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Biomedical subjects

Y H Kao

Publications and source records attributed to Y H Kao.

At least 19 recordsLinked to original sources
PubMed1998

Simultaneous multislice acquisition with arterial-flow tagging (SMART) using echo planar imaging (EPI).

Arterial spin tagging techniques have been used to image tissue perfusion in MR without contrast injection or ionizing radiation. Currently, spin tagging studies are performed primarily using single-slice imaging sequences, which are time consuming. This note reports a multislice echo-planar arterial spin tagging technique (Simultaneous Multislice Acquisition with aRterial-flow Tagging, or "SMART"). Multiband RF encoding (Hadamard) is used to provide simultaneous multislice acquisition capability for spin tagging techniques (such as echo planar imaging signal targeting with alternating radio frequency and flow-sensitive alternative inversion recovery). The method is illustrated with a two-slice pulse sequence that was implemented using the FAIR technique to generate two perfusion weighted images simultaneously. Compared with single-slice sequences, this two-slice sequence provided similar image quality, signal-to-noise ratio, and twice the spatial coverage compared with the single-slice technique within the same scan time.

Blood Flow Velocity↗
PubMed1998

Effects of somatostatin on lipid metabolism of larvae and metamorphosing landlocked sea lamprey, Petromyzon marinus.

This study was designed to examine the role of somatostatin in regulating changes in lipid metabolism of larvae and metamorphosing landlocked sea lamprey, Petromyzon marinus. Larvae and animals in late metamorphosis (stage 6 on a 7-stage scale) were injected intraperitoneally once per day for 2 days with either saline (0.6%) or somatostatin-14 (SS-14; 500 ng/g body wt). Injection of SS-14 into larval and stage 6 metamorphosing animals resulted in elevated plasma fatty acids levels. In larvae, SS-14-induced hyperlipidemia was supported by enhanced lipolysis, as indicated by increased triacylglycerol lipase (TGL) activity in the liver and kidney. Mobilization of larval renal lipid was accompanied by reduced TG synthesis, as indicated by decreased diacylglycerol acyltransferase (DGAT) activity. In stage 6 metamorphosing lamprey, SS-14 did not significantly affect TGL activity; however, SS-14 significantly reduced fatty acid synthesis, as measured by acetyl-CoA carboxylase activity, in kidney, liver, and muscle, as well as muscular TG synthesis. SS-14-stimulated lipid depletion is reminiscent of the pattern of lipid metabolism displayed by P. marinus during their spontaneous metamorphosis-an observation which suggests that somatostatin may play a role in metamorphosis-associated changes in lipid metabolism in this species.

Acyltransferases↗
PubMed1998

In vitro cytotoxicity of IgG antibodies on vascular endothelial cells from patients with endemic peripheral vascular disease in Taiwan.

A unique peripheral vascular disorder called 'blackfoot disease' is endemic in a limited area on the south-west coast of Taiwan. Clinically, the signs and symptoms of blackfoot disease (BFD) are similar to those of arteriosclerosis and Buerger's disease. A destruction of vascular endothelial cells (ECs) takes place at an early stage in the affected limbs. Currently, the cause of BFD is believed to be artesian drinking water containing a high concentration of arsenic and/or humic substances, although the mechanism of EC destruction is not entirely understood. The purpose of the present study was to examine the factors related to EC damage in BFD. Thus, we investigated the effects of purified IgG collected from patients with BFD (BFD-IgG) and from normal controls (N-IgG) on cultured EC. We found that: (1) EC binding activity of BFD-IgG was significantly higher than that of N-IgG; (2) BFD-IgG, at a concentration higher than 100 microg/ml but not N-IgG, induced concentration-dependent EC cytotoxicity; (3) BFD-IgG at a concentration of 100 microg/ml stimulated neither the release of von Willebrand factor nor the expression of intercellular adhesion molecule-1 by EC. Fluorescent video microscopic examination revealed an increase in transcapillary and interstitial diffusion of nailfold capillary loops in clinically normal fingers of BFD patients. These findings strongly suggested that immunological mechanisms played a significant role in the pathogenesis of BFD. We propose that only persons who produce the IgG anti-endothelial cell antibody are potential victims of BFD.

Antibodies, Anti-Idiotypic↗
PubMed1997

Two cholinesterase activities and genes are present in amphioxus.

To obtain information about the evolution of the cholinesterases, acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) in the vertebrates, we investigated the cholinesterase (ChE) activity of the cephalochordate amphioxus (Branchiostoma floridae and Branchiostoma lanceolatum). On the basis of evidence from enzymology, pharmacology, and molecular biology, we conclude that amphioxus possesses two ChE activities and two ChE genes. Two covalent inhibitors of cholinesterases were able to pharmacologically isolate the two activities as drug-sensitive ChE and drug-resistant ChE. Kinetically, in terms of substrate specificity, the drug-sensitive ChE resembles vertebrate AChE, and the drug-resistant ChE resembles the BuChE of cartilaginous and bony fish or the intermediate ChE of protostome invertebrates. We also used the polymerase chain reaction with degenerate oligonucleotide primers and genomic DNA to obtain clones of 1,574 and 1,011 bp corresponding to two cholinesterase genes from amphioxus, which we designated as ChE1 and ChE2. ChE2 codes for an enzyme with an acyl-binding pocket sequence, a portion of the protein that plays an important role in determining substrate specificity, typical of invertebrate ChE. ChE1, which contains a 503-bp intron, encodes a protein with a novel acyl binding site. Phylogenetic analysis of the sequences suggests that the two genes are a result of a duplication event in the lineage leading to amphioxus. We discuss the relevance of our results to the evolution of the cholinesterases in the chordates. Previously, we reported that amphioxus contained a single cholinesterase activity with properties intermediate to AChE and BuChE (Pezzementi et al. [1991] In: Cholinesterases: Structure, Function, Mechanism, Genetics and Cell Biology. J. Massoulié et al., eds. ACS: Washington, D.C., pp. 24-31).

Acetylcholinesterase↗
PubMed1997

Stereoselectivity of the Chinese hamster ovary cell sialidase: sialoside hydrolysis with overall retention of configuration.

The stereochemical course of enzymatic hydrolysis by the soluble sialidase from Chinese hamster ovary cells, expressed as a recombinant protein in insect Sf9 cells, was determined using proton nuclear magnetic resonance spectroscopy. 4-Methyl umbelliferyl-N-acetyl neuraminic acid was employed as substrate, and the stereoselectivity of the enzyme catalysis was ascertained by monitoring the H3 axial and equatorial protons of the sialic acid product over the reaction course. At both high (3 U) and low concentrations (1 U) of the enzyme, the alpha anomer of the sialic acid was clearly observed as the initial reaction product. The corresponding beta anomer of sialic acid appeared much later in the reaction, arising from mutarotation of the alpha anomer. Similar studies were also carried out using the Salmonella typhimurium LT 2 sialidase, a protein of similar size and substrate specificity. Both enzymes apparently cleave the alpha linked sialoside substrate with retention of configuration. Based on the observations of a wide variety of other glycohydrolytic enzymes that have shown a strong correlation of the stereoselectivity of catalysis with active site topology (Gebler et al., J. Biol. Chem. 267, 12559-12561, 1992), the results obtained here suggest that the microbial and mammalian sialidases have a homologous active site architecture even though the molecules do not share significant primary sequence similarities.

Animals↗
PubMed1996

The native state of apomyoglobin described by proton NMR spectroscopy: the A-B-G-H interface of wild-type sperm whale apomyoglobin.

Proton nuclear magnetic resonance spectroscopy was applied to sperm whale apomyoglobin to describe the conformation adopted by the protein under native conditions. The study focused on the A-B-G-H interface, a region known to form a compact subdomain in the apoprotein (Hughson and Baldwin, Biochemistry 28:4415-4422, 1989). Two histidine residues located in this subdomain, His24 and His119, interact and are thought to play a role in the acid denaturation process (Barrick et al., J. Mol. Biol. 237:588-601, 1994). A stable double mutant at these positions (His24Val/His119Phe sperm whale apomyoglobin) was compared with wild-type apomyoglobin. The amino acid replacements result in chemical shift perturbations near the mutations, in particular in the AB interhelical region, and in a deceleration of backbone amide hydrogen exchange in the B helix from position 27 to position 33. The double mutant data were used to expand and confirm the wild-type spectral analysis. Signals from the D helix were identified that demonstrate the formation of holoprotein-like structure. The assigned wild-type nuclear Overhauser effects, although in small number, were sufficient to construct a model of the compact subdomain of the apoprotein. This was achieved by using the structure of the holoprotein and restraining it with the geometrical information on the apoprotein in a simulated annealing procedure. The experimental restraints define a low-resolution model of the A-B-G-H interface in apomyoglobin.

Animals↗
PubMed1996

MR image segmentation using vector decomposition and probability techniques: a general model and its application to dual-echo images.

A general model is developed for segmenting magnetic resonance images using vector decomposition and probability techniques. Each voxel is assigned fractional volumes of q tissues from p differently weighted images (q < or = p + 1) in the presence of partial-volume mixing, random noise, and other tissues. Compared with the eigenimage method, fewer differently weighted images are needed for segmenting the q tissues, and the contrast-to-noise ratio in the calculated fractional volumes is improved. The model can produce composite tissue-type images similar to that of the probability methods, by comparing the fractional volumes assigned to different tissues on each voxel. A three-tissue (p = 2, q = 3) model is illustrated for segmenting three tissues from dual-echo images. It provides statistical analysis to the algebraic method. A three-compartment phantom is segmented for validation. Two clinical examples are presented.

Artifacts↗
PubMed1996

Endoscope--an endodontic application.

The endoscope utilized by otolaryngologists for the past 10 yr has a place in the armamentarium of the endodontist as well. It provides improved visualization of root apicies, especially those not in the line of direct vision. It can illuminate and identify roots in the sinus if such treatment becomes necessary. By allowing a magnified view of the root-end preparation before and after placement of the filling material, any fractures or extraneous material can be identified. This instrument is quite small and readily transportable from one operatory to another. The cost is a fraction of the price of the surgical microscope.

Adult↗
PubMed1996

Imaging the functional organization of zebrafish hindbrain segments during escape behaviors.

Although vertebrate hindbrains are segmented structures, the functional significance of the segmentation is unknown. In zebrafish, the hindbrain segments contain serially repeated classes of individually identifiable neurons. We took advantage of the transparency of larval zebrafish and used confocal calcium imaging in the intact fish to study the activity of one set of individually identified, serially homologous reticulospinal cells (the Mauthner cell, MID2cm, and MID3cm) during behavior. Behavioral studies predicted that differential activity in this set of serially homologous neurons might serve to control the directionality of the escape behavior that fish use to avoid predators. We found that the serially homologous cells are indeed activated during escapes and that the combination of cells activated depends upon the location of the sensory stimulus used to elicit the escape. The patterns of activation we observed were exactly those predicted by behavioral studies. The data suggest that duplication of ancestral hindbrain segments, and subsequent functional diversification, resulted in sets of related neurons whose activity patterns create behavioral variability.

Animals↗
PubMed1995

In-vitro and in-vivo studies of the diclofenac sodium controlled-release matrix tablets.

Controlled release matrix tablets for diclofenac sodium were developed in this study. Five matrix-tablet formulations were prepared by granulating two viscosity grades of HPMC (hydroxylpropylmethylcellulose) in varying ratios with water in the planetary mixer. The in-vitro dissolution tests indicate that all five matrix formulations prolong the release of diclofenac sodium. The main factors controlling drug release were the HPMC viscosity grade and the amount of HPMC used. The larger the amount of high viscosity grade HPMC used, the slower the resultant release rate of diclofenac sodium. There was no significant degradation of diclofenac sodium or change in drug release rate in any of the five formulations during a three-month period of stability testing. The sustained release ability of four formulations was further demonstrated in an in-vivo study in six healthy subjects. There were in-vitro/in-vivo correlations between Cmax, AUC0-14, and the time for 50 or 80% drug to be released.

Adult↗
PubMed1995

Papaverine and prostaglandin E1 gel applications for impotence.

The transdermal permeability of papaverine and prostaglandin E1 (PGE1) could be determined in vitro. A chemical scheme of passive delivery or with enhancer, as well as a physical iontophoretic transdermal delivery system were designed in the laboratory. Clinically, up to 20% papaverine base gel and 500 micrograms PGE1 were applied onto the genital area without any side effect. Only vascular response could be detected by ultrasound. However, immediate erection could not be obtained at the present dosage. Further research on the combination of skin absorption enhancers, the different chemical derivatives of PGE1 or a different administration route is warranted.

Administration, Cutaneous↗
PubMed1994

1H and 15N NMR assignments of PsaE, a photosystem I subunit from the cyanobacterium Synechococcus sp. strain PCC 7002.

PsaE is a highly conserved, water-soluble protein of the photosystem I reaction center complexes of cyanobacteria, algae, and green plants. Along with the PsaC and PsaD proteins, the PsaE protein binds to the stromal surface of photosystem I and is required for cyclic electron transport in Synechococcus sp. strain PCC 7002 [Yu, L., Zhao, J., Mühlenhoff, U., Bryant, D.A., & Golbeck, J.H. (1993) Plant Physiol. 103, 171-180]. The psaE gene from this cyanobacterium encodes a mature protein of 69 amino acid residues and has recently been overexpressed in Escherichia coli [Zhao, J., Snyder, W.B., Mühlenhoff, U., Rhiel, E., Warren, P. V., Golbeck, J. H., & Bryant, D. A. (1993) Mol. Microbiol. 9, 183-194]. By using both unlabeled and uniformly 15N-labeled protein in a series of two- and three-dimensional NMR experiments, complete 1H and 15N amide resonance assignments were made. The major secondary structural element of PsaE is a five-stranded antiparallel beta-sheet. The five strands extend as follows: beta A, residues 7-10; beta B, residues 21-26; beta C, residues 36-39; beta D, residues 57-60; and beta E, residues 65-68. The topology is represented by (+1, +1, +1, -4x); it brings the first and last strands, and consequently the N- and C-termini, together. The protein has an extensive hydrophobic core organized around a conserved phenylalanine residue (Phe-40); another of its distinctive features is a segment extending from residue 42 to residue 56 devoid of dipolar contacts with the beta-sheet. The pK1/2 of the sole histidine residue (His-63) was determined to be 5.4.

Amino Acid Sequence↗
PubMed1994

Three-dimensional solution structure of PsaE from the cyanobacterium Synechococcus sp. strain PCC 7002, a photosystem I protein that shows structural homology with SH3 domains.

PsaE is a 69 amino acid polypeptide from photosystem I present on the stromal side of the thylakoid membrane. The three-dimensional solution structure of this protein from the cyanobacterium Synechococcus sp. strain PCC 7002 was determined at pH 5.8 and room temperature using over 900 experimental restraints derived from two- and three-dimensional NMR experiments. The structure is comprised of a well-defined five-stranded beta-sheet with (+1, +1, +1, -4 alpha) topology. There is no helical region except for a single turn of 3(10) helix between the beta D and beta E strands. PsaE also exhibits a large unrestrained loop spanning residues 42-56. A comparison to known protein structures revealed similarity with the Src homology 3 (SH3) domain, a membrane-associated protein involved in signal transduction in eukaryotes. The match is remarkable as 47 of the alpha-carbons of PsaE can be superimposed onto those of the SH3 domain from chicken brain alpha-spectrin with a root-mean-square deviation of 2.3 A. Although the amino acid sequences have low identity and the loops are different in both proteins, the topology of the beta-sheet and the 3(10) turn is conserved. SH3 domains from other sources show a similar structural homology. The structure of PsaE was used to suggest approaches for elucidating its roles within photosystem I.

Amino Acid Sequence↗
PubMed1994

Dual-echo MRI segmentation using vector decomposition and probability techniques: a two-tissue model.

We combined a vector decomposition technique with Gaussian probability thresholding in feature space to segment normal brain tissues, tumors, or other abnormalities on dual-echo MR images. The vector decomposition technique assigns to each voxel a fractional volume for each of two tissues. A probability threshold, based on an assumed Gaussian probability density function describing random noise, isolates a region in feature space for fractional volume calculation that minimizes contamination from other tissues. The calculated fractional volumes are unbiased estimates of the true fractional volumes. The contrast-to-noise ratio (CNR) between tissues on the segmented images is the same as the Euclidean norm of CNRs in the original images. The method is capable of segmenting more than two tissues from a set of dual-echo images by sequentially analyzing different pairs of tissues. The model is analyzed mathematically and in experiments with a phantom. Two clinical examples are presented.

Adenocarcinoma↗
PubMed1992

Structural comparison of apomyoglobin and metaquomyoglobin: pH titration of histidines by NMR spectroscopy.

Proton NMR spectroscopy was applied to myoglobin in the ferric, water-liganded form (metMbH2O) and the apo form (apoMb) to probe the structure and stability of the latter. Proteins from sperm whale and horse skeletal muscles were studied to simplify the spectral assignment task. Nuclear Overhauser effects and the response of chemical shifts to variations of pH were used as indicators of residual native holoprotein structure in the apoprotein. The investigation was focused in the histidine side chains and their environment. In metMbH2O, the resonances of all imidazole rings not interacting with the heme were assigned by applying standard two-dimensional methods. These assignments were found to differ from those reported elsewhere [Carver, J. A., & Bradbury, J. H. (1984) Biochemistry 23, 4890-4905] except for His-12, -113, and -116. Only one histidine (His-36) has a pK(a) higher than 7, two (His-48 and His-113) have a pK(a) lower than 5.5, and two (His-24 and His-82) appear not to titrate between pH 5.5 and pH 10. In the apoproteins, the signals of His-113 and His-116, as well as those of His-24, -36, -48, and -119 previously assigned in the horse globin [Cocco, M. J.. & Lecomte, J. T. J. (1990) Biochemistry 29, 11067-11072], could be followed between pH 5 and pH 10. A comparison to the holoprotein data indicated that heme removal has limited effect on the pK(a) and the surroundings of these residues. Five additional histidines which occur in the two helices and connecting loops forming the heme binding site were identified in the horse apoprotein. Four of these were found to have pK(a) values lower than that expected of an exposed residue. The NOE and titration data were proposed to reflect the fact that several holoprotein structural elements, in particular outside the heme binding site, are maintained in the apoprotein. In the heme binding region of the apoprotein structure, the low pK(a)'s suggest local environments which are resistant to protonation.

Amino Acid Sequence↗
PubMed1991

Tablet formulation study of spray-dried sodium diclofenac enteric-coated microcapsules.

Sodium diclofenac enteric-coated microcapsules were prepared by a spray-drying technique with Eudragit L 30D as enteric-coating material. The spray-dried powder, mixed with neocel or flo-starch, or the mixture of neocel and flo-starch (weight ratio, 1:1) was directly compressed into a tablet. The micromeritic properties of the spray-dried powder and the mixed powder for tableting were investigated. The flowability of the spray-dried powder was poor but improved after incorporating the excipients. The release rates of sodium diclofenac from the spray-dried powder, the mixed powder before tableting, and the tablets were determined in 0.1 N HCl solution, pH 6.8, phosphate buffer solution, distilled water, and pH-changed medium. The results indicated that the spray-dried powder, the mixed powder before tableting, and the tablets all exhibited enteric-coated release properties; these powders and tablets showed some resistance to stimulated gastric acid and then released drug more rapidly in pH 6.8 buffer solution. The weight ratio of neocel to flo-starch plays an important role in controlling the release of sodium diclofenac from enteric tablets. The 1:1 weight ratio of neocel to flo-starch was more suitable for designing the microdispersed sodium diclofenac enteric-coated tablets.

Acrylates↗
PubMed1990

Preliminary evaluation of the correlation between in vitro release and in vivo bioavailability of two aminophylline slow-release tablets.

An in vitro dissolution study has been carried out with a USP rotating paddle apparatus using the stepwise pH change method. The dissolution kinetics of two different matrix-type aminophylline slow-release (SR) tablets were compared. both aminophylline SR tablets show similar release rates and slow release behavior. The bioavailability of these two aminophylline SR tablets was also evaluated in eight healthy male Chinese volunteers and correlated with in vitro dissolution results by moment analysis. The preliminary results suggest that there is no evidence indicating that the two different matrix types of aminophylline SR tablets are not bioequivalent, and a good in vitro-in vivo correlation for these aminophylline SR tablets may therefore be presumed.

Aminophylline↗