Small Chain Fatty Acids Research Articles

Smoke Points: A Crucial Factor in Cooking Oil Selection for Public Health

: Cooking oils and fats play a significant role in our daily diet and culinary practices by enhancing flavours, textures, and nutritional value. However, overheating these fats can compromise the quality and safety of cooked foods. When oils and fats exceed their smoke points, they undergo chemical breakdown, producing volatile compounds, off-flavours, and undesirable odors, including harmful substances like small chain fatty acids, trans fats, acrylamides, and polycyclic aromatic hydrocarbons. It is crucial to avoid overheating oils to mitigate the formation of these toxic substances and instead opt for those with higher smoke points for high-temperature cooking methods. The smoke point, indicating the temperature at which visible smoke is emitted, serves as a critical indicator of thermal stability and suitability for various cooking oils and fats. Therefore, understanding and considering the smoke points of different oils and fats are essential for maintaining food quality and safety in culinary practices. This review consolidates existing knowledge on the smoke points of various oils and fats and methods for determining smoke points, providing a list of fifty-one oils and fats with their respective smoke points and highlighting their applications in cooking. By considering the smoke point, chefs, cooks, and food manufacturers can select oils that optimize cooking, frying, taste, texture, flavour enhancement, salad dressings, marinades, baking, and overall safety in their culinary practices. Mindfulness of the smoke point helps prevent the degradation of nutritional value and the generation of harmful compounds during the cooking process.

P055 GPR43 and GPR84 play a crucial role in supporting perianal fistula formation and disease progression in Crohn’s Disease

Abstract Background Fistula complication represents one of the most disabling manifestations of Crohn’s Disease and a risk factor for more aggressive disease progression and mucinous adenocarcinoma . However, molecular mechanisms behind this transformation are completely unknown. Growing evidence supported epithelial-to-mesenchymal transition (EMT) as a critical process to replace impaired intestinal fibroblasts in repairing mucosal membrane damage. However, EMT drivers during fistula formation and progression are still not completely known. Here, we investigated whether G-protein coupled receptors serve as new drivers of EMT and fistula disease progression. Methods Surgical specimens (N=9) collected from perianal fistula and non-involved areas of CD patients were analyzed by bulk RNA-sequencing and Lipidomics analysis. Gene set enrichment analysis (GSEA) was used to detect the levels of differentially expressed pathways. GPR43 and GPR84 analysis was performed on perianal fistula; adenocarcinoma; and mucinous adenocarcinoma-associated (MA) CD fistula FFPE tissue section. Caco-2 cell line was stimulated for 24 h with agonists and antagonists of GPRs. Genes associated to EMT were evaluated by RT-PCR and WB. Results Gene sets related to the signatures of epithelial-to-mesenchymal transition, G-protein coupled receptors (GPRs), immune response, lipid oxidation were significantly enriched in the fistula compared to non-involved tissue. Among differentially GPRs expressed genes FFAR2 encoding for GPR43, sensor for Small Chain Fatty Acids (SCFAs), and GPR84 sensor for Medium Chain Fatty Acids (MCFAs), predominantly expressed in immune cells, reported to be upregulated in the context of acute inflammation. Upregulation of GPRs expression correlated positively with enzymes associated to lipid oxidation gen set including PLA2G2D, ALOX5, NR4A3, PLA2G7, ACOXL and negatively with their lipids substrates. Caco2 cells stimulated with SCFAs and MCFAs upregulated not only the expression of GPR43 and GPR84, but also of EMT-transcription factor Twist1 and PLA2G2D, all effects reverted in the presence of their antagonists. An increase expression of GPR43 and GPR84 in association with Twist1 was found in MA-CD tissue section. Conclusion Our results highlighted GPR43 and GPR84 as new potential factors of fistula formation that support the EMT process through increased fatty acid oxidation, which in turn fuels the activation of GPRs. However, the increase expression of both receptors in the fistula oncogenic disease progression suggests that strategies regulating lipid metabolism or targeting GPRs could pave the way for novel therapeutic approaches to prevent fistula complication in CD patients.

Oral Metformin Inhibits Choroidal Neovascularization by Modulating the Gut-Retina Axis.

Emerging data indicate that metformin may prevent the development of age-related macular degeneration (AMD). Whereas the underlying mechanisms of metformin's anti-aging properties remain undetermined, one proposed avenue is the gut microbiome. Using the laser-induced choroidal neovascularization (CNV) model, we investigate the effects of oral metformin on CNV, retinal pigment epithelium (RPE)/choroid transcriptome, and gut microbiota. Specific pathogen free (SPF) male mice were treated via daily oral gavage of metformin 300mg/kg or vehicle. Male mice were selected to minimize sex-specific differences to laser induction and response to metformin. Laser-induced CNV size and macrophage/microglial infiltration were assessed by isolectin and Iba1 immunostaining. High-throughput RNA-seq of the RPE/choroid was performed using Illumina. Fecal pellets were analyzed for gut microbiota composition/pathways with 16S rRNA sequencing/shotgun metagenomics, as well as microbial-derived metabolites, including small-chain fatty acids and bile acids. Investigation was repeated in metformin-treated germ-free (GF) mice and antibiotic-treated/GF mice receiving fecal microbiota transplantation (FMT) from metformin-treated SPF mice. Metformin treatment reduced CNV size (P < 0.01) and decreased Iba1+ macrophage/microglial infiltration (P < 0.005). One hundred forty-five differentially expressed genes were identified in the metformin-treated group (P < 0.05) with a downregulation in pro-angiogenic genes Tie1, Pgf, and Gata2. Furthermore, metformin altered the gut microbiome in favor of Bifidobacterium and Akkermansia, with a significant increase in fecal levels of butyrate, succinate, and cholic acid. Metformin did not suppress CNV in GF mice but colonization of microbiome-depleted mice with metformin-derived FMT suppressed CNV. These data suggest that oral metformin suppresses CNV, the hallmark lesion of advanced neovascular AMD, via gut microbiome modulation.

Butyrate induces oxidative burst mediated apoptosis via Glucose-6-Phosphate Dehydrogenase (G6PDH) in macrophages during mycobacterial infection

Microorganisms present in the gut modulate host defence responses against infections in order to maintain immune homeostasis. This host-microbe crosstalk is regulated by gut metabolites. Butyrate is one such small chain fatty acid produced by gut microbes upon fermentation that has the potential to influence immune responses. Here we investigated the role of butyrate in macrophages during mycobacterial infection. Results demonstrate that butyrate significantly suppresses the growth kinetics of mycobacteria in culture medium as well as inhibits mycobacterial survival inside macrophages. Interestingly, butyrate alters the pentose phosphate pathway by inducing higher expression of Glucose-6-Phosphate Dehydrogenase (G6PDH) resulting in a higher oxidative burst via decreased Sod-2 and increased Nox-2 (NADPH oxidase-2) expression. Butyrate-induced G6PDH also mediated a decrease in mitochondrial membrane potential. This in turn lead to an induction of apoptosis as measured by lower expression of the anti-apoptotic protein Bcl-2 and a higher release of Cytochrome C as a result of induction of apoptosis. These results indicate that butyrate alters the metabolic status of macrophages and induces protective immune responses against mycobacterial infection.

PSII-14 The Effect of Increasing Soluble Dietary Fiber and the Addition of a Stimbiotic in Gestation on Sow Productivity in a Prrs and Non-Prrs Challenge

Abstract This sow study evaluated the effect that sugar beet pulp (SBP), a soluble fiber source, and a stimbiotic (Signis; AB Vista) can have on sow productivity and health when fed in gestation. A stimbiotic is an additive that stimulates fiber-degrading microbiome, resulting in an increase in fiber fermentability even though the additive itself contributes limited small chain fatty acid production. A commercial gestation barn with two feeding lines was utilized to feed sows (n = 2173) two dietary treatments from d 30 to d 90; a corn, soy, soy hulls with (HSDF) or without (LSDF) SBP (50 kg/t) plus stimbiotic (100 g/t) and from d 90 to entering the farrowing pen the LSDF diet with or without a stimbiotic (100 g/day). Sows were fed 2.0 kg per day providing the following fiber intake levels/day, HDSF: TDF; 266g, SDF 55g, IDF, 211g and LDSF: TDF; 240g, SDF 40g, IDF, 200g. The following variables were measured; total born, live born, still born, mummies, pre-weaning mortality, pigs weaned per sow, prolapse rate and sow mortality/culls. A proportion of sows (n = 81) were moved to a GESTAL system for lactation and intake recorded per gestation treatment. During the study the farm became PRRS positive and any sows that farrowed while the farm was PRRS positive were identified as PRRS positive sows and included as a factor. Data were analyzed with ANOVA evaluating the effects of fiber, parity, and PRRS using the fit model platform in JMP16. Significant treatment means were separated using Student’s t-tests, with significance accepted at P ≤ 0.05. Results showed that for born alive there was an interaction between treatment and parity (P =0.02) and treatment and PRRS (P &amp;lt; 0.05) with the HDSF diet increasing born alive in parity 1 (+1.30 pigs; P = 0.03) and parity 2 (+0.71 pigs; P = 0.08) with no effect in parity 3+. HDSF improved born alive in non PRRS pigs (+1.01 pigs; P &amp;lt; 0.01) and had no effect in PRRS pigs. There was a tendency for HDSF program to reduce stillborn (8.8% v 7.4%; P = 0.09) but had no effect on mummies. There was a tendency to increase in pigs weaned with the HSDF treatment (9.15 v 8.86; P = 0.07) with no effect on sow mortality/culls. There was no effect of treatment on prolapses. On the sub-sample of sows recorded in lactation those sows (Parity 2+) that had been on the HSDF in gestation showed an increased ADFI (5.36 kg v 6.02 kg; P = 0.01) compared with the LSDF. It can be concluded that sow productivity can be improved by increasing the fermentative capacity of the gestation feed through the combination of adding a soluble fiber such as SBP along with a stimbiotic.

Utilization of residual fatty acids in matter organic non-glycerol from a soy biodiesel plant in filaments used for 3D printing

Matter organic non-glycerol (MONG) is a considerable waste output (20%−25% of crude glycerol) typically landfilled by soy biodiesel plants. In this work, soy MONG was characterized for potential use as a copolymer to produce filaments for 3D printing with an intent to add value and redirect it from landfills. As a copolymer, MONG was evaluated to reduce the synthetic polymer content of the natural fiber composites (NFC). Even though the general thermal behavior of the MONG was compared to that of a thermoplastic polymer in composite applications, it is dependent on the composition of the MONG, which is a variable depending on plant discharge waste. In order to improve the thermal stability of MONG, we evaluated two pretreatments (acid and acid + peroxide). The acid + peroxide pretreatment resulted in a stabilized paste with decreased soap content, increased crystallinity, low molecular weight small chain fatty acids, and a stable blend as a copolymer with a thermoplastic polymer. This treatment increased formic acid (17.53%) in MONG, along with hydrogen peroxide, led to epoxidation exhibited by the increased concentration of oxirane (5.6%) evaluating treated MONG as a copolymer in polymer processing and 3D printing.

The Association between Dysbiosis and Neurological Conditions Often Manifesting with Chronic Pain.

The prevalence of neurological conditions which manifest with chronic pain is increasing globally, where the World Health Organisation has now classified chronic pain as a risk factor for death by suicide. While many chronic pain conditions have a definitive underlying aetiology, non-somatic conditions represent difficult-to-diagnose and difficult-to-treat public health issues. The interaction of the immune system and nervous system has become an important area in understanding the occurrence of neuroinflammation, nociception, peripheral and central sensitisation seen in chronic pain. More recently, however, the role of the resident microbial species in the human gastrointestinal tract has become evident. Dysbiosis, an alteration in the microbial species present in favour of non-beneficial and pathogenic species has emerged as important in many chronic pain conditions, including functional somatic syndromes, autoimmune disease and neurological diseases. In particular, a decreased abundance of small chain fatty acid, e.g., butyrate-producing bacteria, including Faecalibacterium, Firmicutes and some Bacteroides spp., is frequently evident in morbidities associated with long-term pain. Microbes involved in the production of neurotransmitters serotonin, GABA, glutamate and dopamine, which mediate the gut-brain, axis are also important. This review outlines the dysbiosis present in many disease states manifesting with chronic pain, where an overlap in morbidities is also frequently present in patients.

Emerging non-invasive therapeutic approaches targeting hypocholinergic neural systems in Parkinson's disease.

Emerging non-invasive therapeutic approaches targeting hypocholinergic neural systems in Parkinson's disease.

Investigating Ramadan Like Fasting Effects on the Gut Microbiome in BALB/c Mice.

Recently we reported that in healthy volunteer Ramadan-associated intermittent fasting (RAIF) remodels the gut microbiome and resulted in an increase in small chain fatty acid producing bacteria concomitant with improved metabolic parameters. As interpretation of these results is hampered by the possible psychological effects associated with the study, we now aim to investigate RAIF in experimental animals. To this end, 6-week male BALB/c mice were subjected to RAIF (30 days of a 16-h daily fasting; n = 8) or provided with feed ad libitum (n = 6). Fecal samples were collected before and the end of fasting and bacterial 16S rRNA sequencing was performed. We found that RAIF remodeled the composition of gut microbiota in BALB/c mice (p < 0.01) and especially provoked upregulation of butyrate acid-producing Lachnospireceae and Ruminococcaceae (p < 0.01), resembling the effects seen in human volunteers. Hence we conclude that the effects of RAIF on gut microbiome relate to the timing of food intake and are not likely related to psychological factors possibly at play during Ramadan.

Genetic tools for the redirection of the central carbon flow towards the production of lactate in the human gut bacterium Phocaeicola (Bacteroides) vulgatus

Species of the genera Bacteroides and Phocaeicola play an important role in the human colon. The organisms contribute to the degradation of complex heteropolysaccharides to small chain fatty acids, which are in part utilized by the human body. Furthermore, these organisms are involved in the synthesis of vitamins and other bioactive compounds. Of special interest is Phocaeicola vulgatus, originally classified as a Bacteroides species, due to its abundance in the human intestinal tract and its ability to degrade many plant-derived heteropolysaccharides. We analyzed different tools for the genetic modification of this microorganism, with respect to homologous gene expression of the ldh gene encoding a D-lactate dehydrogenase (LDH). Therefore, the ldh gene was cloned into the integration vector pMM656 and the shuttle vector pG106 for homologous gene expression in P. vulgatus. We determined the ldh copy number, transcript abundance, and the enzyme activity of the wild type and the mutants. The strain containing the shuttle vector showed an approx. 1500-fold increase in the ldh transcript concentration and an enhanced LDH activity that was about 200-fold higher compared to the parental strain. Overall, the proportion of lactate in the general catabolic carbon flow increased from 2.9% (wild type) to 28.5% in the LDH-overproducing mutant. This approach is a proof of concept, verifying the genetic accessibility of P. vulgatus and could form the basis for targeted genetic optimization.Key points• A lactate dehydrogenase was overexpressed in Phocaeicola (Bacteroides) vulgatus.• The ldh transcript abundance and the LDH activity increased sharply in the mutant.• The proportion of lactate in the catabolic carbon flow increased to about 30%.

Not a “they” but a “we”: The microbiome helps promote our well-being

Anaerobic microbes in the human gut produce beneficial and harmful compounds, as well as neutral compounds like trimethylamine, which undergoes microbial metabolism or host-catalyzed transformation into proatherogenic trimethylamine-N-oxide. Ellenbogen et al. identified a microbiome-associated demethylase that short-circuits the production of trimethylamine-N-oxide from the metabolite γ-butyrobetaine and instead produces methyltetrahydrofolate, a key intermediate in the microbial production of beneficial small-chain fatty acids. This article highlights an example of how the microbiome is integrally involved in producing metabolites that support our health and in preventing the formation of compounds that promote disease.

Fatty acid metabolism and acyl-CoA synthetases in the liver-gut axis.

Fatty acids are energy substrates and cell components which participate in regulating signal transduction, transcription factor activity and secretion of bioactive lipid mediators. The acyl-CoA synthetases (ACSs) family containing 26 family members exhibits tissue-specific distribution, distinct fatty acid substrate preferences and diverse biological functions. Increasing evidence indicates that dysregulation of fatty acid metabolism in the liver-gut axis, designated as the bidirectional relationship between the gut, microbiome and liver, is closely associated with a range of human diseases including metabolic disorders, inflammatory disease and carcinoma in the gastrointestinal tract and liver. In this review, we depict the role of ACSs in fatty acid metabolism, possible molecular mechanisms through which they exert functions, and their involvement in hepatocellular and colorectal carcinoma, with particular attention paid to long-chain fatty acids and small-chain fatty acids. Additionally, the liver-gut communication and the liver and gut intersection with the microbiome as well as diseases related to microbiota imbalance in the liver-gut axis are addressed. Moreover, the development of potentially therapeutic small molecules, proteins and compounds targeting ACSs in cancer treatment is summarized.

Microbiota in Health and Disease-Potential Clinical Applications.

Within the last two decades tremendous efforts in biomedicine have been undertaken to understand the interplay of commensal bacteria living in and on our human body with our own human physiology. It became clear that (1) a high diversity especially of the microbial communities in the gut are important to preserve health and that (2) certain bacteria via nutrition-microbe-host metabolic axes are beneficially affecting various functions of the host, including metabolic control, energy balance and immune function. While a large set of evidence indicate a special role for small chain fatty acids (SCFA) in that context, recently also metabolites of amino acids (e.g., tryptophan and arginine) moved into scientific attention. Of interest, microbiome alterations are not only important in nutrition associated diseases like obesity and diabetes, but also in many chronic inflammatory, oncological and neurological abnormalities. From a clinician’s point of view, it should be mentioned, that the microbiome is not only interesting to develop novel therapies, but also as a modifiable factor to improve efficiency of modern pharmaceutics, e.g., immune-therapeutics in oncology. However, so far, most data rely on animal experiments or human association studies, whereas controlled clinical intervention studies are spare. Hence, the translation of the knowledge of the last decades into clinical routine will be the challenge of microbiome based biomedical research for the next years. This review aims to provide examples for future clinical applications in various entities and to suggest bacterial species and/or microbial effector molecules as potential targets for intervention studies.

PSIII-19 The Effect of Xylanase on Finisher Pig Performance

Abstract The breakdown of long chain arabinoxylans into smaller chain xylo-oligomers by the use of xylanase results in a shift towards fiber utilizing bacteria resulting in production of small chain fatty acids and improved pig performance. The objective of this study was to evaluate the effect of xylanase (Econase XT; AB Vista) on finisher pig performance. A total of 598 pigs; (37.4 ± 1.0 kg) were fed a single-phase diet for 60 days. Pigs were assigned to two treatments; 0 (CTL) or 16,000 BXU/kg of xylanase (XYL) with 12 pen replicates and 24/25 pigs (mixed sex; gilts and boars) per treatment. The diet was based on wheat, barley, soybean meal, rapeseed meal, and wheat midds; SID Lys: 0.88%, NDF: 14.7%, and NE: 2090 kcal/kg. Average daily gain (ADG), feed intake (ADFI) and feed conversion ratio (FCR) were evaluated in phase 1 (0-26d), phase 2 (26-60d) and overall (0-60d). Liveability was measured per treatment. Data were analysed using JMP 12 using the standard least square platform and ANOVA was performed to determine significance at P &amp;lt; 0.05. The model included initial BW as a covariant. The results indicated that there was no effect of xylanase on liveweight, ADG or ADFI at any phase of the finisher period. The use of xylanase improved FCR in phase 2 (2.53 v 2.60: P &amp;lt; 0.05) and overall (2.44 v 2.49 P=0.03). No differences were seen in liveability (CTL; 96%; XYL 98%; P = 0.29). It can be concluded that the use of xylanase can be used in finisher feeds to improve FCR which is linked with greater energy utilisation that has been associated with greater fiber breakdown through xylanase use.

Ebola Virus Delta Peptide Is an Enterotoxin

During the 2013-2016 West African Ebola virus (EBOV) outbreak severe gastrointestinal symptoms were common in patients and associated with poor outcome. Delta peptide is a conserved product of post-translational processing of the abundant EBOV soluble glycoprotein (sGP). Here, the murine ligated ileal loop model was used to demonstrate that delta peptide is a potent enterotoxin. Dramatic intestinal fluid secretion followed injection of biologically relevant amounts of delta peptide into ileal loops, along with gross destruction of villous architecture and loss of goblet cell polysaccharides. Transcriptomic analyses showed that delta peptide triggers damage response and cell survival pathways. It also downregulates the expression of transporters and exchangers that mediate absorption of ions, sugars, and small chain fatty acids. Delta peptide induces fluid secretion through pathways that include the ANO1 calcium-activated chloride channel, and prostaglandin signaling. Delta peptide may contribute to EBOV-induced gastrointestinal pathology in humans and presents a potential therapeutic target.

Small Chain Fatty Acid Phenylbutyric Acid Alleviated Inflammation-Induced Endoplasmic Reticulum Stress in Endothelial Cells

Endothelial cells (EC) have dynamic properties and high plasticity in response to microenvironmental change. A proinflammatory cytokine such as tumor necrotizing factor-α (TNF-α) can induce EC phenotype shift to osteoinduction properties by releasing a potent osteogenic cytokine, namely bone morphogenetic protein 2 (BMP2). Normally BMP2 acts as an osteoblast stimulating factor in bone and cartilage tissue. BMP2 activation in vascular tissue will invite osteoblast recruitment and mineralization and generated pathological vascular stiffening and calcification. Recently, endoplasmic reticulum stress (ERS) has been emerging as a new target therapy in many vascular diseases such as vascular stiffening and calcification. Some short-chain fatty acid like 4-phenyl butyric acid has been shown had anti-ERS properties. However, the role of 4-phenyl butyric acid in BMP2 inhibition in endothelial cells is still poorly understood. Hence, we investigated the role of 4-phenyl butyric acid in inflammation-induced BMP2 expression in human vein derived endothelial cells. Endothelial cells obtained from a baby born umbilical vein were cultured and pre-treated with TNF-α (5 ng/ml) as inflammation precondition. Multiple doses of 4-phenyl butyrate acid (4- PBA) 1 nM/mL, 2 nM/mL, and 3 nM/m were used as ERS inhibitors. The expression of two ERS biomarkers, glucose-related protein-8 (GRP78) and activating transcription factor-6 (ATF6), were measured. Statistical analysis was done using one-way ANOVA and Kruskal Wallis tests, and P&lt;0.01 considered as significant. 4- PBA decrease luminal BMP2 at dose one nM/L, GRP78 at dose 1 nM/L, and translocated ATF6 expression at dose 1 nM/L in endothelial culture dose-dependently. Short-chain fatty acid 4-phenylbutyrate acid decreases luminal ERS marker GRP78 and translocated ATF6 expression in endothelial culture. ERS has a role in osteoinductive phenotype shifting in inflammation endothelial cells, which was the novelty of this research. Further research needs to elucidate ERS inhibition in in vivo experiment.

Research Highlights

Research Highlights

Review on the production of medium and small chain fatty acids through waste valorization and CO2 fixation

The developing approaches in the recovery of resources from biowastes for the production of renewable value-added products and fuels, using microbial cultures as bio-catalyst have now became promising aspect. In the path of anaerobic digestion, the microorganisms are assisting transformation of a complex organic feedstock/waste to biomass and biogas. This potentiality consequently leads to the production of intermediate precursors of renewable value-added products. Particularly, a set of anaerobic pathways in the fermentation process, yields small-chain fatty acids (SCFA), and medium-chain fatty acids (MCFA) via chain elongation pathways from waste valorization and CO2 fixation. This review focuses on the production of SCFA and MCFA from CO2, synthetic substrates and waste materials. Moreover, the review introduces the metabolic engineering of Escherichia coli and Saccharomyces cerevisiae for SCFAs/MCFAs production. Furtherly, it concludes that future critical research might target progress of this promising approach as a valorization of complex organic wastes.

The small chain fatty acid butyrate antagonizes the TCR-stimulation-induced metabolic shift in murine epidermal gamma delta T cells.

The metabolic requirements change during cell proliferation and differentiation. Upon antigen-stimulation, effector T cells switch from adenosine-triphospate (ATP)-production by oxidative phosphorylation in the mitochondria to glycolysis. In the gut it was shown that short chain fatty acids (SCFA), fermentation products of the microbiota in colon, ameliorate inflammatory reactions by supporting the differentiation of regulatory T cells. SCFA are a major energy source, but they are also anabolic metabolites, histone-deacetylase-inhibitors and activators of G protein receptors. Recently, it was reported that a topical application of the SCFA butyrate promotes regulatory T cells in the skin. Here we ask if the SCFA butyrate, propionate and acetate affect the energy metabolism and inflammatory potential of dendritic epidermal T cells (DETC), the innate resident skin γδ T cell population. Using the Seahorse™ technology, we measured glycolysis and oxidative phosphorylation (OXPHOS) in a murine DETC cell line, 7-17, upon TCR-stimulation by CD3/CD28 crosslinking, with or without SCFA addition. TCR engagement resulted in a change of the ratio glycolysis/OXPHOS. A similar metabolic shift has been described for activated CD4 T cells. Addition of 5 mM SCFA, in particular butyrate, antagonized the effect. Stimulated DETC secrete cytokines, e.g. the pro-inflammatory cytokine interferon-gamma (IFNγ), and thereby regulate skin homeostasis. Addition of butyrate and propionate to the cultures at non-toxic concentrations decreased secretion of IFNγ by DETC and increased the expression of the immunoregulatory surface receptor CD69. We hypothesize that SCFA can dampen the inflammatory activity of DETC.

Microbial-Derived Metabolites Drive Protective Type-I Interferon Responses in Models of Gut Epithelial Damage and Limit Graft-Versus-Host Disease

Background: Graft-versus-host disease (GVHD) is a dreaded complication after stem-cell transplantation (SCT). Standard treatment relies on immunosuppressants but is associated with an increased risk of infection and relapse. Up 50% of patients develop steroid-refractory GVHD, with dismal impact on SCT outcomes. New studies in mice suggest that induction of type-I interferon (IFN-I) signalling or activation of IFN-I inducing pathways such as cGAS/STING or RIG-I/MAVS can promote gut barrier integrity and limit GVHD. However, the endogenous ligands that drive this "protective" IFN-I response are poorly defined. Recent data in mice and humans suggest that microbial-derived metabolites such as small-chain fatty acids or indoles can decrease GHVD mortality. Here, we describe IFN-I inducing metabolites that improve outcomes in mouse models of gut epithelial damage and acute GVHD via a mechanism dependent on STING signalling. Methods: To investigate which cell types mediate protection and how, we generated intestinal organoids and antigen presenting cells (APC) from bone marrow of WT or genetically deficient mice (MAVS-/-, STING-/-, IFNAR-/-) under steady state conditions versus chemotherapy, total body irradiation and after allogeneic SCT in the presence or absence of microbial metabolites. Analysis was performed by microscopy, immunoblotting, qPCR, ELISA and flow cytometry. Outcomes of gut-injured mice were assessed by clinical scoring, histopathology, flow cytometry and organoid recovery. Results: Metabolite treatment promoted regeneration of intestinal organoids as assayed by organoid numbers as well as proliferation. These effects were dependent on IFN-I and STING signalling. In addition, we found activated pro-inflammatory NFkB signalling and decreased apoptosis as evidenced by reduced caspase-3 cleavage. In APCs, IFN-I responses were enhanced in the presence of metabolites including increased IFN-β production and upregulation of IFN stimulated genes. Metabolite-treated mice showed improved recovery of intestinal stem cells following gut injury by chemotherapy and irradiation and increased survival in acute GVHD. Conclusions: Our findings uncover a mechanism by which microbial metabolites amplify IFN-I signals, promote tissue regeneration and thereby prevent allo-activation and GVHD. We show for the first time that these IFN-I inducing metabolites are protective in diverse models of gut damage -- from chemotherapy and radiation to immune-mediated damage -- via a STING-dependent mechanism. Perhaps the poor prognosis of GVHD patients exhibiting a loss of microbiota diversity can be explained in part by an absence of "protective" metabolites able to amplify critical IFN signals. We are currently studying whether metabolite levels correlate with severity and outcome of GVHD in humans. Figure Disclosures No relevant conflicts of interest to declare.