Biomedical subjects

R Chen

Publications and source records attributed to R Chen.

At least 109 records · Page 6Linked to original sources

PubMed2001

Assignment of the 1511 cm(-1) UV resonance Raman marker band of hemoglobin to tryptophan.

New UV resonance Raman (UVRR) data provide convincing evidence that a characteristic 1511 cm(-1) band in the T - R difference spectra of hemoglobin is due to the overtone of the Trp W18 fundamental at 756 cm(-1). Measured isotope shifts for 2-H and 15-N substitution at the indole NH group are twice as large for the 1511 cm(-1) band as for W18, and the 1511 cm(-1) intensity scales with that of W18 in the difference spectrum. Moreover, the UVRR excitation profile of the 1511 cm(-1) band tracks that of another tryptophan band, W16. Both are redshifted in hemoglobin, relative to aqueous tryptophan, reflecting H bonding within a hydrophobic environment in the protein. The 2xW18 assignment had been thrown into question by the observation of remnant 1511 cm(-1) intensity in the T - R spectra of hemoglobin labeled with tryptophan-d(5), a substitution that shifts W18 over 50 cm(-1). However, reexamination of the data suggests that this remnant intensity may result from a subtraction artifact arising from the downshift of another difference band, W3, from 1549 cm(-1) in unlabeled protein to 1522 cm(-1) in labeled protein. Restoration of the 2xW18 assignment establishes that the 1511 cm(-1) difference band, which is a useful indicator of the extent of T-state formation in hemoglobin, arises from the same residue, Trpbeta37, that gives rise to essentially all of the T - R signal from tryptophan.

Adult↗

PubMed2001

Comparative efficiencies of C-terminal signals of native glycophosphatidylinositol (GPI)-anchored proproteins in conferring GPI-anchoring.

Every protein fated to receive the glycophosphatidylinositol (GPI) anchor post-translational modification has a C-terminal GPI-anchor attachment signal sequence. This signal peptide varies with respect to length, content, and hydrophobicity. With the exception of predictions based on an upstream amino acid triplet termed omega-->omega + 2 which designates the site of GPI uptake, there is no information on how the efficiencies of different native signal sequences compare in the transamidation reaction that catalyzes the substitution of the GPI anchor for the C-terminal peptide. In this study we utilized the placental alkaline phosphatase (PLAP) minigene, miniPLAP, and replaced its native 3' end-sequence encoding omega-2 to the C-terminus with the corresponding C-terminal sequences of nine other human GPI-anchored proteins. The resulting chimeras then were fed into an in vitro processing microsomal system where the cleavages leading to mature product from the nascent preproprotein could be followed by resolution on an SDS-PAGE system after immunoprecipitation. The results showed that the native signal of each protein differed markedly with respect to transamidation efficiency, with the signals of three proteins out-performing the others in GPI-anchor addition and those of two proteins being poorer substrates for the GPI transamidase. The data additionally indicated that the hierarchical order of efficiency of transamidation did not depend solely on the combination of permissible residues at omega-->omega + 2.

Alkaline Phosphatase↗

PubMed2001

Mechanisms underlying human motor system plasticity.

There has been increased interest in the ability of the adult human nervous system to reorganize and adapt to environmental changes throughout life. This ability has been termed "plasticity." Plastic changes in the cerebral cortex have been studied: (a) as modifications of sensory or motor cortical representation of specific body parts (cortical maps, body representation level); and (b) as changes in the efficacy of existing synapses or generation of new synapses (neuronal or synaptic level). In this review, we describe paradigms used to study mechanisms of plasticity in the intact human motor system, the functional relevance of such plasticity, and possible ways to modulate it.

Animals↗

PubMed2001

Auto-regulated hepatic insulin gene expression in type 1 diabetic rats.

Paradigms of insulin gene therapy for type 1 diabetes should incorporate vigorous control for insulin gene expression to be effective in correcting postprandial hyperglycemia and to be safe in preventing fasting hypoglycemia. We hypothesize that hepatic insulin gene expression auto-regulated positively by glucose and negatively by insulin might be both effective and safe in the treatment of type 1 diabetes. Expression of the glucose 6-phosphatase (G6Pase) gene in the liver is both stimulated by glucose and suppressed by insulin. The G6Pase promoter incorporated with intronic enhancers of the aldolase B gene was used to direct insulin gene expression in the liver of streptozotocin-induced diabetic nude rats. In the treated animals, blood insulin levels were elevated after feeding, and nonfasting hyperglycemia was significantly reduced. Glucose tolerance testing also illustrated that the treated animals exhibited accelerated glucose utilization rates. Upon fasting, blood glucose was reduced to normoglycemic range within 4 h and maintained at that level during the prolonged fasting of 16 h. No hypoglycemia was observed in any treated animals at any time throughout the fasting period, as blood insulin gradually declined to the normal range. These results suggest that auto-regulated hepatic insulin expression can potentially be developed as an effective and safe treatment modality for type 1 diabetes.

Adenoviridae↗

PubMed2001

Water diffusion changes in Wallerian degeneration and their dependence on white matter architecture.

This study investigates water diffusion changes in Wallerian degeneration. We measured indices derived from the diffusion tensor (DT) and T2-weighted signal intensities in the descending motor pathways of patients with small chronic lacunar infarcts of the posterior limb of the internal capsule on one side. We compared these measurements in the healthy and lesioned sides at different levels in the brainstem caudal to the primary lesion. We found that secondary white matter degeneration is revealed by a large reduction in diffusion anisotropy only in regions where fibers are arranged in isolated bundles of parallel fibers, such as in the cerebral peduncle. In regions where the degenerated pathway crosses other tracts, such as in the rostral pons, paradoxically there is almost no change in diffusion anisotropy, but a significant change in the measured orientation of fibers. The trace of the diffusion tensor is moderately increased in all affected regions. This allows one to differentiate secondary and primary fiber loss where the increase in trace is considerably higher. We show that DT-MRI is more sensitive than T2-weighted MRI in detecting Wallerian degeneration. Significant diffusion abnormalities are observed over the entire trajectory of the affected pathway in each patient. This finding suggests that mapping degenerated pathways noninvasively with DT-MRI is feasible. However, the interpretation of water diffusion data is complex and requires a priori information about anatomy and architecture of the pathway under investigation. In particular, our study shows that in regions where fibers cross, existing DT-MRI-based fiber tractography algorithms may lead to erroneous conclusion about brain connectivity.

Aged↗

PubMed2001

Expression and purification of Escherichia coli beta-glucuronidase.

A strong and constitutive expression vector of Escherichia coli beta-glucuronidase with the isocitrate dehydrogenase promoter has been developed for producing a large amount of recombinant protein. More than 95% pure enzyme was obtained by a four step purification procedure-ammonium sulfate precipitation, DEAE ion-exchange chromatography, Superose 12 gel filtration, and hydroxyapatite steric ion-exchange chromatography. The overexpressed gene can produce 23 mg of pure enzyme from one liter of bacterial culture.

Chemical Precipitation↗

PubMed2001

Suppression of the motor cortex by magnetic stimulation of the cerebellum.

Conditioning magnetic stimulation of the cerebellum suppresses the motor cortex 5-8 ms later, probably through activation of cerebellar Purkinje cells, which inhibit the dentatothalamocortical pathway. To further characterize this pathway, we examined several factors that may modulate its excitability. We tested the effects of different test motor evoked potential (MEP) amplitudes, voluntary activation of the target muscle, and arm extension that required activation of proximal arm muscles while maintaining relaxation of hand muscles. Surface electromyography was recorded from the right first dorsal interosseous (FDI) muscle. A double-cone coil centered 3 cm lateral to the inion was used for right cerebellar stimulation. The stimulus intensity was set at 5% below the threshold for activation of the corticospinal tract. A figure-of-eight coil was used for left motor cortex stimulation. Interstimulus intervals (ISIs) between 3 and 15 ms were studied. Small test MEPs of about 0.5 mV were markedly inhibited at ISIs of 5-8 ms, but there was much less inhibition for test MEPs of about 2 mV. There was no significant MEP suppression during voluntary activation of the FDI muscle or during right arm extension. Left arm extension did not affect inhibition. Our findings indicate that cerebellar stimulation has a much stronger effect on motor cortex neurons activated near threshold intensities than those activated at higher intensities. Activation of contralateral but not ipsilateral proximal arm muscles during arm extension reduced the excitability of the cerebellothalamocortical projections to the hand area of the motor cortex.

Adult↗

PubMed2001

Studies on the frequencies of vitamin D receptor gene polymorphism in postmenopausal women of Han and Kazak nationality in China.

Polymorphyism of the vitamin D receptor (VDR) gene is reported to play a major role in variations of the genetic regulation of bone mass. The role of VDR polymorphisms within various ethnic populations is also undetermined. The purpose of the present study was to determine the frequencies of VDR genotypes in the Han and Kazak nationalities in China. We analyzed the polymorphism defined by the Bsm1 restriction enzyme using polymerase chain reaction-restriction fragment length polymorphism in 179 healthy postmenopausal Han women and 63 healthy postmenopausal Kazak women. The genotype frequencies of the VDR were calculated later using the Hardy-Weinberg equilibrium formula. The results showed that for women of Han nationality, the bb, Bb, and BB genotypes accounted for 90.5%, 9.5%, and 0%, respectively. In Kazak women, the respective frequencies were 38.1%, 55.56%, and 6.35%. We found that there was a significant difference between women of Han and Kazak nationality in terms of the frequency of distribution of VDR genotype (P < 0.001). There was a similar distribution of VDR genotypes in Kazak women to that seen for the Caucasian population of the USA. The results of the present study provide further evidence on the different pathogeny of osteoporosis in various ethnic groups.

Bone Density↗

PubMed2001

The pharmacology of bimatoprost (Lumigan).

Bimatoprost (Lumigan) is a pharmacologically unique and highly efficacious ocular hypotensive agent. It appears to mimic the activity of a newly discovered family of fatty acid amides, termed prostamides. One biosynthetic route to the prostamides involves anandamide as the precursor. Bimatoprost pharmacology has been extensively characterized by binding and functional studies at more than 100 drug targets, which comprise a diverse variety of receptors, ion channels, and transporters. Bimatoprost exhibited no meaningful activity at receptors known to include antiglaucoma drug targets as follows: adenosine (A(1-3)), adrenergic (alpha(1), alpha(2), beta(1), beta(2)), cannabinoid (CB(1), CB(2)), dopamine (D(1-5)), muscarinic (M(1-5)), prostanoid (DP, EP(1-4), FP, IP, TP), and serotonin (5HT(1-7)). Bimatoprost does, however, exhibit potent inherent pharmacological activity in the feline iris sphincter preparation, which is prostamide-sensitive. Bimatoprost also resembles the prostamides in that it is a potent and highly efficacious ocular hypotensive agent. A single dose of bimatoprost markedly reduces intraocular pressure in dogs and laser-induced ocular hypertensive monkeys. Decreases in intraocular pressure are well maintained for at least 24 hr post-dose. Human studies have demonstrated that systemic exposure to bimatoprost is low and that accumulation does not occur. The sclera is the preferred route of accession to the eye. The high scleral permeability coefficient Papp is a likely contributing factor to the rapid onset and long-acting ocular hypotensive profile of bimatoprost.

Amides↗

PubMed2001

Enzyme engineering: rational redesign versus directed evolution.

Enzyme engineering is undergoing the most profound and exciting transformation in its history (1). It promises unprecedented expansion in the scope and applications of modified or improved enzymes with desired physical and catalytic properties. Two complementary strategies are currently available: rational redesign (2-5) and directed evolution (6,7). Although both approaches have met with great success, each has limitations. In this article, the perspectives for these enzyme-engineering strategies are discussed briefly.

Enzymes↗

PubMed2001

Mutational analysis of patients with p47-phox-deficient chronic granulomatous disease: The significance of recombination events between the p47-phox gene (NCF1) and its highly homologous pseudogenes.

OBJECTIVE: The aim of this study was to determine the molecular basis of p47-phox-deficient chronic granulomatous disease (CGD), the most common autosomal recessive form of the disease. CGD is an inherited condition characterized by defective oxygen radical production due to defects in the phagocyte nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. Mutational analysis of p47-phox-deficient CGD patients previously demonstrated that the majority of patients have a GT dinucleotide (Delta GT) deletion at the start of exon 2, a signature sequence also observed in the highly homologous pseudogenes of NCF1. MATERIALS AND METHODS: We performed genetic analysis of NCF1 and its pseudogenes using genomic DNA in 29 p47-phox-deficient CGD patients from 22 separate families. First-strand cDNA analysis was performed in 17 of the 29 patients. RESULTS: We confirmed the significance of the Delta GT mutation; in 27 of 29 patients, only the Delta GT sequence was detectable. All but one of the 27 had at least one additional signature sequence, specific to the pseudogene, in either intron 1 and/or intron 2. We extended our analysis to look at signature sequence differences in exons 6 and 9 and detected both the wild-type and pseudogene sequences in all patients tested. CONCLUSIONS: Although detection of only Delta GT sequence accounts for over 85% of affected patients, the molecular basis is most likely due to partial cross-over events between the wild-type and pseudogene(s) of p47-phox at different recombination sites. Our results suggest that complete gene conversion or deletion of the p47-phox gene (NCF1) occurs rarely, if it all.

Base Sequence↗

PubMed2001

Application of an integrated matrix-assisted laser desorption/ionization time-of-flight, electrospray ionization mass spectrometry and tandem mass spectrometry approach to characterizing complex polyol mixtures.

Polyols are being used in a wide range of industrial applications including surfactants and precursors for grafted polymers. The characterization of polyols is of significance in correlating compositions and structures with their properties. We illustrate two real world examples where traditional analytical methods including GPC and NMR failed to reveal compositional differences, but the combination of matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF), electrospray ionization mass spectrometry (ESI MS), and MS/MS can produce compositional information required for problem solving. The first example involves failure analysis of four ethylene oxide and propylene oxide (EO/PO) copolymer products. The results from the mass spectrometry analysis unequivocally demonstrate that one of the samples has a small variation in copolymer composition, leading to its abnormal activity. The second example is in the area of deformulation of complex polyol mixtures. Two samples displaying similar properties and activities were found to be two different polyol blends. One of the samples is a more cost-effective product. These examples demonstrate that MALDI, ESI MS, and MS/MS should be seriously considered as an integrated component of an overall polyol characterization program in product failure analysis and deformulation.

Journal Article↗

PubMed2001

Reactions of atomic transition-metal ions with long-chain alkanes.

Understanding metal ion interactions with long-chain alkanes not only is of fundamental importance in the areas of organometallic chemistry, surface chemistry, and catalysis, but also has significant implication in mass spectrometry method development for the analysis of polyethylene. Polyethylene represents one of the most challenging classes of polymers to be analyzed by mass spectrometry. In this work, reactions of several transition-metal ions including Cr+, Mn+, Fe+, Co+, Ni+, Cu+, and Ag+ with long-chain alkanes, C28H58 and C36H74, are reported. A metal powder and the nonvolatile alkane are co-deposited onto a sample target of a laser desorption/ionization (LDI) time-of-flight mass spectrometer. The metal ions generated by LDI react with the vaporized alkane during desorption. It is found that all these metal ions can form adduct ions with the long-chain alkanes. Fe+, Co+, and Ni+ produce in-source fragment ions resulting from dehydrogenation and dealkylation of the adduct ions. The post-source decay (PSD) spectra of the metal-alkane adduct ions are recorded. It is shown that PSD of Ag+ alkane adduct ions produces bare metal ions only, suggesting weak binding between this metal ion and alkane. The PSD spectra of the Fe+, Co+, and Ni+ alkane adduct ions display extensive fragmentation. Fragment ions are also observed in the PSD spectra of Cr+, Mn+, and Cu+ alkane adduct ions. The high reactivity of Fe+, Co+, and Ni+ is consistent with that observed in small alkane systems. The unusually high reactivity of Cr+, Mn+, and Cu+ is rationalized by a reaction scheme where a long-chain alkane first forms a complex with a metal ion via ion/induced dipole interactions. If sufficient internal energy is gained during the complex formation, metal ions can be inserted into C-H and C-C bonds of the alkane, followed by fragmentation. The thermal energy of the neutral alkane is believed to be the main source of the internal energy acquired in the complex. Finally, the implication of this work on mass spectrometry method development for polyethylene analysis is discussed.

Journal Article↗

PubMed2001

Lithium and transition metal ions enable low energy collision-induced dissociation of polyglycols in electrospray ionization mass spectrometry.

Electrospray ionization tandem mass spectrometry has the potential to be widely used as a tool for polymer structural characterization. However, the backbones or molecular chains of many industrial polymers including functional polyglycols are often difficult to dissociate in tandem mass spectrometers using low energy collision-induced dissociation (CID). We present a method that uses Li+ and transition metal ions such as Ag+ as the cationization reagents for electrospray ionization in an ion trap mass spectrometer. It is shown that lithium and transition metal polyglycol adduct ions can be readily fragmented with low energy CID. Comparative results from different cationization reagents in their abilities of producing both MS spectra and CID spectra are shown. This method opens the possibility of using conventional and readily available low energy CID tandem MS to study polyglycol structures.

Carbohydrate Sequence↗

PubMed2001

Laser desorption ionization and MALDI time-of-flight mass spectrometry for low molecular mass polyethylene analysis.

Polyethylene's inert nature and difficulty to dissolve in conventional solvents at room temperature present special problems for sample preparation and ionization in mass spectrometric analysis. We present a study of ionization behavior of several polyethylene samples with molecular masses up to 4000 Da in laser desorption ionization (LDI) time-of-flight mass spectrometers equipped with a 337 nm laser beam. We demonstrate unequivocally that silver or copper ion attachment to saturated polyethylene can occur in the gas phase during the UV LDI process. In LDI spectra of polyethylene with molecular masses above approximately 1000 Da, low mass ions corresponding to metal-alkene structures are observed in addition to the principal distribution. By interrogating a well-characterized polyethylene sample and a long chain alkane, C94H190, these low mass ions are determined to be the fragmentation products of the intact metal-polyethylene adduct ions. It is further illustrated that fragmentation can be reduced by adding matrix molecules to the sample preparation.

Indicators and Reagents↗

PubMed2001

Potentials recorded at the scalp by stimulation near the human subthalamic nucleus.

OBJECTIVE: To record the potentials evoked at the scalp by stimulation through electrodes targeted at the human subthalamic nucleus (STN) and to determine whether the responsible pathways continue to be excited or become blocked with high frequency stimulation. METHODS: We recorded the potentials evoked at the scalp in response to single and multiple stimuli delivered through STN contacts in 6 patients with Parkinson's disease. RESULTS: On 9/11 sides tested, single stimuli elicited a negative potential with latency of approximately 3 ms which was largest over the frontal region. Its short chronaxie (50 micros) and refractory period imply that it arose from the activation of low threshold neural elements, possibly myelinated axons. This potential could follow at 100 Hz. This early potential was sometimes followed by later negative potentials at approximately 5 ms (6/11 sides) and approximately 8 ms (8/11 sides). The responsible neural elements had the same short chronaxie. These potentials were augmented by paired stimuli at separations of 2-7 ms and by trains of stimuli at 200 Hz. CONCLUSIONS: Trains of stimuli delivered to the STN may excite low threshold neural elements which can transmit impulses at frequencies >100 Hz without blocking and which may produce postsynaptic facilitation at the cortex.

Electric Stimulation Therapy↗

PubMed2001

Impairment of motor cortex activation and deactivation in Parkinson's disease.

OBJECTIVES: To examine the time course of corticospinal excitability before and after voluntary movement in Parkinson's disease (PD). METHODS: We studied 9 mild PD patients at least 12 h off medications and 11 healthy volunteers in a simple reaction time (RT) paradigm. Suprathreshold transcranial magnetic stimulation was delivered to the left motor cortex at intervals covering the periods before and after movement. RESULTS: PD patients (284+/-90 ms) and normal subjects (282+/-56 ms) had similar median RT. The time courses of both the premovement increase and the postmovement decrease in corticospinal excitability were significantly different between PD patients and normal subjects. The increase in motor-evoked potential (MEP) amplitudes began earlier for PD patients (200 ms before electromyographic (EMG) onset) than for normal subjects (150 ms before EMG onset), but the rate of increase was slower in PD patients than controls. After EMG offset, MEP amplitudes were increased for about 150 ms in normal subjects, but in PD patients this period was prolonged to about 350 ms. CONCLUSIONS: Impairment of motor cortex activation and deactivation is an early feature of PD and may be a physiological correlate of bradykinesia. The normal RT in our patients may be related to the earlier occurrence of the premovement increase in corticospinal excitability compensating for the slower rate of rise.

Adult↗

PubMed2001

Are singleton assisted reproductive technology pregnancies at risk of prematurity?

PURPOSE: Our purpose was to determine the risk of premature delivery among singleton pregnancies derived from assisted reproduction technology (ART). METHODS: Ninety-five singleton ART pregnancies and 190 matched spontaneous pregnancies were assessed for preterm delivery rates, pregnancy complications, and cesarean section rates in a retrospective study at an academic medical center. RESULTS: Among the ART singleton deliveries group (n = 95), 19 (20%) were preterm, which was statistically significantly higher than the 4% (8 of 190) found in the control group. Among the pregnancies achieved by intracytoplasmic sperm injection (ICSI) in the severe male-factor infertility subgroup (n = 22), only one preterm delivery occurred (4.5%). CONCLUSIONS: Singleton ART pregnancies are at an increased risk of preterm delivery compared to singleton pregnancies after spontaneous conception. The higher rate may be attributed to various infertility cofactors, such as uterine malformations, previous operative procedures that involved cervical dilatation, and a history of pelvic infection. This is supported by the finding that ICSI-derived pregnancies in couples with strict male-factor infertility are not at an increased risk of preterm delivery.

Case-Control Studies↗