DOI
https://doi.org/10.25772/S76N-BA32
Author ORCID Identifier
https://orcid.org/0000-0003-3753-2492
Defense Date
2022
Document Type
Dissertation
Degree Name
Doctor of Philosophy
Department
Pharmacology & Toxicology
First Advisor
S. Stevens Negus
Abstract
One of the largest discrepancies between preclinical and clinical assessment of pain and analgesia is the type of behavioral endpoint used. Although most preclinical research has historically focused on drug effectiveness to block reflexive withdrawal behaviors stimulated by a noxious stimulus, increasing evidence shows that drug-induced restoration of pain-depressed behaviors provides increased clinical translation with decreased susceptibility to false-positives. Accordingly, the first portion of this dissertation designed a behavioral battery that featured pain-depressed behaviors as well as more conventional pain-stimulated behaviors for testing candidate analgesics in male and female mice. The main findings are as follows. (1) Intraperitoneal injection of dilute lactic acid (IP acid) served as an effective visceral chemical noxious stimulus to produce concentration-dependent stimulation of two behaviors (stretching and facial grimace; pain-stimulated behaviors) and depression of two behaviors (rearing and nesting; pain-depressed behaviors). (2) Pharmacological characterization with two positive control analgesics (ketoprofen, oxycodone) and two active negative controls (diazepam, amphetamine) validated a strategy for distinguishing analgesics from nonanalgesics by profiling drug effects in this battery of complementary pain-stimulated and pain-depressed behaviors along with two additional pain-independent behaviors (nesting and locomotor activity in the absence of the IP acid noxious stimulus). (3) A National Institutes of Health mandate for consideration of Sex as a Biological Variable (SABV) was published at the start of this dissertation research. Accordingly, we developed an experimental design for considering SABV when sex differences are not the principle independent variable, with emphases on exploratory power analyses (effect size, power, predicted N) and segregation of data by sex to allow transparent analysis of SABV and help guide future study designs.
The second portion of this dissertation applied this behavioral battery and SABV data-analysis strategy to evaluate a spectrum of endocannabinoid (eCB) catabolic enzyme inhibitors ranging in selectivity for the eCB catabolic enzymes monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH), which have received increasing interest for development of candidate analgesics. The main findings are as follows: (1) antinociceptive effectiveness decreased as MAGL-selectivity decreased, with the most MAGL-selective inhibitor MJN110 producing the most effective antinociceptive profile, (2) time course and antagonism studies for MJN110 showed a long duration of antinociceptive action (40min – 6hrs), mediation by CB1R but not CB2R, a tendency for greater effects in females, and (3) repeated administration of MJN110 produced partial but sustained attenuation of IP acid-induced depression of nesting, with segregation of data by sex demonstrating sustained but weak antinociception in males and variable effects following repeated dosing in females.
Overall, these data provide a framework for predicting the analgesic potential of test drugs in preclinical pain models in male and female mice, and suggest that MJN110 may have only partial effectiveness as a candidate analgesic for treatment of visceral episodic pain.
Rights
© The Author
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
2-1-2022