Beta-amyloid inhibition of MTT reduction is not mimicked by inhibitors of mitochondrial respiration.

Senile plaques, a neuropathological feature of Alzheimer's disease, consist mainly of insoluble aggregates of pamyloid protein I I I . Using rat pheochromocytoma PC12 cells as an irr vitro model. i t has been shown that 8-amyloid potently inhibits the reduction of MTT 12.31. The cellular reduction of M 7 T is thought to be mediated by the mitochondrial respiratory chain, although other NAD(P)H oxidase-type enzymes may also be involved 141. In an attempt to identify an inhibitor which mimics the actions of P-amyloid, the effects of various respiratory and metabolic inhibitors on whole cell respiration, together with MTT, MTS and Alamar Blue reduction were compared. To assess the involvement of mitochondria in whole cell MTT reduction, a range of respiratory inhibitors were used. Rotenone (complex I ) , TTFA (complex 11). antimycin A (complex 111) and azide (complex IV) inhibited whole cell respiration as expected (figure la). The reduction of the redox dyes MTT, MTS and Alamar Blue, however, were not affected (azide was in fact, able to stimulate MTS reduction by 230%; figures 1 h,c,d). P-amyloid (p25-35) inhibits M'IT reduction, but had no effect on MTS or Alamar Blue reduction, or on whole cell respiration. These observations indicate that respiratory inhibitors do not mimic the action of P-amyloid on MTT reduction, that 8-amyloid does not inhibit mitochondrial respiration, and that inhibition of mitochondrial electron transport does not prevent MTT reduction.