In vitro toxicology assessment of cadmium bioavailability on primary porcine oviductal epithelial cells

This study assessed the in vitro effects of cadmium ion (Cd2+) and cadmium–fulvic acid complexes (Cd2+–FA) on porcine oviductal epithelial cells (POEC) using transmission electron microscopy (TEM). Fresh POEC were cultured for 24 h and then exposed for 3 h in the tested solutions. Absorbed cadmium was analyzed by graphite furnace atomic absorption spectrophotometer (AAS). Dissociation and exchange rate constants were determined using the competing ligand, Chelex-100 and predicted cadmium species were calculated using the MINTEQA2 program. The results showed that the dissociation rate constant of Cd2+–FA was equal to 1.023 × 10−3 s−1 which was slower than the exchange rate at 2.062 × 10−3 s−1. Nevertheless, the absorbed concentrations of Cd2+ and Cd2+–FA of POEC were similar and were 47 ± 6.25 μg L−1 and 54 ± 3.61 μg L−1, respectively. Although both levels of absorptions were not significantly different (t-test p = 0.168 at α 0.01), their morphological effects as examined by TEM were substantially different with the effects being most marked with Cd2+ > Cd2+–FA > FA. Aggregations around nuclei and nuclear membranes were observed with FA treatment whilst Cd2+–FA treatment produced more cytoplasmic damage. Cd2+ treatment caused nuclear deformities. In conclusion, FA appears to penetrate the cells but was less likely to enter the nucleus. It also reduced the toxicity of Cd2+ as the nuclei from the Cd2+–FA treatment appeared normal. Nevertheless, some Cd2+ could still enter the nucleus. This might be because there was still 67.8% Cd2+ left unbound from the Cd2+–FA treatment as calculated from the MINTEQA2 program compared to 99.1% Cd2+ with Cd2+ treatment, thus underlining the inherent toxicity of soluble cadmium ion.