Biomedical subjects

H Mao

Publications and source records attributed to H Mao.

At least 19 recordsLinked to original sources

PubMed2002

Electrorheological fluid under elongation, compression, and shearing.

Electrorheological (ER) fluid based on zeolite and silicone oil under elongation, compression, and shearing was investigated at room temperature. Dc electric fields were applied on the ER fluid when elongation and compression were carried out on a self-constructed test system. The shear yield stress, presenting the macroscopic interactions of particles in the ER fluid along the direction of shearing and perpendicular to the direction of the electric field, was also obtained by a HAAKE RV20 rheometer. The tensile yield stress, presenting the macroscopic interactions of particles in the ER fluid along the direction of the electric field, was achieved as the peak value in the elongating curve with an elongating yield strain of 0.15-0.20. A shear yield angle of about 15 degrees -18.5 degrees reasonably connected tensile yield stress with shear yield stress, agreeing with the shear yield angle tested well by other researchers. The compressing tests showed that the ER fluid has a high compressive modulus under a small compressive strain lower than 0.1. The compressive stress has an exponential relationship with the compressive strain when it is higher than 0.1, and it is much higher than shear yield stress.

Journal Article↗

PubMed2002

The ability of an HSV strain to initiate zosteriform spread correlates with its neuroinvasive disease potential.

The requirements for disease development in the mouse epidermal scarification-zosteriform model of HSV infection are likely to parallel those required for primary HSV disease of humans. HSV-1 strains, which are neuroinvasive in the mouse footpad model of HSV encephalitis, caused local site lesions within 3 days and secondary zosteriform lesions along the dermatome within approximately 5 days. HSV-1 strains, which are not neuroinvasive, failed to progress to zosteriform lesion development and local site lesions were mild or absent. Relative differences in the rate and extent of zosteriform lesion development paralleled the behavior of the viruses in the mouse footpad model of neuroinvasion. In conclusion, the viral properties which are important for neuroinvasiveness appear to also determine the ability of an HSV strain to cause zosteriform disease.

Animals↗

PubMed2001

Spectroscopic studies of the vibrational and electronic properties of solid hydrogen to 285 GPa.

We report Raman scattering and visible to near-infrared absorption spectra of solid hydrogen under static pressure up to 285 GPa between 20 and 140 K. We obtain pressure dependences of vibron and phonon modes consistent with results previously determined to lower pressures. The results indicate the stability of the ordered molecular phase III to the highest pressure reached and provide constraints on the insulator-to-metal transition pressure.

Journal Article↗

PubMed2001

Rational design of diflunisal analogues with reduced affinity for human serum albumin.

Many lead compounds bind to serum albumin and exhibit markedly reduced efficacy in vivo as compared to their potency in vitro. To aid in the design of compounds with reduced albumin binding, we performed nuclear magnetic resonance (NMR) structural and binding studies on the complex between domain III of human serum albumin (HSA-III) and diflunisal, a cyclooxygenase inhibitor with antiinflammatory activity. The structural studies indicate that the aromatic rings of diflunisal are involved in extensive and specific interactions with hydrophobic residues that comprise the binding pocket in subdomain IIIA. The carboxylic acid of diflunisal forms electrostatic interactions with the protein similar to those observed in the X-ray structure of HSA complexed to myristic acid. In addition to the structural studies, NMR-derived binding constants were obtained for diflunisal and closely related analogues to develop a structure-affinity relationship for binding to subdomain IIIA. On the basis of the structural and binding data, compounds were synthesized that exhibit more than a 100-fold reduction in binding to domain III of HSA, and nearly a 10-fold reduction in affinity for full length albumin. Significantly, several of these compounds maintain activity against cyclooxygenase-2. These results suggest a rational strategy for designing out albumin binding in potential drug molecules by using structure-based design in conjunction with NMR-based screening.

Amino Acid Sequence↗

PubMed2001

The context of uncertainty modulates the subcortical response to predictability.

Implicit motor learning tasks typically involve comparisons of subject responses during a sequence versus a random condition. In neuroimaging, brain regions that are correlated with a sequence are described, but the temporal relationship of sequence versus nonsequence conditions is often not explored. We present a functional magnetic resonance imaging (fMRI) study describing activation related to sequential predictability in an implicit sensorimotor learning task and the history (context) dependence of these effects. Participants regarded four squares displayed horizontally across a screen and pressed a button when any one of the four targets was illuminated in a particular color. A repeating spatial sequence with varying levels of predictability was embedded within a random color presentation. Both the right dorsolateral prefrontal cortex (R DLPFC) and right caudate displayed a positive correlation to increasing predictability, whereas the left posterior parietal cortex (L PPC) displayed a negative correlation. However, the activation changes within the caudate were significant when transitioning from high predictability to low predictability but not for the reverse case, suggesting a sensitivity not only to predictability but to order effects as well. These results support the hypothesized relationship between basal ganglia and visuomotor sequential learning, but demonstrate the importance of context upon sequence learning.

Adult↗

PubMed2001

Superconductivity in boron.

Metals formed from light elements are predicted to exhibit intriguing states of electronic order. Of these materials, those containing boron are of considerable current interest because of their relatively high superconducting temperatures. We have investigated elemental boron to very high pressure using diamond anvil cell electrical conductivity techniques. We find that boron transforms from a nonmetal to a superconductor at about 160 gigapascals (GPa). The critical temperature of the transition increases from 6 kelvin (K) at 175 GPa to 11.2 K at 250 GPa, giving a positive pressure derivative of 0.05 K/GPa. Although the observed metallization pressure is compatible with the predictions of first-principles calculations, superconductivity in boron remains to be explored theoretically. The present results constitute a record pressure for both electrical conductivity studies and investigations of superconductivity in dense matter.

Journal Article↗

PubMed2001

Fabrication of phospholipid bilayer-coated microchannels for on-chip immunoassays.

Herein we describe a new class of microfluidic immunoassays based upon solid supported lipid bilayers. Two-dimensionally fluid bilayer material, which can accommodate multivalent binding between surface-bound ligands and aqueous receptors, was coated on the surface of poly(dimethylsiloxane) microchannels. The bilayers contained dinitrophenyl (DNP)-conjugated lipids for binding with bivalent anti-DNP antibodies. Twelve independent data points of surface coverage versus bulk protein concentration could be made simultaneously by forming a linear array of channels and flowing fluorescently labeled antibodies into them. This enabled an entire binding curve to be obtained in a single experiment. The measured apparent binding constant for the DNP/anti-DNP system was 1.8 microM. The methodology for performing heterogeneous assays developed here not only produces rapid results but also requires much less protein than traditional procedures and eliminates some standard sources of experimental error.

Immunoassay↗

PubMed2001

Changes in BiP (GRP78) levels upon HSV-1 infection are strain dependent.

BiP (grp78) is a chaperone protein which can also regulate the unfolded protein response of the cell. Levels of BiP increased in cells infected by the small plaque producing, cell associated, neuroinvasive strains of HSV-1 (SP7, 490) but decreased in cells infected with KOS, a large plaque, attenuated strain. BiP protein synthesis continued early in infection and BiP was sequestered and its degradation was limited during SP7 infection. BiP protein synthesis stopped and the protein was degraded in KOS infected cells. These viral strain dependent differences in BiP concentration may influence other aspects of the viral interaction with the target cell and its host.

3T3 Cells↗

PubMed2001

Consolidation of human memory over decades revealed by functional magnetic resonance imaging.

Medial temporal lobe (MTL) lesions typically produce retrograde amnesia characterized by the disproportionate loss of recently acquired memories. Temporally graded memory loss is interpreted traditionally as evidence for a consolidation process guided by the MTL. Here, using functional magnetic resonance imaging (fMRI), we show temporally graded changes in MTL activity in healthy older adults taking a famous faces remote memory test. Evidence for temporally graded change in the hippocampal formation was mixed, suggesting it may participate only in consolidation processes lasting a few years. Entorhinal cortex was associated with temporally graded changes extending up to 20 years. These findings support the basic tenets of consolidation theory and suggest that the entorhinal cortex, rather than the hippocampal formation, participates in memory consolidation over decades.

Aged↗

PubMed2001

Loss of nm23 expression predicts distal metastases and poorer survival for breast cancer.

The nm23 gene, originally identified by differential hybridization of metastatic murine melanoma cell lines has been associated with decreased metastatic potential. In this study, we evaluated the utility of nm23 expression levels as a predictive and a prognostic biomarker for distal metastases and poor survival in a Chinese cohort of 168 breast cancer patients. Our study indicates that high nm23 expression is associated with older age (older than 35 years) and smaller tumor size. There is no statistically significant association between nm23 expression and pathologic type or axillary metastasis. High nm23 expression is associated with the absence of distal metastases. Nearly 80% of women with high nm23 expression are alive after 10 years compared to 25% with low expression; at five years the cumulative survival proportions are 86% and 46%, respectively. The Cox model for survival indicates that controlling for tumor size and presence of axillary metastases at diagnosis, the hazard for women with low nm23 expression is nearly 4 times that of women with high nm23 expression. Low nm23 expression is predictive of distal metastases and appears to be a risk factor that is independent of the presence or absence of positive axillary nodes at diagnosis.

Adult↗

PubMed2001

[Effects of vascular endothelial growth factor on adhesion molecular expression of hepatocellular carcinoma HepG].

OBJECTIVE: To study the effect of vascular endothelial growth factor (VEGF) on homotypic adhesion and E-cadherin of hepatocellular carcinoma cells. METHODS: We measured the function of homotypic adhesion with (3)H-TdR infiltration and the expression of E-cadherin with laser scanning confocal microscope. RESULTS: After 60, 90, 120min, the values (dpm/min) of (3)H-TdR infiltration in HepG(2) cells induced by 1ng/ml, 5ng/ml VEGF were 1758.67+/-289.46, 1380.03+/-328.55, 2657.43 +/- 310.31 and 3124.30+/-262.14, 2245.60+/-273.24, 2091.52+/-213.84. The values by 10ng/ml VEGF were 1232.32+/-201.04, 2337.50+/-333.04, 2236.99 +/- 237.07, which were significantly lower than those in control group (P<0.05 or 0.01). The expression of E-cadherin in hepatocellular carcinoma cells induced by 5ng/ml VEGF was 352+/-56 and much lower than that in control group (757+/-103, P<0.01). CONCLUSIONS: VEGF can decrease homotopic adhesion of hepatocellular carcinoma HepG(2) cell, which is connected with the less expression of E-cadherin in hepatocellular carcinoma HepG(2) cell.

Cadherins↗

PubMed2001

[Expression of nm23 in breast cancer: correlation with distant metastasis and prognosis].

OBJECTIVE: To investigate the relationship between expression of nm23 gene and distant metastasis and prognosis in breast cancer. METHODS: To detect nm23 protein expression in 101 patients with breast cancer by means of immunohistochemistry and nm23 mRNA expression in 68 patients with breast cancer by RT-PCR. RESULTS: Expression of nm23 gene was inversely correlated with distant metastasis and lymph node metastasis. Among 9 patients with negative node but with distant metastasis, 7 had low expression of nm23. In 29 patients with positive nodes but without distant metastasis, 24 had high expression of nm23, while 6 of 6 patients with positive nodes and distant metastasis expressed high levels of nm23 mRNA. CONCLUSION: Expression of nm23 gene, tumor size and status of axillary lymph node are independent prognostic indicators to breast cancer prognosis.

Adult↗

PubMed2000

Elasticity of MgO and a primary pressure scale to 55 GPa.

We have studied the elasticity and pressure-density equation of state of MgO in diamond cells to 55 GPa and have doubled the previous pressure limit of accurate elasticity determinations for crystals. Integrating single-crystal velocity data from Brillouin scattering measurements and density data from polycrystalline x-ray diffraction, we obtained the three principal elastic tensor elements (C(11), C(12), and C(44)) and various secondary elasticity parameters, including single-crystal elastic anisotropy, Cauchy relation, aggregate sound velocities, and Poisson's ratio, as functions of pressure. The present study also provides a direct determination of pressure without recourse to any prior pressure standard, thus creating a primary pressure scale. The commonly used ruby fluorescence pressure scale has thus been improved to 1% accuracy by the new MgO scale.

Journal Article↗

PubMed2000

Transformations in methane hydrates.

Detailed study of pure methane hydrate in a diamond cell with in situ optical, Raman, and x-ray microprobe techniques reveals two previously unknown structures, structure II and structure H, at high pressures. The structure II methane hydrate at 250 MPa has a cubic unit cell of a = 17.158(2) A and volume V = 5051.3(13) A(3); structure H at 600 MPa has a hexagonal unit cell of a = 11.980(2) A, c = 9.992(3) A, and V = 1241.9(5) A(3). The compositions of these two investigated phases are still not known. With the effects of pressure and the presence of other gases in the structure, the structure II phase is likely to dominate over the known structure I methane hydrate within deep hydrate-bearing sediments underlying continental margins.

Journal Article↗

PubMed2000

Moissanite: a window for high-pressure experiments.

We achieved a pressure of 52.1 gigapascals with moissanite anvils, which have optical, thermal, electric, magnetic, and x-ray properties that rival those of diamond. The mode-softening of D(2)O toward the pressure-induced hydrogen bond symmetrization and the Raman shifts of diamond under hydrostatic and nonhydrostatic compressions were studied with moissanite anvils in the spectral regions normally obscured by diamond anvils. Moissanite anvil cells allow maximum sample volumes 1000 times larger than those allowed by diamond anvil cells and may enable the next level of advancement in high-pressure experiments.

Journal Article↗

PubMed2000

Raman spectroscopy of iron to 152 gigapascals: implications for Earth's inner core

Raman spectra of hexagonal close-packed iron (varepsilon-Fe) have been measured from 15 to 152 gigapascals by using diamond-anvil cells with ultrapure synthetic diamond anvils. The results give a Gruneisen parameter gamma(0) = 1.68 (+/-0.20) and q = 0.7 (+/-0.5). Phenomenological modeling shows that the Raman-active mode can be approximately correlated with an acoustic phonon and thus provides direct information about the high-pressure elastic properties of iron, which have been controversial. In particular, the C(44) elastic modulus is found to be lower than previous determinations. This leads to changes of about 35% at core pressures for shear wave anisotropies.

Journal Article↗

PubMed2000

Conscious and unconscious processing of nonverbal predictability in Wernicke's area.

The association of nonverbal predictability and brain activation was examined using functional magnetic resonance imaging in humans. Participants regarded four squares displayed horizontally across a screen and counted the incidence of a particular color. A repeating spatial sequence with varying levels of predictability was embedded within a random color presentation. Both Wernicke's area and its right homolog displayed a negative correlation with temporal predictability, and this effect was independent of individuals' conscious awareness of the sequence. When individuals were made aware of the underlying sequential predictability, a widespread network of cortical regions displayed activity that correlated with the predictability. Conscious processing of predictability resulted in a positive correlation to activity in right prefrontal cortex but a negative correlation in posterior parietal cortex. These results suggest that conscious processing of predictability invokes a large-scale cortical network, but independently of awareness, Wernicke's area processes predictive events in time and may not be exclusively associated with language.

Adult↗

PubMed2000

Expression, refolding, and isotopic labeling of human serum albumin domains for NMR spectroscopy.

Many different compounds bind to human serum albumin (HSA), which can be a significant problem in the drug discovery process. To aid in the design of drug molecules that do not bind to HSA, the structures of HSA/ligand complexes would be very useful. However, little information has been reported on the structures of small molecules complexed to HSA. In this paper, we describe a procedure for preparing isotopically labeled domains of HSA for nuclear magnetic resonance (NMR) studies. The procedure involves the expression in Escherichia coli, refolding, and a multistep purification. Domains I and III are capable of folding into stable structural units and producing well resolved (15)N/(1)H correlation spectra, whereas domain II forms significant aggregates at sub-millimolar concentration. Using our protocols, isotopically labeled and properly folded domains I and III can be effectively produced in large quantities for NMR-based structural studies and NMR-based screening. This provides a valuable tool for obtaining structural information on HSA/ligand complexes by NMR which will be useful in drug discovery.

Cloning, Molecular↗