Transepithelial transfer of phenanthrene, but not of benzo[ a ]pyrene, is inhibited by fatty acids in the proximal intestine of rainbow trout ( Oncorhynchus mykiss )

Abstract

The inclusion of vegetable oils in aquafeeds introduces contaminating polycyclic aromatic hydrocarbons (PAHs) in salmonids. Since lipophilic PAHs solubilize in micelles composed of lipids, bile salts and fatty acids, dietary lipid composition can alter intestinal transepithelial PAH transfer. We studied the uptake of two PAHs, viz. benzo[a]pyrene (BaP) and phenanthrene (PHE), in rainbow trout (Oncorhynchus mykiss) intestine. We also investigated the effects of two fatty acids, viz. fish oil-derived eicosapentaenoic acid (EPA, 20:5n-3) and vegetable oil-derived oleic acid (18:1n-9) on intestinal uptake. Radiolabeled PAHs were solubilized in micelles composed of tritiated EPA and oleic acid, respectively, and administrated to intestinal segments mounted in Ussing chambers. In the absence of micelles, PHE accumulation was two times higher than BaP in the mucosal and serosal layers of proximal and distal intestine. Administration of PHE in micelles composed of oleic acid resulted in a 50% lower accumulation of PHE in the mucosal layers of the proximal intestine compared to EPA-composed micelles. Accumulation of EPA and oleic acid in the proximal intestinal mucosa correlated negatively with the transepithelial transfer of these fatty acids across the proximal intestinal epithelium. Transepithelial PHE transfer across the proximal intestine was reduced by 30% in co-exposure with EPA-composed micelles compared to 80% with oleic acid micelles. BaP was not transferred across the intestine. We conclude that the lipid composition of an aquafeed is an important determinant of PAH bioavailability. Therefore, lipid composition should be an important consideration in choosing vegetable oils as alternatives for fish oil in aquafeeds.

Multicompartmental Toxicokinetic Modeling of Discrete Dietary and Continuous Waterborne Uptake of Two Polycyclic Aromatic Hydrocarbons by Zebrafish Danio rerio

“…The in vitro experiment found that benzo­[a]­pyrene (BaP), pyrene, and phenanthrene could be biotransformed by intestinal Caco-2 cell lines, but phenanthrene was less prone to be biotransformed compared to the other two PAHs . Moreover, it was reported that compared to PAHs with high hydrophobicity, the less hydrophobic phenanthrene from dietary uptake exhibited higher and faster transfer across the GI tract of fish. , It could be inferred from these experimental results that the biotransformation of PAHs in the GI tract of fish was dependent not only on the biotransformation capacity of intestinal cells, but also on the transfer efficiency across the GI tract. These results indicated that the biotransformation in the GI tract of fish was likely toxicant-dependent.…”