DOI
https://doi.org/10.25772/Y497-9W65
Author ORCID Identifier
https://orcid.org/0000-0001-9403-2721
Defense Date
2023
Document Type
Dissertation
Degree Name
Doctor of Philosophy
Department
Pharmacology & Toxicology
First Advisor
Aron Lichtman, PhD
Second Advisor
Joyce Lloyd, PhD
Third Advisor
M Imad Damaj, PhD
Fourth Advisor
Wally Smith, MD
Fifth Advisor
Kurt Hauser, PhD
Abstract
Sickle cell disease (SCD) is associated with significant morbidity and may include both acute and chronic pain contributing to functional disability. Although opioids remain the standard to treat SCD pain, their adverse side effects (e.g., constipation, respiratory depression, abuse liability, dependence) as well as the fact that chronic pain requires prolonged treatment that results in tolerance, severely limits their therapeutic utility and underscores a need for effective non-opioid chronic pain treatments. Berkeley SCD mice (HbSS-BERK) express human sickle hemoglobin, HbS, and display a similar phenotype to SCD patients, and thus represent a useful tool to evaluate disease pathophysiology and progression, as well as investigate novel therapeutic strategies. HbSS-BERK mice exhibit mechanical and thermal hypersensitivity, as well as diminished grip strength compared to HbAA-BERK mice (expressing normal human hemoglobin) at certain ages. These reflexive measures alone insufficiently capture and model the sensory and functional impairments and disruptions of daily life experienced by SCD patients. Moreover, the hyper-nociceptive responses of HbSS-BERK appear to emerge at different ages, but studies systematically examining the influences of age and sex are lacking. Secondly, the myriad adverse effects of opioids underscore a pressing need to identify effective non-opioid analgesic strategies (e.g., cannabinoid-based drugs) to reduce SCD chronic pain. Many SCD patients report using cannabis to help manage their pain; however, obstacles persist for clinical cannabis use due to its abuse liability and psychoactive effects. Provocative evidence suggesting endocannabinoid (eCB) dysregulation in SCD has led us to consider modulation of the eCB system as an analgesic strategy for SCD chronic pain. In particular, diminished 2-arachidonoylglycerol (2-AG) and elevated arachidonic acid in SCD mice sparked our investigation of the 2-AG regulating enzyme, monoacylglycerol lipase (MAGL).
In this dissertation, we test the hypotheses that: 1) the inclusion of both reflexive (stimulus-evoked) and spontaneous (non-evoked) assays of nociception and motor function facilitates enhanced screening of novel analgesic targets in BERK mice; and age and sex represent important covariates, and 2) increased MAGL expression contributes to the HbSS-BERK hyper nociceptive phenotype; and its pharmacological inhibition reduces prominent behaviors through activation of cannabinoid receptors. Thus, we evaluated male and female HbSS- and HbAA-BERK mice for peripheral sensory and functional motor behavior in a battery of assays at various ages. Subsequently, we evaluated the the efficacies of a potent and selective MAGL inhibitor, MJN110, the primary active constituent of cannabis, Δ9-tetrahydrocannabinol (Δ9-THC), and commonly used analgesic, oxycodone, to attenuate a representative subset of prominent hyper-nociceptive and functional behaviors in HbSS-BERK mice. HbSS-BERK mice display mechanical allodynia and thermal hyperalgesia at a young age but show age-related increased magnitudes of mechanical and cold allodynia. HbSS-BERK mice exhibit functional deficits that, in some cases (wheel running, inverted screen, nesting), worsen with age. HbSS-BERK mice also exhibit age-related reductions in nerve conduction velocity and amplitude.
MJN110, Δ9-THC, and oxycodone attenuated mechanical allodynia and thermal hyperalgesia in dose-dependent manners in HbSS-BERK mice. Oxycodone, but not Δ9-THC or MJN110, produced antinociception in HbAA-BERK mice. Interestingly, MJN110 improved grip strength and inverted screen deficits in HbSS-BERK mice, with no significant effect in control mice, while oxycodone decreased grip strength in control mice and worsened inverted screen deficits in HbSS-BERK mice. Irrespective of genotype, Δ9-THC and oxycodone disrupted grip strength and nest-building behavior, respectively.
Using pharmacologic approaches to explore the antinociceptive effects of MJN110 further, we demonstrate that the anti-allodynic effects require both cannabinoid receptors, while the anti-hyperalgesic effects require only the CB1 receptor. Further, improvements in grip strength by MJN110 were mediated by CB2 receptors, particularly in male mice.
As chronic pain required repeated dosing, we demonstrated that repeated administration of 5 mg/kg MJN110 for 7 days produces sustained anti-allodynic, but not anti-hyperalgesic effects in HbSS-BERK mice. Using the conditioned place preference paradigm, we demonstrate that MJN110 produces a CPP in HbSS-, but not HbAA-BERK mice. Lastly, we show that MAGL expression is elevated in the spinal cord of HbSS-BERK mice compared to HbAA-BERK mice. Taken together, these results suggest that this battery of tests provides a framework to investigate novel strategies to prevent and/or treat the various SCD hyper-nociceptive phenotypes, and that MAGL is a viable target for the treatment of chronic pain in SCD.
Rights
© Kennedy Nichelle Goldsborough
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
5-12-2023
Included in
Behavioral Neurobiology Commons, Pharmacology Commons, Translational Medical Research Commons