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Abstract
1. Tangeretin, a polymethoxylated flavone, was studied as a substrate for cytochrome P450-catalysed demethylation reactions by rat and human liver microsomes. Evidence has been presented for the production of formaldehyde in the presence of tangeretin and NAD(P)H. Kinetic studies showed a Km value for tangeretin of about 18 μmlM in both species.
2. The reaction was inhibited by CO, piperonyl butoxide, 7,8-benzoflavone, propyl gallate, aminobenzothiazole and metyrapone.
3. Rats pretreated with classical cytochrome P450 inducers (Aroclor 1254, 3-methylcholanthrene, phenobarbital, dexamethasone and ciprofibrate) or with flavo-noids (flavone, flavanone, quercetin and tangeretin) resulted in increased microsomal demethylation of tangeretin after 3-methylcholanthrene and flavone only. Tangeretin did not enhance its own metabolism.
4. Tangeretin interacted with the oxidized form of cytochrome P450 to produce a reverse type I spectrum.
5. Results indicate that tangeretin is metabolized in liver microsomes by an O-demethylation reaction involving cytochrome P450.