Inhibition Of Small Intestinal Transit Research Articles

Involvement of the Peripheral μ-Opioid Receptor in Tramadol-Induced Constipation in Rodents.

Tramadol is a weak opioid that produces analgesic effect via both the μ-opioid receptor (MOR) and non-opioid targets. Constipation is the most common opioid-related side effect in patients with cancer and non-cancer pain. However, the contribution of MOR to tramadol-induced constipation is unclear. Therefore, we used naldemedine, a peripherally acting MOR antagonist, and MOR-knockout mice to investigate the involvement of peripheral MOR in tramadol-induced constipation using a small intestinal transit model. A single dose of tramadol (3-100 mg/kg, per os (p.o.)) inhibited small intestinal transit dose-dependently in rats. Naldemedine (0.01-10 mg/kg, p.o.) blocked the inhibition of small intestinal transit induced by tramadol (30 mg/kg, p.o.) in rats. The transition rate increased dose-dependently over the range of naldemedine 0.01-0.3 mg/kg, and complete recovery was observed at 0.3-10 m/kg. Additionally, tramadol (30 and 100 mg/kg, subcutaneously (s.c.)) inhibited small intestinal transit in wild-type mice but not in MOR-knockout mice. These results suggest that peripheral MOR participates in tramadol-induced constipation.

Pharmacological Profile of Naldemedine, a Peripherally Acting μ-Opioid Receptor Antagonist: Comparison with Naloxone and Naloxegol.

Opioid-induced constipation (OIC), a typical side effect of opioids, is due to activation of the μ-opioid receptors in the enteric nervous system. Peripherally acting μ-opioid receptor antagonists (PAMORAs) can reverse OIC by inhibiting the peripheral action of opioids without affecting centrally mediated analgesia. Naldemedine is a PAMORA with potent antagonist activity against μ-, δ-, and κ-opioid receptors. In this study, the pharmacological profiles of naldemedine, compared with those of naloxone and naloxegol, were evaluated. In vitro, Schild plot analysis indicated that naldemedine was a noncompetitive antagonist of μ-opioid receptors, whereas other compounds were competitive antagonists. Also, naldemedine showed slower association and dissociation kinetics than the other compounds. In vivo, naldemedine dose-dependently ameliorated morphine-induced inhibition of small intestinal transit (SIT). The dose-response curve was not shifted at 1 and 3 mg/kg morphine. On the contrary, that of naloxegol was significantly shifted to the right from 1 to 3 mg/kg morphine. In morphine-dependent rats, naldemedine caused peripheral withdrawal symptoms (diarrhea) at doses higher than 1 mg/kg, whereas the dose that produced half the maximal preventive effect (ED50) against constipation was 0.03 mg/kg. Naldemedine showed slower onset and a lesser severity of diarrhea than the other compounds at close to the ED50 value in the SIT model. Our results reveal that naldemedine has different pharmacological profiles (type of antagonism and binding kinetics) to the other compounds. This might explain the differential inhibition of morphine-induced SIT and withdrawal symptoms among the three antagonist compounds. SIGNIFICANCE STATEMENT: Naldemedine is a novel peripherally acting μ-opioid receptor antagonist with potent antagonist activity against μ-, δ-, and κ-opioid receptors. Naldemedine showed a noncompetitive antagonism and slower association and dissociation kinetics against μ-opioid receptors than naloxone and naloxegol. Naldemedine showed insurmountable antagonism of morphine-induced inhibition and lower and slower peripheral withdrawal symptoms (diarrhea) than the other compounds. Therefore, naldemedine has a different pharmacological profile (the type of antagonism and binding kinetics) to the other compounds.

Pharmacologic effects of naldemedine, a peripherally acting μ-opioid receptor antagonist, in in vitro and in vivo models of opioid-induced constipation.

BackgroundNaldemedine (S‐297995) is a peripherally acting μ‐opioid receptor antagonist developed as a once‐daily oral drug for opioid‐induced constipation (OIC) in adults with chronic noncancer or cancer pain. This study characterized the pharmacological effects of naldemedine in vitro and in vivo.MethodsThe binding affinity and antagonist activity of naldemedine against recombinant human μ‐, δ‐, and κ‐opioid receptors were assayed in vitro. Pharmacologic effects of naldemedine were investigated using animal models of morphine‐induced inhibition of small and large intestinal transit, castor oil‐induced diarrhea, antinociception, and morphine withdrawal.Key ResultsNaldemedine showed potent binding affinity and antagonist activities for recombinant human μ‐, δ‐, and κ‐opioid receptors. Naldemedine significantly reduced opioid‐induced inhibition of small intestinal transit (0.03‐10 mg kg−1; P < 0.05) and large intestinal transit (0.3‐1 μmol L−1; P < 0.05). Naldemedine (0.03‐1 mg kg−1) pretreatment significantly reversed the inhibition of castor oil‐induced diarrhea by subcutaneous morphine (P < 0.01). Naldemedine (1‐30 mg kg−1) pretreatment (1 or 2 hours) did not alter the analgesic effects of morphine in a model measuring the latency of a rat to flick its tail following thermal stimulation. However, a significant delayed reduction of the analgesic effect of morphine was seen with higher doses of naldemedine (10‐30 mg kg−1). Some centrally mediated and peripherally mediated withdrawal signs in morphine‐dependent rats were seen with naldemedine doses ≥3 and ≥0.3 mg kg−1, respectively.Conclusions & InferencesNaldemedine displayed potent binding affinity to, and antagonistic activity against, μ‐, δ‐, and κ‐opioid receptors. Naldemedine tempered OIC in vivo without compromising opioid analgesia.

Pharmacological profile of TAN-452, a novel peripherally acting opioid receptor antagonist for the treatment of opioid-induced bowel syndromes

AimOpioid-induced bowel syndromes deteriorate patients' quality of life and may lead to nonadherence to opioid schedule and under-treatment of pain. The objective was to characterize the pharmacological profile of 17-cyclopropylmethyl-6,7-didehydro-4,5α-epoxy-6′-ethoxycarbonyl-3,14-dihydroxyindolo [2′,3′-6,7]morphinan (TAN-452), a novel peripherally acting opioid receptor antagonist. Main methodsThe in vitro binding affinity for the μ-, δ-, and κ-opioid receptors (MOR, DOR, and KOR) and the inhibition of [35S]GTPγS binding were examined using membrane preparations from recombinant human (h) MOR, DOR, or KOR expressing cell. In vivo assays were performed to determine the inhibitory effect of TAN-452 on morphine-induced emesis (anti-emetic activity) in ferrets, morphine-induced inhibition of small intestinal transit (anti-constipation activity) in rats, and morphine-induced antinociception (anti-analgesic activity) in rats. A pharmacokinetic study was also performed. Key findingsThe binding affinities of TAN-452 (Ki) were 36.56 ± 1.48 nM, 0.47 ± 0.09 nM, and 5.31 ± 1.80 nM for hMOR, hDOR, and hKOR, respectively. Its antagonistic activities (Kb) were 9.43 ± 0.58 nM, 0.21 ± 0.06 nM, and 7.18 ± 0.75 nM, respectively. The ED50 values (95% Confidence interval) were <1.0 mg/kg p.o. and <0.3 mg/kg s.c. for anti-emetic activity, 9.45 (4.09, 47.79) mg/kg p.o. and 0.52 (0.10, 1.08) mg/kg s.c. for anti-constipation activity, and >300 mg/kg p.o. and >30 mg/kg s.c. for anti-analgesic activity. The pharmacokinetic study demonstrated low brain penetrability of TAN-452. SignificanceTAN-452 is a peripherally acting opioid receptor antagonist with selectivity for DOR that attenuates morphine-induced side effects, such as nausea, vomiting, and constipation, without affecting pain control.

Differences in the morphine-induced inhibition of small and large intestinal transit: Involvement of central and peripheral μ-opioid receptors in mice

Constipation is the most common side effect of morphine. Morphine acts centrally and on peripheral sites within the enteric nervous system. There are a few comprehensive studies on morphine-induced constipation in the small and large intestine by the activation of central and peripheral μ-opioid receptors. We investigated the differences in the inhibition of the small and large intestinal transit in normal and morphine-tolerant mice. Morphine reduced the geometric center in the fluorescein isothiocyanate–dextran assay and prolonged the bead expulsion time in a dose-dependent manner. The inhibitory effects of morphine were blocked by μ-opioid antagonist β-funaltrexamine, but not by δ- and κ-opioid antagonists. The peripheral opioid receptor antagonist, naloxone methiodide, partially blocked morphine's effect in the small intestine and completely blocked its effect in the large intestine. The intracerebroventricular administration of naloxone significantly reversed the delay of small intestinal transit but did not affect morphine-induced inhibition of large intestinal transit. Naloxone methiodide completely reversed the inhibition of large intestinal transit in normal and morphine-tolerant mice. Naloxone methiodide partially reversed the morphine-induced inhibition of small intestinal transit in normal mice but completely reversed the effects of morphine in tolerant mice. Chronic treatment with morphine results in tolerance to its inhibitory effect on field-stimulated contraction in the isolated small intestine but not in the large intestine. These results suggest that peripheral and central opioid receptors are involved in morphine-induced constipation in the small and large intestine during the early stage of treatment, but the peripheral receptors mainly regulate constipation during long-term morphine treatment.

Pharmacological properties of TD-6301, a novel bladder selective muscarinic receptor antagonist

Existing antimuscarinic drugs for overactive bladder have high affinity for M 3/M 1 muscarinic receptors and consequently produce M 3/M 1-mediated adverse effects including dry mouth, constipation, mydriasis and somnolence. TD-6301 is a M 2/4 muscarinic receptor-selective antagonist developed for the treatment of overactive bladder. The present studies characterize the in vitro and in vivo pharmacological properties of this molecule in comparison to other marketed antimuscarinics agents. In radioligand binding studies, TD-6301 was found to possess high affinity for human M 2 muscarinic receptor ( K i = 0.36 nM) and was 31, 36, 2 and 128-fold selective for the human M 2 muscarinic receptor compared to the M 1, M 3, M 4 and M 5 muscarinic receptors, respectively. The in vivo bladder selectivity of TD-6301 in rats was determined to be 26, 28, > 100, 16 and 0.4-fold, respectively, assessed by comparing its potency for inhibition of volume-induced bladder contractions to that for inhibition of oxotremorine-induced salivation, inhibition of small-intestinal transit, decreases in locomotor activity, increases in pupil diameter and increases in heart rate. TD-6301 was more potent in inhibiting volume-induced bladder contractions (ID 50 = 0.075 mg/kg) compared to oxotremorine-induced salivation (ID 50 = 1.0 mg/kg) resulting in a bladder/salivary gland selectivity ratio greater than that observed for tolterodine, oxybutynin, darifenacin and solifenacin. The preclinical properties of TD-6301 suggest that this molecule is likely to be efficacious in overactive bladder patients with a lower propensity to cause M 3 muscarinic receptor mediated adverse effects.

Morphine-6-glucuronide induces contraction of the ileal circular muscle more potently than morphine in mice

It has been reported that morphine-6-glucuronide inhibits small intestinal transit in mice more potently than morphine. In this study, we investigated the effects of morphine, morphine-6-glucuronide and morphine-3-glucuronide on the contractile response of the circular muscle isolated from mouse ileum. Morphine and morphine-6-glucuronide induced tonic contraction dose-dependently, and the contractile force of morphine-6-glucuronide was greater than that of morphine. Morphine-3-glucuronide induced slight contraction at high dose. These results suggest that the strong contraction induced by morphine-6-glucuronide contributed to the inhibition of small intestinal transit in mice.

Inhibition of small intestine motility by cromakalim (BRL 34915)

The effects of the potassium channel activator, cromakalim, on intestine motility were investigated. In vitro, cromakalim inhibits the peristaltic reflex, with the action on longitudinal muscle (pIC 50 = 5.8 ± 0.1) being more potent than that on circular muscle (pIC 50 = 4.8 ± 0.2). In vivo, a half maximal inhibition of small intestinal transit occurred at 1.2 mg/kg (i.p.). These results demonstrate that different gut muscle layers show a different sensitivity to cromakalim and that small intestine smooth muscle is less sensitive to cromakalim than vascular smooth muscle.

Effect of the secretin family of peptides on gastric emptying and small intestinal transit in rats

We have compared the effects of the secretin family of peptides and their synthetic fragments on gastric emptying (GE) and small intestinal transit (SIT) using an unanesthetized rat model which simultaneously measures the GE and SIT of both solids and liquids. The meal consisting of 5% polyethylene glycol w/v, 5% Indian ink v/v and 20 non-digestible plastic beads was given intragastrically 10 minutes after the intraperitoneal injection of 0.5 ml of saline or peptides (2 and 5 μg/kg). Plasma secretin and the immunospecificity of secretin fragments were determined. In control rats, the t 1 2 for the GE of both solids and liquids were 56±3.8 and 19±2.3 minutes, respectively. Liquids emptied faster than the solids and liquids travelled ahead of the solids in the intestine. Secretin (5μg/kg) inhibited GE of both solids and liquids by 33–37%. Secretin delayed the SIT of the meal by approximately 35%. Fragments of secretin and of VIP had no effect on GE and SIT of both solids and liquids. The whole molecule of secretin was required to inhibit GE and to delay SIT of solids and liquids. Glucagon, PHI and growth hormone releasing factor (GHRF 1–44) inhibited GE and SIT of both solids and liquids. For all peptides tested, the inhibition of SIT was proportional to the inhibition of GE suggesting that the prolongation of SIT was secondary to delayed GE. These observations indicate that the peptides of the secretin family inhibit GE and prolong SIT. Thus, the structural requirement required for the secretin family of peptides to effect their motor actions on the stomach is similar to that required for pancreatic enzyme secretion.

Corticotropin-releasing factor directly mediates colonic responses to stress.

A new stress model in rats produced changes in intestinal function that resemble patterns of intestinal dysfunction associated with stress in humans: small intestinal transit was inhibited, large intestinal transit was stimulated, and fecal excretion was stimulated. To evaluate the role of corticotropin-releasing factor (CRF) in mediating the effects of stress on the intestine, we studied the actions of exogenous CRF on small and large intestinal transit in the rat and characterized the effects of pharmacological blockade of CRF receptors on stress-induced intestinal dysfunction. Administration of exogenous CRF (0.3-10.0 micrograms iv or icv) resulted in dose-related inhibition of gastric emptying, inhibition of small intestinal transit, stimulation of colonic transit, and stimulation of fecal excretion. The actions of exogenous CRF mimicked the effects of stress on the motor activity of the gastrointestinal tract. Administration of alpha-helical CRF-(9-41) (50 micrograms iv or icv), an antagonist of CRF, prevented the stress-induced increase in large intestinal transit and the associated increase in fecal excretion. These data suggest that endogenous CRF may mediate stress-induced changes in colonic function.