Mammalian arachidonate 12-lipoxygenases

Targeted profiling of arachidonic acid and eicosanoids in rat tissue by UFLC-MS/MS: Application to identify potential markers for rheumatoid arthritis

We describe a method for the targeted analysis of bioactive arachidonic acid metabolites through cyclooxygenase (COX) and lipoxygenase (LOX) pathway in knee joint, liver, kidney, spleen and heart using an ultra-fast liquid chromatography-tandem mass (UFLC-MS/MS) method. Method validation was investigated, including linearity, precision, accuracy, matrix effect, extraction recovery and stability for the simultaneous analysis of prostaglandins (PGs), thromboxanes (TXs), leukotrienes (LTs) and hydroxyeicosatetraenoic acids (HETEs). The method enables us to chromatographically separate branched-chain species from their straight-chain isomers as well as separate biologically important eicosanoids. The concentrations of the following major eicosanoids were significantly increased in rheumatoid arthritis model rats than in normal ones: 5-HETE, 8-HETE, 12-HETE, 15-HETE, PGF_2α, TXB₂, 5-HpETE, LTE₄, PGE₂, PGD₂, LTB₄. Further multivariate data analysis (partial least square-discriminant analysis) showed COX products (PGs, TXs) were readily distributed towards liver and kidney, LOX products (LTs, HETEs) towards knee joint and spleen, and heart had no characteristic metabolites. The method described here offers a useful tool for the evaluation of complex regulatory eicosanoids responses in RA disease states and provides support for use of dual inhibitors of COX and LOX enzymes on RA treatment.

Simultaneous tissue profiling of eicosanoid and endocannabinoid lipid families in a rat model of osteoarthritis

We describe a novel LC method for the simultaneous and quantitative profiling of 43 oxylipins including eicosanoids, endocannabinoids, and structurally related bioactive lipids with modified acyl groups. The LC-MS/MS method uses switching at a defined time between negative and positive electrospray ionization modes to achieve optimal detection sensitivity for all the lipids. The validated method is linear over a range of 0.01–5 nmol/g (0.1–50 nmol/g for 2-arachidonoyl glycerol) with intra- and interday precision and accuracy between 1.38 and 26.76% and 85.22 and 114.3%, respectively. The method successfully quantified bioactive lipids in different tissue types in the rat, including spinal cord, dorsal root ganglia (DRGs), knee joint, brain, and plasma. Distinct regional differences in the pattern of lipid measured between tissue types were observed using principle component analysis. The method was applied to analyze tissue samples from an established preclinical rat model of osteoarthritis (OA) pain and showed that levels of 12-hydroxyeicosatetraenoic acid were significantly increased in the OA rat knee joint compared with controls, and that 15-hydroxyeicosatetraenoic acid was significantly increased in the DRGs in the model of OA compared with controls. The developed LC-MS/MS method has the potential to provide detailed pathway profiling in tissues and biofluids where the disruption of bioactive oxylipins may be involved in disease states.

DNA hypomethylation at ALOX12 is associated with persistent wheezing in childhood

RATIONALE

Epigenetic changes may play a role in the occurrence of asthma-related phenotypes.

OBJECTIVES

To identify epigenetic marks in terms of DNA methylation of asthma-related phenotypes in childhood, and to assess the effect of prenatal exposures and genetic variation on these epigenetic marks.

METHODS

Data came from two cohorts embedded in the Infancia y Medio Ambiente (INMA) PROJECT: Menorca (n = 122) and Sabadell (n = 236). Wheezing phenotypes were defined at age 4-6 years. Cytosine-guanine (CpG) dinucleotide site DNA methylation differences associated with wheezing phenotypes were screened in children of the Menorca study using the Illumina GoldenGate Panel I. Findings were validated and replicated using pyrosequencing. Information on maternal smoking and folate supplement use was obtained through questionnaires. Dichlorodiphenyldichloroethylene was measured in cord blood or maternal serum. Genotypes were extracted from genome-wide data.

MEASUREMENT AND MAIN RESULTS

Screening identified lower DNA methylation at a CpG site in the arachidonate 12-lipoxygenase (ALOX12) gene in children having persistent wheezing compared with those never wheezed (P = 0.003). DNA hypomethylation at ALOX12 loci was associated with higher risk of persistent wheezing in the Menorca study (odds ratio per 1% methylation decrease, 1.13; 95% confidence interval, 0.99-1.29; P = 0.077) and in the Sabadell study (odds ratio, 1.16; 95% confidence interval, 1.03-1.37; P = 0.017). Higher levels of prenatal dichlorodiphenyldichloroethylene were associated with DNA hypomethylation of ALOX12 in the Menorca study (P = 0.033), but not in the Sabadell study (P = 0.377). ALOX12 DNA methylation was strongly determined by underlying genetic polymorphisms.

CONCLUSIONS

DNA methylation of ALOX12 may be an epigenetic biomarker for the risk of asthma-related phenotypes.

Group IVA phospholipase A₂ is necessary for growth cone repulsion and collapse

The repellent semaphorin 3A (Sema3A) causes growth cone turning or collapse by triggering cytoskeletal rearrangements and detachment of adhesion sites. Growth cone detachment is dependent on eicosanoid activation of protein kinase C epsilon (PKCε), but the characterization of the phospholipase A(2) (PLA(2) ) that releases arachidonic acid (AA) for eicosanoid synthesis has remained elusive. Here, we show, in rat dorsal root ganglion (DRG) neurons, that Sema3A stimulates PLA(2) activity, that Sema3A-induced growth cone turning and collapse are dependent on the release of AA, and that the primary PLA(2) involved is the group IV α isoform (GIVA). Silencing GIVA expression renders growth cones resistant to Sema3A-induced collapse, and GIVA inhibition reverses Sema3A-induced repulsion into attraction. These studies identify a novel, early step in Sema3A-signaling and a PLA(2) necessary for growth cone repulsion and collapse.

Murine 12/15-lipoxygenase regulates ATP-binding cassette transporter G1 protein degradation through p38- and JNK2-dependent pathways

12/15-Lipoxygenase (12/15LO) plays a role in the pathogenesis of atherosclerosis and diabetes and has been implicated in low density lipoprotein oxidation. Murine macrophages express high levels of 12/15LO and are key cells involved in the accumulation and efflux of oxidized low density lipoprotein in the arterial wall. During this process, macrophages up-regulate scavenger receptors that regulate lipid uptake, and ATP-binding cassette (ABC) transporters, that regulate lipid efflux. We have previously demonstrated that 12/15LO enhances the turnover and serine phosphorylation of ABCG1. In the current study, we further elucidate the mechanisms by which 12/15LO regulates ABCG1. Proteasomal inhibitors blocked the down-regulation of ABCG1 expression and resulted in accumulation of phosphorylated ABCG1. Macrophages that lack 12/15LO have enhanced transporter expression, reduced ABCG1 phosphorylation, and increased cholesterol efflux. Conversely, macrophages that overexpress 12/15LO have reduced ABCG1 expression, increased transporter phosphorylation, and reduced cholesterol efflux. 12/15LO plays a key role in activating the MAPK pathway. Inhibition of the p38 or JNK pathways with pharmacological inhibitors or dominant negative constructs blocked 12S-hydroxyeicosatetranoic acid-mediated degradation of ABCG1. Moreover, we isolated macrophages from JNK1-, JNK2-, and MKK3-deficient mice to analyze the involvement of specific MAPK pathways. JNK2- and MKK3-, but not JNK1-deficient macrophages were resistant to the down-regulation of ABCG1 protein, reduction in efflux, and increase in serine phosphorylation by 12S-hydroxyeicosatetranoic acid. These findings provide evidence that 12/15LO regulates ABCG1 expression and function through p38- and JNK2-dependent mechanisms, and that targeting these pathways may provide novel approaches for regulating cholesterol homeostasis.

Oxidative stress in severe pulmonary hypertension

Severe pulmonary hypertension (PH) occurs in a primary or "unexplained" form and in a group of secondary forms associated with a number of diseases. Because the lung tissue from patients with severe PH demonstrates complex vascular lesions, which contain inflammatory cells, we wondered whether the lung tissue from patients with severe PH was "under oxidative stress." We used immunohistochemistry to localize nitrotyrosine and 8-hydroxy guanosine in the lung tissue sections from patients with primary and secondary PH. In some lung tissue extracts, the eicosanoid metabolites 5-oxo-eicosatetraenoic acid, leukotriene B4 5-hydroxyeicosatetraenoic acid (HETE), 12-HETE, and 15-HETE were measured using mass spectroscopy, and superoxide dismutase amount and activity were measured. Nitrotyrosine expression was ubiquitous in all PH lungs, and 5-oxo-eicosatetraenoic acid and HETE levels were elevated in the lungs of patients with severe PH but not in those lungs that were from the patients with severe PH treated chronically with prostacyclin. We conclude that indeed the lungs from patients with severe PH are under oxidative stress and that chronic prostacyclin infusion has an antiinflammatory effect on the lung tissue.

12-hydroxyeicosatetrenoate (12-HETE) attenuates AMPA receptor-mediated neurotoxicity: evidence for a G-protein-coupled HETE receptor

12-hydroxyeicosatetraenoic acid (12-HETE) is a neuromodulator that is synthesized during ischemia. Its neuronal effects include attenuation of calcium influx and glutamate release as well as inhibition of AMPA receptor (AMPA-R) activation. Because 12-HETE reduces ischemic injury in the heart, we examined whether it can also reduce neuronal excitotoxicity. When treated with 12-(S)HETE, cortical neuron cultures subjected to AMPA-R-mediated glutamate toxicity suffered up to 40% less damage than untreated cultures. The protective effect of 12-(S)HETE was concentration-dependent (EC50 = 88 nm) and stereostructurally selective. Maximal protection was conferred by 300 nm 12-(S)HETE; 300 nm 15-(S)HETE was similarly protective, but 300 nm 5-(S)HETE was less effective. The chiral isomer 12-(R)HETE offered no protection; neither did arachidonic acid or 12-(S)hydroperoxyeicosatetraenoic acid. Excitotoxicity was calcium-dependent, and 12-(S)HETE was demonstrated to protect by inactivating N and L (but not P) calcium channels via a pertussis toxin-sensitive mechanism. Calcium imaging demonstrated that 12-(S)HETE also attenuates glutamate-induced calcium influx into neurons via a pertussis toxin-sensitive mechanism, suggesting that it acts via a G-protein-coupled receptor. In addition, 12-(S)HETE stimulates GTPgammaS binding (indicating G-protein activation) and inhibits adenylate cyclase in forskolin-stimulated cultures over the same concentration range as it exerts its anti-excitotoxic and calcium-influx attenuating effects. These studies demonstrate that 12-(S)HETE can protect neurons from excitotoxicity by activating a G(i/o)-protein-coupled receptor, which limits calcium influx through voltage-gated channels.