STRUCTURAL FEATURES OF TANNIC-ACID IMPORTANT FOR DNA-DEGRADATION IN THE PRESENCE OF CU(II)

Tannic acid has numerous food and pharmacological applications, It is an additive in medicinal products and is used as a flavouring agent an d as an antioxidant in various foods and beverages. However, there are reports of its mutagenicity and carcinogenicity in bacterial and anim al test systems. Tannic acid and its structural monomer gallic acid ar e also capable of inducing apoptosis in animal cells. We have earlier shown that tannic acid in the presence of Cu(II) causes DNA degradatio n through generation of reactive oxygen species such as hydroxyl radic als. In order to understand the chemical basis of the various biologic al properties of tannic acid we have studied the structure-activity re lationship between tannic acid and gallic acid using the DNA cleavage assay, Results in the present paper indicate that gallic acid is consi derably more active than tannic acid. However, if two of the three hyd roxyl groups of gallic acid are methylated (syringic acid) the DNA deg rading capacity declines sharply, Further, decarboxylation of gallic a cid (pyrogallol) leads to enhancement of its activity. In conclusion, the results indicate that the DNA cleavage activity of tannic acid is due to its digalloyl moeity and that free hydroxyl groups are essentia l for cleavage.