Biomedical subjects
Publications and source records attributed to Z Cai.
A measurement of the horizontal coherence function of 7.9 keV radiation from an undulator beam line at the Advanced Photon Source is reported. X-ray diffraction from a phase-shifting mask was used, and the coherence function was measured as a function of the width of beam-conditioning slits in the beam line. The coherence distribution is found to be best described by a Lorentzian function.
The induction of endogenous vascular endothelial growth factor (VEGF) production in the skin flap with ischemic injury and the effect of exogenous VEGF on survival of the ischemic skin flap were studied in rats. A dorsal flap model (3x10 cm(2)) was used in this study. In Part I, biopsies were taken from the flap at 2.5, 5.5, and 8.5 cm distances from the distal edge at 0, 6, 12, and 24 h after the flaps were sutured. Malonyldialdehyde (MDA) and VEGF(165) protein level were measured. In Part II, exogenous VEGF (1 microg/ml) was injected subdermally into the flaps in 14 rats before the flaps were replaced. Flaps that received a saline injection were used as the controls. The skin paddle survival was measured on postoperative day five. The results showed that the MDA level in the distal part of the flap significantly increased at 24 h postoperatively when compared to MDA in other parts of the flap. However, VEGF levels in the distal part of the flap significantly decreased when compared to the middle part of the flap. Subdermal injection of exogenous VEGF to the distal area of the flap could significantly improve survival of the distal flap (89% of total skin paddle) when compared to the control, which had a 64% mean percent survival. We conclude that production of endogenous VEGF protein is significantly increased in the skin flap with mild ischemia, but decreased in the flap with severe ischemia. Administration of exogenous VEGF could significantly enhance survival of ischemic flaps.
This study characterized the corrosion behavior of cast CP titanium made with a face-coating method. Wax patterns were coated with oxide slurry of Y(2)O(3) or ZrO(2) before investing with a MgO-based investment. Three surface preparations were tested: ground, sandblasted, and as-cast. Uncoated castings served as controls. Sixteen-hour open circuit potential (OCP) measurement, linear polarization and potentiodynamic cathodic polarization were performed in an aerated modified Tani-Zucchi synthetic saliva at 37 degrees C. Anodic polarization was conducted in the same deaerated medium. Polarization resistance (R(p)) and Tafel slopes were determined. Corrosion current density was calculated for each specimen. Results (n=4) were subjected to nonparametric statistical analysis (alpha=0.05). Cross sections of cast specimens were examined by optical microscopy. Energy dispersive spectroscopy (EDS) spot analysis was performed at various depths below the surface. The OCP stabilized within several hours for all the specimens. Apparent differences in anodic polarization behavior were observed among the different surfaces. A distinctive wide passive region followed by breakdown was seen on specimens with ground and sandblasted surfaces. There were no significant differences in the corrosion resistance among the control and the two face-coating groups for each group. The Mann-Whitney test showed significantly lower OCP and higher R(p) values for ground surfaces. The surface condition significantly affected the corrosion behavior more than the face coating methods. In most cases, specimens with as-cast surfaces exhibited the least corrosion resistance during the potentiodynamic anodic polarization.
Columnar microstructure in step-graded Si(1-x)Ge(x)/Si(001) structures with low threading dislocation densities has been determined using high angular resolution (approximately 0.005 degrees ) x-ray microdiffraction. X-ray rocking curves of a 3-microm-thick strain-relaxed Si(0.83)Ge(0.17) film show many sharp peaks and can be simulated with a model having a set of Gaussians having narrow angular widths (0.013 degrees -0.02 degrees ) and local ranges of tilt angles varying from 0.05 degrees to 0.2 degrees. These peaks correspond to individual tilted rectangular columnar micrograins having similar (001) lattice spacings and average areas of 0.8 to 2.0 microm(2).
Magnetic x-ray diffraction combined with x-ray focusing optics was used to image individual antiferromagnetic spin density wave domains in a chromium single crystal at the micron scale. The cross section for nonresonant magnetic x-ray scattering depends on the antiferromagnetic modulation vector and spin polarization direction and allows these quantities to be extracted independently. The technique was used to show that the broadening of the nominally first-order "spin-flip" transition at 123 kelvin, at which the spins rotate by 90 degrees C, originates at the walls between domains with orthogonal modulation vectors. During cooling, the transition begins at these walls and progresses inward. The modulation vector domains are themselves unchanged.
The complete nucleotide sequence of Beet black scorch virus (BBSV) was determined. The BBSV genome is composed of 3641 nucleotides and has similar organization with Tobacco necrosis virus D of 61% nucleotide identity. The 5'-proximal open reading frame (ORF) encodes a putative 23 kDa protein and a 82 kDa protein by reading-through of an amber termination codon. Three small ORFs located in the center of the genome may encode for a 4.2 kDa protein and two 7 kDa proteins. The 3'-proximal ORF encodes a 24.5 kDa protein equivalent in mass to the viral coat protein. Considering biological and molecular similarities with TNV, it is concluded that BBSV is a new member of the genus Necrovirus.
The aim of this study was to ascertain the minimum sample required to accurately measure the total number of myelinated fibres, mean myelinated fibre density (MFD), myelinated fibre diameter (Ds) and axonal diameter (Da) in morphometric studies of sural nerve biopsies. Measurements were obtained by sampling a single fascicle or systematic sampling of up to 50% of the total transverse fascicular area of two control and eighteen pathological sural nerves showing varying degrees of demyelination and axonal degeneration. MFD and fibre size were heterogeneous between fascicles in both control and pathological sural nerves, and morphometric results from one fascicle and systematic sampling of up to 50% of the total transverse fascicular area did not accurately represent the whole myelinated fibre population in the sural nerve. For accurate morphometric data it is necessary to quantitate all the myelinated fibres in the sural nerve.
Studies of alkylation-induced mutations in Escherichia coli FX-11 revealed that both N-ethyl-N-nitrosourea (ENU) and N-methyl-N-nitrosourea (MNU) produced tRNA suppressor mutations (G:C to A:T) but only ENU produced a significant number of backmutations (A:T to G:C, A:T to T:A and A:T to C:G). Further, the ENU-induced transversions were absent in a UmuC-defective strain. This suggested that transition mutations could result from alkylation of guanine or thymine at the O(6)- and O(4)-positions, respectively, but that transversions might result from alkylation of thymine at the O(2)-position. To test this idea, the gene encoding O(6)-alkylguanine-DNA methyltransferase (ogt) was recombined into a plasmid to overexpress the cellular levels of this enzyme. Ogt protein can de-alkylate O(6)-alkylguanine and O(4)-alkylthymine, but not O(2)-alkylthymine. Cells harboring the plasmid (or a control plasmid lacking the ogt gene) were exposed to different concentrations of MNU or ENU and the resulting mutations were analyzed. With either MNU or ENU, the frequency of GlnV(o) suppressors was reduced about 70-fold in the Ogt-overexpressing cells, suggesting that Ogt eliminated O(6)-alkylguanine. Similarly, GlnU(o) suppressor frequencies were substantially reduced. In contrast, the reduction in frequency for the backmutations was slight, only about 2.5-fold with MNU and less than two-fold for ENU. However, DNA sequence analysis of the backmutations showed that only A:T to G:C transitions were affected by overexpression of Ogt, suggesting repair of O(4)-alkylthymine. The frequency of transversions, in comparison, was essentially unaltered. These results implicate O(2)-alkylthymine as a likely candidate for transversion mutagenesis induced by ENU.
We used cDNA arrays to investigate differentially expressed genes in astrocytes challenged with lipopolysaccharide (LPS). Astrocyte cultures were prepared from 1-day-old rat brains. Purified astrocytes were treated with LPS (1 microg/ml) for 2, 8 and 48 h. Differentially expressed genes in these astrocytes were examined with Atlas rat cDNA arrays. At all the three time points studied, three genes were found consistently up-regulated: I-kappaB alpha chain, NF-kappaB, and interferon induced protein. In addition to these three, six other genes were also up-regulated at 2 and 8 h. They were genes encoding vascular cell adhesion protein 1 (VCAM-1), interferon regulatory factor 1 (IRF-1), mitochondrial hydroxymethylglutaryl-CoA synthase (HMG-CoA synthase), aldehyde dehydrogenase 2, macrophage inflammatory protein 1 (MIP-1) and neurotensin receptor 2. At these two time points, three genes were down-regulated: copper-zinc-containing superoxide dismutase 1 (SOD-1), insulin-like growth factor binding protein 1 (IGFBP-1), and insulin-like growth factor binding protein 3 (IGFBP-3). Expression of several differentially expressed genes in cDNA array (I-kappaB, VCAM-1 and MIP-3) were further confirmed by reverse transcription polymerase chain reaction study. The prominently modulated genes could be classified into three categories: nuclear transcription factors, pro-inflammatory cytokines/chemokines and metabolic enzymes. Application of pyrrolidine dithiocarbamate, an inhibitor of nuclear factor-kB (NF-kappaB), prior to LPS stimulation not only prevented up-regulation of NF-kappaB gene expression, but also completely blocked up-regulation of pro-inflammatory cytokine genes (TNF-alpha and interleukin-1beta) and two chemokine genes: CXC chemokine LIX and CC chemokine MIP-3 alpha. These results indicate that both up-regulation of inflammatory cytokine expression and down-regulation of growth factor expression are probably involved in the response of astrocytes upon exposure to LPS.
Conventional x-ray diffraction topography is currently used to map defects in the bulk of protein crystals, but the lack of sufficient contrast is frequently a limiting factor. We experimentally demonstrate that this barrier can be circumvented using a method that combines phase sensitive and diffraction imaging principles. Details of defects revealed in tetragonal lysozyme and cubic ferritin crystals are presented and discussed. The approach enabling the detection of the phase changes of diffracted x rays should prove to be useful in the study of defect structures in a broad range of biological macromolecular crystals.
Studies of brain acetylcholinesterase (AChE) are traditionally based on biochemical assays, immunoreactivity, and histochemistry. Conventional histochemistry yields rich morphological data from tissue sections but yields quantitative results only with great difficulty. Several histochemical methods developed in recent years, including microdensitometry, microphotometry, and video-based histochemistry, are effective in quantitative and detailed study of AChE in tissue sections. However, they are usually time-consuming. As we report here, we adapted digital scanning densitometry to quantitate AChE histochemical staining in brain sections. The AChE and butyrylcholinesterase (BuChE), as measured by the method, were heterogeneously distributed throughout the brain, results that are consistent with those obtained by biochemical methods. The staining intensity is dependent on section thickness, substrate concentration, and reaction time. The cholinesterase inhibitor methyl paraoxon significantly decreased AChE staining intensity. Furthermore, data acquired from densitometry are similar to those obtained by video-based microscopy or by spectrophotometry. The advantage of the densitometric measurements compared to other quantitative histochemical methods is that it is very rapid while collecting data that are equivalent in quality. Because the digital scanning densitometers provide high quality and sensitive imaging, wide dynamic ranges, and convenient image analysis software, they are very useful tools in quantitative histochemistry.
OBJECTIVE: To investigate the association of the 48 bp variable number tandem repeat (VNTR) polymorphism in the dopamine D4 receptor (DRD4) gene exon III with schizophrenia in Chinese Han population. METHODS: Case-control association study was adopted to analyze the association between the 48 bp VNTR polymorphism of DRD4 gene exon III in 510 DSM-IV schizophrenics and 171 psychiatrically normal controls. RESULTS: (1) The DRD4 gene 48 bp VNTR polymorphism was manifested as 2-7 repeats, with the 4 repeats the most common (78.6% in schizophrenics and 76.9% in controls respectively). The frequency of 2 repeats was 16.2% and 19.3% in the schizophrenics and controls respectively. (2) The genotypic frequency was statistically significantly different between the schizophrenics and the controls. The genotypic frequency of short tandem repeats (2/2 and 2/3 genotype) was lower in patients (3.3%) than in controls (10.5%) (chi 2 = 14.88, df = 2, P = 0.00). (3) the frequency of the genotype with 4-repeat allele in patients was higher (95.9%) than in controls (88.3%) (chi 2 = 13.00, df = 1, P = 0.000). CONCLUSION: The most common allele in Chinese schizophrenics was 4 repeats in the 48 bp VNTR polymorphism of DRD4 gene exon III. The repeat number of 48 bp is probably associated with schizophrenia. Lack of 2-3 repeats or excess of genotype with 4-repeat allele may be associated with increased vulnerability to schizophrenia.
An ion-paring HPLC-MS-MS method with positive ion mode electrospray ionization has been developed to simultaneously quantify Ziagen, carbovir monophosphate, carbovir diphosphate and carbovir triphosphate. N',N'-Dimethylhexylamine was used as the ion-pairing agent. The presence of this ion-pairing agent allowed the retention and separation of the four compounds on a reversed-phase HPLC column as well as the detection of the nucleotides with positive ion mode electrospray ionization. The limits of detection were found to be better than 25 nM for all the analytes. Calibration curves of the analytes showed excellent linearity over the range of 25 nM to 5 microM. The relative standard deviations and accuracies for replicate analyses of quality control samples were less than 15%. The method has been successfully applied to the analysis of these compounds in human liver cells treated with Ziagen.
Chronic ischemic brain injuries were studied in 7- and 14-day-old rat pups, which were subjected to bilateral carotid artery occlusion (BCAO) on postnatal day 1. BCAO preferentially injured white matter in the corpus callosum, subcortex and internal capsule areas while largely spared cortical neurons. White matter rarefaction in the corpus callosum was observed in 12 out of the 17 BCAO rat brains and significantly enlarged lateral ventricles were found in five out of seven P14 BCAO rat brains. These white matter changes were similar to injuries found in newborn infants with periventricular leukomalacia (PVL). White matter injuries in the 7-day-old BCAO rat brain were accompanied with increased activation of microglia/macrophages, as indicated by ED1 and OX42 positive immunostaining. Immature oligodendrocytes in the 7-day-old BCAO rat brain, as indicated by O4+/O1+ staining, were much fewer than in the sham-operated rat brain. Immunostaining for myelin basic protein (MBP) at the fimbria hippocampus and the internal capsule areas in the 7-day-old BACO rat brain was also much less than in the control rat brain. Consistent with the immunostaining data, MBP mRNA expression in the 7-day-old, but not in the 14-day-old, BCAO rat brain was significantly less than in the control rat brain. The overall results suggest that pre-oligodendrocytes and immature oligodendrocytes might be major targets for chronic ischemic insults and activated microglia/macrophages are possibly involved in the process of white matter injury.
A new method is described that enables longitudinal and cross sections of an individual nerve fibre to be cut at multiple specified sites along the fibre by the use of a unique marker system. In this way the internal structure of the fibre can be correlated with the external appearance. Individual myelinated nerve fibres are teased apart in epoxy resin and mounted onto a carbon-coated slide, and after orientation and marking of specific sites of interest are snap frozen to liberate the orientated and marked fibres for embedding on the surface of an epoxy resin block for subsequent longitudinal or transverse sectioning. This method is particularly useful for the correlative study of the myelin-axon relationships.
The application of liquid chromatography/ion-trap mass spectrometry for simultaneous quantification of multiple drugs and detection of their metabolites for in vitro experiments was reported recently. In the current study, the use of these techniques was extended to in vivo pharmacokinetic (PK) studies of alpha-1a antagonists. In combination with limited time-point PK, greatly increased throughput was demonstrated for the in vivo screening and investigation of in vivo-in vitro correlation. In addition to quantitative analyses, the technique allowed simultaneous detection of major in vivo metabolites without having to reanalyze the plasma samples. The drugs were individually dosed in mice intravenously via tail vein injection and the blood samples were collected 5 min and 2 h after dosing. After the plasma samples for the different drugs had been prepared separately, they were pooled for cassette analysis. The concentrations of five test compounds in the plasma samples at 2 h ranged from 36-1062 ng/mL, whereas their 5-min plasma levels were similar. From the same cassette analysis, major metabolites in the samples were also detected simultaneously through the interpretation of full-scan mass spectra. The metabolite identification confirmed the results from a previous report that the major sites of metabolism are hydroxylation of the phenyl ring not bearing the alkylsulfonamide substitutent, piperidine N-dealkylation, and N-demethylation of the alkylsulfonamide group.
In a laboratory study, soil amended with and without wheat straw (2.8 g kg(-1) soil) was incubated under 70% water holding capacity (WHC), continuously flooded and flooded/drained cycle conditions at 30 degrees C for 51 days. Dinitrogen and N2O evolution and ammonia volatilisation were measured during the incubation. Extractable NH4+-N and NO3--N were determined at the end of the incubation. Entrapped N2, N2O, and dissolved NH4+-N and NO3--N in drainage water were measured in the flooded/drained cycle treatment when the floodwater was drained. The results indicated that N loss through ammonia volatilisation was undetected in all treatments due to the low soil pH value (pHH2O= 5.87) and no air movement. The recovery of urea-15N as N2 was lowest in the continuously flooded treatments (0.75% and 0.96% with and without straw amendment, respectively), highest in the 70% WHC treatments (5.65% and 4.41%, respectively), and intermediate in the flooded/drained cycle treatments (1.79% and 2.65%, respectively). The recovery of urea-15N as N2O was in the same order as that of N2, negligible in the continuously flooded treatments, 0.01% and 0.07% in the flooded/drained cycle treatments, and 1.29% and 2.23% in the 70% WHC treatments, respectively. Peak N2O evolution rates were observed after the floodwater was drained but no substantial evolution was found after the soil was reflooded following drained periods. However, peak N2 evolution rates were observed after the onset of both drainage and re-flooding. Considerable quantities of N2 but no detectable N2O were entrapped in the flooded soil.
Some of the major factors influencing ammonia volatilisation in a rice wheat rotation system were studied. A continuous airflow enclosure method was used to measure NH3 volatilisation in a field experiment at an agricultural college in Jiangsu Province. The five treatments comprised application rates of 0, 100, 200 or 300 kg N ha(-1) as urea, per growing season with rice straw amendment when wheat was sown, and 200 kg N ha(-1) without rice straw amendment. There were three replicates in a randomised block design. Ammonia volatilisation was measured immediately after urea application in the three consecutive years 1995 to 1997. The results show that N losses through NH3 volatilisation accounted for 4-19% of N applied during the wheat growing season and for 5-11% during the rice growing season. Ammonia volatilisation was affected significantly by soil moisture and temperature before and after fertiliser application during the wheat growing season. The ratio of volatilised NH3-N to applied N after urea application during the rice growing season was as follows: top-dressing at the onset of tillering > top-dressing at the start of the booting stage > basal fertilization. The results also show that the amount of N lost through NH3 volatilisation increased with increasing N application rate, but the ratio to applied N was not affected significantly by N application rate. Amendment with rice straw had no significant effect on NH3 volatilisation.