Biomedical subjects

L Zhao

Publications and source records attributed to L Zhao.

At least 19 recordsLinked to original sources

PubMed1997

Regulation of ion transport by histamine in mouse cecum.

Histamine levels are elevated in inflammatory bowel disease. We investigated the mechanism by which histamine affects electrolyte transport in the mouse cecum. Using the Ussing-chamber voltage clamp technique, histamine was found to cause a transient concentration-dependent increase in short-circuit current, a measure of total ion transport across the epithelial tissue. This increase was not affected by amiloride pretreatment, but was significantly inhibited by bumetanide and completely inhibited when chloride was substituted in the bathing buffer by gluconate. A histamine-induced increase in short-circuit current was also significantly reduced by inhibitors of the cyclooxygenase pathway indicating the involvement of prostaglandin E2 in its action. Prostaglandin E2 levels were increased in histamine treated tissue and this increase was reversed by indomethacin. These data suggest that histamine causes its effect on mouse cecum largely through increasing arachidonic acid metabolism resulting in increased levels of prostaglandins which in turn increase Cl- secretion in the epithelial cells.

Animals↗

PubMed1997

Direct and GTP-dependent interaction of ADP ribosylation factor 1 with coatomer subunit beta.

A site-directed photocrosslink approach was used to elucidate components that interact directly with ADP- ribosylation factor (ARF)-GTP during coat assembly. Two ARF mutants were generated that contain a photolabile amino acid at positions distant to each other within the ARF molecule. Here we show that one of the two positions specifically interacts with coatomer subunit beta both on Golgi membranes and in isolated coat protein complex type I (COPI)-coated vesicles. Thus, a direct and GTP-dependent interaction of coatomer via beta-coat protein complex (COP) with ARF is involved in the coating of COPI-coated vesicles. These data implicate a bivalent interaction of the complex with the donor membrane during vesicle formation.

ADP-Ribosylation Factors↗

PubMed1997

The human POLD1 gene. Identification of an upstream activator sequence, activation by Sp1 and Sp3, and cell cycle regulation.

The promoter of the human POLD1 gene encoding the catalytic subunit of DNA polymerase delta is G/C-rich and does not contain a TATA box. Transient transfection analysis in HeLa cells employing POLD1-luciferase chimeric plasmids revealed a core promoter region extending 328 base pairs (bp) from the major transcription initiation site. Multiple elements in this region including two 11-bp direct repeats located between nucleotide positions -92 and -22, play an important role in POLD1 promoter activity. Deletion or linker-replacement mutations of the repeats drastically reduced the promoter activity. A 70-bp DNA fragment containing the two repeats could stimulate the expression of the POLD1 or a heterologous promoter in an orientation-independent manner. DNase I footprinting and band-shift assays showed that HeLa nuclear extracts contained proteins specifically binding to the repeat sequences. Southwestern blot and UV cross-linking analyses identified Sp1 and two 85-kDa proteins that bound to the repeats. Additionally, screening of HeLa cDNA expression libraries for the sequence-specific DNA-binding protein using the 11-bp repeat sequences as the probe, identified a cDNA that corresponds to Sp3, a member of the Sp1 family. Cotransfection studies in Drosophila SL2 cells showed that both Sp1 and Sp3, but not Sp2, could activate the POLD1 promoter through the repeat sequences. The POLD1 promoter activity was induced about 4-fold at the late G1/S boundary in serum-stimulated cells. The 11-bp repeats together with an E2F-like sequence, located adjacent to the major transcription initiation site, were important for the stimulation. Taken together, this study provides a direct evidence for transcriptional regulation of the human POLD1 gene.

Base Sequence↗

PubMed1997

Activation of protein kinase C (alpha, beta, and zeta) by insulin in 3T3/L1 cells. Transfection studies suggest a role for PKC-zeta in glucose transport.

We presently studied (a) insulin effects on protein kinase C (PKC) and (b) effects of transfection-induced, stable expression of PKC isoforms on glucose transport in 3T3/L1 cells. In both fibroblasts and adipocytes, insulin provoked increases in membrane PKC enzyme activity and membrane levels of PKC-alpha and PKC-beta. However, insulin-induced increases in PKC enzyme activity were apparent in both non-down-regulated adipocytes and adipocytes that were down-regulated by overnight treatment with 5 microM phorbol ester, which largely depletes PKC-alpha, PKC-beta, and PKC-epsilon, but not PKC-zeta. Moreover, insulin provoked increases in the enzyme activity of immunoprecipitable PKC-zeta. In transfection studies, stable overexpression of wild-type or constitutively active forms of PKC-alpha, PKC-beta1, and PKC-beta2 failed to influence basal or insulin-stimulated glucose transport (2-deoxyglucose uptake) in fibroblasts and adipocytes, despite inhibiting insulin effects on glycogen synthesis. In contrast, stable overexpression of wild-type PKC-zeta increased, and a dominant-negative mutant form of PKC-zeta decreased, basal and insulin-stimulated glucose transport in fibroblasts and adipocytes. These findings suggested that: (a) insulin activates PKC-zeta, as well as PKC-alpha and beta; and (b) PKC-zeta is required for, and may contribute to, insulin effects on glucose transport in 3T3/L1 cells.

3T3 Cells↗

PubMed1997

Actin dynamics and organization during growth cone morphogenesis in Helisoma neurons.

Growth cone formation at the terminal region of severed axons is a fundamental step in neuronal regeneration. To understand the cytoskeletal events underlying this process, we have followed actin organization and dynamics as the severed, axonal stumps of Helisoma neurons transformed into mature growth cones. We identified three stages in growth cone morphogenesis: (1) formation, (2) expansion, and (3) maturation. The formation stage involved cytochalasin B-insensitive terminal swelling formation, followed by cytochalasin B-inhibited filopodial and lamellipodial formation. Time-lapse images of neurons injected with labeled actin showed actin ribs in nascent growth cones formed both by incorporation of filopodial actin bundles and de novo assembly at the leading edge. Phallacidin-stained growth cones revealed F-actin to be organized into bundles (ribs) and a meshwork throughout morphogenesis. Actin ribs represented the dominant F-actin population during the expansion stage and the early phase of maturation, whereas a meshwork organization dominated the late phase of maturation. During the expansion stage, growth cones exhibited a rapid retrograde flow (4.8 microns/min), as assessed with flow-coupled latex beads, and comparatively slow lamellipodial protrusion (0.3 micron/min). During the maturation stage, no net lamellipodial advancement occurred; however, the rate of retrograde flow was significantly faster in the early phase (5.0 microns/min) than the late phase (2.3 microns/min). This decrease in retrograde flow corresponded with a change in actin organization. Lateral movements of actin ribs (2.1 microns/min) also occurred throughout growth cone morphogenesis, but were most prominent during the expansion stage. These experiments provide evidence for de novo actin assembly during growth cone formation and demonstrate that temporal changes in actin organization and dynamics accompany growth cone morphogenesis.

Actins↗

PubMed1997

Role of inducible nitric oxide synthase in pharmacological "preconditioning" with monophosphoryl lipid A.

Pretreatment with monophosphoryl lipid A (MLA) can pharmacologically mimic the second window of ischemic preconditioning (SWOP) to protect the heart from prolonged ischemia and reperfusion injury. Based on the delayed time course for development of MLA associated cardioprotection, this study was designed to test if MLA's cardioprotective effect is mediated by signalling through production of inducible nitric oxide synthase (iNOS), a proposed effector of SWOP. Rabbits were assigned to one of four groups: (1) vehicle control; (2) MLA: (3) vehicle+aminoguanidine (AMG) control; or (4) MLA+AMG. Monophosphoryl lipid A (35 micrograms/kg) or vehicle was given intravenously 24 h before ischemia. The selective iNOS inhibitor AMG (300 mg/ kg) was injected subcutaneously 1 h before ischemia. All rabbits experienced 30 min coronary artery occlusion followed by 3 h of reperfusion. Infarct size was measured by triphenyltetrazolium chloride (TTC) staining. followed by 3 h of reperfusion. Infarct size was measured by triphenyltetrazolium chloride (TTC) staining. Myeloperoxidase activity, an index of neutrophil infiltration, was also quantified in heart tissue collected from the post-ischemic viable border zone surrounding the infarct area. MLA pretreatment significantly reduced infarct size and neutrophil infiltration in rabbit hearts compared to control (P < 0.05). Inhibition of iNOS activity by AMG abolished the infarct size reductive effect of MLA. Aminoguanidine also blocked the ability of MLA to significantly reduce neutrophil infiltration. Although measurement of iNOS activity did not show induction of the enzyme in normal myocardial tissue 24 h after MLA pretreatment, an increase in iNOS activity in ischemic tissue relative to non-ischemic tissue was found after either 15 or 30 min of coronary occlusion in MLA treated rabbits. These results suggest that MLA pretreatment may enhance iNOS enzyme activity by MLA during ischemia which may be responsible for the observed cardioprotection.

Adjuvants, Immunologic↗

PubMed1997

Immunostaining and transcriptional enhancement of interleukin-1 receptor type I in the rat dental follicle.

Interleukin-1alpha (IL-1alpha) enhances the gene expression of colony-stimulating factor-one (CSF-1) in dental follicle cells. In turn, CSF-1 appears to be a critical molecule in stimulating the cellular events of eruption that require the presence of the follicle. Chronologically, the maximal transcription and translation of CSF-1 in the follicle occurs early postnatally, followed by a decline later. Thus, in this study, immunostaining for the interleukin-1 receptor type I (IL-1RI) was used to determine if it paralleled the CSF-1 localization and chronology. The results showed that IL-1RI is primarily localized in the dental follicle, with maximal immunostaining early postnatally and a greatly reduced staining by day 10. In conjunction with this, molecules that enhance the gene expression of IL-1alpha epidermal growth factor (EGF) and transforming growth factor-beta1 (TGF-beta1) were also shown to enhance the expression of IL-1RI, but IL-1alpha did not increase the gene expression of IL-1RI. After injections of EGF at different times postnatally the mRNA of IL-1RI increased over comparable controls. Between days 2 and 5 the IL-1RI mRNA in the follicle decreased. In combination the results suggest that, as the expression of IL-1alpha is enhanced in the stellate reticulum either by EGF or TGF-beta1, these two molecules could also enhance the expression of IL-1RI in the dental follicle such that more receptors would be available to respond to the increased IL-1alpha secreted. The maximal presence of the receptors (IL-1RI) in the dental follicle early postnatally, followed by their subsequent decline, parallels the rise and fall of CSF-1 in the follicle. Thus, regulation of the IL-1RI and IL-1RI gene expression might be a means of regulating changes in CSF-1 in the follicle.

Aging↗

PubMed1997

Delivery of medication by iontophoresis to treat post-burn hypertrophic scars: investigation of a new electronic technique.

At present, direct current (DC) and pulsed direct current (PDC) methods are used for iontophoresis. Although the DC field has high efficiency, it exhibits some side-effects. The PDC field has little side-effects, but the efficiency is lower. In this study, a new iontophoretic drug device was designed for providing the maximal efficiency with the minimal side-effects. Tests of animal and human models showed that the permeation rate of the new field was higher than that of PDC and DC fields, and side-effects were lower than that of the DC field.

Administration, Cutaneous↗

PubMed1997

Coding mutations in p57KIP2 are present in some cases of Beckwith-Wiedemann syndrome but are rare or absent in Wilms tumors.

The Beckwith-Wiedemann syndrome (BWS) is marked by fetal organ overgrowth and conveys a predisposition to certain childhood tumors, including Wilms tumor (WT). The genetics of BWS have implicated a gene that maps to chromosome 11p15 and is paternally imprinted, and the gene encoding the cyclin-cdk inhibitor p57KIP2 has been a strong candidate. By complete sequencing of the coding exons and intron/exon junctions, we found a maternally transmitted coding mutation in the cdk-inhibitor domain of the KIP2 gene in one of five cases of BWS. The BWS mutation was an in-frame three-amino-acid deletion that significantly reduced but did not fully abrogate growth-suppressive activity in a transfection assay. In contrast, no somatic coding mutations in KIP2 were found in a set of 12 primary WTs enriched for cases that expressed KIP2 mRNA, including cases with and without 11p15.5 loss of heterozygosity. Two other 11p15.5 loci, the linked and oppositely imprinted H19 and IGF2 genes, have been previously implicated in WT pathogenesis, and several of the tumors with persistent KIP2 mRNA expression and absence of KIP2 coding mutations showed full inactivation of H19. These data suggest that KIP2 is a BWS gene but that it is not uniquely equivalent to the 11p15.5 "WT2" tumor-suppressor locus.

Beckwith-Wiedemann Syndrome↗

PubMed1997

Patients with cerebellar lesions cannot acquire but are able to retain conditioned eyeblink reflexes.

The purpose of these experiments was to examine the role of the human cerebellum in the acquisition and retention of conditioned reflexes. Normal human subjects and patients with cerebellar lesions were tested for their capacity to acquire, retain and express conditioned eyeblink responses. In acquisition tests, subjects were trained in a delay classical conditioning paradigm using a tone conditioned stimulus and a midline forehead tap as an unconditioned stimulus. While normal subjects developed anticipatory eyeblinks to the tone in one session, patients with cerebellar lesions failed to acquire conditioned responses in four consecutive training sessions. The conditioning deficit was bilateral even in patients with a unilateral cerebellar pathology. The same groups of subjects were tested for the presence of eyeblinks to a visual threat. In these experiments, both normal subjects and patients with cerebellar lesions exhibited a high level of responding when they saw an object approaching their face. These eyeblinks to the visual threat are probably naturally acquired conditioned responses because they extinguish in normal subjects if they are not reinforced by the unconditioned cutaneous stimulus. In addition, the stimulus of seeing an approaching object blocks the acquisition of classically conditioned eyeblinks to a new conditioned stimulus in normal subjects. These data imply that patients with cerebellar lesions who cannot acquire new classically conditioned responses are able to retain and express conditioned eyeblinks which were acquired before the onset of the pathology. Consequently, cerebellum-dependent neural substrates which are involved in learning new conditioned reflexes do not seem to be required for the storage of naturally learned conditioned responses.

Adult↗

PubMed1997

Recombinant advanced glycation end product receptor pharmacokinetics in normal and diabetic rats.

Vascular dysfunction in patients with diabetes mellitus is related to advanced glycation end product (AGE) formation. We previously showed that AGEs produce an increase in vascular permeability and generated an oxidant stress after binding to the receptor (RAGE) present on endothelium. RAGE, a 35-kDa protein that belongs to the immunoglobulin superfamily, has been cloned from a rat lung cDNA library, and recombinant rat soluble RAGE (rR-RAGE) has been produced in insect cells. The sequence of RAGE is highly conserved between human and rat. We studied the biological effect of rR-RAGE and pharmacokinetics of 125I-rR-RAGE after intravenous or intraperitoneal administration in normal and streptozotocin-induced diabetic rats. rR-RAGE prevented albumin or inulin transfer through a bovine aortic endothelial cell monolayer, restored the hyperpermeability observed in diabetic rats or induced in normal rats by diabetic rat red blood cells, and corrected the reactive oxygen intermediate production after intravenous or intraperitoneal administration. After intravenous injection of 125I-rR-RAGE, the distribution half-life was longer (p < or = 0.01) in diabetic (0.15 and 4.01 hr) than in normal (0.02 and 0.21 hr) rats, as was the case for the elimination half-lives (diabetic, 57.17 hr; normal, 26.02 hr; p < or = 0.01). Distribution volume was higher in diabetic than in normal rats (6.94 and 3.24 liter/kg, respectively; p = 0.049). Our study showed that rR-RAGE was biologically active in vivo and slowly cleared, which suggests it could be considered as a potential therapy.

Amino Acid Sequence↗

PubMed1997

Increased expression of transforming growth factor beta s after acute oedematous pancreatitis in rats suggests a role in pancreatic repair.

BACKGROUND: Transforming growth factor beta isoforms (TGF beta s) belong to a family of multifunctional regulators of cellular growth and differentiation. They are mitogenic and chemotactic for fibroblasts and are potent stimulators of extracellular matrix production (collagen) and deposition. Upregulation of TGF beta transcription has been reported for several in vivo systems during repair after injury. AIMS: To study the expression of the three mammalian isoforms of TGF beta (TGF beta 1-3) and their relation to collagen expression as a marker for fibroblast response in acute oedematous pancreatitis in rats. METHODS: Using northern blot analysis and immunohistochemistry, the expression and localisation of TGF beta isoforms, collagen, and amylase were analysed during the course of acute oedematous pancreatitis in rats, experimentally induced by intravenous caerulein infusion. RESULTS: Induction of acute pancreatitis resulted in a biphasic peak pattern of expression of TGF beta 1, beta 2, and beta 3 mRNA, with a pronounced increase from day 1 to day 3 (sixfold, 2.5-fold, fivefold, respectively) and again from day 5 to day 7 (three-fold, 2.3-fold, 3.5-fold, respectively). The temporal changes in TGF beta mRNA identically paralleled the expression in collagen mRNA. In contrast, amylase mRNA expression, used as a general indicator of acinar cell integrity, was slightly decreased after induction of acute pancreatitis. Immunohistochemical analysis of pancreatitis tissue showed that increased expression of TGF beta s was mainly present in the pancreatic acinar and ductal cells; this was evident within one day after pancreatitis induction. CONCLUSION: Overexpression of TGF beta s after induction of acute pancreatitis suggests a role for these proteins in pancreatic repair and remodelling. The increased levels of TGF beta s may help suppress immune activation, and may contribute to the increase in the extracellular matrix including collagen and to the repair of the pancreatic parenchyma.

Acute Disease↗

PubMed1997

IL-1 beta induces synthesis of phospholipase A2-activating protein in rabbit distal colon.

In inflammatory bowel disease, the colonic mucosa is infiltrated by inflammatory cells that secrete a variety of inflammatory mediators such as interleukin-1 beta (IL-1 beta). IL-1 beta caused a delayed increase in Cl- secretion and in prostaglandin E2 (PGE2) release in rabbit distal colon. Both of these effects were abolished with cycloheximide, implying a role for protein synthesis in mediating IL-1 beta's effect. With the use of Western blot assays, the protein was identified as the phospholipase A2 (PLA2)-activating protein (PLAP). IL-1 beta caused a concentration-dependent and a time-dependent increase in PLAP levels as well as in PLA2 activity, with the maximal increase observed at an IL-1 beta concentration between 10 and 30 ng/ml reached in 2-10 min. The PLAP mRNA levels were also regulated by IL-1 beta with a similar time course. PLAP is constitutively present in the epithelial cells and in the subepithelial layer of the distal colon. These findings suggest a direct effect of IL-1 beta on intestinal epithelial cells to cause an increase in PLAP levels and phospholipase A2 activity and subsequent increase in PGE2 levels.

Animals↗

PubMed1997

Disparate effects of preconditioning and MLA on 5'-NT and adenosine levels during coronary occlusion.

Ischemic preconditioning has been proposed to protect the heart against infarction by increasing 5'-nucleotidase (5'-NT) activities and augmenting adenosine levels during sustained coronary artery occlusion. To test this theory, anesthetized dogs received four 5-min episodes of preconditioning ischemia, pretreatment with the pharmacological "preconditioning mimetic" monophosphoryl lipid A (MLA, 35 micrograms/kg i.v.) or no intervention before coronary artery ligation. At 20 min into occlusion (the crucial time at which myocyte death begins in this model), myocardial samples were obtained for measurement (by high-performance liquid chromatography) of ectosolic and cytosolic 5'-NT activity and adenosine levels. Preconditioning and MLA pretreatment limit infarct size in the canine model by 75 and 50%, respectively. However, only MLA augmented 5'-NT activity [i.e., cytosolic 5'-NT in the ischemic subendocardium was 26 +/- 1, 39 +/- 7, and 26 +/- 6 nmol. mg protein-1. min-1 in preconditioned, MLA, and control groups (P < 0.05), respectively]. Moreover, adenosine levels (in nmol/mg protein) were increased with MLA treatment (2.30 +/- 0.44) but attenuated in preconditioned dogs (1.11 +/- 0.23; P < 0.05) versus controls (1.87 +/- 0.29). Thus 5'-NT and adenosine levels need not be increased beyond control values during sustained occlusion to elicit cardioprotection.

5'-Nucleotidase↗

PubMed1997

Localization and expression of CSF-1 receptor in rat dental follicle cells.

Colony-stimulating factor-1 (CSF-1) accelerates tooth eruption in rats and is localized in the dental follicle, a loose connective tissue sac that is necessary for eruption to occur. CSF-1 enhances the cellular events that occur in the follicle prior to eruption--namely, an influx of monocytes into the follicle early post-natally to form the osteoclasts needed to resorb bone for the eruption pathway. Because CSF-1 levels are at a peak at day 3 post-natally, and because CSF-1 has an autocrine effect on its own gene expression, the question remains as to what causes the subsequent decline in CSF-1 protein and mRNA after day 3 post-natally. To determine if the autocrine effect is inhibited through the CSF-1 receptor, analysis of the CSF-1 receptor mRNA levels in cultured dental follicle cells reveals that high concentrations of CSF-1 reduce the gene expression of the CSF-1 receptor. Interleukin 1 alpha, a molecule that enhances CSF-1 gene expression, has no effect on CSF-1 receptor mRNA levels. Immunostaining for the CSF-1 receptor protein shows that it is present in the dental follicle early post-natally and is either absent or greatly reduced by day 10 post-natally. Earlier studies showed that the mRNA levels of the CSF-1 receptor also parallel this time course. Thus, the above results suggest that the feedback inhibition of the autocrine effect of CSF-1 on its own expression is through the effect of CSF-1 inhibiting the translation and transcription of its receptor. In turn, these molecular interactions possibly regulate the cellular events that occur in the follicle prior to and during eruption.

Animals↗

PubMed1997

Comparison of two enzyme-linked immunosorbent assay tests for diagnosis of Helicobacter pylori infection in China.

An ELISA based on a pool of United States strains of Helicobacter pylori was compared with a newly developed ELISA based on a pool of Chinese strains. Both assays were tested using sera from 132 Chinese study subjects with biopsy-proven H. pylori infection. Using cutpoints designed to yield equal specificities of 94.9% in an uninfected control population, the sensitivity of the Chinese assay was 100.0%, compared to 97.7% for the United States assay (P = 0.25 by McNemar test). These results suggest that a H. pylori assay based on pooled antigens from United States strains will perform as well in the rural Chinese population as one based on antigens from Chinese strains.

Adult↗

PubMed1997

[Study on particle contamination produced by syringe needles and rubber stoppers for pharmaceutical solutions].

The contamination of particles produced by syringe needles and rubber stoppers for pharmacal solution of venous transfusion was studied. The results showed that the contamination of particles was positive correlation with the usage frequency of syringe needles, so the syringe needles for single use were suggested. To compare two kinds of syringe needles with different structure (side hole and incline), the result was that the difference of particle contamination between them was similar and without statistic significance. The particles contamination produced by primary and used rubber stoppers which was protected by polyester film was studied. It was shown that the difference between them was no significant statistically. The results of this study supplyed a scientific evidence about repeated use of rubber stoppers.

Drug Contamination↗

PubMed1996

Evidence from Earthquake Data for a Partially Molten Crustal Layer in Southern Tibet

Earthquake data collected by the INDEPTH-II Passive-Source Experiment show that there is a substantial south to north variation in the velocity structure of the crust beneath southern Tibet. North of the Zangbo suture, beneath the southern Lhasa block, a midcrustal low-velocity zone is revealed by inversion of receiver functions, Rayleigh-wave phase velocities, and modeling of the radial component of teleseismic P-waveforms. Conversely, to the south beneath the Tethyan Himalaya, no low-velocity zone was observed. The presence of the midcrustal low-velocity zone in the north implies that a partially molten layer is in the middle crust beneath the northern Yadong-Gulu rift and possibly much of southern Tibet.

Journal Article↗