Comparison of In Vitro Hepatic Scoparone 7-O-Demethylation between Humans and Experimental Animals

Abstract

Scoparone is a natural bioactive compound in Chinese herbal medicines. It has numerous pharmacological actions, including liver protective, hypolipidemic, antitumor, and anti-inflammatory effects. The primary metabolism route of scoparone is O-demethylation to scopoletin or isoscopoletin catalyzed by CYP enzymes. The aims of our study were to identify the human CYP enzymes catalyzing scoparone 7-O-demethylation to scopoletin and to compare this oxidation reaction in liver microsomes among different species. A high throughput fluorescent-based assay method was developed to determine the scoparone 7-O-demethylation to scopoletin rate. The rate was 100 - 400 nmol/(min×g protein) in mouse and rabbit liver microsomes, 10 - 20 nmol/(min×g protein) in pig microsomes, 1 - 3 nmol/(min×g protein) in human and less than 1 nmol/(min×g protein) in rat liver microsomes. Human CYP1A1 (K 13 µM and V 0.8 min), CYP1A2 (K 48 µM and V 0.3 min), and CYP2A13 (K 10 µM and V 22 min) were the most efficient catalysts of the reaction. The CYP2A6 selective inhibitor pilocarpine and an antibody against mouse CYP2A5 inhibited scoparone 7-O-demethylation to scopoletin in rabbit, mouse, and pig liver microsomes, indicating involvement of CYP2A enzymes in the reaction. Hepatic scoparone 7-O-demethylation to scopoletin differed between species both with respect to the rate of reaction and catalyzing enzymes. These species differences need to be taken into account when testing scoparone pharmacokinetics in animals and humans.

Coumarin-Based Profluorescent and Fluorescent Substrates for Determining Xenobiotic-Metabolizing Enzyme Activities In Vitro

“…It is the major active component in the Chinese herbal medicine Yin Chen Hao, a component in many traditional Chinese medicine (TCM) products [ 52 ]. We developed a fluorescent-based assay method to evaluate the rate of scoparone 7-O-demethylation to scopoletin in various species [ 53 ]. The rate was higher in liver microsomes from pigs, mice, and rabbits than in those of humans.…”

Porcine cytochrome 2A19 and 2E1

“…Some phenolic compounds are substrates for CYP2A6 (the human analogy of porcine CYP2A19). In pigs, CYP2A metabolized scoparone, a natural bioactive compound found in Chinese herbal medicines . In human beings, the plant polyphenol curcumin ingested in dose of 1000 mg daily during 14 days, and quercetin in dose of 500 mg daily for 13 days enhanced CYP2A6 activity.…”

“…In pigs, CYP2A metabolized scoparone, a natural bioactive compound found in Chinese herbal medicines. 66 In human beings, the plant polyphenol curcumin ingested in dose of 1000 mg daily during 14 days, 67 and quercetin in dose of 500 mg daily for 13 days 68 enhanced CYP2A6 activity. Because of high similarity between the porcine and human physiology, similar effects can be expected for porcine CYP2A19, which might lead to enhanced skatole metabolism.…”

Metabolism of Scoparone in Experimental Animals and Humans

“…In humans, CYP1A2 was shown to oxidize scoparone to scopoletin [22]. Recently we showed that the human extrahepatic CYP1A1 and CYP2A13 were more efficient catalysts for this reaction than the hepatic CYP1A2 [28]. The rate of in vitro liver microsomal scoparone 7-O-demethylation is lower in humans than in pig, mouse and rabbit.…”

“…The rate of in vitro liver microsomal scoparone 7-O-demethylation is lower in humans than in pig, mouse and rabbit. These results suggested that mouse, rat, pig and rabbit are not suitable surrogate species for evaluating scoparone pharmacokinetics in humans [28].…”