The effects of aminoglycoside antibiotics on phospholipase D (PLD) activity were investigated in permeabilized NG108-15 cells and in isolated rat brain membranes. Neomycin inhibited guanosine 5′-[gamma-thio]triphosphate-stimulated PLD activity in digitonin-permeabilized NG108-15 cells in a concentration-dependent manner (50% inhibition at 100 microM). Neomycin similarly inhibited PLD activity present in rat brain membranes and assayed in vitro with [3H]phosphatidylcholine as substrate (50% inhibition at 65 microM). Other aminoglycosides tested (kanamycin, geneticin and streptomycin) were nearly equipotent inhibitors of rat brain PLD. These results indicate that aminoglycoside antibiotics inhibit phosphatidylcholine-PLD activity with comparable and sometimes greater potency than their well known inhibition of phosphoinositide-phospholipase C. The possibility that PLD inhibition could mediate some of the toxic side effects of aminoglycosides is suggested.

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