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D R Spitz

Publications and source records attributed to D R Spitz.

At least 55 records · Page 3Linked to original sources
PubMed1995

Hyperbilirubinemia results in reduced oxidative injury in neonatal Gunn rats exposed to hyperoxia.

Bilirubin is a potent antioxidant in vitro. To determine whether bilirubin also is an antioxidant in vivo, we studied markers of oxidative injury in the Gunn rat model exposed to hyperoxia. Homozygous jaundiced males were mated with heterozygous nonjaundiced females to obtain both jaundiced and nonjaundiced pups within a litter. Once delivered, the pups and their mother were placed in air (21% O2) or hyperoxia (> 95% O2) for 3 d. Both jaundiced and nonjaundiced pups were removed from the chambers daily. Animals were sacrificed and blood was drawn for determination of serum bilirubin, blood thiobarbituric acid-reactive substances (TBARS) by fluorescence assay, serum hydroperoxides, and serum protein oxidation. Tissues (liver, lung, and brain) were assayed for lipid peroxides (TBARS, conjugated dienes [CD], loss of polyunsaturated fatty acid content [PUFA]). We also measured a wide range of serum antioxidants including superoxide dismutase, catalase, glutathione, vitamins A, C, and E, and uric acid. Blood TBARS were significantly decreased in the jaundiced pups compared to the nonjaundiced pups on day 3 of hyperoxia, and blood TBARS were inversely correlated to serum bilirubin on day 3 of hyperoxia (R2 +/- .89). Similar decreases in serum lipid hydroperoxides and serum protein carbonyl content were detected in the jaundiced pups as compared to their nonjaundiced littermates. Other serum antioxidants were not increased in jaundiced animals compared to nonjaundiced animals. Relative lung weight was lower in jaundiced pups exposed to hyperoxia compared to similarly exposed nonjaundiced pups, suggesting a reduction in hyperoxia-induced lung edema. We detected no significant effects of bilirubin on parameters of lipid peroxidation in solid tissues. We conclude that serum bilirubin protects against serum oxidative damage in the first days of life in neonatal Gunn rats exposed to hyperoxia. We speculate that bilirubin is a functionally important transitional antioxidant in the circulation of human neonates and that it may be involved in modulation of injury due to hyperoxia.

Animals↗
PubMed1995

Nitric oxide-induced cytotoxicity: involvement of cellular resistance to oxidative stress and the role of glutathione in protection.

A series of experiments were designed to examine the potential cytotoxicity of nitric oxide (NO), or reactive species derived from NO, in HA1 fibroblasts and H2O2-resistant variants of this cell line, designated OC14 cells. A 1-h exposure at 37 degrees C to a 1.7 mM bolus dose of NO, prepared in N2-gassed medium, significantly reduced clonogenic survival in the HA1 fibroblasts line to 60% of control cells treated with N2-gassed medium alone. The OC14 cells were found to be completely resistant (100% survival) to NO-mediated injury in comparable experiments. A second set of experiments was designed to determine the role of the intracellular antioxidant, glutathione, in protection against NO-mediated injury. Depletion of total glutathione resulted in a significant reduction in HA1 and OC14 clonogenic survival to 8% and 50% when compared with respective control cells. The effect of total glutathione depletion on NO-initiated toxicity in HA1 cells was dose- and cell-density dependent and was observed to occur within 5 min of exposure to NO. Further evidence of cytotoxicity was demonstrated by loss of trypan blue dye exclusion properties in glutathione-depleted HA1 cells after NO exposure. Other experiments demonstrated that nitrate and nitrite exposure produced no cytotoxicity in glutathione-depleted HA1 cells and that coincubation of NO-saturated medium with oxyhemoglobin inhibited NO-induced cytotoxicity in glutathione-depleted HA1 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Establishment of a hydrogen peroxide resistant variant of renal tubular epithelial cells: role of calcium-independent phospholipase A2 in cell damage.

Renal epithelial cells resistant to oxidant stress mediated by hydrogen peroxide have been isolated and characterized. African green monkey kidney epithelial cell line, BSC-1 cells, chronically exposed to 50 microM hydrogen peroxide for 15 passages exhibited increased catalase (1.5-fold) and glutathione peroxidase (2.4-fold) activity, as well as increased total cellular glutathione (1.6-fold). This was associated with the acquisition of resistance to hydrogen peroxide cytotoxicity, as judged by nuclear staining with ethidium homodimer and clonogenic survival assay. H2O2-adapted and wild-type BSC-1 cells were used to examine the role of elevated cytosolic calcium concentration and the activation of phospholipase A2 in the development of lethal cell injury. Despite dramatic differences in resistance to oxidative stress, both cell types showed similar kinetics of cytosolic calcium increase in response to challenge with hydrogen peroxide. In contrast to this, oxidant-induced release of arachidonic acid correlated with the resistance of both types of BSC-1 cells to oxidative stress. A mechanism-based inhibitor of calcium-independent phospholipase A2 (Hazen et al., J. Biol. Chem. 266, 7227, 1991) reduced oxidant-induced lethal cell injury, suggesting that this class of phospholipases contributes to damage of BSC-1 cells exposed to hydrogen peroxide. H2O2-adapted BSC-1 cells may represent a valuable tool to study adaptation to oxidative stress and various mechanisms of cell injury.

Animals↗
PubMed1993

Cellular resistance to oxidative stress is accompanied by resistance to cisplatin: the significance of increased catalase activity and total glutathione in hydrogen peroxide-resistant fibroblasts.

Studies designed to better understand the involvement of cellular resistance to oxidative stress in mechanisms of cellular resistance to cisplatin were undertaken using H2O2-resistant variants of the HA1 Chinese hamster fibroblast cell line. H2O2-resistant cell lines were resistant to clonogenic inactivation mediated by cisplatin with dose modifying factors at 10% survival of 1.5-3.0, relative to HA1 cells. The most cisplatin resistant of these cell lines (OC5) also demonstrated fewer DNA-DNA crosslinks induced by cisplatin, relative to HA1. Since H2O2-resistant cells contained increased catalase activity as well as total glutathione (GSH) content, the involvement of these cellular antioxidants in the resistance to cisplatin toxicity was evaluated. Treatment of HA1 and H2O2-resistant cell lines (OC5, OC14) with 9 mM aminotriazole reduced catalase activity by 60-65% but had no effect on the cytotoxicity of cisplatin. In contrast, treatment with 5 mM buthionine sulfoximine reduced total GSH by 90% and sensitized the cells to cisplatin cytotoxicity. Furthermore, extracellular reaction of GSH with cisplatin prior to treating HA1 cells reduced the toxicity of the compound, indicating that this reaction is capable of participating in the detoxification of cisplatin. These results indicate that cellular adaptation to oxidative stress renders cells resistant to DNA damage as well as to cytotoxicity associated with cisplatin treatment. Furthermore, increases in total GSH content (but not catalase activity) appear to partially account for cisplatin resistance demonstrated by H2O2-resistant cells.

Animals↗
PubMed1992

Mechanisms of cellular resistance to hydrogen peroxide, hyperoxia, and 4-hydroxy-2-nonenal toxicity: the significance of increased catalase activity in H2O2-resistant fibroblasts.

An H2O2-resistant variant (OC14) of the HA1 Chinese hamster fibroblast cell line which demonstrates a 20-fold increase in catalase activity was utilized in the study of mechanisms responsible for cellular resistance to hydrogen peroxide, oxygen, and 4-hydroxy-2-nonenal toxicity. HA1 and OC14 cells were treated with 9 mM aminotriazole which resulted in a 60 to 80% reduction in catalase activity. Pretreatment with aminotriazole resulted in significant sensitization to the toxicity of 1-h exposures to exogenously applied H2O2, which was proportional to the reduction in catalase activity. Treatment with aminotriazole produced significant sensitization to the toxicity of 95% O2 after 45 h of O2 exposure but no sensitization to the toxicity of a 1-h exposure to 50 microM 4-hydroxy-2-nonenal. Inhibition of catalase activity by aminotriazole had no effect on the metabolism of 4-hydroxy-2-nonenal by either cell line tested. These results support the conclusion that in H2O2-resistant cells, catalase activity is a major determinant of cellular resistance to H2O2 toxicity, whereas catalase activity has a limited role in cellular resistance to an acute exposure to 95% O2 and is unrelated to cellular resistance to 4-hydroxy-2-nonenal.

Aldehydes↗
PubMed1992

A stable O2-resistant cell line: role of lipid peroxidation byproducts in O2-mediated injury.

HA-1 hamster fibroblasts receiving fresh media every 24 h were continuously passaged in progressively increasing O2 concentrations for 18 mo (designated O2R95). These cells were significantly more resistant than parental HA-1 to clonogenic inactivation mediated by 95% O2 without media replacement. The O2R95 cell line exhibited increases in the activities of catalase (CAT), Mn superoxide dismutase (MnSOD), Cu,Zn superoxide dismutase (Cu,Zn SOD), and glutathione peroxidase (GPx). O2R95 cells demonstrated uniformly distributed increased staining for CAT, MnSOD, Cu,Zn SOD, and GPx proteins, as determined by immunohistochemistry. Cellular resistance to and metabolism of 4-hydroxy-2-nonenal (4HNE), a toxic byproduct of lipid peroxidation implicated in mechanisms of O2 toxicity, was examined in HA-1 and O2R95 cell lines. O2R95 cells were significantly more resistant to 4HNE cytotoxicity, which was accompanied by a significant increase in 4HNE metabolism. O2R95 cells also demonstrated an increase in total glutathione (GSH) and glutathione S-transferase (GST) activity, an enzymatic system believed to be involved with 4HNE metabolism. Furthermore, homogenates from O2R95 cells consumed greater quantities of 4HNE in the presence of NADPH (but not NADH, NAD+, or NADP+), suggesting that an enzyme(s) utilizing NADPH contributes to 4HNE metabolism, resistance to 95% O2 and 4HNE as well as increased total GSH, antioxidant enzyme activities, and NADPH-dependent metabolism of 4HNE, persisted in O2R95 cells for 75 days of growth in 21% O2. These findings are compatible with the hypothesis that aldehydic byproducts of lipid peroxidation contribute to mechanisms of O2 toxicity and the selective pressure exerted by exposure of cells to hyperoxia.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

The effect of monosaturated and polyunsaturated fatty acids on oxygen toxicity in cultured cells.

The influence of oleic, linoleic (LIN), and eicosapentaenoic (EPA) acids incorporated into cellular lipids on susceptibility to O2-induced toxicity was evaluated in Chinese hamster fibroblasts (HA1) using a clonogenic cell survival assay. Fatty acid incorporation was achieved by incubating HA1 cells in 21% O2 for 72 h in the presence or absence of media supplemented with 25 microM oleic acid, 25 microM LIN, or 2, 4, and 25 microM EPA. This fatty acid incorporation period increased the percentage of composition in phospholipids 2-fold for oleic acid, 6-fold for LIN, and 6- to 20-fold for EPA. Vitamin E, total glutathione, superoxide dismutase activity, glutathione transferase activity, and catalase activity were unchanged, relative to control, in the 25-microM EPA-treated group, and only total glutathione was elevated in the LIN-treated group. After the incorporation period, the cells were placed in non-fatty acid supplemented media and exposed to 95% O2, and clonogenic survival responses were evaluated at time intervals up to 100 h. Sensitization to O2 toxicity in EPA-treated cells was apparent after 24 h of O2 exposure, whereas LIN-treated cells were significantly (p less than 0.05) sensitized to hyperoxia after 54 h of exposure, indicating that EPA was a more potent sensitizer for O2 injury. Furthermore, cells supplemented with 4 and 25 microM EPA were more sensitive to O2 toxicity than cells supplemented with 2 microM EPA. In contrast, cells treated with 25 microM oleic acid were significantly more resistant to O2 toxicity at 51, 72, and 98 h of O2 exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Hypoxia and resistance to hydrogen peroxide confer resistance to tumor necrosis factor in murine L929 cells.

The mechanism whereby tumor necrosis factor (TNF) kills mammalian cells is not well understood, although oxidative damage has been suggested by several investigators. Further, it is not known why cells vary in their responsiveness to TNF. We show that the cytotoxic effect of TNF toward TNF-sensitive L929 cells is blocked under hypoxic conditions, suggesting a critical role of molecular oxygen and reactive oxygen species. To test whether cellular resistance to reactive oxygen species could provide resistance to TNF, we derived a variant strain from L929 cells by chronic exposure to an oxidizing agent, hydrogen peroxide (H2O2). These cells exhibit marked resistance to TNF as well as to H2O2. This cross-protection provides additional evidence that mechanisms of resistance to oxidative damage are causally related to TNF-induced cell death. Scatchard analysis of TNF binding did not reveal significant differences between the H2O2-resistant line and the wild-type L929 line. On the other hand, analyses of antioxidant enzymes and glutathione levels in cells of the wild-type and the H2O2-resistant lines revealed several potentially important differences. Before exposure to TNF, the H2O2-resistant variants have elevated catalase activity, decreased activity of total glutathione-S-transferase (GST), and similar superoxide dismutase (SOD) activities. Exposure to TNF led to alteration in CuZnSOD activity, and much more so in the variants than in the wild-type L929 cells. However, no significant change in MnSOD activities in cells of either cell line was observed. Total GST activity was not altered appreciably by TNF in either cell line, but Western analysis showed that the level of alpha GST isozyme was increased and mu GST isozyme decreased in the H2O2-resistant variants. Furthermore, alterations in total glutathione content were observed in both the control and the variant cells.

Animals↗
PubMed1991

Replacement of media in cell culture alters oxygen toxicity: possible role of lipid aldehydes and glutathione transferase in oxygen toxicity.

Replacement of media in cell cultures during exposure to hyperoxia was found to alter oxygen toxicity. Following 100 hr of exposure to 95% or 80% O2, the surviving fraction (SF) of Chinese hamster fibroblasts, as assayed by clonogenicity, was less than 1 x 10(-3) when the culture media was replaced only at the onset of the O2 exposure. Media replacement every 24 hr throughout the hyperoxic exposure resulted in SFs of 1.7 x 10(-1) (95% O2) and 1.9 x 10(-1) (80% O2) at 95 hr. Cellular resistance to and metabolism of 4-hydroxy-2-nonenal (4HNE), a cytotoxic byproduct of lipid peroxidation, was examined in cells 24 hr following exposure to 80% O2 for 144 hr with media replacement. These O2-exposed cells were resistant to 4HNE, requiring 2.6 times as long in 80 microM 4HNE to reach 30% survival as compared to density-matched normoxia control. Furthermore, during 40 and 60 min of exposure to 4HNE, the O2-preexposed cells metabolized greater quantities of 4HNE (fmole/cell) relative to control. The activity of glutathione S-transferase (GST), an enzyme believed to be involved with the detoxification of 4HNE, was significantly increased in the O2-preexposed cells compared with controls. Catalase activity was significantly increased, but no change was found in total glutathione content, glutathione peroxidase, manganese superoxide dismutase, and copper-zinc superoxide dismutase activities at the time of 4HNE treatment in the O2-preexposed cells relative to density-matched control. The results demonstrate that in vitro tolerance to the cytotoxic effects of hyperoxia can be achieved through media replacement during O2 exposure. Tolerance to oxygen toxicity conferred resistance to the cytotoxic effects of 4HNE, possibly through GST-catalyzed detoxification. These results provide further support for the hypothesis that toxic aldehydic byproducts of lipid peroxidation contribute to hyperoxic injury.

Aldehydes↗
PubMed1991

Glutathione dependent metabolism and detoxification of 4-hydroxy-2-nonenal.

The involvement of glutathione (GSH) dependent processes in the detoxification of 4-hydroxy-2-nonenal (4HNE) was investigated using Chinese hamster fibroblasts and clonogenic cell survival. GSH reacted, in a dose-dependent fashion, with 4HNE in phosphate buffer at pH 6.5, leading to the disappearance of 4HNE. The addition of glutathione transferase activity (GST) facilitated a more rapid disappearance of 4HNE but the reaction was still dependent on the concentration of GSH. When cell cultures were exposed to the reaction mixtures, 4HNE cytotoxicity was also reduced in a manner which was dependent on the concentration of GSH. When 2.16- or 1.08-mM GSH were incubated in phosphate buffer with 1.08-mM 4HNE in the presence or absence of GST, then mixed with media and placed on cells for 1 h, the cytotoxicity associated with exogenous exposure to free 4HNE was abolished. GSH depletion (greater than 90%) using buthionine sulfoximine (BSO) was accomplished in control (HA1) and H2O2-resistant variants derived from HA1. GSH depletion resulted in enhanced cytotoxicity of 4HNE in all cell lines. This BSO-induced sensitization to 4HNE cytotoxicity was accompanied by a significant reduction in the ability of cells to metabolize 4HNE. The magnitude of the sensitization to 4HNE toxicity caused by GSH depletion was similar to the magnitude of the reduction in the ability of cells to metabolize 4HNE. These results support the hypothesis that GSH and GST provide a biologically significant pathway for protection against aldehydic by-products of lipid peroxidation.

Aldehydes↗
PubMed1990

Cytotoxicity and metabolism of 4-hydroxy-2-nonenal and 2-nonenal in H2O2-resistant cell lines. Do aldehydic by-products of lipid peroxidation contribute to oxidative stress?

Toxic aldehydes, such as 4-hydroxy-2-nonenal (4HNE) and 2-nonenal (2NE), formed during lipid peroxidation have been isolated and implicated in the cytotoxic effects of oxidative stress. We have investigated the cytotoxicity and metabolism of 4HNE and 2NE in control (HA-1) cells and in two H2O2-resistant Chinese hamster fibroblast cell lines. The H2O2-resistant cells were found to be significantly more resistant than HA-1 cells to the cytotoxicity of 4HNE, as determined by clonogenic cell survival (dose-modifying factors at 10% isosurvival of 2.0-3.0). The H2O2-resistant cells demonstrated a significant 2-3-fold increase in the amount of 4HNE removed (mol/cell) from culture media containing 72 microM-4HNE when compared with HA-1 cells. The enhanced ability of H2O2-resistant cells to metabolize 4HNE was abolished by heating the cells at 100 degrees C for 45 min. Similar results were obtained with 2NE. Total glutathione and glutathione transferase activity, believed to be involved in cellular detoxification of 4HNE, were found to be significantly increased (2-3-fold) in the resistant cells when compared with the HA-1 cells. These results show that cell lines adapted and/or selected in a highly peroxidative environment are also resistant to the cytotoxicity of aldehydes formed during lipid peroxidation. This resistance appears to be related to increased cellular metabolism of these aldehydes, possibly through the glutathione transferase system. These findings suggest that the formation of aldehydes due to lipid peroxidation may contribute significantly to the mechanisms of oxidant-induced injury and the selective pressure exerted by H2O2-mediated cytotoxicity in culture.

Aldehydes↗
PubMed1990

Heat-induced cytotoxicity in H2O2-resistant Chinese hamster fibroblasts.

Hydrogen-peroxide-resistant Chinese hamster fibroblasts, derived from the HA-1 cell line, were isolated following continuous culturing in the presence of progressively increasing concentrations of hydrogen peroxide. The hydrogen-peroxide-resistant phenotype has been stable for over 360 days following removal from H2O2 stress. These H2O2-resistant cell lines demonstrate increased resistance to hyperthermic cell killing mediated by continuous heating at 43 degrees C but not 45 degrees C. The relationship between mammalian cellular adaptation to oxidative stress mediated by H2O2 and resistance to 43 degrees C hyperthermia is discussed.

Animals↗
PubMed1990

Oxygen toxicity in control and H2O2-resistant Chinese hamster fibroblast cell lines.

Following exposure to 95% oxygen, clonogenic cell survival was assayed and qualitative morphologic changes were observed in a Chinese hamster fibroblast cell line (HA-1). The time in 95% O2 necessary to clonogenically inactivate 90% of the cells was inversely related to the cell density of the cultures at the beginning of hyperoxic exposure (from 1 to 6 X 10(4) cells/cm2). The O2-induced loss in clonogenicity and evidence of morphologic injury were shown to be significantly delayed (17-22 h) in an H2O2-resistant variant of the parental HA-1 cell line. After the delay in onset of clonogenic cell killing or morphologic injury, the process of injury proceeded in a similar fashion in both cell lines. The H2O2-resistant cell line demonstrated significantly greater catalase activity (20-fold), CuZn superoxide dismutase activity (2-fold), and Se-dependent glutathione peroxidase activity (1.5-fold). The greater activities of CuZn superoxide dismutase and catalase were accompanied by similarly greater quantities of immunoreactive protein as determined by immunoblotting. These data demonstrate that the cells adapted and/or selected for growth in a highly peroxidative environment also became refractory to O2-induced toxicity, which may be related to increased expression of antioxidant enzymes. However, the magnitude of this cross-resistance to O2 toxicity was less than the magnitude of the cellular resistance to the toxicity of exogenous H2O2, suggesting that in this system the toxicity of 95% oxygen is not identical to H2O2-mediated cytotoxicity.

Animals↗
PubMed1990

Does heat shock enhance oxidative stress? Studies with ferrous and ferric iron.

Chinese hamster ovary cells were exposed to FeSO4 or FeCl3 during a 43 degrees C heat shock. Concentrations of iron, which were not toxic when cells were incubated at 37 degrees C, became toxic in a dose-dependent fashion during hyperthermia treatment. The iron chelator EDTA, which supports oxidation/reduction reactions, promoted hyperthermia-induced iron cytotoxicity while the iron chelator desferrioxamine, which has been shown to inhibit iron redox cycling, inhibited cytotoxicity. The presence of exogenous superoxide dismutase, catalase, or mannitol during hyperthermia treatment did not inhibit iron toxicity. Depletion of intracellular glutathione by diethylmaleate increased hyperthermia-induced iron toxicity by 76%. These data are interpreted to mean that heat shock promotes intracellular oxidative damage and intracellular glutathione is necessary for protection.

Animals↗
PubMed1990

Evidence that hydrogen peroxide generated by 365-nm UVA radiation is not important in mammalian cell killing.

We compared measurements of cell survival and DNA single-strand breaks (SSBs) caused by hydrogen peroxide (H2O2) and UVA radiation (365-nm) in both a parental and a H2O2-resistant variant of the Chinese hamster ovary HA1 line derived by culturing cells in progressively higher concentrations of H2O2. Both RNA slot blot analysis and enzyme analysis confirmed that the variant possesses high levels of both catalase activity and mRNA. The variant was completely resistant to the lethal effects of H2O2 over the concentration range tested (up to 480 microM), whereas the parental strain showed less than 1% survival at this concentration. Similarly, the H2O2-resistant strain exhibited far fewer SSBs after exposure to H2O2 than the parental strain. Addition of o-phenanthroline to the parental cells during H2O2 exposure almost completely inhibited SSB induction, evidence that these SSBs are produced via the Fenton pathway of Haber-Weiss reactions. Very little difference was found between the variant and the parent after exposure to 365-nm radiation: only a minor difference in survival kinetics and no difference is SSB induction were observed between the two cell lines. These results are consistent with a hypothesis that most lethal events caused in cells by UVA occur by pathways that do not involve the H2O2 that is produced by sensitized reactions within the cells.

Animals↗
PubMed1989

An assay for superoxide dismutase activity in mammalian tissue homogenates.

During the course of measuring superoxide dismutase (SOD) activity in rat breast tissue, interferences in the nitroblue tetrazolium (NBT) and cytochrome c assay systems were noted. These interferences inhibit accurate measurement of SOD activity in breast tissues, necessitating the development of a new NBT-based assay that includes compounds capable of inhibiting tissue specific interferences. The most effective compounds were metal chelators that were also electron transport chain inhibitors. Bathocuproine sulfonate (BCS) was the most effective of these compounds. The inclusion of BCS in the NBT assay system was shown to make the accurate measurement of SOD activity in tissues with interferences possible.

Adenocarcinoma↗
PubMed1989

Relationship between changes in ploidy and stable cellular resistance to hydrogen peroxide.

Stable hydrogen peroxide (H2O2)-resistant variants of the Chinese hamster ovary HA-1 line have been isolated by culturing cells in progressively increasing concentrations of H2O2 (greater than 200 days, in 50-800 microM H2O2). Increases in catalase activity in these variant cell lines were shown to correlate with increased H2O2 resistance. Stable (greater than 240 days) H2O2-resistant cell lines, seven quasidiploid (21-22 chromosomes/cell) and six quasitetraploid (40-44 chromosomes/cell) were clonally isolated from the 800 microM adapted H2O2-resistant variants which were heterogeneous with respect to ploidy. The H2O2 dose-modifying factors (DMFs) were 3, 5, 8, 13, 15, 26, and 27 for the seven quasidiploid cell lines, and 21, 32, 38, 40, 42, and 49 for the six quasitetraploid cell lines. The mean DMF was 14 +/- 10 for the former and 37 +/- 10 for the latter. Our data show that on the average the quasitetraploid cell lines were significantly more resistant to H2O2-mediated cell killing than the quasidiploid cell lines derived from the same mixed population of 800 microM H2O2-adapted cells. When catalase activities (k units/cell) of the HA-1 cells and three of the clonally derived cell lines (two quasidiploid and one quasitetraploid) were determined and plotted vs. H2O2-DMF, a positive linear correlation was obtained (correlation coefficient = 0.99). This result was further confirmed when immunoreactive catalase protein/cell was detected by Western blots. Our data show that chronic exposure of cells to H2O2 stress (800 microM) was accompanied by increases in quasitetraploid cells within the population. Quasitetraploid cell lines derived from this population demonstrated increased stable H2O2-resistance which may be related to stable increases in the expression of catalase.

Animals↗