Angiotensin II induces a rapid and transient increase of reactive oxygen species

Angiotensin II-Induced Signal Transduction Mechanisms for Cardiac Hypertrophy

Although acute exposure of the heart to angiotensin (Ang II) produces physiological cardiac hypertrophy and chronic exposure results in pathological hypertrophy, the signal transduction mechanisms for these effects are of complex nature. It is now evident that the hypertrophic response is mediated by the activation of Ang type 1 receptors (AT₁R), whereas the activation of Ang type 2 receptors (AT₂R) by Ang II and Mas receptors by Ang-(1-7) exerts antihypertrophic effects. Furthermore, AT₁R-induced activation of phospholipase C for stimulating protein kinase C, influx of Ca²⁺ through sarcolemmal Ca²⁺- channels, release of Ca²⁺ from the sarcoplasmic reticulum, and activation of sarcolemmal NADPH oxidase 2 for altering cardiomyocytes redox status may be involved in physiological hypertrophy. On the other hand, reduction in the expression of AT₂R and Mas receptors, the release of growth factors from fibroblasts for the occurrence of fibrosis, and the development of oxidative stress due to activation of mitochondria NADPH oxidase 4 as well as the depression of nuclear factor erythroid-2 activity for the occurrence of Ca²⁺-overload and activation of calcineurin may be involved in inducing pathological cardiac hypertrophy. These observations support the view that inhibition of AT₁R or activation of AT₂R and Mas receptors as well as depression of oxidative stress may prevent or reverse the Ang II-induced cardiac hypertrophy.

Evaluation of Antioxidant Therapeutic Value of ACE Inhibitor as Adjunct Therapy on Type 2 Diabetes Mellitus Patients with Cardiovascular Disease

Diabetes mellitus (DM) is believed to promote oxidative stress, which potentially provokes and accelerates complications in conditions such as atherosclerotic cardiovascular, peripheral arterial, and cerebrovascular diseases. In this study, we evaluated the antioxidant therapeutic value of adding an angiotensin-converting enzyme (ACE) inhibitor-a low dose of captopril-as adjunct therapy to the treatment regimen of Type 2 diabetes mellitus (T2DM). Participants were distributed among two different groups: control and treated. T2DM patients in the treated group (group 2) were given a supplement of the ACE inhibitor capotopril, 12.5 mg/day, in addition to standard treatment. All subjects were interviewed for clinical examination. All patients in group 2 were re-examined monthly for 3 months to evaluate FBS, HbA1c, MDA, total GSH, reduced GSH, GSSG, and ox-LDL. All parameters were repeated for patients in group 2 after 1 and 3 months. The study showed improvements in the glycemic and oxidative stress status with the addition of a low dose of captopril-not very prominent but statistically significant. Reduced GSH decreased by 73.6% (P = 0.016) and the TBARS level was decreased by 58.3% (P = 0.018) after 3 months of treatment, while ox-LDL was decreased by 26.4% (P = 0.036) at the end of treatment. In summary, the clinical improvements in the disease indices toward normal levels make the use of low doses of ACE inhibitors as adjunct therapy in T2DM worth pursuing. Thus, investigations directed at preventing or protecting against oxidative damage may open a new window for treatment of diabetes mellitus.

Association of Higher Advanced Oxidation Protein Products (AOPPs) Levels in Patients with Diabetic and Hypertensive Nephropathy

Background and Objectives: Diabetes mellitus (DM) and hypertension (HT) are characterized by cell damage caused by inflammatory and metabolic mechanisms induced by alteration in reduction-oxidative status. Serum advanced oxidation protein products (AOPP) are new markers of protein damage induced by oxidative stress. We evaluated serum levels of AOPP in a cohort of patients with DM and HT, with or without renal complications, compared with a control healthy population. Materials and Methods: The study group comprised of 62 patients with type 2 DM and 56 with HT. The 62 patients affected by DM were further distinguished in 24 subjects without renal impairment, 18 with diabetic nephropathy (DN), 20 with chronic kidney disease (CKD) stage 2–3 secondary to DN. The subgroup of 56 patients with primary HT comprised 26 subjects without renal complications and 30 with CKD (stage 2–3) secondary to HT. Thirty healthy controls, matched for age and sex, were recruited among blood donors. Results: Increased AOPP levels were found in DM patients compared with healthy subjects, although not significantly. This index was higher and more significant in patients with DN and CKD secondary to DN than in DM patients without nephropathy (p < 0.05) or controls (p < 0.0001). Patients with HT and with kidney impairment secondary to HT also had significantly higher AOPP serum levels than controls (p < 0.01 and p < 0.0001, respectively). There were no significant differences in mean AOPP levels among DM and HT patients. Conclusion: Our study showed that oxidative stress was higher in diabetic or hypertensive subjects than in healthy controls and, in particular, it appeared to be more severe in patients with renal complications. We suggest that the assessment of AOPP in diabetic and hypertensive patients may be important to predict the onset of renal failure and to open a new perspective on the adoption of antioxidant molecules to prevent CKD in those settings.

Bang-bang model for regulation of local blood flow

The classical model of metabolic regulation of blood flow in muscle tissue implies the maintenance of basal tone in arterioles of resting muscle and their dilation in response to exercise and/or tissue hypoxia via the evoked production of vasodilator metabolites by myocytes. A century-long effort to identify specific metabolites responsible for explaining active and reactive hyperemia has not been successful. Furthermore, the metabolic theory is not compatible with new knowledge on the role of physiological radicals (e.g., nitric oxide, NO, and superoxide anion, O2 (-) ) in the regulation of microvascular tone. We propose a model of regulation in which muscle contraction and active hyperemia are considered the physiologically normal state. We employ the "bang-bang" or "on/off" regulatory model which makes use of a threshold and hysteresis; a float valve to control the water level in a tank is a common example of this type of regulation. Active bang-bang regulation comes into effect when the supply of oxygen and glucose exceeds the demand, leading to activation of membrane NADPH oxidase, release of O2 (-) into the interstitial space and subsequent neutralization of the interstitial NO. Switching arterioles on/off when local blood flow crosses the threshold is realized by a local cell circuit with the properties of a bang-bang controller, determined by its threshold, hysteresis, and dead-band. This model provides a clear and unambiguous interpretation of the mechanism to balance tissue demand with a sufficient supply of nutrients and oxygen.

NADPH oxidase-derived H(2)O(2) contributes to angiotensin II-induced aldosterone synthesis in human and rat adrenal cortical cells

BACKGROUND

The Renin-Angiotensin-Aldosterone-System plays a pivotal role in hypertension. Angiotensin II (Ang II) is a major regulator of aldosterone synthesis and secretion, and it is known to facilitate reactive oxygen species (ROS) generation in many cell types.

AIMS

Here, we assessed the role of ROS signaling in Ang II-induced aldosterone synthesis by focusing on the regulation of aldosterone synthase (CYP11B2), a cytochrome P450 oxidase that catalyzes the final step in aldosterone biosynthetic pathway.

RESULTS

Ang II increased CYP11B2 activity, mRNA and protein with a concomitant elevation of 6-Carboxy- 2',7'-dichlorodihydrofluorescein diacetate fluorescence, malondialdehyde and protein carbonyl levels (indices of ROS), NADPH oxidase (Nox) activity, and H(2)O(2) levels in human and rat adrenal cortical cells. The expression of nuclear receptor related 1 protein, a transcription factor known to regulate CYP11B2 expression, was also augmented by Ang II. These Ang II-evoked effects were either abolished or attenuated by pretreatment of cells with either Ang II type I receptor (AT(1)R) antagonist, or antioxidants or Nox inhibitor or siRNA silencing of Nox1, 2 and 4, or inhibitors of phospholipase C and protein kinase C. Exogenous H(2)O(2) mimicked the facilitatory effects of Ang II on CYP11B2 activity, mRNA, and protein expression, and these changes were significantly reduced by PEG-catalase.

INNOVATION

ROS, particularly H(2)O(2), is identified as a key regulator of aldosterone production.

CONCLUSION

Our results suggest that Ang II facilitates CYP11B2 activity and the ensuing aldosterone production via activation of AT(1)R-Nox-H(2)O(2) signaling pathway.

NADPH oxidases and angiotensin II receptor signaling

Over the last decade many studies have demonstrated the importance of reactive oxygen species (ROS) production by NADPH oxidases in angiotensin II (Ang II) signaling, as well as a role for ROS in the development of different diseases in which Ang II is a central component. In this review, we summarize the mechanism of activation of NADPH oxidases by Ang II and describe the molecular targets of ROS in Ang II signaling in the vasculature, kidney and brain. We also discuss the effects of genetic manipulation of NADPH oxidase function on the physiology and pathophysiology of the renin-angiotensin system.

Central estrogen inhibition of angiotensin II-induced hypertension in male mice and the role of reactive oxygen species

It has been shown that reactive oxygen species (ROS) contribute to the central effect of ANG II on blood pressure (BP). Recent studies have implicated an antihypertensive action of estrogen in ANG II-infused female mice. The present study used in vivo telemetry recording and in vitro living mouse brain slices to test the hypothesis that the central activation of estrogen receptors in male mice inhibits ANG II-induced hypertension via the modulation of the central ROS production. In male wild-type mice, the systemic infusion of ANG II induced a significant increase in BP (Delta30.1 +/- 2.5 mmHg). Either central infusion of Tempol or 17beta-estradiol (E2) attenuated the pressor effect of ANG II (Delta10.9 +/- 2.3 and Delta4.5 +/- 1.4 mmHg), and the protective effect of E2 was prevented by the coadministration of an estrogen receptor, antagonist ICI-182780 (Delta23.6 +/- 3.1 mmHg). Moreover, the ganglionic blockade on day 7 after the start of ANG II infusions resulted in a smaller reduction of BP in central Tempol- and in central E2-treated males, suggesting that estrogen inhibits the central ANG II-induced increases in sympathetic outflow. In subfornical organ slices, the application of ANG II resulted in a 21.5 +/- 2.5% increase in ROS production. The coadministration of irbesartan, an ANG II type 1 receptor antagonist, or the preincubation of brain slices with Tempol blocked ANG II-induced increases in ROS production (-1.8 +/- 1.6% and -1.0 +/- 1.8%). The ROS response to ANG II was also blocked by E2 (-3.2 +/- 2.4%). The results suggest that the central actions of E2 are involved in the protection from ANG II-induced hypertension and that estrogen modulation of the ANG II-induced effects may involve interactions with ROS production.

Signaling mechanisms of angiotensin II-induced attenuation of GABAergic input to hypothalamic presympathetic neurons

The hypothalamic paraventricular nucleus (PVN) is an important site for the regulation of sympathetic outflow. Angiotensin II (Ang II) can activate AT(1) receptors to stimulate PVN presympathetic neurons through inhibition of GABAergic input. However, little is known about the downstream pathway involved in this presynaptic action of Ang II in the PVN. In this study, using whole cell recording from retrogradely labeled PVN neurons in rat brain slices, we determined the signaling mechanisms responsible for the effect of Ang II on synaptic GABA release to spinally projecting PVN neurons. Bath application of Ang II reproducibly decreased the frequency of GABAergic miniature postsynaptic inhibitory currents (mIPSCs) in fluorescence-labeled PVN neurons. Ang II failed to change the frequency of mIPSCs in labeled PVN neurons treated with pertussis toxin. However, Ang II-induced inhibition of mIPSCs persisted in the presence of either CdCl(2), a voltage-gated Ca(2+) channel blocker, or 4-aminopyridine, a blocker of voltage-gated K(+) channels. Interestingly, inhibition of superoxide with superoxide dismutase or Mn(III) tetrakis (4-benzoic acid) prophyrin completely blocked Ang II-induced decrease in mIPSCs. By contrast, inhibition of hydroxyl radical formation with the ion chelator deferoxamine did not significantly alter the effect of Ang II. These findings suggest that the presynaptic action of Ang II on synaptic GABA release in the PVN is mediated by the pertussis toxin-sensitive G(i/o) proteins but not by voltage-gated Ca(2+) and K(+) channels. Ang II attenuates GABAergic input to PVN presympathetic neurons through reactive oxygen species, especially superoxide anions.

Superoxide mediates acute renal vasoconstriction produced by angiotensin II and catecholamines by a mechanism independent of nitric oxide

NAD(P)H oxidases (NOX) and reactive oxygen species (ROS) are involved in vasoconstriction and vascular remodeling during hypertension produced by chronic angiotensin II (ANG II) infusion. These effects are thought to be mediated largely through superoxide anion (O2−) scavenging of nitric oxide (NO). Little is known about the role of ROS in acute vasoconstrictor responses to agonists. We investigated renal blood flow (RBF) reactivity to ANG II (4 ng), norepinephrine (NE, 20 ng), and α1-adrenergic agonist phenylephrine (PE, 200 ng) injected into the renal artery (ira) of anesthetized Sprague-Dawley rats. The NOX inhibitor apocynin (1–4 mg·kg−1·min−1 ira, 2 min) or the superoxide dismutase mimetic Tempol (1.5–5 mg·kg−1·min−1 ira, 2 min) rapidly increased resting RBF by 8 ± 1% ( P < 0.001) or 3 ± 1% ( P < 0.05), respectively. During NO synthase (NOS) inhibition ( Nω-nitro-l-arginine methyl ester, 25 mg/kg iv), the vasodilation tended to increase (apocynin 13 ± 4%, Tempol 10 ± 1%). During control conditions, both ANG II and NE reduced RBF by 24 ± 4%. Apocynin dose dependently reduced the constriction by up to 44% ( P < 0.05). Similarly, Tempol blocked the acute actions of ANG II and NE by up to 48–49% ( P < 0.05). In other animals, apocynin (4 mg·kg−1·min−1 ira) attenuated vasoconstriction to ANG II, NE, and PE by 46–62% ( P < 0.01). During NOS inhibition, apocynin reduced the reactivity to ANG II and NE by 60–72% ( P < 0.01), and Tempol reduced it by 58–66% ( P < 0.001). We conclude that NOX-derived ROS substantially contribute to basal RBF as well as to signaling of acute renal vasoconstrictor responses to ANG II, NE, and PE in normal rats. These effects are due to O2− rather than H2O2, occur rapidly, and are independent of scavenging of NO.

Angiotensin II induces interleukin-6 in humans through a mineralocorticoid receptor-dependent mechanism

This study tested the hypothesis that angiotensin promotes oxidative stress and inflammation in humans via aldosterone and the mineralocorticoid receptor. We measured the effect of intravenous aldosterone (0.7 mug/kg per hour for 10 hours followed by 0.9 mug/kg per hour for 4 hours) and vehicle in a randomized, double-blind crossover study in 11 sodium-restricted normotensive subjects. Aldosterone increased interleukin (IL)-6 (from 4.7+/-4.9 to 9.4+/-7.1 pg/mL; F=4.94; P=0.04) but did not affect blood pressure, serum potassium, or high-sensitivity C-reactive protein. We next conducted a randomized, double-blind, placebo-controlled, crossover study to measure the effect of 3-hour infusion of angiotensin II (2 ng/kg per minute) and norepinephrine (30 ng/kg per minute) on separate days after 2 weeks of placebo or spironolactone (50 mg per day) in 14 salt-replete normotensive subjects. Angiotensin II increased blood pressure (increase in systolic pressure: 13.7+/-7.5 and 15.2+/-9.4 mm Hg during placebo and spironolactone, respectively; P<0.001 for angiotensin II) and decreased renal plasma flow (-202+/-73 and -167+/-112 mL/min/1.73 kg/m(2); P<0.001 for angiotensin II effect) similarly during placebo and spironolactone. Spironolactone enhanced the aldosterone response to angiotensin II (increase of 17.0+/-10.6 versus 9.0+/-5.7 ng/dL; P=0.002). Angiotensin II transiently increased free plasma F(2)-isoprostanes similarly during placebo and spironolactone. Angiotensin II increased serum IL-6 concentrations during placebo (from 1.8+/-1.1 to 2.4+/-1.4 pg/mL; F=4.5; P=0.04) but spironolactone prevented this effect (F=6.4; P=0.03 for spironolactone effect). Norepinephrine increased blood pressure and F(2)-isoprostanes but not aldosterone or IL-6. Aldosterone increases IL-6 in humans. These data suggest that angiotensin II induces IL-6 through a mineralocorticoid receptor-dependent mechanism in humans. In contrast, angiotensin II-induced oxidative stress, as measured by F(2)-isoprostanes, is mineralocorticoid receptor independent and may be pressor dependent.

NO-independent mechanism mediates tempol-induced renal vasodilation in SHR

We investigated whether tempol, a superoxide dismutase mimetic, affected renal hemodynamics and arterial pressure in spontaneously hypertensive rats (SHR) and Sprague-Dawley (SD) rats. We also examined whether tempol affected exaggerated renal vasoconstrictor responses to ANG II in SHR. To test whether the effects of tempol were due to a restored NO system, we used the NOS inhibitor Nw-nitro-l-arginine methyl ester (l-NAME). Renal blood flow (RBF) and mean arterial pressure (MAP) were measured in vivo by electromagnetic flowmetry and arterial catheterization in 10- to 12-wk-old anesthetized SHR and SD rats. Systolic arterial pressure (SAP) was measured in conscious rats using the tail cuff method. Tempol (1 mM) was given in the drinking water to SD (SD-T) and SHR (SHR-T) for 5–7 days for RBF measurements and for 15 days for SAP measurements. Age-matched SD (SD-C) and SHR (SHR-C) were used as controls. ANG II (1–4 ng) was administered as a bolus via a renal artery catheter. l-NAME was administered intravenously for 15–20 min. Renal vascular resistance (RVR) was elevated in SHR-C compared with SD-C. In SHR-T, baseline RVR was not different from SD-C and SD-T rats. Tempol had no effect on RVR in SD. l-NAME elevated RVR to the same extent in all four groups. Arterial pressure was not affected by tempol. The RVR responses to ANG II were higher in SHR-C than in the SD-C group. ANG II responses were not different between SHR-T and SD-T. Overall, tempol reduced the renovascular responses to ANG II in SHR. l-NAME elevated the effects of ANG II in SD-C rats but had no effect on the ANG II responses in the other groups. Thus l-NAME treatment did not influence tempol’s effects on baseline RVR or ANG II responses. We conclude that in SHR, tempol has a significant renal vasodilator effect and that it normalizes the increased renovascular ANG II sensitivity. As the effects of l-NAME are not greater in SHR-T rats, it is not likely that the elevated renal resistance and ANG II sensitivity in SHR are due to reactive oxygen species-induced quenching of nitric oxide.

Differential modulation of MAP kinases by zinc deficiency in IMR-32 cells: role of H(2)O(2)

The influence of zinc deficiency on the modulation of the mitogen-activated protein kinases (MAPKs) extracellular signal-regulated kinase (ERK1/2), p38, and c-Jun N-terminal kinase (JNK) was studied. Using human IMR-32 cells as a model of neuronal cells, the role of oxidants on MAPKs and activator protein-1 (AP-1) activation in zinc deficiency was investigated, characterizing the participation of these events in the triggering of apoptosis. Relative to controls, cells incubated in media with low zinc concentrations showed increased cell oxidants and hydrogen peroxide (H(2)O(2)) release, increased JNK and p38 activation, high nuclear AP-1-DNA binding activity, and AP-1-dependent gene expression. Catalase addition to the media prevented the increase of cellular oxidants and inhibited JNK, p38, and AP-1 activation. Low levels of ERK1/2 phosphorylation were observed in the zinc-deficient cells in association with a reduction in cell proliferation. Catalase treatment did not prevent the above events nor the increased rate of apoptosis in the zinc-deficient cells. It is first demonstrated that a decrease in cellular zinc triggers H(2)O(2)-independent, as well as H(2)O(2)-dependent effects on MAPKs. Zinc deficiency-induced increases in cellular H(2)O(2) can trigger the activation of JNK and p38, leading to AP-1 activation, events that are not involved in zinc deficiency-induced apoptosis.

Angiotensin II, reactive oxygen species, and Ca2+signaling in afferent arterioles

In afferent arteriolar vascular smooth muscle cells, ANG II induces a rise in cytosolic Ca2+([Ca2+]i) via inositol trisphosphate receptor (IP3R) stimulation and by activation of the adenine diphosphate ribose (ADPR) cyclase to form cyclic ADPR, which sensitizes the ryanodine receptor (RyR) to Ca2+. We hypothesize that ANG II stimulation of NAD(P)H oxidases leads to the formation of superoxide anion (O2−·), which, in turn, activates ADPR cyclase. Afferent arterioles were isolated from rat kidney with the magnetized microsphere and sieving technique and loaded with fura-2 to measure [Ca2+]i. ANG II rapidly increased [Ca2+]iby 124 ± 12 nM. In the presence of apocynin, a specific inhibitor of NAD(P)H oxidase assembly, the [Ca2+]iresponse was reduced to 35 ± 5 nM ( P < 0.01). Tempol, a superoxide dismutase mimetic, did not alter the [Ca2+]iresponse to ANG II at a concentration of 10−4M (99 ± 12 nM), but 10−3M tempol reduced the response to 32 ± 3 nM ( P < 0.01). The addition of nicotinamide, an inhibitor of ADPR cyclase, to apocynin or tempol (10−3M) resulted in no further inhibition. Measurement of superoxide production with the fluorescent probe tempo 9-AC showed that ANG II caused an increase of 48 ± 20 arbitrary units; apocynin or diphenyl iodonium (an inhibitor of flavoprotein oxidases) inhibited the response by 94%. Hydrogen peroxide (H2O2) was studied at physiological (10−7M) and higher concentrations. In the presence of H2O2(10−7M), neither baseline [Ca2+]inor the response to ANG II was altered (125 ± 15 nM), whereas H2O2(10−6and 10−5M) inhibited the [Ca2+]iresponse to ANG II by 35 and 46%, respectively. We conclude that ANG II rapidly activates NAD(P)H oxidases of afferent arterioles, leading to the formation of O2−·, which then stimulates ADPR cyclase to form cADPR. cADPR, by sensitizing the RyR to Ca2+, augments the Ca2+response (calcium-induced calcium release) initiated by activation of the IP3R.

Dual pathways for nuclear factor kappaB activation by angiotensin II in vascular smooth muscle: phosphorylation of p65 by IkappaB kinase and ribosomal kinase

Activation of nuclear factor (NF)-kappaB by angiotensin II (Ang II) plays an essential role in stimulating expression of vascular adhesion molecules, which are essential for vascular inflammation. We report that Ang II activates NF-kappaB by phosphorylating its p65 subunit via a pathway mediated partially by ribosomal S6 kinase (RSK). In investigating other pathway(s) that may be involved, we found that the ability of Ang II to activate NF-kappaB in mouse embryonic fibroblast is suppressed (approximately 70%) either by deletion of IkappaB Kinase (IKK) or by inhibiting or knocking down IKK in vascular smooth muscle cells using a dominant-negative IKK adenovirus or small interference RNA to IKKbeta. Thus, Ang II also stimulates NF-kappaB via IKK. In vitro, we found that Ang II stimulates IKK to phosphorylate myelin basic protein and the p65 subunit of NF-kappaB. The mechanism by which Ang II activates IKK is to increase phosphorylation of IKKbeta in its activation loop (Ser181) rather than IkappaB phosphorylation. Inhibiting both the RSK and IKK pathways completely blocks the Ang II-induced p65 phosphorylation and NF-kappaB activation. These 2 pathways are independent: inhibiting IKK does not block Ang II-induced phosphorylation of RSK, whereas inhibiting mitogen-activated protein kinase 1 does not affect phosphorylation of IKK. Finally, we found that Ang II can induce expression of vascular adhesion molecules by 2 pathways; both IKK and RSK lead to phosphorylation of the p65 subunit of NF-kappaB to increase vascular cell adhesion molecule-1 transcription. The 2 pathways are functionally important because inhibiting IKK and RSK in vascular smooth muscle cells blocks Ang II-induced expression of vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 to limit vascular inflammation.

Reactive oxygen species in paraventricular nucleus modulates cardiac sympathetic afferent reflex in rats

Our previous studies showed that angiotensin II (Ang II) in the paraventricular nucleus (PVN) potentiated the cardiac sympathetic afferent reflex (CSAR) in rats. This study investigated whether the reactive oxygen species (ROS) in the PVN modulated the CSAR and contributed to the effect of Ang II on the CSAR in rats. Under alpha-chloralose and urethane anesthesia, renal sympathetic nerve activity (RSNA), mean arterial pressure (MAP) and heart rate were recorded in sinoaortic-denervated and cervical-vagotomized rats. The CSAR was evaluated by the RSNA response to epicardial application of bradykinin (0.04 and 0.4 microCompared with microinjection of saline into the PVN, superoxide anion scavenger, either tempol (20 nmol) or tiron (10 nmol), significantly decreased the CSAR (P < 0.05). Conversely, superoxide dismutase (SOD) inhibitor diethyldithio-carbamic acid (DETC, 10 nmol) potentiated the CSAR (P < 0.05). Microinjection of Ang II (0.3 nmol) into the PVN resulted in an enhanced CSAR (P < 0.05). The effect of Ang II on the CSAR was completely inhibited by pretreatment with either tempol or tiron (P < 0.05) but was not affected by DETC. On the other hand, either tempol or tiron decreased the RSNA (P < 0.05), but DETC increased the RSNA (P < 0.05). Ang II increased the RSNA (P < 0.05) and MAP (P < 0.05). The effect of Ang II on the RSNA and MAP was abolished by pretreatment with either tempol or tiron but was not affected by DETC. These results indicated that the ROS in the PVN modulated the CSAR and contributed to the effect of Ang II in the PVN on the CSAR.

Long-term blood pressure control prevents oxidative renal injury

Arterial hypertension is a leading contributor to the progression of chronic renal disease. Short-term studies had addressed the role of oxidative stress in hypertensive nephropathy. We have now studied oxidative stress and caspase activation in a long-term model of hypertensive renal injury. Nontreated spontaneously hypertensive rats with uninephrectomy displayed severe arterial hypertension over a 36-week follow-up. Uncontrolled high blood pressure in the context of modest renal mass reduction resulted in significant histological renal injury. Blood pressure control by the angiotensin-converting enzyme (ACE) inhibitor, quinapril, or the AT1 receptor antagonist, losartan, decreased the degree of renal injury. Hypertensive renal injury was associated with evidence of activation of the apoptotic pathway (increased activation of caspase-3) and local renal (increased staining for 4-hydroxy-2-nonenal) and systemic [increased serum levels of 8-iso-prostaglandin F2alpha (8-iso-PGF2alpha)] lipid oxidation when compared with normotensive control rats. In addition, severe hypertension decreased the renal antioxidant defenses, as exemplified by decreased expression of Cu/Zn superoxide dismutase. Treatment with quinapril or losartan decreased caspase-3 activation, 4-hydroxy-2-nonenal staining, and 8-iso-PGF2alpha levels and increased Cu/Zn superoxide dismutase expression. These results suggest that hypertension-associated oxidative stress and its consequences may be decreased by either ACE inhibition or AT1 receptor antagonist, emphasizing the role of angiotensin II in hypertensive renal damage.

Inhibition of geranylgeranyltransferase I decreases generation of vascular reactive oxygen species and increases vascular nitric oxide production

BACKGROUND

Vascular injury with endothelial dysfunction results in an imbalance between the production of vasoprotective molecules such as nitric oxide (NO) and deleterious reactive oxygen species (ROS). The purpose of this work was to test the hypothesis that inhibition of geranylgeranyltransferase I (GG Tase I) reduces vascular injury by increasing vascular NO production while decreasing ROS generation.

METHODS AND RESULTS

GGTI-298 decreased the formation of intimal hyperplasia at 14 days following balloon injury. GGTI-298 (10 microm) inhibited activation of RhoA and Rac1 as well as inhibited SMC proliferation. GGTI increased SMC-inducible NO synthase (iNOS) levels and NO production in vitro. Additionally, the activation of NAD(P)H oxidase subunits was decreased by GGTI in vitro. This correlated with a decrease in TNF-alpha- or angiotensin-II-induced ROS production assayed by DCF fluorescence. In vivo, GGTI treatment increased endothelial NOS (eNOS) expression in uninjured arteries and iNOS expression in balloon-injured arteries. Furthermore, GGTI treatment attenuated balloon-injury-induced superoxide generation assayed by MCLA luminescence.

CONCLUSIONS

GGTI decreases the production of ROS and increases the production of NO both in vitro and in vivo. These effects may be mediated via the inhibition of activation of the small GTPases Rac1 and RhoA. Pharmacological inhibition of GGTase I may prove to be a useful clinical adjunct in the treatment of cardiovascular diseases.

Protection from angiotensin II-mediated vasculotoxic and hypertensive response in mice lacking PI3Kgamma

Hypertension affects nearly 20% of the population in Western countries and strongly increases the risk for cardiovascular diseases. In the pathogenesis of hypertension, the vasoactive peptide of the renin-angiotensin system, angiotensin II and its G protein–coupled receptors (GPCRs), play a crucial role by eliciting reactive oxygen species (ROS) and mediating vessel contractility. Here we show that mice lacking the GPCR-activated phosphoinositide 3-kinase (PI3K)γ are protected from hypertension that is induced by administration of angiotensin II in vivo. PI3Kγ was found to play a role in angiotensin II–evoked smooth muscle contraction in two crucial, distinct signaling pathways. In response to angiotensin II, PI3Kγ was required for the activation of Rac and the subsequent triggering of ROS production. Conversely, PI3Kγ was necessary to activate protein kinase B/Akt, which, in turn, enhanced L-type Ca²⁺ channel–mediated extracellular Ca²⁺ entry. These data indicate that PI3Kγ is a key transducer of the intracellular signals that are evoked by angiotensin II and suggest that blocking PI3Kγ function might be exploited to improve therapeutic intervention on hypertension.

Endothelin-1, superoxide and adeninediphosphate ribose cyclase in shark vascular smooth muscle

In vascular smooth muscle (VSM) of Squalus acanthias, endothelin-1(ET-1) signals via the ETB receptor. In both shark and mammalian VSM, ET-1 induces a rise in cytosolic Ca2+ concentration([Ca2+]i) via activation of the inositol trisphosphate (IP3) receptor (IP3R) and subsequent release of Ca2+ from the sarcoplasmic reticulum (SR). IP3R-mediated release of SR Ca2+ causes calcium-induced calcium release (CICR) via the ryanodine receptor (RyR), which can be sensitized by cyclic adeninediphosphate ribose (cADPR). cADPR is synthesized from NAD+ by a membrane-bound bifunctional enzyme, ADPR cyclase. We have previously shown that the antagonists of the RyR, Ruthenium Red, high concentrations of ryanodine and 8-Br cADPR, diminish the[Ca2+]i response to ET-1 in shark VSM. To investigate how ET-1 might influence the activity of the ADPR cyclase, we employed inhibitors of the cyclase. To explore the possibility that ET-1-induced production of superoxide (O2.-) might activate the cyclase, we used an inhibitor of NAD(P)H oxidase (NOX), DPI and a scavenger of O2.-, TEMPOL. Anterior mesenteric artery VSM was loaded with fura-2AM to measure [Ca2+]i. In Ca2+-free shark Ringers, ET-1 increased[Ca2+]i by 104±8 nmol l-1. The VSM ADPR cyclase inhibitors, nicotinamide and Zn2+, diminished the response by 62% and 72%, respectively. Both DPI and TEMPOL reduced the response by 63%. The combination of the IP3R antagonists, 2-APB or TMB-8, with DPI or TEMPOL further reduced the response by 83%. We show for the first time that in shark VSM, inhibition of the ADPR cyclase reduces the[Ca2+]i response to ET-1 and that superoxide may be involved in the activation of the cyclase.

Crosstalk Between Mesangial and Endothelial Cells: Angiotensin II Down-Regulates Endothelin-Converting Enzyme 1

OBJECTIVE

Since mesangial and endothelial cells interact in the kidney, the present experiments were designed to analyze the ability of human mesangial cells (HMC) to modulate endothelin-1 (ET-1) synthesis by human umbilical vein endothelial cells (HuVEC).

METHODS AND RESULTS

The supernatants of HuVEC/HMC contained significantly lower amounts of ET-1 than those of HuVEC alone. This effect was not due to a decreased prepro-ET-1 mRNA expression and was only partially the consequence of HMC-dependent ET-1 degradation. Therefore, we tested the influence of the coculture on endothelin-converting enzyme-1 (ECE-1), and found a significant reduction of its mRNA and protein levels as well as a decreased activity in HuVEC/HMC as compared to HuVEC alone. Using a pharmacological blockade approach (sulotrobam, BN52021, losartan or catalase), losartan was shown to completely abolish down-regulation of ECE-1 observed in HuVEC/HMC. Angiotensin II (AII) induced a dose and time-dependent inhibition of ECE-1 expression in HuVEC.

CONCLUSIONS

These results support the importance of cross-talk among different cell types in the regulation of vascular or renal function. ET-1, and particularly ECE-1, might constitute a target in this regulation. In addition, locally synthesized AII could be one of the mediators involved in the down-regulation of ECE-1.