Butyrylcholinesterase is involved three different enzymatic activities in its structure like its sister enzyme, acetylcholinesterase: esterase, aryl acylamidase and peptidase (or protease). Whereas the clear role of acetylcholinesterase in cholinergic neurotransmission is well defined, the real physiological function of butyrylcholinesterase is still unknown. Both enzymes have similar molecular forms with different tissue distribution. Esteratic activity of butyrylcholinesterase becomes more important in scavenging of organophosphate and carbamate inhibitors before they reach to acetylcholinesterase; in regulating cholinergic transmission in the absence of acetylcholinesterase and in inactivation of some drugs such as cocaine aspirin, amitriptyline or in activation of others such as bambuterol, heroin. It is suggested that aryl acylamidase activity plays a role in crosstalking between seratonergic and cholinergic neurotransmission systems. In addition, peptidase activity of butyrylcholinesterase has a function in the development and progression of Alzheimer disease due to cause the production of β-amyloid protein and to help its diffusion to β-amyloid plaques.

This field study investigates the morphological indices (condition index, hepatosomatic index) and biochemical (catalase (CAT), glutathione S-transferase (GST), acetylcholinesterase (AChE), metallothionein (MT), lipid peroxidation) parameters in liver, gills and kidney of common sole (Solea solea) originating from different sites of the Tunisian coast area impacted by different anthropogenic activities. Differences among sites and tissues for AChE, GST, CAT, MT and TBARS were found and possibly related to known sources of domestic and industrial discharges in the studied sites. Liver, gills and kidney CAT, liver and kidney MT and brain AChE were key biomarkers to discriminate fish of different sites. So, we suggest using these biomarkers in future biomonitoring.