N-3 polyunsaturated fatty acids reduce allergic type mediator release by human mast cells in vitro via inhibition of reactive oxygen species

Background: The increased ratio of n-6/n-3 polyunsaturated fatty acids (PUFA) in Western diets may contribute to the rapid increase in prevalence of allergic diseases. Mast cells (MC) are the key effector cells in allergy. The effect of different PUFA on MC activation and mediator release was investigated and the contribution of reactive oxygen species (ROS) and mitogenactivated protein kinase (MAPK) signaling routes was studied. Method: Human MC lines (LAD2, HMC- 1) were incubated for 24 h with long chain n-6 (arachidonic acid, AA) or n-3 (eicosapentaenoic acid, EPA and docosahexaenoic acid, DHA) PUFA. Effects of PUFA on degranulation, mediator secretion (PGD2, TNF-a, IL-4 and IL-13), and generation of ROS was measured. Result: Incubation with PUFA did not reduce IgE-mediated degranulation by LAD2 cells. However, mediator release of ionomycin/PMA stimulated HMC-1 cells was differentially regulated. AA incubation increased PGD2 and TNF-a (P <0.05) secretion whereas IL-13 (P <0.01 for all PUFA) and IL-4 (P <0.05 for EPA and DHA) secretion were inhibited. The reduction in IL-13 and IL-4 release by PUFA was associated with a reduction in ROS generation (P <0.01). Use of specific ROS inhibitor superoxide dismutase showed that IL-4 secretion is under regulation of superoxide, while IL-13 release was strongly decreased by general ROS inhibitor 1,3-dimethyl-2-thiourea (DMTU). MAPK signaling was found to contribute to IL-13 secretion by activated HMC-1 cells. MC incubation with MAPK inhibitors and PUFA showed differential effects for n-3 vs n-6 PUFA. MAPK inhibitors reduced IL-13 secretion by HMC-1 and only combined incubation of n-3 PUFA with p38 or JNK MAPK inhibitors further suppressed IL-13 production. Conclusion: N-6 PUFA enhanced production of proinflammatory mediators from mast cells, while n-3 PUFA most effectively suppressed ROS generation and IL- 13 and IL-4 release. This suggests that an increase in dietary n-6/n-3 PUFA ratio may increase the susceptibility to develop allergic disease and enhance allergic inflammation.