Biomedical subjects

Z Q Zhang

Publications and source records attributed to Z Q Zhang.

At least 19 recordsLinked to original sources

PubMed2004

Impact of weak localization in the time domain.

We find a renormalized "time-dependent diffusion coefficient," D(t), for pulsed excitation of a nominally diffusive sample by solving the Bethe-Salpeter equation with recurrent scattering. We observe a crossover in dynamics in the transformation from a quasi-1D to a slab geometry implemented by varying the ratio of the radius, R, to the length, L, of the cylindrical sample with reflecting side walls and open ends. Immediately after the peak of the transmitted pulse, D(t) falls linearly with a nonuniversal slope that approaches an asymptotic value for R/L>>1. The value of D(t) extrapolated to t=0 depends only upon the dimensionless conductance g for R/L<<1 and only upon kl(0) for R/L>>1, where k is the wave vector and l(0) is the bare mean free path.

Journal Article↗

PubMed2003

Breakdown of diffusion in dynamics of extended waves in mesoscopic media.

We report the observation of nonexponential decay of pulsed microwave transmission through quasi-one-dimensional random dielectric media signaling the breakdown of the diffusion model. The decay rate of transmission falls nearly linearly in time corresponding to a nearly Gaussian distribution of the coupling strengths of quasinormal electromagnetic modes to free space at the sample surfaces. The peak and width of this distribution scale as L(-2.05) and L(-1.81), respectively.

Journal Article↗

PubMed2003

Fluoride and aluminium concentrations of tea plants and tea products from Sichuan Province, PR China.

Some Tibetans in Sichuan Province in southwestern China have been suffering from fluorosis, due to drinking and eating tea with high fluoride (F) and aluminium (Al) contents. Tea plants, soils of tea plantations and tea products from Yaan, Gaoxian and Yibin Cities in Sichuan Province were investigated to evaluate the factors affecting F and Al contents in tea products. The F and Al concentrations of four commercial brands of brick teas were significantly higher than those of 11 brands of green teas. Chemical analysis indicated that total and available F and Al concentrations in tea plantation soils in Yaan and Gaoxian were within the normal range compared with acid soils in South China and tea soils in Fujian Province. Edaphic conditions did not contribute to the high F and Al concentrations in brick tea. Analysis of raw materials of brick tea indicated that old leaves were the major contributors to the high F and Al contents contained in brick tea. There were also great variations among different tea varieties in accumulating F and Al, and concentrations of F and Al in tea variety of Qianmei 303 were about 2-3-fold higher than the other three varieties. Selection of appropriate varieties would be important to lower F and Al contents in tea products.

Aluminum↗

PubMed2003

Aluminium and fluoride concentrations of three tea varieties growing at Lantau Island, Hong Kong.

The present project aims to investigate aluminium (Al) and fluoride (F) contents in teas (Camellia sinensis (L.) O. Kuntze). Three different commercial tea varieties: Assam variety and two China sub-varieties, a large leafed variety and small leafed variety, were collected in two tea gardens of Lantau Island tea plantation of Hong Kong. In general, high concentrations of Al and F were accumulated in the mature leaves (15.3 and of 2.07 g kg-1 respectively). Among the three varieties, 'the small leafed' variety exhibited the highest Al and F contents followed by the 'large leafed' variety whereas the Assam variety had the lowest Al and F concentrations in its tea bushes. Tea products from a plantation were also analysed and it was noted that black tea had higher Al and F concentrations than green tea. The amount of Al and F released into tea liquor was also tested and the results showed that higher concentrations of Al and F were released into tea liquor under repeated infusion method than continuous infusion method.

Agriculture↗

PubMed2002

Evaluation of major constraints to revegetation of lead/zinc mine tailings using bioassay techniques.

The residues from the extraction of lead/zinc (Pb/Zn) ores of most Pb/Zn mines are permanently stored in tailings ponds, which require revegetation to reduce their environmental impact. This can only be done if the main constraints on plant establishment are evaluated. This can readily be done by field and greenhouse studies. To test this, the properties of different tailings from Lechang Pb/Zn mine located at the north of Guangdong Province in southern China have been studied. Physical and chemical properties including concentrations of metals (Pb, Zn, Cd and Cu) in the tailings and soils collected from different sites have been measured. The results showed that tailings contain low nitrogen (0.016-0.075%), low-organic matter (0.58-1.78%), high salt (3.55-13.85 dS/m), and high total and diethylene-tetramine-pentaacetic acid (DTPA)-extractable metal concentrations (total: 1,019-1,642 microg g(-1) Pb, 3,078-6,773 microg g(-1) Zn, 8-23 microg g(-1) Cd, and 85-192 microg g(-1) Cu; DTPA-extractable: 59-178 microig g(-1) Pb, 21-200 microg g(-1) Zn, 0.30-1.5 mcirog g(-1) Cd, and 4.3-12 microg g(-1) Cu). Aqueous extracts of tailings/soils (10%, 20% and 30%, w/v) from different sites were prepared for testing their effects on seed germination and root elongation of a vegetable crop Brassica chinensis and a grass species Cynodon dactylon. It was found that root elongation provided a better evaluation of toxicity than seed germination. The ranking of toxicity using root elongation was: high-sulfur tailings > tailing dam > sparsely vegetated tailings > densely vegetated tailings > mountain soil for both plants. This order was consistent with DTPA-extractable Pb contents in the tailings and soils. B. chinensis seedlings were then grown in the mixtures of different proportions of tailings and farm soil for 4 weeks, and the results (dry weights of seedlings) were in line with the root elongation test. All these demonstrated that heavy metal toxicity, especially available Pb, low content of nutrient, and poor physical structure were major constraints on plant establishment and colonization on the Pb/Zn mine tailings.

Biodegradation, Environmental↗

PubMed2002

Lead, zinc and copper accumulation and tolerance in populations of Paspalum distichum and Cynodon dactylon.

Both Fankou and Lechang lead/zinc (Pb/Zn) mine tailings located at Guangdong Province contained high levels of total and DTPA-extractable Pb, Zn and Cu. Paspalum distichum and Cynodon dactylon were dominant species colonized naturally on the tailings. Lead, zinc and copper accumulation and tolerance of different populations of the two grasses growing on the tailings were investigated. Tillers of these populations including those from an uncontaminated area were subjected to the following concentrations: 5, 10, 20, 30 and 40 mg l(-1) Pb, 2.5, 5, 10, 20 and 30 mg (l-1) Zn, or 0.25, 0.50, 1 and 2 mg l(-1) Cu for 14 days, respectively, then tolerance index (TI) and EC50 (the concentrations of metals in solutions which reduce 50% of normal root growth) were calculated. The results indicated that both Lechang and Fankou populations of the two grasses showed a greater tolerance to the three metals than those growing on the uncontaminated area, which suggested that co-tolerant ecotypes have evolved in the two grasses. P. distichum collected from Fankou tailings had the highest tolerance to Cu while Lechang population the highest tolerance to Pb and Zn among the tested populations, and tolerance levels in P. distichum were related to metal concentrations in the plants. P. distichum had a better growth performance than C. dactylon when both of them were grown on the tailings sites. Tolerant populations of these species would serve as potential candidates for re-vegetation of wastelands contaminated with Pb, Zn and Cu.

Biodegradation, Environmental↗

PubMed2001

[Protective effects of scopolamine on rabbits with acute brain injury].

OBJECTIVE: To study the protective effects of scopolamine (Sco) (a muscarinic receptor antagonist) on rabbits with acute brain injury, and preliminarily explore the roles of acetylcholine (ACh) in the early pathologic changes of traumatic brain injury(TBI). METHODS: The model of acute brain injury was established by a free-falling device, and the rabbits received Sco intraperitoneally at 5 minutes and 2 hours after brain injury respectively. Transcranial Doppler (TCD) was used to monitor cerebral blood flow velocity (CBV) and pulsatility index (PI) of middle cerebral artery (MCA). The levels of Ca2+, the activities of superoxide dismutase (SOD), the contents of malondiadehyde (MDA) and Evans blue (EB) were measured, and the pathological changes were observed in brain tissue. RESULTS: This model consisted with the pathologic changes of accelerated brain injury. Sco reduced the levels of Ca2+, EB and MDA, increased the activities of SOD, and improved cerebral blood flow following brain injury. CONCLUSIONS: In the early stage of brain injury, ACh can cause neuron calcium overload, oxide free radical reaction, cerebral vasospasm, and increase blood-brain barry(BBB) permeability. Scopolamine, a muscarinic receptor antagonist, can improve these pathologic changes. As a result, Sco has protective effects on brain tissue injury.

Acetylcholine↗

PubMed2001

Anisotropic magnetocaloric effect in nanostructured magnetic clusters.

We report the first experimental observation of anisotropic magnetocaloric effect (MCE) in the Fe8 clusters. It is found that the magnetic anisotropy plays a very important role in the determination of the magnetocaloric effect. The maximum and minimum MCE's are observed when the applied magnetic fields are parallel and perpendicular to the easy axis, respectively. The quantum spin Hamiltonian of a Fe8 cluster is used to calculate the partition function and the magnetization in a range of temperature and magnetic field. Excellent quantitative agreement between the experimental data and calculation is observed.

Journal Article↗

PubMed2001

Residual human immunodeficiency virus (HIV) Type 1 RNA and DNA in lymph nodes and HIV RNA in genital secretions and in cerebrospinal fluid after suppression of viremia for 2 years.

Residual viral replication persists in a significant proportion of human immunodeficiency virus (HIV)-infected patients receiving potent antiretroviral therapy. To determine the source of this virus, levels of HIV RNA and DNA from lymphoid tissues and levels of viral RNA in serum, cerebrospinal fluid (CSF), and genital secretions in 28 patients treated for < or =2.5 years with indinavir, zidovudine, and lamivudine were examined. Both HIV RNA and DNA remained detectable in all lymph nodes. In contrast, HIV RNA was not detected in 20 of 23 genital secretions or in any of 13 CSF samples after 2 years of treatment. HIV envelope sequence data from plasma and lymph nodes from 4 patients demonstrated sequence divergence, which suggests varying degrees of residual viral replication in 3 and absence in 1 patient. In patients receiving potent antiretroviral therapy, the greatest virus burden may continue to be in lymphoid tissues rather than in central nervous system or genitourinary compartments.

Cohort Studies↗

PubMed2001

Large coherence area thin-film photonic stop-band lasers.

We demonstrate that the shift of the stop-band position with increasing oblique angle in periodic structures results in a wide transverse exponential field distribution corresponding to strong angular confinement of the radiation. The beam expansion follows an effective diffusive equation depending only upon the spectral mode width. In the presence of gain, the beam cross section is limited only by the size of the gain area. As an example of an active periodic photonic medium, we calculate and measure laser emission from a dye-doped cholesteric liquid crystal film.

Journal Article↗

PubMed2001

Productive infection of T cells in lymphoid tissues during primary and early human immunodeficiency virus infection.

Current models suggest that during human immunodeficiency virus type 1 (HIV-1) transmission virions are selected that use the CCR5 chemokine receptor on macrophages and/or dendritic cells. A gradual evolution to CXCR4 chemokine receptor use causes a shift in the proportion of productively infected cells to the CD4 cell population. Productively infected cells during acute and early infection in lymphoid tissue were assessed, as well as the impact of productive infection on the T cell population in 21 persons who had biopsies performed on days 2-280 after symptoms of acute HIV-1 seroconversion. Even in the earliest stages of infection, most productively infected cells were T lymphocytes. There were sufficient infected cells in lymphoid tissue (LT) to account for virus production and virus load in plasma. Despite the relatively high frequency of productively infected cells in LT, the impact on the size of the T cell population in LT at this stage was minor.

CD4-Positive T-Lymphocytes↗

PubMed2001

CTNNB1 mutations and beta-catenin protein accumulation in human hepatocellular carcinomas associated with high exposure to aflatoxin B1.

beta-Catenin plays a key role in the Wnt signaling pathway, and mutations of CTNNB1, the gene that encodes beta-catenin, have been identified in about one-fourth of human hepatocellular carcinomas from regions of low aflatoxin B1 exposure. In this study 62 hepatocellular carcinomas (HCCs) from people highly exposed to aflatoxin B1 in Guangxi, People's Republic of China, were laser-capture microdissected and examined for CTNNB1 mutations. In addition, 41 of the HCCs were evaluated for the presence of the beta-catenin protein by immunohistochemical methods. Twenty of the HCCs showed positive results for beta-catenin, with strong membrane staining, while adjacent non-neoplastic liver tissue lacked or showed only weak membrane staining. One HCC, in which a CTNNB1 mutation was not detected, showed nuclear staining for the beta-catenin protein. Mutations of CTNNB1 were identified in five HCCs. These consisted of four point mutations in the glycogen serine kinase-3beta phosphorylation region of codons 32-45 and one deletion of codons 32-38. These mutations were similar to those previously reported for human HCC, although at a lower frequency. A signature mutation profile associated with aflatoxin B1 exposure could not be identified. The immunohistochemical findings indicate a role for accumulation of beta-catenin and possibly increased Wnt signaling in aflatoxin B1-associated HCC. The low frequency of CTNNB1 mutations, however, suggests that mutation of another Wnt signaling component, such as the Wnt scaffolding protein axin or the adenomatous polyposis coli protein, both of which modulate beta-catenin stability, also may be involved in aflatoxin-associated HCC. Published 2001 Wiley-Liss, Inc.

Adult↗

PubMed2001

Acidification of lead/zinc mine tailings and its effect on heavy metal mobility.

The acid-forming potential of lead/zinc (Pb/Zn) mine tailings at Lechang City of Guangdong Province was studied using both net acid generation (NAG) and acid-base accounting (ABA) methods. The pyritic and total sulfur contents of the tailings were 12.6% and 18.7%, respectively. The mean acid neutralization capacity (ANC) was 63.5 kg H2SO4/t while three oxidized tailings samples had an ANC less than zero. The NAG and net acid production potential (NAPP) values were 220 and 326 kg H2SO4/t, and both the NAG and NAPP results indicated that the tailings had a high acid-forming potential. NAG was more accurate than NAPP in predicting acid-forming potential of the tailings due to uncompleted oxidization of pyritic sulfur. Analysis of samples from two profile tests indicated that acidification mainly occurred at the surface (0-20 cm) and had little effects at deep layer of the tailings. Total concentrations of Pb, Zn, Cu, and Cd were increased greatly with depth at the acidified tailings profile, while heavy metal concentrations at different depths of nonacidified tailings profile were similar. The results indicated that depletion of heavy metals at the acidified surface was due to acidification. The diethylenetetramine pentaacetic acid (DTPA)-extractable Pb, Zn, Cu, and Cd concentrations of acidified tailings surface (0-20 cm) were significantly higher than those of nonacidified tailings, which further revealed that acidification enhanced the mobility of heavy metals in the tailings.

Forecasting↗

PubMed2001

Population dynamics of phytophagous and predatory mites (Acari: Tetranychidae, Eriophyidae, Phytoseiidae) on bamboo plants in Fujian, China.

The seasonal cycle and population dynamics of Schizotetranychus nanjingensis Ma and Yuan, Aponychus corpuzae Rimando (Tetranychidae), Aculus hambusae Kuang (Eriophyidae) and their natural enemy Tvphlodromus bambusae Ehara (Phytoseiidae) were studied during 1996-1998 in moso bamboo forests in Nanping, Fujian, China. Damage to bamboo leaves was often caused by mixed populations of the three phytophagous species, which displayed different seasonal dynamics: S. nanjingensis fed actively and reproduced in May and from late July to late October (aestivating from June to mid July), Ap. corpuzae was active and reproduced from mid July to late November, and Ac. bambusae from July to next February. During Spring S. nanjingensis was the dominant species with the greatest niche width, but in Summer Ac. bambusae and Ap. corpuzae became dominant and had greater niche widths. In Autumn, Ac. bambusae decreased but both S. nanjingensis and Ap. corpuzae mites increased and the latter became dominant. In winter all species decreased sharply in number. The two spider mite species (S. nanjingensis and Ap. corpuzae) had high niche overlaps in all four seasons. Niche overlaps between the eriophyid Ac. bambusae and the two spider mites were similarly high except during the spring when Ac. bambusae was absent. The predatory mite (T. bambusae) had higher niche overlap with Ap. corpuzae than with others during Autumn and Winter, but during Spring and Summer niche overlap was higher with S. nanjingensis.

Animals↗

PubMed2001

[A three-domain antibody fragment VH/L specific to tumor blood vessels].

AA98 is a specificaally anti-angiogenic antibody generated in our lab. The heavy chain variable region (VH) attached with mutagenized 36 nucleotides sequence derived from the heavy chain constant region1 (CH1) was amplified VH and light chain (L) were inserted into high-level expression vector pET21a successively, thus pET21a-VH/L was constructed. VH/L was expressed in E. coli BL21 (DE3) after induction with IPTG. The expression of VH/L was 20% of the total bacterial proteins. The refolding of VH/L was conducted by dilution and gel filtration chromatography. The refolded VH/L could bind to HUVEC specifically. Its affinity to the antigen is similar to that of recombinant AA98Fab, but lower than that of the parent antibody AA98.

Angiogenesis Inhibitors↗

PubMed2001

Hepatitis B, aflatoxin B(1), and p53 codon 249 mutation in hepatocellular carcinomas from Guangxi, People's Republic of China, and a meta-analysis of existing studies.

The incidence of hepatocellular carcinomas (HCC) varies widely worldwide, with some of the highest incidence rates found in China. Chronic infection with the hepatitis B virus (HBV) and exposure to aflatoxins in foodstuffs are the main risk factors. A G to T transversion at codon 249 of the p53 gene (249(ser)) is commonly found in HCCs from patients in regions with dietary aflatoxin exposure. Because HBV infection is often endemic in high aflatoxin exposure areas, it is still unclear whether HBV acts as a confounder or as a synergistic partner in the development of the 249(ser) p53 mutation. Our report has two aims. First, we contribute data on HCCs from southern Guangxi, a high aflatoxin exposure area. Using DNA sequencing, we found that 36% (18 of 50) of tumors had a 249(ser) mutation. Also, 50% (30 of 60) were positive for p53 protein accumulation and 78% (28 of 36) were positive for HBV surface antigen, as detected by immunohistochemistry. Second, we present a meta-analysis, using our results along with those from 48 published studies, that examines the interrelationships among aflatoxin exposure, HBV infection, and p53 mutations in HCCs. We used a method that takes into account both within-study and study-to-study variability and found that the mean proportion of HCCs with the 249(ser) mutation was positively correlated with aflatoxin exposure (P = 0.0001). We found little evidence for an HBV-aflatoxin interaction modulating the presence of the p53 249(ser) mutation or any type of p53 mutation.

Aflatoxin B1↗

PubMed2001

[Cloning of VEGF receptor KDR and its expression in insect cells].

The cDNA fragment of the first 3 loops of VEGF receptor, KDR, was cloned by PCR and inserted into a baculovirus expression plasmid pFASTBACI. The competent E. coli DH10BAC cell, which contain another plasmid with baculovirus genome in it, was transformed with pFASTBACI-KDRn3. Homologous recombination in the prokaryotic cells resulted in a recombinant plasmid containing KDRn3 in baculovirus genome. Transfection of the insect cell SF-9 with above plasmid generated a recombinant baculorvirus contain target gene fragment. SDS-PAGE and Western blot analysis of the supernatant of the infected SF-9 cell showed that KDRn3 was secreted in the medium. The recombinant protein was verified with Western blot and tested for their binding activity with VEGF. Its anti-angiogenic activity was assayed on chorionic allantoic membrane(CAM) of fertilized egg. The results showed that the recombinant protein could inhibit new vessel formation on CAM of fertilized eggs.

Angiogenesis Inhibitors↗

PubMed2001

[Expression of extracellular domain of VEGF receptor KDR with recombinant AAV].

New vessel formation plays a key role in tumor growth and transforming, and the Vascular endothelial growth factor (VEGF) is the most important factor inducing tumor vessel formation. The cDNA of extracellular domain of VEGF receptor KDR was cloned from primary cultured HUVEC by RT-PCR and subcloned into AAV vector pSNAV. Recombinant AAV was obtained from BHK cells transformed with pSNAV/KDR after adding helper virus. The recombinant AAV expressing soluble KDR that can bind to VEGF. In vivo experiment demonstrated that the recombinant virus can inhibit the new vessel formation of melanoma in C57 mice model.

Animals↗