One of the three PNAS articles probes the reasons behind this rejuvenation, concluding that the two chemicals "tune up" the energy-producing organelles that power all cells, the mitochondria. Both chemicals are normally used in mitochondria.
Ames calls mitochondria the "weak link in aging." Evidence has been piling up, he said, that deterioration of mitochondria is an important cause of aging. A significant cause of this deterioration, he believes, is the accumulation of destructive free radicals - byproducts of normal metabolism - that disable enzymes and other chemicals.
The combination therapy targets mitochondria to get rid of destructive radicals and to boost the activity of a damaged enzyme, carnitine acetyltransferase, that plays a key role in burning fuel in mitochondria. The researchers hoped that the anti-oxidant alpha-lipoic acid would do the former, and that flooding the cell with acetyl-L-carnitine, one of two proteins that the enzyme acts on, would achieve the latter.
Experiments showed that this regimen worked. Associate researcher Jiankang Liu of CHORI, UC Berkeley postdoctoral fellow David W. Killilea and Ames demonstrated that the enzyme carnitine acetyltransferase is less active in old rats than in young rats, and that it binds less tightly to acetyl-L-carnitine in older rats.
Supplementation with acetyl-L-carnitine or a combination of acetyl-L-carnitine and alpha-lipoic acid restored the enzyme's activity nearly to that found in young rats and substantially restored binding to acetyl-L-carnitine.
"The acetyl-L-carnitine is protecting the protein and the higher levels are enabling the protein to work, while alpha-lipoic acid knocks down oxygen radicals," Ames said. "Each chemical solves a different problem - the two together are better than either one alone."
Ames and Hagen have long had an interest in mitochondria as they relate to aging, and they were
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Contact: Robert Sanders
rls@pa.urel.berkeley.edu
510-643-6998
University of California - Berkeley
18-Feb-2002