Biomedical subjects

C Korth

Publications and source records attributed to C Korth.

14 recordsLinked to original sources

PubMed1997

Prion (PrPSc)-specific epitope defined by a monoclonal antibody.

Prions are infectious particles causing transmissible spongiform encephalopathies (TSEs). They consist, at least in part, of an isoform (PrPSc) of the ubiquitous cellular prion protein (PrPC). Conformational differences between PrPC and PrPSc are evident from increased beta-sheet content and protease resistance in PrPSc. Here we describe a monoclonal antibody, 15B3, that can discriminate between the normal and disease-specific forms of PrP. Such an antibody has been long sought as it should be invaluable for characterizing the infectious particle as well as for diagnosis of TSEs such as bovine spongiform encephalopathy (BSE) or Creutzfeldt-Jakob disease (CJD) in humans. 15B3 specifically precipitates bovine, murine or human PrPSc, but not PrPC, suggesting that it recognizes an epitope common to prions from different species. Using immobilized synthetic peptides, we mapped three polypeptide segments in PrP as the 15B3 epitope. In the NMR structure of recombinant mouse PrP, segments 2 and 3 of the 15B3 epitope are near neighbours in space, and segment 1 is located in a different part of the molecule. We discuss models for the PrPSc-specific epitope that ensure close spatial proximity of all three 15B3 segments, either by intermolecular contacts in oligomeric forms of the prion protein or by intramolecular rearrangement.

Amino Acid Sequence↗

PubMed1997

Recombinant full-length murine prion protein, mPrP(23-231): purification and spectroscopic characterization.

The cellular prion protein of the mouse, mPrP(C), consists of 208 amino acids (residues 23-231). It contains a carboxy-terminal domain, mPrP(121-231), which represents an autonomous folding unit with three alpha-helices and a two-stranded antiparallel beta-sheet. We expressed the complete amino acid sequence of the prion protein, mPrP(23-231), in the cytoplasm of Escherichia coli. mPrP(23-231) was solubilized from inclusion bodies by 8 M urea, oxidatively refolded and purified to homogeneity by conventional chromatographic techniques. Comparison of near-UV circular dichroism, fluorescence and one-dimensional 1H-NMR spectra of mPrP(23-231) and mPrP(121-231) shows that the amino-terminal segment 23-120, which includes the five characteristic octapeptide repeats, does not contribute measurably to the manifestation of three-dimensional structure as detected by these techniques, indicating that the residues 121-231 might be the only polypeptide segment of PrP(C) with a defined three-dimensional structure.

Amino Acid Sequence↗

PubMed1996

Effects of granulocyte colony-stimulating factor on plasma cytokine and cytokine receptor levels and on the in vivo host response to endotoxin in healthy men.

We investigated the effects of granulocyte colony-stimulating factor (G-CSF) on cytokine and cytokine receptor plasma levels and on the in vivo host response to Salmonella abortus equi endotoxin in healthy males. Twenty volunteers received 0.8 ng/kg endotoxin and saline intravenously 1 week apart in randomized order. Twelve hours before both experiments, 10 of these subjects were pretreated with 300 micrograms G-CSF subcutaneously. G-CSF itself increased granulocyte and monocyte counts and the plasma levels of tumor necrosis factor-alpha (TNF-alpha), soluble TNF receptors (sTNF-R) p55, and p75 and interleukin-1 receptor antagonist (IL-1ra). G-CSF did not influence plasma IL-1 beta and IL-6 levels. In the G-CSF-pretreated subjects endotoxin-induced surges in rectal temperature and in the plasma levels of TNF-alpha plasma levels were about 50% increased, and surges in the plasma levels of both sTNF-Rs and IL-1ra were about twice as high as in the control group. Endotoxin-induced increases in IL-6, cortisol, and heart rate were not modified by G-CSF pretreatment. Endotoxin administration induced a transient 50% reduction in leukocyte counts in the G-CSF-pretreated subjects that was not seen in the control group. We conclude that a single stand dose of G-CSF increases the plasma levels of cytokines and cytokine receptors and considerably modifies the host response of healthy humans to a low dose of endotoxin.

Bacterial Toxins↗

PubMed1996

Effects of repeated administration of granulocyte colony-stimulating factor (G-CSF) on neutrophil counts, plasma cytokine, and cytokine receptor levels.

Granulocyte colony-stimulating factor (G-CSF) induces the release of mature neutrophils from storage pools and stimulates differentiation of myeloid progenitor cells. Recently, it has been shown that a standard dose of G-CSF induces immunophenotypical and functional changes of neutrophils that persist for 1 week. The authors investigated the effects of 300 micrograms of G-CSF administered subcutaneously twice, 1 week apart, to 10 healthy volunteers, on neutrophil and monocyte counts and on the plasma levels of interleukin 1 receptor antagonist (IL-1ra), tumour necrosis factor-alpha (TNF-alpha), soluble TNF receptor (sTNF-r) p55 and p75. G-CSF on both occasions increased neutrophil and monocyte counts and the plasma levels of all cytokines and cytokine receptors measured. All parameters assessed had returned to baseline prior to the second administration of G-CSF. The increases in neutrophil counts and plasma IL-1ra levels were larger following the second injection, whereas the increase in plasma sTNF-r p75 levels was smaller. G-CSF induced increases in monocyte counts, TNF-alpha and sTNF-R p55 levels did not differ between the first and second injection. Our finding of an increased response of healthy humans to a second G-CSF challenge 1 week following a first one may be due to long-lasting increases in storage pool neutrophils.

Adult↗

PubMed1996

Prion function and dysfunction: a structure-based scenario.

Prion diseases are transmissible, neurodegenerative disorders associated with as yet incompletely defined isoforms of a cellular protein termed prion protein (PrP). We have now identified in PrP structural information compatible with nucleotide- and nucleic acid-binding. As such, PrP contains a putative nicotinamide adenine dinucleotide (NADH)-binding site. Moreover, the PrP octarepeats reveal homology to the nucleic acid-binding and strand-annealing octarepeats of mammalian heterogeneous ribonucleoprotein (RNP) A1. Therefore, PrP may have NADH-dependent oxidoreductase activity as well as A1-like functions such as nucleic acid annealing and splicing. Moreover, we propose that infectious prions are propagated through a dynamic molecular symbiosis between a ribozyme-like nucleic acid and a conformational isomer of the RNP-like prion protein. Thus, our model has important implications for the understanding and treatment of prion diseases.

Amino Acid Sequence↗

PubMed1996

Diurnal variations in the human host response to endotoxin.

To investigate diurnal variations in the host response to endotoxin, Salmonella abortus equi endotoxin (0.8 ng/kg) was given intravenously to healthy men in a placebo-controlled design at 0900 or 1900 h. The time course of rectal temperature and the plasma levels of tumor necrosis factor- alpha (TNF-alpha), interleukin-6 (IL-6), adrenocorticotropic hormone (ACTH), and cortisol were monitored for 11 h following the injections. The time of day did not affect the endotoxin-induced increase in plasma TNF-alpha or IL-6. However, subjects who received endotoxin in the evening, when endogenous glucocorticoid levels were low, showed about twice the increases in rectal temperature and plasma ACTH and cortisol levels as those who received endotoxin in the morning, when endogenous glucocorticoid levels were high. These results demonstrate diurnal variations in the human susceptibility to endotoxin that may be due to a suppression of the biologic effects of TNF-alpha and IL-6 by endogenous glucocorticoids.

Adrenocorticotropic Hormone↗

PubMed1996

Influence of endotoxin on daytime sleep in humans.

Administration of endotoxin in the evening has been shown to transiently suppress rapid eye movement (REM) and to promote non-REM sleep in humans. In a single-blind placebo-controlled crossover design, we assessed the effects of Salmonella abortus equi endotoxin administered intravenously in the morning on the primary host response and on daytime sleep by use of a multiple napping protocol in healthy volunteers. The extent of the host response achieved by 0.8 ng of endotoxin per kg of body weight given at 0900 h was comparable to that previously reported to result from the administration of 0.4 ng/kg at 1900 h. However, sleep was only slightly influenced. Endotoxin reduced the amount of REM sleep and increased REM latency. Non-REM sleep amount in the first nap, although not significantly changed, correlated negatively with the individual peak levels of interleukin-6 (r = -0.73, P < 0.05). Subjective tiredness, sleep onset latency, total sleep time, and the amounts of slow-wave and non-REM sleep were not affected by endotoxin throughout the entire experiment. Spectral analysis of the electroencephalogram obtained during non-REM sleep yielded no condition differences. We conclude that endotoxin administration in the morning to healthy volunteers, while activating the host defense to the same extent as a lower dose that has been reported to promote non-REM sleep when given in the evening, does not affect non-REM sleep. REM sleep suppression is, to date, the most consistently reported effect of endotoxin on human sleep.

Adult↗

PubMed1995

A co-evolutionary theory of sleep.

Based on recent experimental evidence, a novel theory of sleep function and regulation is advanced, stating that sleep primarily evolved to protect the brain against a wakefulness-dependent increase in the permeability of the blood-brain barrier. A restitutional mechanism for the blood-brain barrier had to co-evolve against the omnipresent gut-derived bacterial cell wall constituents, because these and their elicited cellular responses increase blood-brain barrier permeability and potentially harm nervous tissue. Thus, in order to develop a highly organized cerebral structure, an immune-like response specific for the brain co-evolved during the phylogeny of the symbiosis between animals and gut bacteria to control the detrimental effects of bacterial cell wall constituents. In the course of further evolution, the sleep-associated 'controlled inflammatory state' of the brain employed the growth-factor activities of locally activated cytokines to enforce cerebral development and the maintenance of cognitive functions.

Animals↗

PubMed1995

Influence of host defense activation on sleep in humans.

Despite considerable progress in our understanding of the phenomenology of sleep and wakefulness, their regulation and peculiar functions are poorly understood. Recent animal research has revealed considerable evidence for interactions between host defense and sleep. Therefore, it has been hypothesized that host response mediators, mainly cytokines like interleukin-1 (IL-1), are involved in physiological sleep regulation. Furthermore, it has been suggested that sleep, and non rapid eye movement (NREM) sleep in particular, has an immuno-supportive function. In humans, sleep-host defense interactions are just starting to be understood. There is quite good evidence that some viral diseases cause excessive sleepiness. Other infectious diseases induce, however, serious disturbances of the distribution of sleep and wakefulness rather than excessive sleep. In addition, some disorders with excessive sleep, daytime fatigue or disturbed night sleep as prominent symptoms are thought to involve, at least in part, immuno-pathophysiological mechanisms. Experimental settings have only recently been used to elucidate host defense-sleep interactions in humans. The effects of endotoxin, a cell-wall lipopolysaccharide of gram-negative bacteria, on sleep have been tested in different settings in healthy volunteers. Endotoxin transiently suppresses rapid eye movement (REM) sleep independently of the time of the day of administration. Only low doses, given in the evening, promote NREM sleep. Electorencephalogram (EEG) power in higher frequency bands is enhanced during NREM sleep, whereas delta activity is not affected. In rats and rabbits, on the other hand, the effects of endotoxin and of the mediators of its activity on REM sleep are variable. Enhanced NREM sleep is a common finding and most pronounced during the active part of the nycthemeron and, in general, EEG delta activity is augmented. In view of these species differences, hypotheses regarding the underlying mechanisms and the biological significance of host defense-sleep interactions, primarily derived from the results of animal studies, may not entirely fit human physiology. They should therefore be re-evaluated and probably modified, through the use of additional experimental approaches in humans.

Animals↗

PubMed1985