Page last updated: Tuesday, November 18, 2008
Spare a thought for the catechins and anthocyanins by Gordon Troup
This article complements an article on Resveratrol by Dr. Philip Norrie published in AIM [1].

Resveratrol is a polyphenol belonging to the ‘stilbene’ family, roughly dumbell shaped molecules with a phenolic ring at each end. A phenolic ring is a benzene (hexagonal) hydrogen-carbon ring with at least one hydroxyl (OH) group on it. The more OH groups, the greater the antioxidant action. The term ‘catechins’ in the title includes the various single molecular forms, and their dimers and trimers also. Fig.1 illustrates (-) epicatechin, and shows the three ringed ‘skeleton’ of the catechins (also shared by the anthocyanins, the wine colourants). Fig .2 shows (+) gallocatechin, so called because it has three OH groups on the ‘B’ ring (the phenolic gallic acid has three OH groups on its single phenolic ring). The (-) means that the barred bond to the OH group in fig.1 shows that the group lies below the plane of the page, and the (+) that the same bond darkened in Fig.2 shows that the (OH) is above the plane of the page.

The discussion of the molecular structures is necessary for two reasons. First, to illustrate the statement that the more OH groups there are on the phenolic rings, the greater the antioxidant action. Fig.3 shows the molecule Epigallocatechin gallate (EGCG), The extra three OH groups on the extra phenolic ring are easily seen. This molecule is the major antioxidant in green tea, of which the anticancer and antioxidant properties have been well proven. It also occurs in red wine, from the grapeseed coats, and is leached from the cask or barrels during oak ageing.

The second reason is to show the importance of the geometric 3-dimensional structure of a molecule in chemical reactions. If it is not ‘correct’, certain reactions will not occur, just as if key is not the right shape, it will not open a lock A recent study [2] of the mixture of catechins in (Dark!) chocolate showed that it could relax blood vessels.. The chocolate mix is similar, but not identical to the red wine mix. The researchers then determined what particular molecules/molecule caused the effect. It turned out that it was only due to our first friend, (-) epichatichin (Fig.1).

Does this mean that we should go for dietary supplements of concentrates of the above two molecules? The answer is no, because all the other catechins are antioxidants, and help the ‘special’ ones do their work,. and vice-versa.

Now for the anthocyanins (pigment). These are polyphenols, and have the same A B C ring ‘skeleton’ (Fig.1) as the catechins, but with different chemical groups on them. In red wine there are many anthocyanins, and they are all attached to sugars. The mix of anthocyanins depends on the grape variety, the wine acidity, and other factors as well. A good, short account of this is given by Waterhouse [3]. These sugared molecules are bulky and can carry an electric charge, so some sort of carrie - mediated mechanism of absorption is likely to be necessary from the digestive tract. In blood plasma (both human, and of laboratory rats) they are detected at very low levels (in the milliMole and microMole range), and in fact the majority are excreted (again, in humans and laboratory rats) without metabolisation [4].

So, how and where are these molecules absorbed into the bloodstream? A group in Italy has shown that they are transported directly through the stomach wall, which has cells in it containing a transport protein which they discovered and named Bilitranslocase [5]. This molecule is also used by the body to get the waste product bilirubin out of the bloodstream into the liver, where it is metabolised for excretion: it is the product of the decay (natural) of red bloodcells. Bilirubin causes neonatal jaundice, and is responsible for the yellowish colour around bruises.

It seems quite amazing that bilitranslocase, fortunately, can also interact with anthocyanins, and transport them first into the bloodstream directly from the stomach, and then even into the liver and into brain tissue* These effects have all been verified by experiments on laboratory rats [6], giving them a standardised anthocyanin mix as found in the wine from Cabernet Sauvignon grapes. While the amount absorbed is small, it gets to the named organs very rapidly. This is a good reason for moderate daily drinking of red wine, and the eating of blueberries for example. The human body’s mechanisms becomes more wonderful the more it is researched!

It would be unwise to discount the results of the experiments on laboratory rats as being irrelevant to humans, because: (i), humans and rats behave very similarly physiologically with respect to anthocyanins [4]: and (ii), some of the first experiments to reveal the protective effects of red wine were carried out on laboratory animals.

* This author researched the photophysica of bilirubin for some years. Neonatal jaundice is curedby phototherapy, which changes the bilirubin in the blood to another form, more easily excreted by the liver.

Acknowledgements.

Sincere thanks are due to Professor Sabina Passamonti, Dipartimento Biochimica Biofisica e Chimica delle Macromolecole, Universita‘ di Trieste, Italy, and Dr. Fulvio Mattivi, Istituto Agrario di San Michele, 38010 San Michele all’ Adige, Italy, for their kind correspondence and help with obtaining their publications.

References

1. P. Norrie, Aim-Digest 16 (3), 2005, 8.

2. H. Schroeter et al., Proc. Nat. Acad. Sci.USA 103, 2006, 1024.

3. A.L.Waterhouse, Annals N.Y. Acad. Sci. 957, 2002, 21.

4. T.K. McGhie et al., J. Agric. Food. Chem. 51, 2003, 4539.

5. S. Passamonti & G.L. Sottocasa, Recent research developments in Biochemistry (G.S. Pandalai Ed.) 2002 part 1, (Kerala India Research Signpost) 3, 371.

6. S. Passamonti, U. Vrhovsek and F. Mattivi, Biochem. Biophys. Res, Comm. 296, 2002,631.

S. Passamonti et al.,FEBS Letters 544, 2003, 210.

S. Passamonti et al., Food Res. Int. 38, 2005, 953.

S. Passamonti et al., J.Agri. Food.Chem, 53, 2005, 7029.

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