Apolipoprotein E secreted by astrocytes forms antiparallel dimers in discoidal lipoproteins

The Apolipoprotein E gene (APOE) is of great interest due to its role as a risk factor for late-onset Alzheimer's disease. ApoE is secreted by astrocytes in the central nervous system in high-density lipoprotein (HDL)-like lipoproteins. Structural models of lipidated ApoE of high resolution could aid in a mechanistic understanding of how ApoE functions in health and disease. Using monoclonal Fab and F(ab')2 fragments, we characterize the structure of lipidated ApoE on astrocyte-secreted lipoproteins. Our results provide support for the "double-belt" model of ApoE in nascent discoidal HDL-like lipoproteins, where two ApoE proteins wrap around the nanodisc in an antiparallel conformation. We further show that lipidated, recombinant ApoE accurately models astrocyte-secreted ApoE lipoproteins. Cryogenic electron microscopy of recombinant lipidated ApoE further supports ApoE adopting antiparallel dimers in nascent discoidal lipoproteins.

Structural analyses of β2-glycoprotein I: is there a circular conformation?

BACKGROUND

Antiphospholipid antibodies targeting β2-glycoprotein I (β2GPI) cause thrombosis and pregnancy morbidity in antiphospholipid syndrome (APS) patients. How these antibodies recognize β2GPI remains controversial.

OBJECTIVES

This study aimed to elucidate the structure of β2GPI and evaluate how pathogenic anti-domain I (DI) antibodies recognize it in human plasma.

METHODS

β2GPI was made recombinant and purified from human plasma using different protocols. Structural and functional analyses were conducted using orthogonal techniques, namely, electron microscopy, size-exclusion chromatography, single-molecule Förster resonance energy transfer, and microfluidic diffusional sizing.

RESULTS

Electron microscopy and size-exclusion chromatography showed that the structure of β2GPI produced recombinantly and purified from plasma is elongated, even when subjected to conditions previously reported to favor circularization. Single-molecule Förster resonance energy transfer analyses of β2GPI labeled at positions 88 in DII and 278 in DV showed that these residues are located >90 Å apart, consistent with an elongated form. They also documented that the distance between these 2 residues did not change when the protein was reconstituted in human plasma. Microfluidic diffusional sizing documented that β2GPI binds with moderate affinity to a prototypical anti-DI antibody targeting the epitope G40-R43 despite being elongated.

CONCLUSION

Circulating β2GPI is elongated and, therefore, fully capable of binding to anti-DI antibodies. Binding of β2GPI to negatively charged phospholipids drives autoantibody recognition by increasing the local concentration of the antigen and not by dramatically changing its conformation. These findings clarify the structural properties of β2GPI, which have important implications for understanding APS pathogenesis and the development of APS diagnostics and therapeutics.

222 Rn emanation measurements for the XENON1T experiment

The selection of low-radioactive construction materials is of utmost importance for the success of low-energy rare event search experiments. Besides radioactive contaminants in the bulk, the emanation of radioactive radon atoms from material surfaces attains increasing relevance in the effort to further reduce the background of such experiments. In this work, we present the 222 Rn emanation measurements performed for the XENON1T dark matter experiment. Together with the bulk impurity screening campaign, the results enabled us to select the radio-purest construction materials, targeting a 222 Rn activity concentration of 10 μ Bq / kg in 3.2 t of xenon. The knowledge of the distribution of the 222 Rn sources allowed us to selectively eliminate problematic components in the course of the experiment. The predictions from the emanation measurements were compared to data of the 222 Rn activity concentration in XENON1T. The final 222 Rn activity concentration of ( 4.5 ± 0.1 ) μ Bq / kg in the target of XENON1T is the lowest ever achieved in a xenon dark matter experiment.

The first dual-phase xenon TPC equipped with silicon photomultipliers and characterisation with 37 Ar

For the first time, a small dual-phase (liquid/gas) xenon time projection chamber was equipped with a top array of silicon photomultipliers for light and charge readout. Here we describe the instrument in detail, as well as the data processing and the event position reconstruction algorithms. We obtain a spatial resolution of ∼ 1.5 mm in the horizontal plane. To characterise the detector performance, we show calibration data with internal 83 m Kr and 37 Ar sources, and we detail the production of the latter as well as its introduction into the system. We finally compare the observed light and charge yields down to electronic recoil energies of 2.82 keV to predictions based on NEST v2.0.

Light Dark Matter Search with Ionization Signals in XENON1T

We report constraints on light dark matter (DM) models using ionization signals in the XENON1T experiment. We mitigate backgrounds with strong event selections, rather than requiring a scintillation signal, leaving an effective exposure of (22±3) tonne day. Above ∼0.4  keV_{ee}, we observe <1  event/(tonne day keV_{ee}), which is more than 1000 times lower than in similar searches with other detectors. Despite observing a higher rate at lower energies, no DM or CEvNS detection may be claimed because we cannot model all of our backgrounds. We thus exclude new regions in the parameter spaces for DM-nucleus scattering for DM masses m_{χ} within 3-6  GeV/c^{2}, DM-electron scattering for m_{χ}>30  MeV/c^{2}, and absorption of dark photons and axionlike particles for m_{χ} within 0.186-1  keV/c^{2}.

Search for Light Dark Matter Interactions Enhanced by the Migdal Effect or Bremsstrahlung in XENON1T

Direct dark matter detection experiments based on a liquid xenon target are leading the search for dark matter particles with masses above ∼5  GeV/c^{2}, but have limited sensitivity to lighter masses because of the small momentum transfer in dark matter-nucleus elastic scattering. However, there is an irreducible contribution from inelastic processes accompanying the elastic scattering, which leads to the excitation and ionization of the recoiling atom (the Migdal effect) or the emission of a bremsstrahlung photon. In this Letter, we report on a probe of low-mass dark matter with masses down to about 85  MeV/c^{2} by looking for electronic recoils induced by the Migdal effect and bremsstrahlung using data from the XENON1T experiment. Besides the approach of detecting both scintillation and ionization signals, we exploit an approach that uses ionization signals only, which allows for a lower detection threshold. This analysis significantly enhances the sensitivity of XENON1T to light dark matter previously beyond its reach.

Constraining the Spin-Dependent WIMP-Nucleon Cross Sections with XENON1T

We report the first experimental results on spin-dependent elastic weakly interacting massive particle (WIMP) nucleon scattering from the XENON1T dark matter search experiment. The analysis uses the full ton year exposure of XENON1T to constrain the spin-dependent proton-only and neutron-only cases. No significant signal excess is observed, and a profile likelihood ratio analysis is used to set exclusion limits on the WIMP-nucleon interactions. This includes the most stringent constraint to date on the WIMP-neutron cross section, with a minimum of 6.3×10^{-42}  cm^{2} at 30  GeV/c^{2} and 90% confidence level. The results are compared with those from collider searches and used to exclude new parameter space in an isoscalar theory with an axial-vector mediator.

First Results on the Scalar WIMP-Pion Coupling, Using the XENON1T Experiment

We present first results on the scalar coupling of weakly interacting massive particles (WIMPs) to pions from 1  t yr of exposure with the XENON1T experiment. This interaction is generated when the WIMP couples to a virtual pion exchanged between the nucleons in a nucleus. In contrast to most nonrelativistic operators, these pion-exchange currents can be coherently enhanced by the total number of nucleons and therefore may dominate in scenarios where spin-independent WIMP-nucleon interactions are suppressed. Moreover, for natural values of the couplings, they dominate over the spin-dependent channel due to their coherence in the nucleus. Using the signal model of this new WIMP-pion channel, no significant excess is found, leading to an upper limit cross section of 6.4×10^{-46}  cm^{2} (90% confidence level) at 30  GeV/c^{2} WIMP mass.

Dark Matter Search Results from a One Ton-Year Exposure of XENON1T

We report on a search for weakly interacting massive particles (WIMPs) using 278.8 days of data collected with the XENON1T experiment at LNGS. XENON1T utilizes a liquid xenon time projection chamber with a fiducial mass of (1.30±0.01)  ton, resulting in a 1.0 ton yr exposure. The energy region of interest, [1.4,10.6]  keV_{ee} ([4.9,40.9] keV_{nr}), exhibits an ultralow electron recoil background rate of [82_{-3}^{+5}(syst)±3(stat)]  events/(ton yr keV_{ee}). No significant excess over background is found, and a profile likelihood analysis parametrized in spatial and energy dimensions excludes new parameter space for the WIMP-nucleon spin-independent elastic scatter cross section for WIMP masses above 6  GeV/c^{2}, with a minimum of 4.1×10^{-47}  cm^{2} at 30  GeV/c^{2} and a 90% confidence level.

First Dark Matter Search Results from the XENON1T Experiment

We report the first dark matter search results from XENON1T, a ∼2000-kg-target-mass dual-phase (liquid-gas) xenon time projection chamber in operation at the Laboratori Nazionali del Gran Sasso in Italy and the first ton-scale detector of this kind. The blinded search used 34.2 live days of data acquired between November 2016 and January 2017. Inside the (1042±12)-kg fiducial mass and in the [5,40]  keV_{nr} energy range of interest for weakly interacting massive particle (WIMP) dark matter searches, the electronic recoil background was (1.93±0.25)×10^{-4}  events/(kg×day×keV_{ee}), the lowest ever achieved in such a dark matter detector. A profile likelihood analysis shows that the data are consistent with the background-only hypothesis. We derive the most stringent exclusion limits on the spin-independent WIMP-nucleon interaction cross section for WIMP masses above 10  GeV/c^{2}, with a minimum of 7.7×10^{-47}  cm^{2} for 35-GeV/c^{2} WIMPs at 90% C.L.

Search for Electronic Recoil Event Rate Modulation with 4 Years of XENON100 Data

We report on a search for electronic recoil event rate modulation signatures in the XENON100 data accumulated over a period of 4 yr, from January 2010 to January 2014. A profile likelihood method, which incorporates the stability of the XENON100 detector and the known electronic recoil background model, is used to quantify the significance of periodicity in the time distribution of events. There is a weak modulation signature at a period of 431_{-14}^{+16} day in the low energy region of (2.0-5.8) keV in the single scatter event sample, with a global significance of 1.9σ; however, no other more significant modulation is observed. The significance of an annual modulation signature drops from 2.8σ, from a previous analysis of a subset of this data, to 1.8σ with all data combined. Single scatter events in the low energy region are thus used to exclude the DAMA/LIBRA annual modulation as being due to dark matter electron interactions via axial vector coupling at 5.7σ.

Temperature elevation during simulated polymethylmethacrylate (PMMA) cranioplasty in a cadaver model

The aims of this study were to: (i) obtain temperature measurements during in vitro polymerisation of polymethylmethacrylate (PMMA) disks of a range of thicknesses; and (ii) obtain tissue temperature measurements at various locations within a skull defect during a simulated PMMA cranioplasty procedure using a cadaver. In vitro, higher temperatures were recorded with increasing PMMA thickness. During the simulated cranioplasty, the maximum temperature was observed inside the PMMA sample, with nearby tissues being exposed to temperatures of greater than 50 degrees C over prolonged periods. There is conflicting information in the literature concerning the sensitivity of brain tissue and bone to elevated temperatures. Preoperatively fabricated PMMA cranioplasty prostheses are recommended.

3D surface accuracy of CAD generated skull defect contour

The creation of a satisfactory cosmetic outcome in the repair of cranial defects relies on manual skill. However, computer aided design is gaining acceptance in the creation of custom cranial implants. The purpose of this work is to demonstrate the accuracy of a CAD generated skull defect contours using 3D difference maps. 3D multi-slice CT scanning was carried out on a life size plastic skull. Surface models were generated of the original skull and of temporofrontal and parietal defects. Surface contours were interpolated towards the centre of the defect from the edges where it was blended. The CAD contour deviation ranged from 0.0 mm to 2.0 mm with 80% of the total defect area less than 0.66 mm as measured by difference maps. CAD techniques can be used to produce contours for the repair of cranial defects with minimum deviation from the original skull contour. This enables accurate design and production of cranial implants.

"Virtual unwrapping" of a mummified hand

The purpose of this work is to demonstrate the feasibility of medical virtual reality technologies in the investigation of a mummified hand. The Ulster Museum obtained the mummy hand, which originated from Thebes, without any identifying information. The mummified hand was investigated using conventional X-ray and 3D multi-slice Computed Tomography (CT). Imaging revealed a range of fractures of the wrist, metacarpals and phalanges whilst 3D CT demonstrated internal structures using volume rendering. The absence of any features of bone healing at the fracture sites would imply that they occurred just prior to death or in the mummified state possibly during excavation. Conventional X-ray imaging indicated that the hand, although small, was likely to have originated from an adult. Medical imaging and virtual reality display will enable us to produce a rapid prototyped model using fused deposition technology. Therefore, further paleopathological research can be performed on the replica without the need to handle the original specimen.

CAD generated mold for preoperative implant fabrication in cranioplasty

Intraoperative fabrication of acrylic cranial implants may be difficult and will increase operation time. In addition forming implants directly on the defect, intracranial tissues are exposed to heat of polymerization and residual monomer, that occurs, when autopolymerizing methyl methacrylate is used intraoperatively. Furthermore the cosmetical result may be unacceptable. Preoperatively formed acrylic implants may reduce these disadvantages compared to conventional techniques in cranioplasty. We will present methods for preoperative fabrication of cranial implants for a cadaver specimen. Implants were fabricated using a Rapid prototyping (RP) models of the skull built by Fused Deposition Modeling (FDM). In addition a mold of the defect was generated by CAD techniques, that can serve as a template for implant design.

Surface wear on cervical restorations and adjacent enamel and root cementum caused by simulated long-term maintenance therapy

BACKGROUND

In an in vitro study, the surface wear on cervical restorations and adjacent enamel and root cementum caused by different tooth-cleaning methods in simulated long-term therapy was investigated.

METHODS

Cervical restorations of amalgam (Oralloy), modified composite resin (Dyract), glass-ionomer cement (ChemFill Superior), and composite (Tetric) were instrumented by POL (polishing), CUR+POL (curette and polishing), US+POL (ultrasonic device with polishing) and the polishing agents Cleanic and Proxyt in a computer-controlled test bench. Treatment time corresponding to a real-time period of 5 or 10 years. Substance loss from instrumented surfaces was measured with a digital gauge. A three-way anova was used in the statistical evaluation.

RESULTS

The results showed that POL led to slight substance loss, which was greater using Cleanic (27 microm) than Proxyt (5 microm). CUR+POL produced a significantly greater substance loss than did US+POL, with 186 microm versus 35 microm on glass-ionomer cement, respectively, and 123 microm versus 18 microm, respectively, on root cementum, followed by composite (111 microm versus 27 microm, respectively), polyacid modified composite resin/compomer (89 microm versus 36 microm), amalgam (75 microm versus 19 microm), and enamel (32 microm versus 23 microm).

CONCLUSIONS

As opposed to the use of US+POL or POL, substance loss on cervical restorations and especially root cementum must be expected to result from tooth-cleaning during long-term maintenance treatment using CUR+POL.

Medical biomodelling in surgical applications: results of a multicentric European validation of 466 cases

The study started in September 1999 and ended in April 2002. It is based on a questionnaire [www.phidias.org] assessing case-related questions due to the application of stereolithographic models. Each questionnaire contains over 50 items. These variables take into account diagnosis, indications and benefits of stereolithographic models with view on different steps of the surgical procedures: preoperative planning, intraoperative application and overall outcome after surgical intervervention. These questionnaires were completed by the surgeons who performed operation. Over the time course of our multicentric study (30 months), we evaluated 466 cases. The study population consists of n=231 male and n= 235 female patients. 54 surgeons from 9 European countries were involved. There are main groups of diagnosis that related to the use of a model. Most models were used in maxillofacial surgery. The operative planning may help to determine the resection line of tumor and optimize reconstructive procedures. Correction of large calvarian defects can be simulated and implants can be produced preoperatively. Overall in 58 % of all cases a time- saving effect was reported. The study strongly suggests, that medical modeling has utility in surgical specialities, especially in the craniofacial and maxillofacial area, however increasingly in the orthopedic field. Due to our results, medical modeling optimizes the preoperative surgical planning. Surgeons are enabeled to perform realistic and interactive simulations. The fabrication of implants, its design and fit on the model, allow to reduce operation time and in consequence risk and cost of operation. In addition, the understanging of volumetric data is improved, especially if medical models are combined with standart imaging modalities. Finally, surgeons are able to improve communication between their patientents and colleagues.

In vitro radiosensitivity measured in lymphocytes and fibroblasts by colony formation and comet assay: comparison with clinical acute reactions to radiotherapy in breast cancer patients

PURPOSE

To compare colony-forming and comet assays on fibroblasts and lymphocytes of 32 breast cancer patients irradiated after breast-conserving operations and to correlate the results with acute clinical radiation reactions in the skin.

MATERIAL AND METHODS

Skin fibroblasts were isolated and cultivated before radiotherapy and lymphocytes were drawn prior to the first and directly after the final external irradiation. The colony-forming assay was performed with fibroblasts and the comet assay with lymphocytes and fibroblasts of breast cancer patients according to standard protocols. The clinical radiation reactions of the patients were graded according to the RTOG system.

RESULTS

No significant correlation (p =0.09) was detected between clinical acute skin reactions and the in vitro clonogenic data in fibroblasts. Results of the comet assay in lymphocytes, however, showed a significant correlation (p <0.05) with the clinical data when patients were divided into two groups with average and elevated acute reactions. Apart from initial damage, fibroblasts did not show significant differences between the two patient groups. Repeated comet assays in lymphocytes of the same patient drawn before treatment and before and after external radiotherapy demonstrated good reproducibility of the test and no significant impact of preceding radiation treatment. There was a good correlation (r =0.65) between the comet assay results in fibroblasts and lymphocytes of the same individual.

CONCLUSIONS

In this cohort of patients, a significant correlation between the in vitro results of the comet assay in lymphocytes and clinical acute reactions was detected. The results of the comet assay and of fibroblast colony formation did not correlate with in vitro radiosensitivity.

Stereotactic radiotherapy of targets in the lung and liver

BACKGROUND

Stereotactic irradiation of extracranial targets offers a non-invasive treatment modality for patients with localized tumors, which are not amenable for surgery or other invasive approaches because of age or impaired medical condition. The purpose of the study was the evaluation of the method to achieve local control of irradiated targets in relation to treatment toxicity.

PATIENTS AND METHODS

Irradiation was performed as hypofractionated treatment in three fractions of 10 Gy each, normalized to the PTV enclosing 65% isodose with patient fixation in a stereotactic body frame. The isocenter was localized by stereotactic coordinates. Targets were circumscribed tumors in the lung (n = 27) and liver (n = 24) not amenable for other treatment modalities: primary lung cancer (n = 12), local recurrences of lung cancer (n = 4), lung metastases (n = 11), liver metastases (n = 23) and one cholangiocellular carcinoma. Median CTV/PTV for targets in the lung was 57/113 cm3 (min/max 5-277 cm3/17-343 cm3) and for targets in the liver 50/102 cm3 (min/max 9-516 cm3/42-772 cm3). Median follow-up for targets in the lung was 8 months (2-33) and 9 months (2-28) for liver targets. Local control was defined as complete or partial remission and stable disease, measured by repeated CT scans after 6 weeks and in 3 months intervals. Treatment toxicity was evaluated according to the WHO score.

RESULTS

Crude local control was 85% for pulmonary targets and 83% for hepatic targets. Actuarial local control after 1 and 2 years was 76% and 76% for lung tumors and 76% and 61% for liver tumors. Actuarial overall patient survival was 48% after 1 year and 21% after 2 years for targets in the lung and 71% and 43% for targets in the liver. No acute grade 3-5 side effects were observed. Serious late toxicity occurred in two patients: a chronic ulceration of the esophagus at a target close to the mediastinum after 3 months (grade 3) and fatal bleeding from the pulmonary artery after 9 months (grade 5) in a previously irradiated patient. It remained unclear, whether the bleeding was a side effect of irradiation or due to tumor infiltration.

CONCLUSION

Hypofractionated stereotactic irradiation of targets in the lung and liver is a locally effective treatment with actuarial local control rates of 76% after 1 year and 61-76% after 2 years without relevant acute toxicity. Severe late toxicity did not occur, if targets close to the mediastinum were avoided.

Anatomical accuracy in medical 3D modeling

In complex surgery, medical modeling has become an accepted tool for diagnosis, simulation and the planning of surgical interventions [1]. However, the question concerning the accuracy of the model, i.e. the equivalence between the model itself on the one hand and the original anatomical situation on the other hand, remains unanswererd in the current literature.

The in vitro colony assay: a predictor of clinical outcome

PURPOSE

To determine the predictive power of an in vitro colony assay on the clinical normal-tissue complication rate.

MATERIAL AND METHODS

Primary skin fibroblasts from 88 individuals were generated from the skin biopsies of patients who received a standardized radiotherapy. Tissue was cultured for three to six passages, irradiated with doses between 1 and 8 Gy under defined conditions, seeded and finally the colonies were stained and counted after 10-14 days. The survival curves were fitted by the L-Q model and the SF2, alpha/beta and plating efficiency were calculated.

RESULTS

The parameters SF2 and plating efficiency were stable throughout the 4-year test period. Intra-individual differences between repeated experiments were significantly lower than inter-individual test results. For the observed acute skin and late normal-tissue reactions other than skin the in vitro parameter SF2 correlated significantly (p<0.005). For late skin reactions this correlation was not found.

DISCUSSION

In contrast to other publications, a clear correlation was found between the in vitro test results and clinically observed early reactions. The lack of correlation for late skin reactions suggests that the combination of intrinsic radiation sensitivity and exogenous factors may alter the clinically observed reaction of certain tissues to a different extent.

Stereotactic radiotherapy of extracranial targets: CT-simulation and accuracy of treatment in the stereotactic body frame

BACKGROUND AND PURPOSE

Evaluation of set-up accuracy and analysis of target reproducibility in the stereotactic body frame (SBF), designed by Blomgren and Lax from Karolinska Hospital, Stockholm. Different types of targets were analyzed for the risk of target deviation. The correlation of target deviation to bony structures was analyzed to evaluate the value of bones as reference structures for isocenter verification.

MATERIALS AND METHODS

Thirty patients with 32 targets were treated in the SBF for primary or metastatic peripheral lung cancer, liver metastases, abdominal and pelvic tumor recurrences or bone metastases. Set-up accuracy and target mobility were evaluated by CT-simulation and port films. The contours of the target at isocenter level, bony structures and body outline were compared by matching the CT-slices for treatment planning and simulation using the stereotactic coordinates of the SBF as external reference system. The matching procedure was performed by using a 3D treatment planning program.

RESULTS

Set-up accuracy represented by bony structures revealed standard deviations (SD) of 3.5 mm in longitudinal, 2.2 mm in anterior-posterior and 3.9 mm in lateral directions. Target reproducibility showed a SD of 4.4 mm in longitudinal, 3.4 mm ap and 3.3 mm in lateral direction prior to correction. Correlation of target deviation to bones ranged from 33% (soft tissue targets) to 100% (bones).

CONCLUSION

A security margin of 5 mm for PTV definition is sufficient, if CT simulation is performed prior to each treatment to correct larger target deviations or set-up errors. Isocenter verification relative to bony structures is only safe for bony targets but not for soft tissue targets.

[Results of radiotherapy in rectal carcinoma]

Adjuvant combined radio-chemotherapy in rectal cancer is indicated in stage UICC II and III (pT3/4 and/or pN+) without distant metastases (exception: resectable metastases of the liver). Radiotherapy alone improves local control in the pelvis. A statistical significant improvement of survival is only achievable in combination with systemic chemotherapy. In Germany neo-adjuvant, conventional fractionated radio-chemotherapy over five weeks is applied in patients with surgically inoperable tumors to achieve a "down-staging" with improvement of resectability. Neo-adjuvant radiotherapy of operable rectal cancer in five fractions of high single doses within one week has revealed a statistical significant improvement of survival if compared to surgery alone in the Swedish rectal cancer trial, but is not standard in Germany yet. The influence of technical advances in surgery as total mesorectal excision (TME) on indications of adjuvant therapy is evaluated in prospective randomized studies at this time.

Recent developments in cornea transplantation (1997-1999)

Between 1997 and 1999 a steady increase in cornea donations was achieved, but the number of transplantations remained stable because many grafts did not pass quality control. Intermediate organ culture of entire bulbi was examined as a possible solution to reduce post-mortem times and increase suitability for transplantation.

Unlabeled helper oligonucleotides increase the in situ accessibility to 16S rRNA of fluorescently labeled oligonucleotide probes

Target site inaccessibility represents a significant problem for fluorescence in situ hybridization (FISH) of 16S rRNA with oligonucleotide probes. Here, unlabeled oligonucleotides (helpers) that bind adjacent to the probe target site were evaluated for their potential to increase weak probe hybridization signals in Escherichia coli DSM 30083(T). The use of helpers enhanced the fluorescence signal of all six probes examined at least fourfold. In one case, the signal of probe Eco474 was increased 25-fold with the use of a single helper probe, H440-2. In another case, four unlabeled helpers raised the FISH signal of a formerly weak probe, Eco585, to the level of the brightest monolabeled oligonucleotide probes available for E. coli. The temperature of dissociation and the mismatch discrimination of probes were not significantly influenced by the addition of helpers. Therefore, using helpers should not cause labeling of additional nontarget organisms at a defined stringency of hybridization. However, the helper action is based on sequence-specific binding, and there is thus a potential for narrowing the target group which must be considered when designing helpers. We conclude that helpers can open inaccessible rRNA regions for FISH with oligonucleotide probes and will thereby further improve the applicability of this technique for in situ identification of microorganisms.

Phylogeny and diversity of Achromatium oxaliferum

Achromatium oxaliferum was first described in 1893 by Schewiakoff as an unusually large bacterium living in freshwater sediments. Up to now no pure culture is available. Physical enrichments of achromatia collected from the acidic Lake Fuchskuhle, which houses a peculiar, smaller variety, and the neutral Lake Stechlin were investigated by the cultivation-independent rRNA approach. PCR in combination with cloning and sequencing was used for the retrieval of 24 partial and 4 nearly full-length 16S rRNA sequences that formed two distinct phylogenetic clusters. Fluorescence-in-situ-hybridization (FISH) with four 16S rRNA-targeted oligonucleotide probes unambiguously assigned the different sequences to either regular, large A. oxaliferum cells or to the smaller Lake Fuchskuhle population, tentatively named "A. minus". The two Achromatium sp. 16S rRNA sequence clusters form a stable deep branch in the gamma subclass of the class Proteobacteria. The closest cultivated relatives are Chromatium vinosum, Rhabdochromatium marinum and Ectothiorhodospira halophila with 16S rRNA similarities of 86.2 to 90.5%. Profound differences in the population structure of achromatia were revealed in the two lakes by FISH. In one sample from Lake Stechlin three genotypes could be visualized, and 49% of the cells were assigned to A. oxaliferum clone AST01, 28% to Achromatium sp. genotype AFK192/AFK433 and 23% to Achromatium sp. genotype AFK192/AST433. In contrast, a morphologically and phylogenetically homogeneous population of "A. minus". was present in Lake Fuchskuhle.

[Locally restricted dose escalation in radiotherapy of primary advanced and recurrent rectal cancers]

PURPOSE

Prognosis in patients with resected rectal carcinomas is correlated to local tumor control. Percutaneous (EBRT) and intraoperative boost irradiation (IORT) can improve local control. The aim of this study was to analyse the role of locally restricted dose escalation and the possibility to integrate IORT in a multi-modality adjuvant treatment approach.

PATIENTS AND METHODS

A total of 128 and 71 patients with primary and recurrent disease were eligible for analysis. More than 60% of patients suffered from a stage III carcinoma. Between 26.3 and 38.8% of patients revealed lymphangiosis carcinomatosa in pathohistological examination. A dose of 40.2 Gy was applied using multiple field techniques. Either a percutaneous boost dose of 18.3 Gy or an intraoperative boost dose of 12.1 Gy was given in 97 and 62 patients. 40 patients with non-resectable recurrent carcinomas were treated with radiotherapy alone. In respectively 67.4% and 52.6% of IORT patients (primary and recurrent) a simultaneous chemotherapy was given, whereas only 16.5% and 8.3% of patients with EBRT alone had additional chemotherapy.

RESULTS

Five-year overall survival was 64% and 41% in stage II and III (T2-3) carcinomas. All patients with stage III (T4) carcinomas died within 3 years. Overall the local failure rate was correlated to tumor stage (12.7 to 19.7%) and lymphangiosis carcinomatosa (12.5 vs. 22.9%). In patients with radiotherapy alone, local failure rate decreased with increasing irradiation dose (32%/40 to 48 Gy, 25%/49 to 56 Gy, 20.5%/57 to 66 Gy 0%/40.2 Gy + IORT). The overall 2-year survival was significantly improved after IORT and IORT plus simultaneous chemotherapy in both primary and recurrent disease. Perioperative morbidity was not increased. The toxicity of the multi-modality approach with IORT was low and acceptable.

CONCLUSION

The local tumor control in rectal carcinoma after radiotherapy was dose dependent, IORT could be integrated in an adjuvant multi-modality treatment concept, without increasing morbidity. Local failure rate could be markedly reduced.

[Three-dimensional planned radiotherapy in rectal cancer. Feasibility study and preliminary clinical results]

PURPOSE

Since 1991 the use of three-dimensional planned radiation therapy for rectal cancer was evaluated as a part of a clinical project funded by the Deutsche Krebshilfe at the Radiological Department of the University of Heidelberg. First clinical experiences are reported.

PATIENTS AND METHODS

32 patients who were irradiated loco-regional for rectal cancer were analysed retrospectively. Radiation therapy techniques: patient's position was prone by the use of a belly board. Three-dimensional treatment (3D) planning system was voxelplan. The radiation therapy was started using a 3-field-box technique modified by 3D-technique after 22 to 42 Gy, depending on therapeutic concept.

RESULTS

On average 92% of the planning target volume were encompassed with the 80% isodose. The average maximum dose was 108% (isocenter = 100%), of the small bowel volume received less than 34% of the dose, 70% of the bladder volume less than 40% respectively. Total average dose was 52.4% Gy. Irregular fields were used in all patients, a non-coplanar field was used to optimize dose-distribution in 41% of the patients, 21 patients received chemotherapy simultaneously. Acute side effects according to gastrointestinal tract reached grade 1 (WHO) in 9 patients, grade 2 in 2 patients. Side effects according to bladder reached grade 1 in 5 patients grade 2 in 1 patient respectively. In 4 patients suffered from acute side effects concerning the bladder. In one patient acute side effects grade 1 concerning gastrointestinal tract was observed. Portal films were analysed to evaluate precision of radiation therapy. On average the error was 3.1/4.5/4.0 mm in the x/y/z direction respectively. The standard deviation was 4.4/6.8/6.3 mm for x/y/z respectively. A median time of 2 hours was necessary for all planning procedures.

CONCLUSIONS

Three-dimensional treatment planning optimizes dose-distribution in a relevant number of patients. Its clinical use for treatment of large targets or in order to applicate high doses is justified. Planning target volume should cover the clinical target volume with a margin of 1.5 cm.

Sensitivity changes of photoreceptor cells of Hirudo medicinalis caused by changes in extracellular calcium concentration

Extracellular recordings from the vacuole of photoreceptor cells of Hirudo medicinalis L. were performed using microelectrodes. The cells were adapted by white light flashes given at constant intervals (20 s). Response height versus relative intensity curves obtained from the same cell in physiological saline (PS) and in bathing solutions of either a) lowered calcium contents (2 micron/1 or less) or b) raised calcium contents (15 mM/1) were compared. The cells' adaptation state in PS was operationally defined by the ratio Q = hA/hs where hA is the response height evoked by the adapting flashes, and hs is the corresponding saturation response height. Sensitivity changes were measured by the half saturation intensity shift. Lowering extracellular calcium resulted in: 1. The response height increased and the shape of the response became more rounded and prolonged. 2. The total resistance between the vacuole and outside decreased from 8.2 +/- 1.4 Momega (n = 6) in PS to 4.6 +/- 0.4 Momega (n = 5). The resistance was independent of the cells' adaptation state. 3. A change of the cells' sensitivity occurred either in direction to light adaptation or in direction to dark adaptation. It depended functionally on the ratio Q: a) if Q was less or equal to about 0.6 the cells' sensitivity increased. b) if Q was greater than 0.6 the cells' sensitivity diminished. Raising extracellular calcium decreased the sensitivity of all cells tested independent of their adaptation states in PS. The results can be interpreted under the assumptions that 1. the sensitivity of leech photoreceptor cells is inversely proportional to the intracellular free calcium concentration and 2. intracellular calcium can interact with extracellular calcium in relatively dark adapted cells whereas in relatively light adapted cells the raise of intracellular free calcium is mainly effected by a release from intracellular stores. It is assumed that a Q value of about 0.6 separates relatively light adapted cells from relatively dark adapted cells.

Properties of bilayer membranes in the presence of dipicrylamine. A comparative study by optical absorption and electrical relaxation measurements

In order to test the question if a pool of lipophilic ions may exist in black lipid membranes which cannot be detected by electrical relaxation measurements we have performed simultaneously measurements of the optical absorption of a lipophilic ion. The absorbance of membrane-bound dipicrylamine at 410 nm was measured with a sensitive spectrophotometer which can detect absorbance changes larger than or equal to 4-10(-5). A minimal concentration of about 6-10(11) dipicrylamine ions per cm2 of the membrane could be detected with this instrument. The dipicrylamine concentration in the membrane obtained with the optical method Ntopt is compared with the concentrations Ntel obtained from simultaneous electrical relaxation meausurements. Ntopt and Ntel agreed at low dipicrylamine concentrations (10(-8)--10(-7) M in the aqueous phase) and showed saturation at higher concentrations (up to 5-10(-6) M). In the saturation range Ntopt was maximally four times higher than Ntel. The significance of this difference is discussed together with general aspects of the saturation phenomenon.

Calcium ion-flux across phosphatidylcholine membranes mediated by ionophore A23187

The antibiotic A23187 carries Ca2+ across Müller-Rudin membranes made from 1,2-dierucoyl-sn-glycero-3-phosphocholine and n-decane. The conductance of the membranes is not increased by the Ca2+-transport. The flux depends linearly on Ca2+ concentration and ionophore concentration (above pH 6). It increases with increasing pH, approximately by a factor of 4-5 between pH 6 and pH 8. Maximal Ca2+-fluxes of about 10(-10) mol-cm-2-s-1 were found. A counter transport of H+ could not be detected. The complex formation between A23187 and Ca2+ in egg phosphotidylcholine vesicles was studied spectroscopically. The results are consistent with the formation of a 2:1 complex. Optical absorption measurements on single phophatidylcholine membranes were used to calculate the concentration of membrane-bound ionophore A23187.