Chlorpyrifos inhibitory potency

FIGURE 57.8. Spectrum of log values of relative inhibitory potency (RIP) = 7i(AChE)/ i(NTE), where = himolecular rate constant of inhibition. As log(RIP) becomes more positive, cholinergic potential increases as log(RIP) becomes more negative, delayed neuropathic potential increases. CPMO-chlorpyrifos methyl oxon. DCV derivatives refer to symmetrical dialkyl-2,2-dichlorovinyl phosphate (dichlorvos) compounds. EOPF - ethyl n-octylphosphonofluoridate. Data from Kropp and Richardson (2003) Richardson (1992) and Wu and Casida (1996). 

Kropp, T.J., Richardson, R.J. (2003). Relative inhibitory potencies of chlorpyrifos oxon, chlorpyrifos methyl oxon, and mipafox for acetylcholinesterase versus neuropathy target esterase. J. Toxicol. Environ. Health Part A 66 1145-57. 

The biomolecular inhibition rate constant (ifj) describes both the affinity and the rate of cholinesterase phosphorylation and is an indicator of inhibitory potency (Kousba et al 2004 Kardos and Sultatos, 2000 Amitai et al., 1998 Carr and Chambers, 1996). A typical determination is illustrated in Fig. 10 for the in vitro inhibition of rat BuChE with chlorpyrifos-oxon. In this example, the Kj was determined by incubating BuChE with varying concentrations of ehloropyrifos-oxon (0.25-5 nAf) the maximum inhibition ranged from 10 to 90% during a 7- to 30-min incubation period (Kousba et al., 2003). The slopes obtained from this analy.sis were then analyzed by linear regression to calculate a K (Fig. lOB). Similar in vitro approaches have been used to calculate the spontaneous first-order reactivation... 

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