Distal versus proximal intestinal short-chain fatty acid release in man

Specific dietary fibers steer toward distal colonic saccharolytic fermentation using the microbiota of individuals with overweight/obesity

BACKGROUND

Evidence suggests that increased distal short-chain fatty acid (SCFA) production beneficially impacts metabolic health. However, indigestible carbohydrate availability is limited in the distal colon; consequently, microbes shift toward protein fermentation, often linked to adverse metabolic health effects. We aimed to identify specific fiber(s) that promote saccharolytic fermentation in the distal colon and thereby may (partially) inhibit proteolytic fermentation.

METHODS

Potato-fiber, pectin, and inulin were studied individually and in combination against a high (predigested) protein background using an in vitro model of the colon (TIM-2) inoculated with pooled, standardized fecal microbiota from individuals with overweight/obesity. Microbiota composition and activity were assessed at different timepoints to simulate the travel throughout the colon (proximal: 0-8 h, distal: 8-24 h) and compared to a high protein (HP)_control, receiving only proteins.

RESULTS

Fiber addition increased total SCFA production compared to HP_control (52.11 ± 1.49 vs 27.07 ± 0.26 mmol) whereas total branched-chain fatty acids (BCFA; a marker for protein fermentation) production only slightly decreased (3.31 ± 0.10 vs 4.18 ± 0.40 mmol). Combining potato-fiber and pectin led to the highest total and distal SCFA production and distal SCFA:BCFA. Fiber addition attenuated HP-induced increases in several bacterial taxa including Mogibacterium and Coprococcus, independent of fiber type. Additionally, time- and fiber-specific microbial signatures were identified: inulin increased Bifidobacterium (proximal) relative abundance and pectin and/or potato-fiber increased Prevotella 9 (distal) relative abundance.

CONCLUSION

The most marked increase in distal colonic SCFA production was induced by combining potato-fiber and pectin. Further research should elucidate whether this switch toward saccharolytic fermentation translates into beneficial metabolic health effects in humans.

Sub-chronic exposure of hexaconazole may induce metabolic and neuropathic diseases: The evidence from gut microbiota

The high-frequency detection and long persistence of hexaconazole (Hex) in agricultural products and environment poses potential risk to non-targeted organisms which should pay special attention to. Intestinal flora plays an important role in host health by prevention the occurrence of various diseases. Therefore, in this study, the disturbance of Hex on intestinal function and flora in rats had been studied at environmental related concentrations to evaluate the potential risk of Hex. Our results showed that Hex exposure induced serious oxidative stress and inflammation in intestinal tract. Meanwhile, it notably decreased the tight connectivity in colonic cell leading to the dysfunction of intestinal barrier. Moreover, 16sRNA gene sequencing showed that Hex exposure significantly disturbed the composition and structures of gut microbiota by decrease beneficial bacteria and increase pathogenic bacteria. Further, the metabolites and SCFAs that related to neuropathic and metabolic diseases in colonic contents were also significantly affected by Hex exposure. The pathways of membrane transport, replication and repair, lipid metabolism, and neurodegenerative diseases had been seriously interfered. The obtained results referred that Hex exposure may pose potential risk to metabolic system causing obesity, metabolic syndrome, and cardiovascular as well as nervous system inducing Parkinson's diseases, Alzheimer's diseases, and depression. Our study provided a new sight to study the mechanisms of Hex induced toxicity effects from the aspect of gut microbiota which could help for prevention the risk induced by Hex.

Short-chain fatty acid kinetics and concentrations are higher after inulin supplementation in young and older adults. A randomized trial

BACKGROUND

Beneficial short-chain fatty acids (SCFAs) are produced through intestinal microbial fiber fermentation. Using stable tracer methodology and compartmental modeling, we observed lower SCFA production in older than young adults in both an accessible (i.e. systemic circulation; whole-body production (WBP)) and inaccessible (potentially representing intestine absorbing microbially produced SCFAs (U2)) pool.

OBJECTIVES

We now investigated if fiber supplementation increases SCFA production in older adults and if concentrations reflect production rate changes.

METHODS

In this randomized, placebo controlled, double-blind crossover study, 21 young (YA: 20-29y) and 40 older (OA: 59-87y) adults, were supplemented with inulin or placebo (maltodextrin) for 7d (final intake: 30 g/d). Before and after interventions, participants collected stool and received an intravenous pulse containing [U-13C]-labeled SCFAs followed by blood draws. We measured plasma tracer enrichments, plasma and fecal concentrations by GC-MS and performed compartmental analysis. Data are mean [95% CI].

RESULTS

Inulin evoked a 44% increase in butyrate production (μmol/min) in the inaccessible pool (YA: 28 to 44 (+16.2 [4.3, 28.1]; p=0.038), OA: 14 to 20 (+6.1 [2.2, 9.9]; p=0.011) and were not different between young and older adults. In addition, a 34% increase in propionate production in YA only. We found a 50-60% increase in fecal acetate, propionate and butyrate and a 34% increase in plasma butyrate in OA, while in YA only 34% increase in fecal acetate. Plasma but not fecal concentrations correlated positively with SCFA production in the inaccessible pool (R2 = 0.20-0.45; p<0.001).

CONCLUSION

Older adults have a lower SCFA production. Inulin intake increases SCFA production. Tracer pulse approach detects SCFA metabolism changes more sensitively than plasma or fecal concentration measurements (NCT04459156).

Structure changes of starch complexed with green tea catechin or lemon peel caffeic acid under thermomechanical-assist low moisture and their prebiotics during in vitro digestion and fermentation

This paper highlighted the structural changes of rice starch complexed with green tea catechin and lemon peel caffeic acid under thermomechanical-assist low moisture, and their prebiotics during in vitro digestibility and fermentation were further explained. Extruded starch with caffeic acid, characterized by enhanced short-range order, a distinct fractal structure, and a V-amylose helical arrangement, exhibited slower glucose release due to V-type inclusion crystalline structures and strong hydrogen bondings. Additionally, extruded starch with catechin or caffeic acid changed the composition of gut microbiota by increasing the proliferation of good bacteria and reducing pathogenic microorganisms, which led to a greater synthesis of short-chain fatty acids. According to a PICRUSt2 analysis, the extruded starch with caffeic acid may trigger metabolic alterations via altering the gut microbiota and increasing bile acid metabolism. Thus, extruded starch with caffeic acid demonstrates significant potential as a prebiotic for developing nutritionally tailored starch-based foods.

Dose-Dependent Effects of Short-Chain Fatty Acids on 3T3-L1 Adipocyte Adipokine Secretion and Metabolic Function

BACKGROUND

Short-chain fatty acids (SCFAs) produced from microbial fermentation of non-digestible carbohydrates and protein have been shown to modulate adipocyte adipokine secretion and metabolic function, which has implications for mitigating dysfunction in obese adipose tissue; however, the individual effects of different SCFAs and the optimal concentration required is unknown. The purpose of this study was to dose-dependently determine the effects of individual SCFAs on adipocyte adipokine secretion and metabolic function.

METHODS

We recapitulated the obese adipocyte inflammatory conditions using mature 3T3-L1 adipocytes and a physiological concentration of lipopolysaccharide (LPS) ± individual SCFAs, namely acetate, propionate, and butyrate, in a dose-dependent manner (0.25 mM, 0.5 mM, and 1 mM) for 24 h.

RESULTS

SCFAs dose-dependently affected inflammatory adipokine secretion, wherein at 1 mM, all three SCFAs reduced the secretion of leptin, IL-6 and IL-1β, but only propionate and butyrate reduced MCP-1/CCL2 and MIP-1α/CCL3 compared to control (p < 0.05). Interestingly, 1 mM acetate increased RANTES/CCL5 secretion versus control, whereas propionate and butyrate decreased RANTES/CCL5 secretion, and only 1 mM propionate reduced MCP-3/CCL7 secretion (p < 0.05). At the lower 0.5 mM concentration, both propionate and butyrate reduced IL-6 and IL-1β secretion compared to control (p < 0.05), and there was no difference in adipokine secretion between groups at the 0.25 mM SCFA concentration (p > 0.05). Intracellular protein expression in the ratio of phosphorylated-to-total STAT3 was reduced by all SCFAs at 1 mM and by propionate and butyrate at 0.5 mM versus control (p < 0.05). The ratio fo phosphorylated-to-total NFκB p65 expression was reduced by propionate and butyrate at 1 mM and by butyrate alone at 0.5 mM compared to control (p < 0.05). Basal (no insulin stimulation) and insulin-stimulated glucose uptake did not differ between control and any 1 mM SCFA treatment conditions (p > 0.05).

CONCLUSIONS

Individual SCFAs exert different dose-dependent effects on LPS-stimulated adipocyte function.

Effect of Comparable Carbon Chain Length Short- and Branched-Chain Fatty Acids on Adipokine Secretion from Normoxic and Hypoxic Lipopolysaccharide-Stimulated 3T3-L1 Adipocytes

Background: Microbial fermentation of non-digestible carbohydrates and/or protein produces short-chain fatty acids (SCFA), whereas branched-chain fatty acids (BCFA) are produced from protein fermentation. The effects of individual SCFA and BCFA of comparable carbon chain length on adipocyte inflammation have not been investigated. Objective: To compare the effects of SCFA and BCFA on inflammatory mediator secretion in an adipocyte cell culture model designed to recapitulate obesity-associated adipocyte inflammation under normoxic and hypoxic conditions. Methods: The 3T3-L1 adipocytes were cultured (24 h) without (Control, Con) and with 1 mmol/L of SCFA (butyric acid (But) or valeric acid (Val)) or 1 mmol/L of BCFA (isobutyric acid (IsoBut) or isovaleric acid (IsoVal)) and were unstimulated (cells alone, n = 6/treatment), or stimulated with 10 ng/mL lipopolysaccharide (LPS, inflammatory stimulus, n = 8/treatment) or 10 ng/mL LPS + 100 µmol/L of the hypoxia memetic cobalt chloride (LPS/CC, inflammatory/hypoxic stimulus, n = 8/treatment). Results: Compared to Con + LPS, But + LPS reduced secreted protein levels of interleukin (IL)-1β, IL-6, macrophage chemoattractant protein (MCP)-1/chemokine ligand (CCL)2, MCP3/CCL7, macrophage inflammatory protein (MIP)-1α/CCL3 and regulated upon activation, normal T cell expressed, and secreted (RANTES)/CCL5 and decreased intracellular protein expression of the ratio of phosphorylated to total signal transducer and activator of transcription 3 (STAT3) and nuclear factor kappa B (NFκB) p65 (p < 0.05). Val + LPS reduced IL-6 secretion and increased MCP-1/CCL2 secretion compared to Con + LPS and exhibited a different inflammatory mediator secretory profile from But + LPS (p < 0.05), indicating that individual SCFA exert individual effects. There were no differences in the secretory profile of the BCFA IsoBut + LPS and IsoVal + LPS (p > 0.05). Alternatively, under inflammatory hypoxic conditions (LPS/CC) Val, IsoVal, and IsoBut all increased secretion of IL-6, MCP-1/CCL2 and MIP-1α/CCL3 compared to Con (p < 0.05), whereas mediator secretion did not differ between But and Con (p > 0.05), indicating that the proinflammatory effects of SCFA and BCFA was attenuated by But. Interestingly, But + LPS/CC decreased STAT3 activation versus Con + LPS/CC (p < 0.05). Conclusions: The decreased secretion of inflammatory mediators that is attributable to But highlights the fact that individual SCFA and BCFA exert differential effects on adipocyte inflammation under normoxic and hypoxic conditions.

How the Western Diet Thwarts the Epigenetic Efforts of Gut Microbes in Ulcerative Colitis and Its Association with Colorectal Cancer

Ulcerative colitis (UC) is an autoimmune disease in which the immune system attacks the colon, leading to ulcer development, loss of colon function, and bloody diarrhea. The human gut ecosystem consists of almost 2000 different species of bacteria, forming a bioreactor fueled by dietary micronutrients to produce bioreactive compounds, which are absorbed by our body and signal to distant organs. Studies have shown that the Western diet, with fewer short-chain fatty acids (SCFAs), can alter the gut microbiome composition and cause the host's epigenetic reprogramming. Additionally, overproduction of H2S from the gut microbiome due to changes in diet patterns can further activate pro-inflammatory signaling pathways in UC. This review discusses how the Western diet affects the microbiome's function and alters the host's physiological homeostasis and susceptibility to UC. This article also covers the epidemiology, prognosis, pathophysiology, and current treatment strategies for UC, and how they are linked to colorectal cancer.

Analysis of the fermentation kinetics and gut microbiota modulatory effect of dried chicory root reveals the impact of the plant-cell matrix rationalizing its conversion in the distal colon

Aim: The cell matrix of plant foods has received little attention in prebiotic fiber research. We aimed to understand the impact of the plant cell matrix in dried chicory root on its breakdown in the human gut to explain its reported beneficial effects on gut and metabolic health. Methods: We applied in vitro digestion and fermentation models together with an ex vivo gut barrier integrity model. Plant cell matrix intactness in the upper gastrointestinal tract was investigated by scanning electron microscopy. Colonic breakdown of inulin, and chicory root cubes and powder was assessed by gut microbiota analysis using 16S rRNA gene amplicon sequencing and determining the kinetics of changes in pH, gas, and short-chain fatty acid (SCFA) production. Finally, effects on gut barrier integrity were explored by exposing colonic biopsies to fermentation supernatants in an Ussing chamber model. Results: The plant cell matrix of dried chicory root cubes remained intact throughout upper gastrointestinal transit. Dried chicory root fermentation resulted in higher final relative abundances of pectin-degrading Monoglobus and butyrate-producing Roseburia spp. compared to inulin and a seven-fold increase in Bifidobacterium spp. in donors where these species were present. Dried chicory root cubes yielded similar total SCFAs but higher final butyrate levels than chicory root powder or isolated inulin with less gas produced. No uniform but donor-specific effects of fermentation supernatants on the maintenance of gut barrier integrity were detected. Conclusion: The intact plant cell matrix of dried chicory root affected its colonic breakdown kinetics and microbiota, underpinning its beneficial effect in vivo.

Intraintestinal fermentation of fructo- and galacto-oligosaccharides and the fate of short-chain fatty acids in humans

Consumption of fructo- (FOS) and galacto-oligosaccharides (GOS) has health benefits which have been linked in part to short-chain fatty acids (SCFA) production by the gut microbiota. However, detailed knowledge of this process in the human intestine is lacking. We aimed to determine the acute fermentation kinetics of a FOS:GOS mixture in healthy males using a naso-intestinal catheter for sampling directly in the ileum or colon. We studied the fate of SCFA as substrates for glucose and lipid metabolism by the host after infusion of 13C-SCFA. In the human distal ileum, no fermentation of FOS:GOS, nor SCFA production, or bacterial cross-feeding was observed. The relative composition of intestinal microbiota changed rapidly during the test day, which demonstrates the relevance of postprandial intestinal sampling to track acute responses of the microbial community toward interventions. SCFA were vividly taken up and metabolized by the host as shown by incorporation of 13C in various host metabolites.

Effect of Short-Chain Fatty Acids on Inflammatory and Metabolic Function in an Obese Skeletal Muscle Cell Culture Model

The fermentation of non-digestible carbohydrates produces short-chain fatty acids (SCFAs), which have been shown to impact both skeletal muscle metabolic and inflammatory function; however, their effects within the obese skeletal muscle microenvironment are unknown. In this study, we developed a skeletal muscle in vitro model to mimic the critical features of the obese skeletal muscle microenvironment using L6 myotubes co-treated with 10 ng/mL lipopolysaccharide (LPS) and 500 µM palmitic acid (PA) for 24 h ± individual SCFAs, namely acetate, propionate and butyrate at 0.5 mM and 2.5 mM. At the lower SCFA concentration (0.5 mM), all three SCFA reduced the secreted protein level of RANTES, and only butyrate reduced IL-6 protein secretion and the intracellular protein levels of activated (i.e., ratio of phosphorylated-total) NFκB p65 and STAT3 (p < 0.05). Conversely, at the higher SCFA concentration (2.5 mM), individual SCFAs exerted different effects on inflammatory mediator secretion. Specifically, butyrate reduced IL-6, MCP-1 and RANTES secretion, propionate reduced IL-6 and RANTES, and acetate only reduced RANTES secretion (p < 0.05). All three SCFAs reduced intracellular protein levels of activated NFκB p65 and STAT3 (p < 0.05). Importantly, only the 2.5 mM SCFA concentration resulted in all three SCFAs increasing insulin-stimulated glucose uptake compared to control L6 myotube cultures (p < 0.05). Therefore, SCFAs exert differential effects on inflammatory mediator secretion in a cell culture model, recapitulating the obese skeletal muscle microenvironment; however, all three SCFAs exerted a beneficial metabolic effect only at a higher concentration via increasing insulin-stimulated glucose uptake, collectively exerting differing degrees of a beneficial effect on obesity-associated skeletal muscle dysfunction.

Adipokines and Bacterial Metabolites: A Pivotal Molecular Bridge Linking Obesity and Gut Microbiota Dysbiosis to Target

Adipokines are essential mediators produced by adipose tissue and exert multiple biological functions. In particular, adiponectin, leptin, resistin, IL-6, MCP-1 and PAI-1 play specific roles in the crosstalk between adipose tissue and other organs involved in metabolic, immune and vascular health. During obesity, adipokine imbalance occurs and leads to a low-grade pro-inflammatory status, promoting insulin resistance-related diabetes and its vascular complications. A causal link between obesity and gut microbiota dysbiosis has been demonstrated. The deregulation of gut bacteria communities characterizing this dysbiosis influences the synthesis of bacterial substances including lipopolysaccharides and specific metabolites, generated via the degradation of dietary components, such as short-chain fatty acids, trimethylamine metabolized into trimethylamine-oxide in the liver and indole derivatives. Emerging evidence suggests that these bacterial metabolites modulate signaling pathways involved in adipokine production and action. This review summarizes the current knowledge about the molecular links between gut bacteria-derived metabolites and adipokine imbalance in obesity, and emphasizes their roles in key pathological mechanisms related to oxidative stress, inflammation, insulin resistance and vascular disorder. Given this interaction between adipokines and bacterial metabolites, the review highlights their relevance (i) as complementary clinical biomarkers to better explore the metabolic, inflammatory and vascular complications during obesity and gut microbiota dysbiosis, and (ii) as targets for new antioxidant, anti-inflammatory and prebiotic triple action strategies.

Dietary fiber - a scoping review for Nordic Nutrition Recommendations 2023

Dietary fiber is a term crudely defined as carbohydrates (CHOs) that escape digestion and uptake in the small intestine. Lignin, which is not a CHO, is also a part of the dietary fiber definition. Dietary fibers come in different sizes and forms, with a variety of combinations of monomeric units. Health authorities worldwide have for many years recommended a diet rich in dietary fibers based on consistent findings that dietary fibers are associated with reduced incidences of major non-communicable diseases, including obesity, type 2 diabetes, cardiovascular disease, and colorectal cancer. Most fibers come from common edible foods from the plant kingdom, but fibers are also found in food additives, supplements, and breast milk. The recommended intake in Nordic Nutrition Recommendations 2012 (NNR2012) is 25 g/d for women and 35 g/d for men, whereas the actual intake is significantly lower, ranging from 16 g/d to 22 g/d in women and 18 g/d to 26 g/d in men. New studies since NNR2012 confirm the current view that dietary fiber is beneficial for health, advocating intakes of at least 25 g/day.

Regional changes in intestinal permeability in cirrhosis are associated with mucosal bacteria

BACKGROUND

Several complications of cirrhosis are theorized to result from the translocation of bacteria or their products across the intestinal epithelium. We aimed to assess epithelial permeability and associations with mucosal bacteria in patients with cirrhosis.

APPROACH AND RESULTS

We collected 247 duodenum, ileum, and colon biopsies from 58 consecutive patients with cirrhosis and 33 controls during clinically indicated endoscopies. Patients with cirrhosis were similarly aged to controls (60 vs. 58 y) and had a median Model for End-stage Liver Disease of 8 (interquartile range 7, 10). Biopsies underwent 16S rRNA-encoding gene amplicon sequencing to determine mucosal bacteria composition and transepithelial electrical resistance (TEER) to determine epithelial permeability. In the entire cohort, there were regional differences in TEER with the lowest TEER (ie, more permeable) in the ileum; duodenum TEER was 43% higher and colon TEER 20% higher than ileum TEER (ANOVA p = 0.0004). When comparing patients with cirrhosis and controls, both TEER (26% lower in cirrhosis, p = 0.006) and alpha diversity differed in the duodenum (27% lower in cirrhosis, p = 0.01) but not ileum or colon. A beta-binomial model found that 26 bacteria were significantly associated with TEER. Bifidobacteriaceae Bifidobacterium in duodenal mucosa was protective of epithelial permeability and future hospitalization for hepatic decompensation.

CONCLUSIONS

Duodenal epithelial permeability was higher, and mucosal bacteria alpha diversity was lower in cirrhosis compared to controls, while no such differences were seen in the ileum or colon. Specific bacteria were associated with epithelial permeability and future hepatic decompensation.

2'-fucosyllactose alone or combined with resistant starch increases circulating short-chain fatty acids in lean men and men with prediabetes and obesity

Background

Infusion of short-chain fatty acids (SCFA) to the distal colon beneficially affects human substrate and energy metabolism. Here, we hypothesized that the combination of 2'-fucosyllactose (2'-FL) with resistant starch (RS) increases distal colonic SCFA production and improves metabolic parameters.

Methods

In this randomized, crossover study, 10 lean (BMI 20-24.9 kg/m²) and nine men with prediabetes and overweight/obesity (BMI 25-35 kg/m²) were supplemented with either 2'-FL, 2'-FL+RS, or placebo one day before a clinical investigation day (CID). During the CID, blood samples were collected after a overnight fast and after intake of a liquid high-fat mixed meal to determine plasma SCFA (primary outcomes). Secondary outcomes were fasting and postprandial plasma insulin, glucose, free fatty acid (FFA), glucagon-like peptide-1, and peptide YY concentrations. In addition, fecal SCFA and microbiota composition, energy expenditure and substrate oxidation (indirect calorimetry), and breath hydrogen excretion were determined.

Results

In lean men, supplementation with 2'-FL increased postprandial plasma acetate (P = 0.017) and fasting H₂ excretion (P = 0.041) compared to placebo. Postprandial plasma butyrate concentration increased after 2'-FL and 2'-FL+RS as compared to placebo (P < 0.05) in lean men and men with prediabetes and overweight/obesity. Additionally, 2'-FL+RS decreased fasting and postprandial plasma FFA concentrations compared to placebo (P < 0.05) in lean men.

Conclusion

Supplementation of 2'-FL with/without RS the day before investigation increased systemic butyrate concentrations in lean men as well as in men with prediabetes and obesity, while acetate only increased in lean men. The combination of 2'-FL with RS showed a putatively beneficial metabolic effect by lowering plasma FFA in lean men, indicating a phenotype-specific effect.

Clinical trial registration

nr. NCT04795804.

Can prebiotics help tackle the childhood obesity epidemic?

Globally, excess weight during childhood and adolescence has become a public health crisis with limited treatment options. Emerging evidence suggesting the involvement of gut microbial dysbiosis in obesity instills hope that targeting the gut microbiota could help prevent or treat obesity. In pre-clinical models and adults, prebiotic consumption has been shown to reduce adiposity partially via restoring symbiosis. However, there is a dearth of clinical research into its potential metabolic benefits in the pediatric population. Here, we provide a succinct overview of the common characteristics of the gut microbiota in childhood obesity and mechanisms of action of prebiotics conferring metabolic benefits. We then summarize available clinical trials in children with overweight or obesity investigating the effects of prebiotics on weight management. This review highlights several controversial aspects in the microbiota-dependent mechanisms by which prebiotics are thought to affect host metabolism that warrant future investigation in order to design efficacious interventions for pediatric obesity.

Contribution of skeletal muscle to cancer immunotherapy: A focus on muscle function, inflammation, and microbiota

Sarcopenia, characterized by degenerative and systemic loss of skeletal muscle mass and function, is a multifactorial syndrome commonly observed in individuals with cancer. Additionally, it represents a poor nutritional status and indicates possible presence of cancer cachexia. Recently, with the extensive application of cancer immunotherapy, the effects of sarcopenia/cachexia on cancer immunotherapy, have gained attention. The aim of this review was to summarize the influence of low muscle mass (sarcopenia/cachexia) on the response and immune-related adverse events to immunotherapy from the latest literature. It was revealed that low muscle mass (sarcopenia/cachexia) has detrimental effects on cancer immunotherapy in most cases, although there were results that were not consistent with this finding. This review also discussed potential causes of the paradox, such as different measure methods, research types, muscle indicators, time point, and cancer type. Mechanically, chronic inflammation, immune cells, and microbiota may be critically involved in regulating the efficacy of immunotherapy under the condition of low muscle mass (sarcopenia/cachexia). Thus, nutritional interventions will likely be promising ways for individuals with cancer to increase the efficacy of immunotherapy in the future, for low muscle mass (sarcopenia/cachexia) is an important prognostic factor for cancer immunotherapy.

Enterorenal crosstalks in diabetic nephropathy and novel therapeutics targeting the gut microbiota

The role of gut-kidney crosstalk in the progression of diabetic nephropathy (DN) is receiving increasing concern. On one hand, the decline in renal function increases circulating uremic toxins and affects the composition and function of gut microbiota. On the other hand, intestinal dysbiosis destroys the epithelial barrier, leading to increased exposure to endotoxins, thereby exacerbating kidney damage by inducing systemic inflammation. Dietary inventions, such as higher fiber intake, prebiotics, probiotics, postbiotics, fecal microbial transplantation (FMT), and engineering bacteria and phages, are potential microbiota-based therapies for DN. Furthermore, novel diabetic agents, such as glucagon-like peptide-1 (GLP-1) receptor agonists, dipeptidyl peptidase-4 (DPP-4) inhibitors, and sodium-dependent glucose transporter-2 (SGLT-2) inhibitors, may affect the progression of DN partly through gut microbiota. In the current review, we mainly summarize the evidence concerning the gut-kidney axis in the advancement of DN and discuss therapies targeting the gut microbiota, expecting to provide new insight into the clinical treatment of DN.

Duodenal Permeability Is Associated With Mucosal Microbiota in Compensated Cirrhosis

INTRODUCTION

Several complications of decompensated cirrhosis are believed to result from increased intestinal permeability. However, little is known about the relationship between mucosal bacteria and epithelial permeability in cirrhosis. We aimed to assess epithelial permeability and associations with mucosal bacteria in patients with compensated cirrhosis.

METHODS

We obtained duodenal tissue biopsies from patients with compensated cirrhosis and controls. Patients were excluded if they used antibiotics or immunosuppression. The composition of mucosal microbiota was determined by 16S rRNA gene sequencing and epithelial permeability by transepithelial electrical resistance (TEER) and tight junction protein expression.

RESULTS

We studied 24 patients with compensated cirrhosis and 20 controls. Patients with cirrhosis were older than controls (62 vs 52 years, P = 0.02) but had a similar number of extrahepatic comorbidities (2.2 vs 1.4, P = 0.13). Patients with compensated cirrhosis had lower duodenal TEER (i.e., increased epithelial permeability; 13.3 Ω/cm 2 ± 3.4 vs 18.9 Ω/cm 2 ± 7.1; P = 0.004). Patients with compensated cirrhosis trended toward a distinct mucosal microbiota community structure relative to controls ( P = 0.09). Clustering analysis identified two unique enterotypes. These enterotypes differed in bacterial composition and also TEER. A beta-binomial model found 13 individual bacteria associated with TEER, including Lactobacillus and Bifidobacterium taxa. Thirty-six taxa were associated with tight junction protein expression, including Lactobacillus and Bifidobacterium.

DISCUSSION

Compensated cirrhosis is characterized by increased duodenal epithelial permeability with a distinct mucosal microbial community. Intriguingly, bacteria previously associated with health were protective of duodenal permeability.

Intrinsic dietary fibers and the gut microbiome: Rediscovering the benefits of the plant cell matrix for human health

Dietary fibers contribute to structure and storage reserves of plant foods and fundamentally impact human health, partly by involving the intestinal microbiota, notably in the colon. Considerable attention has been given to unraveling the interaction between fiber type and gut microbiota utilization, focusing mainly on single, purified fibers. Studying these fibers in isolation might give us insights into specific fiber effects, but neglects how dietary fibers are consumed daily and impact our digestive tract: as intrinsic structures that include the cell matrix and content of plant tissues. Like our ancestors we consume fibers that are entangled in a complex network of plants cell walls that further encapsulate and shield intra-cellular fibers, such as fructans and other components from immediate breakdown. Hence, the physiological behavior and consequent microbial breakdown of these intrinsic fibers differs from that of single, purified fibers, potentially entailing unexplored health effects. In this mini-review we explain the difference between intrinsic and isolated fibers and discuss their differential impact on digestion. Subsequently, we elaborate on how food processing influences intrinsic fiber structure and summarize available human intervention studies that used intrinsic fibers to assess gut microbiota modulation and related health outcomes. Finally, we explore current research gaps and consequences of the intrinsic plant tissue structure for future research. We postulate that instead of further processing our already (extensively) processed foods to create new products, we should minimize this processing and exploit the intrinsic health benefits that are associated with the original cell matrix of plant tissues.

Differential Effects of Short-Chain Fatty Acids on L6 Myotube Inflammatory Mediator Production in Response to Lipopolysaccharide- or Palmitic Acid-Stimulation

Short-chain fatty acids (SCFA) produced from dietary non-digestible carbohydrate fermentation have metabolic effects in skeletal muscle; however, their effect on inflammatory mediator production is unknown. In this study, L6 myotubes were cultured with individual SCFA (acetate, propionate, and butyrate) at 0.5 mM and 2.5 mM ± 10 ng/mL lipopolysaccharide (LPS) or ± 500 µM palmitic acid (PA) for 24 h. In response to LPS, only butyrate had an effect at the lower concentration (0.5 mM), whereas at the higher concentration (2.5 mM) both propionate and butyrate reduced MCP-1, MIP-1α, and RANTES secretion (p < 0.05), and only butyrate reduced IL-6 secretion and intracellular protein levels of phospho-STAT3 (p < 0.05). In response to PA, 0.5 mM butyrate reduced protein expression of phospho-NFκB p65 and the secretion of IL-6, MIP-1α, and MCP-1, whereas all three SCFA reduced RANTES secretion (p < 0.05). At the 2.5 mM SCFA concentration combined with PA stimulation, all three SCFA reduced intracellular protein expression of phospho-NFκB p65 and phospho-STAT3 and secreted protein levels of MCP-1, IL-6, and RANTES, whereas only butyrate reduced secretion of MIP-1α (p < 0.05). Thus, SCFA exhibit differential effects on inflammatory mediator expression in response to LPS and PA stimulation, which has implications for their individual impacts on inflammation-mediated skeletal muscle dysfunction.

Host hepatic metabolism is modulated by gut microbiota-derived sphingolipids

Microbially-derived gut metabolites are important contributors to host phenotypes, many of which may link microbiome composition to metabolic disease. However, relatively few metabolites with known bioactivity have been traced from specific microbes to host tissues. Here, we use a labeling strategy to characterize and trace bacterial sphingolipids from the gut symbiont Bacteroides thetaiotaomicron to mouse colons and livers. We find that bacterial sphingolipid synthesis rescues excess lipid accumulation in a mouse model of hepatic steatosis and observe the transit of a previously uncharacterized bacterial sphingolipid to the liver. The addition of this sphingolipid to hepatocytes improves respiration in response to fatty-acid overload, suggesting that sphingolipid transfer to the liver could potentially contribute to microbiota-mediated liver function. This work establishes a role for bacterial sphingolipids in modulating hepatic phenotypes and defines a workflow that permits the characterization of other microbial metabolites with undefined functions in host health.

Intestinal Microbiota-Derived Short Chain Fatty Acids in Host Health and Disease

Intestinal microbiota has its role as an important component of human physiology. It produces metabolites that module key functions to establish a symbiotic crosstalk with their host. Among them, short chain fatty acids (SCFAs), produced by intestinal bacteria during the fermentation of partially and non-digestible polysaccharides, play key roles in regulating colon physiology and changing intestinal environment. Recent research has found that SCFAs not only influence the signal transduction pathway in the gut, but they also reach tissues and organs outside of the gut, through their circulation in the blood. Growing evidence highlights the importance of SCFAs level in influencing health maintenance and disease development. SCFAs are probably involved in the management of host health in a complicated (positive or negative) way. Here, we review the current understanding of SCFAs effects on host physiology and discuss the potential prevention and therapeutics of SCFAs in a variety of disorders. It provides a systematic theoretical basis for the study of mechanisms and precise intake level of SCFAs to promote human health.

Fiber mixture-specific effect on distal colonic fermentation and metabolic health in lean but not in prediabetic men

Infusions of the short-chain fatty acid (SCFA) acetate in the distal colon improved metabolic parameters in men. Here, we hypothesized that combining rapidly and slowly fermentable fibers will enhance distal colonic acetate production and improve metabolic health. In vitro cultivation studies in a validated model of the colon were used to identify fiber mixtures that yielded high distal colonic acetate production. Subsequently, in two randomized crossover studies, lean and prediabetic overweight/obese men were included. In one study, participants received supplements of either long-chain inulin+resistant starch (INU+RS), INU or maltodextrin (PLA) the day prior to a clinical investigation day (CID). The second trial studied beta glucan+RS (BG+RS) versus BG and PLA. During each CID, breath hydrogen, indirect calorimetry, plasma metabolites/hormones were assessed during fasting and postprandial conditions. Additionally, fecal microbiota composition and SCFA were determined. In prediabetic men, INU+RS increased plasma acetate compared to INU or PLA (P < .05), but did not affect metabolic parameters. In lean men, INU+RS increased breath hydrogen and fasting plasma butyrate, which was accompanied by increased energy expenditure, carbohydrate oxidation and PYY and decreased postprandial glucose concentrations (all P < .05) compared to PLA. BG+RS increased plasma butyrate compared to PLA (P < .05) in prediabetic individuals, but did not affect other fermentation/metabolic markers in both phenotypes. Fiber-induced shifts in fecal microbiota were individual-specific and more pronounced with INU+RS versus BG+RS. Administration of INU+RS (not BG+RS) the day prior to investigation improved metabolic parameters in lean but not in prediabetic individuals, demonstrating that effects were phenotype- and fiber-specific. Further research should study whether longer-term supplementation periods are required to elicit beneficial metabolic health in prediabetic individuals. Trial registration numbers: Clinical trial No. NCT03711383 (Inulin study) and Clinical trial No. NCT03714646 (Beta glucan study).

Distinct Effects of Short Chain Fatty Acids on Host Energy Balance and Fuel Homeostasis With Focus on Route of Administration and Host Species

Accumulating evidence implicates gut-microbiota-derived metabolites as important regulators of host energy balance and fuel homeostasis, the underlying mechanisms are currently subject to intense research. In this review, the most important executors, short chain fatty acids, which both directly and indirectly fulfill the interactions between gut microbiota and host will be discussed. Distinct roles of individual short chain fatty acids and the different effects they exert on host metabolism have long been overlooked, which compromises the process of clarifying the sophisticated crosstalk between gut microbiota and its host. Moreover, recent findings suggest that exogenously administered short chain fatty acids affect host metabolism via different mechanisms depending on the routes they enter the host. Although these exogenous routes are often artificial, they may help to comprehend the roles of the short-chain-fatty-acid mechanisms and signaling sites, that would normally occur after intestinal absorption of short chain fatty acids. Cautions should be addressed of generalizing findings, since different results have appeared in different host species, which may imply a host species-specific response to short chain fatty acids.

Transorgan short-chain fatty acid fluxes in the fasted and postprandial state in the pig

The short-chain fatty acids (SCFAs) acetate, propionate, butyrate, isovalerate, and valerate are end products of intestinal bacterial fermentation and important mediators in the interplay between the intestine and peripheral organs. To unravel the transorgan fluxes and mass balance comparisons of SCFAs, we measured their net fluxes across several organs in a translational pig model. In multicatheterized conscious pigs [n = 12, 25.6 (95% CI [24.2, 26.9]) kg, 8-12 wk old], SCFA fluxes across portal-drained viscera (PDV), liver, kidneys, and hindquarter (muscle compartment) were measured after an overnight fast and in the postprandial state, 4 h after administration of a fiber-free, mixed meal. PDV was the main releasing compartment of acetate, propionate, butyrate, isovalerate, and valerate during fasting and in the postprandial state (all P = 0.001). Splanchnic acetate release was high due to the absence of hepatic clearance. All other SCFAs were extensively taken up by the liver (all P < 0.05). Even though only 7% [4, 10] (propionate), 42% [23, 60] (butyrate), 26% [12, 39] (isovalerate), and 3% [0.4, 5] (valerate) of PDV release were excreted from the splanchnic area in the fasted state, splanchnic release of all SCFAs was significant (all P values ≤0.01). Splanchnic propionate, butyrate, isovalerate, and valerate release remained low but significant in the postprandial state (all P values <0.01). We identified muscle and kidneys as main peripheral SCFA metabolizing organs, taking up the majority of all splanchnically released SCFAs in the fasted state and in the postprandial state. We conclude that the PDV is the main SCFA releasing and the liver the main SCFA metabolizing organ. Splanchnically released SCFAs appear to be important energy substrates to peripheral organs not only in the fasted but also in the postprandial state.NEW & NOTEWORTHY Using a multicatheterized pig model, we identified the portal-drained viscera as the main releasing compartment of the short-chain fatty acids acetate, propionate, butyrate, isovalerate, and valerate in the fasted and postprandial states. Low hepatic acetate metabolism resulted in a high splanchnic release, whereas all other SCFAs were extensively cleared resulting in low but significant splanchnic releases. Muscle and kidneys are the main peripheral SCFA metabolizing organs during fasting and in the postprandial state.

The ameliorative effect of Lactobacillus plantarum Y44 oral administration on inflammation and lipid metabolism in obese mice fed with a high fat diet

In our previous studies, Lactobacillus plantarum Y44 showed antioxidant activity and favorable gastric and intestinal transit tolerance. The purpose of this study is to determine whether L. plantarum Y44 could ameliorate intestinal inflammation and lipid metabolism disorder in obese mice fed with a high-fat diet. L. plantarum Y44 was administered by gavage to the mice fed with a high-fat diet for 12 weeks. The mice fed with a high fat diet only showed sustainably elevated body weight, liver lipid metabolism disorder, intestinal inflammation and a lower short chain fatty acid content in feces. Oral administration of L. plantarum Y44 regulated lipid metabolism disorder by inhibiting the expression of fatty acid synthase (FAS) and acetyl-CoA carboxylase (ACC) in the liver of obese mice, reducing the contents of total cholesterol (TC), triacylglycerols (TG), low density lipoprotein cholesterol (LDL-c), alanine aminotransferase (ALT), and aspartate transaminase (AST) and increasing the content of high-density lipoprotein cholesterol (HDL-c) in the serum of obese mice. Oral administration of L. plantarum Y44 up-regulated the expression of colon tight junction protein such as claudin-1 and occludin, down-regulated p38 and phospho-p38 levels and reduced serum interleukin-8 (IL-8) and tumor necrosis factor-α (TNF-α). Oral administration of L. plantarum Y44 increased Muribaculaceae, Rikenellaceae, and Lactobacillaceae levels, reduced the Firmicutes/Bacteroidetes ratio, and Desulfovibrionaceae and Proteobacteria levels in obese mice. Oral administration of L. plantarum Y44 also enhanced the contents of propionic acid, butyric acid, butanoicacid-3-methyl, pentanoic acid and acetic acid in the feces of the obese mice. Correlation analysis of Spearman revealed a significant correlation between changes in intestinal microflora and obesity-related symptoms. L. plantarum Y44 ameliorated intestinal inflammation and lipid metabolism disorders by modulating gut microbiota.

Gut microbiota and metabolic aspects of cancer cachexia

Cancer cachexia is a metabolic syndrome characterized by unintended weight loss and muscle wasting. It has a strong negative impact on survival. Its underlying mechanisms involve systemic inflammation and insulin resistance, which are known to be influenced by the gut microbiota. Preclinical studies support a role for the gut microbiota in cancer cachexia by demonstrating that cachectic mice display: 1) various gut microbiota composition changes; 2) increased gut permeability and translocation of pro-inflammatory microbial compounds; 3) muscle atrophy-related processes linked to gut microbiota properties; 4) positive effects of microbiota-modulating interventions. Data on the relationships between gut microbiota, insulin resistance, and hepatic/adipose tissue metabolism in cachexia models are lacking. Nevertheless, the available data and existing evidence for the impact of gut microbiota on metabolic aberrations in human obesity urge for exploration of its role in human cancer cachexia. We provide practical recommendations and discuss the challenges for such future clinical studies.

Gut Microbiota Influence Lipid Metabolism of Skeletal Muscle in Pigs

Gut microbiota is recognized as a strong determinant of host physiology including fat metabolism and can transfer obesity-associated phenotypes from donors to recipients. However, the relationship between gut microbiota and intramuscular fat (IMF) is still largely unknown. Obese Jinhua pigs (JP) have better meat quality that is associated with higher IMF content than lean Landrace pigs (LP). The present study was conducted to test the contribution of gut microbiota to IMF properties by transplanting fecal microbiota of adult JP and LP to antibiotics-treated mice. Similar to JP donors, the mice receiving JP's microbiota (JM) had elevated lipid and triglyceride levels and the lipoprotein lipase activity, as well as reduced mRNA level of angiopoietin-like 4 (ANGPTL4) in the gastrocnemius muscles, compared to those in mice receiving LP's microbiota (LM). High-throughput 16S rRNA sequencing confirmed that transplantation of JP and LP feces differently reconstructed the gut microbiota in both jejunum and colon of mouse recipients. In colonic samples, we observed an elevated ratio of Firmicutes to Bacteroidetes and increased abundance of genus Romboutsia in JM, which were positively correlated with obesity. Furthermore, the abundance of Akkermansia decreased in JM, which is positively correlated with lean. Colonic concentrations of acetate (P = 0.047) and butyrate (P = 0.014) were significantly lower in JM than in LM, and consistently, the terminal genes for butyrate synthesis, butyryl CoA: acetate CoA transferase were less abundant in colonic microbiota of JM. Taken together, these gut microbiota of obese JP intrinsically promotes IMF accumulation and can transfer the properties to mouse recipients. Manipulation of intestinal microbiota will, therefore, have the potential to improve the meat quality and flavor of pigs and even to ameliorate the metabolic syndrome in human.

The Protective Role of Butyrate against Obesity and Obesity-Related Diseases

Worldwide obesity is a public health concern that has reached pandemic levels. Obesity is the major predisposing factor to comorbidities, including type 2 diabetes, cardiovascular diseases, dyslipidemia, and non-alcoholic fatty liver disease. The common forms of obesity are multifactorial and derive from a complex interplay of environmental changes and the individual genetic predisposition. Increasing evidence suggest a pivotal role played by alterations of gut microbiota (GM) that could represent the causative link between environmental factors and onset of obesity. The beneficial effects of GM are mainly mediated by the secretion of various metabolites. Short-chain fatty acids (SCFAs) acetate, propionate and butyrate are small organic metabolites produced by fermentation of dietary fibers and resistant starch with vast beneficial effects in energy metabolism, intestinal homeostasis and immune responses regulation. An aberrant production of SCFAs has emerged in obesity and metabolic diseases. Among SCFAs, butyrate emerged because it might have a potential in alleviating obesity and related comorbidities. Here we reviewed the preclinical and clinical data that contribute to explain the role of butyrate in this context, highlighting its crucial contribute in the diet-GM-host health axis.

Butyric Acid Added Apically to Intestinal Caco-2 Cells Elevates Hepatic ApoA-I Transcription and Rescues Lower ApoA-I Expression in Inflamed HepG2 Cells Co-Cultured in the Basolateral Compartment

Apolipoprotein A-I (ApoA-I) concentrations are decreased during inflammation, which may reduce high-density lipoprotein (HDL) functionality. Thus, rescuing ApoA-I concentrations during inflammation might help to prevent atherosclerosis. Recent studies have shown that butyric acid (C4) has anti-inflammatory effects and rescues ApoA-I production. However, whether intestinal short chain fatty acids (SCFAs) are able to influence hepatic processes is unknown. Therefore, we investigated C4 anti-inflammatory effects on ApoA-I transcription in the intestine-liver co-culture model. C4 dose-response experiments in the presence or absence of cytokines were performed in a co-culture system including Caco-2 cells, HepG2 cells, or both. Changes in ApoA-I transcription in Caco-2 cells and HepG2 cells were analyzed using qPCR. C4 increased ApoA-I expression in HepG2 cells that cultured alone. When both cells were cultured together, C4 decreased ApoA-I expression in Caco-2 cells and increased ApoA-I expression in HepG2 cells. However, adding C4 to apical Caco-2 cells resulted in a smaller effect in HepG2 cells compared with adding C4 directly to the hepatocytes. Moreover, C4 rescued ApoA-I expression in inflamed HepG2 cells. These findings suggests that intestinal SCFAs can affect hepatic processes. However, the smaller effect in the co-culture experiment indicates cross-talk between intestine and liver.

Acetate Does Not Affect Palmitate Oxidation and AMPK Phosphorylation in Human Primary Skeletal Muscle Cells

Our recent in vivo human studies showed that colonic administration of sodium acetate (SA) resulted in increased circulating acetate levels, which was accompanied by increments in whole-body fat oxidation in overweight-obese men. Since skeletal muscle has a major role in whole-body fat oxidation, we aimed to investigate effects of SA on fat oxidation and underlying mechanisms in human primary skeletal muscle cells (HSkMC). We investigated the dose (0-5 mmol/L) and time (1, 4, 20, and 24 h) effect of SA on complete and incomplete endogenous and exogenous oxidation of ¹⁴C-labeled palmitate in HSkMC derived from a lean insulin sensitive male donor. Both physiological (0.1 and 0.25 mmol/L) and supraphysiological (0.5, 1 and 5 mmol/L) concentrations of SA neither increased endogenous nor exogenous fat oxidation over time in HSkMC. In addition, no effect of SA was observed on Thr¹⁷²-AMPKα phosphorylation. In conclusion, our previously observed in vivo effects of SA on whole-body fat oxidation in men may not be explained via direct effects on HSkMC fat oxidation. Nevertheless, SA-mediated effects on whole-body fat oxidation may be triggered by other mechanisms including gut-derived hormones or may occur in other metabolically active tissues.

Short-chain fatty acids as potential regulators of skeletal muscle metabolism and function

A key metabolic activity of the gut microbiota is the fermentation of non-digestible carbohydrate, which generates short-chain fatty acids (SCFAs) as the principal end products. SCFAs are absorbed from the gut lumen and modulate host metabolic responses at different organ sites. Evidence suggests that these organ sites include skeletal muscle, the largest organ in humans, which plays a pivotal role in whole-body energy metabolism. In this Review, we evaluate the evidence indicating that SCFAs mediate metabolic cross-talk between the gut microbiota and skeletal muscle. We discuss the effects of three primary SCFAs (acetate, propionate and butyrate) on lipid, carbohydrate and protein metabolism in skeletal muscle, and we consider the potential mechanisms involved. Furthermore, we highlight the emerging roles of these gut-derived metabolites in skeletal muscle function and exercise capacity, present limitations in current knowledge and provide suggestions for future work.

The Potential Effects of Probiotics and ω-3 Fatty Acids on Chronic Low-Grade Inflammation

Chronic low-grade inflammation negatively impacts health and is associated with aging and obesity, among other health outcomes. A large number of immune mediators are present in the digestive tract and interact with gut bacteria to impact immune function. The gut microbiota itself is also an important initiator of inflammation, for example by releasing compounds such as lipopolysaccharides (LPS) that may influence cytokine production and immune cell function. Certain nutrients (e.g., probiotics, ω-3 fatty acids [FA]) may increase gut microbiota diversity and reduce inflammation. Lactobacilli and Bifidobacteria, among others, prevent gut hyperpermeability and lower LPS-dependent chronic low-grade inflammation. Furthermore, ω-3 FA generate positive effects on inflammation-related conditions (e.g., hypertriglyceridemia, diabetes) by interacting with immune, metabolic, and inflammatory pathways. Ω-3 FA also increase LPS-suppressing bacteria (i.e., Bifidobacteria) and decrease LPS-producing bacteria (i.e., Enterobacteria). Additionally, ω-3 FA appear to promote short-chain FA production. Therefore, combining probiotics with ω-3 FA presents a promising strategy to promote beneficial immune regulation via the gut microbiota, with potential beneficial effects on conditions of inflammatory origin, as commonly experienced by aged and obese individuals, as well as improvements in gut-brain-axis communication.

Back to the Roots: Revisiting the Use of the Fiber-Rich Cichorium intybusL. Taproots

Fibers are increasingly recognized as an indispensable part of our diet and vital for maintaining health. Notably, complex mixtures of fibers have been found to improve metabolic health. Following an analysis of the fiber content of plant-based products, we found the taproot of the chicory plant (Cichorium intybusL.) to be 1 of the vegetables with the highest fiber content, comprising nearly 90% of its dry weight. Chicory roots consist of a mixture of inulin, pectin, and (hemi-)cellulose and also contain complex phytochemicals, such as sesquiterpene lactones that have been characterized in detail. Nowaday, chicory roots are mainly applied as a source for the extraction of inulin, which is used as prebiotic fiber and food ingredient. Chicory roots, however, have long been consumed as a vegetable by humans. The whole root has been used for thousands of years for nutritional, medicinal, and other purposes, and it is still used in traditional dishes in various parts of the world. Here, we summarize the composition of chicory roots to explain their historic success in the human diet. We revisit the intake of chicory roots by humans and describe the different types of use along with their various methods of preparation. Hereby, we focus on the whole root in its complex, natural form, as well as in relation to its constituents, and discuss aspects regarding legal regulation and the safety of chicory root extracts for human consumption. Finally, we provide an overview of the current and future applications of chicory roots and their contribution to a fiber-rich diet.

Supplementation of a propionate-producing consortium improves markers of insulin resistance in an in vitro model of gut-liver axis

Gut-liver cross talk is an important determinant of human health with profound effects on energy homeostasis. While gut microbes produce a huge range of metabolites, specific compounds such as short-chain fatty acids (SCFAs) can enter the portal circulation and reach the liver (Brandl K, Schnabl B. Curr Opin Gastroenterol 33: 128-133, 2017), a central organ involved in glucose homeostasis and diabetes control. Propionate is a major SCFA involved in activation of intestinal gluconeogenesis (IGN), thereby regulating food intake, enhancing insulin sensitivity, and leading to metabolic homeostasis. Although microbiome-modulating strategies may target the increased microbial production of propionate, it is not clear whether such an effect spreads through to the hepatic cellular level. Here, we designed a propionate-producing consortium using a selection of commensal gut bacteria, and we investigated how their delivered metabolites impact an in vitro enterohepatic model of insulin resistance. Glycogen storage on hepatocyte-like cells and inflammatory markers associated with insulin resistance were evaluated to understand the role of gut metabolites on gut-liver cross talk in a simulated scenario of insulin resistance. The metabolites produced by our consortium increased glycogen synthesis by ~57% and decreased proinflammatory markers such as IL-8 by 12%, thus elucidating the positive effect of our consortium on metabolic function and low-grade inflammation. Our results suggest that microbiota-derived products can be a promising multipurpose strategy to modulate energy homeostasis, with the potential ability to assist in managing metabolic diseases due to their adaptability.

Current metabolic perspective on malnutrition in obesity: towards more subgroup-based nutritional approaches?

Lifestyle intervention may be effective in reducing type 2 diabetes mellitus incidence and cardiometabolic risk. A more personalised nutritional approach based on an individual or subgroup-based metabolic profile may optimise intervention outcome. Whole body insulin resistance (IR) reflects defective insulin action in tissues such as muscle, liver, adipose tissue, gut and brain, which may precede the development of cardiometabolic diseases. IR may develop in different organs but the severity may vary between organs. Individuals with more pronounced hepatic IR have a distinct plasma metabolome and lipidome profile as compared with individuals with more pronounced muscle IR. Additionally, genes related to extracellular modelling were upregulated in abdominal subcutaneous adipose tissue in individuals with more pronounced hepatic IR, whilst genes related to inflammation as well as systemic low-grade inflammation were upregulated in individuals with primarily muscle IR. There are indications that these distinct IR phenotypes may also respond differentially to dietary macronutrient composition. Besides metabolic phenotype, microbial phenotype may be of importance in personalising the response to diet. In particular fibres or fibre mixtures, leading to a high distal acetate and SCFA production may have more pronounced effects on metabolic health. Notably, individuals with prediabetes may have a reduced response to diet-induced microbiota modulation with respect to host insulin sensitivity and metabolic health outcomes. Overall, we need more research to relate metabolic subphenotypes to intervention outcomes to define more optimal diets for individuals with or predisposed to chronic metabolic diseases.

Distal colonic transit is linked to gut microbiota diversity and microbial fermentation in humans with slow colonic transit

Longer colonic transit time and hard stools are associated with increased gut microbiota diversity. Here, we investigate to what extent quantitative measures of (segmental) colonic transit time were related to gut microbiota composition, microbial metabolites, and gut-related parameters in a human cross-sectional study. Using radiopaque markers, (segmental) colonic transit time (CTT) was measured in 48 lean/overweight participants with long colonic transit but without constipation. Fecal microbiota composition was determined using 16S rRNA gene amplicon sequencing. Associations between gastrointestinal transit (segmental CTT and stool frequency and consistency), microbiota diversity and composition, microbial metabolites [short-chain fatty acids (SCFA), branched-chain fatty acids, and breath hydrogen], habitual diet, and gut-related host parameters [lipopolysaccharide-binding protein (LBP) and fecal calprotectin] were investigated using univariate and multivariate approaches. Long descending (i.e., distal) colonic transit was associated with increased microbial α-diversity but not with stool consistency. Using unweighted and weighted UniFrac distance, microbiota variation was not related to (segmental) CTT but to demographics, diet, plasma LBP, and fecal calprotectin. Bray-Curtis dissimilarity related only to stool consistency. Rectosigmoid and descending colonic transit were negatively associated with fecal SCFA and plasma acetate, respectively. This study suggests that the distal colon transit may affect not only microbiota diversity but also microbial metabolism.NEW & NOTEWORTHY We extend previous findings showing that long distal colonic transit time influences microbial diversification and fermentation, whereas stool consistency is related to microbiota composition in humans with a long colonic transit. This study puts the importance of the (distal) colonic site in microbiota ecology forward, which should be considered in future therapeutic studies targeting, for instance, short-chain fatty acid production to improve metabolic health.

Changes in gut microbiota in predigested Hibiscus sabdariffa L calyces and Agave (Agave tequilana weber) fructans assessed in a dynamic in vitro model (TIM-2) of the human colon

Hibiscus sabdariffa (Hb) calyces are a source of dietary fiber (DF) and phenolic compounds. Agave fructans (AF) and oligofructans (OF) are considered as soluble DF. The aim of the study was to investigate changes in gut microbiota upon feeding predigested Hb, AF, OF or Mix (Hb/AF) to a dynamic, validated in vitro model of the human colon (TIM-2), using sequencing of the V3-V4 regions of the 16S rRNA gene. A pooled human fecal microbiota was used. Production of short-chain fatty acids (SCFAs), branched-chain fatty acids (BSCFAs) and ammonia was also assessed. Samples were taken after 0, 24, 48 and 72 h. Principal component (PC) analysis of fermentation metabolites and relative abundance of genera was carried out, and extracted factors were based on eigenvalues >1.0 and explained >60% of variance. Fermentation of samples resulted in different SCFAS concentrations. The highest butyric acid production was on AF and OF, while the molar ratio of SCFAS on Hb was 63:18:18 for acetic, propionic and butyric acid, respectively. BSCFAS were also produced upon feeding the studied substrates, but in much lower concentrations. About 45 bacteria genera were identified and 10 of these were the most abundant changing during the fermentation time, amongst which a high relative abundance in Bifidobacterium, Bacteroides and Catenibacterium, that changed during the fermentation time depending of substrate. Hb feeding after 48 h led to Bifidobacterium being the most abundant genus. Two PCs were identified: after 24 h of fermentation PC1 was highly influenced by Bifidobacterium and Prevotella, which was related with Hb and SIEM feeding. Evaluation of the changes in metabolites and gut microbiota composition during colonic fermentation in a validated in vitro model provides a complete and reliable view of the potential prebiotic effect of different dietary fibers.

The Relationship between Circulating Acetate and Human Insulin Resistance before and after Weight Loss in the DiOGenes Study

Microbially-produced acetate has been reported to beneficially affect metabolic health through effects on satiety, energy expenditure, insulin sensitivity, and substrate utilization. Here, we investigate the association between sex-specific concentrations of acetate and insulin sensitivity/resistance indices (Homeostatic Model Assessment of Insulin Resistance (HOMA-IR), circulating insulin and Matsuda Index) in the Diet, Obesity and Genes (DiOGenes) Dietary study at baseline and after a low-calorie diet (LCD, 800 kcal/d). In this analysis, 692 subjects (Body Mass Index >27 kg/m²) were included, who underwent an LCD for 8 weeks. Linear mixed models were performed, which were adjusted for mean acetate concentration, center (random factor), age, weight loss, and fat-free mass (FFM). At baseline, no associations between plasma acetate and insulin sensitivity/resistance indices were found. We found a slight positive association between changes in acetate and changes in HOMA-IR (std 0.130, p = 0.033) in women, but not in men (std -0.072, p = 0.310) independently of age, weight loss and FFM. We were not able to confirm previously reported associations between acetate and insulin sensitivity in this large European cohort. The mechanisms behind the sex-specific relationship between LCD-induced changes in acetate and insulin sensitivity require further study.

Gut butyrate-producing organisms correlate to Placenta Specific 8 protein: Importance to colorectal cancer progression

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Genes from stools have molecular significance with CRC tumorgenesis.

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SCFAs, the metabolites of microbiota, can suppress CRC tumorigenesis.

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Relationship between colonic genes, gut microbiota, or their metabolites is significant.

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Changes of PLAC8 and butyrate-producing organisms were found in stools of CRC patients.

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Butyrate can reduce the CRC formation through regulating PLAC8 expression.

Tumor metastasis or recurrence often occurs in patients with curative resection of colorectal cancer (CRC). Placental-specific 8 (PLAC8), which has increased expression in stool, may be associated with CRC recurrence. Insights into the role of PLAC8 in CRC recurrence and its clinical significance may support to develop strategies for preventing CRC recurrence and deterioration. Clinical tissues, cell and animal models were used to clarify the roles of PLAC8 in CRC tumorigenesis, invasion, and migration. Next-generation sequencing of 16S ribosomal DNA has been used to assess the gut microbiota in stool of CRC patients. We found that PLAC8 was upregulated in tissues from patients with late-stage CRC. In our in vitro studies, PLAC8 was dynamically regulated in mitotic cells. Overexpressed PLAC8 was nucleated at the centrosome during mitosis, and therefore, PLAC8 overexpression might increase cell growth and migration (all p < 0.05). The tumorigenic and invasive effects of PLAC8 on CRC cells were also confirmed in a xenograft mouse model. We further identified reduced levels of two butyrate-producing organisms, Butyricicoccus and Prevotella spp., in stools from CRC patients. We found that butyrate downregulated PLAC8 expression and induced apoptosis in PLAC8-overexpressing cells. Our data suggests that PLAC8 gene and protein expression and dysbiosis of gut microflora, especially in butyrate-producing microorganisms, may be indicators of CRC progression.

Abundance of Probiotics and Butyrate-Production Microbiome Manages Constipation via Short-Chain Fatty Acids Production and Hormones Secretion

SCOPE

The characteristics of gut microbiota and host metabolism are hypothesized to be associated with constipation status, but the regulation mechanism is not fully understood. Thus, the current study investigates the effect of constipation symptoms on gut functionality following the modulation of gut microbiota and metabolites via dietary fiber intervention.

METHODS AND RESULTS

Constipation causes a significantly reduced short-chain fatty acids (SCFAs) production and a higher level of iso-butyrate. The feces of constipated people are characterized with inhibited Faecalibacterium, Ruminococcaceae and Roseburia abundance. Desulfovibrionaceae is identified to be an important endotoxin producer in constipated patients, and a butyrate-enriched SCFAs profile achieved by dietary fiber supplement accelerates gastrointestinal transit and increases the thickness of the mucosal layer, possibly through triggering the secretion of colonic hormones and enhancing the expression of tight junction proteins for maintaining intestinal barrier integrity. More importantly, an interacting regulatory mechanism among SCFAs, in particular butyrate and propionate, may be involved in signaling between the microbiome and host cells in the colon.

CONCLUSION

Gut microbiota, characterized with enriched butyrate-producing and depressed Desulfovibrionaceae bacteria, attenuates constipation symptoms through promoting intestinal hormones secretion and maintaining gut barrier integrity.

A high-sugar diet rapidly enhances susceptibility to colitis via depletion of luminal short-chain fatty acids in mice

Western-style diets have been implicated in triggering inflammatory bowel disease activity. The aim of this study was to identify the effect of a short-term diet high in sugar on susceptibility to colitis. Adult wild-type mice were placed on chow or a high sugar diet (50% sucrose) ± acetate. After two days of diet, mice were treated with dextran sodium sulfate (DSS) to induce colitis. Disease severity was assessed daily. Colonic tissues were analyzed for cytokine expression using the MesoScale discovery platform. Intestinal dextran permeability and serum lipopolysaccharide levels (LPS) were measured. Gut microbiota were analyzed by 16s rRNA sequencing and short chain fatty acid (SCFA) concentrations by gas chromatography. Bone marrow-derived macrophages (BMDM) were incubated with LPS and cytokine secretion measured. Mice on a high sugar diet had increased gut permeability, decreased microbial diversity and reduced SCFA. BMDM derived from high sugar fed mice were highly responsive to LPS. High sugar fed mice had increased susceptibility to colitis and pro-inflammatory cytokine concentrations. Oral acetate significantly attenuated colitis in mice by restoring permeability. In conclusion, short term exposure to a high sugar diet increases susceptibility to colitis by reducing short-chain fatty acids and increasing gut permeability.

The Short-Chain Fatty Acid Acetate in Body Weight Control and Insulin Sensitivity

The interplay of gut microbiota, host metabolism, and metabolic health has gained increased attention. Gut microbiota may play a regulatory role in gastrointestinal health, substrate metabolism, and peripheral tissues including adipose tissue, skeletal muscle, liver, and pancreas via its metabolites short-chain fatty acids (SCFA). Animal and human data demonstrated that, in particular, acetate beneficially affects host energy and substrate metabolism via secretion of the gut hormones like glucagon-like peptide-1 and peptide YY, which, thereby, affects appetite, via a reduction in whole-body lipolysis, systemic pro-inflammatory cytokine levels, and via an increase in energy expenditure and fat oxidation. Thus, potential therapies to increase gut microbial fermentation and acetate production have been under vigorous scientific scrutiny. In this review, the relevance of the colonically and systemically most abundant SCFA acetate and its effects on the previously mentioned tissues will be discussed in relation to body weight control and glucose homeostasis. We discuss in detail the differential effects of oral acetate administration (vinegar intake), colonic acetate infusions, acetogenic fiber, and acetogenic probiotic administrations as approaches to combat obesity and comorbidities. Notably, human data are scarce, which highlights the necessity for further human research to investigate acetate’s role in host physiology, metabolic, and cardiovascular health.

Regulation of energy expenditure and substrate oxidation by short-chain fatty acids

Short-chain fatty acids (SCFAs) are metabolites produced from the fermentation of dietary fibre by the gut microbiota. High-fibre diets have been associated with lower weight gain and a number of reports have therefore investigated if these positive effects of a dietary fibre on body weight can be replicated through the direct administration of SCFAs. Many of these studies have reported that SCFAs can prevent or attenuate long-term body weight gain by increasing energy expenditure through increased lipid oxidation. The aim of the present review is to therefore evaluate the current evidence for an effect of SCFAs on whole-body energy expenditure and to assess the potential underlying mechanisms. The available data highlights that SCFAs can exert multiple effects at various organ and tissue sites that would cumulatively raise energy expenditure via a promotion of lipid oxidation. In conclusion, the present review proposes that dietary interventions and other therapies that augment gut-derived SCFAs and systemic availability may present an effective strategy to improve long-term energy balance and body weight management.

Diet in the Pathogenesis and Management of Ulcerative Colitis; A Review of Randomized Controlled Dietary Interventions

Epidemiological and experimental studies have suggested that diet is one of the environmental factors that contributes to the onset and pathophysiology of ulcerative colitis. Although many patients suffering from ulcerative colitis attribute their symptoms or disease relapse to dietary factors, only a few well-designed randomized controlled trials have been done to investigate the role of diet in the management of ulcerative colitis. Here, we review the potential mechanisms of the relationship between diet and pathogenesis of ulcerative colitis and summarize randomized controlled dietary interventions that have been conducted in ulcerative colitis patients.

Gut microbial metabolites in obesity, NAFLD and T2DM

Evidence is accumulating that the gut microbiome is involved in the aetiology of obesity and obesity-related complications such as nonalcoholic fatty liver disease (NAFLD), insulin resistance and type 2 diabetes mellitus (T2DM). The gut microbiota is able to ferment indigestible carbohydrates (for example, dietary fibre), thereby yielding important metabolites such as short-chain fatty acids and succinate. Numerous animal studies and a handful of human studies suggest a beneficial role of these metabolites in the prevention and treatment of obesity and its comorbidities. Interestingly, the more distal colonic microbiota primarily ferments peptides and proteins, as availability of fermentable fibre, the major energy source for the microbiota, is limited here. This proteolytic fermentation yields mainly harmful products such as ammonia, phenols and branched-chain fatty acids, which might be detrimental for host gut and metabolic health. Therefore, a switch from proteolytic to saccharolytic fermentation could be of major interest for the prevention and/or treatment of metabolic diseases. This Review focuses on the role of products derived from microbial carbohydrate and protein fermentation in relation to obesity and obesity-associated insulin resistance, T2DM and NAFLD, and discusses the mechanisms involved.

Effects of Inulin Propionate Ester Incorporated into Palatable Food Products on Appetite and Resting Energy Expenditure: A Randomised Crossover Study

Supplementation with inulin-propionate ester (IPE), which delivers propionate to the colon, suppresses ad libitum energy intake and stimulates the release of satiety hormones acutely in humans, and prevents weight gain. In order to determine whether IPE remains effective when incorporated into food products (FP), IPE needs to be added to a widely accepted food system. A bread roll and fruit smoothie were produced. Twenty-one healthy overweight and obese humans participated. Participants attended an acclimatisation visit and a control visit where they consumed un-supplemented food products (FP). Participants then consumed supplemented-FP, containing 10 g/d inulin or IPE for six days followed by a post-supplementation visit in a randomised crossover design. On study visits, supplemented-FP were consumed for the seventh time and ad libitum energy intake was assessed 420 min later. Blood samples were collected to assess hormones and metabolites. Resting energy expenditure (REE) was measured using indirect calorimetry. Taste and appearance ratings were similar between FP. Ad libitum energy intake was significantly different between treatments, due to a decreased intake following IPE-FP. These observations were not related to changes in blood hormones and metabolites. There was an increase in REE following IPE-FP. However, this effect was lost after correcting for changes in fat free mass. Our results suggest that IPE suppresses appetite and may alter REE following its incorporation into palatable food products.

Microbial regulation of organismal energy homeostasis

The gut microbiome has emerged as a key regulator of host metabolism. Here we review the various mechanisms through which the gut microbiome influences the energy metabolism of its host, highlighting the complex interactions between gut microbes, their metabolites and host cells. Among the most important bacterial metabolites are short-chain fatty acids, which serve as a direct energy source for host cells, stimulate the production of gut hormones and act in the brain to regulate food intake. Other microbial metabolites affect systemic energy expenditure by influencing thermogenesis and adipose tissue browning. Both direct and indirect mechanisms of action are known for specific metabolites, such as bile acids, branched chain amino acids, indole propionic acid and endocannabinoids. We also discuss the roles of specific bacteria in the production of specific metabolites and explore how external factors, such as antibiotics and exercise, affect the microbiome and thereby energy homeostasis. Collectively, we present a large body of evidence supporting the concept that gut microbiota-based therapies can be used to modulate host metabolism, and we expect to see such approaches moving from bench to bedside in the near future.