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Biomedical subjects

M Ritter

Publications and source records attributed to M Ritter.

At least 19 recordsLinked to original sources
PubMed2006

siRNA-mediated AML1/MTG8 depletion affects differentiation and proliferation-associated gene expression in t(8;21)-positive cell lines and primary AML blasts.

The chromosomal translocation t(8;21) is associated with 10-15% of all cases of acute myeloid leukaemia (AML). The resultant fusion protein AML1/MTG8 interferes with haematopoietic gene expression and is an important regulator of leukaemogenesis. We studied the effects of small interfering RNA (siRNA)-mediated AML1/MTG8 depletion on global gene expression in t(8;21)-positive leukaemic cell lines and in primary AML blasts using cDNA arrays, oligonucleotide arrays and real-time reverse transcription-polymerase chain reaction (RT-PCR). Suppression of AML1/MTG8 results in the increased expression of genes associated with myeloid differentiation, such as AZU1, BPI, CTSG, LYZ and RNASE2 as well as of antiproliferative genes such as IGFBP7, MS4A3 and SLA both in blasts and in cell lines. Furthermore, expression levels of several genes affiliated with drug resistance or indicative of poor prognosis AML (BAALC, CD34, PRG2, TSPAN7) are affected by AML1/MTG8 depletion. In conclusion, siRNA-mediated suppression of AML1/MTG8 cause very similar changes in gene expression pattern in t(8;21)-positive cell lines and in primary AML blasts. Furthermore, the results suggest that the specific targeting of AML1/MTG8 function may be a promising approach for complementing existing treatment strategies.

Acute Disease↗
PubMed2006

Inhibition of retinoic acid receptor signaling by Ski in acute myeloid leukemia.

Acute myeloid leukemia (AML) is a heterogeneous disease with multiple different cytogenetic and molecular aberrations contributing to leukemic transformation. We compared gene expression profiles of 4608 genes using cDNA-arrays from 20 AML patients (nine with -7/del7q and 11 with normal karyotype) with 23 CD34+ preparations from healthy bone marrow donors. SKI, a nuclear oncogene, was highly up regulated. In a second set of 183 AML patients analyzed with real-time PCR, the highest expression level of SKI in AML with -7/del7q could be confirmed. As previously described, Ski associates with the retinoic acid receptor (RAR) complex and can repress transcription. We wanted to investigate the interference of Ski with RARalpha signaling in AML. Ski was co-immunoprecipitated and colocalized with RARalpha. We also found that overexpression of wild-type Ski inhibited the prodifferentiating effects of retinoic acid in U937 leukemia cells. Mutant Ski, lacking the N-CoR binding, was no more capable of repressing RARalpha signaling. The inhibition by wild-type Ski could partially be reverted by the histone deacetylase blocking agent valproic acid. In conclusion, Ski seems to be involved in the blocking of differentiation in AML via inhibition of RARalpha signaling.

Acute Disease↗
PubMed2006

Location of major histocompatibility complex class II molecules in rafts on dendritic cells enhances the efficiency of T-cell activation and proliferation.

The existence of major histocompatibility complex (MHC) class II molecules in lipid rafts has been described in dendritic cells (DC); however, the importance of rafts in T-cell activation has not been clarified. In this study, the distribution of the lipid raft components (CD59 and GM1 ganglioside) in human monocyte-derived DC was investigated. DC had an even distribution of these components at the cell surface. In addition, raft-associated GM1 ganglioside colocalized with cross-linked MHC class II. This implies coaggregation of raft components with these MHC molecules, which may be important in the interaction between T cells and antigen-presenting cells. In studies carried out to investigate the effect of the DC : T-cell interaction on raft distribution, we found a clustering of the lipid raft component CD59 on DC at the synaptic interface, with associated activation of the interacting T cell. In an antigen-specific response between DC and CD4+ T-cell clones, disruption of lipid rafts resulted in inhibition of both CD59 clustering and T-cell activation. This was most pronounced when limiting amounts of cognate peptide were used. Together, these data demonstrate the association of MHC class II with lipid rafts during DC : T-cell interaction and suggest an important role for DC lipid rafts in T-cell activation.

CD4-Positive T-Lymphocytes↗
PubMed2006

Cell volume regulatory ion transport in the regulation of cell migration.

Cell migration is typically accomplished by the generation of protrusive mechanical forces and is achieved by repeated spatially and temporally coordinated cycles including the formation of a leading edge, the formation of new and disruption of older adhesions to the substratum, actomyosin based contractions and retraction of the trailing edge. Beside the well-described roles of the cytoskeleton and cell adhesions during these processes, a growing body of evidence indicates that the precise regulation of the cell volume is an indispensable prerequisite for coordinated cell migration. On the one hand during cell migration cell volume is continuously tormented by mechanical and morphological alterations, which pose changes to the intracellular hydrostatic pressure, metabolic changes and the formation or degradation of macromolecules like actin, which distort the osmotic equilibrium and the action of chemoattractants, hormones and transmitters, which frequently alter the electrical properties of a cell and thus cause cell swelling or shrinkage, respectively. On the other hand, a migrating cell actively has to govern cell volume regulatory ion transport mechanisms in order to create the appropriate micro- or even nanoenvironment in the intra- and/or extracellular space, which is necessary to guarantee the correct polarity and hence direction of movement of a migrating cell. This chapter will focus on the role of the cell volume regulatory ion transport mechanisms as they participate in the regulation of cell migration and special emphasis is given to their interplay with the cytoskeleton, their meaning for substrate adhesion and to the polarized fashion of their subcellular distribution.

Animals↗
PubMed2005

Local irradiation prior to stem cell harvest has no influence on CD34+ yield: a quantitative analysis.

In patients with multiple myeloma, irradiation of bone marrow prior to mobilization of autologous peripheral blood progenitor cells (PBPCs) may lead to a reduced yield of CD34+ cells. Quantitative effects have not been sufficiently assessed. We retrospectively performed a multivariate analysis in 114 patients (67 men, 47 women) with multiple myeloma, of whom 53 (47%) patients had been irradiated prior to mobilization chemotherapy. High-dose cyclophosphamide followed by granulocyte colony-stimulating factor was used for mobilization in 84% of patients. In addition to previous chemotherapy, we quantitatively evaluated the dose and fractionation of prior irradiation, the volume of the irradiated bone marrow, and the time interval between radiation therapy and mobilization of PBPCs. The median volume of irradiated bone marrow was 9% (range 1-30%) of the estimated total hematopoietic bone marrow. The irradiated bone marrow volume and the number of CD34+ cells per kilogram of body weight in the first leukapheresis product showed no correlation. However, the time between irradiation and mobilization seemed to influence the yield of CD34+ cells. A comparison of irradiated patients with nonirradiated patients revealed no differences with respect to the CD34+ cell counts. We did not find a significant influence of the extent or the total dose of irradiation on the yield of CD34+ cells in the first leukapheresis product in patients with multiple myeloma. However, there may be an inverse correlation between the time elapsed since the last irradiation and the number of mobilized CD34+ cells.

Adult↗
PubMed2005

Caffeine inhibits cytokine expression in lymphocytes.

Caffeine alters intracellular calcium signalling patterns in lymphocytes which are important for the specific regulation of activation and effector function in lymphocytes. The effect of caffeine on calcium signalling is probably mediated via a ryanodine receptor type 3 dependent intracellular calcium store which releases calcium after exposure to caffeine. Also, caffeine decreases lymphocyte cytotoxicity against allogenic myocyte. Which cytotoxic mechanisms are actually altered by caffeine is unknown. In mouse splenocyte cultures containing about 87% lymphocytes we show that concanavalin A (ConA, 5 microg/ml) stimulated cells increase the expression of TNF-alpha, IL-2 and IFN-gamma (ELISA) significantly. Caffeine (3.75 mM) inhibits cytokine expression of ConA stimulated cells almost completely. Ryanodine (1 microM) specifically blocks ryanodine receptors and thereby prevents caffeine induced calcium release. In our experiments, however, ryanodine has no effect on ConA stimulated IL-2 and IFN-gamma expression and only suppresses TNF-alpha expression by 20%. Furthermore, ryanodine does not prevent the inhibitory effect of caffeine on TNF-alpha, IL-2 and IFN-gamma expression in stimulated effector cells. We postulate that caffeine suppresses cytokine expression and thereby contributes to decreased cytotoxicity of lymphocytes against allogenic myocytes. The ryanodine receptor dependent intracellular calcium store does not seem to play a significant role in this process. Possibly, the blockade of IP3 receptors by caffeine is more important for cytokine suppression.

Animals↗
PubMed2005

Ion channels in cell proliferation and apoptotic cell death.

Cell proliferation and apoptosis are paralleled by altered regulation of ion channels that play an active part in the signaling of those fundamental cellular mechanisms. Cell proliferation must--at some time point--increase cell volume and apoptosis is typically paralleled by cell shrinkage. Cell volume changes require the participation of ion transport across the cell membrane, including appropriate activity of Cl- and K+ channels. Besides regulating cytosolic Cl- activity, osmolyte flux and, thus, cell volume, most Cl- channels allow HCO3- exit and cytosolic acidification, which inhibits cell proliferation and favors apoptosis. K+ exit through K+ channels may decrease intracellular K+ concentration, which in turn favors apoptotic cell death. K+ channel activity further maintains the cell membrane potential, a critical determinant of Ca2+ entry through Ca2+ channels. Cytosolic Ca2+ may trigger mechanisms required for cell proliferation and stimulate enzymes executing apoptosis. The switch between cell proliferation and apoptosis apparently depends on the magnitude and temporal organization of Ca2+ entry and on the functional state of the cell. Due to complex interaction with other signaling pathways, a given ion channel may play a dual role in both cell proliferation and apoptosis. Thus, specific ion channel blockers may abrogate both fundamental cellular mechanisms, depending on cell type, regulatory environment and condition of the cell. Clearly, considerable further experimental effort is required to fully understand the complex interplay between ion channels, cell proliferation and apoptosis.

Animals↗
PubMed2005

Interferon-alpha2a is sufficient for promoting dendritic cell immunogenicity.

Type I interferons (IFNs) are widely used therapeutically. IFN-alpha2a in particular is used as an antiviral agent, but its immunomodulatory properties are poorly understood. Dendritic cells (DCs) are the only antigen-presenting cells able to prime naive T cells and therefore play a crucial role in initiating the adaptive phase of the immune response. We studied the effects of IFN-alpha2a on DC maturation and its role in determining Th1/Th2 equilibrium. We found that IFN-alpha2a induced phenotypic maturation of DCs and increased their allostimulatory capacity. When dendritic cells were stimulated simultaneously by CD40 ligation and IFN-alpha2a, the production of interleukin (IL)-10 and IL-12 was increased. In contrast, lipopolysaccharide (LPS) stimulation in the presence of IFN-alpha2a mainly induced IL-10 release. The production of IFN-gamma and IL-5 by the responder naive T cells was also amplified in response to IFN-alpha2a-treated DCs. Furthermore, IL-12 production by IFN-alpha2a-treated DCs was enhanced further in the presence of anti-IL-10 antibody. Different results were obtained when DCs were treated simultaneously with IFN-alpha2a and other maturation factors, in particular LPS, and then stimulated by CD40 ligation 36 h later. Under these circumstances, IFN-alpha2a did not modify the DC phenotype, and the production of IL-10/IL-12 and IFN-gamma/IL-5 by DCs and by DC-stimulated naive T cells, respectively, was inhibited compared to the effects on DCs treated with maturation factors alone. Altogether, this work suggests that IFN-alpha2a in isolation is sufficient to promote DC activation, however, other concomitant events, such as exposure to LPS during a bacterial infection, can inhibit its effects. These results clarify some of the in vivo findings obtained with IFN-alpha2a and have direct implications for the design of IFN-alpha-based vaccines for immunotherapy.

Animals↗
PubMed2004

Lemierre's syndrome: the forgotten disease. An unusual presentation of sepsis.

A 19-year-old girl presented with a septical condition with fever of 40 degrees C, swelling of the right sternocleidomastoid region and abdominal pain. Except for a sore throat with pain strictly localized to the right side of her neck and fever over the last week there were no other clues in her past medical history. An abdominal ultrasound and MRT scan as well as a chest X-ray only showed non-specific findings. The diagnosis of Lemierre's syndrome was established by ultrasonographical detection of right jugular venous thrombosis and perivascular inflammation together with blood cultures positive for Fusobacteria. The patient recovered within days after treatment was initiated with metronidazol according to the antibiogram. Lemierre's syndrome is a life-threatening disease especially in an age group which is less frequently affected by septicaemia. A history of sore throat, Fusobacterium positive blood cultures and ultrasonographical detection of jugular venous thrombophlebitis together with the knowledge of the "forgotten disease" will lead the way to the diagnosis.

Adult↗
PubMed2004

Pneumonia in acute stroke patients fed by nasogastric tube.

BACKGROUND: Aspiration pneumonia is the most important acute complication of stroke related dysphagia. Tube feeding is usually recommended as an effective and safe way to supply nutrition in dysphagic stroke patients. OBJECTIVE: To estimate the frequency of pneumonia in acute stroke patients fed by nasogastric tube, to determine risk factors for this complication, and to examine whether the occurrence of pneumonia is related to outcome. METHODS: Over an 18 month period a prospective study was done on 100 consecutive patients with acute stroke who were given tube feeding because of dysphagia. Intermediate outcomes were pneumonia and artificial ventilation. Functional outcome was assessed at three months. Logistic regression and multivariate regression analyses were used, respectively, to identify variables significantly associated with the occurrence of pneumonia and those related to a poor outcome. RESULTS: Pneumonia was diagnosed in 44% of the tube fed patients. Most patients acquired pneumonia on the second or third day after stroke onset. Patients with pneumonia more often required endotracheal intubation and mechanical ventilation than those without pneumonia. Independent predictors for the occurrence of pneumonia were a decreased level of consciousness and severe facial palsy. The NIH stroke scale score on admission was the only independent predictor of a poor outcome. CONCLUSIONS: Nasogastric tubes offer only limited protection against aspiration pneumonia in patients with dysphagia from acute stroke. Pneumonia occurs mainly in the first days of the illness and patients with decreased consciousness and a severe facial palsy are especially endangered.

Aged↗
PubMed2003

Immunobiology and gene-based immunotherapy of hepatocellular carcinoma.

PURPOSE: Hepatocellular carcinoma (HCC) is one of the major malignancies worldwide. For most patients with advanced or multifocal HCC treatment options are limited resulting in a poor prognosis. Several local ablation methods have been developed as minimally invasive strategies for HCC treatment. It is unclear, until now, whether these therapies will significantly improve the poor prognosis of patients with unresectable HCC. Novel therapeutic strategies and a better understanding of HCC imunobiology are, therefore, urgently required. DESIGN: The scientific literature since 1970 in all languages cited in Medline was systematically reviewed. RESULTS: Until now, a variety of specific and non-specific immunostimulatory strategies against HCC has been applied in preclinical experimental models with some promising results. The molecular characterization of HCC associated tumour antigens such as alpha-fetoprotein (AFP) and the increased understanding of the immunological pathways involved in liver and tumor immunology have paved the way for the design of promising gene-based cancer vaccines. The first phase I and II immunotherapeutic clinical trials based on dendritic cell immunotherapy and peptide vaccines are ongoing in HCC-patients. Clinical trials have, in general, demonstrated the safety of such strategies. Recently, exciting new immunological techniques and tools have been developed which allow to characterize antigen specific T cells at a single-cell level. In future, HCC specific tumor rejection antigens which can be used therapeutically have to be identified using microarray-based analysis. The different therapeutic modalities need to be compared directly resulting in optimised therapeutic approaches and the identification of sub-groups of HCC-patients responding favourably to treatment.

Adjuvants, Immunologic↗
PubMed2001

Automatic classification of HITS into artifacts or solid or gaseous emboli by a wavelet representation combined with dual-gate TCD.

BACKGROUND AND PURPOSE: Transcranial Doppler (TCD) can detect high-intensity transient signals (HITS) in the cerebral circulation. HITS may correspond to artifacts or solid or gaseous emboli. The aim of this study was to develop an offline automated Doppler system allowing the classification of HITS. METHODS: We studied 600 HITS in vivo, including 200 artifacts from normal subjects, 200 solid emboli from patients with symptomatic internal carotid artery stenosis, and 200 gaseous emboli in stroke patients with patent foramen ovale. The study was 2-fold, each part involving 300 HITS (100 of each type). The first 300 HITS (learning set) were used to construct an automated classification algorithm. The remaining 300 HITS (validation set) were used to check the validity of this algorithm. To classify HITS, we combined dual-gate TCD with a wavelet representation and compared it with the current "gold standard," the human experts. RESULTS: A combination of the peak frequency of HITS and the time delay makes it possible to separate artifacts from emboli. On the validation set, we achieved a sensitivity of 97%, a specificity of 98%, a positive predictive value (PPV) of 99%, and a negative predictive value (NPV) of 94%. To distinguish between solid and gaseous emboli, where positive refers now to the solid emboli, we used the peak frequency, the relative power, and the envelope symmetry of HITS. On the validation set, we achieved a sensitivity of 89%, a specificity of 86%, a conditional PPV of 89%, and a conditional NPV of 89%. CONCLUSIONS: An automated wavelet representation combined with dual-gate TCD can reliably reject artifacts from emboli. From a clinical standpoint, however, this approach has only a fair accuracy in differentiating between solid and gaseous emboli.

Adult↗
PubMed2001

Myocyte function and [Ca 2+ ]i homeostasis during early allogenic heart transplant rejection.

BACKGROUND: Recent studies from our laboratory have demonstrated that in vivo contractile function of rejecting mouse heterotopic abdominal heart allografts 5 days after transplantation is depressed to 40% of that of syngenic controls, and that this depression of function is prevented by the nitric oxide synthase (NOS) inhibitor NG-monomethyl-l-arginine. However, the mechanisms of altered myocyte function caused by nitric oxide production in this setting are not established. METHODS: We measured intracellular calcium concentration ([Ca2+]i) transients (fluo-3, confocal microscopy), fractional shortening (video motion), and L-type Ca2+ currents (whole-cell patch clamp) 5 days after transplantation in ventricular myocytes freshly isolated from syngenic (Balb/C into Balb/C) and allogenic (Balb/C into C3H) transplants. RESULTS: L-type Ca2+ currents, [Ca2+]i transient amplitudes, and fractional shortening did not differ between nonrejecting, syngenic and rejecting, allogenic transplants. Catecholamine responsiveness as analyzed by the change in the peak [Ca2+]i transient induced by 100 nM isoproterenol was also similar. Superfusion with l-arginine, an NOS substrate, caused decreased shortening with no change in [Ca2+]i transients in allogenic myocytes, but had no effect in syngenic myocytes. CONCLUSIONS: Depressed contractile function of rejecting allogenic heart transplants in vivo appears to be caused in part by an NOS-dependent decrease in myofilament Ca2+ sensitivity.

Animals↗
PubMed2001

Is alpha/beta for prostate tumors really low?

PURPOSE: Brenner and Hall's 1999 paper estimating an alpha/beta value of 1.5 Gy for prostate tumors has stimulated much interest in the question of whether this ratio (of intrinsic radiosensitivity to repair capacity) is much lower in prostate tumors than in other types of tumors that proliferate faster. The implications for possibly treating prostatic cancer using fewer and larger fractions are important. In this paper we review updated clinical data and present somewhat different calculations to estimate alpha/beta. METHODS AND MATERIALS: Seventeen clinical papers published from 1995 to 2000 were reviewed to obtain estimates of biochemical control from radiotherapy alone using external beam, I-125 implants, or Pd-103 implants. The focus was on intermediate risk patients. Three methods of estimating alpha/beta were employed. First, a simple two-step graphical comparison of isoeffective doses from external beam and implant modalities was made, to see which value of alpha/beta predicted the observed identity of biologic effect. Second, the same data were subjected to Direct Analysis (maximum likelihood estimation), from which an estimate of alpha/beta and also of the T(12) of repair of sublethal damage in the tumors (both with confidence intervals) were obtained. Third, preliminary clinical data comparing two different sizes of high-dose boost doses were analyzed in which significantly different bNED was observed at 2 years. RESULTS: The second method gave the definitive result of alpha/beta = 1.49 Gy (95% CI 1.25-1.76) and T(12) = 1.90 h (95% CI 1.42-2.86 h). The first method gave a range from 1.4 to 1.9 Gy and showed that if mean or median dose were used instead of prescribed dose, the estimate of alpha/beta would be substantially below 1 Gy. The third method, although based on early follow-up, was consistent with low values of alpha/beta in the region of 2 Gy or below. The estimate for T(12) is the first value reported for prostate tumors in situ. CONCLUSIONS: All the estimates point toward low values of alpha/beta, at least as low as the estimates of Brenner and Hall, and possibly lower than the expected values of about 3 Gy for late complications. Hypofractionation trials for intermediate-risk prostatic cancer appear to be indicated.

Algorithms↗