Role of Rho-kinase signaling and endothelial dysfunction in modulating blood flow distribution in pulmonary hypertension

Pediatric Pulmonary Hypertension: Definitions, Mechanisms, Diagnosis, and Treatment

Pediatric pulmonary hypertension (PPH) is a multifactorial disease with diverse etiologies and presenting features. Pulmonary hypertension (PH), defined as elevated pulmonary artery pressure, is the presenting feature for several pulmonary vascular diseases. It is often a hidden component of other lung diseases, such as cystic fibrosis and bronchopulmonary dysplasia. Alterations in lung development and genetic conditions are an important contributor to pediatric pulmonary hypertensive disease, which is a distinct entity from adult PH. Many of the causes of pediatric PH have prenatal onset with altered lung development due to maternal and fetal conditions. Since lung growth is altered in several conditions that lead to PPH, therapy for PPH includes both pulmonary vasodilators and strategies to restore lung growth. These strategies include optimal alveolar recruitment, maintaining physiologic blood gas tension, nutritional support, and addressing contributing factors, such as airway disease and gastroesophageal reflux. The outcome for infants and children with PH is highly variable and largely dependent on the underlying cause. The best outcomes are for neonates with persistent pulmonary hypertension (PPHN) and reversible lung diseases, while some genetic conditions such as alveolar capillary dysplasia are lethal. © 2021 American Physiological Society. Compr Physiol 11:2135-2190, 2021.

Chronic Inhibition of Toll-Like Receptor 9 Ameliorates Pulmonary Hypertension in Rats

Background

Recent accumulating evidence suggests that toll‐like receptor 9 (TLR9) is involved in the pathogenesis of cardiovascular diseases. However, its role in pulmonary hypertension remains uncertain. We hypothesized that TLR9 is involved in the development of pulmonary hypertension.

Methods and Results

A rat model of monocrotaline‐induced pulmonary hypertension was used to investigate the effects of TLR9 on hemodynamic parameters, vascular remodeling, and survival. Monocrotaline‐exposed rats significantly showed increases in plasma levels of mitochondrial DNA markers, which are recognized by TLR9, TLR9 activation in the lung, and interleukin‐6 mRNA level in the lung on day 14 after monocrotaline injection. Meanwhile, monocrotaline‐exposed rats showed elevated right ventricular systolic pressure, total pulmonary vascular resistance index and vascular remodeling, together with macrophage accumulation on day 21. In the preventive protocol, administration (days −3 to 21 after monocrotaline injection) of selective (E6446) or nonselective TLR9 inhibitor (chloroquine) significantly ameliorated the elevations of right ventricular systolic pressure and total pulmonary vascular resistance index as well as vascular remodeling and macrophage accumulation on day 21. These inhibitors also significantly reduced NF‐κB activation and interleukin‐6 mRNA levels to a similar extent. In the short‐term reversal protocol, E646 treatment (days 14–17 after monocrotaline injection) almost normalized NF‐κB activation and interleukin‐6 mRNA level, and reduced macrophage accumulation. In the prolonged reversal protocol, E6446 treatment (days 14–24 after monocrotaline injection) reversed total pulmonary vascular resistance index and vascular remodeling, and improved survival in monocrotaline‐exposed rats.

Conclusions

TLR9 is involved in the development of pulmonary hypertension concomitant via activation of the NF‐κB‒IL‐6 pathway. Inhibition of TLR9 may be a novel therapeutic strategy for pulmonary hypertension.

Concealed role of red blood cells in pathogenesis of pulmonary arterial hypertension: Decreased red blood cell nitric oxide generation and effect of Rho-Kinase inhibitor fasudil

BACKGROUND

Pulmonary arterial hypertension (PAH) is a devastating disease characterized with alterations in pulmonary vasculature yielding increased pulmonary arterial resistance. Emerging evidences suggest important regulatory roles of red blood cells (RBCs) on nitric oxide (NO) bioavailability, mainly by modulating their endothelial nitric oxide synthase (eNOS) enzyme activity.

OBJECTIVE

The aim of this pilot study was to evaluate the alterations in RBC eNOS activity and intracellular NO generation in PAH patients and the modulatory effects of Rho-Kinase (ROCK) inhibitors.

METHODS

RBCs were isolated from patients with PAH and age-matched healthy subjects and were analyzed for their eNOS activity and NO generation capacity under the conditions of the presence or absence of ROCK inhibitor, fasudil. Phosphotidylserine (PS) exposure was also defined.

RESULTS

eNOS activity and intracellular NO generation were lower in RBC from PAH patients. ROCK inhibitor increased basal eNOS activity and improved NO generation capacity of RBC of PAH patients to healthy control levels. PS exposure levels were also higher in RBC of PAH patients.

CONCLUSIONS

This study provides first evidences for decreased RBC eNOS activity due to its ROCK mediated negative regulation in PAH patients. Considering increased ROCK activity contribution to progression of PAH, ROCK inhibition influences NO bioavailability through RBC eNOS, in addition to endothelial eNOS.

Cerium- and Iron-Oxide-Based Nanozymes in Tissue Engineering and Regenerative Medicine

Nanoparticulate materials displaying enzyme-like properties, so-called nanozymes, are explored as substitutes for natural enzymes in several industrial, energy-related, and biomedical applications. Outstanding high stability, enhanced catalytic activities, low cost, and availability at industrial scale are some of the fascinating features of nanozymes. Furthermore, nanozymes can also be equipped with the unique attributes of nanomaterials such as magnetic or optical properties. Due to the impressive development of nanozymes during the last decade, their potential in the context of tissue engineering and regenerative medicine also started to be explored. To highlight the progress, in this review, we discuss the two most representative nanozymes, namely, cerium- and iron-oxide nanomaterials, since they are the most widely studied. Special focus is placed on their applications ranging from cardioprotection to therapeutic angiogenesis, bone tissue engineering, and wound healing. Finally, current challenges and future directions are discussed.

Inhibition of nitric oxide synthase unmasks vigorous vasoconstriction in established pulmonary arterial hypertension

It is widely accepted that impaired bioavailability of endothelial nitric oxide (NO) plays a critical role in the pathophysiology of pulmonary arterial hypertension (PAH). However, there are published data that show that relatively many PAH patients respond favorably to acetylcholine‐induced pulmonary vasodilation during their follow‐up period, when diverse stages of the disorder are included. We hypothesized that NO bioavailability varies depending on the progression of PAH. Adult rats were exposed to the VEGF receptor blocker Sugen5416 and 3 weeks of hypoxia followed by return to normoxia for various additional weeks. All rats developed increased right ventricular systolic pressure (RVSP) and occlusive lesion formation at 1, 3, 5, and 8 weeks after the Sugen5416 injection. Acute NO synthase blockade did not change the elevated RVSP at the 1‐week time point, while it further increased RVSP markedly at the 3‐, 5‐, and 8‐week time points, leading to death in all rats tested at 8 weeks. Acetylcholine caused significant reduction in RVSP at the 8‐week but not the 1‐week time point, whereas sodium nitroprusside decreased the pressure similarly at both time points. Increased NO‐mediated cGMP production was found in lungs from the 8‐week but not the 1‐week time point. In conclusion, despite its initial impairment, NO bioavailability is restored and endogenous NO plays a critical protective role by counteracting severe pulmonary vasoconstriction in established stages of PAH in the Sugen5416/hypoxia/normoxia‐exposed rats. Our results provide solid pharmacological evidence for a major contribution of a NO‐suppressed vasoconstrictor component in the pathophysiology of established PAH.

Hypoxic pulmonary vasoconstriction and vascular contractility in monocrotaline-induced pulmonary arterial hypertensive rats

Pulmonary arterial hypertension (PAH) is a progressive disease characterized by vascular remodeling of pulmonary arteries (PAs) and increased vascular resistance in the lung. Monocrotaline (MCT), a toxic alkaloid, is widely used for developing rat models of PAH caused by injury to pulmonary endothelial cells; however, characteristics of vascular functions in MCT-induced PAH vary and are not fully understood. Here, we investigated hypoxic pulmonary vasoconstriction (HPV) responses and effects of various vasoconstrictors with isolated/perfused lungs of MCT-induced PAH (PAH-MCT) rats. Using hematoxylin and eosin staining, we confirmed vascular remodeling (i.e., medial thickening of PA) and right ventricle hypertrophy in PAH-MCT rats. The basal pulmonary arterial pressure (PAP) and PAP increase by a raised flow rate (40 mL/min) were higher in the PAH-MCT than in the control rats. In addition, both high K⁺ (40 mM KCl)- and angiotensin II-induced PAP increases were higher in the PAH-MCT than in the control rats. Surprisingly, application of a nitric oxide synthase inhibitor, L-N^G-Nitroarginine methyl ester (L-NAME), induced a marked PAP increase in the PAH-MCT rats, suggesting that endothelial functions were recovered in the three-week PAH-MCT rats. In addition, the medial thickening of the PA was similar to that in chronic hypoxia-induced PAH (PAH-CH) rats. However, the HPV response (i.e., PAP increased by acute hypoxia) was not affected in the MCT rats, whereas HPV disappeared in the PAH-CH rats. These results showed that vascular contractility and HPV remain robust in the MCT-induced PAH rat model with vascular remodeling.

Cell permeable peptide conjugated nanoerythrosomes of fasudil prolong pulmonary arterial vasodilation in PAH rats

In this study, we tested the hypothesis that a cell permeable peptide, CARSKNKDC (CAR), conjugated nanoerythrosomes (NERs) containing fasudil, a rho-kinase (ROCK) inhibitor, produces prolonged pulmonary preferential vasodilation. CAR conjugated NERs containing fasudil were prepared by hypotonic lysis and extrusion method, and optimized for various physicochemical properties in-vitro. The formulations were then used to study the hemodynamic efficacy in a monocrotaline-induced rodent model of pulmonary arterial hypertension (PAH). CAR-NERs-Fasudil was spherical in shape with an average vesicle size and entrapment efficiency of 161.3 ± 1.37 nm and 48.81 ± 1.96%, respectively. Formulations were stable for ~3 weeks when stored at 4 °C and the drug was released in a controlled fashion for >48 h. The uptake of CAR-NERs-Fasudil by TGF-b activated pulmonary arterial smooth muscle cell was ~1.5-fold greater than the uptake of NERs-Fasudil. CAR-NERs-Fasudil inhibited ROCK activity and 5-hydroxytryptamine induced cell proliferation. In terms of reduction of pulmonary arterial pressure, intratracheal administration of CAR-NERs-Fasudil was ~2-fold more specific to the lungs compared with plain fasudil. Overall,CAR peptide grafted nanoerythrosomes offers a new platform for improving the therapeutic efficacy ofa rho-kinase inhibitor, fasudil, without affecting peripheral vasodilation.

Existing drugs and agents under investigation for pulmonary arterial hypertension

Pulmonary arterial hypertension is a progressive and debilitating disorder with an associated high morbidity and mortality rate. Significant advances in our understanding of the epidemiology, pathogenesis, and pathophysiology of pulmonary hypertension have occurred over the past several decades. This has allowed the development of new therapeutic options in this disease. Today, our selection of therapeutic modalities is broader, including calcium channel blockers, prostanoids, endothelin receptor antagonists, phosphodiesterase inhibitors, and soluble guanylate cyclase stimulators, but the disease remains fatal. This underscores the need for a continued search for novel therapies. Several potential pharmacologic agents for the treatment of pulmonary arterial hypertension are under clinical development and some promising results with these treatments have been reported. These agents include rho-kinase inhibitors, long-acting nonprostanoid prostacyclin receptor agonists, tyrosine protein kinase inhibitors, endothelial nitric oxide synthase couplers, synthetically produced vasoactive intestinal peptide, antagonists of the 5-HT2 receptors, and others. This article will review several of these promising new therapies and will discuss the current evidence regarding their potential benefit in pulmonary arterial hypertension.

Synchrotron radiation imaging is a powerful tool to image brain microvasculature

Synchrotron radiation (SR) imaging is a powerful experimental tool for micrometer-scale imaging of microcirculation in vivo. This review discusses recent methodological advances and findings from morphological investigations of cerebral vascular networks during several neurovascular pathologies. In particular, it describes recent developments in SR microangiography for real-time assessment of the brain microvasculature under various pathological conditions in small animal models. It also covers studies that employed SR-based phase-contrast imaging to acquire 3D brain images and provide detailed maps of brain vasculature. In addition, a brief introduction of SR technology and current limitations of SR sources are described in this review. In the near future, SR imaging could transform into a common and informative imaging modality to resolve subtle details of cerebrovascular function.

Pulmonary arterial hypertension in adults: novel drugs and catheter ablation techniques show promise? Systematic review on pharmacotherapy and interventional strategies

This systematic review aims to provide an update on pharmacological and interventional strategies for the treatment of pulmonary arterial hypertension in adults. Currently US Food and Drug Administration approved drugs including prostanoids, endothelin-receptor antagonists, phosphodiesterase type-5 inhibitors, and soluble guanylate-cyclase stimulators. These agents have transformed the prognosis for pulmonary arterial hypertension patients from symptomatic improvements in exercise tolerance ten years ago to delayed disease progression today. On the other hand, percutaneous balloon atrioseptostomy by using radiofrequency perforation, cutting balloon dilatation, or insertion of butterfly stents and pulmonary artery catheter-based denervation, both associated with very low rate of major complications and death, should be considered in combination with specific drugs at an earlier stage rather than late in the progression of pulmonary arterial hypertension and before the occurrence of overt right-sided heart failure.

Rho kinases in cardiovascular physiology and pathophysiology: the effect of fasudil

Rho kinase (ROCK) is a major downstream effector of the small GTPase RhoA. ROCK family, consisting of ROCK1 and ROCK2, plays central roles in the organization of actin cytoskeleton and is involved in a wide range of fundamental cellular functions, such as contraction, adhesion, migration, proliferation, and apoptosis. Due to the discovery of effective inhibitors, such as fasudil and Y27632, the biological roles of ROCK have been extensively explored with particular attention on the cardiovascular system. In many preclinical models of cardiovascular diseases, including vasospasm, arteriosclerosis, hypertension, pulmonary hypertension, stroke, ischemia-reperfusion injury, and heart failure, ROCK inhibitors have shown a remarkable efficacy in reducing vascular smooth muscle cell hypercontraction, endothelial dysfunction, inflammatory cell recruitment, vascular remodeling, and cardiac remodeling. Moreover, fasudil has been used in the clinical trials of several cardiovascular diseases. The continuing utilization of available pharmacological inhibitors and the development of more potent or isoform-selective inhibitors in ROCK signaling research and in treating human diseases are escalating. In this review, we discuss the recent molecular, cellular, animal, and clinical studies with a focus on the current understanding of ROCK signaling in cardiovascular physiology and diseases. We particularly note that emerging evidence suggests that selective targeting ROCK isoform based on the disease pathophysiology may represent a novel therapeutic approach for the disease treatment including cardiovascular diseases.

Endothelial progenitor cells and pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease characterised by lung endothelial cell dysfunction and vascular remodelling. A number of studies now suggest that endothelial progenitor cells (EPCs) may induce neovascularisation and could be a promising approach for cell based therapy for PAH. On the contrary EPCs may contribute to pulmonary vascular remodelling, particularly in end-stage pulmonary disease. This review article will provide a brief summary of the relationship between PAH and EPCs, the application of the EPCs to PAH and highlight the potential clinical application of the EPCs cell therapy to PAH.

Assessment of the serotonin pathway as a therapeutic target for pulmonary hypertension

Blockade of the serotonin reuptake transporter (5-HTT), using fluoxetine, has been identified as a potential therapeutic target for preventing and, importantly, reversing pulmonary hypertension (PH). This study utilized synchrotron radiation microangiography to determine whether fluoxetine could prevent or reverse endothelial dysfunction and vessel rarefaction, which underpin PH. PH was induced by a single injection of monocrotaline (MCT; 60 mg kg(-1)). Following MCT administration, rats received daily injections of either saline or fluoxetine (MCT+Fluox; 10 mg kg(-1)) for three weeks. A third group of rats also received the fluoxetine regime, but only three weeks after MCT (MCT+FluoxDelay). Control rats received daily injections of saline. Pulmonary microangiography was performed to assess vessel branching density and visualize dynamic changes in vessel diameter following (i) acute fluoxetine or (ii) acetylcholine, sodium nitroprusside, BQ-123 (ET-1A receptor blocker) and L-NAME (NOS inhibitor). Monocrotaline induced PH that was inevitably terminal. `Delayed' treatment of fluoxetine (MCT+FluoxDelay) was unable to reverse the progression of PH. Early fluoxetine treatment pre-PH (i.e. MCT+Fluox) attenuated but did not completely prevent vascular remodeling, vessel rarefaction and an increase in pulmonary pressure, and it did not prevent pulmonary endothelial dysfunction. Interestingly, fluoxetine treatment did counter-intuitively prevent the onset of right ventricular hypertrophy. Using synchrotron radiation microangiography, selective blockade of the serotonin reuptake transporter alone is highlighted as not being sufficient to prevent pulmonary endothelial dysfunction, which is the primary instigator for the inevitable onset of vascular remodeling and vessel rarefaction. Accordingly, potential therapeutic strategies should aim to target multiple pathways to ensure an optimal outcome.

Acute Rho-kinase inhibition improves coronary dysfunction in vivo, in the early diabetic microcirculation

OBJECTIVES

Activation of RhoA/Rho-kinase (ROCK) is increasingly implicated in acute vasospasm and chronic vasoconstriction in major organ systems. Therefore we aimed to ascertain whether an increase in ROCK activity plays a role in the deterioration of coronary vascular function in early stage diabetes.

METHODS

Synchrotron radiation microangiography was used to determine in vivo coronary responses in diabetic (3 weeks post streptozotocin 65 mg/kg ip) and vehicle treated male Sprague-Dawley rats (n = 8 and 6). Changes in vessel number and calibre during vasodilator stimulation before and after blockade of nitric oxide synthase and cyclooxygenase were compared between rats. Acute responses to ROCK inhibitor, fasudil (10 mg/kg iv) was evaluated. Further, perivascular and myocardial fibrosis, arterial intimal thickening were assessed by histology, and capillary density, nitrotyrosine and ROCK1/2 expressions were evaluated by immunohistochemical staining.

RESULTS

Diabetic rats had significantly elevated plasma glucose (P < 0.001 vs control), but did not differ in fibrotic scores, media to lumen ratio, capillary density or baseline visible vessel number or calibre. Responses to acetylcholine and sodium nitroprusside stimulation were similar between groups. However, in comparison to control rats the diabetic rats showed more segmental constrictions during blockade, which were not completely alleviated by acetylcholine, but were alleviated by fasudil. Further, second order vessel branches in diabetic rats were significantly more dilated relative to baseline (37% vs 12% increase, P < 0.05) after fasudil treatment compared to control rats, while visible vessel number increased in both groups. ROCK2 expression was borderline greater in diabetic rat hearts (P < 0.053).

CONCLUSIONS

We found that ahead of the reported decline in coronary endothelial vasodilator function in diabetic rats there was moderate elevation in ROCK expression, more widespread segmental constriction when nitric oxide and prostacyclin production were inhibited and notably, increased calibre in second and third order small arteries-arterioles following ROCK inhibition. Based on nitrotyrosine staining oxidative stress was not significantly elevated in early diabetic rats. We conclude that tonic ROCK mediated vasoconstriction contributes to coronary vasomotor tone in early diabetes.

Impaired pulmonary blood flow distribution in congestive heart failure assessed using synchrotron radiation microangiography

Synchrotron radiation microangiography is a powerful tool for assessing adverse changes in pulmonary vessel density associated with primary pulmonary hypertension (PH). Congestive heart failure (CHF) leads to a `secondary' onset of PH, yet it is unknown whether secondary PH is also associated with reduced vessel density. This study utilized synchrotron radiation to assess both pulmonary vessel density and endothelial function in a Dahl rat model of CHF with secondary PH. High salt-fed Dahl salt-sensitive (Dahl-S) and salt-resistant (Dahl-R) rats were anesthetized and microangiography was performed to assess the pulmonary vessel density and vascular responses to (i) sodium nitroprusside (5.0 µg kg(-1) min(-1)), (ii) acetylcholine (3.0 µg kg(-1) min(-1)) and (iii) ET-1A receptor blockade, BQ-123 (1 mg kg(-1)). Dahl-S rats developed CHF and secondary PH as evident by endothelial dysfunction, impaired vasodilatory responses to acetylcholine, enhanced vasodilatory responses to BQ-123 and extensive pulmonary vascular remodeling. Consequently, the pulmonary vessel density was adversely reduced. Interestingly, the etiology of secondary PH manifests with structural and functional changes that are comparable with that previously reported for primary PH. One important discrepancy, however, is that ET-1 modulation of pulmonary vessels is most striking in vessels with a diameter range of 100-200 µm in secondary PH, in contrast to a range of 200-300 µm in primary PH. Such discrepancies should be considered in future studies investigating primary and secondary forms of PH.

Mineralocorticoid receptor antagonism attenuates experimental pulmonary hypertension

Mineralocorticoid receptor (MR) activation stimulates systemic vascular and left ventricular remodeling. We hypothesized that MR contributes to pulmonary vascular and right ventricular (RV) remodeling of pulmonary hypertension (PH). We evaluated the efficacy of MR antagonism by spironolactone in two experimental PH models; mouse chronic hypoxia-induced PH (prevention model) and rat monocrotaline-induced PH (prevention and treatment models). Last, the biological function of the MR was analyzed in cultured distal pulmonary artery smooth muscle cells (PASMCs). In hypoxic PH mice, spironolactone attenuated the increase in RV systolic pressure, pulmonary arterial muscularization, and RV fibrosis. In rat monocrotaline-induced PH (prevention arm), spironolactone attenuated pulmonary vascular resistance and pulmonary vascular remodeling. In the established disease (treatment arm), spironolactone decreased RV systolic pressure and pulmonary vascular resistance with no significant effect on histological measures of pulmonary vascular remodeling, or RV fibrosis. Spironolactone decreased RV cardiomyocyte size modestly with no significant effect on RV mass, systemic blood pressure, cardiac output, or body weight, suggesting a predominantly local pulmonary vascular effect. In distal PASMCs, MR was expressed and localized diffusely. Treatment with the MR agonist aldosterone, hypoxia, or platelet-derived growth factor promoted MR translocation to the nucleus, activated MR transcriptional function, and stimulated PASMC proliferation, while spironolactone blocked these effects. In summary, MR is active in distal PASMCs, and its antagonism prevents PASMC proliferation and attenuates experimental PH. These data suggest that MR is involved in the pathogenesis of PH via effects on PASMCs and that MR antagonism may represent a novel therapeutic target for this disease.

Synchrotron radiation imaging for advancing our understanding of cardiovascular function

Synchrotron radiation (SR) is increasingly being used for micro-level and nano-level functional imaging in in vivo animal experiments. This review focuses on the methodology that enables repeated and regional assessment of vessel internal diameter and flow in the resistance vessels of different organ systems. In particular, SR absorption microangiography approaches offer unique opportunities for real-time in vivo vascular imaging in small animals, even during dynamic motion of the heart and lungs. We also describe recent progress in the translation of multiple phase-contrast imaging techniques from ex vivo to in vivo small-animal studies. Furthermore, we also review the utility of SR for multiple pinpoint (dimensions 0.2×0.2 mm) assessments of myocardial function at the cross-bridge level in different regions of the heart using small-angle X-ray scattering, resulting from increases in SR flux at modern facilities. Finally, we present cases for the use of complementary SR approaches to study cardiovascular function, particularly the pathological changes associated with disease using small-animal models.

[Pulmonary hypertension: from molecular pathophysiology to haemodynamic abnormalities]

Pulmonary hypertension (PH) is a complex disorder resulting from many etiologies that cause disturbances of normal pulmonary haemodynamics. Recent breakthroughs have led to a better understanding of the pathophysiology of the disease. In PH, haemodynamic disturbances are closely linked to structural changes and excessive remodeling of pulmonary vessels, leading to progressive narrowing of the pulmonary vascular lumen. Imbalances between pulmonary vasoconstrictors and vasodilators on the one hand, and factors favoring cell proliferation and apoptosis on the other hand, probably account for most cases of PH. This review aims to update readers with the current knowledge on the molecular physiopathology of PH and how this can progress the therapeutic of this disorder.

Animal models of pulmonary hypertension: Rho kinase inhibition

Pulmonary Hypertension is a terminology encompassing a range of etiologically different pulmonary vascular diseases. The most common is that termed pulmonary arterial hypertension or PAH; a rare but often fatal disease characterized by a mean pulmonary arterial pressure of >25 mmHg. PAH is associated with a complex etiology highlighted by core characteristics of increased pulmonary vascular resistance and elevation of mean pulmonary artery pressure. When sustained, pulmonary vascular remodeling occurs and eventually patients pass away due to right heart failure. Hypoxic pulmonary vasoconstriction is an early event occurring in pulmonary hypertension due to chronic exposure to hypoxia. While the underlying mechanisms of hypoxic pulmonary vasoconstriction may be controversial, a role for RhoA/Rho kinase mediated regulation of intracellular Ca(2+) has been recently identified. Further study suggests that RhoA may have an integral role in other pathophysiological processes such as cell proliferation and migration occurring in all forms of PH. Indeed Rho proteins are known to play essential roles in actin cytoskeleton organization in all eukaryotic cells and thus Rho and Rho-GTPases are implicated in fundamental cellular processes such as cellular proliferation, migration, adhesion, apoptosis and gene expression. This review focuses on providing an overview of the role of RhoA/Rho kinase in currently available animal models of pulmonary hypertension.

Targeting RhoA/ROCK pathway in pulmonary arterial hypertension

INTRODUCTION

Pulmonary arterial hypertension (PAH) is a rare disease with a complex pathogenesis. It is often associated with an increased vascular resistance, whilst in the more advanced stages there is a remodelling of the vascular walls. PAH has an intricate involvement of various signaling pathways, including the ras homolog family member A (RhoA)-Rho kinase (ROCK) axis. Currently, available therapies are not always able to significantly slow PAH progression. Therefore, newer approaches are needed.

AREAS COVERED

In this review, areas covered include the role of the RhoA/ROCK in PAH pathogenesis and the plausibility of its therapeutic targeting. Furthermore, various inhibitory compounds are discussed, including Fasudil and SB-772077-B.

EXPERT OPINION

Currently, specific RhoA/ROCK inhibition is the most promising therapeutic approach for PAH. Research has shown that it suppresses both the components of this axis and the upstream upregulating mediators. An inhaled RhoA/ROCK inhibitor may be a successful future therapy; however, further clinical trials are needed to support this approach.

The monocrotaline model of pulmonary hypertension in perspective

Severe forms of pulmonary arterial hypertension (PAH) are characterized by various degrees of remodeling of the pulmonary arterial vessels, which increases the pulmonary vascular resistance and right ventricular afterload, thus contributing to the development of right ventricle dysfunction and failure. Recent years have seen advances in the understanding of the pathobiology of PAH; however, many important questions remain unanswered. Elucidating the pathobiology of PAH continues to be critical to design new effective therapeutic strategies, and appropriate animal models of PAH are necessary to achieve the task. Although the monocrotaline rat model of PAH has contributed to a better understanding of vascular remodeling in pulmonary hypertension, we question the validity of this model as a preclinically relevant model of severe plexogenic PAH. Here we review pertinent publications that either have been forgotten or ignored, and we reexamine the monocrotaline model in the context of human forms of PAH.

Exogenous ghrelin improves blood flow distribution in pulmonary hypertension-assessed using synchrotron radiation microangiography

Ghrelin has cardioprotective properties and, recently, has been shown to improve endothelial function and reduce endothelin-1 (ET-1)-mediated vasoconstriction in peripheral vascular disease. Recently, we reported that ghrelin attenuates pulmonary hypertension (PH) caused by chronic hypoxia (CH), which we hypothesized in this study may be via suppression of the ET-1 pathway. We also aimed to determine whether ghrelin's ability to prevent alterations of the ET-1 pathway also prevented adverse changes in pulmonary blood flow distribution associated with PH. Sprague-Dawley rats were exposed to CH (10% O(2) for 2 weeks) with daily subcutaneous injections of ghrelin (150 μg/kg) or saline. Utilizing synchrotron radiation microangiography, we assessed pulmonary vessel branching structure, which is indicative of blood flow distribution, and dynamic changes in vascular responsiveness to (1) ET-1 (1 nmol/kg), (2) the ET-1(A) receptor antagonist, BQ-123 (1 mg/kg), and (3) ACh (3.0 μg kg⁻¹ min⁻¹). CH impaired blood flow distribution throughout the lung. However, this vessel "rarefaction" was attenuated in ghrelin-treated CH-rats. Moreover, ghrelin (1) reduced the magnitude of endothelial dysfunction, (2) prevented an increase in ET-1-mediated vasoconstriction, and (3) reduced pulmonary vascular remodeling and right ventricular hypertrophy-all adverse consequences associated with CH. These results highlight the beneficial effects of ghrelin for maintaining optimal lung perfusion in the face of a hypoxic insult. Further research is now required to establish whether ghrelin is also an effective therapy for restoring normal pulmonary hemodynamics in patients that already have established PH.

Recent development in pleiotropic effects of statins on cardiovascular disease through regulation of transforming growth factor-beta superfamily

BACKGROUND

3-Hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors, also known as statins, are a drug class that reduce the level of cholesterol in the blood. As a result, statins are used to suppress the progression of cardiovascular disease. Evidence points to another component of statins involving the non-lipid effects of the drug class in preventing cardiovascular disease. One specific mediator of this action is the transforming growth factor β (TGF-β) superfamily. The TGF-β superfamily consists of proteins that include TGF-β and bone morphogenetic proteins (BMPs). These proteins regulate cellular pathways to mediate effects including immunomodulation, cell cycling, and angiogenesis. One pathway that mediates these effects is Ras. Moreover, within this pathway, different functions are possible depending on the activation of the specific receptor subtype. This review discusses the recent development of the non-lipid effects of statins in preventing cardiovascular disease progression by regulating Ras pathway of the TGF-β superfamily, especially RhoA/ROCK pathway.

METHODS

A systematic PubMed database search of all English-language articles up to 2011 was conducted using the following terms: statin, TGF-β, Ras, ROCK, GGPP, inducible nitric oxide synthase, endothelial nitric oxide synthase, actin filament formation, PPARγ, MMP-2, and human trials.

CONCLUSION

With better understanding of the pathway, various mediators were identified; some of these mediators are important biomarkers producing more specific and accurate assessment of the pleiotropic effects of statins. The review of human trials also highlights that more specific biomarkers are employed in recent studies, and the non-lipid effects on human subjects are more accurately documented. Confirmation of the accuracy of these biomarkers by further large-scale studies and further development of new biomarkers may prove an important path leading to better patient selection for treatment, and thus better cost-effectiveness may be achieved.