Gut-derived serotonin contributes to bone deficits in colitis.

Osteoporosis and bone fractures occur at higher frequency in patients with inflammatory bowel disease (IBD), and decreased bone mass is observed in animal models of colitis. Another consistent feature of colitis is increased serotonin (5-HT) availability in the intestinal mucosa. Since gut-derived 5-HT can decrease bone mass, via activation of 5-HT1B receptors on pre-osteoblasts, we tested the hypothesis that 5-HT contributes to bone loss in colitis. Colitis was chronically induced in mice by adding dextran sodium sulfate (DSS) to their drinking water for 21 days. At day 21, circulating 5-HT levels were elevated in DSS-inflamed mice. Micro-computed tomography of femurs showed a decrease in trabecular bone volume fraction, formation, and surface area, due largely to decreased trabecular numbers in DSS-treated mice. The colitis-induced loss of trabecular bone was significantly suppressed in mice treated with the 5-HT synthesis inhibitor, p-chloro-DL-phenylalanine (PCPA; 300 mg/kg/day IP daily), and in mice treated with the 5-HT1B receptor antagonist GR55562 (1 mg/Kg/day SC daily). The 5-HT reuptake transporter (SERT) is critical for moving 5-HT from the interstitial space into enterocytes and from serum into platelets. Mice lacking SERT exhibited significant deficits in trabecular bone mass that are similar to those observed in DSS-inflamed mice, and these deficits were not extensively worsened by DSS-induced colitis in the SERT-/- mice. Taken together, findings from both the DSS and SERT-/- mouse models support a contributing role for 5-HT as a significant factor in bone loss induced by colitis.

Colonic immune cells in irritable bowel syndrome: A systematic review and meta-analysis.

BACKGROUND & AIMS: Increases in mucosal immune cells have frequently been observed in irritable bowel syndrome (IBS) patients. However, this finding is not completely consistent between studies, possibly due to a combination of methodological variability, population differences and small sample sizes. We performed a meta-analysis of case-control studies that compared immune cell counts in colonic biopsies of IBS patients and controls. METHODS: PubMed and Embase were searched in February 2017. Results were pooled using standardized mean difference (SMD) and were considered significant when zero was not within the 95% confidence interval (CI). Heterogeneity was assessed based on I2 statistics where I2  ≤ 50% and I2  > 50% indicated fixed and random effect models, respectively. KEY RESULTS: Twenty-two studies on 706 IBS patients and 401 controls were included. Mast cells were increased in the rectosigmoid (SMD: 0.38 [95% CI: 0.06-0.71]; P = .02) and descending colon (SMD: 1.69 [95% CI: 0.65-2.73]; P = .001) of IBS patients. Increased mast cells were observed in both constipation (IBS-C) and diarrhea predominant IBS (IBS-D). CD3+ T cells were increased in the rectosigmoid (SMD: 0.53 [95% CI: 0.21-0.85]; P = .001) and the descending colon of the IBS patients (SMD: 0.79, 95% CI [0.28-1.30]; P = .002). This was possibly in relation to higher CD4+ T cells in IBS (SMD: 0.33 [95% CI: 0.01-0.65]; P = .04) as there were no differences in CD8+ T cells. CONCLUSIONS & INFERENCES: Mast cells and CD3+ T cells are increased in colonic biopsies of patients with IBS vs non-inflamed controls. These changes are segmental and sometimes IBS-subtype dependent. The diagnostic value of the quantification of colonic mucosal cells in IBS requires further investigation.

NDRG4, an early detection marker for colorectal cancer, is specifically expressed in enteric neurons.

BACKGROUND: Promoter methylation of N-myc Downstream-Regulated Gene 4 (NDRG4) in fecal DNA is an established early detection marker for colorectal cancer (CRC). Despite its connection to CRC, NDRG4 is predominantly studied in brain and heart, with little to no knowledge about its expression or role in other organs. In this study, we aimed to determine the whole-body expression of NDRG4, with a focus on the intestinal tract. METHODS: We investigated NDRG4 expression throughout the body by immunohistochemistry, Western Blotting and in situ mRNA hybridization using tissues from NDRG4 wild-type, heterozygous and knockout mice and humans. In addition, we explored cell-specific expression of NDRG4 in murine whole-mount gut preparations using immunofluorescence and confocal microscopy. KEY RESULTS: NDRG4 is specifically expressed within nervous system structures throughout the body. In the intestinal tract of both mouse and man, NDRG4 immunoreactivity was restricted to the enteric nervous system (ENS), where it labeled cell bodies of the myenteric and submucosal plexuses and interconnecting nerve fibers. More precisely, NDRG4 expression was limited to neurons, as NDRG4 always co-localized with HuC/D (pan-neuronal marker) but never with GFAP (an enteric glial cell marker). Furthermore, NDRG4 was expressed in various neuropeptide Y positive neurons, but was only found in a minority (~10%) of neurons expressing neuronal nitric oxide synthase. CONCLUSIONS AND INFERENCES: NDRG4 is exclusively expressed by central, peripheral and enteric neurons/nerves, suggesting a neuronal-specific role of this protein. Our findings raise the question whether NDRG4, via the ENS, an understudied component of the tumor microenvironment, supports CRC development and/or progression.

Suppression of colitis by adoptive transfer of helminth antigen-treated dendritic cells requires interleukin-4 receptor-α signaling.

Infection with helminth parasites has been explored as a treatment for autoimmune and inflammatory diseases. As helminth antigens have potent immunomodulation properties capable of inducing regulatory programs in a variety of cell types, transferring cells treated with helminth antigens represents a novel extension to helminth therapy. Previous work determined that transfer of bone marrow-derived dendritic cells (DC) pulsed with a crude extract of the tapeworm Hymenolepis diminuta (HD) can suppress colitis in recipient mice. The present study explored the mechanism of disease suppression and the importance of interleukin (IL)-4 signaling. Transfer of HD-DCs suppressed dinitrobenzene sulfonic acid (DNBS)-induced colitis through activation of recipient IL-4 receptor-α. The transferred HD-DCs required IL-4Rα and the capacity to secrete IL-10 to drive IL-4 and IL-10 production and to suppress colitis in recipient mice. Treatment of DCs with IL-4 evokes an alternatively activated phenotype, but adoptive transfer of these cells did not affect the outcome of colitis. Collectively, these studies demonstrate the complexity between IL-4 and IL-10 in donor cells and recipient, and the requirement for parasite- and host-derived factors in this novel form of cell therapy. Thus IL-4Rα signaling is revealed as a pathway that could be exploited for helminth antigen cell-based therapy.

Targeting the gut to treat obesity and its metabolic consequences: view from the Chair.

The neurohumoral signaling systems of the gastrointestinal (GI) tract are considered the most significant of the peripheral inputs controlling both food intake in the short term and energy balance over a longer time course. The importance of the GI tract in the control of energy balance is underscored by the marked beneficial effects of bariatric surgeries for the treatment of obesity. Despite their effectiveness, the mechanisms of bariatric surgery remain to be fully elucidated. Considerable new evidence points to the importance of gut-brain communication, gut barrier function and microbial signaling as three of the most important mechanisms of bariatric surgery-induced weight loss. These mechanisms are reviewed in the present article and the accompanying four papers.

Transient receptor potential vanilloid 4 inhibits mouse colonic motility by activating NO-dependent enteric neurotransmission.

UNLABELLED: Recent studies implicate TRPV4 receptors in visceral pain signaling and intestinal inflammation. Our aim was to evaluate the role of TRPV4 in the control of gastrointestinal (GI) motility and to establish the underlying mechanisms. We used immunohistochemistry and PCR to study TRPV4 expression in the GI tract. The effect of TRPV4 activation on GI motility was characterized using in vitro and in vivo motility assays. Calcium and nitric oxide (NO) imaging were performed to study the intracellular signaling pathways. Finally, TRPV4 expression was examined in the colon of healthy human subjects. We demonstrated that TRPV4 can be found on myenteric neurons of the colon and is co-localized with NO synthase (NOS-1). In vitro, the TRPV4 agonist GSK1016790A reduced colonic contractility and increased inhibitory neurotransmission. In vivo, TRPV4 activation slowed GI motility and reduced stool production in mouse models mimicking pathophysiological conditions. We also showed that TRPV4 activation inhibited GI motility by reducing NO-dependent Ca(2+) release from enteric neurons. In conclusion, TRPV4 is involved in the regulation of GI motility in health and disease. KEY MESSAGES: • Recent studies implicate TRPV4 in pain signaling and intestinal inflammation. • Our aim was to characterize the role of TRPV4 in the control of GI motility. • We found that TRPV4 activation reduced colonic contractility. • Our studies also showed altered TRPV4 mRNA expression in IBS-C patients. • TRPV4 may be a novel pharmacological target in functional GI diseases.

Inhibiting endocannabinoid biosynthesis: a novel approach to the treatment of constipation.

BACKGROUND AND PURPOSE: Endocannabinoids are a family of lipid mediators involved in the regulation of gastrointestinal (GI) motility. The expression, localization and function of their biosynthetic enzymes in the GI tract are not well understood. Here, we examined the expression, localization and function of the enzyme diacylglycerol lipase-α (DAGLα), which is involved in biosynthesis of the endocannabinoid 2-arachidonoylglycerol (2-AG). EXPERIMENTAL APPROACH: Cannabinoid CB1 receptor-deficient, wild-type control and C3H/HeJ mice, a genetically constipated strain, were used. The distribution of DAGLα in the enteric nervous system was examined by immunohistochemistry. Effects of the DAGL inhibitors, orlistat and OMDM-188 on pharmacologically induced GI hypomotility were assessed by measuring intestinal contractility in vitro and whole gut transit or faecal output in vivo. Endocannabinoid levels were measured by mass spectrometry. KEY RESULTS: DAGLα was expressed throughout the GI tract. In the intestine, unlike DAGLß, DAGLα immunoreactivity was prominently expressed in the enteric nervous system. In the myenteric plexus, it was colocalized with the vesicular acetylcholine transporter in cholinergic nerves. In normal mice, inhibiting DAGL reversed both pharmacologically reduced intestinal contractility and pharmacologically prolonged whole gut transit. Moreover, inhibiting DAGL normalized faecal output in constipated C3H/HeJ mice. In colons incubated with scopolamine, 2-AG was elevated while inhibiting DAGL normalized 2-AG levels. CONCLUSIONS AND IMPLICATIONS: DAGLα was expressed in the enteric nervous system of mice and its inhibition reversed slowed GI motility, intestinal contractility and constipation through 2-AG and CB1 receptor-mediated mechanisms. Our data suggest that DAGLα inhibitors may be promising candidates for the treatment of constipation.

AM841, a covalent cannabinoid ligand, powerfully slows gastrointestinal motility in normal and stressed mice in a peripherally restricted manner.

BACKGROUND AND PURPOSE: Cannabinoid (CB) ligands have been demonstrated to have utility as novel therapeutic agents for the treatment of pain, metabolic conditions and gastrointestinal (GI) disorders. However, many of these ligands are centrally active, which limits their usefulness. Here, we examine a unique novel covalent CB receptor ligand, AM841, to assess its potential for use in physiological and pathophysiological in vivo studies. EXPERIMENTAL APPROACH: The covalent nature of AM841 was determined in vitro using electrophysiological and receptor internalization studies on isolated cultured hippocampal neurons. Mouse models were used for behavioural analysis of analgesia, hypothermia and hypolocomotion. The motility of the small and large intestine was assessed in vivo under normal conditions and after acute stress. The brain penetration of AM841 was also determined. KEY RESULTS: AM841 behaved as an irreversible CB1 receptor agonist in vitro. AM841 potently reduced GI motility through an action on CB1 receptors in the small and large intestine under physiological conditions. AM841 was even more potent under conditions of acute stress and was shown to normalize accelerated GI motility under these conditions. This compound behaved as a peripherally restricted ligand, showing very little brain penetration and no characteristic centrally mediated CB1 receptor-mediated effects (analgesia, hypothermia or hypolocomotion). CONCLUSIONS AND IMPLICATIONS: AM841, a novel peripherally restricted covalent CB1 receptor ligand that was shown to be remarkably potent, represents a new class of potential therapeutic agents for the treatment of functional GI disorders.

Cytokine imbalance in irritable bowel syndrome: a systematic review and meta-analysis.

BACKGROUND: Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder of unknown etiology; although infection and inflammation have recently been considered as important etiologic agents. A recent meta-analysis showed correlations between cytokine [interleukin-10 (IL-10) and tumor necrosis factor (TNF)] gene polymorphisms and IBS; however, it is still unknown whether patients with IBS have different cytokine profiles compared to healthy population. METHODS: To determine the relationships between serum/plasma levels or mucosal expression of IL-10/TNF-α and IBS, we conducted a systematic review and meta-analysis based on case-control studies retrieved from PubMed and EMBASE search through August 2013. Standardized mean difference (SMD) was generated by using the inverse variance method. Heterogeneity was assessed based on I(2) values. KEY RESULTS: Serum/plasma levels of TNF-α tended to be higher in IBS vs controls (p = 0.09); this reached significance in IBS subtypes vs controls and in female patients with IBS. However, serum/plasma levels of IL-10 were not significantly different in IBS patients vs controls. Further analysis of serum/plasma IL-10 levels in IBS subtypes did not show any difference; however, analysis based on gender showed a significantly lower serum/plasma IL-10 levels in male patients with IBS vs male controls (p = 0.02). Colonic IL-10 mRNA had a significantly lower expression in IBS vs control (p = 0.001). CONCLUSIONS & INFERENCES: There is an imbalance of proinflammatory TNF-α, and anti-inflammatory IL-10, cytokines in IBS. Stratifying IBS patients based on cytokine profile may represent an opportunity for personalized treatment of this condition.

High fat diet and body weight have different effects on cannabinoid CB(1) receptor expression in rat nodose ganglia.

Energy balance is regulated, in part, by the orexigenic signaling pathways of the vagus nerve. Fasting-induced modifications in the expression of orexigenic signaling systems have been observed in vagal afferents of lean animals. Altered basal cannabinoid (CB1) receptor expression in the nodose ganglia in obesity has been reported. Whether altered body weight or a high fat diet modifies independent or additive changes in CB1 expression is unknown. We investigated the expression of CB1 and orexin 1 receptor (OX-1R) in the nodose ganglia of rats fed ad libitum or food deprived (24h), maintained on low or high fat diets (HFD), with differing body weights. Male Wistar rats were fed chow or HFD (diet-induced obese: DIO or diet-resistant: DR) or were body weight matched to the DR group but fed chow (wmDR). CB1 and OX-1R immunoreactivity were investigated and CB1 mRNA density was determined using in situ hybridization. CB1 immunoreactivity was measured in fasted rats after sulfated cholecystokinin octapeptide (CCK8s) administration. In chow rats, fasting did not modify the level of CB1 mRNA. More CB1 immunoreactive cells were measured in fed DIO, DR and wmDR rats than chow rats; levels increased after fasting in chow and wmDR rats but not in DIO or DR rats. In HFD fasted rats CCK8s did not reduce CB1 immunoreactivity. OX-1R immunoreactivity was modified by fasting only in DR rats. These data suggest that body weight contributes to the proportion of neurons expressing CB1 immunoreactivity in the nodose ganglion, while HFD blunts fasting-induced increases, and CCK-induced suppression of, CB1-immunoreactivity.

Brain CB1 receptor expression following lipopolysaccharide-induced inflammation.

Cannabinoid 1 receptors (CB(1)) are highly expressed on presynaptic terminals in the brain where they are importantly involved in the control of neurotransmitter release. Alteration of CB(1) expression is associated with a variety of neurological and psychiatric disorders. There is now compelling evidence that peripheral inflammatory disorders are associated with depression and cognitive impairments. These can be modeled in rodents with peripheral administration of lipopolysaccharide (LPS), but central effects of this treatment remain to be fully elucidated. As a reduction in endocannabinoid tone is thought to contribute to depression, we asked whether the expression of CB(1) in the CNS is altered following LPS treatment. CD1 mice received LPS (0.1-1mg/kg, ip) and 6h later activated microglial cells were observed only in circumventricular organs and only at the higher dose. At 24h, activated microglial cells were identified in other brain regions, including the hippocampus, a structure implicated in some mood disorders. Immunohistochemistry and real-time polymerase chain reaction (PCR) were utilized to evaluate the change of CB(1) expression 24h after inflammation. LPS induced an increase of CB(1) mRNA in the hippocampus and brainstem. Subsequent immunohistochemical analysis revealed reduced CB(1) in the hippocampus, especially in CA3 pyramidal layer. Analysis of co-localization with markers of excitatory and inhibitory terminals indicated that the decrease in CB(1) expression was restricted to glutamatergic terminals. Despite widespread microglial activation, these results suggest that peripheral LPS treatment leads to limited changes in CB(1) expression in the brain.

Cytokine gene polymorphisms are associated with irritable bowel syndrome: a systematic review and meta-analysis.

BACKGROUND: Low-grade inflammation has been increasingly implicated in the pathophysiology of irritable bowel syndrome (IBS). Imbalances of pro- and anti-inflammatory cytokines and polymorphisms in cytokine genes have been reported in IBS; however, these findings have not been consistently observed. This may be due to small sample sizes and differences in ethnicities. Therefore, we performed a meta-analysis on the studies that investigated cytokine gene polymorphisms in IBS patients compared to healthy controls. METHODS: A PubMed and EMBASE search was performed, and cytokine gene polymorphisms, which had been investigated in at least two case-control studies, were evaluated. Pooled odds ratios (OR) for the genotypes were calculated using random- or fixed-effects models. KEY RESULTS: Five studies that investigated interleukin-10 (IL-10; -1082 G/A), transforming growth factor-ß1 (TGF-ß1; +869 T/C and +915 G/C) and tumor necrosis factor (TNF; -308 G/A) polymorphisms in IBS patients and controls were included. High producer IL-10 (-1082 G/G; OR: 0.64 [95% CI: 0.48-0.87]) was significantly associated with a decreased risk of IBS. The intermediate producer TGF-ß1 (+915 G/C) genotype showed a tendency toward decreasing the risk of IBS. No associations were found between TNF (-308 G/A) genotypes and IBS in the whole meta-analysis although an analysis of Asian studies revealed an association between TNF (-308 G/A and G/G) genotypes and IBS (OR: 0.50 [95% CI: 0.29-0.85]), and 1.82 [95% CI: 1.08-3.07], respectively). CONCLUSIONS & INFERENCES: This meta-analysis indicates a role for IL-10 polymorphisms in IBS in general and TNF in Asian populations. Whether or not gene polymorphisms are associated with alterations in cytokine levels leading to functional effects at the level of the gut needs further investigation.

Endogenous cellular prion protein regulates contractility of the mouse ileum.

BACKGROUND: Cellular prion protein (PrP(C) ) is expressed in the enteric nervous system (ENS), however, its physiological role has not been identified. Studies suggest that PrP(C) can function as a metal-binding protein, as absence of the protein has been linked to altered copper metabolism and atypical synaptic activity. Because copper is known to modulate smooth muscle relaxation, we tested the hypothesis that PrP(C) deficiency would alter intestinal contractility. METHODS: We examined electrically evoked ileal contractility in Prnp(-/-) or wild type littermate mice and the effects of copper or copper chelation. PrP(C) expression was studied in whole mount ileal preparations of mice and guinea pigs by immunohistochemistry. KEY RESULTS: Relative to wild type mice, ileal tissues of Prnp(-/-) mice exhibited reduced electrical field stimulation (EFS)-evoked contractility. Furthermore, EFS-induced relaxation, as a percentage of that induced by a nitric oxide donor, was enhanced. Addition of a copper donor to the organ bath increased, whereas the addition of a copper chelator inhibited, nitric oxide donor-induced ileal relaxation in Prnp(-/-) mice. PrP(C) was expressed on nerve fibers or terminals, and some cell bodies in the myenteric and submucosal plexuses of wild type mice. PrP(C) colocalized with a neuron-specific ectonucleotidase, nucleoside triphosphate diphosphohydrolase 3 (NTPDase3), but to only a limited extent with GFAP, a marker of enteric glia. Guinea pigs expressed PrP(C) in nerve fibers or terminals and enteric glia in the myenteric and submucosal plexuses. CONCLUSIONS & INFERENCES: Our findings suggest that PrP(C) , which is abundant in the ENS, has a role in the regulation of ileal contractility.

Plasticity of mouse enteric synapses mediated through endocannabinoid and purinergic signaling.

BACKGROUND: The enteric nervous system (ENS) possesses extensive synaptic connections which integrate information and provide appropriate outputs to coordinate the activity of the gastrointestinal tract. The regulation of enteric synapses is not well understood. Cannabinoid (CB)(1) receptors inhibit the release of acetylcholine (ACh) in the ENS, but their role in the synapse is not understood. We tested the hypothesis that enteric CB(1) receptors provide inhibitory control of excitatory neurotransmission in the ENS. METHODS: Intracellular microelectrode recordings were obtained from mouse myenteric plexus neurons. Interganglionic fibers were stimulated with a concentric stimulating electrode to elicit synaptic events on to the recorded neuron. Differences between spontaneous and evoked fast synaptic transmission was examined within preparations from CB(1) deficient mice (CB(1)(-/-)) and wild-type (WT) littermate controls. KEY RESULTS: Cannabinoid receptors were colocalized on terminals expressing the vesicular ACh transporter and the synaptic protein synaptotagmin. A greater proportion of CB(1)(-/-) neurons received spontaneous fast excitatory postsynaptic potentials than neurons from WT preparations. The CB(1) agonist WIN55,212 depressed WT synapses without any effect on CB(1)(-/-) synapses. Synaptic activity in response to depolarization was markedly enhanced at CB(1)(-/-) synapses and after treatment with a CB(1) antagonist in WT preparations. Activity-dependent liberation of a retrograde purine messenger was demonstrated to facilitate synaptic transmission in CB(1)(-/-) mice. CONCLUSIONS & INFERENCES: Cannabinoid receptors inhibit transmitter release at enteric synapses and depress synaptic strength basally and in an activity-dependent manner. These actions help explain accelerated intestinal transit observed in the absence of CB(1) receptors.

Inhibiting fatty acid amide hydrolase normalizes endotoxin-induced enhanced gastrointestinal motility in mice.

BACKGROUND AND PURPOSE: Gastrointestinal (GI) motility is regulated in part by fatty acid ethanolamides (FAEs), including the endocannabinoid (EC) anandamide (AEA). The actions of FAEs are terminated by fatty acid amide hydrolase (FAAH). We investigated the actions of the novel FAAH inhibitor AM3506 on normal and enhanced GI motility. EXPERIMENTAL APPROACH: We examined the effect of AM3506 on electrically-evoked contractility in vitro and GI transit and colonic faecal output in vivo, in normal and FAAH-deficient mice treated with saline or LPS (100 µg·kg(-1), i.p.), in the presence and absence of cannabinoid (CB) receptor antagonists. mRNA expression was measured by quantitative real time-PCR, EC levels by liquid chromatography-MS and FAAH activity by the conversion of [(3)H]-AEA to [(3)H]-ethanolamine in intestinal extracts. FAAH expression was examined by immunohistochemistry. KEY RESULTS: FAAH was dominantly expressed in the enteric nervous system; its mRNA levels were higher in the ileum than the colon. LPS enhanced ileal contractility in the absence of overt inflammation. AM3506 reversed the enhanced electrically-evoked contractions of the ileum through CB(1) and CB(2) receptors. LPS increased the rate of upper GI transit and faecal output. AM3506 normalized the enhanced GI transit through CB(1) and CB(2) receptors and faecal output through CB(1) receptors. LPS did not increase GI transit in FAAH-deficient mice. CONCLUSIONS AND IMPLICATIONS: Inhibiting FAAH normalizes various parameters of GI dysmotility in intestinal pathophysiology. Inhibition of FAAH represents a new approach to the treatment of disordered intestinal motility.

Animal models of bariatric/metabolic surgery shed light on the mechanisms of weight control and glucose homeostasis: view from the chair.

Bariatric/metabolic surgeries are remarkably effective in reducing weight over a sustained period of time, and they also have significant beneficial effects on glucose homeostasis. Interestingly, the metabolic benefits of these surgeries frequently occur before significant weight loss. Given these findings, it is perhaps not surprising that obesity researchers are asking, how does bariatric/metabolic surgery work? Establishing these mechanisms can offer new insights into the physiology of energy balance and the control of metabolism. In the second half of the 13(th) International Symposium of the Merck Frosst/CIHR Research Chair in Obesity, four papers that address the mechanisms of bariatric/metabolic surgery were presented. The papers that follow this viewpoint all make use of animal models to reveal the neurohumoral mechanisms underlying weight loss and improved glucose homeostasis after experimental bariatric surgery. The rodent models of the commonly used clinical procedures have shown that energy intake is increased, food reward is altered and that the proximal gut is important in the control of energy balance and glucose homeostasis. Taken together, these models shed light on the mechanisms of bariatric/metabolic surgery and offer new insights that, in the future, may lead to less invasive therapies.

The relationship between inflammation-induced neuronal excitability and disrupted motor activity in the guinea pig distal colon.

BACKGROUND: Colitis is associated with increased excitability of afterhyperpolarization neurons (AH neurons) and facilitated synaptic transmission in the myenteric plexus. These changes are accompanied by disrupted propulsive motility, particularly in ulcerated regions. This study examined the relationship between myenteric AH neuronal hyperexcitability and disrupted propulsive motility. METHODS: The voltage-activated Na(+) channel opener veratridine, the intermediate conductance Ca(2+) -activated K(+) channel inhibitor TRAM-34 and the 5-HT(4) receptor agonist tegaserod were used to evaluate the effects of neuronal hyperexcitability and synaptic facilitation on propulsive motility in normal guinea pig distal colon. Because trinitrobenzene sulfonic acid (TNBS)-colitis-induced hyperexcitability of myenteric afferent neurons involves increases in hyperpolarization-activated, cyclic nucleotide-gated (HCN) channel activity, the HCN channel inhibitors Cs(+) and ZD7288 were used to suppress AH neuronal activity in TNBS-colitis. KEY RESULTS: In non-inflamed preparations, veratridine halted propulsive motility (P<0.001). The rate of propulsive motor activity was significantly reduced following addition of TRAM-34 and tegaserod (P<0.001). In TNBS-inflamed preparations, in which motility was temporarily halted or obstructed at sites of ulceration, both Cs(+) and ZD7288 normalized motility through the inflamed regions. Immunohistochemistry studies demonstrated that the proportion of AH neurons in the myenteric plexus was unchanged in ulcerated regions, but there was a 10% reduction in total number of neurons per ganglion. CONCLUSIONS AND INFERENCES: These findings support the concept that inflammation-induced neuroplasticity in myenteric neurons, involving changes in ion channel activity that lead to enhanced AH neuronal excitability, can contribute to impaired propulsive colonic motility.

A novel peripherally restricted cannabinoid receptor antagonist, AM6545, reduces food intake and body weight, but does not cause malaise, in rodents.

BACKGROUND AND PURPOSE: Cannabinoid CB(1) receptor antagonists reduce food intake and body weight, but clinical use in humans is limited by effects on the CNS. We have evaluated a novel cannabinoid antagonist (AM6545) designed to have limited CNS penetration, to see if it would inhibit food intake in rodents, without aversive effects. EXPERIMENTAL APPROACH: Cannabinoid receptor binding studies, cAMP assays, brain penetration studies and gastrointestinal motility studies were carried out to assess the activity profile of AM6545. The potential for AM6545 to induce malaise in rats and the actions of AM6545 on food intake and body weight were also investigated. KEY RESULTS: AM6545 binds to CB(1) receptors with a K(i) of 1.7 nM and CB(2) receptors with a K(i) of 523 nM. AM6545 is a neutral antagonist, having no effect on cAMP levels in transfected cells and was less centrally penetrant than AM4113, a comparable CB(1) receptor antagonist. AM6545 reversed the effects of WIN55212-2 in an assay of colonic motility. In contrast to AM251, AM6545 did not produce conditioned gaping or conditioned taste avoidance in rats. In rats and mice, AM6545 dose-dependently reduced food intake and induced a sustained reduction in body weight. The effect on food intake was maintained in rats with a complete subdiaphragmatic vagotomy. AM6545 inhibited food intake in CB(1) receptor gene-deficient mice, but not in CB(1)/CB(2) receptor double knockout mice. CONCLUSIONS AND IMPLICATIONS: Peripherally active, cannabinoid receptor antagonists with limited brain penetration may be useful agents for the treatment of obesity and its complications.

The effects of glucagon-like peptide 2 on enteric neurons in intestinal inflammation.

BACKGROUND: Intestinal inflammation alters the structure and function of the enteric nervous system (ENS). Glucagon-like peptide 2 (GLP-2) reduces intestinal inflammation and has trophic effects on isolated neurons. This study examined the effects of GLP-2 treatment on the submucosal plexus of rat colon in the trinitrobenzene sulfonic acid (TNBS) model of colitis. METHODS: After administration of TNBS or saline/ethanol for controls, animals were allocated to treatment with GLP-2 (50 µg kg⁻¹ day⁻¹, s.c.) or sham injection of vehicle, twice daily. Animals were monitored, following clinical parameters, and killed on day 5. The number of neuronal cell bodies per ganglion was quantified using immunohistochemistry on submucosal whole mount preparations, with further characterization of specific subpopulations using antibodies against vasoactive intestinal polypeptide (VIP), neuronal nitric oxide synthase (nNOS), and enteric glial cells with glial fibrillary acid protein and S100. KEY RESULTS: Glucagon-like peptide 2 treatment was associated with a significant amelioration of weight loss, and reduced neutrophil infiltration and microscopic colitis scores in the TNBS animals. Inflammation resulted in a loss of enteric neurons in submucosal ganglia; GLP-2 treatment restored the enteric neuronal populations to normal. In control, non-inflamed animals, GLP-2 treatment increased the number of VIP expressing neurons per ganglion; in TNBS-treated animals, GLP-2 prevented an inflammation-induced reduction in the numbers of VIP expressing neurons per ganglion. Glucagon-like peptide 2 did not change the numbers of nNOS neurons or enteric glial cells in either the control, or inflamed state. CONCLUSIONS & INFERENCES: These findings show that GLP-2 increased the number of VIP expressing neurons in normal animals, and prevents the inflammation-induced loss of neurons in the colonic submucosal ganglia, with an increase in the proportion of VIP expressing neurons. They suggest that GLP-2 may have a role in protecting or regulating the circuitry of the ENS under basal and inflamed states.

Adaptation of intestinal secretomotor function and nutrient absorption in response to diet-induced obesity.

BACKGROUND: The gut plays a significant role in the development of obesity, notably through peptide signaling to the brain. However, few studies have investigated intestinal function per se in a rodent model of diet-induced obesity (DIO). Our aim was to investigate intestinal secretomotor function and glucose transport in DIO and diet-resistant (DR) rat jejunum. METHODS: Male outbred Sprague-Dawley rats were maintained on a medium high fat diet for 9-10 weeks and split into DIO and DR groups based on weight gain. Mucosal-submucosal preparations of the proximal jejunum were mounted in Ussing chambers and voltage-clamped at 0 mV. Glucose (10 mmol L(-1)), 2-deoxy-D-glucose (10 mmol L(-1)), and leptin (10 nmol L(-1)) were added to the luminal side of the tissue and veratridine (30 micromol L(-1)), bethanechol (100 micromol L(-1)), and forskolin (10 micromol L(-1)) were added to the basolateral side of the tissue. KEY RESULTS: Secretomotor responses were significantly decreased in DIO jejunum compared to DR tissues. Glucose-stimulated increases in I(sc) in DR animals, that were sensitive to leptin inhibition, were significantly reduced in DIO rats. Decreased sodium glucose transporter-1 mediated glucose transport was accompanied by a concomitant increase in the expression of jejunal glucose transporter-2. CONCLUSIONS & INFERENCES: These data suggest that submucosal nerve function is compromised in DIO rats and electrogenic glucose transport is significantly decreased. The latter may represent an adaptive response to limit nutrient absorption in the jejunum from DIO rats. However, the loss of secretomotor control may lead to an altered host defense with a resultant change in intestinal flora contributing to the maintenance of obesity.