All of the abovementioned effects of PUFAs

All of the abovementioned effects of PUFAs signal their involvement in a cellular phenotype switching phenomenon, which is increasingly recognized as a potential target for future pharmacotherapies of atherosclerosis, especially for individuals who do not respond to the classical lipid-lowering strategies [18]. Indeed, if atherosclerosis is considered as a low-grade, unresolved inflammation, the phenotype switching approach, favoring a macrophage M2-like activation state, with increased capability for the safe removal of chronically activated cells, could hold promise as an improved atherosclerosis treatment. Our study strengthens these expectations, providing evidence that stimulation of free fatty acids receptors by the administration of their synthetic agonist GW9508 results in the attenuation of atherosclerosis in an apoE-/- mice model by targeting pro-inflammatory M1-like macrophages and shifting the balance within plaques toward Kartogenin of M2-like phenotype. Clearly, our study has a major limitation in that several of the GW9508-treated apoE-/- mice did not reach the end of the experimental protocol. Thus, when taking measurements, we could detect only trends in the changes of several parameters, not reaching statistical significance, thus making our mechanistic conclusions preliminary. This eventuality was somewhat surprising, since the GW9508 compound has been previously used in mice, usually administered intraperitoneally or orally, even at four-fold higher doses than in our setting [19,20]. The major discrepancy, apart from different mouse models investigated, was the duration of the experiments, ranging from seven to 30 days in the abovementioned studies, whereas our study continued for 16 weeks to ensure the development of sufficient atherosclerotic changes on a chow diet. Therefore, further investigation of the anti-atherosclerotic effect of GW9508, as well as exploration of the specific mechanisms elicited by FFAR1/FFAR4 activation in apoE-/- mice, is undoubtedly required. Different formulation of the GW9508 solution and other routes of drug administration should be considered in long-term experiments carried out on the apoE-/- mice model.
Conclusions
Author Contributions
Funding This research was funded by National Science Centre, grant number 2015/17/D/NZ2/01972.
Conflicts of Interest
Introduction Neutrophils represent the first line of host defense against invasive microorganisms and are among the first cells to migrate from the bloodstream to the injured or infected tissues (Smith, 1994). Neutrophils exert several types of defensive responses in invaded or injured tissues, such as superoxide production and the release of degradative enzymes stored in cytoplasmic granules, which contribute to the inflammatory process; however, a sustained and prolonged inflammatory response can also induce potential tissue damage (Nathan, 2006; Paape et al., 2003). The release of matrix metalloproteinase (MMP)-9 granules, a no oxidative response, is triggered by several stimuli that, upon coupling to exposed extracellular receptors, produce signals to increase the intracellular generation of secondary messengers such as intracellular calcium (Faurschou and Borregaard, 2003; Sengelov et al., 1993), which is largely achieved through the endoplasmic reticulum and via calcium influx through the plasma membrane (Burgos et al., 2011; Yin and Heit, 2017). Fatty acids are well-recognized metabolic intermediaries, but recent evidence indicates that they also function as signaling molecules with a clear role in the immune response, thus establishing a link between metabolism and immunity (Lackey and Olefsky, 2016). Indeed, fatty acids have been shown to modulate the functions of macrophages and neutrophils (Rodrigues et al., 2016; Walls et al., 2016). Short-chain fatty acids act as neutrophil chemoattractants that induce granules releases and oxidative response such as reactive oxygen species (ROS) production (Carretta et al., 2013; Maslowski et al., 2009; Vinolo et al., 2009), whereas long-chain fatty acids (LCFAs) induce different responses depending on whether omega-3, omega-6, or omega-9 fatty acids are used. For example, the omega-3 docosahexaenoic acid (DHA) reduces tumor necrosis factor-alpha (TNF-α), interleukin (IL)-6, monocyte chemoattractant protein-1, and IL-1β production along with inflammasome activation in murine macrophages (Oh et al., 2010; Williams-Bey et al., 2014), but increases TNF-α and ROS production in rat neutrophils (Paschoal et al., 2013). Linoleic and oleic acids (omega-6 and omega-9, respectively) induce intracellular calcium release, mitogen-activated protein kinase phosphorylation, cyclooxygenase-2 (COX-2) expression, IL-8 secretion, ROS production, and MMP-9 release in bovine neutrophils (Hidalgo et al., 2011; Mena et al., 2013, 2016), and oleic acids further increase cell the surface expression of CD11b and ROS production in human and rat neutrophils (Hatanaka et al., 2006; Mastrangelo et al., 1998).