Metabolism of acetyl derivatives of polyamines in cultured polyamine-deficient rat hepatoma cells.

The acetyl derivatives of polyamines, N1-acetylspermine (N1-AcSPM) and N1-acetylspermidine (N1-AcSPD), are in vitro better substrates of tissue polyamine oxidase than the corresponding non-acetylated polyamines. Rat hepatoma tissue culture (HTC) cells, depleted of their putrescine (PUT) and spermidine (SPD) content by the use of DL-alpha-difluoromethylornithine (DFMeOrn), an irreversible inhibitor of L-ornithine decarboxylase, were used to study in situ the catabolism of these acetyl derivatives of polyamines. Normal intracellular spermidine content was restored by the addition of N1-acetylspermidine to polyamine-deficient cells. Addition of spermine (SPM) did not restore the spermidine content, although this polyamine elevated the spermine content of the cells. N1-Acetylspermidine reestablished normal spermidine levels of the cells and elevated the cellular putrescine content more efficiently and more rapidly than spermidine. Monoacetylputrescine and N1, N12-diacetylspermine (di-AcSPM) were ineffective in restoring putrescine and spermidine contents. These findings support the concept that N1-acetylspermine and N1-acetylspermidine are natural substrates of tissue polyamine oxidase and suggest poor membrane permeability of monoacetylputrescine (AcPUT) and N1, N12-diacetylspermine. Furthermore, they indicate that acetylation of polyamines by the cytosolic acetyl CoA: polyamine N1-acetyltransferase is the rate-limiting step of polyamine catabolism in rat hepatoma cells. Growth inhibition by DL-alpha-difluoromethylornithine was reversed by N1-acetylspermine and N1-acetylspermidine but not by monoacetylputrescine and N1, N12-diacetylspermine. These results suggest again that the antiproliferative effect of DL-alpha-dilfuoromethylornithine is related to inhibition of polyamine biosynthesis.