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Biomedical subjects

B Li

Publications and source records attributed to B Li.

At least 307 records · Page 17Linked to original sources
PubMed1999

Sol-gel thin-film immobilized soybean peroxidase biosensor for the amperometric determination of hydrogen peroxide in acid medium.

An acid-stable soybean-peroxidase biosensor was developed by immobilizing the enzyme in a sol-gel thin film. Methylene blue was used as a mediator because of its high electron-transfer efficiency. The sol-gel thin film and enzyme membrane were characterized by FT-IR, and the effects of pH, operating potential, and temperature were explored for optimum analytical performance by using the amperometric method. The H2O2 sensor exhibited a fast response (5 s), high sensitivity (27.5 microA/mM), as well as good thermostability and long-term stability. In addition, the performance of the biosensor was investigated using flow-injection analysis (FIA).

Enzymes, Immobilized↗
PubMed1999

Insulin-like growth factor-1 attenuates the detrimental impact of nonocclusive coronary artery constriction on the heart.

Coronary artery narrowing (CAN) induces tissue injury, which may involve myocyte necrosis and apoptosis. Insulin-like growth factor (IGF)-1 may counteract cell death, modifying the detrimental effects of myocardial ischemia. On this basis, CAN was produced in female FVB.Igf+/- mice and nontransgenic littermates, and the animals were euthanized 7 days later. CAN consisted of an 82% reduction in the vessel luminal cross-sectional area in both groups of mice. Severe left ventricular dysfunction was present in CAN nontransgenic and transgenic mice, but heart and left ventricular weights increased more in littermates than in FVB.Igf+/- mice. Similarly, the changes in chamber volume and diastolic wall stress were greater in nontransgenic mice. Subacute tissue injury, represented by foci of replacement fibrosis, was 2.6-fold higher in CAN littermates than in FVB.Igf+/- mice. Ongoing myocyte necrosis was 5-fold greater in nontransgenic mice, whereas apoptosis was low and did not differ in the 2 groups of mice. In CAN nontransgenic mice, myocyte necrosis was 12-fold more frequent than apoptosis but, in CAN transgenic mice, these 2 types of cell death were comparable. alpha-Myosin and beta-myosin isoform mRNAs were affected by CAN, but alpha-myosin mRNA was reduced more in nontransgenic mice. In conclusion, myocyte necrosis and replacement fibrosis are the prevailing forms of myocardial damage induced by CAN. Constitutive overexpression of IGF-1 attenuates myocyte necrosis and tissue injury, having no effect on cell apoptosis. These factors limit ventricular dilation, myocardial loading, cardiac hypertrophy, and alterations in alpha- and beta-myosin isoform expression.

Animals↗
PubMed1999

Ca2+/calmodulin binds to and modulates P/Q-type calcium channels.

Neurotransmitter release at many central synapses is initiated by an influx of calcium ions through P/Q-type calcium channels, which are densely localized in nerve terminals. Because neurotransmitter release is proportional to the fourth power of calcium concentration, regulation of its entry can profoundly influence neurotransmission. N- and P/Q-type calcium channels are inhibited by G proteins, and recent evidence indicates feedback regulation of P/Q-type channels by calcium. Although calcium-dependent inactivation of L-type channels is well documented, little is known about how calcium modulates P/Q-type channels. Here we report a calcium-dependent interaction between calmodulin and a novel site in the carboxy-terminal domain of the alpha1A subunit of P/Q-type channels. In the presence of low concentrations of intracellular calcium chelators, calcium influx through P/Q-type channels enhances channel inactivation, increases recovery from inactivation and produces a long-lasting facilitation of the calcium current. These effects are prevented by overexpression of a calmodulin-binding inhibitor peptide and by deletion of the calmodulin-binding domain. Our results reveal an unexpected association of Ca2+/calmodulin with P/Q-type calcium channels that may contribute to calcium-dependent synaptic plasticity.

Amino Acid Sequence↗
PubMed1999

Molecular cloning and characterization of human AOS1 and UBA2, components of the sentrin-activating enzyme complex.

Sentrin-1/SUMO-1 is a novel ubiquitin-like protein, which can covalently modify a limited number of cellular proteins. Here we report the identification of the sentrin-activating enzyme complex, which consists of two proteins AOS1 and UBA2. Human AOS1 is homologous to the N-terminal half of E1, whereas human UBA2 is homologous to the C-terminal half of E1. The human UBA2 gene is located on chromosome 19q12. Human UBA2 could form a beta-mercaptoethanol-sensitive conjugate with members of the sentrin family, but not with ubiquitin of NEDD8, in the presence of AOS1. Identification of human UBA2 and AOS1 should allow a more detailed analysis of the enzymology of the activation of ubiquitin-like proteins.

Amino Acid Sequence↗
PubMed1999

Potent, orally absorbed glucagon receptor antagonists.

The SAR of 2-pyridyl-3,5-diaryl pyrroles, ligands of the human glucagon receptor and inhibitors of p38 kinase, were investigated. This effort resulted in the identification of 2-(4-pyridyl)-5-(4-chlorophenyl)-3-(5-bromo-2-propyloxyphenyl)pyrr ole 49 (L-168,049), a potent (Kb = 25 nM), selective antagonist of glucagon.

Animals↗
PubMed1999

Correlated variations in EEG pattern and visual responsiveness of cat lateral geniculate relay cells.

1. Simultaneous recordings of the EEG and the visual activity of cat dorsal lateral geniculate nucleus (dLGN) relay cells were analysed for covariance. Sliding time-window analyses were performed in parallel for the EEG power spectrum and single unit visual activity. The EEG power ratio (EEG-PR) of low (1-8 Hz) to high (20-40 Hz) frequencies was chosen to achieve a quantitative measure of the EEG which could be compared with the spike rate of a dLGN unit at any time. A high EEG-PR value indicates a synchronized EEG dominated by low frequencies (delta waves and sleep spindles), a low value indicates a less synchronized EEG. 2. In the anaesthetized animal, two different underlying patterns of activity in the EEG-PR were found: slow gradual changes (slow gradations) and oscillatory changes. In many cases both were accompanied by correlated variations in dLGN spike rate, either for overall activity or for burst firing. 3. The slow gradations appear for long time periods of up to 200 s and, in most cases (76.3 %), show a negative correlation between EEG-PR and overall spike rate, but predominantly a positive correlation for burst firing (85.1 %). 4. The oscillatory changes, which have not previously been reported, appear as temporally well-coupled variations in EEG-PR and spike rate with a stable cycle length within the range 4-10 s. In about 77 % of correlated changes the temporal delay between the change in EEG-PR and that of the spike rate was less than +/- 1.0 s. 5. During simultaneous recordings from two dLGN cells the variations in spike rate tend to show the same sign of correlation with respect to the EEG pattern. This relationship is more pronounced with the slow gradations than with the oscillatory changes. 6. Slow gradations in the spectral composition of the EEG may indicate global transitions between different stages within the sleep-wake cycle, reflecting the well-known influences of the brainstem arousal system. The oscillations in the spectral composition of the EEG are accompanied by gradual variations in thalamic transmission mode and are more likely to be due to involvement of a local feedback system via the thalamo-cortico-thalamic loop. The difference between the effects on overall and burst firing activity supports the notion that phasic (burst firing) and tonic visual responses may play distinctive roles in information processing, which are functionally related to the animal's behavioural state.

Animals↗
PubMed1999

Regulation of IL-4 expression by the transcription factor JunB during T helper cell differentiation.

The molecular basis for restricted cytokine expression by T helper 1 (Th1) and T helper 2 (Th2) cells is unclear. Previous studies found that P1, an element of the interleukin 4 (IL-4) promoter that binds AP-1, is important for Th2-restricted IL-4 expression. Here we show that JunB, but not the other Jun family members, was selectively induced in Th2 cells and not in Th1 cells during differentiation. JunB has previously been considered to be a negative regulator of transcription. However, we show that JunB binds directly to the P1 site and synergizes with c-Maf to activate an IL-4 luciferase reporter gene. JunB-control of IL-4 expression is mediated by the phosphorylation of JunB at Thr102 and -104 by JNK MAP kinase. The synergy between c-Maf and JunB can be attributed to cooperative DNA binding, which is facilitated by JunB phosphorylation. In transgenic mice, elevated JunB levels caused increased expression of several Th2 cytokines in developing Th1 cells. JunB also upregulated IL-4 expression in response to immunization. Thus, the early increase of JunB protein in Th2 cells can provide the specificity for c-Maf in IL-4 expression during T cell development and directs thereby Th2 differentiation.

Animals↗
PubMed1999

Effect of styrene on monoamine oxidase B activity in rat brain.

Previous studies have indicated that workers exposed to styrene present a decreased activity of platelet monoamine oxidase B (MAO B), suggesting that this biochemical assay may represent a biomarker for styrene-induced neurotoxicity. This study was undertaken to determine whether exposure to styrene would cause changes in MAO B activity in the target organ--the brain. Groups of rats were exposed to styrene by inhalation at concentrations of 300 ppm for 4 wk or 50 ppm for 13 wk. Both treatments caused significant decreases of MAO B activity in several brain areas, while MAO A activity was not affected. Decreases in MAO B activity were also found in brainstem of rats given styrene (400 mg/kg) or styrene oxide (100 mg/kg) by i.p. injection for 2 wk. Styrene, styrene oxide, and other styrene metabolites (mandelic acid, phenylglyoxylic acid, and styrene glycol) had no direct inhibitory effect on brain MAO B activity when tested in vitro. These results indicate that exposure to low concentrations of styrene alters MAO B activity in rat brain, suggesting that the observed changes in human platelets may reflect alterations in the nervous system.

Administration, Inhalation↗
PubMed1999

Time Dependent Anchoring of Adsorbed Cationic Surfactant Molecules at Mica/Solution Interface.

The nature of adsorbed cationic amphiphiles at the mica/solution interface was studied by XPS and contact angle measurements. The elemental analyses of freshly cleaved mica surfaces by XPS showed that the potassium atoms on the surface lattice of mica are not necessarily distributed equally to each surface on cleavage. The adsorbed cationic amphiphile molecules remaining on mica surfaces after rinsing with distilled water were found to be anchored to the surface by ion-exchange, replacing surface potassium and/or other cations. The ratio of adsorbed cationic amphiphile molecules with single alkyl chains to the maximum potassium ions on mica surface was estimated to be twice as large as that of amphiphiles having two alkyl chains. The contact angle of water drops placed on the adsorbed surface showed a gradual decrease with the elapse of time due to the dissolution of adsorbed surfactant into the water drop; however, the decrease was not observed for those mica surfaces when aged for more than 3 days in the adsorption bath. The anchoring of adsorbed molecules by ion-exchange was found to occur extremely slowly, however; the anchored molecules may not easily be desorbed when rinsed with deionized water. The time dependent anchoring of adsorbed molecules was studied in terms of adsorption time, alkyl chain length, and concentration of cationic surfactant. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

A new version of the RDP (Ribosomal Database Project).

The Ribosomal Database Project (RDP-II), previously described by Maidak et al. [ Nucleic Acids Res. (1997), 25, 109-111], is now hosted by the Center for Microbial Ecology at Michigan State University. RDP-II is a curated database that offers ribosomal RNA (rRNA) nucleotide sequence data in aligned and unaligned forms, analysis services, and associated computer programs. During the past two years, data alignments have been updated and now include >9700 small subunit rRNA sequences. The recent development of an ObjectStore database will provide more rapid updating of data, better data accuracy and increased user access. RDP-II includes phylogenetically ordered alignments of rRNA sequences, derived phylogenetic trees, rRNA secondary structure diagrams, and various software programs for handling, analyzing and displaying alignments and trees. The data are available via anonymous ftp (ftp.cme.msu. edu) and WWW (http://www.cme.msu.edu/RDP). The WWW server provides ribosomal probe checking, approximate phylogenetic placement of user-submitted sequences, screening for possible chimeric rRNA sequences, automated alignment, and a suggested placement of an unknown sequence on an existing phylogenetic tree. Additional utilities also exist at RDP-II, including distance matrix, T-RFLP, and a Java-based viewer of the phylogenetic trees that can be used to create subtrees.

Base Sequence↗
PubMed1999

Accelerated rejection of Fas ligand-expressing heart grafts.

The Fas/Fas ligand (FasL) system plays an important role in the induction of lymphoid apoptosis and has been implicated in the suppression of immune responses. Recently, there has been renewed interest in immune privilege, as it was shown that two privileged sites (the eye and testes) constitutively express FasL, which kills lymphoid cells that invade these areas. We have established murine FasL-transgenic mice (B6) under the control of the cardiac alpha-myosin heavy chain promotor, and transplanted FasL-expressing F1(B6 x C3H/HeJ) heart grafts into syngeneic (F1) and allogeneic (C3H/HeJ) recipients. FasL-expressing F1 heart allografts placed in C3H/HeJ recipients as well as FasL-expressing F1 isografts placed in nontransgenic and FasL-transgenic F1 were more rapidly rejected, and their survival was much shorter than that of nontransgenic control F1 allografts placed in C3H/HeJ. Native control and FasL-expressing hearts looked normal in mice up to 8 wk of age on hematoxylin-eosin staining. Control heart allografts undergoing ordinally acute rejection showed moderate focal lymphocyte infiltrates, while FasL-expressing F1 allografts and isografts showed massive hemorrhage, edema, and massive neutrophil infiltration as early as 1 day after transplantation. In conclusion, FasL expression and surgical procedure (ischemia/reperfusion) were synergistic in the induction of accelerated heart graft rejection, while allogenicity was not necessary. It may be necessary to find ways of controlling neutrophilic reaction/apoptosis in infiltrating lymphocytes to use FasL in clinical organ transplantation.

Animals↗
PubMed1999

Differing roles of adenosine receptor subtypes in retinal ischemia-reperfusion injury in the rat.

Adenosine has been shown to be a major component of the retina's endogenous reaction to ischemia. In earlier studies, the significant changes in adenosine concentration that occur during ischemia and the ensuing reperfusion period were documented. While previous studies have shown that adenosine is a mediator of the changes in blood flow that occur in response to ischemia, hypoxia, and hypoglycemia in the retina, little is known about other functional effects that result from these changes in adenosine concentration. Accordingly, the influence of adenosine receptor blockade on the functional and histological outcome following ischemia in rats was examined. Specific antagonists of the adenosine A1 and A2a receptors were injected systemically, prior to ischemia of either 5, 30, or 60 min. The recovery of the electroretinogram a and b waves was followed for up to 7 days after ischemia, and retinal structure was examined by light microscopy. The adenosine A1 receptor antagonist DPCPX attenuated recovery after retinal ischemia of either 5 or 30 min, while the A2a receptor antagonist CSC dramatically protected retinal function and structure even with ischemia lasting up to 60 min. It was concluded that blockade of the A2a receptor, possibly combined with stimulation of the A1 receptor, may represent a potential new strategy for the prevention of ischemic damage in the retina.

Animals↗
PubMed1999

Immunohistochemical expression of p53 and bcl-2 proteins is not associated with sarcomatoid change in renal cell carcinoma.

An immunohistochemical study was conducted to examine the expression of p53 and bcl-2 proteins in RCC (renal cell carcinoma) with sarcomatoid change in order to determine whether abnormalities in those proteins are associated with an enhanced malignant potential of RCC. Paraffin-embedded tissues from 11 patients with RCC, in which sarcomatoid change was prominent, were stained using anti-p53, bcl-2 and Ki-67 antibodies. Immunoreactivities for these antibodies were compared between the sarcomatoid components and corresponding basic histologic (clear or papillary) components in individual cases. Measurement of the mean nuclear areas of each component was also performed using an image analyzer system. There was no substantial increase in immunoreactivity for p53 or bcl-2 proteins in sarcomatoid components as compared with basic components. In contrast, the percentage of Ki-67-positive cells and the mean nuclear area were significantly larger in sarcomatous components than in basic components. The expression of p53 and bcl-2 proteins was not likely to play a major role in the sarcomatoid change of RCC.

Adult↗
PubMed1999

Uptake of particulate lead via the gills of fish (Carassius auratus).

Carassius auratus were exposed to mixtures of constant free lead (0. 1 mg/L) and particulate lead (adsorbed on gibbsite particles) at varied concentrations (0, 0.4, 0.8, 1.2, 2.0, and 3.0 mg/L). The concentrations of lead and aluminum in the gills and intestines of the fish were determined after exposure. The gills were examined (after the exposure) with a light microscope for any particles adhering to the surface. The examination results revealed that lead accumulations on the gills increased with increased particulate lead concentrations in the ambient water (under conditions of a constant level of free lead), indicating the bioavailability of lead via the gills. Gibbsite particles were also observed on the gill surface after exposure. The ratio of lead and aluminum in the gills was much higher than that in the particles. Our results suggest that there was a two-step process involved in the uptake of particulate lead by fish gills: (1) adherence of the particles on the gill surface where mucus was attached; and (2) desorption of lead from the particles under conditions of the gill microenvironment.

Animals↗
PubMed1999

CD95 ligand expression enhances growth of murine renal cell carcinoma in vivo.

The CD95/CD95 ligand (CD95L) system plays an important role in the induction of lymphoid apoptosis and has been implicated in the suppression of immune responses. In this system, two murine CD95L-transfected renca clones and a control renca clone transfected only with the vector were implanted into the subcapsule of the left kidney of Balb/c and Balb/c nude mice. Both CD95L-expressing and control renca clones formed macroscopic tumors in all of the Balb/c and Balb/c nude hosts 14 days after implantation. Growth of tumors of murine CD95L-transfected renca cells was significantly better than that of control renca cells in Balb/c mice, while the growth advantage of CD95L transfectants was not observed in Balb/c nude mice. Lymphocytes underwent apoptosis mainly in the periphery of the CD95L-expressing tumors but not in control tumors grown in Balb/c mice, while lymphocytes undergoing apoptosis were not observed in CD95L-expressing tumors or in control tumors grown in Balb/c nude mice. Neutrophilic recruitment was rarely observed in CD95L-expressing or control tumors. CD95L expressed on renca cells possibly suppressed immune responses against renca tumors by inducing apoptosis of the infiltrating lymphocytes. However, CD95L-expressing renca cells did not form tumors in the renal subcapsule of allogeneic C3H/HeJ mice.

Animals↗
PubMed1999

Long-term depot-medroxyprogesterone acetate and bone mineral density.

The association between long-term use of depot-medroxyprogesterone acetate (DMPA) and bone mineral density (BMD) has been controversial, as seen in three case-control studies in New Zealand, Thailand, and the United Kingdom. In the present case-controlled study of BMD, a group of 67 Chinese women who had used DMPA from 5-15 years was compared with 218 women of the same age range who had not used any steroidal hormones. DMPA users were found to have a significantly lower BMD at lumbar vertebra (L2-4) (0.93 g/cm2), neck of femur (0.69 g/cm2), trochanter (0.59 g/cm2), and Ward's triangle (0.58 g/cm2), as compared with the control group, whose corresponding BMD values were 1.03 g/cm2, 0.83 g/cm2, 0.71 g/cm2, and 0.78 g/cm2, respectively (p < 0.001). The average percentage of bone loss per year was estimated to be 1.1% in L2-4, 2.3% in neck of femur, 2.4% in trochanter, and 3.5% in Ward's triangle. The percentage of bone loss in L2-4 was found to be more pronounced with age. This study provided information that the use of DMPA in a Chinese group for > 5 years in associated with bone loss, and a prospective study is needed to confirm these data, which are different from two case-control studies.

Absorptiometry, Photon↗