OBJECTIVETo investigate the effects of hydroquinone (HQ) on expression of topoisomerase IIα (TOPOIIα) in human bone marrow mononuclear cells, and to explore the role and possible regulatory mechanism of TOPOIIα involved in toxicity of HQ to hematopoietic cells.

METHODSAfter human bone marrow mononuclear cells were exposed to 50 µmol/L HQ (used the cells which were exposed to sterile distilled water as control); the activity of TOPOII was measured by TOPOII assay kit; the expression levels of TOPOIIα mRNA and protein were detected by RT-PCR technique and Western blotting method respectively; the chromatin immunoprecipitation (ChIP) assay was carried out to study the possible mechanism of TOPOIIα expression changes.

RESULTS(1) The activity of TOPOII was inhibited obviously; the protein and mRNA expression of TOPOIIα were 0.017 ± 0.029 and 0.610 ± 0.128, significantly lower than that in the control with the significant difference (P < 0.01) after treated with HQ for 10 h; (2) The decreased content of TOPOIIα was associated with descended level of histone H4 acetylation than in the control, from 1.198 ± 0.056 to 0.324 ± 0.229, with the significant difference (P < 0.01), without accompanied descended level of histone H3 acetylation, from 1.253 ± 0.045 to 1.177 ± 0.025 (P > 0.05); (3) TOPOIIα mRNA expression decreased gradually after HQ processing, and the chemical modification (histone H4 acetylation) of TOPOIIα promoter happened prior to the mRNA expression.

CONCLUSIONHQ could repress the expression of TOPOIIα in human bone marrow mononuclear cells; the change of histone chemical modification plays an important role in the benzene's hematopoietic toxicity.

Acetylation ; Adult ; Antigens, Neoplasm ; metabolism ; Bone Marrow Cells ; drug effects ; metabolism ; Cells, Cultured ; DNA Topoisomerases, Type II ; metabolism ; DNA-Binding Proteins ; metabolism ; Female ; Histones ; metabolism ; Humans ; Hydroquinones ; toxicity ; Male ; Young Adult

OBJECTIVETo study the effect of hydroquinone on apoptosis of bone marrow mononuclear cells, and to evaluate the toxic effect of benzene on stem cells.

METHODSCell morphology was observed by HT fluorescent stain method, and DNA fragments were analyzed by agarose gel electrophoresis. Anti-Annexin V FITC plus PI staining for apoptotic and necrotic rate was examined by flow cytometer.

RESULTSAfter adding different concentrations of hydroquinone to the cells for 6 h culture, the fluorescent intensity of nucleus increased, the color of nucleus became deep and inhomogeneous, and the chromatin was condensed and distributed around the neucleus. DNA ladder was detected in all samples. Cell apoptotic rate in different concentration of hydroquinone groups was significantly higher than that in blank control group (P < 0.05). With the increase of the concentration of hydroquinone, the apoptotic and necrotic rate also increased. The optimal concentration of hydroquinone was 50 micro mol/L. When it was >or= 75 micro mol/L, the necrotic rate increased significantly. Hydroquinone-induced apoptosis was associated with culture time at the concentration of 50 micro mol/L, and the peak apoptotic time was 10 h, then the apoptotic rate decreased and necrotic rate increased.

CONCLUSIONHydroquinone can induce apoptosis of bone marrow mononuclear cells in vitro with dose-effect and time-effect relationship.

Apoptosis ; drug effects ; Bone Marrow Cells ; cytology ; Cells, Cultured ; Dose-Response Relationship, Drug ; Humans ; Hydroquinones ; pharmacology ; Leukocytes, Mononuclear ; cytology ; drug effects ; Mutagens ; pharmacology

OBJECTIVETo study the influence of hand-mixed methods on the compressive strength of the zinc phosphate dental cement.

METHODSThree skilled nurses used three kinds of common clinical hand-mixed methods (included the unidirectional rotation method, the alternate pro and con bidirectional rotation method and the pulling and pushing with folding method) to mix the zinc phosphate dental cement on the same condition (i.e. same indoor temperature and humidity, the same mixing ratio, mixing time, mixing frequency and the same mixing instruments and so on). The mixed zinc phosphate cement was packed into the plastic cylinders with 10 mm-high and 5 mm-bore. After the mixed zinc phosphate cement coagulated, compressive strength was tested separately.

RESULTSThe compressive strength of the zinc phosphate dental cement mixed with the alternate pro and con bidirectional rotation method was the best, and the value was (106.11+/- 4.82) MPa. The compressive strength of the zinc phosphate dental cement mixed with the pulling and pushing with folding method was lower, and the value was (77.57 +/- 6.26) MPa. The compressive strength of the zinc phosphate dental cement mixed with the unidirectional rotation method was the lowest, and the value was (54.41 +/- 5.08) MPa. The compressive strength of the zinc phosphate dental cement mixed with the unidirectional rotation method and the pulling and pushing with folding method could not achieve the clinical required compressive strength (about 100 MPa), while the compressive strength mixed with the alternate pro and con bidirectional rotation method was above 100 MPa.

CONCLUSIONThe alternate pro and con bidirectional rotation method to mix the zinc phosphate dental cement is recommended in clinic.

Compressive Strength ; Phosphates ; Zinc Compounds ; Zinc Phosphate Cement