In vitro inhibitory effect of aflatoxin B1 on acetylcholinesterase activity in mouse brain.
Growing concern on the problem of mycotoxins in the alimentary chain underlines the need to investigate the mechanisms explaining the cholinergic effects of aflatoxin B(1) (AFB(1)). We examined the effect of AFB(1), a mycotoxin produced by Aspergillus flavus, on mouse brain acetylcholinesterase (AChE) and specifically on its molecular isoforms (G(1) and G(4)) after in vitro exposure. AFB(1) (from 10(-9) to 10(-4)M), inhibited mouse brain AChE activity (IC(50) = 31.6 x 10(-6)M) and its G(1) and G(4) molecular isoforms in a dose-dependent manner. Michaelis-Menten parameters indicate that the K(m) value increased from 55.2 to 232.2% whereas V(max) decreased by 46.2-75.1%. The direct, the Lineweaver-Burk and the secondary plots indicated a non-competitive-mixed type antagonism, induced when the inhibitor binds to the free enzyme and to the enzyme-substrate complex. AFB(1)-inhibited AChE was partially reactivated by pyridine 2-aldoxime (2-PAM) (10(-4)M) but the AChE-inhibiting time courses of AFB(1) (10(-4)M) and diisopropylfluorophosphate (DFP) (2 x 10(-7)M) differed. Overall these data suggest that AFB(1) non-competitively inhibits mouse brain AChE by blocking access of the substrate to the active site or by inducing a defective conformational change in the enzyme through non-covalent binding interacting with the AChE peripheral binding site, or through both mechanisms.
Cometa
Maria Francesca
MF
Department of Drug Research and Evaluation, Istituto Superiore di Sanità, V.le Regina Elena 299, 00161 Rome, Italy. cometa@iss.it
Lorenzini
Paola
P
Fortuna
Stefano
S
Volpe
Maria Teresa
MT
Meneguz
Annarita
A
Palmery
Maura
M
D000110:Acetylcholinesterase / Q000378:metabolism*; D016604:Aflatoxin B1 / Q000378:metabolism / Q000633:toxicity*; D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000187:drug effects* / Q000201:enzymology; D002800:Cholinesterase Inhibitors / Q000378:metabolism / Q000633:toxicity*; D002801:Cholinesterase Reactivators / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000378:metabolism; D007531:Isoflurophate / Q000378:metabolism / Q000633:toxicity; D007700:Kinetics; D008297:Male; D051379:Mice; D011220:Pralidoxime Compounds / Q000494:pharmacology; D013379:Substrate Specificity; D013997:Time Factors
D002800:Cholinesterase Inhibitors; D002801:Cholinesterase Reactivators; D007527:Isoenzymes; D011220:Pralidoxime Compounds; D007531:Isoflurophate; D016604:Aflatoxin B1; D000110:Acetylcholinesterase; C028797:pralidoxime