Structure-Based SAR in the Design of Selective or Bifunctional Nociceptin (NOP) Receptor Agonists.

The nociceptin opioid receptor (NOP), the fourth member of the opioid receptor family, and its endogenous peptide ligand, nociceptin or orphanin FQ (N/OFQ), play a vital role in several central nervous system pathways regulating pain, reward, feeding, anxiety, motor control and learning/memory. Both selective NOP agonists as well as bifunctional agonists at the NOP and mu opioid receptor (MOP) have potential therapeutic applications in CNS disorders related to these processes. Using Surflex-Dock protocols, we conducted a computational structure-activity study of four scaffold classes of NOP ligands with varying NOP-MOP selectivity. By docking these compounds into the orthosteric binding sites within an active-state NOP homology model, and an active-state MOP crystal structure, the goal of this study was to use a structure-based drug design approach to modulate NOP affinity and NOP vs. MOP selectivity. We first docked four parent compounds (no side chain) to determine their binding interactions within the NOP and MOP binding pockets. Various polar sidechains were added to the heterocyclic A-pharmacophore to modulate NOP ligand affinity. The substitutions mainly contained a 1-2 carbon chain with a polar substituent such as an amine, alcohol, sulfamide, or guanidine. The SAR analysis is focused on the impact of structural changes in the sidechain, such as chain length, hydrogen bonding capability, and basic vs neutral functional groups on binding affinity and selectivity at both NOP and MOP receptors. This study highlights structural modifications that can be leveraged to rationally design both selective NOP and bifunctional NOP-MOP agonists with different ratios of functional efficacy.

Preferred supramolecular organization and dimer interfaces of opioid receptors from simulated self-association.

Substantial evidence in support of the formation of opioid receptor (OR) di-/oligomers suggests previously unknown mechanisms used by these proteins to exert their biological functions. In an attempt to guide experimental assessment of the identity of the minimal signaling unit for ORs, we conducted extensive coarse-grained (CG) molecular dynamics (MD) simulations of different combinations of the three major OR subtypes, i.e., µ-OR, δ-OR, and κ-OR, in an explicit lipid bilayer. Specifically, we ran multiple, independent MD simulations of each homomeric µ-OR/µ-OR, δ-OR/δ-OR, and κ-OR/κ-OR complex, as well as two of the most studied heteromeric complexes, i.e., δ-OR/µ-OR and δ-OR/κ-OR, to derive the preferred supramolecular organization and dimer interfaces of ORs in a cell membrane model. These simulations yielded over 250 microseconds of accumulated data, which correspond to approximately 1 millisecond of effective simulated dynamics according to established scaling factors of the CG model we employed. Analysis of these data indicates similar preferred supramolecular organization and dimer interfaces of ORs across the different receptor subtypes, but also important differences in the kinetics of receptor association at specific dimer interfaces. We also investigated the kinetic properties of interfacial lipids, and explored their possible role in modulating the rate of receptor association and in promoting the formation of filiform aggregates, thus supporting a distinctive role of the membrane in OR oligomerization and, possibly, signaling.

Immunoelectron microscopic localization of the opioid growth factor receptor (OGFr) and OGF in the cornea.

This study was conducted to determine the cellular and subcellular location(s) of the opioid growth factor receptor (OGFr), and the opioid growth factor (OGF), [Met(5)]-enkephalin, in the corneal epithelium. Laser scanning confocal microscopy analysis revealed that both OGFr and OGF were colocalized in the paranuclear cytoplasm and cell nuclei in basal, as well as suprabasal, cells of adult rat corneal epithelium. Using a postembedding immunogold procedure for immunoelectron microscopy that included embedding in Unicryl, both single- and double-face labeling studies were performed. Immunogold labeling of OGFr was detected on the outer nuclear envelope, in the paranuclear cytoplasm proximal to the nuclear envelope, perpendicular to the nuclear envelope in a putative nuclear pore complex, and within the nucleus adjacent to heterochromatin. Immunoreactivity for OGF was noted in locations similar to that for OGFr. In addition, aggregates of staining for OGF were found throughout the cytoplasm, including subjacent to the plasma membrane. Double labeling experiments revealed that complexes of OGF-OGFr were colocalized on the outer nuclear envelope, in the paranuclear cytoplasm, extending across the nuclear pore complex, and in the nucleus. Anti-OGFr IgG by itself, but not anti-OGF IgG alone, was associated with the outer nuclear envelope, and uncomplexed OGF immunoreactivity was detected in the cytoplasm in dual labeling experiments. These results based on complementary approaches of confocal microscopy and immunoelectron microscopy, suggest that: (i) OGFr resides on the outer nuclear envelope, (ii) OGF interacts with OGFr at the outer nuclear envelope, (iii) the colocalized receptor and peptide translocates between the cytoplasm and the nucleus at the nuclear pore, and (iv) signal transduction for modulation of cell proliferation necessitates a peptide-receptor complex that interfaces with chromatin in the nucleus.

[Electrophysiological aspects of the properties of potentially addictive drugs]. / Aspects électrophysiologiques des propriétés des drogues potentiellement addictives.

Considerable progress has been made during the last ten years in the study of the mechanism of action of addictive drugs. In this text, data concerning endogenous opioids and opiates are described. After a brief summary of the physiology of brain opioid systems, the various electrophysiological effects of these substances in the mammalian central nervous system are described. Finally, we summarize some experimental data allowing a better understanding of the development of tolerance and dependence to opiates in the rat.

The role of enkephalins in the pathogenesis of acute myocardial infarction.

Finding opiate receptors in the heart, definition of their role in contractility and blood flow regulation (2) as well as our previous data on the decrease of Leu-enkephalins contents in the blood of patients with myocardial infarction (5) are the theoretical prerequisites for the elucidation of the role of Leu-enkephalins in the pathogenesis of acute myocardial infarction.

Solubilization of adrenal medullary opioid receptors.

The opioid-binding activity of digitonin extract of bovine adrenal medullary membranes was studied. [3H]Diprenorphine binding to the solubilized material was rapid and saturable. The dissociation constant of [3H]diprenorphine binding was 0.76 nM. Several opioids displaced the [3H]diprenorphine binding. The complex of [3H]diprenorphine and the solubilized binding sites was eluted as a single peak on a Sepharose 6B column and showed an apparent molecular weight of 200,000. These results indicate that active opioid receptors are solubilized with digitonin from bovine adrenal medullary membranes.

Sodium ions increase the binding of the antagonist peptide ICI 174864 to the delta-opiate receptor.

The ability of N,N-diallyl-Tyr-Aib-Aib-Phe-Leu-OH (ICI 174864) to displace [3H]-[D-Ala2, D-Leu5]enkephalin bound to the delta-opioid site is increased 8-16 fold by addition of 25mM NaCl. A smaller shift is observed for the related N,N-diallyl-Tyr-Gly-Gly-psi-(CH2S)-Phe-Leu-OH (ICI 154129) but no significant shift is seen with either naloxone or diprenorphine. The results stress the importance of using the correct medium for binding assays, and suggest the changes in delta-receptor conformation induced by Na+ ions also increase peptide antagonist binding.

Specific binding and uptake of opioids in brain slices.

Studies on slices from whole rat brain indicate that the opioid peptide/receptor, but not the opiate drug/receptor, complex is internalized by metabolically-dependent processes. Opiate drugs displace 3H-etorphine from high affinity binding sites with potencies identical to those in brain homogenates. 3H-metenkephalin (ME) binds to a high affinity (IC50 10 nM) and a low affinity (micromolar) site. Opiate drugs and beta-endorphin compete at the high affinity but not at the low affinity binding site for ME. The biological relevance of the low affinity ME-binding site, which like the high affinity site is internalized, remains to be determined. The slice technique should be useful in the characterization of receptor dynamics that may be altered during opiate tolerance and dependence.