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 />
Chlorogenic acid is a product of the phenylpropanoid biochemical pathway and the<br />
first step in the phenylpropanoid pathway involves the deamination of phenylalanine<br />
to cinnamate via the enzyme phenylalanine ammonia lyase (PAL). Phenylalanine<br />
ammonia lyase RNA levels respond to several regulatory signals, and were reported to<br />
be a main factor affecting CGA levels in transgenic systems. Synthesis of CGA from<br />
cinnamate requires four enzymes to complete two hydroxylations on the aromatic ring<br />
and a conjugation of the hydroxycinnamate and quinate moieties: cinnamate-4-<br />
hydroxylase (C4H), 4-coumaroyl-CoA ligase (4CL), coumaroyl-CoA:quinate<br />
hydroxycinnamoyl- transferase (HQT), and coumarate/coumaroylquinate-3-<br />
hydroxylase (C3H). 182,183<br />
Metabolism of chlorogenic acids and health<br />
Dietary polyphenols when tested in animals or humans affect various physiologic and<br />
physiopathologic processes, but the exact nature of the active compounds is still<br />
unknown. Knowledge concerning the absorption of chlorogenic acid in humans is<br />
essential to evaluate possible health effects in vivo because the absorbed fraction of<br />
chlorogenic acid will enter into the blood circulation and thus can induce biological<br />
effects in the blood circulation. Furthermore, the fraction that is not absorbed will<br />
enter into the colon where it might have biological effects.<br />
Like other dietary polyphenols, chlorogenic acids are an antioxidant. In vitro, it<br />
scavenges radicals generated in the aqueous phase, 184,185 increases the resistance of<br />
LDL to lipid peroxidation 186,187,188 and inhibits DNA damage. 189,190 In vivo, when<br />
added to the diet, it inhibits chemically induced carcinogenesis of the large intestine,<br />
liver and tongue in rats and hamsters. 191,192,193,194<br />
Caffeic acid and chlorogenic acids have antioxidant properties, illustrated by their<br />
ability to scavenge various free radicals when tested in vitro. 195,196,197,198,199 In vivo,<br />
when ingested with the diet, caffeic acid and chlorogenic acid increase the plasma<br />
antioxidant capacity, the concentrations of endogenous antioxidants such as vitamin E<br />
and the exvivo resistance of lipoproteins to oxidation. 200,201,202 Chlorogenic acids also<br />
are able to reverse the pro-oxidant effects of drugs such as paraquat. 2<strong>03</strong> Chlorogenic<br />
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