Piperonyl butoxide potentiates the synaptosome ATPase inhibiting effect of pyrethrin

Pyrethrins are widely used insecticides in both agriculture and households. In many commercial formulations piperonyl butoxide (PBO) is used with pyrethrins. PBO is a well-known synergist of pyrethrins, used to intensify their effects. One of the cellular targets of pyrethrins is the sodium channel in the membrane. In the present study, the activity of the membrane-bound integral protein ATPase was studied as a biomarker for the membrane effects of pyrethrin and PBO. Cerebral synaptosomes of rat brain were used in the study. The isolation of synaptosomes was performed with the Percoll gradient method. Both total ATPase and Mg2+ activated ATPase were studied by determining inorganic phosphate. Exposure to 0.1-1000 mu M of pyrethrin and to 0.4-4000 mu M of PBO decreased ATPase activity dose-dependently. The most efficient mixture was the one consisting of one part of pyrethrin and four parts of PBO. The activity of total ATPase decreased 15% in concentrations of 0.1-10 mu M pyrethrin, and a 50% decrease was found at 100 mu M pyrethrin. The mixture of pyrethrin and PBO caused a 15-60% decrease in the total ATPase activity at 0.1-10 mu M pyrethrin and 0.4-40 mu M PBO. A 85% decrease was found after exposure to the mixture of 100 mu M pyrethrin and 400 mu M PBO. PBO alone had no effect at 0.4-40 mu M concentrations, but a marked effect was seen at over 40 mu M concentrations. The results indicate that PBO is an effective synergist of pyrethrin and that it is very toxic in high concentrations. The results also confirm that neuronal sodium homeostasis is one target of the neurotoxic effect of pyrethroid compounds. (C) 1999 Elsevier Science Ltd. All rights reserved.