# A Pilot Study on Blood Concentration of β-Amyloid (40 and 42) and Phospho-Tau 181 in Horses

## TL;DR

This study measures biomarkers of cognitive decline in horses and finds no detectable levels of a key protein linked to Alzheimer's disease.

## Contribution

The study pioneers the investigation of blood-based biomarkers for cognitive degeneration in horses.

## Key findings

- Aβ42 was undetectable in all horse samples.
- A significant positive correlation was found between Aβ40 and pTau181 concentrations.
- No behavioral signs of cognitive dysfunction were observed despite elevated biomarker levels.

## Abstract

Increased life expectancy is a trend observed not only in humans but also in horses. In people, aging is often associated with cognitive deterioration, such as Alzheimer’s disease, which shares similarities with age-related cognitive decline in dogs. However, the aging process in horses remains largely unexplored. This study aims to investigate the presence of blood biomarkers linked to cognitive degeneration in horses. A total of 23 Arabian horses were examined, and serum levels of β-amyloid peptides (Aβ40 and Aβ42) and phosphorylated tau protein (pTau181) were measured, molecules recognized as reliable indicators of cognitive decline in other species. Notably, Aβ42 was undetectable in all samples. While no correlation was found between age and either Aβ40 or pTau181 levels, a significant positive correlation emerged between Aβ40 and pTau181 concentrations. Interestingly, none of the horses showed behavioral changes or clinical signs suggestive of cognitive dysfunction. This absence of symptoms may be attributed to the undetectable levels of Aβ42, the isoform considered key in triggering cognitive degeneration through tau phosphorylation, even if potentially present at higher levels than those typically found in healthy humans.

In humans, aging is often accompanied by cognitive decline, as seen in Alzheimer’s disease. In contrast, the aging process in horses remains poorly characterized. This study aims to explore the presence of blood-based biomarkers associated with cognitive degeneration in this species. Twenty-three Arabian horses were enrolled, and 5 mL of blood was collected from each to measure serum levels of β-amyloid peptides (Aβ40 and Aβ42) and phosphorylated tau protein (pTau181), both considered reliable indicators of cognitive impairment in other species. Aβ42 was undetectable in all samples, while pTau181 ranged from 5.38 to 54.42 pg/mL and Aβ40 from 67.4 to 743.9 pg/mL. Statistical analysis of the data, performed with the non-parametric Spearman test, did not reveal any correlation between age and the concentrations of Aβ40 and pTau. The pTau/Aβ40 ratio also did not appear to be correlated with the age of the subjects. Interestingly, none of the horses exhibited behavioral changes or clinical signs suggestive of cognitive dysfunction. This absence of symptoms may be related to the undetectable levels of Aβ42, the isoform considered crucial in initiating tau phosphorylation and subsequent neurodegeneration, despite possibly being present at concentrations higher than those typically found in healthy humans.