Search PubMed⌕ Search

Biomedical subjects

R Liu

Publications and source records attributed to R Liu.

At least 307 records · Page 17Linked to original sources
PubMed1994

Association of the insulin receptor and phosphatidylinositol 3-kinase requires a third component.

We have studied the interactions between the insulin receptor and PtdIns 3-kinase by a reconstitution system in vitro composed of highly purified PtdIns 3-kinase from rat liver and highly purified insulin receptors bound to insulin-agarose or to antibodies against insulin receptors. As a positive control, receptors for platelet-derived growth factor, which bind and phosphorylate PtdIns 3-kinase, were studied in parallel with insulin receptors. Our results indicate that the insulin receptor, regardless of its phosphorylation state, does not directly associate with purified PtdIns 3-kinase, whereas the autophosphorylated receptor does associate with PtdIns 3-kinase present in the crude CHO-cell lysate. Also, we could not detect phosphorylation of PtdIns 3-kinase by the insulin receptor, even through the receptor readily underwent autophosphorylation and phosphorylated an insulin-receptor substrate, poly(Glu-Tyr) (4:1). These findings argue that one or more cytosolic components link the receptor and the enzyme. Insulin-receptor substrate-1 (IRS-1) was evaluated as a potential linking protein. In the absence of ATP, IRS-1 did not facilitate the coupling of the phosphorylated insulin receptor to PtdIns 3-kinase. Thus IRS-1 is unlikely to be the component in crude CHO-cell lysate that couples PtdIns 3-kinase to the phosphorylated insulin receptor. However, the addition of ATP, which allows phosphorylation of IRS-1 by the insulin receptor, also enhances the coupling of PtdIns 3-kinase to the insulin receptor. In support of this idea, immunoprecipitates of IRS-1 from insulin-treated CHO cells were found to contain both the insulin receptor and PtdIns 3-kinase. In conclusion, the insulin receptor does not appear to phosphorylate or bind directly to PtdIns 3-kinase, regardless of the receptor's state of phosphorylation. Association of PtdIns 3-kinase with the insulin receptor is mediated by one or more components, one of which may involve an unidentified factor in cell lysate and another that apparently involves phosphorylated IRS-1.

Animals↗
PubMed1994

In vitro drug testing of ovarian cancer using the human tumor colony-forming assay: comparison of in vitro response and clinical outcome.

The purpose of this study was to assess the prognostic value of in vitro drug chemosensitivity testing using the Hamburger-Salmon human tumor colony-forming assay (HTCA) in fresh tumor samples obtained from newly diagnosed patients with stage II-IV ovarian cancer undergoing maximum cytoreductive surgery and prior to platinum-based chemotherapy. The HTCA was performed on fresh ovarian cancers obtained from 93 patients at their initial exploratory laparotomy to evaluate in vitro sensitivity to cisplatin, carboplatin, and cyclophosphamide following a 1-hr drug exposure. Prospective clinical follow-up was performed on all patients with the primary study endpoints being pathologically proven complete response at second-look surgery and disease-free and overall survival durations. In vitro drug sensitivity was strongly dose-dependent. At a concentration of 5 micrograms/ml only 23% of tumor samples were sensitive (as defined by a > or = 50% decrease in tumor colony-forming units compared to controls) to cisplatin; 13% of tumors were sensitive to carboplatin at a concentration of 50 micrograms/ml and 11% to 4-OH-cyclophosphamide at a concentration of 1 microgram/ml. At doses which were 10 times the previously stated concentrations, the sensitivity rates to cisplatin, carboplatin, and 4-OH-cyclophosphamide increased to 72, 63, and 53%, respectively. Subjects were categorized as having drug-sensitive disease if HTCA results showed in vitro drug sensitivity to at least one of the agents used in their primary chemotherapy. Multivariate analysis failed to show any advantage in clinical response rate, progression-free interval, or survival duration for patients with drug-sensitive disease compared to drug-resistant disease; however, there was evidence of a trend toward an enhanced pathologically proven complete response rate in patients who had chemosensitive tumors in vitro. Second-look surgery was performed in 28 of 55 patients with optimal surgical resections and no clinical evidence of disease at the completion of their primary chemotherapy. Fifty percent (5/10) of patients with drug-sensitive disease achieved a pathologic complete response, while only 3/18 (17%) patients with drug-resistant tumors had a documented pathologic complete response (P = 0.13). As reported in other ovarian cancer studies, patient characteristics which were found to be significantly associated with survival were stage of disease (II-III vs IV), optimal primary surgical resection (i.e., < 1 cm2 residual tumor) vs suboptimal resection, clinical measurability of disease at initiation of chemotherapy, and response to primary chemotherapy. In conclusion, in vitro drug sensitivity, as measured by the HTCA, does not appear to be an independent prognostic factor for survival in patients with stage II-IV epithelial ovarian cancer who undergo standard treatment with tumor debulking surgery and primary platinum-based chemotherapy.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1994

Quantitative characterization of insulin-glucose response in Watanabe heritable hyperlipidemic and cholesterol-fed rabbits and the effect of cilazapril.

A great deal of evidence suggests that insulin resistance, via hyperinsulinemia, contributes to hyperlipoproteinemia and coronary atherosclerosis. When Watanabe heritable hyperlipidemic (WHHL) rabbits, an animal model of familial hypercholesterolemia (FH), are compared with normolipidemic Japanese White (JW) rabbits, an elevated fasting plasma insulin level and a heightened plasma insulin response to an intravenous (i.v.) glucose challenge are found. To elucidate the mechanism behind this phenomenon, a two-compartment model of the glucose/insulin system was fitted to empirical time courses of glucose and insulin concentrations during an i.v. glucose tolerance test (IVGTT) by nonlinear least-square regression, and the model parameters such as the glucose utilization rate constant, insulin degradation rate constant, and pancreas sensitivity were determined. WHHL rabbits showed decreased values of glucose utilization and insulin degradation rate constants and slightly higher values of pancreas sensitivity. This suggests that insulin resistance occurs in extrapancreatic tissues, and that this may be attributable to insulin receptor and/or post-insulin receptor abnormalities. Cholesterol feeding did not significantly change glucose tolerance or insulin action in JW rabbits. The effects of an angiotensin-converting enzyme (ACE) inhibitor, cilazapril, on insulin resistance were also examined in WHHL and JW rabbits. A decreased insulin response to an i.v. glucose challenge and increased glucose utilization and insulin degradation rate constants were observed in WHHL rabbits that had been treated with cilazapril, indicating that cilazapril improved insulin resistance in WHHL rabbits, possibly by increasing the number of insulin receptors. No significant differences were found in glucose tolerance and insulin action in JW rabbits before and after cilazapril administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Comparative molecular field analysis combined with physicochemical parameters for prediction of polydimethylsiloxane membrane flux in isopropanol.

Comparative molecular field analysis (CoMFA) combined with various physicochemical parameters were used to develop three-dimensional quantitative structure-transportability relationships (3-D QSTR) to predict membrane flux for 108 aromatic and heteroaromatic compounds through polydimethylsiloxane (PDMS) membranes in isopropyl alcohol (IPA). Sybyl, a comprehensive computational molecular modeling package, was used to analyze the data. Optimized molecular models were selected using molecular modeling techniques. Partial least-squares (PLS) regression combined with crossvalidation or bootstrapping was used as the statistical method to establish the predictive models. Prediction was good for the steady-state flux using both steric and electrostatic field descriptors combined with a functional group classification technique. Predictive ability was substantially increased in a model using CoMFA descriptors along with log mole fraction solubility for the penetrants in isopropanol, a hydrophobic term, fchex, which is used to estimate the partition coefficient between cyclohexane and water, and the addition of an intramolecular hydrogen bonding (IHB) term. The crossvalidated r2 and the conventional r2 for this model were 0.951 and 0.973, respectively. Excellent predictions are demonstrated for the membrane flux of the compounds both inside and outside the data domain.

1-Propanol↗
PubMed1994

Regulation of neuropeptide-processing enzymes by nitric oxide in cultured astrocytes.

Nitric oxide (NO), a recently discovered neurotransmitter, has been shown to have a cytostatic effect on cultured glia. A NO-generating agent, S-nitroso-N-acetyl-penicillamine (SNAP), was used to treat C6 glioma and primary cortical astrocytes. The levels of a monobasic peptide-processing enzyme activity and carboxypeptidase E activity were examined. The cellular levels of these two enzymes are specifically reduced in response to treatment with SNAP. A decrease of approximately 30-50% in these two enzyme activities was seen in both primary astrocytes and C6 glioma cells. This decrease in cellular enzyme activities is not due to increased secretion because the secreted activity is also reduced in response to SNAP treatment in both the glioma cells and the primary astrocytes. Removal of SNAP treatment causes the carboxypeptidase enzyme activity to return to control levels within 3 days. Northern and western blot analyses indicate that the reduced cellular level of carboxypeptidase E is not due to reduced expression of the messenger RNA or protein, suggesting that the SNAP treatment is affecting factors that influence carboxypeptidase E activity. Taken together, these results imply that NO is involved in the regulation of peptide biosynthetic enzymes and this could lead to the antimitogenic action of SNAP on glia.

Animals↗
PubMed1994

Effects of background stress and anxiety on postoperative recovery.

The effects of background stress and anxiety on both short- and long-term recovery were measured in 30 healthy patients undergoing general anaesthesia for day-case dental extractions. Standardised questionnaires presented pre-operatively, assessed psychological status in terms of trait and state anxiety and stress levels. State anxiety was again measured postoperatively; recovery was assessed with pre- and postoperative batteries of cognitive tasks. Correlation coefficients revealed that the level of background stress in the preceding 6 months correlated with physical parameters of recovery such as time taken for patients to open their eyes, perceived pain and increased postoperative morbidity. The study also demonstrated that high levels of state anxiety after surgery correlated with postoperative pain. Trait and state anxiety before surgery did not correlate with any parameters of recovery or postoperative morbidity.

Adolescent↗
PubMed1994

gamma-Glutamyl transpeptidase is increased by oxidative stress in rat alveolar L2 epithelial cells.

The tripeptide glutathione (GSH) is used by cells to detoxify hydroperoxides, produced during oxidative stress, and is consumed in the process. Previous studies have indicated that cells can be protected against oxidative stress by extracellular GSH through its degradation catalyzed by the exoenzyme gamma-glutamyl transpeptidase (gamma GT) and its de novo synthesis within the cytosol. We hypothesized that gamma GT would be increased as part of the adaptation of cells to oxidative stress. We examined whether oxidative stress could increase gamma GT activity, protein, and mRNA in a lung epithelial cell line (L2). Cultures were subjected to H2O2-mediated toxicity by 15 min of exposure to the redox cycling quinone, menadione. Menadione (50 microM) caused an initial decrease (27 +/- 9% of baseline after 15 min) in intracellular GSH, followed by resynthesis to levels significantly higher than baseline (335 +/- 40% after 24 h, P < 0.001). This elevation was prevented by acivicin, a gamma GT inhibitor. Menadione also caused a dose-dependent increase in gamma GT enzymatic activity (715 +/- 125% of control at 24 h after 15 min of exposure to 100 microM menadione, P < 0.001) that was prevented by actinomycin D. Western blot analysis indicated increased levels of gamma GT protein with increasing menadione. A concentration-dependent increase in gamma GT-mRNA was also observed. Previous investigation has demonstrated that an increase in gamma GT activity enhances the capacity of cells to utilize extracellular GSH. The findings presented here are consistent with a role for gamma GT in cellular adaptation to oxidative stress.

Animals↗
PubMed1994

Deletion of 3 basepairs resulting in the loss of lysine-121 in the insulin receptor alpha-subunit in a patient with leprechaunism: binding, phosphorylation, and biological activity.

We have identified a novel mutation of the human insulin receptor gene in a previously unreported patient with leprechaunism, leprechaun Rochester. This mutation consists of deletion of three nucleotides (GAA) in exon 2 and results in loss of the lysine-121 in the putative ligand-binding domain of the alpha-subunit. To analyze this mutation, we prepared a corresponding mutant insulin receptor by site-directed mutagenesis and expressed the receptor in Chinese hamster ovary cells. Although the mutant receptor displayed normal insulin binding, abnormalities were found in autophosphorylation and in phosphorylation of endogenous and exogenous protein substrates. These abnormalities consisted of increased basal kinase activity, but blunted insulin-stimulated responsiveness. Importantly, cells that expressed the mutant receptor showed markedly decreased insulin- and serum-stimulated DNA synthesis compared to untransfected control cells and cells transfected with the wild-type insulin receptor. These findings suggest that deletion of lysine-121 in conjunction with a presumed, but thus far unidentified, second mutant allele contributed significantly to the lethal insulin-resistant state in this patient with leprechaunism.

Alleles↗
PubMed1994

Role of tumor necrosis factor in neonatal sepsis.

In order to assess the role of tumor necrosis factor (TNF) in neonatal sepsis, plasma TNF levels were determined by a method using L929 cells at the time of septic work-up in 67 neonates. Thirty-three patients with sepsis were found to have significantly higher TNF levels (533.33 +/- 468.74 U/ml; 1 U corresponding to 1.67 pg recombinant TNF) as compared with 34 non-sepsis patients (100.0 +/- 188.97 U/ml) and 30 healthy newborns (27.33 +/- 16.17 U/ml, P < 0.05, respectively). The upper limit of normal plasma TNF levels was 60 U/ml and the best cutoff value for predicting neonatal sepsis was 160 U/ml. This had remarkable sensitivity (88%), specificity (82%), positive predictive value (83%), and negative predictive value (88%). Plasma TNF levels were significantly associated with the occurrence of shock, organ failure, scleroma and outcome. Thus, anti-TNF antibodies might be used in protecting newborns from septic death.

Acinetobacter Infections↗
PubMed1993

Polymorphic site study at codon 347 of apolipoprotein A-IV in a Japanese population.

In a population of Japanese subjects, we surveyed codon 347 of the apolipoprotein (apo) A-IV gene and found that the frequency of a rare allele at this point was extremely low compared to that in western populations. Only one of 850 unrelated samples showed mutation at the enzyme recognition site by agarose gel electrophoresis. However, direct sequencing of the coding region revealed that it did not result from the ACT (Thr) to TCT (Ser) mutation which has been reported in western countries, but from an ACT to ACG (Thr) mutation, which does not affect the primary structure of apo A-IV. Two additional family members showed the same point mutation at codon 347.

Adult↗
PubMed1993

In vivo conversion of recombinant human proapolipoprotein AI (rh-Met-proapo AI) to apolipoprotein AI in rabbits.

In vivo conversion of recombinant human proapolipoprotein AI (rh-Met-proapo AI) from E. coli to apolipoprotein (apo) AI was investigated. rh-Met-proapo AI was labeled with 125I, and then administered intravenously to rabbits. Blood was sampled periodically for 6 days. The plasma decay curves of radioiodinated rt-Met-proapo AI were similar to those of human mature apo AI (fractional catabolic rate (FCR); 1.018 +/- 0.090/day vs. 0.976 1 0.031/day, respectively). In vivo conversion of rh-Met-proapo AI to mature apo AI was examined by autoradiography of the isoelectric focusing (IEF) slab gel, i.e., the HDL fraction from each sampling point was semiquantitatively applied to IEF. It was found that the radioactivity of rh-Met-proapo AI migrated to more acidic isoproteins, the conversion was complete within 24 h, and the FCR of rh-Met-proapo AI was 9.20 +/- 1.34/day. Although the plasma decay curves of both human pro (rh-Met-proapo AI) and mature apo AI were significantly steeper than those of rabbit mature apo AI4 and apo AI5 (FCR; 0.703 +/- 0.027/day and 0.795 +/- 0.031/day, respectively), the conversion rate of human rt-Met-proapo AI to mature apo AI in rabbit was assumed to be 1:1. In vitro incubation of rh-Met-proapo AI with rabbit serum produced mature apo AI isoproteins, as determined by the apo AI immunoblotting method. Prediction of the amino acid sequence at the NH2 terminus of rabbit proapo AI showed that the prosegment consisted of an alpha helix with a high probability of a beta turn at Pro9, which is close to that in humans. Thus, (1) the proteolytic cleavage of proapo AI is an extracellular event, (2) the converting enzyme in rabbits can also process human proapo AI, (3) this converting enzyme does not specifically and directly attack the Gln6-Asp7 bond which links the carboxyl-terminal residue of the hexapeptide to the amino-terminal residue of human mature apo AI. The conformation of proapo AI at the NH2 terminus (alpha helix of the prosegment and a beta turn at Pro9) may have a key role in this cleavage, and (4) the examination of rh-Met-proapo AI in rabbits helps to explain the early events of HDL biogenesis.

Amino Acid Sequence↗
PubMed1993

Effects of heparin and other glycosaminoglycans on elastin production by cultured neonatal rat lung fibroblasts.

Proteoglycans are important structural elements of the extracellular matrix, and may contribute to the dynamic architecture of the lung and also influence pulmonary gas and solute exchange. The potential for proteoglycans and glycosaminoglycans to modulate the synthesis and deposition of elastin, another important extracellular matrix component of the lung, has not been established. Therefore the effects of glycosaminoglycans on the steady-state level of elastin mRNA, the incorporation of [3H]valine into tropoelastin, the distribution of soluble elastin in the medium and cell layer, and insoluble elastin deposition have been examined using cultured neonatal rat lung fibroblasts. Heparin decreases the soluble elastin content of the culture medium while increasing the soluble elastin content of the cell layer. This altered partitioning of soluble elastin is associated with an increase in steady-state elastin mRNA and an increase in the deposition of insoluble elastin in the extracellular matrix. Some of these effects may result from the binding of heparin to soluble elastin at physiological concentrations of NaCl. The galactosamine-containing glycosaminoglycans, chondroitin sulfate and dermatan sulfate, differ from heparin in that they increase the quantity of soluble elastin in the culture medium and decrease the deposition of insoluble elastin in the extracellular matrix. Proteoglycans, which are present in most elastic tissues, may participate in the regulation of elastin synthesis and deposition during periods of new elastin formation.

Aminopropionitrile↗
PubMed1993

In vivo kinetics of oxidatively modified HDL.

The kinetics of oxidatively modified high-density lipoprotein (HDL) in vivo were investigated. 125I-labeled oxidized (Ox) HDL and 131I-labeled native (N) HDL were injected simultaneously into control and WHHL rabbits. The fractional catabolic rates of 125I-labeled Ox-HDL were significantly greater than those of 131I-labeled N-HDL in both control (2.52 +/- 0.36/day vs 0.94 +/- 0.02/day) and WHHL rabbits (4.07/day vs 1.32/day). Oxidized HDL was catabolized faster than native HDL and was taken up primarily by the liver, spleen, and kidney.

Animals↗