Biomedical subjects

H Li

Publications and source records attributed to H Li.

At least 325 records · Page 18Linked to original sources

PubMed2001

Editors and editing of anti-DNA receptors.

Receptor editing is a means by which immature bone marrow B cells can become self-tolerant. Rearrangements of heavy (H) and/or light (L) chain genes are induced by encounter with autoantigens to change the specificity from self to nonself. We have developed site-directed transgenic mice (sd-tg) whose transgenes code for the H chain of antibodies that bind DNA. B cells that express the transgenic H chain associate mainly with four of the 93 functional Vkappa genes of the mouse. Numerous aspartate residues that might inhibit DNA binding by the V(H) domain distinguish these L chain Vkappa sequences, but engaging these Vkappa editors often requires multiple rearrangements. Among the edited B cells is a subset of multispecific cells that express multiple receptors. One consequence of multispecificity is partial autoreactivity; these multispecific B cells may contribute to autoimmunity.

Amino Acid Sequence↗

PubMed2001

The designability of protein structures.

It has been noted that natural proteins adapt only a limited number of folds. Several researchers have investigated why and how nature has selected this small number of folds. Using simple models of protein folding, we demonstrate systematically that there is a "designability principle" behind nature's selection of protein folds. The designability of a structure (fold) is measured by the number of sequences that can design the structure--that is, sequences that possess the structure as their unique ground state. Structures differ drastically in terms of their designability. A small number of highly designable structures emerge with a number of associated sequences much larger than the average. These highly designable structures possess proteinlike secondary structures, motifs, and even tertiary symmetries. In addition, they are thermodynamically more stable and fold faster than other structures. These results suggest that protein structures are selected in nature because they are readily designed and stable against mutations, and that such a selection simultaneously leads to thermodynamic stability.

Amino Acid Motifs↗

PubMed2001

A permutation procedure for the haplotype method for identification of disease-predisposing variants.

Once a genetic region involved in a complex disease has been localized through linkage or association studies, we need methods to help us identify the actual disease predisposing genetic variant(s) in the region. A large number of single nucleotide polymorphic (SNP) sites may exist in this region. It is important to identify genetic variants directly involved in disease from those in linkage disequilibrium, and thus associated with, the disease predisposing variant(s). A question of great interest is to test whether a SNP, or a combination of SNPs, that influence the trait under investigation have been identified. For many complex HLA-associated diseases, patterns of amino acid site variability raise the possibility that HLA-variation association with a disease may not be due to a given allele but rather one or more variable amino acid sites occurring on several alleles. Here the question is whether an amino acid variant or a combination of amino acid variants involved in disease are identified. To address this question, this paper proposes a permutation procedure for the haplotype method, to test whether all the sites involved in the disease have been identified using the haplotypic data of patients and controls. The method is based on the theoretical result of Valdes and Thomson, that, for each haplotype combination containing all the amino acid sites involved in the disease process, the relative frequencies of amino acid variants at sites not involved in disease, but in linkage disequilibrium with the disease-predisposing sites, are expected to be the same in patients and controls. This procedure takes into account the non-independence of the sites sampled and is robust to mode of inheritance and penetrance of the disease, and can definitely specify when all the disease predisposing sites have not been identified. Application to both simulated data and real data sets on type 1 diabetes and alcoholism indicates that the proposed procedure works well in testing the important null hypothesis of whether all the predisposing sites are identified.

Alcohol Dehydrogenase↗

PubMed2001

Modular chemistry: secondary building units as a basis for the design of highly porous and robust metal-organic carboxylate frameworks.

Secondary building units (SBUs) are molecular complexes and cluster entities in which ligand coordination modes and metal coordination environments can be utilized in the transformation of these fragments into extended porous networks using polytopic linkers (1,4-benzenedicarboxylate, 1,3,5,7-adamantanetetracarboxylate, etc.). Consideration of the geometric and chemical attributes of the SBUs and linkers leads to prediction of the framework topology, and in turn to the design and synthesis of a new class of porous materials with robust structures and high porosity.

Carboxylic Acids↗

PubMed2001

Expression of bone associated macromolecules by gingival and periodontal ligament fibroblasts.

The expression of hard tissue associated proteins may be used to identify periodontal fibroblasts with the capability to facilitate periodontal regeneration. The aim of this study was to describe, by immunohistochemistry, the distribution of osteocalcin, osteopontin, bone sialoprotein and bone morphogenic proteins-2 and -4 (BMP-2 and BMP-4) within the human periodontium. Furthermore, the expression of mRNA for the above proteins and alkaline phosphatase by gingival and periodontal ligament fibroblasts in vitro was also assessed by reverse transcriptase polymerase chain reaction (RT-PCR). Localization of osteopontin, osteocalcin, BMP-2 and BM P-4 within sections of human periodontal structures was stronger in the periodontal ligament compared to the gingiva. Bone sialoprotein was not detected in either of the soft tissues but, along with osteopontin and osteocalcin, it was localized in the cementum and bone. In vitro, both the gingival and periodontal ligament fibroblasts expressed mRNA for alkaline phosphatase, BMP-2, BMP-4 and osteopontin. Although there were no differences in the expression of alkaline phosphatase and BMP-4 mRNA between the two cell types, we noted significantly higher mRNA levels of osteopontin in the periodontal ligament and BM P-2 in the gingival fibroblasts. Osteocalcin and bone sialoprotein mRNA expression was only noted in the cultured periodontal ligament fibroblasts. From these results, it can be concluded that distinct differences exist between the two fibroblast populations in terms of the localization and mRNA expression of the majority of the hard tissue associated proteins. Furthermore, the elevated in vitro mRNA expression for osteocalcin, osteopontin and bone sialoprotein may be used to identify cells with the potential to facilitate hard tissue formation and hence periodontal regeneration.

Alkaline Phosphatase↗

PubMed2001

Regulatory element detection using correlation with expression.

We present here a new computational method for discovering cis-regulatory elements that circumvents the need to cluster genes based on their expression profiles. Based on a model in which upstream motifs contribute additively to the log-expression level of a gene, this method requires a single genome-wide set of expression ratios and the upstream sequence for each gene, and outputs statistically significant motifs. Analysis of publicly available expression data for Saccharomyces cerevisiae reveals several new putative regulatory elements, some of which plausibly control the early, transient induction of genes during sporulation. Known motifs generally have high statistical significance.

Algorithms↗

PubMed2001

Fingerprinting polysaccharides with single-molecule atomic force microscopy.

We report the use of an atomic force microscopy (AFM)-based force spectroscopy technique to identify, at the single-molecule level, the components of mixtures of polysaccharides. Previously, we showed that the elasticity of certain types of polysaccharides is governed by force-induced conformational transitions of the pyranose ring. These transitions produce atomic fingerprints in the force-extension spectrum that are characteristic of the ground-energy conformation of the pyranose ring and the type of glycosidic linkages. Using this approach we find that commercially available agarose and lambda-carrageenan contain molecules that, when stretched in an atomic force microscope, produce a force spectrum characteristic of alpha-(1-->4) d-glucans. We have identified these molecules as amylopectin or floridean starch, a storage polysaccharide in algae. Our methodology can identify individual polysaccharide molecules in solution, which is not possible by any other spectroscopic technique, and therefore is an important addition to the arsenal of analytical techniques used in carbohydrate research.

Amylopectin↗

PubMed2001

Kainate receptor-mediated heterosynaptic facilitation in the amygdala.

Prolonged low-frequency stimulation of excitatory afferents to basolateral amygdala neurons results in enduring enhancement of excitatory synaptic responses. The induction of this form of synaptic plasticity is eliminated by selective antagonists of GluR5 kainate receptors and can be mimicked by the GluR5 agonist ATPA. Kainate receptor-mediated synaptic facilitation generalizes to include inactive afferent synapses on the target neurons, and therefore contrasts with other types of activity-dependent enduring synaptic facilitation that are input-pathway specific. Such heterosynaptic spread of synaptic facilitation could account for adaptive and pathological expansion in the set of critical internal and external stimuli that trigger amygdala-dependent behavioral responses.

Amygdala↗

PubMed2001

Midkine and cyclooxygenase-2 promoters are promising for adenoviral vector gene delivery of pancreatic carcinoma.

Midkine (MK), a heparin binding growth factor, and cyclooxygenase-2 (COX-2), a key enzyme in the conversion of arachidonic acid to prostaglandin, are both up-regulated at the mRNA or protein level in many human malignant tumors. Here, we investigated the tumor specificity of both MK and COX-2 promoters in human pancreatic cancer, with the aim to improve the selectivity of therapeutic gene expression. We constructed recombinant adenoviral (Ad) vectors containing either the luciferase (Luc) reporter gene under the control of the COX-2 or MK promoter or the herpes simplex virus thymidine kinase (HSV Tk) gene under the control of the COX-2 promoter and compared the expression with the cytomegalovirus (CMV) promoter. AdMKLuc achieved moderate to relatively high activity upon infection to both primary and established pancreatic carcinoma cells. Of the two COX-2 promoter regions (COX-2M and COX-2L), both revealed a high activity in primary pancreatic carcinoma cells, whereas in the established pancreatic carcinoma cell lines, COX-2L has an approximately equal high activity compared to CMV. In addition, both AdCOX-2M Tk and AdCOX-2L Tk induced marked cell death in response to ganciclovir (GCV) in three of four established pancreatic carcinoma cell lines. From these results, and because it has been reported that AdMKTk and AdCOX-2L Tk in combination with GCV did not reveal significant liver toxicity, we conclude that the MK as well as the COX-2 promoters are promising tumor-specific promoters for Ad vector-based gene therapy of pancreatic cancer.

Adenoviridae↗

PubMed2001

Norepinephrine transporter (NET) is expressed in cardiac sympathetic ganglia of adult rat.

The sympathetic nervous system plays a cardinal role in regulating cardiac function through releasing the neurotransmitter norepinephrine (NE). In comparison with central nervous system, the molecular mechanism of NE uptake in myocardium is not clear. In present study, we proved that in rat the CNS type of NE transporter (NET) was also expressed in middle cervical-stellate ganglion complex (MC-SG complex) which is considered to control the activity of heart, but not expressed in myocardium. The results also showed that NET expression level in right ganglion was significantly higher than in the left, rendering the greater capacity of NE uptake in right ventricle, a fact which may contribute to the maintenance of right ventricular function under pathologic state.

Animals↗

PubMed2001

Improved gene transfer efficiency to primary and established human pancreatic carcinoma target cells via epidermal growth factor receptor and integrin-targeted adenoviral vectors.

In this study we analyzed two ways of retargeting of Ad-vectors to human pancreatic carcinoma with the aim of enhancing the gene transfer efficiency. First, we analyzed the expression of the epidermal growth factor receptor (EGFR) on primary, as well as established pancreatic carcinoma cells by flow cytometry which revealed high expression levels of EGFR on the surface of these cells. We showed that EGFR-retargeted entry pathway using a bispecific fusion protein formed by a recombinant soluble form of truncated Coxsackie and Adenovirus Receptor (sCAR) genetically fused with human EGF (sCAR-EGF) redirects them to the EGFR leading to an enhanced gene transfer efficiency to pancreatic carcinoma cells. Since flow cytometry revealed absence of CAR expression, but the presence of at least one of both alphav integrins on the pancreatic carcinoma cells, a second way of targeting was investigated using a genetically modified Ad vector which has an RGD (Arg-Gly-Asp)-containing peptide inserted into the HI-loop of the fiber knob. This RGD targeted Ad (AdlucRGD) revealed efficient CAR-independent infection by allowing binding to cellular integrins resulting in a dramatic enhancement of gene transfer. These findings have direct relevance for Ad-vector based gene therapy strategies for pancreatic carcinoma.

Adenoviridae↗

PubMed2001

Determination of sulfur dioxide in vitriol plant wastewater by using a polyNiMe4TAA electrochemically modified Pt microelectrode.

A Pt microelectrode modified with nickel(II) polytetramethyldibenzo[b,i]tetraaza[14]annulene was prepared by electropolymerization of nickel(II) tetramethyldibenzo[b,i]tetraaza[14]annulene monomers and applied to determine sulfur dioxide in vitriol plant wastewater. For determination of SO2 with this electrochemically modified Pt microelectrode, the linear range was from 9.6 x 10(-6) to 2.4 x 10(-4) mol L-1, the sensitivity was 1.8 x 10(-4) A L mol-1, the detection limit was calculated to be 4.8 x 10(-6) mol L-1 (S/N = 3), the response time was less than 20 s and the relative standard deviation was found to be 2.1% on analyzing 4.8 x 10(-5) mol L-1 SO2 solution repeatedly (n = 7). These results demonstrated good accuracy compared with those obtained by the conventional iodimetric method.

Chemical Industry↗

PubMed2001

Preparation of microporous aluminium anodic oxide film modified Pt nano array electrode and application in direct measurement of nitric oxide release from myocardial cells.

A novel method for fabricating a nano array electrode (NAE) by using micropores of aluminium anodic film as templates was investigated. To evaluate the NAE, cyclic scanning of NAE in Fe(CN)6(3-) solution was performed and a sigmoidal shaped voltammogram was obtained. The NAE was designed to measure nitric oxide (NO) in vitro and in vivo. Studies showed that it was a sensitive and selective NO electrochemical sensor. NO release from myocardial cells was directly measured with this NAE and the results were satisfactory.

Aluminum Oxide↗

PubMed2001

The effects of atrial electrical remodeling on atrial defibrillation thresholds.

Electrical remodeling of atrial fibrillation may account for the increase in atrial defibrillation thresholds over time. The aim of this study was to examine the time course of electrical remodeling and the benefit of early defibrillation on the defibrillation threshold. Twenty-six mongrel dogs weighing 27.6 +/- 3.3 kg were induced into AF by repeated high output burst atrial pacing. Eight dogs were paced for multiple time periods of 5, 20, 40, and 60 minutes. Five dogs each had burst pacingfor 4 hours and 8 hours, and eight dogs were paced at a high rate (640 beats/min) for 48 hours. Biphasic atrial defibrillation shocks with a pulse width of 3/3 ms synchronized to the left apical electrogram were delivered to coil electrode catheters positioned in the lateral left and right atria. Defibrillation voltage was increased from 50 V in 20- to 30-V steps until defibrillation was successful. As the pacing period increased, a decrease in atrial fibrillation cycle lengths and atrial effective refractory period was not observed before 8 hours. Similarly, the defibrillation threshold did not change significantly until the 8-hour pacing period was reached. The defibrillation thresholds were 69 +/- 28 V for 5 minutes, 64 +/- 20 V for 20 minutes, 99 +/- 85 V for 40 minutes, 78 +/- 51 V for 60 minutes, 78 +/- 38 V for 4 hours, 124 +/- 33 V for 8 hours, and 133 +/- 32 V for 48 hours (mean +/- SD) (P < 0.05). Atrial electrical remodeling in a rapid atrial pacing canine model is not observed until after 4 hours of burst atrial pacing. The atrial defibrillation threshold increases with increasing duration of burst atrial pacing, and follows a similar time course to other parameters of electrical remodeling.

Animals↗

PubMed2001

Neural stem cells express RET, produce nitric oxide, and survive transplantation in the gastrointestinal tract.

BACKGROUND & AIMS: Transplantation of neural stem cells (NSC) has been shown to be successful in a variety of experimental models of nongastrointestinal diseases. The aim of this study was to assess the potential of NSC transplantation as a therapeutic strategy for neuronal replacement in disorders of the enteric nervous system. METHODS: Central nervous system-derived NSC (CNS-NSC) were obtained from the subventricular zone of rat brain (E17). Expression of RET, GFRalpha1, and neuronal nitric oxide synthase (nNOS) was assessed by Western blot and immunocytochemistry. Nitric oxide (NO) production was assessed using the NO-sensitive fluorescent indicator DAF-2. CNS-NSC (labeled with CM-DiI) were transplanted into the pylorus of mice and fluorescent double-labeling immunostaining for betaIII-tubulin or PGP 9.5 and nNOS was performed at 2, 4, and 8 weeks after transplantation. RESULTS: Our results show that CNS-NSC express both the receptors (RET and GFRalpha1) for the enteric neurotrophin, GDNF; GDNF, in turn, induces expansion of the RET-expressing CNS-NSC population. Furthermore, CNS-NSC express nNOS and produce NO in vitro. When transplanted into the gut, CNS-NSC differentiate into neurons, continue to express nNOS and survive at least 8 weeks. CONCLUSIONS: We conclude that transplantation of CNS-NSC bears promise as a potential cellular replacement strategy for enteric neurons.

Animals↗

PubMed2001

Differential detection of cytomegalovirus immediate-early messenger RNA in clinical samples using ligation-dependent PCR.

BACKGROUND: Cytomegalovirus (CMV) causes life-threatening infections in immunocompromised patients, especially those with acquired immunodeficiency or organ transplants. Therefore, early detection of CMV is important to guide the clinical management of actively infected patients. Because detection of replicative transcripts indicates that the virus is in the process of being replicated in the infected cell, we applied a novel, sensitive, ligation-dependent (LD)-PCR method to detect CMV immediate-early (IE) messenger RNA (mRNA), an indicator of viral replication. METHODS AND RESULTS: Viral mRNAs were released from infected cells by incubation in 5 M guanidinium thiocyanate, and IE mRNAs were captured onto magnetic beads through oligo(dT) capture probes. Two hemiprobes, each containing an IE mRNA-complementary region and a region for PCR primer binding, were captured by binding to the IE mRNA. These hemiprobes, bound on an IE mRNA in juxtaposition to one another, were linked together by a DNA ligase to form a full probe that served as the template for PCR amplification. This approach detected IE mRNAs in CMV-propagating cells, but not in supernatants containing only viral DNAs. Thirty-one clinical specimens were tested by LD-PCR; 18 specimens were positive (ten specimens, bronchoalveolar lavage [BAL]; five specimens, urine; two specimens, blood; one specimen, biopsy), 17 of which were confirmed by culture. Three culture-positive samples (two specimens, urine; one specimen, BAL) were missed by LD-PCR, and one urine sample was positive by LD-PCR but negative by culture. CONCLUSION: LD-PCR assay is a reliable test for the early diagnosis of active CMV infection in patient specimens.

Cytomegalovirus↗

PubMed2001

Transient Bax-protein immunoreactivity prior to apoptosis of spiral ganglion neurons in the postnatal rat.

The apoptosis occurring in the postnatal developing spiral ganglion cells (SGCs) and the concomitant change in Bax-protein immunoreactivity were investigated in rats at postnatal days (P) 1, 3, 5, 7, 10 and 14, and also in adult rats. In P5 and P7 rats, some neurons showed structural features of apoptosis, including cell shrinkage, condensed chromatin around the margin of the nucleus and phagocytosis of apoptotic bodies by satellite cells. The percentage of Bax-protein-positive neurons in the spiral ganglion was significantly higher in P1, P3, P5, and P7 rats compared with adult rats. Our results confirm the occurrence of neuronal cell apoptosis in the spiral ganglion at the end of the first postnatal week, and demonstrate the transient change in Bax-protein immunoreactivity prior to neuronal cell apoptosis. Thus, we speculate that the transient change in Bax protein could be involved in neuronal cell apoptosis of the postnatal developing SGCs of rats.

Animals↗

PubMed2001

Conformation changes in brain calcineurin in diabetic rats with or without treatment with vanadyl sulfate.

Recent studies have shown that vanadium salts are able to reduce blood glucose in diabetics and overcome, to some degree, insulin resistance. This paradigm has been followed to monitor the effects of diabetes and vanadyl treatment on brain calcineurin (CN), an important protein phosphatase. Male rats were rendered diabetic by a single injection of streptozotocin (STZ), resulting in an elevation of blood glucose from 108 +/- 13 to >400 mg/dl. Diabetic animals were given vanadyl sulfate trihydrate (0.5 mg/dl.) in their drinking water for 3 weeks, which led to a fall in blood glucose to 156 +/- 53 mg/ml. Brain CN activity (units/mg brain protein) in diabetic rats was 77% that of control animals, whereas vanadyl-treated diabetic animals were characterized by CN activities like that of controls. CN was purified from brains of control animals, STZ-induced diabetic animals, and STZ-induced diabetic animals receiving vanadyl, then spin-labeled with 3-maleimide-proxyl and studied via electron spin resonance spectroscopy. The rotational correlation time of CN from control animals and vanadyl-treated diabetic animals was 6.4 x 10(-11) s(-1), whereas that from STZ-induced-diabetic animals was 8 x 10(-11) s(-1). Thus, STZ-induced diabetes in rats results in an increase in the rotational correlation time of brain CN relative to control animals, yet vanadyl treatment of STZ-induced diabetic animals reduced the rotational correlation time to that of control. These data suggest that diabetes can lead to apparent conformational changes in brain CN; also, CN conformation in diabetic rats was restored by vanadyl treatment.

Administration, Oral↗