No abstract

The initial transition of amyloid beta (1-42) (Abeta42) soluble monomers/small oligomers from unordered/alpha-helix to a beta-sheet-rich conformation represents a suitable target to design new potent inhibitors and to obtain effective therapeutics for Alzheimer's disease. Under optimized conditions, this reliable and reproducible CD kinetic study showed a three-step sigmoid profile that was characterized by a lag phase (prevailing unordered/alpha-helix conformation), an exponential growth phase (increasing beta-sheet secondary structure) and a plateau phase (prevailing beta-sheet secondary structure). This kinetic analysis brought insight into the inhibitors' mechanism of action. In fact, an increase in the duration of the lag phase can be related to the formation of an inhibitor-Abeta complex, in which the non-amyloidogenic conformation is stabilized. When the exponential rate is affected exclusively, such as in the case of Congo red and tetracycline, then the inhibitor affinity might be higher for the pleated beta-sheet structure. Finally, by adding the inhibitor at the end of the exponential phase, the soluble protofibrils can be disrupted and the Abeta amyloidogenic structure can revert into monomers/small oligomers. Congo red and tetracycline preferentially bind to amyloid in the beta-sheet conformation because both decreased the slope of the exponential growth, even if to a different extent, whereas no effect was observed for tacrine and galantamine. Some very preliminary indications can be derived about the structural requirements for binding to nonamyloidogenic or beta-sheet amyloid secondary structure for the development of potent antiaggregating agents. On these premises, memoquin, a multifunctional molecule that was designed to become a drug candidate for the treatment of Alzheimer's disease, was investigated under the reported circular dichroism assay and its anti-amyloidogenic mechanism of action was elucidated.

The coupling of two different pharmacophores, each endowed with different biological properties, afforded the hybrid compound lipocrine (7), whose biological profile was markedly improved relative to those of prototypes tacrine and lipoic acid. Lipocrine is the first compound that inhibits the catalytic activity of AChE and AChE-induced amyloid-beta aggregation and protects against reactive oxygen species. Thus, it emerged as a valuable pharmacological tool to investigate Alzheimer's disease and as a promising lead compound for new anti-Alzheimer drugs.

In recent years, the investigation of acetylcholinesterase (AChE) inhibitors has gained further interest, because the involvement of the peripheral site of the enzyme in the beta-amyloid (Abeta) aggregation process has been disclosed. We present here, for the first time, a direct evidence of the Abeta antiaggregating action of an AChE inhibitor (AP2238) purposely designed to bind at both the catalytic and the peripheral sites of the human enzyme.

A design strategy to convert a dual-binding site AChE inhibitor into triple functional compounds with promising in vitro profile against multifactorial syndromes, such as Alzheimer's disease, is proposed. The lead compound bis(7)-tacrine (2) was properly modified to confer to the new molecules the ability of chelating metals, involved in the neurodegenerative process. The multifunctional compounds show activity against human AChE, are able to inhibit the AChE-induced amyloid-beta aggregation, and chelate metals, such as iron and copper.