Homocysteine Induces Brain and Retinal Microvascular Endothelial Cell Barrier Damage and Hyperpermeability via NLRP3...

The amino acid homocysteine (HCY) has been implicated in the pathobiology of several conditions, including spaceflight-associated neuro-ocular syndrome (SANS)-a collection of symptoms affecting near vision in astronauts. Blood-retinal barrier (BRB) and blood-brain barrier (BBB) dysfunctions are implicated in the pathobiology of SANS. Our objective was to assess how HCY affects BRB/BBB permeability and the role of the NLRP3 inflammasome in the modulation of such effects.

Human brain and retinal microvascular endothelial cells (HBMECs and HRMECs) were treated with 100 μM HCY alone or in conjunction with NLRP3 inflammasome inhibitor MCC950 at 1 μM. The assays performed included fluorometric assays to measure cell viability, an enzyme assay for caspase-1, expression of BRB/BBB tight junction protein zonula occludens-1 (ZO-1) by RT-PCR, and barrier permeability using FITC-dextran.

In HRMECs and HBMECs, HCY-induced endothelial monolayer hyperpermeability significantly (p < 0.05). In HBMECs, the effect was attenuated by MCC950 (p < 0.05). Increased Caspase-1 activity was observed in both cell types following the addition of HCY. Following HCY addition, gene expression results denoting barrier damage were observed, particularly that of ZO-1 (p < 0.05).

HCY induces hyperpermeability in retinal and brain endothelial cells. NLRP3-mediation in HCY-induced microvascular permeability is prominent in brain endothelial cells compared to retinal endothelial cells.