Author ORCID Identifier

https.orcid.org/0000-0001-7528-291X

Date Available

10-24-2022

Year of Publication

2022

Document Type

Doctoral Dissertation

Degree Name

Doctor of Philosophy (PhD)

College

Agriculture, Food and Environment

Department/School/Program

Veterinary Science

Advisor

Dr. Amanda A. Adams

Abstract

Cannabis sativa L., has been revealed to produce hundreds of phytocannabinoids, of which cannabidiol (CBD) is one of the most desired. It has been revealed that CBD can potentially treat inflammation and act as an analgesic in humans without psychoactive effects of delta-9-tetrahydrocannabinol (THC). Recently, there has been interest in understanding the potential health benefits of CBD for horses. With an increasing senior horse population (< 15 years old), alternatives to the use of non-steroidal anti-inflammatory drugs (NSAIDs) such as phenylbutazone, firocoxib, and flunixin meglumine, are desired as these common anti-inflammatory treatments have negative side effects. Because senior horses may have chronic low-grade inflammation, termed inflamm-aging, they are a natural model to investigate the efficacy of CBD on inflammatory responses as well as other health parameters. Given this interest, and due to the lack of research conducted on CBD in the horse, the overall objective of this dissertation work was to conduct both basic and applied research investigating the effects of CBD on equine immune function and health. The first objective was to determine the in vitro effects of CBD as an anti-inflammatory. Peripheral blood mononuclear cells (PBMCs) from senior horses were cultured in vitro with increasing concentrations of pure CBD dissolved in dimethyl sulfoxide (DMSO). These cells were then stimulated, cell viability and cytokine production were measured. The concentration of CBD that did not affect cell viability was 4 µg/mL. CBD at 4 µg/mL significantly reduced production of TNFα and IFNγ. RT-PCR results for TNFα and IFNγ at 4 µg/mL showed a reduction compared with the positive control and IL-10 showed a similar reduction at 2 µg/mL and 4 µg/mL. RT-PCR gene expression results showed significance at 10 μg/mL CBD with an increase in gene expression of both CB1 and CB2. CBD reduced in vitro production of inflammatory cytokines from senior horses. The second objective was to determine the pharmacokinetics, bioavailability, and pharmacological effects of CBD in senior horses. In a cross-over trial using senior horses, a single oral dose of 2mg/kg CBD in soy oil was compared to a single intravenous (IV) dose of 0.1mg/kg CBD in DMSO. Blood samples were collected at specific time points. Plasma concentrations of CBD and metabolites (7-COH CBD and 7-COOH CBD), were detected in all plasma samples up to 8h post dosing (oral and IV) with 7-COOH CBD being the most predominant metabolite. Pharmacokinetics for CBD oral dosing at 2mg/kg were half-life 7.22 ± 2.86 hours, Cmax was 18.54± 9.80 and Tmax was 2.46 ± 1.62 hours. Oral bioavailability for CBD in senior horses was calculated at 7.92%. There were no significant effects of CBD on CBC, serum chemistry or vitals for all horses. Pharmacokinetics and bioavailability of CBD in senior horses was determined, and no adverse effects were found administering either an oral dose or an IV dose of CBD. Lastly, the third objective was to determine the effects of CBD on immune function by measuring inflammatory cytokines and antibody responses to vaccination, as well as various health parameters of body weight, body condition, lameness, and metabolic responses in senior horses. For 90 days two treatment groups of senior horses were orally-dosed once daily with CBD (treatment: 2mg/kg) or soy oil (control). Peripheral blood samples were collected prior to treatments on day 0 and post-treatment on days 30, 60, and 90. On day 90 all horses were vaccinated with a commercial equine influenza vaccine and blood samples were collected post-vaccination. Plasma concentrations of CBD and metabolites, 7-OH CBD, and 7-COOH CBD were measured with 7-COOH CBD the most significant of the two metabolites in the plasma post-treatment. At day 60 in RT-PCR, a significant reduction in the gene production of IFNγ occurred and IL-6 was also significantly reduced at day 60 and 90 for CBD treated horse when compared with control horses. There were no other significant changes in immune function, nor health parameters measured in response to CBD treatment. This body of work provides the foundation for understanding the effects of CBD on the health and well-being of the senior horse.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2022.374

Funding Information

This dissertation was supported by Enhanced Pet Sciences August 2018-October 2022.

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