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Biomedical subjects

S Lehmann

Publications and source records attributed to S Lehmann.

At least 37 records · Page 2Linked to original sources
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↗
PubMed2000

Effect of Congo red on wild-type and mutated prion proteins in cultured cells.

Transmissible spongiform encephalopathies form a group of fatal neurodegenerative disorders that have the unique property of being infectious, sporadic, or genetic in origin. Although some doubts remain on the nature of the responsible agent of these diseases, it is clear that a protein called PrP(Sc) (which stands for the scrapie isoform of the prion protein) has a central role in their pathology. PrP(Sc) represents a conformational variant of a normal protein of the host: the cellular isoform of the prion protein, or PrP(C). Compounds such as glycosaminoglycans and Congo red (CR) have been shown to interfere with both in vitro and in vivo PrP(Sc) formation. It was hypothesized that CR acts by overstabilizing the conformation of PrP(Sc) molecules or by modifying trafficking of PrP(C). Using transfected cells expressing 3F4-tagged mouse PrPs, we show here that CR does not interfere with conversion of PrP molecules carrying pathogenic mutations. On the contrary, after incubation with the drug, some of their properties, such as insolubility and protease resistance, are enhanced and are even acquired by the wild-type molecule. This last observation suggests an alternative mechanism of action of CR and leads us to reconsider the relationship between the biochemical properties of PrP and conformational alteration of the protein.

Animals↗
PubMed2000

Effect of amphotericin B on wild-type and mutated prion proteins in cultured cells: putative mechanism of action in transmissible spongiform encephalopathies.

Transmissible spongiform encephalopathies form a group of fatal neurodegenerative disorders that have the unique property of being infectious, sporadic, or genetic in origin. Although some doubts remain on the nature of the responsible agent of these diseases, it is clear that a protein called PrP(Sc) [the scrapie isoform of prion protein (PrP)] plays a central role. PrP(Sc) represents a conformational variant of PrP(C) (the cellular isoform of PrP), the normal host protein. Polyene antibiotics, such as amphotericin B, have been shown to delay the accumulation of PrP(Sc) and to increase the incubation time of the disease after experimental transmission in laboratory animals. Unlike agents such as Congo red, the inhibitory effect of amphotericin B on PrP(Sc) generation has not been observed in infected cultures. Using transfected cells expressing wild-type or mutated mouse PrPs, we show here that amphotericin B is able to interfere with the generation of abnormal PrP isoforms in culture. Its action seems related to a modification of PrP trafficking through the association of this glycosylphosphatidylinositol-anchored protein with detergent-resistant microdomains. These results represent a first step toward the comprehension of the mechanism of action of amphotericin B in transmissible spongiform encephalopathies.

Amphotericin B↗
PubMed2000

A model for educating humanistic physicians in the 21st century: the new medicine, patient, and society course at Tel Aviv University.

BACKGROUND: The impact of the social and behavioral sciences on medical education has often been limited due to a variety of organizational, curricular and professional barriers. The new "Medicine, Patient, and Society (MPS)" program in Tel Aviv attempts to rectify this educational shortcoming by exploring new ways to help students acquire the knowledge, attitudes and skills needed for becoming humanistic physicians and for helping patients (and themselves) adopt healthy behaviors. To work toward this goal, this program integrates the biomedical and psychosocial aspects of health care, providing developmentally appropriate learning experiences according to levels of training, together with a variety of educational methods, including learner-centered approaches. OBJECTIVES: To implement and evaluate the MPS pilot program. METHODS: The MPS program uses a "seamless" model of behavioral science education. This integrated curriculum interweaves several elements: behavioral science topics (presented through multiple approaches), clinical experiences, practical medical skills, and an independent project. During the program's first year there is a strong focus on "health" rather than "disease," with activities designed to encourage healthy behaviors, including smoking cessation, stress management, birth control, AIDS education, life cycle and preventive health services. Assessment of the pilot for first-year students included standardized questionnaires, student focus groups, participant observation of educational activities, and committee feedback. RESULTS: Students' quantitative evaluations indicated high levels of satisfaction with the MPS program, but their qualitative evaluations revealed some concerns. Participant observations and focus groups added unexpected insights. Student concerns included performance fears, difficulties with "learner-centered" education, and incompatibilities between more traditional first-year courses and the MPS program. Long-term follow-up will be needed to determine the impact of this emphasis on health during the first year. We assume it serves as a helpful foundation for students before they focus on disease and its sequelae in their later years.

Journal Article↗
PubMed2000

Successful transmission of three mouse-adapted scrapie strains to murine neuroblastoma cell lines overexpressing wild-type mouse prion protein.

Propagation of the agents responsible for transmissible spongiform encephalopathies (TSEs) in cultured cells has been achieved for only a few cell lines. To establish efficient and versatile models for transmission, we developed neuroblastoma cell lines overexpressing type A mouse prion protein, MoPrP(C)-A, and then tested the susceptibility of the cells to several different mouse-adapted scrapie strains. The transfected cell clones expressed up to sixfold-higher levels of PrP(C) than the untransfected cells. Even after 30 passages, we were able to detect an abnormal proteinase K-resistant form of prion protein, PrP(Sc), in the agent-inoculated PrP-overexpressing cells, while no PrP(Sc) was detectable in the untransfected cells after 3 passages. Production of PrP(Sc) in these cells was also higher and more stable than that seen in scrapie-infected neuroblastoma cells (ScN2a). The transfected cells were susceptible to PrP(Sc)-A strains Chandler, 139A, and 22L but not to PrP(Sc)-B strains 87V and 22A. We further demonstrate the successful transmission of PrP(Sc) from infected cells to other uninfected cells. Our results corroborate the hypothesis that the successful transmission of agents ex vivo depends on both expression levels of host PrP(C) and the sequence of PrP(Sc). This new ex vivo transmission model will facilitate research into the mechanism of host-agent interactions, such as the species barrier and strain diversity, and provides a basis for the development of highly susceptible cell lines that could be used in diagnostic and therapeutic approaches to the TSEs.

Animals↗
PubMed2000

Amphotericin B inhibits the generation of the scrapie isoform of the prion protein in infected cultures.

Transmissible spongiform encephalopathies form a group of fatal neurodegenerative disorders that have the unique property of being infectious, sporadic, or genetic in origin. Although some doubts about the nature of the responsible agent of these diseases remain, it is clear that a protein called PrP(Sc) plays a central role. PrP(Sc) is a conformational variant of PrP(C), the normal host protein. Polyene antibiotics such as amphotericin B have been shown to delay the accumulation of PrP(Sc) and to increase the incubation time of the disease after experimental transmission in laboratory animals. Unlike for Congo red and sulfated polyanions, no effect of amphotericin B has been observed in infected cultures. We show here for the first time that amphotericin B can inhibit PrP(Sc) generation in scrapie-infected GT1-7 and N2a cells. Its activity seems to be related to a modification of the properties of detergent-resistant microdomains. These results provide new insights into the mechanism of action of amphotericin B and confirm the usefulness of infected cultures in the therapeutic research of transmissible spongiform encephalopathies.

Amino Acid Sequence↗
PubMed1999

[Arsenic efficient in acute promyelocytic leukemia].

Arsenic compounds have been utilised in medicine for over 2,000 years. Recently, arsenic trioxide has been shown to induce complete remission in up to 90% of patients with acute promyelocytic leukemia (APL), including those resistant to standard therapy. Randomised studies are currently investigating the potential clinical utility of this drug in APL. In vitro, arsenic trioxide exhibits antitumoral properties with respect to various other tumor species as well, although assessment of clinical effects will require further study. This article reviews clinical results and possible mechanisms of action of the drug.

Antineoplastic Agents↗
PubMed1999

Trafficking of the cellular isoform of the prion protein.

Transmissible spongiform encephalopathies form a group of fatal neurodegenerative disorders that have the unique property of being infectious, sporadic or genetic in origin. Although the nature of the responsible agent of these diseases is uncertain, it is clear that a protein called PrPSc has a central role in their pathology. PrPSc is a conformational variant of a normal protein called PrPC. Understanding the transition from PrPC to PrPSc is a major issue in the field. In this article, we will review what is known about the cell biology of PrPC, the understanding of which is crucial considering that trafficking of this molecule governs generation of PrPSc.

Animals↗