Applications cholinesterase activities

Another class of enzymes that has found wide application in the biosensor field in the last decades is that of the cholinesterases which have been mainly used for the detection of pesticides. For the amperometric detection of cholinesterase activity, both the substrates acetylcholine and acetylthiocholine have been extensively used [6-9], the latter being preferred because this avoids the use of another enzyme, choline oxidase, which is usually coupled with acetylcholinesterase. However, the amperometric measurement of thiocholine, produced by... 

Figure 1. Change in blood cholinesterase activities of two mixer-loaders (ML) and three mixer-loader applicators (MLA) from their April 4 baselines during the weeks between May 14 and September 13,1976 (2). Mixer-loaders used the Swampmate (Cherlor Mfg. Co., Inc., Salinas, CA) while mixer-loader applicators used a Model SS 12-4 Closed System (SoilServ, Salinas, CA).

EPA science policy guidelines regarding use and application of cholinesterase activity inhibition data generally consider blood ChE activity inhibition to be an imperfect measure, and there appears to be no fixed percentage of blood ChE activity change that can distinguish adverse from nonadverse effects (USEPA, 2000 Storm et al,... 

Poisoned patients may require monitoring of vital signs, measurement of ventilatory adequacy such as blood gases and pulse oximetry, leukocyte count with differential to assess development of pneumonia, and chest radiographs to assess the degree of pulmonary edema or development of hydrocarbon pneumonitis. Workers involved in the formulation and application of pesticides should be monitored by periodic measurement of cholinesterase activity in their bloodstream. Untreated, anticholinesterase-depressed acetylcholinesterase activity returns to normal values in approximately 120 days. 

Immobilization of cholinesterase, like that of other enzymes, has a number of potentially valuable applications, including active-site studies, economical use of the enzyme as an analytical reagent, and enhancement of the storage life of the enzyme. 

Table 2. Restored cholinesterase activity in dogs after application of 1 lethal dose of the substance on the skin surface...

The toxicity of liquid nerve agents on the skin was studied extensively. In the first study reported (Freeman et al, 1953), 5-mg droplets of sarin (6-129 droplets total doses of 25-550 mg) were placed on the volar aspects of the forearms of 11 subjects. The agent evaporated in 1.5-6 min from the skin when the area was relatively free of hair, and in 6.5-15 min from the skin when placed in areas of heavy hair. The agent was mixed with a dye for visualization, and after evaporation was complete the site was tested for the agent and then decontaminated. Maximal inhibition of erythrocyte cholinesterase activity was 18% (82% of normal). Two subjects (cholinesterase of 82%) had transient diarrhea. Sweating at the site of application continued for as long as 34 days. 

The use of carbaryl has not resulted in illnesses among workers mixing-loading or applying the pesticide and no reentry interval has been established for this pesticide in California. Cholinesterase inhibition is considered to be the major toxic effect of carbaryl. Carbaryl (500 mg/kg) topically applied to the back of the rabbit inhibited 50% of the red cell ChE activity 24 hr after application and activity returned to pretreatment values after 72 hr (21). In the rat study reviewed in this paper, a topical dose of 417 mg/kg did not produce ChE inhibition 24 hr after application indicating that the rate of absorption was low or carbaryl was metabolized in the skin to non-OiE inhibiting products. 

One of the first applicator studies was undertaken by Qulnby al. (17). Cholinesterase activity was measured In aerial applicators together with residues on worker clothing and In respirator pads. 

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