Physiological concentrations of short-chain fatty acids induce the formation of neutrophil extracellular traps in vitro

Abstract

Neutrophils represent the first line of host cellular defense against various pathogens. The most recently described microbicidal mechanism of these cells is the release of neutrophil extracellular traps (NET). Currently, a wide range of chemical and biological stimuli are known to induce this response; however, the effect of short-chain fatty acids (SCFAs) on the induction of NET is still unknown. SCFAs are produced mainly by bacterial fermentation of dietary fiber and are found in host tissues and blood. This study aimed to determine whether physiological levels of SCFAs can induce the formation of NET. Previously reported concentrations of SCFAs (as found in the colonic lumen and peripheral blood in postprandial and basal states) were used to stimulate the neutrophils. In order to determine the signaling pathway utilized by SCFAs, we tested the inhibition of the Free Fatty Acid 2 Receptor (FFA2R) expressed in neutrophils using CATPB, the inhibitor of FFA2R, genistein, an inhibitor of the downstream Gα/q11 proteins and DPI, an inhibitor of the NADPH oxidase complex. The SCFAs at colonic intestinal lumen concentrations were able to induce the formation of NET, and when tested at concentrations found in the peripheral blood, only acetic acid at 100 μM (fasting equivalent) and 700 μM (postprandial equivalent) was found to induce the formation of NET. The administration of the competitive inhibitor against the receptor or blockade of relevant G protein signaling and the inhibition of NADPH oxidase complex decreased NET release. SCFAs stimulate NET formation in vitro and this effect is mediated, in part, by the FFA2R.

Short-Chain Fatty Acids Impair Neutrophil Antiviral Function in an Age-Dependent Manner

“…Furthermore, we detected a delay in NET release after HIV stimulation when neutrophils were challenged in the presence of SCFAs. In contrast to a previous report [ 81 ] showing increased NET release after neutrophil treatment with SCFAs in the mM concentration range, we did not observe any significant differences after SCFA treatment in the absence of HIV stimulation. The reason behind these disparate results remains to be determined but may be due to the different methodologies used to quantify NETs.…”

The emerging role of neutrophilic extracellular traps in intestinal disease

“…Regarding the additional link between the formation of NETs and gut microbes, a study by Liang et al in 2019 revealed that oral administration of Staphylococcal nuclease (SNase), a nuclease that degrades DNA or RNA, was capable of effectively degrading NETs in vitro and in vivo, thereby improving intestinal barrier function. More importantly, SNase alleviated the intestinal inflammatory microenvironment and averted the development of type 1 diabetes (T1D) in non-obese diabetic (NOD) mice by altering the species richness and composition of the intestinal microbiota of NOD mice [ 96 ]. Recently, a study has also shown that dominant microbes ( Acetatifactor, Coprococcus2, Lachnoclostridium_5 and Lachnospiraceae_FCS020_group ) in NOD mice had a positive correlations with neutrophils and could possibly affect T1D via NETs [ 97 ], which inspires us that further works concerning the specific mechanisms of the interaction between intestinal microbiota and NETs require more studies to be revealed.…”

In Vivo Healthy Benefits of Galacto-Oligosaccharides from Lupinus albus (LA-GOS) in Butyrate Production through Intestinal Microbiota

“…In general, neutrophils are implicated in the inflammatory process related with intestinal damage in the UC model [ 111 ]. A lower pH reduced the production of Neutrophil Extracellular Traps (NET) by neutrophils [ 112 ]. The decrease of NET could be associated with an improvement in the intestinal health and anti-inflammatory effects.…”