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Biomedical subjects

M Hofmann

Publications and source records attributed to M Hofmann.

At least 19 recordsLinked to original sources
PubMed1995

Decrease of red cell membrane fluidity and -SH groups due to hyperglycemic conditions is counteracted by alpha-lipoic acid.

Human red cell membranes (ghosts) were treated by 5 min of incubation with fasting or hypo- and hyperglycemic concentrations of D-glucose. This simulation of nondiabetic or diabetic conditions revealed an influence on membrane fluidity and on protein -SH reactivity. Protein -SH groups, measured with Ellman's reagent, generally behave in the same way as membrane fluidity determined with diphenylhexatriene. Maximal values were obtained with 5 mM D-glucose, whereas decrease was observed above 10 mM D-glucose. Addition of alpha-lipoic acid (4 nmol/mg protein) resulted in a significant increase in membrane fluidity and titratable -SH groups at glucose concentrations of 10 mM and above. Dithiothreitol diminished titrable-SH groups and did not restore membrane fluidity. 2-Mercaptopropionylglycine was only effective in restoration of -SH groups. By contrast to D-glucose, other sugars such as L-glucose, D-fructose, or sucrose revealed no comparable changes on membrane fluidity and titratable membrane -SH groups between concentrations of 5 and 10 mM. The hyperglycemic effects of D-glucose were corroborated with isolated, reconstituted membrane proteins and erythrocyte glucose carrier, indicating that, in general, the observed divergent biochemical/biophysical changes of the red cell membrane are influenced by the glucose transport protein GluT1. The natural R-form and the S-form of alpha-lipoic acid were compared with racemic R-/S-forms for their efficiencies in alterations of red cell membrane fluidity. Decreased fluidities in presence of 10 mM glucose were found to be influenced in differentiated ways: the S-form was highly active in increasing fluidity at 4 nmol/mg and increasingly less active up to 20 nmol/mg protein. By contrast the R-form of lipoic acid was moderately efficient in increasing fluidity through a larger concentration range between 4 and 80 nmol/mg protein.

Dithiothreitol↗
PubMed1995

Differential CD44 expression patterns in primary brain tumours and brain metastases.

Splicing variants of CD44 (CD44v) are increasingly recognised as metastasis-promoting factors in rodent and some human cancers. However, the frequency for CD44v expression in human cancers and their metastases and the status of CD44v expression in low or non-metastatic tumours is still uncertain. To address this issue, we investigated CD44 expression patterns in brain metastases (BMTs) spread from more than ten organs and five types of primary brain tumours (PBTs) by Northern blot, reverse transcription-polymerase chain reaction (RT-PCR) and immunocytochemical analysis. The results demonstrated that all of the 56 PBTs examined express standard form of CD44 (CD44s) but none of them express CD44v. In contrast, 22 of 26 BMTs studied were found with CD44v expression. Our data thus present direct evidence of a general distribution of CD44 in BMTs but suggest that such expression is an extremely rare event in PBTs. Therefore, the presence or absence of CD44v expression may be related to high or low metastatic potential of human malignancies.

Adult↗
PubMed1995

Age dependency of changes in cerebral hemoglobin oxygenation during brain activation: a near-infrared spectroscopy study.

We used near-infrared spectroscopy (NIRS) to study noninvasively the influence of aging on changes in the local concentration of oxygenated hemoglobin ([HbO2]), reduced hemoglobin ([HbR]), and total hemoglobin ([HbT] = [HbR] + [HbO2]) during activation of brain function. Young subjects (n = 12; age, 28 +/- 4 years) performing calculation tasks showed an increase in [HbO2] [mean (arbitrary units) +/- SD, 2.36 +/- 1.07] and [HbT] (2.24 +/- 1.13) in the frontal cortex, while [HbR] (-0.11 +/- 0.48) decreased. Elderly subjects (n = 17; age, 52 +/- 10 years) showed a significantly lower mean increase (p < 0.05) in [HbO2] and [HbT] levels (1.21 +/- 1.38 and 0.72 +/- 1.41, respectively). Regression analysis supports the hypothesis of an age-dependent decline in the activation-induced local increase in [HbO2] (y = -0.241x + 20.062; r = -0.431, p < 0.05) as well as [HbT] (y = -0.346x + 22.496; r = -0.568, p < 0.05). We conclude that NIRS is a promising approach for studying changes in Hb oxygenation during brain activation in physiological aging.

Adult↗
PubMed1995

Reduced beta-amyloid response in lymphocytes of patients with Alzheimer's disease.

The beta-amyloid peptide (beta A4) is a principal constituent of senile plaques and is thought to play a major role in the pathophysiology of Alzheimer's disease (AD). Although the mechanism of beta-A4 neurotoxicity is still a matter of debate, one of its effects might be a destabilization of cellular calcium homeostasis, thus promoting neuronal damage. The influence of the toxic fragment beta A25-35 on the mitogen-induced rise in the intracellular calcium concentration ([Ca2+]i) in lymphocytes of AD (n = 13) and depressive patients (n = 14) as well as in healthy controls was therefore investigated (n = 16). The results showed a significant increase in the mitogen-induced calcium signal with lymphocytes of healthy controls and depressive patients. This beta A25-35-induced amplification was significantly lower in AD patients as compared to healthy controls but not as compared to depressive patients. The results thus confirm a postulated decreased beta-amyloid sensitivity in AD lymphocytes. However, this effect might not be as pronounced or as specific as recently described by Eckert et al., (1993b).

Aged↗
PubMed1995

[Computer-assisted individualized memory training in Alzheimer patients].

Memory training programs for cognitively impaired patients have often been criticized for their lack of relevance to everyday activities. We therefore report our experience with two patients suffering from probable Alzheimer's disease who were trained with a new computer-based program recently developed by our research group. An everyday task of personal relevance to the patient was simulated and trained on a PC touch screen using personal photographs of the patient's surroundings and biography. The patient's training performance (time, mistakes, number of advices) improved substantially. While psychopathometric tests showed no significant effects with regard to general cognitive performance, levels of motivation were high and there was a positive acceptance of the training, signs of emotional activation and of a transfer of the trained skills into real situations.

Activities of Daily Living↗
PubMed1995

[Persistent granulocytosis and hyperuricemia after a single G-CSF injection (Filgrastim) in treatment of chemotherapy-induced myelosuppression in metastatic breast carcinoma].

We report about a patient with metastatic breast cancer treated with chemotherapy regime (CMF), who developed a febril leukopenia as well as a hyperuricemia. A single subcutaneous application of 300 micrograms Filgrastim led to a severe overstimulation with leukocytosis of max. 50,000 for about 8 days and hyperuricemia.

Aged↗
PubMed1994

[The recanalization of chronic coronary artery occlusions: what factors influence success?].

Between January 1986 and June 1990, recanalization with guide-wire and balloon angioplasty (PTCA) was attempted in 509 patients (416 men, 93 women; mean age 57.5 +/- 9 years) with chronic coronary artery occlusions. The data recorded were analysed to determine the factors which influenced the outcome. The intervention was initially successful in 284 patients (55.8%; circumflex branch: 50%; right coronary artery: 52%; venous bypass graft: 50%; anterior interventricular branch: 64%). The success rate was markedly reduced if (1) the occlusion had persisted for more than 6 months (9.5%; P < 0.001); (2) occlusion had occurred at or after a vessel kink (28.5%; P < 0.001); (3) there had been no vessel "stump" (36%; P < 0.01) and (4) the occlusion was longer than 10 mm (40.7%; P < 0.05). The success-rate was higher if (1) intracoronary anastomoses were absent (61.2%); (2) occlusion had occurred in a straight vessel (62.6%); (3) there had been a vessel stump (64%); (4) the occlusion had persisted for less than 4 weeks (68.5%) and (5) the length of occlusion was < or = 10 mm (75.8%).-These data indicate that the success of PTCA after chronic coronary artery occlusion depended on the site of occlusion, its duration and length, absence of orthograde collaterals and the presence of a vessel stump. Knowing the extent of these factors helps in delineating the indications.

Aged↗
PubMed1994

Characterization of the essential yeast gene encoding N-acetylglucosamine-phosphate mutase.

A previously cloned gene of Saccharomyces cerevisiae, which complements the growth defect of a phosphoglucomutase (pgm1 delta/pgm2 delta) double deletion mutant on a pure galactose medium [Boles, E., Liebetrau, W., Hofmann, M. & Zimmermann, F. K. (1994) Eur. J. Biochem. 220, 83-96], was identified as the structural gene encoding N-acetylglucosamine-phosphate mutase. The complete nucleotide sequence of the gene, AGM1, and surrounding regions were determined. AGM1 codes for a predicted 62-kDa protein with 557 amino acids and is located on chromosome V adjacent to the known gene PRB1 encoding protease B. No extended nucleotide or amino acid sequence similarities could be found in the databases, except for a small region of amino acids with high similarity to the active-site consensus sequence of hexosephosphate mutases. Three putative pheromone-responsive elements have been identified in the upstream region of the AGM1 gene. The gene is essential for cell viability. An agm1 deletion mutant progresses through only approximately five cell cycles to form a 'string' of undivided cells with an abnormal cell morphology resembling glucosamine auxotrophic mutants. Expression of the AGM1 gene on a multi-copy plasmid led to a significantly increased N-acetylglucosamine-phosphate mutase activity. Unlike over-expression of the AGM1 gene in a pgm1/pgm2 double deletion mutant which could restore phosphoglucomutase activity, over-expression of the PGM2 gene encoding the major isoenzyme of phosphoglucomutase did not increase N-acetylglucosamine-phosphate-mutase activity and did not restore growth of agm1 deletion mutant cells. Our observations indicate that the different hexosephosphate mutases of S. cerevisiae have partially overlapping substrate specificities but, nevertheless, distinct physiological functions.

Amino Acid Sequence↗
PubMed1994

A family of hexosephosphate mutases in Saccharomyces cerevisiae.

The Saccharomyces cerevisiae PGM1 and PGM2 genes encoding two phosphoglucomutase isoenzymes have been isolated and sequenced. The derived protein sequences are closely related to one another and show distinct sequence similarities to the human and rabbit phosphoglucomutases, especially in the region supposed to constitute the active site. PGM1 and PGM2 are located on chromosomes XI and XIII, respectively, just upstream of the known genes YPK1 and YKR2 coding for a pair of closely related putative protein kinases. These observations suggest that an extended region of DNA arose by the process of gene duplication. Cells deleted for both, PGM1 and PGM2, could not grow on galactose. No residual phosphoglucomutase activity could be measured in crude extracts or in permeabilized cells of pgm1/2 double mutants. Unexpectedly, growth with glucose was not impaired and the mutant cells were still able to accumulate trehalose and glycogen, although at a reduced level. Two further genes could be isolated and characterized which when over-expressed on a multi-copy plasmid could restore growth on galactose of the pgm1/2 double deletion mutant. Multi-copy complementation was due to a sharply increased level of phosphoglucomutase activity. Partial sequencing and characterization of the two genes revealed one of them to be SEC53 encoding phosphomannomutase. No extended sequence similarities could be found in the databases for the second gene. However, part of the derived amino acid sequence contained a region of high similarity to the active-site consensus sequence of hexosephosphate mutases from different organism. Further investigations suggest that a complex network of mutases exist in yeast which interact and can partially substitute for each other.

Amino Acid Sequence↗
PubMed1994

Evaluation of liquid chromatography coupled with high-field 1H NMR spectroscopy for drug metabolite detection and characterization: the identification of paracetamol metabolites in urine and bile.

The applicability of coupled reversed-phase high performance liquid chromatography (HPLC)-NMR spectroscopy for the detection and identification of paracetamol (N-(4-hydroxyphenyl)acetamide) and its sulfate, glucuronide and N-acetylcysteinyl metabolites in the unprocessed biological fluids, human urine, rat urine and rat bile, is investigated. Analysis of these samples was performed by gradient HPLC elution and directly coupled 500 MHz 1H NMR spectroscopy detection using a combination of one- and two-dimensional NMR methods in stopped-flow mode. The stopped-flow approach is demonstrated to be an efficient technique for identification of drug metabolites which have, for example, a UV-chromophore. Stopped-flow HPLC analysis with NMR detection is a viable technique and halting the chromatographic process several times during a run has a negligible effect on the separation and NMR characterization. The post-acquisition data processing method of 'quantified maximum entropy' is shown to provide a means of improving the quality of spectra for minor components, thus aiding NMR resonance assignments.

Acetaminophen↗
PubMed1994

In vitro activity of immunoconjugates between cisplatin and an anti-CA125 monoclonal antibody on ovarian cancer cell lines.

Cis-diammine dichloro platinum (II) (CDDP), is a highly potent antineoplastic agent that is used in the treatment of ovarian cancer. However, the clinical use of CDDP is restricted by its severe side effects. In order to reduce these side effects and to enhance its therapeutic efficacy, we developed specific immunoconjugates consisting of the murine monoclonal antibody OC125 and CDDP, using diethylene triamine pentaacetic acid (DTPA) as a linker. The coupling efficiencies of the different preparations synthesized, varied between 1.10 +/- 0.42 and 2.65 +/- 1.60 mol of CDDP per mol of antibody protein. Despite the chemical modification of the antibody molecule, specific binding activity of the OC125-CDDP conjugates toward the CA125 antigen was maintained as was demonstrated by means of immunohisto-/cytochemical staining of frozen sections of ovarian cancer tissue, amniotic epithelium, and the CA125 positive ovarian cancer cell line NIH:OVCAR 3. The antiproliferative activity of the immunoconjugates was tested against the human ovarian cancer cell lines NIH:OVCAR 3 and SKOV 3, applying a kinetic crystal violet microassay. Despite the promising results obtained with the specific immunostaining of the target cells, no significant antiproliferative activity of our immunoconjugates against the cell lines tested was observed. One possible explanation for the lack of antitumor activity could be the fact that CA125 is released in large amounts by the NIH:OVCAR 3 cells. This may have prevented an efficient immunotargeting of the cancer cells by the formation of soluble immune complexes.

Antibodies, Monoclonal↗
PubMed1994

The role of the cAMP pathway in mediating the effect of head activator on nerve-cell determination and differentiation in hydra.

In hydra, head activator (HA) acts as positive signal for nerve-cell determination and differentiation. For both events, HA uses cAMP as the second messenger. Evidence is presented that the cAMP agonist, Sp-cAMPS, is able to mimick the effect of HA on nerve-cell determination and differentiation and that it is blocked by the antagonist Rp-cAMP. An adenylyl cyclase associated protein, CAP, appears to be involved as mediator for transducing the signal from the transmembrane HA receptor to the cAMP system. A cDNA coding for hydra CAP was isolated from the multiheaded mutant of Chlorohydra viridissima. The hydra CAP shows extensive homology with the yeast and, more so, mammalian CAPs. In hydra, CAP mRNA is expressed abundantly in interstitial and epithelial cells. The effect of HA, but not of cAMP, on nerve-cell differentiation was inhibited by pretreatment of hydra with a cap antisense oligonucleotide, suggesting a role for CAP as mediator in the signal transduction cascade between HA and cAMP.

Amino Acid Sequence↗
PubMed1993

The structures of native phosphorylated chicken cystatin and of a recombinant unphosphorylated variant in solution.

The solution structures of the phosphorylated form of native chicken cystatin and the recombinant variant AEF-S1M-M29I-M89L were determined by 2D, 3D and 4D-NMR. The structures turn out to be very similar, despite the substitutions and the phosphorylation of the wild-type. Their dominant feature is a five-stranded beta-sheet, which is wrapped around a five-turn alpha-helix, as shown by X-ray crystallographic studies of wild-type chicken cystatin. However, the NMR analysis shows that the second helix observed in the crystal is not present in solution. The phosphorylation occurs at S80, which is located in a flexible region. For this reason, very few effects on the structure are observed. Comparison of structures of the unphosphorylated variant and the wild-type shows small effects on H84 which is located in the supposed recognition site of the serine kinase. This recognition site appears to be well structured as a large loop-containing bulge of the beta-sheet. The N termini of both mutants, which contribute to a large extent to the binding to the proteinase, are very flexible. A loop structure involving the residues L7 to A10 as found in related inhibitors, such as in the kininogen domains 2 and 3, is not sufficiently populated to be observed.

Amino Acid Sequence↗
PubMed1993

Variant CD44 adhesion molecules are expressed in human brain metastases but not in glioblastomas.

Although human glioblastomas are highly invasive tumors intracerebrally, only rarely do they metastasize outside the central nervous system. In contrast, the brain is a major target for metastatic spread of many systemic tumors. Recently, it was demonstrated that expression of splice variants of CD44 (CD44v), but not standard CD44 (CD44s), was sufficient to confer metastatic potential to low- or nonmetastatic rat tumor cells. Because CD44 is expressed in brain tumors, we examined whether differential expression of CD44 isoforms was correlated with the metastatic behavior of these tumors. We compared CD44s and CD44v expression in 17 human glioblastomas, 18 glioma cell lines, and metastases of 15 other tumors to the brain by reverse transcription/polymerase chain reaction, Northern blotting, and immunocytochemistry. These experiments showed that 0 of 17 glioblastomas and 0 of 18 glioma cell lines expressed CD44v as compared to 12 of 15 brain metastases. These data show a correlation between CD44v expression and the metastatic ability of the tumors analyzed (P < 0.01). This suggests (a) that the biological significance of the lack of CD44v expression in human glioblastomas warrants further examination with regard to their inability to metastasize extraneurally and (b) that CD44v expression may play a role in the intracerebral spread of about 80% [corrected] of the brain metastases. Therefore, CD44v expression should be further considered as a potential marker for differential diagnosis and prognosis of patients with brain metastases.

Base Sequence↗
PubMed1993

Investigation of the human metabolism of antipyrine using coupled liquid chromatography and nuclear magnetic resonance spectroscopy of urine.

The potential of coupled high-performance liquid chromatography-nuclear magnetic resonance spectroscopy for the detection and identification of drug metabolites has been investigated by direct analysis of human urine collected following administration of antipyrine. This approach provided a rapid method of characterizing the major human urinary metabolites of this drug and promises to be of widespread value in structural studies of xenobiotic metabolites.

Antipyrine↗
PubMed1993

[The long-term success after coronary angioplasty in old age].

Long-term results of coronary angioplasty (CAP) were compared between two age-groups of patients. Group 1 had 227 patients (158 men, 69 women) with a mean age of 70 (65-88) years, group 2 had 717 patients (611 men, 106 women), mean age 54 (20-64) years. Unstable angina was more common in group 1 than group 2 (48.9 vs 37.7%, P < 0.05). Multi-vessel disease was present in 50.7% of those in group 1 and 41.9% in group 2. Primary success of CAP was similar in the two groups (group 1: 88.1%, group 2: 90.5%). The long-term effect at the first follow-up angiography 3-4 months after CAP was slightly less favourable in group 1 than 2 (54.9 vs 58.3%; difference not significant). However, there were more patients with unstable angina in group 1. Thus the angiographic long-term results were worse in the older patients (44.6 vs 60.1%; P < 0.05), while there was no difference between the two groups as regards stable angina (64.7 vs 57.2%). After a second CAP (because of recurrence), the long-term angiographic effect was, if anything, slightly better in the older patients (87.0 vs 77.1%). The death-rate (cardiac causes of death) up to one year after CAP was comparable in the two groups (1.7 vs 0.8%), as was the rate of non-fatal myocardial infarction (2.2 vs 1.3%). These data indicate that clinical and angiographic long-term success after CAP is comparable in older and younger patient groups and age alone does not present a higher risk.

Adult↗
PubMed1993

A link between ras and metastatic behavior of tumor cells: ras induces CD44 promoter activity and leads to low-level expression of metastasis-specific variants of CD44 in CREF cells.

The activated oncogene c-Ha-ras induces expression of the surface glycoprotein CD44 in cloned rat embryonic fibroblasts (CREF). Induction is transcriptional as shown by transient cotransfections of c-Ha-ras expression constructs and CD44 promoter reporter gene constructs and depends on the presence of an AP-1 binding site at position -110. Increased transcript levels for the standard isoform of CD44 (CD44s) are accompanied by the appearance of alternatively spliced RNAs and the synthesis of variants of CD44 (CD44v). These CD44v molecules differ from the standard type by the addition of sequences in the extracellular portion of the molecules. The occurrence of CD44v molecules in CREF cells upon induction of the CD44 promoter is probably due to leakiness of the splice control in these cells since stable transfection with c-Ha-ras does not alter the CD44v/total CD44 ratio. Upon ras overexpression, however, using an inducible mouse mammary tumor virus-ras construct, a transient increase of CD44v/total CD44 ratio of 3-4 has been determined suggesting that a burst of ras expression, in the genetic background of CREF cells, influences both promoter activity and splice control or accuracy. The expression of CD44v proteins is responsible for the metastatic potential in a variety of tumors (U. Günthert et al., Cell, 65: 13-24, 1991). Also in CREF cells expression of CD44v correlates with metastatic behavior, ras-transfected CREF cells are not only fully transformed but also give rise to metastatic spread as measured in the spontaneous metastasis assay. The adenoviral oncogene E1A counteracts ras-induced promoter function and, consequently, inhibits metastatic behavior without extinguishing transformation.

Animals↗