Inhibition of Neutrophil Leukotriene B₄ Production by a Novel Synthetic N-3 Polyunsaturated Fatty Acid Analogue, β-Oxa 21:3n-3

We recently reported the synthesis and anti-inflammatory properties of a novel long chain polyunsaturated fatty acid (PUFA) with an oxygen atom in the β-position, β-oxa-21:3 n-3 (Z,Z,Z)-(octadeca-9,12,15-trienyloxy) acetic acid). Our data, from studies aimed at elucidating the mechanism of its action, show that pretreatment of human neutrophils with the β-oxa-PUFA substantially depresses the production of leukotriene B₄ (LTB ₄) in response to calcium ionophore, A23187, comparable to standard leukotriene inhibitors such as zileuton and nordihydroguaiaretic acid. Interestingly, the n-6 equivalent, β-oxa 21:3 n-6, is also a strong inhibitor of LTB₄ production. In contrast, naturally occurring PUFA only slightly reduce, for eicosapentaenoic (20:5n-3) and docosahexaenoic (22:6n-3) acids, or increase, for arachidonic acid (20:4n-6), the formation of LTB₄. The parent β-oxa-21:3n-3 molecule, rather than its derivatives (methyl ester, saturated, monohydroperoxy, or monohydroxy forms), is exclusively responsible for attenuation of LTB₄ formation. β-Oxa-21:3n-3 inhibits the conversion of [³3H]20:4n-6 to [ ³H]5-hydroxyeicosatetraenoic acid and [³H]LTB₄ by neutrophils in the presence of calcium ionophore and also suppresses the activity of purified 5-lipoxygenase, but not cyclooxygenase 1 and 2. β-Oxa-21:3n-3 is taken up by neutrophils and incorporated into phospholipids and neutral lipids. In the presence of calcium ionophore, the leukocytes convert a marginal amount of β-oxa-21:3n-3 to a 16-monohydroxy-β-oxa-21:3n-3 derivative. After administration to rodents by gavage or i.p. injection, β-oxa-21:3n-3 is found to be incorporated into the lipids of various tissues. Thus, β-oxa-21:3n-3 has the potential to be used in the treatment of inflammatory diseases, which are mediated by products of the lipoxygenase pathway.