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Wei Zhao

Publications and source records attributed to Wei Zhao.

At least 127 records · Page 7Linked to original sources
PubMed2005

The essential role of histone H3 Lys9 di-methylation and MeCP2 binding in MGMT silencing with poor DNA methylation of the promoter CpG island.

Silencing of the O (6)-methylguanine-DNA methyltransferase (MGMT) gene, a key to DNA repair, is involved in carcinogenesis. Recent studies have focused on DNA hypermethylation of the promoter CpG island. However, cases showing silencing with DNA hypomethylation certainly exist, and the mechanism involved is not elucidated. To clarify this mechanism, we examined the dynamics of DNA methylation, histone acetylation, histone methylation, and binding of methyl-CpG binding proteins at the MGMT promoter region using four MGMT negative cell lines with various extents of DNA methylation. Histone H3K9 di-methylation (H3me2K9), not tri-methylation, and MeCP2 binding were commonly seen in all MGMT negative cell lines regardless of DNA methylation status. 5Aza-dC, but not TSA, restored gene expression, accompanied by a decrease in H3me2K9 and MeCP2 binding. In SaOS2 cells with the most hypomethylated CpG island, 5Aza-dC decreased H3me2K9 and MeCP2 binding with no effect on DNA methylation or histone acetylation. H3me2K9 and DNA methylation were restricted to in and around the island, indicating that epigenetic modification at the promoter CpG island is critical. We conclude that H3me2K9 and MeCP2 binding are common and more essential for MGMT silencing than DNA hypermethylation or histone deacetylation. The epigenetic mechanism leading to silent heterochromatin at the promoter CpG island may be the same in different types of cancer irrespective of the extent of DNA methylation.

Azacitidine↗
PubMed2005

Temporal performance of amorphous selenium mammography detectors.

We investigated temporal performance of amorphous selenium (a-Se) detectors specifically designed for mammographic imaging. Our goal is to quantify the inherent lag and ghosting of a-Se photoconductor as a function of imaging conditions. Two small area electroded a-Se samples, one positively and the other negatively biased on the entrance side of x rays, were used in the experiments. The study of lag and ghosting was performed by delivering a number of raw exposures as experienced in screening mammography to the samples at different electric field strength E(Se) while measuring the current through the a-Se sample. Ghosting at different operational conditions was quantified as the percentage x-ray sensitivity (x-ray generated photocurrent measured from the sample) reduction compared to before irradiation. Lag was determined by measuring the residual current of a-Se at a given time after the end of each x-ray exposure. Both lag and ghosting were measured as a function of E(Se) and cumulative exposure. The values of E(Se) used in our experiments ranged from 1 to 20 V/microm. It was found that ghosting increases with exposure and decreases with E(Se) for both samples because of the dominant effect of recombination between trapped electrons and x-ray generated holes. Lag on the other hand has different dependence on E(Se) and cumulative exposure. At E(Se) < or = 10 V/microm, the first frame lag for both samples changed slowly with cumulative exposure, with a range of 0.2%-1.7% for the positively biased sample and 0.5%-8% for the negatively biased sample. Overall the positively biased sample has better temporal performance than the negatively biased sample due to the lower density of trapped electrons. The impact of time interval between exposures on the temporal performance was also investigated. Recovery of ghosting with longer time interval was observed, which was attributed to the neutralization of trapped electrons by injected holes through dark current.

Electrodes↗
PubMed2005

Ghosting caused by bulk charge trapping in direct conversion flat-panel detectors using amorphous selenium.

Direct flat-panel detectors using amorphous selenium (a-Se) x-ray photoconductors are gaining wide-spread clinical use. The goal of our investigation is to understand the physical mechanisms responsible for ghosting, i.e., x-ray induced change in sensitivity that results in image persistence, so that the knowledge can be used to consistently minimize ghosting artifacts in a-Se flat-panel detectors. In this paper we will discuss the effect on x-ray sensitivity of charge trapping in a-Se, which is the dominant source for ghosting in a-Se flat-panel detectors. Our approach is to correlate ghosting in electroded a-Se detectors with the trapped charge concentration measured by the "time-of-flight" (TOF) method. All measurements were performed as a function of radiation exposure X of up to approximately 20 R at electric field strength's of E(Se)=5 and 10 V/microm. The results showed that the x-ray sensitivity decreased as a function of X and the amount of ghosting decreased with increasing E(Se). The shape of the TOF curves changed as a result of irradiation in a manner indicating trapped electrons in the bulk of a-Se. The density of trapped electrons n(t) increases as a function of X. A method was developed to determine the values of n(t) in the bulk of a-Se from the TOF measurements, and to predict the corresponding change in x-ray sensitivity. Our results showed that a recombination coefficient consistent with that predicted by Langevin produced good agreement between calculated and measured x-ray sensitivity changes. Thus it can be concluded that the trapping of electrons in the bulk of a-Se and their subsequent recombination with x-ray generated free holes is the dominant mechanism for ghosting in a-Se.

Artifacts↗
PubMed2005

Indirect flat-panel detector with avalanche gain: fundamental feasibility investigation for SHARP-AMFPI (scintillator HARP active matrix flat panel imager).

An indirect flat-panel imager (FPI) with avalanche gain is being investigated for low-dose x-ray imaging. It is made by optically coupling a structured x-ray scintillator CsI(Tl) to an amorphous selenium (a-Se) avalanche photoconductor called HARP (high-gain avalanche rushing photoconductor). The final electronic image is read out using an active matrix array of thin film transistors (TFT). We call the proposed detector SHARP-AMFPI (scintillator HARP active matrix flat panel imager). The advantage of the SHARP-AMFPI is its programmable gain, which can be turned on during low dose fluoroscopy to overcome electronic noise, and turned off during high dose radiography to avoid pixel saturation. The purpose of this paper is to investigate the important design considerations for SHARP-AMFPI such as avalanche gain, which depends on both the thickness d(Se) and the applied electric field E(Se) of the HARP layer. To determine the optimal design parameter and operational conditions for HARP, we measured the E(Se) dependence of both avalanche gain and optical quantum efficiency of an 8 microm HARP layer. The results were used in a physical model of HARP as well as a linear cascaded model of the FPI to determine the following x-ray imaging properties in both the avalanche and nonavalanche modes as a function of E(Se): (1) total gain (which is the product of avalanche gain and optical quantum efficiency); (2) linearity; (3) dynamic range; (4) gain nonuniformity resulting from thickness nonuniformity; and (5) effects of direct x-ray interaction in HARP. Our results showed that a HARP layer thickness of 8 microm can provide adequate avalanche gain and sufficient dynamic range for x-ray imaging applications to permit quantum limited operation over the range of exposures needed for radiography and fluoroscopy.

Cesium↗
PubMed2005

A fungus-specific ras homolog contributes to the hyphal growth and virulence of Aspergillus fumigatus.

The Ras family of GTPase proteins has been shown to control morphogenesis in many organisms, including several species of pathogenic fungi. In a previous study, we identified a gene encoding a fungus-specific Ras subfamily homolog, rasB, in Aspergillus fumigatus. Here we report that deletion of A. fumigatus rasB caused decreased germination and growth rates on solid media but had no effect on total biomass accumulation after 24 h of growth in liquid culture. The DeltarasB mutant had an irregular hyphal morphology characterized by increased branching. Expression of rasBDelta113-135, a mutant transgene lacking the conserved rasB internal amino acid insertion, did not complement the deletion phenotype of delayed growth and germination rates and abnormal hyphal morphology. Virulence of the rasB deletion strain was diminished; mice infected with this strain exhibited approximately 65% survival compared to approximately 10% with wild-type and reconstituted strains. These data support the hypothesis that rasB homologs, which are highly conserved among fungi that undergo hyphal growth, control signaling modules important to the directional growth of fungal hyphae.

Alleles↗
PubMed2005

Epigenetic silencing of the MGMT gene in cancer.

Silencing of the O6-methylguanine-DNA methyltransferase (MGMT) gene, a key to DNA repair, plays a critical role in the development of cancer. The gene product, functioning normally, removes a methyl group from mutagenic O6-methylguanine, which is produced by alkylating agents and can make a mismatched pair with thymine, leading to transition mutation through DNA replication. MGMT is epigenetically silenced in various human tumors. It is well known that DNA hypermethylation at the promoter CpG island plays a pivotal role in the epigenetic silencing of tumor suppressor genes. MGMT silencing, however, occurs without DNA hypermethylation in some cancer cells. Dimethylation of histone H3 lysine 9 and binding of methyl-CpG binding proteins are common and essential in MGMT-silenced cells. Silencing of MGMT has been shown to be a poor prognostic factor but a good predictive marker for chemotherapy when alkylating agents are used. In this review, we describe recent advances in understanding the silencing of MGMT and its role in carcinogenesis; epigenetic mechanisms; and clinical implications.

CpG Islands↗
PubMed2005

Optical pH response of DNA wrapped HiPco carbon nanotubes.

Solubilization of single-walled carbon nanotubes in aqueous solution by surface functionalization is of great interest for biosensor applications and separation of individual nanotubes. Here we have observed that HiPco nanotubes can be stably dispersed into double-stranded DNA aqueous solutions. Interestingly, the first optical interband transitions of the DNA wrapped semiconducting HiPco nanotubes possess a unique pH dependence, a phenomenon observed in SDS-encased and carboxylic group functionalized single-walled carbon nanotubes. The unique optical pH dependence of surface modified semiconducting nanotubes may have promising applications in optical biosensors.

Animals↗
PubMed2005

Synthesis of nanosize mesoporous MCM-48 material.

Nanosize mesoporous material MCM-48 was synthesized under the hydro-thermal system. The results of TEM and SEM show that the obtained MCM-48 is well organized on a 100 A length scale. Both the Nanosize and the superior organization provide this material with good thermal stability.

Crystallization↗
PubMed2005

[Photomacrography of brain surface for evaluating blood-brain barrier disruption within 24 h after focal cerebral ischemia in mice].

OBJECTIVE: To establish a new photomacrographic analysis of morphological changes on brain surface to evaluate blood-brain barrier (BBB) disruption. METHODS: Permanent focal cerebral ischemia was induced by middle cerebral artery occlusion (MCAO) in mice. Brains were removed 10 min, 0.5, 1, 3, 6, 12 and 24 h after MCAO. The whole brains and brain slices were photographed by a digital camera. BBB disruption was evaluated by hemorrhage and traced Evans blue (EB) on the brain surface. Fluoremetric quantitation of EB and water content in the brains were also performed at various time points. RESULT: Photomacrographic morphological analysis showed that hemorrhage and traced EB on the surface of the brains significantly increased from 3 h after focal cerebral ischemia,which were correlated to the results in the brain slices. EB content in the ischemic hemispheres was significantly increased from 0.5 h after MCAO, and water content was increased from 1 h after MCAO. CONCLUSION: Photomacrographic measurement is a simple and useful method for evaluating BBB disruption semi-quantitatively, and can detect BBB disruption earlier after focal cerebral ischemia in mice.

Animals↗
PubMed2005

[Progress in researches on the synthesis of poly (propylene fumarate) and its crosslinking characteristics].

Poly (propylene fumarate) is an unsaturated linear polyester, which degrades, in the presence of water, into propylene glycol and fumaric acid, and the degradation products can be cleared from the human body by normal metabolic processes. In this paper, different methods of the synthesis of PPF are listed, the crosslinking characteristics of polymerizing composite as well as the mechanical properties of cross-linked composite are discussed, and the potentialities of PPF composite used as particularly degradable polymeric cement for orthopedic application are reviewed.

Biocompatible Materials↗
PubMed2005

[The predictive value of the ambulatory blood pressure monitoring parameters on left ventricular hypertrophy and carotid artery intima-media thickness in hypertensives].

OBJECTIVE: To investigate the predictive value of the ambulatory blood pressure monitoring parameters on left ventricular hypertrophy (LVH) and carotid artery intima-media thickness (IMT) in the hypertensives. METHODS: We evaluated 147 hypertensive patients who were never treated regularly before. All patients underwent ultrasound examinations of the heart and the IMT of carotid arteries. We classified them as LVH group (n = 45) or no LVH group (n = 102), and as IMT increased group (n = 52) or no IMT increased group (n = 95). The record of medical history, physical examination and 24 h ambulatory blood pressure monitoring (ABPM) were performed in all the patients. The biochemical parameters such as blood lipids, glucose and so on were tested. Then the data comparison was made. RESULTS: (1) There were no significant differences in clinical manifestations and biochemical parameters between the LVH and no LVH groups (P > 0.05). Age (68.3 +/- 6.2) year vs (65.6 +/- 5.8) year, male 75.6% vs 66.7%, body mass index (24.1 +/- 4.1) vs (23.8 +/- 4.7) (kg/m(2)), diabetes mellitus and(or) impaired glucose tolerance 40.0% vs 38.2%, angina pectoris 42.3% vs 38.9%, cerebral vascular diseases 19.2% vs 15.7%, total cholesterol (5.40 +/- 1.42) vs (5.28 +/- 1.46) mmol/L, triglycerides (1.80 +/- 1.02) vs (1.74 +/- 1.08) mmol/L, low-density lipoprotein cholesterol (4.03 +/- 1.43) vs (4.06 +/- 1.48) mmol/L, high-density lipoprotein cholesterol (1.00 +/- 0.30) vs (0.99 +/- 0.26) mmol/L. (2) The parameters of ABPM in LVH group were higher than those in no LVH group. There were significant differences (P < 0.05) in 24 h mean systolic blood pressure (140.7 +/- 14.1) vs (128.3 +/- 12.3) mm Hg, 24 h mean diastolic blood pressure (86.4 +/- 8.9) vs (81.6 +/- 9.3) mm Hg, daytime mean systolic blood pressure (142.8 +/- 13.9) vs (130.9 +/- 11.1) mm Hg, daytime mean diastolic blood pressure (86.9 +/- 8.8) vs (83.4 +/- 9.0) mm Hg, nighttime mean systolic blood pressure (129.0 +/- 13.2) vs (114.6 +/- 11.4) mm Hg, nighttime mean diastolic blood pressure (77.2 +/- 9.4) vs (67.5 +/- 8.1) mm Hg, 24 h pulse pressure (54.2 +/- 10.2) vs (46.9 +/- 9.6) mm Hg, daytime pulse pressure (55.9 +/- 10.5) vs (47.5 +/- 9.1) mm Hg, nighttime pulse pressure (51.8 +/- 10.7) vs (47.1 +/- 8.7) mm Hg, 24 h systolic blood pressure variance (8.4 +/- 2.0) vs (7.2 +/- 1.9), 24 h diastolic blood pressure variance (9.5 +/- 2.2) vs (8.0 +/- 2.1), the non-dipper rhythm of ambulatory blood pressure 55.6% vs 25.5%. (3) There were also no significant differences in clinical manifestations between the IMT increased and no IMT increased group (P > 0.05). While there were significant differences between the IMT increased and no IMT increased group in those parameters of ABPM (P < 0.05). CONCLUSION: There were more LVH or IMT increased persons in the hypertensives whose ABPM parameters were abnormal.

Aged↗
PubMed2005

[Effects of Icariin on ovariectomized osteoporotic rats].

OBJECTIVE: To observe the effects of Icariin on ovariectomized osteoporotic rats. METHODS: Female Wistar rats were ovariectomized and administered different dosage of Icariin and 17beta-estradiol for eight weeks. Bone mineral density (BMD), indexes of biomechanics and bone metabolism-associated biochemical markers were measured. RESULTS: Icariin increased the BMD, maximum load and flexural rigidity in the osteoporotic rats. The activities of serum tartrate-resistant acid phosphatase (TRACP) and bone alkaline phosphatase (BALP) were decreased in the Icraiin-fed ovariectomized rats. CONCLUSION: Icariin 225mg/kg per day could increase the BMD and improve indexes of bone biomechanics in ovariectomized osteoporotic rats. It was effective in preventing bone loss induced by ovariectomy.

Acid Phosphatase↗
PubMed2005

[Coreceptors CCR5 and CXCR4 expressions on peripheral blood T lymphocytes in HIV/AIDS patients].

OBJECTIVE: To investigate the coreceptors CCR5 and CXCR4 expressions on the peripheral blood T lymphocytes in HIV/AIDS patients, with an analysis of their clinical value. METHODS: Thirty HIV/AIDS patients and 16 normal controls were selected and flow-cytometry was used to detect the coreceptors CCR5 and CXCR4 expressions in whole blood samples taken from the patients and controls. An analysis was made of the correlation of the coreceptor expression with CD4 T cell counts and the activation of CD4+/ CD8+ T cells (HLA-DR+/CD38+). RESULTS: The CCR5 expression on CD8+ lymphocytes and the CXCR4 expression on the CD4+/ CD8+ T lymphocytes of the HIV/AIDS group were higher than those of the normal controls (P < 0.01). The CCR5 and CXCR4 expressions on the CD4+/CD8+ T lymphocytes of the HIV/AIDS patients was significantly correlated with the activation of CD4+/CD8+ T cells (HLA-DR+/CD38+) (P < 0.05). CONCLUSION: The expressions of CCR5 and CXCR4 are significantly correlated with the immune system reaction to HIV and the disease progression in HIV infected patients.

Acquired Immunodeficiency Syndrome↗
PubMed2005

Mechanistic mapping of ontogenetic growth based on biological principles.

Ontogenetic growth can be described by mathematical equations constructed on the goodness of fit. Recently, the biological mechanism underlying mathematical growth equations has been explored using basic cellular properties. Here, we derive a general statistical model for understanding the genetic regulation of ontogenetic growth by integrating those biologically-proven meaningful growth equations into a quantitative trait locus (QTL) mapping framework. We can characterize the dynamic patterns of effects of QTL governing growth curves and estimate the global effect of the underlying QTL throughout the entire course of growth. The model provides the basis for deciphering genetic relationships for growth rates and the timing of life history events for any kind of organisms.

Animals↗
PubMed2005

[Study on the effectiveness and cost-benefit of influenza vaccine on elderly population in Beijing city].

OBJECTIVE: To estimate the effectiveness of inactivated influenza vaccine in elderly population. METHODS: An quasi-experimental study was used. 590 elderly people who volunteered to receive the influenza vaccine were served as vaccine group, while 602 persons who did not want to receive the inoculation but could match the vaccine group were served as controls. One baseline and three follow-up surveys were carried out. RESULTS: The protective rates of influenza like ill (ILI) as 52.38%, 36.84% and 37.89% with the decreasing rates of visits to ILI clinic as 45.16%, 50.54% and 50.54% were found after 1 month, 3 month and 6 month of inoculation of influenza vaccine; The protective rates of common cold, other respiratory tract or chronic disease were 49.54%, 64.54%, and 38.82%, respectively. The benefit-cost ratio was 4.98:1 in elderly population. CONCLUSION: Influenza vaccination could decrease ILI incidence and recurrence rates of related chronic diseases on elderly population to provide better economic benefits for the elderly.

Aged↗
PubMed2005

RNA silencing of Waxy gene results in low levels of amylose in the seeds of transgenic wheat (Triticum aestivum L.).

In this study, the level of amylose was reduced in wheat seeds by RNAi strategy. Because the synthesis of amylose is catalyzed by the granule-bound starch synthase I (GBSSI or WAXY protein), the Waxy gene of wheat was isolated from wheat seeds by using RT-PCR. Southern analysis confirmed that there were three Waxy genes in wheat genome. Northern hybridization showed that Waxy mRNA accumulated in seeds following pollination. By RNAi strategy,the 683 bp sense and antisense fragments in reverse orientation separated by a 150 bp intron were cloned into pCAMBIA 3300 just downstream of the maize ub/1 promoter. By Agrobacteriurn-mediated wheat transformation method, four transgenic plants (Cultivar Yangmai 10) were identified by PCR, RT-PCR and leaf painting assay. The level of amylose in the endosperm were significantly reduced in transgenic seeds as checked by iodine staining and analysis of amylose content. The results indicated that RNA silencing of Waxy gene resulted in low level of amylose in the seeds of transgenic wheat.

Amylose↗