Arachidonic Acid Metabolites in Cardiovascular and Metabolic Diseases

Impact of short-term exposure to fine particulate matter air pollution on urinary metabolome: A randomized, double-blind, crossover trial

BACKGROUND

Metabolomics is a novel tool to explore the biological mechanisms of the health effects of fine particulate matter (PM_2.5) air pollution. Very few studies have examined the urinary metabolomic changes associated with PM_2.5 exposure.

OBJECTIVE

To assess the alternation in urine metabolomics in response to short-term PM_2.5 exposure.

METHODS

We conducted a randomized, double-blind, crossover trial of 9-day real or sham indoor air purification among 45 healthy college students in Shanghai, China. Urine samples were collected immediately at the end of each intervention stage and were analyzed for metabolomics using ultrahigh performance liquid chromatography-mass spectrometry. Orthogonal partial least square-discriminant analysis and linear mixed effect models were used to examine metabolomic changes between interventional scenarios and their associations with continuous PM_2.5 exposure.

RESULTS

The time-weighted average personal PM_2.5 exposure in the real-purified scenario was 50% lower than in the sham-purified air scenario (28.3 μg/m³ VS 56.9 μg/m³). A total of 40 differentiated urinary metabolites at a false discovery rate <0.05 were identified for the effects of both intervention and continuous PM_2.5 exposure, including 16 lipids, 5 purine metabolites, 2 neurotransmitters, and 3 coenzymes.

CONCLUSIONS

This real-world randomized crossover trial demonstrated that short-term PM_2.5 exposure could result in significant changes in urinary metabolomic profile, which may further lead to perturbation in energy metabolism, oxidative stress and inflammation.

Neutral Lipids Are Not a Source of Arachidonic Acid for Lipid Mediator Signaling in Human Foamy Monocytes

Human monocytes exposed to free arachidonic acid (AA), a secretory product of endothelial cells, acquire a foamy phenotype which is due to the accumulation of cytoplasmic lipid droplets with high AA content. Recruitment of foamy monocytes to the inflamed endothelium contributes to the development of atherosclerotic lesions. In this work, we investigated the potential role of AA stored in the neutral lipids of foamy monocytes to be cleaved by lipases and contribute to lipid mediator signaling. To this end, we used mass spectrometry-based lipidomic approaches combined with strategies to generate monocytes with different concentrations of AA. Results from our experiments indicate that the phospholipid AA pool in monocytes is stable and does not change upon exposure of the cells to the external AA. On the contrary, the AA pool in triacylglycerol is expandable and can accommodate relatively large amounts of fatty acid. Stimulation of the cells with opsonized zymosan results in the expected decreases of cellular AA. Under all conditions examined, all of the AA decreases observed in stimulated cells were accounted for by decreases in the phospholipid pool; we failed to detect any contribution of the triacylglycerol pool to the response. Experiments utilizing selective inhibitors of phospholipid or triacylglyerol hydrolysis confirmed that the phospholipid pool is the sole contributor of the AA liberated by stimulated cells. Thus, the AA in the triacylglycerol is not a source of free AA for the lipid mediator signaling during stimulation of human foamy monocytes and may be used for other cellular functions.

Highly sensitive and specific LC–MS/MS method to determine endogenous leukotriene B4 levels in human plasma

Aim: To develop a high sensitivity and specific analytical method to measure endogenous levels of leukotriene B4 (LTB4) in human plasma. Methodology: LC–MS/MS and ELISA. Results: An LC–MS/MS method was developed with a sensitivity of 1.0 pg/ml, and within and between batch precision of <16% and <13% RSD, respectively. Conclusion: We have developed a sensitive LC–MS/MS method that can detect endogenous LTB4 in human plasma. The LC–MS/MS method displayed correlation with a commercial LTB4 ELISA when analyzing in ex vivo ionophore-stimulated blood samples. For untreated plasma this correlation was lost. Endogenous LTB4 was shown to be unstable in plasma during storage at -20°C and subject to stereoisomer formation. Neither of the assays could quantify endogenous plasma LTB4 in samples stored for long term.

The eicosapentaenoic acid:arachidonic acid ratio and its clinical utility in cardiovascular disease

Eicosapentaenoic acid (EPA) is a key anti-inflammatory/anti-aggregatory long-chain polyunsaturated omega-3 fatty acid. Conversely, the omega-6 fatty acid, arachidonic acid (AA) is a precursor to a number of pro-inflammatory/pro-aggregatory mediators. EPA acts competitively with AA for the key cyclooxygenase and lipoxygenase enzymes to form less inflammatory products. As a result, the EPA:AA ratio may be a marker of chronic inflammation, with a lower ratio corresponding to higher levels of inflammation. It is now well established that inflammation plays an important role in cardiovascular disease. This review examines the role of the EPA:AA ratio as a marker of cardiovascular disease and the relationship between changes in the ratio (mediated by EPA intake) and changes in cardiovascular risk. Epidemiological studies have shown that a lower EPA:AA ratio is associated with an increased risk of coronary artery disease, acute coronary syndrome, myocardial infarction, stroke, chronic heart failure, peripheral artery disease, and vascular disease. Increasing the EPA:AA ratio through treatment with purified EPA has been shown in clinical studies to be effective in primary and secondary prevention of coronary artery disease and reduces the risk of cardiovascular events following percutaneous coronary intervention. The EPA:AA ratio is a valuable predictor of cardiovascular risk. Results from ongoing clinical trials will help to define thresholds for EPA treatment associated with better clinical outcomes.