A variety of assay systems have been utilized to evaluate the inhibition of the key enzyme in leukotriene (LT) biosynthesis, 5-lipoxygenase (5-LO). We have developed an assay utilizing a cytosolic preparation of 5-LO from rat basophilic leukemia (RBL-1) cells. Enzyme activity was monitored by continous measurement of oxygen consumption. High performance liquid chromatography (HPLC) analysis of products showed exclusive generation of 5-LO products. The assay proved useful for the evaluation of a variety of chemical classes of lipoxygenase inhibitors and clearly differentiated those compounds which extended the lag phase (e.g. A-64077) as opposed to the propagation phase of the enzyme activity (e.g. SK & F 105561). The data generated were in reasonable agreement with results from the assay of isolated human monocyte 5-LO and, with the exception of compounds which appear to have a significant effect on 5-LO translocation (e.g. MK-886 and Wy-49 232), inhibition of LT production by intact monocytes. This assay system proved to be a convenient and informative method to analyze inhibition of 5-LO activity.
