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U T Brunk

Publications and source records attributed to U T Brunk.

97 records · Page 6Linked to original sources
PubMed1976

Cytoplasmic effects of x-irradiation on cultured cells in a nondividing stage. 1. Establishment of an experimental model.

The investigation was initiated with the aim of establishing a suitable experimental model with respect to mode of radiation and radiation dose for elucidating morphologically the sequential development of radiation induced damage of interphase cells (human glia cells in vitro). Adequately defined and reproducible cellular changes were obtained using X-radiation generated by an 8 MeV linear accelerator at a dose of 20,000 rad. The cellular alterations were studied in the light microscope and by scanning and transmission electron microscopy. The most conspicuous changes--first appreciable about 5 hours after irradiation--occurred in the lysosomal vacuome, and the plasma membrane and associated structures.

Cell Line↗
PubMedDate not supplied

Characterization of residual bodies fromed in phase II cultivated human glia cells.

Residual body-like structures have been shown to occur in small numbers in actively growing in vitro cultivated phase II human glia cells. In contact inhibited phase II glia cells they have been shown to accumulate. Whether such structures are analogous to lipofuscin pigment granules in post-mitotic cells in vivo has been uncertain. We have characterized such bodies in actively growing and contact inhibited cells as to their acid phosphatase content, heavy metal content, autofluorescent characteristics, staining characteristics and morphology. It has been shown that many of these bodies are acid phosphatase positive, contain heavy metals, show the natural and characteristic fluorescence of lipofuscin pigment, are PAS-positive, acid fast with Ziehl-Neelsen and are morphologically similar to lipofuscin. They are thus analogous to the lipofuscin granules found in post-mitotic cells in vivo. The number of such granules was found to increase following contact inhibition of the mitotic activity. We conclude that lipofuscin granules are found continuously in the culture and that the cellular content of these granules can be diluted by cell division.

Acid Phosphatase↗
PubMedDate not supplied

Lysosomal heterogeneity between and within cells with respect to resistance against oxidative stress.

The prevailing opinion on lysosomal endurance is that, as long as the cells are still alive, these organelles are generally quite stable and, thus, do not induce cell damage by leaking their numerous powerful hydrolytic enzymes to the cytosol. We suggest that this opinion is basically wrong and consider that many lysosomes are quite vulnerable, especially to oxidative stress. Moreover, we suggest that cellular degeneration, including apoptosis as well as necrosis, follows upon lysosomal disruption. We have found differing stability of lysosomal membranes to oxidative stress, not only among different cell types, but also between cells of the same type and between lysosomes of individual cells. We suggest that cellular resistance to oxidative stress is mainly a function of three parameters: (i) the capacity to degrade hydrogen peroxide before it reaches, and may diffuse into, the acidic vacuolar compartment; (ii) the resistance to reactive oxygen species of lysosomal membranes; and (iii) the intralysosomal amounts of redox-active, low molecular weight iron. Iron-catalysed intralysosomal reactions, if pronounced enough, result in peroxidation and destabilization of the lysosomal membrane. Owing to differences in the cellular synthesis of hydrogen peroxide-degrading enzymes, degree of autophagocytotic degradation of iron-containing metalloproteins, lysosomal localization within the cytoplasm and intralysosomal iron chelation, the above three parameters may vary between both different and similar cells and between lysosomes of individual cells as well, explaining their observed variability with respect to resistance against oxidative stress.

Acridine Orange↗
PubMedDate not supplied

Starvation-induced autophagocytosis paradoxically decreases the susceptibility to oxidative stress of the extremely oxidative stress-sensitive NIT insulinoma cells.

Glucose and amino acid starvation of cells in culture generally enhances their sensitivity to oxidative stress. This is explained by compensatory autophagocytosis, which results in increased amounts of lysosomal low-molecular-weight, redox-active iron, due to the degradation of metallo-proteins, with a potential increase in iron-catalyzed, intralysosomal oxidative reactions. Such reactions diminish the stability of lysosomal membranes, with resultant leakage of hydrolytic enzymes into the cytosol and ensuing cellular degeneration, often of apoptotic type. However, starvation of NIT insulinoma cells, which are normally remarkably sensitive to oxidative stress, actually attenuated the sensitivity to such stress. We found that starved NIT cells rapidly synthesized ferritin. Moreover, ferritin was found to be autophagocytosed, and the lysosomes were stabilized, as assayed by the acridine orange relocation test. We hypothesize that compensatory autophagocytosis during starvation increases the cytosolic pool of redox-active iron, as a reflection of enhanced transportation of low-molecular-weight iron from autophagic lysosomes to the cytosol, resulting in ferritin induction. The newly formed ferritin would, in turn, become autophagocytosed and bind redox-active lysosomal iron in a non-redox-active form. We also suggest that the proposed mechanism may be a way for oxidative stress-sensitive cells to compensate partly for their failing capacity to degrade hydrogen peroxide before it leaks into the acidic vacuolar apparatus and induces intralysosomal oxidative stress. The insulin-producing beta cell may belong to this type of cells.

Animals↗
PubMedDate not supplied

Intracellular interactions under oxidative stress and aging: a hypothesis.

Oxygen-derived free radicals may result from various reactions, both intra- and extracellularly, but generation of oxygen free radicals from electrons escaping from the electron transport chain in mitochondria is by far the predominant process during the lifetime of a "normal", healthy cell. There is clear evidence that mitochondria are also an important target for oxygen-derived free radicals, and the resulting mitochondrial malfunction has long been suggested as the intracellular basis of aging. Moreover, there is clear evidence that free radical-dependent reactions lead to lipofuscin formation and its accumulation in Lysosomes of post-mitotic cells. Lipofuscin accumulation was demonstrated to be dependent on the probability of iron-catalyzed Fenton reactions. A hypothesis is presented which assumes free radical dependent reactions in mitochondria and lysosomes to be interdependent. Production of hydrogen peroxide in mitochondria and its subsequent diffusion in the cytoplasm, and Fenton reactions in lysosomes, transferring hydrogen peroxide intra-lysosomally to the highly cytotoxic hydroxyl radical, are thought to be necessary intermediary steps in the generation of mitochondrial damage. On the other hand, damage to mitochondria increases both mitochondrial output of hydrogen peroxide and lipofuscin accumulation.

Aged↗