Neoplastic lesions of the kidneys in untreated Long‐Evans Cinnamon (LEC) rats of 57–118 weeks old (85 males and 34 females) and male F344 rats of 64–93 weeks old (59 males) were examined histologically. The incidences of renal cell tumors in male and female LEC rats were 6/80 (8%) in weeks 57–65, 3/19 (16%) in weeks 66–75, 3/8 (38%) in weeks 76–105 and 7/12 (58%) in weeks 106–118. Of these tumors, 13 were microscopic adenomas and 7 were renal cell carcinomas. The copper content of the kidneys was about three times higher in LEC rats than in F344 rats (P<0.001), but the iron content of the kidneys was similar in the two strains.

Spontaneous renal cell tumors in totals of 223 male and female Long-Evans Cinnamon (LEC) rats of 51-120 weeks old, 157 male F344 rats of 51-120 weeks old, and 14 male Long-Evans Agouti (LEA) rats of 51-70 weeks old were examined histologically. The incidences of renal cell tumors increased with age in male and female LEC rats, but no tumors developed in F344 or LEA rats. Dilated atypical tubules of the kidneys were observed at high incidence in aged LEC rats. Copper staining of LEC rat kidneys showed a positive reaction in proximal tubules of the cortex and the outer stripe of the medulla. The renal copper concentration of LEC rats reached a peak in the period of necrotizing hepatitis with renal tubular necrosis, and was higher than that in F344 rats for up to 106 weeks. In contrast, the renal iron concentration of LEC rats was lower than that in F344 rats except in the period of necrotizing hepatitis. Long-term treatment of LEC rats with Dpenicillamine, a copper-chelating agent, inhibited accumulation of copper, but not iron, in the kidneys, and inhibited the development of karyomegaly of proximal tubules and dilated atypical tubules. These results suggest that persistent copper accumulation after toxic necrosis of tubules is the major cause of spontaneous renal carcinogenesis in LEC rats. Key words: Renal carcinogenesis -Spontaneous -Copper -LEC ratThe LEC rat is an inbred strain showing abnormally high copper accumulation in the liver, 1) and has a deletion in the copper-transporting ATPase gene (Atp7b)2) homologous to the human Wilson's disease gene. This mutant rat strain was originally isolated from a closed colony of Long-Evans rats.3) LEC rats develop necrotizing hepatitis with jaundice 4 to 6 months after birth and this hepatitis is inherited in an autosomally recessive manner. 4) About 20-50% of these rats die of fulminant hepatitis, and hepatocellular carcinomas develop in rats of 12 months old or more that recover from the liver injury.4-6) Both the hepatitis and hepatocellular carcinomas can be prevented by treatment with the copper-chelating agent, D-penicillamine or trientine. 7,8) Patients with Wilson's disease are known to have abnormal renal function and penicillamine therapy improves their renal function, 9) but we know of no reports of renal neoplasms in cases of Wilson's disease. We have reported that renal cell tumors develop spontaneously in LEC rats. 10) In the present study, we examined preneoplastic and neoplastic lesions of the kidneys in rats of 51-120 weeks old, and the changes in renal copper and iron concentrations of LEC and F344 rats of 6-106 weeks old. We also investigated the effect of D-penicillamine on spontaneous renal carcinogenesis. MATERIALS AND METHODSAnimals LEC/Tj rats and LEA/Tj rats, a sibling line of the LEC rats, were bred in the Institute for Animal Experimentation of the University of Tokushima, in specific pathogen-free conditions. In our laboratory, the mortality rate of LEC rats during the period of jaundice is 12.4% for males (n=193) and 42.3% for females (n=...

We studied the susceptibilities to N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN)-induced urinary bladder carcinogenesis of male Long-Evans Cinnamon (LEC), F344 and Long-Evans Agouti (LEA) rats. Male rats (n = = = =21) were given 0.1% BBN in their drinking water from week 6, 8 and 10 for one week, and killed in week 56. The incidences of transitional cell tumors (papillomas plus carcinomas) in BBN-treated LEC and F344 rats were 12% and 76%, respectively (P < < < <0.001, experiment 1), and those in LEC and LEA rats were 11% and 95%, respectively (P < < < <0.001, experiment 2). When male LEC and F344 rats were given 0.1% BBN in their drinking water for 7 days, the intake of BBN and the urinary concentration of its active metabolite, N-butyl-N-(3-carboxypropyl)nitrosamine (BCPN), were higher in the LEC rats (P < < < <0.01). The urinary pHs of untreated LEC and F344 rats were similar between week 6 and 30. The urinary copper concentration was lower in LEC rats before jaundice than in F344 rats, but its concentrations in 28-and 50-week-old LEC rats were 1.7 and 2.3 times those in F344 rats. In a two-stage carcinogenesis study using F344 rats, i.p. injections of cupric nitrilotriacetate increased urinary copper excretion, and inhibited BBNinduced bladder carcinogenesis. In a two-stage carcinogenesis study using LEC rats, oral administration of D-penicillamine decreased urinary copper excretion, and increased BBN-induced bladder cancer, although the difference was not significant. These data show that LEC rats are resistant to bladder carcinogenesis and suggest that urinary copper has a significant role in their resistance.

To examine the effect of nongenotoxic chemicals on hepatocarcinogenesis in Long-Evans Cinnamon (LEC) rats, we gave 6-week-old male and female LEC rats (n= = = =18) weekly subcutaneous injections of D-galactosamine hydrochloride (GalN, 300 mg/kg) in 0.9% NaCl or only 0.9% NaCl for 50 weeks, and killed them in week 62. GalN-treated male rats unexpectedly showed no lethal necrotizing hepatitis. GalN treatment increased the incidence of cholangiofibrosis in males and its severity in females, but did not cause significant increases of hepatocellular tumors in either sex. GalN treatment increased the 5-bromo-2′ ′ ′ ′-deoxyuridine (BrdU)-labeling index of hepatocytes and plasma hepatocyte growth factor, and accelerated megalocytic alterations without reduction of the hepatic copper concentration. Next, male and female LEC rats were subjected to two-thirds partial hepatectomy (PH) or sham hepatectomy in week 8 (n = = = =12) or in week 14 (n = = = =9), and killed in week 62.PH in week 14 inhibited lethal hepatitis, but PH in week 8 was less effective. PH reduced the hepatic copper concentration to half that of controls. The present data suggest that induction of hepatocyte regeneration by repeated injections of GalN, or by PH just before the onset of jaundice has a significant effect in prevention of hepatic injury of LEC rats, but not enhancement of spontaneous hepatocarcinogenesis.

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