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Biomedical subjects

N Liu

Publications and source records attributed to N Liu.

268 records · Page 15Linked to original sources
PubMed1990

[Experimental study of glucosylated low density lipoprotein metabolism and atherosclerosis].

The effect of LDL glucosylation on its pathway was assessed. Human serum LDL was isolated by density gradient ultracentrifugation and its purity was identified by polyacrylamide gel electrophoresis. LDL was radioiodinated with 125I by iodine monochloride. LDL radioreceptor assay was performed and intracellular total cholesterol was determined in cultured human fibroblasts. Maximal binding affinity (Bmax) of LDL receptor was 47 ng LDL/mg cell protein, Km was 9.4 micrograms/ml. The receptor mediated binding, internalization and degradation of glucosylated LDL were significantly decreased compared with control LDL, but total cholesterol content of cultured fibroblasts incubated with glucosylated LDL was significantly higher than those incubated with control LDL. The results suggested that glucosylation of LDL might be an important mechanism for the high incidence of disturbed lipid metabolism and atherosclerosis in diabetic patients.

Arteriosclerosis↗
PubMed1988

Physiology of the retrocalcaneal bursa.

To clarify the function of the retrocalcaneal bursa the hindfoot was studied by magnetic resonance imaging at various positions of the ankle joint. In normal individuals a tongue-like extension of the retromalleolar fat pad entered the bursa during plantar flexion as the angle between Achilles tendon and calcaneus widened. The reverse occurred in dorsiflexion. In contrast, in a patient with spondyloarthritis and retrocalcaneal bursitis excessive cavitary fluid prevented the intrusion of the fat pad. The sliding motion of the fat pad in and out of the bursa during ankle motion allows a more caudal, advantageous insertion of the Achilles tendon into the calcaneus.

Achilles Tendon↗
PubMed1986

In vivo and in vitro tyrosine sulfation of a membrane glycoprotein.

A431 cells incorporate 35SO4 into a protein of Mr 61,000 (P61). We examined sulfation of P61 by cells (in vivo) and by a cell-free system (in vitro) which requires only addition of A431 cell membranes and a 3'-phosphoadenosine 5'-phospho[35S]sulfate-generating system prepared from Krebs ascites cells. Sulfate is found exclusively in the form of tyrosine SO4 by two-dimensional high voltage electrophoresis following Pronase digestion. Endoglycosidase F digestion reduces the Mr by 2,000 but does not release the sulfate, indicating that P61 is a glycoprotein but that sulfate is not incorporated into the carbohydrate. Sulfated P61 is not found in the medium from cultured cells and remains associated with the membrane fraction following cell lysis. Treatment of membranes with 0.4 M NaCl, 0.3 M KCl, 15 mM EDTA, or pH 11.0 does not release sulfated P61. P61 is solubilized by Triton X-114 treatment of membranes and partitions into the detergent phase upon warming. Based on these characteristics, we conclude that P61 is an integral membrane protein. Trypsin digestion experiments with intact cells suggest that sulfated P61 is predominantly located in the plasma membrane. This is the first example of an integral membrane protein which is sulfated on tyrosine. The properties of the sulfation reaction are distinct from those reported for secreted proteins and are consistent with the possibility that this modification occurs at the plasma membrane rather than in the Golgi.

Animals↗
PubMed1974

Electrophoretic mobility and agglutinability of red blood cells: a "new" polymorphism in mice.

A quantitative method has been developed to determine agglutinability of mouse red blood cells. Tests with different inbred strains of mice revealed only two phenotypes. The same inbred strains were tested with the cytopherometer to determine the electrophoretic mobility of the corresponding red cells. Again, two phenotypes were uncovered, and faster mobility was found in the red cells that had higher agglutinability. The genetic control of this character is autosomal and codominant, and segregates independently of H-2 and coat color.

Animals↗
PubMedDate not supplied

The nucleus paragigantocellularis and opioid withdrawal-like behavior.

Participation of the nucleus paragigantocellularis (PGi) in mediation of opioid withdrawal was examined in conscious, unrestrained, non-opioid-dependent rats, using electrical stimulation of the PGi. A characteristic series of behaviors, which resembled those seen during naloxone-precipitated withdrawal from dependence on the opioid agonist, butorphanol, was elicited during 30 min of PGi stimulation. Thus, the behavioral syndrome has been termed opioid withdrawal-like. Simultaneous microdialysis measurement of glutamate within the locus ceruleus indicated a positive correlation between extracellular glutamate concentrations and behavioral responses. Behavioral responses were inhibited by 50% during reverse dialysis perfusion of the locus ceruleus with the glutamate receptor antagonist, kynurenic acid, without any effect on glutamate concentrations. Thus, increases in locus ceruleus glutamate partially mediate opioid withdrawal-like behavior. Intracerebroventricular (i.c.v.) injections of the opioid antagonist, naloxone, or of the mu-selective (beta-funaltrexamine) or the delta-selective (naltrindole) opioid antagonists decreased, but did not abolish, stimulation-induced behavioral responses. Similar i.c.v. injections of the kappa-selective antagonist, nor-binaltorphimine, had no effect on behavioral responses to PGi stimulation. Activation of the PGi by electrical stimulation can elicit behaviors similar to those observed during opioid withdrawal. Moreover, additional levels of complexity are evident in the neuropharmacology of PGi stimulation-induced opioid withdrawal-like behavior.

Animals↗
PubMedDate not supplied

Pretargeting with amplification using polymeric peptide nucleic acid.

One goal of this investigation was to develop a polymer conjugated with multiple copies of peptide nucleic acid (PNA) and with pharmacokinetic properties suitable for applications in vivo. The second goal was to establish whether the multiple copies of PNA on the polymer could be targeted by hybridization in vitro and in vivo with (99m)Tc-labeled complementary PNA (cPNA). If successful, this approach could then be considered in further investigations as an alternative to existing pretargeting approaches because of the potential for signal amplification in the target. A 80 KDa poly(methyl vinyl ether-alt-maleic acid) (PA) polymer was conjugated with multiple copies of PNA and with multiple copies of poly(ethylene glycol) (PEG) by reacting the NHS derivative of PA with the amine derivatives of PNA and PEG. Using (99m)Tc-MAG(3)-cPNA, targeting of PNA-PA-PEG was studied in vitro and in vivo in inflammation and tumor mouse models, in both cases relying upon nonspecific diffusion for localization. In addition, cPNA-avidin was considered as a clearing agent with biotinylated PNA-PA-PEG. About 80 PNAs could be conjugated to PA provided that about 200 PEGs were also conjugated to raise the aqueous solubility of the PNA-PA-PEG polymer lowered by the addition of the PNAs. About 70% of the PNAs on this polymer in vitro either in solution or attached to beads could be successfully targeted with (99m)Tc-cPNA. In both the inflammation and tumor mouse models, between 35 and 60% of these PNAs could be targeted in the lesions. The advantage of amplification was evident when less favorable results were obtained with PNA-PA-PEG conjugated with only six PNAs. We conclude that amplification can be achieved in vivo using polymers of PNA followed by radiolabeled complementary PNA and that the application of pretargeting using polymers of PNA for amplification can improve localization.

Animals↗
PubMedDate not supplied

Extraction and simultaneous elution and derivatization of 11-nor-9-carboxy-delta 9-tetrahydrocannabinol using Toxi-Lab SPEC prior to GC/MS analysis of urine.

A new sample preparation procedure is described for the extraction and simultaneous elution and derivation of urine for analysis of 11-nor-9-carboxy-delta 9-tetrahydrocannabinol (THC-COOH) by gas chromatography/ion trap mass spectrometry (GC/MS). Urine samples are extracted for THC-COOH and d6-THC-COOH internal standard onto a hydrophobic membrane. Extracts are simultaneously eluted and derivatized with MSTFA while on the membrane to produce the corresponding trimethylsilane derivative. Using results of blank urine, the limits of detection and quantitation were 1.1 and 2.5 ng/mL, respectively. The linearity of the assay was 250 ng/mL. The within-run and day-to-day precision ranged 3-5%. Compared with a solid-phase column extraction procedure, the overall time for sample preparation was decreased from 3 h down to 1. The SPEC extraction procedure with trimethyl derivatization produces a cleaner total ion chromatogram than the solid-phase column extraction system (minicolumn) and does not require the use of any organic solvents.

Dronabinol↗
PubMedDate not supplied

Design, synthesis, and characterization of HIV-1 enhancer-binding polypeptides derived from bacteriophage 434 repressor.

We have designed and synthesized HIV-1 enhancer-binding polypeptides that were derived from bacteriophage 434 repressor. These peptides were 39-54 residues long and contained either the recognition helix or the entire helix-turn-helix motif of the DNA-binding domain of 434 repressor. The dissociation constant of the complex formed between the standard peptide (R42) and a synthetic 70-bp HIV enhancer DNA was ca. 10(-8) M. The specificity of the interaction of R42 with the two HIV enhancers was demonstrated by competitive band shift assays, stepwise displacement of the p50 subunit of transcription factor NF-kappa B from its two HIV enhancer binding sites, and DNase I footprinting; R42 seemed to protect best the two TTTCC sequences of the HIV enhancers against digestion by DNase I. R42 analogues with mutated recognition helix had lower DNA binding specificity. It remains to be investigated whether our artificial HIV enhancer-binding polypeptides are active in vivo.

Amino Acid Sequence↗
PubMedDate not supplied

Epidural clonidine decreases postoperative requirements for epidural fentanyl.

OBJECTIVE: This study assesses the possibility that clonidine may decrease analgesic opioid demand in postoperative patients. METHODS: Twenty-five patients were allocated randomly after abdominal surgery to receive either an epidural bolus dose of fentanyl (1.0 mcg.kg-1) followed by a 1.0 mcg.kg-1h-1 continuous epidural infusion, or an epidural bolus dose of fentanyl (1.0 mcg.kg-1) followed by a continuous epidural infusion combining fentanyl 0.5 mcg.kg-1 x h-1 and clonidine 0.3 mcg.kg-1 x h-1. Pain was assessed at definite intervals on a visual analog scale (VAS) over 3 postoperative days. Epidural infusion was halved when VAS score was lower than 2. Patients were monitored with a pulse oximeter over 12 hours during the first postoperative night. Plasma fentanyl was measured by radioimmunoassay when patients left the recovery room and at 8 a.m. on the first and the second postoperative days. RESULTS: VAS scores were comparable in the two groups of patients. The amount of fentanyl delivered was significantly lower in the fentanyl + clonidine group, as were the plasma fentanyl concentrations. The duration of SaO2 < 90% episodes was significantly less prolonged in the fentanyl + clonidine group (3.5 +/- 4.8 minutes versus 14.4 +/- 14.6 minutes). CONCLUSIONS: The combination of clonidine to epidural fentanyl allows a decrease in opioid requirements without impairing analgesia. Reduction of opioids administration may have beneficial effects on respiratory function in postoperative patients.

Abdomen↗
PubMedDate not supplied

Prolonged placement of spinal catheters does not prevent postdural puncture headache.

OBJECTIVE: To determine whether leaving an intrathecal catheter in place in the postoperative period prevents postdural puncture headache (PDPH). METHODS: Lumbar puncture was performed with an 18-gauge Tuohy needle. 0.5% bupivacaine spinal anesthesia was given through a 20-gauge catheter in 87 patients having orthopedic surgery. Postoperatively, patients were allocated randomly to have the catheter immediately withdrawn (group 1, N = 47) or kept in place for 12 to 24 hours (group 2, N = 40). Patients were questioned by a blinded observer, about PDPH twice a day on postoperative days 1, 2, 3, and 8. RESULTS: The incidence of PDPH was 9.2%, and this was comparable in the two groups (5 patients in group 1 and 3 patients in group 2). CONCLUSION: Leaving the intrathecal catheter in place in the postoperative period for 12 to 24 hours does not prevent PDPH.

Adult↗
PubMedDate not supplied

Tissue expression of neu differentiation factor/heregulin and its receptor complex in prostate cancer and its biologic effects on prostate cancer cells in vitro.

BACKGROUND: Prostate cancer is the most common cancer in American men and the second leading cause of cancer death. All clinical observations correlate poorly differentiated high-grade prostate cancer with disease-specific mortality. The HER2 cell membrane tyrosine kinase, a member of the epidermal growth factor receptor family that is the transcription product of the erbB2neu oncogene, and HER3, a receptor protein of the same family, are overexpressed in prostate cancer and prostatic intraepithelial neoplasia. The ligand for these receptors and another related family member, HER4, has recently been identified by independent investigator groups and called neu differentiation factor (NDF) or heregulin. In vitro treatment of HER2- and HER3- or HER2- and HER4-expressing breast cancer cells stimulates tyrosine phosphorylation of HER2 and produces changes in the rate of proliferation, degree of cellular differentiation, and synthesis of physiologic secretion products. There are no published reports on the expression of NDF and HER4 in prostate cancer or the in vitro effects of NDF in prostate cancer cells. METHODS: Expression of NDF, HER2, HER3, and HER4 was studied in 24 frozen prostatectomy specimens by immunohistochemistry. The biologic effect of human recombinant NDF was studied in vitro, using the LNCaP, PC3, and DU145 human prostate cancer cell lines. HER and NDF protein expression was studied by immunohistochemistry. NDF mRNA was analyzed using reverse transcriptase polymerase chain reaction from whole RNA. The biologic effects of NDF on prostate cancer cells in vitro included cell proliferation, thymidine synthesis, induction of prostate-specific antigen mRNA, anchorage-dependent and anchorage-independent cell growth, and ploidy analysis. Data analysis was performed using Student's t test. RESULTS: Observations in clinical prostatectomy specimens: Immunohistochemistry studies in clinical prostatectomy specimens demonstrate absence of significant NDF expression in prostate cancer, whereas it is expressed in 100% of the stroma, 100% of basal epithelial cells, and 58% of luminal cells in normal and benign hyperplastic prostatic tissue. The HER4 receptor protein is strongly expressed by normal prostate luminal cells, but not prostate cancer. Benign prostate tissue exhibits strong expression of HER2, HER3, and HER4 by basal cells, but only luminal cells significantly express HER4. Only 23% of prostate cancer specimens express HER4, while 95% express HER3 and 82% HER2. Prostatic intraepithelial neoplasia stained similarly to cancer for all proteins studied. Observations in prostate cancer cell lines: In vitro treatment with NDF significantly reduces aneuploidy and proliferation and growth of androgen-sensitive prostate cancer cells. Incubation with NDF also induces prostate-specific antigen mRNA in prostate cancer cells. In spite of displaying NDF mRNA, prostate cancer cells do not produce detectable NDF protein, but express HER2 and HER3 proteins. DISCUSSION: These data suggest that NDF may be a paracrine differentiation factor involved in normal adult prostate physiology and that functional loss of the NDF/HER ligand/ receptor loop may be an early event associated with prostate tumorigenesis.

Antineoplastic Agents↗