Transthyretin (TTR) binds Aβ peptide, preventing its deposition and toxicity. TTR is decreased in Alzheimer’s disease (AD) patients. Additionally, AD transgenic mice with only one copy of the TTR gene show increased brain and plasma Aβ levels when compared to AD mice with both copies of the gene, suggesting TTR involvement in brain Aβ efflux and/or peripheral clearance. Here we showed that TTR promotes Aβ internalization and efflux in a human cerebral microvascular endothelial cell line, hCMEC/D3. TTR also stimulated brain-to-blood but not blood-to-brain Aβ permeability in hCMEC/D3, suggesting that TTR interacts directly with Aβ at the blood-brain-barrier. We also observed that TTR crosses the monolayer of cells only in the brain-to-blood direction, as confirmed by in vivo studies, suggesting that TTR can transport Aβ from, but not into the brain. Furthermore, TTR increased Aβ internalization by SAHep cells and by primary hepatocytes from TTR+/+ mice when compared to TTR−/− animals. We propose that TTR-mediated Aβ clearance is through LRP1, as lower receptor expression was found in brains and livers of TTR−/− mice and in cells incubated without TTR. Our results suggest that TTR acts as a carrier of Aβ at the blood-brain-barrier and liver, using LRP1.

Several strategies against Alzheimer disease (AD) are directed to target Aβ-peptides. The ability of transthyretin (TTR) to bind Aβ-peptides and the positive effect exerted by some TTR stabilizers for modulating the TTR-Aβ interaction have been previously studied. Herein, key structural features of the interaction between TTR and the Aβ(12-28) peptide (3), the essential recognition element of Aβ, have been unravelled by STD-NMR spectroscopy methods in solution. Molecular aspects related to the role of the TTR stabilizer iododiflunisal (IDIF, 5) on the TTR-Aβ complex have been also examined. The NMR results, assisted by molecular modeling protocols, have provided a structural model for the TTR-Aβ interaction, as well as for the ternary complex formed in the presence of IDIF. This basic structural information could be relevant for providing light on the mechanisms involved in the ameliorating effects of AD symptoms observed in AD/TTR animal models after IDIF treatment and eventually for designing new molecules toward AD therapeutic drugs.

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Transthyretin (TTR) has a well-established role in neuroprotection, evidenced in Alzheimer's Disease (AD). By targeting TTR we have setup a drug discovery program of small-molecule compounds that act as chaperones, enhancing TTR/ amyloid-β peptide (Aβ) interactions. In a first stage, we carried out two computational drug repurposing approaches. In a second stage, the computationally selected compounds were assessed for their ability to bind and stabilize the TTR tetramer, using thyroxine displacement tests, and by assessing the level of monomers, respectively. In a third stage, the selected 53 best performing molecules were run through our in-house validated high-throughput screening ternary test. By targeting TTR in our AD drug discovery program, small-molecule chaperones (SMCs) have been discovered, providing the basis for a novel target for Alzheimer's disease (AD) based on their enhancement of the TTR/A interaction.Among the SMCs, we have found our lead small-molecule compound Iododiflunisal (IDIF), a molecule in the discovery phase, one investigational drug (luteolin), and 3 marketed drugs (sulindac, olsalazine and flufenamic), which could be directly repurposed or repositioned for clinical use. Importantly, we found that not all TTR tetramer stabilizers are good SMCs in vitro, emphasizing the importance of our discovery program. A small set of these SMCs will be prioritized to enter preclinical safety studies, to validate TTR as a target in vivo, and to select one repurposed drug as a candidate to enter clinical trials for AD. We envisage that this new target will feed the currently exhausted pipeline of drugs in phase I for AD with the goal of increasing AD disease-modifying therapies.Compounds assayed in different assays; selected compounds after computational screening; T4 displacement assays; TTR stability assays; selected compounds for ternary assays; results from the HTS assays; kinetics of aggregation of A(12-28) peptide with TTR or TTR complexed with representative comppunds of the 53 selected molecules; ITC studies of the binary interaction A(12-28) + TTR and the ternary interactions [A(12-28) + [(TTR+SMC)]; ITC studies of the binary interactions (TTR+SMC).

Amyloidosis is a generic term that refers to a wide spectrum of diseases that are characterized by the deposition of proteins in different organs, forming insoluble aggregates. Examples include islet amyloid polypeptide (IAPP) associated with diabetes type 2, prion protein (PrP) related with spongiform encephalopathies, (TTR) associated with familial amyloidotic polyneuropathy (FAP), and amyloid-beta (Aβ) peptide linked to Alzheimer's disease (AD), the most common form of dementia. Aβ peptide, thought to be the causative agent in AD, is generated upon sequential cleavage of the amyloid precursor protein (APP), by beta-and gamma-secretases, and it is believed that an imbalance between Aβ production and clearance results in its accumulation in the brain. TTR is a 55 kDa homotetrameric protein synthesized by the liver and choroid plexus of the brain and is involved in the transport of thyroid hormones and retinol. TTR protects against Aβ toxicity by binding the peptide, thus inhibiting its aggregation. Also, increased Aβ levels are found in both brain and plasma of AD mice with only one copy of the TTR gene, when compared to animals with two copies of the gene, suggesting a role for TTR in Aβ clearance. Growing evidence also suggests a wider role for TTR in central nervous system neuroprotection, including in the cases of ischemia, regeneration, and memory.

Transthyretin (TTR) has a well-established role in neuroprotection, evidenced in Alzheimer's Disease (AD). By targeting TTR we have setup a drug discovery program of small-molecule compounds that act as chaperones, enhancing TTR/ amyloid-β peptide (Aβ) interactions. In a first stage, we carried out two computational drug repurposing approaches. In a second stage, the computationally selected compounds were assessed for their ability to bind and stabilize the TTR tetramer, using thyroxine displacement tests, and by assessing the level of monomers, respectively. In a third stage, the selected 53 best performing molecules were run through our in-house validated high-throughput screening ternary test. By targeting TTR in our AD drug discovery program, small-molecule chaperones (SMCs) have been discovered, providing the basis for a novel target for Alzheimer's disease (AD) based on their enhancement of the TTR/A interaction. Among the SMCs, we have found our lead small-molecule compound Iododiflunisal (IDIF), a molecule in the discovery phase, one investigational drug (luteolin), and 3 marketed drugs (sulindac, olsalazine and flufenamic), which could be directly repurposed or repositioned for clinical use. Importantly, we found that not all TTR tetramer stabilizers are good SMCs in vitro, emphasizing the importance of our discovery program. A small set of these SMCs will be prioritized to enter preclinical safety studies, to validate TTR as a target in vivo, and to select one repurposed drug as a candidate to enter clinical trials for AD. We envisage that this new target will feed the currently exhausted pipeline of drugs in phase I for AD with the goal of increasing AD disease-modifying therapies.

Transthyretin (TTR) has a well-established role in neuroprotection, evidenced in Alzheimer’s Disease (AD). By targeting TTR we have setup a drug discovery program of small-molecule compounds that act as chaperones, enhancing TTR/ amyloid-β peptide (Aβ) interactions. In a first stage, we carried out two computational drug repurposing approaches. In a second stage, the computationally selected compounds were assessed for their ability to bind and stabilize the TTR tetramer, using thyroxine displacement tests, and by assessing the level of monomers, respectively. In a third stage, the selected 53 best performing molecules were run through our in-house validated high-throughput screening ternary test. By targeting TTR in our AD drug discovery program, small-molecule chaperones (SMCs) have been discovered, providing the basis for a novel target for Alzheimer’s disease (AD) based on their enhancement of the TTR/Abeta interaction. Among the SMCs, we have found our lead small-molecule compound Iododiflunisal (IDIF), a molecule in the discovery phase, one investigational drug (luteolin), and 3 marketed drugs (sulindac, olsalazine and flufenamic), which could be directly repurposed or repositioned for clinical use. Importantly, we found that not all TTR tetramer stabilizers are good SMCs in vitro, emphasizing the importance of our discovery program. A small set of these SMCs will be prioritized to enter preclinical safety studies, to validate TTR as a target in vivo, and to select one repurposed drug as a candidate to enter clinical trials for AD. We envisage that this new target will feed the currently exhausted pipeline of drugs in phase I for AD with the goal of increasing AD disease-modifying therapies.