Cell culture

Hela cells stably transfected with human PepT1 plasmid (hPepT1-Hela) and vector (mock-Hela) cells were kindly provided by Professor Kexin Liu (Dalian Medical University, Dalian, China). The cells were maintained in high-glucose DMEM supplemented with 10% FBS, 100 U/mL penicillin, and 100 μg/mL streptomycin (Guo et al., 2012, 2014). Porcine ileum Caco-2 cells were obtained from American Type Culture Collection (Rockvile, MD) and cultured in Modified Eagle’s medium (MEM; Invitrogen, Carlsbad, CA) containing 10% FBS, 1 mM sodium pyruvate, 1% non-essential amino acids, 1% L-glutamine, 100 U/mL penicillin, and 100 μg/mL streptomycin. All the cells were grown at 37˚C with an atmosphere of 5% CO₂ and 95% relative humidity.