Validation of an Alzheimer's Disease Marker by Fecal Assay of Amyloid Peptides and Tau Proteins

Alzheimer's disease (AD) is the leading cause of dementia in humans, currently affecting almost one million people in France. It results from an irreversible degeneration of neurons responsible for a progressive decline in the main cognitive and memory functions due to a cerebral accumulation of plaques containing fibrillary amyloid peptide (Aβ) and neurofibrillary tangles composed of truncated, hyperphosphorylated tau protein (pTau). There is currently no curative treatment for this disease in France. However, two treatments aimed at reducing beta-amyloid plaques in the brain have been approved by the U.S. Food and Drug Administration. The failure of the latest therapeutic strategies is largely due to the fact that the disease is diagnosed too late, starting with a long asymptomatic phase, which is the one that needs to be targeted in order to prevent irreversible neurodegenerative mechanisms. The development of diagnostic tools is gradually making it possible to detect such a sequence, but this has its drawbacks (radioactive load, invasive procedure, cumbersome set-up). Over the last ten years, research has focused on the development of plasma or salivary markers. Although encouraging, these studies show either a lack of sensitivity or reproducibility, or a lack of specificity or precocity. The expression of Aβ and Tau proteins has recently been demonstrated in the enteric nervous system and enterocytes. Intestinal Aβ is involved in various gut functions and regulation. What recent work by investigators demonstrates is the essential and hitherto unrecognized role of the gut-brain axis in maintaining brain homeostasis. In a mouse model of AD, the investigators have demonstrated a mechanism for intestinal elimination (clearance) of toxic brain forms of Tau and Aβ proteins, via the lymphatic network. The clearance of cerebral Tau and Aβ proteins in the stool may constitute a reliable and powerful diagnostic signature of AD. Its study would represent a new, non-invasive and easily accessible technique for the early diagnosis of AD in humans.