Anti-Inflammatory Effect of the Endocannabinoid Anandamide in Experimental Periodontitis and Stress in the Rat

Abstract

Objective: Periodontitis is an infectious disease leading to inflammation and destruction of tissue surrounding and supporting the tooth. The progress of the inflammatory response depends on the host’s immune system and risk factors such as stress. The aim of the present study was to investigate the role of the endocannabinoid anandamide (AEA) in experimental periodontitis with restraint stress, since the endocannabinoid system is known to modulate the hypothalamo-pituitary-adrenal axis as well as immune functions and has been found in human gingival tissues. Methods: Experimental periodontitis was induced by ligature around first inferior molars and immobilization stress for 2 h twice daily for 7 days in a rat model. Results: Corticosterone plasma levels, locomotor activity, adrenal gland weight and bone loss were increased in periodontitis and stress groups, and there was also less weight gain. The inflammatory parameters such as prostaglandin E₂ (radioimmunoassay), nitric oxide (radioconversion of ¹⁴C-arginine), tumor necrosis factor (TNF)-α (ELISA) and interleukin (IL)-1β (Western blot) measured in the gingival tissue were significantly increased in the periodontitis groups compared to the control group. Local injection of AEA (10^–8 M, 30 µl) decreased corticosterone plasma levels and the content of the cytokines TNF-α and IL-1β in gingival tissue in periodontitis-stress groups. These AEA-induced inhibitions were mediated by CB₁ and CB₂ cannabinoid receptors since the injection of both antagonists together, AM251 (10^–6 M) and AM630 (10^–6 M) in 30 µl, prevented these effects. Conclusion: The endocannabinoid AEA diminishes the inflammatory response in periodontitis even during a stressful situation.