The neurotoxic effects of the commercial organic solvents n-hexane and methyl n-butyl ketone (MBK), recently discovered to cause profound peripheral neuropathy in man, were studied in neuronal-like cells in tissue culture. These agents are known to induce marked proliferation of 10 nm neurofilaments in peripheral and central axons of both humans and rats. In a murine neuroblastoma cell line, previously reported to show filamentous hyperplasia when exposed to aluminum ions, both MBK and n-hexane induced a highly reproducible series of cytotoxic effects at the light and electron microscopic levels and caused dose-dependent inhibition of cellular proliferation. In contrast, two closely related but clinically non-toxic solvents, methyl isobutyl ketone and methyl ethyl ketone, caused little or no cytopathological or growth inhibiting effects. MBK and its major water soluble derivative, 2,5-hexane dione (HD), produced identical cytotoxic changes in vitro, supporting the postulate that HD is the toxically active agent in victims exposed to MBK
Although MBK and n-hexane adversely affected3 the extension or maintenance of neuritic processes, electron microscopy and immunofluorescent reaction failed to reveal any proliferation of 10 nm cytoplasmic filaments in the intoxicated cells. Also, these agents had no deleterious effect on in vitro brain microtubule polymerization. In contrast, aluminum ions produced a doserelated inhibition of neurotubule assembly, similar to that seen with the filament-inducing agents colchicine and vinblastine. The results suggest that the fibrous cytoskeleton may not be the primary or essential target of MBK, n-hexane and related human neurotoxins.