Bactericidal Permeability Increasing Protein Inhibits Lipopolysaccharide-Mediated Platelet Activation in Vitro

This study was purposed to investigate the inhibitory effect of bactericidal permeability-increasing protein (BPI) on lipopolysaccharide (LPS)-mediated activation of platelets. Venous blood samples were obtained from 10 healthy volunteers and were prepared into platelet-rich plasma (PRP, 1 × 10(8)/ml). Experiments were divided into four groups: normal platelet group (untreated group); LPS group, BPI group and BPI+LPS group. PRP were stimulated by LPS (10 µg/ml) in the presence and absence of BPI (100 µg/ml) or BPI alone. Then platelets were harvested and determined for Toll-like receptor-4 (TLR-4) with flow cytometry (FCM), the supernatant was used for detection of cytokines including tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) with enzyme-linked immunosorbent assay (ELISA). The results showed that as compared with normal platelet group, TLR-4 expression on platelets was significantly increased under LPS stimulation (P < 0.001); the levels of TNF-α and IL-6 in the supernatant were also remarkably elevated (P < 0.001). However, either TLR-4 expression or the cytokine levels significantly decreased in the presence of BPI when platelets underwent LPS-challenge (P < 0.05), but still were higher than that in normal platelet group. Stimulating the platelets with BPI alone could not enhance the TLR-4 expression and cytokine levels. It is concluded that BPI has the ability to inhibit the LPS-induced platelet activation.