Aryl sulfotransferase IV deficiency in rat liver carcinogenesis initiated with diethylnitrosamine and promoted with N-2-fluorenylacetamide or its C-9-oxidized metabolites

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.

Reversibility of cellular and organ pathology in enzyme replacement trials in animal models of lysosomal storage diseases

Enzyme replacement therapy (ERT) has now become a feasible treatment option for several lysosomal storage diseases (LSDs). Although the rationale behind this approach is straightforward, there are many factors that may influence the efficacy of treatment. The reversibility of cellular and organ pathology depends on several factors including the particular organ targeted, the dose and biodistribution of enzyme, the accessibility of the target cell to the infused enzyme, the abundance of receptors for mannose-6-phosphate and other ligands in the target tissue and the activity of endocytosis. In addition, each lysosomal enzyme is unique and its ability to reverse pathology must be individually determined according to source, glycosylation and phosphorylation status. The extent to which cellular pathology may be corrected depends upon the delivery of sufficient enzyme to the diseased tissues.

CONCLUSION

Studies in animal models have identified numerous factors that influence the therapeutic efficacy of ERT. This would suggest that in patients affected by LSDs rigorous evaluation of each therapeutic preparation will be needed.

Reversibility of cellular and organ pathology in enzyme replacement trials in animal models of lysosomal storage diseases

Enzyme replacement therapy (ERT) has now become a feasible treatment option for several lysosomal storage diseases (LSDs). Although the rationale behind this approach is straightforward, there are many factors that may influence the efficacy of treatment. The reversibility of cellular and organ pathology depends on several factors including the particular organ targeted, the dose and biodistribution of enzyme, the accessibility of the target cell to the infused enzyme, the abundance of receptors for mannose-6-phosphate and other ligands in the target tissue and the activity of endocytosis. In addition, each lysosomal enzyme is unique and its ability to reverse pathology must be individually determined according to source, glycosylation and phosphorylation status. The extent to which cellular pathology may be corrected depends upon the delivery of sufficient enzyme to the diseased tissues.

CONCLUSION

Studies in animal models have identified numerous factors that influence the therapeutic efficacy of ERT. This would suggest that in patients affected by LSDs rigorous evaluation of each therapeutic preparation will be needed.