Inhibition of inducible nitric oxide synthase after myocardial ischemia increases coronary flow

S-Nitroso Human Serum Albumin Enhances Left Ventricle Hemodynamic Performance and Reduces Myocardial Damage after Local Ischemia-Reperfusion Injury

Endothelial nitric oxide (NO) production is crucial in maintaining vascular homeostasis. However, in the context of ischemia-reperfusion (I/R) injury, uncoupled endothelial nitric oxide synthase (eNOS) can exacerbate reactive oxygen species (ROS) generation. Supplementation with S-nitroso human serum albumin (S-NO-HSA) offers a potential solution by mitigating eNOS uncoupling, thereby enhancing NO bioavailability. In a study conducted at the University of Verona, male rats underwent thoracotomy followed by 30 min left anterior descendant coronary (LAD) occlusion and subsequent reperfusion. Hemodynamic parameters were meticulously assessed using a conductance catheter inserted via the carotid artery. The rats were stratified into two main groups based on reperfusion duration and the timing of drug infusion, with the effects of S-NO-HSA evaluated after 2 or 24 h. Remarkably, intravenous administration of S-NO-HSA, initiated before or during ischemia, exhibited notable benefits. It significantly improved left ventricular function, safeguarded energetic substrates such as phosphocreatine and ATP, and sustained glutathione levels akin to basal conditions, indicative of diminished oxidative stress. The data from this study strongly suggest a protective role for S-NO-HSA in mitigating I/R injury induced by LAD artery occlusion, a phenomenon observed at both 2 and 24 h post-reperfusion. These findings underscore the promising therapeutic potential of NO supplementation in alleviating myocardial damage subsequent to ischemic insult.

Effect of microRNA-26a on vascular endothelial cell injury caused by lower extremity ischemia-reperfusion injury through the AMPK pathway by targeting PFKFB3

Vascular endothelial cell (VEC) dysfunction plays an important role in the ischemia-reperfusion injury (IRI)-related diseases, and microRNAs (miRNAs) are key factors during this process. We conducted this study to investigate whether miRNA-26a (miR-26a) has effect on the IRI-induced VEC injury via the AMPK pathway by targeting 6-phosphofructo-2-kinase-fructose-2,6-biphosphatase 3 (PFKFB3). IRI rat models were successfully constructed by an abdominal incision. Additionally, the cultured VECs were further treated with miR-26a mimic or inhibitor, and si-PFKFB3. Both the reverse-transcription quantitative polymerase chain reaction and the western blot assay method were carried out to examine the expressions of PFKFB3, endothelial nitric oxide synthase (eNOS), and 5'-adenosine monophosphate-activated protein kinase (AMPK) α1, as well as the extent of the AMPK α1 phosphorylation levels in vascular tissues. Circulating endothelial cell (CEC), von Willebrand factor (VWF), thrombomodulin (TM), superoxide dismutase (SOD), malondialdehyde (MDA), nitric oxide (NO), and endothelin (ET) were all measured. In the rat model of an IRI, a poorly expressed miR-26a and contrarily highly expressed PFKFB3 were identified in vascular tissues. In response to an overexpression of miR-26a or to the PFKFB3 gene silencing, decreased CEC number, TM, VWF, MDA, and ET contents, increased AMPK α1, and eNOS levels, as well as the extent of AMPK α1 phosphorylation coordinate with both increased SOD and NO contents based on the restoration of the AMPK pathway. Overexpression of the miR-26a or si-PFKFB3 provides an elevation in cell proliferation. Our study suggests that the miR-26a RNA alleviates lower extremity IRI-induced VEC injury in rats through the activation of the AMPK pathway by inhibiting PFKFB3.

The effects of IL-18BP on mRNA expression of inflammatory cytokines and apoptotic genes in renal injury induced by infrarenal aortic occlusion

BACKGROUND

Renal injury is an important complication of infrarenal aortic occlusion (IAO), which is mainly encountered during the postoperative period. Aortic clamping procedure may lead to turbulent blood flow and eventually vasoconstriction at renal arterial level of the abdominal aorta. IL-18BP has well-known antioxidant and anti-inflammatory properties. In this study, we aimed to determine whether IL-18BP has anti-inflammatory, antiapoptotic, antioxidant, and protective effects on acute kidney damage induced by IAO rat model.

MATERIALS AND METHODS

A total of 30 adult male Wistar-Albino rats were equally and randomly separated to three groups as follows: SHAM laparotomy, ischemia-reperfusion (IR), and IR + IL-18BP. We applied 30-min IAO and 2-h reperfusion. Inflammatory cytokine levels (TNF-α, IL-1β, IL-18, IL-6, and IFN-γ) and oxidative stress parameters (TAS, TOS, and OSI) were measured. In addition to this, urea and creatinine levels, histopathology of kidney, mRNA expression levels of inflammatory cytokines, and apoptotic genes were investigated.

RESULTS

Urea and creatinine, tissue and serum levels of TNF-α, IL-6, IL-18, IFN-γ, and TOS, and oxidative stress index (OSI) were found significantly lower in IR + IL-18BP group, when compared to the IR group. Moreover, mRNA expression levels of inflammatory cytokines and apoptotic genes were prominently depressed in IR + IL-18BP pre-treatment group in histopathologic examination, there was a significant difference between the IR and other three groups (P < 0.001). These improvements were demonstrated with a total score of histopathologic damage. In our previous studies, we have demonstrated that IL-18BP has antioxidant, inflammatory, and protective effects on liver and spinal cord IR injury. Data established from the present study suggest that IL-18BP may exert anti-inflammatory, antiapoptotic, antioxidant, and protective effects on IAO-induced acute kidney injury in rats, and this would be the first study to be conducted in this field.

CONCLUSIONS

Data established from the present study suggest that IL-18BP may exert anti-inflammatory, antiapoptotic, antioxidant, and protective effects on IAO-induced acute kidney injury in rats.

Ascorbic acid improves renal microcirculatory oxygenation in a rat model of renal I/R injury

Background and objectives

Acute kidney injury (AKI) is a clinical condition associated with a degree of morbidity and mortality despite supportive care, and ischemia/reperfusion injury (I/R) is one of the main causes of AKI. The pathophysiology of I/R injury is a complex cascade of events including the release of free oxygen radicals followed by damage to proteins, lipids, mitochondria, and deranged tissue oxygenation. In this study, we investigated whether the antioxidant ascorbic acid would be able to largely prevent oxidative stress and consequently, reduce I/R-related injury to the kidneys in terms of oxygenation, inflammation, and renal failure.

Materials and methods

Rats were divided into three groups (n = 6/group): (1) a time control group; (2) a group subjected to renal ischemia for 60 min by high aortic occlusion followed by 2 h of reperfusion (I/R); and (3) a group subjected to I/R and treated with an i.v. 100 mg/kg bolus ascorbic acid 15 min before ischemia and continuous infusion of 50 mg/kg/hour for 2 h during reperfusion (I/R + AA). We measured renal tissue oxidative stress, microvascular oxygenation, renal oxygen delivery and consumption, and renal expression of inflammatory and injury markers.

Results

We demonstrated that aortic clamping and release resulted in increased oxidative stress and inflammation that was associated with a significant fall in systemic and renal hemodynamics and oxygenation parameters. The treatment of ascorbic acid completely abrogated oxidative stress and inflammatory parameters. However, it only partly improved microcirculatory oxygenation and was without any effect on anuria.

Conclusion

The ascorbic acid treatment partly improves microcirculatory oxygenation and prevents oxidative stress without restoring urine output in a severe I/R model of AKI.

Protective effect of N-acetylcysteine on kidney as a remote organ after skeletal muscle ischemia-reperfusion

PURPOSE: To investigate whether N-acetylcysteine has a protective effect against renal injury as a remote organ after skeletal muscle ischemia-reperfusion in rats. METHODS: Twenty Wistar male rats were divided randomly into two experimental groups: group ischemia-reperfusion (group I) and group ischemia-reperfusion + N-acetylcysteine (group II). After ketamine and xylazine anesthesia, femoral artery was exposed. All animals were undergone 2h of ischemia by occlusion femoral artery and 24h of reperfusion. Rats that were treated with N-acetylcysteine given IV at a dose of 150 mg/kg-¹, immediately before reperfusion. After 24h of reperfusion, the blood samples were collected and submitted for evaluation of plasmatic urea, creatinine values and then rats were euthanized and left kidney harvested for histopathological analysis under light microscopy. RESULTS: The urea (35±7.84 mg.dL-1), creatinine (1.46±0.47 mg.dL-1) values were significantly lower in group II (P=0.000). Renal histopathologic study in group I showed extensive distal and proximal tubular cells necrosis and sloughing of epithelial cells into the tubular lumen, cast formation in tubule and glomerul, glomerul fibrosis and hemorrhage. Histopathologically, there was a significant difference (p=0.037) between two groups. CONCLUSION: The N-acetylcysteine was able to decrease renal injury induced by skeletal muscle ischemia reperfusion in rats.

The effect of phlebotomy and mannitol on acute renal injury induced by ischemia/reperfusion of lower limbs in rats

BACKGROUND

Abdominal aortic surgery can cause ischemic/reperfusion (I/R) injury not only in the lower limbs but also in remote organs such as kidneys. Venous blood volume exclusion from the inferior vena cava (phlebotomy) or/and mannitol are used as a treatment for I/R injury of kidney in humans, despite the fact that the effectiveness of these treatments is still debated. The aim of this study was to evaluate the effects of phlebotomy or/and mannitol on rat kidneys in a model of lower limbs I/R-induced acute renal injury (ARI).

MATERIAL AND METHODS

Thirty male Wistar albino rats were used and divided into five groups: (I) sham-operated group, laparotomy without I/R injury (group [S], n = 6); (II) I/R group, infrarenal aortic cross-clamp was used for lower limbs I/R, 3 hours of ischemia followed by 2 hours of reperfusion (group [I/R], n = 6); (III) I/R + phlebotomy group, identical to group [I/R] except for 1 mL of blood aspiration from the inferior caval vein just after ischemia (group [P], n = 6); (IV) I/R + mannitol-treated group, these rats were subjected to I/R and received a bolus injection of mannitol (group [M], n = 6); and (V) I/R + phlebotomy + mannitol-treated group (group [P + M], n = 6), the same procedures were performed as those described for previous groups. At the end of 2-hour reperfusion, all rats were sacrificed. Both kidneys were harvested for biochemical assay (myeloperoxidase [MPO] and superoxide dismutase [SOD] activities, and malondialdehyde [MDA] and reduced glutathione levels) and for histopathological examination (tubular necrosis and acute inflammation on kidney [ARI score]).

RESULTS

Aortic I/R significantly increased the level of MDA (reflecting lipid peroxidation), SOD (enzymatic endogenous antioxidant), and MPO (reflecting neutrophil infiltration) activity (p < 0.05). Phlebotomy or/and mannitol treatments significantly decreased the level of MDA, SOD, and MPO activity and increased glutathione level (nonenzymatic antioxidant in the kidney tissues) (p < 0.05). Histological evaluation of ARI score showed that aortic I/R significantly increased (p value for group [S] versus group [I/R] was 0.012), whereas phlebotomy or/and mannitol treatments significantly decreased tubular necrosis and inflammatory infiltration (p values for group [I/R] versus group [P], [M], and [P + M] were 0.043, 0.043, and 0.003, respectively).

CONCLUSION

This experiment clearly indicated that the lower limbs I/R-induced ARI attenuated significantly by phlebotomy or/and mannitol treatments. Phlebotomy plus mannitol is more effective treatment than phlebotomy or mannitol alone in preventing lower limbs I/R-induced ARI in rats. Further clinical studies are required to clarify whether phlebotomy or/and mannitol treatments are beneficial in alleviating of ARI during abdominal aortic surgery.

Should embolectomy be performed in late acute lower extremity arterial occlusions?

Background

We analyzed the embolectomy results and complications of patients who were operated on after a diagnosis of late acute arterial occlusion of lower extremities.

Methods

A total of 122 patients operated on in our clinic between 2004 and 2009 for late acute arterial occlusion were included in the study. Late arterial occlusion was defined as occlusion occuring 72 hours after initial manifestation of the patient complaints related to the affected lower extremity.

Results

Average age of the 122 patients (71 male, 51 female) was 54.2 ± 16.8 years. In this cohort, 64.75% of patients had cardiac pathologies, while 28.68% had extracardiac causes; 1.64% patients had cathetherization, 0.81% patient had malignancy, and 2.46% patients had a history of trauma. In 1.64% of the cases, no reason for thromboembolysis could be found. Thirty-one patients (25.40%) had additional surgical operations, 14 (11.47%) had fasciotomy, and 9 (7.37%) had amputation. Re-embolectomy was performed on 37 patients (30.32%) who had ongoing ischemia after an operation. Additional surgical operations were performed on 31 patients (25.40%) with ongoing ischemia. In 14 of these cases (11.47%), patients were treated with fasciotomy due to development of compartment syndrome. Amputation was performed on a total of 9 patients. Early in the postoperative phase, mortality was observed in 11 patients (9.01%).

Conclusion

We believe that late embolectomies of acute late leg ischemia increases blood flow in the extremity and reduces the number of amputations required.

Post-resuscitation NOS inhibition does not improve hemodynamic recovery of hypoxic newborn pigs

BACKGROUND

Significant improvement in myocardial recovery has been shown previously with interventions to decrease reactive oxygen species after ischemia/hypoxia. We investigated whether co-administration of N-acetylcysteine (NAC, a scavenger for reactive oxygen species) and N (G)-monomethyl-L: -arginine (L-NMMA, a non-selective nitric oxide synthase inhibitor) results in better hemodynamic recovery.

DESIGN

Controlled, block-randomized study.

SETTING

University research laboratory.

SUBJECT

Mixed breed piglets (1-4d, 1.6-2.4 kg).

INTERVENTIONS

Acutely instrumented piglets received normocapnic alveolar hypoxia (10-15% oxygen) for 2 h followed by reoxygenation with 100% oxygen (1 h) then 21% oxygen (3 h). After reoxygenation, hypoxic-reoxygenated piglets were given either saline (controls), NAC [30 mg/kg bolus + 20 mg/(kg h) infusion], NMMA [0.1 mg/kg bolus + 0.1 mg/(kg h) infusion] or NAC + L-NMMA via intravenous infusion in a blinded, randomized fashion (n = 8/group). Sham-operated piglets had no hypoxia-reoxygenation (n = 5).

MEASUREMENTS AND RESULTS

Both cardiac index and stroke volume of hypoxia-reoxygenation controls remained depressed during reoxygenation (vs. normoxic baseline, p < 0.05). Post-resuscitation treatment with L-NMMA alone did not improve systemic hemodynamic recovery, but caused pulmonary hypertension (vs. controls). In contrast, treating the piglets with either NAC or NAC + L-NMMA improved cardiac index and stroke volume, with no effect on heart rate and blood pressure (vs. controls). These treatments also decreased various oxidative stress markers in myocardial tissues (vs. controls). However, there was no significant difference between NAC- and NAC + L-NMMA groups in all examined parameters.

CONCLUSIONS

Post-resuscitation administration of NAC improved cardiac function and reduced oxidative stress in newborn pigs with hypoxia-reoxygenation insult. Low-dose, non-selective inhibitor of nitric oxide synthase activity did not provide any further beneficial effect.

Proteasome inhibition promotes functional recovery after peripheral nerve reperfusion injury

BACKGROUND

The proteasome degrades NF-kappaB blocking protein (I-kappaB) and activates NF-kappaB that plays as a key transcriptional factor to regulate inflammatory factors that are involved in the tissue reperfusion injury. This study was designed to assess whether the proteasome inhibitor can attenuate peripheral nerve ischemia/reperfusion (I/R) injury and consequently promote motor functional recovery after ischemic insult.

METHODS

Rat sciatic nerves were exposed to 2 hour of ischemia followed by various periods of reperfusion. Rats were administered either proteasome inhibitor (bortezomib) or phosphate-buffered saline 30 minutes before reperfusion start. Results were evaluated using a walking track test, and an isolated muscle contraction test, and by muscle weight, and histology.

RESULTS

Bortezomib treatment induced an earlier improvement in sciatic functional index and a more rapid restoration of contractile force and wet weight of extensor digitorum longus muscle. Bortezomib reduced early axonal degeneration and promoted regeneration.

CONCLUSION

This study indicates that bortezomib; a proteasome inhibitor, is effective at promoting the functional recovery of reperfused peripheral nerve. The proteasome inhibition may play a role as one of the clinical strategy in the peripheral nervous system I/R injury with further understanding its mechanism of action.

The effects of iloprost and vitamin C on kidney as a remote organ after ischemia/reperfusion of lower extremities

BACKGROUND

Abdominal aortic surgery can cause ischemic/reperfusion (I/R) injury in not only the lower extremities, but also in the remote organs and tissues such as lungs, kidneys, heart, and liver during abdominal aortic surgery. It can result in mortality and morbidity because of the remote organ injury in early postoperative period. In this study, we investigate the effects of iloprost and vitamin C on the kidney remote organ damage after I/R following abdominal aortic surgery.

MATERIAL AND METHODS

Thirty-four adult male Wistar rats were used and divided into five groups. I/R was studied infrarenally in the abdominal aorta following a median laparotomy. The left kidney was excised immediately following the laparotomy in group I (n = 6, normal group). Group II (n = 6) was the sham group. Group III (n = 6, control group) was subjected to 3 h of ischemia followed by an hour of reperfusion. Group IV (n = 8) was given iloprost 20 ng/kg/min during I/R period before aortic-clamping. Group V (n = 8) was given vitamin C 100 mg/kg during I/R period before aortic-clamping. Arterial blood samples were obtained to determine the levels of blood pH, pO(2) (mmHg), pCO2 (mmHg), HCO(3) (mmol/L), and plasma malondialdehyde (MDA, nmol/mL) at the end of reperfusion period in all groups. The left kidneys were used for remote measurements of tissue MDA (nmol/g.w.t) and scored by histopathological examination for acute inflammation.

RESULTS

While the arterial blood pO(2) and HCO(3) levels significantly increased, the plasma and renal parenchymal MDA levels significantly decreased in both group IV and group V when compared to group III (P < 0.05). Histopathological and acute inflammation scores statistically decreased in both group IV and V compared with group III (P < 0.05). Although MDA levels, histopathologic and acute inflammation scores in group V were lower than group IV, the differences were not statistically significant (P > 0.05).

CONCLUSION

Both iloprost and vitamin C decreased remote organ damage on the kidney after I/R of lower extremities in the rat model. However, vitamin C is more effective than iloprost in preventing postoperative renal dysfunction.

Methylene blue added to a hypertonic–hyperoncotic solution increases short-term survival in experimental cardiac arrest*

OBJECTIVE

Methylene blue (MB), a free-radical scavenger inhibiting the production and actions of nitric oxide, may counteract excessive vasodilatation induced by nitric oxide during cardiac arrest. Effects of MB in cardiac arrest and cardiopulmonary resuscitation were investigated.

DESIGN

Randomized, prospective, laboratory animal study.

SETTING

University animal research laboratory.

SUBJECTS

A total of 63 piglets of both sexes.

INTERVENTIONS

A pig model of extended cardiac arrest (12 mins of untreated cardiac arrest and 8 mins of cardiopulmonary resuscitation) was employed to assess the addition or no addition of MB to a hypertonic saline-dextran solution. These two groups (MB and hypertonic saline-dextran group [MB group] and hypertonic saline-dextran-only group) of 21 animals were each compared with a group receiving isotonic saline (n = 21).

MEASUREMENTS AND MAIN RESULTS

Although the groups were similar in baseline values, 4-hr survival in the MB group was increased (p = .02) in comparison with the isotonic saline group. Hemodynamic variables were somewhat improved at 15 mins after restoration of spontaneous circulation in the MB group compared with the other two groups. The jugular bulb levels of 8-isoprostane-prostaglandin F2alpha and 15-keto-dihydro-prostaglandin F2alpha (indicators of peroxidation and inflammation) were significantly decreased in the MB group compared with the isotonic saline group. Significant differences were recorded between the three groups in levels of protein S-100beta (indicator of neurologic injury), with lower levels in the MB group compared with the isotonic saline and hypertonic saline-dextran-only groups. Troponin I and myocardial muscle creatine kinase isoenzyme arterial concentrations (indicators of myocardial damage) were also significantly lower in the MB group.

CONCLUSIONS

MB co-administered with a hypertonic-hyperoncotic solution increased 4-hr survival vs. saline in an experimental porcine model of cardiac arrest and reduced oxidative, inflammatory, myocardial, and neurologic injury.

Ischaemia or reperfusion: which is a main trigger for changes in nitric oxide mRNA synthases expression?

OBJECTIVE

To investigate alterations in endothelial nitric oxide synthase and inducible nitric oxide synthase mRNA expressions and nitric oxide release in the myocardium during ischaemia/reperfusion and determine whether these changes are ischaemic and/or reperfusion dependent.

MATERIALS AND METHODS

Isolated rat hearts were perfused by a modified Langendorff system. Following 1 h of global cardioplegic ischaemia, left ventricle haemodynamic parameters were recorded at baseline and during 30 min of reperfusion. Levels of endothelial, inducible nitric oxide synthases mRNA expression and nitric oxide release were measured at baseline, after ischaemia and at 30 min of reperfusion.

RESULTS

Global cardioplegic ischaemia caused a significant depression of left ventricular function and a decrease of coronary flow. Postischaemic intensities of the endothelial nitric oxide synthase mRNA bands were significantly lower than at baseline (P < 0.01). There were no significant differences in endothelial nitric oxide synthase mRNA band intensities immediately after ischaemia compared to the end of reperfusion, nor between the intensities of inducible nitric oxide synthase mRNA bands at baseline, at end of ischaemia and at end of reperfusion. Nitric oxide in the myocardial effluent was below detectable levels at all measured points.

CONCLUSION

Ischaemic injury causes down-regulation of endothelial nitric oxide synthase mRNA expression, which is then associated with reduction of coronary flow during reperfusion, representing one possible mechanism of ischaemia/reperfusion injury. We did not find expected elevations of inducible nitric oxide synthase mRNA expression during ischaemia or reperfusion and we suggest that ischaemia/reperfusion injury is not associated with nitric oxide overproduction.

Inhibition of iNOS with 1400W improves contractile function and alters nos gene and protein expression in reperfused skeletal muscle

This study examined the effects of 1400W, an inhibitor of inducible nitric oxide (iNOS), on contractile function and iNOS expression in reperfused skeletal muscle. The right extensor digitorum longus (EDL) muscle of 104 rats underwent a sham operation or 3-h ischemia followed by 3-h or 24-h reperfusion (I/R). Rats received 3 mg/kg 1400W, 10 mg/kg 1400W, or water subcutaneously. Results showed that EDL contractile function in both 1400W-treated groups significantly outperformed the controls at 24-h but not at 3-h reperfusion. Although iNOS expression increased in all three I/R groups during reperfusion, a significantly smaller increase was found in 1400W-treated muscles after 3-h reperfusion, and more dramatically so after 24-h reperfusion. Our results indicate that inhibition of iNOS preserved the contractile function in reperfused skeletal muscle, perhaps via downregulating iNOS expression. Protection by 1400W at 24-h reperfusion suggests that the role of iNOS in exaggerating reperfusion injury is more prominent in the later stages of injury.

Nitric oxide involvement in reperfusion injury of denervated muscle

PURPOSE

To investigate whether inhibition of inducible nitric oxide synthase (iNOS) improves microcirculation in denervated and reperfused skeletal muscle.

METHODS

The cremaster muscles of 52 rats received iNOS inhibitor 1400W (3 mg/kg) or phosphate buffered saline (PBS) and underwent either 3 hours of ischemia and 1.5 hours of reperfusion or a sham operation. During reperfusion the vessel diameters were measured by using intravital videomicroscopy and overall muscle blood flow was measured with laser Doppler flowmetry. The expression of NOS messenger RNA (mRNA) and protein was determined by using real-time reverse-transcription polymerase chain reaction and Western blot, respectively.

RESULTS

1400W treatment significantly increased the mean blood flow of the reperfused muscle compared with controls, and this was associated with significantly less vasospasm in 10 to 20 microm, 21 to 40 microm, and 41 to 70 microm arterioles. The expression of iNOS mRNA and protein in controls increased 23-fold and 6-fold from normal, respectively, but was reduced to only a 2-fold increase in the 1400W-treated muscles. The ischemia/reperfusion (I/R)-induced decrease of endothelial NOS (eNOS) and neuronal NOS (nNOS) expression in controls was not significantly changed after 1400W treatment.

CONCLUSIONS

Our data support a nitric oxide-mediated mechanism in reperfusion injury and show the importance of inhibition of iNOS in reducing reperfusion injury in denervated skeletal muscle. Our results suggest potential benefits via inhibition of iNOS to improve clinical outcomes not only for hand surgeons who work in the microsurgery field, but also for other physicians whose work involves ischemia/reperfusion injury.

Contributions of nitric oxide synthase isozymes to exhaled nitric oxide and hypoxic pulmonary vasoconstriction in rabbit lungs

We investigated the source(s) for exhaled nitric oxide (NO) in isolated, perfused rabbits lungs by using isozyme-specific nitric oxide synthase (NOS) inhibitors and antibodies. Each inhibitor was studied under normoxia and hypoxia. Only nitro-L-arginine methyl ester (L-NAME, a nonselective NOS inhibitor) reduced exhaled NO and increased hypoxic pulmonary vasoconstriction (HPV), in contrast to 1400W, an inhibitor of inducible NOS (iNOS), and 7-nitroindazole, an inhibitor of neuronal NOS (nNOS). Acetylcholine-mediated stimulation of vascular endothelial NOS (eNOS) increased exhaled NO and could only be inhibited by L-NAME. Selective inhibition of airway and alveolar epithelial NO production by nebulized L-NAME decreased exhaled NO and increased hypoxic pulmonary artery pressure. Immunohistochemistry demonstrated extensive staining for eNOS in the epithelia, vasculature, and lymphatic tissue. There was no staining for iNOS but moderate staining for nNOS in the ciliated cells of the epithelia, lymphoid tissue, and cartilage cells. Our findings show virtually all exhaled NO in the rabbit lung is produced by eNOS, which is present throughout the airways, alveoli, and vessels. Both vascular and epithelial-derived NO modulate HPV.

Reperfusion injury is reduced in skeletal muscle by inhibition of inducible nitric oxide synthase

This study evaluated the effects of the selective inducible nitric oxide synthase (iNOS) inhibitor N-[3-(aminomethyl)benzyl]acetamidine (1400W) on the microcirculation in reperfused skeletal muscle. The cremaster muscles from 32 rats underwent 5 h of ischemia followed by 90 min of reperfusion. Rats received either 3 mg/kg 1400W or PBS subcutaneously before reperfusion. We found that blood flow in reperfused muscles was <45% of baseline in controls but sharply recovered to near baseline levels in 1400W-treated animals. There was a significant (P < 0.01 to P < 0.001) difference between the two groups at each time point throughout the 90 min of reperfusion. Vessel diameters remained <80% of baseline in controls during reperfusion, but recovered to the baseline level in the 1400W group by 20 min, and reached a maximum of 121 +/- 14% (mean +/- SD) of baseline in 10- to 20-micro m arterioles, 121 +/- 6% in 21- to 40-micro m arterioles, and 115 +/- 8% in 41- to 70-micro m arteries (P < 0.01 to P < 0.001). The muscle weight ratio between ischemia-reperfused (left) and non-ischemia-reperfused (right) cremaster muscles was 193 +/- 42% of normal in controls and 124 +/- 12% in the 1400W group (P < 0.001). Histology showed that neutrophil extravasation and edema were markedly reduced in 1400W-treated muscles compared with controls. We conclude that ischemia-reperfusion leads to increased generation of NO from iNOS in skeletal muscle and that the selective iNOS inhibitor 1400W reduces the negative effects of ischemia-reperfusion on vessel diameter and muscle blood flow. Thus 1400W may have therapeutic potential in treatment of ischemia-reperfusion injury.

Attenuation of myocardial ischemia/reperfusion injury by superinduction of inducible nitric oxide synthase

BACKGROUND

Nitric oxide (NO) has been implicated as a mediator in myocardial ischemia/reperfusion (I/R) injury, but its functional properties have been conflicting. We investigated whether NO has a protective role against I/R injury.

METHODS AND RESULTS

Using endothelial NO synthase knockout (eNOS KO) mice, inducible NOS KO mice, the NO donor S-nitroso-N-acetylpenicillamine (SNAP), and the NOS inhibitor N-iminoethyl-L-ornithine (L-NIO), we performed studies of isolated perfused hearts subjected to 30 minutes of global ischemia followed by reperfusion. After 60 minutes of reperfusion, nitrite levels in the coronary effluent in the SNAP and eNOS KO groups were significantly elevated compared with other groups. Immunoblot and immunohistochemistry showed that iNOS was markedly induced in the eNOS KO hearts. Under spontaneous beating conditions during reperfusion, increased NO activity was correlated with a prevention of the hyperdynamic contractile response and enhanced myocardial protection, as evidenced by a reduction in myocardial injury and infarct size. During prolonged reperfusion, SNAP-treated hearts were able to preserve contractile functions for 180 minutes, whereas L-NIO-treated hearts showed a sustained deterioration in contractility.

CONCLUSIONS

NO protects against I/R injury by preventing the hyperdynamic response of isolated perfused hearts during early reperfusion. In the eNOS KO hearts, a paradoxical increase in NO production was seen, accompanied by a superinduction of iNOS, possibly due to an adaptive mechanism.

L-NMMA (a nitric oxide synthase inhibitor) is effective in the treatment of cardiogenic shock

BACKGROUND

The objective was to assess the safety and efficacy of L-NMMA in the treatment of cardiogenic shock.

METHODS

We enrolled 11 consecutive patients with cardiogenic shock that persisted after >24 hours from admission, despite coronary catheterization and primary percutaneous transluminal coronary revascularization, when feasible, and treatment with mechanical ventilation, intraaortic balloon pump (IABP), and high doses of catecholamines. L-NMMA was administered as an IV bolus of 1 mg/kg and continuous drip of 1 mg. kg(-1). h(-1) for 5 hours. Treatment with catecholamines, mechanical ventilation, and IABP was kept constant throughout the study.

RESULTS

Within 10 minutes of L-NMMA administration, mean arterial blood pressure (MAP) increased from 76+/-9 to 109+/-22 mm Hg (+43%). Urine output increased within 5 hours from 63+/-25 to 156+/-63 cc/h (+148%). Cardiac index decreased during the steep increase in MAP from 2. 0+/-0.5 to 1.7+/-0.4 L/(min. m(2)) (-15%); however, it gradually increased to 1.85+/-0.4 L/(min. m(2)) after 5 hours. The heart rate and the wedge pressure remained stable. Twenty-four hours after L-NMMA discontinuation, MAP (+36%) and urine output (+189%) remained increased; however, cardiac index returned to pretreatment level. No adverse events were detected. Ten out of eleven patients could be weaned off mechanical ventilation and IABP. Eight patients were discharged from the coronary intensive care unit, and seven (64%) were alive at 1-month follow-up.

CONCLUSIONS

L-NMMA administration in patients with cardiogenic shock is safe and has favorable clinical and hemodynamic effects.

Crucial role of endogenous interleukin-10 production in myocardial ischemia/reperfusion injury

BACKGROUND

The anti-inflammatory cytokine interleukin-10 (IL-10) has been detected in the plasma of patients with myocardial ischemia/reperfusion. The aim of our study was to investigate the role of endogenously produced IL-10 in myocardial ischemia/reperfusion.

METHODS AND RESULTS

In the present study, we used wild-type and IL-10-deficient mice subjected to myocardial ischemia/reperfusion. Significant levels of IL-10 were produced in wild-type mice at 2 to 6 hours after myocardial reperfusion. The genetic deletion of IL-10 enhanced neutrophil infiltration into the reperfused tissues at 6 hours after reperfusion and increased infarct size and myocardial necrosis. Furthermore, in the absence of IL-10, an enhancement of the inflammatory response was seen, as demonstrated by increased plasma levels of tumor necrosis factor-alpha, nitrite/nitrate (breakdown products of NO), and increased tissue expression of intercellular adhesion molecule-1. Reperfusion for 24 hours was associated with a 75% mortality rate in IL-10-deficient mice, whereas no deaths occurred in the wild-type animals.

CONCLUSIONS

The present findings provide the first direct evidence that endogenous IL-10 inhibits the production of tumor necrosis factor-alpha and NO and serves to protect the ischemic and reperfused myocardium through the suppression of neutrophil recruitment.