[3H]R75231; A New Radiolabelled Nucleoside Transporter Probe Related to Mioflazine and Lidoflazine

Abstract

The transport of nucleosides and analogues across the plasma membrane of animal cells is mediated by nucleoside-specific transport proteins, by means of facilitated diffusion. Development of highly potent tritiated transport inhibitors allowed ligand binding studies, performed at various tissues. [³H]Nitrobenzylthioinosine ([³HINBI) and [3H]dipyridamole are used in this respect, yielding a wealth of information about the molecular characteristics of these proteins (1,2).     

Gastro-Intestinal Absorption of Lead in Children and Adults: Overview of Biological and Biophysico-Chemical Aspects

Abstract

Intake and uptake of lead in the general population is mainly via the gastro-intestinal (Gl) tract. Those biological and biophysico-chemical factors operating in the Gl tract are the main determinants of Pb bioavailability. They include sites of Pb uptake, the physiology of uptake/transport to blood, the stage of development, interactions of Pb with nutrients, and Gl biochemical transformations of ingested material. Lead uptake occurs as ion or complex, from micelles and perhaps by pinocytosis in the infant. Uptake is mainly via the duodenum but other sites can participate, e.g. ileum (pinocytosis) and colon. Transport to blood is by active, carrier-mediated transport and passive diffusion. Uptake may include movement through intercellular tight junctions.

Lead uptake is affected by nutrients in the Gl tract, operating synergistically or antagonistically. Iron and calcium interactions are most important and augment those also occurring in vivo in tissues.

Liberation of lead from diverse ingested media, e.g. food, paint, soil and dust, mining waste, is affected by their chemical/physical forms, hydrolytic and oxidative processes in gastric fluid and other Gl sites. Such changes in vivo are poorly simulated by in vitro tests. The downward revision of blood lead (Pb-B) levels considered ‘safe’, to about 0.5 μmol L^?1 (10μg dL^?1) or lower, causes even sources of moderately bioavailable Pb to become important.     

Ultrastructural characteristics of « Diplotaxis erucoides (L.) DC. » suspensor

Abstract

The development and general morphology of Diplotaxis erucoides (L.) DC. suspensor is of the « Onagrad Type », « Alyssum Variation ». Maximum growth of the suspensor occurs from the globular to the early heart stage of embryo development. The suspensor starts then to degenerate disintegrating shortly after the torpedo stage of the embryo.

The wall ingrowths of the long, tapering, basal cell are especially abundant at the cell's micropilar pole which is closely surrounded by well developed wall ingrowths formed by the endosperm. Wall ingrowths and plasmodesmata are present on the suspensor cells cross walls with the exception of the cell closest to the embryo. No such structures in fact are present on the walls separating this last cell both from the embryo and from the rest of the suspensor. Wall ingrowths are generally associated with numerous, large, mitochondria.

The morphological data seem to indicate that absorption and transport of nutrients from the surrounding tissues is a main function of the suspensor. The possibility of an elaborative and secretory function of this structure is discussed.     

Mechano-regulated cell–cell signaling in the context of cardiovascular tissue engineering

Cardiovascular tissue engineering (CVTE) aims to create living tissues, with the ability to grow and remodel, as replacements for diseased blood vessels and heart valves. Despite promising results, the (long-term) functionality of these engineered tissues still needs improvement to reach broad clinical application. The functionality of native tissues is ensured by their specific mechanical properties directly arising from tissue organization. We therefore hypothesize that establishing a native-like tissue organization is vital to overcome the limitations of current CVTE approaches. To achieve this aim, a better understanding of the growth and remodeling (G&R) mechanisms of cardiovascular tissues is necessary. Cells are the main mediators of tissue G&R, and their behavior is strongly influenced by both mechanical stimuli and cell–cell signaling. An increasing number of signaling pathways has also been identified as mechanosensitive. As such, they may have a key underlying role in regulating the G&R of tissues in response to mechanical stimuli. A more detailed understanding of mechano-regulated cell–cell signaling may thus be crucial to advance CVTE, as it could inspire new methods to control tissue G&R and improve the organization and functionality of engineered tissues, thereby accelerating clinical translation. In this review, we discuss the organization and biomechanics of native cardiovascular tissues; recent CVTE studies emphasizing the obtained engineered tissue organization; and the interplay between mechanical stimuli, cell behavior, and cell–cell signaling. In addition, we review past contributions of computational models in understanding and predicting mechano-regulated tissue G&R and cell–cell signaling to highlight their potential role in future CVTE strategies.

     

Storage tissue metabolism and reproduction in marine bivalves—a brief review

Summary

The diversity of storage tissue cell types in bivalve molluscs is evident. In some species there are no specific storage cells, and the adductor muscle plays the role of a reserve tissue (Pectinidae). In others both muscular cells and specific storage cells are involved in storage and release of nutrients for gametogenesis (Veneridae). A few species have a specific storage tissue such as the mantle in Mytilus containing two complementary types of cells. This specialisation can be correlated with the fertility of the species and with the variation of available food organisms. Vesicular connective tissue is found in species with a high level of fecundity which are subject to marked fluctuations in food availability (Mytilidae, Ostreidae). This can be considered as an adaptive behaviour to profit from uncertain supply of food supplies in order to produce the maximum number (and quality) of gametes in a precise period of the year.     

Design criteria for a printed tissue engineering construct: A mathematical homogenization approach

Cartilage tissue repair procedures currently under development aim to create a construct in which patient-derived cells are seeded and expanded ex vivo before implantation back into the body. The key challenge is producing physiologically realistic constructs that mimic real tissue structure and function. One option with vast potential is to print strands of material in a 3D structure called a scaffold that imitates the real tissue structure; the strands are composed of gel seeded with cells and so provide a template for cartilaginous tissue growth. The scaffold is placed in the construct and pumped with nutrient-rich culture medium to supply nutrients to the cells and remove waste products, thus promoting tissue growth.In this paper we use asymptotic homogenization to determine the effective flow and transport properties of such a printed scaffold system. These properties are used to predict the distribution of nutrient/waste products through the construct, and to specify design criteria for the scaffold that will optimize the growth of functional tissue.     

Periodontal tissue regeneration by combined implantation of adipose tissue-derived stem cells and platelet-rich plasma in a canine model

Background aimsOne goal of periodontal therapy is to regenerate periodontal tissues. Stem cells, growth factors and scaffolds and biomaterials are vital for the restoration of the architecture and function of complex tissues. Adipose tissue-derived stem cells (ASCs) are an ideal population of stem cells for practical regenerative medicine. In addition, platelet-rich plasma (PRP) can be useful for its ability to stimulate tissue regeneration. PRP contains various growth factors and may be useful as a cell carrier in stem cell therapies. The purpose of this study was to determine whether a mixture of ASCs and PRP promoted periodontal tissue regeneration in a canine model.MethodsAutologous ASCs and PRP were implanted into areas with periodontal tissue defects. Periodontal tissue defects that received PRP alone or non-implantation were also examined. Histologic, immunohistologic and x-ray studies were performed 1 or 2 months after implantation. The amount of newly formed bone and the scale of newly formed cementum in the region of the periodontal tissue defect were analyzed on tissue sections.ResultsThe areas of newly formed bone and cementum were greater 2 months after implantation of ASCs and PRP than at 1 month after implantation, and the radiopacity in the region of the periodontal tissue defect increased markedly by 2 months after implantation. The ASCs and PRP group exhibited periodontal tissue with the correct architecture, including alveolar bone, cementum-like structures and periodontal ligament-like structures, by 2 months after implantation.ConclusionsThese findings suggest that a combination of autologous ASCs and PRP promotes periodontal tissue regeneration that develops the appropriate architecture for this complex tissue.     

Tissue engineering in the rheumatic diseases

Diseases such as degenerative or rheumatoid arthritis are accompanied by joint destruction. Clinically applied tissue engineering technologies like autologous chondrocyte implantation, matrix-assisted chondrocyte implantation, or in situ recruitment of bone marrow mesenchymal stem cells target the treatment of traumatic defects or of early osteoarthritis. Inflammatory conditions in the joint hamper the application of tissue engineering during chronic joint diseases. Here, most likely, cartilage formation is impaired and engineered neocartilage will be degraded. Based on the observations that mesenchymal stem cells (a) develop into joint tissues and (b) in vitro and in vivo show immunosuppressive and anti-inflammatory qualities indicating a transplant-protecting activity, these cells are prominent candidates for future tissue engineering approaches for the treatment of rheumatic diseases. Tissue engineering also provides highly organized three-dimensional in vitro culture models of human cells and their extracellular matrix for arthritis research.     

Transmural flow bioreactor for vascular tissue engineering

Nutrient transport limitation remains a fundamental issue for in vitro culture of engineered tissues. In this study, perfusion bioreactor configurations were investigated to provide uniform delivery of oxygen to media equivalents (MEs) being developed as the basis for tissue‐engineered arteries. Bioreactor configurations were developed to evaluate oxygen delivery associated with complete transmural flow (through the wall of the ME), complete axial flow (through the lumen), and a combination of these flows. In addition, transport models of the different flow configurations were analyzed to determine the most uniform oxygen profile throughout the tissue, incorporating direct measurements of tissue hydraulic conductivity, cellular O₂ consumption kinetics, and cell density along with ME physical dimensions. Model results indicate that dissolved oxygen (DO) uniformity is improved when a combination of transmural and axial flow is implemented; however, detrimental effects could occur due to lumenal pressure exceeding the burst pressure or damaging interstitial shear stress imparted by excessive transmural flow rates or decreasing hydraulic conductivity due to ME compaction. The model was verified by comparing predicted with measured outlet DO concentrations. Based on these results, the combination of a controlled transmural flow coupled with axial flow presents an attractive means to increase the transport of nutrients to cells within the cultured tissue to improve growth (increased cell and extracellular matrix concentrations) as well as uniformity. Biotechnol. Bioeng. 2009; 104: 1197–1206. © 2009 Wiley Periodicals, Inc.     

A Poroelastic Model Describing Nutrient Transport and Cell Stresses Within a Cyclically Strained Collagen Hydrogel

In the creation of engineered tissue constructs, the successful transport of nutrients and oxygen to the contained cells is a significant challenge. In highly porous scaffolds subject to cyclic strain, the mechanical deformations can induce substantial fluid pressure gradients, which affect the transport of solutes. In this article, we describe a poroelastic model to predict the solid and fluid mechanics of a highly porous hydrogel subject to cyclic strain. The model was validated by matching the predicted penetration of a bead into the hydrogel from the model with experimental observations and provides insight into nutrient transport. Additionally, the model provides estimates of the wall-shear stresses experienced by the cells embedded within the scaffold. These results provide insight into the mechanics of and convective nutrient transport within a cyclically strained hydrogel, which could lead to the improved design of engineered tissues.     

A Poroelastic Model Describing Nutrient Transport and Cell Stresses Within a Cyclically Strained Collagen Hydrogel

In the creation of engineered tissue constructs, the successful transport of nutrients and oxygen to the contained cells is a significant challenge. In highly porous scaffolds subject to cyclic strain, the mechanical deformations can induce substantial fluid pressure gradients, which affect the transport of solutes. In this article, we describe a poroelastic model to predict the solid and fluid mechanics of a highly porous hydrogel subject to cyclic strain. The model was validated by matching the predicted penetration of a bead into the hydrogel from the model with experimental observations and provides insight into nutrient transport. Additionally, the model provides estimates of the wall-shear stresses experienced by the cells embedded within the scaffold. These results provide insight into the mechanics of and convective nutrient transport within a cyclically strained hydrogel, which could lead to the improved design of engineered tissues.     

Windows of operation for bioreactor design for the controlled formation of tissue‐engineered arteries

The availability of large numbers of units of artificial arteries would offer significant benefits to the clinical management of bypass surgery. Tissue engineering offers the potential of providing vessels that can mimic the morphology, function, and physiological environment of native vessels. Ideally this would involve culturing stem cells in vitro within a biodegradable tubular scaffold so as to construct tissue for implantation. Essential to establishing a robust process for the production of tissue‐engineered arteries is the understanding of the impact of changes in the operating conditions and bioreactor design on the construct formation. In this article, models of transport phenomena were developed to predict the critical flow rates and mass transfer requirements of a prototype bioreactor for the formation of tissue‐engineered arteries. The impact of the cell concentration, tube geometry, oxygen effective diffusivity in alginate, substrate and metabolite concentration levels, feed rate, and recycle rate on the design of the bioreactor was visualized using windows of operation and contour plots. The result of this analysis determined the best configuration of the bioreactor that meets the cellular transport requirements as well as being reliable in performance while seeking to reduce the amount of nutrients to be used. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009     

The Anomalous Diffusion of a Tumor Invading with Different Surrounding Tissues

We simulated the invasion of a proliferating, diffusing tumor within different surrounding tissue conditions using a hybrid mathematical model. The in silico invasion of a tumor was addressed systematically for the first time within the framework of a generalized diffusion theory. Our results reveal that a tumor not only migrates using typical Fickian diffusion, but also migrates more generally using subdiffusion, superdiffusion, and even ballistic diffusion, with increasing mobility of the tumor cell when haptotaxis and chemotaxis toward the host tissue surrounding the proliferative tumor are involved. Five functional terms were included in the hybrid model and their effects on a tumor''s invasion were investigated quantitatively: haptotaxis toward the extracellular matrix tissue that is degraded by matrix metalloproteinases; chemotaxis toward nutrients; cell-cell adhesion; the proliferation of the tumor; and the immune response toward the tumor. Haptotaxis and chemotaxis, which are initiated by extracellular matrix and nutrient supply (i.e., glucose) respectively, as well as cell-cell adhesions all drastically affect a tumor''s diffusion mode when a tumor invades its surrounding host tissue and proliferates. We verified the in silico invasive behavior of a tumor by analyzing experimental data gathered from the in vitro culturing of different tumor cells and clinical imaging observations that used the same approach as was used to process the simulation data. The different migration modes of a tumor suggested by the simulations generally conform to the results observed in cell cultures and in clinical imaging. Our study not only discloses some migration modes of a tumor that proliferates and invades under different host tissues conditions, but also provides a heuristic method to characterize the invasion of a tumor in clinical medical imaging analysis.     

Tissue engineering by cell transplantation using degradable polymer substrates.

This paper reviews our research in developing novel matrices for cell transplantation using bioresorbable polymers. We focus on applications to liver and cartilage as paradigms for regeneration of metabolic and structural tissue, but review the approach in the context of cell transplantation as a whole. Important engineering issues in the design of successful devices are the surface chemistry and surface microstructure, which influence the ability of the cells to attach, grow, and function normally; the porosity and macroscopic dimensions, which affect the transport of nutrients to the implanted cells; the shape, which may be necessary for proper function in tissues like cartilage; and the choice of implantation site, which may be dictated by the total mass of the implant and which may influence the dimensions of the device by the available vascularity. Studies show that both liver and cartilage cells can be transplanted in small animals using this approach.     

Reazioni delle piante di Ricinus communis a incisioni sperimentali

Summary

The author has produced wounds in the stem of Ricinus communis, studing the regeneration and cicatrization processes.

The rapidity of the surface cicatrization is in relation with the water loss of the waunded cells.

Both in the stems woumded let free and in those in which an extra tissue has been introduced, the cicatrization processes tacke place. They only take place with different velocity. The healing process lead to the reconstruction of the cortical and the conducting tissues.

The whole reconstruction of the stele may occur, when the flow of the assimilated stuffs is slowed. Sothat it is probable that the regeneration depends more upon the tissue nutrition tham on a specifical properti of the tissues.     

Lignification of cell walls of infected cells in Casuarina glauca nodules that depend on symplastic sugar supply is accompanied by reduction of plasmodesmata number and narrowing of plasmodesmata

The oxygen protection system for the bacterial nitrogen‐fixing enzyme complex nitrogenase in actinorhizal nodules of Casuarina glauca resembles that of legume nodules: infected cells contain large amounts of the oxygen‐binding protein hemoglobin and are surrounded by an oxygen diffusion barrier. However, while in legume nodules infected cells are located in the central tissue, actinorhizal nodules are composed of modified lateral roots with infected cells in the expanded cortex. Since an oxygen diffusion barrier around the entire cortex would also block oxygen access to the central vascular system where it is required to provide energy for transport processes, here each individual infected cell is surrounded with an oxygen diffusion barrier. In order to assess the effect of these oxygen diffusion barriers on oxygen supply for energy production for transport processes, apoplastic and symplastic sugar transport pathways in C. glauca nodules were examined. The results support the idea that sugar transport to and within the nodule cortex relies to a large extent on the less energy‐demanding symplastic mechanism. This is in line with the assumption that oxygen access to the nodule vascular system is substantially restricted. In spite of this dependence on symplastic transport processes to supply sugars to infected cells, plasmodesmal connections between infected cells, and to a lesser degree with uninfected cells, were reduced during the differentiation of infected cells.     

Theoretical analysis of engineered cartilage oxygenation: influence of construct thickness and media flow rate

A novel parallel-plate bioreactor has been shown to modulate the mechanical and biochemical properties of engineered cartilage by the application of fluid-induced shear stress. Flow or perfusion bioreactors may improve tissue development via enhanced transport of nutrients or gases as well as the application of mechanical stimuli, or a combination of these factors. The goal of this study was to complement observed experimental responses to flow by simulating oxygen transport within cartilage constructs of different thicknesses (250 μm or 1 mm). Using numerical computation of convection–diffusion equations, the evaluation of the tissue oxygenation is performed. Four culture conditions are defined based on tissue thickness and flow rates ranging from 0 to ∼25 mL min⁻¹. Under these experimental conditions results show a mean oxygen concentration within the tissue varying from 0.01 to 0.19 mol m⁻³ as a function of the tissue thickness and the magnitude of the applied shear stress. More generally, the influence of shear stress varying (via flow rate modification) from 10⁻³ to 10 dynes cm⁻² on the tissue oxygenation is studied. The influence on the results of important physical parameters such as the maximal oxygen consumption rate of cells is discussed. Lastly, the importance of oxygen concentration in the lower chamber and its relevance to tissue oxygenation are highlighted by the model results.     

Studies on mineral ion absorption by plants

Summary The rate of accumulation of phosphorus in the roots, and its transport to the shoots, of whole plants grown in very dilute nutrient solutions, did not conform to the kinetic models derived from studies with excised roots or tissue slices. The demand for phosphorus associated with the rate of plant growth, or the level of metabolic activity within the tissues, appeared to have a marked influence on the rate of phosphorus uptake at deficient to optimum (1 to 10 μM P) levels of supply. A hypothesis is presented whereby the rate of influx of orthophosphate into the root cortical cells is regulated by the turn-over rate of the pool of inorganic phosphate in the cytoplasm, and by the rate of transport of inorganic phosphate to the shoot. The turn-over rate of this labile pool depends on inherent factors, such as the relative growth rate of the species, and on environmental factors, including the supply of essential nutrients such as nitrogen. re]19720502     

Invasive implantation and intimate placental associations in a placentotrophic african lizard,Trachylepis ivensi (scincidae)

In the viviparous lizard Trachylepis ivensi (Scincidae) of central Africa, reproducing females ovulate tiny ～1 mm eggs and supply the nutrients for development by placental means. Histological study shows that this species has evolved an extraordinary placental pattern long thought to be confined to mammals, in which fetal tissues invade the uterine lining to contact maternal blood vessels. The vestigial shell membrane disappears very early in development, allowing the egg to absorb uterine secretions. The yolk is enveloped precocially by the trilaminar yolk sac and no isolated yolk mass or yolk cleft develops. Early placentas are formed from the chorion and choriovitelline membranes during the neurula through pharyngula stages. During implantation, cells of the chorionic ectoderm penetrate between uterine epithelial cells. The penetrating tissue undergoes hypertrophy and hyperplasia, giving rise to sheets of epithelial tissue that invade beneath the uterine epithelium, stripping it away. As a result, fetal epithelium entirely replaces the uterine epithelium, and lies in direct contact with maternal capillaries and connective tissue. Placentation is endotheliochorial and fundamentally different from that of all other viviparous reptiles known. Further, the pattern of fetal membrane development (with successive loss and re‐establishment of an extensive choriovitelline membrane) is unique among vertebrates. T. ivensi represents a new extreme in placental specializations of reptiles, and is the most striking case of convergence on the developmental features of viviparous mammals known. J. Morphol. 2011. © 2011 Wiley Periodicals, Inc.