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M Loeffler

Publications and source records attributed to M Loeffler.

At least 37 records · Page 2Linked to original sources
PubMed2001

Modelling of chemotherapy: the effective dose approach.

We sketch the development of the effective dose approach which provides a theoretical framework to interpret chemotherapy outcome data. Building on the generalised Skipper model of chemotherapy, a meta-regression method is derived to jointly analyse all chemotherapy comparing randomised clinical trials in a given malignancy in order to explore the slope of the effective dose/outcome relationship and the relative potency of cytostatic drugs. The model is applied to explain why treatment differences in aggressive NHL appear to differ by risk groups in aggressive NHL. A respective meta-subgroup analysis to confirm this interaction hypothesis is proposed.

Algorithms↗
PubMed2001

Dose escalation of cytotoxic drugs using haematopoietic growth factors: a randomized trial to determine the magnitude of increase provided by GM-CSF.

BACKGROUND: The magnitude of chemotherapy dose escalation made possible by the use of recombinant haematopoietic growth factors has not been quantified in a randomized trial. PATIENTS AND METHODS: Patients with refractory or relapsing Hodgkin's disease were randomized to receive the Dexa-BEAM regimen with escalating etoposide doses supported by placebo or granulocyte-macrophage colony-stimulating factor (GM-CSF). Using an adaptive sampling method independently in both arms, the etoposide dose was escalated until the maximal tolerated dose for the first cycle was reached. RESULTS: Thirty patients were randomized to GM-CSF and thirty to placebo. The etoposide dose could be escalated considerably in both treatment arms. Maximal etoposide dose for the first cycle was 1920 mg/m2 for patients receiving GM-CSF and 1160 mg/m2 for patients receiving placebo (P = 0.045 one-sided), corresponding to a 65% higher etoposide dose and a 13% higher dose intensity with GM-CSF. Dose-limiting events were similar in both arms, consisting mainly of prolonged neutropenia and consecutive infections. Treatment efficacy was not different in the two treatment groups. CONCLUSIONS: While GM-CSF permits a somewhat higher dose escalation than placebo, the increase in dose intensity provided by GM-CSF is small. The use of CSF for interval reduction rather than dose escalation is the more effective strategy for dose intensification.

Adolescent↗
PubMed2001

Cell migration and organization in the intestinal crypt using a lattice-free model.

We present a novel class of spatial models of cell movement and arrangement applied to the two-dimensional cellular organization of the intestinal crypt. The model differs from earlier approaches in using a dynamic movement on a lattice-free cylindrical surface. Cell movement is a consequence of mitotic activity. Cells interact by viscoelastic forces. Voronoi tessellation permits simulations of individual cell boundaries. Simulations can be compared with experimental data obtained from cell scoring in sections. Simulation studies show that the model is consistent with the experimental results for the spatial distribution of labelling indices, mitotic indices and other observed phenomena using a fixed number of stem cells and a fixed number of transit cell divisions.

Animals↗
PubMed2001

Dominant cell death induction by extramitochondrially targeted apoptosis-inducing factor.

The complete AIF cDNA comprising the amino-terminal mitochondrial localization sequence (MLS) and the oxidoreductase domain has been fused in its carboxyl terminus to enhanced green fluorescent protein (GFP), thereby engineering an AIF-GFP fusion protein that is selectively targeted to the mitochondrial intermembrane space. Upon induction of apoptosis, the AIF-GFP protein translocates together with cytochrome c (Cyt-c) to the extramitochondrial compartment. Microinjection of recombinant AIF leads to the release of AIF-GFP and Cyt-c-GFP, indicating that ectopic AIF can favor permeabilization of the outer mitochondrial membrane. These mitochondrial effects of AIF are caspase independent, whereas the Cyt-c-microinjection induced translocation of AIF-GFP and Cyt-c-GFP is suppressed by the pan-caspase inhibitor Z-VAD.fmk. Upon prolonged culture, transfection-enforced overexpression of AIF results in spontaneous translocation of AIF-GFP from mitochondria, nuclear chromatin condensation, and cell death. These effects are caspase independent and do not rely on the oxidoreductase function of AIF. Spontaneous AIF-GFP translocation and subsequent nuclear apoptosis can be retarded by overexpression of a Bcl-2 protein selectively targeted to mitochondria, but not by a Bcl-2 protein targeted to the endoplasmic reticulum. Overexpression of a mutant AIF protein in which the MLS has been deleted (AIF Delta 1-100) results in the primary cytosolic accumulation of AIF. AIF Delta 1-100-induced cell death is suppressed by neither Z-VAD.fmk or by Bcl-2. Thus, extramitochondrially targeted AIF is a dominant cell death inducer.

Active Transport, Cell Nucleus↗
PubMed2001

Immunogenetic markers and seropositivity predict radiological progression in early rheumatoid arthritis independent of disease activity.

OBJECTIVE: A prospective clinical study of patients with recent onset rheumatoid arthritis (RA) to examine the relationship between inflammatory disease activity and joint destruction in a 4 year followup, and to evaluate prognostic markers for severe joint erosions early in the disease. METHODS: Eighty-seven patients with RA according to the American College of Rheumatology criteria and a disease duration < 2 years were followed for an observation time of 2 to 4 years (mean 3.1 yrs). Variables of clinical and laboratory disease activity were monitored, and HLA-DRB1 alleles were determined. Hand and foot radiographs were taken every 6 months. RESULTS: Multivariate analysis of independent contributions of covariates to progression of joint destruction resulted in a mixed effect regression model with significant influences for the presence of a shared epitope (SE) positive DR4 allele (SE+ DR4+; p = 0.007), rheumatoid factor (RF) IgA (p = 0.01), and sex (p = 0.059), but not for clinical variables or acute phase reactants. The odds ratio to reach a Larsen score above 32 during the observation period of 4 years was increased in patients positive for RF IgM (OR 2.7, p = 0.019), for the shared epitope on a DR4 allele (OR 8.6, p < 0.005), and in patients with erosions already at study entry (OR 11.9, p = 0.001). The highest sensitivity and specificity for the prediction of severe bone destruction (84% and 79%) were found when the presence of either a SE+ DR4 allele or of early erosions was used as a prognostic marker (OR 20.4, p < 0.0001). CONCLUSION: Our results show the pace of joint destruction in RA to be influenced by the presence of SE+ DR4 alleles, RF production, and sex and by the presence of erosive disease at presentation. Those prognostic markers exert their influence independently from the inflammatory disease activity.

Adult↗
PubMed2000

Bid acts on the permeability transition pore complex to induce apoptosis.

Similar to most if not all pro-apoptotic members of the Bcl-2 family, Bid (and its truncated product t-Bid) triggers cell death via mitochondrial membrane permeabilization (MMP). This effect can be monitored in intact cells, upon microinjection of recombinant Bid protein into the cytoplasm, as well as in purified mitochondria, upon addition of Bid protein. Here we show that Bid-induced MMP can be inhibited, both in cells and in the cell-free system, by three pharmacological inhibitors of the permeability transition pore complex (PTPC), namely cyclosporin A, N-methyl-4-Val-cyclosporin A, and bongkrekic acid (a ligand of the adenine nucleotide translocase, ANT, one of the PTPC components). Bid effects on synthetic membranes were studied either in proteoliposomes or in synthetic bilayers subjected to electrophysiological measurements. Full length Bid preferentially permeabilizes membranes and induces the formation of large conductance channels at neutral pH, when added to liposomes or bilayers containing both purified ANT and Bax, yet has no or little effect combined with ANT or Bax alone. t-Bid acts on membranes containing ANT alone with the same efficiency as on those containing both ANT and Bax. These results suggest that the proapoptotic effects of Bid are mediated, at least in part, by its functional interaction with ANT, one of the major components of PTPC.

Animals↗
PubMed2000

Two distinct pathways leading to nuclear apoptosis.

Apaf-1(-/-) or caspase-3(-/-) cells treated with a variety of apoptosis inducers manifest apoptosis-associated alterations including the translocation of apoptosis-inducing factor (AIF) from mitochondria to nuclei, large scale DNA fragmentation, and initial chromatin condensation (stage I). However, when compared with normal control cells, Apaf-1(-/-) or caspase-3(-/-) cells fail to exhibit oligonucleosomal chromatin digestion and a more advanced pattern of chromatin condensation (stage II). Microinjection of such cells with recombinant AIF only causes peripheral chromatin condensation (stage I), whereas microinjection with activated caspase-3 or its downstream target caspase-activated DNAse (CAD) causes a more pronounced type of chromatin condensation (stage II). Similarly, when added to purified HeLa nuclei, AIF causes stage I chromatin condensation and large-scale DNA fragmentation, whereas CAD induces stage II chromatin condensation and oligonucleosomal DNA degradation. Furthermore, in a cell-free system, concomitant neutralization of AIF and CAD is required to suppress the nuclear DNA loss caused by cytoplasmic extracts from apoptotic wild-type cells. In contrast, AIF depletion alone suffices to suppress the nuclear DNA loss contained in extracts from apoptotic Apaf-1(-/-) or caspase-3(-/-) cells. As a result, at least two redundant parallel pathways may lead to chromatin processing during apoptosis. One of these pathways involves Apaf-1 and caspases, as well as CAD, and leads to oligonucleosomal DNA fragmentation and advanced chromatin condensation. The other pathway, which is caspase-independent, involves AIF and leads to large-scale DNA fragmentation and peripheral chromatin condensation.

Animals↗
PubMed2000

Apoptosis-inducing factor (AIF): a ubiquitous mitochondrial oxidoreductase involved in apoptosis.

Apoptosis-inducing factor (AIF) is encoded by one single gene located on the X chromosome. AIF is ubiquitously expressed, both in normal tissues and in a variety of cancer cell lines. The AIF precursor is synthesized in the cytosol and is imported into mitochondria. The mature AIF protein, a flavoprotein (prosthetic group: flavine adenine dinucleotide) with significant homology to plant ascorbate reductases and bacterial NADH oxidases, is normally confined to the mitochondrial intermembrane space. In a variety of different apoptosis-inducing conditions, AIF translocates through the outer mitochondrial membrane to the cytosol and to the nucleus. Ectopic (extra-mitochondrial) AIF induces nuclear chromatin condensation, as well as large scale ( approximately 50 kb) DNA fragmentation. Thus, similar to cytochrome c, AIF is a phylogenetically old, bifunctional protein with an electron acceptor/donor (oxidoreductase) function and a second apoptogenic function. In contrast to cytochrome c, however, AIF acts in a caspase-independent fashion. The molecular mechanisms via which AIF induces apoptosis are discussed.

Animals↗
PubMed2000

The mitochondrion in cell death control: certainties and incognita.

Apoptosis research has recently experienced a change from a paradigm in which the nucleus determined the apoptotic process to a paradigm in which caspases and, more recently, mitochondria constitute the center of death control. Mitochondria undergo major changes in membrane integrity before classical signs of cell death become manifest. These changes concern both the inner and the outer mitochondrial membranes, leading to the dissipation of the inner transmembrane potential (DeltaPsi(m)) and/or the release of intermembrane proteins through the outer membrane. An ever-increasing number of endogenous, viral, or xenogeneic effectors directly act on mitochondria to trigger permeabilization. At least in some cases, this is achieved by a direct action on the permeability transition pore complex (PTPC), a multiprotein ensemble containing proteins from both mitochondrial membranes, which interact with pro- and antiapoptotic members of the Bcl-2 family. At present, it is elusive whether opening of the PTPC is the only physiological mechanism leading to mitochondrial membrane permeabilization. Proteins released from mitochondria during apoptosis include caspases (mainly caspases 2, 3, and 9), caspase activators (cytochrome c, hsp 10), as well as a caspase-independent death effector, AIF (apoptosis inducing factor). The functional hierarchy among these proteins and their actual impact on the decision between death and life is elusive.

Animals↗
PubMed2000

The HIV-1 viral protein R induces apoptosis via a direct effect on the mitochondrial permeability transition pore.

Viral protein R (Vpr) encoded by HIV-1 is a facultative inducer of apoptosis. When added to intact cells or purified mitochondria, micromolar and submicromolar doses of synthetic Vpr cause a rapid dissipation of the mitochondrial transmembrane potential (DeltaPsi(m)), as well as the mitochondrial release of apoptogenic proteins such as cytochrome c or apoptosis inducing factor. The same structural motifs relevant for cell killing are responsible for the mitochondriotoxic effects of Vpr. Both mitochondrial and cytotoxic Vpr effects are prevented by Bcl-2, an inhibitor of the permeability transition pore complex (PTPC). Coincubation of purified organelles revealed that nuclear apoptosis is only induced by Vpr when mitochondria are present yet can be abolished by PTPC inhibitors. Vpr favors the permeabilization of artificial membranes containing the purified PTPC or defined PTPC components such as the adenine nucleotide translocator (ANT) combined with Bax. Again, this effect is prevented by addition of recombinant Bcl-2. The Vpr COOH terminus binds purified ANT, as well as a molecular complex containing ANT and the voltage-dependent anion channel (VDAC), another PTPC component. Yeast strains lacking ANT or VDAC are less susceptible to Vpr-induced killing than control cells yet recover Vpr sensitivity when retransfected with yeast ANT or human VDAC. Hence, Vpr induces apoptosis via a direct effect on the mitochondrial PTPC.

Apoptosis↗
PubMed2000

Colour Doppler ultrasound in vesicovaginal fistulas.

The purpose was to evaluate the feasibility of diagnosing vesicovaginal fistulas by colour Doppler ultrasound with contrast media. Twelve consecutive patients were examined by vaginoscopy, methylene blue test, cystogram and cystoscopy. For ultrasound examination, the bladder was filled with saline. Then diluted contrast media (Levovist) was instilled. Colour Doppler ultrasound revealed a jet phenomenon through the bladder wall toward the vagina, proving the existence of the fistula. Eleven patients had vesicovaginal fistulas, one patient a vesicoureterovaginal fistula. Colour Doppler ultrasound had correct results in 11 of 12 patients (92%). In follow-up examinations of four patients during a prolonged drainage of the bladder, we could correctly demonstrate the closure of one fistula. Colour Doppler ultrasound with contrast media is a new useful diagnostic tool in the evaluation and follow-up of vesicovaginal fistulas. It is less invasive than cystoscopy and needs no radiation exposure. The examination is well tolerated by the patients.

Adult↗
PubMed2000

Acute hematologic toxicity and practicability of dose-intensified BEACOPP chemotherapy for advanced stage Hodgkin's disease. German Hodgkin's Lymphoma Study Group (GHSG).

BACKGROUND: Evidence is recently accumulating that the novel BEACOPP (bleomycin (B), etoposide (E), adriamycin (A), cyclophosphamide (C), vincristine (O), procarbazine (P), prednisone (P)) chemotherapy is a highly effective treatment for advanced stage Hodgkin's disease. Two dose variants of BEACOPP are currently tested in a phase III randomized multicenter trial of the GHSG. To enable more extensive testing of BEACOPP we characterized its practicability regarding schedule adherence, acute hematotoxicity and need for supportive treatment. PATIENTS AND METHODS: Data of 858 patients (6592 therapy cycles) from 184 participating institutions were evaluated. Planned total drug doses of the baseline variant (arm 1) were 80, 2400, 200, 5200, 11.2, 5600 and 4480 mg/m2 for B, E, A, C, O, P and P, respectively. Compared to arm 1, the doses of E, A and C in the dose-intensified variant (arm 2) were escalated by factor 2.0, 1.4, 1.92, respectively, using G-CSF assistance. Stepwise dose reductions were specified in case of dose-limiting toxicities. Both variants are given in eight three-weekly courses. RESULTS: Median dose adherence (dose actually given relative to planned arm 1 dose) in arm 1 was 1.0 for all drugs. Relative dose escalation of E, A, and C actually maintained in arm 2 was 1.83, 1.37 and 1.77 (medians), respectively, and 70% of patients maintained elevated dose levels throughout the entire treatment. Dose-limiting toxicities occurred in 25% of cycles in arm 2, most frequently due to leukocytopenia and thrombocytopenia. Time courses of leukocytes in arm 2 showed more severe but not more prolonged leukocytopenia compared with arm 1. WHO grades 3-4 infections were documented in 2.1% (arm 1) and 3.1% (arm 2) of all cycles. Erythrocytes were transfused in 61% (arm 1) and 28% (arm 2), platelets in < 1% (arm 1) and 6% (arm 2) of all cycles. CONCLUSIONS: Both BEACOPP schemes are practicable in a large multicenter setting. Despite increased hematotoxicity, moderate dose escalation is safe for the majority of the patients with G-CSF assistance and standard supportive treatment.

Adolescent↗
PubMed2000

Proteasome activation as a critical event of thymocyte apoptosis.

Caspase activation may occur in a direct fashion as a result of CD95 death receptor crosslinking (exogenous pathway) or may be triggered indirectly, via a Bcl-2 inhibitable mitochondrial permeabilization event (endogenous pathway). Thymocyte apoptosis is generally accompanied by proteasome activation. If death is induced by DNA damage, inactivation of p53, overexpression of a Bcl-2 transgene, inhibition of protein synthesis, and antioxidants (N-acetylcyteine, catalase) prevent proteasome activation. Glucocorticoid-induced proteasome activation follows a similar pattern of inhibition except for p53. Caspase inhibition fails to affect proteasome activation induced by topoisomerase inhibition or glucocorticoid receptor ligation. In contrast, caspase activation (but not p53 knockout or Bcl-2 overexpression) does interfere with proteasome activation induced by CD95. Specific inhibition of proteasomes with lactacystin or MG123 blocks caspase activation at a pre-mitochondrial level if thymocyte apoptosis is induced by DNA damage or glucocorticoids. In strict contrast, proteasome inhibition has no inhibitory effect on the mitochondrial and nuclear phases of apoptosis induced via CD95. Thus, proteasome activation is a critical event of thymocyte apoptosis stimulated via the endogenous pathway yet dispensable for CD95-triggered death.

Acetylcysteine↗
PubMed2000

Treatment of anaemia in myelodysplastic syndromes with prolonged administration of recombinant human granulocyte colony-stimulating factor and erythropoietin.

Treatment with recombinant human erythropoietin (rhEPO) improves anaemia in approximately 20% of the patients with myelodysplastic syndromes (MDS). Recent reports suggest that a combination treatment with rhEPO plus recombinant human granulocyte colony-stimulating factor (rhG-CSF) given for up to 18 weeks may result in a higher erythroid response rate than with rhEPO alone. We investigated the potential advantage of an even more prolonged schedule of combined rhG-CSF and rhEPO treatment to obtain and maintain stable responses. In a phase II study, 33 patients with MDS [17 with refractory anaemia (RA), eight with RA with ringed sideroblasts (RARS), eight with RA with excess blasts (RAEB) with bone marrow blast counts less than 20%] were scheduled to receive at least 36 weeks of combined therapy with rhG-CSF and rhEPO. Seventeen of 28 evaluable patients demonstrated an erythroid response [61%; 95% confidence interval (CI) 41-78] after 12 weeks of treatment. The erythroid response rate was 80% (20 of 25 evaluable patients; 95% CI 59-93) after 36 weeks. Seven of these responses developed between week 12 and week 36, whereas two initially responding patients became refractory. The cytokine therapy was generally well tolerated. Nineteen of the 20 patients responding after 36 weeks continued to be treated with both cytokines. After 1 year and 2 years of continuous combined treatment, 50% of the initially included patients showed a continuing response. Our results suggest that a prolonged combination treatment with rhG-CSF and rhEPO is highly effective in achieving a stable and long-lasting erythroid response in many patients with MDS and low blast count.

Adult↗
PubMed2000

Proliferation in murine epidermis after minor mechanical stimulation. Part 1. Sustained increase in keratinocyte production and migration.

It was our objective to obtain an insight into the details and dynamics of the cell proliferative changes following minor barrier disruption, the mechanisms of recovery, and their regulation. Hair of the dorsal area of DBA2-mice was removed and the epidermis was tape stripped. Tritiated thymidine was injected into groups of mice at daily intervals thereafter. Labelling and nuclear densities were measured at several time intervals later in the various epidermal strata to characterize cell production and cell fluxes through the tissue. A dramatic proliferative response was observed at 24 h when the labelling density increased more than sixfold in the basal layer. Labelled cells rapidly appeared in suprabasal layers within a few hours in large quantities while this process took over 2 days in normal skin. Some cycling cells were also found in the suprabasal layer (pulse labelling at 24 h) in contrast with the controls. The cellular flux through the suprabasal layers was drastically (20-fold) increased and the transit time was shortened. Although the nuclear density in the basal layer showed only moderate changes it increased four-fold in the suprabasal layer within 5 days. A kinetic model analysis suggested that the cell cycle time of proliferative cells dropped from a normal value of about 200 h to less than 12 h post tape strip. After 7 days, the proliferative activation still persisted, even though at 3 days post tape strip the stratum corneum had been re-established. Hence, a mild mechanical alteration with removal of some parts of the cornified layer in mouse backskin epidermis triggers a huge proliferative response with massive overproduction of cells that lasts at least 7 days. Our findings suggest that the re-establishment of the cornified layer does not immediately shut down cell proliferation and that more complex, slower (long-term) regulatory processes are involved.

Animals↗
PubMed2000

Proliferation in murine epidermis after minor mechanical stimulation. Part 2. Alterations in keratinocyte cell cycle fluxes.

We have recently shown that a mild mechanical irritation (tape strip) of the epidermis on the back skin of adult mice induces a strong and long lasting increase in proliferative activity and cell production. This was revealed by following the fate of 3HTdR-pulse labelled cells within the basal and suprabasal layers. To obtain further insight into the dynamics of cell kinetic changes we also performed double labelling experiments with 3HTdR and BrdUrd at various times after tape stripping. The technique for analysing the data had to account for a non stationary cell flux. A novel biometrical technique was developed which provides parameter estimates on the S-phase duration, the cell cycle duration and a parameter characterizing the degree of nonstationarity. When applied to the mechanically irritated epidermis we observed that the cell flux through the S-phase in the basal layer was accelerated by a factor of 10 between 18 and 36 h post tape strip. This activation declined slightly in the subsequent days and remained 4-6 fold higher than in the normal steady state for over 7 days post tape strip. The duration of the S-phase was 3-5 h and showed little variation. We conclude that mild mechanical irritation only affecting the stratum corneum has major stimulatory effects on the cell kinetics of proliferative keratinocytes in the basal layer of the epidermis indicating the existence of a powerful regulatory mechanism.

Animals↗
PubMed1999

Molecular characterization of mitochondrial apoptosis-inducing factor.

Mitochondria play a key part in the regulation of apoptosis (cell death). Their intermembrane space contains several proteins that are liberated through the outer membrane in order to participate in the degradation phase of apoptosis. Here we report the identification and cloning of an apoptosis-inducing factor, AIF, which is sufficient to induce apoptosis of isolated nuclei. AIF is a flavoprotein of relative molecular mass 57,000 which shares homology with the bacterial oxidoreductases; it is normally confined to mitochondria but translocates to the nucleus when apoptosis is induced. Recombinant AIF causes chromatin condensation in isolated nuclei and large-scale fragmentation of DNA. It induces purified mitochondria to release the apoptogenic proteins cytochrome c and caspase-9. Microinjection of AIF into the cytoplasm of intact cells induces condensation of chromatin, dissipation of the mitochondrial transmembrane potential, and exposure of phosphatidylserine in the plasma membrane. None of these effects is prevented by the wide-ranging caspase inhibitor known as Z-VAD.fmk. Overexpression of Bcl-2, which controls the opening of mitochondrial permeability transition pores, prevents the release of AIF from the mitochondrion but does not affect its apoptogenic activity. These results indicate that AIF is a mitochondrial effector of apoptotic cell death.

Amino Acid Sequence↗