Abstract
Apoptosis is programed cell death characterized by certain cellular changes and regulated by various gene products including Bcl-2 and caspase-1. The marijuana cannabinoid, Δ9tetrahydrocannabinol (THC), has been reported to suppress in culture the proliferation of splenocytes and increase the release of IL-1 from macrophages; however, the mechanisms of these effects remain unclear. Because cannabinoids have also been reported to induce apoptosis and because the release of IL-1 and suppression of lymphoproliferation are related to apoptosis, we tested for the induction of apoptosis by THC in murine immune cell cultures. Splenocytes cultured with Con A for up to 24 hr showed evidence of DNA fragmentation determined by gel electrophoresis, terminal deoxynucleotide transferase-mediated dUTP-fluorescein nick end labeling and 3H-thymidine labeling and THC (15–30 μM) treatment increased fragmentation under these conditions. Resident peritoneal macrophages cultured with lipopolysaccharides showed no obvious fragmentation unless they were also treated with THC. Time course studies examining DNA fragmentation and cell membrane integrity (assessed by dye exclusion) showed that fragmentation preceded membrane damage indicating that THC induced apoptosis rather than cell necrosis. In addition, THC treatment of splenocytes resulted in a decrease of Bcl-2 mRNA and protein as measured by Northern and Western blotting, respectively, and the drug induced apoptosis was blocked by the caspase inhibitor, Ac-Tyr-Val-Ala-l-aspartic acid aldehyde. These data suggest that THC treatment of cultured immune cells induces apoptosis through the regulation of Bcl-2 and caspase activity.
Footnotes
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Send reprint requests to: Dr. Thomas W. Klein, University of South Florida, Department of Medical Microbiology, MDC Box 10, 12901 Bruce B. Downs Blvd., Tampa, FL 33612.
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↵1 This work was supported by Public Health Service Grant DA03646 from the National Institute on Drug Abuse.
- Abbreviations:
- THC
- Δ9-tetrahydrocannabinol
- IL-1
- interleukin-1
- TUNEL
- terminal deoxynucleotidyl transferase-mediated dUTP-fluorescein nick end labeling
- Con A
- Concanavalin A
- LPS
- lipopolysaccharide
- DMSO
- dimethylsulfoxide
- SDS
- sodium dodecyl sulfate
- PAGE
- polyacrylacrylamide gel electrophoresis
- Received June 20, 1997.
- Accepted April 23, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
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