Biomedical subjects

P Pfeiffer

Publications and source records attributed to P Pfeiffer.

At least 37 records · Page 2Linked to original sources

PubMed2001

Dual modulation of UFT with leucovorin and hydroxyurea in metastatic colorectal cancer.

The aim of the study was to investigate the possibility of dual modulation of UFT with leucovorin and hydroxyurea in a phase II trial of metastatic colorectal cancer. A total of 77 patients with measurable disease were included. UFT (300 mg/m2) was given with a fixed dose of 1-leucovorin (22.5 mg daily) and hydroxyurea (0.5 g daily) for 28 days followed by a 7 days' rest period. Treatment continued until progression or unacceptable toxicity. Sixty-three patients were evaluable for response. One patient (1.6%) had a complete remission and 13 (20.6%) a partial response for an overall response rate of 22.2%. The treatment was well tolerated. No significant bone marrow depression occurred. Grade 2 gastrointestinal toxicity was recorded in 28.5% of the patients, and grade 3 in 12.9%. The median time to progression was 6.8 months and the median crude survival was 11 months. In conclusion, hydroxyurea did not appear to increase either the response rate or the toxicity. Phase III trials along the same line cannot be recommended.

Adult↗

PubMed2000

DNA double-strand break repair in cell-free extracts from Ku80-deficient cells: implications for Ku serving as an alignment factor in non-homologous DNA end joining.

Non-homologous DNA end joining (NHEJ) is considered the major pathway of double-strand break (DSB) repair in mammalian cells and depends, among other things, on the DNA end-binding Ku70/80 hetero-dimer. To investigate the function of Ku in NHEJ we have compared the ability of cell-free extracts from wild-type CHO-K1 cells, Ku80-deficient xrs6 cells and Ku80-cDNA-complemented xrs6 cells (xrs6-Ku80) to rejoin different types of DSB in vitro. While the two Ku80-proficient extracts were highly efficient and accurate in rejoining all types of DNA ends, the xrs6 extract displayed strongly decreased NHEJ efficiency and accuracy. The lack of accuracy is most evident in non-homologous terminus configurations containing 3'-overhangs that abut a 5'-overhang or blunt end. While the sequences of the 3'-overhangs are mostly preserved by fill-in DNA synthesis in the Ku80-proficient extracts, they are always completely lost in the xrs6 extract so that, instead, small deletions displaying microhomology patches at their breakpoints arise. In summary, our results are consistent with previous results from Ku-deficient yeast strains and indicate that Ku may serve as an alignment factor that not only increases NHEJ efficiency but also accuracy. Furthermore, a secondary NHEJ activity is present in the absence of Ku which is error-prone and possibly assisted by base pairing interactions.

Animals↗

PubMed2000

The distribution of group I introns in lichen algae suggests that lichenization facilitates intron lateral transfer.

The nuclear-encoded small subunit ribosomal DNA gene of many lichen-forming green algae in the genus Trebouxia contains a group I intron at Escherichia coli genic position 1512. We studied the evolutionary history of the 1512 intron in Trebouxia spp. (Trebouxiophyceae) by analyzing intron and "host" cell phylogenies. The host trees were constructed by comparing internal transcribed spacer regions of rDNA. Maximum-likelihood, maximum-parsimony, and distance analyses suggest that the 1512 intron was present in the common ancestor of the green algal classes Trebouxiophyceae, Chlorophyceae, and Ulvophyceae. The 1512 intron, however, was laterally transferred at least three times among later-diverging Trebouxia spp. that form lichen partnerships. Intron secondary structure analyses are consistent with this result. Our results support the hypothesis that lichenization may facilitate 1512 group I intron lateral transfer through the close cell-to-cell contact that occurs between the lichen algal and fungal symbionts in the developing lichen thallus.

Alternative Splicing↗

PubMed2000

[Incidence of dental, mouth, and jaw injuries and the efficacy of mouthguards in top ranking athletes].

The aim of the study was to determine the prevalence of orofacial injuries among German top athletes and their attitudes to mouthguards. A questionnaire was mailed to athletes of 10 German contact sports associations. 64.3 percent (303) of the athletes returned questionnaires. 62 percent (188) of the respondents reported that at some time they wore a mouthguard for sports participation. 47.3% (male: 57.8%, female: 38.3%) of these were currently using one. 50% of the mouthguards were custom made by dentists, and 50% were shop bought (boil-and-bite). 32 percent of the participants had, at some time during their sports career, suffered an orofacial injury. The incidence of fractured anterior upper teeth and completely knocked out teeth for athletes without mouthguards was 7 and 14, respectively. Whereas for athletes wearing mouthguards one fractured tooth was reported. Athletes with mouthguards complained of problems with speaking (19.9%) rather than of breathing (3.4%) and fitting difficulties (4.8%). Boil-and-bite mouthguards caused more fitting problems than custom-made ones. As prevalence of oral injuries in body-contact sports is high, athletes should be advised that custom-made mouthguards offer the greatest comfort, fit, durability, and protection against dental injuries.

Adult↗

PubMed2000

Mechanisms of DNA double-strand break repair and their potential to induce chromosomal aberrations.

DNA double-strand breaks (DSB) are considered to be critical primary lesions in the formation of chromosomal aberrations. DSB may be induced by exogenous agents, such as ionizing radiation, but also occur spontaneously during cellular processes at quite significant frequencies. To repair this potentially lethal damage, eukaryotic cells have evolved a variety of repair pathways related to homologous and illegitimate recombination, also called non-homologous DNA end joining, which may induce small scale mutations and chromosomal aberrations. In this paper we review the major cellular sources of spontaneous DSB and the different homologous and illegitimate recombination repair pathways, with particular focus on their potential to induce chromosomal aberrations.

Animals↗

PubMed2000

Phylogenetic analysis of some large double-stranded RNA replicons from plants suggests they evolved from a defective single-stranded RNA virus.

Sequences were recently obtained from four double-stranded (ds) RNAs from different plant species. These dsRNAs are not associated with particles and as they appeared not to be horizontally transmitted, they were thought to be a kind of RNA plasmid. Here we report that the RNA-dependent RNA polymerase (RdRp) and helicase domains encoded by these dsRNAs are related to those of viruses of the alpha-like virus supergroup. Recent work on the RdRp sequences of alpha-like viruses raised doubts about their relatedness, but our analyses confirm that almost all the viruses previously assigned to the supergroup are related. Alpha-like viruses have single-stranded (ss) RNA genomes and produce particles, and they are much more diverse than the dsRNAs. This difference in diversity suggests the ssRNA alpha-like virus form is older, and we speculate that the transformation to a dsRNA form began when an ancestral ssRNA virus lost its virion protein gene. The phylogeny of the dsRNAs indicates this transformation was not recent and features of the dsRNA genome structure and translation strategy suggest it is now irreversible. Our analyses also show some dsRNAs from distantly related plants are closely related, indicating they have not strictly co-speciated with their hosts. In view of the affinities of the dsRNAs, we believe they should be classified as viruses and we suggest they be recognized as members of a new virus genus (Endornavirus) and family (Endoviridae).

Defective Viruses↗

PubMed2000

Effects of different exposure values on diagnostic accuracy of digital images.

OBJECTIVE: The aim of this in vitro study was to compare the effects of different exposure values on the image clarity of 3 digital radiographic systems and 1 conventional direct-exposure emulsion x-ray film. METHOD AND MATERIALS: Three digital radiographic systems, Digora, RVG, and Sidexis, were compared with the conventional dental x-ray film, Ektaspeed Plus. A medullary bone fragment and human teeth were radiographed with varying voltage, exposure time, and focus-receptor distance. Clinical criteria to evaluate image clarity were detail resolution, sharpness, contrast resolution, and artifacts of the different tooth and jaw structures. RESULTS: The optimal exposure times for digital imaging varied between 0.02 and 0.13 seconds and depended on the objects and the imaging systems. Optimal resolution was obtained when a voltage of 60 kV was used. The focus-receptor distance of 33 to 40 cm resulted in the best contrast and sharpness. Digital images did not always provide the detail resolution or sharpness achieved by conventional radiographs. CONCLUSION: The recommended exposure time for digital images amounted to approximately half the time needed for conventional film. Digital images had to be modified by adjusting the contrast and brightness to optimize the visibility of the areas to be diagnosed.

Artifacts↗

PubMed1999

The influence of dsRNA viruses on the biology of plant pathogenic fungi.

Double-stranded RNA viruses are ubiquitous in fungi. They are non-infective and, like most prokaryotic plasmids, are only transmitted to compatible strains via cell fusion. Most are cryptic, but some with an established phenotype, such as the hypoviruses of the chestnut-blight fungus, have been studied for their potential as biological control agents of fungi.

Fungi↗

PubMed1999

Isolation of Desulfovibrio intestinalis sp. nov. from the hindgut' of the lower termite Mastotermes darwiniensis.

A Gram-negative, anaerobic sulfate-reducing bacterium was isolated from hindgut contents of the lower termite Mastotermes darwiniensis Froggatt (strain KMS2). Strain KMS2 is motile by a single polar flagellum. The isolate possesses desulfoviridin and catalase activity. The G+C content of its DNA is in the range of 54.5-55.5 mol% (strain KMS2). It respires hydrogen and different low molecular weight organic compounds in the presence of sulfate, thiosulfate, and sulfite, and also oxygen. The isolated strain ferments pyruvate. Fastest growth with a doubling time of 12.5 h was obtained at 37 degrees C and not at 28 degrees C, the temperature at which the termites were grown. The isolate showed a 16S rDNA sequence homology of 95.9% to Desulfovibrio desulfuricans ATCC 27774 and a DNA-DNA homology of 44.6% to D. desulfuricans Essex 6 (type strain). Based on its biochemical properties and 16S rDNA sequence, the isolate was assigned to a new species named Desulfovibrio intestinalis.

Animals↗

PubMed1998

Rejoining of DNA double-strand breaks in vitro by single-strand annealing.

Nonhomologous DNA end joining (NHEJ) is considered the major pathway of double-strand break (DSB) repair in vertebrate cells. Various studies indicated the existence of at least two different NHEJ pathways; one that joins DNA ends accurately and depends on Ku, a protein heterodimer that binds to DNA ends, and one that generates deletions and is independent of Ku. While the former pathway has been characterised in some detail, only little is known about the latter error-prone. We have partially purified such an NHEJ activity from extracts of Xenopus laevis eggs. End-joined junctions formed in the most extensively purified protein fraction displayed deletions containing short patches of sequence homology at their break points, a feature characteristic of single-strand annealing (SSA). Detailed biochemical characterisation revealed the presence of DNA ligase III, DNA polymerase epsilon, FEN-1 endonuclease, and exonuclease activities of 5'-3' and 3'-5' directionality. We show that these activities are able to correctly process proposed intermediates of SSA. Interestingly, neither Ku nor the associated DNA-dependent protein kinase were detected, indicating that the mechanism can dispense with Ku. Our findings provide evidence for the existence of an error-prone NHEJ pathway that creates deletions by microhomology-driven SSA.

Animals↗

PubMed1998

Cloning, purification and characterization of DNA polymerase beta from Xenopus laevis--studies on its potential role in DNA-end joining.

Double-strand breaks in the DNA of vertebrate cells are joined by mechanisms of non-homologous DNA-end joining (NEJ). In extracts from Xenopus eggs, NEJ is inhibited by dideoxynucleotides, indicating a possible involvement of DNA polymerase beta (Pol beta). Since some types of NEJ products were shown to be formed in vitro by prokaryotic DNA polymerases lacking exonuclease activity, we were interested in whether Pol beta alone would be capable of catalyzing NEJ reactions. Therefore we have cloned the full-length cDNA of the Xenopus laevis Pol beta. The cDNA, predicting a highly conserved 39-kDa protein of 334 amino acids, was tagged with six histidine residues at its N-terminus for overexpression in Escherichia coli, purified to near homogeneity, and shown to have the same catalytic properties as the previously cloned rat and human enzymes. Using oligonucleotides as substrates we show that the recombinant Xenopus Pol beta adds single untemplated nucleotides to blunt ends. However, under conditions that permit efficient NEJ in Xenopus egg extracts, Pol beta does not form those types of NEJ products formed by the prokaryotic polymerases indicating that Pol beta alone is not able to mediate the complex NEJ process in vitro. Using substrates with 3' protruding single strands of increasing length (6-16 nucleotides) we show that Pol beta initiates fill-in DNA synthesis on fold-back structures formed by the longest 3' protruding stand. This unusual feature of beta-type polymerases requires that the loop of the fold-back structure consists of at least six bases and the stem be paired by at least 2 bp to facilitate priming of DNA synthesis.

Amino Acid Sequence↗

PubMed1998

Energy metabolism of underwater swimming in river-otters (Lutra lutra L.).

We used a still-water swim channel in conjunction with open-flow oxygen and carbon dioxide respirometry to examine the energy requirements of river-otters (Lutra lutra L.) swimming voluntarily underwater in Neumünster Zoo (Germany). While at rest on land (5 degrees C), river-otters had a respiratory quotient of 0.77 and a resting metabolic rate of 4.1 W kg-1. This increased to an estimated 6.4 W kg-1 during rest in water (11-15 degrees C) and to 12.3 W kg-1 when the animals were feeding in the channel. River-otters swimming under water preferred a mean speed of 0.89 m s-1, and their energy requirements attained 11.6 W kg-1. Cost of transport, however, was minimal at 1.3 m s-1 and amounted to 0.95 J N-1 m-1.

Animal Welfare↗

PubMed1998

[p53 as a biomarker in radiotherapy of carcinoma of the mouth cavity].

Multimodal therapy of oral squamous cell carcinomas today is based on surgery, radiotherapy and chemotherapy. Despite the combination of all three therapeutic options, there is still a large number of treatment failures and therefore major questions remain. Recent investigations suggest that mutations of the p53 tumor suppressor gene may account for some of the therapeutic failures. Inactivation of the gene may be an important determinant of the efficacy of today's multimodal therapy protocols. In 90 patients with squamous cell carcinomas of the oral cavity biopsy specimens were taken before and after preoperative radiochemotherapy. From all patients, biopsy and resection material was available for immunohistochemical analysis of p53. After radiation treatment, 51 patients (57%) showed a complete response; 39 patients (43%) only showed a partial response or did not respond at all. Among the responders, 82% of the pretherapeutic tumors were p53 positive, whereas among the nonresponders only 56% of the pretherapeutic tumors were p53 positive. The majority of the residual tumors were also p53 negative according to immunohistology after radiation treatment. In our study, detection of p53 protein by immunohistochemistry seemed to be connected with a more radiosensitive reaction of the tumors. Nevertheless, successful strategies for radiation therapy may need to take into account the tissue of origin and the status of p53 in the tumor.

Biomarkers, Tumor↗

PubMed1998

Proliferative activity and loss of function of tumour suppressor genes as 'biomarkers' in diagnosis and prognosis of benign and preneoplastic oral lesions and oral squamous cell carcinoma.

Oral cancer is a disease of the elderly and is closely connected with cigarette smoking and alcohol consumption. Since the successful introduction of multidisciplinary treatment, the survival rate has not changed. Because of the high mortality and potentially disfiguring treatment, today's efforts are aimed at eliminating risk factors, chemoprophylaxis, improvement in diagnostic procedures, and understanding of the genetic mechanisms of oral carcinogenesis. Immunohistochemical and molecular biology analysis of biopsy tissue and cell lines of preneoplastic and neoplastic lesions that originate from the oral mucosa have shown that alterations in tumour suppressor genes such as p53 and Rb gene may have an important role in oral carcinogenesis and may be potentially useful prognostic 'biomarkers' in oral carcinogenesis. Statistical analysis of immunohistochemical data from 216 patients did not identify significant or consistent differences of p53, MDM2, or RB expression with respect to stage of disease, malignant transformation, metastatic node involvement, recurrence, or survival. Nevertheless, p53 overexpression seems to correlate strongly with histological progression of the disease, which confirms the importance of p53 alterations in oral carcinogenesis. Overexpression of p53 is usually found in the less differentiated proliferating cells in benign and malignant oral lesions. Assessment of the proliferating activity is possible by immunohistochemical staining with monoclonal antibodies against proliferating nuclear antigen and Ki-67. Statistical analysis shows that overexpression of p53 combined with high proliferative activity predicts a less favourable course of disease in oral squamous cell carcinoma.

Aged↗

PubMed1998

The mutagenic potential of DNA double-strand break repair.

Numerous environmental pollutants are considered DNA-damaging agents with defined mutagenic potential. Therefore, toxicological studies have focused mainly on the impact of such substances on human health, mutagenesis and carcinogenesis. The possible effects of cellular processes, such as DNA repair and recombination, as causes of spontaneous mutations and genome instability, however, have been less extensively studied but are of major importance for the reliable assessment of human health risk by the exposure to environmental or occupational chemicals and radiation. Of all DNA lesions known double-strand breaks (DSB) are among the most fatal because they disrupt the continuity of the DNA template essential for DNA replication and transcription. Omitted or imprecise repair of DSB may therefore result in cell killing, small scale mutations, chromosome rearrangements, and carcinogenesis. In the following report, the potential of cellular DSB-repair mechanisms to generate mutations in humans will be discussed.

Animals↗

PubMed1998

Dihydroorotate (dhout) and orotate (orout) utilizer mutants in yeast: identification of the dhout mutation and allelism of the DHO and URE2 genes.

We induced by UV mutagenesis a series of yeast mutants that were able to utilize dihydroorotic (dhout) and orotic acid (orout) as precursors for pyrimidine biosynthesis. These recessive mutations defined three complementation groups named dhout, orout1 and orout2. The wild-type allele of the gene responsible for dihydroorotate utilization was cloned using the sensitivity of the dhout mutant to 5-fluoroorotate. The DHO gene was sequenced and found to be identical to the URE2 gene. The dhout mutation resulted from the introduction of a stop codon instead of a glutamine at position 59, which led to the production of a truncated Ure2p. Therefore, the URE2 and DHO genes are alleles in yeast.

Alleles↗

PubMed1998

Enzyme-linked immunosorbent assay of epidermal growth factor receptor in lung cancer: comparisons with immunohistochemistry, clinicopathological features and prognosis.

The prognostic role of epidermal growth factor receptor (EGFR) remains controversial in patients with lung cancer. Previous assays for EGFR have primarily been qualitative or, at best, semiquantitative. In the present study, using fresh-frozen tissue from 190 unselected lung cancer patients, quantification of EGFR (EGFR(ELISA)) using a recently developed enzyme-linked immunosorbent assay (ELISA) technique was compared with results (EGFR(IHC)) obtained using immunohistochemistry (IHC). Correlation between results obtained by the two different techniques was highly significant (r(s) = 0.63, P < 0.001, n = 190). This correlation improved even further (r(s) = 0.76) when sections were estimated using an IHC score that took into account percentage staining, intensity and relative tumour area. Furthermore, the relationship between clinicopathological features and prognosis was identical for the two methods. The expression of EGFR was highest in squamous cell carcinomas, but it was not correlated with other characteristics such as age, sex, histological grading, stage or prognosis. We conclude that evaluation of EGFR content using IHC and ELISA produces comparable results.

Adult↗

PubMed1998

Nucleotide sequence, genetic organization and expression strategy of the double-stranded RNA associated with the '447' cytoplasmic male sterility trait in Vicia faba.

The entire nucleotide sequence of the double-stranded (ds) RNA associated with the unconventional '447' cytoplasmic male sterility (CMS) trait in Vicia faba was determined from overlapping cDNA clones and by RT-PCR. Confirming previous observations, it was found that the negative-strand was continuous and 17,635 nt long, while the positive-strand featured an interruption, probably a nick, that could potentially define two subgenomic RNAs of 2735 nt and 14,900 nt, with the smaller RNA being located on the 5' side. The entire positive-strand could encode a single in-frame ORF starting at the first AUG at position 42-44 and ending with a TGA at 17,517-17,519. This long potential polypeptide with a predicted molecular mass of 654,109 is the largest described to date in the plant kingdom and contains conserved amino acid sequence motifs typical of viral helicases and RNA-dependent RNA polymerases (RDRP). Only limited sequence homology was detected with the ORF B encoded by the hypovirulence-associated dsRNA of chestnut blight fungus, a dsRNA replicon similarly contained in host-derived membranous vesicles and considered to share a common ancestry with potyviruses. By contrast, the helicase and RDRP domains were in the same respective arrangement and shared extensive sequence homologies with those identified in the polyprotein encoded by the dsRNA isolated from Japonica rice, another dsRNA replicon featuring a specific nick in the positive-strand. Although no proteolytic self-cleavage activity has yet been demonstrated, it appears likely that this long ORF is a polyprotein that undergoes proteolytic maturation, with one of the polypeptides derived by self-cleavage being the determinant of the CMS trait.

Amino Acid Sequence↗