Abstract
Scoparone, a major constituent of the Chinese herbal medicine Yin Chen Hao, expresses
beneficial effects in experimental models of various diseases. The intrinsic doses
and effects of scoparone are dependent on its metabolism, both in humans and animals.
We evaluated in detail the metabolism of scoparone in human, mouse, rat, pig, dog,
and rabbit liver microsomes in vitro and in humans in vivo. Oxidation of scoparone to isoscopoletin via 6-O-demethylation was the major metabolic
pathway in liver microsomes from humans, mouse, rat, pig and dog, whereas 7-O-demethylation
to scopoletin was the main reaction in rabbit. The scoparone oxidation rates in liver
microsomes were 0.8 – 1.2 µmol/(min*g protein) in mouse, pig, and rabbit, 0.2 – 0.4 µmol/(min*g
protein) in man and dog, and less than 0.1 µmol/(min*g) in rat. In liver microsomes
of all species, isoscopoletin was oxidized to 3-[4-methoxy-ρ-(3, 6)-benzoquinone]-2-propenoate
and esculetin, which was formed also in the oxidation of scopoletin. Human CYP2A13
exhibited the highest rate of isoscopoletin and scopoletin oxidation, followed by
CYP1A1 and CYP1A2. Glucuronidation of isoscopoletin and scopoletin was catalyzed by
the human UGT1A1, UGT1A6, UGT1A7, UGT1A8, UGT1A9, UGT1A10, and UGT2B17. Dog was most
similar to man in scoparone metabolism. Isoscopoletin glucuronide and sulfate conjugates
were the major scoparone in vivo metabolites in humans, and they were completely excreted within 24 h in urine. Scoparone
and its metabolites did not activate key nuclear receptors regulating CYP and UGT
enzymes. These results outline comprehensively the metabolic pathways of scoparone
in man and key preclinical animal species.
Key words
scoparone - isoscopoletin - scopoletin - esculetin - CYP - UGT