Biomedical subjects

Petr Dvorák

Publications and source records attributed to Petr Dvorák.

10 recordsLinked to original sources

PubMed2006

Radiocesium in mushrooms from selected locations in the Czech Republic and the Slovak Republic.

In this paper, activity concentrations of radiocesium in mushrooms from various locations in the Czech Republic and the Slovak Republic in the years 2000-2004 are presented. Summary reports of Czech regulatory bodies have judged the average activity concentrations in mushrooms to be remarkably below the maximum permissible level of contamination. However, there are certain regions where radiocesium activities have approached the maximum permissible level for contamination of basic foodstuff. For example, the highest activity concentration of (137)Cs measured by gamma-spectrometry was 2,263 Bq kg(-1) (on a dry mass basis), in Xerocomus badius from Staré Ransko (a locality in the Czech-Moravian Highlands, Czech Republic). The highest activity concentration of (137)Cs measured in Slovakia was 966 Bq kg(-1) (on a dry mass basis), for Suillus luteus from Senica. For comparison, the corresponding activity concentration in a sample taken within the 30 km zone around Chernobyl was measured to be 6,000 Bq kg(-1) (on a dry mass basis). Our results have also demonstrated remarkably lower activity concentrations of (137)Cs in Slovakia compared to those in the Czech Republic.

Agaricales↗

PubMed2006

Functional polymer hydrogels for embryonic stem cell support.

Embryonic stem (ES) cells are pluripotent cells with the ability to differentiate among all embryonic and adult cell lineages. Derivation of human ES cells opened up the way for treatment of many serious disorders by stem cell-based transplantation therapy. One of the most exciting challenges in development of transplantation therapies is to repair the damaged part of the organ or tissue by transplantation of undifferentiated ES cells or their differentiated derivatives within three-dimensional polymer scaffold. This method allows both renewal of structure and restoration of function of the organ. To address this issue, new polymer hydrogels were synthesized and tested. Cationic hydrogel slabs were synthesized by bulk radical copolymerization of 2-hydroxyethyl methacrylate (HEMA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) with ethylene dimethacrylate (EDMA) or 1-vinyl-2-pyrrolidone (VP) with N,N'-divinylethyleneurea (DVEU) or EDMA in the presence of saccharose or NaCl as a porogen. Swelling studies of the synthesized copolymers showed a high water content in the swollen state. Biocompatibility was studied with the use of feeder-independent mouse ES cell line D3. Cells grown either on the surface or inside synthesized polymer slabs suggest that the tested slabs are not toxic. The ability of ES cells to proliferate was only partially limited in PHEMA slabs crosslinked with EDMA compared with standard culture conditions. When cultured for a limited period of time, ES cells retained their undifferentiated state independently of properties of the hydrogel slabs, presence or absence of surface charges, type of crosslinking agent and matrix (PHEMA or PVP). Notably, prolonged culture in superporous hydrogel slabs initiated ES cell differentiation. Compared with unmodified PHEMA, the number of proliferating ES cells was still lower in the presence of cationic polymers.

Animals↗

PubMed2006

Posttraumatic pneumopericardium: a sign of severe injury or radiodiagnostic rarity?

We present three cases of pneumopericardium following blunt chest trauma injury. All three patients were victims of road traffic accidents. All had multiple associated injuries and pneumopericardium was found as the additional finding. Pneumopericardium was treated conservatively with thoracic drains placement and patients observation. Transesophageal echocardiography was used as a method of choice for exclusion of cardiac air tamponade. All three patients survived.

Accidents, Traffic↗

PubMed2005

Surface immobilized protein multilayers for cell seeding.

Multilayer assemblies containing various cell-adhesive proteins such as gelatin, collagen IV, and laminin or polycations polylysine and poly(ethyleneimine) were immobilized on the polystyrene surface using the layer-by-layer technique based on hydrophobic and electrostatic interactions between oppositely charged macromolecules. The formation and stability of the assemblies and the adsorption of proteins from a serum containing cell-cultivation media onto their surfaces were observed in real time by Fourier transform infrared multiple internal reflection spectroscopy. The adhesion and growth of mouse embryonic stem cells line D3 were tested in polystyrene culture dishes coated with the assemblies. The cells were seeded in complete serum-containing media or in serum-free media and in the presence (non-differentiated) and/or absence (differentiated) of leukemia inhibitory factor. Proteins from serum-containing cell-cultivation media adsorbed rapidly onto positively charged surfaces. The cells grew best on surfaces coated with gelatin and collagen IV assemblies. There were no significant differences in the growth of the non-differentiated and differentiated cells in complete serum-containing media. When seeded in serum-free media, non-differentiated cells grew better than the differentiated ones. Particularly, polycation surfaces treated with glutaraldehyde promoted the growth of the non-differentiated cells and hindered the growth of the differentiated cells. The layer-by-layer deposition appears to be a practicable technique by which scaffolds for tissue engineering can be coated with biomolecular assemblies tailored to specific cells and applications.

Adsorption↗

PubMed2005

Abnormal development of mouse embryoid bodies lacking p27Kip1 cell cycle regulator.

Cultures of three-dimensional aggregates of embryonic stem cells (ESCs) called embryoid bodies (EBs) provide a valuable system for analyzing molecular mechanisms that regulate differentiation of this unique cell type. Cyclin-dependent kinase inhibitor p27Kip1 (p27) becomes elevated during the differentiation of mouse ESCs (mESCs). In this study, various aspects of differentiation of EBs produced from normal and p27-deficient mESCs were analyzed to address the biological significance of this elevation. It was found that EBs lacking p27 grew significantly bigger, but this was not accompanied by detect-able abnormalities in the activities of cyclin-dependent kinases (CDKs). In most EB cells, downregulation of activating cyclins rather than upregulation of inhibiting p27 is probably responsible for lowering the activity of their CDKs. Abnormalities in the development of specific cell lineages were also observed in p27-deficient EBs. These included elimination of cells positive for cytokeratin endo-A (TROMA-I) and increased proliferation and formation of cavities originating from cells positive for Lewis-X. Our data also suggest that although two different pools of Lewis-X-expressing cells, cluster forming (ESC-like) and cavity forming (neural progenitors), normally exist in EBs, the absence of p27 leads to the enhancement of only the neural pool. No failure was found when the neurogenic capacity of p27-deficient mESCs was tested using various protein markers. Together, our data point to a dual role of p27 in mESCs, with one role being in the regulation of proliferation and the other role in establishing some other aspects of a differentiated phenotype.

Animals↗

PubMed2004

The role of p27(Kip1) in maintaining the levels of D-type cyclins in vivo.

This in vivo study employs p27-deficient mice to investigate the significance of p27 for the metabolism of D-type cyclins in differentiated cells. The absence of p27 results in decreased levels of cyclins D2 and/or D3 in some organs. As demonstrated on Leydig cells of testis, such dependency is only restricted to certain cell types including terminally differentiated ones, and the absence of p27 in these cells can interfere with their differentiation. The decrease of cyclin D caused by the absence of p27 equals the amount of cyclin D physically associated with p27 in non-mutant animals. The data indicate that it is the proportion of p27-associated cyclin D that determines the response to p27 deficiency. Cells in which the level of D-type cyclin is dependent on p27 do not up-regulate the activity of their CDK2 and CDK4 upon loss of p27, and these cells have a negligible amount of p27 bound to CDK2 and/or cyclin A/E under normal conditions. Together, the findings suggest the existence of a dual role for p27, one being a classical regulation of cell cycle via inhibition of cyclin-dependent kinases (CDK), and the other being participation in the establishment and/or maintenance of differentiated status that is realized in conjunction with D-type cyclins.

Animals↗

PubMed2004

Poly(2-hydroxyethyl methacrylate)-based slabs as a mouse embryonic stem cell support.

Poly(2-hydroxyethyl methacrylate) (PHEMA) crosslinked with ethylene dimethacrylate (EDMA) or N,O-dimethacryloylhydroxylamine (DMHA) was obtained in the form of slabs by bulk radical polymerization. Two porosity-inducing methods were investigated, phase separation using a low-molecular-weight porogen and a salt-leaching technique using NaCl and saccharose. Compared with the phase separation, the salt-leaching created open porous structures with voids of the size and shape of crystallites. To address its potentials in the context of stem cell therapies, undifferentiated mouse embryonic stem cells D3 (ES D3 cells) were seeded on the slabs and analyzed for the ability to grow on different types of non-degradable and/or degradable porous PHEMA hydrogels. The cells were able to proliferate only on PHEMA crosslinked with EDMA or 2 wt% DMHA. In order to assess the effect of gelatin, which is routinely used for ES cell cultures, PHEMA slabs were soaked in gelatin solutions and compared the number of cells on gelatin-treated and untreated slabs 4 days after cell seeding. Surprisingly, the number of cells was only slightly higher on gelatin-treated slabs.

Animals↗

PubMed2003

CT-guided stereotaxy: first 10-year experience.

The authors present an overview on CT-guided stereotaxy performed in the last 10 years in the University Hospital Olomouc. During this period a total of 811 stereotactic brain operations were performed. Of these, 710 were done in the field of afunctional and 101 in the field of functional stereotaxy. The majority of procedures were biopsies of intracranial lesions (n = 464), evacuations of intracerebral hematomas with or without drainage and fibrinolysis (n = 147) and thalamotomies in patients with Parkinson's disease (n = 88). With the exception of the two years at the beginning, the number of yearly performed stereotaxies varied between 66-106 (mean, 86.9). Serious complications appeared after three procedures (0.37 %).

Brain↗

PubMed2002

Early cycling-independent changes to p27, cyclin D2, and cyclin D3 in differentiating mouse embryonal carcinoma cells.

Changes to cell cycle-regulating machinery that occur during differentiation of cells are thought to be responsible mostly for withdrawal from cycling. Here, embryonal carcinoma (EC) cell lines were found that differ in their basal levels of p27 inhibitor of cyclin-dependent kinases but not in their growth rates, distribution of cells in phases of cell cycle, and their ability to differentiate. High basal levels of p27 did not substitute for up-regulation of p27 that in EC cells normally occurs early after entering a differentiation pathway. Under both standard and differentiation-supporting culture conditions, variances in the levels of p27 were strictly followed by variances in the levels of cyclins D2 and D3. In EC cells genetically manipulated to overexpress p27 protein, cyclin D3 became up-regulated and vice versa. Supposedly, titration of p27 by D-type cyclins, which prevents its inhibitory action toward cyclin-dependent kinase 2, allows for the maintenance of elevated p27 in proliferating EC cells. Increased levels of p27 in early embryonal cells thus may, at least in certain phases of embryo development, serve a differentiation-associated, rather than proliferation-associated, function.

Animals↗

PubMedDate not supplied

Neural differentiation of mouse embryonic stem cells grown in monolayer.

To drive neural differentiation of mouse embryonic stem (ES) cells, various culture protocols have been previously developed that all require the formation of embryoid bodies, usually combined with a treatment by all-trans retinoic acid (aRA). Here, we investigated whether or not neural differentiation can also occur in a simplified monolayer culture. Mouse ES cells were plated in serum-containing DMEM media with and without aRA and grown under these conditions for 2 days. Then, the cells were transferred to fresh serum-containing DMEM media and/or to serum-free DMEM/F12 media supplemented with a mixture of insulin, transferrin, selenium, and fibronectin (ITSF) for further culture. The changes in cell morphology and in the expression of selected molecular markers were monitored. Generally, in contrast to all the others, the protocol consisting of a 2-day culture in serum-containing DMEM followed by continuous exposure to the ITSF supplement in DMEM/F12 drove a vast majority of ES cells to generate phenotypic signs of neural lineage. Altogether, neural differentiation can be achieved in vitro without the step involving the formation of embryoid bodies as well as the treatment by aRA.

Animals↗