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Pseudocholinesterase is a serine hydrolase enzyme primarily produced in the liver that catalyzes the hydrolysis of choline esters, most prominently succinylcholine and mivacurium.[1] It is crucial to differentiate this enzyme from "true" cholinesterase, also known as acetylcholinesterase. It occurs in higher concentrations within conducting tissues such as the central or peripheral nervous systems and neuromuscular junctions.[2] Due to diverse functions and tissue distribution within the human body, pseudocholinesterase often gets referred to through various enzymatic names, including plasma cholinesterase, serum cholinesterase, acetylcholine acetylhydrolase, and butyrylcholinesterase (BuChE).[3] In addition to possessing multiple names, the enzyme exists in many pharmacogenetic variations, with BuChE operating as the primary human cholinesterase form. When comparing concentrations within the human plasma, the ratio of pseudocholinesterase (BuChE) to true cholinesterase (AChE) overwhelmingly favors BuChE by a ratio of 1000 to 1.[3]

The onset of pseudocholinesterase deficiency may occur through inheritable (genetic) or acquired pathways. Despite its etiology, pseudocholinesterase deficiency usually does not have clinically significant effects until the enzyme activity decreases to less than 75% of normal activity levels.[10] The genetic inheritance of pseudocholinesterase deficiency occurs through an autosomal recessive pattern, with frequencies of approximately 1 in 50 to 1 in 3000 individuals for heterozygotes and homozygotes, respectively.[9] The prevalence of BuChE deficiency is highest amongst those with European ancestry and lowest within the Asian population. Acquired conditions that decrease the activity of the BuChE enzyme include malnutrition, advanced age, malignancy, liver or kidney disease, pregnancy, burns, and organophosphate poisoning. In contrast, obesity and chronic alcoholism are suspected to increase pseudocholinesterase activity levels. Medications such as aspirin, metoclopramide, monoamine oxidase inhibitors, oral contraceptives, and anticholinesterase agents may also influence the enzyme's activity.[9] Through hydrolysis and sequestration of toxic compounds, the broad substrate specificity of BuChE may protect against numerous inhaled and administered substances.[11]