Brain energy metabolizing enzymes in Alzheimer's disease: alpha-ketoglutarate dehydrogenase complex and cytochrome oxidase

Ann N Y Acad Sci. 1997 Sep 26;826:218-28. doi: 10.1111/j.1749-6632.1997.tb48473.x.


PET observations of reduced cerebral glucose metabolism in AD could be explained by a defect in key energy metabolizing enzymes. In particular, levels of two enzymes, cytochrome oxidase (CO) and alpha-ketoglutarate dehydrogenase complex (alpha KGDHC) are generally assumed to be reliably reduced in postmortem brain of patients with AD. How strong is the evidence that brain CO and alpha KGDHC are reduced in AD? In our study CO activity and alpha KGDHC activity and protein subunit levels were measured in cerebral cortex of 19-29 AD patients and 29 control subjects. We found that mean CO activity in cerebral cortex was reduced by 16-26% in the AD group but with almost complete overlap between control and patient ranges. Since our publication in 1992, mean brain CO activity in AD was modestly reduced in 9 independent studies (p < 0.05 in 5). Activity of alpha KGDHC varied widely in control/AD subjects and is not useful as an enzyme marker. Cerebral cortical protein levels of E1-3 subunits, which showed much less variance, were reduced by 23-41% but with large overlap between control/patient groups. We concluded that decreased (i.e., below normal) brain CO and alpha KGDHC is a feature of some, but not all patients with AD. The possible causes and significance of the enzyme changes are discussed.

Publication types

  • Research Support, U.S. Gov't, P.H.S.
  • Review

MeSH terms

  • Alzheimer Disease / enzymology*
  • Alzheimer Disease / metabolism
  • Brain / enzymology*
  • Electron Transport Complex IV / metabolism*
  • Energy Metabolism
  • Humans
  • Ketoglutarate Dehydrogenase Complex / metabolism*
  • Pyruvate Dehydrogenase Complex / metabolism
  • Thiamine Pyrophosphate / metabolism


  • Pyruvate Dehydrogenase Complex
  • Ketoglutarate Dehydrogenase Complex
  • Electron Transport Complex IV
  • Thiamine Pyrophosphate