Enhanced expression of nitric oxide synthase in the early stage after increased pulmonary blood flow in rats

Angiotensin-converting enzyme 2 activation ameliorates pulmonary endothelial dysfunction in rats with pulmonary arterial hypertension through mediating phosphorylation of endothelial nitric oxide synthase

This study aims to investigate the effect of angiotensin-converting enzyme 2 (ACE2) activation on pulmonary endothelial function in the process of preventing pulmonary arterial hypertension (PAH) in rat models and to explore the underlying mechanisms. Specific pathogen free rats were randomly divided into five groups including control group, PAH group, PAH + Resorcinolnaphthalein (Res) group (ACE2 activation), PAH + Res + MLN4760 group (ACE2 inhibition), and PAH + Res + L-NAME group (endothelial nitric oxide synthase [eNOS] inhibition). Rat PAH model was constructed using combined left pneumonectomy with a single dose of monocrotaline injection 1 week after the surgery, and the rats were then given corresponding reagents. Hemodynamics, endothelial function, and pathologic changes were evaluated 3 weeks after monocrotaline injection. The concentration of nitric oxide (NO), expression of eNOS, and phosphorylation of eNOS at Ser1177 and Thr495 in the lung tissues from rats were also investigated.The Res-induced activation of ACE2 led to decreased mean pulmonary arterial pressure (mPAP) and pulmonary artery remodeling in the PAH + Res group comparing with the PAH rats (P < .05). In addition, the reduction in mPAP induced by acetylcholine (Ach) was augmented in PAH + Res group (P < .05), but this was not observed under the treatment with sodium nitroprusside (SNP) (P > .05). The ratio of decrease in mPAP caused by Ach to that caused by SNP (Ach/SNP) was also increased (P < .05) in ACE2-activated rats. However, the protective effects of ACE2 activation on PAH were counteracted by co-administration of MLN4760, an ACE2 antagonist (all P > .05). The mechanistic study showed that the concentration of NO in the lung tissues was downregulated in the PAH group but upregulated in the PAH + Res group (P < .05), whereas the NO concentration in the PAH + Res + MLN4760 group was not obviously different from that in the PAH group (P > .05). Regarding the factors regulating NO release, we found that the eNOS was upregulated in the PAH group, and Res did not affect the expression of eNOS. The phosphorylation of eNOS at Ser1177 was increased but at Thr495 was reduced after Res injection, when compared with the PAH group (P < .05). As expected, co-injection of MLN4760 eliminated these differences (P > .05). The reduction in mPAP induced by Ach was attenuated in the PAH + Res + L-NAME group compared with the PAH + Res group (P < .05), but this was not observed in rats treated with SNP (P > .05). The Ach/SNP ratio of decline in mPAP was also decreased in the PAH + Res + L-NAME group (P < .05). Activation of ACE2 had a protective role in the development of PAH via improving the function of pulmonary arterial endothelium. This effect was potentially mediated by promoted NO release as a consequence of increased phosphorylation of eNOS at Ser1177 and dephosphorylation of eNOS at Thr495.

Gene expressions of nitric oxide synthase and matrix metalloproteinase-2 in monocrotaline-induced pulmonary hypertension in rats after bosentan treatment

Background and Objectives

Nitric oxide (NO) is a major endothelium dependent vasomediator and growth inhibitor. NO synthesis is catalyzed by endothelial nitric oxide synthase (eNOS), and NO can also produce peroxynitrite, which activates matrix metalloproteinases (MMPs). The purpose of this study was to determine the gene expression of eNOS and MMP-2 in the lungs of a rat model of pulmonary hypertension after bosentan treatment.

Materials and Methods

Six-week-old male Sprague-Dawley rats were treated as follows: control group, subcutaneous (sc) injection of saline; monocrotaline (MCT) group, sc injection of MCT (60 mg/kg); and bosentan group, sc injection of MCT (60 mg/kg) plus 20 mg/day bosentan orally. The rats were sacrificed after 1, 5, 7, 14 and 28 days.

Results

The right ventricle/(left ventricle+septum) ratio significantly increased in the MCT group compared to the control group on day 14 and 28. The expression of eNOS messenger ribonucleic acid was significantly increased in the MCT group compared to the control group on day 28. MMP-2 gene expression was significantly increased in the MCT-treated rats compared to the control group on day 5 and 28. Following bosentan treatment to reduce pulmonary hypertension, the expression levels of MMP-2 gene were significantly decreased on day 7 and 28. eNOS and tissue inhibitor of MMPs genes were also significantly decreased on day 28 after bosentan treatment.

Conclusion

These results suggest that elevated eNOS expression may be responsible for MMP-2 activation. The causal relationship between eNOS and MMP-2 and their role in pulmonary hypertension require further investigations.

Gene transfer of endothelial nitric oxide synthase attenuates flow-induced pulmonary hypertension in rabbits

BACKGROUND

Nitric oxide, a potent vasodilator with an important role in the regulation of pulmonary vascular tone, is synthesized by a family of nitric oxide synthases. To determine whether endothelial nitric oxide synthase (eNOS) gene transfer may prevent pulmonary hypertension, the effects of transfer of the eNOS gene to the lung were studied in rabbits with pulmonary hypertension induced by high pulmonary blood flow.

METHODS

Adenoviral vector encoding the eNOS gene was intratracheally transfected into the lung of rabbits with flow-induced pulmonary hypertension. Rabbits instilled intratracheally with adenoviral vector without encoding the eNOS gene served as a control group. Hemodynamic data were recorded before and after transfection, and transgene expression was investigated.

RESULTS

Pulmonary hypertension was significantly attenuated in eNOS gene-transfected rabbits compared with control animals (mean pulmonary arterial pressure, 22.3 +/- 5.5 versus 41.0 +/- 6.9 mm Hg; pulmonary vascular resistance, 326 +/- 42 versus 618 +/- 66 dynes x s x cm(-5); p < 0.01). Systemic arterial pressure and systemic vascular resistance were unaffected. There was an increase in calcium-dependent conversion of L-arginine to L-citrulline in the lung (16.81 +/- 0.72 versus 4.11 +/- 0.41 pmol x mg protein(-1) x h(-1)) and cyclic guanosine monophosphate levels (0.138 +/- 0.015 versus 0.065 +/- 0.003 pmol/mg protein). Immunohistochemical staining showed expression of the eNOS gene was detected mainly in endothelial cells of small pulmonary vessels. Transgene expression was confirmed using Western blot analysis.

CONCLUSIONS

These data suggest that intratracheal adenoviral-mediated eNOS gene transfer can attenuate flow-induced pulmonary hypertension in rabbits and may represent a new form of therapy for the treatment of flow-induced pulmonary hypertension.

Pathophysiology of pulmonary arterial hypertension

The mechanisms leading to elevations in precapillary pulmonary vascular resistance are complex and likely involve multiple pathways, but the histopathologic sequelae of these processes are restricted to a few findings, primarily neoangiogenesis, intimal and smooth muscle proliferation, vasoconstriction, and/or in situ thrombosis. Regardless of the etiology of pulmonary hypertension, abnormalities in endothelial function are often observed and likely play a central role in mediating structural changes.

Functional adaptation and remodeling of pulmonary artery in flow-induced pulmonary hypertension

Patients with left-to-right shunt congenital heart disease may develop pulmonary hypertension. Perioperative mortality of these patients is high due to abnormal vasoreactivity of the pulmonary artery (PA). We studied the changes in the PA induced by high pulmonary blood flow in rats with aortocaval fistula. Eight weeks after surgery, morphological changes of the PA were studied and vasomotor function was assessed by isometric force recording. Expression of endothelial nitric oxide (NO) synthase (eNOS), VEGF, and cyclooxygenase-2 (COX-2) proteins and levels of cGMP in the PA were analyzed. Rats with high pulmonary blood flow developed pulmonary hypertension, medial thickening, and increasing of internal elastic lamina and basement membrane in the PA. When compared with sham-operated animals, rats with fistula had significantly increased contractions in the PA, whereas relaxations to acetylcholine and NO donor were reduced. Concentrations of cGMP were reduced in the PA of rats with pulmonary hypertension (18.4 ± 3.3 vs. 9.4 ± 1.7 pmol/mg protein; P = 0.04). The altered vasomotor function was normalized by treatment with indomethacin. The PA of rats with fistula expressed higher levels of eNOS, phosphorylated eNOS, and COX-2. Sustained high PA blood flow in rats causes pulmonary hypertension that is morphologically and functionally identical with patients with flow-induced pulmonary hypertension. Abnormal vasomotor function of the PA in these animals appears to be mediated by reduced availability and the biological effect of endogenous NO and the high production of vasoconstrictor prostanoids. Increased eNOS and phosphorylated eNOS are most likely the adaptive changes in response to an increase in PA pressure secondary to high blood flow.