Novel membrane target proteins for lipoxygenase-derived mono(S)hydroxy fatty acids

Multicomponent Reductive Coupling for Selective Access to Functional γ-Lactams by a Single-Atom Cobalt Catalyst

Despite their significant importance to numerous fields, the difficulties in direct and diverse synthesis of α-hydroxy-γ-lactams pose substantial obstacles to their practical applications. Here, we designed a nitrogen and TiO2 co-doped graphitic carbon-supported material with atomically dispersed cobalt sites (CoSA-N/NC-TiO2), which was successfully applied as a multifunctional catalyst to establish a general method for direct construction of α-hydroxy-γ-lactams from cheap and abundant nitro(hetero)arenes, aldehydes, and H2O with alkynoates. The striking features of operational simplicity, broad substrate and functionality compatibility (>100 examples), high step and atom efficiency, good selectivity, and exceptional catalyst reusability highlight the practicality of this new catalytic transformation. Mechanistic studies reveal that the active CoN4 species and the dopants exhibit a synergistic effect on the formation of key acid-masked nitrones; their subsequent nucleophilic addition to the alkynoates followed by successive reduction, alkenyl hydration, and intramolecular ester ammonolysis delivers the desired products. In this work, the concept of reduction interruption leading to new reaction route will open a door to further develop useful transformations by rational catalyst design.

High levels of oxidized fatty acids in HDL are associated with impaired HDL function in patients with active rheumatoid arthritis

The objective of this study was to evaluate oxidation products of arachidonic acid and linoleic acid in lipoproteins and synovial fluid (SF) from patients with active rheumatoid arthritis (RA) compared to non-RA controls. High-density lipoproteins (HDL) and low-density lipoproteins (LDL) were isolated from plasma using fast protein liquid chromatography and HDL was isolated from SF using dextran sulfate precipitation. 5-Hydroxyeicosatetraenoic acid (HETE), 12-HETE, 15-HETE, 9 hydroxyoctadecadienoic (HODE), and 13-HODE levels were measured in HDL, LDL, and SF by liquid chromatography-tandem mass spectrometry. HDL's anti-inflammatory function, cholesterol levels, myeloperoxidase (MPO) and paraoxonase 1 (PON1) activities were determined as previously. 5-HETE, 15-HETE, 9-HODE, and 13-HODE levels were significantly increased in HDL and LDL from patients with active RA (n = 10) compared to healthy controls (n = 8) and correlated significantly with measures of systemic inflammation, particularly in HDL (r = 0.65-0.80, p values < 0.004). Higher HETES and HODES in HDL were also significantly correlated with impaired HDL function as measured by the HDL inflammatory index (HII) (r = 0.54-0.58; p values < 0.03). 15-HETE levels and MPO activity were higher in RA SF (n = 10) compared to osteoarthritis (OA) SF(n = 11), and HDL from RA SF had worse function compared to OA SF HDL (HII = 2.1 ± 1.9 and 0.5 ± 0.1), respectively (p < 0.05). Oxidation products of arachidonic acid and linoleic acid are increased in HDL and LDL from patients with active RA compared to healthy controls, and are associated with worse anti-oxidant function of HDL. These results suggest a potential mechanism by which oxidative stress from active RA increases oxidized fatty acids in HDL, promoting HDL dysfunction, and thereby increasing atherosclerotic risk.

Actin filaments-A target for redox regulation

Actin and its ability to polymerize into dynamic filaments is critical for the form and function of cells throughout the body. While multiple proteins have been characterized as affecting actin dynamics through noncovalent means, actin and its protein regulators are also susceptible to covalent modifications of their amino acid residues. In this regard, oxidation-reduction (Redox) intermediates have emerged as key modulators of the actin cytoskeleton with multiple different effects on cellular form and function. Here, we review work implicating Redox intermediates in post-translationally altering actin and discuss what is known regarding how these alterations affect the properties of actin. We also focus on two of the best characterized enzymatic sources of these Redox intermediates-the NADPH oxidase NOX and the flavoprotein monooxygenase MICAL-and detail how they have both been identified as altering actin, but share little similarity and employ different means to regulate actin dynamics. Finally, we discuss the role of these enzymes and redox signaling in regulating the actin cytoskeleton in vivo and highlight their importance for neuronal form and function in health and disease. © 2016 Wiley Periodicals, Inc.

Post-translational modification and regulation of actin

Many of the best-studied actin regulatory proteins use non-covalent means to modulate the properties of actin. Yet, actin is also susceptible to covalent modifications of its amino acids. Recent work is increasingly revealing that actin processing and its covalent modifications regulate important cellular events. In addition, numerous pathogens express enzymes that specifically use actin as a substrate to regulate their hosts' cells. Actin post-translational alterations have been linked to different normal and disease processes and the effects associated with metabolic and environmental stressors. Herein, we highlight specific co-translational and post-translational modifications of actin and discuss the current understanding of the role that these modifications play in regulating actin.

New aspects of the role of hydroxyeicosatetraenoic acids in cell growth and cancer development

Lipoxygenase (LOX) pathway leads to the formation of leukotrienes and also catalyses the conversion of arachidonic acid (AA) to hydroperoxyeicosatetraenoic acids that are then reduced to hydroxyeicosatetraenoic acids (HETE) by glutathione peroxidase. There are four mammalian LOXs that produce 5-, 8-, 12- and 15-HETE, respectively. Cytochrome P-450 isozymes are also capable of metabolising AA to HETEs either by bis-allylic oxidation (lipoxygenase-like reaction) to generate 5-, 8-, 9-, 11-, 12- and 15-HETE; or by varpi/varpi-1 hydroxylation to yield 16-, 17-, 18-, 19- and 20-HETEs. It is now widely recognised that HETEs have important physiological and pathological functions that modulate ion transport, renal and pulmonary functions, vascular tone and reactivity, and inflammatory and growth responses. They can be released during the action of growth factors and cytokines, reaching physiological concentrations higher than that of prostanoids and modulating the functions of these factors. Their effects can occur through receptor or non-receptor mechanisms. Recent reviews have summarised the effects of HETEs in vascular homeostasis or lung and renal physiology. The present review focuses on the emerging effects of HETEs on cell signalling and physiological cell growth. It also discusses current observations regarding the role of HETEs in apoptosis, angiogenesis, the proliferation of cancer cells and metastasis, which constitute a potential area for successful therapeutic intervention.

Antibacterial compounds from Planchonia careya leaf extracts

AIM OF THE STUDY

The leaves of Planchonia careya (F. Muell.) R. Knuth (Lecythidaceae) have been traditionally implemented in the treatment of wounds by the indigenous people of northern Australia, although the compounds responsible for the medicinal properties have not been identified. In this study, antibacterial compounds from the leaf extracts were isolated and characterized, and the biological activity of each compound was assessed.

MATERIALS AND METHODS

Compounds were isolated from the leaf extracts using HPLC-piloted activity-guided fractionation. The minimum inhibitory concentrations (MICs) were assessed with plate-hole diffusion assays, and the cytotoxicity was determined with MTT assays using monkey kidney epithelial (MA104) cells.

RESULTS

Six known compounds were isolated from the leaf extracts and were identified as 1, (+)-gallocatechin; 2, gallocatechin-(4alpha-->8)-gallocatechin; 3, 9(S)-hydroxy-10E,12Z-octadecadienoic acid (alpha-dimorphecolic acid); 4, 2alpha,3beta,24-trihydroxyolean-12-en-28-oic acid (hyptatic acid-A); 5, 3beta-O-cis-p-coumaroyltormentic acid; and 6, 3beta-O-trans-p-coumaroyltormentic acid. Compounds 5 and 6 were weakly selective for vancomycin-resistant Enterococcus (VRE) compared with eukaryotic cells, with an MIC of 59.4microg/mL and a 50% inhibitory concentration (IC(50)) of 72.0microg/mL for MA104 cells.

CONCLUSIONS

The isolation of six antibacterial compounds from the leaves of Planchonia careya validates the use of this species as a topical wound-healing remedy.

Disparate effects of 12-lipoxygenase and 12-hydroxyeicosatetraenoic acid in vascular endothelial and smooth muscle cells and in cardiomyocytes

The expression and activity of the arachidonic acid-metabolizing enzyme leukocyte-type 12-lipoxygenase (12-LO) are augmented in cultured vascular endothelial and smooth muscle cells exposed to high glucose concentrations and in blood vessels of diabetic animals. The product of this enzyme, 12-hydroxyeicosatetraenoic acid (12-HETE), evokes two types of interactions in these cells: on one hand it acts as a pro-inflammatory factor that contributes to the initiation and progression of atherosclerotic lesions. Yet on the other, it protects the same cells against deleterious effects of high levels of intracellular glucose by downregulating the glucose transport system in the cells. In addition, it has been shown that 12-LO and 12-HETE support insulin-dependent glucose transporter-4 translocation to the plasma membrane by maintaining intact actin fiber network in the cardiomyocytes. Here we focus on the disparate cellular interactions by which 12-LO and 12-HETE affect the glucose transport system in vascular endothelial and smooth muscle cells and in cardiomyocytes.

Inflammation and immune regulation by 12/15-lipoxygenases

12/15-Lipoxygenases (12/15-LOX) are members of the LOX family, which are expressed in mammals by monocytes and macrophages following induction by the T helper type 2 cytokines, interleukins-4 and -13. They oxygenate free polyenoic fatty acids but also ester lipids and even complex lipid-protein assemblies such as biomembranes and lipoproteins. The primary oxidation products are either reduced by glutathione peroxidases to corresponding hydroxy derivatives or metabolized into secondary oxidized lipids including leukotrienes, lipoxins and hepoxilins, which act as lipid mediators. Examination of knockout and transgenic animals revealed important roles for 12/15-LOX in inflammatory diseases, including atherosclerosis, cancer, osteoporosis, angiotension II-dependent hypertension and diabetes. In vitro studies suggested 12/15-LOX products as coactivators of peroxisomal proliferator activating-receptors (PPAR), regulators of cytokine generation, and modulators of gene expression related to inflammation resolution. Despite much work in this area, the biochemical mechanisms by which 12/15-LOX regulates physiological and pathological immune cell function are not fully understood. This review will summarize the biochemistry and tissue expression of 12/15-LOX and will describe the current knowledge regarding its immunobiology and regulation of inflammation.

Cellular and molecular events in corneal wound healing: significance of lipid signalling

Alterations in the normal healing process after corneal injury can produce undesirable outcomes that range from corneal haze to ulceration and perforation. Lipids play important roles in the complex inflammatory processes that occur after corneal wounding. While some lipid mediators, such as the lipoxygenase derivatives of arachidonic acid, 12-hydroxyeicosatetraenoic acid (12[S]-HETE and 15[S]-HETE), act as second messengers to promote cell proliferation and are possibly involved in the synthesis of other molecules that suppress inflammation, others, such as platelet-activating factor (PAF), exert their actions through specific receptors, play key roles during sustained corneal inflammation (as might occur with chemical burns), and contribute to tissue destruction and neovascularization. PAF is also a strong inducer of selective metalloproteinases (MMPs) that degrade the extracellular matrix. The use of a new PAF antagonist has shown great promise for the treatment of diffuse lamellar keratitis (DLK) and alkali-burned corneas.

Eicosanoids and the regulation of cardiac glucose transport

Intact actin microfilaments are necessary for insulin-regulated GLUT4 translocation from intracellular pools to the plasma membrane. Products of the lipoxygenase (LO) pathway were shown to be implicated in the regulation of actin cytoskeleton rearrangement. The aim of this study was to examine the role of these LO products for cardiac insulin signaling and glucose uptake, GLUT4 translocation, and actin-based cytoskeleton structure. Exposure of cardiomyocytes to esculetin or NDGA, two structurally different LO inhibitors, induced a complete inhibition of insulin-stimulated glucose uptake, whereas control cells showed a threefold stimulation by insulin. Addition of 12(S)-HETE rendered the NDGA-treated cells insulin-sensitive. Early insulin signaling was not changed in cells exposed to LO inhibitors. Cell surface biotinylation of control cells showed a twofold increase of GLUT4 at the cell surface after insulin stimulation. In contrast, the LO inhibitors induced a complete inhibition of insulin-stimulated GLUT4 translocation. Labeling of the F-actin cytoskeleton revealed a prominent disassembly of actin fibers in cells exposed to the LO inhibitors. In conclusion, we show here that products of the LO reaction participate in the organization of the actin network in ventricular cardiomyocytes. Inhibition of LO blocks GLUT4 translocation without affecting insulin signaling events. These data suggest that products of the LO reaction participate in the regulation of glucose transport by contribution to a rearrangement of actin cytoskeletal elements.

Endogenous anti-inflammatory mediators from arachidonate in human neutrophils

Eicosanoids have been historically involved in the pathogenesis of various inflammatory diseases. Lipoxins (LXs) and epi-LXs show physiological effects relevant to inflammation regulation. In this study, we focused on LX precursors based on the hypothesis that their entrance and metabolism into the cell may facilitate their targeting at the inflammation site. Because compound chirality is of considerable importance in the efficacy of therapeutic agents, our aim was to study the anti-inflammatory effects of various epimers of LXA(4) precursors compared to LXA(4). Blood polymorphonuclear cells (PMNs) were incubated with 15(S)- or 15(R)-hydroxyeicosatetraenoic acid (HETE), 14(R)-,15(S)-, or 14(S),15(S)-diHETE, and LXA(4) and then stimulated with the calcium ionophore A23187. We found that 15(R)-HETE rather than 15(S)-HETE was preferentially metabolized and that 15-epi-LXs were produced in larger amounts than LXs. In contrast, when PMNs were incubated with the diastereoisomers of 14,15(S)-diHETE, 14-epi-LXB(4) was produced in lower amounts than LXB(4). Enantiomers of 15-HETE and diastereoisomers of 14,15-diHETE and LXA(4) were able to significantly decrease LTB(4) release by PMNs. These results suggest a potential resolution of the inflammatory process through endogenous anti-inflammatory mediators released by the way of trans-cellular metabolism.

Eicosanoids participate in the regulation of cardiac glucose transport by contribution to a rearrangement of actin cytoskeletal elements

Intact actin microfilaments are required for insulin-regulated glucose transporter isoform 4 (GLUT4) translocation to the plasma membrane. Lipoxygenase (LO) metabolites have recently been shown to contribute to the regulation of actin cytoskeleton rearrangement. In the present investigation, ventricular cardiomyocytes were used to study the effects of two structurally different LO inhibitors (esculetin and nordihydroguaiaretic acid) on insulin signalling events, glucose uptake, GLUT4 translocation and the actin network organization. Insulin stimulation increased glucose uptake 3-fold in control cells, whereas LO inhibition completely blocked this effect. This was paralleled by a slight reduction in the insulin-induced tyrosine phosphorylation of insulin receptor substrate (IRS)-1 and IRS-2. However, inhibition of 12-LO did not affect the association of phosphatidylinositol 3-kinase with IRS-1 and the phosphorylation of Akt/protein kinase B in response to insulin. Addition of 12(S)-hydroxyeicosatetraenoic acid almost completely restored the insulin action in cells exposed to nordihydroguaiaretic acid. Insulin stimulation increased cell surface GLUT4 2-fold in control cells, whereas LO inhibition abrogated the insulin-stimulated GLUT4 translocation. LO inhibition induced a prominent disassembly of actin fibres compared with control cells. In conclusion, we show here that 12(S)-hydroxyeicosatetraenoic acid plays a role in the organization of the actin network in cardiomyocytes. LO inhibition blocks GLUT4 translocation without affecting downstream insulin signalling. These data suggest that LO metabolites participate in the regulation of glucose transport by contributing to a rearrangement of actin cytoskeletal elements.

12/15-lipoxygenase translocation enhances site-specific actin polymerization in macrophages phagocytosing apoptotic cells

The enzyme 12/15-lipoxygenase (12/15-LO) introduces peroxyl groups in a position-specific manner into unsaturated fatty acids in certain cells, but the role of such enzymatic lipid peroxidation remains poorly defined. Here we report a novel function for 12/15-LO in mouse peritoneal macrophages. When macrophages were coincubated with apoptotic cells, the enzyme translocated from cytosol to the plasma membrane and was more extensively concentrated at sites where macrophages bound apoptotic cells, colocalizing with polymerized actin of emerging filopodia. Disruption of F-actin did not prevent the 12/15-LO translocation. In contrast, inhibition of the 12/15-LO activity, or utilization of genetically engineered macrophages in which the 12/15-LO gene has been disrupted, greatly reduced actin polymerization in phagocytosing macrophages. Lysates of 12/15-LO-deficient macrophages had significantly lower ability to promote in vitro actin polymerization than the lysates of wild type macrophages. These studies suggest that the 12/15-LO enzyme plays a major role in local control of actin polymerization in macrophages in response to interaction with apoptotic cells.

Lipoxygenases and atherosclerosis: protection versus pathogenesis

15 lipoxygenase (15LO) is a lipid-oxidizing enzyme that is considered to contribute to the formation of oxidized lipids in atherosclerotic lesions. Monocyte-macrophages are the key cells that express 15LO in atherosclerotic lesions. In this review, we examine the evidence for 15LO involvement in atherogenesis and explore and evaluate the potential mechanisms whereby 15LO may contribute to the oxidation of LDL by monocyte-macrophages. We also describe several possible pro- versus anti-atherogenic functions that may be mediated by various products of 15LO lipid oxidation. Central pathways involved in regulating 15LO expression and activity that may serve as future targets for intervention and regulation of this enzyme are also reviewed.