Effects of the synergists piperonyl butoxide and S,S,S-tributyl phosphorotrithioate on propoxur pharmacokinetics in Blattella germanica (Blattodea : Blattellidae)
H. Sanchez-arroyo et al., Effects of the synergists piperonyl butoxide and S,S,S-tributyl phosphorotrithioate on propoxur pharmacokinetics in Blattella germanica (Blattodea : Blattellidae), J ECON ENT, 94(5), 2001, pp. 1209-1216
Effects of the synergists piperonyl butoxide (PBO) and S,S,S-tributyl phosp
horotrithioate (DEF) on propoxur pharmacokinetics were examined in the Germ
an cockroach, Blattella germanica (L.). Treatment of adult male German cock
roaches with the cytochrome P450 monooxygenase inhibitor, PBO, or the ester
ase inhibitor, DEF, increased propoxur toxicity by 2- and 6.8-fold, respect
ively, implicating hydrolysis as a major detoxification route of propoxur i
n the Gen-nan cockroach. However, significant hydrolytic metabolism could n
ot be demonstrated conclusively in vitro resulting in a conflict between in
situ bioassay data and in vitro metabolic studies. In vitro propoxur metab
olism with NADPH-fortified microsomes produced at least nine metabolites. F
ormation of metabolites was NADPH-dependent; no quantifiable metabolism was
detected with cytosolic fractions. However, microsomal fractions lacking a
n NADPH source did produce a low, but detectable, quantity of metabolites (
1.6 pmol). PBO inhibited NADPH-dependent propoxur metabolism in a dose-depe
ndent fashion, implicating cytochrome P450 monooxygenases as the enzyme sys
tem responsible for the metabolism. Interestingly, DEF also inhibited the N
ADPH-dependent metabolism of propoxur, albeit to a lower extent. Treatment
with PBO or DEF also caused a significant reduction in the cuticular penetr
ation rate of propoxur. The data demonstrate that unanticipated effects are
possible with synergists and that caution must be exercised when interpret
ing synergist results.