DIFFERENTIATION BETWEEN ORGANOPHOSPHATE AND CARBAMATE POISONING

We propose a novel and simple assay for the real-time differentiation between carbamate and organophosphate inhibition of cholinesterase, ba sed on our observations of the kinetic behavior of inhibited enzyme. T he assay of carbamylated cholinesterase activity over time follows a n on-linear kinetic pattern, whereas that of phosphorylated enzyme activ ity is linear. This feature can be exploited to differentiate between carbamate and organophosphate cholinesterase inhibition. The non-linea r pattern characteristic of carbamates is easily discernible at degree s of inhibition of 40% or more. In this setting, cholinesterase activi ty ought to be measured continuously for about 1 h to obtain the kinet ic pattern of enzyme activity. The initial activity, measured during t he first 5 min of assay, represents the activity of enzyme in vivo. In vitro reactivation of inhibited cholinesterase allows the estimation of full potential activity of enzyme prior to poisoning, so that perce ntage of inhibition can be calculated. Reactivation of carbamylated ch olinesterase is obtained by the incubation of diluted enzyme at 37 deg rees C for 2.5 h prior to assay, whereas phosphorylated (non-aged) enz yme is reactivated by a 30 min incubation with oximes. In cases of mil d exposure to cholinesterase inhibitors (< 40% inhibition), the respon se of enzyme to in vitro reactivation serves as a complementary test f or exposure and for the nature of the inhibitor. All the results prese nted in this work refer to plasma cholinesterase. Erythrocyte cholines terase was found to behave very similarly to plasma enzyme and its res ults have not been reported here.