Biomedical subjects

C Wirbelauer

Publications and source records attributed to C Wirbelauer.

At least 37 records · Page 2Linked to original sources

PubMed2000

Slit-lamp-adapted optical coherence tomography of the anterior segment.

PURPOSE: To evaluate the diagnostic potential of a slit-lamp-adapted optical coherence tomography (OCT) system as an in vivo imaging device for routine clinical examination of the anterior segment of the eye. PATIENTS AND METHODS: In a pilot study, healthy volunteers and patients with different pathologies of the anterior segment were examined with a slit-lamp-adapted OCT system using 100-200 axial scans with 100-Hz line-scan frequency. The scan length is variable up to 7 mm, and the axial depth is 1.5 mm in tissue. RESULTS: The slit-lamp-adapted OCT system allowed direct biomicroscopic imaging of the measured area. Anatomic structures and morphological changes anterior to the attenuating iris pigment epithelium could be visualized with high accuracy. Biometric analyses of the cornea, the chamber angle, the iris and secondary cataract were possible. Complete demonstration of the chamber angle was difficult due to the backscattering properties of the anterior part of the sclera and the consequent shadowing of the most peripheral part of the iris. CONCLUSIONS: Slit-lamp-adapted OCT is a useful diagnostic tool which allows in vivo microscopic cross-sectional imaging of the anterior segment and precise measurement of ocular structures.

Anterior Eye Segment↗

PubMed2000

Corneal optical coherence tomography before and immediately after excimer laser photorefractive keratectomy.

PURPOSE: To investigate the representation of the corneal structure with optical coherence tomography before and immediately after excimer laser photorefractive keratectomy. METHODS: Twenty-four eyes of 24 patients with myopia and myopic astigmatism were prospectively studied. The corneal thickness and the corneal profile were assessed with slit-lamp-adapted optical coherence tomography preoperatively and immediately after excimer laser photorefractive keratectomy. RESULTS: The attempted mean spherical equivalent of the refractive corrections was -6.7 +/- 3.6 (mean +/- SD) diopters with a mean calculated stromal ablation depth of 91 +/- 38 microm. The corneal optical coherence tomography was reproducible in all patients, demonstrating a mean decrease of central corneal thickness after epithelial debridement and excimer laser photorefractive keratectomy of 118 +/- 45 microm. The comparison of the calculated stromal ablation depth and the corneal thickness changes determined by corneal optical coherence tomography revealed a significant linear relationship with a correlation coefficient of 0.88 (P <.001). The flattening of the corneal curvature was confirmed in all patients with the optical coherence tomography system and correlated with the attempted refractive correction (r =.82, P <.001). CONCLUSIONS: The slit-lamp-adapted optical coherence tomography system presented in this study allowed noncontact, cross-sectional, and high-resolution imaging of the corneal configuration. This initial clinical evaluation demonstrated that corneal optical coherence tomography could be a promising diagnostic modality to monitor corneal changes of thickness and curvature before and after excimer laser photorefractive keratectomy.

Adult↗

PubMed2000

Subthreshold (retinal pigment epithelium) photocoagulation in macular diseases: a pilot study.

BACKGROUND: Subthreshold (retinal pigment epithelium) photocoagulation is a new photocoagulation method, which treats the retinal pigment epithelium (RPE) and avoids damage to the neural retina. The initial results in this prospective pilot study on various macular diseases are presented. METHODS: 12 patients with diabetic maculopathy (group I), 10 with soft drusen (group II), and four with central serous retinopathy (CSR) (group III) were treated and followed up for 1 year. Treatment was achieved using a train of repetitive short laser pulses (1.7 micros) of a green Nd:YLF laser (parameters: 527 nm, 100 and 500 pulses, repetition rate: 500 Hz, spot size: 160 microm, energies: 70-100 microJ). Laser energy was based on the visibility of test lesions on fluorescein angiography (50-130 microJ). Patients were examined at various times by ophthalmoscopy, fluorescein and ICG angiography, and infrared imaging. RESULTS: After 6 months hard exudates disappeared in six out of nine patients in group I and leakage disappeared in six out of 12 diabetic patients. In group II drusen were less in seven out of 10 patients. In group III serous detachment disappeared in three out of four cases. Visual acuity was stable in all cases. None of the laser lesions was clinically visible immediately. After 1 day most lesions were visible as yellowish RPE depigmentation. After 3 months some of the lesions were visible as hyperpigmented areas but most were not. Fluorescein angiography showed leakage only in the first week. Infrared imaging showed that most lesions can be visualised in groups I and II after a period longer than 1 week as hyperreflective areas. CONCLUSION: This study showed that subthreshold (RPE) photocoagulation is effective in some cases of diabetic maculopathy, drusens, and in CSR. Visibility of laser burns is not always necessary in the treatment of macular diseases presented here. Infrared imaging is an effective and non-invasive way of visualising subthreshold (RPE) laser burns.

Aged↗

PubMed2000

Association of human ubiquitin-conjugating enzyme CDC34 with the mitotic spindle in anaphase.

Present in organisms ranging from yeast to man, homologues of the Saccharomyces cerevisiae ubiquitin-conjugating enzyme CDC34 have been shown to play important roles in the regulation of cell cycle progression and checkpoint function. Here we analyze the expression and intracellular localization of endogenous CDC34 during mammalian cell cycle progression. We find that CDC34 protein is constitutively expressed during all stages of the cell cycle. Immunofluorescence experiments reveal that during interphase, endogenous CDC34 is localized to distinct speckles in both the nucleus and the cytoplasm. The presence of CDC34 in these compartments has also been established by biochemical fractionation experiments. Interestingly, nuclear localization depends on the presence of specific carboxy-terminal CDC34 sequences that have previously been shown to be required for CDC34's cell cycle function in Saccharomyces cerevisiae. Finally, we find that in anaphase and not during early stages of mitosis, CDC34 colocalizes with (beta)-tubulin at the mitotic spindle, implying that it may contribute to spindle function at later stages of mitosis. Taken together, these results support a model in which CDC34 ubiquitin-conjugating enzyme functions in the regulation of nuclear and cytoplasmic activities as well as in the process of chromosome segregation at the onset of anaphase in mammalian cells.

Anaphase↗

PubMed1999

The von Hippel-Lindau tumor suppressor protein is a component of an E3 ubiquitin-protein ligase activity.

pVHL, the product of the VHL tumor suppressor gene, plays an important role in the regulation of cell growth and differentiation of human kidney cells, and inactivation of the VHL gene is the most frequent genetic event in human kidney cancer. The biochemical function of pVHL is unknown. Here we report that pVHL exists in vivo in a complex that displays ubiquitination-promoting activity in conjunction with the universally required components E1, E2, and ubiquitin. pVHL-associated ubiquitination activity requires, at a minimum, pVHL to bind elongin C and Cul-2, relatives of core components of SCF (Skp1-Cdc53/Cul-1-F-box protein) E3 ligase complexes. Notably, certain tumor-derived mutants of pVHL demonstrate loss of associated ubiquitination promoting activity. These results identify pVHL as a component of a potential SCF-like E3 ubiquitin-protein ligase complex and suggest a direct link between pVHL tumor suppressor and the process of ubiquitination.

Amino Acid Sequence↗

PubMed1999

Increased levels of E2F-1-dependent DNA binding activity after UV- or gamma-irradiation.

In mammalian cells, DNA damage induces robust changes in gene expression and these changes contribute to the proper execution of cellular responses to DNA damage, including DNA repair, cell cycle arrest and apoptosis. The transcription factor E2F-1 has been suggested to play a key role in the regulation of cell cycle-dependent gene expression and apoptosis. These activities depend on the ability of E2F-1 to form functionally active DNA binding complexes. Here we describe an assay that allows one to measure E2F-1 DNA binding activity in naive cells. We find that DNA damage, generated by UV- or gamma-irradiation, prompts increased production of E2F-1 DNA binding activity, which, at least in part, originates from alterations in E2F-1 protein levels. These findings represent an indication for a role of the transcription factor E2F-1 in the DNA damage response pathway.

Amino Acid Sequence↗

PubMed1999

Retinal sparing by selective retinal pigment epithelial photocoagulation.

OBJECTIVE: To investigate whether photocoagulation of the retinal pigment epithelium is possible with sparing of the photoreceptors. METHODS: Mild laser effects of a neodymium:yttrium-lithium-fluoride (Nd:YLF) laser (527 nm) were applied to 17 patients. To establish the necessary energy, test exposures were performed to the lower macula (laser variables: 1.7 microseconds, 100 and 500 pulses applied in a train at 500 Hz, 20-130 microJ, 160 microm). Of 179 test lesions, 73 were followed up at various time intervals up to 1 year by performing microperimetry directly on top of the laser lesions. RESULTS: All of the test lesions were at the threshold of retinal pigment epithelial disruption, and none of the laser effects were visible by ophthalmoscopy during photocoagulation; they were detectable only by fluorescein angiography. After exposure with 500 pulses, retinal defects were detected in up to 73% of the patients (100 microJ) after the first day. Most of these defects were no longer detectable after 3 months. After exposure with 100 pulses, no defects could be detected with 70 and 100 microJ after 1 day. The absence of microscotomas in the follow-up period suggests that retinal damage was minimal or, if it occurred, was functionally repaired. CONCLUSION: By choosing proper energy and number of pulses, it is possible to produce retinal pigment epithelial effects with no subsequent retinal damage detectable by microperimetry.

Adult↗

PubMed1999

[Anisocoria after unilateral photorefractive keratectomy. Result of a lesion of the pupillary sphincter muscle?].

BACKGROUND: After unilateral photorefractive keratectomy (PRK) for myopia correction, relative mydriasis of the treated eye was noticed. The aim of this study was to determine the incidence and possible etiology of this anisocoria. PATIENTS AND METHODS: In a prospective clinical study we examined eight consecutive patients after PRK of a spherical equivalent of -1.0 to -8.5 D with a 6.5-7.0 mm optical zone (Schwind-Keratom) for up to 10 months. Measurements of the pharmacological uninfluenced pupillary diameter were carried out with a Goldmann perimeter under 31.5 asb and under four different room light and distance conditions. In five patients a hard contact lens of 0 D power was fitted to the treated eye, so that the laser-induced central corneal flattening was compensated for by the sublenticular tear film, and the pupillary diameter was measured again. The influence of pilocarpine 0.1% eye drops to the pupil was also examined. RESULTS: Postoperatively, the pupil of the PRK-treated eye measured up to 1.75 mm larger than that of the fellow eye in all patients. The amount of anisocoria showed a small negative correlation with the interval between the PRK procedure and the day of measurement. It did not correlate significantly with the amount of induced refractive change, applied energy, application of pilocarpine 0.1% eye drops or the contact lens fitting. CONCLUSION: After unilateral PRK, anisocoria can regularly be observed. At present its definite pathogenesis is unclear, although certain possible optical and neuronal mechanisms have been excluded. The most probable etiology is a mild lesion of the pupillary sphincter muscle because of its localization in the center of the laser shock wave distribution.

Adolescent↗

PubMed1999

[Diode laser thermokeratoplasty. Initial clinical experiences].

PURPOSE: Pulsed holmium lasers are currently used to correct hyperopia by means of laser thermokeratoplasty (LTK). Series of microsecond laser pulses are applied with a high repetition rate to induce shrinkage of corneal collagen fibers. The pulsed energy application results in intrastromal temperature peaks of up to 200 degrees C. A continuously emitting laser diode can--as we demonstrated recently in an invivo study on minipigs--be used for LTK and may be of advantage because the temperature rise is more steady. The aim of this study was to examine the safety, amount, and stability of hyperopic correction of diode LTK on blind human eyes. METHODS: We used a laserdiode that was set to continuously emit light at lambda = 1.854 microns/mu a = 1.04 mm-1 (group I, n = 4) or 1.87 microns/mu a = 1.92 mm-1 (group II, n = 4). Radiation energy was 100 to 150 mW for 10 s per coagulation. Eight coagulations on a single ring (group I) and 16 coagulations on a double ring (group II) diameter were applied in the cornea concentric to the entrance pupil by means of a vacuum-fixed application mask (group I = conjunctival fixation; group II = corneal fixation) and a handpiece with a focusing optic. Preoperatively as well as 1 week, 1, 2, 3, 6 12 and 18 months postoperative ophthalmologic controls were performed and the corneal refractive power was measured. RESULTS: In group I initial refractive changes of up to +4.9 D were achieved (1 week postoperative). However, due to the great penetration depth of the laser irradiation, large endothelial defects resulted beneath the stromal coagulations. In group II an initial refractive change of up to +6.8 D was achieved and as a result of the reduced penetration depth, the endothelial cell damage was much reduced. Partial regression of the refractive effect occurred in all subjects, which continued in higher refractive changes during the 2nd postoperative year. The refractive effect at 12 months was +0.6 to +1.5 D in group I and +0.9 to +5.7 D in group II. At 12 months the induced astigmatism was 0.5 to 2.2 D in group I and 0.3 to 1.6 D in group II. No serious adverse effects were noticed. CONCLUSION: A continously emitting laser diode working at a wavelength of 1.87 microns can be used to correct hyperopia by means of LTK safely and effectively. Regression occurs predominantly in the first 6 postoperative months. Further studies must be conducted to determine the importance of patient inherent parameters such as age in establishing a nomogram.

Adult↗

PubMed1999

[Thermal damage to the corneal endothelium in diode laser thermokeratoplasty].

Laser thermokeratoplasty (LTK) can be applied for correction of hyperopia and astigmatism by means of concentrically placed coagulations. Because of the temperature rise during coagulation, damage of the endothelial cells directly below the irradiated areas is possible. In this study, we examined the extent of the thermally denatured zones for different laser parameters and the threshold of thermal endothelial damage as a function of of temperature and duration of elevated temperatures. The threshold for thermal damage of endothelial cells was determined in isotonic NaCl solution for temperature exposures of 10 s and 1 min in a water bath. To determine the damage zones, corneas were irradiated under standardized conditions with a continuously emitting infrared (cw-IR) laser diode at various wave-lengths and different power values and were stained after preparation with trypan blue and alizarine red. The extensions of the damage zones were compared with calculated isotherms. Fifty percent cell damage was found at temperatures of 65 degrees C for heating times of 10 s and at 59 degrees C for 1 min. With thicker corneas, less laser power and higher absorption coefficients, the damage zone was reduced. The damage range determined corresponded to the calculated isotherms of 60 degrees C and 70 degrees C. Regarding clinical LTK, a loss of endothelial cells can be predicted and minimized or totally avoided by choosing the appropriate irradiation parameters.

Animals↗

PubMed1999

Variability of RPE reaction in two cases after selective RPE laser effects in prophylactic treatment of drusen.

BACKGROUND: The value of prophylactic photocoagulation of soft drusen is unclear. Photocoagulation is usually performed by a continuous wave laser. METHODS: We report the cases of two patients with age-related macular degeneration with soft drusen who were treated by selective retinal pigment epithelium (RPE) photocoagulation of a pulsed Nd:YLF (527 nm) laser. Laser parameters were: wavelength 527 nm, number of pulses in a train 500, pulse duration 1.7 microseconds, energy per pulse 70 microJ, spot size 160 microns, repetition rate 500 Hz. RESULTS: Dosimetry performed individually showed that in both patients laser photocoagulation was performed at the threshold of RPE disruption. None of the laser effects was visible during photocoagulation. They were detectable only by fluorescein angiography. Despite identical photocoagulation parameters the RPE reaction was completely different. In the first patient RPE hyperpigmentation was notable at most photocoagulation sites and the drusen had disappeared after 6 months. In the second patient the laser effects were not visible after 6 months by biomicroscopy and the drusen stayed unchanged. CONCLUSION: These findings could reflect different repair mechanisms of the RPE after alteration and could represent a sign of a different viable stage in the life of RPE cells. Close attention should be paid to this phenomenon in the various drusen studies currently under way.

Fluorescein Angiography↗

PubMed1999

Systemic levels of lidocaine after intracameral injection during cataract surgery.

PURPOSE: To evaluate the systemic concentrations of lidocaine after intracameral injection of a 1% solution during cataract surgery and the safety of this application mode. SETTING: Department of Ophthalmology, Medical University of Lübeck, Lübeck, Germany. METHODS: This prospective study included 10 patients who had phacoemulsification and posterior chamber lens implantation with a self-sealing scleral tunnel incision. Topical anesthesia was achieved using cocaine 10% eyedrops combined with 0.5mL of unpreserved lidocaine 1% injected into the anterior chamber. Blood samples were taken from all patients at predetermined intervals before and during the procedure. Consecutive analysis for lidocaine was performed with gas chromatography. RESULTS: In all samples, serum lidocaine concentrations were below a minimum detectable level of 100 ng/mL. No local or systemic intraoperative or postoperative complications were noted. CONCLUSIONS: Intracameral injection of 0.5 mL lidocaine 1% revealed no systemic therapeutic concentrations. In patients in whom other forms of needle-delivered local anesthesia are contraindicated, intracameral injection of lidocaine should be considered to enhance topical anesthesia.

Adult↗

PubMed1999

Continuous-wave diode laser thermokeratoplasty: first clinical experience in blind human eyes.

PURPOSE: To evaluate the safety and stability of laser thermokeratoplasty (LTK) with a continuous-wave diode laser in blind human eyes and to optimize parameters for a study in sighted eyes. SETTING: Department of Ophthalmology, Medical University Lübeck, Germany. METHODS: A continuous-wave diode laser was set to emit radiation with a wavelength of 1.854 microns (Group 1, n = 4) or 1.870 microns (Group 2, n = 4) and 100 to 150 mW power for 10 seconds. A focusing handpiece was coupled with an application mask and fixed by partial vacuum to the conjunctiva or cornea. The radiation was focused into the corneal stroma between 400 and 600 microns in Group 1 and set to 1000 microns in Group 2. Eight (Group 1, single ring) or 16 (Group 2, double ring) coagulations were applied. RESULTS: The refractive change increased with higher laser power and smaller ring diameters. Two rings of coagulations provided higher and more stable refractive changes of up to 5.66 diopters (D) than a single ring. The refractive effect stabilized between 3 and 6 months postoperatively. At 1 year, mean refractive change was +0.99 D +/- 0.39 (SD) in Group 1 and +2.32 +/- 2.24 D in Group 2. Extensive endothelial damage occurred in Group 1 but was minimal in Group 2. CONCLUSIONS: Diode LTK was used to treat hyperopia safely and effectively. Regression occurred mainly in the first 3 postoperative months. With a wavelength of 1.870 microns, corneal endothelial damage was limited.

Adult↗

PubMed1999

p45SKP2 promotes p27Kip1 degradation and induces S phase in quiescent cells.

The F-box protein p45SKP2 is the substrate-targeting subunit of the ubiquitin-protein ligase SCFSKP2 and is frequently overexpressed in transformed cells. Here we report that expression of p45SKP2 in untransformed fibroblasts activates DNA synthesis in cells that would otherwise growth-arrest. Expression of p45SKP2 in quiescent fibroblasts promotes p27Kip1 degradation, allows the generation of cyclin-A-dependent kinase activity and induces S phase. Coexpression of a degradation-resistant p27Kip1 mutant suppresses p45SKP2-induced cyclin-A-kinase activation and S-phase entry. We propose that p45SKP2 is important in the progression from quiescence to S phase and that the ability of p45SKP2 to promote p27Kip1 degradation is a key aspect of its S-phase-inducing function. In transformed cells, p45SKP2 may contribute to deregulated initiation of DNA replication by interfering with p27Kip1 function.

Animals↗

PubMed1999

Interaction between ubiquitin-protein ligase SCFSKP2 and E2F-1 underlies the regulation of E2F-1 degradation.

The transcription factor E2F-1 is important in the control of cell proliferation. Its activity must be tightly regulated in a cell-cycle-dependent manner to enable programs of gene expression to be coupled closely with cell-cycle position. Here we show that, following its accumulation in the late G1 phase of the cell cycle, E2F-1 is rapidly degraded in S/G2 phase. This event is linked to a specific interaction of E2F-1 with the F-box-containing protein p45SKP2, which is the cell-cycle-regulated component of the ubiquitin-protein ligase SCFSKP2 that recognizes substrates for this ligase. Disruption of the interaction between E2F-1 and p45SKP2 results in a reduction in ubiquitination of E2F-1 and the stabilization and accumulation of transcriptionally active E2F-1 protein. These results indicate that an SCFSKP2-dependent ubiquitination pathway may be involved in the downregulation of E2F-1 activity in the S/G2 phase of the cell cycle, and suggest a link between SCFSKP2 and cell-cycle-dependent gene control.

3T3 Cells↗

PubMed1999

E2F-1 has properties of a radiosensitizer and its regulation by cyclin A kinase is required for cell survival of fibrosarcoma cells lacking p53.

Negative regulation of E2F-1 DNA binding function by cyclin A kinase represents part of an S-phase checkpoint control system that, when activated, leads to apoptosis. In this study, we examined the cellular sensitivity and resistance of isogenic mouse fibrosarcoma cell lines, differing primarily in their p53 status, to ectopic expression of wild-type (wt) E2F-1 and cyclin A kinase binding-defective mutants of it. We found that E2F-1 (wt) potently affected the survival of p53+/+ tumor cells but not that of p53-/- cells. In contrast, expression of cyclin A kinase binding-defective E2F-1 species interfered with cell survival of fibrosarcoma cells irrespective of their p53 status. Finally, expression of E2F-1 (wt) in p53-/- fibrosarcoma cells enhanced the cytotoxic effect of ionizing radiation in vitro and in vivo in a mouse tumor model. These results suggest that E2F-1-dependent activation of an S-phase checkpoint is p53 independent and that E2F-1 possesses radiosensitizing properties in the absence of p53.

Animals↗

PubMed1998

Association of human CUL-1 and ubiquitin-conjugating enzyme CDC34 with the F-box protein p45(SKP2): evidence for evolutionary conservation in the subunit composition of the CDC34-SCF pathway.

In normal and transformed cells, the F-box protein p45(SKP2) is required for S phase and forms stable complexes with p19(SKP1) and cyclin A-cyclin-dependent kinase (CDK)2. Here we identify human CUL-1, a member of the cullin family, and the ubiquitin-conjugating enzyme CDC34 as additional partners of p45(SKP2) in vivo. CUL-1 also associates with cyclin A and p19(SKP1) in vivo and, with p45(SKP2), they assemble into a large multiprotein complex. In Saccharomyces cerevisiae, a complex of similar molecular composition (an F-box protein, a member of the cullin family and a homolog of p19(SKP1)) forms a functional E3 ubiquitin protein ligase complex, designated SCFCDC4, that facilitates ubiquitination of a CDK inhibitor by CDC34. The data presented here imply that the p45(SKP2)-CUL-1-p19(SKP1) complex may be a human representative of an SCF-type E3 ubiquitin protein ligase. We propose that all eukaryotic cells may use a common ubiquitin conjugation apparatus to promote S phase. Finally, we show that multiprotein complex formation involving p45(SKP2)-CUL-1 and p19(SKP1) is governed, in part, by periodic, S phase-specific accumulation of the p45(SKP2) subunit and by the p45(SKP2)-bound cyclin A-CDK2. The dependency of p45(SKP2)-p19(SKP1) complex formation on cyclin A-CDK2 may ensure tight coordination of the activities of the cell cycle clock with those of a potential ubiquitin conjugation pathway.

Amino Acid Sequence↗

PubMed1998

Corneal endothelial cell changes in pseudoexfoliation syndrome after cataract surgery.

OBJECTIVE: To characterize possible differences in endothelial cell changes after cataract surgery in patients with pseudoexfoliation syndrome (PSX). METHODS: In this prospective, age-matched, controlled clinical study, 25 consecutive patients with PSX and 25 control patients with senile cataracts only were studied. All patients were treated with standardized cataract surgery. Sequential quantitative and qualitative morphometric endothelial cell analyses of the central and paracentral cornea were performed preoperatively and postoperatively at 1 day, 4 weeks, and 6 months using noncontact specular microscopy. RESULTS: Preoperative endothelial cell counts were 9.9% (P<.05) lower in patients with PSX (2387+/-266 cells/mm2) than in controls (2648+/-349 cells/mm2). The mean endothelial cell loss was 11.1% in the PSX group and 10.3% (P<.001 for both) in the control group, with no intergroup differences after 6 months. The mean endothelial cell area increased in both groups. Also, qualitative analysis revealed no significant differences in the endothelial repair mechanisms. CONCLUSIONS: Endothelial cell density is reduced preoperatively in patients with PSX compared with age-matched controls. In patients with PSX, cataract surgery induced similar endothelial cell changes without increased endothelial cell loss postoperatively.

Aged↗