Methylparaben-induced regulation of estrogenic signaling in human neutrophils

Environmental Endocrinology: Parabens Hazardous Effects on Hypothalamic-Pituitary-Thyroid Axis

Parabens are classified as endocrine-disrupting chemicals (EDCs) capable of interfering with the normal functioning of the thyroid, affecting the proper regulation of the biosynthesis of thyroid hormones (THs), which is controlled by the hypothalamic-pituitary-thyroid axis (HPT). Given the crucial role of these hormones in health and the growing evidence of diseases related to thyroid dysfunction, this review looks at the effects of paraben exposure on the thyroid. In this study, we considered research carried out in vitro and in vivo and epidemiological studies published between 1951 and 2023, which demonstrated an association between exposure to parabens and dysfunctions of the HPT axis. In humans, exposure to parabens increases thyroid-stimulating hormone (TSH) levels, while exposure decreases TSH levels in rodents. The effects on THs levels are also poorly described, as well as peripheral metabolism. Regardless, recent studies have shown different actions between different subtypes of parabens on the HPT axis, which allows us to speculate that the mechanism of action of these parabens is different. Furthermore, studies of exposure to parabens are more evident in women than in men. Therefore, future studies are needed to clarify the effects of exposure to parabens and their mechanisms of action on this axis.

Association between urinary methylparaben level and bone mineral density in children and adolescents aged 8-19 years

Previous epidemiological study has explored a positive association between methylparaben (Mep) and bone mineral density (BMD) in adults. Evidence linking Mep and BMD in children and adolescents is very limited. This study examined the association between Mep and BMD in children and adolescents aged 8-19 years. In this cross-sectional study, 1830 children and adolescents aged 8-19 years from NHANES 2011-2016 were analyzed. Mep was ln-transformed for analysis of the skewed distribution. Multiple linear regression analyses were performed to evaluate Mep's association with BMD (containing total BMD, trunk bone BMD, pelvis BMD, lumbar spine BMD, and thoracic spine BMD). Moreover, a generalized additive model (GAM) and a fitted smoothing curve (penalized spline method) were conducted to explore the exact shape of curve between them. In the fully adjusted model, ln-transformed Mep and BMD showed an independent and positive association (total BMD (β = 0.003, 95% CI (0.001, 0.005), P = 0.01), trunk bone BMD (β = 0.002, 95% CI (0.000, 0.005), P = 0.04), pelvis BMD (β = 0.004, 95% CI (0.001, 0.008), P = 0.02), lumbar spine BMD (β = 0.005, 95% CI (0.001, 0.008), P = 0.01), thoracic spine BMD (β = 0.003, 95% CI (0.001, 0.005), P = 0.02)) and a linear association. Subgroup analysis showed positive association between ln-transformed Mep and BMD. Furthermore, the positive association was significant in females and children aged 12-19 years (P for trend < 0.05). This study is the first study to find evidence demonstrating that exposure to Mep may be positively associated with BMD in children and adolescents aged 8-19 years. Validation of our findings will need further research.

Individual and joint association of phenols, parabens, and phthalates with childhood lung function: Exploring the mediating role of peripheral immune responses

The functioning of the respiratory system can be interfered with by exposure to mixtures of environmental chemicals, however, the evidence is still ambiguous. We evaluated the association of exposure to mixtures of 14 chemicals, including 2 phenols, 2 parabens, and 10 phthalates, with four major lung function metrics. Based on data from the National Health and Nutrition Examination Survey 2007-2012, this analysis was conducted among 1462 children aged 6-19 years. Linear regression, Bayesian kernel machine regression, quantile-based g-computation regression, and a generalized additive model were performed to estimate the associations. Mediation analyses were performed to investigate plausible biological pathways mediated by immune cells. Our results indicated that the phenols, parabens, and phthalates mixture was negatively related to lung function parameters. And BPA and PP were identified as important contributors to negative associations with FEV₁, FVC, and PEF, with non-linear relationships observed between BPA and those outcomes. The most influential factor for a probable FEF_{25-75 %} decline was MCNP. BPA, and MCNP had an interaction effect on FEF_{25-75 %}. The association of PP with FVC and FEV₁ has been postulated to be mediated by neutrophils and monocytes. The findings offer insights into the associations of chemical mixtures with respiratory health and the possible driving mechanism, which would be of significance in adding novel evidence of the role of peripheral immune responses, as well as calling for remediation actions to be prioritized during childhood.

Pharmacokinetics of transdermal methyl-, ethyl-, and propylparaben in humans following single dermal administration

Parabens are common chemicals used as preservatives in foods, cosmetics, and personal care products. Although transdermal exposure to parabens occurs, studies on human pharmacokinetics (PK) following dermal exposure to parabens are scarce. In this study, the PK following dermal exposure to parabens was determined and compared with our previous findings on oral exposure. A paraben mixture cream containing 0.8% deuterated methyl-, ethyl-, and propylparaben (MeP-d₄ 0.26%; EtP-d₄ 0.26%, and PrP-d₄ 0.28%) was dermally applied to the whole arm of five male volunteers at a dose of 24 g/person over 30 min. Blood and urine samples were collected at several intervals over the course of 48 h to measure the levels of MeP-d₄, EtP-d₄, and PrP-d₄ and their conjugated metabolites using HPLC-MS/MS. As a result of non-compartmental analysis, the average peak values of total (sum of conjugated and unconjugated metabolites) MeP-d₄, EtP-d_4, and PrP-d₄ were reached at 7.8 h, 10.5 h, and 5.3 h, indicating a slower absorption rate compared to that of oral exposure (<2 h). The terminal elimination half-lives of MeP-d₄, EtP-d₄, and PrP-d₄ were 12.2 h, 12.0 h, and 9.3 h, respectively. Fractional urinary excretion (F_ue) of total MeP-d₄, EtP-d₄, and PrP-d₄ was 1.7%, 2.3%, and 1.9%, respectively. The F_ue of total and unconjugated PrP-d₄ following dermal exposure was five times lower and three times higher, respectively, compared with those after oral exposure, suggesting that PrP is relatively less metabolized to the conjugated form after dermal exposure. Taken together, dermal exposure to paraben leads to a longer apparent half-life and results in higher proportions of biologically active unconjugated parabens in the systemic circulation as compared to oral exposure. This study provides insights into the kinetic properties of parabens and their metabolites in humans.

Endocrine disruption and reproductive impairment of methylparaben in adult zebrafish

Methylparaben (MeP) is one of the most frequently used preservatives in our daily products. However, it is becoming an aquatic pollutant of emerging concern. To reveal the endocrine disruption mechanism and reproductive impairment of MeP, the present study exposed adult zebrafish to 0, 1, 3, and 10 μg/L (0, 6.6, 19.7, and 65.7 nM) of MeP for 28 days. The results showed that subchronic exposure to 10 μg/L of MeP significantly increased the gonadosomatic index in zebrafish. Spermatogenesis and oogenesis were blocked by MeP at concentrations as low as 1 μg/L. Furthermore, parental exposure to MeP induced developmental deficits in offspring larvae, by increasing mortality, stimulating precocious hatching, and elevating heart rate. Blood concentrations of estradiol, testosterone, and 11-keto-testosterone were consistently lowered in MeP exposure groups. Transcriptional results evidenced that the disturbance in steroidogenesis and feedback regulation mechanisms along the hypothalamic-pituitary-gonadal axis underlay the imbalance of sex hormones. In line with the low estradiol level, hepatic production of vitellogenin (VTG) was significantly down-regulated, subsequently leading to a deficiency of VTG supply during oogenesis. To our knowledge, this is the first study to provide systemic insight about the antiestrogenic activity and reproductive toxicity of MeP.

Investigation of estrogen-like effects of parabens on human neutrophils

This study investigated the estrogen-like effects and mechanism of action most commonly used parabens: methyl- (MeP), ethyl- (EtP), propyl- (PrP) and butylparaben (BuP) in human neutrophils. Neutrophils were isolated from 50 blood donors, pre-incubated with antagonists of estrogen receptor α (ERα), ERβ and G-protein coupled estrogen receptor 1 (GPER), then incubated with MeP, EtP, PrP, BuP and 17β-estradiol (E2; 10 nM). Cytotoxic effect was evaluated by MTT test. Neutrophils apoptosis, necrosis and NETs formation were assessed in flow cytometry and confocal microscopy. The ability of the neutrophils for chemotaxis, phagocytosis, NADPH oxidase activity and generation of superoxide anion was assessed in Boyden's chamber, Park's method with latex, the NBT test, and reduction of cytochrome C, respectively. The total nitric oxide concentration was measured in neutrophils supernatants by the Griess reaction. The expression of cathepsin G, neutrophil elastase, proteinase 3, ERα, ERβ and GPER was assessed in Western blot method. In our research, parabens did not cause a cytotoxic effect on human neutrophils nor affect their lifespan. Parabens exposure did not change neutrophils functions (chemotaxis, phagocytosis, NETs formation and oxygen-dependent killing mechanism) and expression of estrogen receptors. Our results suggest that parabens do not cause estrogen receptor-mediated neutrophils-related effects at concentrations measured in the plasma of individuals using products preserved with parabens.

Significant impairment of intestinal health in zebrafish after subchronic exposure to methylparaben

Methylparaben (MeP) is a ubiquitous pollutant in aquatic environment, which has caused severe pollution worldwide. However, aquatic toxicology of MeP is still largely unknown. In the present study, adult zebrafish were exposed to environmentally realistic concentrations of MeP (0, 1, 3, and 10 μg/L) for 28 days. In terms of the antimicrobial nature, dysregulation of gut microbiota and zebrafish health by MeP were elucidated after exposure. High-throughput amplicon sequencing showed that MeP subchronic exposure was able to disrupt the composition and diversity of gut microbial community, which was characterized by the alterations in alpha diversity and divergent distribution by principal component analysis. In addition, MeP exposure increased the body length and body weight of female fish, implying stimulated growth at low doses. In male intestine, consistent increases were notable in goblet cell density, tight junction protein (TJP) 2 expression, and serotonin neurotransmitter concentration after MeP exposure. In contrast, female intestine exposed to MeP had lower density of goblet cells, inhibited expression of TJP2, reduced concentration of serotonin, but up-regulated transcription of pro-inflammatory cytokine. Under the stress of MeP pollutant, intestinal catalase antioxidant enzyme was activated, thus contributing to the removal of oxidative free radicals. Correlation analysis verified the modulation of TJP2 expression by Lactobacillus probiotic bacteria. Disturbances in goblet cell, tight junctions, and serotonin by MeP may be combined to interfere with gut barrier function. Overall, the present study highlights the impairment of intestinal health by environmentally realistic concentrations of MeP, which necessitates an urgent risk assessment.

Hepatotoxicity caused by methylparaben in adult zebrafish

Parabens are a class of aquatic pollutants of emerging concern, among which methylparaben (MeP) causes severe pollution worldwide. However, aquatic toxicology of MeP remains largely unknown, which hinders ecological risk evaluation. In the present study, adult zebrafish were exposed to environmentally realistic concentrations (0, 1, 3, and 10 μg/L) of MeP for 28 days, with objectives to reveal the hepatotoxicity based on transcriptional, biochemical, metabolomics, and histopathological evidences. The results showed that MeP subchronic exposure induced the occurrence of hepatocellular vacuolization in zebrafish. The most severe symptom was noted in 10 μg/L MeP-exposed female liver, which was characterized by rupture of cell membrane and small nuclei. In addition, MeP exposure disturbed the balance between oxidative stress and antioxidant capacity. Lipid metabolism dynamics across gut, blood, and liver system were significantly dysregulated after MeP exposure by altering the transcriptions of lipid nuclear receptors and concentrations of key metabolites. Metabolomic profiling of MeP-exposed liver identified differential metabolites mainly belonging to fatty acyls, steroids, and retinoids. In particular, hepatic concentration of cortisol was increased in male liver by MeP pollutant, implying the activation of stress response. Exposure to MeP also inhibited the synthesis and conjugation of primary bile acid (e.g., 7-ketolithocholic acid and taurochenodeoxycholic acid) in female liver. Furthermore, degradation of biologically active molecules, including retinoic acid and estradiol, was enhanced in the liver by MeP. Overall, the present study highlights the hepatotoxicity caused by MeP pollutant even at environmentally realistic concentrations, which necessitates an urgent and accurate risk assessment.