Biomedical subjects

Y Han

Publications and source records attributed to Y Han.

At least 163 records · Page 9Linked to original sources

PubMed1999

Deglycosylation of a bifunctional lutropin-follitropin agonist reduced its follitropin activity more than its lutropin activity.

OBJECTIVE: To design a drug that blocks the gonadal actions of lutropins and follitropins. DESIGN: Controlled in vitro study. SETTING: Academic laboratory. PATIENT(S): None. INTERVENTION(S): We removed three glycosylation signals from an hCG-hFSH chimera known to have high affinity for LH and FSH receptors, expecting this would create a bifunctional antagonist (dgCFC). To offset the inhibition of subunit combination caused by deglycosylation of alpha-subunit loop 2, we prepared dgCFC as a single-chain fusion protein containing the alpha-subunit downstream of the chimeric beta-subunit. MAIN OUTCOME MEASURE(S): Receptor binding, cyclic adenosine monophosphate accumulation. RESULT(S): dgCFC bound LH or FSH receptors similar to hCG or hFSH. It was a partial agonist and had one tenth the efficacy of hFSH and two thirds the efficacy of hCG. CONCLUSION(S): The surprising high residual lutropin activity of dgCFC indicated that its FSH residues offset the effects of deglycosylation, suggesting this approach to preparing a bifunctional antagonist is unlikely to lead to a useful drug. The increased lutropin efficacy of dgCFC relative to deglycosylated hCG supports the idea that oligosaccharides modulate glycoprotein hormone efficacy through an influence on hormone conformation.

Amino Acid Sequence↗

PubMed1999

Transcriptional regulation of angiotensinogen gene expression.

The renin--angiotensin system (RAS) is an extracellular hormonal system implicated in acute, homeostatic control of peripheral vascular resistance and electrolyte homeostasis. In this tightly regulated system, physiological regulators of blood pressure and fluid balance induce the production of the potent vasoactive angiotensin peptides by sequential proteolysis of the angiotensinogen (AGT) prohormone. AGT is the only known precursor of the angiotensin peptides, whose circulating concentrations influence the tonic activity of the RAS. AGT abundance is regulated at the transcriptional level through hormonal and cell-type specific regulators. In this review, we will discuss the identified mechanisms controlling AGT expression separately for the rodent and human genes. The most intensively investigated gene (rodent AGT) is regulated constitutively by multiple positive- and negative-acting cis factors that function in a cell-type dependent fashion. Inducible rodent AGT expression is mediated through a multihormone-inducible enhancer that integrates signals from steroid and cytokine hormones into AGT transcription. We review recent advances in understanding the mechanism of the nuclear factor-kappa B (NF-kappa B) family in mediating cytokine-induced AGT expression and our recent discoveries on the existence of differentially inducible pools of cytoplasmic NF-kappa B. Constitutive control of the human AGT gene will be discussed; there is surprisingly little information on the cis- and trans-acting regulators controlling inducible expression of human AGT. Finally, we will explore some of the recent developments in gene linkage studies where human AGT alleles have been associated with hypertensive phenotypes through a mechanism that may involve enhanced transcription. These studies have provided a molecular explanation for a subset of heritable hypertensive disorders in humans.

Angiotensinogen↗

PubMed1999

Prostaglandin E2-bisphosphonate conjugates: potential agents for treatment of osteoporosis.

Conjugates of bisphosphonates (potential bone resorption inhibitors) and prostaglandin E2 (a bone formation enhancer) were prepared and evaluated for their ability to bind to bone and to liberate, enzymatically, free PGE2. The conjugate 3, an amide at C-1 of PGE2 proved to be too stable in vivo while conjugate 6, a thioester, was too labile. Several PGE2, C-15 ester-linked conjugates (18, 23, 24 and 31) were prepared and conjugate 23 was found to bind effectively to bone in vitro and in vivo and to liberate PGE2 at an acceptable rate. A 4-week study in a rat model of osteoporosis showed that 23 was better tolerated and more effective as a bone growth stimulant than daily maximum tolerated doses of free PGE2.

Animals↗

PubMed1999

Morphology and composition of hydroxyapatite coatings prepared by hydrothermal treatment on electrodeposited brushite coatings.

Highly pure brushite (CaHPO4.2H2O) coatings on porous Ti6Al4V substrates were prepared by electrodeposition from aqueous electrolytes. The influence of hydrothermal treatment parameters on brushite-to-hydroxyapatite conversion and the morphology and phase composition of hydroxyapatite (HAP) coatings was studied. It was found that the content, Ca/P atomic ratio, grain size and pore size of HAP in coatings increase with increasing hydrothermal treatment temperature, and that increasing the pH value can promote brushite-to-HAP conversion and reduce the grain size of HAP. Under optimal conditions, highly pure HAP coatings with needle-like crystals and non-stoichiometric form, which are similar to those of calcium phosphate in human bone, can be obtained.

Journal Article↗

PubMed1999

Assessment of contrast sensitivity in children aged 3 years 9 months - 6 years with normal vision, visual impairment due to ocular disease and strabismic amblyopia.

The contrast sensitivity function was assessed in children and adults with normal vision, visual impairment due to ocular disease, and strabismic amblyopia. The methods used were: the LH contrast vision test and the ability to detect raisins, puffed rice and white and black sugar strands against a white and black background. The aim of the study was to see whether any of the tests could be used in the detection of subnormal vision, and to compare the results between the different groups of patients. The following parameters of contrast sensitivity function (CSF) were measured with the LH-test: the maximum contrast sensitivity, the total area of CSF, and the area of 8 spatial frequency bands. Difficulty in detecting an object with low versus high contrast was measured with the sugar strands. Subjects with subnormal vision due to ocular disease and strabismic amblyopia had lower contrast sensitivity than subjects with normal vision measured as the total area of the CSF or the area of a specific frequency band. However, the maximum contrast sensitivity value that could be measured with the test was not significantly different between the groups. No subject had difficulties in the detection of raisins and puffed rice on a white and black background. Difficulties in detecting sugar strands on a white background were not seen in the normal children, but approximately 65% of the children with visual impairment had difficulties, as did approximately 25% of the children and adults with strabismus. Most of these subjects also had low visual acuity, but there was no correlation between the level of reduction of visual acuity and the difficulty in detecting sugar strands.

Adult↗

PubMed1999

Candida albicans mannan extract-protein conjugates induce a protective immune response against experimental candidiasis.

Candida albicans mannan extracts encapsulated in liposomes were previously used to stimulate mice to produce antibodies protective against candidiasis. In the present study, mannan-protein conjugates without liposomes were tested as vaccine candidates. Mannan extracts were coupled to bovine serum albumin, and isolated conjugates consisted of carbohydrate and protein at a ratio of 0.7-1.0. Vaccination of mice with the conjugate and an adjuvant yielded antiserum that contained Candida agglutinins. Vaccinated mice challenged with yeast cells had a mean survival time of 56 days, compared with <13 days for control groups. The antiserum protected naive animals against disseminated disease. Naive mice given the antiserum intravaginally developed 79% fewer fungal colony-forming units, compared with control groups. The serum-protective factor was stable at 56 degrees C and was removed by adsorption with yeast cells. It is concluded that the conjugate vaccine can induce protective antibody responses against experimental disseminated candidiasis and Candida vaginal infection.

Animals↗

PubMed1999

Tumor necrosis factor-alpha signals to the IFN-gamma receptor complex to increase Stat1alpha activation.

We describe a novel mechanism of signaling interaction through which tumor necrosis factor-alpha (TNF-alpha) treatment augments interferon-gamma (IFN-gamma)-induced Stat1alpha DNA-binding complexes and transcriptional activation of a Stat-binding element. In TNF-alpha-treated cells, IFN-gamma-induced phosphorylation of Jak2 kinase is increased, Jak2 kinase activity is enhanced, and genetic studies indicate that TNF-alpha requires Jak2 kinase activity to enhance Stat1alpha tyrosine phosphorylation. Increased Jak2 and Stat1alpha phosphorylation are observed within minutes of coexposure to TNF-alpha/IFN-gamma, suggesting a direct signaling interaction. IFN-gamma receptor chain 1 (IFNGR-1) tyrosine phosphorylation is markedly enhanced in cells treated with TNF-alpha/IFN-gamma without alteration in receptor levels. Thus, there exists a direct signaling interaction between TNF-alpha and IFN-gamma, independent of cooperating enhancer elements, that may be relevant for cytokine action during immune-mediated host defense and inflammatory processes.

DNA-Binding Proteins↗

PubMed1999

Spasticity in rats with sacral spinal cord injury.

We have investigated sacral spinal cord lesions in rats with the goal of developing a rat model of muscular spasticity that is minimally disruptive, not interfering with bladder, bowel, or hindlimb locomotor function. Spinal transections were made at the S2 sacral level and, thus, only affected the tail musculature. After spinal transection, the muscles of the tail were inactive for 2 weeks. Following this initial period, hypertonia, hyperreflexia, and clonus developed in the tail, and grew more pronounced with time. These changes were assessed in the awake rat, since the tail is readily accessible and easy to manipulate. Muscle stretch or cutaneous stimulation of the tail produced muscle spasms and marked increases in muscle tone, as measured with force and electromyographic recordings. When the tail was unconstrained, spontaneous or reflex induced flexor and extensor spasms coiled the tail. Movement during the spasms often triggered clonus in the end of the tail. The tail hair and skin were extremely hyperreflexive to light touch, withdrawing quickly at contact, and at times clonus could be entrained by repeated contact of the tail on a surface. Segmental tail muscle reflexes, e.g., Hoffman reflexes (H-reflexes), were measured before and after spinalization, and increased significantly 2 weeks after transection. These results suggest that sacral spinal rats develop symptoms of spasticity in tail muscles with similar characteristics to those seen in limb muscles of humans with spinal cord injury, and thus provide a convenient preparation for studying this condition.

Animals↗

PubMed1999

Exploring the conformational diversity of loops on conserved frameworks.

Loops are structurally variable regions, but the secondary structural elements bracing loops are often conserved. Motifs with similar secondary structures exist in the same and different protein families. In this study, we made an all-PDB-based analysis and produced 495 motif families accessible from the Internet. Every motif family contains some variable loops spanning a common framework (a pair of secondary structures). The diversity of loops and the convergence of frameworks were examined. In addition, we also identified 119 loops with conformational changes in different PDB files. These materials can give some directions for functional loop design and flexible docking.

Computer Simulation↗

PubMed1999

Assessment of a geographically targeted field intervention on gonorrhea incidence in two New York State counties.

BACKGROUND AND OBJECTIVES: Using study findings that demonstrated the importance of core group members in gonorrhea transmission, in 1984, one New York State county changed its approach toward gonorrhea control by targeting its field intervention activities toward infected persons from a geographic core area. In late 1988, New York State experienced an epidemic increase in the number of syphilis cases. In response, the New York State sexually transmitted disease (STD) control program enacted a Syphilis Initiative, which required the diversion of field staff from gonorrhea to syphilis control activities for a 3-year period. Each of these events held the possibility of impacting gonorrhea incidence in this county. GOAL OF THIS STUDY: To evaluate the impact of core interventions on reducing gonorrhea incidence as compared to traditional nontargeted field intervention methods and to determine the influence on gonorrhea incidence of diverting field activities from gonorrhea to syphilis case finding. STUDY DESIGN: A Poisson regression method was used to estimate gonorrhea incidence for a 22-year period in two similar counties: one county that used core intervention and one that applied traditional case-finding methods. The impact of core intervention was estimated in terms of the reduction in the gonorrhea incidence rate from the preintervention incidence rates. RESULTS: After initiation of the core intervention, the relative risk of gonorrhea decreased by 61%. Between 30 % to 40% of the total reported cases were interviewed for contacts annually during the intervention period. In the control county, the relative risk was reduced by 50% despite a significantly higher percentage of annual case interviews (60%-70%). In addition, a small change in the definition of core (from census tracts encompassing 50% of gonorrhea cases to 30%-35%) during the Syphilis Initiative led to a significant increase (16%) in the relative risk of gonorrhea. CONCLUSION: Targeting partner notification activities toward a geographic core area population appears effective in reducing the risk of gonorrhea, and it was more efficient because the overall percentage of cases interviewed was smaller than in a county using a nontargeted approach. Diversion of staff during a syphilis epidemic, combined with a narrowing of the geographic scope of the core intervention, was associated with an increase in gonorrhea incidence.

Contact Tracing↗

PubMed1999

Ascorbate biosynthesis in Arabidopsis cell suspension culture.

The biosynthesis of L-ascorbic acid (L-AA) in an Arabidopsis (L.) Heynh. cell suspension culture was studied by quantifying the effects of incubation with a range of potential biosynthetic precursors, analogs, and inhibitors on the intracellular levels of reduced and oxidized forms of L-AA. Our results support the recently published biosynthetic pathway of L-AA from L-galactose (G.L. Wheeler, M.A. Jones, N. Smirnoff [1998] Nature 393: 365-369), but suggest that Arabidopsis cell suspension culture simultaneously contains two other routes leading to L-AA. The possible physiological significance of these alternate routes is discussed.

Arabidopsis↗

PubMed1999

Expression of an Aspergillus niger phytase gene (phyA) in Saccharomyces cerevisiae.

Phytase improves the bioavailability of phytate phosphorus in plant foods to humans and animals and reduces phosphorus pollution of animal waste. Our objectives were to express an Aspergillus niger phytase gene (phyA) in Saccharomyces cerevisiae and to determine the effects of glycosylation on the phytase's activity and thermostability. A 1.4-kb DNA fragment containing the coding region of the phyA gene was inserted into the expression vector pYES2 and was expressed in S. cerevisiae as an active, extracellular phytase. The yield of total extracellular phytase activity was affected by the signal peptide and the medium composition. The expressed phytase had two pH optima (2 to 2.5 and 5 to 5.5) and a temperature optimum between 55 and 60 degrees C, and it cross-reacted with a rabbit polyclonal antibody against the wild-type enzyme. Due to the heavy glycosylation, the expressed phytase had a molecular size of approximately 120 kDa and appeared to be more thermostable than the commercial enzyme. Deglycosylation of the phytase resulted in losses of 9% of its activity and 40% of its thermostability. The recombinant phytase was effective in hydrolyzing phytate phosphorus from corn or soybean meal in vitro. In conclusion, the phyA gene was expressed as an active, extracellular phytase in S. cerevisiae, and its thermostability was affected by glycosylation.

6-Phytase↗

PubMed1999

Role of the amino-terminal region of Porphyromonas gingivalis fimbriae in adherence to epithelial cells.

Porphyromonas gingivalis fimbriae elicit many responses in eukaryotic cells, including mitogenicity, cytokine production, epithelial cell invasion, and cellular immune response. Specific domains of the major fimbrial protein (FimA) have been shown to be important in triggering some of these functions. The goal of the present study was to identify the domain(s) of P. gingivalis FimA responsible for specific interaction with human mucosal epithelial cells. Fimbriated P. gingivalis strains have been shown to bind to buccal epithelial cells, whereas nonfimbriated strains bind at low levels or not at all. This and other studies provide evidence that FimA mediates the adherence of P. gingivalis to oral epithelial cells. To determine the specific region(s) of P. gingivalis FimA involved in epithelial cell binding, specific antipeptide antibodies were used to inhibit the binding of iodinated purified fimbriae as well as the binding of P. gingivalis cells to epithelial cells. Antibodies directed against peptides 49 to 68 (VVMANTAGAMELVGKTLAEVK) and 69 to 90 (ALTTELTAENQEAAGLIMTAEP) were found to highly inhibit both the binding of fimbriae and the binding of P. gingivalis cells to epithelial cells. The antibody against FimA peptides 69 to 90 also reacted with P. gingivalis fimbriae in immunogold labeling and immunoblot analysis, thereby indicating that this peptide domain is exposed on the surface of fimbriae. Our results suggest that the amino-terminal domain corresponding to amino acid residues 49 to 90 of the fimbrillin protein is a major epithelial cell binding domain of P. gingivalis fimbriae.

Amino Acid Sequence↗

PubMed1999

Interactions of the papovavirus DNA replication initiator proteins, bovine papillomavirus type 1 E1 and simian virus 40 large T antigen, with human replication protein A.

Papovaviruses utilize predominantly cellular DNA replication proteins to replicate their own viral genomes. To appropriate the cellular DNA replication machinery, simian virus 40 (SV40) large T antigen (Tag) binds to three different cellular replication proteins, the DNA polymerase alpha-primase complex, the replication protein A (RPA) complex, and topoisomerase I. The functionally similar papillomavirus E1 protein has also been shown to bind to the DNA polymerase alpha-primase complex. Enzyme-linked immunoassay-based protein interaction assays and protein affinity pull-down assays were used to show that the papillomavirus E1 protein also binds to the cellular RPA complex in vitro. Furthermore, SV40 Tag was able to compete with bovine papillomavirus type 1 E1 for binding to RPA. Each of the three RPA subunits was individually overexpressed in Escherichia coli as a soluble fusion protein. These fusion proteins were used to show that the E1-RPA and Tag-RPA interactions are primarily mediated through the 70-kDa subunit of RPA. These results suggest that different viruses have evolved similar mechanisms for taking control of the cellular DNA replication machinery.

Antigens, Polyomavirus Transforming↗

PubMed1999

Chemokine expression in GKO mice (lacking interferon-gamma) with experimental autoimmune encephalomyelitis.

Experimental autoimmune encephalomyelitis (EAE) is an inflammatory disease of the central nervous system (CNS) considered to be an animal model for multiple sclerosis (MS). The detailed mechanism that specifies accumulation of inflammatory cells within the CNS in these conditions remains a subject of active investigation. Chemokines including IP-10, GRO-alpha, MCP-1 are produced in EAE tissues selectively by parenchymal astrocytes, but the regulatory stimuli that govern this expression remain undetermined. The unexpected occurrence of increased EAE susceptibility in Balb/c GKO mice (lacking IFN-gamma) offered an opportunity to examine the spectrum of chemokine expression during immune-mediated inflammation in the absence of a single regulatory cytokine. We found that chemokines MCP-1 and GRO-alpha were upregulated in the CNS of mice with EAE despite the GKO genotype. IP-10, which is highly expressed in the CNS of mice with an intact IFN-gamma gene and EAE, was strikingly absent. In vitro experiments confirmed that IFNgamma selectively stimulates astrocytes for IP-10 expression. These results indicate that IP-10 is dependent upon IFN-gamma for its upregulation during this model disease, and document directly that astrocyte expression of chemokines during EAE is governed by pro-inflammatory cytokines.

Animals↗

PubMed1999

[Cloning and expression analyses of down-regulated cDNA C6-2A in human esophageal cancer].

OBJECTIVE: To clone genes associated with the genesis of human esophageal cancer. METHODS: Identifying missing or low expressing cDNAs in human esophageal cancer tissues by mRNA differential display and examining its mRNA expression in 4 human cancer cell lines, 9 fetal tissues and other matched esophageal cancer tissues by Northern blot, dot blot and RT-PCR. RESULTS: One cDNA fragment named C6-2A, was cloned and sequenced. There was no identical sequence with C6-2A in BLASTN database; but in querying Genbank EST, the authors found that C6-2A was identical with ne27b03.s1NCI-CGAP-C03 humans sapiens cDNA clone IMAGE:898541 3' and zv30g07.rl Soares ovary tumor NbHOT homo sapiens cDNA clone 755196. 6/6 esophageal cancer tissues in Northern blot and 7/8 in dot blot did not or slightly express C6-2A. RT-PCR analysis showed that C6-2A was expressed much lower in 17/20 esophageal cancer tissues than adjacent microscopically normal mucosa, highly expressed in fetal esophageal mucosa, skin, cerebrum, placenta; moderately expressed in fetal stomach and liver, but not detected in fetal heart, small intestine and kidney. CONCLUSION: The high frequency of deletion of decreased expression of C6-2A in esophageal cell lines and human esophageal cancer tissues suggested that C6-2A might be involved in the carcinogenesis of esophagus.

Cloning, Molecular↗

PubMed1999

[Changes of free radicals in fetal rats brain and liver following intrauterine fetal distress].

OBJECTIVE: To analysis the effect of superoxide dismutase (SOD) and malondialdehyde (MDA) on different organs in intrauterine fetal distress. METHODS: The times of clamping uterine artery in A, B, C groups were 5, 10, 20 minites respectively. By clamping the matenal uterine vessels, we made the model of fetal rat distress. Slam group (13 pups) was used as control. After clamping 10 minutes, Group D (11 pups) was reperfused 5 minutes, and E (8 pups) 20 minutes. We measured the level of SOD and MDA in fetal brains and livers. RESULTS: The activity of cerebral SOD in group B and C decreased significantly than that of control (P < 0.05, P < 0.01). MDA in group C increased significantly than that of control (P < 0.05). As for liver, only SOD in group C decreased significantly (P < 0.05). In that of reperfusion group, only in group E, cerebral SOD and MDA changed significantly (P < 0.01, < 0.05), livers SOD decreased significantly (P < 0.05). CONCLUSION: After severe intrauterine fetal distress, changes of free radicals occurred in brains firstly, which provides the proof of early treatment for neonatal hypoxia ischemia brain damage.

Animals↗

PubMed1999

[Protein kinase a mediated excitatory adrenergic effect on chronically compressed dorsal root ganglion neurons in rats].

With a model of chronically compressed dorsal root ganglion (CCD), the present study was undertaken to test how the plasticity of sympathetic-sensory coupling is and whether the coupling is mediated by intracellular messenger PKA by analysing extracellularly recorded spontaneous activity of single A-fibers originating from the CCD neurons in vitro. Eighty-five out of 95 neurons from injured DRGs during application of norepinephrine (NE) were adrenosensitive. Among the 85 neurons, 44 exhibited excitation, 21 showing excitation followed by suppression, 6 displaying alternated excitation and suppression, and 14 suppression. In addition, adrenosensitivity was observed in 15 silent injured DRGs. The excitatory effect of NE was blocked by alpha 1 and alpha 2 adrenoceptor antagonists yohimbine (10 mumol/L) or prazosin (5 mumol/L). Rp-cAMPS (50-250 mumol/L, n = 6), a specific inhibitor of PKA, and H-89 (10 mumol/L, n = 6), an inhibitor of PKA catalytic subunit, obviously suppressed the NE-evoked excitation. Furthermore, the excitatory effect of NE was attenuated by SQ 22, 536 (1 mmol/L), an adenylate cyclase inhibitor (n = 6). The above results demonstrate that injury to DRG neuron body triggered the adrenosensitivity, which was mediated by alpha 1, alpha 2 adrenoceptors and PKA.

Adrenergic Fibers↗