Inflammation in pulmonary arterial hypertension.

Inflammatory mechanisms appear to play a significant role in some types of pulmonary hypertension (PH), including monocrotaline-induced PH in rats and pulmonary arterial hypertension of various origins in humans, such as connective tissue diseases (scleroderma, systemic lupus erythematosus, mixed connective disease), human immunodeficiency virus infection, or plasma cell dyscrasia with polyneuropathy, organomegaly, endocrinopathy, monoclonal (M) protein and skin changes (POEMS) syndrome. Interestingly, some patients with severe pulmonary arterial hypertension associated with systemic lupus erythematosus have experienced significant improvements with immunosuppressive therapy, emphasising the relevance of inflammation in a subset of patients presenting with PH. Patients with primary PH (PPH) also have some immunological disturbances, suggesting a possible role for inflammation in the pathophysiology of this disease. A subset of PPH patients have been shown to have circulating autoantibodies, including antinuclear antibodies, as well as elevated circulating levels of the pro-infammatory cytokines, interleukins -1 and -6. Lung histology has also revealed inflammatory infiltrates in the range of plexiform lesions in patients displaying severe PPH, as well as an increased expression of the chemokines regulated upon activation, normal T-cell expressed and secreted (RANTES) and fractalkine. Further analysis of the role of inflammatory mechanisms is necessary to understand whether this component of the disease is relevant to its pathophysiology.     

The pathobiology of pulmonary hypertension. Endothelium

Dysfunctional endothelial cells have a central and critical role in the initiation and progression of severe pulmonary hypertension. The elucidation of the mechanisms involved in the control of endothelial cell proliferation and cell death in the pulmonary vasculature, therefore, is fundamentally important in the pathogenesis of severe pulmonary hypertension and of great interest for a better understanding of endothelial cell biology. Because the intravascular growth of endothelial cells resulting in tumorlets is unique to severe pulmonary hypertension, this phenomenon can teach researchers about the factors involved in the formation and maintenance of the normal endothelial cell monolayer. Clearly, in severe pulmonary hypertension, the "law of the endothelial cell monolayer" has been broken. The ultimate level of such a control is at the altered gene expression pattern that is conducive to endothelial cell growth and disruption of pulmonary blood flow. Secondary pulmonary hypertension certainly also is associated with proliferated pulmonary endothelial cells and plexiform lesions that are histologically indistinguishable from those in PPH. What is then the difference in the mechanisms of endothelial cell proliferation between primary and secondary pulmonary hypertension? The authors believe that PPH is a disease caused by somatic mutations in key angiogenesis- or apoptosis-related genes such as the TGF-beta receptor-2 and Bax. The loss of these important cell growth control mechanisms allows for the clonal expansion of endothelial cells from a single cell that has acquired a selective growth advantage. On the other hand, the proliferated endothelial cells in secondary pulmonary hypertension are polyclonal. It follows from this finding that local (vascular) factor(s) (such as increased shear stress), rather than mutations, play a major role in triggering endothelial cell proliferation. In PPH and secondary pulmonary hypertension, the researcher can postulate that the pulmonary vascular bed contains progenitor-like cells with the capacity of dysregulated growth. The main difference in the pathogenesis of primary and secondary pulmonary endothelial cell proliferation therefore may be the initial mechanism involved in the recruitment of an endothelial progenitor-like cell. In PPH, anorexigen-associated, and familial PPH, the proliferation of endothelial cells occurs from a mutated single cell, whereas in secondary pulmonary hypertension, several progenitor-like cells would be activated to grow. The abnormal endothelial cells in both forms of severe pulmonary hypertension expand because of the expression of angiogenesis-related molecules such as VEGF, VEGFR-2, HIF-1 alpha, and HIF-beta. Also important for the expansion of these cells is the down-regulation of expression of apoptosis-related mediators such as TGF-beta receptor-2 or Bax. The success of any therapy for severe pulmonary hypertension requires that the underlying process of endothelial cell proliferation could be controlled or reversed.     

Transforming growth factor-beta type II receptor in pulmonary arteries of patients with very severe COPD.

A mild-to-moderate increase in pulmonary arterial pressure is often associated with severe chronic obstructive pulmonary disease (COPD). Transforming growth factor (TGF)-beta is a cytokine involved in the maintenance of integrity of vasculature. The aim of the study was to investigate whether the TGF-beta pathway might be involved in the development of pulmonary hypertension associated with COPD. Surgical specimens from 14 patients undergoing lung transplantation for very severe COPD (forced expiratory volume in one second 17 +/- 2% of the predicted value) and from seven donors were examined. The expression of TGF-beta1 and TGF-beta type II receptor (TGF-betaRII), cell proliferation index and structural changes in pulmonary arteries were quantified immunohistochemically. In severe COPD patients, increased expression of TGF-betaRII was observed in both the tunica media and intima, which was associated with a normal proliferation index in both layers. Conversely, significant thickening of the tunica intima, which was not present in the tunica media, was observed, suggesting that mechanisms other than cell proliferation may be involved in intimal thickening. In conclusion, in the pulmonary arteries of patients with severe chronic obstructive pulmonary disease, there is upregulation of transforming growth factor-beta type II receptor expression associated with a normal proliferation index. These findings suggest the activation of an antiproliferative pathway, which might explain the relatively low degree of pulmonary hypertension observed in these subjects.     

Inflammation in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is characterized by pulmonary vascular remodeling of the precapillary pulmonary arteries, with excessive proliferation of vascular cells. Although the exact pathophysiology remains unknown, there is increasing evidence to suggest an important role for inflammation. Firstly, pathologic specimens from patients with PAH reveal an accumulation of perivascular inflammatory cells, including macrophages, dendritic cells, T and B lymphocytes, and mast cells. Secondly, circulating levels of certain cytokines and chemokines are elevated, and these may correlate with a worse clinical outcome. Thirdly, certain inflammatory conditions such as connective tissue diseases are associated with an increased incidence of PAH. Finally, treatment of the underlying inflammatory condition may alleviate the associated PAH. Underlying pathologic mechanisms are likely to be "multihit" and complex. For instance, the inflammatory response may be regulated by bone morphogenetic protein receptor type 2 (BMPR II) status, and, in turn, BMPR II expression can be altered by certain cytokines. Although antiinflammatory therapies have been effective in certain connective-tissue-disease-associated PAH, this approach is untested in idiopathic PAH (iPAH). The potential benefit of antiinflammatory therapies in iPAH is of importance and requires further study.     

Current insights on the pathogenesis of pulmonary arterial hypertension

Regardless of the initial trigger, the elevated pulmonary arterial pressure and vascular resistance in patients with pulmonary arterial hypertension are primarily caused by remodeling and thrombosis of small- and medium-sized pulmonary arteries and arterioles, as well as sustained vasoconstriction. The process of pulmonary vascular remodeling involves all layers of the vessel wall and is complicated by cellular heterogeneity within each compartment. Indeed, each cell type (endothelial cells, smooth muscle cells, and fibroblasts), as well as inflammatory cells and platelets, may play significant roles in this condition. Recent studies have emphasized the relevance of several mediators in this condition, including prostaglandin-I (2) (prostacyclin), nitric oxide, endothelin-1, angiopoietin-1, 5-hydroxytryptamine (serotonin), cytokines, chemokines, and members of the transforming growth factor beta (TGF-beta) superfamily. Targeting some of these dysfunctional pathways (prostacyclin, nitric oxide, and endothelin-1) has been beneficial in subjects displaying pulmonary arterial hypertension.     

Possible pathogenic mechanisms in inflammatory myopathies

The limitations associated with the different approaches into the pathogenesis of the IIM have resulted in incomplete knowledge of disease mechanisms in myositis. In most research, in which muscle tissue was used to study the different aspects of disease, biopsies with inflammatory infiltrates have been selected. Although inflammatory cell infiltrates are a characteristic feature of myositis, selecting patients with inflammatory cell infiltrates for investigations naturally introduces a selection bias. Only a few studies have been published on patients without inflammatory infiltrates but with muscle weakness, and few studies have included follow-up biopsies after different therapies. The heterogeneity of the population of patients with myositis is another limitation of the studies of pathogenic mechanisms. Although most studies classify patients according to the Bohan and Peter criteria [118, 119], some studies used histopathologic criteria [6], and only a few studies included characterization with myositis-specific autoantibodies. Because myositis-specific autoantibodies are often associated with certain clinical profiles, classification according to autoantibody profiles could be important to define differences in the pathogenesis of different phenotypes [3]. From available data on pathogenic mechanisms it is evident that cellular and humoral immune responses are involved in disease mechanisms of myositis, but whether there is a muscle-specific immune response cannot be answered by current studies. It is likely that other mechanisms are important for development of muscle weakness, including metabolic disturbances, and muscle weakness could be caused by different mechanisms in different IIM subsets or in patients in different phases of the disease. There could be early changes, which reversibly affect the metabolism, and later, irreversible changes, that could be dependent on muscle fiber damage and replacement of muscle tissue by connective tissue and fat. Current findings suggest that cytokines, which are produced in muscle tissue from different cell sources including inflammatory cells, endothelial cells, and muscle fibers, could affect muscle function. Careful follow-up studies, including the effect of therapies targeting different molecules on molecular expression in muscle tissue, are likely to increase our knowledge on disease mechanisms. A better understanding of which molecules and mechanisms affect muscle function is likely to lead to improved, less toxic therapies in patients with myositis. Many possible target molecules for blocking therapies, especially the proinflammatory cytokines IL-1 and TNF-alpha, have been identified and should be studied in appropriate clinical settings given the currently poor outcomes of many patients with IIM.     

FIBROSING ALVEOLITIS ASSOCIATED WITH PRIMARY ANTIPHOSPHOLIPID SYNDROME

The spectrum of the primary antiphospholipid syndrome has expandedin recent years. It has been associated with a number of non-thromboticsyndromes such as pulmonary hypertension, adrenal insufficiency,chorea and avascular necrosis of bone. Yet, it has not beendescribed in association with inflammatory pulmonary disease.We describe a young male with definite primary antiphospholipidsyndrome who developed insidious diffuse pulmonary infiltrates.The histopathologic examination of the involved lung demonstratedalveolitis and fibrosis. We suggest that this pulmonary involvementmay represent another manifestation of the primary antiphospholipidsyndrome. KEY WORDS: Antiphospholipid syndrome, Fibrosing alveolitis     

Genetics of pulmonary hypertension: from bench to bedside.

Primary pulmonary hypertension has been described as either sporadic or clustered in families. Familial primary pulmonary hypertension segregates as an autosomal dominant trait with markedly reduced disease gene penetrance. Defects within bone morphogenetic protein receptor type II gene, coding for a receptor member of the transforming growth factor-beta family, underlie familial primary pulmonary hypertension. Several lines of evidence point to the potential requirement of additional factors, either environmental or genetic, in the pathogenesis of the disease. In addition, a proportion of so-called sporadic primary pulmonary hypertension turns out to have an inherited basis, as demonstrated by germline bone morphogenetic protein receptor type II gene mutations. Analysis of cases in association with hereditary haemorrhagic telangiectasia led to the demonstration that pulmonary arterial hypertension can involve activin-receptor-like kinase 1 mutations, a type I transforming growth factor-beta receptor. These findings emphasise the critical role of the transforming growth factor-beta signalling pathway in pulmonary arterial hypertension. While this achievement has generated extreme interest, the pathobiology of severe pulmonary arterial hypertension remains unclear and genomic approaches to pulmonary hypertension research may identify additional molecular determinants for this disorder. Finally, there is an urgent need to develop relevant guidelines for genetic counselling to assist patients, their relatives and pulmonary vascular specialists to utilise these recent observations.     

Impaired transforming growth factor-beta signaling in idiopathic pulmonary arterial hypertension

Mutations in transforming growth factor-beta family receptor-II, bone morphogenetic protein receptor-2, and activin-like kinase-1 have been associated with pulmonary hypertension. In the present study, we determined that pulmonary arteries in normal lungs and in lungs of patients with emphysema and idiopathic pulmonary arterial hypertension comparably expressed transforming growth factor-beta receptors I and II, Smad(1, 5, 8), Smad2, Smad3, Smad4, phosphorylated Smad(1, 5, 8), and phosphorylated Smad2 (the latter two both indicative of active in vivo signaling) in endothelial cells, as assessed by immunohistochemistry and quantitative morphometry. Medial or intimal smooth muscle cells had weak or absent expression of these molecules. In clear contrast to endothelial cell expression in pulmonary arteries and in endothelial cells lining incipient vessels within plexiform lesions of hypertensive lungs, endothelial cells present in the core of the lesions lacked expression of all examined members of the signaling molecules. These findings were made irrespective of the mutation status of bone morphogenetic protein receptor-2 in hypertensive patients. Our findings suggest that pulmonary artery endothelial cells in both normal and severely hypertensive lungs have active transforming growth factor-beta family signaling, and that loss of signaling might contribute to the abnormal growth of endothelial cells in plexiform lesions in idiopathic pulmonary arterial hypertension.     

Ca2+ channels and chronic hypoxia

Many chronic lung diseases are associated with prolonged exposure to alveolar hypoxia, resulting in the development of pulmonary hypertension. While the exact mechanisms underlying the pathogenesis of hypoxic pulmonary hypertension remain poorly understood, a key role for changes in Ca2+ homeostasis has emerged. Intracellular Ca2+ concentration controls a variety of pulmonary vascular cell functions, including contraction, gene expression, growth, barrier function and synthesis of vasoactive substances. Several studies indicate that prolonged exposure to hypoxia causes alterations in the expression and activity of several Ca2+ handling pathways in pulmonary arterial smooth muscle cells. In contrast, the effect of chronic hypoxia on Ca2+ homeostasis in pulmonary arterial endothelial cells is relatively unexplored. In this review, we discuss data from our laboratory and others describing the effects of prolonged hypoxia on pulmonary vascular smooth muscle and endothelial cell Ca2+ homeostasis and the various Ca2+ channels and handling pathways involved in these responses. We will also highlight future directions of investigation that might improve our understanding of the response of pulmonary vascular cells to chronic hypoxia.     

Pulmonary vascular involvement in COPD

Alterations in pulmonary vessel structure and function are highly prevalent in patients with COPD. Vascular abnormalities impair gas exchange and may result in pulmonary hypertension, which is one of the principal factors associated with reduced survival in COPD patients. Changes in pulmonary circulation have been identified at initial disease stages, providing new insight into their pathogenesis. Endothelial cell damage and dysfunction produced by the effects of cigarette smoke products or inflammatory elements is now considered to be the primary alteration that initiates the sequence of events resulting in pulmonary hypertension. Cellular and molecular mechanisms involved in this process are being extensively investigated. Progress in the understanding of the pathobiology of pulmonary hypertension associated with COPD may provide the basis for a new therapeutic approach addressed to correct the imbalance between endothelium-derived vasoactive agents. The safety and efficacy of endothelium-targeted therapy in COPD-associated pulmonary hypertension warrants further investigation in randomized clinical trials.     

Plasma monocyte chemoattractant protein-1 and pulmonary vascular resistance in chronic thromboembolic pulmonary hypertension.

The pathogenesis of severe pulmonary hypertension seems to be related to inflammatory response in diseased sites. Monocyte chemoattractant protein-1 (MCP-1) has been reported to play a role in the development of congestive heart failure. In this immunological response, activation and migration of leukocytes including macrophages to the inflammatory region are important factors. We hypothesized that the severity of pulmonary hypertension may be related to MCP-1, which is thought to be upregulated by blood pressure or shear stress in pulmonary vasculature as well as by immunological and inflammatory reactions in chronic thromboembolic pulmonary hypertension (CTEPH). Circulating levels of MCP-1, interleukin-1beta (IL-1beta), and tumor necrosis factor-alpha (TNF-alpha) were measured by sandwich ELISA in 14 patients with CTEPH. The plasma level of MCP-1 was significantly correlated with pulmonary vascular resistance. In IL-1beta and TNF-alpha, on the other hand, there was no correlation between cytokines and pulmonary hemodynamics. Pathological specimens obtained from the patients with CTEPH undergoing thromboendarterectomy demonstrated immunoreactivity of MCP-1 in endothelium, smooth muscle cells, and macrophages within neointima in the hypertensive large elastic pulmonary artery. We conclude that MCP-1 is upregulated in the remodeling of pulmonary arteries in close association with increased pulmonary vascular resistance in CTEPH.     

Myocardiopathy and Takayasu's disease. Apropos of a case

The possibility of cardiac involvement in Takayasu's disease is well known, but this involvement generally appears to be secondary to reno-vascular hypertension or to pulmonary arteritis and, exceptionally, as a result of coronary disease. In the case reported here, the inflammatory myocardial lesion localised to the left ventricle was demonstrated while the patient was still alive. It was responsible for an episode of severe heart failure which finally resolved after 2 years. The inflammatory involvement of the myocardium was associated with laboratory signs of inflammation and with inflammatory arterial lesions. Several haemodynamic investigations were performed to follow the course of the disease. The diagnosis was confirmed by myocardial biopsies and by the pulmonary arterial and renal arterial involvement. A review of the literature revealed that this condition was extremely rare and has only been proven in a few autopsy cases.     

Genetics of pulmonary arterial hypertension: current and future implications

Idiopathic pulmonary arterial hypertension (formerly primary pulmonary hypertension) can affect more than one member of the same family. In the past 25 years scientists have exposed the inheritance pattern and a major element of the molecular basis for inherited pulmonary arterial hypertension. Familial pulmonary arterial hypertension is inherited as an autosomal dominant trait with incomplete penetrance (i.e., several individuals inherit a predisposition to the disease, but never express it). Mutations in the gene that codes for bone morphogenetic protein receptor type II (BMPR-II) are a major predisposition for the development of pulmonary arterial hypertension. These mutations are present in at least half of familial cases of pulmonary arterial hypertension and 10 to 25% of idiopathic pulmonary arterial hypertension patients. Mutations in the gene that codes for activin receptor-like kinase (ALK 1), another transforming growth factor beta (TGF-beta) cell surface receptor, appear responsible for the rare occurrence of pulmonary arterial hypertension in patients with hereditary hemorrhagic telangiectasia. These discoveries coupled with other basic investigations offer opportunities for advances in the management of pulmonary arterial hypertension.     

Antiinflammatory effect of androgen receptor activation in human benign prostatic hyperplasia cells

Progression of benign prostatic hyperplasia (BPH) involves chronic inflammation and immune dysregulation. Preclinical studies have demonstrated that prostate inflammation and tissue remodeling are exacerbated by hypogonadism and prevented by testosterone supplementation. We now investigated whether, in humans, hypogonadism was associated with more severe BPH inflammation and the in vitro effect of the selective androgen receptor agonist dihydrotestosterone (DHT) on cultures of stromal cells derived from BPH patients (hBPH). Histological analysis of inflammatory infiltrates in prostatectomy specimens from a cohort of BPH patients and correlation with serum testosterone level was performed. Even after adjusting for confounding factors, hypogonadism was associated with a fivefold increased risk of intraprostatic inflammation, which was also more severe than that observed in eugonadal BPH patients. Triggering hBPH cells by inflammatory stimuli (tumor necrosis factor α, lipopolysaccharide, or CD4(+)T cells) induced abundant secretion of inflammatory/growth factors (interleukin 6 (IL6), IL8, and basic fibroblast growth factor (bFGF)). Co-culture of CD4(+)T cells with hBPH cells induced secretion of Th1 inducer (IL12), Th1-recruiting chemokine (interferon γ inducible protein 10, IP10), and Th2 (IL9)- and Th17 (IL17)-specific cytokines. Pretreatment with DHT inhibited NF-κB activation and suppressed secretion of several inflammatory/growth factors, with the most pronounced effects on IL8, IL6, and bFGF. Reduced inflammatory cytokine production by T-cells, an increase in IL10, and a significant reduction of T cells proliferation suggested that DHT exerted a broad anti inflammatory effect on testosterone cells [corrected]. In conclusion, our data demonstrate that DHT exerts an immune regulatory role on human prostatic stromal cells, inhibiting their potential to actively induce and/or sustain autoimmune and inflammatory responses.     

Sildenafil decreased pulmonary arterial pressure but may have exacerbated portal hypertension in a patient with cirrhosis and portopulmonary hypertension

Portopulmonary hypertension is a recognized but uncommon complication of cirrhosis. Liver transplantation may be contraindicated in patients with severe portopulmonary hypertension. In order to decrease the pulmonary arterial pressure, intravenous administration of epoprostenol has been shown to provide substantial beneficial results in these patients. Additionally, a recent case report demonstrated that long-term oral administration of sildenafil decreased pulmonary arterial pressure, but its effects on splanchnic hemodynamics were not measured. We report on a patient with cirrhosis and portopulmonary hypertension and the changes in the hemodynamic status after an oral administration of sildenafil. This case report clearly delineates that sildenafil decreases pulmonary arterial pressure but may exacerbate portal hypertension and hyperdynamic circulation in patients with cirrhosis and portopulmonary hypertension.