Biomedical subjects

C Hertel

Publications and source records attributed to C Hertel.

At least 37 records · Page 2Linked to original sources

PubMed1998

Application of lysostaphin-producing lactobacilli to control staphylococcal food poisoning in meat products.

The potential of lysostaphin-producing strains of Lactobacillus curvatus (Lys+) to prevent food-borne illness by Staphylococcus aureus was investigated under practical conditions. A response surface model was developed to estimate the effect of pH, temperature, and salt concentration on the lysostaphin activity. The model was applied to fermenting sausages, and a 90% reduction of lysostaphin activity at ripening was predicted. The residual was sufficiently high to reduce staphylococcal counts by 10(4) to 10(5) CFU/g within 2 to 3 days to below the level of detection. These results were obtained in pilot scale experiments with L. curvatus (Lys+) as a starter culture and S. aureus as well as Staphylococcus carnosus as model contaminants. The applicability of L. curvatus (Lys+) as a protective culture was studied in a mayonnaise-based meat salad. Upon incubation at 25 degrees C the staphylococci were rapidly killed within 24 h, whereas in the presence of the isogenic Lys(-) strain the staphylococci grew up to numbers of 10(7) CFU/g.

Antibiosis↗

PubMed1997

Evidence for natural transformation of Bacillus subtilis in foodstuffs.

The effect of foodstuffs on the natural transformation of Bacillus subtilis was investigated. As examples of complex food matrices milk with various fat contents as well as chocolate milk were used. The frequencies of transformation varied with the fat content and ranged between 3.8 X 10(-4) and 1.4 X 10(-3). Highest frequencies of about 3 X 10(-3) were observed in chocolate milk with 1.5% fat. Development of competence was observed in chocolate milk, resulting in maximal transformation frequencies upon incubation for 10-12 h at 37 degrees C.

Animals↗

PubMed1997

Inhibition of the electrostatic interaction between beta-amyloid peptide and membranes prevents beta-amyloid-induced toxicity.

The accumulation of beta-amyloid peptides (Abeta) into senile plaques is one of the hallmarks of Alzheimer disease. Aggregated Abeta is toxic to cells in culture and this has been considered to be the cause of neurodegeneration that occurs in the Alzheimer disease brain. The discovery of compounds that prevent Abeta toxicity may lead to a better understanding of the processes involved and ultimately to possible therapeutic drugs. Low nanomolar concentrations of Abeta1-42 and the toxic fragment Abeta25-35 have been demonstrated to render cells more sensitive to subsequent insults as manifested by an increased sensitivity to formazan crystals following MTT (3-[4,5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide) reduction. Formation of the toxic beta-sheet conformation by Abeta peptides is increased by negatively charged membranes. Here we demonstrate that phloretin and exifone, dipolar compounds that decrease the effective negative charge of membranes, prevent association of Abeta1-40 and Abeta25-35 to negatively charged lipid vesicles and Abeta induced cell toxicity. These results suggest that Abeta toxicity is mediated through a nonspecific physicochemical interaction with cell membranes.

Amyloid beta-Peptides↗

PubMed1996

Beta-amyloid-induced cell toxicity: enhancement of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide-dependent cell death.

In an attempt to understand the cause of neurodegeneration in Alzheimer's disease, the toxic effects of beta-amyloid (Abeta) peptides have been widely studied. At high micromolar concentrations Abeta peptides have been demonstrated to be acutely toxic to various cell types. At submicromolar concentrations, Abeta peptides have been suggested to inhibit cellular metabolic activity, due to their inhibition of the ability of cells to metabolize the oxidoreductase substrate 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). Here we show, first, that MTT reduction surprisingly leads to a breakdown in PC12 cell membrane integrity and cell death, presumably through the formation of a crystalline formazan product, and, second, that pretreatment of PC12 cells with nanomolar concentrations of Abeta peptide, rather than inhibiting their metabolic activity, increases the susceptibility of these cells to the secondary toxic effect of formazan crystal formation. These results suggest that low nanomolar concentrations of Abeta render membranes more susceptible to damage by a secondary insult, in this case, MTT reduction. It is plausible that such an effect, when combined with additional risk factors, could contribute to the neurodegeneration that occurs in Alzheimer's disease.

Amyloid beta-Peptides↗

PubMed1995

Neuropsychological deficit in newly diagnosed patients with schizophrenia or schizophreniform disorder.

Forty-six patients with schizophrenia or schizophreniform disorder admitted to hospital for the first time were compared with 21 healthy volunteers on neuropsychological tests reflecting prefrontal and left respectively right hemisphere function. The patients with schizophrenia or schizophreniform disorder had a poorer performance on neuropsychological tests (such as Wisconsin Card Sorting) compared with healthy volunteers. Both left and right hemisphere seemed to be involved. Especially poor performance was found on somewhat complicated tests requiring ability of analysis, abstraction and memory, thus indicating dysfunction of prefrontal and temporohippocampal regions. Signs of sulcal enlargement and size of lateral ventricles on computed tomographic scan correlated with poor test performance on some tests both in patients and in healthy volunteers. No correlations were found between performance on neuropsychological test and negative symptoms.

Adolescent↗

PubMed1994

p75 nerve growth factor receptor modulates p140trkA kinase activity, but not ligand internalization, in PC12 cells.

The biological activity of nerve growth factor (NGF) has been shown to be mediated by the p140trkA receptor tyrosine kinase, while the role of the p75 NGF receptor (p75NGFR) is still unresolved. Here we have investigated the relative contribution of p140trkA and p75NGFR to early consequences of NGF binding: ligand internalization, p140trkA autophosphorylation, and tyrosine phosphorylation of Shc, phospholipase C gamma-1 (PLC gamma-1), and extracellular signal-regulated kinases (ERKs). It was found that NGF internalization was neither prevented by blocking p140trkA activity using the protein kinase inhibitors methylthioadenosine, staurosporine, and K-252a, nor by inhibiting NGF binding to p75NGFR with antibodies. However, when NGF binding to p140trkA was reduced by the use of a synthetic peptide corresponding to amino acids 36-53 of human p140trkA, internalization of NGF was decreased. Thus, at least in PC12 cells, internalization appears to require binding of NGF to p140trkA, but occurs irrespective of p140trkA kinase activity and ligand occupancy of p75NGFR. The NGF triple mutant Lys-32/Lys-34/Glu-35 to Ala, which has been demonstrated to bind to p140trkA, but not to p75NGFR, induced tyrosine phosphorylation more rapidly than wild-type NGF. Likewise, NGF-induced tyrosine phosphorylation was accelerated when NGF binding to p75NGFR was prevented with REX-IgG. These findings indicate that NGF bindign by p75NGFR may modulate NGF-induced p140trkA kinase activity.

Adaptor Proteins, Signal Transducing↗

PubMed1994

Protein kinase inhibitor H-7 differentially affects early and delayed nerve growth factor responses in PC12 cells.

The effects of the protein kinase inhibitor H-7 on early and delayed responses to nerve growth factor (NGF) were investigated in PC12 cells. H-7 reduced the NGF-induced expression of c-Fos in a dose-dependent manner without affecting the time course of c-Fos appearance. Conversely, H-7 potentiated delayed NGF effects, i.e., neurite outgrowth and Ca2+/phospholipid-dependent protein kinase (PKC) induction, but not choline acetyltransferase induction. Long-term treatment with NGF resulted in an increase of at least four tyrosine-phosphorylated protein bands with molecular masses between 39 and 48 kDa, which was also potentiated by H-7. In the absence of NGF, H-7 had no significant effect on c-Fos expression, tyrosine phosphorylation of the 45 kDa protein, or choline acetyltransferase activity. However, 4 days of exposure to H-7 alone induced PKC activity and tyrosine phosphorylation of the 39-kDa protein. The action of H-7 derivatives on neurite outgrowth did not correlate with their inhibition profile of cyclic nucleotide-dependent protein kinases. Down-regulation of PKC activity by prolonged exposure to phorbol ester did not completely abolish the effects of NGF and H-7 on induction of c-Fos, choline acetyltransferase activity, and neurite outgrowth, indicating that PKC-independent pathways contribute to these actions. These results suggest that additional pathway(s) sensitive to H-7 may exist, which induce immediate early gene expression and suppress neuronal differentiation of PC12 cells.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1994

Nerve growth factor-induced differentiation in neuroblastoma cells expressing TrkA but lacking p75NGFR.

Nerve growth factor (NGF) binds to two distinct cell surface receptors, TrkA, which is a receptor tyrosine kinase, and p75NGFR, whose role in NGF-induced signal transduction remains unclear. We have found that human neuroblastoma IMR-32 cells express TrkA, but p75NGFR expression was not detectable in these cells by northern blot analysis, immunoblotting, or chemical crosslinking experiments. Despite the lack of p75NGFR expression, subnanomolar concentrations of recombinant human NGF induced neurite outgrowth, tyrosine phosphorylation, and immediate early gene expression in these cells. These results strongly suggest that NGF-induced neuronal differentiation in IMR-32 cells is initiated through TrkA in the absence of p75NGFR. Thus, IMR-32 cells may provide a model for studying neurotrophic effects of NGF on adult striatal cholinergic neurons, which also lack p75NGFR expression.

Adult↗

PubMed1994

Relationship between brain structure and function in disorders of the schizophrenic spectrum: single positron emission computerized tomography, computerized tomography and psychopathology of first episodes.

Fifty newly diagnosed, briefly treated or drug-naive patients with schizophrenia or schizophreniform disorder were examined by psychopathology scales for positive (SAPS), negative (SANS) and overall psychotic symptoms (PSE and BPRS). CT-scan and regional cerebral blood flow (rCBF) measurement by 99mTc-HMPAO SPECT during rest and mental activation by Wisconsin Card Sorting Test was performed as well. Twenty-five age-matched normal healthy volunteers served as controls. Thought disorders and fundamental symptoms correlated positively with relatively high, though subnormal prefrontal (PFC) rCBF and high rCBF in temporal cortex; positive symptoms correlated positively with high rCBF in the striatum and temporal cortex during activation. Negative symptoms correlated with high prefrontal rCBF. The patients had sulcal enlargement and smaller brain volume compared with the healthy volunteers. There were no signs of ventricular enlargement. Neither total negative symptoms, thought disorder nor fundamental symptoms correlated with any CT measurements. Total positive symptoms correlated negatively with the size of the temporal horns. The relatively high rCBF in PFC and temporal cortex of cases with pronounced positive and negative symptoms and thought disorder may imply that an aberrant cortical network has to be active to express a malattuned clinical output. The striatal hyperfunction mainly in productive cases may be a secondary phenomenon and more pronounced in cases where no signs of subcortical atrophy has (yet?) ensued.

Adolescent↗

PubMed1993

Identification and classification of Lactobacillus acidophilus, L. gasseri and L. johnsonii strains by SDS-PAGE and rRNA-targeted oligonucleotide probe hybridization.

Thirty-two strains originally identified as Lactobacillus acidophilus and L. gasseri were screened for their taxonomic homogeneity by SDS-PAGE of whole-cell proteins. After numerical comparison of the resulting protein electrophoretic fingerprints, two well-delineated clusters were detected. The majority of the strains grouped in one electrophoretic cluster, which contained the type strain of L. acidophilus and corresponds to DNA group A1 of Johnson, J. L., Phelps, C. F., Cummins, C. S., London, J. & Gasser, F. (1980; International Journal of Systematic Bacteriology 30, 53-68). Another cluster corresponded to DNA group B. It contained two subclusters, which agreed perfectly with DNA subgroups B1 (L. gasseri) and B2 (L. johnsonii), respectively. The 23S rRNA genes were partially sequenced and 23S-rRNA-targeted oligonucleotide probes were designed for identification of DNA groups A1, B1 and B2. Probe Lbg reacted with all strains of electrophoretic cluster B1 (L. gasseri), probe Lbj hybridized with strains of cluster B2 (L. johnsonii) and probe Lba with strains of cluster A1 (authentic L. acidophilus). The probes were successfully used for the identification of strains belonging to the respective species. The phylogenetic relationship of a representative of L. johnsonii was determined by comparative sequence analysis of the 16S rRNA genes. It is very closely related to L. gasseri.

Bacterial Proteins↗

PubMed1993

Computerised tomography in newly diagnosed schizophrenia and schizophreniform disorder. A controlled blind study.

Patients with newly diagnosed schizophrenia (n = 27) or schizophreniform disorder (n = 22) and 24 healthy volunteers were investigated by CT scan, the investigators being blind to subject status. The patients had never received medication or had been treated only briefly with neuroleptics. The patients had significantly smaller brain volume and brain length than the controls. The patients had greater sulcal enlargement in the case of both Sylvian and interhemispheric fissures and surface sulci in the frontal and parietal regions. The sulcal enlargement was more pronounced in male patients and on the left hemisphere. The study revealed no enlargement of the lateral ventricles and only a trend towards enlargement of the third ventricle in the patients. The findings were not explained by substance abuse or level of education.

Adolescent↗

PubMed1992

Multiple trkA proteins in PC12 cells bind NGF with a slow association rate.

Rat pheochromocytoma (PC12) cells express two distinct nerve growth factor receptors (NGFRs), p75NGFR and trkA (p140trk). In addition to these receptors, by using 125I-mNGF affinity labeling and BS3 chemical cross-linking of PC12 cell protein, we have identified two additional trkA protein bands with apparent molecular weights of 220,000 and 300,000. These bands contain trkA, but were not immunoprecipitated by p75NGFR-specific antisera, suggesting that they do not represent trkA/p75NGFR protein complexes. The 220-kDa trkA band apparently represents trkA with alternate post-translational modification. The appearance of the 300-kDa trkA band was dependent on cross-linker concentration and could be diminished in the presence of reducing agents, suggesting that it represents a trkA dimer. All trkA bands were phosphorylated on tyrosine residues when bound to mNGF, suggesting that they participate in NGF-induced signal transduction. NGF binding kinetics to all three trkA bands were indistinguishable, with slow dissociation rates, and a slow association rate that required approximately 1 h to reach equilibrium levels at 4 degrees C. All three trkA bands bound the related neurotrophin brain-derived neurotrophic factor and neurotrophin-3 with a profile characteristic of trkA.

Animals↗

PubMed1992

The amino terminus of nerve growth factor is involved in the interaction with the receptor tyrosine kinase p140trkA.

The amino terminus of nerve growth factor (NGF) is susceptible to proteolytic cleavage. A comparison of the bioactivity of highly purified full-length recombinant human (1-118)rhNGF and NH2-terminal truncated (10-118)rhNGF revealed lower potency of (10-118)rhNGF with regard to early NGF responses in neuron-like PC12 cells. Approximately 50 times higher concentrations of (10-118)rhNGF than (1-118)rhNGF were required to elicit the same extent of tyrosine phosphorylation of key enzymes in different second messenger pathways, i.e. the NGF receptor tyrosine kinase p140trkA, phospholipase C gamma-1, and the extracellular signal-regulated kinase ERK1. A similar reduced potency for induction of the transcription factor c-Fos was observed with (10-118)rhNGF compared to (1-118)rhNGF. The lower potency of (10-118)rhNGF in triggering early responses correlated with its 40-fold lower affinity for PC12 cells. Whereas (10-118)rhNGF had a more than 300-fold lower affinity for the high affinity receptor p140trkA than (1-118)rhNGF, amino-terminal truncation of NGF changed its affinity for the low affinity receptor p75NGFR only slightly (5-10-fold). These observations suggest that amino acids 1-9 of NGF are important for binding to the signal transducing receptor p140trkA. Proteolytic cleavage of the NGF amino terminus, therefore, reduces its potency in starting several second messenger pathways leading to neuronal differentiation of PC12 cells.

Animals↗

PubMed1992

Nerve growth factor (NGF) receptor on rat glial cell lines. Evidence for NGF internalization via p75NGFR.

Two types of nerve growth factor (NGF) receptors have been described: high affinity (class I) and low affinity (class II). Biological responses to NGF are thought to be mediated by class I receptors, whereas the role of class II receptors is less clear. While some neuronal cells express both receptor types, only class II receptors have been detected on glial cells. Two glial cell lines, peripheral Schwannoma D6P2T and central 33B glioma cells, were employed to investigate the properties of class II receptors in the absence of class I receptors. These cell lines were found to express NGF receptors identified as class II by a low nanomolar dissociation constant, rapid dissociation kinetics at 4 degrees C, and trypsin sensitivity. The receptor was found to bind brain-derived neurotrophic factor with similar affinity as NGF. The responsible binding molecule appeared in sodium dodecyl sulfate-polyacrylamide gel electrophoresis as a heterogeneously glycosylated protein of 60-80 kDa with a tendency to aggregate. All receptor bands affinity-labeled with radioiodinated NGF were immunoprecipitated with anti-p75NGFR antibody, but not with anti-p140prototrk antiserum. In these cells, which express p75NGFR as only NGF receptor, a time- and temperature-dependent appearance of a nondisplaceable, trypsin-resistant, acid wash-stable ligand fraction, followed by an increase of trichloroacetic acid-soluble radiolabel in the medium was observed. This sequestration resembled receptor-mediated internalization with subsequent degradation of NGF. Whether this ligand processing indicates a functional role of p75NGFR in glial cells remains to be shown.

Animals↗

PubMed1992

Nerve growth factor-induced loss of cell-associated nerve growth factor receptor in human melanoma A875 cells.

Human A875 melanoma cells are known to express the low-affinity nerve growth factor receptor p75NGFR in a monomeric and a covalently linked probably dimeric form. Kinetic analysis of the association of nerve growth factor (NGF) with its receptor revealed a rapid loss of binding sites at high ligand concentrations. Using cross-linking and immunoprecipitation with an anti-p75NGFR antibody, this was found to be due to a decrease of the high molecular weight form of the receptor. Mechanisms for such a ligand-induced receptor loss are discussed.

Down-Regulation↗

PubMed1990

A truncation mutation in the avian beta-adrenergic receptor causes agonist-induced internalization and GTP-sensitive agonist binding characteristic of mammalian receptors.

Recombinant turkey erythrocyte beta-adrenergic receptors expressed in murine L cells exhibited characteristic avian subtype selectivity for agonists and antagonists. In 10 of the 11 clones studied, no agonist-induced internalization of receptor was observed, although agonist-induced uncoupling of receptor and adenylyl cyclase occurred rapidly. GTP caused little or no decrease in affinity for beta-adrenergic agonists. Such behavior is commonly observed in avian erythrocytes. In contrast, one clone was susceptible to agonist-induced receptor internalization and down-regulation even though it exhibited characteristic avian beta-adrenergic ligand-binding properties. The affinity of this variant receptor for agonists was also notably reduced by GTP. Electrophoresis of affinity-labeled receptor from this clone indicated an apparent size of about 33 kDa, about 12 kDa less than that of the native or recombinant turkey beta-adrenergic receptor. Genomic DNA from this cell line that encodes the receptor was cloned and partially sequenced. The coding region of the original receptor cDNA was interrupted after codon 412 (out of 483) and was followed by 36 base pairs of novel sequence prior to the first in-frame stop codon. These results suggest that the lack of both hormone-induced internalization and GTP-sensitive, high affinity binding of agonists that is characteristic of the beta-adrenergic receptor in avian erythrocytes is due to intrinsic properties of the receptor. The restoration of these phenomena in a C-terminally truncated mutant receptor suggests the importance of the C-terminal domain in determining these processes.

Adenylyl Cyclases↗

PubMed1990

Xylan degradation by the thermophile Clostridium stercorarium: cloning and expression of xylanase, beta-D-xylosidase, and alpha-L-arabinofuranosidase genes in Escherichia coli.

Seven genes related to arabinoxylan degradation were isolated from a genomic library of the thermophilic bacterium Clostridium stercorarium. The cloned genes include a xylanase gene (xynA), two beta-D-xylosidase genes (bx1A and bx1B), two alpha-L-arabinofuranosidase genes (arfA and arfB), and two genes (celW and celX) encoding enzymes termed celloxylanases, which hydrolyze both xylans and beta-D-cellobiosides. The genes xynA, celX, and bxlB were found to encode the major xylanolytic enzyme activities induced by growth of C. stercorarium on xylan.

Cloning, Molecular↗

PubMed1987

Sequential appearance of epidermal growth factor in plasma membrane-associated and intracellular vesicles during endocytosis.

Receptor-mediated internalization of epidermal growth factor (EGF) occurs by a process involving initially clathrin-coated pits on the cell surface and the subsequent formation of ligand-containing endosomes. Using a modified acid wash technique, cell surface-bound EGF was removed. Utilizing sucrose density centrifugation, the residual cell-associated EGF was separated into plasma membrane-associated and intracellular vesicle-associated forms. Using these procedures we have identified a transient form of cell-associated EGF that is still attached to the plasma membrane but not accessible to the extracellular fluid. This form of EGF appears to be the precursor for endosomic EGF. We suggest that this intermediate form represents the receptor-ligand complex shown by electronmicroscopy to be located in narrow-necked plasma membrane invaginations (Willingham, M. C., and Pastan, I. (1980) Cell 21, 67-77).

Astrocytoma↗