Down regulation of
aryl sulfotransferase IV (AST IV) in promotion/progression of liver
carcinogenesis by
N-2-fluorenylacetamide (2-FAA) has been established. This study examined whether the C-9 oxidized metabolites of 2-FAA, which have recently been shown to promote
diethylnitrosamine (DEN)-initiated liver
carcinogenesis in male Sprague-Dawley rats, effect the above change. Hence, in DEN-initiated rats, the effects of promoting regimens of 9-OH-2-FAA or 9-oxo-2-FAA, 15 oral doses at 50 and 100 mumol/kg of
body weight, were compared to those of 2-FAA at 50 mumol/kg of
body weight and of the vehicle on the activity of N-hydroxy(OH)-2-FAA
sulfotransferase (ST), an
isozyme of AST IV and AST IV expression and distribution. Relative to the vehicle, treatment with the fluorenyl compounds led to decreased levels in hepatic N-OH-2-FAA ST activity and development of hepatic nodules and
tumors which had still lower levels of the ST activity than the respective remnant livers. At approximately 8 months
after treatment with the C-9-oxidized compounds at doses twice that of 2-FAA, the extents of decreases in the hepatic N-OH-2-FAA ST activity and cytosolic AST IV
protein in
tumors were comparable to those with 2-FAA. Immunocytochemical analysis showed close association of AST IV deficiency with neoplastic liver lesions. In comparison to N-OH-2-FAA, 9-OH-2-FAA had only low and 9-oxo-2-FAA lacked
sulfate acceptor activity in the presence of male rat liver cytosol or AST IV. At 3.3-fold greater concentration than N-OH-2-FAA, 9-oxo-2-FAA inhibited (27%) the
sulfate acceptor activity of N-OH-2-FAA in the presence of AST IV, which suggested interference by 9-oxo-2-FAA at the active site. Although the C-9-oxidized compounds do not appear to be substrates for N-OH-2-FAA ST, their ability to cause a decrease in N-OH-2-FAA ST activity and
protein similar to that of 2-FAA supports their role in hepatocarcinogenesis. Whereas 9-OH-2-FAA had a 3.9-fold greater
sulfate acceptor activity in the presence of female than male rat liver cytosol and inhibited
dehydroepiandrosterone ST activity of female rat liver, N-OH-2-FAA and 9-oxo-2-FAA inhibited
estrone ST activity of male rat liver, suggesting that the C-9-oxidized compounds as well as N-OH-2-FAA are substrates for STs other than AST IV.