Modulation of gastrointestinal function by MuDelta, a mixed µ opioid receptor agonist/ µ opioid receptor antagonist

BACKGROUND & PURPOSE

Loperamide is a selective µ opioid receptor agonist acting locally in the gastrointestinal (GI) tract as an effective anti-diarrhoeal but can cause constipation. We tested whether modulating µ opioid receptor agonism with δ opioid receptor antagonism, by combining reference compounds or using a novel compound ('MuDelta'), could normalize GI motility without constipation.

EXPERIMENTAL APPROACH

MuDelta was characterized in vitro as a potent µ opioid receptor agonist and high-affinity δ opioid receptor antagonist. Reference compounds, MuDelta and loperamide were assessed in the following ex vivo and in vivo experiments: guinea pig intestinal smooth muscle contractility, mouse intestinal epithelial ion transport and upper GI tract transit, entire GI transit or faecal output in novel environment stressed mice, or four weeks after intracolonic mustard oil (post-inflammatory). Colonic δ opioid receptor immunoreactivity was quantified.

KEY RESULTS

δ Opioid receptor antagonism opposed µ opioid receptor agonist inhibition of intestinal contractility and motility. MuDelta reduced intestinal contractility and inhibited neurogenically-mediated secretion. Very low plasma levels of MuDelta were detected after oral administration. Stress up-regulated δ opioid receptor expression in colonic epithelial cells. In stressed mice, MuDelta normalized GI transit and faecal output to control levels over a wide dose range, whereas loperamide had a narrow dose range. MuDelta and loperamide reduced upper GI transit in the post-inflammatory model.

CONCLUSIONS AND IMPLICATIONS

MuDelta normalizes, but does not prevent, perturbed GI transit over a wide dose-range in mice. These data support the subsequent assessment of MuDelta in a clinical phase II trial in patients with diarrhoea-predominant irritable bowel syndrome.

Stimulation of neuronal receptors, neuropeptides and cytokines during experimental oil of mustard colitis

Oil of mustard (OM), administered intracolonically, produces severe colitis in mice that is maximized within 3 days. The purpose of this study was to characterize the cytokine response, and to establish expression patterns of enteric neuronal mediators and neuronal receptors affected during active colitis. We measured the changes in the mRNA levels for neuronal receptors and mediators by real-time PCR, and cytokine and chemokine protein levels in the affected tissue. Significant increases in neuronal receptors, such as transient receptor potential A1 (TRPA1), cannabinoid type 1 receptor, neurokinin 1 receptor (NK1R) and delta-opioid receptor; prokineticin-1 receptor; and soluble mediators, such as prodynorphin, proenkephalin1, NK1, prokineticin-1 and secretory leukocyte protease inhibitor, occurred. Significant increases in cytokines, such as interleukin (IL)-1beta, IL-6 and granulocyte macrophage colony stimulating factor (GM-CSF), and in chemokines, such as macrophage chemotactic protein 1 (MCP-1), macrophage inflammatory protein 1 (MIP-1alpha) and Kupffer cell derived chemokine (KC), were detected, with no changes in T-cell-derived cytokines. Furthermore, immunodeficient C57Bl/6 RAG2(-/-) mice exhibited OM colitis of equal severity as seen in wt C57Bl/6 and CD-1 mice. The results demonstrate rapidly increased levels of mRNA for neuronal receptors and soluble mediators associated with pain and inflammation, and increases in cytokines associated with macrophage and neutrophil activation and recruitment. Collectively, the data support a neurogenic component in OM colitis coupled with a myeloid cell-related, T- and B-cell-independent inflammatory component.

Vanilloid receptor 1 antagonists attenuate disease severity in dextran sulphate sodium-induced colitis in mice

Neurogenic mechanisms have been implicated in the induction of inflammatory bowel disease (IBD). Vanilloid receptor type 1 (TRPV1) has been visualized on nerve terminals of intrinsic and extrinsic afferent neurones innervating the gastrointestinal tract and local administration of a TRPV1 antagonist, capsazepine, reduces the severity of dextran sulphate sodium (DSS)-induced colitis in rats (Gut 2003; 52: 713-9(1)). Our aim was to test whether systemically or orally administered TRPV1 antagonists attenuate experimental colitis induced by 5% DSS in Balb/c mice. Intraperitoneal capsazepine (2.5 mg kg(-1), bid), significantly reduced the overall macroscopic damage severity compared with vehicle-treated animals (80% inhibition, P < 0.05); however, there was no effect on myeloperoxidase (MPO) levels. An experimental TRPV1 antagonist given orally was tested against DSS-induced colitis, and shown to reverse the macroscopic damage score at doses of 0.5 and 5.0 mg kg(-1). Epithelial damage assessed microscopically was significantly reduced. MPO levels were attenuated by approximately 50%, and diarrhoea scores were reduced by as much as 70%. These results suggest that pharmacological modulation of TRPV1 attenuates indices of experimental colitis in mice, and that development of orally active TRPV1 antagonists might have therapeutic potential for the treatment of IBD.

Characterization of the maize Globulin-2 gene and analysis of two null alleles

The most abundant proteins present in maize (Zea mays L.) embryos are saline-soluble globulins. A Mr 45,000 globulin component, designated GLB2, is encoded by the Glb2 gene. A cDNA clone corresponding to Glb2 was used as radiolabeled probe to examine the expression of Glb2 in developing embryos and other maize tissues. Glb2 transcripts accumulate during embryo development and are not detectable in germinating kernels. Glb2 transcripts are found only in the developing embryo, and not in endosperm, seedling, or unfertilized ears. Analysis of globulin profiles in embryos homozygous for either a previously described null allele, Glb-2-0, or a novel null allele, Glb2-N1, revealed that these embryos lack not only the GLB2 protein but also globulins of lower molecular mass which may represent processed forms of GLB2. Southern blot analysis of DNA from Glb2-0/0 and Glb2-N1/N1 plants in which a Glb2-specific clone is used as probe indicates that the two null alleles are genetically distinct.

Inhibition of peripheral aromatization in the male cynomolgus monkey by a novel nonsteroidal aromatase inhibitor (R 76713)

R 76713 (6-[(4-chlorophenyl)(1-H-1,2,4-trizol-1-yl)methyl]1-H benzotriazole) is a highly potent and selective inhibitor of the aromatase enzyme both in vitro and in vivo. The ability of R 76713 to inhibit peripheral aromatization of androstenedione (A) to estrone (E1) in vivo was studied in male cynomolgus monkeys (Macaca fascicularis). Peripheral aromatization was measured using a primed constant infusion of [3H] A and [14C]E1 for 3.5 h. Blood samples, collected during the final hour of infusion, were analyzed for plasma radioactivity as infused and product steroids. MCRs, conversion ratios (CR), and percent conversion of A to E1 were calculated. R 76713 (0.03-10 microgram/kg) or vehicle (10% hydroxypropyl-beta-cyclodextrin) were administered iv 90 min before beginning the infusion of radiolabeled steroids. In vehicle-treated monkeys, the aromatization of A (mean +/- SEM, 1.35 +/- 0.11%) was similar to that previously reported for cynomolgus and rhesus monkeys, baboons, and humans. Aromatization of A, measured 4-5 h after injection of R 76713, was dose-dependently decreased from the control value by 87 +/- 3%, 85 +/- 2%, 61 +/- 5%, and 33 +/- 8% (all P less than 0.05) at doses of 10.0, 3.0, 0.3, and 0.03 micrograms/kg, respectively, with an ID50 of 0.13 microgram/kg, iv (95% confidence interval, 0.06-0.21). When measured 15-16 h after iv administration of 3.0 micrograms/kg R 76713, aromatization (0.55 +/- 0.13%) was significantly inhibited by 53 +/- 11% compared to that in control monkeys (1.16 +/- 0.18%). The CRs between androgens, the CRs between estrogens, and the MCRs of A and E1 were not significantly altered by R 76713 compared to those after vehicle treatment. R 76713 potently decreased peripheral conversion of androgen to estrogen in vivo in male cynomolgus monkeys and may be a useful therapeutic agent in treating estrogen-dependent diseases, including post-menopausal breast cancer.

Hypoglycaemic and hypoketonaemic effects of single and repeated oral doses of methyl palmoxirate (methyl 2-tetradecylglycidate) in streptozotocin/alloxan-induced diabetic dogs

1. The hypoglycaemic and hypoketonaemic effects of orally administered methyl palmoxirate were studied in streptozotocin/alloxan-induced diabetic dogs. 2. Single oral 50 mg doses (approximately 7.5 mg kg-1) of methyl palmoxirate produced statistically significant reductions of plasma glucose (32 +/- 6% maximum reduction from baseline) and ketones (74 +/- 12% maximum reduction from baseline), with the peak effect on plasma ketones (3.5 h) preceding that for plasma glucose (6.0 h). 3. Lower doses (0.7-2.0 mg kg-1 daily) of methyl palmoxirate given repeatedly for seven days produced reductions of blood glucose and ketones equivalent to those produced with the higher single dose. Maximal reductions of plasma ketones were generally observed following the first dose of drug, whereas significant lowering of plasma glucose required several days of continuous dosing. 4. Repeated daily doses of methyl palmoxirate markedly reduced the overnight fasting ketone levels but not glucose levels of diabetic dogs. 5. In conclusion, administration of the fatty acid oxidation inhibitor methyl palmoxirate, in the absence of concomitant insulin therapy, was able to lower the plasma glucose and ketone levels of insulin-deficient streptozotocin/alloxan diabetic dogs. Only the plasma ketones were decreased to normal by this treatment.