Cyclooxygenase 2 and prostaglandin E2 are not involved in N-nitrosodiethylamine-initiated early rat hepatocarcinogenesis

Abstract

The present study was undertaken to investigate the effect of dietary supplementation with nimesulide or eugenol on N-nitrosodiethylamine (DEN)-initiated early hepatocarcinogenesis in F344 male rats. Both compounds did not alter the expression of cytochrome P450 (CYP) 2E1, the enzyme that plays a major role in the activation of DEN to genotoxic products; however, nimesulide induced the expression of CYP1A1. Western blot analysis revealed that COX-1 and COX-2 protein expressions were not modulated by DEN compared with normal controls. Furthermore, postinitiation feeding with nimesulide or eugenol did not modulate COX-2 protein expression in normal or DEN-treated rats, whereas eugenol significantly increased the liver prostaglandin E2(PGE2) levels of DEN-injected animals compared with the DEN controls. Ultimately, nimesulide or eugenol did not modify DEN-induced hepatocarcinogenesis as evidenced by insignificant changes in the number and size of preneoplastic placental glutathione S-transferase (GST-P) positive liver foci compared with the DEN controls. These results suggest that COX-2, as well as prostaglandin E2, may play no role in the post-initiation development of DEN-induced rat hepatocarcinogenesis at an early stage.