Fructose malabsorption induces cholecystokinin expression in the ileum and cecum by changing microbiota composition and metabolism

The alteration of fecal microbial and metabolic profile of gallstone patients in Taiwan: Single-center study

BACKGROUND

Gallstone disease is a common health problem worldwide. The role of the gut microbiota in gallstone pathogenesis remains obscure. Our aim was to evaluate the association and crosstalk between gut microbiota, gut metabolomic, and metabolic parameters in cholesterol gallstone patients, pigmented gallstone patients, and controls.

METHODS

We collected stool samples from healthy individuals and patients with gallstones in our hospital from March 2019 to February 2021. 16s rRNA sequencing was performed, followed by differential abundance analyses. Measurement of bile acids and short-chain fatty acids was conducted via targeted metabolomics.

RESULT

Thirty healthy individuals and 20 gallstone patients were recruited. The intergroup difference of microbial composition was significant between control and gallstone patients. The control group had more abundant Faecalibacterium , Prevotella 9 , and Bacteroides plebeius DSM 17135 . The cholesterol stones group had higher Desulfovibrionaceae and Bacteroides uniformis than the other two groups, while the pigment stone group had more abundant Escherichia-Shigella . In the analysis of metabolites, only n-butyric acid had a significantly higher concentration in the controls than in the gallstone group ( p < 0.01). The level of 3α-hydroxy-12 ketolithocholic acid, deoxycholic acid, and cholic acid showed no intergroup differences but was correlated to the serum cholesterol level and bacterial richness and evenness.

CONCLUSION

Our study revealed the key taxa that can discriminate between individuals with or without gallstones. We also identified metabolites that are possibly associated with metabolic parameter and bacterial diversity. However, the correlation of the metabolites to certain clusters of bacteria should be analyzed in a larger cohort.

Cholecystokinin (CCK): a neuromodulator with therapeutic potential in Alzheimer's and Parkinson's disease

Cholecystokinin (CCK) is a neuropeptide modulating digestion, glucose levels, neurotransmitters and memory. Recent studies suggest that CCK exhibits neuroprotective effects in Alzheimer's disease (AD) and Parkinson's disease (PD). Thus, we review the physiological function and therapeutic potential of CCK. The neuropeptide facilitates hippocampal glutamate release and gates GABAergic basket cell activity, which improves declarative memory acquisition, but inhibits consolidation. Cortical CCK alters recognition memory and enhances audio-visual processing. By stimulating CCK-1 receptors (CCK-1Rs), sulphated CCK-8 elicits dopamine release in the substantia nigra and striatum. In the mesolimbic pathway, CCK release is triggered by dopamine and terminates reward responses via CCK-2Rs. Importantly, activation of hippocampal and nigral CCK-2Rs is neuroprotective by evoking AMPK activation, expression of mitochondrial fusion modulators and autophagy. Other benefits include vagus nerve/CCK-1R-mediated expression of brain-derived neurotrophic factor, intestinal protection and suppression of inflammation. We also discuss caveats and the therapeutic combination of CCK with other peptide hormones.

Assessment of dietary interventions including low fermentable oligosaccharides, disaccharides, monosaccharides, and polyols diet as management for fructose intolerance

OBJECTIVES

Abdominal pain remains one of the most common referral reasons to pediatric gastroenterology. Dietary intolerances are often considered but due to various factors are hardly pursued. We observed that diet review in large number of children with abdominal pain was high in sugary foods which led to food intolerance investigation and dietary intervention.

METHODS

A retrospective review was conducted of patients presenting with abdominal pain, diarrhea, or vomiting and negative GI evaluation, who underwent fructose breath testing. Patients younger than 20 years old who were seen between June 1, 2018 and March 1, 2021 were included. Statistical analysis was performed in R.

RESULTS

There were 110 pediatric patients during the study period who underwent fructose breath testing, with 31% male and 69% female. The average age was 12.14 ± 4.01 years, and the average BMI was 21.21 ± 6.12. Abdominal pain was the most common presenting symptom (74.5%) followed by diarrhea and vomiting. Seventy-seven patients (70%) had a positive fructose breath test and were diagnosed with dietary intolerance to fructose. The 56 (67.5%) of those patients experienced symptoms during the breath test. Forty-three patients improved with dietary intervention. Twenty-seven on low fermentable oligosaccharides, disaccharides, monosaccharides, and polyols diet and 16 on other diets.

CONCLUSIONS

Based on analysis of our cohort of children with abdominal pain and high incidence of fructose intolerance as well as improvement in symptoms, following dietary changes, this condition should be considered and treated. Further investigation is needed to improve diagnostic testing but also into understanding mechanisms behind symptom presentation in this population.

Satiety: a gut-brain-relationship

Many hormones act on the hypothalamus to control hunger and satiety through various pathways closely associated with several factors. When food is present in the gastro intestinal (GI) tract, enteroendocrine cells (EECs) emit satiety signals such as cholecystokinin (CCK), glucagon like peptide-1 (GLP-1) and peptide YY (PYY), which can then communicate with the vagus nerve to control food intake. More specifically, satiety has been shown to be particularly affected by the GLP-1 hormone and its receptor agonists that have lately been acknowledged as a promising way to reduce weight. In addition, there is increasing evidence that normal flora is also involved in the peripheral, central, and reward system that impact satiety. Moreover, neurologic pathways control satiety through neurotransmitters. In this review, we discuss the different roles of each of the GLP-1 hormone and its agonist, gut microbiomes, as well as neurotransmitters and their interconnected relation in the regulation of body's satiety homeostasis.

40 years of adding more fructose to high fructose corn syrup than is safe, through the lens of malabsorption and altered gut health-gateways to chronic disease

Labels do not disclose the excess-free-fructose/unpaired-fructose content in foods/beverages. Objective was to estimate excess-free-fructose intake using USDA loss-adjusted-food-availability (LAFA) data (1970-2019) for high fructose corn syrup (HFCS) and apple juice, major sources of excess-free-fructose, for comparison with malabsorption dosages (~ 5 g-children/ ~ 10 g-adults). Unlike sucrose and equimolar fructose/glucose, unpaired-fructose triggers fructose malabsorption and its health consequences. Daily intakes were calculated for HFCS that is generally-recognized-as-safe/ (55% fructose/45% glucose), and variants (65/35, 60/40) with higher fructose-to-glucose ratios (1.9:1, 1.5:1), as measured by independent laboratories. Estimations include consumer-level-loss (CLL) allowances used before (20%), and after, subjective, retroactively-applied increases (34%), as recommended by corn-refiners (~ 2012). No contributions from crystalline-fructose or agave syrup were included due to lack of LAFA data. High-excess-free-fructose-fruits (apples/pears/watermelons/mangoes) were not included. Eaten in moderation they are less likely to trigger malabsorption. Another objective was to identify potential parallel trends between excess-free-fructose intake and the "unexplained" US asthma epidemic. The fructose/gut-dysbiosis/lung axis is well documented, case-study evidence and epidemiological research link HFCS/apple juice intake with asthma, and unlike gut-dysbiosis/gut-fructosylation, childhood asthma prevalence data spans > 40 years. Results Excess-free-fructose daily intake for individuals consuming HFCS with an average 1.5:1 fructose-to-glucose ratio, ranged from 0.10 g/d in 1970, to 11.3 g/d in 1999, to 6.5 g/d in 2019, and for those consuming HFCS with an average 1.9:1 ratio, intakes ranged from 0.13 g/d to 16.9 g/d (1999), to 9.7 g/d in 2019, based upon estimates with a 20% CLL allowance. Intake exceeded dosages that trigger malabsorption (~ 5 g) around ~ 1980. By the early 1980's, tripled apple juice intake had added ~ 0.5 g to average-per-capita excess-free-fructose intake. Contributions were higher (~ 3.8 g /4-oz.) for individuals consuming apple juice consistent with a healthy eating pattern (4-oz. children, 8-oz. adults). The "unexplained" childhood asthma epidemic (1980-present) parallels increasing average-per-capita HFCS/apple juice intake trends and reflects epidemiological research findings. Conclusion Displacement of sucrose with HFCS, its ubiquitous presence in the US food-supply, the industry practice of adding more fructose to HFCS than generally-recognized-as-safe, and increased use of apple juice/crystalline fructose/agave syrup in foods/beverages has contributed to unprecedented excess-free-fructose intake levels, fructose malabsorption, gut-dysbiosis and gut-fructosylation (immunogen burden)-gateways to chronic disease.

Adlercreutzia equolifaciens Is an Anti-Inflammatory Commensal Bacterium with Decreased Abundance in Gut Microbiota of Patients with Metabolic Liver Disease

Non-alcoholic fatty liver disease (NAFLD) affects about 20-40% of the adult population in high-income countries and is now a leading indication for liver transplantation and can lead to hepatocellular carcinoma. The link between gut microbiota dysbiosis and NAFLD is now clearly established. Through analyses of the gut microbiota with shotgun metagenomics, we observe that compared to healthy controls, Adlercreutzia equolifaciens is depleted in patients with liver diseases such as NAFLD. Its abundance also decreases as the disease progresses and eventually disappears in the last stages indicating a strong association with disease severity. Moreover, we show that A. equolifaciens possesses anti-inflammatory properties, both in vitro and in vivo in a humanized mouse model of NAFLD. Therefore, our results demonstrate a link between NAFLD and the severity of liver disease and the presence of A. equolifaciens and its anti-inflammatory actions. Counterbalancing dysbiosis with this bacterium may be a promising live biotherapeutic strategy for liver diseases.

Hepatic but not Intestinal FBP1 Is Required for Fructose Metabolism and Tolerance

Fructose intolerance in mammals is caused by defects in fructose absorption and metabolism. Fructose-1,6-bisphosphatase 1 (FBP1) is a key enzyme in gluconeogenesis, and its deficiency results in hypoglycemia as well as intolerance to fructose. However, the mechanism about fructose intolerance caused by FBP1 deficiency has not been fully elucidated. Here, we demonstrate that hepatic but not intestinal FBP1 is required for fructose metabolism and tolerance. We generated inducible knockout mouse models specifically lacking FBP1 in adult intestine or liver. Intestine-specific deletion of Fbp1 in adult mice does not compromise fructose tolerance, as evidenced by no significant body weight loss, food intake reduction, or morphological changes of the small intestine during 4 weeks of exposure to a high-fructose diet. By contrast, liver-specific deletion of Fbp1 in adult mice leads to fructose intolerance, as manifested by substantial weight loss, hepatomegaly, and liver injury after exposure to a high-fructose diet. Notably, the fructose metabolite fructose-1-phosphate is accumulated in FBP1-deficient liver after fructose challenge, which indicates a defect of fructolysis, probably due to competitive inhibition by fructose-1,6-bisphosphate and may account for the fructose intolerance. In conclusion, these data have clarified the essential role of hepatic but not intestinal FBP1 in fructose metabolism and tolerance.

Integration of Liver Glycogen and Triglyceride NMR Isotopomer Analyses Provides a Comprehensive Coverage of Hepatic Glucose and Fructose Metabolism

Dietary glucose and fructose are both efficiently assimilated by the liver but a comprehensive measurement of this process starting from their conversion to sugar phosphates, involvement of the pentose phosphate pathway (PPP), and conversion to glycogen and lipid storage products, remains incomplete. Mice were fed a chow diet supplemented with 35 g/100 mL drinking water of a 55/45 fructose/glucose mixture for 18 weeks. On the final night, the sugar mixture was enriched with either [U-13C]glucose or [U-13C]fructose, and deuterated water (2H2O) was also administered. 13C-isotopomers representing newly synthesized hepatic glucose-6-phosphate (glucose-6-P), glycerol-3-phosphate, and lipogenic acetyl-CoA were quantified by 2H and 13C NMR analysis of post-mortem liver glycogen and triglyceride. These data were applied to a metabolic model covering glucose-6-P, PPP, triose-P, and de novo lipogenesis (DNL) fluxes. The glucose supplement was converted to glucose-6-P via the direct pathway, while the fructose supplement was metabolized by the liver to gluconeogenic triose-P via fructokinase-aldolase-triokinase. Glucose-6-P from all carbohydrate sources accounted for 40-60% of lipogenic acetyl-CoA and 10-12% was oxidized by the pentose phosphate pathway (PPP). The yield of NADPH from PPP flux accounted for a minority (~30%) of the total DNL requirement. In conclusion, this approach integrates measurements of glucose-6-P, PPP, and DNL fluxes to provide a holistic and informative assessment of hepatic glucose and fructose metabolism.

Molecular cloning of cholecystokinin (CCK) and CCK-A receptor and mechanism of CCK-induced gastrointestinal motility in Suncus murinus

Cholecystokinin (CCK) is a peptide hormone mainly secreted by small intestinal endocrine I-cells and functions as a regulator of gallbladder contraction, gastric emptying, gastrointestinal (GI) motility, and satiety. The cellular effects of CCK in these peripheral tissues are predominantly mediated via CCK-A receptors which are found in smooth muscles, enteric neurons, and vagal afferent neurons in humans and animal models. Although various functions of CCK have been reported to be neurally mediated, it can also stimulate contraction via the CCK receptor on the smooth muscle. However, the entire underlying neural and cellular mechanisms involved in CCK-induced GI contractions are not clearly understood. Here, we first determined the cDNA and amino acid sequences of CCK and CCK-A receptor along with the distributions of cck mRNA and CCK-producing cells in house musk shrew (Suncus murinus, the laboratory strain named as suncus) and examined the mechanism of CCK-induced contraction in the GI tract. Mature suncus CCK-8 was identical to other mammalian species tested here, and suncus CCK-A receptor presented high nucleotide and amino acid homology with that of human, dog, mouse, and rat, respectively. Suncus CCK mRNA and CCK-producing cells were found mainly in small intestine and colon. In the organ bath study, CCK-8 induced dose-dependent contractions in the suncus stomach, duodenum, and jejunum, and these contractions were inhibited by atropine and CCK-A receptor antagonist. These results suggest that CCK-8-induced contraction is mediated in the myenteric cholinergic neural network and that CCK-A receptor is partly responsible for CCK-8-induced contractions. This study indicates that suncus is a useful animal model to study the functions of CCK involved in GI motility.

Are the Effects of Malnutrition on the Gut Microbiota–Brain Axis the Core Pathologies of Anorexia Nervosa?

Anorexia nervosa (AN) is a disabling, costly, and potentially deadly illness. Treatment failure and relapse after treatment are common. Several studies have indicated the involvement of the gut microbiota–brain (GMB) axis. This narrative review hypothesizes that AN is driven by malnutrition-induced alterations in the GMB axis in susceptible individuals. According to this hypothesis, initial weight loss can voluntarily occur through dieting or be caused by somatic or psychiatric diseases. Malnutrition-induced alterations in gut microbiota may increase the sensitivity to anxiety-inducing gastrointestinal hormones released during meals, one of which is cholecystokinin (CCK). The experimental injection of a high dose of its CCK-4 fragment in healthy individuals induces panic attacks, probably via the stimulation of CCK receptors in the brain. Such meal-related anxiety attacks may take part in developing the clinical picture of AN. Malnutrition may also cause increased effects from appetite-reducing hormones that also seem to have roles in AN development and maintenance. The scientific background, including clinical, microbiological, and biochemical factors, of AN is discussed. A novel model for AN development and maintenance in accordance with this hypothesis is presented. Suggestions for future research are also provided.

The Role of Selenoprotein Tissue Homeostasis in MetS Programming: Energy Balance and Cardiometabolic Implications

Selenium (Se) is an essential trace element mainly known for its antioxidant, anti-inflammatory, and anti-apoptotic properties, as it is part of the catalytic center of 25 different selenoproteins. Some of them are related to insulin resistance (IR) and metabolic syndrome (MetS) generation, modulating reactive oxygen species (ROS), and the energetic sensor AMP-activated protein kinase (AMPK); they can also regulate the nuclear transcription factor kappa-B (NF-kB), leading to changes in inflammation production. Selenoproteins are also necessary for the correct synthesis of insulin and thyroid hormones. They are also involved in endocrine central regulation of appetite and energy homeostasis, affecting growth and development. MetS, a complex metabolic disorder, can appear during gestation and lactation in mothers, leading to energetic and metabolic changes in their offspring that, according to the metabolic programming theory, will produce cardiovascular and metabolic diseases later in life. However, there is a gap concerning Se tissue levels and selenoproteins’ implications in MetS generation, which is even greater during MetS programming. This narrative review also provides an overview of the existing evidence, based on experimental research from our laboratory, which strengthens the fact that maternal MetS leads to changes in Se tissue deposits and antioxidant selenoproteins’ expression in their offspring. These changes contribute to alterations in tissues’ oxidative damage, inflammation, energy balance, and tissue function, mainly in the heart. Se imbalance also could modulate appetite and endocrine energy balance, affecting pups’ growth and development. MetS pups present a profile similar to that of diabetes type 1, which also appeared when dams were exposed to low-Se dietary supply. Maternal Se supplementation should be taken into account if, during gestation and/or lactation periods, there are suspicions of endocrine energy imbalance in the offspring, such as MetS. It could be an interesting therapy to induce heart reprogramming. However, more studies are necessary.

Glucose but Not Fructose Alters the Intestinal Paracellular Permeability in Association With Gut Inflammation and Dysbiosis in Mice

A causal correlation between the metabolic disorders associated with sugar intake and disruption of the gastrointestinal (GI) homeostasis has been suggested, but the underlying mechanisms remain unclear. To unravel these mechanisms, we investigated the effect of physiological amounts of fructose and glucose on barrier functions and inflammatory status in various regions of the GI tract and on the cecal microbiota composition. C57BL/6 mice were fed chow diet and given 15% glucose or 15% fructose in drinking water for 9 weeks. We monitored caloric intake, body weight, glucose intolerance, and adiposity. The intestinal paracellular permeability, cytokine, and tight junction protein expression were assessed in the jejunum, cecum, and colon. In the cecum, the microbiota composition was determined. Glucose-fed mice developed a marked increase in total adiposity, glucose intolerance, and paracellular permeability in the jejunum and cecum while fructose absorption did not affect any of these parameters. Fructose-fed mice displayed increased circulation levels of IL6. In the cecum, both glucose and fructose intake were associated with an increase in Il13, Ifnγ, and Tnfα mRNA and MLCK protein levels. To clarify the relationships between monosaccharides and barrier function, we measured the permeability of Caco-2 cell monolayers in response to IFNγ+TNFα in the presence of glucose or fructose. In vitro, IFNγ+TNFα-induced intestinal permeability increase was less pronounced in response to fructose than glucose. Mice treated with glucose showed an enrichment of Lachnospiracae and Desulfovibrionaceae while the fructose increased relative abundance of Lactobacillaceae. Correlations between pro-inflammatory cytokine gene expression and bacterial abundance highlighted the potential role of members of Desulfovibrio and Lachnospiraceae NK4A136 group genera in the inflammation observed in response to glucose intake. The increase in intestinal inflammation and circulating levels of IL6 in response to fructose was observed in the absence of intestinal permeability modification, suggesting that the intestinal permeability alteration does not precede the onset of metabolic outcome (low-grade inflammation, hyperglycemia) associated with chronic fructose consumption. The data also highlight the deleterious effects of glucose on gut barrier function along the GI tract and suggest that Desulfovibrionaceae and Lachnospiraceae play a key role in the onset of GI inflammation in response to glucose.

Fructose intolerance is not associated with malabsorption in patients with functional gastrointestinal disorders

BACKGROUND

Symptoms following fructose ingestion, or fructose intolerance, are common in patients with functional gastrointestinal disorders (FGID) and are generally attributed to intestinal malabsorption. The relationships between absorption, symptoms, and intestinal gas production following fructose ingestion were studied in patients with FGID.

METHODS

Thirty FGID patients ingested a single dose of fructose 35 g or water in a randomized, double-blind, crossover study. Blood and breath gas samples were collected, and gastrointestinal symptoms rated. Plasma fructose metabolites and short-chain fatty acids were quantified by targeted liquid chromatography-tandem mass spectrometry. Patients were classified as fructose intolerant or tolerant based on symptoms following fructose ingestion.

KEY RESULTS

The median (IQR) areas under the curve of fructose plasma concentrations within the first 2 h (AUC_0-2 h ) after fructose ingestion were similar for patients with and without fructose intolerance (578 (70) µM·h vs. 564 (240) µM·h, respectively, p = 0.39), as well as for the main fructose metabolites. There were no statistically significant correlations between the AUC_0-2 h of fructose or its metabolites concentrations and the AUCs of symptoms, breath hydrogen, and breath methane. However, the AUCs of symptoms correlated significantly and positively with the AUC_0-2 h of hydrogen and methane breath concentrations (r = 0.73, r = 0.62, respectively), and the AUCs of hydrogen and methane concentrations were greater in the fructose-intolerant than in the fructose-tolerant patients after fructose ingestion (p ≤ 0.02).

CONCLUSIONS & INFERENCES

Fructose intolerance in FGID is not related to post-ingestion plasma concentrations of fructose and its metabolites. Factors other than malabsorption, such as altered gut microbiota or sensory function, may be important mechanisms.

Microbiota's Role in Diet-Driven Alterations in Food Intake: Satiety, Energy Balance, and Reward

The gut microbiota plays a key role in modulating host physiology and behavior, particularly feeding behavior and energy homeostasis. There is accumulating evidence demonstrating a role for gut microbiota in the etiology of obesity. In human and rodent studies, obesity and high-energy feeding are most consistently found to be associated with decreased bacterial diversity, changes in main phyla relative abundances and increased presence of pro-inflammatory products. Diet-associated alterations in microbiome composition are linked with weight gain, adiposity, and changes in ingestive behavior. There are multiple pathways through which the microbiome influences food intake. This review discusses these pathways, including peripheral mechanisms such as the regulation of gut satiety peptide release and alterations in leptin and cholecystokinin signaling along the vagus nerve, as well as central mechanisms, such as the modulation of hypothalamic neuroinflammation and alterations in reward signaling. Most research currently focuses on determining the role of the microbiome in the development of obesity and using microbiome manipulation to prevent diet-induced increase in food intake. More studies are necessary to determine whether microbiome manipulation after prolonged energy-dense diet exposure and obesity can reduce intake and promote meaningful weight loss.

Vaccarin enhances intestinal barrier function in type 2 diabetic mice

AIMS

Hyperglycemia and insulin resistance drive intestinal barrier dysfunction in type 2 diabetes (T2DM). Vaccarin, the main active component in the semen of traditional Chinese medicine Vaccaria has a definite effect on T2DM mice. The purpose of this study was to investigate whether vaccarin can enhance the intestinal barrier function in T2DM.

MAIN METHODS

The T2DM mice model was established by streptozocin and high-fat diet. Vaccarin at a dose of 1 mg/kg/day was administered. We evaluated the effects of vaccarin on gut microbiota and intestinal barrier function by 16S rRNA sequencing, Western blot, quantitative fluorescent PCR (qPCR), and morphological observation. Moreover, we constructed a single layer of the human intestinal epithelium model to determine the effect of vaccarin in vitro.

RESULTS

The experimental results showed that vaccarin alleviated inflammatory mediators in serum and intestinal tissue of mice (P < 0.05), which may depend on the improvement of tight junctions and gut microbiota (P < 0.05). Activation of extracellular regulated protein kinases (Erk1/2) stimulated myosin light chain kinase (MLCK). By inhibiting ERK expression (P < 0.05), vaccarin had similar effects to ERK inhibitors. In addition, the regulation of tight junction barriers also involved the abovementioned pathways in vivo.

CONCLUSION

Vaccarin could protect the intestinal barrier by inhibiting the ERK/MLCK signaling pathway and modulate the composition of the microbiota. These results suggested that vaccarin may be an effective candidate for improving intestinal barrier changes in T2DM.

Cancer-fighting potentials of algal polysaccharides as nutraceuticals

Cancer has been listed as one of the world's five incurable diseases by the World Health Organization and causes tens of thousands of deaths every year. Unfortunately, anticancer agents either show limited efficacy or show serious side effects. The algae possess high nutritional value and their polysaccharides have a variety of biological activities, especially anti-cancer and immunomodulatory properties. Algal polysaccharides exert anti-cancer effects by inducing apoptosis, cell cycle arrest, anti-angiogenesis, and regulating intestinal flora and immune function. Algal polysaccharides can be combined with nanoparticles and other drugs to reduce the side effects caused by chemotherapy and increase the anticancer effects. This review shows the signal pathways related to the anti-cancer mechanisms of algal polysaccharides, including their influence on intestinal flora and immune regulation, the application of nanoparticles, and the effects on combination therapy and clinical trials of cancer treatments.

The pregnane X receptor drives sexually dimorphic hepatic changes in lipid and xenobiotic metabolism in response to gut microbiota in mice

BACKGROUND

The gut microbiota-intestine-liver relationship is emerging as an important factor in multiple hepatic pathologies, but the hepatic sensors and effectors of microbial signals are not well defined.

RESULTS

By comparing publicly available liver transcriptomics data from conventional vs. germ-free mice, we identified pregnane X receptor (PXR, NR1I2) transcriptional activity as strongly affected by the absence of gut microbes. Microbiota depletion using antibiotics in Pxr^+/+ vs Pxr^-/- C57BL/6J littermate mice followed by hepatic transcriptomics revealed that most microbiota-sensitive genes were PXR-dependent in the liver in males, but not in females. Pathway enrichment analysis suggested that microbiota-PXR interaction controlled fatty acid and xenobiotic metabolism. We confirmed that antibiotic treatment reduced liver triglyceride content and hampered xenobiotic metabolism in the liver from Pxr^+/+ but not Pxr^-/- male mice.

CONCLUSIONS

These findings identify PXR as a hepatic effector of microbiota-derived signals that regulate the host's sexually dimorphic lipid and xenobiotic metabolisms in the liver. Thus, our results reveal a potential new mechanism for unexpected drug-drug or food-drug interactions. Video abstract.

The critical role of CCK in the regulation of food intake and diet-induced obesity

In 1973, Gibbs, Young, and Smith showed that exogenous cholecystokinin (CCK) administration reduces food intake in rats. This initial report has led to thousands of studies investigating the physiological role of CCK in regulating feeding behavior. CCK is released from enteroendocrine I cells present along the gastrointestinal (GI) tract. CCK binding to its receptor CCK1R leads to vagal afferent activation providing post-ingestive feedback to the hindbrain. Vagal afferent neurons' (VAN) sensitivity to CCK is modulated by energy status while CCK signaling regulates gene expression of other feeding related signals and receptors expressed by VAN. In addition to its satiation effects, CCK acts all along the GI tract to optimize digestion and nutrient absorption. Diet-induced obesity (DIO) is characterized by reduced sensitivity to CCK and every part of the CCK system is negatively affected by chronic intake of energy-dense foods. EEC have recently been shown to adapt to diet, CCK1R is affected by dietary fats consumption, and the VAN phenotypic flexibility is lost in DIO. Altered endocannabinoid tone, changes in gut microbiota composition, and chronic inflammation are currently being explored as potential mechanisms for diet driven loss in CCK signaling. This review discusses our current understanding of how CCK controls food intake in conditions of leanness and how control is lost in chronic energy excess and obesity, potentially perpetuating excessive intake.

Dietary switch to Western diet induces hypothalamic adaptation associated with gut microbiota dysbiosis in rats

BACKGROUND

Early hyperphagia and hypothalamic inflammation encountered after Western diet (WD) are linked to rodent propensity to obesity. Inflammation in several brain structures has been associated with gut dysbiosis. Since gut microbiota is highly sensitive to dietary changes, we hypothesised that immediate gut microbiota adaptation to WD in rats is involved in inflammation-related hypothalamic modifications.

METHODS

We evaluated short-term impact of WD consumption (2 h, 1, 2 and 4 days) on hypothalamic metabolome and caecal microbiota composition and metabolome. Data integration analyses were performed to uncover potential relationships among these three datasets. Finally, changes in hypothalamic gene expression in absence of gut microbiota were evaluated in germ-free rats fed WD for 2 days.

RESULTS

WD quickly and profoundly affected the levels of several hypothalamic metabolites, especially oxidative stress markers. In parallel, WD consumption reduced caecal microbiota diversity, modified its composition towards pro-inflammatory profile and changed caecal metabolome. Data integration identified strong correlations between gut microbiota sub-networks, unidentified caecal metabolites and hypothalamic oxidative stress metabolites. Germ-free rats displayed reduced energy intake and no changes in redox homoeostasis machinery expression or pro-inflammatory cytokines after 2 days of WD, in contrast to conventional rats, which exhibited increased SOD2, GLRX and IL-6 mRNA levels.

CONCLUSION

A potentially pro-inflammatory gut microbiota and an early hypothalamic oxidative stress appear shortly after WD introduction. Tripartite data integration highlighted putative links between gut microbiota sub-networks and hypothalamic oxidative stress. Together with the absence of hypothalamic modifications in germ-free rats, this strongly suggests the involvement of the microbiota-hypothalamus axis in rat adaptation to WD introduction and in energy homoeostasis regulation.

Fecal Microbiota Transplant from Human to Mice Gives Insights into the Role of the Gut Microbiota in Non-Alcoholic Fatty Liver Disease (NAFLD)

Non-alcoholic fatty liver diseases (NAFLD) are associated with changes in the composition and metabolic activities of the gut microbiota. However, the causal role played by the gut microbiota in individual susceptibility to NAFLD and particularly at its early stage is still unclear. In this context, we transplanted the microbiota from a patient with fatty liver (NAFL) and from a healthy individual to two groups of mice. We first showed that the microbiota composition in recipient mice resembled the microbiota composition of their respective human donor. Following administration of a high-fructose, high-fat diet, mice that received the human NAFL microbiota (NAFLR) gained more weight and had a higher liver triglycerides level and higher plasma LDL cholesterol than mice that received the human healthy microbiota (HR). Metabolomic analyses revealed that it was associated with lower and higher plasma levels of glycine and 3-Indolepropionic acid in NAFLR mice, respectively. Moreover, several bacterial genera and OTUs were identified as differently represented in the NAFLR and HR microbiota and therefore potentially responsible for the different phenotypes observed. Altogether, our results confirm that the gut bacteria play a role in obesity and steatosis development and that targeting the gut microbiota may be a preventive or therapeutic strategy in NAFLD management.

Perinatal exposure to a dietary pesticide cocktail does not increase susceptibility to high-fat diet-induced metabolic perturbations at adulthood but modifies urinary and fecal metabolic fingerprints in C57Bl6/J mice

BACKGROUND

We recently demonstrated that chronic dietary exposure to a mixture of pesticides at low-doses induced sexually dimorphic obesogenic and diabetogenic effects in adult mice. Perinatal pesticide exposure may also be a factor in metabolic disease etiology. However, the long-term consequences of perinatal pesticide exposure remain controversial and largely unexplored.

OBJECTIVES

Here we assessed how perinatal exposure to the same low-dose pesticide cocktail impacted metabolic homeostasis in adult mice.

METHODS

Six pesticides (boscalid, captan, chlopyrifos, thiachloprid, thiophanate, and ziram) were incorporated in food pellets. During the gestation and lactation periods, female (F0) mice were fed either a pesticide-free or a pesticide-enriched diet at doses exposing them to the tolerable daily intake (TDI) level for each compound, using a 1:1 body weight scaling from humans to mice. All male and female offsprings (F1) were then fed the pesticide-free diet until 18 weeks of age, followed by challenge with a pesticide-free high-fat diet (HFD) for 6 weeks. Metabolic parameters, including body weight, food and water consumption, glucose tolerance, and urinary and fecal metabolomes, were assessed over time. At the end of the experiment, we evaluated energetic metabolism and microbiota activity using biochemical assays, gene expression profiling, and ¹H NMR-based metabolomics in the liver, urine, and feces.

RESULTS

Perinatal pesticide exposure did not affect body weight or energy homeostasis in 6- and 14-week-old mice. As expected, HFD increased body weight and induced metabolic disorders as compared to a low-fat diet. However, HFD-induced metabolic perturbations were similar between mice with and without perinatal pesticide exposure. Interestingly, perinatal pesticide exposure induced time-specific and sex-specific alterations in the urinary and fecal metabolomes of adult mice, suggesting long-lasting changes in gut microbiota.

CONCLUSIONS

Perinatal pesticide exposure induced sustained sexually dimorphic perturbations of the urinary and fecal metabolic fingerprints, but did not significantly influence the development of HFD-induced metabolic diseases.

Short Chain Fatty Acids Enhance Expression and Activity of the Umami Taste Receptor in Enteroendocrine Cells via a Gαi/o Pathway

The short chain fatty acids (SCFAs) acetate, butyrate and propionate, are produced by fermentation of non-digestible carbohydrates by the gut microbiota and regulate appetite, adiposity, metabolism, glycemic control, and immunity. SCFAs act at two distinct G protein coupled receptors (GPCRs), FFAR2 and FFAR3 and are expressed in intestinal enteroendocrine cells (EECs), where they mediate anorectic gut hormone release. EECs also express other GPCRs that act as nutrient sensors, thus SCFAs may elicit some of their health-promoting effects by altering GPCR expression in EECs and enhance gut sensitivity to dietary molecules. Here, we identify that exposure of the murine EEC STC-1 cell line or intestinal organoids to physiological concentrations of SCFAs enhances mRNA levels of the umami taste receptors TASR1 and TASR3, without altering levels of the SCFA GPCRs, FFAR2 and FFAR3. Treatment of EECs with propionate or butyrate, but not acetate, increased levels of umami receptor transcripts, while propionate also reduced CCK expression. This was reversed by inhibiting Gαi/o signaling with pertussis toxin, suggesting that SCFAs act through FFAR2/3 to alter gene expression. Surprisingly, neither a FFAR3 nor a FFAR2 selective ligand could increase TASR1/TASR3 mRNA levels. We assessed the functional impact of increased TASR1/TASR3 expression using unique pharmacological properties of the umami taste receptor; namely, the potentiation of signaling by inosine monophosphate. Activation of umami taste receptor induced inositol-1-phosphate and calcium signaling, and butyrate pretreatment significantly enhanced such signaling. Our study reveals that SCFAs may contribute to EEC adaptation and alter EEC sensitivity to bioactive nutrients.

Bone Growth is Influenced by Fructose in Adolescent Male Mice Lacking Ketohexokinase (KHK)

Fructose is metabolized in the cytoplasm by the enzyme ketohexokinase (KHK), and excessive consumption may affect bone health. Previous work in calcium-restricted, growing mice demonstrated that fructose disrupted intestinal calcium transport. Thus, we hypothesized that the observed effects on bone were dependent on fructose metabolism and took advantage of a KHK knockout (KO) model to assess direct effects of high plasma fructose on the long bones of growing mice. Four groups (n = 12) of 4-week-old, male, C57Bl/6 background, congenic mice with intact KHK (wild-type, WT) or global knockout of both isoforms of KHK-A/C (KHK-KO), were fed 20% glucose (control diet) or fructose for 8 weeks. Dietary fructose increased by 40-fold plasma fructose in KHK-KO compared to the other three groups (p < 0.05). Obesity (no differences in epididymal fat or body weight) or altered insulin was not observed in either genotype. The femurs of KHK-KO mice with the highest levels of plasma fructose were shorter (2%). Surprisingly, despite the long-term blockade of KHK, fructose feeding resulted in greater bone mineral density, percent volume, and number of trabeculae as measured by µCT in the distal femur of KHK-KO. Moreover, higher plasma fructose concentrations correlated with greater trabecular bone volume, greater work-to-fracture in three-point bending of the femur mid-shaft, and greater plasma sclerostin. Since the metabolism of fructose is severely inhibited in the KHK-KO condition, our data suggest mechanism(s) that alter bone growth may be related to the plasma concentration of fructose.

Role of Gut Microbiota in Neuroendocrine Regulation of Carbohydrate and Lipid Metabolism via the Microbiota-Gut-Brain-Liver Axis

Gut microbiota play an important role in maintaining intestinal health and are involved in the metabolism of carbohydrates, lipids, and amino acids. Recent studies have shown that the central nervous system (CNS) and enteric nervous system (ENS) can interact with gut microbiota to regulate nutrient metabolism. The vagal nerve system communicates between the CNS and ENS to control gastrointestinal tract functions and feeding behavior. Vagal afferent neurons also express receptors for gut peptides that are secreted from enteroendocrine cells (EECs), such as cholecystokinin (CCK), ghrelin, leptin, peptide tyrosine tyrosine (PYY), glucagon-like peptide-1 (GLP-1), and 5-hydroxytryptamine (5-HT; serotonin). Gut microbiota can regulate levels of these gut peptides to influence the vagal afferent pathway and thus regulate intestinal metabolism via the microbiota-gut-brain axis. In addition, bile acids, short-chain fatty acids (SCFAs), trimethylamine-N-oxide (TMAO), and Immunoglobulin A (IgA) can also exert metabolic control through the microbiota-gut-liver axis. This review is mainly focused on the role of gut microbiota in neuroendocrine regulation of nutrient metabolism via the microbiota-gut-brain-liver axis.

Important Considerations for Sample Collection in Metabolomics Studies with a Special Focus on Applications to Liver Functions

Metabolomics has found numerous applications in the study of liver metabolism in health and disease. Metabolomics studies can be conducted in a variety of biological matrices ranging from easily accessible biofluids such as urine, blood or feces, to organs, tissues or even cells. Sample collection and storage are critical steps for which standard operating procedures must be followed. Inappropriate sample collection or storage can indeed result in high variability, interferences with instrumentation or degradation of metabolites. In this review, we will first highlight important general factors that should be considered when planning sample collection in the study design of metabolomic studies, such as nutritional status and circadian rhythm. Then, we will discuss in more detail the specific procedures that have been described for optimal pre-analytical handling of the most commonly used matrices (urine, blood, feces, tissues and cells).

Fructose and irritable bowel syndrome

Irritable bowel syndrome (IBS) is a chronic disorder characterised by recurrent abdominal pain or discomfort and transit disturbances with heterogeneous pathophysiological mechanisms. The link between food and gastrointestinal (GI) symptoms is often reported by patients with IBS and the role of fructose has recently been highlighted. Fructose malabsorption can easily be assessed by hydrogen and/or methane breath test in response to 25 g fructose; and its prevalence is about 22 % in patients with IBS. The mechanism of fructose-related symptoms is incompletely understood. Osmotic load, fermentation and visceral hypersensitivity are likely to participate in GI symptoms in the IBS population and may be triggered or worsened by fructose. A low-fructose diet could be integrated in the overall treatment strategy, but its role and implication in the improvement of IBS symptoms should be evaluated. In the present review, we discuss fructose malabsorption in adult patients with IBS and the interest of a low-fructose diet in order to underline the important role of fructose in IBS.

Premises for Cholecystokinin and Gastrin Peptides in Diabetes Therapy

Gastrin and cholecystokinin (CCK) are classical gastrointestinal peptide hormones. Their biogenesis, structures, and intestinal secretory patterns are well-known with the striking feature that their receptor-bound 'active sites' are highly homologous and that this structure is conserved for more than 500 million years during evolution. Consequently, gastrin and CCK are agonists for the same receptor (the CCK2 receptor). But in addition, tyrosyl O-sulphated CCK are also bound to the specific CCK1 receptor. The receptors are widely expressed in the body, including pancreatic islet-cell membranes. Moreover, CCK and gastrin peptides are at various developmental stages and diseases expressed in pancreatic islets; also in human islets. Accordingly, bioactive gastrin and CCK peptides stimulate islet-cell growth as well as insulin and glucagon secretion. In view of their insulinotropic effects, gastrin and CCK peptides have come into focus as drug targets, either alone or in combination with other insulinotropic gut hormones or growth factors. So far, modified CCK and gastrin peptides are being examined as potential drugs for therapy of type 1 as well as type 2 diabetes mellitus.

Demystifying the manipulation of host immunity, metabolism, and extraintestinal tumors by the gut microbiome

The trillions of microorganisms in the gut microbiome have attracted much attention recently owing to their sophisticated and widespread impacts on numerous aspects of host pathophysiology. Remarkable progress in large-scale sequencing and mass spectrometry has increased our understanding of the influence of the microbiome and/or its metabolites on the onset and progression of extraintestinal cancers and the efficacy of cancer immunotherapy. Given the plasticity in microbial composition and function, microbial-based therapeutic interventions, including dietary modulation, prebiotics, and probiotics, as well as fecal microbial transplantation, potentially permit the development of novel strategies for cancer therapy to improve clinical outcomes. Herein, we summarize the latest evidence on the involvement of the gut microbiome in host immunity and metabolism, the effects of the microbiome on extraintestinal cancers and the immune response, and strategies to modulate the gut microbiome, and we discuss ongoing studies and future areas of research that deserve focused research efforts.