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X Liu

Publications and source records attributed to X Liu.

At least 1,171 records · Page 65Linked to original sources
PubMed1997

A modified residual method to estimate the zero-order absorption rate constant in a one-compartment model.

The objective of this work was to develop a simple residual method to estimate the rate constant for actual or apparent zero-order absorption into a one-compartment model. The method is based on the fact that, in theory, a plot of residuals versus e-Kt is linear for a zero-order absorption process, where K represents the elimination rate constant governing the terminal phase of the concentration-time profile. The apparent absorption rate constant (K0) can be calculated from the slope and intercept of the residual plot. Simulated concentration-time data with superimposed random error (CV = 5, 10, 15%, n = 8), as well as data sets from the literature for hydroflumethiazide and theophylline were analyzed with the proposed method of residuals. Parameters derived with the new technique were compared to both the nonlinear least-squares regression and the Wagner-Nelson method, all of which yield comparable K0 estimates. These results indicate that the proposed method of residuals represents a simple approach for estimating the apparent zero-order absorption rate constant analogous to classic residual analysis for first-order absorption.

Administration, Oral↗
PubMed1997

The absence of an apolipoprotein epsilon4 allele is associated with a more aggressive form of Alzheimer's disease.

We investigated the relationship between APOE genotype and rate of disease progression and survival in 99 patients with probable Alzheimer's disease (AD) who were followed biannually for up to 6 years. Patients were stratified into two groups, those with and without at least one APOE epsilon4 allele. The rate of decline in modified Mini-Mental State Examination scores was slower, the presence of extrapyramidal signs was decreased, and the development of myoclonus occurred later among patients with APOE epsilon4 alleles compared with patients with other genotypes. Compared with patients without an APOE epsilon4 allele, the risk of mortality was also decreased in patients with at least one epsilon4 allele (RR = 0.38; CI = 0.17-0.84, p < 0.02). Because the decline in mental ability as well as the development of myoclonus and extrapyramidal signs are consistent manifestations of disease progression, our results imply that APOE epsilon4 is associated with a less aggressive form of AD.

Age of Onset↗
PubMed1997

Analysis of action tremor and impaired control of movement velocity in multiple sclerosis during visually guided wrist-tracking tasks.

We investigated the relationship between action tremor (AT) and impaired control of movement velocity (MV) in visually guided tracking tasks, in normal subjects and in patients with multiple sclerosis (MS) with or without motor deficits. The effects of withdrawing visual feedback of either the target or the cursor were then investigated. Visually cued simple reaction times (SRTs) were also measured. The effects of thalamotomy on motor performance in these tasks were evaluated in seven patients. In the MS patients with tremor, there was no correlation between AT and impairment in control of MV, but the latter was highly correlated with an increased delay in SRT. Withdrawal of visually guiding cues increased the error significantly in MV, but reduced AT by approximately 30% in magnitude. Frequency analysis indicated that the AT had two components: (a) non-visual-dependent, oscillatory movements, mainly at 4 Hz; and (2) visual-dependent, repetitive movements, with significant power at 1-2 Hz. Thalamotomy significantly reduced AT but hardly improved accuracy in MV. These results suggest that visual feedback of a spatial mismatch signal may provoke a visually dependent repetitive movement contributing to AT. Conduction delays along either the cortico-cerebello-cortical or the proprioceptive pathways and impaired working memory caused by MS may be responsible for the movement disorders in these patients.

Adult↗
PubMed1997

Extracellular matrix of retinal pigment epithelium regulates choriocapillaris endothelial survival in vitro.

The role of extracellular matrix of retinal pigment epithelial cells (RPE-ECM) in the regulation of the survival of choriocapillaris endothelial cells (CCE) was investigated in vitro. The CCE survival was evaluated by trypan blue staining, neutral red uptake, and the counting of viable cells. Results showed that CCE cells survived on RPE-ECM. Pre-treatment of RPE-ECM individually with neutralizing antibodies to acidic fibroblast growth factor, vascular endothelial growth factor, platelet-derived growth factor, or transforming growth factor beta(pan specific to TGFbeta1, TGFbeta1.2, TGFbeta2 and TGFbeta5), did not alter the survival rate of CCE cells on RPE-ECM, as compared to that of the control (CCE survival rates on RPE-ECM pretreated with normal rabbit IgG). However, the treatment of RPE-ECM with neutralizing antibody to basic fibroblast growth factor (bFGF) caused CCE death by 77.1+/-15.7%. The CCE death was defined as apoptosis based on the morphological markers (shrinkage in cell size with blebbing of plasma membranes, condensation and fragmentation of nuclei, and DNA fragmentation in multiples of approximately 200 bp). The addition of phorbol 12-myristate 13-acetate (PMA) (2 nM) to the culture medium was effective for complete prevention of CCE apoptosis; the protecting effect of PMA on CCE apoptosis can be abolished by H7 (25 microM), but not HA1004 (50 microM), suggesting the involvement of PKC in protecting CCE from apoptosis. The inhibition of protein synthesis of CCE cells by cycloheximide (0.1 microM) did not affect the apoptotic process of the cells. In a separate experiment, when CCE cells were cultured in a medium saturated with bFGF (5 ng ml-1) without RPE-ECM, the cells also died by apoptosis. However, this apoptotic process was not affected by PMA. Cycloheximide also failed to affect the apoptotic process. These results suggest that both RPE-ECM insoluble molecules and RPE-ECM-bound bFGF modulate choriocapillaris survival by suppressing CCE apoptosis.

Animals↗
PubMed1997

The use of transgenic mice to generate high affinity p53 specific cytolytic T cells.

P53 is an attractive target immunotherapy because it is overexpressed in up to one half of all malignancies, and its overexpression often correlates with a worsened prognosis. We wanted to determine the feasibility of targeting wild-type epitopes p53 on human tumor cells. HLA A2.1 transgenic mice were immunized with the immunodominant wild-type p53 peptide epitopes, p53(149-157) and p53(264-272), along with a pan-DR helper epitope peptide in incomplete Freund's adjuvant (IFA). Twelve days later, splenocytes were harvested and stimulated with syngeneic blast cells that had been acid-treated to remove endogenous peptide and p53 peptide-pulsed. The responding cells were subsequently restimulated weekly with acid washed, peptide-pulsed Jurkat cells transfected with HLA A2.1. Peptide specific activity was tested in a chromium release assay. The resulting cytotoxic T cells (CTL) were cloned by limiting dilution. Peptide specific CTL were generated against both p53(149-157) and p53(264-272. Only p53(149-157) specific CTL were able to recognize and lyse cells that overexpressed endogenous p53. CTL clones derived from the p53(149-157) cell line demonstrated high affinity and specificity for p53(149-157) when presented by HLA A2.1+ cells. The p53(149-157) specific CTL were tested for specificity against a variety of cultured human cell lines. The CTL clones only lysed cells that overexpressed p53 in the context of HLA A2.1 and did not lyse cells with normal p53 expression or cells that lacked HLA A2.1 expression. This study demonstrates the possibility of targeting tumors, which overexpress p53, and raises the possibility transferring the high affinity, p53 specific T cell receptors from the murine CTL to human T cells.

Animals↗
PubMed1997

Bipolar esophageal electrocardiography by using standard limb leads.

The ear-xiphisternum distance (EXD, the distance from the low edge of the ear to the xiphisternal basis in supine position) was used as a reference value for esophageal catheter insertion. ECGs recorded in the esophagus with bipolar electrocardiography using standard limb lead (ESLL) and conventional unipolar lead (ECUL) were compared. 112 patients with sinus rhythm and 76 patients during paroxysmal supraventricular tachycardia (PSVT) whose P-wave and QRS complex did not overlap were studied. The results suggested that in sinus rhythm the amplitude of the P-wave in ESLL was larger and the T-wave was smaller than in ECUL. During PSVT, the P-wave was much clear and higher in each lead of ESLL than that in ECUL. The ideal range of esophageal ECG recording was situated between the end of EXD and 6.5 cm proximal to it.

Adolescent↗
PubMed1997

Effects of propranolol on beta-adrenergic receptor of experimental acute myocardial infarction in rats.

By using receptor autoradiography to observe the distribution and density of receptors, the effects of propranolol, a beta-blocker, on beta-adrenergic receptor of experimental acute myocardial infarction (AMI) were studied. One week after ligation of proximate left anterior descend (LAD) coronary artery, [3H] DHA binding sites were markedly decreased in both infarct region and non-infarct region. After treatment of propranolol (100 micrograms/kg), the [3H] DHA binding sites were obviously increased in the infarct region, and they were further decreased in the non-infarct region. The ratio of [3H] DHA binding sites of the infarct region to non-infarct region was from 0.24 at LAD ligation to 0.87 after propranolol treatment, which was close to 0.97 of control group (sham operation). The results indicated that the propranolol acted directly on myocardial beta- adrenergic through the receptor regulation of the balance of beta-receptors between the infarct region and non-infarct region, and improvement of the myocardial consonation and contraction synergism, thereby protecting the heart affected by AMI.

Adrenergic beta-Antagonists↗
PubMed1997

Biosynthetic production of type II fish antifreeze protein: fermentation by Pichia pastoris.

Sea raven type II antifreeze protein (SRAFP) is one of three different fish antifreeze proteins isolated to date. These proteins are known to bind to the surface of ice and inhibit its growth. To solve the three-dimensional structure of SRAFP, study its ice-binding mechanism, and as a basis for engineering these molecules, an efficient system for its biosynthetic production was developed. Several different expression systems have been tested including baculovirus, Escherichia coli and yeast. The latter, using the methylotrophic organism Pichia pastoris as the host, was the most productive. In shake-flask cultures the levels of SRAFP secreted from Pichia were up to 5 mg/l. The recombinant protein has an identical activity to SRAFP from sea raven serum. In order to increase yields further, four different strategies were tested in 10-l fermentation vessels, including: (1) optimization of pH and dissolved oxygen, (2) mixed feeding of methanol and glycerol with Mut(s) clones, (3) supplementation of amino acid building blocks, and (4) methanol feeding with Mut+ clones. The mixed-feeding/Mut(s) strategy proved to be the most efficient with SRAFP yields reaching 30 mg/l.

Amino Acids↗
PubMed1997

Developmental changes in the subcellular localization of R-cadherin in chick retinal pigment epithelium.

It has been reported that in the chick embryonic retina, N-cadherin first appears at the very early stages and is subsequently substituted by R-cadherin at the middle to late stages of development. To examine the role of R-cadherin in the morphogenesis of chick retinal pigment epithelium (RPE), the distribution of this adhesion molecule was studied by immunofluorescence cytochemistry and immunoelectron microscopy from embryonic day (E) 6 to hatching. R-cadherin immunoreactivity was detected at E6, and was strongest at E12-13. During these stages, R-cadherin was expressed uniformly on the lateral plasma membranes of RPE cells in contact with each other. Thereafter, R-cadherin immunoreactivity was markedly decreased, with intense immunoreactivity restricted to zonulae adherentes in latero-apical regions at E16. R-cadherin immunoreactivity was no longer detectable in the newly hatched chick RPE, even though morphologically well developed zonulae adherentes were present in latero-apical regions. No immunoreactivity was detected on the apical side facing the neural retina or on the basal side facing the basal lamina at any stage of development. These findings indicate that R-cadherin plays an important role as a major cadherin subtype in the morphogenesis of chick embryo RPE, and is involved initially in non-specific cell-cell adhesions, and subsequently in the formation and maintenance of developing zonulae adherentes.

Animals↗
PubMed1997

The relationship between the vas volume and the anatomic size of the vas deferens.

The anatomic sizes of 210 vas segments from 107 volunteers of vasectomy were measured by computerized image graphic technique with microphotography. The mean equivalent-round, outer and inner diameters of the vas were 2.17 +/- 0.20 mm and 0.56 +/- 0.08 mm, respectively. The calculated thickness of vas wall was 0.81 +/- 0.21 mm. The maximal volumes of 124 vas segments (1 cm in length) were tested by injecting colored solution into vas lumen until vas rupture. The mean rupture volume of 1 cm vas lumen was 0.05 +/- 0.007 mL. A significant influence of the thickness of vas wall (p < 0.05) and body height (p < 0.05) on the rupture volume was noticed in stepwise regression analysis. A tunnel-like rupturing pattern was observed in morphological observation. The obtained rupture volume provides a security line in determining the injection volume of occlusive material or the size of the implanted contraceptive device.

Adult↗
PubMed1997

Myosin light-chain phosphorylation in diabetic cardiomyopathy in rats.

The regulatory myosin light chain (MLC) is phosphorylated in cardiac muscle by Ca2+/calmodulin-dependent MLC kinase (MLCK) and is considered to play a modulatory role in the activation of myofibrillar adenosine triphosphatase (ATPase) and the process of force generation. Since the depression in cardiac contractile function in chronic diabetes is associated with a decrease in myofibrillar ATPase activity, we investigated changes in MLC phosphorylation in diabetic heart. Rats were made diabetic by injecting streptozotocin (65 mg/kg intravenously), and the hearts were removed 8 weeks later; some 6-week diabetic animals were injected with insulin (3 U/d) for 2 weeks. Changes in the relative MLC and MLCK protein contents were measured by electrophoresis and immunoblot assay, whereas phosphorylated and unphosphorylated MLCs were separated on 10% acrylamide/urea gel and identified by Western blot. MLC and MLCK contents were decreased markedly (40% to 45%) and MLC phosphorylation was decreased significantly (30% to 45%) in the diabetic rat heart homogenate in comparison to control values. The changes in MLC and MLCK content in diabetic heart were partially reversible, whereas changes in MLC phosphorylation were normalized upon treatment with insulin. These results suggest that decreased protein contents of MLC and MLCK and phosphorylation of MLC may contribute to the depression of cardiac myofibriliar ATPase activity and heart dysfunction in diabetic cardiomyopathy.

Adenosine Triphosphatases↗
PubMed1997

Vitamin A and retinoic acids immunomodulation on human gut lymphocytes.

Epidemiological studies have suggested an important immunomodulatory role for vitamin A and other related vitamin A compounds in adults and children. Although vitamin A is absorbed via the gastrointestinal tract, its affect on the gut mucosal immune cells has not been adequately investigated. We investigated the in-vitro effect of vitamin A (retinol) and its retinoid acid (RA) compounds (13-cis- and all trans-retinoic acids) on the human gut mucosal immune system as represented by colonic lamina propria lymphocyte (LPL) proliferation, and ornithine decarboxylase (ODC) activity. Results showed that retinol suppressed and trans-retinoic acid enhanced thymidine incorporation into LPL. 13-cis retinoic acid did not significantly affect LPL DNA synthesis. Similarly, retinol (0.025 microgram/ml and 10 micrograms/ml) and 13-cis retinoic acid (conc. 10 micrograms/m) suppressed, while all trans-retinoic acid (conc. 10 micrograms/ml) enhanced ODC activity in PHA-stimulated LPL. Interestingly, the effects of retinol and all trans-RA were abolished when LPL were previously depleted of macrophages. Addition of monocyte-associated lymphokines, IL-1 and IL-6, showed that IL-1 partially replaced the enhancing effect of all trans-RA previously observed on LPL thymidine incorporation. IL-6 did not affect LPL DNA synthesis irrespective of the vitamin A compound used. We conclude that retinol and retinoid acids (13-cis, all trans-) may alter the human colonic immune system possibly via IL-1 cytokine, but not via IL-6. The data suggest that vitamin A and its retinoid compounds may participate in the modulation of the gut immune system.

Adjuvants, Immunologic↗
PubMed1997

Histological and physiological effects of the central auditory prosthesis: surface versus penetrating electrodes.

To rehabilitate profoundly deaf patients who are not suitable for cochlear implants, central auditory prostheses have been implanted. To compare two possible electrode configurations - penetrating and surface ones - electrical stimulation of the cochlear nucleus with both types of arrays was tested on guinea pigs and cats. Electrophysiological, autoradiographic and histological measures were used to study effects of the central auditory prostheses on the auditory pathway. The results showed that a successful electrically evoked auditory brainstem response could be recorded with both surface and penetrating electrodes in cats and guinea pigs. In guinea pigs the penetrating electrodes had advantages over surface arrays in the sense of lower thresholds and wider dynamic ranges. In cats penetrating electrodes showed lower thresholds than surface ones. In cats and guinea pigs stimulated with either surface or penetrating electrodes, evoked 2-deoxyglucose (2-DG) label was found in the auditory pathway from the cochlear nucleus to the inferior colliculus. No non-auditory tissues were found with evoked 2-DG label. Histological results showed that in subdivisions of the guinea pig cochlear nucleus stimulated with penetrating electrodes the neurone density was decreased, and the mean soma area was increased compared with the control side. In the cat, penetrating electrodes were associated only with increased mean soma area in parts of the stimulated cochlear nucleus. These results suggest that the physiological advantages of penetrating electrodes over surface ones were achieved with some trade-off in safety, especially in the guinea pig.

Animals↗
PubMed1997

HPCE methods for the identification and quantitation of antibodies, their conjugates and complexes.

We review here much of the existing literature that deals with analysis, resolution, characterization, and (at times) quantitation of antibodies in capillary electrophoresis modes. Each major mode of CE shown applicable to antibody analysis is described, along with the major applications of that mode for antibodies. Discussions are presented as to the mechanisms of antibody resolution in CE, interactions of various buffer components with the proteins leading to resolution, and methods of quantitation for antibodies. The literature is critically reviewed with regard to true application of CE for antibody analysis, limitations, information possible, information implied, and which samples have actually been assayed by CE modes. The literature is critically reviewed up to and including 1996, both for the scientific and commercial literature, especially vendor applications and real world applications possible.

Animals↗
PubMed1997

Peroxynitrite-induced apoptosis in T84 and RAW 264.7 cells: attenuation by L-ascorbic acid.

The free radicals nitric oxide and superoxide react to form peroxynitrite (ONOO-), a potent cytotoxic oxidant. This study was designed to evaluate whether addition of L-Ascorbic acid (AsC) into the culture medium decreases peroxynitrite-induced apoptosis in human intestinal epithelial (T84) and murine macrophage (RAW 264.7) cell lines. In Experiment 1, T84 and RAW 264.7 cells were divided in two protocols: (1) treated with 100-300 microM ONOO- and incubated for 4 h, and (2) treated with 10-100 microM ONOO- and incubated overnight (14 h). In Experiment 2, T84 and RAW 264.7 cells were treated with 300 microM ONOO- and 500 microM AsC and incubated for 4 h. In Experiment 3, T84 and RAW 264.7 cells were preincubated for 2 h with 500 microM AsC then exposed to 300 microM ONOO- for 4 h. Cell viability (necrosis) was assessed by trypan blue dye exclusion. Apoptosis was quantified with a cell death detection ELISA assay. In the 4 h protocol, ONOO- induced apoptosis in T84 and RAW 264.7 cells, at levels of 100-300 microM. Concentrations of ONOO- greater than 300 microM caused necrosis. In contrast, extension of the protocol to 14 h indicated that ONOO- induced apoptosis at lower concentrations (50;-75 microM), with concentrations > 75 microM resulting in necrosis. AsC administered to the media or with preincubation plus washout, decreased peroxynitrite-induced apoptosis in T84 and RAW 264.7 cells. These results indicate that ONOO- may contribute to the pathophysiology of gut inflammation by promoting cell death and ascorbic acid may protect against peroxynitrie-induced damage.

Animals↗
PubMed1997

Role of free radicals in the mechanism of the hydrazine-induced formation of megamitochondria.

The effect of 4-hydroxy-2,2,6,6-tetramethyl-piperidine-1-oxyl(4-OH-TEMPO), a scavenger for free radicals, and 4-hydroxypyrazolo [3,4-d(pyrimidine)allopurinol], a xanthine oxidase inhibitor, on the hydrazine-induced changes of mitochondrial ultrastructure and those in the antioxidant system of the liver were investigated using rats as experimental animals. Animals were placed on a powdered diet containing 0.5% hydrazine for 7 d in the presence and absence of a combined treatment with 4-OH-TEMPO or allopurinol. Results obtained were as follows. 4-OH-TEMPO completely prevented the hydrazine-induced formation of megamitochondria in the liver, while it was partly prevented by allopurinol. The following changes observed in hydrazine-treated animals were improved almost completely by 4-OH-TEMPO:decreases in the body weight and liver weight; lowered rates of ADP-stimulated respiration and coupling efficiency of hepatic mitochondria; remarkable elevation of the level of lipid peroxidation. Improving effects of allopurinol were incomplete. The present results suggest that free radicals may play a key role in the mechanism of the hydrazine-induced formation of megamitochondria and that a part of free radicals generated during the hydrazine intoxication is ascribed to the degradation of purine nucleotides via xanthine oxidase. A general mechanism of the megamitochondria formation induced in various pathological conditions besides the case of hydrazine are discussed.

Allopurinol↗