Quantifying Gut Microbial Short-Chain Fatty Acids and Their Isotopomers in Mechanistic Studies Using a Rapid, Readily Expandable LC-MS Platform

Short-chain fatty acids (SCFAs) comprise the largest group of gut microbial fermentation products. While absorption of most nutrients occurs in the small intestine, indigestible dietary components, such as fiber, reach the colon and are processed by the gut microbiome to produce a wide array of metabolites that influence host physiology. Numerous studies have implicated SCFAs as key modulators of host health, such as in regulating irritable bowel syndrome (IBS). However, robust methods are still required for their detection and quantitation to meet the demands of biological studies probing the complex interplay of the gut-host-health paradigm. In this study, a sensitive, rapid-throughput, and readily expandible UHPLC-QqQ-MS platform using 2-PA derivatization was developed for the quantitation of gut-microbially derived SCFAs, related metabolites, and isotopically labeled homologues. The utility of this platform was then demonstrated by investigating the production of SCFAs in cecal contents from mice feeding studies, human fecal bioreactors, and fecal/bacterial fermentations of isotopically labeled dietary carbohydrates. Overall, the workflow proposed in this study serves as an invaluable tool for the rapidly expanding gut-microbiome and precision nutrition research field.

Milk oligosaccharide-driven persistence of Bifidobacterium pseudocatenulatum modulates local and systemic microbial metabolites upon synbiotic treatment in conventionally colonized mice

BACKGROUND

Bifidobacteria represent an important gut commensal in humans, particularly during initial microbiome assembly in the first year of life. Enrichment of Bifidobacterium is mediated though the utilization of human milk oligosaccharides (HMOs), as several human-adapted species have dedicated genomic loci for transport and metabolism of these glycans. This results in the release of fermentation products into the gut lumen which may offer physiological benefits to the host. Synbiotic pairing of probiotic species with a cognate prebiotic delivers a competitive advantage, as the prebiotic provides a nutrient niche.

METHODS

To determine the fitness advantage and metabolic characteristics of an HMO-catabolizing Bifidobacterium strain in the presence or absence of 2'-fucosyllactose (2'-FL), conventionally colonized mice were gavaged with either Bifidobacterium pseudocatenulatum MP80 (B.p. MP80) (as the probiotic) or saline during the first 3 days of the experiment and received water or water containing 2'-FL (as the prebiotic) throughout the study.

RESULTS

16S rRNA gene sequencing revealed that mice provided only B.p. MP80 were observed to have a similar microbiota composition as control mice throughout the experiment with a consistently low proportion of Bifidobacteriaceae present. Using 1H NMR spectroscopy, similar metabolic profiles of gut luminal contents and serum were observed between the control and B.p. MP80 group. Conversely, synbiotic supplemented mice exhibited dramatic shifts in their community structure across time with an overall increased, yet variable, proportion of Bifidobacteriaceae following oral inoculation. Parsing the synbiotic group into high and moderate bifidobacterial persistence based on the median proportion of Bifidobacteriaceae, significant differences in gut microbial diversity and metabolite profiles were observed. Notably, metabolites associated with the fermentation of 2'-FL by bifidobacteria were significantly greater in mice with a high proportion of Bifidobacteriaceae in the gut suggesting metabolite production scales with population density. Moreover, 1,2-propanediol, a fucose fermentation product, was only observed in the liver and brain of mice harboring high proportions of Bifidobacteriaceae.

CONCLUSIONS

This study reinforces that the colonization of the gut with a commensal microorganism does not guarantee a specific functional output. Video Abstract.

Bifidobacterium catabolism of human milk oligosaccharides overrides endogenous competitive exclusion driving colonization and protection

Understanding how exogenous microbes stably colonize the animal gut is essential to reveal mechanisms of action and tailor effective probiotic treatments. Bifidobacterium species are naturally enriched in the gastrointestinal tract of breast-fed infants. Human milk oligosaccharides (HMOs) are associated with this enrichment. However, direct mechanistic proof of the importance of HMOs in this colonization is lacking given milk contains additional factors that impact the gut microbiota. This study examined mice supplemented with the HMO 2'fucosyllactose (2'FL) together with a 2'FL-consuming strain, Bifidobacterium pseudocatenulatum MP80. 2'FL supplementation creates a niche for high levels of B.p. MP80 persistence, similar to Bifidobacterium levels seen in breast-fed infants. This synergism impacted gut microbiota composition, activated anti-inflammatory pathways and protected against chemically-induced colitis. These results demonstrate that bacterial-milk glycan interactions alone drive enrichment of beneficial Bifidobacterium and provide a model for tunable colonization thus facilitating insight into mechanisms of health promotion by bifidobacteriain neonates.

Microbial metabolites and the vagal afferent pathway in the control of food intake

The gut microbiota is able to influence overall energy balance via effects on both energy intake and expenditure, and is a peripheral target for potential obesity therapies. However, the precise mechanism by which the gut microbiota influences energy intake and body weight regulation is not clear. Microbes use small molecules to communicate with each other; some of these molecules are ligands at mammalian receptors and this may be a mechanism by which microbes communicate with the host. Here we briefly review the literature showing beneficial effects of microbial metabolites on food intake regulation and examine the potential role for vagal afferent neurons, the gut-brain axis.

Region-Specific Cell Membrane N-Glycome of Functional Mouse Brain Areas Revealed by nanoLC-MS Analysis

N-glycosylation is a ubiquitous posttranslational modification that affects protein structure and function, including those of the central nervous system. N-glycans attached to cell membrane proteins play crucial roles in all aspects of biology, including embryogenesis, development, cell-cell recognition and adhesion, and cell signaling and communication. Although brain function and behavior are known to be regulated by the N-glycosylation state of numerous cell surface glycoproteins, our current understanding of brain glycosylation is limited, and glycan variations associated with functional brain regions remain largely unknown. In this work, we used a well-established cell surface glycomic nanoLC-Chip-Q-TOF platform developed in our laboratory to characterize the N-glycome of membrane fractions enriched in cell surface glycoproteins obtained from specific functional brain areas. We report the cell membrane N-glycome of two major developmental divisions of mice brain with specific and distinctive functions, namely the forebrain and hindbrain. Region-specific glycan maps were obtained with ∼120 N-glycan compositions in each region, revealing significant differences in "brain-type" glycans involving high mannose, bisecting, and core and antenna fucosylated species. Additionally, the cell membrane N-glycome of three functional regions of the forebrain and hindbrain, the cerebral cortex, hippocampus, and cerebellum, was characterized. In total, 125 N-glycan compositions were identified, and their region-specific expression profiles were characterized. Over 70 N-glycans contributed to the differentiation of the cerebral cortex, hippocampus, and cerebellum N-glycome, including bisecting and branched glycans with varying degrees of core and antenna fucosylation and sialylation. This study presents a comprehensive spatial distribution of the cell-membrane enriched N-glycomes associated with five discrete anatomical and functional brain areas, providing evidence for the presence of a previously unknown brain glyco-architecture. The region-specific molecular glyco fingerprints identified here will enable a better understanding of the critical biological roles that N-glycans play in the specialized functional brain areas in health and disease.

Human milk oligosaccharide 2'-fucosyllactose supplementation improves gut barrier function and signaling in the vagal afferent pathway in mice

2′-Fucosyllactose (2′-FL) is one of the predominant oligosaccharides found in human milk and has several well-established beneficial effects in the host. It has previously been shown that 2′-FL can improve the metabolic phenotype in high-fat (HF)-fed mice. Here we investigated whether dietary supplementation with 2′-FL was associated with improved intestinal barrier integrity, signaling in the vagal afferent pathway and cognitive function. Mice were fed either a low-fat (LF, 10% fat per kcal) or HF (45% fat per kcal) diet with or without supplementation of 2′-FL (10% w/w) in the diet for 8 weeks. Body weight, energy intake, fat and lean mass, intestinal permeability (ex vivo in Ussing chambers), lipid profiles, gut microbiome and microbial metabolites, and cognitive functions were measured. Vagal afferent activity was measured via immunohistochemical detection of c-Fos protein in the brainstem in response to peripheral administration of cholecystokinin (CCK). 2′-FL significantly attenuated the HF-induced increase in fat mass and energy intake. 2′-FL significantly reduced intestinal permeability and significantly increased expression of interleukin (IL)-22, a cytokine known for its protective role in the intestine. Additionally, 2′-FL led to changes in the gut microbiota composition and in the associated microbial metabolites. Signaling in the vagal afferent pathway was improved but there was no effect on cognitive function. In conclusion, 2′-FL supplementation improved the metabolic profiles, gut barrier integrity, lipid metabolism and signaling in the vagal afferent pathway. These findings support the utility of 2′-FL in the control of gut barrier function and metabolic homeostasis under a metabolic challenge.

2’-Fucosyllactose (2’-FL), a predominant human milk oligosaccharide, attenuates HF diet-induced metabolic and intestinal barrier impairment, improves gut hormone resistance, and alters the intestinal microbiota and microbiota-derived metabolites.

Obesity induces gut microbiota alterations and augments acute graft-versus-host disease after allogeneic stem cell transplantation

The efficacy of allogeneic hematopoietic stem cell transplantation (allo-HSCT) is limited by acute and chronic graft-versus-host disease (GVHD). The impact of obesity on allo-HSCT outcomes is poorly understood. Here, we report that obesity had a negative and selective impact on acute gut GVHD after allo-HSCT in mice with diet-induced obesity (DIO). These animals exhibited increased gut permeability, endotoxin translocation across the gut, and radiation-induced gastrointestinal damage after allo-HSCT. After allo-HSCT, both male and female DIO mouse recipients showed increased proinflammatory cytokine production and expression of the GVHD marker ST2 (IL-33R) and MHC class II molecules; they also exhibited decreased survival associated with acute severe gut GVHD. This rapid-onset, obesity-associated gut GVHD depended on donor CD4⁺ T cells and occurred even with a minor MHC mismatch between donor and recipient animals. Retrospective analysis of clinical cohorts receiving allo-HSCT transplants from unrelated donors revealed that recipients with a high body mass index (BMI, >30) had reduced survival and higher serum ST2 concentrations compared with nonobese transplant recipients. Assessment of both DIO mice and allo-HSCT recipients with a high BMI revealed reduced gut microbiota diversity and decreased Clostridiaceae abundance. Prophylactic antibiotic treatment protected DIO mouse recipients from endotoxin translocation across the gut and increased inflammatory cytokine production, as well as gut pathology and mortality, but did not protect against later development of chronic skin GVHD. These results suggest that obesity-induced alterations of the gut microbiota may affect GVHD after allo-HSCT in DIO mice, which could be ameliorated by prophylactic antibiotic treatment.

Indole-3-lactic acid associated with Bifidobacterium-dominated microbiota significantly decreases inflammation in intestinal epithelial cells

Background

Bifidobacterium longum subsp. infantis (B. infantis) is a commensal bacterium that colonizes the gastrointestinal tract of breast-fed infants. B. infantis can efficiently utilize the abundant supply of oligosaccharides found in human milk (HMO) to help establish residence. We hypothesized that metabolites from B. infantis grown on HMO produce a beneficial effect on the host.

Results

In a previous study, we demonstrated that B. infantis routinely dominated the fecal microbiota of a breast fed Bangladeshi infant cohort (1). Characterization of the fecal metabolome of binned samples representing high and low B. infantis populations from this cohort revealed higher amounts of the tryptophan metabolite indole-3-lactic acid (ILA) in feces with high levels of B. infantis. Further in vitro analysis confirmed that B. infantis produced significantly greater quantities of the ILA when grown on HMO versus lactose, suggesting a growth substrate relationship to ILA production. The direct effects of ILA were assessed in a macrophage cell line and intestinal epithelial cell lines. ILA (1-10 mM) significantly attenuated lipopolysaccharide (LPS)-induced activation of NF-kB in macrophages. ILA significantly attenuated TNF-α- and LPS-induced increase in the pro-inflammatory cytokine IL-8 in intestinal epithelial cells. ILA increased mRNA expression of the aryl hydrogen receptor (AhR)-target gene CYP1A1 and nuclear factor erythroid 2–related factor 2 (Nrf2)-targeted genes glutathione reductase 2 (GPX2), superoxide dismutase 2 (SOD2), and NAD(P) H dehydrogenase (NQO1). Pretreatment with either the AhR antagonist or Nrf-2 antagonist inhibited the response of ILA on downstream effectors.

Conclusions

These findings suggest that ILA, a predominant metabolite from B. infantis grown on HMO and elevated in infant stool high in B. infantis, and protects gut epithelial cells in culture via activation of the AhR and Nrf2 pathway.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-020-02023-y.

Metabolic Responses to Butyrate Supplementation in LF- and HF-Fed Mice Are Cohort-Dependent and Associated with Changes in Composition and Function of the Gut Microbiota

The gut microbiota and associated metabolites have emerged as potential modulators of pathophysiological changes in obesity and related metabolic disorders. Butyrate, a product of bacterial fermentation, has been shown to have beneficial effects in obesity and rodent models of diet-induced obesity. Here, we aimed to determine the beneficial effects of butyrate (as glycerol ester of butyrate monobutyrin, MB) supplementation on metabolic phenotype, intestinal permeability and inflammation, feeding behavior, and the gut microbiota in low-fat (LF)- and high-fat (HF)-fed mice. Two cohorts (separated by 2 weeks) of male C57BL/6J mice (n = 24 in each cohort, 6/group/cohort; 6 weeks old) were separated into four weight-matched groups and fed either a LF (10 % fat/kcal) or HF (45% fat/kcal) with or without supplementation of MB (LF/MB or HF/MB) at 0.25% (w/v) in drinking water for 6 weeks. Metabolic phenotypes (body weight and adiposity), intestinal inflammation, feeding behavior, and fecal microbiome and metabolites were measured. Despite identical genetic and experimental conditions, we found marked differences between cohorts in the response (body weight gain, adiposity, and intestinal permeability) to HF-diet and MB. Notably, the composition of the gut microbiota was significantly different between cohorts, characterized by lower species richness and differential abundance of a large number of taxa, including subtaxa from five phyla, including increased abundance of the genera Bacteroides, Proteobacteria, and Parasutterella in cohort 2 compared to cohort 1. These differences may have contributed to the differential response in intestinal permeability to the HF diet in cohort 2. MB supplementation had no significant effect on metabolic phenotype, but there was a trend to protect from HF-induced impairments in intestinal barrier function in cohort 1 and in sensitivity to cholecystokinin (CCK) in both cohorts. These data support the concept that microbiota composition may have a crucial effect on metabolic responses of a host to dietary interventions and highlight the importance of taking steps to ensure reproducibility in rodent studies.

Estrogen and gut satiety hormones in vagus-hindbrain axis

Estrogens modulate different physiological functions, including reproduction, inflammation, bone formation, energy expenditure, and food intake. In this review, we highlight the effect of estrogens on food intake regulation and the latest literature on intracellular estrogen signaling. In addition, gut satiety hormones, such as cholecystokinin, glucagon-like peptide 1 and leptin are essential to regulate ingestive behaviors in the postprandial period. These peripheral signals are sensed by vagal afferent terminals in the gut wall and transmitted to the hindbrain axis. Here we 1. review the role of the vagus-hindbrain axis in response to gut satiety signals and 2. consider the potential synergistic effects of estrogens on gut satiety signals at the level of vagal afferent neurons and nuclei located in the hindbrain. Understanding the action of estrogens in gut-brain axis provides a potential strategy to develop estrogen-based therapies for metabolic diseases and emphasizes the importance of sex difference in the treatment of obesity.

Leptin signaling in vagal afferent neurons supports the absorption and storage of nutrients from high-fat diet

Objective:

Activation of vagal afferent neurons (VAN) by postprandial gastrointestinal signals terminates feeding and facilitates nutrient digestion and absorption. Leptin modulates responsiveness of VAN to meal-related gastrointestinal signals. Rodents with high-fat diet (HF) feeding develop leptin resistance that impairs responsiveness of VAN. We hypothesized that lack of leptin signaling in VAN reduces responses to meal-related signals, which in turn decreases absorption of nutrients and energy storage from high-fat, calorically dense food.

Methods:

Mice with conditional deletion of the leptin receptor from VAN (Nav1.8-Cre/LepR^fl/fl; KO) were used in this study. Six-week-old male mice were fed a 45% HF for 4 weeks; metabolic phenotype, food intake, and energy expenditure were measured. Absorption and storage of nutrients were investigated in the refed state.

Results:

After 4 weeks of HF feeding, KO mice gained less body weight and fat mass that WT controls, but this was not due to differences in food intake or energy expenditure. KO mice had reduced expression of carbohydrate transporters and absorption of carbohydrate in the jejunum. KO mice had fewer hepatic lipid droplets and decreased expression of de novo lipogenesis-associated enzymes and lipoproteins for endogenous lipoprotein pathway in liver, suggesting decreased long-term storage of carbohydrate in KO mice.

Conclusions:

Impairment of leptin signaling in VAN reduces responsiveness to gastrointestinal signals, which reduces intestinal absorption of carbohydrates and de novo lipogenesis resulting in reduced long-term energy storage. This study reveals a novel role of vagal afferents to support digestion and energy storage that may contribute to the effectiveness of vagal blockade to induce weight loss.

What Should I Eat and Why? The Environmental, Genetic, and Behavioral Determinants of Food Choice: Summary from a Pennington Scientific Symposium

This review details the proceedings of a Pennington Biomedical scientific symposium titled, "What Should I Eat and Why? The Environmental, Genetic, and Behavioral Determinants of Food Choice." The symposium was designed to review the literature about energy homeostasis, particularly related to food choice and feeding behaviors, from psychology to physiology. This review discusses the intrinsic determinants of food choice, including biological mechanisms (genetics), peripheral and central signals, brain correlates, and the potential role of the microbiome. This review also address the extrinsic determinants (environment) of food choice within our physical and social environments. Finally, this review reports the current treatment practices for the clinical management of eating-induced overweight and obesity. An improved understanding of these determinants will inform best practices for the clinical treatment and prevention of obesity. Strategies paired with systemic shifts in our public health policies and changes in our "obesogenic" environment will be most effective at attenuating the obesity epidemic.

Blunted Vagal Cocaine- and Amphetamine-Regulated Transcript Promotes Hyperphagia and Weight Gain

The vagus nerve conveys gastrointestinal cues to the brain to control eating behavior. In obesity, vagally mediated gut-brain signaling is disrupted. Here, we show that the cocaine- and amphetamine-regulated transcript (CART) is a neuropeptide synthesized proportional to the food consumed in vagal afferent neurons (VANs) of chow-fed rats. CART injection into the nucleus tractus solitarii (NTS), the site of vagal afferent central termination, reduces food intake. Conversely, blocking endogenous CART action in the NTS increases food intake in chow-fed rats, and this requires intact VANs. Viral-mediated Cartpt knockdown in VANs increases weight gain and daily food intake via larger meals and faster ingestion rate. In obese rats fed a high-fat, high-sugar diet, meal-induced CART synthesis in VANs is blunted and CART antibody fails to increase food intake. However, CART injection into the NTS retains its anorexigenic effect in obese rats. Restoring disrupted VAN CART signaling in obesity could be a promising therapeutic approach.

Deletion of leptin receptors in vagal afferent neurons disrupts estrogen signaling, body weight, food intake and hormonal controls of feeding in female mice

Deletion of the leptin receptor from vagal afferent neurons (VAN) using a conditional deletion (Nav1.8/LepR^fl/fl) results in an obese phenotype with increased food intake and lack of exogenous cholecystokinin (CCK)-induced satiation in male mice. Female mice are partially protected from weight gain and increased food intake in response to ingestion of high-fat (HF) diets. However, whether the lack of leptin signaling in VAN leads to an obese phenotype or disruption of hypothalamic-pituitary-gonadal axis function in female mice is unclear. Here, we tested the hypothesis that leptin signaling in VAN is essential to maintain estrogen signaling and control of food intake, energy expenditure, and adiposity in female mice. Female Nav1.8/LepR^fl/fl mice gained more weight, had increased gonadal fat mass, increased meal number in the dark phase, and increased total food intake compared with wild-type controls. Resting energy expenditure was unaffected. The decrease in food intake produced by intraperitoneal injection of CCK (3 μg/kg body wt) was attenuated in female Nav1.8/LepR^fl/fl mice compared with wild-type controls. Intraperitoneal injection of ghrelin (100 μg/kg body wt) increased food intake in Nav1.8/LepR^fl/fl mice but not in wild-type controls. Ovarian steroidogenesis was suppressed, resulting in decreased plasma estradiol, which was accompanied by decreased expression of estrogen receptor-1 (Esr1) in VAN but not in the hypothalamic arcuate nucleus. These data suggest that the absence of leptin signaling in VAN is accompanied by disruption of estrogen signaling in female mice, leading to an obese phenotype possibly via altered control of feeding behavior.

Chronic refined low-fat diet consumption reduces cholecystokinin satiation in rats

PURPOSE

Reduced ability of cholecystokinin (CCK) to induce satiation contributes to hyperphagia and weight gain in high-fat/high-sucrose (HF/HS) diet-induced obesity, and has been linked to altered gut microbiota. Rodent models of obesity use chow or low-fat (LF) diets as control diets; the latter has been shown to alter gut microbiota and metabolome. We aimed to determine whether LF-diet consumption impacts CCK satiation in rats and if so, whether this is prevented by addition of inulin to LF diet.

METHODS

Rats (n = 40) were fed, for 8 weeks, a chow diet (chow) or low-fat (10%) or high-fat/high-sucrose (45 and 17%, respectively) refined diets with either 10% cellulose (LF and HF/HS) or 10% inulin (LF-I and HF/HS-I). Caecal metabolome was assessed by ¹H-NMR-based metabolomics. CCK satiation was evaluated by measuring the suppression of food intake after intraperitoneal CCK injection (1 or 3 µg/kg).

RESULTS

LF-diet consumption altered the caecal metabolome, reduced caecal weight, and increased IAP activity, compared to chow. CCK-induced inhibition of food intake was abolished in LF diet-fed rats compared to chow-fed rats, while HF/HS diet-fed rats responded only to the highest CCK dose. Inulin substitution ameliorated caecal atrophy, reduced IAP activity, and modulated caecal metabolome, but did not improve CCK-induced satiety in either LF- or HF/HS-fed rats.

CONCLUSIONS

CCK signaling is impaired by LF-diet consumption, highlighting that caution must be taken when using LF diet until a more suitable refined control diet is identified.

Obesity results in marked increases in gut permeability, inflammatory cytokines, and acute gut graft-versus-host disease after allogeneic hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) remains the most applicable curative option for treating hematologic diseases. In this study, we assessed the impact of obesity on recipient graft-versus-host disease (GVHD) outcome post allogeneic HSCT using a minor histocompatibility antigens (miHA)-mismatched mouse model. Control or diet-induced obese (DIO) BALB/c mice received HSCT from H2-identical B10.D2 mice which is known for resulting in chronic skin GVHD. Strikingly, DIO mice rapidly succumbed to gut GVHD while control mice survived and developed sclerodermatous GVHD much later post-HSCT. The DIO recipient mice had higher expression of pro-inflammatory cytokines (IL-6 and TNF-α) in the gut and serum, as well as higher serum ST2. There were increased numbers of donor CD4+ T cells in the mesenteric lymph nodes of DIO mice compared to control mice. Untreated DIO mice also displayed increased gut permeability and lipopolysaccharide translocation, as well as having less-diverse microbiota which potentially contributed to the severe GVHD post-HSCT. Importantly, administration of anti-IL-6R monoclonal antibody and Enbrel significantly protected DIO mice from lethal gut GVHD, correlating with lower pro-inflammatory cytokine concentrations (IL-6 and TNF-α) and ST2 in the serum. In an initial evaluation, treating DIO mice with broad-spectrum antibiotics 2 weeks before HSCT also ameliorated GVHD. Taken together, these results indicate that obesity exacerbates GVHD, manifested primarily as gut pathology, and therapeutic intervention by blockade of pro-inflammatory cytokine signaling ameliorates GVHD post-HSCT.

Prebiotic milk oligosaccharides prevent development of obese phenotype, impairment of gut permeability, and microbial dysbiosis in high fat-fed mice

Microbial dysbiosis and increased intestinal permeability are targets for prevention or reversal of weight gain in high-fat (HF) diet-induced obesity (DIO). Prebiotic milk oligosaccharides (MO) have been shown to benefit the host intestine but have not been used in DIO. We hypothesized that supplementation with bovine MO would prevent the deleterious effect of HF diet on the gut microbiota and intestinal permeability and attenuate development of the obese phenotype. C57BL/6 mice were fed a control diet, HF (40% fat/kcal), or HF + prebiotic [6%/kg bovine milk oligosaccharides (BMO) or inulin] for 1, 3, or 6 wk. Gut microbiota and intestinal permeability were assessed in the ileum, cecum, and colon. Addition of BMO to the HF diet significantly attenuated weight gain, decreased adiposity, and decreased caloric intake; inulin supplementation also lowered weight gain and adiposity, but this did not reach significance. BMO and inulin completely abolished the HF diet-induced increase in paracellular and transcellular permeability in the small and large intestine. Both BMO and inulin increased abundance of beneficial microbes Bifidobacterium and Lactobacillus in the ileum. However, inulin supplementation altered phylogenetic diversity and decreased species richness. We conclude that addition of BMO to the HF diet completely prevented increases in intestinal permeability and microbial dysbiosis and was partially effective to prevent weight gain in DIO.NEW & NOTEWORTHY This study provides the first report of the effects of prebiotic bovine milk oligosaccharides on the host phenotype of high-fat diet-induced obesity in mice.

Obesity predisposes to rapid gastrointestinal graft-versus-host disease lethality after allogeneic hematopoietic stem cell transplantation in mice

Obesity is a form of chronic inflammation, termed “meta-inflammation”, resulting in the development of many chronic diseases such as diabetes and cancer. In this study, we assessed the impact of obesity on recipient graft-versus-host disease (GVHD) outcome post allogeneic HSCT using mouse models. In a model of sclerodermatous chronic GVHD, lean or diet-induced obese (DIO) BALB/c mice received 800 cGy total body irradiation (TBI), bone marrow cells, and splenocytes from H2-identical but minor MHC-mismatched B10.D2 mice. To mimic major MHC mismatch transplant which results in acute GVHD impacting gut, skin and liver, lean or DIO C57BL/6 mice received 1050 cGy TBI, bone marrow cells, and different doses of purified T cells from BALB/c mice. Strikingly, after the minor mismatch HSCT, all DIO mice succumbed to gut pathology while all lean mice survived and developed sclerodermatous GVHD at week 3 post transplant. In both models, pathological assessment indicated marked gut pathology in DIO mice correlating with lethality. Lean mice in the major MHC mismatch strain combination had significantly increased survival and less severe gut pathology compared to the DIO mice. The DIO mice had higher expression of pro-inflammatory cytokines in the gut, liver, visceral fat, and serum post-HSCT. Flow cytometric analysis demonstrated increased numbers of donor CD8+ T cells in the gut of DIO mice compared to lean mice. In an initial evaluation, untreated DIO mice displayed increased gut permeability as well as having limited diversity in their microbiome which would contribute to severe GVHD post-HSCT. Taken together, these results indicate that obesity exacerbates GVHD after allogeneic HSCT primarily affecting the gastrointestinal tract.

Nopal feeding reduces adiposity, intestinal inflammation and shifts the cecal microbiota and metabolism in high-fat fed rats

Nopal is a cactus plant widely consumed in Mexico that has been used in traditional medicine to aid in the treatment of type-2 diabetes. We previously showed that chronic consumption of dehydrated nopal ameliorated hepatic steatosis in obese (fa/fa) rats; however, description of the effects on other tissues is sparse. The aim of the present study was to investigate the effects of nopal cladode consumption on intestinal physiology, microbial community structure, adipose tissue, and serum biochemistry in diet-induced obese rats. Rats were fed either a normal fat (NF) diet or a HF diet containing 4% of dietary fiber from either nopal or cellulose for 6 weeks. Consumption of nopal counteracted HF-induced adiposity and adipocyte hypertrophy, and induced profound changes in intestinal physiology. Nopal consumption reduced biomarkers of intestinal inflammation (mRNA expression of IL-6) and oxidative stress (ROS), modfied gut microbiota composition, increasing microbial diversity and cecal fermentation (SCFA), and altered the serum metabolome. Interestingly, metabolomic analysis of dehydrated nopal revealed a high choline content, which appeared to generate high levels of serum betaine, that correlated negatively with hepatic triglyceride (TAG) levels. A parallel decrease in some of the taxa associated with the production of trimethylamine, suggest an increase in choline absorption and bioavailability with transformation to betaine. The latter may partially explain the previously observed effect of nopal on the development of hepatic steatosis. In conclusion, this study provides new evidence on the effects of nopal consumption on normal and HF-diet induced changes in the intestine, the liver and systemic metabolism.

Bovine milk oligosaccharides decrease gut permeability and improve inflammation and microbial dysbiosis in diet-induced obese mice

Obesity is characterized by altered gut homeostasis, including dysbiosis and increased gut permeability closely linked to the development of metabolic disorders. Milk oligosaccharides are complex sugars that selectively enhance the growth of specific beneficial bacteria in the gastrointestinal tract and could be used as prebiotics. The aim of the study was to demonstrate the effects of bovine milk oligosaccharides (BMO) and Bifidobacterium longum ssp. infantis (B. infantis) on restoring diet-induced obesity intestinal microbiota and barrier function defects in mice. Male C57/BL6 mice were fed a Western diet (WD, 40% fat/kcal) or normal chow (C, 14% fat/kcal) for 7 wk. During the final 2 wk of the study, the diet of a subgroup of WD-fed mice was supplemented with BMO (7% wt/wt). Weekly gavage of B. infantis was performed in all mice starting at wk 3, yet B. infantis could not be detected in any luminal contents when mice were killed. Supplementation of the WD with BMO normalized the cecal and colonic microbiota with increased abundance of Lactobacillus compared with both WD and C mice and restoration of Allobaculum and Ruminococcus levels to that of C mice. The BMO supplementation reduced WD-induced increase in paracellular and transcellular flux in the large intestine as well as mRNA levels of the inflammatory marker tumor necrosis factor α. In conclusion, BMO are promising prebiotics to modulate gut microbiota and intestinal barrier function for enhanced health.

Curricular Revision and Reform: The Process, What Was Important, and Lessons Learned

Beginning in 2005, the Doctor of Veterinary Medicine program at the University of California underwent major curricular review and reform. To provide information for others that follow, we have documented our process and commented on factors that were critical to success, as well as factors we found surprising, difficult, or problematic. The review and reform were initiated by the Executive Committee, who led the process and commissioned the committees. The planning stage took 6 years and involved four faculty committees, while the implementation stage took 5 years and was led by the Curriculum Committee. We are now in year 2 of the institutionalizing stage and no longer refer to our reform as the "new curriculum." The change was driven by a desire to improve the curriculum and the learning environment of the students by aligning the delivery of information with current teaching methodologies and implementing adult learning strategies. We moved from a department- and discipline-based curriculum to a school-wide integrated block curriculum that emphasized student-centered, inquiry-based learning. A limit was placed on in-class time to allow students to apply classroom knowledge by solving problems and cases. We found the journey long and arduous, requiring tremendous commitment and effort. In the change process, we learned the importance of adequate planning, leadership, communication, and a reward structure for those doing the "heavy lifting." Specific to our curricular design, we learned the importance of the block leader role, of setting clear expectations for students, and of partnering with students on the journey.

Milk with and without lactoferrin can influence intestinal damage in a pig model of malnutrition

Malnutrition remains a leading contributor to the morbidity and mortality of children under the age of five worldwide. However, the underlying mechanisms are not well understood necessitating an appropriate animal model to answer fundamental questions and conduct translational research into optimal interventions. One potential intervention is milk from livestock that more closely mimics human milk by increased levels of bioactive components that can promote a healthy intestinal epithelium. We tested the ability of cow milk and milk from transgenic cows expressing human lactoferrin at levels found in human milk (hLF milk) to mitigate the effects of malnutrition at the level of the intestine in a pig model of malnutrition. Weaned pigs (3 weeks old) were fed a protein and calorie restricted diet for five weeks, receiving cow, hLF or no milk supplementation daily from weeks 3-5. After three weeks, the restricted diet induced changes in growth, blood chemistry and intestinal structure including villous atrophy, increased ex vivo permeability and decreased expression of tight junction proteins. Addition of both cow and hLF milk to the diet increased growth rate and calcium and glucose levels while promoting growth of the intestinal epithelium. In the jejunum hLF milk restored intestinal morphology, reduced permeability and increased expression of anti-inflammatory IL-10. Overall, this pig model of malnutrition mimics salient aspects of the human condition and demonstrates that cow milk can stimulate the repair of damage to the intestinal epithelium caused by protein and calorie restriction with hLF milk improving this recovery to a greater extent.

Bugs, guts and brains, and the regulation of food intake and body weight

The microbiota-gut-brain axis is currently being explored in many types of rodent models, including models of behavioral, neurodegenerative and metabolic disorders. Our laboratory is interested in determining the mechanisms and consequences of activation of vagal afferent neurons that lead to activation of parasympathetic reflexes and changes in feeding behavior in the context of obesity. Obesity is associated with microbial dysbiosis, decreased intestinal barrier function, gut inflammation, metabolic endotoxemia, chronic low-grade systemic inflammation and desensitization of vagal afferent nerves. This review will present the evidence that altered gut microbiota together with decreased gut barrier function allows the passage of bacterial components or metabolites in obese individuals, leading to the disruption of vagal afferent signaling and consequently resulting in an increase in body weight. We first review the most recent descriptions of gut microbial dysbiosis due to a high fat diet and describe changes in the gut barrier and the evidence of increased intestinal permeability in obesity. We then will review the evidence to show how manipulating the gut microbiota via pre and probiotics can restore gut barrier function and prevent weight gain. Lastly, we present possible mechanisms by which the microbe-gut-brain axis may have a role in obesity. The studies mentioned in this review have provided new targets to treat and prevent obesity and have highlighted how the microbiota-gut-brain axis is involved.

Mutations in Durum Wheat SBEII Genes affect Grain Yield Components, Quality, and Fermentation Responses in Rats

Increased amylose in wheat (Triticum ssp.) starch is associated with increased resistant starch, a fermentable dietary fiber. Fermentation of resistant starch in the large intestine produces short-chain fatty acids that are associated with human health benefits. Since wheat foods are an important component of the human diet, increases in amylose and resistant starch in wheat grains have the potential to deliver health benefits to a large number of people. In three replicated field trials we found that mutations in starch branching enzyme II genes (SBEIIa and SBEIIb) in both A and B genomes (SBEIIa/b-AB) of durum wheat [T. turgidum L. subsp. durum (Desf.) Husn.] resulted in large increases of amylose and resistant starch content. The presence of these four mutations was also associated with an average 5% reduction in kernel weight (P = 0.0007) and 15% reduction in grain yield (P = 0.06) compared to the wild type. Complete milling and pasta quality analysis showed that the mutant lines have an acceptable quality with positive effects on pasta firmness and negative effects on semolina extraction and pasta color. Positive fermentation responses were detected in rats (Rattus spp.) fed with diets incorporating mutant wheat flour. This study quantifies benefits and limitations associated with the deployment of the SBEIIa/b-AB mutations in durum wheat and provides the information required to develop realistic strategies to deploy durum wheat varieties with increased levels of amylose and resistant starch.

Changes in intestinal barrier function and gut microbiota in high-fat diet-fed rats are dynamic and region dependent

A causal relationship between the pathophysiological changes in the gut epithelium and altered gut microbiota with the onset of obesity have been suggested but not defined. The aim of this study was to determine the temporal relationship between impaired intestinal barrier function and microbial dysbiosis in the small and large intestine in rodent high-fat (HF) diet-induced obesity. Rats were fed HF diet (45% fat) or normal chow (C, 10% fat) for 1, 3, or 6 wk; food intake, body weight, and adiposity were measured. Barrier function ex vivo using FITC-labeled dextran (4,000 Da, FD-4) and horseradish peroxidase (HRP) probes in Ussing chambers, gene expression, and gut microbial communities was assessed. After 1 wk, there was an immediate but reversible increase in paracellular permeability, decrease in IL-10 expression, and decrease in abundance of genera within the class Clostridia in the ileum. In the large intestine, HRP flux and abundance of genera within the order Bacteroidales increased with time on the HF diet and correlated with the onset of increased body weight and adiposity. The data show immediate insults in the ileum in response to ingestion of a HF diet, which were rapidly restored and preceded increased passage of large molecules across the large intestinal epithelium. This study provides an understanding of microbiota dysbiosis and gut pathophysiology in diet-induced obesity and has identified IL-10 and Oscillospira in the ileum and transcellular flux in the large intestine as potential early impairments in the gut that might lead to obesity and metabolic disorders.

Glucagon-like peptide 1 interacts with ghrelin and leptin to regulate glucose metabolism and food intake through vagal afferent neuron signaling

Emerging evidence has suggested a possible physiologic role for peripheral glucagon-like peptide 1 (GLP-1) in regulating glucose metabolism and food intake. The likely site of action of GLP-1 is on vagal afferent neurons (VANs). The vagal afferent pathway is the major neural pathway by which information about ingested nutrients reaches the central nervous system and influences feeding behavior. Peripheral GLP-1 acts on VANs to inhibit food intake. The mechanism of the GLP-1 receptor (GLP-1R) is unlike other gut-derived receptors; GLP-1Rs change their cellular localization according to feeding status rather than their protein concentrations. It is possible that several gut peptides are involved in mediating GLP-1R translocation. The mechanism of peripheral GLP-1R translocation still needs to be elucidated. We review data supporting the role of peripheral GLP-1 acting on VANs in influencing glucose homeostasis and feeding behavior. We highlight evidence demonstrating that GLP-1 interacts with ghrelin and leptin to induce satiation. Our aim was to understand the mechanism of peripheral GLP-1 in the development of noninvasive antiobesity treatments.

Chronic exposure to low dose bacterial lipopolysaccharide inhibits leptin signaling in vagal afferent neurons

Bacterially derived factors are implicated in the causation and persistence of obesity. Ingestion of a high fat diet in rodents and obesity in human subjects is associated with chronic elevation of low plasma levels of lipopolysaccharide (LPS), a breakdown product of Gram-negative bacteria. The terminals of vagal afferent neurons are positioned within the gut mucosa to convey information from the gut to the brain to regulate food intake and are responsive to LPS. We hypothesized that chronic elevation of LPS could alter vagal afferent signaling. We surgically implanted osmotic mini-pumps that delivered a constant, low-dose of LPS into the intraperitoneal cavity of rats (12.5 μg/kg/hr for 6 weeks). LPS-treated rats developed hyperphagia and showed marked changes in vagal afferent neuron function. Chronic LPS treatment reduced vagal afferent leptin signaling, characterized by a decrease in leptin-induced STAT3 phosphorylation. In addition, LPS treatment decreased cholecystokinin-induced satiety. There was no alteration in leptin signaling in the hypothalamus. These findings offer a mechanism by which a change in gut microflora can promote hyperphagia, possibly leading to obesity.

Deletion of leptin signaling in vagal afferent neurons results in hyperphagia and obesity

The vagal afferent pathway senses hormones released from the gut in response to nutritional cues and relays these signals to the brain. We tested the hypothesis that leptin resistance in vagal afferent neurons (VAN) is responsible for the onset of hyperphagia by developing a novel conditional knockout mouse to delete leptin receptor selectively in sensory neurons (Nav1.8/LepR (fl/fl) mice). Chow fed Nav1.8/LepR (fl/fl) mice weighed significantly more and had increased adiposity compared with wildtype mice. Cumulative food intake, meal size, and meal duration in the dark phase were increased in Nav1.8/LepR (fl/fl) mice; energy expenditure was unaltered. Reduced satiation in Nav1.8/LepR (fl/fl) mice is in part due to reduced sensitivity of VAN to CCK and the subsequent loss of VAN plasticity. Crucially Nav1.8/LepR (l/fl) mice did not gain further weight in response to a high fat diet. We conclude that disruption of leptin signaling in VAN is sufficient and necessary to promote hyperphagia and obesity.

Ability of GLP-1 to decrease food intake is dependent on nutritional status

Gut-derived glucagon like peptide-1 (GLP-1) acts in the postprandial period to stimulate insulin secretion and inhibit gastrointestinal motor and secretory function; whether endogenous peripheral GLP-1 inhibits food intake is less clear. We hypothesized that GLP-1 inhibits food intake in the fed, but not fasted, state. There is evidence that GLP-1 acts via stimulation of vagal afferent neurons (VAN); we further hypothesized that the satiating effects of endogenous GLP-1 in the postprandial period is determined either by a change in GLP-1 receptor (GLP-1R) expression or localization to different cellular compartments in VAN.

METHODS

Food intake was recorded following administration of GLP-1 (50μg/kg or 100μg/kg) or saline (IP) in Wistar rats fasted for 18h or fasted then re-fed with 3g chow. GLP-1R protein expression and localization on VAN were determined by immunocytochemistry and immunoblots in animals fasted for 18h or fasted then re-fed for 40min. GLP-1R mRNA level was detected in animals fasted for 18h or fasted and re-fed ad libitum for 2h.

RESULTS

GLP-1 (100μg/kg) significantly reduced 40min food intake by 38% in re-fed but not fasted rats (p<0.05). GLP-1R mRNA or protein levels in VAN were unchanged in re-fed compared to fasted rats. However, GLP-1R localization to the plasma membrane was significantly increased in VAN by feeding.

CONCLUSION

Feeding changes the ability of peripheral GLP-1 to inhibit food intake. GLP-1Rs are trafficked to the plasma membrane in response to a meal. GLP-1 may play a role in regulating food intake in the postprandial period.

Influence of sucrose ingestion on brainstem and hypothalamic intrinsic oscillations in lean and obese women

BACKGROUND & AIMS

The study of intrinsic fluctuations in the blood oxygen level-dependent signal of functional magnetic resonance imaging can provide insight into the effect of physiologic states on brain processes. In an effort to better understand the brain-gut communication induced by the absorption and metabolism of nutrients in healthy lean and obese individuals, we investigated whether ingestion of nutritive and non-nutritive sweetened beverages differentially engages the hypothalamus and brainstem vagal pathways in lean and obese women.

METHODS

In a 2-day, double-blind crossover study, 11 lean and 11 obese healthy women underwent functional magnetic resonance imaging scans after ingestion of 2 beverages of different sucrose content, but identical sweetness. During scans, subjects rested with eyes closed.

RESULTS

Blood oxygen level-dependent fluctuations demonstrated significantly greater power in the highest frequency band (slow-3: 0.073-0.198 Hz) after ingestion of high-sucrose compared with low-sucrose beverages in the nucleus tractus solitarius for both groups. Obese women had greater connectivity between the right lateral hypothalamus and a reward-related brain region and weaker connectivity with homeostasis and gustatory-related brain regions than lean women.

CONCLUSIONS

In a functional magnetic resonance imaging study, we observed sucrose-related changes in oscillatory dynamics of blood oxygen level-dependent fluctuations in brainstem and hypothalamus in lean and obese women. The observed frequency changes are consistent with a rapid vagally mediated mechanism due to nutrient absorption, rather than sweet taste receptor activation. These findings provide support for altered interaction between homeostatic and reward networks in obese individuals.

CCK1-receptor stimulation protects against gut mediator-induced lung damage during endotoxemia

Background/Aims

Cholecystokinin 1-receptor (CCK1-R) activation by long chain fatty acid (LCFA) absorption stimulates vago-vagal reflex pathways in the brain stem. The present study determines whether this reflex also activates the cholinergic anti-inflammatory pathway, a pathway known to modulate cytokine release during endotoxemia.

Methods

Mesenteric lymph was obtained from wild type (WT) and CCK1-R knockout (CCK1-R^−/−) mice intraperitoneally challenged with Lipopolysaccharid (LPS) (endotoxemic lymph, EL) and intestinally infused with vehicle or LCFA-enriched solution. The lymph was analyzed for TNFα, IL-6 and IL-10 concentration and administered to healthy recipient mice via jugular infusion. Alveolar wall thickness, myeloperoxidase (MPO) and TUNEL positive cells were determined in lung tissue of recipient mice.

Results

LCFA infusion in WT mice reduced TNFα concentration in EL by 49% compared to vehicle infusion, but had no effect in CCK1-R^−/− mice. EL significantly increased the alveolar wall thickness, the number of MPO-positive and TUNEL-positive cells compared to control lymph administration. LCFA infusion in WT, but not in CCK1R^−/− mice, significantly reduced these pathological effects of EL.

Conclusion

During endotoxemia enteral LCFA absorption reduces TNFα release into mesenteric lymph and attenuates histomorphologic parameters of lung dysfunction. Failure to elicit this effect in CCK1R^−/− mice demonstrates that anti-inflammatory properties of LCFAs are mediated through CCK1-Rs.

Leptin resistance in vagal afferent neurons inhibits cholecystokinin signaling and satiation in diet induced obese rats

BACKGROUND AND AIMS

The gastrointestinal hormone cholecystokinin (CCK) plays an important role in regulating meal size and duration by activating CCK1 receptors on vagal afferent neurons (VAN). Leptin enhances CCK signaling in VAN via an early growth response 1 (EGR1) dependent pathway thereby increasing their sensitivity to CCK. In response to a chronic ingestion of a high fat diet, VAN develop leptin resistance and the satiating effects of CCK are reduced. We tested the hypothesis that leptin resistance in VAN is responsible for reducing CCK signaling and satiation.

RESULTS

Lean Zucker rats sensitive to leptin signaling, significantly reduced their food intake following administration of CCK8S (0.22 nmol/kg, i.p.), while obese Zucker rats, insensitive to leptin, did not. CCK signaling in VAN of obese Zucker rats was reduced, preventing CCK-induced up-regulation of Y2 receptor and down-regulation of melanin concentrating hormone 1 receptor (MCH1R) and cannabinoid receptor (CB1). In VAN from diet-induced obese (DIO) Sprague Dawley rats, previously shown to become leptin resistant, we demonstrated that the reduction in EGR1 expression resulted in decreased sensitivity of VAN to CCK and reduced CCK-induced inhibition of food intake. The lowered sensitivity of VAN to CCK in DIO rats resulted in a decrease in Y2 expression and increased CB1 and MCH1R expression. These effects coincided with the onset of hyperphagia in DIO rats.

CONCLUSIONS

Leptin signaling in VAN is required for appropriate CCK signaling and satiation. In response to high fat feeding, the onset of leptin resistance reduces the sensitivity of VAN to CCK thus reducing the satiating effects of CCK.

Gut microbiota, epithelial function and derangements in obesity

The gut epithelium is a barrier between the 'outside' and 'inside' world. The major function of the epithelium is to absorb nutrients, ions and water, yet it must balance these functions with that of protecting the 'inside' world from potentially harmful toxins, irritants, bacteria and other pathogens that also exist in the gut lumen. The health of an individual depends upon the efficient digestion and absorption of all required nutrients from the diet. This requires sensing of meal components by gut enteroendocrine cells, activation of neural and humoral pathways to regulate gastrointestinal motor, secretory and absorptive functions, and also to regulate food intake and plasma levels of glucose. In this way, there is a balance between the delivery of food and the digestive and absorptive capacity of the intestine. Maintenance of the mucosal barrier likewise requires sensory detection of pathogens, toxins and irritants; breakdown of the epithelial barrier is associated with gut inflammation and may ultimately lead to inflammatory bowel disease. However, disruption of the barrier alone is not sufficient to cause frank inflammatory bowel disease. Several recent studies have provided compelling new evidence to suggest that changes in epithelial barrier function and inflammation are associated with and may even lead to altered regulation of body weight and glucose homeostasis. This article provides a brief review of some recent evidence to support the hypothesis that changes in the gut microbiota and alteration of gut epithelial function will perturb the homeostatic humoral and neural pathways controlling food intake and body weight.

Glucose sensing by gut endocrine cells and activation of the vagal afferent pathway is impaired in a rodent model of type 2 diabetes mellitus

Glucose in the gut lumen activates gut endocrine cells to release 5-HT, glucagon-like peptide 1/2 (GLP-1/2), and glucose-dependent insulinotropic polypeptide (GIP), which act to change gastrointestinal function and regulate postprandial plasma glucose. There is evidence that both release and action of incretin hormones is reduced in type 2 diabetes (T2D). We measured cellular activation of enteroendocrine and enterochromaffin cells, enteric neurons, and vagal afferent neurons in response to intestinal glucose in a model of type 2 diabetes mellitus, the UCD-T2DM rat. Prediabetic (PD), recent-diabetic (RD, 2 wk postonset), and 3-mo diabetic (3MD) fasted UCD-T2DM rats were given an orogastric gavage of vehicle (water, 0.5 ml /100 g body wt) or glucose (330 μmol/100 g body wt); after 6 min tissue was removed and cellular activation was determined by immunohistochemistry for phosphorylated calcium calmodulin-dependent kinase II (pCaMKII). In PD rats, pCaMKII immunoreactivity was increased in duodenal 5-HT (P < 0.001), K (P < 0.01) and L (P < 0.01) cells in response to glucose; glucose-induced activation of all three cell types was significantly reduced in RD and 3MD compared with PD rats. Immunoreactivity for GLP-1, but not GIP, was significantly reduced in RD and 3MD compared with PD rats (P < 0.01). Administration of glucose significantly increased pCaMKII in enteric and vagal afferent neurons in PD rats; glucose-induced pCaMKII immunoreactivity was attenuated in enteric and vagal afferent neurons (P < 0.01, P < 0.001, respectively) in RD and 3MD. These data suggest that glucose sensing in enteroendocrine and enterochromaffin cells and activation of neural pathways is markedly impaired in UCD-T2DM rats.

Intestinal glucose-induced calcium-calmodulin kinase signaling in the gut-brain axis in awake rats

BACKGROUND

Lumenal glucose initiates changes in gastrointestinal (GI) function, including inhibition of gastric emptying, stimulation of pancreatic exocrine and endocrine secretion, and intestinal fluid secretion. Glucose stimulates the release of GI hormones and 5-hydroxytryptamine (5-HT), and activates intrinsic and extrinsic neuronal pathways to initiate changes in GI function. The precise mechanisms involved in luminal glucose-sensing are not clear; studying gut endocrine cells is difficult due to their sparse and irregular localization within the epithelium.

METHODS

Here we show a technique to determine activation of gut epithelial cells and the gut-brain pathway in vivo in rats using immunohistochemical detection of the activated, phosphorylated, form of calcium-calmodulin kinase II (pCaMKII).

KEY RESULTS

Perfusion of the gut with glucose (60 mg) increased pCaMKII immunoreactivity in 5-HT-expressing enterochromaffin (EC) cells, cytokeratin-18 immunopositive brush cells, but not in enterocytes or cholecystokinin-expressing cells. Lumenal glucose increased pCaMKII in neurons in the myenteric plexus and nodose ganglion, nucleus of the solitary tract, dorsal motor nucleus of the vagus and the arcuate nucleus. pCaMKII expression in neurons, but not in EC cells, was significantly attenuated by pretreatment with the 5-HT(3) R antagonist ondansetron. Deoxynojirimycin, a selective agonist for the putative glucose sensor, sodium-glucose cotransporter-3 (SGLT-3), mimicked the effects of glucose with increased pCaMKII in ECs and neurons; galactose had no effect.

CONCLUSIONS & INFERENCES

The data suggest that native EC cells in situ respond to glucose, possibly via SGLT-3, to activate intrinsic and extrinsic neurons and thereby regulate GI function.

Diet-induced obesity leads to the development of leptin resistance in vagal afferent neurons

Ingestion of high-fat, high-calorie diets is associated with hyperphagia, increased body fat, and obesity. The mechanisms responsible are currently unclear; however, altered leptin signaling may be an important factor. Vagal afferent neurons (VAN) integrate signals from the gut in response to ingestion of nutrients and express leptin receptors. Therefore, we tested the hypothesis that leptin resistance occurs in VAN in response to a high-fat diet. Sprague-Dawley rats, which exhibit a bimodal distribution of body weight gain, were used after ingestion of a high-fat diet for 8 wk. Body weight, food intake, and plasma leptin levels were measured. Leptin signaling was determined by immunohistochemical localization of phosphorylated STAT3 (pSTAT3) in cultured VAN and by quantifaction of pSTAT3 protein levels by Western blot analysis in nodose ganglia and arcuate nucleus in vivo. To determine the mechanism of leptin resistance in nodose ganglia, cultured VAN were stimulated with leptin alone or with lipopolysaccharide (LPS) and SOCS-3 expression measured. SOCS-3 protein levels in VAN were measured by Western blot following leptin administration in vivo. Leptin resulted in appearance of pSTAT3 in VAN of low-fat-fed rats and rats resistant to diet-induced obesity but not diet-induced obese (DIO) rats. However, leptin signaling was normal in arcuate neurons. SOCS-3 expression was increased in VAN of DIO rats. In cultured VAN, LPS increased SOCS-3 expression and inhibited leptin-induced pSTAT3 in vivo. We conclude that VAN of diet-induced obese rats become leptin resistant; LPS and SOCS-3 may play a role in the development of leptin resistance.

Protein hydrolysate-induced cholecystokinin secretion from enteroendocrine cells is indirectly mediated by the intestinal oligopeptide transporter PepT1

Dietary protein is a major stimulant for cholecystokinin (CCK) secretion by the intestinal I cell, however, the mechanism by which protein is detected is unknown. Indirect functional evidence suggests that PepT1 may play a role in CCK-mediated changes in gastric motor function. However, it is unclear whether this oligopeptide transporter directly or indirectly activates the I cell. Using both the CCK-expressing enteroendocrine STC-1 cell and acutely isolated native I cells from CCK-enhanced green fluorescent protein (eGFP) mice, we aimed to determine whether PepT1 directly activates the enteroendocrine cell to elicit CCK secretion in response to oligopeptides. Both STC-1 cells and isolated CCK-eGFP cells expressed PepT1 transcripts. STC-1 cells were activated, as measured by ERK(1/2) phosphorylation, by both peptone and the PepT1 substrate Cefaclor; however, the PepT1 inhibitor 4-aminomethyl benzoic acid (AMBA) had no effect on STC-1 cell activity. The PepT1-transportable substrate glycyl-sarcosine dose-dependently decreased gastric motility in anesthetized rats but had no affect on activation of STC-1 cells or on CCK secretion by CCK-eGFP cells. CCK secretion was significantly increased in response to peptone but not to Cefaclor, cephalexin, or Phe-Ala in CCK-eGFP cells. Taken together, the data suggest that PepT1 does not directly mediate CCK secretion in response to PepT1 specific substrates. PepT1, instead, may have an indirect role in protein sensing in the intestine.

Cholecystokinin activation of central satiety centers changes seasonally in a mammalian hibernator

Hibernators that rely on lipids during winter exhibit profound changes in food intake over the annual cycle. The mechanisms that regulate appetite changes in seasonal hibernators remain unclear, but likely consist of complex interactions between gut hormones, adipokines, and central processing centers. We hypothesized that seasonal changes in the sensitivity of neurons in the nucleus tractus solitarius (NTS) to the gut hormone cholecystokinin (CCK) may contribute to appetite regulation in ground squirrels. Spring (SPR), late summer (SUM), and winter euthermic hibernating (HIB) 13-lined ground squirrels (Ictidomys tridecemlineatus) were treated with intraperitoneal CCK (100 μg/kg) or vehicle (CON) for 3h and Fos expression in the NTS was quantified. In CON squirrels, numbers of Fos-positive neurons in HIB were low compared to SPR and SUM. CCK treatment increased Fos-positive neurons in the NTS at the levels of the area postrema (AP) and pre AP during all seasons and at the level of the rostral AP in HIB squirrels. The highest absolute levels of Fos-positive neurons were found in SPR CCK squirrels, but the highest relative increase from CON was found in HIB CCK squirrels. Fold-changes in Fos-positive neurons in SUM were intermediate between SPR and HIB. Thus, CCK sensitivity falls from SPR to SUM suggesting that seasonal changes in sensitivity of NTS neurons to vagally-derived CCK may influence appetite in the active phase of the annual cycle in hibernating squirrels. Enhanced sensitivity to CCK signaling in NTS neurons of hibernators indicates that changes in gut-brain signaling may contribute to seasonal changes in food intake during the annual cycle.

Immunonutrition with long-chain fatty acids prevents activation of macrophages in the gut wall

BACKGROUND

Immune cells and inflammatory mediators are released from the gastrointestinal tract into the mesenteric lymph during sepsis causing distant organ dysfunction. Recently, it was demonstrated that macrophages in the gut wall are controlled by the vagus nerve, the so-called cholinergic anti-inflammatory pathway.

AIM

This study aims to investigate whether an enteral diet with lipid prevents the activation of leukocytes in the gut wall.

METHODS

Mesenteric lymph was obtained from rats, receiving an enteral infusion of glucose or glucose + lipid before and after lipopolysaccharide (LPS) injection. Immune cells in mesenteric lymph were analyzed with fluorescence-activated cell sorting before and after LPS injection. Mesenteric lymph leukocytes from rats receiving enteral glucose with or without lipid were stimulated in vitro with LPS and tumor necrosis factor (TNF)α was measured in the supernatant.

RESULTS

The release of macrophages from the gut during sepsis was not significantly different in animals enterally treated with glucose or lipid. However, the release of TNFα from mesenteric lymph leukocytes after in vitro LPS stimulation was more than 3-fold higher in the glucose group compared to the lipid-treated group.

CONCLUSIONS

During sepsis, activated macrophages are released from the gut into mesenteric lymph. However, an enteral diet with lipid is able to suppress the inflammatory cytokine release from mesenteric lymph leukocytes.

The extracellular calcium-sensing receptor is required for cholecystokinin secretion in response to L-phenylalanine in acutely isolated intestinal I cells

The extracellular calcium-sensing receptor (CaSR) has recently been recognized as an L-amino acid sensor and has been implicated in mediating cholecystokinin (CCK) secretion in response to aromatic amino acids. We investigated whether direct detection of L-phenylalanine (L-Phe) by CaSR results in CCK secretion in the native I cell. Fluorescence-activated cell sorting of duodenal I cells from CCK-enhanced green fluorescent protein (eGFP) transgenic mice demonstrated CaSR gene expression. Immunostaining of fixed and fresh duodenal tissue sections confirmed CaSR protein expression. Intracellular calcium fluxes were CaSR dependent, stereoselective for L-Phe over D-Phe, and responsive to type II calcimimetic cinacalcet in CCK-eGFP cells. Additionally, CCK secretion by an isolated I cell population was increased by 30 and 62% in response to L-Phe in the presence of physiological (1.26 mM) and superphysiological (2.5 mM) extracellular calcium concentrations, respectively. While the deletion of CaSR from CCK-eGFP cells did not affect basal CCK secretion, the effect of L-Phe or cinacalcet on intracellular calcium flux was lost. In fact, both secretagogues, as well as superphysiological Ca(2+), evoked an unexpected 20-30% decrease in CCK secretion compared with basal secretion in CaSR(-/-) CCK-eGFP cells. CCK secretion in response to KCl or tryptone was unaffected by the absence of CaSR. The present data suggest that CaSR is required for hormone secretion in the specific response to L-Phe by the native I cell, and that a receptor-mediated mechanism may inhibit hormone secretion in the absence of a fully functional CaSR.

Oligosaccharide binding proteins from Bifidobacterium longum subsp. infantis reveal a preference for host glycans

Bifidobacterium longum subsp. infantis (B. infantis) is a common member of the infant intestinal microbiota, and it has been characterized by its foraging capacity for human milk oligosaccharides (HMO). Its genome sequence revealed an overabundance of the Family 1 of solute binding proteins (F1SBPs), part of ABC transporters and associated with the import of oligosaccharides. In this study we have used the Mammalian Glycan Array to determine the specific affinities of these proteins. This was correlated with binding protein expression induced by different prebiotics including HMO. Half of the F1SBPs in B. infantis were determined to bind mammalian oligosaccharides. Their affinities included different blood group structures and mucin oligosaccharides. Related to HMO, other proteins were specific for oligomers of lacto-N-biose (LNB) and polylactosamines with different degrees of fucosylation. Growth on HMO induced the expression of specific binding proteins that import HMO isomers, but also bind blood group and mucin oligosaccharides, suggesting coregulated transport mechanisms. The prebiotic inulin induced other family 1 binding proteins with affinity for intestinal glycans. Most of the host glycan F1SBPs in B. infantis do not have homologs in other bifidobacteria. Finally, some of these proteins were found to be adherent to intestinal epithelial cells in vitro. In conclusion, this study represents further evidence for the particular adaptations of B. infantis to the infant gut environment, and helps to understand the molecular mechanisms involved in this process.

Vagal afferent neurons in high fat diet-induced obesity; intestinal microflora, gut inflammation and cholecystokinin

The vagal afferent pathway is the major neural pathway by which information about ingested nutrients reaches the CNS and influences both GI function and feeding behavior. Vagal afferent neurons (VAN) express receptors for many of the regulatory peptides and molecules released from the intestinal wall, pancreas, and adipocytes that influence GI function, glucose homeostasis, and regulate food intake and body weight. As such, they play a critical role in both physiology and pathophysiology, such as obesity, where there is evidence that vagal afferent function is altered. This review will summarize recent findings on changes in vagal afferent function in response to ingestion of high fat diets and explore the hypothesis that changes in gut microbiota and integrity of the epithelium may not only be important in inducing these changes but may be the initial events that lead to dysregulation of food intake and body weight in response to high fat, high energy diets.

Effect of ghrelin receptor antagonist on meal patterns in cholecystokinin type 1 receptor null mice

Vagal afferent neurons (VAN) express the cholecystokinin (CCK) type 1 receptor (CCK₁R) and, as predicted by the role of CCK in inducing satiation, CCK₁R⁻/⁻ mice ingest larger and longer meals. However, after a short fast, CCK₁R⁻/⁻ mice ingesting high fat (HF) diets initiate feeding earlier than wild-type mice. We hypothesized that the increased drive to eat in CCK₁R⁻/⁻ mice eating HF diet is mediated by ghrelin, a gut peptide that stimulates food intake. The decrease in time to first meal, and the increase in meal size and duration in CCK₁R⁻/⁻ compared to wild-type mice ingesting high fat (HF) diet were reversed by administration of GHSR1a antagonist D-(Lys3)-GHRP-6 (p<0.05). Administration of the GHSR1a antagonist significantly increased expression of the neuropeptide cocaine and amphetamine-regulated transcript (CART) in VAN of HF-fed CCK₁R⁻/⁻ but not wild-type mice. Administration of the GHSR1a antagonist decreased neuronal activity measured by immunoreactivity for fos protein in the nucleus of the solitary tract (NTS) and the arcuate nucleus of both HF-fed wild-type and CCK₁R⁻/⁻ mice. The data show that hyperphagia in CCK₁R⁻/⁻ mice ingesting HF diet is reversed by blockade of the ghrelin receptor, suggesting that in the absence of the CCK₁R, there is an increased ghrelin-dependent drive to feed. The site of action of ghrelin receptors is unclear, but may involve an increase in expression of CART peptide in VAN in HF-fed CCK₁R⁻/⁻ mice.

Propensity to high-fat diet-induced obesity in rats is associated with changes in the gut microbiota and gut inflammation

Consumption of diets high in fat and calories leads to hyperphagia and obesity, which is associated with chronic "low-grade" systemic inflammation. Ingestion of a high-fat diet alters the gut microbiota, pointing to a possible role in the development of obesity. The present study used Sprague-Dawley rats that, when fed a high-fat diet, exhibit either an obesity-prone (DIO-P) or obesity-resistant (DIO-R) phenotype, to determine whether changes in gut epithelial function and microbiota are diet or obese associated. Food intake and body weight were monitored daily in rats maintained on either low- or high-fat diets. After 8 or 12 wk, tissue was removed to determine adiposity and gut epithelial function and to analyze the gut microbiota using PCR. DIO-P but not DIO-R rats exhibit an increase in toll-like receptor (TLR4) activation associated with ileal inflammation and a decrease in intestinal alkaline phosphatase, a luminal enzyme that detoxifies lipopolysaccharide (LPS). Intestinal permeability and plasma LPS were increased together with phosphorylation of myosin light chain and localization of occludin in the cytoplasm of epithelial cells. Measurement of bacterial 16S rRNA showed a decrease in total bacterial density and an increase in the relative proportion of Bacteroidales and Clostridiales orders in high-fat-fed rats regardless of phenotype; an increase in Enterobacteriales was seen in the microbiota of DIO-P rats only. Consumption of a high-fat diet induces changes in the gut microbiota, but it is the development of inflammation that is associated with the appearance of hyperphagia and an obese phenotype.

Ileal interposition surgery improves glucose and lipid metabolism and delays diabetes onset in the UCD-T2DM rat

BACKGROUND & AIMS

Bariatric surgery has been shown to reverse type 2 diabetes; however, mechanisms by which this occurs remain undefined. Ileal interposition (IT) is a surgical model that isolates the effects of increasing delivery of unabsorbed nutrients to the lower gastrointestinal tract. In this study we investigated effects of IT surgery on glucose tolerance and diabetes onset in UCD-T2DM (University of California at Davis type 2 diabetes mellitus) rats, a polygenic obese animal model of type 2 diabetes.

METHODS

IT or sham surgery was performed on 4-month-old male UCD-T2DM rats. All animals underwent oral glucose tolerance testing (OGTT). A subset was killed 2 months after surgery for tissue analyses. The remainder was followed until diabetes onset and underwent oral fat tolerance testing (OFTT).

RESULTS

IT surgery delayed diabetes onset by 120 +/- 49 days compared with sham surgery (P < .05) without a difference in body weight. During OGTT, IT-operated animals exhibited lower plasma glucose excursions (P < .05), improved early insulin secretion (P < .01), and 3-fold larger plasma glucagon-like peptide-1(7-36) (GLP-1(7-36)) excursions (P < .001), and no difference in glucose-dependent insulinotropic polypeptide responses compared with sham-operated animals. Total plasma peptide YY (PYY) excursions during OFTT were 3-fold larger in IT-operated animals (P < .01). IT-operated animals exhibited lower adiposity (P < .05), smaller adipocyte size (P < .05), 25% less ectopic lipid deposition, lower circulating lipids, and greater pancreatic insulin content compared with sham-operated animals (P < .05).

CONCLUSIONS

IT surgery delays the onset of diabetes in UCD-T2DM rats which may be related to increased nutrient-stimulated secretion of GLP-1(7-36) and PYY and improvements of insulin sensitivity, beta-cell function, and lipid metabolism.

Cholecystokinin knockout mice are resistant to high-fat diet-induced obesity

BACKGROUND & AIMS

Cholecystokinin (CCK) is a satiation peptide released during meals in response to lipid intake; it regulates pancreatic digestive enzymes that are required for absorption of nutrients. We proposed that mice with a disruption in the CCK gene (CCK knockout [CCK-KO] mice) that were fed a diet of 20% butter fat would have altered fat metabolism.

METHODS

We used quantitative magnetic resonance imaging to determine body composition and monitored food intake of CCK-KO mice using an automated measurement system. Intestinal fat absorption and energy expenditure were determined using a noninvasive assessment of intestinal fat absorption and an open circuit calorimeter, respectively.

RESULTS

After consuming a high-fat diet for 10 weeks, CCK-KO mice had reduced body weight gain and body fat mass and enlarged adipocytes, despite the same level of food intake as wild-type mice. CCK-KO mice also had defects in fat absorption, especially of long-chain saturated fatty acids, but pancreatic triglyceride lipase did not appear to have a role in the fat malabsorption. Energy expenditure was higher in CCK-KO than wild-type mice, and CCK-KO mice had greater oxidation of carbohydrates while on the high-fat diet. Plasma leptin levels in the CCK-KO mice fed the high-fat diet were markedly lower than in wild-type mice, although levels of insulin, gastric-inhibitory polypeptide, and glucagon-like peptide-1 were normal.

CONCLUSIONS

CCK is involved in regulating the metabolic rate and is important for lipid absorption and control of body weight in mice placed on a high-fat diet.