title: Effective and less toxic reversal of low-molecular weight heparin anticoagulation by a designer variant of protamine.
abstract: OBJECTIVE
  This investigation assessed protamine reversal of heparin anticoagulation by formation of a protamine-heparin alpha-helix by use of a new designer-variant protamine [+18BE] that was made from an existing protamine variant [+18B] whose non-alpha-helix-forming amino acid proline (P) was replaced by an alpha-helix-forming glutamic acid (E). The rate of administration of the new [+18BE] variant protamine on efficacy and toxicity in comparison to that of [+21] standard protamine and [+18B] was also studied.
  
  
  METHODS
  Acetyl-EAA(K2A2K2A)4K2-Amide [+18BE] was administered intravenously in a 1:1 dose to low-molecular-weight heparin (LMWH)-anticoagulated (intravenous 150 IU antifactor Xa/kg) dogs over 10 seconds or 3 minutes (n = 7, each group). Reversal efficacy was documented by measuring activated clotting time, thrombin clotting time, antifactor Xa, and antifactor IIa. Toxicity was defined by measuring systemic blood pressure, heart rate, cardiac output, pulmonary artery pressure, and oxygen consumption. Measurements were made at baseline, after administration of LMWH, before its reversal, and for 30 minutes thereafter. Results were compared with those after LMWH reversal with [+21] standard protamine and the [+18B] variant. A total toxicity score (TTS) was calculated for each compound from maximal declines in blood pressure, heart rate, cardiac output, and oxygen consumption.
  
  
  RESULTS
  LMWH anticoagulation reversal was significantly (p < 0.01) less toxic over 10 seconds and 3 minutes with the [+18BE] designer variant (TTS -2.3, -2.2) compared with the [+21] standard protamine (TTS -6.4, -7.2). Percent LMWH reversal at 3 minutes revealed [+18BE] to have antifactor Xa activity as high as 91%, compared with 68% for protamine [+21], when given over 3 minutes (p < 0.05).
  
  
  CONCLUSIONS
  This investigation documents that a new designer variant of protamine [+18BE] has superior efficacy compared with [+21] standard protamine for reversal of LMWH anticoagulation and that this occurs with a highly favorable toxicity profile.
authors.affiliation: Jobst Vascular Laboratory, Department of Surgery, University of Michigan, Ann Arbor, USA.
authors.forename: T W
authors.initials: TW
authors.lastname: Wakefield
authors.forename: P C
authors.initials: PC
authors.lastname: Andrews
authors.forename: S K
authors.initials: SK
authors.lastname: Wrobleski
authors.forename: A M
authors.initials: AM
authors.lastname: Kadell
authors.forename: R
authors.initials: R
authors.lastname: Schmidt
authors.forename: S
authors.initials: S
authors.lastname: Tejwani
authors.forename: J C
authors.initials: JC
authors.lastname: Stanley
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001777:Blood Coagulation / Q000187:drug effects; D001794:Blood Pressure / Q000187:drug effects; D002302:Cardiac Output / Q000187:drug effects; D004285:Dogs; D015195:Drug Design; D004347:Drug Interactions; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006495:Heparin, Low-Molecular-Weight / Q000378:metabolism / Q000494:pharmacology*; D007275:Injections, Intravenous; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010101:Oxygen Consumption / Q000187:drug effects; D011479:Protamines / Q000138:chemical synthesis / Q000378:metabolism / Q000494:pharmacology*; D011485:Protein Binding; D013997:Time Factors; D014914:Whole Blood Coagulation Time
chemical_list: D006495:Heparin, Low-Molecular-Weight; C079002:Logiparin; D011479:Protamines