Biomedical subjects

Y Yang

Publications and source records attributed to Y Yang.

At least 595 records · Page 33Linked to original sources

PubMed1999

Effect of ethanol on the activity and conformation of Penaeus penicillatus acid phosphatase.

The effect of ethanol on the activity of Penaeus penicillatus acid phosphatase has been studied. The results show that ethanol significantly inhibits enzyme activity as a non-competitive inhibitor, with Ki 8.75%. The conformational changes of the enzyme molecule induced by ethanol were followed using fluorescence emission, ultraviolet difference and circular dichroism (CD) spectra. Increasing the ethanol concentration caused the fluorescence emission intensity of the enzyme to increase. The ultraviolet difference spectra of the enzyme denatured with ethanol had two negative peaks at 220 and 278 nm, and a positive peak at 240 nm. Increasing the ethanol concentration produced a small shoulder peak at 287 nm in addition to the increases in the negative magnitudes of the 220 and 278 nm peaks. The changes of the fluorescence and ultraviolet difference spectra reflected the changes of the microenvironments of the tryptophan and tyrosine residues of the enzyme. The CD spectrum changes of the enzyme show that the secondary structure of the enzyme also changed. The results suggest that ethanol is a non-competitive inhibitor and the conformational integrity of the enzyme is essential for its activity.

Acid Phosphatase↗

PubMed1999

Class A beta-lactamases--enzyme-inhibitor interactions and resistance.

Beta-Lactamases of Ambler's Class A are the most commonly encountered mechanism of bacterial resistance to beta-lactam antibiotics. In the face of selective pressure arising from use of either newer cephalosporins or beta-lactam/beta-lactamase inhibitor combinations, mutations arose among Class A beta-lactamase genes, leading to resistance. Clavulanic acid, a naturally occurring clavam, and the penicillanic acid sulfones sulbactam and tazobactam are the inhibitors in clinical use. This review focuses on the mechanism of inhibition by these currently marketed beta-lactamase inhibitors and on the mechanism by which specific amino acid substitutions might lead to resistance. The key amino acid positions important for inhibitor-resistance include Met69, Ser130, Arg244, Arg275, and Asn276. Ser130 is vital to the chemical mechanism of inhibition. Arg244 appears to be coordinated to Arg275 and Asp276 by hydrogen bonds. Arg244 is involved in positioning beta-lactams, especially penicillins and beta-lactamase inhibitors, via their carboxyl groups. Site-directed mutagenesis studies confirm the role of Arg244 and its coordinating partners in beta-lactam turnover and in the reactions leading to enzyme inactivation. This mechanism is dependent on the donation of a proton via a water coordinated to Arg244 and Val216 to clavulanic acid to allow formation of a favorable leaving group. This proton donation is probably not required for formation of a favorable leaving group for the sulfone inhibitors sulbactam and tazobactam. Therefore, some amino acid substitutions have differing effects on inhibition by clavulanic acid compared with the penicillanic acid sulfones. Met69 may play a more structural role in beta-lactam positioning within the oxyanion hole.

Anti-Bacterial Agents↗

PubMed1999

Interferons enhance HLA-G mRNA and protein in transfected mouse fibroblasts.

The HLA class Ib gene, HLA-G, has a 16-bp deletion in its Enhancer A/interferon response element (IRE). We used a model system consisting of mouse fibroblasts transfected with 6.0 kb of HLA-G DNA, the S14/8 cells, to test the postulate that this deletion prevents interferons (IFNs) from enhancing transcription. Northern blot hybridization experiments showed that after 48 h of treatment with IFN-alpha, IFN-beta or IFN-gamma, steady-state levels of HLA-G mRNA in the S14/8 cell line were doubled. Proteins were also increased by IFNs as demonstrated in flow cytometry and immunocytochemical experiments that used monoclonal antibodies to all HLA class I antigens (W6/32), HLA-G heavy chains (87G) and light chains (beta2m). Thus, interferons enhance expression of HLA-G and would be expected to improve host defense at the maternal-fetal interface by increasing the ability of maternal immune cells to recognize and destroy infected HLA-G+ cells.

Animals↗

PubMed1999

Residual analysis in random regressions using SAS and S-PLUS.

A program package RRAP: Random Regression Residual Analysis Program using SAS [1] and S-PLUS [2] is available for performing random regression residual analysis. The PROCEDURE MIXED from SAS is used for statistical inference. Both elementary-level and individual-level residuals are used. The S-PLUS programs provide: (1) a transformation to orthogonalize the elementary-level correlated residuals for standard regression residual analyses; and (2) several statistics and plots for checking model assumptions, assessing model fitting and detecting outlying individuals. RRRAP starts with a SAS Macro RRRAPMAC on the data followed by a S-PLUS Program DoRRRAP on a UNIX system.

Models, Statistical↗

PubMed1999

Neuroprotective effects of brain-derived neurotrophic factor in seizures during development.

Although the immature brain is highly susceptible to seizures, it is more resistant to seizure-induced neuronal loss than the adult brain. The developing brain contains high levels of neurotrophins which are involved in growth, differentiation and survival of neurons. To test the hypothesis that neurotrophins may protect the developing brain from seizure-induced neuronal loss, brain-derived neurotrophic factor up-regulation was blocked by intracerebroventricular infusion of an 18mer antisense oligodeoxynucleotide sequence to brain-derived neurotrophic factor in 19-day-old rats using micro-osmotic pumps. Control rats were infused with sense or missense oligodeoxynucleotide. Status epilepticus was induced by intraperitoneal administration of kainic acid 24 h after the start of oligodeoxynucleotide infusion. Seizure duration was significantly increased in the antisense oligodeoxynucleotide plus kainic acid group compared to groups that received kainic acid alone or kainic acid plus sense or missense oligodeoxynucleotide. There was no difference between groups in the latency to forelimb clonus. A twofold increase in brain-derived neurotrophic factor levels was observed in the hippocampus 20 h following kainic acid-induced seizures. This kainic acid-induced increase was absent in animals receiving infusion of antisense oligodeoxynucleotide to brain-derived neurotrophic factor at time of seizure induction. Hippocampi of rats in this group (antisense oligodeoxynucleotide plus kainic acid) showed a loss of CA1 and CA3 pyramidal cells and hilar interneurons. This neuronal loss was not dependent upon seizure duration since animals injected with diazepam to control seizure activity in the antisense plus kainic acid group also showed similar neuronal loss. Administration of kainic acid or infusion of antisense alone did not produce any cell loss in these regions. Induction of seizures at postnatal day 20, in the presence or absence of antisense oligonucleotide, did not produce an impairment in learning and memory when tested 15 days later in the Morris water maze. The hippocampi of these animals did not show any synaptic reorganization as assessed by growth-associated protein-43 immunostaining and Timm staining. Our findings confirm prior studies demonstrating that seizures in the immature brain are associated with little, if any, cell loss. However, when seizure-induced increase in brain-derived neurotrophic factor is blocked, seizures do result in neuronal loss in the developing brain. Thus, brain-derived neurotrophic factor appears to provide protection against kainic acid seizure-induced neuronal damage in the developing brain.

Animals↗

PubMed1999

Consequences of recurrent seizures during early brain development.

It is well documented that prolonged seizures (status epilepticus) can cause neuronal injury and result in synaptic reorganization in certain brain regions. However, the effect of recurrent, relatively short seizures in young animals on subsequent brain development is not known. To study the consequences of recurrent seizures on the developing brain, we subjected immature rats to a total of 50 flurothyl-induced seizures from postnatal day 11 until day 23. Immunohistochemistry for c-fos was performed to characterize the pattern of neuronal activation following the seizures. Cell counting of dentate granule cells, CA3, CA1, and hilar neurons, using unbiased stereological methods, and the silver impregnation method were used to evaluate neuronal death following the recurrent seizures. Timm and Golgi staining were performed four weeks after the 50th seizure to evaluate the effects of recurrent seizures on synaptic organization. Our results show that recurrent flurothyl-induced seizures progressively increased excitability of the brain, as revealed by a dramatic increase in the extent and intensity of c-fos immunostaining. While no cell loss was detected in the hippocampus with either Cresyl Violet or silver stains, animals experiencing multiple daily seizures developed increased mossy fiber sprouting in both the supragranular layer of the dentate gyrus and the infrapyramidale layer of the CA3 region. Golgi staining confirmed that there was an increase in mossy fibers in the pyramidal cell layer. Our results suggest that serial recurrent seizures in the immature brain can lead to significant changes in mossy fiber distribution even though the seizures do not cause significant hippocampal cell loss.

Animals↗

PubMed1999

Effects of hyperthermia and continuous hippocampal stimulation on the immature and adult brain.

Whether febrile seizures lead to hippocampal necrosis is a question of paramount clinical importance. This study attempted to simulate a complex febrile seizure, compared with hyperthermia (HYP) alone and prolonged seizure alone (produced by continuous hippocampal stimulation (CHS)). Four groups of rats were studied at each of two ages, immature (postnatal day, P20) and adult (P60). Group 1 was subjected to 45 min of HYP (body temperature 40 degrees C) plus CHS, Group 2 received 45 min of HYP alone, Group 3 got 45 min of CHS alone, and Group 4 was sham-handled control rats. Baseline and post-session EEGs were recorded in all groups. Subsequently, brains were examined histologically for evidence of hippocampal damage. Both CHS-treated groups (with and without HYP) exhibited behavioral and EEG seizures while the group undergoing HYP alone did not have seizures. There were no gross histological lesions in any group. Cell counts in regions CA1, CA3, dentate gyrus and dentate hilus did not differ in rats under any condition of hyperthermia and CHS, in either P20 or P60 rats compared to age-matched controls. These results indicate that both immature and mature rodents are resistant to hyperthermic brain damage and raises the question of whether febrile seizures play a role in the genesis of mesial temporal sclerosis.

Aging↗

PubMed1999

Inhibitory effect of some triterpenes from cacti on 32Pi-incorporation into phospholipids of HeLa cells promoted by 12-O-tetradecanoylphorbol-13-acetate.

Seventeen triterpenes isolated from cacti and the 10 derivatives were examined for the inhibition of tumor promoter-induced effects in vitro, such as stimulation of 32Pi-incorporation into phospholipids of cultured cells. Betulinic acid (1), cochalic acid (15), erythrodiol (16), oleanolic acid (21) and queretaroic acid (24) inhibited 12-O-tetradecanoylphorbol-13-acetate (TPA) stimulated 32Pi-incorporation into phospholipids of the cultured cells.

Animals↗

PubMed1999

Anti-emetic principles of Pogostemon cablin (Blanco) Benth.

Bioassay-guided fractionation of anti-emetic extracts and constituents of 8 traditional Chinese herbal drugs was performed. Twenty extracts described in Table 1 showed anti-emetic activity on copper sulfate induced-emesis in young chicks. From the n-hexane extract of Pogostemon cablin, patchouli alcohol (1), pogostol (2), stigmast-4-en-3-one (3), retusin (4), and pachypodol (5) were tested and exhibited anti-emetic effects.

Animals↗

PubMed1999

Antigen presentation by MHC class I and its regulation by interferon gamma.

Antigen processing by MHC class I molecules begins with the generation of peptides by proteolytic breakdown of proteins. IFN-gamma upregulates gene expression of several proteasomal subunits as well as the proteasome regulator PA28; this implicated their role in antigen degradation. Crystallographic, mutational and biochemical studies contributed to our understanding of the basic principles of proteasomal protein degradation and the consequences of IFN-gamma induction for proteasome function. In addition, nonproteasomal mechanisms seem to be involved in antigen degradation. Leucine aminopeptidase, which is also upregulated by IFN-gamma, was shown to collaborate with the proteasome for epitope production and unknown proteases seem to compensate for the loss of proteasomal degradation in the presence of proteasome inhibitors. Thus, a rather complex picture emerges for the rules governing peptide production in the presence or absence of IFN-gamma.

Antigen Presentation↗

PubMed1999

Surgical treatment of oligosymptomatic mitral valve incompetence?.

OBJECTIVE: Despite improvements of the surgical technique in NYHA (III)-(IV) mitral valve incompetence (MVI) postoperative long-term results remain poor. As long-term results reflect primarily the ventricular function rather than the quality of the surgical technique the contractile performance of isolated papillary muscles obtained from patients undergoing mitral valve replacement for MVI (n = 25) was analysed in detail. METHODS: Muscle preparations (0.4 x 5.0 mm) obtained from left ventricular papillary muscles (NYHA (I), n = 4; NYHA (II), n = 7; NYHA (III), n = 8; NYHA (IV), n = 6) were loaded for intracellular calcium measurements with FURA-2, stretched to optimal length (Lmax) and electrically stimulated with frequencies ranging from 30 to 180 beats/min (b.p.m.) (10% above threshold, 37 degrees C, Krebs-Henseleit solution). Isometric force development and diastolic intracellular calcium (measured by the 'ratio method'; excitation light: wavelengths alternating 340 and 380 nm, frequency: 250 Hz) were simultaneously recorded as a function of the stimulation frequency. RESULTS: At 60 b.p.m. force development was significantly higher in NYHA (I) myocardium (21.3 +/- 2.8 mN/mm2) than in NYHA (III) myocardium (12.8 +/- 2.2 mN/mm2), (P < 0.0001). In NYHA (I) myocardium force rose with increasing stimulation frequency ('positive staircase'). In contrast the stimulation frequency associated with maximum force was shifted towards lower frequencies in NYHA (II)-(IV) myocardium ('negative staircase'). As compared with NYHA (I) myocardium diastolic intracellular calcium was significantly elevated at 150 b.p.m. in NYHA (II)-(IV) myocardium (P < 0.01). CONCLUSION: The data show, that severe impairment of contractile function ('negative staircase phenomenon', reduced force, elevated diastolic calcium) is present in MVI classified as NYHA (III)-(IV) that may explain the poor long-term results. Most interestingly the data argue for a significant impairment of myocardial function even in NYHA (II) MVI. The results suggest an early surgical treatment of mitral valve incompetence as long as the myocardial function is normal (NYHA (I)) as (1) a reduced perioperative risk, (2) improved long-term results, and (3) a higher probability for mitral valve repair (instead of replacement) may be expected in these early stages of mitral valve disease.

Biopsy, Needle↗

PubMed1999

Two novel anti-emetic principles of Alpinia katsumadai.

Two novel diarylheptanoids named katsumadain A (1) and katsumadain B (2) were isolated from the seeds of Alpinia katsumadai, and their structures were determined by spectroscopic analysis. Both katsumadains A (1) and B (2) showed anti-emetic activities on copper sulfate-induced emesis in young chicks.

Animals↗

PubMed1999

Characterization of conjugated metabolites of benzo[a]pyrene in germ-free rat urine by liquid chromatography/electrospray tandem mass spectrometry.

The characterization of conjugated metabolites of benzo[a]pyrene (BP) in the urine of male germ-free rats given a single intraperitoneal dose of [(14)C]BP is described. Urinary metabolites, constituting 9% of the administered radioactivity, were extracted on a Sep-Pak C(18) cartridge and separated by lipophilic ion-exchange chromatography into neutral and acidic fractions (fractions I-V). Metabolites in the latter fractions, constituting more than 80% of the urinary radioactivity, were characterized by reversed-phase HPLC and capillary column liquid chromatography/electrospray mass spectrometry (LC/ESMS) and tandem mass spectrometry (MS/MS). Relative quantities of BP metabolites were estimated from the distribution of radioactivity. Some coeluting compounds were semiquantified from the ion current chromatograms obtained in the capillary column LC/ESMS analyses. The major conjugated metabolites in fraction II, containing about 50% of the urinary radioactivity, consisted of three tetrahydrotrihydroxy-BP-S-N-acetylcysteines, the major isomer being 7,8,9,10-tetrahydro-8,9, 10-trihydroxy-BP-7-S-N-acetylcysteine, two dihydrotrihydroxy-BP-S-N-acetylcysteines, and a tetrahydrotetrahydroxy-BP-S-N-acetylcysteine. Fraction II also contained three apparently unconjugated compounds whose structures will be described elsewhere. Metabolites characterized in fractions III and IV, containing about 30% of the urinary radioactivity, included three BP-O,O'-disulfates, two monohydroxy-BP-O-sulfates, three dihydrodihydroxy-BP-O-sulfates, three BP-O,O'-diglucuronides, and a BP-O-sulfate-O'-glucuronide. Trace levels of a tetrahydrotrihydroxy-BP-S-glutathione conjugate were detected in fraction V.

Animals↗

PubMed1999

Rapid and efficient retrovirus-mediated gene transfer into B cell lines.

Murine B cell lines such as WEHI-231, BAL17 and M12.4.1 are frequently used as model systems to study signal transduction, cell cycle regulation, and apoptosis. Dissection of these processes often involves expressing exogenous genes in these cells. Electroporation is an inefficient method to express genes in B cell lines and requires several weeks to isolate and analyze clones, followed by an additional one to two weeks to grow sufficient cells for biochemical experiments (e.g. immunoprecipitations). In this report, we describe an optimized procedure for retroviral-mediated gene transfer into murine B cell lines that allows one to obtain a pure population of cells expressing an exogenous gene within 4 days. Two days post-infection, between 10% (BAL17 and M12.4.1 cells) and 70% (WEHI-231 cells) of the cells express the exogenous gene. Culturing the cells for an additional 48 hours with puromycin kills all the non-infected cells and yields a pure population of cells that express the exogenous gene. Sufficient cells for biochemical experiments can be obtained by expanding the cell culture for an additional 5 to 7 days. This rapid and efficient retroviral-mediated gene transfer procedure can greatly expedite the study of signal transduction and other processes in B cells.

Animals↗

PubMed1999

Genetic diversity and taxonomic implication of Cordyceps sinensis as revealed by RAPD markers.

Random amplified polymorphic DNA (RAPD) markers are used to investigate genetic variation and evolutionary relationships of 29 samples of Cordyceps sinensis from different geographical populations on the Qinghai-Tibet plateau. Out of 137 RAPD bands scored, 100 are polymorphic. A correlation is revealed between geographical distance and genetic distance. The molecular phylogenetic tree suggests that the 29 samples are divided into three notable clusters, corresponding to the geographical populations, i.e., the north population (NP), middle population (MP), and south population (SP). The NP consists of 7 northern samples from Menyuan, Maqu, and Luqu, the MP consists of 8 samples from Yushu and Chengduo, and the SP consists of 14 samples from Byma Snow Mountain, Renzhi Snow Mountain, Chongcaoxiwa, and Dacaodi. It is demonstrated that extensive genetic diversity is found among different geographical populations of C. sinensis. The genetic diversity pattern of C. sinensis may be caused by the founder effects. The taxonomic status of NP, MP, and SP populations should be that they are different subspecies rather than different species.

Biological Evolution↗

PubMed1999

Thymocyte apoptosis.

Apoptosis is the fate of most thymocytes. Many molecules participate in the decision of whether a thymocyte is to live or to die, including cell surface receptors, such as the T cell receptor for antigen, Notch-1, and costimulatory receptors, ligand-regulated nuclear transcription factors such as the glucocorticoid receptor, signaling, and effector proteases, and direct regulators of the apoptotic machinery such IAPs. In this review we discuss recent data concerning these molecules and pathways and their implication for understanding the mechanisms underlying thymocyte death, survival, and the generation of inmmunocompetent T cells.

Animals↗

PubMed1999

Kinetics of inhibition of green crab (Scylla serrata) alkaline phosphatase by L-cysteine.

The inhibition of alkaline phosphatase from green crab (Scylla serrata) by L-cysteine has been studied. The results show that L-cysteine gives a mixed-type inhibition. The progress-of-substrate-reaction method previously described by Tsou [(1988), Adv. Enzymol. Related Areas Mol. Biol. 61, 391-436] was used to study the inactivation kinetics of the enzyme by L-cysteine. The microscopic rate constants were determined for reaction of the inhibitor with the free enzyme and the enzyme-substrate complex (ES) The results show that inactivation of the enzyme by L-cysteine is a slow, reversible reaction. Comparison of the inactivation rate constants of free enzyme and ES suggests that the presence of the substrate offers marked protection of this enzyme against inactivation by L-cysteine.

Alkaline Phosphatase↗

PubMed1999

Bacterial death induced by expression of the intracellular portion of human Fas.

In attempting to produce the intracellular portion of human Fas (IC175 - 319) as a GST-fusion protein we found that expression of GST-IC175 - 319, but not GST alone or GST-IC231 - 298 (containing the Fas death domain), rapidly caused the death of host E. coli cells. Expression of GST-IC175 - 319 with a single amino acid substitution (V238N) corresponding to the mouse lprcg mutation, or E245A, which abolishes the ability of Fas to self-associate, did not kill bacteria. Deletional analysis identified a 20-amino acids region (Asp210 - Lys230) as essential for the killing activity, and introduction of a single amino acid substitution (T225P) in this 20 amino acid region markedly decreased the ability of Fas- IC175 - 319 to cause bacterial death. These data indicate that Fas can deliver a death signal in prokaryotic organisms by a means that shares some features with eukaryotic cells, and raise the possibility that certain mechanisms leading to programmed cell death may be conserved from bacteria to mammalian cells.

Animals↗