Intestinal Gluconeogenesis Shapes Gut Microbiota, Fecal and Urine Metabolome in Mice with Gastric Bypass Surgery

Background&Aims: Intestinal gluconeogenesis (IGN), gastric bypass (GBP) and gut microbiota positively regulate glucose homeostasis and diet-induced dysmetabolism. GBP modulates gut microbiota but whether IGN intensity could shape it has not been investigated. Methods: To this aim, we studied gut microbiota and microbiome in wild-type and IGN-deficient mice which underwent GBP and were fed on either a normal chow (NC) or a high-fat/high-sucrose (HFHS) diet. We also studied fecal and urine metabolome in NC-fed mice. Results: IGN and GBP had a peculiar effect on both gut microbiota and microbiome, on NC and HFHS diet. IGN inactivation induced Deltaproteobacteria on NC and higher Proteobacteria such as Helicobacter on HFHS diet. GBP induced higher Firmicutes and Proteobacteria on NC-fed WT mice and Firmicutes, Bacteroidetes and Proteobacteria on HFHS-fed WT mice. The combined effect of IGN inactivation and GBP induced higher Actinobacteria on NC and higher Enterococcaceae and Enterobacteriaceae on HFHS diet. A reduction was observed in short-chain fatty acids in fecal (by GBP) and in both fecal and urine (by IGN inactivation) metabolome. Conclusions: IGN and GBP, alone and in combination, shape gut microbiota and microbiome on NC- and HFHS-fed mice, together with a change in fecal and urine metabolome.

INTESTINAL GLUCONEOGENESIS IS DOWNREGULATED IN PAEDIATRIC PATIENTS WITH COELIAC DISEASE

ABSTRACTObjectiveUntreated coeliac disease (CD) patients have increased levels of blood glutamine and a lower duodenal expression of glutaminase (GLS). Intestinal gluconeogenesis (IGN) is a process through which glutamine is turned into glucose in the small intestine, for which GLS is crucial. Animal studies suggest impaired IGN may have long-term effects on metabolic control and be associated with development of type 2 diabetes and non-alcoholic fatty liver disease (NAFLD). The aim of this study was to thoroughly investigate IGN at the gene expression level in children with untreated coeliac disease.DesignQuantitative polymerase chain reaction (qPCR) was used to quantify expression of 11 target genes related to IGN using the delta-delta Ct method with three reference genes (GUSB, IPO8 and YWHAZ) in duodenal biopsies collected from 84 children with untreated coeliac disease and 58 disease controls.ResultsSignificantly lower expression of nine target genes involved in IGN was seen in duodenal biopsies from CD patients compared with controls: FBP1, G6PC, GLS, GPT1, PCK1, PPARGC1A, SLC2A2, SLC5A1, and SLC6A19. No significant differences in expression were seen for G6PC3 and GOT1.ConclusionChildren with untreated coeliac disease have lower expression of genes important for IGN. Further studies are warranted to disentangle whether this is a consequence of intestinal inflammation or due to an impaired metabolic pathway shared with other chronic metabolic diseases. Impaired IGN could be a mechanism behind the increased risk of NAFLD seen in CD patients.SIGNIFICANCE OF THIS STUDYWhat is already known about this subject?Genome-wide association studies have shown an association between coeliac disease (CD) and glutaminase (GLS).Intestinal gluconeogenesis (IGN) is a process with a recently described important function in energy homeostasis and metabolic disease. GLS is critical for IGN by enabling it to use glutamine, its main substrate.CD patients are at an increased risk of non-alcoholic fatty liver disease (NAFLD) as adults.What are the new findings?Nine genes involved in IGN are downregulated at the gene expression level in the small intestine of children with untreated CD, suggesting impairment of IGN.How might it impact on clinical practice in the foreseeable future?Impaired IGN might be a mechanism behind the increased risk of NAFLD seen in CD patients as adults.Early diagnosis and treatment of CD may restore IGN and prevent CD patients from NAFLD later in adulthood.

The Associations of SCFA with Anthropometric Parameters and Carbohydrate Metabolism in Pregnant Women

Short-chain fatty acids (SCFAs) mediate the transmission of signals between the microbiome and the immune system and are responsible for maintaining balance in the anti-inflammatory reaction. Pregnancy stages alter the gut microbiota community structure, which also synthesizes SCFAs. The study involved 90 pregnant women, divided into two groups: 48 overweight/obese pregnant women (OW) and 42 pregnant women with normal BMI (CG). The blood samples for glucose, insulin, and HBA1c were analyzed as well as stool samples for SCFA isolation (C2:0; C3:0; C4:0i; C4:0n; C5:0i; C5:0n; C6:0i; C6:0n) using gas chromatography. The SCFA profile in the analyzed groups differed significantly. A significant positive correlation between C2:0, C3:0, C4:0n and anthropometric measurements, and between C2:0, C3:0, C4:0n, and C5:0n and parameters of carbohydrate metabolism was found. SCFA levels fluctuate during pregnancy and the course of pregnancy and participate in the change in carbohydrate metabolism as well. The influence of C2:0 during pregnancy on anthropometric parameters was visible in both groups (normal weight and obese). Butyrate and propionate regulate glucose metabolism by stimulating the process of intestinal gluconeogenesis. The level of propionic acid decreases with the course of pregnancy, while its increase is characteristic of obese women, which is associated with many metabolic adaptations. Propionic and linear caproic acid levels can be an important critical point in maintaining lower anthropometric parameters during pregnancy.

Intestinal gluconeogenesis and protein diet: future directions

High-protein meals and foods are promoted for their beneficial effects on satiety, weight loss and glucose homeostasis. However, the mechanisms involved and the long-term benefits of such diets are still debated. We here review how the characterisation of intestinal gluconeogenesis (IGN) sheds new light on the mechanisms by which protein diets exert their beneficial effects on health. The small intestine is the third organ (in addition to the liver and kidney) contributing to endogenous glucose production via gluconeogenesis. The particularity of glucose produced by the intestine is that it is detected in the portal vein and initiates a nervous signal to the hypothalamic nuclei regulating energy homeostasis. In this context, we demonstrated that protein diets initiate their satiety effects indirectly via IGN and portal glucose sensing. This induction results in the activation of brain areas involved in the regulation of food intake. The μ-opioid-antagonistic properties of protein digests, exerted in the portal vein, are a key link between IGN induction and protein-enriched diet in the control of satiety. From our results, IGN can be proposed as a mandatory link between nutrient sensing and the regulation of whole-body homeostasis. The use of specific mouse models targeting IGN should allow us to identify several metabolic functions that could be controlled by protein diets. This will lead to the characterisation of the mechanisms by which protein diets improve whole-body homeostasis. These data could be the basis of novel nutritional strategies targeting the serious metabolic consequences of both obesity and diabetes.

Fructose Consumption by Adult Rats Exposed to Dexamethasone In Utero Changes the Phenotype of Intestinal Epithelial Cells and Exacerbates Intestinal Gluconeogenesis

Fructose consumption by rodents modulates both hepatic and intestinal lipid metabolism and gluconeogenesis. We have previously demonstrated that in utero exposure to dexamethasone (DEX) interacts with fructose consumption during adult life to exacerbate hepatic steatosis in rats. The aim of this study was to clarify if adult rats born to DEX-treated mothers would display differences in intestinal gluconeogenesis after excessive fructose intake. To address this issue, female Wistar rats were treated with DEX during pregnancy and control (CTL) mothers were kept untreated. Adult offspring born to CTL and DEX-treated mothers were assigned to receive either tap water (Control-Standard Chow (CTL-SC) and Dexamethasone-Standard Chow (DEX-SC)) or 10% fructose in the drinking water (CTL-fructose and DEX-fructose). Fructose consumption lasted for 80 days. All rats were subjected to a 40 h fasting before sample collection. We found that DEX-fructose rats have increased glucose and reduced lactate in the portal blood. Jejunum samples of DEX-fructose rats have enhanced phosphoenolpyruvate carboxykinase (PEPCK) expression and activity, higher facilitated glucose transporter member 2 (GLUT2) and facilitated glucose transporter member 5 (GLUT5) content, and increased villous height, crypt depth, and proliferating cell nuclear antigen (PCNA) staining. The current data reveal that rats born to DEX-treated mothers that consume fructose during adult life have increased intestinal gluconeogenesis while recapitulating metabolic and morphological features of the neonatal jejunum phenotype.

Intestinal gluconeogenesis prevents obesity-linked liver steatosis and non-alcoholic fatty liver disease

ObjectiveHepatic steatosis accompanying obesity is a major health concern, since it may initiate non-alcoholic fatty liver disease (NAFLD) and associated complications like cirrhosis or cancer. Intestinal gluconeogenesis (IGN) is a recently described function that contributes to the metabolic benefits of specific macronutrients as protein or soluble fibre, via the initiation of a gut-brain nervous signal triggering brain-dependent regulations of peripheral metabolism. Here, we investigate the effects of IGN on liver metabolism, independently of its induction by the aforementioned macronutrients.DesignTo study the specific effects of IGN on hepatic metabolism, we used two transgenic mouse lines: one is knocked down for and the other overexpresses glucose-6-phosphatase, the key enzyme of endogenous glucose production, specifically in the intestine.ResultsWe report that mice with a genetic overexpression of IGN are notably protected from the development of hepatic steatosis and the initiation of NAFLD on a hypercaloric diet. The protection relates to a diminution of de novo lipogenesis and lipid import, associated with benefits at the level of inflammation and fibrosis and linked to autonomous nervous system. Conversely, mice with genetic suppression of IGN spontaneously exhibit increased hepatic triglyceride storage associated with activated lipogenesis pathway, in the context of standard starch-enriched diet. The latter is corrected by portal glucose infusion mimicking IGN.ConclusionWe conclude that IGN per se has the capacity of preventing hepatic steatosis and its eventual evolution toward NAFLD.

Gut-brain signaling in energy homeostasis: the unexpected role of microbiota-derived succinate

In the context of the obesity epidemic, dietary fibers that are found essentially in fruit and vegetables attract more and more attention, since they exert numerous metabolic benefits resulting in the moderation of body weight. Short-chain fatty acids, such as propionate and butyrate, produced through their fermentation by the intestinal microbiota, have long been thought to be the mediators of these benefits. In fact, propionate and butyrate were recently shown to activate intestinal gluconeogenesis, a function exerting metabolic benefits via its capacity of signaling to the brain by gastrointestinal nerves. Recently, succinate, the precursor of propionate in the bacterial metabolism, has also been shown to exert signaling properties, including the activation of intestinal gluconeogenesis.