Purpose: The role of total cationic charge of synthetic protamine-like peptides in heparin anticoagulation reversal and accompanying adverse hemodynamic effects was studied.
Methods: Five protamine variants having specific total charges of [+8], [+16], [+18], [+20], and [+21] were synthesized by fluorenylmethoxycarbonyl procedures. Each of these lysine-containing peptides plus arginine-containing control salmine native protamine (n-protamine, [+21] charge) was studied in five dogs who received heparin 150 IU/kg intravenously followed by 1.5 mg/kg (intravenously during a 10-second period) of the synthesized peptide or control n-protamine.
Results: Anticoagulation reversal as assessed by a number of coagulation tests was more effective with peptides of greater cationic charge. In this regard, activated clotting time reversal 3 minutes after peptide administration was 7%, [+8]; 54%, [+16]; 81%, [+18]; 92%, [+20]; 81%, [+21]; and greater than 100% [n-protamine]. Reversal of heparin anticoagulation at 3 and 30 minutes, respectively, correlated significantly (*p < or = 0.05, p < or = 0.01 [see corresponding symbols within abstract]) with total cationic charge as assessed by activated clotting time (r = 0.97, 0.99 ), prothrombin time (r = 0.98, 0.87*), activated partial thromboplastin time (r = 0.99, 0.78), thrombin clotting time (r = 0.84,* 0.85*), heparin anti-Xa activity (r = 0.87,* 0.85*), and heparin anti-IIa activity (r = 0.79 at 3 minutes, p = 0.06). Maximum declines in systemic mean arterial pressure (MAP) were greater with more positively charged peptides: -1 mm Hg, [+8]; -3 mm Hg, [+16]; -31 mm Hg; [+18]; -31 mm Hg, [+20]; -35 mm Hg, [+21]; and -34 mm Hg [n-protamine]. Maximum decreases in MAP, cardiac output, and systemic oxygen consumption were highly correlated (p < or = 0.05) with total cationic charge: MAP, r = 0.87; cardiac output, r = 0.87; and systemic oxygen consumption, r = 0.86. A total toxicity score, reflecting adverse hemodynamic effects, was greater with increasing charge: -1.9 +/- 1.1, [+8]; -2.7 +/- 0.8, [+16]; -6.6 +/- 3.3, [+18]; -6.1 +/- 3.5, [+20]; -6.9 +/- 3.8, [+21]; and -7.0 +/- 5.2 [n-protamine]. The correlation of mean peptide total toxicity score to total cationic charge was significant (r = 0.89, p < 0.05).
Conclusions: These data suggest for the first time that effective alternatives to salmine protamine for reversal of heparin anticoagulation can be synthesized. Furthermore, total cationic charge appears to be an important determinant for both anticoagulation reversal and toxicity of protamine-like peptides.