Analysis of the passage of the marine biotoxin okadaic acid through an in vitro human gut barrier.

The marine biotoxin okadaic acid (OA), produced by dinoflagellates, can accumulate in various bivalve molluscs. In humans, oral consumption of shellfish contaminated with OA induces acute toxic effects like diarrhea, nausea, vomiting and abdominal pain. However, tumorigenic and embryotoxic effects of OA have been also described. Current toxicokinetic studies with mice were performed with high cytotoxic oral doses leading presumably to a paracellular passage of OA through the gastrointestinal barrier. There are no studies available analyzing the absorption at low concentrations, which represent a realistic dietary exposure, making a reliable risk assessment difficult. Therefore, we performed a low-dose study using the human intestinal Caco-2 cell model to simulate the intestinal barrier. Low level exposure of 20-200 nM OA to the cell monolayer allows an only limited passage from the "luminal" to the "blood side". Furthermore, we could detect a significant efflux of OA, which led to the suggestion that active transport mechanisms are involved in the elimination process of OA. In conclusion, our results indicate that besides the well known defense mechanisms of humans against this marine biotoxin--vomiting and diarrhea--further detoxification mechanisms are available to limit the absorption of toxic OA.