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Biomedical subjects

H Shen

Publications and source records attributed to H Shen.

At least 235 records · Page 13Linked to original sources
PubMed1998

Color vision defects with variation in the exon 5 of red and green pigment genes.

PURPOSE: To investigate correlation of variation in the exon 5 of red and green pigment genes with color vision defects. METHODS: Exon 5 of the red and green pigment genes in 11 protans, 19 deutans and 38 normal controls were analyzed by heteroduplux-SSCP analysis. RESULTS: In all 11 protans and 8 of the 19 deutans, defects of the red or green pigment gene could be identified. The C polymorphism (A/C at codon 283) in green pigment gene was present in 8 of 44 trichromats and 5 of 24 dichromats. Specific electrophoretic bands were found in 2 normal controls and a deutan. CONCLUSIONS: Variation in the exon 5 of the red and green pigment genes is the most common cause for color vision defects. Heteroduplex-SSCP analysis is a suitable way in screening specific variation in visual pigment genes.

Chromosomes, Human, X↗
PubMed1998

[Analysis of synchronous and derivative synchronous fluorescence spectra of phenol and O-dihydroxybenzene].

In this paper, the analyses of the synchronous flourescence spectra of phenol and O-dihydroxybenzene by quasi-square linear dual combination of multiwavelength data dual-peak multiplication balance, multiwavelength linear regression, first and second order derivative technique are proposed. Five new methods for simultaneous determination of these compounds are constructed. The accuracies and recoveries of the proposed analytical methods are found to be satisfactory.

English Abstract↗
PubMed1998

[Determination of trace Fe in doxycycline hydrochloric acid by flame atomic absorption spectrophotometry].

This paper reports the development of the determination of trace metal Fe in doxycycline hydrochloric acid by flame atomic absorption spectrophotometry. The method is convenient to determine elements in doxycycline hydrochloric acid. The results show that the method offers good precision and accuracy. The relative standard deviation for Fe was 0.54% and the rate of recovery was 99.2%.

Calibration↗
PubMed1997

Monitoring of met-enkephalin in vivo with 5-min temporal resolution using microdialysis sampling and capillary liquid chromatography with electrochemical detection.

A method based on microdialysis sampling and capillary liquid chromatography with electrochemical detection that allows in vivo monitoring of met-enkephalin with 5-min temporal resolution is described. Sampling was achieved using a concentric microdialysis probe made from polycarbonate membrane material with a 20 kDa cut-off. This probe had an in vitro relative recovery for met-enkephalin of 63% at a dialysis flow-rate of 0.6 microl/min. Separations were performed using 7 cm x 25 microm I.D. fused-silica capillary columns packed with 5 microm Alltima C18 particles. A carbon fiber microelectrode was used as the detector electrode. The mass detection limit for met-enkephalin with this system was 40 amol. With on-column preconcentration, up to 2 microl of sample could be loaded onto the column resulting in concentration detection limits as low as 20 pM for met-enkephalin. Direct injection of dialysate, collected at 5-min intervals, allowed determination of met-enkephalin concentrations in the rat globus pallidus under basal and K+-induced depolarization conditions.

Animals↗
PubMed1997

Chicken transcription factor AP-2: cloning, expression and its role in outgrowth of facial prominences and limb buds.

Embryonic facial development in chick embryos involves a sequential activation of genes that control differential growth and patterning of the beak. In the present study we isolate one such gene, the transcription factor, AP-2, that is known to be expressed in the face of mouse embryos. The protein sequence of chick AP-2alpha is 94% homologous to human and mouse AP-2. Wholemount in situ hybridization with a probe for chick AP-2 identifies expression from primitive streak stages up to stage 28. The most striking expression patterns in the head are during neural crest cell migration when AP-2 transcripts follow closely the tracts previously mapped for neural crest cells. Later, expression in the facial mesenchyme is strongest in the frontonasal mass and lateral nasal prominences and is downregulated in the maxillary and mandibular prominences. Once limb buds are visible, high expression is seen in the distal mesenchyme but not in the apical ectodermal ridge. The expression patterns of AP-2 in stage 20 embryos suggested that the gene may be important in "budding out" of facial prominences and limb buds. We implanted beads soaked in retinoic acid in the right nasal pit of stage 20 embryos resulting in a specific inhibition of outgrowth of the frontonasal mass and lateral nasal prominences. AP-2 expression was completely down-regulated in the lateral nasal within 8 hr of bead application. In addition, the normal up-regulation of AP-2 in the frontonasal mass did not occur following retinoic-acid treatment. There was an increase in programmed cell death around the right nasal pit that accompanied the down-regulation of AP-2. Prominences whose morphogenesis were not affected by retinoic acid did not have altered expression patterns. We removed the apical ectodermal ridge in stage 20 limb buds and found that AP-2 expression was partially downregulated 4 hr following ridge removal and completely downregulated 8 hr following stripping. Application of an FGF-4 soaked bead to the apex of the limb bud maintained AP-2 expression. Thus AP-2 is involved in outgrowth and could be regulated by factors such as FGFs that are present in the ectoderm of both the face and limb.

Amino Acid Sequence↗
PubMed1997

Role of neural cell adhesion molecule and polysialic acid in mouse circadian clock function.

The suprachiasmatic nuclei (SCN) express the highly polysialylated form of the neural cell adhesion molecule (NCAM) that has been proposed to promote plasticity in the adult brain. To investigate a role for NCAM in SCN circadian clock function, we examined the daily locomotor rhythm of mice homozygous for a mutation, Ncamtm1Cwr, which results in deletion of the NCAM-180 isoform that in brain carries polysialic acid (PSA). Mutant mice entrained well to a 12 hr light/dark cycle but exhibited a significantly shortened free-running period and longer activity duration under constant darkness (DD) than did wild-type mice. By the third week of DD treatment, circadian rhythmicity in the mutant was abolished. Immunocytochemical analyses of the mutant SCN revealed an abnormal number and distribution of vasoactive intestinal polypeptide-producing neurons, suggesting a developmental effect of the mutant phenotype; however, a direct physiological effect of the mutation on clock function was indicated by the fact that removal of PSA from adult wild-type SCN by microinjection of endoneuraminidase shortened the free-running period to a similar extent as in the mutant. Together, these data indicate critical roles for NCAM and PSA in the development and physiology of the mammalian SCN circadian clock.

Animals↗
PubMed1997

Retinyl ester hydrolysis and retinol efflux from BFC-1beta adipocytes.

Adipose tissue is an important storage depot for retinol, but there are no data regarding retinol mobilization from adipose stores. To address this, dibutyryl cAMP was provided to murine BFC-1beta adipocytes and its effects on retinol efflux assessed. High performance liquid chromatography analysis of retinol and retinyl esters in adipocytes and media indicated that cAMP stimulated, in a time- and dose-dependent manner, retinol accumulation in the culture media and decreased cellular retinyl ester concentrations. Study of adipocyte retinol-binding protein synthesis and secretion indicated that cAMP-stimulated retinol efflux into the media did not result from increased retinol-retinol-binding protein secretion but was dependent on the presence of fetal bovine serum in the culture media. Since our data suggested that retinyl esters can be hydrolyzed by a cAMP-dependent enzyme like hormone-sensitive lipase (HSL), in separate studies, we purified a HSL-containing fraction from BFC-1beta adipocytes and demonstrated that it catalyzed retinyl palmitate hydrolysis. Homogenates of Chinese hamster ovary cells overexpressing HSL catalyzed retinyl palmitate hydrolysis in a time-, protein-, and substrate-dependent manner, with an apparent Km for retinyl palmitate of 161 microM, whereas homogenates from control Chinese hamster ovary cells did not.

Adipocytes↗
PubMed1997

Regulation of phospholipid biosynthetic enzymes by the level of CDP-diacylglycerol synthase activity.

Amine-containing phospholipid synthesis in Saccharomyces cerevisiae starts with the conversion of CDP-diacylglycerol (CDP-DAG) and serine to phosphatidylserine (PS), whereas phosphatidylinositol (PI) is formed from CDP-DAG and inositol (derived from inositol 1-phosphate). In this study the regulation of PS synthase (encoded by CHO1/PSS), PI synthase (encoded by PIS1), and inositol 1-phosphate synthase (encoded by INO1) activities by the in vivo level of CDP-DAG synthase activity (encoded by CDS1) is described. Reduction in the level of CDP-DAG synthase activity from 10-fold over wild type levels to 10% of wild type levels results in a 7-fold increase in PS synthase activity, which follows a similar change in the CHO1/PSS mRNA level. INO1 mRNA also increases but only after CDP-DAG synthase activity falls below the wild type level. PI synthase activity follows the decrease of the CDP-DAG synthase activity, but there is no parallel change in the level of PIS1 mRNA. These changes in CHO1/PSS and INO1 mRNA levels are mediated by a mechanism not dependent on changes in the expression of the INO2-OPI1 regulatory genes. CDS1 expression is repressed in concert with INO2 expression in response to inositol.

CDP-Diacylglycerol-Inositol 3-Phosphatidyltransfer↗
PubMed1997

Role of the multiple T cell receptor (TCR)-zeta chain signaling motifs in selection of the T cell repertoire.

Immature thymocytes undergo a selection process within the thymus based on their T cell antigen receptor (TCR) specificity that results either in their maturation into functionally competent, self-MHC-restricted T cells (positive selection) or their deletion (negative selection). The outcome of thymocyte selection is thought to be controlled by signals transduced by the TCR that vary in relation to the avidity of the TCR-ligand interaction. The TCR is composed of four distinct signal transducing subunits (CD3-gamma, -delta, -epsilon, and zeta) that contain either one (CD3-gamma, -delta, -epsilon) or three (-zeta) signaling motifs (ITAMs) within their intracytoplasmic domains. A possible function for multiple TCR ITAMs could be to amplify signals generated by the TCR during selection. To determine the importance of the multiple TCR-zeta chain ITAMs in thymocyte selection, transgenes encoding alpha/beta TCRs with known specificity were bred into mice in which zeta chains lacking one or more ITAMs had been genetically substituted for endogenous zeta. A direct relationship was observed between the number of zeta chain ITAMs within the TCR complex and the efficiency of both positive and negative selection. These results reveal a role for multiple TCR ITAMs in thymocyte selection and identify a function for TCR signal amplification in formation of the T cell repertoire.

Animals↗
PubMed1997

Dual microcolumn immunoassay applied to determination of insulin secretion from single islets of Langerhans and insulin in serum.

A dual microcolumn immunoassay (DMIA) was developed and applied to determination of insulin in biological samples. The DMIA utilized a protein G capillary column (150 microns I.D.) with covalently attached anti-insulin to selectively capture and concentrate insulins in a sample. Insulins retained in the capillary immunoaffinity column were desorbed and injected onto a reversed-phase capillary column (150 microns I.D.) for further separation from interferences such as cross-reactive antigens and non-specifically adsorbed sample components. Bovine, porcine and rat insulin all cross-reacted with the antibody and could be determined simultaneously. Using a UV absorbance detector, the dual microcolumn system had a detection limit of 10 fmol or 20 pM for 500-microliter sample volumes. The DMIA system was used to measure glucose-stimulated insulin secretion from single rat islets of Langerhans. Because of the separation in the second dimension, both rat I and rat II insulin could be independently determined. The system was also evaluated for determination of insulin in serum. Using microcolumns instead of conventional HPLC columns resulted in several advantages including use of less chromatographic material and improved mass detection limit.

Animals↗
PubMed1997

Idiopathic torsion dystonia linked to chromosome 8 in two Mennonite families.

The DYT1 locus on chromosome 9q34 is responsible for most childhood limb-onset idiopathic torsion dystonia (ITD). Linkage to DYT1 has been excluded in families with adult-onset, and predominantly cranial-cervical, ITD. We mapped a locus (DYT6) associated with prominent cranial-cervical ITD in two large Mennonite families to chromosome 8. An identical haplotype spanning 40-cM segregates with ITD in these families, suggesting a shared mutation from the recent past.

Adolescent↗
PubMed1997

Model systems for modulating the free energy of ATP hydrolysis in normoxically perfused rat hearts.

This study has two objectives; first, to develop perfusion conditions that decrease the free energy of ATP hydrolysis, Delta GATP, in isolated hearts; and, second, to modulate the Delta GATP in these perfused hear models. To accomplish the first goal, a series of inhibitors was employed to restrict acetyl-CoA oxidation. The second goal was accomplished by increasing work demand. Rat hearts were perfused with Krebs-Henseleit solution containing glucose and either; (i) no inhibitors (G group hearts); (ii) 0.3 mm bromo-octanoate (BrO), an inhibitor of beta-oxidation (GB group); (iii) 0.4 mm amino-oxyacetate (AOA), an inhibitor of the malate-aspartate shuttle (GA group); (iv) BrO and AOA (GBA group hearts); or (v) BrO, AOA, and 4 mm butyrate, an alternate substrate (GBA-Bu). Pacing hearts at 300 beats per min (beats/min), at 450 beats/min, and at 450 beats/min in the presence of 80 microgram/l dobutamine allowed three increasing levels of work demand to be attained. The Delta GATP values of the five groups of hearts were calculated for each workstate using the concentrations of high energy phosphate metabolites measured by 31P NMR spectroscopy. At the highest levels of workload demand, the G, GB, and GBA-Bu group hearts had Delta GATP values >/=-53 kJ/mol ATP. At the highest levels of workload demand, the GA and GBA hearts had Delta GATP values </=-49 kJ/mol ATP. The values of Delta GATP and the heart work output during any perfusion conditions were stable for periods of >20 min. The G, GB, and GBA-Bu hearts attained RPPs of >/=54x10(3) mmHg/min at the highest levels of workload demand. The GA and GBA hearts attained RPPs of </=30x10(3) mmHg/min at the highest levels of workload demand. This study establishes stable, non-ischemic, isolated perfused heart preparations with which Delta GATP can be easily varied across the physiological relevant range of -56 to -47 kJ/mol ATP.

Adenosine Triphosphate↗
PubMed1997

Isolation and expression of an isoform of human CDP-diacylglycerol synthase cDNA.

Phosphatidic acid (PA) is a phospholipid involved in signal transduction and in glycerolipid biosynthesis. CDP-diacylglycerol synthase (CDS) or CTP:phosphatidate cytidylyltransferase (EC 2.7.7.41) catalyzes the conversion of PA to CDP-diacylglycerol (CDP-DAG), an important precursor for the synthesis of phosphatidylinositol, phosphatidylglycerol, and cardiolipin. We describe in this study the isolation and characterization of a human cDNA clone that encodes amino acid sequences homologous to Escherichia coli, yeast, and Drosophila CDS sequences. Expression of this human cDNA under the control of a GAL1 promoter in a null cds1 mutant yeast strain complements its growth defect and produces CDS activity when induced with galactose. Transfection of this cDNA into mammalian cells leads to increased CDS activity in cell-free extracts using an in vitro assay that measures the conversion of [alpha-32P]CTP to [32P]CDP-DAG. This increase in CDS activity also leads to increased secretion of tumor necrosis factor-alpha and interleukin-6 from endothelial ECV304 cells upon stimulation with interleukin-1beta, suggesting that CDS overexpression may amplify cellular signaling responses from cytokines.

Amino Acid Sequence↗
PubMed1997

Predicting medical students' academic performances by their cognitive abilities and personality characteristics.

PURPOSE: To utilize multiple regression analyses with both linear and quadratic models to explore and confirm the relationships among students' cognitive abilities, personality traits, and medical school performances at the University of Los Angeles, California, UCLA School of Medicine. METHOD: Ninety-seven "not-disadvantaged" students' pre-medical grade-point averages (GPAs), Medical College Admission Test (MCAT) scores, and personality traits as measured by the Comrey Personality Scales (administered at their application to medical school in 1985) were used to predict their medical school performances according to several criteria. "Disadvantaged" students were excluded from the study because their poor performances on all criteria would confound the relationships of personality, cognitive ability, and performance. RESULTS: The MCAT score was a strong predictor of medical school performances, particularly those criteria measured by medical school GPAs and the National Board of Medical Examiners examination scores, but its predictive power dropped sharply when clinical performance and personal suitability were part of the performance evaluation. Specific personality traits not only strengthened the predictive power of cognitive and personality variables jointly, they became the primary predictors of clinical performance and personal suitability. A single personality-profile index failed to show any power of prediction. As expected, quadratic relationships were found between some personality traits and some medical school performance measures. CONCLUSION: According to these data it is not realistic to use one or two personality traits to predict personal suitability on all medical performance measures. The multiple regression analysis results indicate that different personality characteristics are incorporated in different types of medical performances, which is perhaps why the overall personality-profile score failed to predict any of the studied criteria. Because of the study's relatively small sample size, however, cross-validation studies are necessary to confirm these findings.

Clinical Competence↗
PubMed1997

Recombinant Listeria monocytogenes as a live vaccine vehicle and a probe for studying cell-mediated immunity.

The ability of Listeria monocytogenes (L. monocytogenes) to enter the cytosol of host cells allows secreted proteins to efficiently enter the endogenous antigen-processing pathway leading to presentation by MHC class I molecules. L. monocytogenes has recently been exploited as a live vaccine vehicle for the induction of immunological memory against heterologous antigens. We have established a genetic system for site-specific integration of antigen expression cassettes into the Listeria genome which allows regulated expression and secretion of heterologous proteins. The ability of recombinant strains to stimulate long-term immunological memory and CD8+ T-cell-mediated protective immunity was investigated using the lymphocytic choriomeningitis virus (LCMV) murine infection model. Vaccination of mice with recombinant Listeria strains expressing LCMV antigens induced LCMV-specific CD8+ T cells which protected mice against LCMV challenge. We have also used a cottontail rabbit papillomavirus model to test the ability of recombinant Listeria strains to stimulate protective antitumor immunity in domestic rabbits. These studies have demonstrated the protective efficacy of recombinant L. monocytogenes vaccines and have established an experimental system for systematic analysis of cytotoxic T-cell induction by an intracellular bacterium.

Animals↗
PubMed1997

Recombinant Listeria monocytogenes vaccination eliminates papillomavirus-induced tumors and prevents papilloma formation from viral DNA.

Listeria monocytogenes is a gram-positive, facultative intracellular bacterium that enters the cytoplasm of infected cells and spreads directly into neighboring cells without encountering the extracellular environment. Cytoplasmic L. monocytogenes efficiently presents secreted proteins to the major histocompatibility complex class I pathway which can stimulate protective T-cell-mediated immune responses. We have used a cottontail rabbit papillomavirus (CRPV) rabbit model to test the ability of recombinant L. monocytogenes strains secreting the viral E1 protein (E1-rLm) to protect outbred rabbits against CRPV- and CRPV DNA-induced tumors. CRPV infection of outbred rabbits serves as a model for oncogenic papillomaviruses since CRPV-induced papillomas progress with high frequency to malignant carcinoma. Rabbits were vaccinated with wild-type L. monocytogenes or E1-rLm and then challenged with CRPV or viral DNA. In contrast to 0% papilloma regression in control animals, 77% of E1-rLm-vaccinated rabbits generated protective immunity that controlled and induced complete regression of tumors induced by CRPV. Latent viral DNA was not detected at 71% of the papilloma regression sites examined 4.5 months postregression. E1-rLm responder rabbits were completely resistant to papilloma formation from viral DNA. In contrast to controls, peripheral blood mononuclear cells from E1-rLm responder rabbits were able to proliferate in response to in vitro E1 stimulation. These results indicate that E1-rLm immunization generated a systemic anti-CRPV E1 cell-mediated immune response which protected outbred rabbits from tumors induced by CRPV or CRPV DNA challenge.

Animals↗
PubMed1997

Undetermined manner of death. A comparison with unintentional injury, suicide, and homicide death.

Injury deaths can be grouped into four general categories: accident, homicide, suicide, and undetermined. The present study investigates the use of the "undetermined" category. External cause of death, as well as demographic and other variables, were abstracted from death certificates of the 386,936 Californians who died of an injury between 1969 and 1991. Differences among the four manner-of-death groups were examined, and characteristics of the decedent and the injury event were used to predict a classification of undetermined. Coroners classified 1.9% of the deaths as undetermined in manner. Deaths of women, Blacks, Asians, and Native Americans; the very young and the middle aged; or those involving poisoning or submersion were most likely to be classified as undetermined. Acknowledging that individual coroner judgment may not be free of bias, these findings can help provide a better estimate of the frequency and the epidemiologic features of injury deaths that are assigned to the category of undetermined.

Accidents↗