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Biomedical subjects

Stefan Vielhaber

Publications and source records attributed to Stefan Vielhaber.

At least 19 recordsLinked to original sources
PubMed2007

Variability of the recessive oculopharyngeal muscular dystrophy phenotype.

Oculopharyngeal muscular dystrophy (OPMD) is usually transmitted as an autosomal-dominant trait and characterized by an expansion from 6 to 8 or more GCG/GCA repeats in the poly-(A) binding protein nuclear 1 (PABPN1) gene on chromosome 14q11. Autosomal-recessive OPMD with a homozygous (GCG)7 expansion of PABPN1 has only been described in two Canadian patients, who showed a comparably mild phenotype, suggesting that it is less severe than the dominant form. We clinically and genetically characterized the first two reported cases of autosomal-recessive OPMD in Europe. Remarkably, both patients revealed severe and diverse phenotypes, with an unusual onset and atypical clinical course in one patient. Former studies found a 1%-2% frequency of the (GCG)7 allele, which theoretically produces an incidence of 1:10,000 of autosomal-recessive OPMD in the general population. We conclude that the apparent rarity of the autosomal-recessive form of OPMD may be due to the fact that genetic testing is generally administered only to patients with typical clinical features or a positive family history.

Aged↗
PubMed2006

Binding of copper is a mechanism of homocysteine toxicity leading to COX deficiency and apoptosis in primary neurons, PC12 and SHSY-5Y cells.

Children with hereditary severe hyperhomocysteinemia present with a variety of neurological impairment, and mild hyperhomocysteinemia has been associated with neurodegeneration in the elderly. The link of hyperhomocysteinemia to neurological dysfunction is unknown. We investigated mitochondrial mechanisms of homocysteine (HCys) neurotoxicity in rat dopaminergic pheochromocytoma cells, human neuroblastoma cells and primary rat cerebellar granule neurons. HCys dose dependently impaired cytochrome c oxidase (COX) activity as well as stability and induced reactive oxygen species and apoptotic cell death. We found that HCys binds the COX cofactor Cu(2+), and Cu(2+) supplementation prior to HCys treatment preserved COX activity and prevented cell death. The Cu(2+) chelating action of HCys and impairement of COX activity represent novel mechanisms of HCys neurotoxicity, which might be preventable by supplementation of Cu(2+).

Animals↗
PubMed2006

In vivo quantification of spinal and bulbar motor neuron degeneration in the G93A-SOD1 transgenic mouse model of ALS by T2 relaxation time and apparent diffusion coefficient.

Magnetic resonance imaging (MRI) has provided important information in characterizing amyotrophic lateral sclerosis (ALS) in humans and in animal models. A frequently used animal model to study mechanisms of pathogenesis and the efficacy of drugs in ALS is a transgenic mouse over-expressing the human mutated G93A-superoxide dismutase 1 (G93A-SOD1). In our study, we applied MRI to find suitable progression markers, which can be used to monitor the development of ALS and to evaluate therapeutic approaches at early stages of the disease. Therefore, we generated parameter maps of the spin-spin relaxation time (T2) and the apparent diffusion coefficient (ADC) starting at day 70 after birth, i.e., before motor scores decline around day 90. Depending on the progression of the disease, G93A-SOD1 mice showed significantly increased values of T2 in the brain stem motor nuclei Nc. V (trigeminal nucleus), VII (facial nucleus), and XII (hypoglossal nucleus), and spinal cord compared to non-transgenic wild-type mice and transgenic mice over-expressing the non-mutated wild-type human SOD1 (tg-SOD1). Similar effects in these motor nuclei were revealed by ADC mapping. Furthermore, in the upper spinal cord, a dorsal-ventral difference with significantly higher T2 values in the ventral part was demonstrated by T2 mapping. While both T2 and ADC might prove useful as progression markers and enable the longitudinal non-invasive evaluation of ALS in G93A-SOD1 mice, the potential is limited by age-dependent effects in case of ADC mapping.

Amyotrophic Lateral Sclerosis↗
PubMed2006

Brain 1H magnetic resonance spectroscopic differences in myotonic dystrophy type 2 and type 1.

To evaluate cerebral metabolism and intergroup differences in closely matched patients with myotonic dystrophy type 2 (DM2, n = 15) and type 1 (DM1, n = 14), we performed (1)H magnetic resonance spectroscopic (MRS) analyses of the occipital and temporoparietal cortical regions as well as of subcortical frontal white matter. Relative to healthy subjects, the concentration of N-acetylaspartate was significantly reduced in all tested brain regions in both disease groups. In the DM1 patients we also observed a concomitant depletion of creatine and choline levels, particularly in the frontal white matter. A discriminant analysis based on the (1)H-MRS data distinguished between the DM2, DM1, and control groups with an overall accuracy of 88%. (1)H-MRS indicates that neurochemical alterations involving gray and white matter occur in patients with DM2 and DM1. Although structural abnormalities (cerebral atrophy, white matter lesions) are similar in DM2 and DM1, changes in cerebral metabolites can differentiate these disease groups, suggesting that the diseases differ in their neurocellular pathology.

Adult↗
PubMed2005

Volumetric magnetic resonance imaging of functionally relevant structural alterations in chronic epilepsy after pilocarpine-induced status epilepticus in rats.

PURPOSE: After pilocarpine-induced epilepsy in rats, volumetric magnetic resonance imaging (MRI) reveals significant morphologic changes in functionally relevant structures of the brain. To relate structural changes to functional alteration, we studied the correlation of regional brain atrophy (e.g., of the hippocampus) with lesion-induced learning deficits in the Morris water maze. METHODS: MRI experiments were performed on an MR scanner at 4.7 Tesla. For volumetric analysis, various cerebral structures were segmented in horizontal and coronal T(2)-weighted MR images. Before the MRI investigations, animals were trained for 10 days in a Morris water maze. RESULTS: Volumetric MRI revealed a significant loss in hippocampal size in both the dorsal and ventral parts, correlated with an increase in ventricular size. Furthermore, significant losses were found in the relative size of thalamus, putamen, cortex, and the combined areas of perirhinal, entorhinal, and piriform cortices adjacent to the hippocampus. A significant correlation of learning performance in the Morris water maze with the relative hippocampal area and not with other areas tested was observed in pilocarpine-treated animals. CONCLUSIONS: The data provide a quantitative analysis of functionally relevant structural alterations in rats with chronic epilepsy. Water maze performance of pilocarpine-treated animals correlates with the degree of hippocampal but not with the degree of cortical damage, demonstrating the potential of this method for the investigation of cognitive impairments in relation to cerebral changes. In addition, the data point to an important role of even the residual hippocampus in memory formation.

Animals↗
PubMed2004

Age-dependent changes in MRI of motor brain stem nuclei in a mouse model of ALS.

Mice over-expressing the mutant human G93A-SOD1 are widely used as an animal model of amyotrophic lateral sclerosis (ALS). ALS is characterized by progressive degeneration of motor neurons in the motor cortex, brain stem and spinal cord. The underlying mechanisms for the selective death of motor neurons are still uncertain. To study factors that cause selective neuron degeneration or therapeutic approaches to delay the progression of the disease, a method is required to monitor the state of motor neurons under in-vivo conditions. Here, we demonstrate that in G93A-SOD1 mice the MRI signal intensities of nucleus V, VII, XII, and nucleus ambiguus show a time-dependent increase starting around day 90, parallel to first behavioral signs of a motoneuron disorder.

Aging↗
PubMed2004

The mechanism of neuroprotection by topiramate in an animal model of epilepsy.

PURPOSE: For the antiepileptic drug (AED) topiramate (TPM), neuroprotective effects have been reported in models of focal cerebral ischemia and experimental status epilepticus, but the putative mechanism of action has remained elusive. METHODS: We studied the effects of TPM on mitochondrial function in the pilocarpine rat model of chronic epilepsy and in isolated mitochondria from rat brain. RESULTS: TPM treatment in status epilepticus at doses ranging from 20 to 100 mg/kg considerably improved the survival of rats and improved CA1 and CA3 pyramidal cell survival in a dose-dependent manner. This treatment increased the activity of mitochondrial respiratory chain complex I in the CA1 and CA3 pyramidal subfields and resulted in lower seizure frequencies in chronic epileptic rats. In vitro investigations of the action of TPM on isolated rat brain mitochondria ruled out any direct effects of the drug on mitochondrial oxidative phosphorylation but revealed a protective effect on hippocampal mitochondria against an external calcium challenge. This can explain its observed neuroprotective action in the concentration range tested. The in vitro effects of TPM on the calcium handling of isolated brain mitochondria was found to be comparable to the action of cyclosporin A. CONCLUSIONS: The neuroprotective action of TPM seems to be directly related to its inhibitory effect on the mitochondrial permeability transition pore.

Animals↗
PubMed2003

Improvement of the diagnostic procedure in proximal myotonic myopathy/myotonic dystrophy type 2.

Proximal myotonic myopathy/myotonic dystrophy type 2 (PROMM/DM 2) is caused by an expansion of the (TG)n(TCTG)n(CCTG)n repeat tract in intron 1 of the ZNF9 gene located on chromosome 3q21. Because these expansions show a marked mitotic instability, expanded alleles are often difficult to detect. In order to improve the diagnostic procedure, we applied a combination of pulsed-field gel electrophoresis and semi-quantitative Southern blot analysis with a novel hybridization probe. The combination of these methods led to unequivocal results in about 98% of cases with a clinical diagnosis of PROMM/DM 2. Furthermore, we report the genotype/phenotype correlation in a patient lacking a normal ZNF9 allele and a further proband with a "grey zone" allele.

Adult↗
PubMed2003

Characterization of superoxide-producing sites in isolated brain mitochondria.

Mitochondrial respiratory chain complexes I and III have been shown to produce superoxide but the exact contribution and localization of individual sites have remained unclear. We approached this question investigating the effects of oxygen, substrates, inhibitors, and of the NAD+/NADH redox couple on H2O2 and superoxide production of isolated mitochondria from rat and human brain. Although rat brain mitochondria in the presence of glutamate+malate alone do generate only small amounts of H2O2 (0.04 +/- 0.02 nmol H2O2/min/mg), a substantial production is observed after the addition of the complex I inhibitor rotenone (0.68 +/- 0.25 nmol H2O2/min/mg) or in the presence of the respiratory substrate succinate alone (0.80 +/- 0.27 nmol H2O2/min/mg). The maximal rate of H2O2 generation by respiratory chain complex III observed in the presence of antimycin A was considerably lower (0.14 +/- 0.07 nmol H2O2/min/mg). Similar observations were made for mitochondria isolated from human parahippocampal gyrus. This is an indication that most of the superoxide radicals are produced at complex I and that high rates of production of reactive oxygen species are features of respiratory chain-inhibited mitochondria and of reversed electron flow, respectively. We determined the redox potential of the superoxide production site at complex I to be equal to -295 mV. This and the sensitivity to inhibitors suggest that the site of superoxide generation at complex I is most likely the flavine mononucleotide moiety. Because short-term incubation of rat brain mitochondria with H2O2 induced increased H2O2 production at this site we propose that reactive oxygen species can activate a self-accelerating vicious cycle causing mitochondrial damage and neuronal cell death.

Animals↗
PubMed2003

Mitochondrial dysfunction in myofibrillar myopathy.

'Myofibrillar myopathy' defines a myopathic condition with focal myofibrillar destruction and accumulation of degraded myofibrillar elements. Despite the fact that a number of mutations in different genes as well as cytotoxic agents lead to the disease, abnormal accumulation of desmin is a typical, common feature. Pathological changes of mitochondrial morphology and function have been observed in animal models with intermediate filament pathology. Therefore, in the present study we tested for mitochondrial pathology in skeletal muscle of five patients with the pathohistological diagnosis of myofibrillar myopathy. Screening for large-scale mtDNA deletions and the frequent MERRF (myoclonic epilepsy; ragged red fibres) and MELAS (mitochondrial encephalomyopathy; lactic acidosis; stroke) point mutations was negative in all patients. Histologically, all muscle biopsies showed nonspecific abnormalities of the oxidative/mitochondrial enzyme stainings (histochemistry for reduced nicotinamide adenine dinucleotide, succinic dehydrogenase, cytochrome c oxidase), only one of them had ragged red fibres and a significant number of cytochrome c oxidase-negative fibres. Upon biochemical investigation, four of our patients showed pathologically low respiratory chain complex I activities. Only one of our patients had a pathologically low complex IV activity, while the measurements of the others were within low normal range. The single patient with pathological values for both complex I and IV was the one with the clear histological hallmarks (ragged red and cytochrome c oxidase-negative fibres) of mitochondrial pathology. She also was the only patient with clinical signs hinting at a mitochondrial disorder. Together with data from observations in desmin- and plectin-deficient mice, our results support the view that desmin intermediate filament pathology in these cases is closely linked to mitochondrial dysfunction in skeletal muscle.

Aged↗
PubMed2003

Hippocampal N-acetyl aspartate levels do not mirror neuronal cell densities in creatine-supplemented epileptic rats.

For neuroprotective therapy of neurodegenerative diseases creatine treatment has gained special interest because creatine has been shown to cross the blood-brain barrier, accumulate in the human brain in vivo and cause delayed neuronal cell death in a large number of animal models. Here, we used the pilocarpine model of temporal lobe epilepsy to determine whether creatine administration is able to attenuate the epilepsy-associated decrease in hippocampal N-acetyl aspartate (NAA) concentrations, impairment of mitochondrial function and neuronal cell loss. In vivo1H-NMR spectroscopy showed, in epileptic rats after creatine administration, higher hippocampal NAA concentrations, suggesting improved neuronal survival. However, in vitro observation of hippocampal slices from creatine-treated epileptic rats revealed a more pronounced loss of pyramidal neurons and decrease in activity of mitochondrial enzymes in hippocampal subfields. This indicates that NAA concentrations measured by in vivo1H-NMR spectroscopy reflect alterations of metabolism rather than neuronal cell densities. Our data indicate an adverse effect of creatine on neuronal survival under conditions of enhanced neuronal activity.

Animals↗
PubMed2003

Correlation of hippocampal glucose oxidation capacity and interictal FDG-PET in temporal lobe epilepsy.

PURPOSE: Interictal [18F]fluorodeoxyglucose (FDG) positron emission tomography (PET) demonstrates temporal hypometabolism in the epileptogenic zone of 60-90% of patients with temporal lobe epilepsy. The pathophysiology of this finding is still unknown. Several studies failed to show a correlation between hippocampal FDG-PET hypometabolism and neuronal cell loss. Because FDG is metabolized by hexokinase bound to the outer mitochondrial membrane, we correlated the glucose-oxidation capacity of hippocampal subfields obtained after surgical resection with the corresponding hippocampal presurgical FDG-PET activity. METHODS: In 16 patients with electrophysiologically confirmed temporal lobe epilepsy, we used high-resolution respirometry to determine the basal and maximal glucose-oxidation rates in 400-microm-thick hippocampal subfields obtained after dissection of human hippocampal slices into the CA1 and CA3 pyramidal subfields and the dentate gyrus. RESULTS: We observed a correlation of the FDG-PET activity with the maximal glucose-oxidation rate of the CA3 pyramidal subfields (rp = 0.7, p = 0.003) but not for the regions CA1 and dentate gyrus. In accordance with previous studies, no correlation of the FDG-PET to the neuronal cell density of CA1, CA3, and dentate gyrus was found. CONCLUSIONS: The interictal hippocampal FDG-PET hypometabolism in patients with temporal lobe epilepsy is correlated to the glucose-oxidation capacity of the CA3 hippocampal subfield as result of impaired oxidative metabolism.

Adolescent↗
PubMed2002

Metabolic consequences of a novel missense mutation of the mtDNA CO I gene.

We have identified a novel heteroplasmic C6489A missense mutation in the mitochondrial DNA (mtDNA) CO I gene encoding the cytochrome c oxidase (COX) subunit I in a 17-year-old girl with epilepsia partialis continua. This point mutation leads to an exchange of the highly conserved Leu196 to Ileu196. Muscle biopsy showed in single fibers decreased COX activity and lowered binding of COX antibodies, indicating decreased stability of the mutated enzyme. The analysis of blood mtDNA revealed about 30% mutant mtDNA in the patients blood but about 90% mutant mtDNA in the blood of two non-affected family members. Quantitative analysis of the mutation gene dose effect on COX activity on single muscle fiber level revealed a very high threshold-a COX deficiency was observed only in fibers containing >95% mutant mtDNA. In apparent contrast to this high mutation gene dose threshold, in vivo investigations of mitochondrial function in saponin-permeabilized muscle fibers of the index patient containing approximately 90% mutated mtDNA showed decreased maximal rates of respiration and an increased sensitivity of fiber respiration to cyanide. This is due to a 2-fold increase of COX flux control on muscle fiber respiration and a 30% decrease of COX metabolic threshold, supporting the concept of tight COX control of oxidative phosphorylation in skeletal muscle.

Adolescent↗
PubMed2002

Facioscapulohumeral muscular dystrophy with EcoRI/BlnI fragment size of more than 32 kb.

Facioscapulohumeral muscular dystrophy (FSHD) is associated with the deletion of a variable number of 3.3-kb subunits of a tandemly arranged repeat (D4Z4) on chromosome 4q35. EcoRI/BlnI fragments in the range of 10-35 kb are currently defined as disease-associated. Diagnosis of FSHD is frequently complicated by interchromosomal exchange with a homologous locus on 10q26. We present clinical and laboratory data of six subjects from two unrelated families with a marked FSHD phenotype and EcoRI/BlnI fragments of 39 and 33 kb, respectively. Origin on chromosome 4q35 was confirmed by haplotype analysis in the first family and was supported by pulsed field gel electrophoresis data in the second family. Our data further confirm the existence of a region of overlap of normal and pathological fragments. Fragments from this region can obviously be associated with marked FSHD phenotypes. Furthermore, application of linked markers and resolution of all EcoRI/BlnI fragments by pulsed field gel electrophoresis in addition to routine laboratory tests considerably augments the information obtained from molecular tests, upon which genetic counselling can then be based.

Adult↗
PubMed2002

Differences in flux control and reserve capacity of cytochrome c oxidase (COX) in human skeletal muscle and brain suggest different metabolic effects of mild COX deficiencies.

To evaluate tissue specific control of oxidative phosphorylation by cytochrome c oxidase (COX) we determined the flux control coefficient and the metabolic reserve capacity of this enzyme in human saponin-permeabilised muscle fibers and digitonin-treated parahippocampal homogenates. In these tissue preparations it is possible to investigate mitochondrial function under conditions which are close to the in vivo situation. In the presence of NAD-dependent substrates we observed, under active state conditions, a flux control coefficient of COX over oxidative phosphorylation of 0.24 +/- 0.07 and a 1.9 +/- 0.2-fold excess capacity in human skeletal muscle fibers. In human parahippocampal gyrus we determined, under similar conditions, a flux control coefficient of COX of 0.12 +/- 0.05 and a 3.9 +/- 0.6-fold excess capacity of the enzyme. The observed difference in metabolic control can be attributed to activity differences of COX in human brain and muscle mitochondria. Our results predict stronger metabolic effects of mild COX activity deficits in human skeletal muscle than in brain tissue.

Biological Transport↗
PubMed2002

Seizure-dependent modulation of mitochondrial oxidative phosphorylation in rat hippocampus.

Mitochondrial function is a key determinant of both excitability and viability of neurons. Here, we demonstrate seizure-dependent changes in mitochondrial oxidative phosphorylation in the epileptic rat hippocampus. The intense pathological neuronal activity in pilocarpine-treated rats exhibiting spontaneous seizures resulted in a selective decline of the activities of NADH-CoQ oxidoreductase (complex I of the respiratory chain) and cytochrome c oxidase (complex IV of respiratory chain) in the CA3 and CA1 hippocampal pyramidal subfields. In line with these findings, high-resolution respirometry revealed an increased flux control of complex I on respiration in the CA1 and CA3 subfields and decreased maximal respiration rates in the more severely affected CA3 subfield. Imaging of mitochondrial membrane potential using rhodamine 123 showed a lowered mitochondrial membrane potential in both pyramidal subfields. In contrast to the CA1 and CA3 subfields, mitochondrial oxidative phosphorylation was unaltered in the dentate gyrus and the parahippocampal gyrus. The changes of oxidative phosphorylation in the epileptic rat hippocampus cannot be attributed to oxidative enzyme modifications but are very likely related to a decrease in mitochondrial DNA copy number as shown in the more severely affected CA3 subfield and in cultured PC12 cells partially depleted of mitochondrial DNA. Thus, our results demonstrate that seizure activity downregulates the expression of mitochondrial-encoded enzymes of oxidative phosphorylation. This mechanism could be invoked during diverse forms of pathological neuronal activity and could severely affect both excitability and viability of hippocampal pyramidal neurons.

Animals↗