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Biomedical subjects

C J Koch

Publications and source records attributed to C J Koch.

At least 127 records · Page 7Linked to original sources
PubMed1983

The radiation response of hypoxic cells in EMT6 spheroids in suspension culture does model data from EMT6 tumors.

Radiation survival curves of EMT6/Ed spheroids have been obtained under conditions which eliminate changes in oxygen concentration between growth and irradiation. These curves show a high-dose, resistant component which is nearly parallel to the curves obtained when spheroids were irradiated under nitrogen. Thus EMT6 spheroids appear to model accurately the radiation responses of EMT6 tumors. In contrast, when spheroids were grown to relatively high density (300-400 spheroids per 250-ml spinner flask), then separated into several flasks for irradiation, an increase in oxygen concentration in the medium occurred which fully oxygenated the previously hypoxic cells. The two causes for the oxygen depletion in sealed growth flasks were quantitated. Depletion of total oxygen in the flask occurred, and, more importantly, oxygen consumption kept the growth medium well below equilibrium with the oxygen in the gas phase. Smaller but similar effects on oxygen concentration were found in flasks containing V79 spheroids.

Animals↗
PubMed1980

Buoyant density of EMT6 fibrosarcoma cells: time course of the density changes after growth in hypoxia.

EMT6 fibrosarcoma cells were grown to the exponential phase in tissue culture and incubated at 37 degrees C under hypoxic conditions. Buoyant density was determined as a function of the time in hypoxia. Hypoxia was produced in two ways. The first involved incubation of the cells in sealed aluminum chambers containing 95% N2, 5% CO2 gas, and < 10 ppm oxygen, resulting in the cells rapidly becoming exposed to the hypoxic environment. After incubation at 37 degrees C, they were centrifuged in linear Ficoll gradients to their isopycnic density. A significant decrease in density was found after 4 h, and prolonged incubation up to 24 h did not result in further change. This density change was reversible on transfer back to aerobic conditions, with the hypoxic cells reverting to their aerobic density after about 10 h reincubation in air. The second method of producing hypoxia involved growing about 8 X 10(6) cells in a medium-filled air-tight container. Hypoxia was produced gradually as the oxygen in the medium was consumed by cellular respiration. Similar results were obtained; that is, hypoxic cells became significantly less dense. However, when the level of hypoxia was varied between 4000 and < 10 ppm at 2-h intervals after the cells had depleted all of the original oxygen, no significant difference in density was found between hypoxic and aerobic cells.

Animals↗
PubMed1979

Ascorbate anion potentiates cytotoxicity of nitro-aromatic compounds under hypoxic and anoxic conditions.

The nitro-aromatic radiosensitizing drugs are selectively toxic to hypoxic mammalian cells, and this toxicity can be greatly increased by the addition of ascorbate. The ascorbate itself is not toxic to either hypoxic or aerobic cells (as long as catalase is present to prevent the formation of significant concentrations of hydrogen peroxide) and the mixture of ascorbate plus radiosensitizer is not more toxic to aerobic cells. Sulphydryl reducing agents and dithionite have an effect opposite to ascorbate and decrease the toxicity of nitro-aromatic drugs under hypoxic conditions. Sulphydryl reducing agents are also reported to nullify the radiosensitizing properties of nitro-aromatic drugs, in contrast to ascorbate which has no effect on the radiosensitizing properties. The toxicity of nitro-aromatic drugs decreases rapidly with increasing O2 concentration. This decrease is much less rapid when ascorbate is present. The role of ascorbate in this case may be primarily as an O2 scavenger, although it is also possible that the toxic species produced by radiosensitizer-ascorbate mixtures is less easily removed or detoxified by O2.

Animals↗
PubMed1978

Toxicity, radiation sensitivity modification, and metabolic effects of dehydroascorbate and ascorbate in mammalian cells.

Dehydroascorbate, an electron affinic metabolite of vitamin C, sensitized Ehrlich ascites tumor cells, in vivo, to radiation and was selectively toxic to V79 Chinese hamster lung cells under hypoxic conditions (without radiation). The radiosensitization may involve both the electron affinic nature of dehydroascorbate as well as its ability to oxidize the intracellular NAD(P)H and non-protein sulfhydryl. Dehydroascorbate's oxidation of NAD(P)H required higher concentrations than other sulfhydryl oxidants such as N-ethylmaleimide and diamide. The oxidation of NAD(P)H by dehydroascorbate could be reversed by glucose. Hypoxic cell radiosensitization of V79 cells in tissue culture by dehydroascorbate could not be easily demonstrated because of the rapid breakdown and appreciable cytotoxicity of the drug at high concentration. The cytotoxicity was found to occur with both high and low densities of V79 cells. With low cell densities small amounts of oxygen did not reduce the cytotoxicity of dehydroascorbate, but virtually eliminated the cytotoxicity of nitroaromatic electron affinic compounds (metronidazole and Ro-07-0582). The cytotoxicity to dense cell suspensions was found to depend upon the type of buffer included in the reaction medium. The maximum cytotoxicity was obtained in buffer free saline. The reduced form of dehydroascorbate, vitamin C, was found to be toxic only under aerobic conditions. The aerobic cytotoxicity could be prevented by the addition of catalase to the growth medium or by an increase in cell density, suggesting it was caused entirely by the production of H2O2 from the oxidation of vitamin C.

Aerobiosis↗
PubMed1978

Cell survival in V79 multicell spheroids treated with dehydroascorbate, 5-thio-D-glucose and 2-deoxy-D-glucose.

We found that dehydroascorbic acid (DHA), 5-thio-D-glucose (5TG) and 2-deoxy-D-glucose (2DG) were toxic to monolayers of V79 cells under hypoxic conditions at 37 degree C but not at 0 degree C. Very little toxicity was observed at either temperature under aerobic conditions. When spheroids (600 micrometer diameter) were treated with 7.5 mM of these chemicals for periods up to 3 days, the number of viable cells per spheroid dropped to 70% for DHA, 50% for 5TG and 25% for 2DG relative to controls. These survivals were reduced to much lower values when the experiments were repeated in glucose-free medium.

Ascorbic Acid↗
PubMed1978

Respiration of mammalian cells at low concentrations of oxygen: I. Effect of hypoxic-cell radiosensitizing drugs.

Drugs which sensitize hypoxic mammalian cells to radiation damage in vitro can also affect the cellular respiration rate. This phenomenon was studied in detail to determine whether the changes in oxygen consumption occur at low oxygen concentrations and under optimal nutritional conditions. We have found that cells in tissue culture can undergo adaptive changes in respiration (electron flow) which make them insensitive to the effects of radiosensitizing drugs and even respiration uncouplers such as dinitrophenol, and the inhibitors rotenone and cyanide. At low cell densities, where nutrient depletion in the medium would be negligible, the drugs have reduced effects, particularly at low oxygen concentrations (below 40 mmHg oxygen partial pressure). Parallel cytotoxicity and growht inhibition studies indicate that most drugs are unlikely to have substantial effect on respiration at non-cytotoxic levels.

Cells, Cultured↗
PubMed1977

Energy metabolism and T-cell-mediated cytolysis. I. Synergism between inhibitors of respiration and glycolysis.

The energy requirements for T-cell-mediated cytolysis have been investigated. Cytolytic thymus-derived lymphocytes (CTL) were generated in vitro in mixed leukocyte cultures and assayed for cytotoxicity on 51Cr-labeled mastocytoma target cells. Cytolysis was only slightly reduced in the absence of exogenous glucose (less than 5 micrometer) or under conditions of extreme hypoxia (less than 0.2 micrometer oxygen). Furthermore, neither the glucose analogues 2-deoxy-D-glucose and 5-thio-D-glucose nor the respiratory antagonists sodium azide and 2,4-dinitrophenol were very effective inhibitors of cytolysis when used individually. However, these glucose analogues were highly effective in inhibiting cytolysis in the absence of oxygen, and the respiratory antagonists inhibited cytolysis to a much greater extent in the absence of glucose. In addition, synergistic effects were observed when the glycolytic and respiratory inhibitors were combined. Taken together, these results indicate that T-cell-mediated cytolysis is an energy-dependent process which can be supported by either oxidative or glycolytic energy pathways.

Animals↗
PubMed1975

The oxygen-enhancement ratio for reproductive death induced by 3H or 125I damage in mammalian cells.

The oxygen-enhancement ratio (o.e.r.) for 3H- and 125I-induced cell death at 4 degrees C was determined in cultured Chinese hamster cells. The o.e.r. for cell death induced by 3H-thymidine was 3-2, essentially the same value as that previously reported for X-ray induced cell death. For cell death induced by 125I-iododeoxyuridine (125IdUrd), the o.e.r. was less than 1-4. The lower o.e.r. for 125I-induced death was not due to the presence of the base analogue itself, since cells that had incorporated unlabelled IdUrd and were X-irradiated had an o.e.r. of 2-8 and cells that were inactivated by 3H-IdUrd damage at 4 degrees C had an o.e.r. even greater than 3. These results suggest that 125I-decay damage, like high-linear-energy-transfer radiation damage, is only slightly increased by the presence of oxygen.

Cell Survival↗