The analgesic agent tapentadol inhibits calcitonin gene-related peptide release from isolated rat brainstem via a serotonergic mechanism.

AIMS: In this study we tested the hypothesis that tapentadol inhibits GGRP release from the rat brainstem through a mechanism mediated by the inhibition of NA reuptake; as a second alternative hypothesis, we investigated whether tapentadol inhibits GGRP release via the inhibition of 5-HT reuptake. METHODS: Rat brainstems were explanted and incubated in short-term experiments. CGRP released in the incubation medium was taken as a marker of CGRP release from the central terminals of trigeminal neurons within the brainstem. CGRP levels were measured by radioimmunoassay under basal conditions or in the presence of tapentadol; NA, 5-HT, clonidine, yohimbine and ondansetron were used as pharmacological tools to investigate the action mechanism of tapentadol. RESULTS: The α2-antagonist yohimbine failed to counteract the effects of tapentadol. Moreover, neither NA nor the α2-agonist clonidine per se inhibited K(+)-stimulated CGRP release, thereby indicating that the effects of tapentadol are nor mediated through the block of NA reuptake. Further experiments showed that 5-HT and tramadol, which inhibits both NA and 5-HT reuptake, significantly reduced K(+)-stimulated CGRP release. Moreover, the 5-HT3 antagonist ondansetron was able to counteract the effects of tapentadol in this system. SIGNIFICANCE: This study provided pharmacological evidence that tapentadol inhibits stimulated CGRP release from the rat brainstem in vitro through a mechanism involving an increase in 5-HT levels in the system and the subsequent activation of 5-HT3 receptors.

Tapentadol inhibits calcitonin gene-related peptide release from rat brainstem in vitro.

We have previously developed an in vitro model of rat brainstem explants. The latter release sizable amounts of calcitonin gene-related peptide (CGRP); basal release can be stimulated by such secretagogues as high KCl concentrations, veratridine or capsaicine. In this paradigm we investigated the activity of the analgesic agent tapentadol; the effects of tapentadol were compared to those of a classical opioid receptor agonist, morphine, and the selective noradrenaline reuptake inhibitor reboxetine. Morphine inhibited basal CGRP release, with statistical significance from 1 nM onward and maximal (-44%) inhibition at 100 µM. Morphine also inhibited K(+)-stimulated peptide release, with a significant effect from 1 µM and maximal (-39%) decrease at 100 µM, but failed to inhibit release stimulated by 10 µM capsaicin. At variance, reboxetine had no effect on baseline CGRP outflow, but was able to inhibit both K(+)-stimulated [significant inhibition from 1 µM onward and maximal (-37%) decrease at 100 µM], and capsaicin-stimulated release [significant effect from 1 µM and maximal (-31%) decrease at 100 µM]. Likewise, tapentadol had no effect on baseline CGRP release up to 100 µM, but decreased secretion stimulated by 56 mM KCl or capsaicin, with significant effects from 0.1 and 1 µM respectively; maximal inhibition over 56 mM KCl and capsaicin stimuli was -29% and -31%, respectively. Naloxone antagonized the effect of morphine, but not those of reboxetine and tapentadol, on K(+)-stimulated CGRP secretion. In conclusion the present study provides consistent pharmacological evidence that tapentadol acts as a noradrenaline reuptake inhibitor agent in this experimental model.

Correlation between algogenic effects of calcitonin-gene-related peptide (CGRP) and activation of trigeminal vascular system, in an in vivo experimental model of nitroglycerin-induced sensitization.

The neural mechanism(s) underlying migraine remain poorly defined at present; preclinical and clinical studies show an involvement of CGRP in this disorder. However current evidence pointed out that CGRP does not exert an algogenic action per se, but it is able to mediate migraine pain only if the trigeminal-vascular system is sensitized. The present study was addressed to investigate CGRP-evoked behavior in nitric oxide (NO) sensitized rats, using an experimental model of nitroglycerin induced sensitization of trigeminal system, looking at neuropeptide release from different cerebral areas after the intra-peritoneal (i.p.) administration of NO-donors. CGRP injected into the rat whisker pad did not induce significant changes in face rubbing behavior compared to controls. On the contrary, CGRP injected in animals pre-treated with 10mg/kg nitroglycerin significantly increased the time spent in face rubbing. Nitroglycerin pre-treated animals did not show any rubbing behavior after locally injected saline. Furthermore, the i.p. treatment with nitroglycerin produced an increase of CGRP levels in brainstem and trigeminal ganglia, but not in the hypothalamus and hippocampus. The absolute amounts of CGRP produced in the brainstem were lower compared to those in the trigeminal ganglion; however, after nitroglycerin stimulation the percentage increase was higher in the brainstem. In conclusion, findings presented in this study suggest that CGRP induces a painful behavior in rats only after sensitization of trigeminal system; thus supporting the concept that a genetic as well as acquired predisposition to trigemino- vascular activation represents the neurobiological basis of CGRP nociceptive effects in migraineurs.

Evaluation of efficacy, pharmacokinetics and tolerability of peptidomimetic aspartic proteinase inhibitors as cream formulation in experimental vaginal candidiasis.

OBJECTIVES: It has been previously shown that the treatment with the two protease inhibitors APG12 and APG19 confers protection in a rat model of mucosal candidiasis; in this study, we examined whether these peptidomimetic inhibitors are also effective as a cream formulation in reducing Candida albicans vaginal infection. METHODS: These efficacy studies were performed in a rat model of estrogen-dependent rat vaginitis by C. albicans on both azole-susceptible and azole-resistant C. albicans, and on both caspofungin-susceptible and caspofungin-resistant C. albicans strains. In vivo studies were also conducted in female albino rats and rabbits to obtain information about the safety, local tolerability and principal pharmacokinetics parameters of the two compounds. KEY FINDINGS AND CONCLUSIONS: Both hit compounds showed remarkable results within the 48-h range as effective inhibitors of the infection, particularly causing rapid decay of vaginal C. albicans burden. Importantly, the two compounds showed marked acceleration of fungus clearance in the rats challenged with the fluconazole-resistant as well as with the capsofungin-resistant strain of C. albicans. Both compounds showed fast elimination rates when given by the intravenous route, and poor systemic absorption after intravaginal cream administration. Test drugs were also well tolerated in 7-day local tolerability experiments in the rabbit.

Pharmacokinetic profile of Oncofid-S after intraperitoneal and intravenous administration in the rat.

OBJECTIVES: Oncofid-S is a bio-conjugate molecule obtained from the binding of campthotecin, SN-38, to hyaluronic acid. In view of a possible clinical development for loco-regional treatment of peritoneal carcinomatosis, this study aimed to establish the pharmacokinetic profile of Oncofid-S after single intraperitoneal or intravenous administration in the rat. METHODS: Single-dose intraperitoneal or intravenous administrations of Oncofid-S were performed. Groups of six rats were sacrificed at various times (up to 24 and 72 h in i.p. and i.v. study, respectively) after drug injection. Trunk blood, livers and spleens were collected for subsequent analysis. Total SN-38 was assayed by HPLC. KEY FINDINGS: We found that Oncofid-S was poorly absorbed after intraperitoneal injection, the estimated AUC0­72 being less than 2%. The drug was distributed in liver,but not spleen, and was eliminated with a terminal half-life of 16 h. After intravenous dosing, Oncofid-S was found in liver as well as in spleen. CONCLUSIONS: Here we have demonstrated that Oncofid-S administered intraperitoneally in the rat was poorly absorbed into the systemic circulation, even after the administration of an extremely high dose. This finding reinforces the rationale for developing Oncofid-S in the loco-regional intraperitoneal treatment of peritoneal carcinomatosis in man.

Cortistatin modulates the expression and release of corticotrophin releasing hormone in rat brain. Comparison with somatostatin and octreotide.

Cortistatin (CST) is an endogenous neuropeptide characterized by remarkable structural and functional resemblance to somatostatin (SST), both peptides sharing the ability to bind and activate all five SST receptor subtypes. Evidence is also available showing that CST exerts biological activities independently from SST, perhaps via the activation of specific receptors that remain to be fully characterized at present. Here we have investigated the effects of CST on the gene expression and release of corticotrophin releasing hormone (CRH) from rat hypothalamic and hippocampal explants; moreover, we compared the effects of CST with those of SST and octreotide (OCT) in these models. We found that: (i) CST inhibits the expression and release of CRH from rat hypothalamic and hippocampal explants under basal conditions as well as after CRH stimulation by well known secretagogues; (ii) SST does not modify basal CRH secretion from the hypothalamus or the hippocampus, while it is able to reduce KCl-stimulated CRH release from both brain areas; (iii) OCT inhibits both basal and KCl-induced CRH secretion from rat hypothalamic explants, while it has no effect on CRH release from the hippocampus, either under basal conditions or after stimulation by high K(+) concentrations; (iv) at variance with CST; SST and OCT have not effect whatsoever on veratridine-induced CRH release from the hypothalamus. In conclusion the present findings provide in vitro evidence in support of the hypothesis that CST plays a role in the regulation of endocrine adaptive responses to stress.

Flupirtine inhibits calcitonin-gene related peptide release from rat brainstem in vitro.

We have previously shown that the nonopioid analgesic flupirtine possesses analgesic activity in the orofacial formalin test in vivo in the rat. However, this paradigm does not allow to distinguish between central and peripheral site of action of the drug. In this study we used a recently characterized in vitro model, consisting in acute rat brainstem explants, to investigate whether flupirtine analgesia may be, at least in part, attributed to interference with neurotransmission between the first and the second order neurons of the trigeminal system, occurring within the brainstem. We used acute rat brainstem explants; CGRP released into the incubation medium was taken as a marker of CGRP release from central terminals of trigeminal ganglion afferent neurons within the brainstem. CGRP levels were measured by radioimmunoassay under basal conditions or in the presence of flupirtine, alone or with putative antagonist XE-991. We found that flupirtine inhibits in a concentration-dependent manner both basal and capsaicin-stimulated CGRP release from rat brainstem. This effect is mimicked by the flupirtine analogue retigabine, and is counteracted by the Kv7 blocker XE-991. These findings provide in vitro evidence that the analgesic activity of flupirtine may be related to interference with pain neurotransmission at the brainstem level. Pharmacological data suggests that such effect is related to opening of Kv7 channels on first-order neuronal nerve ending, and the subsequent inhibition of neurotransmitter release, since the effect is mimicked by the Kv7 opener retigabine and is counteracted by the Kv7 blocker XE-991.