The Short-Chain Fatty Acid Butyrate Attenuates Pulmonary Vascular Remodeling and Inflammation in Hypoxia-Induced Pulmonary Hypertension.

Pulmonary hypertension (PH) is a progressive cardiovascular disorder in which local vascular inflammation leads to increased pulmonary vascular remodeling and ultimately to right heart failure. The HDAC inhibitor butyrate, a product of microbial fermentation, is protective in inflammatory intestinal diseases, but little is known regarding its effect on extraintestinal diseases, such as PH. In this study, we tested the hypothesis that butyrate is protective in a Sprague-Dawley (SD) rat model of hypoxic PH. Treatment with butyrate (220 mg/kg intake) prevented hypoxia-induced right ventricular hypertrophy (RVH), hypoxia-induced increases in right ventricular systolic pressure (RVSP), pulmonary vascular remodeling, and permeability. A reversal effect of butyrate (2200 mg/kg intake) was observed on elevated RVH. Butyrate treatment also increased the acetylation of histone H3, 25-34 kDa, and 34-50 kDa proteins in the total lung lysates of butyrate-treated animals. In addition, butyrate decreased hypoxia-induced accumulation of alveolar (mostly CD68+) and interstitial (CD68+ and CD163+) lung macrophages. Analysis of cytokine profiles in lung tissue lysates showed a hypoxia-induced upregulation of TIMP-1, CINC-1, and Fractalkine and downregulation of soluble ICAM (sICAM). The expression of Fractalkine and VEGFα, but not CINC-1, TIMP-1, and sICAM was downregulated by butyrate. In rat microvascular endothelial cells (RMVEC), butyrate (1 mM, 2 and 24 h) exhibited a protective effect against TNFα- and LPS-induced barrier disruption. Butyrate (1 mM, 24 h) also upregulated tight junctional proteins (occludin, cingulin, claudin-1) and increased the acetylation of histone H3 but not α-tubulin. These findings provide evidence of the protective effect of butyrate on hypoxic PH and suggest its potential use as a complementary treatment for PH and other cardiovascular diseases.

Sustained Activation of Rho GTPases Promotes a Synthetic Pulmonary Artery Smooth Muscle Cell Phenotype in Neprilysin Null Mice.

OBJECTIVE: Pulmonary artery smooth muscle cells (PASMCs) from neprilysin (NEP) null mice exhibit a synthetic phenotype and increased activation of Rho GTPases compared with their wild-type counterparts. Although Rho GTPases are known to promote a contractile SMC phenotype, we hypothesize that their sustained activity decreases SM-protein expression in these cells. APPROACH AND RESULTS: PASMCs isolated from wild-type and NEP-/- mice were used to assess levels of SM-proteins (SM-actin, SM-myosin, SM22, and calponin) by Western blotting, and were lower in NEP-/- PASMCs compared with wild-type. Rac and Rho (ras homology family member) levels and activity were higher in NEP-/- PASMCs, and ShRNA to Rac and Rho restored SM-protein, and attenuated the enhanced migration and proliferation of NEP-/- PASMCs. SM-gene repressors, p-Elk-1, and Klf4 (Kruppel lung factor 4), were higher in NEP-/- PASMCs and decreased by shRNA to Rac and Rho. Costimulation of wild-type PASMCs with PDGF (platelet-derived growth factor) and the NEP substrate, ET-1 (endothelin-1), increased Rac and Rho activity, and decreased SM-protein levels mimicking the NEP knock-out phenotype. Activation of Rac and Rho and downstream effectors was observed in lung tissue from NEP-/- mice and humans with chronic obstructive pulmonary disease. CONCLUSIONS: Sustained Rho activation in NEP-/- PASMCs is associated with a decrease in SM-protein levels and increased migration and proliferation. Inactivation of RhoGDI (Rho guanine dissociation inhibitor) and RhoGAP (Rho GTPase activating protein) by phosphorylation may contribute to prolonged activation of Rho in NEP-/- PASMCs. Rho GTPases may thus have a role in integration of signals between vasopeptides and growth factor receptors and could influence pathways that suppress SM-proteins to promote a synthetic phenotype.

Protection against vascular leak in neprilysin transgenic mice with complex overexpression pattern.

Neprilysin (NEP) is a cell surface metallopeptidase found in many tissues. Based mostly on pharmacological manipulations, NEP has been thought to protect blood vessels from plasma extravasation. We have suggested that NEP may protect against pulmonary vascular injury. However, these prior studies did not utilize mice which overexpress NEP. The aims of the present investigation were to develop and characterize doubly transgenic (DT) mice that overexpress NEP universally and conditionally, and to investigate the protective effect that overexpressed NEP may have against plasma extravasation in the vasculature. The duodenum, which is often used to assess vascular permeability, and in which the NEP protein was overexpressed in our DT mice two-fold, was selected as our experimental preparation. We found that substance P-induced plasma extravasation was decreased substantially (3.5-fold) in the duodenums of our doxycycline-treated DT mice, giving independent evidence of NEP's protective effects against plasma extravasation. Transgenic lung NEP protein was not stably expressed in the DT mice, so we were not able to test the effect of NEP overexpression in the lung. Although initially overexpressed nearly nine-fold at that site, pulmonary NEP protein overexpression eventually dissipated. Surprisingly, at a time when there was no lung transgenic NEP protein overexpression, lung NEP mRNA expression was still increased 23-fold, indicating that the expression defect probably is not transcriptional. These studies help to characterize our complex transgenic model of NEP overexpression and further demonstrate NEP's protective effects against plasma extravasation.

Decreased neprilysin and pulmonary vascular remodeling in chronic obstructive pulmonary disease.

RATIONALE: Studies with genetically engineered mice showed that decreased expression of the transmembrane peptidase neprilysin (NEP) increases susceptibility to hypoxic pulmonary vascular remodeling and hypertension; in hypoxic wild-type mice, expression is decreased early in distal pulmonary arteries, where prominent vascular remodeling occurs. Therefore, in humans with smoke- and hypoxia-induced vascular remodeling, as in chronic obstructive pulmonary disease (COPD), pulmonary activity/expression of NEP may likewise be decreased. OBJECTIVES: To test whether NEP activity and expression are reduced in COPD lungs and pulmonary arterial smooth muscle cells (SMCs) exposed to cigarette smoke extract or hypoxia and begin to investigate mechanisms involved. METHODS: Control and advanced COPD lung lysates (n = 13-14) were analyzed for NEP activity and protein and mRNA expression. As a control, dipeptidyl peptidase IV activity was analyzed. Lung sections were assessed for vascular remodeling and oxidant damage. Human pulmonary arterial SMCs were exposed to cigarette smoke extract, hypoxia, or H2O2, and incubated with antioxidants or lysosomal/proteasomal inhibitors. MEASUREMENTS AND MAIN RESULTS: COPD lungs demonstrated areas of vascular rarification, distal muscularization, and variable intimal and prominent medial/adventitial thickening. NEP activity was reduced by 76%; NEP protein expression was decreased in alveolar walls and distal vessels; mRNA expression was also decreased. In SMCs exposed to cigarette smoke extract, hypoxia, and H2O2, NEP activity and expression were also reduced. Reactive oxygen species inactivated NEP activity; NEP protein degradation appeared to be substantially induced. CONCLUSIONS: Mechanisms responsible for reduced NEP activity and protein expression include oxidative reactions and protein degradation. Maintaining or increasing lung NEP may protect against pulmonary vascular remodeling in response to chronic smoke and hypoxia.

Tadalafil for veterans with chronic obstructive pulmonary disease-pulmonary hypertension: A multicenter, placebo-controlled randomized trial.

Treating Veterans with chronic obstructive pulmonary disease complicated by pulmonary hypertension (COPD-PH) using phosphodiesterase type-5 inhibitor pharmacotherapy is common, but efficacy data are lacking. To address this further, patients with COPD-PH from five Department of Veterans Affairs hospitals were randomized (1∶1) to receive placebo or oral tadalafil (40 mg/day) for 12 months. The primary endpoint was changed from baseline in 6-min walk distance at 12 months. Secondary endpoints included change from baseline in pulmonary vascular resistance, mean pulmonary artery pressure, and symptom burden by the University of California San Diego shortness of breath questionnaire scale at 6 months. A total of 42 subjects (all male; 68 ± 7.6 years old) were randomized to placebo (N = 14) or tadalafil (N = 28). The group imbalance was related to under-enrollment. Compared to placebo, no significant difference was observed in the tadalafil group for change from the primary endpoint or change in mean pulmonary artery pressure or pulmonary vascular resistance from baseline at 6 months. A clinically meaningful improvement was observed in the secondary endpoint of shortness of breath questionnaire score in the tadalafil versus placebo group at 6 months. There was no significant difference in major adverse events between treatment groups, and tadalafil was well tolerated overall. For Veterans with COPD-PH enrolled in this study, once-daily treatment with tadalafil did not improve 6-min walk distance or cardiopulmonary hemodynamics although a decrease in shortness of breath was observed. Under-enrollment and imbalanced randomization confound interpreting conclusions from this clinical trial and limit the generalization of our findings.

Metabolite G-Protein Coupled Receptors in Cardio-Metabolic Diseases.

G protein-coupled receptors (GPCRs) have originally been described as a family of receptors activated by hormones, neurotransmitters, and other mediators. However, in recent years GPCRs have shown to bind endogenous metabolites, which serve functions other than as signaling mediators. These receptors respond to fatty acids, mono- and disaccharides, amino acids, or various intermediates and products of metabolism, including ketone bodies, lactate, succinate, or bile acids. Given that many of these metabolic processes are dysregulated under pathological conditions, including diabetes, dyslipidemia, and obesity, receptors of endogenous metabolites have also been recognized as potential drug targets to prevent and/or treat metabolic and cardiovascular diseases. This review describes G protein-coupled receptors activated by endogenous metabolites and summarizes their physiological, pathophysiological, and potential pharmacological roles.

Evidence supporting a role for circulating macrophages in the regression of vascular remodeling following sub-chronic exposure to hemoglobin plus hypoxia.

Macrophages are a heterogeneous population with both pro- and anti-inflammatory functions play an essential role in maintaining tissue homeostasis, promoting inflammation under pathological conditions, and tissue repair after injury. In pulmonary hypertension, the M1 phenotype is more pro-inflammatory compared to the M2 phenotype, which is involved in tissue repair. The role of macrophages in the initiation and progression of pulmonary hypertension is well studied. However, their role in the regression of established pulmonary hypertension is not well known. Rats chronically exposed to hemoglobin (Hb) plus hypoxia (HX) share similarities to humans with pulmonary hypertension associated with hemolytic disease, including the presence of a unique macrophage phenotype surrounding distal vessels that are associated with vascular remodeling. These lung macrophages are characterized by high iron content, HO-1, ET-1, and IL-6, and are recruited from the circulation. Depletion of macrophages in this model prevents the development of pulmonary hypertension and vascular remodeling. In this study, we specifically investigate the regression of pulmonary hypertension over a four-week duration after rats were removed from Hb + HX exposure with and without gadolinium chloride administration. Withdrawal of Hb + HX reversed systolic pressures and right ventricular function after Hb + Hx exposure in four weeks. Our data show that depleting circulating monocytes/macrophages during reversal prevents complete recovery of right ventricular systolic pressure and vascular remodeling in this rat model of pulmonary hypertension at four weeks post exposure. The data presented offer a novel insight into the role of macrophages in the processes of pulmonary hypertension regression in a rodent model of Hb + Hx-driven disease.

Neprilysin null mice develop exaggerated pulmonary vascular remodeling in response to chronic hypoxia.

Neprilysin is a transmembrane metalloendopeptidase that degrades neuropeptides that are important for both growth and contraction. In addition to promoting carcinogenesis, decreased levels of neprilysin increases inflammation and neuroendocrine cell hyperplasia, which may predispose to vascular remodeling. Early pharmacological studies showed a decrease in chronic hypoxic pulmonary hypertension with neprilysin inhibition. We used a genetic approach to test the alternate hypothesis that neprilysin depletion increases chronic hypoxic pulmonary hypertension. Loss of neprilysin had no effect on baseline airway or alveolar wall architecture, vessel density, cardiac function, hematocrit, or other relevant peptidases. Only lung neuroendocrine cell hyperplasia and a subtle neuropeptide imbalance were found. After chronic hypoxia, neprilysin-null mice exhibited exaggerated pulmonary hypertension and striking increases in muscularization of distal vessels. Subtle thickening of proximal media/adventitia not typically seen in mice was also detected. In contrast, adaptive right ventricular hypertrophy was less than anticipated. Hypoxic wild-type pulmonary vessels displayed close temporal and spatial relationships between decreased neprilysin and increased cell growth. Smooth muscle cells from neprilysin-null pulmonary arteries had increased proliferation compared with controls, which was decreased by neprilysin replacement. These data suggest that neprilysin may be protective against chronic hypoxic pulmonary hypertension in the lung, at least in part by attenuating the growth of smooth muscle cells. Lung-targeted strategies to increase neprilysin levels could have therapeutic benefits in the treatment of this disorder.

The Link between Fusobacteria and Colon Cancer: a Fulminant Example and Review of the Evidence.

Systemic infections due to Fusobacterium may originate in the tonsillar/internal jugular veins or from the abdomen. We encountered a patient who presented with bacteremia, fulminant septic shock, and extensive soft tissue pyogenic infection due to Fusobacterium necrophorum. In addition, there was widespread metastatic colon cancer with the unique finding of pre-mortem co-localization of F. necrophorum and cancer cells at a site distant from the colon. We reviewed the literature of the association of F. necrophorum and colon cancer, and discuss the evidence of how each of these 2 distinct entities may mutually augment the development or progression of the other.

c-Jun, Foxo3a, and c-Myc Transcription Factors are Key Regulators of ATP-Mediated Angiogenic Responses in Pulmonary Artery Vasa Vasorum Endothelial Cells.

Angiogenic vasa vasorum (VV) expansion plays an essential role in the pathogenesis of hypoxia-induced pulmonary hypertension (PH), a cardiovascular disease. We previously showed that extracellular ATP released under hypoxic conditions is an autocrine/paracrine, the angiogenic factor for pulmonary artery (PA) VV endothelial cells (VVECs), acting via P2Y purinergic receptors (P2YR) and the Phosphoinositide 3-kinase (PI3K)-Akt-Mammalian Target of Rapamycin (mTOR) signaling. To further elucidate the molecular mechanisms of ATP-mediated VV angiogenesis, we determined the profile of ATP-inducible transcription factors (TFs) in VVECs using a TranSignal protein/DNA array. C-Jun, c-Myc, and Foxo3 were found to be upregulated in most VVEC populations and formed nodes connecting several signaling networks. siRNA-mediated knockdown (KD) of these TFs revealed their critical role in ATP-induced VVEC angiogenic responses and the regulation of downstream targets involved in tissue remodeling, cell cycle control, expression of endothelial markers, cell adhesion, and junction proteins. Our results showed that c-Jun was required for the expression of ATP-stimulated angiogenic genes, c-Myc was repressive to anti-angiogenic genes, and Foxo3a predominantly controlled the expression of anti-apoptotic and junctional proteins. The findings from our study suggest that pharmacological targeting of the components of P2YR-PI3K-Akt-mTOR axis and specific TFs reduced ATP-mediated VVEC angiogenic response and may have a potential translational significance in attenuating pathological vascular remodeling.

Role of Inflammatory Cell Subtypes in Heart Failure.

Inflammation is a well-known feature of heart failure. Studies have shown that while some inflammation is required for repair during injury and is protective, prolonged inflammation leads to myocardial remodeling and apoptosis of cardiac myocytes. Various types of immune cells are implicated in myocardial inflammation and include neutrophils, macrophages, eosinophils, mast cells, natural killer cells, T cells, and B cells. Recent clinical trials have targeted inflammatory cascades as therapy for heart failure with limited success. A better understanding of the temporal course of the infiltration of the different immune cells and their contribution to the inflammatory process may improve the success for therapy. This brief review outlines the major cell types involved in heart failure, and some of their actions are summarized in the supplementary figure.

RhoGTPase in Vascular Disease.

Ras-homologous (Rho)A/Rho-kinase pathway plays an essential role in many cellular functions, including contraction, motility, proliferation, and apoptosis, inflammation, and its excessive activity induces oxidative stress and promotes the development of cardiovascular diseases. Given its role in many physiological and pathological functions, targeting can result in adverse effects and limit its use for therapy. In this review, we have summarized the role of RhoGTPases with an emphasis on RhoA in vascular disease and its impact on endothelial, smooth muscle, and heart and lung fibroblasts. It is clear from the various studies that understanding the regulation of RhoGTPases and their regulators in physiology and pathological conditions is required for effective targeting of Rho.

An Optimized Evans Blue Protocol to Assess Vascular Leak in the Mouse.

Vascular leak, or plasma extravasation, has a number of causes, and may be a serious consequence or symptom of an inflammatory response. This study may ultimately lead to new knowledge concerning the causes of or new ways to inhibit or treat plasma extravasation. It is important that researchers have the proper tools, including the best methods available, for studying plasma extravasation. In this article, we describe a protocol, using the Evans blue dye method, for assessing plasma extravasation in the organs of FVBN mice. This protocol is intentionally simple, to as great a degree as possible, but provides high quality data. Evans blue dye has been chosen primarily because it is easy for the average laboratory to use. We have used this protocol to provide evidence and support for the hypothesis that the enzyme neprilysin may protect the vasculature against plasma extravasation. However, this protocol may be experimentally used and easily adapted for use in other strains of mice or in other species, in many different organs or tissues, for studies which may involve other factors that are important in understanding, preventing, or treating plasma extravasation. This protocol has been extensively optimized and modified from existing protocols, and combines reliability, ease of use, economy, and general availability of materials and equipment, making this protocol superior for the average laboratory to use in quantifying plasma extravasation from organs.

Chronic hypoxia diminishes the proliferative response of Guinea pig uterine artery vascular smooth muscle cells in vitro.

The pregnancy-related size enlargement of the guinea pig uterine artery is partially accomplished by hyperplasia in all layers of the vessel wall. We sought to determine the separate and combined effects of chronic hypoxia and pregnancy on the proliferative capacity of uterine artery vascular smooth muscle cells (UA VSMCs). We established primary UA VSMC cultures from a total of 13 guinea pigs using an enzymatic digestion technique. Animals were bred and kept in normoxia or hypoxia (P(B) = 463 mmHg, simulated elevation = 3962 m) for 45 days, a duration equivalent to midpregnancy in the guinea pig 63-day gestation. Nonpregnant matched controls were included. The proliferative response of UA VSMCs to 1, 3, 5 or 7 days of serum stimulation in vitro was compared. Exposure to hypoxia reduced UA VSMC proliferative response to serum stimulation relative to that seen in cells harvested from normoxic females. The inhibitory effect was present both in cells harvested from nonpregnant and pregnant animals and resulted in a lower UA VSMC proliferative response in the cells harvested from hypoxic compared with normoxic pregnant animals. Our data were consistent with our hypothesis that chronic maternal hypoxia compromises the capacity for growth and remodeling of the uterine artery during pregnancy, perhaps by interfering with the ability of vascular smooth muscle cells to de-differentiate to a proliferative phenotype. Noteworthy was that such effects of chronic hypoxia were retained in cultured cells.

High prevalence of occult endobronchial malignancy in high risk patients with moderate sputum atypia.

Early stage radiographically occult lung cancer has a high cure rate, but comprises a small fraction of all lung cancer. Abnormal sputum cytology is one indication for bronchoscopy in patients with chest imaging that is not suspicious for lung cancer. While there is good evidence that sputum cytologic findings of carcinoma, carcinoma in situ or severe atypia predict high rates of diagnosis of lung cancer, less is known of the frequency in which lung cancer is diagnosed in bronchoscopies carried out for the indication of moderate sputum atypia. One small series, published in abstract form only, reported an 8% rate of diagnosis of lung cancer in subjects bronchoscoped for moderate atypia. We tested the hypothesis that moderate sputum atypia is an indicator of occult central airway cancer in a retrospective analysis of a group of high risk subjects, defined as current or former smokers with >30 pack-years tobacco smoking and airflow obstruction with moderate atypia sputum cytology. Seventy-nine such subjects with no evidence of malignancy on chest radiograph at the time bronchoscopy was scheduled underwent white light and autofluorescence bronchoscopy. Lung cancer was found in five subjects; three had invasive squamous cell carcinomas and two had carcinoma in situ. Seven additional subjects had severe dysplasia found on endobronchial biopsy. Moderate sputum atypia may be an important marker of risk for occult endobronchial malignancy in high risk subjects.

Neprilysin regulates pulmonary artery smooth muscle cell phenotype through a platelet-derived growth factor receptor-dependent mechanism.

Reduced neprilysin (NEP), a cell surface metallopeptidase, which cleaves and inactivates proinflammatory and vasoactive peptides, predisposes the lung vasculature to exaggerated remodeling in response to hypoxia. We hypothesize that loss of NEP in pulmonary artery smooth muscle cells results in increased migration and proliferation. Pulmonary artery smooth muscle cells isolated from NEP(-/-) mice exhibited enhanced migration and proliferation in response to serum and platelet-derived growth factor, which was attenuated by NEP replacement. Inhibition of NEP by overexpression of a peptidase dead mutant or knockdown by small interfering RNA in NEP(+/+) cells increased migration and proliferation. Loss of NEP led to an increase in Src kinase activity and phosphorylation of PTEN, resulting in activation of the platelet-derived growth factor receptor (PDGFR). Knockdown of Src kinase with small interfering RNA or inhibition with PP2, a src kinase inhibitor, decreased PDGFR(Y751) phosphorylation and attenuated migration and proliferation in NEP(-/-) smooth muscle cells. NEP substrates, endothelin 1 or fibroblast growth factor 2, increased activation of Src and PDGFR in NEP(+/+) cells, which was decreased by an endothelin A receptor antagonist, neutralizing antibody to fibroblast growth factor 2 and Src inhibitor. Similar to the observations in pulmonary artery smooth muscle cells, levels of phosphorylated PDGFR, Src, and PTEN were elevated in NEP(-/-) lungs. Endothelin A receptor antagonist also attenuated the enhanced responses in NEP(-/-) pulmonary artery smooth muscle cells and lungs. Taken together our results suggest a novel mechanism for the regulation of PDGFR signaling by NEP substrates involving Src and PTEN. Strategies that increase lung NEP activity/expression or target key downstream effectors, like Src, PTEN, or PDGFR, may be of therapeutic benefit in pulmonary vascular disease.

Alveolar hypoxia promotes murine lung tumor growth through a VEGFR-2/EGFR-dependent mechanism.

Patients with chronic obstructive pulmonary disease (COPD) are at an increased risk for the development of lung cancer, the mechanisms for which are incompletely understood. We hypothesized that the hypoxic pulmonary microenvironment present in COPD would augment lung carcinogenesis. Mice were subjected to chemical carcinogenesis protocols and placed in either hypoxia or normoxia. Mice exposed to chronic hypoxia developed tumors with increased volume compared with normoxic controls. Both lungs and tumors from hypoxic mice showed a preferential stabilization of HIF-2α and increased expression of VEGF-A, FGF2, and their receptors as well as other survival, proliferation, and angiogenic signaling pathways regulated by HIF-2α. We showed that tumors arising in hypoxic animals have increased sensitivity to VEGFR-2/EGFR inhibition, as chemoprevention with vandetanib showed markedly increased activity in hypoxic mice. These studies showed that lung tumors arising in a hypoxic microenvironment express increased growth, angiogenic, and survival signaling that could contribute to the increased lung cancer risk in COPD. Furthermore, the differential sensitivity of tumors arising in hypoxia to VEGFR-2/EGFR inhibition suggests that the altered signaling present in tumors arising in hypoxic lung might be therapeutically exploited in patients with underlying COPD.