PubMed Health⌕ Search

Biomedical subjects

P Muus

Publications and source records attributed to P Muus.

51 records · Page 3Linked to original sources
PubMed1988

Mitochondrial biogenesis and mitochondrial activity during the progression of the cell cycle of human leukemic cells.

Mitochondrial (mt) biogenesis and mt function were investigated during the cell cycle of leukemic cells. The study shows that the activity of enzymes involved in oxidative phosphorylation increases in the early G1 phase. This increase in activity precedes that of other mt enzymes such as citrate synthase and adenylate kinase. Therefore, the synthesis of mt enzymes, needed for the reduplication of the mt mass in the course of the cell cycle, occurs in a sequential order. The enzymes of the system for oxidative phosphorylation are composed of several subunits. Some of these subunits are encoded on mtDNA and synthesized by mt-specific RNA and protein synthesis. This explains why inhibition of mt protein synthesis during the progression of the cell cycle of G1-enriched cells results in an increasing shortage of ATP. This lack of ATP results first in progression delay and, subsequently, in a cell cycle block in early G1. Furthermore, shortage of ATP impairs the increase in activity of at least one mt matrix enzyme. This study offers new information about a number of aspects of mt biogenesis and mt function during cell cycle progression and elucidates the cytostatic mechanism resulting from prolonged inhibition of mt protein synthesis.

Adenosine Diphosphate↗
PubMed1988

GM-CSF enhances sensitivity of leukemic clonogenic cells to long-term low dose cytosine arabinoside with sparing of the normal clonogenic cells.

Leukemic clonogenic cells (CFU-L) and normal myeloid progenitor cells (CFU-GM) were exposed to Ara-C in the presence of crude CSF obtained from placentas (HPCM) or recombinant human GM-CSF for varying periods. The cytotoxicity of Ara-C to CFU-L increased considerably when the exposure time to Ara-C in the presence of HPCM was extended from 20 hours to 10 days. The ID50 of the CFU-L was 1.5 +/- 2.2 x 10(-8) M Ara-C compared to 5.5 +/- 2.9 x 10(-8) M Ara-C for the CFU-GM after an exposure to Ara-C for 10 days (p less than 0.05). Replacement of crude CSF from placenta conditioned medium by rh GM-CSF resulted in identical observations. Interesting was the observation that secondary leukemic colony forming cells were more or at least equally sensitive to Ara-C in the presence of GM-CSF when compared to the primary leukemic clonogenic cells. This contrasted the secondary normal CFU-GM, which were less sensitive to Ara-C than the primary CFU-GM. This indicates that GM-CSF induces leukemic clonogenic cells with selfrenewal capacity into proliferation, and in doing so, it may enhance the cytotoxicity of a cell cycle specific drug like Ara-C with sparing of the normal clonogenic cells.

Bone Marrow↗
PubMed1987

In-vitro studies on phosphorylation and dephosphorylation of cytosine arabinoside in human leukemic cells.

The cytotoxic effect of cytosine arabinoside (ara-C) depends on the capacity of cells to form and retain intracellularly the phosphorylated metabolite cytosine arabinoside triphosphate (ara-CTP). In this study accumulation and cellular retention of ara-CTP have been measured in vitro in the bone marrow cells of 69 patients with acute leukemia. Cells were incubated with 3H-ara-C and the amount of ara-CTP formed was determined after separation of the nucleotides by thin-layer chromatography. Phosphorylation of ara-C to ara-CTP appeared to be a saturable process. The Km-equivalents varied between 1.1 and 16.2 microM ara-C. Maximal ara-CTP formation ranged from 12 to 125 pmol ara-CTP/10(6) cells in 30 min. The phosphorylation activity did not correlate with the percentage of S-phase cells. The intracellular half-life time of ara-CTP measured in vitro ranged from 53 to 210 min. Phosphorylation of ara-C was comparable in patients with acute myeloid leukemia (n = 51) and in patients with acute lymphoblastic leukemia (n = 18). Ara-CTP elimination appeared slower in lymphoblasts than in myeloblasts. The average intracellular ara-CTP level in relapsed patients (n = 34) appeared higher than in previously untreated patients (n = 52). The less favourable outcome of second remission induction therapy with conventional doses of ara-C compared to the first remission induction treatment is not explained by an alteration in the intracellular metabolism of ara-C.

Bone Marrow↗
PubMed1987

Influence of cytarabine on mitochondrial function and mitochondrial biogenesis.

Although replication of nuclear DNA is inhibited by cytarabine (ara-C), protein synthesis in the nucleocytoplasm appears to continue unabated for the duration of at least the time of the normal cell cycle. ara-C treatment of human leukemic cells resulted in increased mitochondrial membrane potential and adenosine-5'-triphosphate (ATP) production and increased activity of enzymes, coded on nuclear DNA (citrate synthetase), as well as of enzymes with subunits coded on mitochondrial DNA (cytochrome c oxidase). These mitochondrial changes occurred during a period of cell-cycle arrest, while cell size and cellular protein content continued to increase. These phenomena appeared to precede the ultimate cell death.

Cell Line↗
PubMed1987

Influence of dose and duration of exposure on the cytotoxic effect of cytarabine toward human hematopoietic clonogenic cells.

The cytotoxic effect of cytarabine (ara-C) on the clonogenic potential of human normal and leukemic hematopoietic cells was investigated. Cells were exposed to ara-C at different concentrations and for periods of one to 120 hours and continuously. Colony growth (CFU-GM/CFU-E/BFU-E) in semisolid culture was assessed after seven and 14 days. The exposure time to ara-C appeared much more important in colony growth inhibition than the drug concentration. For instance, one-hour exposure to 10(-5) mol/L ara-C appeared not cytotoxic, while cocultivation in the presence of 10(-7) mol/L ara-C resulted in a total inhibition of colony growth. Cell fractionation with use of counterflow centrifugation allowed enrichment in subfractions for cells with different amounts of DNA. The inhibition of the clonogenic potential by ara-C was most pronounced in the cell fractions with the highest proliferation activity. Colony-forming cells, assessed after 14 days of culturing appeared less sensitive for ara-C cytotoxicity than seven-day CFUs. This means that ara-C is more cytotoxic to cycling than noncycling cells because compared to the seven-day colonies, 14-day colonies originate from the more resting, more primitive progenitor cells. The cytotoxicity of ara-C to clonogenic cells appears to be related to the proliferating and the cycling state of the progenitor cells and increases with the time of exposure. This phenomenon may be explained by the fact that ara-C is a cycle-specific drug and by the fact that the probability of cells entering the cell cycle is a time-dependent process. The results of this study indicate that development of more effective antileukemic therapy should not aim so much at very high drug levels but rather at prolonged administration of ara-C.

Bone Marrow Cells↗
PubMed1986

The effect of cytosine arabinoside upon mitochondrial staining kinetics in human hematopoietic cells.

The measurement of time correlated intracellular mitochondrial staining with 3,3'-dipentyloxacarbocyanine [Di-O-C5(3)] appeared of interest to define the optimal staining conditions. Mitochondrial staining of lymphocytes, monocytes and granulocytes results in different fluorescence signals, related to the numbers of mitochondria, that are present in the cells of these various cell types. Alterations of Di-O-C(5)3 staining in a distinct cell type are due to changes in the physiological or functional state of the mitochondria. It appeared that such alterations occur in cells, which are cultured in the presence of cytosine arabinoside. The effect of cytotoxic drugs upon the mitochondrial membrane potential may be relevance for the understanding of the mechanism of action, exerted by cytotoxic drugs upon cell biology.

Carbocyanines↗
PubMed1986

Does the metabolite uracil arabinoside inhibit cytosine arabinoside (Ara-C) penetration into the cerebrospinal fluid during high-dose Ara-C therapy?

A patient with acute leukaemia was treated with i.v. 2-h infusions of Ara-C at a dose of 3.0 g/m2 every 12 h. During 6 d of therapy the concentrations of the metabolite Ara-U in the CSF reached rather high levels of between 60 and 70 mumol/l from d 2-6 due to high levels of Ara-U in the plasma. The concentration of Ara-C in the CSF after the first infusion was 10.8 mumol/l. After repetitive doses on d 2-6 the drug concentrations increased from about 3 mumol/l just before infusion to about 8 mumol/l at the end of infusion, indicating inhibition of Ara-C influx into the CSF during prolonged treatment. We suggest that the high levels of Ara-U in the plasma interfere with Ara-C transport across the blood-brain barrier.

Adult↗