Combined effects of okadaic acid and yessotoxin - The role of human CYP metabolism and hepatic transcription factors

Marine biotoxins are produced by microalgae and may concentrate in filter-feeding bivalves. Intoxication can occur after consumption of contaminated shellfish containing several marine biotoxins. Okadaic acid (OA) and yessotoxin (YTX) are two important representatives coexisting in nature in different quantities. The aim of this study was to evaluate combined hepatotoxic effects caused by OA and YTX in HepG2 cells. Additionally, the induction of toxicological relevant transcription factors was investigated by using transactivation assays in regard to mono- vs. co-exposure. Pure OA and YTX were used to treat human liver HepG2 cells including treatments in a proportion of 1:3, 1:1 and 3:1. In addition human CYP enzymes (S9) were included as external metabolic activation system to analyze metabolism dependent effects. Cell viability was measured using neutral red assay. Molecular effects were investigated in mono- and co-exposure on nuclear receptors by using a transactivation assay in HEK-293T- cells. The study clearly showed that combined effects of OA and YTX occur in regard to cytotoxicity in HepG2 cells. The viability decreased with higher YTX than OA concentrations. Such strong effects were not observed for mono-exposure of YTX. Metabolic activation enhanced toxicity after both, mono- and co-exposure. Additionally, co-exposure differently affects the activation of transcription factors compared to mono-exposure. In conclusion, co-exposure of OA and YTX lead to stronger effects than mono-exposure. The proportion of YTX to OA may play a key role in regard to the final resulting toxicity if both toxins are simultaneously present.