Evaluation of 99mTc-MAMA-chrysamine G as an in vivo probe for amyloidosis

99mTc-labeled Small Molecules for Diagnosis of Alzheimer’s Disease: Past, Recent and Future Perspectives

Background:

Alzheimer’s disease (AD) is an age-related progressive neurodegenerative disease. Its prominent hallmarks are extracellular deposition of β-amyloids (amyloid plaques), intracellular neurofibrillary tangles (NTFs), neurodegeneration and finally loss of cognitive function. Hence, AD diagnosis in the early stage and monitoring of the disease are of great importance.

Methods:

In this review article, we have reviewed recent efforts for design, synthesis and evaluation of 99mTc labeled small molecule for AD imaging purposes.

Results:

These small molecules include derivatives of Congo red, benzothiazole, benzofuran, benzoxazole, naphthalene, biphenyl, chalcone, flavone, aurone, stilbene, curcumin, dibenzylideneacetone, quinoxaline, etc. The different aspects of 99mTc-labeled small molecules including chemical structure, their affinity toward amyloid plaques, BBB permeation and in vivo/vitro stability will be discussed.

Conclusion:

The findings of this review confirm the importance of 99mTc-labeled small molecules for AD imaging. Future studies based on the pharmacophore of these designed compounds are needed for improvement of these molecules for clinical application.

Liver transplantation and new therapeutic approaches for familial amyloidotic polyneuropathy (FAP)

Liver transplantation has been considered as a promising therapy to halt the progression of clinical symptoms in familial amyloidotic polyneuropathy (FAP) because most transthyretin (TTR) is produced by the liver. In addition, domino liver transplantation using an FAP patient's liver has been performed because of a shortage of donor livers. However, because the use of liver transplantation as therapy for FAP has given rise to several problems, an alternative treatment is needed. We have tried several other approaches. Recent studies suggested that certain metal ions affect amyloidogenesis. Among metal ions tested in an in vitro amyloid formation study, Cr3+ increased stability of both normal and mutant TTR tetramers and suppressed TTR amyloidogenesis induced by low pH. Our findings indicate that Cr3+ acts to suppress TTR amyloidogenesis. BSB, a Congo red derivative that binds to amyloid fibrils in FAP as well as to those in senile plaques in Alzheimer's disease, effectively suppressed TTR amyloid formation in vitro. BSB may thus be useful for preventing amyloid formation. Free radical scavenger therapy was also tried in FAP patients but yielded no conclusive results. Immunization for transgenic mice having the ATTR V30M gene using ATTR Y78P resulted in suppression of amyloid deposits. Finally, an RNA/DNA chimera and single-stranded oligonucleotides (SSOs) were tested in vitro and in vivo in an attempt to repair the amyloidogenic TTR gene in the liver and retina. On the basis of results achieved so far, SSO is a promising tool for gene therapy.

A novel tool for detecting amyloid deposits in systemic amyloidosis in vitro and in vivo

We synthesized (trans,trans)-1-bromo-2,5-bis-(3-hydroxycarbonyl-4-hydroxy)styrylbenzene (BSB) and used this compound to detect amyloid fibrils in autopsy and biopsy samples from patients with localized amyloidosis, such as familial prion disease, and systemic amyloidosis, such as familial amyloidotic polyneuropathy, amyloid A (AA) amyloidosis, light chain (AL) amyloidosis, and dialysis-related amyloidosis. BSB showed reactions in all Congo red-positive and immunoreactive regions of the samples examined in the study, and some amyloid fibrils in the tissues could be detected more precisely with BSB than with the other methods. In the mouse model of AA amyloidosis, injected BSB reacted with amyloid in all regions in the serial sections in which Congo red staining was positive. A highly sensitive 27-MHz quartz crystal microbalance analysis revealed that BSB showed a significant affinity for amyloid fibrils purified from familial amyloidotic polyneuropathy and dialysis-related amyloidosis samples and suppressed formation of transthyretin amyloid in vitro. These results suggest that BSB may become a valuable tool for detection of amyloid deposits in amyloidosis and of the mechanism of amyloid formation.