Cannabinoid system involves in the analgesic effect of protocatechuic acid

Abstract

Background: Protocatechuic acid is an antioxidant which is shown to have analgesic activity in limited studies. However, the mechanisms of action remain unclear. Objectives: It is aimed to investigate the possible contribution of cannabinoid system that supresses the nociceptive process by the activation of CB1 and CB2 receptors in central and peripheral levels of pain pathways, to the analgesic activity of protocatechuic acid. Methods: The analgesic activity of protocatechuic acid was determined at the doses of 75, 150 and 300 mg/kg (i.p.) by acetic acid-induced writhing and tail-immersion tests in mice. The results were compared to the analgesic effect of 300 mg/kg (i.p.) dipyrone and non-specific CB receptor agonist 5 mg/kg (i.p.) WIN 55,212–2. For investigating the contribution of cannabinoid system to protocatechuic acid analgesia; pre-treatment with 8 mg/kg (i.p.) CB1 antagonist AM251 and 8 mg/kg (i.p.) CB2 antagonist AM630 were performed separately before 300 mg/kg protocatechuic acid administration. Results: It was determined that protocatechuic acid has dose-dependent analgesic effect independently from locomotor activity and is comparable with effects of dipyrone and WIN 55,212–2. Pre-treatment with CB1 receptor antagonist AM251 significantly antagonized the protocatechuic acid-induced analgesia in the tail-immersion and writhing tests, whereas pre-treatment of CB2 receptor antagonist AM630 was found to be effective only in the tail-immersion test. Conclusion: It is concluded that cannabinoid modulation contributes to the analgesic effect of protocatechuic acid in spinal level rather than peripheral. CB1 receptor stimulation rather than CB2 receptor stimulation mediates the analgesic effect of protocatechuic acid in both levels, especially peripheral