Lipoxygenase: an emerging target for stroke therapy

[What is the Initiating Reaction for the Lipid Radical Chain Reaction System That Can Induce Ferroptotic Cell Death at the Lower Oxygen Content?]

The neural cell death in cerebral infarction is suggested to be ferroptosis-like cell death, involving the participation of 15-lipoxygenase (15-LOx). Ferroptosis is induced by lipid radical species generated through the one-electron reduction of lipid hydroperoxides, and it has been shown to propagate intracellularly and intercellularly. At lower oxygen concentration, it appeared that both regiospecificity and stereospecificity of conjugated diene moiety in lipoxygenase-catalysed lipid hydroperoxidation are drastically lost. As a result, in the reaction with linoleic acid, the linoleate 9-peroxyl radical-ferrous lipoxygenase complex dissolves into the linoleate 9-peroxyl radical and ferrous 15-lipoxygenase. Subsequently, the ferrous 15-lipoxygenase then undergoes one-electron reduction of 13-hydroperoxy octadecadienoic acid, generating an alkoxyl radical (pseudoperoxidase reaction). A part of the produced lipid alkoxyl radicals undergoes cleavage of C-C bonds, liberating small molecular hydrocarbon radicals. Particularly, in ω-3 polyunsaturated fatty acids, which are abundant in the vascular and nervous systems, the liberation of small molecular hydrocarbon radicals was more pronounced compared to ω-6 polyunsaturated fatty acids. The involvement of these small molecular hydrocarbon radicals in the propagation of membrane lipid damage is suggested.

Quantitative Assessment of the Post-translational Modifications of Human Serum Albumin by Dimethyl Trisulfide

Some bacteria, such as Fusobacterium nucleatum, act as dimethyl trisulfide (DMTS) producers in the host in vivo. DMTS acts as a sulfane sulfur donor and chemically modifies the sulfhydryl groups. This study explored the post-translational modifications of human serum albumin using DMTS. Quantitative assessments were conducted on mixed disulfides of mercaptoalbumin with mercaptomethane (Alb-SS-CH3) and albumin hydropersulfide (Alb-SSH) as post-translationally modified species. The hydropersulfide group was alkylated with iodoacetamide, resulting in the formation of an albumin-mercaptoacetamide mixed disulfide. The mixed disulfides were subsequently reduced with tris(2-carboxyethyl)phosphine, and the liberated mercaptomethane and mercaptoacetamide were fluorescently labeled with 4-fluoro-7-sulfamoylbenzofurazan (ABD-F). Quantification was performed using HPLC with fluorescence detection. Using this methodology, we examined the formation of Alb-SS-CH3 and Alb-SSH via the reaction between 4% human serum albumin and DMTS at 10-100 µM concentrations. Approximately two molecules of Alb-SS-CH3 and one molecule of Alb-SSH were generated from one DMTS molecule. Moreover, hydrogen sulfide was identified as an intermediate, suggesting its generation and subsequent reaction with intraprotein disulfide bonds, leading to the production of Alb-SSH. These results suggest the production of DMTS in humans in vivo should be involved in the elevation of Alb-SS-CH3 and Alb-SSH contents in plasma samples.

Transgenic mice overexpressing human ALOX15 under the control of the aP2 promoter are partly protected in the complete Freund's adjuvant-induced paw inflammation model

BACKGROUND, OBJECTIVES AND DESIGN

Arachidonic acid 15-lipoxygenase (ALOX15) has been implicated in the pathogenesis of inflammatory diseases but since pro- and anti-inflammatory roles have been suggested, the precise function of this enzyme is still a matter of discussion. To contribute to this discussion, we created transgenic mice, which express human ALOX15 under the control of the activating protein 2 promoter (aP2-ALOX15 mice) and compared the sensitivity of these gain-of-function animals in two independent mouse inflammation models with Alox15-deficient mice (loss-of-function animals) and wildtype control animals.

MATERIALS AND METHODS

Transgenic aP2-ALOX15 mice were tested in comparison with Alox15 knockout mice (Alox15-/-) and corresponding wildtype control animals (C57BL/6J) in the complete Freund's adjuvant induced hind-paw edema model and in the dextran sulfate sodium induced colitis (DSS-colitis) model. In the paw edema model, the degree of paw swelling and the sensitivity of the inflamed hind-paw for mechanic (von Frey test) and thermal (Hargreaves test) stimulation were quantified as clinical readout parameters. In the dextran sodium sulfate induced colitis model the loss of body weight, the colon lengths and the disease activity index were determined.

RESULTS

In the hind-paw edema model, systemic inactivation of the endogenous Alox15 gene intensified the inflammatory symptoms, whereas overexpression of human ALOX15 reduced the degree of hind-paw inflammation. These data suggest anti-inflammatory roles for endogenous and transgenic ALOX15 in this particular inflammation model. As mechanistic reason for the protective effect downregulation of the pro-inflammatory ALOX5 pathways was suggested. However, in the dextran sodium sulfate colitis model, in which systemic inactivation of the Alox15 gene protected female mice from DSS-induced colitis, transgenic overexpression of human ALOX15 did hardly impact the intensity of the inflammatory symptoms.

CONCLUSION

The biological role of ALOX15 in the pathogenesis of inflammation is variable and depends on the kind of the animal inflammation model.

Investigating the in vivo effect of Tribulus terrestris extract in middle cerebral artery occlusion rats using LC-MS-based metabolomics combined with molecular docking

Tribulus terrestris L. fruit (TT) is a traditional Chinese herbal medicine used to treat ischemic stroke (IS). This study aimed to investigate the protective effect of TT extract, named TT15, on middle cerebral artery occlusion (MCAO) rats using metabolomics and molecular docking and find the targets of action and the material basis of TT15 against IS. The results of the infarct volume and neurological defect scores confirmed the efficacy of TT15. Serum metabolomics analysis using LC-MS revealed that model group animals experienced a variety of metabolic disturbances when compared to the sham group. TT15 can restore the MCAO-induced serum metabolite changes by modulating multiple metabolic pathways. Six enzymes were highlighted by the metabolite-reaction-enzyme-gene (M-R-E-G) network analysis, which might be the possible targets for the TT15 against IS. Molecular docking analysis was applied to show the binding affinities between active compounds and these enzymes. The representative docking mode with the lowest binding energy between three compounds and phospholipase A 2 (PLA2) and peroxidase (POD) was displayed by the ribbon binding map. This study profiles the metabolic changes in MCAO-induced IS and investigates the efficacy and the corresponding mechanism of TT15 in the treatment of IS.

J147 Reduces tPA-Induced Brain Hemorrhage in Acute Experimental Stroke in Rats

Background and purpose

J147, a novel neurotrophic compound, was originally developed to treat aging-associated neurological diseases. Based on the broad spectrum of cytoprotective effects exhibited by this compound, we investigated whether J147 has cerebroprotection for acute ischemic stroke and whether it can enhance the effectiveness of thrombolytic therapy with tissue plasminogen activator (tPA).

Methods

Rats were subjected to transient occlusion of the middle cerebral artery (tMCAO) by insertion of an intraluminal suture or embolic middle cerebral artery occlusion (eMCAO), and treated intravenously with J147 alone or in combination with tPA.

Results

We found that J147 treatment significantly reduced infarct volume when administered at 2 h after stroke onset in the tMCAO model, but had no effect in eMCAO without tPA. However, combination treatment with J147 plus tPA at 4 h after stroke onset significantly reduced infarct volume and neurological deficits at 72 h after stroke compared with saline or tPA alone groups in the eMCAO model. Importantly, the combination treatment significantly reduced delayed tPA-associated brain hemorrhage and secondary microvascular thrombosis. These protective effects were associated with J147-mediated inhibition of matrix metalloproteinase-9 (MMP9), 15-lipoxygenase-1, and plasminogen activator inhibitor (PAI) expression in the ischemic hemispheres (predominantly in ischemic cerebral endothelium). Moreover, the combination treatment significantly reduced circulating platelet activation and platelet-leukocyte aggregation compared with saline or tPA alone groups at 24 h after stroke, which might also contribute to reduced microvascular thrombosis and neuroinflammation (as demonstrated by reduced neutrophil brain infiltration and microglial activation).

Conclusion

Our results demonstrate that J147 treatment alone exerts cerebral cytoprotective effects in a suture model of acute ischemic stroke, while in an embolic stroke model co-administration of J147 with tPA reduces delayed tPA-induced intracerebral hemorrhage and confers cerebroprotection. These findings suggest that J147-tPA combination therapy could be a promising approach to improving the treatment of ischemic stroke.

The Nrf2 Pathway in Ischemic Stroke: A Review

Ischemic stroke, characterized by the sudden loss of blood flow in specific area(s) of the brain, is the leading cause of permanent disability and is among the leading causes of death worldwide. The only approved pharmacological treatment for acute ischemic stroke (intravenous thrombolysis with recombinant tissue plasminogen activator) has significant clinical limitations and does not consider the complex set of events taking place after the onset of ischemic stroke (ischemic cascade), which is characterized by significant pro-oxidative events. The transcription factor Nuclear factor erythroid 2-related factor 2 (Nrf2), which regulates the expression of a great number of antioxidant and/or defense proteins, has been pointed as a potential pharmacological target involved in the mitigation of deleterious oxidative events taking place at the ischemic cascade. This review summarizes studies concerning the protective role of Nrf2 in experimental models of ischemic stroke, emphasizing molecular events resulting from ischemic stroke that are, in parallel, modulated by Nrf2. Considering the acute nature of ischemic stroke, we discuss the challenges in using a putative pharmacological strategy (Nrf2 activator) that relies upon transcription, translation and metabolically active cells in treating ischemic stroke patients.

Modulation of the Primary Astrocyte-Enriched Cultures' Oxylipin Profiles Reduces Neurotoxicity

Recently, manipulations with reactive astrocytes have been viewed as a new therapeutic approach that will enable the development of treatments for acute brain injuries and neurodegenerative diseases. Astrocytes can release several substances, which may exert neurotoxic or neuroprotective effects, but the nature of these substances is still largely unknown. In the present work, we tested the hypothesis that these effects may be attributed to oxylipins, which are synthesized from n-3 or n-6 polyunsaturated fatty acids (PUFAs). We used astrocyte-enriched cultures and found that: (1) lipid fractions secreted by lipopolysaccharide (LPS)-stimulated rat primary astrocyte-enriched cultures-possessed neurotoxic activity in rat primary neuronal cultures; (2) both of the tested oxylipin synthesis inhibitors, ML355 and Zileuton, reduce the LPS-stimulated release of interleukin 6 (IL-6) by astrocyte cultures, but only ML355 can change lipid fractions from neurotoxic to non-toxic; and (3) oxylipin profiles, measured by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) from neurotoxic and non-toxic lipid fractions, reveal a group of n-3 docosahexaenoic acid derivatives, hydroxydocosahexaenoic acids (HdoHEs)-4-HdoHE, 8-HdoHE, and 17-HdoHE, which may reflect the neuroprotective features of lipid fractions. Regulating the composition of astrocyte oxylipin profiles may be suggested as an approach for regulation of neurotoxicity in inflammatory processes.

Effects of ML351 and tissue plasminogen activator combination therapy in a rat model of focal embolic stroke

Thrombolytic stroke therapy with tissue plasminogen activator (tPA) is limited by risks of hemorrhagic transformation (HT). We have reported that a new 12/15-lipoxygenase (12/15-LOX) inhibitor ML351 reduced tPA related HT in mice subjected to experimental stroke under anticoagulation. In this study, we asked whether ML351 can ameliorate tPA induced HT in an embolic stroke model. Rats were subjected to embolic middle cerebral artery occlusion with 2 or 3 hr ischemia and tPA infusion, with or without ML351. Regional cerebral blood flow was monitored 2 hr after ischemia and continuously monitored for 1 hr after treatment for determining reperfusion. Hemoglobin was determined in brain homogenates and infarct volume was quantified at 24 hr after stroke.12/15-LOX, cluster of differentiation 68(CD68), immunoglobulin G (IgG), and tight junction proteins expression was detected by immunohistochemistry. ML351 significantly reduced tPA related hemorrhage after stroke without affecting its thrombolytic efficacy. ML351 also reduced blood-brain barrier disruption and improved preservation of junction proteins. ML351 and tPA combination improved neurological deficit of rats even though ML351 did not further reduce the infarct volume compared to tPA alone treated animals. Pro-inflammatory cytokines were suppressed by ML351 both in vivo and in vitro experiments. We further showed that ML351 suppressed the expression of c-Jun-N-terminal kinase (JNK) in brains and microglia cultures, whereas exogenous 12-HETE attenuated this effect in vitro. In conclusion, ML351 and tPA combination therapy is beneficial in ameliorating HT after ischemic stroke. This protective effect is probably because of 12/15-LOX inhibition and suppression of JNK-mediated microglia/macrophage activation.

Inflammation Drives Alzheimer's Disease: Emphasis on 5-lipoxygenase Pathways

It is a known fact that inflammation affects several physiological processes, including the functioning of the central nervous system. Additionally, impairment of lipid mechanisms/pathways have been associated with a number of neurodegenerative disorders and Alzheimer's Disease (AD) is one of them. However, much attention has been given to the link between tau and beta- amyloid hypothesis in AD pathogenesis/prognosis. Increasing evidences suggest that biologically active lipid molecules could influence the pathophysiology of AD via a different mechanism of inflammation. This review intends to highlight the role of inflammatory responses in the context of AD with the emphasis on biochemical pathways of lipid metabolism enzyme, 5-lipoxygenase (5- LO).

Lipoxins, RevD1 and 9, 13 HODE as the most important derivatives after an early incident of ischemic stroke

There is limited information available regarding the association of plasma free fatty acids (FFA) and inflammation mediators with ischemic stroke. At the same time, new treatment strategies are being pursued. The aim of this study was to carry out a thorough analysis of inflammation with multiple FFA-derivative mediators after and ischemic stroke and standard treatment. HPLC separations of 17 eicosanoids were performed using an Agilent Technologies 1,260 liquid chromatograph. The profiles of the esters of fatty acids were labelled by means of gas chromatography. FFA, and eicosanoid profiles in the group of patients after ischemic stroke significantly differed from the profile of the control group. Studies confirmed the involvement of derivative synthesis pathways responsible for the inflammation, especially palmitic acid (9 and 13 HODE), arachidonic acid, EPA and DHA. Arachidonic acid derivatives were synthesised on 5LOX, 15 LOX and COX pathways with the participation of prostaglandins while omega 3 derivatives strengthened the synthesis of resolvins, RevD1 in particular. The ability to accelerate the quenching of inflammation after ischemic stroke seems to be a promising strategy of stroke treatment in its early stage. In this context, our study points to lipoxins, RevD1, and 9, 13 HODE as the most important derivatives.

Cepharanthine attenuates cerebral ischemia/reperfusion injury by reducing NLRP3 inflammasome-induced inflammation and oxidative stress via inhibiting 12/15-LOX signaling

Cepharanthine (CEP) is a potential candidate for treatment of cerebral ischemia/reperfusion (I/R) injury, due to its anti-inflammatory and anti-oxidative properties. To investigate the effect of CEP on cerebral I/R injury, we established a mouse model of transient middle cerebral artery occlusion (tMCAO) and a microglia cell model of oxygen and glucose deprivation/reoxygenation (OGD/R). Administration of CEP attenuated neurological deficits, reduced infarct volume and edema, and decreased microglia activation in MCAO mice. Immunofluorescence staining showed an up-regulation in NLR Family Pyrin Domain Containing 3 (NLRP3) immunoreactivity in Iba1-labled microglia together with total Iba1 and NLRP3 expression in the brain following tMCAO, while down-regulated by CEP treatment. In both tMCAO-induced mice and OGD/R-treated BV-2 cells, CEP exhibited dose-dependent inhibition on the expression of NLRP3, ASC and cleaved caspase-1. Importantly, CEP attenuated tMCAO or OGD/R-induced overproduction of M1 microglia-regulated pro-inflammation cytokines IL-1β and IL-18, suggesting that CEP might involve in suppressing microglia polarization to M1 phenotype in vivo and in vitro. Moreover, CEP dose-dependently inhibited tMCAO-induced arachidonate 15 lipoxygenase (ALOX15) together with Iba1-labled microglia. The subsequent ALOX15-mediated oxidative stress was decreased by CEP treatment in vivo and in vitro, as evidenced by reduced ROS generation and MDA level, and increased SOD activity. Taken together, we demonstrate that CEP attenuates cerebral I/R injury probably by inhibiting microglia activation and NLRP3 inflammasome-induced inflammation and reducing oxidative stress via suppressing 12/15-LOX signaling.

New Quinolylnitrones for Stroke Therapy: Antioxidant and Neuroprotective ( Z)- N- tert-Butyl-1-(2-chloro-6-methoxyquinolin-3-yl)methanimine Oxide as a New Lead-Compound for Ischemic Stroke Treatment

We describe herein the synthesis and neuroprotective capacity of an array of 31 compounds comprising quinolyloximes, quinolylhydrazones, quinolylimines, QNs, and related heterocyclic azolylnitrones. Neuronal cultures subjected to oxygen-glucose deprivation (OGD), as experimental model for ischemic conditions, were treated with our molecules at the onset of recovery period after OGD and showed that most of these QNs, but not the azo molecules, improved neuronal viability 24 h after recovery. Especially, QN ( Z)- N-tert-butyl-1-(2-chloro-6-methoxyquinolin-3-yl)methanimine oxide (23) was shown as a very potent neuroprotective agent. Antioxidant analysis based on the ability of QN 23 to trap different types of toxic radical oxygenated species supported and confirmed its strong neuroprotective capacity. Finally, QN 23 showed also neuroprotection induction in two in vivo models of cerebral ischemia, decreasing neuronal death and reducing infarct size, allowing us to conclude that QN 23 can be considered as new lead-compound for ischemic stroke treatment.

Synthesis, neuroprotective and antioxidant capacity of PBN-related indanonitrones

In this work six PBN-related indanonitrones 1-6 have been designed, synthesized, and their neuroprotection capacity tested in vitro, under OGD conditions, in SH-SY5Y human neuroblastoma cell cultures. As a result, we have identified indanonitrones 1, 3 and 4 (EC₅₀ = 6.64 ± 0.28 μM) as the most neuroprotective agents, and in particular, among them, indanonitrone 4 was also the most potent and balanced nitrone, showing antioxidant activity in three experiments [LOX (100 μM), APPH (51%), DPPH (36.5%)], being clearly more potent antioxidant agent than nitrone PBN. Consequently, we have identified (Z)-5-hydroxy-N-methyl-2,3-dihydro-1H-inden-1-imine oxide (4) as a hit-molecule for further investigation.

CNB-001, a pleiotropic drug is efficacious in embolized agyrencephalic New Zealand white rabbits and ischemic gyrencephalic cynomolgus monkeys

Ischemic stroke is an acute neurodegenerative disease that is extremely devastating to patients, their families and society. Stroke is inadequately treated even with endovascular procedures and reperfusion therapy. Using an extensive translational screening process, we have developed a pleiotropic cytoprotective agent with the potential to positively impact a large population of brain ischemia patients and revolutionize the process used for the development of new drugs to treat complex brain disorders. In this unique translational study article, we document that the novel curcumin-based compound, CNB-001, when administered as a single intravenous dose, has significant efficacy to attenuate clinically relevant behavioral deficits following ischemic events in agyrencephalic rabbits when administered 1 h post-embolization and reduces infarct growth in gyrencephalic non-human primates, when administered 5 min after initiation of middle cerebral artery occlusion. CNB-001 is safe and does not increase morbidity or mortality in either research species. Mechanistically, CNB-001 inhibits human 5- and 15-lipoxygenase in vitro, and can attenuate ischemia-induced inflammatory markers, and oxidative stress markers, while potentially promoting synaptic plasticity mediated by enhanced brain-derived neurotrophic factor (BDNF).

Application of Docking Analysis in the Prediction and Biological Evaluation of the Lipoxygenase Inhibitory Action of Thiazolyl Derivatives of Mycophenolic Acid

5-LOX inhibition is among the desired characteristics of anti-inflammatory drugs, while 15-LOX has also been considered as a drug target. Similarity in inhibition behavior between soybean LOX-1 and human 5-LOX has been observed and soybean LOX (sLOX) type 1b has been used for the evaluation of LOX inhibition in drug screening for years. After prediction of LOX inhibition by PASS and docking as well as toxicity by PROTOX and ToxPredict sixteen (E)-N-(thiazol-2-yl)-6-(4-hydroxy-6-methoxy-7-methyl-3-oxo-1,3-dihydroisobenzofuran-5-yl)-4-methylhex-4-enamide derivatives with lengths varying from about 15⁻20 Å were evaluated in vitro for LOX inhibitory action using the soybean lipoxygenase sLOX 1b. Docking analysis was performed using soybean LOX L-1 (1YGE), soybean LOX-3 (1JNQ), human 5-LOX (3O8Y and 3V99) and mammalian 15-LOX (1LOX) structures. Different dimensions of target center and docking boxes and a cavity prediction algorithm were used. The compounds exhibited inhibitory action between 2.5 μΜ and 165 μΜ. Substituents with an electronegative atom at two-bond proximity to position 4 of the thiazole led to enhanced activity. Docking results indicated that the LOX structures 1JNQ, 3V99 and 1LOX can effectively be used for estimation of LOX inhibition and amino acid interactions of these compounds.

Computational Analysis of LOX1 Inhibition Identifies Descriptors Responsible for Binding Selectivity

Lipoxygenases are a family of cytosolic, peripheral membrane enzymes, which catalyze the hydroperoxidation of polyunsaturated fatty acids and are implicated in the pathogenesis of major human diseases. Over the years, a substantial number of scientific reports have introduced inhibitors active against one or another subtype of the enzyme, but the selectivity issue has proved to be a major challenge for drug design. In the present work, we assembled a dataset of 317 structurally diverse molecules hitherto reported as active against 15S-LOX1, 12S-LOX1, and 15S-LOX2 and identified, using supervised machine learning, a set of structural descriptors responsible for the binding selectivity toward the enzyme 15S-LOX1. We subsequently incorporated these descriptors in the training of QSAR models for LOX1 activity and selectivity. The best performing classifiers are two stacked models that include an ensemble of support vector machine, random forest, and k-nearest neighbor algorithms. These models not only can predict LOX1 activity/inactivity but also can discriminate with high accuracy between molecules that exhibit selective activity toward either one of the isozymes 15S-LOX1 and 12S-LOX1.

Polyunsaturated fatty acids and endocannabinoids in health and disease

Polyunsaturated fatty acids (PUFAs) are lipid derivatives of omega-3 (docosahexaenoic acid, DHA, and eicosapentaenoic acid, EPA) or of omega-6 (arachidonic acid, ARA) synthesized from membrane phospholipids and used as a precursor for endocannabinoids (ECs). They mediate significant effects in the fine-tune adjustment of body homeostasis. Phyto- and synthetic cannabinoids also rule the daily life of billions worldwide, as they are involved in obesity, depression and drug addiction. Consequently, there is growing interest to reveal novel active compounds in this field. Cloning of cannabinoid receptors in the 90s and the identification of the endogenous mediators arachidonylethanolamide (anandamide, AEA) and 2-arachidonyglycerol (2-AG), led to the characterization of the endocannabinoid system (ECS), together with their metabolizing enzymes and membrane transporters. Today, the ECS is known to be involved in diverse functions such as appetite control, food intake, energy balance, neuroprotection, neurodegenerative diseases, stroke, mood disorders, emesis, modulation of pain, inflammatory responses, as well as in cancer therapy. Western diet as well as restriction of micronutrients and fatty acids, such as DHA, could be related to altered production of pro-inflammatory mediators (e.g. eicosanoids) and ECs, contributing to the progression of cardiovascular diseases, diabetes, obesity, depression or impairing conditions, such as Alzheimer' s disease. Here we review how diets based in PUFAs might be linked to ECS and to the maintenance of central and peripheral metabolism, brain plasticity, memory and learning, blood flow, and genesis of neural cells.

CVD and Oxidative Stress

Nowadays, it is known that oxidative stress plays at least two roles within the cell, the generation of cellular damage and the involvement in several signaling pathways in its balanced normal state. So far, a substantial amount of time and effort has been expended in the search for a clear link between cardiovascular disease (CVD) and the effects of oxidative stress. Here, we present an overview of the different sources and types of reactive oxygen species in CVD, highlight the relationship between CVD and oxidative stress and discuss the most prominent molecules that play an important role in CVD pathophysiology. Details are given regarding common pharmacological treatments used for cardiovascular distress and how some of them are acting upon ROS-related pathways and molecules. Novel therapies, recently proposed ROS biomarkers, as well as future challenges in the field are addressed. It is apparent that the search for a better understanding of how ROS are contributing to the pathophysiology of CVD is far from over, and new approaches and more suitable biomarkers are needed for the latter to be accomplished.

12/15-Lipoxygenase Inhibition or Knockout Reduces Warfarin-Associated Hemorrhagic Transformation After Experimental Stroke

BACKGROUND AND PURPOSE

For stroke prevention, patients with atrial fibrillation typically receive oral anticoagulation. The commonly used anticoagulant warfarin increases the risk of hemorrhagic transformation (HT) when a stroke occurs; tissue-type plasminogen activator treatment is therefore restricted in these patients. This study was designed to test the hypothesis that 12/15-lipoxygenase (12/15-LOX) inhibition would reduce HT in warfarin-treated mice subjected to experimental stroke.

METHODS

Warfarin was dosed orally in drinking water, and international normalized ratio values were determined using a Coaguchek device. C57BL6J mice or 12/15-LOX knockout mice were subjected to transient middle cerebral artery occlusion with 3 hours severe ischemia (model A) or 2 hours ischemia and tissue-type plasminogen activator infusion (model B), with or without the 12/15-LOX inhibitor ML351. Hemoglobin was determined in brain homogenates, and hemorrhage areas on the brain surface and in brain sections were measured. 12/15-LOX expression was detected by immunohistochemistry.

RESULTS

Warfarin treatment resulted in reproducible increased international normalized ratio values and significant HT in both models. 12/15-LOX knockout mice suffered less HT after severe ischemia, and ML351 reduced HT in wild-type mice. When normalized to infarct size, ML351 still independently reduced hemorrhage. HT after tissue-type plasminogen activator was similarly reduced by ML351.

CONCLUSIONS

In addition to its benefits in infarct size reduction, 12/15-LOX inhibition also may independently reduce HT in warfarin-treated mice. ML351 should be further evaluated as stroke treatment in anticoagulated patients suffering a stroke, either alone or in conjunction with tissue-type plasminogen activator.

Targeting brain and peripheral plasticity of the lipidome in acute kainic acid-induced epileptic seizures in mice via quantitative mass spectrometry

Epilepsy is a highly common chronic neurological disorder, manifested in many different types, affecting ~1% of the worldwide human population. The molecular mechanisms of epileptogenesis have not yet been clarified, and pharmacoresistance exhibited by 30-40% of epilepsy patients remains a major obstacle in medical care. Growing evidence indicates a role of lipid signalling pathways in epileptogenesis, thus lipid signals emerge as potential biomarkers for the onset and evolving course of the epileptic disorder, as well as potential therapeutic agents and targets. For this purpose, we applied a lipidomic strategy to unravel lipid alterations in brain regions, periphery tissues and plasma that are specific for acute epileptic seizures in mice at 1h after seizure induction by systemic kainic acid injection as compared to vehicle controls. Specifically, levels of (i) selected phospholipids and sphingomyelins, (ii) the endocannabinoids anandamide (AEA) and 2-arachidonoyl glycerol (2-AG), and the endocannabinoid-related compounds oleoylethanolamide (OEA) and palmitoylethanolamide (PEA), (iii) arachidonic acid (AA), (iv) selected eicosanoids, and (v) fatty acyl content of lipidome were determined in pulverized tissues from six brain regions of kainic acid induced epileptic seizure models and vehicle controls: hypothalamus, hippocampus, thalamus, striatum, cerebellum and cerebral cortex, and from peripheral organs, such as heart and lungs, and in plasma. Alterations in lipid levels after acute epileptic seizures as compared to non-seizure controls were found to be brain region- and periphery tissue-specific, including specific plasma lipid correlates, highlighting their value as marker candidates in translational research studies, and/or drug discovery and response monitoring.

Increased 12/15-Lipoxygenase Leads to Widespread Brain Injury Following Global Cerebral Ischemia

Global ischemia following cardiac arrest is characterized by high mortality and significant neurological deficits in long-term survivors. Its mechanisms of neuronal cell death have only partially been elucidated. 12/15-lipoxygenase (12/15-LOX) is a major contributor to delayed neuronal cell death and vascular injury in experimental stroke, but a possible role in brain injury following global ischemia has to date not been investigated. Using a mouse bilateral occlusion model of transient global ischemia which produced surprisingly widespread injury to cortex, striatum, and hippocampus, we show here that 12/15-LOX is increased in a time-dependent manner in the vasculature and neurons of both cortex and hippocampus. Furthermore, 12/15-LOX co-localized with apoptosis-inducing factor (AIF), a mediator of non-caspase-related apoptosis in the cortex. In contrast, caspase-3 activation was more prevalent in the hippocampus. 12/15-lipoxygenase knockout mice were protected against global cerebral ischemia compared to wild-type mice, accompanied by reduced neurologic impairment. The lipoxygenase inhibitor LOXBlock-1 similarly reduced neuronal cell death both when pre-administered and when given at a therapeutically relevant time point 1 h after onset of ischemia. These findings suggest a pivotal role for 12/15-LOX in both caspase-dependent and caspase-independent apoptotic pathways following global cerebral ischemia and suggest a novel therapeutic approach to reduce brain injury following cardiac arrest.

Activity-Based Probes for 15-Lipoxygenase-1

Human 15-lipoxygenase-1 (15-LOX-1) plays an important role in several inflammatory lung diseases, such as asthma, COPD, and chronic bronchitis, as well as various CNS diseases, such as Alzheimer's disease, Parkinson's disease, and stroke. Activity-based probes of 15-LOX-1 are required to explore the role of this enzyme further and to enable drug discovery. In this study, we developed a 15-LOX-1 activity-based probe for the efficient activity-based labeling of recombinant 15-LOX-1. 15-LOX-1-dependent labeling in cell lysates and tissue samples was also possible. To mimic the natural substrate of the enzyme, we designed activity-based probes that covalently bind to the active enzyme and include a terminal alkene as a chemical reporter for the bioorthogonal linkage of a detectable functionality through an oxidative Heck reaction. The activity-based labeling of 15-LOX-1 should enable the investigation and identification of this enzyme in complex biological samples, thus opening up completely new opportunities for drug discovery.

Human 15-LOX-1 active site mutations alter inhibitor binding and decrease potency

Human 15-lipoxygenase-1 (h15-LOX-1 or h12/15-LOX) reacts with polyunsaturated fatty acids and produces bioactive lipid derivatives that are implicated in many important human diseases. One such disease is stroke, which is the fifth leading cause of death and the first leading cause of disability in America. The discovery of h15-LOX-1 inhibitors could potentially lead to novel therapeutics in the treatment of stroke, however, little is known about the inhibitor/active site interaction. This study utilizes site-directed mutagenesis, guided in part by molecular modeling, to gain a better structural understanding of inhibitor interactions within the active site. We have generated eight mutants (R402L, R404L, F414I, F414W, E356Q, Q547L, L407A, I417A) of h15-LOX-1 to determine whether these active site residues interact with two h15-LOX-1 inhibitors, ML351 and an ML094 derivative, compound 18. IC₅₀ values and steady-state inhibition kinetics were determined for the eight mutants, with four of the mutants affecting inhibitor potency relative to wild type h15-LOX-1 (F414I, F414W, E356Q and L407A). The data indicate that ML351 and compound 18, bind in a similar manner in the active site to an aromatic pocket close to F414 but have subtle differences in their specific binding modes. This information establishes the binding mode for ML094 and ML351 and will be leveraged to develop next-generation inhibitors.

Design of a novel thiophene inhibitor of 15-lipoxygenase-1 with both anti-inflammatory and neuroprotective properties

The enzyme 15-lipoxygenase-1 (15-LOX-1) plays a dual role in diseases with an inflammatory component. On one hand 15-LOX-1 plays a role in pro-inflammatory gene expression and on the other hand it has been shown to be involved in central nervous system (CNS) disorders by its ability to mediate oxidative stress and damage of mitochondrial membranes under hypoxic conditions. In order to further explore applications in the CNS, novel 15-LOX-1 inhibitors with favorable physicochemical properties need to be developed. Here, we present Substitution Oriented Screening (SOS) in combination with Multi Component Chemistry (MCR) as an effective strategy to identify a diversely substituted small heterocyclic inhibitors for 15-LOX-1, denoted ThioLox, with physicochemical properties superior to previously identified inhibitors. Ex vivo biological evaluation in precision-cut lung slices (PCLS) showed inhibition of pro-inflammatory gene expression and in vitro studies on neuronal HT-22 cells showed a strong protection against glutamate toxicity for this 15-LOX-1 inhibitor. This provides a novel approach to identify novel small with favorable physicochemical properties for exploring 15-LOX-1 as a drug target in inflammatory diseases and neurodegeneration.

A potent and selective inhibitor targeting human and murine 12/15-LOX

Human reticulocyte 12/15-lipoxygenase (h12/15-LOX) is a lipid-oxidizing enzyme that can directly oxidize lipid membranes in the absence of a phospholipase, leading to a direct attack on organelles, such as the mitochondria. This cytotoxic activity of h12/15-LOX is up-regulated in neurons and endothelial cells after a stroke and thought to contribute to both neuronal cell death and blood-brain barrier leakage. The discovery of inhibitors that selectively target recombinant h12/15-LOX in vitro, as well as possessing activity against the murine ortholog ex vivo, could potentially support a novel therapeutic strategy for the treatment of stroke. Herein, we report a new family of inhibitors discovered in a High Throughput Screen (HTS) that are selective and potent against recombinant h12/15-LOX and cellular mouse 12/15-LOX (m12/15-LOX). MLS000099089 (compound 99089), the parent molecule, exhibits an IC50 potency of 3.4±0.5 μM against h12/15-LOX in vitro and an ex vivo IC50 potency of approximately 10 μM in a mouse neuronal cell line, HT-22. Compound 99089 displays greater than 30-fold selectivity versus h5-LOX and COX-2, 15-fold versus h15-LOX-2 and 10-fold versus h12-LOX, when tested at 20 μM inhibitor concentration. Steady-state inhibition kinetics reveals that the mode of inhibition of 99089 against h12/15-LOX is that of a mixed inhibitor with a Kic of 1.0±0.08 μM and a Kiu of 6.0±3.3 μM. These data indicate that 99089 and related derivatives may serve as a starting point for the development of anti-stroke therapeutics due to their ability to selectively target h12/15-LOX in vitro and m12/15-LOX ex vivo.

LOX1 inhibition with small molecules

Lipoxygenases (LOXs) are nonheme, iron-containing dioxygenases that catalyze the dioxygenation of polyunsaturated fatty acids and are widely distributed among plant and animal species. Human LOXs, now identified as key enzymes in the pathogenesis of major disorders, have increasingly drawn the attention as targets and great effort has been made for the discovery and design of suitable inhibitors, to which end both pharmacological and computational methods have been employed. In the present work, using pharmacophore modeling and docking, we attempt to elucidate the inhibition of LOX1 with a new inhibitor, albidoside, an iridoid glucoside isolated from plants of the Scutellaria genus. Through a pharmacophore approach, complementarities between the ligand and the binding site are explored and a plausible mode of binding with the protein is suggested for albidoside.

STAT-dependent upregulation of 12/15-lipoxygenase contributes to neuronal injury after stroke

Oxidative stress is a major brain injury mechanism after ischemic stroke. 12/15-lipoxygenase (12/15-LOX) is a key mediator of oxidative stress, contributing to neuronal cell death and vascular leakage. Nonetheless, the mechanism leading to its upregulation is currently unknown. We show here that Signal Transducers and Activators of Transcription (STATs), specifically STAT6 and possibly STAT1, increase transcription of 12/15-LOX in neuronal cells. Both p-STAT6 and -1 bound to specific STAT binding sites in the mouse 12/15-LOX promoter. Small interfering RNA (siRNA) knockdown showed STAT6 to be the dominant regulator, reducing 12/15-LOX promoter activation and cell death in oxidatively stressed HT22 cells. STAT6 siRNA efficiently prevented the increase of 12/15-LOX in murine primary neurons, both after induction of oxidative stress and after oxygen-glucose deprivation. Early activation of STAT6 and STAT1 in mice was consistent with a role in regulating 12/15-LOX in focal ischemia. Brains of human stroke patients showed increased p-STAT6 and p-STAT1 in the peri-infarct region, along with 12/15-LOX and markers of apoptosis. These results link STAT6 and STAT1 to the 12/15-LOX damage pathway and suggest disregulation of STAT-dependent transcription as injury mechanism in stroke. Selectively targeting STATs may thus be a novel therapeutic approach to reducing brain injury after a stroke.

The role of lipoxygenases in pathophysiology; new insights and future perspectives

Lipoxygenases (LOXs) are dioxygenases that catalyze the formation of corresponding hydroperoxides from polyunsaturated fatty acids such as linoleic acid and arachidonic acid. LOX enzymes are expressed in immune, epithelial, and tumor cells that display a variety of physiological functions, including inflammation, skin disorder, and tumorigenesis. In the humans and mice, six LOX isoforms have been known. 15-LOX, a prototypical enzyme originally found in reticulocytes shares the similarity of amino acid sequence as well as the biochemical property to plant LOX enzymes. 15-LOX-2, which is expressed in epithelial cells and leukocytes, has different substrate specificity in the humans and mice, therefore, the role of them in mammals has not been established. 12-LOX is an isoform expressed in epithelial cells and myeloid cells including platelets. Many mutations in this isoform are found in epithelial cancers, suggesting a potential link between 12-LOX and tumorigenesis. 12R-LOX can be found in the epithelial cells of the skin. Defects in this gene result in ichthyosis, a cutaneous disorder characterized by pathophysiologically dried skin due to abnormal loss of water from its epithelial cell layer. Similarly, eLOX-3, which is also expressed in the skin epithelial cells acting downstream 12R-LOX, is another causative factor for ichthyosis. 5-LOX is a distinct isoform playing an important role in asthma and inflammation. This isoform causes the constriction of bronchioles in response to cysteinyl leukotrienes such as LTC4, thus leading to asthma. It also induces neutrophilic inflammation by its recruitment in response to LTB4. Importantly, 5-LOX activity is strictly regulated by 5-LOX activating protein (FLAP) though the distribution of 5-LOX in the nucleus. Currently, pharmacological drugs targeting FLAP are actively developing. This review summarized these functions of LOX enzymes under pathophysiological conditions in mammals.

Structural and functional biology of arachidonic acid 15-lipoxygenase-1 (ALOX15)

Lipoxygenases (LOX) form a family of lipid peroxidizing enzymes, which have been implicated in a number of physiological processes and in the pathogenesis of inflammatory, hyperproliferative and neurodegenerative diseases. They occur in two of the three domains of terrestrial life (bacteria, eucarya) and the human genome involves six functional LOX genes, which encode for six different LOX isoforms. One of these isoforms is ALOX15, which has first been described in rabbits in 1974 as enzyme capable of oxidizing membrane phospholipids during the maturational breakdown of mitochondria in immature red blood cells. During the following decades ALOX15 has extensively been characterized and its biological functions have been studied in a number of cellular in vitro systems as well as in various whole animal disease models. This review is aimed at summarizing the current knowledge on the protein-chemical, molecular biological and enzymatic properties of ALOX15 in various species (human, mouse, rabbit, rat) as well as its implication in cellular physiology and in the pathogenesis of various diseases.

Mammalian lipoxygenases and their biological relevance

Lipoxygenases (LOXs) form a heterogeneous class of lipid peroxidizing enzymes, which have been implicated not only in cell proliferation and differentiation but also in the pathogenesis of various diseases with major public health relevance. As other fatty acid dioxygenases LOXs oxidize polyunsaturated fatty acids to their corresponding hydroperoxy derivatives, which are further transformed to bioactive lipid mediators (eicosanoids and related substances). On the other hand, lipoxygenases are key players in the regulation of the cellular redox homeostasis, which is an important element in gene expression regulation. Although the first mammalian lipoxygenases were discovered 40 years ago and although the enzymes have been well characterized with respect to their structural and functional properties the biological roles of the different lipoxygenase isoforms are not completely understood. This review is aimed at summarizing the current knowledge on the physiological roles of different mammalian LOX-isoforms and their patho-physiological function in inflammatory, metabolic, hyperproliferative, neurodegenerative and infectious disorders. This article is part of a Special Issue entitled "Oxygenated metabolism of PUFA: analysis and biological relevance".

Potent and selective inhibitors of human reticulocyte 12/15-lipoxygenase as anti-stroke therapies

A key challenge facing drug discovery today is variability of the drug target between species, such as with 12/15-lipoxygenase (12/15-LOX), which contributes to ischemic brain injury, but its human and rodent isozymes have different inhibitor specificities. In the current work, we have utilized a quantitative high-throughput (qHTS) screen to identify compound 1 (ML351), a novel chemotype for 12/15-LOX inhibition that has nanomolar potency (IC₅₀ = 200 nM) against human 12/15-LOX and is protective against oxidative glutamate toxicity in mouse neuronal HT22 cells. In addition, it exhibited greater than 250-fold selectivity versus related LOX isozymes, was a mixed inhibitor, and did not reduce the active-site ferric ion. Lastly, 1 significantly reduced infarct size following permanent focal ischemia in a mouse model of ischemic stroke. As such, this represents the first report of a selective inhibitor of human 12/15-LOX with demonstrated in vivo activity in proof-of-concept mouse models of stroke.

12/15-lipoxygenase expression is increased in oligodendrocytes and microglia of periventricular leukomalacia

Oxidative stress involving premyelinating oligodendrocytes (OLs) is a major factor in the pathogenesis of preterm white matter injury. In animal and cell culture studies, activation of the lipid-oxidizing enzyme 12/15-lipoxygenase (12/15-LOX) plays a central role as an inflammatory mediator in the pathology of oxidative stress and OL cell death, as well as ischemia and neuronal death. The role of 12/15-LOX, however, is unclear in the developing human brain. The mechanism of 12/15-LOX involves the production of reactive oxygen species through the metabolism of arachidonic acid, as well as direct detrimental effects on organelle membranes. Here we tested the hypothesis that the density of 12/15-LOX-expressing cells is increased in periventricular leukomalacia (PVL). Using immunocytochemistry (ICC) in human paraffin-embedded tissue, 12/15-LOX expression was seen in macrophages of the focally necrotic lesions in the periventricular white matter, as well as in glial cells throughout the surrounding white matter with reactive gliosis. Interestingly, no significant 12/15-LOX expression was detected in neurons in the cerebral cortex overlying the damaged white matter. Using a scoring system from 0 to 3, we assessed the density of 12/15-LOX-expressing cells in diffusely gliotic white matter from 20 to 43 postconceptional (PC) weeks in 19 PVL cases (median = 36 PC weeks) and 10 control (non-PVL) cases (median = 34 PC weeks). The density of 12/15-LOX-positive cells was significantly increased in the diffuse component of PVL (score = 1.17 ± 0.15) compared to controls (score = 0.48 ± 0.21; p = 0.014). Using double-label ICC, 12/15-LOX was observed in PVL in OLs of the O4 and O1 premyelinating stages, as well as in mature OLs as determined with the mature OL marker adenomatous polyposis coli (APC). In addition, 12/15-LOX expression was present in a population of CD68-positive activated microglia. There was no 12/15-LOX expression in reactive astrocytes. Finally we observed terminal deoxynucleotide transferase dUTP nick end-labeling-positive cells within the white matter of PVL that expressed 12/15-LOX and/or within close proximity of 12/15-LOX-positive cells. Our data support a role for 12/15-LOX activation as an inflammatory mediator of injury in PVL, with a contribution of 12/15-LOX to PVL-induced damage to or cell death of OLs, including those at the O1 and O4 stages.