Resolvin E1, an endogenous lipid mediator derived from omega-3 eicosapentaenoic acid, protects against 2,4,6-trinitrobenzene sulfonic acid-induced colitis

Abstract

Resolvin E1 (RvE1; 5S,12R,18R-trihydroxyeicosapentaenoic acid) is an antiinflammatory lipid mediator derived from omega-3 fatty acid eicosapentaenoic acid (EPA). At the local site of inflammation, aspirin treatment enhances EPA conversion to 18R-oxygenated products, including RvE1, which carry potent antiinflammatory signals. Here, we obtained evidence for reduced leukocyte infiltration in a mouse peritonitis model, where the administration of EPA and aspirin initiated the generation of RvE1 in the exudates. Similar results were obtained with the administration of synthetic RvE1, which blocked leukocyte infiltration. RvE1 also protected against the development of 2,4,6-trinitrobenzene sulfonic acid-induced colitis. The beneficial effect was reflected by increased survival rates, sustained body weight, improvement of histologic scores, reduced serum anti-2,4,6-trinitrobenzene sulfonic acid IgG, decreased leukocyte infiltration, and proinflammatory gene expression, including IL-12 p40, TNF-alpha, and inducible nitric oxide synthase. Thus, the endogenous lipid mediator RvE1 counter-regulates leukocyte-mediated tissue injury and proinflammatory gene expression. These findings show an endogenous mechanism that may underlie the beneficial actions of omega-3 EPA and provide targeted approaches for the treatment of intestinal inflammation.

Fig. 1.

RvE1 formation and antiinflammatory actions in peritonitis. (A) Inflammatory exudates from mice treated with EPA and aspirin generate RvE1 in vivo. (B) Inhibition of leukocyte infiltration in zymosan-induced peritonitis treated with EPA and aspirin. Mice were pretreated for 30 min with aspirin (0.5 mg) i.p., followed by EPA (0.3 mg) and zymosan. Peritoneal lavages were collected at 2 h, and cells were enumerated. (n = 4, *, P < 0.05, compared with vehicle control; **, P < 0.05, compared with aspirin alone). (C) Inhibition of leukocyte infiltration in zymosan-induced peritonitis. RvE1 (100 ng) was injected into tail veins, and zymosan A was injected into the peritoneum. Mice were killed, peritoneal lavages were collected (2 h), and cells were enumerated (n = 3; *, P < 0.01 compared with vehicle control).

Fig. 2.

RvE1 dramatically attenuates TNBS-induced colitis. (A) The survival rate of RvE1-treated mice was significantly higher than that of nontreated mice. (B) Wasting disease measured by body weight loss in mice with TNBS colitis is improved by RvE1 treatment. Open diamonds, vehicle control; open circles, TNBS only; filled circles, TNBS treated with RvE1 (1 μg per mouse or 0.05 mg/kg). *, P < 0.01; **, P < 0.001 compared with vehicle control (n = 6). (C) Macroscopic appearance of the colon of mice receiving vehicle, TNBS only, or RvE1 (0.05 mg/kg). (D) Length of the inflamed colons of mice treated with either TNBS alone or RvE1. *, P < 0.01, compared with TNBS alone.

Fig. 3.

Colon histopathology from RvE1- or ATLa-treated mice. (A–D) Colon section of mouse treated with vehicle (A), day 4 after TNB-induced colitis (B), RvE1-treated mouse (C), and ATLa-treated mouse (D). (E) Histological scores of the colon of mice receiving vehicle, TNBS only, TNBS plus RvE1, or TNBS plus ATLa. * and **, P < 0.05 and P < 0.01, respectively.

Fig. 4.

RvE1 reduces leukocyte infiltration and proinflammatory mediators in colitis. (A) Myeloperoxidase activity of colons of mice treated with TNBS alone or RvE1. *, P < 0.0001 vs. mice treated with TNBS alone. (B) Anti-TNBS IgG level in serum on day 4 from mice treated with TNBS alone or RvE1 as noted. *, P < 0.01. (C) Quantitative real-time PCR analysis of mRNA expression of inflammatory mediators in colons obtained on day 4 from control mice (white column), mice treated with TNBS alone (black column), or mice receiving TNBS plus RvE1 (gray column). *, P < 0.01.

Fig. 5.

ChemR23 mRNA is expressed in mouse colon. Total RNA was isolated from control and TNBS-treated colons, and RT-PCR was performed as described in Methods.