Further studies toward a mouse model for biochemical assessment of neuropathic potential of organophosphorus compounds

Abstract

Inhibition and aging of neuropathy target esterase (NTE) by neuropathic organophosphorus (OP) compounds triggers OP compound-induced delayed neuropathy (OPIDN), whereas inhibition of acetylcholinesterase (AChE) produces cholinergic toxicity. The neuropathic potential of an OP compound is defined by its relative inhibitory potency (RIP) toward NTE vs. AChE assessed by enzyme assays following dosing in vivo or after incubations of direct-acting compounds or active metabolites with enzymes in vitro. The standard animal model of OPIDN is the adult hen, but its large size and high husbandry costs make this species a burdensome model for assessing neuropathic potential. Although the mouse does not readily exhibit clinical signs of OPIDN, it displays axonal lesions and expresses brain AChE and NTE. Therefore, the present research was performed as a further test of the hypothesis that inhibition of mouse brain AChE and NTE could be used to assess neuropathic potential using mouse brain preparations in vitro or employing mouse brain assays following dosing of OP compounds in vivo. Excellent correlations were obtained for inhibition kinetics in vitro of mouse brain enzymes versus hen brain and human recombinant enzymes. Furthermore, inhibition of mouse brain AChE and NTE after dosing with OP compounds afforded ED50 ratios that agreed with RIPs assessed in vitro. Taken together, results with mouse brain enzymes demonstrated consistent correspondence between in vitro and in vivo predictors of neuropathic potential, thus adding to previous studies supporting the validity of a mouse model for biochemical assessment of the ability of OP compounds to produce OPIDN.

Neuropathy target esterase in mouse whole blood as a biomarker of exposure to neuropathic organophosphorus compounds

“…Thus, these differences would nearly cancel when the RIP values were calculated. In any event, for both compounds, the brain and blood RIP values are in agreement and the fact that these ratios are greater than one is consistent with the known neuropathic potential of these compounds (Wijeyesakere and Richardson, ; Makhaeva et al , ).…”

“…PrDChVP produces OPIDN in hens with a minimal neuropathic dose of 0.6 mg kg −1 (Lotti and Johnson, ; Makhaeva et al , ). It has a rather high neuropathic potential with an RIP first reported to be 2.6 (Lotti and Johnson, ), in more recent work as 3.47 (Makhaeva et al , ), and in the present study as 3.89 (brain) and 4.80 (blood). In addition, PrDChVP has high acute toxicity, with an LD 50 of 10 mg kg −1 in hens (Albert and Stearns, ) and 15 mg kg −1 in mice (Makhaeva et al , ).…”

“…It is a known neuropathic agent (Lotti and Johnson, , Makhaeva et al , ). In contrast, although diBu‐PFP has a high neuropathic potential in vitro and in vivo , it exhibits very low acute cholinergic toxicity as we have shown previously (Makhaeva et al , ). We compared their inhibitory activities against mouse brain and blood AChE and NTE in vitro and in vivo 1 h after a single intraperitoneal (i.p.)…”

“…However, in contrast to PrDChVP, diBu‐PFP has low acute toxicity, with an LD 50 (i.p.) in mice >2000 mg kg −1 (Makhaeva et al , ; Rudakova et al , ).…”

“…Furthermore, inhibition of mouse brain AChE and NTE after dosing with OP compounds afforded ED 50 ratios that agreed with RIP values assessed in vitro . Thus, mouse brain NTE and AChE could be used for biochemical assessment of the neuropathic potential of OP compounds both in vitro and in vivo (Makhaeva et al , ).…”