'Influence of subclinical generalized spike-wave activity on the heart rate of children with epilepsy'.
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Adolescent↗
Biomedical subjects
Stephan König
Publications and source records attributed to Stephan König.
Capillary microscopy and hemorheology in children during antiepileptic monotherapy with carbamazepine and valproate.
The interactions of epilepsy and antiepileptic therapy an one hand and cardiovascular system on the other hand are multiple and complex. Antiepileptic drugs (AEDs) cause alterations of serum lipids and of the fatty acid composition of the membranes. Homocystein, known to induce vascular endothelial damage was found to be elevated in patients on valproate (VPA) and carbamazepine (CBZ) therapy. Marked coronary artherosclerosis and myocardial infarction may already occur in children treated with CBZ. Community based studies corroborated a higher incidence of myocardial infarction, peripheral vascular diseases hypercholesterinemia, left ventricle hypertrophy and stroke in patients with epilepsy. In this context, we wanted to elevate changes of microcirculation related to AEDs commonly prescribed such as VPA and CBZ. Capillary microscopy is a non-invasive technique for measuring the velocity of red blood cells and for determining nutritional blood flow in the capillaries of the skin. It can easily be performed in children. The aim of this study was to look for possible effects an antiepileptic monotherapy with carbamazepine or valproate has on the peripheral microcirculation in epileptic children. We were able to examine 14 children with CBZ and 24 children with VPA, recruited in our neuropediatric Unit. The results were compared to normative values, determined in former analyses of 207 healthy children. We found significant differences in capillary density, tortuous index of the capillaries, capillary diameter and flow rate of erythrocytes for both antiepileptic drugs. Additionally, there were changes in plasma viscosity and the aggregation of erythrocytes. These microcapillary effects could be of special interest in the relationship of a long-term antiepileptic therapy and the development of vascular diseases. We suggest that the influence of AEDs on microcirculation should also be considered in further studies on cardiovascular changes in patients with antiepileptic long-term medication.
Adolescent↗
18F-FDG PET in a 10-year-old female patient with subacute sclerosing panencephalitis.
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Antibodies, Viral↗
Tracking stimulus processing in Pavlovian pupillary conditioning.
The aim of the present study was to evaluate whether the anticipatory pupillary dilation response is a useful indicator for the examination of complex differential conditioning problems like patterning. A human fear conditioning procedure with six groups (n=20 each) was used to examine conditioned stimulus (CS) processing when a compound stimulus was reinforced, but not its elements (positive patterning) or when the elements were reinforced, but not the compound (negative patterning), as well as modifications in which the compound was replaced by either a new compound or by a new element. We found evidence for conditioning within 2 s after CS onset. Group differences in differential conditioning indicated systematic differences in CS processing due to different discrimination task difficulties. This study showed that the pupil response is a suitable indicator for human Pavlovian conditioning with high time resolution within and between trials.
Adolescent↗
Valproate-associated coagulopathies are frequent and variable in children.
PURPOSE: Valproic acid (VPA) is an antiepileptic drug (AED) commonly used for generalized and focal epilepsies. The clinical relevance of coagulopathies, known as side effects of VPA therapy, especially thrombocytopenia, von Willebrand disease, and a decrease of factor XIII, is still unclear. METHODS: In our institute, we noticed a high incidence of clinically relevant coagulation problems related to VPA in eight patients within 1 year only and a further seven children with significant coagulopathy were identified in the context of planned surgery. RESULTS: We provide an overview of these patients and all six VPA-induced coagulopathies. CONCLUSIONS: At this time, it cannot be recommended to control all hemostatic parameters in every patient. Whenever an increased bleeding tendency is observed, or before surgical procedures, a platelet count, thrombelastography, prothrombin time, activated partial thromboplastin time, TT, fibrinogen, von Willebrand factor, and factor XIII should be examined. With 385 VPA-treated patients per year and 15 cases of coagulation disorders in this period, we estimate the incidence of coagulation disorders related to VPA in children to be nearly 4%.
Age Factors↗
The crystal structure of pyruvate decarboxylase from Kluyveromyces lactis. Implications for the substrate activation mechanism of this enzyme.
The crystal structure of pyruvate decarboxylase from Kluyveromyces lactis has been determined to 2.26 A resolution. Like other yeast enzymes, Kluyveromyces lactis pyruvate decarboxylase is subject to allosteric substrate activation. Binding of substrate at a regulatory site induces catalytic activity. This process is accompanied by conformational changes and subunit rearrangements. In the nonactivated form of the corresponding enzyme from Saccharomyces cerevisiae, all active sites are solvent accessible due to the high flexibility of loop regions 106-113 and 292-301. The binding of the activator pyruvamide arrests these loops. Consequently, two of four active sites become closed. In Kluyveromyces lactis pyruvate decarboxylase, this half-side closed tetramer is present even without any activator. However, one of the loops (residues 105-113), which are flexible in nonactivated Saccharomyces cerevisiae pyruvate decarboxylase, remains flexible. Even though the tetramer assemblies of both enzyme species are different in the absence of activating agents, their substrate activation kinetics are similar. This implies an equilibrium between the open and the half-side closed state of yeast pyruvate decarboxylase tetramers. The completely open enzyme state is favoured for Saccharomyces cerevisiae pyruvate decarboxylase, whereas the half-side closed form is predominant for Kluyveromyces lactis pyruvate decarboxylase. Consequently, the structuring of the flexible loop region 105-113 seems to be the crucial step during the substrate activation process of Kluyveromyces lactis pyruvate decarboxylase.
Allosteric Regulation↗
Maturation of the autonomic nervous system: differences in heart rate variability in premature vs. term infants.
AIMS: Heart rate variability (HRV) reveals information on the functional state of the autonomic nervous system (ANS). This study was initiated to assess the physiological- and maturational development of the ANS by comparing HRV data of healthy prematures with term infants. METHODS: Short-term recordings of HRV in 39 premature healthy infants (29-35 weeks' gestation) were performed and compared with normative data of term infants. Frequency domain HRV parameters are computed in three frequency bands. RESULTS: Gestational age of newborn infants is correlated with HRV. Prematures showed significant lower HRV parameters than term infants. The most significant differences were discerned for HRV parameters reflecting parasympathetic activity, whereas the pulse of the baro-receptor reflex was similar for prematures and term infants at 0.07 Hz (0.1 Hz adults). A respiratory peak in the HF-band according to respiratory sinus arrhythmia (RSA), as is common in adults, was not detected for prematures as it is not detected in term infants. CONCLUSIONS: Maturation of the ANS is accompanied by increasing HRV with a pronounced increase of parasympathetic activity. These changes are measurable by short-term recordings. The physiological pulses concerning baroreceptor reflex activity and respiratory modulation were similar in prematures and term infants.
Analysis of Variance↗
Heart rate variability during extracorporeal membrane oxygenation and recovery in severe neonatal disease.
BACKGROUND: Heart rate variability (HRV) reveals information on the functional state of the autonomic nervous system (ANS) in neonates. During severe illness, heart rate variability is impaired. AIM: This study was initiated to measure the changes in HRV in neonates during extracorporeal membrane oxygenation (ECMO) and recovery from severe respiratory and circulatory failure. Moreover, we compared our data with HRV data of healthy newborns and we investigated the differences in HRV parameters between ECMO-survivors and non-survivors. STUDY DESIGN: This study is of an observational character. We performed short-term recordings of heart rate variability in 14 neonates during ECMO and recovery. We computed time- and frequency-domain HRV parameters. RESULTS: ECMO significantly affects time-domain HRV parameters. Severe neonatal illness causes a significant reduction of all calculated HRV parameters; clinical recovery is accompanied by an increase of HRV. In comparison with normative data of healthy newborns, however, HRV remains impaired. The ECMO-development ratio separated the non-survivors from the survivors during ECMO therapy. CONCLUSIONS: During severe neonatal illness, HRV is impaired. It remains to be clarified whether the impairment of HRV during severe illness can predict the neurological outcome. The ability of the E/D ratio as an HRV parameter to serve as a predictive tool has to be corroborated in larger group of patients.
Case-Control Studies↗
Intermediates and transition states in thiamin diphosphate-dependent decarboxylases. A kinetic and NMR study on wild-type indolepyruvate decarboxylase and variants using indolepyruvate, benzoylformate, and pyruvate as substrates.
The thiamin diphosphate (ThDP)-dependent enzyme indolepyruvate decarboxylase (IPDC) is involved in the biosynthetic pathway of the phytohormone 3-indoleacetic acid and catalyzes the nonoxidative decarboxylation of 3-indolepyruvate to 3-indoleacetaldehyde and carbon dioxide. The steady-state distribution of covalent ThDP intermediates of IPDC reacting with 3-indolepyruvate and the alternative substrates benzoylformate and pyruvate has been analyzed by (1)H NMR spectroscopy. For the first time, we are able to isolate and directly assign covalent intermediates of ThDP with aromatic substrates. The intermediate analysis of IPDC variants is used to infer the involvement of active site side chains and functional groups of the cofactor in distinct catalytic steps during turnover of the different substrates. As a result, three residues (glutamate 468, aspartate 29, and histidine 115) positioned perpendicular to the thiazolium moiety of ThDP are involved in binding of all substrates and decarboxylation of the respective tetrahedral ThDP-substrate adducts. Most likely, interactions of these side chains with the substrate-derived carboxylate account for an optimal orientation of the substrate and/or intermediate in the course of carbon-carbon ligation and decarboxylation supporting the suggested least-motion, maximum overlap mechanism. The active site residue glutamine 383, which is located at the opposite site of the thiazolium nucleus as the "carboxylate pocket" (formed by the Glu-Asp-His triad), is central to the substrate specificity of IPDC, probably through orbital alignment. The Glu51-cofactor proton shuttle is, conjointly with the Glu-Asp-His triad, involved in multiple proton transfer steps, including ylide generation, substrate binding, and product release. Studies with para-substituted benzoylformate substrates demonstrate that the electronic properties of the substrate affect the stabilization or destabilization of the carbanion intermediate or carbanion-like transition state and in that way alter the rate dependence on decarboxylation. In conclusion, general mechanistic principles of catalysis of ThDP-dependent enzymes are discussed.
Amino Acid Substitution↗
The role of Val-265 for flavin adenine dinucleotide (FAD) binding in pyruvate oxidase: FTIR, kinetic, and crystallographic studies on the enzyme variant V265A.
In pyruvate oxidase (POX) from Lactobacillus plantarum, valine 265 participates in binding the cofactor FAD and is responsible for the strained conformation of its isoalloxazine moiety that is visible in the crystal structure of POX. The contrasting effects of the conservative amino acid exchange V265A on the enzyme's catalytic properties, cofactor affinity, and protein structure were investigated. The most prominent effect of the exchange was observed in the 2.2 A crystal structure of the mutant POX. While the overall structures of the wild-type and the variant are similar, flavin binding in particular is clearly different. Local disorder at the isoalloxazine binding site prevents modeling of the complete FAD cofactor and two protein loops of the binding site. Only the ADP moiety shows well-defined electron density, indicating an "anchor" function for this part of the molecule. This notion is corroborated by competition experiments where ADP was used to displace FAD from the variant enzyme. Despite the fact that the affinity of FAD binding in the variant is reduced, the catalytic properties are very similar to the wild-type, and the redox potential of the bound flavin is the same for both proteins. The rate of electron transfer toward the flavin during turnover is reduced to one-third compared to the wild-type, but k(cat) remains unchanged. Redox-triggered FTIR difference spectroscopy of free FAD shows the nu(C(10a)=N(1)) band at 1548 cm(-)(1). In POX-V265A, this band is found at 1538 cm(-)(1) and thus shifted less strongly than in wild-type POX where it is found at 1534 cm(-)(1). Taking these observations together, the conservative exchange V265A in POX has a surprisingly small effect on the catalytic properties of the enzyme, whereas the effect on the three-dimensional structure is rather big.
Base Sequence↗
Short term heart rate variability in healthy neonates: normative data and physiological observations.
BACKGROUND: The measurement of heart rate variability (HRV) reveals information on the functional state of the autonomic nervous system (ANS). Moreover, several diseases are known to be accompanied by a reduction in HRV. Currently, there are no data on HRV within larger samples of healthy neonates. AIM: This study was initiated to establish normative data of HRV parameters and to assess physiological observations in healthy newborn infants. STUDY DESIGN: We performed 10 min recordings of HRV in 80 healthy neonates. We computed time domain parameters. Furthermore power spectrum analysis was calculated by Fourier Transformation in 3 frequency bands. The total power as well as the peak frequencies was estimated for each band. RESULTS: The normative data of each HRV parameter for healthy newborns are presented as mean, standard deviation and the 5th and 95th percentiles. Increasing postnatal age is accompanied by a significant (p<0.05) elevation of HRV parameters. Baroreceptor loop fluctuations were delayed from 0.1 Hz (adults) to 0.07 Hz in healthy newborns. A respiratory peak according to respiratory sinus arrhythmia (RSA) as it is common in adults was not detectable. CONCLUSIONS: Normative data of HRV allows the interpretation of clinical data in neonatal diseases affecting the ANS. Moreover, we observed physiological deviations in healthy newborns in comparison to adults.
Autonomic Nervous System↗
Effect of coenzyme modification on the structural and catalytic properties of wild-type transketolase and of the variant E418A from Saccharomyces cerevisiae.
Transketolase from baker's yeast is a thiamin diphosphate-dependent enzyme in sugar metabolism that reconstitutes with various analogues of the coenzyme. The methylated analogues (4'-methylamino-thiamin diphosphate and N1'-methylated thiamin diphosphate) of the native cofactor were used to investigate the function of the aminopyrimidine moiety of the coenzyme in transketolase catalysis. For the wild-type transketolase complex with the 4'-methylamino analogue, no electron density was found for the methyl group in the X-ray structure, whereas in the complex with the N1'-methylated coenzyme the entire aminopyrimidine ring was disordered. This indicates a high flexibility of the respective parts of the enzyme-bound thiamin diphosphate analogues. In the E418A variant of transketolase reconstituted with N1'-methylated thiamin diphosphate, the electron density of the analogue was well defined and showed the typical V-conformation found in the wild-type holoenzyme [Lindqvist Y, Schneider G, Ermler U, Sundstrom M (1992) EMBO J11, 2373-2379]. The near-UV CD spectrum of the variant E418A reconstituted with N1'-methylated thiamin diphosphate was identical to that of the wild-type holoenzyme, while the CD spectrum of the variant combined with the unmodified cofactor did not overlap with that of the native protein. The activation of the analogues was measured by the H/D-exchange at C2. Methylation at the N1' position of the cofactor activated the enzyme-bound cofactor analogue (as shown by a fast H/D-exchange rate constant). The absorbance changes in the course of substrate turnover of the different complexes investigated (transient kinetics) revealed the stability of the alpha-carbanion/enamine as the key intermediate in cofactor action to be dependent on the functionality of the 4-aminopyrimidine moiety of thiamin diphosphate.
Amino Acid Substitution↗
Factor XIII deficiency associated with valproate treatment.
PURPOSE: We present two children who developed a deficiency of factor XIII with valproate (VPA) treatment. This coagulation disorder has not been described in association with VPA treatment in children, and only very recently in one adult patient. RESULTS: Both patients showed recurrent epistaxis as major clinical sign of a combination of decreased coagulation parameters (factor XIII deficiency with thrombocytopenia and decreased von Willebrand factor, respectively). A few days after reduction or withdrawal of VPA treatment, clinical symptoms disappeared, and laboratory findings were within normal range. CONCLUSIONS: VPA is known to influence the synthetic function of the liver and the number and function of megakaryocytes. Therefore an alteration of the factor XIII level by VPA is conceivable. Our case reports suggest that bleeding symptoms during VPA treatment may be caused or aggravated by a decreased factor XIII activity. A determination of factor XIII activity should be considered before surgical procedures during VPA treatment to minimize the risk of (severe) postsurgical bleeding complications.
Anticonvulsants↗
Crystal structure of thiamindiphosphate-dependent indolepyruvate decarboxylase from Enterobacter cloacae, an enzyme involved in the biosynthesis of the plant hormone indole-3-acetic acid.
The thiamin diphosphate-dependent enzyme indolepyruvate decarboxylase catalyses the formation of indoleacetaldehyde from indolepyruvate, one step in the indolepyruvate pathway of biosynthesis of the plant hormone indole-3-acetic acid. The crystal structure of this enzyme from Enterobacter cloacae has been determined at 2.65 A resolution and refined to a crystallographic R-factor of 20.5% (Rfree 23.6%). The subunit of indolepyruvate decarboxylase contains three domains of open alpha/beta topology, which are similar in structure to that of pyruvate decarboxylase. The tetramer has pseudo 222 symmetry and can be described as a dimer of dimers. It resembles the tetramer of pyruvate decarboxylase from Zymomonas mobilis, but with a relative difference of 20 degrees in the angle between the two dimers. Active site residues are highly conserved in indolepyruvate/pyruvate decarboxylase, suggesting that the interactions with the cofactor thiamin diphosphate and the catalytic mechanisms are very similar. The substrate binding site in indolepyruvate decarboxylase contains a large hydrophobic pocket which can accommodate the bulky indole moiety of the substrate. In pyruvate decarboxylases this pocket is smaller in size and allows discrimination of larger vs. smaller substrates. In most pyruvate decarboxylases, restriction of cavity size is due to replacement of residues at three positions by large, hydrophobic amino acids such as tyrosine or tryptophan.
Amino Acid Sequence↗
Studies on structure-function relationships of indolepyruvate decarboxylase from Enterobacter cloacae, a key enzyme of the indole acetic acid pathway.
Enterobacter cloacae, isolated from the rhizosphere of cucumbers, produces large amounts of indole-3-acetic acid. Indolepyruvate decarboxylase, the key enzyme in the biosynthetic pathway of indole-3-acetic acid, catalyses the formation of indole-3-acetaldehyde and carbon dioxide from indole-3-pyruvic acid. The enzyme requires the cofactors thiamine diphosphate and magnesium ions for catalytic activity. Recombinant indolepyruvate decarboxylase was purified from the host Escherichia coli strain JM109. Specificity of the enzyme for the substrates indole-3-pyruvic acid, pyruvic acid, benzoylformic acid, and seven benzoylformic acid analogues was investigated using a continuous optical assay. Stopped-flow kinetic data showed no indication for substrate activation in the decarboxylation reaction of indole-3-pyruvic acid, pyruvic acid or benzoylformic acid. Size exclusion chromatography and small angle X-ray solution scattering experiments suggested the tetramer as the catalytically active state and a pH-dependent subunit association equilibrium. Analysis of the kinetic constants of the benzoylformic acid analogues according to Hansch et al. [Hansch, C., Leo, A., Unger, S.H., Kim, K.H., Nikaitani, D & Lien, E.J. (1973) J. Med. Chem.16, 1207-1216] and comparison with indole-3-pyruvic acid conversion by pyruvate decarboxylases from Saccharomyces cerevisiae and Zymomonas mobilis provided some insight into the catalytic mechanism of indolepyruvate decarboxylase.
Binding Sites↗
Snapshot of a key intermediate in enzymatic thiamin catalysis: crystal structure of the alpha-carbanion of (alpha,beta-dihydroxyethyl)-thiamin diphosphate in the active site of transketolase from Saccharomyces cerevisiae.
Kinetic and spectroscopic data indicated that addition of the donor substrate hydroxypyruvate to the thiamin diphosphate (ThDP)-dependent enzyme transketolase (TK) led to the accumulation of the alpha-carbanion/enamine of (alpha,beta-dihydroxyethyl) ThDP, the key reaction intermediate in enzymatic thiamin catalysis. The three-dimensional structure of this intermediate trapped in the active site of yeast TK was determined to 1.9-A resolution by using cryocrystallography. The electron density suggests a planar alpha-carbanion/enamine intermediate having the E-configuration. The reaction intermediate is firmly held in place through direct hydrogen bonds to His-103 and His-481 and an indirect hydrogen bond via a water molecule to His-69. The 4-NH(2) group of the amino-pyrimidine ring of ThDP is within 3 A distance to the alpha-hydroxy oxygen atom of the dihydroxyethyl moiety but at an angle unfavorable for a strong hydrogen bond. No structural changes occur in TK on formation of the reaction intermediate, suggesting that the active site is poised for catalysis and conformational changes during the enzyme reaction are not very likely. The intermediate is present with high occupancy in both active sites, arguing against previous proposals of half-of-the-sites reactivity in yeast TK.
Catalytic Domain↗
Pyruvate decarboxylase from Kluyveromyces lactis. An enzyme with an extraordinary substrate activation behaviour.
Pyruvate decarboxylase (EC 4.1.1.1) was isolated and purified from the yeast Kluyveromyces lactis. The properties of this enzyme relating to the native oligomeric state, the subunit size, the nucleotide sequence of the coding gene(s), the catalytic activity, and protein fluorescence as well as circular dichroism are very similar to those of the well characterized pyruvate decarboxylase species from yeast. Remarkable differences were found in the substrate activation behaviour of the two pyruvate decarboxylases using three independent methods: steady-state kinetics, stopped-flow measurements, and kinetic dilution experiments. The dependence of the observed activation rate constant on the substrate concentration of pyruvate decarboxylase from K. lactis showed a minimum at a pyruvate concentration of 1.5 mm. According to the mechanism of substrate activation suggested this local minimum occurs due to the big ratio of the dissociation constants for the binding of the first (regulatory) and the second (catalytic) substrate molecule. The microscopic rate constants of the substrate activation could be determined by a refined fit procedure. The influence of the artificial activator pyruvamide on the activation of the enzyme was studied.
Catalytic Domain↗