Metabolism of N8-monoacetylspermidine in rat hepatoma cells. Investigation of its effect on the activity of L-ornithine decarboxylase.

Recent evidence has indicated a role for the acetyl derivatives of polyamines, particularly N8-monoacetylspermidine, as activators of L-ornithine decarboxylase in rat hepatoma tissue culture (HTC) cells. This is in contrast with the well-described negative regulatory control of ornithine decarboxylase exerted by their non-acetylated counterparts. Because of the possibility of a rapid extracellular and intracellular catabolism of the acetyl derivatives of polyamines, the metabolism of N8-monoacetylspermidine and its effect on HTC cell ornithine decarboxylase have been investigated, under conditions which eliminate its extracellular catabolism. Differing from previous reports, we demonstrate that N8-monoacetylspermidine does not elevate ornithine decarboxylase activity when added at low concentrations to the culture medium of HTC cells. Higher concentrations decrease ornithine decarboxylase activity in a dose-dependent manner. This effect cannot be unambiguously attributed to the effect of the acetyl derivative itself, because of the presence in situ of a very active N8-monoacetylspermidine deacetylase, which generates spermidine intracellularly.