The enzyme xanthine oxidase (XO) has been implicated in the pathogenesis of several disease processes, such as ischemia-reperfusion injury, because of its ability to generate reactive oxygen species. The expression of XO and its precursor xanthine dehydrogenase (XDH) is regulated at pre-and posttranslational levels by agents such as lipopolysaccharide and hypoxia. Posttranslational modification of the protein, for example through thiol oxidation or proteolysis, has been shown to be important in converting XDH to XO. The possibility of posttranslational modification of XDH/XO through phosphorylation has not been adequately investigated in mammalian cells, and studies have reported conflicting results. The present report demonstrates that XDH/XO is phosphorylated in rat pulmonary microvascular endothelial cells (RPMEC) and that phosphorylation is greatly increased (ϳ50-fold) in response to acute hypoxia (4 h). XDH/XO phosphorylation appears to be mediated, at least in part, by casein kinase II and p38 kinase as inhibitors of these kinases partially prevent XDH/XO phosphorylation. In addition, the results indicate that p38 kinase, a stress-activated kinase, becomes activated in response to hypoxia (an ϳ4-fold increase after 1 h of exposure of RPMEC to hypoxia) further supporting a role for this kinase in hypoxia-stimulated XDH/XO phosphorylation. Finally, hypoxia-induced XDH/XO phosphorylation is accompanied by a 2-fold increase in XDH/XO activity, which is prevented by inhibitors of phosphorylation. In summary, this study shows that XDH/XO is phosphorylated in hypoxic RPMEC through a mechanism involving p38 kinase and casein kinase II and that phosphorylation is necessary for hypoxia-induced enzymatic activation.Xanthine dehydrogenase is the rate-limiting step in the catabolism of purines, where it catalyzes the conversion of hypoxanthine to xanthine and xanthine to uric acid. In this reaction, XDH 1 utilizes NAD ϩ preferentially as the electron acceptor. However, when XDH is converted to XO, the preferred electron acceptor becomes molecular oxygen resulting in the formation of superoxide and hydrogen peroxide. This generation of reactive oxygen species is thought to be the basis of XDH/XO involvement in various pathological conditions such as ischemia-reperfusion injury. Reversible conversion of XDH to XO can occur after the oxidation of eight cysteine residues in the molecule into four cystines by agents such as pyrimidines or oxidized glutathione (1, 2). This conversion may be reversed upon the addition of reducing agents such as dithiothreitol. XDH can also be converted into XO irreversibly through proteolysis (3). Experimental proteolysis by trypsin has allowed the identification of three different parts of the molecule: a 20-kDa N-terminal fragment, a 40-kDa flavin-binding fragment, and an 80-kDa molybdopterin-binding fragment, all of which remain attached after proteolysis (3). It is believed that both reversible and irreversible conversion of XDH to XO are due to conformational changes in the molecule that...

Left ventricular (LV) hypertrophy commonly develops in response to chronic hypertension and is a significant risk factor for heart failure and death. The serine-threonine phosphatase, calcineurin (CnA), plays a critical role in the development of pathologic hypertrophy. Previous experimental studies in murine models show that estrogen limits pressure overload-induced hypertrophy; our purpose was to explore further the mechanisms underlying this estrogen effect. Wild type, ovariectomized female mice were treated with placebo or 17β-estradiol (E2), followed by transverse aortic constriction (TAC) to induce pressure overload. At two weeks, mice underwent physiologic evaluation, immediate tissue harvest, or dispersion of cardiomyocytes. E2 replacement limited TAC-induced LV and cardiomyocyte hypertrophy while attenuating deterioration in LV systolic function and contractility. These E2 effects were associated with reduced abundance of CnA. The primary downstream targets of CnA are the nuclear factor of activated T-cell (NFAT) family of transcription factors. In transgenic mice expressing a NFAT-activated promoter-luciferase reporter gene, E2 limited TAC-induced activation of NFAT. Moreover, the inhibitory effects of E2 on LV hypertrophy were absent in CnA knockout mice supporting that CnA is an important target of E2-mediated inhibition. In cultured rat cardiac myocytes, E2 inhibited agonist-induced hypertrophy while also decreasing CnA abundance and NFAT activation. Agonist stimulation also reduced CnA ubiquitination and degradation that was prevented by E2; all in vitro effects of estrogen were reversed by an ER antagonist. These data support that E2 reduces pressure overload induced hypertrophy by an ER-dependent mechanism that increases CnA degradation, unveiling a novel mechanism by which E2 and ERs regulate pathologic LV and cardiomyocyte growth.

New and innovative tools have emerged for the treatment of massive and submassive pulmonary embolism (PE). These novel treatments, when considered alongside existing therapy, such as anticoagulation, systemic intravenous thrombolysis, and open surgical pulmonary embolectomy, have the potential to improve patient outcomes. However, data comparing different treatment modalities are sparse, and guidelines provide only general advice for their use. Treatment decisions rest on clinician expertise and institutional resources. Because various medical and surgical specialties offer different perspectives and expertise, a multidisciplinary approach to patients with massive and submassive PE is required. To address this need, we created a novel multidisciplinary program - the Massachusetts General Hospital (MGH) Pulmonary Embolism Response Team (PERT) - which brings together multiple specialists to rapidly evaluate intermediate- and high-risk patients with PE, formulate a treatment plan, and mobilize the necessary resources to provide the highest level of care. Development of a clinical, educational, and research infrastructure, as well as the creation of a national PERT consortium, will make our experience available to other institutions and serve as a platform for future studies to improve the care of complex patients with massive and submassive PE.

AngioVac thrombectomy is feasible in critically ill patients with acute DVT or PE and large caval thrombi or intracardiac masses.

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Background Hypertension (HTN) causes concentric left ventricular (LV) remodeling, defined as an increased relative wall thickness or overt LV hypertrophy, and associated diastolic dysfunction. HTN and concentric remodeling are also common precursors to heart failure with a preserved ejection fraction (EF). It is not known if the myofilament contributes to diastolic dysfunction in patients with concentric remodeling. Methods and Results Intra-operative myocardial biopsies were obtained in 15 male patients undergoing coronary bypass grafting (CBG), all with normal LV EF and wall motion. Eight patients had a history of HTN and concentric remodeling. Seven without HTN or remodeling served as controls. Myocardial strips were dissected and demembranated with detergent. Isometric tension was measured and sinusoidal length perturbation analysis performed at sarcomere length 2.2μm and pCa 8 –4.5. Sinusoidal analysis provides estimates of cross-bridge dynamics, including rate constants of attachment and detachment and cross-bridge attachment time (ton). The normalized isometric tension-pCa relation was similar in HTN and controls. However, ton was significantly prolonged at submaximal [Ca2+] (pCa ≥ 6.5) in HTN patients. Analysis of protein phosphorylation revealed ~25% reduction in phosphorylation of troponin I in HTN patients (P < 0.05). Conclusions Compared with controls, patients with HTN and concentric remodeling display prolonged ton at submaximal [Ca2+] without a change in the tension-pCa relation. Prolonged ton implicates altered cross-bridge dynamics as a cause of slowed relaxation in these patients. This finding was associated with reduced phosphorylation of troponin I, suggesting decreased phosphorylation of protein kinase A/G sites as a mechanism.

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The effects of hypoxia on the regulation of inducible nitric oxide synthase (NOS) 2 expression were examined in cultured rat pulmonary microvascular endothelial cells (EC). EC did not express NOS 2 mRNA or protein when exposed to normoxia or hypoxia unless they were pretreated with interleukin (IL)-1beta and/or tumor necrosis factor (TNF)-alpha for 24 h. Induction of NOS 2 by IL-1beta+TNF-alpha was significantly attenuated by concomitant exposure of EC to hypoxia or treatment of EC with antioxidants such as tiron, diphenyliodonium, and catalase, suggesting that NOS 2 expression is dependent on the production of reactive oxygen species. Degradation of IkappaB and activation of NF-kappaB, which were both induced by treatment of EC with cytokines, were not altered when the cells were exposed to hypoxia, suggesting that the modulation of NOS 2 expression by hypoxia is unrelated to NF-kappaB activation. Following stimulation with IL-1beta+TNF-alpha for 24 h, incubation of EC in normoxia resulted in a progressive decline in NOS 2 expression and a calculated half-life of approximately 6 h for NOS 2 mRNA. Hypoxia significantly prolonged the half-life of NOS 2 mRNA (17 h, P < 0.05 versus normoxic EC). The half-life of NOS 2 mRNA was also prolonged by actinomycin D treatment (19.5 and 29.5 h for normoxic and hypoxic EC, respectively), suggesting that transcription of an RNA destabilizing factor or RNAse contributes to NOS 2 mRNA degradation. In EC transiently transfected with the rat NOS 2 promoter, hypoxia and the combination of IL-1beta+TNF-alpha independently increased promoter activity 2.2- and 3-fold, respectively. As opposed to the attenuating effect that hypoxia had on IL-1beta+TNF-alpha- dependent induction of NOS 2 gene expression, the concomitant treatment with IL-1beta+TNF-alpha and hypoxia synergistically increased NOS 2 promoter activity 17.6-fold. Taken together, these results suggest that hypoxia alone does not induce NOS 2 expression in cultured pulmonary microvascular EC, but may modulate cytokine induction of this enzyme at pretranscriptional, transcriptional, and posttranscriptional levels.