Determination of leukotriene A4 stabilization by S100A8/A9 proteins using mass spectrometry

Abstract

Leukotriene A4 (LTA4) is the precursor for the formation of bioactive leukotrienes, but is highly susceptible to nonenzymatic hydrolysis. Although it is chemically reactive, LTA4 participates in the process of transcellular metabolism, which requires the transfer of LTA4 from one cell to another for the production of additional leukotrienes. Due to the susceptibility of LTA4 to hydrolysis, various methods have been used to measure the half-life of LTA4 in the presence of different proteins in efforts to understand how it is transported between cells. In this work, a new liquid chromatography mass spectrometry technique was developed to improve upon these previous assays that analyzed LTA4 directly. The new technique derivatizes LTA4 to stable compounds for analysis and removes the potential for sample decomposition between analytical runs. This assay was used in measuring the capabilities of the S100A8/A9 protein complex isolated from human neutrophils to stabilize LTA4. It was determined that the S100A8/A9 protein complex protects LTA4 from hydrolysis in a Ca2+ dependent manner and increases LTA4 half-life to in excess of 35 and 5 min at 4°C and 37°C, respectively.

Keywords

• transcellular metabolism
• leukotriene biosynthesis
• S100 protein