Microbiota: a novel regulator of pain.

Among the various regulators of the nervous system, the gut microbiota has been recently described to have the potential to modulate neuronal cells activation. While bacteria-derived products can induce aversive responses and influence pain perception, recent work suggests that "abnormal" microbiota is associated with neurological diseases such as Alzheimer's, Parkinson's disease or autism spectrum disorder (ASD). Here we review how the gut microbiota modulates afferent sensory neurons function and pain, highlighting the role of the microbiota/gut/brain axis in the control of behaviors and neurological diseases. We outline the changes in gut microbiota, known as dysbiosis, and their influence on painful gastrointestinal disorders. Furthermore, both direct host/microbiota interaction that implicates activation of "pain-sensing" neurons by metabolites, or indirect communication via immune activation is discussed. Finally, treatment options targeting the gut microbiota, including pre- or probiotics, will be proposed. Further studies on microbiota/nervous system interaction should lead to the identification of novel microbial ligands and host receptor-targeted drugs, which could ultimately improve chronic pain management and well-being.

Risk assessment of using off-label morphine sulfate in a population-based retrospective cohort of opioid-dependent patients.

AIMS: Several addictovigilance studies have described the off-label use of morphine sulfate (MS) for nonchronic pain in opioid use disorder (OUD) patients as an alternative to conventional opioid substitution treatments (OSTs). This study primarily sought to compare the incidence of unintentional opioid-related overdose in the year following the prescription initiation in off-label MS users, compared to OST-maintained patients. METHODS: Sequential cohorts of OUD patients who were regularly dispensed MS, buprenorphine, or methadone, between 1 April 2012 and 31 December 2014, were retrospectively identified using the French nationwide healthcare data system. The incidence of overdoses, deaths, doctor shopping, and complications of a viral, bacterial or thrombotic nature, was compared using the Cox regression method. RESULTS: Overall, 1075, 20 834 and 9778 OUD patients without chronic-pain were included in the MS, buprenorphine, and methadone cohorts, respectively. Overdose incidence was 3.8 (P < .01 [95% confidence interval (CI): 2.1-6.8]) and 2.0 (P = .02 [95%CI: 1.1-3.6]) higher in the MS cohort vs buprenorphine and methadone, respectively. Death incidence was 9.1 (P < .01 [95%CI: 3.2-25.9]) and 3.9 (P < .01 [95%CI: 1.4-10.7]) higher in the MS cohort vs buprenorphine and methadone, respectively. The incidences of other associated risks were significantly higher in the MS group vs OSTs, except for hepatitis C viral infection and thrombotic complications. CONCLUSION: This first French comprehensive nationwide study reveals increasing overdose, death, bacterial infection, abuse and diversion risks when off-label MS is initiated as alternative to OST. These results question the relevance of prescribing MS as a safe opioid maintenance treatment, considering its health risk profile.

Increasing spinal 5-HT2A receptor responsiveness mediates anti-allodynic effect and potentiates fluoxetine efficacy in neuropathic rats. Evidence for GABA release.

Antidepressants are one of the first line treatments for neuropathic pain but their use is limited by the incidence and severity of side effects of tricyclics and the weak effectiveness of selective serotonin reuptake inhibitors (SSRIs). Serotonin type 2A (5-HT2A) receptors interact with PDZ proteins that regulate their functionality and SSRI efficacy to alleviate pain. We investigated whether an interfering peptide (TAT-2ASCV) disrupting the interaction between 5-HT2A receptors and associated PDZ proteins would improve the treatment of traumatic neuropathic allodynia. Tactile allodynia was assessed in spinal nerve ligation-induced neuropathic pain in rats using von Frey filaments after acute treatment with TAT-2ASCV and/or 5-HT2A receptor agonist, alone or in combination with repeated treatment with fluoxetine. In vivo microdialysis was performed in order to examine the involvement of GABA in TAT-2ASCV/fluoxetine treatment-associated analgesia. TAT-2ASCV (100ng, single i.t. injection) improved SNL-induced tactile allodynia by increasing 5-HT2A receptor responsiveness to endogenous 5-HT. Fluoxetine alone (10mg/kg, five i.p. injections) slightly increased tactile thresholds and its co-administration with TAT-2ASCV (100ng, single i.t. injection) further enhanced the anti-allodynic effect. This effect depends on the integrity of descending serotonergic bulbospinal pathways and spinal release of GABA. The anti-allodynic effect of fluoxetine can be enhanced by disrupting 5-HT2A receptor-PDZ protein interactions. This enhancement depends on 5-HT2A receptor activation, spinal GABA release and GABAA receptor activation.

Lactobacillus acidophilus modulates intestinal pain and induces opioid and cannabinoid receptors.

Abdominal pain is common in the general population and, in patients with irritable bowel syndrome, is attributed to visceral hypersensitivity. We found that oral administration of specific Lactobacillus strains induced the expression of mu-opioid and cannabinoid receptors in intestinal epithelial cells, and mediated analgesic functions in the gut-similar to the effects of morphine. These results suggest that the microbiology of the intestinal tract influences our visceral perception, and suggest new approaches for the treatment of abdominal pain and irritable bowel syndrome.

T-type calcium channels contribute to colonic hypersensitivity in a rat model of irritable bowel syndrome.

The symptoms of irritable bowel syndrome (IBS) include significant abdominal pain and bloating. Current treatments are empirical and often poorly efficacious, and there is a need for the development of new and efficient analgesics aimed at IBS patients. T-type calcium channels have previously been validated as a potential target to treat certain neuropathic pain pathologies. Here we report that T-type calcium channels encoded by the Ca(V)3.2 isoform are expressed in colonic nociceptive primary afferent neurons and that they contribute to the exaggerated pain perception in a butyrate-mediated rodent model of IBS. Both the selective genetic inhibition of Ca(V)3.2 channels and pharmacological blockade with calcium channel antagonists attenuates IBS-like painful symptoms. Mechanistically, butyrate acts to promote the increased insertion of Ca(V)3.2 channels into primary sensory neuron membranes, likely via a posttranslational effect. The butyrate-mediated regulation can be recapitulated with recombinant Ca(V)3.2 channels expressed in HEK cells and may provide a convenient in vitro screening system for the identification of T-type channel blockers relevant to visceral pain. These results implicate T-type calcium channels in the pathophysiology of chronic visceral pain and suggest Ca(V)3.2 as a promising target for the development of efficient analgesics for the visceral discomfort and pain associated with IBS.

Antihyperalgesic properties of gut microbiota: Parabacteroides distasonis as a new probiotic strategy to alleviate chronic abdominal pain.

ABSTRACT: The potential role of gut microbiota in pain modulation is arousing an emerging interest since recent years. This study investigated neuromodulatory properties of gut microbiota to identify next-generation probiotics to propose alternative therapies for visceral pain management. Neuromodulation ability of 10 bacterial strains isolated from a healthy donor was assessed both on ND7/23 immortalized cell line and primary neuronal cells from rat dorsal root ganglia. This screening highlighted the neuroinhibitory property of Parabacteroides distasonis (F1-2) strain, supported both by its intracellular content and membrane fraction, which was further investigated in visceral pain mouse models. Oral administration of F1-2 resulted in a significant decrease of colonic hypersensitivity (CHS) in dextran sulfate sodium (0.5%) model associated with low-grade inflammation and a significant decrease of CHS in Citrobacter rodentium postinfectious models. No effect of F1-2 oral administration on CHS was observed in a neonatal maternal separation stress model. Antihyperalgesic effect unlikely involved modulation of inflammatory processes or restoration of intestinal barrier. Exploration of direct dialogue mechanisms between this strain and nervous system, assessed by calcium imaging experiments, revealed that F1-2 interacts directly with nociceptors by reducing activation level on capsaicin, inflammatory soup, and bradykinin stimulations. Our study provides new insights about bacteria-host interaction and places P distasonis as a potential therapeutic strategy in the treatment of visceral pain observed in leaky gut-associated pathologies.

Pasteurized akkermansia muciniphila improves irritable bowel syndrome-like symptoms and related behavioral disorders in mice.

Gut - brain communications disorders in irritable bowel syndrome (IBS) are associated with intestinal microbiota composition, increased gut permeability, and psychosocial disturbances. Symptoms of IBS are difficult to medicate, and hence much research is being made into alternative approaches. This study assesses the potential of a treatment with pasteurized Akkermansia muciniphila for alleviating IBS-like symptoms in two mouse models of IBS with different etiologies. Two clinically relevant animal models were used to mimic IBS-like symptoms in C57BL6/J mice: the neonatal maternal separation (NMS) paradigm and the Citrobacter rodentium infection model. In both models, gut permeability, colonic sensitivity, fecal microbiota composition and colonic IL-22 expression were evaluated. The cognitive performance and emotional state of the animals were also assessed by several tests in the C. rodentium infection model. The neuromodulation ability of pasteurized A. muciniphila was assessed on primary neuronal cells from mice dorsal root ganglia using a ratiometric calcium imaging approach. The administration of pasteurized A. muciniphila significantly reduced colonic hypersensitivity in both IBS mouse models, accompanied by a reinforcement of the intestinal barrier function. Beneficial effects of pasteurized A. muciniphila treatment have also been observed on anxiety-like behavior and memory defects in the C. rodentium infection model. Finally, a neuroinhibitory effect exerted by pasteurized A. muciniphila was observed on neuronal cells stimulated with two algogenic substances such as capsaicin and inflammatory soup. Our findings demonstrate novel anti-hyperalgesic and neuroinhibitory properties of pasteurized A. muciniphila, which therefore may have beneficial effects in relieving pain and anxiety in subjects with IBS.

Involvement of toll-like receptor 5 in mouse model of colonic hypersensitivity induced by neonatal maternal separation.

BACKGROUND: Chronic abdominal pain is the most common cause for gastroenterology consultation and is frequently associated with functional gastrointestinal disorders including irritable bowel syndrome and inflammatory bowel disease. These disorders present similar brain/gut/microbiota trialogue alterations, associated with abnormal intestinal permeability, intestinal dysbiosis and colonic hypersensitivity (CHS). Intestinal dysbiosis can alter colon homeostasis leading to abnormal activation of the innate immunity that promotes CHS, perhaps involving the toll-like receptors (TLRs), which play a central role in innate immunity. AIM: To understand the mechanisms between early life event paradigm on intestinal permeability, fecal microbiota composition and CHS development in mice with TLRs expression in colonocytes. METHODS: Maternal separation model (NMS) CHS model, which mimics deleterious events in childhood that can induce a wide range of chronic disorders during adulthood were used. Colonic sensitivity of NMS mice was evaluated by colorectal distension (CRD) coupled with intracolonic pressure variation (IPV) measurement. Fecal microbiota composition was analyzed by 16S rRNA sequencing from weaning to CRD periods. TLR mRNA expression was evaluated in colonocytes. Additionally, the effect of acute intrarectal instillation of the TLR5 agonist flagellin (FliC) on CHS in adult naive wildtype mice was analyzed. RESULTS: Around 50% of NMS mice exhibited increased intestinal permeability and CHS associated with intestinal dysbiosis, characterized by a significant decrease of species richness, an alteration of the core fecal microbiota and a specific increased relative abundance of flagellated bacteria. Only TLR5 mRNA expression was increased in colonocytes of NMS mice with CHS. Acute intrarectal instillation of FliC induced transient increase of IPV, reflecting transient CHS appearance. CONCLUSION: Altogether, these data suggest a pathophysiological continuum between intestinal dysbiosis and CHS, with a role for TLR5.

Tyrosine kinase type A-specific signalling pathways are critical for mechanical allodynia development and bone alterations in a mouse model of rheumatoid arthritis.

ABSTRACT: Rheumatoid arthritis is frequently associated with chronic pain that still remains difficult to treat. Targeting nerve growth factor (NGF) seems very effective to reduce pain in at least osteoarthritis and chronic low back pain but leads to some potential adverse events. Our aim was to better understand the involvement of the intracellular signalling pathways activated by NGF through its specific tyrosine kinase type A (TrkA) receptor in the pathophysiology of rheumatoid arthritis using the complete Freund adjuvant model in our knock-in TrkA/C mice. Our multimodal study demonstrated that knock-in TrkA/C mice exhibited a specific decrease of mechanical allodynia, weight-bearing deficit, peptidergic (CGRP+) and sympathetic (TH+) peripheral nerve sprouting in the joints, a reduction in osteoclast activity and bone resorption markers, and a decrease of CD68-positive cells in the joint with no apparent changes in joint inflammation compared with wild-type mice after arthritis. Finally, transcriptomic analysis shows several differences in dorsal root ganglion mRNA expression of putative mechanotransducers, such as acid-sensing ionic channel 3 and TWIK-related arachidonic acid activated K+ channel, as well as intracellular pathways, such as c-Jun, in the joint or dorsal root ganglia. These results suggest that TrkA-specific intracellular signalling pathways are specifically involved in mechanical hypersensitivity and bone alterations after arthritis using TrkA/C mice.

AhR/IL-22 pathway as new target for the treatment of post-infectious irritable bowel syndrome symptoms.

Alterations in brain/gut/microbiota axis are linked to Irritable Bowel Syndrome (IBS) physiopathology. Upon gastrointestinal infection, chronic abdominal pain and anxio-depressive comorbidities may persist despite pathogen clearance leading to Post-Infectious IBS (PI-IBS). This study assesses the influence of tryptophan metabolism, and particularly the microbiota-induced AhR expression, on intestinal homeostasis disturbance following gastroenteritis resolution, and evaluates the efficacy of IL-22 cytokine vectorization on PI-IBS symptoms. The Citrobacter rodentium infection model in C57BL6/J mice was used to mimic Enterobacteria gastroenteritis. Intestinal homeostasis was evaluated as low-grade inflammation, permeability, mucosa-associated microbiota composition, and colonic sensitivity. Cognitive performances and emotional state of animals were assessed using several tests. Tryptophan metabolism was analyzed by targeted metabolomics. AhR activity was evaluated using a luciferase reporter assay method. One Lactococcus lactis strain carrying an eukaryotic expression plasmid for murine IL-22 (L. lactisIL-22) was used to induce IL-22 production in mouse colonic mucosa. C. rodentium-infected mice exhibited persistent colonic hypersensitivity and cognitive impairments and anxiety-like behaviors after pathogen clearance. These post-infectious disorders were associated with low-grade inflammation, increased intestinal permeability, decrease of Lactobacillaceae abundance associated with the colonic layer, and increase of short-chain fatty acids (SCFAs). During post-infection period, the indole pathway and AhR activity were decreased due to a reduction of tryptophol production. Treatment with L. lactisIL-22 restored gut permeability and normalized colonic sensitivity, restored cognitive performances and decreased anxiety-like behaviors. Data from the video-tracking system suggested an upgrade of welfare for mice receiving the L.lactisIL-22 strain. Our findings revealed that AhR/IL-22 signaling pathway is altered in a preclinical PI-IBS model. IL-22 delivering alleviate PI-IBS symptoms as colonic hypersensitivity, cognitive impairments, and anxiety-like behaviors by acting on intestinal mucosa integrity. Thus, therapeutic strategies targeting this pathway could be developed to treat IBS patients suffering from chronic abdominal pain and associated well-being disorders.

Prevalence of chronic pain in opioid-maintained patients using the capture-recapture method: a nationwide population-based study.

Few studies all based on classical surveys have provided prevalence estimates of chronic pain (CP) in opioid-maintained patients (OMPs) but often had a limited patient sample size and a great variability in the prevalence estimates. This study sought to assess the prevalence of CP in the exhaustive population of OMPs using the capture-recapture method applied to the French nationwide health care database. Capture-recapture methods are increasingly used to estimate the prevalence of chronic conditions but have never been used in the specific context of CP in OMPs. Three large medical-administrative sources were used: the prescription drug database (A-list), the national hospital discharge database (M-list), and the pain center database (C-list). Between 2015 and 2016, 160,429 OMPs aged 15 years and older were identified and age- and sex-matched with 160,429 non-OMPs. All patients treated with analgesic drugs for ≥6 months (A-list) or diagnosed with CP (M- and C-list) were included. Capture-recapture analyses were performed to yield CP estimates with their 95% confidence intervals using log-linear models. In 2015 to 2016, 12,765 OMPs and 2938 non-OMPs with CP were captured. Most patients were male (67%) in OMPs and non-OMPs; median ages for OMPs and non-OMPs were 46 (interquartile range: 38-51) and 48 (41-53) years, respectively. The CP prevalence estimated in OMPs and non-OMPs ranged from 23.6% (14.9-46.2) to 32.1% (28.6-36.3) and from 7.28% (3.98-18.4) to 9.32% (7.42-12.1), respectively. This first study on CP in the exhaustive population of OMPs using the capture-recapture method demonstrated a high prevalence of CP in OMPs, 3- to 4-fold than in the general population.

c-Jun/p38MAPK/ASIC3 pathways specifically activated by nerve growth factor through TrkA are crucial for mechanical allodynia development.

Mechanical allodynia is a cardinal sign of several inflammatory pain disorders where nerve growth factor, a prototypic neurotrophin, plays a crucial role by binding to TrkA receptors. Here, we took the advantage of our generated knock-in mouse model expressing a chimeric TrkA/TrkC receptor that seems to not specifically develop mechanical allodynia after inflammation, to identify the TrkA downstream pathways involved in this phenomenon. We confirmed and extended that disrupting TrkA-specific pathways leads to a specific deficit in mechanical hypersensitivity development after somatic (systemic nerve growth factor administration and paw incision) and, to a lesser extent, visceral injuries. Despite a deficit in thin, mainly peptidergic, fibre innervation in TrkAC mice, thermal hyperalgesia development was not different from WT mice. Inflammatory reaction (oedema, IL-6 content), pain behaviours after intraplantar capsaicin, as well as TRPV1 calcium imaging response of dorsal root ganglion neurons were similar between TrkAC and WT mice. This deficiency in mechanical allodynia development in TrkAC mice is likely due to the alteration of the expression of different TrkA transduction pathways (ie, Akt, p38 MAPK, and c-Jun) especially p38 MAPK, in the dorsal root ganglion cell bodies, ultimately leading to an alteration of at least, ASIC3 channel overexpression, known to participate in nociceptor mechanosensory function.

Fecal dysbiosis associated with colonic hypersensitivity and behavioral alterations in chronically Blastocystis-infected rats.

BACKGROUND: Infectious gastroenteritis is a risk factor for the development of post-infectious Irritable Bowel Syndrome (PI-IBS). Recent clinical studies reported a higher prevalence of the intestinal parasite Blastocystis in IBS patients. Using a rat model, we investigated the possible association between Blastocystis infection, colonic hypersensitivity (CHS), behavioral disturbances and gut microbiota changes. METHODS: Rats were orally infected with Blastocystis subtype 4 (ST4) cysts, isolated from human stool samples. Colonic sensitivity was assessed by colorectal distension and animal behavior with an automatic behavior recognition system (PhenoTyper), the Elevated Plus Maze test and the Forced Swimming tests. Feces were collected at different time points after infection to study microbiota composition by 16 S rRNA amplicon sequencing and for short-chain fatty acid (SFCA) analysis. RESULTS: Blastocystis-infected animals had non-inflammatory CHS with increased serine protease activity. Infection was also associated with anxiety- and depressive-like behaviors. Analysis of fecal microbiota composition showed an increase in bacterial richness associated with altered microbiota composition. These changes included an increase in the relative abundance of Oscillospira and a decrease in Clostridium, which seem to be associated with lower levels of SCFAs in the feces from infected rats. CONCLUSIONS: Our findings suggest that experimental infection of rats with Blastocystis mimics IBS symptoms with the establishment of CHS related to microbiota and metabolic shifts.

Inhibition of Cav 3.2 calcium channels: A new target for colonic hypersensitivity associated with low-grade inflammation.

BACKGROUND AND PURPOSE: Abdominal pain associated with low-grade inflammation is frequently encountered in irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD) during remission. Current treatments are not very effective and new therapeutic approaches are needed. The role of CaV 3.2 channels, which are important in other chronic pain contexts, was investigated in a murine model of colonic hypersensitivity (CHS) associated with low-grade inflammation. EXPERIMENTAL APPROACH: Low doses of dextran sulfate sodium (DSS; 0.5%) were chronically administered to C57BL/6j mice in drinking water. Their inflammatory state was assessed by systemic and local measures of IL-6, myeloperoxidase, and lipocalin-2 using elisa. Colonic sensitivity was evaluated by the visceromotor responses to colorectal distension. Functional involvement of CaV 3.2 channels was assessed with different pharmacological (TTA-A2, ABT-639, and ethosuximide) and genetic tools. KEY RESULTS: DSS induced low-grade inflammation associated with CHS in mice. Genetic or pharmacological inhibition of CaV 3.2 channels reduced CHS. Cav3.2 channel deletion in primary nociceptive neurons in dorsal root ganglia (CaV 3.2Nav1.8 KO mice) suppressed CHS. Spinal, but not systemic, administration of ABT-639, a peripherally acting T-type channel blocker, reduced CHS. ABT-639 given intrathecally to CaV 3.2Nav1.8 KO mice had no effect, demonstrating involvement of CaV 3.2 channels located presynaptically in afferent fibre terminals. Finally, ethosuximide, which is a T-type channel blocker used clinically, reduced CHS. CONCLUSIONS AND IMPLICATIONS: These results suggest that ethosuximide represents a promising drug reposition strategy and that inhibition of CaV 3.2 channels is an attractive therapeutic approach for relieving CHS in IBS or IBD.

Blocking α2δ-1 Subunit Reduces Bladder Hypersensitivity and Inflammation in a Cystitis Mouse Model by Decreasing NF-kB Pathway Activation.

Bladder pain is frequently associated with bladder inflammation, as in conditions like interstitial cystitis (IC), for which current analgesic therapies have limited efficacy. The antinociceptive effect of alpha-2-delta (α2δ) ligands on inflammation-associated visceral pain like that experienced in cystitis has been poorly investigated. To investigate the effect of pregabalin (PGB), an α2δ ligand, we evaluated its impact on mechanical hyperalgesia in a mouse model of cystitis induced by cyclophosphamide (CYP). We further studied its effect on inflammation and NF-kB pathway activation. Acute cystitis was induced by intraperitoneal injection of 150 mg kg-1 of CYP in C57Bl/6J male mice. PGB was subcutaneously injected (30 mg kg-1) 3 h after CYP injection. The effect of PGB on CYP-induced mechanical referred hyperalgesia (abdominal Von Frey test), inflammation (organ weight, cytokine production, α2δ subunit level, NF-kB pathway activation) were assessed 1 h after its injection. In parallel, its effect on cytokine production, α2δ subunit level and NF-kB pathway activation was assessed in vitro on peritoneal exudate cells (PECs) stimulated with LPS. PGB treatment decreased mechanical referred hyperalgesia. Interestingly, it had an anti-inflammatory effect in the cystitis model by reducing pro-inflammatory cytokine production. PGB also inhibited NF-kB pathway activation in the cystitis model and in macrophages stimulated with LPS, in which it blocked the increase in intracellular calcium. This study shows the efficacy of PGB in hypersensitivity and inflammation associated with cystitis. It is therefore of great interest in assessing the benefit of α2δ ligands in patients suffering from cystitis.

Structural and functional alterations in the retrosplenial cortex following neuropathic pain.

Human and animal imaging studies demonstrated that chronic pain profoundly alters the structure and the functionality of several brain regions. In this article, we conducted a longitudinal and multimodal study to assess how chronic pain affects the brain. Using the spared nerve injury model which promotes both long-lasting mechanical and thermal allodynia/hyperalgesia but also pain-associated comorbidities, we showed that neuropathic pain deeply modified the intrinsic organization of the brain functional network 1 and 2 months after injury. We found that both functional metrics and connectivity of the part A of the retrosplenial granular cortex (RSgA) were significantly correlated with the development of neuropathic pain behaviours. In addition, we found that the functional RSgA connectivity to the subiculum and the prelimbic system are significantly increased in spared nerve injury animals and correlated with peripheral pain thresholds. These brain regions were previously linked to the development of comorbidities associated with neuropathic pain. Using a voxel-based morphometry approach, we showed that neuropathic pain induced a significant increase of the gray matter concentration within the RSgA, associated with a significant activation of both astrocytes and microglial cells. Together, functional and morphological imaging metrics of the RSgA could be used as a predictive biomarker of neuropathic pain.

Prevalence of chronic pain with or without neuropathic characteristics in France using the capture-recapture method: a population-based study.

Capture-recapture methods are increasingly used to determine the prevalence of numerous chronic conditions but have never been used in the context of chronic pain (CP). This study sought to provide up-to-date estimates of the prevalence of people experiencing CP ± neuropathic characteristics in France using the capture-recapture method. In 2013 to 2015, 3 data sources were used: the French prescription drug database (D-list), the national hospital discharge database (H-list), and the French pain center database (P-list). Patients aged 18 years and older treated with analgesic drugs for ≥6 months (D-list) or with a diagnosis of CP ± neuropathic characteristics (H- and P-lists) were included. Two successive capture-recapture analyses were conducted, with log-linear regression for each analysis performed. A total of 63,557 and 9852 distinct cases of CP and chronic neuropathic pain were captured, respectively. The estimated prevalence of CP and chronic neuropathic pain in the adults ranged from 27.2% (95% confidence interval: 26.1-28.4) to 32.7% (26.0-43.3) and from 5.55% (2.89-19.0) to 7.30% (6.40-8.41), respectively. Most patients were female, median ages were 67 (55-80) and 63 (51-76) years for chronic and neuropathic pain, respectively. The analgesic drugs most frequently used in CP patients were paracetamol (62.1%), weak opioids (39.7%), and nonsteroidal anti-inflammatory drugs (32.7%), whereas in neuropathic pain patients, anticonvulsants (45.3%), tricyclic antidepressants (18.1%), and serotonin-norepinephrine reuptake inhibitors (13.3%) were more frequently used. This first electronic health record-based study on CP using the capture-recapture method revealed a high prevalence of CP, with a significant proportion of neuropathic pain patients.

Chronic Pain Opioid-Maintained Patients Receive Less Analgesic Opioid Prescriptions.

Treating pain and opioid use disorder represents a clinical challenge. While most studies that have assessed opioid analgesic use in opioid substitution treatment (OST) patients primarily address opioid analgesic misuse (1, 2), only few studies focused on OST patients assessed the prescription of analgesic opioids for chronic pain. We sought to compare the prevalence of analgesic opioid prescription (AOP) in two groups of chronic non-cancer pain (CNCP) patients: OST patients vs. the general population. This was a population-based cross-sectional study based on the French national healthcare claims database SNIIRAM (Système National d'Informations Inter-Régimes de l'Assurance Maladie) covering over 66 million people (98.8% of the French population). Overall, 67,173 participants ≥15 years old undergoing continuous OST in 2015 ("OST patients" group) were included and age- and gender-matched by means of a 1:1 ratio with 67,173 patients without OST ("control" group). In each group, patients with cancer conditions were excluded and those having received opioid and non-opioid analgesics for at least 3 months were identified (CNCP patients). Compared to control patients, CNCP OST patients received less AOP (47.8 vs. 68.0%, p < 0.0001) and more often non-opioid prescription (52.2 vs. 32.0%, p < 0.0001). In multivariate analysis, CNCP OST patients were 2.7 times less likely to be prescribed analgesic opioids (adjusted odds ratio [OR] = 2.7 [2.42-3.01], p < 0.0001) than control patients. AOP correlated in CNCP OST patients with: age ≤ 40 years old, female gender, low-income status, methadone-maintained treatment, mental health disorder, hepatitis C virus (HCV) infection, and alcohol abuse disorder. Opioid analgesics were less often prescribed in CNCP OST patients. AOP prevalence was 2.7-fold lower than in the general population. Chronic pain management in OST patients needs to be reinforced through additional physician training and a multidisciplinary approach.

Adherent-Invasive E. coli enhances colonic hypersensitivity and P2X receptors expression during post-infectious period.

Irritable Bowel Syndrome (IBS) and Inflammatory Bowel Disease (IBD) are related gastrointestinal disorders characterized by abdominal pain associated with colonic hypersensitivity (CHS). Studies in humans have reported an abnormal colonization of Adherent-Invasive E. coli (AIEC) in the ileum of Crohn's disease (CD) patients associated with overexpression of the bacterial colonizing receptor CEACAM6. The aim of the present study was to investigate whether AIEC reference strain LF82 could induce intestinal impairment during infectious and/or post-infectious periods and subsequently the development of CHS. Transgenic mice overexpressing human CEACAM6 protein (TG) and their wild-type littermates were gavaged by CD-associated AIEC bacteria (reference strain LF82) or PBS for 3 d. Colonic hypersensitivity was assessed by colorectal distension (CRD) test during infectious (D4) and post-infectious periods (D21). Several markers of intestinal inflammation were monitored and the colonic expression of purinergic P2X receptors was quantified. At D4, an increased visceromotor response (VMR) to the CRD test was observed in TG mice infected with CD-associated AIEC LF82 in comparison with non-infected TG mice and persisted in a subgroup of infected animals at D21 after bacteria clearance. Increased VMR was associated with low-grade intestinal inflammation, increased intestinal permeability and expression of P2X 3, 4 and 7. This study shows that certain susceptible hosts infected with CD-associated AIEC bacteria can develop persistent CHS associated with low-grade inflammation and increased P2X receptors expression. Thus, CD-associated AIEC infection in CEACAM6 transgenic mice could be used as a novel post-infectious mouse model mimicking quiescent IBD with IBS-like symptoms such as visceral pain.

Efficient and reproducible experimental infections of rats with Blastocystis spp.

Although Blastocystis spp. infect probably more than 1 billion people worldwide, their clinical significance is still controversial and their pathophysiology remains poorly understood. In this study, we describe a protocol for an efficient and reproducible model of chronic infection in rats, laying the groundwork for future work to evaluate the pathogenic potential of this parasite. In our experimental conditions, we were unable to infect rats using vacuolar forms of an axenically cultivated ST4 isolate, but we successfully established chronic infections of 4 week-old rats after oral administration of both ST3 and ST4 purified cysts isolated from human stool samples. The infection protocol was also applied to 4 week-old C57BL/9, BALB/C and C3H mice, but any mouse was found to be infected by Blastocystis. Minimal cyst inoculum required for rat infection was higher with ST3 (105) than with ST4 (102). These results were confirmed by co-housing experiments highlighting a higher contagious potential of ST4 in rats compared to ST3. Finally, experiments mimicking fecal microbiota transfer from infected to healthy animals showed that Blastocystis spp. could easily infect a new host, even though its intestinal microbiota is not disturbed. In conclusion, our results provide a well-documented and robust rat model of Blastocystis chronic infection, reproducing "natural" infection. This model will be of great interest to study host parasite interactions and to better evaluate clinical significance of Blastocystis.