5-lipoxygenase-derived leukotrienes: mediators also of atherosclerotic inflammation

Genetically predicted allergic rhinitis causally increases the risk of erectile dysfunction

Objective

Evidence shows that allergic rhinitis (AR) may increase the risk of erectile dysfunction (ED). This study aims to investigate whether there is a causal relationship between AAR and ED by Mendelian randomization (MR) analysis.

Methods

We performed a two-sample MR analysis using genome-wide association studies (GWAS) summary data. Single nucleotide polymorphisms (SNPs) associated with AR and ED were obtained from the GWAS database. The MR analysis primarily employed the inverse variance weighted (IVW), MR Egger, and weighted median (WM) methods. We assessed pleiotropy using the MR-PRESSO global test and MR-Egger regression. Cochran's Q test was used to evaluate heterogeneity, and a leave-one-out analysis was performed to verify the robustness and reliability of the results.

Results

The IVW analysis demonstrated a positive association between genetic susceptibility to AR and an elevated relative risk of ED (IVW OR = 1.40, p = 0.01, 95% CI 1.08-1.80). The results obtained from MR-Egger regression and WM methods exhibited a consistent trend with the results of the IVW method. Sensitivity analyses showed no evidence of heterogeneity nor horizontal pleiotropy. The leave-one-out analysis showed that the findings remained robust and were unaffected by any instrumental variables.

Conclusion

This study presents genetic evidence that indicates a causal association between AR and ED.

Signaling lipids as diagnostic biomarkers for ocular surface cicatrizing conjunctivitis

Abstract

Metabolomics has been applied to diagnose diseases, predict disease progression, and design therapeutic strategies in various areas of medicine. However, it remains to be applied to the ocular surface diseases, where biological samples are often of limited quantities. We successfully performed proof-of-concept metabolomics assessment of volume-limited cytology samples from a clinical form of chronic inflammatory cicatrizing conjunctivitis, i.e., ocular MMP and discovered metabolic changes of signaling lipid mediators upon disease onset and progression. The metabolomics assessment revealed active oxylipins, lysophospholipids, fatty acids, and endocannabinoids alterations, from which potential biomarkers linked to inflammatory processes were identified. Possible underlying mechanisms such as dysregulated enzyme activities (e.g., lipoxygenases, cytochrome P450, and phospholipases) were suggested which may be considered as potential therapeutic targets in future studies.

Key messages

Metabolic profile of the ocular surface can be measured using impression cytology samples.

Metabolomics analysis of ocular pemphigoid is presented for the first time.

The metabolomics assessment of OCP patients revealed active oxylipins, lysophospholipids, fatty acids, and endocannabinoids alterations.

Several oxylipins are identified as diagnostic biomarkers for OCP.

A Novel Inhibitor of 5-Lipoxygenase (5-LOX) Prevents Oxidative Stress-Induced Cell Death of Retinal Pigment Epithelium (RPE) Cells

PURPOSE

5-Lipoxygenase (5-LOX) oxygenates arachidonic acid to form 5-hydroperoxyeicosatetraenoic acid, which is further converted into biologically detrimental leukotrienes, such as leukotriene B4 (LTB4). The RPE and retina express the PNPLA2 gene for pigment epithelium-derived factor receptor (PEDF-R), a lipase involved in cell survival. The purpose here was to investigate the role of PEDF-R on the 5-LOX pathway in oxidative stress of RPE.

METHODS

Lipoxygenase activity assays were performed with soybean and potato lipoxygenase. Binding was evaluated by peptide-affinity chromatography and pull-down assays with PEDF-R-derived synthetic peptides or recombinant protein. Oxidative stress was induced in human ARPE-19 and primary pig RPE cells with indicated concentrations of H2O2/TNF-α. Reverse transcription-PCR of ALOX5 and PNPLA2 genes was performed. Cell viability and death rates were determined using respective biomarkers. Leukotriene B4 levels were measured by ELISA.

RESULTS

Among five peptides spanning between positions Leu159 and Met325 of human PEDF-R polypeptide, only two overlapping peptides, E5b and P1, bound and inhibited lipoxygenase activity. Human recombinant 5-LOX bound specifically to peptide P1 and to His6/Xpress-tagged PEDF-R via ionic interactions. The two inhibitor peptides E5b and P1 promoted cell viability and decreased cell death of RPE cells undergoing oxidative stress. Oxidative stress decreased the levels of PNPLA2 transcripts with no effect on ALOX5 expression. Exogenous additions of P1 peptide or overexpression of the PNPLA2 gene decreased both LTB4 levels and death of RPE cells undergoing oxidative stress.

CONCLUSIONS

A novel peptide region of PEDF-R inhibits 5-LOX, which intersects with RPE cell death pathways induced by oxidative stress.

Method to Visualize and Analyze Membrane Interacting Proteins by Transmission Electron Microscopy

Monotopic proteins exert their function when attached to a membrane surface, and such interactions depend on the specific lipid composition and on the availability of enough area to perform the function. Nanodiscs are used to provide a membrane surface of controlled size and lipid content. In the absence of bound extrinsic proteins, sodium phosphotungstate-stained nanodiscs appear as stacks of coins when viewed from the side by transmission electron microscopy (TEM). This protocol is therefore designed to intentionally promote stacking; consequently, the prevention of stacking can be interpreted as the binding of the membrane-binding protein to the nanodisc. In a further step, the TEM images of the protein-nanodisc complexes can be processed with standard single-particle methods to yield low-resolution structures as a basis for higher resolution cryoEM work. Furthermore, the nanodiscs provide samples suitable for either TEM or non-denaturing gel electrophoresis. To illustrate the method, Ca²⁺-induced binding of 5-lipoxygenase on nanodiscs is presented.

Metabolic signatures of extreme longevity in northern Italian centenarians reveal a complex remodeling of lipids, amino acids, and gut microbiota metabolism

The aging phenotype in humans has been thoroughly studied but a detailed metabolic profiling capable of shading light on the underpinning biological processes of longevity is still missing. Here using a combined metabonomics approach compromising holistic (1)H-NMR profiling and targeted MS approaches, we report for the first time the metabolic phenotype of longevity in a well characterized human aging cohort compromising mostly female centenarians, elderly, and young individuals. With increasing age, targeted MS profiling of blood serum displayed a marked decrease in tryptophan concentration, while an unique alteration of specific glycerophospholipids and sphingolipids are seen in the longevity phenotype. We hypothesized that the overall lipidome changes specific to longevity putatively reflect centenarians' unique capacity to adapt/respond to the accumulating oxidative and chronic inflammatory conditions characteristic of their extreme aging phenotype. Our data in centenarians support promotion of cellular detoxification mechanisms through specific modulation of the arachidonic acid metabolic cascade as we underpinned increased concentration of 8,9-EpETrE, suggesting enhanced cytochrome P450 (CYP) enzyme activity. Such effective mechanism might result in the activation of an anti-oxidative response, as displayed by decreased circulating levels of 9-HODE and 9-oxoODE, markers of lipid peroxidation and oxidative products of linoleic acid. Lastly, we also revealed that the longevity process deeply affects the structure and composition of the human gut microbiota as shown by the increased extrection of phenylacetylglutamine (PAG) and p-cresol sulfate (PCS) in urine of centenarians. Together, our novel approach in this representative Italian longevity cohort support the hypothesis that a complex remodeling of lipid, amino acid metabolism, and of gut microbiota functionality are key regulatory processes marking exceptional longevity in humans.

Metabolic signatures of extreme longevity in northern Italian centenarians reveal a complex remodeling of lipids, amino acids, and gut microbiota metabolism

The aging phenotype in humans has been thoroughly studied but a detailed metabolic profiling capable of shading light on the underpinning biological processes of longevity is still missing. Here using a combined metabonomics approach compromising holistic ¹H-NMR profiling and targeted MS approaches, we report for the first time the metabolic phenotype of longevity in a well characterized human aging cohort compromising mostly female centenarians, elderly, and young individuals. With increasing age, targeted MS profiling of blood serum displayed a marked decrease in tryptophan concentration, while an unique alteration of specific glycerophospholipids and sphingolipids are seen in the longevity phenotype. We hypothesized that the overall lipidome changes specific to longevity putatively reflect centenarians' unique capacity to adapt/respond to the accumulating oxidative and chronic inflammatory conditions characteristic of their extreme aging phenotype. Our data in centenarians support promotion of cellular detoxification mechanisms through specific modulation of the arachidonic acid metabolic cascade as we underpinned increased concentration of 8,9-EpETrE, suggesting enhanced cytochrome P450 (CYP) enzyme activity. Such effective mechanism might result in the activation of an anti-oxidative response, as displayed by decreased circulating levels of 9-HODE and 9-oxoODE, markers of lipid peroxidation and oxidative products of linoleic acid. Lastly, we also revealed that the longevity process deeply affects the structure and composition of the human gut microbiota as shown by the increased extrection of phenylacetylglutamine (PAG) and p-cresol sulfate (PCS) in urine of centenarians. Together, our novel approach in this representative Italian longevity cohort support the hypothesis that a complex remodeling of lipid, amino acid metabolism, and of gut microbiota functionality are key regulatory processes marking exceptional longevity in humans.

Solid-phase parallel synthesis of drug-like artificial 2H-benzopyran libraries

This review covers the construction of drug-like 2H-benzopyrans and related libraries using solid-phase parallel synthesis. In this context, the preparation of substituted benzopyrans such as mono-, di- and trisubstituted benzopyran derivatives and additional ring-fused benzopyrans such as benzopyranoisoxazoles, benzopyranopyrazoles, six-membered ring-fused benzopyrans, and polycyclic benzopyrans are highlighted.

Association of Sp1 tandem repeat polymorphism of ALOX5 with coronary artery disease in Indian subjects

Lipoxygenases have been implicated in the pathogenesis of coronary artery disease (CAD) for its potent proinflammatory role. The Sp1 addition/deletion polymorphism in promoter region of the 5-lipoxygenase gene (ALOX5) has been associated with increased risk of carotid atherosclerosis and myocardial infarction. To determine the role of this polymorphism in our population we performed a case-control-genetic association study on 117 healthy controls and 119 angiographically verified CAD patients. Biochemical analysis was performed using standard automated assays. High-density lipoprotein cholesterol (HDL-C) and LDL-C subfraction levels were estimated using precipitation methods. Genotyping of polymorphism in the ALOX5 (Sp1 variants) was done using PCR-based heteroduplex analysis and automated sequencing. The Sp1 promoter repeat variants were found to be associated with CAD (p < 0.0001, OR = 4.47, 95% confidence interval = 2.58-7.74). Furthermore, the 5/5 genotype of the ALOX5 polymorphism in the healthy subjects was found to be associated with elevated HDL-C (p= 0.004), HDL(3) -C (p= 0.04), apo A1 (p= 0.011) and sdLDL (p= 0.001). We conclude that this polymorphism influences LDL and HDL subfraction levels and is a risk factor for CAD in our population. Clin Trans Sci 2012; Volume 5: 408-411.

Evidence for activation of inflammatory lipoxygenase pathways in visceral adipose tissue of obese Zucker rats

Central obesity is associated with low-grade inflammation that promotes type 2 diabetes and cardiovascular disease in obese individuals. The 12- and 5-lipoxygenase (12-LO and 5-LO) enzymes have been linked to inflammatory changes, leading to the development of atherosclerosis. 12-LO has also been linked recently to inflammation and insulin resistance in adipocytes. We analyzed the expression of LO and proinflammatory cytokines in adipose tissue and adipocytes in obese Zucker rats, a widely studied genetic model of obesity, insulin resistance, and the metabolic syndrome. mRNA expression of 12-LO, 5-LO, and 5-LO-activating protein (FLAP) was upregulated in adipocytes and adipose tissue from obese Zucker rats compared with those from lean rats. Concomitant with increased LO gene expression, the 12-LO product 12-HETE and the 5-LO products 5-HETE and leukotriene B4 (LTB4) were also increased in adipocytes. Furthermore, upregulation of key proinflammatory markers interleukin (IL)-6, TNFα, and monocyte chemoattractant protein-1 were observed in adipocytes isolated from obese Zucker rats. Immunohistochemistry indicated that the positive 12-LO staining in adipose tissue represents cells in addition to adipocytes. This was confirmed by Western blotting in stromal vascular fractions. These changes were in part reversed by the novel anti-inflammatory drug lisofylline (LSF). LSF also reduced p-STAT4 in visceral adipose tissue from obese Zucker rats and improved the metabolic profile, reducing fasting plasma glucose and increasing insulin sensitivity in obese Zucker rats. In 3T3-L1 adipocytes, LSF abrogated the inflammatory response induced by LO products. Thus, therapeutic agents reducing LO or STAT4 activation may provide novel tools to reduce obesity-induced inflammation.

Functional and pathological roles of the 12- and 15-lipoxygenases

The 12/15-lipoxygenase enzymes react with fatty acids producing active lipid metabolites that are involved in a number of significant disease states. The latter include type 1 and type 2 diabetes (and associated complications), cardiovascular disease, hypertension, renal disease, and the neurological conditions Alzheimer's disease and Parkinson's disease. A number of elegant studies over the last thirty years have contributed to unraveling the role that lipoxygenases play in chronic inflammation. The development of animal models with targeted gene deletions has led to a better understanding of the role that lipoxygenases play in various conditions. Selective inhibitors of the different lipoxygenase isoforms are an active area of investigation, and will be both an important research tool and a promising therapeutic target for treating a wide spectrum of human diseases.

Design and synthesis of an all-in-one 3-(1,1-difluoroprop-2-ynyl)-3H-diazirin-3-yl functional group for photo-affinity labeling

A novel radioisotope-free photo-affinity probe containing the 3-(1,1-difluoroprop-2-ynyl)-3H-diazirin-3-yl functional group was designed and synthesized. This very compact functionality is envisaged to allow photochemically-induced coupling of a compound to its target followed by click reaction coupling with an azido-biotin reagent in order to facilitate purification of the labeled target. In a proof-of-concept study we have shown that 3-(1,1-difluoroprop-2-ynyl)-3H-diazirin-3-yl functional group could be photolyzed to efficiently furnish the methanol adduct 23 and that the generated highly unstable carbene does not react with the neighboring acetylene moiety. A subsequent click reaction with the azido-biotin derivative 25 proceeded smoothly to give triazole 26. This chemical probe should thus be of unique value for facilitating identification of the molecular structure of the target of a bioactive compound.

Insulin and glucose play a role in foam cell formation and function

Background

Foam cell formation in diabetic patients often occurs in the presence of high insulin and glucose levels. To test whether hyperinsulinemic hyperglycemic conditions affect foam cell differentiation, we examined gene expression, cytokine production, and Akt phosphorylation in human monocyte-derived macrophages incubated with two types of oxidized low density lipoprotein (LDL), minimally modified LDL (mmLDL) and extensively oxidized LDL (OxLDL).

Methods and results

Using Affymetrix GeneChip^® arrays, we found that several genes directly related to insulin signaling were changed. The insulin receptor and glucose-6-phosphate dehydrogenase were upregulated by mmLDL and OxLDL, whereas insulin-induced gene 1 was significantly down-regulated. In hyperinsulinemic hyperglycemic conditions, modified LDL upregulated Akt phosphorylation and expression of the insulin-regulated aminopeptidase. The level of proinflammatory cytokines, IL-lβ, IL-12, and IL-6, and of a 5-lipoxygenase eicosanoid, 5-hydroxyeicosatetraenoic acid (5-HETE), was also increased.

Conclusion

These results suggest that the exposure of macrophages to modified low density lipoproteins in hyperglycemic hyperinsulinemic conditions affects insulin signaling and promotes the release of proinflammatory stimuli, such as cytokines and eicosanoids. These in turn may contribute to the development of insulin resistance.

Cholesterol and its anionic derivatives inhibit 5-lipoxygenase activation in polymorphonuclear leukocytes and MonoMac6 cells

5-Lipoxygenase (5-LO) is the key enzyme in the biosynthesis of leukotrienes (LTs), biological mediators of host defense reactions and of inflammatory diseases. While the role of membrane binding in the regulation of 5-LO activity is well established, the effects of lipids on cellular activity when added to the medium has not been characterized. Here, we show such a novel function of the most abundant sulfated sterol in human blood, cholesterol sulfate (CS), to suppress LT production in human polymorphonuclear leukocytes (PMNL) and Mono Mac6 cells. We synthesized another anionic lipid, cholesterol phosphate, which demonstrated a similar capacity in suppression of LT synthesis in PMNL. Cholesteryl acetate was without effect. Cholesterol increased the effect of CS on 5-LO product synthesis. CS and cholesterol also inhibited arachidonic acid (AA) release from PMNL. Addition of exogenous AA increased the threshold concentration of CS required to inhibit LT synthesis. The effect of cholesterol and its anionic derivatives can arise from remodeling of the cell membrane, which interferes with 5-LO activation. The fact that cellular LT production is regulated by sulfated cholesterol highlights a possible regulatory role of sulfotransferases/sulfatases in 5-LO product synthesis.

Development of 5-lipoxygenase inhibitors--lessons from cellular enzyme regulation

5-Lipoxygenase (5-LO) catalyzes the first steps in the conversion of arachidonic acid (AA) into leukotrienes (LTs) that are mediators of inflammatory and allergic reactions. Recently, the 5-LO pathway has also been associated with atherosclerosis and osteoporosis. Thus, in addition to the classical applications including asthma and allergic disorders, LT synthesis inhibitors might be of interest for the treatment of cardiovascular diseases and osteoporosis. Recently, it has been shown that cellular 5-LO activity is regulated in a complex manner that can involve different signalling pathways. 5-LO can be activated by an increase in intracellular Ca2+ concentration, diacylglycerols, phosphorylation by MAPKAP kinase-2 and ERK. Previous work could demonstrate that cellular 5-LO activity is repressed in a protein kinase A-dependent manner and by glutathione peroxidases. This comment focuses on the impact of these stimulatory and inhibitory pathways on the efficacy of 5-LO inhibitors and suggests additional criteria for the development of this class of compounds.

Mutation analysis of the human 5-lipoxygenase C-terminus: support for a stabilizing C-terminal loop

Lipoxygenases contain prosthetic iron, in human 5-lipoxygenase (5LO) the C-terminal isoleucine carboxylate constitutes one of five identified ligands. ATP is one of several factors determining 5LO activity. We compared properties of a series of 5LO C-terminal deletion mutants (one to six amino acid residues deleted). All mutants were enzymatically inactive (expected due to loss of iron), but expression yield (in E. coli) and affinity to ATP-agarose was markedly different. Deletion of up to four C-terminal residues was compatible with good expression and retained affinity to the ATP-column, as for wild-type 5LO. However when also the fifth residue was deleted (Asn-669) expression yield decreased and the affinity to ATP was markedly diminished. This was interpreted as a result of deranged structure and stability, due to loss of a hydrogen bond between Asn-669 and His-399. Mutagenesis of these residues supported this conclusion. In the structure of soybean lipoxygenase-1, a C-terminal loop was pointed out as important for correct orientation of the C-terminus. Accordingly, a hydrogen bond appears to stabilize such a C-terminal loop also in 5LO.

Essential roles of lipoxygenases in LDL oxidation and development of atherosclerosis

Oxidative modification of low-density lipoprotein (LDL) is one of the critical steps for the development of atherosclerosis. Accumulating studies have indicated that 12/15-lipoxygenase highly expressed in macrophages plays an essential role in the oxidation of circulating LDL. It has been demonstrated that LDL needs to bind the LDL receptor-related protein (LRP), a cell-surface receptor, prior to its oxidation by 12/15-lipoxygenase expressed in macrophages. LRP is suggested to mediate the selective transfer of cholesteryl ester in LDL to the plasma membrane of macrophages without endocytosis and degradation of the LDL particle. At the same time, binding of LDL to LRP translocates the 12/15-lipoxygenase from the cytosol to the plasma membrane. It is also demonstrated that 5-lipoxygenase localized in macrophages generates leukotrienes, which exhibit strong proinflammatory activities in cardiovascular tissues and contribute to lesion development. Therefore, the inhibition of these lipoxygenases may be effective in the prevention and treatment of the inflammatory diseases.

Arachidonate 5-lipoxygenase promoter genotype, dietary arachidonic acid, and atherosclerosis

BACKGROUND

Leukotrienes are inflammatory mediators generated from arachidonic acid (polyunsaturated n-6 fatty acid) by the enzyme 5-lipoxygenase. Since atherosclerosis involves arterial inflammation, we hypothesized that a polymorphism in the 5-lipoxygenase gene promoter could relate to atherosclerosis in humans and that this effect could interact with the dietary intake of competing 5-lipoxygenase substrates.

METHODS

We determined 5-lipoxygenase genotypes, carotid-artery intima-media thickness, and markers of inflammation in a randomly sampled cohort of 470 healthy, middle-aged women and men from the Los Angeles Atherosclerosis Study. Dietary arachidonic acid and marine n-3 fatty acids (including a competing 5-lipoxygenase substrate that reduces the production of inflammatory leukotrienes) were measured with the use of six 24-hour recalls of food intake.

RESULTS

Variant 5-lipoxygenase genotypes (lacking the common allele) were found in 6.0 percent of the cohort. Mean (+/-SE) intima-media thickness adjusted for age, sex, height, and racial or ethnic group was increased by 80+/-19 microm (95 percent confidence interval, 43 to 116; P<0.001) among carriers of two variant alleles, as compared with carriers of the common (wild-type) allele. In multivariate analysis, the increase in intima-media thickness among carriers of two variant alleles (62 microm, P<0.001) was similar in this cohort to that associated with diabetes (64 microm, P=0.01), the strongest common cardiovascular risk factor. Increased dietary arachidonic acid significantly enhanced the apparent atherogenic effect of genotype, whereas increased dietary intake of n-3 fatty acids blunted the effect. Finally, the plasma level of C-reactive protein, a marker of inflammation, was increased by a factor of 2 among carriers of two variant alleles as compared with that among carriers of the common allele.

CONCLUSIONS

Variant 5-lipoxygenase genotypes identify a subpopulation with increased atherosclerosis. The observed diet-gene interactions further suggest that dietary n-6 polyunsaturated fatty acids promote, whereas marine n-3 fatty acids inhibit, leukotriene-mediated inflammation that leads to atherosclerosis in this subpopulation.