Early Life Stage Bioactivity Assessment of Short-Chain Chlorinated Paraffins at Environmentally Relevant Concentrations by Concentration-Dependent Transcriptomic Analysis of Zebrafish Embryos

Abstract

Short-chain chlorinated paraffins (SCCPs), a class of ubiquitous pollutants, are considered to be embryotoxic and teratogenic. However, little is known regarding the bioactivity and mechanisms at environmentally relevant concentrations at the embryonic period. Here, a concentration-dependent reduced transcriptomic approach was used to evaluate the environmental dose (<100 ppb) effects of nine SCCP congeners and eight commercial mixtures on zebrafish embryos at 8 hpf. After 24 h of exposure, the overall biological potency of all the SCCPs, in terms of interference with 20% of the differentially expressed genes (POD DEG20 ), in zebrafish embryos ranged from 0.83 to 67.61 ppb. C 10 H 14 Cl 8 (POD GO20 = 3.80 ppb) and C 10−13 51.5% Cl (POD GO20 = 3.31 ppb) exhibited the strongest interference with biological processes compared to other SCCP homologs and mixtures, respectively. The most sensitive early molecular responses induced by SCCPs were associated with pathways of genetic damage, energy metabolite interference, and metal ion binding. Furthermore, the carbon number was positively correlated with the transcriptomic potency (POD GO20 ) of SCCP congeners (with chlorine content > 60%) (p = 0.038), and the chlorine content of SCCP congeners affected the bioactivity associated with genotoxic pathways. The concentration-dependent reduced transcriptomic approach significantly improved the understanding of the ecological risk of environmental contaminants at early life stages.

Cross-Model Comparison of Transcriptomic Dose–Response of Short-Chain Chlorinated Paraffins

“…5 SCCPs with higher chlorine content also showed higher transcriptional potency in ZFEs. 9 There was no significant correlation between carbon length and potency of SCCPs (Figure S5B).…”

“…SCCPs have been shown to elicit DNA damage-related responses in rat liver 44 and ZFEs. 9 The number of GO terms identified by RHT ranged from 112 (SCCP 13) to 2095 (SCCP 18) (Figure S3B and Table S2). REVIGO analysis revealed that the 82 GO terms commonly perturbed by all the 15 SCCPs were primarily involved in cellular response to stress, lipid metabolic process, intracellular signal transduction, and cellular biosynthetic process (Figure S4).…”

“…A previous RZT study has reported positive correlation between POD GO20 and carbon length for SCCPs with chlorine content greater than 60%. 9 Thus, linear correlation analysis was also conducted on POD GO20 and chlorine content/carbon length of SCCPs that had chlorine content greater than 60%.…”

“…Then, 20 ZFEs from two repeated exposures in each treatment were collected for RNA extraction, library construction, and sequencing analysis of mRNA expressions of 1637 zebrafish genes in RZT. 9 The bioinformatic analysis for concentration−response modeling, calculation of POD of pathways, and derivation of biological potency was described as in Section 2.3.2. For further comparison of RHT and RZT, SCCP 13 was not included due to that fact that it had very few perturbed GO pathways to derive the potency value in RZT.…”

“…For further comparison of RHT and RZT, SCCP 13 was not included due to that fact that it had very few perturbed GO pathways to derive the potency value in RZT. 9 For the remaining 14 SCCPs, the identified genes and GO terms of each SCCP were compared between RHT and RZT. Linear correlation analysis was conducted on the POD GO20 values of 14 SCCPs between RHT and RZT.…”