[Show abstract][Hide abstract] ABSTRACT: The gastrointestinal tract is the major source of the related hormones ghrelin and motilin, which act on structurally similar G protein-coupled receptors. Nevertheless, selective receptor agonists are available. The primary roles of endogenous ghrelin and motilin in the digestive system are to increase appetite or hedonic eating (ghrelin) and initiate phase III of gastric migrating myoelectric complexes (motilin). Ghrelin and motilin also both inhibit nausea. In clinical trials, the motilin receptor agonist camicinal increased gastric emptying, but at lower doses reduced gastroparesis symptoms and improved appetite. Ghrelin receptor agonists have been trialled for the treatment of diabetic gastroparesis because of their ability to increase gastric emptying, but with mixed results; however, relamorelin, a ghrelin agonist, reduced nausea and vomiting in patients with this disorder. Treatment of postoperative ileus with a ghrelin receptor agonist proved unsuccessful. Centrally penetrant ghrelin receptor agonists stimulate defecation in animals and humans, although ghrelin itself does not seem to control colorectal function. Thus, the most promising uses of motilin receptor agonists are the treatment of gastroparesis or conditions with slow gastric emptying, and ghrelin receptor agonists hold potential for the reduction of nausea and vomiting, and the treatment of constipation. Therapeutic, gastrointestinal roles for receptor antagonists or inverse agonists have not been identified.
[Show abstract][Hide abstract] ABSTRACT: We discuss the relations of processed foods, especially cooked foods, in the human diet to digestive tract form and function. The modern consumption of over 70 % of foods and beverages in highly refined form favours the diet-related classification of humans as cucinivores, rather than omnivores. Archaeological evidence indicates that humans have consumed cooked food for at least 300–400,000 years, and divergence in genes associated with human subpopulations that utilise different foods has been shown to occur over periods of 10–30,000 years. One such divergence is the greater presence of adult lactase persistence in communities that have consumed dairy products, over periods of about 8,000 years, compared to communities not consuming dairy products. We postulate that 300–400,000 years, or 10,000–14,000 generations, is sufficient time for food processing to have influenced the form and function of the human digestive tract. It is difficult to determine how long humans have prepared foods in other ways, such as pounding, grinding, drying or fermenting, but this appears to be for at least 20,000 years, which has been sufficient time to influence gene expression for digestive enzymes. Cooking and food processing expands the range of food that can be eaten, extends food availability into lean times and enhances digestibility. Cooking also detoxifies food to some extent, destroys infective agents, decreases eating time and slightly increases the efficiency of assimilation of energy substrates. On the other hand, cooking can destroy some nutrients and produce toxic products. The human digestive system is suited to a processed food diet because of its smaller volume, notably smaller colonic volume, relative to the intestines of other species, and because of differences from other primates in dentition and facial muscles that result in lower bite strength. There is no known group of humans which does not consume cooked foods, and the modern diet is dominated by processed foods. We conclude that humans are well adapted as consumers of processed, including cooked, foods.
Journal of Comparative Physiology B 06/2015; DOI:10.1007/s00360-015-0919-3 · 2.62 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Study design: Single centre, single ascending dose study.
Objectives: To compare the pharmacokinetics and assess the safety of capromorelin, a compound that has potential to treat constipation following spinal cord injury (SCI), in groups of able-bodied and SCI volunteers.
Setting: Local population from Victoria, Australia.
Methods: Following initial screening and baseline blood collections, participants received ascending oral doses (20, 50 and then 100mg at least 1-week apart) of capromorelin after pre-dose blood collection, followed by blood collections over the following 12 h for pharmacokinetic analysis and 1-week and 4-week follow-up blood collections for safety evaluations. Blood pressure and heart rate were monitored.
Results: No serious adverse events were recorded following any dose in either the able-bodied group or the SCI group. There were no abnormal blood pressure or heart rate changes. Minor adverse events resolved quickly without the need for treatment. Pharmacokinetic behaviour was broadly similar between groups, with both exhibiting dose-dependent increases in Cmax and AUC0–∞. The SCI participants showed greater variance in pharmacokinetic parameters and had a slightly delayed Tmax and half-life.
Conclusion: Capromorelin at the doses tested was safe and well tolerated in both SCI and able-bodied participants and also showed similar pharmacokinetics with dose-dependent increases in concentration and drug exposure.
Sponsorship: Support for the study was provided by the Victorian State Government Transport Accident Commission.
Spinal Cord advance online publication, 2 December 2014; doi:10.1038/sc.2014.218
[Show abstract][Hide abstract] ABSTRACT: This study has investigated the patterns of colocalisation of the conventional K cell marker, glucagon-like insulinotropic peptide (GIP), and the L cell markers, glucagon like peptide-1 (GLP-1) and peptide YY (PYY), in enteroendocrine cells (EEC) of the small intestine and colon of mouse and pig. All combinations of the hormones, 3 in a cell, 2 in a cell and 1 at a time, were encountered. In both species, the three most common EEC types contained (1) both GLP-1 and PYY but not GIP, (2) GLP-1 alone or (3) GIP plus GLP-1 without PYY. Few GIP plus PYY cells and rare cells containing all 3 hormones were encountered. Gradients of cell types occurred along the intestine. For example, in mouse, there were no PYY cells in the duodenum and few in the jejunum, but >50 % of labelled EEC in the distal ileum and colon were PYY immunoreactive. By contrast, over 40 % of EEC in the pig duodenum contained PYY, and most also contained either GLP-1 or GIP. The gradient in pig was less pronounced. It is concluded that the traditional classification of K and L cells requires revision, and that there are major inter-species differences in the patterns of colocalisation of hormones that have been used to characterise K and L cells.
Cell and Tissue Research 11/2014; 359(2). DOI:10.1007/s00441-014-2033-3 · 3.57 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The only molecularly identified ghrelin receptor is the growth hormone secretagogue receptor GHSR1a. Its natural ligand, ghrelin, is an acylated peptide whose unacylated counterpart (UAG) is almost inactive at GHSR1a. A truncated, nonfunctional receptor, GHSR1b, derives from the same gene. We have critically evaluated evidence for effects of ghrelin receptor ligands that are not consistent with actions at GHSR1a. Effects of ghrelin are observed in cells or tissues where the expression of GHSR1a is not detectable or after the Ghsr gene has been inactivated. In several, effects of ghrelin are mimicked by UAG, and ghrelin binding is competitively reduced by UAG. Effects in the absence of GHSR1a and sites at which ghrelin and UAG have similar potency suggest the presence of novel nonspecific ghrelin receptors (ghrelin receptor-like receptors [GRLRs]). A third class of receptor, the UAG receptors, at which UAG, but not ghrelin, is an agonist has been proposed. None of the novel receptors, with the exception of the glycoprotein CD36, which accounts for ghrelin action at a limited number of sites, have been identified. GHSR1a and GHSR1b combine with other G protein-coupled receptors to form heterodimers, whose pharmacologies differ from their components. Thus, it is feasible some GRLRs and some UAG receptors are heterodimers. Effects mediated through GRLRs or UAG receptors include adipocyte lipid accumulation, myoblast differentiation, osteoblast proliferation, insulin release, cardioprotection, coronary artery constriction, vascular endothelial cell proliferation, and tumor cell proliferation. The molecular identification and pharmacologic characterization of novel ghrelin receptors are thus important objectives.
[Show abstract][Hide abstract] ABSTRACT: The roles of 5-HT3 and 5-HT4 receptors in the modulation of intestinal propulsion by luminal application of 5-HT and augmentation of endogenous 5-HT effects were studied in segments of guinea-pig ileum in vitro. Persistent propulsive contractions evoked by saline distension were examined using a modified Trendelenburg method. When 5-HT (30 nM), fluoxetine (selective serotonin reuptake inhibitor; 1 nM), 2-methyl-5-HT (5-HT3 receptor agonist; 1 mM), or RS 67506 (5-HT4 receptor agonist, 1 μM) was infused into the lumen, the pressure needed to initiate persistent propulsive activity fell significantly. A specific 5-HT4 receptor antagonist, SB 207266 (10 nM in lumen), abolished the effects of 5-HT, fluoxetine, and RS 67506, but not those of 2-methyl-5-HT. Granisetron (5-HT3 receptor antagonist; 1 μM in lumen) abolished the effect of 5-HT, fluoxetine, RS 67506, and 2-methyl-5-HT. The NK3 receptor antagonist SR 142801 (100 nM in lumen) blocked the effects of 5-HT, fluoxetine, and 2-methyl-5-HT. SB 207266, granisetron, and SR 142801 had no effect by themselves. Higher concentrations of fluoxetine (100 and 300 nM) and RS 67506 (3 and 10 μM) had no effect on the distension threshold for propulsive contractions. These results indicate that luminal application of exogenous 5-HT, or increased release of endogenous mucosal 5-HT above basal levels, acts to lower the threshold for propulsive contractions in the guinea-pig ileum via activation of 5-HT3 and 5-HT4 receptors and the release of tachykinins. The results further indicate that basal release of 5-HT is insufficient to alter the threshold for propulsive motor activity.
Frontiers in Neuroscience 09/2014; 8:301. DOI:10.3389/fnins.2014.00301 · 3.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Aromatase converts androgens into estrogens and its expression within adipose stromal cells (ASCs) is believed to be the major driver of estrogen-dependent cancers in older women. Ghrelin is a gut-hormone that is involved in the regulation of appetite and known to bind to and activate the cognate ghrelin receptor, GHSR1a. The unacylated form of ghrelin, des-acyl ghrelin, binds weakly to GHSR1a but has been shown to play an important role in regulating a number of physiological processes. The aim of this study was to determine the effect of ghrelin and des-acyl ghrelin on aromatase in primary human ASCs. Primary human ASCs were isolated from adipose tissue of women undergoing cosmetic surgery. Real-time PCR and tritiated water-release assays were performed to examine the effect of treatment on aromatase transcript expression and aromatase activity, respectively. Treatments included ghrelin, des-acyl ghrelin, obestatin, and capromorelin (GHSR1a agonist). GHSR1a protein expression was assessed by Western blot and effects of treatment on Ca(2+) and cAMP second messenger systems were examined using the Flexstation assay and the Lance Ultra cAMP kit, respectively. Results demonstrate that pM concentrations of ghrelin and des-acyl ghrelin inhibit aromatase transcript expression and activity in ASCs under basal conditions and in PGE2-stimulated cells. Moreover, the effects of ghrelin and des-acyl ghrelin are mediated via effects on aromatase promoter PII-specific transcripts. Neither the GHSR1a-specific agonist capromorelin nor obestatin had any effect on aromatase transcript expression or activity. Moreover, GHSR1a protein was undetectable by Western blot and neither ghrelin nor capromorelin elicited a calcium response in ASCs. Finally, ghrelin caused a significant decrease in basal and forskolin-stimulated cAMP in ASC. These findings suggest that ghrelin acts at alternate receptors in ASCs by decreasing intracellular cAMP levels. Ghrelin mimetics may be useful in the treatment of estrogen-dependent breast cancer.
Breast Cancer Research and Treatment 07/2014; 147(1). DOI:10.1007/s10549-014-3060-1 · 3.94 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The digestive system is innervated through its connections with the central nervous system (CNS) and by the enteric nervous system (ENS) within the wall of the gastrointestinal tract. The ENS works in concert with CNS reflex and command centers and with neural pathways that pass through sympathetic ganglia to control digestive function. There is bidirectional information flow between the ENS and CNS and between the ENS and sympathetic prevertebral ganglia.The ENS in human contains 200-600 million neurons, distributed in many thousands of small ganglia, the great majority of which are found in two plexuses, the myenteric and submucosal plexuses. The myenteric plexus forms a continuous network that extends from the upper esophagus to the internal anal sphincter. Submucosal ganglia and connecting fiber bundles form plexuses in the small and large intestines, but not in the stomach and esophagus. The connections between the ENS and CNS are carried by the vagus and pelvic nerves and sympathetic pathways. Neurons also project from the ENS to prevertebral ganglia, the gallbladder, pancreas and trachea.The relative roles of the ENS and CNS differ considerably along the digestive tract. Movements of the striated muscle esophagus are determined by neural pattern generators in the CNS. Likewise the CNS has a major role in monitoring the state of the stomach and, in turn, controlling its contractile activity and acid secretion, through vago-vagal reflexes. In contrast, the ENS in the small intestine and colon contains full reflex circuits, including sensory neurons, interneurons and several classes of motor neuron, through which muscle activity, transmucosal fluid fluxes, local blood flow and other functions are controlled. The CNS has control of defecation, via the defecation centers in the lumbosacral spinal cord. The importance of the ENS is emphasized by the life-threatening effects of some ENS neuropathies. By contrast, removal of vagal or sympathetic connections with the gastrointestinal tract has minor effects on GI function. Voluntary control of defecation is exerted through pelvic connections, but cutting these connections is not life-threatening and other functions are little affected.
Advances in Experimental Medicine and Biology 07/2014; 817:39-71. DOI:10.1007/978-1-4939-0897-4_3 · 1.96 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Dietary effects of organic Se supplementation in the form of Se-enriched Agaricus bisporus mushroom on ileal mucosal permeability and antioxidant selenoenzymes status in heat induced oxidative stress in rats were evaluated. Acute heat stress (40 °C, 21% relative humidity, 90 min exposure) increased ileum baseline short circuit current (Isc; 2.40-fold) and epithelial conductance (Ge; 2.74-fold). Dietary supplementation with Se-enriched A. bisporus (1 µg Se/g feed) reduced (p < 0.05) ileum Isc and Ge during heat stress to 1.74 and 1.91 fold, respectively, indicating protection from heat stress-induced mucosal permeability increase. The expression of ileum glutathione peroxidase (GPx-) 1 and 2 mRNAs were up-regulated (p < 0.05) by 1.90 and 1.87-fold, respectively, for non-heat stress rats on the Se-enriched diet relative to the control. The interplay between heat stress and dietary Se is complex. For rats on the control diet, heat stress alone increased ileum expression of GPx-1 (2.33-fold) and GPx-2 (2.23-fold) relative to thermoneutral conditions. For rats on the Se-enriched diet, heat stress increased (p < 0.05) GPx-1 expression only. Rats on Se-enriched + α-tocopherol diet exhibited increased expression of both genes (p < 0.05). Thus, dietary Se-enriched A. bisporus protected against increase in ileum permeability and up-regulated GPx-1 and GPx-2 expression, selenoenzymes relevant to mitigating oxidative stress.
[Show abstract][Hide abstract] ABSTRACT: A sub-group of enteroendocrine cells (L cells) release gastrointestinal hormones, GLP-1 and PYY, which have different but overlapping physiological effects, in response to intraluminal nutrients. Whilst their release profiles are not identical, how the plasma levels of these two hormones are differentially regulated is not well understood. We investigate the possibility that GLP-1 and PYY are in separate storage vesicles. In this study, the subcellular location of GLP-1 and PYY storage organelles is investigated using double-labelling immunohistochemistry, super resolution microscopy and high-resolution confocal microscopy. In all species tested, human, pig, rat and mouse, most cytoplasmic stores that exhibited GLP-1 or PYY immunofluorescence were distinct from each other. The volume occupancy, determined by 3D analysis, overlapped by only about 10∼20 %. At the lower resolution achieved by conventional confocal microscopy, there was also evidence of GLP-1 and PYY being in separate storage compartments but, in subcellular regions where there were many storage vesicles, separate storage could not be resolved. The results indicate that different storage vesicles in L cells contain predominantly GLP-1 or predominantly PYY. Whether GLP-1 and PYY storage vesicles are selectively mobilised and their products are selectively released needs to be determined.
Cell and Tissue Research 05/2014; 357(1). DOI:10.1007/s00441-014-1886-9 · 3.57 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Some agonists of ghrelin receptors cause rapid decreases in BP. The mechanisms by which they cause hypotension and the pharmacology of the receptors are unknown.
The effects of ligands of ghrelin receptors were investigated in rats in vivo, on isolated blood vessels and on cells transfected with the only molecularly defined ghrelin receptor, growth hormone secretagogue receptor 1a (GHSR1a).
Three agonists of GHSR1a receptors, ulimorelin, capromorelin and CP464709, caused a rapid decrease in BP in the anaesthetized rat. The effect was not reduced by either of two GHSR1a antagonists, JMV2959 or YIL781, at doses that blocked effects on colorectal motility, in vivo. The rapid hypotension was not mimicked by ghrelin, unacylated ghrelin or the unacylated ghrelin receptor agonist, AZP531. The early hypotension preceded a decrease in sympathetic nerve activity. Early hypotension was not reduced by hexamethonium or by baroreceptor (sino-aortic) denervation. Ulimorelin also relaxed isolated segments of rat mesenteric artery, and, less potently, relaxed aorta segments. The vascular relaxation was not reduced by JMV2959 or YIL781. Ulimorelin, capromorelin and CP464709 activated GHSR1a in transfected HEK293 cells at nanomolar concentrations. JMV2959 and YIL781 both antagonized effects in these cells, with their pA2 values at the GHSR1a receptor being 6.55 and 7.84.
Our results indicate a novel vascular receptor or receptors whose activation by ulimorelin, capromorelin and CP464709 lowered BP. This receptor is activated by low MW GHSR1a agonists, but is not activated by ghrelin.
British Journal of Pharmacology 03/2014; 171(5):1275-86. DOI:10.1111/bph.12527 · 4.84 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: TRPA1 is an ion channel that detects specific chemicals in food and also transduces mechanical, cold and chemical stimulation. Its presence in sensory nerve endings is well known and recent evidence indicates that it is expressed by some gastrointestinal enteroendocrine cells (EEC). The purpose of the present work is to identify and quantify EEC that express TRPA1 in the mouse gastrointestinal tract. Combined in situ hybridisation histochemistry for TRPA1 and immunofluorescence for EEC hormones was used. TRPA1 expressing EEC were common in the duodenum and jejunum, were rare in the distal small intestine and were absent from the stomach and large intestine. In the duodenum and jejunum, TRPA1 occurred in EEC that contained both cholecystokinin (CCK) and 5-hydroxytryptamine (5HT) and in a small number of cells expressing 5HT but not CCK. TRPA1 was absent from CCK cells that did not express 5HT and from EEC containing glucagon-like insulinotropic peptide. Thus TRPA1 is contained in very specific EEC populations. It is suggested that foods such as garlic and cinnamon that contain TRPA1 stimulants may aid digestion by facilitating the release of CCK.
Cell and Tissue Research 01/2014; 356(1). DOI:10.1007/s00441-013-1780-x · 3.57 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Mucosal-associated invariant T cells (MAIT cells) express a semi-invariant T cell receptor (TCR) α-chain, TRAV1-2-TRAJ33, and are activated by vitamin B metabolites bound by the major histocompatibility complex (MHC)-related class I-like molecule, MR1. Understanding MAIT cell biology has been restrained by the lack of reagents to specifically identify and characterize these cells. Furthermore, the use of surrogate markers may misrepresent the MAIT cell population. We show that modified human MR1 tetramers loaded with the potent MAIT cell ligand, reduced 6-hydroxymethyl-8-d-ribityllumazine (rRL-6-CH2OH), specifically detect all human MAIT cells. Tetramer(+) MAIT subsets were predominantly CD8(+) or CD4(-)CD8(-), although a small subset of CD4(+) MAIT cells was also detected. Notably, most human CD8(+) MAIT cells were CD8α(+)CD8β(-/lo), implying predominant expression of CD8αα homodimers. Tetramer-sorted MAIT cells displayed a TH1 cytokine phenotype upon antigen-specific activation. Similarly, mouse MR1-rRL-6-CH2OH tetramers detected CD4(+), CD4(-)CD8(-) and CD8(+) MAIT cells in Vα19 transgenic mice. Both human and mouse MAIT cells expressed a broad TCR-β repertoire, and although the majority of human MAIT cells expressed TRAV1-2-TRAJ33, some expressed TRAJ12 or TRAJ20 genes in conjunction with TRAV1-2. Accordingly, MR1 tetramers allow precise phenotypic characterization of human and mouse MAIT cells and revealed unanticipated TCR heterogeneity in this population.
Journal of Experimental Medicine 10/2013; 210(11). DOI:10.1084/jem.20130958 · 12.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The gastrointestinal tract presents the largest and most vulnerable surface to the outside world. Simultaneously, it must be accessible and permeable to nutrients and must defend against pathogens and potentially injurious chemicals. Integrated responses to these challenges require the gut to sense its environment, which it does through a range of detection systems for specific chemical entities, pathogenic organisms and their products (including toxins), as well as physicochemical properties of its contents. Sensory information is then communicated to four major effector systems: the enteroendocrine hormonal signalling system; the innervation of the gut, both intrinsic and extrinsic; the gut immune system; and the local tissue defence system. Extensive endocrine-neuro-immune-organ-defence interactions are demonstrable, but under-investigated. A major challenge is to develop a comprehensive understanding of the integrated responses of the gut to the sensory information it receives. A major therapeutic opportunity exists to develop agents that target the receptors facing the gut lumen.