Accumulation of pyrethroid compounds in primary cultures from rat cortex.

Recent studies have demonstrated that lipophilic compounds (e.g., methylmercury, polychlorinated biphenyls (PCBs) and polybrominated diphenylethers (PBDEs)) rapidly accumulate in cells in culture to concentrations much higher than in the surrounding media. Primary cultures of neurons have been widely utilized to study the actions of pyrethroids, yet pyrethroid accumulation in these cells has not been studied to date. To test the hypothesis that pyrethroids rapidly accumulate in neurons in vitro, the time (0-90 min) and concentration (0.05-10 μM) dependent accumulation of [(3)H]-deltamethrin (DM), [(3)H]-bifenthrin (BF) and [(14)C]-cis permethrin (PM) into primary cortical cultures was examined. Accumulation of all three pyrethroids was time- and concentration-dependent, with only small differences observed between the compounds. Concentration-dependent accumulation of PM and BF were similar, achieving a of total ∼0.25 nmol in cells after 30 min in a 10 μM solution. DM accumulation was lower, reaching a maximum of 0.14 nmol after 30 min in a 10 μM solution. In 1 μM solutions, DM and PM content in cells were 0.039 and 0.038 nmol after 90 min. At all concentrations and times, pyrethroid accumulation in cells was less than 5% of the total mass applied for DM and PM, and was less than 8% for BF. However, after 90 min, accumulation of all three compounds increased to as much as ∼30-50-fold higher than the surrounding medium. The amount of compound recovered in the media at the end of incubation ranged from ∼77% to 89%; the remainder (6-15%) was presumed to bind to the plastic of the culture plates. These results demonstrate rapid time- and concentration-dependent accumulation of pyrethroids in neurons in vitro. Further, for the three pyrethroids examined, there were not statistically significant differences in their accumulation. This data will be useful for making comparisons between in vivo and in vitro studies regarding effective concentrations of pyrethroids.