Nephrotoxicity and hepatotoxicity of 1,1-dichloro-2,2-difluoroethylene in the rat. Indications for differential mechanisms of bioactivation

1,1-Dichloro-2,2-difluoroethylene (DCDFE) produced marked nephrotoxicity in rats upon an i.p. dose of 150 mumole/kg. At doses higher than 375 mumole/kg, DCDFE also produced hepatotoxicity. Aminooxyacetic acid, an inhibitor of cysteine conjugate beta-lyase, appeared to be slightly nephrotoxic in Wistar rats. Nevertheless it exerted an inhibitory effect on the nephrotoxicity of DCDFE. The N-acetylcysteine conjugate of DCDFE was identified as a major urinary metabolite of DCDFE. When administered as such, this conjugate appeared to be a potent nephrotoxin, without any effect on the liver, indicating that glutathione conjugation of DCDFE is most likely a bioactivation step for nephrotoxicity. The appearance of traces of chlorodifluoroacetic acid in urine of rats treated with higher doses of DCDFE indicates the existence of an oxidative pathway of metabolism of DCDFE, probably involving epoxidation by hepatic mixed-function oxidases. It is speculated that the latter route might account for the hepatotoxicity at higher doses of DCDFE. The nephro- and hepatotoxicity of DCDFE, therefore, most likely are the result of two different mechanisms of bioactivation.

[Transplantation model of human lung oat cell carcinoma in nude mice]

A human lung oat cell carcinoma from a surgical specimen was successfully transplanted into nude mice and has been maintained for over four years through 14 passages. This transplanted tumor had a long latent period of more than one month, slowly growing in the initial inoculation and the following passages. The interval between two passages was about four months. 5 months after the inoculation, the transplanted tumor in nude mice grew to 2 cm in diameter. It was demonstrated that the transplanted tumor possessed the human isoenzyme pattern and human chromosome karyotype. The original human tumor and its transplanted counterparts in the nude mice were strikingly similar by histopathology. Besides, specific neuro-secretory granules in cytoplasm of the transplanted tumor were observed under transmission electron microscope.

[Ultrastructural study on the model of human lung adenocarcinoma heterotransplanted to nude mice]

A human lung adenocarcinoma from surgical biopsy specimen was successfully heterotransplanted into nude mice and has been maintained for 40 generations. The experiments were made on 6-8 week old male or female nude mice with Swiss genetic background cultivated in specific pathogen-free condition. The electron microscopic observation on transplanted tumor of passages 2, 6, 12, 18 and 23 revealed that the ultrastructural features of this tumor were strictly maintained and no obvious change of differentiation was found. But there was a potential prone to regional squamous epithelial metaplasia in the transplanted tumor. The nude mice model of human lung adenocarcinoma so established can be used as a good experimental system of the homologous and reproducible human cancer for the study of basic medical sciences and chemotherapy of human lung carcinoma.

[Changes in protein in bile excretion from rat liver inoculated with BERH-2 hepatoma]

Rocket immunoelectrophoresis was used to assay the change in alpha fetoprotein (AFP) and albumin (Alb) in bile of rats 10 to 14 days after intrahepatic or intraperitoneal inoculation of BERH-2 hepatoma. The bile was collected from the common bile duct cannula. Total protein was determined by the Lowry method. The results showed that the excretion of total protein and Alb was reduced to 54% and 24% of the control in the intrahepatic group, and 65% and 56% of the control in the intraperitoneal group. Bile-AFP can be detected in rats in both groups and its concentration increased gradually during the tumor progression. In the hepatic group, the bile-AFP content per gram of tumor tissue was 29% of that in the intraperitoneal group. It suggests that decreased excretion of AFP, Alb and total protein in bile of rat bearing tumor in the liver be related to local obstruction of excretion by the tumor mass leading to constriction of biliary canaliculi.

The effect of hydroxycamptothecin in the activity of RNA and DNA polymerases prepared from murine hepatoma cells

Hydroxycamptothecin (HCPT) is an antitumor alkaloid isolated from Camptotheca acuminata indigenous to China. It could reduce the activity of nuclear RNA polymerase II and I(III) of hepatoma cells. HCPT at 25-100 microM caused a remarkable inhibition on DNA polymerase alpha whilst only a slight inhibition on beta. The inhibitory action on alpha was restored by increasing amounts of enzyme or DNA template, but unchanged by varying amounts of substrate. It is suggested that HCPT may exert a stronger inhibition on DNA replication process.