Inhibitors of the lipoxygenase pathway block development of Brugia malayi L3 in vitro

Brugia malayi L3 molt to the L4 stage in serum-free cultures: supplemented with arachidonic, linoleic, or linolenic acids and the basidiomycetous yeas t Rhodotorula minuta. These fatty acids are capable of entering the eicosan oid pathway of arachidonate metabolism, the pathway responsible for generat ing a number of biologically active mediators, including prostaglandins, le ukotrienes, and lipoxins. To determine whether this pathway was required fo r L3 development, we added dual inhibitors of cyclooxygenase and lipoxygena se to in vitro cultures containing B.malayi L3. These compounds significant ly inhibited L3 molting. To evaluate whether 1 or both of these pathways of arachidonate metabolism were involved in molting, we tested drugs inhibiti ng either cyclooxygenase or lipoxygenase. Lipoxygenase inhibitors blocked L 3 molting, whereas cyclo oxygenase inhibitors did not. To assess whether en zymes operating downstream of lipoxygenase were also involved in L3 molting , we added inhibitors of enzymes involved in leukotriene synthesis and foun d they were also capable of preventing development. We tested the same inhi bitor panel on Dirofilaria immitis L3. A single lipoxygenase inhibitor and inhibitors of 2 different enzymes operating downstream of lipoxygenase disr upted D. immitis development. These results demonstrate that a lipoxygenase pathway product is required for molting of the infective stage larvae of f ilarial parasites.