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Biomedical subjects

K Post

Publications and source records attributed to K Post.

At least 19 recordsLinked to original sources
PubMed2001

Structural intermediates in the putative pathway from the cellular prion protein to the pathogenic form.

The conversion of the alpha-helical, protease sensitive and noninfectious form of the prion protein (PrP(C)) into an insoluble, protease resistant, predominantly beta-sheeted and infectious form (PrP(Sc)) is the fundamental event in prion formation. In the present work, two soluble and stable intermediate structural states are newly identified for recombinant Syrian hamster PrP(90-231) (recPrP), a dimeric alpha-helical state and a tetra- or oligomeric, beta-sheet rich state. In 0.2% SDS at room temperature, recPrP is soluble and exhibits alpha-helical and random coil secondary structure as determined by circular dichroism. Reduction of the SDS concentration to 0.06% leads first to a small increase in alpha-helical content, whereas further dilution to 0.02% results in the aquisition of beta-sheet structure. The reversible transition curve is sigmoidal within a narrow range of SDS concentrations (0.04 to 0.02%). Size exclusion chromatography and chemical crosslinking revealed that the alpha-helical form is dimeric, while the beta-sheet rich form is tetra- or oligomeric. Both the alpha-helical and beta-sheet rich intermediates are soluble and stable. Thus, they should be accessible to further structural and mechanistic studies. At 0.01% SDS, the oligomeric intermediates aggregated into large, insoluble structures as observed by fluorescence correlation spectroscopy. Our results are discussed with respect to the mechanism of PrP(Sc) formation and the propagation of prions.

Buffers↗
PubMed2000

Neurotoxicity but not infectivity of prion proteins can be induced reversibly in vitro.

Prion diseases include Creutzfeldt-Jakob disease in humans, scrapie in sheep and bovine spongiform encephalopathy. The hallmark of prion diseases is the accumulation of an abnormal isoform (PrP(Sc)) of the cellular prion protein accompanied by neuronal cell death and astroglial proliferation. To characterize the correlation between PrP secondary and quarternary structure and their biological effects we assayed soluble and aggregated forms of PrP 27-30, the N-terminal truncated form of PrP(Sc), as well as the corresponding recombinant PrP(90-231) for their neurotoxicity and infectivity. PrP was kept soluble in 0.2% SDS and subsequently re-aggregated either by diluting the SDS or by adding acetonitril. The neurotoxicity of the re-aggregated states were comparable to that of prion rods (PrP 27-30) whereas the soluble forms had no neurotoxic effects. The solubilized PrP 27-30 showed no significant infection upon re-aggregation as determined by bioassays in Syrian golden hamsters. The recombinant PrP did not exhibit infectivity in any state.

Animals↗
PubMed2000

Prevention of cerebrospinal fluid rhinorrhea in neurotologic surgery.

OBJECTIVE: To determine the efficacy and safety of quick-setting hydroxyapatite cement in eliminating cerebrospinal fluid (CSF) rhinorrhea following neurotologic surgery. STUDY DESIGN: A prospective study of 40 consecutive patients undergoing neurotologic surgery in whom the dura was opened. SETTING: All patients were treated as hospital inpatients at a tertiary referral center. PATIENTS: 25 men and 15 women between the ages of 20 and 72 years (mean age 51 years) underwent neurotologic surgery at the parent institution. INTERVENTION: Various neurotologic procedures were performed for the resection of 25 acoustic tumors, 5 meningiomas, 3 glomus tumors, 2 vestibular nerve sections, 2 chordomas, 1 epidermoid tumor, and 1 meningoencephelocele, and for 2 patients referred to our institution with known CSF leaks following acoustic tumor surgery. A new form of quick-setting hydroxyapatite cement, which that hardens within 3 to 5 minutes was used to seal the air cell tracts of the temporal bone in all cases. MAIN OUTCOME MEASURE: The presence of CSF rhinorrhea postoperatively. RESULTS: CSF rhinorrhea occurred in 2 patients following acoustic tumor surgery, the first through an occult air cell tract at the margin of the drilled internal auditory canal, and the second via an oval window fistula 1 month after a translabyrinthine approach. CONCLUSIONS: This form of hydroxyapatite cement appears safe, reliable, effective, and economical for the prevention of CSF rhinorrhea following neurotologic surgery. CSF rhinorrhea cannot be eliminated unless our ability to identify all potential air cell tract communications improves.

Adult↗
PubMed1999

Fly larvae and pupae as vectors for scrapie.

We analysed experimental transmissibility of the scrapie agent by natural vectors. A fly, Sacrophaga carnaria, fed with brains of scrapie-infected hamsters in different developmental stages caused scrapie in hamsters after they ate fly extracts.

Animals↗
PubMed1999

'Bin bag' study: a survey of the research requests received by general practitioners and the primary health care team.

General practitioners receive a large and increasing number of unsolicited requests to participate in research. This study describes the volume and nature of research requests received by 18 primary care teams in a three-month period. On average, each practice receives 16 to 24 research requests each year. The most frequent request is to complete a questionnaire (32%). Only one-fifth of studies originate from academic or service general practice. Remuneration for participating in a study was only offered for 15% of studies. Although general practice teams feel swamped by research requests, this sensation may be exaggerated by invitations to participate in non-scientific surveys as well as true research projects. Practice teams would welcome help in distinguishing quality research proposals from the remainder.

Data Collection↗
PubMed1998

Rapid acquisition of beta-sheet structure in the prion protein prior to multimer formation.

The N-terminally truncated form of the prion protein, PrP 27-30, and the corresponding recombinant protein, rPrP, were solubilized in 0.2% SDS, and the transitions induced by changing the conditions from 0.2% SDS to physiological conditions, i.e. removing SDS, were characterized with respect to solubility, resistance to proteolysis, secondary structure and multimerization. Circular dichroism, electron microscopy and fluorescence correlation spectroscopy were used to study the structural transitions of PrP. Within one minute the alpha-helical structure of PrP was transformed into one that was enriched in beta-sheets and consisted mainly of dimers. Larger oligomers were found after 20 minutes and larger multimers exhibiting resistance to proteolysis were found after several hours. It was concluded that the monomeric alpha-helical conformation was stable in SDS or when attached to the membrane; however, the state of lowest free energy in aqueous solution at neutral pH seems to be the multimeric, beta-sheet enriched conformation.

Animals↗
PubMed1997

[Direct radiographic magnification mammography with a new microfocus tube. Experimental studies of resolution and radiation exposure].

A recently developed X-ray unit for mammography using microfocal (spot size 0.12-0.05 mm) direct magnification radiography will soon be introduced into clinical practice. Unit arrangement and tube construction have been demonstrated. Mean surface dose was measured using PMMA-phantoms. A dose reduction of up to 50% was obtained in 1.7-fold magnification mammography (full sized views) compared with conventional techniques. The image quality was almost equivalent. However, in comparison with 1.7-fold magnification mammography, a comparable dose range for 4-fold magnifications with the microfocus system was measured with a substantial gain in spatial resolution. These findings satisfy the demands of a modern mammographic unit.

Equipment Design↗
PubMed1997

Degree of carotid artery stenosis. Comparison of selective and non-selective angiographic findings with surgical specimens.

OBJECTIVE: To compare the degree of vessel narrowing seen on selective and non-selective carotid artery catheter angiograms using criteria set by NASCET and ECST with the results obtained from corresponding surgical specimens. SUBJECTS: In 40 preoperative angiograms (20 non-selective, 20 selective) the 'distal' degree of internal carotid artery (ICA) stenosis according to NASCET criteria and the 'local' degree of stenosis according to ECST criteria was assessed. These data were compared with the 'distal' and 'local' degree of ICA stenosis obtained by measuring the specimens and the diameter of the distal ICA intraoperatively. RESULTS: The median 'local' degree of stenosis was 86.5% in the specimen and 83.5% in the selective angiograms (difference not significant). In non-selective angiography the median 'local' degree of stenosis was 77.5% compared to 84% in the corresponding specimens (P < 0.01). The median 'distal' degree of stenosis in selective angiography was 76.5 versus 75.5% in the specimens (n.s.). The median 'distal' degree of non-selective angiography was 67% compared to 77.5% in the corresponding specimens (P = 0.02). The trend to underestimate high grade stenosis (above 90%) was more pronounced in non-selective than in selective angiography. Medium grade stenosis (60-80%) was slightly overestimated in selective angiography. CONCLUSION: Selective angiography is more accurate in determining the 'true' degree of stenosis in internal carotid artery disease, taking into account a slight overestimation of medium grade stenosis. High grade stenosis is underestimated in both selective and non-selective angiography. These observations extend to both the ECST and NASCET criteria of measuring the degree of stenosis, which differ by about 10%.

Aged↗
PubMed1997

[Asymptomatic aneurysm of the ileocolic artery].

Visceral aneurysms are rare and account for only 5% of all abdominal aneurysms. Most often they cause no symptoms and are therefore incidental findings. Doppler ultrasonography is the diagnostic method of choice. Therapeutic procedures can be performed either surgically of by interventional therapeutic techniques. This article presents a patient case with an ileocolic artery aneurysm.

Aged↗
PubMed1996

[The accuracy of angiography and CT angiography of the carotid bifurcation compared to macro-morphological correlation].

PURPOSE: To compare the degree of carotid artery stenosis in angiography and CT angiography with the degree of stenosis measured in an intact eversion endarterectomy specimen. METHODS: Preoperative angiograms (intraarterial DSA, 512 x 512 matrix) and CT-angiograms (24 sec spiral scan, slice thickness 2 mm, pitch 1.5) were taken in 12 patients with symptomatic carotid stenosis. Evaluation of the degree of stenosis was performed according to the NASCET ("distal" degree) and ECST ("local" degree) methods. These data were compared with measurements of the surgical specimens. RESULTS: The median "local" degree of stenosis in angiograms was 81.5% (range: 70-99%), in CT angiograms 83% (59-94%) and in specimens 85.5% (65-96%). The "distal" degree of stenosis was 79% (50-99%) in angiograms, 85.5% (55-99%) in CT angiograms and 81% (52-95%) in specimens. CT angiography slightly overestimated the degree of stenosis compared with the specimen, whereas angiography slightly underestimated the true degree of stenosis. However, these differences were not statistically significant. CONCLUSION: CT angiography is able to predict the degree of internal carotid stenosis when compared with an intact surgical specimen. It is as accurate as the "gold standard" of invasive angiography.

Angiography, Digital Subtraction↗
PubMed1996

Disruption of prion rods generates 10-nm spherical particles having high alpha-helical content and lacking scrapie infectivity.

An abnormal isoform of the prion protein (PrP) designated PrPSc is the major, or possibly the only, component of infectious prions. Structural studies of PrPSc have been impeded by its lack of solubility under conditions in which infectivity is retained. Among the many detergents examined, only treatment with the ionic detergent sodium dodecyl sulfate (SDS) or Sarkosyl followed by sonication dispersed prion rods which are composed of PrP 27-30, an N-terminally truncated form of PrPSc. After ultracentrifugation at 100,000 x g for 1 h, approximately 30% of the PrP 27-30 and scrapie infectivity were found in the supernatant, which was fractionated by sedimentation through 5 to 20% sucrose gradients. Near the top of the gradient, spherical particles with an observed sedimentation coefficient of approximately 6S, approximately 10 mm in diameter and composed of four to six PrP 27-30 molecules, were found. The spheres could be digested with proteinase K and exhibited little, if any, scrapie infectivity. When the prion rods were disrupted in SDS and the entire sample was fractionated by sucrose gradient centrifugation, a lipid-rich fraction at the meniscus composed of fragments of rods and heterogeneous particles containing high levels of prion infectivity was found. Fractions adjacent to the meniscus also contained spherical particles. Circular dichroism of the spheres revealed 60% alpha-helical content; addition of 25% acetonitrile induced aggregates high in beta sheet but remaining devoid of infectivity. Although the highly purified spherical oligomers of PrP 27-30 lack infectivity, they may provide an excellent substrate for determining conditions of renaturation under which prion particles regain infectivity.

Animals↗
PubMed1995

Defects in primer-template binding, processive DNA synthesis, and RNase H activity associated with chimeric reverse transcriptases having the murine leukemia virus polymerase domain joined to Escherichia coli RNase H.

The RNase H domain of murine leukemia virus (MuLV) reverse transcriptase (RT) was replaced with Escherichia coli RNase H, and the effect on RNase H activity and processive DNA synthesis was studied, using RNA-DNA hybrids containing sequences from the MuLV polypurine tract (PPT). Two chimeric RTs, having the entire polymerase domain or all but the last 19 amino acids, were expressed. In both cases, these RTs made multiple cuts in PPT-containing substrates, whereas wild-type cleavages occurred primarily at sites consistent with the distance between the polymerase and RNase H active sites. Primer extension assays performed with the chimeric RTs, an RNase H-minus RT, and wild-type showed that the presence of a wild-type viral RNase H domain facilitates processive DNA synthesis. When wild-type RT was bound to primer-template, two retarded bands could be detected in band-shift assays. In the absence of primer extension, a high proportion of enzyme-bound primer-template was associated with the faster-migrating band, whereas with DNA synthesis, more of the bound radioactivity was in the super-shifted complex. This suggests that the super-shifted complex contains the active form of RT. The mutant RTs were deficient in formation of this complex, but the chimeric RTs were somewhat less defective than the RNase H-minus mutant. Our results demonstrate that in the wild-type enzyme, the RNase H domain is required to stabilize the interaction between RT and primer-template.

Base Sequence↗
PubMed1995

[Determination of the degree of stenosis of the internal carotid artery in the surgical specimen after eversion TEA: comparison with angiography and c-w-Doppler ultrasound].

UNLABELLED: 22 carotid specimens following eversion-endarterectomy were compared with preoperative assessment of carotid stenosis obtained angiographically and by c-w-Doppler-sonography. The intact, unsplit specimens were perfused with a liquid plastic material (Palavit M). After hardening of the plastic material the specimens were removed. The local degree of carotid stenosis with respect to diameter reduction was assessed by direct measurement of the plastic specimens at the narrowest site compared with the diameter of the carotid eversion specimens at the place of the maximum stenosis. The distal degree of carotid stenosis was assessed by comparison of the diameter of the distal internal carotid artery obtained intraoperatively with the measurements of the plastic specimens (1 mm vascular wall thickness of distal internal carotid artery was taken into account). RESULTS: Both the local and the distal degree of carotid stenosis diameter (mean 84.7% +/- 8.4% and 82.1% +/- 9.1% respectively) were underestimated in the preoperative angiogram (79.8 +/- 9% by ECST-criteria and 69 +/- 10.3% by NASCET-criteria) in most of the cases. The difference of the diameter reduction was statistically significant (p < 0.05 and p < 0.01 respectively, Wilcoxon signed rank test). The c-w-Doppler assessments were 82.6 +/- 8.2% (n.s.). CONCLUSION: Our results suggest that the preoperative assessment of internal carotid stenosis obtained angiographically or by c-w-Doppler-sonography easily underestimate the true degree of carotid stenosis.

Adult↗