Dihydroxydocosahexaenoic acids of the neuroprotectin D family: synthesis, structure, and inhibition of human 5-lipoxygenase

During aerobic oxidation of docosahexaenoic acid (DHA), soybean lipoxygenase (sLOX) has been shown to form 7,17(S)-dihydro(pero)xydocosahexaenoic acid [7,17(S)diH(P)DHA] along with its previously described positional isomer, 10,17(S)-dihydro(pero)xydocosahexa-4Z, 7Z, 11E, 13Z, 15E, 19Z-enoic acid. 7,17(S)-diH(P)DHA was also obtained via sLOX-catalyzed oxidation of either 17(S)-hydroperoxydoco-sahexaenoic acid [17(S)-HPDHA] or 17(S)-hydroxydocosahexaenoic acid [17(S)-HDHA]. The structures of the products were elucidated by normal-phase, reverse-phase, and chiral-phase HPLC analyses and by ultraviolet, NMR, and tandem mass spectroscopy and GC-MS. 7,17(S)-diH(P) DHA was shown to have 4Z, 8E, 10Z, 13Z, 15E, 19Z geometry of the double bonds. In addition, a compound apparently identical to the sLOX-derived 7,17(S)-diH(P) DHA was produced by another enzyme, potato tuber LOX, in the reactions of oxygenation of either 17(S)-HPDHA or 17(S)-HDHA. All of the dihydroxy-docosahexaenoic acids (diHDHAs) formed by either of the enzymes were clearly produced through double lipoxygenation of the corresponding substrate. 7,17(S)-diHDHA inhibited human recombinant 5-lipoxygenase in the reaction of arachidonic acid (AA) oxidation. In standard conditions with 100 mu M AA as substrate, the IC50 value for 7,17(S)-diHDHA was found to be 7 mM, whereas IC50 for 10,17(S)-DiHDHA was 15 mM. Similar inhibition by the diHDHAs was observed with sLOX, a quintessential 15LOX, although the strongest inhibition was produced by 10,17(S)-diHDHA (IC50 = 4 mu M). Inhibition of sLOX by 7,17(S)-diHDHA was slightly less potent, with an IC50 value of 9 mM. These findings suggest that 7,17(S)-diHDHA along with its 10,17(S) counterpart might have anti-inflammatory and anticancer activities, which could be exerted, at least in part, through direct inhibition of 15LOX and 15LOX.