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Objective:To explore the relationship and underlying mechanism between exosomes derived from doxorubicin-resistant osteosarcoma cells and MDR1 and miRNAs. Methods:MG63 and U2OS cell lines were selected to construct doxorubicin-resistant strains, and the 50% inhibitory concentration (half maximal inhibitory concentration, IC 50) of drug-resistant and sensitive strains was detected by MTT, and fluorescence staining was performed at intervals of 15 min between 15 and 120 min to detect the change of fluorescence intensity. RT-PCR and Western Blot were used to detect the expression levels of MDR1 P-gp to verify the drug resistance of osteosarcoma cells. Exosomes were identified by particle size analysis and Western Bolt detection. The endocytosis of PKH26-labeled exosomes from doxorubicin-resistant cells was observed, and the proliferation level and migration of exosomes from doxorubicin-resistant cells co-cultured with osteosarcoma cells were detected by MTT assay and cell scratch assay. The differential expression levels of miRNAs in osteosarcoma-sensitive and drug-resistant cells were verified by sequencing and bioinformatics analysis and RT-PCR assay. Tumor growth, serum exosome identification and mRNA expression level of miR-21-5p in tumor-bearing nude mice between normal osteosarcoma cell group and drug-resistant group, drug-resistant+normal exosome group, drug-resistant+drug-resistant+drug-resistant exosome group were observed. MDR1 expression level in tumor tissue was detected by RT-PCR, Western Blot and immunohistochemistry. Results:The IC 50 of two adriamycin resistant strains were 2.21 vs. 11.81 μg/ml and 0.93 vs. 11.81 μg/ml, respectively, and the fluorescence intensity decreased faster than that of normal strains. The relative mRNA expression levels of MDR1 in two cell lines were normal 1.12±0.16, 1.02±0.11 and drug-resistant 2.15±0.10, 2.127±0.12, respectively. The relative protein expression of P-gp was normal 0.92±0.11, 0.73±0.10 and drug-resistant 0.46±0.03, 0.30±0.04, the differences were statistically significant ( P<0.05). Drug-resistant exosomes can enter osteosarcoma cells through endocytosis and concentrate in the cytoplasm when co-cultured with normal strains. Osteosarcoma cells were co-cultured with drug-resistant exosomes at 2, 4, 6, and 8 μg/ml adriamycin, respectively. Compared with normal group, the proliferation level in drug-resistant group was significantly increased. Compared with the normal cell group 35.95±3.92, 6.72±3.55 and the normal exosome group 51.22±5.55, 19.31±1.93, the drug-resistant cell group 54.20±9.32, 19.24±2.88 and drug-resistant exosome group 76.40±5.41, 30.26±4.87, all had significantly higher cell mobility, the difference was statistically significant ( P<0.05). Exosome sequencing and biogenic analysis of 10 highly upregated miRNAs to validate mRNA expression differences between normal and drug-resistant strains by RT-PCR, showing a significant increase in miR-21-5p expression level of drug-resistant strains (5.89±0.26 vs. 0.99±0.06; 1.05±0.07 vs. 8.80±0.93, P<0.05), the difference was statistically significant ( P<0.05). In MG63 and U2OS, the normal cell group and drug-resistant cell group, and the normal exosome group and drug-resistant exosome group were compared, the tumor volume and the terminal tumor weight of nude mice were increased to varying degrees. MRNA relative expression levels of miR-21-5p in serum exosomes of nude mice after drug intervention were 0.86±0.07 and 0.86±0.05 in normal cell group, respectively. The values were 1.13±0.12, 1.14±0.12 in drug-resistant cell group, 0.71±0.05, 0.75±0.03 in normal exosome group, and 0.90±0.07, 0.93±0.04 in drug-resistant exosome group. Compared with normal and drug-resistant strains, the expression levels of normal and drug-resistant exosome groups were increased, with statistical significance ( P<0.05). Conclusion:The exosomes of drug-resistant cells in osteosarcoma could enhance the proliferation level and migration ability of cells through intercellular transfer of MDR1 and miRNAs. The expression of MDR1 and miR-21-5p in drug-resistant cells and tumor-forming nude mouse serum and tumor tissues were up-regulated which suggested that it might be involved in regulating the drug resistance process of osteosarcoma.
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Objective To determine the radiation dose of sensitive organs under different protective methods in lung CT scanning environment, and to explore the best protective scheme of corresponding organs. Methods Annealed thermoluminescence dose elements were placed in the stomach, liver, colon, and thyroid gland of a simulated human body model. The dose effect experiment of protective methods included non-protective group, half lead apron group, and full lead apron group. The dose effect experiment of protective thickness included 0.50 mmpb full lead apron group and 0.35 mmpb full lead apron group. The same exposure conditions of lung CT scan were used in the above experiments. Results Compared with the non-protective group, the exposure dose of the stomach, liver, colon, and thyroid gland increased significantly in the half lead apron group (P < 0.05), and the exposure dose of the thyroid gland and colon decreased significantly in the full lead apron group (P < 0.05). There were no significant differences in the exposure dose of the liver, stomach, and colon in the simulated human body model between the 0.35 mmpb full lead apron group and the 0.50 mmpb full lead apron group. Conclusion For lung CT scan, the protective measure of lead apron may not reduce the exposure dose of subjects. The protective thickness of lead apron does not necessarily have a substantial influence on the exposure dose of human body.