Effects of pre-administration of a
choline-deficient, L-
amino acid-defined (
CDAA) diet on hepatocarcinogenesis initiated with
diethylnitrosamine (DEN) or
N-nitrosobis(2-hydroxypropyl)amine (BHP) in rats were investigated. A pre-administrating period was set as 1 week, because
CDAA diet induces liver
injuries by this time-point. In a time-course study, male Fischer 344 rats, 6 weeks old, received a 1-week pre-administration of
choline-supplemented, L-
amino acid-defined (CSAA) or
CDAA diet, DEN at a dose of 100 mg/kg
body weight by a single
intraperitoneal injection, then CSAA or
CDAA diet for up to 8 weeks, and were sacrificed 4, 6 and 8 weeks after DEN.
CDAA diet administered only after DEN significantly increased the numbers of
glutathione S-transferase placental form (GST-P)-positive lesions 4, 6 and 8 weeks after DEN and their sizes 6 and 8 weeks after DEN.
CDAA diet administered both before and after DEN similarly increased the numbers and sizes of GST-P-positive lesions, but with a significantly greater degree than obtained by the diet administered only after DEN. In a dose response study, rats received vechicle or DEN, at a dose of 0.001, 0.01, 0.1, 1, 10, 20, 50, 100 or 200 mg/kg
body weight, 1 week after the commencement of CSAA or
CDAA diet, and sacrificed 8 weeks after vehicle or DEN. The significant increases of the numbers of GST-P-positive lesions were obtained after 50-200 mg/kg
body weight of DEN under the CSAA diet administration, whereas those were detected after 10-200 mg/kg under
CDAA diet administration. Sizes became significantly larger with only 200 mg/kg
body weight of DEN in the CSAA case but with 50-200 mg/kg in the
CDAA case. Male Wistar rats received a 1-week pre-administration of CSAA or
CDAA diet, vehicle or BHP, at a dose of 600 or 1200 mg/kg
body weight, by a single
intraperitoneal injection, then CSAA or
CDAA diet for 8 weeks, and were then sacrificed. The numbers of GST-P-positive lesions demonstrated significant increment with 1200 mg/kg
body weight of BHP by
CDAA diet administered only after BHP and, to a significantly greater degree, by the diet administered both before and after BHP. While
CDAA diet administered only after BHP did not alter the sizes of GST-P-positive lesions, the diet administered both before and after 600 and 1200 mg/kg
body weight of BHP significantly increased the sizes of the lesions. These results indicate that the pre- plus post-administration of
CDAA diet enhances hepatocarcinogenesis initiated with DEN or BHP, more than the post-administration only, thus providing a sensitive model to detect weak liver carcinogenic potency of environmental chemicals.