The Effects of Ginkgo biloba Extract on Autophagy in Human Macrophages Stimulated by Cigarette Smoke Extract

Abstract

Objective: To investigate the effects of Ginkgo biloba extract (GBE) on autophagy in human macrophages stimulated by cigarette smoke extract (CSE). Methods: The human monocyte cell line U937 was cultured in vitro, and phorbol ester (PMA) was added to the cell culture medium to induce differentiation into human macrophages. CSE was prepared by traditional methods for experiments. The cells were divided into four groups: the blank group, the CSE model group, the GBE + CSE group, and the rapamycin + CSE group. Immunofluorescence was used to identify human macrophages, transmission electron microscopy was used to observe the ultrastructure of human macrophages in each group, ELISA was used to measure the amount of IL-6 and IL-10 in the supernatant from each group of cells, the mRNA levels of p62, ATG5, ATG7, and Rab7 were measured by real-time qPCR, and the protein expression levels of p62, ATG5, ATG7, and Rab7 were measured by Western blotting. Results: U937 cells were successfully differentiated into human macrophages after induction with PMA. The CSE model group had many more autophagosomes than the blank group. Compared with the CSE model group, the GBE + CSE group and the rapamycin + CSE group had significantly more autophagolysosomal. Compared with the other groups, the CSE model group had a higher level of IL-6 but a lower level of IL-10 in the supernatant (p < 0.05). Compared with the blank group, the mRNA and protein expression levels of p62 in the CSE model group were significantly decreased, while the mRNA and protein expression levels of ATG5 and ATG7 were significantly increased in the CSE model group (p < 0.05). No difference was found in the mRNA and protein expression levels of Rab7 between the blank group and the CSE model group. Compared with the CSE model group, the IL-6 level in the GBE + CSE group and the rapamycin + CSE group cell culture supernatant decreased significantly, p62 mRNA and protein expression significantly decreased, while ATG5, ATG7, and Rab7 mRNA and protein expression levels were significantly increased (p < 0.05). Moreover, increased LC3-II/LC3-I ratio were also found in the GBE + CSE group and the rapamycin + CSE group compared with the CSE model group. Conclusions: GBE could promote the fusion of autophagosomes and lysosomes in human macrophages, enhance the autophagy function of human macrophages, and reduce the damaging effect of CSE on the autophagy function of macrophages.