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Kidney Week

Abstract: PO0433

RAP Inhibits Proximal Tubule Endocytosis and Protects Against Gentamicin-Induced Nephrotoxicity

Session Information

Category: Acute Kidney Injury

  • 103 AKI: Mechanisms

Authors

  • Sandoval, Ruben M., Indiana University School of Medicine, Indianapolis, Indiana, United States
  • Wagner, Mark C., Indiana University School of Medicine, Indianapolis, Indiana, United States
  • Yadav, Shiv Pratap Singh, Indiana University School of Medicine, Indianapolis, Indiana, United States
  • Campos-bilderback, Silvia B., Indiana University School of Medicine, Indianapolis, Indiana, United States
  • Molitoris, Bruce A., Indiana University School of Medicine, Indianapolis, Indiana, United States
Background

The proximal tubule (PT) reabsorbs and concentrates filtered nephrotoxins by clathrin mediated (CME) and fluid phase mediated (FPE) endocytosis, leading to PT injury and AKI. The molecular chaperone RAP (Alpha-2-macroglobulin receptor-associated protein) a 39kDa protein inhibits LDL receptor family members ligand binding, including megalin. Our hypothesis was that RAP would inhibit megalin mediated CME, but not FPE, and reduce gentamicin nephrotoxicity.

Methods

We utilized daily injections of gentamicin (100mg/Kg, IP) in a uninephrectomy CKD model in Munich Wistar Fromter rats with a baseline serum creatinine (sCr) of 0.80 + 0.23. Gentamicin was given with or without RAP (40mg/Kg, IV) to evaluate RAP’s impact on function, sCr, 24 hr urinary creatinine clearance and proteinuria, and endocytosis, 2-photon microscopy to determine FPE i.e. 10 kDa Cascade Blue dextran, and Megalin mediated CRE, i.e. albumin, endocytosis.

Results

RAP injections markedly reduced S1 PT albumin uptake over 60 minutes (80%), dextran (67%) and gentamicin (62%) in normal rats in a rapid and fully reversible fashion. In rats treated with or without RAP, daily gentamicin treatment resulted in elevated serum Cr by day 5 (1.4 + 0.2 vs 3.1 + 0.4mg/dl, p<0.01) and day 6 (1.5 + 0.5 vs 5.4 + 0.8mg/dl, p<0.01). CrCl decreased on day 6 to 0.49 + 0.16 ml/min vs 0.09 + 0.07 ml/min and urinary protein increased to 488 mg/ml/100gm wt vs 2,512 mg/ml/100 gm wt in RAP treated and untreated rats, respectively.

Conclusion

These results indicate RAP treatment induced reductions of both CME and FPE PT endocytosis suggesting a link between megalin and FPE. Clinically, RAP may have direct relevance to preventing the harmful nephrotoxic effects of gentamicin treatment, and likely other nephrotoxins, especially in individuals more susceptible to aminoglycoside injury. Future studies will need to explore whether reductions in ototoxicity are also prevented.

Funding

  • Other NIH Support