Pesticide Biochemistry and Physiology 87 (2007) 238–247 www.elsevier.com/locate/ypest 0048-3575/$ - see front matter  2006 Elsevier Inc. All rights reserved. doi:10.1016/j.pestbp.2006.08.002 In vitro metabolism and interaction of profenofos by human, mouse and rat liver preparations Khaled Abass a,¤ , Petri Reponen a,b , Jorma Jalonen b , Olavi Pelkonen a a Department of Pharmacology and Toxicology, P.O. Box 5000, FIN-90014 University of Oulu, Oulu, Finland b Structural Chemistry, Department of Chemistry, P.O. Box 3000, FIN-90014 University of Oulu, Oulu, Finland Received 8 June 2006; accepted 14 August 2006 Available online 22 August 2006 Abstract Biotransformations of profenofos were studied in vitro. Two metabolites, desthiopropylprofenofos and hydroxyprofenofos, were detected by LC–MS after incubation of profenofos with human liver homogenates and diVerent mammalian liver microsomes. The rank order of desthiopropylprofenofos formation in liver microsomes based on intrinsic clearance (V max /K m ) was mouse > human > rat, while for profenofos hydroxylation it was mouse > rat > human. In view of the ratio between desthiopropylation and hydroxylation intrinsic clearance rates, human liver microsomes were most active in profenofos bioactivation. The interspecies diVerences and interindividual variation were within range of the default uncertainty/safety factors for chemical risk assessment. CYP3A4, CYP2B6 and CYP2C19 were identiWed as profenofos-oxidizing enzymes in human liver on the basis of recombinant expressed enzymes and correlation with CYP model activities. The rank order of CYPs in profenofos activation was CYP3A4 > CYP2B6 > CYP2C19, whereas it was the contrary for profenofos hydroxylation. Profenofos inhibited relatively potently several human liver microsomal activities: the lowest IC 50 values were about 3 M for CYP1A1/2 and CYP2B-associated activities. Profenofos is extensively metabolized by liver microsomal CYP enzymes and its interaction potential with several CYP activities is considerable.  2006 Elsevier Inc. All rights reserved. Keywords: Profenofos; Metabolism; Human; Rat; Mouse; Insecticide; In vitro; Toxicology; LC–MS 1. Introduction Currently the development and use of organophosphate compounds is greater than ever before and this trend will most likely continue, because new applications for these compounds have been discovered [1]. One of the organo- phosphorothiolate insecticides used in agriculture for pest control is profenofos (O-4-bromo-2-chlorophenyl O-ethyl S-propyl phosphorothioate). Due to its wide use in control of insects and mites on many diVerent crops, humans are inevitably exposed to its residues in various ways. Profenofos has been classiWed as moderately hazardous (toxicity class II) pesticide by WHO and it has a moderate order of acute toxicity following oral and dermal adminis- tration [2]. Profenofos is extremely toxic to Wsh and macro- invertebrates [3]. The acute toxic action of profenofos is the inhibition of the acetylcholinesterase activity [4], resulting in toxicity also in humans [5]. The bioactivation of both organophosphorothionate (PBS) and organophosphorodithioate (SAPBS) pesti- cides occurs via CYP-mediated desulfuration to their phos- phate oxon metabolites [(PBS) ) (PBO)]. In vitro data have been published on the bioactivation of chlorpyrifos [6–9], diazinon [6,8–10], azinphos-methyl [8] and malathion [11]. Profenofos does not show this behavior due to the absence of the PBS moiety. On the other hand, few data are available about the bio- activation of phosphorothiolate (OBPASAC) pesticides in mammals. However, it has been reported that profenofos like other phosphorothiolate insecticides, is activated to * Corresponding author. Fax: +358 8 537 5247. E-mail address: khaled.megahed@oulu.W (K. Abass).