PubMed Health⌕ Search

Biomedical subjects

Ying Liu

Publications and source records attributed to Ying Liu.

At least 163 records · Page 9Linked to original sources
PubMed2005

Construction of a two-strain system for asymmetric reduction of ethyl 4-chloro-3-oxobutanoate to (S)-4-chloro-3-hydroxybutanoate ethyl ester.

Escherichia coli M15 (pQE30-car0210) was constructed to express carbonyl reductase (CAR) by cloning the car gene from Candida magnoliae and inserting it into pQE30. By cultivating E. coli M15 (pQE30-car0210) and M15 (pQE30-gdh0310), 8.2-fold and 12.3-fold enhancements in specific enzymatic activity over the corresponding original strain were achieved, respectively. After separate cultivations, these two strains were then mixed together at appropriate ratio to construct a novel two-strain system, in which M15 (pQE30-car0210) expressed CAR for ethyl 4-chloro-3-oxobutanoate (COBE) bioreduction and M15 (pQE30-gdh0310) expressed glucose dehydrogenase (GDH) for nicotinamide adenine dinucleotide phosphate (NADPH) regeneration. In this complex system, the effects of substrate concentration, the biomass ratio between two strains as well as reaction temperature were investigated for efficient bioreduction. The results showed that the bioreduction reaction could be completed effectively without any addition of GDH or NADPH/NADP(+). An optical purity of 99% (enantiometric efficiency) was obtained, and the yield of (S)-4-chloro-3-hydroxybutanoate ethyl ester reached 96.6% when initial concentration of COBE was 36.9 mM. The coupling reactions between two different strains were further explored by determining the profile of NADPH in the reaction broth.

Acetoacetates↗
PubMed2005

Characterisation of monoclonal antibodies to the TNF and TNF receptor families.

Tumour necrosis factor (TNF) family ligands and their corresponding receptors play important roles in the immune system and are involved in immune regulation such as lymphoid development, cell proliferation, differentiation, activation and death. Antibodies against these ligands and receptors together with Fc-fusion proteins, have been particularly useful as immunological tools in addressing the underlying involvement of these proteins in these contexts and furthermore, have given us hope in using them as potential therapeutic agents. Over last few years, there have been many additions to these ever-growing TNF family ligands and their receptors. Here, we have generated and characterised a set of monoclonal antibodies, together with mAbs from the HLDA workshop, against DcR1, DcR2, DR4, DR5, TRAIL, APRIL, BAFF, BAFF-R, BCMA, and TACI, which may be useful in phenotypic and functional studies of the role of TNF and TNF receptor family in immune function and regulation in relation to health and disease.

Animals↗
PubMed2005

Association of polymorphism of tumor necrosis factor-alpha gene promoter region with outcome of hepatitis B virus infection.

AIM: To determine whether -238G/A and -857C/T polymorphisms of tumor necrosis factor-alpha (TNF-alpha), gene promoter and hepatitis B (HB) viral genotypes were associated with outcomes of HBV infection. METHODS: A total of 244 HBV self-limited infected subjects, 208 asymptomatic carriers, and 443 chronic HB patients were recruited to conduct a case-control study. TNF-alpha-238G/A and -857C/T gene promoter polymorphisms were examined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP), and HBV genotypes were examined by nested PCR. RESULTS: The positive rate of HBV DNA in asymptomatic carrier group and chronic HB group was 46.6% and 49.9%, respectively. HBV genotype proportion among the asymptomatic carriers was 2.1% for genotype A, 25.8% for genotype B, 68.0% for genotype C, and 4.1% for genotype B+C mixed infection, and 0.9% for genotype A, 21.7% for genotype B, 71.5% for genotype C, 5.9% for genotype B+C mixed infection in chronic HB group. There was no significant difference in genotype distribution between the asymptomatic carrier group and chronic HB group (chi2 = 1.66, P = 0.647). The frequency of -238GG genotype in self-limited group was 95.1%, significantly higher than 90.7% in chronic HB group and 89.0% in asymptomatic carrier group (P = 0.041 and P = 0.016, respectively). The frequency of TNF-alpha-857 CC in chronic HB group was 79.7%, significantly higher than 64.4% in asymptomatic carrier group and 70.9% in self-limited group (P<0.001 and P = 0.023, respectively). A multiple logistic regression analysis revealed that TNF-alpha-238GA and -857CC were independently associated with chronic HB after gender and age were adjusted. CONCLUSION: TNF-alpha promoter variants are likely to play a substantial role in the outcome of HBV infection.

Adenine↗
PubMed2005

Genomic alterations in cultured human embryonic stem cells.

Cultured human embryonic stem cell (hESC) lines are an invaluable resource because they provide a uniform and stable genetic system for functional analyses and therapeutic applications. Nevertheless, these dividing cells, like other cells, probably undergo spontaneous mutation at a rate of 10(-9) per nucleotide. Because each mutant has only a few progeny, the overall biological properties of the cell culture are not altered unless a mutation provides a survival or growth advantage. Clonal evolution that leads to emergence of a dominant mutant genotype may potentially affect cellular phenotype as well. We assessed the genomic fidelity of paired early- and late-passage hESC lines in the course of tissue culture. Relative to early-passage lines, eight of nine late-passage hESC lines had one or more genomic alterations commonly observed in human cancers, including aberrations in copy number (45%), mitochondrial DNA sequence (22%) and gene promoter methylation (90%), although the latter was essentially restricted to 2 of 14 promoters examined. The observation that hESC lines maintained in vitro develop genetic and epigenetic alterations implies that periodic monitoring of these lines will be required before they are used in in vivo applications and that some late-passage hESC lines may be unusable for therapeutic purposes.

Cell Culture Techniques↗
PubMed2005

Early ocular chemokine gene expression and leukocyte infiltration after high-risk corneal transplantation.

PURPOSE: To determine the differential gene expression of chemokine species and leukocyte infiltration of grafts in the early pre-rejection postoperative period after high-risk (HR) compared to normal-risk (NR) corneal transplantation. METHODS: Fully mismatched and syngeneic corneal grafts were performed in NR (avascular) and HR (vascularized) recipient beds of BALB/c murine hosts. Gene expression levels of a panel of chemokines were determined by a multiprobe ribonuclease protection assay system. The profiles of infiltrating cells into the corneal grafts at the same times were determined immunohistochemically. RESULTS: Compared to NR transplantation, HR eyes exhibited significantly higher mRNA levels for macrophage inflammatory protein (MIP)-2 and monocyte chemotactic protein-1 (MCP-1) on day 1, and for eotaxin on days 1 and 3 after transplantation. By day 6 after transplantation, still well before graft rejection, significantly higher levels of RANTES, eotaxin, MIP-1alpha, MIP-1beta, MIP-2, and MCP-1 were detected in HR eyes. The overexpression of MIPs in HR eyes correlated with a significant increase in the number of infiltrating macrophages (p<0.01), and neutrophils (p<0.05) in HR compared to NR recipients. Low levels of eosinophil and mast cell infiltration were observed in all grafts, with a modest increase in mast cell infiltration (p<0.05) in HR compared to NR grafts. CONCLUSIONS: These results suggest that increased expression of gene products for select chemokines, in particular those that mediate recruitment of innate immune cells, in the early period after HR corneal transplantation is related to the enhanced leukocytic infiltration of grafts observed in HR keratoplasty.

Animals↗
PubMed2005

A low-cost biofuel cell with pH-dependent power output based on porous carbon as matrix.

A glucose/O2 biofuel cell (BFC) possessing a pH-dependent power output was fabricated by taking porous carbon (PC) as the matrix to load glucose oxidase or fungi laccase as the catalysts. The electrolytes in the anode and cathode compartments contain ferrocene monocarboxylic acid and 2,2'-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) diammonium salt as the mediators, respectively. The power of the BFC was enhanced significantly by using PC as the matrix, rather than glassy carbon electrode. Additionally, the power output of the BFC decreases as the pH of the solution increases from 4.0 to 7.0, which provides a simple and efficient method to achieve the required power output. More importantly, the BFC can operate at pH 6.0, and even at pH 7.0, which overcomes the requirement for cathode solutions of pH<5.0 when using fungi laccase as a catalyst. Operation of the BFC at neutral pH may provide a means to power medical devices implanted in physiological systems. The facile and low-cost fabrication of this BFC may enable its development for other applications.

Carbon↗
PubMed2005

Hyaluronan accumulates in demyelinated lesions and inhibits oligodendrocyte progenitor maturation.

Demyelination is the hallmark of numerous neurodegenerative conditions, including multiple sclerosis. Oligodendrocyte progenitors (OPCs), which normally mature into myelin-forming oligodendrocytes, are typically present around demyelinated lesions but do not remyelinate affected axons. Here, we find that the glycosaminoglycan hyaluronan accumulates in demyelinated lesions from individuals with multiple sclerosis and in mice with experimental autoimmune encephalomyelitis. A high molecular weight (HMW) form of hyaluronan synthesized by astrocytes accumulates in chronic demyelinated lesions. This form of hyaluronan inhibits remyelination after lysolecithin-induced white matter demyelination. OPCs accrue and do not mature into myelin-forming cells in demyelinating lesions where HMW hyaluronan is present. Furthermore, the addition of HMW hyaluronan to OPC cultures reversibly inhibits progenitor-cell maturation, whereas degrading hyaluronan in astrocyte-OPC cocultures promotes oligodendrocyte maturation. HMW hyaluronan may therefore contribute substantially to remyelination failure by preventing the maturation of OPCs that are recruited to demyelinating lesions.

Animals↗
PubMed2005

Transgenic analysis of the stem cell leukemia +19 stem cell enhancer in adult and embryonic hematopoietic and endothelial cells.

Appropriate transcriptional regulation is critical for the biological functions of many key regulatory genes, including the stem cell leukemia (SCL) gene. As part of a systematic dissection of SCL transcriptional regulation, we have previously identified a 5,245-bp SCL +18/19 enhancer that targeted embryonic endothelium together with embryonic and adult hematopoietic progenitors and stem cells (HSCs). This enhancer is proving to be a powerful tool for manipulating hematopoietic progenitors and stem cells, but the design and interpretation of such transgenic studies require a detailed understanding of enhancer activity in vivo. In this study, we demonstrate that the +18/19 enhancer is active in mast cells, megakaryocytes, and adult endothelium. A 644-bp +19 core enhancer exhibited similar temporal and spatial activity to the 5,245-bp +18/19 fragment both during development and in adult mice. Unlike the +18/19 enhancer, the +19 core enhancer was only active in adult mice when linked to the eukaryotic reporter gene human placental alkaline phosphatase. Activity of a single core enhancer in HSCs, endothelium, mast cells, and megakaryocytes suggests possible overlaps in their respective transcriptional programs. Moreover, activity in a proportion of thymocytes and other SCL-negative cell types suggests the existence of a silencer elsewhere in the SCL locus.

Animals↗
PubMed2005

Saturated fat-rich diet enhances selective uptake of LDL cholesteryl esters in the arterial wall.

Plasma LDL levels and atherosclerosis both increase on a saturated fat-rich (SAT) diet. LDL cholesterol delivery to tissue may occur via uptake of the LDL particles or via selective uptake (SU), wherein cholesteryl ester (CE) enters cells without concomitant whole-particle uptake. It is not known how dietary fats might directly affect arterial LDL-CE uptake and whether SU is involved. Thus, mice that are relatively atherosclerosis resistant (C57BL/6) or susceptible to atherosclerosis (apoE) were fed a chow or SAT diet and injected with double radiolabeled or fluorescent-labeled human LDL to independently trace LDL-CE core and whole-particle uptake, respectively. Our results show that a SAT diet increased contributions of SU to total arterial LDL-CE delivery in C57BL/6 and apoE mice. The SAT diet increased plasma fatty acid and cholesterol levels; cholesterol, but not fatty acid, levels correlated with SU, as did the degree of atherosclerosis. Increased SU did not correlate with arterial scavenger receptor class B type I levels but paralleled increased lipoprotein lipase (LPL) levels and LPL distribution in the arterial wall. These studies suggest that arterial LDL-CE delivery via SU can be an important mechanism in vivo and that dietary influences on arterial LPL levels and atherogenesis modulate arterial LDL-CE delivery, cholesterol deposition, and SU.

Animals↗
PubMed2005

Direct electrochemistry of microperoxidase at Pt microelectrodes modified with carbon nanotubes.

Direct electrochemistry of microperoxidase (MP-11) was found at Pt microelectrodes modified with multi-wall carbon nanotubes (MWNTs). The MWNTs used as the immobilization matrix cooperatively promote the bioactivity of MP-11. When MP-11 was immobilized on MWNTs film-modified Pt microelectrodes, a pair of well-defined redox waves was obtained. The resulted stable microelectrode could be used to catalyze the reduction of H2O2 and O2.

Calibration↗
PubMed2005

The role of phonological activation in the visual semantic retrieval of Chinese characters.

The Stroop paradigm was used to examine the role of phonological activation in semantic access and its development in reading Chinese characters. Subjects (age 7-23 years) of different reading ability were asked to name the display color of Chinese characters. The characters were displayed in four different colors: red, yellow, blue and green. There were five types of relationships between a character and its display color: semantically congruent, phonologically congruent, semantically incongruent, phonologically incongruent and neutral. In addition to the classical Stroop effects, interference and facilitation effects from the homophones of color characters were also observed. The younger children and those with lower reading ability exhibited stronger Stroop effects. These findings suggest that phonological codes are activated automatically in Chinese character recognition. Furthermore, there is more phonological activation in the semantic retrieval of children in lower grades and those with lower reading ability.

Adult↗
PubMed2005

Separation and characterization of underivatized oligosaccharides using liquid chromatography and liquid chromatography-electrospray ionization mass spectrometry.

Native cyclodextrin-based columns are particularly useful for the analysis of oligosaccharides because the retention of these carbohydrates is based mainly on the hydrogen bonding interactions of oligosaccharide hydroxyl groups with the stationary phase. Thus, the retention time predictably increases with the number of analyte hydroxyl groups, which corresponds to the elongation of the oligosaccharide chain. High-performance liquid chromatography (HPLC) coupled to electrospray ionization (ESI) mass spectrometry (MS) was used for the separation and characterization of underivatized oligosaccharide mixtures. With the limits of detection as low as 50 pg, all individual components of oligosaccharide mixtures (up to 11 glucose units long) were baseline resolved on a Cyclobond I 2000 column and detected using ESI-MS. Low flow rates and narrow I.D. columns increase the ESI-MS sensitivity significantly. The method showed potential usefulness for the sensitive and quick analysis of hydrolysis products of polysaccharides, and for trace levels of individual oligosaccharide or oligosaccharide isomers from biological systems.

Acetonitriles↗
PubMed2005

Neisseria gonorrhoeae enhances infection of dendritic cells by HIV type 1.

Clinical studies indicate that Neisseria gonorrhoeae (gonococci (GC)) has the capacity to enhance HIV type 1 (HIV-1) infection. We studied whether GC enhances HIV infection of activated dendritic cells (DCs). The results show that GC can dramatically enhance HIV replication in human DCs during coinfection. The GC component responsible for HIV infection enhancement may be peptidoglycan, which activates TLR2. TLR2 involvement is suggested by bacterial lipoprotein, a TLR2-specific inducer, which stimulates a strong enhancement of HIV infection by human DCs. Moreover, participation of TLR2 is further implicated because GC is unable to stimulate expression of HIV in DCs of TLR2-deficient HIV-1-transgenic mice. These results provide one potential mechanism through which GC infection increases HIV replication in patients infected with both GC and HIV.

Animals↗
PubMed2005

Polybrominated diphenyl ethers (PBDEs) in sediments and mussel tissues from Hong Kong marine waters.

Sediments and green-lipped mussels, Perna viridis, were used to investigate concentrations of polybrominated diphenyl ethers (PBDEs) in Hong Kong's marine environment. PBDEs have been used extensively over the past two decades as flame retardants in polymer additives for a variety of plastics, computers, furniture, building materials, and fabrics. Many measurements of PBDEs in various environmental matrices have been reported from Belgium, Holland, Japan, Europe and North America, but few measurements are available for the southeast Asian region and Hong Kong. PBDE congeners (n=15) were measured in 13 sediments and nine mussel samples, taken from Hong Kong marine waters. The Sigma15PBDEs in sediments ranged between 1.7 and 53.6 ng g(-1) dry wt, with the highest concentrations located around the most heavily populated areas of Victoria Harbour and Sai Kung, while the lowest concentrations of Sigma15PBDEs were found at more remote locations of Sha Tau Kok, Wong Chuk Bay, Castle Peak Bay, and Gold Coast. Sigma15PBDEs ranged from 27.0 to 83.7 ng g(-1) dry wt of mussel tissues. Although not identical, most of the congeners in sediments were found in mussel tissues, with BDE-47, BDE-99, BDE-153 and BDE-183 being the most prominent in both matrices. On the basis of a literature survey, the concentrations of PBDEs reported in Hong Kong sediments and mussel tissues are amongst the highest in the world.

Animals↗
PubMed2005

Haploinsufficiency of cytochrome P450 17alpha-hydroxylase/17,20 lyase (CYP17) causes infertility in male mice.

Cytochrome P450 17alpha-hydroxylase/17,20-lyase (CYP17) is critical in determining cortisol and sex steroid biosynthesis. To investigate how CYP17 functions in vivo, we generated mice with a targeted deletion of CYP17. Although in chimeric mice Leydig cell CYP17 mRNA and intratesticular and circulating testosterone levels were dramatically reduced (80%), the remaining testosterone was sufficient to support spermatogenesis as evidenced by the generation of phenotypical black C57BL/6 mice. However, male chimeras consistently failed to generate heterozygous CYP17 mice and after five matings chimeric mice stopped mating indicating a change in sexual behavior. These results suggested that CYP17 deletion caused a primary phenotype (infertility), probably not due to the anticipated androgen imbalance and a secondary phenotype (change in sexual behavior) due to the androgen imbalance. Surprisingly, CYP17 mRNA was found in mature sperm, and serial analysis of gene expression identified CYP17 mRNA in other testicular germ cells. CYP17 mRNA levels were directly related to percent chimerism. Moreover, more than 50% of the sperm from high-percentage chimeric mice were morphologically abnormal, and half of them failed the swim test. Furthermore, 60% of swimming abnormal sperm was devoid of CYP17. These results suggest that CYP17, in addition to its role in steroidogenesis and androgen formation, is present in germ cells where it is essential for sperm function, and deletion of one allele prevents genetic transmission of mutant and wild-type alleles causing infertility followed by change in sexual behavior due to androgen imbalance.

Alleles↗
PubMed2005

Rac-GAP-dependent inhibition of breast cancer cell proliferation by {beta}2-chimerin.

beta2-Chimerin is a member of the "non-protein kinase C" intracellular receptors for the second messenger diacylglycerol and the phorbol esters that is yet poorly characterized, particularly in the context of signaling pathways involved in proliferation and cancer progression. beta2-Chimerin possesses a C-terminal Rac-GAP (GTPase-activating protein) domain that accelerates the hydrolysis of GTP from the Rac GTPase, leading to its inactivation. We found that beta2-chimerin messenger levels are significantly down-regulated in human breast cancer cell lines as well as in breast tumors. Adenoviral delivery of beta2-chimerin into MCF-7 breast cancer cells leads to inhibition of proliferation and G(1) cell cycle arrest. Mechanistic studies show that the effect involves the reduction in Rac-GTP levels, cyclin D1 expression, and retinoblastoma dephosphorylation. Studies using the mutated forms of beta2-chimerin revealed that these effects were entirely dependent on its C-terminal GAP domain and Rac-GAP activity. Moreover, MCF-7 cells stably expressing active Rac (V12Rac1) but not RhoA (V14RhoA) were insensitive to beta2-chimerin-induced inhibition of proliferation and cell cycle progression. The modulation of G(1)/S progression by beta2-chimerin not only implies an essential role for Rac in breast cancer cell proliferation but also raises the intriguing possibility that diacylglycerol-regulated non-protein kinase C pathways can negatively impact proliferation mechanisms controlled by Rho GTPases.

Adenoviridae↗
PubMed2005

Adaptive evolution of MRGX2, a human sensory neuron specific gene involved in nociception.

MRGX2, a G-protein-coupled receptor, is specifically expressed in the sensory neurons of the human peripheral nervous system and involved in nociception. Here, we studied DNA polymorphism patterns and evolution of the MRGX2 gene in world-wide human populations and the representative nonhuman primate species. Our results demonstrated that MRGX2 had undergone adaptive changes in the path of human evolution, which were likely caused by Darwinian positive selection. The patterns of DNA sequence polymorphisms in human populations showed an excess of derived substitutions, which against the expectation of neutral evolution, implying that the adaptive evolution of MRGX2 in humans was a relatively recent event. The reconstructed secondary structure of the human MRGX2 revealed that three of the four human-specific amino acid substitutions were located in the extra-cellular domains. Such critical substitutions may alter the interactions between MRGX2 protein and its ligand, thus, potentially led to adaptive changes of the pain-perception-related nervous system during human evolution.

Adaptation, Physiological↗