Microvilli-Mediated Transport and Internalization of Extracellularly Assembled Nanoparticles in Kidney Proximal Tubules

Here, using reactive oxygen species (ROS)-responsive glutathione-coated Au₁₁ nanoclusters (∼0.6 nm) as a model, we show that renal-filtered Au₁₁ undergoes extracellular ROS-mediated biotransformation into 2–3 nm gold nanoparticles, followed by their assembly into large nanostructures (∼50–500 nm) within the proximal tubular lumen of healthy kidneys.

Unexpectedly, high-resolution electron microscopy revealed that brush-border microvilli capture these large luminal nanoassemblies, transport them from microvillar tips to the microvillar base, and internalize them through apical pinching-off events. The internalized nanoassemblies subsequently traffic through apical vacuoles to lysosomes, where a second-stage biotransformation produces densely packed flower-like gold nanostructures that are ultimately re-eliminated into the tubular lumen through membrane extrusion.