Comparison of sub-lethal metabolic perturbations of select legacy and novel perfluorinated alkyl substances (PFAS) in Daphnia magna

Sublethal Exposure of Per‐ and Polyfluoroalkyl Substances of Varying Chain Length and Polar Functionality Results in Distinct Metabolic Responses in Daphnia magna

“…The observed biochemical pathway disruptions were supported by Pearson correlation analysis, which highlighted relationships between cysteine and the related metabolites, as well as in the observed downregulations in the percent changes of PFHxA, PFHxS, and PFNA (Figure 3; Supporting Information, Figures S12–S14). The resulting metabolic perturbations stemming from sublethal PFAS exposure are consistent with findings of previous sublethal exposures of PFAS (PFOS, PFOA, and GenX) where metabolic downregulations in cysteine and methionine contributed to disruptions to the pyrimidine metabolism and pantothenate and CoA metabolism pathways (Gebreab et al, 2020; Labine et al, 2022). Pyrimidines and purines are vital structural components in cellular processes including the synthesis of both DNA and RNA and the formation of precursors utilized in protein, lipid, and membrane phospholipid synthesis (Garavito et al, 2015).…”

“…The lack of significance in the middle concentration for PFHxS could be indicative of a non‐monotonic response of the pollutant in D. magna (Figure 1; Supporting Information, Figure S1). The PFAS pollutants have been suggested as potential endocrine‐disrupting chemicals; non‐monotonic responses of PFAS have been observed in aquatic organisms (Hoover et al, 2019; Labine et al, 2022; Panieri et al, 2021; Zhang et al, 2016). Studying the sublethal metabolic perturbations of suspected endocrine disruptors demonstrates the importance and novelty of metabolomics because the observed response cannot be predicted based on traditional toxicity endpoints, such as lethality (Panieri et al, 2022; Vandenberg et al, 2012).…”

“…Although PFHxA and PFHxS shared many similarities in their respective metabolic responses, there were also unique secondary responses observed with each pollutant (Figures 2 and 4). Halogenated carboxylic acid–bearing pollutants have been found to perturb purine and TCA cycle pathways in aquatic organisms including D. magna (Berends et al, 1999; Labine et al, 2022; Labine & Simpson, 2021). The polar functionality of PFAS, including carboxylic acid–bearing pollutants such as PFBA, PFHxA, and PFNA, could lead to the formation of hydrogen bonds between the pollutant and nucleotides, impeding the formation of structural hydrogen bonds between other nucleotides and leading to DNA base‐pair mutations (Chou et al, 2000).…”

“…Although there are no existing 48‐h LC50 measurements for PFHxS, sublethal concentrations of this pollutant were chosen based on the LC50 values of the PFCAs because this would allow for the direct comparison of the sulfonic acid to its carboxylic acid counterpart, PFHxA. Daphnia were exposed to three concentrations of each of PFBA, PFHxA, PFHxS, and PFNA (1, 20, and 45 mg/L); these concentrations could then be directly compared with results from previous findings from sublethal PFOS, PFOA, and GenX (Labine et al, 2022). Preliminary experiments were conducted to ensure the survivability of the organisms during the acute 48‐h exposure, and no mortalities were observed during these tests (data not shown).…”

“…Downregulations in isoleucine concentrations were also observed with exposure of PFOS in the model organism D. magna (Kariuki et al, 2017). Positive relationships were observed between perfluorodecanoic acid concentrations and the response of tyrosine in M. macleaya; similarly, disruptions to tyrosine and related pathways were observed following sublethal exposure to ammonium perfluoro(2-methyl-3-oxahexanoate [GenX]) and PFOA (Labine et al, 2022;Taylor et al, 2019). Environmental metabolomics has revealed the molecularlevel perturbations stemming from sublethal exposure to legacy PFAS (PFOS and PFOA) and the novel replacement GenX and found similarities in the disrupted metabolic profiles as well as unique features in the observed response caused by differences in the chemistry of the pollutants resulting in protein degradation, disruption to protein synthesis (aminoacyl-transfer RNA [tRNA] biosynthesis pathway), and disruptions to energy metabolism (Hagenaars et al, 2013;Kariuki et al, 2017;Kovacevic et al, 2019;Labine et al, 2022;Wagner et al, 2017;Yang et al, 2019).…”