Suppression of acrylamide toxicity by carboxyfullerene in human neuroblastoma cells in vitro

In our previous study, we found that caspase-dependent apoptosis played a role in the genesis of toxicity of acrylamide in human neuroblastoma (SH-SY5Y) cells (Sumizawa and Igisu in Arch Toxicol 81:279-282, 2007). In the present experiment, we examined whether carboxyfullerene may suppress the cytotoxicity of acrylamide because carboxyfullerene has been reported to protect nerve cells from various pathologic processes including apoptosis. Carboxyfullerene lowered lactate dehydrogense leakage and elevated cell viability in SH-SY5Y cells exposed to acrylamide. It also lowered caspase-3 activities and cell population in the sub-G(1) phase induced by acrylamide. Nevertheless, carboxyfullerene enhanced cellular uptake of [C-14]acrylamide. On the other hand, acrylamide markedly decreased glutathione (GSH)-content in cells and carboxyfullerene blocked the decrease. The toxicity of acrylamide was suppressed by adding GSH or GSH monoethyl ester, whereas it was not lowered by carboxyfullerene when GSH synthesis was inhibited by l-buthionine-(S,R)-sulfoximine. Thus, the cytotoxicity of acrylamide including apoptotic processes is closely related to GSH level in SH-SY5Y cells and carboxyfullerene suppresses the toxicity by maintaining GSH content. Neither tricarboxylic acids without fullerene moiety nor hydroxylated fullerene showed comparable effects of carboxyfullerene (60 mu M) against 1-5 mM acrylamide, suggesting the importance of the three malonic acid groups at specific positions in a fullerene molecule for the effects.