Chemical reactivation and aging kinetics of organophosphorus‐inhibited cholinesterases from two earthworm species

Abstract

An in vitro study was conducted to evaluate the ability of pyridine-2-aldoxime methochloride (2-PAM) to recover organophosphorus (OP)-inhibited cholinesterase (ChE) activity of two earthworm species (Eisenia fetida and Lumbricus terrestris). After inhibition of ChE activity by OP pesticides, an alkyl group may be released from the OP-ChE complex. This reaction is termed aging, and the esterase cannot be reactivated either spontaneously or by the action of reactivating agents, such as 2-PAM. We also examined the aging kinetics of OP-inhibited ChE activity to evaluate the suitability of 2-PAM reactivation methodology for field monitoring. A 2-PAM concentration of 5 x 10(-4) M was enough to reactivate the OP-inhibited ChE activity after 60 min of incubation at 25 degrees C. Chemical reactivation kinetics followed an exponential rise to a maximum of 70 to 80% of normal enzyme activity when ChEs were inhibited with methyl paraoxon or dichlorvos and up to 60% for the chlorpyrifos-inhibited ChE of E. fetida. The aging rates (ka) of the inhibited ChEs were strongly affected by the OP type, and these rates decreased for both earthworm species in the following order: Methyl paraoxon (ka = 0.023-0.033/h) > dichlorvos (ka = 0.008-0.009/h) > chlorpyrifos oxon (ka = 0.003-0.006/h). In particular, chlorpyrifos-inhibited ChE activity of L. terrestris aged slowly (median aging time, 190 h), which means that chemical reactivation of esterase activity with 2-PAM seems feasible one week after exposure to OP pesticides. We conclude that reactivation of earthworm ChE activity by treatment with 2-PAM is a complementary and specific methodology for assessing exposure to OP pesticides.

Earthworm biomarkers of pesticide contamination: Current status and perspectives

“…[33][34][35] Reactivation of earthworm phosphorylated ChE activity with 2-PAM has revealed as a promising tool for field monitoring of pesticide. 37) However, this attractive methodology requires field validation to be accepted as a suitable indicator of OP exposure, and furthermore, other oximes (e.g., obidoxime, diacetylmonoxime) and esterases (e.g., CbE) should be tested.…”

“…The potential use of 2-PAM as a complementary methodology to assess exposure of earthworms to OP pesticides has been recently investigated in E. fetida and L. terrestris. 37) Phosphorylated earthworm ChE activity was reactivated with 5ϫ10 Ϫ4 M of 2-PAM, and the efficiency of the oxime to induce ChE reactivation was dependent on the OP type involved in the enzyme inhibition. Moreover, this study showed that chlorpyrifos-inhibited ChE activity displayed a slow aging rate and consequently 2-PAM-induced reactivation was possible for as long as one week after chlorpyrifos inhibition.…”

Biochemical characterization of cholinesterases in Enchytraeus albidus and assessment of in vivo and in vitro effects of different soil properties, copper and phenmedipham

“…Among these species, studies of ChE activities in earthworms, including Eisenia fetida, Aporrectodea calignosa, Lumbricus terrestris and Drawida willsi, have shown that they are inhibited by several classes of pesticides and have allowed the linkage with behaviour (Stenersen 1979a, b, c;Drewes and Vining 1984;Drewes et al 1987;Booth et al 2000;Panda and Sahu 2004;Rodríguez-Castellanos and Sanchez-Hernandez 2007).…”

The relationship between total cholinesterase activity and mortality in four butterfly species

“…These esterases hydrolyze the neurotransmitter acetylcholine concluding the transmission of the nervous impulse in the cholinergic synapses. The rapid recovery of ChE activity following OP exposure (i.e., synthesis of a new enzyme) among other factors means that ChE inhibition may not always lead to effects at higher levels of biological organization [15][16][17][18][19]. In fact, ChE activity in organisms is often measured to assess their exposure to organophosphate pesticides in the field [10][11][12][13].…”

“…However, measurement of ChE inhibition alone to assess adverse effects from pesticides is not always a suitable approach. The rapid recovery of ChE activity following OP exposure (i.e., synthesis of a new enzyme) among other factors means that ChE inhibition may not always lead to effects at higher levels of biological organization [15][16][17][18][19].…”