Renal targeting of captopril using captopril-lysozyme conjugate enhances its antiproteinuric effect in adriamycin-induced nephrosis

Introduction: High-sodium intake blunts the renoprotective efficacy of angiotensin-converting enzyme (ACE) inhibitors. We investigated whether targeting the drug to the kidneys may attenuate the inferior response to ACE inhibitor (ACE-I) under high-sodium conditions. The ACE-I, captopril, was coupled to the low molecular weight protein (LMWP) lysozyme, yielding captopril-lysozyme conjugates that accumulate specifically in the proximal tubular cells of the kidneys. We compared the antiproteinuric efficacy of captopril to that of the captopril-lysozyme conjugate in adriamycin-induced proteinuric rats fed with a high-sodium diet. Materials and methods: Rats with adriamycin (single injection 2 mg/kg)-induced proteinuria were put on a high-sodium diet (HS; 3% NaCl). When stable proteinuria developed at 5.5 weeks, animals were assigned to the following subcutaneous treatments: (1) vehicle (n=7); (2) lysozyme (equivalent to the amount in conjugate) (n=7); (3) captopril (5 mg/kg/24 hours) (n=8); (4) captopril-lysozyme conjugate (captopril content equivalent to 1mg captopril/kg/24 hours) (n=7). Blood pressure and proteinuria were monitored. After 10 days of treatment the rats were sacrificed and kidneys and plasma were removed. Results: Results are given as mean ± S.E.M. After injection with adriamycin at t=0, stable proteinuria developed, amounting to 547±79 mg/24 hours at week 5.5. Subsequently, after seven and nine days of treatment, no reduction of proteinuria was observed in the captopril-treated group. In contrast, a significant reduction in proteinuria, amounting to 35±4% (day seven) and 25±2% (day nine), was observed in the captopril-lysozyme conjugate group (p