Fig. 4: Fluvoxamine-induced transcytosis boosts permeability of the blood-brain barrier.

A Representative image of cultured brain-like endothelial cells treated with fluvoxamine for 1 h and immunostained for EEA1 and LAMP1. Scale bar, 20 µm. B Permeability of 4 kDa FITC-dextran across the human co-culture model of the blood-brain barrier in the presence of 80 nM fluvoxamine after 1, 2, and 4 h of incubation. Values presented are means ± SD. **P < 0.01, *P < 0.05, two-way ANOVA, with Bonferroni posttest; n = 4. C Representative images of brain sections from mice injected intraperitoneally 24 h prior with 4 kDa FITC-dextran, Evans blue, and fluvoxamine. Arrows denote accumulation of dextran in multiple punctate intracellular structures. Scale bar, 20 µm. D Quantification of FITC signal in brain sections from mice injected intraperitoneally 24 h prior with 4 kDa FITC-dextran, Evans blue, and fluvoxamine. **P < 0.01, One-way ANOVA with Tukey’s post test. N = 3 independent experiments, 9 animals/condition. E Quantification of Evans Blue signal in brain sections from fluvoxamine-treated mice. ns - P = 0.23, Kruskal–Wallis test with Dunn’s multiple comparisons test. F Schematic model of fluvoxamine-induced transcytotic dextran delivery into the brain. Under normal conditions (left) transcytosis in the blood-brain barrier cells is inactive, limiting delivery of cargo from the bloodstream into the brain milieu. Treatment with the therapeutic concentration of fluvoxamine (right) triggers fluid-phase transcytosis across the blood-brain barrier, resulting in enhanced delivery of non-charged hydrophilic cargo. Blue arrows denote fluvoxamine-induced bloodstream-to-brain flow of blood-brain barrier transcytosis; gray arrows denote speculated compensatory increase in the brain-to-bloodstream flow. For the sake of simplicity, putative effects of fluvoxamine on uptake of negatively charged cargo are not pictured.