Monocyte-platelet complexes on CD14/CD16 monocyte subsets: relationship with ApoA-I levels. A preliminary study

Platelet-Monocyte Aggregates: Understanding Mechanisms and Functions in Sepsis

ABSTRACT

Platelets have been shown to play an important immunomodulatory role in the pathogenesis of various diseases through their interactions with other immune and nonimmune cells. Sepsis is a major cause of death in the United States, and many of the mechanisms driving sepsis pathology are still unresolved. Monocytes have recently received increasing attention in sepsis pathogenesis, and multiple studies have associated increased levels of platelet-monocyte aggregates observed early in sepsis with clinical outcomes in sepsis patients. These findings suggest platelet-monocyte aggregates may be an important prognostic indicator. However, the mechanisms leading to platelet interaction and aggregation with monocytes, and the effects of aggregation during sepsis are still poorly defined. There are few studies that have really investigated functions of platelets and monocytes together, despite a large body of research showing separate functions of platelets and monocytes in inflammation and immune responses during sepsis. The goal of this review is to provide insights into what we do know about mechanisms and biological meanings of platelet-monocyte interactions, as well as some of the technical challenges and limitations involved in studying this important potential mechanism in sepsis pathogenesis. Improving our understanding of platelet and monocyte biology in sepsis may result in identification of novel targets that can be used to positively affect outcomes in sepsis.

L-4F alters hyperlipidemic (but not healthy) mouse plasma to reduce platelet aggregation

Background and Purpose- Hyperlipidemia is associated with platelet hyperreactivity. We hypothesized that L-4F, an apolipoprotein A-I mimetic peptide, would inhibit platelet aggregation in hyperlipidemic mice.

METHODS AND RESULTS

Injecting L-4F into apolipoprotein E (apoE)-null and low-density lipoprotein receptor-null mice resulted in a significant reduction in platelet aggregation in response to agonists; however, there was no reduction in platelet aggregation after injection of L-4F into wild-type (WT) mice. Consistent with these results, injection of L-4F into apoE-null mice prolonged bleeding time; the same result was not found in WT mice. Incubating L-4F in vitro with apoE-null platelet-rich plasma also resulted in decreased platelet aggregation. However, incubating washed platelets from either apoE-null or WT mice with L-4F did not alter aggregation. Compared with WT mice, unstimulated platelets from apoE-null mice contained significantly more 12-hydroxy 5,8,10,14-eicosatetraenoic acid, thromboxane A(2), and prostaglandins D(2) and E(2). In response to agonists, platelets from L-4F-treated apoE-null mice formed significantly less thromboxane A(2), prostaglandins D(2) and E(2), and 12-hydroxy 5,8,10,14-eicosatetraenoic acid.

CONCLUSIONS

By binding plasma-oxidized lipids that cause platelet hyperreactivity in hyperlipidemic mice, L-4F decreases platelet aggregation.