LDH isoenzyme pattern, lactate/pyruvate, and ultrastructure of fibrinogenic and epithelial cell lines exposed to 3% oxygen

Total LD and isozyme variations during in vitro fibroblast aging with a discussion of its theoretical implication

Dermal fibroblast cultures were obtained from 18 patients. Total lactic dehydrogenase (LD) and LD isozymes were determined after each population doubling (PD). The lactic dehydrogenase was assayed by the method of Wacker, Ulmer and Vallee. The isozymes were analyzed by gel electrophoresis. Some investigators have reported conflicting results as to the quantity of LD produced during in vitro aging. These researchers sampled a small number of PDs. We found that the total LD varied with each PD. A distinct isozyme pattern has been described for adult, fetal and neoplastic fibroblasts. We have found all three patterns occurring during the in vitro aging of our normal diploid fibroblasts. In spite of our asynchronous population of cells the LD and its isozymes continually fluctuate. An asynchronous population of cells would be expected to produce a dampening of the total LD. In order to explain this finding we speculate a synchrony is established in a "gated" entrance from subcycle Gq into the S stage or from G1 and G0 into the S stage. In order to evaluate, accurately, changes occurring during in vitro aging it is imperative to assay each PD.

Influence of the oxygen pressure in the culture medium on the oxygenation of different types of multicellular spheroids

Six different types of spheroids of both human and rodent origin were cultured, using the liquid-overlay technique. Oxygen gradients were measured with micro-electrodes, when the spheroids were attached to thin cover-glasses. The gradients were measured from the upper surface towards the center of the spheroids. Stable and reproducible gradients were obtained. Large variations were seen in the steepness of the gradients, depending both on the type and on the size of the spheroids. An interesting phenomenon was discovered. When some types of spheroids were cultured in a medium with a low oxygen pressure (medium equilibrated with gas containing 4-5% O2), the gradients continuously changed and became flatter. Detailed studies showed that most of the changes occurred within 2 days after the transfer to the low oxygen pressure. After 2 days, no further dramatic changes took place. This phenomenon was seen in two types of human glioma (U-118 MG and U-178 MG) and two types of embryonic, hamster lung-cell (V-79-379A and CHEL) spheroids. In the cases of human-osteosarcoma (U-393 OS) and human thyroid-cancer (HTh7) spheroids, no such changes could be seen. The low oxygen tension in the culture medium was chosen to mimic the environmental conditions in solid tumors.

Modulation of epithelial cell proliferation in culture by dissolved oxygen

Modulation of epithelial cell proliferation by the dissolved oxygen concentration (PO2) of the growth medium was assessed with primary human foreskin epithelium and a continuous monkey kidney epithelial cell line (LLC-MK2). Direct measurement of the growth medium PO2 provides the first quantitative evaluation of epithelial cell proliferation as a function of PO2. Sustained proliferation of LLC-MK2 cells occurs in serum-free medium equilibrated with a gas phase containing 18% or 30% O2 v/v. Mid-logarithmic phase cultures rapidly consume dissolved oxygen; this results in a 60-70 mm Hg decline in PO2, and leads to a stable growth medium PO2 between 70 and 100 mm Hg, well above anoxic values. In contrast, if culture medium is equilibrated with a gass phase containing 0% or 1% O2 v/v to yield a growth medium PO2 - approximately 20-40 mm Hg, proliferation of LLC-MK2 and primary foreskin epithelial cells is retarded, and LLC-MK2 cells use little dissolved oxygen. Gentle, continuous rocking to prevent diffusion gradient formation enhances proliferation slightly at the higher PO2, but neither periodic fluid renewals nor continued rocking stimulates cells retarded by a lowered oxygen concentration to resume proliferation. The data collectively demonstrate that epithelial cell proliferation requires a PO2 greater than 40 mm Hg, and threshold requirements are probably closer to 70 mm Hg. Glycolysis continues at a PO2 insufficient for proliferation, but more lactic acid accumulates in actively proliferating cultures than in cultures equilibrated with 0% oxygen. We conclude that epithelial cells in vitro both consume more oxygen and require a higher PO2 for continued proliferation, and that the oxygen requirement for epithelial cell proliferation exceeds that of a comparable population of fibroblasts for which low oxygen may enhance survival and proliferation.

The effect of hypoxia on collagen synthesis in cultured 3T6 fibroblasts and its relationship to the mode of action of ascorbate

When exposed to low oxygen tension, in the absence of added ascorbic acid 3T6 mouse fibroblast cultures in late log phase respond by increased lactate production and increased hydroxylation of proline in nascent collagen, which is paralleled by an increase in prolyl hydroxylase activity. After 6 h recovery from the anoxic stimulus, however, cultures still yield more prolyl hydroxylase than controls, but the effect on hydroxylation of nascent collagen has disappeared. These observations help to dissect the dual role of ascorbate which can stimulate hydroxylation both by increasing the amount of active enzyme and by a cofactor-like role; in addition, these observations may be relevant to wound healing.