The n–3 polyunsaturated fatty acids contained in fish oil provide it with anti-inflammatory effects on different inflammatory diseases⁽Reference Kremer^1, Reference Soyland, Funk and Pajka²⁾. Several mechanisms can be involved in the influence of the degree of unsaturation of dietary fatty acids on the development of inflammatory diseases⁽Reference Moreno and Mitjavila³⁾. The beneficial effects of fish oil on inflammatory diseases have been attributed to the EPA/docosahexaenoic acid (DHA) content. EPA is also substrate for AA cascade enzymes, but induced the production of alternative eicosanoids such as 3-serie prostanoids and 5-serie leukotrienes that are considered to be less pro-inflammatory compared with AA metabolites. Thus, fish oil diet reduced AA mobilization and the subsequent prostaglandin (PG)E₂ synthesis⁽Reference Moreno, Carbonell and Sáncehz⁴⁾. However, the molecular basis of beneficial effect of EPA supplementation is poorly understood as well as the comparative biological effects of AA and EPA metabolites.

Leucocyte recruitment to inflamed areas is a pivotal event in the development of the inflammatory processes⁽Reference Lloret and Moreno⁵⁾. In this work, we studied the effects of PGE₂ and PGE₃ on endothelium permeability, the effects of leukotriene B₄ (LTB₄) and LTB₅ on endothelium permeability as well as mononuclear adhesion and migration.

Endothelial monolayer permeability to albumin was measured in ECV304 cell cultures using the Casnocha et al. methodology⁽Reference Casnocha, Eskin and Hall⁶⁾. Polymorphonuclear (PMN) granulocytes were isolated from human blood samples using Histopaque-1077. ECV304 cell confluent cultures were plated with PMN in the presence of eicosanoids and allowed to attach at 37°C for 3 h. Non-adherent cells were removed, cultures were fixed and PMN adhered to ECV304 monolayer were counted under a phase-contrast microscope. LFA-1 and MAC-1, and E-selectin and ICAM-1 expression on PMN and ECV304 surface, respectively, were analysed with a fluorescein-activated cell sorter analyser using the corresponding antibodies to each adhesion molecule. PMN chemotaxis was measured using the modified Boyden chamber technique⁽Reference Boyden⁷⁾ and a locomotion index was calculated using Maderazo and Woronick method⁽Reference Maderazo and Woronick⁸⁾. Results are means±se of three independent experiments performed in duplicate. Student's t test was used to determine the significance.

Our results show that both prostaglandins (PGE₂ and PGE₃, 0.1–100 nM) increased trans-endothelial Evans blue-albumin (EBA) permeability in a concentration-dependent manner, reaching a maximum plateau effect at 100 nM. Interestingly, the effect of PGE₃ (increased 115±3% v. control) (P<0.001) was slight higher than PGE₂ (90±4%) (P<0.001) action and both were significantly antagonised by EP₁ (SC19200, 1 μM) and EP₂ (AH6809, 1 μM) antagonist, but not by EP₃ and EP₄ antagonist. LTB₄ and LTB₅ presented a slight effect on EBA extravasation (32±2% and 21±1.5%, respectively.

LTB₄ (1–100 nM) caused significant increases in the number of PMN cell adhering to endothelial cells (280±13%–405±21%) (P<0.001 in all concentrations), whereas LTB₅ was not able to induce an appreciable effect. This effect of LTB₄ was mediated through the enhancement of adhesion molecules such as LFA-1 and MAC-1 on PMN surface and E-selectin and ICAM-1 expression on surface of endothelial cells. Finally, we observed that LTB₄ (10–100 nM) is a highly potent chemoattractant (migration index 1.25±0.05 and 1.68±0.1 v. migration index of 1 in control condition) (P<0.05 and P<0.001, respectively), whereas LTB₅ presents a weak effect (migration index of 1.15±0.06 at 100 nM).

In conclusion, the summation of these differences in the LTB₄/LTB₅ effect on PMN transmigration may contribute to explain the beneficial impact of omega-3 in inflammatory processes.