Assessment of the toxicity of styrene, styrene oxide, and styrene glycol in primary cultures of motor and sensory neurons

Chronic occupational exposure to styrene is associated with a number of adverse effects on the nervous system, including sensory neuropathy and neurophysiological alterations. In order to test styrene for neurotoxic potential and investigate its mechanism of action, primary co-cultures of murine spinal cord-dorsal root ganglia (DRG)-skeletal muscle were used in a simple in vitro neurotoxicity screen. The neurotoxicity of styrene and its major metabolites, styrene oxide and styrene glycol was evaluated after both short and long-term exposure. Endpoints used to characterize neurotoxicity were both morphological and neurophysiological, and included: (1) chromatolysis, (2) axonopathy, and (3) interference with action potential generation. The major findings of this study were: (1) styrene and oxide were acutely cytotoxic to all cell types at concentrations in excess of 2.0 mM and 0.2 mM respectively. (2) There was no evidence of neurotoxicity attributable to styrene or its metabolites, with the exception of a slight chromatolytic effect induced by 0.2 mM styrene oxide in DRG neurons after long-term exposure. It is therefore possible that cytotoxic mechanisms rather than effects on neuron specific processes, underlie styrene's damage to cells of the nervous system. (3) Surprisingly, dimethyl sulfoxide (DMSO), a common in vitro solubility vehicle, was neurotoxic after long-term exposure, producing both chromatolysis and axonopathy. This study, therefore also established the upper limit of DMSO recommended for use as a solubility vehicle in long-term in vitro tests