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Biomedical subjects

G Zhang

Publications and source records attributed to G Zhang.

At least 271 records · Page 15Linked to original sources
PubMed2000

[The effective dielectric function of porous SiO2 glass].

In this paper, we discussed the effective dielectric function of porous SiO2 glass with pore size 7.5 nm. We briefly discussed different formulae proposed by different theoretical models of porous systems, and compared the relationship of effective dielectric functions changing with different porosity of porous SiO2 of each formula. Through comparing the experimental spectra and the theoretical spectra of each formula, we found the equation ln epsilon e = theta 1 ln epsilon 1 + theta 2 + theta 2 ln epsilon 2 best indicates the effective dielectric function of porous SiO2. This work is helpful in selecting special absorption materials.

English Abstract↗
PubMed2000

[Determination of Al, B, Ba, Ca, Cr, Cu, Fe, Mg, Mn, Ni, Sr, Ti, V and Zn impurities in silicon metal by ICP-AES].

In this paper, an ICP-AES method for determining Al, B, Ba, Ca ets impurities in silicon metal is described. The interference factors in the analysis of impurity elements in silicon metal has been studied. The problems of background interference, organic matter (mannitol) interference, major elements interference are discussed. In the procedure of sample preparation, a proper volume of mannitol solution was added to sample, and this can protect B from volatilization. The feasibility of the proposed method is evaluated by analyzing one national geochemical reference samples (GSR-4), The results are satisfactory.

English Abstract↗
PubMed2000

[Kinetic fluorimetric determination of trace oxalate].

A new kinetic fluorimetric method for the determination of trace oxalate is described. The method is based on the enhancing effect of oxalate on the oxidation of butyl rhodamine B by potassium dichromate in the solution of hydrochloric acid. The linear range of the determination is 1.20-10.0 micrograms.mL-1. This method has been used to determine trace oxalate in spinach with satisfactory results.

Fluorometry↗
PubMed1999

Transcriptional regulatory elements of the human gene for cytochrome P450c21 (steroid 21-hydroxylase) lie within intron 35 of the linked C4B gene.

The CYP21 gene, which encodes P450c21, the adrenal steroid 21-hydroxylase needed for glucocorticoid synthesis, lies in the major histocompatibility locus only 2.3 kilobase pairs (kb) downstream from the C4 gene. A 300-base pair (bp) proximal promoter and two upstream regions within C4 are needed for expression of mouse CYP21; the human gene also has a proximal promoter, but upstream elements have not been studied. To search for upstream regulatory elements in human CYP21B, we examined up to 9 kb of 5'-flanking DNA by transient transfection into human adrenal NCI-H295A cells. The 300-bp proximal promoter had substantial activity, but constructs retaining the DNA between -4.6 and -5.6 kb had increased activity, indicating the presence of distal elements. This region does not correspond to the mouse upstream regions, lying further upstream within intron 35 of C4B, which encompasses the previously described "Z promoter." DNase I footprinting located two elements, F1 and F2, lying -186 to -195 bp and -142 to -151 bp upstream from the Z cap site (-4862 to -4871 and -4818 to -4827 bp upstream of the CYP21B cap site). Each element formed a specific DNA-protein complex and conferred orientation-independent expression to a heterologous promoter. Mutations abolished formation of the DNA-protein complexes but only partially decreased expression. We identified a third site, F3, lying at -33 to -42 bp from Z. Competitive gel mobility supershift assays and co-transfection studies with SF-1 produced in vitro indicate F2 and F3 bind SF-1; BLAST searches and Southwestern blotting suggest that NF-W2 may bind F1. These results indicate that the Z promoter is a component of the CYP21 promoter needed to drive its adrenal-specific expression and that CYP21 transcription elements within C4 have kept these two genes linked during evolution.

Animals↗
PubMed1999

Echocardiographic determination of left atrial function and its application for assessment of mitral flow velocity pattern.

We determined left atrial (LA) volume changes to evaluate LA function, and to correlate the Doppler-determined mitral flow velocity (MFV) pattern. Twenty-four patients with ischemic heart disease who showed 'normal' MFV pattern by pulsed Doppler echocardiography were studied. The patients were divided into 14 patients with left ventricular end diastolic pressure < 18 mmHg (true normals) and 10 patients with > or = 18 mmHg (pseudo normals). The changes in LA volume were determined by echocardiography from apical two- and four-chamber views with modified Simpson's method. The volume measurements were done at the time of mitral valve opening (Vmax), at onset of atrial systole (Va) and at mitral valve closure (Vmin). Then the passive LA emptying volume was calculated by subtracting Va from Vmax, and the active LA emptying volume by subtracting Vmin from Va. The LA ejection fraction was calculated by the formula: [(Va-Vmin)Va] x 100. There was no significant difference in LA ejection fraction in pseudo normal (39+/-6%) and in true normal (41+/-13%) patients. Although the passive LA emptying volume was 16+/-4 ml/beat in true normal and was 11+/-3 ml/beat in pseudo normal (NS), the active LA emptying volume was significantly greater in pseudo normals (22+/-4 m/beat) than in true normals (12+/-2 ml/beat, P<0.001). Thus, the ratio of passive and active LA emptying volume was markedly greater in true normals (1.28+/-0.35) than in pseudo normals (0.52+/-0.19, P<0.001), facilitating the differentiation of these two groups. These results indicate that two-dimensional echocardiographic measurement of LA volume can be valuable in assessing the LA function, providing an alternative method for differentiating pseudo normal from true normal MFV pattern in clinical settings, although several technological shortcomings should be resolved.

Adult↗
PubMed1999

[A sero-epidemiological study of HCV and HBV infection among intravenous drug abusers].

OBJECTIVE: To investigate hepatitis B and C virus infection in drug addicts in Guangzhou. METHODS: Serum samples from drug users and normal control people were collected. Serum antibodies against hepatitis C virus (HCV) and hepatitis B virus (HBV) were detected by ELISA. RESULTS: The results showed that hepatitis prevalence is significantly higher among the drug users than that in normal control group (for HCV 67.49% to 3.75%, for HBV 90.48% to 55.63%, and for the mixed infections 62.73% to 3.75%). CONCLUSION: In Guangzhou, the very high infection rates of HBV and HCV were found in drug addicts. Our results emphasize intravenous drug use is the major risk factor for HBV and HCV infections.

Adult↗
PubMed1999

Crystal structure of Thermus aquaticus core RNA polymerase at 3.3 A resolution.

The X-ray crystal structure of Thermus aquaticus core RNA polymerase reveals a "crab claw"-shaped molecule with a 27 A wide internal channel. Located on the back wall of the channel is a Mg2+ ion required for catalytic activity, which is chelated by an absolutely conserved motif from all bacterial and eukaryotic cellular RNA polymerases. The structure places key functional sites, defined by mutational and cross-linking analysis, on the inner walls of the channel in close proximity to the active center Mg2+. Further out from the catalytic center, structural features are found that may be involved in maintaining the melted transcription bubble, clamping onto the RNA product and/or DNA template to assure processivity, and delivering nucleotide substrates to the active center.

Catalytic Domain↗
PubMed1999

Cloning and characterization of the gene for a new epithelial beta-defensin. Genomic structure, chromosomal localization, and evidence for its constitutive expression.

Mammalian beta-defensins are endogenous cysteine-rich peptide antibiotics that are produced either by epithelial cells lining the respiratory, digestive, and urogenital tracts or by granulocytes and macrophages. A growing body of evidence has implicated these peptides in host defense, particularly mucosal innate immunity. We previously reported the cloning of the full-length cDNA for a porcine beta-defensin (pBD-1), which was found to be expressed throughout the airway and oral mucosa. Here, we provide the structural organization of the pBD-1 gene, showing that the entire gene spans approximately 1.9 kilobases with two short exons separated by a 1.5-kilobase intron. Fluorescence in situ hybridization mapped the pBD-1 gene to porcine chromosome 15q14-q15. 1 within a region of conserved synteny to the chromosomal locations of human and mouse alpha- and beta-defensins. We also provide several independent lines of evidence showing that the pBD-1 gene is expressed constitutively during inflammation and infection, despite its resemblance to many inducible epithelial beta-defensins in amino acid sequence, genomic structure, and sites of expression. First, stimulation of primary porcine tongue epithelial cells with lipopolysaccharide, tumor necrosis factor-alpha, and interleukin (IL)-1beta failed to up-regulate the expression of pBD-1 mRNA. Second, pBD-1 gene expression was not enhanced in either digestive or respiratory mucosa of pigs following a 2-day infection with Salmonella typhimurium or Actinobacillus pleuropneumoniae. Last, direct transfection of the pBD-1 gene promoter into NIH/3T3 cells showed no difference in reporter gene activity in response to stimulation by lipopolysaccharide and IL-1beta. The constitutive expression of pBD-1 in airway and oral mucosa, which is consistent with a lack of consensus binding sites for nuclear factor-kappaB or NF-IL-6 in its promoter region, suggests that it may play a surveillance role in maintaining the steady state of microflora on mucosal surfaces.

3T3 Cells↗
PubMed1999

High levels of foreign gene expression in hepatocytes after tail vein injections of naked plasmid DNA.

We have previously shown that the intramuscular injection of naked plasmid DNA enables foreign gene expression in muscle. Further studies showed that the intravascular delivery of naked plasmid DNA enables high levels of expression not only in muscle but also in hepatocytes. For the liver, this technique required injection directly into the liver vessels (portal vein, hepatic vein, or bile duct) and occlusion of outflow. The present study now demonstrates that high levels of plasmid DNA expression in hepatocytes can be easily obtained by tail vein injections. The highest levels of expression are achieved by rapidly injecting the plasmid DNA in large volumes, approximately 2.5 ml. This technique has great potential for a wide variety of laboratory studies.

Animals↗
PubMed1999

Mortality risk in selenium-deficient HIV-positive children.

OBJECTIVE: To determine the independent contribution of specific nutritional factors on disease progression and survival in HIV-1-infected children. POPULATION: HIV-infected children (N = 24), who were perinatally exposed to the virus and symptomatic, were recruited between October and December of 1990 from the Jackson Memorial Pediatric Immunology Clinic, Miami, Florida, and observed for 5 years. METHODS: Immune status was measured by CD4 cell count; nutritional status was determined using serum albumin and plasma trace elements including iron, zinc, and selenium. Cox proportional hazards regression models were used to evaluate the relationship of these parameters to survival. Use of antiretroviral treatment was considered in the statistical model, and age at death was considered a parameter of disease progression. RESULTS: Over the course of the study, 12 children died of HIV-related causes. The final Cox multivariate analysis indicated that, of the variables evaluated, only CD4 cell count below 200 (risk ratio [RR] = 7.05; 95% confidence interval [CI], 1.87-26.5); p = .004], and low levels of plasma selenium (RR = 5.96; 95% CI, 1.32-26.81; p = .02) were significantly and independently related to mortality. Among the children who died, those with low selenium levels (< or =85 microg/L), died at a younger age, suggesting more rapid disease progression. CONCLUSIONS: In pediatric HIV-infection, low plasma level of selenium is an independent predictor of mortality, and appears to be associated with faster disease progression.

Child↗
PubMed1999

Nonpeptide glycoprotein IIB/IIIA inhibitors. 19. A new design paradigm employing linearly minimized, centrally constrained, exosite inhibitors.

A new series of potent, linearly-minimized, orally active, selective GPIIb/IIIa inhibitors is identified. Thus 15 (L-750,034) achieves interaction via a constrained, non-turned conformation that maintains the proper distance between its charged termini and full sulfonamide exosite interaction. The diminutive stature and the proposed linear conformation of L-750,034 define a new paradigm for the conceptualization of RGD mimics.

Benzamides↗
PubMed1999

Studies on the interactions between human replication factor C and human proliferating cell nuclear antigen.

Proliferating cell nuclear antigen (PCNA) is a processivity factor required for DNA polymerase delta (or epsilon)-catalyzed DNA synthesis. When loaded onto primed DNA templates by replication factor C (RFC), PCNA acts to tether the polymerase to DNA, resulting in processive DNA chain elongation. In this report, we describe the identification of two separate peptide regions of human PCNA spanning amino acids 36-55 and 196-215 that bind RFC by using the surface plasmon resonance technique. Site-directed mutagenesis of residues within these regions in human PCNA identified two specific sites that affected the biological activity of PCNA. Replacement of the aspartate 41 residue by an alanine, serine, or asparagine significantly impaired the ability of PCNA to (i) support the RFC/PCNA-dependent polymerase delta-catalyzed elongation of a singly primed DNA template; (ii) stimulate RFC-catalyzed DNA-dependent hydrolysis of ATP; (iii) be loaded onto DNA by RFC; and (iv) activate RFC-independent polymerase delta-catalyzed synthesis of poly dT. Introduction of an alanine at position 210 in place of an arginine also reduced the efficiency of PCNA in supporting RFC-dependent polymerase delta-catalyzed elongation of a singly primed DNA template. However, this mutation did not significantly alter the ability of PCNA to stimulate DNA polymerase delta in the absence of RFC but substantially lowered the efficiency of RFC-catalyzed reactions. These results are in keeping with a model in which surface exposed regions of PCNA interact with RFC and the subsequent loading of PCNA onto DNA orients the elongation complex in a manner essential for processive DNA synthesis.

Amino Acid Substitution↗
PubMed1999

Identity of heart and liver L-3-hydroxyacyl coenzyme A dehydrogenase.

Rat heart and liver cDNAs for precursor of L-3-hydroxyacyl-CoA dehydrogenase have been cloned and sequenced. The results indicate that these different rat organs express identical dehydrogenases. Furthermore, pig heart mRNA for L-3-hydroxyacyl-CoA dehydrogenase precursor was amplified by reverse transcription-polymerase chain reaction, and all the cDNA clones were found to encode a precursor of liver L-3-hydroxyacyl-CoA dehydrogenase (X.-Y. He, S.-Y. Yang, Biochim. Biophys. Acta 1392 (1998) 119-126) but not the well-documented heart form of the dehydrogenase (K.G. Bitar et al., FEBS Lett. 116 (1980) 196-198). Sequencing data and other evidence establish that the pig, like the rat, has the same dehydrogenase in heart and liver. Since the size and structure of pig heart L-3-hydroxyacyl-CoA dehydrogenase are identical to the pig liver dehydrogenase, reports that relied on the published sequence of the pig heart dehydrogenase need to be re-evaluated. For example, the signature pattern of the L-3-hydroxyacyl-CoA dehydrogenase family is HXFXPX3MXLXE. Furthermore, the published crystal structure of the pig heart dehydrogenase that substantiated each subunit comprising 307 residues with a mercury-binding residue at position 204 (J.J. Birktoft et al., Proc. Natl. Acad. Sci. U.S.A. 84 (1987) 8262-8266) must be re-examined in accordance with this revelation.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1999

Comparative analysis of three murine G-protein coupled receptors activated by sphingosine-1-phosphate.

The cloning and analysis of the first identified lysophosphatidic acid (LPA) receptor gene, lpA1 (also referred to as vzg-1 or edg-2), led us to identify homologous murine genes that might also encode receptors for related lysophospholipid ligands. Three murine genomic clones (designated lpB1, lpB2, and lpB3) were isolated, corresponding to human/rat Edg-1, rat H218/AGR16, and human edg-3, respectively. Based on the amino acid similarities of their predicted proteins (44-52% identical), the three lpB genes could be grouped into a separate G-protein coupled receptor subfamily, distinct from that containing the LPA receptor genes lpA1 and lpA2. Unlike lpA1 and lpA2, which contain multiple coding exons, all lpB members contained a single coding exon. Heterologous expression of individual lpB members in a hepatoma cell line (RH7777), followed by 35S-GTPgammaS incorporation assays demonstrated that each of the three LPB receptors conferred sphingosine-1-phosphate-dependent, but not lysophosphatidic acid-dependent, G-protein activation. Northern blot and in situ hybridization analyses revealed overlapping as well as distinct expression patterns in both embryonic and adult tissues. This comparative characterization of multiple sphingosine-1-phosphate receptor genes and their spatiotemporal expression patterns will aid in understanding the biological roles of this enlarging lysophospholipid receptor family.

Amino Acid Sequence↗
PubMed1999

Inhibitory effect of recombinant FN polypeptide CH50 on the metastasis and tumor growth.

The inhibition of CH50, a recombinant polypeptide of human fibronectin, on the formation of tumor metastases in vivo was studied by inoculation of melanoma B16/F1 cells by hypodermic or intraperitoneal injection, and the size and amount of tumor nodes after therapy were measured. In the treatment of hypodermic tumor, local injection of CH50 produced much better efficacy than distance injection of CH50 did. The inhibitory effect of CH50 on the growth of tumor reached 50%. In the treatment of peritoneal metastasis, the inhibition of CH50 on metastases smaller than 1 mm was above 80%, and above 50% on metastases larger than 1 mm. A better efficacy was achieved if CH50 was used in combination with hydroxycamptothecine (HCPT), a chemotherapeutic agent. CH50 displayed a strong inhibitory effect on the formation of small metastasis and growth of larger nodes of tumor, suggesting that CH50 plays a very important role in combined treatment of tumor therapy.

Fibronectins↗
PubMed1999

Mitochondrial tRNA(leu)(UUR) gene mutation and the decreased activity of cytochrome c oxidase in preeclampsia.

To explore the roles of mitochondria tRNA(leu)(UUR) gene mutation at nucleotide 3243 and the activity of cytochrome c oxidase in pathogenesis of preeclampsia, 57 patients with preeclampsia and 60 normotension pregnancy women were screened for tRNA(leu)(UUR) nt3243 A-->G mutation with the method of polymers chain reaction (PCR) and restriction fragment length polymorphism. Cytochrome c oxidase activity was determined by measuring the rate of cyanide-sensitive oxidation of reduced cytochrome c using luminosity photographer. The results showed that cytochrome c oxidase activity was significantly lower in the preeclampsia group (0.30 +/- 0.39/min, n = 32) than that in the controls (0.73 +/- 0.54/min, n = 26, P < 0.01). The mitochondria DNA mutation at position 3243 was not found in our series. The results suggested that the decreased activity of cytochrome c oxidase might impair the energy production, leading to the mitochondria dysfunction and placenta dysfunction in preeclampsia patients. Mitochondria dysfunction may be involved in the pathogenesis of preeclampsia. The mutation of mitochondria DNA may not be the common contributor of preeclampsia in our series.

Adult↗