Lack of Chemoprevention Effects of the Monoterpene d‐Limonene in a Rat Multi‐organ Carcinogenesis Model

Modifying effects of dietary administration of the monoterpene d‐limonene were examined using a multi‐organ carcinogenesis model. Groups of twenty F344 male rats were treated sequentially with N‐diethylnitrosamine (DEN, i.p.), N‐methyl‐N‐nitrosourea (MNU, i.p.), 1,2‐dimethylhydrazine (DMH, s.c.), N‐butyl‐N‐(4‐hydroxybutyl)nitrosamine (BBN, in drinking water) and dihydroxy‐di‐N‐propylnitrosamine (DHPN, in drinking water) during the first 4 weeks (DMBDD treatment), and then (d‐limonene was administered in the diet, at the dose of 2.0, 1.0 or 0.5%. The maximal tolerable dose was 2.0% under the present conditions. Further groups were treated with DMBDD or 2.0%d‐limonene alone as controls. All surviving animals were killed at week 28, and major organs were examined histopathologically for development of preneoplastic and neoplastic lesions. The incidences and/or multiplicities of renal atypical tubules and adenomas were increased in animals fed 2.0%d‐limonene. The immunohistochemical reactivity for α(2u)‐globulin in the proximal tubules was greater in rats fed d‐limonene than in the carcinogen alone group. No enhancing or inhibitory effect was noted for tumor development in other organs. The present results indicate a lack of any chemopreventive effect of (d‐limonene in any organ of male rats under the present experimental conditions.