V. Theodorou

Guanylate cyclase C‐mediated antinociceptive effects of linaclotide in rodent models of visceral pain

Background  Linaclotide is a novel, orally administered investigational drug currently in clinical development for the treatment of constipation‐predominant irritable bowel syndrome (IBS‐C) and chronic idiopathic constipation. Visceral hyperalgesia is a major pathophysiological mechanism in IBS‐C. Therefore, we investigated the anti‐nociceptive properties of linaclotide in rodent models of inflammatory and non‐inflammatory visceral pain and determined whether these pharmacological effects are linked to the activation of guanylate cyclase C (GC‐C).

Nitric oxide released by Lactobacillus farciminis improves tnbs-induced colitis in Rats

Background: Beneficial effects of lactobacilli have been reported in experimental colitis. On the other hand, despite the controversial role of nitric oxide (NO) in the inflammatory gut process, a protective action of exogenous NO in inflammation has been suggested. Consequently, this study aimed to determine the effect of (i) sodium nitroprusside (SNP), a NO donor and (ii) treatment with Lactobacillus farciminis, which produces NO in vitro, on trinitrobenzene sulphonic acid (TNBS)‐induced colitis in rats and to evaluate the role of exogenous NO in this effect. Methods: Rats were divided into three groups receiving one of the following: (i) a continuous intracolonic (IC) infusion of SNP for 4 days, (ii) L. farciminis orally for 19 days, or (iii) saline. On day 1 and day 15, respectively, TNBS and saline were administrated IC, followed by a continuous IC infusion of saline or haemoglobin, a NO scavenger. At the end of treatments, the following parameters were evaluated: macroscopic damage of colonic mucosa, myeloperoxidase and nitric oxide synthase activities and colonic luminal NO production. Results: In colitic rats, SNP and L. farciminis treatment significantly (P < 0.05) reduced macroscopic damage scores, myeloperoxidase and nitric oxide synthase activities compared to controls. Haemoglobin infusion abolished the anti‐inflammatory effect of both NO donor treatments, but had no effect per se on colitis. Conclusion: NO released intraluminally by SNP infusion or by L. farciminis given orally improves TNBS‐induced colitis in rats. These results indicate a protective role of NO donation in colonic inflammation and show for the first time a mechanism involving NO delivery by a bacterial strain reducing an experimental colitis.

Colonic responses to Lactobacillus farciminis treatment in trinitrobenzene sulphonic acid-induced colitis in rats

Background: It has recently been shown that Lactobacillus farciminis treatment exerts an anti-inflammatory effect in trinitrobenzene sulphonic acid (TNBS)-induced colitis partly through a nitric oxide release by this strain. The aim of this study was to evaluate whether L. farciminis treatment shares also the general mechanisms of action involved in the beneficial effect of probiotics in the colonic inflammatory process. Methods: Rats received L. farciminis for 15 days before and 4 days after intracolonic administration of TNBS or vehicle. The following parameters were evaluated: macroscopic damage of colonic mucosa, myeloperoxidase activity, cytokine mucosal levels, bacterial profile in colonic content and mucosa, bacterial translocation and colonic paracellular permeability. Results: In the absence of TNBS, L. farciminis treatment reduced colonic paracellular permeability and increased the IL-10 level in the colonic wall. TNBS administration induced colonic macroscopic damage, associated with an increase of myeloperoxidase activity, bacterial translocation, colonic paracellular permeability and IL-1β mucosal level, and a decrease in IL-10 mucosal level. Moreover, the bacterial profile of colonic content and mucosa was modified. All these alterations were abolished or significantly reduced by L. farciminis treatment. Conclusions: As previously shown, L. farciminis treatment improves TNBS-induced colitis. This study indicates that, in addition to the nitric oxide released by this bacterial strain, the anti-inflammatory action of L. farciminis involves also normalization of colonic microflora, prevention of bacterial translocation, enhancement of barrier integrity and a decrease in the IL-1β mucosal level.

Lactobacillus farciminis treatment attenuates stress‐induced overexpression of Fos protein in spinal and supraspinal sites after colorectal distension in rats

Abstract  Irritable bowel syndrome (IBS), frequently associated with psychological distress, is characterized by hypersensitivity to gut wall distension. Some probiotics are able to alleviate IBS symptoms and reduce visceromotor response to mechanical stimuli in animals. Moreover, we have previously shown that Lactobacillus farciminis treatment abolished the hyperalgesia to colorectal distension (CRD) induced by acute stress. The aims of the present study were to determine whether (i) stress‐induced visceral hyperalgesia modifies the expression of Fos, a marker of general neuronal activation, induced by CRD, (ii) this activation can be modulated by L. farciminis treatment. Female rats were treated by L. farciminis and CRD was performed after partial restraint stress (PRS) or sham‐PRS. The expression of Fos protein was measured by immunohistochemistry. After CRD or PRS, Fos expression was increased in spinal cord section (S1), nucleus tractus solitarius (NTS), paraventricular nucleus (PVN) of the hypothalamus, and in the medial nucleus of the amygdala (MeA). The combination of both stimuli, PRS and CRD, markedly increased this Fos overexpression in the sacral spinal cord section, PVN and MeA, but not in NTS. By contrast, a pretreatment with L. farciminis significantly reduced the number of Fos positive cells in these area. This study shows that PRS enhances Fos protein expression induced by CRD at the spinal and supraspinal levels in rats. Lactobacillus farciminis treatment inhibited this enhancing effect, suggesting that the antinociceptive effect of this probiotic strain results from a decrease of the stress‐induced activation/sensitization of sensory neurons at the spinal and supraspinal level.

Peripheral anti-nociceptive effect of nociceptin/orphanin FQ in inflammation and stress-induced colonic hyperalgesia in rats

ABSTRACT Nociceptin/orphanin FQ (N/OFQ) and its NOP receptors are present in the central nervous system and in the periphery playing important roles in the modulation of gastrointestinal functions and pain. The aim of this study was to investigate the role of central and peripheral N/OFQ–NOP receptor system in the nociceptive response to colorectal distension (CRD) in basal condition and in two models of gut hypersensitivity triggered by both inflammation and stress. Male Wistar rats were tested in basal and in post‐inflammatory conditions, i.e., 5 days after IC TNBS instillation (80 mg/Kg) and received N/OFQ (2 nmol/Kg IP), UFP‐101 (a selective NOP receptor antagonist, 10 nmol/Kg IP), N/OFQ+UFP‐101, N/OFQ (0.5 nmol/rat ICV) or vehicle. Female rats were tested in basal and after partial restraint stress receiving the same pharmacological treatment. CRD was performed using barostat and abdominal contractions were recorded by electromyography. In basal condition, N/OFQ, ICV and IP injected, did not modify basal visceral sensitivity. Both in TNBS and stress‐induced hyperalgesia, IP but not ICV injection of N/OFQ significantly decreased the number of abdominal contractions. Peripheral injection of UFP‐101 antagonized N/OFQ effect. Moreover, in post‐inflammatory colitis, UFP‐101, injected alone, exacerbated visceral hyperalgesia to CRD compared with vehicle. These findings indicate that in rats, N/OFQ, only peripherally injected, reduces visceral hypersensitivity triggered by inflammation or stress without affecting basal sensitivity. N/OFQ visceral anti‐hyperalgesic effect involves peripheral NOP receptors. In a post‐inflammatory, but not in an acute stress colitis model, N/OFQergic system is endogenously activated.

Evidence of Central and Peripheral Sensitization in a Rat Model of Narcotic Bowel-Like Syndrome

BACKGROUND & AIMS Narcotic bowel syndrome (NBS) is a subset of opioid bowel dysfunctions that results from prolonged treatment with narcotics and is characterized by chronic abdominal pain. NBS is under-recognized and its molecular mechanisms are unknown. We aimed to (1) develop a rat model of NBS and (2) to investigate its peripheral and central neurobiological mechanisms. METHODS Male Wistar rats were given a slow-release emulsion that did or did not contain morphine (10 mg/kg) for 8 days. Visceral sensitivity to colorectal distension (CRD) was evaluated during and after multiple administrations of morphine or vehicle (controls). The effects of minocycline (a microglia inhibitor), nor-binaltorphimine (a kappa-opioid antagonist), and doxantrazole (a mast-cell inhibitor) were observed on morphine-induced visceral hyperalgesia. Levels of OX-42, P-p38 mitogen-activated protein kinase, rat mast cell protease II, and protein gene product 9.5 were assessed at different spinal segments (lumbar 6 to sacral 1) or colonic mucosa by immunohistochemistry. RESULTS On day 8 of morphine administration, rats developed visceral hyperalgesia to CRD (incipient response) that lasted for 8 more days (delayed response). Minocycline reduced the incipient morphine-induced hypersensitivity response to CRD whereas nor-binaltorphimine and doxantrazole antagonized the delayed hyperalgesia. Levels of OX-42 and P-p38 increased in the spinal sections, whereas rat mast cell protease II and protein gene product 9.5 increased in the colonic mucosa of rats that were given morphine compared with controls. CONCLUSIONS We developed a rat model of narcotic bowel-like syndrome and showed that spinal microglia activation mediates the development of morphine-induced visceral hyperalgesia; peripheral neuroimmune activation and spinal dynorphin release represent an important mechanism in the delayed and long-lasting morphine-induced colonic hypersensitivity response to CRD.

Central α2‐Adrenergic Control of Colonic Transit in Rats

The effects of central and peripheral administration of α2‐adrenoceptor agonists on colonic propulsion were examined in conscious rats chronically fitted with a catheter inserted in the lumen of the proximal colon and a cannula placed in a cerebral lateral ventricle. The mean retention time of a marker in the colon was determined by administration of a bolus of [51Cr]sodium chromate into the proximal colon and collection of the feces at hourly intervals. In control studies the colonic mean retention time was 7.5 ± 1.6 hours. Clonidine administered intraperitonedy or intracerebroventricularly produced a dose‐dependent increase in mean retention time but was more potent when given intracerebroventricularly. St‐91, a quaternary derivative of clonidine which poorly crosses the blood‐brain barrier, delayed colonic transit after intracerebroventricular, but not after intraperitoneal, administration at the same dose. The increase in colonic mean retention time induced by intraperitonedy administered clonidine was antagonized by intracerebroventricular administration of yohimhine but not of prazosin, an α1‐adrenoceptor antagonist. Yohimbine intracerebroventricularly or intraperitonedy administered alone at the same dose accelerated the colonic transit. Such data suggest a possible role of central α2‐adrenoceptors in the regulation of colonic motility in rats.

Anaphylactic colonic hypersecretion in cow's milk sensitized guinea‐pigs depends upon release of Interleukin‐1, prostaglandins and mast cell degranulation

Methods: The effect of β‐lactoglobulin (β‐LGI) challenge on net water movements into the proximal colon and the role of Interleukin‐1 (IL‐1), prostaglandins and mast cell degranulation on the challenge‐induced net water changes were assessed in vivo using isolated colonic loops in anaesthetized guinea‐pigs immunized to bovine milk.

Proteinase‐activated receptor‐4 evoked colorectal analgesia in mice: an endogenously activated feed‐back loop in visceral inflammatory pain

Background  Activation of proteinase‐activated receptor‐4 (PAR‐4) from the colonic lumen has an antinociceptive effect to colorectal distension (CRD) in mice in basal conditions. We aimed to determine the functional localization of the responsible receptors and to test their role in two different hyperalgesia models.

Protective action of diosmectite treatment on digestive disturbances induced by intestinal anaphylaxis in the guinea-pig

Methods: Colonic transit time, faecal moisture and intestinal permeability were assessed in guinea‐pigs sensitized intraperitoneally with cows milk and challenged with an oral administration of β‐lactoglobulin. One group of animals was treated for 1 week with diosmectite (500 mg.kg/day) and another with placebo. A control group was not sensitized but treated with diosmectite.