Biomedical subjects

Ondrej Hovorka

Publications and source records attributed to Ondrej Hovorka.

4 recordsLinked to original sources

PubMed2006

Cytogenetic evidence for diversity of two nuclei within a single diplomonad cell of Giardia.

Giardia intestinalis is an ancient protist that causes the most commonly reported human diarrheal disease of parasitic origin worldwide. An intriguing feature of the Giardia cell is the presence of two morphologically similar nuclei, generally considered equivalent, in spite of the fact that their karyotypes are unknown. We found that within a single cell, the two nuclei differ both in the number and the size of chromosomes and that representatives of two major genetic groups of G. intestinalis possess different karyotypes. Odd chromosome numbers indicate aneuploidy of Giardia nuclei, and their stable occurrence is suggestive of a long-term asexuality. A semi-open type of Giardia mitosis excludes a chromosome interfusion between the nuclei. Differences in karyotype and DNA content, and cell cycle-dependent asynchrony are indicative of diversity of the two Giardia nuclei.

Animals↗

PubMed2006

HPMA based macromolecular therapeutics: internalization, intracellular pathway and cell death depend on the character of covalent bond between the drug and the peptidic spacer and also on spacer composition.

Polymeric conjugates based on N-(2-hydroxypropyl)methacrylamide (HPMA) have been tested as potential carrier for anticancer drug - doxorubicin (Dox). Two types of conjugates were synthesized: (a) conjugates containing Dox bound through an amidic bond to an oligopeptidic side-chain (usually GFLG) and (b) hydrolytically cleavable conjugates wherein Dox is bound to the polymeric carrier through a pH sensitive bond. The mechanism of action of both conjugates is different and reflects the diverse way and intensity of their intracellular accumulation. All conjugates containing doxorubicin bound via an amidic bond directly penetrate the plasma membrane and are detectable in all associated cellular membranes, i.e. membranes of the endocytic compartment, a nuclear membrane as well as membranes of Golgi and endoplasmic reticulum. We have never been able to detect released doxorubicin inside the nuclei of the treated cells. The cytotoxicity of these conjugates seems to be primarily caused by the damage of cellular membranes. Necrosis is the main mechanism of the cell death. Conjugates containing hydrolytically bound doxorubicin are internalized by endocytosis and fluid phase pinocytosis and doxorubicin is cleaved from the polymeric carrier at low pH in late endosomes and lysosomes. An apoptosis is the main mechanism of the cell death. The spacer influences the rate of the intracellular release of the drug rather than the rate of internalization.

3T3 Cells↗

PubMed2005

Arranging matter by magnetic nanoparticle assemblers.

We introduce a method for transporting colloidal particles, large molecules, cells, and other materials across surfaces and for assembling them into highly regular patterns. In this method, nonmagnetic materials are manipulated by a fluid dispersion of magnetic nanoparticles. Manipulation of materials is guided by a program of magnetic information stored in a substrate. Dynamic control over the motion of nonmagnetic particles can be achieved by reprogramming the substrate magnetization on the fly. The unexpectedly large degree of control over particle motion can be used to manipulate large ensembles of particles in parallel, potentially with local control over particle trajectory.

Journal Article↗

PubMed2002

Differences in the intracellular fate of free and polymer-bound doxorubicin.

Internalization and subcellular fate of free doxorubicin or its polymeric conjugates based on poly N-(2-hydroxypropyl)methacrylamide (pHPMA), either non-targeted or targeted with anti-Thy1.2 or anti-CD71 monoclonal antibody was tested on EL-4 mouse T-cell lymphoma, SW620 human colorectal carcinoma and OVCAR-3 human ovarian adenocarcinoma. Doxorubicin fluorescence allowed us to follow the internalization and intracellular distribution of tested conjugates by laser scanning confocal microscopy and/or by fluorescent microscopy. Whereas free doxorubicin was always detectable only in the nuclei of treated cells, detectable fluorescence of doxorubicin bound to a polymeric carrier, targeted or non-targeted, was detectable up to 3 days of incubation only in the cytoplasmatic structures. While free doxorubicin causes apoptosis in the populations of tested cancer cell lines, significant number of apoptotic cells was never found in cell cultures exposed to targeted or non-targeted polymeric conjugates. In contrast to free doxorubicin, which is a strong inducer of p53 expression, increased p53 expression was never observed after the treatment with the polymeric drug. High-performance liquid chromatographic analysis shows that the percentage of cleaved doxorubicin is very low even after 48 h of incubation of tested cells with the polymeric conjugate, and cannot be the only reason for the toxicity of the conjugate. We suggest that: (a) after the treatment with pHPMA-bound drug, the cells die by necrosis and (b) the toxicity of pHPMA-based conjugates is a combination of the toxic effect of released doxorubicin and the toxic effect of doxorubicin in polymer-bound form directed against cell membranes.

Animals↗