Spermine induces cell death in cultured human embryonic cerebral cortical neurons through N-methyl-D-aspartate receptor activation

The polyamines putrescine, spermidine, and spermine play important roles in cell proliferation, differentiation, and modulation of ion channel receptors. However, the function of increased concentrations of these compounds in brain injury and disease is unclear, in that they have been proposed as being both neuroprotective and neurotoxic. The effects of spermine and putrescine were studied in human primary cerebral cortical cultures containing both neurons and glia. No toxic effects were induced at 8 days in vitro (DIV) by either of the two polyamines at concentrations ranging from 0.3 microM to 2 mM. However, when the oxidative metabolism of spermine that generates toxic byproducts was induced by the presence of fetal calf serum, spermine caused cellular death with an LC(50) of approximately 50 microM. At 14 DIV, the coapplication of spermine 2 mM and glutamate 5 mM induced neuron cell death, but the effect of applying both components separately was null. Both spermine and glutamate were toxic to older neurons (26-42 DIV cultures), and here the coapplication of glutamate was found always to intensify the effect of spermine. Spermine showed greater toxicity than glutamate in neurons. Another effect observed is that glutamate, but not spermine, induced astrocyte swelling. Spermine toxicity was inhibited by both MK801 and ifenprodil, indicating a mechanism involving N-methyl-D-aspartate (NMDA) receptor activation. Moreover, a strong spermine modulation of the NMDA receptor was demonstrated by the inhibition of glutamate toxicity by ifenprodil. Putrescine induced minor effects also as a neurotoxic agent. In conclusion, neuronal death by spermine can be induced by its toxic byproducts as well as through NMDA receptor action. The present results confirm the potentially harmful role of the polyamines in excitotoxicity-related human disorders.