Adherent Mononuclear Cells And Activated Protein C (APC)

Abstract

Addition of bovine APC to dilute whole blood or euglobulin assays of fibrinolytic activity produces little effect on rates of clot lysis. However, addition of APC to undiluted non anti coagulated or to 3.2% citrated whole blood followed by 125I-fibrinogen and thrombin produces clots which release fibrin degradation products and lyse within 24 hours. Ordinarily clotted non-anticoagulated whole blood does not lyse.Addition of increasing amounts of APC from 12-100ug/ml increases the rate of whole blood clot lysis at least 20 fold over a 3.2% citrate control. This response is dose dependent with no evidence of saturation. Addition of increasing amounts of APC (25-200ug/ml) to platelet poor plasma (PPP) increases the rate of clot lysis only twofold. This increase is also dose dependent but is saturated at 80-100ug/ml. Addition of APC (60ug/ml) to 3.2% citrated PPP plus adherent mononuclear cells (1,000-2,000/MM3) again increases the rate of clot lysis at least 20 fold as with the whole blood system. However, this increase in rate is delayed. Substitution of platelet rich plasma (PRP) for PPP eliminates the lag phase. Substitution of non-adherent cells (1,000 MM3), RBC (3 million/MM3) or polymorphonuclear cells produces no acceleration of PPP clot lysis above the PPP-APC control. When deoxyglucose (1.4 × 10-1M) and anti-mycin (2.9 × 10-5M) are added to the PPP plus adherentxells before APC, the cell dependent acceleration of clot lysis is abolished. Removal of plasminogen activator (PA) and plasminogen (P) from PPP by lysine agarose adsorbtion also inhibits the effect of APC and adherent cells whereas reconstitution restores activity to 60%.We conclude that adherent mononuclear cells are required for expression of optimal APC pro-fibrinolytic activity and that this may require both P and PA. This suggests another role for mononuclear cells (monocytes) found in inflamatory and thrombotic lesions.

Activated protein C in sepsis

“…A subsequent study (1985) demonstrated that infusion of thrombin with endotoxin also protected the dogs, suggesting that this was the case [59]. This work was closely followed by studies demonstrating the prophylactic [9] and therapeutic [10,60] efficacy of plasma APC and rhAPC in treatment of baboons infused with LD 100 E. coli (1986–87).…”

“…In spite of our increasing understanding of the biochemistry [1,2] and physiology [3–8] of the protein C network and the anticoagulant and anti‐inflammatory [9,10] functions of activated protein C in primate models of sepsis, our knowledge of how it protects patients with severe sepsis remains more limited. What is not fully recognized, however, is our equally limited knowledge of the various pathophysiologic processes that constitute the severe sepsis syndrome on which activated protein C has been shown to act.…”

“…Severe sepsis at least initially is an acute inflammatory coagulopathic disorder of the microvascular endothelium [19,20]. The endothelium is rendered dysfunctional such that it becomes more permeable [10,46], hypercoagulable [10,47], and itself contributes to the cycle of inflammation and thrombosis by expressing both procoagulant and pro‐inflammatory mediators [48]. This starts with the organisms triggering a defense response by the host's plasma factors and reticular elements that, if left unregulated, result in an aberrant attack on the endothelium by toxins [49–51] and neutrophils [41–43, 52–55].…”

“…This starts with the organisms triggering a defense response by the host's plasma factors and reticular elements that, if left unregulated, result in an aberrant attack on the endothelium by toxins [49–51] and neutrophils [41–43, 52–55]. As observed in the baboon model of Escherichia coli sepsis, the dysfunction of the endothelium [10,46,47] arising from this attack can assume several clinical forms depending on which pathophysiologic process is dominant. These include (i) cardiovascular organ failure with capillary leak syndrome and shock within hours such as is seen in severe sepsis and toxic shock syndrome; (ii) consumptive coagulopathy with hemorrhage/ecchymosis within hours such as is seen in severe sepsis arising from septic abortion; (iii) multiple organ failure that progresses over a period of days in which elements of coagulopathy and capillary leak appear such as is seen in less intense but still lethal cases of severe sepsis; (iv) multiple organ failure that does not progress such as is seen in severe sepsis patients most of whom recover; and (v) multiple organ failure over a period of weeks with irreversible microvascular thrombosis such as is seen in severe sepsis patients and patients with hemolytic uremic syndrome.…”

Activation of Protein C In Vivo

“…Phospholipid and Ca2' accelerate the inactivation of Factor Va and VIIIa by protein Ca (4)(5)(6)(7)(8)(9). Protein Ca also generates fibrinolytic activity in blood both in vitro (10)(11)(12) and in vivo (13)(14). The in vivo effects are mediated, at least in part, by increased levels of circulating plasminogen activator (14).…”