Objective: To determine whether hippocampal neurons and choroidal epithelia
l cells demonstrate a mitochondrial enzyme deficiency in AD more frequently
than in normal aging. Background: High levels of mutant mitochondrial DNA
(mtDNA) cause a deficiency in cytochrome c oxidase (COX) (complex IV activi
ty) because three of its 13 subunits are encoded for by mtDNA. In contrast,
succinate dehydrogenase (SDH) (complex II activity) remains intact because
all of its subunits are nuclear encoded. The histologic hallmark of cells
containing high levels of mtDNA mutation in both primary mtDNA disorders an
d normal aging muscle is the presence of COX-deficient SDH-positive cells.
Methods: The authors applied a sequential histochemical method for COX and
SDH to hippocampal sections in 17 AD and 17 age-matched control brains. Thi
s confers the advantages of both looking at individual cells in situ and me
asuring the actual mitochondrial complex activity rather than simply the co
mplex quantity. Results: COX-deficient SDH-positive hippocampal neurons and
choroidal epithelial cells are more prevalent in patients with AD than in
controls. In addition the COX-deficient SDH-positive choroidal cells are as
sociated with an enlargement in size. Conclusion: This increase in number o
f COX-deficient SDH-positive hippocampal pyramidal neurons and choroid epit
helial cells provides strong evidence that a substantial mitochondrial enzy
me activity defect occurs in individual cells more frequently in AD than in
normal aging and that mitochondria may play a significant role in the path
ogenesis of AD.