RESUMO
Diabetic neuropathic pain is one of the most common and debilitating complications of diabetes whose available treatments are poorly effective. Currently, omega-3 polyunsaturated fatty acids (ω-3 PUFAs) have been widely studied as a treatment of many types of pain, including inflammatory, spontaneous and neuropathic pain. However, little is known about the potential antinociceptive effect of ω-3 PUFAs (fish oil; FO or its major fatty acids, eicosapentaenoic -EPA and docosahexaenoic acids-DHA), in diabetic neuropathic pain as well as the mechanisms involved. To test, streptozotocin (STZ) -induced diabetic male Wistar rats were submitted to acute treatment with FO, EPA or DHA at the second and fourth weeks after diabetes induction (at the beginning and peak of development of mechanical allodynia, respectively). The cumulative effect of these compounds after a sub-chronic treatment for two weeks was also evaluated as well as the role of central µ-opioid receptors. It was observed that acute oral treatment with FO (0.5, 1 or 3â¯g/kg), EPA or DHA (100, 200 or 400â¯mg/kg) at the 2nd or at the 4th week after STZ significantly reverted the mechanical allodynia of diabetic animals, without altering the hyperglycemia or reduced weight gain. Moreover, the sub-chronic treatment with FO, EPA or DHA induced a sustained antinociceptive effect in diabetic animals. Intriguingly, the intrathecal treatment with a µ-opioid receptor antagonist (CTOP; 10⯵g/rat) completely prevented the acute effect of FO, EPA or DHA. Taken together, our data suggest that ω-3 PUFAs may represent a promising therapeutic outcome for diabetic neuropathic pain, probably acting through the opioid system activation.
Assuntos
Neuropatias Diabéticas/tratamento farmacológico , Ácidos Docosa-Hexaenoicos/farmacologia , Ácido Eicosapentaenoico/farmacologia , Analgésicos/farmacologia , Analgésicos Opioides/uso terapêutico , Animais , Diabetes Mellitus/metabolismo , Ácidos Graxos/metabolismo , Ácidos Graxos Ômega-3/administração & dosagem , Ácidos Graxos Ômega-3/metabolismo , Óleos de Peixe/administração & dosagem , Óleos de Peixe/farmacologia , Hiperalgesia/tratamento farmacológico , Masculino , Antagonistas de Entorpecentes/uso terapêutico , Neuralgia/tratamento farmacológico , Ratos , Ratos Wistar , Receptores Opioides mu/efeitos dos fármacos , Receptores Opioides mu/metabolismoRESUMO
(R/S)-Salsolinol is a full agonist of the µ-opioid receptor (µOR) Gi protein pathway via its (S)-enantiomer and is functionally selective as it does not promote ß-arrestin recruitment. Compared to (S)-salsolinol, the (R)-enantiomer is a less potent agonist of the Gi protein pathway. We have now studied the interactions of the salsolinol enantiomers docked in the binding pocket of the µOR to determine the molecular interactions that promote enantiomeric specificity and functional selectivity of (R/S)-salsolinol. Molecular dynamics simulations showed that (S)-salsolinol interacted with 8 of the 11 residues of the µOR binding site, enough to stabilize the molecule. (R)-Salsolinol showed higher mobility with fewer prevalent bonds. Hence, the methyl group bound to the (S)-stereogenic center promoted more favorable interactions in the µOR binding site than in the (R)-orientation. Because (S)-salsolinol is a small molecule (179.2 Da), it did not interact with residues implicated in the binding of larger morphinan agonists that are located toward the extracellular portion of the binding pocket: W3187.35 , I3227.39 , and Y3267.43 . Our results suggest that contact with residues which (S)-salsolinol interacts with are enough to elicit Gi protein activation, and possibly define a minimum set required by µOR ligands to promote activation of the Gi protein pathway.
Assuntos
Isoquinolinas/química , Simulação de Dinâmica Molecular , Receptores Opioides mu/agonistas , Sítios de Ligação , Subunidades alfa Gi-Go de Proteínas de Ligação ao GTP/metabolismo , Humanos , Receptores Opioides mu/química , Receptores Opioides mu/metabolismo , Transdução de Sinais/efeitos dos fármacosRESUMO
Numerous studies demonstrate the significant role of central ß-endorphin and its receptor, the µ-opioid receptor (MOR), in sodium intake regulation. The present study aimed to investigate the possible relationship between chronic high-NaCl intake and brain endogenous MOR functioning. We examined whether short-term (4 days) obligatory salt intake (2% NaCl solution) in rats induces changes in MOR mRNA expression, G-protein activity and MOR binding capacity in brain regions involved in salt intake regulation. Plasma osmolality and electrolyte concentrations after sodium overload and the initial and final body weight of the animals were also examined. After 4 days of obligatory hypertonic sodium chloride intake, there was clearly no difference in MOR mRNA expression and G-protein activity in the median preoptic nucleus (MnPO). In the brainstem, MOR binding capacity also remained unaltered, although the maximal efficacy of MOR G-protein significantly increased. Finally, no significant alterations were observed in plasma osmolality and electrolyte concentrations. Interestingly, animals that received sodium gained significantly less weight than control animals. In conclusion, we found no significant alterations in the MnPO and brainstem in the number of available cell surface MORs or de novo syntheses of MOR after hypertonic sodium intake. The increased MOR G-protein activity following acute sodium overconsumption may participate in the maintenance of normal blood pressure levels and/or in enhancing sodium taste aversion and sodium overload-induced anorexia.
Assuntos
Encéfalo/efeitos dos fármacos , Receptores Opioides mu/metabolismo , Transdução de Sinais/efeitos dos fármacos , Cloreto de Sódio/administração & dosagem , Animais , Encéfalo/metabolismo , Área Pré-Óptica/efeitos dos fármacos , Área Pré-Óptica/metabolismo , Ratos , Ratos Sprague-DawleyRESUMO
BACKGROUND: Some peptides purified from the venom of the spider Phoneutria nigriventer have been identified as potential sources of drugs for pain treatment. In this study, we characterized the antinociceptive effect of the peptide PnPP-19 on the central nervous system and investigated the possible involvement of opioid and cannabinoid systems in its action mechanism. METHODS: Nociceptive threshold to thermal stimulation was measured according to the tail-flick test in Swiss mice. All drugs were administered by the intracerebroventricular route. RESULTS: PnPP-19 induced central antinociception in mice in the doses of 0.5 and 1 µg. The non-selective opioid receptor antagonist naloxone (2.5 and 5 µg), µ-opioid receptor antagonist clocinnamox (2 and 4 µg), δ-opioid receptor antagonist naltrindole (6 and 12 µg) and CB1 receptor antagonist AM251 (2 and 4 µg) partially inhibited the antinociceptive effect of PnPP-19 (1 µg). Additionally, the anandamide amidase inhibitor MAFP (0.2 µg), the anandamide uptake inhibitor VDM11 (4 µg) and the aminopeptidase inhibitor bestatin (20 µg) significantly enhanced the antinociception induced by a low dose of PnPP-19 (0.5 µg). In contrast, the κ-opioid receptor antagonist nor-binaltorphimine (10 µg and 20 µg) and the CB2 receptor antagonist AM630 (2 and 4 µg) do not appear to be involved in this effect. CONCLUSIONS: PnPP-19-induced central antinociception involves the activation of CB1 cannabinoid, µ- and δ-opioid receptors. Mobilization of endogenous opioids and cannabinoids might be required for the activation of those receptors, since inhibitors of endogenous substances potentiate the effect of PnPP-19. Our results contribute to elucidating the action of the peptide PnPP-19 in the antinociceptive pathway.
RESUMO
Background: Some peptides purified from the venom of the spider Phoneutria nigriventer have been identified as potential sources of drugs for pain treatment. In this study, we characterized the antinociceptive effect of the peptide PnPP-19 on the central nervous system and investigated the possible involvement of opioid and cannabinoid systems in its action mechanism. Methods: Nociceptive threshold to thermal stimulation was measured according to the tail-flick test in Swiss mice. All drugs were administered by the intracerebroventricular route.Results: PnPP-19 induced central antinociception in mice in the doses of 0.5 and 1 µg. The non-selective opioid receptor antagonist naloxone (2.5 and 5 µg), µ-opioid receptor antagonist clocinnamox (2 and 4 µg), δ-opioid receptor antagonist naltrindole (6 and 12 µg) and CB1 receptor antagonist AM251 (2 and 4 µg) partially inhibited the antinociceptive effect of PnPP-19 (1 µg). Additionally, the anandamide amidase inhibitor MAFP (0.2 µg), the anandamide uptake inhibitor VDM11 (4 µg) and the aminopeptidase inhibitor bestatin (20 µg) significantly enhanced the antinociception induced by a low dose of PnPP-19 (0.5 µg). In contrast, the κ-opioid receptor antagonist nor-binaltorphimine (10 µg and 20 µg) and the CB2 receptor antagonist AM630 (2 and 4 µg) do not appear to be involved in this effect. Conclusions: PnPP-19-induced central antinociception involves the activation of CB1 cannabinoid, µ- and δ-opioid receptors. Mobilization of endogenous opioids and cannabinoids might be required for the activation of those receptors, since inhibitors of endogenous substances potentiate the effect of PnPP-19. Our results contribute to elucidating the action of the peptide PnPP-19 in the antinociceptive pathway.(AU)
Assuntos
Animais , Peptídeos , Aranhas , Canabinoides , Sistema Nervoso Central , Analgésicos Opioides , Receptor CB1 de Canabinoide , Receptor CB2 de CanabinoideRESUMO
Important inhibitory mechanisms for the control of water and sodium intake are present in the lateral parabrachial nucleus (LPBN). Opioid receptors are expressed by LPBN neurons and injections of ß-endorphin (nonspecific opioid receptor agonist) in this area induce 0.3M NaCl and water intake in satiated rats. In the present study, we investigated the effects of the injections of endomorphin-1 (µ opioid receptor agonist) alone or combined with the blockade of µ, κ or δ opioid receptors into the LPBN on 0.3M NaCl and water intake induced by subcutaneous injections of the diuretic furosemide (FURO) combined with low dose of the angiotensin converting enzyme inhibitor captopril (CAP). Male Holtzman rats with stainless steel cannulas implanted bilaterally in the LPBN were used. Bilateral injections of endomorphin-1 (0.1, 0.25, 0.5, 1.0, 2.0 and 4.0nmol/0.2µl) into the LPBN increased 0.3M NaCl and water intake induced by FURO+CAP. The previous blockade of µ opioid receptor with CTAP (1.0nmol/0.2µl) into the LPBN reduced the effect of endomorphin-1 on FURO+CAP-induced 0.3M NaCl. GNTI (κ opioid receptor antagonist; 2.0nmol/0.2µl) and naltrindole (δ opioid receptor antagonist; 2.0nmol/0.2µl) injected into the LPBN did not change the effects of endomorphin-1 on FURO+CAP-induced 0.3M NaCl. The results suggest that µ opioid receptors in the LPBN are involved in the control of sodium intake.
Assuntos
Regulação do Apetite/fisiologia , Ingestão de Líquidos/fisiologia , Núcleos Parabraquiais/metabolismo , Receptores Opioides mu/metabolismo , Sódio na Dieta , Analgésicos Opioides/farmacologia , Inibidores da Enzima Conversora de Angiotensina/farmacologia , Animais , Regulação do Apetite/efeitos dos fármacos , Diuréticos/farmacologia , Relação Dose-Resposta a Droga , Ingestão de Líquidos/efeitos dos fármacos , Água Potável , Masculino , Antagonistas de Entorpecentes/farmacologia , Oligopeptídeos/farmacologia , Núcleos Parabraquiais/efeitos dos fármacos , Ratos Sprague-Dawley , Receptores Opioides delta/antagonistas & inibidores , Receptores Opioides delta/metabolismo , Receptores Opioides kappa/antagonistas & inibidores , Receptores Opioides kappa/metabolismo , Receptores Opioides mu/agonistas , Receptores Opioides mu/antagonistas & inibidores , Cloreto de SódioRESUMO
A wealth of evidence indicates that the activation of 5-HT1A and 5-HT2A receptors in the dorsal periaqueductal grey matter (dPAG) inhibits escape, a panic-related defensive behaviour. Results that were previously obtained with the elevated T-maze test of anxiety/panic suggest that 5-HT1A and µ-opioid receptors in this midbrain area work together to regulate this response. To investigate the generality of this finding, we assessed whether the same cooperative mechanism is engaged when escape is evoked by a different aversive stimulus electrical stimulation of the dPAG. Administration of the µ-receptor blocker CTOP into the dPAG did not change the escape threshold, but microinjection of the µ-receptor agonist DAMGO (0.3 and 0.5 nmol) or the 5-HT1A receptor agonist 8-OHDPAT (1.6 nmol) increased this index, indicating a panicolytic-like effect. Pretreatment with CTOP antagonised the anti-escape effect of 8-OHDPAT. Additionally, combined administration of subeffective doses of DAMGO and 8-OHDPAT increased the escape threshold, indicating drug synergism. Therefore, regardless of the aversive nature of the stimulus, µ-opioid and 5-HT1A receptors cooperatively act to regulate escape behaviour. A better comprehension of this mechanism might allow for new therapeutic strategies for panic disorder.
Assuntos
Reação de Fuga/fisiologia , Pânico/fisiologia , Substância Cinzenta Periaquedutal/fisiologia , Receptor 5-HT1A de Serotonina/fisiologia , Receptores Opioides mu/fisiologia , 8-Hidroxi-2-(di-n-propilamino)tetralina/antagonistas & inibidores , 8-Hidroxi-2-(di-n-propilamino)tetralina/farmacologia , Animais , Estimulação Elétrica , Ala(2)-MePhe(4)-Gly(5)-Encefalina/farmacologia , Reação de Fuga/efeitos dos fármacos , Masculino , Microinjeções , Pânico/efeitos dos fármacos , Substância Cinzenta Periaquedutal/efeitos dos fármacos , Ratos , Receptor 5-HT1A de Serotonina/efeitos dos fármacos , Receptor 5-HT2A de Serotonina , Receptores Opioides mu/antagonistas & inibidores , Somatostatina/administração & dosagem , Somatostatina/análogos & derivados , Somatostatina/farmacologiaRESUMO
Previous results with the elevated T-maze (ETM) test indicate that the antipanic action of serotonin (5-HT) in the dorsal periaqueductal grey (dPAG) depends on the activation endogenous opioid peptides. The aim of the present work was to investigate the interaction between opioid- and serotonin-mediated neurotransmission in the modulation of defensive responses in rats submitted to the ETM. The obtained results showed that intra-dPAG administration of morphine significantly increased escape latency, a panicolytic-like effect that was blocked by pre-treatment with intra-dPAG injection of either naloxone or the 5-HT1A antagonist N-[2-[4-(2-methoxyphenyl)-1 piperazinyl] ethyl] -N- 2- pyridinyl-ciclohexanecarboxamide maleate (WAY-100635). In addition, previous administration of naloxone antagonized both the anti-escape and the anti-avoidance (anxiolytic-like) effect of the 5-HT1A agonist (±)-8-hydroxy-2-(di-n-propylamino)tetralin hydrobromide (8-OH-DPAT), but did not affect the anti-escape effect of the 5-HT2A agonist (±)-2,5-dimethoxy-4-iodoamphetamine hydrochloride (DOI). Moreover, the combination of sub-effective doses of locally administered 5-HT and morphine significantly impaired ETM escape performance. Finally, the µ-antagonist D-PHE-CYS-TYR-D-TRP-ORN-THR-PEN (CTOP) blocked the anti-avoidance as well as the anti-escape effect of 8-OHDPAT, and the association of sub-effective doses of the µ-opioid receptor agonist [D-Ala(2), N-Me-Phe(4), Gly(5)-ol]-enkephalin acetate salt (DAMGO) and of 8-OHDPAT had anti-escape and anti-avoidance effects in the ETM. These results suggest a synergic interaction between the 5-HT1A and the µ-opioid receptor at post-synaptic level on neurons of the dPAG that regulate proximal defense, theoretically related to panic attacks.