Inhibitory effect of naringin on the micronuclei induced by ifosfamide in mouse, and evaluation of its modulatory effect on the Cyp3a subfamily

Naringin (Nar) is a flavonone found in high amount in grapefruit. In in vitro studies to determine its antimutagenicity results have been both positive and negative. On the other hand, an increase in the bioavailability of some medicaments have been observed when these are ingested together with grapefruit. It has been suggested that the effect may be related to the inhibition of the human enzyme Cytochrome P450 (CYP) 3A4 by Nar, an enzyme with a high aminoacid sequence homology with the Cyp3a in mouse. The present study was designed for three main purposes: (1) to determine whether Nar has a genotoxic effect in mouse in vivo. This was evaluated by measuring the rate of micronucleated polychromatic erythrocytes (MNPE); (2) to determine its antigenotoxic and its anticytotoxic potential on the damage produced by ifosfamide (Ifos). The first study was done by scoring the rate of MNPE, and the second one by establishing the index polychromatic erythrocytes/normochromatic erythrocytes (PE/NE); and (3) to explore whether its antigenotoxic mechanism of action is related to an inhibitory effect of Nar on the expression of the Cyp3a enzyme, an effect which could avoid the biotransformation of Ifos. A single oral administration was used for all groups in the experiment: three groups were given different doses of Nar (50, 250, and 500 mg/kg), other groups received the same doses of Nar plus an administration of Ifos (60 mg/kg), another group treated with distilled water and another with Ifos (60 mg/kg) were used as negative and positive controls, respectively. The micronuclei and the cell scoring were made in blood samples taken from the tail of the animals at 0, 24, 48, 72, and 96h. The results showed that Nar was neither genotoxic nor cytotoxic with the doses tested, but Ifos produced an increase in the rate of MNPE at 24 and 48 h. The highest value was 24 +/- 1.57 MNPE%, cells at 48 h. The index PE/NE was significantly reduced by Ifos at 24 and 48 h. Concerning the antigenotoxic capacity of Nar, a significant decrease was observed in the MNPE produced by Ifos at the three tested doses. This effect was dose-dependent, showing the highest reduction in MNPE frequency (54.2%) at 48 h with 500 mg/kg of Nar. However, no protection on the cytotoxicity produced by Ifos was observed. Immunoblot analysis was used to assess the Cyp3a expression in liver and intestinal microsomes from mouse exposed orally to Nar. An induction in the Cyp3a protein was observed in both intestinal and hepatic microsomes from treated mice. This induction correlated with an increase in erythromycin N-demethylase activity. These data suggest that other mechanism(s) are involved in the antigenotoxic action of naringin. (C) 2001 Elsevier Science B.V. All rights reserved.