In vitro human cell-based TTR-TR\u03b2 CALUX assay indicates thyroid hormone transport disruption of short-chain, medium-chain, and long-chain chlorinated paraffins

Jannik Sprengel,Harrie Besselink,Abraham Brouwer,Peter A Behnisch,Walter Vetter

doi:10.1007/s00204-021-02994-5

Abstract

Over the last decades, short-chain chlorinated paraffins (SCCPs), medium-chain chlorinated paraffins (MCCPs), and long-chain chlorinated paraffins (LCCPs) have become the most heavily produced monomeric organohalogen compound class of environmental concern. However, knowledge about their toxicology is still scarce, although SCCPs were shown to have effects on the thyroid hormone system. The lack of data in the case of MCCPs and LCCPs and the structural similarity with perfluoroalkyl substances (PFAS) prompted us to test CPs in the novel TTR-TR CALUX assay for their thyroid hormone transport disrupting potential. Four self-synthesized and additionally purified single chain length CP mixtures (C10-CPs, C11-CPs, C14-CPs and C16-CPs) and two each of industrial MCCP and LCCP products were tested in parallel with PFOA. All CP mixtures influenced the TTR binding of T4, giving activities of 1,300 to 17,000 µg/g PFOA equivalents and lowest observable effect concentrations (LOELs) of 0.95 to 0.029 mM/L incubate. Highest activities and lowest LOELs were observed for C16-CPs (48.3% Cl content, activity 17,000, LOEL 0.047 mM/L) and a LCCP mixture (71.7% Cl content; activity 10,000; LOEL 0.029 mM/L). A trend of higher activities and lower LOELs towards longer chains and higher chlorination degrees was implied, but could not be statistically confirmed. Irrespectively, the less well examined and current-use LCCPs showed the highest response in the TTR-TRβ CALUX assay.

Highlights

Chlorinated paraffins (CPs) are a group of current-use anthropogenic organohalogenated chemicals ubiquitously detected in the environment (Glüge et al 2016, 2018; van Mourik et al 2016)
Given the structural similarity with perfluorooctanoic acid (PFOA), we reasoned that CPs may give response in the TTR-TRβ CALUX bioassay and that this test could be used to monitor thyroidal responses induced by CPs
To exclude that these could affect the measurements, the four single chain CP mixtures were further purified by CCC before they were applied to the TTRTRβ CALUX bioassay (section Clean-up of self-synthesized CPs via countercurrent chromatography (CCC))

Summary

Introduction

Chlorinated paraffins (CPs) are a group of current-use anthropogenic organohalogenated chemicals ubiquitously detected in the environment (Glüge et al 2016, 2018; van Mourik et al 2016). Compared to that only one technical MCCP product (40% Cl) was shown to interfere with thyroid hormones similar to SCCPs (Wyatt et al 1993), and no data existed on the thyroid disruptive potential of LCCPs. Recently, poly- and perfluoroalkyl substances (PFAS) like perfluorooctanoic acid (PFOA) were shown to competitively bind to the thyroid transport protein transthyretin (TTR), which can lead to reduced thyroid hormone levels (Weiss et al 2009). Given the structural similarity with PFOA (both consisting of long, unbranched carbon chains with a high level of halogenation), we reasoned that CPs may give response in the TTR-TRβ CALUX bioassay and that this test could be used to monitor thyroidal responses induced by CPs

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Conclusion