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Biomedical subjects

D Lohmann

Publications and source records attributed to D Lohmann.

At least 19 recordsLinked to original sources
PubMed2006

[Retinoblastoma].

Retinoblastomas are the most frequent intraocular tumors in childhood. Untreated, the tumor is almost always fatal. Using a multidisciplinary approach combining the efforts of ophthalmologists, radiation oncologists, pediatric oncologists and geneticists a survival rate of more than 95% can be achieved. Molecular genetic research on the origin of retinoblastomas has substantially helped in our understanding of the origin of malignant tumors in general, as well as to the key role of the Rb-1 gene as a tumor suppressor.

Diagnosis, Differential↗
PubMed2003

Polymer design for corneal epithelial tissue adhesion: pore density.

A porous polymer is required to sustain corneal epithelial tissue on the anterior surface of an implantable contact lens (corneal onlay). Porosity creates topography on the polymer surface and, if defined, this can be manipulated to elicit a particular tissue response. Previous work identified pores of 100-nm diameter to be the critical size of a discontinuity in a polymer surface to facilitate the migration, stratification, and sustained adhesion of corneal epithelial tissue. Now we address the issue of pore density. Corneal epithelial tissue was grown for 21 days on nonporous polycarbonate and polycarbonate track-etched with pores 100-nm diameter with pore densities ranging from 0.27 and 14.4% of the total polymer surface area. Histology was used to score epithelial structure, and electron microscopy was used to quantitate the formation of adhesive structures (basal lamina and hemidesmosomes) at the tissue-polymer interface. Data showed that epithelial tissue stratified and epithelial adhesive structures formed on polycarbonate surfaces with pore densities between 0.52 and 14.4% inclusive. This means that epithelial tissue can be maintained on a polymer where up to 14.4% of the surface is dedicated to small discontinuities in the form of pores 100-nm diameter. These figures can be used to specify the design of a polymer for applications requiring epithelial cover.

Animals↗
PubMed2002

Efficiency of rotary nickel-titanium FlexMaster instruments compared with stainless steel hand K-Flexofile--Part 1. Shaping ability in simulated curved canals.

AIM: The purpose of this study was to compare the shaping ability of FlexMaster rotary nickel-titanium instruments with stainless steel hand K-Flexofiles. This part of the two-part report describes the efficiency of these two instruments in simulated curved root canals. METHODOLOGY: Simulated 28 degree- and 35 degree-curved canals were prepared by the FlexMaster instruments with a rotational speed of 250 rpm using a crown-down preparation technique. and by the K-Flexofiles using a reaming motion (n = 24 canals in each case). All canals were prepared up to size 35. The pre- and post-instrumentation images were recorded and assessment of the canal shape was completed with a computer image analysis program. The material removal was measured at 20 measuring points, beginning 1 mm away from the apex. Incidence of canal aberrations, preparation time,changes of working length and instrument failures were also recorded. RESULTS: In comparison with stainless steel K-Flexofiles, the rotary FlexMaster instruments achieved bet-ter canal geometry, showed less canal transportation and created fewer canal aberrations in both the canal types. Two FlexMaster instruments were separated, and 15 FlexMaster instruments and 11 K-Flexofiles were permanently deformed during preparation. However, these differences were not significant (P > 0.05). Between both the canal types, FlexMaster was significantly faster (P < 0.001) than K-Flexofiles. Both instruments maintained a good working distance. CONCLUSIONS: FlexMaster instruments prepared curved canals rapidly, and with minimal transportation towards the outer aspect of the curve.

Dental Instruments↗
PubMed2002

Efficiency of rotary nickel-titanium FlexMaster instruments compared with stainless steel hand K-Flexofile--Part 2. Cleaning effectiveness and instrumentation results in severely curved root canals of extracted teeth.

AIM: To determine the cleaning effectiveness and the shaping ability of FlexMaster nickel-titanium rotary instruments and stainless steel hand K-Flexofiles during the preparation of curved root canals in extracted human teeth. METHODOLOGY: A total of 48 root canals with curvatures ranging between 25 degrees and 35 degrees were divided into two groups of 24 canals. Based on radiographs taken prior to the instrumentation with the initial instrument inserted into the canal, the groups were balanced with respect to the angle and the radius of canal curvature. Canals were prepared by FlexMaster instruments using a crown-down preparation technique or by K-Flexofiles using a reaming working motion up to size 35. After each instrument, the root canals were flushed with 5 mL of a 2.5% NaOCl solution and at the end of instrumentation with 5 mL of NaCl. Using the pre- and post-instrumentation radiographs, straightening of the canal curvatures was determined with a computer image analysis program. After splitting the roots longitudinally, the amount of debris and smear layer were quantified on the basis of a numerical evaluation scale, using a scanning electron microscope. RESULTS: Completely cleaned root canals were not found with any of the two instruments. In general, K-Flexofiles resulted in significantly less debris(P < 0.001) and less smear layer (P < 0.05) than Flex-Master instruments, but these differences were not significant in the apical third of the canals (P > 0.05). FlexMaster instruments maintained the original canal curvature significantly better (P < 0.0001) than K-Flexofiles. No significant differences were detected between the instruments (P > 0.05) for the time taken to prepare the canals. CONCLUSIONS: Under the conditions of this study, K-Flexofiles allowed significantly better canal cleaning than FlexMaster instruments. FlexMaster instruments maintained the original curvature significantly better.

Dental Instruments↗
PubMed1999

Detection of homozygous deletions in tumors by hybridization of representational difference analysis (RDA) products to chromosome-specific YAC clone arrays.

Representational difference analysis (RDA), a subtractive hybridization method that enriches differences between complex genomes, can be used to isolate fragments deleted in tumor genomes. Usually, most of the clones obtained by this approach result from polymorphic fragments. Therefore, identification of homozygously deleted fragments, which can indicate the presence of tumor suppressor loci, is often tedious. To overcome this limitation, we devised a novel strategy in which labeled RDA products are hybridized in toto against membranes spotted with YAC clones covering a region of interest. In such a way, identified YAC clones provide positional information on homozygous deletions and loss of heterozygosity (LOH) regions. We have tested this approach with a tumor known to have a homozygous deletion within a region of LOH on chromosome 13. RDA was performed using representations generated with restriction enzymes Bgl II, Nco I and Xba I, and the difference products of each experiment were separately hybridized to chromosome 13 YAC filters. When collating the map positions of positive YACs from three different RDA experiments a cluster of hits clearly identified the region on chromosome 13 which comprised the homozygous deletion. This shows that our novel approach can be effective.

Bacterial Proteins↗
PubMed1999

Human TRH-degrading ectoenzyme cDNA cloning, functional expression, genomic structure and chromosomal assignment.

Thyrotropin-Releasing Hormone (TRH) is an important extracellular signal substance that acts as a stimulator of hormone secretion from adenohypophyseal target cells and fulfills many criteria for the function of a neuromodulator/neurotransmitter within the central and peripheral nervous systems. The inactivation of TRH-signals is catalysed by a highly specific ectoenzyme. Here, we characterize the human TRH-degrading ectoenzyme (TRH-DE) by primary sequence, functional expression, genomic structure and chromosomal assignment. By screening a cDNA-library constructed from human lung, 5.7 kb of cDNA were identified. The longest open reading frame predicts a type II integral membrane protein of 117 kDa. The extracellular domain contains the HEXXH + E motif that is characteristic of a certain family of Zn-dependent aminopeptidases. Within this family, the sequences of human and rat TRH-DE reveal an unusual high degree of conservation (96% identical residues). Specific enzymatic activity was observed after transfecting COS-7 cells with human TRH-DE cDNA yielding a Km for TRH hydrolysis of 29.7 microM. Northern blot analysis demonstrated a restricted tissue distribution with highest transcript levels in the brain. Using fluorescent in situ hybridization with the cDNA and a genomic lambda clone, respectively, we localized the TRH-DE gene to the long arm of human chromosome 12. Five independent P1 artificial chromosome clones were required to span the complete cDNA sequence and revealed that it is distributed on 19 exons. Interspecies Southern analysis suggests that the gene is present as a single copy in human, monkey, rat, mouse, dog, bovine, rabbit and chicken DNA. All of these data further the notion that the TRH-DE is not an ordinary enzyme but a specific neuropeptidase that has been highly conserved among species.

Amino Acid Sequence↗
PubMed1998

[Genetic and molecular diagnostics in retinoblastoma].

Retinoblastoma is a childhood malignancy of the eye. Almost all patients with familial or bilateral disease suffer from the hereditary form of the disease that is caused by germline mutations in one allele of the RB1 gene. Tumor development is initiated by the loss of the second RB allele in a retinal progenitor cell. Most patients with isolated unilateral disease have nonhereditary retinoblastoma and thus do not carry a mutant allele in their germline. In no patient, the presence of a germline mutation can be excluded clinically. Consequently, relatives are at an increased risk for retinoblastoma. Molecular testing, however, enables accurate risk prediction provided that samples are available. In some relatives an increased risk can be excluded by segregation analysis. Most often, however, identification of the disease causing mutation is necessary for accurate risk prediction. Mutation analysis, which is impeded by the size and complexity of the RB gene, is facilitated by use of efficient screening methods. Using these methods, the oncogenic mutation can be identified in most patients. Therefore, predictive testing has become an integral part of contemporary management of retinoblastoma.

Female↗
PubMed1995

Genotype-phenotype correlation in a series of 167 deletion and non-deletion patients with Prader-Willi syndrome.

A total of 167 patients with Prader-Willi syndrome (PWS) was studied at the clinical and molecular level. Diagnosis was confirmed by the PW71 methylation test. Quantitative Southern blot hybridizations with a probe for the small nuclear ribonucleoprotein N were performed to distinguish between patients with a deletion (116 patient or 69.5%) and patients without a deletion (51 patients or 30.5%). These two types of patients differed with respect to the presence of hypopigmentation, which was more frequent in patients with a deletion (52%) than in patients without (23%), and to average birth weight of females and males, which was lower in patients with a deletion than in patients without. Newborns with PWS had a lower birth weight and length at term, but normal head circumference in comparison with a control group. This finding aids the identification of the neonatal phenotype. In addition, our data confirm an increased maternal age in the non-deletion group.

Adolescent↗
PubMed1994

Frequency and parental origin of hypermethylated RB1 alleles in retinoblastoma.

The retinoblastoma susceptibility (RB1) gene contains an unmethylated CpG-rich island at its 5' end. Using methylation-sensitive restriction enzymes, we have investigated the methylation status of this island in 21 sporadic unilateral retinoblastomas and 30 hereditary retinoblastomas. Three sporadic unilateral tumors were found to have hypermethylated RB1 alleles. In two tumors, the paternal allele was methylated, whereas the maternal allele had been lost. Cultured cells from one of these tumors were studied by the reverse transcription polymerase chain reaction and found to have a reduced level of RB1 mRNA. The third tumor had retained constitutional heterozygosity, and the paternal allele was specifically methylated. The combined data from previously published reports and from this study show that hypermethylation of the RB1 gene occurs in 13% of sporadic unilateral tumors and may reduce gene activity.

Base Sequence↗
PubMed1994

Inflammatory islet damage in patients bearing HLA-DR 3 and/or DR 4 haplotypes does not lead to islet autoimmunity.

The hypothesis was tested that islet autoimmunity is induced by ongoing islet cell destruction in subjects with susceptibility genes HLA-DR 3 and/or DR 4. Sixty-one patients with confirmed chronic pancreatitis were analysed, 30 of whom expressed HLA-DR 3 and/or DR 4. Electron microscopy studies in 10 patients showed that the inflammatory process also affected islets, as recognisable from islet cell lysis, intrainsular fibrosis and immune cell infiltrates. None of the sera tested contained any of three markers of islet autoimmunity, ICA, IAA or GAD antibodies. A correlation was seen between the loss of exocrine function, as determined by the ALTAB-test, and of beta-cell function, as determined by the C-peptide response to i.v. glucagon. However, there was no preferential loss of beta-cell function in patients with HLA-DR 3 and/or DR 4. We conclude that islet cell destruction occurs during chronic pancreatitis, but does not trigger islet autoimmunity, even in the presence of HLA-DR 3 and/or DR 4.

Adult↗
PubMed1993

Detection of HER-2 oncogene amplification in breast cancer by differential polymerase chain reaction from single cryosections.

Amplification of genomic DNA encoding oncogenes such as HER-2 (syn.c-erbB2/c-neu) may be substantially involved in the initiation and progression of breast cancer. In order to refine and facilitate the quantitative analysis of HER-2 amplification in breast cancer, differential polymerase chain reaction (PCR) was performed on DNA derived from single cryosections of tumor tissue. This technique is based on the simultaneous amplification of a potentially amplified oncogene (HER-2) and a reference gene (IFN-gamma). Differential PCR yielded reproducible results that were in agreement with gene copy quantification using the dot blot technique. Thus we suggest differential PCR to be a reliable and rapid method for determining relative gene dosage in a minute amount of tumour tissue.

Base Sequence↗
PubMed1993

Accumulation of p53 protein as an indicator for p53 gene mutation in breast cancer. Occurrence of false-positives and false-negatives.

Accumulation of p53 protein resulting in levels detectable by immunohistochemistry (IHC) has been proposed as an indicator of mutation of the p53 gene. We have investigated a panel of 23 fresh-frozen breast cancers by IHC (PAb 1801), Southern and Northern blot analysis, and direct sequencing of the mutation hot spot regions (exons 5-8) of the p53 gene. Three tumors (13%) showed an intense nuclear staining in the majority of malignant cells, but only one of these showed a mutation of the p53 gene (codon 237, Arg to His). Furthermore, a mutation (5-bp deletion) was identified in a tumor that showed no p53 immunoreactivity. Our results indicate that accumulation of p53 protein, as detectable by IHC, is not a reliable indicator for p53 gene mutation in human breast cancer.

Base Sequence↗
PubMed1993

Mutational spectrum of the p53 gene in human small-cell lung cancer and relationship to clinicopathological data.

The spectrum of p53 gene mutations was determined in formalin-fixed, paraffin-embedded samples of small-cell lung cancer derived from 28 patients. By direct sequencing of exons 5, 7, and 8, including their flanking intron sequences, 18 mutations were identified in 17 tumors (61%), and in all but two of these the wild type allele was lost. In 8 cases, the mutation detected in the tumor was absent from the corresponding normal tissue, indicating that these mutations were somatically acquired. In two patients, identical mutations were found in the primary tumor and corresponding metastases. In a further case, an intrapulmonary metastasis did not show the mutation detected in the primary tumor. The local distribution of the mutations resembled that reported in non-small cell lung cancer and gave no indication of distinct bot spot regions. G-to-T transversions were the predominant type of mutation, reflecting a possible genotoxic influence of carcinogens contained in tobacco smoke. Mutations were equally distributed among tumors with intermediate and oat cell histology and did not show a significant association to age and gender of the patients. Also, no significant relationship was observed between the presence of a mutation and tumor stage (T, N, M) or survival. However, transitions at CpG dinucleotides were restricted to tumors without detectable metastases at the time of biopsy, whereas all other mutations occurred in metastasizing small cell lung cancer.

Base Sequence↗
PubMed1992

Detection of small RB1 gene deletions in retinoblastoma by multiplex PCR and high-resolution gel electrophoresis.

Loss of function of both copies of the RB1 gene is a causal event in the development of retinoblastoma. The predisposition to this tumor can be inherited as an autosomal dominant trait. Direct detection of the genetic defect is important for presymptomatic DNA diagnosis and genetic counseling in families with hereditary retinoblastoma. We have used multiplex polymerase chain reaction and high-resolution polyacrylamide gel electrophoresis to detect RB1 gene deletions as small as one base pair. By using three independent sets of amplification reactions, which cover 26% of the RB1 gene coding region, we identified RB1 gene deletions in the DNA of peripheral blood cells in 3 out of 24 (12.5%) unrelated patients with hereditary retinoblastoma. In one case, formalin-fixed paraffin-embedded tumor material was also used to detect the mutation. Sequencing of the mutated alleles revealed deletions of 1, 3 and 10 base pairs. Each deleted region was flanked by direct repeats.

Amino Acid Sequence↗
PubMed1991

Identification of cells responsible for the suppression of anti-beta-cell cytotoxicity in type I (insulin-dependent) diabetes mellitus.

Peripheral blood mononuclear cells (PBMC) from newly diagnosed type I diabetic patients induced a significantly higher cytotoxic insulin leakage from isolated rat islets during a 20-h incubation. compared with PBMC from healthy controls (13.9 +/- 7.7 versus 2.6 +/- 3.2 ng insulin/islet/20 h). The addition of PBMC from healthy subjects in a ratio of 1:4 suppressed the cytotoxic effect (13.9 +/- 7.7 to 6.7 +/- 4.4 ng insulin/islet/20 h). Depletion of CD8+ T lymphocytes from the PBMC of healthy subjects abolished their suppressive capacity, while depletion of CD4+ T lymphocytes and pre-incubation with CD3 monoclonal antibodies had no effect.

Adolescent↗
PubMed1990

Lymphocyte transfusion in recent onset type I diabetes mellitus--a one-year follow-up of cell-mediated anti-islet cytotoxicity and C-peptide secretion.

In 19 patients with newly diagnosed Type I diabetes mellitus a single transfusion of 1.9 x 10(9) to 1.5 x 10(10) lymphocytes was performed. Fifteen Type I diabetic patients who did not receive a transfusion were used as controls. Anti-beta-cell cell-mediated cytotoxicity was measured using an insulin release assay. Stimulated C-peptide secretion (100 g glucose orally, 1 mg glucagon i.v.) was used to estimate residual beta-cell function. Both parameters were measured prior to transfusion and after 12 months. The transfusions were followed by a fall of cytotoxicity below the 95% confidence limit of the controls in 11 of the 19 patients ('responders') (15.7 +/- 1.7 ng insulin/islet/20 h vs 6.7 +/- 1.3 P less than 0.001), while the other eight transfused patients ('non-responders') (13.5 +/- 1.9 vs 17.1 +/- 2.9, ns) and the non-transfused control patients (11.6 +/- 1.1 vs 14.2 +/- 2.4, ns) displayed persistently high cytotoxicity levels. In the responder group a slight improvement in stimulated C-peptide secretion was observed (136 +/- 43 pmol/dl vs 148 +/- 38, ns) whereas in the non-responder (127 +/- 28 vs 106 +/- 25, ns) and in the control group (130 +/- 17 vs 97 +/- 19, P less than 0.05) the stimulated C-peptide responses declined during the 12-month follow-up. Thus, lymphocyte transfusion may have beneficial effects by suppressing anti-beta-cell cytotoxicity and preserving C-peptide secretion.

Adolescent↗