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Biomedical subjects

L Dai

Publications and source records attributed to L Dai.

At least 19 recordsLinked to original sources
PubMed2006

Light extraction efficiency of a top-emission organic light-emitting diode with an Yb/Au double-layer cathode and an opaque Si anode.

We have computed the transmittances of four types of cathode--Yb/Au, Al/Au, Yb/Ag, and Al/Ag double layers--and the light extraction efficiencies of the top-emission organic light-emitting diodes with these cathodes, respectively, based on the characteristic matrix method and the dissipation spectrum model. Computations show that the Yb/Au cathode has a markedly higher transmittance than the other three types of cathode when the Yb and Au thicknesses in the Yb/Au cathode are, respectively, equal to the Al (or Yb) and Au (or Ag) thicknesses in the other three types of cathode. The power lost to the Yb/Au cathode due to the surface plasmon polaritons is the lowest, and hence the device with the Yb/Au cathode has the highest extraction efficiency. The transmittances for the four cathodes are also measured experimentally.

Journal Article↗
PubMed2006

Synthesis and optical properties of ZnTe single-crystalline nanowires.

Single-crystalline ZnTe nanowires with the zincblende structure have been synthesized on silicon (Si) substrates via a vapor phase transport method. The ZnTe (99.99%) powders were used as the source, and 10 nm-thick thermal evaporated gold (Au) film was used as the catalyst. The as-prepared ZnTe nanowires have diameters of 30-80 nm and lengths of more than 10 microm. The products were analyzed by X-ray diffraction, field emission scanning electron microscopy, and high-resolution transmission electron microscopy. Optical properties of these nanowires were investigated by room-temperature Raman scattering spectrum and temperature-dependent photoluminescence measurements. The results show that the as-prepared ZnTe nanowires are of high crystal quality.

Electric Wiring↗
PubMed2005

Detection and initial characterization of synovial lining fragments in synovial fluid.

OBJECTIVE: Free fragments of synovium have occasionally been seen in synovial fluid but have not been studied systematically. We wished to establish a method for the reliable detection of these fragments in joint and bursa effusions and begin to characterize them by histochemical and immunohistochemical methods. METHODS: Cell smears, wet drop preparations and cytospins were prepared from 39 consecutive joint and bursa effusions. Paraffin cell blocks were prepared from a subset. Analysis encompassed standard and polarized light microscopy, histochemistry, immunohistochemistry and transmission electron microscopy (EM). Synovial biopsy tissue from one different patient was examined for comparison. RESULTS: Tissue fragments were not seen in Wright-stained cell smears and only rarely in wet drop preparations. In contrast, variously sized fragments with the histological appearance of hyperplastic synovial lining were detected in ethanol-fixed, haematoxylin/eosin-stained cytospins from bursitis and all arthropathies studied [17/24 (71%) of non-inflammatory and 12/15 (80%) of inflammatory specimens]. Immunostaining revealed CD68 expression in a subset of cells in a pattern characteristic of hyperplastic synovial lining. Juxtaposed cells with morphological features of macrophage-like and fibroblast-like synoviocytes were seen by EM. CONCLUSIONS: Synovial lining fragments can be detected in effusions from diverse arthropathies and bursitis. They maintain important properties of the synovial lining and can be analysed by immunohistochemistry. They may afford the opportunity to study a relatively pure preparation of synovial lining cells without the need for cell culture, and to evaluate their possible role in augmenting or perpetuating synovitis or joint damage.

Aged↗
PubMed2005

The spectrum of renal tubular acidosis in paediatric Sjögren syndrome.

OBJECTIVES: Renal tubular acidosis (RTA) is a well-recognized extraglandular complication of adult Sjögren syndrome (SS) but has been reported only rarely in paediatric SS. We wished to describe the natural history of RTA in paediatric SS. METHODS: We performed a chart and literature review. Inclusion criteria were primary or secondary SS with onset before 18 yr of age, complicated by RTA before 18 yr of age. RESULTS: Twelve cases were identified: two from chart review and 10 from the literature. RTA was mostly associated with primary SS. RTA was detected at the onset of SS or up to 9 yr later. The clinical spectrum ranged from nearly silent to life-threatening, with plasma pH and serum potassium as low as 7.0 and 1.2 mEq/l, respectively. Hypokalaemia was present in 92%. Half the patients presented with profound weakness or paralysis, most likely from hypokalaemia. Proximal, distal and mixed RTA were detected, reflecting a diffuse 'tubulopathy' from interstitial nephritis, which was the predominant histopathological finding. Diabetes insipidus was the most frequent renal comorbidity. The RTA stabilized in 82% of the cases and resolved in one case. Only one patient had long-term unstable RTA. CONCLUSIONS: RTA is an under-recognized complication of paediatric SS. It can be life-threatening in the acute phase but generally has a good long-term renal outcome. SS should be considered in the older child with otherwise unexplained RTA. Likewise, RTA should be excluded in children and adolescents with SS who develop weakness, fatigue or growth failure. Early recognition would reduce long-term complications such as growth failure.

Acidosis, Renal Tubular↗
PubMed2005

NFAT transcription factors--new players in the pathogenesis of inflammatory arthropathies?

Inflammatory arthropathies are characterized by major changes in gene expression, which-ultimately-result from differential activities of intracellular signaling pathways and their associated inducible transcription factors. The nuclear factor of activated T cells' (NFAT) family of transcription factors plays diverse roles in a variety of processes in the immune system and other tissues. Preliminary evidence has recently emerged implicating NFAT family members directly in the pathogenesis of inflammatory arthropathies. Specific anti-NFAT drug therapy may add to the pharmacologic armamentarium against rheumatoid arthritis, other inflammatory arthropathies, and related autoimmune disorders.

Antirheumatic Agents↗
PubMed2005

Synthesis of GaN nanotip triangle pyramids on 3C-SiC epilayer/Si substrates via an in situ In-doping technique.

GaN nanotip triangle pyramids were synthesized on 3C-SiC epilayer via an isoelectronic In-doping technique. The synthesis was carried out in a specially designed two-hot-boat chemical vapor deposition system. In (99.999%) and molten Ga (99.99%) with a mass ratio of about 1:4 were used as the source, and pieces of Si (111) wafer covered with 400-500 nm 3C-SiC epilayer were used as the substrates. The products were analyzed by x-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy, selected area electron diffraction, Raman spectroscopy, and photoluminescence measurements. Our results show that the as-synthesized GaN pyramids are perfect single crystal with wurtzite structure, which may have potential applications in electronic/photonic devices.

Journal Article↗
PubMed2005

Synthesis and ab initio X-ray powder diffraction structure of the new alkali and alkali earth metal borate NaCa(BO3).

A sodium calcium borate, NaCaBO3, has been synthesized by the solid-state reaction method and the structure solved from X-ray powder diffraction data. The compound crystallizes in space group Pmmn and has a desired structure type containing isolated planar BO3(3-) anions. Mixed occupancy is found to exist in the Ca site, with partial replacement by Na. One Ca/Na mixed atom and one Na atom are at sites with mm2 symmetry, and a second Ca/Na mixed atom, an Na atom, two B and two O atoms are on mirror planes.

Journal Article↗
PubMed2004

The profibrinolytic effect of plasma thrombomodulin in factor XI deficiency and its implications in hemostasis.

Bleeding tendency in factor (F)XI deficiency may result from premature clot lysis due to insufficient thrombin activatable fibrinolysis inhibitor (TAFI) activation. Thrombomodulin (TM), upon binding to thrombin, is capable of modulating TAFI activation. In this study, we investigated the effects of plasma TM on fibrinolysis in FXI-deficient patients. A clot lysis assay showed the defective down-regulation of fibrinolysis in FXI-deficient patients as compared with normal controls. To evaluate the effects of plasma TM on fibrinolysis, a monoclonal anti-TM IgG was preincubated with plasma for 30 min. The presence of anti-TM IgG significantly prolonged the clot lysis times both in the FXI-deficient and normal plasma, indicating that plasma TM stimulated fibrinolysis. Furthermore, the presence of anti-TM IgG not only reduced protein C activation, but also increased thrombin generation and TAFI activation. The profibrinolytic effect of plasma TM was inhibited in the assay by including either a monoclonal anti-TAFI IgG or a specific TAFI inhibitor--carboxypeptidase inhibitor (CPI). Our results indicate that the impaired thrombin generation in FXI-deficient patients leads to the defective down-regulation of fibrinolysis, and that plasma TM stimulates fibrinolysis through APC pathway which inhibits TAFI activation. The profibrinolytic effect of plasma TM may contribute to the bleeding tendency observed in some FXI-deficient patients.

Adolescent↗
PubMed2003

Amelioration of antigen-induced arthritis in rats by transfer of extracellular superoxide dismutase and catalase genes.

Reactive oxygen species (ROS) have been implicated in the pathogenesis of rheumatoid arthritis (RA), while antioxidant enzymes, such as extracellular superoxide dismutase (EC-SOD) and catalase, block radical-induced events. The present study tested if the ex vivo transfer of EC-SOD and catalase genes alone or in combination in the knee joint of rats with monoarticular antigen-induced arthritis (AIA) was anti-inflammatory, and examined the potential mechanisms involved. Synoviocytes isolated from female Wistar rats were immortalized with a retroviral vector SUV19.5. These cells were permanently transfected with an EC-SOD expression plasmid (pEC-SODZeo) or a catalase expression plasmid (pCatalaseZeo) to create cells overexpressing EC-SOD or catalase, as measured by RT-PCR and Western blots. The cells were engrafted in knee joints of animals at the time of the induction of AIA. Three gene transfer groups, an EC-SOD group, a catalase group and a combined therapy group (EC-SOD and catalase) were included in these experiments. Animals in the control group were engrafted with synoviocytes transfected with the plasmid pZeoSV2 without an insert. Clinical and histological assessments were performed, as well as tissue measurements of SOD, catalase and gelatinase activities. Ex vivo gene transfer of EC-SOD and catalase into rat knee joints produced about a six- to seven-fold increase in EC-SOD activity and a two- to three-fold increase in catalase activity compared with the control animals. Rats treated with cells overexpressing EC-SOD, catalase or a combination of EC-SOD and catalase showed significant suppression of knee joint swelling, decreased infiltration of inflammatory cells within the synovial membrane and reduced gelatinase activity in knee joints, compared with animals receiving cells transfected with the plasmid alone. No statistically significant difference was found between the groups treated with cells overexpressing EC-SOD, catalase or a combination of both. Gene therapy involving the local intra-articular overexpression of two antioxidant enzymes, EC-SOD and catalase, was anti-inflammatory in AIA. One mechanism appears to be the suppression of gelatinase activities by both EC-SOD and catalase.

Animals↗
PubMed2001

Quantitative analysis of DNA binding by the Escherichia coli arginine repressor.

Allosteric activation of the hexameric arginine repressor (ArgR) for specific operator DNA binding appears to involve alteration in its quaternary structure. Current models for activation include subunit assembly and/or domain rearrangements in response to binding of the coeffector l-arginine. To investigate the molecular basis for ArgR operator interactions, we have carried out a series of quantitative analyses of ArgR subunit assembly and of the affinity, stoichiometry, cooperativity, and l-arginine- and DNA sequence-dependence of ArgR-DNA binding. The results indicate that subunit assembly plays no role in activation, although communication among subunits of the ArgR hexamer is required for specific DNA binding. The data suggest that DNA is also an allosteric effector of ArgR.

Allosteric Regulation↗
PubMed2001

IsCT, a novel cytotoxic linear peptide from scorpion Opisthacanthus madagascariensis.

A novel cytotoxic linear peptide, IsCT, was characterized from scorpion Opisthacanthus madagascariensis. It is a linear peptide with a molecular weight of 1501.9 Da composed of 13 amino acid residues without cysteines. MS/MS analysis showed that its C-terminal is amidated. The identity of IsCT is re-confirmed by comparing the chemical synthesized peptide with the natural one. IsCT demonstrated antimicrobial activity against both gram-positive and gram-negative bacteria and hemolytic activity to sheep red blood cells. Also, it can release histamine from rat peritoneal mast cells. The CD absorption suggested that IsCT had an alpha-helix configuration in aqueous TFE. IsCT is one of the shortest natural cytotoxic peptides described, and it will be a suitable model for studying peptide-lipid interactions.

Amino Acid Sequence↗
PubMed2001

Increased sensitivity of mitochondrial respiration to inhibition by nitric oxide in cardiac hypertrophy.

Cardiac hypertrophy is a significant risk factor for the development of congestive heart failure (CHF). Mitochondrial defects are reported in CHF, but no consistent mitochondrial alterations have yet been identified in hypertrophy. In this study selective metabolic inhibitors were used to determine thresholds for respiratory inhibition and to reveal novel mitochondrial defects in hypertrophy. Cardiac hypertrophy was produced in rats by aortic banding. Mitochondria were isolated from left ventricular tissue and the effects of inhibiting respiratory complexes I and IV on mitochondrial oxygen consumption were measured. At 8 weeks post-surgery, 65+/-2% complex IV inhibition was required to inhibit respiration half maximally in control mitochondria. In contrast, only 52+/-6% complex IV inhibition was required to inhibit respiration half maximally in mitochondria from hypertrophied hearts (P=0.046). This effect persisted at 22 weeks post-surgery and was accompanied by a significant upregulation of inducible nitric oxide synthase (iNOS, 3.0+/-0.7-fold, P=0.006). We conclude that respiration is more sensitive to complex IV inhibition in hypertrophy. Nitric oxide is a well documented inhibitor of complex IV, and thus the combination of increased NO(.)from iNOS and an increased sensitivity to inhibition of one of its targets could result in a bioenergetic defect in hypertrophy that may be a harbinger of CHF.

Animals↗
PubMed2001

Modeling and analysis of the structure of the thermostable catechol 2,3-dioxygenase from Bacillus Stearothermophilus.

The three-dimensional structure of thermostable catechol 2,3-dioxygenase(TC230) from Bacillus Stearothermophilus has been modeled basing on the known x-ray structure of catechol 2,3-dioxygenase(metapyrocatechase) from Pseudomonas putida mt-2, using computer graphics energy minimization techniques. The rationality of the resulting model was validated by Ramachandran plot and Profile-3D. The structure-functionally important residues, such as M++ binding residues and the substrate binding residues, were identified from the model. These residues are candidates for further site-directed mutagenesis experiments. The reason that the thermostability of TC230 is greater than metapyrocatechase(MPC) has been found, which may be due to the specific structure of the TC230 in the C-end mainly.

Amino Acid Sequence↗
PubMed2001

Bioenergetics in cardiac hypertrophy: mitochondrial respiration as a pathological target of NO*.

A rat aortic banding model of cardiac hypertrophy was used to test the hypothesis that reversible inhibition of mitochondrial respiration by nitric oxide (NO*) elicits a bioenergetic defect in the hypertrophied heart. In support of this hypothesis, the respiration of myocytes isolated from hypertrophied hearts was more sensitive to exogenous NO* (IC(50) 200 +/- 10 nM vs. 290 +/- 30 nM in controls, P = 0.0064). Hypertrophied myocytes also exhibited significantly elevated inducible NO* synthase (iNOS). Consistent with this endogenous source for NO*, the respiration of hypertrophied myocytes was significantly inhibited at physiological O(2) tensions versus controls. Both the nonspecific NOS inhibitor nitro-L-arginine and the iNOS-specific inhibitor N-[3-(aminomethyl)- benzyl]acetamidine. 2HCl reversed this inhibition, with no effect on respiration of control myocytes. Consistent with an NO*-mediated mitochondrial dysfunction, the ability of intact perfused hearts to respond to a pacing workload was impaired in hypertrophy, and this effect was reversed by NOS inhibition. We conclude that endogenously generated NO* can modulate mitochondrial function in the hypertrophied heart and suggest that this bioenergetic defect may underlie certain pathological features of hypertrophy.

Amidines↗
PubMed2001

Three-dimensional micropatterns of well-aligned carbon nanotubes produced by photolithography.

Three-dimensional micropatterns of well-aligned carbon nanotubes were prepared on photolithographically prepatterned substrates by pyrolysis of iron(II) phthalocyanine (FePc) under an Ar/H2 atmosphere at 800-1100 degrees C. The photopatterning was achieved by photolithographic cross-linking of a chemically amplified photoresist layer spin-cast on a quartz plate or a silicon wafer, coupled with solution development. Owing to an appropriate surface characteristic, the patterned photoresist layer was found in this case to support aligned carbon nanotube growth by pyrolysis of FePc, as were the photoresist-free substrate surfaces. The difference in chemical nature between the surface areas covered and uncovered by the photoresist film, however, caused a region-specific growth of the nanotubes with different tubular lengths and packing densities, leading to the formation of three-dimensional aligned nanotube patterns suitable for various device applications.

Crystallization↗