Blood-Brain Barrier Dysfunction and Aβ42/40 Ratio Dose-Dependent Modulation with the ApoE Genotype within the ATN Framework

Association of APOE genotype with blood-brain barrier permeability in neurodegenerative disorders

Apolipoprotein E (APOE) is recognized for its role in modulating blood-brain barrier (BBB) permeability in vitro, which may have significant implications for the pathogenesis and progression of neurodegenerative disorders. However, evidence in vivo is contrasting. This study explores the impact of APOE genotypes on BBB integrity among 230 participants experiencing cognitive impairment, encompassing cases of Alzheimer's disease (AD) as well as various non-AD neurodegenerative conditions. To assess BBB integrity, we utilized cerebrospinal fluid (CSF)/serum albumin ratios and CSF/serum kappa and lambda free light chains (FLCs) as indirect markers. Our findings show a dose-dependent increase in BBB permeability in individuals carrying the APOE ε4 allele, marked by elevated CSF/serum albumin and FLCs ratios, with this trend being especially pronounced in AD patients. These results highlight the association of APOE ε4 with BBB permeability, providing valuable insights into the pathophysiology of neurodegenerative diseases.

Is blood pTau a reliable indicator of the CSF status? A narrative review

BACKGROUND

The identification of biomarkers for the early diagnosis of Alzheimer's disease (AD) is a crucial goal of the current research. Blood biomarkers are less invasive, easier to obtain and achievable by a cheaper means than those on cerebrospinal fluid (CSF) and significantly more economic than functional neuroimaging investigations; thus, a great interest is focused on blood isoforms of the phosphorylated Tau protein (pTau), indicators of ongoing tau pathology (i.e. neurofibrillary tangles, NFTs, an AD neuropathological hallmark) in the central nervous system (CNS). However, current data often highlight discordant results about the ability of blood pTau to predict CSF status.

OBJECTIVE

We aim to synthesise the studies that compared pTau levels on CSF and blood to assess their correlation in AD continuum.

METHODS

We performed a narrative literature review using, first, MEDLINE (via PubMed) by means of MeSH terms, and then, we expanded the reults by means of Scopus and Web of Sciences to be as inclusive as possible. Finally, we added work following an expert opinion. Only papers presenting original data on pTau values on both blood and CSF were included.

RESULTS

The 33 included studies show an extreme heterogeneity in terms of pTau isoform (pTau181, 217 and 231), laboratory methods, diagnostic criteria and choice of comparison groups. Most studies evaluated plasma pTau181, while data on other isoforms and serum are scarcer.

DISCUSSION

Most papers identify a correlation between CSF and blood measurements. Furthermore, even when not specified, it is often possible to show an increase in blood pTau values as AD-related damage progresses in the AD continuum and higher values in AD than in other neurodegenerative diseases. Notably, plasma pTau231 seems the first biomarker to look for in the earliest and pre-clinical stages, quickly followed by pTau217 and, finally, by pTau181.

CONCLUSIONS

Our results encourage the use of blood pTau for the early identification of patients with AD continuum.