Influence of puerarin, paeoniflorin, and menthol on structure and barrier function of tight junctions in MDCK and MDCK-MDR1 Cells

ObjectiveIn this study, the influence of puerarin, paeoniflorin, and menthol on the structure and barrier function of tight junctions (TJs) in Madin–Darby canine kidney epithelial (MDCK) and MDCK-multi-drug resistance 1 (MDR1) cells was evaluated to determine the mechanisms by which the drugs cross the blood–brain barrier (BBB).MethodCells were treated with puerarin, paeoniflorin, and menthol followed by immunohistochemical staining with occludin, claudin-1, and F-actin. The cells were then observed using laser-scanning confocal microscopy. Average optical density (AOD) of the immunofluorescence images of the proteins were analyzed using ImageJ software while Transepithelial electrical resistance (TEER) was measured using an epithelial voltohmmeter.ResultsConfocal microscopy revealed that puerarin- and paeoniflorin-treated tight junction proteins were conspicuous while menthol suppressed their expression. Correspondingly, AOD values of cells treated with puerarin or paeoniflorin, or both showed no difference compared to the control group (P > .05) while the menthol group value was downregulated. In 3 h, TEER of cells not treated with menthol were similar to the control group, while treatment with menthol significantly decreased TEER value (P < .05). In addition, application of menthol decreased TEER in MDCK cells earlier than in MDCK-MDR1 cells.ConclusionMenthol but not puerarin and paeoniflorin may enhance paracellular transport and improve drug penetration of the BBB by disrupting the structure and, thereby, weakening the barrier function of TJs.