Study of in vitro human intestinal palytoxin absorption

DA Fernández1, B Espiña1, N Vilariño1, MC Louzao1, MR Vieytes2, M Poli3, LM Botana1. 1Universidad de Santiago de Compostela, Facultad de Veterinaria, Farmacología y Terapéutica, 27002, Spain, 2Universidad de Santiago de Compostela, Facultad de Veterinaria, Fisiología Animal, 27002, Spain, 3U.S. Army Medical Research Institute of Infectious Diseases, Integrated Toxicology Division, Frederick, Maryland MD 21702-5011, USA

Palytoxin (PLTX) is one of the most poisonous marine toxins know to date. Moreover, it is one of the biggest natural non-peptide molecules. It was first isolated in 1971 form coral Palythoa toxica and later from dinoflagellates of Ostreopsis genus. This molecule was discovered in Hawaiian and Japanese waters but nowadays is distributed worldwide, supposing a serious human health risk linked to contaminated-shellfish consumption. PLTX targets the Na+-K+ pump, allowing passive transport of both ions and destroying normal cell gradient resulting in cell death. It also damages actin cytoskeleton and it is a potent tumor promoter. In animals PLTX toxicity is highly dependent on the administration route. Oral administration is much less toxic than intra peritoneal or parenteral injection. In humans, there are no reliable quantitative data for acute toxicity. Likewise, long-term toxicity studies are also inexistent. Precise data regarding oral PLTX toxicity for humans is important to establish safe regulation limits in the seafood and seawater monitoring.

In this study we performed a reliable modelization of the human intestinal trans-epithelial permeability to PLTX that uses CaCo-2 cell monolayers. PLTX is a demonstrated highly cytotoxic compound and could affect the CaCo-2 monolayer integrity. Taking this into account we analyzed the effect that increasing PLTX concentrations induces in the Trans-Epithelial Electric Resistance of the CaCo-2 monolayer as a function of time. Our results showed that PLTX disrupts the CaCo-2 monolayer integrity at concentrations higher than 0.15 nM. To determine the permeability of Caco-2 to PLTX, inserts of Caco-2 cells monolayer attached to the PET membrane were incubated with the toxin. After that we evaluated the toxin absorbed by the cell. Results indicated that PLTX do not go through the CaCo-2 monolayer despite the lack of epithelium integrity. Therefore, PLTX could not be well absorbed by the intestinal epithelium and as a result, would not be transported to blood. This explains its lower oral toxicity and may help to achieve a better understanding of PLTX poisoning.