Effects of sub-chronic cannabis smoke exposure on inflammatory markers in serum and brain in younger and older mice.

Aging is associated with chronic low-grade inflammation, which is thought to contribute to both cognitive decline and various neurodegenerative diseases. Cannabinoids are reported to reduce levels of inflammatory markers; however, these effects have not been thoroughly assessed in older subjects. To address this gap, we evaluated the effects of sub-chronic cannabis smoke exposure on serum and brain inflammatory markers in younger and older mice. Younger (4 month old) and older (22 month old) C57Bl/6J mice were exposed to smoke from burning either cannabis (5.5-6.2% THC) or placebo (0% THC) cigarettes daily for 30 consecutive days. Following exposure sessions, both blood and brain tissue from the prefrontal cortex (PFC) and hippocampus (HPC) were collected and analyzed for multiple markers of inflammation. Overall, the patterns of inflammatory markers varied across serum, PFC, and HPC. Both comparisons of individual cytokines and global cytokine profiles revealed that aging caused increases in cytokine levels in all three sample types. Global cytokine analysis showed increases in PFC inflammatory markers in younger and older mice exposed to cannabis smoke. In contrast, HPC samples had significant Age x Drug interactions, such that cannabis smoke exposure tended to increase cytokine levels in younger mice but decrease them in older mice. These findings point to general age-related increases in serum and brain inflammatory markers in this mouse strain; however, age-dependent cannabis effects were largely restricted to the HPC.