Increased MAO-A Activity Promotes Progression of Pulmonary Arterial Hypertension

Does Cell-Type-Specific Silencing of Monoamine Oxidase B Interfere with the Development of Right Ventricle (RV) Hypertrophy or Right Ventricle Failure in Pulmonary Hypertension?

Increased mitochondrial reactive oxygen species (ROS) formation is important for the development of right ventricular (RV) hypertrophy (RVH) and failure (RVF) during pulmonary hypertension (PH). ROS molecules are produced in different compartments within the cell, with mitochondria known to produce the strongest ROS signal. Among ROS-forming mitochondrial proteins, outer-mitochondrial-membrane-located monoamine oxidases (MAOs, type A or B) are capable of degrading neurotransmitters, thereby producing large amounts of ROS. In mice, MAO-B is the dominant isoform, which is present in almost all cell types within the heart. We analyzed the effect of an inducible cardiomyocyte-specific knockout of MAO-B (cmMAO-B KO) for the development of RVH and RVF in mice. Right ventricular hypertrophy was induced by pulmonary artery banding (PAB). RV dimensions and function were measured through echocardiography. ROS production (dihydroethidium staining), protein kinase activity (PamStation device), and systemic hemodynamics (in vivo catheterization) were assessed. A significant decrease in ROS formation was measured in cmMAO-B KO mice during PAB compared to Cre-negative littermates, which was associated with reduced activity of protein kinases involved in hypertrophic growth. In contrast to littermates in which the RV was dilated and hypertrophied following PAB, RV dimensions were unaffected in response to PAB in cmMAO-B KO mice, and no decline in RV systolic function otherwise seen in littermates during PAB was measured in cmMAO-B KO mice. In conclusion, cmMAO-B KO mice are protected against RV dilatation, hypertrophy, and dysfunction following RV pressure overload compared to littermates. These results support the hypothesis that cmMAO-B is a key player in causing RV hypertrophy and failure during PH.

Therapeutic Approaches in Pulmonary Arterial Hypertension with Beneficial Effects on Right Ventricular Function-Preclinical Studies

Pulmonary hypertension (PH) is a progressive condition that affects the pulmonary vessels, but its main prognostic factor is the right ventricle (RV) function. Many mice/rat models are used for research in PAH, but results fail to translate to clinical trials. This study reviews studies that test interventions on pulmonary artery banding (PAB), a model of isolated RV disfunction, and PH models. Multiple tested drugs both improved pulmonary vascular hemodynamics in PH models and improved RV structure and function in PAB animals. PH models and PAB animals frequently exhibited similar results (73.1% concordance). Macitentan, sildenafil, and tadalafil improved most tested pathophysiological parameters in PH models, but almost none in PAB animals. Results are frequently not consistent with other studies, possibly due to the methodology, which greatly varied. Some research groups start treating the animals immediately, and others wait up to 4 weeks from model induction. Treatment duration and choice of anaesthetic are other important differences. This review shows that many drugs currently under research for PAH have a cardioprotective effect on animals that may translate to humans. However, a uniformization of methods may increase comparability between studies and, thus, improve translation to clinical trials.

Pulmonary Hypertension: A Contemporary Review

Major advances in pulmonary arterial hypertension, pulmonary hypertension (PH) associated with lung disease, and chronic thromboembolic PH cast new light on the pathogenetic mechanisms, epidemiology, diagnostic approach, and therapeutic armamentarium for pulmonary vascular disease. Here, we summarize key basic, translational, and clinical PH reports, emphasizing findings that build on current state-of-the-art research. This review includes cutting-edge progress in translational pulmonary vascular biology, with a guide to the diagnosis of patients in clinical practice, incorporating recent PH definition revisions that continue emphasis on early detection of disease. PH management is reviewed including an overview of the evolving considerations for the approach to treatment of PH in patients with cardiopulmonary comorbidities, as well as a discussion of the groundbreaking sotatercept data for the treatment of pulmonary arterial hypertension.

Monoamine Oxidase A Contributes to Serotonin-But Not Norepinephrine-Dependent Damage of Rat Ventricular Myocytes

Serotonin effects on cardiac hypertrophy, senescence, and failure are dependent either on activation of specific receptors or serotonin uptake and serotonin degradation by monoamine oxidases (MAOs). Receptor-dependent effects are specific for serotonin, but MAO-dependent effects are nonspecific as MAOs also metabolize other substrates such as catecholamines. Our study evaluates the role of MAO-A in serotonin- and norepinephrine-dependent cell damage. Experiments were performed in vivo to study the regulation of MAOA and MAOB expression and in vitro on isolated cultured adult rat ventricular cardiomyocytes (cultured for 24 h) to study the function of MAO-A. MAOA but not MAOB expression increased in maladaptive hypertrophic stages. Serotonin and norepinephrine induced morphologic cell damage (loss of rod-shaped cell structure). However, MAO-A inhibition suppressed serotonin-dependent but not norepinephrine-dependent damages. Serotonin but not norepinephrine caused a reduction in cell shortening in nondamaged cells. Serotonin induced mitochondria-dependent oxidative stress. In vivo, MAOA was induced during aging and hypertension but the expression of the corresponding serotonin uptake receptor (SLC6A4) was reduced and enzymes that reduce either oxidative stress (CAT) or accumulation of 5-hydroxyindolacetaldehyde (ALDH2) were induced. In summary, the data show that MAO-A potentially affects cardiomyocytes' function but that serotonin is not necessarily the native substrate.

Oxidative Stress and Antioxidant Therapy in Pulmonary Hypertension

Pulmonary hypertension (PH) is a progressive disease characterized by elevated artery pressures and pulmonary vascular resistance. Underlying mechanisms comprise endothelial dysfunction, pulmonary artery remodeling and vasoconstriction. Several studies have shown evidence of the critical role of oxidative stress in PH pathophysiology. Alteration of redox homeostasis produces excessive generation of reactive oxygen species, inducing oxidative stress and the subsequent alteration of biological molecules. Exacerbations in oxidative stress production can lead to alterations in nitric oxide signaling pathways, contributing to the proliferation of pulmonary arterial endothelial cells and smooth muscle cells, inducing PH development. Recently, antioxidant therapy has been suggested as a novel therapeutic strategy for PH pathology. However, the favorable outcomes observed in preclinical studies have not been consistently reproduced in clinical practice. Therefore, targeting oxidative stress as a therapeutic intervention for PH is an area that is still being explored. This review summarizes the contribution of oxidative stress to the pathogenesis of the different types of PH and suggests antioxidant therapy as a promising strategy for PH treatment.

Importance of Mitochondria in Cardiac Pathologies: Focus on Uncoupling Proteins and Monoamine Oxidases

On the one hand, reactive oxygen species (ROS) are involved in the onset and progression of a wide array of diseases. On the other hand, these are a part of signaling pathways related to cell metabolism, growth and survival. While ROS are produced at various cellular sites, in cardiomyocytes the largest amount of ROS is generated by mitochondria. Apart from the electron transport chain and various other proteins, uncoupling protein (UCP) and monoamine oxidases (MAO) have been proposed to modify mitochondrial ROS formation. Here, we review the recent information on UCP and MAO in cardiac injuries induced by ischemia-reperfusion (I/R) as well as protection from I/R and heart failure secondary to I/R injury or pressure overload. The current data in the literature suggest that I/R will preferentially upregulate UCP2 in cardiac tissue but not UCP3. Studies addressing the consequences of such induction are currently inconclusive because the precise function of UCP2 in cardiac tissue is not well understood, and tissue- and species-specific aspects complicate the situation. In general, UCP2 may reduce oxidative stress by mild uncoupling and both UCP2 and UCP3 affect substrate utilization in cardiac tissue, thereby modifying post-ischemic remodeling. MAOs are important for the physiological regulation of substrate concentrations. Upon increased expression and or activity of MAOs, however, the increased production of ROS and reactive aldehydes contribute to cardiac alterations such as hypertrophy, inflammation, irreversible cardiomyocyte injury, and failure.

Myocardial ischemia-reperfusion injury is probably due to the excessive production of mitochondrial ROS caused by the activation of 5-HT degradation system mediated by PAF receptor

AIM

Previously, we revealed a crucial role of 5-HT degradation system (5DS), consisting of 5-HT2A receptor (5-HT2AR), 5-HT synthases and monoamine oxidase A (MAO-A), in ischemia-reperfusion (IR)-caused organ injury. Whereas, platelet activating factor receptor (PAFR) also mediates myocardial ischemia-reperfusion injury (MIRI). Here, we try to clarify the relationship between 5DS and PAFR in mediating MIRI.

METHODS

H9c2 cell injury and rat MIRI were caused by hypoxia/reoxygenation (H/R) or PAF, and by ligating the left anterior descending coronary artery then untying, respectively. 5-HT_2AR and PAFR antagonists [sarpogrelate hydrochloride (SH) and BN52021], MAO-A, AKT, mTOR and 5-HT synthase inhibitors (clorgyline, perifosine, rapamycin and carbidopa), and gene-silencing PKCε were used in experiments RESULTS: The mitochondrial ROS production, respiratory chain damage, inflammation, apoptosis and myocardial infarction were significantly prevented by BN52021, SH and clorgyline in H/R and PAF-treated cells and in IR myocardium. BN52021 also significantly suppressed the upregulation of PAFR, 5-HT_2AR, 5-HT synthases and MAO-A expression (mRNA and protein), and Gα_q and PKCε (in plasmalemma) expression induced by H/R, PAF or IR; the effects of SH were similar to that of BN52021 except for no affecting the expression of PAFR and 5-HT_2AR. Gene-silencing PKCε suppressed H/R and PAF-induced upregulation of 5-HT synthases and MAO-A expression in cells; perifosine and rapamycin had not such effects; however, clorgyline suppressed H/R and PAF-induced phosphorylation of AKT and mTOR.

CONCLUSION

MIRI is probably due to PAFR-mediated 5-HT_2AR activation, which further activates PKCε-mediated 5-HT synthesis and degradation, leading to mitochondrial ROS production.

Metformin and empagliflozin modulate monoamine oxidase-related oxidative stress and improve vascular function in human mammary arteries

Monoamine oxidases (MAOs), mitochondrial enzymes with two isoforms, A and B, have been recently recognized as significant contributors to oxidative stress in the cardiovascular system. The present study was purported to assess the effect of metformin and empagliflozin on MAO expression, oxidative stress and vascular reactivity in internal mammary arteries harvested from overweight patients with coronary heart disease subjected to bypass grafting. Vascular rings were prepared and acutely incubated (12 h) with high glucose (GLUC, 400 mg/dL) or angiotensin II (AII, 100 nM) and metformin (10 µM) and/or empagliflozin (10 µM) and used for the assessment of MAO expression (qRT-PCR and immune histochemistry), reactive oxygen species (ROS, confocal microscopy and spectrophotometry), and vasomotor function (myograph). Ex vivo stimulation with GLUC or AII increased both MAOs expression, ROS production and impaired relaxation to acetylcholine (ACh) of the vascular rings. All effects were alleviated by incubation with each antidiabetic drug; no cumulative effect was obtained when the drugs were applied together. In conclusion, MAO-A and B are upregulated in mammary arteries after acute stimulation with GLUC and AII. Endothelial dysfunction and oxidative stress were alleviated by either metformin or empagliflozin in both stimulated and non-stimulated vascular samples harvested from overweight cardiac patients.

Chronic Sigma 1 receptor activation alleviates right ventricular dysfunction secondary to pulmonary arterial hypertension

Sigma 1 receptor (S1R) has shown a preferable protective effect on left ventricular function, but whether it protects right ventricular (RV) function is still elusive.This study aimed to determine the effects of S1R on RV dysfunction secondary to pulmonary arterial hypertension.Sixty wild-type male Sprague–Dawley rats were randomly divided into the control group, the fluvoxamine group, the pulmonary arterial hypertension group and the pulmonary arterial hypertension combined with fluvoxamine group. Monocrotaline (60 mg/kg) was administered to induce pulmonary arterial hypertension, and fluvoxamine was given for 21 consecutive days to activate S1R after one week of monocrotaline administration. Echocardiographic, serologic, and histologic parameters, qRT-PCR, and western blotting were conducted after 4 weeks of monocrotaline administration.The expression of S1R was decreased in the right ventricle in pulmonary arterial hypertension. TAPSE, and the FAC of the right ventricle were significantly decreased, and RV EDP and the plasma concentration of N-terminal pro-B-type natriuretic peptide was increased in the pulmonary arterial hypertension group, but fluvoxamine partly restored those abnormalities (all P < 0.05). Moreover, pulmonary arteriole remodeling, and fibrosis and hypertrophy in the RV were shown in the pulmonary arterial hypertension group; interestingly, fluvoxamine recovered RV structural remodeling (all P < 0.05) but neither alleviated pulmonary arteriole remodeling nor reduced pulmonary artery pressure. Furthermore, S1R activation protects RV function by upgrading the NRF 2/HO 1-mediated antioxidant stress pathway. In conclusion, chronic S1R activation ameliorates structural remodeling and RV dysfunction secondary to pulmonary arterial hypertension without altering pulmonary artery pressure.

Mitochondrial Metabolism, Redox, and Calcium Homeostasis in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease characterized by elevated pulmonary arterial pressure due to increased pulmonary vascular resistance, secondary to sustained pulmonary vasoconstriction and excessive obliterative pulmonary vascular remodeling. Work over the last decade has led to the identification of a critical role for metabolic reprogramming in the PAH pathogenesis. It is becoming clear that in addition to its role in ATP generation, the mitochondrion is an important organelle that regulates complex and integrative metabolic- and signal transduction pathways. This review focuses on mitochondrial metabolism alterations that occur in deranged pulmonary vessels and the right ventricle, including abnormalities in glycolysis and glucose oxidation, fatty acid oxidation, glutaminolysis, redox homeostasis, as well as iron and calcium metabolism. Further understanding of these mitochondrial metabolic mechanisms could provide viable therapeutic approaches for PAH patients.

Sex Dimorphism in Pulmonary Hypertension: The Role of the Sex Chromosomes

Pulmonary hypertension (PH) is a condition characterised by an abnormal elevation of pulmonary artery pressure caused by an increased pulmonary vascular resistance, frequently leading to right ventricular failure and reduced survival. Marked sexual dimorphism is observed in patients with pulmonary arterial hypertension, a form of pulmonary hypertension with a particularly severe clinical course. The incidence in females is 2-4 times greater than in males, although the disease is less severe in females. We review the contribution of the sex chromosomes to this sex dimorphism highlighting the impact of proteins, microRNAs and long non-coding RNAs encoded on the X and Y chromosomes. These genes are centrally involved in the cellular pathways that cause increased pulmonary vascular resistance including the production of reactive oxygen species, altered metabolism, apoptosis, inflammation, vasoconstriction and vascular remodelling. The interaction with genetic mutations on autosomal genes that cause heritable pulmonary arterial hypertension such as bone morphogenetic protein 2 (BMPR2) are examined. The mechanisms that can lead to differences in the expression of genes located on the X chromosomes between females and males are also reviewed. A better understanding of the mechanisms of sex dimorphism in this disease will contribute to the development of more effective therapies for both women and men.