Endothelium-specific sepiapterin reductase deficiency in DOCA-salt hypertension.

The endothelial nitric oxide synthase (eNOS) requires tetrahydrobiopterin (H(4)B) as a cofactor and, in its absence, produces superoxide (O(2)(·-)) rather than nitric oxide (NO(·)), a condition referred to as eNOS uncoupling. DOCA-salt-induced hypertension is associated with H(4)B oxidation and uncoupling of eNOS. The present study investigated whether administration of sepiapterin or H(4)B recouples eNOS in DOCA-salt hypertension. Bioavailable NO(·) detected by electron spin resonance was markedly reduced in aortas of DOCA-salt hypertensive mice. Preincubation with sepiapterin (10 µmol/l for 30 min) failed to improve NO(·) bioavailability in hypertensive aortas while it augmented NO(·) production from control vessels, implicating a hypertension-associated deficiency in sepiapterin reductase (SPR), the rate-limiting enzyme for sepiapterin conversion to H(4)B. Indeed, a decreased SPR expression was observed in aortic endothelial cells, but not in endothelium-denuded aortic remains, implicating an endothelium-specific SPR deficiency. Administration of hypertensive aortas with H(4)B (10 µmol/l, 30 min) partially restored vascular NO(·) production. Combined administration of H(4)B and the NADPH oxidase inhibitor apocynin (100 µmol/l, 30 min) fully restored NO(·) bioavailability while reducing O(2)(·-) production. In angiotensin II-induced hypertension, however, aortic endothelial SPR expression was not affected. In summary, administration of sepiapterin is not effective in recoupling eNOS in DOCA-salt hypertension, due to an endothelium-specific loss in SPR, whereas coadministration of H(4)B and apocynin is highly efficient in recoupling eNOS. This is consistent with our previous observations that in angiotensin II hypertension, endothelial deficiency in dihydrofolate reductase is alternatively responsible for uncoupling of eNOS. Taken together, these data indicate that strategies specifically targeting at different H(4)B metabolic enzymes might be necessary in restoring eNOS function in different types of hypertension.

Effectiveness of artificial tears in the management of evaporative dry eye.

PURPOSE: To compare the efficacies of sodium hyaluronate, hydroxypropyl methylcellulose (HPMC), and a new oil-in-water emulsion (Emustil unidose; SIFI) in the management of lipid-deficient dry eye. METHODS: Seventy-five subjects with dry eye were randomly divided into 3 groups. Each was allocated sodium hyaluronate, HPMC, or emulsion eyedrops to be used four times daily for 90 days. Parameters were measured at baseline, 30 days, and 90 days. A compliance visit was performed at days 7 and 60. RESULTS: Significant reduction (P < 0.05) in evaporation and improvement in symptoms in all groups were found. No statistically significant increase in tear turnover rate (TTR) was found with any solution. A significant difference in tear stability and noninvasive tear break-up time (NITBUT) was found in the emulsion and sodium hyaluronate groups but not in the HPMC group (P > 0.05). There was a significant decrease in osmolarity and corneal staining in the emulsion group (P < 0.001) but not in the sodium hyaluronate or HPMC group (P > 0.05). CONCLUSIONS: A significant reduction in evaporation and improvement in symptoms in all therapy groups were found from baseline to 90 days. However, no significant effect was seen on TTR for any group. The emulsion drops were shown to perform best, improving tear stability, and decreasing osmolarity and corneal staining. These results are consistent with improvements in the lipid layer of the tear film as a result of prolonged use of emulsion drops.

Comparison of human tear film osmolarity measured by electrical impedance and freezing point depression techniques.

PURPOSE: Tear hyperosmolarity is diagnostic of dry eye disease (DED), yet difficulty in measurement has limited its utility; development of new instruments could facilitate its clinical application. This study compares the new OcuSense TearLab osmometer (OcuSense, Inc, San Diego, CA), based on electrical impedance "lab-on-a-chip" nanoliter technology, with the freezing point depression Clifton Osmometer (Clifton Technical Physics, Hartford, NY). METHODS: Thirty-six subjects were recruited: 15 DED (9 women, 6 men age: 41 +/- 16 years) and 21 controls (12 women, 9 men age: 35 +/- 12 years); criteria for DED were noninvasive tear breakup time <10 seconds, Schirmer I test <5 mm, and positive symptoms. Samples were collected from the inferior tear meniscus for testing with both osmometers. RESULTS: Osmolarity values measured with OcuSense TearLab were 308 +/- 6 and 321 +/- 16 mOsm/L for controls and dry eye, respectively, and those measured with Clifton were 310 +/- 7 and 323 +/- 14 mOsm/L for controls and dry eye, respectively; these values were significantly different. Significant correlation was found between OcuSense and Clifton measurements (r = 0.904; P = 0.006). Bland-Altman analysis revealed agreement between techniques; the majority of points fell within the 95% confidence limits, and actual values differed by less than 1%. A cutoff value of >316 mOsm/L, derived from the distribution of osmolarity values, was used to diagnose DED with an effectiveness of 73% sensitivity, 90% specificity, and 85% positive predictive value for the OcuSense and 73% sensitivity, 71% specificity, and 65% positive predictive value for the Clifton in the study samples. CONCLUSIONS: Tear film osmolarity measured with the OcuSense TearLab system correlates well with the Clifton Osmometer. The new instrument has the potential to provide clinicians with a readily available clinically applicable measure, which could become the gold standard in DED.

Central and peripheral mechanisms of T-lymphocyte activation and vascular inflammation produced by angiotensin II-induced hypertension.

RATIONALE: We have previously found that T lymphocytes are essential for development of angiotensin II-induced hypertension; however, the mechanisms responsible for T-cell activation in hypertension remain undefined. OBJECTIVE: We sought to study the roles of the CNS and pressure elevation in T-cell activation and vascular inflammation caused by angiotensin II. METHODS AND RESULTS: To prevent the central actions of angiotensin II, we created anteroventral third cerebral ventricle (AV3V) lesions in mice. The elevation in blood pressure in response to angiotensin II was virtually eliminated by AV3V lesions, as was activation of circulating T cells and the vascular infiltration of leukocytes. In contrast, AV3V lesioning did not prevent the hypertension and T-cell activation caused by the peripheral acting agonist norepinephrine. To determine whether T-cell activation and vascular inflammation are attributable to central influences or are mediated by blood pressure elevation, we administered hydralazine (250 mg/L) in the drinking water. Hydralazine prevented the hypertension and abrogated the increase in circulating activated T cells and vascular infiltration of leukocytes caused by angiotensin II. CONCLUSIONS: We conclude that the central and pressor effects of angiotensin II are critical for T-cell activation and development of vascular inflammation. These findings also support a feed-forward mechanism in which modest degrees of blood pressure elevation lead to T-cell activation, which in turn promotes inflammation and further raises blood pressure, leading to severe hypertension.

A clinical alternative to fluorophotometry for measuring tear production in the diagnosis of dry eye.

PURPOSE: To determine the utility of the tear function index (Liverpool modification TFI) in assessing tear turnover rate (TTR), evaluate association of tear clearance rate (TCR) and TFI with measurements of TTR by fluorophotometry, and determine effectivity of these test measures in dry eye (DE) diagnosis. METHODS: Forty-one subjects with DE and 15 control subjects participated. Tests included symptoms, fluorophotometry (by automated scanning fluorophotometry), and TCR and TFI from a prepared Liverpool modification TFI strip. RESULTS: Significant differences between subjects with DE and control subjects were found for all tests. Although wetting length values gave highest sensitivity (SS) and specificity (SP) (71% and 73%, respectively), this resulted from a high degree of selection bias because the Schirmer test was one of the inclusion criteria for patients entering the study. Therefore, the best tear production test was found to be TTR (SS 71% and SP 60%). The TTR test is not readily available in clinical settings; therefore, associations between the TTR test and other tests were determined. Significant correlations were found between TTR and wetting length/TCR/TFI, indicating these latter clinical tests useful as surrogates. The strongest correlations, TTR/TCR at 0.69 (P = 0.000) and TTR/TFI at 0.65 (P = 0.000), indicate TCR/TFI with the Liverpool test can be used as an alternative to TTR by fluorophotometry. The diagnostic effectiveness between these tests was compared, with both TCR and TFI found to have equal effectivity of 78% SS and 40% SP (TCR) and 83% SS and 40% SP (TFI). CONCLUSIONS: TCR measured by the commercially available Liverpool modification TFI strip is an acceptable alternative to TTR by fluorophotometry as a measure of tear production. It is effective as a single test for the discrimination of those with DE from those without the condition.

Therapeutic targeting of mitochondrial superoxide in hypertension.

RATIONALE: Superoxide (O2(-) ) has been implicated in the pathogenesis of many human diseases including hypertension; however, commonly used antioxidants have proven ineffective in clinical trials. It is possible that these agents are not adequately delivered to the subcellular sites of superoxide production. OBJECTIVE: Because the mitochondria are important sources of reactive oxygen species, we postulated that mitochondrial targeting of superoxide scavenging would have therapeutic benefit. METHODS AND RESULTS: In this study, we found that the hormone angiotensin (Ang II) increased endothelial mitochondrial superoxide production. Treatment with the mitochondria-targeted antioxidant mitoTEMPO decreased mitochondrial O2(-), inhibited the total cellular O2(-), reduced cellular NADPH oxidase activity, and restored the level of bioavailable NO. These effects were mimicked by overexpressing the mitochondrial MnSOD (SOD2), whereas SOD2 depletion with small interfering RNA increased both basal and Ang II-stimulated cellular O2(-). Treatment of mice in vivo with mitoTEMPO attenuated hypertension when given at the onset of Ang II infusion and decreased blood pressure by 30 mm Hg following establishment of both Ang II-induced and DOCA salt hypertension, whereas a similar dose of nontargeted TEMPOL was not effective. In vivo, mitoTEMPO decreased vascular O2(-), increased vascular NO production and improved endothelial-dependent relaxation. Interestingly, transgenic mice overexpressing mitochondrial SOD2 demonstrated attenuated Ang II-induced hypertension and vascular oxidative stress similar to mice treated with mitoTEMPO. CONCLUSIONS: These studies show that mitochondrial O2(-) is important for the development of hypertension and that antioxidant strategies specifically targeting this organelle could have therapeutic benefit in this and possibly other diseases.

Interleukin 17 promotes angiotensin II-induced hypertension and vascular dysfunction.

We have shown previously that T cells are required for the full development of angiotensin II-induced hypertension. However, the specific subsets of T cells that are important in this process are unknown. T helper 17 cells represent a novel subset that produces the proinflammatory cytokine interleukin 17 (IL-17). We found that angiotensin II infusion increased IL-17 production from T cells and IL-17 protein in the aortic media. To determine the effect of IL-17 on blood pressure and vascular function, we studied IL-17(-/-) mice. The initial hypertensive response to angiotensin II infusion was similar in IL-17(-/-) and C57BL/6J mice. However, hypertension was not sustained in IL-17(-/-) mice, reaching levels 30-mm Hg lower than in wild-type mice by 4 weeks of angiotensin II infusion. Vessels from IL-17(-/-) mice displayed preserved vascular function, decreased superoxide production, and reduced T-cell infiltration in response to angiotensin II. Gene array analysis of cultured human aortic smooth muscle cells revealed that IL-17, in conjunction with tumor necrosis factor-alpha, modulated expression of >30 genes, including a number of inflammatory cytokines/chemokines. Examination of IL-17 in diabetic humans showed that serum levels of this cytokine were significantly increased in those with hypertension compared with normotensive subjects. We conclude that IL-17 is critical for the maintenance of angiotensin II-induced hypertension and vascular dysfunction and might be a therapeutic target for this widespread disease.

Induction of hypertension and peripheral inflammation by reduction of extracellular superoxide dismutase in the central nervous system.

The circumventricular organs (CVOs) lack a well-formed blood-brain barrier and produce superoxide in response to angiotensin II and other hypertensive stimuli. This increase in central superoxide has been implicated in the regulation of blood pressure. The extracellular superoxide dismutase (SOD3) is highly expressed in cells associated with CVOs and particularly with tanycytes lining this region. To understand the role of SOD3 in the CVOs in blood pressure regulation, we performed intracerebroventricular injection an adenovirus encoding Cre-recombinase (5x10(8) particles per milliliter) in mice with loxP sites flanking the SOD3 coding region (SOD3(loxp/loxp) mice). An adenovirus encoding red-fluorescent protein was injected as a control. Deletion of CVO SOD3 increased baseline blood pressure modestly and markedly augmented the hypertensive response to low-dose angiotensin II (140 ng/kg per day), whereas intracerebroventricular injection of adenovirus encoding red-fluorescent protein had minimal effects on these parameters. Adenovirus encoding Cre-recombinase-treated mice exhibited increased sympathetic modulation of heart rate and blood pressure variability, increased vascular superoxide production, and T-cell activation as characterized by increased circulating CD69(+)/CD3(+) cells. Deletion of CVO SOD3 also markedly increased vascular T-cell and leukocyte infiltration caused by angiotensin II. We conclude that SOD3 in the CVO plays a critical role in the regulation of blood pressure, and its loss promotes T-cell activation and vascular inflammation, in part by modulating sympathetic outflow. These findings provide insight into how central signals produce vascular inflammation in response to hypertensive stimuli, such as angiotensin II.

Tear and meibomian gland function in blepharitis and normals.

PURPOSE: To determine the differential features of tear physiology and meibomian gland function in blepharitics for ascertaining the diagnostic potential of a number of clinical tests. METHODS: Two groups of subjects, 15 with clinically diagnosed blepharitis (11 women and 5 men mol/L; age 60.9 +/- 12.5; range 41-79) and 15 age- and sex-matched controls (11 women and 5 men mol/L; age 60.7 +/- 12.6; range 40-78), were included in the study. Tear physiology was assessed by evaporimetry and interferometry and the meibomian glands by expression and meibography. RESULTS: Tear evaporation rate was significantly higher (P<0.001) in blepharitics (46.3 +/- 22.9 g/m/hr) than that in normals (18.0 +/- 10.7 g/m/hr). The lipid pattern was found to be significantly less stable (P=0.001) in the blepharitic group compared with that in the normal group. By meibography, meibomian gland dropout was scored and found to be significantly greater (P=0.001) in blepharitics in both the upper eyelids (blepharitis 1.0 +/- 0.8; normal 0.1 +/- 0.3) and lower eyelids (blepharitis 2.1 +/- 8.3; normal 1.0 +/- 0.8). The dropout score was the same or greater for the lower lids than for the upper lids, in all cases. A significant difference (P=0.000) in meibomian gland expression was found between blepharitics and normals; meibum was significantly thicker and more opaque in blepharitics in both the upper (blepharitis 2.2 +/- 0.7; normal 1.0 +/- 0.2) and lower (blepharitis 2.6 +/- 0.7; normal 1.3 +/- 0.4) eyelids. CONCLUSIONS: There are significant differences in tear physiology and meibomian gland function in patients with blepharitis when compared with those without. All the tests employed would be useful as single tests in the diagnosis of blepharitis, with meibomian gland dropout of the lower eyelid offering the greatest effectiveness as a single measure.

Role of the T cell in the genesis of angiotensin II induced hypertension and vascular dysfunction.

Hypertension promotes atherosclerosis and is a major source of morbidity and mortality. We show that mice lacking T and B cells (RAG-1-/- mice) have blunted hypertension and do not develop abnormalities of vascular function during angiotensin II infusion or desoxycorticosterone acetate (DOCA)-salt. Adoptive transfer of T, but not B, cells restored these abnormalities. Angiotensin II is known to stimulate reactive oxygen species production via the nicotinamide adenosine dinucleotide phosphate (NADPH) oxidase in several cells, including some immune cells. Accordingly, adoptive transfer of T cells lacking the angiotensin type I receptor or a functional NADPH oxidase resulted in blunted angiotensin II-dependent hypertension and decreased aortic superoxide production. Angiotensin II increased T cell markers of activation and tissue homing in wild-type, but not NADPH oxidase-deficient, mice. Angiotensin II markedly increased T cells in the perivascular adipose tissue (periadventitial fat) and, to a lesser extent the adventitia. These cells expressed high levels of CC chemokine receptor 5 and were commonly double negative (CD3+CD4-CD8-). This infiltration was associated with an increase in intercellular adhesion molecule-1 and RANTES in the aorta. Hypertension also increased T lymphocyte production of tumor necrosis factor (TNF) alpha, and treatment with the TNFalpha antagonist etanercept prevented the hypertension and increase in vascular superoxide caused by angiotensin II. These studies identify a previously undefined role for T cells in the genesis of hypertension and support a role of inflammation in the basis of this prevalent disease. T cells might represent a novel therapeutic target for the treatment of high blood pressure.

Role of extracellular superoxide dismutase in hypertension.

We previously found that angiotensin II-induced hypertension increases vascular extracellular superoxide dismutase (ecSOD), and proposed that this is a compensatory mechanism that blunts the hypertensive response and preserves endothelium-dependent vasodilatation. To test this hypothesis, we studied ecSOD-deficient mice. ecSOD(-/-) and C57Blk/6 mice had similar blood pressure at baseline; however, the hypertension caused by angiotensin II was greater in ecSOD(-/-) compared with wild-type mice (168 versus 147 mm Hg, respectively; P<0.01). In keeping with this, angiotensin II increased superoxide and reduced endothelium-dependent vasodilatation in small mesenteric arterioles to a greater extent in ecSOD(-/-) than in wild-type mice. In contrast to these findings in resistance vessels, angiotensin II paradoxically improved endothelium-dependent vasodilatation, reduced intracellular and extracellular superoxide, and increased NO production in aortas of ecSOD(-/-) mice. Whereas aortic expression of endothelial NO synthase, Cu/ZnSOD, and MnSOD were not altered in ecSOD(-/-) mice, the activity of Cu/ZnSOD was increased by 80% after angiotensin II infusion. This was associated with a concomitant increase in expression of the copper chaperone for Cu/ZnSOD in the aorta but not in the mesenteric arteries. Moreover, the angiotensin II-induced increase in aortic reduced nicotinamide-adenine dinucleotide phosphate oxidase activity was diminished in ecSOD(-/-) mice as compared with controls. Thus, during angiotensin II infusion, ecSOD reduces hypertension, minimizes vascular superoxide production, and preserves endothelial function in resistance arterioles. We also identified novel compensatory mechanisms involving upregulation of copper chaperone for Cu/ZnSOD, increased Cu/ZnSOD activity, and decreased reduced nicotinamide-adenine dinucleotide phosphate oxidase activity in larger vessels. These compensatory mechanisms preserve large vessel function when ecSOD is absent in hypertension.

Atrial fibrillation increases production of superoxide by the left atrium and left atrial appendage: role of the NADPH and xanthine oxidases.

BACKGROUND: Atrial fibrillation (AF) is associated with an increased risk of stroke due almost exclusively to emboli from left atrial appendage (LAA) thrombi. Recently, we reported that AF was associated with endocardial dysfunction, limited to the left atrium (LA) and LAA and manifest as reduced nitric oxide (NO*) production and increased expression of plasminogen activator inhibitor-1. We hypothesized that reduced LAA NO* levels observed in AF may be associated with increased superoxide (O2*-) production. METHODS AND RESULTS: After a week of AF induced by rapid atrial pacing in pigs, O2*- production from acutely isolated heart tissue was measured by 2 independent techniques, electron spin resonance and superoxide dismutase-inhibitable cytochrome C reduction assays. Compared with control animals with equivalent ventricular heart rates, basal O2*- production was increased 2.7-fold (P<0.01) and 3.0-fold (P<0.02) in the LA and LAA, respectively. A similar 3.0-fold (P<0.01) increase in LAA O2*- production was observed using a cytochrome C reduction assay. The increases could not be explained by changes in atrial total superoxide dismutase activity. Addition of either apocyanin or oxypurinol reduced LAA O2*-, implying that NADPH and xanthine oxidases both contributed to increased O2*- production in AF. Enzyme assays of atrial tissue homogenates confirmed increases in LAA NAD(P)H oxidase (P=0.04) and xanthine oxidase (P=0.01) activities. Although there were no changes in expression of the NADPH oxidase subunits, the increase in superoxide production was accompanied by an increase in GTP-loaded Rac1, an activator of the NADPH oxidase. CONCLUSIONS: AF increased O2*- production in both the LA and LAA. Increased NAD(P)H oxidase and xanthine oxidase activities contributed to the observed increase in LAA O2*- production. This increase in O2*- and its reactive metabolites may contribute to the pathological consequences of AF such as thrombosis, inflammation, and tissue remodeling.

The role of the multidrug resistance protein-1 in modulation of endothelial cell oxidative stress.

Glutathione (GSH) is the major source of intracellular sulfhydryl groups. Oxidized GSH (GSSG) can be recycled to GSH by the GSH reductase or exported from the cell. The mechanism by which GSSG is exported and the consequence of its export from endothelial cells has not been defined previously. We found that human endothelial cells express the multidrug resistance protein-1 (MRP1) and use this as their major exporter of GSSG. Oscillatory shear stress, which is known to stimulate endothelial cell production of reactive oxygen species, decreased intracellular GSH. In contrast, laminar shear significantly increased intracellular GSH. Oscillatory shear also caused a robust export of GSSG that was prevented by the MRP1 inhibitor MK571 and by MRP1 small interfering RNA. MRP1 inhibition prevented the decline in intracellular GSH, preserved the intracellular GSH Nernst potential, and reduced apoptosis caused by oscillatory shear. In aortas of hypertensive mice, endothelial disulfide export was doubled, and this was prevented by MK571 and was not observed in aortas of hypertensive MRP1-/- mice. Further, the altered endothelium-dependent vasodilatation caused by hypertension was ameliorated in MRP1-/- mice. GSSG export by MRP1 leads to a perturbation of endothelial redox state and ultimately endothelial cell apoptosis. Endothelial MRP1 may provide a novel therapeutic target for prevention of vascular disease.

Hemodynamic and biochemical adaptations to vascular smooth muscle overexpression of p22phox in mice.

Protein levels and polymorphisms of p22(phox) have been suggested to modulate vascular NAD(P)H oxidase activity and vascular production of reactive oxygen species (ROS). We sought to determine whether increasing p22(phox) expression would alter vascular ROS production and hemodynamics by targeting p22(phox) expression to smooth muscle in transgenic (Tg) mice. Aortas of Tg(p22smc) mice had increased p22(phox) and Nox1 protein levels and produced more superoxide and H(2)O(2). Surprisingly, endothelium-dependent relaxation and blood pressure in Tg(p22smc) mice were normal. Aortas of Tg(p22smc) mice produced twofold more nitric oxide (NO) at baseline and sevenfold more NO in response to calcium ionophore as detected by electron spin resonance. Western blot analysis revealed a twofold increase in endothelial NO synthase (eNOS) protein expression in Tg(p22smc) mice. Both eNOS expression and NO production were normalized by infusion of the glutathione peroxidase mimetic ebselen or by crossing Tg(p22smc) mice with mice overexpressing catalase. We have previously found that NO stimulates extracellular superoxide dismutase (ecSOD) expression in vascular smooth muscle. In keeping with this, aortic segments from Tg(p22smc) mice expressed twofold more ecSOD, and chronic treatment with the NOS inhibitor N(G)-nitro-L-arginine methyl ester normalized this, suggesting that NO regulates ecSOD protein expression in vivo. These data indicate that chronic oxidative stress caused by excessive H(2)O(2) production evokes a compensatory response involving increased eNOS expression and NO production. NO in turn increases ecSOD protein expression and counterbalances increased ROS production leading to the maintenance of normal vascular function and hemodynamics.

Detection of intracellular superoxide formation in endothelial cells and intact tissues using dihydroethidium and an HPLC-based assay.

Recently, it was demonstrated that superoxide oxidizes dihydroethidium to a specific fluorescent product (oxyethidium) that differs from ethidium by the presence of an additional oxygen atom in its molecular structure. We have adapted this new HPLC-based assay to quantify this product as a tool to estimate intracellular superoxide in intact tissues. Ethidium and oxyethidium were separated using a C-18 column and quantified using fluorescence detection. Initial cell-free experiments with potassium superoxide and xanthine oxidase confirmed the formation of oxyethidium from dihydroethidium. The formation of oxyethidium was inhibited by superoxide dismutase but not catalase and did not occur upon the addition of H(2)O(2), peroxynitrite, or hypochlorous acid. In bovine aortic endothelial cells (BAEC) and murine aortas, the redox cycling drug menadione increased the formation of oxyethidium from dihydroethidium ninefold (0.4 nmol/mg in control vs. 3.6 nmol/mg with 20 microM menadione), and polyethylene glycol-conjugated superoxide dismutase (PEG-SOD) significantly inhibited this effect. Treatment of BAEC with angiotensin II caused a twofold increase in oxyethidium formation, and this effect also was reduced by PEG-SOD (0.5 nmol/mg). In addition, in the aortas of mice with angiotensin II-induced hypertension and DOCA-salt hypertension, the formation of oxyethidium was increased in a manner corresponding to superoxide production estimated on the basis of cytochrome c reduction. Detection of oxyethidium using HPLC represents a new, convenient, quantitative method for the detection of superoxide in intact cells and tissues.

Oxidation of tetrahydrobiopterin leads to uncoupling of endothelial cell nitric oxide synthase in hypertension.

Tetrahydrobiopterin is a critical cofactor for the NO synthases, and in its absence these enzymes become "uncoupled," producing reactive oxygen species (ROSs) rather than NO. In aortas of mice with deoxycorticosterone acetate-salt (DOCA-salt) hypertension, ROS production from NO synthase is markedly increased, and tetrahydrobiopterin oxidation is evident. Using mice deficient in the NADPH oxidase subunit p47(phox) and mice lacking either the endothelial or neuronal NO synthase, we obtained evidence that hypertension produces a cascade involving production of ROSs from the NADPH oxidase leading to oxidation of tetrahydrobiopterin and uncoupling of endothelial NO synthase (eNOS). This decreases NO production and increases ROS production from eNOS. Treatment of mice with oral tetrahydrobiopterin reduces vascular ROS production, increases NO production as determined by electron spin resonance measurements of nitrosyl hemoglobin, and blunts the increase in blood pressure due to DOCA-salt hypertension. Endothelium-dependent vasodilation is only minimally altered in vessels of mice with DOCA-salt hypertension but seems to be mediated by hydrogen peroxide released from uncoupled eNOS, since it is inhibited by catalase. Tetrahydrobiopterin oxidation may represent an important abnormality in hypertension. Treatment strategies that increase tetrahydrobiopterin or prevent its oxidation may prove useful in preventing vascular complications of this common disease.

Role of c-Src in regulation of endothelial nitric oxide synthase expression during exercise training.

We have shown that c-Src plays a role in shear stress stimulation of endothelial nitric oxide synthase (eNOS) expression in cultured cells. To examine the role of c-Src in vivo, we exercised C57Blk/6 and c-Src heterozygous (c-Src(+/-)) mice on a treadmill for 3 wk. Western analysis demonstrated that c-Src(+/-) mice express less than one-half the normal amount of c-Src. Exercise increased heart rate and blood pressure to identical levels in both strains as determined using radiotelemetry. Exercise training increased eNOS protein >2-fold in the aorta and 1.7-fold in the heart in C57Blk/6 mice but had no effect on eNOS protein levels in c-Src(+/-) mice. In contrast to exercise, treatment of mice with mevastatin, which stimulates expression of eNOS posttranscriptionally, increased eNOS protein in both strains. Training also increased aortic extracellular superoxide dismutase protein expression, which is regulated by nitric oxide, in C57Blk/6 mice but not in c-Src(+/-)mice. These data indicate that c-Src has an important role in modulating vascular adaptations to exercise training, in particular increasing eNOS and extracellular superoxide dismutase protein expression.

Role of p47(phox) in vascular oxidative stress and hypertension caused by angiotensin II.

Hypertension caused by angiotensin II is dependent on vascular superoxide (O2*-) production. The nicotinamide adenine dinucleotide phosphate (NAD[P]H) oxidase is a major source of vascular O2*- and is activated by angiotensin II in vitro. However, its role in angiotensin II-induced hypertension in vivo is less clear. In the present studies, we used mice deficient in p47(phox), a cytosolic subunit of the NADPH oxidase, to study the role of this enzyme system in vivo. In vivo, angiotensin II infusion (0.7 mg/kg per day for 7 days) increased systolic blood pressure from 105+/-2 to 151+/-6 mm Hg and increased vascular O2*- formation 2- to 3-fold in wild-type (WT) mice. In contrast, in p47(phox-/-) mice the hypertensive response to angiotensin II infusion (122+/-4 mm Hg; P<0.05) was markedly blunted, and there was no increase of vascular O2*- production. In situ staining for O2*- using dihydroethidium revealed a marked increase of O2*-production in both endothelial and vascular smooth muscle cells of angiotensin II-treated WT mice, but not in those of p47(phox-/-) mice. To directly examine the role of the NAD(P)H oxidase in endothelial production of O2*-, endothelial cells from WT and p47(phox-/-) mice were cultured. Western blotting confirmed the absence of p47(phox) in p47(phox-/-) mice. Angiotensin II increased O2*- production in endothelial cells from WT mice, but not in those from p47(phox-/-) mice, as determined by electron spin resonance spectroscopy. These results suggest a pivotal role of the NAD(P)H oxidase and its subunit p47(phox) in the vascular oxidant stress and the blood pressure response to angiotensin II in vivo.

Peroxidase properties of extracellular superoxide dismutase: role of uric acid in modulating in vivo activity.

OBJECTIVE: The cytosolic form of Cu/Zn-containing superoxide dismutase (SOD1) has peroxidase activity, with H2O2 used as a substrate to oxidize other molecules. We examined peroxidase properties of the extracellular form of SOD (SOD3), a major isoform of SOD in the vessel wall, by using recombinant SOD3 and an in vivo model of atherosclerosis. METHODS AND RESULTS: In the presence of HCO3-, SOD3 reacted with H2O2 to produce a hydroxyl radical adduct of the spin trap 5-diethoxyphosphoryl-5methyl-1-pyrroline N-oxide (DEMPO). SOD1 and SOD3 were inactivated by H2O2 in a dose- and time-dependent fashion, and this was prevented by physiological levels of uric acid. To examine the in vivo role of uric acid on SOD1 and SOD3, control and apolipoprotein E-deficient (ApoE(-/-)) mice were treated with oxonic acid, which inhibits urate metabolism. This treatment increased plasma levels of uric acid in control and ApoE(-/-) mice by approximately 3-fold. Although increasing uric acid levels did not alter aortic SOD1 and SOD3 protein expression, aortic SOD1 and SOD3 activities were increased by 2- to 3-fold in aortas from ApoE(-/-) mice but not in aortas from control mice. CONCLUSIONS: These studies show that SOD1 and SOD3 are partially inactivated in atherosclerotic vessels of ApoE(-/-) mice and that levels of uric acid commonly encountered in vivo may regulate vascular redox state by preserving the activity of these enzymes.