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Biomedical subjects

L Peng

Publications and source records attributed to L Peng.

At least 73 records · Page 4Linked to original sources
PubMed1999

[Study on conformational changes of GP IIb/IIIa complex during platelet activation].

OBJECTIVE: To determine whether a conformational change in GPIIb/IIIa occurs during platelet activation. METHODS: Epitopes on GPIIb/IIIa complex were labeled with McAbs to GPIIb (SZ-22) and GPIIIa (SZ-21) conjugated to either a donor fluorescein (FITC-labeled) or an acceptor (TR-labeled) chromophore. The FRET between platelet-bound FITC and TR was measured and calculated by flow cytometry during platelet activation induced by some agonists. RESULTS: In unstimulated platelets, a small but consistent change of FRET (5.5%) was detected, regardless of which antibody served as FRET donor. Platelet activation resulted in an obvious increase in FRET, suggesting a significant change in the separation or orientation of the epitopes within GPIIb/IIIa. This kind of changes could also occur on removing the extracellular calcium, and was independent of receptor occupancy. CONCLUSION: The increase in FRET can reflect the rearrangement of the chromophore-labeled McAbs bound to GPIIb/IIIa during platelet activation, and this kind of structural rearrangement subunits of GPIIb/IIIa complex subunits can induce fibrinogen receptor expression.

Flow Cytometry↗
PubMed1999

[Investigation of inhibitory effect of ramipril on apoptosis in spontaneously hypertensive rats].

To explore the effect of angiotensin converting enzyme (ACE) inhibitor on apoptosis in spontaneously hypertensive rats(SHR), and normotensive control rats (WKY) at different ages were used. Ramipril (1 mg.kg-1.d-1) was administered orally to male SHR from 3 or 5 weeks to 10 weeks of age. Male and age-matched untreated SHR and WKY were used as controls. Experiments determined. Apoptosis in cardiomyocytes of SHR was quantified by a maximal labeling (Lmax) method and the characteristic features of apoptosis were identified by electron microscopy (EM), in situ labeling of DNA strand breaks with terminal deoxynucleotidyl transferase mediated dUTP end labeling (TUNEL) and autoradiographic analysis of DNA fragments. The results of the quantitative method showed an age-dependent increase in apoptosis in the cardiac tissues of SHR. A significant increase in DNA breaks occurred as early as age 4 weeks and continued to increase up to a plateau at age 16 weeks in the cardiac tissue of SHR, whereas there was no significant change in apoptosis in WKY up to 64 weeks. Moreover, after the treatment of SHR with ramipril, an inhibitor of ACE, the DNA fragmentation, like BP and HW/BW, was reduced significantly (70.7%) as compared with that of untreated SHR(P < 0.01); and similar to that of the WKY (P > 0.1), the DNA ladder disappeared, which was very obvious in the untreated SHR. These studies demonstrate that ramipril can prevent the development of hypertension and myocardial hypertrophy and can inhibit the increase in the apoptosis of SHR cardiac myocytes, suggesting that apoptosis may be involved in the pathogenesis of genetic hypertension.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1998

Analysis of the human RAD51L1 promoter region and its activation by UV light.

The human REC2/RAD51B gene (HGMW-approved symbol RAD51L1) encodes a 350-amino-acid protein with regional homologies to members of the RAD52 epistasis group. It is induced by DNA-damaging agents, and the overexpression of this gene product causes G1/S cell cycle arrest. In this report, the promoter region, containing the UV-responsive element, is revealed. Deletion analyses of a 1699-base fragment at the 5' end of the human REC2/RAD51B cDNA identified a 116-base sequence that appears to be responsible for radiation induction. This fragment contains many DNA sequences that have been identified in the promoter regions of other radiation-inducible genes in yeast and humans. Within this region are "consensus" binding sites for both the AP2 and the p53 proteins that may act to regulate the expression of the human REC2/RAD51B gene. Five putative transcripts have been identified from regions 5' of the promoter element that splice near the ATG translation start site. None of the transcripts contain the UV-inducible element nor the consensus transcription factor binding sites.

Base Sequence↗
PubMed1998

[Cytogenetic study in eight cases of Fanconi anemia].

OBJECTIVE: To study the clinical, hematological and cytogenetical characteristics in Fanconi anemia (FA). METHODS: Culture the peripheral lymphocytes with Mitomycin C (MMC) induction to count the chromosome breakages and to count the sister chromatid exchanges (SCE) in FA. RESULTS: The clinical and hematological manifestations in FA varied at all. Spontaneous chromosome break and MMC induced break in FA were significantly higher than those in normal. Spontaneous and induced SCE were also higher in FA. CONCLUSION: Owing to genetic heterogeneity in FA, the phenotypes in FA are diversified also. So, chromosome breakage study is a very important method in the diagnosis of FA, and gene complementation analysis may identify which complementation group the patient carries.

Adolescent↗
PubMed1998

Lipopolysaccharide differentially regulates microglial trk receptor and neurotrophin expression.

Activated brain microglia play a pivotal role in inflammatory and degenerative disorders, mediating immune function and producing toxic and trophic agents. We previously reported that microglia express neurotrophins and that neurotrophin-3 (NT-3) increases microglial proliferation and phagocytosis, processes associated with cellular activation. However, mechanisms regulating responsiveness to NT-3 and expression of NT-3 in activated microglia remain undefined. To investigate mechanisms governing microglial responsiveness to neurotrophins, we determined whether microglia express trk C, the high-affinity receptor for NT-3, and whether the inflammatory agent lipopolysaccharide (LPS) regulates receptor expression. Trk C mRNA was expressed by unstimulated microglia, and both trk C mRNA and protein were dramatically increased by LPS. In contrast, expression of trk A, the high-affinity receptor for nerve growth factor (NGF), was down-regulated by LPS. Consequently, the same stimulus differentially influences responsiveness of microglia to distinct trophins. In addition, LPS induced microglial NT-3 expression, suggesting that increases in both the ligand and receptor modulate NT-3 effects on microglia. Regulation was specific, since brain-derived neurotrophic factor (BDNF) and NT-4/5 expression were unaltered by LPS. In sum, our findings raise the possibility that microglial NT-3 regulates their response to inflammation through autocrine mechanisms: LPS modulates both trk C and NT-3 which, in turn, regulate microglial function.

Blotting, Western↗
PubMed1998

A method for assessing strand breaks in DNA.

A simple method has been developed to assess strand breaks in extracted DNA. The method uses the enzyme terminal deoxynucleotidyl transferase (TDT) to incorporate labeled deoxycytidine triphosphate (dCTP) in the presence of dideoxy-CTP (ddCTP) which is added to ensure that the reaction goes to completion. Following development of the method, the extent of DNA degradation in 21 blood or bone marrow samples, which had varying degrees of DNA degradation, was measured by the TDT assay, by gel electrophoresis, or by a laborious PCR-based method which quantifies the number of amplifiable N-ras targets in a sample. The TDT assay was more sensitive at detecting strand breaks than electrophoresis and there was good correlation between the results of the TDT assay and the N-ras assay. The TDT assay was also used to demonstrate the development of strand breaks during induced apoptosis. The TDT assay is thus a simple and semiquantitative method to study strand breaks produced by DNA damage.

Apoptosis↗
PubMed1998

Molecular analysis of cellulose biosynthesis in Arabidopsis.

Cellulose, an abundant, crystalline polysaccharide, is central to plant morphogenesis and to many industries. Chemical and ultrastructural analyses together with map-based cloning indicate that the RSW1 locus of Arabidopsis encodes the catalytic subunit of cellulose synthase. The cloned gene complements the rsw1 mutant whose temperature-sensitive allele is changed in one amino acid. The mutant allele causes a specific reduction in cellulose synthesis, accumulation of noncrystalline beta-1,4-glucan, disassembly of cellulose synthase, and widespread morphological abnormalities. Microfibril crystallization may require proper assembly of the RSW1 gene product into synthase complexes whereas glucan biosynthesis per se does not.

Amino Acid Sequence↗
PubMed1998

Plasticity of Na,K-ATPase isoform expression in cultures of flat astrocytes: species differences in gene expression.

The Na,K-ATPase plays an active role in glial physiology, contributing to K+ uptake as well as to the Na+ gradients used by other membrane carriers. There are multiple isoforms of Na,K-ATPase alpha and beta subunits, and different combinations result in different affinities for Na+ and K+. Isoform choice should thus influence K+ and Na+ homeostasis in astrocytes. Prior studies of astrocyte Na,K-ATPase subunit composition have produced apparently conflicting results, suggesting plasticity of gene expression. Purified flat astrocytes from the cerebral cortex and cerebellum of both mouse and rat were systematically investigated here. Using antibodies specific for the alpha1, alpha2, alpha3, beta1, beta2, and beta3 subunits, isoform level was assessed with Western blots, and cellular distribution was visualized with immunofluorescence. Although alpha1 was always expressed, differences were observed in the expression of alpha2 and beta2, subunits that can be expressed in astrocytes in vivo and in coculture with neurons. In addition, abundant alpha subunit was expressed in rat astrocytes and in mouse cerebellar astrocytes without an equivalent level of any of the known beta isoforms, suggesting that an additional beta subunit important for glia is yet to be discovered. Conditions that have been shown to increase Na,K-ATPase activity in astrocyte cultures, such as dibutyryl cAMP, high extracellular K+, and glutamate, did not specifically induce missing subunits, suggesting that cellular interactions are required to alter the ion transporter phenotype.

Animals↗
PubMed1998

Functional studies in cultured astrocytes.

Studies using primary cultures of astrocytes have made essential contributions to the understanding of astrocytic functions and neuronal-astrocytic interactions. The purposes of this article are to (i) outline principles and methodologies used in the preparation of such cultures and caveats for the interpretation of the observations made; (ii) summarize astrocytic functions in turnover of the amino acid transmitters glutamate and gamma-aminobutyric acid (GABA), in energy metabolism and in Na+,K+-ATPase-catalyzed processes and emphasize the degree to which the observations have been confirmed in intact tissue; (iii) describe regulations of astrocytic functions by transmitters and by calcium channel activity; and (iv) indicate suggestions for future functional studies using astrocytes in primary cultures and emphasize that some of the conclusions about neuronal-astrocytic interactions reached on the basis of studies in cultured cells and confirmed in intact tissue may not yet have been completely integrated into general neuroscience knowledge.

Adenosine Triphosphatases↗
PubMed1998

Gene expression in activated brain microglia: identification of a proteinase inhibitor that increases microglial cell number.

Microglia, the intrinsic immune cells of the central nervous system, are activated in a variety of inflammatory brain diseases in which they play a pathogenetic role. However, mechanisms underlying activation are largely unknown. To begin elucidating molecular mechanisms associated with activation, we characterized the pattern of gene expression in virtually pure dissociated microglial cultures, using RT-PCR differential display. Microglia were activated with bacterial lipopolysaccharide (LPS), a traditional stimulant, and the profile of gene expression was compared to that in basal, control cultures. Activation resulted in altered expression of six genes. The cDNAs were isolated, sequenced and characterized. Homology searches identified three novel genes, and two that exhibited very high sequence similarity to the gene encoding squamous cell carcinoma antigen (SCCA). SCCA (1 and 2) are tandemly arranged genes that encode two serine proteinase inhibitors (serpins). SCCA has been detected exclusively in cancer cells, and is a plasma marker for squamous cell carcinoma. Immunoblot analysis indicated that gene expression was accompanied by a 5-fold increase in the synthesis of SCCA protein in LPS-activated microglia. To assess potential biological actions of the SCCA serpins, SCCA1 protein was added to cultures. SCCA1 altered microglial morphology, and elicited a dramatic, 5-fold increase in cell number within 72 h. The effects appeared to be cell-specific, since the protein had no effect on other cell types: cortical astrocytes and neurons from cortex or basal forebrain were unaffected. We tentatively conclude that SCCA1 may play a cell-specific role in increasing cell number, a critical early step in microglial activation and brain inflammation. More generally, differential display of genes in the microglial model system may help define patterns of expression associated with CNS disease, thereby identifying pathogenetic mechanisms and new therapeutic targets.

Animals↗
PubMed1998

Validity of diagnostic and drug data in standardized nursing home resident assessments: potential for geriatric pharmacoepidemiology. SAGE Study Group. Systematic Assessment of Geriatric drug use via Epidemiology.

OBJECTIVES: The Health Care Financing Administration requires that patients admitted to certified nursing homes be assessed with the Minimum Data Set, a data collection instrument containing more than 300 demographic, diagnostic, clinical, and treatment variables. Long-term care databases potentially may be used to assess the outcomes of specific treatments as well as drug effectiveness. The authors sought to ascertain reliability and validity of diagnostic and drug data in a database obtained by merging the Minimum Data Set with detailed information on drugs consumed by each resident. METHODS: A population of 296,379 residents of 1,492 nursing homes in Kansas, Maine, Mississippi, New York, and South Dakota participated in the study between 1992 and 1994. Minimum Data Set clinical diagnoses were contrasted with selected resident characteristics and a variety of symptoms and treatments. Limited to individuals who had been hospitalized in the 6 months preceding the first assessment, Minimum Data Set diagnoses were compared with those on the hospital discharge claims maintained in the Medicare Provider Analysis and Review database. Finally, the probability that the use of selected drugs predicted the correspondent gender-specific, age-specific, or unique labeled indication was estimated. RESULTS: The positive predictive value for Minimum Data Set diagnoses compared with gender or function measures exceeded 0.9, and it was 0.8 for specific symptoms and 0.6 for virtually all other comparisons. The positive predictive value for Minimum Data Set diagnoses compared with those from hospital claims was approximately 0.7 for all chronic medical conditions, except for depression and asthma/chronic obstructive pulmonary disease/emphysema. The positive predictive value for acute/subacute diagnoses (ie, pneumonia, urinary tract infection, anemia) that may resolve during hospital stay was less than 0.5. The positive predictive value for selected drugs, except estrogens, compared with age and gender was close to 1.0 in all cases. When compared to their labeled indication, the positive predictive value was more than 0.6 for all drugs considered, with 0.97, 0.91, and 0.87 for tacrine and Alzheimer's disease, antidiabetics and diabetes mellitus, and L-dopa and Parkinson's disease, respectively. CONCLUSIONS: These findings point to the overall validity of the drug and clinical data in this Minimum Data Set-based data set. Additional validation efforts will determine whether this data set can be used for studies of geriatric pharmacoepidemiology and for analyses of the influence of different policies and practices on residents' outcomes.

Aged↗
PubMed1998

Molecular and genetic analysis of two closely linked genes that encode, respectively, a protein phosphatase 1/2A/2B homolog and a protein kinase homolog in the cyanobacterium Anabaena sp. strain PCC 7120.

Reversible protein phosphorylation plays important roles in signal transduction. One gene, prpA, encoding a protein similar to eukaryotic types of phosphoprotein phosphatases PP1, PP2A, and PP2B, was cloned from the nitrogen-fixing cyanobacterium Anabaena sp. strain PCC 7120. Interestingly, a eukaryotic-type protein kinase gene, pknE, was found 301 bp downstream of prpA. This unusual genetic arrangement provides the opportunity for study about how the balance between protein phosphorylation and dephosphorylation can regulate cellular activities. Both proteins were overproduced in Escherichia coli and used to raise polyclonal antibodies. Immunodetection and RNA/DNA hybridization experiments suggest that these two genes are unlikely to be coexpressed, despite their close genetic linkage. PrpA is expressed constitutively under different nitrogen conditions, while PknE expression varies according to the nature of the nitrogen source. Inactivation analysis in vivo suggests that PrpA and PknE function to ensure a correct level of phosphorylation of the targets in order to regulate similar biological processes such as heterocyst structure formation and nitrogen fixation.

Amino Acid Sequence↗
PubMed1998

Can experimental conditions explain the discrepancy over glutamate stimulation of aerobic glycolysis?

Uncertainty reigns over whether or not glutamate uptake in astrocytes leads to strong stimulation of glucose utilization, measured as accumulation of radioactive deoxyglucose-6-phosphate. This is an important issue, not only because glutamate is the major excitatory transmitter, but also because it has been postulated that glutamate-induced stimulation of glycolysis links brain excitation with activation of energy production. The effect of glutamate on deoxyglucose utilization in cultured rat and mouse astrocytes grown in different media and incubated under various conditions during the deoxyglucose assay has, therefore, been studied. Under most conditions, no stimulation occurred but rather a decrease in deoxyglucose utilization during exposure to glutamate; under certain conditions, the contribution of non-metabolized deoxyglucose to the intracellular 14C signal was significant.

Aerobiosis↗
PubMed1998

[Behavioral-teratological effects of caffeine on mice].

Pregnant ICR mice were exposed to caffeine at levels of 0, 4, 20 and 100 mg/kg during pregnancy. The behavioral-teratological tests indicated that the retardation of development, the obstruction of early reflexes and sensation and decline of learning ability existed in the offsprings of 20 and 100 mg/kg groups. The number of the dead fetus increased in the group of 100 mg/kg coffeine treated mice. No morphological changes were found.

Animals↗
PubMed1998

[Apoptosis of leukemic lymphocytes mediated by purinergic P2z receptors].

OBJECTIVE: To investigate the role of purinergic P2z receptors for apoptosis of human leukemic lymphocytes induced by extracellular adenosine triphosphate (ATP). METHODS: A total of 11 B-CLL patients were studied with regard to exposure of leukemic lymphocytes with (n = 8) or without (n = 3) P2z receptors to ATP, benzoylbenzoic-ATP (BzATP), 2-methylthio-ATP (2MeSATP), adenosine-5'-[gamma-thio] triphosphate (ATP-gamma S), and other nucleosides for 8 h in vitro. Apoptosis was detected by electron microscopy (EM), agarose gel electrophoresis, and quantitative assay-TdT assay. RESULTS: Apoptosis was detected only in leukemic lymphocytes with P2z receptors. Using a quantitative assay, we found that ATP-induced DNA strand breaks occur specifically with BzATP, ATP and 2MeSATP, but not for analogue ATP-gamma S nor other nucleosides. Meanwhile, ATP-induced DNA fragmentation was fully blocked by pretreatment with oxidized ATP (OxATP), a compound recently shown to block P2z receptors. Also, the Ca2+/calmodulin complex played a role in the regulation of the apoptosis induced by ATP on CLL cells, because an antagonist of this complex, 1-[N,O-bis (5-isoquinolinesulfonyl)-N-methyl-L-tyrosyl]-4-phenylpiperazine (KN-62) was found to inhibit the ATP-induced apoptosis. CONCLUSION: These data indicate that P2z receptors on lymphocytes play an important role in apoptosis induced by ATP in vitro.

Adenosine Triphosphate↗
PubMed1998

[Study on apoptosis of leukemic lymphocytes mediated by purinergic P2z receptors].

OBJECTIVE: To investigate the role of purinergic P2z receptors in human leukemic lymphocyte apoptosis induced by extracellular adenosine triphosphate (ATP). METHODS: Eleven B-CLL patients were studied. Leukemic lymphocytes with (n = 8) or without (n = 3) P2z receptors were exposed in vitro to ATP, benzoyl-benzoic-ATP (BzATP), 2-methylthio-ATP(2MeSATP), adenosine-5'-[gamma-thio] triphosphate (ATP-gamma S), and other nucleosides for 8 h. Apoptosis was detected by electron microscopy (EM), agarose gel electrophoresis, and quantitative TdT assay. RESULTS: Apoptosis was detected only in leukemic lymphocytes with P2z receptors. By using the quantitative assay, ATP-inducing DNA strand breaks were found to occur specifically for BzATP, ATP and 2MeSATP, but not for ATP-gamma S and other nucleosides. Meanwhile, ATP-inducing DNA fragmentation was fully blocked by pretreatment with oxidized ATP (OxATP), a compound recently shown to block P2z receptors. Ca2+/Calmodulin complex played a role in the regulation of the CLL cell apoptosis induced by ATP, because an antagonist of this complex, 1-[N,O-bis (5-isoquinolinesulfonyl)-N-methyl-L-tyrosyl]-4-phenylpiperazine (KN-62), was found to inhibit the ATP-inducing apoptosis. CONCLUSION: P2z receptors on lymphocytes play an important role in the apoptosis induced by ATP in vitro.

Adenosine Triphosphate↗