Ethanol induces transient arrest of cell division (G2 + M block) followed by G0/G1 block: dose effects of short- and longer-term ethanol exposure on cell cycle and cell functions.

To study the cytophysiological effects of ethanol systematically, L929 cells, a fibroblastic cell line derived from mouse connective tissue, were exposed to various concentrations of ethanol (12.5, 50, 100 and 200 mM) for short (3 and 6 h) and longer (24 or 26 h) durations. Ethanol-induced cellular responses were analysed by a combination of the following assays: number of cells, amounts of DNA and protein, MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay and cell cycle. Ethanol dose-dependently suppressed these cellular functions, except that 12.5 mM exposures for both 6 and 26 h increased the amount of protein in spite of almost no change in other cellular functions, compared to the control. The most marked dose-dependency was observed in a reduction of formazan product in an MTT assay after both 6 and 26 h exposures to ethanol, being independent of the number of cells and probably reflecting dose-dependent depression of mitochondrial respiration. A G2 + M block in the cell cycle, an inhibition of cell division, was induced after short-term exposures (3 and 6 h) to 100 and 200 mM ethanol, but the block was released before 24 h had passed. Alternatively, prolonged exposures (24 h) to 50-200 mM ethanol induced a G0/G1 block, resulting in a decrease in the amount of DNA below the control value. Moreover, the percentage of the S phase was decreased gradually and dose-dependently throughout the 24 h exposure. Thus, high concentrations of ethanol (50, 100 and 200 mM) perturbed the cell cycle progression by causing both a transient G2 + M block (an inhibition of mitosis) and a continuous G0/G1 block, though the latter was masked by the G2 + M block during short-term exposure. The cells seem finally to acquire some tolerance to ethanol so as to pass through mitosis, but much less tolerance to pass through the checkpoint from the G1 to the S phase, which results in a decline in proliferation.