| Description |
Recent epidemiological data support a protective effect of vegetables, fruits, tea and wine intake against cancer or cardiovascular diseases. The protective effect can be also attributed to antioxidant polyphenolic compounds, such as flavonoids or phenolic acids, found in the plants in the high amounts. The flavonoids show a strong antioxidant activity in vitro and intake of flavonoids was inversely correlated to coronary heart disease mortality in 3 out of 5 epidemiological prospective cohort studies1. However, little is known about the antioxidative activity, bioavaibility and health effect of dietary phenolic acids, such as hydroxycinnamates (e.g. caffeic and chlorogenic acid), components of many plant-derived foods. In this work, we determined an antiradical activity of dietary caffeoylquinic acids, 5-caffeoylquinic acid (5-CQA, trivial name chlorogenic acid, Fluka), 1,3-dicaffeoylquinic acid (1,3-DiCQA, trivial name cynarin), 1,5-dicaffeoylquinic acid (1,5-DiCQA) and caffeic acid (Sigma). The antiradical activity of caffeic acid derivatives was compared with that of L-ascorbic acid and flavonoids luteolin and luteolin-7-O-glucoside that contain like caffeic acid the catechol group. Chlorogenic acid is only one commercially available caffeoylquinic acid, 1,3-DiCQA and 1,5-DiCQA were together with flavonoids luteolin and luteolin-7-O-glucoside isolated from the leaves of Cynara cardunculus (Asteraceae). The radical scavenging activity was measured using free stable 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical. The antiradical effects of all phenolic acids and flavonoids were stronger than that of L-ascorbic acid (EC50 = 10.3 umol/L). The ability to scavenge the free stable DPPH radical increased with the number of the catechol groups in the order: caffeic acid (EC50 = 5.8 umol/L) < chlorogenic acid (5.0 umol/L) < luteolin (4.8 umol/L) < luteolin-7-glucoside (4.3 umol/L) < 1,3-DiCQA (3.9 umol/L) < 1,5-DiCQA (2.8 umol/L). The stronger antiradical activity of 1,5-DiCQA than that of 1,3-DiCQA may be rationalized by the presence of one equatorial caffeoyl group in 1,5-DiCQA, whereas 1,3-DiCQA has both axial caffeoyl groups. Comparing the scavenging activities, 1 mole of ascorbic acid reacted with approximately 2 moles of DPPH radical and 1 mole of 1,5-DiCQA scavenged about 6 moles of the radical. This is in good accordance to results obtained with 3,5-DiCQA5. Our findings show that DiCQAs have the strong radical scavenging activity in vitro. The interest in research of caffeoylquinic acids has increased greatly in the last years not only for their presence in the diet, but also for their significant biological activity, e.g. DiCQAs has been recently found as potent and selective inhibitors of HIV-1 integrase and HIV-1 replication6. However, very limited data are known about their bioavaibility and metabolism in humans.
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