Increased free radical production in hypertension due to increased expression of the NADPH oxidase subunit p22(phox) in lymphoblast cell lines

CYBA encoding p22(phox), the cytochrome b558 alpha polypeptide: gene structure, expression, role and physiopathology

P22(phox) is a ubiquitous protein encoded by the CYBA gene located on the long arm of chromosome 16 at position 24, containing six exons and spanning 8.5 kb. P22(phox) is a critical component of the superoxide-generating nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOXs). It is associated with NOX2 to form cytochrome b558 expressed mainly in phagocytes and responsible for the killing of microorganisms when bacterial and fungal infections occur. CYBA mutations lead to one of the autosomal recessive forms of chronic granulomatous disease (AR22(0)CGD) clinically characterized by recurrent and severe infections in early childhood. However, p22(phox) is also the partner of NOX1, NOX3 and NOX4, but not NOX5, which are analogs of NOX2, the first identified member of the NOX family. P22(phox)-NOX complexes have emerged as one of the most relevant sources of reactive oxygen species (ROS) in tissues and cells, and are associated with several diseases such as cardiovascular and cerebrovascular diseases. The p22(phox)-deficient mouse strain nmf333 has made it possible to highlight the role of p22(phox) in the control of inner ear balance in association with NOX3. However, the relevance of p22(phox) for NOX3 function remains uncertain because AR22(0)CGD patients do not suffer from vestibular dysfunction. Finally, a large number of genetic variations of CYBA have been reported, among them the C242T polymorphism, which has been extensively studied in association with coronary artery and heart diseases, but conflicting results continue to be reported.

Insulin resistance determines phagocytic nicotinamide adenine dinucleotide phosphate oxidase overactivation in metabolic syndrome patients

OBJECTIVE

Metabolic syndrome (MetS) is associated with insulin resistance and increases the cardiovascular risk. Oxidative stress constitutes a potential mechanism that links insulin resistance and cardiovascular disease. The aim of this study was to analyze the relationship of NADPH oxidase activation with insulin resistance, and the effect of this interaction on the cardiovascular risk in MetS patients.

METHODS

NADPH oxidase-dependent superoxide production and expression was evaluated by luminescence and western blot, respectively, in peripheral blood mononuclear cells obtained from 125 patients with MetS. Insulin resistance was defined by the homeostasis model assessment index. Matrix metalloproteinase-9 was quantified by enzyme-linked immunosorbent assay in plasma samples. To ascertain the mechanisms involved in vivo, we performed in-vitro experiments in cultured macrophages.

RESULTS

Fifty-six percent of patients with MetS showed insulin resistance. Plasma matrix metalloproteinase-9 levels were higher (P < 0.05) in insulin-resistant patients than in patients with insulin sensitivity. NADPH oxidase-dependent superoxide production was augmented (P < 0.05) in insulin-resistant patients with respect to insulin-sensitive patients. The interaction between insulin resistance and abnormally high NADPH oxidase-mediated superoxide production was associated with the highest matrix metalloproteinase-9 values. Increased NADPH oxidase-dependent superoxide production was significantly associated with higher NADPH oxidase p22phox expression in insulin-resistant than in insulin-sensitive patients. Interestingly, insulin upregulated p22phox in peripheral blood mononuclear cells and in murine macrophages.

CONCLUSION

Insulin resistance is associated with phagocytic NADPH oxidase activation. This association results in the highest cardiovascular risk in MetS patients.

Losartan metabolite EXP3179 blocks NADPH oxidase-mediated superoxide production by inhibiting protein kinase C: potential clinical implications in hypertension

Oxidative stress plays a critical role in the pathogenesis of hypertension. The NADPH oxidase constitutes a major source of superoxide anion in phagocytic cells, and its activation is associated with matrix metalloproteinase (MMP)-9 secretion by these cells. We investigated the effects of the angiotensin II type 1 receptor antagonist losartan and its metabolites (EXP3174 and EXP3179) on NADPH oxidase activity and MMP-9 secretion in human phagocytic cells. EXP3179, but not losartan and EXP3174, dose-dependently inhibited (P<0.05) phorbol myristate acetate and insulin-stimulated NADPH oxidase activity. EXP3179 also inhibited phorbol myristate acetate-induced NADPH oxidase in endothelial cells. In addition, EXP3179 inhibited (P<0.05) both phorbol myristate acetate-stimulated p47phox translocation from cytosol to membranes and protein kinase C activity. Affinity experiments and enzymatic assays confirmed that EXP3179 inhibited several protein kinase C isoforms. EXP3179 also inhibited (P<0.05) phorbol myristate acetate-stimulated MMP-9 secretion. In a study performed in 153 hypertensive patients, phagocytic NADPH oxidase activity was lower (P<0.05) in losartan-treated compared with untreated patients and in patients treated with other angiotensin II type 1 receptor antagonists or with angiotensin-converting enzyme inhibitors. Plasma levels of MMP-9 were lower (P<0.05) in losartan-treated hypertensives compared with the other group of patients. Thus, EXP3179 acts as a blocker of the NADPH oxidase in phagocytic cells by a potential mechanism that targets the protein kinase C signaling pathway. This effect can be involved in reduced MMP-9 secretion by these cells. It is proposed that the EXP3179 metabolite may confer to losartan the specific capacity to reduce oxidative stress mediated by phagocytic cells in hypertensive patients.

The angiotensin-converting enzyme insertion/deletion polymorphism is associated with phagocytic NADPH oxidase-dependent superoxide generation: potential implication in hypertension

The objective of the present study was to analyse the influence of the ACE (angiotensin-converting enzyme) gene I/D (insertion/deletion) polymorphism on NADPH oxidase-dependent O(2)(*-) (superoxide radical) production, and to investigate the clinical implication of this association in hypertensive subjects. A case-control study was performed in a random sample of the general population composed of 189 normotensive subjects and 223 hypertensive subjects. The ACE polymorphism was determined by PCR. NADPH oxidase-dependent O(2)(*-) production was quantified in phagocytic cells by chemiluminescence. MMP-9 (matrix metalloproteinase-9), a marker of atherosclerosis previously reported to be associated with NADPH oxidase overactivity, was quantified by ELISA in plasma samples. The distribution of genotypes was in Hardy-Weinberg equilibrium. The I/D polymorphism was not associated with hypertension. NADPH oxidase-dependent O(2)(*-) production was significantly higher in D/D (deletion/deletion) than in I/I (insertion/insertion) and I/D, both in normotensive and hypertensive subjects. Interestingly, plasma levels of angiotensin II were significantly higher in D/D than in I/I and I/D, both in normotensive and hypertensive subjects. Plasma levels of MMP-9 and systolic blood pressure values were significantly higher in D/D than in I/I and I/D hypertensive subjects, whereas no differences were found among genotypes in normotensive subjects. Interestingly, NADPH oxidase-dependent O(2)(*-) production positively associated with plasma MMP-9 levels in hypertensive subjects, which remained significant after adjustment for age and gender. In conclusion, in the present study we have reported for the first time an association of the D/D genotype of the ACE I/D polymorphism with phagocytic NADPH oxidase-mediated O(2)(*-) overproduction. Within the group of hypertensive patients, D/D cases also associated with increased blood pressure values and with enhanced plasma levels of MMP-9.

Redox signaling, vascular function, and hypertension

Accumulating evidence supports the importance of redox signaling in the pathogenesis and progression of hypertension. Redox signaling is implicated in many different physiological and pathological processes in the vasculature. High blood pressure is in part determined by elevated total peripheral vascular resistance, which is ascribed to dysregulation of vasomotor function and structural remodeling of blood vessels. Aberrant redox signaling, usually induced by excessive production of reactive oxygen species (ROS) and/or by decreases in antioxidant activity, can induce alteration of vascular function. ROS increase vascular tone by influencing the regulatory role of endothelium and by direct effects on the contractility of vascular smooth muscle. ROS contribute to vascular remodeling by influencing phenotype modulation of vascular smooth muscle cells, aberrant growth and death of vascular cells, cell migration, and extracellular matrix (ECM) reorganization. Thus, there are diverse roles of the vascular redox system in hypertension, suggesting that the complexity of redox signaling in distinct spatial spectrums should be considered for a better understanding of hypertension.

NADPH oxidase inhibitors: new antihypertensive agents?

NADPH oxidases have recently been shown to contribute to the pathogenesis of hypertension. The development of specific inhibitors of these enzymes has focused attention on their potential therapeutic use in hypertensive disease. Two of the most specific inhibitors, gp91ds-tat and apocynin, have been shown to decrease blood pressure in animal models of hypertension. Other inhibitors, including diphenylene iodonium, aminoethyl benzenesulfono fluoride, S17834, PR39, protein kinase C inhibitors, and VAS2870, have shown promise in vitro, but their in vivo specificity, pharmacokinetics, and effectiveness in hypertension remains to be determined. Of importance, the currently available antihypertensive agents angiotensin-converting enzyme inhibitors and angiotensin receptor blockers also effectively inhibit NADPH oxidase activation. Similarly, the cholesterol-lowering agents, statins, have been shown to attenuate NADPH oxidase activation. Although, antioxidants act to scavenge the reactive oxygen species produced by these enzymes, their effectiveness is limited. Targeting NADPH homologues may have a distinct advantage over current therapies because it would specifically prevent the pathophysiological formation of reactive oxygen species that contributes to hypertension.

A novel CYBA variant, the -675A/T polymorphism, is associated with essential hypertension

OBJECTIVE

Oxidative stress is implicated in hypertension and the NADPH oxidase systems constitute the main source of superoxide in vascular wall. We searched for new polymorphisms within the CYBA promoter, the human gene that encodes the p22phox protein, and studied their potential association with essential hypertension.

DESIGN

A case-control study in a random sample of the general population.

METHODS

CYBA polymorphisms were determined by restriction fragment length polymorphism and allelic discrimination. NADPH oxidase activity was quantified in phagocytic cells by chemiluminescence.

RESULTS

We identified three novel polymorphisms, at positions -852, -675 and -536 from the ATG codon. Only the -675(A/T) polymorphism associated with essential hypertension. The prevalence of the TT genotype and the T allele frequency were significantly higher (P < 0.05) in hypertensives than in normotensives. Furthermore, TT hypertensives exhibited higher (P < 0.05) systolic blood pressure values than TA/AA hypertensives. Increased phagocytic NADPH oxidase activity was observed in TT subjects compared to TA and AA individuals (P < 0.05). Enhanced carotid intima-media thickness, a surrogate marker of atherosclerosis, was found in TT subjects compared to TA and AA individuals (P < 0.05). Finally, mutagenesis experiments demonstrated a functional role of this polymorphism on the CYBA promoter activity.

CONCLUSION

The -675 (A/T) CYBA polymorphism may be a novel genetic marker associated with essential hypertension. Furthermore, TT subjects exhibit features of NADPH oxidase-mediated oxidative stress and asymptomatic atherosclerosis.

The NOX family of ROS-generating NADPH oxidases: physiology and pathophysiology

For a long time, superoxide generation by an NADPH oxidase was considered as an oddity only found in professional phagocytes. Over the last years, six homologs of the cytochrome subunit of the phagocyte NADPH oxidase were found: NOX1, NOX3, NOX4, NOX5, DUOX1, and DUOX2. Together with the phagocyte NADPH oxidase itself (NOX2/gp91(phox)), the homologs are now referred to as the NOX family of NADPH oxidases. These enzymes share the capacity to transport electrons across the plasma membrane and to generate superoxide and other downstream reactive oxygen species (ROS). Activation mechanisms and tissue distribution of the different members of the family are markedly different. The physiological functions of NOX family enzymes include host defense, posttranlational processing of proteins, cellular signaling, regulation of gene expression, and cell differentiation. NOX enzymes also contribute to a wide range of pathological processes. NOX deficiency may lead to immunosuppresion, lack of otoconogenesis, or hypothyroidism. Increased NOX activity also contributes to a large number or pathologies, in particular cardiovascular diseases and neurodegeneration. This review summarizes the current state of knowledge of the functions of NOX enzymes in physiology and pathology.

Production of extracellular superoxide by human lymphoblast cell lines: comparison of electron spin resonance techniques and cytochrome C reduction assay

Superoxide production by NADPH oxidases plays an important role in the development and progression of cardiovascular disease (CVD). However, measurement of superoxide (O(2)(-)), a marker of oxidative stress, remains a challenging task in clinical and translational studies. In this study we analyzed O(2)(-) production in cultured human lymphoblast cell lines by three different methods: (a) superoxide dismutase (SOD)-inhibitable cytochrome C reduction, (b) spin trapping of superoxide with 5-(ethoxycarbonyl)-5-methyl-1-pyrroline N-oxide (EMPO) and 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide (DEPMPO), and (c) using electron spin resonance (ESR) with the cell-permeable spin probe 1-hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine (CMH). Lymphocytes were isolated and immortalized by an Epstein-Barr Virus (EBV)-transformation procedure. Superoxide was measured in cultured lymphoblast cell lines at baseline and upon stimulation with phorbol 12-myristate 13-acetate (PMA). Cytochrome C and the spin traps EMPO and DEPMPO detected two to five times less superoxide compared to CMH. Thus, CMH provided the most quantitative measurement of superoxide generation in human lymphoblast cell lines. Superoxide detection with CMH was linear dependent on cell concentration and was inhibited by SOD but not by catalase. Both cell-permeable polyethylene glycol (PEG)-SOD and extracellular Cu,Zn-SOD inhibited O(2)(-) detection by 90% in PMA-stimulated cells, suggesting a predominantly extracellular O(2)(-) generation in human lymphoblasts. Our study describes a new technique for O(2)(-) measurement in cultured human lymphoblasts using ESR and CMH. A highly sensitive in vitro measurement of O(2)(-) in human cell lines would allow investigators to study genotype/phenotype interactions in translational studies.

NADPH oxidases in the kidney

NADPH oxidases have a distinct cellular localization in the kidney. Reactive oxygen species (ROS) are produced in the kidney by fibroblasts, endothelial cells (EC), vascular smooth muscle cells (VSMC), mesangial cells (MCs), tubular cells, and podocyte cells. All components of the phagocytic NADPH oxidase, as well as the Nox-1 and -4, are expressed in the kidney, with a prominent expression in renal vessels, glomeruli, and podocytes, and cells of the thick ascending limb of the loop of Henle (TAL), macula densa, distal tubules, collecting ducts, and cortical interstitial fibroblasts. NADPH oxidase activity is upregulated by prolonged infusion of angiotensin II (Ang II) or a high salt diet. Since these are major factors underlying the development of hypertension, renal NADPH oxidase may have an important pathophysiological role. Indeed, recent studies with small interference RNAs (siRNAs) targeted to p22( phox ) implicate p22( phox ) in Ang II-induced activation of renal NADPH oxidase and the development of oxidative stress and hypertension, while studies with apocynin implicate activation of p47( phox ) in the development of nephropathy in a rat model of type 1 diabetes mellitus (DM). Experimental studies of the distribution, signaling, and function of NADPH oxidases in the kidney are described.

Effects of D-amino acids on lipoperoxidation in rat liver and kidney mitochondria

The effects of the amino acids D-ser, D-asp, and D-ala on lipoperoxidation under conditions of hypertension, alcoholism, and ammonemia in rat liver and kidney mitochondria were studied. Under normal conditions, D-alanine increased in 54% free radicals production in liver mitochondria (p < 0.05). The D-amino acids had no effect on kidney mitochondria. D-ser and D-ala increased lipoperoxidation in spontaneously hypertensive rats (SHR) as compared with their normotensive genetic control Wistar-Kyoto (WKY) rats (p < 0.05). During hypertension and in oxidative stress in the presence of calcium, only D-ala produced 46% and 29% free radicals in liver and kidney mitochondria (p < 0.05), respectively. During chronic alcoholism, D-ser increased lipoperoxidation in 80% in kidney mitochondria (p < 0.05), as compared to control. During ammonemia, D-ser produced 41% free radicals.

The C242T CYBA polymorphism of NADPH oxidase is associated with essential hypertension

OBJECTIVE

Oxidative stress is implicated in hypertension. The reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidases are the main source of superoxide in phagocytic and vascular cells. The C242T polymorphism of CYBA, the human gene that encodes p22phox, has been found to be functionally associated with vascular NADPH oxidase activity in atherosclerotic patients. We investigated the association of the C242T polymorphism with hypertension and its potential impact on NADPH oxidase activity. We also analysed the interaction of C242T polymorphism with the -930A/G CYBA variant.

DESIGN

Case-control study in a random sample of 623 subjects (326 hypertensive patients and 297 normotensive controls) from the general population.

METHODS

CYBA polymorphisms were determined by restriction fragment length polymorphism (RFLP) or allelic discrimination. NADPH oxidase activity and p22phox expression were quantified in phagocytic cells by chemiluminescence and by northern and western blots, respectively.

RESULTS

The prevalence of the CC genotype and the C allele frequency were significantly higher (P < 0.05) in hypertensives than in normotensives. CC genotype remained associated with hypertension after adjusting for potential confounders in a logistic regression analysis. Increased phagocytic NADPH oxidase activity was observed in CC hypertensives compared with CT and TT hypertensives (P < 0.05). Enhanced plasma levels of von Willebrand factor were found in CC hypertensives compared with TT hypertensives (P < 0.05). The C242T polymorphism was not in linkage disequilibrium with the -930A/G CYBA promoter variation, which also associates with hypertension.

CONCLUSION

The C242T CYBA polymorphism is associated with essential hypertension. Furthermore, hypertensives carrying the CC genotype of this polymorphism exhibit features of NADPH oxidase-mediated oxidative stress and endothelial damage.

Phagocytic NADPH oxidase overactivity underlies oxidative stress in metabolic syndrome

Oxidative stress plays a critical role in the pathogenesis of atherosclerosis in patients with metabolic syndrome. This study aimed to investigate whether a relationship exists between phagocytic NADPH oxidase activity and oxidative stress and atherosclerosis in metabolic syndrome patients. The study was performed in 56 metabolic syndrome patients (metabolic syndrome group), 99 patients with one or two cardiovascular risk factors (cardiovascular risk factor group), and 28 healthy subjects (control group). NADPH oxidase expression and activity was augmented (P < 0.05) in metabolic syndrome compared with cardiovascular risk factor and control groups. Insulin was enhanced (P < 0.05) in metabolic syndrome patients compared with cardiovascular risk factor and control groups and correlated with NADPH oxidase activity in the overall population. Insulin stimulated NADPH oxidase activity; this effect was abolished by a specific protein kinase C inhibitor. Oxidized LDL and nitrotyrosine levels and carotid intima-media thickness were increased (P < 0.05) in the metabolic syndrome group compared with cardiovascular risk factor and control groups and correlated with NADPH oxidase activity in the overall population. These findings suggest that phagocytic NADPH oxidase overactivity is involved in oxidative stress and atherosclerosis in metabolic syndrome patients. Our findings also suggest that hyperinsulinemia may contribute to oxidative stress in metabolic syndrome patients through activation of NADPH oxidase.

NADPH oxidase-mediated oxidative stress: genetic studies of the p22(phox) gene in hypertension

Increased vascular production of reactive oxygen species, especially superoxide anion, significantly contributes to the oxidative stress associated with hypertension. An enhanced superoxide production causes an increased inactivation of nitric oxide that diminishes nitric oxide bioavailability, thus contributing to endothelial dysfunction and hypertrophy of vascular cells. It has been shown that NADPH oxidases play a major role as the most important sources of superoxide anion in phagocytic and vascular cells. Several experimental observations have described an enhanced superoxide generation as a result of NADPH oxidase activation in hypertension. Although these enzymes respond to stimuli such as vasoactive factors, growth factors, and cytokines, recent data suggest a significant role of the genetic background in the modulation of the expression of its different components. Several polymorphisms have been identified in the promoter and in the coding region of CYBA, the gene that encodes the essential subunit of the NADPH oxidase p22phox, some of which seem to influence significantly the activity of these enzymes in the context of cardiovascular diseases. Among CYBA polymorphisms, genetic investigations have provided a novel marker, the -930(A/G) polymorphism, which determines the genetic susceptibility of hypertensive patients to oxidative stress.

Regulation of reactive oxygen species (ROS) production by C18 fatty acids in Jurkat and Raji cells

In the present study, the effects of C18 fatty acids with different numbers of double bonds, SA (stearic acid; C18:0), OA (oleic acid; C18:1), LA (linoleic acid; C18:2) and gamma-LNA (gamma-linolenic acid; C18:3), on ROS (reactive oxygen species) production by Jurkat (a human T-lymphocyte-derived cell line) and Raji (a human B-lymphocyte-derived cell line) cells were investigated. ROS production was determined by NBT (Nitro Blue Tetrazolium) reduction (intracellular and extracellular ROS production) and by dihydroethidium oxidation using flow cytometry (intracellular ROS production). The effectiveness on ROS production was gamma-LNA<SA<OA<LA in Jurkat cells and SA<gamma-LNA<OA<LA in Raji cells. LA (found in corn, soya bean and sunflower oils) was more potent than OA (found in olive oil) in stimulating ROS production in both Raji and Jurkat cells. The lower ROS production by OA compared with LA may be one of the benefits of olive oil consumption. As SA and gamma-LNA acids had little or no effect, further studies on the site of ROS production in these cells were carried out with OA and LA only. Activation of NADPH oxidase via PKC (protein kinase C) was found to be the major mechanism of ROS production induced by OA and LA in Jurkat and Raji cells.

High glucose-induced oxidative stress inhibits Na+/glucose cotransporter activity in renal proximal tubule cells

Oxidative stress plays an important role in the pathogenesis of renal diseases such as diabetic nephropathy. The metabolism of excessive intracellular glucose may involve a number of processes. One consequence of excessive intracellular glucose levels is an increased rate of oxidative phosphorylation under hyperglycemic conditions, whereas another consequence is an increase in the metabolism of glucose to sorbitol by aldose reductase. In addition, hyperglycemia may result in the activation of NADPH oxidase, the production of superoxide anion, and hydrogen peroxide (H2O2). In this report, we investigate the mechanisms responsible for the H2O2 production that occurs as the consequence of hyperglycemia and the effect of H2O2 on the activity of the Na+/glucose cotransport system (SGLT) in primary cultures of renal proximal tubule cells (PTCs). When primary PTCs were cultured in the presence of high glucose, one consequence was that the Na+/glucose cotransport system was inhibited, as indicated by uptake studies utilizing alpha-methyl-D-glucoside (alpha-MG), a nonmetabolizable analog of D-glucose. Pretreatment of the cultures with either 1) aminoguanidine or pyridoxamine [inhibitors of the accumulation of advanced glycation end products (AGEs)], 2) rotenone (an inhibitor of the mitochondrial electron transport chain), or 3) apocynin or diphenylene iodonium (DPI; inhibitors of NADPH oxidase) blocked the observed changes that occurred as a consequence of the incubation of the PTCs with high glucose. Included among these changes were the observed increase in H2O2 levels, as well as an increase in lipid peroxide production, and a decrease both in the activity of catalase and in the level of glutathione (GSH), endogenous antioxidants. The high glucose-induced decrease in the level of the Na+/glucose cotransporter was similarly prevented by either aminoguanidine, rotenone, or apocynin. Thus the inhibitory effect of high glucose on both the level of the Na+/glucose cotransport system and the activity of the Na+/glucose cotransport system can be explained, at least in part, as being due to the effects of the H2O2, the consequent formation of AGEs, the increase in mitochondrial metabolism, and in NADPH oxidase activity in the PTCs. Other related changes observed in the PTCs that could be reversed by treatment with either aminoguanidine, pyridoxamine, rotenone, apocynin, or DPI included an increase in transforming growth factor-beta1 secretion and the activation of the NF-kappaB signal transduction pathway.

Association of increased phagocytic NADPH oxidase-dependent superoxide production with diminished nitric oxide generation in essential hypertension

OBJECTIVE

Oxidative stress has been implicated in the pathogenesis of hypertension and its complications through alterations in nitric oxide (NO) metabolism. This study was designed to investigate whether a relationship exists between phagocytic nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-dependent superoxide anion (*O2-) production and NO generation in patients with essential hypertension.

METHODS

Superoxide production was assayed by chemiluminescence under baseline and stimulated conditions on mononuclear cells obtained from hypertensives (n=51) and normotensives (n=43). NO production was evaluated by determining serum NO metabolites, nitrate plus nitrite (NOx).

RESULTS

Although there were no differences in baseline *O2- production between normotensives and hypertensives, the *O2- production in phorbol myristate acetate (PMA)-stimulated mononuclear cells was increased (P <0.05) in hypertensives compared with normotensives. The PMA-induced *O2- production was completely abolished by apocynin, a specific inhibitor of NADPH oxidase. Moreover, stimulation of *O2- production by angiotensin II and endothelin-1 was higher (P <0.05) in cells from hypertensives than in cells from normotensives. In addition, diminished (P <0.001) serum NOx was detected in hypertensives compared with normotensives. Interestingly, an inverse correlation (r=0.493, P <0.01) was found between *O2- production and NOx in hypertensives.

CONCLUSIONS

Generation of *O2- mainly dependent on NADPH oxidase is abnormally enhanced in stimulated mononuclear cells from hypertensives. It is suggested that this alteration could be involved in the diminished NO production observed in these patients.

Functional Effect of the p22 phox −930 A/G Polymorphism on p22 phox Expression and NADPH Oxidase Activity in Hypertension

Oxidative stress induced by superoxide is implicated in hypertension. NADPH oxidase is the main source of superoxide in phagocytic and vascular cells, and the p22 phox subunit is involved in NADPH oxidase activation. Recently we reported an association of −930 A/G polymorphism in the human p22 phox gene promoter with hypertension. This study was designed to investigate the functional role of this polymorphism in hypertension. We thus investigated the relationships between the −930 A/G polymorphism and p22 phox expression and NADPH oxidase–mediated superoxide production in phagocytic cells from 70 patients with essential hypertension and 70 normotensive controls. Genotyping of the polymorphism was performed by restriction fragment length polymorphism. NADPH oxidase activity was determined by chemiluminescence assays, and p22 phox mRNA and protein expression was measured by Northern and Western blotting, respectively. Compared with hypertensive subjects with the AA/AG genotype, hypertensive subjects with the GG genotype exhibited increased ( P <0.05) phagocytic p22 phox mRNA (1.26±0.06 arbitrary unit [AU] versus 0.99±0.03 AU) and protein levels (0.58±0.05 AU versus 0.34±0.04 AU) and enhanced NADPH oxidase activity (1998±181 counts/s versus 1322±112 counts/s). No differences in these parameters were observed among genotypes in normotensive cells. Transfection experiments on vascular smooth muscle cells showed that the A -to- G substitution of this polymorphism produced an increased reporter gene expression in hypertensive cells. Nitric oxide production, as assessed by measurement of serum nitric oxide metabolites, was lower in GG hypertensive subjects than in AA/AG hypertensive subjects. In conclusion, these results suggest that hypertensive subjects carrying the GG genotype of the p22 phox −930 A/G polymorphism are highly exposed to NADPH oxidase-mediated oxidative stress.

Vascular NAD(P)H oxidases: specific features, expression, and regulation

The importance of reactive oxygen species (ROS) in vascular physiology and pathology is becoming increasingly evident. All cell types in the vascular wall produce ROS derived from superoxide-generating protein complexes similar to the leukocyte NADPH oxidase. Specific features of the vascular enzymes include constitutive and inducible activities, substrate specificity, and intracellular superoxide production. Most phagocyte enzyme subunits are found in vascular cells, including the catalytic gp91phox (aka, nox2), which was the earliest member of the newly discovered nox family. However, smooth muscle frequently expresses nox1 rather than gp91phox, and nox4 is additionally present in all cell types. In cell culture, agonists increase ROS production by activating multiple signals, including protein kinase C and Rac, and by upregulating oxidase subunits. The oxidases are also upregulated in vascular disease and are involved in the development of atherosclerosis and a significant part of angiotensin II-induced hypertension, possibly via nox1 and nox4. Likewise, enhanced vascular oxidase activity is associated with diabetes. Therefore, members of this enzyme family appear to be important in vascular biology and disease and constitute promising targets for future therapeutic interventions.

NADPH oxidase activity in preeclampsia with immortalized lymphoblasts used as models

Upon activation, neutrophils release reactive oxygen species that are believed to contribute to the widespread manifestation of preeclampsia. Neutrophils have an NADPH oxidase enzyme that catalyzes the production of reactive oxygen species. Little is known about the manifestations of the activated response and the upstream signaling pathways that regulate this process in preeclampsia. It is hypothesized that genetic factors may contribute to the release of reactive oxygen species and consequently the pathophysiology of the disease. We used Epstein-Barr virus-immortalized lymphoblasts from third-trimester, preeclamptic, postpartum preeclamptic women and their respective control subjects to assess NADPH oxidase-mediated reactive oxygen species production by using luminol-derived chemiluminescence and dihydrorhodamine-123 fluorescence. There was no effect of pregnancy status on the lymphoblast phorbol ester-stimulated luminol chemiluminescence area under the curve. However, lymphoblasts from preeclamptic patients had significant elevation of the lymphoblast phorbol ester-stimulated luminol area under the curve (F statistic 10.922, P<0.002). Similar findings were evident with dihydrorhodamine-123. No differences were revealed between preeclamptic and control cells when measuring the abundance of the phox proteins using Western blotting. Studies with genistein and tyrphostin implicated tyrosine kinase-dependent mechanisms in the control of NADPH oxidase-associated increased reactive oxygen species production in preeclampsia. These data show that preeclampsia is associated with a predisposition to increased agonist-stimulated NADPH oxidase-mediated reactive oxygen species production. The enhancement of reactive oxygen species generation may be important in mediating the endothelial dysfunction seen in preeclampsia.

Neutrophil activation and production of reactive oxygen species in pre-eclampsia

OBJECTIVE

To investigate neutrophil NADPH oxidase activation and subsequent production of reactive oxygen species (ROS) in pre-eclampsia.

DESIGN

Baseline values and the activated response of neutrophils upon stimulation of the NADPH oxidase with the agonists was measured. Neutrophils from 17 third-trimester pre-eclamptic and 17 age- and gestation-matched normal pregnant women were examined.

METHODS

Neutrophil ROS production was measured by both lucigenin- and luminol-derived chemiluminescence. The abundance of the various phox proteins was examined using Western blotting techniques. Lucigenin-derived ROS generation was significantly increased in neutrophils isolated from women with pre-eclampsia compared with normotensive controls in the case of both agonists [n-formyl-met-leu-phe (fMLP): pre-eclamptic 2.071 +/- 0.336 relative light units seconds (RLU.s) and normotensive 1.141 +/- 0.249 RLU.s, P = 0.035; phorbol-12-myristate-13-acetate (PMA): pre-eclamptic 34.954 +/- 2.634 RLU.s and normotensive 17.208 +/- 3.325 RLU.s, P = 0.0001]. Luminol-derived ROS generation was also significantly increased in the neutrophils isolated from the women with pre-eclampsia compared with the normotensive controls in the case of both agonists (fMLP: pre-eclamptic 1.955 +/- 0.316 RLU.s and normotensive 1.058 +/- 0.191 RLU.s, P = 0.023; PMA: pre-eclamptic 4.108 +/- 0.351 RLU.s and normotensive 3.073 +/- 0.332 RLU.s, P = 0.042). There were no differences between the relative abundance of the phox proteins in the two groups.

CONCLUSIONS

Neutrophils isolated from women with pre-eclampsia during the third trimester showed increased sensitivity to agonist stimulation and produced significantly more ROS than age-matched normotensive controls. This was not due to an increased abundance of any of the phox proteins. Increased ROS production in pre-eclampsia may highlight a role for neutrophils in the oxidative stress and associated endothelial dysfunction that are characteristic of the condition.

Genomic association/linkage of sodium lithium countertransport in CEPH pedigrees

Little is known about genetic determinants explaining variation in the erythrocyte sodium-lithium countertransport (SLC), an intermediate phenotype of essential hypertension. We characterized the SLC in immortalized lymphoblasts and showed that its behavior is similar to that of erythrocyte SLC. We then performed association and linkage analyses of the SLC in immortalized lymphoblasts from 5 large pedigrees from the Center d'Etude du Polymorphisme Humain (CEPH) genomics repository. The results of these analyses showed that a number of genomic regions harboring genes involved in glutathione metabolism might explain variations in SLC activity. These findings support evidence that thiol groups play a central role in SLC activity.