The synthetic peptide PnPP-19 induces peripheral antinociception via activation of NO/cGMP/KATP pathway: Role of eNOS and nNOS

BACKGROUND

and purpose: The peptide PnPP-19, derived from the spider toxin PnTx2-6 (renamed as δ-CNTX-Pn1c), potentiates erectile function by activating the nitrergic system. Since NO has been studied as an antinociceptive molecule and PnPP-19 is known to induce peripheral antinociception, we intended to evaluate whether PnPP-19 could induce peripheral antinociception through activation of this pathway.

EXPERIMENTAL APPROACH

Nociceptive thresholds were measured by paw pressure test. PGE₂ (2 μg/paw) was administered intraplantarly together with PnPP-19 and inhibitors/blockers of NOS, guanylyl cyclase and K_ATP channels. The nitrite concentration was accessed by Griess test. The expression and phosphorylation of eNOS and nNOS were determined by western blot.

KEY RESULTS

PnPP-19 (5, 10 and 20 μg/paw) induced peripheral antinociception in rats. Administration of NOS inhibitor (L-NOarg), selective nNOS inhibitor (L-NPA), guanylyl cyclase inhibitor (ODQ) and the blocker of K_ATP (glibenclamide) partially inhibited the antinociceptive effect of PnPP-19 (10 μg/paw). Tissue nitrite concentration increased after PnPP-19 (10 μg/paw) administration. Expression of eNOS and nNOS remained the same in all tested groups, however the phosphorylation of nNOS Ser852 (inactivation site) increased and phosphorylation of eNOS Ser1177 (activation site) decreased after PGE₂ injection. Administration of PnPP-19 reverted this PGE₂-induced effect.

CONCLUSIONS AND IMPLICATIONS

The peripheral antinociceptive effect induced by PnPP-19 is resulting from activation of NO-cGMP-K_ATP pathway. Activation of eNOS and nNOS might be required for such effect. Our results suggest PnPP-19 as a new drug candidate to treat pain and reinforce the importance of nNOS and eNOS activation, as well as endogenous NO release, for induction of peripheral antinociception.

PnPP-19, a spider toxin peptide, induces peripheral antinociception through opioid and cannabinoid receptors and inhibition of neutral endopeptidase

BACKGROUND AND PURPOSE

The synthetic peptide PnPP-19 has been studied as a new drug candidate to treat erectile dysfunction. However, PnTx2-6, the spider toxin from which the peptide was designed, induces hyperalgesia. Therefore, we intended to investigate the role of PnPP-19 in the nociceptive pathway.

EXPERIMENTAL APPROACH

Nociceptive thresholds were measured by paw pressure test. PnPP-19 was administered intraplantarly alone or with selective cannabinoid or opioid receptor antagonists. The hydrolysis of PnPP-19 by neutral endopeptidase (NEP) (EC 3.4.24.11), an enzyme that cleaves enkephalin, was monitored by HPLC and the cleavage sites were deduced by LC-MS. Inhibition by PnPP-19 and Leu-enkephalin of NEP enzyme activity was determined spectrofluorimetrically.

KEY RESULTS

PnPP-19 (5, 10 and 20 μg per paw) induced peripheral antinociception in rats. Specific antagonists of μ opioid receptors (clocinnamox), δ opioid receptors (naltrindole) and CB1 receptors (AM251) partly inhibited the antinociceptive effect of PnPP-19. Inhibition of fatty acid amide hydrolase by MAFP or of anandamide uptake by VDM11 enhanced PnPP-19-induced antinociception. NEP cleaved PnPP-19 only after a long incubation, and Ki values of 35.6 ± 1.4 and 14.6 ± 0.44 μmol·L(-1) were determined for PnPP-19 and Leu-enkephalin respectively as inhibitors of NEP activity.

CONCLUSIONS AND IMPLICATIONS

Antinociception induced by PnPP-19 appears to involve the inhibition of NEP and activation of CB1, μ and δ opioid receptors. Our data provide a greater understanding of the antinociceptive effects of PnPP-19. This peptide could be useful as a new antinociceptive drug candidate.

Crucial role of peripheral kappa-opioid receptors in a model of periodontal disease in rats

BACKGROUND AND OBJECTIVE

Periodontal disease is a chronic inflammatory condition of the tooth supporting tissues, the periodontium. Opioids have been shown to account for the relief of various chronic and acute inflammatory conditions. The aim of the present study was to investigate the participation of peripheral opioid receptors in development of periodontal disease.

MATERIAL AND METHODS

Morphine and selective agonists and antagonists of opioid receptors were used in an experimental model of ligature-induced periodontal disease in rats. To evaluate the development of disease, the loss of fiber attachment, alveolar bone and number of cells in periodontal tissues were assessed. Measurements of these indicators were obtained by morphometric analysis of histological sections of periodontal-diseased tissues stained with hematoxylin and eosin.

RESULTS

Local administration of either morphine or a selective kappa-opioid agonist for three consecutive days from the onset of periodontal disease reduced the loss of periodontal tissues, without changing the number of leukocytes in inflamed periodontium. Nor-binaltorphimine, a selective kappa-antagonist, reversed the beneficial effects of both morphine and the compound U-50,488 in this model. The use of either an agonist or an antagonist of delta-opioid receptors, however, did not affect disease progression.

CONCLUSION

Our results showed that the beneficial effect of opioids in periodontal disease depended mainly on the activation of specific kappa-opioid receptors located in the periphery. Activation of such receptors could be considered in the management of periodontal disease, since it would not present the classical central side-effects associated with opioid use.

Combined hamartoma of the retina and retinal pigment epithelium associated with neurofibromatosis type-1

BACKGROUND

Retinal tumors are occasionally seen in patients with neurofibromatosis type-1 (NF-1). These are usually astrocytic hamartomas or angiomas. Combined hamartoma of the retina and retinal pigment epithelium are tumors also described in NF-1, but this association has not been definitively established yet.

METHOD

We report on a child with NF-1, who presented a combined hamartoma of the retina and retinal pigment epithelium in both eyes.

RESULTS

The diagnosis of bilateral combined hamartoma of the retina and retinal pigment epithelium in our patient was performed on the basis of the ophthalmoscopic appearance of the lesions. NF-1 was diagnosed following the current international clinical criterion, supplemented by neuroimaging findings.

CONCLUSION

Despite the extreme rarity of this association, we believe that it is not coincidental, as the presence of a hamartomatous retinal lesion in a patient with a systemic hamartomatous neuroectodermic disease would be, at least, rational. Thus, NF-1 must be excluded in patients with combined hamartoma of the retina and retinal pigment epithelium.