Oral Treatment with Iododiflunisal Delays Hippocampal Amyloid-β Formation in a Transgenic Mouse Model of Alzheimer's Disease: A Longitudinal in vivo Molecular Imaging Study1

Synthesis and PET Imaging Biodistribution Studies of Radiolabeled Iododiflunisal, a Transthyretin Tetramer Stabilizer, Candidate Drug for Alzheimer's Disease

The small-molecule iododiflunisal (IDIF) is a transthyretin (TTR) tetramer stabilizer and acts as a chaperone of the TTR-Amyloid beta interaction. Oral administration of IDIF improves Alzheimer's Disease (AD)-like pathology in mice, although the mechanism of action and pharmacokinetics remain unknown. Radiolabeling IDIF with positron or gamma emitters may aid in the in vivo evaluation of IDIF using non-invasive nuclear imaging techniques. In this work, we report an isotopic exchange reaction to obtain IDIF radiolabeled with 18F. [19F/18F]exchange reaction over IDIF in dimethyl sulfoxide at 160 °C resulted in the formation of [18F]IDIF in 7 ± 3% radiochemical yield in a 20 min reaction time, with a final radiochemical purity of >99%. Biodistribution studies after intravenous administration of [18F]IDIF in wild-type mice using positron emission tomography (PET) imaging showed capacity to cross the blood-brain barrier (ca. 1% of injected dose per gram of tissue in the brain at t > 10 min post administration), rapid accumulation in the liver, long circulation time, and progressive elimination via urine. Our results open opportunities for future studies in larger animal species or human subjects.

Endogenous Human Proteins Interfering with Amyloid Formation

Amyloid formation is a pathological process associated with a wide range of degenerative disorders, including Alzheimer’s disease, Parkinson’s disease, and diabetes mellitus type 2. During disease progression, abnormal accumulation and deposition of proteinaceous material are accompanied by tissue degradation, inflammation, and dysfunction. Agents that can interfere with the process of amyloid formation or target already formed amyloid assemblies are consequently of therapeutic interest. In this context, a few endogenous proteins have been associated with an anti-amyloidogenic activity. Here, we review the properties of transthyretin, apolipoprotein E, clusterin, and BRICHOS protein domain which all effectively interfere with amyloid in vitro, as well as displaying a clinical impact in humans or animal models. Their involvement in the amyloid formation process is discussed, which may aid and inspire new strategies for therapeutic interventions.

Static discrete disorder in the crystal structure of iododiflunisal: on the importance of hydrogen bond, halogen bond and π-stacking interactions

We report a combined computational/crystallographic analysis focused on the static discrete disorder shown by the drug iododiflunisal.

Neuroprotection in early stages of Alzheimer's disease is promoted by transthyretin angiogenic properties

Background

While still controversial, it has been demonstrated that vascular defects can precede the onset of other AD hallmarks features, making it an important therapeutic target. Given that the protein transthyretin (TTR) has been established as neuroprotective in AD, here we investigated the influence of TTR in the vasculature.

Methods

We evaluated the thickness of the basement membrane and the length of brain microvessels, by immunohistochemistry, in AβPPswe/PS1A246E (AD) transgenic mice and non-transgenic mice (NT) bearing one (TTR+/−) or two (TTR+/+) copies of the TTR gene. The angiogenic potential of TTR was evaluated in vitro using the tube formation assay, and in vivo using the chick chorioallantoic membrane (CAM) assay.

Results

AD transgenic mice with TTR genetic reduction, AD/TTR+/−, exhibited a thicker BM in brain microvessels and decreased vessel length than animals with normal TTR levels, AD/TTR+/+. Further in vivo investigation, using the CAM assay, revealed that TTR is a pro-angiogenic molecule, and the neovessels formed are functional. Also, TTR increased the expression of key angiogenic molecules such as proteins interleukins 6 and 8, angiopoietin 2, and vascular endothelial growth factor, by endothelial cells, in vitro, under tube formation conditions. We showed that while TTR reduction also leads to a thicker BM in NT mice, this effect is more pronounced in AD mice than in NT animals, strengthening the idea that TTR is a neuroprotective protein. We also studied the effect of TTR tetrameric stabilization on BM thickness, showing that AD mice treated with the TTR tetrameric stabilizer iododiflunisal (IDIF) displayed a significant reduction of BM thickness and increased vessel length, when compared to non-treated littermates.

Conclusion

Our in vivo results demonstrate the involvement of TTR in angiogenesis, particularly as a modulator of vascular alterations occurring in AD. Since TTR is decreased early in AD, its tetrameric stabilization can represent a therapeutic avenue for the early treatment of AD through the maintenance of the vascular structure.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-021-00883-8.

Longitudinal evaluation of a novel BChE PET tracer as an early in vivo biomarker in the brain of a mouse model for Alzheimer disease

Purpose: The increase in butyrylcholinesterase (BChE) activity in the brain of Alzheimer disease (AD) patients and animal models of AD position this enzyme as a potential biomarker of the disease. However, the information on the ability of BChE to serve as AD biomarker is contradicting, also due to scarce longitudinal studies of BChE activity abundance. Here, we report ¹¹C-labeling, in vivo stability, biodistribution, and longitudinal study on BChE abundance in the brains of control and 5xFAD (AD model) animals, using a potent BChE selective inhibitor, [¹¹C]4, and positron emission tomography (PET) in combination with computerised tomography (CT). We correlate the results with in vivo amyloid beta (Aβ) deposition, longitudinally assessed by [¹⁸F]florbetaben-PET imaging.

Methods: [¹¹C]4 was radiolabelled through ¹¹C-methylation. Metabolism studies were performed on blood and brain samples of female wild type (WT) mice. Biodistribution studies were performed in female WT mice using dynamic PET-CT imaging. Specific binding was demonstrated by ex vivo and in vivo PET imaging blocking studies in female WT and 5xFAD mice at the age of 7 months. Longitudinal PET imaging of BChE was conducted in female 5xFAD mice at 4, 6, 8, 10 and 12 months of age and compared to age-matched control animals. Additionally, Aβ plaque distribution was assessed in the same mice using [¹⁸F]florbetaben at the ages of 2, 5, 7 and 11 months. The results were validated by ex vivo staining of BChE at 4, 8, and 12 months and Aβ at 12 months on brain samples.

Results: [¹¹C]4 was produced in sufficient radiochemical yield and molar activity for the use in PET imaging. Metabolism and biodistribution studies confirmed sufficient stability in vivo, the ability of [¹¹C]4 to cross the blood brain barrier (BBB) and rapid washout from the brain. Blocking studies confirmed specificity of the binding. Longitudinal PET studies showed increased levels of BChE in the cerebral cortex, hippocampus, striatum, thalamus, cerebellum and brain stem in aged AD mice compared to WT littermates. [¹⁸F]Florbetaben-PET imaging showed similar trend of Aβ plaques accumulation in the cerebral cortex and the hippocampus of AD animals as the one observed for BChE at ages 4 to 8 months. Contrarily to the results obtained by ex vivo staining, lower abundance of BChE was observed in vivo at 10 and 12 months than at 8 months of age.

Conclusions: The BChE inhibitor [¹¹C]4 crosses the BBB and is quickly washed out of the brain of WT mice. Comparison between AD and WT mice shows accumulation of the radiotracer in the AD-affected areas of the brain over time during the early disease progression. The results correspond well with Aβ accumulation, suggesting that BChE is a promising early biomarker for incipient AD.

An Assay for Screening Potential Drug Candidates for Alzheimer's Disease That Act as Chaperones of the Transthyretin and Amyloid-β Peptides Interaction

The protein transthyretin (TTR) modulates amyloid-β (Aβ) peptides deposition and processing and this physiological effect is further enhanced by treatment with iododiflunisal (IDIF), a small-molecule compound (SMC) with TTR tetramer stabilization properties, which behaves as chaperone of the complex. This knowledge has prompted us to design and optimize a rapid and simple high-throughput assay that relies on the ability of test compounds to form ternary soluble complexes TTR/Aβ/SMC that prevent Aβ aggregation. The method uses the shorter Aβ(12-28) sequence which is cheaper and simpler to use while retaining the aggregation properties of their parents Aβ(1-40) and Aβ(1-42). The test is carried out in 96-plate wells that are UV monitored for turbidity during 6 h. Given its reproducibility, we propose that this test can be a powerful tool for efficient screening of SMCs that act as chaperones of the TTR/Aβ interaction that may led to potential AD therapies.