A. Chacon1, B. E. Phillips1, S. Kelleher1, M. Chacon1, D. Brunke-Reese1, D. Soybel1 1Penn State University College Of Medicine,Hershey, PA, USA
Introduction: Chemical and mechanical irritation of the peritoneum lead to acute inflammation, delaying recovery of intestinal motor coordination and increasing susceptibility to secondary infection. Recent studies in a variety of settings have provided evidence that targeted therapy with purified omega-3 fatty acids or synthetic pro-resolution lipids may attenuate acute inflammation and hasten the transition to healing. Administration of highly processed nutraceutical agents may, however, be attended with unanticipated toxicities or undesirable pharmacologic effects. In this study, we tested the hypothesis that resolution of peritoneal inflammation would be enhanced by pre-treatment with fish oil rich in docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), precursors to more potent lipid mediators of resolution.
Methods: C57/BL6 mice were begun on a daily oral gavage of 200uL Marinol® C-38, a fish oil blend containing 17% DHA and 22% EPA (FO) or saline as a control (C). At day 7, 3% thioglycollate media was injected into the peritoneum to create a chemical peritonitis, and exudates were collected by peritoneal lavage at 0hr (no injection), 48hr, and 96hr. Lipid inflammatory mediators in lavage fluid were assessed via ELISA (Leukotriene B4 {LTB4}, Resolvin D1 {RvD1}). Cells harvested via lavage were isolated for differential Wright-Giemsa staining, and cells collected at 96hr (95% macrophages) were assessed for macrophage differentiation markers via quantitative PCR. Additional cells were incubated in media alone for 16hr or with the addition of LPS (100ng/ml). Ex vivo cytokine secretion was assessed in culture media via ELISA (IL-6, IL-10, IL-1β, TNFα), and phagocytic capacity was assessed via uptake of fluorescent E. coli bioparticles.
Results: Fish Oil (FO) increased the ratio of RvD1/LTB4 in the peritoneal cavity at 0hr. No significant changes were observed in total counts of polymorphonuclear cells, macrophages or lymphocytes in the lavage fluid, and FO did not significantly alter mRNA markers of macrophage phenotype. FO interestingly increased ex vivo TNFα secretion after stimulation with LPS in cells harvested at 96hr. No effect of FO was seen on LPS-stimulated particle phagocytosis.
Conclusion: Our findings provide evidence that nutraceutically relevant doses of FO supplements enhance production of pro-resolution lipid mediators such as RvD1 relative to that of pro-inflammation mediators such as LTB4 following induction of chemical peritonitis, without altering counts or transition states of local innate immune cell populations. These observations stand in contrast to more powerful and global effects of purified compounds, suggesting that the latter may be more effective in enhancing resolution, but also in inviting unwanted pharmacologic sequelae. Further studies will be required to determine whether FO-induced alterations in the RvD1/LTB4 ratio can hasten resolution without compromising other homeostatic functions.