Biomedical subjects

A Richter

Publications and source records attributed to A Richter.

At least 19 recordsLinked to original sources

PubMed1997

Prodystonic effects of riluzole in an animal model of idiopathic dystonia related to decreased total power in the red nucleus?

The effects of riluzole (2-amino-6-trifluoromethoxy benzothiazole) on the severity of dystonia were examined in mutant hamsters (dtsz), an animal model of idiopathic dystonia in which dystonic attacks can be age dependently induced by mild stress. Previous studies in hamsters have shown antidystonic activity of various glutamate receptor antagonists whereas lamotrigine, considered as an inhibitor of glutamate release, exerted prodystonic effects. The latter, unexpected, finding prompted us to investigate riluzole which is thought to possess antiglutamatergic properties with mechanisms similar to those of lamotrigine. Riluzole (2, 5, 10 or 20 mg/kg i.p.) dose dependently decreased the latency to onset of dystonic attacks. A dose of 10 or 20 mg/kg significantly increased the severity of dystonia. Even in dtsz hamsters older than 70 days, i.e., after spontaneous remission of age-dependent dystonia, riluzole (10 or 20 mg/kg) provoked severe long-lasting (> 4 h) dystonic attacks. At a dose of 20 mg/kg, riluzole provoked short-lasting (< 1 h) dystonic disturbances also in non-dystonic control hamsters. Electroencephalographic recordings from depth electrodes in the red nucleus, where recent studies have shown abnormal neural activity before and during dystonic attacks in dtsz hamsters, revealed that riluzole (10 mg/kg) tended to cause a further decrease of the total power in dtsz hamsters and significantly reduced the total power in control animals. This finding may indicate that the prodystonic effects of riluzole are related to alterations of rubrospinal activity. With regard to antidystonic effects of glutamate receptor antagonists demonstrated in previous studies, the prodystonic effects of riluzole and, as shown by recent experiments, of lamotrigine also, may be due to the lack of selectivity of these drugs to inhibit glutamate release.

Animals↗

PubMed1997

High-molecular-mass complexes of human minichromosome-maintenance proteins in mitotic cells.

Minichromosome-maintenance (Mcm) proteins perform essential functions regulating the replication of eukaryotic genomes. In interphase cells they are either bound to a nuclear structure, most probably chromatin, or occur as free multiprotein complexes in the nucleoplasm. Mcm proteins are displaced from their chromatin sites during S phase, and several become highly phosphorylated during mitosis. We investigated whether phosphorylation affects the ability of mitotic Mcm proteins to form multiprotein complexes. Our results clearly show that phosphorylated mitotic Mcm proteins form a 14-15-S complex, probably consisting of one molecule each of the six known human Mcm proteins.

Amino Acid Sequence↗

PubMed1997

The electrical activity is impaired in the red nucleus of dt(sz) mutant hamsters with paroxysmal dystonia: an EEG power spectrum analysis of depth electrode recordings.

The genetically dystonic (dt(sz)) hamster is an animal model of paroxysmal dystonia that displays attacks of sustained abnormal movements and postures in response to mild stress. Dysfunctions within the basal ganglia may be critically involved in the pathophysiology of dystonia in mutant hamsters. Furthermore, previous observations from autoradiographic studies pointed to an altered neural activity in the red nucleus (RN). In the present study, computerized EEG spectral analysis of depth electrode recordings from the RN was performed before and after dystonic attacks in freely moving dt(sz) hamsters and compared to age-matched non-dystonic controls. No epileptic activity was seen in any of the recordings, substantiating previous notions that paroxysmal dystonia in these mutants has no epileptogenic basis. The predominant EEG changes in RN of dystonic hamsters were a decrease in total power over the range of 1.25-42.00 Hz, a decrease in maximum power and a shift of frequency at maximum power to lower frequencies. With regard to selected frequency bands, there was a decrease in the alpha, beta and gamma band. Although the observed changes of neural activity in the RN are probably based on a primary dysfunction in related structures, the present data demonstrate its importance in the expression of dystonic movements.

Animals↗

PubMed1997

Increased levels of lipid oxidation products in low density lipoproteins of patients suffering from rheumatoid arthritis.

9-Hydroxy-10,12-octadecadienoic acid (9-HODE) and 13-hydroxy-9,11-octadecadienoic acid (13-HODE) are accumulated in the low density lipoproteins of patients suffering from rheumatoid arthritis for a factor of 20-50 compared to healthy individuals of the same age. Both acids, derived by lipid peroxidation of linoleic acid, induce the release of interleukin 1 beta. The latter induces bone degression. The genesis of 9- and 13-HODE seems therefore to be an important factor in the development and progression of rheuma; in addition 9-HODE was reported to be a stimulus of inflammation, comparable to leukotrienes.

Adult↗

PubMed1997

Dextrorphan, but not dextromethorphan, exerts weak antidystonic effects in mutant dystonic hamsters.

The effects of dextromethorphan and its metabolite dextrorphan on severity of dystonia were examined in mutant dystonic hamsters, an animal model of idiopathic paroxysmal dystonia, in which recent examinations have shown antidystonic effects of selective N-methyl-D-aspartate (NMDA) receptor antagonists. Dextromethorphan and dextrorphan are non-competitive NMDA receptor antagonists which additionally exhibit affinity for sigma receptors. Dextrorphan (20 and 40 mg/kg i.p.) significantly retarded the progression of dystonia at the higher dose, whereas dextromethorphan (20, 40, 60 mg/kg i.p.) failed to exert any antidystonic effects even at high doses which caused severe effects. The lack of antidystonic efficacy of dextromethorphan may be related to its higher affinity to sigma receptors compared with dextrorphan.

Animals↗

PubMed1997

Alterations in N-methyl-D-aspartate receptor binding in dystonic hamster brains.

The genetically dystonic hamster is an animal model of idiopathic dystonia that displays sustained abnormal movements and postures either spontaneously or in response to mild environmental stimuli. Previous pharmacological studies have shown that competitive and non-competitive N-methyl-D-aspartate (NMDA) receptor antagonists exert potent antidystonic activity in this model, indicating that abnormal NMDA receptor function may be involved in the pathophysiology of this movement disorder. Autoradiographic analysis of NMDA receptor density in 67 brain regions, using the ligand [3H] N-(1-[2-thienyl]cyclohexyl)3,4-piperidine, which binds to the phencyclidine (PCP) site in the ion channel of the NMDA receptor channel complex, revealed that NMDA receptor binding is not substantially altered in dystonic hamster brains compared to age-matched controls. Nevertheless, there was a tendency towards enhanced binding during a dystonic attack in several regions, including a 25% increase in the ventrolateral thalamic nucleus (P < 0.05), which may be associated with altered basal ganglia output. While the data do not indicate widespread abnormalities in the PCP site of the NMDA complex, they do not exclude the possibility of more pronounced changes at other regulatory binding sites of the NMDA complex or other types of glutamate receptors in dystonia.

Animals↗

PubMed1997

Phenotypic variability in Friedreich ataxia: role of the associated GAA triplet repeat expansion.

We studied genotype-phenotype correlations in a group of 100 patients with typical Friedreich ataxia (FRDA), and in three groups of patients with atypical clinical presentations, including 44 Acadian FRDA, 8 late-onset FRDA (LOFA), and 6 FRDA with retained reflexes (FARR). All patients, except 3 with typical FRDA, carried two copies of the FRDA-associated GAA triplet repeat expansion. Overall, the phenotypic spectrum of FRDA appeared to be wider than defined by the currently used diagnostic criteria. Our study indicated the existence of several sources of variability in FRDA. Patients with larger GAA expansions tended to have earlier onset and were more likely to show additional manifestations of the disease. Mitotic instability of the expanded GAA repeats may partially account for the limited degree of correlation between expansion sizes as determined in lymphocytes and clinical parameters. Some clinical variants associated with specific FRDA haplotypes, such as Acadian FRDA and FARR, turned out to be unrelated to expansion sizes. No polymorphism in the frataxin coding sequence could be associated with these clinical variants.

Adolescent↗

PubMed1997

[In vivo imaging of corneal innervation in the human using confocal microscopy].

To date, descriptions of the structure of corneal innervation have only been possible on the basis of histological techniques. Confocal microscopy represents a new method for the structural examination of the cornea in vivo. Through our examinations we first defined the control group and then proceeded to record the reinnervation of donor tissue after perforating keratoplasty. We used the confocal slit-scanning video-microscope Microphthal to examine 40 corneas from 20 normal volunteers, 15 donor corneas and 5 eyes after enucleation for ocular tumors. These results were compared to our findings from postoperative checks on 14 patients after perforating keratoplasty (from 1 month to 2 years). With this system we were able to see nerves in the middle and in the superficial stroma. The course of these nerves can be followed, as well as their branching in the subepithelial plexus. Nerve fibers from superficial stromal nerves penetrate Bowman's membrane and create the basal epithelial plexus in the region of the basal epithelium. Seven months after perforating keratoplasty the first stromal nerves could be seen in the central corneal area. The first central reinnervation in the region of Bowman's membrane as well as in the basal epithelium was not detected until 15 months after operation. With confocal microscopy we have the potential to study the morphology of corneal innervation in vivo and in fresh donor tissue. For the first time it is possible to perform non-invasive morphological studies of reinnervation of the human cornea after surgical treatment.

Adolescent↗

PubMed1997

[Detection of morphological corneal changes caused by chloroquine therapy using confocal in vivo microscopy].

BACKGROUND: Chloroquine keratopathy is known as a disease with epithelial deposits in the cornea. The appearance of corneal changes does not seem to be related to dose and duration of treatment. Chloroquine accumulates in lysosomes. The purpose of this study was to investigate microscopic changes of corneal morphology in patients treated with chloroquine in vivo. PATIENTS AND METHODS: Using the confocal slit scanning microscope, we examined 16 patients during chloroquine treatment and 4 patients after treatment. The patients' age was between 33 and 75 years. They were treated with chloroquine over a minimum period of 2 months up to a maximum period of 10 years. RESULTS: In 12 of 20 patients, corneal changes were visible. An atypical inverse reflectivity of basal cells in comparison to healthy volunteers was found. There were also deposits in the wing cell layer. We saw a higher density in the anterior stroma before the appearance of epithelial opacities, as well as in cases of keratopathy on slit-lamp examination and also after the cessation of chloroquine treatment. In one patient with long-term therapy, there were atypically shaped and branched nerves in the anterior stroma. CONCLUSIONS: Using confocal microscopy, it was in some cases possible to detect changes in the corneal morphology before these changes could be detected by slit-lamp examination. As a result of this study we found that chloroquine keratopathy is not limited to the epithelium but can affect the anterior stroma and possibly neural structures.

Adult↗

PubMed1997

The Friedreich ataxia GAA triplet repeat: premutation and normal alleles.

The most common mutation causing Friedreich ataxia (FRDA), an autosomal recessive neurodegenerative disease, is the hyperexpansion of a polymorphic GAA triplet repeat localized within an Alu sequence (GAA-Alu) in the first intron of the frataxin (X25) gene. GAA-Alu belongs to the AluSx subfamily and contains several polymorphisms in strong linkage disequilibrium either with a subgroup of normal alleles, or with hyperexpanded FRDA-associated alleles. GAA repeat sizes in 300 normal chromosomes (97 from carriers and 203 from controls) were distributed in two separate groups: 83% of them contained between six and 10 triplets (small normal alleles), while the remaining 17% had more than 12 triplets, up to 36 (large normal alleles). Sequence analysis showed that no normal, stable allele contained more than 27 uninterrupted GAA triplets. All longer normal alleles were interrupted by a hexanucleotide repeat (GAGGAA). An allele containing an uninterrupted run of 34 GAA triplets was stably transmitted in four instances, but in one case underwent hyperexpansion to 650 triplets. Overall, our results suggest that the FRDA-associated expanded GAA repeats originate from normal alleles by recurrent expansions of alleles at risk.

Alleles↗

PubMed1997

Synthesis and in vitro trypanocidal activity of some novel iron chelating agents.

This report describes the syntheses and in vitro trypanocidal activity of a number of iron (III) chelators against epimastigotes of Trypanosoma cruzi. The compounds examined included a number of lipophilic N-alkyl derivatives of 2-ethyl- and 2-methyl-3-hydroxypyrid-4-ones, N,N'-bis(o-hydroxybenzyl)-(+/-)-trans-1,2-diaminocyclohexane, cyclotetrachromotropylene and four commercially available carboxy derivatives of pyridine, pyrazine, and pyarazole. Benznidazole, the drug clinically used in the treatment of Chagas' disease in humans, served as standard. All compounds were screened in vitro against Trypanosoma cruzi epimastigotes at 50 and 100 micrograms/ml for 72 h of exposure. At 100 micrograms/ml dosage, at least 4 compounds exhibited high epimastigote growth inhibition (65-69%) comparable to benznidazole (72%), whereas 9 compounds showed moderate to fair activity (53-64%) in the in vitro assay. At the lower concentration (50 micrograms/ml), the inhibitory activity of the best of these compounds was reduced significantly (39-48%) compared to the standard drug (59%). The activity of all the carboxylic acids remained in the lower range (4-25%). It is hypothesized that the enhanced activity of some of the compounds is due to their increased lipophilicity which enables them to successfully pass through the cellular membrane of Trypanosoma cruzi epimastigotes. The trypanocidal activities of the most effective compounds were significantly reduced when tested in the presence of added ferric ion.

Animals↗

PubMed1997

The in vitro biological activities of synthetic 18-O-methyl mycalamide B, 10-epi-18-O-methyl mycalamide B and pederin.

Mycalamides A and B, which were originally isolated from a marine sponge, show close structural similarity to the insect toxin pederin, and exhibit potent cytotoxicity and antitumour activity. Detailed investigation of the clinical potential of these compounds has been hampered because they are available in only minute quantities from natural sources. We now describe the biological activities of 18-O-methyl mycalamide B, 10-epi-18-O-methyl mycalamide and pederin, all prepared by total synthesis. The activities of 18-O-methyl mycalamide B and pederin were virtually indistinguishable when evaluated in DNA or protein synthesis assays, and in cytotoxicity assays using human carcinoma cell lines (IC50s 0.2-0.6 nM). In all assays, 10-epi-18-O-methyl mycalamide B was 10(3) times less toxic than its diastereoisomer, demonstrating that the cytotoxicity of 18-O-methyl mycalamide B is inseparable from its ability to inhibit protein synthesis. Short-term exposure of squamous carcinoma cells to 18-O-methyl mycalamide B or pederin caused an irreversible inhibition of cellular proliferation and induced cellular necrosis. In contrast, the antiproliferative effects of the compounds on human fibroblasts were reversible and there was no evidence of necrosis. Demonstration that 18-O-methyl mycalamide B and the synthetically less complex molecule, pederin, show some tumour cell toxicity indicates that this novel class of compounds should be subjected to preclinical evaluation.

Animals↗

PubMed1996

Friedreich ataxia in Acadian families from eastern Canada: clinical diversity with conserved haplotypes.

The gene for Friedreich ataxia (FRDA), an autosomal-recessive neurodegenerative disease, remains elusive. The current candidate region of about 150 kb lies between loci FR2 and F8101 near the D9S15/D9S5 linkage group at 9q13-21.1. Linkage homogeneity between classical FRDA and a milder, slowly progressive Acadian variant (FRDA-Acad) has been demonstrated. An extended D9S15-D9S5 haplotype (C6) predominates in FRDA-Acad chromosomes from Louisiana. We studied 10 Acadian families from New Brunswick, Canada. In eight families, affected individuals conformed to the clinical description of FRDA-Acad; in one, 2 sibs presented with spastic ataxia (SPA-Acad). In the last family, 2 sibs had FRDA-Acad, and one had SPA-Acad. We found that SPA-Acad is linked to the FRDA gene region. The C6 haplotype and a second major haplotype (B7) were identified. The same ataxia-linked haplotypes segregated with both FRDA-Acad and SPA-Acad in two unrelated families. The parental origins of these haplotypes were different. Our observation of different phenotypes associated with the same combination of haplotypes may point to the influence of the parent of origin on gene expression, indicate the effect of modifier genes, or reflect the presence of different mutations on the same haplotypes. Our findings underline the need to investigate families with autosomal-recessive ataxias for linkage to the FRDA region, despite lack of key diagnostic manifestations such as cardiomyopathy or absent deep-tendon reflexes.

Canada↗

PubMed1996

Abnormal c-fos expression in the lateral habenula during dystonic attacks in a hamster model of idiopathic dystonia.

The genetically dystonic hamster (dtsz), an animal model of idiopathic dystonia, displays sustained twisting movements and postures either spontaneously or in response to mild stress. In the present study the expression of c-fos immunoreactive neurons (Fos-ir), used as an indicator of neuronal activity, was investigated within various brain regions in dtsz hamsters and non-dystonic control hamsters. Under baseline condition, i.e. in the absence of dystonia, the expression of Fos-ir did not reveal any differences between dtsz hamsters and controls. However, in response to mild stress several brain regions, particularly the lateral habenula (LHb), exhibited differences in c-fos induction in dtsz hamsters and controls. Whereas in the LHb the expression of Fos-ir was markedly enhanced in controls, it showed almost no increase in dystonic hamsters, indicating impaired neuronal activity. Since the lateral habenula receives major input from the basal ganglia via the entopeduncular nucleus, the present data might indicate that basal ganglia are involved in the dystonic syndrome in mutant hamsters.

Animals↗

PubMed1996

The significance of valine 33 as a ligand-specific epitope of transforming growth factor alpha.

Although binding of epidermal growth factor (EGF) and transforming growth factor alpha (TGFalpha) to the EGF receptor (EGFR) is mutually competitive, their binding is not identical, and their biological activities are not always equivalent. To probe for ligand-specific interactions, we have synthesized analogues of TGFalpha with modifications to the residue lying between the fourth and fifth cysteines (the "hinge"). Although this residue lies in a structurally conserved region of the protein, it is not conserved within the EGFR ligand family. Our results show that in TGFalpha there is a preference for a bulky hydrophobic hinge residue; this contrasts with EGF, for which a hydrogen bond donor functionality is preferred. Sequence analysis of the human EGFR ligands revealed that the nature of the hinge residue correlated with the sequence in the B-loop beta-sheet. As this region is an important determinant in recognition of TGFalpha by the chicken EGFR, we assessed the mitogenicity of the TGFalpha hinge mutants, as well as the other EGFR ligands, using chicken embryo fibroblasts. The preference of the chicken EGFR for TGFalpha hinge mutants with hydrophobic side chains paralleled that of the human EGFR. Betacellulin and heparin-binding EGF-like growth factor also possess an hydrophobic hinge; both were at least as potent as TGFalpha for chicken embryo fibroblasts. EGF and amphiregulin, both with hydrogen bond donor functionalities at their hinge, displayed markedly decreased in potency by comparison with TGFalpha. We propose that EGFR ligands can be subclassified into TGFalpha-like and EGF-like and that this is of functional significance, identifying a potential mechanism whereby EGFR can discriminate between its ligands.

Amino Acid Sequence↗

PubMed1996

Antidystonic effects of L-type Ca2+ channel antagonists in a hamster model of idiopathic dystonia.

The effects of selective L-type Ca2+ channel antagonists on severity of dystonia were investigated in a mutant hamster model of idiopathic generalized dystonia. Nimodipine and diltiazem significantly decreased the severity of dystonia. Nimodipine was more potent in this respect and did not cause any behavioral side effects. The present data therefore suggest that Ca2+ channel antagonists could be useful in the treatment of idiopathic dystonia. The antidystonic effect of diltiazem and nimodipine may be based on their antidopaminergic action. However, the lack of significant effects of the L-type channel agonist (+/-)-BAY k-8644 (1-5 mg/kg; methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoro-methylphenyl) -pyridine-5-carboxylate)) on severity of dystonia may indicate that voltage-gated Ca2+ channels are not critically involved in the pathophysiology of dystonia in mutant hamsters.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1996

Increased levels of kynurenic acid in brains of genetically dystonic hamsters.

Recent pharmacological studies have shown antidystonic effects of NMDA and non-NMDA receptor antagonists in an inbred line of Syrian hamsters (dt(sz)) with primary generalized dystonia, i.e. a neurological syndrome of sustained muscle contractions which occurs in the absence of any pathomorphological alterations. This prompted us to examine the levels of kynurenic acid (KYNA), the endogenous broad spectrum antagonist of the excitatory amino acid receptors. The concentrations of KYNA were determined by HPLC in forebrain, cerebellum, brainstem and plasma in dystonic hamsters and age-matched non-dystonic controls. Dystonia in mutant hamsters is transient and disappears completely at the age of 70 days. In order to examine if neurochemical changes are associated with dystonia, KYNA was determined at the age of maximum severity (30 days) and after remission (70 days). The levels of KYNA were significantly increased in forebrain, cerebellum and brainstem (37-130 percent) in dystonic hamsters at the age of maximum severity of dystonia (30 days of life) compared to both a genetically related non-dystonic inbred line and a non-related outbred line of hamsters. The increase of KYNA in brain regions was accompanied by enhanced plasma levels. However, there was no correlation between brain and plasma levels. Since the changes in KYNA levels disappeared in parallel with dystonia (70 days), the present data provide further evidence that abnormal activity of excitatory amino acids may be pathogenetically involved in dystonia in mutant hamsters. With regard to the recent finding of antidystonic effects of glutamate receptor antagonists the increased levels of kynurenic acid may be interpreted as a counteracting process to an overactivity of the glutamatergic system.

Aging↗

PubMed1996

Properties of the human nuclear protein p85Mcm. Expression, nuclear localization and interaction with other Mcm proteins.

Recently we identified a cDNA fragment encoding a conserved part of a new human minichromosome maintenance (Mcm) protein, provisionally termed P1.1Mcm3. Here, we report that the protein is most highly related to a yeast cell-division-cycle protein, Cdc47, encoded by the open reading frame YBR1441 on chromosome 11 of Saccharomyces cerevisiae. The human protein migrates on a polyacrylamide gel with an apparent molecular mass of 85 kDa and shares areas of significant similarity with the Mcm family of replication proteins. It is, therefore, designated as p85Mcm. Microscopic immuno-fluorescence studies revealed that protein p85Mcm is located in the nuclei of interphase cells, but is evenly distributed throughout the cell during mitosis. The amounts of p85Mcm do not significantly change during the cell cycle, but mRNA levels rise with the beginning of the S phase. However, in vitro differentiation of HL60 cells results in a striking decrease of both p85Mcm mRNA and protein levels, suggesting a role for p85Mcm in proliferating, but not in differentiated cells. Under physiological salt conditions, p85Mcm is a component of a high molecular-mass complex including other Mcm proteins. The complex dissociates at high ionic strength giving rise to stable subcomplexes, one of which contains protein p85Mcm together with Mcm proteins hCdc21 and p1O5Mcm.

Amino Acid Sequence↗