Assessing Blood-Brain Barrier Permeability

To investigate the effects of AlNPs on the tightness of BBB, we assessed the permeability rate of 40 kDa FITC–dextran (Sigma-Aldrich) with or without treatment of AlNPs. Upon the completion of AlNP treatment, we added 10 μg/mL of 40 kDa FITC-dextran to L.C. of hNVUI and collected the conditioned medium from R.C. side every 6 h up to 24 h. We measured the concentration of BBB-penetrating FITC-dextran by Bio Tek Gen5 (Agilent Technologies, Santa Clara, CA, USA). The apparent permeability of each sample across the BBB (P_BBB) was calculated by Eq. 1 as described previously^{15 (link),46 (link)}: $${\text{P}}_{\text{BBB}}=\frac{C_L}{C_0}\times \frac{V}{S·t}$$
In this equation, C_L (μg/mL), C₀ (μg/mL), V (cm³), S (cm²), and t (s) represent the concentration of FITC-dextran in R.C., the initial concentration of FITC-dextran in L.C., the volume of R.C., the surface area of microchannels connecting L.C. and R.C., and the time for BBB penetration, respectively.