Effect of Chrysin and Natural Coumarins on UGT1A1 and 1A6 Activities in Rat and Human Hepatocytes in Primary Culture

Abstract

Flavonoids and coumarins are naturally occurring compounds that are widely distributed in vegetables and have a broad pharmacological activity. Inducibility of UDP-glucuronosyltransferases (UGTs) by xenobiotics is well documented and can be considered beneficial for health. In particular, UGT1A1-dependent bilirubin conjugation plays a critical role in the detoxification of neurotoxic bilirubin and phenobarbital-mediated UGT1A1 induction therapy is commonly used in the treatment of unconjugated hyperbilirubinemic diseases such as Crigler-Najjar type II disease. In the present study, the effects of the flavone chrysin and six natural coumarins isolated from various Rutaceous plants on UGT1A6-dependent p-nitrophenol and/or UGT1A1-dependent bilirubin glucuronoconjugation activities were evaluated in cultured rat and human hepatocytes and compared to those of the prototypical UGT1A inducers β-naphthoflavone, phenobarbital and clofibric acid. After 3 days of treatment at a concentration of 25 μM, the pyranocoumarins avicennin and cis-avicennol, and the furocoumarins bergapten and imperatorin, increased by 2-fold UGT1A1-dependent activity, equivalent to the increases obtained with chrysin at 25 μM, whereas in the presence of the simple coumarins such as coumarin or umbelliferone, UGT1A1-dependent activity was not modified. In terms of structural requirements for UGT1A1 induction, the present study suggests that the B-ring (phenyl) for chrysin and the furan or pyran rings for coumarins are essential for the biological activity.

Abbreviations

BCA:bicinchoninic acid

Bili:biliribin

BSA:bovine serum albumin

CLO:clofibric acid

FCS:foetal calf serum

HBSS:Hank’s buffered salt solution

HEPES:4-(2-hydroxyethyl)piperazine-1-ethane sulfonic acid

NF:β-naphthoflavone

PB:Phenobarbital

PBS:phosphate buffered saline

PNP:p-nitrophenol

UDPGA:Uridine 5′-diphosphoglucuronic acid

UGTs:UD-glucuronosyltransferases

Key words

Coumarins - Rutaceae - chrysin - avicennin - cis-avicennol - imperatorin - bergapten - umbelliferone - UGT1A1 - UGT1A6 - hepatocytes

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