Central and peripheral modulation of gastrointestinal transit in mice by DN‐9, a multifunctional opioid/NPFF receptor agonist

Abstract

Background The nonapeptide DN‐9 functions as a multifunctional agonist to opioid and neuropeptide FF (NPFF) receptors and exhibits antinociceptive effects at the central and peripheral levels. Methods The effects of DN‐9 on small and colonic intestinal transit were evaluated using the upper gastrointestinal (GI) transit test and colonic bead expulsion assay, respectively. Opioid and NPFF receptor antagonists were used to investigate the mechanisms of DN‐9‐induced GI inhibition. Furthermore, the agonism of the DN‐9 analog [Phg9]‐DN‐9 to opioid and NPFF receptors was tested by the cAMP assay. Key results Intracerebroventricular administration of DN‐9 dose‐dependently slowed upper GI transit and colonic expulsion via mu‐ and kappa‐opioid receptors in the brain, independent of the delta‐opioid receptor. Similarly, intraperitoneal injection of DN‐9 dose‐dependently inhibited GI propulsion via the peripheral opioid receptors. DN‐9‐induced GI transit inhibitions were significantly aggravated by the NPFF receptor antagonist RF9. Moreover, the DN‐9 analog [Phg9]‐DN‐9, an agonist at mu‐, delta‐, and kappa‐opioid receptors but not NPFF receptors, inhibited GI more potently than DN‐9. In addition, intracerebroventricular NPFF significantly attenuated the central inhibitory effects induced by [Phg9]‐DN‐9 and morphine. However, central and peripheral injections of NPFF or RF9 almost had no significant effects on GI transit by itself. Conclusion and Inferences Intracerebroventricular and intraperitoneal administrations of DN‐9 inhibit GI transit via opioid receptors in mice by central and peripheral mechanisms, respectively. In addition, the NPFF agonism of DN‐9 possesses antiopioid effects on GI transit, which might explain the reduced constipation at the antinociceptive doses.

Development of Multifunctional and Orally Active Cyclic Peptide Agonists of Opioid/Neuropeptide FF Receptors that Produce Potent, Long-Lasting, and Peripherally Restricted Antinociception with Diminished Side Effects

“…An increasing number of groups reported that mixed agonists/antagonists exhibited potent analgesia with reduced opioid-like side effects. − A recent study suggests that the NPFF receptor agonist activity of DN-9 exhibits anti-opioid effects on the GIT and may help to reduce its constipation side effects . The present study showed that oral analogue 1 induced GIT inhibition at a dose of 2520-fold higher than the effective analgesic dose.…”

“…Therefore, these results suggest that the limited side effects of analogue 1 on constipation after p.o. administration are associated with its NPFF receptor agonism property, which is consistent with our recent study . Taken together, the reduced side effects of oral analogue 1 may be explained by its peripheral activities and multifunctional agonism of opioid and NPFF receptors.…”

“…63−65 A recent study suggests that the NPFF receptor agonist activity of DN-9 exhibits anti-opioid effects on the GIT and may help to reduce its constipation side effects. 66 The present study showed that oral analogue 1 induced GIT inhibition at a dose of 2520-fold higher than the effective analgesic dose. Oral analogue 1-induced GIT inhibition was significantly aggravated by pretreatment with RF9.…”

“…All compounds were injected intracerebroventricularly, subcutaneously, intravenously, or orally following our previous reports. ,, …”

“…was injected at 5 min prior to analogues. The doses and pretreatment times were determined according to previous reports. ,,− …”