Protamine Protects Against Vancomycin Induced Kidney Injury

Introduction: Vancomycin causes kidney injury by accumulating in the proximal tubule, likely mediated by megalin uptake. Protamine is a putative megalin inhibitor that shares binding sites with heparin and is approved for heparin overdose in patients. Methods: We employed a well characterized Sprague Dawley rat model to assess kidney injury and function in animals that received vancomycin, protamine alone, or vancomycin plus protamine over 5 days. Urinary KIM-1 was used as the primary measure for kidney injury while iohexol clearance was calculated to assess kidney function. Animals had samples drawn pre-treatment to serve as their own controls. Additionally, since protamine is not a known nephrotoxin, the protamine group also served as a control. Cellular inhibition studies were performed to assess the ability of protamine to inhibit OAT1, OAT3, and OCT2. Results: Rats that received vancomycin had significantly increased urinary KIM-1 on day 2 (24.9 ng/24h, 95% CI 1.87 to 48.0) compared to the protamine alone group. By day 4, animals that received protamine with vancomycin had urinary KIM-1 amounts that were elevated compared to protamine alone (KIM-1 29.0 ng/24h, 95% CI 5.0 to 53.0). No statistically significant differences were identified for iohexol clearance changes between drug groups or when comparing clearance change from baseline (P>0.05). No substantial inhibition of OAT1, OAT3, or OCT2 was observed with protamine. IC50 values for protamine were 1e-4 M for OAT1 and OAT3 and 4.3e-5 M for OCT2. Conclusion: Protamine, when added to vancomycin therapy, delays vancomycin induced kidney injury as defined by urinary KIM-1 in the rat model by one to three days. Protamine putatively acts through blockade of megalin and does not appear to have significant inhibition on OAT1, OAT3, or OCT2. Since protamine is an approved FDA medication, it has clinical potential as a therapeutic to reduce vancomycin related kidney injury; however, greater utility may be found by pursuing compounds with fewer adverse event liabilities.