Fenitrothion toxicity in Triatoma infestans synergized by quercetin or thymol blue

Quercetin and thymol blue were shown to synergize the toxicity of fenitroth ion to Triatoma infestans with synergistic ratios of 1.89 and 2.65 respecti vely. These synergistic ratios were statistically significant at P < 0.05. Both compounds inhibited glutathione S-transferases (GST) in vitro, with pI (50) values of 6.1 and 5.1 respectively. Quercetin or thymol blue caused in -vivo GST inhibition without affecting non-specific esterase (NSE) or acety lcholinesterase (AChE) activity. Incubation of [C-14]fenitrothion with T. infestans or rabbit liver GST prod uced desmethyl-fenitrothion as the major metabolite, which was specifically diminished in the presence of 0.3 mM quercetin. [C-14]Fenitrothion toxicokinetics study showed a significant decrease (P < 0.05) in radioactivity due to polar metabolites when insects were pre-treat ed with quercetin. These facts suggest that both assayed chemicals may be a ctive in synergizing fenitrothion toxicity due to their ability to prevent the detoxification of organophosphorus insecticides by GSH conjugation. (C) 1999 Society of Chemical Industry.