Biomedical subjects

L Liu

Publications and source records attributed to L Liu.

At least 883 records · Page 49Linked to original sources

PubMed1996

Molecular cloning and structural organization of the human inducible nitric oxide synthase gene (NOS2).

Previously, we reported the isolation and molecular cloning of human inducible nitric oxide synthase gene (NOS2) sequences from human chromosome 17 cosmid libraries. Here we describe the further characterization and sequencing of the NOS2 gene. The genomic structure of the NOS2 gene was determined from two overlapping cosmid clones, namely, pcos4A and pcos20. the NOS2 open reading frame is encoded by 27 exons, with translation initiation and termination in exon 2 and exon 27, respectively. These results differ from the previously reported organization of the iNOS gene, where 26 exons were reported for the genomic structure of NOS2.

Alternative Splicing↗

PubMed1996

The 145-kDa protein induced to associate with Shc by multiple cytokines is an inositol tetraphosphate and phosphatidylinositol 3,4,5-triphosphate 5-phosphatase.

A 145-kDa tyrosine-phosphorylated protein that becomes associated with Shc in response to multiple cytokines has been purified from the murine hemopoietic cell line B6SUtA1. Amino acid sequence data were used to clone the cDNA encoding this protein from a B6SUtA1 library. The predicted amino acid sequence encodes a unique protein containing an N-terminal src homology 2 domain, two consensus sequences that are targets for phosphotyrosine binding domains, a proline-rich region, and two motifs highly conserved among inositol polyphosphate 5-phosphatases. Cell lysates immunoprecipitated with antiserum to this protein exhibited both phosphatidylinositol 3,4,5-trisphosphate and inositol 1,3,4,5-tetrakisphosphate polyphosphate 5-phosphatase activity. This novel signal transduction intermediate may serve to modulate both Ras and inositol signaling pathways. Based on its properties, we suggest the 145-kDa protein be called SHIP for SH2-containing inositol phosphatase.

Adaptor Proteins, Signal Transducing↗

PubMed1996

Development of an avian model for restenosis.

Recurrence of atherosclerotic plaque growth after interventional therapy, restenosis, is a significant clinical problem occurring in 20%-50% of cases. We have developed a new avian model for the investigation of restenosis after arterial injury in cholesterol fed White Leghorn roosters. Atherosclerotic plaque growth 1-30 weeks after angioplasty balloon mediated endothelial injury in the abdominal aorta was studied in 37 roosters. Roosters were maintained on either normal poultry diet or high cholesterol diet. Twelve cholesterol fed roosters were also fed a hormone supplemented diet in order to modify plaque morphology. The procedural success rate was high. Angiographic stenoses (mean 36% with maximum of 74%) were detectable in cholesterol fed roosters after balloon angioplasty with associated histological evidence of plaque growth (P < 0.017). Cholesterol feeding enhanced fatty plaque growth; hormone manipulation increased calcific and ulcerated plaque but with high associated morbidity. Three interventional devices were subsequently examined in 32 roosters (16 laser angioplasty, 7 atherectomy, and 9 stent implant). Plaque development was again assessed by contrast angiography and histological analysis. We conclude that balloon mediated arterial injury in cholesterol fed roosters produces early proliferative and late, complex atherosclerotic lesions providing an inexpensive model for plaque development after intimal injury.

Angioplasty, Balloon↗

PubMed1996

Biochemical characterization of the human cyclin-dependent protein kinase activating kinase. Identification of p35 as a novel regulatory subunit.

The activation of cyclin-dependent protein kinases (Cdks) is dependent upon site-specific phosphorylation and dephosphorylation reactions, as well as positive and negative regulatory subunits. The human Cdk-activating protein kinase (Cak1) is itself a Cdc2-related cyclin-dependent protein kinase that associates with cyclin H. The present study utilized specific anti-Cak1 antibodies and immunoaffinity chromatography to identify additional Cak1-associated proteins and potential target substrates. Immunoprecipitation of metabolically labeled human osteosarcoma cells revealed a number of Cak1-associated proteins, including p95, p37 (cyclin H), and a 35-kDa protein that was further characterized herein. Microsequence analysis obtained after limited proteolysis revealed peptide fragments that are similar, but not identical to, human and yeast cyclins, thus identifying p35 as a cyclin-like regulatory subunit. The greatest sequence similarity of human p35 is with Mcs2, a yeast cyclin that is essential for cell cycle progression. Immunoaffinity chromatography performed under nondenaturing conditions afforded the isolation of enzymatically active Cak1 from cell lysates, enabling studies of kinase autophosphorylation and comparative substrate utilization. Immunoaffinity-purified Cak1 phosphorylated monomeric Cdc2 and Cdk2, but not Cdk4; the phosphorylation of both Cdc2 and Cdk2 were increased in the presence of recombinant cyclin A. These studies indicate that the Cak1 catalytic subunit, like Cdc2 and Cdk2, associates with multiple regulatory partners and suggests that subunit composition may be an important determinant of this multifunctional enzyme.

Amino Acid Sequence↗

PubMed1996

Thymidine kinase deficient cells with decreased TTP pools are hypersensitive to DNA alkylating agents.

The effect of mutational loss of thymidine kinase (TK) on the sensitivity to alkylating agents was investigated in promyelocytic, HL-60, and T-lymphoblastoid, Molt-3, human leukemia cell lines. Although both cell lines exhibited approx. 1% residual TK activity, only HL-60 TK deficient cells had a decreased intracellular TTP pool, i.e., 20% of that of the wild-type. When treated with N-methyl-N'-nitronitrosoguanidine or ethyl methanesulfonate, HL-60 TK deficient cells showed significantly increased killing and mutation frequencies at the hypoxanthine-guanine phosphoribosyl transferase (HGPRT) locus relative than did wild-type. Pretreatment of cells with O6-benzylguanine, an inhibitor of O6-alkylguanine-DNA alkyltransferase, partially abolished those differences. Molt-3 wild-type and TK deficient cells had similar cell survivals and HGPRT mutation frequencies following treatment with alkylating agents. These results indicate that TK deficiency, only when a concomitant decrease of TTP pool is detected, plays a pivotal role in the sensitivity to the cytotoxic and mutagenic effects of alkylating agents.

Antineoplastic Agents↗

PubMed1996

The differentiating agent phenylacetate increases prostate-specific antigen production by prostate cancer cells.

The prostatic-specific antigen (PSA) is the tumor marker most widely relied upon for the monitoring of patients with prostate cancer. Recently, declines in the serum concentrations of PSA have been advocated as a surrogate marker of tumor response in clinical trials of investigational antitumor agents. We examined the hypothesis that this postulate may not apply to the evaluation of drugs such as phenylacetate, a differentiating agent endowed with mechanisms of action different from those of classic cytotoxic chemotherapy. Using human prostatic carcinoma LNCaP cells as a model, we show that phenylacetate induces PSA production despite inhibition of tumor cell proliferation. Incubation of LNCaP cultures with cytostatic doses of phenylacetate (3-10 mM) resulted in a three- to fourfold increase in PSA secretion per cell. This appears to result from upregulation of PSA gene expression, as indicated by elevated PSA mRNA steady-state levels in treated cells. The increase in PSA production per cell was confirmed in rats bearing subcutaneous LNCaP tumor implants that were treated systemically with phenylacetate. Further comparative studies indicate that upregulation of PSA is common to various differentiation inducers, including all-trans-retinoic acid, 1,25-dihydroxyvitamin D3, and butyrate but is not induced by other antitumor agents of clinical interest such as suramin. We conclude that declines in PSA may be treatment specific and that the exclusive use of this criterion as a marker of disease response may mislead the proper evaluation of differentiating agents in prostate cancer patients.

Animals↗

PubMed1996

Complement activation on thiol-modified gold surfaces.

To evaluate the importance of protein adsorption and chemical composition of the solid surface on complement activation, we used mercaptoglycerol (MG) and mercaptopropionic acid (MPA) modified gold surfaces as model surfaces. The complement activation by these surfaces was determined by measuring fluid phase iC3b and C5b-9 in serum that had been in contact with the surfaces. In addition, "active" C3 deposition at the modified surfaces was measured with the use of ellipsometry, an optical technique. It was found that the MG surface caused pronounced productions of iC3b and C5b-9 in serum as well as increased C3 deposition on the surface. In contrast, the bare gold surface and the MPA surface caused very little complement activation. The MG surface seems to have a high affinity with immunoglobulin G (IgG) that may be one explanation for the high complement activation ability of the MG surface. However, complement activation at the MG surface was relatively insensitive to Mg-EGTA buffer at a high serum concentration, indicating alternative pathway activation when classical pathway activation was inhibited. Corresponding control experiments performed with Mg-EGTA serum at hydrophobic silicon surfaces precoated with IgG showed no sign of alternative pathway activation. At a lower serum concentration, classical pathway activation seemed to dominate at the MG surface and the hydrophobic silicon surface precoated with IgG. Most probably, it is the hydroxyl groups at the MG surface that are associated with alternative pathway activation.

3-Mercaptopropionic Acid↗

PubMed1996

Different mechanism of saturation of acetaminophen sulfate conjugation in mice and rats.

Sulfation of acetaminophen is a high-affinity and low-capacity conjugation pathway in rats. It is thought that sulfation becomes saturated in rats at high doses of acetaminophen because of limited availability of the active sulfate donor, 3'-phosphoadenosine 5'-phosphosulfate (PAPS), the supply of which is, in turn, limited by the availability of its precursor, inorganic sulfate. The present study was designed to determine whether a similar mechanism is responsible for capacity-limited sulfation in mice. Saturation of acetaminophen sulfation occurs in both species; however, at the maximal rate of sulfation, sulfate and PAPS concentrations were markedly decreased in rats but not in mice. Administration of sodium sulfate and the sulfate precursor N-acetylcysteine enhanced the formation of acetaminophen sulfate in rats, but not in mice. Mice exhibited lower activities of hepatic PAPS synthetic enzymes (i.e., ATP sulfurylase and APS kinase) and sulfotransferase than rats, which may in part be responsible for their lower capacity to sulfate acetaminophen. In addition, administration of acetaminophen further decreased phenolsulfotransferase activity in mice. In rats, administration of acetaminophen did not influence hepatic sulfotransferase activity. These observations suggest that while the capacity of rats to sulfate acetaminophen is limited by the availability of PAPS, in mice it is limited by sulfotransferase activity.

Acetaminophen↗

PubMed1996

Role of DNA repair in resistance to drugs that alkylate O6 of guanine.

The mechanism of cytotoxicity of a number of chemotherapeutic agents involves alkylation at the O6 position of guanine, a site that strongly influences cytotoxicity. Repair of these lesions by the alkyltransferase protects from cytotoxicity and is a major mechanism of resistance to these agents. O6-benzylguanine inhibition of alkyltransferase sensitizes tumor cells, and clinical trials are underway to determine its efficacy. The use of gene therapy to enhance the expression of alkyltransferase in hematopoietic cells may prevent dose-limiting myelosuppression and may enhance the utility of this class of chemotherapeutic agents.

Amino Acid Sequence↗

PubMed1996

In-vivo microdialysis study of extracellular glutamate response to temperature variance in subarachnoid hemorrhage.

Neurochemical changes may precede the development of clinical signs in neurological disease. Early identification of such changes may offer an opportunity to avoid or treat complications. Under experimental conditions, extracellular levels of glutamate and other amino acids can be monitored by in-vivo microdialysis in cerebral ischemia, head trauma and epilepsy. Data on the release of glutamate under ischemic conditions in humans are limited. There is no published data on the effects of temperature variation or other manipulations on the extracellular glutamate levels in humans. We report for the first time, the effects of changes in temperature on the extracellular cerebral glutamate levels as measured by in-vivo microdialysis, the dialysate being collected before, during and after cooling in four patients with subarachnoid hemorrhage. Three of the patients had in-vivo microdialysis carried out postoperatively. One patient underwent microdialysis three days prior to the surgical clipping of the aneurysm. In all patients, mild head cooling resulted in a significant decrease in extracellular glutamate levels. The effect of cooling was most apparent when the extracellular glutamate concentrations were high. In two patients, the extracellular glutamate levels increased sharply with fever but returned to normal once the temperature normalized. In vivo microdialysis can be used to measure extracellular glutamate and other neurotransmitters with minimal discomfort in awake humans. This technique offers a unique opportunity to monitor the neurochemistry in critically ill patients and it may aid in developing therapeutic intervention strategies to minimize undesired chemical responses.

Cold Temperature↗

PubMed1996

A correlation study of averaged and single trial MEG signals: the average describes multiple histories each in a different set of single trials.

Our understanding of the link between electrical events in the brain and behaviour is based on indirect measures. Positron Emission Tomography (PET) and functional Magnetic Resonance Imaging (fMRI) rely on haemodynamic processes which are slower by two to three orders of magnitude than the processes characterizing normal and pathological brain function. Direct invasive measurements of the electrical activity on the other hand produce too local a view which fails to show the large scale coherence which sustains awareness and cognition. On the opposite extreme, gross measures of the electrical activity like Electroencephalography (EEG) and single or few channel Magetoencephalography (MEG) had until recently to rely on simplistic point like models extracted from the averages of many repetitions of physiologically irrelevant stimuli. The introduction of multichannel probes with over 30 channels (Hämälainen et al. 1993), and the use of distributed source analysis (Ioannides et al. 1990a) opened up for the first time the possibility to study the response of single trials. In this work we address directly the question how representative is the description of events extracted from the analysis of the average signal. We use the simplest possible example: the cortical response to a simple 1 kHz tone, focusing on the early and by general admission "automatic" response around 100 ms after stimulus onset. To avoid the confounding inter-subject variability we have studied the responses over the left and right cortical areas to ipsi- and contralateral stimulation in a single subject; for testing reproducibility, we have used both the eyes open and eyes closed conditions. Since the computational demands involved in extracting a full three dimensional description from each trial are too great, we have complemented the distributed source analysis with special techniques, which allow us to scan through each and every single trial and identify each cortical activation similar to the ones picked out in the average signal. We are thus able to show conclusively that the sequence of events suggested by the analysis of the average signal is not representative of what is happening in individual trials. The sequence is made up of events which occurred in different trials reflecting probably the existence of many parallel routes each of which leads from the input at the ear to a final "computation".

Adult↗

PubMed1996

The value of perioperative echocardiography in percutaneous balloon mitral valvuloplasty.

In order to investigate the value of perioperative echocardiography in percutaneous balloon mitral valvuloplasty (PBMV), two-dimensional echocardiography (2-DE), Doppler echocardiography and color Doppler flow imaging (CDFI) were employed prior to PBMV in 52 patients and during or after PBMV in 15 patients. The results showed that TTE and TEE were helpful in the selection of candidates for 2-DE transseptal and balloon dilation procedures. Continuous monitoring of 2-DE, Doppler echocardiography and CDFI during PBMV could make this procedure safer and more effective, reduce X-ray exposure and avoid complications. Echocardiography was useful in fluoroscopy and could be used for evaluation of the effects of operation.

Adult↗

PubMed1996

Saturation revealed by clamping the gain of the retinal light response.

The saturation nonlinearity of the retinal light response in human was measured by a psychophysical technique in which the adaptive gain control mechanism was clamped by the presence of a fixed surround in a small (7') foveal test field. Gain clamping was established by showing that the normal variation in temporal summation properties with test intensity was abolished in the gain clamping paradigm. The static saturation function constructed from the increment/decrement asymmetries around a range of base intensities was shown to conform more closely to the Naka-Rushton hyperbolic saturation equation than to three other candidate nonlinearities.

Adaptation, Ocular↗

PubMed1996

Capsaicin activated currents in rat dorsal root ganglion cells.

Capsaicin is a pungent-tasting compound produced by plants in the Capsium family that activates a subset of primary afferent neurons associated with pain and thermoreception. Previous studies from dorsal root ganglion (DRGs) neurons suggest that many of capsaicin's physiological responses are a consequence of its activating a cation-selective current. To further characterize the responses to capsaicin whole-cell patch-clamp measurements were performed on rat DRGs to which 0.1-10 microM capsaicin was continuously applied. The capsaicin-activated currents exhibited marked variability in their thresholds, amplitude (to 15 nA), rates of desensitization, and the number of distinct maxima in the evoked current. Similar responses were found in rat trigeminal ganglion cells. The heterogeneity in the magnitude of the currents evoked by 0.1 microM capsaicin likely reflects different types of capsaicin-sensitive neurons; a result consistent with in vitro extracellular recordings from capsaicin-sensitive sensory afferents (Seno and Dray 1993).

Animals↗

PubMed1996

In vivo evidence of hydroxyl radical formation induced by elevation of extracellular glutamate after cerebral ischemia in the cortex of anesthetized rats.

The in vivo interrelation between excitotoxicity and oxidative stress following cerebral ischemia in the cortex of anesthetized rats was investigated. Cerebral ischemia was induced by ligation of the bilateral common carotid arteries and the unilateral middle cerebral artery. Microdialysis perfusion with on-line high-performance liquid chromatography was used to monitor the hydroxyl radical levels. Extracellular hydroxyl radical levels were quantitated as the increased formation of 2.3 and 2.5 dihydroxybenzoic acid (DHBA), the hydroxylative products of salicylic acid contained in the microdialysis perfusion solutions. Elevated cortex extracellular glutamate content, resulting from the cerebral ischemia, caused an increase in the formation of hydroxyl radicals. Exogenous perfusion of authentic glutamate solutions through implanted microdialysis probes also resulted in increased hydroxyl radical formation in the cortex. The 2.3 and 2.5 DHBA levels remained elevated for an entire 80-min ischemic period. These results suggest that, after cerebral ischemia, increased oxidative stress did occur in anesthetized rats, and the oxidative stress may result from increased excitotoxicity.

Animals↗

PubMed1996

Selective screening for dyslipidemia in a Canadian population.

The study assesses the clinical features of individuals that best enable an effective selective screening of the adult population for dyslipidemia. The results of the population-based 1990 Saskatchewan Heart Health Survey were examined. Dyslipidemia was defined as a total cholesterol (TC) to high-density lipoprotein cholesterol (HDL) ratio of > or = 5. In total, 805 men and 782 women, 18-74 years of age, had their plasma cholesterol measured. Using TC screening of the entire population as recommended by the Canadian Consensus Conference on Cholesterol would correctly identify 79% of those with dyslipidemia (sensitivity) and 67% of those with a normal profile (specificity). However, if one performs lipoprotein analysis on only those with a high waist-to-hip circumference ratio (WHR), 44% of the population would need to be screened to correctly identify 71% of those with dyslipidemia (sensitivity) and 66% of those with a normal profile (specificity). A high WHR is an especially strong predictor of dyslipidemia in young adults. In conclusion, a high WHR may provide an effective means of selective screening of the adult population for dyslipidemia.

Adolescent↗

PubMed1996

Four-dimensional echocardiography: methods and clinical application.

4DE (i.e., dynamic three-dimensional) echocardiography is a new developing technique in recent years. In our study, a three-dimensional echo scan computer system was used to acquire and store the two-dimensional information, then to reconstruct the stereoscopic image of the heart according to its space-time continuum. It can yield a better approach, which can help identify the various structures of the heart and great arteries and facilitate understanding of spatial relations and motion. In addition, it can display physiologic information such as the direction, course, size, and shape of the blood flow. We have examined 138 patients by both transthoracic and transesophageal approaches. Our preliminary experience shows that 4DE is of great value in diagnosing congenital heart disease and valvular disease.

Adolescent↗

PubMed1996

Amelioration of rat experimental arthritides by treatment with the alkaloid sinomenine.

The effects of treatment with sinomenine, a pure alkaloid extracted from the chinese medical plant Sinomenium acutum, were investigated in rat adjuvant arthritis (AA) and antigen-induced arthritis (AIA). In AA, long-term, intraperitoneal (i.p.) treatment induced significant improvement of arthritic score, hind paw swelling, body weight and erythrocyte sedimentation rate (ESR) beginning past the clinical peak of the disease. In-acute AIA, short and middle-term treatment with sinomenine around and following induction of arthritis induced a dose-dependent decrease of both joint swelling and ESR, starting after the peak of arthritis, and a significant reduction of joint destruction on day 3. There was no rebound of the arthritic signs following suspension of treatment. Long-term treatment of chronic AIA partially ameliorated clinical parameters and significantly counteracted joint destruction. Maximal plasma concentrations of 22.5 micrograms/ml, fast wash out (half-life 4.24 +/- 0.99 h; mean +/- S.E.M.) and no evidence of accumulation of sinomenine were observed following single or repeated i.p. injection of 150 mg/kg. In vitro, sinomenine markedly inhibited proliferation of synovial fibroblasts from AIA or normal rats, both at rest and following activation with either transforming growth factor beta 2 (TGF-beta 2) or interleukin-1 beta (IL-1 beta). The effect was dose-dependent and half-maximal inhibition of proliferation occurred at 20.6 micrograms/ml, that is, within the in vivo therapeutic range of the drug. Late therapeutic effects of sinomenine in rat arthritic models despite early start of treatment may be related to its antiproliferative effects on synovial fibroblasts in addition to its previously reported anti-inflammatory properties.

Adjuvants, Immunologic↗