Biomedical subjects

X Li

Publications and source records attributed to X Li.

At least 235 records · Page 13Linked to original sources

PubMed2001

Analysis of terpene compounds in Cimicifuga foetida L. by reversed-phase high-performance liquid chromatography with evaporative light scattering detection.

An RP-HPLC method with evaporative light scattering detection (ELSD) was developed for the analysis of terpene compounds in traditional Chinese medicine. Actein, 27-deoxyactein and cimicifugoside in a typical Chinese medicine of Cimicifuga foetida L. were quantitatively analyzed. Comparing ELSD with UV detection under the same eluent conditions, the former showed better sensitivity and a more stable baseline. The ELSD responses versus sample size of three terpenes and those in double logarithmic were investigated. The good calibration curves in double logarithmic coordinator for actein, 27-deoxyactein and cimicifugoside were obtained. Three solutions for the extraction of the terpene compounds were also compared, the results indicated that methanol-water (80:20) is the best among them. The method was applied to quantify actein, 27-deoxyactein and cimicifugoside in Cimicifuga foetida L. from Hunan, China. It was shown that ELSD is an effective detection method for the analysis of the non-volatile terpenes in traditional Chinese medicine.

Calibration↗

PubMed2001

Galanin synaptic input to gonadotropin-releasing hormone perikarya in juvenile and adult female mice: implications for sexual maturity.

Changes in connectivity of the gonadotropin-releasing hormone (GnRH) neuronal system are believed to occur during the transition from juvenile to adulthood in females. Experiments were designed to investigate whether there is any difference in the number of galanin inputs to GnRH cells located in the organum vasculosum of lamina terminalis-rostral preoptic area (OVLT-rPOA) between juvenile (2 weeks old) and adult (10 weeks old) female mice. Triple label immunofluorescence staining of brain sections for galanin, GnRH and the presynaptic vesicle marker synaptophysin coupled with confocal microscopy was employed to identify galanin synapses to GnRH perikarya. The number of galanin synapses to GnRH cells and the proportion of GnRH cells with galanin input were significantly higher in adults than in juvenile mice. In adult mice, the proportions of GnRH cells with 0, 1, 2, 3, 4, 5 or 6 galanin synapses/cell were comparable to each other whereas in the juveniles the vast majority of them received no galanin synaptic input. A greater number of galanin synapses in adult as compared with juvenile female mice suggests a functional role for galanin in the maturation of the GnRH system.

Age Factors↗

PubMed2001

Cellular automaton model considering the velocity effect of a car on the successive car.

In this paper we present a cellular automata model for one-lane traffic flow. The update rules of velocity of a car depend not only on the positions of this car and the car ahead of it, but also on the velocities of the two cars. Using computer simulations we obtain some basic qualitative results and the fundamental diagram of the proposed model. In comparison with those of the existing models in the literature, we find that the fundamental diagram of the proposed model is more consistent with the results measured in the real traffic, and the model is able to reproduce some relevant macroscopic states that are found in the real traffic flow but cannot be predicted by the existing models.

Journal Article↗

PubMed2001

Selenium spares ascorbate and alpha-tocopherol in cultured liver cell lines under oxidant stress.

The selenoenzyme thioredoxin reductase (TR) can recycle ascorbic acid, which in turn can recycle alpha-tocopherol. Therefore, we evaluated the role of selenium in ascorbic acid recycling and in protection against oxidant-induced loss of alpha-tocopherol in cultured liver cells. Treatment of HepG2 or H4IIE cultured liver cells for 48 h with sodium selenite (0-116 nmol/l) tripled the activity of the selenoenzyme TR, measured as aurothioglucose-sensitive dehydroascorbic acid (DHA) reduction. However, selenium did not increase the ability of H4IIE cells to take up and reduce 2 mM DHA, despite a 25% increase in ascorbate-dependent ferricyanide reduction (which reflects cellular ascorbate recycling). Nonetheless, selenium supplements both spared ascorbate in overnight cultures of H4IIE cells, and prevented loss of cellular alpha-tocopherol in response to an oxidant stress induced by either ferricyanide or diazobenzene sulfonate. Whereas TR contributes little to ascorbate recycling in H4IIE cells, selenium spares ascorbate in culture and alpha-tocopherol in response to an oxidant stress.

Animals↗

PubMed2001

Receptor binding kinetics of human IL-3 variants with altered proliferative activity.

The binding kinetics of native IL-3 and a set of truncated IL-3 variants to the alpha subunit of the IL-3 receptor (IL-3Ralpha) were studied using surface plasmon resonance. These variants, with amino acid substitutions at residues, 22, 42, 43, 45, 46, 113, or 116, have previously been identified to have altered capacity to stimulate cell proliferation compared to native IL-3(1-133). In this study, variants E43N and F113Y exhibited >100-fold slower association rates than IL-3(15-125) consistent with residues 43 and 113 being essential for the binding of IL-3 to the IL-3Ralpha. Variants G42A, G42D, Q45V, D46S, K116V, and K116W exhibited increased association rates (up to 15-fold relative to IL-3(15-125)) and decreased dissociation rates (up to 7-fold). The results demonstrate that both the association and dissociation rates for the binding of IL-3 to the IL-3Ralpha are altered by truncation and by amino acid substitution at individual sites. Intracellular signaling studies using K116W and E43N demonstrate that differences in the IL-3alpha binding characteristics are reflected in magnitude and kinetics of STAT5 phosphorylation.

Amino Acid Substitution↗

PubMed2001

Role of the alpha(v)beta6 integrin in human oral squamous cell carcinoma growth in vivo and in vitro.

Expression of the alpha(v)beta6 integrin is strikingly upregulated in several types of carcinoma, including human oral squamous cell carcinoma (SCC). Employing a neutralizing monoclonal antibody to alpha(v)beta6, we investigated its role in cell adhesion, proliferation, migration, and in vivo growth of an invasive human SCC line, termed HSC-3. We found that alpha(v)beta6 is strictly required for HSC-3 cell growth in a three-dimensional collagen gel and also prominently contributes to cell migration in two different assay systems. In addition, the anti-alpha(v)beta6 antibody inhibited the invasive growth of HSC-3 cells transorally injected into nude mice. In the presence of the coinjected antibody, the average tumor size at 10 days was reduced by 59%. Histologically, antibody-treated tumors appeared less invasive than control tumors. Furthermore, intravenous application of a neutralizing antibody to the alpha(v) integrin subunit retarded HSC-3 tumor growth. These results point to a possible critical role of the alpha(v)beta6 integrin in controlling growth and invasion of human oral cancer cells.

Animals↗

PubMed2001

Familial carcinoid tumors and subsequent cancers: a nation-wide epidemiologic study from Sweden.

Carcinoids are rare neuroendocrine tumors, mainly located in the bowel, stomach and lung. Familial risks in carcinoid tumours are not well known apart from multiple endocrine neoplasia 1 (MEN1). We used the nation-wide Swedish Family-Cancer Database on 10.1 million individuals for assessment. Carcinoid tumors were retrieved from the Cancer Registry covering the years 1958-1998. The offspring generation, aged 0-66 years, accumulated 190 million person-years at risk. The age-adjusted incidence rates were 0.76 for men and 1.29/100,000 for women. Standardized incidence ratios (SIRs) were calculated for offspring when their parents had a carcinoid or any other cancer. When parents presented with carcinoids, SIRs for offspring were 4.35 (n = 8, 95% CI 1.86-7.89) for small intestinal and 4.65 (n = 4, 95% CI 1.21-10.32) for colon carcinoids. If both offspring and parents presented with small intestinal carcinoids, the SIR was 12.31 (n = 4, 95% CI 3.20-27.34). Offspring carcinoids were also increased if parents presented with bladder and endocrine gland tumors, the latter association probably partially due to MEN1. Risks for second cancers were increased, particularly at sites where familial risks were found, including carcinoids in the small intestine.

Adolescent↗

PubMed2001

Unilateral left prefrontal transcranial magnetic stimulation (TMS) produces intensity-dependent bilateral effects as measured by interleaved BOLD fMRI.

Transcranial magnetic stimulation (TMS) administered over the prefrontal cortex has been shown to subtly influence neuropsychological tasks, and has antidepressant effects when applied daily for several weeks. Prefrontal TMS does not, however, produce an immediate easily observable effect, making it hard to determine if one has stimulated the cortex. Most prefrontal TMS studies have stimulated using intensity relative to the more easily determined motor threshold (MT) over motor cortex. Five healthy adults were studied in a 1.5 T MRI scanner during short trains of 1 Hz TMS delivered with a figure eight MR compatible TMS coil followed by rest epochs. In a randomized manner, left prefrontal TMS was delivered at 80%, 100% and 120% of MT interleaved with BOLD fMRI acquisition. Compared to rest, all TMS epochs activated auditory cortex, with 80% MT having no other areas of significant activation. 100% MT showed contralateral activation and 120% MT showed bilateral prefrontal activation. Higher intensity TMS, compared to lower, in general produced more activity both under the coil and contralaterally. Higher prefrontal TMS stimulation intensity produces greater local and contralateral activation. Importantly, unilateral prefrontal TMS produces bilateral effects, and TMS at 80% MT produces only minimal prefrontal cortex activation.

Adult↗

PubMed2001

Spinal cord nitric oxide synthase and heme oxygenase limit morphine induced analgesia.

Spinal cord tissue contains two enzyme systems capable of producing monoxide gases which in turn are linked to the stimulation of soluble guanylate cyclase, nitric oxide synthase (NOS) which produces NO and heme oxygenase (HO) which produces CO. Reports from several laboratories link these two enzyme systems to pain of inflammatory and neuropathic etiologies. Additional studies have demonstrated that the activation of the NOS system by morphine limits the spinal analgesic action of this drug. In this study we first employed the hot plate model of pain to demonstrate that the NOS inhibitor L-NAME and the HO inhibitor Sn-P potentiate the analgesic actions of intrathecally administered morphine while having no intrinsic analgesic action at the doses used. We then determined that L-NAME loses its ability to potentiate morphine in nNOS null-mutant mice, while Sn-P no longer potentiates morphine in mice lacking a functional HO-2 gene. The intrathecal injection of the cGMP analog 8-Br cGMP caused hyperalgesia in the hot plate assay. Focusing on the possible involvement of cGMP metabolism, we documented that morphine stimulates cGMP production in a spinal cord slice model in a concentration dependent and naloxone reversible manner. Both L-NAME and Sn-P were potent inhibitors of morphine-stimulated cGMP production. Buffer containing either CO or the NO donor compound SNAP stimulated cGMP production as well. In spinal cord slices from either nNOS or HO-2 null-mutant animals morphine did not stimulate cGMP production. Taken together our data suggest that spinal monoxide generation modifies the acute analgesic actions of morphine.

Analgesics, Opioid↗

PubMed2001

Zinc-mediated thermal stabilization of carboxypeptidase A.

In this study we investigated the contribution of Zn ions to the catalytic and structural thermostability of carboxypeptidase A (CPA). Structural studies on CPA molecule, performed in the presence of a number of ligands, demonstrated the multiple binding models around Zn ions which may affect the enzyme functions. Zinc was reported to bind at various sites in the CPA molecule at room temperature leading to inhibition of its enzymic activity. In this study we found that binding of Zn to CPA molecule followed by exposure to 50 degrees C did not inhibit the enzymic activity but activates and protects it against heat denaturation. The stabilization effect was found to be dependent on the increasing Zn/CPA ratios. The moderate changes of CPA activity as well as the UV and fluorescence spectra analyses indicate that the main function of the newly introduced zinc atoms is structural rather than catalytical.

Carboxypeptidases↗

PubMed2001

Cysteine-25 of adenylate kinase reacts with dithiothreitol to form an adduct upon aging of the enzyme.

Adenylate kinase (AK) ages in solution in the presence of DL-dithiothreitol (DTT) with a gradual activity decrease. Upon dilution with 4 M guanidine hydrochloride denatured native and aged AK, both recover to the same activity as the fresh enzyme. Mass spectroscopy and 7-chloro-4-nitrobenz-2-oxa-1,3-diazole chloride modification kinetics studies identify that the residue cysteine-25 of the enzyme reacts with DTT to form an adduct. The formation of the unusual bridging DTT adduct of AK appears to be the result of a stable DTT-protein complex. The K(M) for AMP, ADP and MgATP of the DTT-modified enzyme does not differ significantly from that of the intact enzyme, whereas the secondary and tertiary structures of the enzyme change obviously. These results indicate that cysteine-25 may not be involved directly in substrate binding, but may play an important role in maintaining secondary and tertiary structures of native AK, as well as the conformation interconversion in the catalytic cycle.

Adenylate Kinase↗

PubMed2001

Identification of sequence, protein isoforms, and distribution of the hyaluronan-binding protein RHAMM in adult and developing rat brain.

The protein RHAMM (for "receptor for hyaluronan-mediated motility"; CD168) is a member of the hyaladherin family of hyaluronan-binding proteins. RHAMM has a role in cell signaling, migration, and adhesion via interactions with hyaluronan, microtubules, actin, calmodulin, and components of the extracellular regulated kinase (erk) signaling pathway. Based on previous findings of potentially similar roles in neural cells in culture, we investigated the molecular characteristics, protein expression profile, and distribution of RHAMM in rat brain. Reverse transcriptase-polymerase chain reaction (RT-PCR) using RNA isolated from adult rat brain yielded a single RHAMM sequence of 2.1 kilobases encoding a protein of 82.4 kDa. RHAMM is subject to alternate splicing in other systems, but no RT-PCR evidence was found for splice variants in brain, although our analysis does not rule out this possibility. The amino acid sequence displayed homology with human and murine RHAMM (74% and 80%, respectively) but contained only one copy of a 21-amino-acid sequence that is repeated five times in the murine homologue. By using anti-RHAMM antibodies, several RHAMM isoforms were identified in brain. Immunohistochemically, RHAMM was found in the vast majority of neurons and in many oligodendrocytes throughout brain, with heterogeneous levels among cell populations, and was confined to the somata and initial processes of these cells. RHAMM was detected in neurons of cerebral cortex and most subcortical and brainstem structures at postnatal day 1 and exhibited an adult distribution pattern by postnatal day 5. High levels were detected in oligodendrocytes by postnatal day 10. The widespread expression of RHAMM in adult and developing brain implies a role for this protein and its ligand hyaluronan in key events of cell signaling and cytoskeletal regulation in the CNS.

Aging↗

PubMed2001

Incidence trends and risk factors of carcinoid tumors: a nationwide epidemiologic study from Sweden.

BACKGROUND: Carcinoids are rare indolent neuroendocrine tumors, mainly located in bowel, stomach, and lung. Their etiology is virtually unknown although a family history is a minor cause. METHODS: Site specific incidence trends and several risk factors of carcinoid tumors were studied based on the nationwide Swedish Family-Cancer Database of 10.2 million individuals and their more than 1 million tumors. Data on a total of 5184 carcinoid tumors were retrieved from the Cancer Registry covering years 1958-1998. RESULTS: The overall age-adjusted incidence rates were 2.0 for men and 2.4/100,000 for women in 1983-1998. Appendix was the main site for women whereas small intestine was the main site for men. The incidence of all carcinoids, including those at the main sites increased during the follow-up period but appeared to plateau in the middle of the 1980s. Appendiceal carcinoids showed an unusually early onset with a maximum incidence at age 15-19 years for women and 20-29 years for men. Among women, parity was not related to the age specific incidence of carcinoid tumors. A Poisson regression analysis showed that family history of carcinoids in first-degree relatives (relative risk, 3.6), well educated social background (relative risk for professionals, 2.8), and birth in large cities were risk factors. CONCLUSIONS: The data suggest that the increase in carcinoid tumors may be largely ascribed to the application of advanced medical viewing techniques that detect asymptomatic tumors. However, the difference in incidence between men and women in appendiceal tumor may be real and independent of parity.

Adolescent↗

PubMed2001

A role for NF-kappa B in the induction of beta-R1 by interferon-beta.

Previous experiments have suggested that induction of the beta-R1 gene by interferon (IFN)-beta required transcription factor ISGF-3 (IFN-stimulated gene factor-3) and an additional component. We now provide evidence that nuclear factor-kappaB (NF-kappaB) can serve as this component. Site-directed mutagenesis of an NF-kappaB binding site in the beta-R1 promoter or over-expression of an IkappaBalpha super-repressor abrogated IFN-beta-mediated induction of a beta-R1 promoter-reporter. IFN-beta treatment did not augment abundance of NF-kappaB but did lead to phosphorylation of the p65 NF-kappaB subunit. It is proposed that IFN-beta-mediated enhancement of the transactivation competence of NF-kappaB components is required for inducible transcription of the beta-R1 promoter. These results provide a novel insight into the role of NF-kappaB in the transcriptional response to IFN-beta.

Binding Sites↗

PubMed2001

Strain selection of Metarrhizium anisopliae by image analysis of colony morphology for consistency of steroid biotransformation.

Quantitative description of colony morphological images of the fungus Metarrhizium anisopliae was done by means of computer image analysis based on fractal analysis. Compared with simple fractal analysis, the differences in the morphological features of colonies were expressed more accurately by multifractal analysis. The use of multifractal analysis markedly improved the reliability of colony image analysis, which could be extended to morphological characterization for colony recognition and classification. First, the multifractal spectrum was calculated from each morphological image and 14 features were defined on the spectrum to describe the spectral line profile. Second, three features, alpha-right, alpha-width, and f-start, were selected from the 14 features in two-dimensional feature vector spaces and a feature augmented vector (alpha-right, alpha-width, and f-start, 1)(T) was generated and used for classifier design. Third, a statistical least mean square error (LMSE) algorithm was applied to design a piecewise-linear classifier, which consists of two linear classifiers, d(1)(x) and d(2)(x). Representative colony samples were used as training and test sample sets, which were previously classified into a high-activity class and another class by a training person. After passing the training phase, the piecewise-linear classifier could be used for automated classification of unknown colony samples. A correct recognition rate of 96% was achieved in this manner. Compared with conventional strain selection methods, this new method has the advantage of less subjectivity, reduced labor and time, and improved ability to deal with a large number of colonies.

Algorithms↗

PubMed2001

Rapid activation of ERK1/2 mitogen-activated protein kinase by corticosterone in PC12 cells.

Although the nongenomic effects of glucocorticoids have been well acknowledged, its precise intracellular signal transduction pathway remains to be elucidated. The present study using Western immunoblot and protein kinase activity assay, for the first time, showed that corticosterone (B) can induce a rapid activation of Erk1/2 mitogen-activated protein kinase (MAPK) in PC12 cells. The dose-response curve was bell shaped, with the maximal activation at 10(-9) M in 15 min. The results from immunofluorescence staining also revealed that the activated Erk1/2 MAPK was translocated from cytoplasm to nucleus of PC12 cells in 15 min. Activation of Erk1/2 MAPK by B was apparently not mediated by the classical cytosolic steroid receptors, for B-BSA can induce the phosphorylation of Erk1/2 MAPK, but the antagonist (RU38486) cannot block the phosphorylation of Erk1/2 MAPK induced by B. Phosphorylation of Erk1/2 MAPK induced by B was not affected by a tyrosine kinase inhibitor (genistein), suggesting that the pathway did not involve the tyrosine kinase activity. On the other hand, protein kinase C activator (PMA) can activate and protein kinase C inhibitor (Gö6976) can block the activation of Erk1/2 MAPK induced by B. Taken together, these data clearly demonstrated that B might act via putative membrane receptor and rapidly activate Erk1/2 MAPK through protein kinase C alpha in PC12 cells.

Active Transport, Cell Nucleus↗

PubMed2001

Structure of human holocarboxylase synthetase gene and mutation spectrum of holocarboxylase synthetase deficiency.

Holocarboxylase synthetase (HLCS) is an enzyme that catalyzes the incorporation of biotin into apo-carboxylases, and its deficiency causes biotin-responsive multiple carboxylase deficiency. The reported sequences of cDNA for human HLCS from liver, lymphocyte, and KG-1 myeloid cell lines differ at their 5' regions. To elucidate variations of the human HLCS mRNA and longer 5' cDNA ends, we performed screening of the human liver cDNA library and rapid amplification of the cDNA ends (RACE). Our results suggest the existence of three types of HLCS mRNA that start at different exons. The first type starts at exon 1, and the second type starts at exon 3, and both are found in various human tissues. The third type, corresponding to the cDNA from the KG-1 cell, starts at exon 2 of the HLCS gene. Various splicing patterns from exons 3-6 were also observed. None of the variations of cDNA found created a new initiation codon. Mutation screening from exons 6-14, therefore, was sufficient to detect amino acid changes in HLCS in patients. Our direct sequencing strategy for screening mutations in the HLCS gene revealed mutations in five Japanese patients and seven non-Japanese patients. Our analyses involving 12 Japanese and 13 non-Japanese patients and studies by others indicate that (1) there is no panethnically prevalent mutation; (2) the Arg508Trp, Gly581Ser, and Val550Met mutations are found in both Japanese and non-Japanese populations; (3) the IVS10+5G-->A mutation is predominant and probably a founder mutation in European patients; (4) the 655-656insA, Leu237Pro, and 780delG mutations are unique in Japanese patients; (5) the spectrum of the mutations in the HLCS gene may vary substantially among different ethnic groups.

Base Sequence↗

PubMed2001

Requirement for GSH in recycling of ascorbic acid in endothelial cells.

Ascorbic acid may be involved in the defense against oxidant stress in endothelial cells. Such a role requires that the cells effectively recycle the vitamin from its oxidized forms. In this work, we studied the ability of cultured bovine aortic endothelial cells (BAECs) to take up and reduce dehydroascorbic acid (DHA) to ascorbate, as well as the dependence of ascorbate recycling on intracellular GSH. BAECs took up and reduced DHA to ascorbate much more readily than they took up ascorbate. Although BAECs in culture did not contain ascorbate, ascorbate accumulated to concentrations of 2-3 mM in BAECs following incubation with 400 microM DHA. Extracellular ferricyanide oxidized intracellular ascorbate, which was recycled by the cells. Reduction of DHA, either when added to the cells or when generated in response to ferricyanide, caused significant decreases in intracellular GSH concentrations. Depletion of intracellular GSH with 1-chloro-2,4-dinitrobenzene, diethylmaleate, and diamide almost abolished the ability of the cells to reduce DHA to ascorbate. DHA reduction by thioredoxin reductase was evident in dialyzed cell extracts, but occurred at rates far lower than direct GSH reduction of DHA. These results suggest that maximal rates of DHA reduction, and thus recycling of ascorbate from DHA, are dependent upon GSH in these cells.

Animals↗