A role for heterodimerization of μ and δ opiate receptors in enhancing morphine analgesia

Abstract

Opiates such as morphine are the choice analgesic in the treatment of chronic pain. However their long-term use is limited because of the development of tolerance and dependence. Due to its importance in therapy, different strategies have been considered for making opiates such as morphine more effective, while curbing its liability to be abused. One such strategy has been to use a combination of drugs to improve the effectiveness of morphine. In particular, ␦ opioid receptor ligands have been useful in enhancing morphine's potency. The underlying molecular basis for these observations is not understood. We propose the modulation of receptor function by physical association between and ␦ opioid receptors as a potential mechanism. In support of this hypothesis, we show that -␦ interacting complexes exist in live cells and native membranes and that the occupancy of ␦ receptors (by antagonists) is sufficient to enhance opioid receptor binding and signaling activity. Furthermore, ␦ receptor antagonists enhance morphine-mediated intrathecal analgesia. Thus, heterodimeric associations between -␦ opioid receptors can be used as a model for the development of novel combination therapies for the treatment of chronic pain and other pathologies. Opioid receptors belong to the rhodopsin family of G proteincoupled receptors (GPCRs). Like many GPCRs, these receptors were thought to function as single units. This notion has been revised in recent years by a number of studies showing that GPCRs associate with each other to form dimers and͞or oligomers (1-3). Of particular significance are the studies with rhodopsin, a prototypical member of the GPCR family, where infrared-laser atomic-force microscopy of native mouse disk membranes showed the receptors to be arranged in crystalline arrays of dimeric units (4, 5). Also, data from x-ray crystallographic studies with rhodopsin (6, 7) and the N terminus of metabotropic glutamate receptors (8), support the notion that dimerization is an integral feature of these receptors and could play a key role in modulating their function.The three types of opioid receptors (, ␦, and ) have been shown to associate with each other in a homotypic or heterotypic fashion when expressed in heterologous cells (9-11). Furthermore, heterotypic interactions appear to alter the ligand-binding and signaling properties of these receptors (12). However, until now, it was not clear whether these interactions occurred in live cells and in endogenous tissues and whether they were physiologically relevant. In this study, we addressed these questions by using multiple approaches. We used the bioluminescence resonance energy transfer (BRET) assay to show that and ␦ receptors interact in living cells. In addition, we show that signaling by clinically relevant drugs, such as morphine, fentanyl, and methadone can be enhanced by ␦ receptor ligands. This potentiation of receptor signaling by the ␦ receptor antagonist is seen in membranes from WT mice and not in membranes from ␦ receptor lacking mice (␦ k͞o). Finally, w...

Knockout subtraction autoradiography: A novel ex vivo method to detect heteromers finds sparse KOP receptor/DOP receptor heterodimerization in the brain

“…Western blotting have been developed to investigate the existence of heterodimer/heteroligomers in vitro (Gomes et al, 2004;Gomes et al, 2000;Harrison and van der Graaf, 2006;Jordan and Devi, 1999), proving the existence of heteromers in physiological systems has been a more challenging task. Gupta et al (2010) KSA robust for opioid receptor systems, and this would be an important validation criteria for using the model for other G-protein coupled receptor systems.…”

“…Cell studies over more than a decade have suggested that mu opioid receptors (MOPr) and delta opioid receptors (DOPr), as well as kappa opioid receptors (KOPr) and DOPr may exist as heteromers (Gomes et al, 2004;Gomes et al, 2000;Jordan and Devi, 1999). In cell studies, co-expression of KOPr/DOPr heteromers (Jordan and Devi, 1999) or MOPr/DOPr heteromers (Gomes et al, 2004;Gomes et al, 2000) exhibited distinct ligand binding and signaling characteristics compared to cells individually expressing the monomeric form of these receptors, suggesting dimerisation between the different subtypes of opioid receptors could modulate receptor function. More recent studies have focused on conditions that might drive the process of opioid heterodimerisation and evidence has been provided that chronic morphine treatment increases the abundance of heteromers (Gupta et al, 2010), which might be of relevance to the treatment of addiction disorders (Stockton and Devi, 2012).…”

A gene-based method for detecting gene–gene co-association in a case–control association study

“…In the analysis of the heroin addiction data, CCU suggested that gene-gene co-association between OPRD1 and OPRM1 and that between OPRD1 and OPRK1 were significant (Table 4), as with LD-based statistic suggesting that SNP-SNP interaction in OPRD1 and OPRM1 was significant but not in OPRD1 and OPRK1. Gene-gene interaction between OPRD1 and OPRM1 had been detected in many studies [34][35][36][37][38][39] and for that between OPRD1 and OPRK1, Jordan and Devi 40 had provided biochemical and pharmacological evidence for the heterodimerization of the two fully functional opioid receptors, which suggests the result of CCU is credible. Analysis of the RA data showed that CCU is much more efficient than traditional logistic regression analysis (Table 5).…”

In Vivo Characterization of (−)(−)MCL-144 and (+)(−)MCL-193: Isomeric, Bivalent Ligands with Mu/Kappa Agonist Properties

“…Studies have demonstrated that opioid receptor dimerization alters signaling (5)(6)(7)(8), trafficking (5,9), and internalization (10). It also has been suggested that opioid receptor heterodimers could explain pharmacological subtypes (3), such as δ 1 (Deltorphin II) respectively, yet, these same subtypes have not been found utilizing cloning methods.…”