No Activation of Human Pregnane X Receptor by Hyperforin-Related Phloroglucinols

Abstract

The acylated phloroglucinol, hyperforin, the main active ingredient of St. John's Wort, exerts antidepressant properties via indirect inhibition of serotonin reuptake by selectively activating the canonical transient receptor potential channel 6 (TRPC6). Hyperforin treatment can lead to drug-drug interactions due to potent activation of the nuclear receptor PXR (NR1I2), a key transcriptional regulator of genes involved in drug metabolism and transport. It was previously shown that synthetic acylated phloroglucinol derivatives activate TRPC6 with similar potency as hyperforin. However, their interaction potential with PXR remained unknown. Here we investigated five synthetic TRPC6-activating phloroglucinol derivatives and four TRPC6-nonactivating compounds compared with hyperforin and rifampicin for their potential to activate PXR in silico and in vitro. Computational PXR pharmacophore modeling did not indicate potent agonist or antagonist interactions for the TRPC6-activating derivatives, whereas one of them was suggested by docking studies to show both agonist and antagonist interactions. Hyperforin and rifampicin treatment of HepG2 cells cotransfected with human PXR expression vector and a CYP3A4 promoter-reporter construct resulted in potent PXR-dependent induction, whereas all TRPC6-activating compounds failed to show any PXR activation or to antagonize rifampicin-mediated CYP3A4 promoter induction. Hyperforin and rifampicin treatment of primary human hepatocytes resulted in highly correlated induction of PXR target genes, whereas treatment with the phloroglucinol derivatives elicited moderate gene expression changes that were only weakly correlated with those of rifampicin and hyperforin treatment. These results show that TRPC6-activating phloroglucinols do not activate PXR and should therefore be promising new candidates for further drug development.

Mechanosensitive ATP release from hemichannels and Ca2+ influx through TRPC6 accelerate wound closure in keratinocytes

“…Hyperforin increased the Ca 2+ influx by activating or upregulating TRPC6 channels, and possibly increased the ATP release through mechanosensitive hemichannels, although the underlying mechanism remains to be elucidated. Hyperforin is known to exert a variety of effects on cells, including activation of the pregnane X nuclear receptor (PXR) (Moore et al, 2000, Kandel et al, 2014. In our HaCaT cell system, hyperforin treatment resulted in reduced cell proliferation and a decreased basic Ca 2+ influx (non-stimulated or non-TRPC6), but did not affect the expression level of ATP receptors (e.g.…”

Clinical relevance of St. John's wort drug interactions revisited

“…However, considering that drug elimination is based on an interplay of multiple mechanisms, increased clearance can only be achieved if phase I and phase II biotransformation and cellular efflux are modulated at the same time (Figure ). Testing the influence of in vitro treatment with hyperforin on the mRNA expression in human hepatocytes revealed significantly enhanced expression of CYP2B6, CYP2C9, CYP3A4, CYP3A5, UGT1A1, and ABCB1 (Kandel et al, ). For CYP2B6, Goodwin et al had previously shown the binding of PXR to the promotor.…”

Hyperforin: To Be or Not to Be an Activator of TRPC(6)

“…1d) blocked serotonin uptake in murine synaptosomes and were able to mimic nearly all features shown for hyperforin, e.g., induction of neurite growth and TRPC6 activation [ (Leuner et al 2010) for further aspects see below]. However, the absence of PXR binding is the most impressive feature of the 2,4-diacylphloroglucinol compounds (Kandel et al 2014). Docking studies, modeling the compounds into the crystal structure of PXR provided evidence for the inefficiency of the compounds to bind to PXR (Kandel et al 2014).…”

“…However, the absence of PXR binding is the most impressive feature of the 2,4-diacylphloroglucinol compounds (Kandel et al 2014). Docking studies, modeling the compounds into the crystal structure of PXR provided evidence for the inefficiency of the compounds to bind to PXR (Kandel et al 2014). The modeling results could be validated by biochemical experiments testing the induction of the expression of drug metabolizing proteins.…”

“…The modeling results could be validated by biochemical experiments testing the induction of the expression of drug metabolizing proteins. While hyperforin and rifampicin efficiently elevated CYP3A4 mRNA transcription, this effect was absent in side-byside experiment using 2,4-diacylphloroglucinol compounds (Kandel et al 2014). The 2,4-diacylphloroglucinol structure provide an interesting lead in the development of a new generation of antidepressants acting via a quite different mechanism (see below) compared to the known synthetic antidepressants of today.…”