Differential effects of novel protamine variants on myocyte contractile function with left ventricular failure Monty H. Cox, BS, Seung-Jun O, MD, Mark J. Clair, BS, Rupak Mukherjee, PhD, Thomas W. Wakefield, MD, Philip C. Andrews, Phi), James C. Stanley, MD, Fred A. Crawford, Jr., MD, and Francis G. Spinale, MD, Phi), Charleston, S.C., and Ann Arbor, Mich. Background. Protamine administration can cause left ventricular (L IO dysfunction, which may have clinical significance in the setting of congestive heart failure (CHF). Protamine variants have recently been constructed with heparin reversal capacity similar to protamine. The purpose of this study was to examine the potential differential effects of these protamine variants on isolated myocyte contractile function in normal myocytes and in myocytes after the development of CHF. Methods, Contractile function was measured by means of computer-aided videomicroscopy in myocytes from five normal pigs and five pigs with CHF induced by rapid pacing (240 beats/min for 3 weeks). Myocyte contractility was examined in the presence of 40 tzg/ml native protamine or one of three protamine variants: (1) reduced charge (+18) and lysine substituted for arginine; (2) lysine-substituted variant with glutamic acid substituted for the initial proline; or (3) arginine-rich peptide with a terminal arginine-glycine-aspartic acid (RGD) amino acid sequence. Results. In the presence of native protamine, myocyte percent shortening feU from baseline in both the normal (2.86 + 0.15 versus 4.58 +_ 0.08, p < 0.05) and the CItF groups (1.01 + 0.06 versus 2.07 +- 0.05, p < 0.05). With both of the lysine-substituted protamine variants, percent shortening fell from baseline in the normal group (3.42 + 0.20for arginine and 3. 74 +- 0.20for glutamic acid versus 4.58 + 0.08, p < 0.05), and was unchanged in the CHF group (1.94 + 0.13 versus 2.07 +- 0.05, p = 0.34for arginine; and 1.96 +- 0.10 versus 2.07 +_ 0.05, p = 0.31, for glutamic acid). However, with the arginine/RGD variant, percent shortening fell from baseline in both the normal (2.86 + 0.23 versus 4.58 + 0.08, p < 0.05) and the CHF groups (1.32 +- 0.10 versus 2.07 + 0.05, p < 0.05). Conclusions. Specific changes in the primary and secondary structures of protamine had different effects on myocyte contractile function. Furthermore, the negative effects of lysine-substituted protamine variants on myocyte contractility were less pronounced in both CItF and normal myocytes. Thus protamine variants may be of clinical use, particularly in the setting of preexisting L V dysfunction. (Surgery 1997;121:304-13.) From the Division of Cardiothoracic Surgery, Medical University of South Carolina, Charleston, S.C.; the Section of Vascular Surgery, Jobst Vascular Research Laboratory, University of Michigan, and the Department of Biochemistry, University of Michigan, Ann Arbor, Mich. AN ESTIMATED 500,000 CARDIAC and vascular surgical procedures performed each year require anticoagula- Supported by National Institutes of Health grant HL-45024, a basic re- search grant from Pfizer Inc., a grant-in-aid from the South Carolina Heart Association,a grant-in-aid from the American Heart Association, and Veterans Administration merit reviewgrant 331. F.G.S.is an estab- lished investigator of the American Heart Association. M.H.C. is a medical student research fellow of the American Heart Association. Accepted for publication July 31, 1996. Reprint requests: Francis G. Spinale, MD, PhD. Divisionof Cardiotho- racic Surgery, Medical University of South Carolina, 171 Ashley Avenue, Charleston, SC 29425. Copyright 9 1997 by Mosby-YearBook, Inc. 0039-6060/97/$5.00 + 0 11/56/77008 304 SURGERY tion with heparin. 1 Protamine sulfate is a polycationic peptide routinely used to reverse the anticoagulant ef- fects of heparin. However, past studies have reported decreased systemic vascular resistance, elevated pulmo- nary vascular resistance, and reduced left ventricular (LV) pump performance after the intravascular admin- istration ofprotamine3 -1~This laboratory has previously demonstrated that protamine has direct and negative effects on myocyte contractile performance, suggesting a potential contributory mechanism for the decreased LV pump function after protamine administration. 14-17 Wakefield et al. 18-21 have synthesized several protamine variants with altered primary and secondary structure and reduced overall charge. These protamine variants