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The effect of opioids on the signalling of the µ-opioid receptor and some variants

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posted on 28.03.2022, 01:35 authored by Preeti Manandhar
Opioid analgesics are the most effective medications used for the treatment of moderate to severe nociceptive pain. However, their clinical utility is limited by their adverse effects and prevalence of tolerance and dependence on chronic use. Moreover, the degree of pain relief varies in individuals and studies suggest genetic variation as one of the cause. In this project, we focus on comparing the effect of pethidine, O-desmethyl tramadol and TRV 130 on signalling of µ-opioid receptor (MOR) and some common polymorphisms of MOR (A118G and C17T). In addition, we sought to compare the efficacy of these opioids with enkephalin analog, DAMGO and commonly studied opioid-morphine in K channel activation assay in AtT20 transfected cells. FLIPR membrane potential assay is used to determine the change in membrane potential caused by different opioids. The highest concentration tested for pethidine and O-desmethyl tramadol showed a reduced inhibition of forskolin response in CHO cells expressing C17T as compared to WT (P<0.05) whereas no significant difference was observed in A118G. TRV 130 showed a significantly reduced inhibition of forskolin response (P<0.05) in the CHO cells expressing A118G and C17T than in WT. Pethidine, )-desmethyl tramadol and TRV 130 activated K channel in AtT20 hMOR cells with pEC50 of 5.7 ± 0.1, 6.3 ± 0.1, 8.1 ± 0.1 respectively, as compared to morphine (7.1 ± 0.1) and DAMGO (8.3 ± 0.1). Depleting MOR with an irreversible antagonist, ß-CNA, allowed us to calculate a measure of transduction efficiency (tau), which elates receptor occupancy to effect, forboth control and depleted cases for DAMGO (67.6, 7.1), morphine (11.1, 1.5) and TRV 130 (5.5, 0.6). demonstrating the lower efficacy of TRV 130 compared to morphine. All the opioids under study appeared to be lower efficacy agonist than morphine, and their efficacy may be further reduced at common MOR polymorphisms. It remains to be established whether the findings of this project, yields similar clinical effects.

History

Table of Contents

1. General introduction -- 2. Experimental methodology -- 3. Effect of Pethidine on signalling of µ-opioid receptor and its variants -- 4. Effect of genotype variation on Tramadol signalling -- 5. Signalling of TRV 130 on µ-opioid receptor and variants -- 6. General discussion, limitations and future directions.

Notes

Bibliography: Pages 69-86 Theoretical thesis.

Awarding Institution

Macquarie University

Degree Type

Thesis MRes

Degree

MRes, Macquarie University, Faculty of Medicine and Health Sciences, Department of Biomedical Sciences

Department, Centre or School

Department of Biomedical Sciences

Year of Award

2017

Principal Supervisor

Mark Connor

Rights

Copyright Preeti Manandhar 2017. Copyright disclaimer: http://mq.edu.au/library/copyright

Language

English

Extent

1 online resource (xii, 86 pages) illustrations

Former Identifiers

mq:70261 http://hdl.handle.net/1959.14/1261858