Toxicogenomic Screening of Replacements for Di(2-Ethylhexyl) Phthalate (DEHP) Using the Immortalized TM4 Sertoli Cell Line

Exposure to the non-phthalate plasticizer di-heptyl succinate is less disruptive to C57bl/6N mouse recovery from a myocardial infarction than DEHP, TOTM or related di-octyl succinate

Phthalate plasticizers are incorporated into plastics to make them soft and malleable, but are known to leach out of the final product into their surroundings with potential detrimental effects to human and ecological health. The replacement of widely-used phthalate plasticizers, such as di-ethylhexyl phthalate (DEHP), that are of known toxicity, by the commercially-available alternative Tris(2-ethylhexyl) tri-mellitate (TOTM) is increasing. Additionally, several newly designed "green" plasticizers, including di-heptyl succinate (DHPS) and di-octyl succinate (DOS) have been identified as potential replacements. However, the impact of plasticizer exposure from medical devices on patient recovery is unknown and, moreover, the safety of TOTM, DHPS, and DOS is not well established in the context of patient recovery. To study the direct effect of clinically based chemical exposures, we exposed C57bl/6 N male and female mice to DEHP, TOTM, DOS, and DHPS during recovery from cardiac surgery and assessed survival, cardiac structure and function, immune cell infiltration into the cardiac wound and activation of the NLRP3 inflammasome. Male, but not female, mice treated in vivo with DEHP and TOTM had greater cardiac dilation, reduced cardiac function, increased infiltration of neutrophils, monocytes, and macrophages and increased expression of inflammasome receptors and effectors, thereby suggesting impaired recovery in exposed mice. In contrast, no impact was detected in female mice and male mice exposed to DOS and DHPS. To examine the direct effects in cells involved in wound healing, we treated human THP-1 macrophages with the plasticizers in vitro and found DEHP induced greater NLRP3 expression and activation. These results suggest that replacing current plasticizers with non-phthalate-based plasticizers may improve patient recovery, especially in the male population. In our assessment, DHPS is a promising possibility for a non-toxic biocompatible plasticizer.

Phthalate metabolite concentrations and effects on albuminuria in the US population

BACKGROUND

The usage pattern of phthalates has changed with the introduction of new alternatives such as 1,2-cyclohexane dicarboxylic acid, diisononyl ester (DINCH) and di-isodecyl phthalate (DiDP). However, the concentrations of these alternatives at the population level and their effects on endothelial function are under-studied.

OBJECTIVES

We examined the concentrations of the new alternatives and their previous counterparts, as well as the associations between phthalate exposure and albuminuria in the general US population.

METHODS

In total, 2672 participants from the National Health and Nutrition Examination Survey (NHANES) 2017-2018 were enrolled in this study, and we obtained data on 19 urinary phthalate metabolites, albumin, and creatinine. The distributions of urinary phthalates were studied by age and sex. Linear and logistic regressions were used to estimate the association between urinary phthalate metabolites and albumin.

RESULTS

The geometric mean of the total phthalate concentrations in males and females was 124.97 and 113.09 ng/mL respectively. The detection rates of most urinary phthalate metabolites were greater than 95 %. The major phthalate metabolites found in the US population were MEP (24.20 %) and MECPTP (23.76 %). More positive relationships between phthalate and micro- plus albuminuria were found in females aged ≥ 60 years group（1.49 (95 % CI: 1.08-1.90), 1.44 (95 % CI: 1.06-1.81), 1.52 (95 % CI: 1.14-1.90), 1.41(95 % CI: 1.04-1.78), 1.29(95 % CI: 1.01-1.58), 1.60(95 % CI: 1.20-2.01), 1.45(95 % CI:1.14-1.77), and 1.55(95 % CI: 1.22-1.87) in MECPP, MEHHP, MEOHP, MEHP, MCPP, MHBP, MHNCH and MCOCH respectively）. In total population, logistic regression showed that all traditional phthalate metabolites were associated with an increased proportion of albuminuria (OR range from 1.19 to 1.40, all p < 0.05). However, three new alternatives were not associated with albuminuria (OR range from 1.01 to 1.05, all p > 0.05), and six new alternatives were associated with an increased proportion of albuminuria (OR range from 1.14 to 1.30, all p < 0.05).

CONCLUSIONS

Children have higher metabolite concentrations than adults. Exposure to certain phthalates may disrupt albuminuria homeostasis, especially in older females. Alternative phthalates may have a lower impact on albuminuria than conventional phthalates. The safety of the new alternatives should be interpreted with caution, as more research is still required.

Screening of Potential Plasticizer Alternatives for Their Toxic Effects on Male Germline Stem Cells

Plasticizers give flexibility to a wide range of consumer and medical plastic products. Among them, phthalate esters are recognized as endocrine disruptors that target male reproductive functions. With this notion, past studies designed and produced alternative plasticizers that could replace phthalates with limited toxicity to the environment and to male reproductive functions. Here, we focused on one reproductive cell type that was not investigated in past studies-spermatogonial stem cells (SSCs)-and examined in vitro the effects on 22 compounds (seven plasticizers currently in use and 15 newly synthesized potential alternative plasticizers) for their effects on SSCs. Our in vitro compound screening analyses showed that a majority of the compounds examined had a limited level of toxicity to SSCs. Yet, some commercial plasticizers and their derivatives, such as DEHP (di-(2-ethylhexyl) phthalate) and MEHP (mono-(2-ethylhexyl) phthalate), were detrimental at 10^-5 to 10^-4 M. Among new compounds, some of maleate- and fumarate-derivatives showed toxic effects. In contrast, no detrimental effects were detected with two new compounds, BDDB (1,4 butanediol dibenzoate) and DOS (dioctyl succinate). Furthermore, SSCs that were exposed to BDDB and DOS in vitro successfully established spermatogenic colonies in testes of recipient mice after transplantation. These results demonstrate that SSC culture acts as an effective platform for toxicological tests on SSC function and provide novel information that two new compounds, BDDB and DOS, are alternative plasticizers that do not have significant negative impacts on SSC integrity.

Alteration of the N6-methyladenosine epitranscriptomic profile in synthetic phthalate-treated human induced pluripotent stem cell-derived endothelial cells

Background: This study aimed to characterize the N6-methyladenosine epitranscriptomic profile induced by mono(2-ethylhexyl) phthalate (MEHP) exposure using a human-induced pluripotent stem cell-derived endothelial cell model. Methods: A multiomic approach was employed by performing RNA sequencing in parallel with an N6-methyladenosine-specific microarray to identify mRNAs, lncRNAs, and miRNAs affected by MEHP exposure. Results: An integrative multiomic analysis identified relevant biological features affected by MEHP, while functional assays provided a phenotypic characterization of these effects. Transcripts regulated by the epitranscriptome were validated with quantitative PCR and methylated RNA immunoprecipitation. Conclusion: The authors' profiling of the epitranscriptome expands the scope of toxicological insights into known environmental toxins to under surveyed cellular contexts and emerging domains of regulation and is, therefore, a valuable resource to human health.

Gestational and lactational exposure to the emergent alternative plasticizer 1,2-cyclohexane dicarboxylic acid diisononyl ester (DINCH) impairs lipid metabolism to a greater extent than the commonly used Di(2-ethylhexyl) phthalate (DEHP) in the adult rat mammary gland

Due to their endocrine disruption properties, phthalate plasticizers such as di(2-ethylhexyl) phthalate (DEHP) can affect the hormone-dependent development of the mammary gland. Over the past few years, DEHP has been partially replaced by 1,2-cyclohexane dicarboxylic acid diisononyl ester (DINCH) which also have potential endocrine disrupting properties. The goal of the present study is to understand the impact of a gestational and lactational exposure to DEHP and DINCH on mammary gland development using Sprague-Dawley rats. Both plasticizers altered the adipocytes of the mammary gland fat pad of adult progeny, as demonstrated by a decrease in their size, folding of their membrane and modulations of the lipid profiles. DEHP treatments decreased the expression of Rxrα and Scd1 at the low and high dose, respectively, but did not affect any of the other genes studied. DINCH modulation of lipid metabolism could be observed at puberty by a decreased expression of genes implicated in triglyceride synthesis, lipid transport and lipolysis, but by an increased expression of genes of the β-oxidation pathway and of genes involved in lipid storage and fatty acid synthesis at adulthood, compared to control and DEHP-treated rats. A strong upregulation of different inflammatory markers was observed following DINCH exposure only. Together, our results indicate that a gestational and lactational exposure to DINCH has earlier and more significant effects on lipid homeostasis, adipogenesis and the inflammatory state of the adult mammary gland than DEHP exposure. The long-term consequence of these effects on mammary gland health remained to be determined.

High Content Imaging Analyses of the Effects of Bisphenols and Organophosphate Esters on TM4 Mouse Sertoli Cells

The endocrine disruptive effects of bisphenol A (BPA) and brominated flame retardants (BDE-47) have led to restrictions to their use and increased the pressure to identify safe replacements for these chemicals. Although there is evidence that some of these alternatives may be toxic to spermatogonial and Leydig cells, little is known about the toxicity of emerging replacements on Sertoli cells, one of the major testicular cell types. We used high-content imaging to compare the effects of legacy chemicals, BPA and BDE-47, to their corresponding replacements. TM4 Sertoli cells were exposed for 48 h to each chemical (0.001-100 μM) followed by cytotoxicity and phenotypic endpoint assessment. The benchmark concentration (BMC) potency ranking for bisphenols based on cytotoxicity was BPTMC>BPM > BPAF>BPF > BPS > BPA. Human administered equivalent dose (AED) determination ranked BPS as most potent alternative replacement studied. The BMC potency ranking of BDE-47 and organophosphate esters based on cytotoxicity was TDtBPP>BDMPP>TBOEP>TDCPP>TMPP>TPHP> BDE47 > IPPP=BPDP = TCPP. Additionally, TM4 cell exposure to BDE-47 increased Calcein intensity (57.9 μM) and affected lysosomes (21.6 μM), while exposure to TPHP and TMPP resulted in cellular oxidative stress changes at BMC values as low as 0.01 μM and 0.4 μM, respectively. Overall bioactivity considerations of the chemicals on TM4 via ToxPi analyses and AED modeling further validated emerging replacements as highly potent chemicals in comparison to BPA and BDE-47. These findings demonstrate that many bisphenol and flame retardant replacements are more potent in Sertoli cells than the legacy chemical they are replacing, and that phenotypic parameter assessment is an effective tool in chemical toxicity assessment.

A review of atmospheric microplastics pollution: In-depth sighting of sources, analytical methods, physiognomies, transport and risks

Micro-sized plastics were first examined for atmospheric environment in 2016. From then on, they have been detected in both indoor and outdoor atmospheric samples, with indoor environments demonstrated as containing a big proportion of these particles. The sparse distribution of these particles, is attributed to their swift and long distance transportation that is mainly eased by their tiny size (1 μm to 5 mm) and low density. Due to ongoing limitation on detectable size, analysis methods together with a lack of standardized sampling and analytical procedures, few studies were conducted on airborne microplastics (MPs). Thus, the facts regarding the occurrence, global spatial distribution, fate, and threats to ecosystem and human health of airborne MPs, are still far from being fully clarified. This literature review is a broad depiction of a state of knowledge on atmospheric MPs. Within it, robust and concise information on the sources, inspection, transport, and threats pertaining to airborne MPs are presented. Particularly, the paper entails some information concerning traffic-generated MPs pollution, which has not been frequently discussed within previously published reports. In addition, this paper has widely unveiled sectors and aspects in need of further attention, with the gaps to be filled pinpointed.

DEHP induces ferroptosis in testes via p38α-lipid ROS circulation and destroys the BTB integrity

Exposure to Di (2-ethylhexyl) phthalate (DEHP) has been associated with toxic effects of the reproductive system. However, the exact mechanism remains to be elucidated. In this study we explored the testicular toxicity induced by DEHP, and the probable molecular mechanism in the process. In vivo, the results demonstrated that DEHP affected testosterone levels and blood-testosterone barrier (BTB) integrity and caused ferroptosis. We further demonstrated that DEHP up-regulated the expression of p38α, p-p38α, p53, p-p53, SAT1, ALOX15. This view has also been confirmed in TM4 cells. After pre-treatment with fer-1 or si-MAPK14, the expression of either p53, p-p53, SAT1 and ALOX15 up-regulated by MEHP was inhibited in vitro. Interestingly, p38α can prevent the accumulation of lipid ROS, and the production of lipid ROS in turn promoted the expression of p38α, thus forming a feedback loop during the ferroptosis. In this process, a vicious cycle consisting of p38α, p53, SAT1, ALOX15, lipid ROS was involved. This study provides new mechanistic insights into DEHP-induced toxicity of the reproductive system.

Phthalates and Alternative Plasticizers Differentially affect Phenotypic Parameters in Gonadal Somatic and Germ Cell Lines

The developmental and reproductive toxicity associated with exposure to phthalates has motivated a search for alternatives. However, there is limited knowledge regarding the adverse effects of some of these chemicals. We used high-content imaging to compare the effects of mono (2-ethylhexyl) phthalate (MEHP) with six alternative plasticizers: di-2-ethylhexyl terephthalate (DEHTP); diisononyl-phthalate (DINP); di-isononylcyclohexane-1,2-dicarboxylate (DINCH); 2-ethylhexyl adipate (DEHA); 2,2,4-trimethyl 1,3-pentanediol diisobutyrate (TXIB) and di-iso-decyl-adipate (DIDA). A male germ spermatogonial cell line (C18-4), a Sertoli cell line (TM4) and two steroidogenic cell lines (MA-10 Leydig and KGN granulosa) were exposed for 48h to each chemical (0.001-100 μM). Cell images were analyzed to assess cytotoxicity and effects on phenotypic endpoints. Only MEHP (100 μM) was cytotoxic and only in C18-4 cells. However, several plasticizers had distinct phenotypic effects in all four cell lines. DINP increased Calcein intensity in C18-4 cells, whereas DIDA induced oxidative stress. In TM4 cells, MEHP, and DINCH affected lipid droplet numbers, while DEHTP and DINCH increased oxidative stress. In MA-10 cells, MEHP increased lipid droplet areas and oxidative stress; DINP decreased the number of lysosomes, while DINP, DEHA and DIDA altered mitochondrial activity. In KGN cells, MEHP, DINP and DINCH increased the number of lipid droplets, whereas DINP decreased the number of lysosomes, increased oxidative stress and affected mitochondria. The Toxicological Priority Index (ToxPi) provided a visual illustration of the cell line specificity of the effects on phenotypic parameters. The lowest administered equivalent doses were observed for MEHP. We propose that this approach may assist in screening alternative plasticizers.

Di(isononyl) cyclohexane-1,2-dicarboxylate (DINCH) alters transcriptional profiles, lipid metabolism and behavior in zebrafish larvae

Plasticizers are commonly used in different consumer goods and personal care products to provide flexibility, durability and elasticity to polymers. Due to their reported toxicity, the use of several plasticizers, including phthalates has been regulated and/or banned from the market. Di(isononyl) cyclohexane-1,2-dicarboxylate (DINCH) is an alternative plasticizer that was introduced to replace toxic plasticizers. Increasing global demand and lack of toxicity data and safety assessment of DINCH have raised the concern to human and animal health. Hence, in the present study, we investigated the adverse effects of DINCH (at concentrations ranging from 0.01 to 10 μM) in early developmental stages of zebrafish using different endpoints such as hatching rate, developmental abnormalities, lipid content, behavior analysis and gene expression. We found that DINCH caused hatching delay in a dose-dependent manner and altered the expression of genes involved in stress response. Lipid staining using Oil Red O stain showed a slight lipid accumulation around the yolk, brain, eye and neck with increasing concentration. Genes associated with lipid transport such as fatty acid synthesis, β-oxidation, elongation, lipid transport were significantly altered by DINCH. Genes involved in cholesterol biosynthesis and homeostasis were also affected by DINCH indicating possible developmental neurotoxicity. Behavioral analysis of larvae demonstrated a distinct locomotor activity upon exposure to DINCH. The present data shows that DINCH could induce physiological and metabolic toxicity to aquatic organisms. Hence, further analyses and environmental monitoring of DINCH should be conducted to determine its safety and toxicity levels.

The inhibition of microtubule dynamics instability alters lipid homeostasis in TM4 Sertoli cells

Sertoli cells (SC) structurally support and transport nutrients to germ cells during spermatogenesis facilitated by an active cytoskeleton. Chemical perturbation of SC microtubule (MT) dynamics instability leads to premature germ cell exfoliation demonstrating that this process is essential for male fertility, yet the effects of MT damaging drugs on SC lipid metabolism have been less explored. The aim of this study was to advance our understanding of how adequate SC MT dynamicity is needed to finely tune lipid homeostasis. To elucidate the role of MT dynamics instability on the latter, we suppressed MT dynamicity by long-term exposures to 10 nM of nocodazole (NCZ) on TM4-SC cultures. Inhibition of MT dynamics instability affected the distribution of [³H] arachidonate on TM4-SC. Triacylglycerols (TAG) exhibited a higher proportion of the [³H] label, with significantly lower percentages in the mitochondrial phospholipid cardiolipin, and notably, also in phosphatidylethanolamine. A noteworthy and progressive accumulation of lipid droplets during the period of exposure to NCZ was accompanied by increased TAG levels but not cholesterol levels in TM4-SC. NCZ-exposed cells reduced their mitochondrial membrane potential and increased ROS production without triggering apoptosis, had a compromised autophagic flux, and lost their transferrin expression. Although SC morphology was preserved, the NCZ-exposed cells displayed alteration of the normal organization of microfilaments (f-actin) and intermediate filaments (vimentin). Our findings suggest that a preserved MT dynamicity is essential in the maintenance of lipid and fatty acids homeostasis in SC, and thus highlights a novel target in these cells for drugs that impair MT dynamicity.

In vitro evaluation of cytotoxic effects of di (2-ethylhexyl) phthalate (DEHP) produced by Bacillus velezensis strain RP137 isolated from Persian Gulf

Phthalates are widely used in polymer science and have potential toxicity related to their chemical structures. However, lots of evidence indicate that phthalate derivatives are undoubtedly produced as secondary metabolites by organisms, including plants, animals, and microorganisms. In the present study, Bacillus velezensis strain RP137 was cultured under optimized conditions. Its biomass was extracted with ethyl acetate with one fraction showing cytotoxic properties. A pure compound was isolated from the active fraction using combined silica gel and LH20 size exclusion column chromatography. Structural evaluation including FT-IR, ¹H NMR, ¹³C NMR, HR-MS and CHN analysis identified the purified compound as di(2-ethylhexyl)phthalate (DEHP) with the formula C₂₄H₃₈O₄ and the molecular weight of 389.29 Da. The microorganism-derived (stereospecific) DEHP was strongly reduced the proliferation and induced cytotoxic effects on various eukaryotic cell lines in compare to the synthetic racemic mixture of the compound when assessed by MTT assay. Furthermore, crystal violet assay and morphological changes confirmed the cytotoxic effect of DEHP. Interestingly, non-malignant SV40-immortalized fibroblast cells were less affected by the purified DEHP. Further evaluation on the antibacterial activity of DEHP documented no effect toward Gram-positive (S. aureus) and Gram-negative (E. coli and P. aeruginosa) pathogens even at a high concentration of 100 μM. In conclusion, existence of DEHP as byproduct of microorganism's metabolism can seriously be considered as a warning to human health.

The oxidative stress responses caused by phthalate acid esters increases mRNA abundance of base excision repair (BER) genes in vivo and in vitro

The base excision repair (BER) pathway is an important defense response to oxidative DNA damage. It is known that exposures to phthalate esters (PAEs), including Dibutyl phthalate (DBP), Mono-(2-ethylhexyl) phthalate (MEHP), and Di-(2-ethylhexyl) phthalate (DEHP), cause reactive oxygen species-induced DNA damage and oxidative stress. Here, we determined the mRNA levels of BER pathway-related genes (ogg1, nthl1, apex1, parp1, xrcc1, lig3, ung, pcna, polb, pold, fen1, and lig1), pro-apoptotic gene (bax), and apoptotic suppressor gene (bcl2) in different PAEs-exposed zebrafish larvae and HEK293T cells. Further investigations were performed to examine reactive oxygen species (ROS) accumulation, superoxide dismutase (SOD) activity, developmental toxicity, and cell viability after PAEs exposure in vivo and in vitro. The results showed that PAEs exposure can induce developmental abnormalities in zebrafish larvae, and inhibit cell viability in HEK293T cells. Additionally, we found that PAEs exposure results in the accumulation of ROS and the inhibition of SOD activation in vivo and in vitro. Notably, the mRNA levels of BER pathway-related genes (OGG1, NTHL1, APEX1, XRCC1, UNG, POLB, POLD, FEN1) were significantly upregulated after DBP or MEHP exposure, whereas the mRNA levels of NTHL1, UNG, POLB, POLD, and FEN1 were significantly altered in DEHP-treated HEK293T cells. In zebrafish, the mRNA levels of ogg1, pcna, fen1 and lig1 genes were increased after DBP or DEHP exposure, whereas the mRNA levels of nthl1, apex1, parp1, lig3, pcna and polb were decreased after MEHP exposure, respectively. Thus, our findings indicated that PAEs exposure can induce developmental toxicity, cytotoxicity, and oxidative stress, as well as activate BER pathway in vivo and in vitro, suggesting that BER pathway might play critical roles in PAEs-induced oxidative stress through repairing oxidative DNA damage.

Biomonitoring of emerging DINCH metabolites in pregnant women in charleston, SC: 2011-2014

Due to the mounting evidence that phthalates, specifically di-2-ethylhexyl phthalate and dibutyl phthalate, produce adverse endocrine effects in humans and wildlife, the use of other chemicals as replacements has increased. One of the most commonly encountered phthalate replacements is di(isononyl)cyclohexane-1,2-dicarboxylate (DINCH). Currently, little is known about the prevalence of human exposure, bioactivity, and endocrine disrupting potential of DINCH. We sampled urine from 100 pregnant women during the second trimester of pregnancy living in Charleston, SC between 2011 and 2014 and measured the following DINCH metabolites by LC-MS/MS: cyclohexane-1,2-dicarboxylic acid-mono(hydroxy-isononyl) ester (OH-MINCH), cyclohexane-1,2-dicarboxylic acid-mono(oxo-isononyl) ester (oxo-MINCH), and cyclohexane-1,2-dicarboxylic acid-monocarboxy isooctyl ester (cx-MINCH). These metabolites were also tested on human estrogen receptor alpha and progesterone receptor beta transactivation assays in vitro. OH-MINCH was detected in 98% of urine samples. The specific gravity-adjusted median (interquartile range) OH-MINCH concentration was 0.20 (0.25) ng/mL, and concentrations were significantly higher in African American women compared to Caucasian women (p = 0.01). DINCH metabolite concentrations were consistent between years, and they did not exhibit estrogenic or progestogenic activity in vitro. Human exposure to these emerging compounds should continue to be monitored, especially in vulnerable populations, to ensure the replacement of phthalates by DINCH is not a case of regrettable substitution.

Trends for plasticizers in German freshwater environments - Evidence for the substitution of DEHP with emerging phthalate and non-phthalate alternatives

Plasticizers are marketed in high volumes and Di(2-ethylhexyl) phthalate (DEHP) is frequently detected in the environment and human populations. Industry had largely relied on DEHP until regulation started to restrict its marketing in 1999 due to environmental and human health concerns. The aim of this study was to obtain spatial-temporal trends for DEHP and its substitutes in German rivers. We have investigated suspended particulate matter (SPM) samples from the German Environmental Specimen Bank (ESB) for the presence of 23 plasticizers, i.e. 17 phthalates and 6 non-phthalates. The samples were collected in the last 10 years at 13 sites in large river basins in Germany such as the Rhine, Elbe and Danube. A decrease in DEHP concentrations was observed at all sampling sites between the mid-2000s and 2017. The maximum concentration for DEHP was determined in 2006 in samples from Rehlingen/Saar (6720 ng/g dry weight (dw)). By 2017, the DEHP concentration in Rehlingen had dropped to 2080 ng/g dw. Currently, Diisononyl phthalate (DINP) is the plasticizer with the highest levels in the SPM samples (maximum value 4150 ng/g dw in Rehlingen/Saar). Our results show that novel plasticizers such as Diisononylcyclohexane-1,2-dicarboxylate (DINCH) spread rapidly in surface waters after their market introduction. We have found several plasticizers of emerging concern in the environmental samples, the further use of which is currently under review under the EU chemicals regulation (REACH, registration, evaluation, authorisation and restriction of chemicals). In particular for Di(2-propylheptyl) phthalate (DPHP) a significant increase in concentration was observed at almost all sites between the mid-2000s and 2017, for example in Prossen/Elbe from 24 ng/g dw (2005) to 1380 ng/g dw (2017).

Effect of subacute and prenatal DINCH plasticizer exposure on rat dams and male offspring hepatic function: The role of PPAR-α

Plasticizers are compounds added to plastics to modify their physical proprieties. The most well-known class of plasticizers, the phthalates, has been shown to possess antiandrogenic and tumor promoting activities. 1,2-Cyclohexane dicarboxylic acid diisononyl ester (DINCH) was approved for use in food contact containers in 2006 and has been used as a replacement for phthalates in toys and children products. However, we reported previously that the DINCH metabolite MINCH acts on primary rat adipocytes through the peroxisome proliferator activated receptor (PPAR)-α pathway in a manner similar to phthalates. Evidence from our studies, as well as from the current bibliography on DINCH, suggests that the liver might be one of its target organs. In the present study, we collected tissues from dams exposed subacutely and progeny at postnatal day (PND) 3 and 60 exposed in utero to DINCH (1, 10 and 100 mg/kg bw/day). Exposure to DINCH drastically affected liver gene expression in all 3 age groups tested and in particular at the dose of 1 mg/kg bw/day. The PPAR-α pathway along with other metabolic and DNA replication pathways were affected by DINCH. Modifications in PPAR-α and superoxide dismutase (SOD)-1 protein levels were observed in dams at PND21, as well as male progeny at PND3 and 60. No sign of fibrosis or direct liver toxicity was observed after 8 days of stimulus with low doses of DINCH. This study provides evidence that DINCH is not a biologically inert molecule in the rat, and in the liver its actions are mediated, at least in part, by PPAR-α.

In vitro exposure to the next-generation plasticizer diisononyl cyclohexane-1,2-dicarboxylate (DINCH): cytotoxicity and genotoxicity assessment in human cells

Plasticizers are currently present in many consumer products, particularly food packaging, children's toys, and medical devices. There are concerns regarding potential leaching to environment or food, thus increasing the risk of human exposure by inhalation, ingestion and/or dermal absorption potentially leading to adverse health consequences. Hexamoll diisononyl cyclohexane-1,2-dicarboxylate (Hexamoll® DINCH®), a non-phthalate plasticizer, has been used as a safer alternative to hazardous phthalates. In contrast to phthalates, evidence indicates that DINCH did not produce endocrine disruption, reproductive dysfunctions, genotoxicity or mutagenicity. However, there are limited data available regarding safety assessment, especially with respect to genotoxicity in human cells. The aim of this study was to assess DINCH cytotoxic and genotoxic effects in human liver and kidney cell lines following several exposure periods. For this purpose, the MTT cell viability, micronucleus, conventional and formamidopyrimidine DNA glycosylase (FPG)-modified comet assays were employed to detect cell death and genotoxicity, respectively. Data demonstrated that DINCH induced cytotoxicity in kidney cells exposed for 48hr, but not in liver cells. No marked chromosomal damage was noted after short-term or longer following treatment of both cell lines. However, DINCH produced oxidative DNA damage in liver cells exposed for 3 h, which decreased after a more prolonged incubation period. The occurrence of oxidative lesions, even transiently, indicates that mutation fixation may occur leading to adverse effects in liver. Therefore, these findings suggest that DINCH may be hazardous to humans and that further investigation is necessary to warrant its safety.

Transcriptome profiling and pathway analysis of the effects of mono-(2-ethylhexyl) phthalate in mouse Sertoli cells

Phthalates are confirmed to have toxic effects on the reproductive system and are likely to have further damaging actions in humans. The present study explored the molecular mechanisms of the toxic effect of mono-(2-ethylhexyl) phthalate (MEHP) on mouse Sertoli cells. Cell apoptosis and proliferation assays were used to assess the effects of MEHP on the TM4 Sertoli cell line derived from mouse testes. TM4 cells were treated with two doses of MEHP or left untreated as a control group, followed by RNA extraction and analysis using high-throughput transcriptome sequencing technology. The gene expression profile obtained was then subjected to a bioinformatics analysis to explore the molecular mechanisms of reproductive toxicity. The results revealed that 528 and 269 genes were upregulated in the high- and low-dose MEHP groups of cells compared with the control group, while 148 and 173 genes were downregulated. Gene ontology (GO) analysis indicated that the differently expressed genes were associated with the GO term 'extracellular region' of the cellular component domain in the high and low MEHP groups. Compared with the control group, eight common pathway changes were identified in the high- and low-dose MEHP groups, including 'terpenoid backbone biosynthesis'. Reverse transcription-quantitative polymerase chain reaction analysis was used to validation, and hermetic effects were observed for certain genes. These results provide an important basis and experimental data for further research into the mechanisms of phthalate-induced toxicity.

Identifying Greener and Safer Plasticizers: A 4-Step Approach

The health and economic burden of endocrine disrupting chemicals, such as the plasticizer di(2-ethylhexyl) phthalate (DEHP), is prompting industry to develop alternatives. However, the absence of requirements for manufacturers to ensure the safety of these alternatives has led to the generation of replacements that may have similar or worse effects than the original chemicals. Consequently, there is increasing recognition by scientists, regulators and industry that proactive approaches are needed to develop safe chemical substitutes. We propose a 4-step approach for the design, characterization and toxicological testing of responsible alternative chemicals that we illustrate with our ongoing studies on DEHP replacements. Our approach is comprised of: (1) the design and characterization of alternative chemicals based on innovative chemical structures and environmental considerations; (2) large-scale in vitro cell-based high throughput and selective ex vivo studies to preselect the most innocuous alternatives; (3) an acute toxicity in vivo study to rule out overt toxicity of the selected candidates; and (4) an in utero and lactational exposure study comparing the effects of selected candidates to those currently in use, emphasizing commonly described phenotypes after exposure to the latter. Using this 4-step approach, we have identified 2 alternative chemicals displaying good plasticizing properties, better biodegradability, and less leaching than DEHP without any apparent toxicity in vivo. This process has thus far proven useful in the proactive identification of responsible chemical replacements for DEHP.

PVC flooring at home and uptake of phthalates in pregnant women

Phthalates are used as plasticizers in polyvinyl chloride (PVC) materials and it is known that phthalates may migrate into the surrounding environment and then become a source for human uptake. The aim of the study was to investigate whether residential PVC flooring was related to the urinary levels of phthalate metabolites determined in pregnant women. The data were from the Swedish SELMA study where sampling was conducted during the time period 2007-2010. Spot urine samples from 1674 women at the end of the first trimester were analyzed for 14 metabolites from seven phthalates and one phthalate alternative. Data on flooring material in the kitchen and the parents' bedrooms as well as potential confounders were collected by postal questionnaires at the same time as the urine samples were taken. Multiple regression modeling by least square geometric mean and weighted quantile sum regression was applied to log-transformed and creatinine-adjusted phthalate metabolite concentrations adjusted for potential confounders from questionnaire data. This study has found significantly higher urinary levels of the BBzP metabolite (MBzP) in pregnant women living in homes with PVC flooring as compared to homes with other flooring materials.

How Green is Your Plasticizer?

Plasticizers are additives that are used to impart flexibility to polymer blends and improve their processability. Plasticizers are typically not covalently bound to the polymers, allowing them to leach out over time, which results in human exposure and environmental contamination. Phthalates, in particular, have been the subject of increasing concern due to their established ubiquity in the environment and their suspected negative health effects, including endocrine disrupting and anti-androgenic effects. As there is mounting pressure to find safe replacement compounds, this review addresses the design and experimental elements that should be considered in order for a new or existing plasticizer to be considered green. Specifically, a multi-disciplinary and holistic approach should be taken which includes toxicity testing (both in vitro and in vivo), biodegradation testing (with attention to metabolites), as well as leaching studies. Special consideration should also be given to the design stages of producing a new molecule and the synthetic and scale-up processes should also be optimized. Only by taking a multi-faceted approach can a plasticizer be considered truly green.

Effects of In Utero and Lactational Exposure to New Generation Green Plasticizers on Adult Male Rats: A Comparative Study With Di(2-Ethylhexyl) Phthalate

Di(2-ethylhexyl) phthalate (DEHP), a widely used plasticizer, is a ubiquitous environmental contaminant and may act as an endocrine disruptor. Early life exposures to DEHP may result in anti-androgenic effects, impairing the development of the male reproductive tract. However, data on the long-lasting consequences of such DEHP exposures on adult male reproductive function are still rare and discrepant. Previously, we identified 2 novel plasticizers, 1,4-butanediol dibenzoate (BDB) and dioctyl succinate (DOS), as potential substitutes for DEHP that did not reproduce classically described endocrine disrupting phenotypes in prepubertal male offspring after maternal exposure. Here, we investigated the consequences of in utero and lactational exposure to BDB and DOS on adult male rat reproductive function in a comparative study with DEHP and a commercially available alternative plasticizer, 1,2-cyclohexane dicarboxylic acid diisononyl ester (DINCH). Timed pregnant Sprague Dawley rats were gavaged with vehicle or a test chemical (30 or 300 mg/kg/day) from gestation day 8 to postnatal day 21. While DEHP exposure (300 mg/kg/day) significantly increased epididymal weight in the adult, exposure to DINCH, BDB, or DOS did not affect reproductive organ weights, steroid levels, or sperm quality. Using a toxicogenomic microarray approach, we found that adult testicular gene expression was affected by exposure to the higher dose of DEHP; transcripts such as Nr5a2, Ltf, or Runx2 were significantly downregulated, suggesting that DEHP was targeting estrogen signaling. Lesser effects were observed after treatment with either DINCH or BDB. DOS exposure did not produce such effects, confirming its potential as a responsible substitute for DEHP.

Designing Green Plasticizers: Linear Alkyl Diol Dibenzoate Plasticizers and a Thermally Reversible Plasticizer

Several linear alkyl diol dibenzoate compounds, ranging from C3 to C6 in central diol length, were evaluated for their plasticizing effectiveness in blends with poly(vinyl chloride) (PVC). The results were compared to blends of PVC/di(2-ethylhexyl) phthalate (DEHP), the most commonly used commercial plasticizer. DEHP has come under scrutiny, due to its suspected endocrine-disrupting behaviour, and the proposed diol dibenzoates have previously been shown to have the potential to be green, safe candidates for DEHP replacement. The thermal and mechanical properties of PVC/dibenzoate blends were determined, and include glass transition temperature (T_g), the elongation at break, maximum stress, apparent moduli, torsional modulus, and surface hardness. The C3, C5, and C6 dibenzoates performed as well as or better than DEHP, with the exception of torsional modulus, further supporting their use as green plasticizers. For blends with 1,4-butanediol dibenzoate, differential scanning calorimetry and torsional temperature sweeps suggested that the compound partly crystallizes within PVC blends over the course of two days, thereby losing the ability to effectively plasticize PVC. However, upon heating to temperatures above 60 °C, effective plasticization was again observed. 1,4-Butanediol dibenzoate is thereby a reversible heat-activated plasticizer or processing aid with excellent plasticizer properties at mildly elevated temperatures.

Essential roles of Akt/Snail pathway in microcystin-LR-induced tight junction toxicity in Sertoli cell

Microcystin (MC)-LR is a cyclic heptapeptide that acts as a potent reproductive system toxin. However, the underlying pathways of MCLR-induced reproductive system toxicity have not been well elucidated. The blood-testis barrier is mainly constituted by tight junctions (TJs) between adjacent Sertoli cells in the seminiferous epithelium near the basement membrane. The present study was designed to investigate changes in TJs and the underlying pathway in MC-LR-induced TJs toxicity in Sertoli cell. In our study, the transepithelial electrical resistance (TER) value was decreased in a dose dependent manner due to the markers of TJs occludin, claudin and zonula occludens-1 (ZO-1) expression decline. MC-LR is shown to induce cytotoxicity by inhibiting protein phosphatase 2A (PP2A) activity. Our results also showed that the PP2A activity presented a dose-dependent decline. Moreover, MC-LR stimulated protein expression of snail by Akt/GSK-3β activation. The activated Akt/GSK-3β and snail signaling pathway largely accounted for MC-LRinduced TJs toxicity, which could be partially reversed by snail siRNA interference or AKT chemical inhibitor in TM4 cells. These findings indicated that MC-LR inhibit the protein expression of TJs, and the activation of Akt/Snail signaling pathways due to PP2A inhibition is proposed to participate in this process.

Effect of prenatal DINCH plasticizer exposure on rat offspring testicular function and metabolism

In 2002, the plasticizer 1,2-cyclohexane dicarboxylic acid diisononyl ester (DINCH) was introduced in the European market as a substitute for endocrine-disrupting phthalates. We found that in utero exposure of rats to DINCH from gestational day 14 until parturition affected reproductive organ physiology and reduced circulating testosterone levels at post-natal day 60, indicating a long-term effect on Leydig cells of the testis. Metabolically, animals exhibited randomly increased serum glucose concentrations not associated with impaired glucose utilization. Analysis of liver markers in the serum showed a hepatic effect; e.g. reduced bilirubin levels and albumin/globulin ratio. At post-natal day 200, random appearance of testicular atrophy was noted in exposed offspring, and limited changes in other reproductive parameters were observed. In conclusion, DINCH exposure appears to directly affect Leydig cell function, likely causing premature aging of the testes and impaired liver metabolic capacity. These effects might be attenuated with physiologic aging.

In Utero and Lactational Exposure Study in Rats to Identify Replacements for Di(2-ethylhexyl) Phthalate

Di(2-ethylhexyl) phthalate (DEHP) and other phthalates are ubiquitous environmental contaminants with endocrine disrupting properties. Two novel plasticizers, 1,4 butanediol dibenzoate (BDB) and dioctyl succinate (DOS), have been proposed as potential replacements. Both have desirable properties as plasticizers and minimal in vitro biological effects. Herein, we present an in utero and lactational exposure study comparing DEHP with BDB, DOS, and 1,2-cyclohexane dicarboxylic acid diisononyl ester (DINCH), a commercial alternative. Timed-pregnant Sprague-Dawley rats were gavaged with vehicle or one of these chemicals at 30 or 300 mg/kg/day from gestational day 8 until postnatal day (PND) 21. The offspring were examined for effects on developmental and endocrine markers until PND 46. DEHP treatment (300 mg/kg) decreased heart weights in dams and induced a significant decrease in anogenital index and an increase in hemorrhagic testes and multinucleated gonocytes in PND 3 male pups. An increase in the incidence of hemorrhagic testes was also observed on PND 8 after exposure to DINCH (30 and 300 mg/kg). The only other effects observed were decreases in serum alanine transaminase and magnesium in BDB 30 exposed dams. These data suggest that both BDB and DOS are viable alternative plasticizers.

Increased Sat2 expression is associated with busulfan-induced testicular Sertoli cell injury

Busulfan is a chemotherapeutic agent used to treat chronic myelogenous leukemia and other myeloproliferative disorders. Increasing evidence has demonstrated that busulfan may induce testicular dysfunction by targeting genes that are expressed in the testis. Here, we showed that spermidine/spermine N1-acetyltransferase 2 (Sat2) was present in testicular Sertoli cells, and its expression was significantly increased by busulfan treatment. To investigate the implications of Sat2 upregulation for cell growth and function, a Sat2-overexpressing TM4 Sertoli cell model was established. Increased Sat2 expression led to inhibited cell proliferation and arrested cell cycle. Based on iTRAQ proteomics analysis, we revealed that Sat2 overexpression is detrimental to cell cycle progression and cell communication, and notably, Sat2 may disturb protein metabolic processes by altering translation regulation and protein complex subunit organization. In summary, the present study provides evidence that Sat2 upregulation induces alterations in the growth and function of Sertoli cells. In testis tissue subjected to busulfan, increased expression of Sat2 can cause cellular injury and subsequent organ damage, which could lead to male infertility. Therefore, Sat2 may be a novel molecular target for treating busulfan-induced testicular toxicity.

In vitro functional screening as a means to identify new plasticizers devoid of reproductive toxicity

Plasticizers are indispensable additives providing flexibility and malleability to plastics. Among them, several phthalates, including di (2-ethylhexyl) phthalate (DEHP), have emerged as endocrine disruptors, leading to their restriction in consumer products and creating a need for new, safer plasticizers. The goal of this project was to use in vitro functional screening tools to select novel non-toxic plasticizers suitable for further in vivo evaluation. A panel of novel compounds with satisfactory plasticizer properties and biodegradability were tested, along with several commercial plasticizers, such as diisononyl-cyclohexane-1,2-dicarboxylate (DINCH®). MEHP, the monoester metabolite of DEHP was also included as reference compound. Because phthalates target mainly testicular function, including androgen production and spermatogenesis, we used the mouse MA-10 Leydig and C18-4 spermatogonial cell lines as surrogates to examine cell survival, proliferation, steroidogenesis and mitochondrial integrity. The most promising compounds were further assessed on organ cultures of rat fetal and neonatal testes, corresponding to sensitive developmental windows. Dose-response studies revealed the toxicity of most maleates and fumarates, while identifying several dibenzoate and succinate plasticizers as innocuous on Leydig and germ cells. Interestingly, DINCH®, a plasticizer marketed as a safe alternative to phthalates, exerted a biphasic effect on steroid production in MA-10 and fetal Leydig cells. MEHP was the only plasticizer inducing the formation of multinucleated germ cells (MNG) in organ culture. Overall, organ cultures corroborated the cell line data, identifying one dibenzoate and one succinate as the most promising candidates. The adoption of such collaborative approaches for developing new chemicals should help prevent the development of compounds potentially harmful to human health.