Chronic Visceral Pain: New Peripheral Mechanistic Insights and Resulting Treatments

Chronic visceral pain is one of the most common reasons for patients with gastrointestinal disorders, such as inflammatory bowel disease or disorders of brain-gut interaction, to seek medical attention. It represents a substantial burden to patients and is associated with anxiety, depression, reductions in quality of life, and impaired social functioning, as well as increased direct and indirect health care costs to society. Unfortunately, the diagnosis and treatment of chronic visceral pain is difficult, in part because our understanding of the underlying pathophysiologic basis is incomplete. In this review, we highlight recent advances in peripheral pain signaling and specific physiologic and pathophysiologic preclinical mechanisms that result in the sensitization of peripheral pain pathways. We focus on preclinical mechanisms that have been translated into treatment approaches and summarize the current evidence base for directing treatment toward these mechanisms of chronic visceral pain derived from clinical trials. The effective management of chronic visceral pain remains of critical importance for the quality of life of suffers. A deeper understanding of peripheral pain mechanisms is necessary and may provide the basis for novel therapeutic interventions.

Face-to-face interviews versus Internet surveys: Comparison of two data collection methods in the Rome foundation global epidemiology study: Implications for population-based research

BACKGROUND AND AIMS

The Rome Foundation Global Epidemiology Study (RFGES) assessed the prevalence, burden, and associated factors of Disorders of Gut-Brain Interaction (DGBI) in 33 countries around the world. Achieving worldwide sampling necessitated use of two different surveying methods: In-person household interviews (9 countries) and Internet surveys (26 countries). Two countries, China and Turkey, were surveyed with both methods. This paper examines the differences in the survey results with the two methods, as well as likely reasons for those differences.

METHODS

The two RFGES survey methods are described in detail, and differences in DGBI findings summarized for household versus Internet surveys globally, and in more detail for China and Turkey. Logistic regression analysis was used to elucidate factors contributing to these differences.

RESULTS

Overall, DGBI were only half as prevalent when assessed with household vs Internet surveys. Similar patterns of methodology-related DGBI differences were seen within both China and Turkey, but prevalence differences between the survey methods were dramatically larger in Turkey. No clear reasons for outcome differences by survey method were identified, although greater relative reduction in bowel and anorectal versus upper gastrointestinal disorders when household versus Internet surveying was used suggests an inhibiting influence of social sensitivity.

CONCLUSIONS

The findings strongly indicate that besides affecting data quality, manpower needs and data collection time and costs, the choice of survey method is a substantial determinant of symptom reporting and DGBI prevalence outcomes. This has important implications for future DGBI research and epidemiological research more broadly.

Asymptomatic surveillance testing for COVID-19 in health care professional students: lessons learned from a low prevalence setting

The novel coronavirus disease of 2019 (COVID-19) pandemic has severely impacted the training of health care professional students because of concerns of potential asymptomatic transmission to colleagues and vulnerable patients. From May 27th, 2020, to June 23rd 2021; at a time when B.1.1.7 (alpha) and B.1.617.2 (delta) were the dominant circulating variants, PCR testing was conducted on 1,237 nasopharyngeal swabs collected from 454 asymptomatic health care professional students as they returned to their studies from across Canada to Kingston, ON, a low prevalence area during that period for COVID-19. Despite 46.7% of COVID-19 infections occurring in the 18-29 age group in Kingston, severe-acute-respiratory coronavirus-2 was not detected in any of the samples suggesting that negligible asymptomatic infection occurred in this group and that PCR testing in this setting may not be warranted as a screening tool.

A272 EVIDENCE OF SEX DIFFERENCES IMPACTING PAIN SIGNALING BY LUMINAL MEDIATORS IN IRRITABLE BOWEL SYNDROME

Background

Irritable bowel syndrome (IBS) is more than twice as common in women and female patients report more severe abdominal pain. This suggests that sex-specific mechanisms may contribute to the pathophysiology of IBS. Many IBS patients have altered gut microbiota and luminal meditators, implicating the gut microbiota in abdominal pain. These luminal mediators can alter excitability of visceral nociceptors, thus potentially contributing to abdominal pain in IBS. Furthermore, in a subset of IBS patients a low FODMAP diet (LFD) reduces the effect of luminal mediators on pain sensing neurons. The LFD may improve abdominal pain at greater rates in women, and numerous putative mechanisms contributing to abdominal pain in IBS are susceptible to sex-specific mediators. However, it is unknown whether luminal mediators have similar effects on visceral pain signaling in both males and females. We hypothesize that luminal mediators will cause greater differences in neuronal excitability and pain signaling in female mice due to sex-specific factors.

Purpose

To determine whether FS from IBS patients (IBS FS) affects nociceptors from female mice more than nociceptors from male mice.

Method

Neurons from dorsal root ganglia from male and female mice were incubated overnight in media containing fecal supernatant (FS) from IBS patients (N=2 females) before and after the LFD, or healthy controls (HC, N=1 female and 1 male). Ratiometric Ca²⁺ imaging with FURA-2-AM was employed to quantify TRPV1 channel sensitization following application of capsaicin (100nM for 1 minute) as a measure of neuronal excitability. Data was analyzed using chi-squared test as well as two-way and mixed-effects model ANOVA as appropriate, followed by Sidak’s multiple comparisons test.

Result(s)

IBS FS caused a 177% larger Ca²⁺ influx in response to capsaicin compared to HC FS in female mice (p=0.0148, N=6-7 mice, neurons=43-49). In male mice, IBS FS increased Ca²⁺ influx by only 13% compared to HC FS (p=0.79, N=5 mice, neurons=28-35). In female mice, 117% more neurons responded to capsaicin after incubation with IBS FS versus HC FS (p=0.0004), while in male mice, only 17% more neurons responded following incubation with IBS FS (p=0.46). Finally, FS from the same IBS patients following a LFD reduced neuronal Ca²⁺ influx by 39% compared to IBS FS in female mice (p=0.0434, N=4-6 mice, neurons=18-49). In male mice, LFD FS reduced Ca²⁺ influx by 11% versus IBS FS (p=0.98, N=5 mice, neurons=28-35).

Conclusion(s)

Nociceptive neurons from female mice are more sensitive to the pro-nociceptive effects of FS from IBS patients, as well as a reduction of these excitatory effects following the LFD. This suggests a potential role of sex hormones in pain signaling in IBS.

Disclosure of Interest

None Declared

A17 EVIDENCE OF PROTEASE-MEDIATED PRO-NOCICEPTIVE EFFECTS OF FECAL SUPERNATANTS FROM CROHN'S DISEASE PATIENTS

Background

Abdominal pain is a debilitating symptom of Crohn’s disease (CD). Despite the current treatment options for this disease, abdominal pain is an unresolved problem that commonly persists in the absence of active inflammation. This suggests that something other than inflammation is driving the pain during the quiescent phase. We have previously reported that microbial proteases can directly modulate the excitability of dorsal root ganglia (DRG) neurons, many of which are pain-sensing. We hypothesize that luminal proteases of CD patients are contributing to their abdominal pain.

Purpose

Determine whether luminal mediators in CD fecal samples induce changes in pain signalling.

Method

The effects of patient (active CD [n = 3] and healthy volunteer (HV) [n = 3]) fecal supernatant (FS) samples on pain-sensing neurons were assessed using ex-vivo single unit afferent nerve recordings from mouse colons. Each sample was tested in colonic preparations from a least 5 mice. To further examine cellular mechanisms, DRG neurons were isolated and incubated overnight in media containing CD FS or HV FS media. Changes in neuronal excitability were recorded by determining the rheobase (lower rheobase=increased excitability) using patch clamp recordings (n ≥ 9 DRG neurons/group). Protease inhibitors were applied in both bioassays to determine whether these inhibited the excitatory effect of FS. Lastly, total proteolytic activity in the CD and HV fecal samples was calculated using a casein colorimetric protease detection assay.

Result(s)

FS from HV had no effect on afferent nerve excitability (p = 0.8920). FS from active CD patients increased action potential discharge from colonic afferent nerves by 85% (p<0.0001) and selectively increased the activation of high-threshold units, which are putative nociceptors, by 44% (p=0.0074). A protease inhibitor cocktail (1:1000) and protease-activated receptor (PAR)-2 antagonist GB83 (10µM) both blocked the excitatory effects of CD FS (p<0.05). Overnight incubation with CD FS also had an excitatory effect on DRG neurons compared to HV FS (rheobase decreased by 46%, p<0.05). The effect of CD FS was blocked by GB83 (10µM) (p<0.001) and a serine protease inhibitor (FUT175; 100µM) (p<0.05) independently, but the activity was not blocked by E64 (30nM) a cysteine protease inhibitor. A 200-fold increase (p<0.0001) in total proteolytic activity was found in CD FS compared to HV FS.

Conclusion(s)

Luminal serine proteases, but not cysteine proteases, appear to be driving nociceptive signalling in CD patients. This provides insight into the generation of pain in CD patients and may be a potential target to mitigate this action. Further research is required to elucidate whether these pro-nociceptive proteases are of bacterial or host origin and their effects in the quiescent phase.

Disclosure of Interest

None Declared

A278 SEX DIFFERENCES IN THE EFFECT OF THE MICROBIOTA FROM IRRITABLE BOWEL SYNDROME PATIENTS ON ABDOMINAL PAIN

Background

Irritable bowel syndrome (IBS) is a chronic abdominal pain disorder that affects women twice as often as men. The gut microbiota has been implicated as a key player in the modulation of abdominal pain in IBS. Given this, we hypothesised that the production of pro-nociceptive mediators within the gut lumen are increased in females, and this contributes to the female predominance of IBS.

Purpose

Compare the effects of FS from male and female IBS patients on abdominal pain pathways and identify the impact of female mouse estrous cycle on abdominal pain.

Method

Fecal supernatants (FS) were perfused through murine colonic preparations while performing extracellular colonic afferent nerve recordings to measure changes in action potential frequency in response to colonic distension. Phase of estrous cycle in female mice was determined through vaginal swabs. FS from male and female IBS patients reporting low, moderate, and high levels of abdominal pain were used.

Result(s)

FS from female IBS patients (N=6) increased afferent nerve discharge (p < 0.05) whereas FS from male IBS patients has no effect (N=4). However, single unit analysis of nociceptive axons revealed that male IBS FS increased nociceptor activity in female mice taken during the proestrus/estrus stage (p < 0.05), but not female mice taken during the metestrus/diestrus stage or male mice. Further investigation found that IBS FS from female patients with high abdominal pain (N=6), but not patients with moderate (N=5) or low pain (N=3), increased visceral afferent nerve discharge by 70%. Single unit analysis of nociceptive axons showed that their activation was increased by almost 50% following FS perfusion from high abdominal pain patients only (p < 0.05). Histamine concentrations and proteolytic activity are increased in FS from female IBS patients with high abdominal pain compared to male IBS patients.

Conclusion(s)

This work suggests that luminal mediators that impact abdominal pain are increased in female IBS patients compared to male IBS patients, and females appear to be more sensitive to their pro-nociceptive effects. Together, these sex differences may contribute to the female predominance of IBS.

Disclosure of Interest

None Declared

Gut bacteria interact directly with colonic mast cells in a humanized mouse model of IBS

Both mast cells and microbiota play important roles in the pathogenesis of Irritable Bowel Syndrome (IBS), however the precise mechanisms are unknown. Using microbiota-humanized IBS mouse model, we show that colonic mast cells and mast cells co-localized with neurons were higher in mice colonized with IBS microbiota compared with those with healthy control (HC) microbiota. In situ hybridization showed presence of IBS, but not control microbiota, in the lamina propria and RNAscope demonstrated frequent co-localization of IBS bacteria and mast cells. TLR4 and H₄ receptor expression was higher in mice with IBS microbiota, and in peritoneal-derived and bone marrow-derived mast cells (BMMCs) stimulated with IBS bacterial supernatant, which also increased BMMCs degranulation, chemotaxis, adherence and histamine release. While both TLR4 and H₄ receptor inhibitors prevented BMMCs degranulation, only the latter attenuated their chemotaxis. We provide novel insights into the mechanisms, which contribute to gut dysfunction and visceral hypersensitivity in IBS.

Small-molecule metabolome identifies potential therapeutic targets against COVID-19

Respiratory viruses are transmitted and acquired via the nasal mucosa, and thereby may influence the nasal metabolome composed of biochemical products produced by both host cells and microbes. Studies of the nasal metabolome demonstrate virus-specific changes that sometimes correlate with viral load and disease severity. Here, we evaluate the nasopharyngeal metabolome of COVID-19 infected individuals and report several small molecules that may be used as potential therapeutic targets. Specimens were tested by qRT-PCR with target primers for three viruses: Influenza A (INFA), respiratory syncytial virus (RSV), and SARS-CoV-2, along with unaffected controls. The nasopharyngeal metabolome was characterized using an LC–MS/MS-based screening kit capable of quantifying 141 analytes. A machine learning model identified 28 discriminating analytes and correctly categorized patients with a viral infection with an accuracy of 96% (R² = 0.771, Q² = 0.72). A second model identified 5 analytes to differentiate COVID19-infected patients from those with INFA or RSV with an accuracy of 85% (R² = 0.442, Q² = 0.301). Specifically, Lysophosphatidylcholines-a-C18:2 (LysoPCaC18:2) concentration was significantly increased in COVID19 patients (P < 0.0001), whereas beta-hydroxybutyric acid, Methionine sulfoxide, succinic acid, and carnosine concentrations were significantly decreased (P < 0.0001). This study demonstrates that COVID19 infection results in a unique nasopharyngeal metabolomic signature with carnosine and LysoPCaC18:2 as potential therapeutic targets.

A240 OPIOID-INDUCED HYPEREXCITABILITY IN DRG NEURONS IS MEDIATED BY DOR-DEPENDENT ENDOCYTOSIS

Background

Opioids are effective for the treatment of abdominal pain but are also associated with tolerance, and increased dosing leads to severe side effects. We previously showed that prolonged exposure to high doses of opioids evoked paradoxical hyperexcitability of colonic afferent nerves that was mediated by δ-opioid receptor (DOR) signaling. Recent studies suggest that DOR-dependent analgesia is mediated not only by G proteins but also via receptor endocytosis and downstream signaling, but it is unclear what intracellular signaling mechanisms are underlying opioid-induced hyperexcitability.

Aims

To examine the mechanisms underlying DOR-mediated hyperexcitability of dorsal root ganglia (DRG) neurons.

Methods

We assessed the excitability of DRG neurons isolated from C57BL/6 mice by measuring the rheobase (minimal current to elicit an action potential, i.e. lower rheobase=increased excitability) using perforated patch-clamp recordings. Dissociated neurons were exposed to a high concentration (10 µM) of the μ-opioid receptor agonist DAMGO, the DOR agonist DADLE, or the weakly internalizing DOR agonist ARM390 overnight. To examine the role of receptor endocytosis and intracellular receptor activation underlying the excitatory effect by opioids, DRG neurons exposed to DAMGO or DADLE were preincubated with the membrane-permeable opioid receptor antagonist naloxone or the endocytosis inhibitor Pitstop2. To further understand the mechanisms involved in the hyperexcitability evoked by opioid re-exposure, following overnight incubation with high concentrations of DAMGO or DADLE, neurons were washed for 1 hr and treated either with the PKA inhibitor H89 or the PKC inhibitor GFX before re-exposure to DAMGO or DADLE at a low concentration (10 nM).

Results

Neurons exposed to 10 µM DAMGO or DADLE were hyperexcitable (rheobase decreased 25 % and 26 % compared to controls respectively; p≤0.05, 2-way ANOVA). Naloxone and Pitstop2 blocked the increased excitability of DRG neurons induced by overnight incubations with either DAMGO or DADLE. In contrast to the hyperexcitability induced by DAMGO and DADLE, overnight incubation with 10 µM ARM390 decreased excitability (rheobase increased 31%, p≤0.05, unpaired t-test). The hyperexcitability induced by DAMGO and DADLE was reversed after a 1 hr washout but acute reapplication of a low concentration of DAMGO or DADLE (10nM) now evoked hyperexcitability (rheobase decreased 34 and 35 % respectively, p≤0.05, 2-way ANOVA). This effect was prevented by inhibiting PKC but not PKA.

Conclusions

Our data suggest that the DOR-dependent hyperexcitability evoked by prolonged exposure to high concentrations of opioids is dependent on receptor endocytosis and downstream PKC signaling. Targeting these pathways could mitigate the hyperexcitability of pain signaling neurons caused by high doses of opioids.

Funding Agencies

CCC

A242 STOOL FROM IBS-D PATIENT WITH A HISTORY OF A DYSBIOTIC AND NON-DYSBIOTIC ONSET MODULATE NEURONAL EXCITABILITY VIA DIFFERENT MECHANISMS

Background

We have shown that Irritable Bowel Syndrome diarrhea-predominant (IBS-D) patients with a history of a dysbiotic-like onset have distinct stool metabolomic profiles versus those with a non-dysbiotic-like onset. IBS stool supernatants can sensitize mouse colonic afferent nerves via both histamine and proteases. However, it is unknown if stool supernatants from the two IBS-D subgroups modulate the excitability of nociceptive neurons via different neuroactive mediators

Aims

To evaluate whether there are differences in neuroactive mediators within stool supernatants from subgroups of IBS-D patients that can modulate the excitability of nociceptive neurons.

Methods

Stool samples from healthy control (HC) (N=5) and IBS-D patients with a dysbiotic (N=7) or non-dysbiotic-like (N=7) onset, was homogenized with Krebs solution and filtered. Proteolytic activity was assessed using casein as a substrate with and without protease inhibitors. Histamine was quantified by ELISA. DRG neurons from C57BL/6 mice were incubated overnight or acutely (30 min) with stool supernatants. Some neurons were pre-incubated with PAR2 (GB83, 10 μM) or H1R (pyrilamine, 1μM) antagonists prior to supernatant incubation. Changes in neuronal excitability were assessed with perforated patch-clamp by measuring the rheobase (current that elicits an action potential).

Results

Proteolytic activity in dysbiotic-like (57.9 U/μg, p&lt;0.05) but not non-dysbiotic like (37.4 U/μg) stool supernatant was increased compared to HC (25.2 U/μg). Serine inhibitor decreased proteolytic activity of dysbiotic (46.6%, p&lt;0.05) and non-dysbiotic (34.2%, p&lt;0.01) supernatant whereas cysteine, aspartic and metalloproteases inhibitors had no effect. Histamine was increased 78% (p&lt;0.05) in IBS-D compared to HC. No differences in proteolytic activity and histamine concentration between IBS-D subtypes were found. In patch-clamp recordings, overnight incubation with dysbiotic (19%, p&lt;0.05) and non-dysbiotic (22%, p&lt; 0.01) stool supernatant decreased rheobase of DRG neurons compared to HC. No difference in rheobase was observed between IBS-D subtypes. GB83 blocked the overnight actions of supernatants from both subgroups, but pyrilamine had no effect. In contrast, following acute incubation, pyrilamine blocked the hyperexcitability evoked by dysbiotic like supernatant (60pA vs 48pA, p&lt;0.001) but had no effect on non-dysbiotic like supernatants.

Conclusions

Proteases in stool supernatants from IBS-D patients increase neuronal excitability but only those with a history of dysbiotic like onset acutely increase neuronal excitability through H1 receptors. These findings suggest that stool supernatants from subgroups of IBS-D may modulate nociceptor excitability via different mechanisms.

Funding Agencies

CIHRAmerican Neurogastroenterology and Motility Society

A243 HISTAMINE H1-RECEPTOR ANTAGONISTS SUPPRESS THE HYPEREXCITABILITY OF NOCICEPTIVE NEURONS EXPOSED TO IBS-C PATIENT STOOL SUPERNATANTS

Background

Abdominal pain is the primary cause of morbidity in many chronic GI disorders such as IBS, but the molecular mechanisms contributing to pain signaling are unclear. Stool supernatants from patients with diarrhea-predominant IBS increase the excitability of DRG neurons compared to supernatants from healthy controls, suggesting that mediators in the stool may sensitize nociceptors. Additionally, histamine has been implicated as a mediator of hypersensitivity in IBS patients. However, it is unclear if stool supernatants from constipation-predominant IBS (IBS-C) patients affect the excitability of DRG neurons. Furthermore, it is unknown if specific neuro-mediators in stool such as histamine impact the excitability of nociceptive neurons in this subgroup of IBS patients.

Aims

To evaluate whether IBS-C stool supernatants induce nociceptive signaling in DRG neurons compared to healthy control (HC) stool supernatants.

If so, to evaluate the role of histamine 1 (H1) receptors in DRG neuron nociceptive signaling initiated by mediators in IBS-C stool supernatants.

Methods

IBS-C (n=5) and HC (n=2) patient stool was collected, filtered, and dissolved with Krebs solution in a 1:8 (g/v) dilution. Dorsal root ganglion (DRG) neurons from C57BL/6 mice were incubated with HC or IBS-C stool supernatant for 30 minutes. To evaluate whether histamine in stool supernatants can sensitize H1 receptors on nociceptors, DRG neurons were pre-incubated with the H1-receptor antagonist pyrilamine (1μM, 30 min) before stool supernatants. Changes in DRG neuronal excitability were recorded using perforated patch-clamp techniques to measure the rheobase (minimum input current needed to elicit an action potential) and the resting membrane potential (RMP).

Results

In neurons incubated with IBS-C stool supernatants (n=28) the rheobase decreased (63%) compared to healthy controls (78 ± 13.7 pA; n=6). This effect was reversed in DRG neurons pre-incubated with the H1 receptor antagonist, pyrilamine, (n=26) (77 ± 5.9 pA, p&lt;0.001) compared to neurons incubated with IBS-C supernatant alone (50 ± 5.13 pA; n=28). No changes were found in the RMP. The data were analyzed with the non-parametric Kruskal-Wallis test.

Conclusions

IBS-C stool supernatants increase the excitability of DRG neurons compared to HC. Furthermore, the H1-receptor antagonist pyrilamine inhibits the neuronal hyperexcitability evoked by mediators in IBS-C patient stool. These findings suggest that the neuroactive metabolite histamine may contribute to visceral pain experienced by patients with IBS-C. Further studies are needed to examine whether similar signaling to nociceptive neurons by stool supernatants occurs in other subtypes of IBS.

Funding Agencies

CAG, CIHR

A239 COMBINED CANNABINOID RECEPTOR 1 AND MU-OPIOID RECEPTOR AGONISTS SYNERGISTICALLY INHIBIT VISCERAL PAIN IN VIVO WITHOUT ADVERSE SIDE EFFECTS OR TOLERANCE

Background

Previously we have shown that both cannabinoid 1 receptor (CB1R) and mu-opioid receptor (MOR) agonists inhibit mechanosensitivity of colonic nociceptive nerves. However, it is unknown whether agonists of cannabinoid and opioid receptors have a synergistic interaction, such that very low doses of these agonists can be employed to reduce visceral pain and side effects.

Aims

To determine the effects of combined cannabinoid and opioid receptor agonists on visceral pain and its side effects.

Methods

Telemetric transmitters were surgically implanted into the abdominal cavity of C57/BL6 mice, with electrodes sutured to the external oblique muscle to measure the visceromotor response (VMR) to colorectal distention using a 4F arterial embolectomy catheter (volume range 20–80 µL). Mice were injected intraperitoneally with vehicle, arachidonyl-2’-chloroethylamide (ACEA), a selective CB1R agonist (0.3, 1, 3 mg/kg), HU-308, a selective CB2R agonist (0.3, 1, 3mg/kg), morphine, a MOR agonist (0.3, 3 mg/kg), or a combination, 30-minutes prior to distention. To assess side effects, pulse oximetry, heart rate, fecal pelleting, and locomotion (via an open-field maze) were measured. Data was analyzed with one or two-way ANOVA with post-hoc Bonferroni multiple comparisons test.

Results

ACEA dose-dependently reduced VMR (P&lt;0.01 vs. vehicle, N=5); at the 80 µL distention, reductions of 35% (P&lt;0.01) and 62% (P&lt;0.01) were observed for 1 mg/kg and 3 mg/kg respectively. In contrast, HU-308 did not reduce VMR at any dose (P=0.17, N=8). Morphine (0.3 mg/kg) did not reduce VMR (P&gt;0.99), while a higher dose (3 mg/kg) attenuated VMR (P&lt;0.01 vs. vehicle, N=5); reductions of 32% (P&lt;0.01) and 61% (P&lt;0.01) at 60 and 80 µL distentions respectively. Interestingly, a combination of sub-analgesic doses of ACEA (0.3 mg/kg) and morphine (0.3 mg/kg) significantly reduced VMR (P&lt;0.01 vs vehicle, N=5); compared to vehicle, VMR was reduced by 21% at 40 µL (P&lt;0.05), 27% at 60 µL (P&lt;0.01) and 60% at 80 µL (P&lt;0.01). Chronic administration (2x/day for 6 days) of this combination did not alter the magnitude of its inhibitory effect (P=0.67, N=5), suggesting tolerance did not develop. While analgesic doses of morphine (3mg/kg) decreased oxygen saturation (P&lt;0.01), heart rate (P&lt;0.01) and fecal pelleting (i.e., GI motility; P&lt;0.05), the sub-analgesic combination of ACEA and morphine had no effect (P&gt;0.99 for all, N=5). Locomotion was unchanged by the agonists alone or combined (P=0.17).

Conclusions

A combination of sub-analgesic doses of CB1R and MOR agonists significantly inhibits visceral pain in vivo, without development of sides effects or tolerance with chronic use. Thus, combining low doses of CB1R and MOR agonists may be an effective visceral pain management strategy.

Funding Agencies

NSERC

A80 CANADIAN NEUROGASTROENTEROLOGY NETWORK (CNN) SURVEY ON PH/MOTILITY TESTING IN CANADA

Background

Anecdotal reports suggest that access to pH/motility testing is problematic in Canada, but to date there is little data documenting this.

Aims

To assess the volume and accessibility of motility lab testing in Canada.

Methods

The CNN developed a questionnaire directed at the scope, volume and accessibility of pH/motility testing in Canadian labs. Fifty-three labs were identified using lists provided by companies that supply pH/motility recording equipment in Canada. Of these, 12 labs were excluded (10 had incorrect or absent contact information, 1 had recently closed and 1 had just opened). Questionnaires were sent in early 2020 to the remaining 41 labs, and respondents were asked to use data from their last fiscal year pre-pandemic.

Results

26 completed questionnaires were returned (i.e., 63% response rate, but representing ~ 51% of active labs): 23 adult units (7 community, 15 academic and 1 private) and 3 academic pediatric units. Of the adult units, 6 performed studies in children <12 yrs old. All 3 pediatric units provided both esophageal and anorectal high-resolution manometry (HRM) and pH/Impedance recording, with wait times of < 3 months. All 23 adult labs provided esophageal HRM, but just 50% performed anorectal manometry and only 3 anorectal manometry with biofeedback. Ambulatory pH/Impedance was performed in all but 1 adult unit. 15 of 23 adult centres reported access to colon transit studies and only one performed colonic manometry. No units performed antroduodenal manometry. Five units offered Bravo wireless pH recording and 4 performed ENDOFLIP. In adult units, the median number of procedures per year were as follows: esophageal HRMs - 278 (range: 50–1140); pH/impedance - 225 (range: 40–634); anorectal manometry - 90 (range: 10–450). Corresponding median wait times in months were as follows: esophageal HRM - 4 (range: 0.5–14); pH/Impedance - 4.5 (range: 0.5–14); anorectal manometry - 4.6 (range: 2–9). Only 6 of the 23 adult units met recommended wait time targets of <2 months. Testing was performed by a nurse in ~ 80% of centres, while testing was done by technicians in 2 units and physicians in 3 units. 8 units accepted referrals from primary care physicians, whereas the remainder only accepted specialist referrals. 50% screened referrals for appropriateness and restricted access accordingly.

Conclusions

The scope of motility and pH testing across Canada is variable, with lower GI testing lacking in many regions. Wait times vary significantly across labs and the majority of centres exceed recommended limits of 2 months. The reasons underlying the identified limitations to pH/motility testing access warrant further study.

Funding Agencies

None

A53 A NOVEL PH-SENSITIVE OPIOID ANALOGUE PROVIDES SUSTAINED ANALGESIA DURING COLONIC INFLAMMATION AND LACKS COMMON SIDE EFFECTS

Background

Opioids provide effective pain relief during flares of inflammatory bowel disease but are limited by serious side effects. We showed that acute administration of a novel pH-sensitive opioid agonist, NFEPP, had potent analgesic effects in inflamed acidified colonic tissues without opioid typical side effects. However, the effects of repeated application of NFEPP during the course of an acute flare of colonic inflammation are unknown.

Aims

To assess the analgesic and side effect profile resulting from repeated NFEPP applications during the course of acute colitis.

Methods

Acute colitis in C57BL/6 mice was induced via 2.5% dextran sulfate sodium dissolved in drinking water for 5 days. Mice were then randomly group assigned to either vehicle, fentanyl or NFEPP. Drugs and vehicle were administered sc. BID for 5 days (0.4 mg/kg), with a final injection on Day 6 (Day 1–6). Visceral nociception was evaluated by performing visceromotor responses (VMRs) to colorectal distension at different time points during colitis. Side effects were assessed using 1) a combination of oral contrast-enhanced abdominal CT-scans (before/after treatment) and defecation assessments to analyze gastrointestinal transit and isometric tension recordings to evaluate colon motility 2) pulse oximeter measurements to reveal cardiorespiratory effects. Inflammation was assessed by histological scoring, myeloperoxidase activity assay and tissue pH measurement of colon samples.

Results

NFEPP decreased VMRs to colorectal distension over the entire period of acute DSS colitis (Day 6: 40.54%, p&lt;0.001, reduction compared to baseline). However, strongest VMR inhibition was observed at Day 3 (66.7%, p&lt;0.05), concordant with the peak of inflammation (MPO: 3.5 U/mg tissue, p&lt;0.001; tissue Damage-Score: 3.0, p&lt;0.001; tissue pH: ΔpH= -0.28, p=0.001, all compared to healthy control). Treatment with NFEPP did not delay gastrointestinal transit (GIT, p=0.37, compared to baseline) nor fecal output (p=0.45, compared to vehicle) whereas fentanyl decreased transit (GIT: p&lt;0.05; fecal output: p&lt;0.05). Colonic contractile responses evoked by electrical field stimulation were reduced in fentanyl treated mice compared to NFEPP (10 Hz: p&lt;0.05). Fentanyl significantly reduced oxygen saturation (15 min: 85% SpO2, p&lt;0.01) and caused a sustained reduction in heart rate at Day 2 (60 min: Δ BPM -91.8 from baseline, p=0.001) whereas NFEPP did not affect oxygen saturation (p=0.95) and revealed minor, transient effects on heart rate (15 min: Δ BPM -75.6, p&lt;0.01) which recovered after 60 min.

Conclusions

Prolonged NFEPP administration effectively inhibits visceral nociception during acute colitis in a preclinical mouse model without altering gastrointestinal transit, colon motility and oxygen saturation.

Funding Agencies

CCC

Targeting G protein-coupled receptors for the treatment of chronic pain in the digestive system

Chronic pain is a hallmark of functional disorders, inflammatory diseases and cancer of the digestive system. The mechanisms that initiate and sustain chronic pain are incompletely understood, and available therapies are inadequate. This review highlights recent advances in the structure and function of pronociceptive and antinociceptive G protein-coupled receptors (GPCRs) that provide insights into the mechanisms and treatment of chronic pain. This knowledge, derived from studies of somatic pain, can guide research into visceral pain. Mediators from injured tissues transiently activate GPCRs at the plasma membrane of neurons, leading to sensitisation of ion channels and acute hyperexcitability and nociception. Sustained agonist release evokes GPCR redistribution to endosomes, where persistent signalling regulates activity of channels and genes that control chronic hyperexcitability and nociception. Endosomally targeted GPCR antagonists provide superior pain relief in preclinical models. Biased agonists stabilise GPCR conformations that favour signalling of beneficial actions at the expense of detrimental side effects. Biased agonists of µ-opioid receptors (MOPrs) can provide analgesia without addiction, respiratory depression and constipation. Opioids that preferentially bind to MOPrs in the acidic microenvironment of diseased tissues produce analgesia without side effects. Allosteric modulators of GPCRs fine-tune actions of endogenous ligands, offering the prospect of refined pain control. GPCR dimers might function as distinct therapeutic targets for nociception. The discovery that GPCRs that control itch also mediate irritant sensation in the colon has revealed new targets. A deeper understanding of GPCR structure and function in different microenvironments offers the potential of developing superior treatments for GI pain.

A45 A NOVEL PH-SENSITIVE OPIOID ANALGESIC THAT SELECTIVELY INHIBITS NOCICEPTION IN DSS-INDUCED COLITIS

Background

Opioid drugs are used to treat pain in inflammatory bowel disease (IBD) but their side effects can cause serious morbidity. Therefore, we tested a novel opioid analgesic, ±)-N-(3-fluoro-1-phenethylpiperidine-4-yl)-N-phenylpropionamide (NFEPP) which selectively activates peripheral µ-opioid receptors at acidic pH, as occurs in inflamed tissue.

Aims

Evaluate whether NFEPP causes analgesia in the inflamed colon of DSS-colitis mice using both in vitro and in vivo techniques.

Methods

To measure the visceral motor reflex (VMR) in response to colorectal distention, EMG electrodes connected to a telemetric transmitter were implanted in mice (c57BL/6), after 10 days recovery acute dextran sodium sulfate (DSS) colitis was induced (5 days 2.5% DSS, 2 days water). VMR was measured 30 min after s.c. injection of vehicle or 0.2 mg/kg of NFEPP or fentanyl. Motility was assessed by fecal pellet count 1 hour after NFEPP. Colonic tissue pH was evaluated using the SNARF-4F-5 carboxylic acid probe. Excitability of mouse dorsal root ganglia (DRG) neurons was measured by recording the rheobase (minimum input current to fire an action potential) after superfusion of NFEPP (300 nM, 10 min) or vehicle at pH 6.5 or 7.4. Colonic afferent nerve responses to probing with a von Frey filament (1 gm) were examined before and after exposure to NFEPP (300 nM, 5 min superfusion) at pH 6.5 and 7.4 respectively. The data was analyzed with Welch’s t-test, 1- or 2-way ANOVA with post hoc Dunnett or Bonferroni or Tukey’s test.

Results

NFEPP significantly inhibited the VMR in response to distension in mice with colitis compared to vehicle (decreased response by 65%, P&lt;0.001). NFEPP had no effect in control mice. Conversely, fentanyl caused a similar decreased response in both groups (DSS 79% and control 67%, P&lt;0.001). Pelleting was not affected by NFEPP injection in either group compared to vehicle. The pH measurement revealed a more acidic environment in DSS colonic tissue (ΔpH0.37±0.14, P&lt;0.05) compared to controls. In patch-clamp studies, NFEPP decreased DRG excitability at pH 6.5 compared to the baseline and vehicle (increased rheobase 53.84%, P&lt;0.01 and 36.36%, P&lt;0.05 respectively) but had no effect at pH 7.4. In colonic afferent nerve recordings, NFEPP significantly attenuated afferent responses (28.9% P&lt;0.01) to probing at pH 6.5 but also had no effect at pH 7.4.

Conclusions

This pH-selective opioid agonist significantly inhibits pain at the site of inflammation where the tissue pH is acidic but has no effect in tissues where the pH is in the physiological range. Thus, NFEPP could be an effective opioid analgesic in IBD while being devoid of any unwanted side effects.

Funding Agencies

CCC

A234 EVALUATING THE EFFECT OF STOOL SUPERNATANTS FROM IBS PATIENTS AND HEALTHY CONTROLS ON THE EXCITABILITY OF DRG NEURONS

Background

Abdominal pain is commonly described in chronic disorders such as irritable bowel syndrome (IBS), but the underlying mechanisms are currently unclear. The stool metabolomic and microbiota profiles of IBS and healthy patients have shown distinct differences. Additionally, IBS stool supernatants have previously been demonstrated to induce hypersensitivity of nociceptive nerves in the ex vivo mouse colon, suggesting that mediators in the stool can sensitize nociceptors. However, the effects of healthy control (HC) or IBS patient stool supernatants on the excitability of DRG neurons have not been clarified.

Aims

To evaluate the effect of HC and IBS supernatant on DRG neurons.

Methods

HC (n=8 patients) or IBS (n=10 patients) stool was collected, dissolved and homogenized with bicarbonate-buffered Krebs solution at 37°C in a 1/10 dilution. DRG neurons from C57BL/6 mice were dissociated and incubated overnight with HC or IBS supernatant in a Krebs dissolution. Changes in DRG neuronal excitability were recorded using perforated patch-clamp techniques to measure the rheobase (amount of current needed to elicit an action potential). The effect of the IBS and HC stool supernatants on the resting membrane potential (RMP) was also recorded.

Results

Overnight incubations with supernatant of HC stool diluted in Krebs solution (n=28 neurons) did not significantly decrease the rheobase compared to control neurons (n=22) (62.7 ± 3.9 pA vs 64.2 ± 2.7 pA). In a parallel experiment, we evaluated the effect of IBS stool supernatants diluted in Krebs (n=52 neurons) and found that they significantly decreased the rheobase compared to the supernatant of HC diluted in Krebs and control neurons (52.3 ± 2.3; p&lt;0.05). The data were analyzed with a one-way ANOVA and Tukey’s test. Incubations with IBS supernatant decreased the RMP compared to HC supernatant (-42.6 ± 0.6 mV vs. -46.0 ± 0.9 mV; p&lt;0.01), which was calculated with an unpaired t-test.

Conclusions

These findings suggest that mediators in IBS stool increase the excitability of DRG neurons compared to HC stool supernatant, and thus may contribute to pain signaling in IBS patients.

Funding Agencies

CIHR

A10 FOOD ANTIGEN-STRESS INTERACTION LEADS TO INCREASE PAIN SIGNALING IN ILEUM AND COLON VIA STAT6 IN AN IBS MODEL

Background

Abdominal pain can be triggered by food ingestion in IBS patients. Previously we have shown that a food antigen induces local release of immune mediators in the colon that increase dorsal root ganglion (DRG) neuron excitability when there is previous antigen exposure in the presence of psychological stress. However, it is unknown if this effect is limited to the colon. Furthermore, the involvement of histamine in the neuronal hyperexcitability suggests that the stress-food antigen interaction evokes a Th2 immune response. Thus, we sought to investigate the role of STAT6, a transcription factor downstream of Th2 cytokines and important for IgE production.

Aims

1) Determine if stress-food antigen interaction leads to release of mediators within the small intestine that increase DRG neuron excitability. 2) Determine the involvement of STAT6 on neuronal hyperexcitability induced by the stress-food antigen interaction.

Methods

BALB/c mice were exposed to water avoidance stress (WAS) or sham stress (SHAM) for 1 hr daily for 10 days. On day 2–10, mice were exposed to ovalbumin (OVA) or saline (SAL). Seven days later, mice were re-exposed to either OVA or SAL every 2 days for 2 weeks yielding 3 groups: WAS/OVA+OVA, WAS/SAL+OVA, and SHAM/OVA+OVA. STAT6 deficient mice were also exposed to WAS/OVA+OVA protocol. Ileum or colonic supernatants were obtained 4 hours after tissue collection. DRG neurons were incubated overnight with supernatants prior to perforated patch clamp recordings. Neuronal excitability was evaluated by measuring the rheobase (minimum current to elicit an action potential, decreased rheobase indicates increased excitability). Mechanosensitivity of extrinsic afferent nerves innervating distal ileum was examined using ex vivo extracellular afferent nerve recordings. Data was analyzed by one or two-way ANOVA with Bonferroni post-hoc test.

Results

Ileum supernatants from WAS/OVA+OVA mice increased DRG neuron excitability compared to WAS/SAL+OVA and SHAM/OVA+OVA mice (63.3 ± 6.2 pA vs 83.2 ± 5.4 pA, 86.7 ± 4.5 pA, p&lt;0.05). Ileum afferent nerve response to distention was significantly augmented in WAS/OVA+OVA mice compared to WAS/SAL+OVA and SHAM/OVA+OVA (P&lt;0.05, n=4–7). DRG neurons incubated with WAS/OVA+OVA supernatant from STAT6 deficient mice were less excitable compared to neurons incubated with colonic supernatants from wild type mice (86.5 ± 4.1 pA vs 67.6 ± 4.8 pA, p&lt;0.05).

Conclusions

Stress-food antigen interaction releases mediators in both the small intestine and colon to increase nociceptive signaling, an important finding as IBS can involve both areas. The release of excitatory mediators within the gut appears to involve STAT6. Thus, a stress-food antigen interaction evoking a Th2 immune response in the gut may be a mechanism underlying food induced symptoms in IBS.

Funding Agencies

Queen’s University, Department of Medicine

Worldwide Prevalence and Burden of Functional Gastrointestinal Disorders, Results of Rome Foundation Global Study

BACKGROUND & AIMS

Although functional gastrointestinal disorders (FGIDs), now called disorders of gut-brain interaction, have major economic effects on health care systems and adversely affect quality of life, little is known about their global prevalence and distribution. We investigated the prevalence of and factors associated with 22 FGIDs, in 33 countries on 6 continents.

METHODS

Data were collected via the Internet in 24 countries, personal interviews in 7 countries, and both in 2 countries, using the Rome IV diagnostic questionnaire, Rome III irritable bowel syndrome questions, and 80 items to identify variables associated with FGIDs. Data collection methods differed for Internet and household groups, so data analyses were conducted and reported separately.

RESULTS

Among the 73,076 adult respondents (49.5% women), diagnostic criteria were met for at least 1 FGID by 40.3% persons who completed the Internet surveys (95% confidence interval [CI], 39.9-40.7) and 20.7% of persons who completed the household surveys (95% CI, 20.2-21.3). FGIDs were more prevalent among women than men, based on responses to the Internet survey (odds ratio, 1.7; 95% CI, 1.6-1.7) and household survey (odds ratio, 1.3; 95% CI, 1.3-1.4). FGIDs were associated with lower quality of life and more frequent doctor visits. Proportions of subjects with irritable bowel syndrome were lower when the Rome IV criteria were used, compared with the Rome III criteria, in the Internet survey (4.1% vs 10.1%) and household survey (1.5% vs 3.5%).

CONCLUSIONS

In a large-scale multinational study, we found that more than 40% of persons worldwide have FGIDs, which affect quality of life and health care use. Although the absolute prevalence was higher among Internet respondents, similar trends and relative distributions were found in people who completed Internet vs personal interviews.

IMAGINE Network's Mind And Gut Interactions Cohort (MAGIC) Study: a protocol for a prospective observational multicentre cohort study in inflammatory bowel disease and irritable bowel syndrome

INTRODUCTION

Gut microbiome and diet may be important in irritable bowel syndrome (IBS), inflammatory bowel disease (IBD) and comorbid psychiatric conditions, but the mechanisms are unclear. We will create a large cohort of patients with IBS, IBD and healthy controls, and follow them over time, collecting dietary and mental health information and biological samples, to assess their gastrointestinal (GI) and psychological symptoms in association with their diet, gut microbiome and metabolome.

METHODS AND ANALYSIS

This 5-year observational prospective cohort study is recruiting 8000 participants from 15 Canadian centres. Persons with IBS who are 13 years of age and older or IBD ≥5 years will be recruited. Healthy controls will be recruited from the general public and from friends or relatives of those with IBD or IBS who do not have GI symptoms. Participants answer surveys and provide blood, urine and stool samples annually. Surveys assess disease activity, quality of life, physical pain, lifestyle factors, psychological status and diet. The main outcomes evaluated will be the association between the diet, inflammatory, genetic, microbiome and metabolomic profiles in those with IBD and IBS compared with healthy controls using multivariate logistic regression. We will also compare these profiles in those with active versus quiescent disease and those with and without psychological comorbidity.

ETHICS AND DISSEMINATION

Approval has been obtained from the institutional review boards of all centres taking part in the study. We will develop evidence-based knowledge translation initiatives for patients, clinicians and policymakers to disseminate results to relevant stakeholders.Trial registration number: NCT03131414.

A124 SYNERGISTIC INTERACTION OF CANNABINOIDS AND OPIOIDS REDUCES PAIN SIGNALING IN COLONIC NOCICEPTIVE NERVES

Background

With the recent legalization of recreational marijuana in Canada, increasing numbers of patients with gastrointestinal (GI) disorders are using cannabis to treat their pain, either alone or together with opioids. However, little is known about potential benefits of cannabinoids for treating visceral pain originating within the GI tract and whether the combined use of cannabinoids and opioids could enable the reduction or even discontinuation of opioids.

Aims

To investigate the effects of cannabinoids alone or in combination with opioids on colonic nociceptive nerves.

Methods

Extracellular afferent nerve recordings were obtained from ex vivo flat sheet preparations of male C57BL/6 mouse distal colons. Single unit analysis discriminated individual afferent neuron responses to mechanical probing of the colon with a 1g von Frey hair before and after superfusion of HU-210, a selective CB1 receptor agonist, HU-308, a selective CB2 receptor agonist, DAMGO, a selective mu-opioid receptor (MOR) agonist, or a combination. In parallel studies, perforated patch clamp techniques were employed to assess the rheobase as a measure of neuronal excitability in acutely dissociated dorsal root ganglia (DRG) neurons in the presence of one or more of these agonists. Data were analyzed using a one-way ANOVA with Bonferroni multiple comparisons test.

Results

Superfusion of HU-210 (1 μM), caused significant inhibition in afferent nerve mechanosensitivity compared to control (6.2±1.1 vs. 13.7±2.5 Hz, p=0.005, n=10); lower concentrations (10 nM and 100 nM) had no effect (p&gt;0.99, n=11; p=0.600, n=10 respectively). Conversely, the CB2 agonist HU-308 (1 μM and 10 μM), did not alter mechanosensitivity (p&gt;0.9, n=8 for both concentrations). Superfusion of HU-210 alone (100 nM) or DAMGO (1 nM) alone in the same recording had no effect, but when both agonists were superfused together, there was a significant reduction in mechanosensitivity (8.1±1.7 vs. 14.8±2.3 Hz, p&lt;0.01, n=10). In patch clamp recordings of DRG neurons, HU-210 (1 μM) decreased excitability (i.e. increased rheobase, 94.4±9.4 vs. 62.7±6.4 pA; p=0.031, n=9), whereas a lower concentration (100 nM) had no effect. Similar to afferent nerve recordings, when applied alone, DAMGO (1 nM) and HU-210 (100 nM) did not affect rheobase (DAMGO: p&gt;0.99, n=9; HU-210: p&gt;0.99, n=10), whereas the combination of both agonists significantly decreased excitability (123.0±13.4 vs. 62.7±6.4 pA, p&lt;0.01, n=10).

Conclusions

Activation of CB1 receptors inhibits mechanosensitivity of colonic afferent nerves while a CB2 agonist had no effect. Interestingly, combination of sub-threshold concentrations of CB1 and MOR agonists inhibited colonic afferent nerves and thus, may suggest that cannabinoids could enable opioid dose reduction or discontinuation.

Funding Agencies

None

A11 MICROBIAL AND METABOLOMIC PROFILES IDENTIFY SUBSETS OF DIARRHEA PREDOMINANT IRRITABLE BOWEL SYNDROME

Background

Irritable bowel syndrome (IBS) patients are subtyped by predominant bowel habit rather than pathophysiological mechanisms and this may underlie challenges in identifying more effective targets for designing new treatments. Metabolomics and microbial analysis can distinguish IBS patients from healthy controls but it is unknown if they can identify pathophysiological IBS subgroups.

Aims

To phenotype subgroups of IBS patients using metabolomics and microbial analysis and determine if these subgroups have different underlying pain signalling mechanisms.

Methods

Symptom history, stool and urine were collected from 30 diarrhea predominant (IBS-D) and 30 constipation predominant (IBS-C) IBS patients (Rome IV). Liquid Chromatography-Mass Spectrometry quantified 130 metabolites in stool and urine. The GA-map™ Dysbiosis Test targeting ≥300 bacteria on different taxonomic levels was used to identify stool microbial composition. Multivariate OPLS discriminatory analysis assessed metabolomics and microbial profiles. To assess potential effects on pain signalling, the effect of stool supernatant on dissociated dorsal root ganglia (DRG) neuron responses to capsaicin (10nM) was assessed using Ca2+ imaging.

Results

Within both IBS-D and IBS-C, combined stool/urine metabolomic profiles of patients with a dysbiosis-like (DL) IBS (onset following antibiotics, enteric infection, or travel) were distinct from patients with a non-DL IBS onset (IBS-D R2=0.7, Q2=0.5; IBS-C R2=0.5, Q2=0.4); fecal glutamic acid and urinary pyruvic acid were the main metabolites driving separation. However, microbial profiles of DL vs non-DL onset could only be discriminated in IBS-D (R2=0.8, Q2=0.4). In the patients with a DL IBS onset, stool metabolomic profiles of the 7 IBS-C discriminated from the 8 IBS-D patients (R2=0.9, Q2=0.8). Profile differences were not seen between IBS-C and IBS-D with a non-DL onset of IBS. In preliminary studies, incubation of DRG neurons with stool supernatant from 1 DL IBS-D and 1 non-DL IBS-D increased peak [Ca2+]i responses to capsaicin compared to incubation with media (DL: 5.5±0.9 vs 2.3±0.7; non-DL: 6.9±0.7 vs 3.9±0.4% ΔF/F). Similarly, the number of responsive neurons to capsaicin was increased after incubation with IBS stool supernatant vs media (DL: 27% vs 8%; non-DL 19% vs 12%).

Conclusions

Different metabolomic and bacterial profiles between DL and non-DL onset of IBS-D suggests a novel means to better phenotype clinically defined IBS subgroups. While initial results with stool supernatants from both a DL and non-DL IBS-D patient suggest increased pain signalling in DRG neurons, more studies are needed to determine if there are differences between these two subgroups as well as healthy controls.

Funding Agencies

CIHRSoutheastern Ontario Academic Medical Organization (SEAMO)

A54 DELTA OPIOID RECEPTOR SIGNALING MEDIATES OPIOID INDUCED TOLERANCE AND HYPERALGESIA IN COLONIC SENSORY NERVES

Background

While opioid drugs are widely used for treating abdominal pain, prolonged exposure to opioids can induce tolerance and paradoxically increase pain. We previously showed in colonic afferent nerves that chronic morphine treatment causes tolerance and paradoxical hyperalgesia, however the mechanisms are unknown.

Aims

To evaluate the role of delta opioid receptor (DOR) signaling in opioid induced tolerance and hyperalgesia in colonic nerves during chronic morphine exposure.

Methods

C57BL/6 mice were injected (i.p.) twice daily for 7 days with escalating doses of morphine (10, 20, 30 mg/kg for the first 3 days, then 40mg/kg on 4th to 7th day); a subset of mice were also injected with 2.5 mg/kg naltrindole (NTI), a DOR antagonist. The analgesic response in vivo was monitored daily using the tail-flick test. To assess the effect of chronic morphine exposure, mice were euthanized on day 8, and the dorsal root ganglia (DRGs) and colons were harvested. Isolated DRG neurons were incubated with 1μM morphine (30 min) and neuronal excitability was determined by measuring the rheobase (amount of current required to elicit an action potential) using perforated patch clamp. To assess changes in colonic afferent nerve excitability, ex vivo afferent nerve recordings were obtained from flat-sheet colon preparations to determine the effects of 1μM morphine (10 min perfusion) on mechanosensitivity by probing with 1g von Frey hair.

Results

The tail flick test showed that the DOR antagonist NTI inhibited (30%) the maximal antinociceptive effect of morphine and reduced morphine tolerance. In patch clamp recordings, 1μM morphine paradoxically increased the excitability of small DRG neurons from morphine mice (rheobase decreased 28%; p&lt;0.05, 2-way ANOVA), whereas this excitatory effect was absent on neurons from NTI+morphine mice. Acute application of 1μM morphine had no effect on afferent nerve responses to probing in morphine mice (14.9 vs 16.7 Hz; p=ns, paired t test, n=15) whereas it inhibited the afferent nerve response to probing in NTI+morphine mice (15.2 vs 9.9 Hz; p&lt;0.001, paired t test, n=16). Furthermore, most single units from morphine mice had an increased response to probing following acute morphine application (7/15 vs 2/16 units excited), whereas most units form NTI-morphine mice were inhibited (14/16 vs. 3/15 units inhibited, P&lt;0.001, Chi-square).

Conclusions

These findings suggest that DOR signaling plays a significant role in the development of opioid tolerance and hyperalgesia in colonic afferent nerves induced by chronic morphine treatment. Thus, antagonists of DOR may help to mitigate these side effects induced by opioids.

Funding Agencies

CCC

A102 MONOSODIUM GLUTAMATE INCREASES VISCERAL SENSITIVITY IN A MURINE MODEL OF IRRITABLE BOWEL SYNDROME

Background

Over 70% of patients suffering from symptoms of the irritable bowel syndrome (IBS) report that food is the most common trigger. Patients have identified that monosodium glutamate (MSG) is one food component that they suspect can trigger symptoms, but this remains unproven. As a first step towards establishing a potential role, we sought to examine whether there was a plausible mechanism of how MSG ingestion could underlie exaggerated pain signaling in IBS.

Aims

To examine the effects of MSG on visceral sensitivity in a murine model of IBS.

Methods

Balb/c mice were subjected to 6-days of water-avoidance stress (WAS) to create a pre-clinical model for IBS. To assess changes in visceral afferent nerve sensitivity in control and WAS mice, responses to ramp distension (0–60 mmHg), in the absence and presence 10 μM MSG perfused into the intestinal lumen (concentration based on diet analysis of MSG human ingestion), were recorded from afferent nerves innervating the jejunum ex vivo. To quantify these responses, the baseline firing frequency (spikes/second) was subtracted from the maximum response at each distending pressure. The relative distension response was calculated as a percentage of the control distension response (absence of MSG) (Figure 1). Jejunal preparations from the same WAS-treated mice were also used to measure ex vivo changes in mucosal permeability to MSG using Ussing chambers. We also ran the same distension protocol; however, we applied 10 μM MSG directly to the organ bath outside intestine obtained from control mice. This direct application would allow the MSG to have direct access to the nerve terminals without having to traverse the mucosa.

Results

The intraluminal administration of 10 μM MSG significantly increased afferent nerve sensitivity in WAS-treated jejunum but not controls. This response was significantly greater (23%) at pressures between 40 and 60 mmHg (p&lt;0.01) (Figure 1). WAS-treated mouse jejunum was also significantly more permeable to MSG (p&lt;0.05). Furthermore, the application of 10 μM MSG directly to the bath containing healthy jejunum significantly increased by 25% the sensitivity of afferent nerves specifically at 60 mmHg (p&lt;0.01).

Conclusions

Our findings demonstrate that MSG increases visceral sensitivity to distension in our pre-clinical model of IBS. The increased permeability to MSG in WAS tissue and increased distension response in healthy control tissue when MSG is applied directly to the bath rather than intraluminally, suggests that MSG signals to the immune compartment or directly to the afferent nerve terminals. These findings support the rationale for future in vivo studies with this model to further clarify the mechanism.

Funding Agencies

CCC, CIHR

A213 A NOVEL PH-SENSITIVE OPIOID ANALGESIC THAT IS SELECTIVELY ACTIVATED IN ACIDIC INFLAMMATORY ENVIRONMENTS

Background

Opioids drugs are effective analgesics for inflammatory disorders such as inflammatory bowel disease (IBD) but their effects at non-inflammed sites can cause serious morbidity and even death. Exploiting the knowledge that tissue pH in inflamed tissues is acidic (e.g. 6.5–7.0), a novel opioid analgesic, ±)-N-(3-fluoro-1-phenethylpiperidine-4-yl)-N-phenylpropionamide (NFEPP), with a low acid dissociation constant, was developed that selectively activates peripheral µ-opioid receptor (MOPr) at acidic pH. Thus, pH-sensitive binding of NFEPP could selectively inhibit nociceptive nerves in the inflamed colon and have no effect on non-inflamed tissues outside the GI tract.

Aims

Evaluate whether NFEPP causes inhibition of colonic nociceptors at acidic pH’s, which mimic the inflamed colon.

Methods

To evaluate pH sensitive property of NFEPP to activate MOPr, dorsal root ganglia (DRG) neurons from C57BL/6 mice were exposed to the MOPr agonists NFEPP (300nM, 15 min) or DAMGO (100nM, 15 min) or vehicle at pH 6.5 or 6.8 or 7.4. Neuronal excitability was measured by recording the rheobase (minimum current to fire an action potential) using patch clamp recordings of isolated dorsal root ganglia neurons. In parallel ex vivo studies of mouse colon, extracellular recordings were obtained from afferent nerves innervating the distal colon. Afferent responses to probing with von Frey hair (1 gm) were examined before and after exposure to NFEPP (300nM, 5 min superfusion) at pH 6.5 and 7.4 respectively. Oneway ANOVA and post hoc Dunnett and Bonferroni tests were used to analyze the data.

Results

In patch clamp studies, NFEPP caused a decrease in DRG excitability at pH 6.5 and 6.8 (increased rheobase 21.3%, p&lt;0.05 and 28.9%, p&lt;0.05 respectively compared to vehicle) but had no effect at physiological pH 7.4. DAMGO, a MOPr agonist, caused inhibition of nociceptor excitability at pH 7.4 (increased rheobase 25.2%, p&lt;0.05 compared to vehicle) as shown in previous experiments, but had no effect at pH 6.5 and 6.8. Vehicle had no effect at the different pH’s. In colonic afferent nerve recordings, NFEPP significantly attenuated afferent response (28.9% P&lt;0.01) to probing at pH 6.5 and this effect was reversed after a 15 min washout. At pH 7.4 NFEPP had no effect on afferent nerve firing.

Conclusions

NFEPP activated MOPr at acidic pH causing inhibition of colonic nociceptors. This pH-selective agonist provides a new strategy to relieve pain at the site of inflammation while being devoid of any of unwanted activity in non-inflamed organs.

Funding Agencies

CCC

A55 LACK OF EXPERIMENTAL REPRODUCIBILITY IN PRECLINICAL RESEARCH IS INFLUENCED BY THE NUTRITIONAL PROFILE OF STANDARD RODENT CHOWS

Background

Lack of experimental reproducibility, particularly in studies investigating the microbiota, is of growing concern to the scientific community. Factors such as environment, stress, and sex have been identified as contributors, whereas dietary composition has received less attention.

Aims

To profile the use of standard rodent chows in research institutions, analyze the nutrient content of common rodent chows, and assess the impact of different chows on microbiota profiles.

Methods

A survey was conducted to evaluate which rodent chows are used by research institutions worldwide. Seven standard rodent chows were selected for analysis of ingredients, fermentable carbohydrate (FODMAP) and gluten content. FODMAP content was measured by high-performance liquid-chromatography and enzymatic assays, and gluten content was assessed by a commercial kit using G12 antibody. Forty C57BL/6 mice were randomized to 4 groups of 10 mice (5 male, 5 female). Group A was euthanized at baseline. Group B received the breeding institution chow (LabDiet 5066). Group C received ResearchDiets AIN93G (low FODMAP and gluten content). Group D received LabDiet 5001 (high FODMAP and gluten content). After 3 weeks, cecal contents were collected and analyzed by 16S rRNA gene sequencing; short- and branched-chain fatty acids (SCFA, BCFAs) content was also determined.

Results

Twenty-eight different types of rodent chows were reported to be used by 45 international survey respondents. Ingredient composition of the standard chows varied widely, resulting in differences in FODMAP and gluten content. Microbiota analysis of cecal contents revealed that gut microbiota composition was altered by the standard chows, as reflected by significantly different clusters in β-diversity analysis as well as by altered α-diversity. Microbiota diversity was also influenced by sex in Groups A and B (p&lt;0.01). Total SCFA levels were lower (p=0.03) and BCFA levels were higher (p=0.01) in Group C compared to Group B.

Conclusions

Our results suggest that the composition of the diet not only significantly impacts gut microbiota profiles and fermentation patterns but may also emphasize sex differences in preclinical studies, with major implications for the reproducibility of results across laboratories.

Funding Agencies

CIHRThe Canadian Nutrition Society

A127 THE ROLE OF ENDOGENOUS OPIOIDS IN MITIGATING OPIOID TOLERANCE IN A PRE-CLINICAL MODEL OF IBD

Background

While opioid drugs are used to treat pain in IBD patients, escalating doses can induce tolerance and paradoxical increased pain signaling. Endogenous opioids are released by immune cells during chronic colitis and have an analgesic action but it is unknown whether they can mitigate the development of tolerance to opioid drugs in IBD.

Aims

To evaluate whether endogenous opioids released during chronic inflammation prevent the development of tolerance and/or increased pain signaling following chronic morphine treatment.

Methods

Three groups of C57BL/6 mice were studied: 1) control, 2) chronic colitis induced with 3 cycles of 2% DSS (cDSS mice) and 3) chronic DSS mice injected with escalating doses of morphine on the last 7 days of DSS (10, 20, 30 mg/kg for the first 3 days, then 40mg/kg on 4 to 7 day) (cDSS-morphine mice). Ex vivo afferent nerve recordings were obtained from flat-sheet distal colon preparations (day 31) to determine their mechanosensitivity by probing with a 1g von Frey hair before and after acute morphine (1μM, 10 min perfusion). In parallel experiments, supernatants were obtained from the proximal colon and incubated overnight with isolated dorsal root ganglia (DRG) neurons from control mice. Neuronal excitability was then examined by measuring the rheobase using perforated patch clamp.

Results

In afferent nerve recordings, acute application of 1μM morphine inhibited the colonic afferent response to probing in control mice (17.86 vs 12.31 Hz; p&lt;0.05), whereas no effect of morphine was seen in cDSS mice. In cDSS-morphine mice acute morphine perfusion paradoxically increased the mean afferent response to probing (13.99 vs 17.28 Hz, p&lt;0.05). Single units were analyzed to identify how many mechanosensitive responses were increased, decreased or not affected by acute morphine perfusion. Compared to control mice, cDSS mice exhibited increased numbers of unaffected units (6/18 vs 1/14) whereas cDSS-morphine mice had decreased number of inhibited units (1/17 vs 11/14) and increased number of excited units (8/17 vs. 2/14) (Figure 1). In patch clamp recordings, colonic supernatants from cDSS mice reduced the excitability of DRG neurons (rheobase increased 28%; p&lt;0.05), however, this effect was lost in neurons incubated with cDSS-morphine supernatants.

Conclusions

Endogenous opioids released during cDSS colitis do not mitigate tolerance to chronic morphine exposure and may diminish the response to acute morphine. Moreover, the paradoxical hyperexcitable response to acute morphine induced by chronic morphine was not blocked by endogenous opioids. Our patch clamp data suggest that endogenous opioid actions are lost following chronic morphine exposure and could result from inhibition of their release from immune cells.

Funding Agencies

CCC

Colonoscopy Trainers Experience Greater Stress During Insertion than Withdrawal: Implications for Endoscopic Curricula

Background

Optimal colonoscopy training curricula should minimize stress and cognitive load. This study aimed to determine whether withdrawal or insertion colonoscopy skills training is associated with less stress or cognitive load for trainees or trainers.

Methods

In Phase I, participants were randomized to train on either insertion or withdrawal in a simulated environment. In Phase II, participants were randomized to begin with either insertion or withdrawal in patient encounters. Salivary cortisol levels, heart rate, and State-Trait Anxiety Inventory (STAI) surveys were used to assess stress in trainees and trainers. NASA Task Load Index (TLX) survey was used to assess cognitive workload in trainees.

Results

In Phase I, trainee stress increased during the simulation training during both withdrawal and insertion compared to baseline, while trainer stress changed minimally. Cognitive load was higher for trainees during withdrawal (P = 0.005). In Phase II, trainers’ STAI scores were greater during insertion training (P = 0.013). Trainees’ stress was highest prior to beginning patient training and decreased during training, while trainer’s stress increased during training. Trainees reported insertion training being of greater value (70.0%), while trainers reported withdrawal was preferred (77.8%).

Conclusion

Trainees and trainers exhibit important differences in stress during colonoscopy skills training. Trainees reported more stress during simulation training and greatest cognitive load during simulation withdrawal, whereas trainers reported greatest stress during patient encounters, particularly training of insertion techniques. Attention to the effect of stress on trainees and trainers and the drivers of stress is warranted and could be incorporated in competency based medical education.

Review article: biological mechanisms for symptom causation by individual FODMAP subgroups - the case for a more personalised approach to dietary restriction

BACKGROUND

Due to the paucity of targeted therapy for irritable bowel syndrome (IBS), many patients turn to dietary modifications for symptom management. The combination of five subgroups of poorly absorbed and rapidly fermented carbohydrates-fructans, galacto-oligosaccharides, lactose, excess fructose and polyols-are thought to trigger gastrointestinal symptoms and are referred to collectively as "FODMAPs".

AIMS

To examine the biological plausibility and mechanisms by which foods high in specific FODMAP subgroups cause symptoms, and to use this information to explore the possibility of targeting select dietary components to allow for a more personalised approach to dietary adjustment METHODS: Recent literature was analysed via search databases including Medline, PubMed and Scopus.

RESULTS

Lactose, fructans and galacto-oligosaccharides have strong biologic plausibility for symptom generation due to lack of hydrolases resulting in distention from osmosis and rapid fermentation. However, excess fructose and polyols may only cause symptoms in specific individuals when consumed in high doses, but this remains to be established. There is evidence to suggest that certain patient characteristics such as ethnicity may predict response to lactose, but differentiation of other subgroups is difficult prior to dietary manipulation.

CONCLUSIONS

While some clear mechanisms of action for symptom generation have been established, further research is needed to understand which patients will respond to specific FODMAP subgroup restriction. We suggest that clinicians consider in some patients a tailored, personalised "bottom-up" approach to the low-FODMAP diet, such as dietary restriction relevant to the patients' ethnicity, symptom profile and usual dietary intake.

Canadian Association of Gastroenterology Clinical Practice Guideline for the Management of Irritable Bowel Syndrome (IBS)

BACKGROUND & AIMS

Irritable bowel syndrome (IBS) is one of the most common gastrointestinal (GI) disorders, affecting about 10% of the general population globally. The aim of this consensus was to develop guidelines for the management of IBS.

METHODS

A systematic literature search identified studies on the management of IBS. The quality of evidence and strength of recommendations were rated according to the Grading of Recommendation Assessment, Development and Evaluation (GRADE) approach. Statements were developed through an iterative online platform and then finalized and voted on by a multidisciplinary group of clinicians and a patient.

RESULTS

Consensus was reached on 28 of 31 statements. Irritable bowel syndrome is diagnosed based on symptoms; serological testing is suggested to exclude celiac disease, but routine testing for C-reactive protein (CRP), fecal calprotectin or food allergies is not recommended. A trial of a low fermentable oligosaccharides, disaccharides, monosaccharides, polyols (FODMAP) diet is suggested, while a gluten-free diet is not. Psyllium, but not wheat bran, supplementation may help reduce symptoms. Alternative therapies such as peppermint oil and probiotics are suggested, while herbal therapies and acupuncture are not. Cognitive behavioural therapy and hypnotherapy are suggested psychological therapies. Among the suggested or recommended pharmacological therapies are antispasmodics, certain antidepressants, eluxadoline, lubiprostone, and linaclotide. Loperamide, cholestyramine and osmotic laxatives are not recommended for overall IBS symptoms. The nature of the IBS symptoms (diarrhea-predominant or constipation-predominant) should be considered in the choice of pharmacological treatments.

CONCLUSIONS

Patients with IBS may benefit from a multipronged, individualized approach to treatment, including dietary modifications, psychological and pharmacological therapies.