The Effects of Chronic Vaping Delta-9-Tetrahydrocannabinol (THC) in Traumatic Femur Fracture in Mice

Abstract

The growing trend of vaping delta-9-tetrahydrocannabinol (THC) has raised concerns about its potential effects on various aspects of health. Extensive research has delved into the adverse effects of tobacco smoking on wound and fracture healing in both animals and humans. Concurrently, the growing prevalence of nicotine e-cigarette use has prompted studies to explore the repercussions of e-cigarette vaping on bone health, but the potential effects of vaping THC on bone healing remain a topic of scientific inquiry. As vaping has become increasingly popular, substantial concerns have emerged regarding its potential health risks, especially among adolescents. We utilized THC vape distillate with a total THC purity of 93.4% obtained from an Arizona State Licensed Dispensary. In our study we report the effects of chronic THC vaping (18.68 mg/mL) on bone healing following a traumatic femur fracture in mice, comparing the outcomes to those of non-exposed fracture mice. We also investigated the impact of both chronic and acute vaping of THC (18.68 mg/mL), nicotine (5 mg/mL), and chronic vehicle in the absence of fracture. The analysis includes the evaluation of callus size, serum levels of bone turnover markers (OPG/TRANCE,RANKL) and bone microstructures. Radiograph imaging showed THC exposure in mice with a fracture of the femur initially resulted in a greater callus diameter 1 week post-fracture compared to non-exposed fractured mice. The diameter of the callus was reduced at 2 weeks post-fracture and sustained this characteristic through 8 weeks post-fracture as compared to controls. Micro-computed tomography (µCT) revealed a significantly smaller callus volume in the THC-exposed fracture group compared to the non-exposed fracture group at 8 weeks post-fracture. Blood serum levels were analyzed for bone molecules, OPG and TRANCE(RANKL), that are crucial signaling molecules in fracture healing and bone homeostasis. Data revealed a non-significant change in OPG serum levels between both fracture groups, THC-exposed and non-exposed. TRANCE(RANKL) serum levels showed a statistically significant increase in the chronic THC-exposed fracture group compared to non-exposed fracture group and may be why a smaller callus diameter and volume was seen since TRANCE(RANKL) levels favor bone remodeling. In the absence of fracture, whether animals were exposed acute or chronically to THC or chronically to vehicle a non-significant change was seen in OPG serum levels. Similar results were obtained with chronic or acute vaping of nicotine. Of the available serums to measure, there was a non-significant change in TRANCE(RANKL) levels in animals exposed to THC or vehicle. Studies with nicotine vaping only included serum from two animals from each cohort, therefore samples were excluded in the statistical analysis of TRANCE(RANKL) serum levels. Taken together, our data demonstrates vaping THC at 18.68 mg/mL influences fracture callus size and TRANCE(RANKL) serum levels in animals that underwent a femur fracture. In the absence of fracture, vaping THC does not appear to influence OPG or TRANCE(RANKL) serum levels. Although preliminary due to a small number of animals tested, non-fracture µCT data revealed chronic nicotine vape exposure decreased trabecular marrow and spacing, while increasing trabecular bone volume fraction (BV/TV). Additionally, µCT data of the non-fracture groups showed that acute exposure to THC or nicotine and chronic exposure to THC or nicotine resulted in elevation in cortical BV/TV when compared to chronic vehicle exposure.