Omega-6 docosapentaenoic acid-derived resolvins and 17-hydroxydocosahexaenoic acid modulate macrophage function and alleviate experimental colitis.

OBJECTIVE: Enzymatically oxygenated lipid products derived from omega-3 and omega-6 fatty acids play an important role in inflammation dampening. This study examined the anti-inflammatory effects of n-6 docosapentaenoic acid-derived (17S)-hydroxy-docosapentaenoic acid (17-HDPAn-6) and (10,17S)-dihydroxy-docosapentaenoic acid (10,17-HDPAn-6) as well as n-3 docosahexaenoic acid-derived 17(R/S)-hydroxy-docosahexaenoic acid (17-HDHA). MATERIALS AND METHODS: The effects of 17-HDPAn-6, 10,17-HDPAn-6 or 17-HDHA on activity and M1/M2 polarization of murine macrophage cell line RAW 264.7 were examined by phagocytosis assay and real-time PCR. To assess anti-inflammatory effects in vivo, dextran sodium sulfate (DSS) colitis was induced in mice treated with 17-HDPAn-6, 10,17-HDPAn-6, 17-HDHA or NaCl. RESULTS: Our results show that 17-HDPAn-6, 10,17-HDPAn-6 and 17-HDHA increase phagocytosis in macrophages in vitro and promote polarization towards the anti-inflammatory M2 phenotype with decreased gene expression of TNF-α and inducible Nitric oxide synthase and increased expression of the chemokine IL-1 receptor antagonist and the Scavenger receptor Type A. Intraperitoneal treatment with 17-HDPAn-6, 10,17-HDPAn-6, or 17-HDHA alleviated DSS-colitis and significantly improved body weight loss, colon epithelial damage, and macrophage infiltration. CONCLUSION: These results suggest that DPAn-6-derived 17-HDPAn-6 and 10,17-HDPAn-6 as well as the DHA-derived 17-HDHA have inflammation-dampening and resolution-promoting effects that could be used to treat inflammatory conditions such as inflammatory bowel disease.

Omega-3 fatty acids and their lipid mediators: towards an understanding of resolvin and protectin formation.

Omega-3 polyunsaturated fatty acids (n-3 PUFAs) have long been associated with decreased inflammation and are also implicated in the prevention of tumorigenesis. Conventional thinking attributed this mainly to a suppressive effect of these fatty acids on the formation of arachidonic acid-derived prostaglandins and leukotrienes. Recent years have seen the discovery of a new class of inflammation-dampening and resolution-promoting n-3 PUFA-derived lipid mediators called resolvins and protectins. Chemically, these compounds are hydroxylated derivatives of the parent n-3 PUFA eicosapentaenoic acid (EPA) for the E-resolvins, and docosahexaenoic acid (DHA) for the D-resolvins and protectin D1. While a relatively large number of these compounds have been identified and characterized until now, with differences in the positions of the hydroxyl-groups as well as in the chirality at the different carbon atoms, all compounds share common precursor metabolites, 17-hydroperoxydocosahexaenoic acid (17-H(p)DHA) for the DHA-derived compounds and 18-hydroperoxyeicosapentaenoic acid (18-H(p)EPE) for the EPA-derived compounds. In this review we summarize the current knowledge about EPA- and DHA-derived resolvins and protectins and explore the potential use of the pro-resolvins 17-hydroxydocosahexaenoic acid (17-HDHA) and 18-hydroxyeicosapentaenoic acid (18-HEPE) as indicators of anti-inflammatory n-3 PUFA mediator formation.

Suppressed liver tumorigenesis in fat-1 mice with elevated omega-3 fatty acids is associated with increased omega-3 derived lipid mediators and reduced TNF-α.

Liver tumors, particularly hepatocellular carcinoma (HCC), are a major cause of morbidity and mortality worldwide. The development of HCC is mostly associated with chronic inflammatory liver disease of various etiologies. Previous studies have shown that omega-3 (n-3) polyunsaturated fatty acids (PUFAs) dampen inflammation in the liver and decrease formation of tumor necrosis factor (TNF)-α. In this study, we used the fat-1 transgenic mouse model, which endogenously forms n-3 PUFA from n-6 PUFA to determine the effect of an increased n-3 PUFA tissue status on tumor formation in the diethylnitrosamine (DEN)-induced liver tumor model. Our results showed a decrease in tumor formation, in terms of size and number, in fat-1 mice compared with wild-type littermates. Plasma TNF-α levels and liver cyclooxygenase-2 expression were markedly lower in fat-1 mice. Furthermore, there was a decreased fibrotic activity in the livers of fat-1 mice. Lipidomics analyses of lipid mediators revealed significantly increased levels of the n-3 PUFA-derived 18-hydroxyeicosapentaenoic acid (18-HEPE) and 17-hydroxydocosahexaenoic acid (17-HDHA) in the livers of fat-1 animals treated with DEN. In vitro experiments showed that 18-HEPE and 17-HDHA could effectively suppress lipopolysacharide-triggered TNF-α formation in a murine macrophage cell line. The results of this study provide evidence that an increased tissue status of n-3 PUFA suppresses liver tumorigenesis, probably through inhibiting liver inflammation. The findings also point to a potential anticancer role for the n-3 PUFA-derived lipid mediators 18-HEPE and 17-HDHA, which can downregulate the important proinflammatory and proproliferative factor TNF-α.

Analysis of omega-3 and omega-6 fatty acid-derived lipid metabolite formation in human and mouse blood samples.

Mass spectrometry techniques have enabled the identification of different lipid metabolites and mediators derived from omega-6 and omega-3 polyunsaturated fatty acids (n-6 and n-3 PUFA) that are implicated in various biological processes. However, the broad-spectrum assessment of physiologically formed lipid metabolites and mediators in blood samples has not been presented so far. Here lipid mediators and metabolites of the n-6 PUFA arachidonic acid as well as the long-chain n-3 PUFA eicosapentaenoic acids (EPA) and docosahexaenoic acid (DHA) were measured in human blood samples as well as in mouse blood. There were detectable but mostly very low amounts of the assayed compounds in human native plasma samples, whereas in vitro activation of whole blood with the calcium ionophore A23187 led to highly significant increases of metabolite formation, with a predominance of the 12-lipoxygenase (12-LOX) products 12-hydroxyeicosatetraenoic acid (12-HETE), 12-hydroxyeicosapentaenoic acid (12-HEPE) and 14-hydroxydocosahexaenoic acid (14-HDHA). A23187 activation also led to significant increases in the formation of 5-LOX products including leukotriene B(4) (LTB(4)), leukotriene B(5) (LTB(5)) as well as of 15-LOX products and prostaglandin E(2) (PGE(2)) and thromboxane B(2) (TXB(2)). Levels were similar or even higher in A23187-activated mouse blood. The approach presented here thus provides a protocol for the comprehensive and concomitant assessment of the generation capacity of n-3 and n-6 PUFA-derived lipid metabolites as well as thromboxanes and prostaglandins in human and murine blood samples. Further studies will now have to evaluate lipid metabolite generation capacity in different physiological and pathophysiological contexts.

Acetylsalicylic Acid reduces the severity of dextran sodium sulfate-induced colitis and increases the formation of anti-inflammatory lipid mediators.

The role of non-steroidal anti-inflammatory drugs in inflammatory bowel disease is controversial, as they have been implicated in disease aggravation. Different from other cyclooxygenase inhibitors, acetylsalicylic acid (ASA) enhances the formation of anti-inflammatory and proresolution lipoxins derived from arachidonic acid as well as resolvins from omega-3 polyunsaturated fatty acids such as docosahexaenoic acid (DHA). In this study, we examined the effect of ASA on murine dextran sodium sulfate colitis. A mouse magnetic resonance imaging (MRI) protocol and post mortem assessment were used to assess disease severity, and lipid metabolites were measured using liquid chromatography-coupled tandem mass spectrometry. Decreased colitis activity was demonstrated by phenotype and MRI assessment in mice treated with ASA, and confirmed in postmortem analysis. Analysis of lipid mediators showed sustained formation of lipoxin A4 and an increase of DHA-derived 17-hydroxydocosahexaenoic acid (17-HDHA) after treatment with ASA. Furthermore, in vitro experiments in RAW264.7 murine macrophages demonstrated significantly increased phagocytosis activity after incubation with 17-HDHA, supporting its proresolution effect. These results show a protective effect of ASA in a murine colitis model and could give a rationale for a careful reassessment of ASA therapy in patients with inflammatory bowel disease and particularly ulcerative colitis, possibly combined with DHA supplementation.