The Beneficial Effects of -3 Polyunsaturated Fatty Acids on Proliferative Retinopathies Are Mediated via the 5-Lipoxygenase Pathway

Abstract

Purpose: : Vaso-proliferative retinopathies are the principal causes of blindness across all age groups. The propensity of ω-3 polyunsaturated fatty acids (PUFAs) to ameliorate conditions linked to ocular neovascularization has been reported in both experimental and clinical settings. However, the mechanisms and effectors governing these beneficial effects have remained largely elusive. Here we investigate the involvement of the lipoxygenase pathways (5-LO & 12/15-LO) in mediating the anti-proliferative effects of ω-3 PUFAs in a mouse oxygen-induced retinopathy model (OIR).

Methods: : Wild-type, 5-LO-/- and 12/15-LO-/- mouse mothers were fed isocaloric diets enriched in either ω-3 PUFAs or conversely ω-6 PUFAs (otherwise matched). Proliferative retinopathy was induced in their pups using a mouse model of OIR where pups were exposed to 75% O2 from postnatal day (P) 7 to P12 and returned to room air until P17 (maximal neovascularization (NV)). The inflammatory status of retinas was assessed by RT-PCR for TNF-α, IL-6, IL-10, E-Selectin and ICAM. Retinas and serum were collected and lipid-derived mediators analysed by gas chromatography/mass spectrometry.

Results: : Retinal NV at P17 was significantly reduced (~45%) in ω-3-fed wild-type and 12/15-LO-/- animals when compared to ω-6-fed controls. This protective effect of ω-3 PUFAs was largely abolished in 5-LO-/- mice (non-significant 7% reduction in NV) suggesting an anti-proliferative role for ω-3-derived 5-LO lipid metabolites. Consistent with a role for inflammation in preventing NV reduction, ω-3-fed 5-LO-/- mice failed to show the ω-3-induced reduction of retinal pro-inflammatory mediators seen in wild-type mice. In line, ω-3-fed 5-LO-/- mice did not display the ω-3-associated increase in anti-inflammatory IL-10 seen in wild-type mice. Accordingly, lipidomic analysis of retinas and serum from ω-3-fed 5-LO-/- mice revealed 3-fold lower concentrations of the DHA metabolites 4-HDHA and 7-HDHA (established markers of the protective/anti-inflammatory resolvin pathway) compared to ω-3-fed wild-type controls.

Conclusions: : Our data disclose a prominent role for 5-LO and its ω-3 derived metabolites in mediating the beneficial anti-angiogenic effects of ω-3 PUFAs. These findings provide the ground work for streamlining lipid-based therapeutic applications to curtail ocular neovascularization.

Keywords: retinal neovascularization • retinal neovascularization • pathobiology