Antioxidant properties of Rosmarinus officinalis and its effects on xenobiotic biotransformation

Rosmarinus officinalis (rosemary) extracts display antioxidant properties mainly due to the presence of polyphenols. These properties have yet to be systematically studied in biological systems. In this study, we used rat liver microsomes to evaluate the antioxidant capacity of a dry extract from rosemary leaves. Noteworthy, compounds occurring in herbal extracts are xenobiotics to animals, thus mainly biotransformed in the hepatic endoplasmic reticulum. Thus, we also studied the ability of this extract to inhibit different xenobiotics biotransformation pathways. The rosemary extract prevented all tested oxidative processes that were evaluated in rat liver microsomes. It also inhibited the activities of: 1) UDP-glucuronyltransferase; 2) microsomal GSH-transferase; and 3) cytochrome P450 system (N-demethylating activity). Our results indicate that herbal extracts, in addition to act as antioxidants, display a significant interaction with the metabolism of xenobiotics and/or endogenous compounds. Considerations about such interaction are discussed.