Tetramethylenedisulfotetramine Neurotoxicity: In Vivo Validation of In Vitro Screen to Identify Potential Countermeasures

Tetramethylenedisulfotetramine (TMDT), a synthetic neurotoxin, induces a seizure syndrome by blocking Cl- influx through the GABAA channel. This process leads to uncontrolled depolarization followed by excessive Ca2+ entry into neurons and potential excitotoxicity. No standardized, effective treatment for TMDT poisoning currently exists. Primary neuronal cultures were used to screen candidate countermeasures for alleviation of TMDT-provoked hyperexcitability by monitoring changes in intracellular Ca2+ levels ([Ca2+]i). Agents antagonizing NMDA or β-adrenergic receptors reversed TMDT-induced increases in [Ca2+]i and displayed the best counteracting potential. We have commenced testing these in vitro leads in vivo. Adult male mice were injected with 0.25 mg/kg TMDT subcutaneously followed by intraperitoneal monotherapy immediately after the first clonic seizure observed. They were continuously monitored over 1 hr, for the occurrence and severity of clonic and tonic-clonic seizures, and for 24-hr mortality. Our current results indicate that MK-801 is superior, completely eliminating tonic-clonic seizures and 24-hr mortality. At 40 mg/kg, memantine decreased mortality by 75%, however delayed tonic-clonic seizures were observed. Although both procyclidine and ketamine prevented tonic-clonic seizures at higher doses (60 and 70 mg/kg, respectively), they were not as effective in preventing TMDT-induced lethality. Propranolol was the least effective at reducing seizure severity and mortality rate. Altogether, our in vitro assay provides a useful screen to identify potential countermeasures against TMDT neurotoxicity. Positive leads are being tested and show activity in vivo, supporting utility of the screen