*2.3. Cell Culture*

The Caco-2 (HTB-37™) cells were purchased from the American Type Culture Collection (ATCC, Manassas, VA, USA). OATP1A2/SLCO1A2 transfected HEK293 cells were purchased from Corning (New York, NY, USA). The Caco-2 cells were cultured in high glucose added DMEM with 10% FBS, 1% NEAA, 10-mM HEPES, 4-mM glutamine, 100 U/mL of penicillin and 100 μg/mL of streptomycin, and maintained in humidified 5% CO2 at 37 ◦C. The medium of the Caco-2 cells was replaced 2–3 times per week.

The transfected HEK293 cells were cultured in high glucose added DMEM with 10% FBS and 1% NEAA, and maintained in 8% CO2 with low humidity at 37 ◦C for 4 h. After incubation for 4 h, the medium of the transfected HEK293 cells was replaced with high glucose added DMEM with 10% FBS, 1% NEAA and 2-mM sodium butyrate, and incubated for 24 h.
