Platelet Antistaphylococcal Responses Occur through P2X ₁ and P2Y ₁₂ Receptor-Induced Activation and Kinocidin Release

Abstract

Platelets (PLTs) act in antimicrobial host defense by releasing PLT microbicidal proteins (PMPs) or PLT kinocidins (PKs). Receptors mediating staphylocidal efficacy and PMP or PK release versus isogenic PMP-susceptible (ISP479C) and -resistant (ISP479R) Staphylococcus aureus strains were examined in vitro. Isolated PLTs were incubated with ISP479C or ISP479R (PLT/S. aureus ratio range, 1:1 to 10,000:1) in the presence or absence of a panel of PLT inhibitors, including P2X and P2Y receptor antagonists of increasingly narrow specificity, and PLT adhesion receptors (CD41, CD42b, and CD62P). PLT-to-S. aureus exposure ratios of >10:1 yielded significant reductions in the viability of both strains. Results from reversed-phase high-performance liquid chromatography indicated that staphylocidal PLT releasates contained PMPs and PKs. At ratios below 10:1, the PLT antistaphylococcal efficacy relative to the intrinsic S. aureus PMP-susceptible or -resistant phenotype diminished. Apyrase (an agent of ADP degradation), suramin (a general P2 receptor antagonist), pyridoxal 5-phosphonucleotide derivative (a specific P2X 1 antagonist), and cangrelor (a specific P2Y 12 antagonist) mitigated the PLT staphylocidal response against both strains, correlating with reduced levels of PMP and PK release. Specific inhibition occurred in the presence and absence of homologous plasma. The antagonism of the thromboxane A 2 , cyclooxygenase-1/ cyclooxygenase-2, or phospholipase C pathway or the hindrance of surface adhesion receptors failed to impede PLT anti-S. aureus responses. These results suggest a multifactorial PLT anti-S. aureus response mechanism involving (i) a PLT-to-S. aureus ratio sufficient for activation; (ii) the ensuing degranulation of PMPs, PKs, ADP, and/or ATP; (iii) the activation of P2X 1 /P2Y 12 receptors on adjacent PLTs; and (iv) the recursive amplification of PMP and PK release from these PLTs.

In vitro bactericidal activity of equine platelet concentrates, platelet poor plasma, and plasma against methicillin-resistant Staphylococcus aureus

“…We believe that the microbicidal proteins stored in platelets (Blair y Flaumenhaft 2009, Yeaman 2010 of the equine cellular blood components evaluated, are potentially the main mediators of antibacterial effects in this study. Possibly, the bactericidal mechanism of action for ePCs and PPP against MRSA could in part be related with a receptor saturable system of the bacterial cell wall (Trier et al 2008). This notion may explain how counts of PLTs as low as those observed in the equine PPP of this study were enough to induce bactericidal activity.…”

“…The mechanism of the antibacterial effect of PRP is not fully understood, although some evidence suggests that platelets could play pivotal role in antimicrobial host defence, since these cell fragments contain molecules with microbicidal effect, mainly, thrombin-induced platelet microbicidal protein-1 (tPMP-1), a protein similar to human platelet factor 4 (PF-4) (Yount et al 2004). tPMP-1 has an important antibacterial effect against Staphylococcus aureus (Mukhopadhyay et al 2007, Trier et al 2008. Platelets release other microbicidal proteins such as thymosin-b4, the derivatives of CXCL7, (PBP, CTAP-III, NAP-2), and CCL5 (RANTES) (Trier et al 2008).…”

“…tPMP-1 has an important antibacterial effect against Staphylococcus aureus (Mukhopadhyay et al 2007, Trier et al 2008. Platelets release other microbicidal proteins such as thymosin-b4, the derivatives of CXCL7, (PBP, CTAP-III, NAP-2), and CCL5 (RANTES) (Trier et al 2008). Platelet alpha-granules also contain complement and complement binding proteins, such as precursor of the complements C3 and C4 that participate in the complement pathway activation (Blair and Flaumenhaft 2009).…”

In Vitro Cross-Resistance to Daptomycin and Host Defense Cationic Antimicrobial Peptides in Clinical Methicillin-Resistant Staphylococcus aureus Isolates

“…Cationic antimicrobial host defense peptides (HDPs), including those of hematogenous origin, such as platelets and neutrophils, kill many important blood-borne pathogens, especially S. aureus (35). Although most HDPs initially interact with the bacterial cell membrane, their overall mechanism(s) of action can be quite distinct and multifactorial, involving the cell membrane, the cell wall, and intracellular targets (37).…”

Efficacy of Synthetic Peptides RP-1 and AA-RP-1 against Leishmania Species In Vitro and In Vivo

“…They have been identified in humans and rabbits and exhibit rapid and potent in vitro microbicidal activity against Gram-positive bacteria, Gramnegative bacteria, and fungi (38,39,(47)(48)(49). In addition to direct antimicrobial activity, certain PMPs have been identified as chemokines (e.g., CXCL4 or platelet factor-4).…”