Cytochrome P450 inhibition impedes the insecticide pyrethroid effects on insects through Nav channels regulation

Insecticides in various formulations are indispensable for agricultural pest control and the prevention of vector-borne diseases. Piperonyl butoxide (PBO) is a synergist widely used to enhance the effectiveness of insecticides, notably pyrethroids, by inhibiting the detoxifying cytochrome P450 enzymes, thus reducing the capacity of insects to metabolize and resist insecticides. Recent studies have revealed an unexpectedly weak enhancement of pyrethroid efficacy by PBO, which may have serious implications for insect control. The underlying mechanism of this effect remains unclear.

Here, we demonstrate that the PBO-induced inhibition of cytochrome P450 impedes the effect of deltamethrin by mainly affecting its interaction with the inactivated state of voltage-gated sodium channels (Nav). We describe a new octopamine-dependent regulatory mechanism involving Gαs, PKA, DARPP-32, and PP1-2A, which affect the cytochrome P450 conformation, thus limiting the effect of PBO and modulating the Nav gating. As a result, deltamethrin cannot reach its final binding site in the fenestration to exert its full effect. We confirmed in vivo that the octopamine level is elevated in insects under the treatment with a chemical stressor, which decreases the deltamethrin efficacy.

Our findings reveal a novel adaptive mechanism that increases insect survival by reducing insecticide efficacy, underscoring the need to develop more effective formulations and technologies for pest and vector control.