Biomedical subjects

W Li

Publications and source records attributed to W Li.

At least 451 records · Page 25Linked to original sources

PubMed2000

Captopril MR renography in a swine model: toward a comprehensive evaluation of renal arterial stenosis.

PURPOSE: To test the feasibility of captopril magnetic resonance (MR) renography and to validate the technique in an animal model of renal arterial stenosis. MATERIALS AND METHODS: Seven pigs with induced renal arterial stenosis were studied. MR renography was performed with a T1-weighted approach by using three-dimensional fast imaging with steady-state precession, or FISP, sequences after administration of a bolus of 0.1 mmol of gadopentetate dimeglumine per kilogram of body weight. Captopril was administered to improve the specificity. RESULTS: The results demonstrate that differences in renographic curves and indices are observed only if an anatomically substantial stenosis, typically a diameter reduction of more than 70%, is present and captopril is administered. CONCLUSION: In this preliminary experience in an animal model, captopril MR renography provided data consistent with expectations based on conventional renographic results.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed2000

Sphingomyelinase and ceramide analogs induce contraction and rises in [Ca(2+)](i) in canine cerebral vascular muscle.

Studies were designed to investigate effects of neutral sphingomyelinase (N-SMase) and ceramide analogs as well as phosphorylcholine on vascular tone and Ca(2+) mobilization in isolated canine cerebral arterial smooth muscle. N-SMase (0.001-0.1 U/ml) provoked a gradual but sustained vasoconstriction of arterial rings in a concentration-related manner that was endothelium independent. Incubation of denuded arterial rings in Ca(2+)-free medium or pretreatment with verapamil in extracellular Ca(2+) resulted in a reduction of the N-SMase-evoked constriction. Exposure of arterial rings to 1,2-bis(2-aminophenoxy)ethane-N,N,N', N'-tetraacetic acid (BAPTA)-AM did not, however, result in a reduction of N-SMase-induced constriction. Both staurosporine and bisindolymaleimide I attenuated N-SMase-induced contractions to 66% and 72% of control, respectively. N-SMase caused gradual and sustained rises in intracellular Ca(2+) concentration ([Ca(2+)](i)) in primary cultured cerebral vascular smooth muscle cells. Pretreatment of these cultured cells with nimodipine and verapamil caused a steady decline in N-SMase-induced rises in [Ca(2+)](i). Exposure of the cells to Ca(2+)-free solution reversed the [Ca(2+)](i)-induced rise triggered by N-SMase to the resting baseline. Both C(8) and C(16) ceramide (10(-9)-10(-6) M), but not phosphorylcholine, constricted denuded canine arterial rings in a concentration-related manner and elevated [Ca(2+)](i). Our results suggest that the sphingomyelin-signaling pathway, via a probable release of ceramide molecules, may play an important role in regulation of cerebral arterial wall tone.

Animals↗

PubMed2000

Effects of exercise training on cardiac function, gene expression, and apoptosis in rats.

This study determined the effects of exercise training on cardiac function, gene expression, and apoptosis. Rats exposed to a regimen of treadmill exercise for 13 wk had a significant increase in cardiac index and stroke volume index and a concomitant decrease in systemic vascular resistance compared with both age-matched and body weight-matched sedentary controls in the conscious state at rest. In exercise-trained animals, there was no change in the expression of several marker genes known to be associated with pathological cardiac adaptation, including atrial natriuretic factor, beta-myosin heavy chain, alpha-skeletal and smooth muscle actins, and collagens I and III. Exercise training, however, produced a significant induction of alpha-myosin heavy chain, which was not observed in rats with myocardial infarction. No histological features of cardiac apoptosis were observed in the treadmill-trained rats. In contrast, apoptotic myocytes were detected in animals with myocardial infarction. In summary, exercise training improves cardiac function without evidence of cardiac apoptosis and produces a pattern of cardiac gene expression distinct from pathological cardiac adaptation.

Actins↗

PubMed2000

Contextual influence on orientation discrimination of humans and responses of neurons in V1 of alert monkeys.

We studied the effects of various patterns as contextual stimuli on human orientation discrimination, and on responses of neurons in V1 of alert monkeys. When a target line is presented along with various contextual stimuli (masks), human orientation discrimination is impaired. For most V1 neurons, responses elicited by a line in the receptive field (RF) center are suppressed by these contextual patterns. Orientation discrimination thresholds of human observers are elevated slightly when the target line is surrounded by orthogonal lines. For randomly oriented lines, thresholds are elevated further and even more so for lines parallel to the target. Correspondingly, responses of most V1 neurons to a line are suppressed. Although contextual lines inhibit the amplitude of orientation tuning functions of most V1 neurons, they do not systematically alter the tuning width. Elevation of human orientation discrimination thresholds decreases with increasing curvature of masking lines, so does the inhibition of V1 neuronal responses. A mask made of straight lines yields the strongest interference with human orientation discrimination and produces the strongest suppression of neuronal responses. Elevation of human orientation discrimination thresholds is highest when a mask covers only the immediate vicinity of the target line. Increasing the masking area results in less interference. On the contrary, suppression of neuronal responses in V1 increases with increasing mask size. Our data imply that contextual interference observed in human orientation discrimination is in part directly related to contextual inhibition of neuronal activity in V1. However, the finding that interference with orientation discrimination is weaker for larger masks suggests a figure-ground segregation process that is not located in V1.

Action Potentials↗

PubMed2000

Noggin is a negative regulator of neuronal differentiation in developing neocortex.

Bone morphogenetic proteins (BMPs) trigger neuronal differentiation of neocortical precursors within the ventricular zone (VZ) [Li et al. (1998): J Neurosci 18:8853-8862]. BMP-2/4 protein is concentrated at the VZ surface and BMPs rapidly promote the differentiation of neocortical precursors in both dissociated cell and explant cultures. Noggin binds to BMP-2/4 with high affinity, and prevents binding to cell surface receptors. In the present study, we used human recombinant noggin protein to determine whether endogenous BMP-2/4 triggers neuronal differentiation in dissociated cell culture. We find that noggin inhibits the differentiation of neocortical neurons: noggin decreases the number of MAP-2- and TUJ1-positive cells after 24 h of treatment, yet has no effect on either proliferation or cell survival. Noggin also significantly decreases neurite growth of MAP-2-positive cells. In addition, using Western blot analysis we show that noggin protein is present in developing cortex at E15. These results are consistent with previous results showing that endogenous BMPs trigger neuronal differentiation in the neocortical VZ and also indicate that a balance of noggin and BMP may regulate the differentiation of neocortical neurons in vivo.

Animals↗

PubMed2000

A single amino acid deletion in the carboxy terminal of apolipoprotein A-I impairs lipid binding and cellular interaction.

The carboxy-terminal region of apolipoprotein (apo) A-I has been shown by mutagenesis or synthetic peptides to play an important role in lipid binding. However, the precise functional domain of the C-terminal remains to be defined. In this study, apoA-I Nichinan, a naturally occurring human apoA-I variant with a deletion of glutamic acid 235, was expressed in Escherichia coli to examine the effect of this mutation on the functional domain of apoA-I for lipid binding and related consequences. A dimyristoyl phosphatidylcholine binding study with recombinant (r-) proapoA-I Nichinan showed a significantly slow initial rate of lipid binding. On preincubation with human plasma lipoprotein fractions (d<1.225 g/mL) at 37 degrees C for 1 hour, (125)I-labeled normal r-proapoA-I was chromatographed as a single peak at the high density lipoprotein (HDL) fraction, whereas (125)I-labeled r-proapoA-I Nichinan was chromatographed into the HDL fraction as well as the free r-proapoA-I fraction (23% of radioactivity). Circular dichroism measurements showed that the alpha-helix content of lipid-bound r-proapoA-I Nichinan was reduced, being 62% (versus 73%) of normal r-proapoA-I. Nondenaturing gradient gel electrophoresis of reconstituted HDL particles assembled with r-proapoA-I Nichinan and normal r-proapoA-I showed similar particle size. To study cholesterol efflux, human skin fibroblasts were labeled with [(3)H]cholesterol, followed by incubation with either lipid-free r-proapoA-I or DMPC/r-proapoA-I complex. Fractional cholesterol efflux from [(3)H]cholesterol-labeled fibroblasts to lipid-free r-proapoA-I Nichinan or DMPC/r-proapoA-I Nichinan complexes was significantly reduced relative to that of normal r-proapoA-I or DMPC/r-proapoA-I during the 6-hour incubation. Binding assays of human skin fibroblasts by lipid-free r-proapoA-I showed that r-proapoA-I Nichinan was 32% less bound to fibroblasts than was normal r-proapoA-I. Our data demonstrate that the deletion of glutamic acid 235 at the C-terminus substantially reduces the lipid-binding properties of r-proapoA-I Nichinan, which may cause a reduction in its capacity to interact with plasma membranes as well as to promote cholesterol efflux from cultured fibroblasts.

Apolipoprotein A-I↗

PubMed2000

Measuring the VC-dimension using optimized experimental design.

VC-dimension is the measure of model complexity (capacity) used in VC-theory. The knowledge of the VC-dimension of an estimator is necessary for rigorous complexity control using analytic VC generalization bounds. Unfortunately, it is not possible to obtain the analytic estimates of the VC-dimension in most cases. Hence, a recent proposal is to measure the VC-dimension of an estimator experimentally by fitting the theoretical formula to a set of experimental measurements of the frequency of errors on artificially generated data sets of varying sizes (Vapnik, Levin, & Le Cun, 1994). However, it may be difficult to obtain an accurate estimate of the VC-dimension due to the variability of random samples in the experimental procedure proposed by Vapnik et al. (1994). We address this problem by proposing an improved design procedure for specifying the measurement points (i.e., the sample size and the number of repeated experiments at a given sample size). Our approach leads to a nonuniform design structure as opposed to the uniform design structure used in the original article (Vapnik et al., 1994). Our simulation results show that the proposed optimized design structure leads to a more accurate estimation of the VC-dimension using the experimental procedure. The results also show that a more accurate estimation of VC-dimension leads to improved complexity control using analytic VC-generalization bounds and, hence, better prediction accuracy.

Algorithms↗

PubMed2000

Brush border myosin I (BBMI): a basally localized transcript in human jejunal enterocytes.

To extend our recent observation that villin mRNA, encoding an apical microvillous protein, is dichotomously localized in the basal region of human enterocytes, we examined the localization of mRNAs for brush border myosin I (BBMI) and intestinal fimbrin (I-fim). In situ hybridization indicated that BBMI mRNA localized to the basal region of human enterocytes, whereas the mRNA for I-fim distributed diffusely. To facilitate study of potential mechanisms of mRNA targeting, we cloned a full-length cDNA for BBMI including its 5'- and 3'-untranslated regions (UTRs). This cDNA shares 86% sequence identity with bovine BBMI and 85% with rat BBMI. Sequence analysis revealed no obvious similarity between the 3'-UTRs of BBMI and villin. This study provides evidence of novel sorting pathways for intestinal microvillous cytoskeletal proteins.

Base Sequence↗

PubMed2000

Inhibition by ginseng of 1,2-dimethylhydrazine induction of aberrant crypt foci in the rat colon.

The modifying effects of dietary administration of ginseng on the induction and development of 1,2-dimethylhydrazine (DMH)-induced aberrant crypt foci (ACF) were investigated in Fischer 344 (F-344) rats. In Experiment 1, starting at six weeks of age, 65 rats were injected with DMH or saline alone once a week for four weeks. Rats in Groups 1 and 2 were fed diets containing 1% ginseng for five weeks, starting one week before the first dose of DMH. Animals in Groups 3 and 4 received ginseng for eight weeks after DMH treatment; Group 5 served as a carcinogen control group. In Experiment 2, 60 rats were injected with DMH or saline alone four times at one-week intervals. They were also fed diets containing 1% ginseng or the control diet throughout the 30 days of the experiment. In Experiment 1, numbers of foci with at least four crypts were significantly reduced in Group 2 treated with red ginseng during the initiation phase (p < 0.005). In Experiment 2, treatment with red ginseng also resulted in a decrease in the total number of DMH-induced ACF accompanied by a reduction in 5-bromo-2'-deoxyuridine labeling indexes in colonic crypts comprising ACF (p < 0.005 and p < 0.05, respectively). These findings suggest that dietary administration of red ginseng in combination with DMH suppresses colon carcinogenesis of rats, and the inhibition may be associated, in part, with suppression of cell proliferation in the colonic mucosa.

1,2-Dimethylhydrazine↗

PubMed2000

Liquid chromatography-atmospheric pressure chemical ionization mass spectrometry as a tool for the characterization of anthraquinone derivatives from Chinese herbal medicine.

We have examined the anthraquinone derivatives of a Chinese herb medicine 'Rhubarb' by using HPLC/MS/MS, equipped with an atmospheric pressure chemical ionization source. The simultaneous determination of five ingredients in the sample extracts by HPLC/MS/MS was demonstrated. Product ion spectra of these components in the extracts were obtained and matched against known standards. Concentrations of these active ingredients were estimated by multiple reaction monitoring in the negative ion mode using a single HPLC run.

Anthraquinones↗

PubMed2000

VEGF nuclear accumulation correlates with phenotypical changes in endothelial cells.

Vascular endothelial growth factor (VEGF) is a multifunctional cytokine that plays a prominent role in normal vascular biology and pathology. In an experimental wound model, the mechanical disruption of monolayers of cultured endothelial cells resulted in two phenotypically distinct cell subpopulations in which VEGF was internalized by alternative endocytotic pathways and delivered to different subcellular compartments. In the cells away from the wound, VEGF was internalized via the classical receptor-mediated endocytosis pathway and accumulated in the endosomal compartment, whereas in the cells situated at the edges of a wound, VEGF was rapidly taken up and translocated to the nucleus. VEGF internalization and subsequent nuclear accumulation only occurred for a short period of time after the wounding and was specifically abolished by antibodies that bind to the KDR binding site of VEGF. In the cells with VEGF nuclear accumulation, the levels of wound healing related proteins, such as Factor VIII (FVIII), tissue factor (TF) and tissue plasminogen activator, rapidly and dramatically increased compared to the cells that internalized VEGF via the classical endocytotic pathway. The increase in FVIII and TF was abolished when the nuclear transport is blocked. These data suggest that nuclear VEGF accumulation may be involved in modulating the levels of the proteins of the coagulation and fibrinolysis pathways.

Adrenal Cortex↗

PubMed2000

Plasma endothelin-1 levels and circulating endothelial cells in patients with aortoarteritis.

To investigate the correlation between plasma endothelin-1 (ET-1), circulating endothelial cells (CECs), and the disease activity in patients with aortoarteritis. In this study, radioimmunoassay was used to measure plasma levels of ET-1 in 56 patients with aortoarteritis. Circulating endothelial cell counts were also carried out as an indicator of vessel wall lesions. The plasma levels of ET-1 and CECs in the active disease patient group were significantly higher than those in inactive patient group (p<0.001). A significant positive correlation was found between plasma ET-1 levels and erythrocyte sedimentation rates (ESRs) in patients with aortoarteritis (r=0.645, p<0.001), as well as CECs (r=0.876, p<0.001). These results suggested that the ET-1 secreted during the active stages of aortoarteritis may cause constriction and proliferation of vascular smooth muscle cells, thus contributing to the pathogenesis of luminal narrowing. The increased CECs might serve as a marker of disease activity.

Adult↗

PubMed2000

The SH2 and SH3 adapter Nck: a two-gene family and a linker between tyrosine kinases and multiple signaling networks.

SH2 and SH3 adapter proteins connect cell surface tyrosine kinases to intracellular signaling networks. For instance, the SH3-SH2-SH3 adapter Grb2 links receptor tyrosine kinases to the Ras pathway. Nck, composed of three SH3 domains and one SH2 domain, represents a two-gene (alpha and beta) family in mammals. Nckalpha and Nckbeta are expressed in the same cells and appear to have distinct signaling specificity. Studies show that Nck plays a role in cell mitogenesis and morphogenesis. The former uses Ras-dependent and Ras-independent pathways. The latter appears to coordinate with the Cdc42/Rac>PAK1/WASp>actin cytoskeleton pathway. Understanding the specificity of Nckalpha and Nckbeta signal transduction will provide answers for the previously often conflicting observations.

Actins↗

PubMed2000

Evaluation of potato tuber moth (Lepidoptera: Gelechiidae) resistance in tubers of Bt-cry5 transgenic potato lines.

The potato tuber moth, Phthorimaea operculella (Zeller), in tropical and subtropical countries, is the most destructive pest of potato, Solanum tuberosum L. The larvae attack foliage and tubers in the field and in storage. The purpose of this study was to evaluate the efficacy of a Bt-cry5 transgene to control the potato tuber moth in tuber tissues. Tuber bioassays using stored (11-12 mo old) and newly harvested tubers of Bt-cry5-Lemhi Russet and Bt-cry5-Atlantic potato lines showed up to 100% mortality of 1st instars. Mortality was lowest in the newly harvested tubers of Bt-cry5-Atlantic lines (47.1-67.6%). Potato tuber moth mortality was 100% in the Bt-cry5-Spunta lines that were transformed with Bt-cry5 gene controlled by the CaMV 35S promoter (pBIML5 vector) and in 2 of 3 lines transformed with Bt-cry5 gene controlled by the Gelvin super promoter (pBIML1 vector). The transgenic Spunta lines expressing Bt-cry5 controlled by the patatin promoter (pBMIL2 vector) showed the lowest tuber moth mortality (25.6 and 31.1%). The Bt-cry5 transgenic lines with high tuber expression of B. thuringiensis have value in an integrated pest management system to control potato tuber moth.

Animals↗

PubMed2000

Expression and regulation of connexin43 in rat Leydig cells.

Gap junctions are intercellular protein channels which provide a pathway for the exchange of ions and small molecules. This exchange of materials allows metabolic coupling of cells. Gap junction channels are made up of connexins, integral membrane proteins encoded by a multigene family. Rat testes contain mRNAs for at least five different connexins: Cx26, Cx32, Cx33, Cx37 and Cx43. Immunocytochemical studies have shown that Cx43 assembles gap junctions between Leydig cells. The present study investigated the expression and regulation of the Cx43 gene in rat Leydig cells. Purified Leydig cells were obtained from 40- to 80-day-old Sprague-Dawley rats using a combination of arterial perfusion, collagenase digestion, centrifugal elutriation and Percoll gradient centrifugation. Leydig cells from 20- and 30-day-old rats were isolated without arterial perfusion or centrifugal elutriation. Cx43 mRNA was present in 20-day-old rat Leydig cells, reached a plateau at day 40, and remained at high levels in 65- and 80-day-old rat Leydig cells. To evaluate the regulation of Cx43 gene expression, Leydig cells were cultured overnight and then treated with human chorionic gonadotropin (hCG) for variable periods of time. Addition of hCG (10 ng/ml) increased cytochrome P450 side-chain cleavage and steroidogenic acute regulatory protein mRNA levels and testosterone formation. However, Cx43 mRNA levels were inhibited by hCG in a time- and dose-dependent manner. Cx43 mRNA levels decreased 27% as early as 2 h after the addition of hCG and decreased 60% by 24 h. Treatment of Leydig cells with 8-bromo-cAMP (0.1 mM) for 6 and 24 h also reduced Cx43 mRNA levels by 36 and 56% respectively. Primary cultured Leydig cells stained strongly positive with anti-Cx43 monoclonal antibody. Treatment with hCG for 24 h reduced Cx43 signals and caused Cx43 to redistribute to the periphery of the cells. To evaluate the regulation of Cx43 in vivo, rats were treated with hCG (300 ng i.p.) and testes were removed 24 h later. Frozen section of testes revealed that these interstitial cells stained positive for 3beta-hydroxysteroid dehydrogenase (3beta-HSD) by histochemical staining and were positive for Cx43 by immunofluorescence staining. The adjacent seminiferous tubules stained only weakly positive for Cx43. Twenty-four hours after hCG treatment, 3beta-HSD activity increased while Cx43 immunostaining of Leydig cells was reduced. In conclusion, gap junction channels of Leydig cells are regulated by hCG both in vivo and in vitro. hCG increased Leydig cell steroidogenesis and steroidogenic enzyme mRNA levels but caused a redistribution of Cx43.

3-Hydroxysteroid Dehydrogenases↗

PubMed2000

Computational methods for gene expression-based tumor classification.

Gene expression profiles may offer more or additional information than classic morphologic- and histologic-based tumor classification systems. Because the number of tissue samples examined is usually much smaller than the number of genes examined, efficient data reduction and analysis methods are critical. In this report, we propose a principal component and discriminant analysis method of tumor classification using gene expression profile data. Expression of 2000 genes in 40 tumor and 22 normal colon tissue samples is used to examine the feasibility of gene expression-based tumor classification systems. Using this method, the percentage of correctly classified normal and tumor tissue was 87.0%. The combined approach using principal components and discriminant analysis provided superior sensitivity and specificity compared to an approach using simple differences in the expression levels of individual genes.

Analysis of Variance↗

PubMed2000

Inhibition of oncogene STAT3 phosphorylation by a prolactin antagonist, hPRL-G129R, in T-47D human breast cancer cells.

We have previously demonstrated that a hPRL antagonist (hPRL-G129R) was able to inhibit PRL induced breast cancer cell proliferation through induction of apoptosis. In the present study, we test the hypothesis that the inhibitory effect of hPRL-G129R in breast cancer cells occurs, at least in part, through the inhibition of oncogene STAT3 activation. We first demonstrated that STAT5 and STAT3 could be activated by either hGH or hPRL in T-47D breast cancer cells. Although the patterns of STAT5 activation by hGH and hPRL are similar, we observed a nearly 10-fold greater efficacy of hPRL in STAT3 activation as compared to that of hGH. More importantly, we have demonstrated that activation of STAT3 by hPRL could be inhibited by hPRL-G129R. Since T-47D cells coexpress GHR and PRLR, an attempt was made to dissect the molecular events mediated through hGHR or hPRLR using mouse L-cells expressing a single population of receptors (hGHR or hPRLR). To our surprise, only STAT5, not STAT3 phosphorylation was observed in these L-cells. In conclusion, our results suggest that: a) STAT3 is preferably activated through hPRLR in T-47D cells; b) hPRL-G129R is effective in inhibiting STAT3 phosphorylation; and c) the mechanism of STAT3 activation is different from that of STAT5.

Amino Acid Substitution↗

PubMed2000

Structural and functional properties of apolipoprotein A-I mutants.

Apolipoprotein (apo) A-I is composed of 243 amino acid residues that fold into amphipathic helixes, and plays a central role in the high density lipoprotein (HDL) metabolism. Familial apoA-I deficiency is a rare metabolic disorder of which three cases have been characterized at a molecular level in western Japan. However, in subjects with apoA-I deficiency, coronary artery disease was not always present. One apo A-I deficiency was compound heterozygous apoA-I mutant for a TATA box mutation and a structural nonsense mutation. To date, screening analysis in our laboratory has identified nine genetically-determined structural mutations of apo A-I. We have also characterized these apo A-I mutations, including apoA-I (Glu235del) Nichinan. Few structural mutations were associated with altered HDL cholesterol levels.

Apolipoprotein A-I↗