15(S)-Lipoxygenase-1 associates with neutral lipid droplets in macrophage foam cells: evidence of lipid droplet metabolism

15(S)-Lipoxygenase-1 associates with neutral lipid droplets in macrophage foam cells: evidence of lipid droplet metabolism

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15(S)-lipoxygenase-1 (15-LO-1) was present in the whole-cell homogenate of an acute human monocytic leukemia cell line (THP-1).Additionally, 15-LO-1 was detected on neutral lipid False Eyelashes droplets isolated from THP-1 foam cells.To investigate if 15-LO-1 is active on lipid droplets, we used the mouse leukemic monocytic macrophage cell line (RAW 264.7), which are stably transfected with human 15-LO-1.The RAW 15-LO-1 cells were incubated with acetylated low density lipoprotein to generate foam cells.

15(S)-hydroxyeicosatetraenoic acid [15(S)-HETE], the major 15-LO-1 metabolite of arachidonic acid, was produced in the 15-LO-1 RAW but not in the mock transfected cells when incubated with arachidonic acid.Lipid droplets were isolated from the cells and incubated with arachidonic acid, and production of 15(S)-HETE was measured over 2 h.15(S)-HETE was produced in the incubations with the lipid droplets, and this production was attenuated when the lipid droplet fraction was subjected to enzyme inactivation through heating.Efflux of 15(S)-HETE from cholesteryl ester-enriched 15-LO RAW cells, when lipid droplets are present, was significantly reduced compared with that from cells enriched with free cholesterol (lipid droplets are absent).We propose that 15-LO-1 is present and functional on cytoplasmic neutral lipid IC CPU droplets in macrophage foam cells, and these droplets may act to accumulate the anti-inflammatory lipid mediator 15(S)-HETE.