PubMed Health⌕ Search

Biomedical subjects

Ulrich Hahn

Publications and source records attributed to Ulrich Hahn.

12 recordsLinked to original sources
PubMed2006

Bivalent monoclonal IgY antibody formats by conversion of recombinant antibody fragments.

Monoclonal IgY have the potential to become unique tools for diagnostic research and therapeutic purposes since avian antibodies provide several advantages due to their phylogenetic difference when compared to mammalian antibodies. The mechanism of avian immunoglobulin gene diversification renders chicken an excellent source for the generation of recombinant scFv as well as Fab antibody libraries of high diversity. One major limitation of these antibody fragments, however, is their monovalent format, impairing the functional affinity of the molecules and, thereby, their applicability in prevalent laboratory methods. In this study, we generated vectors for conversion of avian recombinant antibody fragments into different types of bivalent IgY antibody formats. To combine the properties of established mammalian monoclonal antibodies with those of IgY constant domains, we additionally generated bivalent murine/avian chimeric antibody constructs. When expressed in HEK-293 cells, all constructs yielded bivalent disulfide-linked antibodies, which exhibit a glycosylation pattern similar to that of native IgY as assessed by lectin blot analysis. After purification by one step procedures, the chimeric and the entire avian bivalent antibody formats were analyzed for antigen binding and interaction with secondary reagents. The data demonstrate that all antibody formats provide comparable antigen binding characteristics and the well established properties of avian constant domains.

Animals↗
PubMed2005

Degradation of poly-L/DL-lactide versus TCP composite pins: a three-year animal study.

Biodegradable polylactide implants allow secure fixation of osteochondral fractures. This quasirandomized parallel-group animal study investigates whether a composite implant of poly-L/DL-lactide (PLDLLA) with additional 10% beta-tricalcium phosphate produces an osteoconductive effect, whether the admixture positively influences implant degradation (assessed by comparing time to implant degradation), and whether the pin sites of degraded implants are replaced with bone tissue. On 36 medial femoral condyles of sheep, osteotomies were fixed with either three PLDLLA pins or three composite pins. At 3, 18, and 36 months, the pin sites were measured histologically and the state of degradation assessed according to Pistner's classification. All fractures healed without clinically relevant complications and without displacement. Both pin types led to asymptomatic pin-site enlargement at 18 months, which disappeared by 36 months. At 18 months, 14 of 18 PLDLLA pins were no longer evident, whereas 16 of 18 composite pins showed only peripheral degradation. By 36 months, all implants from both groups were completely degraded and replaced with scar (2/18) or bone tissue (16/18). At 36 months there was no evidence for significant improvement of either degradation performance or osseointegration through use of the 10% TCP composite mixture.

Animals↗
PubMed2005

A comparative radiological assessment of polylactide pins over 3 years in vivo.

Biodegradable polylactide implants allow secure fixation of osteochondral fractures with minimal adverse effects. The goal of this prospective, randomized animal study was to show whether osteoconductive effects can be achieved through the development of poly-L/DL(70/30)lactide composite implants with 10% beta-tricalcium phosphate, and whether degradation can be positively influenced and adverse effects minimized using such implants. An additional goal was to clarify which radiological procedure is most suitable to observe the course of follow-up. Thirtysix medial femoral condyle osteotomies of sheep were fixed with either 3 poly-L/DL-lactide pins or 3 composite pins, and the pin canal widths were measured with conventional radiographs, with CT, MRI, and histologically after 3, 18, and 36 months. All fractures healed completely without displacement or clinically relevant complications. The pin canals dilated secondary to pin degradation at the 12th month, and then decreased in size later. At 36 months, the pins had microscopically disappeared, and the canals were filled with bone or scar tissue. There were no statistically significant differences between the pin-types. Poly-L/DL-lactide pins and composite C-pins are suitable for secure fixation of small osteochondral fractures. Osteoconductive effects of biocompatibility or osseous integration relating to composite development were not evident. Conventional radiography and computer tomography were suitable techniques for observation of pin canals. Due to frequently observed artifact, MRI was not suitable to observe the course of the implants.

Absorbable Implants↗
PubMed2005

Biodegradable implants for Pipkin fractures.

The current study was designed to clarify whether biodegradable poly-L/DL lactide pins provide an operative alternative for fixation of Pipkin fractures. Nine patients with Pipkin fractures (one with Pipkin Type I, one with Pipkin Type II, and seven with Pipkin Type IV fractures) were treated surgically between 1996 and 2002. In all patients, the femoral head fractures were fixed with biodegradable, 2.7-mm and 2.0-mm polylactide pins. Eight patients were followed up for an average of 54.2 months. One patient died before the final followup. Eight fractures healed uneventfully. In one patient, a persisting femoral head defect led to posttraumatic arthritis requiring insertion of a femoral endoprosthesis at 1 year. The average range of motion of the affected hips of all patients at followup was 109 degrees -0 degrees -0 degrees in flexion and extension. External and internal rotation averaged 37 degrees -0 degrees -29 degrees . One patient had Brooker Grade I heterotopic ossification develop, and another had a Grade II heterotopic develop. Merle d'Aubigne and Postel ratings showed two excellent and five satisfactory results (average score, 13.1). Adverse effects from the polylactide implants were not observed. Pipkin fractures can be fixed successfully with biodegradable polylactide pins.

Absorbable Implants↗
PubMed2004

RNase T1 variant RV cleaves single-stranded RNA after purines due to specific recognition by the Asn46 side chain amide.

Attempts to alter the guanine specificity of ribonuclease T1 (RNase T1) by rational or random mutagenesis have failed so far. The RNase T1 variant RV (Lys41Glu, Tyr42Phe, Asn43Arg, Tyr45Trp, and Glu46Asn) designed by combination of a random and a rational mutagenesis approach, however, exhibits a stronger preference toward adenosine residues than wild-type RNase T1. Steady state kinetics of the cleavage reaction of the two dinucleoside phosphate substrates adenylyl-3',5'-cytidine and guanylyl-3',5'-cytidine revealed that the ApC/GpC ratio of the specificity coefficient (k(cat)/K(m)) was increased approximately 7250-fold compared to that of the wild-type. The crystal structure of the nucleotide-free RV variant has been refined in space group P6(1) to a crystallographic R-factor of 19.9% at 1.7 A resolution. The primary recognition site of the RV variant adopts a similar conformation as already known from crystal structures of RNase T1 not complexed to any nucleotide. Noteworthy is a high flexibility of Trp45 and Asn46 within the three individual molecules in the asymmetric unit. In addition to the kinetic studies, these data indicate the participation of Asn46 in the specific recognition of the base and therefore a specific binding of adenosine.

Adenine↗
PubMed2004

Addressing the challenge of changing the specificity of RNase T1 with rational and evolutionary approaches.

Although ribonuclease T1 (RNase T1) is one of the best-characterized proteins with respect to structure and enzymatic action, numerous attempts at altering the specificity of the enzyme to cleave single-stranded RNA at the 3'-side of adenylic instead of guanylic residues by rational approaches have failed so far. Recently we generated and characterized the RNase T1 variant RV with a 7200-fold increase in adenylyl-3',5'-cytidine (ApC)/guanylyl-3',5'-cytidine (GpC) preference, with the guanine-binding loop changed from 41-KYNNYE-46 (wt) to 41-EFRNWN-46. Now we have introduced the asparagine residue at position 46 of the wild-type enzyme as a single-point mutation in variant E46N and in combination with the Y45W exchange also occurring in RV. Both variants show an improved ApC/GpC preference with a 1450-fold increase for E46N and a 2100-fold increase for Y45W/E46N in comparison to wild-type activity. We also addressed the challenge of altering enzyme specificity with an evolutionary approach. We have randomly introduced point mutations into the RNase T1 wild-type gene and into the gene of the variant RV with different mutation rates. Altogether we have screened about 100,000 individual clones for activity on RNase indicator plates; 533 of these clones were active. A significant change in substrate specificity towards an ApC preference could not be observed for any of these active variants; this demonstrated the magnitude of the challenge to alter the specificity of this evolutionary perfected enzyme.

Amino Acids↗
PubMed2002

MR imaging at rest early after myocardial infarction: detection of preserved function in regions with evidence for ischemic injury and non-transmural myocardial infarction.

Patients with subacute myocardial infarction were studied to detect regions of ischemic injury but with preserved myocardial function combining different MRI techniques. On a 1.5-T imaging system 27 patients were examined 7-14 days after acute myocardial infarction. The imaging protocol included T2-weighted fast spin-echo imaging, a cine fast low-angle shot (FLASH) 2D technique to determine regional function at rest, and a first pass as well as late contrast enhancement perfusion study injecting 0.1 mmol/kg Gd-DTPA. Preserved function was compared with the transmural extent of first-pass perfusion phenomena, increased T2 signal intensity (SI), and late contrast enhancement. Semi-quantitative first-pass perfusion parameters were correlated with quantitative myocardial wall thickening (MWT) and degree of coronary artery stenosis. Indicating ischemic injury increased T2 SI and late enhancement was present in 29 and 26% of segments. Preserved function was found predominantly in segments with non-transmural late enhancement (112 of 338 segments with late enhancement) and transmural increase of T2 SI (129 of 386 segments with increased T2 SI). A high-grade perfusion deficit was detected in 4% of all segments and regularly associated with markedly decreased systolic function. Correlation of first-pass perfusion parameters was observed with MWT (r=0.50-0.90, p<0.001) but not with the degree of coronary artery stenosis. Our data suggest that preserved function was detected in non-transmural myocardial infarction demonstrated by non-transmural late enhancement and increase of T2 SI.

Aged↗
PubMed2002

Impact of four (13)C-proline isotope labels on the infrared spectra of ribonuclease T1.

Ribonuclease T1 was biosynthesized, with all four prolines (13)C-labeled in the peptide C[double bond]O bond, using a proline auxotrophic yeast strain of Saccharomyces cerevisiae. The (13)C- and (12)C-proline isotopomers of ribonuclease T1 were investigated by infrared spectroscopy in the thermally unfolded and natively folded state at 80 and 20 degrees C, respectively. In the thermally unfolded state, both proteins established almost indistinguishable spectral features in the secondary structure sensitive amide I region. In contrast, the spectra measured at 20 degrees C revealed substantial qualitative and quantitative differences, though parallel analysis by circular dichroism suggested identical native folds for both isotopomers. Major spectral differences in the infrared spectra were detected at 1626 and 1679 cm(-1), which are diagnostic marker bands for antiparallel beta-sheets in ribonuclease T1 and at 1645 cm(-1), a region that is characteristic for the infrared absorption of irregular structures. Starting with the known three-dimensional structure of ribonuclease T1, the observed effects of the isotope labeling are discussed on the basis of transition dipole coupling between the (12)C[double bond]O and (13)C[double bond]O groups. The experimental results were confirmed by transition dipole coupling calculations of the amide I manifold of the labeled and unlabeled variant.

Aspergillus oryzae↗
PubMedDate not supplied

Frequent embolization in peripheral angioplasty: detection with an embolism protection device (AngioGuard) and electron microscopy.

PURPOSE: To evaluate the deliverability and protection capabilities of an embolism protection filter in angioplasty of peripheral arteries. METHODS: The Angioguard emboli capture guidewire system was applied in 11 patients with femoropopliteal lesions (6 stenoses, 3 occlusions, 2 controls). Data on lesion crossing, flow deceleration and macroembolization were recorded. Filter membranes were evaluated with scanning electron microscopy (SEM). RESULTS: System delivery was successful in all patients. Primary lesion crossing was feasible in four of six stenoses; predilatation was required in two of six. Marked flow deceleration was recorded in six patients. Emboli next to the filter were detected in each patient with concentric plaques, but could not reliably be removed with the filter. Downstream macroembolization was also present in all patients with concentric stenoses, but in none with chronic occlusion. None of the patients had clinical signs of ischemia. SEM analysis demonstrated only small particles on control group filters and non-obliterating fibrinous conglomerates on filters used in chronic occlusion. Substantial obliteration was seen on several filters used in stenotic lesions. CONCLUSION: Microembolization of fibrin aggregates is a common incident in balloon angioplasty of femoropopliteal stenoses. Macroembolization occurred more frequently than previously reported. The use of embolism protection filters aided in the detection but not in the removal of larger emboli.

Aged↗
PubMedDate not supplied

Aptamers that recognize the lipid moiety of the antibiotic moenomycin A.

Moenomycin A is an amphiphilic phosphoglycolipid antibiotic that interferes with the transglycosylation step in peptidoglycan biosynthesis. The antibiotic consists of a branched pentasaccharide moiety, connected to the moenocinol lipid via a glycerophosphate linker. We have previously described the selection of aptamers that require the lipid group and the disaccharide epitopes of the oligosaccharide moiety for moenomycin binding. Here we report that the enriched moenomycin-binding library contains sequences that evolved for specific recognition of the unpolar lipid group of the antibiotic. These results suggest that the evolution of hydrophobic binding pockets in RNA molecules may be much more common than previously assumed.

Anti-Bacterial Agents↗
PubMedDate not supplied

Retroclival ecchordosis physaliphora: MR imaging and review of the literature.

BACKGROUND AND PURPOSE: Ecchordosis physaliphora (EP), found in about 2% of autopsies, is a clinically inconspicuous notochordal remnant appearing at the dorsal wall of the clivus. To our knowledge, a systematic review of its MR features does not exist. The aim of this study was to describe the MR imaging findings of incidentally found retroclival EP with special respect to its differentiation from intradural chordomas. METHODS: We reviewed 300 consecutive 1.5-T MR imaging studies that included thin-section transverse T2-weighted images of the skull base for the presence of a retroclival EP. In cases in which an EP was identified, two neuroradiologists observed MR signal intensity characteristics, contrast enhancement, size, form, stalk of EP, and signal intensity changes of the adjacent clivus. RESULTS: Five cases with retroclival EP were found (incidence, 1.7%). In all cases, the ecchordoses was hyperintense on T2-weighted images and hypointense on T1-weighted images. Contrary to the reported findings in chordomas, none of the lesions showed contrast enhancement. In four cases, there were signal intensity changes in the adjacent clivus. A stalklike connection between clivus and EP was seen in three patients. CONCLUSION: Because of the benign character of EP and the difficulties in its histopathologic differentiation from chordomas, precise knowledge of the radiologic characteristics of EP is important. On the basis of these five cases and a review of literature, contrast enhancement and the presence of clinical symptoms seem to be highly reliable parameters in the differential diagnosis of intradural chordoma and EP.

Adult↗