title: Effects of intrinsic fluorescence and quenching on fluorescence-based screening of natural products.
abstract: To evaluate the effects of intrinsic (natural) fluorescence and quenching as confounding variables in fluorescence-based enzyme inhibition assays of natural products, we measured the fluorescence and quenching properties of 25 components of popular herbal products. The analyses were performed under conditions typically employed in drug-drug interaction studies that use c-DNA-derived P450 isoforms and surrogate fluorogenic substrates. Four of the 25 compounds tested (isorhamnetin, quercetin, vitexin, and yangonin) fluoresced or quenched sufficiently to interfere with these assays. Intrinsic fluorescence had a greater effect on these assays than quenching and for one compound, yangonin, was sufficient to mask inhibition and potentially produce a false negative result. Quenching had less of an effect on these assays, but was significant enough for one compound, quercetin, to mimic "weak" inhibition. Therefore, because intrinsic fluorescence or quenching could render some natural products unsuitable for testing in certain fluorometric assays, it would be prudent to include an evaluation of these properties in experimental protocols.
authors.affiliation: Department of Medical Pharmacology and Toxicology, School of Medicine, University of California, Davis 95616, USA.
authors.forename: L
authors.initials: L
authors.lastname: Zou
authors.forename: M R
authors.initials: MR
authors.lastname: Harkey
authors.forename: G L
authors.initials: GL
authors.lastname: Henderson
mesh_terms: D047310:Apigenin; D001189:Aryl Hydrocarbon Hydroxylases / Q000187:drug effects; D019388:Cytochrome P-450 CYP1A2 / Q000187:drug effects; D065731:Cytochrome P-450 CYP2C19; D019389:Cytochrome P-450 CYP2D6 / Q000187:drug effects; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000187:drug effects; D004798:Enzymes / Q000187:drug effects*; D005419:Flavonoids / Q000494:pharmacology; D044948:Flavonols; D005453:Fluorescence; D006801:Humans; D006899:Mixed Function Oxygenases / Q000187:drug effects; D008517:Phytotherapy; D010936:Plant Extracts / Q000737:chemistry / Q000494:pharmacology*; D011753:Pyrones / Q000494:pharmacology; D011794:Quercetin / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D004798:Enzymes; D005419:Flavonoids; D044948:Flavonols; D010936:Plant Extracts; D011753:Pyrones; C047368:3-methylquercetin; D047310:Apigenin; D003577:Cytochrome P-450 Enzyme System; D011794:Quercetin; C032731:vitexin; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C045793:CYP2C19 protein, human; C104464:CYP3A protein, human; D019388:Cytochrome P-450 CYP1A2; D065731:Cytochrome P-450 CYP2C19; D019389:Cytochrome P-450 CYP2D6; D051544:Cytochrome P-450 CYP3A; C110481:yangonin