S14-03 Comparison of Metabolism and Transport of Thiabendazole in Human and Rat In vitroModels

Abstract

Introduction:

Thiabendazole (TBZ) is a food preservative, anti-fungal agent and anthelmintic drug which prevents the polymerization of beta-tubulins. Its major metabolite 5-hydroxy-thiabendazole (5-OH-TBZ) has been found in the urine of over 90% of the Swedish population between 2000–2017. Traditionally human health risk assessment is conducted in vivo, but there are indications that TBZ is only hepatotoxic in rats while being hepato- and nephrotoxic in mice and humans. In human liver microsomes it has been shown that the major metabolite 5-OH-TBZ can undergo metabolic activation to form nephrotoxic molecules. Organic cation transporter (OCT) is believed to be involved in the uptake in the proximal tubule cells. TBZ is first metabolized by CYP1A2 in the liver and then further metabolized by UGT, SULT and GST.

Aims:

We aim to investigate interspecies differences in the absorption, distribution, metabolism and excretion (ADME) of TBZ in liver, kidney and gut microbiome in vitro systems using a tiered approach.

Materials and Methods:

In vitro models including human and rat renal subcellular fractions, RPTEC/TERT1 cells, human and rat primary hepatocytes and human gut microbiome samples were exposed to TBZ or 5-OH-TBZ at different timepoints. The formation of different metabolites over time was explored using LC-MS. Additionally the renal transporter involved in the uptake of TBZ will be studied using suitable OCT inhibitors and quantified by transported TBZ.

Results and Discussion:

Exposure of 99 μM TBZ induced thioredoxin reductase 1 (TXNRD1) in RPTEC/TERT1 after 24 h exposure. Kinetic experiments in RPTEC/TERT1 and primary hepatocytes were performed with non-toxic maximum concentrations of 10 μM TBZ. Phase I metabolite 5-OH-TBZ was detected in rat liver microsomes. Phase II 5-OH-glucuronide formation was detected in human and rat renal microsomes. There was no 5-OH-sulfate measured in human and rat renal cytosol. Additionally, TBZ does not seem to be metabolized by the human gut microbiome.

Conclusion:

Phase I and II metabolites of TBZ were detected in human and rat liver and kidney in vitro models. The experimental data will be integrated into physiologically based kinetic (PBK) models. This will help to improve these in silico models and lead to more accurate xenobiotic human health risk assessment.