Chronic alcohol exposure and thiamine transport in BBB in Alcohol Use Disorder

Background:

Thiamine transport between blood and cells only occurs via active transport involving transporters, like thiamine transporter 1 (Thtr1) and Thtr2. Patients with severe alcohol use disorder have been identified to have reduced intestine absorption of thiamine, however, it is still unclear if thiamine absorption is impaired at the human brain level. To act in central nervous system (CNS) targets, thiamine must overcome the blood-brain barrier (BBB). The effect of chronic ethanol exposure on BBB cells is still under investigation.

Methods:

Using a human brain endothelial (HBEC-5i) in vitro model, we tested the effect of chronic ethanol exposure to BBB cells. To achieve an optimal and adequate model to mimic the human BBB HBEC-5i cells were left to grow a monolayer for 9 days. According to the timeline, on day 6, 7, or 8 (24h, 48h, or 72h before the endpoint), test compounds were included in the system to simulate a drug abuse chronicity state. Cell viability assay, integrity assay, transendothelial electrical resistance (TEER), western blot and immunofluorescence technics were conducted. Quantitative data and statistical analysis were processed using the Excel Microsoft 365 (Microsoft, New York, USA) and GraphPad Prism 8.0 software package.

Results:

A chronic ethanol exposure affects the BBB viability at high concentrations and affects the BBB permeability for selected timepoints and dose regimens. Also, a chronic ethanol exposure reduces the expression of the tight junction proteins ZO-1, occludin, and claudin-5 and reduces the expression of Thtr2, but not Thtr1. 

Conclusions:

Using a human brain endothelial (HBEC-5i) in vitro model, we demonstrated that ethanol decreased the cell viability, integrity, and expression of tight junction proteins and Thtr2.