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 B1 (AFB1). We examined the effect of AFB1, a mycotoxin produced by Aspergillus flavus, on mouse brain acetylcholinesterase (AChE) and specifically on its molecular isoforms (G1 and G4) after in vitro exposure. AFB1 (from 10?9 to 10?4 M), inhibited mouse brain AChE activity (IC50 = 31.6 × 10?6 M) and its G1 and G4 molecular isoforms in a dose-dependent manner. Michaelis-Menten parameters indicate that the Km value increased from 55.2 to 232.2% whereas Vmax 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. AFB1-inhibited AChE was partially reactivated by pyridine 2-aldoxime (2-PAM) (10?4 M) but the AChE-inhibiting time courses of AFB1 (10?4 M) and diisopropylfluorophosphate (DFP) (2 × 10?7 M) differed. Overall these data suggest that AFB1 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.