Cholinesterase classification

A classification of organophosphate poisoning has been proposed by Tafuri and Roberts (1987) modified from Namba et al. (1971). Clinical signs and symptoms of intoxication may occur when serum cholinesterase levels drop to below 50% of the normal value. Mild poisoning, with the patient still ambulatory, may occur when serum cholinesterase levels are 20-50% of normal moderate poisoning with inability to walk with levels 10-20% of normal and severe poisoning with respiratory distress and unconsciousness with serum cholinesterase levels <10% of normal. 

As given in classification, these agents are of two type e.g. reversible and irreversible. The reversible anticholinesterases have a structural resemblance to acetylcholine, are capable of combining with anionic and esteratic sites of cholinesterase as well as with acetylcholine receptor. The complex formed with the esteratic site of cholinesterase is less readily hydrolyzed than the acetyl esteratic site complex formed with acetylcholine. Edrophonium forms reversible complex with the anionic site and has shorter duration of action. Also, neostigmine and edrophonium have a direct stimulating action at cholinergic sites. 

The organophosphorus insecticides are all structurally related and undergo similar reactions. The chemical classification of the most widely used compounds of this type is given in Table V. These compounds can also be differentiated on the basis of whether they are largely effective per se or undergo oxidative conversions in plants or animals. All are inhibitors of the enzyme, cholinesterase. Their potency depends not only upon their intrinsic enzyme affinity but also on anticholinesterase properties acquired through in vivo metabolism. 

DOT CLASSIFICATION 6.1 Label Poison SAFETY PROFILE Poison by inhalation, ingestion, skin contact, subcutaneous, intravenous, and intraperitoneal routes. Fatal poisoning can result from skin or eye contact after very brief exposure to concentrated solution. Experimental teratogenic and reproductive effects. Questionable carcinogen. Human mutation data reported. A cholinesterase inhibitor type of insecticide. When heated to decomposition it emits very toxic fumes of NOx, POx, and SOx. See also PARATHION. 

A27. Augustinsson, K. B., Classification and comparative enzymology of the cholinesterases and methods for their determination. In Handbuch der experimentellen Pharmacologic XV. Cholinesterase and anticholinesterase agents (C. B. Koelle, ed.), pp. 89-128. Springer-Verlag, Berlin and New York, 1963. 

Methods have been published that allow the classification of two types of esterases, the carboxylic ester hydrolases (CEHs) and the phosphoric triester hydrolases (PTEHs) (Anspaugh and Roe, 2004). The CEHs contain the B-esterases, which are inhibited by organophosphates. B-esierases include many other esterases, such as CarbE, acetylcholinesterase (AChE), cholinesterases (ChE), aryleslerases, sterol esterases, insect juvenile hormone esterases, aixl others. The determination of A-esterases uses a protocol for the detection of PTEHs. The PTEH assay allows for the identification of two subclasses of esterases, the A-esterase (known as aiyldialkylphos-phatase) and ditsopropyl fluorophosphatase. Both these enzymes metabolize OP compounds. 

If the client does not respond to one of the cholinesterase inhibitors, then another may be tried because the drugs are not identical. The client may be responsive to a different medication in the same classification. 

Although the term monoamine oxidase suggests a single enzyme species, it is now apparent that there are a variety of enzymes which oxidatively deaminate amines. The classification into diamine oxidase and MAO is also not absolute since MAO will metabolize diamines including histamine (Fonts et al., 1957). Amine-oxidizing enzymes are also present in the blood of certain species (Tabor et al., 1954 Blaschko et al., 1958). These enzymes are not like the mitochondrial MAO. It may well be that there are a large number of amine oxidases, some of which are fairly specific for a given amine and others quite nonspecific. A similar situation exists with respect to cholinesterase activity. 

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