Evaluation of arsenic metabolism and tight junction injury after exposure to arsenite and monomethylarsonous acid using a rat in vitro blood–Brain barrier model

Experimental verification of impairment to cognitive abilities and cognitive dysfunction resulting from inorganic arsenic (iAs) exposure in children and adults is challenging. This study aimed to elucidate the effects of arsenite (iAs(III); 1, 10 and 20 μM) or monomethylarsonous acid (MMA(III); 0.1, 1 and 2 μM) exposure on arsenic metabolism and tight junction (TJ) function in the blood–brain barrier (BBB) using a rat in vitro-BBB model. The results showed that a small percentage (~15%) of iAs(III) was oxidized or methylated within the BBB, suggesting the persistence of toxicity as iAs(III). Approximately 65% of MMA(III) was converted to low-toxicity monomethylarsonic acid and dimethylarsenic acid via oxidation and methylation. Therefore, it is estimated that MMA(III) causes TJ injury to the BBB at approximately 35% of the unconverted level. TJ injury of BBB after iAs(III) or MMA(III) exposure could be significantly assessed from decreased expression of claudin-5 and decreased transepithelial electrical resistance values. TJ injury in BBB was found to be significantly affected by MMA(III) than iAs(III). Relatedly, the penetration rate in the BBB by 24 h of exposure was higher for MMA(III) (53.1% ± 2.72%) than for iAs(III) (43.3% ± 0.71%) (p < 0.01). Exposure to iAs(III) or MMA(III) induced an antioxidant stress response, with concentration-dependent increases in the expression of nuclear factor-erythroid 2-related factor 2 in astrocytes and heme oxygenase-1 in a group of vascular endothelial cells and pericytes, respectively. This study found that TJ injury at the BBB is closely related to the chemical form and species of arsenic; we believe that elucidation of methylation in the brain is essential to verify the impairment of cognitive abilities and cognitive dysfunction caused by iAs exposure.