Changes in mitochondrial structure and function in 9l rat brain tumor cells treated in vitro with alpha-difluoromethylornithine, a polyamine biosynthesis inhibitor.

Abstract

Mitochondrial structure and function were studied in 9L rat brain tumor cells depleted of polyamines by alpha-difluoromethylornithine, an enzyme-activated irreversible inhibitor of ornithine decarboxylase. Cells treated with methylglyoxal bis(guanylhydrazone), a reversible inhibitor of S-adenosylmethionine decarboxylase, were used for comparison because this polyamine biosynthesis inhibitor is known to cause structural and functional disruption of mitochondria. A significant increase in mitochondrial size, measured quantitatively, was found in alpha-difluoromethylornithine-treated cells (10 mM for 72 hr) compared with untreated cells (P < 0.001). This increase in mitochondrial size was reversed when putrescine was added to the cultures for 24 hr after alpha-difluoromethylornithine treatment. Putrescine alone had no effect on the size of mitochondria. Treatment of cells with methylglyoxal bis(guanylhydrazone) (80 muM for 48 hr) caused only a slight increase in mitochondrial size compared with mitochondria in untreated cells (P < 0.05) and failed to produce the dramatic ultrastructural changes reported in other cell lines. Ultrastructural examination revealed an increase in cytoplasmic and membrane-associated ribosomes in alpha-difluoromethylornithine-treated cells, an increase in cytoplasmic ribosomes in methylglyoxal bis(guanylhydrazone)-treated cells, and an increase in membrane-bound ribosomes in putrescine-treated cells. In cells treated first with alpha-difluoromethylornithine and then with putrescine, the distribution of ribosomes was normal. The distributions of ribosomes were not quantitatively assessed. Pyruvate utilization, a measure of mitochondrial function, was decreased in cells treated with 10 mM alpha-difluoromethylornithine for 72 hr, compared with untreated cells. Restoration of intracellular polyamine levels by the addition of putrescine 24 hr before analysis reversed this phenomenon. Putrescine treatment alone did not affect pyruvate utilization. Pyruvate utilization in methylglyoxal bis(guanylhydrazone)-treated cells was depressed to a greater extent than that in alpha-difluoromethylornithine-treated cells.