How Oliceridine (TRV-130) Binds and Stabilizes a μ‑Opioid Receptor Conformational State That Selectively Triggers G Protein Signaling Pathways

Substantial attention has recently been devoted to G protein-biased agonism of the μ-opioid receptor (MOR) as an ideal new mechanism for the design of analgesics devoid of serious side effects. However, designing opioids with appropriate efficacy and bias is challenging because it requires an understanding of the ligand binding process and of the allosteric modulation of the receptor. Here, we investigated these phenomena for TRV-130, a G protein-biased MOR small-molecule agonist that has been shown to exert analgesia with less respiratory depression and constipation than morphine and that is currently being evaluated in human clinical trials for acute pain management. Specifically, we carried out multimicrosecond, all-atom molecular dynamics (MD) simulations of the binding of this ligand to the activated MOR crystal structure. Analysis of >50 μs of these MD simulations provides insights into the energetically preferred binding pathway of TRV-130 and its stable pose at the orthosteric binding site of MOR. Information transfer from the TRV-130 binding pocket to the intracellular region of the receptor was also analyzed, and was compared to a similar analysis carried out on the receptor bound to the classical unbiased agonist morphine. Taken together, these studies lead to a series of testable hypotheses of ligand–receptor interactions that are expected to inform the structure-based design of improved opioid analgesics

Mechanistic Insights into the Allosteric Modulation of Opioid Receptors by Sodium Ions

The idea of sodium ions altering G-protein-coupled receptor (GPCR) ligand binding and signaling was first suggested for opioid receptors (ORs) in the 1970s and subsequently extended to other GPCRs. Recently published ultra-high-resolution crystal structures of GPCRs, including that of the δ-OR subtype, have started to shed light on the mechanism underlying sodium control in GPCR signaling by revealing details of the sodium binding site. Whether sodium accesses different receptor subtypes from the extra- or intracellular sides, following similar or different pathways, is still an open question. Earlier experiments in brain homogenates suggested a differential sodium regulation of ligand binding to the three major OR subtypes, in spite of their high degree of sequence similarity. Intrigued by this possibility, we explored the dynamic nature of sodium binding to δ-OR, μ-OR, and κ-OR by means of microsecond-scale, all-atom molecular dynamics (MD) simulations. Rapid sodium permeation was observed exclusively from the extracellular milieu, and following similar binding pathways in all three ligand-free OR systems, notwithstanding extra densities of sodium observed near nonconserved residues of κ-OR and δ-OR, but not in μ-OR. We speculate that these differences may be responsible for the differential increase in antagonist binding affinity of μ-OR by sodium resulting from specific ligand binding experiments in transfected cells. On the other hand, sodium reduced the level of binding of subtype-specific agonists to all OR subtypes. Additional biased and unbiased MD simulations were conducted using the δ-OR ultra-high-resolution crystal structure as a model system to provide a mechanistic explanation for this experimental observation

The Stress-Strain Data of the Hip Capsule Ligaments Are Gender and Side Independent Suggesting a Smaller Contribution to Passive Stiffness

<div><p>Background</p><p>The ligaments in coherence with the capsule of the hip joint are known to contribute to hip stability. Nevertheless, the contribution of the mechanical properties of the ligaments and gender- or side-specific differences are still not completely clear. To date, comparisons of the hip capsule ligaments to other tissues stabilizing the pelvis and hip joint, e.g. the iliotibial tract, were not performed.</p><p>Materials & Methods</p><p>Hip capsule ligaments were obtained from 17 human cadavers (9 females, 7 males, 13 left and 8 right sides, mean age 83.65 ± 10.54 years). 18 iliofemoral, 9 ischiofemoral and 17 pubofemoral ligaments were prepared. Uniaxial stress-strain properties were obtained from the load-deformation curves before the secant elastic modulus was computed. Strain, elastic modulus and cross sections were compared.</p><p>Results</p><p>Strain and elastic modulus revealed no significant differences between the iliofemoral (strain 129.8 ± 11.1%, elastic modulus 48.8 ± 21.4 N/mm²), ischiofemoral (strain 128.7 ± 13.7%, elastic modulus 37.5 ± 20.4 N/mm²) and pubofemoral (strain 133.2 ± 23.7%, elastic modulus 49.0 ± 32.1 N/mm²) ligaments. The iliofemoral ligament (53.5 ± 15.1 mm²) yielded a significantly higher cross section compared to the ischiofemoral (19.2 ± 13.2 mm²) and pubofemoral (15.2 ± 7.2 mm²) ligament. No significant gender- or side-specific differences were determined. A comparison to the published data on the iliotibial tract revealed lower elasticity and less variation in the ligaments of the hip joint.</p><p>Conclusion</p><p>Comparison of the mechanical data of the hip joint ligaments indicates that their role may likely exceed a function as a mechanical stabilizer. Uniaxial testing of interwoven collagen fibers might lead to a misinterpretation of the mechanical properties of the hip capsule ligaments in the given setup, concealing its uniaxial properties. This underlines the need for a polyaxial test setup using fresh and non-embalmed tissues.</p></div

The ligaments of the hip capsule revealed similar mechanical properties except of significant differences in the cross-sectional area.

<p>Hip capsules of 17 cadavers were used and dissected related to their anatomical origin. From these tissue samples 17 ilio-, 9 ischio- and 17 pubofemoral were investigated regarding their elastic modulus, strain and cross-sectional area. (A) The cross-section of the iliofemoral ligament (IL) is significant higher compared to ischio- (IS) or pubofemoral (PF) ligament (* indicates p<0.05 adjusted p values: IF vs. IS 0.0016, IF vs. PB <0.0001, IS vs. PB >0.999). (B) Analysis of strain values revealed non-significant differences between the hip capsule ligaments. (C) Elastic Modulus was generated related to the strain and stress values measured over ten cycles and present no significant differences between iliofemoral, ischiofemoral and pubofemoral ligament.</p

Investigation of side-specific differences of the hip capsule ligaments regarding strain, cross section and elastic modulus.

<p>No Statistical differences were determined (p>0.05).</p

The ligaments of the hip joint capsule have a lower elasticity and less variation compared to the iliotibial tract (* indicates p<0.0001).

<p>The ligaments of the hip joint capsule have a lower elasticity and less variation compared to the iliotibial tract (* indicates p<0.0001).</p

Baseline data of the hip joint capsule specimens.

<p>Mean values ± standard deviation are given in the captions for all tested tissue samples (∑).</p

Preparation and material testing setup for the investigation of the stress-strain properties of the ilio-, ischio- and pubofemoral ligaments.

<p>(A) Partially plastinated ligaments of hip capsule. (B) Attached partially-plastinated tissue sample to the testing machine (C) Example of a stress-strain curve. The elastic modulus was represented by means of a secant modulus. It was calculated as ratio of Δσ10% (last 10% of stress values) and according strain values Δε: elastic modulus = Δσ10% / Δε.</p

Synthetic Studies of Neoclerodane Diterpenes from Salvia divinorum: Identification of a Potent and Centrally Acting μ Opioid Analgesic with Reduced Abuse Liability

Opioids are widely used to treat millions suffering from pain, but their analgesic utility is limited due to associated side effects. Herein we report the development and evaluation of a chemical probe exhibiting analgesia and reduced opioid-induced side effects. This compound, kurkinorin (<b>5</b>), is a potent and selective μ-opioid receptor (MOR) agonist (EC₅₀ = 1.2 nM, >8000 μ/κ selectivity). <b>5</b> is a biased activator of MOR-induced G-protein signaling over β-arrestin-2 recruitment. Metadynamics simulations of <b>5</b>’s binding to a MOR crystal structure suggest energetically preferred binding modes that differ from crystallographic ligands. In vivo studies with <b>5</b> demonstrate centrally mediated antinociception, significantly reduced rewarding effects, tolerance, and sedation. We propose that this novel MOR agonist may represent a valuable tool in distinguishing the pathways involved in MOR-induced analgesia from its side effects