Evolution of iron carbides during tempering of low-alloy tool steel studied with polarized small angle neutron scattering, electron microscopy and atom probe

The magnetic scattering of iron carbides in low-alloy tool steel was investigated ex-situ by polarized small angle neutron scattering measurements after tempering the steel at 550 \ub0C and 600 \ub0C. Magnetic features could be detected in the as-quenched sample resulting in a negative interference term, believed to be either θ-Fe3C, η-Fe2C, or ε-Fe2-3C. During tempering the evolution of cementite could be studied by the variation of the interference term and in γ-ratio, which is the ratio of the magnetic to nuclear scattering length density contrast. From scanning transmission electron microscopy (STEM) and atom probe tomography, it is evident that cementite (θ-Fe3C) is present directly when reaching the tempering temperature of either 550 \ub0C or 600 \ub0C. At longer tempering times, cementite gets enriched with substitutional elements like chromium and manganese, forming an enriched shell on the cementite particles. STEM and energy dispersive x-ray spectrometry show that the chemical composition of small cementite particles approaches that of Cr-rich M7C3 carbides after 24 h at 600 \ub0C. It is also seen that small non-magnetic particles precipitate during tempering and these correspond well with molybdenum and vanadium-rich carbides

Carbide Precipitation during Processing of Two Low-Alloyed Martensitic Tool Steels with 0.11 and 0.17 V/Mo Ratios Studied by Neutron Scattering, Electron Microscopy and Atom Probe

Two industrially processed low-alloyed martensitic tool steel alloys with compositions Fe-0.3C-1.1Si-0.81Mn-1.5Cr-1.4Ni-1.1Mo-0.13V and Fe-0.3C-1.1Si-0.81Mn-1.4Cr-0.7Ni-0.8Mo-0.14V (wt.%) were characterized using small-angle neutron scattering (SANS), scanning electron microscopy (SEM), Scanning transmission electron microscopy (STEM), and atom probe tomography (APT). The combination of methods enables an understanding of the complex precipitation sequences that occur in these materials during the processing. Nb-rich primary carbides form at hot working, while Fe-rich auto-tempering carbides precipitate upon quenching, and cementite carbides grow during tempering when Mo-rich secondary carbides also nucleate and grow. The number density of Mo-rich carbides increases with tempering time, and after 24 h, it is two to three orders of magnitude higher than the Fe-rich carbides. A high number density of Mo-rich carbides is important to strengthen these low-alloyed tool steels through precipitation hardening. The results indicate that the Mo-rich secondary carbide precipitates are initially of MC character, whilst later they start to appear as M2C. This change of the secondary carbides is diffusion driven and is therefore mainly seen for longer tempering times at the higher tempering temperature of 600◦C

Expression of 5-lipoxygenase and 15-lipoxygenase in rheumatoid arthritis synovium and effects of intraarticular glucocorticoids

The past years have witnessed tremendous progress in the treatment of rheumatoid arthritis, a chronic debilitating autoimmune disease mainly characterized by joint inflammation with progressive tissue destruction and loss of function. This condition affects 0.5-1% of the population, is associated with important co-morbidities and represents a heavy economical burden. New strategies, employing early and aggressive therapies with classical drugs or new agents, have resulted in impressive improvements in controlling disease activity. In some cases they even lead to clinical remission. Despite potent and efficient biological agents that specifically modulate distinct pathological pathways a large proportion of patients remain unresponsive to these therapies; drug-free remission is also difficult to achieve since attempting discontinuation of treatment usually results in disease flare. In rheumatoid arthritis joints there is a constant activation of complex networks of cytokines and factors mediating immune interactions and inflammation, in which prostaglandin E2 (PGE2) and leukotriene B4 (LTB4) are important players and contributors to pathogenesis. Our research aimed to investigate the synovial expression of enzymes controlling prostaglandin E2 synthesis and degradation – cyclooxygenase (COX) 1 and 2, microsomal prostaglandin E2 synthase 1 (MPGES1) and 15-prostaglandin dihydrogenase (15-PGDH) as well as enzymes involved in leukotriene synthesis, such as 5-lipoxygenase (LO) and 15-LO. In addition, we evaluated how traditional and new therapies influence these pathways, by analyzing enzyme expression before and after systemic treatment with tumor necrosis factor (TNF) antagonists, rituximab or methotrexate, as well as before and after intra-articular treatment with glucocorticoids. We also evaluated the in vitro effects of TNF antagonists and glucocorticoids on synovial fluid cells and that of methotrexate on synovial fibroblasts. We demonstrated that synovial tissue from RA patients displayed an important expression of enzymes involved in the metabolism of PGE2, as well as 5-LO and 15-LO. MPGES1 and COX-2, the inflammation-inducible enzymes co-localized mainly in fibroblasts and macrophage-like cells and accounted for the local PGE2 production. Intra-articular glucocorticoids significantly reduced all enzymes involved in the PGE2 cascade – COX-1 and COX-2, MPGES1 and 15-PGDH, but also 5-LO, responsible for leukotriene formation. However, they did not influence the expression of 15-LO, an enzyme involved in the formation of both pro-and anti-inflammatory lipid mediators. Regarding the effects of TNF blockers, rituximab or methotrexate, they did not alter the expression profile of enzymes involved in PGE2 metabolism despite showing clinical efficiency in improving disease activity. Although anti-TNF agents reduced the in vitro expression of MPGES1 and COX-2 in synovial fluid cells, the lack of effect ex vivo in biopsies emphasized once again the differences between synovial compartments and possibly the difficulty in mimicking the micro-environment at the site of inflammation in vitro. In conclusion, this thesis demonstrates that potent anti-rheumatic drugs currently used in the clinic with good efficiency also leave inflammatory pathways un-affected, which may account for subclinical ongoing disease activity. Blocking the PGE2 pathway by using MPGES1 inhibitors as combination therapy may show benefit in dampening ongoing local inflammation

High expression of 5-lipoxygenase in normal and malignant mantle zone B lymphocytes

<p>Abstract</p> <p>Background</p> <p>Human B lymphocytes can produce leukotriene B₄but the biological function of the 5-lipoxygenase (5-LO) pathway in B cells is unclear. In order to better understand and define the role of 5-LO in B cells, we investigated the expression of 5-LO mRNA and protein in subsets of B cells from human tonsils and different types of B cell lymphoma.</p> <p>Results</p> <p>Based on RT-PCR and western blot/immunohistochemical staining, with a polyclonal antibody raised against 5-LO, high expression of 5-LO was found in mantle zone B cells from tonsils. By contrast, only a weak expression of 5-LO was detected in germinal centre cells and no expression in plasma cells from tonsils. This pattern of 5-LO expression was preserved in malignant lymphoma with high expression in mantle B cell lymphoma (MCL) and weak or no expression in follicular lymphoma. Primary leukemized MCL, so called B-prolymphocytic leukaemia cells, and MCL cell lines also expressed 5-LO and readily produced LTB₄after activation.</p> <p>Conclusion</p> <p>The present report demonstrates the expression of 5-LO mainly in normal and malignant mantle zone B cells while the expression is low or absent in germinal centre B cells and plasma cells, indicating a role of the 5-LO pathway in B cells before the cells finally differentiate to plasma cells.</p

Preferential Generation of 15-HETE-PE Induced by IL-13 Regulates Goblet Cell Differentiation in Human Airway Epithelial Cells

Type 2–associated goblet cell hyperplasia and mucus hypersecretion are well known features of asthma. 15-Lipoxygenase-1 (15LO1) is induced by the type 2 cytokine IL-13 in human airway epithelial cells (HAECs) in vitro and is increased in fresh asthmatic HAECs ex vivo. 15LO1 generates a variety of products, including 15-hydroxyeicosatetraenoic acid (15-HETE), 15-HETE-phosphatidylethanolamine (15-HETE-PE), and 13-hydroxyoctadecadienoic acid (13-HODE). In this study, we investigated the 15LO1 metabolite profile at baseline and after IL-13 treatment, as well as its influence on goblet cell differentiation in HAECs. Primary HAECs obtained from bronchial brushings of asthmatic and healthy subjects were cultured under air–liquid interface culture supplemented with arachidonic acid and linoleic acid (10 μM each) and exposed to IL-13 for 7 days. Short interfering RNA transfection and 15LO1 inhibition were applied to suppress 15LO1 expression and activity. IL-13 stimulation induced expression of 15LO1 and preferentially generated 15-HETE-PE in vitro, both of which persisted after removal of IL-13. 15LO1 inhibition (by short interfering RNA and chemical inhibitor) decreased IL-13–induced forkhead box protein A3 (FOXA3) expression and enhanced FOXA2 expression. These changes were associated with reductions in both mucin 5AC and periostin. Exogenous 15-HETE-PE stimulation (alone) recapitulated IL-13–induced FOXA3, mucin 5AC, and periostin expression. The results of this study confirm the central importance of 15LO1 and its primary product, 15-HETE-PE, for epithelial cell remodeling in HAEC

Mice Lacking 12/15-Lipoxygenase have Attenuated Airway Allergic Inflammation and Remodeling.

Arachidonate 15-lipoxygenase (LO)-1 has been implicated in allergic inflammation and asthma. The overall effect of 15-LO in allergic inflammation in vivo is, however, unclear. This study investigates systemic allergen sensitization and local allergic airway inflammation and remodeling in mice lacking the murine 12/15-LO, the ortholog to human 15-LO-1. Upon systemic sensitization with intraperitoneal ovalbumin, 12/15 LO(-/-) mice produced elevated levels of allergen-specific IgE compared to wild type (Wt) controls. However, when challenged with repeated aerosolized allergen sensitized 12/15 LO(-/-) mice had an impaired development of airway allergic inflammation compared to Wt controls, as indicated by reduced BAL fluid leukocytes (eosinophils, lymphocytes macrophages) and Th2 cytokines (IL-4, IL-5, IL-13) as well as tissue eosinophils. Allergen-induced airway epithelial proliferation was also significantly attenuated in 12/15 LO(-/-) mice whereas goblet cell hyperplasia was unaffected. However, 12/15 LO(-/-) mice had significantly reduced luminal mucus secretions compared to Wt controls. The repeated allergen challenges resulted in a dramatic increase of alpha-smooth muscle-actin positive alveolar cells in the peripheral airways, a phenomenon that was significantly less developed in 12/15 LO(-/-) mice. In conclusion, our data suggest that 12/15 LO(-/-) mice, although having a fully developed systemic sensitization, did not establish a fully developed allergic airway inflammation and associated manifestations of central and peripheral airway remodeling. These data suggest that 12/15-LO derived metabolites play an important pathophysiological role in allergen-induced inflammation and remodeling. Hence, pharmacologic targeting of the human 15-LO-1 may represent an attractive therapeutic strategy to control inflammation and remodeling in asthma