100 muM H2O2 increases intracellular O2 levels in PAEC. In addition, we demonstrate that l-NAME, an inhibitor of NOS, and apocynin, an inhibitor of NADPH oxidase, reduced O2 levels in PAEC treated with H2O2 under physiologic shear suggesting that both NOS and NADPH oxidase contribute to H2O2-induced O2 in PAEC. Co-inhibition of NOS and NADPH oxidase also reduced intracellular O2 levels under shear. We conclude that H2O2-induced oxidative stress in endothelial cells exhibits increased intracellular O2 levels through NOS and NADPH oxidase under shear. The inhibition of NOS and NADPH with H2O2 exposure is nonlinear, suggesting some interdependent or compensating system within endothelial cells. These findings suggest a complex interaction between H2O2 and oxidant-generating enzymes that may contribute to endothelial dysfunction in cardiovascular diseases.     

Oscillatory shear stress induces mitochondrial superoxide production: implication of NADPH oxidase and c-Jun NH2-terminal kinase signaling

Fluid shear stress is intimately linked with vascular oxidative stress and atherosclerosis. We posited that atherogenic oscillatory shear stress (OSS) induced mitochondrial superoxide (mtO2?-) production via NADPH oxidase and c-Jun NH(2)-terminal kinase (JNK-1 and JNK-2) signaling. In bovine aortic endothelial cells, OSS (±3?dyn/cm2) induced JNK activation, which peaked at 1?h, accompanied by an increase in fluorescein isothiocyanate-conjugated JNK fluorescent and MitoSOX Red (specific for mtO2?- production) intensities. Pretreatment with apocynin (NADPH oxidase inhibitor) or N-acetyl cysteine (antioxidant) significantly attenuated OSS-induced JNK activation. Apocynin further reduced OSS-mediated dihydroethidium and MitoSOX Red intensities specific for cytosolic O2?- and mtO2?- production, respectively. As a corollary, transfecting bovine aortic endothelial cells with JNK siRNA (siJNK) and pretreating with SP600125 (JNK inhibitor) significantly attenuated OSS-mediated mtO2?- production. Immunohistochemistry on explants of human coronary arteries further revealed prominent phosphorylated JNK staining in OSS-exposed regions. These findings indicate that OSS induces mtO2?- production via NADPH oxidase and JNK activation relevant for vascular oxidative stress.     

Renal and vascular oxidative stress and salt-sensitivity of arterial pressure

Oxidative stress occurs in a tissue or in the whole body when the total oxidant production exceeds the antioxidant capacity. Recent studies in human essential hypertension indicate that free radical production is increased and antioxidant levels are decreased, and more than one-half of these hypertensives have a salt-sensitive type of hypertension with progressive renal damage. Increased oxidative stress may also play a critical role in animal models of salt-sensitive hypertension. The stroke-prone spontaneously hypertensive rats (SHRSP) exhibits salt-sensitivity, vascular release of superoxide is increased, and total plasma antioxidant capacity is decreased. The superoxide release in the SHRSP rats inactivates nitric oxide, and superoxide dismutase (SOD) administration returns the bioactive nitric oxide levels to normal. The deoxycorticosterone acetate (DOCA)-salt hypertensive rat is salt-sensitive, aortic superoxide production is increased, and renal inflammation is significant. Treatment of the DOCA-salt rats with apocynin, an NADPH oxidase inhibitor, decreased aortic superoxide production and decreased arterial pressure. The Dahl salt-sensitive (S) rat has increased mesenteric microvascular and renal superoxide production and increased plasma levels of H2O2. The renal protein expression of SOD is decreased in the kidney of Dahl S rats, and long-term administration of Tempol, a superoxide mimetic, significantly decreased arterial pressure and renal damage. In conclusion, both human hypertension and experimental models of salt-sensitive hypertension have increased superoxide release, decreased antioxidant capacity and elevated renal damage.     

Enhancement of reactive oxygen species and induction of apoptosis in streptozotocin-induced diabetic rats under hyperbaric oxygen exposure

An important source of reactive oxygen species (ROS) production is nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, which on activation induces superoxide production via oxidation in the mitochondria, inflammation and stress; such ROS are implicated in the pathogenesis of diabetic complications, including neuropathy. Hyperbaric oxygen (HBO) treatments are applied various diseases including diabetic patients with unhealing foot ulcers, however, and also increases the formation of ROS. In a previous study, we showed that a clinically recommended HBO treatment significantly enhanced oxidative stress of pancreatic tissue in the diabetic rats. However, no study has been undertaken with regard to the effects of HBO on the activity and gene expression of the NADPH oxidase complex and on apoptosis in the pancreas of diabetic animals. The purpose of this study was to investigate the effect of HBO exposure on gene expression of the NADPH complex, and pancreatic expression of genes related to apoptosis via the mitochondria, using the NADPH oxidase inhibitor apocynin. The mRNA expression of genes related to NADPH oxidase complex and apoptosis increased significantly (P < 0.05) in the pancreas of diabetic rats under HBO exposure. Similarly, activities of NADPH oxidase and caspase-3 changed in parallel with mRNA levels. These results suggest that oxidative stress caused by HBO exposure in diabetic animals induces further ROS production and apoptosis, potentially through the up-regulation of NADPH oxidase complex. Thus, this study can contribute to development of a better understanding of the molecular mechanisms of apoptosis via the mitochondria in diabetes, under HBO exposure.     

Minodronate, a nitrogen-containing bisphosphonate, inhibits advanced glycation end product-induced vascular cell adhesion molecule-1 expression in endothelial cells by suppressing reactive oxygen species generation

Advanced glycation end products (AGEs), the senescent macroprotein derivatives that form in increased amounts in diabetes, have been implicated in the pathogenesis of diabetic vascular complications. Indeed, AGEs elicit oxidative stress generation in vascular wall cells through an interaction with their receptor (RAGE), thus playing an important role in vascular inflammation and altered gene expression of growth factors and cytokines. We have previously shown that minodronate, a nitrogen-containing bisphosphonate, blocked the angiogenic signaling of vascular endothelial growth factor in ECs through its antioxidative properties. However, the effects of minodronate on AGE-exposed ECs remain to be elucidated. In this study, we investigated whether and how minodronate could inhibit AGE-induced reactive oxygen species (ROS) generation and subsequent vascular cell adhesion molecule-1 (VCAM-1) gene expression in human umbilical vein endothelial cells (HUVEC). Minodronate or an NADPH oxidase inhibitor, diphenylene iodonium, completely inhibited the AGE-induced ROS generation in HUVEC. Geranylgeranyl pyrophosphate reversed the antioxidative properties of minodronate in AGE-exposed ECs. Furthermore, minodronate was found to prevent AGE-induced nuclear factor--KB activation and subsequently suppress VCAM-1 gene expression in HUVEC. These results demonstrate that minodronate could inhibit VCAM- 1 expression in AGE-exposed ECs by suppressing NADPH oxidase-derived ROS generation, probably via inhibition of geranylgeranylation of Rac, a component of endothelial NADPH oxidase. Our present study suggests that minodronate may have a therapeutic potential in the treatment of patients with diabetic vascular complications.     

NADPH oxidase in endothelial cells: impact on atherosclerosis

An elevated vascular superoxide anion formation has been implicated in the initiation and progression of hypertension and atherosclerosis. In this review, we would like to discuss the generation of superoxide anions by an NADPH oxidase complex in vascular cells. Special focus is on the induction of endothelial NADPH oxidase by proatherosclerotic stimuli. We propose a proatherosclerotic vicious cycle of increased NADPH oxidase-dependent superoxide anion formation, augmented generation and uptake of oxidatively modified low-density lipoprotein, and further potentiation of oxidative stress by oxidized low-density lipoprotein itself, angiotensin II, and endothelin-1 in endothelial cells. Furthermore, novel homologues of NADPH oxidase subunit gp91(phox) are summarized. Future directions of research for a better understanding of the role of NADPH oxidase in the pathogenesis of atherosclerosis and clinical implications are discussed.     

Hormonal and nutritional enhancement of Na-K-ATPase activity may aid the prevention and treatment of essential hypertension

Subnormal activity of the Na⁺-K⁺-ATPase appears to be a common feature of essential hypertension, and may in fact play a pathogenic role in this disorder. If so, methods which relieve inhibition or enhance the activity of the sodium pump should have therapeutic or preventive value. Diuretics enhance the activity of the sodium pump in hypertensives, apparently by suppressing secretion of an inhibitory natriuretic factor, and it is likely that low-sodium diets have a similar effect. Activity of the Na⁺-K⁺-ATPase is also stimulated by thyroid hormone and insulin, and there are indications that thyroid therapy, as well as various measures which increase tissue insulin sensitivity, may have therapeutic value in essential hypertension. Nutritional measures which may enhance sodium pump activity include potassium supplementation, insurance of adequate magnesium intake, and consumption of rich sources of gammalinolenic acid.     

Apocynin administration does not improve behavioral and neuropathological deficits in a transgenic mouse model of Alzheimer's disease

In addition to mitochondria, NADPH oxidase (NOX) is a source of oxidative stress, which can induce oxidative damage in Alzheimer's disease (AD). For this reason, several groups have investigated the effect of its inhibition. In AD mice, NADPH oxidase 2 (NOX2) deficiency improved behavior and cerebrovascular function, and reduced oxidative stress. In our study, we administered the NOX inhibitor apocynin to Tg19959 mice, and found that it did not improve cognitive and synaptic deficits, and did not decrease amyloid deposition, microgliosis and hyperphosphorylated tau. However, apocynin reduced carbonyl levels in the cerebral cortex but not the hippocampus, which may have not been sufficient to ameliorate symptoms. Also, the reduction of NOX-mediated oxidative stress may not be sufficient to prevent AD, since other sources of reactive oxygen species such as mitochondria may be more important.     

The microglial NADPH oxidase complex as a source of oxidative stress in Alzheimer's disease

Alzheimer's disease is the most common cause of dementia in the elderly, and manifests as progressive cognitive decline and profound neuronal loss. The principal neuropathological hallmarks of Alzheimer's disease are the senile plaques and the neurofibrillary tangles. The senile plaques are surrounded by activated microglia, which are largely responsible for the proinflammatory environment within the diseased brain. Microglia are the resident innate immune cells in the brain. In response to contact with fibrillar beta-amyloid, microglia secrete a diverse array of proinflammatory molecules. Evidence suggests that oxidative stress emanating from activated microglia contribute to the neuronal loss characteristic of this disease. The source of fibrillar beta-amyloid induced reactive oxygen species is primarily the microglial nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. The NADPH oxidase is a multicomponent enzyme complex that, upon activation, produces the highly reactive free radical superoxide. The cascade of intracellular signaling events leading to NADPH oxidase assembly and the subsequent release of superoxide in fibrillar beta-amyloid stimulated microglia has recently been elucidated. The induction of reactive oxygen species, as well as nitric oxide, from activated microglia can enhance the production of more potent free radicals such as peroxynitrite. The formation of peroxynitrite causes protein oxidation, lipid peroxidation and DNA damage, which ultimately lead to neuronal cell death. The elimination of beta-amyloid-induced oxidative damage through the inhibition of the NADPH oxidase represents an attractive therapeutic target for the treatment of Alzheimer's disease.     

Nutraceutical strategies for ameliorating the toxic effects of alcohol

Rodent studies reveal that oxidative stress, much of it generated via induction/activation of NADPH oxidase, is a key mediator of a number of the pathogenic effects of chronic ethanol overconsumption. The highly reactive ethanol metabolite acetaldehyde is a key driver of this oxidative stress, and doubtless works in other ways to promote alcohol-induced pathology. Effective antioxidant measure may therefore be useful for mitigating the adverse health consequences of alcohol consumption; spirulina may have particular utility in this regard, as its chief phycochemical phycocyanobilin has recently been shown to function as an inhibitor of certain NADPH oxidase complexes, mimicking the physiological role of its chemical relatives biliverdin/bilirubin in this respect. Moreover, certain nutraceuticals, including taurine, pantethine, and lipoic acid, may have the potential to boost the activity of the mitochondrial isoform of aldehyde dehydrogenase, ALDH-2, accelerating conversion of acetaldehyde to acetate (which arguably has protective health effects). Little noticed clinical studies conducted nearly three decades ago reported that pre-ingestion of either taurine or pantethine could blunt the rise in blood acetaldehyde following ethanol consumption. Other evidence suggests that lipoic acid may function within mitochondria to maintain aldehyde dehydrogenase in a reduced active conformation; the impact of this agent on ethanol metabolism has however received little or no study. Studies evaluating the impact of nutracetical strategies on prevention of hangovers – which likely are mediated by acetaldehyde – may represent a quick, low-cost way to identify nutraceutical regimens that merit further attention for their potential impact on alcohol-induced pathology. Measures which boost or preserve ALDH-2 activity may also have important antioxidant potential, as this enzyme functions physiologically to protect cells from toxic aldehydes generated by oxidant stress.     

Nitric oxide, tetrahydrobiopterin, oxidative stress, and endothelial dysfunction in hypertension

Endothelial dysfunction in the setting of cardiovascular risk factors such as hypercholesterolemia, diabetes mellitus, chronic smoking, as well hypertension, is, at least in part, dependent of the production of reactive oxygen species (ROS) and the subsequent decrease in vascular bioavailability of nitric oxide (NO). ROS-producing enzymes involved in increased oxidative stress within vascular tissue include NADPH oxidase, xanthine oxidase, and mitochondrial superoxide producing enzymes. Superoxide produced by the NADPH oxidase may react with NO, thereby stimulating the production of the NO/superoxide reaction product peroxynitrite. Peroxynitrite in turn has been shown to uncouple eNOS, therefore switching an antiatherosclerotic NO producing enzyme to an enzyme that may accelerate the atherosclerotic process by producing superoxide. Increased oxidative stress in the vasculature, however, is not restricted to the endothelium and also occurs within the smooth muscle cell layer. Increased superoxide production has important consequences with respect to signaling by the soluble guanylate cyclase and the cGMP-dependent kinase I, which activity and expression is regulated in a redox-sensitive fashion. The present review will summarize current concepts concerning eNOS uncoupling, with special focus on the role of tetrahydrobiopterin in mediating eNOS uncoupling.     

The NADPH oxidase family and its inhibitors

The classical nicotinamide adenine dinucleotide phosphate (NADPH) oxidase was originally detected in neutrophils as a multicomponent enzyme that catalyzes the generation of superoxide from oxygen and the reduced form of NADPH. This enzyme is composed of two membrane-bound subunits (p22phox and gp91phox), three cytosolic subunits (p67phox, p47phox, and p40phox) and a small G-protein Rac (Rac1 and Rac2). Recently, it has been demonstrated that there are several isoforms of nonphagocytic NADPH oxidase. Endothelial cells, vascular smooth muscle cells or adventitial fibroblasts possess multiple isoforms of this enzyme. The new homologs, along with gp91phox are now designated the Nox family of NADPH oxidases and are key sources of reactive oxygen species in the vasculature. Reactive oxygen species play a significant role in regulating endothelial function and vascular tone. However, besides the participation in the processes of physiological cell, these enzymes can also be the perpetrator of oxidative stress that causes endothelial dysfunction. This review summarizes the current state of knowledge of the structure and functions of NADPH oxidase and NADPH oxidase inhibitors in the treatment of disorders with endothelial damage.     

Regulation of hypothalamic renin-angiotensin system and oxidative stress by aldosterone

In rats with salt-induced hypertension or postmyocardial infarction, angiotensin II type 1 receptor (AT(1)R) densities and oxidative stress increase and neuronal NO synthase (nNOS) levels decrease in the paraventricular nucleus (PVN). The present study was designed to determine whether these changes may depend on activation of the aldosterone -'ouabain' neuromodulatory pathway. After intracerebroventricular (i.c.v.) infusion of aldosterone (20 ng h(-1)) for 14 days, blood pressure (BP) and heart rate (HR) were recorded in conscious Wistar rats, and mRNA and protein for nNOS, endothelial NO synthase (eNOS), AT(1)R and NADPH oxidase subunits were assessed in brain tissue. Blood pressure and HR were significantly increased by aldosterone. Aldosterone significantly increased mRNA and protein of AT(1)R, P22phox, P47phox, P67phox and Nox2, and decreased nNOS but not eNOS mRNA and protein in the PVN, as well as increased the angiotensin-converting enzyme and AT(1)R binding densities in the PVN and supraoptic nucleus. The increases in BP and HR, as well as the changes in mRNA, proteins and angiotensin-converting enzyme and AT(1)R binding densities were all largely prevented by concomitant i.c.v. infusion of Digibind (to bind 'ouabain') or benzamil (to block presumed epithelial sodium channels). These data indicate that aldosterone, via 'ouabain', increases in the PVN angiotensin-converting enzyme, AT(1)R and oxidative stress, but decreases nNOS, and suggest that endogenous aldosterone may cause the similar pattern of changes observed in salt-sensitive hypertension and heart failure postmyocardial infarction.     

Mechanisms regulating superoxide generation in experimental models of phenylketonuria: an essential role of NADPH oxidase

This study was designed to investigate whether nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, a superoxide-producing enzyme, could be involved in phenylketonuria (PKU)-associated oxidative stress. A Pah^enu2-BTBR PKU mouse model, and an in vitro cell culture model of PKU mimicking high phenylalanine insults in PKU, were employed for this study. The concentration of phenylalanine in mouse cerebral cortex was determined by liquid chromatography-tandem mass spectrometry. Superoxide production was displayed with dihydroethidium staining. NADPH oxidase expression level was measured by real-time RT-PCR, Western blotting and immunofluorescence. NADPH oxidase activity was measured by the colorimetric method. The phenylalanine concentrations in cerebral cortices of PKU mice were significantly higher than those in wild-type control mice. Similar results concerning superoxide production and NADPH oxidase protein expression and activity, were also found in this brain region. In addition, it was found that cerebral cortical neurons subjected to an in vitro high phenylalanine insult, displayed increased superoxide production accompanied by increases of NADPH oxidase protein expression and activity. Pretreatment with the inhibitor of this oxidase (diphenylene iodonium or apocynin) prevented this superoxide-increasing effect. Collectively, these findings provide evidence that NADPH oxidase might be a key enzyme involved in enhanced superoxide production in PKU and suggest that it may be a potential therapeutic target in neuroprotective strategies against phenylalanine-evoked oxidative brain injury in PKU.     

Nitric oxide and oxidative stress in vascular disease

Endothelium-derived nitric oxide (NO) is a paracrine factor that controls vascular tone, inhibits platelet function, prevents adhesion of leukocytes, and reduces proliferation of the intima. An enhanced inactivation and/or reduced synthesis of NO is seen in conjunction with risk factors for cardiovascular disease. This condition, referred to as endothelial dysfunction, can promote vasospasm, thrombosis, vascular inflammation, and proliferation of vascular smooth muscle cells. Vascular oxidative stress with an increased production of reactive oxygen species (ROS) contributes to mechanisms of vascular dysfunction. Oxidative stress is mainly caused by an imbalance between the activity of endogenous pro-oxidative enzymes (such as NADPH oxidase, xanthine oxidase, or the mitochondrial respiratory chain) and anti-oxidative enzymes (such as superoxide dismutase, glutathione peroxidase, heme oxygenase, thioredoxin peroxidase/peroxiredoxin, catalase, and paraoxonase) in favor of the former. Also, small molecular weight antioxidants may play a role in the defense against oxidative stress. Increased ROS concentrations reduce the amount of bioactive NO by chemical inactivation to form toxic peroxynitrite. Peroxynitrite—in turn—can “uncouple” endothelial NO synthase to become a dysfunctional superoxide-generating enzyme that contributes to vascular oxidative stress. Oxidative stress and endothelial dysfunction can promote atherogenesis. Therapeutically, drugs in clinical use such as ACE inhibitors, AT₁ receptor blockers, and statins have pleiotropic actions that can improve endothelial function. Also, dietary polyphenolic antioxidants can reduce oxidative stress, whereas clinical trials with antioxidant vitamins C and E failed to show an improved cardiovascular outcome.     

NADPH oxidases in cardiovascular health and disease

Increased oxidative stress plays an important role in the pathophysiology of cardiovascular diseases such as hypertension, atherosclerosis, diabetes, cardiac hypertrophy, heart failure, and ischemia-reperfusion. Although several sources of reactive oxygen species (ROS) may be involved, a family of NADPH oxidases appears to be especially important for redox signaling and may be amenable to specific therapeutic targeting. These include the prototypic Nox2 isoform-based NADPH oxidase, which was first characterized in neutrophils, as well as other NADPH oxidases such as Nox1 and Nox4. These Nox isoforms are expressed in a cell- and tissue-specific fashion, are subject to independent activation and regulation, and may subserve distinct functions. This article reviews the potential roles of NADPH oxidases in both cardiovascular physiological processes (such as the regulation of vascular tone and oxygen sensing) and pathophysiological processes such as endothelial dysfunction, inflammation, hypertrophy, apoptosis, migration, angiogenesis, and vascular and cardiac remodeling. The complexity of regulation of NADPH oxidases in these conditions may provide the possibility of targeted therapeutic manipulation in a cell-, tissue- and/or pathway-specific manner at appropriate points in the disease process.