Jean Ruel

Is the Incidence of Congenital Hypothyroidism Really Increasing? A 20-Year Retrospective Population-Based Study in Québec

CONTEXT Congenital hypothyroidism (CH) is reportedly increasing in the United States, possibly reflecting changes in screening methods. In Québec, the same initial TSH cutoff (15 mU/liter) has been used for the last 20 yr, but in 2001, the cutoff was decreased from 15 to 5 mU/liter for the second test, which is requested when TSH is intermediate (15-30 mU/liter) on the first. OBJECTIVES Our objective was to assess the incidence of CH over the last 20 yr in Québec. DESIGN, SETTING, PATIENTS, AND MAIN OUTCOME MEASURE This is a population-based retrospective study. Incidences by etiology based on thyroid scintigraphy with technetium were compared between 1990-2000 and 2001-2009. RESULTS Of 1,660,857 newborns over 20 yr, 620 had CH (incidence 1:2679). Etiology was dysgenesis (n = 389, 1:4270), either ectopy (n = 290) or athyreosis (n = 99), goiter (n = 52, 1:31,940), normal-size gland in situ (n = 115, 1:14,442), and unknown (n = 64, 1:25,950). The new screening algorithm identified 49 additional cases (i.e. 25 normal-size gland in situ, 12 unknown etiology, 10 ectopies, and two goiters). Consequently, the incidence of normal-size gland in situ or of unknown etiology more than doubled (1:22,222 to 1:9,836, P = 0.0015; and 1:43,824 to 1:17,143, P = 0.0018, respectively) but that of dysgenesis and goiter remained stable. Had the 1990-2000 algorithm been applied in 2001-2009, no change in incidence would have been observed in any category. CONCLUSION Estimating the incidence of CH is influenced by minimal changes in TSH screening cutoffs. Lower cutoffs identify additional cases that have predominantly functional disorders whose impact on intellectual disability, if left untreated, remains to be determined.

Regional distribution of nuclear T3 receptors in rat brain and evidence for preferential localization in neurons1

We examined the distribution of nuclear T3 in mature rat brain with the aim of determining specific targets of thyroid hormones within this tissue. Saturation experiments, performed in 9 different structures of the brain and in 4 parts of the cortex, revealed the presence of a single class of binding sites with a mean Ka of 0.53 × 1010 M1. The highest concentrations of receptors were found in the amygdala (0.523 +0.025 ng T3/mg DNA, Mean ± SE) and the hippocampus (0.438 ± 0.071 ng T3/mg DNA) while the lowest were in the brain stem (0.058 ± 0.003 ngT3/mg DNA) and the cerebellum (0.079 ± 0.026 ngT3/ml DNA). The receptor was not uniformal-ly distributed within the cerebrel cortex, its concentration being relatively high in the central sections and intermediate in the remaining portions. The cell type distribution of the T3 receptor was studied by separating glial and neuronal nuclei on a discontinuous sucrose gradient. There was no detectable specific T3binding in the fraction of oligodendrocyte nuclei (~ 95% pure). Conversely, the neuron-enriched fraction (~ 60%) showed a significant increase in receptor concentration compared to total nuclei (35-40% neurons): 0.857 + 0.196 vs 0.511 + 0.095 ng T3/mg DNA (p < 0.01) in the cortex and 0.425 ± 0.018 vs 0.234 ± 0.24 ngT3/mg DNA (p < 0.01) in the forebrain. The absence of nuclear T3 receptors in oligodendrocytes may have important implications on the mechanism of action of thyroid hormone in myelination.

Triiodothyronine increases glutamine synthetase activity in primary cultures of rat cerebellum.

Dissociated cells from 2-3 day-old rat cerebella were cultured in absence of thyroid hormones using conditions yielding mainly glial cells. After 7, 14 and 21 days in vitro, triiodothyronine (60 nM) was added to a set of dishes and glutamine synthetase activity was measured after 24, 48, and 72 h in both control and triiodothyronine-treated cultures. Basal glutamine synthetase activity increased more than 6 X between 7 and 21 days of culture. Triiodothyronine produced significant increases of glutamine synthetase activity after 72 h in 7-day-old cultures (+ 16%), after 48 h in 14-day-old cultures (+ 45%) and after 24 h in 21-day-old cultures (+ 27%). This effect depends on the initial plating density and is not observed if cells are plated at less than 1 cerebellum equivalent per 60 mm dish. Dose-response experiments indicated that 10(-8) M of triiodothyronine induces maximal response whereas half-maximal response is achieved around 10(-10) M. These results show that physiological amounts of thyroid hormone can influence the maturation of astrocytes in culture.

A New Bioreactor for the Development of Tissue-Engineered Heart Valves

This paper reports the design, manufacturing, and characterization of a new bioreactor dedicated to the development of tissue-engineered heart valve substitutes. First, a comprehensive review of the state of the art in bioreactors is presented and a rigorous classification is put forward. The existing bioreactors found in literature are organized in three groups and discussed with respect to their quality of reproduction compared to the physiological environment. The bioreactor architecture is then decomposed into basic components which may be grouped together in different arrangements, and the well-known Windkessel approach is used to study the global behavior of the system. Then, the new design, which is based on a synthesis of the features of the most evolved systems as well as on new improvements, is explained in detail. Optimal fluid dynamics are obtained with the presented bioreactor through carefully designed components and an advanced computer-controlled actuator. This allows a very accurate reproduction of physiological parameters, namely the pulsating flow rate and pressure. Finally, experimental results of flow rate and pressure waveforms are presented, where an excellent correlation with physiological measurements can be observed.

Endothelial cells exposed to erythrocytes under shear stress : An in vitro study

After injury and vascular replacement, endothelial cell recovery is limited and could lead to thrombosis. Seeding small diameter vascular prosthesis with endothelial cells has been proposed to fulfil cell lining and improve surface hemocompatibility. However, detachment of seeded cells occurs following implantation. Previous in vitro studies have looked at the fluid shear stress as a major cause of cell detachment. To our knowledge, the role of erythrocyte collisions has not been investigated. The present in vitro study aims at investigating whether endothelial cell adhesion depends on (i) the presence of erythrocytes in flow and (ii) the latent culture period (1, 24 and 48 h) between seeding and exposure to flow. Endothelial cells were exposed to culture media containing different erythrocyte concentrations using a steady laminar flow of 1350 ml min(-1) in a parallel plate flow chamber. Endothelial cell morphology in dynamic conditions was quantified and compared to that in static conditions. The projected area of cells were mostly found smaller under dynamic than static conditions, particularly at a wall shear stress of 23 dyn cm(-2). Cells from the 1 h latent culture period were oriented parallel to the flow axis and were more elongated than under static conditions. Conversely, endothelial cell shape was slightly modified when either the latent period or the wall shear stress was increased. Disparate orientation was observed on confluent endothelial cells (24-48 h latent period) exposed to shear stress with or without erythrocytes. Increasing fluid viscous forces due to erythrocytes play a critical role on the behaviour of freshly seeded endothelial cells upon exposure to blood flow.

Development of a parallel plate flow chamber for studying cell behavior under pulsatile flow.

&NA; The design of a new parallel plate perfusion chamber for cell behavior studies involving pulsatile flowrates is presented. It was based on fluid mechanical considerations to ensure a region of regular and uniform shear stress at the wall. A numeric solution of the flow was performed to study the effect of pulsating flow on the entrance length. Dye injection investigations in the chamber showed laminar and uniform flow in the culture region under steady state conditions. ASAIO Journal 1995;41:876‐883.

A transient method for measuring the DC streaming potential coefficient of porous and fractured rocks

High-quality streaming potential coupling coefficient measurements have been carried out using a newly designed cell with both a steady state methodology and a new pressure transient approach. The pressure transient approach has shown itself to be particularly good at providing high-quality streaming potential coefficient measurements as each transient increase or decrease allows thousands of measurements to be made at different pressures to which a good linear regression can be fitted. Nevertheless, the transient method can be up to 5 times as fast as the conventional measurement approaches because data from all flow rates are taken in the same transient measurement rather than separately. Test measurements have been made on samples of Berea and Boise sandstone as a function of salinity (approximately 18 salinities between 10 -5 mol/dm3 and 2 mol/dm3). The data have also been inverted to obtain the zeta potential. The streaming potential coefficient becomes greater (more negative) for fluids with lower salinities, which is consistent with existing measurements. Our measurements are also consistent with the high-salinity streaming potential coefficient measurements made by Vinogradov et al. (2010). Both the streaming potential coefficient and the zeta potential have also been modeled using the theoretical approach of Glover (2012). This modeling allows the microstructural, electrochemical, and fluid properties of the saturated rock to be taken into account in order to provide a relationship that is unique to each particular rock sample. In all cases, we found that the experimental data were a good match to the theoretical model.

Mechanical properties of endothelialized fibroblast-derived vascular scaffolds stimulated in a bioreactor

There is an ongoing clinical need for tissue-engineered small-diameter (<6mm) vascular grafts since clinical applications are restricted by the limited availability of autologous living grafts or the lack of suitability of synthetic grafts. The present study uses our self-assembly approach to produce a fibroblast-derived decellularized vascular scaffold that can then be available off-the-shelf. Briefly, scaffolds were produced using human dermal fibroblasts sheets rolled around a mandrel, maintained in culture to allow for the formation of cohesive and three-dimensional tubular constructs, and then decellularized by immersion in deionized water. Constructs were then endothelialized and perfused for 1week in an appropriate bioreactor. Mechanical testing results showed that the decellularization process did not influence the resistance of the tissue and an increase in ultimate tensile strength was observed following the perfusion of the construct in the bioreactor. These fibroblast-derived vascular scaffolds could be stored and later used to deliver readily implantable grafts within 4weeks including an autologous endothelial cell isolation and seeding process. This technology could greatly accelerate the clinical availability of tissue-engineered blood vessels.

Comparison of the direct burst pressure and the ring tensile test methods for mechanical characterization of tissue-engineered vascular substitutes

Tissue engineering provides a promising alternative for small diameter vascular grafts, especially with the self-assembly method. It is crucial that these grafts possess mechanical properties that allow them to withstand physiological flow and pressure without being damaged. Therefore, an accurate assessment of their mechanical properties, especially the burst pressure, is essential prior to clinical release. In this study, the burst pressure of self-assembled tissue-engineered vascular substitutes was first measured by the direct method, which consists in pressurizing the construct with fluid until tissue failure. It was then compared to the burst pressure estimated by Laplace׳s law using data from a ring tensile test. The major advantage of this last method is that it requires a significantly smaller tissue sample. However, it has been reported as overestimating the burst pressure compared to a direct measurement. In the present report, it was found that an accurate estimation of the burst pressure may be obtained from a ring tensile test when failure internal diameter is used as the diameter parameter in Laplace׳s law. Overestimation occurs with the method previously reported, i.e. when the unloaded internal diameter is used for calculations. The estimation of other mechanical properties was also investigated. It was demonstrated that data from a ring tensile test provide an accurate estimate of the failure strain and the stiffness of the constructs when compared to measurements with the direct method.

A new construction technique for tissue-engineered heart valves using the self-assembly method.

Tissue engineering appears as a promising option to create new heart valve substitutes able to overcome the serious drawbacks encountered with mechanical substitutes or tissue valves. The objective of this article is to present the construction method of a new entirely biological stentless aortic valve using the self-assembly method and also a first assessment of its behavior in a bioreactor when exposed to a pulsatile flow. A thick tissue was created by stacking several fibroblast sheets produced with the self-assembly technique. Different sets of custom-made templates were designed to confer to the thick tissue a three-dimensional (3D) shape similar to that of a native aortic valve. The construction of the valve was divided in two sequential steps. The first step was the installation of the thick tissue in a flat preshaping template followed by a 4-week maturation period. The second step was the actual cylindrical 3D forming of the valve. The microscopic tissue structure was assessed using histological cross sections stained with Massons Trichrome and Picrosirius Red. The thick tissue remained uniformly populated with cells throughout the construction steps and the dense extracellular matrix presented corrugated fibers of collagen. This first prototype of tissue-engineered heart valve was installed in a bioreactor to assess its capacity to sustain a light pulsatile flow at a frequency of 0.5 Hz. Under the light pulsed flow, it was observed that the leaflets opened and closed according to the flow variations. This study demonstrates that the self-assembly method is a viable option for the construction of complex 3D shapes, such as heart valves, with an entirely biological material.