Abstract
Although the cause of the Alzheimer´s disease is still
unknown, it is supposed to be closely related with the deposition of amyloid
peptides in the brain of patients. The amyloid is thus a major target in the
search for novel diagnostics and therapeutic approaches. This work employs
RNA-technologies to develop new tools for the study of the Alzheimer´s disease.
The in vitro selection enables the design of specific nucleic acids
(aptamers) against almost any target molecule. The aptamers have similar
properties as monoclonal antibodies, but several advantages. The chemical
synthesis of these nucleic acids enables tailor-made modifications. By
introduction of specific reporter groups these RNAs become suitable tools for
analytical and diagnostic purposes. Since a change of the amyloid concentration
has been reported in the blood of Alzheimer´s disease patients, the use of
amyloid-specific aptamers for diagnosing the disease seems conceivable.
Moreover, antibodies have been reported that prevent the aggregation of amyloid
into senile plaques. This points towards a potential therapeutic application of
the amyloid-specific aptamers.
High affinity RNA aptamers against the b A4(1-40) and a fragment b
A4(1-16) were isolated from a combinatorial library of 1015
different molecules by using in vitro selection. For this purpose a DNA
library containing 70 randomised nucleotides was chemically synthesised and
transcribed into RNA. Affinic molecules were isolated after 8 rounds of
selection and amplification. The apparent dissociation constants of these
aptamers were 29-48 nM for the long peptide and 758 nM for the short
b A4(1-16) fragment. The binding constants for the
aptamers against the amyloid are within the range of the highest affinities so
far described for peptide-specific aptamers.
This work introduces a new approach for the study and
diagnosis of the Alzheimer´s disease. In future experiments, the efficacy of
the aptamers needs to be tested. In addition, identifying the minimal binding
motifs and enhancing the stability of the aptamers against RNase degradation
are necessary steps to render these aptamers into reliable tools.
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