Synthetic lipopeptide Pam3CysSer(Lys)4 is an effective activator of human platelets

Abstract

Lipopeptide analogues of the NH2-terminus of bacterial lipoprotein are known to induce activation of macrophages, neutrophils, and lymphocytes. We studied the effect of the lipopeptide N-palmitoyl-S-[2,3-bis(palmitoyloxy)-(2RS)-propyl]-(R)-cysteinyl-( S)-seryl-(S)-lysyl-(S)-lysyl-(S)-lysyl-(S)-lysine [Pam3CysSer(Lys)4] on several functions of human platelets. Pam3CysSer(Lys)4 led to the aggregation of platelets and induced the secretion of serotonin with an effectiveness similar to thrombin. These cellular effects of Pam3CysSer(Lys)4 were concentration dependent, being half maximal at 2-3 microM and maximal at 10-30 microM. Another lipopeptide also induced platelet aggregation and serotonin secretion but was less potent and less effective than Pam3CysSer(Lys)4. The lipid moiety and the peptide moiety of Pam3CysSer(Lys)4 alone were without any effect. Lipopeptides also stimulated tyrosine phosphorylation of several proteins with molecular masses similar to those found to be tyrosine phosphorylated in response to thrombin, and Pam3CysSer(Lys)4 led to an increase in the cytosolic calcium concentration. All studied responses of platelets to lipopeptides were inhibited by the prostacyclin receptor agonist cicaprost. Taken together, our data show that lipopeptides are effective activators of human platelets and that this activation is susceptible to the action of physiological platelet inhibitors.

The Toll-like receptor 2/1 (TLR2/1) complex initiates human platelet activation via the src/Syk/LAT/PLCγ2 signalling cascade

“…Whereas it has been shown that human platelet TLR4 signalling engages MyD88 [33], TLR2/1 activation by Pam3CSK4 was reported to not induce IRAK-1 phosphorylation [12]. Although several former studies demonstrated that the bacterial lipopeptide-mimicking TLR2/1-heterodimer agonist Pam3CSK4 concentration-dependently triggers prominent platelet activation and full aggregation [11][12][13], the underlying initial signalling pathway, however, has not been defined in detail so far.…”

“…The synthetic triacylated lipopeptide Pam3CSK4 that mimics the acylated amino terminus of bacterial lipopeptides, today recognized as a highly specific agonist of the TLR2/1 complex, has already in 1994 been reported to be an effective activator of human platelets inducing cytosolic calcium (Ca 2+ ) mobilization, protein tyrosine phosphorylation, dense granule secretion, and aggregation [11]. Interestingly, the diacylated macrophage activating lipoprotein-2 (MALP-2), which selectively induces TLR2/6 complex signalling, was recently reported to not induce any activation of human platelets, but rather exerted inhibitory effects on platelets subsequently challenged with Pam3CSK4 [12].…”

Pattern Recognition Receptors Based Immune Adjuvants: Their Role and Importance in Vaccine Design

“…Synthetic analogues of the Nterminal lipopentapeptide (sLP) 3 of the lipoprotein of E. coli proved to be as active as the native lipoprotein (Fig 5). They activate B-cells, monocytes, neutrophils and platelets and act as potent immunoadjuvants in-vivo and in-vitro (Seifert, Schultz et al 1990;Wiesmüller, Bessler et al 1992;Berg, Offermanns et al 1994;Bessler, Cox et al 1998;Hoffmann, Heinle et al 1998). Synthetic lipopeptides with the RR stereoisomer (N-palmitoyl-S-[2,3-bis(palmitoyloxy)-(2R)-propyl]-[R]-cysteine), showed higher B-cell mitogenicity and protective activity when introduced into vaccines than the mixture of other stereoisomers (Wiesmüller, Jung et al 1989;Wiesmüller, Bessler et al 1992).…”

Evidence that inhibition of phorbol ester-induced superoxide anion formation by cyclosporin a in phagocytes is not mediated by direct inhibition of protein kinase C

“…Isolation of platelets from healthy drug-free volunteers was performed as described previously [17]. Platelet aggregation was studied in an Aggrecorder II PA-3220 (Kyoto Daiichi Kagaku, Kyoto, Japan) according to Berg et al [17].…”