The opioid and neuropeptide FF pharmacophore-containing chimeric peptide 0 (BN-9) was recently developed and produced potent nontolerance forming analgesia. In this study, 11 analogues of 0 were designed and synthesized. An in vitro cAMP assay demonstrated that these analogues behaved as multifunctional agonists at both opioid and NPFF receptors. In mouse tail-flick test, most of the analogues produced potent nontolerance forming antinociception. Notably, 11 (DN-9) was 33-fold more potent than 0 at analgesic effects, which was mediated by μ- and κ-opioid receptors. In addition, 11 also produced powerful analgesic effects in the formalin pain and CFA-induced chronic inflammatory pain models. Strikingly, following its repeated administration for 6 days, 11 did not produce antinociceptive tolerance in the tail-flick test and CFA-induced pain model. The present work indicates that it is reasonable to design multifunctional peptide ligands for opioid and NPFF receptors in a single molecule producing effective nontolerance forming antinociception.

The cannabinoid system has been demonstrated to modulate the acute and chronic pain of multiple origins. Mouse VD-hemopressin (a) [(m)VD-Hpa], an 11-residue a-hemoglobin-derived peptide, was recently reported to function as a selective agonist of the cannabinoid receptor type 1 (CB 1 ) in vitro. To characterize its behavioral and physiological properties, we investigated the in vivo effects of (m)VD-Hpa in mice. In the mouse tail-flick test, (m) VD-Hpa dose-dependently induced antinociception after supraspinal (EC 50 5 6.69 nmol) and spinal (EC 50 5 2.88 nmol) administration. The antinociceptive effects of (m)VD-Hpa (intracerebroventricularly and intrathecally) were completely blocked by N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM251; CB 1 antagonist), but not by 6-iodo-2-methyl-1-[2-(4-morpholinyl)ethyl]-1H-indol-3-yl (4-methoxyphenyl)-methanone (AM630; CB 2 antagonist) or naloxone (opioid antagonist), showing its selectivity to the CB 1 receptor. Furthermore, the central nervous system (CNS) effects of (m)VD-Hpa were evaluated in body temperature, locomotor activity, tolerance development, reward, and food intake assays. At the highly antinociceptive dose (3 Â EC 50 ), (m)VD-Hpa markedly exerted hypothermia and hypoactivity after supraspinal administration. Repeated intracerebroventricular injection of (m)VD-Hpa resulted in both development of tolerance to antinociception and conditioned place aversion. In addition, central injection of (m)VD-Hpa dosedependently stimulated food consumption. These findings demonstrate that this novel cannabinoid peptide agonist induces CB 1 -mediated central antinociception with some CNS effects, which further supports a CB 1 agonist character of (m)VD-Hpa. Moreover, the current study will be helpful to understand the in vivo properties of the endogenous peptide agonist of the cannabinoid CB 1 receptor.

No abstract

Neuropeptide FF (NPFF) is known to be an endogenous opioid-modulating peptide. Nevertheless, very few researches focused on the interaction between NPFF and endogenous opioid peptides. In the present study, we have investigated the effects of NPFF system on the supraspinal antinociceptive effects induced by the endogenous µ-opioid receptor agonists, endomorphin-1 (EM-1) and endomorphin-2 (EM-2). In the mouse tail-flick assay, intracerebroventricular injection of EM-1 induced antinociception via µ-opioid receptor while the antinociception of intracerebroventricular injected EM-2 was mediated by both µ- and κ-opioid receptors. In addition, central administration of NPFF significantly reduced EM-1-induced central antinociception, but enhanced EM-2-induced central antinociception. The results using the selective NPFF1 and NPFF2 receptor agonists indicated that the EM-1-modulating action of NPFF was mainly mediated by NPFF2 receptor, while NPFF potentiated EM-2-induecd antinociception via both NPFF1 and NPFF2 receptors. To further investigate the roles of µ- and κ-opioid systems in the opposite effects of NPFF on central antinociception of endomprphins, the µ- and κ-opioid receptors selective agonists DAMGO and U69593, respectively, were used. Our results showed that NPFF could reduce the central antinociception of DAMGO via NPFF2 receptor and enhance the central antinociception of U69593 via both NPFF1 and NPFF2 receptors. Taken together, our data demonstrate that NPFF exerts opposite effects on central antinociception of endomorphins and provide the first evidence that NPFF potentiate antinociception of EM-2, which might result from the interaction between NPFF and κ-opioid systems.

No abstract