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Biomedical subjects

Z Liu

Publications and source records attributed to Z Liu.

At least 415 records · Page 23Linked to original sources
PubMed2000

Antioxidative effects of green tea polyphenols on free radical initiated and photosensitized peroxidation of human low density lipoprotein.

Antioxidative effects of the main polyphenolic components extracted from green tea leaves, i.e. (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECG), (-)-epigallocatechin gallate (EGCG) and gallic acid (GA), against free radical initiated peroxidation of human low density lipoprotein (LDL) were studied. The peroxidation was initiated either thermally by a water-soluble initiator 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH), or photochemically by a triplet sensitizer benzophenone (BP). The reaction kinetics was monitored by the uptake of oxygen and the depletion of alpha-tocopherol (TOH) presented in the native LDL. Kinetic analysis of the antioxidation process demonstrates that these green tea polyphenols are effective antioxidants against both AAPH-initiated and BP-photosensitized LDL peroxidation. The antioxidative action of the green tea polyphenols includes trapping the initiating and/or propagating peroxyl radicals with the activity sequence EC>EGCG>ECG>EGC>GA for the AAPH initiated peroxidation, and reducing the alpha-tocopheroxyl radical to regenerate alpha-tocopherol with the activity sequence of ECG>EC>EGCG>EGC>GA and ECG>EGCG>GA>EC>EGC for the AAPH-initiated and BP-photosensitized peroxidations respectively.

Antioxidants↗
PubMed2000

Rescue intracytoplasmic sperm injection (ICSI)-salvaging in vitro fertilization (IVF) cycles after total or near-total fertilization failure.

OBJECTIVE: To evaluate the effectiveness of delayed oocyte reinsemination by ICSI (rescue ICSI) after total or near-total fertilization failure (</=25%) in IVF. DESIGN: A retrospective clinical study. SETTING: Non-hospital-based IVF program. PATIENT(S): Thirty IVF cycles with total fertilization failure and two cycles with </=25% initial fertilization. MAIN OUTCOME MEASURE(S): Fertilization and pregnancy rates after rescue ICSI. INTERVENTION(S): Rescue ICSI 19-22 hours after initial oocyte insemination. RESULT(S): A fertilization rate of 60.2% was achieved with rescue ICSI (141 of 234 oocytes, 29 of 32 patients). Of 30 patients with total fertilization failure, 27 had fresh transfers with rescue ICSI embryos. Two additional patients with </=25% initial fertilization had subsequent replacement of frozen-thawed rescue ICSI embryos. Six pregnancies resulted, including three singleton, one twin, one missed abortion, and one ectopic pregnancy (20.7%). One of the singleton pregnancies resulted from replacement of four frozen-thawed embryos and is the first known pregnancy achieved from cryopreserved rescue ICSI embryos. CONCLUSION(S): Rescue ICSI should be considered in the presence of total or near-total fertilization failure in IVF. Early application of rescue ICSI (19-22 hours after insemination) may be critical for establishing fertilization within an optimal window and producing viable embryos and pregnancies.

Adult↗
PubMed2000

Mechanisms of generalization in perceptual learning.

Learning in many visual perceptual tasks has been shown to be specific to practiced stimuli, while new stimuli have to be learned from scratch. Here we demonstrate generalization using a novel paradigm in motion discrimination where learning has been previously shown to be specific. We trained subjects to discriminate directions of moving dots, and verified the previous results that learning does not transfer from a trained direction to a new one. However, by tracking the subjects' performance across time in the new direction, we found that their speed of learning doubled. Therefore, we found generalization in a task previously considered too difficult to generalize. We also replicated, in a second experiment, transfer following training with 'easy' stimuli, when the difference between motion directions is enlarged. In a third experiment we found a new mode of generalization: after mastering the task with an easy stimulus, subjects who have practiced briefly to discriminate the easy stimulus in a new direction generalize to a difficult stimulus in that direction. This generalization depends on both the mastering and the brief practice. The specificity of perceptual learning and the dichotomy between learning of 'easy' versus 'difficult' tasks have been assumed to involve different learning processes at different cortical areas. Here we show how to interpret these results in terms of signal detection theory. With the assumption of limited computational capacity, we obtain the observed phenomena--direct transfer and acceleration of learning--for increasing levels of task difficulty. Human perceptual learning and generalization, therefore, concur with a generic discrimination system.

Discrimination, Psychological↗
PubMed2000

Preparation of macroporous poly(2-hydroxyethyl methacrylate) hydrogels by enhanced phase separation.

Macroporous poly(2-hydroxyethyl methacrylate) (p(HEMA)) hydrogels were prepared in the presence of a 0.3-0.7 M NaCl solution. The pore morphology of the p(HEMA) hydrogels was dependent on the concentration of NaCl for a constant monomer solution to aqueous solution ratio. Swelling studies showed an increase in equilibrium water content and hydrogel porosity as the NaCl concentration in the polymerization medium increased from 0 to 0.7 M. The equilibrium water content, however, decreased as the NaCl concentration in the swelling medium increased. The frozen water content increased and non-frozen water decreased with an increase in the NaCl concentration in the polymerization medium. Mechanical testing indicated that the elastic modulus of the hydrogels was not affected by the increased porosity until the pores became interconnected. These data suggest that the addition of NaCl to the polymerization medium results in a multi-phase separation during fabrication that produces macroporous hydrogels of controlled morphology.

Calorimetry, Differential Scanning↗
PubMed2000

The effects of long-term contact lens wear on corneal thickness, curvature, and surface regularity.

PURPOSE: To evaluate the effect of long-term contact lens wear on corneal thickness, curvature, and surface regularity. DESIGN: A prospective, clinic-based, case-control study. PARTICIPANTS: A total of 40 eyes of 20 normal subjects and 64 eyes of 35 subjects wearing contact lenses for more than 5 years were evaluated. METHODS: The Orbscan Corneal Topography System was used to evaluate the entire corneal thickness and curvature, anterior curvature and the anterior and posterior elevation topographic patterns in normal eyes and subjects wearing contact lenses on a regular basis for more than 5 years. Indices of TMS-1 Corneal Topography System were used to determine corneal surface regularity in subjects wearing contact lenses and normal eyes. All topographic examinations were performed after contact lenses had been removed for at least 2 weeks. MAIN OUTCOME MEASURES: The entire corneal thickness, curvature, surface regularity index (SRI), surface asymmetry index (SAI), potential visual acuity (PVA) and topographic patterns were compared between normal eyes and subjects wearing contact lenses for more than 5 years. RESULTS: The 64 eyes of 35 subjects evaluated by the Orbscan instrument had an average of 13.45 +/- 6.42 years of contact lens wear. The mean corneal thickness in the center and in eight peripheral areas measured in contact lens wearing subjects was significantly reduced by about 30 to 50 microm compared to normal subjects (P < 0.001 for central and peripheral sites). No correlation was noted between central corneal thickness and degree of myopia in diopters (r = 0.15, 0.10 < P < 0.25). The corneal curvature, maximum keratometry (Max K) and minimum keratometry (Min K) readings, were significantly steeper in eyes wearing contact lenses than normal eyes (P < 0.01 for Max K and Min K measured by both instruments). No difference in the mean corneal astigmatism was noted between groups. The SRI and SAI, but not the PVA index, of the TMS-1 were significantly greater in contact lens wearers than in the control group (P < 0.01 for both SRI and SAI, P = 0.15 for PVA). The color-coded patterns of all curvature and elevation maps made with both instruments showed no significant difference between subjects wearing contact lenses and the control group. There was no significant difference between corneal curvature measurements taken with the Orbscan System or the TMS-1 System in both normal and contact lens groups. CONCLUSIONS: Long-term contact lens wear appears to decrease the entire corneal thickness and increase the corneal curvature and surface irregularity.

Adult↗
PubMed2000

A high-recovery extraction procedure for quantitative analysis of substance P and opioid peptides in human cerebrospinal fluid.

This study reports an improved approach for the determination of neuropeptide levels in human cerebrospinal fluid (CSF). The method is based on sample acidification followed by liquid-liquid extraction (LLE) combined with radioimmunoassay. It was applied to study the recovery and level of some opioid peptides (Met-enkephalin-Arg(6)-Phe(7) and Leu-enkephalin-Arg(6)), substance P and the substance P(1-7) fragment, which are all compounds known to be present in human CSF. The results indicated that the use of LLE highly improved the recovery of these peptides compared to current liquid-solid-phase extraction methods by using silica gel cartridges or mini-columns for ion-exchange chromatography. Peptides added to CSF in concentrations down to 10 fmol/ml were recovered in yields exceeding 80%. The mean recovery of synthetic peptides as recorded by radioimmunoassay in the LLE procedure was significantly improved when HCl was added to the sample. In contrast, when the (125)I-labeled analogues of the peptides were added to CSF samples, the mean recovery of the four labeled peptides using the LLE procedure was markedly reduced in acidified samples. We also found that the inclusion of HCl effectively improved the removal of proteins present in the samples. As an application the levels of substance P and Met-enkephalin-Arg(6)-Phe(7) in CSF samples from patients with chronic pain (fibromyalgia syndrome) were measured using the new procedure. It was possible to confirm a significant difference in the CSF levels of both peptides when comparing patients and controls.

Fibromyalgia↗
PubMed2000

Novel point mutations in the German cockroach para sodium channel gene are associated with knockdown resistance (kdr) to pyrethroid insecticides.

Knockdown resistance (kdr) to pyrethroid insecticides has been attributed to point mutations in the para sodium channel gene in more than a half dozen insect pest species. In this study, we identified two novel para mutations in five highly resistant kdr-type German cockroach strains. The two mutations, from glutamic acid (E434) to lysine (K434) and from cysteine (C764) to arginine (R764), respectively, are located in the first intracellular linker connecting domains I and II. E434K is located near the beginning of the linker (closest to domain I), whereas C764R is found toward the end of the linker (closest to domain II). Two additional mutations from aspartic acid (D58) to glycine (G58), and from proline (P1880) to leucine (L1888), respectively, were found in one of the resistant strains. The four mutations coexist with the previously identified leucine to phenylalanine (L993F) kdr mutation in IIS6, and are present only in the highly resistant individuals of a given strain. These findings suggest that these mutations might be responsible for high levels of knockdown resistance toward pyrethroid insecticides in the German cockroach.

Amino Acid Sequence↗
PubMed2000

The distinct roles of TRAF2 and RIP in IKK activation by TNF-R1: TRAF2 recruits IKK to TNF-R1 while RIP mediates IKK activation.

The death domain kinase RIP and the TNF receptor-associated factor 2 (TRAF2) are essential effectors in TNF signaling. To understand the mechanism by which RIP and TRAF2 regulate TNF-induced activation of the transcription factor NF-kappaB, we investigated their respective roles in TNF-R1-mediated IKK activation using both RIP-/- and TRAF2-/- fibroblasts. We found that TNF-R1-mediated IKK activation requires both RIP and TRAF2 proteins. Although TRAF2 or RIP can be independently recruited to the TNF-R1 complex, neither one of them alone is capable of transducing the TNF signal that leads to IKK activation. Moreover, we demonstrated that IKK is recruited to the TNF-R1 complex through TRAF2 upon TNF treatment and that IKK activation requires the presence of RIP in the same complex.

Antigens, CD↗
PubMed2000

The lin-41 RBCC gene acts in the C. elegans heterochronic pathway between the let-7 regulatory RNA and the LIN-29 transcription factor.

Null mutations in the C. elegans heterochronic gene lin-41 cause precocious expression of adult fates at larval stages. Increased lin-41 activity causes the opposite phenotype, reiteration of larval fates. let-7 mutations cause similar reiterated heterochronic phenotypes that are suppressed by lin-41 mutations, showing that lin-41 is negatively regulated by let-7. lin-41 negatively regulates the timing of LIN-29 adult specification transcription factor expression. lin-41 encodes an RBCC protein, and two elements in the lin-413'UTR are complementary to the 21 nucleotide let-7 regulatory RNA. A lin-41::GFP fusion gene is downregulated in the tissues affected by lin-41 at the time that the let-7 regulatory RNA is upregulated. We suggest that late larval activation of let-7 RNA expression downregulates LIN-41 to relieve inhibition of lin-29.

3' Untranslated Regions↗
PubMed2000

Study on three-dimensional fluorescent spectral characteristics of fluoroquinolones in varying media.

Behaviors of fluoroquinolones in varying media were observed by employing their intrinsic fluorescence. Spectral characteristics in reversed micelles (Aerosol OT/n-octane) were compared with those in aqueous solution and micelles (sodium dodecyl sulfonate). Those differences in interactions between fluoroquinolones and the various media were clearly illustrated by three-dimensional fluorescent spectra. The influences of other environmental factors on spectral characteristics (pH, SDS concentration, etc.) were also investigated.

Acids↗
PubMed2000

Acute obstructive cholangiopathy in interleukin-6 deficient mice: compensation by leukemia inhibitory factor (LIF) suggests importance of gp-130 signaling in the ductular reaction.

AIM: The hypothesis that interleukin-6-IL-6/gp130 signaling is involved in liver and biliary epithelial cell (BEC) biology and growth control was tested by subjecting homozygous IL-6 deficient mice (IL-6-/-) and wild type (IL-6+/+) littermate controls to bile duct ligation (BDL). MATERIALS AND METHODS: During the first week after BDL, the two groups were compared with respect to routine liver injury tests, liver histology, BEC and hepatocyte DNA synthesis, together with the expression of mRNA and protein of IL-6 as well as related growth factors, and their receptors. RESULTS: During the first week after BDL, there was marked upregulation of IL-6 mRNA and protein in the IL-6+/+ mice only in the vicinity of the biliary tree; whereas, biliary/peri-biliary IL-6R, HGF and met mRNA and protein increased in both groups. IL-6, HGF mRNA and protein localized to periductal inflammatory cells and stellate cells, while met and IL-6R protein were upregulated in the BEC and, to a lesser extent, in hepatocytes. This occurred during maximal proliferation of the BEC. Despite the absence of IL-6 in the IL-6-/- mice, there were only mildly phenotypic differences between the two groups, and no differences in mortality. Compared to IL-6+/+ controls, IL-6-/- mice showed slightly less BEC proliferation, a trend toward more liver injury, and significantly higher total serum bilirubin (TB) levels, suggestive of impaired biliary tree integrity. These changes were associated with slightly less HGF mRNA and protein expression in the IL-6-/- mice, but the differences were not significant. Leukemia inhibitory factor (LIF), another gp-130 ligand, also showed marked peri-biliary upregulation after BDL in both groups, and also induced BEC DNA synthesis, in vitro. CONCLUSIONS: The mild phenotypical differences between IL-6+/+ and IL-6-/- mice in the acute response to BDL is most likely attributable to the redundancy of the gp-130 signaling system. However, the long-term response to BDL results in a distinct phenotype in the IL-6-/- mice, marked by a relentless rise in serum total bilirubin and an inability to maintain compensatory increase in liver mass.

Acute Disease↗
PubMed2000

A functional role for VAP-33 in insulin-stimulated GLUT4 traffic.

Soluble N-ethylmaleimide sensitive factor attachment protein receptors (SNAREs) are critical proteins in membrane fusion, in both regulated and constitutive vesicular traffic. In addition, proteins that interact with the SNAREs are thought to regulate fusion. Vesicle-associated membrane protein-2 (VAMP-2) is a SNARE protein involved in insulin-dependent glucose transporter 4 (GLUT4) traffic. VAMP-2 is required for productive GLUT4 incorporation into the plasma membrane. VAMP-associated protein of 33 kDa (VAP-33) is an integral membrane protein that binds VAMPs in vitro, and is hypothesized to be a regulator of VAMPs. In L6 skeletal myoblasts, which display insulin-dependent traffic of GLUT4, we show that VAP-33 colocalized significantly with VAMP-2 using indirect confocal immunofluorescence and biochemical cosegregation. Overexpression of wild-type VAP-33 in L6 myoblasts attenuated the insulin-dependent incorporation of myc-tagged GLUT4 into the plasma membrane, and this response was restored by co-overexpression of VAMP-2 linked to green fluorescent protein. Antibodies to VAP-33 microinjected into 3T3-L1 adipocytes abrogated the insulin-stimulated translocation of GLUT4 to the plasma membrane, as measured in adhered plasma membrane lawns. Immunopurified VAMP-2-containing compartments from L6 myotubes and 3T3-L1 adipocytes showed significant levels of VAP-33. We propose that VAP-33 may be a regulator of VAMP-2 availability for GLUT4 traffic and other vesicle fusion events.

Animals↗
PubMed2000

Drosophila Lis1 is required for neuroblast proliferation, dendritic elaboration and axonal transport.

Haplo-insufficiency of human Lis1 causes lissencephaly. Reduced Lis1 activity in both humans and mice results in a neuronal migration defect. Here we show that Drosophila Lis1 is highly expressed in the nervous system. Lis1 is essential for neuroblast proliferation and axonal transport, as shown by a mosaic analysis using a Lis1 null mutation. Moreover, it is cell-autonomously required for dendritic growth, branching and maturation. Analogous mosaic analysis shows that neurons containing a mutated cytoplasmic-dynein heavy chain (Dhc64C) exhibit phenotypes similar to Lis1 mutants. These results implicate Lis1 as a regulator of the microtubule cytoskeleton and show that it is important for diverse physiological functions in the nervous system.

Animals↗
PubMed2000

Learning motivational significance of visual cues for reward schedules requires rhinal cortex.

The limbic system is necessary to associate stimuli with their motivational and emotional significance. The perirhinal cortex is directly connected to this system, and neurons in this region carry signals related to a monkey's progress through visually cued reward schedules. This task manipulates motivation by displaying different visual cues to indicate the amount of work remaining until reward delivery. We asked whether rhinal (that is, entorhinal and perirhinal) cortex is necessary to associate the visual cues with reward schedules. When faced with new visual cues in reward schedules, intact monkeys adjusted their motivation in the schedules, whereas monkeys with rhinal cortex removals failed to do so. Thus, the rhinal cortex is critical for forming associations between visual stimuli and their motivational significance.

Animals↗
PubMed2000

Study of the fluorescence characteristics of norfloxacin in reversed micelles and application in analysis.

The fluorescence characteristics of norfloxacin (NFLX) were studied in reversed micelles which formed with sodium bis(2-ethylhexyl) sulfosuccinate (AOT)-water-octane. The influences of the environmental factors, such as the water content, AOT concentration and pH, on the fluorescence of NFLX were investigated. A novel spectrofluorimetric method for the direct determination of NFLX is proposed based on the enhancement effect of reversed micelles on the native fluorescence of NFLX, which showed a much lower detection limit (0.0032 microgram mL-1) and a wider linear range (0.015-3.8 micrograms mL-1) compared with aqueous solution.

Anti-Infective Agents↗
PubMed2000

Repair of UV damage in plants by nucleotide excision repair: Arabidopsis UVH1 DNA repair gene is a homolog of Saccharomyces cerevisiae Rad1.

To analyze plant mechanisms for resistance to UV radiation, mutants of Arabidopsis that are hypersensitive to UV radiation (designated uvh and uvr) have been isolated. UVR2 and UVR3 products were previously identified as photolyases that remove UV-induced pyrimidine dimers in the presence of visible light. Plants also remove dimers in the absence of light by an as yet unidentified dark repair mechanism and uvh1 mutants are defective in this mechanism. The UVH1 locus was mapped to chromosome 5 and the position of the UVH1 gene was further delineated by Agrobacterium-mediated transformation of the uvh1-1 mutant with cosmids from this location. Cosmid NC23 complemented the UV hypersensitive phenotype and restored dimer removal in the uvh1-1 mutant. The cosmid encodes a protein similar to the S. cerevisiae RAD1 and human XPF products, components of an endonuclease that excises dimers by nucleotide excision repair (NER). The uvh1-1 mutation creates a G to A transition in intron 5 of this gene, resulting in a new 3' splice site and introducing an in-frame termination codon. These results provide evidence that the Arabidopsis UVH1/AtRAD1 product is a subunit of a repair endonuclease. The previous discovery in Lilium longiflorum of a homolog of human ERCC1 protein that comprises the second subunit of the repair endonuclease provides additional evidence for the existence of the repair endonuclease in plants. The UVH1 gene is strongly expressed in flower tissue and also in other tissues, suggesting that the repair endonuclease is widely utilized for repair of DNA damage in plant tissues.

Amino Acid Sequence↗
PubMed2000

Intracellular signaling in the developing blastocyst as a consequence of the maternal-embryonic dialogue.

The success of blastocyst implantation is dependent on signaling between the embryo and the receptive endometrium. Intercellular signaling molecules, which include hormones, growth factors, and cytokines, have been identified that participate in the maternal-embryonic dialogue. These biologically active molecules may target uterine and/or embryonic tissues in a biochemical cascade that coordinates the two developmental programs during implantation. Two notable uterine products are calcitonin and heparin-binding epidermal growth factor-like growth factor, which are both expressed during the receptive phase of the endometrium in humans and in rodent models. We review data that demonstrate the ability of these molecules to accelerate blastocyst differentiation and delineate the respective intracellular signaling pathways that advance the embryonic developmental program. An understanding of the mediators regulating embryonic development in utero and their biochemical mechanisms of the action may provide insights for improvement of embryo culture in vitro prior to blastocyst transfer.

Animals↗