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Biomedical subjects

L Xu

Publications and source records attributed to L Xu.

At least 271 records · Page 15Linked to original sources
PubMed2000

Neuronal nitric oxide synthase and systemic vasodilation in rats with cirrhosis.

Cirrhosis is typically associated with a hyperdynamic circulation consisting of low blood pressure, low systemic vascular resistance (SVR), and high cardiac output. We have recently reported that nonspecific inhibition of nitric oxide synthase (NOS) with nitro-L-arginine methyl ester reverses the hyperdynamic circulation in rats with advanced liver cirrhosis induced by carbon tetrachloride (CCl(4)). Although an important role for endothelial NOS (eNOS) is documented in cirrhosis, the role of neuronal NOS (nNOS) has not been investigated. The present study was carried out to specifically investigate the role of nNOS during liver cirrhosis. Specifically, physiological, biochemical, and molecular approaches were employed to evaluate the contribution of nNOS to the cirrhosis-related hyperdynamic circulation in CCl(4)-induced cirrhotic rats with ascites. Cirrhotic animals had a significant increase in water and sodium retention. In the aorta from cirrhotic animals, both nNOS protein expression and cGMP concentration were significantly elevated compared with control. Treatment of cirrhotic rats for 7 days with the specific nNOS inhibitor 7-nitroindazole (7-NI) normalized the low SVR and mean arterial pressure, elevated cardiac index, and reversed the positive sodium balance. Increased plasma arginine vasopressin concentrations in the cirrhotic animals were also repressed with 7-NI in association with diminished water retention. The circulatory changes were associated with a reduction in aortic nNOS expression and cGMP. However, 7-NI treatment did not restore renal function in cirrhotic rats (creatinine clearance: 0.76 +/- 0.03 ml. min(-1). 100 g body wt(-1) in cirrhotic rats vs. 0.79 +/- 0.05 ml. min(-1). 100 g body wt(-1) in cirrhotic rats+7-NI; P NS. ). Taken together, these results indicate that nNOS-derived NO contributes to the development of the hyperdynamic circulation and fluid retention in cirrhosis.

Animals↗
PubMed2000

Pulmonary expression of early growth response-1: biphasic time course and effect of oxygen concentration.

Hypoxia induces complex adaptive responses. In this report, induction of early growth response-1 (Egr-1) transcripts in lungs of mice subjected to hypoxia is shown to be dose and time dependent. Within 30 min of hypoxia, Egr-1 transcripts were approximately 20-fold elevated in 6% oxygen, approximately 5.2-fold increased by 10% oxygen, and returned to the normoxic baseline by 12% oxygen. Time course studies up to 48 h showed a biphasic profile with an initial steep rise in Egr-1 transcripts after 0.5 h of hypoxia and a second elevation beginning after 20-24 h. Hypoxic induction of Egr-1 was paralleled by enhanced expression of the downstream target gene tissue factor. Egr-1 and tissue factor antigen were visualized in bronchial and vascular smooth muscle and in alveolar macrophages. Egr-1 has the capacity to modulate expression of genes involved in the remodeling of the extracellular matrix and properties of smooth muscle, thus possibly contributing to the pulmonary response to chronic hypoxia.

Animals↗
PubMed2000

Aging reduces adaptive capacity and stress protein expression in the liver after heat stress.

A decline in an organism's ability to cope with stress through acute response protein expression may contribute to stress intolerance with aging. We investigated the influence of aging on stress tolerance and the capacity to synthesize the 70-kDa heat shock protein (HSP70) in young and old rats exposed to an environmental heating protocol. Livers were assessed for injury and HSP70 expression after heat stress by use of immunohistochemical and immunoblotting techniques. The inducible HSP70 response in the cytoplasm and nucleus was markedly reduced with age at several time points over a 48-h recovery period, although senescent rats were able to strongly express HSP70 early in recovery. Older animals had extensive zone-specific liver injury, which corresponded to the diminished HSP70 response observed in these regions, and a significant reduction in thermotolerance compared with their young counterparts. These data highlight the regional nature of stress-induced injury and HSP70 expression in the liver and the impact of aging on these responses. Furthermore, the results suggest a functional link between the age-related decrements in the expression of inducible HSP70 and the pathophysiological responses to heat stress.

Adaptation, Physiological↗
PubMed2000

Inhaled budesonide inhibits OVA-induced airway narrowing, inflammation, and cys-LT synthesis in BN rats.

The objective of the present investigation was to examine the effects of an inhaled glucocorticoid, budesonide, on antigen-induced production of cysteinyl leukotrienes (cys-LTs) and pulmonary inflammatory cell infiltration in the Brown Norway rat, an animal model of asthma. Two weeks after sensitization to ovalbumin, rats were treated with budesonide (2.5 mg/kg) 18 and 1 h before challenge with antigen. Budesonide abolished the late response to ovalbumin (P<0.02) and strongly inhibited the in vivo synthesis of N-acetyl-leukotriene E(4), an indicator of cys-LT synthesis, during this period (P<0.005). Both total bronchoalveolar lavage (BAL) cells (P<0.01) and BAL macrophages (P<0.005) were markedly reduced to approximately 25% of their control levels after treatment with budesonide. It can be concluded that inhibition of the antigen-induced late response in Brown Norway rats by budesonide is associated with reductions in both BAL macrophages and cys-LT synthesis. It is possible that the effect of budesonide on cys-LT synthesis is related to its effects on pulmonary macrophages.

Administration, Inhalation↗
PubMed2000

Asymptotic convergence rate of the EM algorithm for gaussian mixtures

It is well known that the convergence rate of the expectation-maximization (EM) algorithm can be faster than those of convention first-order iterative algorithms when the overlap in the given mixture is small. But this argument has not been mathematically proved yet. This article studies this problem asymptotically in the setting of gaussian mixtures under the theoretical framework of Xu and Jordan (1996). It has been proved that the asymptotic convergence rate of the EM algorithm for gaussian mixtures locally around the true solution Theta* is o(e(0. 5-epsilon)(Theta*)), where epsilon > 0 is an arbitrarily small number, o(x) means that it is a higher-order infinitesimal as x --> 0, and e(Theta*) is a measure of the average overlap of gaussians in the mixture. In other words, the large sample local convergence rate for the EM algorithm tends to be asymptotically superlinear when e(Theta*) tends to zero.

Journal Article↗
PubMed2000

Identification of human lung and skin proteins conjugated with hexamethylene diisocyanate in vitro and in vivo.

Diisocyanates are asthma-causing chemicals used in the commercial production of polyurethane. We have previously shown that human lung epithelial cell proteins can become conjugated with hexamethylene diisocyanate (HDI) and may be biologically important in diisocyanate-induced asthma. The objective of this study was to identify specific human lung and skin proteins that become conjugated with diisocyanate after in vitro and in vivo exposure. Following in vitro exposure of human airway epithelial cells (A549), keratin 18, the 78-kD glucose-regulated protein, trans-1, 2-dihyrobenzene-1,2-diol dehydrogenase, and actin were identified as prominent diisocyanate-conjugated proteins through use of a combination of immunocytochemical and mass spectrometric techniques. Following in vivo inhalation of an HDI aerosol, keratin 18 was also identified as the predominant diisocyanate-conjugated protein in human endobronchial biopsy samples, whereas albumin was the predominant diisocyanate-conjugated protein in bronchoalveolar lavage fluid. Keratin was also identified as a predominant diisocyanate-conjugated protein in human skin biopsy samples after epicutaneous exposure to liquid-phase HDI, although the major skin diisocyanate-conjugated protein (56-kD) differed from the predominant lung diisocyanate-conjugated keratin (47-kD). The data from this study identify keratin and other proteins as potential "carriers" for diisocyanates in vivo, and suggest that HDI conjugation of these proteins may play a role in the pathogenesis of diisocyanate-induced asthma.

Adult↗
PubMed2000

Formation of corneal endothelium is essential for anterior segment development - a transgenic mouse model of anterior segment dysgenesis.

The anterior segment of the vertebrate eye is constructed by proper spatial development of cells derived from the surface ectoderm, which become corneal epithelium and lens, neuroectoderm (posterior iris and ciliary body) and cranial neural crest (corneal stroma, corneal endothelium and anterior iris). Although coordinated interactions between these different cell types are presumed to be essential for proper spatial positioning and differentiation, the requisite intercellular signals remain undefined. We have generated transgenic mice that express either transforming growth factor (alpha) (TGF(alpha)) or epidermal growth factor (EGF) in the ocular lens using the mouse (alpha)A-crystallin promoter. Expression of either growth factor alters the normal developmental fate of the innermost corneal mesenchymal cells so that these cells often fail to differentiate into corneal endothelial cells. Both sets of transgenic mice subsequently manifest multiple anterior segment defects, including attachment of the iris and lens to the cornea, a reduction in the thickness of the corneal epithelium, corneal opacity, and modest disorganization in the corneal stroma. Our data suggest that formation of a corneal endothelium during early ocular morphogenesis is required to prevent attachment of the lens and iris to the corneal stroma, therefore permitting the normal formation of the anterior segment.

Animals↗
PubMed2000

Authentication of an animal crude drug, Zaocys, by diagnostic PCR.

A pair of diagnostic primers for distinguishing the Chinese crude drug Zaocys (Zaocys dhumandes) from its substitutes was designed based on the sequence data of the original animal of the drug and substitutes. Total DNAs were extracted from genuine crude drug and 5 of its substitutes, as well as from 12 species of original animal of the snake crude drug. Diagnostic PCRs were performed using the primers with these total DNAs as a template, annealing at 60-65 degrees C. Positive amplifications were obtained from all DNA templates of Zaocys, whereas negative amplifications were obtained from that of others. The results indicate that Zaocys samples could be definitely distinguished from its substitutes by diagnostic PCR, and no incorrect discrimination was found under the same reaction conditions. The advantages of the method in the authentication of crude drugs are also discussed in the present paper.

Animals↗
PubMed2000

Interleukin 8: an autocrine growth factor for human ovarian cancer.

We determined whether interleukin-8 (IL-8) plays a direct role in the progressive growth of ovarian cancer cells by isolating high- and low-IL-8-producing clones from the parental Hey-A8 human ovarian cancer cell line and compared their proliferative activity and tumorigenicity in nude mice. The effect of exogenous IL-8 and mouse antihuman IL-8 neutralizing antibody on ovarian cancer cell proliferation was investigated. Finally, we studied the modulation of IL-8 production in ovarian cancer cells by sense and antisense IL-8 expression vector transfection and its effect on proliferation. The Hey-A8(H) clone was selected for its overexpression of IL-8. It has a significantly higher proliferation rate than the low-IL-8-producing clone, Hey-A8(L). Recombinant IL-8 (50 ng/ml) caused a significant increase in proliferation of Hey-A8(L) clones, and 10 microg/ml neutralizing antibody against IL-8 significantly decreased proliferative activity of both Hey-A8(H) and Hey-A8(L) clones. Enforced IL-8 expression by IL-8 expression vector transfection in Hey-A8(L) clones significantly increased tumor cell proliferation, microvessel density, and hence, tumorigenicity. We conclude that IL-8 has a direct and indirect growth-potentiating activity in human ovarian cancer cells.

Animals↗
PubMed2000

Inhibition of malignant ascites and growth of human ovarian carcinoma by oral administration of a potent inhibitor of the vascular endothelial growth factor receptor tyrosine kinases.

We determined whether inhibition of the catalytic tyrosine kinase activity of the receptors for vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) inhibits the formation of malignant ascites and the progressive growth of human ovarian carcinoma cells implanted into the peritoneal cavity of nude mice. The novel protein tyrosine inhibitor PTK 787 was evaluated in two models of human ovarian cancer: Hey-A8 cells, which express low levels of VEGF/VPF and grow as solid tumor foci on the surface of peritoneal organs, and SKOV3 i.p.1 cells, which express high levels of VEGF/VPF and grow as solid peritoneal tumors and ascites. Treatment of nude mice by daily oral administration of 50 mg/kg PTK 787 was not effective against Hey-A8 tumors. In sharp contrast, it significantly inhibited growth of SKOV3 i.p.1 cells and formation of ascites, significantly increasing survival of mice with the implants. Tumor-induced vascular hyperpermeability in the peritoneum of tumor-bearing mice was inhibited by PTK 787, which accounted for its inhibition of ascites formation. Our results suggest that blockade of the VEGF/VPF receptor may be an efficient strategy to inhibit formation of malignant ascites and growth of VEGF/VPF-dependent human ovarian carcinomas.

Administration, Oral↗
PubMed2000

Effect of mibefradil on voltage-dependent gating and kinetics of T-type Ca(2+) channels in cortisol-secreting cells.

We have studied the effect of the Ca(2+) antagonist mibefradil on low voltage-activated T-type Ca(2+) channels in whole-cell patch clamp recordings from bovine adrenal zona fasciculata (AZF) cells. AZF cells are distinctive in expressing only T-type Ca(2+) channels, allowing the mechanism of pharmacological agents to be explored without interference from other Ca(2+) channels. The inhibition of T-type Ca(2+) channels by mibefradil was voltage- and use-dependent. When Ca(2+) currents were activated from holding potentials of -80 and -60 mV, mibefradil inhibited currents with IC(50) values of 1.0 and 0.17 microM, respectively. When T-type Ca(2+) current (I(T)) was activated from a holding potential of -90 mV in the presence of 2 microM mibefradil, a single voltage step to -10 mV inhibited I(T) by 16.2% +/- 2.9% (n = 10). With subsequent voltage steps, applied at 10-s intervals, block reached a steady-state value of 51.9% +/- 5.0% (n = 5). Mibefradil (1 microM) produced a leftward shift of 5.7 mV (n = 4) in the voltage-dependent steady-state availability curve such that T-type Ca(2+) channels inactivated at more negative potentials, but this drug did not change the voltage-dependence of T channel opening. Mibefradil failed to alter the kinetics of T channel activation, inactivation, or deactivation, but markedly slowed T channel recovery following an inactivating prepulse. Mibefradil inhibited adrenocorticotropin-stimulated cortisol secretion from AZF cells with an IC(50) value of 3.5 microM. These results show that mibefradil is a relatively potent antagonist of T-type Ca(2+) channels in cortisol-secreting cells. The enhanced potency of mibefradil with sustained or repetitive depolarizations, its shifting of the steady-state inactivation curve, and its slowing of recovery all indicate that this drug preferentially interacts with Ca(2+) channels in the open or inactivated state. The inhibition of cortisol secretion by mibefradil at concentrations similar to those that block I(T) is consistent with a requirement for these channels in corticosteroidogenesis.

Adrenocorticotropic Hormone↗
PubMed2000

Immunohistochemical analyses of focal adhesion kinase expression in benign and malignant human breast and colon tissues: correlation with preinvasive and invasive phenotypes.

The focal adhesion kinase (FAK) is a protein tyrosine kinase linked to signaling events between cells and the extracellular matrix. Studies at the Western blot level have demonstrated up-regulation of FAK expression in invasive breast and colon cancers. To assess p125FAK expression at the cellular level, we developed monoclonal antibodies that specifically detected FAK in formalin-fixed, paraffin-embedded tissue sections and analyzed the levels of FAK expression in human breast and colon tissues. Monoclonal antibody 4.47 demonstrated FAK-specific focal adhesion staining by immunofluorescence assays on BT-474 breast cancer cells and detected a Mr 125,000 protein by both Western blotting and immunoprecipitation analyses. Using immunohistochemical techniques, the expression of p125FAK was analyzed in 36 normal and 43 preinvasive or invasive human breast and colon tissues from individual patients. FAK was weakly expressed in most benign breast epithelium but was up-regulated at moderate or strong levels in 14 of 18 invasive breast carcinomas. In seven samples of ductal carcinoma-in situ, FAK was overexpressed. Borderline-to-weak expression of FAK was detected in the normal colonic epithelium. In the invasive colon cancers, FAK was overexpressed at moderate or strong levels in 13 of 15 tumors. Furthermore, FAK expression was up-regulated in areas of dysplastic, premalignant colon epithelium. These results provide the first evidence at the cellular level that FAK expression is variably overexpressed in breast and colon cancer and suggest that up-regulation occurs at an early stage of tumorigenesis.

Animals↗
PubMed2000

Antineoplastic effect of intracellular expression of a single-chain antibody directed against type IV collagenase.

It has been shown that the type IV collagenase with its two subtypes, 72 kDa/ MMP-2 and 92 kDa/MMP-9, plays an important role in tumor invasion and metastasis formation that occur through a mechanism of proteolytic degradation of collagen IV in the basement membrane. One possible method to specifically inhibit the function of the targeted protein of a cell is to express intracellular antibody combining site that can block the function or prevent the expression of the targeted molecule. Accordingly, intracellular antibodies against type IV collagenase may have a therapeutic use against tumor invasion and metastasis. As described in our previous reports, an anti-type IV collagenase monoclonal antibody (3D6) was obtained using the hybridoma approach, and its functional single-chain Fv fragment (scFv) named M97 was constructed based on recombinant phage display techniques. In this study, the endoplasmic reticulum (ER)-retained scFv antibody fragment was used to inhibit the function of type IV collagenase. For expression in mammalian cells, the assembled scFv M97 gene with ER retention signal encoding 6 additional amino acid (SEKDEL) was reamplified by PCR. The amplified fragments were cloned into the pcDNA3.1 vector containing the CMV early-intermediate promoter/enhancer. The resulting plasmid was sequenced and then introduced by the lipofectamine method into PG cells, a highly metastatic human lung cancer cell line and G418-resistant cells were obtained by G418 selection. After transfection, the M97 mRNA expression was observed and the type IV collagenase expression was downregulated significantly as measured by ELISA. The biological behavior of PG cells, such as the ability of in vitro invasion of colony formation on soft agar through Matrigel, were also inhibited by scFv M97 transfection. The results indicate that intracellular antibody technology represents a novel and efficient way to selectively abrogate the activity of type IV collagenase, at least in vitro. We are presently exploring the efficacy of this approach in a xenograft model of human lung cancer.

3T3 Cells↗
PubMed2000

Study on polymorphism of MICA exon 5 microsatellite in Shanghai Han population.

OBJECTIVE: To investigate the polymorphism distribution of MICA gene exon 5 microsatellite in Shanghai Han population and study the relationship of MICA gene and its closely linked gene HLA B. METHODS: The microsatellite polymorphism of MICA exon 5 in 175 unrelated healthy individuals were investigated using PCR-heteroduplex analysis. RESULTS: (1)There are 5 alleles of the microsatellite polymorphism in exon 5 of the MICA gene in Shanghai Han population, the gene frequency of MICA*A5 is the highest(39.14%), the next is MICA*A5.1(22.29%). (2)There is strong linkage disequilibrium between the HLA-B and MICA STR loci, e.g. MICA*A5 and HLA-B15, MICA*A4 and HLA-B27. CONCLUSION: The polymorphism distribution of MICA gene and the linkage disequilibrium between MICA and HLA-B have deviations in different ethnic groups.

China↗