Thesis-Final 03 June 2011 pdf - Jacobs University
Thesis-Final 03 June 2011 pdf - Jacobs University
Thesis-Final 03 June 2011 pdf - Jacobs University
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Background Chapter 2<br />
acid and caffeic acid have been reported to prevent different cancers and CVD in<br />
several experimental studies on animal models. 204,205,206,207,208 The biological<br />
properties of hydroxycinnamic acids depend on their absorption in the gut and on their<br />
metabolism. The absorption of caffeic acid in the small intestine has been well<br />
characterized in both experimental animals and in man, 209,210,211 but the bioavailability<br />
of chlorogenic acid is more controversial. In some studies, chlorogenic acid has been<br />
detected in urine with a recovery varying from 0·3% to 2·3%, suggesting absorption<br />
without structural modification. 212,213 Other authors have failed to detect chlorogenic<br />
acid in the plasma of both rats and man after its ingestion as a pure compound or in<br />
coffee. 214,215,216 Caffeic acid and its O-methylated metabolites are commonly found in<br />
plasma and urine after ingestion of chlorogenic acid in rats and man, showing that<br />
chlorogenic acid is hydrolysed in the body. 217,218 Such a reaction could either take<br />
place in the gut mucosa or arise from catalysis by the gut microflora. No esterase<br />
activity able to hydrolyse chlorogenic acid could be detected in human tissues<br />
(intestinal mucosa, liver) or biological fluids (plasma, gastric juice, duodenal fluid) in<br />
rats or man. 219,220,221,222,223 On the other hand, microflora in the large intestine possess<br />
esterase activity towards chlorogenic acid. 224,225 These results suggest that caffeic acid<br />
found in plasma originates from the hydrolysis of chlorogenic acid in the colon.<br />
Mechanisms of absorption<br />
The absorption of caffeic acid esterified with quinic acid (chlorogenic acid) was less<br />
than that of caffeic acid itself. It is possible that chlorogenic acid and caffeic acid are<br />
absorbed through different absorption mechanisms. There are two possible<br />
mechanisms for the absorption of chlorogenic acid in humans. The first mechanism<br />
might involve absorption of chlorogenic acid as an intact molecule as indicated by the<br />
presence of traces of chlorogenic acid in urine after ingestion of chlorogenic. 226 The<br />
second mechanism might involve hydrolysis of chlorogenic acid in the stomach<br />
and/or small intestine into caffeic acid and quinic acid before absorption. The caffeic<br />
acid moiety and the quinic acid moiety are subsequently absorbed. 227,228 .The general<br />
pathway of chlorogenic acid metabolism in rats is shown in Figure 14.<br />
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