ABSTRACT
The naturally occurring acylated phloroglucinol derivative hyperforin was recently identified as the first specific canonical transient receptor potential-6 (TRPC6) activator. Hyperforin is the major antidepressant component of St. John's wort, which mediates its antidepressant-like properties via TRPC6 channel activation. However, its pharmacophore moiety for activating TRPC6 channels is unknown. We hypothesized that the phloroglucinol moiety could be the essential pharmacophore of hyperforin and that its activity profile could be due to structural similarities with diacylglycerol (DAG), an endogenous nonselective activator of TRPC3, TRPC6, and TRPC7. Accordingly, a few 2-acyl and 2,4-diacylphloroglucinols were tested for their hyperforin-like activity profiles. We used a battery of experimental models to investigate all functional aspects of TRPC6 activation, including ion channel recordings, Ca(2+) imaging, neurite outgrowth, and inhibition of synaptosomal uptake. Phloroglucinol itself was inactive in all of our assays, which was also the case for 2-acylphloroglucinols. For TRPC6 activation, the presence of two symmetrically acyl-substitutions with appropriate alkyl chains in the phloroglucinol moiety seems to be an essential prerequisite. Potencies of these compounds in all assays were comparable with that of hyperforin for activating the TRPC6 channel. Finally, using structure-based modeling techniques, we suggest a binding mode for hyperforin to TRPC6. Based on this modeling approach, we propose that DAG is able to activate TRPC3, TRPC6, and TRPC7 because of higher flexibility within the chemical structure of DAG compared with the rather rigid structures of hyperforin and the 2,4-diacylphloroglucinol derivatives.
