losartan-potassium and Hypertrophy--Right-Ventricular

Upregulation of the erythropoietin (EPO)/EPO receptor (EPOR) system plays a protective role against chronic hypoxia-induced pulmonary hypertension (hypoxic PH) through enhancement of endothelial nitric oxide (NO)-mediated signaling. Genistein (Gen), a phytoestrogen, is considered to ameliorate NO-mediated signaling. We hypothesized that Gen attenuates and prevents hypoxic PH. In vivo, Sprague-Dawley rats raised in a hypobaric chamber were treated with Gen (60 mkg/kg) for 21 days. Pulmonary hemodynamics and vascular remodeling were ameliorated in Gen-treated hypoxic PH rats. Gen also restored cGMP levels and phosphorylated endothelial NO synthase (p-eNOS) at Ser(1177) and p-Akt at Ser(473) expression in the lungs. Additionally, Gen potentiated plasma EPO concentration and EPOR-positive endothelial cell counts. In experiments with hypoxic PH rats' isolated perfused lungs, Gen caused NO- and phosphatidylinositol 3-kinase (PI3K)/Akt-dependent vasodilation that reversed abnormal vasoconstriction. In vitro, a combination of EPO and Gen increased the p-eNOS and the EPOR expression in human umbilical vein endothelial cells under a hypoxic environment. Moreover, Gen potentiated the hypoxic increase in EPO production from human hepatoma cells. We conclude that Gen may be effective for the prevention of hypoxic PH through the improvement of PI3K/Akt-dependent, NO-mediated signaling in association with enhancement of the EPO/EPOR system.

Topics: Animals; Antihypertensive Agents; Blood Pressure; Cell Hypoxia; Cyclic GMP; Drug Evaluation, Preclinical; Erythropoietin; Genistein; Hep G2 Cells; Human Umbilical Vein Endothelial Cells; Humans; Hypertension, Pulmonary; Hypertrophy, Right Ventricular; Male; Nitric Oxide; Nitric Oxide Synthase Type III; Phosphorylation; Protein Processing, Post-Translational; Proto-Oncogene Proteins c-akt; Rats; Rats, Sprague-Dawley; Signal Transduction; Vasodilator Agents; Ventricular Pressure

The central pathway for oxygen-dependent control of red cell mass is the prolyl hydroxylase domain protein (PHD):hypoxia inducible factor (HIF) pathway. PHD site specifically prolyl hydroxylates the transcription factor HIF-α, thereby targeting the latter for degradation. Under hypoxia, this modification is attenuated, allowing stabilized HIF-α to activate target genes, including that for erythropoietin (EPO). Studies employing genetically modified mice point to Hif-2α, one of two main Hif-α isoforms, as being the critical regulator of Epo in the adult mouse. More recently, erythrocytosis patients with heterozygous point mutations in the HIF2A gene have been identified; whether these mutations were polymorphisms unrelated to the phenotype could not be ruled out. In the present report, we characterize a mouse line bearing a G536W missense mutation in the Hif2a gene that corresponds to the first such human mutation identified (G537W). We obtained mice bearing both heterozygous and homozygous mutations at this locus. We find that these mice display, in a mutation dose-dependent manner, erythrocytosis and pulmonary hypertension with a high degree of penetrance. These findings firmly establish missense mutations in HIF-2α as a cause of erythrocytosis, highlight the importance of this HIF-α isoform in erythropoiesis, and point to physiologic consequences of HIF-2α dysregulation.

Topics: Animals; Basic Helix-Loop-Helix Transcription Factors; Blood Gas Analysis; Cells, Cultured; Disease Models, Animal; Endothelin-1; Erythropoiesis; Erythropoietin; Gene Expression; Gene Knock-In Techniques; Genetic Association Studies; Humans; Hypertension, Pulmonary; Hypertrophy, Right Ventricular; Kidney; Lung; Mice; Mice, Inbred C57BL; Mutagenesis; Mutation, Missense; Polycythemia; Proto-Oncogene Proteins c-sis; Respiratory Rate; RNA, Messenger; Up-Regulation; Vascular Endothelial Growth Factor A

Recent studies have suggested that endogenous erythropoietin (Epo) plays an important role in the mobilization of bone marrow-derived endothelial progenitor cells (EPCs). However, it remains to be elucidated whether the Epo system exerts protective effects on pulmonary hypertension (PH), a fatal disorder encountered in cardiovascular medicine.. A mouse model of hypoxia-induced PH was used for study. We evaluated right ventricular systolic pressure, right ventricular hypertrophy, and pulmonary vascular remodeling in mice lacking the Epo receptor (EpoR) in nonerythroid lineages (EpoR(-/-) rescued mice) after 3 weeks of exposure to hypoxia. Those mice lack EpoR in the cardiovascular system but not in the hematopoietic system. The development of PH and pulmonary vascular remodeling were accelerated in EpoR(-/-) rescued mice compared with wild-type mice. The mobilization of EPCs and their recruitment to the pulmonary endothelium were significantly impaired in EpoR(-/-) rescued mice. By contrast, reconstitution of the bone marrow with wild-type bone marrow cells ameliorated PH in the EpoR(-/-) rescued mice. Hypoxia enhanced the expression of EpoR on pulmonary endothelial cells in wild-type but not EpoR(-/-) rescued mice. Finally, hypoxia activated endothelial nitric oxide synthase in the lungs in wild-type mice but not in EpoR(-/-) rescued mice.. These results indicate that the endogenous Epo/EpoR system plays an important role in the recruitment of EPCs and prevents the development of PH during chronic hypoxia in mice in vivo, suggesting the therapeutic importance of the system for the treatment of PH.

Topics: Animals; Bone Marrow Transplantation; Cell Movement; Cells, Cultured; Chronic Disease; Endothelial Cells; Endothelium; Endothelium, Vascular; Enzyme Activation; Erythroid Precursor Cells; Erythropoietin; GATA1 Transcription Factor; Heart Failure; Hematopoietic Stem Cells; Hypertension, Pulmonary; Hypertrophy, Right Ventricular; Hypoxia; Lung; Male; Mice; Mice, Knockout; Mice, Transgenic; Muscle, Smooth, Vascular; Nitric Oxide Synthase Type III; Organ Specificity; Radiation Chimera; Receptor, TIE-2; Receptors, Erythropoietin; Systole; Ventricular Dysfunction, Right

Acute alveolar hypoxia causes pulmonary vasoconstriction that matches lung perfusion to ventilation to optimize gas exchange. Chronic alveolar hypoxia induces pulmonary hypertension, characterized by increased muscularization of the pulmonary vasculature and right ventricular hypertrophy. Elevated erythropoietin (EPO) plasma levels increase hematocrit and blood viscosity and may affect structure and function of the pulmonary circulation. To differentiate between the direct effects of hypoxia and those linked to a hypoxia-induced increase in EPO/hematocrit levels, we investigated the lung vasculature in transgenic mice constitutively over-expressing EPO (termed tg6) upon exposure to normoxia and chronic hypoxia. Despite increased hematocrit levels (approximately 0.86),tg6 mice kept in normoxia did not develop selective right ventricular hypertrophy. The portion of vessels with a diameter of 51-95 microm and >155 microm was increased whereas the portion of small vessels (30-50 microm) was decreased. Pulmonary vascular resistance and the strength of hypoxic vasoconstriction measured in isolated perfused lungs were decreased. Vasoconstrictions induced by the thromboxane mimetic U46619 tended to be reduced. After chronic hypoxia (FiO2 = 0.10, 21 days), vascular resistance and vasoconstrictor responses to acute hypoxia and U46619 were reduced in tg6 mice compared to wildtype controls. Chronic hypoxia increased the degree of pulmonary vascular muscularization in wildtype but not in tg6 mice that already exhibited less muscularization in normoxia. In conclusion, congenital over-expression of EPO exerts an "anti-pulmonary hypertensive" effect, both structurally and functionally, particularly obvious upon chronic hypoxia.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Aspirin; Blood Pressure; Blood Vessels; Blood Viscosity; Cyclooxygenase Inhibitors; Erythropoietin; Hematocrit; Hypertension, Pulmonary; Hypertrophy, Left Ventricular; Hypertrophy, Right Ventricular; Hypoxia; Lung; Mice; Mice, Inbred C57BL; Mice, Transgenic; Muscle, Smooth, Vascular; Nitric Oxide Synthase; omega-N-Methylarginine; Up-Regulation; Vascular Resistance; Vasoconstriction; Vasoconstrictor Agents

In two rat strains (H and M) with differing susceptibilities to chronic hypoxia we examined the role of polycythemia in the differing hypoxic pulmonary hemodynamic responses. We hypothesized that augmentation of hematocrit (Hct) during hypoxia in the resistant M strain would render cardiopulmonary responses similar to those obtained in the susceptible H strain. Administration of human recombinant erythropoietin (EPO) in doses of 100, 250 and 500 U.kg-1 s.c. thrice weekly for three weeks raised Hct similarly in both strains indicating that normoxic rats had similar sensitivities to EPO. In rats exposed to hypobaric hypoxia (0.5 atm) for 21 days, EPO (500 U.kg-1 thrice weekly) significantly increased Hct and whole blood viscosity as expected. Surprisingly, right ventricular (RV) to body weight (BW) ratio as an index of right ventricular hypertrophy (RVH) and RV peak systolic pressure did not increase in EPO-injected rats of either strain compared to hypoxic controls. Among hypoxic animals, Hct correlated highly with viscosity but not with RV/BW. We conclude, contrary to our hypothesis, that polycythemia does not appear to be responsible for the strain difference in RVH and pulmonary hypertension.

Topics: Animals; Erythropoietin; Hematocrit; Hypertension, Pulmonary; Hypertrophy, Right Ventricular; Hypoxia; Polycythemia; Pulmonary Circulation; Rats; Rats, Sprague-Dawley; Species Specificity