6-PPD quinone-inhibited retinoic acid synthesis mediates toxicity through feedback loop between ALH-3/DHS-19-SEX-1 axis and intestinal signals in Caenorhabditis elegans

Abstract

Due to its widespread occurrence in environments, the exposure risk to 6-PPD quinone (6-PPDQ) is receiving increasing attention. Considering the crucial role of retinoic acid in regulating physiological state, we investigated the effects of 6-PPDQ on retinoic acid synthesis and the underlying mechanisms in nematodes. Retinoic acid content was reduced by 6-PPDQ (0.1-10 μg/L). Expression of enzyme genes alh-3 governing retinoic acid synthesis and dhs-19 governing retinal synthesis was decreased by 6-PPDQ. Retinoic acid content was reduced by alh-3 and dhs-19 RNA interference (RNAi). Additionally, alh-3 and dhs-19 RNAi conferred susceptibility to 6-PPDQ toxicity, and these two genes functioned in intestine to modulate 6-PPDQ toxicity. In the intestine, alh-3 and dhs-19 expressions were decreased by intestinal pmk-1, bar-1, and daf-16 RNAi, and pmk-1, bar-1, and daf-16 RNAi reduced retinoic acid content and induced susceptibility to 6-PPDQ toxicity. Additionally, 6-PPDQ decreased expression of sex-1 encoding retinoic acid receptor. After 6-PPDQ exposure, sex-1 expression was decreased by alh-3 and dhs-19 RNAi, and sex-1 RNAi further inhibited pmk-1, bar-1, and daf-16 expressions. sex-1 RNAi caused susceptibility to 6-PPDQ toxicity. Moreover, 6-PPDQ-induced toxicity and decrease in sex-1 expression were suppressed by retinoic acid treatment. Therefore, 6-PPDQ disrupted retinoic acid synthesis, which was linked to toxicity induction through the formation of a feedback loop between the alh-3/dhs-19-sex-1 axis and intestinal signals.

Keywords

6-PPD quinone / exposure risk / retinoic acid / nematodes

References

[1] Tian Z,Peter KT.A ubiquitous tire rubber-derived chemical induces acute mortality in coho salmon.Science2021;371:185-9

[2] Hua X.Tire-rubber related pollutant 6-PPD quinone: a review of its transformation, environmental distribution, bioavailability, and toxicity.J Hazard Mater2023;459:132265

[3] Zhao HN,Tian Z.Transformation products of tire rubber antioxidant 6PPD in heterogeneous gas-phase ozonation: identification and environmental occurrence.Environ Sci Technol2023;57:5621-32

[4] Li K,Chen Z.Accelerated transformation of 6PPD to 6PPD-Q in tire wear particles driven by roadway manganese oxides and dry-wet cycles: interfacial catalysis coupled with climatic stressors.Water Res2025;288:124741

[5] Kazmi SSUH,Tayyab M.Navigating the environmental dynamics, toxicity to aquatic organisms and human associated risks of an emerging tire wear contaminant 6PPD-quinone.Environ Pollut2024;356:124313

[6] Liang Y,Li J.P-phenylenediamine antioxidants and their quinone derivatives: a review of their environmental occurrence, accessibility, potential toxicity, and human exposure.Sci Total Environ2024;948:174449

[7] Chen X,Yang X.Analysis, environmental occurrence, fate and potential toxicity of tire wear compounds 6PPD and 6PPD-quinone.J Hazard Mater2023;452:131245

[8] Zhang Y,Wang L,Chen J.A nation-wide study for the occurrence of PPD antioxidants and 6PPD-quinone in road dusts of China.Sci Total Environ2024;922:171393

[9] Ren S,Wang X.Development and application of diffusive gradients in thin-films for in-situ monitoring of 6PPD-Quinone in urban waters.Water Res2024;266:122408

[10] Ihenetu SC,Khan ZH.Environmental fate of tire-rubber related pollutants 6PPD and 6PPD-Q: a review.Environ Res2024;258:119492

[11] Jin R,Chen Q,Liu M.Amino antioxidants: a review of their environmental behavior, human exposure, and aquatic toxicity.Chemosphere2023;317:137913

[12] Bohara K,Adhikari K.A mini review on 6PPD quinone: a new threat to aquaculture and fisheries.Environ Pollut2024;340:122828

[13] Wang W,Miao F,Cai Z.Biotransformation of tire-derived 6PPD and 6PPD-Q in soil nematode caenorhabditis elegans: unraveling novel Phosphorylation Products and Distinct Kinetic Profiles.Environ Sci Technol2025;59:14625-36 PMCID:PMC12288073

[14] He W,Wang D.Four-week repeated exposure to tire-derived 6-PPD quinone causes multiple organ injury in male BALB/c mice.Sci Total Environ2023;894:164842.

[15] Yu H,Wang D.Exposure to 6PPD-Q induces dysfunctions of ovarian granulosa cells: its potential role in PCOS.J Hazard Mater2025;486:137037

[16] Yao K,Liu W,Wang L.Chronic exposure to tire rubber-derived contaminant 6PPD-quinone impairs sperm quality and induces the damage of reproductive capacity in male mice.J Hazard Mater2024;470:134165

[17] Zhao HN,Zylka MJ,Hu W.Urine excretion, organ distribution, and placental transfer of 6PPD and 6PPD-quinone in mice and potential developmental toxicity through nuclear receptor pathways.Environ Sci Technol2023;57:13429-38 PMCID:PMC11648498

[18] Fang L,Di S.Oral exposure to tire rubber-derived contaminant 6PPD and 6PPD-quinone induce hepatotoxicity in mice.Sci Total Environ2023;869:161836

[19] Yang Y,Lv J.Environmentally realistic dose of tire-derived metabolite 6PPD-Q exposure causes intestinal jejunum and ileum damage in mice via cannabinoid receptor-activated inflammation.Sci Total Environ2024;918:170679

[20] Shi R,Zeb A.Environmental occurrence, fate, human exposure, and human health risks of p-phenylenediamines and their quinones.Sci Total Environ2024;957:177742

[21] Deng M,Peng B.In vitro and in vivo biotransformation profiling of 6PPD-quinone toward their detection in human urine.Environ Sci Technol2024;58:9113-24

[22] Wan X,Wang D.Potential human health risk of the emerging environmental contaminant 6-PPD quinone.Sci Total Environ2024;949:175057

[23] Black GP,Uychutin M,Orlando JL.6PPD-quinone in water from the San Francisco-San Joaquin Delta, California, 2018-2024.Environ Monit Assess2025;197:369

[24] Xu S,Lao JY.Typical tire additives in river water: leaching, transformation, and environmental risk assessment.Environ Sci Technol2024;58:18940-9

[25] Rauert C,Okoffo ED.Concentrations of tire additive chemicals and tire road wear particles in an Australian urban tributary.Environ Sci Technol2022;56:2421-31

[26] McDonough CM,Guo TL.Toxicity of bisphenol analogues on the reproductive, nervous, and immune systems, and their relationships to gut microbiome and metabolism: insights from a multi-species comparison.Crit Rev Toxicol2021;51:283-300

[27] Wu J,Hua X,Wang D.Photo-aged polylactic acid microplastics causes severe transgenerational decline in reproductive capacity in C. elegans: insight into activation of DNA damage checkpoints affected by multiple germline histone methyltransferases.Environ Pollut2025;382:126697

[28] Yang YF,Liao VH.Nanoscale zerovalent iron (nZVI) at environmentally relevant concentrations induced multigenerational reproductive toxicity in Caenorhabditis elegans.Chemosphere2016;150:615-23

[29] Song M,Wang D.Comparison of transgenerational neurotoxicity between pristine and amino-modified nanoplastics in C. elegans.Toxics2024;12:555 PMCID:PMC11358997

[30] Shang Y,Ni H.Environmentally relevant concentrations of perfluorobutane sulfonate impair locomotion behaviors and healthspan by downregulating mitophagy in C. elegans.J Hazard Mater2024;480:135938

[31] Liu H,Wang Z.Long-term exposure to polystyrene nanoparticles at environmentally relevant concentration causes suppression in heme homeostasis signal associated with transgenerational toxicity induction in Caenorhabditis elegans.J Hazard Mater2023;459:132124

[32] Wang X,Cao Z,Zhao Q.Multigenerational toxicity and transcriptomic changes induced by environmentally relevant concentrations of microcystin-LR and -RR in Caenorhabditis elegans.Toxicol Lett2025;410:58-66. Erratum in: Toxicol Lett 2025;411:122

[33] Liu Z,Wang D.6-PPD quinone induces response of nuclear hormone receptors in the germline associated with formation of reproductive toxicity in Caenorhabditis elegans.J Hazard Mater2025;495:138815

[34] Wang Y.Transgenerational intestinal toxicity of 6-PPD quinone in causing ROS production, enhancement in intestinal permeability and suppression in innate immunity in C. elegans.Environ Pollut2024;363:125208

[35] Song M,Wang D.Paeoniflorin alleviates toxicity and accumulation of 6-PPD quinone by activating ACS-22 in Caenorhabditis elegans.Ecotoxicol Environ Saf2024;286:117226

[36] Hua X.6-PPD quinone causes alteration in ubiquinone-mediated complex III associated with toxicity on mitochondrial function and longevity in Caenorhabditis elegans.J Environ Chem Eng2025;13:116571

[37] Hua X,Chao J.Exposure to 6-PPD quinone causes damage on mitochondrial complex I/II associated with lifespan reduction in Caenorhabditis elegans.J Hazard Mater2024;472:134598

[38] Hua X.6-PPD quinone at environmentally relevant concentrations activates feedback response of electron transport chain to mediate damage on mitochondrial function and longevity in Caenorhabditis elegans.Environ Chem Ecotox2025;7:2356-65

[39] Hua X.Transgenerational response of germline histone acetyltransferases and deacetylases to nanoplastics at predicted environmental doses in Caenorhabditis elegans.Sci Total Environ2024;952:175903

[40] Hua X.An environmentally relevant concentration of 6-PPD quinone inhibits two types of mitophagy to cause mitochondrial dysfunction and lifespan reduction in Caenorhabditis elegans.Environ Sci Process Impacts2025;27:1928-40

[41] Hua X.6-PPD quinone at environmentally relevant concentrations induced damage on longevity in C. elegans: mechanistic insight from inhibition in mitochondrial UPR response.Sci Total Environ2024;954:176275

[42] Salzer L.Quo Vadis Caenorhabditis elegans metabolomics-a review of current methods and applications to explore metabolism in the nematode.Metabolites2021;11:284 PMCID:PMC8146106

[43] Rubio-Tomás T.Lipid metabolism and ageing in Caenorhabditis elegans: a complex interplay.Biogerontology2022;23:541-57

[44] Wang W,Wang D.Exposure to 6-PPD quinone disrupts adsorption and catabolism of leucine and causes mitochondrial dysfunction in Caenorhabditis elegans.Toxics2025;13:544 PMCID:PMC12300368

[45] Wang Y,Wang D.Increased S-adenosyl methionine strengthens the suppression in mitochondrial unfolded protein response induced by 6-PPD quinone at environmentally relevant concentrations in Caenorhabditis elegans.Environ Pollut2025;386:127231

[46] Wu J,Hu D,Bian Q.Environmentally relevant concentrations of 6-PPDQ disrupt vitamin D3 adsorption and receptor function in Caenorhabditis elegans.Environ Sci Process Impacts2025;27:2798-808

[47] Wan X,Wang D.6-PPD quinone at environmentally relevant concentrations disrupts citric acid cycle in Caenorhabditis elegans: role of reduction in acetyl CoA and pyruvate contents.Environ Chem Ecotox2025;7:1119-29

[48] Liu Z,Wang D.Transgenerational response of glucose metabolism in Caenorhabditis elegans exposed to 6-PPD quinone.Chemosphere2024;367:143653

[49] Wang Y,Wang D.6-PPD quinone causes lipid accumulation across multiple generations differentially affected by metabolic sensors and components of COMPASS complex in Caenorhabditis elegans.Environ Pollut2025;366:125539

[50] Ott DB.Retinoic acid - a review.Am J Clin Nutr1979;32:2522-31

[51] Ghyselinck NB.Retinoic acid signaling pathways.Development2019;146:dev167502 PMCID:PMC6633611

[52] Mohanty R,Patri M.Modulation of benzo[a]pyrene induced anxiolytic-like behavior by retinoic acid in zebrafish: involvement of oxidative stress and antioxidant defense system.Neurotox Res2017;31:493-504

[53] Joseph PA,Gumienny TL. Establishing C. elegans as a model to study the function of vitamin A metabolism. TWUSJ 2021;1:16-30. Available from: https://twusj-ojs-twu.tdl.org/twusj/article/view/11 (accessed 2025-11-17)

[54] Brenner S.The genetics of Caenorhabditis elegans.Genetics1974;77:71-94 PMCID:PMC1213120

[55] Wang Y.Effect of disruption in the intestinal barrier function during the transgenerational process on nanoplastic toxicity induction in Caenorhabditis elegans.Environ Sci: Nano2025;12:2741-9

[56] Wang W,Wang D.Long-Term Exposure to 6-PPD quinone inhibits glutamate synthesis and glutamate receptor function associated with its toxicity induction in Caenorhabditis elegans.Toxics2025;13:434 PMCID:PMC12197550

[57] Wu T,Ye Z.Aged biodegradable nanoplastics enhance body accumulation associated with worse neuronal damage in Caenorhabditis elegans.Environ Sci Technol2025;59:4352-63

[58] Wu J,Hua X.Activated hedgehog and insulin ligands by decreased transcriptional factor DAF-16 mediate transgenerational nanoplastic toxicity in Caenorhabditis elegans.J Hazard Mater2024;480:135909

[59] Wu J,Hua X,Wang D.Nanoplastic at environmentally relevant concentrations induces toxicity across multiple generations associated with inhibition in germline G protein-coupled receptor CED-1 in Caenorhabditis elegans.Chemosphere2024;364:143011

[60] Wu J,Wang D.6-PPD quinone at environmentally relevant concentrations induces immunosenescenece by causing immunosuppression during the aging process.Chemosphere2024;368:143719

[61] Joshi P,Yang X.Combinations of vitamin A and vitamin E metabolites confer resilience against amyloid-β aggregation.ACS Chem Neurosci2023;14:657-66 PMCID:PMC9936541

[62] Hua X,Liang G,Wang D.Exposure to 6-PPD quinone at environmentally relevant concentrations causes abnormal locomotion behaviors and neurodegeneration in Caenorhabditis elegans.Environ Sci Technol2023;57:4940-50

[63] Bang YJ.Vitamin A: a key coordinator of host-microbe interactions in the intestine.BMB Rep2023;56:133-9 PMCID:PMC10068342

[64] Li Y,Hodges JK,Ross AC.Priming with retinoic acid, an active metabolite of vitamin A, increases vitamin A uptake in the small intestine of neonatal rats.Nutrients2021;13:4275 PMCID:PMC8703606

[65] Wang DY.Target organ toxicology in Caenorhabditis elegans. Springer Nature Singapore Pte Ltd, 2019.

[66] Qu M,Xu K.Activation of p38 MAPK signaling-mediated endoplasmic reticulum unfolded protein response by nanopolystyrene particles.Adv Biosyst2019;3:e1800325

[67] Shao H,Wang D.Response of intestinal signaling communication between the nucleus and peroxisome to nanopolystyrene at a predicted environmental concentration.Environ Sci: Nano2020;7:250-61

[68] Shao H,Krasteva N.Identification of signaling cascade in the insulin signaling pathway in response to nanopolystyrene particles.Nanotoxicology2019;13:174-88

[69] Jia K,Du Q.Mass spectrometry imaging unveils the metabolic effect of 6ppd-quinone in exposed mice.Environ Sci Technol2025;59:4282-91

[70] Wang L,Sun N.Low-dose tire wear chemical 6PPD-Q exposure elicit fatty liver via promoting fatty acid biosynthesis in ICR mice.J Hazard Mater2025;489:137574

[71] Liu Y,Zhang C.Hydroxysteroid dehydrogenase family proteins on lipid droplets through bacteria, C. elegans, and mammals.Biochim Biophys Acta Mol Cell Biol Lipids2018;1863:881-94

[72] Wang DY.Toxicology at environmentally relevant concentrations in Caenorhabditis elegans. Springer Nature Singapore Pte Ltd, 2022.

[73] Carmi I,Meyer BJ.The nuclear hormone receptor SEX-1 is an X-chromosome signal that determines nematode sex.Nature1998;396:168-73

[74] Farboud B,Jow MM,Meyer BJ.Molecular antagonism between X-chromosome and autosome signals determines nematode sex.Genes Dev2013;27:1159-78 PMCID:PMC3672649