Pulmonary arterial hypertension and the potential roles of metallothioneins: A focused review

Pulmonary hypertension and the potential of 'drug' repurposing: A case for African medicinal plants

Abstract

Pulmonary hypertension (PH) is a haemodynamic disorder in which elevated blood pressure in the pulmonary circulation is caused by abnormal vascular tone. Despite advances in treatment, PH mortality remains high, and drug repurposing has been proposed as a mitigating approach. This article reviews the studies that have investigated drug repurposing as a viable option for PH. We provide an overview of PH and highlight pharmaceutical drugs with repurposing potential, based on limited evidence of their mechanisms of action. Moreover, studies have demonstrated the benefits of medicinal plants in PH, most of which are of Indian or Asian origin. Africa is a rich source of many medicinal plants that have been scientifically proven to counteract myriad pathologies. When perusing these studies, one will notice that some African medicinal plants can counteract the molecular pathways (e.g. proliferation, vasoconstriction, inflammation, oxidative stress and mitochondrial dysfunction) that are also involved in the pathogenesis of PH. We review the actions of these plants with actions applicable to PH and highlight that they could be repurposed as adjunct PH therapies. However, these plants have either never been tested in PH, or there is little evidence of their actions against PH. We therefore encourage caution, as more research is needed to study these plants further in experimental models of PH while acknowledging that the outcomes of such proof of-concept studies may not always yield promising findings. Regardless, this article aims to stimulate future research that could make timely contributions to the field.

Study synopsis

What the study adds. Pulmonary hypertension (PH) remains a fatal disease, and 80% of the patients live in developing countries where resources are scarce and specialised therapies are often unavailable. Drug repurposing is a viable option to try to improve treatment outcomes.Implications of the findings. We propose that another form of 'drug' repurposing is the use of medicinal plants, many of which have demonstrated benefits against pathological processes that are also key in PH, e.g. apoptosis, tumour-like growth of cells, proliferation, oxidative stress and mitochondrial dysfunction.

Immunolocalization of zinc transporters and metallothioneins reveals links to microvascular morphology and functions

Zinc homeostasis is vital to immune and other organ system functions, yet over a quarter of the world’s population is zinc deficient. Abnormal zinc transport or storage protein expression has been linked to diseases, such as cancer and chronic obstructive pulmonary disorder. Although recent studies indicate a role for zinc regulation in vascular functions and diseases, detailed knowledge of the mechanisms involved remains unknown. This study aimed to assess protein expression and localization of zinc transporters of the SLC39A/ZIP family (ZIPs) and metallothioneins (MTs) in human subcutaneous microvessels and to relate them to morphological features and expression of function-related molecules in the microvasculature. Microvessels in paraffin biopsies of subcutaneous adipose tissues from 14 patients undergoing hernia reconstruction surgery were analysed for 9 ZIPs and 3 MT proteins by MQCM (multifluorescence quantitative confocal microscopy). Zinc regulation proteins detected in human microvasculature included ZIP1, ZIP2, ZIP8, ZIP10, ZIP12, ZIP14 and MT1-3, which showed differential localization among endothelial and smooth muscle cells. ZIP1, ZIP2, ZIP12 and MT3 showed significantly (p < 0.05) increased immunoreactivities, in association with increased microvascular muscularization, and upregulated ET-1, α-SMA and the active form of p38 MAPK (Thr180/Tyr182 phosphorylated, p38 MAPK-P). These findings support roles of the zinc regulation system in microvascular physiology and diseases.

Reviewing the suitability of mitochondrial transplantation as therapeutic approach for pulmonary hypertension in the era of personalised medicine

Pulmonary hypertension (PH) is a fatal disease, defined as a mean pulmonary artery pressure ≥ 25 mm Hg. It is caused, in part, by mitochondrial dysfunction. Among the various biological therapies proposed to rescue mitochondrial dysfunction, evidence going back as far as 2009, suggests that mitochondrial transplantation is an alternative. Although scant, recent PH findings and other literature supports a role for mitochondrial transplantation as a therapeutic approach in the context of PH. In experimental models of PH, it confers beneficial effects that include reduced pulmonary vasoconstriction, reduced pulmonary vascular remodelling, and improved right ventricular function. It also reduces the proliferation of pulmonary artery smooth muscle cells. However, first, we must understand that more research is needed before mitochondrial transplantation can be considered an effective therapy in the clinical setting, as many of the mechanisms or potential long-term risks are still unknown. Second, the current challenges of mitochondrial transplantation are surmountable and should not deter researchers from further investigating its effectiveness and trying to overcome these challenges in creative ways.

Dysregulated zinc and sphingosine-1-phosphate signaling in pulmonary hypertension: Potential effects by targeting of bone morphogenetic protein receptor type 2 in pulmonary microvessels

Recently identified molecular targets in pulmonary artery hypertension (PAH) include sphingosine-1-phosphate (S1P) and zinc transporter ZIP12 signaling. This study sought to determine linkages between these pathways, and with BMPR2 signaling. Lung tissues from a rat model of monocrotaline-induced PAH and therapeutic treatment with bone marrow-derived endothelial-like progenitor cells transduced to overexpress BMPR2 were studied. Multifluorescence quantitative confocal microscopy (MQCM) was applied for analysis of protein expression and localization of markers of vascular remodeling (αSMA and BMPR2), parameters of zinc homeostasis (zinc transporter SLC39A/ZIP family members 1, 10, 12 and 14; and metallothionein MT3) and S1P extracellular signaling (SPHK1, SPNS2, S1P receptor isoforms 1, 2, 3, 5) in 20-200 µm pulmonary microvessels. ZIP12 expression in whole lung tissue lysates was assessed by western blot. Spearman nonparametric correlations between MQCM readouts and hemodynamic parameters, Fulton index (FI), and right ventricular systolic pressure (RVSP) were measured. In line with PAH status, pulmonary microvessels in monocrotaline-treated animals demonstrated significant (p < .05, n = 6 per group) upregulation of αSMA (twofold) and downregulation of BMPR2 (20%). Upregulated ZIP12 (92%), MT3 (57.7%), S1PR2 (54.8%), and S1PR3 (30.3%) were also observed. Significant positive and negative correlations were demonstrated between parameters of zinc homeostasis (ZIP12, MT3), S1P signaling (S1PRs, SPNS2), and vascular remodeling (αSMA, FI, RVSP). MQCM and western blot analysis showed that monocrotaline-induced ZIP12 upregulation could be partially negated by BMPR2-targeted therapy. Our results indicate that altered zinc transport/storage and S1P signaling in the monocrotaline-induced PAH rat model are linked to each other, and could be alleviated by BMPR2-targeted therapy.

Single-cell transcriptomic profile of human pulmonary artery endothelial cells in health and pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is an insidious disease characterized by severe remodeling of the pulmonary vasculature caused in part by pathologic changes of endothelial cell functions. Although heterogeneity of endothelial cells across various vascular beds is well known, the diversity among endothelial cells in the healthy pulmonary vascular bed and the pathologic diversity among pulmonary arterial endothelial cells (PAEC) in PAH is unknown and previously unexplored. Here single-cell RNA sequencing technology was used to decipher the cellular heterogeneity among PAEC in the human pulmonary arteries isolated from explanted lungs from three patients with PAH undergoing lung transplantation and three healthy donor lungs not utilized for transplantation. Datasets of 36,368 PAH individual endothelial cells and 36,086 healthy cells were analyzed using the SeqGeq bioinformatics program. Total population differential gene expression analyses identified 629 differentially expressed genes between PAH and controls. Gene Ontology and Canonical Ingenuity analysis revealed pathways that are known to be involved in pathogenesis, as well as unique new pathways. At the individual cell level, dimensionality reduction followed by density based clustering revealed the presence of eight unique PAEC clusters that were typified by proliferative, angiogenic or quiescent phenotypes. While control and PAH harbored many similar subgroups of endothelial cells, PAH had greater proportions of angiogenic and proliferative subsets. These findings identify that only specific subgroups of PAH PAEC have gene expression different than healthy PAEC, and suggest these subpopulations lead to the pathologic functions leading to remodeling.

Zinc Homeostasis Alters Zinc Transporter Protein Expression in Vascular Endothelial and Smooth Muscle Cells

INTRODUCTION

Zinc is an important essential micronutrient with anti-oxidative and anti-inflammatory properties in humans. The role of zinc in signalling has been characterized in the nervous, endocrine, gastrointestinal, renal and reproductive systems. Relatively little is known regarding its role in the vascular system, but the role of zinc homeostasis in augmenting vascular health and vasorelaxation is emerging. Zinc transport proteins are integral to the protective function of zinc, but knowledge of their expression in vascular endothelial and smooth muscle cells is lacking.

METHODOLOGY

Human coronary artery endothelial cells and pulmonary artery smooth muscle cells were assessed for gene expression (RT-PCR) of SLC39A (ZIP), SLC30A (ZnT) and metallothionein (MT) families of Zn transporters and storage proteins. Protein expression (fluorescence confocal microscopy) was then analysed for the proteins of interest that changed mRNA expression: ZIP2, ZIP12, ZnT1, ZnT2 and MT1/2.

RESULTS

Endothelial and smooth muscle cell mRNA expression of ZnT1, ZnT2 and MT1 was significantly downregulated by low and high Zn conditions, while ZIP2 and ZIP12 expression was induced by Zn depletion with the Zn chelator, TPEN. Changes in gene expression were consistent with protein expression levels for ZIP2, ZIP12 and MT1, where ZIP2 was localized to intracellular bodies and ZIP12 to lamellipodia.

CONCLUSION

Vascular endothelial and smooth muscle cells actively regulate specific Zn transport and metallothionein gene and protein expressions to achieve Zn homeostasis.

Pulmonary hypertension in majority countries: opportunities amidst challenges

PURPOSE OF REVIEW

Pulmonary hypertension is a deadly disease, the causes of which vary between geographical regions. Eighty four percentage of the world's population lives in majority countries (also called low-income and middle-income countries), yet data on pulmonary hypertension in these settings are proportionally scarce. This article provides a review of pulmonary hypertension in majority countries, focusing in detail on the most common causes in these regions, and highlights contextual challenges faced.

RECENT FINDINGS

Epidemiological data confirms a complex and overlapping array of causes, with pulmonary hypertension because of conditions such as rheumatic heart disease, HIV, schistosomiasis, chronic lung disease and sickle cell disease. Delayed pulmonary hypertension diagnosis remains a concern and is ascribed to a lack of resources and lack of pulmonary hypertension awareness by health professionals. Pulmonary hypertension diagnosis is frequently considered once signs of right heart failure emerge, while echocardiography and right heart catheterization are unavailable in many settings. Accurate data on the prevalence of pulmonary hypertension in many of these regions are needed and could be achieved by establishing and frequent review of national databases where the incident and prevalent pulmonary hypertension cases are captured.

SUMMARY

There is urgent need for pulmonary hypertension advocacy among clinicians in the primary, secondary and tertiary healthcare sectors of majority countries, and validated noninvasive diagnostic algorithms are needed. Increased awareness and early diagnosis are likely to improve outcomes of pulmonary hypertension patients in these regions, and potentially stimulate locally relevant research.