Ghrelin and the brain-gut axis as a pharmacological target for appetite control

Appetite regulation is highly complex and involves a large number of orexigenic and anorexigenic peptide hormones. These are small, processed, secreted peptides derived from larger prepropeptide precursors. These peptides are important targets for the development of therapeutics for obesity, a global health epidemic. As a case study, we consider the ghrelin axis. The ghrelin axis is likely to be a particularly useful drug target, as it also plays a role in energy homeostasis, adipogenesis, insulin regulation and reward associated with food intake. Ghrelin is the only known circulating gut orexigenic peptide hormone. As it appears to play a role in diet-induced obesity, blocking the action of ghrelin is likely to be effective for treating and preventing obesity. The ghrelin peptide has been targeted using a number of approaches, with ghrelin mirror-image oligonucleotides (Spiegelmers) and immunotherapy showing some promise. The ghrelin receptor, the growth hormone secretagogue receptor, may also provide a useful target and a number of antagonists and inverse agonists have been developed. A particularly promising new target is the enzyme which octanoylates ghrelin, ghrelin O-acyltransferase (GOAT), and drugs that inhibit GOAT are likely to circumvent pharmacological issues associated with approaches that directly target ghrelin or its receptor.

Towards a cognitive neurobiology of brain-gut axis disorders

The past two decades have seen substantial gains in our understanding of the complex processes underlying disturbed brain-gut communication in disorders such as irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD). Despite a growing understanding of the neurobiology of brain-gut axis dysfunction, there is a relative paucity of investigations into how the various factors involved in dysregulating the brain-gut axis, including stress, immune activation and pain, could impact on fundamental brain processes such as cognitive performance. To this end, we proposed a cognitive neurobiology of brain-gut axis dysfunction and took a novel approach to examine how disturbed brain-gut interactions may manifest as altered cognitive performance in IBS and IBD, both cross-sectionally and prospectively. We have demonstrated that, disorders of the brain-gut axis are characterised by stable deficits in specific cognitive domains. Specifically, patients with IBS exhibit a consistent hippocampal mediated visuospatial memory impairment. In addition we have found evidence to suggest a similar visuospatial impairment in IBD. However, our most consistent finding within this population was that patients with Crohn’s disease exhibit impaired selective attention/ response inhibition on the classic Stroop interference test. These cognitive deficits may serve to perpetuate and sustain brain-gut axis dysfunction. Furthermore, this research has shed light on some of the underlying neurobiological mechanisms that may be mediating cognitive dysfunction in IBS. Our findings may have significant implications for the individual who suffers from a brain-gut axis disorder and may also inform future treatment strategies. Taken together, these findings can be incorporated into existing neurobiological models of brain-gut axis dysfunction, to develop a more comprehensive model accounting for the cognitive-neurobiology of brain-gut axis disorders. This has furthered our understanding of disease pathophysiology and may ultimately aid in both the diagnosis and treatment of these highly prevalent, but poorly understood disorders.

A remarkable, precisely timed release of hyperglycemic hormone from endocrine cells in the gut is associated with ecdysis in the crab Carcinus maenas

Molting or ecdysis is the most fundamentally important process in arthropod life history, because shedding of the exoskeleton is an absolute prerequisite for growth and metamorphosis. Although the hormonal mechanisms driving ecdysis in insects have been studied extensively, nothing is known about these processes in crustaceans. During late premolt and during ecdysis in the crab Carcinus maenas, we observed a precise and reproducible surge in hemolymph hyperglycemic hormone (CHH) levels, which was over 100-fold greater than levels seen in intermolt animals. The source of this hormone surge was not from the eyestalk neurosecretory tissues but from previously undescribed endocrine cells (paraneurons), in defined areas of the foregut and hindgut. During premolt (the only time when CHH is expressed by these tissues), the gut is the largest endocrine tissue in the crab. The CHH surge, which is a result of an unusual, almost complete discharge of the contents of the gut endocrine cell, regulates water and ion uptake during molting, thus allowing the swelling necessary for successful ecdysis and the subsequent increase in size during postmolt. This study defines an endocrine brain/gut axis in the arthropods. We propose that the ionoregulatory process controlled by CHH may be common to arthropods, in that, for insects, a similar mechanism seems to be involved in antidiuresis. It also seems likely that a cascade of very precisely coordinated release of (neuro) hormones controls ecdysis.

Tryptophan degradation in irritable bowel syndrome: evidence of indoleamine 2,3-dioxygenase activation in a male cohort

Background: Irritable bowel syndrome (IBS) is a common disorder that affects 10–15% of the population. Although characterised by a lack of reliable biological markers, the disease state is increasingly viewed as a disorder of the brain-gut axis. In particular, accumulating evidence points to the involvement of both the central and peripheral serotonergic systems in disease symptomatology. Furthermore, altered tryptophan metabolism and indoleamine 2,3-dioxygenase (IDO) activity are hallmarks of many stress-related disorders. The kynurenine pathway of tryptophan degradation may serve to link these findings to the low level immune activation recently described in IBS. In this study, we investigated tryptophan degradation in a male IBS cohort (n = 10) and control subjects (n = 26). Methods: Plasma samples were obtained from patients and healthy controls. Tryptophan and its metabolites were measured by high performance liquid chromatography (HPLC) and neopterin, a sensitive marker of immune activation, was measured using a commercially available ELISA assay. Results: Both kynurenine levels and the kynurenine:tryptophan ratio were significantly increased in the IBS cohort compared with healthy controls. Neopterin was also increased in the IBS subjects and the concentration of the neuroprotective metabolite kynurenic acid was decreased, as was the kynurenic acid:kynurenine ratio. Conclusion: These findings suggest that the activity of IDO, the immunoresponsive enzyme which is responsible for the degradation of tryptophan along this pathway, is enhanced in IBS patients relative to controls. This study provides novel evidence for an immune-mediated degradation of tryptophan in a male IBS population and identifies the kynurenine pathway as a potential source of biomarkers in this debilitating condition.

An investigation into mechanisms of visceral pain in rodents

Visceral pain is a debilitating symptom of irritable bowel syndrome (IBS), a disorder affecting up to 30% of adults. A better understanding of the mechanisms underlying visceral hypersensitivity may facilitate development of more targeted therapies, improving the quality of life of these individuals. The studies performed in this thesis were designed to investigate important factors of visceral pain, including early-life manipulations, genetic predisposition and sex hormones. Maternal separation (MS) consistently reproduces visceral hypersensitivity and altered anxiety-like behaviours in rats, symptoms associated with IBS. It has been found that 5-HT2B receptor antagonism blocks visceral pain but no difference in relative 5-HT2B receptor mRNA expression was found in hippocampus, amygdala and colon. The neuronal activation patterns of prefrontal cortex and amygdala of MS rats were then investigated. MS animals are characterised by differential activation of the prefrontal cortex (anterior cingulate cortex (ACC), infralibic cortex, prelimbic cortex) as well as the central nucleus of the amygdala (CeA). Genetic factors also contribute to pain syndromes such as IBS. We utilised the Wistar Kyoto (WKY) rat, a stress-sensitive strain, as an animal model of brain-gut axis dysfunction. WKY rats have a lower expression of the glutamate transporter EAAT2 and mGlu4 receptor in the ACC. Another early-life factor that can increase susceptibility to functional gastrointestinal symptoms later life is disruption of the gut microbiota, thus early-life antibiotic treatment was used to assess this effect. Antibiotic treatment induced visceral hypersensitivity in adulthood and may be related to observed reductions in spinal cord alpha-2A adrenoreceptor (adra2A) mRNA. Lastly, we investigated sex differences in visceral sensitivity. EAAT1 & 2 mRNA levels are lower in females, potentially increasing glutamatergic concentration at the symaptic level. Moreover, NR1 and NR2B subunits mRNA of NMDA receptor were increased in caudal ACC of females. These findings may account for sex differences in visceral sensitivity.

Water deprivation induces appetite and alters metabolic strategy in Notomys alexis : unique mechanisms for water production in the desert

Like many desert animals, the spinifex hopping mouse, Notomys alexis, can maintain water balance without drinking water. The role of the kidney in producing a small volume of highly concentrated urine has been well-documented, but little is known about the physiological mechanisms underpinning the metabolic production of water to offset obligatory water loss. In Notomys, we found that water deprivation (WD) induced a sustained high food intake that exceeded the pre-deprivation level, which was driven by parallel changes in plasma leptin and ghrelin and the expression of orexigenic and anorectic neuropeptide genes in the hypothalamus; these changed in a direction that would stimulate appetite. As the period of WD was prolonged, body fat disappeared but body mass increased gradually, which was attributed to hepatic glycogen storage. Switching metabolic strategy from lipids to carbohydrates would enhance metabolic water production per oxygen molecule, thus providing a mechanism to minimize respiratory water loss. The changes observed in appetite control and metabolic strategy in Notomys were absent or less prominent in laboratory mice. This study reveals novel mechanisms for appetite regulation and energy metabolism that could be essential for desert rodents to survive in xeric environments.

A novel method for studying the cortical processing of human swallowing using Synthetic Aperture Magnetometry(SAM)

Background/Aims: Positron emission tomography has been applied to study cortical activation during human swallowing, but employs radio-isotopes precluding repeated experiments and has to be performed supine, making the task of swallowing difficult. Here we now describe Synthetic Aperture Magnetometry (SAM) as a novel method of localising and imaging the brain's neuronal activity from magnetoencephalographic (MEG) signals to study the cortical processing of human volitional swallowing in the more physiological prone position. Methods: In 3 healthy male volunteers (age 28–36), 151-channel whole cortex MEG (Omega-151, CTF Systems Inc.) was recorded whilst seated during the conditions of repeated volitional wet swallowing (5mls boluses at 0.2Hz) or rest. SAM analysis was then performed using varying spatial filters (5–60Hz) before co-registration with individual MRI brain images. Activation areas were then identified using standard sterotactic space neuro-anatomical maps. In one subject repeat studies were performed to confirm the initial study findings. Results: In all subjects, cortical activation maps for swallowing could be generated using SAM, the strongest activations being seen with 10–20Hz filter settings. The main cortical activations associated with swallowing were in: sensorimotor cortex (BA 3,4), insular cortex and lateral premotor cortex (BA 6,8). Of relevance, each cortical region displayed consistent inter-hemispheric asymmetry, to one or other hemisphere, this being different for each region and for each subject. Intra-subject comparisons of activation localisation and asymmetry showed impressive reproducibility. Conclusion: SAM analysis using MEG is an accurate, repeatable, and reproducible method for studying the brain processing of human swallowing in a more physiological manner and provides novel opportunities for future studies of the brain-gut axis in health and disease.

Lost in translation? The potential psychobiotic Lactobacillus rhamnosus (JB-1) fails to modulate stress or cognitive performance in healthy male subjects

Background: Preclinical studies have identified certain probiotics as psychobiotics a live microorganisms with a potential mental health benefit. Lactobacillus rhamnosus (JB-1) has been shown to reduce stress-related behaviour, corticosterone release and alter central expression of GABA receptors in an anxious mouse strain. However, it is unclear if this single putative psychobiotic strain has psychotropic activity in humans. Consequently, we aimed to examine if these promising preclinical findings could be translated to healthy human volunteers. Objectives: To determine the impact of L. rhamnosus on stress-related behaviours, physiology, inflammatory response, cognitive performance and brain activity patterns in healthy male participants. An 8 week, randomized, placebo-controlled, cross-over design was employed. Twenty-nine healthy male volunteers participated. Participants completed self-report stress measures, cognitive assessments and resting electroencephalography (EEG). Plasma IL10, IL1β, IL6, IL8 and TNFα levels and whole blood Toll-like 4 (TLR-4) agonist-induced cytokine release were determined by multiplex ELISA. Salivary cortisol was determined by ELISA and subjective stress measures were assessed before, during and after a socially evaluated cold pressor test (SECPT). Results: There was no overall effect of probiotic treatment on measures of mood, anxiety, stress or sleep quality and no significant effect of probiotic over placebo on subjective stress measures, or the HPA response to the SECPT. Visuospatial memory performance, attention switching, rapid visual information processing, emotion recognition and associated EEG measures did not show improvement over placebo. No significant anti-inflammatory effects were seen as assessed by basal and stimulated cytokine levels. Conclusions: L. rhamnosus was not superior to placebo in modifying stress-related measures, HPA response, inflammation or cognitive performance in healthy male participants. These findings highlight the challenges associated with moving promising preclinical studies, conducted in an anxious mouse strain, to healthy human participants. Future interventional studies investigating the effect of this psychobiotic in populations with stress-related disorders are required.

Gastrointestinal diseases: psycho-social aspects

An interconnection between psychological and gastrointestinal (GI) functioning has long been recognized, incorporating multiple mechanisms and considering bidirectional processes. However, exciting discoveries regarding the role of stress and depression in etiology and disease course have shed new light on the understanding of biopsychosocial processes in chronic GI conditions. This article provides an introduction to GI tract functioning, GI disorders, and stress mechanisms in the gut, followed by an overview and discussion of the psychosocial impact of these disorders, the role of stress and mental comorbidity in GI disorders, and the current knowledge regarding psychological interventions for GI disorders.

The Gut Microbiome and Cirrhosis: Basic Aspects

In this chapter the basic aspects helping to understand the microbiome in terms of quantity, diversity, complexity, function, and interaction with the host are discussed. First the nomenclature, definitions of taxa, and measures of diversity as well as methods to unravel this kingdom are outlined. A brief summary on its physiological relevance for general health and the functions exerted specifically by the microbiome is presented. Differences in the composition of the microbiome along the gastrointestinal tract and across the gut wall and its interindividual variations, enterotypes, and stability are highlighted. The reader will be familiarized with all different modulators impacting on the microbiome, namely, intrinsic and extrinsic factors. Intrinsic factors include gastrointestinal secretions (gastric acid, bile, pancreatic juice, mucus), antimicrobial peptides, motility, enteric nervous system, and host genotype. Extrinsic factors are mainly dietary choices, hygiene, stress, alcohol consumption, exercise, and medications. The second part of the chapter focuses on quantitative and qualitative changes in microbiome in liver cirrhosis. The mechanisms contributing to dysbiosis, small intestinal bacterial overgrowth, and bacterial translocation are delineated underscoring their role for the liver-gut axis.

Corticosteroides vs dosis bajas de adrenocorticotropina en el tratamiento de espasmos infantiles. Revisión sistemática de la literatura

Antecedentes: El tratamiento de los espasmos infantiles generalmente se realiza con ACTH a pesar de perfil de efectos secundarios y el alto costo financiero. Se ha propuesto el uso de los corticoides como primera línea de tratamiento para la enfermedad, no obstante no existe certeza sobre la eficacia de este esquema. Objetivos: Evaluar la eficacia del uso de los corticoides comparados con la ACTH como primera línea de tratamiento en el manejo de pacientes con espasmos infantiles. Metodología: Se realizó una revisión sistemática de la literatura. La búsqueda se efectuó en las bases de datos Pubmed, Embase, Ovid, LiLaCs y en el registro de ensayos clínicos de Estados Unidos. Se incluyeron estudios en portugués, ingles y español, no se fijo límite de tiempo para la publicación. Se realizó un análisis de riesgo de sesgo y de calidad de la evidencia utilizando el programa GRADEPRO. Se estimaron OR y sus respectivos intervalos de confianza al 95%. Resultados: Se incluyeron 4 estudios, un ensayo clínico y tres estudios de cohorte retrospectiva. Dos estudios aportaron evidencia de calidad moderada y alta. No se encontraron diferencias en la eficacia a corto plazo entre el uso de los corticoides y la ACTH sobre desenlaces clínicos o electroencefalográficos. No se encontraron estudios de seguridad a largo plazo. La seguridad a corto plazo no mostró diferencias. Conclusiones: Es muy probable que el uso de los corticoides como primera línea de tratamiento puedan reemplazar el uso de la ACTH, se requiere estudios de seguridad a largo plazo. La decisión de su uso rutinario debería estar basada en un análisis de costo efectividad y bajo la mirada del balance riesgo/beneficio.

Intestinal bacterial translocation in rats with cirrhosis is related to compromised Paneth cell antimicrobial host defense

Liver cirrhosis is associated with bacterial translocation (BT) and endotoxemia. Most translocating bacteria belong to the common intestinal microbiota, suggesting a breakdown of intestinal barrier function. We hypothesized that diminished mucosal antimicrobial host defense could predispose to BT. Two rodent models of portal hypertension with increased BT were used, CCl(4)-induced ascitic cirrhosis and 2-day portal vein-ligated (PVL) animals. BT was assessed by standard microbiological techniques on mesenteric lymph nodes. Total RNA was isolated systematically throughout the intestinal tract, and expression of Paneth cell α-cryptdins and β-defensins was determined by real-time quantitative polymerase chain reaction (qPCR). To determine functional consequences, mucosal antimicrobial activity was assessed with a fluorescence-activated cell sorting assay. BT was detectable in 40% of rats with cirrhosis. Compared with the group without BT, these animals exhibited diminished intestinal Paneth cell α-cryptdin 5 and 7 expression. In contrast, PVL was associated with BT in all animals but did not affect antimicrobial peptides. The decrease in Paneth cell antimicrobials was most pronounced in the ileum and the coecum. Other antimicrobials showed no changes or even an induction in the case of BT at different sites. Antimicrobial activity toward different commensal strains was reduced, especially in the distal ileum and the cecum in experimental cirrhosis with BT (excluding PVL). Conclusion: Compromised Paneth cell antimicrobial host defense seems to predispose to BT in experimental cirrhosis. Understanding this liver-gut axis including the underlying mechanisms could help us to find new treatment avenues.

Growth hormone as a cytokine

1. The growth hormone (GH) receptor was the first of the class 1 cytokine receptors to be cloned. It shares a number of structural characteristics with other family members and common signalling mechanisms based on common usage of the Janus kinase 2 (JAK2). 2. Growth hormone receptor activation is initiated by GH-induced homodimerization of receptor molecules. This has enabled the creation of specific hormone antagonists that block receptor dimerization. 3. The details of the transcription factors used by the activated receptor are being revealed as a result of promoter analyses and electrophoretic mobility gelshift analysis. 4. Growth hormone receptors are widespread and their discovery in certain tissues has led to the assignment of new physiological roles for GH, Some of these involve local or paracrine roles for GH, as befits its cytokine status. 5. Four examples of such novel roles are discussed, These are: (i) the brain GH axis; (ii) GH and the vitamin B-12 axis; (iii) GH in early pre-implantation development; and (iv) GH in development of the tooth. 6. We propose that the view that GH acts through the intermediacy of insulin-like growth factor-1 is simplistic; rather, GH acts to induce an array of growth factors and their receptors and the composition of this array varies with tissue type and, probably, stage of development.

Maternal weaning modulates emotional behavior and regulates the gut-brain axis

Evidence shows that nutritional and environmental stress stimuli during postnatal period influence brain development and interactions between gut and brain. In this study we show that in rats, prevention of weaning from maternal milk results in depressive-like behavior, which is accompanied by changes in the gut bacteria and host metabolism. Depressive-like behavior was studied using the forced-swim test on postnatal day (PND) 25 in rats either weaned on PND 21, or left with their mother until PND 25 (non-weaned). Non-weaned rats showed an increased immobility time consistent with a depressive phenotype. Fluorescence in situ hybridization showed non-weaned rats to harbor significantly lowered Clostridium histolyticum bacterial groups but exhibit marked stress-induced increases. Metabonomic analysis of urine from these animals revealed significant differences in the metabolic profiles, with biochemical phenotypes indicative of depression in the non-weaned animals. In addition, non-weaned rats showed resistance to stress-induced modulation of oxytocin receptors in amygdala nuclei, which is indicative of passive stress-coping mechanism. We conclude that delaying weaning results in alterations to the gut microbiota and global metabolic profiles which may contribute to a depressive phenotype and raise the issue that mood disorders at early developmental ages may reflect interplay between mammalian host and resident bacteria.

Growing up in a bubble: using germ-free animals to assess the influence of the gut microbiota on brain and behavior

There is a growing recognition of the importance of the commensal intestinal microbiota in the development and later function of the central nervous system. Research using germ-free mice (mice raised without any exposure to microorganisms) has provided some of the most persuasive evidence for a role of these bacteria in gut-brain signalling. Key findings show that the microbiota is necessary for normal stress responsivity, anxiety-like behaviors, sociability, and cognition. Furthermore, the microbiota maintains central nervous system homeostasis by regulating immune function and blood brain barrier integrity. Studies have also found that the gut microbiota influences neurotransmitter, synaptic, and neurotrophic signalling systems and neurogenesis. The principle advantage of the germ-free mouse model is in proof-of-principle studies and that a complete microbiota or defined consortiums of bacteria can be introduced at various developmental time points. However, a germ-free upbringing can induce permanent neurodevelopmental deficits that may deem the model unsuitable for specific scientific queries that do not involve early-life microbial deficiency. As such, alternatives and complementary strategies to the germ-free model are warranted and include antibiotic treatment to create microbiota-deficient animals at distinct time points across the lifespan. Increasing our understanding of the impact of the gut microbiota on brain and behavior has the potential to inform novel management strategies for stress-related gastrointestinal and neuropsychiatric disorders.