Arachidonic acid 5-lipoxygenase (ALOX5) is the key enzyme in the biosynthesis of pro-inflammatory leukotrienes. We recently created knock-in mice (Alox5-KI) which express an arachidonic acid 15-lipoxygenating Alox5 mutant instead of the 5-lipoxygenating wildtype enzyme. These mice were leukotriene deficient but exhibited an elevated linoleic acid oxygenase activity. Here we characterized the polyenoic fatty acid metabolism of these mice in more detail and tested the animals in three different experimental inflammation models. In experimental autoimmune encephalomyelitis (EAE), Alox5-KI mice displayed an earlier disease onset and a significantly higher cumulative incidence rate than wildtype controls but the clinical score kinetics were not significantly different. In dextran sodium sulfate-induced colitis (DSS) and in the chronic constriction nerve injury model (CCI), Alox5-KI mice performed like wildtype controls with similar genetic background. These results were somewhat surprising since in previous loss-of-function studies targeting leukotriene biosynthesis (Alox5^−/− mice, inhibitor studies), more severe inflammatory symptoms were observed in the EAE model but the degree of inflammation in DSS colitis was attenuated. Taken together, our data indicate that these mutant Alox5-KI mice respond differently in two models of experimental inflammation than Alox5^−/− animals tested previously in similar experimental setups.

Evidence suggests beneficial effects of long‐chain n–3 polyunsaturated fatty acids (PUFAs) in inflammatory diseases. However, the underlying mechanisms are still subject of research. For this purpose, we developed an ex vivo n–3 PUFA supplementation strategy. M2‐like macrophages were supplemented for 2–3 days with 20–40 µM docosahexaenoic acid (DHA) during differentiation. Quality parameters include <3% oxylipins for PUFA‐preparation, total fatty acids (FAs) <10 mM, and low oxylipins in plasma, n–3 PUFA <0.25 mM for the selection of donors of plasma as well as %n–6 in highly unsaturated fatty acids (HUFAs) ≥70% for donors of cells. Following supplementation, PUFA pattern of cells was shifted toward one described for blood and tissue from subjects with higher n–3 and lower n–6 PUFAs. This was accompanied by a decrease of arachidonic acid‐derived oxylipins in a dose‐ and time‐dependent manner in favor of n–3 PUFA ones. Stimulation with LPS resulted in decreased levels of pro‐inflammatory prostaglandins in the DHA‐supplemented cells, but no changes in cytokines. In vitro supplementation studies with n–3 PUFA need rigorous controls to exclude the background formation of oxylipins. By accounting for these possible confounders the described approach allows the mechanistic investigation of n–3 PUFAs in primary human immune cells, offering an alternative for intervention studies.

Colorectal cancer (CRC) is one of the most prevalent cancers worldwide, ranking as the third most malignant. The incidence of CRC has been increasing with time, and it is reported that Westernized diet and lifestyle play a significant role in its higher incidence and rapid progression. The intake of high amounts of omega-6 (n − 6) PUFAs and low levels of omega-3 (n − 3) PUFAs has an important role in chronic inflammation and cancer progression, which could be associated with the increase in CRC prevalence. Oxylipins generated from PUFAs are bioactive lipid mediators and have various functions, especially in inflammation and proliferation. Carcinogenesis is often a consequence of chronic inflammation, and evidence has shown the particular involvement of n − 6 PUFA arachidonic acid-derived oxylipins in CRC, which is further described in this review. A deeper understanding of the role and metabolism of PUFAs by their modifying enzymes, their pathways, and the corresponding oxylipins may allow us to identify new approaches to employ oxylipin-associated immunomodulation to enhance immunotherapy in cancer. This paper summarizes oxylipins identified in the context of the initiation, development, and metastasis of CRC. We further explore CRC chemo-prevention strategies that involve oxylipins as potential therapeutics.

The ketogenic diet (KD) is a high-fat, low-carbohydrate diet that has been reported to have neuroprotective effects. The health effects of KD might be linked to an altered gut microbiome, which plays a major role in host health, leading to neuroprotective effects via the gut-brain axis. However, results from different studies, most often based on the 16S rRNA gene and metagenome sequencing, have been inconsistent. In this study, we assessed the effect of a 4-week KD compared to a western diet (WD) on the colonic microbiome of female C57Bl/6J mice by analyzing fecal samples using fluorescence in situ hybridization. Our results showed distinct changes in the total number of gut bacteria following the 4-week KD, in addition to changes in the composition of the microbiome. KD-fed mice showed higher absolute numbers of Actinobacteria (especially Bifidobacteria spp.) and lower absolute levels of Proteobacteria, often linked to gut inflammation, in comparison with WD-fed mice. Furthermore, an increased abundance of the typically rare genus Atopobium was observed. These changes may indicate the possible anti-inflammatory effects of the KD. However, since the overall changes in the microbiota seem low, the KD effects might be linked to the differential abundance of only a few key genera in mice.

Background, objectives and design: Arachidonic acid 15-lipoxygenase (ALOX15) has been implicated in the pathogenesis of inflammatory diseases but since pro- and anti-inflammatory roles have been suggested, the precise function of this enzyme is still a matter of discussion. To contribute to this discussion, we created transgenic mice, which express human ALOX15 under the control of the activating protein 2 promoter (aP2-ALOX15 mice) and compared the sensitivity of these gain-of-function animals in two independent mouse inflammation models with Alox15-deficient mice (loss-of-function animals) and wildtype control animals. Materials and methods: Transgenic aP2-ALOX15 mice were tested in comparison with Alox15 knockout mice (Alox15^−/−) and corresponding wildtype control animals (C57BL/6J) in the complete Freund’s adjuvant induced hind-paw edema model and in the dextran sulfate sodium induced colitis (DSS-colitis) model. In the paw edema model, the degree of paw swelling and the sensitivity of the inflamed hind-paw for mechanic (von Frey test) and thermal (Hargreaves test) stimulation were quantified as clinical readout parameters. In the dextran sodium sulfate induced colitis model the loss of body weight, the colon lengths and the disease activity index were determined. Results: In the hind-paw edema model, systemic inactivation of the endogenous Alox15 gene intensified the inflammatory symptoms, whereas overexpression of human ALOX15 reduced the degree of hind-paw inflammation. These data suggest anti-inflammatory roles for endogenous and transgenic ALOX15 in this particular inflammation model. As mechanistic reason for the protective effect downregulation of the pro-inflammatory ALOX5 pathways was suggested. However, in the dextran sodium sulfate colitis model, in which systemic inactivation of the Alox15 gene protected female mice from DSS-induced colitis, transgenic overexpression of human ALOX15 did hardly impact the intensity of the inflammatory symptoms. Conclusion: The biological role of ALOX15 in the pathogenesis of inflammation is variable and depends on the kind of the animal inflammation model.

Purpose: A ketogenic diet (KD), high in fat and low in carbohydrates, induces ketosis characterized by elevated circulating ketone bodies. While both KD and ketone bodies have demonstrated therapeutic potential in various pathophysiological conditions, their effect on inflammatory bowel diseases remains controversial. This study aimed to investigate the impact of a KD and ketone ester (KE), an ingestible form of ketone bodies, on intestinal inflammation. Methods: Acute dextran sodium sulfate (DSS)- and 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced murine colitis models were used to evaluate and compare the effects of KD feeding and KE supplementation on intestinal inflammation, the mucus barrier and gut microbiota composition. Results: KD feeding did not significantly affect colitis activity, whereas KE supplementation alleviated colitis in both models investigated. KE-induced mitigation of colitis was associated with increased mucin2 expression, indicating enhanced colonic mucus barrier integrity. KE supplementation also improved goblet cell function and differentiation, as evidenced by increased goblet cell numbers and the upregulation of goblet cell differentiation markers. Furthermore, 16S rRNA sequencing analysis revealed that KE supplementation resulted in higher abundances of mucus-degrading Akkermansia , a genus believed to play a key role in maintaining intestinal homeostasis. Conclusion: The present study suggests that KE represent an effective anti-inflammatory dietary supplement in the context of acute colitis, potentially by modulating mucin2 expression, goblet cell differentiation, and the abundance of Akkermansia . Although promising, these findings remain preliminary, and further investigations are needed to explore the therapeutic potential of KE as a dietary supplement in patients with inflammatory bowel disease.