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Biomedical subjects

X L Li

Publications and source records attributed to X L Li.

At least 109 records · Page 6Linked to original sources
PubMed1993

Quality assurance in the biological monitoring of lead exposure in China.

Based on the statistical data of the nationwide occupational diseases reporting in 1986-1988, lead poisoning stood the first place of chronic occupational poisonings in China. Biological monitoring of lead exposure is of paramount importance in both occupational and environmental health. In order to ensure lead testing data valid enough for taking actions of prevention and control, a quality assurance scheme including selection of reliable analytical techniques, establishing reference laboratory, application of standard reference materials, and conducting internal and external quality control program was implemented in China. Since the rigid assurance procedure was conducted during studies on "background levels of lead in non-exposure population" and "revision of the diagnostic criteria for lead", compatible and reliable results were obtained.

Aminolevulinic Acid↗
PubMed1993

The changes of metabolism balance of zinc and copper in gastric juice with widely varying dietary zinc intake.

The concentrations of zinc and copper in gastric juice of humans who had widely varying dietary zinc intake were evaluated. In order to compare this with zinc and copper levels of normal dietary individuals, we also determined the zinc and copper levels in healthy individuals' plasma and in cancer patient's natural tissue, all of whom had normal diets. The correlation coefficients between zinc and copper were 0.71, 0.45, and 0.55, respectively, in gastric juice, plasma, and tissue of normal dietary subjects. Such correlation changed and was destroyed when there was a high zinc level in gastric juice. When gastric juice zinc level changed from mean value 16.8 mumol/L to 262.5 mumol/L, the correlation coefficient varied from 0.71 to -0.04, and the copper level also varied from mean value 8.96 mumol/L to 4.89 mumol/L. These findings probably give the evidence to suggest that a high zinc level will restrain the copper level and break the balance of the human body's zinc and copper metabolism.

Adult↗
PubMed1993

Purification and characterization of a new xylanase (APX-II) from the fungus Aureobasidium pullulans Y-2311-1.

Aureobasidium pullulans Y-2311-1 produced four major xylanases (EC 3.2.1.8) with pI values of 4.0, 7.3, 7.9, and 9.4 as revealed by isoelectric focusing and zymogram analysis when grown for 4 days on 1.0% oat spelt xylan. The enzyme with a pI of 9.4 was purified by ammonium sulfate precipitation, chromatography on a DEAE-Sephadex A-50 column, and gel filtration with a Sephadex G-75 column. The enzyme had a mass of about 25 kDa as determined by both sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel filtration chromatography. The purified enzyme had a Km of 7.6 mg . ml(-1) and Vmax of 2,650 micromol . min(-1) . mg(-1) for birchwood xylan at 28 degrees C and pH 4.5. It lacked activity towards carboxymethylcellulose, cellobiose, starch, mannan, p-nitrophenyl (pNP)-beta-D-xylopyranoside, pNP-beta-D-glucopyranoside, pNP-alpha-D-glucopyranoside, pNP-beta-D-cellobioside, pNP-beta-D-fucopyranoside, or pNP-alpha-D-galactopyranoside. The predominant end products of birchwood xylan or xylohexaose hydrolysis were xylobiose and xylose. The enzyme had the highest activity of pH 4.8 and 54 degrees C. Sixty percent of the activity remained after the enzyme had been incubated at 55 degrees C and pH 4.5 for 30 min. The sequence of the first 68 amino acid residues at the amino terminus showed homology to those of several other xylonases. Immunoblot analysis with antiserum raised against the purified xylanase revealed that two immunologically related polypeptides of 25 and 22 kDa were produced in A. pullulans cultures containing oat spelt xylan or xylose as carbon sources but not in cultures containing glycerol or glucose.

Amino Acid Sequence↗
PubMed1993

[Expression of human multidrug resistance gene (mdr1) cDNA in murine ES cells and in chimeric mice].

Human multidrug resistance gene (mdr1) was introduced into mouse embryonic stem cells (ES-5 line) by calcium phosphate mediated transfection, and transfected ES-5 cells were then selected by stepwise increase in colchicine concentration (30, 50, 100, and 200 ng/ml respectively). Finally, we obtained 4 clones that could be stably grown in culture medium with colchicine at 200 ng/ml and designated as ES-mdr1 clones A, B, C, and D. Southern blot analysis of DNA from ES-mdr1 A and D cells digested by Hind III and hybridized with mdr1 cDNA 5 A probe was shown in Fig. 3. Characteristic 4.8 and 2.4 kb fragments of mdr1 gene were found as expected and their amplification under increased concentration of colchicine in culture medium was also evident from the figure. Slot blot and Northern analysis of total RNA and poly A+ RNA extracted from ES-mdr1 cells were shown in Fig. 4 and 5, demonstrating that ES-mdr1 cells could express mdr1 mRNA. Indirect immunofluorescence analysis with antibodies against p170 glycoprotein indicated that p170 protein translated from mdr1 mRNA was present at the surface of ES-mdr1 cells (Plate I, Fig. 2). The biological characteristics of ES-mdr1 cells cultured in medium containing 200 ng/ml colchicine were investigated. The cells maintained their undifferentiated morphology and grew in nests (Plate I, Fig. 1), like the parental ES-5 cells. When ES-mdr1 cells were cultured in suspension in vitro, these cells were still capable of producing simple and cystic embryoid bodies. ES-mdr1 cells injected subcutaneously into 129 mice formed tumor-like outgrowths giving a great variety of cell types (Plate I, Fig. 4). These results indicated that the integration and expression of human mdr1 gene and selection against colchicine did not affect the pluripotency of ES-mdr1 cells both in vitro and in vivo. However, ES-mdr1 cells, unlike their parental ES-5 cells, could no longer be induced to differentiate by either RA or HMBA (Plate I, Figs. 3a, 3b), indicating that the human mdr1 gene transfected ES cells had changed their competence of inducible response to differentiation in vitro. The details and possible significance of such change require further studies. From the above preliminary data, we are of the opinion that ES-mdr1 cells may serve as a model to study the mode of action of p170 glycoprotein at cellular level and to screen possible means to counteract the action of mdr1 gene.(ABSTRACT TRUNCATED AT 400 WORDS)

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1993

[Determination of trace elements in several hemostatic medicinal plants and their boiling water extracts].

The experimental results indicate that the amounts of Cu, Zn, Fe and Mn in Rubia cordifolia and Agrimonia pilosa var. japonica are very small in boiling water extracts (only 6%). But after digestion they may rise to 30%. It was found that the amounts of four trace elements decreased with the increase of extracting time, but the ratios of Mn/Zn and Zn/Cu were almost the same.

Copper↗
PubMed1993

[Experimental study of corneal endothelial damage by Nd:YAG laser].

Evaluation by scanning electron microscopy revealed that rabbit eyes that underwent experimental anterior capsulotomy by Q-switched Nd:YAG laser suffered no endothelial damage, while the endothelium was focally denuded in those that received laser shots focussed within 0.8 mm behind it, and the Descemet's membrane was disrupted by laser shots focussed at the endothelium. The implications of clinical laser application were discussed.

Animals↗
PubMed1993

[Study of quality control on herbal drugs and preparations of daqingye and banlangen].

This paper first suggests that 2,4 (1H,3H) quinazolinedione (QZL) may be used as a quality control standard for the Chinese herbal drugs Daqingye (Folium Strobilanthis et Polygoni) and Banlangen (Radix Strobilanthis) as well as its preparations. QZL was found for the first time from the above mentioned two Chinese herbal drugs which has a representative property. Its content is stable. This made it possible to solve the difficulty of quality control for the preparations "antipyretic and common cold granules" and "Banlangan granules" and provide a reliable assay method to evaluate the quality of the herbal preparations. By changing the wavelength and using gradient elution in HPLC, 3 constituents can be determined through one injection by the present method, thus the time of determination may be shortened and the efficiency of assay increased. The method showed good linearity (r = 0.99998, n = 4) in the range of 0.2-3.2 micrograms/ml of QZL, the average recovery was above 95% with RSD < 1.5% (n = 3). HPLC condition: Column: LiChrosorb RP 18; elution gradient: methanol from 35% to 90% in water solution; determination wavelength: 226 nm and 288 nm.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1992

Microvascular salvage procedures with adjuvant antithrombotic therapy for restitution of patency in a rat model.

Thrombosis following microvascular anastomosis requires further surgical intervention, involving anastomotic resection and reanastomosis or interpositional vein grafting. This study was undertaken to investigate different methods of salvaging thrombosed vessels, using a rat-vein model of error-induced thrombosis. Vessels were reconstructed 4 hr after the onset of thrombosis, using one of three methods: Group 1--removal of the erroneously placed stitch; Group 2--anastomotic resection and re-anastomosis; and Group 3--resection and replacement with a vein graft. Adjuvant antithrombotic therapy was simultaneously evaluated, assessing the influence of systemic Iloprost or heparin. Patency rates at one day postoperatively were 0 percent, 12.5 percent and 37.5 percent for Groups 1, 2, and 3, respectively. Following Iloprost infusion, these rates increased to 25 percent, 25 percent, and 56.3 percent, respectively and, following heparin administration, to 50 percent, 68.8 percent, and 81.8 percent, respectively. Significant increases were found for vein grafting (Group 3), and for the heparin-treated subgroups using all three methods. Effective levels of both Iloprost and heparin were confirmed by increases noted in rat-tail bleeding times. Significant rates of recanalization by three days following one-day occlusion were found in Groups 1 and 2. These results support the application of vein-graft replacement for thrombosed veins, concurrently with systemic heparinization. This study further confirms the high rate of recanalization seen in thrombosed rat femoral veins.

Anastomosis, Surgical↗
PubMed1992

[Determination of oleanolic acid in Achyranthes bidentata BLume and its preparations by supercritical fluid chromatography].

Capillary SFC was used for the determination of oleanolic acid in Achyranthes bidentata BLume and its preparations Tianmawan, Jinguishenqiwan and Hechedazaowan. The amount of oleanolic acid in the root of Achyranthes bidentata BLume was 1.75-2.19% (mean +/- SD = 1.94 +/- 0.17%). The limit of detection was 9.605 x 10(-11) g. The method is highly sensitive, accurate, reproducible, simple, rapid and specific, so, it can be extensively used for the determination of other preparations and crude herbs.

Chromatography↗
PubMed1992

[Effect of intracerebroventricular injections of ANG II and ANG II antibody on renal sodium excretion and Na+.K(+)-ATPase in rat].

In anesthetized rats, it was observed that intracerebroventricular (I.C.V.) microinjection of angiotensin II (ANG II) in a dose of 16 pg evoked a significant increase in renal sodium excretion which began within 15 min and lasted for 90 min. The activity of Na+.K(+)-ATPase in renal cortex after I.C.V. microinjection of ANG II (1.51 +/- 0.26 mumol Pi/mg Pro.h) was inhibited as compared with that of the control injecting of artificial cerebrospinal fluid (2.66 +/- 0.28 mumol Pi/mg Pro.h, P less than 0.01). There was no change in mean arterial pressure. Within 15 min after I.C.V. administration of ANG II antibody, however, and antinatriuretic period of 135 min and a higher activity of Na+.K(+)-ATPase in renal cortex (3.61 +/- 0.34 mumol Pi/mg Pro.h, P less than 0.05 compared with control) were observed. There was no natriuresis in the animals microinjected with ANG II either into femoral vein or into spinal subarachnoid space. The result of the present investigation suggests that brain endogenous ANG II may possess some natriuretic activity possibly through inhibiting renal Na+.K(+)-ATPase activity.

Angiotensin II↗
PubMed1991

Kinetic study of a cellobiase purified from Neocallimastix frontalis EB188.

A cellobiase was purified from the culture supernatant of Neocallimastix frontalis EB188. This enzyme possessed a molecular weight of 85,000 and an isoelectric point of 6.95. The enzyme rapidly hydrolyzed cellobiose, p-nitrophenyl (pNP) beta-D-glucopyranoside (pNPG) and cellotriose and slowly hydrolyzed cellopentaose and salicin. The enzyme did not hydrolyze pNP alpha-D-glucopyranoside or pNP beta-D-cellobioside. Substrate inhibition was observed when cellobiose or pNPG were used as the substrates and glucose production was measured. The kinetic parameters were: K = 0.053 mM, V = 5.88 U/mg of protein and Ki = 0.95 mM for cellobiose; K = 0.36 mM, V = 1.05 U/mg and Ki = 8.86 mM for pNPG. Substrate inhibition was not detected during the hydrolysis of pNPG when pNP production was measured. The kinetic parameters for pNPG were: K = 0.67 mM and V = 1.49 U/mg of protein. The presence of an enzyme.glucose.substrate complex and transglucosylation was evident during the catalysis. Glucose, cellobiose, glucono-delta-lactone, galactose, lactose, maltose and salicin acted as competitive inhibitors during the hydrolysis of pNPG with the apparent inhibition constants (Kis) of 4.8 mM, 0.035 mM, 0.062 mM, 28.5 mM, 0.38 mM, 15.0 mm and 31.0 mM, respectively.

Animals↗
PubMed1991

Another discontinuous epitope on glycoprotein gp120 that is important in human immunodeficiency virus type 1 neutralization is identified by a monoclonal antibody.

To define the domains in the envelope glycoprotein important for antibody neutralization of the human immunodeficiency virus type 1 (HIV-1), monoclonal antibodies (mAbs) were generated by immunizing mice with purified glycoprotein gp120 of the IIIB isolate. One mAb, G3-4, reacted with the gp120 of homologous (IIIB) and heterologous (RF) isolates. In addition, mAb G3-4 efficiently neutralized both IIIB and RF viruses in vitro, as well as four of nine primary HIV-1 isolates. In competition immunoassays, mAb G3-4 and soluble CD4 were found to inhibit one another in binding to gp120. However, no competition was seen between mAb G3-4 and mAbs directed to the third variable region or the fourth conserved region of gp120. In particular, mAb G3-4 did not compete with our human mAb 15e, which identifies a discontinuous epitope on gp120 involved in group-specific neutralization of HIV-1 and in gp120-CD4 binding. Epitope-mapping studies on mAb G3-4 with synthetic or unglycosylated recombinant peptides were negative, suggesting that its epitope may be discontinuous. Indeed, this hypothesis was confirmed by showing the loss of mAb G3-4 serologic reactivity when gp120 was first denatured. We conclude that the site recognized by mAb G3-4 represents another discontinuous epitope on gp120 important for neutralization of HIV-1.

Animals↗
PubMed1991

Synthesis of poly(hydroxypropylglutamine-prazosin carbamate) and release studies.

Prazosin, an antihypertensive drug with postsynaptic alpha 1-adrenergic blocking activity, has been coupled to poly-N5-(3-hydroxypropyl-L-glutamine) (PHPG) via a carbamate linkage. PHPG was activated by p-nitrophenyl chloroformate and then reacted with prazosin to form p(HPG-prazosin carbamate) conjugate. Drug loading was 23.9% (w/w). Activated polymer and conjugates were characterized by infrared spectroscopy and differential scanning calorimetry. In vitro studies proceeded in pH 7.4 isotonic phosphate-buffered saline solution. Prazosin was released at a rate of 0.92 mg/day/100 mg conjugate from p(HPG-prazosin carbamate) particles. In vivo studies were performed with New Zealand White rabbits. P(HPG-prazosin carbamate) conjugate particles (100 mg) were suspended in 2 ml saline and injected subcutaneously into both flanks of rabbits. P(HPG-prazosin carbamate) conjugates, following an initial burst, demonstrated a nearly constant plasma prazosin concentration profile above 2 ng/ml, which was maintained for 10 days.

Animals↗
PubMed1991

Fractionation of cellulases from the ruminal fungus Neocallimastix frontalis EB188.

Cellulases from the ruminal fungus Neocallimastix frontalis EB188 were separated by using hydroxylapatite column chromatography. Seven carboxymethylcellulases, six avicelases, and four beta-glucosidases accounted for the majority of the activities. The separation of enzymes was confirmed by using polyacrylamide gel electrophoresis. Electrophoretic migration, analysis of hydrolysis products, and substrate specificity measurements suggested that several different cellulases were secreted in N. frontalis EB188. The possible relationship of cellulase diversity to protein glycosylation is discussed.

Animals↗
PubMed1991

Conformational epitope on gp120 important in CD4 binding and human immunodeficiency virus type 1 neutralization identified by a human monoclonal antibody.

A human monoclonal antibody designated 15e is reactive with the envelope glycoprotein (gp120) of multiple isolates of human immunodeficiency virus type 1 (HIV-1). Antibody 15e also neutralizes HIV-1 with broad specificity and blocks gp120 binding to CD4. Characterization of the 15e epitope shows that it is conformation dependent and is distinct from previously recognized functional domains of gp120, suggesting that this epitope represents a novel site important for HIV-1 neutralization and CD4 binding. These findings have implications for the development of a vaccine for AIDS.

Antibodies, Monoclonal↗
PubMed1991

[Determination of panaxadiol and panaxatriol in radix notoginseng and Yunnan baiyao by capillary supercritical fluid chromatography].

Capillary supercritical fluid chromatography (SFC) was developed for the determination of panaxadiol and panaxatriol in Radix notoginseng and Yunnan baiyao. 0.1g Radix notoginseng powder or 0.5g Yunnan baiyao was mixed with 10 ml 15% H2SO4 ethanol-water (1:1) solution, adding 1 mg cholesterol as internal standard. The mixture was refluxed for 4 h, then adding 15 ml 15% NaOH solution, refluxed for 0.5 h. The mixture was extracted 3 times with 10 ml portions of cyclohexane. The cyclohexane extracts were purified by partition column and concentrated by adsorption column and then analysed by SFC. The proposed method is sensitive, accurate, precise, simple and rapid; all the process can be done in 8 h.

Chromatography↗
PubMed1991

[Determination of ergosterol in Cordyceps sinensis and Cordyceps black-bone chicken capsules by HPLC].

A high performance liquid chromatographic method (HPLC) was developed for the determination of ergosterol in Cordyceps sinensis and Cordyceps black-bone chicken capsules. The sample was mixed with 0.5 ml of saturated KOH solution and 5 ml of ethanol, and refluxed for 1 h. The saponified mixture was diluted with 5 ml of 10% NACl solution and extracted 3 times with 5 ml portions of cyclohexane. The cyclohexane extracts were purified by partition column and concentrated by adsorption column and then analysed by HPLC. The other components of the Cordyceps black-bone chicken capsules have no interference to the determination of ergosterol. The proposed method is rapid, precise, accurate and sensitive. The whole process can be done in 2 h.

Ascomycota↗