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Biomedical subjects

X Hu

Publications and source records attributed to X Hu.

At least 397 records · Page 22Linked to original sources
PubMed1995

Predicting the structure of the light-harvesting complex II of Rhodospirillum molischianum.

We attempted to predict through computer modeling the structure of the light-harvesting complex II (LH-II) of Rhodospirillum molischianum, before the impending publication of the structure of a homologous protein solved by means of X-ray diffraction. The protein studied is an integral membrane protein of 16 independent polypeptides, 8 alpha-apoproteins and 8 beta-apoproteins, which aggregate and bind to 24 bacteriochlorophyll-a's and 12 lycopenes. Available diffraction data of a crystal of the protein, which could not be phased due to a lack of heavy metal derivatives, served to test the predicted structure, guiding the search. In order to determine the secondary structure, hydropathy analysis was performed to identify the putative transmembrane segments and multiple sequence alignment propensity analyses were used to pinpoint the exact sites of the 20-residue-long transmembrane segment and the 4-residue-long terminal sequence at both ends, which were independently verified and improved by homology modeling. A consensus assignment for the secondary structure was derived from a combination of all the prediction methods used. Three-dimensional structures for the alpha- and the beta-apoprotein were built by comparative modeling. The resulting tertiary structures are combined, using X-PLOR, into an alpha beta dimer pair with bacteriochlorophyll-a's attached under constraints provided by site-directed mutagenesis and spectral data. The alpha beta dimer pairs were then aggregated into a quaternary structure through further molecular dynamics simulations and energy minimization. The structure of LH-II so determined is an octamer of alpha beta heterodimers forming a ring with a diameter of 70 A.

Amino Acid Sequence↗
PubMed1995

Three-dimensional structure prediction of the NAD binding site of proton-pumping transhydrogenase from Escherichia coli.

A three-dimensional structure of the NAD site of Escherichia coli transhydrogenase has been predicted. The model is based on analysis of conserved residues among the transhydrogenases from five different sources, homologies with enzymes using NAD as cofactors or substrates, hydrophilicity profiles, and secondary structure predictions. The present model supports the hypothesis that there is one binding site, located relatively close to the N-terminus of the alpha-subunit. The proposed structure spans residues alpha 145 to alpha 287, and it includes five beta-strands and five alpha-helices oriented in a typical open twisted alpha/beta conformation. The amino acid sequence following the GXGXXG dinucleotide binding consensus sequence (residues alpha 172 to alpha 177) correlates exactly to a typical fingerprint region for ADP binding beta alpha beta folds in dinucleotide binding enzymes. In the model, aspartic acid alpha 195 forms hydrogen bonds to one or both hydroxyl groups on the adenosine ribose sugar moiety. Threonine alpha 196 and alanine alpha 256, located at the end of beta B and beta D, respectively, create a hydrophobic sandwich with the adenine part of NAD buried inside. The nicotinamide part is located in a hydrophobic cleft between alpha A and beta E. Mutagenesis work has been carried out in order to test the predicted model and to determine whether residues within this domain are important for proton pumping directly. All data support the predicted structure, and no residue crucial for proton pumping was detected. Since no three-dimensional structure of transhydrogenase has been solved, a well based tertiary structure prediction is of great value for further experimental design in trying to elucidate the mechanism of the energy-linked proton pump.

Amino Acid Sequence↗
PubMed1995

Functional MRI of brain during breath holding at 4 T.

Both theoretical considerations and animal experiments predict increased signal intensity in brain cortex on T2*-weighted images that develops over a breath hold period. This has not been observed in recent human studies performed at 1.0 and 1.5 T. To clarify this inconsistency, we undertook a study in normal volunteers at 4.0 T. Unlike the earlier studies, we observed a 3-10% signal intensity increase in the gray matter. Possible reasons for the discrepant results are discussed. We conclude that regional cerebral hemodynamics are observable by fMRI in man and this may have clinical applications.

Artifacts↗
PubMed1995

Tissue-regulated differentiation and maturation of a v-abl-immortalized mast cell-committed progenitor.

An immature v-abl-transformed mast cell line (V3-MC) was derived from a mouse that developed systemic mastocytosis after transplantation of v-abl-infected bone marrow cells. V3-MCs injected intravenously into adult BALB/c mice infiltrated the liver, spleen, and intestine by day 6 and underwent progressive differentiation and maturation, eventually resembling indigenous mast cells. In terms of their protease content, the V3-MCs that localized in the liver and spleen differed from those in the intestine, and both differed from the cultured V3-MCs. The acquired expression of certain proteases and the loss of expression of other proteases in these tissue V3-MCs defines particular phenotypes and indicates that the differentiation and maturation of mast cell-committed progenitor cells are primarily regulated by factors in the different tissue microenvironments.

Animals↗
PubMed1995

A measurement-theoretic analysis of the fuzzy logic model of perception.

The fuzzy logic model of perception (FLMP) is analyzed from a measurement-theoretic perspective. FLMP has an impressive history of fitting factorial data, suggesting that its probabilistic form is valid. The authors raise questions about the underlying processing assumptions of FLMP. Although FLMP parameters are interpreted as fuzzy logic truth values, the authors demonstrate that for several factorial designs widely used in choice experiments, most desirable fuzzy truth value properties fail to hold under permissible rescalings, suggesting that the fuzzy logic interpretation may be unwarranted. The authors show that FLMP's choice rule is equivalent to a version of G. Rasch's (1960) item response theory model, and the nature of FLMP measurement scales is transparent when stated in this form. Statistical inference theory exists for the Rasch model and its equivalent forms. In fact, FLMP can be reparameterized as a simple 2-category logit model, thereby facilitating interpretation of its measurement scales and allowing access to commercially available software for performing statistical inference.

Attention↗
PubMed1995

Cytokine-containing liposomes as adjuvants for HIV subunit vaccines.

Dehydration-rehydration liposome vesicles (DRVs) containing various cytokines were evaluated for their ability to induce delayed-type hypersensitivity (DTH) and humoral immunity to the recombinant envelope protein rgp120 of the MN strain of human immunodeficiency virus type 1 (HIV-1). The DRVs trapped approximately 25% of the radiolabeled cytokines and approximately 17% of the radiolabeled rgp120 that were added. The level of trapping was greater than the aqueous volume of the DRVs, indicating association of the proteins with the lipid bilayer. Flow cytometric analysis using antibody to rgp120 or the V3 loop of rgp120 showed the diameter of the DRVs to be 2-7.5 microns. Transmission electron microscopy confirmed the heterogeneity in size of the DRVs and revealed morphological heterogeneity. Transmission electron microscopy with immunogold labeling also revealed the presence of rgp120 on the surface of the DRVs. In vitro bioassays demonstrated slow leakage of biologically active cytokines from DRVs soaked in tissue culture medium containing serum. Mice injected subcutaneously three times at 14-day intervals with DRVs containing 15 micrograms of rgp120 plus interleukin 6 (IL-6) or interferon gamma (IFN-gamma) produced significantly greater DTH responses than mice injected with DRVs containing rgp120 alone. Soluble rgp120 plus soluble IFN-gamma produced DTH in some experiments, but of lower magnitude than the comparable DRVs. Interleukin 6, but not IFN-gamma, increased the antibody titer to rgp120 when included in the DRVs. The mice did not develop antibodies to IFN-gamma or IL-6. Induction of DTH by vaccines may increase protection from viral pathogens such as HIV. Cytokine-containing liposomes may be an effective adjuvant for the induction of a DTH response to envelope-antigen subunit vaccines.

Adjuvants, Pharmaceutic↗
PubMed1995

Persistence of replication-deficient adenovirus-mediated gene transfer in lungs of immune-deficient (nu/nu) mice.

To evaluate the role of cell-mediated immunity during gene transfer to the respiratory epithelium, the time course of luciferase activity was assessed after intratracheal administration of Av1Luc1, an E1a-E3-deleted adenoviral (Ad5) vector expressing firefly luciferase, to FVB/N, BALB/c and BALB/c-nu/nu adult mice. Adenovirus-mediated luciferase activity was rapidly lost from the respiratory tract between 2 and 14 days after treatment of both FVB/N and BALB/c wild-type mice. In the wild-type mice, loss of luciferase activity was associated with an early inflammatory response consisting of infiltration with macrophages and polymorphonuclear leukocytes and a more prolonged response characterized by lymphocytic infiltration. In the immune-deficient nu/nu mice, luciferase activity was maintained at higher levels than in immune-competent mice after exposure to virus and was associated with a distinct pattern of inflammation, consisting primarily of macrophages and polymorphonuclear cells but lacking the lymphocytic infiltrates typical of the inflammation in wild-type mice. Adenoviral DNA was rapidly cleared from the lungs of both nu/nu and wild-type mice. Markedly increased expression of proliferating cell nuclear antigen (PCNA) was observed in bronchiolar and alveolar epithelial cells and in inflammatory cells after exposure to Av1LUc1. The proliferative response of the respiratory epithelium was more extensive and persistent in wild-type than in nu/nu mice. To assess further the impact of the immune system on adenovirus-mediated gene expression, cotton rats treated with cyclosporin A or dexamethasone were exposed to Av1Luc1. Both agents decreased lung inflammation and significantly increased lung luciferase activity. The loss of lung luciferase activity is dependent, in part, on the immune-mediated clearance of respiratory epithelial cells, which may limit the extent and duration of gene expression with recombinant adenoviral vectors.

Adenoviridae Infections↗
PubMed1995

Molecular analysis of scabrous mutant alleles from Drosophila melanogaster indicates a secreted protein with two functional domains.

Mutations at the scabrous locus (sca) affect cell-cell signaling during neural development. Twenty-one mutant alleles of scabrous have been analyzed. Many synthesize no sca protein. In others, a defective protein is arrested intracellularly. Two mutants in which protein is not arrested must affect sca protein function outside the cell. Both affect the fibrinogen related domain (FReD), a 200-amino acid segment conserved in fibrinogen, tenascins, and other proteins. In fibrinogen, this region is involved in protein interactions and is altered in human mutations affecting blood clotting. In sca(UM2), an invariant Asp residue is replaced by Asn. In sca(MSKF) allele has dominant negative properties, indicating that the truncated amino-terminal portion interferes with the function of so me other gene product. These mutations show that the conserved FReD is essential for wild-type sca function, but suggest that the amino-terminal domain also interacts with other proteins, but other neural mutations were without effect. Models for the role of a two-domain protein in neural development are discussed.

Alleles↗
PubMed1995

Typing Neisseria meningitidis by analysis of restriction fragment length polymorphisms in the gene encoding the class 1 outer membrane protein: application to assessment of epidemics throughout the last 4 decades in China.

A typing method was developed for Neisseria meningitidis serogroup A by analysis of restriction fragment length polymorphisms (RFLP) of the class 1 outer membrane protein gene (porA). By using appropriate primers, an approximately 1,116-bp fragment of the porA gene was amplified by PCR and then was digested with the restriction endonuclease MspI. The digestion products were separated on 10% polyacrylamide gels and were stained with silver. One hundred three clinical isolates of group A N. meningitidis from 17 provinces of China collected over a 26-year period were analyzed. Results of MspI-generated RFLP profiles of PCR-amplified porA genes were compared with those obtained by conventional serosubtyping. There was a band of about 400 bp common to all strains examined, and the 103 strains of serogroup A resulted in 22 unique RFLP patterns. The differences in bands could be observed mainly in the range of 120 to 280 bp. The smaller fragments were useful in distinguishing meningococci with the same serosubtype. Three epidemic periods were characterized by the presence of three distinct genotypes (a1, a2, and a3), accounting for 74.5% of the strains examined (3.88, 26.21, and 44.66%, respectively). Three predominant RFLP patterns were correlated epidemiologically with cycles of epidemic meningococcal meningitis and were well-matched to the predominant serosubtypes (P1.9, P1.7, 10, and P1.9) that presented at the same prevalence cycles. The genotyping yielded information that allowed strains from one epidemic to be distinguished from those from another that would have been indistinguishable if only serotyping and serosubtyping were available. Therefore, the PCR-RFLP typing method was very useful in the epidemiologic investigation of group A meningococcal meningitis.

Antibodies, Monoclonal↗
PubMed1995

Dysregulation of interleukin-6 responses in ectopic endometrial stromal cells: correlation with decreased soluble receptor levels in peritoneal fluid of women with endometriosis.

Endometriosis (EM) is characterized by the aberrant growth of endometrial cells at sites outside the uterus. We showed previously that peritoneal leukocyte interleukin-6 (IL-6) production is altered in women with EM relative to that in normal control women. Because studies suggest that IL-6 may be growth regulatory for endometrial cells, we examined IL-6 and IL-6 soluble receptor (IL-6sR) in the peritoneal fluid of 40 women. In addition, the growth responsiveness of ectopic endometrial stromal cells to IL-6 was evaluated. The severity of EM correlated with increased levels of IL-6 accompanied by decreased IL-6sR in peritoneal fluid (controls, 1.0 +/- 0.1 and 525.4 +/- 53; stage I-II EM, 1.4 +/- 0.2 and 274.6 +/- 26; stage III-IV EM, 19.3 +/- 4.6 and 319.4 +/- 26; adhesions, 1.9 +/- 0.4 and 324.7 +/- 26 pmol/L IL-6 and IL-6sR, respectively). Additional studies revealed that unstimulated endometrial stromal cells from ectopic implants secreted this cytokine in vitro. Furthermore, these cells were resistant to growth inhibition induced by exposure to additional IL-6; this response correlated with weak expression of IL-6 receptor. Taken together, these findings lend further support to the hypothesis that dysregulation of IL-6 responses plays a role in the pathophysiology of EM.

Adolescent↗
PubMed1995

Functional magnetic resonance imaging as a management tool for cerebral arteriovenous malformations.

The location of eloquent cortex, such as the motor strip, the visual cortex, or Broca's area, may be difficult to predict even with multiprojectional magnetic resonance imaging (MRI). Distortion and displacement of this cortex may occur with a congenital lesion, such as an arteriovenous malformation, or by an acquired disease, such as a neoplasm. A desire to avoid damaging these eloquent areas by conventional surgery, radiosurgery, or endovascular surgery makes their accurate identification an important part of the pretherapeutic planning process. Blood oxygen level dependent functional MRI is a technique that uses the local increase of oxyhemoglobin concentration in the patient that occurs as a result of the increase in flow rate and blood volume in eloquent cortex undergoing stimulation from, for example, flashing lights, hand movements, or speech. We have used the blood oxygen level dependent technique to localize eloquent cortex relative to arteriovenous malformations and tumors. Using a 4.0-T magnetic resonance (MR) system, there is a sufficiently high degree of spatial resolution of the MR signal intensity changes during stimulation to allow the identification of eloquent cortex. Alternative, non-MR, invasive techniques for functional localization include electrocorticography and stimulation from subdural grids and strips. Noninvasive, non-MR technologies, such as positron emission tomography and magnetoencephalography, can also provide functional localization of eloquent cortex. However, the perfection of functional MRI at the 1.5-T field strength and the large number of such MR systems in operation mean that a highly accurate cerebral cortical localization technique can be available to most neuroscientists without the need to purchase alternative expensive technology.

Adult↗
PubMed1995

Evaluation of a subsidy program to increase bicycle helmet use by children of low-income families.

OBJECTIVE: We have previously shown that an educational program was not effective in increasing bicycle helmet use in children of low-income families. The objective of this study was to evaluate a combined educational and helmet subsidy program in the same population, while controlling for secular trends. The secondary objective was to complete a third year of surveying children's bicycle helmet use throughout the study community. DESIGN: A prospective, controlled, before-and-after study. SUBJECTS: Bicycling children 5 to 14 years of age from areas of low average family income. SETTING: A defined geographic community within a large urban Canadian city. INTERVENTION: In April 1992, students in three schools located in the area of lowest average family income were offered $10 helmets and an educational program; three other low-income areas served as control areas. MAIN OUTCOME MEASURE: Helmet use was determined by direct observation of more than 1800 bicycling children. RESULTS: Nine hundred ten helmets were sold to a school population of 1415 (64%). Reported helmet ownership increased from 10% to 47%. However, observed helmet use in the low-income intervention area was no different from the rate in the three low-income control areas (18% versus 19%). There was no difference in the trend in helmet use during the period of 1990 through 1992 in the intervention area (4% to 18%) compared with the control areas (3% to 19%). Helmet use rates from all income areas have increased from 3.4% in 1990, to 16% in 1991, to 28% in 1992. In 1992, helmet use in the high-income areas was 48% and in the low-income areas was 20%. CONCLUSIONS: There has been a trend toward increasing helmet use in all income areas during the 3-year period. Despite encouraging helmet sales and increases in reported helmet ownership, the results of the observational study do not support the efficacy of a helmet subsidy program in increasing helmet use in children residing in areas of low average family income. Strategies to increase helmet use in children of low average family income remain a priority.

Adolescent↗
PubMed1995

The real incidence of pediatric trauma.

Trauma care is one of the major components of modern surgery. This is especially true of pediatric surgery, because injuries are by far the leading cause of death for children from early childhood through adolescence. Recently, the epidemiological model of host, agent, and environment has been applied to the study of childhood injuries to increase understanding of their causes and to provide a basis for primary and secondary prevention strategies. We now know that injury patterns vary with age, sex, race, place of residence, and family income, and that the rates of fatal injury from violence, whether interpersonal or self inflicted, are increasing. We also know that firearms are involved in an ever-increasing proportion of cases. As trauma care has improved, the key to further reductions in the toll of injuries on our children is prevention.

Burns↗
PubMed1995

Functional MR imaging of perceptual and cognitive functions.

Functional MR imaging using the blood oxygen level dependent technique as an endogenous contrast agent localizes eloquent cortex when stimulated by a variety of motor or sensory tasks. To date, visual, motor, speech, and cerebellar studies have been conducted, revealing significant information regarding cortical localization and control of various functions. The technique is also an important management tool for localizing eloquent cortex contiguous to a tumor or arteriovenous malformation, so that injury can be avoided if ablation of the lesion is contemplated.

Cerebellum↗
PubMed1995

[Reduced intracellular drug accumulation related to overexpression of P-glycoprotein cannot explain the complete drug resistance in MDR cell variant K562/Dox].

The purpose of this study was to determine what proportion of drug resistance of MDR cell variant K562/Dox was attributed to the reduced steady state intracellular drug accumulation related to overexpression of P-glycoprotein. K562/Dox was derived from repeated exposure of human erythroleukaemic cell line K562 cell to doxorubicin. As assessed with MTT assay, the resistance of K562/Dox to 7 cytotoxic drugs increased variably in the range between 1200 and 11 folds. K562/Dox cells were positively stained with anti-human p-glycoprotein monoclonal antibody JSB-1, indicating overexpression of P-gp. Intracellular drug accumulation in K562/Dox, though significantly reduced as compared with that in K562 cells, was maximally restored by concurrent exposure of cells to 6 mumol/L verapamil and 1.72 mumol/L either of the doxorubicin, epirubicin or daunorubicin. Similar results were obtained by exposure of cells to 12 mumol/L verapamil and 8.62 mumol/L drug, indicating that restoration of intracellular drug accumulation in MDR cells was dependent on the relative concentrations of verapamil to drug. However, the resistances of K562/Dox cells to epirubicin and daunorubicin still remained for about 5.6 and > 6.6 folds, respectively, even at verapamil concentration of 6 mumol/L, suggesting at least a relatively big fraction of drug resistance was not directly related to the altered cellular pharmacokinetics associated with overexpression of P-glycoprotein.

ATP Binding Cassette Transporter, Subfamily B, Mem↗