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Biomedical subjects

Hao Chen

Publications and source records attributed to Hao Chen.

At least 127 records · Page 7Linked to original sources
PubMed2004

A method to extract algae toxin of microcystin-LR.

A simple and low-cost method to obtain cyanobacterial toxin microcystin-LR (MC-LR) was developed. A new strain of Microcystis aeruginosa, named DC-1, producing microcystin-LR but not microcystin-RR, was separated from the field blooming algae samples of Dianchi Lake, in southwest of China. Following three times' freeze and thaw treatment, the cultivated DC-1 cells were extracted with 40% methanol in water. The extract was centrifuged and the supernatant applied to a Hydrophilic-Lipophilic Balance (HLB) SPE cartridge. Eluted impurities with a certain gradient from 30% to 50% methanol in water, MC-LR was finally eluted from the HLB cartridge with 60% methanol in water, and samples containing 3.85% to 14.8% of MC-LR were obtained. These MC-LR samples may be used in adsorption and biodegradation experiments instead of using expensive standard reagents.

Bacterial Toxins↗
PubMed2004

[Study on constituents in rhizome of Astilbe chinensis].

OBJECTIVE: To study the chemical constituents in rhizome of Astilbe chinensis. METHOD: The constituents were isolated with column chromatographies and the structures were identified by physicochemical properties and spectral analysis (UV, IR, MS, 1H-NMR, 13C-NMR and 2D-NMR). RESULT: The structures were identified as bergenin (1), 11-O-galloylbergenin (2), 4-O-galloylbergenin (3), catechin (4), respectively. CONCLUSION: Compound 3 was isolated from Astilbe for the first time.

Benzopyrans↗
PubMed2004

[Quantitative analysis of circulating DNA in serum of cancer patients].

OBJECTIVE: To develop a method for ng quantitation of circulating DNA in serum and explore the value in the diagnosis of cancer. METHODS: Serum DNA was extracted by commercial "genomic DNA extraction kit" and detected by fluorescent dye (SYBR green I) staining. Loss of heterozygosity (LOH) at BRCA1 (D17S579, D17S855) and p53 (TP53, D17S786) in serum DNA was analyzed by PCR-based method. RESULTS: SYBR green I dot staining could detect DNA as low as 2 ng. Using this method, we detected serum samples from 483 patients with various types of cancer and 150 healthy individuals. The mean DNA concentration in the normal controls was 22.2 +/- 13.4 ng/ml, while that in cancer patients was 81.3 +/- 98.3 ng/ml (P < 0.001). In 33 ovarian cancer patients with increased DNA level, 27(81.8%) displayed LOH in at least one of the four loci analyzed. CONCLUSION: Circulating DNA in serum may become additional tumor marker for the diagnosis of cancer.

BRCA1 Protein↗
PubMed2004

[Flocculation and removal of water bloom cells Microcystis aeruginosa by chitosan-modified clays].

The kinetics of flocculation and removal of Microcystis aeruginosa by chitosan-modified clays was studied. The efficiency of flocculating and removing of algal cells was greatly improved after the modification of the clays. About 80% of algae cell was removed in 0.5 hour, and 90% in 2 hours, when 11 mg/L modified sepiolite was added. Algae-removal capacities of different clays were all improved to a similar level of >90% at a total loading of 11 mg/L after being modified with chitosan. The efficiency of algae-removing was reduced when the clay loading was larger or smaller than the optimum loading.

Aluminum Silicates↗
PubMed2004

[Effect of growth phase on the flocculation of algal cells using clays].

Four different growth phases, late lag phase, middle logarithmic phase, late logarithmic phase and early senescence phase of Microcystis aeruginosa 469 were studied for their surface hydrophobicity (xylene-water system) and surface charge (Zeta potential), followed by flocculation tests with sepiolite of 0.2 g/L. The results showed that the values of hydrophobicity were 64%, 48%, 58% and 70%, and the algal removal efficiencies after 60 min were 97%, 87%, 81% and 99% respectively, indicating a good relationship between surface hydrophobicity and removal efficiency (R = 0.7-0.8), but not the surface charge. Surface hydrophobicity and removal efficiency for the algal cells of Microcystis aeruginosa both varied with growth phase in a sequence of senescence phase > lag phase > logarithmic phase.

Aluminum Silicates↗
PubMed2003

Gas-phase reactions for selective detection of the explosives TNT and RDX.

Highly selective gas-phase reactions with ethyl vinyl ether (EVE) of major electron (EI) and chemical ionization (CI) fragment ions of the explosives TNT and RDX have been uncovered. The fragment ion of m/z 210 from TNT undergoes [4(+)+ 2] cycloaddition with EVE to form an oxo-iminium ion of m/z 282, which dissociates by acetaldehyde loss after a [1,5-H] shift to form a quinolynium ion of m/z 238. The fragment ion of m/z 149 from RDX reacts with EVE by a formal vinylation reaction, that is, the elusive cyclic adduct loses ethanol to yield a nitro-iminium ion of m/z 175, which reacts further with EVE to form a second cyclic product ion of m/z 247. Calculations and MS/MS experiments support the proposed structures. These highly characteristic reactions of diagnostic EI and CI fragment ions improve selectivity for TNT and RDX detection.

Journal Article↗
PubMed2003

Broadband saturable absorber with cobalt-doped tellurite glasses.

A robust solid-state saturable absorber was developed with cobalt-ion-doped tellurite glasses that has a broad saturable-absorption band in the near-infrared. A nonlinear optical absorber was measured by the Z-scan technique. Numerically fitting the Z-scan experimental data yields excited-state absorption cross sections at a 1064-nm laser wavelength of sigma(es) = 1.45 x 10(-20) and sigma(es) = 1.15 x 10(-20) cm2 for 1.0- and 2.5-at. % Co2+-doped glasses, respectively.

Journal Article↗
PubMed2003

Antioxidant status and mineral contents in tissues of rutin and baicalin fed rats.

The versatile benefit effects of flavonoids lead some nutritionists to believe that they are micronutrients. However, excess intake of flavonoids may cause side effects. In this paper, the effects produced by a higher intake of rutin and baicalin on antioxidant status as well as trace minerals such as iron, copper and zinc in rat tissues were studied. When rats were fed a rutin or baicalin containing diet (1%) for 20 days, the body weight gain was lower than that of the control group. Both rutin and baicalin caused significant a decrease of catalase activity and a moderate increase of total superoxide dismutase activity in the liver. The total antioxidant status of flavonoid fed rats was increased in the liver but decreased in the serum. In comparison to the control group, the lipid peroxidation level in the liver of the rutin fed group was significantly decreased; however, there was no statistical significance in the liver of the baicalin fed group and the brain of both flavonoids groups. The liver homogenates of both flavonoid fed rats significantly inhibited alkyl radical-induced lipid peroxidation. The iron contents in the liver of flavonoid fed rats were significantly decreased; rutin also caused zinc and copper decrease in the liver. These results indicated that high flavonoid intake can improve rat antioxidant systems in the liver; while it can also cause a trace mineral decrease and, in turn, reduce the activities of some metal-containing enzymes and may cause harmful effects on health.

Animals↗
PubMed2003

[Modeling of the SARS coronavirus main proteinase and conformational flexibility of the active site].

SARS coronavirus 3CL proteinase is the key enzyme for virus replication which may serve as the target for drug discovery against SARS. A 3D structure model has been built for SARS coronavirus 3CL proteinase by comparative protein modeling. A homodimer model of the proteinase was also built. Analysis of the dimeric interface suggests the 3CL proteinase may have dimer form in solution. The conformational flexibility of the active site has been simulated by molecular dynamics combined with multi-canonical sampling. The active site loops have two typical conformations which may be related to the conformational movement associated with the enzymatic reaction.

Amino Acid Sequence↗
PubMed2003

[Immune tolerance inducing effects of soluble human leucocyte antigen G1 on natural killer cells and T cells].

OBJECTIVE: To investigate the immune tolerance inducing effects of soluble human leucocyte antigen G1 (sHLA-G1) on natural killer (NK) cells and T cells. METHODS: A recombinant plasmid expressing sHLA-G1 was constructed and transfected into human lymphoblastoid cells LCL721.221. sHLA-G1 in the supernatant was purified by immuno-affinity chromatography and then added into the culture of NK cells obtained from the peripheral blood mononuclear cells of 3 unrelated individuals. Target cells, K562 cells, were added too. The killing rate of NK was calculated. Peripheral blood lymphocytes (PBLs) were obtained and stimulated by Ebstein-Barr-virus-transformed B lymphoblastoid cell line (EBV-LCL). The proliferation of the T cells in the mixed lymphocyte culture was examined by enzyme linked immunosorbent assay. The antigen-specific T cells in the peripheral blood was activated. sHLA-G1 was added into the culture. Then the T cells were suspended in the solution of fluorescence isothiocyanate (FITC)-annexin-V. Flow cytometry was used to detect the fluorescent intensity of FITC so as to examine the apoptosis of T cells. RESULTS: sHLAG-1 inhibited the cytotoxicity of NK cells dose-dependently. sHLAG-1 inhibited the proliferation of activated T cells, and induced the apoptosis of T cells dose-dependently, with a dose-saturation character and without antigen-specificity. CONCLUSION: sHLAG-1 is a kind of immune tolerance inducing molecule.

Apoptosis↗
PubMed2003

Beyond the rotamer library: genetic algorithm combined with the disturbing mutation process for upbuilding protein side-chains.

The disturbing genetic algorithm, incorporating the disturbing mutation process into the genetic algorithm flow, has been developed to extend the searching space of side-chain conformations and to improve the quality of the rotamer library. Moreover, the growing generation amount idea, simulating the real situation of the natural evolution, is introduced to improve the searching speed. In the calculations using the pseudo energy scoring function of the root mean squared deviation, the disturbing genetic algorithm method has been shown to be highly efficient. With the real energy function based on AMBER force field, the program has been applied to rebuilding side-chain conformations of 25 high-quality crystallographic structures of single-protein and protein-protein complexes. The averaged root mean standard deviation of atom coordinates in side-chains and veracities of the torsion angles of chi(1) and chi(1) + chi(2) are 1.165 A, 88.2 and 72.9% for the buried residues, respectively, and 1.493 A, 79.2 and 64.7% for all residues, showing that the method has equal precision to the program SCWRL, whereas it performs better in the prediction of buried residues and protein-protein interfaces. This method has been successfully used in redesigning the interface of the Basnase-Barstar complex, indicating that it will have extensive application in protein design, protein sequence and structure relationship studies, and research on protein-protein interaction.

Algorithms↗
PubMed2003

Ketalization of phosphonium ions by 1,4-dioxane: selective detection of the chemical warfare agent simulant DMMP in mixtures using ion/molecule reactions.

Phosphonium ions CH(3)P(O)OCH(3)(+) (93 Th) and CH(3)OP(O)OCH(3)(+) (109 Th) react with 1,4-dioxane to form unique cyclic ketalization products, 1,3,2-dioxaphospholanium ions. By contrast, a variety of other types of ions having multiple bonds, including the acylium ions CH(3)CO(+) (43 Th), CH(3)OCO(+) (59 Th), (CH(3))(2)NCO(+) (72 Th), and PhCO(+) (105 Th), the iminium ion H(2)C[double bond]NHC(2)H(5)(+) (58 Th) and the carbosulfonium ion H(2)C[double bond]SC(2)H(5)(+) (75 Th) do not react with 1,4-dioxane under the same conditions. The characteristic ketalization reaction can also be observed when CH(3)P(OH)(OCH(3))(2)(+), viz. protonated dimethyl methylphosphonate (DMMP), collides with 1,4-dioxane, as a result of fragmentation to yield the reactive phosphonium ion CH(3)P(O)OCH(3)(+) (93 Th). This novel ion/molecule reaction is highly selective to phosphonium ions and can be applied to identify DMMP selectively in the presence of ketone, ester, and amide compounds using a neutral gain MS/MS scan. This method of DMMP analysis can be applied to aqueous solutions using electrospray ionization; it shows a detection limit in the low ppb range and a linear response over the range 10 to 500 ppb.

Chemical Warfare Agents↗
PubMed2003

Functional interaction between RNA polymerase alpha subunit C-terminal domain and sigma70 in UP-element- and activator-dependent transcription.

We show that the Escherichia coli RNA polymerase (RNAP) alpha subunit C-terminal domain (alphaCTD) functionally interacts with sigma(70) at a subset of UP-element- and activator-dependent promoters, we define the determinants of alphaCTD and sigma(70) required for the interaction, and we present a structural model for the interaction. The alphaCTD-sigma(70) interaction spans the upstream promoter and core promoter, thereby linking recognition of UP-elements and activators in the upstream promoter with recognition of the -35 element in the core promoter. We propose that the alphaCTD-sigma(70) interaction permits UP-elements and activators not only to "recruit" RNAP through direct interaction with alphaCTD, but also to "remodel" RNAP-core-promoter interaction through indirect, alphaCTD-bridged interactions with sigma(70).

Alanine↗
PubMed2003

Co-C bond dissociation energy and reaction volume change of 2',5'-dideoxyadenosylcobalamin studied by laser-induced time-resolved photoacoustic calorimetry.

Time resolved photoacoustic calorimetry (PAC) was applied to a study of the photolysis of a coenzyme B(12) analog 2',5'-dideoxyadenosylcobalamin, which lacks an -OH group at the 2' position of ribofuranose ring. In aqueous solution, we report for the first time the quantum yield Phi(d) (0.25+/-0.02), Co-C bond dissociation energy (BDE; 31.8+/-2.5 kcal mol(-1)) and reaction volume change deltaV(R) (6.5+/-0.5 ml mol(-1)) due to conformation changes of the corrin ring and its side chains accompanying the cleavage of the Co-C bond. These values for the analog are very similar to those for the natural cofactor. Based our results and previous studies, a possible explanation for the similarity in their structure and properties versus the large difference in their enzymatic activity is discussed.

Calorimetry↗
PubMed2003

Ion/molecule reactions performed in a miniature cylindrical ion trap mass spectrometer.

A recently constructed miniature mass spectrometer, based on a cylindrical ion trap (CIT) mass analyzer, is used to perform ion/molecule reactions in order to improve selectivity for in situ analysis of explosives and chemical warfare agent simulants. Six different reactions are explored, including several of the Eberlin reaction type (M. N. Eberlin and R. G. Cooks, Org. Mass Spectrom., 1993, 28, 679-687) as well as novel gas-phase Meerwein reactions. The reactions include (1) Eberlin transacetalization of the benzoyl, 2,2-dimethyloximinium, and 2,2-dimethylthiooximinium cations with 2,2-dimethyl-1,3-dioxolane to form 2-phenyl-1,3-dioxolanylium cations, 2,2-dimethylamine-1,3-dioxolanylium cations and the 2,2-dimethylamin-1,3-oxathiolanylium cations, respectively; (2) Eberlin reaction of the phosphonium ion CH3P(O)OCH3+, formed from the chemical warfare agent simulant dimethyl methylphosphonate (DMMP), with 1,4-dioxane to yield the 1,3,2-dioxaphospholanium ion, a new characteristic reaction for phosphate ester detection; (3) the novel Meerwein reaction of the ion CH3P(O)OCH3+ with propylene sulfide forming 1,3,2-oxathionylphospholanium ion; (4) the Meerwein reaction of the benzoyl cation with propylene oxide and propylene sulfide to form 4-methyl-2-phenyl-1,3-dioxolane and its thio analog, respectively; (5) ketalization of the benzoyl cation with ethylene glycol to form the 2-phenyl-1,3-dioxolanylium cation; (6) addition/NO2 elimination involving benzonitrile radical cation in reaction with nitrobenzene to form an arylated nitrile, a diagnostic reaction for explosives detection and (7) simple methanol addition to the C7H7+ ion, formed by NO2 loss from the molecular ion of p-nitrotoluene to form an intact adduct. Evidence is provided that these reactions occur to give the products described and their potential analytical utility is discussed.

Chemical Warfare Agents↗
PubMed2003

Toxicity and pharmacokinetics of stampidine in mice and rats.

The in vivo toxicity and pharmacokinetics of stampidine (CAS 217178-62-6), an aryl phosphate derivative of stavudine (CAS 3056-17-5) under development as a new anti-human immunodeficiency virus (anti-HIV) agent, were studied in mice and rats. Stampide was very well tolerated by both mice and rats without any toxicity at cumulative dose levels > 1 g/kg. Therapeutic micromolar plasma concentrations of stampidine and its active metabolites ala-STV-MP (CAS 180076-92-0) and STV were rapidly achieved and maintained several hours after i.p. administration of the nontoxic 25-50 mg/kg bolus doses of stampidine. The remarkable in vivo safety of stampidine warrants the further development of this promising new antiviral agent for possible clinical use in HIV-infected patients.

Animals↗