Functional Selectivity of Kappa Opioid Receptor Agonists in Peripheral Sensory Neurons

Abstract

Activation of kappa opioid receptors (KORs) expressed by peripheral sensory neurons that respond to noxious stimuli (nociceptors) can reduce neurotransmission of pain stimuli from the periphery to the central nervous system. We have previously shown that the antinociception dose-response curve for peripherally restricted doses of the KOR agonist (-)-(trans)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]benzeneacetamide (U50488) has an inverted U shape. Here, we found that the downward phase of the U50488 dose-response curve was blocked by an inhibitor of extracellular signal-regulated kinase (ERK) activation U0126. Local administration of the selective KOR agonist salvinorin A (Sal-A), also resulted in an inverted U-shaped curve; however, the downward phase was insensitive to U0126. By contrast, inhibition of c-Jun N-terminal kinase (JNK) partially blocked the downward phase of the doseresponse curve to Sal-A, suggesting a role for JNK. In cultures of peripheral sensory neurons, U50488 and Sal-A inhibited adenylyl cyclase activity with similar efficacies; however, their ability to activate ERK and JNK differed. Whereas U50488 activated ERK but not JNK, Sal-A activated JNK but not ERK. Moreover, although both U50488 and Sal-A produced homologous desensitization, desensitization to U50488 was blocked by inhibition of ERK activation, whereas desensitization to Sal-A was blocked by inhibition of JNK. Substitution of an ethoxymethyl ether for the C2 position acetyl group of Sal-A reduced stimulation of JNK, prevented desensitization by ethoxymethyl ether for the C2 position acetyl group of Sal-A, and resulted in a monotonic antinociception dose-response curve. Collectively, these data demonstrate the functional selectivity of KOR ligands for signaling in peripheral sensory neurons, which results in differential effects on behavioral responses in vivo.

Long-Term Reduction of Kappa Opioid Receptor Function by the Biased Ligand, Norbinaltorphimine, Requires c-Jun N-Terminal Kinase Activity and New Protein Synthesis in Peripheral Sensory Neurons

“…After baseline PWL was determined, animals were pretreated with BK (25 mg) via intraplantar (i.pl.) injection to induce KOR functional competence (Rowan et al, 2009;Berg et al, 2011Berg et al, , 2012Jamshidi et al, 2015;Sullivan et al, 2015). To assess KOR-mediated antinociception, rats received coinjections (i.pl.)…”

“…Opioid receptor-mediated inhibition of adenylyl cyclase activity was determined by measuring the amount of cAMP accumulated (15 minutes) in the presence of the phosphodiesterase inhibitor, rolipram, and PGE 2 (1 mM) with or without the indicated opioid receptor ligands, as described previously (Patwardhan et al, 2005(Patwardhan et al, , 2006Berg et al, 2007Berg et al, , 2011Jamshidi et al, 2015;Sullivan et al, 2015). For all experiments, cells were pretreated with BK (10 mM, 15 minutes, 37°C) to induce KOR functional competence (Berg et al, 2007(Berg et al, , 2012Jamshidi et al, 2015;Sullivan et al, 2015). To assess long-term effects of norBNI on KOR agonist-mediated inhibition of PGE 2 -stimulated cAMP accumulation, cells were treated with norBNI (3 nM) for 1 hour, washed three times with 500 ml/well serum-free media (a total wash period of 30 minutes), and then incubated further for 24 hours (37°C, 5% CO 2 ) before testing KOR agonist efficacy.…”

“…Opioid agonist-mediated changes in paw withdrawal latency (PWL) to a radiant heat stimulus were measured with a plantar test apparatus (Hargreaves et al, 1988), as described previously Jamshidi et al, 2015). The radiant heat stimulus was set to produce baseline PWL of 10 6 2 seconds with a cutoff time of 25 seconds to prevent tissue damage.…”

“…Primary cultures derived from rat trigeminal ganglion were prepared, as described previously (Patwardhan et al, 2005(Patwardhan et al, , 2006Berg et al, 2007Berg et al, , 2011Jamshidi et al, 2015;Sullivan et al, 2015), and maintained in culture for 5 days. For all experiments, cells were refed with serum-free Dulbecco's modified Eagle's medium without nerve growth factor on day 5 and used for experiments on the sixth day of culture (i.e., after a 24-hour serum-and nerve growth factor-free period).…”

“…KORs are also expressed by pain-sensing neurons (nociceptors) of the peripheral nervous system, where they function to inhibit transmission of pain stimuli to the CNS (Fields et al, 1980;Chen et al, 1997;Stein and Lang, 2009;Stein and Zollner, 2009;Berg et al, 2011;Jamshidi et al, 2015). It has been suggested that peripherally-restricted KOR agonists may provide for improved treatment of some forms of pain that would be devoid of CNS-mediated adverse effects (Kivell and Prisinzano, 2010;Vanderah, 2010;Berg et al, 2011;Vadivelu et al, 2011;Jamshidi et al, 2015), and some clinical studies have demonstrated efficacy of peripherally-restricted KOR agonists in a variety of pain conditions (Riviere, 2004;Arendt-Nielsen et al, 2009).…”