Combined effect of cadmium and sulfonamides on sea urchin development

Echinoderms play a key role in the maintenance of the integrity of the ecosystem where they live. They are constantly exposed to pollutants, particularly in their early planktonic life stages. Sulfamethoxazole with trimethoprim (TMP/SMX) is a fixed antibiotic combination whose concentration is significantly increasing in the coastal waters due to human medicine and also intensive husbandry and aquaculture activities. Previously, we studied the defense strategies activated by P. lividus embryos in response to sublethal doses of CdCl2. Although toxic effects of cadmium on embryo development are not morphologically detectable before 24 hours of exposure, we found upregulation in mRNAs related to intracellular signaling component pathways, redox enzymes, and metal detoxification (including 5 metallothioneins) in response to cadmium. In this study, we investigated the putative morphological and molecular malfunctions in embryos exposed to different doses of TMP/SMX and cadmium, with the aim of simulating embryonic vulnerability that could occurred in polluted seawaters. The morphological analysis showed that embryos grown in the presence of TMP/SMX at the concentration used in aquaculture develop normally and gastrulate. Instead the embryos grown with a combination of TMP/SMX and low concentrations of cadmium show inhibition of development and arrest at the morula/blastula transition. RT-qPCR analysis was used to assess the extent of gene expression. Target mRNA were selected from the previously isolated mRNAs or from an in silico EST database search of sequences coding for apoptosis and stress markers. RT-qPCR results show that TMP/SMX treatment causes a remarkable increase in mRNAs coding for enzymes of Nitric Oxide pathway, detox enzymes and antiproliferative proteins. Co-treatment with TMP/SMX and cadmium blocks the response impairing development. Combined effect of TMP/SMX and cadmium could suppress the physiological protective response and activate the apoptotic program.