Biomedical subjects

L Xu

Publications and source records attributed to L Xu.

At least 505 records · Page 28Linked to original sources

PubMed1997

RBI-257: a highly potent dopamine D4 receptor-selective ligand.

RBI-257 (1-[4-iodobenzyl]-4-[N-(3-isopropoxy-2-pyridinyl)-N-methyl]-aminopiperid ine), the p-iodobenzyl analog of U-101,958 (1-benzyl-4-[N-(3-isopropoxy-2-pyridinyl)-N-methyl]-aminopiperidine) had a lower dissociation constant (Ki = 0.3 vs. 2.7 nM) and higher selectivity than U-101,958 at dopamine D4 receptors, over dopamine D2 and D3 receptors in transfected cell membranes and D2-like sites in rat forebrain. Dopamine D4 receptor affinity of iodo-isomers of RBI-257 ranked: para > meta > ortho. RBI-257 had much lower affinity at D1 and D5 dopamine receptors in transfected cells, as well as dopamine D1-like receptors, alpha1, alpha2 or beta(1,2) adrenoceptors, sigma(1,2) receptors and 5-HT1A or 5-HT2A receptors, and transporters for dopamine, norepinephrine or serotonin in rat forebrain tissue. RBI-257 may be a useful probe or radioligand for brain dopamine D4 receptors.

Aminopyridines↗

PubMed1997

Fractal Dimensions of Coals and Cokes

Using adsorption data, we get formulas for the calculation of fractal dimensions: log[A CO2 (DP) /A N2 (BET) ] = -5.3984(2 - D 1 )/2 and log[A CO2 (BET) /A N2 (BET) ] = -4.9569(2 - D 2 )/2. The fractal dimensions (D ) of 27 coals and 2 cokes have been obtained. The D of coals decreased with the increase of fa and reached a maximum at H/C equal to 0.66 (or C daf about 86%). The fractal dimension is relative to ash and volatiles of coal: D = 2.2237 + 0.6249V daf + 0.8863A d . The relationship between D of coal coke and its conversions (X ) obeys the following equation: D = a exp(-bX ) + c .

Journal Article↗

PubMed1997

Behavioural stress facilitates the induction of long-term depression in the hippocampus.

The induction of activity-dependent persistent increases in synaptic efficacy, such as long-term potentiation (LTP), is inhibited by behavioural stress. The question arises whether stress also affects the ability to induce persistent decreases in synaptic efficacy, such as long-term depression (LTD). We now report that the induction of stable homosynaptic LTD in the CA1 area of the hippocampus of awake adult rats is facilitated, rather than inhibited, by exposure to mild naturalistic stress. The same stress blocked the induction of LTP. The effects of such stress were short lasting: acclimatization to, or removal from, the conditions that facilitated LTD induction led to a rapid loss of the ability to elicit this form of plasticity. The time window in which LTD could be reliably elicited was prolonged by inducing anaesthesia immediately after the stress. These data reveal that even brief exposure to mild stress can produce a striking shift in the susceptibility to synaptic plasticity in the awake animal.

Animals↗

PubMed1997

Transduction of cytosine deaminase gene makes rat glioma cells highly sensitive to 5-fluorocytosine.

To investigate the potential use of E. coli cytosine deaminase (CD) gene instead of the commonly used HSV-TK gene in the gene therapy of brain tumors, we constructed a retrovirus vector carrying the CD gene. We then transduced a rat glioma cell line C6 with CD gene by the retrovirus vector. Transduction of the CD gene made C6 cells become highly sensitive to the anti-fungi drug 5-fluorocytosine (5FC). IC50 for 5FC was 6,000 microM in CD-negative cells, while it was 3 microM in CD-positive cells. Mixed cellular assay showed that CD-positive cells had a strong "bystander effect" on CD-negative cells when exposed to 5FC. Significant anti-tumor effects were observed in nude mice bearing s.c. tumors derived from CD-positive cells when these animals were given 250 mg/kg 5FC twice a day for 20 consecutive days. A marked decrease in tumor weight occurred when a mixture containing 50% CD-positive and 50% CD-negative C6 cells was injected s.c., followed by 5FC treatment, suggesting the bystander effect in vivo. Concerning the pharmacokinetics of 5FC, especially its high oral bio-availability and good penetration into cerebrospinal fluid, we suppose that the combination of CD-gene transfer and 5FC oral administration may have potential use in the gene therapy of brain tumors.

Animals↗

PubMed1997

Pharmacology of ABT-491, a highly potent platelet-activating factor receptor antagonist.

ABT-491 (4-ethynyl-N, N-dimethyl-3-[3-fluoro-4-[(2-methyl-1H-imidazo-[4,5-c]pyridin-1-yl)methy l]benzoyl]-1H- indole-1-carboxamide hydrochloride) is a novel PAF (platelet-activating factor) receptor antagonist with a K(i) for inhibiting PAF binding to human platelets of 0.6 nM. Binding kinetics of ABT-491 to the PAF receptor is consistent with a relatively slow off-rate of the antagonist when compared to PAF. Inhibition of PAF binding is selective and is correlated with functional antagonism of PAF-mediated cellular responses (Ca2+ mobilization, priming, and degranulation). Administration of ABT-491 in vivo leads to potent inhibition of PAF-induced inflammatory responses (increased vascular permeability, hypotension, and edema) and PAF-induced lethality. Oral potency (ED50) was between 0.03 and 0.4 mg/kg in rat, mouse, and guinea-pig. When administered intravenously in these species, ABT-491 exhibited ED50 values between 0.005 and 0.016 mg/kg. An oral dose of 0.5 mg/kg in rat provided > 50% protection for 8 h against cutaneous PAF challenge. ABT-491 administered orally was also effective in inhibiting lipopolysaccharide-induced hypotension (ED50 = 0.04 mg/kg), gastrointestinal damage (0.05 mg/kg, 79% inhibition), and lethality (1 mg/kg, 85% vs. 57% survival). The potency of this novel antagonist suggests that ABT-491 will be useful in the treatment of PAF-mediated diseases.

Acute Disease↗

PubMed1997

Effect of the histone deacetylase inhibitor trichostatin A on the responsiveness of rat hepatocytes to dioxin.

Since histone acetylation has been implicated in the facilitation of specific gene transcription, we investigated the effect of increasing histone acetylation through inhibition of histone deacetylase on 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induction of P4501A activity in cultured rat hepatocytes. Inhibition of histone deacetylation was accomplished with addition of trichostatin A (TSA) to the incubation medium, and P4501A activity was measured spectrofluorometrically by determination of the rate of resorufin formation by ethoxyresorufin-O-deethylase (EROD). While TSA alone (5-200 ng/mL) had no effect on EROD activity, TSA potentiated the effect of various concentrations (10(-12) to 10(-10) M) of TCDD. Addition of 200 ng TSA/mL with TCDD resulted in an increased EROD activity of approximately 200% compared with TCDD alone. When TSA was removed from the cells after various incubation times (2, 6, 24 hr) by successive washings with TSA-free medium, it was determined that TSA was required for 24 hr in order to potentiate the effects of a 48-hr incubation with TCDD. In addition to measurement of EROD activity, P4501A1 and 1A2 microsomal protein were determined by western immunoblotting analysis. While neither P4501A1 nor 1A2 was detectable in the presence of TSA alone, P4501A1 was present after incubation of cells with TCDD in the presence or absence of TSA. TCDD plus TSA also resulted in the formation of P4501A2. The results of this study suggest an important role for histone acetylation in the action of TCDD on induction of P4501A enzymes.

Animals↗

PubMed1997

Effect of repeated ipsapirone treatment on hippocampal excitatory synaptic transmission in the freely behaving rat: role of 5-HT1A receptors and relationship to anxiolytic effect.

The effects of acute and repeated treatment with the 5-HT1A receptor ligand ipsapirone on hippocampal excitatory synaptic transmission and in an ultrasonic vocalization anxiety test were investigated in the rat. Synaptic responses in the CA1 region of the dorsal hippocampus of alert, freely behaving male Wistar rats were reduced after acute injection of ipsapirone (1 or 2 mg/kg, i.p.). This effect was prevented by pretreatment with the 5-HT1A receptor antagonist WAY-100635 (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclo-hexanecarboxamide trihydrochloride, 0.25 or 0.5 mg/kg, i.p.) but not by the 5-HT-depleting agent para-chlorophenylalanine (300 mg/kg per day for 3 days, i.p.). WAY-100635 (0.1-0.3 mg/kg, i.p.) also blocked the acute anti-aversive effects of ipsapirone (3 mg/kg, i.p.) in the anxiety test. Repeated administration of ipsapirone (1 or 2 mg/kg per day for 7-8 days, i.p.) produced a gradual reduction in baseline synaptic transmission which was transiently reversed by WAY-100635 (0.25 mg/kg, i.p.). Ipsapirone (1 mg/kg per day for 7 days) produced a gradual and sustained reduction in the duration of vocalizations in the anxiety test which paralleled the reduction in baseline synaptic responses in the same animals. The data indicate that with repeated administration of ipsapirone, a prolongation and enhancement of the 5-HT1A receptor-mediated reduction in hippocampal excitatory synaptic transmission occurs. This delayed effect may contribute to the sustained anxiolytic and/or antidepressant effect of ipsapirone.

Animals↗

PubMed1997

Synthesis, dopamine transporter affinity, dopamine uptake inhibition, and locomotor stimulant activity of 2-substituted 3 beta-phenyltropane derivatives.

A series of 2 beta-substituted 3 beta-phenyltropanes were synthesized as analogs of cocaine and tested in vitro for their ability to displace bound [3H]WIN 35,428 (2b) and inhibit dopamine uptake in rat caudate-putamen tissue. The analogs bound with high affinity (Ki = 11-22 nM) to the dopamine transporter. Increased lipophilicity at the beta-C(2)-position was found to lead to increased binding affinity and increased dopamine uptake potency. However, a direct correlation between clogP values and binding affinity and potency of uptake inhibition was not observed. The unsaturated ester 7 was found to possess weak dopamine uptake inhibition relative to the high binding affinity (IC50/Ki = 10.2). In vivo measurement of stimulated locomotor activity and drug discrimination against cocaine (10 mg/kg, ip) with selected analogs (4, 6, and 7) demonstrated that the behavioral effects of these drugs were approximately equipotent with those of cocaine. The structure-activity relationships of this series of cocaine analogs supports a pharmacophore model in which lipophilic interactions between the beta-C(2)-position of 3 beta-phenyltropanes and the cocaine binding site on the dopamine transporter lead to enhanced potency while electrostatic interactions have a nonspecific effect.

Animals↗

PubMed1997

HSP70 protects murine astrocytes from glucose deprivation injury.

Expression of the 70 kDa heat shock protein (HSP70) induced by a first insult is associated with protection from a subsequent ischemic insult in brain. Expression of the human inducible HSP70 was previously shown to protect astrocytes in primary culture from combined oxygen-glucose deprivation. These studies have now been extended to demonstrate that HSP70 expression also protects from isolated glucose deprivation. Slight protection was seen against hydrogen peroxide (H2O2) exposure. Glutathione levels decrease less after glucose deprivation or H2O2 exposure (200 microM) in the cells overexpressing HSP70, compared to either beta-galactosidase expressing or uninfected controls (P < 0.01). These data suggest that the HSP70-expressing cells suffered less oxidative stress since their glutathione levels were better preserved.

Animals↗

PubMed1997

Transferrin-liposome-mediated p53 sensitization of squamous cell carcinoma of the head and neck to radiation in vitro.

Wild-type (wt) p53 DNA was transfected into the radioresistant human cell line JSQ-3, established from a squamous cell carcinoma of the head and neck (SCCHN), using a transferrin-liposome system, and the ability of the introduced wt p53 to sensitize the transfected JSQ-3 cells to ionizing radiation was examined. Transferrin increased the in vitro transfection efficiency of cationic liposomes up to 70-80% in JSQ-3 cells, representing a 6- to 10-fold increase over liposome transfection alone. The exogenous wt p53 was expressed at high levels in transferrin-liposome-DNA-transfected cells and resulted in the reversion of the radioresistant phenotype of the JSQ-3 cells in a DNA dose-dependent manner. The D10 values were reduced from 6.36 +/- 0.54 Gy to 4.13 +/- 0.06 Gy, a value in the radiosensitive range. In vivo, the intratumoral injection of the transferrin-liposome system resulted in a higher number of transfected tumor cells in the JSQ-3 induced nude mouse xenografts when compared with transfection by liposome alone. The results indicate that the combination of p53 replacement gene transduction, mediated by the relatively safe transferrin-liposome system, and conventional ionizing radiation may provide a more effective treatment for head and neck cancer.

Animals↗

PubMed1997

A new expression vector for high level protein production, one step purification and direct isotopic labeling of calmodulin-binding peptide fusion proteins.

Calmodulin-binding peptide (CBP), a peptide of 26 amino acids derived from muscle myosin light chain kinase (MLCK), binds to calmodulin with nanomolar affinity. Proteins fused in frame with CBP can be purified from crude E. coli lysates in a single step using calmodulin affinity chromatography (Stofko-Hahn et al., 1992). Because the binding between CBP and calmodulin is calcium-dependent, the fusion protein can be eluted from the resin with virtually any buffer containing EGTA (2 mM) and used directly for many applications. To take full advantage of this affinity purification system, we constructed the versatile CBP fusion protein expression vector pCAL-n. The CBP coding sequence was positioned for fusion at the N-terminus, an advantage that ensures consistent high level synthesis of fusion proteins due to the efficient translation of the CBP in E. coli. The production of fusion proteins from pCAL-n is controlled by the tightly regulated T7(lac)O promoter. A versatile multiple cloning site (MCS) was included to facilitate the cloning of genes of interest. The protein coding sequence for the enzyme c-Jun N-terminal kinase (JNK) was inserted into the MCS of pCAL-n, and the resulting fusion protein CBP-JNK synthesized in E. coli cells at 15-20 mg/1 culture. CBP-JNK was purified to near homogeneity in one step with calmodulin affinity resin. Purified CBP-JNK is fully active, and the CBP peptide tag can be removed by cleavage with thrombin. We also show that CBP can be efficiently phosphorylated by cAMP-dependent protein kinase. Hence, the purified fusion proteins can be labeled directly with [gamma-32P]ATP and used to probe protein-protein or protein-nucleic acid interactions.

Adenosine Triphosphate↗

PubMed1997

Nuclear integration of JAK/STAT and Ras/AP-1 signaling by CBP and p300.

We report that interferon gamma (IFN-gamma) inhibits transcription of the macrophage scavenger receptor gene by antagonizing the Ras-dependent activities of AP-1 and cooperating ets domain transcription factors, apparently as a result of competition between AP-1/ets factors and activated STAT1 for limiting amounts of CBP and p300. Consistent with this model, STAT1 alpha interacts directly with CBP in cells, and microinjection of anti-CBP and anti-p300 antibodies blocks transcriptional responses to IFN-gamma. Cells lacking STAT1 fail to inhibit AP-1/ets activity, and overexpression of CBP both potentiates IFN-gamma-dependent transcription and relieves AP-1/ets repression. Thus, CBP and p300 integrate both positive and negative effects of IFN-gamma on gene expression by serving as essential coactivators of STAT1 alpha, modulating gene-specific responses to simultaneous activation of two or more signal transduction pathways.

Acetyltransferases↗

PubMed1997

Meiotic cells monitor the status of the interhomolog recombination complex.

During meiosis, mutations that cause defects at intermediate stages in the recombination process confer arrest at the end of prophase (e.g., pachytene). In yeast, mutations of this type include rad50S, dmc1, rad51, and zip1. Rad50 is likely part of a recombination initiation complex. DMC1, RAD51, and ZIP1 encode two RecA homologs and a synaptonemal complex protein, respectively. We report here the effects of mutations in two other (meiosis-specific) genes, RED1 and MEK1/MRE4, that encode a chromosome structure component and a protein kinase, respectively. A red1 or mek1/mre4 mutation alleviates completely rad50S, dmc1, rad51, and zip1 arrest. Furthermore, the red1 and mek1/mre4 mutations define a unique, previously unrecognized aspect of recombination imposed very early in the process, during DSB formation. Finally, the red1 and mek1/mre4 mutations appear to alleviate prophase arrest directly rather than by eliminating, or permitting bypass of, the rad50S, dmc1, rad51, or zip1 defects. These and other observations suggest that a meiosis-specific regulatory surveillance process monitors the status of the protein/DNA interhomolog recombination machinery as an integral entity, in its proper chromosomal context, and dependent upon its appropriate Red1 and Mek1/Mre4-promoted development. We speculate that a properly developed recombination complex emits an inhibitory signal to delay progression of meiotic cells out of prophase until or unless the recombination process has progressed, at least past certain critical steps, and perhaps to completion.

Blotting, Southern↗

PubMed1997

Detection via laser desorption and mass spectrometry of multiplex electrophore-labeled albumin.

Albumin was reacted with a mixture of six electrophore N-hydroxysuccinimide esters, each of which possessed an interior glycolketo linkage. The purpose of this linkage is to release the attached electrophore as a ketone when heated, due to a thermal retro-aldol reaction. The multiplex electrophore-labeled albumin was detected as a dried spot deposited on a polyimide membrane by laser desorption/capillary collection (of the released ketone electrophores)/off-line gas chromatography/electron capture-mass spectrometry. This encourages further study of such electrophore labels in immunoassays and related techniques, where there is a need to make advances in multi-analyte detection.

Albumins↗

PubMed1997

Regulation of CCR2 chemokine receptor mRNA stability.

During inflammatory and immunological responses, leukocytes respond to external stimuli by altering the stability of cytokine and cytokine receptor messages. Change in message stability is an effective mechanism for rapidly regulating steady state levels of mRNA. Cytokine messages containing A-U-rich elements located in the 3' untranslated region (ARE) are the best studied examples of this process. AREs have been shown to act as targeting motifs for degradation of cytokine and transcription factor messages. We have recently observed that the interleukin-8 (IL-8) receptor messages, IL-8RA and B (CXCR1 and CXCR2), also undergo changes in stability in response to the inflammatory stimulator lipopolysaccharide (LPS). To determine whether regulation of message stability is a common mechanism for modulation of chemokine receptor mRNA we explored whether the stability of the CC chemokine receptor message for CCR2 (monocyte chemotactic protein-1 receptor) is also regulated by LPS. We found that LPS induces a rapid loss of steady state levels of CCR2 message through message degradation. Furthermore, LPS stimulated the decay of Poly(A) CCR2 mRNA faster than total CCR2 RNA, indicating that deadenylation is the first step in LPS-induced CCR2 RNA degradation. We conclude from these experiments that LPS stimulates the rapid degradation of CCR2 messages through a two-step process, deadenylation followed by degradation of the message body. In contrast to the results obtained for CCR2 mRNA, macrophage inflammatory protein-1alpha messages, which contain an ARE motif, were stabilized by LPS stimulation, indicating that chemokine and chemokine receptor mRNA stability are regulated by different and opposing mechanisms.

Adenine↗

PubMed1997

Temperature Regulation of Supercooling and Gut Nucleation in Relation to Diapause of Pyrrhocoris apterus (L.) (Heteroptera)

The heteropteran Pyrrhocoris apterus (L.) does not survive freezing of its body fluids; there is a good correlation between values of survival at subzero temperatures and the supercooling point (SCP), i.e., the temperature at which body fluids start to freeze. The decrease of the SCP and thus the increase in cold hardiness is regulated by photoperiod and temperature. The relative importance of these factors depends on the physiological state of the insect. The SCP is about -7°C at the onset of prediapause and a decrease of about 4-5°C is associated with the development of the diapause syndrome in adults; these processes both are induced by a short-day photoperiod with temperature playing a secondary role. The induction of the diapause syndrome is a prerequisite for the subsequent decrease of the SCP by about 5-6°C during cold acclimation. An intermediate temperature of 15°C, or fluctuating outdoor temperatures and short-day photoperiods, are more suitable for the decrease of SCP than 5°C in continuous darkness. The sensitivity to photoperiod gradually disappears during the development of diapause; after the termination of diapause around the winter solstice the SCP irreversibly increases at a high temperature of 26°C even if exposed to a short-day photoperiod. The SCPs of hemolymph, gut, fat body, and gonads were compared to whole-body SCP. The gut was identified as the primary site of ice nucleation because its SCP value was very similar to the value for the whole body in both short-day and long-day insects. The SCPs of other organs, including the hemolymph, were always lower than the whole body SCP. Food was not a source of ice nucleating agents because the SCP of freshly ecdysed adults remained high after 2 weeks of starvation. In contrast, feeding was a prerequisite for the decrease of the SCP during prediapause. In postdiapause insects, the SCP increased at high temperatures in spite of the absence of food.

Journal Article↗

PubMed1997

IL-8 and NAP-2 differ in their capacities to bind and chemoattract 293 cells transfected with either IL-8 receptor type A or type B.

Two receptors for interleukin 8 (IL-8), IL-8rA and IL-8rB, have been cloned. Previous studies of neutrophils indicated that the two C-X-C chemokines, IL-8 and NAP-2, bind to IL-8rB with high affinity but that only IL-8 binds to IL-8rA with high affinity. In this study, human kidney embryonal 293 cells were transfected to express solely IL-8rA or IL-8rB (the cells are designated IL-8rA/293 and IL-8rB/293, respectively). The authors show that NAP-2 bound both IL-8rA and IL-9rB specifically. While NAP-2 and IL-8 bound IL-8rB with comparable high affinity (2.9 +/- 0.5 and 2.8 +/- 0.8 nM, respectively), NAP-2 showed a lower binding affinity to IL-8rA (9 +/- 2 nM) compared with IL-8 (1.3 +/- 0.5 nM). A lower number of binding sites was detected for NAP-2 than for IL-8 on IL-8rA/293 cells as well on IL-8rB/293 cells. On both cell types (IL-8rA/293 and IL-8rb/293), NAP-2 and IL-8 could completely inhibit [125I]NAP-2 binding, while unlabelled NAP-2 could only partially compete for [125I]IL-8 binding. Functional assays revealed that although NAP-2 is chemotactic for both IL-8rA/293 and IL-8rB/293 cells, it is less potent than IL-8. While NAP-2 induced chemotaxis of IL-8rB/293 cells at the same optimal concentrations as IL-8 (10-100 ng/ml), the induction of optimal migratory response of IL-8rA/293 cells required much higher concentrations of NAP-2 than IL-8 (1000-3000 ng/ml and 10-100 ng/ml, respectively). The dose-response curve of the IL-8rB/293 cells to IL-8 was bell shaped, while the response to NAP-2 was sustained at a plateau level even at concentrations as high as 3000 ng/ml. It is likely that tertiary structural differences between NAP-2 and IL-8 account for their divergent abilities to bind and chemoattract 293 cells transfected with either IL-8 receptor type A or type B.

Antigens, CD↗

PubMed1997

Permeation through the calcium release channel of cardiac muscle.

Current voltage (I-V) relations were measured from the calcium release channel (CRC) of the sarcoplasmic reticulum of cardiac muscle in 12 KCl solutions, symmetrical and asymmetrical, from 25 mM to 2 M. I-V curves are nearly linear, in the voltage range +/- 150 mV approximately 12kT/e, even in asymmetrical solutions, e.g., 2 M // 100 mM. It is awkward to describe straight lines as sums of exponentials in a wide range of solutions and potentials, and so traditional barrier models have difficulty fitting this data. Diffusion theories with constant fields predict curvilinear I-V relations, and so they are also unsatisfactory. The Poisson and Nernst-Planck equations (PNP) form a diffusion theory with variable fields. They fit the data by using adjustable parameters for the diffusion constant of each ion and for the effective density of fixed (i.e., permanent) charge P(x) along the channel's "filter" (7-A diameter, 10 A long). If P(x) is described by just one parameter, independent of x (i.e., P(x) = P0 = -4.2 M), the fits are satisfactory (RMS error/RMS current = 6.4/67), and the estimates of diffusion coefficients are reasonable D(K) = 1.3 x 10(-6) cm2/s, D(Cl) = 3.9 x 10(-6) cm2/s. The CRC seems to have a small selectivity filter with a very high density of permanent charge. This may be a design principle of channels specialized for large flux. The Appendix derives barrier models, and their prefactor, from diffusion theories (with variable fields) and argues that barrier models are poor descriptions of CRCs in particular and open channels in general.

Calcium↗