Calcitriol decreases live Porphyromonas gingivalis internalized into epithelial cells and monocytes by promoting autophagy

Background The present study aimed to explore the effects of the active form of vitamin D (calcitriol, 1 alpha,25-dihydroxyvitamin D-3, 1 alpha,25 (OH)(2)D-3, 1,25D) on live Porphyromonas gingivalis internalized into KB cells and U937 cells. Methods Quantitative real-time polymerase chain reaction method was used to evaluate the number of surviving P. gingivalis internalized into KB cells and U937 cells. Transmission electron microscopy was used to detect P. gingivalis in cells. A western blot analysis was performed to observe LC3 expressions. Results 1) Treatment with 1,25D decreased the number of live P. gingivalis in KB cells and U937 cells in a dose-dependent manner. 2) Dividing P. gingivalis were found only in KB cells but not in U937 cells. The cell walls of most P. gingivalis in KB cells were intact, while those in U937 cells were disrupted. Treatment with 1,25D promoted the encapsulation of P. gingivalis in autophagosomes in both KB and U937 cells. 3) Both 1,25D treatment and P. gingivalis infection increased the LC3 II/I ratio. Furthermore, 1,25D treatment increased the P. gingivalis-upregulated LC3 II/I ratio. 4) Treatment with 3-methyladenine (3-MA) decreased the number of P. gingivalis by 11.41% in KB cells, while increased that by 121.51% in U937 cells. Under 1,25D treatment conditions, 3-MA treatment increased the number of P. gingivalis by 88.71% in KB cells and by 284.70% in U937 cells. Conclusions Autophagy may facilitate P. gingivalis survival in KB cells and eliminate P. gingivalis in U937 cells. Treatment with 1,25D may help decrease the number of live P. gingivalis in KB cells and U937 cells by promoting functional autophagy.