Screening thyroid hormone disrupting effects of benzophenones using GH3, FRTL-5 cells and zebrafish

Abstract

Benzophenones (BPs) are UV protection agents frequently used in various personal care products (PCPs). BPs have been widely detected in the environment and biota. Endocrine disrupting effects of some BPs have been documented. However, significant knowledge gaps are present for thyroid disrupting effects of these compounds. Thyroid disruption of various BPs was investigated using rat pituitary and thyroid follicle cell lines, and zebrafish. First, in vitro assays employing a rat pituitary cell line (GH3) and a rat follicular cell line were conducted on six BPs, i.e., benzophenone (BP), benzophenone-1 (BP-1), benzophenone-2 (BP-2), benzophenone-3 (BP-3), benzophenone-4 (BP-4), and benzophenone-8 (BP-8). Then, BP-3, mainly used BP-type UV filter, and its major metabolites BP-1 and –8 were employed for subsequent in vivo tests with zebrafish (Danio rerio) embryo. Following in vitro GH3 exposure, all six BPs except BP-4 down-regulated Tshβ, Trhr, and Trβ genes and up-regulated Dio2 gene in the rat pituitary cells. In addition, some BPs significantly up-regulated Nisand Tg genes while down-regulating Tpo gene on various level in FRTL-5 cells. In zebrafish embryo, significantly decreases of whole-body T4 and T3 level were observed following exposure to each BP until 144 hour post fertilization (hpf). BP-3 and –8 decreased T3 in zebrafish at lower exposure concentrations compared to that for BP-1, implying greater thyroid hormone disrupting potencies of both BPs. Transcriptional changes in several thyroid hormone regulating genes in hypothalamic-pituitary-thyroid axis were observed as well. The results of this study showed that all tested BPs caused thyroid disrupting responses in a rat pituitary gland and a thyroid gland, crucial organs regulating homeostasis of thyroid system. Embryo-larval exposure of zebrafish also demonstrated that BP-1, -3, and –8 could alter thyroid hormone levels. Since thyroid hormone regulation plays key role in early development and normal physiology, consequences of this thyroid hormone disruption in later life stages of the fish warrant further investigation.