Differential effects of azinphos-methyl and chlorpyrifos on polyamine oxidative metabolism during the embryonic development of Rhinella arenarum and its relation to oxidative stress

Abstract

The organophosphorus pesticides azinphos-methyl (AZM) and chlorpyrifos (CPF)exert their toxic action by inhibition of acetylcholinesterase,but non-target processes such as polyamine metabolism can also be affected. Ourobjective was to evaluate the effects of different concentrations of AZM(0.5-, 2-and 9 mg L-1)and CPF (0.5-and 1 mg L-1)on polyamine oxidativemetabolism along hinellaarenarumembryonic developmentand to explore its relationship to oxidative stress.Free and conjugated polyamines were measured by HPLC. The activity of spermine oxidase (SMOX), N1-acetylpolyamine oxidase (PAOX) and diamine oxidase (DAO) were measured through kinetic spectrofluorometry. Freeputrescine and sperminewere significantly increased in openmouth embryos exposed to AZM.Free polyaminelevels were not affected byCPF exposure. In embryos exposed to AZM,DAO was increased in tailbudstage and SMOXwas increased in openmouth stage,while embryos exposed to CPF showed an increase ofPAOXactivity in tailbudstageand a decrease of DAO and SMOXactivity in openmouth stage. Polyaminelevels and oxidativedegradation enzymes respond differently ifR. arenarumembryos are exposed toAZM orCPF, despite that both insecticides belong to the same chemical family. The early increase of DAO and PAOXwould play a protective role to guarantee the normal progression of embryonic development.Theincreased production of reactive species might contribute to anoxidative stress situationgeneratedby exposure to the insecticidesand to the alteration ofthe antioxidant defense system.In tail bud stage embryos,PAOX and SMOX were positively correlated to acetylcholinesteraseactivity and reduced glutathione levels(GSH),and negatively correlated to the antioxidant enzymes catalase (CAT)and glutathione S-transferase (GST). In complete operculum embryos, a negative correlation between antioxidant parameters and polyamine levels and polyamine oxidative metabolism was observed, except forSMOX,which showed a low positive correlation with CAT and GSH and a negative correlation to PAOX and DAO. We suggest the use of DAO and PAOX as biomarkers of exposure to AZM and CPF, respectively, as they respond earlier than the classical biomarker acetylcholinesterase.