Robert Horvath

Characterization of [3H]naltrindole binding to delta opioid receptors in rat brain

[3H]Naltrindole binding characteristics were determined using homogenized rat brain tissue. Saturation binding studies at 25 degrees C measured an equilibrium dissociation constant (Kd) value of 37.0 +/- 3.0 pM and a receptor density (Bmax) value of 63.4 +/- 2.0 fmol/mg protein. Association binding studies showed that equilibrium was reached within 90 min at a radioligand concentration of 30 pM. Naltrindole, as well as the ligands selective for delta (delta) opioid receptors, such as pCI-DPDPE and Deltorphin II inhibited [3H]naltrindole binding with nanomolar IC50 values. Ligands selective for mu (mu) and kappa (kappa) opioid receptors were only effective in inhibiting [3H]naltrindole binding at micromolar concentrations. From these data, we conclude that [3H]naltrindole is a high affinity, selective radioligand for delta opioid receptors.

A new approach to enhance bioavailability of biologically active peptides: conjugation of a δ opioid agonist to β-cyclodextrin

Abstract The cyclic δ opioid against [p-I-Phe4]DPDPE, 1, was conjugated to mono-6-amino-permethyl-β-cyclodextrin at the C-terminus to improve the bioavailability of 1. In the rat brain building assay, the conjugate 8 showed an IC50 = 134 nM vs. a δ ligand and IC50 > 10 μM at the μ receptor, making it less potent and selective than 1. However, 8 shows antinociceptive properties (i.v.) in the mouse tail flick test and prolonged activity.

Topographical requirements for delta opioid ligands: The synthesis and biological properties of a cyclic analogue of deltorphin I

Abstract A cyclic constrained analogue of deltorphin, has been proposed on the basis of an energetically favored model of a delta-selective conformation for deltorphin. The biological properties of this synthetic analogue demonstrate that incorporation of a disulfide bridge into Deltorphin I does not affect its high affinity for delta opioid receptors. The analogue shows low receptor selectivity as a result of a large increase in its affinity for mu receptors when compared to the parent deltorphin.

Increased expression of opioid delta receptors by deoxy conformation heme proteins in NG108-15 cells

Adaptations to prolonged hypoxia include an increase in the expression of proteins that may facilitate survival. One mechanism by which hypoxia increases protein expression involves a change of heme proteins from oxygenated to deoxygenated conformations. In the present study, we tested the hypothesis that treatment of NG108-15 cells with metallic cations, which are known to induce a deoxygenated conformation of heme proteins, would increase delta opioid receptor (DOR) expression. Cells were treated with cobalt and nickel, which induce deoxygenated heme protein conformation, or zinc as a control for 48 h prior to quantifying DOR expression. Cobalt and nickel, but not zinc, significantly increased DOR expression. Heme synthesis inhibitors would block the synthesis of cobalt-substituted heme proteins which are locked in a deoxygenated conformation. The cobalt-induced increase in DOR expression was blocked by the heme synthesis inhibitor, 4,6-dioxoheptanoic acid. These experiments indicate that deoxygenated conformation heme proteins, which are thought to partially mimic hypoxia, increase DOR expression. The increase in DOR expression suggests that the DOR gene may be hypoxia-sensitive. Further, the increase in DOR expression suggests a potential adaptation strategy to hypoxia and may represent one of the first findings of physiological regulation of DOR expression.

Structure-activity relationships of analogues of higly potent opioid peptide, biphalin

For SAR study of biphalin ((Tyr-D-Ala-Gly-PheNH-) 2 ] we have synthesized several analogues with modifications of amino acid residues 3 position 3 and 4. The introduction of halogenated phenylalanine residues in position 4 increases affinity to delta receptors. Introducing basic aromatic amino acid residues in position 4 resulted in decrease in affinity to mu receptors, but preserve affinity to delta receptors

Topographic model of delta opioid selective ligands; DPLPE-deltorphin hybrid analogues

They are attempts to correlate the topography of the bioactive structures of DPDPE and deltorphins, two delta active peptide families. One of the methods utilized by us is the hybridization of necesary elements for bioactivity of these opioid peptide groups. We have found that a major point determining high activity of hybrid analogues is also the chirality of the amino acid residue in position 5. Replacing D-Pen(5) with L-Pen(5) resulted in dramatic increases in affinity for opioid delta receptors