Activation of κ Opioid Receptors in Cutaneous Nerve Endings by Conorphin-1, a Novel Subtype-Selective Conopeptide, Does Not Mediate Peripheral Analgesia

Abstract

Selective activation of peripheral κ opioid receptors (KORs) may overcome the dose-limiting adverse effects of conventional opioid analgesics. We recently developed a vicinal disulfide-stabilized class of peptides with subnanomolar potency at the KOR. The aim of this study was to assess the analgesic effects of one of these peptides, named conorphin-1, in comparison with the prototypical KOR-selective small molecule agonist U-50488, in several rodent pain models. Surprisingly, neither conorphin-1 nor U-50488 were analgesic when delivered peripherally by intraplantar injection at local concentrations expected to fully activate the KOR at cutaneous nerve endings. While U-50488 was analgesic when delivered at high local concentrations, this effect could not be reversed by coadministration with the selective KOR antagonist ML190 or the nonselective opioid antagonist naloxone. Instead, U-50488 likely mediated its peripheral analgesic effect through nonselective inhibition of voltage-gated sodium channels, including peripheral sensory neuron isoforms NaV1.8 and NaV1.7. Our study suggests that targeting the KOR in peripheral sensory nerve endings innervating the skin is not an alternative analgesic approach.

Pharmacological characterisation of the highly NaV1.7 selective spider venom peptide Pn3a

“…Venom fractions were assessed for activity at rNa V 1.3 stably expressed in HEK293 cells using a FLIPR TETRA (Molecular Devices) membrane potential assay as previously described58. Active fractions were further fractionated to near-purity and peptide masses were determined using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) MS using a Model 4700 Proteomics Analyser (Applied Biosystems, Foster City, CA, USA) by spotting HPLC fractions with α-cyano-4-hydroxycinnamic acid (7 mg/mL in 50% ACN).…”

Methods Used to Evaluate Pain Behaviors in Rodents

“…This therefore provides measure of paw withdrawal threshold on a continual scale, as the force is applied continuously and not in steps. In addition, the experimental time is dramatically reduced, as few applications (usually 3–4) are needed to determine the paw withdrawal threshold (Deuis et al, 2014 , 2015 ). Despite these advantages of automation, experimenters still need to be experienced to distinguish true responses from “touch-on” responses and ambulation.…”

Conopeptide-Derived κ-Opioid Agonists (Conorphins): Potent, Selective, and Metabolic Stable Dynorphin A Mimetics with Antinociceptive Properties

“…The pharmacophore of this novel series of KOR agonist peptides 33 is represented using the most potent analogue 39 in Figure 5. The pharmacophore is defined by an aromatic N-terminal residue …”

“…29,32 Development of peripherally restricted selective ligands for the KOR is of considerable therapeutic interest as potential analgesic. 29,32,33 In general KOR agonists are of interest for a variety of other therapeutic applications. KOR agonists produce analgesia without MOR agonist related side effects; in addition to their anti-inflammatory 34 and neuroprotective effects, they suppress the rewarding effects of opiates and cocaine.…”