Enhanced liver tumor promotion activity in rats subjected to combined administration of phenobarbital and orphenadrine

Abstract

-Phenobarbital (PB) and orphenadrine (ORPH) are cytochrome P450 (CYP) 2B inducers and have liver tumor-promoting effects in rats. In this study, we performed a rat two-stage liver carcinogenesis bioassay to examine the tumor-promoting effect of PB and ORPH co-administration. Twelve male rats per group were given an intraperitoneal injection of N-diethylnitrosamine (DEN) for initiation. Twoweek after DEN administration, rats were given PB (60 or 120 ppm in drinking water), ORPH (750 or 1,500 ppm in diet) or 60 ppm PB+750 ppm ORPH for 6-week. One-week after the PB/ORPH treatment, all rats were subjected to two-thirds partial hepatectomy. To evaluate the effect of the combined administration, we used two statistical models: a heteroadditive model and an isoadditive model. In the heteroadditive model, the net values of the number and area of glutathione S-transferase placental form (GST-P) positive foci, Cyp2b1/2, Gstm3 and Gpx2 mRNA levels, microsomal reactive oxygen species (ROS) production and thiobarbituric acid-reactive substances level in the PB+ORPH group were significantly higher than the sum of the net values of those in the Low PB and Low ORPH groups. In the isoadditive model, the average values of the area of GST-P positive foci and PCNA positive hepatocyte ratio and Gstm3 mRNA level in the PB+ORPH group were significantly higher than the average values of those in the High PB and High ORPH groups. These results suggest that PB and ORPH co-administration causes synergistic effects in liver tumor-promoting activity in rats resulting from oxidative stress due to enhanced microsomal ROS production.

Modifying effects of liver tumor promotion in rats subjected to co-administration of indole-3-carbinol and phenobarbital

“…On the other hand, our previous studies demonstrated that the co-administration of CYP1A inducers, OPZ and BNF, at low doses induced increased numbers and area of GST-P + foci when compared with the respective administration of OPZ and BNF at high doses and the administration of OPZ at high doses, respectively (Hayashi et al, 2012b). In addition, our group demonstrated that the co-administration of CYP2B inducers, PB and ORPH, at low doses significantly increased the numbers and area of GST-P + foci compared with the respective administration of PB at low or high dose and of ORPH at a low dose, respectively (Morita et al, 2013). Therefore, there may be no modifying effect in terms of liver tumor promotion in rats subjected to combined administration of different types of CYP inducers, unlike the combined administration of the same type of CYP inducers.…”

“…However, the combined administration of two different CYP1A inducers causes a synergistic effect in liver tumor promoting in rats (Hayashi et al, 2012b), and the combined liver tumorpromoting effect of two different CYP2B inducers is synergistic in rats (Morita et al, 2013). Therefore, particular attention in risk assessments should be paid to the combined exposure of plural chemicals that are recognized as CYP inducers inducing the same CYP family.…”

“…It has been demonstrated that co-administration of several hepatocarcinogens at doses lower than the apparent carcinogenic doses results in carcinogenic actions in rats (Hasegawa et al, 1989). Our group previously reported the modifying effect of liver tumor promotion by coadministration of CYP inducers in rats (Hayashi et al, 2012b;Morita et al, 2013). Hayashi et al (2012b) reported that co-administration of CYP1A inducers, OPZ and BNF, resulted in synergistic effects in liver tumor promotion probably because of increased COX-2 expression.…”

“…Hayashi et al (2012b) reported that co-administration of CYP1A inducers, OPZ and BNF, resulted in synergistic effects in liver tumor promotion probably because of increased COX-2 expression. Co-administration of CYP2B inducers, PB and ORPH, also caused synergistic effects in liver tumor promotion resulting from oxidative stress following enhanced microsomal ROS production (Morita et al, 2013). Therefore, we hypothesized that the combined administration of CYP1A and CYP2B inducers also enhances CYP inductions resulting in oxidative stress and enhances liver tumor promotion in rats.…”

“…Morita et al (2011) recently reported that production of microsomal ROS and thiobarbituric acid-reactive substances (TBARS) with increased Cyp2b induction resulting from PB treatment is involved in the effects of liver tumor promotion in rats. Orphenadrine (ORPH), a derivative of the antihistamine diphenhydramine, also induces CYP2B in the livers of rats (Murray et al, 2003) and has a liver tumor-promoting effect in rats attributable to oxidative DNA damage resulting from increased microsomal ROS production (Morita et al, 2013). It has been demonstrated that co-administration of several hepatocarcinogens at doses lower than the apparent carcinogenic doses results in carcinogenic actions in rats (Hasegawa et al, 1989).…”