Biomedical subjects

W Li

Publications and source records attributed to W Li.

At least 235 records · Page 13Linked to original sources

PubMed2001

Parathyroid hormone-stimulated resorption in calvaria cultured in serum-free medium is enhanced by the calcium-mobilizing activity of 1,25-dihydroxyvitamin D(3).

1,25(OH)(2)D(3) enhances parathyroid hormone (PTH)-induced Ca(2+) signaling in osteoblasts by activating plasma membrane voltage-sensitive Ca(2+) channels (VSCCs). The ability of 1,25(OH)(2)D(3) or the VSCC-activating analog AT (25-hydroxy-16-ene-23-yne-D(3)) to enhance parathyroid hormone-stimulated (45)Ca(2+) release from cultured new-born rat calvaria was measured. Analog BT (1,24-dihydroxy-22-ene-24-cyclopropyl-D(3)), that does not mobilize Ca(2+), also was tested along with PTH. Control experiments were performed with and without PTH and with and without serum. Individual calvaria labeled in utero with (45)Ca(2+) were cultivated in serum-free medium on filters at the medium/air interface of 24-well culture plates and (45)Ca(2+) release followed over 72 h. The results demonstrated that 1,25(OH)(2)D(3) and the Ca(2+)-mobilizing analog, AT, but not the nuclear receptor-binding analog, BT, enhanced PTH-stimulated (45)Ca(2+) release under serum-free conditions. This enhancement effect of the seco-steroids was not evident in the presence of 10% fetal calf serum. The effect of analog AT was faster than that of 1,25(OH)(2)D(3). Nitrendipine, a specific L-type VSCC blocker, attenuated enhancement by vitamin D compounds, indicating that the high-threshold L-type VSCC is a molecular transducer of costimulation. These results emphasize the synergy between the calcitropic hormones 1,25(OH)(2)D(3) and PTH in cultures containing osteoblasts and osteoclasts, and suggest that the Ca(2+)-mobilizing activity of 1,25(OH)(2)D(3) enhances Ca(2+) release from bone.

Animals↗

PubMed2001

Polishing and whitening properties of toothpaste containing hydroxyapatite.

Toothpastes containing hydroxyapatite (HA-toothpaste) have demonstrated efficacy in preventing caries, treating hypersensitivity and curing periodontal diseases, however, their effects on whitening teeth have not been investigated. In this study, the polishing and whitening properties of hydroxyapatite contained toothpastes were evaluated in a combined experimental and clinical study. The polishing properties were evaluated in artificial teeth by polishing with different toothpastes, while the brightening and whitening properties were examined in volunteers using two colorimeters with two specially made fiberscopes. The results revealed that the addition of hydroxyapatite to toothpaste did not alter its polishing properties, while it did result in a marked increase in tooth-whiting. It was also found that the brightening and whitening properties increased as the amount of hydroxyapatite in the toothpaste increased. It is concluded that toothpaste containing hydroxyapatite are effective at whitening tooth and that whitening was not due to their polishing effect on tooth surface.

Journal Article↗

PubMed2001

Proteomic detection of changes in protein synthesis induced by NGX6 transfected in human nasopharyngeal carcinoma cells.

In the previous study, we cloned a new gene, named NGX6, related to nasopharyngeal carcinoma (NPC) at 9p. To study its function in the pathogenesis of NPC, we have investigated changes in protein synthesis between NPC cell line HNE1 and that transfected with the gene. Using high-resolution two-dimensional electrophoresis, we found that 22 protein spots showed variations that were significant and reproducible. Analysis of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and database searches identified seven proteins that were upregulated and seven proteins that were downregulated. These proteins included Fas, zinc-finger protein (ZNF), RAB, and Ah receptor-interacting protein (AIP). The functional implications of the identified proteins are discussed.

Down-Regulation↗

PubMed2001

Hepatitis B virus genomes of chronic hepatitis patients do not contain specific mutations related to acute exacerbation.

To determine the specific viral variants associated with acute exacerbation of chronic hepatitis from hepatitis B virus (HBV) infection, we analyzed the complete nucleotide sequences of the HBV genome in serial serum samples from two chronic active hepatitis patients who seroconverted from HBeAg to anti-HBe. HBV DNA was amplified by polymerase chain reaction (PCR) and sequenced. A 1896 precore stop codon mutant (G to A at nt 1896) coexisting with the wild sequence was found in both patients prior to seroconversion from HBeAg to anti-HBe. Core promoter mutations at nucleotide positions 1762 (A to T) and 1764 (G to A) were found in both patients throughout the observation period. Mutations were observed in the HBV genome of the two patients at different time points, and there was no correlation between the mutations and liver disease or DNA polymerase levels. The nucleotide divergence rate and the composition of quasispecies in the HBV sequence at the time of acute exacerbation were almost the same as were found at other time points. These results suggest that acute exacerbation does not appear to be caused by a characteristic HBV species. The multiple factors that cause generalized HBV replication activation may contribute to acute exacerbation.

Child, Preschool↗

PubMed2001

Cortical brain regions engaged by masked emotional faces in adolescents and adults: an fMRI study.

Face-emotion processing has shown signs of developmental change during adolescence. Functional magnetic resonance imaging (fMRI) was used on 10 adolescents and 10 adults to contrast brain regions engaged by a masked emotional-face task (viewing a fixation cross and a series of masked happy and masked fearful faces), while blood oxygen level dependent signal was monitored by a 1.5-T MRI scanner. Brain regions differentially engaged in the 2 age groups were mapped by using statistical parametric mapping. Summed across groups, the contrast of masked face versus fixation-cross viewing generated activations in occipital-temporal regions previously activated in passive face-viewing tasks. Adolescents showed higher maxima for activations in posterior association cortex for 3 of the 4 statistical contrasts. Adolescents and adults differed in the degree to which posterior hemisphere brain areas were engaged by viewing masked facial displays of emotion.

Adolescent↗

PubMed2001

A 5-bp deletion in ELOVL4 is associated with two related forms of autosomal dominant macular dystrophy.

Stargardt-like macular dystrophy (STGD3, MIM 600110) and autosomal dominant macular dystrophy (adMD) are inherited forms of macular degeneration characterized by decreased visual acuity, macular atrophy and extensive fundus flecks. Genetic mapping data suggest that mutations in a single gene may be responsible for both conditions, already known to bear clinical resemblance. Here we limit the minimum genetic region for STGD3 and adMD to a 0.6-cM interval by recombination breakpoint mapping and identify a single 5-bp deletion within the protein-coding region of a new retinal photoreceptor-specific gene, ELOVL4, in all affected members of STGD3 and adMD families. Bioinformatic analysis of ELOVL4 revealed that it has homology to a group of yeast proteins that function in the biosynthesis of very long chain fatty acids. Our results are therefore the first to implicate the biosynthesis of fatty acids in the pathogenesis of inherited macular degeneration.

Amino Acid Sequence↗

PubMed2001

Learning to see: experience and attention in primary visual cortex.

The response properties of neurons in primary sensory cortices remain malleable throughout life. The existence of such plasticity, and the characteristics of a form of implicit learning known as perceptual learning, suggest that changes in primary sensory cortex may mediate learning. We explored whether modification of the functional properties of primary visual cortex (V1) accompanies perceptual learning. Basic receptive field properties, such as location, size and orientation selectivity, were unaffected by perceptual training, and visual topography (as measured by magnification factor) was indistinguishable between trained and untrained animals. On the other hand, the influence of contextual stimuli placed outside the receptive field showed a change consistent with the trained discrimination. Furthermore, this property showed task dependence, only being manifest when the animal was performing the trained discrimination.

Animals↗

PubMed2001

Interplay between insulin and nutrients in the regulation of translation factors.

Protein synthesis in mammalian cells is regulated through alterations in the states of phosphorylation of eukaryotic initiation factors and elongation factors (eIFs and eEFs respectively) and of other regulatory proteins. This modulates their activities or their abilities to interact with one another. Insulin activates several of these proteins including the following: the guanine-nucleotide exchange factor eIF2B; the eIF4F complex, which (through eIF4E) interacts with the cap of the mRNA; p70 S6 kinase; and elongation factor eEF2, which mediates the translocation step of elongation. Control of the last three of these is linked to mTOR (mammalian target of rapamycin). In Chinese hamster ovary cells, regulation of all these proteins by insulin is modulated by the presence of amino acids and/or glucose in the medium. For example, p70 S6 kinase activity declines in the absence of amino acids and cannot be stimulated by insulin under this condition. The readdition of amino acids, especially leucine, restores activity and sensitivity to insulin. With eIF2B and eEF2, both amino acids and glucose must be provided for insulin to regulate their activities. In contrast, insulin-stimulation of the formation of eIF4F complexes requires glucose but not amino acids. Glucose metabolism is required for this permissive effect. Our recent studies have also identified the mechanism by which mTOR signalling regulates the phosphorylation of eEF2. eEF2 kinase is phosphorylated by p70 S6 kinase at Ser-366; this results in the inactivation of eEF2 kinase, especially at low (micromolar) Ca concentrations.

Adaptor Proteins, Signal Transducing↗

PubMed2001

The p38-MAPK/SAPK pathway is required for human keratinocyte migration on dermal collagen.

Human keratinocyte motility plays an important role in the re-epithelialization of human skin wounds. The wound bed over which human keratinocytes migrate is rich in extracellular matrices, such as fibrin, fibronectin, and collagen, and serum factors, such as platelet-derived growth factor and transforming growth factor beta 1. Extracellular matrices and the serum factors bind to cell surface receptors and initiate a cascade of intracellular signaling events that regulate cell migration. In this study, we identified an intracellular signaling pathway that mediates collagen- driven motility of human keratinocytes. Pharmaco logic inhibition of the activation of p38-alpha and p38-beta mitogen-activated protein kinase activation potently blocked collagen-driven human keratinocyte migration. Transfection of the same keratinocytes with the kinase-negative mutants of p38-alpha or p38-beta mitogen-activated protein kinase markedly inhibited keratinocyte migration on collagen. Attachment of keratinocytes to collagen activated p38 mitogen- activated protein kinase, as well as p44/p42 ERKs. Interestingly, activation of the p38 mitogen-activated protein kinase cascade by overexpressing the constitutively active MKK3 and MKK6, MKK3b(E) and MKK6b(E), could neither initiate migration in the absence of collagen nor enhance collagen-driven migration. This study provides evidence that the p38-MAPK/SAPK pathway is necessary, but insufficient, for mediating human keratinocyte migration on collagen.

Calcium-Calmodulin-Dependent Protein Kinases↗

PubMed2001

Mutational analysis of RsrA, a zinc-binding anti-sigma factor with a thiol-disulphide redox switch.

In the Gram-positive bacterium, Streptomyces coelicolor A3(2), expression of the thioredoxin system is modulated by a sigma factor called sigmaR in response to changes in the cytoplasmic thiol-disulphide status, and the activity of sigmaR is controlled post-translationally by an anti-sigma factor, RsrA. In vitro, the anti-sigma factor activity of RsrA, which contains seven cysteines, correlates with its thiol-disulphide redox status. Here, we investigate the function of RsrA in vivo. A constructed rsrA null mutant had very high constitutive levels of disulphide reductase activity and sigmaR-dependent transcription, confirming that RsrA is a negative regulator of sigmaR and a key sensor of thiol-disulphide status. Targeted mutagenesis revealed that three of the seven cysteines in RsrA (C11, C41 and C44) were essential for anti-sigma factor activity and that a mutant RsrA protein containing only these three cysteines was active and still redox sensitive in vivo. We also show that RsrA is a metalloprotein, containing near-stoichiometric amounts of zinc. On the basis of these data, we propose that a thiol-disulphide redox switch is formed between two of C11, C41 and C44, and that all three residues play an essential role in anti-sigma factor activity in their reduced state, perhaps by acting as ligands for zinc. Unexpectedly, rsrA null mutants were blocked in sporulation, probably as a consequence of an increase in the level of free sigmaR.

Amino Acid Sequence↗

PubMed2001

Regulation of plant water loss by manipulating the expression of phospholipase Dalpha.

Phospholipase D (PLD) has been implicated in various processes, including signal transduction, membrane trafficking, and membrane degradation. Multiple forms of PLD with distinct biochemical properties have been described in the cell. In Arabidopsis, PLDalpha and PLDgamma, but not PLDbeta, were detected in guard cells, and antisense suppression resulted in a specific loss of PLDalpha. The abrogation of PLDalpha rendered plants less sensitive to abscisic acid and impaired stomatal closure induced by water deficits. PLDalpha-depleted plants exhibited accelerated transpirational water loss and a decreased ability to tolerate drought stress. Overexpression of PLDalpha enhanced the leaf's sensitivity to abscisic acid. These findings provide molecular and physiological evidence that PLDalpha plays a crucial role in regulating stomatal movement and plant-water status.

Abscisic Acid↗

PubMed2001

Global changes in interleukin-6-dependent gene expression patterns in mouse livers after partial hepatectomy.

Liver regeneration following 70% partial hepatectomy leads to rapid activation of genes in the remnant liver. Interleukin-6 deficient (IL-6 -/-) mice have impaired liver regeneration and abnormalities in immediate early gene expression. In this study, the gene expression program in the IL-6 +/+ and -/- livers at 2 hours posthepatectomy was examined with a cDNA array representing 588 highly regulated mouse genes. Thirty-six percent of the 103 immediate early genes were induced differently in IL-6 +/+ compared with IL-6 -/- livers, implying regulation by IL-6. IL-6 treatment of the IL-6 -/- mice in the absence of hepatectomy induced a much smaller set of genes in the liver, suggesting that IL-6 cooperates with other hepatectomy-induced factors to activate the large number of genes. Northern blot analyses were used to verify gene expression data obtained from the arrays. The expression of urokinase type plasminogen activator receptor (uPAR) and plasminogen activator inhibitor-1 (PAI-1), critical components of the urokinase plasminogen activator (uPA) system, was lower and delayed in IL-6 -/- livers. Despite the fact that active uPAR/uPA complex is critical for hepatocyte growth factor (HGF) activation, no differences were detected between the IL-6 +/+ and -/- livers in HGF activation as measured by receptor phosphorylation. On the contrary, the mitogen-activated protein kinase (MAPK) pathway was activated in IL-6 +/+ livers early during regeneration but remarkably delayed in IL-6 -/- livers. Defective liver regeneration may be explained by the large number of gene activation pathways altered in IL-6 -/- livers and further supports the finding that IL-6 is necessary for normal liver regeneration.

Animals↗

PubMed2001

Atrial and ventricular electromechanical function in 1-ventricle hearts: influence of atrial flutter and Fontan procedure.

OBJECTIVE: Echocardiography was used to study electromechanical atrial and ventricular function in adult patients with a 1-ventricle heart who were in sinus rhythm to better understand the recurrence of atrial flutter in these conditions. Patients who had recent atrial flutter, with and without the Fontan procedure, were compared with those who had no arrhythmia. METHODS: This was a prospective study that used M-mode and 2-dimensional Doppler echocardiography and electrocardiography. Conventional measurements were used to evaluate ventricular long-axis function. Basic data were drawn from case notes. The setting was a designated quaternary service for grown-up congenital heart patients (GUCH) in a tertiary referral center for cardiology and cardiac surgery. From January 1997 to February 1998, 26 consecutive adult patients (aged >16 years) with a heart with one functioning ventricle and a history of atrial flutter were studied: group 1, with non-Fontan palliative surgery or no surgery (10 patients), and group 2, with Fontan-type repair (16 patients). Also studied were 20 patients with a 1-ventricle heart but no history of atrial flutter. These 20 patients were divided into 2 groups: control 1, which comprised 14 patients with previous shunts or no surgery, and control 2, which consisted of 6 patients with Fontan repair. RESULTS: P-wave duration on the electrocardiogram was similar in the 4 patient groups, but the amplitude was reduced in group 2 and control 2 (patients with Fontan surgery) (P <.016). Bifid P wave was seen in 5 (50%) of 10 patients in group 1 and in 6 (43%) of 14 patients in control 1, but it was not seen in patients with Fontan (P <.01). Ventricular systolic and diastolic dimensions and fractional shortening were not different between patients and controls. Right atrial transverse dimensions were greater in group 2 patients compared with those in controls. Significant atrioventricular valve regurgitation was seen in 9 of 10 group 1 patients but in none of the others. Right-sided total long-axis excursion and atrial A-wave amplitude were depressed in group 2 patients compared with the values in the others. The onset of right atrial shortening was delayed by 50 ms in group 2 compared with control 2, whereas the left atrial shortening was delayed by 30 ms in group 1 compared with control 1. This particular disturbance remained 6 months after cardioversion. CONCLUSION: In 1-ventricle hearts, significant atrioventricular valve regurgitation is commonly associated with atrial flutter in patients who did not undergo the Fontan procedure, and with electromechanical disturbances in those who did. Recognition of disturbances in ventricular long-axis function may thus assist in the identification of patients with a 1-ventricle heart who are prone to atrial flutter.

Adolescent↗

PubMed2001

Disturbed atrioventricular electromechanical function long after Mustard operation for transposition of great arteries: a potential contributing factor to atrial flutter.

OBJECTIVE: The objectives were to study atrial and ventricular electromechanical function in patients long after Mustard repair for transposition of great arteries and to identify possible causes and physiologic disturbances in those with recurrent atrial flutter. METHODS: Electromechanical atrial and ventricular function was assessed in 22 patients (11 women) aged 27 +/- 5 years, 10 to 29 (mean 24) years after initial Mustard operation with electrocardiography and echocardiography. The study subjects involved 12 patients with documented atrial flutter and the remaining 10 without history of atrial arrhythmia served as controls. All patients were studied while in sinus rhythm. RESULTS: There was no difference in age, gender, or age at original Mustard surgery between the 2 patient groups. The P wave and QRS duration were significantly broader in patients compared with controls (128 +/- 14 ms vs 100 +/- 10 ms, P <.05 and 120 +/- 20 ms vs 93 +/- 6 ms, P <.01). Right ventricular end diastolic dimension was not different, whereas left ventricular fraction shortening was less (20% +/- 10% vs 35% +/- 12%, P <.01) in the patient group. Left and septal total ventricular long axes amplitude were significantly lower in patients compared with controls (1.4 +/- 0.4 cm vs 1.7 +/- 0.3 cm, P <.05 and 0.6 +/- 0.2 cm vs 1.0 +/- 0.3 cm, P <.01). Right-sided total long axis excursion was equally reduced in the 2 groups (1.0 +/- 0.3 cm). Septal and right-sided but not left-sided "a" wave was smaller in the patients (1.2 +/- 1 mm vs 3 +/- 1.2 mm, P <.001 and 1 +/- 1.3 mm vs 3 +/- 0.9 mm, P <.01). Right atrial electromechanical delay was significantly longer in patients with respect to controls (110 +/- 14 ms vs 84 +/- 25 ms, P <.001), but on the left there was no difference. The P wave duration correlated closely with right atrial electromechanical delay, r = 0.79, P <.003. Significant tricuspid regurgitation was found in 9 of 12 patients but none of the controls. CONCLUSION: Right ventricular dysfunction is present long after Mustard operation for transposition of great arteries whether flutter occurs. However, in patients with history of atrial flutter, evidence of left ventricular dysfunction, significant tricuspid regurgitation, impaired right atrial electrical and mechanical function, and reversed onset of atrial systole is also present. The consistent association of the disturbed atrial and ventricular electromechanical behavior suggests a multifactorial etiology for atrial arrhythmia.

Adult↗

PubMed2001

Molecular dynamics simulations of the denaturation and refolding of an RNA tetraloop.

Tetraloops are very abundant structural elements of RNA that are formed by four nucleotides in a hairpin loop which is closed by a double stranded helical stem with some Watson-Crick base pairs. A tetraloop r(GCGAAGGC) was identified from the crystal structure of the central domain of 16S rRNA (727-730) in the Thermus thermophilus 30S ribosomal complex. The crystal structure of the 30S complex includes a total of 104 nucleotides from the central domain of the 16S rRNA and three ribosomal proteins S6, S15 and S18. Independent biochemical experiments have demonstrated that protein S15 plays the role in initiating the formation of the central domain of this complex. In the crystal, the tetraloop interacts with the protein S15 at two sites: one of them is associated with hydrogen bond interactions between residue His50 and nucleotide G730, and the other is associated with the occurrence of residue Arg53 beside A728. This paper uses molecular dynamics (MD) simulations to investigate the protein-dependent structural stability of the tetraloop and demonstrates the folding pathway of this tetraloop via melting denaturation and its subsequent refolding. Three important results are derived from these simulations: (i) The stability of nucleotide A728 appears to be protein dependent. Without the interaction with S15, A728 flips away from stacking with A729. (ii) The melting temperature demonstrated by the simulations is analogous to the results of thermodynamic experiments. In addition, the simulated folding of the tetraloop is stepwise: the native shape of the backbone is formed first; this is then followed by the formation of the Watson- Crick base pairs in the stem; and finally the hydrogen bonds and base stacking in the loop are formed. (iii) The tetraloop structure is similar to the crystal structure at salt concentrations of 0.1 M and 1.0 M used for the simulations, but the refolded structure at 0.1 M salt is more comparable to the crystal structure than at 1.0 M. The results from the simulations using both the Generalized Born continuum model and explicit solvent model (Particle Mesh Ewald) generate a similar pathway for unfolding/refolding of the tetraloop.

Arginine↗

PubMed2001

The Chinese version of the Parenting Stress Index: a psychometric study.

UNLABELLED: This study examined the psychometric properties of a Chinese version of the Parenting Stress Index/Short Form (PSI/SF). A 15-item simplified PSI/SF (S-PSI/SF) was subsequently developed which maintained a level of reliability and validity similar to the full version. The Chinese PSI/SF was tested on 149 parents (100 mothers, 49 fathers) of pediatric cancer patients in Taiwan. Psychometric testing was conducted using item analysis, Cronbach's alpha and confirmatory factor analysis. The S-PSI/SF was constructed based on the item analysis of the PSI/SF. Both the PSI/SF and S-PSI/SF produced good reliability coefficients. Confirmatory factor analyses indicated that both PSI/SF and S-PSI/SF met all criteria for goodness of fit. Compared with the PSI/SF, the S-PSI/SF demonstrated better internal consistency and overall fit at the one-subscale level, and satisfactory overall fit at two- and three-subscale levels. Despite the limited number of items included, the S-PSI/SF had a very good factor structure. No gender difference in parenting distress index was observed between mothers and fathers of pediatric cancer patients. CONCLUSION: The 15-item S-PSI/SF is a brief, easily administered instrument that has evidence of reliability and validity in Taiwanese parents of children with cancer. It could serve as a valuable assessment tool in clinical practice to identify parenting stress with a need for intervention.

Adolescent↗

PubMed2001

Quinquenoside L9 from leaves and stems of Panax quinquefolium L.

During additional chemical investigation on the saponin composition of leaves and stems of Panax quinquefolium L, a new minor dammarane saponin, quinquenoside L9 (1) has been obtained. By means of physico-chemical evidences and spectral analysis, its structure was elucidated 6-O-[alpha-L-rhamnopyranosyl-(1-2)-beta-D-glucopyranosyl]-dammara-3beta, 6beta,12beta,20(S),24zeta,25-hexaol (1).

Chromatography, Gel↗

PubMed2001

Triterpenoid saponins from leaves and stems of Panax quinquefolium L.

In the chemical investigation on the saponin composition of leaves and stems of Panax quinquefolium L., two new minor dammarane saponins, quinquenoside L1 (1) and L2 (2) have been isolated. By means of physico-chemical evidences and spectral analysis their structures were established as 3-O-[beta-D-glucopyranosyl-(1-2)-beta-D-glucopyranosyl]-20-O-beta-D-glucopyranosyl-dammara-23,25-diene-3beta, 12beta, 20(S)-triol (1) and 3-O-[beta-D-glucopyranosyl-(1-2)-beta-D-glucopyranosyl]-20-O-beta-D-glucopyranosyl-(24Z)-dammar-24-ene-3beta, 12beta, 20(S), 26-tetraol (2).

Carbohydrate Sequence↗