Ma. Pappolla et al., Alzheimer beta protein mediated oxidative damage of mitochondrial DNA: Prevention by melatonin, J PINEAL R, 27(4), 1999, pp. 226-229
Most contemporary progress in Alzheimer's disease (AD) stems from the study
of a 42-43 amino acid peptide, called the amyloid beta protein (A beta), a
s the main neuropathololgic marker of the disorder, It has been demonstrate
d that A beta has neurotoxic properties and that such effects are mediated
by free-radicals, Exposure of neuronal cells to A beta results in a spectru
m of oxidative lesions that are profoundly harmful to neuronal homeostasis.
We had previously shown that. A beta 25-35 induces oxidative damage to mit
ochondrial DNA (mtDNA) and that this, modality of injury is prevented by me
latonin. Because A beta 25-35 does not occur in AD and because the mode of
toxicity by A beta 25-35 may be different from that of A beta 1-42 (the phy
siologically relevant form of A beta), we extended our initial observations
to determine whether oxidative damage to mtDNA could also be induced by A
beta 1-42 and whether this type of injury is prevented by melatonin. Exposu
re of human neuroblastoma cells to A beta 1-42 resulted in marked oxidative
damage to mtDNA as determined by a quantitative polymerase chain reaction
method. Addition of melatonin to cell cultures along with A beta completely
prevented the damage. This study supports previous findings with A beta 25
-35, including a causative role for A beta in the mitochondrial oxidative:
lesions present in AD brains. Most important, the data confirms the neuropr
otective role of melatonin in A beta-mediated oxidative injury. Because mel
atonin also inhibits amyloid aggregation, lacks toxicity, and efficiently c
rosses the blood-brain barrier, this hormone appears superior to other avai
lable antioxidants as a candidate for pharmacologic intervention in AD.