p22phox mRNA expression and NADPH oxidase activity are increased in aortas from hypertensive rats

Regulation of the vascular extracellular superoxide dismutase by nitric oxide and exercise training

The bioactivity of endothelium-derived nitric oxide (NO) reflects its rates of production and of inactivation by superoxide (O(2)(*-)), a reactive species dismutated by extracellular superoxide dismutase (ecSOD). We have now examined the complementary hypothesis, namely that NO modulates ecSOD expression. The NO donor DETA-NO increased ecSOD expression in a time- and dose-dependent manner in human aortic smooth muscle cells. This effect was prevented by the guanylate cyclase inhibitor ODQ and by the protein kinase G (PKG) inhibitor Rp-8-CPT-cGMP. Expression of ecSOD was also increased by 8-bromo-cGMP, but not by 8-bromo-cAMP. Interestingly, the effect of NO on ecSOD expression was prevented by inhibition of the MAP kinase p38 but not of the MAP kinase kinase p42/44, suggesting that NO modulates ecSOD expression via cGMP/PKG and p38MAP kinase-dependent pathways, but not through p42/44MAP kinase. In aortas from mice lacking the endothelial nitric oxide synthase (eNOS), ecSOD was reduced more than twofold compared to controls. Treadmill exercise training increased eNOS and ecSOD expression in wild-type mice but had no effect on ecSOD expression in mice lacking eNOS, suggesting that this effect of exercise is meditated by endothelium-derived NO. Upregulation of ecSOD expression by NO may represent an important feed-forward mechanism whereby endothelial NO stimulates ecSOD expression in adjacent smooth muscle cells, thus preventing O(2)(*-)-mediated degradation of NO as it traverses between the two cell types.

Genetic, biochemical, and clinical features of chronic granulomatous disease

The reduced nicotinamide dinucleotide phosphate (NADPH) oxidase complex allows phagocytes to rapidly convert O2 to superoxide anion which then generates other antimicrobial reactive oxygen intermediates, such as H2O2, hydroxyl anion, and peroxynitrite anion. Chronic granulomatous disease (CGD) results from a defect in any of the 4 subunits of the NADPH oxidase and is characterized by recurrent life-threatening bacterial and fungal infections and abnormal tissue granuloma formation. Activation of the NADPH oxidase requires translocation of the cytosolic subunits p47phox (phagocyte oxidase), p67phox, and the low molecular weight GT-Pase Rac, to the membrane-bound flavocytochrome, a heterodimer composed of the heavy chain gp91phox and the light chain p22phox. This complex transfers electrons from NADPH on the cytoplasmic side to O2 on the vacuolar or extracellular side, thereby generating superoxide anion. Activation of the NADPH oxidase requires complex rearrangements between the protein subunits, which are in part mediated by noncovalent binding between src-homology 3 domains (SH3 domains) and proline-rich motifs. Outpatient management of CGD patients relies on the use of prophylactic antibiotics and interferon-gamma. When infection is suspected, aggressive effort to obtain culture material is required. Treatment of infections involves prolonged use of systemic antibiotics, surgical debridement when feasible, and, in severe infections, use of granulocyte transfusions. Mouse knockout models of CGD have been created in which to examine aspects of pathophysiology and therapy. Gene therapy and bone marrow transplantation trials in CGD patients are ongoing and show great promise.

Dietary troglitazone decreases oxidative stress in early stage type II diabetic rats

Oxidative stress is involved in the initiation and development of atherosclerosis in diabetes. We tested the hypothesis that oxidative stress is already increased in early stage type II diabetes, and that troglitazone may prevent the increase. Three groups of 20 week old rats were studied: untreated Otsuka Long-Evans Tokushima Fatty (OLETF) rats, as an animal model of type II diabetes, OLETF rats treated with troglitazone, and control Long-Evans Tokushima Otsuka (LETO) rats. Plasma lipid hydroperoxides (LOOH) concentration, as an indication of lipid peroxidation, and superoxide dismutase (SOD) activity in the thoracic aorta were measured. Plasma LOOH concentration was significantly higher in non-treated OLETF rats compared to LETO rats and treatment with troglitazone completely prevented this increase. SOD activity was significantly decreased in non-treated OLETF rats compared to LETO rats and troglitazone attenuated the diminution of it. These observations demonstrate oxidative stress is already increased in the early stage of type II diabetes and we confirmed troglitazone has the effect of an antioxidant in vivo.

Free radical production and angiotensin

Angiotensin II (ANG II) has multiple effects on cardiovascular and renal cells, including vasoconstriction, cell growth, induction of proinflammatory cytokines, and profibrogenic actions. Recent studies provide evidence that ANG II could stimulate intracellular formation of reactive oxygen species (ROS) such as the superoxide anion (O2-). This ANG II-mediated ROS formation exhibits different kinetic and lower absolute concentrations than those traditionally observed during the respiratory burst of phagocytic cells, but it likely involves similar membrane-bound NAD(P)H-oxidases. Current evidence suggests that ANG II, through AT1-receptor activation, upregulates several subunits of this multienzyme complex, resulting in an increase in intracellular O2- concentration. ROS are involved in several signal pathways, and redox-sensitive transcriptional factors (AP-1, NF-kappaB) have been characterized. ANG II-induced ROS play a pivotal role in several pathophysiologic situations of vascular and renal cells such as hypertension, endothelial dysfunction, nitrate tolerance, atherosclerosis, and cellular remodeling. Although these perceptions suggest that drugs interfering with ANG II effects (ACE inhibitors, AT1 -receptor antagonist) may serve as antioxidants, preventing vascular and renal changes, the clinical studies are not so straightforward. In fact, only specific risk groups, such as patients with diabetes mellitus or renal insufficiency, may benefit from ACE inhibitors, whereas hard endpoints showed no advantage for ACE inhibitors in patients with essential hypertension.

Inhibition of arterial thrombogenesis by quinapril but not losartan

The cardioprotective effect of angiotensin converting enzyme (ACE) inhibitors and angiotensin type I (AT1) receptor blockers may relate to their antithrombotic effect. We determined the differential effects of the ACE inhibitor quinapril and the AT1 receptor blocker losartan on arterial thrombus formation in the rat. Sprague-Dawley rats were fed regular chow or chow mixed with low-dose quinapril (0. 6 mg/kg/day), high-dose quinapril (1.2 mg/kg/day), or losartan (10 mg/kg/day) for 15 days. Abdominal aorta was exposed and wrapped with Whatman paper impregnated with 29% FeCl(3) (ferric chloride). Time to occlusive thrombus formation and weight of the thrombus were recorded. Aortic superoxide anion generation, platelet aggregation, plasma angiotensin II levels, and morphology of the thrombus were also examined. Both losartan and quinapril caused similar reductions in arterial pressure. Losartan did not affect the time to thrombus formation, whereas quinapril (both low and high doses) delayed the time to thrombus formation (P<.01 vs control). Weight of the thrombus was similar in all groups of rats. Platelet aggregation was inhibited by approximately 50 in both quinapril- and losartan-treated rats. The high-dose quinapril-treated rats showed markedly reduced vascular superoxide anion generation compared with the control rats (P<.05). Plasma angiotensin II levels were unaffected by quinapril treatment but were elevated 7-fold in losartan-treated rats (P <.001 vs. control rats). The thrombi in the control rats consisted of platelet aggregates, fibrin, and red blood cells. The intravascular platelet aggregates were much smaller in the quinapril-treated rats (P<.05 vs. control), but were similar in control and losartan-treated rats. In conclusion, quinapril but not losartan prolongs time to arterial thrombus formation and results in smaller platelet aggregates in the thrombus. Both quinapril and losartan decrease platelet aggregation, but only quinapril decreases superoxide anion generation. This effect on superoxide anion generation as well as mechanisms other than AT1 receptor blockade may underlie the salutary effect of quinapril on arterial thrombogenesis.

Vascular oxidant stress: molecular mechanisms and pathophysiological implications

The term oxidative stress refers to a situation in which cells are exposed to excessive levels of either molecular oxygen or chemical derivatives of oxygen (ie, reactive oxygen species). Three enzyme systems produce reactive oxygen species in the vascular wall: NADH/NADPH oxidase, xanthine oxidoreductase, and endothelial nitric oxide synthase. Among vascular reactive oxygen species superoxide anion plays a critical role in vascular biology because it is the source for many other reactive oxygen species and various vascular cell functions. It is currently thought that increases in oxidant stress, namely excessive production of superoxide anion, are involved in the pathophysiology of endothelial dysfunction that accompanies a number of cardiovascular risk factors including hypercholesterolemia, hypertension and cigarette smoking. On the other hand, vascular oxidant stress plays a pivotal role in the evolution of clinical conditions such as atherosclerosis, diabetes and heart failure.

Pitfalls of using lucigenin in endothelial cells: implications for NAD(P)H dependent superoxide formation

Since an increased endothelial superoxide formation plays an important role in the pathogenesis of endothelial dysfunction its specific detection is of particular interest. The widely used superoxide probe lucigenin, however, has been reported to induce superoxide under certain conditions, especially in the presence of NADH. This raises questions as to the conclusion of a NAD(P)H oxidase as the major source of endothelial superoxide. Using independent methods, we showed that lucigenin in the presence of NADH leads to the production of substantial amount of superoxide (approximately 15-fold of control) in endothelial cell homogenates. On the other hand, these independent methods revealed that endothelial cells without lucigenin still produce superoxide in a NAD(P)H-dependent manner. This was blocked by inhibitors of the neutrophil NADPH oxidase diphenyleniodonium and phenylarsine oxide. Our results demonstrate that a NAD(P)H-dependent oxidase is an important source for endothelial superoxide but the latter, however, cannot be measured reliably by lucigenin.

Acute production of vascular superoxide by angiotensin II but not by catecholamines

OBJECTIVE

To determine whether vascular superoxide is rapidly released by angiotensin II and is involved in vascular contraction.

DESIGN

The effect of superoxide dismutase (SOD) on angiotensin II induced elevation of mean arterial blood pressure was measured. Subsequently, acute production of vascular superoxide by angiotensin II and its effect on isometric tension were measured in rat aortic rings. The effects of catecholamines were concomitantly measured.

METHODS AND RESULTS

The acute pressor effects of angiotensin II were significantly reduced when rats were pretreated intravenously with SOD. When angiotensin II was added on aortic segments in the presence of Cypridina luciferin analog, immediate elevations of chemiluminescence were observed which were inhibited by SOD. Furthermore, angiotensin II-induced elevations of isometric tension in aortic rings were significantly reduced by SOD. The effects of epinephrine and norepinephrine were concomitantly measured and were not significant

CONCLUSIONS

The acute superoxide producing effect is likely to be specific to angiotensin II, because such a significant modification of the effects was not observed for catecholamines. Our results suggest that angiotensin II causes acute vascular superoxide production, which may be involved in the acute pressor effects.

Oxidative stress and vascular damage in hypertension

Metabolism of oxygen by cells generates potentially deleterious reactive oxygen species, including superoxide anion radical, hydrogen peroxide, and hydroxyl radical. Under normal physiologic conditions the rate and magnitude of oxidant formation is balanced by the rate of oxidant elimination. However, an imbalance between prooxidants and antioxidants results in oxidative stress, which is the pathogenic outcome of the overproduction of oxidants that overwhelms the cellular antioxidant capacity. There is increasing evidence that an elevation of oxidative stress and associated oxidative damages are mediators of vascular injury in various cardiovascular pathologies, including hypertension, atherosclerosis, and ischemia-reperfusion. This review focuses on the vascular effects of reactive oxygen species and the role of oxidative stress in vascular damage in hypertension.

The p22 phox polymorphism C242T is not associated with CHD risk in Asian Indians and Chinese

BACKGROUND

Oxygen free radicals such as superoxide anion have been implicated in the pathogenesis of atherosclerosis and coronary heart disease (CHD). The nonglycosylated 22 kDa alpha-subunit of the NADH/NADPH oxidase (p22 phox) of the vasculature acts as the final electron transporter in the generation of superoxide anion. Recently, a common polymorphism (C242T) at codon 72 in the p22 phox gene has been reported to be associated with CHD risk.

STUDY DESIGN

We examined the role of the C242T polymorphism with the risk of CHD in a biracial sample of Asian Indians and Chinese from Singapore. The sample comprised angiographically confirmed CHD patients (126 Asian Indians and 151 Chinese) and age- and sex-matched healthy control subjects (154 Asian Indians and 167 Chinese).

RESULTS

The frequency of the T allele was significantly higher in Asian Indian control subjects than in Chinese control subjects (0.38 vs. 0.09; P < 0. 0001). However, there was no difference in the frequency of this allele between case patients and control subjects either in Chinese (0.10 vs. 0.09) or Asian Indians (0.38 vs. 0.40). This polymorphism was also not associated with plasma lipid and apolipoprotein levels in any group.

CONCLUSIONS

The p22 phox codon 72 polymorphism is not associated with the risk of CHD in the present samples of Asian Indians and Chinese.

NADH/NADPH oxidase p22 phox C242T polymorphism and coronary artery disease in the Australian population

BACKGROUND

Oxidative stress induced by the superoxide anion (.O2-) has been implicated in atherogenesis. The NADH/NADPH oxidase system is involved in.O2- production and p22 phox is an essential component of that system.

MATERIAL AND METHODS

We analysed the p22 phox C242T polymorphism in 689 consecutive Australian Caucasians aged </= 65 years with and without angiographically documented coronary artery disease (CAD) RESULTS: We report the rare T allele frequency of 0.33, which is 3 fold higher than that reported in the Japanese population by Inoue et al. [7]. The genotype distributions were not different among patients with CAD (CC:0.422, CT:0.459 and TT: 0.119 in men; 0.447, 0.439 and 0.114 in women) and without CAD (0.479, 0. 420 and 0.101%, chi2 = 0.794, P = 0.672 in men; 0.443, 0.471 and 0. 86, chi2 = 0.442, P = 0.802 in women). The frequencies of the rare TT homozygotes or of the 'T' allele frequency were also not associated with the number of significantly stenosed vessels (chi2 = 4.466, P = 0.614 in men; chi2 = 4.736, P = 0.578 in women) or with a myocardial infarction (MI) history (chi2 = 2.310, P = 0.315 in men; chi2 = 1.178, P = 0.555 in women). However, when the analysis was conducted in young male patients aged </= 45 years (n = 44), TT + TC patients tended to have an increased risk for CAD (odds ratio: 5.71 95% CI: 1.22-26.75, P = 0.0271).

CONCLUSION

The p22 phox C242T polymorphism is not associated with the occurrence or severity of CAD or with a history of MI in Australian Caucasian patients aged </= 65 years. However, the polymorphism could be associated with an increased CAD risk in young patients, which requires confirmation in large populations.

Endothelial dysfunction and hypertensive vasoconstriction

A change in endothelial function is a common phenomenon in patients with essential hypertension and in animals with hypertension, whether primary or induced by a salt-rich diet. In hypertensive subjects, there may be a change in the synthesis, or the effect, of nitric oxide. Nevertheless, hypertensive vasoconstriction is at present associated, above all, with the degradation of this mediator by free radicals, such as the superoxide anion, released in the dysfunctional vascular endothelium. These radicals are also formed when hypoxanthine is turned into xanthine, and when the latter becomes uric acid, both having been catalysed by the enzyme xanthine oxidase. In physiological conditions, the concentration of superoxide radicals remains low within the organism as a result of its reaction with the superoxide dismutase enzyme. However, in pathological situations, such as arterial hypertension, there may be an increase in the production of these radicals or a deficiency of the superoxide dismutase enzyme. In hypertensive patients, the release of vasoconstrictor peroxides derived from the activity of cyclo-oxygenase in the endothelium and the vascular smooth muscle is also important. The excess free radicals released by the dysfunctional endothelium also stimulate the synthesis of these contracting agents. Moreover, it should not be forgotten that endothelin-1, which is similarly synthesized and released in the vascular endothelium, is the most powerful known endogenous vasoconstrictor. This peptide would therefore play a prominent part in some forms of hypertension. Although no changes in endothelin plasma levels have been found in essential hypertension, there may be an increase in its local concentration. It should be borne in mind that endothelin could strengthen the effect of other vasoconstrictors. Moreover, it may also provoke the release of free radicals and of cyclo-oxygenase-derived vasoconstrictor factors. The latest theories therefore indicate that the increase in vasoconstriction, which characterizes arterial hypertension, is associated with a greater production of free radicals. At the present time, antioxidant agents and xanthine oxydase-inhibiting compounds are being used to treat hypertension and other pathologies linked to endothelial dysfunction. In addition, it is thought that the therapeutic benefit of some anti-hypertensive drugs, such as calcium antagonists and angiotensin-converting enzyme inhibitors, could be in part due to the inhibition of the production of free radicals that they provoke.

Stimulation of a vascular smooth muscle cell NAD(P)H oxidase by thrombin. Evidence that p47(phox) may participate in forming this oxidase in vitro and in vivo

Thrombin is a potent vascular smooth muscle cell (VSMC) mitogen. Because recent evidence implicates reactive oxygen intermediates (ROI) in VSMC proliferation in general and atherogenesis in particular, we investigated whether ROI generation is necessary for thrombin-induced mitogenesis. Treatment of human aortic smooth muscle cells with thrombin increased DNA synthesis, an effect that was antagonized by diphenyleneiodonium but not by other inhibitors of cellular oxidase systems. This effect of thrombin was accompanied by increased O-2 and H2O2 generation and NADH/NADPH consumption. ROI generation in response to thrombin pretreatment could also be blocked by diphenyleneiodonium, suggesting that the NAD(P)H oxidase was necessary for ROI generation and thrombin-induced mitogenesis. Because of observed differences between the VSMC and neutrophil oxidase, we examined whether the cytosolic components of the phagocytic NAD(P)H oxidase were present in VSMC. p47(phox) and Rac2 were present in VSMC. Furthermore, thrombin increased expression of p47(phox) and Rac2 and stimulated their translocation to the cell membrane. We examined whether p47(phox) might be similarly regulated in vivo in a rat aorta balloon injury model and found that p47(phox) protein was increased after injury. Immunocytochemistry localized expression of p47(phox) to the neointima and media of injured arteries. Our data demonstrate that generation of O-2 and H2O2 is required for thrombin-mediated mitogenesis in VSMC and that p47(phox) is regulated by thrombin in vitro and is associated with vascular lesion formation in vivo.

Role of superoxide dismutase in in vivo and in vitro nitrate tolerance

We assessed whether pharmacological inhibition of CuZn-superoxide dismutase (SOD) mimics the molecular mechanism of either in vitro or in vivo nitrovasodilator tolerance. In endothelium-intact aortic rings from in vivo tolerant rabbits the GTN- and acetylcholine (ACh)-induced maximal relaxation was attenuated by 36 and 23%, respectively. In vitro treatment of control rings with GTN (1 h 10 microM) similarly attenuated the vasorelaxant response to GTN, but not to ACh. Formation of superoxide radicals (*O2-) in endothelium-intact rings (lucigenin-chemiluminescence) increased 2.5 fold in in vivo tolerance, but significantly decreased in in vitro tolerance. The membrane associated NADH oxidase activity was increased 2.5 fold in homogenates of in vivo tolerant aortae, but was not changed in in vitro tolerant aorta. Conversely, SOD activity and protein expression was halved in in vivo tolerance, but SOD activity was not altered by in vitro tolerance. The *O2- scavenger tiron (10 mM) effectively restored the vasorelaxant response to GTN in in vivo tolerant aortic rings, but not the reduced response to GTN in in vitro tolerant rings. Pretreatment (1 h) of vessels with diethyldithiocarbamate (DETC; 10 mM) attenuated vasorelaxant responses to GTN and ACh, increased vascular *O2- production, and inhibited SOD activity in vessel homogenates to a similar degree as observed in in vivo tolerance. DETC-treatment of in vivo-tolerant vessels induced an additional increase in *O2- production. Increased *O2- production in in vivo nitrate tolerant aorta is associated with activation of vascular NADH oxidase and inactivation of CuZnSOD. Therefore, in vivo tolerance can be mimicked by in vitro inhibition of CuZnSOD, but not by in vitro exposure to GTN, which does not affect vascular *O2- production, NADH oxidase and CuZnSOD.

Role for NADPH/NADH oxidase in the modulation of vascular tone

The endothelium modulates vascular tone by producing vasodilator and vasconstrictor substances. Of these, the best characterized and potentially most important are nitric oxide (NO.) and O2-.. These small molecules exhibit opposing effects on vascular tone and chemically react with each other in a fashion that negates their individual effects and leads to the production of potentially toxic substances, such as peroxynitrite (ONOO-). These dynamic interactions may likely have important implications, altering not only tissue perfusion but also contributing to the process of atherosclerosis. The precise O2-. source within vascular tissue remains to be determined. Recent work demonstrated that in endothelial cells as well as in vascular smooth muscle cells, a membrane-associated NAD(P)H-dependent oxidase represents the most significant O2-. source. Interestingly, this oxidase is activated upon stimulation with angiotension II, suggesting that under all conditions of an activated circulating and/or local renin-angiotensin system endothelial dysfunction secondary to increased vascular O2-. production is expected.

Increased oxidative DNA damage in stroke-prone spontaneously hypertensive rats

1. The amount of urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG), a biomarker of the total systemic oxidative stress in vivo, in stroke-prone spontaneously hypertensive rats (SHRSP) was not different from that in control normotensive Wistar-Kyoto (WKY) rats at 6 weeks of age, but became higher than control values after the development of severe hypertension at 14-17 weeks of age. 2. The amount of urinary 8-OHdG was not significantly different between SHRSP treated with anti-hypertensive agents and those not treated at 14 weeks of age. 3. Stroke-prone spontaneously hypertensive rats were exposed to DNA damage by oxidative stress at the early stage when they developed severe hypertension, but this increase in DNA damage was not the secondary effect of hypertension.

Increased NAD(P)H oxidase-mediated superoxide production in renovascular hypertension: evidence for an involvement of protein kinase C

BACKGROUND

Angiotensin II infusion has been shown to cause hypertension and endothelial dysfunction and to increase superoxide (O-.2) production in vascular tissue, mainly via an activation of nicotinamide adenine dinucleotide (phosphate) [NAD(P)H]-dependent oxidase, the most significant O-.2 source in endothelial and/or smooth muscle cells. With these studies, we sought to determine whether endothelial dysfunction in renovascular hypertension is secondary to an activation of these oxidases.

METHODS

Endothelial function in aortas from rats with two kidney-one clip (2K-1C) hypertension and age-matched controls was assessed using isometric tension studies in organ chambers. Changes in vascular O-.2 production were measured using lucigenin-enhanced chemiluminescence and electron spin resonance spectroscopy.

RESULTS

In hypertensive animals, relaxation to endothelium-dependent (acetylcholine) and endothelium-independent nitrovasodilators (nitroglycerin) was impaired. Constriction to a direct activator of protein kinase C (PKC) phorbol ester 12,13 dibutyrate (PDBu) was enhanced, and vascular O-.2 was significantly increased compared with controls. Vascular O-.2 was normalized by the PKC inhibitor calphostin C, by the inhibitor of flavin-dependent oxidases, diphenylene iodonium, and recombinant heparin-binding superoxide dismutase, whereas inhibitors of the xanthine oxidase (oxypurinol), nitric oxide synthase (NG-nitro-l-arginine) and mitochondrial NADH dehydrogenase (rotenone) were ineffective. Studies of vascular homogenates demonstrated that the major source of O-.2 was a NAD(P)H-dependent oxidase. Incubation of intact tissue with PDBu markedly increased O-. 2, the increase being significantly stronger in vessels from hypertensive animals as compared with vessels from controls. Endothelial dysfunction was improved by preincubation of vascular tissue with superoxide dismutase and calphostin C.

CONCLUSIONS

We therefore conclude that renovascular hypertension in 2K-1C rats is associated with increased vascular O-.2 leading to impaired vasodilator responses to endogenous and exogenous nitrovasodilators. Increased vascular O-.2 is likely secondary to a PKC-mediated activation of a membrane-associated NAD(P)H-dependent oxidase.

Diabetes mellitus and vascular lesions

Cardiovascular complications represent by far the most severe manifestations of diabetes mellitus. Treatment aimed at stopping progression of vascular lesions may fall short if initiated when the disease becomes clinically evident. Therefore, identification of the earliest vascular disfunctions may offer the best opportunity to interfere with pathogenic mechanisms and avoid progression of diabetic vasculopathy. In this report, we present a few mechanisms that alter hemodynamic and metabolic homeostasis in the course of diabetes mellitus. Endothelial function with special emphasis on nitric oxide and oxidative stress, advanced glycation end products, and the renin angiotensin system are briefly discussed. New pharmacological agents that may favorably influence these parameters are presently undergoing clinical trials. However, tight control of plasma glucose and cardiovascular risk factors represent the cornerstone of the treatment in diabetes to slow progression of vascular disease.

Angiotensin II-mediated expression of p27Kip1 and induction of cellular hypertrophy in renal tubular cells depend on the generation of oxygen radicals

BACKGROUND

Angiotensin II (Ang II) induces hypertrophy of cultured proximal tubular cells. We have previously demonstrated that this Ang II-mediated hypertrophy occurs in the G1-phase of the cell cycle and depends on the induction of p27Kip1, an inhibitor of G1-phase cyclin/cyclin-dependent kinase complexes. The present study was undertaken to investigate whether Ang II may stimulate superoxide anions (O2.) formation in cultured LLC-PK1 and cultured mouse proximal tubule (MCT) cells, and to gain further insight into a potential relationship between O2. and cell cycle regulation.

METHODS

Reactive oxygen species were measured with the lucigenin method in intact cells. The effects of various inhibitors were tested on Ang II-induced O2. production. Cells were transiently transfected with phosphorothioate-modified rat p22phox antisense oligonucleotides to investigate the potential role of NAD(P)H oxidase. Expression of p22phox mRNA after Ang II-treatment was detected with Northern blots. Incorporation of [3H]leucine into de novo synthesized proteins was used as a parameter of cell hypertrophy. Expression of p27Kip1 was evaluated in cell lysates by Western blotting.

RESULTS

Ang II stimulated the accumulation of O2. in tubular cells; however, an addition of two different antioxidants completely abolished measurable O2. This effect was transduced by angiotensin receptor type-1 (AT1) and was inhibited by a flavoprotein inhibitor (DIP) or p22phox antisense oligonucleotides, indicating the involvement of membrane NAD(P)H oxidase. Ang II-stimulated de novo protein synthesis was attenuated by DIP, antioxidants, and p22phox antisense oligonucleotides. The Ang II-induced expression of p27Kip1 protein and cellular hypertrophy were reduced by similar treatments. Generation of O2. by xanthine supplementation also stimulated p27Kip1 expression and induced hypertrophy in LLC-PK1 cells.

CONCLUSIONS

This study provides the first evidence, to our knowledge, that Ang II induces O2. in cultured tubular cells. Ang II-mediated activation of membrane bound NAD(P)H oxidase, probably by an increase in p22phox transcripts, is likely responsible for this induction. Generation of O2. subsequently induces p27Kip1 expression and stimulates hypertrophy, suggesting a novel mechanism of how Ang II can modulate cell cycle regulation.

Role of oxygen radicals generated by NADPH oxidase in apoptosis induced in human leukemia cells

We have used a human leukemia cell line that, after homologous recombination knockout of the gp91-phox subunit of the phagocyte respiratory-burst oxidase cytochrome b-558, mimics chronic granulomatous disease (X-CGD) to study the role of oxygen radicals in apoptosis. Camptothecin (CPT), a topoisomerase I inhibitor, induced significantly more apoptosis in PLB-985 cells than in X-CGD cells. Sensitivity to CPT was enhanced after neutrophilic differentiation, but was lost after monocytic differentiation. No difference between the two cell lines was observed after treatment with other apoptosis inducers, including etoposide, ultraviolet radiation, ionizing radiation, hydrogen peroxide, or 7-hydroxystaurosporine. After granulocytic differentiation of both cell lines, CPT still induced apoptosis, suggesting independence from replication in fully differentiated and growth-arrested cells. Pyrrolidine dithiocarbamate (an antioxidant inhibitor of NF-kappaB) and catalase partially inhibited CPT-induced DNA fragmentation in granulocytic-differentiated PLB-985 cells, but had no effect in X-CGD cells. Flow cytometry analysis revealed that reactive oxygen intermediates were generated in CPT-treated PLB-985 cells. These data indicate that oxygen radicals generated by NADPH oxidase may contribute directly or indirectly to CPT-induced apoptosis in human leukemia and in neutrophilic-differentiated cells.

Alterations in the vasoreactivity of hypertensive rat aortic rings: role of nitric oxide and superoxide radicals

OBJECTIVES

Present study was undertaken to investigate involvement of nitric oxide (NO) and superoxide radicals in the modulation of vasoreactivity in a model of renal hypertension.

METHOD

Hypertension was induced in the male Sprague Dawley rats by aortic banding just above the left kidney. Relaxation or contraction following cumulative addition of acetylcholine (Ach, 1 x 10(-8) to 1 x 10(-5) M) or phenylephrine (PE, 1 x 10(-8) to 1 x 10(-5) mol/l) was studied in the aortic rings obtained from sham operated normotensive, hypertensive and captopril pretreated rats. Ach and PE responses were taken in the presence or absence of NO synthase inhibitor (L-NAME; 1 x 10(-5) and 1 x 10(-4) mol/l). Spontaneous release of NO from the aortic rings was evaluated by studying the inhibition of adenosine diphosphate stimulated platelet aggregation, while superoxide radicals were estimated by cytochrome c reduction method.

RESULTS

Ach induced vasorelaxation in PE precontracted rings was impaired following 8 wk after aortic banding, while spontaneous release of NO remained unaffected. Captopril pretreatment restored the aortic ring responsiveness to Ach. An increase in the superoxide radical generation and PE induced contraction following L-NAME treatment in the hypertensive rat aortic rings was observed.

CONCLUSION

Attenuation in the Ach induced NO release and augmentation in the superoxide radical generation seems to play an important role in the modulation of vasoreactivity following renal hypertension in rats.

Mechanical deformation of the arterial wall in hypertension: a mechanism for vascular pathology

Hypertension is an independent risk factor for atherosclerotic disease. It has been proposed that the atherogenic potential of hypertension is due to the development of a proinflammatory state within the arterial wall that is, at least in part, a result of the generation of reactive oxygen species. This article proposes that mechanical deformation of the arterial wall is a critical stimulus in this scheme. Data is reviewed that demonstrate that mechanical deformation of the arterial wall stimulates the generation of reactive oxygen species and subsequently results in the upregulation of redox-sensitive proinflammatory gene products.

Pathophysiology of nitric oxide and related species: free radical reactions and modification of biomolecules

Since its initial discovery as an endogenously produced bioactive mediator, nitric oxide (.NO) has been found to play a critical role in the cellular function of nearly all organ systems. Furthermore, aberrant production of .NO or reactive nitrogen species (RNS) derived from .NO, has been implicated in a number of pathological conditions, such as acute lung disease, atherosclerosis and septic shock. While .NO itself is fairly non-toxic, secondary RNS are oxidants and nitrating agents that can modify both the structure and function of numerous biomolecules both in vitro, and in vivo. The mechanisms by which RNS mediate toxicity are largely dictated by its unique reactivity. The study of how reactive nitrogen species (RNS) derived from .NO interact with biomolecules such as proteins, carbohydrates and lipids, to modify both their structure and function is an area of active research, which is lending major new insights into the mechanisms underlying their pathophysiological role in human disease. In the context of .NO-dependent pathophysiology, these biochemical reactions will play a major role since they: (i) lead to removal of .NO and decreased efficiency of .NO as an endothelial-derived relaxation factor (e.g. in hypertension, atherosclerosis) and (ii) lead to production of other intermediate species and covalently modified biomolecules that cause injury and cellular dysfunction during inflammation. Although the physical and chemical properties of .NO and .NO-derived RNS are well characterised, extrapolating this fundamental knowledge to a complicated biological environment is a current challenge for researchers in the field of .NO and free radical research. In this review, we describe the impact of .NO and .NO-derived RNS on biological processes primarily from a biochemical standpoint. In this way, it is our intention to outline the most pertinent and relevant reactions of RNS, as they apply to a diverse array of pathophysiological states. Since reactions of RNS in vivo are likely to be vast and complex, our aim in this review is threefold: (i) address the major sources and reactions of .NO-derived RNS in biological systems, (ii) describe current knowledge regarding the functional consequences underlying .NO-dependent covalent modification of specific biomolecules, and (iii) to summarise and critically evaluate the available evidence implicating these reactions in human pathology. To this end, three areas of special interest have been chosen for detailed description, namely, formation and role of S-nitrosothiols, modulation of lipid oxidation/nitration by RNS, and tyrosine nitration mechanisms and consequences.

Redox control of vascular smooth muscle proliferation

Recent evidence suggests a role for reactive oxygen species in the control of vascular smooth muscle proliferation both in vitro and in vivo. Oxidative stress increases cell proliferation, mediates hormone-induced hypertrophy, and-under some circumstances-induces apoptosis. Smooth muscle cells contain a reduced nicotinamide adenine dinucleotide/reduced nicotinamide adenine dinucleotide phosphate oxidase that is responsible for the majority of the superoxide produced by the vessel wall. This enzyme has been characterized biochemically, but only limited information is available regarding its molecular structure. High levels of oxidative stress are apparently involved in the pathogenesis of vascular diseases such as hypertension and atherosclerosis, along with abnormal vascular growth after balloon injury. Thus the pathways responsible for oxidative stress, as well as the antioxidant defenses in the vessel wall, may provide novel therapeutic targets.

Extracellular and intracellular arachidonic acid-induced contractions in rat aorta

Arachidonic acid induced contractions of de-endothelized rat aortic rings. A more potent effect was obtained after intracellular administration of arachidonic acid using liposomes. Contractions induced by extracellular arachidonic acid were inhibited similarly to phenylephrine-induced contractions by the L-type Ca2+ channel blocker, methoxyverapamil (D600), and the calmodulin inhibitor, calmidazolium. In contrast, contractions induced by arachidonic acid-filled liposomes were not affected by these compounds. Indomethacin did not affect the contractions induced by either extra- or intracellular arachidonic acid, whereas nordihydroguaiaretic acid relaxed contractions induced by extracellular arachidonic acid but not those induced by arachidonic acid-filled liposomes. Apart from a relaxing effect on contractions induced by extracellular arachidonic acid or by phenylephrine, protein kinase C inhibition with 1-(5-isoquinolinesulphonyl-2-methylpiperazine (H7)) had an even more prominent relaxing effect on contractions induced by arachidonic acid-filled liposomes. Therefore, arachidonic acid exerts a contractile effect on rat aorta, and this effect is regulated differently depending on the site of application.

Oxygen radicals and signaling

Recent evidence suggests that reactive oxygen species, such as superoxide anions and hydrogen peroxide, function as intracellular second messengers. This review will discuss the progress in understanding the intracellular pathways leading from ligand stimulation to the generation of oxidants, as well as some of the increasing number of cellular processes that appear to be subject to redox regulation.

Tumour necrosis factor alpha activates a p22phox-based NADH oxidase in vascular smooth muscle

Increasing experimental evidence suggests that non-phagocytic cells express a potent superoxide (O2-.)-producing NADH oxidase that might be related to the phagocytic NADPH oxidase. Here we show that the cytokine tumour necrosis factor alpha (TNF-alpha) activates, in a time- and dose-dependent manner, a O2-.-producing NADH oxidase in cultured rat aortic smooth-muscle cells. Dose-response experiments for NADH showed an upward shift of the curve for TNF-alpha-treated cells, suggesting that TNF-alpha increased the amount of available enzyme. Using the anti-sense transfection technique, we further demonstrate that the molecular identity of this oxidase includes p22(phox) (the alpha subunit of cytochrome b558 and part of the electron transfer component of the phagocytic NADPH oxidase), which we recently cloned from a rat vascular smooth-muscle cell cDNA library. In addition, prolonged treatment with TNF-alpha increased p22phox mRNA expression without affecting p22phox mRNA stability, and only when transcriptional activity was intact. These findings identify a p22phox-containing NADH oxidase as a source for cytokine-induced free radical production in vascular smooth-muscle cells and clarify some of the mechanisms involved in the regulation of vascular oxidase activity.

G protein-coupled receptor kinase 5 in cultured vascular smooth muscle cells and rat aorta. Regulation by angiotensin II and hypertension

GRK5, a recently cloned member of the G protein-coupled receptor kinase family, has been shown to phosphorylate and participate in the desensitization of angiotensin II (Ang II) type 1A (AT1A) receptors. In this study, the effect of angiotensin II on GRK5 expression was examined in cultured vascular smooth muscle cells and aortas of Ang II-infused hypertensive rats. In vascular smooth muscle cells, Ang II (100 nM) up-regulated GRK5 mRNA as early as 1 h, with a peak at 16 h. This up-regulation was dose- and calcium-dependent. The increase in GRK5 mRNA was reflected in a smaller increase in protein expression, which nonetheless had functional significance since AT1 receptor phosphorylation was increased and phospholipase C activation was decreased following prolonged incubation with Ang II. In aortas of Ang II-infused hypertensive rats, both GRK5 mRNA and protein levels increased approximately 3-fold compared with sham-operated rats at 5 and 7 days, respectively. This up-regulation was blocked either by losartan or by the nonspecific vasodilator hydralazine. Since a subpressor dose of Ang II did not increase GRK5 mRNA levels and norepinephrine infusion also increased GRK5 mRNA expression, we conclude that Ang II-induced GRK5 up-regulation in rat aortas may be due to hypertension per se. Hormone- and hemodynamic stress-induced GRK5 regulation may provide a novel molecular basis for long-term regulation of agonist sensitivity of vascular cells.

Angiotensin receptor antagonists delay nitric oxide-deficient stroke in stroke-prone rats

We investigated whether chronic deficiency of nitric oxide (NO) in stroke-prone spontaneously hypertensive rats (SHRSP) precipitates stroke and whether exogenous nitrates and other pharmacological agents can prevent stroke. Groups of five-week-old male SHRSP rats chronically received saline, L-nitro-arginine methyl ester (L-NAME) in saline, L-NAME along with pharmacological agents (L-arginine, isosorbide dinitrate, enalapril maleate and L-158,809; angiotensin receptor antagonist; 5,7-dimethyl-2-ethyl-3(-)[[2'-(1H-tetrazol-5-yl)biphenyl-4-yl]meth yl]-imidazo[4,5-b]pyridine) in saline to drink. The development of visible neurological deficits following various treatments was considered as an occurrence of stroke. Within hours following onset of stroke, the rats were anesthetized, catheterized and attached to a Cardiomax blood pressure recorder. SHRSP treated with L-NAME (10+/-2 mg/day) developed stroke in 11+/-2 days while no neurological deficit was seen in animals receiving saline till the end of the study period (35 days). Blockade of the renin-angiotensin system with enalapril or L-158,809 significantly delayed the onset of stroke (19+/-2 and 20+/-2 days, respectively), but caused only slight reductions in mean arterial blood pressure. These results suggest that chronic inhibition of NO synthase in SHRSP is associated with the development of stroke and such stroke appears to be renin-angiotensin system-dependent.