Matas Lecture. Heparin--controversies and misconceptions

Porous Polymers as Universal Reversal Agents for Heparin Anticoagulants through an Inclusion-Sequestration Mechanism

Heparins are widely used anticoagulants for surgical procedures and extracorporeal therapies. However, all of them have bleeding risks. Protamine sulfate, the only clinically approved antidote for unfractionated heparin (UFH), has adverse effects. Moreover, protamine can only partially neutralize low-molecular-weight heparins (LMWHs) and is not effective for fondaparinux. Here, an inclusion-sequestration strategy for efficient neutralization of heparin anticoagulants by cationic porous supramolecular organic frameworks (SOFs) and porous organic polymers (POPs) is reported. Isothermal titration calorimetric and fluorescence experiments show strong binding affinities of these porous polymers toward heparins, whereas dynamic light scattering and zeta potential analysis confirm that the heparin sequences are adsorbed into the interior of the porous hosts. Activated partial thromboplastin time, anti-FXa, and thromboelastography assays indicate that their neutralization efficacies are higher than or as high as that of protamine for UFH and generally superior to protamine for LMWHs and fondaparinux, which is further confirmed by tail-transection model in mice and ex vivo aPTT or anti-FXa analysis in rats. Acute toxicity evaluations reveal that one of the SOFs displays outstanding biocompatibility. This work suggests that porous polymers can supply safe and rapid reversal of clinically used heparins, as protamine surrogates, providing an improved approach for their neutralization.

Activated platelets in heparinized shed blood: the "second hit" of acute lung injury in trauma/hemorrhagic shock models

The return of heparinized shed blood (SB) in trauma/hemorrhagic shock (T/HS) models remains controversial because of potential anti-inflammatory properties. Although ubiquitous as an anticoagulant, heparin is ineffective on cellular coagulation as an antithrombotic agent. Therefore, we hypothesized that returning heparinized SB would paradoxically enhance acute lung injury (ALI) after T/HS because of the infusion of activated platelets. Sprague-Dawley rats, anesthetized with pentobarbital, underwent laparotomy and hemorrhage-induced shock (MAP of 30 mmHg × 45 min). Animals were resuscitated with a combination of normal saline and returned SB. Shed blood was collected in either 80 U/kg of heparin, 800 U/kg of heparin, or citrate or diluted 1:8 with normal saline. An additional group of animals were pretreated with a platelet P2Y12 receptor antagonist (clopidogrel) before T/HS. Bronchoalveolar lavage, lung myeloperoxidase assays, pulmonary immunofluorescence, and blood smears were conducted. Bronchoalveolar lavage protein increased in animals resuscitated with heparinized SB (T/HS + 80 U/kg Hep 1.62 ± 0.29, T/HS + 800 U/kg Hep 1.30 ± 0.15 vs. T/SS 0.51 ± 0.16 and T/HS Citrate 0.7 ± 0.09) (P < 0.0001). Blood smears and platelet function assays revealed platelet aggregates and increased platelet activation. Animals pretreated with a platelet P2Y12 receptor antagonist were protected from postinjury ALI (P < 0.0001). Animals with return of SB had increased pulmonary polymorphonuclear leukocyte sequestration (P < 0.0001). Pulmonary immunofluorescence demonstrated microthrombi only in the T/HS group receiving heparinized SB (P < 0.0001). The return of heparinized SB functions as a "second hit" to enhance ALI, with activated platelets propagating microthrombi and pulmonary polymorphonuclear leukocyte recruitment.

Citrate anticoagulation in a piglet model of pediatric continuous renal replacement therapy

OBJECTIVE

To develop pediatric guidelines for the use of citrate as a regional anticoagulant for continuous renal replacement therapy (CRRT) using a neonatal piglet model.

DESIGN

Prospective observational study.

SETTING

Animal laboratory in the research center of a tertiary-level children's hospital.

SUBJECTS

Ten neonatal piglets.

INTERVENTIONS AND MEASUREMENTS

Using a venovenous CRRT circuit and filter, we randomly altered the filter blood flow rate, replacement flow rate, and citrate flow rate over conventional pediatric ranges. Measured end points were prefilter serum ionized calcium and citrate levels.

MAIN RESULTS

A prefilter serum citrate concentration of 6 mmol/L is required to maintain the prefilter ionized calcium < or =0.4 mmol/L. Using multiple regression analysis on collected data, we derived a formula to predict prefilter serum citrate for combinations of replacement flow rate, blood flow rate, and citrate flow rate.

CONCLUSIONS

The available literature and our past experience indicate that a prefilter ionized calcium < or =0.4 mmol/L is required to anticoagulate a CRRT circuit; a prefilter serum citrate concentration of 6 mmol/L is required to achieve this. Our multiple regression analysis can be expressed graphically to allow easy calculation of the required citrate flow rate, given the knowledge of the replacement flow rate and blood flow rate. Our results provide the first guidelines for the use of citrate as a regional anticoagulant in a pediatric-size model of CRRT.