Biomedical subjects

T Li

Publications and source records attributed to T Li.

At least 127 records · Page 7Linked to original sources

PubMed2001

[Effects of repeated high +Gz exposure on several enzyme activities in cardiomyocytes in rats and some protective measures].

Objective. To determine the changes of several myocardial enzymes in rats after repeated high +Gz exposure and the protective effects of preconditioning of low-G exposure and tea polyphenols (TP). Method. Thirty-two male Wistar rats were randomly divided into 4 groups (n = 8 each): control group (group A), +10 Gz group (group B), low-G preconditioning group (group C) and TP protection group (group D). Group B, C and D were exposed to repeated +10 Gz stress (each for 30s, 5 times/d with +1 Gz 1 min intervals, 3 d/wk, 3 weeks in total), but group A was only submitted to +1 Gz for 5 min. Group C was exposed to +2 Gz for 5 min about 1 h prior to +10 Gz stress. Additionally, TP (200 mg/kg) was given orally to group D about 1 h prior to the +Gz experiment, while distilled water was given to groups A, B and C instead. On the next day after the last centrifuge run, the hearts were taken out immediately for making frozen tissue sections. Enzyme histochemical staining and image analysis were carried out for acid phosphatase (ACP), succinate dehydrogenase (SDH), cytochromeoxidase (Cyt aa3) and adenosine triphosphatase (ATPase). Result. As compared with the control, the activities of ACP and SDH in +10 Gz stressed rats decreased significantly (P<0.05), and there was a declining trend for Cyt aa3. But, low-G preconditioning and TP had protective effects on +10 Gz stress-induced reduction of these enzymatic activities (P<0.05). Conclusion. The results showed that repeated high +Gz exposure could bring about decreases of activities in ACP (the marker enzyme of lysosome) and SDH (the marker enzyme of mitochondrial endomembrane), which indicated a reduction of oxidative metabolism in myocardial tissue; but preconditioning with low-G and natural antioxidant TP had protective effects.

Acceleration↗

PubMed2001

[Observation on the changes in nasopharyngeal carcinoma patients' olfactory before and after radiotherapy].

OBJECTIVE: Detecting nasopharyngeal carcinoma (NPC) patients' olfactory before and after radiotherapy for investigating the infection of radiotherapy on these patients' olfactory. METHOD: 100 NPC patients' olfactory were detected before the start of radiotherapy and after the termination of therapy in 3, 6, 12, 24 and 36 months. RESULT: Patients' smell acuity decreased sharply 3 months after therapy, but varying degrees of recovery were noted in 6 and 12 months. However their smell acuity became worse in the following time. CONCLUSION: NPC patients' smell acuity can be profoundly affected by radiotherapy. And after radiotherapy, their smell acuity will decrease wave-likely and cannot fully recover.

Adult↗

PubMed2001

[Determination of volatile organic compounds in atmospheric environment].

It is well known that volatile organic compounds (VOCs) are the main photochemical pollutants and ozone precursors of the photochemical smog. Investigation of photochemical pollution in the ambient air must focus on VOCs, but the concentration of VOCs in ambient air is in a very low level (10(-9)-10(-12), volume fraction), so there are difficulties in the determination of VOCs. In this work, based on the TO14A and TO15 methods recommended by the Environmental Protection Agency of United States, an improved method for the determination of fifty-six VOCs, mainly O3 precursors, in atmospheric environment was developed. Operating conditions of VOCs preconcentrator, gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) were optimized. Air sample was first frozen by liquid nitrogen, and then H2O and CO2 were eliminated in the VOCs preconcentrator. The preconcentrated VOCs sample was injected to GC and detected by MS or hydrogen flame ionization detector (FID). The C2-C10 hydrocarbons were separated effectively in capillary columns under the high concentration of CO2. The detection limits were 0.1 microgram.m-3 and the relative standard deviations were in the range from 2.57% to 9.82%. This method has been used for the determination of VOCs in real samples. The results were satisfactory.

Air Pollutants↗

PubMed2000

Retinitis pigmentosa GTPase regulator (RPGRr)-interacting protein is stably associated with the photoreceptor ciliary axoneme and anchors RPGR to the connecting cilium.

Retinitis pigmentosa (RP) is a blinding retinal disease in which the photoreceptor cells degenerate. Mutations in the gene for retinitis pigmentosa GTPase regulator (RPGR) are a frequent cause of RP. The function of RPGR is not well understood, but it is thought to be a putative guanine nucleotide exchange factor for an unknown G protein. Ablation of the RPGR gene in mice suggested a role in maintaining the polarized distribution of opsin across the cilia. To investigate its function, we used a protein interaction screen to identify candidate proteins that may interact physiologically with RPGR. One such protein, designated RPGR-interacting protein (RPGRIP), is expressed specifically in rod and cone photoreceptors. It consists of an N-terminal region predicted to form coiled coil structures linked to a C-terminal tail that binds RPGR. In vivo, both proteins co-localize in the photoreceptor connecting cilia. RPGRIP is stably associated with the ciliary axoneme independent of RPGR and is resistant to extraction under conditions that partially solubilized other cytoskeletal components. When over-expressed in heterologous cell lines, RPGRIP appears in insoluble punctate and filamentous structures. These data suggest that RPGRIP is a structural component of the ciliary axoneme, and one of its functions is to anchor RPGR within the cilium. RPGRIP is the only protein known to localize specifically in the photoreceptor connecting cilium. As such, it is a candidate gene for human photoreceptor disease. The tissue-specific expression of RPGRIP explains why mutations in the ubiquitously expressed RPGR confer a photoreceptor-specific phenotype.

Amino Acid Sequence↗

PubMed2000

Metallothioneins, oxidative stress and the cardiovascular system.

Metallothioneins (MTs) discovered four decades ago as metal binding low molecular weight thiol proteins, in recent years, have generated immense interest due to their involvement in various physiological and pathophysiological events. In spite of the recent advances in the knowledge base in MTs, no specific study on the isolation or characterization of MTs isoforms and their precise function in the heart has been conducted. Although most stress conditions in the heart do not produce much change in myocardial MTs, TNF-alpha and IL-6 do induce MT in the heart to the extent comparable with the liver. Cardiotoxicity of anticancer drugs and vulnerability of the heart to other oxidative stress conditions may partially be due to lack of inducibility of MT in the heart by these interventions. A clear understanding of induction of MTs in the heart may help in the development of better approaches to modulate the pathogenesis of cardiomyopathies and heart failure.

Animals↗

PubMed2000

Tissue-specific expression of antisense and sense transcripts at the imprinted Gnas locus.

The mouse Gnas gene encodes an important signal transduction protein, the alpha subunit of the stimulatory G protein, G(s). In humans, partial deficiency of G(s)alpha, the alpha subunit of G(s), results in the hormone-resistance syndrome pseudohypoparathyroidism type 1a. The mouse Gnas (and the human GNAS1) locus is transcribed from three promoter regions. Transcripts from P1, which encode Nesp55, are derived from the maternal allele only. Transcripts from P2 encode Xlalphas and are derived only from the paternal allele, while transcripts from P3 encode the alpha subunit and are from both parental alleles. The close proximity of reciprocal imprinting suggests the presence of important putative imprinting elements in this region. In this report, we demonstrate that the reciprocal imprinting occurs in normal tissues of interspecific (Mus spretus x C57BL/6) mice. Transcripts from P1 are most abundant in CNS (pons and medulla) in contrast to the more ubiquitous expression from P2 and P3. In the P1-P2 genomic region, we have identified an antisense transcript that starts 2.2 kb upstream of the P2 exon and spans the P1 region. While the P1 transcript is derived from the maternal allele, the P1-antisense (Gnas-as) is derived only from the paternal allele in most but not all tissues. Although both the Nesp55 region and the Gnas-as transcripts are present in cerebral cortex, adrenal, and spleen, Gnas-as is abundant in some tissues in which transcription from the Nesp55 region is negligible. Furthermore, the Nesp55 region transcripts remain strictly imprinted in tissues that lack Gnas-as. Our results suggest that multiple imprinting elements, including the unique Gnas-as, regulate the allelic expression of the Nesp55 region sense transcript.

Animals↗

PubMed2000

Identification of chiral selectors from a 200-member parallel combinatorial library.

Selection of chiral selectors for the resolution of racemic N-(1-naphthyl)leucine ester 1 was studied with a 200-member parallel library prepared on polymeric synthesis resin. Through this study, the library screening procedure developed previously is improved and other pertinent issues concerning the screening process are also addressed. The equilibration time required for screening is reduced from 24 h to approximately 3 h. Excellent correlation of the outcome between the resin batch equilibration experiment and chromatographic separation is further demonstrated. It is also demonstrated that selectors with separation factors as low as 1.4 could be identified by this batch screening process. In addition, a great deal of information regarding enantioselective interactions was obtained in this parallel library study. Such information should prove useful in improving future library designs.

Chromatography, High Pressure Liquid↗

PubMed2000

An alternative procedure to screen mixture combinatorial libraries for selectors for chiral chromatography.

An alternative process for the analysis of mixture library components for their potential as selectors for chiral chromatography is described. The procedure involves the immobilization of each enantiomer of the target racemic analyte to silica gel, followed by incubation of each resulting stationary phase with a mixture library. The adsorbed library components on the two stationary phases are then analyzed by reversed-phase liquid chromatography. A comparison of the resulting two chromatograms is made. Any peak of identical retention time but with a significant difference in intensity in the two chromatograms indicates that this component is most likely a chiral selector. Its chemical structure is then determined by LC-MS or LC-MS-MS. This new screening method significantly increases the efficiency of chiral selector determination by eliminating the need for multilibrary syntheses, as opposed to our previous method. This technique should also allow for the screening of much larger libraries as compared to our previous work.

Chemistry, Organic↗

PubMed2000

Adriamycin-induced early changes in myocardial antioxidant enzymes and their modulation by probucol.

BACKGROUND: The clinical usefulness of adriamycin is restricted by the development of congestive heart failure. It has been suggested that probucol, a strong antioxidant, completely prevents adriamycin-induced cardiomyopathy without interfering with its antitumor properties. The present study investigated the effects of adriamycin and probucol on myocardial antioxidant enzyme activities and immunoreactive protein levels in rats. METHODS AND RESULTS: Activities and protein levels of glutathione peroxidase (GSHPx) were significantly decreased from 2 to 24 hours, and those of manganese superoxide dismutase were decreased at 1 and 2 hours after adriamycin treatment. These changes were prevented by probucol. Catalase activity was increased from 2 to 24 hours after adriamycin treatment, but its protein levels were not significantly changed. Copper zinc superoxide dismutase activity and protein level were not changed at any time. Myocardial lipid peroxidation was found to be significantly higher at all time points, and this change was also prevented by probucol. Treatment with probucol alone increased GSHPx activity at 2 weeks, and in these hearts, lipid peroxidation was lower than the control value. Within 24 hours, there was no mortality in any of the groups. CONCLUSIONS: It is suggested that an early and persistent decrease in GSHPx activity and protein may play an important role in the pathogenesis of adriamycin-induced cardiomyopathy, worsening heart failure and mortality.

Animals↗

PubMed2000

Nitric-oxide dioxygenase activity and function of flavohemoglobins. sensitivity to nitric oxide and carbon monoxide inhibition.

Widely distributed flavohemoglobins (flavoHbs) function as NO dioxygenases and confer upon cells a resistance to NO toxicity. FlavoHbs from Saccharomyces cerevisiae, Alcaligenes eutrophus, and Escherichia coli share similar spectra, O(2), NO, and CO binding kinetics, and steady-state NO dioxygenation kinetics. Turnover numbers (V(max)) for S. cerevisiae, A. eutrophus, and E. coli flavoHbs are 112, 290, and 365 NO heme(-1) s(-1), respectively, at 37 degrees C with 200 microm O(2). The K(M) values for NO are low and range from 0.1 to 0.25 microm. V(max)/K(M)(NO) ratios of 900-2900 microm(-1) s(-1) indicate an extremely efficient dioxygenation mechanism. Approximate K(M) values for O(2) range from 60 to 90 microm. NO inhibits the dioxygenases at NO:O(2) ratios of > or =1:100 and makes true K(M)(O(2)) values difficult to determine. High and roughly equal second order rate constants for O(2) and NO association with the reduced flavoHbs (17-50 microm(-1) s(-1)) and small NO dissociation rate constants suggest that NO inhibits the dioxygenase reaction by forming inactive flavoHbNO complexes. Carbon monoxide also binds reduced flavoHbs with high affinity and competitively inhibits NO dioxygenases with respect to O(2) (K(I)(CO) = approximately 1 microm). These results suggest that flavoHbs and related hemoglobins evolved as NO detoxifying components of nitrogen metabolism capable of discriminating O(2) from inhibitory NO and CO.

Alcaligenes↗

PubMed2000

Association analysis of polymorphisms in the DRD4 gene and heroin abuse in Chinese subjects.

Heroin abuse is a major social and public health problem in many parts of the world, yet relatively little is known about its etiology. Although genes play a role in determining susceptibility, they are expected to be of small effect with considerable heterogeneity. Because the dopamine system is involved in reward, its neurotransmitter receptors are candidates for etiological involvement in addiction. In the present study, we examine two polymorphisms in the dopamine D4 receptor, a VNTR in exon III and a point mutation in the promoter (-512C/T) that affects transcriptional efficiency. We examined a sample of 405 heroin-abusing subjects and 304 controls from Sichuan Province, Southwest China. One hundred twenty-one of these cases and 154 controls were previously used in a study of the DRD4 VNTR [Li et al., 1997], and the remainder are newly ascertained. The two polymorphisms were in weak but detectable linkage disequilibrium (1, 418 chromosomes, P < 0.00001, D' = 0.17). When we compared the heroin-abuse group with controls, we found no significant difference between the patients and controls for either polymorphism in the DRD4 gene or their haplotypes. We were also unable to replicate our earlier association between "long" DRD4 alleles and heroin abuse. However, division of the sample by route of administration (nasal inhalers or injectors) produced a significant difference between inhalers and controls for the DRD4 VNTR (six-fold corrected P = 0. 018 by allele) but not for injectors of heroin. The association we observed between inhalers and the DRD4 polymorphism is difficult to interpret, although it is possible that the association is explained by different levels of novelty seeking between the two subgroups.

Administration, Inhalation↗

PubMed2000

Recovery of sodium dodecyl sulfate-proteins from gel electrophoretic bands in a single electroelution step for mass spectrometric analysis.

Mass spectrometric analysis of proteins derived from bands in gel electrophoresis is incompatible with the covalent fluorescent labeling of the protein. Thus, if one wishes to take advantage of the capacity for computer-directed electroelution of electrophoresis apparatus with intermittent fluorescent scanning of the migration path, the protein must be labeled fluorescently in a noncovalent, reversible fashion. This was recently achieved by staining of SDS-proteins with Cascade blue and electrophoresis in barbital buffer. However, the method was not a practical one for the purpose of isolating proteins from gel electrophoretic bands and their transfer into the mass spectrometer for three reasons: (i) Ten consecutive electroelution steps were required to obviate pH changes in the electroelution chamber; (ii) electroeluates from six gel electrophoretic lanes needed to be pooled; (iii) excessive protein loads ranging from 7 to 33 microg/pool were required. The present study reports the solution to those three problems. Mass spectrometric (MALDI-TOF) characterization of five proteins was demonstrated (i) after a single electroelution step; (ii) using electroelution from a single gel of 0.3-cm(2) cross-sectional area; and (iii) using a protein load of 2 (in one case 4) microg. However, the migration rates of the Cascade blue-SDS-protein-barbital complexes derived from proteins with widely varying molecular weights proved to be the same. Thus, despite the three advances made, the method to date remains restricted to samples of single proteins.

Electrophoresis, Agar Gel↗

PubMed2000

Comparative Study on the Structure of Water in Reverse Micelles Stabilized with Sodium Bis(2-ethylhexyl) Sulfosuccinate or Sodium Bis(2-ethylhexyl) Phosphate in n-Heptane.

The microstructure of water solubilized in H(2)O/surfactant/n-heptane ternary systems has been investigated by employing (1)H-NMR and FT-IR spectroscopic techniques. Two reverse micellar systems were prepared and studied, i.e., sodium bis(2-ethylhexyl) sulfosuccinate in n-heptane (H(2)O/AOT/n-heptane) and sodium bis(2-ethylhexyl) phosphate in n-heptane (H(2)O/NaDEHP/n-heptane). (1)H-NMR data showed that the chemical shift of water protons for the AOT and NaDEHP reverse micelles varied downfield and upfield, respectively, with an increase of the water content. The opposite shift directions with increasing water content are interpreted as due to a composition change of the solubilized water associated with head-groups and sodium counterions in reverse micellar systems. On the basis of deconvolution results of FT-IR spectra, a four-component model is proposed to interpret the FT-IR and (1)H-NMR results. Copyright 2000 Academic Press.

Journal Article↗

PubMed2000

Combined (1)H MR spectroscopy and diffusion-weighted MRI improves the prediction of stroke outcome.

BACKGROUND: The prognostic value of the biochemical changes seen with proton MR spectroscopy (1H MRS) in ischemic stroke was examined. Acute diffusion-weighted imaging (DWI) was used to identify regions of ischemia for 1H MRS voxel localization. METHODS: Nineteen patients had 36 1H MRS studies, 13 patients acutely (mean, 11.1 hours), 10 subacutely (mean, 3.9 days), and 13 at outcome (mean, 82 days). Single-voxel, long-echo, timepoint-resolved spectroscopy was used to obtain lactate, n-acetylaspartate (NAA), choline, and creatine levels from the infarct core. Outcome measures were final infarct volume and clinical assessment scales (Canadian Neurological Scale, Barthel Index, and Rankin Scale). RESULTS: Acute lactate/choline ratio correlated more strongly with clinical outcome scores (r = 0.76 to 0.83; p < 0.01) and final infarct size (r = 0. 96; p < 0.01) than acute DWI lesion volume or acute NAA/choline ratio. Combination of acute lactate/choline ratio with acute DWI lesion volume improved prediction of all outcome scores (R2 = 0.80 to 0.90). The predictive effect of acute lactate/choline ratio was independent of acute DWI lesion volume (p < 0.001). In subacute and chronic infarction, both lactate/choline and NAA/choline ratios continued to correlate with outcome (p < 0.05). At the chronic stage, persistent lactate/choline ratio elevation strongly correlated with outcome measures (r = 0.71 to 0.87). CONCLUSION: Lactate/choline ratio measured in the acute infarct core by 1H MRS improves the prediction of stroke outcome and provides prognostic information complementary to DWI. Lactate/choline ratio could be used as an additional marker to select patients for acute and chronic therapies.

Aged↗

PubMed2000

Low frequency of HLA-A*0201 allele in patients with Epstein-Barr virus-positive nasal lymphomas with polymorphic reticulosis morphology.

Lymphoproliferative diseases of the nasal cavity and paranasal sinuses occur frequently in Asian countries and are histologically categorized as monomorphic ordinary lymphoma and polymorphic reticulosis (PR) with apparent inflammatory cell infiltration. The large atypical cells in PR show natural-killer cell nature and frequently contain Epstein-Barr virus (EBV) DNA. Among the EBV genes involved in latent infection, those encoding EBV latent membrane proteins are frequently expressed in PR. Several cytotoxic T-lymphocyte (CTL) defined epitopes have been mapped to latent membrane proteins restricted with HLA-A2, -A11 or -A24 antigens. Thus, the HLA-A allele may affect the development of PR. To examine this possibility, HLA-A alleles of 25 patients with EBV(+) PR were determined with low-resolution polymerase chain reaction-based typing using HLA-A locus sequence-specific primer combinations. The frequency of HLA-A alleles including HLA-A2 and -A24 antigens in PR patients was lower than that in the normal Japanese population, but the difference was not significant. Since HLA-A2-restricted CTL responses are well delineated at the A2-subtype level, the A2-subtype of PR cases with HLA-A2 antigen was further determined by high-resolution genetic typing. The frequency of HLA-A*0201 in PR was significantly lower than in the normal population (p=0.0314). The HLA-A*0201-restricted CTL responses may thus function in vivo to suppress the development of overt lymphoma.

Adult↗

PubMed2000

Identification of a Drosophila vitamin K-dependent gamma-glutamyl carboxylase.

Using reduced vitamin K, oxygen, and carbon dioxide, gamma-glutamyl carboxylase post-translationally modifies certain glutamates by adding carbon dioxide to the gamma position of those amino acids. In vertebrates, the modification of glutamate residues of target proteins is facilitated by an interaction between a propeptide present on target proteins and the gamma-glutamyl carboxylase. Previously, the gastropod Conus was the only known invertebrate with a demonstrated vitamin K-dependent carboxylase. We report here the discovery of a gamma-glutamyl carboxylase in Drosophila. This Drosophila enzyme is remarkably similar in amino acid sequence to the known mammalian carboxylases; it has 33% sequence identity and 45% sequence similarity to human gamma-glutamyl carboxylase. The Drosophila carboxylase is vitamin K-dependent, and it has a K(m) toward a model pentapeptide substrate, FLEEL, of about 4 mm. However, unlike the human gamma-glutamyl carboxylase, it is not stimulated by human blood coagulation factor IX propeptides. We found the mRNA for Drosophila gamma-glutamyl carboxylase in virtually every embryonic and adult stage that we investigated, with the highest concentration evident in the adult head.

Adult↗

PubMed2000

CP1 domain in Escherichia coli leucyl-tRNA synthetase is crucial for its editing function.

The amino acid discrimination by aminoacyl-tRNA synthetase is achieved through two sifting steps; amino acids larger than the cognate substrate are rejected by a "coarse sieve", while the reaction products of amino acids smaller than the cognate substrate will go through a "fine sieve" and be hydrolyzed. This "double-sieve" mechanism has been proposed for IleRS, a class I aminoacyl-tRNA synthetase. In this study, we created LeuRS-B, a mutant leucyl-tRNA synthetase from Escherichia coli with a duplication of the peptide fragment from Met328 to Pro368 (within its CP1 domain). This mutant has 50% of the leucylation activity of the wild-type enzyme and has the same ability to discriminate noncognate amino acids in the first step of the reaction. However, LeuRS-B can catalyze mischarging of tRNA(Leu) by methionine or isoleucine, suggesting that it is impaired in the ability to edit incorrect products. Wild-type leucyl-tRNA synthetase can edit the mischarged tRNA(Leu) made by LeuRS-B, while a separated CP1 domain cannot. These data suggest that the CP1 domain of leucyl-tRNA synthetase is crucial to the second editing sieve and that CP1 needs the structural context in leucyl-tRNA synthetase to fulfill its editing function.

Amino Acyl-tRNA Synthetases↗

PubMed2000

Identification of a 26S proteasome-associated UCH in fission yeast.

We have identified a 26S proteasome-associated ubiquitin carboxyl-terminal hydrolase (UCH) in Schizosaccharomyces pombe. The gene (designated uch2+) encodes a protein containing a UCH catalytic domain at its N-terminus and a short extension at its C-terminus. uch2+ is nonessential as the uch2 null mutant strain showed no significant difference from the wild-type strain. The GFP-tagged Uch2p is localized predominantly to the nuclear periphery, which is similar to the 26S proteasome localization. Deletion of the C-terminal extension of Uch2p resulted in a drastic change of its subcellular localization: it showed a generally diffused distribution instead of a perinuclear pattern. Glycerol gradient centrifugation analysis and coimmunoprecipitation studies of fission yeast extracts using anti-Mts4p antiserum suggest that Uch2p is associated with the 26S proteasome and the association of Uch2p with the 26S proteasome is mediated by its C-terminal extension.

Amino Acid Sequence↗