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Biomedical subjects

X Hu

Publications and source records attributed to X Hu.

At least 199 records · Page 11Linked to original sources
PubMed1999

An extension of a phenomenological model for dental composites.

OBJECTIVES: The aims of this study are firstly to demonstrate the limitations of a phenomenological model proposed for filler/resin dental composites, and secondly, to modify the model to accommodate these limitations. METHODS: A power-law rule of mixtures (ROM) is established by a simple modification of the elastic contact mechanics. A scaling parameter from the modification links the composite modulus Ec to the filler and resin moduli, Ef and Er. Computer simulation results available in the literature are used to determine the scaling parameter. Difference between the previous phenomenological model and the current approach is evaluated using correlation coefficients and standard errors. RESULTS: The results demonstrate that the previous phenomenological model is deficient if the modulus ratio Ef/Er is higher than 10 (the normal Ef/Er ratio for filler/resin dental composites is around 20-30). A modified approach keeps the simplicity of the previous model, gives much improved predictions for composite moduli and satisfies the boundary conditions for bulk filler and resin materials. SIGNIFICANCE: Dental researchers investigating a variety of combinations of different fillers and resins can have accurate first-hand estimates of the potential composite modulus even before the composites are actually made. Therefore, the dental researchers will be able to tailor their composite modulus more purposefully to match either the dentin or enamel modulus. Such a useful design tool would obviously promote much wanted further research and application of polymeric dental composites.

Composite Resins↗
PubMed1999

The influence of cyclic loading on the wear of a dental composite.

The load applied to a tooth surface during mastication is not a constant force and the objective of the research reported in this paper was to evaluate the impact of variable masticatory loads on the mechanisms involved in the wear of a dental composite. A new wear testing machine has therefore been developed, which incorporates a sine cam mechanical system to generate an alternating sine curve load at the wear surfaces to simulate the loading produced by masticatory process. The basic wear pattern is generated by positioning a disc shaped specimen against a rotating cylindrical ring with a normal load applied to the upper surface of the specimen. This approach allows different combinations of static and sine curve loads to be applied, thereby facilitating the study of different wear situations. It was found that the wear behaviour associated with variable loading patterns differed from that of static loading.

Composite Resins↗
PubMed1999

Transforming growth factor beta inhibits growth of more differentiated myeloid leukemia cells and retinoblastoma protein phosphorylation at serine 795.

Transforming growth factor beta (TGF-beta) has been shown to be a specific inhibitor of early human myeloid progenitors. We show here that TGF-beta1 potentially inhibited not only the growth of primitive but also more mature myeloid leukemic cells. Surprisingly, those apparently more mature progenitor cells, such as MV4-11 and Mo7e cells, are very sensitive to the action of TGF-beta. The addition of TGF-beta1 to liquid cultures of these cells significantly inhibited their proliferation, with as much as 72% inhibition of growth of MV4-11 cells. The suppressive effect by TGF-beta1 was not reversed or prevented by granulocyte-macrophage colony-stimulating factor or interleukin 3 used to promote cell growth in TF-1a and MV4-11 cells. TGF-beta1 completely abolished the clonal growth of MV4-11 cells in soft agar and inhibited Mo7e, KG-1, K562, TF-1, and TF-1a colony growth by 99%, 90%, 63%, 53%, and 43%, respectively. The cells treated with TGF-beta1 showed progressive accumulation in the G1 phase of cell cycle. Maximal G1 arrest (93%) was observed in MV4-11 cells. Using anti-retinoblastoma protein (pRb) and anti-specific phosphorylated-pRb antibodies, we demonstrated that TGF-beta1 greatly inhibited pRb phosphorylation at serine 795 in MV4-11 and Mo7e cells. Taken together, our data suggest that the sensitivity of myeloid leukemic progenitor cells to growth inhibition by TGF-beta may not be inversely correlated with their maturation stage, and the inhibition of the cells appeared to be linked to the suppression of pRb phosphorylation at serine 795.

Cell Differentiation↗
PubMed1999

A hybrid technique for spectroscopic imaging with reduced truncation artifact.

Traditionally, Fourier spectroscopic imaging is associated with a small k-space coverage which leads to truncation artifacts such as "bleeding" and ringing in the resultant image. Because substantial truncation artifacts mainly arise from regions having intense signals, such as the subcutaneous lipid in the head, effective reduction of truncation artifacts can be achieved by obtaining an extended k-space coverage for these regions. In this paper, a hybrid technique which employs phase-encoded spectroscopic imaging (SI) to cover the central portion of the k-space and echo-planar spectroscopic imaging (EPSI) to measure the peripheral portion of the k-space is developed. EPSI, despite its inherently low SNR characteristics, provides a sufficient SNR for outer high-spatial frequency components of the aforementioned high signal regions and supplies an extended k-space coverage of these regions for the reduction of truncation artifacts. The data processing includes steps designed to remove inconsistency between the two types of data and a previously described technique for selectively retaining only outer k-space information for the high signal regions during the reconstruction. Experimental studies, in both phantoms and normal volunteers, demonstrate that the hybrid technique provides significant reduction in truncation artifacts.

Artifacts↗
PubMed1999

Effect of lidocaine on improving cerebral protection provided by retrograde cerebral perfusion: a neuropathologic study.

OBJECTIVE: To determine whether lidocaine can improve the neuropathologic results in canine brains after retrograde cerebral perfusion (RCP). DESIGN: Randomized, blinded, experimental study. SETTING: University animal laboratory. PARTICIPANTS: Mongrel dogs. INTERVENTIONS: Fourteen mongrel dogs were placed on 120 minutes of hypothermic (20 degrees C) RCP. Following the RPC, they then resumed cardiopulmonary bypass and rewarming for 60 minutes. In the lidocaine group (n = 8), lidocaine was administered continuously; in the control group (n = 6), normal saline was administered. Cerebral perfusion fixation was performed at the end of the experiment. MEASUREMENTS AND MAIN RESULTS: The number of ischemic cells in 200 neurons was counted in the parietal cortex, CA1 sector of the hippocampus, CA3 sector of the hippocampus, ventral posterolateral nucleus of the thalamus, and Purkinje cells of the cerebellar cortex. Those in the parietal cortex, CA1 sector of the hippocampus, and ventral posterolateral nucleus of the thalamus were significantly less in the lidocaine group than in the control group (25.8+/-17.3 v 53.7+/-12.0; p < 0.01; 17.0+/-8.5 v 54.7+/-22.1; p < 0.01; and 16.9+/-17.8 v 49.7+/-28.4; p < 0.05, respectively). The total number of ischemic cells in the five examined regions was also significantly less in the lidocaine group than in the control group (89.5+/-19.4 v 219.5+/-45.5; p < 0.01). CONCLUSION: Continuous lidocaine significantly alleviated the ischemic neuropathologic injury after RCP and thus possibly improved cerebral protection.

Anesthetics, Local↗
PubMed1999

Specificity of murine glutathione S-transferase isozymes in the glutathione conjugation of (-)-anti- and (+)-syn-stereoisomers of benzo[g]chrysene 11,12-diol 13,14-epoxide.

Specificities of murine glutathione (GSH) S-transferase (GST) isozymes mGSTA1-1, mGSTA2-2, mGSTA3-3 and mGSTA4-4 (alpha class), mGSTP1-1 (pi class) and mGSTM1-1 (mu class) for GSH conjugation of (-)-anti- and (+)-syn-stereoisomers of benzo[g]chrysene 11, 12-diol 13,14-epoxide (B[g]CDE), the activated metabolites of the environmental pollutant benzo[g]chrysene (B[g]C), have been determined. When GST activity was determined as a function of varying (-)-anti- or (+)-syn-B[g]CDE concentration (10-320 microM) at a fixed saturating concentration of GSH (2 mM), each isozyme obeyed Michaelis-Menten kinetics. mGSTA1-1 was significantly more efficient than other murine GSTs in the GSH conjugation of not only (-)-anti-stereoisomer but also (+)-syn-B[g]CDE. For example, the catalytic efficiency (k(cat)/K(m)) of mGSTA1-1 towards (-)-anti-B[g]CDE was approximately 2.3- to 16.6-fold higher compared with other murine GSTs. Likewise, mGSTA1-1 was approximately 2.7-, 6.7-, 4.4- and 12.4-fold more efficient than mGSTA2-2, mGSTA3-3, mGSTP1-1 and mGSTM1-1, respectively, in catalyzing the GSH conjugation of (+)-syn-B[g]CDE. Interestingly, mGSTA4-4, which also belongs to class alpha, was virtually inactive towards both stereoisomers of B[g]CDE. The results of the present study indicate that murine GSTs, especially alpha class isozymes, significantly differ in their ability to detoxify B[g]CDE stereoisomers and that mGSTA1-1 plays a major role in the detoxification of both (-)-anti- and (+)-syn-B[g]CDE, which among four B[g]CDE stereoisomers are formed from the carcinogen B[g]C as major DNA binding metabolites.

Animals↗
PubMed1999

Activation of a delayed-early gene encoding MHR3 by the ecdysone receptor heterodimer EcR-B1-USP-1 but not by EcR-B1-USP-2.

MHR3, a homolog of the retinoid orphan receptor (ROR), is a transcription factor in the nuclear hormone receptor family that is induced by 20-hydroxyecdysone (20E) in the epidermis of the tobacco hornworm, Manduca sexta. Its 2.7-kb 5' flanking region was found to contain four putative ecdysone receptor response elements (EcREs) and a monomeric (GGGTCA) nuclear receptor binding site. Activation of this promoter fused to a chloramphenicol acetyltransferase (CAT) reporter by 2 micrograms of 20E per ml in Manduca GV1 cells was similar to that of endogenous MHR3, with detectable CAT by 3 h. When the ecdysone receptor B1 (EcR-B1) and Ultraspiracle 1 (USP-1) were expressed at high levels under the control of a constitutive promoter, CAT levels after a 3-h exposure to 20E increased two- to sixfold. In contrast, high expression of EcR-B1 and USP-2 caused little increase in CAT levels in response to 20E. Moreover, expression of USP-2 prevented activation by EcR-B1-USP-1. Deletion experiments showed that the upstream region, including the three most proximal putative EcREs, was responsible for most of the 20E activation, with the EcRE3 at -671 and the adjacent GGGTCA being most critical. The EcRE1 at -342 was necessary but not sufficient for the activational response but was the only one of the three putative EcREs to bind the EcR-B1-USP-1 complex in gel mobility shift assays and was responsible for the silencing action of EcR-B1-USP-1 in the absence of hormone. EcRE2 and EcRE3 each specifically bound other protein(s) in the cell extract, but not EcR and USP, and so are not EcREs in this cellular context. When cell extracts were used, the EcR-B1-USP-2 heterodimer showed no binding to EcRE1, and the presence of excess USP-2 prevented the binding of EcR-B1-USP-1 to this element. In contrast, in vitro-transcribed-translated USP-1 and USP-2 both formed heterodimeric complexes with EcR-B1 that bound ponasterone A with the same Kd (7 x 10(-10) M) and bound to both EcRE1 and heat shock protein 27 EcRE. Thus, factors present in the cell extract appear to modulate the differential actions of the two USP isoforms.

Animals↗
PubMed1999

A novel role for helix 12 of retinoid X receptor in regulating repression.

Nutrients, drugs, and hormones influence transcription during differentiation and metabolism by binding to high-affinity nuclear receptors. In the absence of ligand, some but not all nuclear receptors repress transcription as a heterodimer with retinoid X receptor (RXR). Here we define a novel role for helix 12 (H12) in sterically masking the corepressor (CoR) binding site in apo-RXR. Removing H12 converts RXR to a potent transcriptional repressor. The length but not the specific sequence of H12 is critical for masking RXR's intrinsic repression function. This contrasts with the amphipathic character required for mediating ligand-dependent activation and coactivator recruitment. Physiologically, we show that heterodimerization of RXR with apo-thyroid hormone receptor (TR) unmasks the CoR binding site in RXR and allows the TR-RXR heterodimer to repress. A molecular mechanism that involves sequence-specific interaction between RXR H12 and the coactivator-binding surface of the nuclear receptor is proposed for this heterodimerization-mediated unmasking. Peroxisome proliferator-activated receptor gamma does not interact as well with RXR H12, thus explaining its inability to repress transcription as an RXR heterodimer. The requirement to unmask RXR's latent repression function explains why only certain RXR partners repress transcription.

Amino Acid Sequence↗
PubMed1999

Insulin-like growth factor I stimulates cardiac myosin heavy chain and actin synthesis in the awake rat.

To determine the effect of insulin-like growth factor I (IGF-I) on cardiac contractile protein synthesis in vivo, we measured L-[ring-2, 6-3H]phenylalanine incorporation into myosin heavy chain and actin during intravenous infusions (4 h) of either saline or IGF-I (1 microgram. kg-1. min-1) in awake rats. After an overnight fast, IGF-I increased myosin synthesis by 29% compared with saline (11.5 +/- 0.8 vs. 8.9 +/- 0.6%/day, P < 0.01) and actin synthesis by 26% (7.2 +/- 0.3 vs. 5.7 +/- 0.3%/day, P < 0.01), with similar effects in left and right ventricles and a comparable effect on mixed cardiac protein. When amino acids were infused with IGF-I, a further increase in myosin synthesis was observed (P < 0.01). In fed rats, despite higher baseline synthesis rates than in fasted rats (P < 0. 01), IGF-I also increased the synthesis of myosin (12.3 +/- 0.5 vs. 9.9 +/- 0.5%/day, P < 0.01) and actin (8.8 +/- 0.3 vs. 7.5 +/- 0. 2%/day, P < 0.01) compared with saline. IGF-I infusion had no hypoglycemic effect and did not change heart rate or blood pressure. Thus relatively low-dose IGF-I has a direct action in vivo to acutely increase heart contractile protein synthesis in both fasted and fed awake rats.

Actins↗
PubMed1999

Direct visualization of organ of corti kinematics in a hemicochlea.

The basilar membrane in the mammalian cochlea vibrates when the cochlea receives a sound stimulus. This mechanical vibration is transduced into hair cell receptor potentials and thereafter encoded by action potentials in the auditory nerve. Knowledge of the mechanical transformation that converts basilar membrane vibration into hair cell stimulation has been limited, until recently, to hypothetical geometric models. Experimental observations are largely lacking to prove or disprove the validity of these models. We have developed a hemicochlea preparation to visualize the kinematics of the cochlear micromechanism. Direct mechanical drive of 1-2 Hz sinusoidal command was applied to the basilar membrane. Vibration patterns of the basilar membrane, inner and outer hair cells, supporting cells, and tectorial membrane have been recorded concurrently by means of a video optical flow technique. Basilar membrane vibration was driven in a direction transversal to its plane. However, the direction of the resulting vibration was found to be essentially radial at the level of the reticular lamina and cuticular plates of inner and outer hair cells. The tectorial membrane vibration was mainly transversal. The transmission ratio between cilia displacement of inner and outer hair cells and basilar membrane vibration is in the range of 0.7-1.1. These observations support, in part, the classical geometric models at low frequencies. However, there appears to be less tectorial membrane motion than predicted, and it is largely in the transversal direction.

Animals↗
PubMed1999

Selectin blockade prevents antigen-induced late bronchial responses and airway hyperresponsiveness in allergic sheep.

Antigen challenge can elicit an allergic inflammatory response in the airways that involves eosinophils, basophils, and neutrophils and that is expressed physiologically as a late airway response (LAR) and airway hyperresponsiveness (AHR). Although previous studies have suggested that E-selectin participates in these allergic airway responses, there is little information concerning the role of L-selectin. To address this question, we examined the effects of administering an L-selectin-specific monoclonal antibody, DU1-29, as well as three small molecule selectin binding inhibitors, on the development of early airway responses (EAR), LAR and AHR in allergic sheep undergoing airway challenge with Ascaris suum antigen. Sheep treated with aerosol DU1-29 before antigen challenge had a significantly reduced LAR and did not develop postchallenge AHR. No protective effect was seen when sheep were treated with a nonspecific control monoclonal antibody. Treatment with DU1-29 also reduced the severity of the EAR to antigen. Similar results were obtained with each of the three small molecule selectin inhibitors at doses that depended on their L-, but not necessarily E-selectin inhibitory capacity. The inhibition of the EAR with one of the inhibitors, TBC-1269, was associated with a reduction in histamine release. Likewise, treatment with TBC-1269 reduced the number of neutrophils recovered in bronchoalveolar lavage (BAL) during the time of LAR and AHR. TBC-1269, given 90 min after antigen challenge also blocked the LAR and the AHR, but this protection was lost if the treatment was withheld until 4 h after challenge, a result consistent with the proposed time course of L-selectin involvement in leukocyte trafficking. These are the first data indicating that L-selectin may have a unique cellular function that modulates allergen-induced pulmonary responses.

Aerosols↗
PubMed1999

Coactivators for the orphan nuclear receptor RORalpha.

A mutation in the nuclear orphan receptor RORalpha results in a severe impairment of cerebellar development by unknown mechanisms. We have shown previously that RORalpha contains a strong constitutive activation domain in its C terminus. We therefore searched for mammalian RORalpha coactivators using the minimal activation domain as bait in a two-hybrid screen. Several known and putative coactivators were isolated, including glucocorticoid receptor-interacting protein-1 (GRIP-1) and peroxisome proliferator-activated receptor (PPAR)-binding protein (PBP/TRAP220/DRIP205). These interactions were confirmed in vitro and require the intact activation domain of RORalpha although different requirements for interaction with GRIP-1 and PBP were detected. Even in the absence of exogenous ligand, RORalpha interacts with a complex or complexes of endogenous proteins, similar to those that bind to ligand-occupied thyroid hormone and vitamin D receptors. Both PBP and GRIP-1 were shown to be present in these complexes. Thus we have identified several potential RORalpha coactivators that, in contrast to the interactions with hormone receptors, interact with RORalpha in yeast, in bacterial extracts, and in mammalian cells in vivo and in vitro in the absence of exogenous ligand. GRIP-1 functioned as a coactivator for the RORalpha both in yeast and in mammalian cells. Thus, GRIP-1 is the first proven coactivator for RORalpha.

ATPases Associated with Diverse Cellular Activitie↗
PubMed1999

Multinomial processing tree models: an implementation.

Multinomial processing tree (MPT) models have been widely used by researchers in cognitive psychology. This paper introduces MBT.EXE, a computer program that makes MPT easy to use for researchers. MBT.EXE implements the statistical theory developed by Hu and Batchelder (1994). This user-friendly software can be used to construct MPT models and conduct statistical inferences, including point and interval estimation, hypothesis testing, and goodness of fit. Furthermore, this program can be used to examine the robustness of MPT models. Algorithms for parameter estimation, hypothesis testing, and Monte Carlo simulation are presented.

Algorithms↗
PubMed1999

GPT.EXE: a powerful tool for the visualization and analysis of general processing tree models.

This paper introduces GPT.EXE, a computer program for designing and implementing general processing tree (GPT) models. First, designing and building GPT models using this program is discussed. The second major emphasis is a description of various statistical procedures that can be carried out with GPT.EXE. There is also a brief section on the on-line documentation of this program. Throughout the text, pictures of windows from the program are displayed to help explain the procedures being described by the text.

Cognition↗
PubMed1999

Neural correlates of visual form and visual spatial processing.

Cortico-cortical projections for visual processing that originate from the striate cortex are organized into two streams. The dorsal stream projects to the parietal region and the ventral stream to the inferior temporal region. One hypothesis is that the dorsal stream processes visual spatial information, and the ventral stream processes visual object information. Although recognition of human faces or common objects has been shown preferentially to activate the ventral stream, the issue of when such processing starts to engage the ventral or the dorsal stream is not clear. The question explored in this study is whether processing of visual form per se without evoking the brain mechanisms that are associated with recognition of human faces or common objects is sufficient to activate the ventral stream more significantly relative to the condition when only visual spatial processing is involved. Functional magnetic resonance images were acquired while subjects performed a delayed comparison task in which either visual spatial or visual form information was processed. Cortical areas that were preferentially activated in visual spatial or visual form processing showed not only ventral-dorsal segregation, but also hemispheric laterality. The results extended previous findings by showing that preferential activation in the ventral pathway is not contingent upon such powerful stimuli as faces and common objects. Processing of simple visual form information is cause enough for such activation to be observed. A strong left hemisphere dominance in visual form recognition was also revealed. The observed laterality may be a reflection that the left hemisphere is more important in symbolic and/or semantic coding of visual form information.

Adult↗
PubMed1999

[An investigation of small marker chromosome in eight Turner syndrome patients by fluorescence in situ hybridization and DNA analysis].

OBJECTIVE: To direct genetic counseling and identify the origin of small marker chromosome in patients with Turner syndrome stigmata. METHODS: The specific primer on the sex determining region on Y (SRY) and biotin labeled X- and Y-chromosome DNA probes were utilized in the analysis of sex chromosome-derived markers. The PCR product from the amplification was detected on agarose gel, and fluorescence in situ hybridization (FISH) was conducted to metaphase chromosome. RESULTS: In 8 patients who had a small marker chromosome, five markers were derived from the X chromosome and three from the Y chromosome. Two patients with a Y-derived marker were determined by Y-chromosome probe as well as by SRY sequences amplification. One patient with a Y-derived marker was only demonstrated by FISH. CONCLUSION: The findings of this study demonstrate successfully the value and necessity of FISH utilizing DNA probes combined with specific amplification on SRY gene in the identification of sex chromosome marker. Such identification is important not only for clinical care, but also for understanding phenotype-karyotype correlations.

DNA-Binding Proteins↗
PubMed1999

[Investigation of erythrocyte immune function of patients with endometriosis].

OBJECTIVE: To study erythrocyte immune function of patients with endometriosis and explore the pathogenesis of endometriosis. METHODS: 38 patients with endometriosis diagnosed by laparoscopy or laparotomy and 21 normal women as the control were studied. The patients were divided into three groups by revised American Fertility Society (RAFS) classification: group one (stage I, II; n = 13), group two(stage III, n = 15), and group three(stage IV, n = 10). Using rosette formation test and polyethyleneglycol sedimentation methods, the erythrocyte immune function including C3b receptor rosette rate (C3bRR), immune complex rosette rate(ICR), erythrocyte rosette forming enhancing rate (RFER) and inhibitory rate (RFIR), and circulatory immune complex (CIC) was determined. RESULTS: The C3bRR, ICR, and RFER of group one, two, and three were decreased (P < 0.05 or P < 0.01), and RFIR and CIC of group one, two, and three were increased (P < 0.05) when compared with those of the control. All parameters had no significant difference among group one, two and three. In addition, these parameters had no significant difference in infertile groups of endometriosis as compared with those of fertile group. CONCLUSION: The erythrocyte immune function of patients with endometriosis is depressed, resulting from decreased erythrocyte immune adherence enhancer and increased inhibitor. These changes of erythrocyte immune function may be related to the pathogenesis of endometriosis.

Adult↗