Flavonoid conjugates identified in plasma and urine

A summary of the data in the various reports concerned with the structures of flavonoid conjugates in vivo has been published recently (Kroon et al. 2004) therefore, only a brief summary will be provided here, and the reader is advised to refer to this citation for a more detailed account. As mentioned, more detailed investigations are emerging as technology permits (Mullen etal. 2004,2006 Jaganath etal. 2006). 

For the flavones, there is some evidence to indicate a luteolin monoglucuronide is obtained (Shimoi etal. 1998, 2000). Chrysin-7-0-sulphate and chrysin-7-O-glucuronide 

The concentration of 4, 4 -di-0-methyl-epigallocatechin gallate was about 15% that of unmethylated epigallocatechin gallate in human plasma. It is likely that the gallated flavan-3-ols produce numerous combinations of conjugated metabolites. The structures of the predominant forms of these metabolites in plasma after green tea consumption need to be determined. 

Approximately one hundred studies have been published to date on the bioavailability and pharmacokinetics of individual polyphenols following a single dose of pure compound, plant extract or whole food/beverage to healthy volunteers. We recently reviewed the pharmacokinetic data available for each class to estimate average pharmacokinetic parameters including the maximum concentration in plasma (Qnax) Tmax the area under the plasma concentration versus time curve (Al/Q, ehmination half-life (Ti/2) and percent of dose excreted in urine (Manach and Donovan 2004). Here, we present a summary of that data 

Only two studies are available in humans on proanthocyanidins (Holt etal. 2002 Sano et al. 2003). They both showed that the C ax in plasma for dimers Bi and B2 was in the 10-20 nM range even after consumption of two of the richest food sources, chocolate and grape seed extract. Due to the low plasma concentrations it has not been possible to determine other pharmacokinetic parameters such as elimination half-life. As discussed above, absorption of trimers or proanthocyanidins with higher degree of polymerization has never been reported and is unlikely to occur according to the size and polarity of the compounds and their strong binding capacity to proteins. 

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