Biomedical subjects

P Chen

Publications and source records attributed to P Chen.

At least 37 records · Page 2Linked to original sources

PubMed2005

Effect of NaCl and peptide concentration on the self-assembly of an ionic-complementary peptide EAK16-II.

Previous work has examined the effects of such factors as pH and peptide concentration on the self-assembly of ionic-complementary peptides. This work focused on the effect of sodium chloride on the molecular self-assembly of an ionic-complementary peptide EAK16-II (AEAEAKAKAEAEAKAK). Surface tensions and dimensions of the self-assembled nanostructures were determined for a wide range of peptide and sodium chloride concentrations using axisymmetric drop shape analysis-profile (ADSA-P) and atomic force microscopy (AFM), respectively. The critical aggregation concentration, or critical self-assembly concentration (CSAC), of EAK16-II was not significantly affected by the presence of NaCl. However, the analysis of size variations in self-assembled nanostructures in response to changes in NaCl concentration indicated that the presence of NaCl does influence the resulting dimensions of the peptide nanostructures when the peptide concentration is below its CSAC. A critical NaCl concentration was identified at approximately 20mM, below which the equivalent radius of the peptide fibrils increased with increasing salt concentration, and above which the opposite response was observed. This critical NaCl concentration was further confirmed in the surface tension measurements, where the equilibrium surface tension and induction time of the peptide at low concentrations (<CSAC) decreased with increasing NaCl concentration up to approximately 20mM and a further increase caused the opposite trend.

Amino Acid Sequence↗

PubMed2005

A simple method for determining the probability a new vertebral fracture is present in postmenopausal women with osteoporosis.

The vertebral fracture status of women with osteoporosis has strong prognostic implications that may influence clinical decisions. We developed a simple method for estimating the probability that a new vertebral fracture has occurred in postmenopausal women with osteoporosis. Data was from the placebo groups of the Fracture Prevention Trial (median observation =21 months) and the MORE Trial at 2 years. A logistic regression analysis identified prior vertebral fracture (yes/no), new or worsening back pain (yes/no), and height loss (> or =2 cm, yes/no) as significant predictors for the presence of a new vertebral fracture. The actual probability of a new vertebral fracture in patients without these predictors, over the median observation period of 23 months, was 2.1%. Presence of back pain increased this probability fourfold; prior vertebral fracture increased this probability threefold, and height loss > or =2 cm increased this probability threefold. The predicted probabilities of a new vertebral fracture being present for each subgroup representing each of the eight possible combinations of back pain, prior vertebral fracture, and height loss were highly correlated with both the multivariate logistic regression-derived probabilities (r=0.98, p <0.001) and with the actual probabilities (r=0.99, p <0.001). The validity of this simple method was confirmed in patients from the MORE trial at both 2 years and 3 years, and in the Fracture Prevention Trial alone. This simple method provides clinicians with an estimate of the probability that a new vertebral fracture has occurred in postmenopausal women with osteoporosis.

Adult↗

PubMed2005

Thermodynamic modeling of contact angles on rough, heterogeneous surfaces.

Theoretical modelling for contact angle hysteresis carried out to date has been mostly limited to several idealized surface configurations, either rough or heterogeneous surfaces. This paper presents a preliminary study on the thermodynamics of contact angles on rough and heterogeneous surfaces by employing the principle of minimum free energy and the concept of liquid front. Based on a two-dimensional regular model surface, a set of relations were obtained, which correlate advancing, receding and system equilibrium contact angles to surface topography, roughness and heterogeneity. It was found that system equilibrium contact angles (theta(ES)) can be expressed as a function of surface roughness factor (delta) and the Cassie contact angle (theta(C)): costheta(ES) = deltacostheta(C). This expression can be reduced to the classical Wenzel equation.: theta(ES) = theta(W) for rough but homogeneous surfaces, and the classical Cassie equation theta(ES) = theta(C) for heterogeneous but smooth surfaces. A non-dimensional parameter called surface feature factor (omega) was proposed to classify surfaces into three categories (types): roughness-dominated, heterogeneity-dominated and mixed-rough-heterogeneous. The prediction of advancing and receding contact angles of a surface is dependent on which category the surface belongs to. The thermodynamic analysis of contact angle hysteresis was further extended from the regular model surface to irregular surfaces; consistent results were obtained. The current model not only agrees well with the models previously studied by other researchers for idealized surfaces, but also explores more possibilities to explain the reported experimental results/observations that most existing theories could not explain.

Colloids↗

PubMed2005

Modeling of adsorption dynamics at air-liquid interfaces using statistical rate theory (SRT).

A large number of natural and technological processes involve mass transfer at interfaces. Interfacial properties, e.g., adsorption, play a key role in such applications as wetting, foaming, coating, and stabilizing of liquid films. The mechanistic understanding of surface adsorption often assumes molecular diffusion in the bulk liquid and subsequent adsorption at the interface. Diffusion is well described by Fick's law, while adsorption kinetics is less understood and is commonly described using Langmuir-type empirical equations. In this study, a general theoretical model for adsorption kinetics/dynamics at the air-liquid interface is developed; in particular, a new kinetic equation based on the statistical rate theory (SRT) is derived. Similar to many reported kinetic equations, the new kinetic equation also involves a number of parameters, but all these parameters are theoretically obtainable. In the present model, the adsorption dynamics is governed by three dimensionless numbers: psi (ratio of adsorption thickness to diffusion length), lambda (ratio of square of the adsorption thickness to the ratio of adsorption to desorption rate constant), and Nk (ratio of the adsorption rate constant to the product of diffusion coefficient and bulk concentration). Numerical simulations for surface adsorption using the proposed model are carried out and verified. The difference in surface adsorption between the general and the diffusion controlled model is estimated and presented graphically as contours of deviation. Three different regions of adsorption dynamics are identified: diffusion controlled (deviation less than 10%), mixed diffusion and transfer controlled (deviation in the range of 10-90%), and transfer controlled (deviation more than 90%). These three different modes predominantly depend on the value of Nk. The corresponding ranges of Nk for the studied values of psi (10(-2)<psi<10(4)) and lambda (10(-12)<lambda<10(8)) are 10(1)<Nk<10(4) for the diffusion controlled, 10(-3)<Nk<10(1) for the mixed diffusion and transfer controlled, and 10(-4)<Nk<10(-3) for the transfer controlled, respectively. The study also shows that lower values of psi and lambda are favorable for maximum surface adsorption and consequently surface tension reduction.

Journal Article↗

PubMed2005

Majority rule dynamics in finite dimensions.

We investigate the long-time behavior of a majority rule opinion dynamics model in finite spatial dimensions. Each site of the system is endowed with a two-state spin variable that evolves by majority rule. In a single update event, a group of spins with a fixed (odd) size is specified and all members of the group adopt the local majority state. Repeated application of this update step leads to a coarsening mosaic of spin domains and ultimate consensus in a finite system. The approach to consensus is governed by two disparate time scales, with the longer time scale arising from realizations in which spins organize into coherent single-opinion bands. The consequences of this geometrical organization on the long-time kinetics are explored.

Journal Article↗

PubMed2005

Vitronectin stabilizes thrombi and vessel occlusion but plays a dual role in platelet aggregation.

The role of vitronectin (Vn) in thrombosis is currently controversial; both inhibitory and supportive roles have been reported. To monitor directly the function of Vn in thrombotic events at the site of vascular injury, we studied Vn-deficient (Vn-/-) and wild-type (WT) control mice with two real-time intravital microscopy thrombosis models. In the mesenteric arteriole model, vessel injury was induced by ferric chloride. We observed unstable thrombi and a significantly greater number of emboli in Vn-/- mice. Vessel occlusion was also delayed and frequent vessel re-opening occurred. In the cremaster muscle arteriole model, vessel injury was induced by a nitrogen dye laser. We observed significantly fewer platelets, lower fibrin content, and unstable fibrin within the thrombi of Vn-/- mice. To define further the role of Vn in thrombus growth, we studied platelet aggregation in vitro. Consistent with our in vivo data, the second wave of thrombin-induced aggregation of gel-filtered platelets was abolished at a low concentration of thrombin in Vn-/- platelets. Interestingly, adenosine diphosphate (ADP)-induced platelet aggregation was significantly increased in Vn-/- platelet-rich plasma (PRP) and this effect was attenuated by adding purified plasma Vn. We also observed increased platelet aggregation induced by shear stress in Vn-/- whole blood. These data demonstrate that Vn is a thrombus stabilizer. However, in contrast to released platelet granule Vn which enhances platelet aggregation, plasma Vn inhibits platelet aggregation.

Adenosine Diphosphate↗

PubMed2005

The relationship between HPV16 and expression of CD44v6, nm23H1 in esophageal squamous cell carcinoma.

The esophageal squamous cell carcinoma (ESCC) has high incidence in Shaanxi Province of China. More and more researches indicated that human papillomavirus type 16 (HPV16) might play an important role in carcinogenesis of ESCC but the relationship between HPV16 and CD44v6, nm23H1 has not been elucidated. HPV16 was detected by amplifying HPV16 E6 gene through polymerase chain reaction (PCR) method and the expression of CD44v6, nm23H1 in 40 ESCCs and fifteen normal esophageal mucosa (NEM) from Shaanxi Province was examined by Streptavidin-Peroxidase (SP) method using monoclonal antibody specific to CD44v6 and nm23H1. The positive rates of HPV16 E6 gene, CD44v6 and nm23H1 were 60% (24/40), 65% (26/40) and 45% (18/40) respectively in ESCCs and 26.67% (4/15), 33.33% (5/15) and 86.67% (13/15) respectively in NEMs. There exited statistical difference for HPV16, CD44v6 and nm23H1 between NEMs and ESCCs respectively (p < 0.05). The relationship between HPV16 and the expression of CD44v6 in ESCCs was statistical significance (P = 0.021), but no significant correlation was found between HPV16 and the expression of nm23H1 (P = 0.436) in ESCCs. The infection rate of HPV16 had no statistical difference in all pathological features we observed, but the expression rates of CD44v6 and nm23H1 had statistical correlation with invasion (p = 0.001, 0.013) and lymph nodes metastasis (p = 0.014, 0.002) respectively. In different histology grade of ESSCs, the relationship between HPV16 and CD44v6 was statistical significance in grade I (p = 0.044) but was not in grade II (p = 0.165) and grade III (p = 0.658), however as to the expression of nm23H1 there exited no statistical significance in all histology grades of ESCC (p > 0.05). The expression rates of CD44v6 and nm23H1 were statistically different between grade I and II (p = 0.004, 0.016) respectively and between grade I and grade III (p = 0.014, 0.020), but not statistically different between grade II and III (p = 0.792, 0.943) respectively. Our data firstly suggested that there existed the statistical relationship between the infection of HPV16 and the expression of CD44v6 in ESCCs and that HPV16 may be involved in invasion and metastasis of ESCC.

Carcinoma, Squamous Cell↗

PubMed2005

Emergence of Rsv-resistance breaking Soybean mosaic virus isolates from Korean soybean cultivars.

Twelve Rsv resistance-breaking (RB) isolates of Soybean mosaic virus (SMV) were obtained from field-grown soybean plants showing mosaic symptoms and subsequently examined biologically and molecularly. All of these RB isolates were identified as SMV based on serological and infectivity assays, and the amplification of P1 gene products by reverse transcription-polymerase chain reaction (RT-PCR). Differential soybean cultivars, lines or accessions Lee 68 (rsv), PI 96983, York, Marshall, Ogden, Kwanggyo, Suweon 97 (Rsv1 alleles), L29 (Rsv3), and V94-5152 (Rsv4), following inoculation with each RB isolate, showed similar systemic symptoms suggesting that these RB isolates can overcome Rsv resistance at three loci. To differentiate the 12 RB isolates molecularly, the P1 coding region for each isolate was amplified, cloned, sequenced and compared to known SMV strains. The P1 region from the RB isolates shared 86-90% and 90-99% similarities in amino acid (aa) and nucleotide sequence, respectively, with known SMV strains. Comparison of aa sequences indicated that these RB isolates are newly emerging isolates capable of breaking Rsv resistance. Phylogenetic analysis further suggested that the RB isolates can be classified as three major types. However, recombination was not observed within the coding region of P1 protein among the types. This is the first report on the emergence of SMV isolates capable of overcoming all of the known resistance alleles at the Rsv1 locus, as well as distinct resistance genes at Rsv3 and Rsv4.

Amino Acid Sequence↗

PubMed2005

In vitro and in vivo induction of bone formation based on ex vivo gene therapy using rat adipose-derived adult stem cells expressing BMP-7.

BACKGROUND: Adipose-derived adult stem (ADAS) cells are multipotent cells capable of differentiating into osteoblasts, adipocytes and chondrocytes. The aim of this study was to determine whether BMP-7-expressing ADAS cells would elicit bone formation invitro and in vivo. METHODS: ADAS cells were harvested from Lewis rats and transduced with adenovirus carrying the recombinant human bone morphogenetic protein-7 (Ad-BMP-7) gene. Untransduced cells and cells transduced with adenovirus carrying the enhanced green fluorescence protein (Ad-EGFP) gene served as controls. BMP-7 expression was assessed by RT-PCR, immunofluorescence on day 1, and Western blot on days 4, 8 and 12. Alkaline phosphatase (ALP) activity was assayed on days 2, 4, 6, 8, 10 and 12. Osteocalcin production and bone nodule formation were detected by immunohistochemistry and von Kossa stain on day 12. A total of 1 x 10(6) cells mixed with type I collagen were implanted into the subcutaneous pocket in Lewis rat and subjected to histologic analysis 1, 2 and 4 weeks post-implantation. RESULTS: The Ad-BMP-7-transduced ADAS cells expressed BMP-7 at both mRNA and protein levels. ALP activity was detected in Ad-BMP-7-transduced cells from day 2 to day 12, peaking on day 8. Osteocalcin production and matrix mineralization further confirmed that these cells differentiated into osteoblasts and induced bone formation in vitro. Histologic examination revealed that implantation of BMP-7-expressing ADAS cells could induce new bone formation in vivo. DISCUSSION: ADAS cells would be a promising source of adult autologous stem cells for BMP gene therapy and tissue engineering.

Adenoviridae↗

PubMed2005

Cancer screening beliefs and reactions to an innovative colorectal cancer screening kit among Chinese worksite population.

OBJECTIVES: This study assessed the relationships between cancer screening beliefs (perceived pros, cons, and susceptibility) and reactions (acceptance, self-efficacy, intention to purchase) to an innovative home-administered kit (HAK) for fecal occult blood test (FOBT) among Chinese worksite population. METHODS: A total of 450 Chinese people aged 40 and older were recruited from ten worksites in Taiwan (2002), with response rate of 83% (375/450). RESULTS: All the belief scales of cancer screening in general showed good internal consistency (Cronbach alphas >0.70). Perceived benefits and barriers towards cancer screening were significantly correlated with the acceptance, self-efficacy, and order intention towards the FOBT-HAK (p-values <0.001). Perceived susceptibility of cancer was associated with intention to purchase. After taking gender into consideration, the regression analyses showed similar relationships. CONCLUSIONS: Screening beliefs were significantly associated with reactions toward the innovative FOBT-HAK. Intervention programs addressing these beliefs could potentially promote positive reactions to innovative CRC screening strategies.

Adult↗

PubMed2004

Differential effects of estrogen and raloxifene on messenger RNA and matrix metalloproteinase 2 activity in the rat uterus.

A detailed analysis of the differential effects of estrogen (E) compared to raloxifene (Ral), a selective estrogen receptor modulator (SERM), following estrogen receptor (ER) binding in gynecological tissues was conducted using gene microarrays, Northern blot analysis, and matrix metalloproteinase (MMP) 2 activity studies. We profiled gene expression in the uterus following acute (1 day) and prolonged daily (5 wk) treatment of E and Ral in ovariectomized rats. Estrogen regulated twice as many genes as Ral, largely those associated with catalysis and metabolism, whereas Ral induced genes associated with cell death and negative cell regulation. Follow-up studies confirmed that genes associated with matrix integrity were differentially regulated by Ral and E at various time points in uterine and vaginal tissues. Additional experiments were conducted to determine the levels of MMP2 activity in uterus explants from ovariectomized rats following 2 wk of treatment with E, Ral, or one of two additional SERMs: lasofoxifene, and levormeloxifene. Both E and lasofoxifene stimulated uterine MMP2 activity to a level twofold that of Ral, whereas levormeloxifene elevated MMP2 activity to a level 12-fold that of Ral. These data show that one of the significant differences between E and Ral signaling in the uterus is the regulation of genes and proteins associated with matrix integrity. This may be a potential key difference between the action of SERMs in the uterus of postmenopausal women.

Animals↗

PubMed2004

Coherently photoinduced ferromagnetism in diluted magnetic semiconductors.

Ferromagnetism is predicted in undoped diluted magnetic semiconductors illuminated by intense sub-band-gap laser radiation. The mechanism for photoinduced ferromagnetism is coherence between conduction and valence bands induced by the light which leads to an optical exchange interaction. The ferromagnetic critical temperature T(C) depends both on the properties of the material and on the frequency and intensity of the laser and could be above 1K.

Journal Article↗

PubMed2004

Radiation exposure assessment for portsmouth naval shipyard health studies.

Occupational radiation exposures of 13,475 civilian nuclear shipyard workers were investigated as part of a retrospective mortality study. Estimates of annual, cumulative and collective doses were tabulated for future dose-response analysis. Record sets were assembled and amended through range checks, examination of distributions and inspection. Methods were developed to adjust for administrative overestimates and dose from previous employment. Uncertainties from doses below the recording threshold were estimated. Low-dose protracted radiation exposures from submarine overhaul and repair predominated. Cumulative doses are best approximated by a hybrid log-normal distribution with arithmetic mean and median values of 20.59 and 3.24 mSv, respectively. The distribution is highly skewed with more than half the workers having cumulative doses <10 mSv and >95% having doses <100 mSv. The maximum cumulative dose is estimated at 649.39 mSv from 15 person-years of exposure. The collective dose was 277.42 person-Sv with 96.8% attributed to employment at Portsmouth Naval Shipyard.

Algorithms↗

PubMed2004

Self-assembling peptide as a potential carrier of hydrophobic compounds.

Microcrystals of a hydrophobic cargo were stabilized by EAK16 II, a self-assembling oligopeptide, and suspended in aqueous solution. Pyrene was used as a model hydrophobic compound. Egg phosphatidylcholine (EPC) vesicles were prepared to mimic a cell membrane. Pyrene was released from its EAK16 II coating into EPC vesicles. The excimer decay profiles were acquired. They showed that pyrene is present in the crystalline form when stabilized by EAK16 II, it is molecularly dispersed in EPC vesicles, and it is completely released from its EAK16 II coating into the membrane bilayers. The release of pyrene from the microcrystals coated with EAK16 II into the EPC membrane was followed by fluorescence as a function of time. The amount of pyrene released into the EPC vesicles at a given time was quantified using a calibration curve. The concentration of pyrene released was determined as a function of time, and the concentration-versus-time profile was fitted with one exponential. The rate of pyrene release was found to depend on the peptide-to-pyrene molecular ratio. Higher peptide-to-pyrene ratios lead to slower transfer of pyrene to the lipophilic environment. Scanning electron micrographs demonstrated that a thicker coating on the pyrene crystals results in a slower release. The data presented in this work demonstrate that the self-assembling EAK16 II can stabilize a hydrophobic cargo in aqueous solution and deliver it into a lipophilic environment, and that the rate of transfer can be adjusted by tuning the peptide-to-pyrene ratio.

Drug Carriers↗

PubMed2004

Laparoscopic left hemihepatectomy for hepatolithiasis.

To assess the feasibility of hepatolithiasis treatment using laparoscopic liver resections, a prospective study of laparoscopic liver resections was undertaken in selected patients with left intrahepatic stone disease. The patients underwent a laparoscopic left lobectomy to try to alleviate the symptoms of their disease. Two patients were operated on successfully. Mean blood loss was 400-600 ml. Laparoscopic resections are feasible methods of treatment for selected patients with left intrahepatic stone disease.

Adult↗

PubMed2004

Group I metabotropic glutamate receptors in spiral ganglion neurons contribute to excitatory neurotransmissions in the cochlea.

Evidence has accumulated over the years supporting glutamate as the primary neurotransmitter used by hair cells in afferent cochlear neurotransmission. Besides acting on ionotropic glutamate receptors, glutamate also activates second messenger systems via G-protein-coupled metabotropic glutamate receptors (mGluRs) to modulate neuronal excitability. However, it is unclear whether mGluRs participate in cochlear neurotransmission. We present evidence directly supporting a functional role for group I metabotropic glutamate receptors (mGluRIs) in spiral ganglion (SG) neurons. The presence of mGluRI and downstream G-protein subunits was demonstrated by molecular biology and immunolabeling methods. Direct activation of mGluRIs in cultured SG neurons resulted in transient increases of intracellular Ca(++) concentration and transient inward currents that gave rise to firings of multiple action potentials. These responses showed mGluRI pharmacological specificity and quickly desensitized. We next examined changes in cochlear function after noise exposure as a result of pharmacologically manipulating cochlear glutamate neurotransmission. These in vivo tests showed that blocking non-N-methyl-D-aspartic acid glutamate receptors was sufficient to eliminate compound action potentials of the auditory nerve, and pharmacologically inhibiting mGluRIs in the cochlea did not significantly affect the hearing threshold. In contrast, blocking mGluRIs lowered the amplitude of compound action potentials at louder sound levels and reduced the noise-induced temporary threshold shift. Our results suggest that although mGluRIs did not initiate fast excitatory cochlear neurotransmission, their activation contributed to the growth of excitatory responses of the cochlea. As a result, the cochlea was more resistant to noise-induced temporary hearing losses without the activation of mGluRIs in SG neurons.

Action Potentials↗

PubMed2004

Altered CNS response to injury in the MRL/MpJ mouse.

The MRL/MpJ mouse has a greatly enhanced healing response and an absence of scarring compared with other mouse strains. Following lesions to the CNS mammals show a scarring response known as reactive gliosis, and this CNS scar tissue blocks regeneration of cut axons. We have therefore compared reactive gliosis in the MRL/MpJ mouse and the Swiss Webster mouse, which exhibits normal scarring in the periphery. The lesion model was a stab lesion to the cortex, in which reactive gliosis has previously been quantified. Axon regeneration was examined following a cut lesion to the dopaminergic projection from the substantia nigra to the striatum used in previous regeneration experiments. In the MRL/MpJ following the lesion compared with Swiss Webster mice there was greater cell loss around the lesion followed by greater and more widespread and more prolonged cellular proliferation. Early after the lesion there was a greater loss of glial fibrillary acidic protein (GFAP)-positive astrocytes around the injury site in the MRL/MpJ, and an enhancement and prolongation of the microglial inflammatory response. This was accompanied by greater and more widespread blood-brain barrier leakage following injury. RNA levels for the matrix metalloproteinases (MMP)-2 and MMP-9 as well as for the thrombin receptors PAR-1 and PAR-4 were also greater at the MRL/MpJ injury site. All of these differences were transient and by 14 days post-injury there were no differences observed between MRL/MpJ and control mice. No axonal regeneration was observed following axotomy to the nigrostriatal pathway of the MRL/MpJ or the Swiss Webster mice at any time point.

Animals↗

PubMed2004

Bifunctional killing activity encoded by conserved reaper proteins.

Drosophila activators of apoptosis mapping to the Reaper region function, in part, by antagonizing IAP proteins through a shared RHG motif. We isolated Reaper from the Blowfly L. cuprina, which triggered extensive apoptosis in Drosophila cells. Conserved regions of Reaper were tested in the context of GFP fusions and a second killing activity, distinct from the RHG, was identified. A 20 amino-acid peptide, designated R3, conferred targeting to a focal compartment and promoted membrane blebbing. Killing by the R3 fragment did not correlate with translational suppression or with reduced DIAP1 levels. Likewise, R3-induced cell deaths were only modestly suppressed by silencing of Dronc and involved no detectable association with DIAP1. Instead, a second IAP-binding domain, distinct from the R3, was identified at the C terminus of Reaper that bound to DIAP1 but failed to trigger apoptosis. Collectively, these findings are inconsistent with single effector models for cell killing by Reaper and suggest, instead, that Reaper encodes conserved bifunctional death activities that propagate through distinct effector pathways.

Amino Acid Motifs↗