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Biomedical subjects

L Chen

Publications and source records attributed to L Chen.

At least 883 records · Page 49Linked to original sources
PubMed1997

[Molecular characterization of genetic defects in hemophilia in Shanghai].

OBJECTIVE: To detect gene mutations in hemophilia A in Shanghai. METHODS: PCR, denaturing gradient gel electrophoresis (DGGE) and DNA sequencing were used. Fifty Chinese cases of hemophilia A without intron 22 inversion, including 24 severe, 9 moderate and 17 mild cases, were screened. Genomic DNA was amplified using GC-clamped primers covering all the exons and flanking intron regions, excluding the middle portion of extron 14 encoding the B domain, but including the thrombin cleavage sites at AA740 and 1689. The amplified GC-clamped PCR fragments were then electrophoresed on DGGE. The abnormal bands were sequenced. RESULTS: Eleven different mutations were identified, including 5 nonsense mutations, 5 missense mutations and one small deletion. Among them, 3 mutations, 466Lys (AAG)-Thr (ACG), 719Tyr (TAC)-Stop (TAG) and 312Ile (ATC)-xxC have not been reported before. CONCLUSION: Apart from intron 22 inversion, most gene mutations in hemophilia A were point mutations resulted from single base substitution. Generally the genetic defects correspond to the clinical manifestations.

Asian People↗
PubMed1997

[The combinations of separation modes in multidimensional high performance liquid chromatography (MDHPLC)].

MDHPLC is a new chromatographic technique, in which fractions from a separation system are selectively transferred to one or more secondary chromatographic systems with different separation mechanism to enhance resolution and sensitivity, or to decrease analysis times. In this review, the principle, characteristics and developments of MDHPLC are discussed. The various possible combinations of separation modes in HPLC [such as, size exclusion chromatography/reversed-phase chromatography (SEC/RPC), ion exchange chromatography/reversed-phase chromatography (IEC/RPC), normal bonded phase chromatography/reversed-phase chromatography (NPC/RPC), size exclusion chromatography/ion exchange chromatography (SEC/IEC), liquid-solid chromatography/reversed-phase chromatography (LSC/RPC), affinity chromatography/reversed-phase chromatography (AC/RPC) and achiral column/chiral column] and their applications are systematically reviewed with 63 references.

English Abstract↗
PubMed1997

[Determination of beta-carotene in Fructus lycii by nonaqueous reversed-phase high performance liquid chromatography].

A simple, rapid and accurate quantitative method was established for the determination of beta-carotene in Fructus lycii by isocratic nonaqueous RP-HPLC. Separation was obtained by using Shim-Pack CLC-ODS column (6 mm i.d. x 150 mm, 5 microm) and mobile phase of methanol/ethyl acetate (50:55, V/V) with flow rate of 1 mL/min. The eluates were monitored with UV/VIS detector at 448 nm. The retention time for beta-carotene was 7.33 min. The calibration curve was linear in the range of 1.0-5.0 mg/L with r=0.9998. The average recovery for beta-carotene was 97.1% with a coefficient of variation of 1.9%. The content of beta-carotene in Fructus lycii from different areas was also determined.

Chromatography, High Pressure Liquid↗
PubMed1997

[Brush-type chiral stationary phase for chiral resolution in high performance liquid chromatography].

A review is presented about brush-type chiral stationary phase in high performance liquid chromatography chiral resolution, dealing with design, synthesis and applications, of various brush-type chiral stationary phases (CSP). The advances of study of chiral recognition mechanism are introduced and the development trends of the brush-type chiral stationary phase in the future proposed. Eighty-four references are cited in this paper.

English Abstract↗
PubMed1997

[Identification of volatile compounds of hawthorn by gas chromatography/mass spectrometry (GC/MS)].

The volatile compounds of three cultivars of hawthorn were studied. Changko (Crataegus pinnatifida Bge.) hawthorn fruit was harvested after ripening from Hubei Province and those of Heihong and Dajinxing were from Shandong Province. The volatile compounds of each hawthorn cultivars were obtained by SDE (simultaneous distillation-extraction) equipment, by using CH2Cl2 as extracting solvent. The volatile extract was concentrated at 40-50 degrees C under vacuum to 0. 05mL or so and was ready for GC and GC/MS analysis. A DB-Wax fused silica capillary column (50m x 0.32mm i.d.; 1microm thickness) and a flame ionization detector (FID) was employed in GC analysis. The temperature program included of a 5 min isothermal period at 40 degrees C, temperature increases of 2 degrees C/min from 40 degrees C to 240 degrees C, and a 60 min isothermal period at 240 degrees C. Mass spectra were obtained by electron impact at 70eV and a source temperature of 250 degrees C. Thirty-two volatile compounds of the hawthorn fruit were identified, which comprised 61%-68% of the volatile fraction. The ten major components were cis-3-hexenol, cis-3-hexenyl acetate, alpha-terpineol, furfural, hexanol, hexyl acetate, nonanal, citral, 3-penten-2-one and trans-2-decenal. The molecular weight range of the major volatile fraction covers from C3 to C10. Both qualitative and quantitative differences in the volatile constituents among the three cultivars were not remarkable.

Crataegus↗
PubMed1997

[Analysis of hexamethylene bisacetamide in biological fluids and tissues by RP-HPLC].

This paper describes the analysis of anticancer drug hexamethylene bisacetamide (HMBA) in biological fluids and tissues by RP-HPLC. The samples of plasmas, urine and tissues from cancer mice and rabbits were first used with methanol for pretreatment to remove protein impurity, then analyzed by RP-HPLC on an ODS column. The mobile phase was methanol/water (70/30, V/V), UV detection is employed at 210 nm. 153 samples were analyzed and good results were obtained. The recoveries of 93.3%-104% with a relative standard deviation of 0.04%. The regression equation is: Y = 0.32X - 1.07, with a linear correlation coefficient of 0.998 and the linear range of HMBA is 0 to 1000 mg/L. A sample analysis can be completed within 13 minutes. This method could be satisfactorily applied not only for the analysis of HMBA but probably also for the analysis of other drugs in biological fluids and tissues.

Acetamides↗
PubMed1997

[Some considerations in the designed scheme of WLY100 sequential scanning ICP spectrometer].

The designed scheme of China made sequential scanning ICP spectrometer was described in this paper. The considerations of monochromater, RE generator, scanning machine, intensity measurement, the utility of far ultra vioiet region, the controlling of temperature and carrier ags flow, and the software were discussed detailly. A good designed seheme promoted the manufacturing and performed in short period.

English Abstract↗
PubMed1997

[Fluorescence spectra study on 2, 3, 7, 8-tetrachloro-n-ethyl-phenothiazine].

In this paper we gave been discussed the variation law of fluorescence intensity of 2, 3, 7, 8-tetracloro-N-ethyl-phenothazine under different conditions. The experimental results show the best emit light system of fluorescence. It has theoretical significance and practical value on raising seneitivity of organic photoconductor.

English Abstract↗
PubMed1997

[Study on fluorescence method of pefloxacin].

Pefloxacin is a new kind of antibiotic. In this paper, a sensitive fluorescence method has been developed for the analysis of Pefloxacin. It has stronger fluorescence excitation. The fluorescence of Pefloxacin was measured at excitation wavelength 282nm and emission wavelength 440nm. The method is highly sensitive with lower limit of detection, calibration curves were linear between 1 x 10(-9) - 1 x 10(-6)mol/L, with a regression coefficient of 0.9999. At the same time, recoveries of pefloxacin in Human serum Albumin and Urine are 95% and 105% respectively.

Anti-Infective Agents↗
PubMed1997

Growth hormone, insulin-like growth factor I, and motoneuron size.

In this study we asked whether growth hormone (GH) and one of its key mediators, insulin-like growth factor I (IGF-I), influence spinal motoneuron size in conjunction with whole body size. We present evidence that GH has such a role, possibly without the mediation of IGF-I. Both lumbar motoneuron and body size were found to be increased relative to littermate controls in transgenic mice overexpressing GH, while body size, but not motoneuron size, was increased in mice overexpressing IGF-I. GH overexpression coordinately increased nucleolar, nuclear, and cell body size in lumbar spinal motoneurons, so that their normal size relationships were preserved in the transgenic mice. In addition, spinal cord and brain weights were significantly increased in both types of transgenic animal. We conclude that GH can regulate motoneuron, central nervous system, and body size in the same animal, and that IGF-I can mimic the effects of GH on at least two of these three parameters.

Animals↗
PubMed1997

Oxidative modification of low density lipoprotein in normal and hyperlipidemic patients: effect of lysophosphatidylcholine composition on vascular relaxation.

The elevated level of plasma low density lipoprotein (LDL) in hyperlipidemic patients is an important risk factor for the production of atherosclerosis. Plasma LDL must be modified before it can produce an impairment of endothelium-dependent relaxation in aortic rings or enhancement of uptake by macrophages. The dramatic increase in lysophosphatidylcholine (lysoPC) content in oxidatively modified LDL has been touted as an important biochemical factor for the impairment of endothelium-dependent relaxation. The present study was designed to examine the lysoPC composition of oxidized LDL samples from normal and hyperlipidemic subjects, and their effects on the impairment of endothelium-dependent relaxation. Oxidatively modified LDL from hyperlipidemic patients contained a slightly higher level (17%) of lysoPC, but produced a disproportionately greater impairment of endothelium-dependent relaxation than that from normal subjects. As lysoPC is composed of many molecular species, its composition in oxidized LDL samples was analyzed. In hyperlipidemic patients, lysoPC samples were found to contain a higher proportion of long-chain acyl groups. Subsequent studies revealed that only long-chain lysoPC (C > 16:0) were effective in impairing endothelium-dependent relaxation. Experimental loading of oxidized LDL from normal subjects with long chain lysoPC to mimic levels observed in oxidized LDL from hyperlipidemic patients resulted in further impairment of endothelium-dependent relaxation. We conclude that the greater proportion of long-chain lysoPC found in the oxidized LDL of hyperlipidemic subjects is responsible for the increased impairment of endothelium-dependent vascular relaxation. We propose that the high level of LDL found in the plasma of hyperlipidemic patients, coupled with its enhanced ability to generate long chain species of lysoPC during oxidative modification, are important factors for the development of atherosclerosis in these patients.

Adult↗
PubMed1997

Coexpression of cytochrome P4502A6 and human NADPH-P450 oxidoreductase in the baculovirus system.

Heterologous expression using baculovirus vectors has become a popular method for the production of catalytically active cytochrome P450s (CYPs). We have systematically optimized the multiplicity of infection (MOI) for a coinfection approach for the coexpression of CYP2A6 (viral vector designated v2A6) and NADPH-P450 oxidoreductase (OR; viral vector designated vOR) using Sf9 insect cells. A 3000-fold range of MOI was examined in stationary culture and stirred suspension culture. Surprisingly, our results indicate that the best CYP2A6 catalytic activity (850-1300 pmol/ min/mg total lysate protein as measured by coumarin 7-hydroxylase activity) was obtained only when using a low MOI of v2A6 (1.5-3 x 10(-2)) and a vOR of 10- to 20-fold less. This activity was approximately 7- to 11-fold higher than the best activity obtained when infecting cells with v2A6 alone. At this level of coinfection, the P450 content ranged from 180 to 250 pmol/mg total lysate protein, and the NADPH cytochrome c reductase activity ranged from 350 to 520 nmol/min/mg total lysate protein. Increasing the MOI of both viruses to 50-fold higher resulted in lower overall activity with the optimum (250 pmol/min/mg total lysate protein) being seen earlier postinfection (60 vs. 72 hr). Increasing the MOI of vOR to levels comparable with those of v2A6, decreased coumarin 7-hydroxylase activity 14-fold. These results suggest that the best CYP2A6 catalytic activity depends on properly posttranslationally modified proteins accumulating in a right ratio as a result of primary, secondary, and possibly tertiary infection of both viruses. These results also suggest that high OR expression results in degradation of P450.

Animals↗
PubMed1997

Manipulation of T cell response to tumors by targeting on costimulatory pathway.

T cells require at least two signals to be fully activated: one is generated by interactions between antigen-specific receptor on T cell and peptide-MHC complexes on tumor cells and second signal is delivered by costimulatory molecules on antigen presenting cells to their counter-receptor on T cells. We demonstrated previously that expression of T cell costimulatory molecule B7-1, a counterreceptor for CD28, on tumors led to tumor regression in syngeneic mice. We have used retrovirus to transfer B7-1 into a variety of murine tumor lines to examine their ability to stimulate CTL in vivo and in vitro. Expression of B7 results in increased immunogenicity in immunogenic, but not poorly-immunogenic tumors, suggesting a deficiency of tumor cells on antigen presentation. We analyze tumor epitopes associated with MHC molecules by HPLC combining with specific CTL clones and the results indicate that many non-immunodominant epitopes do not normally induce a response unless B7 costimulation is provided. Furthermore, increased T cell receptor signaling, such as co-expression of CD2 ligand with B7-1, can convert some poorly-immunogenic tumours to become immunogenic. Our results indicate that deficiency on antigenic signaling in many tumors could be a quantitative phenomenon. Induction of T cell immunity by targeting on both antigen receptor and costimulatory pathway thus may be useful for cancer treatment.

Animals↗
PubMed1997

Further evidence of an association between attention-deficit/hyperactivity disorder and cigarette smoking. Findings from a high-risk sample of siblings.

The authors investigated the relationship between attention-deficit/hyperactivity disorder (ADHD) and cigarette smoking in siblings of ADHD and non-ADHD probands. They conducted a 4-year follow-up of siblings from ADHD and control-group families. In the siblings of ADHD probands, ADHD was associated with higher rates and earlier onset of cigarette smoking. There was also a significant positive association between cigarette smoking and conduct disorder, major depression, and drug abuse in the siblings, even after adjusting for confounding variables. Moreover, smoking was found to be familial among ADHD families but not control-group families. Our findings indicate that ADHD is a risk factor for early initiation of cigarette smoking in the high-risk siblings of ADHD probands.

Adolescent↗
PubMed1997

Anionic sites of charge barrier in the guinea pig crista ampullaris.

In present studies we obtained anionic sites in the epithelial and capillary basement membranes in the dark cell area of the crista ampullaris in the guinea pig. The immersion method with cationic tracer polyethyleneimine (PEI) was applied. Electronmicroscopically, the arrangement of PEI particles was observed as two strata along the basement membrane. The number of particles could be counted and compared in each portion. The control test with protamine sulfate showed that the number of PEI particles decreased in both the epithelium and capillaries of the dark cell area. In the experiment using furosemide, the stria vascularis and the dark cells had changed, with pathological findings of interstitial edema and PEI particles reduced in number. It is suggested that the PEI particles reflect different conditions of charge in the basement membrane, which influences the production or absorption of the inner ear fluid.

Absorption↗
PubMed1997

Absorption, distribution, elimination of tea polyphenols in rats.

Tea polyphenols-including (-)-epigallocatechin-3-gallate (EGCG), (-)-epigallocatechin (EGC), and (-)-epicatechin (EC)-are believed to be responsible for the beneficial effects of tea. This study was conducted to investigate the absorption, distribution, and elimination of EGCG, EGC, and EC in rats after administration of decaffeinated green tea (DGT). For comparison, pure EGCG was also studied. The plasma and tissue levels of EGCG, EGC, and EC were quantified by HPLC, and the results were analyzed by the PCNONLIN program. Following intravenous injection of DGT (25 mg/kg), the plasma concentration-time curves of EGCG, EGC, and EC were fitted in a two-compartment model. The beta-elimination half-lives (t1/2beta) were 212, 45, and 41 min for EGCG, EGC, and EC, respectively; the clearances were 2.0, 7.0, and 13.9 ml x min/kg, and the apparent distribution volumes (V(d)) were 1.5, 2.1, and 3.6 dl/kg. When pure EGCG (10 mg/kg) was given, however, a shorter t1/2beta (135 min), a larger clearance (72.5 ml x min/kg), and a larger V(d) (22.5 dl/kg) for EGCG were observed, suggesting that other components in DGT could affect the plasma concentration and elimination of EGCG. After intragastric administration of DGT (200 mg/kg), approximately 13.7% of EGC and 31.2% of EC were shown in the plasma, but only 0.1% of EGCG was bioavailable as judged by the ratio of AUC(i.g.)/AUC(i.v.). After intravenous administration of DGT (25 mg/kg), the level of EGCG was found to be the highest in the intestine samples, and the intestinal EGCG level declined with a t1/2 of 173 min. The highest levels of EGC and EC were observed in the kidney, and the levels declined rapidly with t1/2 of 29 and 28 min, respectively. The AUC of EGCG in the intestine was 4-fold higher than that in the kidney, but the AUCs of EGC and EC in the intestine were similar to those in the kidney. The liver and lung levels of EGCG, EGC, and EC were generally lower than those in the intestine and the kidney. The distribution results suggest that EGCG is mainly excreted through bile, and that EGC and EC are excreted through both the bile and urine.

Administration, Oral↗
PubMed1997

Proteinuria and tubulointerstitial injury.

These studies have demonstrated pathways whereby one urinary protein, holotransferrin, may alter proximal tubular cell function and cause tubular cytotoxicity, and at least two urinary proteins, albumin and transferrin, may mediate the development of interstitial inflammation in proteinuric renal disease.

Animals↗