Tissue Of Interest Research Articles

A Comparison of the Dynamics of S100B, S100A1, and S100A6 mRNA Expression in Hippocampal CA1 Area of Rats during Long-Term Potentiation and after Low-Frequency Stimulation

The interest in tissue- and cell-specific S100 proteins physiological roles in the brain remains high. However, necessary experimental data for the assessment of their dynamics in one of the most important brain activities, its plasticity, is not sufficient. We studied the expression of S100B, S100A1, and S100A6 mRNA in the subfield CA1 of rat hippocampal slices after tetanic and low-frequency stimulation by real-time PCR. Within 30 min after tetanization, a 2–4 fold increase of the S100B mRNA level was observed as compared to the control (intact slices) or to low-frequency stimulation. Subsequently, the S100B mRNA content gradually returned to baseline. The amount of S100A1 mRNA gradually increased during first hour and maintained at the achieved level in the course of second hour after tetanization. The level of S100A6 mRNA did not change following tetanization or low-frequency stimulation.

Incorporating a vascular term into a reference region model for the analysis of DCE-MRI data: a simulation study

A vascular term was incorporated into a reference region (RR) model analysis of DCE-MRI data, and its effect on the accuracy of the model in estimating tissue kinetic parameters in a tissue of interest (TOI) was systematically investigated through computer simulations. Errors in the TOI volume transfer constant (Ktrans,TOI) and TOI extravascular extracellular volume (ve,TOI) that result when the fractional plasma volume (vp) was included in (1) neither region, (2) TOI only (3) both regions were investigated. For nominal values of tumor kinetic parameters (ve,TOI = 0.40 and Ktrans,TOI = 0.25 min−1), if the vascular term was included in neither region or the TOI only, Ktrans,TOI error was within 20% for 0.03 < vp,TOI < 0.10, and ve,TOI error was within 20% for the range of vp,TOI studied (0.01–0.10). The effects of temporal resolution were shown to be complex, and in some cases errors increased with increasing temporal resolution.

Repeatability of a reference region model for analysis of murine DCE‐MRI data at 7T

To test the repeatability of a reference region (RR) model for the analysis of dynamic contrast-enhanced MRI (DCE-MRI) in a mouse model of cancer at high field. Seven mice were injected with 10(6) 4T1 mammary carcinoma cells and imaged eight to 10 days later on a Varian 7.0T scanner. Two DCE-MRI studies were performed for each mouse (separated by 2.5 hours). The RR model was used to analyze the data, and returned estimates on the perfusion-permeability index (Ktrans) for the RR and the tissue of interest (TOI), as well as the extravascular extracellular volume fraction (ve) for the TOI. When the first injection was compared with the second injection, all parameters tested were highly correlated (r2=0.90, 0.62, 0.82 for the RR Ktrans, TOI Ktrans, and TOI ve, respectively, with P<0.001 for all). To observe a statistically significant change (at the 5% level) in a treatment study with seven animals in each group, log10 changes of 0.084 and 0.077 in the tumor Ktrans and ve, respectively, are required. If a reliable arterial input function (AIF) is unavailable, the RR model is a reasonable alternative to measuring MRI contrast-agent (CA) kinetics in mouse models of cancer at high field.

Quantitative pharmacokinetic analysis of DCE-MRI data without an arterial input function: a reference region model

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) can assess tumor perfusion, microvascular vessel wall permeability and extravascular-extracellular volume fraction. Analysis of DCE-MRI data is usually based on indicator dilution theory that requires knowledge of the concentration of the contrast agent in the blood plasma, the arterial input function (AIF). A method is presented that compares the tissues of interest (TOI) curve shape to that of a reference region (RR), thereby eliminating the need for direct AIF measurement. By assigning literature values for Ktrans (the blood perfusion-vessel permeability product) and v(e) (extravascular-extracellular volume fraction) in a reference tissue, it is possible to extract the Ktrans and v(e) values for a TOI without knowledge of the AIF. The operational RR equation for DCE-MRI analysis is derived, and its sensitivity to noise and incorrect assignment of the RR parameters is tested via simulations. The method is robust at noise levels of 10%, returning accurate (+/-20% in the worst case) and precise (+/-15% in the worst case) values. Errors in the TOI Ktrans and v(e) values scale approximately linearly with the errors in the assigned RR Ktrans and v(e) values. The methodology is then applied to a Lewis Lung Carcinoma mouse tumor model. A slowly enhancing TOI yielded Ktrans=0.039+/-0.002 min-1 and v(e)=0.46+/-0.01, while a rapidly enhancing region yielded Ktrans=0.35+/-0.05 min-1 and v(e)=0.31+/-0.01. Parametric Ktrans and v(e) mappings manifested a tumor periphery with elevated Ktrans (>0.30 min-1) and v(e) (>0.30) values. The main advantage of the RR approach is that it allows for quantitative assessment of tissue properties without having to obtain high temporal resolution images to characterize an AIF. This allows for acquiring images with higher spatial resolution and/or SNR, and therefore, increased ability to probe tissue heterogeneity.

Anterior cruciate ligament regeneration using braided biodegradable scaffolds: in vitro optimization studies

The anterior cruciate ligament (ACL) is the most commonly injured intra-articular ligament of the knee, and limitations in existing reconstruction grafts have prompted an interest in tissue engineered solutions. Previously, we reported on a tissue-engineered ACL scaffold fabricated using a novel, three-dimensional braiding technology. A critical factor in determining cellular response to such a graft is material selection. The objective of this in vitro study was to optimize the braided scaffold, focusing on material composition and the identification of an appropriate polymer. The selection criteria are based on cellular response, construct degradation, and the associated mechanical properties. Three compositions of poly- α-hydroxyester fibers, namely polyglycolic acid (PGA), poly- L-lactic acid (PLLA), and polylactic- co-glycolic acid 82:18 (PLAGA) were examined. The effects of polymer composition on scaffold mechanical properties and degradation were evaluated in physiologically relevant solutions. Prior to culturing with primary rabbit ACL cells, scaffolds were pre-coated with fibronectin (Fn, PGA-Fn, PLAGA-Fn, PLLA-Fn), an important protein which is upregulated during ligament healing. Cell attachment and growth were examined as a function of time and polymer composition. While PGA scaffolds measured the highest tensile strength followed by PLLA and PLAGA, its rapid degradation in vitro resulted in matrix disruption and cell death over time. PLLA-based scaffolds maintained their structural integrity and exhibited superior mechanical properties over time. The response of ACL cells was found to be dependent on polymer composition, with the highest cell number measured on PLLA-Fn scaffolds. Surface modification of polymer scaffolds with Fn improved cell attachment efficiency and effected the long-term matrix production by ACL cells on PLLA and PLAGA scaffolds. Therefore based on the overall cellular response and its temporal mechanical and degradation properties in vitro, the PLLA braided scaffold pre-coated with Fn was found to be the most suitable substrate for ACL tissue engineering.

The current situation in human pancreatic islet transplantation: problems and prospects

In 2000, seven cases of pancreatic islet transplantation were documented by the researchers at the University of Alberta (Edmonton, Canada). The transplantation was performed using a protocol with a novel immunosuppressive regimen later named the Edmonton Protocol. The results showed that all seven patients became free of the need for insulin therapy. The success of the Edmonton Protocol has enhanced expectations for and interest in islet transplantation all over the world. Islet transplantation seems to be an almost ideal therapy for insulin-dependent patients. In our recent participation in transplant-related conferences in Europe or the USA, we have felt great enthusiasm for islet transplantation among clinicians, researchers, as well as medical staff. In Japan, the Organ Transplant Law that allows transplants from brain-dead patients was enacted in 1997. Since the passing of the law, people's interest in tissue and organ transplantation, particularly islet transplantation, has been growing. Here we present general information on islet transplantation and discuss its problems and prospects.

A dispersion model for viral transport in tissues

Gene therapy of cancer is the transfer of genetic material to correct genetic mutations in malignant cells or destroy cancer cells through cytolysis or other mechanisms. Intratumoural injection is often used for direct delivery of viral particles (VP) into tumours. The temporal and spatial distributions of VP in the tissue of interest (TOI) following the injection may closely correlate with the therapeutic results. Thus, a theoretical model as a dispersion process is introduced to describe VP transport processes in the TOI. Which include mechanical flow, molecular diffusion, blood uptake, cellular absorption, and viral death and replication.

Estimation of the shear stress on the surface of an aortic valve leaflet.

The limited durability of xenograft heart valves and the limited supply of allografts have sparked interest in tissue engineered replacement valves. A bioreactor for tissue engineered valves must operate at conditions that optimize the biosynthetic abilities of seeded cells while promoting their adherence to the leaflet matrix. An important parameter is shear stress, which is known to influence cellular behavior and may thus be crucial in bioreactor optimization. Therefore, an accurate estimate of the shear stress on the leaflet surface would not only improve our understanding of the mechanical environment of aortic valve leaflets, but it would also aid in bioreactor design. To estimate the shear stress on the leaflet surface, two-component laser-Doppler velocimetry measurements have been conducted inside a transparent polyurethane valve with a trileaflet structure similar to the native aortic valve. Steady flow rates of 7.5, 15.0, and 22.5 L/min were examined to cover the complete range possible during the cardiac cycle. The laminar shear stresses were calculated by linear regression of four axial velocity measurements near the surface of the leaflet. The maximum shear stress recorded was 79 dyne/cm2, in agreement with boundary layer theory and previous experimental and computational studies. This study has provided a range of shear stresses to be explored in bioreactor design and has defined a maximum shear stress at which cells must remain adherent upon a tissue engineered construct.

Detection of genes of interest in tissues and cells by in situ hybridization

In situ hybridization (ISH) is a powerful technique for assessing the expression of particular genes of interest within individual cells in tissues or cytospins. The only limitations of the technique are the availability of appropriate probes and tissues. When coupled with routine histology and DNA analysis, characterization and classification of tissues can be greatly extended. Future applications include the identification of tumor-specific markers that can be combined with ISH in diagnostic strategies.

Quality factor and dose equivalent in radiation protection.

In considering the present state of radiation units for protection purposes, we shall start from proposals made by the International Commission on Radiation Units and Measurements. In ICRU Report 11 (ICRU, 1968), and again in Report 19 (ICRU, 1971), dose equivalent is defined as the product of absorbed dose, quality factor, and any other necessary modifying factors, at the point of interest in tissue. However, the quality factor is not denned, apart from indicating its dependence on linear energy transfer, and there is an apparent uncertainty relating to the dimensions of the dose equivalent. Criticism of the definitions has already appeared from some quarters. As members of the British Committee on Radiation Units and Measurements, we have discussed these issues at considerable length and come to conclusions which, while not supporting some of the criticisms made, should clarify the position.