Jan Neuwirt
Charles University in Prague
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Jan Neuwirt.
Biochimica et Biophysica Acta | 1979
P. Poňka; Jitka Borová; Jan Neuwirt; Ota Fuchs; Emanuel Necas
Abstract 1. 1. Rabbit reticulocytes with a high level of non-heme radioiron induced by preincubation with isonicotinic acid hydrazide and transferrin-bound 59Fe, were reincubated with various synthetic chelating agents and the amount of radioiron released from the cells was determined. Some substances, especially derivatives of pyridoxal or 2-hydroxybenzaldehyde and isonicotinic acid hydrazide or benzhydrazide, were found to mobilize significantly iron from 59Fe-labeled reticulocytes. The effectiveness of the compounds tested decreases in the following order: pyridoxal isonicotinoyl hydrazone, pyridoxal benzoyl hydrazone, 2-hydroxybenzal isonicotinoyl hydrazone, 2-hydroxybenzal benzoyl hydrazone, pyridoxal-valine Schiff base, pyridoxal. The efficiency of these compounds exceeded the ability of common chelators such as desferrioxamine, 2,2′-bipyridine, nitrolotriacetic acid, etc., to mobilize iron from reticulocytes. 2. 2. Iron mobilization from reticulocytes by pyridoxal isonicotinoyl hydrazone requires ATP to be produced by cells and is completely blocked by low temperature (4°C). Although the effect of desferrioxamine is also prevented by low temperature, modest iron mobilization due to this chelator seems to occur independently of ATP production in reticulocytes. 3. 3. Pyridoxal isonicotinoyl hydrazone mobilizes iron mainly from mitochondria and in part also from ferritin. Although 2,2′-bipyridine seems to enter reticulocyte mitochondria and bind iron there, this chelator is not able to release iron either from mitochondria or from the cells. 4. 4. Reticulocytes with a high level of non-heme radioiron are envisaged as a useful system for testing biological effectiveness of various iron chelators. 5. 5. Pyridoxal isonicotinoyl hydrazone was shown to be an effective in vivo chelator since its administration to mice decreased 59Fe radioactivity in liver, spleen and kidney.
Biochimica et Biophysica Acta | 1973
Jitka Borová; P. Poňka; Jan Neuwirt
Abstract Iron compartments in which iron accumulates during the inhibited heme synthesis after treatment with isonicotinic acid hydrazide were studied in rabbit reticulocytes. A great accumulation of 59Fe radioactivity was found in mitochondria, low molecular weight iron compounds and non-hemoglobin proteins, especially ferritin. In a chase experiment, approximately 50% of the 59Fe radioactivity accumulated in mitochondria and low molecular weight iron compounds was re-utilized for the synthesis of hemoglobin. Although some iron is incorporated into ferritin, it apparently is not utilized for heme synthesis. In control reticulocytes, only traces of 59Fe radioactivity were detected in mitochondria and only a minute amount of 59Fe radioactivity was detected in low molecular weight iron compounds. The release of low molecular weight iron from 59Fe-transferrin occured in intact reticulocytes to a larger extent than in the stroma-free hemolysate. An attempt to establish the possible pathway of iron transport inside the reticulocyte was made. It is suggested that an iron-transferrin complexes enters the reticulocyte cytoplasm, and the majority of released iron is taken up by mitochondria for heme synthesis. When protoporphyrin IX is not available, iron accumulates inside the mitochondria.
British Journal of Haematology | 1980
M. Cikrt; P. Poňka; Emanuel Necas; Jan Neuwirt
Summary Biliary excretion of iron after administration of pyridoxal isonicotinoyl hydrazone (PIH), a recently identified effective iron‐chelating agent, was investigated in rats. PIH administered both intraperitoneally and orally was shown to increase significantly 59Fe excretion into bile of rats which had previously been injected with 59Fe‐transferrin to label hepatic parenchymal cells. 59Fe‐PIH appears in bile as early as 15 min after chelator administration and the peak of 59Fe‐radioactivity in bile is seen 1–5 h following intraperitoneal PIH injection. PIH, administered intraperitoneally, 125–250 mg/kg, increased 24 h biliary radioiron excretion about 35 times and in addition increased urinary and faecal iron excretion. When PIH was given immediately before 59Fe‐transferrin, 24 h cumulative biliary 59Fe excretion was even higher. PIH was also demonstrated to increase biliary excretion of radioiron released from 59Fe‐haemoglobin catabolysed in reticuloendothelial cells. The effect of PIH was confirmed by estimation of biliary iron concentration using the method of atomic absorption spectrophotometry. Repeated PIH administration to rats decreased 59Fe radioactivity in liver and kidney and increased urinary and faecal iron excretion.
British Journal of Haematology | 1970
P. Poňka; Jan Neuwirt
Summary One‐hour incubation of reticulocytes with 10−2m isonicotinic acid hydrazide (INH) and transferrin‐bound 59Fe changes the normal distribution of radioiron inside the cell. About 10% of 59Fe is found in haem and 90% is present in the non‐haem iron pool. The accumulated non‐haem radioiron may be utilized for haem synthesis. This is demonstrated by the reincubation of washed reticulocytes with a high non‐haem radioiron pool induced by INH under optimal conditions. The incorporation of radioiron from intracellular non‐haem pool into haem is used as a method for the estimation of the rate of haem synthesis in the presence of various inhibitors. INH reduces haem synthesis from non‐haem iron to a greater extent than that from transferrin iron. On the other hand, haemin, which inhibits the incorporation of 59Fe from transferrin into haem, does not significantly decrease the utilization of intracellular non‐haem iron for haem synthesis. These results are considered as further evidence for the inhibitory effect of haem on the membrane transport of iron. Cells with an artificially increased non‐haem iron pool incorporate more [2‐14C]glycine into haem than normal reticulocytes. These results are in accordance with the possibility that the supply of iron to the critical sites of haem synthesis may be a limiting factor controlling the rate of haem synthesis.
Biochimica et Biophysica Acta | 1972
Jan Neuwirt; P. Poňka; Jitka Borová
Abstract In the hemolysate of reticulocytes incubated with 59 Fe or [2– 14 C]glycine a radioactivity is found also in nonhemoglobin heme. About 96% of the radioactivity of nonhemoglobin heme is associated with proteins and approx. 4% is in a free form. Labeled free heme is removed from the reticulocyte hemolysate on the column of Sephadex G-25. Retained heme is eluted from the column of Sephadex G-25 by means of the special eluting solution containing serum albumin. Protein-bound nonhemoglobin heme radioactivity is recovered in hermin isolated from nonhemoglobin proteins separated by means of the chromatography on CM-Sephadex. Isonicotinic acid hydrazide which specifically inhibits heme synthesis prevents the incorporation of 59 Fe into hemoglobin heme. In the hemolysate of cycloheximide incubated reticulocytes the radioactivity in both free and protein-bound nonhemoglobin heme increases essentially. The accumulation of 59 Fe-labeled heme in the nonhemoglobin proteins in reticulocytes incubated with cycloheximide provides evidence for an existence of an increased pool of heme which is not incorporated into hemoglobin or catalase. The finding of the existence of free heme in reticulocytes might contribute to recent theories of regulation of hemoglobin synthesis.
Biochimica et Biophysica Acta | 1973
P. Poňka; Jitka Borová; Jan Neuwirt
Incubation of rabbit reticulocytes with cycloheximide and 59Fe bound to transferrin in plasma induces excessive non-hemoglobin 59Fe-labeled heme accumulation in mitochondria. During incubation of these mitochondria in vitro a part of 59Fe-labeled heme is released into the surrounding medium. The addition of globin or bovine serum albumin to the incubation mixture essentially increases the amount of heme released from mitochondria.
Biochimica et Biophysica Acta | 1992
Daniel Vyoral; Antonín Hradilek; Jan Neuwirt
Iron distribution in subcellular fractions was investigated at different times after a single cohort of 59Fe-125 I-labeled transferrin (Tf) endocytosis in K562 cells. Cell homogenates prepared by hypotonic lysis and deoxyribonuclease (DNAase) treatment were fractionated on Percoll density gradients. Iron-containing components in the postmitochondrial supernatant were further fractionated according to their molecular weight using gel chromatography and membrane filtration. In the initial phases of endocytosis, both iron and Tf were found in the light vesicular fraction. After 3 min the labels diverged, with iron appearing in the postmitochondrial supernatant and Tf in the heavy fraction containing mitochondria, lysosomes and nuclei. Iron released from Tf-containing vesicles appeared both in low- and high-molecular-weight fractions in the postmitochondrial supernatant. After 5 min of endocytosis 59Fe activity in the low-molecular-weight fraction remained constant and 59Fe accumulated in a high-molecular-weight fraction susceptible to desferrioxamine chelation. After 10 min, 59Fe radioactivity in this fraction decreased and a majority of cytosolic 59Fe was found in ferritin. These results do not support the concept of the cytosolic low-molecular-weight iron pool as a kinetic intermediate between transferrin and ferritin iron in K562 cells.
Cell Proliferation | 1976
Emanuel Necas; Jan Neuwirt
The haemopoietic tissue of mice was damaged by different cell‐cycle‐stage specific and cell‐cycle‐stage non‐specific cytostatic agents. The proliferation rate among the surviving pluripotential stem cells, i.e. those cells forming colonies in spleens of lethally irradiated mice (CFUs), was then investigated.
Cell Proliferation | 1978
Emanuel Necas; P. Poňka; Jan Neuwirt
Hydroxyurea injection kills only approximately 10% of CFU, which are in the S phase of the cell cycle. In mice given a single injection of hydroxyurea CFUs in the femur decreased only about 50% in 2–4 days after hydroxyurea, and then started to return to normal levels with an overshoot evident after the eighth day after hydroxyurea. CFUs in spleens of mice given a single injection of hydroxyurea show an evident overshoot as early as 3 days after the drug, reaching levels which are about 300% of normal. CFUs from blood disappear rapidly, but equally rapidly return to normal values followed by a significant overshoot. the radioresistance of mice increased up to 4 days after hydroxyurea.
British Journal of Haematology | 1976
E. Nečas; Jan Neuwirt
Summary. It has been demonstrated that for the slowly proliferating population of the haemopoietic pluripotent stem cells (CFUs) the response after damage by hydroxyurea to cells synthesizing DNA differs from that after damage by colchicine to cells entering mitosis. The killing of DNA synthesizing cells elicits increased proliferation in the CFUs population. From this it has been inferred that cells in the S phase may inhibit the entry of nonproliferating G0 cells into the cell cycle and in this way control cellular proliferation.