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L Witte

Publications and source records attributed to L Witte.

At least 55 records · Page 3Linked to original sources
PubMed1998

Four new bioactive lobane diterpenes of the soft coral Lobophytum pauciflorum from Mindoro, Philippines.

The marine soft coral Lobophytum pauciflorum collected from Mindoro Island, Philippines, yielded four new lobane diterpene derivatives: the acetate congeners of epoxylobatrienol and lobatrienediol (2 and 7, respectively), a methoxyl congener of lobatetraene (10), and an oxepin congener of lobatrienetriol (11), and six known derivatives (1, 3-6, and 8). The structures of the new compounds were unambiguously established on the basis of NMR spectroscopic (1H, 13C, COSY, 1H-detected direct, and long-range 13C-1H correlations) and mass spectrometric (EIMS) data. All of the compounds were active against the phytopathogenic fungus Cladosporium cucumerinum. Compound 1 was found to be active against the Gram-positive bacteria Bacillus subtilis and the yeast Saccharomyces cerevisiae. The isolated lobane diterpenes were also active in the brine shrimp lethality test. In the latter bioassay, compounds 8 and 10 were the most active congeners with LC50's of 0.64 and 4.18 micrograms/mL, respectively.

Animals↗
PubMed1998

A new meroditerpenoid dimer from an undescribed Philippine marine sponge of the genus Strongylophora.

An undescribed Philippine marine sponge of the genus Strongylophora yielded a new meroditerpenoid-strongylophorine dimer (1) and the known meroditerpenoids, strongylophorine-2 (2), strongylophorine-3 (3), and strongylophorine-4 (4). The structures of the compounds were established on the basis of NMR spectroscopic and mass spectrometric data. The position of the inter-unit linkage in the new compound was elucidated after methylation and 1D 1H NOE difference experiments. This is the first report wherein the1H and 13C NMR data of the strongylophorine congeners are fully and unambiguously assigned on the basis of 2D NMR spectroscopy. Compounds 2 and 3 exhibited slight activity against Micrococcus luteus and Salmonella typhii, respectively. Compound 3 was active against the phytopathogenic fungusCladosporium cucumerinum and also against the neonate larvae of the polyphagous pest insectSpodoptera littoralis (EC50 of 69 [+/-0.48 (S.E.)] ppm) when incorporated into artificial diet. Compound 1 was found to be the most active in the brine shrimp lethality test with a LC50 of 10.5 [+/-0.43 (S.E.)] microg/mL.

Animals↗
PubMed1998

Monoclonal antibodies targeting the VEGF receptor-2 (Flk1/KDR) as an anti-angiogenic therapeutic strategy.

Biological evidence suggests that interference with the function of the angiogenic growth factor receptor VEGFR2 (flk1/KDR) is a particularly promising strategy to inhibit tumor-induced angiogenesis. Proof of concept was established by developing a monoclonal rat anti-mouse VEGFR2 antibody (DC101) and showing that it potently blocked the binding of VEGF to its receptor, inhibited VEGF-induced signaling, and strongly blocked tumor growth in mice through an anti-angiogenic mechanism. Since DC101 does not cross-react with the human VEGFR2 KDR, anti-KDR monoclonal antibodies were generated by standard hybridoma technology and by using phage display library. High affinity antibodies (Kd = 4.9 x 10(-10)-1.1 x 10(-9) M) were found with both approaches. The anti-KDR antibodies compete on an equimolar basis with VEGF for binding to KDR and inhibit with similar potency the VEGF-induced signaling and mitogenesis in human endothelial cells. Although these antibodies cannot be tested for in vivo efficacy in standard murine tumor models because of lack of species cross-reactivity, the similarity of their in vitro properties with those of DC101 suggests that they may be effective in blocking KDR function in vivo.

Animals↗
PubMed1998

Catalytic activities, protein- and mRNA-expression of cytochrome P450 isoenzymes in intestinal cell lines.

1. Certain chemicals and drugs in addition to metabolically activated carcinogens are substrates for intestinal cytochrome P450s (CYPs) and a number of cell lines are available which could be used in metabolism studies. These include the rat duodenal cell line IEC 6, rat ileal IEC 18, foetal human HuTu 80, foetal human small intestinal FHS 74, human duodenal HCT 8 and human colon CaCo-2 cells, but they lack thorough biochemical characterization. 2. The aim of the present study was therefore to investigate the mRNA and protein expression of CYP1A1, CYP1A2, CYP2C9/10, CYP2E1 and CYP3A. In addition, the metabolism of the immunosuppressant drug tacrolimus and of the procarcinogen 7,12-dimethyl-benz[a]anthracene (DMBA) was studied to obtain information on the functional activity on these cell lines. 3. Of all the cell lines tested only CaCo-2 cells expressed CYP1A1 at the protein and mRNA level, but the CYP2E1 and CYP3A protein was also detected in CaCo-2 and FHS 74 cells. It is of considerable interest that none of the other cell lines expressed CYP1A1, CYP1A2, CYP2C9/10 or CYP3A4 at the protein and mRNA level. 4. When the metabolism of DMBA (a model carcinogen) was studied, CaCo-2 cells produced the following metabolites: 7,12-dihydroxymethylbenz[a]anthracene, 7,12-dimethylbenz-[a]anthracene-di-hydrodiol, 7-methyl-12-hydroxymethylbenz[a]anthracene, 7-hydroxy-methyl-12-benz[a]anthracene and possibly the dihydrated product of the latter two derivatives. 5. CaCo-2 cells also catalysed the metabolism of the immunosuppressant drug tacrolimus resulting in the formation of 13-O-demethyl-tacrolimus bisdemethyl-hydroxy-tacrolimus and demethyl-dihydroxy-tacrolimus. Neither the foetal human small intestinal FHS 74 cell line nor any of the other cell lines were able to catalyse the biotransformation of tacrolimus. 6. In conclusion, only CaCo-2 cells were able to produce metabolites similar to those observed in in vivo metabolism studies, whereas all other cell lines were metabolically incompetent. Therefore, this cell line may be used in studies of intestinal biotransformation.

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

Hematopoietic activity of a stromal cell transmembrane protein containing epidermal growth factor-like repeat motifs.

Primitive hematopoietic stem cells are closely associated with discrete in vivo microenvironments. These "niches" are thought to provide the molecular signals that mediate stem cell differentiation and self-renewal. We have dissected the fetal liver microenvironment into distinct cellular components by establishing an extensive panel of stromal cell lines. One particular cell line maintains repopulating stem cells for prolonged in vitro culture periods. A subtraction cloning strategy has yielded a cDNA that encodes a cell surface glycoprotein with a restricted pattern of expression among stromal cell lines. This molecule, previously identified as delta-like/preadipocyte factor-1, contains epidermal growth factor-like repeats that are related to those in the notch/delta/serrate family of proteins. We have investigated the potential role of this molecule in hematopoietic stem/progenitor cell regulation. We show that the delta-like protein displays activity on purified stem cells by promoting the formation of "cobblestone areas" of proliferation. These cobblestone areas contain both primitive high-proliferative potential progenitors and in vivo repopulating stem cells.

Animals↗
PubMed1997

Four new bioactive polybrominated diphenyl ethers of the sponge Dysidea herbacea from West Sumatra, Indonesia.

The marine sponge Dysidea herbacea collected from Indonesia yielded four new polybrominated diphenyl ether congeners 2-5 and the known derivatives 1, 6, and 7. The structures of the new compounds were unambiguously established on the basis of NMR spectroscopic (1H, 13C, COSY, 1H-detected direct and long-range 13C-1H correlations) and mass spectrometric (EIMS) data. All of the compounds were active against the Gram-positive bacteria Bacillus subtilis and the phytopathogenic fungus Cladosporium cucumerinum. The isolated polybrominated compounds were also active in the brine shrimp lethality test. In the latter bioassay, compounds 1 and 6 were the most active with LC50's of 0.96 [SE +/- 0.19] and 0.94 [SE +/- 0.70] microg/mL, respectively.

Animals↗
PubMed1996

Expression of the hematopoietic growth factor receptor FLT3 (STK-1/Flk2) in human leukemias.

Normal expression of the hematopoietic growth factor receptor FLT3 (STK-1@Flk2) is limited to CD34+ stem/progenitor cells. We have evaluated the expression of FLT3 by RNase protection assay and Western blotting in 161 primary bone marrow (BM) samples from patients with leukemia. FLT3 RNA was found to be expressed at a higher level than in normal BM controls in 33 of 33 B-lineage acute leukemias, 11 of 12 acute myeloid leukemias (AMLs), and 3 of 11 T-cell acute leukemias (T-ALLs). Expression of FLT3 RNA was also observed in some cases of blast crisis CML. The FLT3 signal resulted from expression on the leukemic blasts, and was not caused by increased FLT3 expression on normal CD34+ stem/progenitor cells in the leukemic samples. To determine if FLT3 protein was also overexpressed, proteins were extracted from leukemic BM samples and screened by Western blotting with anti-FLT3 antisera. FLT3 protein was not detected in normal BM controls, but was found in 14 of 14 B-lineage ALLs, 36 of 41 AMLs, and 1 of 4 T-ALLs. Stimulation of patient samples with FLT3 ligand resulted in autophosphorylation of the FLT3 receptor, suggesting the receptor is functional in these cells. These data show that FLT3 RNA and protein are aberrantly expressed by AML and ALL cells in that CD34 expression and FLT3 expression are no longer synchronous, and suggest the possibility that overexpression of FLT3 could play a role in the survival and/or proliferation of malignant clones in acute myeloid and lymphoid leukemias.

Antigens, CD34↗
PubMed1996

Four new bioactive manzamine-type alkaloids from the Philippine marine sponge Xestospongia ashmorica.

Analysis of the Philippine marine sponge Xestospongia ashmorica afforded four new manzamine congeners 1-4 and four known compounds 5 and 7-9. Compound 1 is the 6-deoxy derivative of manzamine X, while 2-4 are the N-oxides of manzamine J (5), 3,4-dihydromanzamine A (6), and manzamine A (7), respectively. The structures of the new compounds were unambiguously established on the basis of NMR spectroscopic (1H, 13C, COSY, 1H-detected direct, and long-range 13C-1H correlations) and mass spectrometric (EI, FAB-MS, and electrospray ionization) data. Alkaloid N-oxide structures were confirmed by conversion to the corresponding tertiary bases by reduction with Zn/HCl. This is the first report of the occurrence of bioactive manzamine N-oxides in marine sponges. Compound 7 exhibited insecticidal activity toward neonate larvae of the polyphagous pest insect Spodoptera littoralis (with an ED50 of 35 ppm) when incorporated in artificial diet and offered to larvae in a chronic feeding bioassay. Compound 7 was also active against the Gram-positive bacteria Bacillus subtilis and Staphylococcus aureus. Cytotoxicity was studied in vitro using L1578y mouse lymphoma cells. From the alkaloids studied, the N-oxides 3 and 4 were the most active (ED50 = 1.6 micrograms/mL) followed by compound 7 (ED50 = 1.8 micrograms/mL).

Alkaloids↗
PubMed1996

The effects of Flk-2/flt3 ligand as compared with c-kit ligand on short-term and long-term proliferation of CD34+ hematopoietic progenitors elicited from human fetal liver, umbilical cord blood, bone marrow, and mobilized peripheral blood.

The Flk-2/flt3 ligand (FL) was evaluated and compared with c-kit ligand (KL) for its in vitro proliferative effects on CD34+ cells from human fetal liver, umbilical cord blood, bone marrow, and mobilized peripheral blood. Using a 7-day liquid culture system, FL in combination with interleukin-3 (IL-3), interleukin-6 (IL-6), and granulocyte colony-stimulating factor (G-CSF) was comparable with KL in combination with IL-3, IL-6, and G-CSF for the expansion of hematopoietic progenitors. When FL-containing cultures were assayed after 21 or 28 days, a greater number of progenitors were generated as compared with KL-containing cultures. Using bone marrow microvascular endothelial cells as support stroma, cultures supplemented with FL generated a greater number of progenitors in both the nonadherent and adherent layers at day 35. These data suggest that FL ligand, in combination with other cytokines, can be used for short-term ex vivo expansion of hematopoietic progenitors and facilitates the preservation and possible expansion of primitive cells capable of long-term generation of progenitors.

Antigens, CD34↗
PubMed1995

Hypoxia-mediated induction of acidic/basic fibroblast growth factor and platelet-derived growth factor in mononuclear phagocytes stimulates growth of hypoxic endothelial cells.

Wound repair and tumor vascularization depend upon blood vessel growth into hypoxic tissue. Although hypoxia slows endothelial cell (EC) proliferation and suppresses EC basic fibroblast growth factor (bFGF) expression, we report that macrophages (MPs) exposed to PO2 approximately 12-14 torr (1 torr = 133.3 Pa) synthesize and release in a time-dependent manner platelet-derived growth factor (PDGF) and acidic/basic FGFs (a/bFGFs), which stimulate the growth of hypoxic ECs. Chromatography of hypoxic MP-conditioned medium on immobilized heparin with an ascending NaCl gradient resolved three peaks of mitogenic activity: activity of the first peak was neutralized by antibody to PDGF; activity of the second peak was neutralized by antibody to aFGF; and activity of the third peak was neutralized by antibody to bFGF. Metabolically labeled lysates and supernatants from MPs exposed to hypoxia showed increased synthesis and release of immunoprecipitable PDGF and a/bFGF in the absence of changes in cell viability. Possible involvement of a heme-containing oxygen sensor in MP elaboration of growth factors was suggested by the induction of bFGF and PDGF by normoxic MPs exposed to nickel or cobalt, although metabolic inhibitors such as sodium azide were without effect. These results suggest a paracrine model in which hypoxia stimulates MP release of PDGF and a/bFGF, inducing EC proliferation and potentially promoting angiogenesis in hypoxic environments.

Animals↗
PubMed1994

Heparin modulates the interaction of VEGF165 with soluble and cell associated flk-1 receptors.

The 165-amino acid form of vascular endothelial growth factor (VEGF165) is a mitogen for vascular endothelial cells and a potent angiogenic factor. Expression of a chimeric receptor containing the extracellular domain of the flk-1 receptor fused to the transmembrane and intracellular domains of the human c-fms receptor in NIH-3T3 cells, resulted in the appearance of high affinity binding sites for 125I-VEGF165 on transfected cells. The binding of 125I-VEGF165 to the flk-1/fms chimeric receptor of the transfected cells as well as the VEGF165-induced autophosphorylation of the chimeric receptors were inhibited in the presence of low concentrations of heparin (1-10 micrograms/ml). In contrast, similar concentrations of heparin potentiated the binding of 125I-VEGF165 to the endogenous VEGF receptors of the transfected cells, indicating that to some extent, the effect of heparin on 125I-VEGF165 binding is receptor type-dependent. A soluble fusion protein containing the extracellular domain of flk-1 fused to alkaline phosphatase (flk-1/SEAP) was used to study the effects of heparin on the binding of 125I-VEGF165 to flk-1 in a cell-free environment. The fusion protein specifically inhibited VEGF165-induced proliferation of vascular endothelial cells, but bound 125I-VEGF165 inefficiently in the absence of heparin. Addition of low concentrations of heparin or heparan sulfate (0.1-1 microgram/ml) resulted in a strong potentiation of 125I-VEGF165 binding, whereas higher heparin or heparan sulfate concentrations inhibited the binding. The effect of heparin on the binding of 125I-VEGF165 to flk-1/SEAP could not be mimicked by desulfated heparin or by chondroitin sulfate. Both bFGF and aFGF inhibited the binding when low concentrations of heparin were added to the binding reaction. However, higher concentrations of heparin abolished the inhibition, indicating that the inhibition is probably caused by competition for available heparin. Taken as a whole, these results indicate that heparin-like molecules regulate the binding of VEGF165 to its receptors in complex ways which depend on the heparin binding properties of VEGF165, on the specific VEGF receptor type involved, and on the amount and composition of heparin-like molecules that are present on the cell surface of VEGF receptor containing cells.

3T3 Cells↗
PubMed1994

STK-1, the human homolog of Flk-2/Flt-3, is selectively expressed in CD34+ human bone marrow cells and is involved in the proliferation of early progenitor/stem cells.

We cloned the cDNA for stem cell tyrosine kinase 1 (STK-1), the human homolog of murine Flk-2/Flt-3, from a CD34+ hematopoietic stem cell-enriched library and investigated its expression in subsets of normal human bone marrow. The cDNA encodes a protein of 993 aa with 85% identity and 92% similarity to Flk-2/Flt-3. STK-1 is a member of the type III receptor tyrosine kinase family that includes KIT (steel factor receptor), FMS (colony-stimulating factor 1R), and platelet-derived growth factor receptor. STK-1 expression in human blood and marrow is restricted to CD34+ cells, a population greatly enriched for stem/progenitor cells. Anti-STK-1 antiserum recognizes polypeptides of 160 and 130 kDa in several STK-1-expressing cell lines and in 3T3 cells transfected with a STK-1 expression vector. Antisense oligonucleotides directed against STK-1 sequences inhibited hematopoietic colony formation, most strongly in long-term bone marrow cultures. These data suggest that STK-1 may function as a growth factor receptor on hematopoietic stem and/or progenitor cells.

Amino Acid Sequence↗
PubMed1994

Apoprotein B structure and receptor recognition of triglyceride-rich low density lipoprotein (LDL) is modified in small LDL but not in triglyceride-rich LDL of normal size.

We compared the effect of lipid composition and particle size of triglyceride-rich low density lipoprotein (LDL) upon apoprotein B conformation and binding to the LDL receptor. Three groups of triglyceride-rich LDL were studied: (a) LDL isolated from chronic hypertriglyceridemic individuals (HTG-LDL); (b) normal LDL made triglyceride-rich by in vitro incubation with triglyceride emulsion and the neutral lipid transfer protein (R-LDL); and (c) LDL from normolipidemic individuals made acutely hypertriglyceridemic by intravenous infusion of 10% Intralipid (IV-LDL). HTG-LDL was small and dense, whereas R-LDL and IV-LDL had normal size. HTG-LDL, but not R-LDL or IV-LDL, exhibited decreased binding to the LDL receptor on human skin fibroblasts in studies at 4 degrees C and reduced degradation at 37 degrees C. Apoprotein B conformation was assessed by circular dichroism and by analyzing the immunoreactivity of different monoclonal antibodies. HTG-LDL but not R-LDL or IV-LDL showed a change in the CD spectra and a consistent decrease in the immunoreactivity of monoclonal antibody 3F5 (2.5-fold) which recognizes an epitope adjacent to the receptor binding domain of apoprotein B. These findings suggest that in triglyceride-rich LDL, the relative content of neutral lipid in the core of LDL in the absence of changes in the size of the particle does not significantly affect apoprotein B conformation or its affinity for the LDL receptor.

Antibodies, Monoclonal↗
PubMed1992

Ten statements on the motivation of medical teachers to teach.

Not only high number of students, increasing disintegration of curricula, lack of resources or hindering state regulations and laws seem to be the crucial problem in medical education worldwide but in particular substantially reduced interest and poor commitment in educational matters. Ten statements on possible reasons for the teachers' lack of motivation to teach are given and proposals for promoting their commitment are made.

Career Choice↗
PubMed1991

Autocrine effects of fibroblast growth factor in repair of radiation damage in endothelial cells.

The study demonstrates that basic fibroblast growth factor (bFGF) serves as an inducer of radiation damage repair in bovine aortic endothelial cells (BAEC). Radiation dose-survival curves were generated with plateau-phase BAEC using culture dishes precoated with HR9-bFGF/extracellular matrix (ECM) for the postradiation colony formation assay. This natural basement membrane-like ECM is enriched with ECM-bound bFGF. Under these conditions the cells exhibited increased repair of radiation damage as compared to cells plated on top of the bFGF-free isotype of this extracellular matrix (the HR9/ECM). While the slopes of the curves did not differ significantly (Do 107 +/- 6.8 cGy on the HR9/ECM, compared to 112 +/- 1.3 cGy on the HR9-bFGF/ECM), there was a nearly complete elimination of the threshold shoulder in the curves generated on the bFGF-free HR9/ECM (Dq 29 +/- 19 cGy, compared to 174 +/- 22 cGy on the HR9-bFGF/ECM; P less than 0.05). Delayed plating experiments, in which the cells were irradiated under bFGF-free conditions (while adherent as contact-inhibited monolayers to the HR9/ECM in bFGF-free medium) and maintained after irradiation in the same culture for various periods of time, showed that the cells performed repair of potentially lethal damage (PLDR) and restored clonogenic ability, with a 24 h to immediate postradiation recovery ratio of 3.27. This expression of PLDR was inhibited by neutralizing monoclonal antibodies against bFGF, indicating that the irradiated cells secreted bFGF into their conditioned medium. Northern blot hybridization showed a 5.6-fold increase of the 3.7-kilobase species and a 4.7-fold increase of the 7.0-kilobase species of the bFGF-specific mRNA within 6 h after delivery of a single dose of 400 cGy. The data suggest that radiation induces a complete cycle of an autoregulated damage-repair pathway in BAEC, initiated by radiation-induced damage to cellular DNA and followed by stimulation of bFGF synthesis and its secretion into the medium. The newly synthesized bFGF stimulates the PLDR pathway, acting via an extracellular autocrine loop (inhibitable by specific anti-bFGF antibodies), leading to recovery of cells from radiation lesions and restoration of their clonogenic capacity.

Animals↗
PubMed1991

Qualitative and Quantitative Analysis of the Phenolic Constituents from Orthosiphon aristatus.

ORTHOSIPHON ARISTATUS (Orthosiphonis folium DAB 9) was studied with regard to its phenolic constituents. Twenty compounds were isolated and identified on the basis of their spectral characteristics. The compounds included nine lipophilic flavones, two flavonol glycosides, and nine caffeic acid derivatives. The presence of the recently reported methylripariochromene A could not be confirmed. All compounds identified were quantified by HPLC. The caffeic acid derivatives including the major compounds rosmarinic acid and 2,3-dicaffeoyltartaric acid (67% of total identified phenolics) predominated over the flavones (33%) in an aqueous MeOH extract. The predominance of the caffeic acid derivatives was even more pronounced in a hot water extract (94.5% of total identified phenolics) that was comparable to a herbal tea.

Journal Article↗
PubMed1989

Effects of irradiation on the release of growth factors from cultured bovine, porcine, and human endothelial cells.

The effects of radiation on the release of mitogenic factors into the media of cultured endothelial cells of bovine, porcine, and human origins were studied. Although unirradiated controls revealed a significant background activity, single doses of irradiation (20-60 Gy) resulted in a dose-related increased release of growth factor activity, measured by the mitogenic effects of the conditioned media on both 3T3 mouse fibroblasts and unirradiated endothelial cells serving as target cells. Receptor binding competition assays for the platelet-derived growth factor receptor revealed that 12-28% of the total mitogenic activity was due to platelet-derived growth factor-like mitogens. Mitogenic assays using endothelial cells and specific antibody mediated inhibition assays suggested that another component of the mitogenic activity was due to a fibroblast growth factor-like factor. Although radiation resulted in a significant increase in cell death, the enhanced growth factor activities did not appear to result from cell lysis-related leakage of intracellular stores of growth factor. Instead, our data suggest that the growth factors were synthesized de novo and secreted at elevated levels by the cells which maintained postradiation a high level of metabolic activity. Time course studies demonstrated that the growth factors accumulation in the conditioned media started within the first 24 h after radiation and reached a plateau within 72 h after treatment. Radiation-induced release of endothelial cell-derived growth factors may be involved in the pathogenesis of both early vascular damage and the late fibrosis which represents a prominent feature of late radiation damage in normal tissues.

Animals↗