The Effect of Omega-3 Polyunsaturated Fatty Acids on the Resolution of Inflammation in the Rodent Brain

Resolution of inflammation in the periphery is believed to be mediated by omega- 3 polyunsaturated fatty acids (n-3 PUFA) derived specialized pro-resolving lipid mediators. However, the resolution of neuroinflammation, and the role of n-3 PUFA and their specialized pro-resolving lipid mediators in the resolution of neuroinflammation have yet to be studied. Moreover, while ischemia induces the production of various mediators in the brain, this effect has yet to be demonstrated for specialized pro-resolving lipid mediators. The first objective of this thesis was to develop a lipidomic approach to measure the rodent neurolipidome without the effect of ischemia using head-focused microwave fixation. Once a lipidomic approach was developed, we attempted to develop a selfresolving model of neuroinflammation and to determine the effect of increasing brain docosahexaenoic acid (DHA) on resolution of neuroinflammation. We demonstrated that microwave-fixation inhibits ischemia-induced production of bioactive mediators, including specialized pro-resolving lipid mediators, and changes in various intact lipid species. We then developed a self-resolving model of neuroinflammation using intracerebroventricular injections of lipopolysaccharide (LPS). Following LPS injection, microglia activation peaked at 5 days and returned to baseline by 21 days. Using a microarray, we illustrated that various markers had varying time courses of inflammation. Interestingly, no neutrophil infiltration was detected. Since neutrophils carry the lipoxygenase enzyme, which produces specialized pro-resolving lipid mediators, we also did not detect specialized pro-resolving mediator production following LPS injection as measured by our new lipidomic approach combined with microwave fixation. In order to increase brain DHA, we compared a wildtype mouse fed a safflower diet deficient in n-3 PUFA to the fat-1 mouse and a wildtype mouse fed a fish oil diet high in n-3 PUFA. Increasing brain DHA resulted in modest increases in resolution of microglia activation and cyclooxygenase (COX)-2 mRNA expression. However, many other inflammatory markers were unaffected by the increased brain DHA. In conclusion, we illustrated that microwave fixation inhibits the ischemiainduced changes on the rodent neurolipidome and that n-3 PUFA have small proresolving properties in a self-resolving model of neuroinflammation. These appear to be independent of specialized pro-resolving mediator production.Ph.D.2017-11-30 00:00:0