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Biomedical subjects

J G Chen

Publications and source records attributed to J G Chen.

At least 55 records · Page 3Linked to original sources
PubMed1996

Trace elements and lipid peroxidation in uremic patients on hemodialysis.

Trace elements and lipid peroxidation in 26 patients with chronic renal failure treated with hemodialysis and 25 healthy subjects were observed. Both plasma and erythrocyte trace elements and plasma malon dialdehyde (MDA) were examined immediately before and after hemodialysis. Increased levels of plasma Cu, MDA, and erythrocyte Pb, Mn, Zn, and a significantly decreased plasma Se, Zn, and erythrocyte Se were found in patients before hemodialysis. After a single hemodialysis, erythrocyte Mn, Cu, Zn, and plasma Cu, Al, and MDA were significantly increased whereas both plasma and erythrocyte Se were lower in patients than in healthy subjects. The level of MDA was not significantly changed during the single hemodialysis. Both plasma and erythrocyte Zn levels and plasma Cu and Al were significantly higher after hemodialysis than before hemodialysis. In conclusion, levels of trace elements are altered by hemodialysis, which may increase patient susceptibility to lipid peroxidation in uremia.

Adult↗
PubMed1996

Hypertonic activation and recovery of system A amino acid transport in renal MDCK cells.

Amino compounds are abundant within the renal inner medulla, but their possible role during hypertonic stress is not clear. Renal epithelial Madin-Darby canine kidney cells were used to examine the osmoregulation of system A transport, a major Na(+)-dependent process for neutral amino acid transport. System A activity was markedly increased after 6 h of hypertonic challenge, and intracellular alanine content increased more than twofold. The activation of system A was reversed after 24 h of hypertonic challenge. This downregulation was accompanied by the activation of betaine transport, as measured by gamma-aminobutyric acid uptake. Extracellular betaine prevented the early activation of system A. The hypertonic activation of system A was blocked by actinomycin D and cycloheximide. When cells were returned to isotonic medium after hypertonic activation, the recovery of system A transport also was partially inhibited by actinomycin D and puromycin. The results are consistent with the possibility that hypertonicity, by disrupting a repressor protein, leads to increased synthesis of a system A-related protein. The isotonic recovery may require synthesis of new repressor proteins.

Amino Acids↗
PubMed1996

Color-Doppler Ultrasound-assisted endoscopic neurosurgery for intracerebral hemorrhage.

BACKGROUND: Over the past few years, the use of endoscopy in neurosurgery has gradually gained importance. In this study we described the performance of Color Doppler Ultrasound (CDU)-guided endoscopic neurosurgery in ten patients with intracerebral hemorrhage. The completeness of hematoma evacuation was also evaluated. METHODS: CDU, resectoscope, cutting loops, biopsy forcep, and the irrigation and suction device were the main instruments used in treating intracerebral hematoma. The CDU probe was utilized to locate the exact position of the hematoma and to provide direct visual control of the operation. The cutting loops and biopsy forcep were applied to morcellate and fragment the hematoma. Next, the fragmented hematoma was aspirated by a suction and irrigation device. CDU was then re-used to verify the completeness of hematoma resection and hemostasis as well as evaluate the position of midline shifting. RESULTS: The completeness of hematoma evacuation in our patient series was over 90% in three patients, over 50% in five patients, and less than 50% in two patients. One patient showed signs of rebleeding two days post-operatively and underwent conventional craniotomy. CONCLUSIONS: This endoscopic neurosurgical procedure caused less trauma around and along the route to the hematoma, and inflicted less damage to healthy brain tissue. Sonography, especially CDU, is quite helpful in the localization of hematoma and evaluation of intra- or post-operative bleeding. The operation time was also significantly shortened as compared to conventional craniotomy, thereby reducing the risk of operation.

Aged↗
PubMed1995

Detection of bioactive oligopeptides after microbore HPLC with electrochemical detection of their Cu(II) complexes: effect of operating parameters on sensitivity and selectivity.

We used a microbore reversed phase column for acetonitrile/0.1% aqueous TFA gradient elution separation of peptides with the detection of their copper complexes by electrochemical detection. The copper complexes are formed in a short (1 or 1.5 min) postcolumn reactor following mixing of the eluent with the postcolumn reaction phase. Detection can be at an upstream anode or a downstream cathode of a dual-electrode electrochemical detector. The following parameters have been investigated for their effect on the sensitivity and the selectivity of the procedure: postcolumn pH, buffer type, temperature, reaction time, and anode potential. Of the 23 bioactive peptides used, there are several that fall into classes according to their chemical and electrochemical behavior with copper(II): those with a blocked terminal amine, those with aspartate in the third position, those that have an electroactive amino acid, and those that have a cyclic structure formed by the amide backbone through a Cys-Cys disulfide bridge. Depending on these attributes, the operating parameters have an influence on the sensitivity of the determination. Among the more well-defined results are the following. Uncomplicated peptides with a free amine terminus react rapidly in the postcolumn reactor and give signals in the range predicted by theory. There is evidence that longer peptides, and those with a blocked amine terminus, have a sensitivity limited by kinetic factors. The oxidations of tyrosine and tryptophan in peptides are dramatically influenced by buffer type at pH 9.8. At pH 8.0, there is no signal from several peptides in phosphate buffer, while in borate there is a signal.

Amino Acid Sequence↗
PubMed1995

Optimization of a modified electrode for the sensitive and selective detection of alpha-dipeptides.

Sensitive and selective detection of dipeptides is important in neurochemistry. We have developed a flexible detection scheme for dipeptides based on a modified carbon electrode. The modification arises from the anodic treatment of the carbon electrode in alkaline solution. The flexibility of the detection scheme arises from the different conditions used in both the modification and the detection. It is shown that the modification step requires the presence of cupric ion, while the detection step does not. On the other hand, it is shown that the presence of copper in the detection eluent, as well as the pH of the environment, can be used in controlling the selectivity of the modified electrode. For example, the modified electrode is more selective for alpha-dipeptides over beta- and gamma-dipeptides as well as amino acids at pH 9.8, whereas it is selective for all dipeptides over amino acids at pH 8.0. Detection limits of dipeptides on the order of 10 nM were achieved at pH 8.0 by flow-injection analysis with a knotted Teflon tubing connecting the injector and the detector that gave a typical peak volume of about 0.50 ml at 1.0 ml/min. From surface analysis it is shown that the oxygenation of the glassy carbon electrode gives rise to the selectivity. The oxidation of dipeptides at the modified electrode is completely inhibited by 10 mM Mg2+ in the eluent.

Chromatography, Liquid↗
PubMed1995

Sensitivity and selectivity of the electrochemical detection of the copper(II) complexes of bioactive peptides, and comparison to model studies by rotating ring-disc electrode.

Post-column reaction of peptides with Cu(II) can be used for the electrochemical detection of peptides as their biuret complexes. Understanding of the behavior (sensitivity at the anode and cathode in the dual-series electrochemical detector) of the system is facilitated through the observation of the rotating ring disc voltammetry of some model compounds. In operation, the anodic signal from the oxidation of the Cu(II)-peptide to the Cu(III) form can be used to detect peptides, or the downstream cathode can be used to detect the Cu(III) form. The signals appear at about 0.4 V (anode) for tetra- and longer peptides, 0.65 V for tripeptides. The anode signal is augmented by tyrosine (oxidation at 0.4-0.5 V) and tryptophan (0.5-0.6 V). If the cathode is used as the detector in a two working electrode cell, the sensitivity depends on the stability of the Cu(III) product. This is peptide dependent, but the signal is significant and useful analytically. Twenty-three bioactive peptides in two groups, naturally electrochemically active and naturally electrochemically silent, and several model compounds have been studied. Both naturally electrochemically active peptides (contain tyrosine and/or tryptophan) and naturally electrochemically silent peptides have been studied. Chromatography with an acetonitrile gradient has been used to separate the peptides in each group. Detection limits are for non-electroactive peptides in the range of 16-100 fmol (10- microliters injection 1.6-10 nM, 100 microliters injection 0.16-1.0 nM), and for electroactive peptides in the range of 6-40 fmol (0.6-4.0 nM for a 10- microliters injection and 60-400 pM for a 100- microliters injection). A tryptic digest of bovine cytochrome c is easily seen at 100 nM.

Amino Acid Sequence↗
PubMed1995

Determination of the pharmaceutical peptide TP9201 by post-column reaction with copper(II) followed by electrochemical detection.

An electrochemical detection method was applied to the determination of the synthetic peptide TP9201 (Telios Pharmaceuticals). The method utilizes reversed-phase HPLC, followed by post-column formation of Cu(II)-peptide complexes to render peptides electrochemically active via the Cu(III/II) couple. TP9201 is cyclic and N-amidated; the lack of a free amine precludes the use of typical fluorescent labeling reagents. Neither the cyclic structure nor the N-amidation prevented the copper complexation reaction, however. The detection limit in bovine serum was 20 nM, limited by interfering sample peaks, and the detector response was linear in a range 10-400 nM.

Amino Acid Sequence↗
PubMed1995

Microtubule disruption stimulates system A transport in cultured vascular smooth muscle cells.

This study has focused on the possible influence of microtubules for the regulation of Na(+)-dependent system A neutral amino acid transport in A10 cells, a cultured cell line derived from rat aortic vascular smooth muscle. When microtubules were disrupted by incubating cells for 5 h in serum-free medium containing colchicine, nocodazole, or vinblastine, there was a twofold increase in system A transport (Vmax change). The dose for the disruption of microtubules by colchicine was similar to the dose required for the stimulation of system A. The time course showed that system A stimulation did not occur until widespread disruption of microtubules was established. The stimulation was specific for system A; there were no changes in glucose transport and Na(+)-dependent transport of phosphate and glutamate. Serum refeeding of quiescent cells from 2 days of serum starvation led to stimulation of system A, glucose, and phosphate transport. However, only system A was activated when colchicine was added to the serum-free medium. Addition of colchicine during serum refeeding had no additive effect for the stimulation of system A. The stimulation by both colchicine and serum was blocked by cycloheximide and actinomycin D. These findings suggest that microtubule disruption may activate system A gene expression.

Animals↗
PubMed1995

Osmoregulation of neutral amino acid transport.

Neutral amino acids are important organic osmolytes found in most osmotically stressed cells. During prolonged hypertonic stress, accumulation of neutral amino acids contributes to the cell volume recovery and may protect cellular proteins against salt denaturation. Hypertonicity activates system A transport, a major neutral amino acid transporter in mammalian cells, by a microtubule-dependent mechanism. Similar to the regulation of amino acid efflux induced by hypotonic-swelling, influx via system A may be under the control of intracellular ionic strength. An osmotically sensitive repressor may negatively regulate the gene expression of a regulatory protein which activates the preexisting system A transporter protein. Hypertonically activated protein kinases may be involved in this osmoregulation of amino acid transport.

Amino Acids↗
PubMed1994

Hypertonic upregulation of amino acid transport system A in vascular smooth muscle cells.

The A10 line of vascular smooth muscle cells has Na+ dependent transport systems for alanine, proline, and Pi, whereas uptake of leucine, myo-inositol and D-glucose is Na+ independent. When A10 cells were incubated for 4 h in medium made hypertonic by addition of sucrose, there was a marked increase in Na(+)-dependent transport of alanine and proline but no change in Na(+)-dependent Pi uptake or Na(+)-independent uptake of leucine and inositol. Intracellular alanine content was increased 61% by the hypertonic treatment. Other nonpenetrating solutes, such as cellobiose and mannitol, reproduced the effect of sucrose, but urea, a penetrating solute, did not. Studies with 2-(methylamino)-isobutyric acid revealed that the upregulation by hypertonicity involved only system A. Increases in alanine and proline uptake also occurred after incubating the cells in isotonic medium containing 0.1 mM ouabain, suggesting that an increase in intracellular Na+ may be part of the intracellular signal for upregulation of system A. Hypertonic upregulation of Na(+)-dependent alanine transport occurred also in primary cultures of vascular smooth muscle cells. The response was blocked by actinomycin D and cycloheximide, indicating that gene transcription and protein synthesis play important roles in the mechanism leading to increased alanine uptake. We conclude that vascular smooth muscle cells, during prolonged hypertonic stress, activate system A and accumulate specific neutral amino acids which may act as organic osmolytes to help maintain normal cell volume.

Alanine↗
PubMed1994

[Influence of endothelin-1 on ventricular fibrillation threshold in acute myocardial ischemic rats].

The influence of endothelin-1 on ventricular fibrillation threshold was studied in acute myocardial ischemic rats. Endothelin-1 (1.5-3.0 micrograms.kg-1 i.v.) given 5 min before ischemia reduced the ventricular fibrillation threshold in a dose- and time-dependent manner. Its effect lasted at least 60 min. A marked increase of spontaneous ventricular tachycardia and myocardial infarct size was seen and the arterial blood pressure was at a higher level (18.5-20.1/14.4-15.8 kPa) after 3.0 micrograms.kg-1. Diltiazem prevented partially from reduction of ventricular fibrillation threshold, eliminated completely the vasopressor response and limited the extension of myocardial necrosis induced by endothelin-1.

Animals↗
PubMed1993

Electrical double-layer models of ion-modified (ion-pair) reversed-phase liquid chromatography.

Stoichiometric models of ion-modified reversed-phase liquid chromatography are based on chemical equilibria between ionic modifiers and analyte. These are briefly discussed. Non-stoichiometric models portray the ionic solute as being under the summed influence of all of the ions in the system. Chromatographic theories have been developed that are based on the Poisson-Boltzmann equation, which quantitates the summed influence of the ions in the system on the solute. These ideas and quantitative predictions are described and are critically discussed.

Chromatography, Liquid↗
PubMed1993

Phosphate deprivation inhibits NH4+ transport in OK cells.

Deprivation of dietary phosphate leads to a decrease in urinary excretion of ammonium in rats which may be mediated through an alteration in ammonium transport in the proximal tubule. In the present study the OK renal epithelial cell line, a model for the proximal tubule, was used to determine if NH4+ transport was changed during acute phosphate deprivation. The intracellular pH after perfusion with NH4Cl solution was used for calculation of intracellular NH4+ concentration. Intracellular [NH4+] increased linearly during the first 2 min of acidification with NH4Cl. NH4+ transport, defined by the initial rate of the increase in intracellular [NH4+], was decreased by 32% (P < 0.005) in phosphate-deprived cells. This transport process was inhibited by barium chloride, but not by DIDS, amiloride or ouabain, suggesting that the NH4+ transport pathway may utilize K+ channels. Acute phosphate deprivation may inhibit NH4+ transport in OK cells by decreasing membrane K+ permeability.

Ammonia↗
PubMed1993

Exercise countermeasure protocol management expert system.

Exercise will be used primarily to countermeasure against deconditioning on extended space flight. In this paper we describe the development and evaluation of an expert system for exercise countermeasure protocol management. Currently, the system includes two major subsystems: baseline prescription and prescription adjustment. The baseline prescription subsystem is designed to provide initial exercise prescriptions while prescription adjustment subsystem is designed to modify the initial prescription based on the exercised progress. The system runs under three different environments: PC, SUN workstation, and Symbolic machine. The inference engine, baseline prescription module, prescription adjustment module and explanation module are developed under the Symbolic environment by using the ART (Automated Reasoning Tool) software. The Sun environment handles database management features and interfaces with PC environment to obtain physical and physiological data from exercise units on-board during the flight. Eight subjects' data have been used to evaluate the system performance by comparing the prescription of nine experienced exercise physiologists and the one prescribed by the expert system. The results of the validation test indicated that the performance of the expert system was acceptable.

Analysis of Variance↗
PubMed1993

[Comparison of Enterobius vermicularis infection among preschool children in Ta-Liao District of Kaohsiung County with that in Kaohsiung City].

To compare the rate of E. vermicularis infection among preschool children in Ta-Liao District of Kaohsiung County, with that in Kaohsiung City, a total of 532 preschool children from 7 kindergartens in Ta-Liao District, Kaohsiung County and 544 preschool children from Kaohsiung City kindergartens were randomly collected. The preschool children were examined for E. vermicularis infection with a scotch tape perianal swab technique (S.T.P.S.T.). After examination, the preschool childrens' parents were also interviewed. The interview included the following factors: personal data of the preschool children (age, sex and birthplace); the size of the living quarters (measured in "Ping") and the number of rooms in the living quarters; the play area floor material (e.g. carpet, wood, tile, etc.); the total number of family members; the distribution of family members in bedrooms; the frequency of finger-sucking and the frequency of hand-washing before eating meals and after using toilets; the preschool childrens' primary caregiver; the occupations of both parents; and the means and times of bathing. The obtained data were analyzed and E. vermicularis infection among the preschool children in Ta-Liao District and Kaohsiung City were compared using the Mantel-Haenszel statistical program in Statistical Analysis System (S.A.S) software. The present results indicated that the rate of E. vermicularis infection among preschool children was higher in Ta-Liao District than in Kaohsiung City.

Child↗
PubMed1992

[Changes in cardiac contractility induced by stimulation of hypothalamic ventromedial nucleus].

Experiments were performed on anesthetized cats to observe the effect of electrical stimulation of the hypothalamic ventromedial nucleus (VMH) on cardiac contractility as judged by the change in LVSP, dp/dtmax, Vmax, P-dp/dt, P-lndp/dt. Electrical stimulation of VMH induced an augment response in cardiac force, while stimulation of an area between VMH and the third ventricle led only to a decrease in cardiac contractile force. All these changes were not accompanied by significant changes in heart rate and unaffected by bilateral vagotomy. The present experiment indicates that the inotropic and chronotropic regulation centers of cardiac function exist in different hypothalamic areas.

Animals↗