ABSTRACT
Objective To investigate the mitochondrial energy metabolism in D-galactoseinduced cell ageing model.Methods MRC-5 cells were cultivated for 72 hours in a medium containing 55 mmol/L D-galactose.The analysis of cell proliferation capacity by CCK8 method,β-galactosidase staining and detection of p21 protein expression level were performed for identifying cell senescence.The cell oxidation-reduction state was evaluated by an analysis of cellular ROS levels,SOD activity,MDA content and oxidative damage level of mitochondrial DNA(mtDNA).For purpose of detecting mitochondrial function and its impairment,mitochondrial morphology was observed by electron microscope,mitochondrial quantity was analyzed by flow cytometry,mitochondrial membrane potential(△Ψm) was measured by JC-1 staining,and ATP content was analyzed by HPLC,and mitochondrial oxygen consumption rate was detected by Seahorse cell energy metabolism detection system.Results The decreased MRC-5 cell proliferation,up-expression of p21 protein,increased β-galactosidase activity were observed in D-Gal-treated cells,which indicated the cell premature senescence.When treated with D-Gal,the significantly increased ROS and MDA level,decreased SOD activity and increased oxidized mtDNA proved that the cells kept higher oxidative stress.D-Gal induced-mitochondrial impairment was evidenced by the dimming of mitochondrial cristae and double membrane structure,decrease of transmembrane potential and ATP synthesis,and decrease of its oxygen consumption rate(OCR).Conclusions The 55 mmol/L D-Gal causes an impairment of mitochondrial structure and a decrease of function of energy metabolism,which is associated with cellular senescence induced by D-Gal.
ABSTRACT
Objective To investigate the mechanisms of tigecycline nonsusceptibility in carbapen-ems-resistant Acinetobacter baumannii ( CRAB) strains in order to provide a theoretical basis for a reasonable use of antibiotics and the control of nosocomial infection .Methods Susceptibility testing of 120 non-dupli-cate CRAB strains to tigecycline was performed by using the broth microdilution method .Minimal inhibitory concentrations ( MIC) of tigecycline against the A.baumannii strains were determined by using the broth mi-crodilution method before and after exposing the strains to Carbonylcyanide-m-chlorophenylhydrazone (CCCP), which was the efflux pump inhibitor .Polymerase chain reaction (PCR) was used to amply the ef-flux pumps genes including adeB, adeJ, adeG, abeM, adeE, adeRS, tetX and tetX1.The real-time PCR was performed to measure the expression of efflux pumps genes including adeB, adeJ, adeG, abeM and adeE.Results A total of 120 CRAB strains were collected including 13 (10.8%) tigecycline non-suscep-tible A.baumannii (TNAB) strains and 107 (89.2%) tigecycline susceptible A.baumannii (TSAB) strains.The MIC values of tigecline to the 120 CRAB strains were in a range of 0.25 μg/ml to 8 μg/ml. The adeR and adeJ genes were detected in 90.0%and 92.5%of the 120 CRAB strains, respectively.The positive rates of adeB, adeS, adeG and abeM genes among the 120 CRAB strains were all 94.2%.None of the three genes including adeE, tetX and tetX1 were detected .The mean expression levels of adeB and adeJ in TNAB strains were respectively increased by 18.69 folds and 5.46 folds as compared with those in sensi-tive strains.No significant increase in the expression of adeG and abeM genes was observed in TNAB strains . A 4-fold decrease in the MIC was observed in 8 out of 13 TNAB isolates treated with 10 μg/ml of CCCP .The CCCP could partially reverse the resistance pattern of tigecycline .Conclusion The efflux pump sys-tems of adeABC and adeIJK rather than the abeFGH and abeM systems might play an important role in reduc-ing the tigecycline susceptibility in carbapenems-resistant A.baumannii strains.