Interaction With the Lipid Membrane Influences Fentanyl Pharmacology

Abstract

Overdose deaths from fentanyl have reached epidemic proportions in the USA and are increasing worldwide. Fentanyl is a potent opioid agonist that is less well reversed by naloxone than morphine. Due to fentanyl’s high lipophilicity and elongated structure we hypothesised that its unusual pharmacology may be explained by its interactions with the lipid membrane on route to binding to the µ-opioid receptor (MOPr). Through coarse-grained molecular dynamics simulations, electrophysiological recordings and cell signalling assays, we determined how fentanyl and morphine access the orthosteric pocket of MOPr. Morphine accesses MOPr via the aqueous pathway; first binding to an extracellular vestibule, then diffusing into the orthosteric pocket. In contrast, fentanyl may take a novel route; first partitioning into the membrane, before accessing the orthosteric site by diffusing through a ligand-induced gap between the transmembrane helices. In electrophysiological recordings fentanyl-induced currents returned after washout, suggesting fentanyl deposits in the lipid membrane. However, mutation of residues forming the potential MOPr transmembrane access site did not alter fentanyl’s pharmacological profile in vitro. A high local concentration of fentanyl in the lipid membrane, possibly in combination with a novel lipophilic binding route, may explain the high potency and lower susceptibility of fentanyl to reversal by naloxone.

Medium-Chain Lipid Conjugation Facilitates Cell-Permeability and Bioactivity

“…Lipid-conjugation can modulate membrane permeability but could also play key roles in targeting proteins that are embedded in or associated with biological membranes. − These include G protein-coupled receptors (GPCRs), receptor-linked enzymes, ion channels, transporters, pumps, and many transiently membrane-localized proteins (e.g., RAS, PI3K, PKC), which together represent the majority of known drug targets . In the case of transmembrane proteins, lipophilic drugs can bind a target directly via lateral diffusion from the intramembrane space of the lipid bilayer, as has been recently established for a number of endogenous and synthetic GPCR and ion channel ligands. ,,− …”

Coarse-Grained MD Simulations of Opioid Interactions with the μ-Opioid Receptor and the Surrounding Lipid Membrane

“…The protonated form of fentanyl, and the protonated and deprotonated forms of NFEPP [1], were sketched and parameterised using the CHARMM-GUI Ligand Reader & Modeler [31]. To parameterise these ligands in MARTINI, initially, 1 µs FA MD simulations of a single ligand in TIP3P water and 0.15 M NaCl were conducted using the CHARMM36m force field [10]. System pressure was maintained at 1 bar with the Parrinello-Rahman barostat using an isotropic scheme, where pressures along all three orthonormal directions were coupled together.…”

“…A recent study [10] examined the interaction of fentanyl with MOR embedded in a lipid bilayer using coarse-grained (CG) molecular dynamics (MD) simulations. With fully atomistic (FA) simulations, time scales of milliseconds or higher are usually required to observe rare events such as ligand binding.…”

“…CG force fields combine groups of atoms into interaction sites or beads and thereby diminish the computational costs compared with simulations with FA force fields [11]. Hence, CG MD simulations were employed to deal with such sampling issues by attaining significant computational acceleration relative to FA MD simulations [10,11].…”

“…It was earlier noted that fentanyl demonstrates high lipid solubility, and thus, has a tendency to partition into the lipid bilayer without passing through the entire membrane [10]. In the present work, we tweaked the ligand modelling as per the FA atom to CG bead mapping MARTINI 2.0 guidelines [12].…”