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Biomedical subjects

J Chen

Publications and source records attributed to J Chen.

At least 487 records · Page 27Linked to original sources
PubMed2001

Multimodal standardization of voice among four multicultural populations: fundamental frequency and spectral characteristics.

A stratified random sample of 20 males and 20 females matched for physiological factors and cultural-linguistic markers were examined to determine differences in fundamental frequency and spectral characteristics during prolongation of three vowels: [a], [i], and [u]. The ethnic-gender breakdown included four sets of five male and five female subjects comprised of Caucasian and African-American speakers of standard American English, native Hindi Indian speakers, and native Mandarin Chinese speakers. Acoustic measures were analyzed using the Multidimensional Voice Program (Kay Elemetrics, Lincoln Park, NJ) (Model 4305) from which fundamental frequency and associated acoustic spectra were extracted from a 200-ms sample of each vowel token. Statistically significant group differences for the main effects of culture, race, and gender were found. The acoustic differences found are attributed to biomechanical, physiological, cultural, and linguistic factors.

Adult↗
PubMed2001

Synthesis and DNA nicking studies of a novel cyclic peptide: cyclo[Lys-Trp-Lys-Ahx-].

Two novel cyclic tetrapeptides: cyclo[Lys-Tyr-Lys-Ahx-] 7a and cyclo[Lys-Trp-Lys-Ahx-] 7b were synthesized by coupling protected amino acid in solution and the subsequent cyclization effected by the pentafluorophenyl ester method as described in previous papers. These cyclic peptides were designed and synthesized to study their interaction with DNA, based on previous reports that linear peptides Lys-Tyr-Lys and Lys-Trp-Lys could bind to various forms of DNA and cleaved supercoiled DNA at apurinic sites. Ethidium bromide displacement assay showed that the apparent DNA binding constant of linear Lys-Tyr-Lys and cyclic peptide 7a are far below 1 x 10(3) M(-1), whereas those of cyclic peptide 7b and linear Lys-Trp-Lys are 1.9 x 10(4) M(-1) and 9.5 x 10(3) M(-1), respectively. Kinetic studies using agarose gel electrophoresis showed that cyclic peptide 7b and Lys-Trp-Lys possessed DNA nicking activity on natural supercoiled phi X174 DNA with nicking rate of 50.7 and 75.6 pM min(-1) at 65 degrees C, respectively, whereas cyclic peptide 7a and linear Lys-Tyr-Lys were devoid of the corresponding activity. The DNA nicking rate increased significantly with increase in reaction temperature. At reaction temperatures lower than 65 degrees C, the DNA nicking rate of cyclic peptide 7b exceeded that of linear Lys-Trp-Lys. The addition of 1 microM ferrous ion did not give significant enhancement effect on the DNA nicking rate by the peptides. UV irradiation gave a marked rate enhancement on the DNA nicking rate of linear Lys-Trp-Lys and a moderate enhancement on the DNA nicking rate of cyclic peptide 7b.

DNA↗
PubMed2001

Photon radiation dose enhancement at material interfaces.

Experimental radiation dose-effect studies at a material's interface require high-resolution dose measurements resulting from the exposure of mounted samples on a supporting substrate. Reflections of photons and electrons from the substrate increase the effective dose to the sample relative to dose from the direct beam incident on the unbacked sample. This difficult-to-measure enhancement of effective dose can be calculated easily with Monte Carlo transport codes. We have used the Monte Carlo code, CYLTRAN, to carry out radiation transport and dose calculations in very thin water layers backed by different substrate materials. We present cases with an incident photon beam (15-100 keV) on a water medium with five different substrates--mylar, aluminum, copper, silver, and gold.

Journal Article↗
PubMed2001

Bleeding complications associated with the use of rt-PA versus r-PA for peripheral arterial and venous thromboembolic occlusions.

This article analyzes the early experience with alteplase (rt-PA) and reteplase (r-PA) to identify noteworthy differences in bleeding and to determine correlations with dosage, concomitant anticoagulation, and duration of infusion. A retrospective review of the medical records was unavailable for the initial 82 patients who were treated with either rt-PA (44) or r-PA (38) for peripheral arterial or venous occlusions after urokinase therapy. Successful recanalization was achieved in 31/44 (70%) of the patients treated with rt-PA and in 34/38 (89%) of the patients treated with r-PA. Significant bleeding was documented in 20/44 (45%) of the rt-PA-treated patients (including 14 transfusions) versus 3/38 (8%) of the r-PA-treated patients (3 transfusions). Concomitant anticoagulation with either preceding warfarin (international normalized ratio > 1.1) or a bolus of heparin at the outset of the infusion was associated with significant bleeding in 13/17 (76%) of the rt-PA-treated patients (including 9 transfusions) versus 0/17 in the r-PA-treated patients. No significant correlation between either mean dose or total dose and bleeding was shown for either drug. Early experience indicates that r-PA is at least as effective as rt-PA for the thrombolysis of peripheral arterial and venous occlusions. It also appears that r-PA is less likely than rt-PA to be associated with significant bleeding during such infusions, especially if the patient is concomitantly anticoagulated.

Adolescent↗
PubMed2001

Fatty acid composition and dynamics of selected fungal-feeding nematodes and fungi.

Fatty acid profiles of fungal-feeding nematodes, Aphelenchus avenae and Aphelenchoides composticola, and selected fungi were determined in microcosm cultures of agar, broth, or sand amended with organic matter. Fatty acids of A. avenae and A. composticola included 16:0 18:0, 18:1omega7, 18:1omega9, 18:2, 20:0, 20:1, 20:2, 20:3 and 20:4 phospholipid fatty acids (PLFAs) and neutral lipid fatty acids (NLFAs). The nematodes differed in relative amounts of saturated and C(18) fatty acids. Similar C(16) and C(18) PLFAs and whole-cell fatty acids were found in Rhizoctonia solani, Fusarium oxysporum and Trichoderma sp. with 18:2omega6 as the major component. The C(20) fatty acids were not found in these fungi. Although only present in the nematodes, C(20) PLFAs were only detected when nematode population levels were > or =22 per gram of sand, suggesting that there is a detection threshold that might limit their use as biomarkers in the soil community. After removal of nematodes from a food source, the relative amount of C(20) PLFAs (structural components of nematode cell membranes) decreased more slowly than the C(16) and C(18) PLFAs, which may have reflected ingested fungal cytoplasm in the nematode intestine. In the early stage of organic matter decomposition, total and fungal PLFAs were lower in the presence of A. composticola then in its absence at C:N ratios > or =30:1.

Animals↗
PubMed2001

Computational tools in rehabilitation of erectile dysfunction.

Erectile dysfunction (ED) is defined as the inability to achieve and maintain an erection adequate for satisfactory intercourse. It is a common problem among approximately 50% of men between the ages of 40 and 70. Erectile dysfunction is not only stressful to both the affected individual and his partner, but it can also negatively affect self-esteem. Biomechanical models have recently been developed to study both the structural and hemodynamic factors involved in normal and pathological erectile conditions. These computational models, which are reviewed in the present paper, allow for better understanding of the mechanisms acting in ED and provide a suitable basis for development of state-of-the-art interdisciplinary treatment approaches aimed to improve the quality of life for these men.

Adult↗
PubMed2001

Vibrational spectra and normal coordinate analysis of a weak ligand complex, Co(p-DMABA)2Cl2 x 2H2O.

The complex Co(p-DMABA)2Cl2 x 2H2O (p-dimethylaminobenzaldehyde, p-DMABA) was prepared from the solid-state reaction of a weak ligand p-DMABA and CoCl2 x 6H2O at lower heating temperature (60 degrees C). It is very difficult to obtain the title complex using solution reaction method, less than isolating single crystals. In order to determine the crystal structure of the title compound, we have to rely on the X-ray powder diffraction data. That is, the crystal structure can be solved directly from powder data, which crucial step is to constitute the structure model. Indirect spectroscopic methods, such as infrared and Raman spectroscopes, and further vibrational assignments made with the aid of normal coordinate calculations by using a modified Urey-Bradley force field, were analyzed to proposed molecular structure. One hundred and fifty-seven internal coordinates were established and 129 theoretical vibrational frequencies were calculated. An appropriate set of internal coordinates and force constants in the course of calculation were introduced, so that the calculated vibration frequencies are good agreement with the observed values. The average difference and the maximum deviation between theoretic and experimental frequencies are 2.44 and 8.0 cm(-1), respectively. Thus the normal coordinate analysis is a powerful tool to the molecular structure. Other structural and spectral properties are also discussed in this paper. The purpose of the present paper is to obtain a good structural model. This model was used as starting model for crystal structure determination from powder X-ray diffraction (XRD) data.

Crystallization↗
PubMed2001

Pooled exposure-response analyses and risk assessment for lung cancer in 10 cohorts of silica-exposed workers: an IARC multicentre study.

OBJECTIVES: Silica is one of the most common occupational exposures worldwide. In 1997 the International Agency for Research on Cancer (IARC) classified inhaled crystalline silica as a human carcinogen (group 1), but acknowledged limitations in the epidemiologic data, including inconsistencies across studies and the lack of extensive exposure-response data. We have conducted a pooled exposure-response analysis of 10 silica-exposed cohorts to investigate lung cancer. METHODS: The pooled cohort included 65,980 workers (44,160 miners, 21,820 nominees), and 1,072 lung cancer deaths (663 miners, 409 nonminers). Follow-up has been extended for five of these cohorts beyond published data. Quantitative exposure estimates by job and calendar time were adopted, modified, or developed to permit common analyses by respirable silica (mg/m3) across cohorts. RESULTS: The log of cumulative exposure, with a 15-year lag, was a strong predictor of lung cancer (p = 0.0001), with consistency across studies (test for heterogeneity, p = 0.34). Results for the log of cumulative exposure were consistent between underground mines and other facilities. Categorical analyses by quintile of cumulative exposure resulted in a monotonic trend with odds ratios of 1.0. 1.0, 1.3, 1.5, 1.6. Analyses using a spline curve also showed a monotonic increase in risk with increasing exposure. The estimated excess lifetime risk (through age 75) of lung cancer for a worker exposed from age 20 to 65 at 0.1 mg/m3 respirable crystalline silica (the permissible level in many countries) was 1.1-1.7%, above background risks of 3-6%. CONCLUSIONS: Our results support the decision by the IARC to classify inhaled silica in occupational settings as a carcinogen, and suggest that the current exposure limits in many countries may be inadequate. These data represent the first quantitative exposure-response analysis and risk assessment for silica using data from multiple studies.

Air Pollutants, Occupational↗
PubMed2001

Production of poly-3-hydroxybutyrate by Bacillus sp. JMa5 cultivated in molasses media.

A strain of Bacillus sp. coded JMa5 was isolated from molasses contaminated soil. The strain was able to grow at a temperature as high as 45 degrees C and in 250 g/l molasses although the optimal growth temperature was 35-37 degrees C. Cell density reached 30 g/l 8 h after inoculation in a batch culture with an initial concentration of 210 g/l molasses. Under fed-batch conditions, the cells grew to a dry weight of 70 g/l after 30 h of fermentation. The strain accumulated 25-35%, (w/w) polyhydroxybutyrate (PHB) during fermentation. PHB accumulation was a growth-associated process. Factors that normally promote PHB production include high ratios of carbon to nitrogen, and carbon to phosphorus in growth media. Low dissolved oxygen supply resulted in sporulation, which reduced PHB contents and dry weights of the cells. It seems that sporulation induced by reduced supply of nutrients is the reason that PHB content is generally low in the Bacillus strain.

3-Hydroxybutyric Acid↗
PubMed2001

Caution in the use of 2-iminothiolane (Traut's reagent) as a cross-linking agent for peptides. The formation of N-peptidyl-2-iminothiolanes with bombesin (BN) antagonist (D-Trp(6),Leu(13)-psi[CH(2)NH]-Phe(14))BN(6-14) and D-Trp-Gln-Trp-NH(2).

During a study aimed at generating a bispecific molecule between BN antagonist (D-Trp(6),Leu(13)-psi[CH(2)NH]-Phe(14))BN(6-14) (Antag1) and mAb22 (anti-FcgammaRI), we attempted to cross-link the two molecules by introducing a thiol group into Antag1 via 2-iminothiolane (2-IT, Traut's reagent). We found that reaction of Antag1 with 2-IT, when observed using HPLC, affords two products, but that the later eluting peptide is rapidly transformed into the earlier eluting peptide. To understand what was occurring we synthesized a model peptide, D-Trp-Gln-Trp-NH(2) (TP1), the N-terminal tripeptide of Antag1. Reaction of TP1 with 2-IT for 5 min gave products 1a and 3a; the concentration of 1a decreased with reaction time, whereas that of 3a increased. Thiol 1a, the expected Traut product, was identified by collecting it in a vial containing N-methylmaleimide and then isolating the resultant Michael addition product 2a, which was confirmed by mass spectrometry. Thiol 1a is stable at acidic pH, but is unstable at pH 7.8, cyclizes and loses NH3 to give N-TP1-2-iminothiolane (3a), ES-MS (m/z) [602.1 (M+H)(+)], as well as regenerating TP1. Repeat reaction with Antag1 and 2-IT allowed us to isolate N-Antag1-2-iminothiolane (3b), FAB-MS (m/z) [1212.8 (M+H)(+)] and trap the normal Traut product 1b as its N-methylmaleimide Michael addition product 2b, ES-MS (m/z) [1340.8 (M+H)(+)]. Thiol 1b is also stable at acidic pH, but when neutralized is unstable and cyclizes, forming 3b and Antag1.

Antibodies, Monoclonal↗
PubMed2001

Periodontal infections and pre-term birth: early findings from a cohort of young minority women in New York.

The aim of this report is to provide early data from an ongoing study examining (i) the relationship between periodontal infections and pre-term low birth weight (PLBW) in a cohort of young, minority, pregnant and post-partum women; and (ii) the effect of periodontal interventions on pregnancy outcome. During the first 2 yr of the study, 213 women were enrolled and examined clinically for dental plaque, calculus, bleeding on probing, and probing depth. Birth outcome data were available for 164 women, including one group (n = 74) subjected to oral prophylaxis during pregnancy, and a second group (n=90) who received no prenatal periodontal treatment. Subgingival plaque samples were available from 145 subjects (4 samples/subject) and were analyzed by checkerboard DNA hybridization with respect to 12 bacterial species. The prevalence of PLBW was 16.5% (27 cases) in this cohort. No differences in clinical periodontal status were observed between PLBW cases and women with normal birth outcome. However, PLBW mothers had significantly higher levels of Bacteroides forsythus and Campylobacter rectus, and consistently elevated counts for the other species examined. PLBW occurred in 18.9% of the women who did not receive periodontal intervention (17 cases), and in 13.5% (10 cases) of those who received such therapy.

Adolescent↗
PubMed2001

Cofilin/ADF is required for cell motility during Drosophila ovary development and oogenesis.

The driving force behind cell motility is the actin cytoskeleton. Filopodia and lamellipodia are formed by the polymerization and extension of actin filaments towards the cell membrane. This polymerization at the barbed end of the filament is balanced by depolymerization at the pointed end, recycling the actin in a 'treadmilling' process. One protein involved in this process is cofilin/actin-depolymerizing factor (ADF), which can depolymerize actin filaments, allowing treadmilling to occur at an accelerated rate. Cofilin/ADF is an actin-binding protein that is required for actin-filament disassembly, cytokinesis and the organization of muscle actin filaments. There is also evidence that cofilin/ADF enhances cell motility, although a direct requirement in vivo has not yet been shown. Here we show that Drosophila cofilin/ADF, which is encoded by the twinstar (tsr) gene, promotes cell movements during ovary development and oogenesis. During larval development, cofilin/ADF is required for the cell rearrangement needed for formation of terminal filaments, stacks of somatic cells that are important for the initiation of ovarioles. It is also required for the migration of border cells during oogenesis. These results show that cofilin/ADF is an important regulator of actin-based cell motility during Drosophila development.

Actin Depolymerizing Factors↗
PubMed2001

A photic visual cycle of rhodopsin regeneration is dependent on Rgr.

During visual excitation, rhodopsin undergoes photoactivation and bleaches to opsin and all-trans-retinal. To regenerate rhodopsin and maintain normal visual sensitivity, the all-trans isomer must be metabolized and reisomerized to produce the chromophore 11-cis-retinal in biochemical steps that constitute the visual cycle and involve the retinal pigment epithelium (RPE; refs. 3-8). A key step in the visual cycle is isomerization of an all-trans retinoid to 11-cis-retinol in the RPE (refs. 9-11). It could be that the retinochrome-like opsins, peropsin, or the retinal G protein-coupled receptor (RGR) opsin12-16 are isomerases in the RPE. In contrast to visual pigments, RGR is bound predominantly to endogenous all-trans-retinal, and irradiation of RGR in vitro results in stereospecific conversion of the bound all-trans isomer to 11-cis-retinal. Here we show that RGR is involved in the formation of 11-cis-retinal in mice and functions in a light-dependent pathway of the rod visual cycle. Mutations in the human gene encoding RGR are associated with retinitis pigmentosa.

Animals↗
PubMed2001

Folding of malate dehydrogenase inside the GroEL-GroES cavity.

The chaperonin GroEL binds nonnative substrate protein in the hydrophobic central cavity of an open ring. ATP and GroES binding to the same ring converts this cavity into an encapsulated, hydrophilic chamber that mediates productive folding. A 'rack' mechanism of initial protein unfolding proposes that, upon GroES and ATP binding, the polypeptide is stretched between the binding sites on the twisting apical domains of GroEL before complete release into the chamber. Here, the structure of malate dehydrogenase (MDH) subunit during folding is monitored by deuterium exchange, peptic fragment production and mass spectrometry. When bound to GroEL, MDH exhibits a core of partially protected secondary structure that is only modestly deprotected upon ATP and GroES binding. Moreover, deprotection is broadly distributed throughout MDH, suggesting that it results from breaking hydrogen bonds between MDH and the cavity wall or global destabilization, as opposed to forced mechanical unfolding.

Adenosine Triphosphate↗
PubMed2001

Epigenetic regulation of gene structure and function with a cell-permeable Cre recombinase.

Studies of mammalian gene function are hampered by temporal limitations in which phenotypes occurring at one stage of development interfere with analysis at later stages. Moreover, phenotypes resulting from altered gene activity include both direct and indirect effects that may be difficult to distinguish. In the present study, recombinant fusion proteins bearing the 12 amino acid membrane translocation sequence (MTS) from the Kaposi fibroblast growth factor (FGF-4) were used to transduce enzymatically active Cre proteins directly into mammalian cells. High levels of recombination were observed in a variety of cultured cell types and in all tissues examined in mice following intraperitoneal administration. This represents the first use of protein transduction to induce the enzymatic conversion of a substrate in living cells and animals and provides a rapid and efficient means to manipulate mammalian gene structure and function.

Animals↗
PubMed2001

Absence of pressure overload induced myocardial hypertrophy after conditional inactivation of Galphaq/Galpha11 in cardiomyocytes.

Myocardial hypertrophy is an adaptational response of the heart to increased work load, but it is also associated with a high risk of cardiac mortality due to its established role in the development of cardiac failure, one of the leading causes of death in developed countries. Multiple growth factors and various downstream signaling pathways involving, for example, ras, gp-130 (ref. 4), JNK/p38 (refs. 5,6) and calcineurin/NFAT/CaM-kinase have been implicated in the hypertrophic response. However, there is evidence that the initial phase in the development of myocardial hypertrophy involves the formation of cardiac para- and/or autocrine factors like endothelin-1, norepinephrine or angiotensin II (refs. 7,8), the receptors of which are coupled to G-proteins of the Gq/11-, G12/13- and Gi/o-families. Cardiomyocyte-specific transgenic overexpression of alpha1-adrenergic or angiotensin (AT1)-receptors as well as of the Gq alpha-subunit, Galphaq, results in myocardial hypertrophy. These data demonstrate that chronic activation of the Gq/G11-family is sufficient to induce myocardial hypertrophy. In order to test whether Gq/G11 mediate the physiological hypertrophy response to pressure overload, we generated a mouse line lacking both Galphaq and Galpha11 in cardiomyocytes. These mice showed no detectable ventricular hypertrophy in response to pressure-overload induced by aortic constriction. The complete lack of a hypertrophic response proves that the Gq/G11-mediated pathway is essential for cardiac hypertrophy induced by pressure overload and makes this signaling process an interesting target for interventions to prevent myocardial hypertrophy.

Animals↗