11-Hydroperoxide eicosanoid-mediated 2(E),4(E)-decadienal production from arachidonic acid in the brown algae, Saccharina angustata

This work aims to propose a pathway for the production of 2(E),4(E)-decadienal from arachidonic acid (ARA) via 11-hydroperoxide eicosanoid (11 hydroperoxyeicosatetraenoic acid, 11-HPETE) through lipoxygenase (LOX) and hydroperoxide lyase (HPL) in the brown alga, Saccharina angustata, by identifying pathway intermediates through three studies. The first study investigated the biogeneration of 2(E),4(E)-decadienal in crude homogenates of fronds (CHF), while the second and third investigated whether ARA is the precursor of the pathway and if 11-HPETE is produced from ARA as an intermediate in 2(E),4(E)-decadienal generation, respectively. The results showed that 2(E),4(E)-decadienal was formed in CHF and its concentration increased after incubation. This finding led to the hypothesis that 2(E),4(E)-decadienal is formed enzymatically via LOX-HPL and consequently its biogeneration was determined. ARA was indicated to be a precursor of the pathway since, after CHF was incubated with ARA as a substrate, the amount of aldehyde increased significantly compared with that produced by CHF without ARA and without incubation. The production of 11-HPETE from ARA was also demonstrated as an intermediate reaction in 2(E),4(E)-decadienal formation via the LOX-HPL pathway. The hydroxy isomer of 11-HPETE was produced, and ARA was incubated with homogenated fronds in combination with glutathione peroxidase and glutathione to control its stability during identification. The compound was identified as 11-HPETE because the purified isomer showed the same retention time when co-injected with the standard using an HPLC technique; moreover, the same indicated mass spectrum was obtained as that of the standard via a GC/GCMS technique. The indicated pathway and the pathway for the production of short chain aldehydes [n-hexanal, 2(E),3(Z)-nonenal and 2(E),4(E)-decadienal] from ARA and linoleic acid through theirs hydroperoxides are proposed.