Biomedical subjects

Lei Zhang

Publications and source records attributed to Lei Zhang.

At least 127 records · Page 7Linked to original sources

PubMed2006

Influence of peak viral load on the extent of CD4+ T-cell depletion in simian HIV infection.

Simian HIV (SHIV) infection of macaques with CXCR4 tropic viruses results in early and profound CD4 T-cell depletion in the first few weeks of infection. Analyzing data from a large study of vaccination and SHIV-89.6P challenge, we observe a strong correlation between peak viral load and the extent of CD4 T-cell depletion in acute infection, consistent with a simple kinetic model of viral infection of CD4 T cells. We have modeled the dynamics of the interaction of virus and CD4 T cells over time to investigate the rate of CD4 T-cell infection and death. This analysis indicates that up to 80% of CD4 T cells are infected at peak viremia and that the proportion of CD4 T cells destroyed is correlated with the peak viral load. The simple relation between viral load and CD4 T-cell depletion allows prediction of the level of viral control required to prevent CD4 T-cell depletion in acute SHIV infection. Whether such a simple relation also holds for HIV or simian immunodeficiency virus infections remains to be determined, particularly in the gut and other anatomic sites in which most early T-cell depletion occurs.

Animals↗

PubMed2006

An edge-guided image interpolation algorithm via directional filtering and data fusion.

Preserving edge structures is a challenge to image interpolation algorithms that reconstruct a high-resolution image from a low-resolution counterpart. We propose a new edge-guided nonlinear interpolation technique through directional filtering and data fusion. For a pixel to be interpolated, two observation sets are defined in two orthogonal directions, and each set produces an estimate of the pixel value. These directional estimates, modeled as different noisy measurements of the missing pixel are fused by the linear minimum mean square-error estimation (LMMSE) technique into a more robust estimate, using the statistics of the two observation sets. We also present a simplified version of the LMMSE-based interpolation algorithm to reduce computational cost without sacrificing much the interpolation performance. Experiments show that the new interpolation techniques can preserve edge sharpness and reduce ringing artifacts.

Algorithms↗

PubMed2006

Improvement of color video demosaicking in temporal domain.

Color demosaicking is critical to the image quality of digital still and video cameras that use a single-sensor array. Limited by the mosaic sampling pattern of the color filter array (CFA), color artifacts may occur in a demosaicked image in areas of high-frequency and/or sharp color transition structures. However, a color digital video camera captures a sequence of mosaic images and the temporal dimension of the color signals provides a rich source of information about the scene via camera and object motions. This paper proposes an inter-frame demosaicking approach to take advantage of all three forms of pixel correlations: spatial, spectral, and temporal. By motion estimation and statistical data fusion between adjacent mosaic frames, the new approach can remove much of the color artifacts that survive intra-frame demosaicking and also improve tone reproduction accuracy. Empirical results show that the proposed inter-frame demosaicking approach consistently outperforms its intra-frame counterparts both in peak signal-to-noise measure and subjective visual quality.

Algorithms↗

PubMed2006

Face recognition from a single training image under arbitrary unknown lighting using spherical harmonics.

In this paper, we propose two novel methods for face recognition under arbitrary unknown lighting by using spherical harmonics illumination representation, which require only one training image per subject and no 3D shape information. Our methods are based on the recent result which demonstrated that the set of images of a convex Lambertian object obtained under a wide variety of lighting conditions can be approximated accurately by a low-dimensional linear subspace. We provide two methods to estimate the spherical harmonic basis images spanning this space from just one image. Our first method builds the statistical model based on a collection of 2D basis images. We demonstrate that, by using the learned statistics, we can estimate the spherical harmonic basis images from just one image taken under arbitrary illumination conditions if there is no pose variation. Compared to the first method, the second method builds the statistical models directly in 3D spaces by combining the spherical harmonic illumination representation and a 3D morphable model of human faces to recover basis images from images across both poses and illuminations. After estimating the basis images, we use the same recognition scheme for both methods: we recognize the face for which there exists a weighted combination of basis images that is the closest to the test face image. We provide a series of experiments that achieve high recognition rates, under a wide range of illumination conditions, including multiple sources of illumination. Our methods achieve comparable levels of accuracy with methods that have much more onerous training data requirements. Comparison of the two methods is also provided.

Algorithms↗

PubMed2006

Output convergence analysis for a class of delayed recurrent neural networks with time-varying inputs.

This paper studies the output convergence of a class of recurrent neural networks with time-varying inputs. The model of the studied neural networks has different dynamic structure from that in the well known Hopfield model, it does not contain linear terms. Since different structures of differential equations usually result in quite different dynamic behaviors, the convergence of this model is quite different from that of Hopfield model. This class of neural networks has been found many successful applications in solving some optimization problems. Some sufficient conditions to guarantee output convergence of the networks are derived.

Algorithms↗

PubMed2006

Comparative studies on the effect of a protein-synthesis inhibitor on aluminium-induced secretion of organic acids from Fagopyrum esculentum Moench and Cassia tora L. roots.

Aluminium (Al)-induced secretion of organic acids from plant roots is considered a mechanism of Al resistance, but the processes leading to the secretion of organic acids are still unknown. In the present study, a protein-synthesis inhibitor, cycloheximide (CHM), was used to investigate its effect on Al-induced organic acid secretion in a pattern I (rapid exudation of organic acids under Al stress) plant buckwheat (Fagopyrum esculentum Moench) and a pattern II (exudation of organic acids was delayed by several hours under Al stress) plant Cassia tora L. A dose-response experiment showed that the secretion of oxalate by buckwheat roots was not affected by CHM when added in the range from 0 to 50 microM, with or without exposure to 100 microm Al, but the secretion of citrate was completely inhibited by 30 microM CHM in C. tora. A time-course experiment showed that even prolonged exposure to 20 microM CHM did not affect oxalate secretion in buckwheat, but significantly inhibited citrate secretion in C. tora. However, citrate synthase (CS) activity in C. tora was not affected during 12 h exposure to 100 microM Al when compared with that in control roots, although CHM can inhibit CS activity effectively. These results indicated that CS activity was not related to Al-regulated citrate efflux in C. tora. The total protein was decreased by 14.0% and 32.3% in C. tora and buckwheat root tip, respectively, after 3-h treatment with 20 microM CHM. A 3-h pulse with 20 microM CHM completely inhibited citrate efflux in C. tora during the next 6-h exposure to Al, although a small amount of citrate was exuded after 9-h exposure. However, oxalate efflux in buckwheat was not influenced by a similar treatment. In buckwheat, a 3-h pulse with 100 microM Al maintained oxalate secretion at a high level during the next 9 h, with or without CHM treatment. Conversely, in C. tora a 6-h pulse with 100 microM Al induced significant secretion of citrate which was inhibited by the CHM. Taken together, these findings suggest that both de novo synthesis and activation of an anion channel are needed for Al-induced secretion of citrate in C. tora, but in buckwheat the plasma membrane protein responsible for oxalate secretion pre-exists.

Aluminum↗

PubMed2006

Expression patterns of 5-lipoxygenase in human brain with traumatic injury and astrocytoma.

5-Lipoxygenase (5-LOX) is a key enzyme in the metabolism of arachidonic acid to leukotrienes. The levels of leukotrienes increase after brain injury and when tumors are present. It has been reported that 5-LOX is widely expressed in the brain and that 5-LOX inhibition provides neuroprotection. However, there is still no information available for the expression patterns of 5-LOX in human brain following trauma or with astrocytomas. We investigated its expression patterns by immunohistochemistry. We found that 5-LOX is normally expressed in neurons and glial cells. In neurons, it was expressed in two patterns: in the cytosol and nucleus or only in the cytosol. In traumatic brain injury, 5-LOX expression increased in glial cells and neutrophils. Double-labeling immunohistochemistry showed that part of the 5-LOX-positive glial cells were GFAP positive. No 5-LOX expression was found in brain microvessel endothelia, except in the regenerated endothelia of a patient 8 days following brain trauma. Furthermore, 5-LOX expression increased and showed a granular pattern in high-grade (grade III/IV) astrocytoma. These results indicate that 5-LOX has multiple expression patterns, and can be induced by brain injury, which implies that 5-LOX might have pathophysiological roles in the human brain.

Adult↗

PubMed2006

Transplantation of umbilical cord blood-derived endothelial progenitor cells: a promising method of therapeutic revascularisation.

Therapeutic neovascularisation by endothelial progenitor cells (EPCs) mediated vascular regeneration is becoming a novel option for the treatment of ischaemic diseases. Recently, human umbilical cord blood (CB) has been found to contain a large number of EPCs and transplantation of CB EPCs led to a successful salvage of the ischaemic limbs through improvement in blood perfusion, indicating the feasibility of using CB cells for therapeutic revascularisation. This review will summarise recent studies in therapeutic revascularisation using CB cells and discuss the potential clinical utilisation of CB cells in ischaemic diseases.

Animals↗

PubMed2006

Cysteinyl leukotriene receptors CysLT1 and CysLT2 are upregulated in acute neuronal injury after focal cerebral ischemia in mice.

AIM: To determine whether cysteinyl leukotriene receptors (CysLT1 and CysLT2) are upregulated in acute neuronal injury after focal cerebral ischemia in mice, and to confirm CysLT1 receptor localization. METHODS: After permanent focal cerebral ischemia was induced by middle cerebral artery occlusion (MCAO), neurological deficits and neuron loss were determined at various time points within 48 h. The mRNA expressions of CysLT1 and CysLT2 receptors in the brain were analyzed by RT-PCR. CysLT1 receptor localization was detected by double immunofluorescence. RESULTS: Neurological deficits and neuron loss were found 6, 24 and 48 h after MCAO. The mRNA expressions of both CysLT1 and CysLT2 receptors were upregulated in the ischemic hemisphere 1, 24, and 48 h after MCAO with peaks at 24 h. The CysLT1 receptor was selectively localized in neurons 24 h after MCAO. CONCLUSION: CysLT1 and CysLT2 receptors are upregulated in acute neuronal injury after focal cerebral ischemia, and the CysLT1 receptor is localized in neurons after ischemia.

Animals↗

PubMed2006

Immunomodulating effects of fractioned polysaccharides isolated from Yu-Ping-Feng-Powder in cyclophosphamide-treated mice.

Yu-Ping-Feng-Powder (YP), a traditional Chinese medicine prescription, is widely applied in China for the cure and prevention of diseases related to immunodeficiency. To test whether the fractioned polysaccharides (YPF-P) isolated from YP have immunomodulating activities, the effects of YPF-P on cyclophosphamide (Cy)-treated mice were studied in relation to phagocytosis of macrophage, splenocyte proliferation, and humoral, and cellular immunity parameters. It was found that YPF-P enhances phagocytic activity, augments ConA- or LPS-stimulated T cell proliferation, increases the quantitative haemolysis of SRBC (QHS) and delayed-type hypersensitivity reaction (DTH) to dinitrofluorobenzene. Hence, YPF-P restored the immuno-competence suppressed by Cy. YPF-P also augmented IL-2 and IFN-gamma production, but failed to increase IL-4 production, which indicates that there is high probability that it enhance Th1 function. These results suggested that YPF-P has immunomodulating effects and that the polysaccharides constitute one of the active components of YP.

Administration, Oral↗

PubMed2006

Biological effects of thyrotropin receptor activation on human orbital preadipocytes.

PURPOSE: Thyrotropin receptor (TSHR) expression is upregulated in the orbits of patients with Graves ophthalmopathy (GO), most of whom have TSHR-stimulating antibodies. The authors investigated the biological effects of TSHR activation in vitro in adipose tissue, the site of orbital TSHR expression. METHODS: Activating mutant TSHR (TSHR*) or wild-type (WT) was introduced into human orbital preadipocytes using retroviral vectors. Their proliferation (Coulter counting), basal cAMP accumulation (radioimmunoassay), and spontaneous and peroxisome proliferator-activated receptor (PPARgamma)-induced adipogenesis (quantitative oil red O staining) were assessed and compared with those of nonmodified cells. QRT-PCR was used to measure transcripts of CCAT/enhancer binding protein (C/EBP)beta, PPARgamma, and lipoprotein lipase (LPL; early, intermediate, and late markers of adipogenesis) and for uncoupling protein (UCP)-1 (brown adipose tissue [BAT]). RESULTS: Expression of TSHR* significantly inhibited the proliferation of preadipocytes and produced an increase in unstimulated cAMP of 200% to 600%. Basal lipid levels were significantly increased in TSHR* (127%-275%) compared with nonmodified (100%) or WT-expressing (104%-187%) cells. This was accompanied by 2- to 10-fold increases in early-intermediate markers and UCP-1 transcripts (2- to 8-fold); LPL was at the limit of detection. In nonmodified cells, adipogenesis produced significant increases in transcripts of all markers, including LPL (approximately 30-fold). This was not the case in TSHR*-expressing cells, which also displayed 67% to 84% reductions in lipid levels. CONCLUSIONS: TSHR activation stimulates early differentiation (favoring BAT formation?) but renders preadipocytes refractory to PPARgamma-induced adipogenesis. In neither case did lipid-containing vacuoles accumulate, suggesting that terminal stages of differentiation were inhibited.

Adipocytes↗

PubMed2006

TRPM8 in prostate cancer cells: a potential diagnostic and prognostic marker with a secretory function?

During the past 5 years it has emerged that the transient receptor potential (TRP) family of Ca(2+)-and Na(+)-permeable channels plays a diverse and important role in cell biology and in pathology. One member of this family, TRPM8, is highly expressed in prostate cancer cells but the physiological and pathological functions of TRPM8 in these cells are not known. Here we address these questions, and the issue of whether or not TRPM8 is an effective diagnostic and prognostic marker in prostate cancer. TRPM8 is known to be activated by cool stimuli (17-25 degrees C) and cooling compounds such as menthol. The activation mechanism(s) involves voltage sensing of membrane potential, phosphatidylinositol 4,5-bisphosphate and Ca(2+). In addition to prostate cancer cells, TRPM8 is expressed in sensory neurons where it acts as a sensor of cold. In prostate epithelial cells, expression of TRPM8 is regulated by androgen and is elevated in androgen-sensitive cancerous cells compared with normal cells. While there is some evidence that in prostate cancer cells Ca(2+) and Na(+) inflow through TRPM8 is necessary for survival and function, including secretion at the apical membrane, the function of TRPM8 in these cells is not really known. It may well differ from the role of TRPM8 as a cool sensor in sensory nerve cells. Androgen unresponsive prostate cancer is difficult to treat effectively and there are limited diagnostic and prognostic markers available. TRPM8 is a potential tissue marker in differential diagnosis and a potential prognostic marker for androgen-unresponsive and metastatic prostate cancer. As a consequence of its ability to convey Ca(2+) and Na(+) and its expression in only a limited number of cell types, TRPM8 is considered to be a promising target for pharmaceutical, immunological and genetic interventions for the treatment of prostate cancer.

Biomarkers, Tumor↗

PubMed2006

Synthesis of N-o-methylphenyl-N'-(sodium p-aminobenzene-sulfonate) thiourea and its chromogenic reaction with palladium(II).

A new chromogenic reagent, N-o-methylphenyl-N'-(sodium p-aminobenzenesulfonate)thiourea (MSAT), has been synthesized and characterized by elemental analysis, (1)H-NMR, FT-IR and UV-Vis spectra. Based on the absorption spectrum of the colored complex of MSAT with palladium(II), a novel spectrophotometric method for the determination of palladium has been developed. In a pH 4.0 - 5.5 HAc-NaAc buffer solution, palladium(II) reacted with MSAT to form a stable yellow water-soluble complex with an apparent molar absorptivity of epsilon = 2.04 x 10(5) L mol(-1) cm(-1) at the maximum absorption of 318.0 nm. Beer's law was obeyed in the concentration range of 1.2 - 11.8 microg per 25 mL for palladium(II) with a correlation coefficient of 0.9997. The probable interfering ions and their tolerable limits have also been investigated in detail. The proposed method is simple, rapid, and sensitive, and has been applied to the determination of palladium in anode mud and ore samples with satisfactory results.

Hydrogen-Ion Concentration↗

PubMed2006

Gene transfer of an engineered transcription factor promoting expression of VEGF-A protects against experimental diabetic neuropathy.

Peripheral neuropathy is a common, irreversible complication of diabetes. We investigated whether gene transfer of an engineered zinc finger protein transcription factor (ZFP-TF) designed to upregulate expression of the endogenous vascular endothelial growth factor (VEGF)-A gene could protect against experimental diabetic neuropathy. ZFP-TF-driven activation of the endogenous gene results in expression of all of the VEGF-A isoforms, a fact that may be of significance for recapitulation of the proper biological responses stimulated by this potent neuroprotective growth factor. We show here that this engineered ZFP-TF activates VEGF-A in appropriate cells in culture and that the secreted VEGF-A protein induced by the ZFP protects neuroblastoma cell lines from a serum starvation insult in vitro. Importantly, single and repeat intramuscular injections of formulated plasmid DNA encoding the VEGF-A-activating ZFP-TF resulted in protection of both sensory and motor nerve conduction velocities in a streptozotocin-induced rat model of diabetes. These data suggest that VEGF-A-activating ZFP-TFs may ultimately be of clinical utility in the treatment of this disease.

Animals↗

PubMed2006

Participation of an abnormality in the transforming growth factor-beta signaling pathway in resistance of malignant glioma cells to growth inhibition induced by that factor.

OBJECT: Malignant glioma cells secrete and activate transforming growth factor-beta (TGFbeta) and are resistant to growth inhibition by that factor. Nevertheless, the mechanism underlying this effect remains poorly understood. In this study, the mechanism of the resistance to growth inhibition induced by TGFbeta was investigated. METHODS: The authors examined the expression of downstream components of the TGFbeta receptor, including Smad2, Smad3, Smad4, and Smad7, and the effect of TGFbeta1 treatment on the phosphorylation of Smad2 and the nuclear translocation of Smad2 and Smad3 by using 10 glioma cell lines and the A549 cell line, which is sensitive to TGFbeta-mediated growth inhibition. The expression of two transcriptional corepressor proteins, SnoN and Ski, and the effect of TGFbeta1 treatment on the expression of the SnoN protein and the cell cycle regulators p21, p15, cyclin-dependent kinase-4 (CDK4), and cyclin D1 were also examined. Expression of the Smad2 and Smad3 proteins was lower in the glioma cell lines than in the A549 cell line and in normal astrocytes. In particular, Smad3 expression was low or very low in nine of the 10 malignant glioma cell lines. Expression of Smad4 was low in four glioma cell lines, and expression of the Smad7 protein was similar when compared with protein expression in the A549 cell line and in normal astrocytes. The levels of Smad2 phosphorylation after TGFbeta1 treatment were lower in glioma cell lines than in the A549 cell line, except for one glioma cell line. Seven of the 10 glioma cell lines exhibited lower levels of nuclear translocation of Smad2 and Smad3, and two cell lines that expressed very low levels of Smad3 protein showed no nuclear translocation. All glioma cell lines expressed the SnoN protein and its expression was unaltered by treatment with TGFbeta1. Three glioma cell lines expressed high levels of the Ski protein. The expression of the p21(cip1), p15(INK4B), CDK4, and cyclin D1 proteins was not altered by TGFbeta1, treatment, except in one cell line that displayed a slight increase in p21 protein. Overall, the expression of the Smad2 and Smad3 proteins was low in the glioma cell lines, the phosphorylation and nuclear translocation of Smad2 and Smad3 were impaired, and the TGFbeta receptor signal did not affect the expression of the SnoN, p21, p15, cyclin D1, and CDK4 proteins. CONCLUSIONS: These results suggest that the ability to resist TGFbeta-mediated growth inhibition in malignant glioma cells is due to abnormalities in the TGFbeta signaling pathway.

Cell Culture Techniques↗

PubMed2006

[Protective effects of glycyrrhizin on adriamycin nephropathy in rats].

OBJECTIVE: To observe the effects of glycyrrhizin on laminin (LN) expression in kidney tissue and excretory quantity of urine protein of rats with adriamycin nephropathy, and to explore the protective effects of glycyrrhizin on glomerulosclerosis. METHODS: Eighteen SD rats were randomly divided into 3 groups: normal control group (n=6), untreated group (n=6) and glycyrrhizin-treated group (n=6). Adriamycin nephropathy was induced in rats in the last two groups by intravenous injection of adriamycin. The rats in the glycyrrhizin-treated group were fed glycyrrhizin for eight weeks, whereas the rats in the normal control group and untreated group were fed normal saline solution for eight weeks too. The levels of 24 h urine protein (Upr), serum creatinine (sCr), blood urea nitrogen (BUN) and serum cholesterol (Ch) of rats in each group were examined before treatment and after the treatment for four and eight weeks. The renal morphological changes were observed under a microscope. The expression level of LN in renal tissue was detected by streptavidin-biotin peroxidase complex (SABC) method. RESULTS: The levels of 24 h Upr after the treatment for four and eight weeks in the glycyrrhizin-treated group were both significantly decreased as compared with those in the untreated group. The pathological morphological changes of renal tissue in the glycyrrhizin-treated group were remarkably alleviated, and the expression level of LN in renal tissue was also decreased in the glycyrrhizin-treated group as compared with those in the untreated group. CONCLUSION: The glycyrrhizin exerts certain protective effects on adriamycin nephropathy in rats by reducing excretory quantity of urine protein, decreasing expression level of LN in renal tissue, improving renal function and lessening the severity degree of glomerulosclerosis so as to retard the development of glomerulosclerosis.

Animals↗

PubMed2006

[Homeostatic conditions affect the protective effect of edaravone on ischemic injury in neurons].

OBJECTIVE: To determine whether homeostatic conditions (pH, glycine or ion concentration) affect the protective effects of edaravone on ischemic injury in rat cortical neurons. METHODS: In cultured rat cortical neurons, the compositions in the experimental solutions were changed to mimic the disturbance of homeostasis after cerebral ischemia. In vitro ischemic injury was induced by oxygen-glucose deprivation (OGD) for 3 h and reperfusion for 12 h, and the neuron injury was evaluated by 3-(4, 5-dimethylthiazol-2yl)-2, 5-diphenyl tetrazolium bromide (MTT) reduction assay and lactate dehydrogenase (LDH) release. Effect of edaravone on OGD injury was observed in different experimental solutions. RESULT: In weak alkalified solution (pH 7.8) or the solution containing glycine (10 micromol/L), OGD injury became more serious; but in weak acidic (pH 6.5) or higher Mg(2+) (1.8 mmol/L) solutions, OGD injury was attenuated. Edaravone (1 micromol/L) reversed the injury in the solutions with pH 6.1,7.4 and 7.8 or the solution containing glycine, but did not show protective effect in the solution with pH 6.5 and the higher Mg(2+) or lower Ca(2+) solution. CONCLUSION: The changes of homeostatic conditions affect the severity of ischemic injury of neurons and the protective effect of edaravone.

Animals↗

PubMed2006

[Incomplete protective effects of minocycline on traumatic brain injury in rats and mice].

OBJECTIVE: To evaluate protective effect of minocycline,a semisynthetic tetracycline derivative on different traumatic brain injuries in rats and mice. METHODS: The opened brain trauma was induced in rats and the closed head injury and cold brain injury were induced in mice. In 3 brain trauma models, minocycline (45 mg/kg, ip) was administered twice daily for 2 d before the operation, at 30 min before and 1 h after the operation, and once daily for 2 d following the operation (totally 8 doses in 5 d). After the operation, the behavioral alteration was observed daily, lesion area and survival neuron density were measured at the end of the experiments (14 d after the injuries). RESULT: For rat opened traumatic injury, minocycline promoted the recovery of hindlimb motor activity (inclined board angle), but did not alter other indexes. For mouse closed head traumatic injury, minocycline reduced the neuron loss, but did not improve behavioral dysfunction. For mouse cold injury-induced trauma, minocycline reduced death rate and lesion area, but did not remarkably improve behavior and neuron loss. CONCLUSION: Minocycline only has an incomplete neuroprotective effect on different brain traumatic injuries in rats and mice.

Animals↗