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Biomedical subjects

L Huang

Publications and source records attributed to L Huang.

At least 541 records · Page 30Linked to original sources
PubMed1994

A biphasic poroelastic analysis of the flow dependent subcutaneous tissue pressure and compaction due to epidermal loadings: issues in pressure sore.

A layer of skin and subcutaneous tissue on a bony substratum was modeled as a homogeneous layer of biphasic poroelastic material with uniform thickness. The epidermal surface and the bony interface were taken to be impervious. The soft tissue on the bony interface was assumed either fully adhered or completely free to slide on the bone. The cases for surface pressure loadings and displacement controlled indentations were simulated. The resultant biomechanical responses of the layer, including the transient tissue hydrostatic pressure and the tissue compaction, were presented. A new hypothesis is offered to interpret the threshold pressure-time curve for pressure sores in term of the time required for a particular area in the tissue layer to reach a critical compaction for a given level of applied pressure.

Biomechanical Phenomena↗
PubMed1994

A human cytomegalovirus early promoter with upstream negative and positive cis-acting elements: IE2 negates the effect of the negative element, and NF-Y binds to the positive element.

The human cytomegalovirus early promoter for the UL4 gene, which codes for an early viral envelope glycoprotein designated gpUL4, requires immediate-early viral protein two (IE2) synthesis to be activated (C.-P. Chang, C. L. Malone, and M. F. Stinski, J. Virol. 63:281, 1989). We investigated the cis-acting and trans-acting factors that regulate transcription from this UL4 promoter. In transient transfection assays, the viral IE2 protein negated the effect of an upstream cis-acting negative element and enhanced downstream gene expression. A cis-acting positive element contributed to the activity of the viral promoter when an upstream cis-acting negative element was deleted or when the viral IE2 protein was present. The cellular protein(s) that binds to the cis-acting negative element requires further investigation. The cellular protein that binds to the cis-acting positive element was characterized. Two DNA sequence-specific protein complexes were detected with DNA probes spanning the region containing the cis-acting positive element and human cytomegalovirus-infected human fibroblast cell nuclear extracts. The more slowly migrating complex was labeled complex A, and the faster was labeled complex B. Only complex B was detected with mock-infected cell nuclear extracts. Competition experiments confirmed the specificity of the A and B complexes. The protein bound to the DNA in both the complexes contacts a CCAAT box imperfect dyad symmetry (5'CCAATCACTGG3'). Either CCAAT box within the dyad symmetry could compete for binding the nuclear factor. Mutation of the CCAAT box dyad symmetry resulted in a decrease of the transcriptional activity from the UL4 promoter. A cellular transcription factor, antigenically related to nuclear factor-Y (NF-Y), was found in both complexes A and B. Events associated with viral infection caused phosphorylation of protein complex A. Dephosphorylation of the DNA-binding protein converts complex A to complex B. The effect of phosphorylation of NF-Y is not known.

Acid Phosphatase↗
PubMed1994

Preferred sequences for DNA recognition by the TAL1 helix-loop-helix proteins.

Tumor-specific activation of the TAL1 gene is the most common genetic alteration seen in patients with T-cell acute lymphoblastic leukemia. The TAL1 gene products contain the basic helix-loop-helix (bHLH) domain, a protein dimerization and DNA-binding motif common to several known transcription factors. A binding-site selection procedure has now been used to evaluate the DNA recognition properties of TAL1. These studies demonstrate that TAL1 polypeptides do not have intrinsic DNA-binding activity, presumably because of their inability to form bHLH homodimers. However, TAL1 readily interacts with any of the known class A bHLH proteins (E12, E47, E2-2, and HEB) to form heterodimers that bind DNA in a sequence-specific manner. The TAL1 heterodimers preferentially recognize a subset of E-box elements (CANNTG) that can be represented by the consensus sequence AACAGATGGT. This consensus is composed of half-sites for recognition by the participating class A bHLH polypeptide (AACAG) and the TAL1 polypeptide (ATGGT). TAL1 heterodimers with DNA-binding activity are readily detected in nuclear extracts of Jurkat, a leukemic cell line derived from a patient with T-cell acute lymphoblastic leukemia. Hence, TAL1 is likely to bind and regulate the transcription of a unique subset of subordinate target genes, some of which may mediate the malignant function of TAL1 during T-cell leukemogenesis.

Amino Acid Sequence↗
PubMed1994

Inhibition of carbon tetrachloride-induced liver injury by liposomes containing vitamin E.

We tested a variety of antioxidants as possible therapeutic agents in an acute CCl4 mouse model of hepatotoxicity. Liver damage, gauged by the amount of serum aminotransferase released into the blood, morphological changes, lethal dose response, and presence of thiobarbituric acid-reactive substances (TBARS), were significantly inhibited in a dose-dependent manner by liposomes containing vitamin E (LVE) or by Rocavit E, a water-soluble emulsion of alpha-tocopherol. Serum aminotransferase levels in LVE- or Rocavit E-treated animals were always > 10-fold lower than levels in corresponding CCl4 controls. Other liposome-associated antioxidants, butylated hydroxytoluene, vitamin E succinate, catalase, desferoxamine, superoxide dismutase, and ascorbic acid 6-palmitate, were also able to elicit a decrease in damage; however, they were substantially less effective. Intravenous therapy with LVE decreased mortality by nearly 90% when a lethal dose of CCl4 was given. When the biodistribution of the liposomes was examined, it was determined that the vast majority were localized in the Kupffer cell population. This approach of delivering nontoxic therapeutic agents selectively to the liver offers a variety of clinical applications in humans.

Animals↗
PubMed1994

Regulation of rat renal alpha 2 B-adrenergic receptors by potassium depletion.

Potassium depletion and alpha 2-adrenergic receptor (alpha 2-AR) agonists produce similar physiological effects on renal function. Both stimuli increase Na-H exchange in proximal tubule cells, inhibit water transport in collecting tubule cells, and alter blood pressure regulation. The purpose of this study was to determine whether potassium depletion and renal alpha 2-AR subtype expression were linked. Kidney membrane proteins and RNA were harvested from anesthetized rats fed a potassium-deficient diet for 4-20 days (LK 4 to LK 20). Using a selective alpha 2-AR antagonist, [3H]MK-912, we observed that potassium depletion led to a dramatic increase in maximum binding (270% of control) without a change in dissociation constant. Competitive binding studies in LK 14 kidney membranes employing chlorpromazine, prazosin, and oxymetazoline suggested that the increase in alpha 2-ARs in response to potassium depletion was due primarily to an increase in the B subtype of alpha 2-AR. Northern blot analysis demonstrated that renal alpha 2B-AR mRNA levels increased (190% of control) after 4 or 14 days on a potassium-deficient diet. In contrast, there was no difference in steady-state alpha 2A-receptor protein levels by Western blot analysis. We conclude that potassium depletion selectively increases the expression of the B subtype of alpha 2-AR with no detectable effect on alpha 2A-AR expression.

Adrenergic alpha-Antagonists↗
PubMed1994

Apical membrane and intracellular distribution of endogenous alpha 2A-adrenergic receptors in MDCK cells.

The purpose of the current studies was to characterize the endogenous alpha 2-adrenergic receptor (AR) subtypes present in Madin-Darby canine kidney (MDCK) cells and to determine their level of expression and pattern of distribution. By saturation binding analysis with [3H]MK-912, MDCK cells expressed high levels of alpha 2-ARs with a maximum receptor density (Bmax) of 798 +/- 55 fmol/mg protein and an equilibrium dissociation constant (Kd) of 0.98 +/- 0.32 nM. Competitive binding studies using prazosin, oxymetazoline, phentolamine, and epinephrine to displace [3H]MK-912 demonstrated inhibition constant (Ki) values of 1,270 +/- 250, 5.0 +/- 0.4, 5.5 +/- 0.3, and 392 +/- 150 nM (n = 3), respectively. In Northern blot analysis we found that MDCK cells expressed transcripts encoding alpha 2A-AR and not alpha 2B-AR or alpha 2C-AR. Surface binding experiments suggested that approximately 60% of alpha 2A-ARs are distributed at the cell surface domain. Specific binding of [3H]MK-912 to soluble apical and basolateral surface proteins isolated by surface biotinylation indicated the expression of surface alpha 2A-ARs was limited to the apical domain of MDCK cells. No alpha 2A-ARs were detected on the basolateral surface. We conclude that endogenous alpha 2A-ARs are targeted to the apical domain of MDCK cells and that the intracellular compartment may contain ARs as a reservoir for de novo cell surface expression or, alternatively, may represent internalized receptors.

Adrenergic alpha-Antagonists↗
PubMed1994

Nasal application of the cationic liposome DC-Chol:DOPE does not alter ion transport, lung function or bacterial growth.

Liposome-mediated gene transfer is commonly used for in vitro transfection of deoxyribonucleic acid (DNA) into mammalian cells. We and others have recently demonstrated that this can be an effective method for in vivo delivery of plasmid DNA containing the human cystic fibrosis transmembrane conductance regulator (CFTR) gene to mouse models of cystic fibrosis (CF). This suggests that cationic liposomes may be useful for transferring CFTR complementary DNA (cDNA) into the airways of CF subjects. In such trials, measurement of nasal potential difference (PD) will be used to monitor the efficacy of correction of the CF bioelectric defect and to provide a sensitive assay of epithelial integrity [corrected]. We therefore assessed whether the cationic liposome DC-Chol: DOPE altered nasal ion transport parameters, in six normal and three CF subjects. Lung function was also measured as a further marker of safety. Finally, as CF airways are chronically infected, we studied whether DC-Chol:DOPE or DC-Chol:DOPE-DNA complexes altered the bacterial growth and sensitivities of CF sputum. No significant effect was seen on any of these parameters, suggesting that DC-Chol:DOPE may be appropriate for use in human trials of liposome-mediated gene therapy for CF.

Administration, Intranasal↗
PubMed1994

Degradation of native and oxidized beta- and gamma-crystallin using bovine lens epithelial cell and rabbit reticulocyte extracts.

In many types of cells, modified proteins are selectively and rapidly removed by various proteolytic systems. In eye lens, as in most cells, there appears to be a multiplicity of proteolytic pathways, including ubiquitin-dependent, ATP-dependent and ATP-independent pathways. Each of these appears to be involved in the degradation of alpha-crystallins. The objective of this study was to determine if oxidized beta- and gamma-crystallins would be selectively degraded and which proteolytic systems might be involved. beta- and gamma-crystallins were oxidized by exposure to 137Cs radiation under N2O. This system generates *OH primarily. Oxidation of beta- and gamma-crystallins was indicated by decreased protein sulfhydryl content and tryptophan fluorescence, as well as by increased levels of carbonyl and high molecular weight aggregates with increasing radiation dose. gamma-crystallin was more susceptible than beta-crystallin to oxidation based on loss of native crystallin, increase in aggregates and fragmentation products, and loss of tryptophan. Low molecular mass polymers (dimers) appear to be the precursors of high mass aggregates induced upon oxidation. At a specific level of oxidative insult interchain covalent bonds in addition to disulfides were more extensive in the polymers of gamma-crystallin as compared to beta-crystallin. Except for beta-crystallin irradiated with 1 krad, the degradation rate of crystallins using both reticulocyte and bovine lens epithelial cells (BLEC) proteolytic systems increased in proportion to the extent of oxidation. Proteolysis of oxidized gamma-crystallins increased 1775% and 900%, respectively, using reticulocytes and BLEC supernatants as the source of proteases.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1994

The preparation of zaragozic acid A analogues by directed biosynthesis.

Zaragozic acid A analogues are produced by an unidentified sterile fungus when it is exogenously supplied with 2-thiophenecarboxylic acid, 3-thiophenecarboxylic acid, 2-furoic acid, 2-fluorobenzoic acid, 3-fluorobenzoic acid, or 4-fluorobenzoic acid. The analogues carry 2-thiophenyl, 3-thiophenyl, 2-furyl, o-fluorophenyl, m-fluorophenyl, or p-fluorophenyl group, respectively, at C-6' of the C-1 alkyl side chain replacing the phenyl group of natural zaragozic acid A. All the new analogues of zaragozic acid A possess picomolar inhibitory activity against squalene synthase in vitro.

Bridged Bicyclo Compounds↗
PubMed1994

[The origin of channel syndromes].

Originally, "Shi Dong" disease, one of the Channel Syndromes, first appeared in Moxibustion Canon of Eleven-channels of Yin-yang System is a manifestation in pulse diagnosis. The two pulse-syncope (mai jue) syndromes in On Syncope of Plain Question are also the summary from different scholars far pulse manifestation. On the other hand, the "Suo Sheng" disease is the summary of ancient scholar on the lesions at the superficial running courses of channels and the disease condition of its underlying viscera, which would also be changed with the changes of channels and viscera.

China↗
PubMed1994

Biochemical and pharmacological comparison of a cytosolic, high molecular weight phospholipase A2, human synovial fluid phospholipase A2 and CoA-independent transacylase.

We have compared biochemical and pharmacological characteristics of CoA-independent transacylase (CoA-IT) activity of microsomes from U937 cells to those of two other enzymes involved in arachidonate metabolism, a human type II low molecular weight (M(r) 14,000, LMW) PLA2 isolated from synovial fluid of patients with inflammatory joint disease and a high molecular weight (M(r) 85,000, HMW) PLA2 enzyme isolated from the cytosol of human monocytic U937 cells. Activities of HMW PLA2 and CoA-IT were reduced by treatment with acid, heat or acetonitrile but were not altered by treatment with the sulfhydryl reducing agent dithiothreitol (DTT). In contrast, the activity of LMW PLA2 enzyme was inactivated by DTT, but was insensitive to treatment with acid, heat or acetonitrile. HMW PLA2 activity decreased as NaCl concentration was increased in the assay buffer from 0 to 150 mM, unlike LMW PLA2 and CoA-IT activities, which increased as NaCl increased. Compounds that inhibit LMW PLA2 activity were examined for their effects on HMW PLA2 and CoA-IT activities. The compounds examined (nordihydroguaiaretic acid, manoalide, p-bromophenacyl bromide, arachidonic acid, gossypol, aristologic acid and a mimic of a transition state phospholipid) had different rank orders for inhibition of the three enzymes. Taken together, these data show that these three enzymes, although unpurified, can be biochemically and pharmacologically distinguished.

Acyltransferases↗
PubMed1994

Platelet-activating factor and endotoxin induce tumour necrosis factor gene expression in rat intestine and liver.

We have shown previously that endotoxin, tumour necrosis factor (TNF) and platelet-activating factor (PAF) are important in the pathogenesis of bowel injury, and that endotoxin and TNF induce PAF formation in bowel tissue. In the present study we investigated the effects of endotoxin and PAF on TNF gene expression. Adult rats were injected with endotoxin (2 mg/kg), PAF (1 microgram/kg) or endotoxin plus PAF, and were killed after 30 min. Endotoxin had little systemic effect. PAF induced transient hypotension and mild bowel injury. Endotoxin plus PAF caused profound shock, severe haemoconcentration, leukopenia and intestinal necrosis. Sham-operated rats had barely detectable TNF mRNA in the liver or intestine. Endotoxin or PAF induced a marked increase in TNF mRNA, especially in the distal ileum and in the liver, but much less in the jejunum. Endotoxin plus PAF did not further increase TNF mRNA, probably due to development of tissue injury. Serum TNF levels in animals treated with endotoxin, PAF and endotoxin plus PAF were elevated. Endotoxin induces TNF gene expression probably via both PAF-dependent and PAF-independent pathways, since TNF mRNA formation was only partially blocked by PAF antagonist.

Animals↗
PubMed1994

Seroepidemiological study of coxsackievirus type A24 variant (CA24v) in Taiwan.

In October 1985 and June 1986, for the first time, Taiwan experienced two outbreaks of acute hemorrhagic conjunctivitis (AHC) caused by a variant of coxsackievirus A24 (CA24v). Sera of virologically and clinically confirmed cases were studied together with the pre- and post-epidemic serum samples by the microneutralization method (cut-off titer, 1:8). The serum samples included 16 cases of virologically confirmed AHC and 18 cases of clinically diagnosed AHC which were collected during the period of January to July, 1987 (i.e., 7 to 21 months after the epidemic). In the same period of time, 374 serum samples were randomly collected as a post-epidemic control group. Meanwhile, 206 serum samples, which were randomly collected in 1980, were studied as a pre-epidemic control group. The results showed that in terms of CA24v neutralizing antibody (NTAb) positivity, a significant difference was found between the pre- and post-epidemic random sample groups (5.3% vs. 28.1%, P < 0.001) while no significant differences among the virologically confirmed, the clinically diagnosed and the post-epidemic random sample groups were noticed (31.3% vs. 28.1%; 44.4% vs. 28.1%, P > 0.05). For comparison, the enterovirus 70 (EV70) NTAb of the samples was studied simultaneously. The results showed that the positive rate and geometric mean titer of CA24v NTAb were lower than those of EV70 even in the post-epidemic serum samples collected shortly after the CA24v epidemic.

Adolescent↗
PubMed1994

Characterization of the human MSX-1 promoter and an enhancer responsible for retinoic acid induction.

Previous studies have shown that the expression of some human HOX genes can be induced by retinoic acid (RA) in cultured embryonal carcinoma (EC) cells. However, the mechanisms for the regulation of HOX gene expression by RA are still unclear. We have examined the effects of RA on the human MSX-1 (formerly named HOX-7) gene expression in cultured EC cells (NT2/D1). Furthermore, we have cloned and characterized the human MSX-1 promoter and analyzed the activities of the promoter in response to RA. Our results demonstrate that transcription of human MSX-1 is activated by RA in cultured EC cells. This activation is dose and time responsive. The MSX-1 promoter was shown to be TATA-box independent and able to promote transcription in RA-treated EC cells. DNase-I footprinting studies revealed protection of several GAGA factor binding sites and an NF-kappa B site upstream to the transcription start site by nuclear extracts prepared from EC cells. A downstream sequence was differentially protected by the nuclear extract from RA treated cells. This differential binding of the sequence with the nuclear extract was further confirmed by gel shift assays. This sequence confers to a heterologous promoter with the ability to respond to RA induction. Point mutation within this DNA fragment abolished the binding of the fragment to the nuclear extract and the response of this element in a heterologous promoter to RA induction. Deletion of this enhancer element together with the adjacent NF-kappa B and GAGA sites abolished the ability of the promoter to direct transcription in RA-treated EC cells. However, removal of a downstream DNA fragment from the promoter endowed the promoter with the ability to direct transcription in RA-untreated cells. Taken together, both positive and negative regulatory cis-elements are involved in the regulation of the MSX-1 promoter and coordinate to control the gene expression.

Animals↗
PubMed1994

Sequencing for 4 single-copy DNA segments from human chromosome 8q24.1.

A successful method for constructing human chromosome 8q24.1 band specific probe pool by microdissection and microcloning is described in this paper. The probe pool was proved to be band-specific by fluorescence in situ hybridization. Through Southern blot analysis, 34 single copy DNA segments were obtained and four of them were sequenced. It is possible to provide useful landmarks for constructing human chromosome 8q24.1 physical map and STSs map.

Base Sequence↗
PubMed1993

CC-1065 functional analogues possessing different electron-withdrawing substituents and leaving groups: synthesis, kinetics, and sequence specificity of reaction with DNA and biological evaluation.

Antitumor agent CC-1065 functional analogues possessing different electron-withdrawing substituents and leaving groups have been synthesized. The extent and the relative rates of DNA cleavage following alkylation by these CPI structures and thermal treatment were determined independently by an ethidium binding assay and by agarose gel electrophoresis experiments. The anticipated preferential covalent binding to adenine sites within the minor groove was confirmed by sequencing determination of selected agents on high-resolution gels. Certain of the synthetic agents, unlike CC-1065, also bind covalently to G sites with weaker intensity. The cytotoxicities of these compounds were also determined against KB cells in vitro. Compounds bearing a bromo or nitro group in the benzene ring and a methylsulfonyl as a leaving group are 10 and 5 times more potent than their unsubstituted counterparts, respectively. Compounds bearing a methylsulfonyl as a leaving group are more potent than those bearing a chlorine.

Alkylation↗
PubMed1993

A serum-derived hyaluronan-associated protein (SHAP) is the heavy chain of the inter alpha-trypsin inhibitor.

We showed previously that hyaluronan (HA) synthesized by cultured fibroblasts firmly bound 85-kDa proteins. The proteins were derived from serum used for the culture and appeared to be covalently linked to HA (Yoneda, M., Suzuki, S., and Kimata, K. (1990) J. Biol. Chem. 265, 5247-5257). In these regards, we named this molecule SHAP (serum-derived HA associated proteins). Incubation of serum with exogenous HA under physiological conditions enabled us to prepare SHAP.HA complex without cell cultivation. The complex thus obtained from bovine or human serum was served for the characterization of SHAP. Digestion with HA-lyase and subsequent separation on SDS-polyacrylamide gel electrophoresis yielded two components, X and Y. Because of the block of their NH2 termini, peptides were obtained by the digestion of X and Y with V8 protease, separated on SDS-polyacryl-amide gel electrophoresis and then subjected to the analysis. Peptides from X and Y showed a high degree of sequence similarity to the two heavy chains, HC2 and HC1, of human inter-alpha-trypsin inhibitor (ITI), respectively (over 80% with bovine SHAP and essentially 100% with human SHAP). Cross-reactivity with antibodies against ITI supported the findings. Direct digestion of the complex with V8 protease and the subsequent purification of the HA-resistant fragment complex were performed to identify the HA-binding domains. NH2-terminal sequences of the fragments suggested the participation of the COOH-terminal half of ITI with an amphipathic alpha helix structure in the HA binding.

Alpha-Globulins↗