Spermine cytotoxicity to human colon carcinoma-derived cells (CaCo-2)

Spermine is a constituent of all vertebrate cells. Nevertheless, it exerts toxic effects if it accumulates in cells. Spermine is a natural substrate o f the FAD-dependent polyamine oxidase, a constitutive enzyme of many cell t ypes. It has been reported that the toxicity of spermine was enhanced if po lyamine oxidase was inhibited. We were interested to examine spermine toxic ity to human colon carcinoma-derived CaCo-2 cells because, in contrast to m ost tumor cell lines, CaCo-2 cells undergo differentiation, which is parall eled by changes in polyamine metabolism. CaCo-2 cells were remarkably resis tant to spermine accumulation, presumably because spermine is degraded by p olyamine oxidase at a rate sufficient to provide spermidine for the mainten ance of growth. Inactivation of polyamine oxidase increased the sensitivity to spermine. A major reason for the enhanced spermine cytotoxicity at low polyamine oxidase activity is presumably the profound depletion of spermidi ne, and the consequent occupation of spermidine binding sites by spermine. Hydrogen peroxide and the aldehydes 3-aminopropanal and 3-acetamidopropanal , the products of polyamine oxidase-catalyzed splitting of spermine and N-1 -acetylspermine, contribute little to spermine cytotoxicity. Activation of caspase by spermine was insignificant, and the formation of DNA ladders, an other indicator of apoptotic cell death, could not be observed. Thus it app ears that cell death due to excessive accumulation of spermine in CaCo-2 ce lls was mainly nonapoptotic. The content of brush border membranes did not change between days 6 and 8 after seeding, and it was not affected by expos ure of the cells to spermine. However, the activities of alkaline phosphata se, sucrase, and aminopeptidase in nontreated cells were considerably enhan ced during this period, but remained low if cells were exposed to spermine. These changes appear to indicate that differentiation is prevented by into xication with spermine, although other explanations cannot be excluded.