Butyrylcholinesterase (BChE) is an enzyme found throughout the human body, involved in various biological processes. It performs specific actions that impact how the body handles certain substances and maintains health. Understanding BChE’s role offers insights into its medical significance and influence on well-being.
What is Butyrylcholinesterase?
Butyrylcholinesterase (BChE) is a nonspecific cholinesterase enzyme. It is primarily synthesized in the liver and is most abundant in blood plasma, but also found in tissues like the brain, lungs, heart, and intestines.
BChE is also known as pseudocholinesterase (PChE) or plasma cholinesterase. This distinguishes it from acetylcholinesterase (AChE), which has a more defined role in nerve impulse transmission. While both enzymes break down choline esters, BChE acts on a broader range of substrates.
How Butyrylcholinesterase Functions
BChE functions as a hydrolase, breaking down compounds by adding water. It catalyzes the hydrolysis of various ester-containing compounds and choline esters. This enzymatic action involves a catalytic triad of amino acids—serine, histidine, and glutamate—within its active site.
When a substrate enters BChE’s active site, serine initiates the breakdown. This process allows BChE to metabolize a wide array of substances, including naturally occurring compounds. For example, BChE can hydrolyze ghrelin, a hormone influencing appetite and metabolism, converting it into an inactive form.
Butyrylcholinesterase’s Relevance to Health
BChE plays a role in the metabolism of several clinically used medications, impacting their effectiveness and duration. A notable example is succinylcholine, a muscle relaxant used in anesthesia to induce short-term muscle paralysis. BChE rapidly breaks down succinylcholine, determining how long its effects last. Mivacurium, another muscle relaxant, is also metabolized by BChE.
Beyond drug metabolism, BChE serves as a biomarker for certain health conditions. Its activity levels can indicate liver damage, as it is primarily synthesized in the liver. Altered BChE levels are also observed in organophosphate poisoning, where it acts as a scavenger, binding to these toxic compounds and preventing them from affecting other enzymes. BChE’s potential roles in neurodevelopment and detoxification pathways are areas of ongoing investigation.
Factors Affecting Butyrylcholinesterase Levels
Butyrylcholinesterase levels and activity are influenced by both genetic predispositions and acquired conditions. Genetic variations in the BCHE gene, which encodes for BChE, can alter enzyme function. For example, the “atypical” BChE variant (D70G) significantly reduces enzyme activity and concentration, often leading to prolonged paralysis after succinylcholine administration. The K-variant (A539T) is another common genetic variant, associated with a 30-33% reduction in plasma BChE activity, potentially causing a slightly prolonged response to succinylcholine.
Acquired conditions also impact BChE levels. Liver diseases, such as acute and chronic liver damage or cirrhosis, often decrease BChE activity due to impaired synthesis. Malnutrition, inflammation, and certain infections can also lower BChE levels. Additionally, exposure to organophosphate pesticides can significantly inhibit BChE activity, often used as a diagnostic indicator for such poisoning. Some chemotherapy agents and pregnancy can also influence BChE levels.