DIAFENTHIURON ACTION - CARBODIIMIDE FORMATION AND ATPASE INHIBITION

Diafenthiuron (a thiourea insecticide/acaricide) is proposed by scient ists at Ciba-Geigy to act in insects as a mitochondrial adenosine trip hosphatase (ATPase) inhibitor following metabolic activation to the co rresponding carbodiimide. The present research establishes methods for thin-layer chromatography and high-pressure liquid chromatography ana lyses of diafenthiuron and its carbodiimide and urea derivatives in en zyme preparations and tissues without artifacts from abiotic decomposi tion. The carbodiimide, but not the urea, is detected and quantitated as a diafenthiuron metabolite in mouse and housefly microsomal oxidase systems and in the liver, lung, and brain of intraperitoneally (ip)-t reated mice. Carbodiimide formation by microsomes in vitro is dependen t on the reduced form of nicotinamide adenine dinucleotide phosphate a nd inhibited by piperonyl butoxide (PB). Another microsomal oxidase me tabolite of [H-3]diafenthiuron cochromatographs with a major reaction product of hydrogen peroxide with diafenthiuron. This compound, propos ed to be diafenthiuron sulfoxide, decomposes abiotically to the corres ponding formamidine identified by X-ray crystallography. The carbodiim ide, but not the thiourea itself, inhibits mouse liver mitochondrial o ligomycin-sensitive ATPase activity in vitro with an IC50 of 0.18 mu M . Diafenthiuron, its carbodiimide, and two classical ATPase inhibitors (dicyclohexylcarbodiimide and oligomycin A) at lethal ip doses strong ly inhibit mouse liver mitochondrial oligomycin-sensitive ATPase in vi vo at 1-6 hr after treatment. Although PB inhibits metabolism of the t hiourea in vitro, it acts in vivo to increase the rate of poisoning an d toxicity of diafenthiuron to mice by 2-fold consistent with the obse rved elevation in carbodiimide levels in liver, lung, and brain by 2- to 14-fold. Diafenthiuron and its carbodiimide act slowly in ip-treate d mice with LD(50) values of 15 and 0.3 mg/kg, respectively, and death 3-7 days after treatment; this delayed toxicity (also observed with d icyclohexylcarbodiimide but not oligomycin A) is not correlated with p rolonged inhibition of liver ATPase activity. (C) 1995 Academic Press, Inc.