Inhibition of neutrophil leukotriene B-4 production by a novel synthetic N-3 polyunsaturated fatty acid analogue, beta-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 beta-position, beta-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 beta-oxa-PUFA substantially depresses the production of leukotriene B-4 (LTB4) in response to calcium ionophore, A23187, comparable to standard leukotriene inhibitors such as Menton and nordihydroguaiaretic acid. Interestingly, the n-6 equivalent, beta-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 beta-oxa-21:3n-3 molecule, rather than its derivatives (methyl ester, saturated, monohydroperoxy, or monohydroxy forms), is exclusively responsible for attenuation of LTB4 formation. beta-Oxa-21:3n-3 inhibits the conversion of [H-3]20:4n-6 to [H-3]5-hydroxyeicosatetraenoic acid and [H-3]LTB4 by neutrophils in the presence of calcium ionophore and also suppresses the activity of purified 5-lipoxygenase, but not cyclooxygenase 1 and 2. beta-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 beta-oxa-21:3n-3 to a 16-monohydroxy-beta-oxa-21:3n-3 derivative. After administration to rodents by gavage or i.p. injection, beta-oxa-21:3n-3 is found to be incorporated into the lipids of various tissues. Thus, 6-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.