Neutralization of heparin by protamine. Time for a change?

Abstract

T he DNA of eukaryotic chromosomes forms a complex called chromatin with histones and other nucleic acid-binding proteins. In certain structures like sperm heads in which chromatin is present in a very condensed form, histones are replaced by smaller proteins, the protamines.' The structure-function relations of protamines have been studied in detail: they contain between 31 and 34 amino acid residues, two thirds of them basic, most of them arginine. When complexed to nucleic acids, protamines are folded into four a-helical domains, the cross-linking of DNA double helixes being achieved through arginine-phosphate interactions.1"2 A therapeutic role for protamine was first envisioned by Hagedorn et al,3 who observed that protamine-insulin suspensions are relatively insoluble in water or serum at neutral pH. This contrasts with regular insulin, which because of its acidic isoelectric point is extremely soluble under these conditions. The relative insolubility of protamineinsulin slows the rate at which the hormone is absorbed; consquently, its biological activity persists for 24-36 hours after subcutaneous injection (for comparison, the half-life of regular insulin after subcutaneous injection is about 4 hours).3'4 Because insulin and heparin have similar electric charges, Chargaff and Olson5 speculated that protamine might also prolong the anticoagulant effect of heparin. This, however, is not the case, because protamine efficiently inhibits the action of heparin both in vitro and in vivo. cytopenia in the dog9 was followed by studies of cardiovascular protamine toxicity after extracorporeal circulation in humans.10"'1 Jastrzebski et al10 observed a 37% increase in the mean pulmonary artery pressure of 15 patients who received protamine (6 mg/kg over a period of about 5 minutes) immediately after bypass. More recently, Lowenstein et al"l described five patients who experienced severe systemic hypotension and pulmonary vasoconstriction with 20-30 mg intravenous bolus doses of this compound. Subsequent studies involving 904 consecutive patients revealed that the incidence of protamine-induced pulmonary artery vasoconstriction after bypass was about 1%12 and that this reaction was accompanied by the generation of thromboxane and C5a, the anaphylatoxin derived from the fifth component of complement.13 In nondiabetic patients, the pathogenesis of protamineinduced pulmonary artery vasoconstriction is still poorly understood. In diabetic patients who have IgE or IgG antibodies against protamine because they have been treated with protamine-insulin preparations, the syndrome of pulmonary artery vasoconstriction and systemic hypotension is probably mediated by antibody-dependent reactions.'4

A natural motif approach to protein design: a synthetic leucine zipper peptide mimics the biological function of the platelet factor 4 protein

“…For example, efficient reversal of heparin anticoagulation is essential for a successful completion of open heart surgery in patients with cardiopulmonary bypass. Routinely, protamine sulfate is being used for this purpose, but this may result in a number of complications [29,30]. Recombinant PF4 appears to be a safer and more efficient drug as shown in a study in rats and baboons.…”

Investigation of Prothrombin Time in Human Whole-Blood Samples with a Quartz Crystal Biosensor

“…32 It has been used after cardiopulmonary bypass and has been recommended as an alternative neutralizing agent besides protamine. 33 As shown in the measurements, QCM sensors can be used to monitor heparin and antiheparin effect (polybrene) with respect to PT analysis even in whole-blood samples. In conclusion, this series of QCM measurements reveals the possibility to clinicians to decide on the basis of QCM data if the anticoagulant therapy is still sufficient (M1-M2) or if the heparin concentration in the sample is so high that no further coagulation processes can occur (M4).…”

Influence of Heparin, Protamine and Polybrene on the Time Integral of Thrombin Generation (Endogenous Thrombin Potential)

“…Polybrene is a positively charged quaternary nitrogen poly mer, used as a safe alternative heparin neu tralizer in patients with a protamine allergy [12,13], in spite of its reported nephrotoxicity [14], Polybrene is mainly used for in vitro heparin titration experiments [15,16]. In the late 60s, several articles reported polybrene to be superior to protamine [17][18][19].…”