Biomedical subjects

P Novák

Publications and source records attributed to P Novák.

At least 19 recordsLinked to original sources

PubMed2006

Detection of magnetic circular dichroism using a transmission electron microscope.

A material is said to exhibit dichroism if its photon absorption spectrum depends on the polarization of the incident radiation. In the case of X-ray magnetic circular dichroism (XMCD), the absorption cross-section of a ferromagnet or a paramagnet in a magnetic field changes when the helicity of a circularly polarized photon is reversed relative to the magnetization direction. Although similarities between X-ray absorption and electron energy-loss spectroscopy in a transmission electron microscope (TEM) have long been recognized, it has been assumed that extending such equivalence to circular dichroism would require the electron beam in the TEM to be spin-polarized. Recently, it was argued on theoretical grounds that this assumption is probably wrong. Here we report the direct experimental detection of magnetic circular dichroism in a TEM. We compare our measurements of electron energy-loss magnetic chiral dichroism (EMCD) with XMCD spectra obtained from the same specimen that, together with theoretical calculations, show that chiral atomic transitions in a specimen are accessible with inelastic electron scattering under particular scattering conditions. This finding could have important consequences for the study of magnetism on the nanometre and subnanometre scales, as EMCD offers the potential for such spatial resolution down to the nanometre scale while providing depth information--in contrast to X-ray methods, which are mainly surface-sensitive.

Journal Article↗

PubMed2006

[Peripheral primitive neuroectodermal tumor -- PNET].

The authors describe three cases of peripheral primitive neuroectodermal tumor. The tumor was found in soft tissues of the crus, shoulder girdle and perineum, and was also located paravertebrally and epidurally at the level of L1-L2 vertebrae. Radiological findings were not specific for this disease. The results of imaging methods (sonography, CT, MRI, DSA) were important for the assessment of tumor size, its boundary and invasion of the surrounding tissues, and for the evaluation of tumor response to therapy and detection of recurrent disease. The PNET diagnosis was based on immunohistochemical, biochemical and cytogenetic examinations. One patient died 5 months after the first clinical signs were manifested; the two patients surviving for 2 and 1 3/4 years after first sign manifestation, respectively, remained in the care of cancer specialists. Key words: skeletal Ewing's sarcoma, extra-skeletal Ewing's sarcoma, Ewing's sarcoma family of tumors, peripheral primitive neuroectodermal tumor.

Adolescent↗

PubMed2006

PrP gene polymorphism in sheep breeds in Slovakia and susceptibility to scrapie.

We analyzed the prion protein (PrP) genotype based on the codons 136, 154 and 171 and assigned to five risk groups (R1-R5) in healthy and scrapie-affected sheep in Slovakia. In healthy (asymptomatic) population, 119 Merino, 106 Improved Valachian, 117 Tsigai, and 48 Suffolk breeds were tested. Among the asymptomatic sheep, the low-risk genotypes R1 and R2 were most abundant in Suffolk (94%) and Merino (84%) breeds, followed by Tsigai (58%) and Improved Valachian (40%) breeds. The medium-risk group R3 was most frequent in Improved Valachian (31%) breed, followed by Tsigai (21%), Merino (10%), and Suffolk (6%) breeds. The occurrence of high-risk groups R4 and R5 was none in Suffolk breed, followed by Merino (6%), Tsigai (21%), and Improved Valachian (30%) breeds. Since 2003, altogether 48 cases of scrapie have been confirmed in Tsigai (38), Merino (4), Improved Valachian (2), Improved Valachian x Tsigai (3), and Suffolk (1) breeds. Among sheep with scrapie, Merino breed belonged to the medium-risk group R3. The majority of scrapie-affected Tsigai sheep were classified into high-risk R5 (50%) and medium-risk R3 (42%) groups. We showed an association of scrapie with medium- and high-risk groups of PrP genotype in Slovakia. In particular, the glutamine at position 171 appears to be of major importance for the susceptibility to scrapie.

Animals↗

PubMed2005

Experience with a small animal hyperthermia ultrasound system (SAHUS): report on 83 tumours.

An external local ultrasound (US) system was developed to induce controlled hyperthermia of subcutaneously implanted tumours in small animals (e.g., mice and rats). It was designed to be compatible with a small animal positron emission tomography scanner (microPET) to facilitate studies of hyperthermia-induced tumour re-oxygenation using a PET radiopharmaceutical, but it is applicable for any small animal study requiring controlled heating. The system consists of an acrylic applicator bed with up to four independent 5 MHz planar disc US transducers of 1 cm in diameter, a four-channel radiofrequency (RF) generator, a multiple thermocouple thermometry unit, and a personal computer with custom monitoring and controlling software. Although the system presented here was developed to target tumours of up to 1 cm in diameter, the applicator design allows for different piezoelectric transducers to be exchanged and operated within the 3.5-6.5 MHz band to target different tumour sizes. Temperature feedback control software was developed on the basis of a proportional-integral-derivative (PID) approach when the measured temperatures were within a selectable temperature band about the target temperature. Outside this band, an on/off control action was applied. Perfused tissue-mimicking phantom experiments were performed to determine optimum controller gain constants, which were later employed successfully in animal experiments. The performance of the SAHUS (small animal hyperthermia ultrasound system) was tested using several tumour types grown in thighs of female nude (nu/nu) mice. To date, the system has successfully treated 83 tumours to target temperatures in the range of 41-43 degrees C for periods of 65 min on average.

Algorithms↗

PubMed2005

[Infectious complications after arthroscopic replacement of the cruciate ligaments].

PURPOSE OF THE STUDY: Infection following replacement of the cruciate ligaments of the knee joint may result in not only graft failure but also complete destruction of the joint. The aim of this study was to report the authors' experience with the diagnosis and therapy of this, fortunately occasional, complication. MATERIAL: In the period from October 1999 till June 2003, a total of 2372 arthroscopic operations of the knee joint were carried out; of these, 908 were cruciate ligament replacements. Three surgeons using the same technique were involved. An autologous graft taken from the ligamentum patellae and fixed with interference screws was used in 857 knees, and a graft derived from the tendon of the semitendinosus or the gracilis muscle, with "endobutton" fixation, was employed. Two kinds of inflammatory complications were recorded in the early post-operative period, i. e., infection of the articular cavity and infected subcutaneous hematoma at site of graft collection. METHODS: When infection of the articular cavity was suspected because of severe pain, perspiration, motion restriction, articular exudate and increased temperature, arthrocentesis was performed and a sample of the fluid withdrawn was sent for cultivation; laboratory tests (blood counts, erythrocyte sedimentation rate, C-reactive protein) were carried out and antibiotic therapy was started. When there was no subsidence of signs within 24 h, revision surgery was carried out without waiting for the results of laboratory examination. Coagula from inside of the cavity were removed through a short incision on the lateral side of the suprapatellar recess and, after repeated thorough irrigation, a suction drain was inserted. Antibiotic therapy was administered parenterally. Infected subcutaneous hematoma, associated with edema, reddening and tension of the skin, pain, fluctuation and, in some cases, high temperature, was treated by disintegration of the wound, removal of the hematoma, debridement and thorough irrigation. After drain insertion, the wound was closed by suture. The development of infectious complications was assessed in relation to the risk factors described in the literature, namely, patient's age, operating room time and tourniquet application, previous infections of the upper respiratory or urinary tracts, previous surgery on the same joint and the season in which the operation was performed. RESULTS: A total of 37 revision operations following replacement of the cruciate ligaments of the knee joint were carried out; of these, 29 involved the articular cavity. An infectious agent was found in six cases (0.7 % of the total number of cruciate ligament replacements). Eight knees were treated for hematoma in the wound at site of graft collection and, in seven of them, Staphylococcus aureus was isolated (0.8 % of the total number of crucial ligament replacements). For recurrent problems the distal fixation material had to be removed in two patients at 6 and 12 months, respectively. Afterwards the patients were free from symptoms. The only risk factor for the development of infection was found to be previous surgery on the same joint. DISCUSSION: The authors prefer early revision surgery in the cases showing signs of developing infection in the articular cavity or hematoma in the wound after graft collection. Therefore the results of positive cultivation were fewer in comparison with other relevant reports. In revision surgery on the articular cavity, the authors made a 2-cm incision on the lateral side of the suprapatellar recess, which enabled them to wash out all coagula, in comparison to other authors who recommend irrigation with the use of arthroscopic apparatus only. The early intervention made it possible to keep all grafts in situ. The only factor associated with a higher occurrence of complications in our patients was a previous operation on the same joint. CONCLUSIONS: On the basis of their experience with arthroscopic replacement of the cruciate ligaments, the authors recommend an active approach if the development of infectious complications is suspected. In our patients, no persisting sequelae were recorded.

Anterior Cruciate Ligament↗

PubMed2005

Computer-aided formation of the whole-cell patch-clamp recording configuration.

The conventional patch-clamp technique requires well-trained experimenter. Few commercial automated patch-clamp systems, designed for drug development, are better suited for large-scale research then for standard electrophysiological experiments. Here we describe a state machine for automated recognition of recording states of the patch-clamp experiment. The principle of the state machine is based on evaluation of the charge carried by membrane current during specific time segments in responses to square wave voltage stimulation. The state machine may serve for generating various sound alerts, signals for automated control of other devices, assistance in micromanipulation, internal pipette pressure control, and holding potential adjustments. Algorithm of the state machine, designed to cover wide variety of cell types, was successfully tested on rat ventricular myocytes.

Algorithms↗

PubMed2004

Mass spectrometry is a powerful tool for identification of proteins associated with lipid rafts of Jurkat T-cell line.

Many proteins involved in signal-transduction pathways are concentrated in membrane microdomains enriched in lipids with distinct physical properties. Since these microdomains are insoluble in non-ionic detergents in cold, proteins associated with them could be efficiently purified by techniques such as sucrose-density gradient centrifugation. The complexity of the resulting protein mixture requires powerful MS technique for its analysis. We have found that successful identification of biologically relevant proteins is critically dependent on the enrichment of the starting material (plasma membranes), and on the extraction procedure. Applying these conditions in combination with microHPLC-ESI (electrospray ionization)-MS/MS, we have identified proteins involved in signalling, cytoskeletal association and cellular adhesion in Jurkat cells that are not stimulated by any antibody incubation.

Cell Adhesion↗

PubMed2004

Lymphocyte activation receptors: new structural paradigms in group V of C-type animal lectins.

The structure-function relationship in group V of C-type animal lectins remains incompletely understood despite the new structures of NK (natural killer) cell receptors that have been solved recently. Recombinant, soluble forms of rat and human NKR-P1 and CD69 that we obtained after in vitro refolding were analysed by Fourier transform-ion cyclotron resonance MS and heteronuclear NMR ((1)H-(15)N correlation). In NKR-P1, calcium may not be removed by chelating agents because of the very high affinity of binding. In CD69, incorporation of calcium causes a structural shift in several amino acids important for the interaction with carbohydrates. Structural studies have also allowed us to understand an interesting preference of these receptors for either linear (NKR-P1) or branched (CD69) carbohydrate sequences.

Amino Acid Sequence↗

PubMed2004

[Isolated rupture of the gall bladder following a blunt abdominal injury].

The study presents a rare isolated rupture of the gall bladder following a blunt abdominal injury. The diagnostics was complicated by inaccurate anamnestic data, because the patient was injured in the drunken state and could not remember it. The clinical picture was extremely nonspecific. Repetitive ultrasound examinations aided a correct clinical decision making and an adequate management. A possibility of the gall bladder perforation following blunt injuries of the abdomen must be considered mainly in younger patients with nonspecific abdominal pains. The risk increases after abuse of alcohol or after prolonged starvation.

Abdominal Injuries↗

PubMed2004

Evaluation of comparative cytochrome P450 2B4 model by photoaffinity labeling.

A homology model of rabbit CYP 2B4 was constructed on the basis of the crystallographic structure of truncated mammalian CYP 2C5/3 and bacterial soluble CYPs. To validate the CYP 2B4 homology model photoaffinity labeling was employed. Three probes (I-III) containing a photo-labile azido-group and an amino-group on opposite ends of the molecule were designed for photoaffinity labeling of the CYP 2B4 in increasing distance from the heme iron. Spectroscopic data proved probes I (the shortest) and II (a middle sized) to be coordinated with the heme iron via their amino-groups in the enzyme active center while the probe III (the longest) was not bound in this way. This binding orientation of probes I and II is in accordance with the model predicting ion-pairing of the negatively charged side chain of CYP 2B4 Asp 105 and a positively charged nitrogen located in an appropriate position in structures of probes I and II, only. The lack of heme binding of the probe III is clear from its docking into the CYP 2B4 model since no Asp 105 ion-pairing is possible. The target of photoactivated probe II, Arg 197, in a distance of about 16.5 A from the heme iron, exactly matches the position of that amino acid residue, predicted from the CYP 2B4 homology model. Moreover, using this technique, a substrate access channel has been identified. To assess the predicted substrate-binding pocket, an interaction of a specific CYP 2B4 substrate, diamantane, was examined. In "silico" docking revealed strong binding of diamantane in an orientation allowing experimentally observed C4-hydroxylation. Our homology model of CYP 2B4 is thus consistent with experimental metabolic and photoaffinity labeling data.

Amino Acid Sequence↗

PubMed2003

[Indications for refractive procedures in adult patients with strabismus and results of the subsequent therapeutic procedures].

The authors estimated the contribution of the refraction intervention and a possible evolution in the position of eyes in 102 adult individuals considering a refraction intervention. The indications for this intervention were a disorder in eye position or amblyopia in those who were interested in this operation and were examined in the years 1996 to 2002. The basic refraction examination was always supplemented by a detailed orthoptic analysis. Based on this examination the intervention was not recommended in 14 examined subjects (14%). ARK represented the contraindication of the refraction intervention in 9 patients, since subsequent changes in the size of the deviation or operation adjustment of strabismus could result in diplopia. An excessive convergence with a high AC/A in hyperopia was also considered as an unsuitable indication, since a lasting cosmetic and functional significant convergent deviation into near distances could not be excluded. Five patients declined from the refraction intervention on the basis of this explanation. The paper is mainly dealing with an analysis of the development of position of the eyes and binocular functions in 46 adult patients, who decided to undergo a refraction intervention and further orthoptic care after a complex stroboscopic and refraction examination. The adjustment of refractive error was made by the LASIK methods (Laser in Situ Keratomileusis) on 69 eyes (80%) and CLE (Cleans Lens Extraction) on 17 eyes (20%). The orthoptic analyses before and the refraction intervention revealed that in all 29 even only partially accommodating esotropia, the deviation was diminished after the refraction intervention on the average by +11.2 degrees (in the rage of +2 degrees to +30 degrees) to 5.4 degrees (in the range of parallel position to +20 degrees) in the predominantly represented hyperopia, but also in 6 myopias. The improved position of the bulbs was not directly associated with the degree of hyperopia with the original deviation. The deviation after the refraction intervention in 23 patients (79%) with esotropia was not higher than degrees. The cosmetic position of the eyes was completely satisfactory and did not therefore represent even indication for the operation. The 9 patients (35%) with esotropia and hyperopia there were an improvement of binocular functions. It could be theoretically due to the newly developed emetropia making permanent optimal sensory information possible. In all 17 exotropias there were not any significant changes in the size of deviation and the binocular functions were not reestablished, if they were not retained before. The position of eyes was solved surgically in 12 patients, while exotropia predominated in two thirds of them. The weakening or strengthening interventions on horizontal straight muscles were selected according to character of strabismus in 11 patients. Recession of the lower oblique muscle was indicated one case only for the simultaneously present torticollis with exotropia. The residual deviation was not greater than 5 degrees immediately after the operation or during the following months. Binocular functions were not reestablished in any patients. A alternate suppression or suppression of perception on one eye were proved.

Adult↗

PubMed2002

Large orbital moments and internal magnetic fields in lithium nitridoferrate(I).

The iron nitridometalates Li2[(Li(1-x)Fe(I)(x))N] display ferromagnetic ordering and spin freezing. Large magnetic moments up to 5.0mu(B)/Fe are found in the magnetization. In Mössbauer effect studies huge hyperfine magnetic fields up to 696 kOe are observed at specific Fe sites. These extraordinary fields and moments originate in an unusual ligand field splitting for those Fe species leading [within local spin density approximation (LSDA)] to a localized orbitally degenerate doublet. Including spin-orbit interaction and strong intra-atomic electron correlation (LDA+SO+U) gives rise to a large orbital momentum.

Journal Article↗

PubMed2001

Correlation induced paramagnetic ground state in FeAl.

Experimentally the intermetallic compound FeAl is known to be nonmagnetic, whereas conventional density functional theory calculations within the local density approximation always yield a ferromagnetic ground state with a magnetic moment at the Fe site of about 0.7 mu(B). We show that a correlation correction within the LDA+U scheme yields a nonmagnetic ground state for U>or=3.7 eV using two different implementations. The disappearance of the magnetic ground state occurs since Fe-t(2g) and Fe-e(g) manifolds are affected differently by a common U. For large values of U a magnetic solution reappears as expected for strong correlation.

Journal Article↗

PubMed2001

Two-phase character of metallic ferromagnetism in manganites.

(55)Mn NMR spectra of several ferromagnetic manganites, including La(0.7)Ca(0.3)MnO(3) and La(0.7)Sr(0.3) MnO(3), were measured as a function of temperature. A thorough analysis of the spin-spin relaxation and the NMR line shape revealed that in these compounds two different ferromagnetic phases coexist below T(C) in a certain temperature interval which depends on the composition. The phase with lower hyperfine field has faster nuclear relaxation, its characteristic dimension is a few nm, and its volume decreases with decreasing temperature. The NMR lines of both phases are motionally narrowed, i.e., the electron holes are mobile.

Journal Article↗

PubMed2001

A proteolytically truncated form of free CD18, the common chain of leukocyte integrins, as a novel marker of activated myeloid cells.

An unusual CD18 monoclonal antibody (mAb) MEM-148 binds, in contrast to standard CD18 mAbs, specifically to peripheral blood monocytes and neutrophils activated by various stimuli such as phorbol myristate acetate, opsonized zymosan, heat-aggregated immunoglobulin, and (after priming with lipopolysaccharide, tumor necrosis factor, or granulocyte-macrophage colony-stimulating factor) also by formyl-methionyl-leucyl-phenylalanine. In addition, in vivo activated neutrophils obtained from urine of patients following recent prostatectomy were also strongly positive for MEM-148. On the activated myeloid cells the mAb recognized a 65- to 70-kd protein identified immunochemically and by mass spectrometric peptide sequencing as a membrane-anchored fragment of CD18 (the common chain of leukocyte integrins) produced by proteolytic cleavage. The CD18 fragment originated mainly from integrin molecules stored intracellularly in resting cells, it was unassociated with CD11 chains, and its formation was inhibited by several types of protease inhibitors. Thus, the 65- to 70-kd CD18 fragment represents a novel abundant activation marker of myeloid cells of so far unknown function but possibly involved in conformational changes in leukocyte integrin molecules resulting in increased affinity to their ligands.

Antibodies, Monoclonal↗

PubMed2001

Synthesis of chitooligomer-based glycoconjugates and their binding to the rat natural killer cell activation receptor NKR-P1.

NKR-P1 protein is an important activating receptor at the surface of the rat natural killer cells. GlcNAc and chitooligomers were identified as strong activation ligands in vitro and in vivo. Their clustering brings about increase of their affinity to the NKR-P1 by 3-6 orders. Here we describe novel methodology for preparation of neoglycoproteins based on BSA carrying the chitooligomers (n = 2-5). Further on we developed novel methodology of the coupling of glycosylamines via aromatic-SCN activated linker both to protein or synthetic cores. Inhibition studies of chitooligomer glycoconjugates with the NKR-P1 receptor show that our neoglycoproteins are very strong ligands with high binding affinity (-log IC(50) = 13-15). In analogy with our previous observations with GlcNAc clustered on protein or PAMAM backbones the synthetic chitooligomer clusters should provide considerably better ligands in the in vivo antitumor treatment.

Amines↗

PubMed2001

30% complications with adjustable gastric banding: what did we do wrong?

BACKGROUND: The authors analyzed the complications in patients following laparoscopic adjustable gastric banding (LAGB) for morbid obesity. METHODS: Retrospective analysis of the 36 LAGB patients was done. The operations were performed from December 1997 to the December 1999 using the Lap-Band. RESULTS: 11 complications occurred. Most common was port-site infection or port migration (5 patients). These complications were termed minor. In 3 patients, slippage of the gastric wall was observed, all corrected laparoscopically. In another 3 patients, removal of the band was necessary for poor patient compliance (1), for intussusception of the gastric wall through the band with occlusion of the stoma (1), and for infection of the band (1). These complications were termed major. The overall complication rate was 30.5%. CONCLUSION: Compared to the literature, our complication rate was rather high. Based on our analysis, the following measures are recommended: 1) antibiotic prophylaxis; 2) drainage of the port-site; 3) proper band and port placement and fixation; 4) closer psychological evaluation and follow-up. By these measures, hopefully we can obtain better results in the future.

Adult↗

PubMed2001

[Treatment of intermediate hypermetropia using laser in situ keratomileusis--retrospective study (1995-1999)].

In this study, the authors present their findings concerning the usage of the LASIK method in 225 cases of hyperopia. This method has been used in our ELAS refractive centre from 1995 in the treatment of hyperopia up to +7.0 D. The average preoperative spherical equivalent in this group was +4.91 D, and in cycloplegic refraction 20 D (+/- 1.94 D). The postoperative average spherical equivalent was 0.53 D (+/- 0.58 D). Uncorrected visual acuity is used as the main criterion in assessing the effectiveness of the refractive procedure. The average uncorrected visual acuity was improved from a preoperative value of 0.4 (+/- 0.27) to a postoperative one of 0.8 (+/- 0.24). The average value of the best correct visual acuity worsened from 0.98 (+/- 0.31) preoperatively to 0.88 (+/- 0.23) postoperatively. This was perhaps caused by the side-effects of laser ablation (glare), which occurred in using LASIK with cases of hyperopia of over 0 D. For this reason, the choice of the LASIK method for correction of middle hyperopia should be made with caution.

Astigmatism↗