Megalin‐Mediated Direct and Indirect Pathways for the Development of Contrast‐Induced Proximal Tubule Epithelial Cell Injury

Megalin is a multiligand endocytic receptor in proximal tubule epithelial cells (PTECs) that facilitates the reabsorption of certain nephrotoxic drugs. Notably, cilastatin competes with these drugs for binding to megalin. Patients with chronic kidney disease are at increased risk of contrast-induced (CI) acute kidney injury, in which iodine-mediated PTEC toxicity is a crucial pathogenic factor. This study investigated the interplay between megalin and CI-PTEC injury, along with the protective effect of cilastatin, utilizing electron probe microanalysis, a mouse CI-PTEC injury model, quartz crystal microbalance analysis, and binding assays with magnetic beads immobilized with iomeprol, a water-soluble nonionic contrast medium (CM). Electron probe microanalysis revealed the reduced renal uptake of CMs in the kidney cortex of kidney-specific conditional megalin-knockout mice compared with controls. In the CI-PTEC injury model using kidney-specific conditional or mosaic megalin-knockout mice, a significant reduction of vacuolization was observed in PTECs in the cortex compared with controls in the former, while co-expression of megalin and kidney injury molecule-1 was observed in the latter. These findings indicate that megalin is involved in the development of CI-PTEC injury. Cilastatin inhibited the renal uptake of CMs and ameliorated CI-PTEC injury in wild-type mice. Of note, two distinct pathways of renal CM uptake were delineated, both of which cilastatin inhibited: the direct binding of CMs to megalin and an indirect route involving transcobalamin-2, an endocytic megalin ligand, functioning as a CM carrier. Collectively, megalin governs the direct and indirect pathways in the development of CI-PTEC injury, and cilastatin effectively impedes both.