Effects of hyperoxia on human endothelial cell proliferation and morphology in vitro

The effects of hyperoxia on endothelial cells from human umbilical veins were studied in vitro by flow cytometric DNA analysis, cell proliferation, and morphology. Exposure of the cells to PO2 of approximately 400 and 500 mmHg (corresponding to O2 concentrations of 65 and 95%, respectively) caused, after 24 h, an increase in the proportion of S-phase cells from 18 to 33%. This was followed by a dramatic decrease of S-phase cells to about 4% after 48 h of O2 exposure. This decrease was also sustained after 72 h of O2 treatment. Concomitant with the depletion of S-phase cells was an increase from 13 to 21% in the proportion of cells in the G2M phase, indicating that cells were unable to undergo cell division after a 48-h exposure to 65 and 95% O2. Cells exposed to various PO2 levels (124, 248, 400, and 500 mmHg) showed a dose-dependent reduction in cell proliferation leading to a total inhibition of cell growth after exposure to PO2 of 400 and 500 mmHg. Cells exposed to 248 mmHg PO2 exhibited similar growth rates as the control cells during the first 3 days. Thereafter there was a 50% reduction in cell density as compared to the control cells. Light and scanning electron microscopy showed that the hyperoxic cells underwent morphologic changes characterized by cell contraction and swelling. Thus it is shown that exposure to very high PO2 tensions first stimulates the cells to enter the S phase of the cell cycle. Thereafter changes take place leading to a nearly complete reduction of cell proliferation.