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S Ding

Publications and source records attributed to S Ding.

At least 19 recordsLinked to original sources
PubMed1999

DENSE: displacement encoding with stimulated echoes in cardiac functional MRI.

Displacement encoding with stimulated echoes (DENSE) was developed for high-resolution myocardial displacement mapping. Pixel phase is modulated by myocardial displacement and data spatial resolution is limited only by pixel size. 2D displacement vector maps were generated for the systolic action in canines with 0.94 x 1.9 mm nominal in-plane resolution and 2.3 mm/pi displacement encoding. A radial strain of 0.208 was measured across the free left ventricular wall over 105 ms during systole. DENSE displacement maps require small first-order gradient moments for encoding. DENSE magnitude images exhibit black-blood contrast which allows for better myocardial definition and reduced motion-related artifacts.

Animals↗
PubMed1999

Distinct mutation patterns of breast cancer-associated alleles of the HRAS1 minisatellite locus.

DNA sequence analysis of 130 alleles of the HRAS1 minisatellite has demonstrated that breast cancer-associated variants arise as a consequence of both replication errors and gene conversions. Unlike mutations at other variable number of tandem repeats (VNTRs), high-risk variants of the HRAS1 minisatellite do not demonstrate positional polarity. Instead, most mutations occur at three hotspots, with replication errors confined to one hotspot, gene conversions to a second and a mixed pattern of mutation at the third. DNA sequence analysis of 66 low-risk a1 alleles revealed no evidence for hypermutation. Therefore, while the HRAS1 minisatellite may serve as a reporter for a broad-based group of mutational mechanisms, these results are consistent with a direct pathogenetic contribution by high-risk alleles as the biological basis underlying cancer association of this VNTR.

Alleles↗
PubMed1999

Cloning and expression of the Ca2+ channel alpha1C and beta2a subunits from guinea pig heart.

Complimentary DNA clones encoding the alpha1C and beta2a subunits of guinea-pig cardiac L-type Ca2+ channels were isolated using the PCR method. The open reading frame encoded 2,169 amino acids for the alpha1C and 597 amino acids for the beta2a subunit. The proteins showed 94.2 and 94.8%, respectively, identity to the respective subunit of the rabbit protein. The message size of the guinea pig alpha1C and beta2a subunits was 8.0 and 3.5/4.0 kb, respectively. RT-PCR analysis revealed that the alpha1C subunit is expressed exclusively in the heart, while the beta2a subunit is expressed in the heart, cerebellum, whole brain, and stomach. The alpha1C and beta2a subunits are transiently expressed in BHK (baby hamster kidney) cells, and the channel currents were studied using the whole-cell patch clamp technique in medium containing 30 mM Ba2+. In cells expressing alpha1C alone, the Ba2+ current was activated at -30 mV and more positive potentials and peaked at about 10 mV. The co-expression of beta2a with alpha1C did not affect the voltage-dependence of the current, but increased the peak current and accelerated current decay. In cells transfected with guinea pig alpha1C and rabbit beta1+alpha2/delta, a Ba2+ current comparable to those in native myocytes was observed. The Ba2+ current can be blocked completely by nifedipine and is enhanced 3-fold by Bay K 8644. On the other hand, neither forskolin nor okadaic acid affects the Ba2+ current, suggesting that cAMP-mediated modulation is not easily reproduced in transfected cells, unlike that seen in native cardiac myocytes.

Amino Acid Sequence↗
PubMed1998

High-resolution in vivo measurements of transverse relaxation times in rats at 7 Tesla.

A multi-echo imaging sequence suitable for high-resolution and accurate in vivo transverse relaxation time (T2) mapping has been implemented. The sequence was tested on phantoms and was used to measure T2 values in vivo in the rat brain, muscle, and fat at 7 T. Brain T2 maps are shown and regional variations in brain T2 are reported (41.8 ms in cortex, 47.9 ms in hippocampus). Results are compared to literature values obtained at lower field in vivo as well as high-field T2 measurements on excised rat tissues. The reported T2 values are generally smaller compared to lower-field-strength literature values. A discussion of the possible causes of these field effects on T2 is included (dipolar interaction, fast chemical exchange, and diffusion in susceptibility gradients).

Adipose Tissue↗
PubMed1998

Improved coverage in dynamic contrast-enhanced cardiac MRI using interleaved gradient-echo EPI.

An interleaved gradient-echo echo-planar imaging (IGEPI) sequence was modified for and applied to dynamic contrast-enhanced imaging of the heart. Using IGEPI, images with 3.0 x 3.9 mm nominal in-plane resolution are acquired in 100 ms, enabling eight slices per heartbeat for a heart rate of 60 beats/min. The acquisition speed and use of saturation prepulses allows acquisition of short- and long-axis images during the same contrast bolus. IGEPI maintains the acquisition characteristics required for performing a quantitative first-pass perfusion analysis as well as providing improved coverage compared with conventional fast gradient echo.

Contrast Media↗
PubMed1998

Multiple-quantum MAS NMR spectroscopy of spin-3/2 quadrupolar spin systems using shaped pulses.

An investigation of the effect of shaping the pulses in multiple-quantum magic-angle nuclear magnetic resonance experiments was carried out on polycrystalline samples containing spin-32 quadrupolar nuclear spins. Both theoretical analysis and numerical simulations show that there exist types of shaped pulses that are more advantageous than the usual rectangular pulses in exciting multiple-quantum coherences and converting these into single-quantum coherences or zero-quantum coherences (in z-filtering cases). The sensitivities can be enhanced without loss of resolution or increasing the RF offset dependences. Moreover, properly shaped pulses can moderate the requirements on the RF power and sample spinning speeds. Especially important for application purposes is the finding that lattice site quantification can also be improved by the use of certain shaped pulses.

Magnetic Resonance Spectroscopy↗
PubMed1998

Potassium tetracyanoplatinate (II) trihydrate (K2Pt(CN)4 x 3H2O) studied by high resolution solid state 13C MAS NMR.

Prudent analysis of the solid state 13C MAS NMR spectra of polycrystalline K2Pt(CN)4 x 3H2O (KTCP)- reveals that in crystals of this compound there are two types of carbon nuclei with slightly different 13C chemical shift tensors, contrary to what is found for the solution NMR spectrum and previous static powder NMR studies on this compound and the high resolution solid state NMR studies on other similar compounds. The 13C MAS spectra measured at different rotor spinning speeds are satisfactorily simulated though the use of a newly developed computer program based on a novel density matrix formulation. The present method is eminently successful even though the spectra are rather complicated because of (1) the relatively large anisotropies of the chemical shift tensors; (2) the high-order dipolar interactions between 13C and 14N nuclei because of the strong quadrupolar coupling constants of 14N nuclei; and (3) the indirect J-coupling between the 13C and 195Pt. The principal elements as well as their orientations of the two 13C chemical shift tensors are evaluated from the spectral simulations.

Carbon Isotopes↗
PubMed1998

p53 mutation is a poor prognostic indicator for survival in patients with hepatocellular carcinoma undergoing surgical tumour ablation.

Forty-two patients with hepatocellular carcinoma (HCC) were resected and their tumours were analysed for p53 mutations by GC-clamped denaturing gradient gel electrophoresis (DGGE), single-strand conformation polymorphism (SSCP) and gene sequencing. All the exons have been analysed in this study. Eight of 12 HCCs with cirrhosis due to viral hepatitis and the two patients with sarcomatoid changes displayed p53 mutations. In contrast, no mutation was observed in the fibrolamellar variant (n = 9), non-cirrhotics (n = 13) and alcoholic cirrhosis (n = 6). The mutations observed were in exons 5-8. Two mutations were observed in codons 136 and 213 as well as a T insertion between residues 156 and 157 (exon 5) and these are reported for the first time in HCC. Likewise, the silent mutation polymorphism in codon 213 was noticed in 3 of the 42 patients. Survival analysis of these patients after surgery showed the mean and median survival in patients with wild-type p53 to be 60 and 43 months respectively. In the group with p53 mutations, the mean and median survival was 15 and 12 months. The difference was statistically significant (P= 0.003).

Adolescent↗
PubMed1997

High levels of recombinant CYP3A4 expression in Chinese hamster ovary cells are modulated by coexpressed human P450 reductase and hemin supplementation.

Expression of recombinant cytochrome P450s (P450s) in mammalian cells has been used as a powerful tool to study these enzymes. However, the activity of CYP3A4 expressed in several stable mammalian cell lines was much lower than native enzyme in human liver. The low level of recombinant CYP3A4 may have been due to the low copy number of the cDNA. In addition, the low activity is caused by the low level of P450 reductase in these cells. To achieve high levels of CYP3A4 expression, we employed gene amplification of the CYP3A4 cDNA in Chinese hamster ovary (CHO) cells followed by transfection of the P450 reductase cDNA. Using this strategy, we have obtained a cell line, designated D3A4, with high levels of recombinant CYP3A4. The content of spectrally active P450 was 14 pmol/mg total cellular protein. Hemin treatment increased the P450 content 2-fold. Upon coexpression of P450 reductase in DHR/3A4 cells, enzyme activity of CYP3A4 was stimulated 15-fold, despite a 40% decrease in spectrally active P450. Interestingly, the latter effect was not due to a decrease in CYP3A4 mRNA. Treatment of these cells with hemin, however, counteracted the P450 reductase-mediated decrease of spectrally active P450. These data demonstrate that P450 reductase has a strong influence on the levels of recombinant P450 holoenzyme, possibly by modulating the level of heme in CHO cells. Concomitantly our results show that the gene amplification strategy provides a powerful approach to obtain a high level of functional recombinant P450.

Animals↗
PubMed1997

Molecular cloning of a new unc-33-like cDNA from rat brain and its relation to paraneoplastic neurological syndromes.

Anti-CV2-autoantibodies from patients with paraneoplastic neurological syndromes were used to purify protein(s) related to this disease. A novel cDNA, c-22, was obtained by PCR with primers based on amino-acid sequence of peptides obtained from this protein and rat brain cDNA as template. The deduced amino-acid sequence of c-22 shows homology to the Unc-33 gene from C. elegans in which mutations lead to defects in neuritic outgrowth and axonal guidance and cause uncoordinated movements of the nematode. Several consensus sites for putative protein kinase C phosphorylation were found, suggesting that the c-22 gene product may be a phosphoprotein. Northern hybridizations show that the apparently unique 3.8-kb mRNA of c-22 is present in rat brain tissue and its expression is developmentally regulated: the levels of C-22 mRNA, detectable in brain at embryonic day 17 (E17), increase up to post-natal day 7 (P7) and decline rapidly to an almost undetectable level in adult.

Amino Acid Sequence↗
PubMed1997

Two novel subgenomic RNAs derived from RNA 3 of tomato aspermy cucumovirus.

Two abundant subgenomic RNAs, designated RNA 3B and RNA 5, were found to be associated with the V strain of tomato aspermy cucumovirus (V-TAV). Sequence determination showed that the 3'-terminal 323 nucleotides (nt) of RNA 3B was identical to RNA 5, whereas its 5'-terminal 163 nt was a direct repeat (one nt difference) of the 5'-half of RNA 5, and that both RNAs are completely homologous to the 3'-terminal untranslated region of TAV RNA 3. TAV RNAs 3B and 5 were also detected in the infection of a pseudorecombinant virus consisting of TAV RNA 3 and RNAs 1 and 2 from cucumber mosaic virus. Furthermore, only RNA 5, not RNA 3B, was detected in a TAV mutant in which one of the repeats was deleted from RNA 3. These genetic studies clearly show that both RNA species are derived from TAV RNA 3. However, in contrast to TAV RNAs 4 and 4A, which encode coat protein and 2b protein, respectively, RNAs 3B and 5 represent a novel class of subgenomic RNAs from TAV that do not function as mRNAs. Possible functional roles for such a class of viral subgenomic RNAs are discussed.

Base Sequence↗
PubMed1996

Coexpression of a human P450 (CYP3A4) and P450 reductase generates a highly functional monooxygenase system in Escherichia coli.

The catalytic activities of recombinant cytochrome P450s expressed in E. coli have been impeded by the absence of endogenous P450 reductase. To solve this problem, we coexpressed P450 reductase with CYP3A4. Membranes from this strain contained 215 pmol P450/mg protein and a reductase activity of 1315 nmol cytochrome c reduced/min per mg. We detected 6beta-hydroxylation of testosterone and oxidation of nifedipine in vivo with turnover numbers of 15.2 and 17.3 min(-1), respectively. These values compare favourably with those obtained using an optimally reconstituted system. Our data demonstrate that a catalytically efficient human P450 system can be generated in E. coli.

Base Sequence↗
PubMed1996

A modified sub-second fast-STEAM sequence incorporating bipolar gradients for in vivo diffusion imaging.

A modified high-speed stimulated-echo acquisition mode (STEAM) diffusion sequence (90 degrees-TE/2-90 degrees-TM-[alpha-TE/2-STE]n) incorporating bipolar diffusion gradients that are less sensitive to macroscopic motion-induced artifacts is presented. Diffusion encoding was performed only during the first echo interval (TE1) with bipolar gradients that were implemented on all three mutually orthogonal axes. Calibration measurements on phantoms filled with water, isopropanol, and dimethyl sulfoxide yielded apparent diffusion coefficients (ADC) consistent with published values. Non-ECG-triggered in vivo images acquired on rat brain with relatively high b values (approximately 450 s/mm2) indicated minimal motion artifacts. Evaluated ADCs averaged over the cortex, left mid-brain, right mid-brain, regions yielded (0.91 +/- 0.02), (1.06 +/- 0.02), (1.01 +/- 0.03) x 10(-3) mm2s-1, respectively.

Animals↗
PubMed1995

Expression and alternative splicing of the cytochrome P-450 CYP2A7.

In order to investigate the relative levels of expression of human cytochrome P-450 (P-450) CYP2A genes and determine how this relates to polymorphism in coumarin hydroxylase activity, cDNA clones for members of the CYP2A gene family were isolated. These clones were CYP2A6, CYP2A7 and an alternatively spliced version of CYP2A7 (CYP2A7AS). The latter clone was missing exon 2, but contained a 10 bp segment of intron 1. Translation of CYP2A7AS resulted in an in-frame deletion of 51 amino acids. The expression of these cDNAs in COS-7 cells showed that both CYP2A6 and CYP2A7 generated a protein of molecular mass 49 kDa, whereas the protein product of CYP2A7AS was about 44 kDa. Only the CYP2A6 had coumarin hydroxylase activity. The relative level of CYP2A7 and CYP2A7AS mRNA was investigated by reverse transcription followed by PCR (RT-PCR) using human liver RNAs and an RNA sample from a human skin fibroblast cell line. In one of five liver RNAs studied, the aberrantly spliced CYP2A7 mRNA was 3-4-fold more abundant than the normal mRNA. The other samples contained very low levels of this mRNA species. Interestingly, CYP2A7AS mRNA was the major CYP2A7 mRNA detected in the fibroblast cell line. In this case only a protein band of 44 kDa was observed by Western-blot analysis. The relative of mRNA encoding CYP2A6 and CYP2A7 was established in seven human liver samples by RT-PCR and found to range between 1:0.5 and 1:3. These data strength the previous findings that alternative splicing is an important factor in determining the levels of many human P-450s and that this may be subject to tissue-specific effects. Whether in this case the protein product has some function remains to be determined.

Alternative Splicing↗
PubMed1995

The apparent diffusion constant measured by MRI correlates with pO2 in a RIF-1 tumor.

As tissue oxygen tension (pO2) is an important variable in cancer therapy, it would be of major clinical benefit to be able to measure pO2 noninvasively. Current methods for determining pO2 in clinical settings are limited to superficial tumors. The authors measured the apparent diffusion constant (ADC) in an implanted murine fibrosarcoma (RIF-1) using magnetic resonance imaging and correlated the ADC with tissue pO2 measured by electron paramagnetic resonance oximetry. The ADC correlates significantly with tissue pO2 in this tumor (r = 0.89; n = 14) and so may provide a noninvasive index of pO2 in tumors.

Animals↗
PubMed1995

High resolution renal diffusion imaging using a modified steady-state free precession sequence.

A modified steady-state free precession (SSFP) diffusion sequence is proposed for high resolution renal imaging. A pair of bipolar diffusion gradients was used to minimize the errors in measured apparent diffusion coefficient (ADC) caused by variations in T1, T2, and RF flip angle that have been observed with previously employed SSFP diffusion sequences. Motion sensitivity was reduced by the use of compensated gradients, frame-by-frame averaging, and a repetition time of 22 ms, which for a single-acquisition 128 x 128 image requires only 3 s. High resolution was achieved by signal averaging. The modified sequence was applied to in vivo diffusion measurements. In six normal rat kidneys the ADCs (mean +/- SD; x 10(-3) mm2/s) of the cortex, outer medulla, and inner medulla were 2.28 +/- 0.05, 2.38 +/- 0.10, and 2.95 +/- 0.05, respectively. The technique requires relatively large gradients to achieve adequate diffusion weighting.

1-Propanol↗
PubMed1995

A longitudinal study on electrophysiological properties of atrioventricular accessory pathways in infants and children.

In this study the electrophysiological developmental changes of accessory pathway (AP) properties in infants and children are examined. Intracardiac and/or transesophageal electrophysiological studies were performed on seven infants (group 1, mean age 2 months) and four children (group 2, mean age 9 y; study 1), and documented orthodromic atrioventricular tachycardia in all cases. At follow-up study (study 2), supraventricular tachycardia was induced in three of seven (43%) cases in group 1 and in all four cases in group 2. Changes in antegrade conduction properties of AP were documented by loss of pre-excitation (two of four cases in group 1) or change to intermittent pre-excitation (one of two cases in group 2).

Age of Onset↗