Tyr-W-MIF-1 Attenuates Down-Regulation of Opiate Receptors in SH-SY5Y Human Neuroblastoma Cells 1

ABSTRACT Down-regulation of opiate receptors is demonstrated more easily in vitro than in vivo. The possible role of endogenous opiate-modulating peptides in preventing such down-regulation was investigated by addition of Tyr-W-MIF-1 to an in vitro preparation, the human neuroblastoma cell line SH-SY5Y, in which down-regulation of opiate receptors has been demonstrated previously. Although both morphine and Met-enkephalin down-regulated mu and delta receptors after chronic (24 h) exposure in serum-free medium, Tyr-W-MIF-1, at doses of up to 100 M, did not affect receptor number when administered alone. This lack of effect could not be attributed to degradation of the peptide during chronic treatment because high-performance liquid chromatography showed that 79% of the peptide remained intact after a 24-h incubation. When coadministered with 3 M morphine, Tyr-W-MIF-1 dose-dependently attenuated morphine-induced down-regulation of both mu and delta receptors. Down-regulation of mu receptors by the selective agonist PL017 was also attenuated by Tyr-W-MIF-1, but downregulation of delta receptors by the selective agonist DPDPE was not. These studies indicate that endogenous opiate modulators may play a role in opiate tolerance at the level of receptor down-regulation

Dissociation of effects of LH-RH analogs on pituitary regulation and reproductive behavior

Analogs of LH-RH were studied for their effect on lordosis in ovariectomized rats primed with estrogen. Classified by their gonadotropin-releasing activity, representatives of three types of analogs were tested for facilitation of lordotic (L) responses of preselected females to mounting (M) by male studs. Positive responses (L/M>0.5) were found after SC administration of LH-RH peptides modified so as to be inhibitory, stimulatory, or inactive in releasing LH and FSH. The results further support the concept of a dissociation between the endocrine and extra-endocrine effects of peripherally injected hypothalamic peptides

MIF-1 Attenuates Apomorphine Stereotypies in Adult Rats After Neonatal 6-Hydroxydopamine

Since prolyl-leucyl-glycinamide (MIF-1) modifies the behavior of adult rats after treatment with neuroleptics, we examined whether MIF-1 would also modify adult behavior after treatment of neonatal rats with 6-hydroxydopamine (6-OHDA). Rats received 6-OHDA (100 μg i.c.v.) or diluent at 3 days after birth and either MIF-1 (2.0 mg/kg per day s.c. × 10 days) or diluent beginning at 28 or 29 days after birth. At 5 weeks, a low dose (0.1 mg/kg s.c.) of apomorphine increased the distance traveled, time in ambulation, number of stereotypic movements, and number of movements per time in stereotypy, but decreased the time in stereotypy in the 6-OHDA group. MIF-1 (× 7 or 8 days) showed a tendency to attenuate the increased number of movements and significantly (P \u3c 0.05) reduced all of the other effects of neonatal 6-OHDA. Behavior induced by higher doses of apomorphine in the 6-OHDA group (reduced licking and head nodding; increased paw treading, taffy pulling and self-biting) were not attenuated by MIF-1. At 38 or 39 days, total in vitro binding of [3H]SCH-23390 and [3H]spiroperidol to striatal homogenates was not altered in any of the groups. The findings demonstrate that specific early developmental alterations in apomorphine-induced behaviors can be modified by treatment of adult rats with MIF-1, even in the absence of overt changes in the binding of striatal dopamine D-1 and D-2 receptors

Novel Endomorphin Analogs Are More Potent and Longer-Lasting Analgesics in Neuropathic, Inflammatory, Postoperative, and Visceral Pain Relative to Morphine.

Activation of the mu-opioid receptor provides the gold standard for pain relief, but most opioids used clinically have adverse effects that have contributed to an epidemic of overdose deaths. We recently characterized mu-opioid receptor selective endomorphin (EM) analogs that provide potent antinociception with reduction or absence of a number of side effects of traditionally prescribed opioids including abuse liability, respiratory depression, motor impairment, tolerance, and inflammation. The current study explores the effectiveness of these EM analogs relative to morphine in four major pain models by intrathecal as well as intravenous administration in male Sprague Dawley rats and subcutaneous administration in male CD-1 mice. In the spared nerve injury model of neuropathic pain, mechanical allodynia and mechanical hyperalgesia were assessed with von Frey and Randall-Selitto tests, respectively. In the paw incision model of postoperative pain, von Frey testing was used to assess mechanical allodynia and thermal hyperalgesia was evaluated with Hargreaves testing. In the Complete Freund\u27s Adjuvant model of inflammatory pain, thermal hyperalgesia was assessed using Hargreaves testing. In CD-1 mice, visceral pain was assessed with the acetic acid writhing test. In all cases, EM analogs had equal or greater potency and longer duration of action relative to morphine. The data suggest that EM analogs, particularly analog 4 (ZH853), could provide effective therapy for a diverse spectrum of pain conditions with low risk of adverse side effects compared with currently used opioids such as morphine. PERSPECTIVE: Novel EM analogs show equal or greater potency and effectiveness relative to morphine in multiple pain models. Together with substantially reduced side effects, including abuse liability, the compounds show promise for addressing the critical need for effective pain relief as well as reducing the opioid overdose epidemic. J Pain 2017 Dec; 18(12):1526-1541

Naloxone-like actions of MIF-1 do not require the presence of the pituitary

The actions of peripherally administered MIF-1 (Pro-Leu-Gly-NH 2) and naloxone in blocking the effects of morphine in the tail-flick test were measured across a wide range of five doses in hypophysectomized and intact mice. The presence of the pituitary gland failed to influence the response to MIF-1 or naloxone. Both hypophysectomized and intact mice were significantly affected by these two compounds at doses of 0.01, 0.1, 1.0, and 10.0 mg/kg IP. The greatest effect of MIF-1 occurred at 100 mg/kg, but naloxone was lethal at this dose. Preliminary experiments with other tests showed that at 10 mg/kg, naloxone, but not MIF-1, was effective in preventing the Straub-tail reflex and in precipitating withdrawal-jumping in mice implanted with morphine pellets. Only minimal activity was shown by MIF-1 in preventing blockade of electrically induced contractions of the guinea pig ileum by morphine. Neither compound was active in the frog-righting test. In summary, the results emphasize the differential actions of MIF-1 as an opiate antagonist and demonstrate that the pituitary is not required for their mediation

Endomorphins inhibit high-threshold Ca2+ channel currents in rodent NG108-15 cells overexpressing μ-opioid receptors

Extracellular application of the novel brain peptides endomorphin 1 (EM1) and endomorphin 2 (EM2) inhibited high-threshold Ca2+ channel currents in NGMO-251 cells, a daughter clone of NG108-15 mouse neuroblastoma × rat glioma hybrid cells, in which μ-opioid receptors are overexpressed.In contrast, EM1 and EM2 did not induce this inhibition in the parental NG108-15 cells that predominantly express endogenous δ-receptors.The IC50 for EM1 and EM2 was 7.7 and 23.1 nm, respectively.EM-induced Ca2+ channel current inhibition was blocked by treatment or pretreatment of the cells with 100 μmN-methylmaleimide or 100 ng ml−1 pertussis toxin.These results show that a decrease in conductance of Ca2+ channels results following interaction of EMs with cloned μ-receptors, which couple via Gi/Go-type G proteins, and that EMs fulfill one of the necessary synaptic conditions for them to be identified as neurotransmitters