Stearidonic acid, an inhibitor of the 5‐lipoxygenase pathway. A comparison with timnodonic and dihomogammalinolenic acid

Leukotrienes have been shown to play an important role as mediators in various disease processes, including asthma and inflammation; thus, their synthesis is tightly regulated. The major precursor of leukotrienes is arachidonic acid (20∶4n−6). Fatty acids which are structurally similar to 20∶4n−6, such as eicosatrienoic acid (20∶3n−6; dihomogammalinolenic acid) and eicosapentaenoic acid (20∶5n−3; timnodonic acid) have been found to inhibit leukotriene biosynthesis. Because of the structural similarity of octadecatetraenoic acid (18∶4n−3; stearidonic acid) with 20∶4n−6, the present study was undertaken to determine whether stearidonic acid also exerts an inhibitory effect on the 5‐lipoxygenase pathway. Human leukocytes were incubated with 18∶4n−3 (20 μM or 10 μM), 20∶5n−3 (20 μM) or 20∶3n−6 (20 μM) and subsequently stimulated with 1 μM ionophore A23187 and 20∶4n−6 (20 μM or 10 μM). The 5‐lipoxygenase products were then measured by high‐performance liquid chromatography. Leukotriene synthesis was reduced by 50% with 20 μM 18∶4n−3 and by 35% with 10 μM 18∶4n−3. Formation of 5 S ,12 S ‐di‐hydroxy‐eicosatetraenoic acid and of 5‐hydroxy‐eicosatetraenoic acid was decreased by 25% with 20 μM 18∶4n−3 and by 3% with 10 μM 18∶4n−3. The inhibition observed with 20 μM 18∶4n−3 appeared to be of the same order as that observed with 20 μM 20∶5n−3; the inhibition observed with 18∶4n−3 was shown to be dosedependent. The inhibition produced by 20 μM 20∶3n−6 was greater than that observed with either 20 μM 18∶4n−3 or with 20 μM 20∶5n−3. The results suggest that stearidonic acid, which is found, for example, in blackcurrant seed oil (which also contains the 20∶3n−6 precursor), may play a role in suppressing inflammation.