Acute sacral nerve stimulation reduces visceral mechanosensitivity in a cross-organ sensitization model

Involvement of acid sensing ion channel (ASIC)-3 in an acute urinary bladder-colon cross sensitization model in rodent

Introduction

Irritable bowel syndrome and bladder pain syndrome are both characterized by pain in response to organ distension. Epidemiologic studies showed that these two syndromes are often overlapped. Such overlap may be due to sharing of common extrinsic innervations between the colorectum and the urinary bladder, where cross-sensitization of the urinary bladder and the colon would occur in response to mechanical distension of either organ. The aim of this project was to develop and characterize a rodent model of urinary bladder-colon sensitization and to assess the role of the acid sensing ion channel (ASIC)-3.

Methods

Double retrograde labelling was performed to identify extrinsic primary afferent neurons innervating both the colon (Fluororuby) and urinary bladder (Fluorogold) in the L6-S1 dorsal root ganglia (DRG) in Sprague Dawley rats. The phenotype of the colon/urinary bladder co-innervating primary afferent neurons was assessed using immunohistochemistry directed against ASIC-3. Cross-organ sensitization was induced in Sprague Dawley rats by using an echography-guided intravesical administration of acetic acid (0.75%) under brief isoflurane anesthesia. Colonic sensitivity was assessed in conscious rats by measuring abdominal contraction during isobaric colorectal distension (CRD). Measurement of urinary bladder and colonic paracellular permeabilities and tissue myeloperoxidase assay were performed. The involvement of ASIC-3 was assessed by use of S1 intrathecal administration of the ASIC-3 blocker, APETx2 (2.2 µM).

Results

Immunohistochemistry showed that 73.1% of extrinsic primary afferent neurons co-innervating the colon and the urinary bladder express ASIC-3. By contrast, extrinsic primary afferent neurons innervating the colon only or the urinary bladder only were positive for ASIC-3 in 39.3% and 42.6%, respectively. Echography-guided intravesical administration of acetic acid resulted in colonic hypersensitivity to colorectal distension. This effect started 1 h post-injection and lasted up to 24 h, and was not longer seen after 3 days after injection. No colonic hyperpermeability and no difference in urinary bladder and colon MPO activity was observed between control and acetic acid-treated rats. Colonic sensitization by intravesical acetic acid administration was prevented by S1 intrathecal administration of APETx2.

Conclusion

We developed an acute pelvic cross-organ sensitization model in conscious rat. In this model, cross-organ sensitization is likely to involve S1-L6 extrinsic primary afferents co-innervating the colon and urinary bladder through an ASIC-3 pathway.

Update on treatment of abdominal pain in irritable bowel syndrome: A narrative review

The objectives of this narrative review are to update readers on the current state-of-the-art regarding diverse approaches for the treatment of pain, global symptoms, or adequate relief in irritable bowel syndrome (IBS). The article appraises medications, dietary interventions including low fermentable oligosaccharides, disaccharides, and monosaccharides and polyols (FODMAP) diet, fecal microbial transplantation (FMT), electrical approaches, and behavioral therapies including cognitive behavioral therapy (CBT), gut-directed hypnotherapy (GDH), mindfulness, and open-label placebo. Current evidence demonstrates only modest benefit in global IBS symptoms and pain relief. A future approach that identifies pathophysiological mechanisms of IBS through validated biomarkers has the potential to individualize treatment of patients rather than sequential therapeutic trial and error approaches.

Electrical devices for functional visceral pain

Several studies have documented correction of dysmotility in several regions of the gastrointestinal tract based on electrical stimulation of extrinsic nerves supplying those regions. In this issue of Neurogastroenterology and Motility, Ma et al. (2023) document the effect of transcutaneous neuromodulation applied by acustimulation at ST36 for ineffective esophageal motility in patients with gastroesophageal reflux disease. In addition to motor effects, there were also significant effects on GERD symptoms, raising the question whether extrinsic electrical nerve stimulation of the gut can reduce symptoms through effects that target sensation. This brief review summarizes evidence regarding the application of electrical acustimulation, transauricular electrical stimulation, and sacral electrical or magnetic stimulation to reduce abdominal or pelvic pain.

Bladder-colon chronic cross-sensitization involves neuro-glial pathways in male mice

BACKGROUND

Irritable bowel syndrome and bladder pain syndrome often overlap and are both characterized by visceral hypersensitivity. Since pelvic organs share common sensory pathways, it is likely that those syndromes involve a cross-sensitization of the bladder and the colon. The precise pathophysiology remains poorly understood.

AIM

To develop a model of chronic bladder-colon cross-sensitization and to investigate the mech-anisms involved.

METHODS

Chronic cross-organ visceral sensitization was obtained in C57BL/6 mice using ultrasound-guided intravesical injections of acetic acid under brief isoflurane anesthesia. Colorectal sensitivity was assessed in conscious mice by measuring intracolonic pressure during isobaric colorectal distensions. Myeloperoxidase, used as a marker of colorectal inflammation, was measured in the colon, and colorectal permeability was measured using chambers. c-Fos protein expression, used as a marker of neuronal activation, was assessed in the spinal cord (L6-S1 level) using immunohistochemistry. Green fluorescent protein on the fractalkine receptor-positive mice were used to identify and count microglia cells in the L6-S1 dorsal horn of the spinal cord. The expression of NK1 receptors and MAPK-p38 were quantified in the spinal cord using western blot.

RESULTS

Visceral hypersensitivity to colorectal distension was observed after the intravesical injection of acetic acid vs saline (P < 0.0001). This effect started 1 h post-injection and lasted up to 7 d post-injection. No increased permeability or inflammation was shown in the bladder or colon 7 d post-injection. Visceral hypersensitivity was associated with the increased expression of c-Fos protein in the spinal cord (P < 0.0001). In green fluorescent protein on the fractalkine receptor-positive mice, intravesical acetic acid injection resulted in an increased number of microglia cells in the L6-S1 dorsal horn of the spinal cord (P < 0.0001). NK1 receptor and MAPK-p38 levels were increased in the spinal cord up to 7 d after injection (P = 0.007 and 0.023 respectively). Colorectal sensitization was prevented by intrathecal or intracerebroventricular injections of minocycline, a microglia inhibitor, by intracerebroventricular injection of CP-99994 dihydrochloride, a NK1 antagonist, and by intracerebroventricular injection of SB203580, a MAPK-p38 inhibitor.

CONCLUSION

We describe a new model of cross-organ visceral sensitization between the bladder and the colon in mice. Intravesical injections of acetic acid induced a long-lasting colorectal hypersensitivity to distension, mediated by neuroglial interactions, MAPK-p38 phosphorylation and the NK1 receptor.

Overlaps with bladder pain syndrome and irritable bowel syndrome are associated with higher symptom burden and reduced quality of life in functional dyspepsia

BACKGROUND

Functional dyspepsia and bladder pain syndrome are well-known to overlap with irritable bowel syndrome. Whether functional dyspepsia overlaps with bladder pain syndrome remains unknown. Our aim was to evaluate the presence of bladder pain syndrome in functional dyspepsia patients and its impact.

METHODS

All consecutive patients with investigated dyspeptic symptoms in our tertiary care center between March 2015 and November 2018 were studied. Functional dyspepsia and irritable bowel syndrome were diagnosed according to Rome III and IV criteria while bladder pain syndrome was diagnosed using ESSIC criteria. Validated questionnaires were filled to assess quality of life (GIQLI), anxiety and depression (HADS), sleep (PSQI), and insomnia (ISI). Dyspeptic symptoms severity was assessed individually for eight dyspeptic complaints.

KEY RESULTS

Among 1453 patients with dyspeptic symptoms, 61.4% fulfilled Rome criteria for functional dyspepsia. Bladder pain syndrome was present in 16.0% of the patients not fulfilling diagnostic criteria for functional dyspepsia, 22.2% of patients with functional dyspepsia alone, and 36.4% of patients with overlapping functional dyspepsia and irritable bowel syndrome (p-values &lt;0.0001). In patients with bladder pain syndrome overlapping with functional dyspepsia, dyspeptic symptoms severity, anxiety, depression, and insomnia levels were higher while quality of life and sleep quality were reduced (p-values &lt;0.0001). These results were even more pronounced in case of overlap with irritable bowel syndrome (p-values &lt;0.0001).

CONCLUSIONS AND INFERENCES

Bladder pain syndrome is present in 26.9% of functional dyspepsia patients and is associated with higher gastrointestinal, psychological distresses, and sleep symptom burdens, and with reduced quality of life.

Progress in research of sacral nerve stimulation

Sacral nerve stimulation (SNS) is well-known as a minimally invasive treatment. Originally, it was mainly used to treat urinary system diseases such as urge urinary incontinence. Gradually, it is used to treat digestive system diseases such as fecal incontinence and chronic constipation. SNS is a method in which electrical pulse signals are sent out through pulse generators to stimulate the sacral nerve directly or indirectly, thus modulating the nerve reflex of the bladder, urethra, anus, colon, and rectum and improving abnormal nerve regulation to achieve the therapeutic effect. The regulation of the sacral nerve is often carried out by inserting electrodes into the sacral spinal canal S_2-4 (mostly S₃), and the symptoms are improved by complex regulation of spinal reflex and supraspinal reflex. However, the exact mechanism is still unclear. Many studies have shown that SNS plays a key role in the treatment of many diseases of the urinary system and digestive system. This paper reviews the progress in the research of SNS.

Sacral nerve modulation for irritable bowel syndrome: A randomized, double-blinded, placebo-controlled crossover study

BACKGROUND

Irritable bowel syndrome (IBS) is among the most common gastrointestinal disorders, and a substantial proportion of patients have an insufficient response to treatment. In a single-blinded study, sacral nerve modulation (SNM) significantly reduced symptoms of IBS. The aim of the present double-blinded, randomized, placebo-controlled study was to evaluate the effect of SNM for IBS.

METHODS

We included patients with diarrhea-predominant or mixed IBS and a minimum baseline IBS-specific symptom score of 40 points (Gastrointestinal Symptom Rating Scale-IBS version). Patients underwent a 6-week period of SNM. In the first 4 weeks, the patients were randomized 1:1 to have the neurostimulator set subsensory or OFF for 2 weeks and then the opposite for another 2 weeks. Patients and investigators were blinded to settings. In the remaining 2 weeks, the stimulation was set suprasensory. IBS-specific symptoms and quality of life were assessed with validated questionnaires and bowel diaries.

KEY RESULTS

Twenty-one patients were randomized and eligible for analysis. The IBS-specific symptom score was reduced with borderline significance during stimulation (subsensory-OFF median change -1 (-26, 9), OFF-subsensory median change 8 (-11, 36); P = 0.0572). Pain was significantly reduced during stimulation (subsensory-OFF median change -1.5 (-4, 1), OFF-subsensory median change 1 (-4, 3); P = 0.0188), along with the number of daily bowel movements (subsensory-OFF median change 0 (-1.8, 0.2), OFF-subsensory median change 0.2 (-0.5, 1.1); P = 0.0373). The median placebo effect was 14% (0, 55).

CONCLUSION AND INFERENCES

Sacral nerve modulation for IBS seems promising but should be considered experimental until larger multicenter studies have been performed.

The efficacy of botulinum toxin A and sacral neuromodulation in the management of interstitial cystitis (IC)/bladder pain syndrome (BPS), what do we know? ICI-RS 2017 think thank, Bristol

AIMS

This manuscript aims to address the evidence availale in the literature on the efficacy of Botulinum Toxin A (BoNT-A) and sacral neuromodulation (SNM) in patients suffering from Interstitial Cystitis (IC)/BPS and propose further research to identify mechanisms of action and establish the clinical efficacy of either therapy.

METHODS

At the International Consultation on Incontinence-Research Society (ICI-RS) in 2017, a panel of Functional Urologists and Urogynaecologists participated in a Think Tank (TT) discussing the management of IC/BPS by BoNT-A and SNM, using available data from both PubMed and Medicine literature searches.

RESULTS

The role of BoNT-A and SNM in the treatment of IC/BPS are discussed and mechanisms of actions are proposed. Despite the available randomized trial data on the effect of intravesical BoNT-A treatment on symptoms of IC/BPS, a consistent conclusion of a positive effect cannot be drawn at the moment, as the published studies are small and heterogeneous in design. There is substantive evidence for the positive effects of SNM on symptoms of IC/BPS patients however, during patient selection, it is important to distinguish the degree and the location of pain in order to tailor the best therapy to the right patients.

CONCLUSIONS

Both intravesical BoNT-A treatment and SNM have been shown to have positive effects in patients with IC/BPS. However, firm conclusions cannot yet be drawn. Patient-reported outcomes and quality of life should be assessed in addition to urinary and pain symptoms. Since current treatments mainly focus on symptomatic relief, future research should also focus on clarifying the pathogenic mechanisms involved in IC/BPS.