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Biomedical subjects

H Yu

Publications and source records attributed to H Yu.

At least 487 records · Page 27Linked to original sources
PubMed1997

Computational contact analysis of joint congruency.

Joint contact analysis of the musculoskeletal system is an important biomedical research topic due to its significant clinical relevance. In this research, the finite element method was used to study the effect of joint congruencies (various radii, R1 and R2), contact area (angles theta), and contact stresses of articular joints (the far-field applied pressure, P = 10,000 Pa). In total, 12 joint congruency cases, ranging from R1/R2 = 100% (congruent) to R1/R2 = -100% (highly incongruent) were analyzed. The linear finite element (quasi-static/equilibrium) results show that peak contact stress delta r of a congruent joint (R1 = R2 theta = 90 degrees) is -13,068 Pa. However, with a slight change of joint congruency (R1/R2 = 99.7%), the contact area decreases dramatically (theta = 30 degrees) and leads to a much higher concentrated contact stress, delta r = -27,894 Pa. When R1/R2 = -100%, the finite element result shows that the contact region is only theta = 3 degrees and the associate peak contact stress delta r is -229,943 Pa.

Computer Simulation↗
PubMed1997

[Behaviour after transplantation of brain cells into monkey models of Parkinson's disease].

OBJECTIVE: To observe the improved degree of pathogenic behaviour in monkey models of Parkinson's disease after transplantation of substantia nigra cells of human fetus. METHOD: 1-methy-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) was used to prepare monkey models of hemiparkinson's disease, i.e., early substantia nigra cells of human fetus were stereotaxically transplanted into PD monkey's behaviour for six months, using immuno-electromicroscopy to prove the transplanted survived neuron. RESULTS: After transplantation, the model monkey's motion slow and muscle hypertonia was apparently improved. Limb tremor almost disappeared, Right spontaneous rotation behavior relieved. Rotating frequency caused by APO became less than before transplanytation, and its effect could last a year. Under the immunoelectromicroscope, we observed that transplanted tyrosine hydroxylase positive neuron was connected with the host brain cells in synapse. CONCLUSION: Substantia nigra neuron transplanted into the PD monkey brain can establish synaptic connection with the host nervous cells. Pathogenic symptoms are improved and the effect may remain for a longer time.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1997

[Genetic subtyping of HIV-1 strains by heteroduplex mobility assay].

DNA fragments of HIV-1 env gene were amplified by nested PCR from uncultured peripheral blood mononuclear cells (PBMCs) obtained from 24 HIV-1 infected individuals. The PCR products were separated by melting and annealing with denatured PCR product prepared from reference plasimd of representative subtypes. Heteroduplex were then formed between the single-stranded DNA from the two sources and were analysed on polyacrylamide gels. The results from heteroduplex mobility assay (HMA) were compared with HIV-1 subtype results determined by DNA sequencing. With advantages of high speed, low cost and high specificity, HMA is a reliable screening method for HIV-1 subtyping.

Acquired Immunodeficiency Syndrome↗
PubMed1996

The Conductivity Confined Temperature Dependence of Water-Free Electrorheological Fluids

The shear stresses and the current densities of four sorts of water-free ER fluids, two oxidized polyacrylonitriles-based and two aluminosilicates-based, were investigated at elevated and reduced temperatures in order to elucidate the operating mechanism. The complicated relationships among the mechanical properties, the current density, and temperature were especially addressed. The Wagner model was introduced to interpret our observations, instead of the commonly used conductivity model. It is found that the conductivity of the dispersed particles determines the temperature dependence of the shear stress and the current density of an ER fluid. Our findings have direct implication for the design of industrially required ER fluids and would be significant for ER applications.

Journal Article↗
PubMed1996

CDC42 and Rac1 are implicated in the activation of the Nef-associated kinase and replication of HIV-1.

BACKGROUND: The negative factor (Nef) of human and simian immunodeficiency viruses (HIV-1, HIV-2 and SIV) is required for high levels of viremia and progression to AIDS. Additionally, Nef leads to cellular activation, increased viral infectivity and decreased expression of CD4 on the cell surface. Previously, we and others demonstrated that Nef associates with a cellular serine kinase (NAK) activity. Recently, it was demonstrated that NAK bears structural and functional similarity to p21-activated kinases (PAKs). RESULTS: In this study, we demonstrate that Nef not only binds to but also activates NAK via the small GTPases CDC42 and Rac1. First, the dominant-negative PAK (PAKR), via its GTPase-binding domain, and dominant-negative GTPases (CDC42Hs-N17 and Rac1-N17) block the ability of Nef to associate with and activate NAK. Second, constitutively active small GTPases (CDC42Hs-V12 and Rac1-V12) potentiate the effects of Nef. Third, interactions between Nef and NAK result in several cellular effector functions, such as activation of the serum-response pathway. And finally, PAKR, CDC42Hs-N17 and Rac1-N17 decrease levels of HIV-1 production to those of virus from which the nef gene is deleted. CONCLUSIONS: By activating NAK via small GTPases and their downstream effectors, Nef interacts with regulatory pathways required for cell growth, cytoskeletal rearrangement and endocytosis. Thus, NAK could participate in the budding of new virions, the modification of viral proteins and the increased endocytosis of surface molecules such as CD4. Moreover, blocking the activity of these GTPases could lead to new therapeutic interventions against AIDS.

3T3 Cells↗
PubMed1996

Activation of a novel calcium-dependent protein-tyrosine kinase. Correlation with c-Jun N-terminal kinase but not mitogen-activated protein kinase activation.

Many G protein-coupled receptors (e.g. that of angiotensin II) activate phospholipase Cbeta, initially increasing intracellular calcium and activating protein kinase C. In the WB and GN4 rat liver epithelial cell lines, agonist-induced calcium signals also stimulate tyrosine phosphorylation and subsequently increase the activity of c-Jun N-terminal kinase (JNK). We have now purified the major calcium-dependent tyrosine kinase (CADTK), and by peptide and nucleic acid sequencing identified it as a rat homologue of human PYK2. CADTK/PYK2 is most closely related to p125(FAK) and both enzymes are expressed in WB and GN4 cells. Angiotensin II, which only slightly increases p125(FAK) tyrosine phosphorylation in GN4 cells, substantially increased CADTK tyrosine autophosphorylation and kinase activity. Agonists for other G protein-coupled receptors (e.g. LPA), or those increasing intracellular calcium (thapsigargin), also stimulated CADTK. In comparing the two rat liver cell lines, GN4 cells exhibited approximately 5-fold greater angiotensin II- and thapsigargin-dependent CADTK activation than WB cells. Although maximal JNK activation by stress-dependent pathways (e.g. UV and anisomycin) was equivalent in the two cell lines, calcium-dependent JNK activation was 5-fold greater in GN4, correlating with CADTK activation. In contrast to JNK, the thapsigargin-dependent calcium signal did not activate mitogen-activated protein kinase and Ang II-dependent mitogen-activated protein kinase activation was not correlated with CADTK activation. Finally, while some stress-dependent activators of the JNK pathway (NaCl and sorbitol) stimulated CADTK, others (anisomycin, UV, and TNFalpha) did not. In summary, cells expressing CADTK/PYK2 appear to have two alternative JNK activation pathways: one stress-activated and the other calcium-dependent.

Amino Acid Sequence↗
PubMed1996

Circulating antibodies against p53 protein in patients with ovarian carcinoma. Correlation with clinicopathologic features and survival.

BACKGROUND: Genetic alterations of the p53 tumor suppressor protein are the most frequent molecular events in human carcinogenesis. For as yet unknown reasons, mutant p53 often acts as an immunogen for autoantibody generation. These autoantibodies can be detected in the serum of cancer patients. The presence of such antibodies has been identified in a subset of patients with ovarian carcinoma, but their clinical significance has not been investigated. METHODS: Serum samples from patients with ovarian carcinoma were quantitatively analyzed for the presence of p53 autoantibodies with a time-resolved immunofluorometric procedure. Tumor p53 overexpression was assessed by immunohistochemical analysis of tissue sections. Kaplan-Meier survival curves were calculated for p53 antibody positive and negative patients, and the Cox model was used to evaluate the strength of the associations between the presence of serum p53 antibodies and cancer relapse or death, and also between the presence of such antibodies and other clinicopathologic features. RESULTS: p53 antibodies were detected in the serum of 41 of 174 patients with ovarian carcinoma (24%). Antibody levels ranged from a few hundred to 9 x 10(6) arbitrary Units/L, and fluctuated during the course of the disease. p53 antibody positive patients tended to have tumors overexpressing p53, but the association between the two parameters was not statistically significant (P = 0.13). There was also no association between the presence of p53 antibodies and clinical stage, tumor histologic type, or overall patient survival. However, these antibodies were more frequently present in patients older than 50 years (P = 0.001), in patients with moderately or poorly differentiated tumors (P = 0.001), and in patients who received chemotherapy (P = 0.015), and who suffered relapse after surgery (P = 0.018). In univariate analysis, p53 antibody positive patients were at an increased risk for relapse but not death. In multivariate analysis, the differences in disease free and overall survival between patients who were p53 antibody positive or negative were not statistically significant. CONCLUSIONS: p53 autoantibodies are found frequently in the serum of patients with ovarian carcinoma. The presence of such autoantibodies was associated with older patient age, more aggressive tumors, and reduced patient disease free survival. In multivariate analysis the prognostic value of p53 autoantibodies was not statistically significant.

Adolescent↗
PubMed1996

Iron-ascorbate-phospholipid mediated modification of low density lipoprotein.

LDL can be oxidized by a variety of agents to form a modified lipoprotein which is capable of being avidly metabolized by macrophages. While previous in vitro studies have focused exclusively on the oxidation of LDL, other lipids found in the atheroma are also subject to oxidation and its lipoperoxide byproducts may contribute to the process of LDL modification. To examine the relationship between the oxidation of phospholipids and the subsequent modification of LDL, we incubated 250 microM phosphatidylcholine with 10 microM ferrous sulfate and 50 microM ascorbic acid in 10 mM Tris (pH 7.0). After 18 h at 37 degrees C, significant amounts of thiobarbituric acid reactive substances (TBARS) were formed. The inclusion of LDL (100 micrograms protein/ml) elevated the TBARS and increased the electrophoretic mobility of the lipoprotein. LDL treated with iron and ascorbate in the absence of phosphatidylcholine did not result in the modification of this lipoprotein. LDL that was incubated with phosphatidylcholine, iron and ascorbate was found to be metabolized by macrophages to a far greater extent than native LDL or LDL treated with phosphatidylcholine alone. Probucol (10 microM) inhibited the LDL modification process. These results demonstrate that while iron and ascorbate cannot oxidize LDL directly, the addition of phosphatidylcholine to these initiators of lipid peroxidation can mediate and lead to the modification of LDL.

Animals↗
PubMed1996

Enhancing immunoelectrochemiluminescence (IECL) for sensitive bacterial detection.

Immunoelectrochemiluminescence (IECL) as an alternative method versus immunochemiluminescent and immunofluorescent methods can be used for versatile applications in biological agent detection. Although IECL offered high reproducibility and sensitive detection capability for soluble antigens and nucleic acids in aqueous phase, the IECL assays are not optimal and many factors which can affect the IECL performance still remain unclear. Further IECL kinetic studies, improvement of antibody biotinylation, magnetic particle selection and reducing non-specific binding have shown that the enhanced IECL sensitivities (signal to background noise ratios) can be potentially increased at least ten-fold compared to the sensitivities with general IECL assay procedures for bacterial detection.

Antigens, Bacterial↗
PubMed1996

Differential serotoninergic and dopaminergic activities of the (R)- and the (S)-enantiomers of 2-(di-n-propylamino)tetralin.

Racemic 2-(di-n-propylamino)tetralin ((R,S)-DPAT), which lacks phenolic or other aromatic substituents, induces both dopaminergic (sniffing, licking and gnawing) and serotoninergic (forepaw treading and flat body posture) behavioural responses. The present study shows that s.c. administration of (R)-DPAT induces typical 5-HT1A receptor agonist behaviours. These effects are blocked by the 5-HT1A receptor antagonist (S)-5-fluoro-8-hydroxy-2-(di-n-propylamino)tetralin ((S)-UH-301). Administration of (S)-DPAT induces dopaminergic behaviours, which are fully antagonised by raclopride, a dopamine D2 receptor antagonist. Both enantiomers induce hypothermia, (R)-DPAT being antagonised by (S)-UH-301, whereas (S)-DPAT is antagonised by raclopride. The accumulation of 5-hydroxytryptophan and DOPA (3,4-dihydroxyphenylalanine) after decarboxylase inhibition that reflects presynaptic actions on 5-HT (5-hydroxytryptamine, serotonin) and dopamine neurons, respectively, are inhibited by both enantiomers of DPAT. (R)-DPAT is more potent than (S)-DPAT as an inhibitor of 5-hydroxytryptophan accumulation whereas (S)-DPAT is more potent than (R)-DPAT as an inhibitor of DOPA accumulation. Thus, in functional tests of postsynaptic actions (R)-DPAT behaves as a 5-HT1A receptor agonist and (S)-DPAT as a dopamine D2 receptor agonist. Presynaptically, (R)-DPAT shows selectivity for 5-HT1A receptors and (S)-DPAT for dopamine D2 receptors. Receptor binding studies, utilizing [3H]8-hydroxy-2-(di-n-propylamino)tetralin and [3H]quinpirole as radioligands for 5-HT1A and dopamine D2 receptors, respectively, showed (R)-DPAT to have a 3-fold higher affinity than (S)-DPAT for 5-HT1A receptors, whereas (S)-DPAT had a 6-fold higher affinity than (R)-DPAT for dopamine D2 receptors. Thus, the results from receptor binding studies support the conclusion that (R)- and (S)-DPAT are agonists showing selectivity for 5-HT1A and dopamine D2 receptors, respectively. Taken together, these findings may explain previous controversies with regard to the pharmacology of racemic DPAT and re-emphasise the necessity to study pure enantiomers of chiral compounds.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1996

Identification of a novel ubiquitin-conjugating enzyme involved in mitotic cyclin degradation.

BACKGROUND: The destruction of cyclin B is required for exit from mitosis, and is mediated by the ubiquitin pathway. Recently, a 20S complex, termed the anaphase-promoting complex (APC) or the cyclosome, has been genetically and biochemically identified as the cyclin-specific ubiquitin ligase (E3). In addition, a ubiquitin-conjugating enzyme (E2), UBC4, was shown to be involved in cyclin ubiquitination in Xenopus egg extracts. Another E2 activity, designated UBCx, can independently support cyclin ubiquitination in Xenopus. A similar activity (E2-C) has also been observed in clams. However, the molecular identity of Xenopus UBCx or clam E2-C has not been established. RESULTS: We have purified and cloned Xenopus UBCx. Sequence comparisons with known E2s reveal that UBCx is a novel ubiquitin-conjugating enzyme. Purified recombinant UBCx is sufficient to complement purified APC and E1 in destruction box-dependent cyclin ubiquitination. UBCx and UBC4 are active in a similar concentration range and with similar kinetics. At saturating enzyme concentrations, UBCx converts twice as much substrate into ubiquitin conjugates, but generates conjugates of lower molecular mass than UBC4. CONCLUSIONS: UBCx is a novel ubiquitin-conjugating enzyme involved in cyclin ubiquitination in Xenopus. Like UBC4, ubiquitination catalyzed by UBCx is dependent on both the destruction box and the APC, suggesting that these E2s function through a similar mechanism. However, as the patterns of conjugates generated by these E2s are distinct, these enzymes may play different roles in promoting cyclin proteolysis in mitosis.

Amino Acid Sequence↗
PubMed1996

Photolyase of Myxococcus xanthus, a Gram-negative eubacterium, is more similar to photolyases found in Archaea and "higher" eukaryotes than to photolyases of other eubacteria.

We report the identification of the gene encoding a DNA photolyase (phrA) from the Gram-negative eubacterium Myxococcus xanthus. The deduced amino acid sequence of M. xanthus photolyase indicates that the protein contains 401 amino acids (Mr 45,071). By comparison of the amino acid and DNA sequences with those of other known photolyases, it has been found that it is more similar to the deduced amino acid sequences of the photolyases of "higher" eukaryotes than to the photolyases of other eubacteria. Recombinant plasmids carrying M. xanthus phrA rescue the photoreactivation activity of an irradiated strain of Escherichia coli with a deletion in phrA. This rescue is light-dependent.

Amino Acid Sequence↗
PubMed1996

A new phospholipase C delta 4 is induced at S-phase of the cell cycle and appears in the nucleus.

To discover a new phospholipase C (PLC) related to cell growth, we screened a cDNA library prepared from regenerating rat liver. A novel PLC (PLC delta 4) encoding a polypeptide of 770 amino acids with structural similarity to PLC delta-type isozymes was isolated. PLC delta 4 mRNA is expressed more remarkably in regenerating liver than in normal resting liver. It is also distributed abundantly in tumor cells such as hepatoma and src-transformed cells. Furthermore, its expression can be induced markedly by serum treatment and reaches a maximum at 8 h. Western blot analysis and immunocytochemical staining showed that PLC delta 4 is dominantly present in nucleus. Nuclear PLC delta 4 dramatically increases at the transition from G1- to S-phase, and the high content continues to the end of M-phase. PLC delta 4 almost disappears when cells re-enter the next G1-phase. On the other hand, the contents of PLC beta 1, PLC gamma 1, and PLC delta 1 do not change significantly during the cell cycle. These results suggest that PLC delta 4 is expressed in nucleus in response to mitogenic stimulation and plays important roles in cell growth as one of the early genes expressed during the transition from G1- to S-phase in the cell cycle.

3T3 Cells↗
PubMed1996

Body dissatisfaction among Chinese undergraduates and its implications for eating disorders in Hong Kong.

OBJECTIVES: To study the body dissatisfaction of Chinese undergraduates and its implications for eating disorders in Hong Kong. METHOD: A large sample of 1,581 subjects completed a "Body Dissatisfaction Questionnaire" (BDQ) which included 25 items about various body parts and questions on body indices, body shape dissatisfaction, and dieting. RESULTS: Whereas male subjects wanted to be taller and stronger in their upper body, the majority of female subjects felt fat in their lower body and were cognitively inclined to weigh less even though they were not obese. They desired a slimming of the stomach, thighs, waist and hip, but not the breasts. Body dissatisfaction was substantially intensified in females who reported a history of dieting in the previous year. Factor analysis of the BDQ affirmed the gender specificity and multidimensionality of body dissatisfaction. DISCUSSION: The typically "Western" pattern of body dissatisfaction has overshadowed the traditional Chinese notions of female beauty based on the face and other nontruncal features. In the context of a rapidly urbanizing Chinese society, this will predispose more females to weight control behavior and eating disorders.

Adolescent↗