Summary
In this study, Gram-positive Staphylococcus aureus lipoteichoic acid (LTA) dose-dependently (0.1-1.0 µg/ml) and time-dependently (10-60
min) inhibited platelet aggregation in human platelets stimulated by agonists. LTA
also dose-dependently inhibited phosphoinositide breakdown and intracellular Ca+2 mobilization in human platelets stimulated by collagen. LTA (0.5 and 1.0 µg/ml) also
significantly inhibited thromboxane A2 formation stimulated by collagen in human platelets. Moreover, LTA (0.1-1.0 µg/ml)
dose-dependently decreased the fluorescence of platelet membranes tagged with diphenylhexatrience.
Rapid phosphorylation of a platelet protein of Mr. 47,000 (P47), a marker of protein kinase C activation, was triggered by PDBu (30
nM). This phosphorylation was markedly inhibited by LTA (0.5 and 1.0 µg/ml) within
a 10-min incubation period.
These results indicate that the antiplatelet activity of LTA may be involved in the
following pathways: LTA’s effects may initially be due to induction of conformational
changes in the platelet membrane, leading to a change in the activity of phospholipase
C, and subsequent inhibition of phosphoinositide breakdown and thromboxane A2 formation, thereby leading to inhibition of both intracellular Ca+2 mobilization and phosphorylation of P47 protein. Therefore, LTA-mediated alteration
of platelet function may contribute to bleeding diathesis in Gram-positive septicemic
and endotoxemic patients.
Key words
Gram-positive bacteria - lipoteichoic acid - platelet aggregation - membrane fluidity
- protein kinase C