In vitro and in vivo opioid activity of [DPro(6)]dermorphin, a new dermorphin analogue

Novel Cyclic Endomorphin Analogues with Multiple Modifications and Oligoarginine Vector Exhibit Potent Antinociception with Reduced Opioid-like Side Effects

Endomorphins (EMs) are potent pharmaceuticals for the treatment of pain. Herein, we investigated several novel EM analogues with multiple modifications and oligoarginine conjugation. Our results showed that analogues 1-6 behaved as potent μ-opioid agonists and enhanced stability and lipophilicity. Analogues 5 and 6 administered centrally and peripherally induced significant and prolonged antinociceptive effects in acute pain. Both analogues also produced long-acting antiallodynic effects against neuropathic and inflammatory pain. Furthermore, they showed a reduced acute antinociceptive tolerance. Analogue 6 decreased the extent of chronic antinociceptive tolerance, and analogue 5 exhibited no tolerance at the supraspinal level. Particularly, they displayed nontolerance-forming antinociception at the peripheral level. In addition, analogues 5 and 6 exhibited reduced or no opioid-like side effects on gastrointestinal transit, conditioned place preference (CPP), and motor impairment. The present investigation established that multiple modifications and oligoarginine-vector conjugation of EMs would be helpful in developing novel analgesics with fewer side effects.

Novel endomorphin-1 analogs with C-terminal oligoarginine-conjugation display systemic antinociceptive activity with less gastrointestinal side effects

In recent study, in order to improve the bioavailability of endomorphin-1 (EM-1), we designed and synthesized a series of novel EM-1 analogs by replacement of L-Pro(2) by β-Pro, D-Ala or Sar, together with C-terminal oligoarginine-conjugation. Our results indicated that the introduction of D-Ala and β-Pro in position 2, along with oligoarginine-conjugation, didn't significantly decrease the μ-affinity and in vitro bioactivity, and the enhancement of arginine residues did not markedly influence the μ-affinity of these analogs. All analogs displayed a significant enhancement of stability, which may be due to increased resistance to proline-specific enzymatic degradation. Moreover, following intracerebroventricular (i.c.v.) administration, analogs 1, 2, 4 and 5 produced significant antinociception and increased duration of action, with the ED50 values being about 1.8- to 4.2-fold less potent than that of EM-1. In addition, our results indicated that no significant antinociceptive activity of EM-1 was seen following subcutaneous (s.c.) injection, whereas analogs 1, 2, 4 and 5 with equimolar dose induced significant and prolonged antinociception by an opioid and central mechanism. Herein, we further examined the gastrointestinal transit and colonic propulsive latencies of EM-1 and its four analogs administered centrally and peripherally. I.c.v. administration of EM-1 and analogs 1, 2, 4 and 5 significantly delayed gastrointestinal transit and colonic bead propulsion in mice, but the inhibitory effects induced by these analogs were largely attenuated. It is noteworthy that no significant gastrointestinal side effects induced by these four analogs were observed after s.c. administration. Our results demonstrated that combined modifications of EM-1 with unnatural amino acid substitutions and oligoarginine-conjugation gave an efficient strategy to improve the analgesic profile of EM-1 analogs but with less gastrointestinal side effects when administered peripherally.

Intracerebroventricular administration of neuronostatin delays gastric emptying and gastrointestinal transit in mice

Neuronostatin is a 13-amino acid amidated peptide widely distributed in various organs including gastrointestinal tract. However, the effect of neuronostatin on gastrointestinal motility has not been well characterized. In the present work, effects of central administration of neuronostatin on gastric emptying and gastrointestinal transit were investigated. The results indicated that intracerebroventricular (i.c.v.) administration of neuronostatin (1, 5, 10 or 20nmol/mouse) delayed gastric emptying and gastrointestinal transit in a dose-related manner in mice. The effects were significantly reversed by melanocortin 3/4 receptor antagonist SHU9119 or classical opioid receptor antagonist naloxone, suggesting that the central melanocortin system and opioid system may be involved in the gastrointestinal effects elicited by i.c.v. administration of neuronostatin. In addition, we found that C-terminal amidation modification of neuronostatin is essential to exert its gastrointestinal effects. These results indicated that neuronostatin may play an important role in regulating gastrointestinal function.

Effect of centrally administered apelin-13 on gastric emptying and gastrointestinal transit in mice

Apelin, as the endogenous ligand for the APJ, regulates many biological functions, including blood pressure, neuroendocrine, drinking behavior, food intake and colonic motility. The present study was designed to investigate the effect of central apelin-13 on gastric emptying and gastrointestinal transit in mice. Intracerebroventricular (i.c.v.) injection of apelin-13 (3 and 10 μg/mouse) decreased gastric emptying rate by 10.9% and 17.1%. This effect was significantly antagonized by the APJ receptor antagonist apelin-13(F13A) and the opioid receptor antagonist naloxone, respectively. However, intraperitoneal (i.p.) injection of apelin-13 (10-100 μg/mouse) did not affect gastric emptying. Apelin-13 (0.3, 1 and 3 μg/mouse, i.c.v.) inhibited gastrointestinal transit by 16.8%, 23.4% and 19.2%. Apelin-13(F13A) and naloxone could also reverse this antitransit effect induced by apelin-13. Taken together, these results suggest that i.c.v. injected apelin-13 inhibits gastric emptying and gastrointestinal transit and it seems that APJ receptor and opioid receptor might be involved in these processes.

Synthesis and biological evaluation of 14-alkoxymorphinans. 22.(1) Influence of the 14-alkoxy group and the substitution in position 5 in 14-alkoxymorphinan-6-ones on in vitro and in vivo activities

Novel 14-alkoxy-substituted (e.g. allyloxy, benzyloxy, naphthylmethoxy) morphinan-6-one derivatives were synthesized and biologically evaluated. Compounds 6-9 and 11 displayed affinities in the subnanomolar range to mu opioid receptors which were comparable to 14-O-methyloxymorphone (1) and 14-methoxymetopon (3), and higher than oxymorphone (2). Opioid binding affinity was sensitive to the character and length of the substituent in position 14. In smooth muscle preparations they behaved as potent agonists. Antinociceptive potencies of compounds 6-11 in the hot-plate test after sc administration in mice were considerably greater than the potency of morphine. In the colonic propulsion test, the most potent analgesic compound 7 showed negligible constipating activity at the analgesic dose. These findings provide further evidence that the nature of the substituent at position 14 has a major impact on the abilities of morphinans to interact with opioid receptors. Introduction of a 5-methyl group has no significant effect on in vitro biological activities, but resulted in decreased antinociceptive potency.

Effects of peptides, with emphasis on feeding, pain, and behavior A 5-year (1999-2003) review of publications in Peptides

Novel effects of naturally occurring peptides are continuing to be discovered, and their mechanisms of actions as well as interactions with other substances, organs, and systems have been elucidated. Synthetic analogs may have actions similar or antagonistic to the endogenous peptides, and both the native peptides and analogs have potential as drugs or drug targets. The journal Peptides publishes many leading articles on the structure-activity relationship of peptides as well as outstanding reviews on some families of peptides. Complementary to the reviews, here we extract information from the original papers published during the past five years in Peptides (1999-2003) to summarize the effects of different classes of peptides, their modulation by other chemicals and various pathophysiological states, and the mechanisms by which the effects are exerted. Special attention is given to peptides related to feeding, pain, and other behaviors. By presenting in condensed form the effects of peptides which are essential for systems biology, we hope that this summary of existing knowledge will encourage additional novel research to be presented in Peptides.