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  • In vitro effects of myricetin, morin, apigenin, (+)-taxifolin, (+)-catechin, (-)-epicatechin, naringenin and naringin on cytochrome b5 reduction by purified NADH-cytochrome b5 reductase.

In vitro effects of myricetin, morin, apigenin, (+)-taxifolin, (+)-catechin, (-)-epicatechin, naringenin and naringin on cytochrome b5 reduction by purified NADH-cytochrome b5 reductase.

Toxicology (2013-04-10)
Haydar Çelik, Müberra Koşar, Emel Arinç
ABSTRACT

The microsomal NADH-dependent electron transport system consisting of cytochrome b5 reductase and cytochrome b5 participates in a number of physiologically important processes including lipid metabolism as well as is involved in the metabolism of various drug and xenobiotics. In the present study, we assessed the inhibitory effects of eight dietary flavonoids representing five distinct chemical classes on cytochrome b5 reduction by purified cytochrome b5 reductase. From the flavonoids tested, myricetin was the most potent in inhibiting cytochrome b5 reduction with an IC50 value of 0.35μM. Myricetin inhibited b5 reductase noncompetitively with a Ki of 0.21μM with respect to cofactor NADH, and exhibited a non-linear relationship indicating non-Michaelis-Menten kinetic binding with respect to cytochrome b5. In contrast to the potent inhibitory activity of myricetin, (+)-taxifolin was found to be a weak inhibitor (IC50=9.8μM). The remaining flavonoids were inactive within the concentration range tested (1-50μM). Analysis of structure-activity data suggested that simultaneous presence of three OH groups in ring B is a primary structural determinant for a potent enzyme inhibition. Our results suggest that inhibition of the activity of this system by myricetin or myricetin containing diets may influence the metabolism of therapeutic drugs as well as detoxification of xenobiotics.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Apigenin, ≥95.0% (HPLC)
Sigma-Aldrich
(−)-Epicatechin, ≥90% (HPLC)
Sigma-Aldrich
(−)-Epicatechin, ≥98% (HPLC), from green tea
Epicatechin, primary reference standard
Supelco
(−)-Epicatechin, analytical standard
Supelco
Apigenin, analytical standard
Sigma-Aldrich
Naringin, ≥90% (HPLC), from citrus fruit
Sigma-Aldrich
Myricetin, ≥96.0%, crystalline
Sigma-Aldrich
Myricetin, ≥96.0% (HPLC)
Sigma-Aldrich
Naringin, ≥95% (HPLC)
Supelco
Naringin, analytical standard
Supelco
(+)-Catechin, analytical standard
Supelco
Myricetin, analytical standard
Supelco
Taxifolin, analytical standard