Comparison of the sensitivity of different toxicological endpoints in Caco-2 cells after cadmium chloride treatment

The human colorectal adenocarcinoma cell line Caco-2 is a widely used in vitro model of the intestinal barrier. Cadmium chloride (CdCl2) is a highly toxic metal compound, ubiquitous in the biosphere, able to enter the food chain and to reach the intestinal epithelium, causing structural and functional damages. The aim of this work was to characterise cadmium toxicity in Caco-2 cells and, in particular, to compare the sensitivity of different endpoints revealing damage both on the epithelial barrier and at the cellular or molecular level. After 24-h exposure of the cells to CdCl2, lactate dehydrogenase (LDH) leakage showed cadmium-induced cell toxicity, significant from 25 muM CdCl2 and above, and analysis of different cell death pathways indicated the presence of necrosis after treatment with 50 muM CdCl2. At the molecular level, we observed an increase in the protective protein heat shock protein 70 (HSP70), starting at 10 muM CdCl2. At the barrier level, transepithelial electrical resistance (TEER) decreased while paracellular permeability (PCP) significantly increased after the treatment, showing an EC50 of 6 and 16 muM CdCl2, respectively, and indicating the loss of barrier integrity. In conclusion, our data reveal that CdCl2 toxicity in Caco-2 cells can be detected at the barrier level at very low concentrations; also, HSP70 was shown to be a sensitive marker for detecting in vitro cadmium-induced toxicity.