Analysis of bioactive eicosanoids in equine plasma by stable isotope dilution reversed-phase liquid chromatography/multiple reaction monitoring mass spectrometry.

This research article explores an examination method for understanding the influence of arachidonic acid (AA) metabolites in inflammation. Particularly, the study focuses on the formation of eicosanoids, derivative compounds of AA thought to contribute to inflammation. A new analytical approach involving liquid chromatography and mass spectrometry was developed and used to detect and quantify these compounds in horse plasma.

Research Methodology

• The researchers investigated how cycloxygenases (COXs) and lipoxygenases (LOs), both of which are enzymes, metabolize arachidonic acid (AA) into eicosanoids in horse plasma.
• To extract eicosanoids from the plasma, two liquid-liquid extraction steps were employed, involving the use of chloroform/isopropanol and methyl-tert-butyl ether.
• A unique analysis technique combining stable isotope dilution with liquid chromatography (LC) and multiple reaction monitoring (MRM) mass spectrometric (MS) method was developed.
• To prevent artificial formation of eicosanoids due to potentially remaining traces of metal ions, a compound named deferoxamine was introduced to the plasma.

Results

• The researchers found excellent linearity in the calibration curve within the 0.1 to 10 ng/mL range, suggesting accurate results.
• The limit of detection (LOD) for the method ranged from 1 to 10 pg on-column for different eicosanoids, indicating high sensitivity.
• The technique demonstrated good inter-day and intra-day accuracy and precision.
• The formation of eicosanoids was tested using exogenous AA or by releasing endogenous AA from esterified lipids through treatment with calcium ionophore (CI) A23187 in horse blood.
• Dexamethasone, a type of glucocorticoid, significantly inhibited the formation of eicosanoids when applied to horse blood prior to the administration of AA or CI A23187.

Conclusion

• The method created by the researchers proved to be specific, selective, and sensitive enough to determine and identify 25 different eicosanoids.
• The research indicates a potential role for glucocorticoids in the control or mitigation of inflammatory responses caused by the formation of eicosanoids.
• As a result, the validated method is being used in ongoing studies to further explore the mechanisms of action and the pharmacokinetics/pharmacodynamics of eicosanoids post-glucocorticoids administration in horses.
• This research lays important foundation for future studies focused on understanding the contribution of eicosanoids to inflammation in horses and potentially other animals and humans.