Apolipoprotein E and antioxidants have different mechanisms of inhibiting Alzheimer's beta-amyloid fibril formation in vitro

We compared the mechanisms of apolipoprotein E- (apoE-) and antioxidant- (A O-) mediated inhibition of beta-amyloid fibril (fA beta) formation in vitro , based on a nucleation-dependent polymerization model using fluorescence s pectroscopy with thioflavin T, We first applied a kinetic plot to transform a sigmoidal time-course curve of fA beta formation from freshly prepared a myloid beta-peptides (A beta) into a straight line, Mathematical treatment of this plot demonstrated that the above-described sigmoidal curve is a log istic curve and provided us with a kinetic parameter tilt, the time when th e rate of fA beta formation is maximum. t(1/2) Of beta-amyloids (A beta) (1 -42) and (1-40) were 18.7 +/- 1.7 min and 6.3 +/- 0.2 h, respectively (mean +/- SD, Il = 3) and were independent of the initial A beta concentration e xamined. Although apoE extended t(1/2) of both A beta s in a dose-dependent manner, AO did not. On the other hand, the final amount of fA beta formed was decreased by both apoE and AO dose-dependently. We then analyzed the ef fect of apoE and AO on the extension reaction of fA beta, based on a first- order kinetic model. Although apoE extended the time to proceed to equilibr ium in a dose-dependent manner, AO did not, On the other hand, both apoE an d AO dose-dependently decreased the final amount of fA beta formed. These r esults indicate that apoE and AO inhibit fA beta formation in vitro by diff erent mechanisms and suggest the existence of multiple pharmacological targ ets for the prevention of fA beta formation.