Effects of amino acid-derived luminal metabolites on the colonic epithelium and physiopathological consequences

Exercise-induced stress behavior, gut-microbiota-brain axis and diet: a systematic review for athletes

Fatigue, mood disturbances, under performance and gastrointestinal distress are common among athletes during training and competition. The psychosocial and physical demands during intense exercise can initiate a stress response activating the sympathetic-adrenomedullary and hypothalamus-pituitary-adrenal (HPA) axes, resulting in the release of stress and catabolic hormones, inflammatory cytokines and microbial molecules. The gut is home to trillions of microorganisms that have fundamental roles in many aspects of human biology, including metabolism, endocrine, neuronal and immune function. The gut microbiome and its influence on host behavior, intestinal barrier and immune function are believed to be a critical aspect of the brain-gut axis. Recent evidence in murine models shows that there is a high correlation between physical and emotional stress during exercise and changes in gastrointestinal microbiota composition. For instance, induced exercise-stress decreased cecal levels of Turicibacter spp and increased Ruminococcus gnavus, which have well defined roles in intestinal mucus degradation and immune function.

Diet is known to dramatically modulate the composition of the gut microbiota. Due to the considerable complexity of stress responses in elite athletes (from leaky gut to increased catabolism and depression), defining standard diet regimes is difficult. However, some preliminary experimental data obtained from studies using probiotics and prebiotics studies show some interesting results, indicating that the microbiota acts like an endocrine organ (e.g. secreting serotonin, dopamine or other neurotransmitters) and may control the HPA axis in athletes. What is troubling is that dietary recommendations for elite athletes are primarily based on a low consumption of plant polysaccharides, which is associated with reduced microbiota diversity and functionality (e.g. less synthesis of byproducts such as short chain fatty acids and neurotransmitters). As more elite athletes suffer from psychological and gastrointestinal conditions that can be linked to the gut, targeting the microbiota therapeutically may need to be incorporated in athletes’ diets that take into consideration dietary fiber as well as microbial taxa not currently present in athlete’s gut.

Dual effects of a high-protein diet on DSS-treated mice during colitis resolution phase

The impact of the dietary protein level on the process of colonic mucosal inflammation and subsequent recovery remains largely unknown. In this study, we fed DSS-treated mice with either a normoproteic (NP) or a high-protein (HP) isocaloric diet from the beginning of the 5-day dextran sulfate sodium (DSS) treatment to 14 days later. Measurements of colitis indicators (colon weight:length ratio, myeloperoxidase activity, cytokine expressions) showed a similar level of colonic inflammation in both DSS groups during the colitis induction phase. However, during the colitis resolution phase, inflammation intensity was higher in the DSS-HP group than in the DSS-NP group as evidenced by higher inflammatory score and body weight loss. This coincided with a higher mortality rate. In surviving animals, an increase in colonic crypt height associated with a higher number of colon epithelial cells per crypt, and TGF-β3 content was observed in the DSS-HP vs. DSS-NP group. Moreover, colonic expression patterns of tight junction proteins and E-cadherin were also different according to the diet. Altogether, our results indicate that the HP diet, when given during both the induction and resolution periods of DSS-induced colitis, showed deleterious effects during the post-induction phase. However, HP diet ingestion was also associated with morphological and biochemical differences compatible with higher colonic epithelium restoration in surviving animals, indicating an effect of the dietary protein level on colonic crypt repair after acute inflammation. These data highlight the potential impact of the dietary protein amount during the colitis course.

Health relevance of intestinal protein fermentation in young pigs

The physiological role of the gastrointestinal microbiota has become an important subject of nutrition research in pigs in the past years, and the importance of intestinal microbial activity in the etiology of disease is doubtless. This review summarizes the recent knowledge related to the microbial ecology of protein fermentation and the appearance of protein-derived metabolites along the pig intestine. The amount of fermentable protein depends on factors such as dietary protein concentration, protein digestibility due to secondary or tertiary structure, the interaction with dietary compounds or anti-nutritional factors, and the secretion of endogenous proteins into the gut lumen. High protein diets increase the luminal concentrations and epithelial exposure to putatively toxic metabolites and increase the risk for post-weaning diarrhea, but the mechanisms are not yet clarified. Although the use of fermentable carbohydrates to reduce harmful protein-derived metabolites in pigs is well-established, recent studies suggest that the inclusion of fermentable carbohydrates into diets with low protein digestibility or high dietary protein level may not ameliorate all negative effects with regard to epithelial response. Based on the current knowledge, the use of diets with low levels of high-quality protein may help to reduce the risk for intestinal disease in young pigs.

Compared with Raw Bovine Meat, Boiling but Not Grilling, Barbecuing, or Roasting Decreases Protein Digestibility without Any Major Consequences for Intestinal Mucosa in Rats, although the Daily Ingestion of Bovine Meat Induces Histologic Modifications in the Colon

BACKGROUND

Cooking may impair meat protein digestibility. When undigested proteins are fermented by the colon microbiota, they can generate compounds that potentially are harmful to the mucosa.

OBJECTIVES

This study addressed the effects of typical cooking processes and the amount of bovine meat intake on the quantity of undigested proteins entering the colon, as well as their effects on the intestinal mucosa.

METHODS

Male Wistar rats (n = 88) aged 8 wk were fed 11 different diets containing protein as 20% of energy. In 10 diets, bovine meat proteins represented 5% [low-meat diet (LMD)] or 15% [high-meat diet (HMD)] of energy, with the rest as total milk proteins. Meat was raw or cooked according to 4 processes (boiled, barbecued, grilled, or roasted). A meat-free diet contained only milk proteins. After 3 wk, rats ingested a (15)N-labeled meat meal and were killed 6 h later after receiving a (13)C-valine injection. Meat protein digestibility was determined from (15)N enrichments in intestinal contents. Cecal short- and branched-chain fatty acids and hydrogen sulfide were measured. Intestinal tissues were used for the assessment of protein synthesis rates, inflammation, and histopathology.

RESULTS

Meat protein digestibility was lower in rats fed boiled meat (94.5% ± 0.281%) than in the other 4 groups (97.5% ± 0.0581%, P < 0.001). Cecal and colonic bacterial metabolites, inflammation indicators, and protein synthesis rates were not affected by cooking processes. The meat protein amount had a significant effect on cecal protein synthesis rates (LMD > HMD) and on myeloperoxidase activity in the proximal colon (HMD > LMD), but not on other outcomes. The ingestion of bovine meat, whatever the cooking process and the intake amount, resulted in discrete histologic modifications of the colon (epithelium abrasion, excessive mucus secretion, and inflammation).

CONCLUSIONS

Boiling bovine meat at a high temperature (100°C) for a long time (3 h) moderately lowered protein digestibility compared with raw meat and other cooking processes, but did not affect cecal bacterial metabolites related to protein fermentation. The daily ingestion of raw or cooked bovine meat had no marked effect on intestinal tissues, despite some slight histologic modifications on distal colon.

Altered gut microbiota in Rett syndrome

BACKGROUND

The human gut microbiota directly affects human health, and its alteration can lead to gastrointestinal abnormalities and inflammation. Rett syndrome (RTT), a progressive neurological disorder mainly caused by mutations in MeCP2 gene, is commonly associated with gastrointestinal dysfunctions and constipation, suggesting a link between RTT's gastrointestinal abnormalities and the gut microbiota. The aim of this study was to evaluate the bacterial and fungal gut microbiota in a cohort of RTT subjects integrating clinical, metabolomics and metagenomics data to understand if changes in the gut microbiota of RTT subjects could be associated with gastrointestinal abnormalities and inflammatory status.

RESULTS

Our findings revealed the occurrence of an intestinal sub-inflammatory status in RTT subjects as measured by the elevated values of faecal calprotectin and erythrocyte sedimentation rate. We showed that, overall, RTT subjects harbour bacterial and fungal microbiota altered in terms of relative abundances from those of healthy controls, with a reduced microbial richness and dominated by microbial taxa belonging to Bifidobacterium, several Clostridia (among which Anaerostipes, Clostridium XIVa, Clostridium XIVb) as well as Erysipelotrichaceae, Actinomyces, Lactobacillus, Enterococcus, Eggerthella, Escherichia/Shigella and the fungal genus Candida. We further observed that alterations of the gut microbiota do not depend on the constipation status of RTT subjects and that this dysbiotic microbiota produced altered short chain fatty acids profiles.

CONCLUSIONS

We demonstrated for the first time that RTT is associated with a dysbiosis of both the bacterial and fungal component of the gut microbiota, suggesting that impairments of MeCP2 functioning favour the establishment of a microbial community adapted to the costive gastrointestinal niche of RTT subjects. The altered production of short chain fatty acids associated with this microbiota might reinforce the constipation status of RTT subjects and contribute to RTT gastrointestinal physiopathology.

Transcriptome Analysis and Postprandial Expression of Amino Acid Transporter Genes in the Fast Muscles and Gut of Chinese Perch (Siniperca chuatsi)

The characterization of the expression and regulation of growth-related genes in the muscles of Chinese perch is of great interest to aquaculturists because of the commercial value of the species. The transcriptome annotation of the skeletal muscles is a crucial step in muscle growth-related gene analysis. In this study, we generated 52 504 230 reads of mRNA sequence data from the fast muscles of the Chinese perch by using Solexa/Illumina RNA-seq. Twenty-one amino acid transporter genes were annotated by searching protein and gene ontology databases, and postprandial changes in their transcript abundance were assayed after administering a single satiating meal to Chinese perch juveniles (body mass, approximately 100 g), following fasting for 1 week. The gut content of the Chinese perch increased significantly after 1 h and remained high for 6 h following the meal and emptied within 48-96 h. Expression of eight amino acid transporter genes was assayed in the fast muscles through quantitative real-time polymerase chain reaction at 0, 1, 3, 6, 12, 24, 48, and 96 h. Among the genes, five transporter transcripts were markedly up-regulated within 1 h of refeeding, indicating that they may be potential candidate genes involved in the rapid-response signaling system regulating fish myotomal muscle growth. These genes display coordinated regulation favoring the resumption of myogenesis responding to feeding.

Gut Microbiota of Nonalcoholic Fatty Liver Disease

The prevalence of nonalcoholic fatty liver disease has been rapidly increasing worldwide. It has become a leading cause of liver transplantation. Accumulating evidence suggests a significant role for gut microbiota in its development and progression. Here we review the effect of gut microbiota on developing hepatic fatty infiltration and its progression. Current literature supports a possible role for gut microbiota in the development of liver steatosis, inflammation and fibrosis. We also review the literature on possible interventions for NAFLD that target the gut microbiota.

Detrimental effects for colonocytes of an increased exposure to luminal hydrogen sulfide: The adaptive response

Protein fermentation by the gut microbiota releases in the large intestine lumen various amino-acid derived metabolites. Among them, hydrogen sulfide (H2S) in excess has been suspected to be detrimental for colonic epithelium energy metabolism and DNA integrity. The first objective of this study was to evaluate in rats the epithelial response to an increased exposure to H2S. Experiments from colonocyte incubation and intra-colonic instillation indicate that low millimolar concentrations of the sulfide donor NaHS reversibly inhibited colonocyte mitochondrial oxygen consumption and increased gene expression of hypoxia inducible factor 1α (Hif-1α) together with inflammation-related genes namely inducible nitric oxide synthase (iNos) and interleukin-6 (Il-6). Additionally, rat colonocyte H2S detoxification capacity was severely impaired in the presence of nitric oxide. Based on the γH2AX ICW technique, NaHS did not induce DNA damage in colonocytes. Since H2S is notably produced by the gut microbiota from sulfur containing amino acids, the second objective of the study was to investigate the effects of a high protein diet (HPD) on large intestine luminal sulfide content and on the expression of genes involved in H2S detoxification in colonocytes. We found that HPD markedly increased H2S content in the large intestine but the concomitant increase of the content mass maintained the luminal sulfide concentration. HPD also provoked an increase of sulfide quinone reductase (Sqr) gene expression in colonocytes, indicating an adaptive response to increased H2S bacterial production. In conclusion, low millimolar NaHS concentration severely affects colonocyte respiration in association with increased expression of genes associated with intestinal inflammation. Although HPD increases the sulfide content of the large intestine, the colonic adaptive responses to this modification limit the epithelial exposure to this deleterious bacterial metabolite.

Changes of Mouse Gut Microbiota Diversity and Composition by Modulating Dietary Protein and Carbohydrate Contents: A Pilot Study

Dietary proteins influence colorectal cancer (CRC) risk, depending on their quantity and quality. Here, using pyrosequencing, we compared the fecal microbiota composition in Balb/c mice fed either a normal protein/carbohydrate diet (ND, 20% casein and 68% carbohydrate) or a high-protein/low-carbohydrate diet (HPLCD, 30% casein and 57% carbohydrate). The results showed that HPLCD feeding for 2 weeks reduced the diversity and altered the composition of the microbiota compared with the ND mice, which included a decrease in the proportion of the family Lachnospiraceae and Ruminococcaceae and increases in the proportions of the genus Bacteroides and Parabacteroides, especially the species EF09600_s and EF604598_s. Similar changes were reported in patients with inflammatory bowel disease, and in mouse models of CRC and colitis, respectively. This suggests that HPLCD may lead to a deleterious luminal environment and may have adverse effects on the intestinal health of individuals consuming such a diet.

Review article: insights into colonic protein fermentation, its modulation and potential health implications

BACKGROUND

Beneficial effects of carbohydrate fermentation on gastrointestinal health are well established. Conversely, protein fermentation generates harmful metabolites but their relevance to gastrointestinal health is poorly understood.

AIM

To review the effects of increased protein fermentation on biomarkers of colonic health, factors influencing fermentative activity and potential for dietary modulation to minimise detrimental effects.

METHODS

A literature search was performed in PubMed, Medline, EMBASE and Google scholar for clinical and pre-clinical studies using search terms - 'dietary protein', 'fermentation', 'putrefaction', 'phenols', 'sulphide', 'branched-chain fatty acid', 'carbohydrate fermentation', 'gastrointestinal'.

RESULTS

High protein, reduced carbohydrate diets alter the colonic microbiome, favouring a potentially pathogenic and pro-inflammatory microbiota profile, decreased short-chain fatty acid production and increased ammonia, phenols and hydrogen sulphide concentrations. These metabolites largely compromise the colonic epithelium structure, causing mucosal inflammation but may also directly modulate the enteric nervous system and intestinal motility. Increased protein fermentation as a result of a high-protein intake can be attenuated by addition of oligosaccharides, resistant starch and nonstarch polysaccharides and a reduction in total protein or specifically, aromatic and sulphur-containing amino acids. These factors may have clinical importance as novel therapeutic approaches to problems, in which protein fermentation may be implicated, such as malodorous flatus, irritable bowel syndrome, ulcerative colitis and prevention of colorectal cancer.

CONCLUSIONS

The direct clinical relevance of excessive protein fermentation in the pathogenesis of irritable bowel syndrome, malodorous flatus and ulcerative colitis are underexplored. Manipulating dietary carbohydrate and protein intake have potential therapeutic applications in such settings and warrant further clinical studies.

Effects of the dietary protein level on the microbial composition and metabolomic profile in the hindgut of the pig

The aim of this study was to investigate the effects of a long-term low protein diet on the microbial composition and metabolomic profile in the hindgut of the pig. Thirty-six Duroc × Landrace × Large White growing barrows (70 days of age, 23.57 ± 1.77 kg) were randomly allocated to normal protein diet (NP) and low protein diet (LP) groups using a randomized block design. At the age of 170 days, the digesta in the hindguts of the pigs were collected for microbial and metabolomic analysis. The results showed that there were no significant differences in the average daily gain, average daily feed intake, or feed:gain ratio between the NP and LP groups. The concentrations of isobutyrate, isovalerate, and branched-chain fatty acids (BCFAs)/short-chain fatty acids (SCFAs) in the cecum decreased with the reduction of dietary protein. Pyrosequencing of the V1-V3 region of the 16S rRNA genes showed that LP diet significantly decreased the relative abundance of Lactobacillus in the cecum, and Streptococcus in the colon; however, the relative abundance of Prevotella and Coprococcus in the LP group was significantly higher than in the NP group in the cecum, and Sarcina, Peptostreptococcaceae incertae sedis, Mogibacterium, Subdoligranulum, and Coprococcus was higher in the colon. The gas chromatography-mass spectrometry (GC-MS) analysis showed that the dietary protein level mainly affected phenylalanine metabolism; glycine, serine, and threonine metabolism; the citrate cycle; pyruvate metabolism; and the alanine, aspartate, and glutamate metabolism. Moreover, the correlation analysis of the combined datasets revealed some potential relationships between the colonic metabolites and certain microbial species. These results suggest that a low protein diet may modulate the microbial composition and metabolites of the hindgut, without affecting the growth performance of pigs; however, potential roles of this modulation to the health of pigs remains unknown.

Interactive Effects of Indigestible Carbohydrates, Protein Type, and Protein Level on Biomarkers of Large Intestine Health in Rats

The effects of indigestible carbohydrates, protein type, and protein level on large intestine health were examined in rats. For 21 days, 12 groups of six 12-week-old male Wistar rats were fed diets with casein (CAS), or potato protein concentrate (PPC), providing 14% (lower protein level; LP), or 20% (higher protein level; HP) protein, and containing cellulose, resistant potato starch, or pectin. Fermentation end-products, pH, and β-glucuronidase levels in cecal digesta, and ammonia levels in colonic digesta were determined. Cecal digesta, tissue weights, cecal and colon morphology, and colonocyte DNA damage were also analyzed. Digesta pH was lower, whereas relative mass of cecal tissue and digesta were higher in rats fed pectin diets than in those fed cellulose. Cecal parameters were greater in rats fed PPC and HP diets than in those fed CAS and LP diets, respectively. Short-chain fatty acid (SCFA) concentrations were unaffected by protein or carbohydrate type. Total SCFA, acetic acid, and propionic acid concentrations were greater in rats fed LP diets than in those fed HP. Cecal pool of isobutyric and isovaleric acids was greater in rats fed PPC than in those fed CAS diets. PPC diets decreased phenol concentration and increased ammonia concentration in cecal and colonic digesta, respectively. Cecal crypt depth was greater in rats fed PPC and HP diets, and was unaffected by carbohydrates; whereas colonic crypt depth was greater in rats fed cellulose. Myenteron thickness in the cecum was unaffected by nutrition, but was greater in the colon of rats fed cellulose. Colonocyte DNA damage was greater in rats fed LP diets than in those fed HP diets, and was unaffected by carbohydrate or protein type. It was found that nutritional factors decreasing cecal digesta weight contribute to greater phenol production, increased DNA damage, and reduced ammonia concentration in the colon.

Diet drives quick changes in the metabolic activity and composition of human gut microbiota in a validated in vitro gut model

The aim of this study was to screen how rapidly the human gut microbiota responds to diet in an in vitro model of the proximal colon (TIM-2 system). Two experimental diets were provided to the gut bacteria: a high carbohydrate and a high protein diet. The metabolic response and the composition of the microbiota were compared to a control diet simulating an average western meal. Short-chain and branched-chain fatty acids (SCFA and BCFA, respectively) production, in addition to changes in the community composition (profiling), were measured. The activity of the microbiota reflected differences between diets, exhibiting a trade-off between saccharolytic and proteolytic fermentation when compared to the control. Diversity analysis revealed a phylum-specific response depending on the diet tested. Most changes in the microbiome composition occurred during the first 24 h of the experiment. The outcome of this study elucidates the fact that human gut bacteria quickly respond to changes in diet. In addition, it confirms that variations in the concentration of carbohydrates and proteins modify the activity and composition of the microbiota, and these changes can potentially have an impact on the health of the host.

Dietary flaxseed modulates the colonic microenvironment in healthy C57Bl/6 male mice which may alter susceptibility to gut-associated diseases

Understanding how dietary components alter the healthy baseline colonic microenvironment is important in determining their roles in influencing gut health and gut-associated diseases. Dietary flaxseed (FS) has demonstrated anti-colon cancer effects in numerous rodent models, however, exacerbated acute colonic mucosal injury and inflammation in a colitis model. This study investigates whether FS alters critical aspects of gut health in healthy unchallenged mice, which may help explain some of the divergent effects observed following different gut-associated disease challenges. Four-week-old C57Bl/6 male mice were fed an AIN-93G basal diet (BD) or an isocaloric BD+10% ground FS diet for 3 weeks. FS enhanced colon goblet cell density, mucus production, MUC2 mRNA expression, and cecal short chain fatty acid levels, indicative of beneficial intestinal barrier integrity responses. Additionally, FS enhanced colonic regenerating islet-derived protein 3 gamma (RegIIIγ) and reduced MUC1 and resistin-like molecule beta (RELMβ) mRNA expression which may indicate altered responses in regulating microbial defense and injury repair responses. FS diet altered the fecal microbial community structure (16S rRNA gene profiling), including a 20-fold increase in Prevotella spp. and a 30-fold reduction in Akkermansia muciniphila abundance. A 10-fold reduction in A. muciniphila abundance by FS was also demonstrated in the colon tissue-associated microbiota (quantitative PCR). Furthermore, fecal branched chain fatty acids were increased by FS, indicative of increased microbial-derived putrefactive compounds. In conclusion, consumption of a FS-supplemented diet alters the baseline colonic microenvironment of healthy mice which may modify subsequent mucosal microbial defense and injury-repair responses leading to altered susceptibility to different gut-associated diseases.

High True Ileal Digestibility but Not Postprandial Utilization of Nitrogen from Bovine Meat Protein in Humans Is Moderately Decreased by High-Temperature, Long-Duration Cooking

BACKGROUND

Meat protein digestibility can be impaired because of indigestible protein aggregates that form during cooking. When the aggregates are subsequently fermented by the microbiota, they can generate potentially harmful compounds for the colonic mucosa.

OBJECTIVE

This study evaluated the quantity of bovine meat protein escaping digestion in the human small intestine and the metabolic fate of exogenous nitrogen, depending on cooking processes.

METHODS

Sixteen volunteers (5 women and 11 men; aged 28 ± 8 y) were equipped with a double lumen intestinal tube positioned at the ileal level. They received a test meal exclusively composed of 120 g of intrinsically (15)N-labeled bovine meat, cooked either at 55°C for 5 min (n = 8) or at 90°C for 30 min (n = 8). Ileal effluents and blood and urine samples were collected over an 8-h period after the meal ingestion, and (15)N enrichments were measured to assess the digestibility of meat proteins and the transfer of dietary nitrogen into the metabolic pools.

RESULTS

Proteins tended to be less digestible for the meat cooked at 90°C for 30 min than at 55°C for 5 min (90.1% ± 2.1% vs. 94.1% ± 0.7% of ingested N; P = 0.08). However, the particle number and size in ileal digesta did not differ between groups. The appearance of variable amounts of intact fibers was observed by microscopy. The kinetics of (15)N appearance in plasma proteins, amino acids, and urea were similar between groups. The amount of exogenous nitrogen lost through deamination did not differ between groups (21.2% ± 0.8% of ingested N).

CONCLUSIONS

Cooking bovine meat at a high temperature for a long time can moderately decrease protein digestibility compared with cooking at a lower temperature for a short time and does not affect postprandial exogenous protein metabolism in young adults. The study was registered at www.clinicaltrials.gov as NCT01685307.

Short-chain fatty acids in control of body weight and insulin sensitivity

The connection between the gut microbiota and the aetiology of obesity and cardiometabolic disorders is increasingly being recognized by clinicians. Our gut microbiota might affect the cardiometabolic phenotype by fermenting indigestible dietary components and thereby producing short-chain fatty acids (SCFA). These SCFA are not only of importance in gut health and as signalling molecules, but might also enter the systemic circulation and directly affect metabolism or the function of peripheral tissues. In this Review, we discuss the effects of three SCFA (acetate, propionate and butyrate) on energy homeostasis and metabolism, as well as how these SCFA can beneficially modulate adipose tissue, skeletal muscle and liver tissue function. As a result, these SCFA contribute to improved glucose homeostasis and insulin sensitivity. Furthermore, we also summarize the increasing evidence for a potential role of SCFA as metabolic targets to prevent and counteract obesity and its associated disorders in glucose metabolism and insulin resistance. However, most data are derived from animal and in vitro studies, and consequently the importance of SCFA and differential SCFA availability in human energy and substrate metabolism remains to be fully established. Well-controlled human intervention studies investigating the role of SCFA on cardiometabolic health are, therefore, eagerly awaited.

Metabolic and Microbial Modulation of the Large Intestine Ecosystem by Non-Absorbed Diet Phenolic Compounds: A Review

Phenolic compounds represent a diverse group of phytochemicals whose intake is associated with a wide spectrum of health benefits. As consequence of their low bioavailability, most of them reach the large intestine where, mediated by the action of local microbiota, a series of related microbial metabolites are accumulated. In the present review, gut microbial transformations of non-absorbed phenolic compounds are summarized. Several studies have reached a general consensus that unbalanced diets are associated with undesirable changes in gut metabolism that could be detrimental to intestinal health. In terms of explaining the possible effects of non-absorbed phenolic compounds, we have also gathered information regarded their influence on the local metabolism. For this purpose, a number of issues are discussed. Firstly, we consider the possible implications of phenolic compounds in the metabolism of colonic products, such as short chain fatty acids (SCFA), sterols (cholesterol and bile acids), and microbial products of non-absorbed proteins. Due to their being recognized as affective antioxidant and anti-inflammatory agents, the ability of phenolic compounds to counteract or suppress pro-oxidant and/or pro-inflammatory responses, triggered by bowel diseases, is also presented. The modulation of gut microbiota through dietetic maneuvers including phenolic compounds is also commented on. Although the available data seems to assume positive effects in terms of gut health protection, it is still insufficient for solid conclusions to be extracted, basically due to the lack of human trials to confirm the results obtained by the in vitro and animal studies. We consider that more emphasis should be focused on the study of phenolic compounds, particularly in their microbial metabolites, and their power to influence different aspects of gut health.

Co-dependence of genotype and dietary protein intake to affect expression on amino acid/peptide transporters in porcine skeletal muscle

A total of 96 barrows (48 pure-bred Bama mini-pigs representing fatty genotype, and 48 Landrace pigs representing lean genotype) were randomly assigned to either a low- or adequate-protein treatment diet. The experimental period commenced at 5 weeks of age and extended to the finishing period. After euthanasia, blood and skeletal muscle samples were collected from pigs at the nursery, growing, and finishing phases. Our results indicate that the concentrations of free AAs in the plasma and muscle decreased as the age of the pigs increased. In addition, a strain × growth phase interaction (P < 0.05) was observed for the free AA pool in the plasma and muscle. The low-protein diet upregulated (P < 0.05) the mRNA levels for T1R1/T1R3 involved in glutamate binding, but downregulated (P < 0.05) the mRNA levels for PAT1, PAT2, and ASCT2, which transport neutral AAs into muscles. Bama mini-pigs had higher (P < 0.05) mRNA levels for LAT1, SNAT2, and EAAC1, but a lower (P < 0.05) mRNA level for PepT1, compared with Landrace pigs. Collectively, our findings indicate that adequate provision of dietary protein plays an important role in regulating profiles of free AA pools and expression of key AA/peptide transporters/transceptors in a genotype- and tissue-specific manner.

Effects of Dietary Different Doses of Copper and High Fructose Feeding on Rat Fecal Metabolome

The gut microbiota plays a critical role in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). Increased fructose consumption and inadequate copper intake are two critical risk factors in the development of NAFLD. To gain insight into the role of gut microbiota, fecal metabolites, obtained from rats exposed to different dietary levels of copper with and without high fructose intake for 4 weeks, were analyzed by comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC × GC-TOF MS). In parallel, liver tissues were assessed by histology and triglyceride assay. Our data showed that high fructose feeding led to obvious hepatic steatosis in both marginal copper deficient rats and copper supplementation rats. Among the 38 metabolites detected with significant abundance alteration between groups, short chain fatty acids were markedly decreased with excessive fructose intake irrespective of copper levels. C15:0 and C17:0 long chain fatty acids, produced only by bacteria, were increased by either high copper level or high fructose intake. In addition, increased fecal urea and malic acid paralleled the increased hepatic fat accumulation. Collectively, GC × GC-TOF MS analysis of rat fecal samples revealed distinct fecal metabolome profiles associated with the dietary high fructose and copper level, with some metabolites possibly serving as potential noninvasive biomarkers of fructose induced-NAFLD.

The deleterious metabolic and genotoxic effects of the bacterial metabolite p-cresol on colonic epithelial cells

p-Cresol that is produced by the intestinal microbiota from the amino acid tyrosine is found at millimolar concentrations in the human feces. The effects of this metabolite on colonic epithelial cells were tested in this study. Using the human colonic epithelial HT-29 Glc(-/+) cell line, we found that 0.8mM p-cresol inhibits cell proliferation, an effect concomitant with an accumulation of the cells in the S phase and with a slight increase of cell detachment without necrotic effect. At this concentration, p-cresol inhibited oxygen consumption in HT-29 Glc(-/+) cells. In rat normal colonocytes, p-cresol also inhibited respiration. Pretreatment of HT-29 Glc(-/+) cells with 0.8mM p-cresol for 1 day resulted in an increase of the state 3 oxygen consumption and of the cell maximal respiratory capacity with concomitant increased anion superoxide production. At higher concentrations (1.6 and 3.2mM), p-cresol showed similar effects but additionally increased after 1 day the proton leak through the inner mitochondrial membrane, decreasing the mitochondrial bioenergetic activity. At these concentrations, p-cresol was found to be genotoxic toward HT-29 Glc(-/+) and also LS-174T intestinal cells. Lastly, a decreased ATP intracellular content was observed after 3 days treatment. p-Cresol at 0.8mM concentration inhibits colonocyte respiration and proliferation. In response, cells can mobilize their "respiratory reserve." At higher concentrations, p-cresol pretreatment uncouples cell respiration and ATP synthesis, increases DNA damage, and finally decreases the ATP cell content. Thus, we have identified p-cresol as a metabolic troublemaker and as a genotoxic agent toward colonocytes.

Towards microbial fermentation metabolites as markers for health benefits of prebiotics

Available evidence on the bioactive, nutritional and putative detrimental properties of gut microbial metabolites has been evaluated to support a more integrated view of how prebiotics might affect host health throughout life. The present literature inventory targeted evidence for the physiological and nutritional effects of metabolites, for example, SCFA, the potential toxicity of other metabolites and attempted to determine normal concentration ranges. Furthermore, the biological relevance of more holistic approaches like faecal water toxicity assays and metabolomics and the limitations of faecal measurements were addressed. Existing literature indicates that protein fermentation metabolites (phenol, p-cresol, indole, ammonia), typically considered as potentially harmful, occur at concentration ranges in the colon such that no toxic effects are expected either locally or following systemic absorption. The endproducts of saccharolytic fermentation, SCFA, may have effects on colonic health, host physiology, immunity, lipid and protein metabolism and appetite control. However, measuring SCFA concentrations in faeces is insufficient to assess the dynamic processes of their nutrikinetics. Existing literature on the usefulness of faecal water toxicity measures as indicators of cancer risk seems limited. In conclusion, at present there is insufficient evidence to use changes in faecal bacterial metabolite concentrations as markers of prebiotic effectiveness. Integration of results from metabolomics and metagenomics holds promise for understanding the health implications of prebiotic microbiome modulation but adequate tools for data integration and interpretation are currently lacking. Similarly, studies measuring metabolite fluxes in different body compartments to provide a more accurate picture of their nutrikinetics are needed.

Effects of low dietary protein on the metabolites and microbial communities in the caecal digesta of piglets

Thirty-six healthy piglets (weighing 10 ± 1 kg; three animals per pen) were randomly allocated to two treatments: (i) a low protein diet (14% crude protein [CP]) supplemented with lysine, methionine, threonine and tryptophan (Group LP) and (ii) a normal protein diet (20% CP, Group NP), resulting in six replicate pens per treatment. One piglet from each pen was slaughtered at days 10, 25 and 45 of the experiment. For the whole experimental period of 45 d, Group LP had lower feed intake and daily gain and a higher feed-to-gain ratio compared with Group NP. At day 10, no effects on measured caecum metabolites were observed, but at days 25 and 45 in Group LP the concentration of ammonia-N, cadaverine, branched chain fatty acids and acetate were reduced. This was also true for the concentration of short chain fatty acids at day 45. The results of denaturing gradient gel electrophoresis showed that microbial diversity in Group LP was less abundant at day 25, but there was no difference at days 10 and 45. An unweighted pair group mean average analysis showed that the similarities were lower between Groups LP and NP at day 10 and higher at days 25 and 45. Quantitation results indicated that the numbers of Firmicutes and Clostridium cluster IV were lower in Group LP than in Group NP at day 25, but there were no differences at days 10 and 45. In conclusion, the low protein diet markedly reduced the metabolites of protein and carbohydrate fermentation and altered microbial communities in the caecal digesta of piglets.

The role of microbial amino acid metabolism in host metabolism

Disruptions in gut microbiota composition and function are increasingly implicated in the pathogenesis of obesity, insulin resistance, and type 2 diabetes mellitus. The functional output of the gut microbiota, including short-chain fatty acids and amino acids, are thought to be important modulators underlying the development of these disorders. Gut bacteria can alter the bioavailability of amino acids by utilization of several amino acids originating from both alimentary and endogenous proteins. In turn, gut bacteria also provide amino acids to the host. This could have significant implications in the context of insulin resistance and type 2 diabetes mellitus, conditions associated with elevated systemic concentrations of certain amino acids, in particular the aromatic and branched-chain amino acids. Moreover, several amino acids released by gut bacteria can serve as precursors for the synthesis of short-chain fatty acids, which also play a role in the development of obesity. In this review, we aim to compile the available evidence on the contribution of microbial amino acids to host amino acid homeostasis, and to assess the role of the gut microbiota as a determinant of amino acid and short-chain fatty acid perturbations in human obesity and type 2 diabetes mellitus.

The risks of self-made diets: the case of an amateur bodybuilder

BACKGROUND

Following DIY (do it yourself) diets as well as consuming supplements exceeding by far the recommended daily intake levels, is common among athletes; these dietary habits often lead to an overconsumption of some macro and/or micronutrients, exposing athletes to potential health risks. The aim of this study is to document the development of possible adverse effects in a 33 year-old amateur bodybuilder who consumed for 16 years a DIY high protein diet associated to nutrient supplementation. Body composition, biochemical measures and anamnestic findings were evaluated. We present this case to put on alert about the possible risks of such behavior repeated over time, focusing on the adverse gastrointestinal effects. We discuss the energy and nutrient composition of his DIY diet as well as the use of supplements.

CONCLUSION

This study provides preliminary data of the potential risks of a long-term DIY dietary supplementation and a high protein diet. In this case, permanent abdominal discomfort was evidenced in an amateur body builder with an intake exceeding tolerable upper limit for vitamin A, selenium and zinc, according to our national and updated recommendations. As many amateur athletes usually adopt self-made diets and supplementation, it would be advisable for them to be supervised in order to prevent health risks due to a long-term DIY diet and over-supplementation.

Pilot dietary intervention with heat-stabilized rice bran modulates stool microbiota and metabolites in healthy adults

Heat-stabilized rice bran (SRB) has been shown to regulate blood lipids and glucose, modulate gut mucosal immunity and inhibit colorectal cancer in animal and human studies. However, SRB’s effects on gut microbial composition and metabolism and the resulting implications for health remain largely unknown. A pilot, randomized-controlled trial was developed to investigate the effects of eating 30 g/day SRB on the stool microbiome and metabolome. Seven healthy participants consumed a study meal and snack daily for 28 days. The microbiome and metabolome were characterized using 454 pyrosequencing and gas chromatography-mass spectrometry (GC-MS) at baseline, two and four weeks post-intervention. Increases in eight operational taxonomic units (OTUs), including three from Bifidobacterium and Ruminococcus genera, were observed after two and four weeks of SRB consumption (p < 0.01). Branched chain fatty acids, secondary bile acids and eleven other putative microbial metabolites were significantly elevated in the SRB group after four weeks. The largest metabolite change was a rice bran component, indole-2-carboxylic acid, which showed a mean 12% increase with SRB consumption. These data support the feasibility of dietary SRB intervention in adults and support that SRB consumption can affect gut microbial metabolism. These findings warrant future investigations of larger cohorts evaluating SRB’s effects on intestinal health.

Down-regulation of monocarboxylate transporter 1 (MCT1) gene expression in the colon of piglets is linked to bacterial protein fermentation and pro-inflammatory cytokine-mediated signalling

The present study investigated the influence of bacterial metabolites on monocarboxylate transporter 1 (MCT1) expression in pigs using in vivo, ex vivo and in vitro approaches. Piglets (n 24) were fed high-protein (26 %) or low-protein (18 %) diets with or without fermentable carbohydrates. Colonic digesta samples were analysed for a broad range of bacterial metabolites. The expression of MCT1, TNF-α, interferon γ (IFN-γ) and IL-8 was determined in colonic tissue. The expression of MCT1 was lower and of TNF-α and IL-8 was higher with high-protein diets (P< 0·05). MCT1 expression was positively correlated with l-lactate, whereas negatively correlated with NH₃ and putrescine (P< 0·05). The expression of IL-8 and TNF-α was negatively correlated with l-lactate and positively correlated with NH₃ and putrescine, whereas the expression of IFN-γ was positively correlated with histamine and 4-ethylphenol (P< 0·05). Subsequently, porcine colonic tissue and Caco-2 cells were incubated with Na-butyrate, NH₄Cl or TNF-α as selected bacterial metabolites or mediators of inflammation. Colonic MCT1 expression was higher after incubation with Na-butyrate (P< 0·05) and lower after incubation with NH₄Cl or TNF-α (P< 0·05). Incubation of Caco-2 cells with increasing concentrations of these metabolites confirmed the up-regulation of MCT1 expression by Na-butyrate (linear, P< 0·05) and down-regulation by TNF-α and NH₄Cl (linear, P< 0·05). The high-protein diet decreased the expression of MCT1 in the colon of pigs, which appears to be linked to NH₃- and TNF-α-mediated signalling.

Amino acid metabolism in intestinal bacteria and its potential implications for mammalian reproduction

Reproduction is vital for producing offspring and preserving genetic resources. However, incidences of many reproductive disorders (e.g. miscarriage, intrauterine growth restriction, premature delivery and lower sperm quality) have either increased dramatically or remained at high rates over the last decades. Mounting evidence shows a strong correlation between enteral protein nutrition and reproduction. Besides serving as major nutrients in the diet, amino acids (AA) are signaling molecules in the regulation of diverse physiological processes, ranging from spermatogenesis to oocyte fertilization and to embryo implantation. Notably, the numbers of bacteria in the intestine exceed the numbers of host cells by 10 times. Microbes in the small-intestinal lumen actively metabolize large amounts of dietary AA and, therefore, affect the entry of AA into the portal circulation for whole-body utilization. Changes in the composition and abundance of AA-metabolizing bacteria in the gut during pregnancy, as well as their translocation to the uterus, may alter uterine function and epigenetic modifications of maternal physiology and metabolism, which are crucial for pregnancy recognition and fetal development. Thus, the presence of the maternal gut microbiota and AA metabolites in the intrauterine environments (e.g. endometrium and placenta) and breast milk is likely a unique signature for the programming of the whole-body microbiome and metabolism in both the fetus and infant. Dietary intervention with functional AA, probiotics and prebiotics to alter the abundance and activity of intestinal bacteria may ameliorate or prevent the development of metabolic syndrome, while improving reproductive performance in both males and females as well as their offspring.

Alteration of the fecal microbiota and serum metabolite profiles in dogs with idiopathic inflammatory bowel disease

Idiopathic inflammatory bowel disease (IBD) is a common cause of chronic gastrointestinal (GI) disease in dogs. The combination of an underlying host genetic susceptibility, an intestinal dysbiosis, and dietary/environmental factors are suspected as main contributing factors in the pathogenesis of canine IBD. However, actual mechanisms of the host-microbe interactions remain elusive. The aim of this study was to compare the fecal microbiota and serum metabolite profiles between healthy dogs (n = 10) and dogs with IBD before and after 3 weeks of medical therapy (n = 12). Fecal microbiota and metabolite profiles were characterized by 454-pyrosequencing of 16 S rRNA genes and by an untargeted metabolomics approach, respectively. Significantly lower bacterial diversity and distinct microbial communities were observed in dogs with IBD compared to the healthy control dogs. While Gammaproteobacteria were overrepresented, Erysipelotrichia, Clostridia, and Bacteroidia were underrepresented in dogs with IBD. The functional gene content was predicted from the 16 S rRNA gene data using PICRUSt, and revealed overrepresented bacterial secretion system and transcription factors, and underrepresented amino acid metabolism in dogs with IBD. The serum metabolites 3-hydroxybutyrate, hexuronic acid, ribose, and gluconic acid lactone were significantly more abundant in dogs with IBD. Although a clinical improvement was observed after medical therapy in all dogs with IBD, this was not accompanied by significant changes in the fecal microbiota or in serum metabolite profiles. These results suggest the presence of oxidative stress and a functional alteration of the GI microbiota in dogs with IBD, which persisted even in the face of a clinical response to medical therapy.

Dietary fibre and crude protein: impact on gastrointestinal microbial fermentation characteristics and host response

The role of the gastrointestinal tract microbiota in animal health and nutrition has become the subject of intensive research. Carbohydrates and crude protein are major components of swine diets and numerous studies have been performed looking at the effect of inclusion of dietary fibre with possible functional properties. In recent years, our understanding of the diversity and functionality of the gastrointestinal tract microbiota has increased further enabling the possibility for their targeted modulation. However, favouring potential beneficial bacteria, inhibiting possible pathogens or promotion of the formation of desired metabolites, is complex and underlies many factors and uncertainties. Approaches targeting this complex ecosystem (and discussed in this review) include the utilisation of fermentable carbohydrates such as resistant starch, cereal 1–3/1–4 β-glucans, arabinoxylans, inulin or other sources from legumes and industrial by-products. In addition, strategies regarding protein level and the protein : carbohydrate ratio are discussed briefly. Results are both promising and sometimes rather disillusioning considering the dietary concentrations needed to show biologically relevant effects. Deriving recommendations for an optimal inclusion rate of dietary fibre for weaning, growing pigs and sows and maximum levels for dietary crude protein may be one of the main challenges in the near future in the swine industry.

Functional short-chain carbohydrates (prebiotics) in the diet to improve the microbiome and health of the gastrointestinal tract

Advancement in technologies to identify and quantify bacterial species in the gastrointestinal tract has escalated interest in its microbiome worldwide. There is enormous interest in understanding the roles that bacterial species play in gastrointestinal health and overall wellbeing. What constitutes a ‘healthy gut microbiome’ includes: favourable fermentation-dependent characteristics such as butyrate supply to all regions, minimisation of putrefaction of proteins, and adequate laxation. The relative abundance of specific bacterial species with certain functional characteristics is also important and include: traditional prebiotic bacteria – Bifidobacteria; strongly butyrate-producing – Clostridium coccoides and Faecalibacterium prausnitzi as well as a mucus-associated bacterium Akkermansia muciniphila. Manipulation of diet and dietary factors may be essential to favourably influence these fermentation-dependent parameters and select for growth of beneficial bacterial species. In this regard, this laboratory has identified indigestible oligosaccharides with prebiotic effects and now has an extensive database that quantifies indigestible oligosaccharides in a wide variety of foods including whole grains, cereals, legumes, seeds, nuts, fruits and vegetables. Future research in this area should consider the role of dietary components that best establish and maintain a ‘healthy gut microbiome’.

Mucosal healing in inflammatory bowel diseases: is there a place for nutritional supplementation?

Advanced mucosal healing (MH) after intestinal mucosal inflammation coincides with sustained clinical remission and reduced rates of hospitalization and surgical resection, explaining why MH is increasingly considered as a full therapeutic goal and as an endpoint for clinical trials. Intestinal MH is a complex phenomenon viewed as a succession of steps necessary to restore tissue structure and function. These steps include epithelial cell migration and proliferation, cell differentiation, restoration of epithelial barrier functions, and modulation of cell apoptosis. Few clinical studies have evaluated the needs for specific macronutrients and micronutrients and their effects on intestinal MH, most data having been obtained from animal and cell studies. These data suggest that supplementation with specific amino acids including arginine, glutamine, glutamate, threonine, methionine, serine, proline, and the amino acid-derived compounds, polyamines can favorably influence MH. Short-chain fatty acids, which are produced by the microbiota from undigested polysaccharides and protein-derived amino acids, also exert beneficial effects on the process of intestinal MH in experimental models. Regarding supplementation with lipids, although the effects of ω-3 and ω-6 fatty acids remain controversial, endogenous prostaglandin synthesis seems to be necessary for MH. Finally, among micronutrients, several vitamin and mineral deficiencies with different frequencies have been observed in patients with inflammatory bowel diseases and supplementation with some of them (vitamin A, vitamin D3, vitamin C, and zinc) are presumed to favor MH. Future work, including clinical studies, should evaluate the efficiency of supplementation with combination of dietary compounds as adjuvant nutritional intervention for MH of the inflamed intestinal mucosa.

High-protein diet differently modifies intestinal goblet cell characteristics and mucosal cytokine expression in ileum and colon

We have previously shown that high-protein (HP) diet ingestion causes marked changes in the luminal environment of the colonic epithelium. This study aimed to evaluate the impact of such modifications on small intestinal and colonic mucosa, two segments with different transit time and physiological functions. Rats were fed with either normal protein (NP; 14% protein) or HP (53% protein) isocaloric diet for 2 weeks, and parameters related to intestinal mucous-secreting cells and to several innate/adaptive immune characteristics (myeloperoxidase activity, cytokine and epithelial TLR expression, proportion of immune cells in gut-associated lymphoid tissues) were measured in the ileum and colon. In ileum from HP animals, we observed hyperplasia of mucus-producing cells concomitant with an increased expression of Muc2 at both gene and protein levels, reduction of mucosal myeloperoxidase activity, down-regulation of Tlr4 gene expression in enterocytes and down-regulation of mucosal Th cytokines associated with CD4+ lymphocyte reduction in mesenteric lymph nodes. These changes coincided with an increased amount of acetate in the ileal luminal content. In colon, HP diet ingestion resulted in a lower number of goblet cells at the epithelial surface but increased goblet cell number in colonic crypts together with an increased Muc3 and a slight reduction of Il-6 gene expression. Our data suggest that HP diet modifies the goblet cell distribution in colon and, in ileum, increases goblet cell activity and decreases parameters related to basal gut inflammatory status. The impact of HP diet on intestinal mucosa in terms of beneficial or deleterious effects is discussed.

Dietary supplementation with soybean oligosaccharides increases short-chain fatty acids but decreases protein-derived catabolites in the intestinal luminal content of weaned Huanjiang mini-piglets

The improvement of gut health and function with prebiotic supplements after weaning is an active area of research in pig nutrition. The present study was conducted to test the working hypothesis that medium-term dietary supplementation with soybean oligosaccharides (SBOS) can affect the gut ecosystem in terms of microbiota composition, luminal bacterial short-chain fatty acid and ammonia concentrations, and intestinal expression of genes related to intestinal immunity and barrier function. Ten Huanjiang mini-piglets, weaned at 21 days of age, were randomly assigned to 2 groups. Each group received a standard diet containing either dietary supplementation with 0.5% corn starch (control group) or 0.5% SBOS (experimental group). The results showed that dietary supplementation with SBOS increased the diversity of intestinal microflora and elevated (P < .05) the numbers of some presumably beneficial intestinal bacteria (e.g., Bifidobacterium sp, Faecalibacterium prausnitzii, Fusobacterium prausnitzii, and Roseburia). Soybean oligosaccharide supplementation also increased the concentration of short-chain fatty acid in the intestinal lumen, and it reduced (P < .05) the numbers of bacteria with pathogenic potential (e.g., Escherichia coli, Clostridium, and Streptococcus) and the concentration of several protein-derived catabolites (e.g., isobutyrate, isovalerate, and ammonia). In addition, SBOS supplementation increased (P < .05) expression of zonula occludens 1 messenger RNA, and it decreased (P < .05) expression of tumor necrosis factor α, interleukin 1β, and interleukin 8 messenger RNA in the ileum and colon. These findings suggest that SBOS supplementation modifies the intestinal ecosystem in weaned Huanjiang mini-piglets and has potentially beneficial effects on the gut.

High-protein diet modifies colonic microbiota and luminal environment but not colonocyte metabolism in the rat model: the increased luminal bulk connection

High-protein diets are used for body weight reduction, but consequences on the large intestine ecosystem are poorly known. Here, rats were fed for 15 days with either a normoproteic diet (NP, 14% protein) or a hyperproteic-hypoglucidic isocaloric diet (HP, 53% protein). Cecum and colon were recovered for analysis. Short- and branched-chain fatty acids, as well as lactate, succinate, formate, and ethanol contents, were markedly increased in the colonic luminal contents of HP rats (P < 0.05 or less) but to a lower extent in the cecal luminal content. This was associated with reduced concentrations of the Clostridium coccoides and C. leptum groups and Faecalibacterium prausnitzii in both the cecum and colon (P < 0.05 or less). In addition, the microbiota diversity was found to be higher in the cecum of HP rats but was lower in the colon compared with NP rats. In HP rats, the colonic and cecal luminal content weights were markedly higher than in NP rats (P < 0.001), resulting in similar butyrate, acetate, and propionate concentrations. Accordingly, the expression of monocarboxylate transporter 1 and sodium monocarboxylate transporter 1 (which is increased by higher butyrate concentration) as well as the colonocyte capacity for butyrate oxidation were not modified by the HP diet, whereas the amount of butyrate in feces was increased (P < 0.01). It is concluded that an increased bulk in the large intestine content following HP diet consumption allows maintenance in the luminal butyrate concentration and thus its metabolism in colonocytes despite modified microbiota composition and increased substrate availability.

Chlorogenic acid decreases intestinal permeability and increases expression of intestinal tight junction proteins in weaned rats challenged with LPS

Chlorogenic acid, a natural phenolic acid present in fruits and plants, provides beneficial effects for human health. The objectives of this study were to investigate whether chlorogenic acid (CHA) could improve the intestinal barrier integrity for weaned rats with lipopolysaccharide (LPS) challenge. Thirty-two weaned male Sprague Dawley rats (21±1 d of age; 62.26±2.73 g) were selected and randomly allotted to four treatments, including weaned rat control, LPS-challenged and chlorogenic acid (CHA) supplemented group (orally 20 mg/kg and 50 mg/kg body). Dietary supplementation with CHA decreased (P<0.05) the concentrations of urea and albumin in the serum, compared to the LPS-challenged group. The levels of IFN-γ and TNF-α were lower (P<0.05) in the jejunal and colon of weaned rats receiving CHA supplementation, in comparison with the control group. CHA supplementation increased (P<0.05) villus height and the ratio of villus height to crypt depth in the jejunal and ileal mucosae under condictions of LPS challenge. CHA supplementation decreased (P<0.05) intestinal permeability, which was indicated by the ratio of lactulose to mannitol and serum DAO activity, when compared to weaned rats with LPS challenge. Immunohistochemical analysis of tight junction proteins revealed that ZO-1 and occludin protein abundances in the jejunum and colon were increased (P<0.05) by CHA supplementation. Additionally, results of immunoblot analysis revealed that the amount of occludin in the colon was also increased (P<0.05) in CHA-supplemented rats. In conclusion, CHA decreases intestinal permeability and increases intestinal expression of tight junction proteins in weaned rats challenged with LPS.

Nonprotein nitrogen is absorbed from the large intestine and increases nitrogen balance in growing pigs fed a valine-limiting diet

Nitrogen absorption from the large intestine, largely as ammonia and possibly as amino acids (AAs), is generally thought to be of little nutritional value to nonruminant animals and humans. Ammonia-nitrogen absorbed from the large intestine, however, may be recycled into the small intestine as urea and incorporated into microbial AAs, which may then be used by the host. A cecal infusion study was performed to determine the form in which nitrogen is absorbed from the large intestine and the impact of large intestine nitrogen supply on nitrogen balance in growing pigs. Eighteen cecally cannulated barrows (initial body weight: 22.4 ± 1.2 kg) were used to determine the effect of supplying nitrogen into the large intestine from either casein or urea on whole-body nitrogen retention and urea kinetics. Treatments were cecal infusions of saline (control), casein, or urea with nitrogen infused at a rate of 40% of nitrogen intake. In a subsample of 9 pigs, (15)N(15)N-urea was infused via i.v. during the nitrogen-balance period to determine urea kinetics. All pigs were fed a valine-limiting cornstarch-soybean meal-based diet. More than 80% of infused nitrogen was apparently absorbed. Urea flux and urinary nitrogen excretion increased (P ≤ 0.05) by the same amount for both nitrogen sources, but this increase did not fully account for the increase in nitrogen absorption from the large intestine. Whole-body nitrogen retention improved with nitrogen infusions (129 vs. 114 g/d; P < 0.01) and did not differ (P > 0.05) between nitrogen sources. Absorption of nitrogen from the large intestine appears to be in the form of nonprotein nitrogen, which appears to be returned to the small intestine via urea and used there for microbial AA production and should therefore be considered when determining nitrogen and AA supply and requirements.

Commensal bacteria-dependent indole production enhances epithelial barrier function in the colon

Microbiota have been shown to have a great influence on functions of intestinal epithelial cells (ECs). The role of indole as a quorum-sensing (QS) molecule mediating intercellular signals in bacteria has been well appreciated. However, it remains unknown whether indole has beneficial effects on maintaining intestinal barriers in vivo. In this study, we analyzed the effect of indole on ECs using a germ free (GF) mouse model. GF mice showed decreased expression of junctional complex molecules in colonic ECs. The feces of specific pathogen-free (SPF) mice contained a high amount of indole; however the amount was significantly decreased in the feces of GF mice by 27-fold. Oral administration of indole-containing capsules resulted in increased expression of both tight junction (TJ)- and adherens junction (AJ)-associated molecules in colonic ECs in GF mice. In accordance with the increased expression of these junctional complex molecules, GF mice given indole-containing capsules showed higher resistance to dextran sodium sulfate (DSS)-induced colitis. A similar protective effect of indole on DSS-induced epithelial damage was also observed in mice bred in SPF conditions. These findings highlight the beneficial role of indole in establishing an epithelial barrier in vivo.

Caecal fermentation, putrefaction and microbiotas in rats fed milk casein, soy protein or fish meal

To clarify the effect of soy protein (SP) and fish meal (FM), compared to milk casein (MC), on the intestinal environment, we examined caecal environment of rats fed the test diets. Four-week-old rats were fed AIN-76-based diet containing 20 %, w/w MC, SP or FM for 16 days. Caecal organic acids were analysed by HPLC. Caecal putrefactive compounds (indole, phenol, H2S and ammonia) were analysed by colorimetric assays. Caecal microflora was determined by 16S rRNA gene-DGGE and pyrosequencing with bar-coded primers targeting the bacterial 16S rRNA gene. n-Butyric and lactic acid levels were high in rats fed SP and FM, respectively. Butyrate-producing bacteria, such as Oscillibacter, and lactate-producing bacteria, such as Lactobacillus, were detected in each diet group. Also, the putrefactive compound contents were high in rats fed SP and FM. In this study, both DGGE and pyrosequencing analyses were able to evaluate the dynamics of the intestinal microbiota. The results indicate that dietary proteins can alter the intestinal environment, affecting fermentation by the intestinal microbiota and the generation of putrefactive compounds.

Metabolomics approaches for characterizing metabolic interactions between host and its commensal microbes

It is increasingly evident that the gut microbiota is involved in the regulation of multiple mammalian metabolic pathways through a series of interactive host-microbiota metabolic, signaling, and immune-inflammatory axes that physiologically connect the gut, liver, brain, and other organs. Correlation of the metabotypes with the gut microbial profiles derived from culture-independent molecular techniques is increasingly useful for deciphering inherent and intimate host-microbe relationships. Real-time analysis of the small molecule metabolites derived from gut microbial-host co-metabolism is essential for understanding the metabolic functions of the gut microbiome and has tremendous implications for personalized healthcare strategies. Metabolomics, an array of analytical techniques that includes high resolution NMR spectroscopy and chromatography-MS in conjunction with chemometrics and bioinformatics tools, enables characterization of the metabolic footprints of mammalian hosts that correlate with the microbial community in the intestinal tract. The metabolomics approach provides important information of a complete spectrum of metabolites produced from the gut microbial-mammalian co-metabolism and is improving our understanding of the molecular mechanisms underlying multilevel host-microbe interactions. In this review, the interactions of gut microbiota with their host are discussed and some examples of NMR- or MS-based metabolomics applications for characterizing the metabolic footprints of gut microbial-host co-metabolism are described. Advances in the metabolomic analysis of bile acids, short-chain fatty acids, and choline metabolism are also summarized.

Dietary protein excess during neonatal life alters colonic microbiota and mucosal response to inflammatory mediators later in life in female pigs

The interplay between the colonic microbiota and gut epithelial and immune cells during the neonatal period, which establishes the structure of the microbiota and programs mucosal immunity, is affected by the diet. We hypothesized that protein-enriched milk formula would disturb this interplay through greater flux of protein entering the colon, with consequences later in life. Piglets were fed from postnatal day (PND) 2 to 28 either a normal-protein formula (NP; 51 g protein/L) or high-protein formula (HP; 77 g protein/L) and weaned at PND28, when they received standard diets until PND160. HP feeding transiently increased the quantity of protein entering the colon (PND7) but did not change the microbiota composition at PND28, except for a higher production of branched-chain fatty acids (BCFAs) in an in vitro fermentation test (P < 0.05). HP piglets had greater colonic mucosa densities of cluster of differentiation (CD) 3(+) and CD172(+) cells and lower Il-1β and Tnfα mRNA levels at PND28 (P < 0.05). Later in life (PND160), HP females, but not males, had a higher increase in colonic permeability after ex vivo oxidative stress and higher cytokine secretion in response to lipopolysaccharide in colonic explant cultures than NP females (P < 0.05). HP females also had lower colonic amounts of F. prausnitzii and BCFAs (P < 0.05). BCFAs displayed a dose-dependent protection against inflammation-induced alteration of barrier function in Caco-2 cells (P < 0.05). In conclusion, protein-enriched formula had little impact on colonic microbiota, but it modified colonic immune cell development and had a long-term effect on adult colonic mucosa sensitivity to inflammatory insults, probably through microbiotal and hormonal factors.