Angiotensin II AT1 receptor antagonists inhibit platelet adhesion and aggregation by nitric oxide release

This study investigated the process of nitric oxide (NO) release from platelets after stimulation with different angiotensin II type 1 (AT1)-receptor antagonists and its effect on platelet adhesion and aggregation. Angiotensin II AT1-receptor antagonist-stimulated NO release in platelets was compared with that in human umbilical vein endothelial cells by using a highly sensitive porphyrinic microsensor. In vitro and ex vivo effects of angiotensin II AT1-receptor antagonists on platelet adhesion to collagen and thromboxane A2 analog U46619-induced aggregation were evaluated. Losartan, EXP3174, and valsartan alone caused NO release from platelets and endothelial cells in a dose-dependent manner in the range of 0.01 to 100 micro mol/L, which was attenuated by NO synthase inhibitor N(G)-nitro-L-arginine methyl ester. The angiotensin II AT1-receptor antagonists had more than 70% greater potency in NO release in platelets than in endothelial cells. The degree of inhibition of platelet adhesion (collagen-stimulated) and aggregation (U46619-stimulated) elicited by losartan, EXP3174, and valsartan, either in vitro or ex vivo, closely correlated with the NO levels produced by each of these drugs alone. The inhibiting effects of angiotensin II AT1-receptor antagonists on collagen-stimulated adhesion and U46619-stimulated aggregation of platelets were significantly reduced by pretreatment with N(G)-nitro-L-arginine methyl ester. Neither the AT2 receptor antagonist PD123319, the cyclooxygenase synthase inhibitor indomethacin, nor the selective thromboxane A2/prostaglandin H2 receptor antagonist SQ29,548 had any effect on angiotensin II AT1-receptor antagonist-stimulated NO release in platelets and endothelial cells. The presented studies clearly indicate a crucial role of NO in the arterial antithrombotic effects of angiotensin II AT1-receptor antagonists.

S-nitroso human serum albumin treatment reduces ischemia/reperfusion injury in skeletal muscle via nitric oxide release

BACKGROUND

Peroxynitrite generated from nitric oxide (NO) and superoxide (O2-) contributes to ischemia/reperfusion (I/R) injury. Feedback inhibition of endothelial NO synthase by NO may inhibit O2- production generated also by endothelial NO synthase at diminished local L-arginine concentrations accompanying I/R.

METHODS AND RESULTS

During hindlimb I/R (2.5 hours/2 hours), in vivo NO was monitored continuously (porphyrinic sensor), and high-energy phosphates, reduced and oxidized glutathione (chromatography), and I/R injury were measured intermittently. Rabbits receiving human serum albumin (HSA) (controls) were compared with those receiving S-nitroso human serum albumin (S-NO-HSA) beginning 30 minutes before reperfusion for 1 hour or 30 minutes before ischemia for 3.5 hours (0.1 micromol x kg(-1) x h(- 1)). The onset of ischemia led to a rapid increase of NO from its basal level (50+/-12 nmol/L) to 120+/-20 and 220+/-15 nmol/L in the control and S-NO-HSA-treated groups, respectively. In control animals, NO dropped below basal levels at the end of ischemia and to undetectable levels (<1 nmol/L) during reperfusion. In S-NO-HSA-treated animals, maximal NO levels never decreased below basal concentration and on reperfusion were 100+/-15 nmol/L (S-NO-HSA preischemia group, 175+/-15 nmol/L). NO supplementation by S-NO-HSA led to partial and in the preischemia group to total preservation of high-energy phosphates and glutathione status in reperfused muscle (eg, preischemia groups: ATP, 30.23+/-5.02 micromol/g versus control, 15.75+/-4.33 micromol/g, P<0.0005; % oxidized glutathione, 4.49+/- 1.87% versus control, 22.84+/-6.39%, P<0.0001). S-NO-HSA treatment in all groups led to protection from vasoconstriction and reduced edema formation after reperfusion (eg, preischemia groups: interfiber area, 12.94+/-1.36% versus control, 27.83+/-1.95%, P< 0.00001).

CONCLUSIONS

Long-lasting release of NO by S-NO-HSA provides significant protection of skeletal muscle from I/R injury.

Increased nitric oxide bioavailability in endothelial cells contributes to the pleiotropic effect of cerivastatin

BACKGROUND

Although statins preserve endothelial function by reducing serum cholesterol levels, it has been suggested they may also stimulate nitric oxide (NO) synthase in endothelium with concurrent increase in superoxide (O2-) generation, leading to impairment of NO activity. Therefore, measurements of biologically active NO and O2- in endothelium after exposure to the HMG-CoA reductase inhibitor cerivastatin were undertaken to evaluate its potential effect on NO biological activity.

METHODS AND RESULTS

Highly sensitive electrochemical NO and O2- microsensors were placed near the surface of a single human umbilical vein endothelial cell, and the kinetics of NO and O2- release were recorded in vitro. Cerivastatin demonstrated a time-dependent effect on NO release in endothelial cells. The initial release (approximately the first 3 minutes) was concentration-dependent (0.01 to 10 micromol/L) and was similar to that observed for typical NO synthase agonists calcium ionophore or acetylcholine. Cerivastatin stimulated NO release at a favorable rate and scavenged O2-, which led to the preservation of the active concentration of NO. The sustained effect (after approximately 6 hours) of cerivastatin on endothelium was associated with an approximately 35% increase in NO release as compared with the initial effect. In contrast to the initial effect, the sustained effect of cerivastatin was shown at concentrations approximately 100-fold lower and was dependent on inhibition of endothelial HMG-CoA reductase.

CONCLUSIONS

These data provide direct evidence to prove that in the presence of cerivastatin, the NOS system in endothelium operates with high efficiency toward increasing NO activity by activation of NO release and by concurrent inactivation of O2-.

Decreased nitric oxide availability in normotensive and hypertensive rats with failing hearts after myocardial infarction

Endothelial NO synthase, being deficient in arginine and/or tetrahydrobiopterin, produces in addition to NO a significant concentration of superoxide (O2)(-)). We investigated whether such an imbalance between O2(-) and NO production is present in dysfunctional aortas of Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) with failing hearts after myocardial infarction. Heart failure was induced by permanent occlusion of the left coronary artery, resulting in a large infarction of the free left ventricular wall. Eight weeks after myocardial infarction, when WKY and SHR had compensated heart failure and congestive heart failure, respectively, calcium ionophore-induced NO release (assessed by a NO-sensitive microsensor) from aortic endothelial cells was significantly reduced from 478+/-48 to 216+/-16 nmol/L and 693+/-131 to 257+/-53 nmol/L in WKY and SHR, respectively. Concomitantly, significant increases in calcium ionophore-stimulated O2(-) production (assessed by an electrochemical sensor) could be observed in aortic endothelial cells from infarcted WKY rats (22+/-3.2 versus sham, 10.1+/-1.2 nmol/L) and SHR (102+/-8 versus sham, 67+/-5 nmol/L). A dramatic increase in endothelial peroxynitrite concentration (chemiluminescence method) from 35+/-4 to 90+/-3 nmol/L for WKY and from 60+/-5 to 170+/-10 nmol/L for SHR also was detected. Thus, the markedly decreased NO availability probably caused by impaired endothelial NO synthase activity with enhanced O2(-) and peroxynitrite production appears to be attributable to endothelial dysfunction in normotensive rats with chronic heart failure and especially in hypertensive rats with severe congestive heart failure.

Central hypotensive action of clonidine requires nitric oxide

Background- Clonidine has an antihypertensive effect by its action in the brain and, because we observed that the tonic production of nitric oxide (NO) in the brain is required to maintain blood pressure at its low, normotensive level, the current study was designed to determine whether the hypotensive action of clonidine resulted from its stimulation of excess NO in the brain. Methods and Results- Porphyritic microsensors were used to quantify NO concentration in the nucleus tractus solitarius (NTS) in vitro in brain slices and in vivo in the anesthetized rat. In both preparations, the basal production of NO in the NTS was 15+/-3 nmol/L. In vitro stimulation of the NTS with clonidine (50 nmol/L) resulted in an increase in the NO concentration to 84+/-7 nmol/L. In vivo, the intracerebroventricular (ICV) infusion of clonidine (0.03 microgram) caused an increase in NO concentration in the NTS to 128+/-17 nmol/L. This ICV injection of clonidine caused a fall in mean arterial pressure of -22+/-1 mm Hg and a decrease of heart rate of -18+/-2%. The blockade of NO production with N(G)-nitro-L-arginine-methyl ester (2 micromol; delivered ICV, 30 minutes before the clonidine) reduced responses to clonidine for both mean arterial pressure and heart rate (-3+/-1 mm Hg and -2+/-1% change, respectively). Conclusion- The stimulation of the release of NO in the brain by clonidine contributes to its central antihypertensive action.

Nitric oxide as a second messenger in parathyroid hormone-related protein signaling

Parathyroid hormone (PTH)-related protein (PTHrP) is produced in smooth muscles and endothelial cells and is believed to participate in the local regulation of vascular tone. No direct evidence for the activation of endothelium-derived nitric oxide (NO) signaling pathway by PTHrP has been found despite attempts to identify it. Based on direct in situ measurements, it is reported here for the first time that the human PTH/PTHrP receptor analogs, hPTH(1--34) and hPTHrP(1--34), stimulate NO release from a single endothelial cell. A highly sensitive porphyrinic microsensor with a response time of 0.1 ms and a detection limit of 1 nmol/l was used for the measurement of NO. Both hPTH(1--34) and hPTHrP(1--34) stimulated NO release at nanomolar concentrations. The peak concentration of 0.1 micromol/l hPTH(1--34)- and 0.1 micromol/l hPTHrP(1--34)-stimulated NO release was 175+/-9 and 248+/-13 nmol/l respectively. This represents about 30%--40% of maximum NO concentration recorded in the presence of (0.1 micromol/l) calcium ionophore. Two competitive PTH/PTHrP receptor antagonists, 10 micromol/l [Leu(11),d -Trp(12)]-hPTHrP(7--34)amide and 10 micromol/l [Nle(8,18),Tyr(34)]-bPTH(3--34)amide, were equipotent in antagonizing hPTH(1--34)-stimulated NO release; [Leu(11),d -Trp(12)]-hPTHrP(7--34)amide was more potent than [Nle(8,18),Tyr(34)]-bPTH(3--34)amide in inhibiting hPTHrP(1--34)-stimulated NO release. The PKC inhibitor, H-7 (50 micromol/l), did not change hPTH(1--34)- and hPTHrP(1--34)-stimulated NO release, whereas the combined effect of 10 micromol/l of the cAMP antagonist, Rp-cAMPS, and 50 micromol/l of the calmodulin inhibitor, W-7, was additive. The present studies show that both hPTH(1--34) and hPTHrP(1--34) activate NO production in endothelial cells. The activation of NO release is through PTH/PTHrP receptors and is mediated via the calcium/calmodulin pathway.

Statin-stimulated nitric oxide release from endothelium

BACKGROUND

There is increasing evidence that loss of endothelium-derived NO is a major factor in cardiovascular complication events, and that NO might exert antiatherosclerotic actions. The beneficial effects of HMG CoA reductase inhibitors (statins) therapy in atherosclerosis outweigh those expected from simply lowering low-density lipoprotein (LDL) cholesterol, and may be related to the direct action in the endothelium. Based on these concepts, in the studies described here, the effect of new statin derivatives on nitric oxide (NO) and superoxide (O2-) release in bovine endothelial cells was tested.

MATERIAL AND METHODS

Highly sensitive electrochemical NO and O2--microsensors were placed near the surface of endothelial cells, and the concurrent kinetics of NO and O2-- release were measured in situ.

RESULTS

All tested statins stimulated NO release. The peak concentration of NO after stimulation with 1 Kmol/l Lovastatin, 1 Kmol/l Atorvastatin, 1 Kmol/l Pravastatin, or 1 Kmol/l Simvastatin was about 77%, 73%, 72%, and 44% lower, respectively, as compared with the NO peak concentration after stimulation with 1 Kmol/l calcium ionophore A23187 (receptor-independent agonist). The tested statins stimulated NO release in a modest way, which resulted in diminishing O2- generation during activation of nitric oxide synthase. Moreover, the kinetics of O2- release after administration of the statins suggested that these compounds may also scavenge O2-. The NO/O2- peak concentration ratio after the NOS agonists administration was as follows: 7.51 for CaI, 6.56 for Lovastatin, 6.00 for Atorvastatin, 4.17 for Pravastatin and 6.25 for Simvastatin.

CONCLUSIONS

The tested statins, i.e. Lovastatin, Atorvastatin, Pravastatin and Simvastatin demonstrate variable potency to enhance the NO/O2- concentration ratio after stimulation of NOS, resulting in an increase of NO bioavailability in endothelial cells.

Nitric oxide measurements during endotoxemia

BACKGROUND

Excessive continuous NO release from inducible NO synthase over prolonged periods under pathological conditions, such as endotoxemia, contributes significantly to circulatory failure, hypotension, and septic shock. This NO production during endotoxemia is accompanied by superoxide release, which contributes to the fast decay of NO. Therefore, the amount of NO that diffuses to target sites may be much lower than the total amount released under pathological conditions.

METHODS

We performed in vivo and ex vivo measurements of NO (electrochemical) and ex vivo in situ measurements of superoxide, peroxynitrite (chemiluminescence), and nitrite and nitrate (ultraviolet-visible spectroscopy). We determined the effect of lipopolysaccharide administration (20 mg/kg) on diffusible NO, total NO (diffusible plus consumed in chemical reactions), and superoxide and peroxynitrite release in the pulmonary arteries of rats.

RESULTS

An increase in diffusible NO generated by constitutive NO synthase was observed immediately after administration of lipopolysaccharide, reaching a plateau (145 +/- 18 nmol/L) after 540 +/- 25 s. The plateau was followed by a decrease in NO concentration and its subsequent gradual increase after 45 min because of NO production by inducible NO synthase. The concentration of superoxide increased from 16 +/- 2 nmol/L to 30 +/- 3 nmol/L after 1 h and reached a plateau of 41 +/- 4 nmol/L after 6 h. In contrast to the periodic changes in the concentration of diffusible NO, the total concentration of NO measured as a sum of nitrite and nitrate increased steadily during the entire period of endotoxemia, from 2.8 +/- 0.2 micromol/L to 10 +/- 1.8 micromol/L.

CONCLUSIONS

The direct measurement of NO concentrations in the rat pulmonary artery demonstrates dynamic changes throughout endotoxemia, which are related to the production of superoxide and the subsequent increase in peroxynitrite. Monitoring endotoxemia with total nitrate plus nitrite is not sensitive to these fluctuations in NO concentration.

Cicletanine stimulates nitric oxide release and scavenges superoxide in endothelial cells

Cicletanine ((+/-)3-(4-chlorophenyl)-1,3-dihydro-7-hydroxy-6-methylfuro-[3,4-c] pyridine) 3-(4-chlorophenyl)-1,3-dihydro-7-hydroxy-6-methylfuro-[3,4-c] pyridine) is a novel antihypertensive vasodilator with an incompletely understood mechanism of action. In the studies described here, the release of nitric oxide and superoxide (O2-) stimulated by cicletanine was measured simultaneously in the endothelium of isolated rat aortic rings. Highly sensitive electrochemical nitric oxide and O2- microsensors were placed near the surface of endothelial cells and the kinetics of nitric oxide and O2- release were monitored in situ. The response times for nitric oxide and O2- microsensors were 100 micros and 50 micros, respectively, and detection limit was 10(-9) M. Cicletanine stimulated nitric oxide release in aorta endothelium at (micromolar) therapeutic concentrations that were consistent with the concentrations of the compound to induce endothelium-dependent vasorelaxation in isolated rat aorta. The peak concentration of nitric oxide was 160+/-8 nM. This concentration was about 70% and was 60% lower as compared with the nitric oxide peak concentration observed after stimulation with receptor-independent agonist (calcium ionophore A23187) and receptor-dependent agonist (acetylcholine), respectively. However, after administration of cicletanine, only a small concentration of O2- was recorded (peak 3.1+/-0.2 nM) contrary to a large concentration (27+/-1.35 nM) observed after stimulation with A23187). Cicletanine not only stimulated nitric oxide release but also was a potent scavenger of O2- at nanomolar level. Both of these effects may contribute to potent vasorelaxation properties of cicletanine and its long-term therapeutic actions, resulting in cardiovascular tissue protection.

Nitric Oxide Measurements during Endotoxemia

Background: Excessive continuous NO release from inducible NO synthase over prolonged periods under pathological conditions, such as endotoxemia, contributes significantly to circulatory failure, hypotension, and septic shock. This NO production during endotoxemia is accompanied by superoxide release, which contributes to the fast decay of NO. Therefore, the amount of NO that diffuses to target sites may be much lower than the total amount released under pathological conditions.

Methods: We performed in vivo and ex vivo measurements of NO (electrochemical) and ex vivo in situ measurements of superoxide, peroxynitrite (chemiluminescence), and nitrite and nitrate (ultraviolet-visible spectroscopy). We determined the effect of lipopolysaccharide administration (20 mg/kg) on diffusible NO, total NO (diffusible plus consumed in chemical reactions), and superoxide and peroxynitrite release in the pulmonary arteries of rats.

Results: An increase in diffusible NO generated by constitutive NO synthase was observed immediately after administration of lipopolysaccharide, reaching a plateau (145 ± 18 nmol/L) after 540 ± 25 s. The plateau was followed by a decrease in NO concentration and its subsequent gradual increase after 45 min because of NO production by inducible NO synthase. The concentration of superoxide increased from 16 ± 2 nmol/L to 30 ± 3 nmol/L after 1 h and reached a plateau of 41 ± 4 nmol/L after 6 h. In contrast to the periodic changes in the concentration of diffusible NO, the total concentration of NO measured as a sum of nitrite and nitrate increased steadily during the entire period of endotoxemia, from 2.8 ± 0.2 μmol/L to 10 ± 1.8 μmol/L.

Conclusions: The direct measurement of NO concentrations in the rat pulmonary artery demonstrates dynamic changes throughout endotoxemia, which are related to the production of superoxide and the subsequent increase in peroxynitrite. Monitoring endotoxemia with total nitrate plus nitrite is not sensitive to these fluctuations in NO concentration.

Measurement of nitric oxide in single cells and tissue using a porphyrinic microsensor

This unit describes the preparation and applications of porphyrinic sensors for quantitative measurement of nitric oxide (NO) in single cells and in tissues. The determination of NO is based on the electrochemical oxidation of NO on a carbon fiber electrode covered with a thin layer of a conducting polymeric metalloporphyrin catalyst, overlaid with another thin film of Nafion, a cation exchange material. The electric current generated during NO oxidation on the surface of the polymeric porphyrin is linearly proportional to the concentration of NO, so this current is used as an analytical signal which can be measured in either the amperometric or the voltammetric mode. Both methods provide a quantitative signal. This unit describes the electrochemical setup for measurement of NO in single cells and tissue. Support protocols describe porphyrin synthesis, sensor preparation, and sensor calibration.

Angiotensin-(1-7)-Stimulated Nitric Oxide and Superoxide Release From Endothelial Cells

-The stimulation of endothelium-dependent NO release by angiotensin-(1-7) [Ang-(1-7)] has been indirectly shown in terms of vasodilation, which was diminished by NO synthase inhibition or removal of the endothelium. However, direct measurement of endothelium-derived NO has not been analyzed. With a selective porphyrinic microsensor, NO release was directly assessed from single primary cultured bovine aortic endothelial cells. Ang-(1-7) caused a concentration-dependent release of NO of 1 to 10 µmol/L, which was attenuated by NO synthase inhibition. [D-Ala(7)]Ang-(1-7) (5 µmol/L), described as a selective antagonist of Ang-(1-7) receptors, inhibited Ang-(1-7)-induced NO release only by approximately 50%, whereas preincubation of bovine aortic endothelial cells with the angiotensin II subtype 1 and 2 receptor antagonists EXP 3174 and PD 123,177 (both at 0.1 µmol/L) led to an inhibition of 60% and 90%, respectively. A complete blockade of the Ang-(1-7)-induced NO release was observed on preincubation of the cells with 1 µmol/L concentration of the bradykinin subtype 2 receptor antagonist icatibant (HOE 140), suggesting an important role of local kinins in the action of Ang-(1-7). Simultaneous direct measurement of superoxide (O(2)(-)) detected by an O(2)(-)-sensitive microsensor revealed that the moderately Ang-(1-7)-stimulated NO release was accompanied by a very slow concomitant O(2)(-) production with a relative low peak concentration in comparison to the O(2)(-) production of the strong NO releasers bradykinin and, especially, calcium ionophore. Thus, Ang-(1-7) might preserve the vascular system, among others, due to its low formation of cytotoxic peroxynitrite by the reaction between NO and O(2)(-).

Synergistic Antihypertensive Effects of Nifedipine on Endothelium : Concurrent Release of NO and Scavenging of Superoxide

Recent studies have suggested that part of the vasorelaxation caused by nifedipine, a 1,4-dihydropyridine Ca(2+) antagonist, depends on the endothelium. To study the effect of endothelium-dependent vasorelaxation, the release of NO and superoxide (O(2)(-)) in the presence of nifedipine in isolated cultured rabbit endothelial cells was measured. Highly sensitive electrochemical microsensors were placed onto the cell membrane, and the kinetics of NO and O(2)(-) were measured simultaneously with time resolutions of 0.1 and 0.05 ms, respectively. Nifedipine at its therapeutical concentrations stimulated NO release and scavenged O(2)(-) in endothelial cells. The linear relationship between NO concentration and nifedipine concentration was observed in the range between 0.01 and 1 nmol/L. NO concentration reached a maximum of 200+/-10 nmol/L at 1.2 nmol/L of nifedipine. The NO concentration was approximately 50% and 30% of the concentration measured in the presence of receptor-dependent (acetylcholine) and the receptor-independent (Ca(2+) ionophore A23187) NO synthase (eNOS) agonists, respectively. NO release stimulated by eNOS agonists was followed by the generation of the NO scavenger superoxide. The concentration of O(2)(-) was significantly lower after stimulation with nifedipine (peak 5+/-0.5 nmol/L) than after stimulation with acetylcholine (15+/-1 nmol/L) and Ca(2+) ionophore (25+/-1 nmol/L). The average rate of NO release by nifedipine is relatively slow (17 nmol/L per second). This is in sharp contrast to the fast rate of NO release by acetylcholine and Ca(2+) ionophore (40 and 300 nmol/L per second, respectively). These experiments show that nifedipine, apart from its well-known Ca(2+) antagonistic properties in vascular smooth muscle cells, stimulates the release of significant concentration of NO in endothelium and also preserves NO concentration. Both these effects may be beneficial in the treatment of hypertension.

Enhanced peroxynitrite formation is associated with vascular aging

Vascular aging is mainly characterized by endothelial dysfunction. We found decreased free nitric oxide (NO) levels in aged rat aortas, in conjunction with a sevenfold higher expression and activity of endothelial NO synthase (eNOS). This is shown to be a consequence of age-associated enhanced superoxide (.O(2)(-)) production with concomitant quenching of NO by the formation of peroxynitrite leading to nitrotyrosilation of mitochondrial manganese superoxide dismutase (MnSOD), a molecular footprint of increased peroxynitrite levels, which also increased with age. Thus, vascular aging appears to be initiated by augmented.O(2)(-) release, trapping of vasorelaxant NO, and subsequent peroxynitrite formation, followed by the nitration and inhibition of MnSOD. Increased eNOS expression and activity is a compensatory, but eventually futile, mechanism to counter regulate the loss of NO. The ultrastructural distribution of 3-nitrotyrosyl suggests that mitochondrial dysfunction plays a major role in the vascular aging process.

The protective role of nitric oxide in the brain ischemia

A role of nitric oxide in ischemia/reperfusion (I/R) injury of brain in normotensive (Sprague-Dowley rats, SD) and stroke-prone spontaneously hypertensive rats (SHR-SP) was studied. Cerebral ischemia was produced in rats by occlusion of the middle cerebral artery (MCA). NO and O2- releases in the brain in response to MCA occlusion followed by reperfusion were simultaneously monitored (2h) using electrochemical microsensors. The size of infarct was evaluated in the course of I/R from images of brain slices stained with 2,3,5-triphenyltetrazolium chloride. Similar patterns of NO and O2- releases were exhibited for SD and SHR-SP rats in the entire course of the experiments. However, the concentration of NO release was significantly lower during I/R in SHR-SP than in SD rats (the maximal NO concentration was 2.61 +/- 0.22 micromol/L for SD and 1.51 +/- 0.16 micromol/L for SHR-SP rats; *P < 0.01). In contrast, the concentration of O2- release during cerebral ischemia was significantly higher in SHR-SP than SD rats (the maximal increase was 122 +/- 24 nmol/L for SD and 220 +/- 44 nmol/L for SHR-SP rats; *P<0.01). The infarct sizes revealed in the course of I/R were larger in SHR-SP than SD rats (1.8 +/- 0.4% vs. 1.1 +/- 0.4% at 30 min., 2.84 +/- 0.8% vs. 2.21 +/- 0.6% at 100 min. and 9.20 +/- 1.1% vs. 5.8 +/- 0.6% at 180 min. ofthe brain weights, respectively; *P < 0.01 for each time-point). These studies indicate that nitric oxide plays a protective role during I/R and deficiency of NO in SHR-SP rats is due to excess of O2- production. The deficiency in NO concentration correlates positively with the increase of cerebral I/R injury.

HMG-CoA reductase inhibition improves endothelial cell function and inhibits smooth muscle cell proliferation in human saphenous veins

OBJECTIVES

This study examined effects of 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase inhibitor cerivastatin on human saphenous vein (SV), endothelial cells (EC) and smooth muscle cells (SMC).

BACKGROUND

Venous bypass graft failure involves EC dysfunction and SMC proliferation. Substances that improve EC function and inhibit SMC proliferation would be of clinical relevance.

METHODS

Both EC and SMC were isolated from SV. Endothelial nitric oxide synthase (eNOS) expression and nitric oxide (NO) production were analyzed by immunoblotting and porphyrinic microsensor. The SMC proliferation was assayed by 3H-thymidine incorporation. Protein kinases and cell cycle regulators were analyzed by immunoblotting.

RESULTS

Cerivastatin (10(-9) to 10(-6) mol/liter) enhanced eNOS protein expression and NO release (about two-fold) in EC in response to Ca2+ ionophore (10(-6) mol/liter). This was fully abrogated by the HMG-CoA product mevanolate (2 x 10(-4) mol/liter). In SMC, platelet-derived growth factor (5 ng/ml) enhanced 3H-thymidine incorporation (298 +/- 23%, n = 4), activated cyclin-dependent kinase (Cdk2), phosphorylated Rb and down-regulated p27Kip1 (but not p21CiP1). Cerivastatin reduced the 3H-thymidine incorporation (164 +/- 11%, p < 0.01), inhibited Cdk2 activation and Rb phosphorylation, but did not prevent p27Kip1 down-regulation, nor p42mapk and p70S6K activation. Mevalonate abrogated the effects of cerivastatin on Cdk2 and Rb but only partially rescued the 3H-thymidine incorporation (from 164 +/- 11% to 211 +/- 13%, n = 4, p < 0.01).

CONCLUSIONS

In humans, SVEC inhibition of HMG-CoA/mevalonate pathway contributes to the enhanced eNOS expression and NO release by cerivastatin, whereas in SMC, inhibition of this pathway only partially explains cerivastatin-induced cell growth arrest. Inhibition of mechanisms other than p42mapk and p70S6K or Cdk2 are also involved. These effects of cerivastatin could be important in treating venous bypass graft disease.

Prostaglandin E1 reduces ischemia/reperfusion injury by normalizing nitric oxide and superoxide release

To test the effects of prostaglandin E1 on 2.5 h of ischemia followed by 2 h of reperfusion, continuous nitric oxide measurements (electrochemical) were correlated with intermittent assays of superoxide and peroxynitrite levels (chemiluminescence) and ischemia/reperfusion injury in rabbit adductor magnus muscle. Administering prostaglandin E1 (1 microg/kg) before or during ischemia/reperfusion caused normalization of the release of nitric oxide, superoxide, and peroxynitrite to slightly above preischemic levels. This pattern was dramatically different from that observed during ischemia/reperfusion alone, where nitric oxide concentration increased three times above its basal level. Normalization of constitutive nitric oxide synthase activity in the presence of prostaglandin E1 was associated with a significant reduction of superoxide and peroxynitrite production and subsequent reduction of ischemia/reperfusion injury. At 2 h of reperfusion, vasoconstriction associated with ischemia/reperfusion injury was eliminated, and edema was significantly mollified but still apparent. Prostaglandin E1 treatment does not directly inhibit constitutive nitric oxide synthase, like the inhibitor N(omega)-monomethyl-L-arginine. Some phenomenon associated with ischemia turns on endothelial constitutive nitric oxide synthase to start transforming L-arginine and oxygen into nitric oxide, but prostaglandin E1 seems to inhibit this phenomenon. Thus, essential local L-arginine pools are not depleted, and normal basal levels of essential nitric oxide are maintained, whereas cytotoxic superoxide and peroxynitrite production by L-arginine-deficient constitutive nitric oxide synthase is prevented.

cAMP pulse during preservation inhibits the late development of cardiac isograft and allograft vasculopathy

The causes of transplant-associated coronary artery disease remain obscure, and there is no known treatment. Preservation injury of murine heterotopic vascularized cardiac isografts caused a small, albeit significant, increase in neointimal formation; preservation injury of allografts markedly increased both the incidence and severity of transplant-associated coronary artery disease. As cAMP is an important vascular homeostatic mediator the levels of which decline during organ preservation, buttressing cAMP levels solely during initial preservation both improved acute allograft function and reduced the severity of transplant-associated coronary artery disease in grafts examined 2 months later. Inhibiting the cAMP-dependent protein kinase abrogated these beneficial effects. cAMP treatment was associated with an early reduction in leukocyte infiltration and a reciprocal decrease in superoxide and increase in NO levels. These data indicate that alloantigen-independent injury to the graft, which occurs at the time of cardiac preservation, can set in motion pathological vascular events that are manifest months later. Furthermore, a cAMP pulse during cardiac preservation reduces the incidence and severity of transplant-associated coronary artery disease.

Nitric oxide deficiency contributes to large cerebral infarct size

The purpose of this study was to examine the role played by a deficit in nitric oxide (NO) in contributing to the large cerebral infarcts seen in hypertension. Cerebral infarction was produced in rats by occlusion of the middle cerebral artery (MCA). Studies were performed in Sprague-Dawley (SD) rats subjected to NO synthase blockade (N(G)-nitro-L-arginine [L-NNA], 20 mg x kg(-1) x d(-1) in drinking water) and in spontaneously hypertensive stroke-prone rats (SHRSP). NO released in the brain in response to MCA occlusion was monitored with a porphyrinic microsensor in Wistar-Kyoto rats. The increment in NO released with MCA occlusion was 1.31+/-0.05 micromol/L in L-NNA-treated rats, 1.25+/-0.04 micromol/L in SHRSP, 2. 24+/-0.07 micromol/L in control SD rats, and 2.25+/-0.06 micromol/L in Wistar-Kyoto rats (P<0.0001 for control versus the other groups). Infarct sizes in the L-NNA-treated and control SD rats were 8.50+/-0. 8% and 5.22+/-0.7% of the brain weights, respectively (P<0.05). The basilar arterial wall was significantly thicker in L-NNA-treated rats compared with their controls. We conclude that both the deficit in NO and the greater wall thickness contribute to the larger infarct size resulting from MCA occlusion in SHRSP and in L-NNA-treated rats compared with their respective controls.

Effect of native and oxidized low-density lipoprotein on endothelial nitric oxide and superoxide production : key role of L-arginine availability

BACKGROUND

Native and oxidized LDLs (n-LDL and ox-LDL) are involved in the atherogenic process and affect endothelium-dependent vascular tone through their interaction with nitric oxide (NO).

METHODS AND RESULTS

In this study we evaluated directly, by using a porphyrinic microsensor, the effect of increasing lipoprotein concentrations on endothelial NO and superoxide (O(2)(-)) production. We investigated where lipoproteins may affect the L-arginine-NO pathway by pretreating cells with L-arginine, L-N-arginine methyl ester (L-NAME), and superoxide dismutase. Bovine aortic endothelial cells were exposed for 1 hour to increasing concentrations of n-LDL (from 0 to 240 mg cholesterol/dL) and ox-LDL (from 0 to 140 mg cholesterol/dL). A stimulated (calcium ionophore) NO concentration decreased to 29% of the control at n-LDL concentration of 80 mg cholesterol/dL and to 15% of the control at 20 mg cholesterol/dL of ox-LDL. L-Arginine partially neutralized the inhibitory effect of n-LDL and ox-LDL on the NO generation. Superoxide dismutase pretreatment did not modify NO production, whereas L-NAME blunted NO generation at all LDL concentrations. O(2)(-) production was increased at low n-LDL and very low ox-LDL concentrations; this was reversed by L-arginine.

CONCLUSIONS

These findings confirm the inhibitory role of n-LDL and ox-LDL on NO generation and suggest that lipoproteins may induce a decreased uptake of L-arginine. The local depletion of the L-arginine substrate may derange the NO synthase, leading to overproduction of O(2)(-) from oxygen, the other substrate of NO synthase.

Ischemic preconditioning and infarct mass: the effect of hypercholesterolemia and endothelial dysfunction

In an experimental model of atherosclerosis we investigated whether rabbits fed an atherogenic diet (0.25% cholesterol, 3% coconut oil) develop endothelial dysfunction accompanied with increased infarct mass compared to normal fed rabbits and, whether hypercholesterolemia would interfere with the beneficial outcome of ischemic preconditioning observed in normal rabbits. After four weeks on either a normal or an atherogenic diet, New Zealand White rabbits (n=7 in each group) were subjected to 30 min of myocardial ischemia by occlusion of a branch of the left anterior descending coronary artery (LAD) followed by 2 hours of reperfusion (infarct studies). For ischemic preconditioning experiments, LAD was additionally occluded twice for 5 min followed by 10 min reperfusion before the long-lasting (30 min) ischemia. Infarct mass was evaluated by triphenyl-tetrazolium staining. Besides the assessment of aortic endothelium-dependent function and NO-release, aortic and cardiac vessels were inspected for atherosclerotic lesions. Total cholesterol serum levels in rabbits on an atherogenic diet were significantly higher (15.3+/-2.7 mmol/L) than those on a standard diet (0.65+/-0.08 mmol/L). The aortas and heart vessels were without any histological evidence of atherosclerosis, whereas endothelial dysfunction and significantly reduced calcium-ionophore stimulated endothelial NO-release were found in isolated aortic rings of hypercholesterolemic animals. Rabbits on a standard diet showed an infarct mass (related to the area at risk) of 41+/-33%, which was reduced to 21+/-2% by ischemic preconditioning (49% decrease, p<0.05). In rabbits on an atherogenic diet, infarct mass was significantly increased to 63+/-3% (52% increase versus standard diet). Interestingly, hypercholesterolemia did not affect the beneficial influence of ischemic preconditioning; infarct mass (21+/-3%, p<0.05 vs hypercholesterolemia) was similar to rabbits on a standard diet with ischemic preconditioning. Our results show that experimental hypercholesterolemia increases infarct mass in nonpreconditioned hearts but it does not interfere with the reduction of infarct mass elicited by preconditioning. This may suggest that NO produced by the endothelium is not a prime factor in the cardioprotective mechanism of preconditioning.

Nitric oxide release from normal and dysfunctional endothelium

The endothelium plays a critical role in maintaining vascular tone by releasing vasoconstrictor and vasodilator substances. Endothelium - derived nitric oxide (NO) is a vasodilator rapidly inactivated by superoxide (O2-) found in significant quantities. The porphyrinic sensor (0.5-8 microm diameter) and chemiluminescence methods were used to measure NO and (O2-) respectively. Effects of hypertension, low density lipoprotein (LDL), and heart preservation on the release of NO and O2- were delineated. In the single endothelial cell (rat aorta) NO concentration was the highest in the cell membrane decreasing exponentially with distance from cell, and becoming undetectable beyond 50 microm and 25 microm for normotensive (WKY) and hypertensive (SHR) rats respectively. The endothelium of SHR released 40% less NO (300+/-25 nmol L(-1)) than that of normotensive rats (500+20 nmol L(-1)), due to the higher production of O2- in SHR rats. An exponentially decreasing NO production (from 1.20 +/- 0.15 to 0.16 +/- 0.05 micromol (L-1)) and concomitant increase of O2- generation (from 10 +/- 0.3 to 300 +/- 25 nmol L(-1) were observed in left ventricle of stored (eight hours) rabbit heart. Native and oxidized low density lipoproteins (nLDL and oxLDL) inhibited NO generation and increased O2- production. The local depletion of the L-arginine substrate may disarrange the nitric oxide synthase, leading to production of O2- from oxygen.

Release of nitric oxide from endothelial cells stimulated by YC-1, an activator of soluble guanylyl cyclase

1 In this study we examined the endothelium-dependent effect of YC-1 - a benzyl indazole derivative which directly activates soluble guanylyl cyclase (sGC) - on vascular relaxation and nitric oxide (NO) and guanosine-3',5'-cyclic monophosphate (cyclic GMP) in endothelial cells. 2 In preconstricted rat aortic rings with intact endothelium, YC-1 produced a concentration-dependent relaxation. However, the concentration response curve was shifted rightward to higher concentrations of YC-1, when (i) the aortas were pre-treated with L-NG-nitroarginine methylester (L-NAME) or (ii) the endothelium was removed. 3 Incubation of bovine aortic endothelial cells (BAEC) with YC-1 produced a concentration-dependent NO synthesis and release as assessed using a porphyrinic microsensor. Pre-incubating cells with L-NAME or with 8-bromo-cyclic GMP decreased this effect indicating that the YC-1 stimulation of NO synthesis is due to an activation of nitric oxide synthase, but not to an elevation of cyclic GMP. No direct effect of YC-1 on recombinant endothelial constitutive NO synthase activity was observed. 4 The YC-1 stimulated NO release was reduced by 90%, when extracellular free calcium was diminished. 5 In human umbilical vein endothelial cells (HUVEC), YC-1 stimulated intracellular cyclic GMP production in a concentration- and time-dependent manner. Stimulation of cyclic GMP was greater with a maximum concentration of YC-1 compared to calcium ionophore A23187. Similar effects were observed in BAEC and rat microvascular coronary endothelial cells (RMCEC). 6 When HUVEC and RMCEC were pre-treated with L-NG-nitroarginine (L-NOARG), the maximum YC-1 stimulated cyclic GMP increase was reduced by >/=50%. 7 These results indicate, that beside being a direct activator of sGC, YC-1 stimulates a NO-synthesis and release in endothelial cells which is independent of elevation of cyclic GMP but strictly dependent on extracellular calcium. The underlying mechanism needs to be determined further.

Late treatment with ramipril increases survival in old spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR) begin to die from cardiovascular complications at approximately 15 months of age. We tested whether chronic ACE-inhibitor treatment would extend the lifespan of such old animals. We also studied cardiac hypertrophy and function, endothelial function and expression, and activity of NO synthase (eNOS). One hundred 15-month-old SHR were randomized into 3 groups, control (n=10), placebo-treated (n=45), and ramipril-treated with an antihypertensive dose of 1 mg. kg(-1). d(-1) in drinking water (n=45). Ex vivo experiments were performed after 15 months (control) and 21 months, when approximately 80% of the placebo group had died. Late treatment with ramipril significantly extended lifespan of the animals from 21 to 30 months. Fully established cardiac hypertrophy, observed in placebo-treated animals and in controls, was significantly reversed by ramipril treatment. In isolated working hearts, a significantly improved function associated with increased cardiac eNOS expression was seen versus placebo and control hearts. Endothelial dysfunction in isolated aortic rings from control and placebo-treated SHR was significantly improved by ACE inhibition and associated with enhanced NO release. Late treatment of SHR with the ACE inhibitor ramipril extended lifespan from 21 to 30 months, which is comparable to the lifespan of untreated normotensive Wistar-Kyoto rats. This lifespan extension, probably due to blood pressure reduction, correlated with increased eNOS expression and activity followed by a regression of left ventricular hypertrophy and cardiac and vascular dysfunction.

Direct microsensor measurement of nitric oxide production by the osteoclast

Nitric oxide (NO) triggers marked osteoclast retraction which closely resembles that due to Ca2+. The effect of Ca2+ has been attributed to a stimulated release of NO. Here, we show for the first time, by direct measurement with a microsensor, that osteoclasts do indeed produce NO and that this production is enhanced by a high Ca2+. We also show that the Ca2+ ionophore, A23187, mimics the latter. Furthermore, osteoclasts on dentine produce more NO than osteoclasts on glass and NO release from dentine-plated osteoclasts is much less sensitive to stimulation by Ca2+. Finally, the microsomal Ca2+ store-depleting agent, thapsigargin, attenuates NO release only from osteoclasts on glass, suggesting that stored Ca2+ has the dominant effect in modulating NO release from non-resorbing cells. NO is a powerful inhibitor of bone resorption: a direct demonstration of its production is therefore strong evidence for a role in modulating osteoclast function.

Angiotensin II-stimulated nitric oxide release from porcine pulmonary endothelium is mediated by angiotensin IV

In this study, a nitric oxide (NO) sensor was used to examine the ability of angiotensin II (AngII), AngIV, and bradykinin (Bk) to stimulate NO release from porcine pulmonary artery (PPAE) and porcine aortic endothelial (PAE) cells and to explore the mechanism of the AngII-stimulated NO release. Physiologic concentrations of AngII, but not Bk, caused release of NO from PPAE cells. In contrast, Bk, but not AngII, stimulated NO release from PAE cells. AngIII-stimulated NO release from PPAE cells required extracellular L-arginine and was inhibited by L-nitro-arginine methyl ester. AT1 and AT2 receptor inhibition had no affect on AngII-mediated NO release or activation of NO synthase (NOS). AngIV, an AngII metabolite with binding sites that are pharmacologically distinct from the classic AngII receptors, stimulated considerably greater NO release and greater endothelial-type constitutive NOS activity than the same amount of AngII. The AngIV receptor antagonist, divalinal AngIV, blocked both AngII- and AngIV-mediated NO release as well as NOS activation. The results demonstrate that AngIV and the AngIV receptor are responsible, at least in part, for AngII-stimulated NO release and the associated endothelium-dependent vasorelaxation. Furthermore, these results suggest that differences exist in both AngII- and Bk-mediated NO release between PPAE and PAE cells, which may reflect important differences in response to these hormones between vascular beds.

Direct electrochemical measurement of nitric oxide in vascular endothelium

The endothelium plays a critical role in maintaining vascular tone by releasing vasoconstrictor and vasodilator substances. Endothelium-derived nitric oxide (NO) is a vasodilator rapidly inactivated by superoxide and by Fe(II) and Fe(III), all found in significant quantities in biological systems. Thus due to the short life of NO in tissue (t1/2 = 3-6 s), in situ quantification of NO is a challenging problem. We designed the present study to perform direct measurements of nitric oxide using the electrochemical porphyrinic sensor. The most significant advantages of this sensor is small size (0.5-8 microm), rapid response time (0.1-1 ms), and low detection limit (10(-9) mol l(-1)). The porphyrinic sensor was used for in vitro and in vivo measurements of NO in an isolated single cell or tissue. Effects of hypertension, endotoxemia, and ischemia/reperfusion on the release of NO and/or its interaction with superoxide (O2-) were delineated. In the single endothelial cell (rabbit endocardium), NO concentration was highest at the cell membrane (950 +/- 50 nmol l(-1)), decreasing exponentially with distance from cell, and becoming undetectable at distances beyond 50 microm. The endothelium of spontaneously hypertensive rats (SHR) released 35% less NO (580 +/- 30 nmol l(-1)) than that of normotensive rats (920 +/- 50 nmol l(-1)), due to the higher production of O2- in SHR rats. Endothelial NO synthase (eNOS) generated NO (140 +/- 20 nmol l(-1)) in lung during the acute phase (first 10-15 min) of endotoxemia, followed by production of NO by inducible NOS. High production of O2- was observed during the entire period of endotoxemia. Ischemia (lower limb of rabbit) caused a significant increase of NO peaking at 15 min and decreasing thereafter, also due to O2- production.

The molecular pathology laboratory of the 21st century

Human cells contain deoxyribonucleic acid in mitochondria and nuclei. Human diseases may be caused by mutations in mitochondrial DNA, nuclear DNA or both. The volume of work performed in the diagnostic molecular pathology laboratory will continue to grow as more disease-related mutations are discovered. Many factors will influence the diagnostic molecular pathology laboratory in the 21st century, such as future clinical laboratory organization, amplification methods, specimen integrity, ethical guidelines and opportunities to expand service. In the evaluation of a patient suspected of a mitochondrial DNA mutation, care must be exercised in the selection of a primer for amplification and of the specimen to be examined for the mutation. The uneven distribution of normal and abnormal mitochondrial DNA within the various tissues (heteroplasmy) may result in a normal mitochondrial DNA sequence if the wrong tissue is examined. The presence of mitochondrial-like sequences (pseudogenes) within nuclear DNA may result in amplification of nuclear genes if generic primers are used to duplicate a mitochondrial DNA gene. Diabetes mellitus is a heterogeneous disease with mutations occurring in a variety of proteins leading to either prereceptor, receptor or postreceptor defects. In this example, the diagnostic molecular pathology laboratory may be asked to define the specific genotype a specific patient with this common phenotype may possess.

NO concentration in the periendothelial area of the femoral artery of the dog measured in vivo

.NO concentration was measured in the periendothelial area of the femoral artery by Malinski's porphyrinic .NO sensor in seven anaesthetized dogs. The basal concentration was 154.2 +/- 5.6 nM and two-minute intraarterial infusions of acetylcholine (3-4 micrograms/ml/min) or bradykinin (30-40 ng/ml/min) increased this value significantly to 204.3 +/- 16.4 and 266.5 +/- 16.4 nM (P < 0.01), respectively. Inhibition of .NO synthase by L-NAME (50 mg/kg) declined the basal .NO concentration only to 137.2 +/- 3.3 nM (P < 0.01). Subsequent administration of acetylcholine and bradykinin attenuated significantly the increase in .NO concentration. Surprisingly, both agonists still induced a significant increase of .NO concentration by 125.3 +/- 8.3 and 156.6 +/- 26.9 nM, respectively (P < 0.01). One of the possible explanations may be that besides arginine-citrulline plus the .NO pathway other sources of .NO could be involved in the high level of .NO after .NO synthase blockade by L-NAME.

Normal and pathological distribution of nitric oxide in the cardiovascular system

Using microsensors, it is possible to quantify the amount and concentration of nitric oxide (NO) release throughout the cardiovascular system in veins, arteries and the heart. Under normal physiological conditions a well defined distribution of NO is maintained. This concentration depends++ on the laminar, turbulent, or pulsatile flow rate of blood. Significantly reduced production of NO is observed in the pathogenesis of cardiovascular disorders like hypertension, atherosclerosis and diabetes. This is due to increased generation of superoxide by a dysfunctional endothelium and the rapid formation of peroxynitrite followed by formation of peroxynitrite followed by the formation of highly reactive OH and NO2 radicals and NO2+. Elevated concentration or improved mass transport of L-arginine and (6)-5,6,7,8-tetrahydrobiopterin can be applied to increase/decrease NO/superoxide release by the dysfunctional endothelium.

New strategy for prolonging the preservation time of hearts for transplantation

Our study concerned the findings that rat and rabbit heart transplants do not survive after six hours. They become dark, hard and fail to contract within 2 min after reperfusion and never regain their function. We tested the supplementation of solutions for heart transplant preservation with tetrahydrobiopterin (H4B) and L-arginine (L-ARG) to maintain the oxidative and reductive domains of the endocardial NO synthase. We decided to study the excised rabbit hearts preserved in Hank's balanced salt solution (HBSS) at 0 degrees C supplemented with different concentrations of H4B (0, 1, 5, 10 or 100 microM). At desired time intervals, successive pieces stored in the above solutions were warmed to rabbit body temperature in 4 ml of HBSS and maximally agonized by direct application of 20 microl of 200 microM bradykinin (or other agonist) onto the exposed endocardium. Nitric oxide bursts were monitored with a porphyrinic NO sensor lying on the exposed endocardium. Our goal was to find the lowest H4B concentration which would maximally agonize NO. and prolong the time of heart preservation to more than 6 hours. Ten microM are a minimum H4B concentration which achieves maximum prolongation of heart preservation time up to 90 hours. This effect was based upon maximal potentiation of NO. release and minimizing of superoxide production.