A mitral allograft is us ed exceptionally in the mitral, as well as in the tricuspid position, mostly as an experimental surgical procedure. The authors decided to evaluate the possibility of inserting a cryopreserved mitral allograft into the tricuspid position in a sheep experimental model. Within the framework of this experimental project the mechanical properties of the cryopreserved mitral allograft were tested. A novel methodology studying the functional unit composed of mitral annulus, leaflet, chordae tendinaea, and papillary muscle is presented. A five-parameter Maxwell model was applied to characterize the viscoelastic behavior of sheep mitral valves. A control group of 39 fresh mitral specimens and a test group of 13 cryopreserved mitral allografts from tissue bank were tested. The testing protocol consisted of six loading cycles with 1 mm elongation every 5 min. There was no significant difference in the mean values of the determined parameters (p> 0.05) which confirms the main hypothesis that cryopreservation does not influence significantly material parameters characterizing the tissue mechanics. Slight discrepancy is observed in variances of viscous parameters suggesting that the values of the test group may be spread over larger interval due to the treatment., J. Hlubocký ... [et al.]., and Obsahuje bibliografii a bibliografické odkazy
a1_Mechanical properties of scaffolds seeded with mesenchymal stem cells used for cartilage repair seem to be one of the critical factors in possible joint resurfacing. In this paper, the effect of adding hyaluronic acid, hydroxyapatite nanoparticles or chitosan nanofibers into the cross-linked collagen I on the mechanical response of the lyophilized porous scaffold has been investigated in the dry state at 37 oC under tensile loading. Statistical significance of the results was evaluated using ANOVA analysis. The results showed that the addition of hyaluronic acid significantly (p<<0.05) reduced the tensile elastic modulus and enhanced the strength and deformation to failure of the modified cross-linked collagen I under the used test conditions. On the other hand, addition of hydroxyapatite nanoparticles and chitosan nanofibers, respectively, increased the elastic modulus of the modified collagen ten-fold and four-fold, respectively. Hydroxyapatite caused significant reduction in the ultimate deformation at break while chitosan nanofibers enhanced the ultimate deformation under tensile loading substantially (p<<0.05). The ultimate tensile deformation was significantly (p<<0.05) increased by addition of the chitosan nanofibers. The enhanced elastic modulus of the scaffold was translated into enhanced resistance of the porous scaffolds against mechanical load compared to scaffolds based on cross-linked neat collagen or collagen with hyaluronic acid with similar porosity. It can be concluded that enhancing the rigidity of the compact scaffold material by adding rigid chitosan nanofibers can improve the resistance of the porous scaffolds against compressive loading, which can provide more structural protection to the seeded mesenchymal stem cells when the construct is implanted into a lesion., a2_Moreover, scaffolds with chitosan nanofibers seemed to enhance cell growth compared to the neat collagen I when tested in vitro as well as the scaffold stability, extending its resorption to more than 10 weeks., J. Jančář, A. Slovíková, E. Amler, P. Krupa, H. Kecová, L. Plánka, P. Gál, A. Nečas., and Obsahuje bibliografii
In the article, the actions of homocysteine (Hcys) and its metabolite - cyclic thioester – homocysteine thiolactone (HTL) on complex process of hemostasis, which regulates the flowing properties of blood, are described. Possible interaction of Hcys and HTL with endothelial cells, blood platelets, plasmatic fibrinogen and plasminogen, as the important major components of hemostasis are also discussed. The modification of hemostatic proteins (N-homocysteinylated or S-homocysteinylated proteins) induced by Hcys or its thiolactone, and links of homocysteine or homocysteine thiolactone to •NO metabolism seem to be the main reason of biotoxicty of homocysteine in cardiovascular diseases., K. Karolczak, B. Olas., and Obsahuje seznam literatury
We have studied the mechanism of Na+ deprivation-induced catecholamine secretion from freshly isolated bovine adrenal chromaffin cells. Na+ deprivation-induced catecholamine secretion depended on free extracellular Ca2+ concentrations and was almost parallel to 45Ca2+ influx into the cells under various experimental conditions. Furthermore, Na+ deprivation-induced 45Ca2+ influx and catecholamine secretion were actually induced by a relative Na+ concentration gradient across the plasma membrane, but not by simple omission of Na+ from the medium. These results indicate that the deprivation of Na+ from the medium changes the relative Na+ gradient across the plasma membrane and results in Ca2+ influx via a reverse mode of Na+-Ca2+ exchange rather than by inducing Ca2+ entry through Ca2+ channels by eliminating the competition between extracellular Na+ and Ca2+., M. Isosaki, T. Nakashima., and Obsahuje bibliografii
More than 50 % of end-stage renal disease (ESRD) patients treated by chronic hemodialysis die from cardiovascular diseases, including congestive heart failure (CHF). The incidence of CHF is rising in both general and ESRD population. However, the mechanisms, which lead to the development of CHF in dialyzed patients, differ considerably. First, there are several factors leading to increase of the left ventricular afterload: volume overload between dialyses, hypertension, increased arterial stiffness, anemia, vascular access flow (arteriovenous fistula) and sympathetic activation. Second, hypertension, left ventricular hypertrophy, anemia and frequently present coronary artery disease worsen myocardial oxygenation. The combination of these factors explains the high incidence of CHF in dialyzed patients and their roles are reviewed in this article., J. Malík ... [et al.]., and Obsahuje seznam literatury
Neurogenic pulmonary edema is a life-threatening complication, known for almost 100 years, but its etiopathogenesis is still not completely understood. This review summarizes current knowledge about the etiology and pathophysiology of neurogenic pulmonary edema. The roles of systemic sympathetic discharge, central nervous system trigger zones, intracranial pressure, inflammation and anesthesia in the etiopathogenesis of neurogenic pulmonary edema are considered in detail. The management of the patient and experimental models of neurogenic pulmonary edema are also discussed., J. Šedý, J. Zicha, J. Kuneš, P. Jendelová, E. Syková., and Obsahuje bibliografii a bibliografické odkazy
Many aspects of protein function regulation require specific protein-protein interactions to carry out the exact biochemical and cellular functions. The highly conserved members of the 14-3-3 protein family mediate such interactions and through binding to hundreds of other proteins provide multitude of regulatory functions, thus playing key roles in many cellular processes. The 14-3-3 protein binding can affect the function of the target protein in many ways including the modulation of its enzyme activity, its subcellular localization, its structure and stability, or its molecular interactions. In this minireview, we focus on mechanisms of the 14-3- 3 protein-dependent regulation of three important 14-3-3 binding partners: yeast neutral trehalase Nth1, regulator of G-protein signaling 3 (RGS3), and phosducin., V. Obsilova ... [et al.]., and Obsahuje bibliografii a bibliografické odkazy
Leptin-melanocortin pathway plays an essential role in the body weight regulation. Enhanced melanocortin signaling in the hypothalamus results in both decreased food intake and increased energy expenditure. The discovery of monogenic obesities with dysfunction of melanocortin-4 receptor (MC4R) greatly contributed to understanding of energy balance regulation. This review presents phenotypical characterization and prevalence of the MC4R gene mutations. Genome-wide association studies revealed that MC4R gene is significantly related not only to monogenic obesities but also to common obesity. An interaction of variants in the MC4R gene with fat mass and obesity associated (FTO) gene significantly increases the risk for obesity, particularly in adolescence. On the other hand, about 15 % of the MC4R gene variants result in a gain of function that protects against obesity and is associated with favorable metabolic profile. Long-term attempts to activate the MC4R have recently been finalized by a discovery of setmelanotide, a novel specific MC4R agonist that is devoid of untoward cardiovascular side-effects. The employment of specific MC4R agonists may open new horizons not only in the treatment of rare monogenic obesities but also in some common obesities where stimulation of MC4R could be achieved., Vojtěch Hainer, Irena Aldhoon Hainerová, Marie Kunešová, Radka Taxová Braunerová, Hana Zamrazilová, Běla Bendlová., and Obsahuje bibliografii