Disclosing Environmental Ligands of hL-FABP and PPARγ: Should We Re-evaluate the Chemical Safety of Hydrocarbon Surfactants?

Abstract

Environmental obesogens can cause adverse health effects through activation of peroxisome proliferator-activated nuclear receptor γ (PPARγ). However, only a small portion of PPARγ ligands in the environment have been discovered to date, due to the co-occurrence of thousands of compounds. In this study, protein Affinity Purification with Nontargeted Analysis (APNA) was employed to identify ligands of human liver fatty acid binding protein (hL-FABP) and PPARγ in indoor dust and sewage sludge. A total of 84 features were “pulled out” by His-tagged hL-FABP as putative ligands, among which 13 were assigned as fatty acids and hydrocarbon surfactants. The binding of hydrocarbon surfactants to hL-FABP/PPARγ was confirmed using both recombinant proteins and reporter cells. These hydrocarbon surfactants, along with >50 homologues and isomers, were detected in dust and sludge at high concentrations. Fatty acids and hydrocarbon surfactants explained the majority of hL-FABP (57.7 ± 32.9%) and PPARγ (66.0 ± 27.1%) activities in the sludge. Notably, hydrocarbon surfactants contributed to PPARγ activities at comparable or even higher levels than fatty acids, with alkylbenzene sulfonates being the predominant PPARγ ligands in sludge. This study revealed hydrocarbon surfactants as the predominant synthetic ligands of hL-FABP/PPARγ, highlighting the importance of re-evaluating their chemical safety as putative obesogens.

Building the Environmental Chemical-Protein Interaction Network (eCPIN): An Exposome-Wide Strategy for Bioactive Chemical Contaminant Identification

“…For instance, hydrocarbon surfactants were recently identified as the predominant synthetic PPARγ ligands in sewage sludge and house dust, among >40,000 mass spectrometry features . This class of compounds, together with fatty acids, explained 66.0 ± 27.1% of PPARγ activity in sewage sludge (Figure g) . In another very recent study, triclosan was exclusively identified as the sole inhibitor of FabI as well as the predominant antibacterial compound in sewage sludge, despite the co-occurrence of numerous other antibiotics and nonantibiotics (Figure h) .…”

“…As mentioned above, we have already successfully applied the APNA method to multiple proteins including NRs, bacterial proteins, and transporter proteins. − Unexpectedly, we have found that a very small number of chemicals often contributed to the majority of bioactivity. For instance, hydrocarbon surfactants were recently identified as the predominant synthetic PPARγ ligands in sewage sludge and house dust, among >40,000 mass spectrometry features . This class of compounds, together with fatty acids, explained 66.0 ± 27.1% of PPARγ activity in sewage sludge (Figure g) .…”

“…In contrast, eCPIN could help to build a direct relationship between chemical contaminants and the protein targets with which they physically interact on the proteome scale. As highlighted above, thus far, the progress of eCPIN has effectively discovered new protein targets for hydrocarbon surfactants (PPARγ), TPHP (LXRα), and 6-OH-BDE-47 (FabI) . Once more protein targets are tested using APNA, the eCPIN strategy could benefit the comprehensive annotation of the MIEs of toxic chemical contaminants.…”

“…While a few chemicals exert toxicities by attacking nucleotides (e.g., polycyclic aromatic hydrocarbons and aromatic amines) or cell membranes (e.g., baseline toxicity), proteins mediate the toxicity of the majority of chemical contaminants . For instance, endocrine-disrupting chemicals (EDCs) exert their adverse effects primarily by interacting with NRs. , Considering this fundamental biochemistry principle, we highlighted a bioanalytical method “protein A ffinity P urification with N ontargeted A nalysis (APNA)” for the “ top-down ” screening of bioactive chemical contaminants at the exposome-wide level. − APNA uses a tagged protein of interest (e.g., a His-tagged NR) as a “bait” to directly isolate bioactive chemical contaminants from the extracts of environmental samples consisting of thousands of chemicals. Figure outlines the general steps involved in the APNA workflow.…”

“…Third, the identification of chemical contaminants remains highly challenging due to their distinct fragmentation pathways within mass spectrometers and the lack of comprehensive databases. Because of these challenges, no studies had successfully applied this concept for the screening of toxic contaminants until our development of the APNA method. − …”