Schistosomiasis Pulmonary Arterial Hypertension

Characterization of long-term interleukin-33 administration as an animal model of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is characterized by the severe obstruction of the small pulmonary arteries and concomitant high pulmonary arterial pressure, resulting in progressive right ventricular failure. Previously, we demonstrated that long-term interleukin (IL)-33 administration in mice induces severe occlusive medial hypertrophy of pulmonary arteries (PA) in the lungs, which is mediated by group 2 innate lymphoid cells (ILC2s). In response to IL-33, ILC2s accumulate around the blood vessels and produce IL-5, leading to perivascular eosinophil recruitment. In this study, we characterized IL-33-induced medial hypertrophy of PA. We demonstrated that long-term IL-33 administration causes an increase in right ventricular pressure. In IL-33-deficient mice, medial hypertrophy of PA mediated by eggs of Schistosoma mansoni was attenuated, accompanied by a partial reduction in ILC2s, eosinophils, and CD4+ T cells. In addition, proteomic analysis revealed dramatic changes in the urine samples from mice treated with IL-33 or S. mansoni eggs. Resistin-like alpha (RELMα), a pulmonary hypertension-related molecule, was commonly detected in the urine in both treatments. Large amounts of RELMα were observed in the lungs of the IL-33-treated mice. These observations suggest that IL-33-induced medial hypertrophy of PA is a useful model for studying the mechanism underlying the development of PAH and finding biomarkers to indicate the onset of PAH.

Treatment algorithm for pulmonary arterial hypertension

Pulmonary arterial hypertension leads to significant impairment in haemodynamics, right heart function, exercise capacity, quality of life and survival. Current therapies have mechanisms of action involving signalling via one of four pathways: endothelin-1, nitric oxide, prostacyclin and bone morphogenetic protein/activin signalling. Efficacy has generally been greater with therapeutic combinations and with parenteral therapy compared with monotherapy or nonparenteral therapies, and maximal medical therapy is now four-drug therapy. Lung transplantation remains an option for selected patients with an inadequate response to therapies.

Infection and pulmonary vascular diseases consortium: United against a global health challenge

Leveraging the potential of virtual platforms in the post-COVID-19 era, the Infection and Pulmonary Vascular Diseases Consortium (iPVDc), with the support of the Pulmonary Vascular Research Institute (PVRI), launched a globally accessible educational program to highlight top-notch research on inflammation and infectious diseases affecting the lung vasculature. This innovative virtual series has already successfully brought together distinguished investigators across five continents - Asia, Europe, South and North America, and Africa. Moreover, these open global forums have contributed to a comprehensive understanding of the complex interplay among immunology, inflammation, infection, and cardiopulmonary health, especially concerning pulmonary hypertension and related pulmonary disorders. These enlightening discussions have not only heightened awareness about the impact of various pathogenic microorganisms, including fungi, parasites, and viruses, on the onset and development of pulmonary vascular diseases but have also cast a spotlight on co-infections and neglected illnesses like schistosomiasis - a disease that continues to impose a heavy socioeconomic burden in numerous regions worldwide. Thus, the overall goal of this review article is to present the most recent breakthroughs from infectious PVDs as well as bring to light the scientific and educational insights from the 2023 iPVDc/PVRI virtual symposium series, shaping our understanding of these crucial health issues in this more than ever interconnected world.

Interstitial macrophage phenotypes in Schistosoma-induced pulmonary hypertension

Background

Schistosomiasis is a common cause of pulmonary hypertension (PH) worldwide. Type 2 inflammation contributes to the development of Schistosoma-induced PH. Specifically, interstitial macrophages (IMs) derived from monocytes play a pivotal role by producing thrombospondin-1 (TSP-1), which in turn activates TGF-β, thereby driving the pathology of PH. Resident and recruited IM subpopulations have recently been identified. We hypothesized that in Schistosoma-PH, one IM subpopulation expresses monocyte recruitment factors, whereas recruited monocytes become a separate IM subpopulation that expresses TSP-1.

Methods

Mice were intraperitoneally sensitized and then intravenously challenged with S. mansoni eggs. Flow cytometry on lungs and blood was performed on wildtype and reporter mice to identify IM subpopulations and protein expression. Single-cell RNA sequencing (scRNAseq) was performed on flow-sorted IMs from unexposed and at day 1, 3 and 7 following Schistosoma exposure to complement flow cytometry based IM characterization and identify gene expression.

Results

Flow cytometry and scRNAseq both identified 3 IM subpopulations, characterized by CCR2, MHCII, and FOLR2 expression. Following Schistosoma exposure, the CCR2+ IM subpopulation expanded, suggestive of circulating monocyte recruitment. Schistosoma exposure caused increased monocyte-recruitment ligand CCL2 expression in the resident FOLR2+ IM subpopulation. In contrast, the vascular pathology-driving protein TSP-1 was greatest in the CCR2+ IM subpopulation.

Conclusion

Schistosoma-induced PH involves crosstalk between IM subpopulations, with increased expression of monocyte recruitment ligands by resident FOLR2+ IMs, and the recruitment of CCR2+ IMs which express TSP-1 that activates TGF-β and causes PH.

Non-cirrhotic portal hypertension in pregnancy due to schistosomiasis: A case series

The presence of non-cirrhotic portal hypertension in pregnancy poses a challenging clinical scenario as it predisposes women to several life-threatening complications such as variceal haemorrhage, splenic artery aneurysm, pulmonary hypertension and bacterial peritonitis. The haemodynamic changes in pregnancy along with the demands of a growing fetus may worsen the severity of pre-existing non-cirrhotic portal hypertension. In this case series, we discuss four cases of non-cirrhotic portal hypertension in pregnancy in a low to middle income setting and review the literature related to this condition.

Experimental Schistosoma haematobium pulmonary hypertension

Whether all Schistosoma species cause pulmonary hypertension (PH) is unclear. Experimentally exposing mice to Schistosoma haematobium eggs caused PH, which was less severe than that induced by S. mansoni exposure. These findings align with the relatively uncommon reports of pulmonary arterial hypertension associated with S. haematobium.

Gut-Lung Axis in Focus: Deciphering the Impact of Gut Microbiota on Pulmonary Arterial Hypertension

Recent advancements in the understanding of pulmonary arterial hypertension (PAH) have highlighted the significant role of the gut microbiota (GM) in its pathogenesis. This comprehensive review delves into the intricate relationship between the GM and PAH, emphasizing the influence of gut microbial composition and the critical metabolites produced. We particularly focus on the dynamic interaction between the gut and lung, examining how microbial dysbiosis contributes to PAH development through inflammation, altered immune responses, and changes in the gut-lung axis. Noteworthy findings include variations in the ratios of key bacterial groups such as Firmicutes and Bacteroidetes in PAH and the pivotal roles of metabolites like trimethylamine N-oxide (TMAO), short-chain fatty acids (SCFAs), and serotonin in the disease's progression. Additionally, the review elucidates potential diagnostic biomarkers and novel therapeutic approaches, including the use of probiotics and fecal microbiota transplantation, which leverage the gut microbiota for managing PAH. This review encapsulates the current state of research in this field, offering insights into the potential of gut microbiota modulation as a promising strategy in PAH diagnosing and treatment.

Is pulmonary arterial hypertension associated with schistosomiasis distinct from pulmonary arterial hypertension associated with portal hypertension?

Pulmonary arterial hypertension associated with schistosomiasis (SchPAH) and pulmonary arterial hypertension associated with portal hypertension (PoPAH) are lung diseases that develop in the presence of liver diseases. However, mechanistic pathways by which the underlying liver conditions and other drivers contribute to the development and progression of pulmonary arterial hypertension (PAH) are unclear for both etiologies. In turn, these unknowns limit certainty of strategies to prevent, diagnose, and reverse the resultant PAH. Here we consider specific mechanisms that contribute to SchPAH and PoPAH, identifying those that may be shared and those that appear to be unique to each etiology, in the hope that this exploration will both highlight known causal drivers and identify knowledge gaps appropriate for future research. Overall, the key pathophysiologic differences that we identify between SchPAH and PoPAH suggest that they are not variants of a single condition.

Respiratory morbidity in Schistosoma mansoni infection: a rapid review of literature

Background

Schistosomiasis contributes to 2.5 million disability-adjusted life years globally. Acute and chronic respiratory morbidity of Schistosoma mansoni (S. mansoni) is poorly documented in the literature. We conducted a rapid literature review of the burden of respiratory symptoms and lung function abnormalities among patients with S. mansoni. We also report the immunologic and lung imaging findings from the studies reviewed.

Methods

We carried out a comprehensive literature search in Embase and MEDLINE from the inception of the databases to 13th March 2023.

Results

A total of 2243 patients with S. mansoni were reported from 24 case reports, 11 cross-sectional studies, 7 case series, 2 cohort studies and 2 randomized controlled trials. The prevalence of any respiratory symptom was 13.3-63.3% (total number of patients studied, n = 149). The prevalence of the individual symptoms among patients with S. mansoni in whom respiratory symptoms were sought for was as follows: cough (8.3-80.6%, n = 338), dyspnea (1.7-100.0%, n = 200), chest pain (9.0-57.1%, n = 86), sputum production (20.0-23.3%, n = 30) and wheezing (0.0 - 20.0%, n = 1396). The frequency of the symptoms tended to be higher in acute schistosomiasis. Restrictive lung disease was prevalent in 29.0% (9/31). The commonest chest imaging findings reported were nodules (20-90%, n = 103) and interstitial infiltrates (12.5-23.0%, n = 89). Peripheral blood eosinophilia was prevalent in 72.0-100.0% of patients (n = 130) with acute schistosomiasis and correlated with symptoms and imaging abnormalities. Three case reports in chronic S. mansoni reported elevated C-reactive protein, leucocyte, neutrophil and absolute eosinophil counts, eosinophil percentage, IgE and IgG4.

Conclusion

There is a high prevalence of respiratory morbidity among patients with S. mansoni, particularly in the acute stage of the infection, although the studies are relatively small. Larger studies are needed to characterize respiratory morbidity in chronic schistosomiasis and determine the underlying clinical and immunological mechanisms.

Parasitic lung diseases

Parasitic lung diseases are caused by a number of parasites as a result of transient passage in the lung or as a result of an immunologic reaction. The clinical presentation may be in the form of focal or cystic lesions, pleural effusion or diffuse pulmonary infiltrates. With increasing globalisation, it is important to consider parasitic infections in the differential diagnosis of lung diseases. This is particularly important since early identification and prompt therapy result in full cure of these conditions. In this review, we summarise the most common parasitic lung diseases.

Regnase-1 Prevents Pulmonary Arterial Hypertension Through mRNA Degradation of Interleukin-6 and Platelet-Derived Growth Factor in Alveolar Macrophages

BACKGROUND

Pulmonary arterial hypertension (PAH) is a type of pulmonary hypertension (PH) characterized by obliterative pulmonary vascular remodeling, resulting in right-sided heart failure. Although the pathogenesis of PAH is not fully understood, inflammatory responses and cytokines have been shown to be associated with PAH, in particular, with connective tissue disease-PAH. In this sense, Regnase-1, an RNase that regulates mRNAs encoding genes related to immune reactions, was investigated in relation to the pathogenesis of PH.

METHODS

We first examined the expression levels of ZC3H12A (encoding Regnase-1) in peripheral blood mononuclear cells from patients with PH classified under various types of PH, searching for an association between the ZC3H12A expression and clinical features. We then generated mice lacking Regnase-1 in myeloid cells, including alveolar macrophages, and examined right ventricular systolic pressures and histological changes in the lung. We further performed a comprehensive analysis of the transcriptome of alveolar macrophages and pulmonary arteries to identify genes regulated by Regnase-1 in alveolar macrophages.

RESULTS

ZC3H12A expression in peripheral blood mononuclear cells was inversely correlated with the prognosis and severity of disease in patients with PH, in particular, in connective tissue disease-PAH. The critical role of Regnase-1 in controlling PAH was also reinforced by the analysis of mice lacking Regnase-1 in alveolar macrophages. These mice spontaneously developed severe PAH, characterized by the elevated right ventricular systolic pressures and irreversible pulmonary vascular remodeling, which recapitulated the pathology of patients with PAH. Transcriptomic analysis of alveolar macrophages and pulmonary arteries of these PAH mice revealed that Il6, Il1b, and Pdgfa/b are potential targets of Regnase-1 in alveolar macrophages in the regulation of PAH. The inhibition of IL-6 (interleukin-6) by an anti-IL-6 receptor antibody or platelet-derived growth factor by imatinib but not IL-1β (interleukin-1β) by anakinra, ameliorated the pathogenesis of PAH.

CONCLUSIONS

Regnase-1 maintains lung innate immune homeostasis through the control of IL-6 and platelet-derived growth factor in alveolar macrophages, thereby suppressing the development of PAH in mice. Furthermore, the decreased expression of Regnase-1 in various types of PH implies its involvement in PH pathogenesis and may serve as a disease biomarker, and a therapeutic target for PH as well.

Molecular Pathways in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension is a multifactorial, chronic disease process that leads to pulmonary arterial endothelial dysfunction and smooth muscular hypertrophy, resulting in impaired pliability and hemodynamics of the pulmonary vascular system, and consequent right ventricular dysfunction. Existing treatments target limited pathways with only modest improvement in disease morbidity, and little or no improvement in mortality. Ongoing research has focused on the molecular basis of pulmonary arterial hypertension and is going to be important in the discovery of new treatments and genetic pathways involved. This review focuses on the molecular pathogenesis of pulmonary arterial hypertension.

The role of helminths in the development of non-communicable diseases

Non-communicable diseases (NCDs) like cardiovascular disease, chronic respiratory diseases, cancers, diabetes, and neuropsychiatric diseases cause significant global morbidity and mortality which disproportionately affect those living in low resource regions including low- and middle-income countries (LMICs). In order to reduce NCD morbidity and mortality in LMIC it is imperative to understand risk factors associated with the development of NCDs. Certain infections are known risk factors for many NCDs. Several parasitic helminth infections, which occur most commonly in LMICs, have been identified as potential drivers of NCDs in parasite-endemic regions. Though understudied, the impact of helminth infections on the development of NCDs is likely related to helminth-specific factors, including species, developmental stage and disease burden. Mechanical and chemical damage induced by the helminth in combination with pathologic host immune responses contribute to the long-term inflammation that increases risk for NCD development. Robust studies from animal models and human clinical trials are needed to understand the immunologic mechanisms of helminth-induced NCDs. Understanding the complex connection between helminths and NCDs will aid in targeted public health programs to reduce helminth-induced NCDs and reduce the high rates of morbidity that affects millions of people living in parasite-endemic, LMICs globally.

The prevalence of Schistosoma mansoni infection among adults with chronic non-communicable diseases in Malawi

BACKGROUND

Schistosomiasis is a parasitic infectious disease caused by flatworms of the Schistosoma genus. The global burden of schistosomiasis is high. In Malawi, schistosomiasis is among the top 20 causes of outpatient department visits in health facilities. Schistosomiasis is among the most important but neglected causes of non-communicable diseases (NCD) peculiar to tropical endemic settings. While much is known about the contribution of S. haematobium to the NCD burden in Malawi, the role of S. mansoni remains largely unknown.

METHODS

We conducted a cross-sectional study at Mangochi District Hospital. Adults over 18 years diagnosed with NCDs (n = 414), admitted or attending weekly outpatient clinics were recruited between August 2021 and February 2022. Data were collected on sociodemographic characteristics, medical history, body weight, blood pressure, and fasting blood glucose. Stool and midstream urine were collected for Kato-Katz (KK) microscopy and urine point of care-circulating cathodic antigen (POC-CCA) tests, respectively. We computed prevalence of S. mansoni as number of positive KK and CCA tests, each divided by total submitted samples. Univariate and multivariable logistic regression were done to evaluate risk factors of NCDs and association between S. mansoni infection and NCDs.

RESULTS

We recruited 414 participants, mean age 57 years (SD 16), 67% of whom were female. Prevalence of S. mansoni based on urine CCA was 15% (95% CI: 11-19) and 0% on KK microscopy. Hypertension was the most common condition with a prevalence of 85% (95% CI: 81-89), followed by diabetes mellitus with a prevalence of 42% (95% CI: 37-46) and heart disease with a prevalence of 3% (95% CI: 2-5). S. mansoni infection was not significantly associated with hypertension (OR: 1.2, 95% CI: 0.5-3.1), diabetes (OR: 0.6, 95% CI: 0.3-1.10) or heart disease (OR: 2.0, 95% CI: 0.4-10).

CONCLUSIONS

We observed moderate prevalence of S. mansoni infection among adults in the study per WHO classification of endemicity. This is within the range observed in children in Mangochi from 10 to 56.7%.

HIV and Schistosoma Co-Exposure Leads to Exacerbated Pulmonary Endothelial Remodeling and Dysfunction Associated with Altered Cytokine Landscape

HIV and Schistosoma infections have been individually associated with pulmonary vascular disease. Co-infection with these pathogens is very common in tropical areas, with an estimate of six million people co-infected worldwide. However, the effects of HIV and Schistosoma co-exposure on the pulmonary vasculature and its impact on the development of pulmonary vascular disease are largely unknown. Here, we have approached these questions by using a non-infectious animal model based on lung embolization of Schistosoma mansoni eggs in HIV-1 transgenic (HIV) mice. Schistosome-exposed HIV mice but not wild-type (Wt) counterparts showed augmented pulmonary arterial pressure associated with markedly suppressed endothelial-dependent vasodilation, increased endothelial remodeling and vessel obliterations, formation of plexiform-like lesions and a higher degree of perivascular fibrosis. In contrast, medial wall muscularization was similarly increased in both types of mice. Moreover, HIV mice displayed an impaired immune response to parasite eggs in the lung, as suggested by decreased pulmonary leukocyte infiltration, small-sized granulomas, and augmented residual egg burden. Notably, vascular changes in co-exposed mice were associated with increased expression of proinflammatory and profibrotic cytokines, including IFN-γ and IL-17A in CD4⁺ and γδ T cells and IL-13 in myeloid cells. Collectively, our study shows for the first time that combined pulmonary persistence of HIV proteins and Schistosoma eggs, as it may occur in co-infected people, alters the cytokine landscape and targets the vascular endothelium for aggravated pulmonary vascular pathology. Furthermore, it provides an experimental model for the understanding of pulmonary vascular disease associated with HIV and Schistosoma co-morbidity.

Diagnosis and Treatment of Pulmonary Arterial Hypertension: A Review

IMPORTANCE

Pulmonary arterial hypertension (PAH) is a subtype of pulmonary hypertension (PH), characterized by pulmonary arterial remodeling. The prevalence of PAH is approximately 10.6 cases per 1 million adults in the US. Untreated, PAH progresses to right heart failure and death.

OBSERVATIONS

Pulmonary hypertension is defined by a mean pulmonary artery pressure greater than 20 mm Hg and is classified into 5 clinical groups based on etiology, pathophysiology, and treatment. Pulmonary arterial hypertension is 1 of the 5 groups of PH and is hemodynamically defined by right heart catheterization demonstrating a mean pulmonary artery pressure greater than 20 mm Hg, a pulmonary artery wedge pressure of 15 mm Hg or lower, and a pulmonary vascular resistance of 3 Wood units or greater. Pulmonary arterial hypertension is further divided into subgroups based on underlying etiology, consisting of idiopathic PAH, heritable PAH, drug- and toxin-associated PAH, pulmonary veno-occlusive disease, PAH in long-term responders to calcium channel blockers, and persistent PH of the newborn, as well as PAH associated with other medical conditions including connective tissue disease, HIV, and congenital heart disease. Early presenting symptoms are nonspecific and typically consist of dyspnea on exertion and fatigue. Currently approved therapy for PAH consists of drugs that enhance the nitric oxide-cyclic guanosine monophosphate biological pathway (sildenafil, tadalafil, or riociguat), prostacyclin pathway agonists (epoprostenol or treprostinil), and endothelin pathway antagonists (bosentan and ambrisentan). With these PAH-specific therapies, 5-year survival has improved from 34% in 1991 to more than 60% in 2015. Current treatment consists of combination drug therapy that targets more than 1 biological pathway, such as the nitric oxide-cyclic guanosine monophosphate and endothelin pathways (eg, ambrisentan and tadalafil), and has shown demonstrable improvement in morbidity and mortality compared with the previous conventional single-pathway targeted monotherapy.

CONCLUSIONS AND RELEVANCE

Pulmonary arterial hypertension affects an estimated 10.6 per 1 million adults in the US and, without treatment, typically progresses to right heart failure and death. First-line therapy with drug combinations that target multiple biological pathways are associated with improved survival.

Rationale and design of a screening study to detect schistosomiasis-associated pulmonary hypertension in Ethiopia and Zambia

Schistosomiasis is a major cause of pulmonary arterial hypertension (PAH) worldwide, but the prevalence and risk factors for schistosomiasis-associated PAH (SchPAH) development are not well understood. Schistosomiasis-associated hepatosplenic disease (SchHSD) is thought to be a major risk factor for PAH development. Herein, we describe our plans for prospectively screening SchHSD subjects for clinical evidence of PAH at two major academic medical centers and national referral hospitals in Addis Ababa, Ethiopia and Lusaka, Zambia. The screening study will primarily be conducted by echocardiography, in addition to clinical assessments. Plasma samples will be drawn and banked for subsequent analysis based on preclinical animal model rationale. If successful, this study will demonstrate feasibility of conducting prospective cohort studies of SchPAH screening in schistosomiasis-endemic regions of Africa, and provide initial data on clinic-based disease prevalence and potential mechanistic biomarkers underlying disease pathogenesis.

Experimental Schistosoma japonicum-induced pulmonary hypertension

BACKGROUND

Schistosomiasis, a major cause of pulmonary arterial hypertension (PAH) worldwide, is most clearly described complicating infection by one species, Schistosoma mansoni. Controlled exposure of mice can be used to induce Type 2 inflammation-dependent S. mansoni pulmonary hypertension (PH). We sought to determine if another common species, S. japonicum, can also cause experimental PH.

METHODS

Schistosome eggs were obtained from infected mice, and administered by intraperitoneal sensitization followed by intravenous challenge to experimental mice, which underwent right heart catheterization and tissue analysis.

RESULTS

S. japonicum sensitized and challenged mice developed PH, which was milder than that following S. mansoni sensitization and challenge. The degree of pulmonary vascular remodeling and Type 2 inflammation in the lungs was similarly proportionate. Cross-sensitization revealed that antigens from either species are sufficient to sensitize for intravenous challenge with either egg, and the degree of PH severity depended on primarily the species used for intravenous challenge. Compared to a relatively uniform distribution of S. mansoni eggs, S. japonicum eggs were observed in clusters in the lungs.

CONCLUSIONS

S. japonicum can induce experimental PH, which is milder than that resulting from comparable S. mansoni exposure. This difference may result from the distribution of eggs in the lungs, and is independent of which species is used for sensitization. This result is consistent with the clearer association between S. mansoni infection and the development of schistosomiasis-associated PAH in humans.

Signature network-based survey of the effects of a traditional Chinese medicine on heart failure

ETHNOPHARMACOLOGICAL RELEVANCE

Heart failure (HF) after myocardial infarction (MI) is one of the most common disabling and painful diseases. A traditional Chinese medicine (TCM) formula, Shengmaisan, is known as a multitarget medicine that is widely used clinically to treat heart failure (HF) in Asian countries. However, its mechanism has not been comprehensively demonstrated.

AIM OF THE STUDY

To use a prediction network to figure out which disease link SMZ mainly alleviates in HF and find biomarkers related to myocardial fibrosis in the serum for clinical reference.

MATERIALS AND METHODS

In this article, we collected a large amount of actual measurement data and our own proteomics data, along with the biomarkers of heart failure staging under study to establish a precise network. Then, we tested and verified the medicinal effect of SMZ in treatment of HF after MI by Measurement of left ventricular wall thickness and ejection fraction by echocardiography. Then we tested the serum level of the potential targets of SMZ predicting by the network we developed using ELISA.

RESULTS

the cardiac ejection fraction and retarding the thinning of the anterior wall of the left ventricle increased after treating with SMZ. The serum level of EGFR and MAPK1 decreased in the groups treated with SMZ.

CONCLUSION

SMZ can improve the cardiac function of rats with MI by increasing the cardiac ejection fraction and retarding the thinning of the anterior wall of the left ventricle. In addition, SMZ could delay heart failure mainly by inhibiting the progression of myocardial fibrosis through decreasing the EGFR and MAPK1 levels.

Schistosome-Associated Pulmonary Arterial Hypertension: A Review Emphasizing Pathogenesis

Schistosomiasis, especially due to Schistosoma mansoni, is a well-recognized cause of pulmonary arterial hypertension (PAH). The high prevalence of this helminthiasis makes schistosome-related PAH (Sch-PAH) one of the most common causes of this disorder worldwide. The pathogenic mechanisms underlying Sch-PAH remain largely unknown. Available evidence suggests that schistosome eggs reach the lung via portocaval shunts formed as a consequence of portal hypertension due to hepatosplenic schistosomiasis. Once deposited into the lungs, the eggs elicit an immune response resulting in periovular granuloma formation. Immune mediators drive transforming growth factor-β (TGF-β) release, which gives rise to pulmonary vascular inflammation with subsequent remodeling and development of angiomatoid and plexiform lesions. These mechanisms elicited by the eggs seem to become autonomous and the vascular lesions progress independently of the antigen. Portopulmonary hypertension, which pathogenesis is still uncertain, may also play a role in the genesis of Sch-PAH. Recently, there have been substantial advances in the diagnosis and treatment of PAH, but it remains a difficult condition to recognize and manage, and patients still die prematurely from right-heart failure. Echocardiography is used for screening, and the formal diagnosis requires right-heart catheterization. The experience in treating Sch-PAH is largely limited to the phosphodiesterase type 5 inhibitors, with evidence suggesting that these vasodilators improve symptoms and may also improve survival. Considering the great deal of uncertainty about Sch-PAH pathogenesis, course, and treatment, the aim of this review is to summarize current knowledge on this condition emphasizing its pathogenesis.

Animal models of pulmonary hypertension: Getting to the heart of the problem

Despite recent therapeutic advances, pulmonary hypertension (PH) remains a fatal disease due to the development of right ventricular (RV) failure. At present, no treatments targeted at the right ventricle are available, and RV function is not widely considered in the preclinical assessment of new therapeutics. Several small animal models are used in the study of PH, including the classic models of exposure to either hypoxia or monocrotaline, newer combinational and genetic models, and pulmonary artery banding, a surgical model of pure RV pressure overload. These models reproduce selected features of the structural remodelling and functional decline seen in patients and have provided valuable insight into the pathophysiology of RV failure. However, significant reversal of remodelling and improvement in RV function remains a therapeutic obstacle. Emerging animal models will provide a deeper understanding of the mechanisms governing the transition from adaptive remodelling to a failing right ventricle, aiding the hunt for druggable molecular targets.