Inducible nitric oxide synthase activation after ischemia/reperfusion contributes to myocardial dysfunction and extent of infarct size in rabbits: evidence for a late phase of nitric oxide-mediated reperfusion injury

Cardiomyocyte-Specific Overexpression of NO Synthase-3 Protects Against Myocardial Ischemia-Reperfusion Injury

OBJECTIVE

The protective effect of NO synthase-3 (eNOS)-derived NO in limiting myocardial ischemia-reperfusion (MI-R) injury is well established. We reported previously that systemic genetic overexpression of eNOS attenuates MI-R injury. The purpose of the current study was to investigate tissue-specific genetic overexpression of the human eNOS gene.

METHODS AND RESULTS

To accomplish this, we used 2 distinct murine models of transgenic overexpression, a cardiomyocyte-specific eNOS overexpresser (CS eNOS-Tg) under the control of the alpha-myosin heavy chain promoter, and a systemic eNOS transgenic mouse (SYS eNOS-Tg) under control of the native eNOS promoter with an upstream endothelial enhancer element. Mice were subjected to 30 or 45 minutes of left coronary artery ischemia and 24 or 72 hours of reperfusion. CS eNOS-Tg mice displayed significantly decreased infarct size beyond that of mice with systemic overexpression. Additionally, CS eNOS-Tg mice exhibited better preservation of cardiac function compared with SYS eNOS-Tg mice after myocardial infarction.

CONCLUSIONS

These results provide evidence that site-specific targeting of eNOS gene therapy may be more advantageous in limiting MI-R injury and subsequent cardiac dysfunction.

Effects of aminoguanidine against renal ischaemia-reperfusion injury in rats

Aminoguanidine is an inhibitor of nitric oxide synthase (NOS), with high selectivity for the inducible isoform (iNOS). In addition to being an inhibitor of NOS, aminoguanidine also exhibits antioxidant activity. Recent studies suggest that aminoguanidine reduces ischaemia-reperfusion (I/R)-induced damage. However, the role of aminoguanidine, in renal injury associated with I/R remains unknown. This study was designed to investigate the effects of aminoguanidine on renal I/R injury. There were three groups of eight rats each. I/R was induced by occlusion of the left renal vessels for 60 min, followed by 24 h reperfusion in rats. Malondialdehyde (MDA) levels, a stable metabolite of the free radical-mediated lipid peroxidation cascade, were found to be significantly higher in the I/R group (30.3 +/- 0.1 nmol g(-1) tissue) than in the control group (10 +/- 0.05 nmol g(-1)). Aminoguanidine (100 mg kg(-1)) administration to rats significantly reduced the MDA values. We also demonstrated that I/R leads to structural change but aminoguanidine did not reverse this change. Aminoguanidine, according to the biochemical finding is protective but histopathological findings did not reveal protection against I/R injury in kidney. The effects of aminoguanidine on I/R-induced damage remain a subject for future investigations.

Suppression of angioplasty-related inflammation by pre-procedural treatment with trimetazidine

Percutaneous transluminal coronary angioplasty (PTCA) has been recognized as a reliable treatment procedure for acute reversible ischemia and reperfusion. Ischemic reperfusion cycle in PTCA leads to the systemic inflammation and extensive tissue injury by the production of reactive oxygen species including nitric oxide (NO) radicals. In patients with coronary artery disease, undergoing PTCA, the effects of trimetazidine (TMZ), a piperazine-derivative anti-anginal drug, were studied on several indirect markers of systemic inflammatory response: tumor necrosis factor-alpha (TNF-alpha), C-reactive protein (CRP) and NO products (nitrite and nitrate). Patients (n = 11 each group) were untreated or pre-treated with TMZ (20 mg per orally three times a day), begun three days prior to PTCA, and marker levels were measured before the start of TMZ therapy (baseline), just before PTCA (0 hr), and 4, 24, and 48 hrs after PTCA. The baseline levels of markers were not significantly different between the untreated and pre-treated patients. In contrast, all parameters were lower in the TMZ-treated group than those in the matched control group in the pre- and post-angioplasty periods. Interestingly, in the TMZ group, CRP and nitrite levels were significantly lower than in the control group at each time point of the pre- and post-angioplasty periods, but the TNF-alpha levels were significantly decreased only in the post-angioplasty period. Pre-procedural treatment with oral TMZ for three days significantly suppressed the elevation of inflammatory markers before and shortly after PTCA. We suggest the usefulness of TMZ in preventing inflammatory cardiovascular events after PTCA.

Stimulation of A2A-adenosine receptors after myocardial infarction suppresses inflammatory activation and attenuates contractile dysfunction in the remote left ventricle

Following myocardial infarction (MI), contractile dysfunction develops not only in the infarct zone but also in noninfarcted regions of the left ventricle remote from the infarct zone. Inflammatory activation secondary to MI stimulates inducible nitric oxide synthase (iNOS) induction with excess production of nitric oxide. We hypothesized that the anti-inflammatory effects of selective A2A-adenosine receptor (A2AAR) stimulation would suppress inflammation and preserve cardiac function in the remote zone early after MI. A total of 53 mice underwent 60 min of coronary occlusion followed by 24 h of reperfusion. The A2AAR agonist (ATL146e, 2.4 μg/kg) was administered intraperitoneally 1, 3, and 6 h postreperfusion. Because of the 1-h delay in treatment after MI, ATL146e had no effect on infarct size, as demonstrated by contrast-enhanced cardiac MRI ( n = 18) performed 24 h post-MI. ATL146e did however preserve global cardiac function at that time by limiting contractile dysfunction in remote regions [left ventricle wall thickening: 51 ± 4% in treated ( n = 9) vs. 29 ± 3% in nontreated groups ( n = 9), P < 0.01]. RT-PCR, immunohistochemistry, and Western blot analysis indicated that iNOS mRNA and protein expression were significantly reduced by ATL146e treatment in both infarcted and noninfarcted zones. Similarly, elevations in plasma nitrate-nitrite after MI were substantially blunted by ATL146e ( P < 0.01). Finally, treatment with ATL146e reduced NF-κB activation in the myocardium by over 50%, not only in the infarct zone but also in noninfarcted regions ( P < 0.05). In conclusion, A2AAR stimulation after MI suppresses inflammatory activation and preserves cardiac function, suggesting the potential utility of A2AAR agonists against acute heart failure in the immediate post-MI period.

Receptor for Advanced-Glycation End Products

Background— The beneficial effects of reperfusion therapies have been limited by the amount of ischemic damage that occurs before reperfusion. To enable development of interventions to reduce cell injury, our research has focused on understanding mechanisms involved in cardiac cell death after ischemia/reperfusion (I/R) injury. In this context, our laboratory has been investigating the role of the receptor for advanced-glycation end products (RAGE) in myocardial I/R injury.

Methods and Results— In this study we tested the hypothesis that RAGE is a key modulator of I/R injury in the myocardium. In ischemic rat hearts, expression of RAGE and its ligands was significantly enhanced. Pretreatment of rats with sRAGE, a decoy soluble part of RAGE receptor, reduced ischemic injury and improved functional recovery of myocardium. To specifically dissect the impact of RAGE, hearts from homozygous RAGE-null mice were isolated, perfused, and subjected to I/R. RAGE-null mice were strikingly protected from the adverse impact of I/R injury in the heart, as indicated by decreased release of LDH, improved functional recovery, and increased adenosine triphosphate (ATP). In rats and mice, activation of the RAGE axis was associated with increases in inducible nitric oxide synthase expression and levels of nitric oxide, cyclic guanosine monophosphate (cGMP), and nitrotyrosine.

Conclusions— These findings demonstrate novel and key roles for RAGE in I/R injury in the heart. The findings also demonstrate that the interaction of RAGE with advanced-glycation end products affects myocardial energy metabolism and function during I/R.

Physiogenomic resources for rat models of heart, lung and blood disorders

Cardiovascular disorders are influenced by genetic and environmental factors. The TIGR rodent expression web-based resource (TREX) contains over 2,200 microarray hybridizations, involving over 800 animals from 18 different rat strains. These strains comprise genetically diverse parental animals and a panel of chromosomal substitution strains derived by introgressing individual chromosomes from normotensive Brown Norway (BN/NHsdMcwi) rats into the background of Dahl salt sensitive (SS/JrHsdMcwi) rats. The profiles document gene-expression changes in both genders, four tissues (heart, lung, liver, kidney) and two environmental conditions (normoxia, hypoxia). This translates into almost 400 high-quality direct comparisons (not including replicates) and over 100,000 pairwise comparisons. As each individual chromosomal substitution strain represents on average less than a 5% change from the parental genome, consomic strains provide a useful mechanism to dissect complex traits and identify causative genes. We performed a variety of data-mining manipulations on the profiles and used complementary physiological data from the PhysGen resource to demonstrate how TREX can be used by the cardiovascular community for hypothesis generation.

Inhibition of iNOS protects the aging heart against beta-adrenergic receptor stimulation-induced cardiac dysfunction and myocardial ischemic injury

BACKGROUND

beta-adrenergic receptor (AR) and aging are two major contributors to pathogenesis of perioperative myocardial ischemia and infarction. This study compared the response to beta-AR stimulation in the young and aging heart and examined the role of inducible nitric oxide synthase (iNOS) in aging related myocardial ischemic injury and its relation to beta-AR stimulation.

MATERIAL AND METHODS

Isolated perfused hearts from young (3-5 months) and aging (24-25 months) rats were subjected to 60 min of 50% coronary flow reduction and 30 min of isoproterenol (Iso) stimulation starting at 30 min of ischemia. The rats were randomized to receive vehicle or 1400W (a selective iNOS inhibitor) at 24 h (2 mg/kg, i.p.) and 1 h (1 mg/kg, i.p.) pre-ischemia.

RESULTS

The 30 min of myocardial ischemia resulted in cardiac dysfunction as indicated by a 13 to 45% of reduction in left ventricular developed pressure (LVDP) and +/- dp/dtmax in either young or aging rats. Infusion of Iso for 30 min caused a partial recovery of cardiac function in hearts from young animals receiving either vehicle or 1400W as evidenced by improvements in LVDP and +/- dp/dtmax. In striking contrast, Iso infusion to hearts from aging animals receiving vehicle not only failed to improve ischemia-induced cardiac depression but worsened cardiac function as indicated by a 43 to 60% further reduction in LVDP and +/- dp/dtmax at the end of 30-min Iso infusion, which was also associated with a significant increase in myocardial NO production, ONOO- formation, caspase-3 activation and creatine kinase (CK) release. However, the treatment with a selective iNOS inhibitor-1400W blocked NO production and ONOO- formation, attenuated caspase-3 activation and CK release, and improved LV function in the aging heart, demonstrating a critical link between iNOS generated NO production and aging myocardial ischemic injury. A significant increase of iNOS protein expression, activity and immunoreactivity was found in the baseline aging LV tissues versus their young counterparts.

CONCLUSIONS

Aging induces phenotypic up-regulation of iNOS in the heart, in which beta-AR stimulation interacts with ischemia and triggers a markedly increased NO production, which creates a nitrative stress, generates toxic peroxynitrite, activates apoptosis, and eventually causes cardiac dysfunction and myocardial injury. An iNOS inhibitor-1400W can markedly attenuate these adverse effects in the aging heart.

Preconditioning of salvaged myocardium in conscious rabbits with postinfarction dysfunction

Protection against postinfarction myocardial dysfunction is modest with classic preconditioning (PC). We investigated whether multiple cycles of PC could improve this protection and whether postinfarction dysfunction only depends on the amount of viable tissue. Eighteen rabbits were chronically instrumented with coronary occluders and ultrasonic crystals (segment shortening, SH) in the ischemic zone. A control group underwent 30-min coronary artery occlusion (CAO) with 72-h reperfusion (CAR). In two other groups, PC was induced by six 4-min CAO/4-min CAR cycles (PC×6) or one 5-min CAO/10-min CAR cycle (PC×1). After 72-h CAR, depression in SH was reduced in PC×1 (−68 ± 7% from baseline) and to a greater extent in PC×6 (−18 ± 10%) vs. control (−99 ± 7%; all P < 0.05). Infarct sizes were reduced in PC×1 (15 ± 2%) and to a greater extent in PC×6 (3 ± 1%) vs. control (46 ± 5%; P < 0.05). Contractility of salvaged myocardium was evaluated by calculating the ratio between SH at 72-h CAR and the amount of viable tissue. This index was enhanced in PC×1 (0.39 ± 0.07, P < 0.05) and to a greater extent in PC×6 (0.82 ± 0.09) vs. control (0.0 ± 0.10). This differential effect of PC was not related to changes in apoptosis, endothelial nitric oxide synthase (NOS) expression, or macrophages infiltration but, rather, to blunted inducible NOS expression in PC×6 vs. control and PC×1. Thus multiple cycles of PC induced an almost complete protection against postinfarction dysfunction, potentially involving beneficial effects on salvaged myocardium.

Metabolic and functional protection by selective inhibition of nitric oxide synthase 2 during ischemia-reperfusion in isolated perfused hearts

BACKGROUND

Drugs that selectively block nitric oxide synthase (NOS) 2 enzyme activity by inhibiting dimerization of NOS2 monomers have recently been developed.

METHODS AND RESULTS

To investigate whether selective inhibition of NOS2 is cardioprotective, rats were pretreated for 2 days with BBS2, an inhibitor of NOS2 dimerization, at 15 mg/kg SC. Isolated buffer-perfused hearts from treated (n=9) and control (n=7) hearts were subjected to 20 minutes of ischemia followed by 60 minutes of reperfusion. NOS2 protein was upregulated in all hearts at the end of ischemia and of reperfusion; NOS2 enzyme activity was 60% lower in hearts from the treated animals. In the treated hearts, the increase in end-diastolic pressure was significantly attenuated at the end of ischemia, and the return of developed pressure at reperfusion was greater (P<0.05). Creatine kinase release at reperfusion was lower in treated hearts than in controls (P=0.02). At the end of ischemia and of reperfusion, myocardial ATP levels were significantly higher in the treated hearts than in controls (P<0.05). In the treated hearts under ischemic conditions, lactate content was higher and the lactate/pyruvate ratio was lower than in controls (P<0.05); GAPDH activity was higher; and G-3-P and aldose reductase activity were lower. At reperfusion, in the treated hearts, there was less histological damage and less apoptosis of cardiac muscle cells.

CONCLUSIONS

Pretreatment with BBS2, a selective inhibitor of NOS2, improves contractile performance, preserves myocardial ATP, and reduces damage and death of cardiac myocytes during ischemia and reperfusion of isolated buffer-perfused rat hearts.

Lipopolysaccharide and inflammatory cytokines cause an inducible nitric oxide synthase-dependent bladder smooth muscle fibrotic response

PURPOSE

Bladder wall fibrosis is a sequela of recurrent urinary tract infection (UTI). Inducible nitric oxide synthase (iNOS) has been shown to mediate the fibrotic response to inflammation in other tissues. We determined if iNOS could be involved in the fibrotic response to recurrent UTI.

MATERIALS AND METHODS

Human bladder smooth muscle cells (SMC) were treated with bacterial lipopolysaccharides (LPS) and a mixture of inflammatory cytokines. The level of collagen type III, and the levels of iNOS mRNA, protein and activity were determined. The effect of the iNOS inhibitor aminoguanidine on collagen type III expression was then assessed.

RESULTS

Expression of collagen type III, iNOS mRNA and iNOS protein as well as iNOS activity were increased in bladder SMC treated with the combination of LPS and cytokines. The increase in collagen type III expression was inhibited by pretreatment of cells with aminoguanidine.

CONCLUSIONS

LPS and inflammatory cytokines induce collagen type III expression in an iNOS dependent manner in human bladder SMC. This finding suggests that iNOS may be a critical mediator of the bladder wall fibrotic response to chronic UTI and iNOS inhibitors may be of therapeutic value in patients with chronic UTI.

Relation of preexisting anti-beta2GPI antibodies to infarct size in a rat model

BACKGROUND

Anti-beta2-glycoprotein I (beta2GPI) antibodies (a subpopulation of antiphospholipid (aPL) antibodies) are associated with a procoagulant state in humans and with enhanced atherosclerosis in experimental animal models. Moreover, the presence of high titers of aPL antibodies in relatively young patients is associated with higher incidence of subsequent myocardial infarction. Herein, we evaluated the role of preexisting high levels of aPL antibodies in determining the size of the infarct induced by permanent ligation of the left anterior descending artery (LAD) in a rat model.

METHODS AND RESULTS

A total of 11 Wistar rats were immunized and boosted with 10 microg of the phospholipid binding protein -beta2GPI (a method commonly applied for induction of aPL antibodies). Rats in the control group (n=9) were immunized and boosted with a Freund's adjuvant. Upon development of high anti-beta2GPI antibodies levels, myocardial infarction was induced by ligation of the LAD coronary artery. Rats were sacrificed 7 days later, their lymph nodes were collected for evaluation of cellular immunity to beta2GPI and their hearts were removed for assessment of infarct size and for immunohistochemical stains for iNOS and TGF-beta. beta2GPI-immunized rats exhibited high levels of aPL antibodies (mean optical density of 1.3+/-0.3) as compared with the control group (mean optical density of 0.12+/-0.03; P<.0001). Cellular immunity to beta2GPI was also pronounced as evident by an increased thymidine uptake and by increased interferon gamma secretion by the lymph node cells from beta2GPI-immunized rats. Myocardial infarct size has shown a tendency to be increased in rats induced to develop anti-beta2GPI antibodies (mean size 23+/-9%) as compared with controls (17+/-12%; P<.23). iNOS positive cells in the infarct area of beta2GPI-immunized rats were significantly increased in comparison to the control group (P<.01). Similarly, TGF-beta cell expression was significantly increased in the infarct area of the immunized rats in comparison to the control group (22.6+/-5.1 and 7+/-2.1 per 100 mononuclear inflammatory cells, respectively; P=.01).

CONCLUSION

The presence of high levels of aPL antibodies is associated with higher expression of iNOS and TGF-beta and may contribute to myocardial damage.

Gene therapy with inducible nitric oxide synthase protects against myocardial infarction via a cyclooxygenase-2-dependent mechanism

Although the inducible isoform of NO synthase (iNOS) mediates late preconditioning (PC), it is unknown whether iNOS gene transfer can replicate the cardioprotective effects of late PC, and the role of this protein in myocardial ischemia is controversial. Thus, the cDNA for human iNOS was cloned behind the Rous sarcoma virus (RSV) promoter to create adenovirus (Ad) 5/iNOS lacking E1, E2a, and E3 regions. Intramyocardial injection of Ad5/iNOS in mice increased local iNOS protein expression and activity and markedly reduced infarct size. The infarct-sparing effects of Ad5/iNOS were at least as powerful as those of ischemic PC. The increased iNOS expression was associated with increased cyclooxygenase-2 (COX-2) protein expression and prostanoid levels. Pretreatment with the COX-2-selective inhibitor NS-398 completely abrogated the infarct-sparing actions of Ad5/iNOS, demonstrating that COX-2 is an obligatory downstream effector of iNOS-dependent cardioprotection. We conclude that gene transfer of iNOS (an enzyme commonly thought to be detrimental) affords powerful cardioprotection the magnitude of which is equivalent to that of late PC. This is the first report that upregulation of iNOS, in itself, is sufficient to reduce infarct size. The results provide proof-of-principle for gene therapy against ischemia/reperfusion injury, which increases local myocardial NO synthase levels without the need for continuous intravenous infusion of NO donors and without altering systemic hemodynamics. The data also reveal the existence of a close coupling between iNOS and COX-2, whereby induction of the former enzyme leads to secondary induction of the latter, which in turn mediates the cytoprotective effects of iNOS. We propose that iNOS and COX-2 form a stress-responsive functional module that mitigates ischemia/reperfusion injury.

The role of nitric oxide after a short period of liver ischemia-reperfusion

BACKGROUND

Liver ischemia-reperfusion injury is a serious problem during liver resection and transplantation. Nitric oxide (NO) has been suggested to have a cytoprotective effect for microcirculation, while the interaction of active oxygen species and NO produces peroxynitrite anion. The present study attempts to clarify the role of NO in liver ischemia-reperfusion injury.

METHODS

Wistar male rats were subjected to 30 min of hepatic ischemia followed by reperfusion. The model rats were divided into the three following groups: a control group that was not administered NO synthase inhibitors, and two experimental groups that were administered either N(omega)-nitro-L-arginine methyl ester (L-NAME) or aminoguanidine. In each group, we examined active oxygen species and nitric oxide production, and investigated liver function by measuring serum transaminase levels. In addition, we conducted histopathologic examinations and microcirculation examinations using intravital videomicroscopy.

RESULTS

In the control group, NO concentrations in the plasma increased with time after reperfusion. A decrease in NO production was detected in the groups administered NO synthase inhibitors. Elevated serum transaminase levels became more prominent after L-NAME administration, while aminoguanidine administration reduced its level. The degree of microcirculation failure was found to be more prominent in the L-NAME-administered group over both the control group and the aminoguanidine-administered group. A significantly lower survival rate was observed at 6 h after reperfusion in the L-NAME-administered group over that of the other groups.

CONCLUSIONS

A reduction of the ischemia-reperfusion injury is important in inhibiting the production of high-output NO and peroxynitrite, and in maintaining NO levels necessary for maintenance of microcirculation.

Aminoguanidine inhibits mitogen-activated protein kinase and improves cardiac performance and cardiovascular remodeling in failing hearts of salt-sensitive hypertensive rats

OBJECTIVES

Congestive heart failure (CHF) is associated with inducible nitric oxide synthase (iNOS) expression in the failing human heart, and recently we have also demonstrated that iNOS expression was upregulated in Dahl salt-sensitive hypertensive (DS) rats with cardiac dysfunction and vascular remodeling. Thus, we evaluated whether aminoguanidine (AG), a selective iNOS inhibitor, protects against cardiac dysfunction and vascular remodeling in DS rats receiving a high-salt diet.

METHODS

AG (DSHF-AG, 150 mg/kg per day) or vehicle (DSHF-V) were given from left ventricular hypertrophy stage (11 weeks) to CHF stage (18 weeks) for 7 weeks. The left ventricular end-systolic pressure-volume relationship (contractility: E(es)) was measured by conductance catheter.

RESULTS

Decreased E(es) in DSHF-V was significantly ameliorated by AG treatment. The iNOS mRNA and protein expression and phospho-p42/p44 extracellular signal-regulated kinase (ERK) activities in the left ventricle were significantly upregulated in DSHF-V compared with control rats, and significantly suppressed in DSHF-AG compared with DSHF-V. DSHF-V showed a significant increase of perivascular fibrosis and myocardial fibrosis, with all these parameters being significantly improved by AG treatment.

CONCLUSIONS

We demonstrated that the selective iNOS inhibitor, AG, may be at least a potential therapeutic strategy for treating CHF and cardiovascular remodeling.

Oxidative stress and neutrophil activation—the two keystones of ischemia/reperfusion injury

The widespread introduction of fibrinolytics and recently also PTCA in the treatment of myocardial infarction has changed the picture of modern cardiology. But this therapy also raises new problems and challenges. One of them is the occurrence of extensive tissue injury caused by reperfusion. Reinstitution of oxygen to the ischemic tissues initiates various processes leading to generation of reactive oxygen species (ROSs). Acting on the plasma membrane ROS damage its organization and release various proinflammatory agents. Different proteins, including receptors, ionic channels, transporters or components of transduction pathways are substrates of oxidation by ROSs. Their changed structure results in altered functioning and disruption of vital cellular processes. Another key factor of reperfusion injury is activation and infiltration of infarcted area by polymorphonuclear leukocytes (PMNs). Multiple studies identified consecutive stages of PMN activation and substances being involved in it. Main interest lies in cellular adhesion molecules, particularly selectins and beta2 integrins, as their antagonists were repeatedly found to diminish neutrophil activation and infarct size. Nevertheless new publications strike at the foundations of the established order and confront the relation between neutrophil infiltration and infarct size. PMNs are linked by close ties to other cells involved in inflammatory response. Seemingly also in cardiac ischemia-reperfusion injury, the activity of neutrophils is modulated by lymphocytes and macrophages. The article describes mutual interactions between different factors involved in the reperfusion injury that may enable preparing new treatments, hopefully as effective and successful as reperfusion therapy.

Inhibition of NOS II prevents cardiac dysfunction in myocardial infarction and congestive heart failure

Strong expression of the inducible form of nitric oxide synthase (NOS II) has been shown in the myocardium of patients with myocardial infarction (MI). We hypothesized that NOS II plays an important role in the development of MI and subsequent heart failure and that inhibition of NOS II may beneficially alter the course of the disease. Long-term administration (2 mo) of the selective NOS II inhibitor S-methylisothiourea (SMT) to rats with MI significantly improved cardiac function. A significant drop in mortality, lung water content, infarct size, and cardiomyocyte hypertrophy was also associated with the use of SMT. Plasma concentration of nitrite and nitrate was also reduced by SMT. Short-term administration of SMT (first 2 wk only) significantly reduced infarct size; however, it did not improve cardiac dysfunction measured 2 mo after MI. These findings demonstrate that induction of NOS II during MI exerts negative effects on cardiac function and structure. Long-term administration of a selective NOS II inhibitor may prove to be beneficial in the treatment of MI and congestive heart failure.

Nitric oxide production is maintained in exercising swine with chronic left ventricular dysfunction

Left ventricular (LV) dysfunction caused by myocardial infarction (MI) is accompanied by endothelial dysfunction, most notably a loss of nitric oxide (NO) availability. We tested the hypothesis that endothelial dysfunction contributes to impaired tissue perfusion during increased metabolic demands as produced by exercise, and we determined the contribution of NO to regulation of regional systemic, pulmonary, and coronary vasomotor tone in exercising swine with LV dysfunction produced by a 2- to 3-wk-old MI. LV dysfunction resulted in blunted systemic and coronary vasodilator responses to ATP, whereas the responses to nitroprusside were maintained. Exercise resulted in blunted systemic and pulmonary vasodilator responses in MI that resembled the vasodilator responses in normal (N) swine following blockade of NO synthase with N(omega)-nitro-L-arginine (L-NNA, 20 mg/kg iv). However, L-NNA resulted in similar decreases in systemic (43 +/- 3% in N swine and 49 +/- 4% in MI swine), pulmonary (45 +/- 5% in N swine and 49 +/- 4% in MI swine), and coronary (28 +/- 4% in N and 35 +/- 3% in MI) vascular conductances in N and MI swine under resting conditions; similar effects were observed during treadmill exercise. Selective inhibition of inducible NO synthase with aminoguanidine (20 mg/kg iv) had no effect on vascular tone in MI. These findings indicate that while agonist-induced vasodilation is already blunted early after myocardial infarction, the contribution of endothelial NO synthase-derived NO to regulation of vascular tone under basal conditions and during exercise is maintained.

Differential response to myocardial reperfusion injury in eNOS-deficient mice

Two strains of endothelial nitric oxide synthase (eNOS)-deficient (-/-) mice have been developed that respond differently to myocardial ischemia-reperfusion (MI/R). We evaluated both strains of eNOS(-/-) mice in an in vivo model of MI/R. Harvard (Har) eNOS(-/-) mice (n = 12) experienced an 84% increase in myocardial necrosis compared with wild-type controls (P < 0.05). University of North Carolina (UNC) eNOS(-/-) (n = 10) exhibited a 52% reduction in myocardial injury versus wild-type controls (P < 0.05). PCR analysis of myocardial inducible NO synthase (iNOS) mRNA levels revealed a significant (P < 0.05) increase in the UNC eNOS(-/-) mice compared with wild-type mice, and there was no significant difference between the Har eNOS(-/-) and wild-type mice. UNC eNOS(-/-) mice treated with an iNOS inhibitor (1400W) exacerbated the extent of myocardial necrosis. When treated with 1400W, Har eNOS(-/-) did not exhibit a significant increase in myocardial necrosis. These data demonstrate that two distinct strains of eNOS(-/-) mice display opposite responses to MI/R. Although the protection seen in the UNC eNOS(-/-) mouse may result from compensatory increases in iNOS, other genes may be involved.

Absence of inducible nitric oxide synthase modulates early reperfusion-induced NF-kappaB and AP-1 activation and enhances myocardial damage

The role of nitric oxide (NO) generated by the inducible NO synthase (iNOS) during myocardial ischemia and reperfusion is not understood. We investigated the role of iNOS during early reperfusion damage induced in genetically deficient iNOS (iNOS-/-) mice and wild-type littermates. In wild-type mice, ischemia (60 min) and reperfusion (60 min) induced an elevation in serum levels of creatine phosphokinase and myocardial injury characterized by the presence of scattered apoptotic myocytes and mild neutrophil infiltration. Northern blot analysis showed increased expression of iNOS, whose activity was markedly elevated after reperfusion. Immunohistochemistry showed staining for nitrotyrosine; Western blot analysis showed elevated expression of heat shock protein 70 (HSP70), a putative cardioprotective mediator. Plasma levels of nitrite and nitrate, tumor necrosis factor alpha (TNF-alpha), interleukin 6 (IL-6), and IL-10 were also increased. These events were preceded by degradation of inhibitor kappaBalpha (IkappaBalpha), activation of IkappaB kinase complex (IKK) and c-Jun-NH2-terminal kinase (JNK), and subsequently activation of nuclear factor-kappaB (NF-kappaB) and activator protein 1 (AP-1) as early as 15 min after reperfusion. In contrast, iNOS-/- mice experienced 35% mortality after reperfusion. The extensive myocardial injury was associated with marked apoptosis and infiltration of neutrophils whereas expression of HSP70 was less pronounced. Nitrotyrosine formation and plasma levels of nitrite and nitrate were undetectable. TNF-alpha and IL-6 were increased and IL-10 was reduced in earlier stages of reperfusion. Activation of IKK and JNK and binding activity of NF-kappaB and AP-1 were significantly reduced. Thus, we conclude that iNOS plays a beneficial role in modulating the early defensive inflammatory response against reperfusion injury through regulation of signal transduction.

Enhanced iNOS function in myocytes one day after brief ischemic episode

There is increasing evidence that nitric oxide (NO) produced by inducible NO synthase (iNOS) plays a key role in cadioprotection during the "second window of protection" (SWOP). The goals of this study were to determine 1) whether a transient ischemic episode [10-min coronary artery occlusion (CAO), followed by full reperfusion] enhances NOS function in cardiac myocytes, 2) which specific NOS isoform is responsible for the enhanced NOS function in myocytes, and 3) to localize iNOS expression during SWOP. To address these questions, 10 dogs were instrumented to measure aortic and left ventricular pressures and wall thickness. At 1-2 wk after recovery, myocardial ischemia was induced regionally by a 10-min left circumflex CAO. After 24-h reperfusion, cardiac myocytes were isolated from the previously ischemic and nonischemic regions (n = 6). Myocyte contractile function was assessed using a video motion detector at 1 Hz (35 +/- 2 degrees C). At baseline, myocyte contractile function (% contraction) was similar in the two regions (ischemic 7.8 +/- 0.5% vs. nonischemic 7.8 +/- 0.2%). L-Arginine (1 mM) significantly reduced (P < 0.05) myocyte contraction in the ischemic (-34 +/- 3%, P < 0.05) but not (-7 +/- 4%) nonischemic regions; these responses were abolished by N(G)-nitro-L-arginine (1 mM), a nonspecific NOS inhibitor, as well as 2-amino-5,6-dihydro-6-methy-4H-1,3,thiazine (1 mM), a specific iNOS inhibitor. Immunohistochemistry also revealed enhanced iNOS expression in the myocardium and in particular the interstitial spaces in the ischemic zone. These results indicate that a brief ischemic episode upregulates iNOS function in myocytes as well as in the interstitial space between blood vessels and myocytes, strategically where it can regulate both vascular and myocyte function during the SWOP.

Inducible nitric oxide synthase plays a role in LPS-induced hyperglycemia and insulin resistance

The molecular mechanisms underlying endotoxin-induced insulin resistance remain unclear. Endotoxin or lipopolysaccharide (LPS) injection is a potent stimulator of inducible nitric oxide synthase (iNOS). This study in rats, using the specific iNOS inhibitor aminoguanidine, investigated the role of iNOS in endotoxin-induced hyperglycemia and insulin resistance. LPS injection led to hyperglycemia, insulin resistance, and increased iNOS protein expression and activity. Aminoguanidine prevented LPS-induced hyperglycemia without affecting insulin levels or iNOS expression. Aminoguanidine attenuated the LPS-induced insulin resistance, reflected by the requirement for a higher glucose infusion rate to maintain euglycemia during a hyperinsulinemic clamp study. Aminoguanidine completely blocked the LPS-elevated hepatic glucose output and also inhibited LPS-induced increases in hepatic glycogen phosphorylase activities and phosphoenolpyruvate carboxykinase (PEPCK) mRNA expression, key enzymes for glycogenolysis and gluconeogenesis, respectively. Thus, these data demonstrate an important role for iNOS in LPS-induced insulin resistance, evidenced by the attenuation of LPS-induced hyperglycemia and reversal of increased hepatic glucose output by aminoguanidine. The protective effect of aminoguanidine on insulin resistance is probably by attenuation of hepatic glucose output via its inhibition of key enzymes for glycogenolysis and gluconeogenesis, including glycogen phosphorylase and PEPCK.

Activation of cardiac endothelium as a compensatory component in endotoxin-induced cardiomyopathy: role of endothelin, prostaglandins, and nitric oxide

BACKGROUND

In view of growing evidence of an important endothelial paracrine regulation of cardiac function, the present study investigated the role of cardiac endothelium-derived endothelin-1 (ET-1), prostaglandins, and nitric oxide (NO) during endotoxin-induced cardiomyopathy in rabbits.

METHODS AND RESULTS

Immunohistochemical studies showed a marked transient coinduction of the inducible isoforms of NO synthase (NOS-2) and cyclooxygenase (COX-2) in endocardial endothelium and coronary arteriolar endothelium of hearts 12 hours after intravenous administration of lipopolysaccharide (LPS+12h); staining for both isoforms was much weaker 24 hours later (LPS+36h). Nitrotyrosine localization was similar to that of NOS-2, suggesting a NOS-2-related endothelial formation of peroxynitrite in septic hearts. Contractile performance of papillary muscles was depressed in both LPS-treated groups. In the LPS+12h group, however, isometric twitches were significantly prolonged (482+/-14 versus 420+/-14 ms in the saline-treated group, P<0.005). This twitch prolongation was completely reversed by simultaneous administration of BQ-123 and indomethacin to block endogenous ET-1 and prostaglandins, respectively. In addition, in the LPS+12h group, myocardial inotropic responsiveness to exogenous ET-1 was enhanced (P<0.01).

CONCLUSIONS

Cardiac endothelial activation and myocardial sensitization to endothelium-derived mediators may be part of an adaptive response in the early (12 hours) stages of septic cardiomyopathy.

TGF-beta(1) modulates NOS expression and phosphorylation of Akt/PKB in rat myocytes exposed to hypoxia-reoxygenation

Myocardial hypoxia-reoxygenation (H-R) is associated with upregulation of inducible nitric oxide synthase (iNOS), decrease in endothelial NOS (eNOS), and increase in protein kinase B (PKB). Previous work also shows that transforming growth factor-beta(1) (TGF-beta(1)) can attenuate myocardial injury induced by H-R. We examined the modulation of NOS and PKB expression in response to H-R by TGF- beta(1). Myocytes from Sprague-Dawley rat hearts were cultured and exposed to hypoxia (95% N(2)-5% CO(2), PO(2) ~30 mmHg) for 24 h and reoxygenation (95% air-5% CO(2)) for 3 h. Myocytes were then examined for lactate dehydrogenase (LDH) release, iNOS activity (conversion of L-[(3)H]arginine to L-[(3)H]citrulline), iNOS and eNOS expression, and PKB phosphorylation. H-R alone resulted in myocyte injury, upregulation of iNOS activity and expression, decrease in eNOS expression, and increase in PKB phosphorylation (all P < 0.05 vs. cells cultured in normoxic conditions). Treatment of myocytes with TGF-beta(1) (1 ng/ml) resulted in a reduction in LDH release, attenuation of the alterations in NOS expression (both iNOS and eNOS), and PKB phosphorylation in response to H-R (all P < 0.05 vs. H-R alone). These observations suggest that TGF-beta(1) decreases H-R injury and attenuates alterations in NOS and PKB phosphorylation in myocytes exposed to H-R.

Apoptosis in myocardial ischemia, infarction, and altered myocardial states

The work ahead necessary to develop and refine clinically useful antiapoptotic therapy in ischemic-reperfusion injury is daunting. There are many unanswered questions. What is the best method of detecting apoptosis in the cardiac myocytes? What will be the most practical method to deliver this therapy to the cardiac myocyte? Will antiapoptotic agents act selectively on affected myocytes to provide clinical efficacy? Will antiapoptotic agents be effective, or will they be limited by dose heterogeneity? If antiapoptotic is proven to have long lasting efficacy, should it be used for all patients with myocardial infarction or confined only to patients with left ventricular dysfunction. Will antiapoptotic therapy be so effective that it replaces ACE inhibitors and betablockers, or will it always be used as an adjunct to an ACE inhibitor or a betablocker? These questions lay the foundation for investigation for the next decade.