Sami I. Said

Background: Pulmonary Arterial Hypertension (PAH) remains a therapeutic challenge, and the search continues for more effective drugs and drug combinations. We recently reported that deletion of the vasoactive intestinal peptide (VIP) gene caused the spontaneous expression of a PH phenotype that was fully corrected by VIP. The objectives of this investigation were to answer the questions: 1) Can VIP protect against PH in other experimental models? and 2) Does combining VIP with an endothelin (ET) receptor antagonist bosentan enhance its efficacy? Methods: Within 3 weeks of a single injection of monocrotaline (MCT, s.c.) in Sprague Dawley rats, PAH developed, manifested by pulmonary vascular remodeling, lung inflammation, RV hypertrophy, and death within the next 2 weeks. MCT-injected animals were either untreated, treated with bosentan (p.o.) alone, with VIP (i.p.) alone, or with both together. We selected this particular combination upon finding that VIP down-regulates endothelin receptor expression which is further suppressed by bosentan. Therapeutic outcomes were compared as to hemodynamics, pulmonary vascular pathology, and survival. Results: Treatment with VIP, every other day for 3 weeks, begun on the same day as MCT, almost totally prevented PAH pathology, and eliminated mortality for 45 days. Begun 3 weeks after MCT, however, VIP only partially reversed PAH pathology, though more effectively than bosentan. Combined therapy with both drugs fully reversed the pathology, while preventing mortality for at least 45 days. Conclusions: 1) VIP completely prevented and significantly reversed MCT-induced PAH; 2) VIP was more effective than bosentan, probably because it targets a wider range of pro-remodeling pathways; and 3) combination therapy with VIP plus bosentan was more effective than either drug alone, probably because both drugs synergistically suppressed ET-ET receptor pathway.

Beyond their classical role as a class of female sex hormones, estrogens (e.g. 17β-estradiol) exert important biological actions, both protective and undesirable. We have investigated the ability of estradiol to protect the lung in three models of acute injury induced by 1) oxidant stress due to the herbicide paraquat; 2) excitotoxicity, caused by glutamate agonist N-methyl-d-aspartate; and 3) acute alveolar anoxia. We also assessed the role of estrogen receptors (ER) ERα and ERβ and the neuropeptide vasoactive intestinal peptide (VIP) in mediating this protection. Isolated guinea pig or rat lungs were perfused in situ at constant flow and mechanically ventilated. The onset and severity of lung injury were monitored by increases in pulmonary arterial and airway pressures, wet/dry lung weight ratio, and bronchoalveolar lavage fluid protein content. Estradiol was infused into the pulmonary circulation, beginning 10 min before induction of injury and continued for 60–90 min. Lung injury was marked by significant increases in the above measurements, with paraquat producing the most severe, and excitotoxicity the least severe, injury. Estradiol significantly attenuated the injury in each model. Both ER were constitutively expressed and immunohistochemically demonstrable in normal lung, and their selective agonists reduced anoxic injury, the only model in which they were tested. As it protected against injury, estradiol rapidly and significantly stimulated VIP mRNA expression in rat lung. Estradiol attenuated acute lung injury in three experimental models while stimulating VIP gene expression, a known mechanism of lung protection. The up-regulated VIP expression could have partially mediated the protection by estrogen.

Pharmacogenomics is the study of how genetic variations influence the response to drugs, by correlating gene expression with the drug's efficacy and toxicity. This concept has recently been success...

Although largely distinct and seemingly unrelated, asthma and pulmonary arterial hypertension (PAH) have important pathological features in common, including inflammation, smooth muscle contraction and remodelling.We hypothesised that these common features could be explained by one shared mechanism of pathogenesis: activation of the transcription factor NFAT (nuclear factor of activated T-cells). If this concept is validated, it could lead to the introduction of novel therapeutic strategies against both lung disorders.In several experimental models, airway remodelling is accompanied by remodelling of smaller pulmonary arteries, validating the hypothesis of their similar pathogenesis. In addition, lungs of vasoactive intestinal peptide (VIP) knockout mice express airway hyperresponsiveness with airway inflammation and PAH with vascular remodelling, with both sets of pathological findings being reversible with VIP treatment. Preliminary data suggest that absence of the VIP gene leads to activation of the calcineurin–NFAT pathway, and that VIP is probably a physiological inhibitor of this pathway.Enough evidence exists to support the views that asthma and PAH share important pathological features, probably related to NFAT activation, and that VIP may be a physiological modulator of this mechanism.

Pulmonary vascular remodeling and inflammation often coexist in clinical and experimentally induced pulmonary arterial hypertension (PAH). In some instances, the pulmonary hypertension may be the primary, or at least the initial, problem, while inflammatory or autoimmune responses appear to initiate or dominate the picture in other cases. Based on studies in a model of PAH resulting from targeted deletion of the neuropeptide vasoactive intestinal peptide (VIP) gene, we propose that, at least in this experimental model, but possibly also in other situations, both vascular remodeling and inflammation may be mediated by one and the same mechanism: uncontrolled activation of calcineurin–NFAT (nuclear factor of activated T cells) signaling. If this hypothesis is validated, VIP would emerge as an endogenous modulator of pulmonary vascular remodeling and inflammation, through its suppression of NFAT activation.

The pathogenesis of idiopathic pulmonary arterial hypertension (PAH) remains poorly understood. The present authors recently reported that mice with vasoactive intestinal peptide (VIP) gene disruption show a spontaneous phenotype of PAH, with pulmonary vascular remodelling and lung inflammation.To explore the underlying molecular mechanisms in this model, it was examined whether absence of the VIP gene might alter the expression of additional genes involved in the pathogenesis of PAH, as single-gene deletions, in the absence of hypoxia, rarely result in significant pulmonary vascular remodelling.Lung tissue from mice with targeted disruption of the vasoactive intestinal peptide gene (VIP^-/-mice) and from control mice was subjected to whole-genome gene microarray analysis, and the results validated with quantitative, real-time PCR. Lungs from VIP^-/-mice showed a wide range of significant gene expression alterations, including overexpression of genes that promote pulmonary vascular smooth muscle cell proliferation, underexpression of antiproliferative genes and upregulation of pro-inflammatory genes.In conclusion, vasoactive intestinal peptide is a pivotal modulator of genes controlling the pulmonary vasculature, its deficiency alone resulting in gene expression alterations that can readily explain both the vascular remodelling and associated inflammatory response in pulmonary arterial hypertension. The present findings shed more light on the molecular mechanisms of pulmonary arterial hypertension, and could lead to better understanding of the pathogenesis of human pulmonary arterial hypertension, and hence to improved therapy.

Background—Vasoactive intestinal peptide (VIP), a pulmonary vasodilator and inhibitor of vascular smooth muscle proliferation, has been reported absent in pulmonary arteries from patients with idiopathic pulmonary arterial hypertension (PAH). We have tested the hypothesis that targeted deletion of the VIP gene may lead to PAH with pulmonary vascular remodeling.Methods and Results—We examined VIP knockout (VIP^−/−) mice for evidence of PAH, right ventricular (RV) hypertrophy, and pulmonary vascular remodeling. Relative to wild-type control mice, VIP^−/−mice showed moderate RV hypertension, RV hypertrophy confirmed by increased ratio of RV to left ventricle plus septum weight, and enlarged, thickened pulmonary artery and smaller branches with increased muscularization and narrowed lumen. Lung sections also showed perivascular inflammatory cell infiltrates. No systemic hypertension and no arterial hypoxemia existed to explain the PAH. The condition was associated with increased mortality. Both the vascular remodeling and RV remodeling were attenuated after a 4-week treatment with VIP.Conclusions—Deletion of the VIP gene leads to spontaneous expression of moderately severe PAH in mice during air breathing. Although not an exact model of idiopathic PAH, the VIP^−/−mouse should be useful for studying molecular mechanisms of PAH and evaluating potential therapeutic agents. VIP replacement therapy holds promise for the treatment of PAH, and mutations of the VIP gene may be a factor in the pathogenesis of idiopathic PAH.

Pulmonary hypertension (PH), defined as a mean pulmonary arterial (PA) pressure of >25 mmHg at rest or >30 mmHg during exercise, is characterized by a progressive and sustained increase in pulmonary vascular resistance that eventually leads to right ventricular failure. Clinically, PH may result from a variety of underlying diseases ( Table 1 and Refs. 50 , 113 , 124 ). Pulmonary arterial hypertension (PAH) may be familial (FPAH) or sporadic (idiopathic, IPAH), formerly known as primary pulmonary hypertension, i.e., for which there is no demonstrable cause. More often, PAH is due to a variety of identifiable diseases including scleroderma and other collagen disorders, liver disease, human immunodeficiency virus, and the intake of appetite-suppressant drugs such as phentermine and fenfluramine ( 72 ). Other, more common, causes of PAH include left ventricular failure (perhaps the most common cause), valvular lesions, chronic pulmonary diseases, sleep-disordered breathing, and prolonged residence at high altitude. This classification, now widely accepted, was first proposed at a meeting in Evian, France, in 1998, and modified in Venice, Italy, in 2003 ( 124 ).

We have taken advantage of the availability of vasoactive intestinal polypeptide (VIP) knockout (KO) mice to examine the possible influence of deletion of the VIP gene on: (a) airway reactivity and airway inflammation, as indicators of bronchial asthma; (b) mortality from endotoxemia, a model of septic shock; and (c) the pulmonary circulation. VIP KO mice showed: (a) airway hyperresponsiveness to the cholinergic agonist methacholine, as well as peribronchial and perivascular inflammation; (b) a greater susceptibility to death from endotoxemia; and (c) evidence suggestive of pulmonary hypertension.