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Biomedical subjects

R S Chen

Publications and source records attributed to R S Chen.

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

Electronic energy levels and hopping conductivity of an entire molecule of hagfish insulin.

The quantum-chemical calculation of an entire molecule of hagfish insulin was done by the ENFC method in which the matrix elements were calculated at the ab initio level using a minimal basis set with simulation of the aqueous solution environment. The ac conductivity for hagfish insulin was also calculated at the ab initio level by random walk theory. All the results were compared with those of pig insulin. It is shown that the reduction of HOMOs and LUMOs localized on the active sites of hagfish insulin agrees with the decrease in the biological reactivity of the insulin. The analysis of primary hopping events showed that a different sequence could influence the biological activity of insulin through the distribution of the hopping centers and the quantities of the hopping frequencies. The curve of the frequency versus ac conductivity of hagfish insulin shows that the different amino acid sequences of proteins influence the hopping conductivity. However, the electronic properties of native proteins are dominated by the three-dimensional conformations. Finally, the electronic mechanism of trans-membrane signal transforms by insulin and its receptor, which had been proposed by Ye and Ladik, was clearly described.

Amino Acid Sequence↗
PubMed1996

Modeling of the three-dimensional structure of luffin-alpha and its simulated reaction with the substrate oligoribonucleotide GAGA.

A fundamental problem in biochemistry and molecular biology is understanding the spatial structure of macromolecules and then analyzing their functions. In this study, the three-dimensional structure of a ribosome-inactivating protein luffin-alpha was predicted using a neural network method and molecular dynamics simulation. A feedforward neural network with the backpropagation learning algorithm were trained on model class of homologous proteins including trichosanthin and alpha-momorcharin. The distance constraints for the C alpha atoms in the protein backbone were utilized to generate a folded crude conformation of luffin-alpha by model building and the steepest descent minimization approach. The crude conformation was refined by molecular dynamics techniques and a simulated annealing procedure. The interaction between luffin-alpha and its analogous substrate GAGA was also simulated to understand its action mechanism.

Algorithms↗
PubMed1996

Dopa-responsive dystonia: clinical and family study in Taiwanese.

We report the clinical features of four female patients with dopa-responsive dystonia (DRD), and the survey of the family members. The patients were 2 sisters and 2 sporadic patients from 3 families. Their age of onset ranged between 5 and 13 years. The clinical manifestation was characterized by limb dystonia which was relieved by L-dopa treatment. Diurnal fluctuation disappeared 15 years later in one patient. There was a wide spectrum of Parkinsonian features and variability of dystonia. Response of L-dopa was still excellent 20 years later. In survey of the family members, there was neither bradykinesia, rigidity, tremor nor dystonia.

Adult↗
PubMed1996

Sexual reproduction plays a major role in the genetic structure of populations of the fungus Mycosphaerella graminicola.

The relative contributions of sexual and asexual reproduction to the genetic structure of populations can be difficult to determine for fungi that use a mixture of both types of propagation. Nuclear RFLPs and DNA fingerprints were used to make indirect and direct measures of departures from random mating in a population of the plant pathogenic fungus Mycosphaerella graminicola during the course of an epidemic cycle. DNA fingerprints resolved 617 different genotypes among 673 isolates sampled from a single field over a 3-month period. Only 7% of the isolates represented asexual clones that were found more than once in the sample. The most common clone was found four times. Genotypic diversity averaged 85% of its maximum possible value during the course of the epidemic. Analyses of multilocus structure showed that allelic distributions among RFLP loci were independent. Pairwise comparisons between individual RFLP loci showed that the majority of alleles at these loci were in gametic equilibrium. Though this fungus has the capacity for a significant level of asexual reproduction, each analysis suggested that M. graminicola populations maintain a genetic structure more consistent with random-mating over the course of an epidemic cycle.

Ascomycota↗
PubMed1996

Botulinum toxin A injection in the treatment of hemifacial spasm.

UNLABELLED: There are conflicting reports concerning the variation in duration of symptoms relief for patients with hemifacial spasm who have undergone several injections of botulinum A toxin (BOTX-A). We present our experience of BOTX-A injections in Taiwanese patients to analyze this issues, and to inspect whether the efficacy of treatment depends on the pre-injection severity. MATERIAL AND METHOD: From July 1992 to December 1994, 137 patients received injections of BOTX-A. We used objective and subjective score system to evaluate the efficacy and side effects of BOTX-A injection. RESULTS: The overall successful rate of substantial relief of spasm was 88%. The mean duration of response was 20 weeks. Patents with more severe spasm tended to have shorter duration of improvement. The effects of consecutive injections remained fairly constant over the first 4 injections. CONCLUSION: The BOTX-A injection is an effective and safe treatment for patients with hemifacial spasm and the effect could be sustained over the consecutive injections.

Adult↗
PubMed1996

Chronic carbon disulfide encephalopathy.

To understand central nervous damage after long-term exposure to carbon disulfide (CS2), 10 patients who had polyneuropathy with various neuropsychiatric symptoms in a viscose rayon plant were studied. Clinical and laboratory examinations including electroencephalography (EEG), brain computed tomography (CT), brain magnetic resonance images (MRI), and carotid duplex sonography were carried out. Clinically, headache, unpleasant dreams, memory impairment, fatigue, anorexia and emotional lability were common in these patients while 2 patients had stroke episodes. EEGs were all normal. Brain CT scan showed mild cortical atrophy in 3 and low density lesions in the basal ganglia in 3. Brain MRI studies also disclosed mild cortical atrophy in 4 and multiple lesions involving the basal ganglia and corona radiata in 4. Carotid duplex sonography revealed mild atherosclerosis with plaques (< 20% stenosis) of extracranial vessels in 6. However there was no significant difference in flow velocities and flow volumes in the extracranial carotid arteries between patients and the normal controls. Interestingly, 2 patients had multiple brain lesions in the subcortical white matter but without strokes. In conclusion, encephalopathy with possible strokes may occur after chronic exposure to CS2, as well as polyneuropathy. The lesions usually involve the basal ganglia and subcortical white matter. Furthermore, MRI study may detect brain lesions particularly in the subcortical white matter areas before the occurrence of stroke.

Brain Diseases↗
PubMed1996

Leg manifestation in alien hand syndrome.

A patient with left alien hand syndrome (AHS) accompanied by leg symptoms due to right anterior cerebral artery territory infarction is reported. Magnetic resonance imaging demonstrated that the responsible lesion involved the right anterior cingulate gyrus, supplementary motor area, medical prefrontal cortex and corpus callosum extending from the genu to the isthmus. The leg symptoms included: 1) motor perseveration manifesting as compulsive straight walking with difficulty stopping on command; 2) dissociation between mind and action resulting in going to unintended places with subsequent complaints of poor memory not due to spatial disorientation; 3) discrepancy between verbal and actual leg motor responses to auditory verbal suggestions; and 4) movement dissociation between the legs resulting in transient standing still or brief sticking to the ground, a situation simulating akinesia. As the legs usually perform together to coordinate movements of standing and walking, unlike the hands performing well-learned, skilled unimanual or bimanual coordinating movements, the counterpart in the leg of the alien hand sign in AHS was not manifested. Nevertheless, in the presence of AHS, the associated leg symptoms bear similar neurobehavioral features and should be dealt with on equal terms.

Cerebral Infarction↗
PubMed1996

Nerve growth factors prevent glutamate toxicity in cortical neuronal cultures.

AIM: To determine if nerve growth factors (NGF) can protect against glutamate-induced cortical neuron damage. METHODS: Neuron viability and lactate dehydrogenase (LDH) efflux in the bathing medium in primary cultures from 17-d-old mouse fetal cortex were measured to assay NGF effect. Imaging of the calcium indicator dye Fura-2 was used to measure the [Ca2+]i. RESULTS: The LD50 for NGF-free glutamate was 0.2 mmol.L-1 (95% confidence limits 0-1.6 mmol.L-1). In the presence of NGF 60 micrograms.L-1, 59% of the neurons survived in glutamate 1.6 mmol.L-1. The protective effect afforded by NGF was maximal at 60 micrograms.L-1, at which it prevented the elevation in [Ca2+]i. CONCLUSION: NGF protect cortical neurons against glutamate-induced toxicity via "stabilizing" [Ca2+]i level or suppression of the rise in [Ca2+]i.

Animals↗
PubMed1995

Reciprocal inhibition in writer's cramp.

We studied the inhibition of median H-reflexes by conditioning stimuli on the radial nerve in 13 patients with writer's cramp, eight of the simple type and five of the dystonic type, and in 14 normal volunteers. The patients and controls were right-handed, and their right arms were studied. Asymptomatic left arms were also studied in nine of 13 patients. In the control group we identified three periods of inhibition, with maximum peaks at conditioning-test intervals of 0 ms (41 +/- 17%), 20 ms (40 +/- 13%), and 100 ms (36 +/- 20%). In the patient group, the amplitudes of inhibition of these three periods in both arms were significantly less than those in the control group. However, there were no significant differences in the amplitudes of inhibition of these three periods between symptomatic and asymptomatic arms. There were also no significant differences between simple and dystonic writer's cramps. Our results indicate that the attenuation of reciprocal inhibition was present not only in symptomatic arms but also in asymptomatic arms of patients with writer's cramp. The defect of reciprocal inhibition in the asymptomatic hand has never been documented. We suggest that the preexistent electrophysiological abnormality may provide an explanation for the development of hand cramp after shifted writing.

Adult↗
PubMed1995

Analysis of tRNA gene sequences by neural network.

The quantitative similarity among tRNA gene sequences was acquired by analysis with an artificial neural network. The evolutionary relationship derived from our results was consistent with those from other methods. A new sequence was recognized to be a tRNA-like gene by a neural network on the analysis of similarity. All of our results showed the efficiency of the artificial neural network method in the sequence analysis for biological molecules.

Animals↗
PubMed1995

Family environment and the interrelation of family structure, child behavior, and metabolic control for children with diabetes.

Examined perceptions of the family environment in a cross-regional sample of 90 families who had children with diabetes and 89 controls. Families were classified as either traditional (intact) or nontraditional (single-parent or blended families). Parents of children with diabetes reported less family expressiveness, which was a predictor of clinically higher levels of child behavior problems than controls. Parents in nontraditional families reported lower levels of organization, less emphasis on active-recreational pursuits, and more child behavior problems than traditional families. An additive effect of diabetes and nontraditional family structure was found for children with diabetes from nontraditional families, who reported substantially less cohesion than all other groups. Nontraditional family structure was more disruptive for children with diabetes than for controls; it was the best predictor of behavior problems and was related to poorer metabolic control.

Adolescent↗
PubMed1995

Polyneuropathy induced by carbon disulphide in viscose rayon workers.

OBJECTIVES: To understand the prevalence of polyneuropathy and correlations among the clinical manifestations, electrophysiological findings, and degree of exposure to carbon disulphide (CS2) in workers who were exposed to variable concentrations of CS2 in a viscose rayon factory. METHODS: All the 163 workers received a detailed physical and neurological evaluation. Fixed point air samples were analysed for CS2. Nerve conduction velocity was studied in 26 workers with symptoms similar to neuropathy. RESULTS: Nine workers (53%) with overt polyneuropathy from the fibre cutting department and 19 workers (13%) with oligosymptoms similar to polyneuropathy from various jobs were noted. The fixed point air concentrations of CS2 were 150-300 ppm in the cutting areas and 15 to 100 ppm in the spinning areas. The estimated eight hour time weighted averages in the fibre cutting areas were 40-67 ppm. The occurrence of polyneuropathy was generally correlated with the degree of exposure to CS2. Nerve conduction velocities (NCVs) were significantly different in the overt polyneuropathy and subclinical polyneuropathy groups from the normal controls. The sensitive indicators for CS2 polyneuropathy were distal latency, motor NCV, and amplitude of sensory nerve action potentials in sensory NCVs. CONCLUSION: The outbreak of polyneuropathy was attributed to higher concentrations of CS2 in fibre cutting areas. Even in other jobs with relatively lower concentrations of CS2, the hazard of subclinical polyneuropathy cannot be overlooked.

Adult↗
PubMed1995

Double-blind, placebo-controlled study of botulinum toxin injections in the treatment of cervical dystonia.

Botulinum toxin injections were given to 23 patients with cervical dystonia in a double-blind, placebo-controlled, crossover study. Each patient was randomly given 100 units of botulinum A toxin and placebo in two respective sets of injections into the two most active contracting neck muscles at least 3 months apart. Before and 3 weeks after each set of injections, the cervical dystonia was "blindly" scored by the investigator. Each patient was also asked to independently score the improvement of the dystonia and neck pain. Four patients dropped out and one patient showed spontaneous remission. The remaining 18 patients completed the study and showed a significant improvement after the injections of botulinum toxin in comparison with that of the placebo. The effect started about 1 week after injection and the maximal effect lasted about 11 weeks in patients with a satisfactory response. The neck pain was satisfactorily relieved in 9 of 10 patients affected. There were no significant side effects. Thus, botulinum toxin injection is effective in treating cervical dystonias; injection of a higher dose of botulinum toxin in a greater number of neck muscles is required for those patients with complex cervical dystonia.

Adult↗
PubMed1994

Myoclonic epilepsy with ragged-red fibers (MERRF) syndrome: report of a Chinese family with mitochondrial DNA point mutation in tRNA(Lys) gene.

We report myoclonic epilepsy with ragged-red fibers (MERRF) syndrome in a Chinese family with confirmed mitochondrial DNA point mutation. Six members of the family including the grandmother, two siblings, and three grandchildren were affected. Among them, action myoclonus was seen in five; short stature, muscle weakness, and mental retardation in four; lactic acidosis, hearing impairment, and ataxia in two; and seizures in one. Muscle biopsy from two affected siblings revealed ragged-red fibers and abundant subsarcolemmal mitochondria with paracrystalline inclusions. Pedigree analysis suggests a maternal transmission. Analysis of mitochondrial DNA showed a point mutation from A to G at the 8344th nucleotide position located in the tRNA(Lys) gene. To our knowledge, this is the first report of MERRF syndrome with such genetic defect from a Chinese family. The present and previous reports support the notion that mitochondrial DNA point mutation at the 8344th nucleotide position is the most common cause of MERRF syndrome.

Adult↗
PubMed1994

ATP evokes calcium transients in single pulmonary artery endothelial cell in primary cultures.

Effects of ATP on cytosolic free calcium ([Ca2+]i) in single porcine pulmonary artery endothelial cell were studied. Using a dual-wavelength excitation microflurometry, it was found that ATP evoked a rapid transient in [Ca2+]i which was then followed by a maintained elevation of [Ca2+]i. The removal of extracellular Ca2+ abolished the maintained plateform, but exerted no obvious effect on the initial-transient. These results suggest that ATP stimulates both calcium release from intracellular calcium pool(s) and calcium influx across the plasma membrane from extracellular space.

Adenosine Triphosphate↗
PubMed1994

MELAS syndrome with mitochondrial tRNA(Leu(UUR)) gene mutation in a Chinese family.

The clinical features of a patient in a Chinese family with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS syndrome) are reported. The study revealed that hearing and visual impairments and miscarriages may be early clinical presentations in MELAS. A heteroplasmic A to G transition in the tRNA(Leu(UUR)) gene was noted at the nucleotide pair 3243 in the mitochondrial DNA of muscle, blood, and hair follicles of the proband and his maternal relatives. Quantitative analysis of the mutated mitochondrial DNA revealed variable proportions in different tissues and subjects of maternal lineage in the family. Muscle tissue contained a higher proportion of the mutant mitochondria than other tissues examined. The function of the reproductive system of the proband seems to be impaired. In one clinically healthy sibling, the 3243rd point mutation was found in sperm mitochondrial DNA, although sperm motility was not affected. It seems that biochemical defects in mitochondrial respiration and oxidative phosphorylation are tissue specific expressions of the 3243rd point mutation in the mitochondrial DNA of the affected target tissues.

Adolescent↗
PubMed1994

Comparison of physical properties of light-curing and self-curing dental impression materials.

A light-curing polyether urethane dimethacrylate impression material was recently developed. Its polymerization reaction is activated by intensified visible light; therefore, the on-demand set allows operators to work at their own pace. Furthermore, its constant viscosity provides a constant flow rate at the critical stages of taking impressions. The purposes of this study were to evaluate the physical properties and accuracy of this light-curing impression material and to compare it with those of self-curing impression materials currently used in our dental clinic. Physical properties such as strain in compression, compression set, dimensional stability, and tear strength of the impression materials were measured according to test methods stipulated in ADA Specification No. 19 for elastomeric impression materials. The template-coping method developed by Lewinstein and Craig was used to evaluate the accuracy of the impression materials. It was found that the strain in compression of the polyether urethane dimethacrylate was higher than that of the condensation silicones, but lower than that of the addition silicones. The compression set of the condensation silicones was more than that of the polyether urethane dimethacrylate, but much less than that of the polysulfides. The dimensional stability showed that all of the impression materials, except the polyether urethane dimethacrylate, had a negative dimensional change 24 hours after mixing. The sequence is: polysulfide < condensation silicone < addition silicone. The expansion rate of the light-curing material was measured under 0.07% one day after curing. The polyether urethane dimethacrylate had extraordinary tear resistance compared to the other impression materials.(ABSTRACT TRUNCATED AT 250 WORDS)

Biomechanical Phenomena↗