Bile acid mediated effects on gut integrity and performance of early-weaned piglets

Effects of adding bile acids to dietary storage japonica brown rice on growth performance, meat quality, and intestinal microbiota of growing-finishing Min pigs

Introduction

This study investigated the effects of storage japonica brown rice (SJBR) and bile acids (BA) on the growth performance, meat quality, and intestinal microbiota of growing-finishing Min pigs.

Methods

A total of 24 healthy Min pigs with a similar body weight of 42.25 ± 2.13 kg were randomly divided into three groups with eight replicates of one pig each. The groups were as follows: CON (50% corn), SJBR (25% corn +25% SJBR), and SJBR + BA (25% corn +25% SJBR +0.025% hyodeoxycholic acid). The experimental period lasted from day 90 (the end of the nursery phase) to day 210 (the end of the finishing phase).

Results

The results showed the following: (1) Compared with the CON group, there was no significant difference in the average daily gain (ADG) and average daily feed intake (ADFI) of the SJBR and SJBR + BA groups, and the feed conversion ratio (FCR) was significantly decreased (p < 0.05). (2) Compared with the CON group, the total protein (TP) content in the serum was significantly increased, and the blood urea nitrogen (BUN) content was significantly decreased (p < 0.05) in the SJBR and SJBR + BA groups; moreover, HDL-C was significantly higher by 35% (p < 0.05) in the SJBR + BA group. (3) There were no significant differences in carcass weight, carcass length, pH, drip loss, cooking loss, and shear force among the groups; the eye muscle area was significantly increased in the SJBR group compared with the CON group (p < 0.05); back fat thickness was significantly decreased in the SJBR + BA group compared with the SJBR group (p < 0.05); and the addition of SJBR significantly increased the mRNA expression of MyHC I in the longissimus dorsi (LD) muscle of growing-finishing Min pigs (p < 0.05). (4) The cecal bacteria were detected using 16S rDNA, and the proportion of Lactobacillus was increased gradually at the genus level, but there was no significant difference among the different groups.

Conclusion

In conclusion, 25% SJBR can improve the growth performance and increase the abundance of intestinal beneficial bacteria, and based on this, adding bile acids can reduce the back fat thickness of growing-finishing Min pigs.

Combined transcriptome and metabolome analysis reveals breed-specific regulatory mechanisms in Dorper and Tan sheep

BACKGROUND

Dorper and Tan sheep are renowned for their rapid growth and exceptional meat quality, respectively. Previous research has provided evidence of the impact of gut microbiota on breed characteristics. The precise correlation between the gastrointestinal tract and peripheral organs in each breed is still unclear. Investigating the metabolic network of the intestinal organ has the potential to improve animal growth performance and enhance economic benefits through the regulation of intestinal metabolites.

RESULTS

In this study, we identified the growth advantage of Dorper sheep and the high fat content of Tan sheep. A transcriptome study of the brain, liver, skeletal muscle, and intestinal tissues of both breeds revealed 3,750 differentially expressed genes (DEGs). The genes PPARGC1A, LPL, and PHGDH were found to be highly expressed in Doper, resulting in the up-regulation of pathways related to lipid oxidation, glycerophospholipid metabolism, and amino acid anabolism. Tan sheep highly express the BSEP, LDLR, and ACHE genes, which up-regulate the pathways involved in bile transport and cholesterol homeostasis. Hindgut content analysis identified 200 differentially accumulated metabolites (DAMs). Purines, pyrimidines, bile acids, and fatty acid substances were more abundant in Dorper sheep. Based on combined gene and metabolite analyses, we have identified glycine, serine, and threonine metabolism, tryptophan metabolism, bile secretion, cholesterol metabolism, and neuroactive ligand-receptor interaction as key factors contributing to the differences among the breeds.

CONCLUSIONS

This study indicates that different breeds of sheep exhibit unique breed characteristics through various physiological regulatory methods. Dorper sheep upregulate metabolic signals related to glycine, serine, and threonine, resulting in an increase in purine and pyrimidine substances. This, in turn, promotes the synthesis of amino acids and facilitates body development, resulting in a faster rate of weight gain. Tan sheep accelerate bile transport, reduce bile accumulation in the intestine, and upregulate cholesterol homeostasis signals in skeletal muscles. This promotes the accumulation of peripheral and intramuscular fat, resulting in improved meat quality. This work adopts a joint analysis method of multi-tissue transcriptome and gut metabolome, providing a successful case for analyzing the mechanisms underlying the formation of various traits.

Growth performance, blood lipids, and fat digestibility of broilers fed diets supplemented with bile acid and xylanase

This study aimed to show the effect of bile acid (BA) and xylanase (Xyl) supplementation on the growth, fat digestibility, serum lipid metabolites, and ileal digesta viscosity of broilers. A total of 720 1 d old male broilers were allocated to one of nine treatments with four replicates in each under a factorial design arrangement of three levels of BA (0 %, 0.25 %, and 0.50 %) and three levels of Xyl (0 %, 0.05 %, and 0.10 %) supplementation. The duration of the experiment was 35 d (7-42 d). Growth performance, blood lipids, fat digestibility, and ileal digesta viscosity were determined. The experimental treatments did not affect feed intake (FI) and weight gain (WG). Supplementation of BA or Xyl did not significantly ameliorate the feed conversion rate (FCR) (p < 0.05 ). The addition of BA linearly increased fat digestibility. At 7-21 d of age, the addition of BA or Xyl had a significant (p < 0.05 ) increase in serum cholesterol (Chol) but no significant difference for other serum lipid parameters in broiler chickens fed with Xyl in the starter and grower periods. However, the supplementation of 0.5 % BA at 7-21 d of age significantly increased the Chol and low-density-lipoprotein (LDL) levels. The results of this trial revealed that the supplementation of xylanases had a great effect on the degradation of arabinoxylan from wheat, which led to a relatively greater reduction in ileal digesta viscosity; it was also found that supplementation of BA significantly increased the concentration of serum lipid metabolites, whereas BA and Xyl supplementation linearly increased the fat digestibility of the birds fed wheat and tallow diets.

Microbiome-liver crosstalk: A multihit therapeutic target for liver disease

Liver disease has become a leading cause of death, particularly in the West, where it is attributed to more than two million deaths annually. The correlation between gut microbiota and liver disease is still not fully understood. However, it is well known that gut dysbiosis accompanied by a leaky gut causes an increase in lipopolysaccharides in circulation, which in turn evoke massive hepatic inflammation promoting liver cirrhosis. Microbial dysbiosis also leads to poor bile acid metabolism and low short-chain fatty acids, all of which exacerbate the inflammatory response of liver cells. Gut microbial homeostasis is maintained through intricate processes that ensure that commensal microbes adapt to the low oxygen potential of the gut and that they rapidly occupy all the intestinal niches, thus outcompeting any potential pathogens for available nutrients. The crosstalk between the gut microbiota and its metabolites also guarantee an intact gut barrier. These processes that protect against destabilization of gut microbes by potential entry of pathogenic bacteria are collectively called colonization resistance and are equally essential for liver health. In this review, we shall investigate how the mechanisms of colonization resistance influence the liver in health and disease and the microbial-liver crosstalk potential as therapeutic target areas.

Growth performance, bile acid profile, fecal microbiome and serum metabolomics of growing-finishing pigs fed diets with bile acids supplementation

The present experiment was conducted to determine the effect of bile acids (BAs) supplementation on growth performance, BAs profile, fecal microbiome, and serum metabolomics in growing-finishing pigs. A total of 60 pigs [Duroc × (Landrace × Yorkshire)] with an average body weight of 27.0 ± 1.5 kg were selected and allotted into one of 2 groups (castrated male to female ratio = 1:1), with 10 replicates per treatment and 3 pigs per replicate. The 2 treatments were the control group (control) and a porcine bile extract-supplemented group dosed at 0.5 g/kg feed (BA). After a 16-wk treatment, growth performance, BAs profiles in serum and feces, and fecal microbial composition were determined. An untargeted metabolomics approach using gas chromatography with a time-of-flight mass spectrometer was conducted to identify the metabolic pathways and associated metabolites in the serum of pigs. We found that BAs supplementation had no effect on the growth performance of the growing-finishing pig. However, it tended to increase the gain-to-feed ratio for the whole period (P = 0.07). BAs supplementation resulted in elevated serum concentrations of secondary bile acids, including hyodeoxycholic acid (HDCA), glycoursodeoxycholic acid, and tauro-hyodeoxycholic acid, as well as fecal concentration of HDCA (P < 0.05). Fecal microbiota analysis revealed no differences in alpha and beta diversity indices or the relative abundance of operational taxonomic units (OTUs) at both phylum and genus levels between groups. Metabolic pathway analysis revealed that the differential metabolites between control and BA groups are mainly involved in purine metabolism, ether lipid metabolism, glycerophospholipid metabolism, and amino sugar and nucleotide sugar metabolism, as well as primary bile acid biosynthesis. Our findings indicate that BAs supplementation tended to improve the feed efficiency, and significantly altered the BA profile in the serum and feces of growing-finished pigs, regardless of any changes in the gut microbial composition. The altered metabolic pathways could potentially play a vital role in improving the feed efficiency of growing-finished pigs with BAs supplementation.

Bile acids as modulators of gut microbiota composition and function

Changes in the composition of gut-associated microbial communities are associated with many human illnesses, but the factors driving dysbiosis remain incompletely understood. One factor governing the microbiota composition in the gut is bile. Bile acids shape the microbiota composition through their antimicrobial activity and by activating host signaling pathways that maintain gut homeostasis. Although bile acids are host-derived, their functions are integrally linked to bacterial metabolism, which shapes the composition of the intestinal bile acid pool. Conditions that change the size or composition of the bile acid pool can trigger alterations in the microbiota composition that exacerbate inflammation or favor infection with opportunistic pathogens. Therefore, manipulating the composition or size of the bile acid pool might be a promising strategy to remediate dysbiosis.

Microbiota in a long survival discourse with the human host

The relationship between human health and gut microbiota is becoming more apparent. It is now widely believed that healthy gut flora plays a vital role in the overall well-being of the individual. There are spatial and temporal variations in the distribution of microbes from the esophagus to the rectum throughout an individual's lifetime. Through the development of genome sequencing technologies, scientists have been able to study the interactions between different microorganisms and their hosts to improve the health and disease of individuals. The normal gut microbiota provides various functions to the host, whereas the host, in turn, provides nutrients and promotes the development of healthy and resilient microbiota communities. Thus, the microbiota provides and maintains the gut's structural integrity and protects the gut against pathogens. The development of the normal gut microbiota is influenced by various factors. Some of these include the mode of delivery, diet, and antibiotics. In addition, the environment can also affect the development of the gut microbiota. For example, one of the main concerns of antibiotic use is the alteration of the gut microbiota, which could lead to the development of multidrug-resistant organisms. When microbes are disturbed, it can potentially lead to various diseases. Depending on the species' ability to adapt to the human body's environment, the fate of the microbes in the host and their relationship with the human body are decided. This review aims to provide a comprehensive analysis of microbe, microbes-host immune interactions, and factors that can disturb their interactions.

Food and Gut Microbiota-Derived Metabolites in Nonalcoholic Fatty Liver Disease

Diet and lifestyle are crucial factors that influence the susceptibility of humans to nonalcoholic fatty liver disease (NAFLD). Personalized diet patterns chronically affect the composition and activity of microbiota in the human gut; consequently, nutrition-related dysbiosis exacerbates NAFLD via the gut–liver axis. Recent advances in diagnostic technology for gut microbes and microbiota-derived metabolites have led to advances in the diagnosis, treatment, and prognosis of NAFLD. Microbiota-derived metabolites, including tryptophan, short-chain fatty acid, fat, fructose, or bile acid, regulate the pathophysiology of NAFLD. The microbiota metabolize nutrients, and metabolites are closely related to the development of NAFLD. In this review, we discuss the influence of nutrients, gut microbes, their corresponding metabolites, and metabolism in the pathogenesis of NAFLD.

High-fidelity porcine models of metabolic syndrome: a contemporary synthesis

This review aims to describe and compare porcine models of metabolic syndrome. This syndrome and its associated secondary comorbidities are set to become the greatest challenge to healthcare providers and policy makers in the coming century. However, an incomplete understanding of the pathogenesis has left significant knowledge gaps in terms of efficacious therapeutics. To further our comprehension and, in turn, management of metabolic syndrome, appropriate high-fidelity models of the disease complex are of great importance. In this context, our review aims to assess the most promising porcine models of metabolic syndrome currently available for their similarity to the human phenotype. In addition, we aim to highlight the strengths and shortcomings of each model in an attempt to identify the most appropriate application of each. Although no porcine model perfectly recapitulates the human metabolic syndrome, several pose satisfactory approximations. The Ossabaw miniature swine in particular represents a highly translatable model that develops each of the core parameters of the syndrome with many of the associated secondary comorbidities. Future high-fidelity porcine models of metabolic syndrome need to focus on secondary sequelae replication, which may require extended induction period to reveal.

Regulation of Intestinal Barrier Function by Microbial Metabolites

The human gastrointestinal tract (GI) harbors a diverse population of microbial life that continually shapes host pathophysiological responses. Despite readily available abundant metagenomic data, the functional dynamics of gut microbiota remain to be explored in various health and disease conditions. Microbiota generate a variety of metabolites from dietary products that influence host health and pathophysiological functions. Since gut microbial metabolites are produced in close proximity to gut epithelium, presumably they have significant impact on gut barrier function and immune responses. The goal of this review is to discuss recent advances on gut microbial metabolites in the regulation of intestinal barrier function. While the mechanisms of action of these metabolites are only beginning to emerge, they mainly point to a small group of shared pathways that control gut barrier functions. Amidst expanding technology and broadening knowledge, exploitation of beneficial microbiota and their metabolites to restore pathophysiological balance will likely prove to be an extremely useful remedial tool.

Supplemental Choline Modulates Growth Performance and Gut Inflammation by Altering the Gut Microbiota and Lipid Metabolism in Weaned Piglets

BACKGROUND

Whether dietary choline and bile acids affect lipid use via gut microbiota is unclear.

OBJECTIVES

This study aimed to investigate the effect of choline and bile acids on growth performance, lipid use, intestinal immunology, gut microbiota, and bacterial metabolites in weaned piglets.

METHODS

A total of 128 weaned piglets [Duroc × (Landrace × Yorkshire), 21-d-old, 8.21 ± 0.20 kg body weight (BW)] were randomly allocated to 4 treatments (8 replicate pens per treatment, each pen containing 2 males and 2 females; n = 32 per treatment) for 28 d. Piglets were fed a control diet (CON) or the CON diet supplemented with 597 mg choline/kg (C), 500 mg bile acids/kg (BA) or both (C + BA) in a 2 × 2 factorial design. Growth performance, intestinal function, gut microbiota, and metabolites were determined.

RESULTS

Compared with diets without choline, choline supplementation increased BW gain (6.13%), average daily gain (9.45%), gain per feed (8.18%), jejunal lipase activity (60.2%), and duodenal IL10 gene expression (51%), and decreased the mRNA abundance of duodenal TNFA (TNFα) (40.7%) and jejunal toll-like receptor 4 (32.9%) (P < 0.05); additionally, choline increased colonic butyrate (29.1%) and the abundance of Lactobacillus (42.3%), while decreasing the bile acid profile (55.8% to 57.6%) and the abundance of Parabacteroides (75.8%), Bacteroides (80.7%), and unidentified-Ruminococcaceae (32.5%) (P ≤ 0.05). Compared with diets without BA, BA supplementation decreased the mRNA abundance of colonic TNFA (37.4%), NF-κB p65 (42.4%), and myeloid differentiation factor 88 (42.5%) (P ≤ 0.01); BA also increased colonic butyrate (20.9%) and the abundance of Lactobacillus (39.7%) and Faecalibacterium (71.6%) and decreased that of Parabacteroides (67.7%) (P < 0.05).

CONCLUSIONS

Choline supplementation improved growth performance and prevented gut inflammation in weaned piglets by altering gut microbiota and lipid metabolism. BA supplementation suppressed intestinal inflammation with no effect on growth performance, which was associated with changed gut microbiota and metabolites.

Microbiome Analysis Investigating the Impacts of Fermented Spent Mushroom Substrates on the Composition of Microbiota in Weaned Piglets Hindgut

The purpose of this study was to investigate the effects of fermented spent mushroom substrates (FSMS) on growth performance, serum biochemical, gut digestive enzyme activity, microbial community, genes expression of tight junction proteins, and volatile fatty acids in the hindgut (colon and cecum) of weaned piglets. A total of 100 weaned Yihao native pigs (native × Duroc, 50 males and 50 females) were allocated to two groups with five replicates and 10 pigs per replicate. Pigs in the control group were fed a basal diet (BD group), and the others were fed basal diets supplemented with 3% FSMS (FSMS group). Relative to the BD group, it had better results for final weight, average daily gain, and feed conversion ratio in the FSMS group but not significant (p > 0.05), which was accompanied by improved serum triiodothyronine, immunoglobulin G, and immunoglobulin A (p < 0.05) but lower serum total protein, albumin, total cholesterol, and total triglyceride during the overall period (p < 0.05). Similarly, FSMS significantly upregulated (p < 0.05) the messenger RNA expression of duodenal tight junction proteins such as tight junction protein 1, tight junction protein 2, and occludin. Meanwhile, isobutyric acid, valeric acid, and isovaleric acid levels were increased, whereas propanoic acid was decreased (p < 0.05) in the FSMS group than the BD group. In addition, the piglets in the FSMS group changed the microbial diversity in the colon and cecum. 16S rRNA gene sequencing-based compositional analysis of the colonic and cecal microbiota showed differences in the relative abundance of bacterial phyla (Firmicutes, Bacteroidetes, etc.), genus (Lactobacillus, Streptococcus, Roseburia, etc.), and species (Lactobacillus gasseri, Clostridium disporicum, etc.) between the BD and FSMS fed piglets. In conclusion, dietary supplementation with FSMS benefited to the intestinal mucosal barrier, immunity, and composition of the microbiota.

Effect of fosfomycin, Cynara scolymus extract, deoxynivalenol and their combinations on intestinal health of weaned piglets

Weaning is a challenging stage of pig farming. Animals undergo environmental, social and dietary changes leading to weaning stress syndrome. In order to compensate for the detrimental effects of weaning stress, antibiotics and natural extracts are used as feed additives, sometimes without fully understanding the interactions between them or even with low concentrations of mycotoxins that are frequently present in feed. The aim of this study was to evaluate the effect of fosfomycin (FOS), Cynara scolymus extract (CSE), deoxynivalenol (DON) and their combined administration on intestinal health of weaned piglets. The experiment was designed as a 2 × 2 × 2 factorial arrangement with 3 factors (FOS, CSE and DON treatments), 2 levels each (presence and absence) and 3 repeats. Weaned piglets (n = 24) were randomly divided in groups to receive the different treatments, namely DON administered in diet (50 μg/kg BW), FOS administered into the drinking water (30 mg/kg BW), CSE administered in diet (15 mg/kg BW) and all their combinations. After 15 d, the animals were euthanized and gastrointestinal tract samples were immediately taken to evaluate gastrointestinal pH, Enterobacteriaceae to lactic acid bacteria (E:L) ratio, volatile fatty acid (VFA) concentrations, disaccharidase (lactase, sucrase and maltase) activity, histology (intestinal absorptive area [IAA] and goblet cells count) and mucus ability to adhere pathogenic Escherichia coli. From our results, FOS and CSE treatments, individually or combined, produced a lower E:L ratio, an enhanced production of butyrate, increased disaccharidase activity (particularly maltase), and a greater IAA and goblet cells count along with an increase in pathogenic bacteria adherence to intestinal mucus. Deoxynivalenol did not show interactions with the other factors and its administration produced decreases on VFA, disaccharidase activity and goblet cells count. In conclusion, weaning piglets receiving diets containing FOS, CSE or both exhibited evident beneficial intestinal effects compared to animals receiving diets free from these compounds. On the contrary, the presence of DON at sub-toxic concentrations produced detrimental effects on intestinal health. The knowledge of the physiological and pathological gut changes produced by these compounds contributes to understand their potential productive consequences.

The effects of dietary supplementation with hyodeoxycholic acid on the differentiation and function of enteroendocrine cells and the serum biochemical indices in weaned piglets

Bile acid, a cholesterol metabolite, promotes gastrointestinal tract digestion and absorption of cholesterol, lipids, and fat-soluble vitamins. It is a signaling regulatory molecule that influences a variety of endocrinal and metabolic activities. This study investigated the effects hyodeoxycholic acid (HDCA) as a dietary supplement on endocrine cell differentiation and function and weaned piglet serum biochemical indices. Sixteen piglets (Duroc × [Landrace × Yorkshire]) were individually housed and weaned at 21 days of age (body weight of 6.14 ± 0.22 kg). Uniform weight animals were randomly assigned to one of two treatments (eight replicate pens per treatment and one piglet per pen). The treatments were 1) base diet (control); and 2) base diet supplemented with 2 g/kg of HDCA. Control and HDCA piglet numbers of CgA-positive cells per crypt did not differ. HDCA CgA-positive cells numbers decreased (P < 0.05) in the jejunal villi, showed a tendency to decrease (P < 0.10) in the ileal villi, and showed tendency toward an increase (P < 0.10) in the duodenal villi compared to the controls. The HDCA diet led to a decline in GLP-2 (P < 0.01) concentrations, but did not affect plasma GLP-1. HDCA supplementation increased (P < 0.05) the mRNA expression of jejunal Insm1, Sst, PG, and Gast, but decreased (P < 0.05) duodenal expression of Insm1, jejunal Pdx1, and ileal NeuroD1. HDCA elevated GLO and IgA (P < 0.05) serum concentrations and decreased the A/G ratio (P < 0.05). TP and IgG serum levels tended to increase compared to the control group. These results indicate that dietary HDCA at 2 g/kg may regulate enteroendocrine cell differentiation and play a role in increasing weaned piglet humoral immunity.

Antimicrobial promotion of pig growth is associated with tissue-specific remodeling of bile acid signature and signaling

The spread of bacterial resistance to antimicrobials (AMA) have intensified efforts to discontinue the non-therapeutic use of AMA in animal production. Finding alternatives to AMA, however, is currently encumbered by the obscure mechanism that underlies their growth-promoting action. In this report, we demonstrate that combinations of antibiotics and zinc oxide at doses commonly used for stimulating growth or preventing post-weaning enteritis in pigs converge in promoting microbial production of bile acids (BA) in the intestine. This leads to tissue-specific modifications in the proportion of BA, thereby amplifying BA signaling in intestine, liver, and white adipose tissue (WAT). Activation of BA-regulated pathways ultimately reinforces the intestinal protection against bacterial infection and pathological secretion of fluids and electrolytes, attenuates inflammation in colon and WAT, alters protein and lipid metabolism in liver, and increases the circulating levels of the hormone FGF19. Conceivably, these alterations could spare nutrients for growth and improve the metabolic efficiency of AMA-treated animals. This work provides evidence that BA act as signaling molecules that mediate host physiological, metabolic, and immune responses to the AMA-induced alterations in gut microbial metabolism, eventually permitting the growth-promoting action of AMA. Consequently, BA emerge as a promising target for developing efficacious alternatives to AMA.

Developmental regulation of the intestinal FGF19 system in domestic pigs

Fibroblast growth factor-19 (FGF19) is an emerging endocrine factor involved in the regulation of bile acid homeostasis and energy metabolism in rodents and humans. In pigs, however, the FGF19 system remains largely unexplored. This study was designed to investigate the developmental regulation of the FGF19 system in domestic pigs. Samples of intestinal sections, liver, and plasma were collected from 24 pigs ( n = 6) at four developmental stages (birth, preweaning, postweaning, and adulthood). In the intestine, expression of the farnesoid X receptor (FXR) and FGF19 showed a congruent time- and region-dependent regulation, beginning soon after birth to achieve maximal expression in ileum during adulthood. The same temporal pattern was followed by the circulating concentration of FGF19, and these changes were accompanied by a time-related increase in the ileal proportion of bile acids that potently activate FXR. Conversely, genes belonging to the FGF19 signaling machinery achieved maximal expression in the small intestine at birth to decrease sharply afterward. In the liver, gene expression of FGF19 receptors and enzymes involved in bile acid biosynthesis paralleled after-birth changes in plasma concentration of this enterokine and attained a maximum during postweaning when plasma FGF19 was the lowest. Although detectable at birth, the hepatic expression of genes belonging to the bile acid-FXR-FGF19 pathway was low before the onset of enteral feeding. In summary, the porcine FGF19 system is present from birth, operative before the onset of enteral feeding, and regulated in a temporal and section-specific manner. NEW & NOTEWORTHY Fibroblast growth factor-19 (FGF19) is an emerging endocrine factor. The domestic pig is a translational model of value in biomedical research. We show for the first time that in pigs the intestinal FGF19 system is present from birth, operative before the onset of enteral feeding, and regulated in a temporal and section-specific manner. This work identifies pigs as a suitable model for investigating the implications of FGF19 signaling within and beyond the gut-liver axis.

The human microbiome and metabolomics: Current concepts and applications

The mammalian gastrointestinal tract has co-developed with a large number of microbes in a symbiotic relationship over millions of years. Recent studies indicate that indigenous bacteria are intimate with the intestine and play essential roles in health and disease. In the quest to maintain a stable niche, these prokaryotes influence multiple host metabolic pathways, resulting from an interactive host-microbiota metabolic signaling and impacting strongly on the metabolic phenotypes of the host. Since dysbiosis of the gut bacteria result in alteration in the levels of certain microbial and host co-metabolites, identifying these markers could enhance early detection of diseases. Also, identification of these metabolic fingerprints could give us clues as to how to manipulate the microbiome to promote health or treat diseases. This review provides an overview of our current knowledge of the microbiome and metablomics, applications and the future perspectives.

Glucagon-like peptide-2 promotes gallbladder refilling via a TGR5-independent, GLP-2R-dependent pathway

OBJECTIVE

Glucagon-like peptides (GLPs) are secreted from enteroendocrine cells in response to nutrients and bile acids and control metabolism via actions on structurally-related yet distinct G protein coupled receptors. GLP-1 regulates gut motility, appetite, islet function, and glucose homeostasis, whereas GLP-2 enhances intestinal nutrient absorption. GLP-1R agonists are used to treat diabetes and obesity, and a GLP-2R agonist is approved to treat short bowel syndrome. Unexpectedly, reports of gallbladder disease have been associated with the use of both GLP-1R and GLP-2R agonists and after bariatric surgery, although the mechanisms remain unknown.

METHODS

We investigated whether GLP-1 or GLP-2 acutely controls gallbladder (GB) volume and whether GLP-2 regulates GB muscle activity in mice. The expression of Tgr5, Glp2r, and Glp1r was assessed in mouse GB, and the effects of GLP-2 on hepatic bile acid (BA) flow, intestinal and liver BA uptake, and GB gene expression were determined. GLP-2 regulation of GB volume was assessed in wildtype, Glp2r^-/- and Tgr5^-/- mice. The effect of GLP-2 on GB smooth muscle (GBSM) calcium transients was characterized ex vivo.

RESULTS

Acute administration of the GLP-1R agonist exendin-4 lowered glucose but had no effect on GB volume in mice. In contrast, GLP-2 rapidly enhanced GB filling in a dose-dependent manner, actions maintained in the presence of cholecystokinin, and mediated through the canonical GLP-2R. GLP-2 also rapidly induced immediate early gene expression in GB, consistent with detection of the endogenous Glp2r in GB RNA. The ability of GLP-2 to increase GB volume was not abrogated by systemic administration of hexamethonium, propranolol, a vasoactive peptide receptor antagonist or N-Nitroarginine methyl ester, and was maintained in Tgr5^-/- mice. In contrast, lithocholic acid, a Tgr5 agonist, increased GB filling in Glp2r^-/- but not in Tgr5^-/- mice. GLP-2 had no effect on ileal uptake or hepatic clearance of taurocholic acid or on hepatic bile flow, yet reduced the frequency of spontaneous calcium transients in murine GBSM ex vivo, in a tetrodotoxin-sensitive manner.

CONCLUSIONS

Our data extend endocrine concepts of regulation of GB filling beyond FXR-FGF15/19 and the direct effects of BA via Tgr5, to encompass a novel BA-Tgr5-L cell GLP-2 axis providing nutrient-mediated feedback from BA to terminate meal-related GB contraction. These findings have implications for conditions characterized by elevated circulating levels of GLP-2 such as after bariatric surgery and the development and use of agents that promote Tgr5 activation, L cell secretion, or GLP-2R agonism for the treatment of metabolic disease.

Epidermal Growth Factor and Intestinal Barrier Function

Epidermal growth factor (EGF) is a 53-amino acid peptide that plays an important role in regulating cell growth, survival, migration, apoptosis, proliferation, and differentiation. In addition, EGF has been established to be an effective intestinal regulator helping to protect intestinal barrier integrity, which was essential for the absorption of nutrients and health in humans and animals. Several researches have demonstrated that EGF via binding to the EGF receptor and subsequent activation of Ras/MAPK, PI3K/AKT, PLC-γ/PKC, and STATS signal pathways regulates intestinal barrier function. In this review, the relationship between epidermal growth factor and intestinal development and intestinal barrier is described, to provide a better understanding of the effects of EGF on intestine development and health.

Chenodeoxycholic acid reduces feed intake and modulates the expression of hypothalamic neuropeptides and hepatic lipogenic genes in broiler chickens

Bile acids have recently become an emerging research hot spot in mammals due to their roles as metabolic regulators and molecular signatures controlling whole-body metabolic homeostasis. Such effects are still unknown in avian (non-mammalian) species. We, therefore, undertook this study to determine the effect of chenodeoxycholic acid (CDCA) on growth performance and on the expression of hypothalamic neuropeptides and hepatic lipogenic genes in broiler chickens. Chickens fed with diet-containing 0.1% or 0.5% CDCA for two weeks exhibited a significant and a dose dependent reduction of feed intake and body weight compared to the control (standard diet). These changes were accompanied with a significant decrease in plasma glucose levels at d10 and d15 post-treatment. At molecular levels, CDCA treatment significantly up-regulated the expression of feeding-related hypothalamic neuropeptides (NPY, AgRP, ORX, CRH, Ghrl, and MC1R) and down-regulated the hypothalamic expression of SOCS3. CDCA treatment also decreased the mRNA levels of key hepatic lipogenic genes (FAS, ACCα, ME, ATPcl, and SCD-1) and their related transcription factors SREBP-1/2 and PPARα. In addition, CDCA reduced the hepatic expression of FXR and the adipokine, visfatin, and adiponectin genes compared to the control. Together, our data provide evidence that CDCA alters growth performances in broilers and modulates the expression of hypothalamic neuropeptides and hepatic lipogenic and adipocytokine genes.