Cellular lipid extraction for targeted stable isotope dilution liquid chromatography-mass spectrometry analysis

Enantioselectivity Effects in Clinical Metabolomics and Lipidomics

Metabolomics and lipidomics have demonstrated increasing importance in underlying biochemical mechanisms involved in the pathogenesis of diseases to identify novel drug targets and/or biomarkers for establishing therapeutic approaches for human health. Particularly, bioactive metabolites and lipids have biological activity and have been implicated in various biological processes in physiological conditions. Thus, comprehensive metabolites, and lipids profiling are required to obtain further advances in understanding pathophysiological changes that occur in cells and tissues. Chirality is one of the most important phenomena in living organisms and has attracted long-term interest in medical and natural science. Enantioselective separation plays a pivotal role in understanding the distribution and physiological function of a diversity of chiral bioactive molecules. In this context, it has been the goal of method development for targeted and untargeted metabolomics and lipidomic assays. Herein we will highlight the benefits and challenges involved in these stereoselective analyses for clinical samples.

Cellular uptake and antiproliferative effects of 11-oxo-eicosatetraenoic acid

Cyclooxygenases (COX) metabolize arachidonic acid (AA) to hydroxyeicosatetraenoic acids (HETE), which can then be oxidized by dehydrogenases, such as 15-hydroxyprostaglandin dehydrogenase (15-PGDH), to oxo-eicosatetraenoic acids (ETE). We have previously established that 11-oxo-eicosatetraenoic acid (oxo-ETE) and 15-oxo-ETE are COX-2/15-PGDH-derived metabolites. Stable isotope dilution (SID) chiral liquid chromatography coupled with electron capture atmospheric pressure chemical ionization (ECAPCI) single reaction monitoring (SRM) MS has been used to quantify uptake of 11-oxo-ETE and 15-oxo-ETE in both LoVo cells and human umbilical vein endothelial cells (HUVEC). Intracellular 11-oxo- and 15-oxo-ETE concentrations reached maximum levels within 1 h and declined rapidly, with significant quantitative differences in uptake between the LoVo cells and the HUVECs. Maximal intracellular concentrations of 11-oxo-ETE were 0.02 ng/4 × 10⁵ cells in the LoVo cells and 0.58 ng/4 × 10⁵ cells in the HUVECs. Conversely, maximal levels of 15-oxo-ETE were 0.21 ng/4 × 10⁵ in the LoVo cells and 0.01 ng/4 × 10⁵ in the HUVECs. The methyl esters of both 11-oxo- and 15-oxo-ETE increased the intracellular concentrations of the corresponding free oxo-ETEs by 3- to 8-fold. 11-oxo-ETE, 15-oxo-ETE, and their methyl esters inhibited proliferation in both HUVECs and LoVo cells at concentrations of 2–10 μM, with 11-oxo-ETE methyl ester being the most potent inhibitor. Cotreatment with probenecid, an inhibitor of multiple drug resistance transporters (MRP)1 and 4, increased the antiproliferative effect of 11-oxo-ETE methyl ester in LoVo cells and increased the intracellular concentration of 11-oxo-ETE from 0.05 ng/4 × 10⁵ cells to 0.18 ng/4 × 10⁵ cells. Therefore, this study has established that the COX-2/15-PGDH-derived eicosanoids 11-oxo- and 15-oxo-ETE enter target cells, that they inhibit cellular proliferation, and that their inhibitory effects are modulated by MRP exporters.

Untargeted metabolomics from biological sources using ultraperformance liquid chromatography-high resolution mass spectrometry (UPLC-HRMS)

Here we present a workflow to analyze the metabolic profiles for biological samples of interest including; cells, serum, or tissue. The sample is first separated into polar and non-polar fractions by a liquid-liquid phase extraction, and partially purified to facilitate downstream analysis. Both aqueous (polar metabolites) and organic (non-polar metabolites) phases of the initial extraction are processed to survey a broad range of metabolites. Metabolites are separated by different liquid chromatography methods based upon their partition properties. In this method, we present microflow ultra-performance (UP)LC methods, but the protocol is scalable to higher flows and lower pressures. Introduction into the mass spectrometer can be through either general or compound optimized source conditions. Detection of a broad range of ions is carried out in full scan mode in both positive and negative mode over a broad m/z range using high resolution on a recently calibrated instrument. Label-free differential analysis is carried out on bioinformatics platforms. Applications of this approach include metabolic pathway screening, biomarker discovery, and drug development.

Resuscitation with supplementary oxygen induces oxidative injury in the cerebral cortex

Isoprostanes, neuroprostanes, isofurans, and neurofurans have all become attractive biomarkers of oxidative damage and lipid peroxidation in brain tissue. Asphyxia and subsequent reoxygenation cause a burst of oxygen free radicals. Isoprostanes and isofurans are generated by free radical attacks of esterified arachidonic acid. Neuroprostanes and neurofurans are derived from the peroxidation of docosahexanoic acid, which is abundant in neurons and could therefore more selectively represent oxidative brain injury. Newborn piglets (age 12-36 h) underwent hypoxia until the base excess reached -20 mmol/L or the mean arterial blood pressure dropped below 15 mm Hg. They were randomly assigned to receive resuscitation with 21, 40, or 100% oxygen for 30 min and then ventilation with air. The levels of isoprostanes, isofurans, neuroprostanes, and neurofurans were determined in brain tissue (ng/g) isolated from the prefrontal cortex using gas chromatography-mass spectrometry (GC/MS) with negative ion chemical ionization (NICI) techniques. A control group underwent the same procedures and observations but was not submitted to hypoxia or hyperoxia. Hypoxia and reoxygenation significantly increased the levels of isoprostanes, isofurans, neuroprostanes, and neurofurans in the cerebral cortex. Nine hours after resuscitation with 100% oxygen for 30 min, there was nearly a 4-fold increase in the levels of isoprostanes and isofurans compared to the control group (P=0.007 and P=0.001) and more than a 2-fold increase in neuroprostane levels (P=0.002). The levels of neuroprostanes and neurofurans were significantly higher in the piglets that were resuscitated with supplementary oxygen (40 and 100%) compared to the group treated with air (21%). The significance levels of the observed differences in neuroprostanes for the 21% vs 40% comparison and the 21% vs 100% comparison were P<0.001 and P=0.001, respectively. For neurofurans, the P values of the 21% vs 40% comparison and the 21% vs 100% comparison were P=0.036 and P=0.025, respectively. Supplementary oxygen used for the resuscitation of newborns increases lipid peroxidation in brain cortical neurons, a result that is indicative of oxidative brain damage. These novel findings provide new knowledge regarding the relationships between oxidative brain injury and resuscitation with oxygen.