Characterization of the delta-opioid receptor found in SH-SY5Y neuroblastoma cells

Pregnane steroidogenesis is altered by HIV-1 Tat and morphine: Physiological allopregnanolone is protective against neurotoxic and psychomotor effects

Pregnane steroids, particularly allopregnanolone (AlloP), are neuroprotective in response to central insult. While unexplored in vivo, AlloP may confer protection against the neurological dysfunction associated with human immunodeficiency virus type 1 (HIV-1). The HIV-1 regulatory protein, trans-activator of transcription (Tat), is neurotoxic and its expression in mice increases anxiety-like behavior; an effect that can be ameliorated by progesterone, but not when 5α-reduction is blocked. Given that Tat's neurotoxic effects involve mitochondrial dysfunction and can be worsened with opioid exposure, we hypothesized that Tat and/or combined morphine would perturb steroidogenesis in mice, promoting neuronal death, and that exogenous AlloP would rescue these effects. Like other models of neural injury, conditionally inducing HIV-1 Tat in transgenic mice significantly increased the central synthesis of pregnenolone and progesterone's 5α-reduced metabolites, including AlloP, while decreasing central deoxycorticosterone (independent of changes in plasma). Morphine significantly increased brain and plasma concentrations of several steroids (including progesterone, deoxycorticosterone, corticosterone, and their metabolites) likely via activation of the hypothalamic-pituitary-adrenal stress axis. Tat, but not morphine, caused glucocorticoid resistance in primary splenocytes. In neurons, Tat depolarized mitochondrial membrane potential and increased cell death. Physiological concentrations of AlloP (0.1, 1, or 10 nM) reversed these effects. High-concentration AlloP (100 nM) was neurotoxic in combination with morphine. Tat induction in transgenic mice potentiated the psychomotor effects of acute morphine, while exogenous AlloP (1.0 mg/kg, but not 0.5 mg/kg) was ameliorative. Data demonstrate that steroidogenesis is altered by HIV-1 Tat or morphine and that physiological AlloP attenuates resulting neurotoxic and psychomotor effects.

The delta opioid receptor antagonist, SoRI-9409, decreases yohimbine stress-induced reinstatement of ethanol-seeking

A major problem in treating alcohol use disorders (AUDs) is the high rate of relapse due to stress and re-exposure to cues or an environment previously associated with alcohol use. Stressors can induce relapse to alcohol-seeking in humans or reinstatement in rodents. Delta opioid peptide receptors (DOP-Rs) play a role in cue-induced reinstatement of ethanol-seeking; however, their role in stress-induced reinstatement of ethanol-seeking is not known. The objective of this study was to determine the role of DOP-Rs in yohimbine-stress-induced reinstatement of ethanol-seeking. Male, Long-Evans rats were trained to self-administer 10% ethanol in daily 30-minute operant self-administration sessions using a FR3 schedule of reinforcement, followed by extinction training. Once extinction criteria were met, we examined the effects of the DOP-R antagonist, SoRI-9409 (0-5 mg/kg, i.p.) on yohimbine (2 mg/kg, i.p.) stress-induced reinstatement. Additionally, DOP-R-stimulated [(35) S]GTPγS binding was measured in brain membranes and plasma levels of corticosterone (CORT) were determined. Pre-treatment with SoRI-9409 decreased yohimbine stress-induced reinstatement of ethanol-seeking but did not affect yohimbine-induced increases in plasma CORT levels. Additionally, yohimbine increased DOP-R-stimulated (35) [S]GTPγS binding in brain membranes of ethanol-trained rats, an effect that was inhibited by SoRI-9409. This suggests that the DOP-R plays an important role in yohimbine-stress-induced reinstatement of ethanol-seeking behavior, and DOP-R antagonists may be promising candidates for further development as a treatment for AUDs.

Neuropeptide FF (NPFF) analogs functionally antagonize opioid activities in NPFF2 receptor-transfected SH-SY5Y neuroblastoma cells

To elucidate the mechanism of the cellular antiopioid activity of neuropeptide FF (NPFF), we have transfected the SH-SY5Y neuroblastoma cell line, which expresses mu-and delta-opioid receptors, with the human NPFF2receptor. The selected clone, SH2-D9, expressed high-affinity NPFF2 receptors in the same range order as mu- and delta-opioid receptors (100-300 fmol/mg of protein). The NPFF analog [D-Tyr1, (NMe)Phe3]NPFF (1DMe) did not modify the binding parameters of the mu- and delta-specific agonists [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin and deltorphin-I, respectively. 1DMe dose dependently inhibited 75 to 80% of the cAMP production stimulated by forskolin. Preincubation with 1DMe halved the maximal inhibition of N-type Ca2+ channels by opioid agonists. In the presence of carbachol, acting on muscarinic receptors to release Ca2+ from the intracellular stores, deltorphin-I and 1DMe enhanced this release. Preincubation with 1DMe reduced the maximal effect of deltorphin-I by 40%, demonstrating an antiopioid effect in this experimental model for the first time. By using peptides corresponding to the carboxyl terminus of the alphai1,2, alphai3, alphao, and alphas subunits of G proteins, which specifically uncouple receptors from G proteins, we demonstrated that mu-opioid and NPFF2 receptors couple to the four subunits assayed. The Ca2+ release from the intracellular stores by 1DMe resulted from the coupling of NPFF2 receptors with Galphao and Galphai1,2, whereas the coupling with Galphas reduced the antiopioid effect of 1DMe in the modulation of N-type channels. This SH2-D9 cell line now provides the opportunity to study the interaction between both receptors.

Tyr-c[D-Orn-Tyr(Bzl)-Pro-Gly]: a novel antiproliferative acting somatostatin receptor agonist with mu-opioid receptor-sensitizing properties

(1) Here, we introduce a beta-casomorphin-5-derived cyclic pentapeptide, cCD-2 (Tyr-cyclo[d-Orn-Tyr(Bzl)-Pro-Gly]), which inhibits the cell growth of a variety of human cancer cell lines. (2) This opioid-derived peptide possesses only low affinity for mu-receptors, but enhances the agonist binding to mu-receptors in vitro and potentiates the analgesic effect of morphin in vivo. The molecular mechanism of mu-receptor sensitization by cCD-2 is not yet known. (3) The antiproliferative effect of cCD-2 is independent of mu-, delta-, and kappa-receptors. (4) Using SH-SY5Y cells as model, we can demonstrate that cCD-2 specifically binds to somatostatin receptors and stimulates the activity of protein tyrosine phosphatases, which are early downstream targets of SST receptors. (5) In SH-SY5Y cells, cCD-2 specifically increases the activity of the cytosolic PTP SHP-2, stimulates the activity of mitogen-activated protein kinase (MAPK), and elevates the expression of the cyclin-dependent kinase inhibitor p21 (WAF1/Cip1), suggesting the involvement of SSTR1 receptor subtype in cCD-2 action in this cell type. (6) In COS-7 cells, for comparison, we found a stimulation of SHP-2 as well as SHP-1 in response to cCD-2. The activation of SHP-1, which is attributed to the SSTR2 receptor and negatively regulates the EGF receptor, corresponds with the ability of cCD-2 to inhibit the EGF-induced MAPK activation in COS-7 cells. (7) Our results show that in SH-SY5Y cells cCD-2 inhibits cell growth via the SSTR1 receptor-signalling pathway but may, in other cells, also use other SSTR subtypes and their signalling mechanisms. (8) cCD-2 represents a novel type of opioid-derived antiproliferative SST receptor agonist, which possesses low mu-receptor affinity but may induce mu-receptor sensitization and is structurally different from the hitherto known SST receptor agonists.

Several delta-opioid receptor ligands display no subtype selectivity to the human delta-opioid receptor

Pharmacological studies performed in vivo suggested that the delta-opioid receptor could exist as two distinct subtypes, delta(1) and delta(2), while in vitro studies are inconclusive. Therefore, we measured the binding and functional selectivity of several putative delta(1)- and delta(2)-opioid receptor-selective compounds in membranes from Chinese hamster ovary cells stably expressing the human delta-opioid receptor. The compounds characterized were the agonists [D-Pen(2),D-Pen(5)]enkephalin (DPDPE, delta(1)) and deltorphin II (delta(2)), and the antagonists 7-benzylidenenaltrexone (BNTX, delta(1)), naltriben (delta(2)), naltrindole 5'-isothiocyanate (delta(2)), and naltrindole (delta(1) and delta(2)). In competition binding assays, all compounds tested showed no preference for the [3H]DPDPE, [3H]deltorphin II, or [3H]naltrindole binding sites. BNTX also showed no selectivity for the delta-opioid receptor over the mu-opioid receptor. In functional assays, the stimulation of [35S]GTPgammaS binding induced by either DPDPE or deltorphin II was potently inhibited by both delta(1)- and delta(2)-opioid receptor-selective antagonists. Together, these results indicate that these compounds are not selective for either the delta(1)- or delta(2)-opioid receptor binding sites in binding or functional assays.

Pharmacological delta1- and delta2-opioid receptor subtypes in the human neuroblastoma cell line SK-N-BE: no evidence for distinct molecular entities

The two pharmacological delta-opioid receptor subtypes, delta1 and delta2, have been defined on the basis of pharmacological tools but remain to be characterized at the molecular level, since only a single cDNA has been cloned. The present study aimed to investigate the pharmacological properties of delta1- and delta2-opioid subtypes expressed in the human neuroblastoma cell line SK-N-BE and to characterize their putative corresponding mRNAs. Binding experiments using "selective" delta1- and delta2-opioid agonists and antagonists revealed the presence of two binding sites, demonstrating the presence of these delta1-opioid subtypes as they were previously described. The activation of these pharmacological subtypes by the selective agonists induced the incorporation of [alpha-(32)P]azidoanilide-GTP into Galpha(i2)/Galpha(0) subunits with the same efficiency and potency and inhibited adenosine 3', 5'-cyclic monophosphate (cAMP) accumulation with similar efficiency, while their sustained activation for 15 min induced a cross-desensitization. The "selective" delta1 and delta2 antagonists, 7-benzylidenenaltrexone and naltrindole benzofuran, respectively, were found to be as potent in blocking the inhibition of cAMP accumulation induced by both [D-Pen(2,5)]enkephalin and Tyr-D-Ala-Phe-Asp-Val-Val-Gly-NH(2). The possibility that delta-opioid subtypes could arise from alternative splicing was ruled out by reverse transcription-polymerase chain reaction (RT-PCR) experiments and the sequencing of PCR products, which revealed the presence of a single transcript encoding for the delta-opioid receptor. Different possibilities which could account for the delta-opioid receptor heterogeneity observed in the SN-N-BE cell line are discussed.

delta opioid receptor modulation of several voltage-dependent Ca(2+) currents in rat sensory neurons

Endogenous enkephalins and delta opiates affect sensory function and pain sensation by inhibiting synaptic transmission in sensory circuits via delta opioid receptors (DORs). DORs have long been suspected of mediating these effects by modulating voltage-dependent Ca(2+) entry in primary sensory neurons. However, not only has this hypothesis never been validated in these cells, but in fact several previous studies have only turned up negative results. By using whole-cell current recordings, we show that the delta enkephalin analog [D-Ala(2), D-Leu(5)]-enkephalin (DADLE) inhibits, via DORs, L-, N-, P-, and Q-high voltage-activated Ca(2+) channel currents in cultured rat dorsal root ganglion (DRG) neurons. The percentage of responding cells was remarkably high (75%) within a novel subpopulation of substance P-containing neurons compared with the other cells (18-35%). DADLE (1 microM) inhibited 32% of the total barium current through calcium channels (I(Ba)). A delta (naltrindole, 1 microM), but not a mu (beta-funaltrexamine, 5 microM), antagonist prevented the DADLE response, whereas a DOR-2 subtype (deltorphin-II, 100 nM), but not a DOR-1 (DPDPE, 1 microM), agonist mimicked the response. L-, N-, P-, and Q-type currents contributed, on average, 18, 48, 14, and 16% to the total I(Ba) and 19, 50, 26, and 20% to the DADLE-sensitive current, respectively. The drug-insensitive R-type current component was not affected by the agonist. This work represents the first demonstration that DORs modulate Ca(2+) entry in sensory neurons and suggests that delta opioids could affect diverse Ca(2+)-dependent processes linked to Ca(2+) influx through different high-voltage-activated channel types.