In vitro Evaluation of The Effects of Cadmium on Endocytic Uptakes of Proteins into Cultured Proximal Tubule Epithelial Cells.

Hitomi Fujishiro,Mei Jinno,Seiichiro Himeno,Nanae Oka,Nobuki Otera,Hazuki Yamamoto

doi:10.3390/toxics8020024

Abstract

Cadmium (Cd) is an environmental pollutant known to cause dysfunctions of the tubular reabsorption of biomolecules in the kidney. Elevated levels of urinary excretion of low-molecular-weight proteins such as β2-microglobulin (β2-MG) have been used as an indicator of Cd-induced renal tubular dysfunctions. However, very few studies have examined the direct effects of Cd on the reabsorption efficiency of proteins using cultured renal cells. Here, we developed an in vitro assay system for quantifying the endocytic uptakes of fluorescent-labeled proteins by flow cytometry in S1 and S2 cells derived from mouse kidney proximal tubules. Endocytic uptakes of fluorescent-labeled albumin, transferrin, β2-MG, and metallothionein into S1 cells were confirmed by fluorescence imaging and flow cytometry. The exposure of S1 and S2 cells to Cd at 1 and 3 µM for 3 days resulted in significant decreases in the uptakes of β2-MG and metallothionein but not in those of albumin or transferrin. These results suggest that Cd affects the tubular reabsorption of low-molecular-weight proteins even at nonlethal concentrations. The in vitro assay system developed in this study to evaluate the endocytic uptakes of proteins may serve as a useful tool for detecting toxicants that cause renal tubular dysfunctions.

Highlights

Cadmium (Cd) is an environmental pollutant that causes renal toxicity in animals and humans after chronic exposure in the diet [1]
Cd accumulation in the proximal tubules of the kidney has been believed to disturb the reabsorption of the luminal biomolecules, which are filtered through the glomerulus into proximal tubule epithelial cells (PTECs)
Disturbances in the tubular reabsorption of glomerular-filtered biomolecules by PTECS in kidney are a hallmark of Cd-induced nephrotoxicity

Summary

Introduction

Cadmium (Cd) is an environmental pollutant that causes renal toxicity in animals and humans after chronic exposure in the diet [1]. Due to both the high affinity of Cd for sulfhydryl moieties in biomolecules within cells and the difficulty of excretion from cells, the biological half-life of Cd in the human kidney has been calculated to be more than 25 years [2]. Animals and humans exposed to Cd for a long time show increased urinary excretion of glucose, amino acids, and low-molecular-weight (LMW) proteins such as β2 -microglobulin (β2 -MG). Enhanced urinary levels of β2 -MG have been used as sensitive and reliable indicators of Cd-induced renal tubular damage [9,10]

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