Suppression of ovalbumin-induced allergic diarrhea by diminished intestinal peristalsis in RAMP1-deficient mice

Synergistic effects of L-theanine and epigallocatechin gallate in alleviating ovalbumin allergy by regulating intestinal immunity through inhibition of mast cell degranulation

Ovalbumin (OVA), a commonly consumed food protein, can cause severe allergies and intestinal immune disorders. L-Theanine (LTA) and epigallocatechin gallate (EGCG) regulate intestinal immunity. However, it is unclear whether an LTA and EGCG combined intervention can alleviate OVA allergy (OVA-A) by modulating intestinal-specific immunity, and it is unknown whether there is a synergistic effect between LTA and EGCG. Therefore, we treated BALB/c OVA-sensitized mice with LTA, EGCG, or a combination of both (LTA + EGCG) to investigate the effects of LTA and EGCG on intestinal-specific immunity regulation and underlying mechanisms. Female mice were intraperitoneally injected with OVA to establish OVA-sensitive mouse models. MLEO LTA + EGCG (20 mg kg^-1 d^-1 LTA + 80 mg kg^-1 d^-1 EGCG) and HLEO (30 mg kg^-1 d^-1 LTA + 120 mg kg^-1 d^-1 EGCG) exerted more beneficial effects on alleviating OVA-A (weight gain, allergy score, jejunum structure, mast cell [MC] degranulation, thymus and spleen indices) than LTA or EGCG alone (p < 0.01). Based on the alleviation of OVA-A by LTA + EGCG, we selected MLEO mice for 16S rDNA, flow cytometry, and western blot analyses. The 16S rDNA results showed that MLEO increased the abundance of Lactobacillaceae, Lachnospiraceae, and Ruminococcaceae, and decreased that of Helicobacteraceae (p < 0.01). The flow cytometry and western blotting results indicated that MLEO reduced the number of dendritic cells available to capture OVA, thereby lowering the Th2 immune response and decreasing the IL-4 and IL-13 levels. Meanwhile, the attenuation of the Th2 immune response inhibits the cross-linking of OVA and FcεRI, thus reducing MC degranulation and decreasing the serum HIS and mMCPT-1 levels through the FcεRI/Btk/PLCγ signaling pathway. LTA + EGCG also inhibits the Th2 immune response through the FcεRI/Lyn/Syk/PI3K/AKT signaling pathway and decreases the serum IL-4 and IL-13 levels. Notably, LTA + EGCG promotes the Treg and Th1 immune responses and inhibits the Th17 immune response, altering the levels of the corresponding cytokines. Therefore, LTA + EGCG can synergistically alleviate OVA-A by regulating intestinal immunity through MC degranulation inhibition.

Constipation Caused by Anti-calcitonin Gene-Related Peptide Migraine Therapeutics Explained by Antagonism of Calcitonin Gene-Related Peptide's Motor-Stimulating and Prosecretory Function in the Intestine

The development of small-molecule calcitonin gene-related peptide (CGRP) receptor antagonists (gepants) and of monoclonal antibodies targeting the CGRP system has been a major advance in the management of migraine. In the randomized controlled trials before regulatory approval, the safety of these anti-CGRP migraine therapeutics was considered favorable and to stay within the expected profile. Post-approval real-world surveys reveal, however, constipation to be a major adverse event which may affect more than 50% of patients treated with erenumab (an antibody targeting the CGRP receptor), fremanezumab or galcanezumab (antibodies targeting CGRP). In this review article we address the question whether constipation caused by inhibition of CGRP signaling can be mechanistically deduced from the known pharmacological actions and pathophysiological implications of CGRP in the digestive tract. CGRP in the gut is expressed by two distinct neuronal populations: extrinsic primary afferent nerve fibers and distinct neurons of the intrinsic enteric nervous system. In particular, CGRP is a major messenger of enteric sensory neurons which in response to mucosal stimulation activate both ascending excitatory and descending inhibitory neuronal pathways that enable propulsive (peristaltic) motor activity to take place. In addition, CGRP is able to stimulate ion and water secretion into the intestinal lumen. The motor-stimulating and prosecretory actions of CGRP combine in accelerating intestinal transit, an activity profile that has been confirmed by the ability of CGRP to induce diarrhea in mice, dogs and humans. We therefore conclude that the constipation elicited by antibodies targeting CGRP or its receptor results from interference with the physiological function of CGRP in the small and large intestine in which it contributes to the maintenance of peristaltic motor activity, ion and water secretion and intestinal transit.

Advances in reconstructing intestinal functionalities in vitro: From two/three dimensional-cell culture platforms to human intestine-on-a-chip

Standard two/three dimensional (2D/3D)-cell culture platforms have facilitated the understanding of the communications between various cell types and their microenvironments. However, they are still limited in recapitulating the complex functionalities in vivo, such as tissue formation, tissue-tissue interface, and mechanical/biochemical microenvironments of tissues and organs. Intestine-on-a-chip platforms offer a new way to mimic intestinal behaviors and functionalities by constructing in vitro intestinal models in microfluidic devices. This review summarizes the advances and limitations of the state-of-the-art 2D/3D-cell culture platforms, animal models, intestine chips, and the combined multi-organ chips related with intestines. Their applications to studying intestinal functions, drug testing, and disease modeling are introduced. Different intestinal cell sources are compared in terms of gene expression abilities and the recapitulated intestinal morphologies. Among these cells, cells isolated form human intestinal tissues and derived from pluripotent stem cells appear to be more suitable for in vitro reconstruction of intestinal organs. Key challenges of current intestine-on-a-chip platforms and future directions are also discussed.

The DH31/CGRP enteroendocrine peptide triggers intestinal contractions favoring the elimination of opportunistic bacteria

The digestive tract is the first organ affected by the ingestion of foodborne bacteria. While commensal bacteria become resident, opportunistic or virulent bacteria are eliminated from the gut by the local innate immune system. Here we characterize a new mechanism of defense, independent of the immune system, in Drosophila melanogaster. We observed strong contractions of longitudinal visceral muscle fibers for the first 2 hours following bacterial ingestion. We showed that these visceral muscle contractions are induced by immune reactive oxygen species (ROS) that accumulate in the lumen and depend on the ROS-sensing TRPA1 receptor. We then demonstrate that both ROS and TRPA1 are required in a subset of anterior enteroendocrine cells for the release of the DH31 neuropeptide which activates its receptor in the neighboring visceral muscles. The resulting contractions of the visceral muscles favors quick expulsion of the bacteria, limiting their presence in the gut. Our results unveil a precocious mechanism of defense against ingested opportunistic bacteria, whether they are Gram-positive like Bacillus thuringiensis or Gram-negative like Erwinia carotovora carotovora. Finally, we found that the human homolog of DH31, CGRP, has a conserved function in Drosophila.

The intestine is the first barrier to fight non-commensal bacteria ingested along with the food. The innate immune system is the main mean mounted by the gut lining in response to ill-causing bacteria to avoid detrimental impact. Intestinal cells produce chlorine bleach and antimicrobial peptides that destroy exogenous bacteria. Here, we identified and characterized a new mechanism of gut defense that occurs rapidly after ingestion of exogenous bacteria. We found that the enteroendocrine cells perceive the presence of chlorine bleach in the lumen thanks to a sensor. This sensor promotes a calcium flux within enteroendocrine cells that allows the release of a hormone. This hormone acts locally on the visceral muscle surrounding the intestine by provoking its strong contractions (or spasms). We show that these strong but brief visceral contractions are helping to the quick expulsion of the ingested bacteria thus limiting their potential detrimental impact on the intestine. Markedly, the bleach-sensor is well known to be involved in pain. Therefore we have deciphered in this study a biological mechanism that has so far been described only empirically by medicine, potentially explaining intestinal pain and visceral spasms upon food poisoning.

The Influence of Inflammation and Nerve Damage on the Neurochemical Characterization of Calcitonin Gene-Related Peptide-Like Immunoreactive (CGRP-LI) Neurons in the Enteric Nervous System of the Porcine Descending Colon

The enteric nervous system (ENS), localized in the wall of the gastrointestinal tract, regulates the functions of the intestine using a wide range of neuronally-active substances. One of them is the calcitonin gene-related peptide (CGRP), whose participation in pathological states in the large intestine remains unclear. Therefore, the aim of this study was to investigate the influence of inflammation and nerve damage using a double immunofluorescence technique to neurochemically characterize CGRP-positive enteric nervous structures in the porcine descending colon. Both pathological factors caused an increase in the percentage of CGRP-positive enteric neurons, and these changes were the most visible in the myenteric plexus after nerve damage. Moreover, both pathological states change the degree of co-localization of CGRP with other neurochemical factors, including substance P, the neuronal isoform of nitric oxide synthase, galanin, cocaine- and amphetamine-regulated transcript peptide and vesicular acetylcholine transporter. The character and severity of these changes depended on the pathological factor and the type of enteric plexus. The obtained results show that CGRP-positive enteric neurons are varied in terms of neurochemical characterization and take part in adaptive processes in the descending colon during inflammation and after nerve damage.

Anti-CGRP antibodies block CGRP-induced diarrhea in mice

The multifunctional neuropeptide calcitonin gene-related peptide (CGRP) and its receptor are expressed throughout the gastrointestinal tract. Previous studies have shown that CGRP has roles in intestinal motility, water secretion, and inflammation. Furthermore, animal studies have demonstrated CGRP involvement in diarrhea secondary to C. difficile and food allergies. Diarrhea thus provides a convenient bioassay of CGRP activity in the GI system. In this proof of principle study, we report that prophylactic administration of an anti-CGRP antibody is able to block CGRP-induced diarrhea in mice. As a control, the CGRP-receptor antagonist olcegepant also attenuated the diarrhea response to CGRP. This preclinical study indicates that anti-CGRP antibodies may provide a new preventative therapy for gastrointestinal disorders involving CGRP.

RAMP1 suppresses mucosal injury from dextran sodium sulfate-induced colitis in mice

BACKGROUND AND AIMS

Calcitonin gene-related peptide (CGRP) is thought to be involved in the modulation of intestinal motility. CGRP receptor is composed of receptor activity-modifying protein (RAMP) 1 combined with calcitonin receptor-like receptor (CRLR) for CGRP. The study investigated the role of CGRP in mice with experimentally induced colitis.

METHODS

The study used dextran sodium sulfate (DSS) to induce colitis in mice. The study compared the severity of colitis in wild-type (WT) mice, mice treated with a CGRP receptor antagonist (CGRP_8-37 ), and RAMP1 knockout (^-/- ) mice. Pathological changes in the mucosa were assessed, and inflammatory cells and cytokine levels were measured.

RESULTS

The severity of inflammation in DSS-induced colitis increased markedly in CGRP_8-37 -treated mice and RAMP1^-/- mice compared with WT mice. RAMP1^-/- mice showed more severe damage compared with CGRP_8-37 -treated mice. The number of periodic acid-Schiff-positive cells decreased in CGRP_8-37 -treated mice compared with WT mice and was even further decreased in RAMP1^-/- mice. RAMP1 was expressed by macrophages, mast cells, and T-cells. RAMP1^-/- mice exhibited excessive accumulation of macrophages and mast cells into the colonic tissue with increased levels of tumor necrosis factor-α and interleukin-1β as compared with WT mice. Infiltration of T-cells into the colonic mucosa, which was associated with the expression of T helper (Th) cytokines including Th1 (interferon gamma) and Th17 (IL-17), was augmented in RAMP1^-/- mice.

CONCLUSIONS

The findings of this study suggest that RAMP1 exerted mucosal protection in DSS-induced colitis via attenuation of recruitment of inflammatory cells and of pro-inflammatory cytokines.

Calcitonin gene-related peptide and cyclic adenosine 5'-monophosphate/protein kinase A pathway promote IL-9 production in Th9 differentiation process

Th9 cells are a novel Th cell subset that produces IL-9 and is involved in type I hypersensitivity such as airway inflammation. Although its critical roles in asthma have attracted interest, the physiological regulatory mechanisms of Th9 cell differentiation and function are largely unknown. Asthma is easily affected by psychological factors. Therefore, we investigated one of the physiological mediators derived from the nervous system, calcitonin gene-related peptide (CGRP), in asthma and Th9 cells because CGRP and activation of the cAMP/protein kinase A (PKA) pathway by CGRP are known to be important regulators in several immune responses and allergic diseases. In this study, we demonstrated that the CGRP/cAMP/PKA pathway promotes IL-9 production via NFATc2 activation by PKA-dependent glycogen synthase kinase-3β inactivation. Moreover, CGRP also induces the expression of PU.1, a critical transcriptional factor in Th9 cells, which depends on PKA, but not NFATc2. Additionally, we demonstrated the physiological importance of CGRP in IL-9 production and Th9 differentiation using an OVA-induced airway inflammation model and T cell-specific CGRP receptor-deficient mice. The present study revealed a novel regulatory mechanism comprising G protein-coupled receptor ligands and nervous system-derived substances in Th9 cell differentiation and type I hypersensitivity.