Background and purpose: Inhibitors of fatty acid amide hydrolase (FAAH), the enzyme responsible for the metabolism of the endogenous cannabinoid (CB) receptor ligand anandamide (AEA), are effective in a number of animal models of pain. Here, we investigated a series of isoflavones with respect to their abilities to inhibit FAAH. Experimental approach: In vitro assays of FAAH activity and affinity for CB receptors were used to characterize key compounds. In vivo assays used were biochemical responses to formalin in anaesthetized mice and the 'tetrad' test for central CB receptor activation. Key results: Of the compounds tested, biochanin A was adjudged to be the most promising. Biochanin A inhibited the hydrolysis of 0.5 μM AEA by mouse, rat and human FAAH with IC50 values of 1.8, 1.4 and 2.4 μM respectively. The compound did not interact to any major extent with CB1 or CB2 receptors, nor with FAAH-2. In anaesthetized mice, URB597 (30 μg i.pl.) and biochanin A (100 μg i.pl.) both inhibited the spinal phosphorylation of extracellular signal-regulated kinase produced by the intraplantar injection of formalin. The effects of both compounds were significantly reduced by the CB1 receptor antagonist/inverse agonist AM251 (30 μg i.pl.). Biochanin A (15 mg·kg-1 i.v.) did not increase brain AEA concentrations, but produced a modest potentiation of the effects of 10 mg·kg-1 i.v. AEA in the tetrad test. Conclusions and implications: It is concluded that biochanin A, in addition to its other biochemical properties, inhibits FAAH both in vitro and peripherally in vivo.
- Biochanin A
- Fatty acid amide hydrolase