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Antibiotic-induced dysbiosis is a key predisposing factor for Clostridium difficile infections (CDIs), which cause intestinal disease ranging from mild diarrhea to pseudomembranous colitis. Here, we examined the impact of a microbiota-derived metabolite, short-chain fatty acid acetate, on an acute mouse model of CDI. We found that administration of acetate is remarkably beneficial in ameliorating disease. Mechanistically, we show that acetate enhances innate immune responses by acting on both neutrophils and ILC3s through its cognate receptor free fatty acid receptor 2 (FFAR2). In neutrophils, acetate-FFAR2 signaling accelerates their recruitment to the inflammatory sites, facilitates inflammasome activation, and promotes the release of IL-1β; in ILC3s, acetate-FFAR2 augments expression of the IL-1 receptor, which boosts IL-22 secretion in response to IL-1β. We conclude that microbiota-derived acetate promotes host innate responses to C. difficile through coordinate action on neutrophils and ILC3s., Competing Interests: Disclosures: The authors declare no competing interests exist., (© 2019 Fachi et al.)

Short-chain fatty acids (SCFAs), predominantly acetic, propionic, and butyric acids, are bacterial metabolites with an important role in the maintenance of homeostasis due to their metabolic and immunomodulatory actions. Some evidence suggests that they may also be relevant during infections. Therefore, we aimed to investigate the effects of SCFAs in the effector functions of neutrophils to an opportunistic pathogenic bacterium, Aggregatibacter actinomycetemcomitans. Using a subcutaneous model to generate a mono, isolated infection of A. actinomycetemcomitans, we demonstrated that the presence of the SCFAs in situ did not affect leukocyte accumulation but altered the effector mechanisms of migrating neutrophils by downregulating the production of cytokines, their phagocytic capacity, and killing the bacteria, thus impairing the containment of A. actinomycetemcomitans. Similar effects were observed with bacteria-stimulated neutrophils incubated with SCFAs in vitro. These effects were independent of free-fatty acid receptor 2 (FFAR2) activation, the main SCFA receptor expressed on neutrophils, occurring possibly through inhibition of histone deacetylases because similar effects were obtained by using histone deacetylase inhibitors, such as SAHA, MS-275, and RGFP 966. Considering the findings of this study, we hypothesized that in an infectious condition, SCFAs may exert a detrimental effect on the host by inhibiting neutrophil's effector functions., (© 2017 John Wiley & Sons Ltd.)

Neutrophils are well-known to act in the destruction of invading microorganisms. They have also been implicated in the activation of other immune cells including B- and T-lymphocytes and in the resolution of inflammation and tissue regeneration. Neutrophils are produced in the bone marrow and released into the circulation from where they migrate to tissues to perform their effector functions. Neutrophils are in constant contact with fatty acids that can modulate their function, activation and fate (survival or cell death) through different mechanisms. In this review, the effects of fatty acids pertaining to five classes, namely, long-chain saturated fatty acids (LCSFAs), short-chain fatty acids (SCFAs), and omega-3 (n-3), omega-6 (n-6) and omega-9 (n-9) unsaturated fatty acids, on neutrophils and the relevance of these effects for disease development are discussed., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Short chain fatty acids (SCFAs) are fermentation products of anaerobic bacteria. More than just being an important energy source for intestinal epithelial cells, these compounds are modulators of leukocyte function and potential targets for the development of new drugs. The aim of this study was to evaluate the effects of SCFAs (acetate, propionate and butyrate) on production of nitric oxide (NO) and proinflammatory cytokines [tumor necrosis factor α (TNF-α) and cytokine-induced neutrophil chemoattractant-2 (CINC-2αβ)] by rat neutrophils. The involvement of nuclear factor κB (NF-κB) and histone deacetylase (HDAC) was examined. The effect of butyrate was also investigated in vivo after oral administration of tributyrin (a pro-drug of butyrate). Propionate and butyrate diminished TNF-α, CINC-2αβ and NO production by LPS-stimulated neutrophils. We also observed that these fatty acids inhibit HDAC activity and NF-κB activation, which might be involved in the attenuation of the LPS response. Products of cyclooxygenase and 5-lipoxygenase are not involved in the effects of SCFAs as indicated by the results obtained with the inhibitors of these enzymes. The recruitment of neutrophils to the peritonium after intraperitoneal administration of a glycogen solution (1%) and the ex vivo production of cytokines and NO by neutrophils were attenuated in rats that previously received tributyrin. These results argue that this triglyceride may be effective in the treatment of inflammatory conditions., (Crown Copyright © 2011. Published by Elsevier Inc. All rights reserved.)

The high ingestion of oleic (OLA) and linoleic (LNA) acids by Western populations, the presence of inflammatory diseases in these populations, and the importance of neutrophils in the inflammatory process led us to investigate the effects of oral ingestion of unesterified OLA and LNA on rat neutrophil function. Pure OLA and LNA were administered by gavage over 10 days. The doses used (0.11, 0.22 and 0.44 g/kg of body weight) were based on the Western consumption of OLA and LNA. Neither fatty acid affected food, calorie or water intake. The fatty acids were not toxic to neutrophils as evaluated by cytometry using propidium iodide (membrane integrity and DNA fragmentation). Neutrophil migration in response to intraperitoneal injection of glycogen and in the air pouch assay, was elevated after administration of either OLA or LNA. This effect was associated with enhancement of rolling and increased release of the chemokine CINC-2alphabeta. Both fatty acids elevated L-selectin expression, whereas no effect on beta(2)-integrin expression was observed, as evaluated by flow cytometry. LNA increased the production of proinflammatory cytokines (IL-1beta and CINC-2alphabeta) by neutrophils after 4 h in culture and both fatty acids decreased the release of the same cytokines after 18 h. In conclusion, OLA and LNA modulate several functions of neutrophils and can influence the inflammatory process.