Non-enzymatic degradation of acid-soluble calf skin collagen by superoxide ion: protective effect of flavonoids.

Calf skin acid-soluble collagen in microfibrillar form was incubated with free oxygen radicals produced by the system xanthine oxidase + hypoxanthine. This incubation liberated peptides of a size smaller than that of alpha-chains, as demonstrated by SDS-PAGE and by evaluation of the 4-hydroxyproline contained in small peptides. The amount of liberated peptides was found to increase with time. The process was inhibited by addition of superoxide dismutase to the medium but not by addition of catalase. Two flavonoids extracted from bilberries and a third one from grapes were demonstrated to protect collagen against this non-enzymatic proteolytic activity. This work confirms that collagen may be degraded during the process of inflammation and that some flavonoids are endowed with protective properties.