Modulatory effect of opioid administration on the activity of cholinesterase enzyme: a systematic review of mice/rat models

We aimed to review the literature to find the specific effect of opioids on the activity of cholinesterase (ChE) enzyme which plays a substantial role in the functioning of cholinergic system. Literature search was performed by two independent reviewers in order to find relevant articles about the changes in the activity of ChE in mice or rat following opioid administration. Based on findings from literature review, opioid administration is able to induce cholinergic modulation via decreasing or increasing the activity of ChE enzyme. However, the degree of variation of ChE in various brain regions is different. No gender differences was reported in the effect of opioids on ChE activity. Although chronic opioid administration may decrease enzyme function, ChE activity might be unchanged following opioid withdrawal using naloxone or the development of tolerance. Opioid type affects whether or not naloxone can reverse the changes of ChE. Direct inhibitory action of morphine and the other opioid ligands believed responsible for the decrease in the ChE activity. Moreover, the potency of codeine to induce allosteric enhancement of acetylcholine receptor signaling might be involved in the cholinergic modulation of codeine and other opioids. Animal studies on rat and mice showed that opioids may change the activity of ChE. These changes can pertain an increase or decrease in enzyme activity; as there might be no change. The type of opioid used may have an effect on the cholinergic modulation. It is beneficial to conduct cross-sectional and cohort studies on addicted individuals, especially opium abusers, to find the precise association of opioids with alterations in human acetyl cholinesterase or butyrylcholinesterase. Simulation studies can also examine the structure-function relationships and provide important details to better understand the mechanism of action of opioid compounds on ChE activity. In addition, understanding how opioids impact ChE activity may help perform proper interventions for drug abstinence.