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Oliver Frank

Publications and source records attributed to Oliver Frank.

At least 19 recordsLinked to original sources
PubMed2006

Altered transcriptional activity of human endogenous retroviruses in neuroepithelial cells after infection with Toxoplasma gondii.

Human endogenous retroviruses (HERVs) arose in antiquity from stable integration into the human genome. The mechanism for activation of HERVs has not been fully elucidated. Toxoplasmosis, caused by Toxoplasma gondii, is a medically important parasitic infection with worldwide distribution. To search for a tentative link between toxoplasmosis and HERV activation, HERV expression profiles of human neuroepithelial SK-N-MC cells infected with T. gondii were analyzed. Increased transcriptional activity of class I, II, and III HERV elements was observed in infected cells, suggesting that T. gondii can influence the transcription of HERVs in neuronal cells.

Animals↗
PubMed2006

The potential of retroviral vectors to cotransfer human endogenous retroviruses (HERVs) from human packaging cell lines.

Using a versatile and highly sensitive retroviral microarray, we have investigated particle preparations from three different human packaging cell lines harboring retroviral vector systems based on human immunodeficiency virus (HIV) and murine leukemia virus (MLV). 293Rev/Gag/Pol(i) cells inducibly express high titers of HIV-derived particles for packaging of HIV vectors. The Phoenix-GP and the Anjou 65 cell lines constitutively express MLV vector particles. We compared the transcription profiles of human endogenous retroviruses (HERVs) in all cell lines with the HERV sequences present in the particles. In addition, the influence of the transfected vector plasmid on the copackaging of HERVs was investigated. All particle preparations showed a defined pattern of endogenous retroviral sequences that differed from the cellular HERV expression pattern. HERV transcripts were observed in the particle preparations independent of whether a vector construct was coexpressed or not. Furthermore, our results suggest that particle preparations are frequently contaminated by cellular vesicles (exosomes) containing cellular RNAs including HERV transcripts.

Animals↗
PubMed2006

Prion infection influences murine endogenous retrovirus expression in neuronal cells.

Prions as causative agents of transmissible spongiform encephalopathies have been well investigated in experimental and modelling work. However, little is known about the molecular pathogenesis of prion-induced encephalopathies, the role of co-factors, and the interaction of prions with cellular components. We investigated the influence of prion infection on expression of murine endogenous retroviruses (ERVs), which compose approximately 10% of the mouse genome. Hypothalamic neuronal cells (GT1) and neuroblastoma cells (N2a) were examined. Both cell lines can be persistently infected with mouse adapted prion strains, i.e., RML. Using a mammalian retrovirus-specific DNA microarray and quantitative PCR methods, we compared the expression profiles of ERVs in prion-infected, uninfected, and anti-prion compound-treated murine neuronal cell lines, including clonal cell populations. The results suggest that prion infection influences ERV expression in neuronal cell lines, that this influence is cell line-specific, ERV-specific, and responsive to anti-prion compound treatment.

Animals↗
PubMed2006

Modulation of chondrocyte phenotype for tissue engineering by designing the biologic-polymer carrier interface.

Therapeutic strategies based on cell and tissue engineering can be advanced by developing material substrates that effectively interrogate the biological compartment, with or without the complimentary local release of growth factors. Poly(ether ester) segmented copolymers were engineered as model material systems to elucidate the interfacial molecular events that govern the function of adhered cells. Surface chemistry was modulated by varying poly(ethylene glycol) (PEG) length and mole fraction with poly(butylene terephthalate) (PBT), leading to differential competitive protein adsorption of fibronectin and vitronectin from serum and consequently to different cell attachment modes. Adhesion within the hydrogel-like milieu of longer surface PEG was mediated via binding to the CD44 transmembrane receptor, rather than the RGD-integrin mechanism, whereas greater substrate-bound fibronectin resulted in cell adhesion via integrins. These adhesion modalities differentially impacted morphological cell phenotype (spread or spheroid) and the subsequent expression of mRNA transcripts (collagen types II, I) characteristic of phenotypically differentiated or dedifferentiated chondrocytes, respectively. These results demonstrate that materials can be designed to directly elicit the membrane bound receptor apparatus desired for downstream cellular response, without requiring exogenous biological growth factors to enable differentiated potential.

Blotting, Western↗
PubMed2006

Fatness.

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Body Mass Index↗
PubMed2006

Item 291.

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Australia↗
PubMed2005

Comprehensive analysis of human endogenous retrovirus transcriptional activity in human tissues with a retrovirus-specific microarray.

Retrovirus-like sequences account for 8 to 9% of the human genome. Among these sequences, about 8,000 pol-containing proviral elements have been identified to date. As part of our ongoing search for active and possibly disease-relevant human endogenous retroviruses (HERVs), we have recently developed an oligonucleotide-based microarray. The assay allows for both the detection and the identification of most known retroviral reverse transcriptase (RT)-related nucleic acids in biological samples. In the present study, we have investigated the transcriptional activity of representative members of 20 HERV families in 19 different normal human tissues. Qualitative evaluation of chip hybridization signals and quantitative analysis by real-time RT-PCR revealed distinct HERV activity in the human tissues under investigation, suggesting that HERV elements are active in human cells in a tissue-specific manner. Most active members of HERV families were found in mRNA prepared from skin, thyroid gland, placenta, and tissues of reproductive organs. In contrast, only few active HERVs were detectable in muscle cells. Human tissues that lack HERV transcription could not be found, confirming that human endogenous retroviruses are permanent components of the human transcriptome. Distinct activity patterns may reflect the characteristics of the regulatory machinery in these cells, e.g., cell type-dependent occurrence of transcriptional regulatory factors.

Endogenous Retroviruses↗
PubMed2005

Human endogenous retrovirus expression profiles in samples from brains of patients with schizophrenia and bipolar disorders.

The detection and identification of retroviral transcripts in brain samples, cerebrospinal fluid, and plasma of individuals with recent-onset schizophrenia and schizoaffective disorders suggest that activation or upregulation of distinct human endogenous retroviruses (HERVs) may play a role in the etiopathogenesis of neuropsychiatric diseases. To test this hypothesis, we performed a comprehensive microarray-based analysis of HERV transcriptional activity in human brains. We investigated 50 representative members of 20 HERV families in a total of 215 brain samples derived from individuals with schizophrenia or bipolar disorders and matched controls. A characteristic brain-specific retroviral activity profile was found that consists of members of the class I families HERV-E, HERV-F, and ERV9 and members of HERV-K taxa. In addition to these constitutively expressed HERVs, a number of differentially active HERV elements were identified in all brain samples independent of the disease pattern that may reflect differences in the genetic background of the tested individuals. Only a subgroup of the HML-2 family (HERV-K10) was significantly overrepresented in both bipolar-disorder- and schizophrenia-associated samples compared to healthy brains, suggesting a potential association with disease. Real-time PCR analysis of HERV env transcripts with coding capacity potentially involved in neuroinflammatory conditions revealed that env expression of HERV-W, HERV-FRD, and HML-2 remains unaffected regardless of the clinical picture. Our data suggest that HERV transcription in brains is weakly correlated with schizophrenia and related diseases but may be influenced by the individual genetic background, brain-infiltrating immune cells, or medical treatment.

Animals↗
PubMed2005

Dietary bread crust advanced glycation end products bind to the receptor for AGEs in HEK-293 kidney cells but are rapidly excreted after oral administration to healthy and subtotally nephrectomized rats.

In renal HEK-293 cells, the dietary Maillard reaction compounds casein-linked Nepsilon-carboxymethyllysine (CML), CML, bread crust (BC), and pronyl-glycine (a key compound formed in association with the process-induced heat impact applied to bread dough) all showed activation of p38-MAP kinase. Expression of the C-terminus truncated receptor for advanced glycation end products (RAGE) resulted in a reduction of HEK-293-MAP kinase activation. As these findings suggested a RAGE-mediated activating effect of CML, BC, and pronyl-glycine on kidney cellular signal transduction pathways, an in vivo study was performed. Male Wistar rats were subjected to a sham operation (CTRL, n = 20) or to 5/6 nephrectomy (NX, n = 20). Both groups were randomized into two subgroups and fed 20 g of a diet containing either 25% by weight BC or wheat starch (WS). GC-MS analyses of CML, carboxyethyllysine (CEL), and pentosidine revealed increased levels of CML and CEL in the liver but decreased levels of CML in the kidneys of CTRL and NX rats fed the BC diet compared to those on the WS diet. However, urinary levels of CML were also elevated in the CTRL and NX rats on the BC diet, pointing to enhanced excretion of AGEs after BC administration. Although renal insufficiency in the NX rats was reflected by proteinuria, the renal handling of CML and, presumably, other AGEs was not impaired.

Animals↗
PubMed2005

Preventive activities during consultations in general practice: influences on performance.

BACKGROUND: The relationship between the performance of opportunistic preventive activities in general practice consultations and characteristics of patients, general practitioners, consultations and preventive opportunities is poorly understood. METHODS: We recorded the performance of 11 preventive care activities by 10 GPs in one practice and examined the associations of performance of the preventive activities and the characteristics of the patients, GPs, consultations and preventive opportunities. RESULTS: Every patient, GP, consultation and preventive opportunity characteristic studied was independently significantly associated with the performance of at least two of the preventive activities. DISCUSSION: These findings suggest ways of designing more effective reminders, particularly for patients least likely to receive prevention counselling.

Adult↗
PubMed2004

Bitter taste receptors for saccharin and acesulfame K.

Weight-conscious subjects and diabetics use the sulfonyl amide sweeteners saccharin and acesulfame K to reduce their calorie and sugar intake. However, the intrinsic bitter aftertaste, which is caused by unknown mechanisms, limits the use of these sweeteners. Here, we show by functional expression experiments in human embryonic kidney cells that saccharin and acesulfame K activate two members of the human TAS2R family (hTAS2R43 and hTAS2R44) at concentrations known to stimulate bitter taste. These receptors are expressed in tongue taste papillae. Moreover, the sweet inhibitor lactisole did not block the responses of cells transfected with TAS2R43 and TAS2R44, whereas it did block the response of cells expressing the sweet taste receptor heteromer hTAS1R2-hTAS1R3. The two receptors were also activated by nanomolar concentrations of aristolochic acid, a purely bitter-tasting compound. Thus, hTAS2R43 and hTAS2R44 function as cognate bitter taste receptors and do not contribute to the sweet taste of saccharin and acesulfame K. Consistent with the in vitro data, cross-adaptation studies in human subjects also support the existence of common receptors for both sulfonyl amide sweeteners.

Aristolochic Acids↗
PubMed2004

Tumor cells escape suicide gene therapy by genetic and epigenetic instability.

Transfer and expression of suicide genes is one cornerstone of cancer gene therapy and is also considered as a proactive tool to enhance the safety of somatic transgenesis. Here we addressed whether retrovirus-mediated suicide gene therapy would result in a predictable antitumor efficiency, given that problems related to gene transfer are solved or that the suicide gene is used in a proactive approach. Using retroviral vectors encoding the thymidine kinase gene of herpes simplex virus, we transduced EL-4 lymphoma cells and induced experimental tumors in congeneic C57Bl/6 mice. Systemic administration of ganciclovir (GCV) resulted in remission of transduced clonal and polyclonal tumors in vivo. However, GCV-resistant relapses occurred and were found to be associated with postinsertional alterations of transgene structure or loss of the entire transgene. Complete loss of a retrovirally marked fusion chromosome was confirmed by spectral karyotyping. Transgene silencing occurred in another clone. We conclude that genetic as well as epigenetic instability related to biologic features of the tumor, the insertion site, and the vector represent relevant limitations of retroviral suicide gene therapy. Considering the mechanisms of escape identified here, the proactive use of suicide genes to prevent complications of insertional mutagenesis may still be efficient.

Animals↗
PubMed2004

Systematic studies of structure and physiological activity of alapyridaine. A novel food-born taste enhancer.

By application of taste dilution analysis (+)-(S)-1-(1-carboxyethyl)-5-hydroxy-2-(hydroxymethyl)-pyridinium inner salt was recently successfully identified as a multimodal taste enhancer in beef bouillon. While being taste-less on its own, this so-called alapyridaine was found to intensify the human perception of sweet, salty, and umami taste. To gain information on the molecular requirements of this novel class of taste enhancer, a range of structurally related pyridinium betaines were synthesized, purified, and their physiological activities sensorially evaluated. Removal or modification of the hydroxyl and the hydroxymethyl group, respectively, induced a loss in bioactivity, thus indicating the 2-(hydroxymethyl)-5-hydroxypyridinium moiety as an essential structural element for taste enhancement. Regarding the amino substituent, neither the prolongation or removal of the alkyl chain or the carboxy function in the 1-(1-carboxy-2-ethyl)-moiety, nor the incorporation of an additional carboxy function led to any active derivative, thus demonstrating that also the structure of the nitrogen substituent is rather conserved for taste enhancement. But substitution of the methyl group by a benzyl group yielded a compound showing similar taste enhancing activities as found for alapyridaine. Interestingly, additional insertion of glycine between the 1-(1-carboxy-2-phenylethyl)-moiety and the pyridinium ring resulted in a compound eliciting comparable taste enhancing effects as shown for the compound lacking the glycine spacer. In contrast to these multimodal taste enhancers, substitution of the alanine moiety in alapyridaine by an arginine moiety revealed an one-dimensional taste enhancer exclusively increasing the human sensitivity for salty taste.

Alanine↗
PubMed2003

Activity-guided identification of a chemopreventive compound in coffee beverage using in vitro and in vivo techniques.

The aim of the present study was to apply an activity-guided screening procedure to coffee brew to identify a key chemopreventive compound by means of in vitro antioxidant tests as well as cell culture experiments and to prove the in vivo activity of that compound by an animal feeding experiment. Solvent fractionation, followed by multiple-step ultrafiltration, revealed that the polar coffee compounds with molecular weights below 1 kDa show the major inhibitory effect on the in vitro peroxidation of linoleic acid as well as the predominant chemopreventive enzyme modulating activity on the NADPH-cytochrome c reductase (CCR) and glutathione S-transferase (GST) in human intestinal Caco-2 cells. To identify the chemical structure of the most active antioxidants and chemopreventive compounds, the polar compounds were further separated by HPLC techniques, followed by the activity-guided screening of the individual HPLC fraction. These experiments demonstrated 5-chlorogenic acid to be the most powerful antioxidant in vitro, whereas, in contrast, chemopreventive effects on the GST activity were found for the N-methylpyridinium ion, the structure of which was elucidated by LC-MS and NMR experiments and confirmed by synthesis. The in vivo activities of coffee beverage and N-methylpyridinium ions were tested in a 15-day feeding experiment on rats. In the liver, feeding of 4.5% coffee beverage resulted in increases of GST and UDP-GT activities by 24 and 40% compared to animals fed the control diet (p > 0.05), respectively. Plasma total antioxidant capacity and plasma tocopherol were elevated in animals fed the coffee beverage and the N-methylpyridinium-containing diet. In summary, the results demonstrating a strong in vitro antioxidant activity for coffee were confirmed by the feeding study. Surprisingly, feeding of N-methylpyridinium also resulted in an increased total antioxidant capacity in the plasma. The data indicate that the mode of action demonstrated for N-methylpyridinium in biological systems is different from that in foods.

Animals↗
PubMed2003

Sensory activity, chemical structure, and synthesis of Maillard generated bitter-tasting 1-oxo-2,3-dihydro-1H-indolizinium-6-olates.

Thermal treatment of aqueous solutions of xylose, rhamnose, and l-alanine led to a rapid development of a bitter taste of the reaction mixture. To characterize the key compounds causing this bitter taste, the recently developed taste dilution analysis (TDA), which is based on the determination of the taste threshold of reaction products in serial dilutions of HPLC fractions, was performed to locate the most intense taste compounds in the complex mixture of Maillard reaction products. By application of this TDA, 26 fractions were obtained, among which seven fractions were evaluated with a high taste impact. LC/MS and NMR spectroscopy as well as synthetic experiments revealed the 1-oxo-2,3-dihydro-1H-indolizinium-6-olates 1-5 as the key compounds contributing the most to the intense bitter taste of the Maillard mixture. Calculation of the taste impact of these compounds based on a dose/activity relationship indicated that these five compounds already accounted for 56.8% of the overall bitterness of the Maillard mixture, thus demonstrating this class of 1-oxo-2,3-dihydro-1H-indolizinium-6-olates as the key bitter compounds. First synthetic studies on the relationship between the chemical structure and the human psychobiological activity of 1-oxo-2,3-dihydro-1H-indolizinium-6-olates revealed that substitution of the furan rings of 1 by 5-methylfuryl moieties (compounds 3-5) or by 5-(hydroxymethyl)furyl groups (compound 6) led to a significant increase of the bitter threshold. In contrast, the substitution of the oxygen atoms in the furan rings of 1 by sulfur atoms induced a significant decrease of the detection threshold of the 1-oxo-2,3-dihydro-1H-indolizinium-6-olate; for example, the thiophene derivative 7 showed the extraordinarily low bitter detection threshold of 6.3 x 10(-5) mmol/kg (water).

Alanine↗
PubMed2003

RAGE-mediated MAPK activation by food-derived AGE and non-AGE products.

Investigating the cellular effects of food compounds formed by heat treatment during processing, we recently demonstrated the expression of the receptor for advanced glycation endproducts (RAGE) and the p44/42 MAP kinase activation by casein-N(epsilon )-(carboxymethyl)lysine (casein-CML), a food-derived AGE, in the intestinal cell line Caco-2. In this work, we report a Caco-2 p44/42 MAP kinase activation by bread crust and coffee extract. After identification, quantification, and synthesis of two key compounds formed in association with the process-induced heat impact applied to bread dough and coffee beans, those compounds, namely the AGE pronyl-glycine and the non-AGE N-methylpyridinium, were also demonstrated for the first time to activate the p44/42 MAP kinase through binding to RAGE in Caco-2 cells. Blocking of RAGE by an antagonistic antibody and expression of C-terminally truncated RAGE resulted in a reduced Caco-2- and HEK-293-MAP kinase activation. These findings unequivocally point to a RAGE-mediated activating effect of chemically defined food-derived, thermally generated products, both, AGEs and non-AGEs, on cellular signal transduction pathways involved in inflammatory response and cellular proliferation.

Antibodies↗
PubMed2003

Maillard reaction products modulating the growth of human tumor cells in vitro.

We investigated the effect of a series of Maillard reaction products formed from carbohydrates under household heating conditions on the growth of human tumor cells in vitro. 4-Hydroxy-5-methyl-3-(2H)-furanone (1) was found to potently enhance the proliferation of human tumor cells. In contrast, the Maillard-type chromophores 2-(2-furyl)methylidene-4-hydroxy-5-methyl-2H-furan-3-one (2), 4-(2-furyl)-7-[(2-furyl)methylidene]-2-hydroxy-2H,7H,8aH-pyrano[2,3-b]- pyran-3-one (6), and 3-hydroxy-4[(E)-(2-furyl)methylidene]methyl-3-cyclopentene-1,2 dione (13) inhibited the growth of human tumor cells in vitro in the low micromolar range. GXF251L cells (gastric carcinoma), synchronized by serum deprivation, were retained in the G1-phase of the cell cycle after treatment with 2, 6, or 13 for 24 h. Concomitantly, a distinct sub-G1 peak was observed, indicative for apoptosis induction. DNA fragmentation was further investigated by ELISA using antibodies raised against histones and DNA. 2 induced a significant increase of fragmented DNA at concentrations > or = 30 microM. After treatment with compound 6, DNA fragmentation was observed at a higher concentration range (> or = 50 microM), whereas incubation with 13 resulted in a marked DNA fragmentation already at 20 microM. On the protein level, the activation of caspase 3, as an early marker for apoptosis induction, was determined. The results were almost identical to those obtained in the DNA fragmentation ELISA. In summary, Maillard reaction products potently modulating the growth of human tumor cells were identified. The Maillard-type chromophores 2, 6, and 13 were found to interfere with the proliferation of gastric carcinoma cells, causing cell cycle arrest and apoptosis induction.

Antineoplastic Agents↗