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Biomedical subjects

A J García

Publications and source records attributed to A J García.

At least 19 recordsLinked to original sources
PubMed2006

Evaluation of fruit-vegetable and fish wastes as alternative feedstuffs in pig diets.

Fruit-vegetable and fish wastes were evaluated as potential feedstuffs for growing-finishing pigs. Wastes were collected from shops in the city of Salamanca (Spain) and their nutritional composition, mineral content and digestibility were determined. The dry matter of the wastes under study was relatively low (12% for fruit-vegetable waste and 26% for fish waste), but they presented all of the nutrient requirements for swine diets. The fish waste contained 58% crude protein, 22% ash, 19% ether extract and 1% crude fibre, whereas the fruit-vegetable waste contained 65% nitrogen free extract, 13% crude fibre, 12% crude protein, 8% ash and 2% ether extract. Waste digestibility decreased with temperature, and hence temperatures over 65 degrees C for fruit-vegetable waste and 105 degrees C for fish waste should not be used in the treatment to reduce the moisture and to ensure the microbiology quality. Therefore, two diets were formulated using linear programming. The analysed waste was included in approximately 20% of one of the diets, while another diet was formulated without any type of waste. These data showed that this part of biodegradable municipal waste could be managed as alternative feedstuffs in swine diets, reducing the amount of biodegradable municipal waste going to landfills.

Animal Feed↗
PubMed2006

Inducible regulation of Runx2-stimulated osteogenesis.

Ex vivo gene therapy is a promising approach to orthopedic regenerative medicine. These strategies typically focus on the constitutive overexpression of osteogenic factors to induce osteoblastic differentiation and matrix mineralization. However, the unregulated production of osteoinductive molecules has also resulted in abnormal bone formation and tumorigenesis. To address these limitations, this work describes a retroviral system to deliver the Runx2 osteoblastic transcription factor under control of the tetracycline-inducible (tet-off) promoter in primary skeletal myoblasts. Runx2 expression was tightly regulated by anhydrotetracyline (aTc) concentration in cell culture media. Osteoblastic gene expression, alkaline phosphatase activity, and matrix mineralization were also controlled by aTc in a dose-dependent manner. Additionally, osteoblastic differentiation was temporally regulated by adding and removing aTc from the culture media. Engineered cells were seeded onto collagen scaffolds and implanted intramuscularly in the hind limbs of syngeneic mice. In vivo mineralization by these constructs was regulated by supplementing the drinking water with aTc, as demonstrated by micro-computed tomography and histological analyses. Collectively, these results present a novel system for regulating osteoblastic differentiation of a clinically relevant autologous cell source. This system is significant to developing controlled and effective orthopedic gene therapy strategies and studying the regulation of osteoblastic differentiation.

Animals↗
PubMed2006

The application of reproductive technologies to natural populations of red deer.

Over the past decade, there has been increasing interest in the application of reproductive technology to the conservation and management of natural populations of deer. The application of assisted reproduction technologies within natural population of deer is in its infancy. However, its future potential is enormous, particularly in relation to genetic management or conservation. This paper reviews the present state of such technologies for a wild subspecies of red deer, the Iberian red deer (Cervus elaphus hispanicus), by discussing the major components of oestrous synchronization, semen collection/cryopreservation and insemination techniques. In addition, findings made during the course of studies on natural populations have enormous potential for the understanding of novel reproductive mechanism that may not be uncovered by livestock or human studies. A summary of these results are also reviewed here.

Animals↗
PubMed2005

Biodegradable municipal solid waste: characterization and potential use as animal feedstuffs.

Five different fractions of the biodegradable municipal solid waste (BMSW) were evaluated as potential animal feedstuffs. For each source of waste (meat waste (MW), fish waste (FW), fruit and vegetables waste (FVW), restaurant waste (RW), household waste (HW)), samples were obtained from small shops (butchers, fishmongers, fruit and vegetable shops), restaurants and a MSW treatment plant (household waste). The chemical composition, microbiological characterization, dioxins, furans, PCB's and mineral content were determined for every type of waste fraction. The analysed biodegradable waste presented high moisture content (from 60% to 90%). Some fractions were dense in one nutrient: meat waste in ether extract, fish waste in crude protein, fruit and vegetable waste in nitrogen free extract. The other studied fractions (restaurant fraction and household fraction) presented a more balanced composition, but the presence of toxic concentrations of contaminants such as metals was higher than European legislation permitted values in animal feeding. From a microbiological standpoint, a heat treatment at 65 degrees C for 20 min was sufficient to ensure microbiological quality of the samples. This treatment was also advisable to reduce the moisture content: a lower moisture content facilitates the waste handling and processing and, therefore, the inclusion of these waste fractions in commercial animal diets. This paper presents a potential alternative for the recovery of organic matter content in municipal solid waste. The results obtained in this research and the feedstuffs legislation in force related to animal feed, indicated that some of the studied biodegradable waste fractions (meat waste, fruit and vegetable waste and fish waste) could be considered as alternatives to typical raw materials used in animal feeds.

Animal Feed↗
PubMed2005

Bio-adhesive surfaces to promote osteoblast differentiation and bone formation.

Binding of integrin adhesion receptors to extracellular matrix components, such as fibronectin and type I collagen, activates signaling pathways directing osteoblast survival, cell-cycle progression, gene expression, and matrix mineralization. Biomimetic strategies exploit these adhesive interactions to engineer bio-inspired surfaces that promote osteoblast adhesion and differentiation, bone formation, and osseointegration. These emerging initiatives focus on directing integrin binding through presentation of bio-adhesive motifs derived from extracellular matrices. These biomolecular approaches provide promising strategies for the development of biologically active implants and grafting substrates for enhanced bone repair.

Biomimetic Materials↗
PubMed2004

Chondrocyte phenotypes on different extracellular matrix monolayers.

Chondrocytes undergo a process of dedifferentiation in monolayer culture that is characterized by a transition to a fibroblast-like phenotype. This behavioral change poses a challenge for tissue-engineered cartilage constructs, as approaches using autologous cells require expansion in vitro. Because chondrocytes express a variety of integrin receptors specific to different adhesive proteins, we hypothesized that chondrocytes expanded on various underlying protein monolayers would have different phenotypic responses. Bovine articular chondrocytes were cultured for up to 2 weeks on tissue culture plastic, fibronectin, collagen type I or collagen type II substrate in the presence or absence of ascorbate. Contrary to our hypothesis, the extracellular matrix protein substrates used in this study did not significantly alter the changes in chondrocyte morphology, gene expression, matrix formation, or cytoskeletal organization. Cells on all substrates assembled equivalent matrices, which may have subsequently regulated cell behavior. In cultures with ascorbate, populations of round and spread cells emerged after 1 week, with round cells expressing collagen type II and the differentiated phenotype and spread cells dedifferentiating. In cultures without ascorbate, chondrocytes rapidly adhered and spread onto organized fibronectin matrices via the alpha5beta1 integrin, which has been associated with survival and proliferation of chondrocytes in vitro. These findings indicate that expanding chondrocytes on protein monolayers may not be an effective solution to preventing dedifferentiation and improving autologous chondrocyte transplantation.

Animals↗
PubMed2002

Reproductive seasonality in female Iberian red deer (Cervus elaphus hispanicus).

This study characterized the seasonal pattern of luteal cyclicity in Iberian red deer (n=16), by measuring plasma progesterone concentrations in hinds (female red deer) twice per week from calving (May and June) 1996 until May 1997. In eight of these hinds we also examined plasma prolactin profiles to assess seasonal responses to photoperiod. Plasma progesterone concentration in the 16 hinds studied indicated that the reproductive pattern is seasonal, and lasts for 5.73 +/- 0.27 months. After calving, progesterone levels remained basal (no luteal activity) for several months, except in a hind that lost her calf just after calving, and thus did not have to suckle it. This hind showed two consecutive estrus cycles in the month following calving, which suggests that suckling has an inhibiting effect on the resumption of ovarian activity. These results also showed that as long as the hinds do not become pregnant, they show between 5 and 10 estrus cycles per reproductive season (8.06 +/- 0.35), ranging between 105 and 249 days from onset of the first cycle to end of the last one. Uninterrupted cycling lasted for 3.5-6.4 months (mean, 4.6 +/- 0.24). Cyclic luteal activity was found from October to February in all hinds, with a smaller, but notable proportion in September (56.25%) and March (68.8%), whereas it was negligible in the remaining period. Our results show a reproductive season similar to or longer than that recorded by other authors. Prolactin plasma concentrations showed a yearly trend following that of photoperiod, with peak concentrations from April to July, a decrease in August, minimal concentrations from September to February and a sharp increase in March.

Animals↗
PubMed1999

Integrin-fibronectin interactions at the cell-material interface: initial integrin binding and signaling.

Integrin receptors mediate cell adhesion to extracellular matrices and provide signals that direct proliferation and differentiation. Integrin binding involves receptor-ligand interactions at the cell-substrate interface and assembly and reorganization of structural and signaling elements at the cytoplasmic face. Using a cross-linking/extraction/reversal method to quantify bound integrins, we demonstrate that the density of alpha5beta1 integrin-fibronectin bonds increases linearly with ligand density, as predicted by simple receptor-ligand equilibrium. This linear relationship is consistent with linear increases in cell adhesion strength with receptor and ligand surface densities. Furthermore, we show that phosphorylation of FAK, a tyrosine kinase involved in early integrin-mediated signaling, increases linearly with the number of integrin-Fn bonds. These linear relationships suggest the absence of cooperative effects in the initial stages of mechanical coupling and adhesion-mediated signaling.

Cell Adhesion↗
PubMed1999

Modulation of cell proliferation and differentiation through substrate-dependent changes in fibronectin conformation.

Integrin-mediated cell adhesion to extracellular matrices provides signals essential for cell cycle progression and differentiation. We demonstrate that substrate-dependent changes in the conformation of adsorbed fibronectin (Fn) modulated integrin binding and controlled switching between proliferation and differentiation. Adsorption of Fn onto bacterial polystyrene (B), tissue culture polystyrene (T), and collagen (C) resulted in differences in Fn conformation as indicated by antibody binding. Using a biochemical method to quantify bound integrins in cultured cells, we found that differences in Fn conformation altered the quantity of bound alpha5 and beta1 integrin subunits but not alphav or beta3. C2C12 myoblasts grown on these Fn-coated substrates proliferated to different levels (B > T > C). Immunostaining for muscle-specific myosin revealed minimal differentiation on B, significant levels on T, and extensive differentiation on C. Differentiation required binding to the RGD cell binding site in Fn and was blocked by antibodies specific for this site. Switching between proliferation and differentiation was controlled by the levels of alpha5beta1 integrin bound to Fn, and differentiation was inhibited by anti-alpha5, but not anti-alphav, antibodies, suggesting distinct integrin-mediated signaling pathways. Control of cell proliferation and differentiation through conformational changes in extracellular matrix proteins represents a versatile mechanism to elicit specific cellular responses for biological and biotechnological applications.

Adsorption↗
PubMed1998

Two-stage activation for alpha5beta1 integrin binding to surface-adsorbed fibronectin.

By analyzing the functional binding of alpha5beta1 integrin to adsorbed fibronectin in intact cells, we demonstrate that integrin activation results in linear increases in adhesion strength as a function of ligand density, suggesting that modulation of the receptor-ligand interaction is the dominant mechanism for adhesion during the initial stages of adhesion and that cooperative binding contributes little to initial adhesion strength. Using this experimental framework, we show the existence of three distinct activation states for alpha5beta1 integrin binding to adsorbed fibronectin for both passive, antibody-induced and active, cell-controlled activation. During the initial phase of adhesion, alpha5beta1 integrin is activated in an energy-dependent process from the nonbinding ground state to an intermediate state in which the receptor binds fibronectin and provides significant mechanical coupling. In later stages of adhesion maturation, alpha5beta1 integrin is activated to a higher binding state, which provides significant increases in adhesion strength compared with the intermediate state. These multiple binding states most likely result from different integrin conformations and reflect distinct interactions between alpha5beta1 and sites on adsorbed fibronectin. Multiple activation states for alpha5beta1 suggest the existence of distinct stages in adhesion signaling and strengthening and can provide a versatile mechanism for the regulation of adhesive interactions.

Adsorption↗
PubMed1998

Force required to break alpha5beta1 integrin-fibronectin bonds in intact adherent cells is sensitive to integrin activation state.

Binding of integrin receptors to extracellular ligands is a complex process involving receptor-ligand interactions at the cell-substrate interface, signals activating the receptors, and assembly of cytoskeletal and adhesion plaque proteins at the cytoplasmic face. To analyze the contribution of these elements to overall cell adhesion, we have developed a model system that characterizes the functional binding characteristic for adhesion receptors as the force required to separate the integrin-ligand bond. A spinning disk device was used to apply a range of controlled hydrodynamic forces to adherent cells. The adhesion of K562 erythroleukemia cells, a cell line expressing a single fibronectin receptor, integrin alpha5beta1, which was uniformly activated with the monoclonal antibody TS2/16, to defined fibronectin surface densities was examined. Cell adhesion strength increased linearly with receptor and ligand densities. Based on chemical equilibrium principles, it is shown that adhesion strength is directly proportional to the number of receptor-ligand bonds. This analysis provides for the definition of a new physical parameter, the adhesion constant psi, which is related to the bond strength and binding equilibrium constant and has units of force-length2. This parameter can be measured by the experimental system presented and is governed by the activation state of integrin receptors. This simplified model isolates the integrin receptor-ligand binding parameters and provides a basis for analysis of the functions of signaling and cytoskeletal elements in the adhesion process.

Cell Adhesion↗
PubMed1998

Effect of surface reaction stage on fibronectin-mediated adhesion of osteoblast-like cells to bioactive glass.

Bioactive glasses and ceramics enhance bone formation and bond directly to bone, and have emerged as promising substrates for bone tissue engineering applications. Bone bioactivity involves physicochemical surface reactions and cellular events, including cell attachment to adsorbed extracellular matrix proteins. The effects of fibronectin (Fn) adsorption and glass surface reaction stage on the attachment of osteoblast-like cells (ROS 17/2.8) to bioactive glass were analyzed. Bioactive glass disks were pretreated in a simulated physiologic solution to produce three reaction layers: unreacted glass (BG0), amorphous calcium phosphate (BG1d), and carbonated hydroxyapatite (BG7d). Synthetic hydroxyapatite (sHA) and nonreactive borosilicate glass (CG) were used as controls. A spinning disk device which applied a linear range of forces to attached cells while maintaining uniform chemical conditions at the interface was used to quantify cell adhesion. The number of adherent cells decreased in a sigmoidal fashion with applied force, and the resulting detachment profile provided measurements of adhesion strength. For the same amount of adsorbed Fn, cell adhesion was higher on surface-reacted bioactive glasses (BG1d and BG7d) than on BG0, CG, and sHA. For all substrates, cell attachment was primarily mediated by the RGD binding site of Fn, as demonstrated by blocking experiments with antibodies and RGD peptides. Cell adhesion strength increased linearly with adsorbed Fn surface density. Analysis of this fundamental relationship revealed that improved adhesion to reacted bioactive glasses resulted from enhanced cell receptor-Fn interactions, suggesting substrate-dependent conformational changes in the adsorbed Fn.

Biocompatible Materials↗
PubMed1997

Quantification of cell adhesion using a spinning disc device and application to surface-reactive materials.

Quantitative analysis of cell adhesion is essential in understanding physiological phenomena and developing biotechnological applications. Electrochemical measurements demonstrated that the transport patterns associated with a spinning disc device approximate the fluid flow and mass transport fields for a disc spinning in an infinite fluid. Therefore, this device applies a linear range of forces to attached cells under uniform and constant chemical conditions at the interface. The application of this apparatus for examining cell adhesion to surface-active materials was illustrated by investigating the attachment of osteoblast-like cells to fibronectin adsorbed onto bioactive and non-reactive glasses for different chemical environments. Cells were seeded on fibronectin-coated substrates for 15 min and then subjected to detachment forces for 10 min. The number of adherent cells decreased non-linearly with applied force and the detachment profile was accurately described by a sigmoidal curve fit, as expected for a cell population with normally distributed adhesion properties.

Adsorption↗
PubMed1997

Development of Graves' disease nine years after total thyroidectomy due to follicular carcinoma of the thyroid.

We report a 49-year-old woman with Marfan syndrome who underwent total thyroidectomy for follicular carcinoma. The patient was given 100 mCi of radioactive iodine (131I) followed by levothyroxine (LT4) 0.2 mg/day after surgery. The subsequent five total body scans were negative and thyroglobulin (TG) measurements ranged between undetectable levels to 12 ng/mL. Nine years after thyroidectomy the patient developed bilateral exophthalmos with markedly positive thyroid-stimulating immunoglobulins (TSI), indicating the presence of Graves' disease. TG levels increased and concurrently pulmonary metastases that did not concentrate radioiodine at tracer doses, were diagnosed. Due to these metastatic lesions, the patient received a therapeutic dose of 150 mCi of 131I 1 month after LT4 withdrawal, and a total body scan was made 10 days later. Slight uptake of 131I was found in the right side of the neck, whereas predominant uptake occurred in the right lung base. We suggest that the elevated TSI played a role in the growth of metastases.

Adenocarcinoma, Follicular↗
PubMed1996

[Tc-99-sestamibi scan in the preoperative localization of abnormal hyperfunctioning parathyroid glands].

Hyperparathyroidism is a relatively frequent condition mostly due to a solitary parathyroid adenoma. Although it has been claimed that surgical exploration is the best way to visualize the abnormal parathyroid gland, several imaging techniques have been proposed to localize it in order to simplify and shorten the surgical procedure. Echography, thalium-technetium scintigraphy, computerized tomography and nuclear magnetic resonance have shown a mean sensitivity of 75% which can be increased to about 90% by combining 2 or more of these procedures. In this study, we evaluated the utility of Tc-99m-sestamibi scintigraphy in 13 patients with hyperparathyroidism (11 primary, 2 secondary). High resolution neck echography was carried out in all of the cases. Cervical scans were obtained 10-15 min and 3 hours after giving an i.v. injection of 25 mCi Tc-99m-sestamibi in all the patients; suppression studies with combined 131-I were also done. Positive scans were obtained in 11 out of the 13 patients. Abnormal parathyroid glands were found and surgically excised in all the cases (10 adenomas, 1 carcinoma, 2 hyperplasias). Echographic localization had a sensitivity of only 33.3%. On the contrary, Tc-99m-sestamibi showed a sensitivity of 56% for the whole group, increasing to 82% in the 11 patients with primary hyperparathyroidism whereas the positive predictive value was of 91% and 90%, respectively. We conclude that Tc-99m-sestamibi is a very useful tool in localizing abnormal parathyroid glands and should be the first choice before reoperation after surgical failure or before the first parathyroid surgery whenever it is desired to shorten the surgical and anesthetic duration.

Adenoma↗
PubMed1994

Numerical analysis of extracellular fluid flow and chemical species transport around and within porous bioactive glass.

Modeling of the physical phenomena present at the biomaterial-tissue interface provides a valuable tool for examining the underlying mechanisms which influence the overall behavior of the implant-host system. Based on histological data from a previous implantation study (E. Schepers, M. De Clercq, P. Ducheyne, and R. Kempeneers, "Bioactive glass particulate materials as a filler for bone lesions," J. Oral Rehab.; 18, 439-452, 1991, Ref. 1) which documented the differentiation of mesenchymal cells to cells expressing the osteoblastic phenotype in porous bioactive glass, a finite element momentum and mass transport model was constructed. In this analysis, the extracellular compositional variations and fluid flow conditions around and within porous bioactive glass granules were determined. Numerical simulations demonstrated that the interstitial fluid flow around these granules (300-360 microns) is viscosity dominated (low Reynolds number flow) and that the fluid inside the granules remains stagnant. This velocity field results in shear stresses proportional to the velocity gradient at the granule-fluid interface outside the particles and no shear stresses inside the particles. A parametric study on the effect of interstitial fluid flow on chemical species (Na+, Ca+2, HPO(4)-2) transport outside the granules revealed three domains. At low velocities (0-0.1 micron/s), the transport of species is diffusion controlled. At intermediate velocities (1.0-10 microns/s), diffusion and convection contribute to the species transport. The concentration of chemical species is nearly uniform at high velocities (100-800 microns/s). For all three cases, the transport of chemical species within the granules is diffusion controlled. The differences in transport mechanisms and interstitial fluid flow conditions lead to variations in concentrations, reaction rates, and shear stresses between the inside and the outside of the glass granules. These differences may influence cellular migration, attachment, differentiation, and the overall response to these bioactive materials.

Animals↗
PubMedDate not supplied

[Generic drugs: good or bad? Physician's knowledge of generic drugs and prescribing habits].

In this article we analyze the responses of 1220 Spanish physicians who participated in a survery about generic drugs. A previously validated questionnaire was sent to physicians through the Spanish Medical Councils of the different provinces. Four items were analyzed: what doctors know about generic drugs (knowledge); physicians' prescribing habits concerning these drugs (attitude and professional competence); how prescription of generic drugs effects pharmaceutical costs amd, finally, what doctors believe a generic drug should be. The influence of physician-related variables (age, type of contract, specialty, workload, etc.) on prescribing of generic drugs was also analyzed. In view of the results, we believe that to rationalize expenditure through and appropriate policy on generic drugs Spanish health authorities should offer more and better training and information (clear and independent) about what generic drugs are.

Adult↗