Occurrence and Distribution of Phthalate Esters and Their Major Metabolites in Porcine Tissues

Phthalate monoesters accumulation in residential indoor dust and influence factors

Phthalate monoesters (mPAEs) possess biological activity that matches or even exceeds that of their parent compounds, phthalate esters (PAEs), negatively impacting humans. Indoor dust is the main carrier of indoor pollutants. In this study, indoor dust samples were collected from 46 households in Changchun City, Jilin Province, in May 2019, and particulate and flocculent fibrous dust was used as the research target to analyze the concentration and compositional characteristics of mPAEs, primary metabolites of five significant PAEs. The influence of factors such as architectural features and living habits in residential areas on exposure to mPAEs was explored. Ten suspected enzyme genes along with two metabolic pathways with the ability to degrade PAEs were screened using PICRUSt2. The results showed that the total concentrations of the five mPAEs in the indoor dust samples were particulate dust (11.49-78.69 μg/g) and flocculent fibrous dust (21.61-72.63 μg/g), respectively. The molar concentration ratio (RC) of mPAEs to corresponding PAEs significantly differed among chemicals, with MMP/DMP and MEP/DEP sporting the highest RC values. Different bacterial types have shown distinct influences against mPAEs and PAEs. Enzyme function and metabolic pathway abundance had a significant effect on the concentration of some mPAEs, mPAEs are most likely derived from microbial degradation of PAEs.

Environmental monobutyl phthalate exposure promotes liver cancer via reprogrammed cholesterol metabolism and activation of the IRE1α-XBP1s pathway

Humans are widely exposed to phthalates, a major chemical plasticizer that accumulates in the liver. However, little is known about the impact of chronic phthalate exposure on liver cancer development. In this study, we applied a long-term cell culture model by treating the liver cancer cell HepG2 and normal hepatocyte L02 to environmental dosage of monobutyl phthalate (MBP), the main metabolite of phthalates. Interestingly, we found that long-term MBP exposure significantly accelerated the growth of HepG2 cells in vitro and in vivo, but barely altered the function of L02 cells. MBP exposure triggered reprogramming of lipid metabolism in HepG2 cells, where cholesterol accumulation subsequently activated the IRE1α-XBP1s axis of the unfolded protein response. As a result, the XBP1s-regulated gene sets and pathways contributed to the increased aggressiveness of HepG2 cells. In addition, we also showed that MBP-induced cholesterol accumulation fostered an immunosuppressive microenvironment by promoting tumor-associated macrophage polarization toward the M2 type. Together, these results suggest that environmental phthalates exposure may facilitate liver cancer progression, and alerts phthalates exposure to patients who already harbor liver tumors.

Facile fabrication of carbon nanotube hollow microspheres as a fiber coating for ultrasensitive solid-phase microextraction of phthalic acid esters in tea beverages

The efficient extraction of phthalic acid esters (PAEs) is challenging due to their extremely low concentration, complicated matrices and hydrophilicity. Herein, hollow microspheres, as an ideal coating, possess significant potential for solid-phase microextraction (SPME) due to their fascinating properties. In this study, multiwalled carbon nanotube hollow microspheres (MWCNT-HMs) were utilized as a fiber coating for the SPME of PAEs from tea beverages. MWCNT-HMs were obtained by dissolving the polystyrene (PS) cores with organic solvents. Interestingly, MWCNT-HMs well maintain the morphology of the MWCNTs@PS precursors. The layer-by-layer (LBL) assembly of MWCNTs on PS microsphere templates was achieved through electrostatic interactions. Six PAEs, di-ethyl phthalate (DEP), di-iso-butyl phthalate (DIBP), di-n-butyl phthalate (DBP), benzyl butyl phthalate (BBP), di-2-ethylhexyl phthalate (DEHP) and di-n-octyl phthalate (DOP), were selected as target analytes for assessing the efficiency of the coating for SPME. The stirring rate, sample solution pH and extraction time were optimized by using the Box-Behnken design. Under optimal working conditions, the proposed MWCNT-HMs/SPME was coupled with gas chromatography-tandem mass spectrometry (GC-MS/MS) to achieve high enrichment factors (118-2137), wide linearity (0.0004-10 μg L-1), low limits of detection (0.00011-0.0026 μg L-1) and acceptable recovery (80.2-108.5%) for the detection of PAEs. Therefore, the MWCNT-HM coated fibers are promising alternatives in the SPME method for the sensitive detection of PAEs at trace levels in tea beverages.

Environmental health risks induced by interaction between phthalic acid esters (PAEs) and biological macromolecules: A review

As a kind of compounds abused in industry productions, phthalic acid esters (PAEs) cause serious problems in natural environment. PAEs pollution has penetrated into environmental media and human food chain. This review consolidates the updated information to assess the occurrence and distribution of PAEs in each transmission section. It is found that micrograms per kilogram of PAEs are exposed to humans through daily diets. After entering the human body, PAEs often undergo the metabolic process of hydrolysis to monoesters phthalates and conjugation process. Unfortunately, in the process of systemic circulation, PAEs will interact with biological macromolecules in vivo under the action of non-covalent binding, which is also the essence of biological toxicity. The interactions usually operate in the following pathways: (a) competitive binding; (b) functional interference; and (c) abnormal signal transduction. While the non-covalent binding forces mainly contain hydrophobic interaction, hydrogen bond, electrostatic interaction, and π interaction. As a typical endocrine disruptor, the health risks of PAEs often start with endocrine disorder, further leading to metabolic disruption, reproductive disorders, and nerve injury. Besides, genotoxicity and carcinogenicity are also attributed to the interaction between PAEs and genetic materials. This review also pointed out that the molecular mechanism study on biological toxicity of PAEs are deficient. Future toxicological research should pay more attention to the intermolecular interactions. This will be beneficial for evaluating and predicting the biological toxicity of pollutants at molecular scale.

Phthalate esters and their metabolites in paired soil-crop systems from farmland in major provinces of eastern China: Pollution characteristics and implications for human exposure

The extensive application of phthalate esters (PAEs) as plasticizers has raised considerable concern regarding their environmental load, but the associated occurrence of PAE metabolites has often been ignored. The soil-plant system is a vital source of human exposure to PAEs via crop intake. Here, paired soil-plant samples were collected from eastern China to investigate the occurrence characteristics of seven PAE congeners and two primary monoester phthalate metabolites (mPAEs) in farmland. The detection frequencies of PAEs and mPAEs in the investigated soil-plant systems were 100 %. The total concentrations of PAEs in the collected soil and plant samples ranged from 0.07 to 1.83 mg/kg (dw) and from 3.9 to 24 mg/kg (dw), respectively. Moreover, di-(2-ethylhexyl) phthalate, diisobutyl phthalate and di-n-butyl phthalate were the predominant PAE congeners in the farmlands of eastern China, collectively accounting for >90 % of the total concentration of PAEs. In addition, the total concentrations of the two mPAEs were markedly higher in plant samples (49 ng/g dw to 549 ng/g dw) than in soil samples (3 ng/g dw to 22 ng/g dw), indicating that PAEs are readily metabolized in plants. The hazard index (HI) values of all PAEs in all crops were <1, demonstrating that the risks of PAEs in the crops were acceptable. However, the daily intake of mPAEs from the consumption of cabbage was higher than or comparable to that of some PAEs (such as di-n-octyl phthalate). This highlights the importance of taking metabolites into consideration in further environmental investigations and risk assessments of PAEs.

Wide occurrence of seven phthalate plasticizers and two typical microplastics in pig feed

Plastics are widely used as packaging and engineering materials in feed processing, which leads to the potential contamination of plasticizers and microplastics (MPs) in animal feeds. In this study, the concentrations of two typical MPs, i.e., polyethylene terephthalate (PET) and polycarbonate (PC), and seven phthalates (PAEs) as well as their corresponding monoester metabolites (mPAEs) in 45 pig feed samples in China were analyzed by mass spectrometers. Among PAEs, dibutyl phthalate (DBP) and bis(2-ethylhexyl) phthalate (DEHP) were detected in all samples, and DEHP showed the highest concentrations of 8.26-2464 μg/kg, which accounted for 65.6% of the total detected PAEs. PET MPs (<MDL-302 μg/kg) were detected in 97.8% of samples. Meanwhile, mPAEs were also detected in feed samples with high detection rates but of much lower concentrations. A significantly positive correlation was observed between DEHP and PET MPs. This indicates that the sources of DEHP and MPs in feeds are homologous, mainly from processing and packaging. Besides, the significantly positive correlations between DBP/DEHP and mBP/mEHP indicated the degradation of PAEs to mPAEs during feed production and transportation. The estimated daily intake (EDI) of PAEs and PET MPs were 2.40-70.3 and 0.800-7.79 μg/kg-bw-day, respectively. The results of this study provided new insight into the first evidence of the co-occurrence and risk of MPs, PAE, and mPAEs in pig feed.

Alterations in the conformation and function of human serum albumin induced by the binding of methyl hydrogen phthalate

Phthalate esters (PAEs) are widely used as plasticizer components in production. Methyl hydrogen phthalate (MHP) is a metabolite of dimethyl phthalate (DMP, a kind of PAEs), and its toxic residues accumulate in the nature and can enter the human body. Here, the interaction between MHP and human serum albumin (HSA) was probed by using multi-spectral, computer simulations, and biochemical techniques. The results showed that MHP was spontaneously embedded in site I of HSA to form a complex by H-bonds and van der Waals forces (ΔH < 0, ΔS < 0). The binding constant (K_a) of the HSA-MHP system was 1.136 ± 0.026 × 10⁴ M^-1 (298 K). The combination of MHP produced conformational variations of HSA, as shown by the 3D fluorescence spectrum, CD spectra, and molecular dynamics simulation. Additionally, molecular docking indicated that MHP was surrounded by multiple residues, such as Lys199, Leu203, Phe206, and Trp214. Specifically, Lys199 and Trp214 exerted a crucial effect on the interaction of HSA and MHP. The residues with important energy contribution were mostly located in site I. The ASA values of the aromatic amino acids of HSA changed after combining with MHP. The R_g and SASA values of HSA increased after adding MHP, suggesting that the structure of HSA was less compact. Moreover, the esterase-like activity of HSA increased after adding MHP to HSA, indicating that MHP may disturb the normal physiological activities in the human body. This study was helpful to understand the biological function of MHP and provided some insights for its side effect in the human body.

A novel porphyrin-based conjugated microporous nanomaterial for solid-phase microextraction of phthalate esters residues in children's food

A novel porphyrin-based conjugated microporous polymer (PCMP) with microporous structure and nitrogen-rich pyrrole building blocks was synthesized. The PCMP was used as a coating material to prepare solid-phase microextraction (SPME) fibers by sol-gel technique. Due to the toxicity of the phthalate esters (PAEs) and the necessity for their sensitive determinations in some food samples, the SPME fiber was investigated for the extraction of eleven PAEs from six different children's milk beverages prior to their detection by gas chromatography-mass spectrometry. Under the optimal conditions, the linear response range for the PAEs was in the range from 0.03 to 200 µg L^-1 and the limits of detection (S/N = 3) for the analytes were 0.01-3.00 μg L^-1. The method recoveries for the PAEs were between 80% and 120%, with the relative standard deviations varying from 1.3% to 9.8%. The method was successfully applied for the determination of PAEs in children's milk beverages.

Dibutyl phthalate-induced oxidative stress and apoptosis in swine testis cells and therapy of naringenin via PTEN/PI3K/AKT signaling pathway

Dibutyl phthalate (DBP) is a phthalic acid ester (PAE) that has posed a health hazard to the organisms. Naringenin (NRG) is a flavanone compound that has shown protection against several environmental chemicals through suppression of oxidative stress and activation of phosphatidylinositol 3-kinase/threonine kinase (PI3K/AKT) signaling pathway. Herein, swine testis (ST) cells were treated with 1.8 μM of DBP or/and 25.39 nM of NRG for 24 h, we described the discovery path of NRG inhibition on apoptosis in DBP-exposed ST cells through targeting phosphatase and tensin homologue deleted on chromosome 10 (PTEN). We first found that the anti-apoptosis effect of NRG is dependent on mitochondrial pathway through flow cytometry and related gene/protein expression, and then we detected PI3K/AKT pathway-related gene/protein expression, and established a computational docking assay between NRG and PTEN. We found that NRG specifically binds to three basic residues (His93, Lys125, Lys128) of P loop in PTEN, as well as phosphatase domains (Asp92, His93, Cys124, Lys125, Ala126, Lys128, and Arg130) in active dephosphorylation pockets, thereby reducing PTEN level and activating PI3K/AKT signaling pathway, and further inhibiting oxidative stress and mitochondrial pathway apoptosis. Taken together, our results push forward that NRG deserves further attention as a potential antagonistic therapy against DBP through targeting PTEN to inhibit oxidative stress and activate PI3K/AKT signaling pathway.

Tissue distribution of phthalates in celery under different cultivation patterns and associated dietary exposure

To investigate tissue distribution, spatial difference, temperature variation, and potential health risks of PAEs in vegetables, celery was used as a model plant. Celery samples were collected from open fields and greenhouses from two provinces in China over four seasons. Celery tissues were analyzed for 16 PAE compounds by gas chromatography-tandem mass spectrometry. The total content of PAEs was 89.0-1130.3 μg kg^-1 dry weight (dw) in stems and 155.0-2730.8 μg kg^-1 dw in leaves. Concentrations of PAEs in celeries showed notable spatial differences (P < 0.05), and the levels in samples from open fields were lower than those in samples from plastic greenhouses. In celeries from greenhouses, higher PAE concentrations were observed for plants grown at high temperatures than in plants grown at low temperatures. Discrepancies in tissue distribution indicated different uptake pathways of PAE contaminants. Risk assessments to humans found that both carcinogenic risks and non-carcinogenic risks of PAEs via celery consumption were at an acceptable level. Further research should consider other exposure pathways of PAEs and pay special attention to reducing PAE contents in vegetables.

Allicin alleviated acrylamide-induced NLRP3 inflammasome activation via oxidative stress and endoplasmic reticulum stress in Kupffer cells and SD rats liver

Acrylamide (AA) in heat-processed food leads to widespread concerns due to its hepatotoxicity. Allicin, a plant-derived antioxidant, possesses a significant protective effect on AA-induced hepatotoxicity, but the mechanism is still unclear. Herein, we investigated the mechanism in Kupffer cells and SD rats liver. Molecular docking, molecular dynamics simulation and LigPlus software speculated that allicin inhibited the activity of CYP2E1 expression by binding to its amino acid residues Phe116, Phe207, Leu210, Phe298, Ala299, Thr303, Val364 and Phe478 through hydrophobic interactions. Allicin decreased the reactive oxygen species (ROS) release and CYP2E1 protein expression and then alleviated the appearance of OS. Meanwhile, allicin significantly reduced ERS characteristic proteins GRP78, CHOP and UPR branch IRE1α pathway key proteins p-IRE, p-ASK, TRAF2 and XBP-1s expression. Simultaneously, allicin ameliorated OS and ERS activation, which inhibited the activation of the MAPK and NF-κB pathways, and down-regulated JNK, ERK, p38, p65 and IκBα phosphorylation. Allicin pre-treatment inhibited AA-induced inflammation as evidenced by reducing NLRP3 inflammasome activation, decreasing Cleaved-Caspase-1 expression as well as IL-1β, IL-18, IL-6 and TNF-α secretion. Taken together, our data provide new insights into possible signaling pathways involved in allicin attenuating AA-induced hepatotoxicity in vivo and in vitro.