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Biomedical subjects

J Yuan

Publications and source records attributed to J Yuan.

At least 271 records · Page 15Linked to original sources
PubMed1996

Prevention of apoptosis in CNTF-dependent neurons by a mutant ICE and by viral protein CrmA but not by proto-oncogene product Bcl-2.

The interleukin-1beta converting enzyme (ICE) gene family, (homologues of C. elegans cell death gene product Ced-3) plays an important role in controlling programmed cell death. Nerve growth factor (NGF) promotes survival of cultured embryonic chicken dorsal root ganglion neurons. Ciliary ganglion neurons depend exclusively on ciliary neurotrophic factor (CNTF) for survival. Complete depletion of NGF or CNTF from culture medium induces apoptosis in both types of neurons. We can prevent apoptosis, due either to NGF or CNTF withdrawal and in either type of neuron, by overexpression of a mutant inactive ICE and an ICE inhibitor, the product of cowpox virus gene crmA. Bcl-2 does not prevent apoptosis in CNTF-dependent ciliary neurons or DRG neurons as it does in NGF-dependent neurons. These results suggest that neuronal cell death is mediated through a common effector mechanism involving the Ice family of genes, whereas different suppression mechanisms are engaged depending upon the specific neurotrophic factors present.

Journal Article↗
PubMed1996

Neurotoxic and pharmacologic studies on enantiomers of the N-methylated analog of cathinone (methcathinone): a new drug of abuse.

These studies evaluated neurotoxic and pharmacologic properties of the R(+) and S(-) enantiomers of methcathinone, a psychostimulant drug that has surfaced in the illicit drug market, primarily in the S(-) form. Neurotoxic potential toward brain dopamine (DA) and serotonin (5-HT) neurons was assessed by measuring DA and 5-HT axonal markers and by means of silver degeneration studies; pharmacologic effects were evaluated by measuring locomotor stimulation. Methcathinone produced dose-related neurotoxic and locomotor stimulant effects which were species- and enantiomer-dependent. In mice, although both enantiomers produced toxic effects on DA neurons, the R(+) enantiomer was more potent, and neither enantiomer produced long-term effects on 5-HT neurons. By contrast, in behavioral studies, both enantiomers increased mouse locomotor activity, but the S(-) enantiomer was more potent, which suggests that methcathinone's neurotoxic and locomotor stimulant effects may be separable. Additional studies were done with rats, because mice are often refractory to 5-HT neurotoxicity induced by amphetamines. In the rat, both enantiomers produced toxic effects on DA neurons, only S(-)-methcathinone produced toxic effects on 5-HT neurons, and both enantiomers produced comparable locomotor stimulant effects. Together, these results indicate that: 1) Methcathinone has the potential to damage DA and 5-HT neurons; 2) Methcathinone neurotoxicity is enantiomer and species dependent; 3) Methcathinone's neurotoxic and locomotor stimulant effects are dissociable in mice but not rats; and 4) N-methylation confers 5-HT toxic activity onto cathinone, the N-desmethyl derivative of methcathinone, which is known to lack 5-HT neurotoxic activity.

Animals↗
PubMed1996

[A study of the expression and localization of tumor necrosis factor mRNA in small intestine of rats after severe burn].

In this study, the dot blotting and in situ hybridization, collaborated with determination of contents of endotoxin and TNF in plasma, were used to study the expression and localization of TNF mRNA in the intestine. The results showed that, the expression of TNF mRNA in the small intestine increased rapidly and reached maximum at 6 h postburn, being 5.56 times higher than that of normal control. The TNF mRNA-producing cells in normal animal were mononuclear phagocytes located in lamina propria. After burn, the number of positive cells in lamina propria increased significantly, and the TNF gene-expressing cells were vascular endothelium. Many positive cells were found in the crypts of the intestine. It suggested that the expression of TNF correlated well with bacterial translocation in the early stage of burn. The mononuclear phagocytes and endothelial cells located in lamina propria and interstitial tissue were the chief TNF mRNA-producing cells in the intestine. The overproduction of TNF could provoke microvascular injury or induce the production of oxygen free radical to damage the gut mucosal barrier.

Animals↗
PubMed1996

[Clinical trial of an anti-fertility method with testosterone enanthate in normal men].

OBJECTIVE: To establish the feasibility of anti-fertility by ultraphysiological-dosage testosterone in male. METHODS: Ten healthy, fertile men received 200 mg testosterone enanthate weekly by intramuscular injection based on international standard protocol. RESULTS: After 3-month injection, severe oligospermia was achieved. After 6-month injection, azoospermia was achieved. The total consecutive administration lasted for 12 months. During the period of severe oligospermia and azoospermia no partner was pregnant. After stopping injection, the sperm output returned to normal (20 x 10(8)/ml) in 2-3 months up to individual's own level before administration in 6 months. CONCLUSION: Severe oligospermia and azoospermia can be induced by ultra-pathological-dosage tesosterone through inhibiting FSH, LH to cause spermatogenesis inhibition. The sperm output would recover to its previous level in 6 months after stopping injection. It is suggested that there is a strong possibility that high-dosage testosterone may act as a male contraceptive.

Adult↗
PubMed1996

[Selenium levels in human bodies and environment in Qinghai province].

To study selenium level, its distribution in human bodies and environment and its effects on health, 3,035 specimens of human hair, blood, urine, and environmetal water, soil, food were collected from 91 sampling spots in 23 cities and counties of Qinghai Province and determined for selenium levels with fluorescence analysis. Results showed overall biological selenium level of human bodies in Qinghai Province was low and blood selenium level was lower than the normal reference value in 84.73% of the population, same as that in selenium-poor nations. Environmental selenium was poor or in a deficient status in Qinghai Province, 69.57% of the areas in the Province was in low, poor, or severely deficient selenium. Selenium level in vegetable food correlated closely with that in human blood, which indicated low selenium level in environment caused human selenium deficient in their internal environment via food chain. There were difference in biological selenium levels of human bodies in seven districts and six ethnic nationalities, which suggests selenium levels in human bodies correlate closely with economic development, selenium intake, geographical environment, living habits and customs, etc., and are nothing to do with the altitude above sea level.

Adolescent↗
PubMed1995

Interleukin-1 beta-converting enzyme mediates cisplatin-induced apoptosis in malignant glioma cells.

Increasing the susceptibility of tumor cells to apoptotic cell death following chemotherapy is of importance to the outcome of cancer treatment. Although the tumor suppressor gene p53 is required for efficient induction of apoptosis by chemotherapeutic agents, it is not the only apoptosis mediator gene. The molecular mechanisms mediating apoptosis following chemotherapy via p53-dependent or p53-independent pathways remain unclear. We show here that cis-diamminedichloroplatinum (cisplatin) induces the expression of interleukin-1 beta-converting enzyme (ICE), a mammalian homologue of the Caenorhabditis elegans cell death gene ced-3, in murine and human malignant glioma cells during apoptosis regardless of their p53 status. Furthermore, overexpression of the murine ICE gene induces apoptosis in these tumor cells. The apoptosis induced by cisplatin treatment or murine ICE overexpression can be suppressed by the tetrapeptide ICE inhibitor Ac-YVAD-CMK or the apoptosis inhibitors bcl-2 or bcl-2-related bcl-XL gene. These findings suggest that ICE may mediate apoptosis induced by chemotherapy, and its induction could represent a novel approach for the effective treatment of malignant glioma.

Amino Acid Sequence↗
PubMed1995

The instability of the membrane skeleton in thalassemic red blood cells.

The thalassemias are a heterogeneous group of disorders characterized by accumulation either of unmatched alpha or beta globin chains. These in turn cause the intramedullary and peripheral hemolysis that leads to varying anemia. A partial explanation for the hemolysis came our of our studies on material properties that showed that beta-thalassemia (beta-thal) intermedia ghosts were very rigid but unstable. A clue to this instability came from the observation that the spectrin/band 3 ratio was low in red blood cells (RBCs) of splenectomized beta-thal intermedia patients. The possible explanations for the apparent decrease in spectrin content included deficient or defective spectrin synthesis in thalassemic erythroid precursors or globin chain-induced membrane changes that lead to spectrin dissociation from the membrane during ghost preparation. To explore the latter alternative, samples from different thalassemic variants were obtained, ie, beta-thal intermedia, HbE/beta-thal, HbH (alpha-thal-1/alpha-thal-2), HbH/Constant Spring (CS), and homozygous HbCS/CS. We searched for the presence of spectrin in the first lysate of the standard ghost preparation. Normal individuals and patients with autoimmune hemolytic anemia, sickle cell anemia, and anemia due to chemotherapy served as controls. Using gradient sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis, no spectrin was detected in identical aliquots of the supernatants of normals and these control samples. Varying amounts of spectrin were detected in the first lysate supernatants of almost all thalassemic patients. The identification of spectrin was confirmed by Western blotting using an affinity-purified, monospecific, rabbit polyclonal antispectrin antibody. Relative amounts of spectrin detected were as follows in decreasing order: splenectomized beta-thal intermedia including HbE/beta-thal; HbCS/CS; nonsplenectomized beta-thal intermedia, HbH/CS; and, lastly, HbH. These findings were generally confirmed when we used an enzyme-linked immunosorbent assay technique to measure spectrin in the first lysate. Subsequent analyses showed that small amounts of actin and band 4.1 also appeared in lysates of thalassemic RBCs. Therefore, the three major membrane skeletal proteins are, to a varying degree, unstably attached in severe thalassemia. From these studies we could postulate that membrane association of abnormal or partially oxidized alpha-globin chains has a more deleterious effect on the membrane skeleton than do beta-globin chains.

Actins↗
PubMed1995

Rat neutrophil defensins. Precursor structures and expression during neutrophilic myelopoiesis.

Defensins constitute a family of 3- to 4-kDa antimicrobial peptides that are stored in the cytoplasmic granules of neutrophils, some macrophages, and intestinal Paneth cells. We have assessed defensin gene expression during myeloid differentiation by first characterizing cDNAs for each of the four known rat neutrophil defensins (RatNP 1-4). The cDNA sequences revealed that the peptides are synthesized as 87-94 amino acid precursors, each containing signal, pro-, and mature peptide segments. RatNP-3 and -4 mRNAs, but not those for RatNP-1 and -2 or other myeloid defensins, contained unique polypurine tracts located close to the termination codon in the 3' untranslated region. By using cDNA probes and/or riboprobes, we evaluated defensin transcript levels in a variety of tissues and in the full spectrum of neutrophil precursors. By in situ hybridization, defensin mRNAs were localized to neutrophil precursors in the bone marrow, with the highest mRNA levels occurring in promyelocytes and somewhat lower signals occurring in myeloblasts and myelocytes. Defensin mRNAs were not detectable in bands or mature neutrophils, nor at significant levels in tissues other than bone marrow. The accumulation of defensin protein in bone marrow cells was assessed by immunohistochemical staining with anti-RatNP-1 Ab. RatNP 1-4 mRNAs and protein levels were then correlated for each stage of neutrophilic differentiation to reveal the maturational profile of myeloid defensin gene expression in the rat.

Amino Acid Sequence↗
PubMed1995

p53 inactivation by HPV16 E6 results in increased mutagenesis in human cells.

To study the pathways associated with genomic instability in cancer, we examined UV-induced and spontaneous mutagenesis in clonal cell lines expressing human papillomavirus (HPV) proteins, either high-risk (HPV16) E6 or E7 or low-risk (HPV11) E6, in comparison to the parental RKO cells, a colon carcinoma cell line expressing only normal p53. High-risk E6 and E7 bind and functionally inactivate tumor suppressor proteins p53 and Rb, respectively, and both disrupt the G1 arrest in response to DNA damage. Low-risk HPV E6 proteins bind p53 with much lower affinity than high-risk E6 and fail to mediate p53 degradation or to disrupt the G1 checkpoint. We found that cells expressing HPV16 E6 had reduced survival and increased mutagenesis at the hprt locus when treated with low doses of UV. However, this analysis was complicated by the unexpected observation of a very high background of spontaneous mutagenesis in the unirradiated cells expressing the HPV16 E6 gene. Fluctuation analysis revealed a 5-fold elevated mutation rate in the cells expressing HPV16 E6. HPV11 E6 conferred a 2-fold elevation in the mutation rate, but HPV16 E7 had no effect. The increased spontaneous mutagenesis, therefore, appeared to be mediated by p53 inactivation and to be independent of Rb (which acts downstream of p53 in the G1 arrest pathway following DNA damage). Taken together, these findings suggest that the effect of p53 inactivation on spontaneous mutagenesis is manifested at the level of DNA repair, recombination, or coupling of transcription with one of these processes instead of by an alteration in G1 arrest.

Cell Survival↗
PubMed1995

Fenfluramine's appetite suppression and serotonin neurotoxicity are separable.

To determine whether fenfluramine's anorectic and neurotoxic effects could be dissociated, rats were treated with fenfluramine or the serotonin transporter blocker fluoxetine, alone or in combination. Fenfluramine alone produced anorexia, weight loss and lasting depletions of brain serotonin axon markers. Fluoxetine prevented fenfluramine-induced long-term serotonergic deficits, yet did not diminish fenfluramine's acute anorectic effects. These findings indicate that fenfluramine's anorectic and neurotoxic actions are distinct and separable.

Animals↗
PubMed1995

Tumor necrosis factor-induced apoptosis is mediated by a CrmA-sensitive cell death pathway.

We report here that the activation of the interleukin 1 beta (IL-1 beta)-converting enzyme (ICE) family is likely to be one of the crucial events of tumor necrosis factor (TNF) cytotoxicity. The cowpox virus CrmA protein, a member of the serpin superfamily, inhibits the enzymatic activity of ICE and ICE-mediated apoptosis. HeLa cells overexpressing crmA are resistant to apoptosis induced by Ice but not by Ich-1, another member of the Ice/ced-3 family of genes. We found that the CrmA-expressing HeLa cells are resistant to TNF-alpha/cycloheximide (CHX)-induced apoptosis. Induction of apoptosis in HeLa cells by TNF-alpha/CHX is associated with secretion of mature IL-1 beta, suggesting that an IL-1 beta-processing enzyme, most likely ICE itself, is activated by TNF-alpha/CHX stimulation. These results suggest that one or more members of the ICE family sensitive to CrmA inhibition are activated and play a critical role in apoptosis induced by TNF.

Apoptosis↗
PubMed1995

Influence of an anti-angiogenic treatment on 9L gliosarcoma: oxygenation and response to cytotoxic therapy.

Tissue oxygen tensions were measured in subcutaneously growing rat 9L gliosarcoma under normal air and carbogen breathing conditions prior to and after i.v. administration of a perflubron emulsion. When these animals were treated with the anti-angiogenic agents TNP-470 and minocycline for 5 days prior to oxygen measurement, tumor hypoxia was decreased compared with untreated tumors. Hypoxia, defined as the percent of pO2 readings < or = 5 mm Hg, was decreased from 71% in untreated air-breathing controls to 34% in animals treated with the anti-angiogenic agents, the perflubron emulsion and carbogen breathing. These effects were manifest in the increased response of the tumor to single-dose (10, 20 and 30 Gy) radiation therapy. Twenty-four hours after treatment with BCNU oxygenation of the tumors was not altered; however, 24 hr after administration of adriamycin oxygenation of the tumors was increased such that hypoxia in adriamycin-treated tumors in animals receiving the perflubron emulsion and carbogen was reduced to 21%. Tumor growth delay in the s.c. tumors was increased by the addition of treatment with the anti-angiogenic agents from day 4 through day 18 post-tumor cell implantation along with BCNU or adriamycin on days 7-11. Administration of the perflubron emulsion and carbogen breathing resulted in increased tumor growth delay with the chemotherapeutic agents alone and in combination with the anti-angiogenic agents. Life span in animals bearing intracranially implanted 9L gliosarcoma progressively increased with administration of the anti-angiogenic agents and then the anti-angiogenic agents and perflubron emulsion/carbogen compared to treatment with BCNU or adriamycin.

Animals↗
PubMed1995

A chloroplast homologue of the signal recognition particle subunit SRP54 is involved in the posttranslational integration of a protein into thylakoid membranes.

The mechanisms involved in the integration of proteins into the thylakoid membrane are largely unknown. However, many of the steps of this process for the light-harvesting chlorophyll a/b protein (LHCP) have been described and reconstituted in vitro. LHCP is synthesized as a precursor in the cytosol and posttranslationally imported into chloroplasts. Upon translocation across the envelope membranes, the N-terminal transit peptide is cleaved, and the apoprotein is assembled into a soluble "transit complex" and then integrated into the thylakoid membrane via three transmembrane helices. Here we show that 54CP, a chloroplast homologue of the 54-kDa subunit of the mammalian signal recognition particle (SRP54), is essential for transit complex formation, is present in the complex, and is required for LHCP integration into the thylakoid membrane. Our data indicate that 54CP functions posttranslationally as a molecular chaperone and potentially pilots LHCP to the thylakoids. These results demonstrate that one of several pathways for protein routing to the thylakoids is homologous to the SRP pathway and point to a common evolutionary origin for the protein transport systems of the endoplasmic reticulum and the thylakoid membrane.

Animals↗
PubMed1995

Interleukin-6-induced serine phosphorylation of transcription factor APRF: evidence for a role in interleukin-6 target gene induction.

The cytokine interleukin-6 (IL-6) rapidly activates a latent cytoplasmic transcription factor, acute-phase response factor (APRF), by tyrosine phosphorylation. Activation and DNA binding of APRF are inhibited by inhibitors of protein tyrosine kinases but not serine/threonine kinases. However, immediate-early gene induction by IL-6 and, as we show here, stimulation of the promoters of the genes for alpha 2-macroglobulin, Jun-B, and intercellular adhesion molecule-1 (ICAM-1) are blocked by the serine/threonine kinase inhibitor H7. We now show that IL-6 triggers a delayed phosphorylation of APRF at serine resudues which can be reversed in vitro by protein phosphatase 2A and is also inhibited by H7. Therefore, APRF serine phosphorylation is likely to represent a crucial event in IL-6 signal transduction leading to target gene induction.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1995

Characterization of polymorphism within the H2-M MHC class II loci.

The products of the class II-like H2-M genes of the major histocompatibility complex are required for class II antigen processing. We sequenced H2-Ma and Mb from several mouse strains to determine whether these genes are polymorphic like the classical H2-A and E genes, or are oligomorphic, like H2-O. Both Mb loci appear to be transcribed and are distinct from each other. Mb1 and Mb2 differ by about 11% at the nucleotide level and are most dissimilar in their second exons (corresponding to the beta 1 domain). Relative to the published Mb1d haplotype sequence, the products of the b, g7, f, and k2 alleles of Mb1 from Mus musculus domesticus and the separate mouse species Mus spretus differ by only one to four amino acids. The majority of the changes occurred in the second exon of Mb1, in contrast to HLA-DMB, the human orthologue. Little polymorphism was seen for Mb2, and Ma was invariant in all strains tested. The similarity of the g7 allele to those from other haplotypes makes it unlikely that the M class II genes play a role in the autoimmune diabetes of NOD strain mice. The M genes are regulated in a manner similar to classical class II genes, in that they are upregulated by IFN-gamma in macrophages, and to a lesser extent by IL4 in B cells. When modeled on the crystal structure of the HLA-DR1 class II molecule, nearly all of the differences between M beta 1 and M beta 2 affect residues facing away from the putative peptide binding groove.

Amino Acid Sequence↗
PubMed1995

Determination of protein binding by in vitro charcoal adsorption.

Certain compounds such as SC-52151 have extensive nonspecific adsorption to the ultrafiltration devices or to dialysis membranes and therefore can not be measured by the conventional ultrafiltration or equilibrium dialysis methods. A new method based on charcoal adsorption was developed to overcome this difficulty. Unlike many conventional methods, which are based on the separation of free drug from bound drug under equilibrium conditions, the new method is operated under nonequilibrium conditions and involves measuring the time course of decline of the percentage of bound drug remaining in plasma while the free drug is being removed by charcoal adsorption. Theoretical aspects of the method and the data processing procedure are presented. SC-98A, a compound with minimal nonspecific adsorption to the ultrafiltration membrane, was used to demonstrate the applicability of this method against the ultrafiltration method. Using this method, the protein binding of SC-52151 in human plasma at 1.0 microgram/ml was determined to be in the range of 91.4-97.7% at room temperature.

Adsorption↗