Quantitative analysis of 5-oxo-6,8,11,14-eicosatetraenoic acid by electrospray mass spectrometry using a deuterium-labeled internal standard

Non-Targeted LC-MS/MS Assay for Screening Over 100 Lipid Mediators from ARA, EPA, and DHA in Biological Samples Based on Mass Spectral Fragmentations

A non-targeted strategy to simultaneously screen for over 100 lipid mediators from ω-6 ARA and ω-3 EPA and DHA fatty acids is presented. The method based on an extensive study of fragmentation patterns obtained by SPE-LC-MS/MS analysis-provided fingerprints to comprehensively elucidate and identify lipid mediators in biological samples. Many of these metabolites are associated to metabolic disorders, inflammatory, immune and oxidative stress. The methodology consisted of a three-step procedure. (1) SPE extraction of compounds from plasma and adipose tissue was followed by LC-MS/MS analysis operating in full scan mode. The methodology was validated for a group of 65 metabolites using standards. SPE recoveries ranged from 29–134% and matrix effect from 10–580%. LOD and LOQ ranged from 0.01 to 1765 ng/mL and 0.03 to 5884 ng/mL respectively, similarly than current analytical strategies based on MRM mode. (2) An extensive study of the mass spectra of a wide range of compounds was done to stablish a specific fragmentation pattern. Interestingly, illustrative fragmentations and new specific transitions to identify EPA and DHA lipid mediators have been innovatively established. (3) After analysis, 30 lipid mediators were tentatively identified in plasma and 35 in adipose tissue of rats according to the pre stablished fragmentation patterns. The hypothetical identification of compounds was validated by using reference standards. Around 85–90% of proposed identifications were correctly assigned and only 4 and 3 identifications failed in adipose tissue and plasma, respectively. The method allowed the identification of these metabolites without losing information by the use of predefined ions list. Therefore, the use of full scan mode together with the study of fragmentation patterns provided a novel and stronger analytical tool to study the complete profile of lipid mediators in biological samples than the analysis through MRM based methods. Importantly, no analytical standards were required at this qualitative screening stage and the performance and sensitivity of the assay were very similar to that of a MRM method.

5-Oxo-ETE receptor antagonists

5-Oxo-ETE is the most powerful eosinophil chemoattractant among lipid mediators. Eosinophil infiltration into the lungs of asthmatics may be responsible for the late phase of inflammatory asthma. We have designed and synthesized a 5-oxo-ETE receptor antagonist, the purpose of which is to prevent eosinophil migration to the lung during an asthma attack and thereby reduce asthma symptoms.

Nitration of respiratory epithelial cells by myeloperoxidase depends on extracellular nitrite

To investigate peroxidase induced 3'-nitrotyrosine (3NT) formation, neutrophil derived myeloperoxidase (MPO) (0.025 microM) was directly administered to A549 epithelial cells with or without H(2)O(2) (150 microM). Little evidence of 3NT was found. In contrast, there was a dose dependent increase in intracellular NO (p<0.001, n=8) following MPO (0.025 microM) treatment, which was further enhanced (p<0.0003, n=8) by addition of H(2)O(2). Extracellular NO also increased after MPO (p<0.002, n=5) and with MPO and H(2)O(2) (p<0.004, n=5). Substantial 3NT formation was only detected following addition of nitrite (NO(2)(-), > or =100 microM), which induced a dose dependent increase in epithelial 3NT. In contrast, protein carbonyl formation and increased GSSG/GSH ratios were associated with MPO treatment even in the absence of NO(2)(-). Co-culture of A549 epithelial cells with polymorphonuclear leukocytes (PMN) (10(6)/ml) led to immunocytochemical detection of epithelial 3NT and induction of nitric oxide synthase (NOS2). However, in a Transwell system direct contact between PMN and A549 cells was necessary for immunodetection of 3NT but not of NOS2 consistent with a role for high local nitrite concentrations. These findings demonstrate dissociation between epithelial endogenous NO production and 3NT formation. Although MPO can influence cellular oxidative stress, particularly in the presence of H(2)O(2), 3NT formation requires the presence of high concentrations of NO(2)(-) in the milieu.

Airway epithelial cells synthesize the lipid mediator 5-oxo-ETE in response to oxidative stress

5-Oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) is a potent eosinophil chemoattractant that is synthesized from the 5-lipoxygenase product 5S-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE) by the NADP+-dependent enzyme 5-hydroxyeicosanoid dehydrogenase (5-HEDH), previously reported only in inflammatory cells. Because of their critical location at the interface of the lung with the external environment, we sought to determine whether epithelial cells could also synthesize this substance. We found that HEp-2, T84, A549, and BEAS-2B cells all synthesize 5-oxo-ETE from 5-HETE in amounts comparable to leukocytes. The epithelial dehydrogenase is localized in the microsomal fraction, requires NADP+, and is selective for the S-isomer of 5-HETE, suggesting that it is identical to leukocyte 5-HEDH. Normal human bronchial epithelial cells have an even greater capacity to synthesize 5-oxo-ETE. H2O2 dramatically stimulates its synthesis in association with increased levels of intracellular GSSG and NADP+. These responses were all blocked by removal of GSH/GSSG with N-ethylmaleimide, suggesting that H2O2 stimulates 5-oxo-ETE synthesis by raising NADP+ levels through activation of the GSH redox cycle. Airway smooth muscle cells can also synthesize 5-oxo-ETE, but to a lesser extent. These results suggest that epithelial cells may be a major source of 5-oxo-ETE under conditions of oxidative stress, which may contribute to eosinophil infiltration in allergic diseases.

The OXE receptor: a new therapeutic approach for asthma?

The eicosanoid 5-oxo-6E,8Z,11Z,14Z-eicosatetraenoic acid (5-oxo-ETE) has recently been identified as the ligand for the oxoeicosanoid (OXE) receptor. In vitro and in vivo studies have suggested that 5-oxo-ETE has a role in the asthmatic inflammatory response and it has been shown to stimulate eosinophil migration to the airways. New data suggest that eosinophils have an important role in the pathogenesis of asthma, being required for mucus accumulation, airway hyperresponsiveness and remodelling of the airways. However, there are several mediators that can stimulate the recruitment of eosinophils to the airways and the development of antagonists against the OXE receptor is required to evaluate the potential of the OXE receptor as a new therapeutic approach for asthma.