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Biomedical subjects

Ivan Miksík

Publications and source records attributed to Ivan Miksík.

At least 19 recordsLinked to original sources

Separation and investigation of structure-mobility relationship of gonadotropin-releasing hormones by capillary zone electrophoresis in conventional and isoelectric acidic background electrolytes.

Capillary zone electrophoresis (CZE) has been applied to qualitative and quantitative analysis, separation and physicochemical characterization of synthetic gonadotropin-releasing hormones (GnRHs) and their analogs and fragments. Structurally related peptides were separated in conventional and isoelectric acidic background electrolytes (BGEs), pH 2.18-2.50. Best separation was achieved in isoelectric BGE composed of 200 mM iminodiacetic acid, pH 2.32. The effective electrophoretic mobilities, m(ep), of GnRHs in five BGEs were determined and four semiempirical models correlating effective mobility with charge, q, and relative molecular mass, M(r), (m(ep) versus q/M(r)(k), where k is related to the molecular shape) were tested to describe the migration behavior of GnRHs in CZE. None of the models was found to be quite definitively applicable for the whole set of 10 GnRHs differing in size (tetrapeptide-decapeptide) and positive charge (0.91-3.00 elementary charges). Nevertheless, for the dependence of m(ep) on q/M(r)(k), the highest coefficient of correlation, R=0.995-0.999, was obtained for k close to the value 0.5 in all five acidic BGEs. This indicates that the most probable structure of GnRHs in these BGEs can be predicted as a random coil.

Electrolytes↗

Capillary electromigration methods for the study of collagen.

This review paper gives an overview of capillary electromigration methods used in the analysis of collagen. Analyses of the parent chains as well as of the bromcyane and collagenase fragments of collagens are presented. Methods include capillary zone electrophoresis, capillary gel electrophoresis, micellar electrokinetic chromatography as well as combinations of HPLC and capillary electrophoresis, and capillary electrophoresis with mass spectrometry.

Chromatography, High Pressure Liquid↗

Posttranslational modifications of collagen studied by off-line coupling of HPLC and CE.

A typical example of non-enzymatic change of collagen is glycation (the Maillard reaction, formation of advanced glycation end products) resulting from the reaction of sugars with the epsilon-amino group of lysine. Posttranslational non-enzymatic modifications of collagen by sugars were studied. Collagenous tissues were incubated as a test protein separately with both glucose and ribose. The collagen mixture was digested by bacterial collagenase and separated by reversed-phase HPLC (in a Jupiter Proteo 90 A column). The eluate from this HPLC separation was collected as seven fractions and consecutively analysed by CE in a bare fused silica capillary (57/50 cm x 75 mm id) using 100 mM sodium 1-heptanesulfonate in 100 mM phosphate buffer, pH 2.5 (NaH2PO4 adjusted to pH by phosphoric acid). The chromatographic and electromigration behaviour of individual peptides varied considerably. This off-line HPLC-CE coupling made it possible to discover minor changes in the structure of collagen caused by posttranslational modifications. A new HPLC-CE technique for peptide analysis was developed, and applied to the identification of posttranslational modifications in slowly metabolised test proteins.

Animals↗

11beta-Hydroxysteroid dehydrogenase in the heart of normotensive and hypertensive rats.

Corticosteroids have been shown to play a role in cardiac remodeling, with the possibility of a direct effect of overexpression of 11beta-hydroxysteroid dehydrogenase (11HSD) isoform 2 at the level of the cardiomyocytes. The aim of this study was to examine cardiac steroid metabolism in hypertensive rats with hearts that are hypertrophied and fibrotic and have structural alterations in the coronary circulation. To assess possible alterations of cardiac steroid metabolism the expression and activity of both isoforms of 11beta-hydroxysteroid dehydrogenase (11HSD) were studied in spontaneously hypertensive rats (SHR), their normotensive controls Wistar-Kyoto (WKY), and in Dahl salt-sensitive (DS) and salt-resistant rats (DR) kept on a low- or high-salt diet. Using real-time quantitative RT-PCR and enzyme activity assay we found strain-dependent differences in cardiac metabolism of glucocorticoids. In Dahl rats expression of 11HSD1 and 11HSD2 mRNA was lower in DS than in DR rats and was not influenced by dietary salt intake; 11HSD1 mRNA was expressed at higher level than 11HSD2 mRNA. NADP(+)-dependent cardiac 11HSD activity showed similar distribution as 11HSD1 mRNA-lower activity in DS than in DR rats and no effect of salt intake. In SHR and WKY strains 11HSD2 mRNA expression was significantly higher in WKY than in SHR but no differences were observed in 11HSD1 mRNA abundance and NADP(+)-dependent 11HSD activity. These results show that the heart is able to metabolize glucocorticoids and that this metabolism is strain-dependent but do not support the notion of association between cardiac hypertrophy and changes of 11HSD1 and 11HSD2 expression.

11-beta-Hydroxysteroid Dehydrogenase Type 1↗

Non-enzymatic posttranslational modifications of bovine serum albumin by oxo-compounds investigated by chromatographic and electrophoretic methods.

Non-enzymatic posttranslational modifications of bovine serum albumin (BSA) by oxo-compounds, particularly glucose, ribose, glyoxal and glutardialdehyde, have been investigated using a set of modern chromatographic and electrophoretic separation methods. High-performance liquid chromatography (HPLC) alternatively with UV spectrophotometric (diode array) or mass spectrometric (MS) detection, polyacrylamide gel electrophoresis (PAGE) with Coomassie brilliant blue staining detection, and capillary zone electrophoresis (CZE) with UV spectrophotometric detection have been employed for the investigation of the chemical and structural changes of BSA caused by its reaction with the above oxo-compounds exhibiting different degree of reactivity. The extent of modifications was found to be dependent on the nature of the oxo-compound used and progressed in the glucose<ribose<glyoxal<glutaraldehyde order. With the aid of HPLC/UV/MS and CZE/UV tryptic peptide mapping and amino acid analysis of both unmodified and modified BSA it was revealed that the mildest modification resulted from the reaction of BSA with glucose, in this case presumably only monofunctional derivatives have arisen, whereas the most intensive modifications were found after BSA reaction with glutardialdehyde, which resulted in high degree of both inter- and intra-molecular cross-linking, due to which no unmodified peptides were detected after tryptic cleavage of BSA modified by this agent.

Aldehydes↗

Glucocorticoid metabolism and Na+ transport in chicken intestine.

The role of aldosterone in regulation of electrogenic Na+ transport is well established, though mineralocorticoid receptors bind glucocorticoids with similar binding affinity as aldosterone and plasma concentration of aldosterone is much lower than glucocorticoids. In mammals, the aldosterone specificity is conferred on the low-selective mineralocorticoid receptors by glucocorticoid inactivating enzyme 11beta-hydroxysteroid dehydrogenase (11HSD) that converts cortisol or corticosterone into metabolites (cortisone, 11-dehydrocorticosterone) with lower affinity for these receptors. The present study examined the chicken intestine, whether changes in 11HSD activity are able to modulate the effect of corticosterone on Na+ transport, and how the metabolism of this hormone is distributed within the intestinal wall. This study shows that not only aldosterone, but also corticosterone (B), was able to increase the electrogenic Na+ transport in chicken caecum in vitro. The effect of corticosterone was higher in the presence of carbenoxolone, an inhibitor of steroid dehydrogenases, and was comparable to the effect of aldosterone. The metabolism of B in the intestine was studied; results showed oxidation of this steroid to 11-dehydrocorticosterone (A) and reduction to 11-dehydro-20beta-dihydrocorticosterone (20diA) as the main metabolic products at low nanomolar concentration of the substrate. In contrast, 20beta-dihydrocorticosterone and 20diA were the major products at micromolar concentration of B. Progesterone was converted to 20beta-dihydroprogesterone. The metabolism of corticosterone was localized predominantly in the intestinal mucosa (enterocytes). In conclusion, the oxidation at position C11 and reduction at position C20 suggest that both 11HSD and 20beta-hydroxysteroid dehydrogenase (20HSD) operate in the chicken intestine and that the mucosa of avian intestine possesses a partly different system of modulation of corticosteroid signals than mammals. This system seems to protect the aldosterone target tissue against excessive concentration of corticosterone and progesterone.

11-beta-Hydroxysteroid Dehydrogenases↗

Separation of low-molecular mass peptides by capillary electrophoresis with the use of alkylamines as dynamic coating agents at low pH.

Modification of the silanophilic activity of the inner surface of the capillary wall was studied in a capillary electrophoretic system using alkylamines containing background electrolytes at acid pH. The effect of the following amine additives was investigated: (1) alkyl-alpha,omega-diamines (1,2-diaminoethane, 1,4-diaminobutane, 1,7-diaminoheptane, spermine), (2) polymeric amines (polyethylenimine, polybrene), (3) cationic amine surfactants (cetrimide, hexamethonium bromide). A seven membered test mixture of peptides (Gly-Pro-Ala, Pro-hPro, Gly-Pro-Arg, Gly-Pro-Gln, Lys-Pro-Gly, Asn-Pro-Gly, His-Pro-Gly) possessing one or more amino groups was used for selectivity evaluation. Under optimised concentration of the amine modifiers the selectivity was always improved (except for polybrene), particularly with the fast moving analytes. The best results were obtained with 1,2-diaminoethane and 1,7-diaminoheptane. On the other hand with slowly moving peaks the best separations were obtained with 1,7-diaminoheptane, hexadecyltrimethylammonium bromide and hexamethonium bromide, i.e. with modifiers possessing large aliphatic domains which are likely to be hydrophobically bonded with the separated solutes. The selectivity improvement with fast moving members of the test mixture can be ascribed to the decrease of the electroosmotic flow, while the improved separation with slowly moving peaks appears to reflect the altered interaction with the hydrophobized capillary wall. As expected the endoosmotic flow was in all cases decreased. The practical applicability of using amine based dynamic modifiers of the capillary wall was demonstrated on a natural peptide mixture (bacterial collagenase hydrolysate of collagen types I and III).

Electrophoresis, Capillary↗

Application of liquid chromatography-electrospray ionization mass spectrometry for study of steroid-converting enzymes.

A high-performance liquid chromatography-atmospheric pressure ionization-electrospray ionization mass spectrometry (HPLC-API-ESI-MS) method was developed for the analysis of steroids in a study of steroid-converting enzymes. Separations ware done on a Zorbax Eclipse XDB-C18 column (eluted with a linear methanol-water-acetic acid gradient) and identification of the steroids involved was done by API-ESI-MS using positive ion mode and extracted ion analysis. The applicability of the present method for studying steroid metabolism was proven in assaying two steroid-converting enzymes (20beta-hydroxysteroid dehydrogenase and 11beta-hydroxysteroid dehydrogenase) in various biological samples (rat and chicken intestine, chicken oviduct).

11-beta-Hydroxysteroid Dehydrogenases↗

Peptide mapping by capillary electrophoresis with Pluronic F127.

Separation of peptides and proteins by capillary zone electrophoresis suffers from the interaction of these solutes with the capillary wall which results in the formation of broad peaks and low resolution. To minimize the protein/peptide-capillary wall interaction we tried to use Pluronic F127, a triblock copolymer of the general formula (polyethylene oxide)(x)(polypropylene oxide)(y)(polyethylene oxide)(z) when x=106, y=70 and z=106 which can be considered a surfactant capable of self-association both into isotropic and anisotropic gels. The analytes studied were enzymatic digests (obtained by trypsin or pepsin treatment) of insoluble matrix proteins from avian eggshell. The best separations were obtained by a system exploiting 10% Pluronic F127 in 20 mmol/l phosphate buffer, pH 2.5. Electrophoretic peptide profiles obtained were very complex owing to the complicated nature of the samples (the exact composition of the proteinous insoluble part of the eggshell is still unknown). The separation in phosphate buffer only offered complex maps of incompletely resolved peaks. The use of Pluronic F127 distinctly improved the separation with a considerably better resolution regarding both the number of peaks obtained and the quality of the separation.

Buffers↗

Plastic substrates based separation channels in electromigration techniques.

Three types of plastic materials (polyester, polyurethane and polymethylmethacrylate) were tested as materials for manufacturing separation columns (polyester and polyurethane capillaries were used) or separation channels (polymethylmethacrylate) in the chip format. A set of 11 fluorescein isothiocyanate amino acid derivatives was used as the test mixture. Using alpha-cyclodextrin additive to the background electrolyte in the case of the chip separation was also tested. The main problem with all plastic separation media was the selectivity of the separation. The best results, practically identical with bare fused silica capillary, were obtained with the polymethylmethacrylate chip, provided that alpha-cyclodextrin in a concentration 40 mmol/l was added to the background electrolyte. An important observation was that in SDS containing background electrolyte all the plastic materials used exhibited a distinct electroosmotic flow, which was ascribe to the sorption of the negatively charged constituents of the background electrolyte to the capillary wall. Regarding the order in which the individual components of the test mixture were brought to the detector only a single change was observed. Histidine migrated in the polystyrene and polymethylmethacrylate separation channels more slowly than in the bare silica or polyurethane based capillaries.

Electrophoresis, Capillary↗

Comparison of the electrophoretic separation of proteins in capillaries with different inner diameter.

Two fused-silica capillaries of considerably different inner diameter (75 and 10 microm) were used for the separation of a set of five standard proteins. The separations were run in acid pH (50 mM phosphate buffer, pH 2.5). Generally better separations (with minor tailing only) were obtained using a standard capillary [27 cm (20 cm effective length)x 75 microm I.D.] in comparison with a narrow bore capillary [27 cm (20 cm effective length)x 10 microm I.D.]. The conditions of the electrophoretic separation were the same for both types of capillaries (25 degrees C; 10 kV; positive polarity at the inlet). The sequence of the proteins was cytochrome c, albumin, transferrin followed by a partly resolved peak of catalase and chymotrypsinogen A. In the narrow bore capillary severe tailing was observed--tailing factor ranged from 2.11 to 5.54 or 1.67 to 2.53 depending on the concentration of the analytes injected (2 or 0.2 mg/ml of each test compound injected). The relative [delta(deltaG(0))] values of the interaction with the capillary wall in the small bore capillary (with cytochrome c taken as initial standard) ranged from -0.74 to -1.04 kJ/mol. The problem of assaying the speed of the endoosmotic flow (EOF) in both capillary types was thoroughly investigated using thiourea and dithiothreitol as EOF markers. It was revealed that if thiourea is used as the EOF marker, the obtained value was dependent on the concentration of the marker injected. Optimum conditions for the EOF determination in acid buffer were specified. The higher speed of the EOF in the narrow bore capillary (10 microm) as compared to the 75 microm I.D. capillary is discussed.

Electrophoresis, Capillary↗

Separation of structurally related peptides by open-tubular capillary electrochromatography using (metallo)porphyrins as the adsorbed stationary phase.

Several (metallo)porphyrins, particularly the porphyrin derivative tetraphenylporphyrin, and complexes of porphyrin derivatives with metal ions (Zn2+, Cu2+, Ni2+, Co2+, Co3+) have been employed as the stationary phase physically adsorbed onto the inner fused-silica capillary surface for open-tubular capillary electrochromatography, and applied for the separation of structurally related peptides. Four octapeptides, derivatives of the B23-B30 fragment of the B-chain of human insulin with minor changes in their sequences (presence of lysine or ornithine in position B-29, presence or absence of phenylacetyl protecting group on the amino group of lysine/ornithine or N-terminal amino group of glycine), were studied as model analytes. Separations were performed both in alkaline (pH 9.0) and in acidic (pH 2.25) background electrolytes, and the changes in the migration/retention behaviour of the model set of peptides were investigated with respect to the porphyrin periphery/central metal atom and the charge of the octapeptides modified. The key moment of successful separation of these peptides seems to be the accessibility of functional groups of the peptides to the interaction with the modifiers tested herein.

Adsorption↗

Comparison of standard capillary and chip separations of sodium dodecylsulfate-protein complexes.

Conditions for converting a set of five standard proteins to electrochemically active sodium dodecylsulfate (SDS) complexes were worked out with the aim of using such complexes for conductivity detection with a a chip electrophoresis system. The results obtained were compared with standard capillary electrophoresis (37 cm (effective length 30 cm) x 75 microm I.D. capillary, 10 kV, negative polarity at the inlet). The chip separations were run at 500 V per chip (100 V/cm) as compared to the standard capillary arrangement, which was run at 266.6 V/cm. For the capillary set-up the protein complexes were prepared in aqueous solution (Milli-Q water) made 10 mM with respect to SDS. If the SDS concentration was increased to 50 mM, the separation in the capillary was incomplete. On the other hand with the chip system both approaches yielded acceptable results. The chip separations were slightly (but not distinctly) shorter and offered better separations than the standard set-up. The concentration of the surfactant used for the preparation the complexes results in alternations of the elution sequence, which is preserved if the chip separation is used instead of the capillary set-up. Apparently the full capacity of protein-SDS binding is not exploited for the preparation of the adducts.

Electrophoresis, Capillary↗

Insoluble eggshell matrix proteins--their peptide mapping and partial characterization by capillary electrophoresis and high-performance liquid chromatography.

Avian eggshell matrix proteins were studied by two analytical approaches. Peptide mapping was done by trypsin and pepsin followed by collagenase cleavage; analyses were carried out by capillary electrophoresis and reversed-phase high-performance liquid chromatography (HPLC). Comparison of peptide maps obtained by both methods revealed a complex mixture of peptides in the insoluble layers of the eggshell; it was concluded that there are at least three different insoluble protein/peptide layers in the avian eggshell (cuticle, palisade, and mammillary layer). Partial characterization of peptides in each layer was made by HPLC-mass spectrometry analysis. There is an evidence that the eggshell insoluble proteins contain species susceptible to collagenase cleavage, however, the sequences split by this enzyme probably are not those typical for the main triple-helical core of collagenous proteins. It is proposed that the action of collagenase upon eggshell proteins is caused by the side effect of collagenase described previously with synthetic peptides. Some of the proteins present are probably glycosylated. Fatty acid content in the insoluble eggshell layers (after decalcification) was in the range of 2-4% (which reflected both lipid and lipoproteins bound fatty acids). Porphyrin pigments are dominant in the cuticle layer.

Animals↗

Sexual dimorphism of 11beta-hydroxysteroid dehydrogenase in hypertensive and normotensive rats.

To evaluate the role of sexually dimorphic tissue expression of 11beta-oxidase activity of 11beta-hydroxysteroid dehydrogenase (11betaHSD) in gender-associated blood pressure differences, we have studied female and male hypertensive rats of two different strains and their normotensive controls: spontaneously hypertensive rats (SHR), Wistar-Kyoto rats (WKY) and Dahl salt-sensitive (SS/Jr) and salt-resistant rats (SR/Jr). In hypertensive SHR and SS/Jr, but not in normotensive strains WKY and SR/Jr, blood pressure reached a higher level in males than in females. The activity of 11betaHSD was higher in the renal cortex, medulla, colon and aorta of males than of females in all investigated strains with the exception of aortic 11betaHSD in SHR and WKY rats, both of which had very low 11beta-oxidase activity. In contrast to gender-dependent differences, strain differences of 11betaHSD were observed in a limited number of tissues only. Renal medullary 11betaHSD showed significantly lower activity in WKY than in SHR, whereas no difference was observed in the renal cortex. Similarly, colonic 11betaHSD activity was lower in WKY than in SHR. In Dahl rats the strain differences were observed in aortic 11betaHSD that had higher activity in SR/Jr than in SS/Jr rats; no difference was observed in the kidney or colon. These data demonstrate the following. 1) Sexual dimorphism of 11betaHSD activity exists in the kidney, colon, and aorta. 2) The sexual dimorphism of 11betaHSD does not play a role in gender-associated differences in blood pressure. 3) The reduced 11betaHSD activity in the aorta of hypertensive SS/Jr compared to SR/Jr rats suggests that this enzyme might play a role in the pathogenesis of salt-sensitive hypertension in Dahl rats.

11-beta-Hydroxysteroid Dehydrogenases↗

Impaired noradrenaline-induced lipolysis in white fat of aP2-Ucp1 transgenic mice is associated with changes in G-protein levels.

In vitro experiments suggest that stimulation of lipolysis by catecholamines in adipocytes depends on the energy status of these cells. We tested whether mitochondrial uncoupling proteins (UCPs) that control the efficiency of ATP production could affect lipolysis and noradrenaline signalling in white fat in vivo. The lipolytic effect of noradrenaline was lowered by ectopic UCP1 in white adipocytes of aP2-Ucp1 transgenic mice, overexpressing the UCP1 gene from the aP2 gene promoter, reflecting the magnitude of UCP1 expression, the impaired stimulation of cAMP levels by noradrenaline and the reduction of the ATP/ADP ratio in different fat depots. Thus only subcutaneous but not epididymal fat was affected. UCP1 also down-regulated the expression of hormone-sensitive lipase and lowered its activity, and altered the expression of trimeric G-proteins in adipocytes. The adipose tissue content of the stimulatory G-protein alpha subunit was increased while that of the inhibitory G-protein alpha subunits decreased in response to UCP1 expression. Our results support the idea that the energy status of cells, and the ATP/ADP ratio in particular, modulates the lipolytic effects of noradrenaline in adipose tissue in vivo. They also demonstrate changes at the G-protein level that tend to overcome the reduction of lipolysis when ATP level in adipocytes is low. Therefore, respiratory uncoupling may exert a broad effect on hormonal signalling in adipocytes.

Adenosine Diphosphate↗

The effect of sodium dodecyl sulfate and Pluronic F127 on the electrophoretic separation of protein and polypeptide test mixtures at acid pH.

Using a test mixture consisting of standard proteins (cytochrome c, chymotrypsinogen A, hen egg albumin, bovine serum albumin, aldolase, catalase and ferritin) and synthetic polypeptides (polylysine, polyaspartic, polyglutamic acid and polyproline) it was revealed that using sodium dodecyl sulfate (SDS) as background electrolyte modifier at acid pH (2.5) allows selective separation of highly positively charged polypeptides (polylysine) provided that their relative molecular mass is sufficiently low (3300 Da). The altered elution sequence of standard proteins as compared to a separation done without SDS may help their identification. Addition of Pluronic F127 offers clear-cut separations of standard proteins up to a relative molecular mass of 5 x 10(4) Da and allows to reveal protein/polypeptide microheterogeneity where applicable. None of the systems tested is suitable for the separation of acidic polypeptides and polyproline.

Buffers↗

Effect of cellular differentiation on 11beta-hydroxysteroid dehydrogenase activity in the intestine.

11beta-Hydroxysteroid dehydrogenase (11betaHSD) converts endogenous glucocorticoids to their biologically inactive 11-dehydro derivatives and is therefore able to determine, at least in part, the biological action of glucocorticoids. Type 1 11betaHSD has both oxidase and reductase activities interconverting corticosterone and 11-dehydrocorticosterone, whereas type 2 11betaHSD has only oxidase activity converting corticosterone to 11-dehydrocorticosterone. Since 11betaHSD expression is regulated during development and by hormones in a tissue-specific manner and since glucocorticoids play an important role in postnatal intestinal maturation, we investigated the role of corticosteroids and cytodifferentiation in the regulation of intestinal 11betaHSD. Using rat intestinal organ cultures and epithelial cell lines derived from rat small intestine (IEC-6, IEC-18) and from human colon adenocarcinoma (Caco-2, HT-29), we analyzed the effect of corticosteroids and cytodifferentiation on 11betaHSD. Screening of the clonal cell lines showed that Caco-2 cells expressed by far the greatest 11betaHSD2 oxidase activity, lower activity was observed in HT-29 cells, and lowest activity was seen in IEC cells. Treatment with dexamethasone (50 nM) increased the activity of 11betaHSD2 in IEC-6 cells (+59%) and HT-29 cells (+31%), whereas aldosterone (50 nM) stimulated 11betaHSD2 in IEC-6 cells only (+31%). Caco-2 cells and IEC-18 cells did not respond to corticosteroids. Growth of IEC-6 cells on Matrigel, treatment of HT-29 cells with butyrate, and postconfluency of Caco-2 cells increased not only the markers of cytodifferentiation, such as alkaline phosphatase and sucrase, but also the activity of 11betaHSD2 in all of these cell lines (IEC-6, +96%; HT-29, +139%; Caco-2, +95%). Addition of corticosteroids to these more differentiated cell cultures did not enhance 11betaHSD2 activity. In intestinal organ cultures of suckling rat small intestine, dexamethasone and aldosterone stimulated 11betaHSD by more than 300%. We conclude that corticosteroids markedly and differentially regulate intestinal 11betaHSD2 and that cytodifferentiation of intestinal epithelial cells is associated with upregulation of 11betaHSD2 activity that is independent of corticosteroids.

11-beta-Hydroxysteroid Dehydrogenase Type 1↗