DHA-derived oxylipins, neuroprostanes and protectins, differentially and dose-dependently modulate the inflammatory response in human macrophages: Putative mechanisms through PPAR activation

Whereas the anti-inflammatory properties and mechanisms of action of long chain ω3 PUFAs have been abundantly investigated, research gaps remain regarding the respective contribution and mechanisms of action of their oxygenated metabolites collectively known as oxylipins. We conducted a dose-dependent and comparative study in human primary macrophages aiming to compare the anti-inflammatory activity of two types of DHA-derived oxylipins including the well-described protectins (NPD1 and PDX), formed through lipoxygenase pathway and the neuroprostanes (14-A_4t- and 4-F_4t-NeuroP) formed through free-radical mediated oxygenation and expected to be new anti-inflammatory mediators. Considering the potential ability of these DHA-derived oxylipins to bind PPARs and knowing the central role of these transcription factors in the regulation of macrophage inflammatory response, we performed transactivation assays to compare the ability of protectins and neuroprostanes to activate PPARs. All molecules significantly reduced mRNA levels of cytokines such as IL-6 and TNF-α, however not at the same doses. NPD1 showed the most effect at 0.1µM (-14.9%, p<0.05 for IL-6 and -26.7%, p<0.05 for TNF-α) while the three other molecules had greater effects at 10µM, with the strongest result due to the cyclopentenone neuroprostane, 14-A_4t-NeuroP (-49.8%, p<0.001 and -40.8%, p<0.001, respectively). Part of the anti-inflammatory properties of the DHA-derived oxylipins investigated could be linked to their activation of PPARs. Indeed, all tested oxylipins significantly activated PPARγ, with 14-A_4t-NeuroP leading to the strongest activation, and NPD1 and PDX also activated PPARα. In conclusion, our results show that neuroprostanes and more especially cyclopentenone neuroprostanes have potent anti-inflammatory activities similar or even more pronounced than protectins supporting that neuroprostanes should be considered as important contributors to the anti-inflammatory effects of DHA.