Received for publication March 6, 2008.
Revised April 2, 2008.
Accepted for publication April 2, 2008.

Attenuation of experimental autoimmune hepatitis by exogenous and endogenous cannabinoids: Involvement of regulatory T cells

Abstract

Immune-mediated liver diseases including autoimmune and viral hepatitis are a major health problem worldwide. Natural cannabinoids such as ⁹-tetrahydrocannabinol (THC) effectively modulate immune cell function and have shown therapeutic potential in treating inflammatory diseases. We investigated the effects of THC in a murine model of Concanavalin A-induced hepatitis. Intraperitoneal administration of THC after ConA challenge inhibited hepatitis as shown by significant decrease in liver enzymes and reduced liver tissue injury. Furthermore, THC treatment resulted in significant suppression of crucial inflammatory cytokines in ConA-hepatitis. Interestingly, THC treatment in ConA-injected mice led to significant increase in absolute number of Foxp3⁺ T regulatory cells in liver. Surprisingly, select cannabinoid receptor (CB1 or CB2) agonists were not able to block hepatitis either independently or in combination. However, CB1/CB2 mixed agonists were able to efficiently attenuate hepatitis similar to THC. The modulatory effect of THC in ConA-induced hepatitis was reversed by both CB1 and CB2 antagonists. We also observed that endogenous cannabinoid anandamide was able to reduce hepatitis by suppressing cytokine levels. Also, deficiency or inhibition of endocannabinoid hydrolyzing enzyme, fatty acid amide hydrolase (FAAH), which leads to increased levels of endogenous cannabinoids, resulted in decreased liver injury upon ConA challenge. Our data demonstrate that targeting cannabinoid receptors using exogenous or endogenous cannabinoids and use of FAAH inhibitors may constitute novel therapeutic modalities to treat immune-mediated liver inflammation.

Key words: Cannabinoid, Interferons, Interleukins, Apoptosis, Leukocytes/Mast cells