Aminoglycosides Induced Activation of Saponin-permeabilized Platelets

Abstract

Neomycin, an aminoglycoside antibiotic, binds more strongly to inositol polyphospholipid than to other membrane phospholipids. Therefore, this antibiotic is commonly used as a relatively specific inhibitor of inositol phospholipid metabolism in studies regarding the involvement of inositol phospholipids in various cell functions. The mechanism of action of neomycin is presumed to be inhibition of phospholipase C. However, the mode of inhibition remains obscure. Other aminoglycosides, including gentamicin and streptomycin, may also possess phospholipid binding affinity and platelet activity, but their effects are less potent than those of neomycin. The present study investigated both the direct action of aminoglycoside antibiotics and the activation of platelets rendered semi-permeable with saponin, which allows polar aminoglycoside antibiotics access to the innerleaf let of the plasma membrane, where the phosphoinositides are located. With semi-permeabilized platelets, relatively low concentrations of aminoglycoside antibiotics stimulated secretion, aggregation, arachidonic acid release and generation of inositol trisphosphate. All of the above-mentioned effects on semi-permeabilized platelets were fully inhibited by high concentrations of the aminoglycoside antibiotics. By acetylsalicylic acid pretreatment, aggregation, secretion and generation of inositol trisphosphate were fully inhibited. In contrast, arachidonic acid release was only slightly inhibited by this treatment. These data therefore suggest that the mechanism of action of aminoglycosids antibiotics on semipermeabilized platelets is not related to phospholipase C, but to phospholipase A2. These results provide evidence that aminoglycoside antibiotics activate phospholipase A2, which leads to the release of arachidonic acid in semi-permeabilized platelets. But whether themechanism of activation of phospolipase A2 by aminoglycoside antibiotics is direct or not is yet unclear.