Zinc induced damage to kidney proximal tubular cells: studies on chemical speciation leading to a mechanism of damage

This study was carried out to investigate whether zinc can potentiate renal toxicity using monolayer cultures of kidney proximal tubular cells and if so to establish the chemical species and the mechanism involved.

METHODS

Zinc was prepared as the citrate complex at pH 7.4 in phosphate buffered saline. Monolayers of kidney proximal tubular cells under standard cell culture conditions were exposed to zinc concentrations of 0, 5 10, 20, 50 and 100 μmol/L. To assess cellular damage, thiazol blue (MTT) uptake, NAG and LDH release, DAPI staining and Tunel assay were used. Cytoprotective agents: trolox, cysteine, glutathione, ascorbic acid and sodium selenite were used to investigate if the damage was reversible.

RESULTS

Incubation of kidney cells with zinc citrate showed a dose related reduction in cell viability (p<0.005) associated with cellular uptake of zinc ions. After 24 h incubation with 100 μmol/L Zn citrate, NAG release was not significantly different compared to the control whereas LDH increased 3 fold. DAPI staining showed apoptotic bodies within the cells confirmed by Tunel assay using flow cytometry. Electron microscopy showed significant morphological changes including loss of brush border, vacuolated cytoplasm and condensed nuclei. Trolox almost completely (>85±5%) and sodium selenite partially recovered (40±4%) the viability of cells exposed to Zn but no protection was observed with other cytoprotectants, e.g. glutathione, cysteine or ascorbic acid. In conclusion zinc can induce damage to kidney cells by a mechanism dependent on zinc ions entering the cell, binding to the cell organelles and disrupting cellular processes rather than damage initiated by free radical and ROS production.