The cytochrome P450 CYP6P4 is responsible for the high pyrethroid resistance in knockdown resistance-free Anopheles arabiensis

Abstract

Pyrethroid insecticides are the front line vector control tools used in bed nets to reduce malaria transmission and its burden. However, resistance in major vectors such as Anopheles arabiensis is posing a serious challenge to the success of malaria control.Herein, we elucidated the molecular and biochemical basis of pyrethroid resistance in a knockdown resistance-free Anopheles arabiensis population from Chad, Central Africa. Using heterologous expression of P450s in Escherichia coli coupled with metabolism assays we established that the over-expressed P450 CYP6P4, located in the major pyrethroid resistance (rp1) quantitative trait locus (QTL), is responsible for resistance to Type I and Type II pyrethroid insecticides, with the exception of deltamethrin, in correlation with field resistance profile. However, CYP6P4 exhibited no metabolic activity towards non-pyrethroid insecticides, including DDT, bendiocarb, propoxur and malathion. Combining fluorescent probes inhibition assays with molecular docking simulation, we established that CYP6P4 can bind deltamethrin but cannot metabolise it. This is possibly due to steric hindrance because of the large vdW radius of bromine atoms of the dihalovinyl group of deltamethrin which docks into the heme catalytic centre.The establishment of CYP6P4 as a partial pyrethroid resistance gene explained the observed field resistance to permethrin, and its inability to metabolise deltamethrin probably explained the high mortality from deltamethrin exposure in the field populations of this Sudano-Sahelian An. arabiensis. These findings describe the heterogeneity in resistance towards insecticides, even from the same class, highlighting the need to thoroughly understand the molecular basis of resistance before implementing resistance management/control tools.

Genome-wide gene expression profiling reveals that cuticle alterations and P450 detoxification are associated with pyrethroid resistance in Anopheles arabiensis populations from Ethiopia

“…arabiensis . 31, 32 Ibrahim et al 2016 showed that CYP6P4 plays a key role in pyrethroid resistance of An. arabiensis populations from Central Africa (Chad), and that it can metabolize the pyrethroids permethrin, bifenthrin and λ-cyhalothrin, but not deltamethrin.…”

Cytochrome P450s in Anopheles gambiae (Diptera: Culicidae) and Insecticide Resistance in Africa: A Mini Review

“…It has been well documented that P450-mediated pyrethroid resistant insects strains have higher levels or more efficient enzyme forms of one or more P450s compared to susceptible strains [11][12][13]. Cytochrome P450s are therefore generally associated with the enzymatic metabolism of insecticides [14].…”

Identification of permethrin and etofenprox cross‐tolerance in Rhipicephalus sanguineus sensu lato (Acari: Ixodidae)

“…Although increased esterase activity confers permethrin resistance in R. sanguineus , it is not a likely candidate to explain etofenprox tolerance as etofenprox is a non‐ester pesticide . However, cytochrome P450's, such as CYP6P4 , do detoxify permethrin and etofenprox in the malaria vector, Anopheles arabiensis (Patton; Diptera: Culicidae) , and warrant further investigation in R. sanguineus . Future research should include synergist bioassays to investigate the level of metabolic detoxification of etofenprox in resistant populations and the occurrence of other resistance conferring sodium channel SNP's.…”