The metabolism of arachidonic acid by human cells generates a number of eicosanoid derivatives that may be of importance not only to the endogenous functioning of cells but also as mediators of inflammation and immunity. The proposed research will investigate the role of lipid bodies in the metabolism of arachidonic acid by human neutrophilic and eosinophilic leukocytes. Lipid bodies are non-membrane bound, roughly spherical cytoplasmic inclusions that may be identified by light and transmission electron microscopy in a variety of cell types. Although believed to be composed of lipid, the nature and function of these intracellular structures have been unknown. Recent findings indicate that these lipid bodies, which increase in number in vivo when cells are involved in inflammatory reactions, are active in the uptake and incorporation of arachidonic acid. In order to define the role of lipid bodies in the metabolism of arachidonic acid, methods of subcellular fractionation will be developed to isolate lipid bodies from human neutrophils and eosinophils. The lipid and protein content of lipid bodies purified from these two types of leukocytes will be determined. In addition, using purified, isolated lipid bodies, the presence of enzymes involved in the esterification of arachidonic acid, the release of arachidonic acid from phospholipids and in the generation of eicosanoid derivatives, especially leukotrienes C4 (for eosinophils) and B4 (for neutrophils), from arachidonic acid will be evaluated. Utilizing purified human eosinophils and neutrophils, the formation of lipid bodies in these cells will be induced in vitro, and the temporal incorporation of radiolabeled phospholipid precursors and fatty acids into lipid bodies will be evaluated both by electron microscopic autoradiography and by analyses of neutral lipids and phospholipids in isolated lipid bodies. The presence of leukotrienes and other eicosanoids in these induced lipid bodies will be assessed. These studies will define the composition of cytoplasmic lipid bodies in these two leukocytes and will evaluate the previously unappreciated role of lipid bodies in the metabolism of arachidonic acid by these cells. Because lipid bodies are found in many different cells, these studies, in addition to assessing the function of these cytoplasmic inclusions in granulocyte generation of eicosanoid mediators pertinent to inflammation and immunity, may elucidate a more general role for these often overlooked organelles in cellular arachidonic acid metabolism.
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