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Biomedical subjects

D Yeung

Publications and source records attributed to D Yeung.

At least 19 recordsLinked to original sources
PubMed2000

The telomerase reverse transcriptase is limiting and necessary for telomerase function in vivo.

Mammalian telomerase is essential for the maintenance of telomere length [1-5]. Its catalytic core comprises a reverse transcriptase component (TERT) and an RNA component. While the biochemical role of mammalian TERT is well established [6-11], it is unknown whether it is sufficient for telomere-length maintenance, chromosome stability or other cellular processes. Cells from mice in which the mTert gene had been disrupted showed progressive loss of telomere DNA, a phenotype similar to cells in which the gene encoding the telomerase RNA component (mTR) has been disrupted [1,12]. On prolonged growth, mTert-deficient embryonic stem (ES) cells exhibited genomic instability, aneuploidy and telomeric fusions. ES cells heterozygous for the mTert disruption also showed telomere attrition, a phenotype that differs from heterozygous mTR cells [12]. Thus, telomere maintenance in mammals is carried out by a single, limiting TERT.

Animals↗
PubMed2000

Telomerase-associated protein TEP1 is not essential for telomerase activity or telomere length maintenance in vivo.

TEP1 is a mammalian telomerase-associated protein with similarity to the Tetrahymena telomerase protein p80. Like p80, TEP1 is associated with telomerase activity and the telomerase reverse transcriptase, and it specifically interacts with the telomerase RNA. To determine the role of mTep1 in telomerase function in vivo, we generated mouse embryonic stem (ES) cells and mice lacking mTep1. The mTep1-deficient (mTep1(-/-)) mice were viable and were bred for seven successive generations with no obvious phenotypic abnormalities. All murine tissues from mTep1(-/-) mice possessed a level of telomerase activity comparable to that in wild-type mice. In addition, analysis of several tissues that normally lack telomerase activity revealed no reactivation of telomerase activity in mTep1(-/-) mice. Telomere length, even in later generations of mTep1(-/-) mice, was equivalent to that in wild-type animals. ES cells deficient in mTep1 also showed no detectable alteration in telomerase activity or telomere length with increased passage in culture. Thus, mTep1 appears to be completely dispensable for telomerase function in vivo. Recently, TEP1 has been identified within a second ribonucleoprotein (RNP) complex, the vault particle. TEP1 can also specifically bind to a small RNA, vRNA, which is associated with the vault particle and is unrelated in sequence to mammalian telomerase RNA. These results reveal that TEP1 is an RNA binding protein that is not restricted to the telomerase complex and that TEP1 plays a redundant role in the assembly or localization of the telomerase RNP in vivo.

Animals↗
PubMed2000

Arytenoid adduction: controlling vertical position.

In flaccid laryngeal paralysis, the vocal process (VP) is displaced laterally and superiorly. The arytenoid adduction procedure (AA) moves the VP medially and caudally, closing the glottic gap. However, clinical evidence suggests that the VP is more caudal after AA than in physiological phonation. The neurally intact arytenoid is supported by tonic and phonatory activity of the posterior cricoarytenoid muscle (PCA). We hypothesize that a posterior anchoring suture could replace PCA support, achieving a more natural VP location. Cadaver larynges were scanned with computed tomography at rest and after AA, alone or in combination with a second arytenoid suture anchored to either the posterior midline cricoid (PC) or the inferior thyroid cornu (IC). Each posterior suture reduced caudal displacement of the VP during AA, but the glottic gap was wider with the PC suture. In 3 patients undergoing AA for laryngeal paralysis, the IC suture improved arytenoid posture and voice quality.

Female↗
PubMed1998

Is there a relationship between delta sleep at night and afternoon cerebral blood flow, assessed by HMPAO-SPECT in depressed patients and normal control subjects? Preliminary data.

We wished to explore the relationships between waking HMPAO uptake and visually scored polysomnography. We hypothesized that HMPAO activity would correlate positively with slow wave sleep measures the same night. Eight unmedicated unipolar patients with current DSM-IV major depression (17-item Hamilton Depression Rating Scale score 21.5+/-2.9) and seven control subjects received polysomnography on 2 consecutive nights. On the afternoon following the adaptation night, subjects received cerebral SPECT, with 15 mCi Tc-99m-HMPAO injected while subjects performed the Continuous Performance Task. Patients and control subjects did not significantly differ on demographic, polysomnographic, and SPECT variables. Slow wave sleep measures correlated positively (Spearman's) with global and regional tracer activity for depressed (n = 8), control (n = 7) and combined groups (n = 15); in other words, the greater the global or regional afternoon HMPAO uptake, the greater the slow wave sleep measures were the same night. In addition, the greater the waking afternoon global or regional HMPAO activity, the faster subjects fell asleep and the less Stage 2% they had. In patients, global and regional HMPAO activity correlated positively with REM density. Positive correlations between waking tracer activity and subsequent slow wave measures are consistent with previous hypotheses linking slow wave sleep with brain energy conservation and restoration. Further study is needed to determine whether these functional relationships differ in depression.

Adult↗
PubMed1998

New approaches for the analysis of molecular recognition using the IAsys evanescent wave biosensor.

Trends in the analysis of molecular recognition using the IAsys evanescent wave biosensor are outlined. Diversification of sensor surface chemistry, an open cuvette format and the advent of robotics controlled by intelligent software are widening the range and throughput of applications. Analyses of binding and dissociation are now carried out across a wide spectrum of biomolecules, including protein, nucleic acid, carbohydrate and lipid. Determinations are obtained from a range of experimental formats. These include qualitative 'yes/no' screening assays, through semi quantitative ranking of kinetic association, dissociation and equilibrium constants for a family of binding partners, to deriving constants comparable with those which would be obtained in free solution. A dependence of the initial rate of biomolecular association on concentration allows analyte concentration to be measured--an increasingly common application class. This is often employed in situations where a rapid determination is required The ability to recover bound analyte from the sensor surface in sufficient amounts for subsequent characterization is opening up new routes to the parallel analysis of structure and function.

Animals↗
PubMed1998

Unilateral cricothyroid contraction and glottic configuration.

It is frequently stated that unilateral cricothyroid muscle (CT) paralysis can be diagnosed by physical examination, noting rotation of the glottis, and shortening and vertical displacement of the ipsilateral vocal fold. These signs, however, are inconsistently observed, and there is considerable controversy regarding the direction of glottic rotation. To determine the effects of CT contraction on three-dimensional glottic configuration, we performed computerized tomography on cadaver larynges before and after simulated CT contraction. Radiopaque makers were used to compute distances. Unilateral CT contraction equally increased the length of both membranous vocal folds, and rotated the posterior glottis less than 1 mm. CT contraction neither adducted the vocal processes, nor significantly their altered vertical level. These results suggest that unilateral CT paralysis cannot be diagnosed on the basis of any clinically apparent change in glottal configuration.

Cricoid Cartilage↗
PubMed1998

Design, construction and use of a large-sample field-cycled PEDRI imager.

The design, construction and use of a large-scale field-cycled proton-electron double-resonance imaging (FC-PEDRI) imager is described. The imager is based on a whole-body sized, vertical field, 59 mT permanent magnet. Field cycling is accomplished by the field compensation method, and uses a secondary, resistive magnet with an internal diameter of 52 cm. The magnetic field can be switched from zero to 59 mT or vice versa in 40 ms. It is used with a double-resonance coil assembly (NMR/EPR) comprising a solenoidal NMR transmit/receive coil and a coaxial, external birdcage resonator for EPR irradiation. Experiments to image the distribution of an exogenous nitroxide free radical in anaesthetized rabbits are described.

Animals↗
PubMed1997

The stability of recombinant human growth hormone in poly(lactic-co-glycolic acid) (PLGA) microspheres.

PURPOSE: The development of a sustained release formulation for recombinant human growth hormone (rhGH) as well as other proteins requires that the protein be stable at physiological conditions during its in vivo lifetime. Poly(lactic-co-glycolic acid) (PLGA) microspheres may provide an excellent sustained release formulation for proteins, if protein stability can be maintained. METHODS: rhGH was encapsulated in PLGA microspheres using a double emulsion process. Protein released from the microspheres was assessed by several chromatrographic assays, circular dichroism, and a cell-based bioassay. The rates of aggregation, oxidation, diketopiperazine formation, and deamidation were then determined for rhGH released from PLGA microspheres and rhGH in solution (control) during incubation in isotonic buffer, pH 7.4 and 37 degrees C. RESULTS: rhGH PLGA formulations were produced with a low initial burst (< 20%) and a continuous release of rhGH for 30 days. rhGH was released initially from PLGA microspheres in its native form as measured by several assays. In isotonic buffer, pH 7.4 and 37 degrees C, the rates of rhGH oxidation, diketopiperazine formation, and deamidation in the PLGA microspheres were equivalent to the rhGH in solution, but aggregation (dimer formation) occurred at a slightly faster rate for protein released from the PLGA microspheres. This difference in aggregation rate was likely due to the high protein concentration used in the encapsulation process. The rhGH released was biologically active throughout the incubation at these conditions which are equivalent to physiological ionic strength and pH. CONCLUSIONS: rhGH was successfully encapsulated and released in its fully bioactive form from PLGA microspheres over 30 days. The chemical degradation rates of rhGH were not affected by the PLGA microspheres, indicating that the internal environment of the microspheres was similar to the bulk solution. After administration, the microspheres should become fully hydrated in the subcutaneous space and should experience similar isotonic conditions and pH. Therefore, if a protein formulation provides stability in isotonic buffer, pH 7.4 and 37 degrees C, it should allow for a safe and efficacious sustained release dosage form in PLGA microspheres.

Chromatography, Gel↗
PubMed1997

Changes in length and spatial orientation of the vocal fold with arytenoid adduction in cadaver larynges.

Videoendoscopy suggests that arytenoid adduction (AA) surgery not only medializes the paralyzed vocal fold, but increases the length of its membranous portion so that it more closely resembles the normal side. This could represent either real length change or out-of-plane rotation. Computed tomography scanning was performed on adult male cadaver larynges before and after the AA procedure to measure changes in length and spatial orientation of the vocal fold. Three-dimensional coordinates of radiopaque markers on the anterior commissure, posterior glottic midline, and vocal processes were determined. The distance between the vocal processes was 3.9 mm before, and 0.8 mm after AA. The mean vocal fold length was 12.4 mm before, and 13.4 mm after AA (p = .14). The vocal process moved consistently caudally, an average of 3.5 mm (p = .02). The data suggest that clinically apparent vocal fold length changes with AA could be an illusion due to vertical displacement of the vocal process, and not actual lengthening.

Adult↗
PubMed1996

Human posterior cricoarytenoid muscle compartments. Anatomy and mechanics.

OBJECTIVE: To document the presence and functional significance of distinct anatomical compartments in the human posterior cricoarytenoid muscle (PCA). DESIGN: Anatomic study of human cadaver larynges. SUBJECTS: Seventeen fresh larynges, harvested at autopsy from 8 men and 9 women, with no history of laryngeal disease or surgery. INTERVENTIONS: Twenty-three PCA muscles from 12 human cadaver larynges were dissected. Computed tomographic scanning and rigid body mechanical analysis were used to compute 3-dimensional motion with simulated individual contraction of PCA compartments in 5 fresh larynges. RESULTS: Discrete medial and lateral bellies with different orientations of muscle fibers were found in every muscle. The 2 bellies insert on opposing aspects of the muscular process of the arytenoid. Very little linear translation was effected by either muscle. The axes of rotation attributable to the 2 bellies differed significantly, with the medial belly effecting rotation about a more vertical axis. The axis of rotation for the lateral muscle belly was nearer the anterior posterior axis than that of the medial belly. CONCLUSIONS: These data indicate that PCA muscle contraction results in arytenoid rotation about a variable oblique axis without significant lateral gliding. There are 2 bellies within the human PCA muscle with differing mechanical actions on the cricoarytenoid joint.

Aged↗
PubMed1996

Three-dimensional reconstruction of arteriovenous malformations from multiple stereotactic angiograms.

Stereotactic angiography is the preferred imaging modality in the radiosurgical treatment of arteriovenous malformations (AVM). A major limitation of this technique is the inability to determine the three-dimensional shape and the volume of the AVM. We developed a technique for reconstructing the AVM from multiple stereotactic angiograms. The fiducial marks and the identified target area are digitized for each view. The 2-D target area is then stereotactically backprojected into a 3-D volume. The spatial boundary of the target volume is defined by superimposing the backprojections from each of the views. In feasibility studies with a phantom, this technique accurately reconstructed complex 3-D structures, depicting fine details as small as 1 mm. Clinical studies in two patients indicated that this novel technique is very useful for the 3-D reconstruction of AVM for radiosurgical treatment. The number of views required depends on the complexity of the object. In general, six to eight views appear adequate. The accuracy of the reconstruction can be compromised if the view angles are limited as with the current radiographic frame. A new frame design with practically unlimited view angles is proposed to avoid this potential limitation. However, structures that are always obscured (such as concavity) could not be accurately reconstructed, leading to overestimates of the object size. This "limitation" has a positive side, in that the technique will not underestimate the actual target volume. The ability to delineate both the shape and volume of the lesion should facilitate optimal target coverage while sparing a significant amount of normal tissue.

Arteriovenous Malformations↗
PubMed1995

Real-time detection and quantification of DNA hybridization by an optical biosensor.

The use of an optical biosensor, the resonant mirror, for direct and rapid detection of DNA-DNA hybridization has been demonstrated. Biotinylated oligonucleotide probes were immobilized on the sensor surface, via streptavidin, and the hybridization of a complementary target oligonucleotide (40-mer) was monitored in real time. The interaction at the sensor surface was shown to be sequence specific under conditions of low stringency. Regeneration of the surface-immobilized probe was possible, allowing reuse without a significant loss of hybridization activity. A comparison of probes indicated that the relative position of complementary sequence and the length of probe affected the hybridization response obtained. The potential of the sensor for quantitation of a hybridized DNA target was investigated. From radiolabeling data, the lowest amount of hybridized target sequence which could be determined directly was 19.9 fmol/mm2 (263 pg/mm2) of sensor surface. The dependence of the sensor response on the concentration of probe and target oligonucleotide was established. Utilizing the assay as an end-point determination method, the lowest detectable concentration of target oligonucleotide (40-mer) was 9.2 nM. This compares favorably to other sensor methods described previously without the requirement for labels.

Base Sequence↗
PubMed1994

Systematic analysis of errors in target localization and treatment delivery in stereotactic radiosurgery (SRS).

PURPOSE: To systematically analyze the spatial uncertainties associated with each step of the stereotactic radiosurgery (SRS) procedure and the overall spatial accuracy in the treatment delivery. METHODS AND MATERIALS: A special test device has been designed and fabricated to permit accurate simulation, localization and treatment portal verification of a SRS target. This device with simulated targets dispersed in 3-D space can be rigidly attached to the BRW CT or angio frame for localization, to the BRW phantom base for target coordinate determination, and to the floor stand for portal verification. The setup allows evaluation of the accuracy of each procedure separately as well as the overall accuracy in the delivery of SRS treatment. RESULTS: Biplanar film localizations reveal a systematic error in the phantom base pointer of the order of 0.1 mm that is applied as a correction to the measured target coordinates. Targets localized by planar film angiography had a mean positional error of 0.38 +/- 0.1 mm compared to 1.0 +/- 0.7 mm for digital angiographic localization. The positional accuracy associated with CT localization was superior when a 2 mm vs. 4 mm slice thickness was used (0.9 +/- 0.3 mm vs. 1.6 +/- 0.5 mm error). Cumulative mean errors, including inaccuracies associated with treatment setup, were 1.0 +/- 0.4 mm for radiographic localization, 1.2 +/- 0.5 mm for CT with a 512 x 512 matrix and 2 mm slice thickness, and 2.0 +/- 0.6 mm for CT at a 4 mm slice thickness (256 x 256 matrix). Larger errors would be expected in the clinical setting. CONCLUSION: Spatial errors in stereotactic radiosurgery are best estimated using a systematic approach to isolate independent contributing factors. The accuracy in target localization determines the overall accuracy of SRS procedure, provided the mechanical accuracy of the treatment apparatus is assured. Biplanar treatment portal verification with a fiducial localization frame is an accurate method of verifying the target coordinates before delivering treatment.

Humans↗
PubMed1990

Immunoassays and nucleic acid detection with a biosensor based on surface plasmon resonance.

A technique based on surface plasmon resonance is described which can be used to detect changes of refractive index that occur when one partner of a molecular binding pair diffuses from solution to bind the other partner which is immobilised on a silver surface. Results for the molecular binding pairs; protein-antibody, hapten-antibody and DNA-DNA are described. Instrumentation necessary for implementation of the technique is detailed. Immunoassay of proteins and haptens is possible in less than one minute with a sensitivity of 10(-9) mol/l. Hybridisation of 10 fmoles of a 97 base target sequence on the 1 mm2 area of detection to an immobilised oligonucleotide probe can be detected in less than five minutes. Advantages of the technique include the ability to record the kinetics of binding reactions in "real time" and the lack of labels in this simple assay format. Methods of improving the sensitivity are discussed.

Animals↗