Immune activation may underlie the pathogenesis of irritable bowel syndrome (IBS), but the evidence is conflicting. We examined whether peripheral CD4+ T-cells from IBS patients demonstrated immune ...activation and changes in cytokine production. To gain mechanistic insight, we examined whether immune activation correlated with psychological stress and changing symptoms over time. IBS patients (n = 29) and healthy volunteers (HV; n = 29) completed symptom and psychological questionnaires. IBS patients had a significant increase in CD4+ T-cells expressing the gut homing marker integrin β7 (p = 0.023) and lymphoid marker CD62L (p = 0.026) compared to HV. Furthermore, phytohaemagglutinin stimulated CD4+ T-cells from IBS-D patients demonstrated increased TNFα secretion when compared to HV (p = 0.044). Increased psychological scores in IBS did not correlate with TNFα production, while stress hormones inhibited cytokine secretion from CD4+ T-cells of HV in vitro. IBS symptoms, but not markers of immune activation, decreased over time. CD4+ T-cells from IBS-D patients exhibit immune activation, but this did not appear to correlate with psychological stress measurements or changing symptoms over time. This could suggest that immune activation is a surrogate of an initial trigger and/or ongoing parallel peripheral mechanisms.
This study examined enteric neural reflexes activating submucosal cholinergic vasodilator motoneurons, which innervate the
final resistance vessels regulating mucosal blood flow. Videomicroscopy was ...employed to monitor dilatation of submucosal arterioles
in in vitro preparations from guinea-pig ileum. Balloon distension of intact lumen evoked reflex vasodilatation and flat sheet preparations
were employed to separate mucosal mechanical stimulation from intestinal distension. Mucosal stroking and balloon distension
of the orad segment evoked vasodilatations > 1.5 cm from the stimulating site. Mucosal stimulation was blocked by combined
5-HT 3 /5HT 4 antagonists but distension-evoked responses were unaffected. Distension-evoked responses were also unaffected by nifedipine
(5 μ m ) or nifedipine (1 μ m ) and wortmannin (300 n m ), suggesting stretch activation rather than stretch-activated contraction was involved. Mucosal and distension-evoked responses
were completely blocked when the myenteric plexus was surgically lesioned and were significantly inhibited by hexamethonium.
The muscarinic antagonist 4-DAMP, which inhibits vasodilatations evoked by submucosal cholinergic vasodilator neurons, blocked
dilatations elicited by mucosal stimulation and balloon distension. Maximal dilatations evoked with either sensory modality
could be further enhanced when stimulated with the second modality. Dilatations evoked by stimulation of the aborad segment
were similar to those elicited in the orad segment. In conclusion, sensory mechanisms in the mucosa and muscularis propria
activate vasodilator pathways in the myenteric plexus which project for significant distances in both ascending and descending
directions before innervating submucosal arterioles. These reflexes could co-ordinate mucosal blood flow during multiple motor
events such as peristalsis and intestinal mixing between propulsive events.
Psychological stress accompanies chronic inflammatory diseases such as IBD, and stress hormones can exacerbate pain signalling. In contrast, the endogenous opioid system has an important analgesic ...action during chronic inflammation. This study examined the interaction of these pathways.
Mouse nociceptive dorsal root ganglia (DRG) neurons were incubated with supernatants from segments of inflamed colon collected from patients with chronic UC and mice with dextran sodium sulfate (cDSS)-induced chronic colitis. Stress effects were studied by adding stress hormones (epinephrine and corticosterone) to dissociated neurons or by exposing cDSS mice to water avoidance stress. Changes in excitability of colonic DRG nociceptors were measured using patch clamp and Ca
imaging techniques.
Supernatants from patients with chronic UC and from colons of mice with chronic colitis caused a naloxone-sensitive inhibition of neuronal excitability and capsaicin-evoked Ca
responses. Stress hormones decreased signalling induced by human and mouse supernatants. This effect resulted from stress hormones signalling directly to DRG neurons and indirectly through signalling to the immune system, leading to decreased opioid levels and increased acute inflammation. The net effect of stress was a change endogenous opioid signalling in DRG neurons from an inhibitory to an excitatory effect. This switch was associated with a change in G protein-coupled receptor excitatory signalling to a pathway sensitive to inhibitors of protein kinase A-protein, phospholipase C-protein and G protein βϒ subunits.
Stress hormones block the inhibitory actions of endogenous opioids and can change the effect of opioid signalling in DRG neurons to excitation. Targeting these pathways may prevent heavy opioid use in IBD.
Emerging studies of human visceral nociceptors Reed, David E; Vanner, Stephen J
American journal of physiology: Gastrointestinal and liver physiology,
2017-Mar-01, Letnik:
312, Številka:
3
Journal Article
Recenzirano
Animal studies have led to significant advances in our understanding of pain mechanisms in the intestine that could lead to altered signaling in disorders such as irritable bowel syndrome. However, ...how these translate to the human afferent nervous system is unclear. Recent studies have demonstrated that it is possible to use a variety of techniques, including electrophysiological recordings, to begin to examine these concepts in humans. This mini-review examines these studies to explore how well animal studies translate to humans suffering from irritable bowel syndrome, highlights some of the advantages and technical limitations of these approaches, and identifies some priorities for future studies using human tissues.
The Canadian Digestive Health Foundation initiated a scientific program to assess the incidence, prevalence, mortality and economic impact of digestive disorders across Canada in 2009. The current ...article presents the updated findings from the study concerning irritable bowel syndrome.
Neutrophil elastase is a serine protease that has been implicated in the pathogenesis of inflammatory bowel disease. Due to post-translational control of its activation and high expression of its ...inhibitors in the gut, measurements of total expression poorly reflect the pool of active, functional neutrophil elastase. Fluorogenic substrate probes have been used to measure neutrophil elastase activity, though these tools lack specificity and traceability. PK105 is a recently described fluorescent activity-based probe, which binds to neutrophil elastase in an activity-dependent manner. The irreversible nature of this probe allows for accurate identification of its targets in complex protein mixtures. We describe the reactivity profile of PK105b, a new analogue of PK105, against recombinant serine proteases and in tissue extracts from healthy mice and from models of inflammation induced by oral cancer and Legionella pneumophila infection. We apply PK105b to measure neutrophil elastase activation in an acute model of experimental colitis. Neutrophil elastase activity is detected in inflamed, but not healthy, colons. We corroborate this finding in mucosal biopsies from patients with ulcerative colitis. Thus, PK105b facilitates detection of neutrophil elastase activity in tissue lysates, and we have applied it to demonstrate that this protease is unequivocally activated during colitis.
Proteases sustain hyperexcitability and pain by cleaving protease-activated receptor-2 (PAR2) on nociceptors through distinct mechanisms. Whereas trypsin induces PAR2 coupling to Gαq, Gαs, and ...β-arrestins, cathepsin-S (CS) and neutrophil elastase (NE) cleave PAR2 at distinct sites and activate it by biased mechanisms that induce coupling to Gαs, but not to Gαq or β-arrestins. Because proteases activate PAR2 by irreversible cleavage, and activated PAR2 is degraded in lysosomes, sustained extracellular protease-mediated signaling requires mobilization of intact PAR2 from the Golgi apparatus or de novo synthesis of new receptors by incompletely understood mechanisms. We found here that trypsin, CS, and NE stimulate PAR2-dependent activation of protein kinase D (PKD) in the Golgi of HEK293 cells, in which PKD regulates protein trafficking. The proteases stimulated translocation of the PKD activator Gβγ to the Golgi, coinciding with PAR2 mobilization from the Golgi. Proteases also induced translocation of a photoconverted PAR2-Kaede fusion protein from the Golgi to the plasma membrane of KNRK cells. After incubation of HEK293 cells and dorsal root ganglia neurons with CS, NE, or trypsin, PAR2 responsiveness initially declined, consistent with PAR2 cleavage and desensitization, and then gradually recovered. Inhibitors of PKD, Gβγ, and protein translation inhibited recovery of PAR2 responsiveness. PKD and Gβγ inhibitors also attenuated protease-evoked mechanical allodynia in mice. We conclude that proteases that activate PAR2 by canonical and biased mechanisms stimulate PKD in the Golgi; PAR2 mobilization and de novo synthesis repopulate the cell surface with intact receptors and sustain nociceptive signaling by extracellular proteases.
Background
Monosodium glutamate (MSG) has been identified as a trigger of abdominal pain in irritable bowel syndrome (IBS), but the mechanism is unknown. This study examined whether MSG causes ...visceral hypersensitivity using a water‐avoidance stress (WAS) mouse model of visceral pain.
Methods
Mice were divided into four groups receiving treatment for 6 days: WAS + MSG gavage, WAS + saline gavage, sham‐WAS + MSG gavage, and sham‐WAS + saline gavage. The acute effects of intraluminal administration of 10 μM MSG on jejunal extrinsic afferent nerve sensitivity to distension (0–60 mmHg) were examined using ex vivo extracellular recordings. MSG was also applied directly to jejunal afferents from untreated mice. Glutamate concentration was measured in serum, and in the serosal compartment of Ussing chambers following apical administration.
Key Results
Acute intraluminal MSG application increased distension responses of jejunal afferent nerves from mice exposed to WAS + MSG. This effect was mediated by wide dynamic range and high‐threshold units at both physiologic and noxious pressures (10–60 mmHg, p < 0.05). No effect of MSG was observed in the other groups, or when applied directly to the jejunal afferent nerves. Serum glutamate was increased in mice exposed to WAS + MSG compared to sham‐WAS + saline, and serosal glutamate increased using WAS tissue (p = 0.0433).
Conclusions and Inferences
These findings demonstrate that repeated exposure to MSG in mice leads to sensitization of jejunal afferent nerves to acute ex vivo exposure to MSG. This may contribute to visceral hypersensitivity reported in response to MSG in patients with IBS.
Proposed mechanisms of how chronic MSG exposure can exacerbate pain in IBS patients. Chronic psychological stress and MSG exposure leads to increased responsiveness to an intraluminal infusion of MSG during distension (as postulated in the circle with the “?”) Permeability changes and/or increased MSG transport across the epithelium result in increased tissue levels of glutamate. Speculatively, glutamate (purple dots) may activate receptors on an intermediary pathway via immune cells or through signaling from enterochromaffin cells (blue) or enterocytes releasing pronociceptive mediators and/or interact directly with terminals of nociceptive dorsal root ganglion (DRG) neurons. One or more of these pathways are sensitized to reexposure to MSG, which results in visceral hypersensitivity and ultimately greater abdominal pain. Created with BioRender.com.
Capsaicin-sensitive extrinsic sensory nerves and submucosal vasodilator neurons provide important vasodilator input to submucosal arterioles, but relatively little is known about the signaling ...between these populations and the sympathetic vasoconstrictor innervation. This study examined whether release of sympathetic purines can modulate dilator nerves. In vitro submucosal preparations from guinea pig ileum were modified to leave the parent mesenteric artery intact so that perivascular sympathetic and extrinsic afferent nerves could be activated by a bipolar stimulating electrode placed on the parent artery, and submucosal vasodilator neurons were activated using focal electrodes placed on submucosal ganglia. The outside diameter of submucosal arterioles was monitored using videomicroscopy, and dilator responses were examined after preconstricting vessels 80-95% with prostaglandin F(2alpha) (400 nM). Mesenteric nerve stimulation evoked a frequency-dependent dilation, with suramin (100 microM) present throughout to inhibit P(2X) receptor-mediated vasoconstrictions. In the presence of guanethidine (10 microM) to inhibit sympathetic purine release, superfusion of ATP (200 nM-6 microM) caused a concentration-dependent inhibition of nerve-evoked dilations. Vasodilations to substance P (10 nM) were not inhibited by ATP in the presence of guanethidine, implicating a presynaptic effect of ATP on neurotransmitter release. The inhibitory effect of ATP was blocked by the adenosine receptor antagonist 8-phenyltheophylline (8-PT; 10 microM). In addition, 8-PT increased the amplitude of nerve-evoked dilations, suggesting a tonic inhibitory effect of adenosine receptors on vasodilator release. Dilations evoked by electrical stimulation of submucosal ganglia were also inhibited almost 50% by ATP (2 microM) and its nonhydrolyzable analog, alpha,beta-methylene-ATP (10 microM). These data suggest that sympathetic varicosities release ATP or a related purine that can act at presynaptic adenosine receptors on extrinsic sensory and submucosal vasodilator neurons to inhibit neurotransmitter release.
This study examined whether Pico-Salax alone or Pico-Salax plus bisacodyl tablets for two nights before colonoscopy afford superior efficacy, patient tolerance, and safety compared with oral sodium ...phosphate.
Patients undergoing outpatient colonoscopy were randomized to receive either Pico-Salax at 5 and 10 PM the night before colonoscopy plus bisacodyl 10 mg at 5 PM in the two earlier evenings (n=105), Pico-Salax alone at 5 and 10 PM the night before colonoscopy (n=109), or oral sodium phosphate at 5 and 10 PM the night (n=101) before colonoscopy. All groups were encouraged to drink 3-4 l of Gatorade or other clear fluids the night before the colonoscopy.
Global scoring of cleansing efficacy using the Ottawa scale did not reveal differences among groups, but Pico-Salax plus bisacodyl was superior in cleansing the right colon compared with the other regimens (P=0.003), providing almost 50% improvement over oral sodium phosphate. Patient tolerance of Pico-Salax plus bisacodyl did not differ from Pico-Salax alone but was much better than oral sodium phosphate (P<0.0001). Hemodynamic and biochemical monitoring of patients on Pico-Salax plus bisacodyl suggests this regimen has a very strong safety profile. It does not differ from Pico-Salax alone, which lacks the hyperphosphatemia and hypocalcemia associated with oral sodium phosphate.
Together, these data suggest that Pico-Salax plus bisacodyl provides enhanced colon cleansing in the right colon compared with Pico-Salax alone or oral sodium phosphate, but this finding does not compromise the much greater tolerability or the safety profile of Pico-Salax alone.
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