PubMed Health⌕ Search

Biomedical subjects

S Lehmann

Publications and source records attributed to S Lehmann.

At least 19 recordsLinked to original sources
PubMed2003

Prion-like protein Doppel expression is not modified in scrapie-infected cells and in the brains of patients with Creutzfeldt-Jakob disease.

Doppel protein has been discovered in prnp knock-out mouse lines, with overproduction of this protein in the brain causing ataxia and neurodegeneration. We investigated whether Doppel expression (i) affected or was affected by the course of prion propagation in neuroblastoma cells, or (ii) modulated Creutzfeldt-Jakob disease pathogenesis. No change in Doppel production was detected in N2a cells, before or after infection. Transient murine Doppel gene expression had no effect on N2a viability or PrP(Sc) production. A sensitive immunometric assay revealed low levels of Doppel in human brain, reflecting weak transcription of the corresponding gene. No difference in brain Doppel levels was observed between Creutzfeldt-Jakob disease patients and controls, adding further evidence that Doppel is unlikely to be involved in prion disease pathogenesis.

Animals↗
PubMed2002

The expression of cellular retinoid binding proteins in non-APL leukemic cells and its association with retinoid sensitivity.

Retinoic acid (RA) has important effects on cell differentiation and cell growth and on normal embryonic development. Intracellular retinoid signaling induced by endogenous or exogenous RA is regulated by retinoid binding proteins such as CRBPI, CRABPI and CRABPII and there are data suggesting that the expression of these proteins can influence the sensitivity to the growth inhibitory effects of ATRA. In this study, we investigated the basal and ATRA-induced expression of CRBPI and CRABPI and II in leukemic cell lines and in cells from patients with acute myeloid leukemia (AML). CRBPI as well as CRABPI and II were expressed in all tested cell lines and in leukemic cells from all 18 AML-patients. CRABPII mRNA expression was more abundant than CRBPI and CRABPI in both the cell lines and the patient cells but the levels compared the house keeping gene was lower in the patient cells. In all cell lines and in 69% of the patient samples, ATRA did upregulate CRABPII whereas CRBPI exhibited a varying response and CRABPI was more commonly downregulated. The sensitivity to the growth inhibitory effects of ATRA did not correlate with the basal expression of any of these proteins. However, ATRA-induced upregulation of CRABPII did significantly correlate with the ATRA sensitivity (p < 0.005) as well as with ATRA-induced upregulation of the retinoid receptor RARbeta (p < 0.05). We conclude that the retinoid binding proteins CRBPI and CRABPI and II are expressed in myeloid leukemic cells of non-M3 type but that the level of expression does not affect ATRA sensitivity.

Gene Expression↗
PubMed2001

Cell culture models of transmissible spongiform encephalopathies.

In this review, we describe the generation and use of cell culture models of transmissible spongiform encephalopathies, also known as prion diseases. These models include chronically prion-infected cell lines, as well as cultures expressing variable amounts of wild-type, mutated, or chimeric prion proteins. These cell lines have been widely used to investigate the biology of both the normal and the pathological isoform of the prion protein. They have also contributed to the comprehension of the pathogenic processes occurring in transmissible spongiform encephalopathies and in the development of new therapeutic approaches of these diseases.

Animals↗
PubMed2001

Ex vivo propagation of infectious sheep scrapie agent in heterologous epithelial cells expressing ovine prion protein.

Transmissible spongiform encephalopathies, or prion diseases, are fatal degenerative disorders of the central nervous system that affect humans and animals. Prions are nonconventional infectious agents whose replication depends on the host prion protein (PrP). Transmission of prions to cultured cells has proved to be a particularly difficult task, and with a few exceptions, their experimental propagation relies on inoculation to laboratory animals. Here, we report on the development of a permanent cell line supporting propagation of natural sheep scrapie. This model was obtained by stable expression of a tetracycline-regulatable ovine PrP gene in a rabbit epithelial cell line. After exposure to scrapie agent, cultures were repeatedly found to accumulate high levels of abnormal PrP (PrPres). Cell extracts induced a scrapie-like disease in transgenic mice overexpressing ovine PrP. These cultures remained healthy and stably infected upon subpassaging. Such data show that (i) cultivated cells from a nonneuronal origin can efficiently replicate prions; and (ii) species barrier can be crossed ex vivo through the expression of a relevant PrP gene. This approach led to the ex vivo propagation of a natural transmissible spongiform encephalopathy agent (i.e., without previous experimental adaptation to rodents) and might be applied to human or bovine prions.

Animals↗
PubMed2001

Automated 5' nuclease assay for detection of virulence factors in porcine Escherichia coli.

This paper describes the development of a 5' nuclease assay for detection of virulence factor genes responsible for colonization factors and toxins in Escherichia coli isolated from pigs. Colonization factors were F4, F5, F6, F18, F41 and the outer membrane protein intimin. Toxins were heat stable (STa, STb, EAST1) and heat labile (LT) enterotoxins and the verocytotoxin variant 2e (VT2e). To correctly identify false negative results, an endogenous internal control targeting the E. coli 16 S rRNA gene was incorporated in each test tube. The assay was evaluated using a collection of E. coli reference strains which have previously been examined with phenotypical assays or DNA hybridization. Furthermore, the assay was evaluated by testing porcine E. coli field strains, previously characterized. The 5' nuclease assay correctly detected the presence of virulence genes in all reference strains. When testing field strains there was generally excellent agreement with results obtained by laboratories in Belgium and Germany. In conclusion, the 5' nuclease assay developed is a fast and specific tool for detection of E. coli virulence genes in the veterinary diagnostic laboratory.

5'-Nucleotidase↗
PubMed2001

Landscape metrics for assessment of landscape destruction and rehabilitation.

This investigation tested the usefulness of geometry-based landscape metrics for monitoring landscapes in a heavily disturbed environment. Research was carried out in a 75 sq km study area in Saxony, eastern Germany, where the landscape has been affected by surface mining and agricultural intensification. Landscape metrics were calculated from digital maps (1912, 1944, 1973, 1989) for the entire study area and for subregions (river valleys, plains), which were defined using the original geology and topography of the region. Correlation and factor analyses were used to select a set of landscape metrics suitable for landscape monitoring. Little land-use change occurred in the first half of the century, but political decisions and technological developments led to considerable change later. Metrics showed a similar pattern with almost no change between 1912 and 1944, but dramatic changes after 1944. Nonparametric statistical methods were used to test whether metrics differed between river valleys and plains. Significant differences in the metrics for these regions were found in the early maps (1912, 1944), but these differences were not significant in 1973 or 1989. These findings indicate that anthropogenic influences created a more home geneous landscape.

Animals↗
PubMed2001

Effects of arsenic trioxide (As2O3) on leukemic cells from patients with non-M3 acute myelogenous leukemia: studies of cytotoxicity, apoptosis and the pattern of resistance.

Arsenic oxide (As2O3) has recently been reported to induce remission in a high percentage of patients with acute promyelocytic leukemia (APL). The aim of this study was to investigate the effects of As2O3 at therapeutic concentrations on cell viability and apoptosis on leukemic cells from patients with non-M3 acute myelogenous leukemia (AML) and to study the resistance profile compared to conventional AML drugs. Cells from 20 patients were exposed to therapeutic concentrations of As2O3 continuously for 96 h. As2O3 reduced the viability in blast cells from all the 20 tested patients compared to unexposed controls (p-value: 0.02 at 0.05 microM; <0.005 at 1.0 microM and higher concentrations). An increase in the apoptotic rate was also seen after incubation with As2O3. Parallel to the incubation with arsenic the in vitro sensitivity to a number of chemotherapeutic agents commonly used in AML was studied. Correlation coefficients for the in vitro sensitivity were highly significant between the conventional AML drugs except for Ara-C. For As2O3, all the correlation coefficients were negative and ranged between -0.05 and -0.51. Furthermore, increased P-gp expression in a multidrug resistant HL-60 cell line did not decrease the sensitivity to As2O3 as compared to the parental cell line. Neither did a P-gp-transfected variant of the K562 cell line show decreased sensitivity to As2O3. We conclude that As2O3 at therapeutic concentrations induces apoptosis and cytotoxic effects in blast cells from patients with non-M3 AML, and that As2O3 differs from conventional AML drugs with respect to the mechanisms that confer resistance to the drugs.

ATP Binding Cassette Transporter, Subfamily B↗
PubMed2001

Retinoid receptor expression and its correlation to retinoid sensitivity in non-M3 acute myeloid leukemia blast cells.

All-trans-retinoic acid (ATRA) has significantly improved the treatment results in acute promyelocytic leukemia (M3). In non-M3 acute myeloid leukemia (AML), the effects are less clear, and there is a pronounced heterogeneity in the sensitivity to the growth-inhibitory effects of retinoids in leukemic cells from different non-M3 AML patients. Retinoids exert their effects through a number of nuclear receptors [retinoic acid receptors (RARs) and retinoid X receptors (RXRs)]. In this study, we determined the expression of RAR alpha, RAR beta, RAR gamma, and RXR alpha by real-time PCR in four cell lines and in blast cells from patients with non-M3 AML before and after ATRA incubation. All four receptors were expressed in cells from all 18 tested patient samples and in four myeloid cell lines. In the majority of the patient samples as well as in the cell lines, there was a pattern of high expression of RAR alpha and RXR alpha and low expression of RAR beta and RAR gamma. There was no correlation between the basal expression of any of the retinoid receptors and sensitivity to ATRA. A 24-h exposure to ATRA increased the expression of RAR alpha, RAR beta, RAR gamma, and RXR alpha in 46%, 77%, 30%, and 38% of the samples, respectively. The mean increase in receptor expression was most pronounced for RAR beta and RXR alpha. There was a significant correlation between an increase in RAR beta expression in response to ATRA and sensitivity to ATRA (P < 0.014). No such correlations were found for RAR alpha, RAR gamma, and RXR alpha. The expression of the monocytoid marker CD14 was significantly correlated with increased expression of RAR alpha (P = 0.03). We conclude that RAR alpha, RAR beta, RAR gamma, and RXR alpha are expressed in non-M3 AML blast cells and that ATRA-induced expression of RAR beta may be a marker for retinoid sensitivity.

Adult↗
PubMed2000

Prion infection impairs the cellular response to oxidative stress.

The molecular mechanism of neurodegeneration in transmissible spongiform encephalopathies remains uncertain. In this study, it was demonstrated that prion-infected hypothalamic neuronal GT1 cells displayed a higher sensitivity to induced oxidative stress over noninfected cells. In addition, the infected cells presented an increased lipid peroxidation and signs of apoptosis associated with a dramatic reduction in the activities of the glutathione-dependent and superoxide dismutase antioxidant systems. This study indicates for the first time that prion infection results in an alteration of the molecular mechanisms promoting cellular resistance to reactive oxygen species. This finding is vital for future therapeutic approaches in transmissible spongiform encephalopathies and the understanding of the function of the prion protein.

Blotting, Western↗
PubMed2000

Phorbol ester-regulated cleavage of normal prion protein in HEK293 human cells and murine neurons.

Cellular prion protein (PrP(c)) undergoes a proteolytic attack at the 110/111 downward arrow112 peptide bond, whereas the PrP isoform (PrP(res)) that accumulates in the brain tissue in Creutzfeldt-Jakob disease reveals an alternate cleavage site at about residue 90. Interestingly, the normal processing of PrP occurs inside the 106-126 amino acid region thought to be responsible for the neurotoxicity of the pathogenic prions, whereas PrP(res) cleavage preserves this potentially toxic domain. Therefore, any molecular mechanisms leading to enhanced cleavage at the 110/111 downward arrow112 peptide bond could be of potential interest. We set up TSM1 neurons and HEK293 stable transfectants overexpressing the wild-type or 3F4-tagged murine PrP(c), respectively. Both mock-transfected and PrP(c)-expressing cell lines produced an 11-12-kDa PrP fragment (referred to as N1), the immunological characterization of which strongly suggests that it corresponds to the N-terminal PrP(c) fragment derived from normal processing. We have established that the recovery of secreted N1 is increased by the protein kinase C agonists PDBu and PMA in a time- and dose-dependent manner in both cell lines. In contrast, secretion of N1 remains unaffected by the inactive PDBu analog alphaPDD and by the protein kinase A effectors dibutyryl cAMP and forskolin. Overall, our data indicate that the normal processing of PrP(c) is up-regulated by protein kinase C but not protein kinase A in human cells and murine neurons.

Amino Acid Sequence↗
PubMed2000

Cleavage of the amino terminus of the prion protein by reactive oxygen species.

Relatively limited information is available on the processing and function of the normal cellular prion protein, PrP(C). Here it is reported for the first time that PrP(C) undergoes a site-specific cleavage of the octapeptide repeat region of the amino terminus on exposure to reactive oxygen species. This cleavage was both copper- and pH-dependent and was retarded by the presence of other divalent metal ions. The oxidative state of the cell also decreased detection of full-length PrP(C) and increased detection of amino-terminally fragmented PrP(C) within cells. Such a post-translational modification has vast implications for PrP(C), in its processing, because such cleavage could alter further proteolysis, and in the formation of the scrapie isoform of the prion protein, PrP(Sc), because abnormal cleavage of PrP(Sc) occurs into the octapeptide repeat region.

Animals↗
PubMed2000

Signal transduction through prion protein.

The cellular prion protein PrPc is a glycosylphosphatidylinositol-anchored cell-surface protein whose biological function is unclear. We used the murine 1C11 neuronal differentiation model to search for PrPc-dependent signal transduction through antibody-mediated cross-linking. A caveolin-1-dependent coupling of PrPc to the tyrosine kinase Fyn was observed. Clathrin might also contribute to this coupling. The ability of the 1C11 cell line to trigger PrPc-dependent Fyn activation was restricted to its fully differentiated serotonergic or noradrenergic progenies. Moreover, the signaling activity of PrPc occurred mainly at neurites. Thus, PrPc may be a signal transduction protein.

Animals↗
PubMed2000

Effects of retinoids on cell toxicity and apoptosis in leukemic blast cells from patients with non-M3 AML.

All-trans retinoic acid (ATRA) induces complete remission in acute promyelocytic leukemia (APL or M3). In this study we measured the effect of retinoids alone and in combination with daunorubicin (DNR) on cell growth and apoptosis in blast cells from patients with non-M3 AML. Cells from 21 patients were incubated in 0.2 microM daunorubicin for 1 h or in 1 microM ATRA or 9-cis-RA continuously and in the combinations of DNR with both retinoids. Cell toxicity and apoptosis were analyzed after 96 h. Both ATRA and 9-cis-RA reduced the viability significantly to 86 and 84%, respectively (P = 0.003 for ATRA and 0.02 for 9-cis-RA). The expression of CD34 correlated to a higher sensitivity to ATRA (P = 0.003). When retinoids were added to DNR the mean decrease in viability was 11 percentage points with ATRA (P = 0.003) and nine percentage points with 9-cis-RA (P = 0.02). Apoptosis was induced by both retinoids and the percentage of apoptotic cells was increased from 16% in the controls to 24% with ATRA (P = 0.03) and to 26% with 9-cis-RA (P = 0.04). When the retinoids were added to DNR the apoptotic rate increased from 41% with DNR alone to 51% with ATRA (P = 0.01) and to 49% with 9-cis-RA (P = 0.03). We conclude that ATRA and RA exert a slight but clear cytotoxic and apoptotic effect on AML blast cells after 96 h incubation and that retinoids can have an additive or synergistic effects on cell toxicity when added to daunorubicin.

Acute Disease↗
PubMed2000

Glycosylation of prions and its effects on protein conformation relevant to amino acid mutations.

The three-dimensional coordinates from a nuclear magnetic resonance (NMR)-averaged structure containing residues 121-226 of mouse prion were used as the starting geometry for MD of prion either with or without glycan in both mutant and wild-type forms. The following mutants were studied: Asp-178 to Asn, Thr-183 to Ala, Phe-198 to Ser, Glu-200 to Lys, and Gln-217 to Arg. NMR data vs structural models were compared to observe any major differences. Simulations of the change in protein structure with and without glycan were performed, as they cannot be tested by NMR analysis. Several mutants were expressed and analyzed for altered glycosylation and the results interpreted in terms of molecular modeling. N-linked glycosylation is likely to play an important role in prion biology as shown by visualization of glycoprotein conformation.

Amino Acid Sequence↗
PubMed2000

N-acetylcysteine for hepatic veno-occlusive disease after allogeneic stem cell transplantation.

Three patients developed veno-occlusive disease of the liver (VOD) after allogeneic stem cell transplantation. On the day after diagnosis, N-acetylcysteine (NAC) was given, initially in loading doses and thereafter 50-150 mg/kg/day for 12 to 31 days. The maximum bilirubin levels were 137, 58 and 138 mmol/l in the three patients, respectively. After the introduction of NAC, bilirubin, aspartate aminotransferase, sIL-2 receptor and IL-8 decreased. All three patients achieved normal bilirubin levels and prothrombin times. To conclude, NAC may be useful for treatment of VOD.

Acetylcysteine↗
PubMed2000

Cardiac systolic function before and after hematopoietic stem cell transplantation.

In order to examine the effect of hematopoietic stem cell transplantation (HSCT) on cardiac systolic function, we measured left ventricular ejection fraction (LVEF) by radioventriculography (RVG) before and after the transplantation procedure. One hundred and forty-eight patients were examined, 96 undergoing allogeneic grafting and 52 autologous. Fifty patients had CML, 48 AML, 21 ALL, 18 multiple myeloma and 11 breast cancer. The second RVG examination was performed 22 to 227 days (median 60 days) after HSCT. The mean LVEF value in the whole patient group was 60.2% (range 39-81%) before and 61.1% (35-86%) after transplantation. Patients with CML had significantly higher LVEF before transplantation than patients with acute leukemia (P = 0.007) and multiple myeloma (P = 0.005). No significant changes in mean LVEF between the pre- and post-transplant measurements were seen in any of the diagnostic subgroups or in allogeneic or autologous recipients. None of the 148 patients in the study has shown any signs of clinical heart failure at 2, 5 to 10 years follow-up. Patients who had received anthracyclines in the previous treatment had significantly lower LVEF before transplantation but showed no increased risk of decline in cardiac function. In conclusion, the HSCT procedure does not seem to affect myocardial function 1-7 months after transplantation.

Adolescent↗