The resolvin D2 and omega-3 polyunsaturated fatty acid as a new possible therapeutic approach for inflammatory bowel diseases

Abstract

Inflammatory bowel diseases (IBD) are idiopathic disorders characterized by chronic gastrointestinal inflammation. Given conventional therapies' adverse effects and clinical failures, novel approaches are being investigated. Recent studies have highlighted the role of specialized pro-resolving lipid mediators (SPMs) in the active resolution of chronic inflammation. In this regard, omega-3 fatty acid-derived Resolvin D2 (RvD2) appears to play a protective role in the pathophysiology of IBD. Therefore, we characterized the RvD2 pathway and its receptor expression in the intestinal mucosa of experimental colitis induced by dextran sulfate sodium. We also evaluated the preventive impact of an omega-3-enriched diet and the therapeutic efficacy of RvD2 compared with anti-TNF-α treatment. We found an increase in TNFα and IL22 expression and decreased levels of enzymes involved in RvD2 biosynthesis, such as PLA₂, 15-LOX, 5-LOX, and its receptor GPR18 in experimental colitis. Omega-3 supplementation reduced the Disease Activity Index (DAI), weight loss, colonic shortening, and inflammation. These results and the increased IL-10 transcriptional levels after RvD2 treatment suggest that this mediator attenuated experimental colitis. These results enhance our understanding of the molecular mechanisms involved in the exacerbated inflammatory response present in experimental colitis and suggest that RvD2 and its omega-3 precursor offer a promising therapeutic approach for IBD.

Keywords: Chronic inflammation; Fatty acid; Inflammatory bowel disease; Omega-3; Pro-resolving lipid mediators; Resolvins.

Fig. 1

Evaluation of metabolic and histologic parameters in the DSS-induced colitis. Variation in mean body weight (grams per day) of mice with experimental colitis compared to the control group (A,B). Variation in average dietary intake of the group (grams per day) of mice with experimental colitis compared to the control group (C,D). Evolution of Disease Activity Index (E). Variation in colon length after 7 days of exposure to DSS (F,G). Histopathological characteristics of mice’s colonic tissue. Staining with Hematoxylin and Eosin (H&E) and Masson’s Trichrome. Presence of inflammatory cell infiltrate (black arrow) and collagen deposits (white arrow) in the lamina propria. Scale bars: 30 and 100 μm, labeled in each respective photomicrography (H). Results were graphically represented as Mean with SEM. CTR control group, DSS DSS-induced colitis group, DSS Dextran Sulfate Sodium. n = 6, *p < 0.05, **p < 0.01, and ***p < 0.001 were considered statistically significant compared to the control group.

Fig. 2

Inflammatory mediators and the RvD2 biosynthesis pathway in the intestinal mucosa of DSS-induced colitis. Diagram of RvD2 synthesis and its binding to the GPR18 receptor (A). PLA2 (B),15-LOX (C), 5-LOX (D), and GPR18 (E) mRNA levels (RT-qPCR) in the mice intestinal mucosa from the DSS group when compared to the CTR group. TNFα, IL1β, IL22, IL6, and IL10 mRNA levels (RT-qPCR) in the mice intestinal mucosa from the DSS group compared to the CTR group (F). Results were graphically represented as Mean with SEM. CTR control group, DSS DSS-induced colitis group, DSS Dextran Sulfate Sodium. n = 6, *p < 0.05, **p < 0.01, and ***p < 0.001 were considered statistically significant compared to the control group.

Fig. 3

Effect of omega-3 supplementation on the clinical profile of DSS-induced colitis. Variation in body weight of the experimental groups (A). Final variation in body weight of all groups (B). Evolution of Disease Activity Index (C). Colon specimens in all experimental groups (D). Variation in colon length after 7 days of exposure to DSS (E). Histopathological characteristics of mice’s colonic tissue. Staining with Hematoxylin and Eosin (H&E). Scale bars: 30 and 100 μm, labeled in each respective photomicrography (F). Histological score of colitis (G). Protein levels of IL1β (H), IFNϒ (I), IL17 (J), and IL10 (K) cytokines in the colonic tissue through multiplex analysis. Results were graphically represented as Mean with SEM. CTR control group with the standard diet, DSS DSS-induced colitis with the standard diet group, n-3 omega-3 supplemented diet group, n-3_DSS DSS-induced colitis with omega-3 enriched diet group. n = 6, *p < 0.05, **p < 0.01 were considered statistically significant compared to the DSS group; ^&p < 0.01 was considered statistically significant n-3 vs. DSS group; and *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001 were considered statistically significant compared to the control group and n-3 group.

Fig. 4

Clinical and inflammatory parameters of experimental colitis after treatment with intraperitoneal RvD2 or anti-TNFα. Variation in mean body weight (grams) of mice with experimental colitis treated with anti-TNFα (5 mg/Kg, single dose) or RvD2 (0.3 µg, 1.0 µg for 4 days) compared to the DSS group (A,B). Evolution of Disease Activity Index (C). Variation in colon length after exposure to DSS and the treatment with anti-TNFα or RvD2 (D). Histological score of colitis (E). CXCL1 mRNA levels (RT-qPCR) in the mice intestinal mucosa from the anti-TNFα and RvD2 treatment groups compared to the DSS group (F). IL10 mRNA levels (RT-qPCR) in the mice intestinal mucosa from the anti-TNFα and RvD2 treatment groups compared to the DSS group (G). Results were graphically represented as Mean with SEM. DSS DSS-induced colitis that received intraperitoneal injection of saline solution, DSS + anti-TNF DSS-induced colitis treated with an intraperitoneal injection of anti-TNFα, DSS + RvD2 0.3 DSS-induced colitis treated with an intraperitoneal injection of 0.3 µg RvD2, DSS + RvD2 1 DSS-induced colitis treated with an intraperitoneal injection of 1 µg RvD2. n = 6, *p < 0.05, **p < 0.01, ***p < 0.001 were considered statistically significant compared to the DSS group. ^&p < 0.05 was considered statistically significant between DSS + RvD2 0.3 vs. DSS group.