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Biomedical subjects

W Jelkmann

Publications and source records attributed to W Jelkmann.

At least 91 records · Page 5Linked to original sources
PubMed1994

Prevalence of paraneoplastic erythropoietin production by renal cell carcinomas.

The prevalence of increased serum immunoreactive erythropoietin (Epo) was determined in a prospective study of 49 patients with renal cell carcinoma. Measured by a monoclonal antibody based commercial enzyme-linked immunoassay, the Epo concentration was above the normal range, determined in nonanemic humans, in four of the renal carcinoma patients. Since three of these were anemic, their increased Epo level was considered to be appropriate. The high estimate of serum Epo (218 U/l) in the fourth patient, who was not anemic, was not confirmed when tested by radioimmunoassay. Thus, in contrast with earlier studies, our results indicate that increased Epo is not a clear serological renal cell carcinoma marker. In addition, when monolayer cell cultures of 14 different established human renal carcinoma lines were screened, none of these released immunoreactive Epo in measurable amounts.

Adult↗
PubMed1994

Nucleotide sequences of apple stem pitting virus and of the coat protein gene of a similar virus from pear associated with vein yellows disease and their relationship with potex- and carlaviruses.

The nucleotide sequence (9306 nucleotides) of cDNA clones of apple stem pitting virus (ASPV) obtained from a double-stranded RNA template, extracted from diseased plant tissue, was determined. The genome is composed of five open reading frames (ORFs) encoding putative proteins with M(r)s of 247083, 25147, 12832, 7429 and 43712, and has a poly(A) tail. Using two oligonucleotides designed from the ASPV sequence information a 1598 bp fragment from near the 3' terminus of the viral RNA, containing the coat protein of M(r) 43,766, was amplified from vein yellows (VY)-infected pear plants by PCR. The sequence determined showed eight nucleotide changes resulting in five amino acid substitutions compared with the sequence of ASPV. When compared to potex-, carla-, clostero- and capilloviruses, the ASPV genome organization appeared to be most closely related to that of potexviruses, but with a larger coat protein of M(r) 44K (ORF5). The predicted coat protein size was confirmed by immunoblot analysis. The results show that ASPV does not fall into subgroup A of the closteroviruses but that it probably belongs in an as yet undefined group of viruses. They also suggest that the virus associated with VY is a strain of ASPV.

Amino Acid Sequence↗
PubMed1994

Serum immunoreactive erythropoietin in hyper- and hypothyroidism: clinical observations related to cell culture studies.

Laboratory experiments have demonstrated that tetra- and triiodothyronine (T4, T3) enhance hypoxia-induced erythropoietin (Epo) production. In the present study serum immunoreactive Epo was measured in 29 patients with hyperthyroidism and in 10 patients with hypothyroidism. Epo levels were inversely correlated to the blood haemoglobin concentration [Hb] in both groups of patients. However, Epo levels at given [Hb] were significantly higher in the hyperthyroid state. In vitro studies confirmed that T4 and T3 stimulate Epo synthesis in the human liver cell line HepG2. This stimulating effect persisted for at least 1 day after the removal of T4 and T3 from the cultures. Thus, while thyroidal disorders affect steady-state levels of circulating Epo, it seems unlikely that thyroid hormones play a major role in abrupt adjustments of Epo production, such as the diurnal changes.

Carcinoma, Hepatocellular↗
PubMed1994

Thyroid hormones enhance hypoxia-induced erythropoietin production in vitro.

Effects of thyroid hormones on the production of erythropoietin (Epo) were investigated in isolated perfused rat kidneys and in the human hepatoma cell line, HepG2. Epo protein was measured by radioimmunoassay. L-triiodothyronine and L-thyroxine stimulated hypoxia-induced Epo formation both in the kidney and in HepG2 cells in a dose-dependent fashion. Quantitation of Epo mRNA by competitive polymerase chain reaction (PCR) showed that hypoxic HepG2 cells had three-fold higher Epo messenger RNA levels when treated with thyroid hormones for 3 hours. Measurements of oxygen consumption revealed that this effect was not due to an increase in the degree of hypoxia. Thus, apart from the known direct effect on erythroid precursors, thyroid hormones appear to stimulate erythropoiesis by a noncalorigenic increase in Epo production.

Animals↗
PubMed1994

Biology of erythropoietin.

The glycoprotein hormone erythropoietin is an essential survival and growth factor for the erythrocytic progenitors in the bone marrow. Its peptide sequence of 165 amino acids is stabilized by 4 carbohydrate side chains (total molecular mass 30 kDa, 60% protein). Erythropoietin is synthesized mainly in the kidney. Its formation increases greatly in response to hypoxia. The mechanism by which lack of oxygen induces erythropoietin gene expression is only partly understood. Erythropoietin deficiency is the primary cause of the anemia in chronic renal failure. Erythropoietin production is lowered in severe acidosis and in inflammatory states. Genetical engineering has enabled the isolation of the human erythropoietin gene and its in vitro expression in mammalian cell cultures. Recombinant human erythropoietin has been approved to be an efficient and safe drug for treatment of renal anemia. This paper reviews some of the recent advances in the understanding of the biology of erythropoietin with respect to its possible application as an alternative to blood transfusion in surgical patients.

Animals↗
PubMed1993

Photometric characteristics of haem proteins in erythropoietin-producing hepatoma cells (HepG2).

Erythropoietin (Epo)-producing hepatoma cells (HepG2) reveal, in addition to the cytochromes of the respiratory chain, a photometrically measurable haem signal with absorbance maxima at 559 nm and 427 nm, suggesting the presence of a b-type cytochrome. This activity exhibited a low midpoint potential, CO-binding spectra and reduction which was insensitive to both cyanide and antimycin. This haem possessed a 22 kDa subunit and might be part of an electron transfer chain similar to the NADPH oxidase, since the NADPH oxidase cytosolic activating factor (p47) could be identified by Western blot analysis. H2O2, which was detected inside the cells by confocal microscopy, might therefore be produced by the suggested electron transfer chain. This cyanide- and antimycin-insensitive but hypoxia-sensitive cytochrome b would be an attractive candidate for controlled Epo production in response to pO2.

Blotting, Western↗
PubMed1993

Immunocytochemical demonstration of erythropoietin in hypoxic human hepatoma cultures.

The possibility of demonstrating erythropoietin at the light microscopic level was examined in homogenous cultures of the erythropoietin-producing human hepatoma cell lines HepG2 and Hep3B. Immunoperoxidase staining was applied in combination with several mono- and polyclonal antibodies. Sufficiently strong colour responses were obtained with all three polyclonal antibodies and with one of three monoclonal antibodies raised against recombinant human erythropoietin. The staining intensity was increased in hypoxic versus nonhypoxic hepatoma cultures. Intracellular erythropoietin immunoreactivity was confirmed by Western blot analysis of HepG2 extracts. The effect of oxygen supply on erythropoietin gene expression was confirmed by competitive polymerase chain reaction of erythropoietin mRNA and by radioimmunoassay of secreted erythropoietin.

Animals↗
PubMed1993

Effects of chemotherapeutic and immunosuppressive drugs on the production of erythropoietin in human hepatoma cultures.

The effects of agents used in combination chemotherapy were studied on erythropoietin synthesis in cultures of the human hepatoma cell line, HepG2. Erythropoietin was measured by radioimmunoassay in the culture media after 24-h treatment periods. The RNA synthesis-inhibiting drugs daunorubicin, cyclophosphamide, ifosfamide, and cis-diamine-dichloroplatinum produced a dose-dependent decrease of the production of erythropoietin. Inhibition was also induced by the tubulin-binding agents vincristine and colchicine and the immunosuppressive agents azathioprine and cyclosporin A. The DNA synthesis-inhibiting drugs methotrexate and cytosine arabinoside, the antimycotics 5-fluorocytosine and amphotericin B, and glucocorticoids did not inhibit. Viability studies showed that the inhibition of erythropoietin production was partly correlated with cytotoxicity. These data could be relevant with respect to recombinant erythropoietin replacement therapy in tumor-associated anemia.

Animals↗
PubMed1993

Microelectrode measurements of pericellular PO2 in erythropoietin-producing human hepatoma cell cultures.

On the basis of Fick's law of gas diffusion, it has been proposed that cells in conventional monolayer cultures may be severely hypoxic. Because knowledge of the cellular O2 availability is important for the interpretation of biochemical and toxicological cell culture work, microelectrode measurements of the pericellular PO2 were carried out using the erythropoietin (Epo)-producing human hepatoma cell lines Hep G2 and Hep 3B as an in vitro model. In confluent hepatoma cultures grown in polystyrene dishes and incubated in air with 5% CO2, the pericellular steady-state PO2 was < 1 mmHg. The rates of the production of immunoreactive Epo and lactate were high due to a misproportion between O2 supply and O2 requirements. Epo production decreased when shaken instead of static cultures were studied, or when the O2 concentration in the gas atmosphere was increased gradually up to 95%. In cultures grown on gas-permeable supports, pericellular and gas PO2 values were very similar, with increased Epo production at lowered PO2. In agreement with mathematical models, our experimental data make PO2 measurements desirable for studies of O2-dependent biological functions in cell cultures.

Carcinoma, Hepatocellular↗
PubMed1992

Monokines inhibiting erythropoietin production in human hepatoma cultures and in isolated perfused rat kidneys.

The blood level of erythropoietin (Epo) is often anomalously low in anemic patients with inflammatory or malignant diseases. Therefore, we studied effects of pure recombinant immunomodulatory peptides on Epo formation in cultures of the human hepatoma cell line, HepG2. Interleukin (IL)-1 beta, IL-1 alpha, and tumor necrosis factor alpha lowered Epo production with half-maximal inhibition at 2, 5, and 20 U/ml, respectively. IL-6, transforming growth factor beta 2 and interferon gamma did not inhibit. Furthermore, IL-1 beta (10 U/ml) proved to block Epo formation in isolated serum-free perfused rat kidneys. Proposedly, monokines play a role in the pathogenesis of Epo deficiency in various diseases.

Animals↗
PubMed1992

The nucleotide sequence and genome organization of strawberry mild yellow edge-associated potexvirus.

The nucleotide sequence (5966 nucleotides) of cDNA clones of strawberry mild yellow edge-associated potexvirus was determined. The genome contains six open reading frames (ORFs) encoding putative proteins with Mrs of 149,423, 25,344, 11,576, 8079, 25,714 and 11,216. In the first three putative proteins and the coat protein considerable similarity was found to comparable polypeptides of the potexviruses potato virus X, clover yellow mosaic virus, narcissus mosaic virus, papaya mosaic virus, white clover mosaic virus and lily virus X.

Amino Acid Sequence↗
PubMed1991

Inhibition of erythropoietin production by phorbol ester is associated with down-regulation of protein kinase C-alpha isoenzyme in hepatoma cells.

The role of protein kinase C (PKC) in the control of erythropoietin (Epo) production was studied using the human hepatoma cell line HepG2. Inhibition of PKC by staurosporine and the selective PKC inhibitor CGP 41251 significantly reduced Epo formation. No inhibition occurred with the inactive staurosporine derivative CGP 42700. Treatment with phorbol 12-myristate 13-acetate (PMA) for 24 h dose-dependently inhibited Epo formation, thus suggesting that down-regulation of PKC might be responsible for this inhibition. Immunoblotting experiments showed that incubation of HepG2 cells with PMA for 24 h resulted in a selective and almost complete down-regulation of PKC-alpha. Thus, PKC-alpha may play a permissive role in Epo synthesis in HepG2 cells.

Alkaloids↗