Olive leaf (Olea europaea L. folium) extract influences liver microsomal detoxifying enzymes in rats orally exposed to 2-amino-l-methyI-6-phenyI-imidazo pyridine (PhIP)

Abstract

Olive tree (Olea europaea, Oleaceae) leaf extract (OLE) exerts many biological activities. One of the most common polycyclic aromatic hydrocarbons (PAHs) that pollute the environment is 2-amino-l-methyI-6-phenyI-imidazo pyridine (PhIP). It is a food-derived carcinogen that is present in fish and meat that has been cooked at high temperatures. Due to the generation of reactive electrophilic species, phase I enzymes have the potential to cause oxidative damage. In order to safely remove these reactive species from the body, phase II detoxification (conjugation) enzymes are necessary. It is not known whether OLE could influence their activities and hence reduce the carcinogenic effects of PhIP. This study evaluated whether OLE could modulate phase I detoxifying enzymes as well as phase II enzymes that metabolize PhIP in rat liver microsomes. Four groups of rats were used: group I: no treatment; group II: OLE (10 mg/kg bw orally); group III: PhIP (0.1 mg/kg bw orally); and group IV: PhIP followed by OLE. After 4 weeks, the activities of phase I enzymes such as CYP1A1 (ethoxyresorufin O-deethylase), CYP2E1 (p-nitrophenol hydroxylase), CYP1A2 (methoxyresorufin O-demethylase), UDP-glucuronyl transferase, sulphotransferase, and glutathione-S transferase were evaluated in rat liver microsomes. Analysis of OLE by gas chromatography-mass spectrometry (GC/MS) showed various active ingredients in OLE, including 3,5-Heptadienal (C10H14O), 3,4-dimethoxy benzoic acid (C8H10O3), 4-hydroxy-3-methoxy (C8H8O4), 1,3,5-Benzenetriol (C6H6O3), hexadecanoic acid (C16H32O2), and hexadecanoic acid ethyl ester (C18H36O2). Our results showed that rats given PhIP were found to have a statistically significant (p < 0.001) reduction in the activities of CYP1A1, CYP1A2, and CYP2E1 in comparison with the control group. However, treatment with OLE enhanced their activities but not to a normal level compared with untreated groups. Administration of PhIP decreased the activities of phase II enzymes (glutathione S-transferase, UDP-glucuronyltransferase, or sulphotransferase) (p < 0.01) in comparison with the control group. Histological examination of rat livers was consistent with the biochemical changes. The administration of OLE improved the phase II enzyme activities in animals injected with PhIP. We conclude that OLE influences phase I and phase II detoxification enzymes exposed to PhIP, which may represent a new approach to attenuating carcinogenesis induced by it.

Keywords: Cytochrom P450; Detoxifying enzymes; Olive leaf extract; PAHs; PhIP.