Inhibition of tissue angiotensin-converting enzyme with quinapril reduces hypoxic pulmonary hypertension and pulmonary vascular remodeling

Angiotensin-converting enzyme inhibition and pre-superior cavopulmonary connection haemodynamics in infants with single-ventricle physiology

INTRODUCTION

Preliminary animal and human data suggest that angiotensin-converting enzyme inhibition has a role in pulmonary vascular remodelling. We sought to assess the effect of ACEi versus placebo on pulmonary artery pressure and transpulmonary gradient amongst infants undergoing single-ventricle palliation.

MATERIALS AND METHODS

Using the publicly available Pediatric Heart Network Infant Single-Ventricle trial dataset, we compared mean PA pressure at pre-superior cavopulmonary connection catheterisation (primary outcome), transpulmonary gradient, pulmonary-to-systemic flow ratio, and post-SCPC oxygen saturation (secondary outcomes) in infants receiving enalapril versus placebo.

RESULTS

A total of 179 infants underwent pre-SCPC catheterisation, of which 85 (47%) received enalapril. There was no difference between the enalapril and placebo group in the primary and the secondary outcomes. Mean PA pressure in the enalapril group was 13.1 ± 2.9 compared to 13.7 ± 3.4 mmHg in the placebo group. The transpulmonary gradient was 6.7 ± 2.5 versus 6.9 ± 3.2 mmHg in the enalapril and placebo groups, respectively. The pulmonary-to-systemic flow ratio was 1.1 ± 0.5 in the enalapril group versus 1.0 ± 0.5 in the placebo group and the post-SCPC saturation was 83.1 ± 5.0% in the enalapril group versus 82.2 ± 5.3% in the placebo group. In the pre-specified subgroup analyses comparing enalapril and placebo according to ventricular morphology and shunt type, there was no difference in the primary and secondary outcomes.

CONCLUSION

ACEi did not impact mean pulmonary artery pressure or transpulmonary gradient amongst infants with single-ventricle physiology prior to SCPC palliation.

Hypoxia Inducible Factors as Central Players in the Pathogenesis and Pathophysiology of Cardiovascular Diseases

Cardiovascular (CV) diseases are the major cause of death in industrialized countries. The main function of the CV system is to deliver nutrients and oxygen to all tissues. During most CV pathologies, oxygen and nutrient delivery is decreased or completely halted. Several mechanisms, including increased oxygen transport and delivery, as well as increased blood flow are triggered to compensate for the hypoxic state. If the compensatory mechanisms fail to sufficiently correct the hypoxia, irreversible damage can occur. Thus, hypoxia plays a central role in the pathogenesis and pathophysiology of CV diseases. Hypoxia inducible factors (HIFs) orchestrate the gene transcription for hundreds of proteins involved in erythropoiesis, glucose transport, angiogenesis, glycolytic metabolism, reactive oxygen species (ROS) handling, cell proliferation and survival, among others. The overall regulation of the expression of HIF-dependent genes depends on the severity, duration, and location of hypoxia. In the present review, common CV diseases were selected to illustrate that HIFs, and proteins derived directly or indirectly from their stabilization and activation, are related to the development and perpetuation of hypoxia in these pathologies. We further classify CV diseases into acute and chronic hypoxic states to better understand the temporal relevance of HIFs in the pathogenesis, disease progression and clinical outcomes of these diseases. We conclude that HIFs and their derived factors are fundamental in the genesis and progression of CV diseases. Understanding these mechanisms will lead to more effective treatment strategies leading to reduced morbidity and mortality.

Effects of Recombinant Human Angiotensin-Converting Enzyme 2 on Response to Acute Hypoxia and Exercise: A Randomised, Placebo-Controlled Study

Introduction

Angiotensin-converting enzyme 2 (ACE2) is a key enzyme of the renin-angiotensin system (RAS) that has been implicated in the pathogenesis of acute respiratory distress syndrome (ARDS). Enhancing ACE2 activity using GSK2586881, a recombinant form of human ACE2, could be beneficial in diseases such as ARDS but may blunt the hypoxic pulmonary vasoconstriction (HPV) response and potentially impact systemic and tissue oxygenation. This study aimed to evaluate the effect of GSK2586881 0.8 mg/kg on HPV response in healthy adult volunteers during exercise under hypoxic conditions.

Methods

In this phase I, randomised, double-blind (sponsor open) study, GSK2586881 or placebo was administered as a single intravenous (IV) dose in a two-period crossover design. Treatment periods were separated by a washout period of 3–14 days. The primary endpoint was change from baseline in pulmonary artery systolic pressure (PASP) measured by echocardiography. Secondary endpoints included RAS peptides and oxygen saturation.

Results

Seventeen adults aged 18–40 years were randomised to treatment. There were no clinically relevant differences (defined as a reduction of ≥ 5 mmHg) in change from baseline in PASP between GSK2586881 and placebo. GSK2586881 was well tolerated, with no serious adverse events, no worsening of hypoxaemia and no evidence of immunogenicity. The study was terminated early after review of the data, which showed that the predefined success criteria had not been met. Following GSK2586881 administration, levels of the RAS peptide angiotensin II decreased while angiotensin (1-7) increased, as expected, indicating that GSK2586881 was pharmacologically active.

Conclusions

A single IV dose of GSK2586881 0.8 mg/kg was well tolerated but did not impact the acute HPV response in healthy volunteers.

Supplementary Information

The online version contains supplementary material available at 10.1007/s41030-021-00164-7.

Neurohormonal modulation in pulmonary arterial hypertension

Pulmonary hypertension is a fatal condition of elevated pulmonary pressures, complicated by right heart failure. Pulmonary hypertension appears in various forms; one of those is pulmonary arterial hypertension (PAH) and is particularly characterised by progressive remodelling and obstruction of the smaller pulmonary vessels. Neurohormonal imbalance in PAH patients is associated with worse prognosis and survival. In this back-to-basics article on neurohormonal modulation in PAH, we provide an overview of the pharmacological and nonpharmacological strategies that have been tested pre-clinically and clinically. The benefit of neurohormonal modulation strategies in PAH patients has been limited by lack of insight into how the neurohormonal system is changed throughout the disease and difficulties in translation from animal models to human trials. We propose that longitudinal and individual assessments of neurohormonal status are required to improve the timing and specificity of neurohormonal modulation strategies. Ongoing developments in imaging techniques such as positron emission tomography may become helpful to determine neurohormonal status in PAH patients in different disease stages and optimise individual treatment responses.

Mechanisms of Pulmonary Hypertension in Acute Respiratory Distress Syndrome (ARDS)

Background: Acute respiratory distress syndrome (ARDS) is a severe and often fatal disease. The causes that lead to ARDS are multiple and include inhalation of salt water, smoke particles, or as a result of damage caused by respiratory viruses. ARDS can also arise due to systemic complications such as blood transfusions, sepsis, or pancreatitis. Unfortunately, despite a high mortality rate of 40%, there are limited treatment options available for ARDS outside of last resort options such as mechanical ventilation and extracorporeal support strategies. Aim of review: A complication of ARDS is the development of pulmonary hypertension (PH); however, the mechanisms that lead to PH in ARDS are not fully understood. In this review, we summarize the known mechanisms that promote PH in ARDS. Key scientific concepts of review: (1) Provide an overview of acute respiratory distress syndrome; (2) delineate the mechanisms that contribute to the development of PH in ARDS; (3) address the implications of PH in the setting of coronavirus disease 2019 (COVID-19).

Angiotensin Converting Enzyme Inhibitors and Angiotensin Receptor Blockers: A Promising Medication for Chronic Obstructive Pulmonary Disease?

Chronic obstructive pulmonary disease (COPD) is a complex disorder that primarily affects the lungs and is characterized not only by local pulmonary, but also by systemic inflammation which promotes the development of extrapulmonary and cardiovascular co-morbidities. Angiotensin converting enzyme (ACE) inhibitors and ARBs (angiotensin receptor blockers) are widely used drugs in the treatment of cardiovascular diseases, with growing evidence suggesting potential benefits in COPD patients. The purpose of this review is to describe the correlation of renin-angiotensin system (RAS) with COPD pathophysiology and to present the latest data regarding the potential role of RAS blockers in COPD.

Combinatory Evaluation of Transcriptome and Metabolome Profiles of Low Temperature-induced Resistant Ascites Syndrome in Broiler Chickens

To select metabolic biomarkers and differentially expressed genes (DEGs) associated with resistant-ascites syndrome (resistant-AS), we used innovative techniques such as metabolomics and transcriptomics to comparatively examine resistant-AS chickens and AS controls. Metabolomic evaluation of chicken serum using ultra-performance liquid chromatography-quadruple time-of-flight high-sensitivity mass spectrometry (UPLC-QTOF/HSMS) showed significantly altered lysoPC(18:1), PE(18:3/16:0), PC(20:1/18:3), DG(24:1/22:6/0:0), PS(18:2/18:0), PI(16:0/16:0), PS(18:0/18:1), PS(14:1/14:0), dihydroxyacetone, ursodeoxycholic acid, tryptophan, L-valine, cycloserine, hypoxanthine, and 4-O-Methylmelleolide concentrations on day 21 and LysoPC(18:0), LysoPE(20:1/0:0), LysoPC(16:0), LysoPE(16:0/0:0), hypoxanthine, dihydroxyacetone, 4-O-Methylmelleolide, LysoPC(18:2), and PC(14:1/22:1) concentrations on day 35, between the susceptible and resistant groups. Compared to the susceptible group, transcriptomic analysis of liver samples using RNA-seq revealed 413 DEGs on day 21 and 214 DEGs on day 35 in the resistant group. Additional evaluations using gene ontology (GO) indicate that significant enrichment occurred in the oxygen transportation, defensive reactions, and protein modifications of the decreased DEGs as well as in the cell morphological formation, neural development, and transforming growth factor (TGF)-beta signalling of the increased DEGs on day 21. Oxygen transportation was also significantly enriched for downregulated DEGs on day 35. The combinatory evaluation of the metabolome and the transcriptome suggests the possible involvement of glycerophospholipid metabolism in the development of resistant-AS in broilers.

The principal pathways involved in the in vivo modulation of hypoxic pulmonary vasoconstriction, pulmonary arterial remodelling and pulmonary hypertension

Hypoxic pulmonary vasoconstriction (HPV) serves to optimize ventilation-perfusion matching in focal hypoxia and thereby enhances pulmonary gas exchange. During global hypoxia, however, HPV induces general pulmonary vasoconstriction, which may lead to pulmonary hypertension (PH), impaired exercise capacity, right-heart failure and pulmonary oedema at high altitude. In chronic hypoxia, generalized HPV together with hypoxic pulmonary arterial remodelling, contribute to the development of PH. The present article reviews the principal pathways in the in vivo modulation of HPV, hypoxic pulmonary arterial remodelling and PH with primary focus on the endothelin-1, nitric oxide, cyclooxygenase and adenine nucleotide pathways. In summary, endothelin-1 and thromboxane A₂ may enhance, whereas nitric oxide and prostacyclin may moderate, HPV as well as hypoxic pulmonary arterial remodelling and PH. The production of prostacyclin seems to be coupled primarily to cyclooxygenase-1 in acute hypoxia, but to cyclooxygenase-2 in chronic hypoxia. The potential role of adenine nucleotides in modulating HPV is unclear, but warrants further study. Additional modulators of the pulmonary vascular responses to hypoxia may include angiotensin II, histamine, serotonin/5-hydroxytryptamine, leukotrienes and epoxyeicosatrienoic acids. Drugs targeting these pathways may reduce acute and/or chronic hypoxic PH. Endothelin receptor antagonists and phosphodiesterase-5 inhibitors may additionally improve exercise capacity in hypoxia. Importantly, the modulation of the pulmonary vascular responses to hypoxia varies between species and individuals, with hypoxic duration and age. The review also define how drugs targeting the endothelin-1, nitric oxide, cyclooxygenase and adenine nucleotide pathways may improve pulmonary haemodynamics, but also impair pulmonary gas exchange by interference with HPV in chronic lung diseases.

Effect of Angiotensin-converting Enzyme Inhibitors on Phenylephrine Responsiveness in Patients with Valvular Heart Disease

We studied patients with valvular heart disease to investigate whether chronic pre-operative treatment with angiotensin-converting enzyme (ACE) inhibitors modulates the effect of phenylephrine (PE) on anaesthesia-induced hypotension. Sixty-five patients were enrolled in the study and hypotension developed after anaesthesia in 36 (18 in the control group and 18 in the ACE inhibitor group). These patients received PE infusions, which were increased in a stepwise fashion at 10-min intervals. Increased mean arterial pressure due to PE infusion was significant only in the control group. There was no significant difference in pressor response or change in haemodynamic variables with PE infusion between the two groups. Treatment with ACE inhibitors did not increase the incidence of hypotensive episodes or significantly modify pressor response after anaesthesia in patients with valvular heart disease.

Effects of captopril on cardiovascular reflexes and respiratory mechanisms in rats submitted to monocrotaline-induced pulmonary arterial hypertension

BACKGROUND

Pulmonary Arterial Hypertension (PAH) is a disease associated with increased arteriolar resistance in the lungs. Due to hypoxemia, some physiological mechanisms can be posteriorly affected, including respiratory and cardiovascular reflexes, but this has not yet been fully investigated. This study aimed to evaluate how these mechanisms were affected by monocrotaline (MCT)-induced PAH and the possible therapeutic role of angiotensin converting enzyme inhibitor (ACEi), captopril, in reversing this remodeling process.

METHODS AND RESULTS

Groups of Wistar rats received MCT injections (60 mg kg(-1)). Three weeks later, they received captopril (CPT, 100 mg kg(-1)) in their drinking water (MCT + CPT) or water alone (MCT) for 2 weeks. As control, saline-treated animals received captopril in their drinking water (CPT) or water alone (CON), also for 2 weeks. Results showed that PAH was fully induced in the MCT group, evidenced by a high pulmonary index. Gasometrical and respiratory analyses showed hypoxemia and compensatory hyperventilation. CPT treatment brought these parameters to similar values to those observed in the CON group. We observed that autonomic dysfunction in the MCT group was suppressed by CPT. Finally, cardiovascular reflexes analysis showed increased chemoreflex responses in the MCT group, while baroreflex sensibility was decreased. Surprisingly, CPT normalized these reflex responses to values similar to the CON group.

CONCLUSIONS

The present study demonstrates that MCT-induced PAH induces compensatory respiratory responses, dysautonomia, and baroreflex dysfunction and increases chemoreflex responses. The data also indicate that CPT was effective in reversing these cardio-respiratory disorders, suggesting that ACEi could be a potential therapeutic target for PAH.

Relationship between angiotensin-converting enzyme gene polymorphism and respiratory distress syndrome in premature neonates

OBJECTIVE

The aim of this study was to investigate the possible relationship between angiotensin-converting enzyme (ACE) gene polymorphism (D/D and I/D genotypes) and respiratory distress syndrome (RDS) in preterm neonates.

STUDY DESIGN

Our study included 120 preterm neonates (<37 weeks of gestation) with RDS (the patient group) and 120 preterm neonates without RDS (the control group). Blood samples were obtained from patients and control groups, and ACE gene polymorphism was analysed using the polymerase chain reaction method.

RESULTS

D/D genotype was highly significant in the patient group compared with the control group (48.3% of RDS group vs 20% of the control group, P < 0.001). Meanwhile, I/D and I/I genotypes were significantly higher in the control group (75% and 5% of the control group vs 50% and 1.7% of the patient group, P < 0.001). D/D genotype was highly significant in neonates with bronchopulmonary dysplasia (BPD) compared with I/D genotype (P = 0.001).

CONCLUSION

Our results may suggest that D/D genotype is associated with increased risk of RDS and BPD development in preterm neonates.

Chronic obstructive pulmonary disease and cardiovascular disease

Chronic obstructive pulmonary disease (COPD) is an inflammatory disease of the lung associated with progressive airflow limitation and punctuated by episodes of acute exacerbation. There is growing recognition that the inflammatory state associated with COPD is not confined to the lungs but also involves the systemic circulation and can impact nonpulmonary organs. Epidemiologic and mechanistic studies indicate that COPD is associated with a high frequency of coronary artery disease, congestive heart failure and cardiac arrhythmias, independent of shared risk factors. Possible pathways include complex interrelationships between chronic low-grade systemic inflammation and oxidative stress as well as shared risk factors such as age, cigarette smoking, and environmental pollutants. In this review, we provide an overview of the epidemiologic data linking COPD with cardiovascular disease, comment on the interrelationships among COPD, inflammation, and cardiovascular disease, and highlight diagnostic and therapeutic challenges.

Sodium tanshinone IIA sulfonate inhibits canonical transient receptor potential expression in pulmonary arterial smooth muscle from pulmonary hypertensive rats

Danshen, the dried root of Salvia miltiorrhiza, is widely used in clinics in China for treating various diseases, including cardiovascular diseases. Sodium tanshinone IIA sulfonate (STS), a water-soluble derivative of tanshinone IIA isolated as the major active component from Danshen, was recently reported to be effective in attenuating the characteristic pulmonary vascular changes associated with chronically hypoxic pulmonary hypertension (CHPH); however, the underlying detailed mechanisms are poorly understood. In this study, we investigated the effects of STS on basal intracellular Ca(2+) concentration ([Ca(2+)](i)) and store-operated Ca(2+) entry (SOCE) in distal pulmonary arterial smooth muscle cells (PASMCs) exposed to prolonged hypoxia or isolated from CHPH rats. SOCE measured by Mn(2+) quenching of Fura-2 fluorescence in PASMCs from rats exposed to chronic hypoxia (10% O(2), 21 d) was increased by 59%, and basal [Ca(2+)](i) was increased by 119%; this effect was inhibited by intraperitoneal injection of STS. These inhibitory effects of STS on hypoxic increases of SOCE and basal [Ca(2+)](i) were associated with reduced expression of canonical transient receptor potential (TRPC)1 and TRPC6 in distal pulmonary arterial smooth muscle and decreases on right ventricular pressure, right ventricular hypertrophy, and peripheral pulmonary vessel thickening. In ex vivo cultured distal PASMCs from normoxic rats, STS (0-25 μM) dose-dependently inhibited hypoxia-induced cell proliferation and migration, paralleled with attenuation in increases of basal [Ca(2+)](i), SOCE, mRNA, and protein expression of TRPC1 and TRPC6. STS also relieved right ventricular systolic pressure, right ventricular hypertrophy, and TRPC1 and TRPC6 protein expression in distal pulmonary arteries in a monocrotaline-induced rat model of pulmonary arterial hypertension. These results indicate that STS prevents pulmonary arterial hypertension development likely by inhibiting TRPC1 and TRPC6 expression, resulting in normalized basal [Ca(2+)](i) and attenuated proliferation and migration of PASMCs.

Reactive oxygen and nitrogen species in pulmonary hypertension

Pulmonary vascular disease can be defined as either a disease affecting the pulmonary capillaries and pulmonary arterioles, termed pulmonary arterial hypertension, or a disease affecting the left ventricle, called pulmonary venous hypertension. Pulmonary arterial hypertension (PAH) is a disorder of the pulmonary circulation characterized by endothelial dysfunction, as well as intimal and smooth muscle proliferation. Progressive increases in pulmonary vascular resistance and pressure impair the performance of the right ventricle, resulting in declining cardiac output, reduced exercise capacity, right-heart failure, and ultimately death. While the primary and heritable forms of the disease are thought to affect over 5000 patients in the United States, the disease can occur secondary to congenital heart disease, most advanced lung diseases, and many systemic diseases. Multiple studies implicate oxidative stress in the development of PAH. Further, this oxidative stress has been shown to be associated with alterations in reactive oxygen species (ROS), reactive nitrogen species (RNS), and nitric oxide (NO) signaling pathways, whereby bioavailable NO is decreased and ROS and RNS production are increased. Many canonical ROS and NO signaling pathways are simultaneously disrupted in PAH, with increased expression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases and xanthine oxidoreductase, uncoupling of endothelial NO synthase (eNOS), and reduction in mitochondrial number, as well as impaired mitochondrial function. Upstream dysregulation of ROS/NO redox homeostasis impairs vascular tone and contributes to the pathological activation of antiapoptotic and mitogenic pathways, leading to cell proliferation and obliteration of the vasculature. This paper will review the available data regarding the role of oxidative and nitrosative stress and endothelial dysfunction in the pathophysiology of pulmonary hypertension, and provide a description of targeted therapies for this disease.

Treatment of COPD: moving beyond the lungs

We still do not know whether the successful treatment of the comorbid diseases associated with COPD, mainly cardiovascular disease, also positively influences the course of the lung disease because so far there are few definite data documenting that treatment of COPD comorbidities will reduce morbidity and mortality rates in these patients. Observational studies suggest that COPD patients treated with statins, angiotensin-converting enzyme inhibitors and angiotensin II type 1 receptor blockers, and β-adrenoceptor blockers may have improved survival and reduced hospitalisation from exacerbations. Progress in basic and translational research has led to a better understanding of pharmacological mechanisms that may explain the effects of these drugs on COPD and some small clinical trial activity is beginning to generate promising results.

Losartan exerts no protective effects against acute pulmonary embolism-induced hemodynamic changes

The acute obstruction of pulmonary vessels by venous thrombi is a critical condition named acute pulmonary embolism (APE). During massive APE, severe pulmonary hypertension may lead to death secondary to right heart failure and circulatory shock. APE-induced pulmonary hypertension is aggravated by active pulmonary vasoconstriction. While blocking the effects of some vasoconstrictors exerts beneficial effects, no previous study has examined whether angiotensin II receptor blockers protect against the hemodynamic changes associated with APE. We examined the effects exerted by losartan on APE-induced hemodynamic changes. Hemodynamic evaluations were performed in non-embolized lambs treated with saline (n = 4) and in lambs that were embolized with silicon microspheres and treated with losartan (30 mg/kg followed by 1 mg/kg/h, n = 5) or saline (n = 7) infusions. The plasma and lung angiotensin-converting enzyme (ACE) activity were assessed using a fluorometric method. APE increased mean pulmonary arterial pressure (MPAP) and pulmonary vascular resistance index (PVRI) by 21 ± 2 mmHg and 375 ± 20 dyn s cm⁻⁵ m⁻², respectively (P < 0.05). Losartan decreased MPAP significantly (by approximately 15%), without significant changes in PVRI and tended to decrease cardiac index (P > 0.05). Lung and plasma ACE activity were similar in both embolized and non-embolized animals. Our findings show evidence of lack of activation of the renin-angiotensin system during APE. The lack of significant effects of losartan on the pulmonary vascular resistance suggests that losartan does not protect against the hemodynamic changes found during APE.

Antenatal maternal hypoxic stress: adaptations in fetal lung Renin-Angiotensin system

Antenatal maternal hypoxia (AMH) can lead to intrauterine growth restriction (IUGR), as well as idiopathic pulmonary hypertension of newborn and adult, the latter of which may be a consequence of alterations in the local pulmonary renin-angiotensin system (RAS). Little is known of these adaptations, however. Thus, we tested the hypothesis that antenatal maternal hypoxia is associated with alterations in gene and protein expression of the pulmonary renin-angiotensin system, which may play an important role in pulmonary disorders in the offspring. In FVB/NJ mice, we studied messenger RNA (mRNA) and protein expression, as well as promoter DNA methylation and microRNA (miRNA) levels in response to 48 hours hypoxia (10.5% O(2)) at 15.5 day post coitum (DPC). In response to AMH, the pulmonary mRNA levels of angiotensin-converting enzyme (ACE) 1.2, ACE-2, and angiotensin II type 1b (AT-1b) receptors were increased significantly, as compared to controls (N = 4). In response to antenatal hypoxia, pulmonary protein levels of renin and ACE-2 also were increased significantly, whereas ACE-1 protein expression was reduced. In fetal lungs, we also observed reduced expression of the miRNAs: mmu-mir -199b, -27b, -200b, and -468 that putatively increase the translation of renin, ACE-1, ACE-2, and AT-1 receptors, respectively. In response to AMH, promoter methylation of ACE was unchanged. We conclude that AMH leads to changes in expression of pulmonary RAS of fetal mice. The possible implications of these changes for the regulation of pulmonary vascular contractility in later life remain to be explored.

Losartan attenuates chronic cigarette smoke exposure-induced pulmonary arterial hypertension in rats: possible involvement of angiotensin-converting enzyme-2

Chronic cigarette smoking induces pulmonary arterial hypertension (PAH) by largely unknown mechanisms. Renin–angiotensin system (RAS) is known to function in the development of PAH. Losartan, a specific angiotensin II receptor antagonist, is a well-known antihypertensive drug with a potential role in regulating angiotensin-converting enzyme-2 (ACE2), a recently found regulator of RAS. To determine the effect of losartan on smoke-induced PAH and its possible mechanism, rats were daily exposed to cigarette smoke for 6 months in the absence and in the presence of losartan. Elevated right ventricular systolic pressure (RVSP), thickened wall of pulmonary arteries with apparent medial hypertrophy along with increased angiotensin II (Ang II) and decreased ACE2 levels were observed in smoke-exposed-only rats. Losartan administration ameliorated pulmonary vascular remodeling, inhibited the smoke-induced RVSP and Ang II elevation and partially reversed the ACE2 decrease in rat lungs. In cultured primary pulmonary artery smooth muscle cells (PASMCs) from 3- and 6-month smoke-exposed rats, ACE2 levels were significantly lower than in those from the control rats. Moreover, PASMCs from 6-month exposed rats proliferated more rapidly than those from 3-month exposed or control rats, and cells grew even more rapidly in the presence of DX600, an ACE2 inhibitor. Consistent with the in vivo study, in vitro losartan pretreatment also inhibited cigarette smoke extract (CSE)-induced cell proliferation and ACE2 reduction in rat PASMCs. The results suggest that losartan may be therapeutically useful in the chronic smoking-induced pulmonary vascular remodeling and PAH and ACE2 may be involved as part of its mechanism. Our study might provide insight into the development of new therapeutic interventions for PAH smokers.

Role of HIF-1alpha in the regulation ACE and ACE2 expression in hypoxic human pulmonary artery smooth muscle cells

Angiotensin-converting enzyme (ACE) enhances the proliferation and migration of pulmonary artery smooth muscle cells (PASMCs), which contribute to the pathogenesis of hypoxic pulmonary hypertension (HPH). Previous reports have demonstrated that hypoxia upregulates ACE expression, but the underlying mechanism is unknown. Here, we found that ACE is persistently upregulated in PASMCs on the transcriptional level during hypoxia. Hypoxia-inducible factor 1alpha (HIF-1alpha), a key transcription factor activated during hypoxia, was able to upregulate ACE protein expression under normoxia, whereas knockdown of HIF-1alpha expression in PASMCs inhibited hypoxia-induced ACE upregulation. Furthermore, HIF-1alpha can bind and transactivate the ACE promoter directly. Therefore, we report that ACE is a novel target of HIF-1alpha. Recently, a homolog of ACE, ACE2, was reported to counterbalance the function of ACE. In contrast to ACE, we found that ACE2 mRNA and protein levels increased during the early stages of hypoxia and decreased to near-baseline levels at the later stages after HIF-1alpha accumulation. Thus HIF-1alpha inhibited ACE2 expression, and the accumulated ANG II catalyzed by ACE is a key mediator in the downregulation of ACE2 by HIF-1alpha. Moreover, a reduction of ACE2 expression in PASMCs by RNA interference was accompanied by significantly enhanced proliferation and migration during hypoxia. We conclude that ACE is directly regulated by HIF-1alpha, whereas ACE2 is regulated in a bidirectional way during hypoxia and may play a protective role during the development of HPH. In sum, these findings contribute to the understanding of the pathogenesis of HPH.

Pulmonary hypertension associated with COPD

Although the prevalence of pulmonary hypertension (PH) in individuals with chronic obstructive pulmonary disease (COPD) is not known precisely, approximately 10%–30% of patients with moderate to severe COPD have elevated pulmonary pressures. The vast majority of PH associated with COPD is mild to moderate and severe PH occurs in <5% of patients. When COPD is associated with PH, both mortality and morbidity are increased. There are no clinical or physical examination findings that accurately identify patients with underlying PH. Radiographic imaging findings are specific but not sensitive indicators of PH. Echocardiography is the principle noninvasive diagnostic test but may be technically limited in a significant proportion of patients with COPD. Right heart catheterization is required for accurate measurement of pulmonary pressures. The combined effects of inflammation, endothelial cell dysfunction, and angiogenesis appear to contribute to the development of PH associated with COPD. Systemic vasodilators have not been found to be effective therapy. Selective pulmonary vasodilators including inhaled nitric oxide and phosphodiesterase inhibitors are promising treatments for patients with COPD associated PH but further evaluation of these medications is needed prior to their routine use.

Oxidative stress contributes to pulmonary hypertension in the transgenic (mRen2)27 rat

The transgenic (mRen2)27 (Ren2) rat overexpresses mouse renin in extrarenal tissues, causing increased local synthesis of ANG II, oxidative stress, and hypertension. However, little is known about the role of oxidative stress induced by the tissue renin-angiotensin system (RAS) as a contributing factor in pulmonary hypertension (PH). Using male Ren2 rats, we test the hypothesis that lung tissue RAS overexpression and resultant oxidative stress contribute to PH and pulmonary vascular remodeling. Mean arterial pressure (MAP), right ventricular systolic pressure (RVSP), and wall thickness of small pulmonary arteries (PA), as well as intrapulmonary NADPH oxidase activity and subunit protein expression and reactive oxygen species (ROS), were compared in age-matched Ren2 and Sprague-Dawley (SD) rats pretreated with the SOD/catalase mimetic tempol for 21 days. In placebo-treated Ren2 rats, MAP and RVSP, as well as intrapulmonary NADPH oxidase activity and subunits (Nox2, p22phox, and Rac-1) and ROS, were elevated compared with placebo-treated SD rats (P < 0.05). Tempol decreased RVSP (P < 0.05), but not MAP, in Ren2 rats. Tempol also reduced intrapulmonary NADPH oxidase activity, Nox2, p22phox, and Rac-1 protein expression, and ROS in Ren2 rats (P < 0.05). Compared with SD rats, the cross-sectional surface area of small PA was 38% greater (P < 0.001) and luminal surface area was 54% less (P < 0.001) in Ren2 rats. Wall surface area was reduced and luminal area was increased in tempol-treated SD and Ren2 rats compared with untreated controls (P < 0.05). Collectively, the results of this investigation support a seminal role for enhanced tissue RAS/oxidative stress as factors in development of PH and pulmonary vascular remodeling.

A study of the effect of hemorrhage on the cardiorespiratory actions of halothane, isoflurane and sevoflurane in the dog

OBJECTIVE

To compare the cardiorespiratory changes induced by equipotent concentrations of halothane (HAL), isoflurane (ISO) and sevoflurane (SEVO) before and after hemorrhage.

STUDY DESIGN

Prospective, randomized clinical trial.

ANIMALS

Twenty-four healthy adult dogs weighing 15.4 +/- 3.4 kg (mean +/- SD).

METHODS

Animals were randomly allocated to one of three groups (n = 8 per group). In each group, anesthesia was maintained with 1.5 minimum alveolar concentration of HAL (1.3%), ISO (1.9%) and SEVO (3.5%) in oxygen. Controlled ventilation was performed to maintain eucapnia. Cardiorespiratory variables were evaluated at baseline (between 60 and 90 minutes after induction), immediately after and 30 minutes after the withdrawal of 32 mL kg(-1) of blood (40% of the estimated blood volume) over a 30-minute period.

RESULTS

During baseline conditions, ISO and SEVO resulted in higher cardiac index (CI) than HAL. Heart rates were higher with SEVO at baseline, while mean arterial pressure (MAP) and mean pulmonary arterial pressure did not differ between groups. Although heart rate values were higher for ISO and SEVO after hemorrhage, only ISO resulted in a higher CI when compared with HAL. In ISO-anesthetized dogs, MAP was higher immediately after hemorrhage, and this was related to better maintenance of CI and to an increase in systemic vascular resistance index from baseline.

CONCLUSIONS

Although the hemodynamic responses of ISO and SEVO are similar in normovolaemic dogs, ISO results in better maintenance of circulatory function during the early period following a massive blood loss.

CLINICAL RELEVANCE

Inhaled anesthetics should be used judiciously in animals presented with blood loss. However, if an inhalational agent is to be used under these circumstances, ISO may provide better hemodynamic stability than SEVO or HAL.

Effects of olmesartan, an AT1 receptor antagonist, on hypoxia-induced activation of ERK1/2 and pro-inflammatory signals in the mouse lung

The present study aimed to investigate the effects of olmesartan, an antagonist for angiotensin II receptor type 1(AT1), on the activation of extracellular signal-regulated kinases (ERK)1/2, tissue remodeling, and pro-inflammatory signals in the right ventricle and lung of mice during the early phase of hypobaric hypoxia. Phosphorylation of ERK1/2 in both tissue types in response to hypoxia peaked at 1-3 days, and declined rapidly in the right ventricle, whereas in the lung it was sustained for at least 8 days. Upregulation of angiotensinogen mRNA was observed in the hypoxic lung at 4-9 days, but not in the hypoxic right ventricle and pulmonary artery. Olmesartan inhibited the hypoxia-induced phosphorylation of ERK1/2 in the lung, but not in the right ventricle. Neither right ventricular hypertrophy nor the thickening of the intrapulmonary arterial wall was ameliorated by olmesartan. However, this drug inhibited the expression of the mRNA for angiotensinogen and several pro-inflammatory factors, including interleukin-6 and inducible nitric oxide synthase in the hypoxic lung. These results suggest that olmesartan blocks a potential positive feedback loop of the angiotensin II-AT1 receptor system, which may lead to attenuate pro-inflammatory signals in the mouse lung, that are associated with hypoxic pulmonary hypertension, without inducing any appreciable effects on the compensatory cardiopulmonary hypertrophy at an early phase of exposure to a hypobaric hypoxic environment.

Effects of chronic angiotensin II receptor antagonist and angiotensin-converting enzyme inhibitor treatments on neurohormonal levels and haemodynamics during cardiopulmonary bypass

BACKGROUND

Chronic treatment with renin-angiotensin system (RAS) antagonists frequently causes deleterious hypotension during anaesthesia. We compared the effects of angiotensin II receptor antagonists (ARA) and angiotensin-converting enzyme inhibitors (ACEI) on neurohormonal levels and haemodynamics during cardiopulmonary bypass (CPB).

METHODS

Forty-four patients undergoing mitral valvular surgery who were treated with either ARA (ARA group, n=14) or ACEI (ACEI group, n=15) over 12 weeks or who were not treated with any RAS antagonist (control group, n=15) were enrolled. The plasma levels of epinephrine, norepinephrine, arginine vasopressin (AVP) and angiotensin II, and haemodynamic variables were measured before (T1) and 15 min after (T2) the start of CPB, before aortic unclamping (T3) and at skin closure (T4). Mean arterial pressure (MAP) was maintained above 60 mm Hg with phenylephrine administration during CPB.

RESULTS

The plasma epinephrine, norepinephrine, AVP and angiotensin II levels increased during CPB in all groups. Compared with the control group, the AVP level was lower at T1 in the ARA group and at T2 in the ARA and ACEI groups. The angiotensin II level was higher at T1, T2 and T3 in ARA group compared with ACEI and control groups. There were no significant differences in the epinephrine and norepinephrine levels among the three groups. The amount of administered phenylephrine during CPB was greater and MAP was lower in the ARA group compared with the ACEI and control groups.

CONCLUSIONS

Chronic ARA treatment resulted in more profound hypotension than ACEI treatment during CPB, and this may be associated with the blockade of angiotensin II receptors by ARA.

How valid are animal models to evaluate treatments for pulmonary hypertension?

Various animal models of pulmonary hypertension (PH) exist, among which injection of monocrotaline (MCT) and exposure to hypoxia are used most frequently. These animal models have not only been used to characterize the pathophysiology of PH and its sequelae such as right ventricular hypertrophy and failure, but also to test novel therapeutic strategies. This manuscript summarizes the available treatment studies in animal models of PH, and compares the findings to those obtained in patients with PH. The analysis shows that all approaches which have proven successful in patients, most notably prostacyclin and its analogs and endothelin receptor antagonists, are also effective in various animal models. However, the opposite it not always true. Therefore, promising results in animals have to be interpreted carefully until confirmed in clinical studies.

Angiotensin-converting enzyme 2 in lung diseases

The renin-angiotensin system (RAS) plays a key role in maintaining blood pressure homeostasis, as well as fluid and salt balance. Angiotensin II, a key effector peptide of the system, causes vasoconstriction and exerts multiple biological functions. Angiotensin-converting enzyme (ACE) plays a central role in generating angiotensin II from angiotensin I, and capillary blood vessels in the lung are one of the major sites of ACE expression and angiotensin II production in the human body. The RAS has been implicated in the pathogenesis of pulmonary hypertension and pulmonary fibrosis, both commonly seen in chronic lung diseases such as chronic obstructive lung disease. Recent studies indicate that the RAS also plays a critical role in acute lung diseases, especially acute respiratory distress syndrome (ARDS). ACE2, a close homologue of ACE, functions as a negative regulator of the angiotensin system and was identified as a key receptor for SARS (severe acute respiratory syndrome) coronavirus infections. In the lung, ACE2 protects against acute lung injury in several animal models of ARDS. Thus, the RAS appears to play a critical role in the pathogenesis of acute lung injury. Indeed, increasing ACE2 activity might be a novel approach for the treatment of acute lung failure in several diseases.

Pilot study of losartan for pulmonary hypertension in chronic obstructive pulmonary disease

BACKGROUND

Morbidity in COPD results from a combination of factors including hypoxia-induced pulmonary hypertension, in part due to pulmonary vascular remodelling. Animal studies suggest a role of angiotensin II and acute studies in man concur. Whether chronic angiotensin-II blockade is beneficial is unknown. We studied the effects of an angiotensin-II antagonist losartan, on haemodynamic variables, exercise capacity and symptoms.

METHODS

This was a double-blind, randomized, parallel group, placebo- controlled study of 48 weeks duration. Forty patients with COPD and pulmonary hypertension (Tran tricuspid pressure gradient (TTPG) = 30 mmHg) were randomised to losartan 50 mg or placebo. Changes in TTPG were assessed at 3, 6 and 12 months.

RESULTS

There was a trend for TTPG to increase in the placebo group (baseline 43.4 versus 48.4 mmHg at endpoint) and stay constant in the losartan group (baseline 42.8 versus 43.6 mmHg). More patients in the losartan group (50%) than in the placebo group (22%) showed a clinically meaningful reduction in TTPG at any timepoint; these effects seemed more marked in patients with higher baseline TTPG. There were no clear improvements in exercise capacity or symptoms.

CONCLUSION

In this 12-month pilot study, losartan 50 mg had no statistically significant beneficial effect on TTPG, exercise capacity or symptoms in pulmonary hypertension secondary to obstructive disease. A sub-group of patients with higher TTPG may benefit.

Antiproliferative Action of an Angiotensin I-Converting Enzyme Inhibitory Peptide, Val-Tyr, via an L-Type Ca2+ Channel Inhibition in Cultured Vascular Smooth Muscle Cells

Recent antihypertensive studies have demonstrated that small peptides with angiotensin I-converting enzyme (ACE) inhibitory activity had an ability to lower or to modulate a pressor blood pressure response in mild hypertensive subjects. However, the underlying mechanisms still remain unclear. Based on our previous finding that a small peptide, Val-Tyr (VY), was accumulated in the rat aorta and kidney as well as in the circulating blood system, we here investigated whether antihypertensive small peptides exert an antiproliferative effect on serum- or mitogen-induced human vascular smooth muscle cells (VSMCs). Treatment with some ACE inhibitory small peptides (VY, Ile-Trp [IW], and Ile-Val-Tyr [IVY]) had diverse effects on serum-stimulated VSMC proliferation that were independent of their ACE inhibitory activity, though only VY exerted a potent antiproliferative action. VY also showed a greater inhibition of WST-8 incorporation in response to angiotensin (Ang) II-stimulation than the other two small peptides. The attenuation of Ang II-stimulated WST-8 incorporation by VY was not affected by Ang II receptor antagonists (losartan and saralasin ([Sar1, Ile8]-Ang II)), indicating that the antiproliferative action of VY may not be due to the peptide's antagonistic effect against Ang II receptors. Treatment with VY had a significant inhibitory effect on the WST-8 incorporation induced by the stimulation of a voltage-gated L-type Ca2+ channel agonist, Bay K 8644. Even in the presence of a K+ channel blocker (paxillin) the inhibition was apparent, suggesting that VY inhibited the proliferation of VSMCs by serving as a natural L-type Ca2+ channel blocker, but not as a K+ channel agonist.

Endogenous angiotensin II in the regulation of hypoxic pulmonary vasoconstriction in anaesthetized dogs

Introduction

The role played by several vasoactive mediators that are synthesized and released by the pulmonary vascular endothelium in the regulation of hypoxic pulmonary vasoconstriction (HPV) remains unclear. As a potent vasoconstrictor, angiotensin II could be involved. We tested the hypothesis that angiotensin-converting enzyme inhibition by enalaprilat and type 1 angiotensin II receptor blockade by candesartan would inhibit HPV.

Methods

HPV was evaluated in anaesthetized dogs, with an intact pulmonary circulation, by examining the increase in the Ppa–Ppao gradient (mean pulmonary artery pressure minus occluded pulmonary artery pressure) that occurred in response to hypoxia (inspiratory oxygen fraction of 0.1) at constant pulmonary blood flow. Plasma renin activity and angiotensin II immunoreactivity were measured to determine whether activation or inhibition of the renin–angiotensin system was present.

Results

Administration of enalaprilat and candesartan did not affect the Ppa–Ppao gradient at baseline or during hypoxia. Plasma renin activity and angiotensin II immunoreactivity increased during hypoxia, and subsequent measurements were consistent with effective angiotensin-converting enzyme inhibition after administration of enalaprilat, and with angiotensin receptor blockade after administration of candesartan.

Conclusion

These results suggest that, although the renin–angiotensin system was activated in hypoxia, angiotensin II is not normally involved in mediating acute HPV.

Characterization of high-altitude pulmonary hypertension in the Kyrgyz: association with angiotensin-converting enzyme genotype

Previous studies have suggested a genetic component in susceptibility to hypoxia-induced pulmonary hypertension. We therefore estimated the prevalence of high-altitude pulmonary hypertension (HAPH) in a Kyrgyz population and whether the insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme (ACE) gene associates with HAPH. An electrocardiographic survey of 741 highlanders demonstrated electrocardiogram signs of cor pulmonale in 14% of subjects. Pulmonary artery hemodynamics measured in an independent group of 136 male highlanders with symptoms of dyspnea at altitude revealed established pulmonary hypertension (mean pulmonary artery pressure [MPAP] > or = 25 mm Hg) in 20%. However, 26% of the normal subjects demonstrated an exaggerated response (twofold or greater increase in MPAP) to inhalation of 11% oxygen, and were classified as hyperresponsive. Ten-year follow-up of this group revealed increases in the MPAP, but not in normal subjects. Comparison of ACE I/D genotypes in the catheterized group revealed a threefold higher frequency of the I/I genotype in highlanders with HAPH, compared with normal highlanders (chi2 = 11.59, p = 0.003). In addition, MPAP was higher in highlanders with the I/I genotype (26.9 +/- 4.0 mm Hg) compared with the I/D genotype (20.6 +/- 1.2 mm Hg) or the D/D genotype (18.3 +/- 0.9 mm Hg) (p < 0.05). We conclude that HAPH is associated with ACE I/D genotype among Kyrgyz highlanders and the development of HAPH in this population and may be predicted by hyperresponsiveness to acute hypoxia.

Insertion/deletion polymorphism of the angiotensin I-converting enzyme gene and arterial oxygen saturation at high altitude

There is a significant genetic influence on arterial oxygen saturation (Sa(O(2))) in high-altitude (HA) residents. It is not known whether this is true of lowlanders ascending to HA. The I allele of the angiotensin-converting enzyme (ACE) gene is associated with low ACE activity and elite endurance performance. An excess of the I allele has also been reported in South American natives living over 3,000 m and among elite HA mountaineers who demonstrate extreme endurance in a hypoxic environment, where maintenance of Sa(O(2)) is crucial to performance. We postulated that the I allele may confer an advantage at HA through genotype-dependent alterations in Sa(O(2)). Rapid ascent (n = 32) and slow ascent groups (n = 40), ascending to approximately 5,000 m over 12.0 and 18.5 days, respectively, had their Sa(O(2)) assessed throughout and compared with their ACE genotype. Resting Sa(O(2)) was independent of the ACE genotype and remained so for the slow ascent group, in whom the fall in Sa(O(2)) with ascent was genotype independent. However, Sa(O(2)) with ascent was significantly associated with the ACE genotype in the rapid ascent group (p = 0.01) with a relatively sustained Sa(O(2)) in the II subjects. These data are the first to report an association of the I allele with the maintenance of Sa(O(2)) at HA.

Cardiac modulations of ANG II receptor expression in rats with hypoxic pulmonary hypertension

Right ventricular myocardial hypertrophy during hypoxic pulmonary hypertension is associated with local renin-angiotensin system activation. The expression of angiotensin II type 1 (AT(1)) and type 2 (AT(2)) receptors in this setting has never been investigated. We have therefore examined the chronic hypoxia pattern of AT(1) and AT(2) expression in the right and left cardiac ventricles, using in situ binding and RT-PCR assays. Hypoxia produced right, but not left, ventricular hypertrophy after 7, 14, and 21 days, respectively. Hypoxia for 2 days was associated in each ventricle with a simultaneous and transient increase (P < 0.05) in AT(1) binding and AT(1) mRNA levels in the absence of any significant change in AT(2) expression level. Only after 14 days of hypoxia, AT(2) binding increased (P < 0.05) in the two ventricles, concomitantly with a right ventricular decrease (P < 0.05) in AT(2) mRNA. Along these data, AT(1) and AT(2) binding remained unchanged in both the left and hypertrophied right ventricles from rats treated with monocrotaline for 30 days. These results indicate that chronic hypoxia induces modulations of AT(1) and AT(2) receptors in both cardiac ventricles probably through direct and indirect mechanisms, respectively, which modulations may participate in myogenic (at the level of smooth or striated myocytes) rather than in the growth response of the heart to hypoxia.

Enalapril protects mice from pulmonary hypertension by inhibiting TNF-mediated activation of NF-kappaB and AP-1

The present study was undertaken to investigate the effects of treatment with the angiotensin-converting enzyme (ACE) inhibitor enalapril in a mouse model of pulmonary hypertension induced by bleomycin. Bleomycin-induced lung injury in mice is mediated by enhanced tumor necrosis factor-alpha (TNF) expression in the lung, which determines the murine strain sensitivity to bleomycin, and murine strains are sensitive (C57BL/6) or resistant (BALB/c). Bleomycin induced significant pulmonary hypertension in C57BL/6, but not in BALB/c, mice; average pulmonary arterial pressure (PAP) was 26.4 +/- 2.5 mmHg (P < 0.05) vs. 15.2 +/- 3 mmHg, respectively. Bleomycin treatment induced activation of nuclear factor (NF)-kappaB and activator protein (AP)-1 and enhanced collagen and TNF mRNA expression in the lung of C57BL/6 but not in BALB/c mice. Double TNF receptor-deficient mice (in a C57BL/6 background) that do not activate NF-kappaB or AP-1 in response to bleomycin did not develop bleomycin-induced pulmonary hypertension (PAP 14 +/- 3 mmHg). Treatment of C57BL/6 mice with enalapril significantly (P < 0.05) inhibited the development of pulmonary hypertension after bleomycin exposure. Enalapril treatment inhibited NF-kappaB and AP-1 activation, the enhanced TNF and collagen mRNA expression, and the deposition of collagen in bleomycin-exposed C57BL/6 mice. These results suggest that ACE inhibitor treatment decreases lung injury and the development of pulmonary hypertension in bleomycin-treated mice.

Pulmonary vascular remodeling: a target for therapeutic intervention in pulmonary hypertension

Pulmonary vascular remodelling is an important pathological feature of pulmonary hypertension, leading to increased pulmonary vascular resistance and reduced compliance. It involves thickening of all three layers of the blood vessel wall (due to hypertrophy and/or hyperplasia of the predominant cell type within each layer), as well as extracellular matrix deposition. Neomuscularisation of non-muscular arteries and formation of plexiform and neointimal lesions also occur. Stimuli responsible for remodelling involve transmural pressure, stretch, shear stress, hypoxia, various mediators [angiotensin II, endothelin (ET)-1, 5-hydroxytryptamine, growth factors, and inflammatory cytokines], increased serine elastase activity, and tenascin-C. In addition, there are reductions in the endothelium-derived antimitogenic substances, nitric oxide, and prostacyclin. Intracellular signalling mechanisms involved in pulmonary vascular remodelling include elevations in intracellular Ca2+ and activation of the phosphatidylinositol pathway, protein kinase C, and mitogen-activated protein kinase. In animal models of pulmonary hypertension, various drugs have been shown to attenuate pulmonary vascular remodelling. These include angiotensin-converting enzyme inhibitors, angiotensin receptor antagonists, ET receptor antagonists, ET-converting enzyme inhibitors, nitric oxide, phosphodiesterase 5 inhibitors, prostacyclin, Ca2+ -channel antagonists, heparin, and serine elastase inhibitors. Inhibition of remodelling is generally accompanied by reductions in pulmonary artery pressure. The efficacy of some of the drugs varies, depending on the animal model of the disease. In view of the complexity of the remodelling process and the diverse aetiology of pulmonary hypertension in humans, it is to be anticipated that successful anti-remodelling therapy in the clinic will require a range of different drug options.

Angiotensin-converting enzyme and genetics at high altitude

As part of the renin-angiotensin system (RAS), angiotensin-converting enzyme (ACE) plays a key role in circulatory homeostasis. ACE degrades vasodilator kinins and generates angiotensin II. A polymorphism in intron 16 of the human ACE gene has been identified in which the presence (insertion, I allele) rather than the absence (deletion, D allele) of a 287 bp fragment is associated with lower serum and tissue ACE activity. The I allele has been associated with some aspects of endurance performance, being found with excess frequency in elite distance runners, rowers, and other elite athletes. Mountaineers also demonstrate an allele skew with a significant excess of the I allele and II genotype in elite, male, British mountaineers who have ascended beyond 7000 m without the use of supplemental oxygen. This review evaluates the evidence for and against an association of the I allele with human endurance, and performance at high altitude. We conclude that the I allele does confer an advantage, most likely mediated via improved muscle efficiency with secondary benefits in terms of conservation of non-fat mass.

Effect of chronic hypoxia on agonist-induced tone and calcium signaling in rat pulmonary artery

The effect of chronic hypoxia (CH) for 14 days on Ca2+ signaling and contraction induced by agonists in the rat main pulmonary artery (MPA) was investigated. In MPA myocytes obtained from control (normoxic) rats, endothelin (ET)-1, angiotensin II (ANG II), and ATP induced oscillations in intracellular Ca2+ concentration ([Ca2+]i) in 85-90% of cells, whereas they disappeared in myocytes from chronically hypoxic rats together with a decrease in the percentage of responding cells. However, both the amount of mobilized Ca2+ and the sources of Ca2+ implicated in the agonist-induced response were not changed. Analysis of the transient caffeine-induced [Ca2+]i response revealed that recovery of the resting [Ca2+]i value was delayed in myocytes from chronically hypoxic rats. The maximal contraction induced by ET-1 or ANG II in MPA rings from chronically hypoxic rats was decreased by 30% compared with control values. Moreover, the D-600- and thapsigargin-resistant component of contraction was decreased by 40% in chronically hypoxic rats. These data indicate that CH alters pulmonary arterial reactivity as a consequence of an effect on both Ca2+ signaling and Ca2+ sensitivity of the contractile apparatus. A Ca2+ reuptake mechanism appears as a CH-sensitive phenomenon that may account for the main effect of CH on Ca2+ signaling.

Dissociation of pulmonary vascular remodeling and right ventricular pressure in tissue angiotensin-converting enzyme-deficient mice under conditions of chronic alveolar hypoxia

The present study was designed to characterize the role of tissue angiotensin-converting enzyme (ACE) on pulmonary vascular remodeling and its functional consequences in chronic hypoxia. On the basis of data obtained by pharmacological inhibition of ACE in rats we hypothesized that, under chronic hypoxic conditions, tissue ACE-deficient mice show less remodeling of pulmonary arterioles as compared with wild-type mice, but have equally increased right ventricular pressures. Wild-type and tissue ACE-deficient mice were exposed to chronic hypoxia for 4 wk. Absence of tissue ACE did not affect the increase in the mean right ventricular pressures (MRVP) and the extent of right ventricular hypertrophy under chronic hypoxic conditions. Chronic hypoxia induced significant remodeling of pulmonary arterioles in tissue ACE-deficient mice. The percentage of completely muscularized arterioles was, however, lower in tissue ACE-deficient mice compared with wild-type animals (29 +/- 12 versus 41 +/- 18%, p < 0.05), whereas the percentage of partially muscularized arterioles had increased (48 +/- 11 versus 39 +/- 11%, p < 0.05). No sex-based effects were found. We conclude that the absence of tissue ACE does not prevent the MRVP and right ventricular weight from increasing during chronic hypoxia in the mouse. Also, pulmonary vascular remodeling occurs in hypoxic tissue ACE-deficient mice, albeit to a lower level than in mice that do have an intact ACE gene.

Pulmonary vascular remodelling in hypoxic rats: effects of amlodipine, alone and with perindopril

This study investigated whether pulmonary vascular remodelling in hypoxic pulmonary hypertensive rats (10% oxygen; 4 weeks) could be prevented by treatment, during hypoxia, with amlodipine (10 mg/kg/day, p.o.), either alone or in combination with the angiotensin converting enzyme inhibitor, perindopril (30 mg/kg/day, p.o.). Medial thickening of pulmonary arteries (30-500 microm o.d.) was attenuated by amlodipine whereas it was totally prevented by the combination treatment (amlodipine plus perindopril); neomuscularisation of small alveolar arteries (assessed from critical closing pressure in isolated perfused lungs) was not affected. Pulmonary vascular resistance (isolated perfused lungs) was reduced by both treatment regimes but only combination treatment reduced right ventricular hypertrophy. Thus, amlodipine has anti-remodelling properties in pulmonary hypertensive rats. The finding that combining amlodipine with another anti-remodelling drug produced effects on vascular structure that were additive raises the question of whether combination therapy with two different anti-remodelling drugs may be of value in the treatment of patients with hypoxic (and possibly other forms of) pulmonary hypertension.

Pulmonary angiotensin-converting enzyme (ACE) binding and inhibition in humans. A positron emission tomography study

Angiotensin-converting enzyme (ACE) inhibition attenuates pulmonary hypertension and delays the development of pulmonary vascular remodeling in animal models. Thus, ACE inhibition might be a useful treatment for primary pulmonary hypertension (PPH). To determine the dose of ACE inhibitor required to specifically block pulmonary ACE in humans, we measured the combined forward rate constant (CFRC) for [(18)F]-fluorocaptopril, which is proportional to the mass of ACE in the lung, using positron emission tomography (PET). In five normal subjects, CFRC was measured twice, 1 wk apart, to assess measurement reproducibility. The CFRC was 0.151 +/- 0.067 for the first measurement and 0.140 +/- 0.060 for the second measurement (p = not significant [NS]). In five normals, CFRC decreased on average 84%, from 0.177 +/- 0.053/s to 0.028 +/- 0.017/s (p < 0.05), after 1 wk ingestion of 5 mg enalapril orally once a day (the scans were performed 24 h after the last medication). Similarly, in five patients with PPH, CFRC decreased on average 76%, from 0.052 +/- 0. 020/s to 0.012 +/- 0.003 (p < 0.01), after 1 wk enalapril, despite much lower baseline values. We conclude that the total mass of pulmonary ACE appears to be significantly reduced in PPH and that only low doses of ACE inhibitors may be needed to block the effects of ACE on vascular remodeling in PPH.

Modulation of angiotensin II receptor expression during development and regression of hypoxic pulmonary hypertension

Lung vessel muscularization during hypoxic pulmonary hypertension is associated with local renin-angiotensin system activation. The expression of angiotensin II (Ang II) AT1 and AT2 receptors in this setting is not well known and has never been investigated during normoxia recovery. We determined both chronic hypoxia and normoxia recovery patterns of AT1 and AT2 expression and distal muscularization in the same lungs using in situ binding, reverse transcriptase/polymerase chain reaction, and histology. We also used an isolated perfused lung system to evaluate the vasotonic effects of AT1 and AT2 during chronic exposure to hypoxia with and without subsequent normoxia recovery. Hypoxia produced right ventricular hypertrophy of about 100% after 3 wk, which reversed with normoxia recovery. Hypoxia for 2 wk was associated with simultaneous increases (P<0.05) in AT1 and AT2 binding (16-fold and 18-fold, respectively) and in muscularized vessels in alveolar ducts (2. 8-fold) and walls (3.7-fold). An increase in AT2 messenger RNA (mRNA) (P<0.05) was also observed, whereas AT1 mRNA remained unchanged. After 3 wk of hypoxia, muscularization was at its peak, whereas all receptors and transcripts showed decreases (P<0.05 versus hypoxia 2 wk for AT1 mRNA), which became significant after 1 wk of normoxia recovery (P<0.05 versus hypoxia 2 wk). Significant reversal of muscularization (P<0.01) was found only after 3 wk of normoxia recovery in alveolar wall vessels. Finally, the AT1 antagonist losartan completely inhibited the vasopressor effect of Ang II in hypoxic and normoxia-restored lungs, whereas the AT2 agonist CGP42112A had no effect. Our data indicate that in lungs, chronic hypoxia-induced distal muscularization is associated with early and transient increases in AT2 and AT1 receptors probably owing to hypoxia- dependent transcriptional and post-transcriptional regulatory mechanisms, respectively. They also indicate that the vasotonic response to Ang II is mainly due to the AT1 subtype.

Perindopril, an angiotensin converting enzyme inhibitor, in pulmonary hypertensive rats: comparative effects on pulmonary vascular structure and function

1. Hypoxic pulmonary hypertension in rats (10% O2, 4 weeks) is characterized by changes in pulmonary vascular structure and function. The effects of the angiotensin converting enzyme inhibitor perindopril (oral gavage, once daily for the 4 weeks of hypoxia) on these changes were examined. 2. Perindopril (30 mg kg-1 d-1) caused an 18% reduction in pulmonary artery pressure in hypoxic rats. 3. Structural changes (remodelling) in hypoxic rats included increases in (i) critical closing pressure in isolated perfused lungs (remodelling of arteries <50 microm o.d.) and (ii) medial wall thickness of intralobar pulmonary arteries, assessed histologically (vessels 30 - 100 and 101 - 500 microm o.d.). Perindopril 10 and 30 mg kg-1 d-1 attenuated remodelling in vessels < or = 100 microm (lungs and histology), 30 mg kg-1 d-1 was effective in vessels 101 - 500 microm but neither dose prevented hypertrophy of main pulmonary artery. 3 mg kg-1 d-1 was without effect. 4. Perindopril (30 mg kg-1 d-1) prevented the exaggerated hypoxic pulmonary vasoconstrictor response seen in perfused lungs from hypoxic rats but did not prevent any of the functional changes (i.e. the increased contractions to 5-HT, U46619 (thromboxane-mimetic) and K+ and diminished contractions to angiotensins I and II) seen in isolated intralobar or main pulmonary arteries. Acetylcholine responses were unaltered in hypoxic rats. 5. We conclude that, in hypoxic rats, altered pulmonary vascular function is largely independent of remodelling. Hence any drug that affects only remodelling is unlikely to restore pulmonary vascular function to normal and, like perindopril, may have only a modest effect on pulmonary artery pressure.

Chronic hypoxia alters effects of endothelin and angiotensin on K+ currents in pulmonary arterial myocytes

We tested the hypothesis that chronic hypoxia alters the regulation of K+ channels in intrapulmonary arterial smooth muscle cells (PASMCs). Charybdotoxin-insensitive, 4-aminopyridine-sensitive voltage-gated K+ (K(V,CI)) and Ca2+-activated K+ (KCa) currents were measured in freshly isolated PASMCs from rats exposed to 21 or 10% O2 for 17-21 days. In chronically hypoxic PASMCs, K(V, CI) current was reduced and KCa current was enhanced. 4-Aminopyridine (10 mM) depolarized both normoxic and chronically hypoxic PASMCs, whereas charybdotoxin (100 nM) had no effect in either group. The inhibitory effect of endothelin (ET)-1 (10(-7) M) on K(V,CI) current was significantly reduced in PASMCs from chronically hypoxic rats, whereas inhibition by angiotensin (ANG) II (10(-7) M) was enhanced. Neither ET-1 nor ANG II altered K(Ca) current in normoxic PASMCs; however, both stimulated K(Ca) current at positive potentials in chronically hypoxic PASMCs. These results suggest that although modulation of K(V,CI) and KCa channels by ET-1 and ANG II is altered by chronic hypoxia, the role of these channels in the regulation of resting membrane potential was not changed.

Acute hypoxic pulmonary vasoconstriction in conscious dogs decreases renin and is unaffected by losartan

Acute hypoxic pulmonary vasoconstriction (HPV) may be mediated by vasoactive peptides. We studied eight conscious, chronically tracheostomized dogs kept on a standardized dietary sodium intake. Normoxia (40 min) was followed by hypoxia (40 min, breathing 10% oxygen, arterial oxygen pressures 36 +/- 1 Torr) during both control (Con) and losartan experiments (Los; iv infusion of 100 microg. min-1. kg-1 losartan). During hypoxia, minute ventilation (by 0.9 l/min in Con, by 1.3 l/min in Los), cardiac output (by 0.36 l/min in Con, by 0.30 l/min in Los), heart rate (by 11 beats/min in Con, by 30 beats/min in Los), pulmonary artery pressure (by 9 mmHg in both protocols), and pulmonary vascular resistance (by 280 and 254 dyn. s. cm-5 in Con and Los, respectively) increased. Mean arterial pressure and systemic vascular resistance did not change. In Con, PRA decreased from 4.2 +/- 0.7 to 2.5 +/- 0.5 ng ANG I. ml-1. h-1, and plasma ANG II decreased from 11.9 +/- 3.0 to 8.2 +/- 2.1 pg/ml. The renin-angiotensin system is inhibited during acute hypoxia despite sympathetic activation. Under these conditions, ANG II AT1-receptor antagonism does not attenuate HPV.