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Biomedical subjects

J Y Chen

Publications and source records attributed to J Y Chen.

At least 19 recordsLinked to original sources
PubMed1992

Long-term results of percutaneous mitral valvuloplasty with the Inoue balloon catheter.

The initial 85 patients who successfully underwent percutaneous mitral valvuloplasty (PMV) with the Inoue balloon catheter at the Guangdong Cardiovascular Institute between November 1985 and November 1988 had a mean follow-up period of 5 +/- 1 year (range 43 to 79 months). Before and after PMV and at follow-up, mean diastolic mitral gradients by the catheter method were 17.5 +/- 6.2, 3.1 +/- 3.3 and 3.3 +/- 3.4 mm Hg, respectively (p < 0.001 before vs after PMV and before vs follow-up; and p > 0.05 after PMV vs follow-up). Mean diastolic mitral gradients by the Doppler method were 18 +/- 6, 8 +/- 5 and 9 +/- 5 mm Hg, respectively (p < 0.001 before vs after PMV and before vs follow-up; and p > 0.05 after PMV vs follow-up). Mean diastolic mitral gradients by the Doppler method were 18 +/- 6, 8 +/- 5 and 9 +/- 5 mm Hg, respectively (p < 0.001 before vs after PMV and before vs follow-up; and p > 0.05 after PMV vs follow-up). Mitral valve areas by the echo-Doppler method were 1.1 +/- 0.3, 2.0 +/- 0.4 and 1.8 +/- 0.5 cm2, respectively (p < 0.001 before vs after PMV and before vs follow-up; and p > 0.05 after PMV vs follow-up). Phonocardiographic and vectorcardiographic studies, and cardiopulmonary exercise testing showed significant improvement after PMV and at follow-up.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Characterization and purification of human retinoic acid receptor-gamma 1 overexpressed in the baculovirus-insect cell system.

The full-length cDNA for the human retinoic acid receptor-gamma 1 (RAR-gamma 1) has been expressed to high levels in Spodoptera frugiferda (Sf9) cells using the baculovirus expression system. Western blot analysis revealed that RAR-gamma 1 expression increased between 32 and 60 h post-infection. The recombinant receptor was expressed primarily as a nuclear protein and displayed a molecular mass of 50 kDa as determined by SDS/PAGE and gel-filtration chromatography, consistent with its cDNA-deduced size. Based on ligand binding, 2 x 10(6) RAR-gamma 1 molecules were expressed per Sf9 cell, a level approx. 2000 times greater than in mammalian cells. The receptor was partially purified 300-fold by sequential anion-exchange, gel-filtration and DNA affinity chromatographies. The overexpressed receptor specifically bound all-trans-retinoic acid (RA) and the synthetic retinoid CD367 with high affinity (Kd 0.15 nM and 0.23 nM respectively). The RA metabolites 4-hydroxy-RA and 4-oxo-RA were poor competitors for [3H]CD367 binding to recombinant RAR-gamma 1 (K(i) > 1 microM), indicating that 4-oxidation of RA greatly reduces its affinity for RAR-gamma 1. Gel-retardation analysis demonstrated that RAR-gamma 1 specifically bound the RA response element of the mouse RAR-beta gene. RAR-gamma 1 species expressed from recombinant baculovirus (in Sf9 cells) and vaccinia virus (in HeLa cells) exhibited similar affinities for RA and CD367 and had comparable DNA-binding properties in gel-retardation experiments. Moreover, a similar requirement for additional DNA-binding stimulatory factor(s) was observed in both cases. These results provide a basis for the use of baculovirus-expressed RAR-gamma 1 in further functional and structural studies.

Amino Acid Sequence↗
PubMed1992

Synthesis of a biospecific adsorbent for the purification of the three human retinoic acid receptors by affinity chromatography.

The total synthesis of an affinity gel suitable for the purification of retinoic acid receptors (hRARs) is reported. A chalcone derived from a potent retinobenzoic acid (Ch55) was chosen as the ligand and fixed to an immobilized matrix by coupling with the N-hydroxysuccinimide ester of agarose (Affi-Gel 10, Bio-Rad Laboratories). Efficiencies of purification of the different human RARs were tested, using recombinant receptors produced with the baculovirus expression system.

Carrier Proteins↗
PubMed1992

Cytoplasmic and mitochondrial tRNA nucleotidyltransferase activities are derived from the same gene in the yeast Saccharomyces cerevisiae.

ATP (CTP):tRNA-specific tRNA nucleotidyltransferase is an enzyme required for the synthesis of functional tRNAs in eukaryotic cells. Neither the tRNA genes in the nucleus nor in organelles encode the CCA end, so it must be added post-transcriptionally. The gene that codes for the enzyme that adds the CCA end to nuclear coded tRNAs in Saccharomyces cerevisiae has been isolated (Aebi, M., Kirchner, G., Chen, J.-Y., Vijayraghavan, U., Jacobson, A., Martin, N. C., and Abelson, J. (1990) J. Biol. Chem. 265, 16216-16220). We now demonstrate that there is a mitochondrial tRNA nucleotidyltransferase activity in yeast and that it is a matrix enzyme. A comparison of purified mitochondrial enzyme with its cytoplasmic counterpart revealed no differences. These results suggest that proteins responsible for this step in the maturation of tRNAs in the nucleus and mitochondria might be identical and coded by the same nuclear gene. Accumulation of shortened mitochondrial as well as cytoplasmic tRNAs in a strain with a temperature-sensitive tRNA nucleotidyltransferase is consistent with this hypothesis. Alteration of the wild type gene such that amino-terminal truncated proteins are produced leads to a defect in mitochondrial function and a decrease in mitochondrial nucleotidyltransferase activity. This provides a direct demonstration that one gene provides this enzyme activity for the biosynthesis of tRNAs in both the nuclear/cytoplasmic and mitochondrial compartments in yeast.

Amino Acid Sequence↗
PubMed1992

An infrequent point mutation of the p53 gene in human nasopharyngeal carcinoma.

Point mutations in the p53 gene have been detected in a variety of human cancers; the mutations are clustered in four "hot-spots" located in the coding region of exons 5, 7, and 8, which coincide with the four most highly conserved regions of the gene. We report the finding of a heterozygous G----C mutation at codon 280 (exon 8), position 2, of the p53 gene in a nasopharyngeal carcinoma (NPC) cell line, originating from Guangdong, a province in the People's Republic of China that leads the world in NPC incidence. A survey of nasopharyngeal tissues and NPC biopsies revealed that 1 out of 12 NPC samples from Hunan, another province in the People's Republic of China with high NPC incidence, had the same heterozygous mutation at codon 280 of p53, and none of 10 biopsies from Taiwan showed a mutation within exons 5-8 of the p53 gene. No other alteration of gene structure, including gross rearrangement or loss of heterozygosity or abnormality of gene expression was detected in NPC cell lines or NPC biopsies. We conclude from this study that mutational or other alterations of the p53 gene are not common in nasopharyngeal carcinogenesis and that a codon-280 mutation of p53 may be involved in less than 10% of NPC cases. This result contrasts with the relatively high frequency of p53 mutations associated with several other human carcinomas and suggests the importance of other genes in NPC genesis.

Base Sequence↗
PubMed1992

Two promoters in the bovine adrenodoxin gene and the role of associated, unique cAMP-responsive sequences.

The bovine adrenodoxin gene gives rise to two species of mRNA differing only at their 5'-ends. The synthesis of these two types of mRNA in bovine adrenal cortical cells is regulated transcriptionally in part by ACTH via the action of cAMP. Examination of the 5'-end of the adrenodoxin gene revealed that each mRNA contains sequences derived from a different exon encoding the mitochondrial leader sequence. To define the sequences necessary for the synthesis of these two types of mRNA and to determine if the synthesis of each is driven by a separate promoter, 5'-regions of the adrenodoxin gene were inserted upstream from two different reporter genes and tested for promoter/enhancer regulatory activity by transient transfection into mouse adrenocortical Y1 tumor cells. The results clearly demonstrated that the bovine adrenodoxin gene contains two functional promoters; one, ADXP1, located in the 5'-flanking region gives rise to the minor form of mRNA, and a second, stronger promoter, ADXP2, which maps within intron 1 gives rise to the major form of mRNA. Unique cAMP-responsive sequences were found upstream from each promoter which share no sequence homology to the consensus CRE (cAMP-responsive element). Upon transient expression, the cAMP-responsive sequence associated with the ADXP2 promoter, termed CRS2, confers the cAMP responsiveness to stimulate the transcription of the linked beta-globin reporter gene regardless of whether the adrenodoxin ADXP2 promoter or the beta-globin promoter was utilized.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenodoxin↗
PubMed1992

Purification, cloning, and RXR identity of the HeLa cell factor with which RAR or TR heterodimerizes to bind target sequences efficiently.

We have purified and cloned a HeLa cell nuclear protein that strongly stimulates binding of retinoic acid and thyroid hormone receptors (RARs and TRs) to response elements. The purified protein is a human retinoid X receptor beta (hRXR beta). Three murine members of the RXR family (mRXR alpha, beta, and gamma) have also been cloned, and their interactions with RARs and TRs have been investigated. Under conditions where RAR, RXR, and TR bound poorly as homodimers to various response elements, strongly cooperative RAR-RXR and TR-RXR binding was observed. The binding efficiency was dependent on the sequence, relative orientation, and spacing of the repeated motifs of response elements. We show also that unstable RAR-RXR heterodimers were formed in solution, and that C-terminal sequences and the DNA-binding domains of both receptors were required for efficient formation of stable heterodimers on response elements. These findings suggest a convergence of the signaling pathways of some members of the nuclear receptor superfamily.

Amino Acid Sequence↗
PubMed1992

A frequency-dependent finite-difference time-domain formulation for induced current calculations in human beings.

The finite-difference time-domain (FDTD) method has been used to calculate SARs and induced currents involving whole-body or partial-body exposures of models to spatially uniform or nonuniform (far-field or near-field), to sinusoidally varying EM fields, or to transient fields such as those associated with electromagnetic pulses. However, a weakness of the FDTD algorithm is that the dispersion of the tissue's dielectric properties is ignored and frequency-independent properties are assumed. Although this is permissible for continuous-wave or narrow-band irradiation, the results may be highly erroneous for short pulses, in which ultra-wide bandwidths are involved. In some recent publications, procedures are described for one- and two-dimensional problems for media in which the complex permittivity epsilon * (omega) may be described by a single-order Debye relaxation equation or a modified version thereof. These procedures based on a convolution integral describing D(t) in terms of E(t) cannot be extended to human tissues for which multiterm Debye relaxation equations must generally be used. We describe here a new differential-equation approach that can be used for general dispersive media. We illustrate the use of this approach by one- and three-dimensional examples of media for which epsilon * (omega) is given by a multiterm Debye equation, and for an approximate two-thirds muscle-equivalent model of the human body. Based on a single run involving a Gaussian pulse, the frequency-dependent FDTD [(FD)2TD] method allows calculations of SARs and induced currents at various frequencies by taking the Fourier components of the induced E fields. The (FD)2TD method can also be used to calculate coupling of the short (ultra-wideband) pulses to the human body.

Electromagnetic Phenomena↗
PubMed1992

Numerical dosimetry at power-line frequencies using anatomically based models.

We have used the finite-difference time-domain (FDTD) method to calculate induced current densities in a 1.31-cm (nominal 1/2 in) resolution anatomically based model of the human body for exposure to purely electric, purely magnetic, and combined electric and magnetic fields at 60 Hz. This model based on anatomic sectional diagrams consists of 45,024 cubic cells of dimension 1.31 cm for which the volume-averaged tissue properties are prescribed. It is recognized that the conductivities of several tissues (skeletal muscle, bone, etc.) are highly anisotropic for power-line frequencies. This has, however, been neglected in the first instance and will be included in future calculations. Because of the quasi-static nature of coupling at the power-line frequencies, a higher quasi-static frequency f' may be used for irradiation of the model, and the internal fields E' thus calculated can be scaled back to the frequency of interest, e.g., 60 Hz. Since in the FDTD method one needs to calculate in the time domain until convergence is obtained (typically 3-4 time periods), this frequency scaling to 5-10 MHz for f' reduces the needed number of iterations by over 5 orders of magnitude. The data calculated for the induced current and its variation as a function of height are in excellent agreement with the data published in the literature. The average current densities calculated for the various sections of the body for the magnetic field component (H) are considerably smaller (by a factor of 20-50) than those due to the vertically polarized electric field component when the ratio E/H is 377 ohms. We have also used the previously described impedance method to calculate the induced current densities for the anatomically based model of the human body for the various orientations of the time-varying magnetic fields, namely from side to side, front to back, or from top to bottom of the model, respectively.

Electromagnetic Fields↗
PubMed1992

The extraction of penicillin G with aliphatic amines in organic solvents of different polarities.

The equilibrium constants of the extraction, the molar ratios of amines to penicillin G in the extract and the bonding structures of the extracted species were studied with chemical analysis and the absorbance shift of FT-IR spectra of the functional groups in penicillin G. Extraction of penicillin G from the filtrate of fermentation broth indicates that amines will be difficult to use as the industrial solvent for the production of penicillin G because of the poor quality of the final crystalline product obtained and the difficulties involved in the stripping and solvent recovery.

Amines↗
PubMed1992

Detection of human herpesvirus-6 DNA by polymerase chain reaction in serum or plasma.

Human herpesvirus-6 (HHV-6) is a newly identified human pathogen. Currently clinicians rely mainly on blood lymphocyte culture and serological tests to diagnose HHV-6 infection. The polymerase chain reaction (PCR) was carried out on the plasma or sera of patients to determine the value of PCR in the diagnosis of HHV-6 infection. A total of 30 patients entered the study; 10 were experiencing acute HHV-6 infections and 20 were healthy and served as controls. HHV-6 DNA was detected by PCR in the serum or plasma of the 10 cases with acute HHV-6 infections. All 20 controls had no HHV-6 DNA in their sera. The time for serum to become PCR-positive coincided with the appearance of IgG HHV-6 antibody. The relatively late presence of HHV-6 DNA in serum might result from late lysis of infected cells by immune responses. It is concluded that detection of HHV-6 DNA by PCR in the serum is a valuable tool for the diagnosis of acute and/or active viral infection.

Adult↗
PubMed1992

Use of antigen expressed in bacteria for detection of EBV-specific thymidine kinase antibodies in sera from patients with nasopharyngeal carcinoma.

Two cDNA clones covering the N- and C-terminal portions of the EBV BXLF1 open reading frame were selected from a cDNA library derived from P3HR1 cells. The two clones were ligated, the N-terminal untranslated region truncated, and the product inserted into an E. coli expression vector, pET3CP*. The fusion protein was expressed under control of the T7 phage phi 10 gene promoter and shown to possess thymidine kinase activity. The protein was then used as an antigen to detect antibody reactivities in serum samples of nasopharyngeal carcinoma patients and healthy blood donors. Using a 1:400 dilution of serum samples in Western blot analyses, it was possible to differentiate the reactivities of serum IgA of NPC patients and healthy donors. The prevalence of positive reactivity to EBV TK in NPC was around 84%. The test was compared to others used for early diagnosis of NPC and was able to detect some patients who were negative in those tests.

Antibodies, Viral↗
PubMed1992

Cloning and expression of a cDNA encoding the Epstein-Barr virus thymidine kinase gene.

A clone of the Epstein-Barr virus (EBV) thymidine kinase (TK) gene was derived from a cDNA library of P3HR1 cells. The gene product was expressed as a fusion protein in a procaryotic system by using T7 RNA polymerase. The recombinant TK showed a molecular mass of 67 kDa and was biologically active. Antiserum raised in mice immunized with partially purified TK recognized an antigen present in EBV-superinfected Raji cells using an indirect immunofluorescence assay.

Animals↗
PubMed1992

Specific absorption rates and induced current distributions in an anatomically based human model for plane-wave exposures.

We have previously reported local, layer-averaged, and whole-body-averaged specific absorption rates and induced currents for a 5,628-cell anatomically based model of a human for plane-wave exposures 20-100 MHz (Chen and Gandhi 1989). Using a higher resolution, 45,024-cell model of the human body, calculations have now been extended to 915 MHz using the finite-difference time-domain method. Because of the higher resolution of the model, it has been possible to calculate specific absorption rates for various organs (brain, eyes, heart, lungs, liver, kidneys, and intestines) and for various parts of the body (head, neck, torso, legs, and arms) as a function of frequency in the band 100-915 MHz. Consistent with some of the experimental data in the literature, the highest part-body-averaged specific absorption rate for the head and neck region (as well as for the eyes and brain) occurs at 200 MHz for the isolated condition and at 150 MHz for the grounded condition of the model. Also observed is an increasing specific absorption rate for the eyes for frequencies above 350 MHz due to the superficial nature of power deposition at increasing frequencies.

Algorithms↗