Mechanistic Toxicity Assessment of Hexahydroisohumulone in Canine Hepatocytes

Abstract In vitro test methods are used primarily for rapid screening of chemicals based on mechanistic understanding of toxicity to predict hazards and potential risks. We investigated organ-specific oxidative stress and the molecular mechanism of toxicity using the pathway-focused DNA array of the hop ingredient hexahydroisohumulone (HEX) with canine hepatocytes, canine proximal tubule cells (CPTC), bone marrow-derived mesenchymal stem cells (BMSC) and enterocyte-like cells (ELC). Free radical species were produced in HEX-treated hepatocytes and to a lesser extent in CPTC, BMSC and ELC. Transcriptional profiles showed 30.5% (113 genes) out of 370 genes were differentially expressed in hepatocytes followed by CPTC (21.6%, 80 genes), ELC (4.8%, 18 genes) and BMSC (1.0%, 4 genes). HEX predominantly affected DNA damage/ repair pathways in hepatocytes and CPTC, while for ELC endoplasmic reticulum (ER) stress/unfolded protein response (UPR) dominated. Cyclooxygenase-2 (COX-2) and C/EBP homologous protein (CHOP) were most abundant genes in HEX-treated hepatocytes and CPTC; networked complementary between various pathways resulting in its adverse effect on oxidative stress, ER stress/UPR, mitochondrial metabolism and apoptosis. This work contributes to the understanding of the molecular effects of HEX, cellular response to oxidative stress and provides insight into genes altered with HEX exposure and the cell-type specific responses in dogs