Introduction. Platelets actively fight infections by producing antibacterial substances, enhancing immune activity, and form clots to prevent bacterial dissemination. Previous studies have observed platelet activation following incubation with various bacterial toxins (1,2) that might potentially result in transition to a procoagulant state promoting thrombus formation.

Goals. We hypothesized that under sublytic conditions S. pneumoniae proteins pneumolysin (Ply) and S. aureus proteins a-hemolysin (Hla), EapD3D4, CHIPS, FlipR, and AtlA trigger reactive oxygen species (ROS) generation in platelets, leading to increased lipid oxidation to favour procoagulant activation.

Methods. To test this hypothesis, toxins were incubated with washed platelets. ROS (DCFH2-DA), and mitochondrial superoxide (MitoSOX) generation, intraplatelet oxidized low-density lipoprotein-(anti-oxLDL-FITC) levels, platelet activation (degranulation-CD62P), and phosphatidylserine (PS; Annexin V) exposure were measured via flow cytometry.

Results. While all proteins increased platelet activation, toxins Ply and Hla preferably induced PS exposure substantiating a procoagulant state, along with increased ROS generation. Superoxide production also increased in the presence of toxins and S. aureus EapD3D4. Intraplatelet oxLDL levels were enhanced following incubation with CHIPS.

Summary. Our data suggest that Ply and Hla toxins turn platelets procoagulant without implying nonenzymatic lipid oxidation. Staphylococcal proteins activated platelets but did not induce a procoagulant state. Notably, CHIPS and EapD3D4 induced intraplatelet lipid oxidation without inducing a procoagulant phenotype. Such differential impact of bacteria and bacterial toxins may prevent bacterial dissemination, but could also contribute to increased organ damage through platelet derived oxidized (phospho)lipids and procoagulant platelet-assisted thrombosis, necessitating further research in this direction.

References:

Li, C., Li, J., & Ni, H. (2020). Frontiers in Immunology, 11, 1962.Jahn, K., T.P. Kohler, L.S. Swiatek, S. Wiebe, and S. Hammerschmidt. 2022. Cells 11(7):1121.