Enhancement of cell growth in tissue-engineering constructs under direct perfusion: Modeling and simulation

Perfusion bioreactors improve mass transfer in cell-scaffold constructs. We developed a mathematical model to simulate nutrient flow through cellular constructs. Interactions among cell proliferation, nutrient consumption, and culture medium circulation were investigated. The model incorporated modified Contois cell-growth kinetics that includes effects of nutrient saturation and limited cell growth. Nutrient uptake was depicted through the Michaelis-Menton kinetics. To describe the culture medium convection, the fluid flow outside the cell-scaffold construct was described by the Navier-Stokes equations, while the fluid dynamics within the construct was modeled by Brinkman's equation for porous media flow. Effects of the media perfusion were examined by including time-dependant porosity and permeability changes due to cell growth. The overall cell volume was considered to consist of cells and extracellular matrices (ECM) as a whole without treating ECM separately. Numerical simulations show when cells were cultured subjected to direct perfusion, they penetrated to a greater extent into the scaffold and resulted in a more uniform spatial distribution. The cell amount was increased by perfusion and ultimately approached an asymptotic value as the perfusion rates increased in terms of the dimensionless Peclet number that accounts for the ratio of nutrient perfusion to diffusion. In addition to enhancing the nutrient delivery, perfusion simultaneously imposes flow-mediated shear stress to the engineered cells. Shear stresses were found to increase with cell growth as the scaffold void space was occupied by the cell and ECM volumes. The macro average stresses increased from 0.2 mPa to 1 mPa at a perfusion rate of 20 microm/s with the overall cell volume fraction growing from 0.4 to 0.7, which made the overall permeability value decrease from 1.35 x 10(-2)cm(2) to 5.51 x 10(-4)cm(2). Relating the simulation results with perfusion experiments in literature, the average shear stresses were below the critical value that would induce the chondrocyte necrosis.     

Clinical Outcomes of Patients with Oral Cavity Squamous Cell Carcinoma and Retropharyngeal Lymph Node Metastasis Identified by FDG PET/CT

Purpose

Retropharyngeal lymph node (RPLN) metastasis is an uncommon finding in patients with oral cavity squamous carcinoma (OSCC). We sought to investigate the clinical outcomes, clinicopathological characteristics, and the priority of treatment with curative intent in OSCC patients with RPLN involvement.

Methods and Materials

Between January 2007 and January 2011, we identified 36 patients with primary RPLN metastases (n = 10) or RPLN relapse (n = 26). The follow-up continued until June 2013. Disease-specific survival (DSS), disease-free survival (DFS), and the potential benefits of salvage therapy served as the main outcome measures.

Results

The 2-year DSS and DFS rates of untreated patients with RPLN involvement were 20% and 24%, respectively. Level IV/V neck lymph node involvement was an adverse prognostic factor for DSS (P = 0.048) and DFS (P = 0.018). All of the patients presenting with neck lymph node involvement at level IV/V died within 6 months. Among patients who were treated for RPLN relapse, the 2-year DSS and DFS rates from the relapse day were 12.8% and 9.6%, respectively. Concomitant contralateral neck lymph node metastases (N2c) were associated with lower 2-year DSS (P = 0.005) and DFS (P = 0.011) rates. Moreover, five (55%) of the nine patients with recurrent disease in the contralateral RPLN had distant metastases within 6 months. Salvage therapy yielded the maximum survival benefit in patients without N2c disease and ipsilateral RPLN involvement alone (P = 0.005).

Conclusion

OSCC patients with RPLN involvement have poor outcomes. The risk factor for definitive treatment in OSCC patients with FDG PET/CT defined RPLN disease in primary disease was neck lymph node involvement at level IV/V and N2c and/or contralateral RPLN disease in recurrent disease. Treatment efforts with curative intent should be tailored according to individual risk factors.     

Disabled-2 small interfering RNA modulates cellular adhesive function and MAPK activity during megakaryocytic differentiation of K562 cells

Previous studies have shown that Disabled-2 (DAB2) is up-regulated during megakaryocytic differentiation of human K562 cells. To delineate the consequences of DAB2 induction, a DNA vector-based small interfering RNA (siRNA) was designed to intervene in DAB2 expression. We found that DAB2 siRNA specifically inhibited DAB2 induction, resulting in the modulation of cell-cell adhesion and mitogen-activated protein kinase (MAPK) phosphorylation. The morphological changes and beta3 integrin expression associated with megakaryocytic differentiation were not affected. Since the MAPK pathway has been shown to involve DAB2 induction [Tseng et al., Biochem. Biophys. Res. Commun. 285 (2001) 129-135], our results suggest a reciprocal regulation between DAB2 and MAPK in the differentiation of K562 cells. In addition, we have demonstrated for the first time that DAB2 siRNA is a valuable tool for unveiling the biological consequences of DAB2 expression.     

Effects of amphetamine on schedule-induced polydipsia

A series of experiments examined the effects of amphetamine (AMPH) at various doses administration for different length of time on a schedule-induced polydipsia (SIP) and possible associations with behavioral activation. Two stages of a two-week AMPH treatment were introduced with interposed interval of two months. In terms of behavioral activation, AMPH induced a robust depression across stages but with less potency in the second one. As for the SIP performance, the effects manifested qualitative difference in the two stages. For the first stage, there were no differential effects of AMPH on stereotypy intensity during the facultative phase of the inter-rewarding interval. However, AMPH reduced the high frequency of licks in the adjunctive (schedule-induced) phase and increased the low frequency of nose pokes in the terminal (schedule-dependent) phase. In the second stage, AMPH had no effect on the frequency of licking whereas the efficiency of licking and the frequency of nose pokes were reduced. These results were interpreted to support the current viewpoint that the behavior of SIP displaying is relevant to the function of central dopaminergic systems. The results were further discussed in the considerations of behavioral competition, stress coping strategy, and also the impact of AMPH at different time.     

A molten globule-to-ordered structure transition of Drosophila melanogaster crammer is required for its ability to inhibit cathepsin

Drosophila melanogaster crammer is a novel cathepsin inhibitor that is involved in LTM (long-term memory) formation. The mechanism by which the inhibitory activity is regulated remains unclear. In the present paper we have shown that the oligomeric state of crammer is pH dependent. At neutral pH, crammer is predominantly dimeric in vitro as a result of disulfide bond formation, and is monomeric at acidic pH. Our inhibition assay shows that monomeric crammer, not disulfide-bonded dimer, is a strong competitive inhibitor of cathepsin L. Crammer is a monomeric molten globule in acidic solution, a condition that is similar to the environment in the lysosome where crammer is probably located. Upon binding to cathepsin L, however, crammer undergoes a molten globule-to-ordered structural transition. Using high-resolution NMR spectroscopy, we have shown that a cysteine-to-serine point mutation at position 72 (C72S) renders crammer monomeric at pH 6.0 and that the structure of the C72S variant highly resembles that of wild-type crammer in complex with cathepsin L at pH 4.0. We have determined the first solution structure of propeptide-like protease inhibitor in its active form and examined in detail using a variety of spectroscopic methods the folding properties of crammer in order to delineate its biomolecular recognition of cathepsin.     

Human β-endorphin: Development of tolerance and behavioral activity in rats

Human β-endorphin produced a potent antinociceptive response as estimated by the tail-flick test in rats after intraventricular injection. On a molar basis, the peptide was 21 times more potent than morphine and in addition, the peptide produced morphine-like catatonia and hypothermia. These responses were blocked by naloxone. Repeated injections of the peptide induced tolerance to analgesic response, catatonia and hypothermia. Cross tolerance to morphine was also observed.     

Evaluation and comparison of gene clustering methods in microarray analysis

MOTIVATION: Microarray technology has been widely applied in biological and clinical studies for simultaneous monitoring of gene expression in thousands of genes. Gene clustering analysis is found useful for discovering groups of correlated genes potentially co-regulated or associated to the disease or conditions under investigation. Many clustering methods including hierarchical clustering, K-means, PAM, SOM, mixture model-based clustering and tight clustering have been widely used in the literature. Yet no comprehensive comparative study has been performed to evaluate the effectiveness of these methods. RESULTS: In this paper, six gene clustering methods are evaluated by simulated data from a hierarchical log-normal model with various degrees of perturbation as well as four real datasets. A weighted Rand index is proposed for measuring similarity of two clustering results with possible scattered genes (i.e. a set of noise genes not being clustered). Performance of the methods in the real data is assessed by a predictive accuracy analysis through verified gene annotations. Our results show that tight clustering and model-based clustering consistently outperform other clustering methods both in simulated and real data while hierarchical clustering and SOM perform among the worst. Our analysis provides deep insight to the complicated gene clustering problem of expression profile and serves as a practical guideline for routine microarray cluster analysis.