Estradiol metabolites attenuate monocrotaline-induced pulmonary hypertension in rats

Low Thyroid Hormones Level Attenuates Mitochondrial Dysfunction and Right Ventricular Failure in Pulmonary Hypertensive Rats

PURPOSE

This study is to investigate the repercussions of hypothyroidism in the pathophysiological progression of pulmonary arterial hypertension (PAH).

METHODS

While the control (CTL, n = 5) male Wistar rats received vehicle, PAH was induced with monocrotaline (MCT group, n = 15). Hypothyroidism was induced in a subset of rats by methimazole 3 weeks prior to the MCT injection (MMZ + MCT group, n = 15). Plasma thyroid hormones were measured by radioimmunoassay. Electrocardiographic, echocardiographic, and hemodynamic analyses were performed to evaluate the progression of PAH. Gene expression of antioxidant enzymes and cardiac hypertrophy markers were assessed by qPCR. Mitochondrial respiration, ATP levels, and ROS production were measured in right ventricular (RV) samples.

RESULTS

Plasma T3 and T4 decreased in both MCT and MMZ + MCT groups (p < 0.05). Right ventricular systolic pressure (RVSP) increased, and RV - dP/dt, + dP/dt, and contractility index decreased in the MCT versus the CTL group and remained within control levels in the MMZ + MCT group (p < 0.05). Relative RV weight, RV wall thickness, RV diastolic area, and relative lung weight were augmented in the MCT versus the CTL group, whereas all parameters were improved to the CTL levels in the MMZ + MCT group (p < 0.05). Only the MCT group exhibited an increased duration of QTc interval compared to the baseline period (p < 0.05). ADP-induced mitochondrial respiration and ATP levels were decreased, and ROS production was increased in MCT versus the CTL group (p < 0.05), while the MMZ + MCT group exhibited increased mitochondrial respiration versus the MCT group (p < 0.05).

CONCLUSION

Hypothyroidism attenuated the RV mitochondrial dysfunction and the pathophysiological progression of MCT-induced PAH.

[Protective effects of 2-methoxyestradiol against hypoxic pulmonary hypertension in neonatal rats]

OBJECTIVES

To investigate the protective effects of 2-methoxyestradiol (2ME) against hypoxic pulmonary hypertension (HPH) in neonatal rats.

METHODS

Ninety-six Wistar neonatal rats were randomly divided into a normoxia group, a hypoxia group, and a hypoxia + 2ME group, with each group further subdivided into 3-day, 7-day, 14-day, and 21-day subgroups, containing eight rats each. The hypoxia and hypoxia + 2ME groups received daily subcutaneous injections of saline and 2ME (240 μg/kg), respectively, while the normoxia group was raised in a normoxic environment with daily saline injections. Right ventricular systolic pressure (RVSP) was measured using the direct pressure method. Pulmonary vascular morphology was assessed using hematoxylin and eosin staining, with metrics including the percentage of medial thickness of small pulmonary arteries relative to the external diameter (MT%) and the cross-sectional area of the media of small pulmonary arteries relative to the total cross-sectional area (MA%). Immunohistochemistry was used to detect the expression levels of hypoxia-inducible factor-1α (HIF-1α) and proliferating cell nuclear antigen (PCNA) proteins, while real-time quantitative PCR was used to to assess HIF-1α and PCNA mRNA levels.

RESULTS

Compared to the normoxia group, the hypoxia and hypoxia + 2ME groups showed increased RVSP and upregulated HIF-1α and PCNA protein and mRNA expression levels at 3, 7, 14, and 21 days after hypoxia (P<0.05). Furthermore, at 7, 14, and 21 days after hypoxia, the hypoxia group showed increased MT% and MA% (P<0.05). In comparison to the hypoxia group, the hypoxia + 2ME group exhibited reduced RVSP and downregulated HIF-1α and PCNA protein and mRNA expression levels, along with decreased MT% and MA% at 7, 14, and 21 days after hypoxia (P<0.05).

CONCLUSIONS

2ME may protect against HPH in neonatal rats by inhibiting the expression of HIF-1α and PCNA and reducing pulmonary vascular remodeling. Citation:Chinese Journal of Contemporary Pediatrics, 2024, 26(7): 757-764.

Pulmonary arterial hypertension: Sex matters

Pulmonary arterial hypertension (PAH) is a complex disease of multifactorial origin. While registries have demonstrated that women are more susceptible to the disease, females with PAH have superior right ventricle (RV) function and a better prognosis than their male counterparts, a phenomenon referred to as the 'estrogen paradox'. Numerous pre-clinical studies have investigated the involvement of sex hormones in PAH pathobiology, often with conflicting results. However, recent advances suggest that abnormal estrogen synthesis, metabolism and signalling underpin the sexual dimorphism of this disease. Other sex hormones, such as progesterone, testosterone and dehydroepiandrosterone may also play a role. Several non-hormonal factor including sex chromosomes and epigenetics have also been implicated. Though the underlying pathophysiological mechanisms are complex, several compounds that modulate sex hormones levels and signalling are under investigation in PAH patients. Further elucidation of the estrogen paradox will set the stage for the identification of additional therapeutic targets for this disease.

Gender-based research underscores sex differences in biological processes, clinical disorders and pharmacological interventions

Earlier research has presumed that the male and female biology is similar in most organs except the reproductive system, leading to major misconceptions in research interpretations and clinical implications, with serious disorders being overlooked or misdiagnosed. Careful research has now identified sex differences in the cardiovascular, renal, endocrine, gastrointestinal, immune, nervous, and musculoskeletal systems. Also, several cardiovascular, immunological, and neurological disorders have shown differences in prevalence and severity between males and females. Genetic variations in the sex chromosomes have been implicated in several disorders at young age and before puberty. The levels of the gonadal hormones estrogen, progesterone and testosterone and their receptors play a role in the sex differences between adult males and premenopausal women. Hormonal deficiencies and cell senescence have been implicated in differences between postmenopausal and premenopausal women. Specifically, cardiovascular disorders are more common in adult men vs premenopausal women, but the trend is reversed with age with the incidence being greater in postmenopausal women than age-matched men. Gender-specific disorders in females such as polycystic ovary syndrome, hypertension-in-pregnancy and gestational diabetes have attained further research recognition. Other gender-related research areas include menopausal hormone therapy, the "Estrogen Paradox" in pulmonary arterial hypertension being more predominant but less severe in young females, and how testosterone may cause deleterious effects in the kidney while having vasodilator effects in the coronary circulation. This has prompted the National Institutes of Health (NIH) initiative to consider sex as a biological variable in research. The NIH and other funding agencies have provided resources to establish state-of-the-art centers for women health and sex differences in biology and disease in several academic institutions. Scientific societies and journals have taken similar steps to organize specialized conferences and publish special issues on gender-based research. These combined efforts should promote research to enhance our understanding of the sex differences in biological systems beyond just the reproductive system, and provide better guidance and pharmacological tools for the management of various clinical disorders in a gender-specific manner.

Pulmonary Circulation Under Pressure: Pathophysiological and Therapeutic Implications of BK Channel

The large-conductance Ca2+-activated K+ (BK) channel is widely expressed in the pulmonary blood vessels and plays a significant role in regulating pulmonary vascular tonus. It opens under membrane depolarization, increased intracellular Ca+2 concentration, and chronic hypoxia, resulting in massive K+ efflux, membrane hyperpolarization, decreased L-type Ca+2 channel opening, and smooth muscle relaxation. Several reports have demonstrated an association between BK channel dysfunction and pulmonary hypertension (PH) development. Decreased BK channel subunit expression and impaired regulation by paracrine hormones result in decreased BK channel opening, increased pulmonary vascular resistance, and pulmonary arterial pressure being the cornerstone of PH. The resulting right ventricular pressure overload ultimately leads to ventricular remodeling and failure. Therefore, it is unsurprising that the BK channel has arisen as a potential target for treating PH. Recently, a series of selective, synthetic BK channel agonists have proven effective in attenuating the pathophysiological progression of PH without adverse effects in animal models.

Dimethyl Sulfoxide Induces Hemolysis and Pulmonary Hypertension

Vascular and lung injury are well established complications associated with hemolytic disorders, and hemolysis associated pulmonary hypertension (PH) has emerged as the most serious complication of sickle cell disease. The causal relationship between intravascular hemolysis and the development of PH is still under investigation. Previously we have shown that repetitive administration of hemolyzed autologous blood causes PH in rats. Dimethyl sulfoxide (DMSO), a widely used solvent and anti-inflammatory agent, induces hemolysis in vivo. We hypothesized that repetitive administration of DMSO would induce PH in rats. We also examined hemolysis-induced release of adenosine deaminase (ADA) and arginase from red blood cells, which may amplify hemolysis-mediated vascular injury. Acute administration of DMSO (1.5ml/30 min into the right atrium) induced intravascular hemolysis and pulmonary vasoconstriction. DMSO-induced increase in right ventricular peak systolic pressure (RVPSP) was associated with increased release of ADA. Notably, the acute increase in RVPSP was attenuated by administration of an adenosine A2A receptor agonist or by pretreatment of animals with ADA inhibitor erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA). Repetitive administration of DMSO for 10 days produced anemia, hemoglobinuria, hemoglobinemia, splenomegaly, and development of PH. Histopathological analysis revealed pulmonary vascular remodeling. The presented data describe a new model of hemolysis induced PH, suggesting that hemolysis is mechanistically related to pulmonary hypertension, and pointing to a potential pathogenic role that adenosine deaminase and accelerated adenosine metabolism may play in hemolysis associated pulmonary hypertension.

Role of miR-21-5p/FilGAP axis in estradiol alleviating the progression of monocrotaline-induced pulmonary hypertension

Background

Aberrant expression of microRNAs (miRNAs) has been associated with the pathogenesis of pulmonary hypertension (PH). It is, however, not clear whether miRNAs are involved in estrogen rescue of PH.

Methods

Fresh plasma samples were prepared from 12 idiopathic pulmonary arterial hypertension (IPAH) patients and 12 healthy controls undergoing right heart catheterization in Shanghai Pulmonary Hospital. From each sample, 5 μg of total RNA was tagged and hybridized on microRNA microarray chips. Monocrotaline‐induced PH (MCT‐PH) male rats were treated with 17β‐estradiol (E₂) or vehicle. Subgroups were cotreated with estrogen receptor (ER) antagonist or with antagonist of miRNA.

Results

Many circulating miRNAs, including miR‐21‐5p and miR‐574‐5p, were markedly expressed in patients and of interest in predicting mean pulmonary arterial pressure elevation in patients. The expression of miR‐21‐5p in the lungs was significantly upregulated in MCT‐PH rats compared with the controls. However, miR‐574‐5p showed no difference in the lungs of MCT‐PH rats and controls. miR‐21‐5p was selected for further analysis in rats as E₂ strongly regulated it. E₂ decreased miR‐21‐5p expression in the lungs of MCT‐PH rats by ERβ. E₂ reversed miR‐21‐5p target gene FilGAP downregulation in the lungs of MCT‐PH rats. The abnormal expression of RhoA, ROCK2, Rac1 and c‐Jun in the lungs of MCT‐PH rats was inhibited by E₂ and miR‐21‐5p antagonist.

Conclusions

miR‐21‐5p level was remarkably associated with PH severity in patients. Moreover, the miR‐21‐5p/FilGAP signaling pathway modulated the protective effect of E₂ on MCT‐PH through ERβ.

Sex Differences in Pulmonary Hypertension

Pulmonary hypertension (PH) includes multiple diseases that share as common characteristic an elevated pulmonary artery pressure and right ventricular involvement. Sex differences are observed in practically all causes of PH. The most studied type is pulmonary arterial hypertension (PAH) which presents a gender bias regarding its prevalence, prognosis, and response to treatment. Although this disease is more frequent in women, once affected they present a better prognosis compared to men. Even if estrogens seem to be the key to understand these differences, animal models have shown contradictory results leading to the birth of the estrogen paradox. In this review we will summarize the evidence regarding sex differences in experimental animal models and, very specially, in patients suffering from PAH or PH from other etiologies.

Bioactivities and mechanisms of natural medicines in the management of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a progressive and rare disease without obvious clinical symptoms that shares characteristics with pulmonary vascular remodeling. Right heart failure in the terminal phase of PAH seriously threatens the lives of patients. This review attempts to comprehensively outline the current state of knowledge on PAH its pathology, pathogenesis, natural medicines therapy, mechanisms and clinical studies to provide potential treatment strategies. Although PAH and pulmonary hypertension have similar pathological features, PAH exhibits significantly elevated pulmonary vascular resistance caused by vascular stenosis and occlusion. Currently, the pathogenesis of PAH is thought to involve multiple factors, primarily including genetic/epigenetic factors, vascular cellular dysregulation, metabolic dysfunction, even inflammation and immunization. Yet many issues regarding PAH need to be clarified, such as the "oestrogen paradox". About 25 kinds monomers derived from natural medicine have been verified to protect against to PAH via modulating BMPR2/Smad, HIF-1α, PI3K/Akt/mTOR and eNOS/NO/cGMP signalling pathways. Yet limited and single PAH animal models may not corroborate the efficacy of natural medicines, and those natural compounds how to regulate crucial genes, proteins and even microRNA and lncRNA still need to put great attention. Additionally, pharmacokinetic studies and safety evaluation of natural medicines for the treatment of PAH should be undertaken in future studies. Meanwhile, methods for validating the efficacy of natural drugs in multiple PAH animal models and precise clinical design are also urgently needed to promote advances in PAH.

Sex and gender in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare disease characterised by pulmonary vascular remodelling and elevated pulmonary pressure, which eventually leads to right heart failure and death. Registries worldwide have noted a female predominance of the disease, spurring particular interest in hormonal involvement in the disease pathobiology. Several experimental models have shown both protective and deleterious effects of oestrogens, suggesting that complex mechanisms participate in PAH pathogenesis. In fact, oestrogen metabolites as well as receptors and enzymes implicated in oestrogen signalling pathways and associated conditions such as BMPR2 mutation contribute to PAH penetrance more specifically in women. Conversely, females have better right ventricular function, translating to a better prognosis. Along with right ventricular adaptation, women tend to respond to PAH treatment differently from men. As some young women suffer from PAH, contraception is of particular importance, considering that pregnancy in patients with PAH is strongly discouraged due to high risk of death. When contraception measures fail, pregnant women need a multidisciplinary team-based approach. This article aims to review epidemiology, mechanisms underlying the higher female predominance, but better prognosis and the intricacies in management of women affected by PAH.

2-Methoxyestradiol Attenuates the Development and Retards the Progression of Hypoxia-And Alpha-Naphthylthiourea-Induced Pulmonary Hypertension

Pulmonary arterial hypertension (PH), a progressive, incurable, and deadly disease, predominantly develops in women. Growing body of evidence suggest that dysregulated estradiol (E2) metabolism influences the development of PH and that some of the biological effects of E2 are mediated by its major non-estrogenic metabolite, 2-metyhoxyestradiol (2ME). The objective of this study was to examine effects of 2ME in chronic hypoxia (CH)-induced PH and alpha-naphthylthiourea (ANTU)-induced acute lung injury and PH. In addition, we investigated the effects of exposure to different levels of CH on development of PH. Chronic exposure to 15% or 10% oxygen produced similar increases in right ventricle peak systolic pressure (RVPSP) and pulmonary vascular remodeling, but oxygen concentration-dependent increase in hematocrit. Notably, right ventricle (RV) hypertrophy correlated with level of hypoxia and hematocrit, rather than with magnitude of RVPSP. The latter suggests that, in addition to increased afterload, hypoxia (via increased hematocrit) significantly contributes to RV hypertrophy in CH model of PH. In CH-PH rats, preventive and curative 2ME treatments reduced both elevated RVPSP and pulmonary vascular remodeling. Curative treatment with 2ME was more effective in reducing hematocrit and right ventricular hypertrophy, as compared to preventive treatment. Single ANTU injection produced lung injury, i.e., increased lungs weight and induced pleural effusion. Treatment with 2ME significantly reduced pleural effusion and, more importantly, eliminated acute mortality induced by ANTU (33% vs 0%, ANTU vs. ANTU+2ME group). Chronic treatment with ANTU induced PH and RV hypertrophy and increased lungs weight. 2-ME significantly attenuated severity of disease (i.e., reduced RVPSP, RV hypertrophy and pulmonary vascular injury). This study demonstrates that 2ME has beneficial effects in chronic hypoxia- and acute lung injury-induced PH and provides preclinical justification for clinical evaluation of 2ME in pulmonary hypertension.

Sex Differences in Pulmonary Hypertension

Pulmonary arterial hypertension (PAH) occurs in women more than men whereas survival in men is worse than in women. In recent years, much research has been carried out to understand these sex differences in PAH. This article discusses clinical and preclinical studies that have investigated the influences of sex, serotonin, obesity, estrogen, estrogen synthesis, and estrogen metabolism on bone morphogenetic protein receptor type II signaling, the pulmonary circulation and right ventricle in both heritable and idiopathic pulmonary hypertension.

Impact of liver damage on blood-borne variables and pulmonary hemodynamic responses to hypoxia and hyperoxia in anesthetized rats

BACKGROUND

Liver disorders may be associated with normal pulmonary hemodynamic, hepatopulmonary syndrome (HPS), or portopulmonary hypertension (POPH). In this study, we aimed to investigate the effect of the severity of liver dysfunctions on blood-borne variables, and pulmonary hemodynamic during repeated ventilation with hyperoxic and hypoxic gases.

METHODS

Female Sprague Dawley rats were assigned into four groups of Sham (n = 7), portal vein ligation (PPVL, n = 7), common bile duct ligation (CBDL, n = 7), and combination of them (CBDL+ PPVL, n = 7). Twenty-eight days later, right ventricular systolic pressure (RVSP) and systemic blood pressure were recorded in anesthetized animals subjected to repeated maneuvers of hyperoxia (O₂ 50%) and hypoxia (O₂ 10%). Besides, we assessed blood parameters and liver histology.

RESULTS

Liver histology score, liver enzymes, WBC and plasma malondialdehyde in the CBDL+PPVL group were higher than those in the CBDL group. Also, the plasma platelet level in the CBDL+PPVL group was lower than those in the other groups. On the other hand, the serum estradiol in the CBDL group was higher than that in the CBDL+PPVL group. All the above parameters in the PPVL group were similar to those in the Sham group. During ventilation with hyperoxia gas, RVSP in the CBDL+PPVL group was higher than the ones in the other groups, and in the CBDL group, it was more than those in the PPVL and Sham groups. Hypoxic pulmonary vasoconstriction (HPV) was not detected in both CBDL+PPVL and CBDL groups, whereas, it retained in the PPVL group.

CONCLUSION

Severe liver damage increases RVSP in the CBDL+PPVL group linked to the high level of ROS, low levels of serum estradiol and platelets or a combination of them. Furthermore, the high RVSP at the noted group could present a reliable animal model for POPH in female rats.

Estradiol Metabolism: Crossroads in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a debilitating and progressive disease that predominantly develops in women. Over the past 15 years, cumulating evidence has pointed toward dysregulated metabolism of sex hormones in animal models and patients with PAH. 17β-estradiol (E2) is metabolized at positions C2, C4, and C16, which leads to the formation of metabolites with different biological/estrogenic activity. Since the first report that 2-methoxyestradiol, a major non-estrogenic metabolite of E2, attenuates the development and progression of experimental pulmonary hypertension (PH), it has become increasingly clear that E2, E2 precursors, and E2 metabolites exhibit both protective and detrimental effects in PH. Furthermore, both experimental and clinical data suggest that E2 has divergent effects in the pulmonary vasculature versus right ventricle (estrogen paradox in PAH). The estrogen paradox is of significant clinical relevance for understanding the development, progression, and prognosis of PAH. This review updates experimental and clinical findings and provides insights into: (1) the potential impacts that pathways of estradiol metabolism (EMet) may have in PAH; (2) the beneficial and adverse effects of estrogens and their precursors/metabolites in experimental PH and human PAH; (3) the co-morbidities and pathological conditions that may alter EMet and influence the development/progression of PAH; (4) the relevance of the intracrinology of sex hormones to vascular remodeling in PAH; and (5) the advantages/disadvantages of different approaches to modulate EMet in PAH. Finally, we propose the three-tier-estrogen effects in PAH concept, which may offer reconciliation of the opposing effects of E2 in PAH and may provide a better understanding of the complex mechanisms by which EMet affects the pulmonary circulation–right ventricular interaction in PAH.

Sex, Gender, and Sex Hormones in Pulmonary Hypertension and Right Ventricular Failure

Pulmonary hypertension (PH) encompasses a syndrome of diseases that are characterized by elevated pulmonary artery pressure and pulmonary vascular remodeling and that frequently lead to right ventricular (RV) failure and death. Several types of PH exhibit sexually dimorphic features in disease penetrance, presentation, and progression. Most sexually dimorphic features in PH have been described in pulmonary arterial hypertension (PAH), a devastating and progressive pulmonary vasculopathy with a 3-year survival rate <60%. While patient registries show that women are more susceptible to development of PAH, female PAH patients display better RV function and increased survival compared to their male counterparts, a phenomenon referred to as the "estrogen paradox" or "estrogen puzzle" of PAH. Recent advances in the field have demonstrated that multiple sex hormones, receptors, and metabolites play a role in the estrogen puzzle and that the effects of hormone signaling may be time and compartment specific. While the underlying physiological mechanisms are complex, unraveling the estrogen puzzle may reveal novel therapeutic strategies to treat and reverse the effects of PAH/PH. In this article, we (i) review PH classification and pathophysiology; (ii) discuss sex/gender differences observed in patients and animal models; (iii) review sex hormone synthesis and metabolism; (iv) review in detail the scientific literature of sex hormone signaling in PAH/PH, particularly estrogen-, testosterone-, progesterone-, and dehydroepiandrosterone (DHEA)-mediated effects in the pulmonary vasculature and RV; (v) discuss hormone-independent variables contributing to sexually dimorphic disease presentation; and (vi) identify knowledge gaps and pathways forward. © 2020 American Physiological Society. Compr Physiol 10:125-170, 2020.

The Role of Sex in the Pathophysiology of Pulmonary Hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease characterised by increased pulmonary vascular resistance and pulmonary artery remodelling as result of increased vascular tone and vascular cell proliferation, respectively. Eventually, this leads to right heart failure. Heritable PAH is caused by a mutation in the bone morphogenetic protein receptor-II (BMPR-II). Female susceptibility to PAH has been known for some time, and most recent figures show a female-to-male ratio of 4:1. Variations in the female sex hormone estrogen and estrogen metabolism modify FPAH risk, and penetrance of the disease in BMPR-II mutation carriers is increased in females. Several lines of evidence point towards estrogen being pathogenic in the pulmonary circulation, and thus increasing the risk of females developing PAH. Recent studies have also suggested that estrogen metabolism may be crucial in the development and progression of PAH with studies indicating that downstream metabolites such as 16α-hydroxyestrone are upregulated in several forms of experimental pulmonary hypertension (PH) and can cause pulmonary artery smooth muscle cell proliferation and subsequent vascular remodelling. Conversely, other estrogen metabolites such as 2-methoxyestradiol have been shown to be protective in the context of PAH. Estrogen may also upregulate the signalling pathways of other key mediators of PAH such as serotonin.

Influence of 2-Methoxyestradiol and Sex on Hypoxia-Induced Pulmonary Hypertension and Hypoxia-Inducible Factor-1-α

Background Women are at greater risk of developing pulmonary arterial hypertension, with estrogen and its downstream metabolites playing a potential role in the pathogenesis of the disease. Hypoxia-inducible factor-1-α (HIF 1α) is a pro-proliferative mediator and may be involved in the development of human pulmonary arterial hypertension . The estrogen metabolite 2-methoxyestradiol (2 ME 2) has antiproliferative properties and is also an inhibitor of HIF 1α. Here, we examine sex differences in  HIF 1α signaling in the rat and human pulmonary circulation and determine if 2 ME 2 can inhibit HIF 1α in vivo and in vitro. Methods and Results HIF 1α signaling was assessed in male and female distal human pulmonary artery smooth muscle cells ( hPASMC s), and the effects of 2 ME 2 were also studied in female hPASMC s. The in vivo effects of 2 ME 2 in the chronic hypoxic rat (male and female) model of pulmonary hypertension were also determined. Basal HIF 1α protein expression was higher in female hPASMC s compared with male. Both factor-inhibiting HIF and prolyl hydroxylase-2 (hydroxylates HIF leading to proteosomal degradation) protein levels were significantly lower in female hPASMC s when compared with males. In vivo, 2 ME 2 ablated hypoxia-induced pulmonary hypertension in male and female rats while decreasing protein expression of HIF 1α. 2 ME 2 reduced proliferation in hPASMC s and reduced basal protein expression of HIF 1α. Furthermore, 2 ME 2 caused apoptosis and significant disruption to the microtubule network. Conclusions Higher basal HIF 1α in female hPASMC s may increase susceptibility to developing pulmonary arterial hypertension . These data also demonstrate that the antiproliferative and therapeutic effects of 2 ME 2 in pulmonary hypertension may involve inhibition of HIF 1α and/or microtubular disruption in PASMC s.

Sex differences in pulmonary arterial hypertension: role of infection and autoimmunity in the pathogenesis of disease

Registry data worldwide indicate an overall female predominance for pulmonary arterial hypertension (PAH) of 2–4 over men. Genetic predisposition accounts for only 1–5% of PAH cases, while autoimmune diseases and infections are closely linked to PAH. Idiopathic PAH may include patients with undiagnosed autoimmune diseases based on the relatively high presence of autoantibodies in this group. The two largest PAH registries to date report a sex ratio for autoimmune connective tissue disease-associated PAH of 9:1 female to male, highlighting the need for future studies to analyze subgroup data according to sex. Autoimmune diseases that have been associated with PAH include female-dominant systemic sclerosis, systemic lupus erythematosus, rheumatoid arthritis, Sjögren’s syndrome, and thyroiditis as well as male-dominant autoimmune diseases like myocarditis which has been linked to HIV-associated PAH. The sex-specific association of PAH to certain infections and autoimmune diseases suggests that sex hormones and inflammation may play an important role in driving the pathogenesis of disease. However, there is a paucity of data on sex differences in inflammation in PAH, and more research is needed to better understand the pathogenesis underlying PAH in men and women. This review uses data on sex differences in PAH and PAH-associated autoimmune diseases from registries to provide insight into the pathogenesis of disease.

Pathobiology of pulmonary arterial hypertension: understanding the roads less travelled

The pathobiology of pulmonary arterial hypertension (PAH) is complex and incompletely understood. Although three pathogenic pathways have been relatively well characterised, it is widely accepted that dysfunction in a multitude of other cellular processes is likely to play a critical role in driving the development of PAH. Currently available therapies, which all target one of the three well-characterised pathways, provide significant benefits for patients; however, PAH remains a progressive and ultimately fatal disease. The development of drugs to target alternative pathogenic pathways is, therefore, an attractive proposition and one that may complement existing treatment regimens to improve outcomes for patients. Considerable research has been undertaken to identify the role of the less well-understood pathways and in this review we will highlight some of the key discoveries and the potential for utility as therapeutic targets.

Anastrozole in Pulmonary Arterial Hypertension. A Randomized, Double-Blind, Placebo-controlled Trial

RATIONALE

The aromatase inhibitor anastrozole blocks the conversion of androgens to estrogen and blunts pulmonary hypertension in animals, but its efficacy in treating patients with pulmonary arterial hypertension (PAH) is unknown.

OBJECTIVES

We aimed to determine the safety and efficacy of anastrozole in PAH.

METHODS

We performed a randomized, double-blind, placebo-controlled trial of anastrozole in patients with PAH who received background therapy at two centers.

MEASUREMENTS AND MAIN RESULTS

A total of 18 patients with PAH were randomized to anastrozole 1 mg or matching placebo in a 2:1 ratio. The two co-primary outcomes were percent change from baseline in 17β-estradiol levels (E2) and tricuspid annular plane systolic excursion (TAPSE) at 3 months. Anastrozole significantly reduced E2 levels compared with placebo (percent change: -40%; interquartile range [IQR], -61 to -26% vs. -4%; IQR, -14 to +4%; P = 0.003), but there was no difference in TAPSE. Anastrozole significantly increased the 6-minute-walk distance (median change = +26 m) compared with placebo (median change = -12 m) (median percent change: anastrozole group, 8%; IQR, 2 to 17% vs. placebo -2%; IQR, -7 to +1%; P = 0.042). Anastrozole had no effect on circulating biomarkers, functional class, or health-related quality of life. There was no difference in adverse events.

CONCLUSIONS

Anastrozole significantly reduced E2 levels in patients with PAH but had no effect on TAPSE. Anastrozole was safe, well tolerated, and improved 6-minute-walk distance in this small "proof-of-principle" study. Larger and longer phase II clinical trials of anastrozole may be warranted in patients with PAH. Clinical trial registered with www.clinicaltrials.gov (NCT 1545336).

Pulmonary arterial hypertension: the clinical syndrome

Pulmonary arterial hypertension is a progressive disorder in which endothelial dysfunction and vascular remodeling obstruct small pulmonary arteries, resulting in increased pulmonary vascular resistance and pulmonary pressures. This leads to reduced cardiac output, right heart failure, and ultimately death. In this review, we attempt to answer some important questions commonly asked by patients diagnosed with pulmonary arterial hypertension pertaining to the disease, and aim to provide an explanation in terms of classification, diagnosis, pathophysiology, genetic causes, demographics, and prognostic factors. Furthermore, important molecular pathways that are central to the pathogenesis of pulmonary arterial hypertension are reviewed, including nitric oxide, prostacyclin, endothelin-1, reactive oxygen species, and endothelial and smooth muscle proliferation.

Progress in solving the sex hormone paradox in pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a devastating and progressive disease with marked morbidity and mortality. Even though being female represents one of the most powerful risk factors for PAH, multiple questions about the underlying mechanisms remain, and two "estrogen paradoxes" in PAH exist. First, it is puzzling why estrogens have been found to be protective in various animal models of PAH, whereas PAH registries uniformly demonstrate a female susceptibility to the disease. Second, despite the pronounced tendency for the disease to develop in women, female PAH patients exhibit better survival than men. Recent mechanistic studies in classical and in novel animal models of PAH, as well as recent studies in PAH patients, have significantly advanced the field. In particular, it is now accepted that estrogen metabolism and receptor signaling, as well as estrogen interactions with key pathways in PAH development, appear to be potent disease modifiers. A better understanding of these interactions may lead to novel PAH therapies. It is the purpose of this review to 1) review sex hormone synthesis, metabolism, and receptor physiology; 2) assess the context in which sex hormones affect PAH pathogenesis; 3) provide a potential explanation for the observed estrogen paradoxes and gender differences in PAH; and 4) identify knowledge gaps and future research opportunities. Because the majority of published studies investigated 17β-estradiol and/or its metabolites, this review will primarily focus on pulmonary vascular and right ventricular effects of estrogens. Data for other sex hormones will be discussed very briefly.

Sex differences in the pulmonary circulation: implications for pulmonary hypertension

Pulmonary arterial hypertension (PAH), a form of pulmonary hypertension, is a complex disease of multifactorial origin. While new developments regarding pathophysiological features and therapeutic options in PAH are being reported, one important fact has emerged over the years: there is a sex difference in the incidence of this disease such that while there is a higher incidence in females, disease outcomes are much worse in males. Accordingly, recent attention has been focused on understanding the features of sex differences in the pulmonary circulation and the contributory mechanisms, particularly sex hormones and their role in the pathological and pathophysiological features of PAH. However, to date, there is no clear consensus whether sex hormones (particularly female sex steroids) are beneficial or detrimental in PAH. In this review, we highlight some of the most recent evidence regarding the influence of sex hormones (estrogen, testosterone, progesterone, dehydroepiandrosterone) and estrogen metabolites on key pathophysiological features of PAH such as proliferation, vascular remodeling, vasodilation/constriction, and inflammation, thus setting the stage for research avenues to identify novel therapeutic target for PAH as well as potentially other forms of pulmonary hypertension.

The effects of gender difference on monocrotaline-induced pulmonary hypertension in rats

The present study aimed to compare the effect of gender difference on hemodynamic consequences in the development of monocrotaline (MCT)-induced pulmonary hypertension in rat. The effect of antioxidant enzyme systems on the development of pulmonary hypertension mediated by the phytotoxin MCT and the effect of gender on these antioxidant systems were also investigated. For this purpose, the right ventricular pressures (RVPs) and right ventricular/heart weight (HW) ratios were compared between groups and the glutathione (GSH) level and superoxide dismutase (SOD), catalase (CAT) and glutathione-S-transferase (GST) activities were determined in lung and liver tissue samples of rats. RVP and right ventricular/HW ratios significantly increased in the MCT group compared to the control group. In the MCT group, RVP was significantly higher in males than females. MCT-induced pulmonary hypertension resulted in decreased GSH level, decreased GST and SOD activities and increased CAT activity in lung and liver tissues of both male and female rats. In addition, the lung and liver GSH level and GST and SOD levels were higher in female control rats compared to male control rats. The results of the present study, that antioxidant enzyme activities were different between the groups, highlight the possible role of oxidative stress in the pathogenesis of MCT-induced pulmonary hypertension in rats. Moreover, the lower antioxidant defense capacity of male rats than female rats may be considered as a cause of more aggressive course of MCT-induced pulmonary hypertension in males compared to females.

Gender, sex hormones and pulmonary hypertension

Most subtypes of pulmonary arterial hypertension (PAH) are characterized by a greater susceptibility to disease among females, although females with PAH appear to live longer after diagnosis. While this "estrogen paradoxȍ of enhanced female survival despite increased female susceptibility remains a mystery, recent progress has begun to shed light upon the interplay of sex hormones, the pathogenesis of pulmonary hypertension, and the right ventricular response to stress. For example, emerging data in humans and experimental models suggest that estrogens or differential sex hormone metabolism may modify disease risk among susceptible subjects, and that estrogens may interact with additional local factors such as serotonin to enhance the potentially damaging chronic effects of estrogens on the pulmonary vasculature. Regardless, it remains unclear why not all estrogenic compounds behave equally, nor why estrogens appear to be protective in certain settings but detrimental in others. The contribution of androgens and other compounds, such as dehydroepiandrosterone, to pathogenesis and possibly treatment must be considered as well. In this review, we will discuss the recent understandings on how estrogens, estrogen metabolism, dehydroepiandrosterone, and additional susceptibility factors may all contribute to the pathogenesis or potentially to the treatment of pulmonary hypertension, by evaluating current human, cell-based, and experimental model data.

Effects of Developmental Exposure to Mixtures of Environmental Contaminants on the Hepatic Metabolism of Estradiol-17β in Immature Female Sprague Dawley Rats

Exposure to environmental contaminants induces the activation of cytochrome P450s (CYP) which lead to the hydroxylation of contaminants and endogenous hormones such as estrogens. The hydroxylation of estrogens forms catecholestrogens (CEs), one of them being the mutagenic 4-hydroxyestradiol-17β (4−OH−E2). Catecholestrogens are transformed by catechol -o-methyltransferases (COMTs) into nonreactive methoxyestrogens. To investigate the hepatic metabolism of estradiol-17β in female offspring at postnatal day (PND) 21, pregnant rats were dosed daily from gestation day 1 until PND 21 with 2 dose levels of organochlorine pesticides (OCPs; 0.019 or 1.9 mg/kg per d), methylmercury (MeHg; 0.02 or 2 mg/kg per d), polychlorinated biphenyls (PCBs; 0.011 or 1.1 mg/kg per d), or a mixture (M; 0.05 or 5 mg/kg per d) including all 3 groups of chemicals. Concentrations of organochlorines in the mixture M were based on their proportions in serum of the Canadian Arctic population. The messenger RNA (mRNA) expressions of CYP and COMT were analyzed by quantitative reverse transcriptase–polymerase chain reaction (qRT-PCR). High-performance thin layer chromatography and phosphor imaging were used to measure the transformation of 14C substrates into estrogen metabolites. The low-dose treatments or the MeHg groups had no effect. The high-dose OCP, PCB, and M group increased the production of 2-OH-E2 and 6α-OH-E2, while only the PCB and M groups increased the 2-OH-CE/methoxyestrogen ratio. In all groups, the cytosolic COMT activity exceeded the microsomal production rate of 4-OH-E2. Although the M treatment included the PCB and OCP mixtures, it did not modify the estrogen metabolism more than did the PCB mixture alone. This endocrine disruption information contributes to our understanding of chemical interactions in the toxicology of chemical mixtures.

Activity of the estrogen-metabolizing enzyme cytochrome P450 1B1 influences the development of pulmonary arterial hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH) is a hyperproliferative vascular disorder observed predominantly in women. Estrogen is a potent mitogen in human pulmonary artery smooth muscle cells and contributes to PAH in vivo; however, the mechanisms attributed to this causation remain obscure. Curiously, heightened expression of the estrogen-metabolizing enzyme cytochrome P450 1B1 (CYP1B1) is reported in idiopathic PAH and murine models of PAH.

METHODS AND RESULTS

Here, we investigated the putative pathogenic role of CYP1B1 in PAH. Quantitative reverse transcription-polymerase chain reaction, immunoblotting, and in situ analysis revealed that pulmonary CYP1B1 is increased in hypoxic PAH, hypoxic+SU5416 PAH, and human PAH and is highly expressed within the pulmonary vascular wall. PAH was assessed in mice via measurement of right ventricular hypertrophy, pulmonary vascular remodeling, and right ventricular systolic pressure. Hypoxic PAH was attenuated in CYP1B1(-/-) mice, and the potent CYP1B1 inhibitor 2,3',4,5'-tetramethoxystilbene (TMS; 3 mg · kg(-1) · d(-1) IP) significantly attenuated hypoxic PAH and hypoxic+SU5416 PAH in vivo. TMS also abolished estrogen-induced proliferation in human pulmonary artery smooth muscle cells and PAH-pulmonary artery smooth muscle cells. The estrogen metabolite 16α-hydroxyestrone provoked human pulmonary artery smooth muscle cell proliferation, and this mitogenic effect was greatly pronounced in PAH-pulmonary artery smooth muscle cells. ELISA analysis revealed that 16α-hydroxyestrone concentration was elevated in PAH, consistent with CYP1B1 overexpression and activity. Finally, administration of the CYP1B1 metabolite 16α-hydroxyestrone (1.5 mg · kg(-1) · d(-1) IP) caused the development of PAH in mice.

CONCLUSIONS

Increased CYP1B1-mediated estrogen metabolism promotes the development of PAH, likely via the formation of mitogens, including 16α-hydroxyestrone. Collectively, this study reveals a possible novel therapeutic target in clinical PAH.

Genistein, a soy phytoestrogen, reverses severe pulmonary hypertension and prevents right heart failure in rats

Pretreatment with a phytoestrogen genistein has been shown to attenuate the development of pulmonary hypertension (PH). Because PH is not always diagnosed early, we examined whether genistein could also reverse preexisting established PH and prevent associated right heart failure (RHF). PH was induced in male rats by 60 mg/kg of monocrotaline. After 21 days, when PH was well established, rats received daily injection of genistein (1 mg/kg per day) for 10 days or were left untreated to develop RHF by day 30. Effects of genistein on human pulmonary artery smooth muscle cell and endothelial cell proliferation and neonatal rat ventricular myocyte hypertrophy were assessed in vitro. Severe PH was evident 21 days after monocrotaline, as peak systolic right ventricular pressure increased to 66.35±1.03 mm Hg and right ventricular ejection fraction reduced to 41.99±1.27%. PH progressed to RHF by day 30 (right ventricular pressure, 72.41±1.87 mm Hg; RV ejection fraction, 29.25±0.88%), and mortality was ≈75% in RHF rats. Genistein therapy resulted in significant improvement in lung and heart function as right ventricular pressure was significantly reduced to 43.34±4.08 mm Hg and right ventricular ejection fraction was fully restored to 65.67±1.08% similar to control. Genistein reversed PH-induced pulmonary vascular remodeling in vivo and inhibited human pulmonary artery smooth muscle cell proliferation by ≈50% in vitro likely through estrogen receptor-β. Genistein also reversed right ventricular hypertrophy (right ventricular hypertrophy index, 0.35±0.029 versus 0.70±0.080 in RHF), inhibited neonatal rat ventricular myocyte hypertrophy, and restored PH-induced loss of capillaries in the right ventricle. These improvements in cardiopulmonary function and structure resulted in 100% survival by day 30. Genistein restored PH-induced downregulation of estrogen receptor-β expression in the right ventricle and lung. In conclusion, genistein therapy not only rescues preexisting severe PH but also prevents the progression of severe PH to RHF.

Estrogen paradox in pulmonary hypertension: current controversies and future perspectives

Although the incidence of pulmonary hypertension is higher in female patients, numerous experimental studies have demonstrated better outcome in female animals, exacerbation of the disease after ovariectomy, and a strong protective effect of estrogen: a phenomenon known as the "estrogen paradox" of pulmonary hypertension. On the other hand, some clinical studies have indirectly linked estrogen to increased risk of portopulmonary hypertension, whereas others implicate increased estrogen metabolism and high levels of certain estrogen metabolites in promoting pulmonary vascular remodeling in familial pulmonary arterial hypertension. In this review we investigate the estrogen paradox through highlighting the differential receptor-mediated effects of estrogen. Although estrogen and estrogen receptor-based therapies have shown promise in rescuing preexisting pulmonary hypertension in animals, their role is yet to be defined in humans.

17β-Estradiol attenuates hypoxic pulmonary hypertension via estrogen receptor-mediated effects

RATIONALE

17β-Estradiol (E2) attenuates hypoxic pulmonary vasoconstriction and hypoxic pulmonary hypertension (HPH) through an unknown mechanism that may involve estrogen receptors (ER) or E2 conversion to catecholestradiols and methoxyestradiols with previously unrecognized effects on cardiopulmonary vascular remodeling.

OBJECTIVES

To determine the mechanism by which E2 exerts protective effects in HPH.

METHODS

Male rats were exposed to hypobaric hypoxia while treated with E2 (75 μg/kg/d) or vehicle. Subgroups were cotreated with pharmacologic ER-antagonist or with inhibitors of E2-metabolite conversion. Complementary studies were performed in rats cotreated with selective ERα- or ERβ-antagonist. Hemodynamic and pulmonary artery (PA) and right ventricular (RV) remodeling parameters, including cell proliferation, cell cycle, and autophagy, were measured in vivo and in cultured primary rat PA endothelial cells.

MEASUREMENTS AND MAIN RESULTS

E2 significantly attenuated HPH endpoints. Hypoxia increased ERβ but not ERα lung vascular expression. Co-treatment with nonselective ER inhibitor or ERα-specific antagonist rendered hypoxic animals resistant to the beneficial effects of E2 on cardiopulmonary hemodynamics, whereas ERα- and ERβ-specific antagonists opposed the remodeling effects of E2. In contrast, inhibition of E2-metabolite conversion did not abolish E2 protection. E2-treated hypoxic animals exhibited reduced ERK1/2 activation and increased expression of cell-cycle inhibitor p27(Kip1) in lungs and RV, with up-regulation of lung autophagy. E2-induced signaling was recapitulated in hypoxic but not normoxic endothelial cells, and was associated with decreased vascular endothelial growth factor secretion and cell proliferation.

CONCLUSIONS

E2 attenuates hemodynamic and remodeling parameters in HPH in an ER-dependent manner, through direct antiproliferative mechanisms on vascular cells, which may provide novel nonhormonal therapeutic targets for HPH.

Targeting energetic metabolism: a new frontier in the pathogenesis and treatment of pulmonary hypertension

This perspective highlights advances in the understanding of the role of cellular metabolism in the pathogenesis of pulmonary hypertension. Insights gained in the past 20 years have revealed several similarities between the cellular processes underlying the pulmonary vascular remodeling in pulmonary hypertension and those seen in cancer processes. In line with these insights, there is increasing recognition that abnormal cellular metabolism, notably of aerobic glycolysis (the "Warburg effect"), the potential involvement of hypoxia-inducible factor in this process, and alterations in mitochondrial function, are key elements in the pathogenesis of this disease. The glycolytic shift may underlie the resistance to apoptosis and increased vascular cell proliferation, which are hallmarks of pulmonary hypertension. These investigations have led to novel approaches in the diagnosis and therapy of pulmonary hypertension.

Synergistic therapeutic effects of 2-methoxyestradiol with either sildenafil or bosentan on amelioration of monocrotaline-induced pulmonary hypertension and vascular remodeling

2-Methoxyestradiol (2ME) is a major nonestrogenic metabolite of estradiol. Our previous studies suggest that 2ME, in several models of cardiac and/or vascular injury, strongly inhibits cardiac and vascular remodeling. Furthermore, our most recent study shows that in male rats, 2ME attenuates the development and retards the progression of monocrotaline (MCT)-induced pulmonary arterial hypertension (PAH), and in female rats, 2ME eliminates the exacerbation of PAH and the increased mortality due to ovariectomy. The current standard of care of patients with PAH includes treatment with an endothelin receptor antagonist (eg, bosentan) or a phosphodiesterase5 inhibitor (eg, sildenafil). Moreover, combination therapy is often prescribed. Therefore, in the present study, we compared the efficacy of 2ME (10 μg · kg(-1) · h(-1), 2ME-10) to the effects of bosentan (200 mg/kg; BOS), sildenafil (50 mg/kg; SIL), and their respective combinations with 2ME-10 (2ME + BOS and 2ME + SIL groups, respectively). Treatments were initiated 12 days after administration of MCT (60 mg/kg). Twenty-eight days after MCT administration, right ventricular peak systolic pressure was measured and morphometric analysis was conducted. 2ME exhibited beneficial effects in pulmonary hypertensive animals and had efficacy comparable to that of BOS and SIL. Importantly, combination treatments had favorable effects on survival, vascular remodeling, and inflammatory response, and the 2ME + SIL combination was significantly more efficacious than any other treatment. These results indicate that 2ME is effective in experimental PAH and suggests that 2ME may provide additional therapeutic benefit over existing drugs used for the treatment of pulmonary hypertension.

Role of lipoxygenase metabolites of arachidonic acid in enhanced pulmonary artery contractions of female rabbits

Pulmonary arterial hypertension is characterized by elevated pulmonary artery pressure and vascular resistance. In women the incidence is 4-fold greater than that in men. Studies suggest that sustained vasoconstriction is a factor in increased vascular resistance. Possible vasoconstrictor mediators include arachidonic acid-derived lipoxygenase (LO) metabolites. Our studies in rabbits showed enhanced endothelium-dependent contractions to arachidonic acid in pulmonary arteries from females compared with males. Because treatment with a nonspecific LO inhibitor reduced contractions in females but not males, the present study identified which LO isoform contributes to sex-specific pulmonary artery vasoconstriction. The 15- and 5- but not 12-LO protein expressions were greater in females. Basal and A23187-stimulated release of 15-, 5-, and 12-hydroxyeicosatetraenoic acids (HETEs) from females and males were measured by liquid chromatography/mass spectrometry. Only 15-HETE synthesis was greater in females compared with males under both basal and stimulated conditions. Vascular contractions to 15-HETE were enhanced in females compared with males (maximal contraction: 44±6%versus 25±3%). The specific 15-LO inhibitor PD146176 (12 μmol/L) decreased arachidonic acid-induced contractions in females (maximal contraction: 93±4% versus 57±10%). If male pulmonary arteries were incubated with estrogen (1 μmol/L, 18 hours), protein expression of 15-LO and 15-HETE production increased. Mechanisms to explain the increased incidence of pulmonary hypertension in women are not known. Results suggest that the 15-LO pathway is different between females and males and is regulated by estrogen. Understanding this novel sex-specific mechanism may provide insight into the increased incidence of pulmonary hypertension in females.

Estrogens and development of pulmonary hypertension: interaction of estradiol metabolism and pulmonary vascular disease

Severe pulmonary arterial hypertension (PAH) is characterized by clustered proliferation of endothelial cells (ECs) in the lumina of small size pulmonary arteries resulting in concentric obliteration of the lumina and formation of complex vascular structures known as plexiform lesions. This debilitating disease occurs more frequently in women, yet both animal studies in classical models of PAH and limited clinical data suggest protective effects of estrogens: the estrogen paradox in pulmonary hypertension. Little is known about the role of estrogens in PAH, but one line of evidence strongly suggests that the vascular protective effects of 17β-estradiol (estradiol; E2) are mediated largely by its downstream metabolites. Estradiol is metabolized to 2-hydroxyestradiol (2HE) by CYP1A1/CYP1B1, and 2HE is converted to 2-methoxyestradiol (2ME) by catechol-O-methyl transferase. 2ME is extensively metabolized to 2-methoxyestrone, a metabolite that lacks biologic activity, but which may be converted back to 2ME. 2ME has no estrogenic activity, and its effects are mediated by estrogen receptors–independent mechanism(s). Notably, in systemic and pulmonary vascular ECs, smooth muscle cells, and fibroblasts, 2ME exerts stronger antimitotic effects than E2 itself. E2 and 2ME, despite having similar effects on other cardiovascular cells, have opposing effects on ECs; that is, in ECs, E2 is promitogenic, proangiogenic, and antiapoptotic, whereas 2ME is antimitogenic, antiangiogenic, and proapoptotic. This may have significant ramifications in severe PAH that involves uncontrolled proliferation of monoclonal apoptosis-resistant ECs. Based on its cellular effects, 2ME should be expected to attenuate the progression of disease and provide protection in severe PAH. In contrast, E2, due to its mitogenic, angiogenic, and antiapoptotic effects (otherwise desirable in normal quiescent ECs), may even adversely affect endothelial remodeling in PAH, and this may be even more significant if the E2's effects on injured endothelium are not opposed by 2ME (eg, in the event of reduced E2 conversion to 2ME due to hypoxia, inflammation, drugs, environmental factors, or genetic polymorphism of metabolizing enzymes). This review focuses on the effects of estrogens and their metabolites on pulmonary vascular pathobiology and the development of experimental PAH and offers potential explanation for the estrogen paradox in PAH. Furthermore, we propose that unbalanced estradiol metabolism may lead to the development of PAH. Recent animal data and studies in patients with PAH support this concept.

New therapies for pulmonary arterial hypertension: an update on current bench to bedside translation

IMPORTANCE OF THE FIELD

Treatments of pulmonary arterial hypertension (PAH) that have so far proven efficacious are all based on the restoration of endothelium control of pulmonary vascular tone and structure, by administration of prostacyclins, endothelin receptor antagonists and phosphodiesterase-5 inhibitors. However, results remain unsatisfactory, with persistent high mortality, insufficient clinical improvement and no convincing report of any reversal of the disease process.

AREAS COVERED IN THIS REVIEW

New antiproliferative approaches that aim to actively limit pulmonary vascular remodeling are being sought. Several such treatments have shown promise in experimental models and in preliminary clinical studies. Noteworthy among these are dichloroacetate, survivin antagonists, nuclear factor of activated T-cell inhibitors, PPAR-gamma agonists, tyrosine kinase inhibitors, Rho-kinase inhibitors, statins, vasoactive intestinal peptide, soluble guanylate cyclase stimulators/activators, adrenomedullin, elastase inhibitors, serotonin reuptake inhibitors, anti-inflammatory agents, and bone marrow-derived progenitor cells.

WHAT THE READER WILL GAIN

Update on various strategies targeting proliferative, inflammatory and regenerating processes currently under evaluation in patients with PAH.

TAKE HOME MESSAGE

In spite of favorable results in experimental models, none of these strategies has achieved the ultimate goal of curing PAH. Further developments will depend on progress made in our pathobiological understanding of the disease and carefully designed randomized, controlled trials.

Novel approaches to treat experimental pulmonary arterial hypertension: a review

Background. Pulmonary arterial hypertension (PAH) is a life-threatening disease characterized by an increase in pulmonary artery pressure leading to right ventricular (RV) hypertrophy, RV failure, and ultimately death. Current treatments can improve symptoms and reduce severity of the hemodynamic disorder but gradual deterioration in their condition often necessitates a lung transplant. Methods and Results. In experimental models of PAH, particularly the model of monocrotaline-induced pulmonary hypertension, efficacious treatment options tested so far include a spectrum of pharmacologic agents with actions such as anti-mitogenic, proendothelial function, proangiogenic, antiinflammatory and antioxidative. Emerging trends in PAH treatment are gene and cell therapy and their combination, like (progenitor) cells enriched with eNOS or VEGF gene. More animal data should be collected to investigate optimal cell type, in vitro cell transduction, route of administration, and number of cells to inject. Several recently discovered and experimentally tested interventions bear potential for therapeutic purposes in humans or have been shown already to be effective in PAH patients leading to improved life expectation and better quality of life. Conclusion. Since many patients remain symptomatic despite therapy, we should encourage research in animal models of PAH and implement promising treatments in homogeneous groups of PAH patients.

Hypoxia inducible-factor1alpha regulates the metabolic shift of pulmonary hypertensive endothelial cells

Severe pulmonary hypertension is irreversible and often fatal. Abnormal proliferation and resistance to apoptosis of endothelial cells (ECs) and hypertrophy of smooth muscle cells in this disease are linked to decreased mitochondria and preferential energy generation by glycolysis. We hypothesized this metabolic shift of pulmonary hypertensive ECs is due to greater hypoxia inducible-factor1alpha (HIF-1alpha) expression caused by low levels of nitric oxide combined with low superoxide dismutase activity. We show that cultured ECs from patients with idiopathic pulmonary arterial hypertension (IPAH-ECs) have greater HIF-1alpha expression and transcriptional activity than controls under normoxia or hypoxia, and pulmonary arteries from affected patients have increased expression of HIF-1alpha and its target carbonic anhydrase IX. Decreased expression of manganese superoxide dismutase (MnSOD) in IPAH-ECs paralleled increased HIF-1alpha levels and small interfering (SI) RNA knockdown of MnSOD, but not of the copper-zinc SOD, increased HIF-1 protein expression and hypoxia response element (HRE)-driven luciferase activity in normoxic ECs. MnSOD siRNA also reduced nitric oxide production in supernatants of IPAH-ECs. Conversely, low levels of a nitric oxide donor reduced HIF-1alpha expression in normoxic IPAH-ECs. Finally, mitochondria numbers increased in IPAH-ECs with knockdown of HIF-1alpha. These findings indicate that alterations of nitric oxide and MnSOD contribute to pathological HIF-1alpha expression and account for lower numbers of mitochondria in IPAH-ECs.

Potential vascular actions of 2-methoxyestradiol

2-Methoxyestradiol (2-ME) is a biologically active metabolite of 17beta-estradiol that appears to inhibit key processes associated with cell replication in vitro. The molecule has been suggested to have potent growth-inhibitory effects on proliferating cells, including smooth muscle cells and endothelial cells, and may be antiangiogenic. Because of these potential roles for 2-ME, its lack of cytotoxicity and low estrogenic activity, we hypothesize that 2-ME could be a valuable therapeutic molecule for prevention and treatment of cardiovascular diseases. Whether 2-ME is as effective in vivo as it is in vitro at modulating vascular processes remains controversial. Here we discuss recent developments regarding mechanisms by which 2-ME might regulate vascular activity and angiogenesis and speculate on the therapeutic implications of these developments.

2-methoxyestradiol attenuates bleomycin-induced pulmonary hypertension and fibrosis in estrogen-deficient rats

Pulmonary hypertension (PH) is a common and life-threatening complication of pulmonary fibrosis. Estradiol (E2) is protective in experimental PH, and its non-estrogenic metabolite 2-methoxyestradiol (2ME) prevents the development and retards the progression of monocrotaline-induced PH in male and female rats. However, the effects of E2 and 2ME on pulmonary fibrosis and associated PH have not been examined. Therefore, we compared the growth inhibitory effects of E2 and 2ME in human lung fibroblasts (hLFs) and pulmonary vascular smooth muscle cells (hPASMCs), and we investigated the effects of estrogen deficiency and 2ME on bleomycin-induced pulmonary fibrosis and PH. Intact and ovariectomized (OVX) female Sprague-Dawley rats were administered intratracheally either saline or bleomycin (15IU/kg), and a subset of OVX bleomycin-treated rats received 2ME (10microg/kg/h) for 21days. Estradiol had only limited inhibitory effects on growth in hPASMCs and no effect in hLFs, whereas 2ME exhibited strong and concentration-dependent (1-10microM) antimitogenic effects in both cell types. Bleomycin caused lung injury/PH (significantly increased lung and right ventricle (RV) weights, RV peak systolic pressure (RVPSP), and RV/left ventricle + septum ratio (RV/LV + S); caused medial hypertrophy and adventitial widening of pulmonary arteries; induced marked focal/diffuse fibrosis with diffuse infiltration of inflammatory (ED1+) cells; and resulted in 30% mortality). OVX exacerbated the disease and increased mortality (to 75%); whereas 2ME tended to reduce mortality (55.5%) and in surviving animals reduced RVPSP and RV/LV + S ratio, and attenuated vascular remodeling, pulmonary inflammation and fibrosis. This study suggests that 2ME may have protective effects in bleomycin-induced PH and fibrosis. Further investigation of 2ME in pulmonary fibrosis and PH is warranted.

2-Methoxyestradiol attenuates hypertension and coronary vascular remodeling in spontaneously hypertensive rats

OBJECTIVES

Accumulating data provide evidence that some metabolites of 17beta-estradiol are biologically active and mediate multiple effects on the cardiovascular and renal systems. We investigated the effect of 2-methoxyestradiol (an active metabolite of estradiol with non-feminizing activity) on the development of hypertension and myocardial vascular remodeling in male and female ovarectomized SHR.

METHODS

Rats were divided into five groups: intact females, ovarectomized (OVX), OVX+ 2-methoxyestradiol (2ME), control males, and male+2ME. Systolic blood pressure was determined from 10 to 18 weeks. Structural changes in coronary vessels were quantified by an image analyzer. Immunoblotting of phosphorylated ERK1/2 and NADPH oxidase activity were performed on mesenteric arteries.

RESULTS

Treatment with 2ME reduced the increase in systolic blood pressure in male and ovarectomized rats to values not different from those obtained in intact females. Myocardial arterioles and small arteries showed significant increases in wall-to-lumen ratio and perivascular fibrosis in male and ovarectomized rats when compared with intact females. NADPH oxidase activity was increased in mesenteric arteries from males and ovarectomized females as compared with intact females. Finally, the expression of phosphorilated ERK1/2 were significantly higher in mesenteric arteries from male and ovariectomized animals than in those from intact females. Those effects of ovarectomy and gender differences were totally or partially prevented by treatment with 2-methoxyestradiol.

CONCLUSIONS

These data demonstrate that 2-methoxyestradiol protects the vasculature from hypertension-induced myocardial arterial remodeling in male and ovarectomized SHR, and that might be in part related to decreased superoxide generation and ERK1/2 activation.

Therapeutic targets in pulmonary arterial hypertension

Pulmonary arterial hypertension is a progressive, fatal disease. Current treatments including prostanoids, endothelin-1 (ET-1) antagonists, and phosphodiesterase (PDE) inhibitors, have sought to address the pulmonary vascular endothelial dysfunction and vasoconstriction associated with the condition. These treatments may slow the progression of the disease but do not afford a cure. Future treatments must target more directly the structural vascular changes that impair blood flow through the pulmonary circulation. Several novel therapeutic targets have been proposed and are under active investigation, including soluble guanylyl cyclase, phosphodiesterases, tetrahydrobiopterin, 5-HT2B receptors, vasoactive intestinal peptide, receptor tyrosine kinases, adrenomedullin, Rho kinase, elastases, endogenous steroids, endothelial progenitor cells, immune cells, bone morphogenetic protein and its receptors, potassium channels, metabolic pathways, and nuclear factor of activated T cells. Tyrosine kinase inhibitors, statins, 5-HT2B receptor antagonists, EPCs and soluble guanylyl cyclase activators are among the most advanced, having produced encouraging results in animal models, and human trials are underway. This review summarises the current research in this area and speculates on their likely success.

Estrogen is a modulator of vascular inflammation

Vascular inflammation underlies the pathogenesis of atherosclerosis. Atherosclerotic changes in the vasculature lead to conditions such as coronary artery disease and stroke, which are the major causes of morbidity and mortality worldwide. Epidemiological studies in premenopausal women suggest a beneficial role for estrogen in preventing vascular inflammation and consequent atherosclerosis. However, the benefits of estrogen areabsent or even reversed in older postmenopausal subjects. The modulation of inflammation by estrogen under different conditions might explain this discrepancy. Estrogen exerts its antiinflammatory effects on the vasculature through different mechanisms such as direct antioxidant effect, generation of nitric oxide, prevention of apoptosis in vascular cells and suppression of cytokines and the renin-angiotensin system. On the other hand, estrogen also elicits proinflammatory changes under certain conditions, which are less completely understood. Some of the mechanisms underlying a possible proinflammatory role for estrogen include increased expression of the proinflammatory receptor for advanced glycation end products, increased tyrosine nitration of cellular proteins, and generation of reactive oxygen species through an uncoupled eNOS. In this review, we have presented evidence for both antiinflammatory and proinflammatory pathways modulated by estrogen and how interactions among such pathways might determine the effects of estrogen on the vascular system.

The effects of estrogen on pulmonary artery vasoreactivity and hypoxic pulmonary vasoconstriction: potential new clinical implications for an old hormone

BACKGROUND AND OBJECTIVES

Recent research recognizes gender as a major factor determining the outcomes in trauma, ischemia/reperfusion, shock, and sepsis. In particular, estrogen has been demonstrated to exert protective effects in these settings. The effects of estrogens on the pulmonary vasculature are potent and complex yet not fully understood. A better mechanistic understanding may allow for future therapeutic interventions in pulmonary hypertensive crises after cardiac surgery and during acute lung injury as well as in patients with pulmonary arterial hypertension.

DATA SOURCES AND STUDY SELECTION

We searched PubMed for articles in the English language by using the search words pulmonary hypertension, hypoxic pulmonary vasoconstriction, estrogen, estradiol, inflammation, acute injury, ischemia reperfusion, sepsis, trauma, and burns. These were used in various combinations. We read the abstracts of the relevant titles to confirm their relevance, and the full articles were then extracted. References from extracted articles were checked for any additional relevant articles.

DATA EXTRACTION AND SYNTHESIS

Estrogen plays a critical role in the improved outcomes in the settings of trauma, shock, sepsis, myocardial ischemia/reperfusion, and acute lung injury. Several new mechanisms of action have been identified. In the pulmonary vasculature, estrogen causes vasodilation and attenuates the vasoconstrictor response to various stimuli, including hypoxia. This is mediated by increased levels of prostacyclin and nitric oxide as well as decreased levels of endothelin-1. In addition, effects on intracellular signaling pathways and several kinases as well as anti-inflammatory mechanisms may contribute as well. Recent studies suggest the importance of acute, nongenomic effects.

CONCLUSION

Estrogen exerts a variety of nongenomic actions, which may allow for future therapeutic interventions in pulmonary vascular disease.