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Biomedical subjects

D Liu

Publications and source records attributed to D Liu.

At least 397 records · Page 22Linked to original sources
PubMed1998

Free liposomes enhance the transfection activity of DNA/lipid complexes in vivo by intravenous administration.

Factors that regulate the transfection efficiency of cationic lipid-based carriers are still largely unknown. We have shown in a previous report [F. Liu, H.W. Qi, L. Huang, D. Liu, Factors controlling the efficiency of cationic lipid-mediated transfection in vivo via intravenous administration, Gene Ther., 4 (1997) 517-523. ] that the transfection efficiency, to the lung, of a lipid formulation composed of N-[1-(2,3-dioleoyloxy)propyl-N,N, N-trimethylammonium chloride (DOTMA) and Tween 80 is directly proportional to the ratio of DOTMA to DNA. In this study, we investigated the mechanism underlying the high cationic lipid to DNA ratio dependent transfection activity. Specifically, we have examined the role of free cationic liposomes in affecting the transfection efficiency of the DNA/lipid complexes in vivo by intravenous administration. The data show that greater transfection activity of DNA/lipid complexes in the lung at a higher cationic lipid to DNA ratio is due to the function of free liposomes present in the DNA/lipid mixture. Free liposomes enhance the transfection activity of DNA/lipid complexes by increasing the retention time of DNA and decreasing transgene degradation in different organs. In addition to DOTMA liposomes, liposomes composed of 1,2-dioleoyl-3-trimethylammonium propane chloride (DOTAP) and 3beta[N-(N', N'-dimethylaminoethane) carbamoyl] cholesterol (DC-Chol) also enhance the level of gene expression in animals transfected by DNA/DOTMA complexes. These results suggest that inclusion of free liposomes into the DNA/lipid complexes may be important in achieving an optimal transfection activity in vivo.

Animals↗
PubMed1998

Human general transcription factor TFIIB: conformational variability and interaction with VP16 activation domain.

Human TFIIB, an essential factor in transcription of protein-coding genes by RNA polymerase II, consists of an amino-terminal zinc binding domain (TFIIBn) connected by a linker of about 60 residues to a carboxy-terminal core domain (TFIIBc). The TFIIB core domain has two internally repeated motifs, each comprising five alpha-helices arranged as in the cyclin box. Compared to the crystal structure of TFIIBc in complex with TBP and a TATA-containing oligonucleotide, the NMR-derived solution structure of free TFIIBc is more compact, with a different repeat-repeat orientation and a significantly shorter first helix in the second repeat. Analysis of backbone 15N relaxation parameters indicates the presence of relatively large amplitude, nanosecond time-scale motions in the TFIIBc interrepeat linker and structural fluctuations throughout the backbone. Interaction of TFIIBc with the acidic activation domain of VP16 or with TFIIBn induces 1H-15N chemical shift and line width changes concentrated in the first repeat, interrepeat linker and the first helix of the second repeat. These results suggest that TFIIB is somewhat pliable and that the conformation of the C-terminal core domain can be modulated by interaction with the N-terminal zinc binding domain. Furthermore, binding of the VP16 activation domain may promote TFIIBc conformations primed for binding to a TBP-DNA complex.

Binding Sites↗
PubMed1998

Peptides derived from the complementarity-determining regions of anti-Mac-1 antibodies block intercellular adhesion molecule-1 interaction with Mac-1.

Peptides or small molecules that can block the interaction of the integrin Mac-1 with its receptor, intercellular adhesion molecule-1 (ICAM-1), have not previously been developed. We studied this interaction by measuring the adherence of ICAM-1-expressing Chinese hamster ovary (CHO) cells to immobilized, purified Mac-1. Nucleotide sequence information was obtained for the complementarity determining regions (CDRs) of three antibodies (44aacb, MY904, and 118.1) shown to block Mac-1-mediated cell adherence. Peptides were synthesized based on the predicted amino acid sequences of the CDRs and tested for the ability to block cell adhesion to Mac-1. Peptides derived from CDR1 of 44aacb, CDR2 of 118.1, and CDRs 1 and 3 of MY904 heavy chains were found to possess blocking activity at 10-100 muM. This may indicate that one or two CDRs contribute disproportionately to the antibody binding affinity. The binding of ligands to Mac-1 has been shown to require a region of the alpha-chain known as the I- or A-domain. We have recombinantly produced Mac-1 I-domain, and show that it is also capable of supporting the adherence of ICAM-1-expressing CHO cells. The adherence of ICAM-1-CHO cells to the I-domain is inhibited by 44aacb and 118.1 and by the CDR peptides from 44aacb and 118.1. By using phage display of peptide libraries based on the 118.1 CDR peptide with five residues randomized, we were able to identify a novel peptide inhibitor of Mac-1 with substitutions at all five positions. These peptides provide lead structures for development of Mac-1 antagonists.

Amino Acid Sequence↗
PubMed1998

Prevalence and causes of undernutrition in medical outpatients.

PURPOSE: To assess the prevalence, common causes, and frequency of recognition and treatment of undernutrition in older and younger medical outpatients using a cross-sectional survey design with 2-year follow-up of undernourished subjects. PATIENTS AND METHODS: Charts of 1017 adult patients attending a hospital outpatient department were reviewed for the presence of undernutrition, and 85 patients meeting inclusion criteria for undernutrition were evaluated and followed for 2 years. An initial evaluation focused on nutritional, cognitive, and affective status and on nutritional attitudes using two subscales of the EAT-26 eating disorder inventory. After 2 years, initial data plus outpatient records were evaluated by 2 independent reviewers to determine a primary cause of undernutrition and to assess the recognition and treatment of undernutrition by the primary physician. RESULTS: Undernutrition was identified in 46 (11%) and 44 (7%) of older and younger subjects respectively; odds ratio (OR) (95% [confidence interval (CI)]) for older versus younger=1.65 (1.06 to 2.51). The primary cause of undernutrition differed between age groups but was deemed treatable in nearly 90% of all subjects. Undernutrition was recognized in 19 (43%) older subjects and 5 (12%) younger subjects (OR=5.47 [1.87 to 16.0]), and appropriate intervention(s) were instituted in 6 (14%) and 2 (5%) of older and younger subjects, respectively (OR=3.08 [0.668 to 14.21]). Older subjects scored higher on the EAT-26 oral control subscale than did younger subjects (4.7 versus 2.5, P=0.004) but similarly on the EAT-26 dieting subscale (5.2 versus 6.3, P=0.332); these relationships did not change with control for potentially confounding variables. CONCLUSIONS: In this study, undernutrition was relatively common, usually amenable to treatment, but frequently undetected and undertreated in both older and younger medical outpatients. Older undernourished subjects exhibited higher oral control needs than younger persons, which may have implications for the pathophysiology and treatment of their malnutrition. Further improvement in detection and intervention is warranted in both younger and older age groups.

Adult↗
PubMed1998

Pulmonary metastasectomy for testicular germ cell tumors: a 28-year experience.

BACKGROUND: The role of surgery in patients with pulmonary metastatic germ cell tumors has been evolving since the 1970s. To evaluate the results of pulmonary resection, we reviewed our 28-year experience. METHODS: Between July 1967 and May 1995, 157 patients with testicular germ cell tumors underwent pulmonary resections for suspected metastases. Their clinical and pathological data were reviewed. Kaplan-Meier and Cox regression models were used to analyze prognostic factors for survival after resection of metastatic disease. RESULTS: All patients were male with median age of 27 years (range 15-65). Complete resection was accomplished in 155 (99%) patients. Viable carcinoma was present in 44% (70) of the patients. Forty-one (26%) patients had metastases to other sites after pulmonary metastasectomy. The overall actuarial survival 5 years after pulmonary resection was 68% for the entire group and 82% for patients diagnosed after 1985. On multivariate analysis, the adverse prognostic factors were metastases to nonpulmonary visceral sites (p = 0.0069) and the presence of viable carcinoma in the resected specimen (p < 0.0001). CONCLUSIONS: With current chemotherapy regimens, almost 85% of the patients with testicular germ cell tumors undergoing complete resection of their pulmonary metastases can be expected to achieve long-term survival.

Adolescent↗
PubMed1998

A novel expression system based on host-range expansion of baculovirus.

A host range expanded recombinant Autographa californica multiple-nucleocapsid nucleopolyhedrosis virus AcMNPV/r2 was obtained by cotransfection of the bacmid DNA from Escherichia coli DH10Bac along with a plasmid pBmH-M containing HindIII M fragment of Bombyx mori nuclear polyhedrosis virus (BmNPV) genomic DNA. A recombinant transposon vector carrying a mutant green fluorescent protein gene (GFP) and a polyhedrin gene was constructed. Transposition was carried out in both E. coli DH10Bac and E. coli DH10BmH, which contains AcMNPV/r2 and a helper plasmid. Recombinant DNAs were transfected into Sf-9 cells to generate recombinant virus AcMNPV/r3 and AcMNPV/r4 respectively. Viral stock of AcMNPV/r4 was then infected into Bombyx mori cells (BmN) and Bombyx mori larvae (silkworm). Analysis shows that GFP was highly expressed in Bombyx mori larvae. This expression system, is practicable therefore for mass production of foreign gene products.

Animals↗
PubMed1998

Aluminum treatment induces nitric oxide synthase in the rat brain.

In an attempt to delineate the capacity of aluminum to promote pro-oxidant events in the central nervous system, levels of nitric oxide synthase (NOS) have been determined in the cerebellum of rats exposed to an aluminum salt, either alone or in combination with an iron compound. Relatively acute treatment with aluminum over a three-day period, increased cerebellar levels of NOS. Parallel results were obtained when animals were dosed over a more extended three-week period. Dosing with an iron compound resulted in no changes in levels of this enzyme. Concurrent treatment with aluminum and iron did not potentiate the NOS-inducing effects of aluminum. By use of selective inhibitors, the specific induction of iNOS by aluminum treatment was found. The results suggest that the presence of aluminum can induce cerebellar NOS and that these changes are independent of any interaction between aluminum and erogenous iron.

Aluminum↗
PubMed1998

Metabotropic glutamate receptors are involved in calcium-induced LTP of AMPA and NMDA receptor-mediated responses in the rat hippocampus.

Effects of metabotropic glutamate (mGlu) receptors on calcium-induced long-term potentiation (LTP) of alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionate (AMPA) and N-methyl-D-aspartate (NMDA) receptor-mediated components were investigated in rat hippocampal slices using whole-cell patch-clamp recordings of excitatory postsynaptic currents (EPSCs). Calcium-induced LTP comprises a parallel, long-lasting increase of AMPA and NMDA receptor-mediated components. The calcium-induced LTP of the AMPA receptor-mediated component can be significantly attenuated by the use of a selective NMDA antagonist. (R.S)-alpha-methyl-4-carboxyphenylglycine (MCPG), a selective antagonist of mGlu receptors, abolished the long-lasting increase of both AMPA and NMDA receptor-mediated components observed in calcium-induced LTP. In current clamp mode, the application of a high calcium alone or Schaffer fiber stimulation alone (20 Hz) only generated a short-term increase in the firing rate of evoked action potentials. Conversely, a long-term increase in the firing rate was observed if Schaffer fiber stimulation (20 Hz) accompanied the perfusion of high calcium. These results suggest that calcium-induced LTP involves a parallel, long-lasting enhancement in ionotropic AMPA and NMDA receptor-mediated components. More importantly, the mGlu receptor plays a critical role in the establishment of both AMPA and NMDA receptor-mediated components underlying calcium-induced LTP. In addition, the present study also described an experimental condition in which the coapplication of the high calcium pulse and Schaffer fiber stimulation (20 Hz) can synergistically elicit a long-term increase of neuronal excitability.

Action Potentials↗
PubMed1998

Modulation of American ginseng on brainstem GABAergic effects in rats.

Single neurons in the region of the medial nucleus tractus solitarius (NTS), responding or not responding to gastric vagal branch stimulation, were recorded in an in vitro neonatal rat brainstem-gastric preparation. The spontaneous activity of the majority of these two types of NTS units was inhibited by GABA(A) receptor agonist, muscimol (30 microM), and this inhibition (approximately 52% compared to 100% of the control level) could be antagonized by selective GABA(A) receptor antagonist, bicuculline (10 microM). Application of Panax quinquefolium L. extracts (3.0 microg/ml) into the brainstem compartment of the preparation also significantly reduced the discharge rate of these NTS neurons (approximately 27% compared to the control level), but this reduction could not be reversed by bicuculline (10 microM). Pretreatment with Panax quinquefolium L. (3.0 microg/ml) significantly decreased the NTS inhibitory effects induced by muscimol (30 microM), approximately from 51 to 33%. Our results demonstrated the interactions of Panax quinquefolium L. with ligand-bindings of GABA(A) receptors, and the modulation of the brainstem GABAergic mechanism by Panax quinquefolium L. Our data suggest that the regulation of GABAergic neurotransmission may be an important action of Panax quinquefolium L.

Animals↗
PubMed1998

"Stunning" of the left atrium after spontaneous conversion of atrial fibrillation to sinus rhythm: demonstration by transesophageal Doppler techniques in a canine model.

OBJECTIVES: This study compared left atrial and left atrial appendage contraction velocities in sinus rhythm before and after a brief period of atrial fibrillation in a canine model. BACKGROUND: In patients, left atrial appendage contraction velocities measured during sinus rhythm after cardioversion from atrial fibrillation are depressed relative to left atrial appendage emptying velocities measured during atrial fibrillation, suggesting that the left atrial appendage is mechanically "stunned." METHODS: This phenomenon was studied in a canine model of acute (60 min) pacing-induced atrial fibrillation followed by spontaneous reversion to sinus rhythm using epicardial and transesophageal pulsed wave Doppler. Unique features of the model include: 1) comparison of left atrial function postconversion to baseline sinus rhythm rather than to measurements during atrial fibrillation, 2) control of the duration of atrial fibrillation and 3) elimination of the extraneous influences of direct current shock and antiarrhythmic agents, which may independently depress left atrial function. RESULTS: Hemodynamic conditions (heart rate, mean arterial pressure, cardiac output, mean pulmonary artery pressure, mean right atrial pressure and mean left atrial pressure) at baseline, during 60 min of atrial fibrillation and after reversion to sinus rhythm were constant throughout the study period. Peak left atrial contraction velocities (measured from the transmitral flow velocity profile) were significantly (p < 0.02) reduced to 64+/-22% of baseline values upon spontaneous conversion of atrial fibrillation to sinus rhythm and recovered to basal values by 20 min after resumption of sinus rhythm. Peak left atrial appendage contraction velocities were significantly (p < 0.001) reduced to 49+/-24% of baseline values upon spontaneous conversion of atrial fibrillation to sinus rhythm and recovered to basal values by 40 min after reversion to sinus rhythm. CONCLUSIONS: Even brief (60 min) periods of atrial fibrillation in normal canine hearts result in marked depression of global left atrial systolic function and regional left atrial (left atrial appendage) systolic function upon resumption of sinus rhythm. This "mechanical stunning" of left atrial systolic function appears to be more profound and of longer duration for the left atrial appendage compared with the left atrium as a whole, which may predispose the appendage to blood stasis and thrombus formation. Chronic models of atrial fibrillation need to be developed to examine the impact of longer periods of atrial fibrillation upon the magnitude and duration of postconversion left atrial "stunning."

Animals↗
PubMed1998

Corneal topography in Ehlers-Danlos syndrome.

PURPOSE: To assess the use of corneal topography in conjunction with slitlamp biomicroscopy and retinoscopy to diagnose keratoconus in a large group of patients with Ehlers-Danlos syndrome (EDS). SETTING: Kresge Eye Institute, Wayne State University, Detroit, Michigan, USA. METHODS: Thirty-six patients (72 eyes) with genetically typed EDS had slitlamp biomicroscopy, retinoscopy, and videokeratography with the EyeSys instrument. The presence or absence of slitlamp keratoconus findings was correlated to a presumptive diagnosis based on corneal topography using derived topographic indexes associated with keratoconus. These topographic indexes included central corneal power, (CCP), difference in CCP, inferosuperior asymmetry (I-S) value, and asphericity (Q). Axial and profile difference maps were generated and analyzed for findings suggestive of keratoconus. RESULTS: In 72 eyes, no keratoconus was found using slitlamp biomicroscopy. No eye had an I-S value greater than 1.60 diopters (D), 2 eyes had a CCP greater than 46.50 D, and 2 eyes had a Q value less than -1.00. Eight of 36 pairs of eyes had an intereye CCP greater than 0.92 D. In both eyes of the patient with Q values less than -1.00 the profile difference maps were mildly abnormal. CONCLUSIONS: Slitlamp biomicroscopy of the cornea was unremarkable in all patients. Only 1 patient had Q values and profile difference maps that were mildly suggestive of keratoconus. Even after adding topography to the examination, it appears that keratoconus in a known population of patients with EDS remains rare.

Cornea↗
PubMed1998

Superoxide production after spinal injury detected by microperfusion of cytochrome c.

Highly reactive oxygen-containing species may form upon CNS injury and cause oxidative damage to important cellular components, thereby destroying cells. To test this hypothesis, free radical formation following such insults should be characterized first. In this study, we measured the time course of superoxide production following impact injury to the rat spinal cord using a novel microcannula perfusion technique developed by us. Cytochrome c (50 microM in artificial cerebrospinal fluid) was perfused into the rat spinal cord through the cannula inserted laterally into the gray matter of the cord, and reduced cytochrome c was measured from perfusates spectrophotometrically. We found that the levels of superoxide in the extracellular space increased to approximately twice the basal level and remained elevated for over 10 h. Superoxide dismutase (60 U/ml) significantly reduced the elevation of superoxide levels (p = .016) and ferric chloride (0.1 mM)/EDTA (0.25 mM) infused together with cytochrome c completely removed the superoxide measured, validating the measurement of superoxide. The relatively long-lasting formation of superoxide reported herein suggests that removal of superoxide may be a realistic treatment strategy for reducing injury caused by free radicals.

Animals↗
PubMed1998

Patients' expectations of outcome of hysterectomy and alternative treatments for menstrual problems.

Patients can influence treatment to the extent of securing surgery in the absence of medical need, but their expectations of effects of surgery are poorly understood. Interviews with 26 patients presenting menstrual problems without confirmed pathology were used to construct a questionnaire to measure expectations of effects of treatment. Principal-components analysis of responses of 200 similar patients identified six discrete areas in which improvement was expected, including general well-being, menstrual function, and physical symptoms. Expectations of harm were nonspecific and unidimensional. Component-based scale scores showed that patients who anticipated hysterectomy expected more benefit, but also more harm, than those anticipating conservative procedures. In study 2, these different expectations were largely replicated in patients who were randomly allocated to provide their expectations of specific procedures. Patients' uniquely positive expectations of hysterectomy may help to explain its frequent use in the absence of pathology.

Adolescent↗
PubMed1998

Induction of specific T-cell tolerance by adenovirus-transfected, Fas ligand-producing antigen presenting cells.

A major problem associated with adenovirus gene therapy is the T cell-mediated immune response, which is elicited by inoculation of the adenovirus vector and leads to rapid clearance of the virus and loss of transgene expression. In this study, the immune response to adenovirus was prevented by induction of specific T-cell tolerance by pretreatment with adenovirus-infected antigen-presenting cells (APC) that express Fas ligand. Compared with control-treated mice, the tolerized mice showed prolonged expression of lacZ upon administration of AdCMVlacZ 1 week after tolerance induction. In contrast to the control mice, the tolerized mice did not display proliferation of CD3+ T cells in the spleen in response to AdCMVlacZ. Tolerance induction also was indicated by the lower production of interferon-gamma and interleukin-2 by peripheral T cells isolated from AdCMVlacZ-challenged tolerized mice than by AdCMVlacZ-challenged control-treated mice. The T-cell tolerance was specific for the adenovirus as the T-cell responses to irrelative murine cytomegalovirus remained unimpaired. Our results indicate that adenovirus-specific T-cell tolerance can be induced by APCs that coexpress Fas ligand and adenovirus antigens. We propose that this new strategy can be used to induce tolerance to adenovirus vector gene therapy with resultant prolonged expression of the transgene.

Adenoviridae↗
PubMed1998

Cyclin A1 is required for meiosis in the male mouse.

The mammalian A-type cyclin family consists of two members, cyclin A1 (encoded by Ccna1) and cyclin A2 (encoded by Ccna2). Cyclin A2 promotes both G1/S and G2/M transitions, and targeted deletion of Ccna2 in mouse is embryonic lethal3. Cyclin A1 is expressed in mice exclusively in the germ cell lineage and is expressed in humans at highest levels in the testis and certain myeloid leukaemia cells. To investigate the role of cyclin A1 and possible redundancy among the cyclins in vivo, we generated mice bearing a null mutation of Ccna1. Ccna1-/- males were sterile due to a block of spermatogenesis before the first meiotic division, whereas females were normal. Meiosis arrest in Ccna1-/- males was associated with increased germ cell apoptosis, desynapsis abnormalities and reduction of Cdc2 kinase activation at the end of meiotic prophase. Cyclin A1 is therefore essential for spermatocyte passage into the first meiotic division in male mice, a function that cannot be complemented by the concurrently expressed B-type cyclins.

Animals↗
PubMed1998

Enhanced gene expression in mouse lung by prolonging the retention time of intravenously injected plasmid DNA.

The effect of retention time of plasmid DNA in mouse lung on the level of transgene expression after intravenous administration was examined. Using CMV driven expression system with luciferase gene as a reporter and preinjection of free cationic liposomes into the animal as means of manipulating the retention time of plasmid DNA, we demonstrated that naked plasmid DNA is effective in transfecting cells in the lung by intravenous administration. An increase in DNA retention time in the lung results in a higher level of gene expression. Liposomes composed of cationic lipids with alkyl chains exhibited better activity than cholesterol-based cationic liposomes to retain the plasmid DNA in the lung. The level and patterns of gene expression obtained appeared similar to those seen in animals transfected by DNA-liposome complexes. These results suggest that prolonging the exposure time of DNA to the target cells in vivo may be an important strategy in achieving a high level of gene expression. Our data also introduce a possibility that the function of cationic liposomes in lipoplex-mediated transfection in vivo is to extend the interaction time of DNA with the cells.

Animals↗
PubMed1998

Microbial adsorption of cyanazine and metolachlor.

A laboratory experiment was performed to study the role of microorganisms in producing the non-extractable residues by anaerobically incubating cyanazine (2-[[4-chloro-6-(ethylamino)-1,3,5,-triazin-2-yl]-amino]-2-methoxy -l- methylethyl)acetamide] and metolachlor [2-chloro-N-(2-ethyl-6-methoxy-l- methylethyl)acetamide] in culture media that had been inoculated with sewage bacteria from anaerobic sludge. Based on the gas chromatographic analyses of extracts from the degradation, adsorption, and abiotic controls for the parent herbicide and its possible metabolites, this study provided the first direct evidence that bacterial biomass, rather than metabolism, was mainly involved in the formation of bound residues with cyanazine. Anaerobic bacteria appeared to be incapable of forming bound residues with metolachlor. The common phenomenon of age-dependent extractability for bound residues was observed with cyanazine. These results imply that bacteria may adsorb pesticides selectively with preference for certain chemical structures over others.

Acetamides↗