Transthyretin Stabilization by Iododiflunisal Promotes Amyloid-β Peptide Clearance,Decreases its Deposition,and Ameliorates Cognitive Deficits in an Alzheimer's Disease Mouse Model

Abstract

Alzheimer's disease (AD) is the most common form of dementia and now represents 50–70% of total dementia cases. Over the last two decades, transthyretin (TTR) has been associated with AD and, very recently, a novel concept of TTR stability has been established in vitro as a key factor in TTR/amyloid-β (Aβ) interaction. Small compounds, TTR stabilizers (usually non-steroid anti-inflammatory drugs), bind to the thyroxine (T₄) central binding channel, increasing TTR tetrameric stability and TTR/Aβ interaction. In this work, we evaluated in vivo the effects of one of the TTR stabilizers identified as improving TTR/Aβ interaction, iododiflunisal (IDIF), in Aβ deposition and other AD features, using AβPPswe/PS1A246E transgenic mice, either carrying two or just one copy of the TTR gene (AD/TTR^+/+ or AD/TTR^+/−, respectively), available and characterized in our laboratory. The results showed that IDIF administered orally bound TTR in plasma and stabilized the protein, as assessed by T₄ displacement assays, and was able to enter the brain as revealed by mass spectrometry analysis of cerebrospinal fluid. TTR levels, both in plasma and cerebrospinal fluid, were not altered. In AD/TTR^+/− mice, IDIF administration resulted not only in decreased brain Aβ levels and deposition but also in improved cognitive function associated with the AD-like neuropathology in this mouse model, although no improvements were detectable in the AD/TTR^+/+ animals. Further, in AD/TTR^+/− mice, Aβ levels were reduced in plasma suggesting TTR promoted Aβ clearance from the brain and from the periphery. Taken together, these results strengthen the importance of TTR stability in the design of therapeutic drugs, highlighting the capacity of IDIF to be used in AD treatment to prevent and to slow the progression of the disease.