Modulation of epithelial cell proliferation in culture by dissolved oxygen

Finite cell lines of turkey sperm storage tubule cells: ultrastructure and protein analysis

Cell lines of turkey sperm storage tubule (SST) epithelial cells were established. Turkey SSTs were dissected from freshly obtained uterovaginal junction (UVJ) tissue and placed in explant culture on various substrates and media. Primary cultures of SST epithelium only survived and grew from SST explants that were cultured on inactivated Sandoz inbred strain, thioguanine- and ouabain-resistance (STO) mouse feeder-cell layers in 12% fetal bovine serum-supplemented Dulbecco's Modified Eagle Medium mixed 1:1 with F12 nutrient mixture. Three independent primary colonies gave rise to 3 finite cell lines, SST-1, -2, and -3, which were continuously cultured for 8 to 16 passages at 1:3 passage ratios over a period of 3 to 4 mo. The cells were passaged by pretreatment with Y27632 and dissociation with Accutase. The SST cells grew as tightly knit monolayers on top of the feeder cells at a slow rate (approximately 96 h doubling time) at a medium pH of approximately 6.9. Lipid vacuoles were visible by light microscopy in the cells particularly at the periphery of growth. Transmission electron microscopy revealed the cells to be a polarized epithelium with apical microvilli and to have lateral tight-junction-like unions and associated desmosomes. Numerous secretory vesicles filled the upper portion of the cells’ cytoplasm, and nuclei and other major organelles such as mitochondria, rough endoplasmic reticulum, and Golgi apparatus were distributed somewhat lower in the cytoplasm. The secretory vesicles resembled mucin secretory vesicles. Proteomic analysis by mass spectroscopy of the conditioned medium of the cells, and of the cells themselves, showed the cell lines did not secrete large amounts of any particular protein, and the analysis confirmed their epithelial character. In conclusion, the SST-derived cell lines resembled the mucus-secreting cells found in the epithelium lining the UVJ of the turkey's reproductive tract.

Hypoxia limits mouse follicle growth in vitro

Ovarian follicle culture is useful for elucidation of factors involved in the regulation of follicular function. We examined the effects of gas phase oxygen concentration, an oil overlay, serum type and medium supplementation with FSH, insulin-transferrin-selenium (ITS) and l-ascorbic acid on cultured preantral mouse follicle growth in a spherical, non-attached follicle culture system. Follicle growth in 5% oxygen was significantly (P < 0.01) inferior to growth in 20% oxygen in terms of follicle diameter. This was likely due to hypoxia, as evidenced by significantly (P < 0.05) increased follicle secretion of vascular endothelial growth factor (VEGF), a marker of cell hypoxia. Follicular growth was not (P > 0.05) affected by an oil overlay, ITS supplementation or serum type. Culture in medium with 5% mouse serum, 1 IU mL-1 FSH, 25 μg mL-1 l-ascorbic acid and 20% oxygen without an oil overlay supported the growth of follicles to a maximum diameter of 380 μm in 6 days. Compared with mature preovulatory mouse follicles in vivo that often have diameters >500 μm within the same time frame, in vitro-grown follicles clearly exhibit limited growth. Thus, adequate oxygenation is an essential factor in the process of optimising follicle growth.

Characteristics of human infant primary fibroblast cultures from Achilles tendons removed post-mortem

Primary cell cultures were investigated as a tool for molecular diagnostics in a forensic setting. Fibroblast cultures had been established from human Achilles tendon resected at autopsies, from cases of sudden infant death syndrome and control infants who died in traumatic events (n=41). After isolation of primary cultures cells were stored at -135°C, and re-established up to 15 years later for experimental intervention. Growth characteristics in cultures were evaluated in relation to the age of the donor, the post mortem interval before sampling, and the storage interval of cells before entry into the study. High interpersonal variation in growth rates and cell doubling time was seen, but no statistically significant differences were found with increasing age of the donor (mean 19 weeks), length of post-mortem interval prior to sampling (6-100 h), or increase in years of storage. Fibroblast cultures established from post-mortem tissue are renewable sources of biological material; they can be the foundation for genetic, metabolic and other functional studies and thus constitute a valuable tool for molecular and pathophysiological investigations in biomedical and forensic sciences.

The pursuit of ES cell lines of domesticated ungulates

In contrast to differentiated cells, embryonic stem cells (ESC) maintain an undifferentiated state, have the ability to self-renew, and exhibit pluripotency, i.e., they can give rise to most if not all somatic cell types and to the germ cells, egg and sperm. These characteristics make ES cell lines important resources for the advancement of human regenerative medicine, and, if established for domesticated ungulates, would help make possible the improvement of farm animals through their contribution to genetic engineering technology. Combining other genetic engineering technologies, such as somatic cell nuclear transfer with ESC technology may result in synergistic gains in the ability to precisely make and study genetic alterations in mammals. Unfortunately, despite significant advances in our understanding of human and mouse ESC, the derivation of ES cell lines from ungulate species has been unsuccessful. This may result from a lack of understanding of species-specific mechanisms that promote or influence cell pluripotency. Thorough molecular characterizations, including the elucidation of stem cell "marker" signaling cascade hierarchy, species-appropriate pluripotency markers, and pluripotency-associated chromatin alterations in the genomes of ungulate species, should improve the chances of developing efficient, reproducible technologies for the establishment of ES cell lines of economically important species like the pig, cow, goat, sheep and horse.

Oxidative phosphorylation and the tricarboxylic acid cycle are essential for normal development of mouse ovarian follicles

BACKGROUND

Mouse ovarian follicles are typically grown in upright drops of culture medium. Recently we found that culture of follicles at the medium-gas interface in inverted drops markedly improved follicular development, possibly due to improved access of oxygen to the follicle. In this study, we examined the importance of aerobic energy metabolism for follicle development by culturing mouse follicles (198 6 16.5 initial microm diameter, mean 6 SD) in the presence of phosphorylation and tricarboxylic acid (TCA) cycle inhibitors.

METHODS

All inhibitors were tested in the inverted system using 100 microl medium drops in 96-well plates; certain inhibitors were also tested in upright drops with or without an oil overlay.

RESULTS

The oxidative phosphorylation inhibitor rotenone (0.1, 0.5 and 1 micromol/l) totally abolished follicle growth in the inverted system; cyanide (1 mmol/l) totally abolished growth in the upright with oil system but not in the inverted system (possibly due to loss of cyanide gas due to the absence of an oil overlay). The mitochondrial uncoupler 2,4-dinitrophenol (0.5 and 1 mmol/l) also abolished growth in the inverted system. The TCA cycle inhibitor monofluoroacetate (10 mmol/l), significantly inhibited growth in all three culture systems (P < 0.01) but malonate (10 mmol/l) had no effect.

CONCLUSIONS

Aerobic metabolism and an adequate oxygen supply are essential for normal follicular development.

Method for determining oxygen consumption rates of static cultures from microplate measurements of pericellular dissolved oxygen concentration

We describe a simple protocol for determining the oxygen consumption of cells in static culture. The protocol is based on a noninvasive oxygen-sensing microplate and a simple mathematical model derived from Fick's Law. The applicability of the model is confirmed by showing the correlation of computed oxygen consumption rate (OCR) values to actual cell densities ascertained by direct cell counting and/or MTT for HL60 and U937 cells cultured in suspension. Correlation between computed OCR and these other indications of cell number was quite good, as long as the cultures were not diffusion-limited for oxygen. The impact of the geometric factors of media depth and well size were confirmed to be consistent with the model. Based on this demonstrated correlation, we also developed a simple, completely noninvasive algorithm for ascertaining the per-cell oxygen utilization rate (OUR), which is the ratio of OCR to cell number, and a fundamental cell characteristic. This is accomplished by correlating the known seed densities to extrapolated determinations of OCR at time zero. Such determinations were performed for numerous cell types, in varying well sizes. Resulting OUR values are consistent with literature values acquired by far more painstaking methods, and ranged from <0.01 fmol.min(-1).cell(-1) for bacteria to 0.1-10 fmol.min(-1).cell(-1) for immortalized mammalian and insect cell lines to >10 fmol.min(-1).cell(-1) for primary hepatocytes. This protocol for determining OCR and OUR is extremely simple and broadly applicable and can afford rapid, informative, and noninvasive insight into the state of the culture.

Comparison of Colony-Formation Efficiency of Bovine Fetal Fibroblast Cell Lines Cultured with Low Oxygen, Hydrocortisone, L-Carnosine, bFGF, or Different Levels of FBS

A comparison of colony-formation efficiency (CFE) was made between six independent bovine fetal fibroblast (BFF) cell lines used in somatic cell nuclear transfer. Variation in CFE was assessed under different culture conditions. The conditions examined were ambient atmosphere (approximately 20% oxygen) culture versus 5% oxygen culture, three levels of fetal bovine serum (FBS) in the medium (5%, 10% or 20%), and the amendment of 10% FBS medium with basic fibroblast growth factor (1 ng/mL), L-carnosine (20 mM), or hydrocortisone (1 microM). The six BFF cell lines showed significant differences from one another in CFE. No significant difference in CFE was found with reduced oxygen culture. L-Carnosine also had no significant effect on CFE. A FBS concentration of 10% was found to produce the best overall CFE. Hydrocortisone treatment reduced the size of colonies although the number of colonies formed was not affected. Basic FGF increased the size of colonies but the number of colonies formed was not affected. The results showed that different BFF cell lines varied significantly in their CFE. Also, some medium supplements or culture conditions that have shown positive CFE effects on the fibroblasts of other species failed to show significant positive CFE effects on the BFF cell lines tested.

Oxygen Conformance of Cellular Respiration

Oxygen pressure declines from normoxic air-level to the microenvironment of mitochondria where cytochrome c oxidase (COX) reduces oxygen to water at oxygen levels as low as 0.3 kPa (2 Torr; 3 microM; 1.5 % air saturation). Intracellular hypoxia is defined as (1) local oxygen pressure below normoxic reference states, or (2) limitation of mitochondrial respiration by oxygen levels below kinetic saturation, resulting in oxyconformance. High-resolution respirometry provides the methodology to measure mitochondrial and cellular oxygen kinetics in the relevant low oxygen range < 1 kPa (7.5 mmHg; 9-10 microM; 5% air saturation). Respiration of isolated heart mitochondria follows hyperbolic oxygen kinetics with half-saturating oxygen pressure, p50, of 0.04 kPa (0.3 Torr; 0.4 microM) in ADP-stimulated state 3. Thus mitochondrial respiration proceeds at 90% of its hyperbolic maximum at the p50 of myoglobin, suggesting the possibility of a small but significant oxygen limitation even under normoxia in active muscle. Any impairment of oxygen delivery, therefore, induces oxyconformance. In addition, a shift of mitochondrial oxygen kinetics to the right, particularly by competitive inhibition of COX by NO, causes a further depression of respiration and a compensatory increase of local oxygen pressure. Above 1 kPa, mitochondrial oxygen uptake increases above hyperbolic saturation, which is probably due to oxygen radical production rather than the kinetics of COX. In cultured cells, the pronounced oxygen uptake above mitochondrial saturation at air-level oxygen pressure cannot be inhibited by rotenone and antimycin A, amounting to > 20 % of routine respiration in fibroblasts. Biochemical models of oxyconformance of COX are evaluated relative to patterns of intracellular oxygen distribution in the tissue and enzyme turnover in vivo, considering the kinetic effects of COX excess capacity on flux through the mitochondrial electron transport chain.

Microaerophilic conditions permit to mimic in vitro events occurring during in vivo Helicobacter pylori infection and to identify Rho/Ras-associated proteins in cellular signaling

Molecular dissection of the mechanisms underlying Helicobacter pylori infection suffers from the lack of in vitro systems mimicking in vivo observations. A system was developed whereby human epithelial cells (Caco-2) grown as polarized monolayers and bacteria can communicate with each other under culture conditions optimal for each partner. Caco-2 cells grown on filter supports were inserted in a vertical position into diffusion chambers equilibrated with air and 5% CO(2) at their basolateral surface (aerophilic conditions) and 5% CO(2), 5% O(2), 90% N(2) (microaerophilic conditions) in the apical compartment. Remarkably, the epithelial polarized layer was stable under these asymmetric culture conditions for at least 24 h, and the presence of Caco-2 cells was necessary to maintain H. pylori growth. In contrast to previous studies conducted with non-polarized Caco-2 cells and other cell lines kept under aerophilic conditions, we found H. pylori-dependent stimulation of cytokine secretion (MCP-1 (monocyte chemoattractant protein-1), GRO-alpha (growth-regulated oncogene-alpha), RANTES (regulated on activation normal T cell expressed and secreted)). This correlated with nuclear translocation of NF-kappaB p50 and p65 subunits. Tyrosine phosphorylation of nine cellular proteins was induced or enhanced; we identified p120(RasGAP), p190(RhoGAP), p62dok (downstream of tyrosine kinases), and cortactin as H. pylori-inducible targets. Moreover, reduction of H. pylori urease expression was observed in adherent bacteria as compared with bacteria in suspension. In addition to mimicking several observations seen in the inflamed gastric mucosa, the novel in vitro system was allowed to underscore complex cellular events not seen in classical in vitro analyses of microaerophilic bacteria-epithelial cell cross-talk.

Chronic hypoxia impairs the differentiation of 3T3-L1 fibroblast in culture: role of sustained protein kinase C activation

The effect of hypoxia on 3T3-L1 cell differentiation was examined in confluent cultures incubated with differentiation medium (DM) followed by incubation in growth medium (GM). Control cultures remained in GM throughout the incubation period. Eight days after the incubation, cells were assessed either for changes in morphology by staining with Oil Red O/hematoxylin or harvested to measure protein kinase C activity. Morphological examination of stained cells showed almost complete differentiation of normoxic cells to adipocytes when exposed to DM. By contrast hypoxia caused a dramatic inhibition of differentiation under similar media conditions with only 34 +/- 4% of cells accumulating fat deposits. Cultures sustained in GM under normoxic or hypoxic conditions were devoid of any fat deposits, reflecting an undifferentiated phenotype. Normoxic cells exposed to DM exhibited a significantly lower membrane to cytosolic ratio of protein kinase C in comparison with cells maintained in GM, which is consistent with differentiated and undifferentiated phenotypes, respectively. In comparison with normoxic cells incubated in DM, cells exposed to hypoxia under similar media conditions exhibited a significantly higher membrane to cytosolic ratio of protein kinase C, indicating sustained activation of the enzyme. In addition, cells in differentiation medium exposed to hypoxia in the presence of the protein kinase C inhibitors staurosporine or H7 exhibited a significant increase in the number of fat accumulating cells when compared with hypoxic controls. These studies indicate that chronic hypoxia impairs the differentiation of 3T3-L1 cells to adipocytes in association with the sustained activation of protein kinase C, which appears to play a role in mediating this process.

Oxygen concentration and asexual development of Eimeria tenella in cell cultures

Primary chicken kidney cells in Flexiperm cultures were either inoculated with Eimeria tenella sporozoites or incubated as noninoculated controls. Oxygen concentration was reduced (10 or 15 vol% O2, 5 vol% CO2) or increased (25 or 30 vol% O2, 5 vol% CO2) in a triple gas incubator (Heraeus B 5061 EK/O2) and retained in a CO2-air incubator (20 vol% O2, 5 vol% CO2) 24 hours post inoculation (hpi). Mature second generation schizonts (mS2) were counted microscopically at 120 hpi and numbers were compared either as mS2 or mS2/cm2 confluent cells. Asexual development of Eimeria tenella was neither stimulated nor inhibited by different oxygen concentrations, indicating that higher numbers of schizonts in cultures under reducing conditions reported earlier are probably a result of increased invasion rates of sporozoites.

Physiological oxygen tension modulates the chemically induced mitogenic response of cultured rat hepatocytes

Freshly isolated rat hepatocytes were cultured at periportal- (13% O2) or perivenous-like (4% O2) oxygen tension and exposed to subtoxic exposure levels of cyproterone acetate (CPA: 10-330 microM), phenobarbital (PB: 0.75-6 mM), and dimethylsulfoxide (DMSO: 0.1-3.3%) from 24-72 h after seeding. Induced alterations in ploidy, in the number of S-phase cells, the degree of binuclearity, and cellular protein content were determined by twin parameter protein/DNA flow cytometry analysis of intact cells and isolated nuclei. CPA and PB increased whereas DMSO decreased dose dependently the total number of S-phase cells. The changes differed within individual ploidy classes and were modulated by the oxygen tension. CPA increased and DMSO decreased the number of S-phase cells preferentially among the diploid hepatocytes at periportal-like oxygen tension. In contrast, PB increased binuclearity and S-phase cells mainly among the tetraploid hepatocytes at perivenous-like oxygen tension. Cellular protein content increased dose dependently after exposure to the hepatomitogens (CPA, PB) and decreased after exposure to DMSO at both oxygen tensions. Comparison with in vitro data proves that chemicals which interact with cells from the progenitor liver compartment (CPA, DMSO) exert their mitogenic activity best in cultures at periportal-like oxygen tension preferentially in diploid hepatocytes, whereas chemicals which affect cells from the functional compartment show a higher activity at perivenous-like oxygen tension. Physiological oxygen tension seems to be an effective modulator of the proliferative response of cultured rat hepatocytes similar to that expected for periportally or perivenously derived hepatocytes.

Hypoxia-mediated impaired differentiation by LLC-PK1 cells: evidence based on the protein kinase C profile

We recently reported that mild hypoxia in LLC-PK1 cells, grown in standard fashion under a still layer of overlying medium at 5% CO2/18% O2 environment, result in decreased oxidative metabolism and impaired differentiated functions in comparison to adequately oxygenated cultures maintained either under a higher oxygen (36% O2) environment or conditions of continuous rocking of the media fluid. In the present study, subcellular distribution of a regulatory enzyme protein kinase C (PKC) was examined between hypoxic still and normoxic rocked LLC-PK1 cells. Subconfluent cultures of hypoxic LLC-PK1 cells exhibited significantly lower and predominantly membrane-bound PKC activity in comparison to mostly cytosolic localization of this enzyme in normoxic rocked cells. One hour of exposure of adequately oxygenated-rocked LLC-PK1 cells with the phorbol ester TPA, a dedifferentiating agent that did not effect the cell ATP content, resulted in significant inhibition of dome formation and sodium-dependent glucose transport activity, a partial loss of pH-responsive ammoniagenesis, and almost complete translocation of protein kinase C activity from cytosol to the membrane pool; all of which resembles the behavior of hypoxic still cultured cells. In addition, acute re-oxygenation of hypoxic still cultures by rocking the media fluid for one hour resulted in an increase in cell ATP content to the cellular levels of ATP observed in normoxic rocked cells. However, all the parameters of differentiation were unaffected by re-oxygenation. These studies support the notion that hypoxia can act in some primary fashion, independent of its effects on energy metabolism, to impair cellular differentiation in LLC-PK1 cells. They also raise the possibility that activation of protein kinase C may act as an important mediator in this process.

Defect in generation of LAK cell activity under oxygen-limited conditions

In general, the in vitro induction of lymphokine activated killer (LAK) cell activities by interleukin 2 (IL-2) in human peripheral blood mononuclear cells (PMNC) has been performed in an atmosphere of 5% CO2 in air (20% O2), whereas IL-2-induced LAK cell activities are considerably reduced under concentrations of 5% O2 equal to arterial blood oxygen tension (100 mmHg) and 2% O2 equal to venous blood oxygen tension (40 mmHg). Cultured cell viability, IL-2 receptor-beta expression on large granular lymphocytes (LGL), the percentage of IL-2 receptor-beta positive LGLs and cell proliferation were not affected by oxygen-limited conditions. LAK cells were induced by IL-2 over 5 days at 20% O2, at which time the LAK cells were further stimulated by IL-2 in 2% O2 and 20% O2. Under these conditions the activity of LAK cells in 2% O2 decreased day by day, while that of LAK cells induced in 20% O2 was maintained at least until day 10 of the original culture. LAK effector cell-mediated lysis was not influenced by oxygen-limited conditions. These results point to more successful applications of the combination of oxygen therapy and adoptive cellular immunotherapy in the clinic.

A deficient function of the antioxidative system of the organism as an aetiopathogenetic factor in psoriasis

The main idea of a new hypothesis about the aetiopathogenesis of psoriasis concerns the significance of interrelation between pro- and antioxidants, vitamin A-dependent keratin synthesis and proliferation of keratinocytes. On the basis of postulated deregulation in the antioxidative system of the organism, we explain the predisposition, the initiation and pathogenesis of lesions, their persistence and resolution and the operation mechanisms of antipsoriatics.

Oxygen concentration regulates EGF-induced proliferation and EGF-receptor down regulation

Reducing oxygen from 20% to 2.5% increases EGF-induced DNA synthesis and cell proliferation in cultures of human diploid fibroblasts. Reducing oxygen also changes the pattern of EGF binding to the cell surface. The loss of surface binding that follows EGF attachment to cells in 20% oxygen does not occur in 2.5% oxygen.

The influence of oxygen tension on the long-term growth in vitro of haematopoietic progenitor cells from human cord blood

Growth of low density human cord blood cells in long-term suspension culture was evaluated at incubation conditions of 5% carbon dioxide in approximately 20% (normal incubator) oxygen tension or in 5% (low) oxygen tension. During the first 5 weeks there was no difference in the numbers of morphologically recognizable cells grown at either oxygen tension, while growth was superior from weeks 5 to 8 at approximately 20% oxygen tension. For the first 5 weeks, growth of granulocyte-macrophage progenitors (CFU-GM) was superior at 5% oxygen tension during the long-term and semi-solid culture phases and least impressive in the long-term and semi-solid cultures incubated at approximately 20% oxygen. This trend was reversed after 5 weeks and after 8 weeks there were no detectable CFU-GM in suspension cultures at 5% oxygen while steady state levels of CFU-GM were maintained for greater than 12 weeks in suspension cultures at approximately 20% oxygen. Semi-solid cultures for erythroid (BFU-E) and multipotential (CFU-GEMM) progenitors were incubated at approximately 20% oxygen only. During the first 4 weeks, the growth of BFU-E and CFU-GEMM was superior at 5% oxygen during long-term culture. Numbers of these cells decreased by week 5 and at this time growth was better in the long-term cultures grown at approximately 20% oxygen. By week 6, no BFU-E or CFU-GEMM were detectable. Thus, growth of cord blood at low oxygen tension gives an initial enhancement in output of progenitor cells, but this appears to be at the expense of continued production.

Effect of oxygen on the growth of human epidermal keratinocytes

We studied the growth of secondary cultures of neonatal human keratinocytes at oxygen concentrations between 1 and 89%. Keratinocytes were grown in MCDB medium with 5% fetal bovine serum, 10 ng/ml epidermal growth factor, 5 micrograms/ml insulin, 0.5 microgram/ml hydrocortisone, and 0.1 mM ethanolamine and phosphorylethanolamine. Medium in the flasks was equilibrated with gas mixtures containing 5% CO2, various percentages of oxygen from 0-95% and nitrogen to balance. Cells were seeded at 10(4) cells/cm2 in sealed flasks (25 cm2). These were incubated at 37 degrees C in incubators maintained at the experimental oxygen tensions. Cells grew best at PO2 (partial pressure of oxygen) 133 mm Hg (18% O2), with a mean population doubling time of 2.8 days. Growth was retarded by 60% at PO2 38 mm Hg (5% O2) and by 98% at PO2 7 mm Hg (1% O2). However, the oxygen tension that resulted in the best plating efficiency was at PO2 12 mm Hg (2% O2). When oxygen tensions were shifted to 78-133 mm Hg, cells seeded under low oxygen tensions began to proliferate. These data suggest that a better harvest of keratinocytes is obtained when cells are seeded under low oxygen tension and then shifted to ambient oxygen tensions. At high oxygen tensions, above 20%, growth was inhibited by 75% at PO2 241 mm Hg (34% O2) and 98% at PO2 374 mm Hg (52% O2). At PO2 637 mm Hg (89% O2) no cell growth occurred. These findings showed that high oxygen tensions, above 20%, have no beneficial effect on the growth of keratinocytes.

Influence of added catalase on chromosome stability and neoplastic transformation of mouse cells in culture

The generation of hydrogen peroxide (H2O2) and the derivative free hydroxyl radical (. OH) in cultures of mouse cells grown in the presence of visible light and ambient oxygen was shown previously to be implicated in chromatid damage. Furthermore, chromosome alterations appear to be associated with the spontaneous neoplastic transformation of mouse cells in culture. An attempt was made in this study to reduce the incidence of chromosomal aberrations and delay or prevent the onset of spontaneous neoplastic transformation of freshly isolated mouse cells, both fibroblasts and epidermal keratinocytes, by adding catalase to the culture medium, shielding the cultures from wavelengths less than 500 nm and providing a gas phase of 0-1% O2. These conditions significantly decreased the incidence of chromosomal aberrations in both cell types, and in fibroblasts prevented tumourigenicity in non-irradiated syngeneic mice, and increased latent periods for tumour development in X-irradiated mice. The epidermal keratinocytes were particularly resistant to spontaneous neoplastic transformation under all conditions tested. These observations on the protective effect of extracellular catalase suggest that H2O2, a normal metabolite, and/or the derivative .OH can directly or indirectly produce genetic damage and neoplastic transformation in mouse fibroblasts.

Free radical damage to cultured porcine aortic endothelial cells and lung fibroblasts: modulation by culture conditions

Culture conditions modulating cell damage from xanthine plus xanthine oxidase-derived partially reduced oxygen species were studied. Porcine thoracic aorta endothelial cells and porcine lung fibroblasts were maintained in monolayer culture. Cells were prelabeled with 51Cr before xanthine plus xanthine oxidase exposure. Endothelial cells showed 30 to 100% more lysis than fibroblasts and thus seemed more sensitive to this oxidant stress. The effect of cell culture age, as indicated by population doubling level (PDL), was examined. Response of low PDL endothelial cells and fibroblasts subjected to oxidant stress was compared with the response of PDL 15 cells. Both low PDL endothelial cells and fibroblasts responded differently to the lytic effect of xanthine oxidase-derived free radicals than did higher PDL cells. Specific activities of the antioxidant enzymes catalase, manganese superoxide dismutase, copper-zinc superoxide dismutase, glutathione peroxidase, and glucose-6-phosphate dehydrogenase were measured in both low and high PDL fibroblasts and endothelial cells. Antioxidant enzyme specific activities could only partially explain the differences in response to oxidant stress between fibroblasts and endothelial cells and between low and high PDL cells. Cell culture medium composition modulated the rate of production, and relative proportions of xanthine plus xanthine oxidase-derived partially reduced species of oxygen, i.e. superoxide, hydrogen peroxide, and hydroxyl radical. Serum content of medium was important in modulating free radical generation; superoxide production rates decreased 32%, H2O2 became undetectable, and hydroxyl radical generation decreased 54% in the presence of 10% serum. The medium protein and iron content also modulated free radical generation. The data suggest that cell culture media constituents, cell type, and cell culture age greatly affect in vitro response of cells subjected to oxidant stress.

Oxygen dependence of cellular metabolism: the effect of O2 tension on gluconeogenesis and urea synthesis in isolated rat hepatocytes

The dependencies of gluconeogenesis and urea synthesis on oxygen concentration were measured in suspensions of isolated rat hepatocytes and compared with the O2 dependence of cellular energy supply (reduction of cytochrome c, respiratory rate, mitochondrial [NAD+]/[NADH], lactate production, and [ATP]/[ADP] [Pi]). As the oxygen concentration was decreased, production of both glucose and urea declined; the changes were observable at 20 microM oxygen and below, with the apparent Km values for both processes of near 5 microM. The similar dependence of gluconeogenesis and urea synthesis on oxygen concentration indicates that the two pathways have equal access to the cellular ATP supply, i.e., there is no evidence that either pathway is preferentially turned off to spare ATP for the other. The cellular energy state had an oxygen dependence similar to that of glucose and urea synthesis. It is suggested that the behavior of gluconeogenesis and urea production is a reflection of homeostatic regulation of cellular metabolism which is designed to respond to changes in [ATP]/[ADP][Pi].

The propagation of cancer, a process of tissue remodeling

Effective study of the malignant phenotype at the tissue level requires model systems that are intelligible both to cell biologists and to pathologists, and that also observe the spatial imperatives intrinsic to tissues in nature. Malignant cells commonly appear in multicellular units, and growth of tumor tissue is seen as an increase in the number of cells and multicellular units. The supporting stroma frequently has an abnormal appearance, and this component of the tissue also increases in mass as the tumor enlarges and spreads. The direction of invasion is influenced by the direction of available metabolites. Histophysiologic gradient culture complies with nature's spatial rationale, since at the substrate-parenchymal interface three functions coincide. These are anchorage, initiation of epithelial renewal, and complete exchange of metabolites. Our model system provides a setting for reconstructing and manipulating many features of the malignant phenotype seen in cancer tissues in nature, such as abnormalities in the sequence of maturation of stratified epithelium, hyperplasias, dysplasias, interaction between different types of epithelium, aggregate formation, tumor angiogenesis, and neoplastic blockade.

Serum-independent modulation of hemicyst formation by dissolved oxygen in postconfluent epithelial monolayers

Hemicyst formation is considered a manifestation of either transepithelial solute and fluid movement or secretory activity in culture. This study shows that hemicyst formation in postconfluent monolayers of rhesus monkey kidney (LLC-MK2) cells is modulated by the dissolved oxygen concentration (PO2) of the culture medium. Either daily replacement of serum-free medium or displacement of the gas phase with 18% vol/vol O2 (initial medium PO2 = 125 to 135 mm Hg) enhances formation of hemicysts. Use of 30% O2 (medium PO2 approximately equal to 175 mm Hg) does not further increase the incidence, but neither 10% O2 (medium PO2 = 90 to 95 mm Hg) nor 1% O2 (medium PO2 = 35 to 50 mm Hg), the approximate range of dissolved oxygen values in blood, supports hemicyst formation unless cultures are gently rocked to disrupt diffusion gradients. Phase photomicrography of living cultures shows that the surface of a turgid hemicyst is furrowed, and cinephotomicrography reveals that the walls vibrate subtly. When hypoxic conditions (0 to 1% O2) are introduced this vibration ceases within 2 to 3 h, whereas collapse and disappearance of turgid hemicysts requires 18 to 20 h, seems virtually synchronous, and is reversible. Hemicysts form in a broad osmotic range, and increased electrolyte concentration increases the incidence. Hemicysts persist in locally dense areas when cell-free strips are etched in the postconfluent monolayer; no DNA synthesis is detected under these conditions, but two-dimensional cell spreading into the denuded area is seen along the edge of the wound. We conclude that the dissolved oxygen supply in the cellular microenvironment modulates functional expression by differentiated kidney epithelial cells in culture and that increased electrolyte concentration also enhances expression of this phenotypic marker.

Decreased oxygen supply enhances growth in culture of human mid-trimester amniotic fluid cells

Human mid-trimester amniotic fluid cells were cultivated under conditions of decreased oxygen supply. Compared to control cultures the low-oxygen group showed improved growth which was quantitated by three independent assays (1) direct cell counts, (2) bromodeoxyuridine (BrdU)-Hoechst flow-cytometry, and (3) cloning efficiency. The growth promoting effects of lowered oxygen hold for all major morphologic categories of amniotic fluid cells.

Modulation of proliferation in epidermal keratinocyte cultures by lowered oxygen tension

The modulation of proliferation and differentiation in primary epidermal keratinocyte cultures by lowered gas phase oxygen tensions was studied. Neonatal mouse epidermal keratinocyte cultures were grown in an Heraeus type B 5060 EK/O2 incubator in oxygen tensions between 5% and 15% (within the physiologic range); the oxygen tension of ambient air being 21%. Cell morphology was studied using histochemical stains and electron microscopy. Differentiation was assessed using autoradiography of SDS PAGE gels of six serially extracted cell protein fractions with [3H]leucine as a marker. Autoradiographs using [14C]glucosamine and 32Pi as markers were also assessed as a measure of other cell functions. Proliferation was studied using autoradiography of [3H]thymidine ([3H]TdR) pulse-labeled cultures and [3H]TdR incorporation into isolated DNA fractions. The results of these studies showed that lowering the oxygen tension in the gas phase reversibly inhibited cell proliferation. There was a direct arithmetic relationship between the proliferative rate of the cultures and the oxygen tension. No change in differentiation as defined by [3H]leucine indexing of protein synthesis was seen. Other markers of cell function, such as [14C]glucosamine glycosylation and [32P] phosphorylation of proteins were also unchanged. These results suggest that oxygen tension regulates only proliferation in epidermal keratinocytes. This epidermal response is well adapted to its role in the healing wound, and is an example of a tissue-specific modification of a regulatory function.