Sex-dependent influence of endogenous estrogen in pulmonary hypertension.

RATIONALE: The incidence of pulmonary arterial hypertension is greater in women, suggesting estrogens may play a role in the disease pathogenesis. Experimentally, in males, exogenously administered estrogen can protect against pulmonary hypertension (PH). However, in models that display female susceptibility, estrogens may play a causative role. OBJECTIVES: To clarify the influence of endogenous estrogen and sex in PH and assess the therapeutic potential of a clinically available aromatase inhibitor. METHODS: We interrogated the effect of reduced endogenous estrogen in males and females using the aromatase inhibitor, anastrozole, in two models of PH: the hypoxic mouse and Sugen 5416/hypoxic rat. We also determined the effects of sex on pulmonary expression of aromatase in these models and in lungs from patients with pulmonary arterial hypertension. MEASUREMENTS AND MAIN RESULTS: Anastrozole attenuated PH in both models studied, but only in females. To verify this effect was caused by reduced estrogenic activity we confirmed that in hypoxic mice inhibition of estrogen receptor α also has a therapeutic effect specifically in females. Female rodent lung displays increased aromatase and decreased bone morphogenetic protein receptor 2 and Id1 expression compared with male. Anastrozole treatment reversed the impaired bone morphogenetic protein receptor 2 pathway in females. Increased aromatase expression was also detected in female human pulmonary artery smooth muscle cells compared with male. CONCLUSIONS: The unique phenotype of female pulmonary arteries facilitates the therapeutic effects of anastrozole in experimental PH confirming a role for endogenous estrogen in the disease pathogenesis in females and suggests aromatase inhibitors may have therapeutic potential.

Imatinib attenuates hypoxia-induced pulmonary arterial hypertension pathology via reduction in 5-hydroxytryptamine through inhibition of tryptophan hydroxylase 1 expression.

RATIONALE: Whether idiopathic, familial, or secondary to another disease, pulmonary arterial hypertension (PAH) is characterized by increased vascular tone, neointimal hyperplasia, medial hypertrophy, and adventitial fibrosis. Imatinib, a potent receptor tyrosine kinase inhibitor, reverses pulmonary remodeling in animal models of PAH and improves hemodynamics and exercise capacity in selected patients with PAH. OBJECTIVES: Here we use both imatinib and knockout animals to determine the relationship between platelet-derived growth factor receptor (PDGFR) and serotonin signaling and investigate the PAH pathologies each mediates. METHODS: We investigated the effects of imatinib (100 mg/kg) on hemodynamics, vascular remodeling, and downstream molecular signatures in the chronic hypoxia/SU5416 murine model of PAH. MEASUREMENTS AND MAIN RESULTS: Treatment with imatinib reduced all measures of PAH pathology observed in hypoxia/SU5416 mice. In addition, 5-hydroxytryptamine (5-HT) and tryptophan hydroxylase 1 (Tph1) expression were reduced compared with the normoxia/SU5416 control group. Imatinib attenuated hypoxia-induced increases in Tph1 expression in pulmonary endothelial cells in vitro via inhibition of the PDGFR-ß pathway. To better understand the consequences of this novel mode of action for imatinib, we examined the development of PAH after hypoxic/SU5416 exposure in Tph1-deficient mice (Tph1(-/-)). The extensive changes in pulmonary vascular remodeling and hemodynamics in response to hypoxia/SU5416 were attenuated in Tph1(-/-) mice and further decreased after imatinib treatment. However, imatinib did not significantly further impact collagen deposition and collagen 3a1 expression in hypoxic Tph1(-/-) mice. Post hoc subgroup analysis suggests that patients with PAH with greater hemodynamic impairment showed significantly reduced 5-HT plasma levels after imatinib treatment compared with placebo. CONCLUSIONS: We report a novel mode of action for imatinib, demonstrating TPH1 down-regulation via inhibition of PDGFR-ß signaling. Our data reveal interplay between PDGF and 5-HT pathways within PAH, demonstrating TPH1-dependent imatinib efficacy in collagen-mediated mechanisms of fibrosis.

Targeting the serotonin pathway for the treatment of pulmonary arterial hypertension.

As we uncover the complex pathophysiology underlying idiopathic and familial pulmonary arterial hypertension, multiple disease associated pathways, cell types and processes reveal links to elements of the serotonin system. Beyond the original 'serotonin hypothesis' observed with anorexigens, and the latterly demonstrated association with vascular tone and pulmonary artery smooth muscle cell proliferation, recent studies suggest links to BMPR2, PDGF and RhoK pathways, as well as an impact upon more complex lesion formation and pathologic bone marrow progenitor mobilization. Clinical experience with antagonists targeting the various elements of the serotonin pathway has been unsatisfactory, yet perhaps this is less than surprising given our expanding knowledge around serotonin production and signaling biology, which indicate opportunities for novel therapeutic options.

Reduced response to the formalin test and lowered spinal NMDA glutamate receptor binding in adenosine A2A receptor knockout mice.

Adenosine is a neuromodulator with complex effects on pain pathways. Mice lacking the adenosine A2A receptor are hypoalgesic, and have altered analgesic responses to receptor-selective opioid agonists. These and other findings suggest a role for the adenosine A2A receptor in sensitizing afferent fibres projecting to the spinal cord. To test this hypothesis formalin (20 microl, 5%) was injected into the paw and nociceptive responses were measured in wildtype and adenosine A2A receptor knockout mice. There was a significant reduction in nociception associated with sensory nerve activation in the knockout mice as measured by time spent biting/licking the formalin-injected paw and number of flinches seen during the first phase, but only the number of flinches was reduced during the second inflammatory phase. In addition, the selective adenosine A2A antagonist SCH58261 (3 and 10 mg/kg) also antagonised both phases of the formalin test. We also labelled NMDA glutamate and NK1 receptors in spinal cord sections as an indirect measure of nociceptive transmission from peripheral sites to the spinal cord. [3H]-Substance P binding to NK1 receptors was unaltered but there was a substantial reduction in binding of [3H]-MK801 to NMDA glutamate receptors in all regions of the spinal cord from knockout mice. The decrease in NMDA glutamate receptor binding may reflect reduced peripheral sensory input to the spinal cord during development and could relate to the hypoalgesia in this genotype. These results support a key role for the adenosine A2A receptor in peripheral nociceptive pathways.