9-Hydroxyoctadecadienoic acid

9-Hydroxyoctadecadienoic acid (or 9-HODE) has been used in the literature to designate either or both of two stereoisomer metabolites of the essential fatty acid, linoleic acid: 9(S)-hydroxy-10(E),12(Z)-octadecadienoic acid (9(S)-HODE) and 9(R)-hydroxy-10(E),12(Z)-octadecadienoic acid (9(R)-HODE); these two metabolites differ in having their hydroxy residues in the S or R configurations, respectively. The accompanying figure gives the structure for 9(S)-HETE. Two other 9-hydroxy linoleic acid derivatives occur in nature, the 10E,12E isomers of 9(S)-HODE and 9(R)-HODE viz., 9(S)-hydroxy-10E,12E-octadecadienoic acid (9(S)-EE-HODE) and 9(R)-hydroxy-10E,12E-octadecadienoic acid (13(R)-EE-HODE); these two derivatives have their double bond at carbon 12 in the E or trans configuration as opposed to the Z or cis configuration. The four 9-HODE isomers, particularly under conditions of oxidative stress, may form together in cells and tissues; they have overlapping but not identical biological activities and significances. Because many studies have not distinguished between the S and R stereoisomers and, particularly in identifying tissue levels, the two EE isomers, 9-HODE is used here when the isomer studied is unclear.

A similar set of 13-Hydroxyoctadecadienoic acid (13-HODE) metabolites (13(S)-HODE), 13(R)-HODE, 13(S)-EE-HODE), and 13(R)-EE-HODE) also occurs naturally and, again particularly under conditions of oxidative stress, may form concurrently with 9-HODEs; these 13-HODEs also have overlapping and complementary but not identical activities with the 9-HODEs. Some recent studies measuring HODE levels in tissue have lumped the four 9-HODEs and four 13-HODEs together to report only on total HODEs (tHODEs): tHODEs have been proposed to be markers for certain human disease. Other recent studies have lumped together the 9-(S), 9(R), 13 (S)-, and 13(R)-HODE along with the two ketone metabolites of these HODEs, 9-oxoODE (9-oxo-10(E),12(Z)-octadecadienoic acid) and 13-oxoODE, reporting only on total OXLAMs (oxidized linoleic acid metabolites); the OXLAMs have been implicated in working together to signal for pain perception.