Role of esterases in enhanced detoxication of pyrethoids in Pediculus humanus capitis from Buenos Aires (Argentina)

PAOLA GONZÁLEZ AUDINO, S. BARRIOS, MARÍA I. PICOLLO & EDUARDO N. ZERBA

Buenos Aires

Congreso; International Congress on Phthiraptera; 2006

CIPEIN

Enhanced metabolism by oxidative enzymes is known to be a major cause of pyrethroid resistance in insects. We demonstrated in a previous work the importance of enhanced metabolism by monooxygenases in populations of head lice from Buenos Aires, Argentina exhibiting different levels of resistance to permethrin. A positive correlation was established between enzyme activity and the LD50 to permethrin in the resistant field populations. In this work, we evaluated the role of specific and non-specific esterase in head lice populations of Buenos Aires with different levels of resistance to permethrin. Taking into account that esterase activity is substrate dependent, four different esters were used as unspecific substrates in order to give a better characterization of the possible role of these enzymes in the resistance phenomena. The unspecific substrates were phenylthioacetate, a- and b- naphtyl-acetate, and p-nitrophenyl acetate. All the resistant head lice populations studied in this work showed detoxifying activity of esterase significantly greater than the susceptible one with all the substrates used for the determination. Accordingly, esterase activity seems to be a contributive mechanism to the pyrethoids detoxification in resistant head lice. Unspecific substrates could be no enough good model of the real pyrethroid esterase activity. Thus, with the aim of obtaining a specific substrate for pyrethroid esterases, 7-coumaryl permethrate was synthesized, an ester structurally similar to permethrin, with the same acid moiety. The hydrolysis of this ester yields fluorescent 7-OH coumaryl, what allows the use of microfluorometric methods for quantification of esterase activity. This method is highly sensitive and the substrate has a structure similar to pyrethroid insecticides. Results of pyrethroid esterases activity obtained with the new substrate showed that these enzymes contribute to the detoxifying activity in resistant populations, although a correlation between pyrethroid esterase activity and resistance ratios was not found. Therefore, in this work we established that esterase activity against specific and non-specific substrates is increased in pyrethroid resistant populations of head lice from Buenos Aires