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Biomedical subjects

L Huang

Publications and source records attributed to L Huang.

At least 433 records · Page 24Linked to original sources
PubMed1996

AIDS and the lung.

Respiratory symptoms are common in HIV-infected persons. The challenge facing clinicians is to determine whether these respiratory symptoms are due to an opportunistic infection or to a chronic process, such as asthma, chronic bronchitis, bronchiectasis, or emphysema. This article reviewed the clinical presentation, diagnosis, and treatment of two important opportunistic infections, PCP and bacterial pneumonia. It also reviewed the current data on obstructive lung diseases as they relate to HIV.

AIDS-Related Opportunistic Infections↗
PubMed1996

Effect of matrix lipid chain length on liposomes containing cholesterol and ganglioside GM1: implications in drug delivery.

Incorporation of ganglioside GM1 into liposomes composed of phosphatidylcholine (PC) and cholesterol significantly increases their blood circulation time. Dipalmitoyl PC (DPPC) and distearoyl PC (DSPC) are the most commonly used saturated phospholipids employed in the preparation of long-circulating liposome formulations. Physical studies were performed on different formulations of these liposomes in an attempt to understand the effects of the matrix lipid chain length and GM1 concentration on the use of these liposomes as long-circulating drug delivery systems. The GM1/PC mixtures existed in different physical states: a lamellar state with components exhibiting miscibility (which is the desired state for drug delivery), a mixed micellar phase, and also a smectic mesophase. GM1 is miscible with DSPC bilayers up to a concentration of 25 mol%, beyond which conversion into the metastable mesophase occurs. By 30 mol%, solubilization into the mixed micellar state occurs. With DPPC, the metastable mesophase occurs at 33-38 mol% of GM1, with mixed micelles being formed at higher concentrations. The addition of cholesterol led to an inhibition of micelle formation. This study also indicates that GM1 stabilizes DPPC bilayers while destabilizing DSPC bilayers. On the basis of the interactions of GM1 with DPPC and DSPC, a new hypothesis for stabilization of PC bilayers is proposed, which also explains the destabilization of PC with C18.0 and higher. The longest circulating GM1 liposome formulations are predicted from this study.

Calorimetry, Differential Scanning↗
PubMed1996

A new prenylated flavonol from the root of Petalostemon purpureus.

A new prenylated flavonol, petalopurpurenol (1), and a known dihydroflavonol, petalostemumol (2), have been isolated by DNA scission-guided fractionation of the organic portion of a 20% MeOH/CHCl3/H2O partition of a 50% MeOH/CHCl3 extract of the roots of Petalostemon purpureus. Compound 2 displayed moderate activity in DNA-scission assay. Both compounds 1 and 2 were evaluated for cytotoxicity in a panel of human cancer cell lines. The structures of petalopurpurenol (1) and petalostemumol (2) were determined by spectroscopic analysis.

Antineoplastic Agents, Phytogenic↗
PubMed1996

New cationic lipid formulations for gene transfer.

PURPOSE: To develop appropriate dosage forms of DNA for gene delivery. METHODS: 3 beta [N-(N', N' dimethylaminoethane) carbamoyl] cholesterol (DC-Chol) was mixed either with Tween 80 alone, or with additional lipid components including castor oil and phosphatidylcholine (PC) or dioleoylphosphatidylethanolamine (DOPE) to make different lipid formulations. The particle size and the physical stability of the formulations upon mixing with plasmid DNA containing the luciferase cDNA were examined using laser light scattering measurement. The transfection activity of the DNA/lipid complexes was tested in presence or absence of serum using a cell culture system. RESULTS: We demonstrated that many favorable properties as a gene carrier could be achieved by formulating DNA into new dosage forms using Tween 80 as the major emulsifier. Compared to the cationic liposomes, these new formulations transfected different cell lines with an equivalent or higher efficiency. Not only are they resistant to serum, but also form stable DNA complexes which could be stored for longer periods of time without losing transfection activity. CONCLUSIONS: Cationic lipids formulated into different lipid formulations using Tween 80 as a surfactant appeared to have more favorable physical and biological activities than traditional cationic liposomes as a carrier for gene delivery.

Cell Line↗
PubMed1996

Interaction of polyethyleneglycol-phospholipid conjugates with cholesterol-phosphatidylcholine mixtures: sterically stabilized liposome formulations.

PURPOSE: The purpose of this study was to investigate polyethyleneglycol (PEG)-phosphatidylethanolamine (PE) conjugate interaction with cholesterol-phospholipid mixtures in an attempt to explain the effect of cholesterol on liposome circulation time. METHODS: Differential scanning calorimetry, NMR, electron microscopy, dynamic light scattering and fluorescence spectroscopy were the major methods used. RESULTS: Studies performed in the absence of cholesterol indicated the formation of three distinct physical states depending on the chain length of PEG in PEG-PE. Mixed micelle formation was observed at concentrations of PEG(1,000)-DPPE above 7 mol-% of lipid. Phase separated lamellae were observed at all concentrations of PEG( 12,000)-DPPE (Bedu-Addo et al. Pharm. Res. 13:710-717 (1996)). Upon incorporation of high concentrations of cholesterol >30 mol% into the lipid bilayer, the formation of phase separated lamellae was completely inhibited and the formation of mixed micelles significantly reduced. At high concentrations of PEG(1,000)-PE, solubilization of the bilayer occurred with preferential solubilization of cholesterol over phosphatidylcholine. Maximum steric stabilization (surface protection) was observed with low concentrations of short chain PEG-PE and high concentrations of cholesterol. CONCLUSIONS: The study provides a physical mechanism for the following observations: the blood circulation time is significantly increased or decreased with liposomes highly enriched with cholesterol or PEG-PE respectively.

Calorimetry, Differential Scanning↗
PubMed1996

Effects of polyethyleneglycol chain length and phospholipid acyl chain composition on the interaction of polyethyleneglycol-phospholipid conjugates with phospholipid: implications in liposomal drug delivery.

PURPOSE: The purpose of this study was to investigate polyethyleneglycol(PEG)-phosphatidylethanolamine(PE) conjugate interaction with phospholipid bilayers, in an attempt to explain the dependence of liposome circulation time on formulation. METHODS: Differential scanning calorimetry, electron microscopy, dynamic light scattering and NMR were the major methods used in the study. RESULTS: Mixtures of PEG-phospholipid conjugates and phosphatidylcholine existed in three different physical states: a lamellar phase with components exhibiting some miscibility, a lamellar phase with components phase separated, and mixed micelles. Beyond 7 mol-percent of PEG(1,000-3,000)-dipalmitoyl phosphatidylethanolamine (DPPE), and 11 mol% PEG(5,000)-DPPE in dipalmitoyl phosphatidylcholine (DPPC), a strong tendency towards mixed micelle formation was observed. All concentrations of PEG(12,000)-DPPE and PEG(5,000)-DPPE beyond 8 mol% formed phase separated lamellae with phosphatidylcholine. Decreasing the acyl chain length from C(16:0) to C(14:0) caused a decrease in tendency towards micelle formation and phase separation. These tendencies increased upon increasing acyl chain length to C(18:0). Phase separation was at least partly due to PEG chain-chain interaction. This was supported by an increased fraction of PEG chains exhibiting a fast NMR transverse relaxation in DPPC/PEG(5,000)-DPPE mixtures as compared to that in distearoyl phosphatidylcholine (DSPC)/PEG(5,000)-dioleoyl-PE (DOPE). CONCLUSIONS: These phenomena are discussed in relation to both bilayer and steric stabilization of liposomes, and the lack of prolonged circulation with certain formulations is discussed.

Calorimetry, Differential Scanning↗
PubMed1996

Effect of non-ionic surfactants on the formation of DNA/emulsion complexes and emulsion-mediated gene transfer.

PURPOSE: To study the structure-function relationship of non-ionic surfactants in emulsion-mediated gene delivery. METHODS: Four different types of non-ionic surfactants including Tween, Span, Brij and pluronic copolymers were used as co-emulsifiers for preparation of emulsions composed of Castor oil, dioleoylphosphatidylethanolamine (DOPE) and 3 beta [N-(N', N'-dimethylaminoethane) carbamoyl] cholesterol (DC-Chol). The effect of different surfactants on the formation of DNA/emulsion complexes and transfection activity were analyzed using plasmid DNA containing luciferase cDNA as a reporter gene. RESULTS: Non-ionic surfactants containing branched polyoxyethylene chains as the hydrophilic head group were more effective in preventing the formation of large DNA/emulsion complexes than those containing one or no polyoxyethylene chain. All emulsion formulations except those containing Brij 700 exhibited high activity in transfecting mouse BL-6 cells in the absence of serum. In the presence of serum, however, transfection activity of each formulation varied significantly. Emulsions containing Tween, Brij 72, pluronic F68 and F127 demonstrated increased activity in transfecting cells in the presence of 20% serum. In contrast to emulsions containing Span, long chain polyoxyethylene of Brij showed decreased transfection activity. The particle size of the DNA/emulsion complexes and their ability to transfect cells are dependent on the concentration of non-ionic surfactant in the formulation. CONCLUSIONS: The structure of the hydrophilic head group of the non-ionic surfactants in the emulsion is important in determining how DNA molecules interact with emulsions and the extent to which DNA is transferred inside the cell.

Animals↗
PubMed1996

Vesicular quantal size measured by amperometry at chromaffin, mast, pheochromocytoma, and pancreatic beta-cells.

Amperometric detection of exocytosis at single chromaffin cells has shown that the distribution of spike areas, or quantal size, is dependent on the volume and catecholamine concentration of individual secretory vesicles. The present work offers an alternate, simplified model to analyze the current spikes due to single exocytotic events. When the cube root of these spike areas is plotted as a histogram, a Gaussian distribution is obtained for chromaffin cells and also mast, pheochromocytoma, and pancreatic beta-cells. It was found that the relative SD of these distributions is similar to that for the vesicular radii, which also have a Gaussian distribution in all four cell types. In addition, this model was used to evaluate conditions where the quantal size of individual events was altered. When chromaffin cells were maintained in culture for < 6 days, spikes of approximately double the quantal size were obtained on repeated exposure to 60 mM K+. The results suggest a heterogeneous distribution of catecholamine-containing vesicles at later days in culture is responsible for this alteration.

Animals↗
PubMed1996

Limiting impairment of muscle function following ischemia and reperfusion in rabbits.

Reperfusion injury is a phenomenon complicating microvascular reconstruction. Extensive investigations of free-radical scavengers exist in the literature. The potential beneficial effects of verapamil, deferoxamine, and dimethylsulfoxide were studied in the rabbit forelimb subjected to 3 hr of tourniquet ischemia, followed by a period of reperfusion. Five minutes prior to tourniquet release, rabbits were given single intravenous infusions of normal saline, verapamil (0.2 mg/kg), deferoxamine (50 mg/kg), or dimethylsulfoxide (100 mg/kg). Following reperfusion, neither light microscopy nor laser Doppler flowmetry revealed significant differences between the sham and treated limbs. Muscle function was evaluated by measuring maximal twitch tensions in the flexor digitorum superficialis. Deterioration of muscle contractile function at 0.5, 3, and 24 hr after reperfusion was significantly improved by treatment with verapamil or deferoxamine. Conversely, dimethylsulfoxide worsened muscle function post ischemia. Dimethylsulfoxide does not appear to be beneficial, while verapamil and deferoxamine may be of benefit in mitigating reperfusion injury in microvascular transplantation.

Animals↗
PubMed1996

No change in insulin mediators in human skeletal muscle during isometric contraction or recovery.

The rapid activation of glycogen synthase in human skeletal muscle during recovery from isometric contraction is dependent on an intact circulation, which suggests the requirement of an activating humoral factor. To determine whether the activating factor is insulin, muscle biopsies were obtained from subjects at rest, at fatigue, 3 min postexercise with an intact circulation, and 3 min postexercise during which circulation to the muscle was occluded. Two inositol phosphoglycan mediators of insulin action were isolated from the biopsies, and bioactivity was measured by determining the effects of the isolated mediators on the activities of purified cyclic AMP-dependent protein kinase, pyruvate dehydrogenase phosphatase and glycogen synthase phosphatase in vitro. Bioactivity was not altered by any condition compared with rest. These data suggest that changes in inositol phosphoglycans are not responsible for the circulation-dependent activation of glycogen synthase during recovery from exercise.

Adult↗
PubMed1996

A physical map of chromosome 2 of Arabidopsis thaliana.

A yeast artificial chromosome (YAC) physical map of chromosome 2 of Arabidopsis thaliana has been constructed by hybridization of 69 DNA markers and 61 YAC end probes to gridded arrays of YAC clones. Thirty-four YACs in four contigs define the chromosome. Complete closure of the map was not attained because some regions of the chromosome were repetitive or were not represented in the YAC library. Based on the sizes of the YACs and their coverage of the chromosome, the length of chromosome 2 is estimated to be at least 18 Mb. These data provide the means for immediately identifying the YACs containing a genetic locus mapped on Arabidopsis chromosome 2.

Arabidopsis↗
PubMed1996

The differentiation of snoring mechanisms using sound analysis.

Ten subjects known to suffer from heavy snoring but not obstructive sleep apnoea were studied using the technique of sleep nasendoscopy. The mechanism of snoring was noted for each and sound recordings of the snoring noise were made. Six subjects were observed to snore using their soft palate only, three snored using only their tongue base and one snored using a combination of palate and tongue base. The sound recordings were subjected to computer analysis of waveform and frequency. Palatal flutter snoring and tongue base snoring appear to have distinct waveform and frequency patterns which allows them to be differentiated from each other.

Confounding Factors, Epidemiologic↗
PubMed1996

Four of eleven loci required for transient complementation of human cytomegalovirus DNA replication cooperate to activate expression of replication genes.

As previously shown, 11 loci are required to complement human cytomegalovirus (HCMV) DNA replication in a transient-transfection assay (G. S. Pari and D. G. Anders, J. Virol. 67:6979-6988, 1993). Six of these loci encode known or candidate replication fork proteins, as judged by sequence and biochemical similarities to herpes simplex virus homologs of known function; three encode known immediate early regulatory proteins (UL36-38, IRS1/TRS1, and the major immediate early region spanning UL122-123); and two encode early, nucleus-localized proteins of unknown functions (UL84 and UL112-113). We speculated that proteins of the latter five loci might cooperate to promote and regulate expression of the six replication fork proteins. To test this hypothesis we made luciferase reporter plasmids for each of the replication fork gene promoters and measured their activation by the candidate effectors, expressed under the control of their respective native promoters, using a transient-cooperativity assay in which the candidate effectors were subtracted individually from a transfection mixture containing all five loci. The combination of UL36-38, UL112-113, IRS1, or TRS1 and the major immediate early region produced as much as 100-fold-higher expression than the major immediate early region alone; omitting any one of these four loci from complementing mixtures produced a significant reduction in expression. In contrast, omitting UL84 had insignificant (less than twofold), promoter-dependent effects on reporter activity, and these data do not implicate UL84 in regulating HCMV early-gene expression. Most of the effector interactions showed significant positive cooperativity, producing synergistic enhancement of expression. Similar responses to these effectors were observed for the each of the promoters controlling expression of replication fork proteins. However, subtracting UL112-113 had little if any effect on expression by the UL112-113 promoter or by the simian virus 40 promoter-enhancer under the same conditions. Several lines of evidence argue that the cooperative interactions observed in our transient-transfection assays are important to viral replication in permissive cells. Therefore, the data suggest a model in which coordinate expression of multiple essential replication proteins during permissive infection is vitally dependent upon the cooperative regulatory interactions of proteins encoded by multiple loci and thus have broad implications for our understanding of HCMV biology.

Base Sequence↗
PubMed1996

Cellular or viral protein binding to a cytomegalovirus promoter transcription initiation site: effects on transcription.

We have previously shown that the IE2 protein of human cytomegalovirus (CMV) represses its own synthesis by binding to the major immediate-early promoter (M. P. Macias and M. F. Stinski, Proc. Natl. Acad. Sci. USA 90:707-711, 1993). The binding of a viral protein (IE2) and a cellular protein in the region of the transcription start site was investigated by site-specific mutational analysis and electrophoretic mobility shift assay. The viral protein and the cellular protein require different but adjacent core DNA sequence elements for binding. In situ chemical footprinting analysis of DNA-protein interactions with purified CMV IE2 protein or HeLa cell nuclear extracts demonstrated binding sites that overlap the transcription start site. The IE2 protein footprint was between bp -15 and +2, relative to the transcription start site, and the cellular protein was between bp -16 and +7. The ability of the unknown human cellular protein of approximately 150 kDa to bind the CMV major immediate-early promoter correlates with an increase in the level of transcription efficiency. Mutations in the core DNA sequence element for cellular protein binding significantly reduced the level of in vitro transcription efficiency. Mutations upstream and downstream of the core sequence moderately reduced the transcription efficiency level. Negative autoregulation of the CMV promoter by the viral IE2 protein may involve both binding to the DNA template and interference with the function of a cellular protein that binds to the transcription start site and enhances transcription efficiency.

Antigens, Viral↗
PubMed1996

The variable 3' ends of a human cytomegalovirus oriLyt transcript (SRT) overlap an essential, conserved replicator element.

The genetically defined human cytomegalovirus (HCMV) lytic-phase replicator, oriLyt, comprises more than 2 kb in a structurally complex region that spans a variety of potential transcription control signals. Several transcripts originate within or cross oriLyt, and we are studying these oriLyt transcription units to determine whether they participate in initiating or regulating lytic-phase DNA synthesis. Results presented here establish the temporal accumulation and structure of the smallest replicator transcript, which we call SRT, and identify a single-sequence element essential to replicator function. SRT was detected as early as 2 h after HCMV infection of human fibroblast cells; transcript levels increased by 24 h and continued to increase thereafter. Consistent with its early appearance, treatment of HCMV-infected cells with the viral DNA polymerase inhibitor phosphonoformic acid had no effect on SRT accumulation; however, no SRT was detected in RNA preparations from cycloheximide-treated infected cells. Additional Northern (RNA) analysis localized the 0.2- to 0.25-kb SRT to an apparently noncoding segment near the center of the oriLyt core region. Reverse transcriptase PCR (rapid amplification of cDNA 5' ends [5'-RACE]) identified a single 5' end. In transient-transfection assays, the sequence immediately upstream of SRT functioned as a promoter responsive to HCMV infection when placed upstream of a reporter gene, suggesting that SRT is the product of a discrete transcription unit. RNA ligase-mediated 3'-RACE showed that SRT is not polyadenylated and has heterogeneous 3' ends within a roughly 45-nucleotide window overlapping an oligopyrimidine sequence having counterparts in the lytic-phase replicators of several herpesviruses. Mutation of the oligopyrimidine element showed that it is essential to oriLyt replicator function; it is the only essential single-sequence HCMV oriLyt replicator element described to date. Collectively, the location of SRT near the center of the oriLyt core region, its early expression, its overlapping relationship with a sequence element essential to replicator function, and its similarities to replicator transcripts in other systems suggest the possibility that SRT plays a role in initiating or regulating HCMV lytic-phase DNA synthesis.

Base Sequence↗
PubMed1996

Alpha 2B-adrenergic receptors: immunolocalization and regulation by potassium depletion in rat kidney.

Regulation of transport processes in renal epithelial cells in response to alpha 2-adrenergic receptor (alpha 2-AR) stimulation is likely due to specific effects of the A-, B-, or C-subtype alpha 2-AR. The purpose of the present study was 1) to examine the precise localization, using subtype-specific antibodies, the B-subtype alpha 2-AR protein, the most abundant alpha 2-AR in rat kidney; and 2) to determine the effect of dietary potassium restriction, a factor known to increase alpha 2B-ARs, on the distribution of receptors. We employed a method to generate a specific antibody to the third intracellular loop of the alpha 2B-AR and demonstrated the specificity of this antibody. Our results demonstrated, for the first time, evidence for the alpha 2B-receptor protein in the basolateral membrane of proximal convoluted and straight tubules. No specific immunoreactivity was detected in other nephron segments. Finally, the increase in alpha 2B-AR expression observed previously was due to the recruitment of alpha 2B-ARs to the basolateral membrane of proximal tubules.

Animals↗
PubMed1996

Presentation of AIDS-related pulmonary Kaposi's sarcoma diagnosed by bronchoscopy.

Kaposi's sarcoma (KS) is the most common neoplasm in persons infected with the human immunodeficiency virus (HIV). However, information about the presenting features of pulmonary KS is limited. To describe the clinical, laboratory, and radiographic features of pulmonary KS, medical records and chest radiographs of 168 patients with pulmonary KS diagnosed by bronchoscopy during a 7-yr period were reviewed. All of the patients were HIV-seropositive males, of whom 95% identified homosexual or bisexual sex as a risk factor for HIV infection. The median CD4 lymphocyte count was 19 cells/microliter. The most common symptoms were cough, dyspnea, and fever. Patients with a concurrent opportunistic pneumonia had a higher median serum lactate dehydrogenase (LDH) concentration than did those with pulmonary KS alone (p<0.001). The most common chest radiograph findings were bronchial-wall thickening, nodules, Kerley B lines, and pleural effusions. The presence of granular opacities or cystic spaces usually indicated concomitant Pneumocystitis carinii pneumonia (p < 0.001). Twenty-six patients (15.5%, 95% CI = 10.2% to 20.8%) had pulmonary KS in the absence of mucocutaneous involvement. The presentation of pulmonary KS is characterized by symptoms that cannot be distinguished from those of a superimposed infection. An elevated serum LDH concentration or a chest radiograph with granular opacities or cystic spaces should raise the suspicion of concurrent opportunistic pneumonia. The diagnosis of pulmonary KS should be considered in an HIV-infected homosexual or bisexual male with respiratory symptoms even in the absence of mucocutaneous lesions.

Acquired Immunodeficiency Syndrome↗