The mechanism of inhibitory effect of eicosapentaenoic acid on phagocytic activity and chemotaxis of human neutrophil granulocytes.

Free eicosapentaenoic acid (EPA) was found to inhibit dose dependently the chemiluminescence of human neutrophil granulocytes phagocytosing zymosan and their chemotaxis induced by C5a-containing zymosan-activated serum (ZAS) and platelet-activating factor. Rigidification of plasma membranes in the ZAS-treated cells could be observed by measuring the fluorescence anisotropy. The cells were labeled by 3-[p-(6-phenyl-1,3,5-hexatrienoil) phenyl] propionic acid, reporting plasma membrane for determination of membrane fluidity. In resting, nonstimulated neutrophils, EPA dose dependently increased the fluidity of plasma membrane. In zymosan-activated cells, however, after a short fluidization, the basic effect of EPA was a rigidification compared to very low fluorescence anisotropy values of activated control cells. This diminished fluidity, increased membrane stability of plasma membranes can be one of the reasons for the decreased functions (phagocytosis and chemotaxis) of human EPA-treated neutrophils.