The Entomopathogenic Nematodes H. bacteriophora and S. carpocapsae Inhibit the Activation of proPO System of the Nipa Palm Hispid Octodonta nipae (Coleoptera: Chrysomelidae)

Entomopathogenic nematodes are biocontrol agents of invasive insect pests in soil and cryptic habitats. Nipa palm hispid, Octodonta nipae, is a pest of palm trees in Sothern China. To address its increasing damage, environmentally friendly control methods are required. This study aimed to test efficacy of Heterorhabditis bacteriophora and Steinernema carpocapsae on O. nipae and investigated the influence of secondary metabolites, nematodes, and their isolated cuticles on the activation of O. nipae’s prophenoloxidase system using qPCR analysis. Our data revealed that O. nipae were less susceptible to H. bacteriophora than S. carpocapsae and penetrations of infective juveniles were higher with S. carpocapsae treatment than H. bacteriophora. Moreover, expression levels of the serine protease P56, prophenoloxidase activation factor 1, PPO and serine protease inhibitor 28 upon S. carpocapsae and H. bacteriophora infections were generally downregulated at all times. However, upon heating, the cuticles lost their inhibitory effects and resulted in upregulation of the PPO gene. Similarly, the addition of arachidonic acid reversed the process and resulted in the upregulation of the PPO gene compared to the control. Further work is needed to identify toxic substances secreted by these EPNs to evade O. nipae’s immune system.

"HETE"ing up mitochondria in human heart failure

A decade of research has established the phospholipase iPLA₂γ as being involved in cardiomyocyte dysfunction and necrosis leading to heart failure, but the mechanisms by which iPLA₂γ acts and its interaction with the mitochondrial permeability transition pore (mPTP) that is critical for cardiac homeostasis are unclear. New investigations by Moon et al. demonstrate that mitochondria in failing hearts undergo dynamic shifts in PLA₂ isoform expression, leading to a redistribution of eicosanoid composition that contributes to pathologic mPTP opening.

Epoxide hydrolase 1 (EPHX1) hydrolyzes epoxyeicosanoids and impairs cardiac recovery after ischemia

Stimuli such as inflammation or hypoxia induce cytochrome P450 epoxygenase-mediated production of arachidonic acid-derived epoxyeicosatrienoic acids (EETs). EETs have cardioprotective, vasodilatory, angiogenic, anti-inflammatory, and analgesic effects, which are diminished by EET hydrolysis yielding biologically less active dihydroxyeicosatrienoic acids (DHETs). Previous in vitro assays have suggested that epoxide hydrolase 2 (EPHX2) is responsible for nearly all EET hydrolysis. EPHX1, which exhibits slow EET hydrolysis in vitro, is thought to contribute only marginally to EET hydrolysis. Using Ephx1^-/-, Ephx2^-/-, and Ephx1^-/-Ephx2^-/- mice, we show here that EPHX1 significantly contributes to EET hydrolysis in vivo Disruption of Ephx1 and/or Ephx2 genes did not induce compensatory changes in expression of other Ephx genes or CYP2 family epoxygenases. Plasma levels of 8,9-, 11,12-, and 14,15-DHET were reduced by 38, 44, and 67% in Ephx2^-/- mice compared with wildtype (WT) mice, respectively; however, plasma from Ephx1^-/-Ephx2^-/- mice exhibited significantly greater reduction (100, 99, and 96%) of those respective DHETs. Kinetic assays and FRET experiments indicated that EPHX1 is a slow EET scavenger, but hydrolyzes EETs in a coupled reaction with cytochrome P450 to limit basal EET levels. Moreover, we also found that EPHX1 activities are biologically relevant, as Ephx1^-/-Ephx2^-/- hearts had significantly better postischemic functional recovery (71%) than both WT (31%) and Ephx2^-/- (51%) hearts. These findings indicate that Ephx1^-/-Ephx2^-/- mice are a valuable model for assessing EET-mediated effects, uncover a new paradigm for EET metabolism, and suggest that dual EPHX1 and EPHX2 inhibition may represent a therapeutic approach to manage human pathologies such as myocardial infarction.

Liberating Chiral Lipid Mediators, Inflammatory Enzymes, and LIPID MAPS from Biological Grease

In 1970, it was well accepted that the central role of lipids was in energy storage and metabolism, and it was assumed that amphipathic lipids simply served a passive structural role as the backbone of biological membranes. As a result, the scientific community was focused on nucleic acids, proteins, and carbohydrates as information-containing molecules. It took considerable effort until scientists accepted that lipids also "encode" specific and unique biological information and play a central role in cell signaling. Along with this realization came the recognition that the enzymes that act on lipid substrates residing in or on membranes and micelles must also have important signaling roles, spurring curiosity into their potentially unique modes of action differing from those acting on water-soluble substrates. This led to the creation of the concept of "surface dilution kinetics" for describing the mechanism of enzymes acting on lipid substrates, as well as the demonstration that lipid enzymes such as phospholipase A₂ (PLA₂) contain allosteric activator sites for specific phospholipids as well as for membranes. As our understanding of phospholipases advanced, so did the understanding that many of the lipids released by these enzymes are chiral information-containing signaling molecules; for example, PLA₂ regulates the generation of precursors for the biosynthesis of eicosanoids and other bioactive lipid mediators of inflammation and resolution underlying disease progression. The creation of the LIPID MAPS initiative in 2003 and the ensuing development of the lipidomics field have revealed that lipid metabolites are central to human metabolism. Today lipids are recognized as key mediators of health and disease as we enter a new era of biomarkers and personalized medicine. This article is my personal "reflection" on these scientific advances.

Human Platelets Utilize Cycloxygenase-1 to Generate Dioxolane A3, a Neutrophil-activating Eicosanoid

Eicosanoids are important mediators of fever, pain, and inflammation that modulate cell signaling during acute and chronic disease. We show by using lipidomics that thrombin-activated human platelets generate a new type of eicosanoid that both stimulates and primes human neutrophil integrin (Mac-1) expression, in response to formylmethionylleucylphenylalanine. Detailed characterization proposes a dioxolane structure, 8-hydroxy-9,11-dioxolane eicosatetraenoic acid (dioxolane A₃, DXA₃). The lipid is generated in nanogram amounts by platelets from endogenous arachidonate during physiological activation, with inhibition by aspirin in vitro or in vivo, implicating cyclooxygenase-1 (COX). Pharmacological and genetic studies on human/murine platelets revealed that DXA₃ formation requires protease-activated receptors 1 and 4, cytosolic phospholipase A₂ (cPLA₂), Src tyrosine kinases, p38 MAPK, phospholipase C, and intracellular calcium. From data generated by purified COX isoforms and chemical oxidation, we propose that DXA₃ is generated by release of an intermediate from the active site followed by oxygenation at C8. In summary, a new neutrophil-activating platelet-derived lipid generated by COX-1 is presented that can activate or prime human neutrophils, suggesting a role in innate immunity and acute inflammation.

A Catalase-related Hemoprotein in Coral Is Specialized for Synthesis of Short-chain Aldehydes: DISCOVERY OF P450-TYPE HYDROPEROXIDE LYASE ACTIVITY IN A CATALASE

In corals a catalase-lipoxygenase fusion protein transforms arachidonic acid to the allene oxide 8R,9-epoxy-5,9,11,14-eicosatetraenoic acid from which arise cyclopentenones such as the prostanoid-related clavulones. Recently we cloned two catalase-lipoxygenase fusion protein genes (a and b) from the coral Capnella imbricata, form a being an allene oxide synthase and form b giving uncharacterized polar products (Lõhelaid, H., Teder, T., Tõldsepp, K., Ekins, M., and Samel, N. (2014) PloS ONE 9, e89215). Here, using HPLC-UV, LC-MS, and NMR methods, we identify a novel activity of fusion protein b, establishing its role in cleaving the lipoxygenase product 8R-hydroperoxy-eicosatetraenoic acid into the short-chain aldehydes (5Z)-8-oxo-octenoic acid and (3Z,6Z)-dodecadienal; these primary products readily isomerize in an aqueous medium to the corresponding 6E- and 2E,6Z derivatives. This type of enzymatic cleavage, splitting the carbon chain within the conjugated diene of the hydroperoxide substrate, is known only in plant cytochrome P450 hydroperoxide lyases. In mechanistic studies using (18)O-labeled substrate and incubations in H2(18)O, we established synthesis of the C8-oxo acid and C12 aldehyde with the retention of the hydroperoxy oxygens, consistent with synthesis of a short-lived hemiacetal intermediate that breaks down spontaneously into the two aldehydes. Taken together with our initial studies indicating differing gene regulation of the allene oxide synthase and the newly identified catalase-related hydroperoxide lyase and given the role of aldehydes in plant defense, this work uncovers a potential pathway in coral stress signaling and a novel enzymatic activity in the animal kingdom.

Phenotyping drug polypharmacology via eicosanoid profiling of blood

It is widely accepted that small-molecule drugs, despite their selectivity at primary targets, exert pharmacological effects (and safety liabilities) through a multiplicity of pathways. As such, it has proved extremely difficult to experimentally assess polypharmacology in an agnostic fashion. Profiling of metabolites produced as part of physiological responses to pharmacological stimuli provides a unique opportunity to explore drug pharmacology. A total of 122 eicosanoid lipids in human whole blood were monitored from 10 different donors upon stimulation with several inducers of immunological responses and treatment with modulators of prostaglandin (PG) and leukotriene biosynthesis, including clinical and investigational molecules. Such analysis revealed differentiation between drugs nominally targeting different eicosanoid biosynthetic enzymes, or even those designed to target the same enzyme. Profiled agents, some of them marketed products, affect eicosanoid biosynthesis in ways that cannot be predicted from information on their intended targets. As an example, we used this platform to discriminate drugs based on their ability to silence PG biosynthesis in response to bacterial lipopolysaccharide, resulting in differential pharmacological activity in an in vivo model of endotoxemia. Some of the observed effects are subject to variability among individuals, indicating a potential application of this methodology to the patient stratification, based on their responses to benchmark drugs and experimental compounds read on the eicosanome via a simple blood test.