Biomedical subjects

H Liu

Publications and source records attributed to H Liu.

At least 199 records · Page 11Linked to original sources

PubMed2001

Precursor supply for polyketide biosynthesis: the role of crotonyl-CoA reductase.

Crotonyl-CoA reductase (CCR), which catalyzes the reduction of crotonyl-CoA to butyryl-CoA, is common to most streptomycetes and appears to be inducible by either lysine or its catabolites in Streptomyces cinnamonensis grown in chemically defined medium. A major role of CCR in providing butyryl-CoA from acetate for monensin A biosynthesis has been demonstrated by the observation of a change in the monensin A/monensin B ratio in the parent C730.1 strain (50/50) and a ccr (encoding CCR) disruptant (12:88) of S. cinnamonensis in a complex medium. Both strains produce significantly higher monensin A/monensin B ratios in a chemically defined medium containing valine as a major carbon source than in either complex medium or chemically defined medium containing alternate amino acids. This observation demonstrates that under certain growth conditions valine catabolism may have a more significant role than CCR in providing butyryl-CoA. Such a process most likely involves an isomerization of the valine catabolite isobutyryl-CoA, catalyzed by the coenzyme B(12)-dependent isobutyryl-CoA mutase. Monensin labeling experiments using dual (13)C-labeled acetate in the ccr-disrupted S. cinnamonensis indicate the presence of an additional coenzyme B(12)-dependent mutase linking branched and straight-chain C(4) compounds by a new pathway.

Acetic Acid↗

PubMed2001

Molecular systematics of Xenocyprinae (teleostei: cyprinidae): taxonomy, biogeography, and coevolution of a special group restricted in East Asia.

We surveyed mitochondrial DNA (mtDNA) sequence variation in the subfamily Xenocyprinae from China and used these data to estimate intraspecific, interspecific, and intergeneric phylogeny and assess biogeographic scenarios underlying the geographic structure of lineages. We sequenced 1140 bp of cytochrome b from 30 individuals of Xenocyprinae and one putative outgroup (Myxocypris asiaticus) and also sequenced 297 bp of ND4L, 1380 bp of ND4, 68 bp of tRNA(His), and 69 bp of tRNA(Ser) from 17 individuals of Xenocyprinae and the outgroup (M. asiaticus). We detected high levels of nucleotide variation among populations, species, and genera. The phylogenetic analysis suggested that Distoechodon hupeinensis might be transferred to the genus Xenocypris, the taxonomic status of the genus Plagiognathops might be preserved, and species of Xenocypris and Plagiognathops form a monophyletic group that is sister to the genus Distoechodon and Pseudobrama. The introgressive hybridization might occur among the populations of X. argentea and X. davidi, causing the two species to not be separated by mtDNA patterns according to their species identification, and the process and direction of hybridization are discussed. The spatial distributions of mtDNA lineages among populations of Xenocypris were compatible with the major geographic region, which indicated that the relationship between Hubei + Hunan and Fujian is closer than that between Hubei + Hunan and Sichuan. From a perspective of parasite investigation, our data suggested that the fauna of Hexamita in Xenocyprinae could be used to infer the phylogeny of their hosts.

Animals↗

PubMed2001

Tail-vein injection of mannan-binding lectin DNA leads to high expression levels of multimeric protein in liver.

The human plasma protein mannan-binding lectin (MBL) is an essential part of the innate immune defense system. Low levels of MBL are associated with recurrent infections and other clinically significant signs of a compromised immune defense. Previous studies have addressed the possibility of reconstitution therapy by the use of recombinant or plasma-derived protein. Natural MBL is a multimeric protein, which consists of up to 18 identical polypeptide chains. Synthesis by in vitro methods of MBL with the proper multimeric structure is difficult. We here report that mice obtain MBL levels comparable to those found in normal human plasma when injected with an MBL expression construct as naked plasmid DNA contained in a large volume of physiologic salt solution. The expression was confined to the liver and high MBL expression levels were obtained with less than 5% of the liver cells transfected. The multimeric structure of the MBL found in plasma of injected mice was similar to that of natural MBL. Thus, liver expression following injection of naked DNA is an alternative to reconstitution therapy with a protein having a complex quaternary structure.

Animals↗

PubMed2001

Study on the role of interleukin-4 in experimental murine systemic candidiasis.

In order to investigate the role of interleukin-4 (IL-4) in experimental murine systemic Candidiasis, we created the intact and dexamethasone-induced immunosuppressed murine systemic Candidiasis models. In these models, two-site ELISA and RT-PCR were applied to determine the level of IL-4 protein and mRNA expression in spleens respectively, clone forming units (CFUs) of infected kidneys were determined with the plating dilution method, and mean survival time (MST) of the mice was recorded. The results showed that, when compared with the controls, protein level of IL-4 increased in both intact mice infected with lethal doses of yeast (day 3, P < 0.05; day 7, P < 0.001) and immunosuppressed mice infected with sublethal doses of yeast (day 3, P > 0.05; day 7, P < 0.05). Furthermore, the level of IL-4 was higher on day 7 than on day 3 after infection (P < 0.001 and P < 0.05 respectively in two groups). The tendency of IL-4 mRNA expression was similar with that of IL-4 protein. As for fungal loads in kidneys, CFUs were significantly higher on day 7 than on day 3 after infection (P < 0.001 in both groups). Mice in both groups succumbed to infection within several days. It was suggested that IL-4 might play a promoting role in the development of murine systemic Candidiasis.

Animals↗

PubMed2001

The expression of Fas/FasL in peripheral blood lymphocytes and the level of IL-2 in serum of patients with condyloma acuminata.

In order to investigate the role of the expression of the Fas/FasL in peripheral blood lymphocytes (PBLC) and the level of IL-2 in serum of patients with condyloma acuminata (CA) in the immune pathogenesis of CA, flow cytometry, indirect immunofluorescence labeling and ELISA were performed to detect the expression of the apoptotic regulatory proteins Fas/FasL in PBLC and the level of IL-2 in serum of 60 patients with different course of CA. The results showed that the expression of Fas/FasL in PBLC of the group of short course in CA was significantly higher than that of the normal controls (P < 0.05); the expression of Fas, FasL in PBLC of the group of long course CA was significantly higher than that of the group of short course and the normal controls (P < 0.05 and P < 0.01, respectively); the level of IL-2 in serum of the group of short and long course CA was significantly lower than that of the group of normal controls (P < 0.01); the negative relation was revealed between the expression of Fas/FasL in PBLC and the level of IL-2 in serum of patients with CA (r = -0.76, P < 0.01). It was suggested that the abnormal apoptosis in PBLC and decreased level of IL-2 in serum of CA might play an important role in the course of CA.

Adolescent↗

PubMed2001

Fasting limits the increase in intracellular calcium during ischemia in isolated rat hearts.

INTRODUCTION: Fasting has been shown to limit ischemic injury and improve functional activity after global ischemia. Because calcium overload is considered a mechanism of ischemic injury, we hypothesized that fasting would limit the accumulation of intracellular calcium [Ca]i during ischemia, potentially due to reduced accumulation of intracellular sodium [Na]i. METHODS: To address this hypothesis, hearts isolated from rats fed either a normal diet or fasted for 24 hours underwent 20 min of global ischemia at 37 degrees. In addition to functional parameters, [Na]i and [Ca]i were measured using 21Na and 19F spectroscopy using thulium-DOTP-5 and 5F-BAPTA, respectively. In vitro measurement of sarcoplasmic reticulum calcium uptake and release, as well as activity of the sarcolemmal Na-Ca exchanger, was performed in hearts from fed and fasted animals under baseline and ischemic conditions. RESULTS: Hearts from fasted animals showed greater recovery of developed pressure (37+/-9 vs. 11+/-6 cm H2O, p < 0.05) and less contracture (end-diastolic pressure 25+/-2 vs. 47+/-2 cm H2O, p < 0.05) by the end of the reperfusion period. [Na]i was similar in the 2 groups during the first half of the ischemic period, albeit with a higher concentration of [Na]i in hearts from fed compared to fasted animals at reperfusion. Fasting markedly limited calcium accumulation during ischemia, with end-ischemic calcium being 419+/-46 nM in the hearts from fasted animals and 858+/-140 nM in the hearts from fed animals (p < 0.01). There was no significant effect of fasting on calcium uptake or release by the SR, nor on sarcolemmal Na-Ca exchange activity. CONCLUSIONS: Fasting for 24 hours improves functional recovery and markedly limits [Ca]i accumulation during ischemia and early reperfusion. The mechanism for this phenomenon remains to be elucidated.

Animals↗

PubMed2001

Molecular typing of HLA-A, -B, and DRB using a high throughput micro array format.

The goal of this study was to develop a DNA micro array procedure for molecular human leukocyte antigen (HLA) typing of a large number of samples. DNA was isolated from peripheral blood samples and polymerase chain reaction (PCR) amplified for HLA-A, -B, and -DRB. Amplified DNA samples were spotted on silane-treated glass slides using a micro array spotter. The spotter was capable of spotting multiple slides with up to 9216 samples per slide or 2304 samples in quadruplicate. The allele specific oligo nucleotide probes for HLA-A, -B, and -DRB were labeled with the fluorescent dye Cy3, while a control probe, to quantitate the total amount of PCR product in a sample, was labeled with Cy5. Each slide was hybridized with a mixture of an allele specific Cy3 probe plus the control Cy5 probe. Following hybridization and wash, the amount of probe hybridizing to each DNA sample on the slide was measured with a micro array scanner. A computer program was used for image analysis, to calculate the average Cy3/Cy5 ratios and to identify the positive and negative samples. In turn, this information was used to determine the HLA phenotype of each sample. There was very good concordance between the results obtained for all three loci using Cy-labeled probes as compared with those previously obtained by chemiluminescent detection of alkaline phosphatase labeled probes. This methodology has the potential of greatly simplifying HLA molecular typing of large number of samples.

Alleles↗

PubMed2001

Molecular cloning and characterization of four scorpion K(+)-toxin-like peptides: a new subfamily of venom peptides (alpha-KTx14) and genomic analysis of a member.

Four full-length cDNAs encoding the precursors of four K(+)-toxin-like peptides (named BmKK(1), BmKK(2), BmKK(3) and BmmKK(4), respectively) were first isolated from a venom gland cDNA library of the Chinese scorpion Buthus martensii Karsch. The deduced precursors of BmKK(1), BmKK(2) and BmKK(3) are all made of 54 amino acid residues including a signal peptide of 23 residues, and a mature toxin of 31 residues with three disulfide bridges. The precursor of BmKK(4) is composed of 55 amino acid residues including a signal peptide of 23 residues, a mature toxin of 30 residues cross-linked by three disulfide bridges, and an extra Gly-Lys tail which should be removed in the processing step. The four peptides displayed 24-97% sequence identity with each other, and less than 27% homology with any other scorpion toxins described. However, they shared a common disulfide bridge pattern, which was consistent with that of most short-chain K(+)-toxins, suggesting they represent a new class of scorpion toxins and their target receptors may be a subfamily of K(+) channels. We classified the BmKK toxin subfamily as alpha-KTx14 according to the classification rules. The genomic sequence of BmKK(2) was also cloned and sequenced. It consisted of two exons, disrupted by an intron of 79 bp inserted in the region encoding the C-terminal part of the signal peptide. This structure was very similar to that of other K(+)-toxins described previously.

3' Untranslated Regions↗

PubMed2001

Migration and metalloproteinases determine the invasive potential of mouse melanoma cells, but not melanin and telomerase.

The biological characteristic cell locomotion and invasion, melanin content, metalloproteinases and telomerase activity were studied in a parental mouse melanoma cell line B16 and two descendents B16BL6 and B16F10. The invasive potential of melanoma cells was assayed in a transwell cell culture chamber. Melanin content was determined by the absorbance value at 470 nm per 10(6) cells. Tumor cells migration within the 3-D collagen matrix was microscopically recorded with a time-lapse video recorder and analyzed by computer-assisted cell tracking. Gelatin zymography was adopted to assay the metalloproteinases secretion. A polymerase chain reaction-based telomeric repeat amplification protocol (TRAP) was used for measuring telomerase activity. The results demonstrated that B16BL6 and B16F10 cells were highly invasive compared to B16 cells, but the melanin content of B16F10 was very low. B16F10 and B16BL6 were hypermotile and secreted much more metalloproteinases than B16. No differences were observed in telomerase activity among the three melanoma cell lines. Invasion of mouse melanoma was closely correlated to tumor cell migration and secretion of metalloproteinases. Melanin content and telomerase activity were phenotypically not related to invasiveness in these three mouse melanoma cell lines.

Animals↗

PubMed2001

Structural characterization of the oxidative degradation products of an antifungal agent SCH 56592 by LC-NMR and LC-MS.

LC-NMR and LC-MS were used to characterize the structures of four major degradation products of SCH 56592, an antifungal drug candidate in clinical trials. These compounds were formed under stress conditions in which the bulk drug substance was heated in air at 150 degrees C for 12 days, and were separated from SCH 56592 as a mixture using a semi-preparative HPLC method. The data from LC-NMR, LC-ESI-MS (electrospray ionization mass spectrometry) and LC-ESI-MS/MS indicate that the oxidation occurred at the piperazine ring in the center of the drug molecule. The structures of the degradation products were determined from the 1H NMR spectra obtained via LC-NMR, which were supported by LC-ESI-MS and LC-ESI-MS/MS analyses. A novel degradation pathway of SCH 56592 was proposed based on these characterized structures.

Antifungal Agents↗

PubMed2001

Amplification of the DNA polymerase I gene of Treponema pallidum from whole blood of persons with syphilis.

Previous reports suggest that Treponema pallidum bacteremia occurs in persons with syphilis exposure ('incubating syphilis') and in persons with primary or secondary syphilis. During a recent syphilis outbreak, whole blood samples from 32 persons with suspected syphilis or syphilis exposure were screened using polymerase chain reaction (PCR) to amplify the DNA polymerase I gene (polA) of T. pallidum. Of the 32 samples, polA was amplified from 13 (41%). Of these 13, three were determined to have incubating syphilis; two had primary or secondary syphilis and eight had latent syphilis. This study demonstrates that spirochetemia can occur throughout the course of T. pallidum infection.

Adult↗

PubMed2001

Toxic endothelial cell destruction from intraocular benzalkonium chloride.

PURPOSE: To present a cluster of cases of corneal edema occurring after phacoemulsification. SETTING: Regional hospital in rural Australia. METHODS: This retrospective case series comprised 12 patients from a single surgical list comprising 19 cases who developed persistent corneal edema after having phacoemulsification. RESULTS: After 6 months, the edema improved in 1 patient. Inadvertent intraocular use of balanced salt solution (BSS) preserved with benzalkonium chloride was found to be the cause of this serious complication. CONCLUSIONS: Benzalkonium chloride in concentrations commonly used extraocularly is highly toxic to the corneal endothelium. Every possible safeguard should be taken to prevent inadvertent intraocular use of such preserved solutions.

Acetates↗

PubMed2001

Estrogen receptor alpha mediated induction of the transforming growth factor alpha gene by estradiol and 4-hydroxytamoxifen in MDA-MB-231 breast cancer cells.

The selective estrogen receptor modulator, 4-hydroxytamoxifen (4-OHT) is a full agonist at the transforming growth factor (TGF) alpha gene in ER negative breast cancer cells stably transfected with ER alpha cDNA (Levenson et al., Br. J. Cancer 77 (1998) 1812-1819). E(2) and 4-OHT increase TGF alpha mRNA and protein in a concentration dependent manner. The responses to E(2) and 4-OHT are blocked by the pure antiestrogen ICI 182,780, which does not induce TGF alpha. Transfected MDA-MB-231 cells contain functional ER alpha but no ER beta function was detected. Neo transfected cells that did not express ER alpha or cells stably transfected with the DNA binding domain mutant C202R/E203V which prevents gene activation did not induce TGF alpha mRNA after either E(2) or 4-OHT treatment. An examination of the time course for either 10 nM E(2) or 1 microM 4-OHT for MDA-MB-231 cells stably transfected with cDNA for ER alpha showed increases in TGF alpha mRNA within 2 or 3 h respectively. Cells pretreated with cycloheximide (1 microg/ml) showed induced TGF alpha mRNA in response to E(2) or 4-OHT but TGF alpha mRNA induction was blocked by actinomycin D (1 microg/ml). We conclude that both E(2) and 4-OHT induce TGF alpha by direct interaction of ER alpha with DNA and that ER beta is not involved in the estrogen-like response to 4-OHT in the MDA-MB-231 cells.

Blotting, Northern↗

PubMed2001

Evaluation of [(99m)Tc] liposomes as lymphoscintigraphic agents: comparison with [(99m)Tc] sulfur colloid and [(99m)Tc] human serum albumin.

This study investigates the use of [(99m)Tc] liposomes for the detection of sentinel lymph nodes. A variety of [(99m)Tc] liposome formulations were compared with common lymphoscintigraphic agents including [(99m)Tc] regular-sulfur colloid (SC), [(99m)Tc] 0.22 microfiltered-SC, [(99m)Tc] reduced heating time 0.22 microfiltered-SC, and [(99m)Tc] human serum albumin (HSA) in rabbits. Images were acquired for the first 60 minutes and at 24 hours, followed by tissue biodistribution study. All agents except [(99m)Tc] regular SC demonstrated good migration from the injection site. Agents were retained in the popliteal node at 24 hours to varying degrees as follows: both [(99m)Tc] filtered SC preparations > [(99m)Tc] regular SC > [(99m)Tc] liposomes > [(99m)Tc] HSA. [(99m)Tc] liposome imaging can be used to develop novel liposome compositions with improved lymph node diagnostic and drug delivery characteristics.

Animals↗

PubMed2001

A novel TNF receptor family member binds TWEAK and is implicated in angiogenesis.

TWEAK is a member of the TNF ligand family that induces angiogenesis in vivo. We report cloning of a receptor for TWEAK (TweakR) from a human umbilical vein endothelial cell (HUVEC) library. The mature form of TweakR has only one hundred and two amino acids and six cysteine residues in its extracellular region. Five different assays demonstrate TWEAK-TweakR binding, and the interaction affinity constant (Kd) is within a physiologically relevant range of 2.3 +/- 0.1 nM. The TweakR cytoplasmic domain binds TRAFs 1, 2, and 3. Cross-linking of TweakR induces HUVEC growth, and mRNA levels are upregulated in vitro by a variety of agents and in vivo following arterial injury. Soluble TweakR inhibits endothelial cell migration in vitro and corneal angiogenesis in vivo.

Amino Acid Sequence↗

PubMed2001

Localization error analysis for stereo X-ray image guidance with probability method.

The mean value and standard deviation of localization error for the stereo imaging systems are derived based on probability theory. Compared with the maximum error analysis method used in our previous study, the new approach yields more informative and precise results as the guidance for X-ray imaging system design and protocol optimization. The prototype for our current study is a CCD based monoplane digital stereo X-ray imaging system. The imaging model consists of two X-ray sources and one detector plane. With perspective geometry, the least-square solution is derived to reconstruct 3-dimensional object points, such as a biopsy needle tip, from a pair of 2-dimensional digital radiographs. Under the conditions of our specific prototype, the measurement errors of interested points in the radiographs are modeled as random variables with Gaussian distribution. Such variables account for finite image system noise and positioning errors. Then, the 3D localization error, in terms of mean value and standard deviation, is formulated using measurement error, feature point location, and separation between the two X-ray sources and distance from source to detector. Both theoretical analysis and numerical simulation are performed. The mean value and standard deviation of the localization error are first evaluated using numerical simulation under practical imaging conditions. Then, the error estimates are given in simply analytic forms. Simulation and theoretical results are in excellent agreement. The results show that our prototype X-ray stereological imaging system is accurate and reliable to locate feature points in 3D for medical intervention. Imaging protocols can be effectively optimized through the 3D localization error analysis using the approximate formulas proposed in this study.

Algorithms↗

PubMed2001

Transcriptional control of dimorphism in Candida albicans.

Candida albicans uses a network of multiple signaling pathways to control the yeast-->hypha transition. These include a mitogen-activated protein kinase pathway through Cph1, the cAMP-dependent protein kinase pathway via Efg1, a pH-responsive pathway through Rim101, the Tup1-mediated repression through Rfg1 and Nrg1, and pathways represented by transcription factors Cph2, Tec1 and Czf1. These pathways control the transcription of a common set of hypha-specific genes, many of which encode known virulence factors. The link between the signaling pathways and hyphal elongation is currently unknown, but there is evidence to suggest that Cdc42 likely plays a key role in hyphal morphogenesis. Unlike pseudohyphal growth in Saccharomyces cerevisiae, hyphal elongation is regulated independently of the cell cycle. Cellular differences between pseudohyphae and hyphae are further revealed by septin localization.

Bacterial Proteins↗

PubMed2001

Reaction of fumonisin with glucose prevents promotion of hepatocarcinogenesis in female F344/N rats while maintaining normal hepatic sphinganine/sphingosine ratios.

The reaction of the primary amine of fumonisin B(1) (FB(1)) with glucose was hypothesized to detoxify this mycotoxin. Eighty 10-day-old female F344/N rats were injected intraperitoneally with diethylnitrosamine (DEN; 15 mg/kg of body weight). At 4 weeks of age, the weaned rats were randomly assigned to one of four treatment groups with 20 rats each. At 9 weeks of age, four rats from each treatment group were killed. At 12 weeks, another five rats from each group were killed. At 20 weeks of age, the remaining rats were killed. In comparison with the rats fed basal diet or FB(1)-glucose (containing 25 ppm of FB(1)), rats fed 8 ppm (residual amount of free FB(1) in the FB(1)-glucose mixture) or 25 ppm of FB(1) had greater alanine aminotransferase activity at 9 and 20 weeks of age (P < 0.001), greater endogenous hepatic prostaglandin E(2) production at 20 weeks of age (P < 0.05), and significantly lower plasma cholesterol at 20 weeks of age (P < 0.01). Placental glutathione S-transferase (PGST)-positive and gamma-glutamyltransferase (GGT)-positive altered hepatic foci (AHF) occurred only in rats fed 25 ppm of FB(1) at 20 weeks of age. Hepatic natural killer (NK) cell activities were similar among the four groups, but the percentage of total liver-associated mononuclear cells exhibiting the NKR-P1(bright) marker was significantly greater in rats fed FB(1)-glucose, FB(1) (8 ppm) and FB(1) (25 ppm) than in control rats at 9 weeks of age, and FB(1)-glucose-treated rats had significantly lower NKR-P1(bright) cells as a percentage of total liver-associated mononuclear cells than rats fed 25 ppm of FB(1) at 20 weeks of age (P < 0.05). PGST- or GGT-positive AHF were not detected in any treatment group at 9 or 12 weeks of age. At 20 weeks of age, half of the rats fed 25 ppm of FB(1) had PGST- and GGT-positive AHF. The sphinganine (Sa) concentration and the Sa/sphingosine (So) ratio were significantly greater in the rats fed 25 ppm of FB(1) diet as compared with the control groups at, respectively, 12 or 20 weeks of age. Therefore, modifying FB(1) with glucose seems to prevent FB(1)-induced hepatotoxicity and promotion of hepatocarcinogenesis. The Sa/So ratio was not the most sensitive biomarker of FB(1) toxicity.

Alkylating Agents↗