Comparative in vitro study of the inhibition of human and hen esterases by methamidophos enantiomers

Abstract

The current Organisation for Economic Co-operation and Development (OECD) guidelines for evaluating organophosphorus-induced delayed neuropathy (OPIDN) require the observation of dosed animals over several days and the sacrifice of 48 hens. Adhering to these protocols in tests with enantiomers is difficult because large quantities of the compound are needed and many animals must be utilized. Thus, developing an in vitro screening protocol to evaluate chiral organophosphorus pesticides (OPs) that can induce delayed neuropathy is important. This work aimed to evaluate, in blood and brain samples from hens, human blood, and human cell culture samples, the potential of the enantiomeric forms of methamidophos to induce acetylcholinesterase (AChE) inhibition and/or delayed neurotoxicity. Calpain activation was also evaluated in the hen brain and SH-SY5Y human neuroblastoma cells. The ratio between the inhibition of neuropathy target esterase (NTE) and AChE activities by the methamidophos enantiomers was evaluated as a possible indicator of the enantiomers' abilities to induce OPIDN. The (-)-methamidophos exhibited an IC(50) value approximately 6 times greater than that of the (+)-methamidophos for the lymphocyte NTE (LNTE) of hens, and (+)-methamidophos exhibited an IC(50) value approximately 7 times larger than that of the (-)-methamidophos for the hen brain AChE. The IC(50) values were 7 times higher for the human erythrocyte AChE and 5 times higher for AChE in the SH-SY5Y human neuroblastoma cells. Considering the esterases inhibition and calpain results, (+)-methamidophos would be expected to have a greater ability to induce OPIDN than the (-)-methamidophos in humans and in hens.

In vitro study of the neuropathic potential of the organophosphorus compounds trichlorfon and acephate

“…Some studies (Ehrich et al, 1997;Sogorb et al, 2010;Emerick et al, 2012b) have proposed in vitro screenings for the evaluation of the ability of OPs to generate OPIDN. The parameters evaluated in these studies are: aging of NTE and IC 50 NTE/IC 50 AChE ratio (ratios higher than five are incompatible with generation of OPIDN).…”

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

“…These in vitro findings confirm and extend previous work using mouse brain homogenates (Quistad et al ., 2002), hen or human brain homogenates (Capodicasa et al ., 1991; Emerick et al ., 2012; Lotti and Johnson, 1978; Richardson et al ., 1993) hen brain particulate fractions (Makhaeva et al ., 2013; Malygin et al ., 2003; Sogorb et al ., 2010) or preparations from human or murine cell cultures (Ehrich et al ., 1997; Li and Casida, 1997; Sogorb et al ., 2010). In addition, the present work provides new in vitro and in vivo data on the neuropathic potential of PrDChVP and two new compounds, diEt-PFP and diBu-PFP.…”

“…Currently, the most widely accepted animal model for the study of OPIDN or assessment of the neuropathic potential of OP compounds is the adult hen (Doherty, 2006; Emerick et al ., 2012). However, compared to the usual laboratory rodents (e.g., rats or mice), hens are difficult to acquire and maintain for laboratory studies, and their substantially larger size requires considerably greater amounts of test materials for dosing.…”

Organophosphate neurotoxicity to the voluntary motor system on the trail of environment-caused amyotrophic lateral sclerosis: the known, the misknown, and the unknown

“…Both were focused on OP acute cholinergic neurotoxicity; the first investigated the short term inhibition of AchE in spinal cells (Goldberg et al 1980), and the second performed electrophysiological and video recordings of muscle relaxation in co-culture with spinal motor neurons to evaluate the efficacy of AchE reactivation therapy (Drexler et al 2011). In the context of OPIDN, various efforts were reported as focusing towards the development of in vitro models that could help predict whether a particular OP is capable of causing OPIDN in humans (Emerick et al 2012; Fernandes et al 2015; Emerick et al 2015). Each of these studies used a neuroblastoma clonal cell line (SH-SY5Y) originally derived from a metastatic bone tumor, which exhibits only partial cholinergic features after differentiation.…”