Stability and biotransformation of various dietary anthocyanins in vitro.
BACKGROUND
Anthocyanins, which are found in high concentrations in fruit and vegetable, may play a beneficial role in retarding or reversing the course of chronic degenerative diseases. However, little is known about the biotransformation and the metabolism of anthocyanins so far.


OBJECTIVE
The aim of the study was to investigate possible transformation pathways of anthocyanins by human faecal microflora and by rat liver microsomes as a source of cytochrome P450 enzymes as well as of glucuronyltransferases.


METHODS
Pure anthocyanins, an aqueous extract of red radish as well as the assumed degradation products were incubated with human faecal suspension. The incubation mixtures were purified by solid-phase extraction and analysed by HPLC/DAD/MS and GC/MS. Quantification was done by the external standard method. Furthermore the biotransformation of anthocyanins by incubation with rat liver microsomes in the presence of the cofactor NADPH (as a model for the phase I oxidation) and in the presence of activated glucuronic acid (as a model for the phase II glucuronidation) was investigated.


RESULTS
Glycosylated and acylated anthocyanins were rapidly degraded by the intestinal microflora after anaerobic incubation with a human faecal suspension. The major stable products of anthocyanin degradation are the corresponding phenolic acids derived from the B-ring of the anthocyanin skeleton. Anthocyanins were not metabolised by cytochrome P450 enzymes, neither hydroxylated nor demethylated. However they were glucuronidated by rat liver microsomes to several products.


CONCLUSIONS
The gut microflora seem to play an important role in the biotransformation of anthocyanins. A rapid degradation could be one major reason for the poor bioavailability of anthocyanins in pharmacokinetic studies described so far in the literature. The formation of phenolic acids as the major stable degradation products gives an important hint to the fate of anthocyanins in vivo.
Fleschhut
Jens
J
Institute for Nutritional Physiology, Federal Research Centre for Nutrition and Food, Karlsruhe, Germany.
Kratzer
Frank
F
Rechkemmer
Gerhard
G
Kulling
Sabine E
SE
D000818:Animals; D000872:Anthocyanins / Q000378:metabolism* / Q000493:pharmacokinetics; D000975:Antioxidants / Q000378:metabolism* / Q000493:pharmacokinetics; D001711:Biotransformation; D002851:Chromatography, High Pressure Liquid; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D005243:Feces / Q000382:microbiology*; D008401:Gas Chromatography-Mass Spectrometry; D014453:Glucuronosyltransferase / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D008862:Microsomes, Liver / Q000378:metabolism*; D051381:Rats
D000872:Anthocyanins; D000975:Antioxidants; D003577:Cytochrome P-450 Enzyme System; D014453:Glucuronosyltransferase