The Effect of Protein Kinase C and G Protein-Coupled Receptor Kinase Inhibition on Tolerance Induced by μ-Opioid Agonists of Different Efficacy

Abstract

Differences in the mechanisms underlying tolerance and -opioid receptor desensitization resulting from exposure to opioid agonists of different efficacy have been suggested previously. The objective of this study was to determine the effects of protein kinase C (PKC) and G protein-coupled receptor kinase (GRK) inhibition on antinociceptive tolerance in vivo to opioid agonists of different efficacy. A rapid (8-h) tolerance-induction model was used where each opioid was repeatedly administered to naive mice. Animals were then challenged with the opioid after injection of a kinase inhibitor to determine its effects on the level of tolerance. Tolerance to meperidine, morphine, or fentanyl was fully reversed by the PKC inhibitor 12-(2-cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo(2,3-a)pyrrolo (3,4-c) maleimide (Ro 32-0432) did not reverse the tolerance to meperidine, fentanyl, or morphine but did reverse the tolerance to DAMGO. To correlate GRK-dependent DAMGO-induced tolerance with -opioid receptor desensitization, we used in vitro whole-cell patch-clamp recording from mouse locus coeruleus neurons and observed that the GRK inhibitors reduced DAMGO-induced desensitization of -opioid receptors, whereas the PKC inhibitor had no effect. These results suggest that tolerance induced by low-and moderate-efficacy -opioid receptor agonists is dependent on PKC, whereas tolerance induced by the high-efficacy agonist DAMGO is dependent on GRK.Opioid analgesics are the most widely used drugs for the management of moderate to severe pain. One of the main drawbacks to this class of drugs is the development of tolerance during chronic use; that is, a decrease in the analgesic effect during prolonged use of the drug. The mechanisms of tolerance to any one opiate are multifaceted and not fully understood. We and others have proposed that -opioid receptor desensitization plays an important role in opioid tolerance (Bohn et al., 2000;Zuo, 2005;Bailey et al., 2006). -Opioid receptor desensitization can occur in at least two ways, through phosphorylation by G-protein coupled receptor kinase (GRK) and subsequent arrestin binding or by phosphorylation by second messenger kinases such as PKC (for review, see Bailey et al., 2006).Previous studies have suggested that the intrinsic efficacy of an opioid determines its ability to cause desensitization and that the mechanisms underlying such desensitization

Analgesic Tolerance to High-Efficacy Agonists But Not to Morphine Is Diminished in Phosphorylation-Deficient S375A μ-Opioid Receptor Knock-In Mice

“…The phenotype we observed in S375A knock-in mice resembles closely that reported for GRK3 knock-out mice, in which the development of tolerance to the high-efficacy agonist fentanyl is strongly reduced, whereas acute and chronic tolerance to morphine is retained (Terman et al, 2004). Similar, intracerebroventricular injection of a smallmolecule GRK2 inhibitor reversed tolerance to DAMGO but not to morphine (Hull et al, 2010). Conversely, mice lacking ␤-arrestin-2 show diminished antinociceptive tolerance to morphine only but not to high-efficacy agonists such as fentanyl or methadone (Bohn et al, 1999(Bohn et al, , 2000Dang et al, 2011;Raehal and Bohn, 2011).…”

“…Conversely, mice lacking ␤-arrestin-2 show diminished antinociceptive tolerance to morphine only but not to high-efficacy agonists such as fentanyl or methadone (Bohn et al, 1999(Bohn et al, , 2000Dang et al, 2011;Raehal and Bohn, 2011). Moreover, inhibition of PKC reversed tolerance to morphine but not to DAMGO (Bailey et al, 2006(Bailey et al, , 2009Hull et al, 2010).…”

Association of Mu-opioid and NMDA Receptors in the Periaqueductal Gray: What Does it Mean for Pain Control?

“…Similarly, PKC inhibition reverses the expression of acute tolerance to morphine. These results are consistent with prior data showing that antinociceptive tolerance to morphine is sensitive to PKC inhibition, but tolerance induced by other opioid agonists, such as DAMGO is not (Hull et al, 2011). Thus, it will be interesting to examine whether other opioid agonists disrupt the MOR/NR1 complex.…”

“…These results provide evidence that acute tolerance may be associated with activation of delayed nociceptive processes in the PAG, following opioid administration or stress. Interestingly, tolerance to clinically used opioids, such as morphine and fentanyl, are dependent on PKC mechanisms, but tolerance to other opioid agonists, such as DAMGO, are not affected by inhibition of PKC (Hull et al, 2011), suggesting that other opioid agonists may be more useful in neuropathic pain conditions, because they do not stimulate PKC and potentiate NMDA responses.…”

Differential Phosphorylation, Desensitization, and Internalization ofα1A−Adrenoceptors Activated by Norepinephrine and Oxymetazoline

“…Similar agonist-dependent recruitment of kinases is well described for CCR7 and m-opioid receptors; CCR7 receptors are phosphorylated by GRK3 and GRK6 on exposure to the endogenous chemokine CCL19 and undergo internalization, whereas receptors exposed to the chemokine CCL21 are phosphorylated only by GRK6 and this is not followed by internalization (Zidar et al, 2009). Also, m-opioid receptors activated by DAMGO are phosphorylated by GRK2 and undergo internalization, whereas PKC phosphorylates the receptors activated by morphine or fentanyl, which in turn are not internalized (Johnson et al, 2006;Hull et al, 2010). Such barcoding in receptor phosphorylation and the respective kinases involved have been elucidated for the m-opioid receptor (Doll et al, 2011(Doll et al, , 2012.…”