Abstract:

Objective To discuss the enhancing effect of cordycepin on ferroptosis inducer RSL3-induced ferroptosis in the hepatocellular carcinoma HepG2 cells， and to clarify its potential mechanism. Methods The HepG2 cells were divided into control group， RSL3 group， low， medium and high doses of cordycepin groups， RSL3+low， medium and high doses of cordycepin groups， RSL3+medium-dose cordycepin+ferroptosis inhibitor Ferrostatin-1 （Fer-1） group， and RSL3+medium-dose cordycepin+ferroptosis inhibitor Liproxstatin-1 （Lip-1） group. The HepG2， Huh-7 and HCCLM3 cells were treated with 0， 1， 5， 10， 15 and 20 μmol·L^-1 RSL3 for 24， 48 and 72 h， respectively. Cell counting kit-8（CCK-8） method was used to detect cell viability and determine the optimal concentration and treatment time of RSL3. The HepG2 cells were treated with 0， 50， 100， 200， 400， 600， 800， 1 000， and 1 200 μmol·L^-1 cordycepin for 24， 48 and 72 h， respectively. CCK-8 method was used to detect the survival rate of the cells and the half maximal inhibitory concentration （IC₅₀） was calculated to determine the optimal concentration and treatment time of cordycepin； the apoptosis inhibitor Z-VAD-FMK， autophagy inhibitor Chloroquine （CQ）， necroptosis inhibitor Necrostatin-1 （Nec-1）， Fer-1， Lip-1， Deferasirox and 2，2，6，6-tetramethylpiper idinoxy（TEMPO） were used to treat HepG2 cells， and the survival rate of the cells was calculated； 2'，7'-Dichlorodihydrofluorescein diacetate （DCFH-DA） fluorescence probe was used to detect reactive oxygen species （ROS） levels in the HepG2 cells in various groups； C11 BODIPY 581/591 fluorescence probe was used to detect lipid peroxidation （LPO） levels in the HepG2 cells in various groups； FeRhoNox-1 fluorescent probe was used to detect ferrous ion （Fe²⁺） levels in the HepG2 cells in various groups； kits were used to detect glutathione （GSH） and malondialdehyde （MDA） levels in the HepG2 cells； Western blotting method was used to detect the expression levels of ferroptosis-related proteins， nuclear factor erythroid 2-related factor 2 （Nrf2） and heme oxygenase-1 （HO-1） proteins in the hepG2 cells in various groups； transmission electron microscope was used to observe the ultrastructural morphology of the HepG2 cells in various groups. Results The CCK-8 results showed that when the cells were treated with 0.56 μmol·L?1 RSL3， the viabilities of the three cell types differed significantly. Compared with 0 μmol·L?1 RSL3 group， the survival rates of the cells in 6.4 and 12.8 μmol·L^-1 RSL3 groups were significantly decreased （P<0.05）. The HepG2 cells had the highest IC₅₀ value and were selected for subsequent experiments. Compared with 0 μmol·L^-1 cordycepin group， the survival rates of the HepG2 cells in 200， 400， 600， 800， 1 000， and 2 000 μmol·L^-1 cordycepin groups were significantly decreased （P<0.05 or P<0.01）. 0.5×IC₅₀ （267.9 μmol·L^-1）， 1×IC₅₀ （535.8 μmol·L^-1） and 1.5×IC₅₀ （803.7 μmol·L^-1） were selected as low， medium and high doses of cordycepin groups， respectively， with an intervention time of 24 h. Compared with control group， the survival rates of the HepG2 cells in low， medium， and high doses of cordycepin groups were significantly decreased （P<0.05）. Compared with low， medium， and high doses of cordycepin groups， the survival rates of the HepG2 cells in Z-VAD-FMK+low， medium， and high doses of cordycepin groups were significantly increased （P<0.01）， and those in Fer-1+medium and high doses of cordycepin groups and Lip-1+low， medium， and high doses of cordycepin groups were significantly increased （P<0.05）. Compared with control group， the survival rates of the HepG2 cells in RSL3 group， RSL3+low， medium， and high doses of cordycepin groups， RSL3+cordycepin+Fer-1 group and RSL3+cordycepin+Lip-1 group were significantly decreased （P<0.05 or P<0.01）. Compared with RSL3 group， the survival rates of the HepG2 cells in RSL3+low， medium， and high doses of cordycepin groups were significantly decreased （P<0.05）. The DCFH-DA results showed that compared with control group， the ROS levels in the cells in medium and high doses of cordycepin groups， RSL3 group and RSL3+low， medium， and high doses of cordycepin groups were significantly increased （P<0.05 or P<0.01）. The C11 BODIPY 581/591 results showed that compared with control group， the LPO levels in the HepG2 cells in medium and high doses of cordycepin groups， RSL3 group and RSL3+low， medium and high doses of cordycepin groups were significantly increased （P<0.05 or P<0.01）. Compared with RSL3 group， the LPO levels in the HepG2 cells in RSL3+low， medium， and high doses of cordycepin groups were significantly increased （P<0.05 or P<0.01）. The FeRhoNox-1 results showed that compared with control group， the Fe²⁺ levels in the HepG2 cells in medium and high doses of cordycepin groups， RSL3 group and RSL3+low， medium， and high doses of cordycepin groups were significantly increased （P<0.05 or P<0.01）. Compared with RSL3 group， the Fe²⁺ levels in the HepG2 cells in RSL3+low， medium， and high doses of cordycepin groups were significantly increased （P<0.05 or P<0.01）. Compared with control group， the MDA levels in the HepG2 cells in high doses of cordycepin group， RSL3 group and RSL3+low， medium， and high doses of cordycepin groups were significantly increased （P<0.05 or P<0.01）. Compared with RSL3 group， the MDA levels in the HepG2 cells in RSL3+low， medium， and high doses of cordycepin groups were significantly increased （P<0.05 or P<0.01）. Compared with control group， the GSH levels in the HepG2 cells in medium and high doses of cordycepin groups， RSL3 group and RSL3+low， medium， and high doses of cordycepin groups were significantly decreased （P<0.05 or P<0.01）. Compared with RSL3 group， the GSH levels in the HepG2 cells in RSL3+low， medium， and high doses cordycepin groups were significantly decreased （P<0.05 or P<0.01）. Compared with control group， the ultrastructure of the HepG2 cells in low and medium doses of cordycepin groups showed no significant changes， while the cells in high dose of cordycepin group exhibited reduced mitochondrial cristae， mild swelling and increased membrane density， with slightly distorted inner membrane structure. The cells in RSL3 group and RSL3+low， medium， and high doses of cordycepin groups all showed ultrastructural changes characteristic of ferroptosis. Compared with RSL3 group， the cells in RSL3+low， medium， and high doses of cordycepin groups exhibited ruptured mitochondrial membranes with increased membrane density， abnormally twisted or expanded inner membrane structures， and reduced or even disappeared mitochondrial cristae. The Western blotting results showed that compared with control group， the expression levels of FTH1 and GPX4 proteins in the HepG2 cells in medium and high doses of cordycepin groups were significantly decreased （P<0.05 or P<0.01）， while the expression levels of Nrf2 and HO-1 proteins were significantly decreased （P<0.05 or P<0.01）. Compared with control group， the expression levels of GPX4 protein in the HepG2 cells in low， medium and high doses of cordycepin groups， RSL3 group， and RSL3+cordycepin+Fer-1 group were significantly decreased （P<0.05）. Compared with RSL3 group， the expression levels of GPX4 protein in the HepG2 cells in RSL3+low， medium， and high doses of cordycepin groups were significantly decreased （P<0.05）. Conclusion Cordycepin can significantly enhance RSL3-induced ferroptosis in the hepatocellular carcinoma HepG2 cells and down-regulate the expression of Nrf2 and HO-1 proteins in the HepG2 cells.

Key words: Hepatocellular carcinoma, Cordycepin, Ferroptosis, RSL3, Nuclear factor erythroid 2-related factor 2/heme oxygenase-1 signaling pathway