Biomedical subjects

H Xu

Publications and source records attributed to H Xu.

At least 487 records · Page 27Linked to original sources

PubMed1997

Integrins (alpha7beta1) in muscle function and survival. Disrupted expression in merosin-deficient congenital muscular dystrophy.

Mutations in genes coding for dystrophin, for alpha, beta, gamma, and delta-sarcoglycans, or for the alpha2 chain of the basement membrane component merosin (laminin-2/4) cause various forms of muscular dystrophy. Analyses of integrins showed an abnormal expression and localization of alpha7beta1 isoforms in myofibers of merosin-deficient human patients and mice, but not in dystrophin-deficient or sarcoglycan-deficient humans and animals. It was shown previously that skeletal muscle fibers require merosin for survival and function (Vachon, P.H., F. Loechel, H. Xu, U.M. Wewer, and E. Engvall. 1996. J. Cell Biol. 134:1483-1497). Correction of merosin deficiency in vitro through cell transfection with the merosin alpha2 chain restored the normal localization of alpha7beta1D integrins as well as myotube survival. Overexpression of the apoptosis-suppressing molecule Bcl-2 also promoted the survival of merosin-deficient myotubes, but did not restore a normal expression of alpha7beta1D integrins. Blocking of beta1 integrins in normal myotubes induced apoptosis and severely reduced their survival. These findings (a) identify alpha7beta1D integrins as the de facto receptors for merosin in skeletal muscle; (b) indicate a merosin dependence for the accurate expression and membrane localization of alpha7beta1D integrins in myofibers; (c) provide a molecular basis for the critical role of merosin in myofiber survival; and (d) add new insights to the pathogenesis of neuromuscular disorders.

Animals↗

PubMed1997

Probes for narcotic receptor-mediated phenomena. 25. Synthesis and evaluation of N-alkyl-substituted (alpha-piperazinylbenzyl)benzamides as novel, highly selective delta opioid receptor agonists.

A series of N-alkyl- and N,N-dialkyl-4-[alpha-[(2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl] benzyl]-benzamides were synthesized and evaluated for binding affinities at mu, delta, and kappa opioid receptor subtypes. Several compounds (2e,f,h,i,m) strongly bound to the delta receptor with IC50 values in the nanomolar range. On the other hand, the binding affinities of these compounds for the mu and kappa receptors were in the micromolar or greater range indicating excellent delta opioid receptor subtype selectivities. In this series, two important structure-activity relationships were found for the delta receptor binding affinity. First, the spatial orientation of the alpha-benzylic position influenced the affinities with the alpha R derivatives 2a-n generally showing more than 10-fold greater affinity than the alpha S derivatives 3a-n. Second, the binding affinities were strongly influenced by the number of alkyl substituents on the amide nitrogen. N-Monoalkylbenzamide derivatives 2b-d showed lower affinity than N,N-dialkylbenzamide derivatives 2e-n, and the N-unsubstituted benzamide derivative 2a had the lowest affinity for the delta receptor in the series. The dramatic effect of the amide group substitution pattern on the binding affinity for the delta receptor strongly suggests that the amide function is an important structural element in the interaction of this series of compounds at the delta receptor. Selective compounds in this series were examined for binding affinity in cloned human mu and delta receptors. The results obtained generally paralleled those from the rat brain binding assay. Compounds 2e,f with potent delta binding affinities and high delta selectivities were shown to be delta agonists with high selectivity by studies in the guinea pig ileum (GPI) and mouse vas deferens (MVD) preparations. Compound 2f was the most selective compound in the rat brain and GPI/MVD assays with 1755- and 958-fold delta vs mu selectivity, respectively.

Alkylation↗

PubMed1997

Chiral separation of primary amino compounds using a non-chiral crown ether with beta-cyclodextrin by capillary electrophoresis.

A non-chiral crown ether (18-crown-6) along with beta-cyclodextrin (beta-CD) was used to achieve enantioselective separations of primary amino compounds in capillary electrophoresis. In this new method, the amino group of these compounds is protonated in a low pH separation buffer and forms a selective host-guest complex with the crown ether (amino compound+18-crown-6). The hydrophobic portion of the host-guest complex is then incorporated into the cavity of the beta-cyclodextrin. The amino compound is sandwiched between the crown ether and the cyclodextrin (18-crown-6+amino compound+beta-CD) and thus determines or enhances the enantioselective recognition. It is postulated that the formation of this sandwich results in a more selective chiral interaction between the molecule and beta-cyclodextrin. The chiral recognition is dependent upon the formation of this sandwich complex. This method has been used to achieve enantioselectivity of primary amino compounds with a wide variety of substitutions.

Amines↗

PubMed1997

Mouse adhalin: primary structure and expression during late stages of muscle differentiation in vitro.

Adhalin, or alpha-sarcoglycan, is a 50-kDa glycoprotein that was originally characterized as a muscle membrane protein. The importance of adhalin is suggested by the diseases associated with its absence, notably the limb-girdle muscular dystrophies. However, the function of adhalin is unknown. To analyze the biological roles of adhalin, we cloned the mouse adhalin cDNA, raised peptide-specific antibodies to its cytoplasmic domain, and examined its expression and localization in vivo and in vitro. The mouse adhalin sequence was 80% identical to that of human, rabbit, and hamster. Adhalin was specifically expressed in striated muscle cells and their immediate precursors, and absent in many other cell types. Adhalin expression in embryonic mouse muscle was coincident with primary myogenesis. Its expression was found to be up-regulated at mRNA and protein levels during myogenic differentiation in vitro. The proper localization of adhalin to the muscle cell membrane was observed only in late stages of myotube maturation, coincident with the re-distribution of caveolin-3 and dystrophin. These data suggest that adhalin is highly specific for striated muscle and that it is linked with the formation of a fully functional muscle fiber.

Amino Acid Sequence↗

PubMed1997

Mutations in the GAP-related domain impair the ability of neurofibromin to associate with microtubules.

The neurofibromatosis 1 (NF1) gene encodes a cytoplasmic protein with structural and functional homology to GTPase activating proteins (GAPs) for p21-ras. Double-labeling immunofluorescence experiments using neurofibromin antibodies and in vitro microtubule assembly have demonstrated that the NF1 gene product, neurofibromin, interacts with cytoplasmic microtubules. The region critical for this interaction was shown to reside within the NF1-GAP-related domain (NF1GRD). Examination of the NFIGRD reveals a number of residues that are highly conserved amongst all GAP molecules. Mutational analysis of a representative number of these conserved residues demonstrated differential effects on NF1GRD p21-ras GAP activity. In this study, we examined the effect of these selected NF1GRD mutations on the ability of neurofibromin to associate with microtubules. Mutations at residues R1391, P1400 and K1423 disrupted microtubule association. In contrast, mutations at residues E1264, Q1426 and the insertion of exon 23a, critical for p21-ras regulation, did not impair microtubule association. These results demonstrate that some residues important for p21-ras regulation are also required for microtubule binding while other residues within the NF1GRD differentially affect p21-ras regulation and microtubule association.

Animals↗

PubMed1997

Uveitogenicity is associated with a Th1-like lymphokine profile: cytokine-dependent modulation of early and committed effector T cells in experimental autoimmune uveitis.

This study addresses the nature of the pathogenic effector T cell in experimental autoimmune uveoretinitis and the effect of different cytokines on these cells in vitro. Lymph node cells of B10.RIII mice immunized with the uveitogenic peptide 161-180 of interphotoreceptor retinoid binding protein were cultured with the peptide with or without IL-12, IL-4, or anti-IL-4. An antigen-specific T cell line was subsequently derived from these cells. Primary cultures of immune lymph node cells stimulated with the peptide proliferated and produced IL-2 and some IL-4, but no IFN-gamma. The addition of recombinant IL-12 resulted in abundant production of IFN-gamma, which was blocked by the addition of IL-4 and was enhanced by anti-IL-4. Only those cultures that produced IFN-gamma in vitro were uveitogenic in vivo. A long-term uveitogenic T cell line, initially derived in the presence of IL-12, produced IFN-gamma and IL-2, but not IL-4, and was CD4+ (Th1-like). Antigen-specific proliferation and IFN-gamma production of the line were enhanced by exogenous IL-4, TGF-beta, IL-2, IL-6, IL-7, and IL-9 and were inhibited by IL-10 and TNF-alpha. Our results provide support for the hypothesis that the uveitogenic effector T cell has a Th1-like phenotype. Furthermore, the data suggest that the effects of the cytokine milieu on fully differentiated Th1 effectors may differ considerably from their effects on less mature stages of antigen-specific T cells.

Amino Acid Sequence↗

PubMed1997

Development of effector CD8+ T cells in contact hypersensitivity occurs independently of CD4+ T cells.

Contact hypersensitivity (CHS) is a T cell-mediated response to hapten sensitization of the epidermis. Recent results from this laboratory indicated that hapten sensitization induces two populations of hapten-reactive T cells: CD8+ T cells producing IFN-gamma, which mediate the response, and CD4+ T cells producing IL-4 and IL-10, which function to limit the magnitude and the duration of the response. In the current report we first examined the hapten-presenting cell priming each of these T cell populations and then examined the influence of CD4+ T cell priming on the development of the CD8+ effector T cells. Isolation of hapten-presenting Langerhans cells from the lymph nodes of oxazolone-sensitized mice and transfer to naive mice resulted in the induction of both the regulatory CD4+ and the effector CD8+ T populations. Both CD4+ and CD8+ T cells expressing high levels of the activation determinants CD11a and CD44 appeared in the lymph nodes 3 days after hapten sensitization. The CD8+ T cells producing IFN-gamma and mediating CHS responses following transfer to naive mice were restricted to the high CD44-expressing population. In vitro activation of hapten-immune CD8+ T cells resulted in very low amounts (3 U/ml) of IL-2 production, whereas production of IL-2 by immune CD4+ T cells was approximately 70-fold higher (208 U/ml). Despite this discrepancy in IL-2 production and the coincidental priming of CD4+ and CD8+ T cells by hapten-presenting Langerhans cells during hapten sensitization, the numbers of CD8+/high CD44-expressing T cells in the lymph nodes were nearly identical when CD4+ T cells were present or absent during hapten priming. These results indicate that coincidental priming of CD4+ (and CD8+) T cells by LC does not augment CD8+ T cell development in CHS.

Animals↗

PubMed1997

Generation of Alzheimer beta-amyloid protein in the trans-Golgi network in the apparent absence of vesicle formation.

beta-amyloid protein (A beta) formation was reconstituted in permeabilized neuroblastoma cells expressing human Alzheimer beta-amyloid precursor protein (beta APP) harboring the Swedish double mutation associated with familial early-onset Alzheimer disease. Permeabilized cells were prepared following metabolic labeling and incubation at 20 degrees C, a temperature that allows beta APP to accumulate in the trans-Golgi network (TGN) without concomitant A beta formation. Subsequent incubation at 37 degrees C led to the generation of A beta. A beta production in the TGN persisted even under conditions in which formation of nascent post-TGN vesicles was inhibited by addition of guanosine 5'-O-(3-thiotriphosphate), a nonhydrolyzable GTP analogue, or by omission of cytosol. These and other results indicate that vesicle budding and trafficking may not be required for proteolytic metabolism of beta APP to A beta, a process that includes "gamma-secretase" cleavage within the beta APP transmembrane domain.

Amyloid beta-Peptides↗

PubMed1997

Probes for narcotic receptor mediated phenomena. 23. Synthesis, opioid receptor binding, and bioassay of the highly selective delta agonist (+)-4-[(alpha R)-alpha-((2S,5R)-4-Allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]- N,N-diethylbenzamide (SNC 80) and related novel nonpeptide delta opioid receptor ligands.

The highly selective delta (delta) opioid receptor agonist SNC 80 [(+)-4- [(alpha R)-alpha-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N ,N- diethylbenzamide, (+)-21] and novel optically pure derivatives were synthesized from the enantiomers of 1-allyl-trans-2,5-dimethylpiperazine (2). The piperazine (+/-)-2 was synthesized, and its enantiomers were obtained on a multigram scale in > 99% optical purity by optical resolution of the racemate with the camphoric acids. The absolute configuration of (+)-2 was determined to be 2S,5R by X-ray analysis of the salt with (+)-camphoric acid. Since the chirality of the starting material was known, and the relative configuration of compounds (-)-21, (-)-22, and (+)-23 were obtained by single-crystal X-ray analysis, the assignment of the absolute stereochemistry of the entire series could be made. Radioreceptor binding studies in rat brain preparations showed that methyl ethers (+)-21 (SNC 80) and (-)-25 exhibited strong selectivity for rat delta receptors with low nanomolar affinity to delta receptors and only micromolar affinity for rat mu (mu) opioid receptors. Compounds (-)-21, (-)-22, and (-)-23 showed micromolar affinities for delta opioid receptors. The unsubstituted derivative (+)-22 and the fluorinated derivative (-)-27 showed > 2659- and > 2105-fold delta/mu binding selectivity, respectively. The latter derivatives are the most selective ligands described in the new series. Studies with some of the compounds described in the isolated mouse vas deferens and guinea pig ileum bioassays revealed that all were agonists with different degrees of selectivity for the delta opioid receptor. These data show that (+)-21 and (+)-22 are potent delta receptor agonists and suggest that these compounds will be valuable tools for further study of the delta opioid receptor at the molecular level, including its function and role in analgesia and drug abuse.

Animals↗

PubMed1997

Structure and expression of a novel filarial gene for glia maturation factor.

Factors that influence neural growth and development in parasitic nematodes have not yet been identified. We have isolated and sequenced a Brugia malayi nematode 3.4-kb genomic DNA fragment and its corresponding cDNA, which encode a predicted protein of 138 amino acids with 52% identity and 75% similarity to the mammalian neuroglial growth factor, glia maturation factor-beta (GMF). GMF promotes the differentiation of mammalian glia and neurons and stimulates axonal regeneration. The filarial nematode gene Bmgmf for Brugia malayi glia maturation factor contains six predicted exons, with the first exon encoding only the initiation methionine. Brugia malayi GMF (BmGMF) is also related to a large family of eukaryotic actin depolymerizing factors (ADFs). Although BmGMF does not contain the consensus actin-depolymerizing motif of ADFs, it does share a similar intron exon structure, including the unusual first exon, with the unc-60 ADF gene of the nematode Caenorhabditis elegans. RT-PCR experiments reveal that BmGMF is trans-spliced with the nematode spliced leader sequence SL1 and is expressed in microfilariae but not in third-stage larvae or adult worms. We speculate that BmGMF may function as a stage-specific neuroglial growth factor.

Actin Depolymerizing Factors↗

PubMed1997

Engagement of the Lewis X antigen (CD15) results in monocyte activation.

We previously reported that monocyte adhesion to tumor necrosis factor-alpha (TNF-alpha)-treated endothelial cells increased expression of tissue factor and CD36 on monocytes. Using immunological cross-linking to mimic receptor engagement by natural ligands, we now show that CD15 (Lewis X), a monocyte counter-receptor for endothelial selectins may participate in this response. We used cytokine production as a readout for monocyte activation and found that CD15 cross-linking induced TNF-alpha release from peripheral blood monocytes and cells from the monocytic cell line MM6. Quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) showed an increase in steady-state TNF-alpha mRNA after 3 to 4 hours of cross-linking. CD15 cross-linking also concomitantly increased interleukin-1 beta (IL-1 beta) mRNA, while no apparent change was observed in the levels of beta-actin mRNA, indicating specificity. To examine transcriptional regulation of cytokine genes by CD15 engagement, a CAT plasmid reporter construct containing IL-1 beta promoter/enhancer sequences was introduced into MM6. Subsequent cross-linking of CD15 increased CAT activity. CD15 engagement by monoclonal antibody also attenuated IL-1 beta transcript degradation, demonstrating that signaling via CD15 also had posttranscriptional effects. Nuclear extracts of anti-CD15 cross-linked cells demonstrated enhanced levels of the transcriptional factor activator protein-1, minimally changed nuclear factor-kappa B, and did not affect SV40 promoter specific protein-1. We conclude that engagement of CD15 on monocytes results in monocyte activation. In addition to its well-recognized adhesive role, CD15 may function as an important signaling molecule capable of initiating proinflammatory events in monocytes that come into contact with activated endothelium.

Antibodies, Monoclonal↗

PubMed1997

Evidence for the induction of apoptosis in thymocytes by 2,3,7,8-tetrachlorodibenzo-p-dioxin in vivo.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is well known for its immunotoxic effects particularly on the thymus. The exact mechanism by which TCDD induces thymic atrophy is not clear. In the current study, we investigated whether TCDD triggers apoptosis in thymocytes, when administered in vivo, by using the TdT-mediated FITC-dUTP nick end labeling method and analyzing the cell flow cytometrically. Significant apoptosis was detected at 8-12 hr after the TCDD injection but not at 24 hr or beyond, up to 120 hr of study. Furthermore, the induction of apoptosis was confirmed using the JAM test in which thymocytes from TCDD-treated mice, labeled with [3H]thymidine, exhibited increased DNA fragmentation when compared to the controls. Similar to TCDD treatment, administration of dexamethasone (5 or 100 mg/kg) into C57BL/6 mice triggered apoptosis that was only detected at 12 hr after administration of the drug and not thereafter. When thymocytes from TCDD- or dexamethasone-treated mice were cultured in vitro for 24 hr, they exhibited marked increase in apoptosis when compared to the vehicle-treated controls. However, TCDD, when added to in vitro cultures of thymocytes, failed to trigger apoptosis. Together, our studies demonstrate that TCDD can induce apoptosis in thymocytes in vivo. This can be detected only at an early stage following TCDD administration, possibly because of rapid clearance of apoptotic cells by the phagocytic cells in vivo.

Animals↗

PubMed1997

Inhibition of lipid peroxidation.

Lipid peroxy radicals (ROO.) were detected by electron spin resonance (ESR) at low temperature after formation by addition of H2O2 into a suspension of mice lymphocytes. If lymphocytes were treated with selenomethionine (Se-Met) prior to addition of H2O2, ROO. formation was inhibited in a fashion that was dependent on Se-Met concentration. Formation of ROO. in the spleen of mice was induced by 60Co irradiation. Animals that were supplemented with Na2SeO3 prior to irradiation exhibited a lower ROO. concentration than that of nontreated animals. Based on our experiments, we have concluded that Se has an oxygen-free radical scavenging effect. This should be a protective effect against lipid peroxy radical cellular attack.

Animals↗

PubMed1997

Effect of selenium supplementation on mice infected with LP-BM5 MuLV, a murine AIDS model.

LP-BM5 Murine leukemia virus (MuLV) infection of C57BL/6 mice develop a disease that has many features in common with human acquired immunodeficiency syndrome (AIDS), in particular abnormal lymphoproliferation and severe immunodeficiency. Thus, this MAIDS model may be useful for evaluation of potent antirival agents in vivo. Deficiency in antioxidant micronutrients such as selenium, zinc, and glutathione have been observed in AIDs and AIDS-related complex (ARC) patients. In the present study, the MAIDS model was used to evaluate immunological and oxidative effect of Se as sodium selenite. Results indicated that Se treatment 0.1 mg/kg/d (p.o.) inhibited splenomegaly and sera IgG elevation effectively. In addition to abnormal immunity, oxidative imbalance possibly existed in MAIDS model, as lipid peroxide increased significantly in spleen and whole blood glutathione peroxidase (GSH-Px) activity decreased markedly. Se supplementation had good protective effect.

Animals↗

PubMed1997

Effects of ligustrazine on bone marrow microvessel system in the early period of acute radiation injury in mice.

Sublethally irradiated mice were immediately treated with 250 mg/kg Ligustrazine Phosphiatis intraperitoneally twice a day for seven days, and the bone marrow microvessels of the Ligustrazine group was much greater than that of the control group. On the 7th day, the amount of the control group decreased to normal, while the ligustrazine group was still increasing, and the microvessel area was enlarged obviously.. The percentage of the hematopoietic tissue volume in bone marrow between the two groups had no significant difference in the first 7 days. On the 7th day after irradiation, the peripheral neutrophilic granulocytes increased in the Ligustrazine group. The results suggested that early use of Ligustrazine after acute radiation injury might improve the blood supply of bone marrow, and be helpful for recovery of hematopoiesis.

Animals↗

PubMed1997

Study on immunoregulation by interleukin-1 receptor antagonist in NZB/W F mice.

The immunoregulating effect of Interleukin-1-receptor antagonist (IL-1ra) in lupus-like NZB/W F1 mice was investigated to find possible approach to prevent lupus nephritis. 12 female NZB/W F1 mice of 13 weeks were randomly divided into 2 groups. Each mouse in the treated group was intraperitoneally injected with IL-1ra once every 2 weeks for 3 times at the dosage of 100 micrograms each time, while the control group was given injection of 0.1 ml normal saline. All the mice were killed at the age of 9 months and the immunologic function was examined. Results showed that this dosage could not completely prevent the development of lupus nephritis, but the renal damage was alleviated and the urine protein was decreased. Moreover, it could improve the immunofunction by significantly reducing the levels of serum IL-1 and obviously increase the activities of NK cells and IL-2 induced by ConA in mononuclear cells of spleen. There was no significant difference in the levels of serum IL-6 and TNF-alpha between the treated group and control group. It is concluded that IL-1ra has certain regulatory effect on the immunologic function of lupus-like NZB/W F1 mice.

Animals↗

PubMed1997

Percutaneous implantation of non-small-cell lung carcinoma: technique and observations.

RATIONALE AND OBJECTIVES: The authors performed this study to determine whether intrathoracic inoculation of non-small-cell lung carcinoma with fluoroscopic guidance would provide for more accurate implantation. MATERIALS AND METHODS: A tumor cell inoculum (2 x 10(6) cells per 0.15 mL) was injected percutaneously under fluoroscopic guidance at the posterior midaxillary line in 22 athymic nude mice. The mice underwent imaging with a mammographic unit at 3, 5, and 8 weeks after implantation. The mice were sacrificed at 8 weeks, and autopsy was performed to determine tumor yield. RESULTS: The use of a percutaneous technique under fluoroscopic guidance greatly facilitated the accurate implantation of xenografts. Tumor growth was seen at radiography in 18 of the 22 (82%) mice at 8 weeks. Necropsy revealed a 100% tumor yield. Histologic examination confirmed adenocarcinoma of the lung. The average number of tumors found in the lung parenchyma was 1.05 +/- 0.35; the average number of tumors found in the mediastinum was 0.59 +/- 0.67. The average tumor weight was 389 mg +/- 64.3. The average tumor size was 300 mm3 +/- 66.23. CONCLUSION: With fluoroscopic guidance, percutaneous implantation of tumor cells in athymic nude mice is simple and effective.

Adenocarcinoma↗

PubMed1997

Proteoglycan expression by human trabecular meshworks.

PURPOSE: Proteoglycans may serve important roles in trabecular meshwork structure or function. Detailed molecular characterization and identification of specific trabecular proteoglycan core proteins has been limited. METHODS: Radiolabeled proteoglycans were extracted from cultured human trabecular meshworks and subjected to ion exchange and molecular sieve chromatography. Peaks were subjected to glycosaminoglycan content analysis. Reverse transcription with polymerase chain reaction was used to identify trabecular mRNAs of several common proteoglycan core proteins. Western immunoblots of trabecular extracts were also utilized to identify these proteoglycan core proteins. RESULTS: The proteoglycans elute from ion exchange columns at high salt and molecular sieve column profiles, and they exhibit broad peaks typical of the proteoglycan microheterogeneity seen in other tissues. The four common glycosaminoglycan side-chains were identified on these proteoglycans. Trabecular cells in organ or cell culture contain mRNAs coding for decorin, biglycan, versican, perlecan and a basement membrane glycoprotein, SPARC. Syndecan-1 transcripts were present at very low levels, while aggrecan transcripts were not detectable. Decorin, biglycan, versican and perlecan core proteins were also identified by immunoblots of trabecular cell extracts. CONCLUSIONS: Several common proteoglycans are expressed by trabecular cells in organ explant or cell culture. Their general characteristics are not unlike those found in other tissues. These proteoglycans may serve important functions in the trabecular outflow pathway.

Aggrecans↗