PubMed Health⌕ Search

Biomedical subjects

N Li

Publications and source records attributed to N Li.

At least 19 recordsLinked to original sources
PubMed2002

Site-specific forms of antifreeze protein in the beetle Dendroides canadensis.

It was known previously that overwintering larvae of the beetle Dendroides canadensis produce antifreeze proteins (DAFPs) consisting of a family of 12 similar proteins, and based on sequence variations the DAFPs may be separated into three groups. DAFPs were known to be present in hemolymph, midgut fluid and in/on epidermal cells located immediately under the cuticle. However, only DAFPs-1, 2, and 4 were known to be present in the hemolymph, leaving the location of the others unknown. In this study, matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry of hemolymph confirmed the presence of DAFPs-1, 2, and 4 (Group I), plus a protein consistent with the mass of DAFP-6 (Group I). Also, a review of older data revealed the co-purification of DAFP-6 along with DAFP-4 in hemolymph. However, none of the other DAFPs (Groups II and III) were present in hemolymph. In contrast, mass spectrometry of midgut fluid demonstrated the absence of DAFPs-1, 2, 4, or 6, however, proteins consistent with the masses of all, or a subset of, Groups II and/or III were present. Reverse transcriptase polymerase chain reaction (RT-PCR) showed that transcripts of all 12 DAFPs were present in the fat body. However, consistent with the MALDI-TOF data, only Groups II (8, 9, 10, 11) and III (3, 5, 7, 12) transcripts were found in midgut epithelia. RT-PCR of epidermal tissue identified dafps- 4, 6, 8 and 11 (and sometimes 1 and/or 2) as the major transcripts. These data suggest that various DAFPs may have evolved to function best in certain sites.

Amino Acid Sequence↗
PubMed2002

Regulation of medial prefrontal cortex dopamine by alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate/kainate receptors.

In the medial prefrontal cortex, repeated cocaine produces tolerance of the extracellular dopamine response to subsequent cocaine injection. These studies characterized the influence of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate/kainate receptors on the medial prefrontal cortex dopamine response to acute cocaine, amphetamine and potassium chloride as a first step to assess whether these receptor subtypes may be candidates for mediating dopamine tolerance after repeated cocaine. Local infusion of 10 microM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) produced an approximate 40% increase in dopamine levels in the medial prefrontal cortex, while a 30 microM dose did not alter basal levels infused over a 3-h period. Thus, 30 microM CNQX was chosen for the remaining experiments, and was infused for 1 h prior to and during all in vivo treatments. Local medial prefrontal cortex infusion of the 30 microM dose blocked the small increase in dopamine levels elicited by systemic saline injection (maximum of 26%), as well as the much larger increase in response to acute cocaine injection (maximum of 340%). Local infusion of D-amphetamine (3 and 30 microM) through the probe increased dopamine to 300 and 600% of basal levels, respectively. Co-infusion of CNQX partially blocked the response for the first 40 min, but dopamine levels recovered by 60 min later. Local infusion of 100 mM potassium chloride elicited a 600% increase in dopamine levels, which was attenuated approximately 50% by CNQX co-infusion. Potassium-stimulated release of dopamine was also measured in vitro in medial prefrontal cortical and striatal tissue. By 30 s after potassium addition, dopamine levels increased to 800% above baseline in the medial prefrontal cortex, and this increase was blocked by the presence of 30 microM CNQX. In contrast, potassium-stimulated dopamine release in striatal tissue was approximately 250% above basal levels, with no effect of CNQX on dopamine release. Locomotor behavior collected during dialysis experiments demonstrated that increased activity induced by local infusion of potassium chloride was severely attenuated by co-infusion of 30 microM CNQX, while no effects of this drug were found for cocaine-elicited behavior. These results suggest a potent influence of glutamate via alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate/kainate receptors on extracellular dopamine in the medial prefrontal cortex, and these receptors may regulate dopamine release through a presynaptic mechanism. The findings may help elucidate the role of medial prefrontal cortex dopamine-glutamate interactions in drug abuse and stress- and drug-precipitated psychosis.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed2002

Cloning and sequencing of quail and pigeon prion genes.

Quail and pigeon PrP genes were cloned and sequenced. Like mammalian PrP genes, quail and pigeon genes are encoded by a single exon of a single copy gene in the genome. All of the structural features of mammalian PrP genes were found in the quail and pigeon PrP gene. Compared with the nucleotide sequences of mammalian PrP, they display generally 30% similarity. When compared with chicken PrP's DNA sequence, they show a higher homology (90%), and an even higher homology (99%) when compared to each other. A phylogenetic tree was constructed to trace the evolution of the prion gene in animals.

Animals↗
PubMed2002

Identification of three SNPs in the porcine myostatin gene (MSTN).

Thirteen pairs of primers were designed for the entire porcine MSTN gene to enable PCR amplification for the detection of single nucleotide polymorphisms (SNPs) by a PCR-SSCP approach. Altogether 96.5% (1089/1128) of the encoding regions and 971 bp of the non-coding regions were screened. A total of three polymorphisms were identified with PCR-SSCP. They were located in the promoter, intron one and exon three regions of the gene. These polymorphisms were then confirmed to be point mutations (T --> A transversion, G --> A transition and C --> T transition respectively) by sequencing. Allele frequencies were determined for all three SNPs in several different pig breed populations. The polymorphisms were found to be rare in Western breeds, but much more common in Chinese breeds. Whether they have any relationship with the marked difference in lean meat mass between Western and Chinese breeds requires further study.

Alleles↗
PubMed2001

Assessment of colloid formation and physical state distribution of trace polycyclic aromatic hydrocarbons in aqueous samples.

A tandem-cartridge system was established for studying colloid formation and physical state distribution of trace polycycic aromatic hydrocarbons (PAHs) in water. The effectiveness of the method for measuring the trace PAH colloids was demonstrated. With aqueous samples prepared by adding the PAH solutes with a small amount of organic solvent carrier, the potential of colloid formation increased with the hydrophobicity and concentration of the solute, but the incipient concentration for the colloid formation may be far lower than the aqueous solubility of the solute. After formation in water, the colloids showed remarkable stability at room temperature, and the stability was greatly reduced by elevated temperature and the presence of a small amount of inorganic electrolytes. The possible mechanism of destabilization of the colloids was discussed, and the mechanism might be of utility in providing insights into the physical state distribution of the solutes in various water samples. However, further effort to investigate the mechanism through fluorescence spectrophotometry was unsuccessful. The significance of the colloid formation in methods of preparation of aqueous samples and for measuring aqueous solubilities of PAHs and other hydrophobic compounds was illustrated. The results of this work demonstrate that it is undesirable to prepare aqueous solutions of PAHs or similarly hydrophobic compounds by vigorous mixing or the use of cosolvents, methods that are widely used in many studies for which aqueous solutions of such analytes are required.

Chromatography, Gas↗
PubMed2001

Insulin enhances platelet activation in vitro.

Diabetes mellitus is associated with an increased risk of atherothrombotic complications. There is accumulating evidence of platelet hyperreactivity in diabetes, which may be of importance in the pathogenesis of diabetic vascular complications. Platelets possess insulin receptors, but their physiological relevance is not clear, and data on insulin effects on platelet function in the literature are less than consistent. We therefore investigated the influence of insulin on platelet activation in vitro. Fasting blood samples were collected in 20 healthy males, using citrate or hirudin as anticoagulants. Platelet activation was measured as platelet P-selectin expression and fibrinogen binding using whole blood flow cytometry in unstimulated and adenosine diphosphate (ADP) stimulated samples, incubated with 0-10000 microU/ml insulin for 20 min. The effect of insulin (30 or 300 microU/ml, incubated for 3 min) on platelet aggregation was studied using Born aggregometry in platelet-rich plasma (PRP). Insulin enhanced platelet fibrinogen binding more than P-selectin expression in unstimulated and ADP stimulated samples (P<.001 by analysis of variance [ANOVA]; n=20). Insulin (30 or 300 microU/ml) also enhanced ADP-induced platelet aggregation in PRP (P<.01 or P<.001; n=14). The platelet activating effect of insulin was verified in hirudinized samples (n=12), indicating that it was not dependent on unphysiologically low extracellular calcium concentrations. Thus, insulin enhances platelet activation in vitro, independently of extracellular calcium concentrations. Beneficial effects of insulin treatment on platelet function in vivo are probably related to improved metabolic control, rather than to direct platelet stabilizing effects.

Adult↗
PubMed2001

Quantification of epimeric budesonide and fluticasone propionate in human plasma by liquid chromatography-atmospheric pressure chemical ionization tandem mass spectrometry.

A highly sensitive and selective liquid chromatography-atmospheric pressure chemical ionization tandem mass spectrometry assay was developed and validated for simultaneous determination of epimeric budesonide (BUD) and fluticasone propionate (FP) in plasma. The drugs were isolated from human plasma using C18 solid-phase extraction cartridges, and epimeric BUD was acetylated with a mixture of 12.5% acetic anhydride and 12.5% triethylamine in acetonitrile to form the 21-acetyl derivatives following the solid-phase extraction. Deuterium-labelled BUD acetate with an isotopic purity >99% was synthesized and used as the internal standard. The assay was linear over the ranges 0.05-10.0 ng/ml for epimeric BUD, and 0.02-4.0 ng/ml for FP. The inter- and intra-day relative standard deviations were <14.3% in the assay concentration range.

Androstadienes↗
PubMed2001

DIgR1, a novel membrane receptor of the immunoglobulin gene superfamily, is preferentially expressed by antigen-presenting cells.

A novel membrane receptor of immunoglobulin gene superfamily (IgSF) has been identified from mouse dendritic cells (DC) and designated as DC-derived Ig-like receptor 1 (DIgR1). It encodes a 228-amino-acid (aa) residue polypeptide with a 21-aa signal peptide, a 20-aa transmembrane region, a 189-aa extracellular region, and a 19 aa intracellular region. Its extracellular region contains a single V domain of Ig. So it is a novel type I transmembrane glycoprotein of IgSF. DIgR1 shows significant homologies to human CMRF-35 antigens and polymeric immunoglobulin receptors (pIgR). The mRNA expression of DIgR1 was highly abundant in mouse spleen. The preferential expression of DIgR1 mRNA is observed in the known antigen-presenting cells (APC) including DC, monocytes/macrophages, and B lymphocytes. A 40 kDa of protein in NIH/3T3 cells transfected with the DIgR1 cDNA was detected by Western blot analysis using anti-DIgR1 polyclonal antibodies. The expression of DIgR1 protein on DC is not regulated by LPS stimulation. Further study should be conducted to investigate what were biological functions of DIgR1 in the immunobiology of APC.

Amino Acid Sequence↗
PubMed2001

Calcium-sensitive regions of GCAP1 as observed by chemical modifications, fluorescence, and EPR spectroscopies.

Guanylyl cyclase-activating proteins are EF-hand Ca(2+)-binding proteins that belong to the calmodulin superfamily. They are involved in the regulation of photoreceptor membrane-associated guanylyl cyclases that produce cGMP, a second messenger of vertebrate vision. Here, we investigated changes in GCAP1 structure using mutagenesis, chemical modifications, and spectroscopic methods. Two Cys residues of GCAP1 situated in spatially distinct regions of the N-terminal domain (positions 18 and 29) and two Cys residues located within the C-terminal lobe (positions 106 and 125) were employed to detect conformational changes upon Ca(2+) binding. GCAP1 mutants with only a single Cys residue at each of these positions, modified with N,N'-dimethyl-N-(iodoacetyl)-N'-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)ethylenediamine, an environmentally sensitive fluorophore, and with (1-oxy-2,2,5,5-tetramethylpyrroline-3-methyl)methanethiosulfonate, a spin label reagent, were studied using fluorescence and EPR spectroscopy, respectively. Only minor structural changes around Cys(18), Cys(29), Cys(106), and Cys(125) were observed as a function of Ca(2+) concentration. No Ca(2+)-dependent oligomerization of GCAP1 was observed at physiologically relevant Ca(2+) concentrations, in contrast to the observation reported by others for GCAP2. Based on these results and previous studies, we propose a photoreceptor activation model that assumes changes within the flexible central helix upon Ca(2+) dissociation, causing relative reorientation of two structural domains containing a pair of EF-hand motifs and thus switching its partner, guanylyl cyclase, from an inactive (or low activity) to an active conformation.

Amino Acid Motifs↗
PubMed2001

Resonance Rayleigh scattering study of the interaction of heparin with some basic diphenyl naphthylmethane dyes.

In a near-neutral medium, a combination of heparin with some basic diphenyl naphthylmethane dyes such as victoria blue 4R (VB4R), victoria blue B (VBB), or night blue (NB) can result in a significant enhancement of resonance. Rayleigh scattering (RRS) and their maximum scattering wavelengths lambdamax appear at 523, 534, and 540 nm for VB4R, VBB, and NB, respectively. The characteristics of RRS spectra of the heparin-dye complexes, the influencing factors, and the optimum conditions of these reactions have been investigated. The RRS intensity is directly proportional to the concentration of heparin in the range of approximately 0 to 0.4 microg/mL for all systems. The methods exhibit high sensitivities, and the detection limits for heparin are 3.35 ng/mL for the VB4R system, 6.62 ng/ mL for the VBB system, and 6.29 ng/mL for the NB system. Because the VB4R system is the most sensitive, it was taken as an example to study the selectivity of the method. A new method for the determination of trace amounts of heparin based on RRS technique has been developed. Moreover, the enhancement reasons of RRS and the relationship between RRS spectral characteristics of the heparin-dye complex and its absorption spectra have been primarily discussed.

Benzhydryl Compounds↗
PubMed2001

[Rehabilitation therapy for short bowel syndrome].

OBJECTIVE: To investigate the effect of rehabilitation therapy for short bowel syndrome on patients' nutritional status and intestinal adaptation. METHODS: Twenty seven patients with short bowel syndrome with the average age of 38.5 +/- 19.3 years, the residual small intestine of the length of 15 to 80 cm, ileocecal valve being preserved in 15 cases, and an average time between the onset of short bowel syndrome and rehabilitation therapy of 86 +/- 105 d received 29 courses of rehabilitation therapy including enteral or parenteral nutrition, glutamine, recombinant human growth hormone and rehabilitation diet from January 1997 to July 2000. RESULTS: After the treatment, the patients' nutritional status improved markedly, their intestinal absorptive capacity improved too. Eight patients were followed up for more than 2 y, 4 of them (50%) had weaned from total parenteral nutrition. Thirteen patients were followed up for more than 1 y, 10 of them (76.9%) had weaned from total parenteral nutrition. CONCLUSION: Rehabilitation therapy for short bowel syndrome improves patients' nutritional status effectively and promote intestinal adaptation. Early initiation of rehabilitation therapy promotes intestinal adaptation, and increases patients' liability to wean from total parenteral nutrition.

Adolescent↗
PubMed2001

Molecular cloning and characterization of a novel calcium/calmodulin-dependent protein kinase II inhibitor from human dendritic cells.

Calcium/calmodulin-dependent protein kinase II (CaMKII) is a widely distributed protein kinase that regulates numerous physiological functions. Inhibitors of CaMKII are useful tools for investigating the CaMKII functions. Here we identified a novel CaMKII inhibitor protein (CaM-KIIN) from the human dendritic cell cDNA library by large-scale random sequencing. Human CaM-KIIN contains 79 amino acids, which shares 98% identity and 98% positives with rat CaMKII inhibitor protein beta and 65% identity and 78% positives with rat CaMKII inhibitor alpha. Human CaM-KIIN mRNA expression was detectable in various tissues and cell lines by Northern blot and RT-PCR. To investigate its biological functions, full-length human CaM-KIIN was overexpressed in colon adenocarcinoma LoVo cells. When expressed in LoVo cells, it could inhibit cell proliferation, block cell growth, and decrease the viable cell number. These results characterize a potential cellular inhibitor protein of CaMKII that plays an important role in the regulation of cell growth.

Adenocarcinoma↗
PubMed2001

Genes and mechanisms related to RNA interference regulate expression of the small temporal RNAs that control C. elegans developmental timing.

RNAi is a gene-silencing phenomenon triggered by double-stranded (ds) RNA and involves the generation of 21 to 26 nt RNA segments that guide mRNA destruction. In Caenorhabditis elegans, lin-4 and let-7 encode small temporal RNAs (stRNAs) of 22 nt that regulate stage-specific development. Here we show that inactivation of genes related to RNAi pathway genes, a homolog of Drosophila Dicer (dcr-1), and two homologs of rde-1 (alg-1 and alg-2), cause heterochronic phenotypes similar to lin-4 and let-7 mutations. Further we show that dcr-1, alg-1, and alg-2 are necessary for the maturation and activity of the lin-4 and let-7 stRNAs. Our findings suggest that a common processing machinery generates guide RNAs that mediate both RNAi and endogenous gene regulation.

Animals↗
PubMed2001

Solid-phase extraction of polycyclic aromatic hydrocarbons in surface water. Negative effect of humic acid.

The effect of humic acid on solid-phase extraction of polycyclic aromatic hydrocarbons (PAHs) from surface water was studied. The hydrophobic PAHs show significant association with humic acid, and this was confirmed to be the cause of negative effect when conventional reversed-phase solid-phase extraction (RP-SPE) was employed to extract the analytes from aqueous samples. As an alternative, dynamic ion-exchange (DIE) SPE could simultaneously extract both the fraction of the analytes which was associated with humic acid, and that which was freely dissolved. Using the 16 US Environmental Protection Agency priority PAHs as model compounds, the recoveries of the highly hydrophobic components by DIE-SPE were 10-30% higher than those by RP-SPE for a 1000-ml water sample dissolved with Aldrich humic acid (of 4.1 mg/l dissolved organic carbon content). A similar result was also obtained for 500 ml of natural surface water although the difference in recoveries between the two methods for this sample was smaller than that for the simulated sample. For validation of the method, the artifacts in connection with DIE-SPE in extracting the fraction of analytes which was freely dissolved and that which was associated with humic acid were investigated.

Humic Substances↗
PubMed2001

Crystal structures of 1-aminocyclopropane-1-carboxylate (ACC) synthase in complex with aminoethoxyvinylglycine and pyridoxal-5'-phosphate provide new insight into catalytic mechanisms.

The structures of tomato 1-aminocyclopropane-1-carboxylate synthase (ACS) in complex with either cofactor pyridoxal-5'-phosphate (PLP) or both PLP and inhibitor aminoethoxyvinylglycine have been determined by x-ray crystallography. The structures showed good conservation of the catalytic residues, suggesting a similar catalytic mechanism for ACS and other PLP-dependent enzymes. However, the proximity of Tyr152 to the C-gamma-S bond of model substrate S-adenosylmethionine implies its critical role in the catalysis. The concerted accomplishment of catalysis by cofactor PLP and a protein residue, as proposed on the basis of the ACS structures in this paper, may represent a general scheme for the diversity of PLP-dependent catalyses. PLP-dependent enzymes have been categorized into four types of folds. A structural comparison revealed that a core fragment of ACS in fold type I is superimposable over tryptophan synthase beta subunit in fold type II and mouse ornithine decarboxylase in fold type III, thus suggesting a divergent evolution of PLP-dependent enzymes.

Amino Acid Sequence↗
PubMed2001

Involvement of CGRP and CGRP1 receptor in nociception in the nucleus accumbens of rats.

The present study was performed to investigate the role of calcitonin gene-related peptide (CGRP) and its antagonist CGRP8-37 on nociception in the nucleus accumbens of rats. Hindpaw withdrawal latencies (HWLs) to noxious stimulation induced by hot plate and Randall Selitto tests were measured. The HWL to both thermal and mechanical stimulation increased significantly after intra-nucleus accumbens administration of 0.5 or 1 nmol of CGRP, but not 0.1 nmol, indicating that CGRP plays an anti-nociceptive effect in the nucleus accumbens of rats. The anti-nociceptive effect induced by intra-nucleus accumbens administration of 1 nmol of CGRP was blocked significantly by following intra-nucleus accumbens administration of 1 nmol of CGRP8-37, a selective antagonist of CGRP1 receptor. Furthermore, the HWLs to both thermal and mechanical stimulation decreased significantly after intra-nucleus accumbens administration of 0.02, 0.1 and 0.5 nmol of CGRP8-37 alone. The hyperalgesic effect of intra-nucleus accumbens administration of CGRP8-37 lasted for more than 60 min after the injection, suggesting that CGRP1 receptor is involved in anti-nociception in the nucleus accumbens of rats. The results indicate that CGRP and CGRP1 receptor have important roles in nociceptive modulation in the nucleus accumbens of rats.

Animals↗
PubMed2001

Cloning and characterization of Siglec-10, a novel sialic acid binding member of the Ig superfamily, from human dendritic cells.

The Siglecs (sialic acid-binding Ig-like lectins) are a subfamily of I-type lectins, which specifically recognize sialic acids. Nine members of the family have been identified thus far. We have obtained a novel cDNA clone from a human dendritic cell cDNA library encoding a protein with sequence and structural features of the Siglec family, hence designated as Siglec-10. The full-length Siglec-10 cDNA encodes a type 1 transmembrane protein containing four extracellular immunoglobulin-like domains, a transmembrane region, and a cytoplasmic tail with two classical immunoreceptor tyrosine-based inhibitory motifs. The N-terminal V-set Ig domain has most of the amino acid residues typical of the Siglecs. Siglec-10 shows the closest homology to Siglec-5 and Siglec-3/CD33. Various cells and cell lines including monocytes and dendritic cells express Siglec-10. High levels of mRNA expression were seen in peripheral blood leukocytes, spleen, and liver. When expressed on COS-7 cells, Siglec-10 was able to bind human red blood cells and soluble sialoglycoconjugates in a sialic acid-dependent manner. The identification of Siglec-10 as a new Siglec family member and its expression profile, together with its sialic acid-dependent binding capacity, suggest that it may be involved in cell-cell recognition by interacting with sialylated ligands expressed on specific cell populations.

Amino Acid Motifs↗