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Biomedical subjects

A Kraemer

Publications and source records attributed to A Kraemer.

16 recordsLinked to original sources
PubMed2004

Reliability of non-invasively acquired human genomic DNA as a substrate for real-time PCR-assisted analysis of genetic polymorphisms.

Molecular epidemiological studies require high numbers of participants. The combination of an non-invasive access to human DNA with a rapid genotyping analysis, e.g. by use of LightCycler assisted real-time polymerase chain reaction (PCR), can be helpful in conducting such trials. The aim of our study was to define, for the first time, the use of LightCycler technology in analysis of non-invasively derived DNA. DNA extracted from blood, mouthwash and buccal cytobrush samples from 100 volunteers was analyzed for the genotypes of cytochrome P450 CYP1B1, and glutathione S-transferases GSTT1, GSTM1 and GSTP1. The median amounts of DNA isolated from blood, mouthwash and buccal cytobrush samples were 95, 11 and 8 microg, respectively. While genotyping for CYP1B1 codon 432 polymorphism and GSTP1 codon 105 polymorphism resulted in a complete correspondence for all three modes of sampling, the identification of individuals with null-genotype for GSTT1 or GSTM1 failed in some cases due to atypical courses of the corresponding melting curves, leading to high false-positive rates in the group of non-invasively derived samples. Thus, the results presented here call for caution in using LightCycler assisted real-time PCR in non-invasively collected samples, at least when appropriate control strategies are not implemented.

Adult↗
PubMed2004

Clinical risk factors and prognostic significance of local recurrence in cutaneous melanoma.

BACKGROUND: True local recurrence (LR) means clinically detectable regrowth of parts of the tumour which were not completely excised. In the literature the term 'LR' has been used in a vague and inconsistent manner that may include satellite and in-transit metastasis. OBJECTIVE: The aim of this study was to establish clinical, histological and surgical risk factors for the manifestation of LR and to evaluate the prognostic significance of LR. STUDY DESIGN: Data from 3960 Stage I and II melanoma patients who visited the melanoma clinic of the Department of Dermatology at the University of Tuebingen from 1980 to 1999 were documented in a prospective manner. A retrospective comparative analysis of patients with and without LR was performed. RESULTS: Of all patients 1.4% had a LR as a first recurrence and 1.7% had a LR in the course of the follow-up period. LR were most frequent after previous clinical or histological misdiagnosis and inadequate therapy. In the univariate analysis significant risk factors for LR-free survival were age, tumour surface area, locality, tumour thickness, level of invasion, histological type, associated naevus, surgery (one step vs. multiple steps) and compliance with recommended excision margins. In the multivarate analysis the factors locality (P < 0.0001), tumour thickness (P = 0.0086) and compliance with recommendations on excision margins (P = 0.014) were significant independent risk factors for the manifestation of LR. The overall survival of patients with LR as first progression did not significantly differ from the overall survival of the other patients with melanoma (P = 0.60). CONCLUSION: True LR is a rare event for which tumour locality, tumour thickness and surgery are independent risk factors. The occurrence of LR might not impair the prognosis of melanoma patients. However, in the published literature numerous definitions of 'LR', including lymphogenic metastasis, complicate comparison.

Female↗
PubMed2003

Remarkable response to rituximab in a patient with atypical CD20(++) mantle cell lymphoma of the bone marrow leading to severe pancytopenia.

Rituximab, a chimeric monoclonal antibody which binds to the CD20 antigen, has been reported in several studies to induce remissions in low- and high-grade non-Hodgkin's lymphoma without causing myelosuppression. We report here a case of a 68-year-old female patient with an atypical mantle cell lymphoma infiltrating only the bone marrow without leukemic involvement or any other nodal or extranodal manifestations. Progressive severe pancytopenia due to the diffuse bone marrow infiltration led to life-threatening infections following oral chlorambucil treatment. No response to chlorambucil was noted. The patient attained a complete remission after salvage therapy with four weekly infusions of single-agent rituximab at a standard dose of 375 mg/m(2). Thus, anti-CD20 antibody may be the treatment of choice for patients with CD20(+) B-non-Hodgkin's lymphoma who cannot tolerate chemotherapy due to high risk of infectious complications as a result of severe pancytopenia.

Aged↗
PubMed2002

Occurrence of sarcoidosis subsequent to chemotherapy for non-Hodgkin's lymphoma: report of two cases.

Sarcoidosis-lymphoma syndrome is a well-established syndrome where sarcoidosis is followed by the development of a lymphoproliferative disease such as non-Hodgkin's lymphoma (NHL). Here we report two patients with NHL who developed sarcoidosis subsequent to the diagnosis of lymphoproliferative disease. In both cases, chemotherapeutic treatment had already been initiated or was completed when sarcoidosis occurred. In these patients, sarcoidosis may have been triggered by immunologic aberrations induced by antineoplastic therapy or as a consequence of an underlying immunologic disturbance associated with the lymphoma. When a suspected relapse of lymphoma presents with signs and symptoms compatible with sarcoidosis, this rare immunologic disorder has to be ruled out by careful clinical and histopathologic analysis to prevent mistreatment.

Adult↗
PubMed2001

Search for x-ray induced acceleration of the decay of the 31-yr isomer of (178)Hf using synchrotron radiation.

Enhanced decay of the 31-yr isomer of (178)Hf induced by x-ray irradiation has been reported previously. Here we describe an attempt to reproduce this result with an intense "white" x-ray beam from the Advanced Photon Source. No induced decay was observed. The upper limits for the energy-integrated cross sections for such a process, over the range of energies of 20--60 keV x rays, are less than 2 x 10(-27) cm(2) keV, below the previously reported values by more than 5 orders of magnitude; at 8 keV the limit is 5 x 10(-26) cm(2) keV.

Journal Article↗
PubMed2001

Dynamic interaction of cAMP with the Rap guanine-nucleotide exchange factor Epac1.

Epac1 is a Rap-specific guanine-nucleotide exchange factor (GEF) which is activated by the binding of cAMP to a cyclic nucleotide monophosphate (cNMP)-binding domain. We investigated the equilibrium and dynamics of the interaction of cAMP and Epac1 using a newly designed fluorescence analogue of cAMP, 8-MABA-cAMP. We observed that the interaction of cAMP, measured by competition with 8-MABA-cAMP, with an isolated cNMP binding domain of Epac1 has an overall equilibrium constant (Kd) of 4 microM and that the kinetics of the interaction are highly dynamic. The binding properties of cAMP are apparently not affected when the catalytic domain is present, despite the fact that binding of cAMP results in activation of Epac1. This indicates that for the activation process, no appreciable binding energy is required. However, when bound to Rap1b, the apparent Kd of Epac to cAMP was about fivefold lower, suggesting that substrate interaction stabilizes cAMP binding. Since the fluorescent analogues used here were either less able or unable to induce activation of Epac1, we concluded that the binding of nucleotide to Epac and the activation of GEF activity are uncoupled processes and that thus appropriate cAMP analogues can be used as inhibitors of the Epac1-mediated signal transduction pathway of Rap.

Binding Sites↗
PubMed2001

Response to thalidomide in progressive multiple myeloma is not mediated by inhibition of angiogenic cytokine secretion.

Thalidomide (Thal) is a drug with anti-angiogenic properties. To explore whether the effect of Thal on angiogenesis is associated with a reduction of angiogenic cytokine levels in progressive multiple myeloma (MM), plasma levels of basic fibroblast growth factor, vascular endothelial growth factor, interleukin 6, tumour necrosis factor-alpha and hepatocyte growth factor (HGF) were measured in 51 patients at 0, 3 and 6 months of Thal therapy. After 6 months of treatment, 26 patients were considered to be responsive to Thal therapy, including 17 minimal responses, eight partial responses and one complete response. Only HGF (decreasing, P = 0.02) in the group of responsive patients showed a statistically significant change over a period of 6 months. Because HGF levels are known to correlate to MM tumour burden, we conclude that the mechanism of action of Thal in MM is not caused by a specific inhibition of angiogenic cytokine secretion.

Adult↗
PubMed2001

Conformational switch and role of phosphorylation in PAK activation.

p21-activated protein kinases (PAKs) are involved in signal transduction processes initiating a variety of biological responses. They become activated by interaction with Rho-type small GTP-binding proteins Rac and Cdc42 in the GTP-bound conformation, thereby relieving the inhibition of the regulatory domain (RD) on the catalytic domain (CD). Here we report on the mechanism of activation and show that proteolytic digestion of PAK produces a heterodimeric RD-CD complex consisting of a regulatory fragment (residues 57 to 200) and a catalytic fragment (residues 201 to 491), which is active in the absence of Cdc42. Cdc42-GppNHp binds with low affinity (K(d) 0.6 microM) to intact kinase, whereas the affinity to the isolated regulatory fragment is much higher (K(d) 18 nM), suggesting that the difference in binding energy is used for the conformational change leading to activation. The full-length kinase, the isolated RD, and surprisingly also their complexes with Cdc42 behave as dimers on a gel filtration column. Cdc42-GppNHp interaction with the RD-CD complex is also of low affinity and does not dissociate the RD from the CD. After autophosphorylation of the kinase domain, Cdc42 binds with high (14 nM) affinity and dissociates the RD-CD complex. Assuming that the RD-CD complex mimics the interaction in native PAK, this indicates that the small G protein may not simply release the RD from the CD. It acts in a more subtle allosteric control mechanism to induce autophosphorylation, which in turn induces the release of the RD and thus full activation.

Animals↗
PubMed2001

High plasma basic fibroblast growth factor concentration is associated with response to thalidomide in progressive multiple myeloma.

The aim of this study was to define prognostic factors that might be predictive for response to thalidomide (Thal) in progressive multiple myeloma (n = 54). We examined the concentration of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF), two potent heparin-binding mediators of angiogenesis in peripheral blood (PB; PB-VEGF and PB-bFGF) and bone marrow (BM; BM-VEGF and BM-bFGF), in combination with well-characterized predictors for response and survival to chemotherapy. After a median follow-up time of 15 months (range, 0.3-20), 29 patients (pts.) showed at least a minimal response to Thal therapy, whereas 25 pts. were nonresponsive. As shown by univariate analysis, responsive pts. had statistically significant higher concentrations of PB-bFGF (P = 0.009) and beta2-microglobulin (P = 0.03) before therapy, as well as lower hemoglobin (P = 0.008) and albumin (P = 0.02) levels, whereas no statistically significant difference was found for PB-VEGF (P = 0.93). When a multiple logistic regression analysis was performed, PB-bFGF was the only statistically significant predictor for response to therapy (P = 0.01). None of these variables was associated with a prolonged progression-free survival. In conclusion, our findings indicate that high pretreatment plasma bFGF levels in pts. with progressive multiple myeloma are associated with unfavorable parameters of response and survival but nevertheless predict for response to Thal therapy.

Adult↗
PubMed2000

Aneuploidy precedes and segregates with chemical carcinogenesis.

A century ago, Boveri proposed that cancer is caused by aneuploidy, an abnormal balance of chromosomes, because aneuploidy correlates with cancer and because experimental aneuploidy generates "pathological" phenotypes. Half a century later, when cancers were found to be nonclonal for aneuploidy, but clonal for somatic gene mutations, this hypothesis was abandoned. As a result, aneuploidy is now generally viewed as a consequence, and mutated genes as a cause of cancer. However, we have recently proposed a two-stage mechanism of carcinogenesis that resolves the discrepancy between clonal mutation and nonclonal karyotypes. The proposal is as follows: in stage 1, a carcinogen "initiates" carcinogenesis by generating a preneoplastic aneuploidy; in stage 2, aneuploidy causes asymmetric mitosis because it biases balance-sensitive spindle and chromosomal proteins and alters centrosomes both numerically and structurally (in proportion to the degree of aneuploidy). Therefore, the karyotype of an initiated cell evolves autocatalytically, generating ever-new chromosome combinations, including neoplastic ones. Accordingly, the heterogeneous karyotypes of "clonal" cancers are an inevitable consequence of the karyotypic instability of aneuploid cells. The notorious long latent periods, of months to decades, from carcinogen to carcinogenesis, would reflect the low probability of evolving by chance karyotypes that compete favorably with normal cells, in principle analagous to natural evolution. Here, we have confirmed experimentally five predictions of the aneuploidy hypothesis: (1) the carcinogens dimethylbenzanthracene and cytosine arabinoside induced aneuploidy in a fraction of treated Chinese hamster embryo cells; (2) aneuploidy preceded malignant transformation; (3) transformation of carcinogen-treated cells occurred only months after carcinogen treatment, i.e., autocatalytically; (4) preneoplastic aneuploidy segregated with malignant transformation in vitro and with 14 of 14 tumors in animals; and (5) karyotypes of tumors were heterogeneous. We conclude that, with the carcinogens studied, aneuploidy precedes cancer and is necessary for carcinogenesis.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1997

Aneuploidy correlated 100% with chemical transformation of Chinese hamster cells.

Aneuploidy or chromosome imbalance is the most massive genetic abnormality of cancer cells. It used to be considered the cause of cancer when it was discovered more than 100 years ago. Since the discovery of the gene, the aneuploidy hypothesis has lost ground to the hypothesis that mutation of cellular genes causes cancer. According to this hypothesis, cancers are diploid and aneuploidy is secondary or nonessential. Here we reexamine the aneuploidy hypothesis in view of the fact that nearly all solid cancers are aneuploid, that many carcinogens are nongenotoxic, and that mutated genes from cancer cells do not transform diploid human or animal cells. By regrouping the gene pool-as in speciation-aneuploidy inevitably will alter many genetic programs. This genetic revolution can explain the numerous unique properties of cancer cells, such as invasiveness, dedifferentiation, distinct morphology, and specific surface antigens, much better than gene mutation, which is limited by the conservation of the existing chromosome structure. To determine whether aneuploidy is a cause or a consequence of transformation, we have analyzed the chromosomes of Chinese hamster embryo (CHE) cells transformed in vitro. This system allows (i) detection of transformation within 2 months and thus about 5 months sooner than carcinogenesis and (ii) the generation of many more transformants per cost than carcinogenesis. To minimize mutation of cellular genes, we have used nongenotoxic carcinogens. It was found that 44 out of 44 colonies of CHE cells transformed by benz[a]pyrene, methylcholanthrene, dimethylbenzanthracene, and colcemid, or spontaneously were between 50 and 100% aneuploid. Thus, aneuploidy originated with transformation. Two of two chemically transformed colonies tested were tumorigenic 2 months after inoculation into hamsters. The cells of transformed colonies were heterogeneous in chromosome number, consistent with the hypothesis that aneuploidy can perpetually destabilize the chromosome number because it unbalances the elements of the mitotic apparatus. Considering that all 44 transformed colonies analyzed were aneuploid, and the early association between aneuploidy, transformation, and tumorigenicity, we conclude that aneuploidy is the cause rather than a consequence of transformation.

Aneuploidy↗
PubMed1997

Autocrine interleukin-1 receptor antagonist can support malignant growth of glioblastoma by blocking growth-inhibiting autocrine loop of interleukin-1.

In situ hybridization (ISH) of human glioblastoma tissue sections revealed expression of interleukin-1 (IL-1)alpha and/or beta and IL-1 receptor types I and II (IL-1R I and II) in the majority of cases evaluable. To understand the function of IL-1-family members in human glioblastomas, we have studied 6 glioblastoma cell lines. RT-PCR, ISH, ELISA and 125I-IL-1-binding assays revealed expression of IL-1 and high-affinity receptors for human (h)IL-1 in all but 1 cell line. Using a colony growth assay in semi-solid media for testing serial plating efficacy (PE, number of colonies per number of cells seeded in %), only the IL-1R-negative cell line was not influenced by recombinant human (rh)IL-1alpha or -beta, whereas IL-1 down-regulated the self-renewal of clonogenic cells of the other glioblastomas. Tritiated thymidine uptake was down-regulated by rhIL-1 in all cell lines studied. Cell viability remained unchanged by rhIL-1. Wherever growth modulation by rhIL-1 was detected, it could be reversed by either soluble IL-1R I or II or by rhIL-1 receptor antagonist (ra). IL-1ra not only was able to reverse rhIL-1-induced growth modulation but alone could modulate glioblastoma growth in comparison with control in cell lines producing IL-1. Our results show the presence of public autocrine loops for IL-1 leading to growth inhibition in some glioblastomas. To understand these loops, we have studied expression and function of IL-1ra in glioblastomas. ISH of human glioblastoma tissue sections revealed expression of hIL-1ra in all 8 cases evaluable. In 4 of 6 cell lines, IL-1ra was found in the supernatant under constitutive conditions, the IL-1R-negative line being among the 2 non-producers. The other non-producing cell line, HTB 17, showed expression of hIL-1R II. Most interestingly, a neutralizing antibody against IL-1ra down-regulated growth of IL-1- and IL-1ra-producing glioblastoma cells to approx. 30% of the controls. Thus, public autocrine loops for IL-1 in human glioblastomas exist and result in growth inhibition. An autocrine production of IL-1-antagonizing molecules such as IL-1ra by these tumors can counteract this IL-1 function and represent a basic escape mechanism supporting malignant growth in some glioblastomas.

Binding Sites↗
PubMed1990

[Description of a special form of postprandial hyperlipidemia: possible cause of premature coronary heart disease].

We have studied the metabolism of post-prandial lipoproteins in four male patients who suffered from premature (less than 60 years) angiographically proven coronary heart disease. They had normal to low total and low density lipoprotein cholesterol levels. Other risk factors were absent. Using the vitamin A fat loading test we were able to show that the clearance of chylomicron remnants was delayed compared to three healthy control subjects. Since these postprandial lipoproteins have been implicated in atherogenesis, we conclude that this defect contributed to the development of coronary heart disease in these patients.

Adult↗