Differences in Toxic Response induced by three Variants of the Diarrheic Shellfish Poisoning Phycotoxins in Human Intestinal Caco-2 Cells

Diarrheic shellfish poisoning (DSP) is caused by the consumption of shellfish contaminated with a group of phycotoxins that includes okadaic acid (OA), dinophysistoxin-1 (DTX-1), and dinophysistoxin-2 (DTX-2). These toxins are inhibitors of serine/threonine protein phosphatases 1 (PP1) and 2A (PP2A), but show distinct levels of toxicity. Aside from a difference in PP inhibition potency that would explain these differences in toxicity, others mechanisms of action are thought to be involved. Therefore, we investigated and compared which mechanisms are involved in the toxicity of these three analogues. As the intestine is one of the target organs, we studied the transcriptomic profiles of human intestinal Caco-2 cells exposed to OA, DTX-1, and DTX-2. The pathways specifically affected by each toxin treatment were further confirmed through the expression of key genes and markers of toxicity. Our results did not identify any distinct biological mechanism for OA and DTX-2. However, only DTX-1 induced up-regulation of the MAPK transduction signalling pathway, and down-regulation of gene products involved in the regulation of DNA repair. As a consequence, based on transcriptomic results, we demonstrated that the higher toxicity of DTX-1 compared to OA and DTX-2 was consistent with certain specific pathways involved in intestinal cell response. Modulation of gene expression in undifferentiated Caco-2 cells was measured at 24 hours after exposure to doses of 0, 13.8 nM of okadaic acid, 6.9 nM of dinophysistoxin-1, and 27.7 nM of dinophysistoxin-2. Six independent experiments were performed, and 24 samples (6 controls, 6 exposed to okadaic acid, 6 exposed to dinophysistoxin-1, 6 exposed to dinophysistoxin-2) had an RNA quality indicator ≥ 9 and were used for the microarray experiments.