Online background cleanup followed by high-performance liquid chromatography with tandem mass spectrometry for the analysis of perfluorinated compounds in human blood

Metabolic characteristics and pathogenesis of precocious puberty in girls: the role of perfluorinated compounds

BACKGROUND

Precocious puberty (PP) in girls is traditionally defined as the onset of breast development before the age of 8 years. The specific biomarkers of premature thelarche (PT) and central precocious puberty (CPP) girls are uncertain, and little is known about their metabolic characteristics driven by perfluorinated compounds (PFCs) and clinical phenotype. This study aimed to screen specific biomarkers of PT and CPP and elucidate their underlying pathogenesis. The relationships of clinical phenotype-serum PFCs-metabolic characteristics were also explored to reveal the relationship between PFCs and the occurrence and development of PT and CPP.

METHODS

Nuclear magnetic resonance (NMR)-based cross-metabolomics strategy was performed on serum from 146 PP (including 30 CPP, 40 PT, and 76 unspecified PP) girls and 64 healthy girls (including 36 prepubertal and 28 adolescent). Specific biomarkers were screened by the uni- and multivariate statistical analyses. The relationships between serum PFCs and clinical phenotype were performed by correlation analysis and weighted gene co-expression network analysis to explore the link of clinical phenotype-PFCs-metabolic characteristics in PT and CPP.

RESULTS

The disordered trend of pyruvate and butyrate metabolisms (metabolites mapped as formate, ethanol, and 3-hydroxybutyrate) were shared and kept almost consistent in PT and CPP. Eight and eleven specific biomarkers were screened for PT and CPP, respectively. The area under curve of specific biomarker combination was 0.721 in CPP vs. prepubertal, 0.972 in PT vs. prepubertal, 0.646 in CPP vs. prepubertal integrated adolescent, and 0.822 in PT vs. prepubertal integrated adolescent, respectively. Perfluoro-n-heptanoic acid and perfluoro-n-hexanoic acid were statistically different between PT and CPP. Estradiol and prolactin were significantly correlated with PFCs in CPP and PT. Clinical phenotypes and PFCs drive the metabolic characteristics and cause metabolic disturbances in CPP and PT.

CONCLUSIONS

The elevation of formate, ethanol, and 3-hydroxybutyrate may serve as the early diagnostic indicator for PP in girls. But the stratification of PP still needs to be further determined based on the specific biomarkers. Specific biomarkers of CPP and PT exhibited good sensitivity and can facilitate the classification diagnosis of CPP and PT. PFC exposure is associated with endocrine homeostasis imbalance. PFC exposure and/or endocrine disturbance directly or indirectly drive metabolic changes and form overall metabolic network perturbations in CPP and PT.

Optimization and application of a method to determine 24 perfluorinated compounds in umbilical cord serum by using liquid chromatography tandem mass spectrometry

Perfluorinated compounds (PFCs) are a group of widely used synthetic chemicals. Owing to their unique chemical properties, PFCs can accumulate in the environment and living organisms. In vitro and in vivo studies have demonstrated the adverse effects of exposure to PFCs, resulting in increased concern. Therefore, a fast, reliable analytical method is crucial for human biomonitoring and health risk assessment. This study used two isotope internal standards to identify and quantify 24 PFCs in umbilical cord serum samples, based on classical liquid-liquid extraction (LLE) with liquid chromatography tandem mass spectrometry (LC-MS/MS). According to our review of the literature, this study is the first to determine the TFHSA, S4hPDS, S4hPOS, S4hPHS, SPHeS, SPNoS, and SPPeS by using this developed method. The average spiked recoveries of 24 PFCs were acceptable, ranging from approximately 64.0% to 124%; RSDs ranged from 0.74% to 11.2%; LOD and LOQ ranged from 0.013 to 0.248 μg/L and from 0.030 to 0.747 μg/L, respectively. This method was applied to measure the PFCs in umbilical cord serum samples; 24 PFCs were detected in the investigated samples, which are comparable to those reported in the literature. TFHSA, S4hPDS, S4hPOS, S4hPHS, SPHeS, SPNoS, and SPPeS were also detected in the samples, which should be investigated in further research. The sensitivity, accuracy, and precision of the developed method are sufficient for its application in large-scale biomonitoring studies.

Low Levels of Perfluorooctanoic Acid Exposure Activates Steroid Hormone Biosynthesis through Repressing Histone Methylation in Rats

Perfluorooctanoic acid (PFOA) is a persistent organic pollutant, which has endocrine-disrupting properties and can interfere with the synthesis and secretion of testicular steroid hormones, but the underlying molecular mechanisms are still not fully understood. In this study, we investigated the effects of low doses of PFOA exposure on testicular steroidogenesis in rats and revealed the role of histone modifications. It was found that the serum levels of progesterone, testosterone, and estradiol were significantly increased after 0.015 and 0.15 mg/kg of PFOA exposure, and the expression of Star, a key rate-limiting gene, was up-regulated, while other steroidogenic genes Cyp11a1, Hsd3b, Cyp17a1, and Hsd17b were down-regulated. In addition, the levels of multiple histone modifications (H3K9me1/2/3 and H3K9/18/23ac) were all significantly reduced by PFOA in rat testis. Histone H3K9 methylation is associated with gene silencing, while histone acetylation leads to gene activation. ChIP analysis further showed that H3K9me1/3 was significantly decreased in the promoter region of Star, while H3K18ac levels were down-regulated in other gene promoters. Accordingly, we suggest that low-level PFOA enhances StAR expression through the repression of H3K9me1/3, which stimulates steroid hormone production in rat testis. These results are expected to shed new light on the molecular mechanisms by which low-dose PFOA disturbs male reproductive endocrine from an epigenetic aspect and may be useful for human health risk assessment regarding environmental PFOA exposure.

Chronic low-level perfluorooctane sulfonate (PFOS) exposure promotes testicular steroidogenesis through enhanced histone acetylation

Perfluorooctane sulfonate (PFOS), an artificial perfluorinated compound, has been associated with male reproductive disorders. Histone modifications are important epigenetic mediators; however, the impact of PFOS exposure on testicular steroidogenesis through histone modification regulations remains to be elucidated. In this study, we examined the roles of histone modifications in regulating steroid hormone production in male rats chronically exposed to low-level PFOS. The results indicate that PFOS exposure significantly up-regulated the expressions of StAR, CYP11A1 and 3β-HSD, while CYP17A1 and 17β-HSD were down-regulated, thus contributing to the elevated progesterone and testosterone levels. Furthermore, PFOS significantly increased the histones H3K9me2, H3K9ac and H3K18ac while reduced H3K9me3 in rat testis. It is known that histone modifications are closely involved in gene transcription. Therefore, to investigate the association between histone modifications and steroidogenic gene regulation, the levels of these histone marks were further measured in steroidogenic gene promoter regions by ChIP. It was found that H3K18ac was augmented in Cyp11a1 promoter, and H3K9ac was increased in Hsd3b after PFOS exposure, which is proposed to result in the activation of CYP11A1 and 3β-HSD, respectively. To sum up, chronic low-level PFOS exposure activated key steroidogenic gene expression through enhancing histone acetylation (H3K9ac and H3K18ac), ultimately stimulating steroid hormone biosynthesis in rat testis.

Liquid-Chromatographic Methods for Carboxylic Acids in Biological Samples

Carboxyl-bearing low-molecular-weight compounds such as keto acids, fatty acids, and other organic acids are involved in a myriad of metabolic pathways owing to their high polarity and solubility in biological fluids. Various disease areas such as cancer, myeloid leukemia, heart disease, liver disease, and lifestyle diseases (obesity and diabetes) were found to be related to certain metabolic pathways and changes in the concentrations of the compounds involved in those pathways. Therefore, the quantification of such compounds provides useful information pertaining to diagnosis, pathological conditions, and disease mechanisms, spurring the development of numerous analytical methods for this purpose. This review article addresses analytical methods for the quantification of carboxylic acids, which were classified into fatty acids, tricarboxylic acid cycle and glycolysis-related compounds, amino acid metabolites, perfluorinated carboxylic acids, α-keto acids and their metabolites, thiazole-containing carboxylic acids, and miscellaneous, in biological samples from 2000 to date. Methods involving liquid chromatography coupled with ultraviolet, fluorescence, mass spectrometry, and electrochemical detection were summarized.

Elevated bioaccumulation of PFAAs in Oryzias melastigma following the increase of salinity is associated with the up-regulated expression of PFAA-binding proteins

Perfluoroalkyl acids (PFAAs) are widely detected in the environment, especially in estuarine and coastal areas where fluctuation of salinity occurs. Salinity alteration affected the distribution of PFAAs and even the bioaccumulation in organisms. However, the inner mechanism is still unclear. In this study, the marine medaka (Oryzias melastigma), a euryhaline fish model, was exposed to four PFAAs congeners under three different salinities (0, 15 and 35 psu). Results showed that the bioaccumulation of PFAAs increased in fish as the water salinity increased. PFAAs with longer lengths of carbon‑fluorine bond showed higher bioaccumulation in the fish. Salinity did not alter the levels of PFAAs in water media, however, the uptake rate of PFAAs from gills did increase with the salinity. Further analysis of the mechanism showed that PFAA bound to branchial proteins as confirmed by fluorescence spectroscopy. Higher expressions of proteins binding to PFAAs including organic anion transporter 1 (OAT1) and fatty acid-binding protein (FABP) facilitated the uptake of PFAAs through gills in fish culturing under higher salinity. In all, our study showed that elevation of salinity can induce the expression of proteins binding to PFAAs in gills, thus facilitate the uptake of water PFAAs. Salinity fluctuation should be taken into consideration when assessing the chemical risk in the estuarine and coastal areas.

Seminal plasma metabolites mediate the associations of multiple environmental pollutants with semen quality in Chinese men

Environmental exposure to arsenic, phthalate esters (PAEs) and perfluorinated compounds (PFCs) has been associated with human semen quality. However, the epidemiological "black-box" of these associations remains poorly uncovered. In this study, based on the association analysis between arsenic, PAE and PFC exposure and semen quality parameters (i.e., semen volume, sperm concentration, sperm count, progressive motility, total motility and normal morphology) in a Chinese male population, we explored the seminal plasma metabolic signatures that may mediate the exposure-outcome relations by using the meet-in-metabolite-analysis (MIMA) approach. As a result, a negative association was found between DMA and sperm concentration, whereas MEHP and PFHxS were positively associated with sperm count and concentration, respectively. Metabolomics analysis revealed that sixteen and twenty-two seminal plasma metabolites were related to sperm concentration and count, respectively, and they are mainly involved in fatty acid, lipid and amino acid metabolism. Moreover, it was further indicated that eicosatetraenoate, carnitines and DHA may impact the inverse association between DMA and sperm concentration, while eicosatetraenoate, carnitines, DHA, PGB2 and tocotrienol are possible mediators of the positive association between PFHxS and sperm concentration. As these metabolic biomarkers are relevant to antioxidation and fatty acid β-oxidation, we suggest that redox balance and energy generation shifts in seminal plasma are involved in the association of human semen quality with environmental DMA and PFHxS exposure.

Biphasic effects of perfluorooctanoic acid on steroidogenesis in mouse Leydig tumour cells

Perfluorooctanoic acid (PFOA) is a persistent organic pollutant, which may possess endocrine disrupting properties. Herein, we investigated the possible mechanism(s) of toxicity and steroidogenesis in mouse Leydig cells. MLTC-1 (mouse Leydig tumour cells) cells were exposed to 0, 50, 100 or 200 μM PFOA for 48 h to ascertain their effects on the nuclear (membrane) receptor responses, steroidogenesis pathway and related regulated gene expression and steroid hormone secretion profiles. Our results reveal that nuclear receptors PXR, SR-B1 and LHR are sensitive to PFOA exposure. PFOA can accumulate in mitochondria and alter cholesterol precursor (fatty acid) mitochondrial transport process-related gene expression and thus inhibit steroid hormone precursor (cholesterol) production. In particular, PFOA exhibits biphasic effects on testosterone and progesterone production at differing levels of exposure. These findings indicate the potential endocrine-related effects of PFOA on steroid hormone secretion in Leydig cells and point to a novel disruption model.

Serum metabolome biomarkers associate low-level environmental perfluorinated compound exposure with oxidative /nitrosative stress in humans

Previous in vivo and in vitro studies have linked perfluorinated compound (PFC) exposure with metabolic interruption, but the inter-species difference and high treatment doses usually make the results difficult to be extrapolated to humans directly. The best strategy for identifying the metabolic interruption may be to establish the direct correlations between monitored PFCs data and metabolic data on human samples. In this study, serum metabolome data and PFC concentrations were acquired for a Chinese adult male cohort. The most abundant PFCs are PFOA and PFOS with concentration medians 7.56 and 12.78 nM, respectively; in together they count around 81.6% of the total PFCs. PFC concentration-related serum metabolic profile changes and the related metabolic biomarkers were explored by using partial least squares-discriminant analysis (PLS-DA). Respectively taking PFOS, PFOA and total PFC as the classifiers, serum metabolome can be differentiated between the lowest dose group (1st quartile PFCs) and the highest PFC dose group (4th quartile PFCs). Ten potential PFC biomarkers were identified, mainly involving in pollutant detoxification, antioxidation and nitric oxide (NO) signal pathways. These suggested that low-level environmental PFC exposure has significantly adverse impacts on glutathione (GSH) cycle, Krebs cycle, nitric oxide (NO) generation and purine oxidation in humans. To the best of our knowledge, this is the first report investigating the association of environmental PFC exposure with human serum metabolome alteration. Given the important biological functions of the identified biomarkers, we suggest that PFC could increase the metabolism syndromes risk including diabetes and cardiovascular diseases.

Analysis of perfluorinated compounds in human serum from the general population in Shanghai by liquid chromatography-tandem mass spectrometry (LC-MS/MS)

Perfluorinated compounds (PFCs) have potential health risk to human. In this paper, human serum samples collected from Jiading District, Shanghai aged from 23 to 87 years old (12 male and 33 female) were analyzed for 17 perfluorinated compounds (PFCs). A novel method for the elimination of background contamination of perfluorooctanoic acid (PFOA) generated from instrument by the modification of high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) has also been developed and validated. The limit of detection (LOD) for all monitored PFCs range from 0.02 to 0.18 ng mL^-1. The limit of quantitation (LOQ) for PFOS and PFOA was 2.23 and 1.60 ng mL^-1, respectively, and for other PFCs it ranged from 0.04 to 0.88 ng mL^-1. Of the 17 PFCs analyzed in Shanghai serum, eleven were found. The dominating PFCs in all samples were perfluorooctanesulfonate (PFOS) and PFOA with a fraction of 49.5%, 34.2%, respectively. The median total concentration of each serum samples was 53.43 ng mL^-1 with a range from <LOD to 99.37 ng mL^-1. The results indicate a high human exposure to PFCs in Shanghai region. Compared with other cities in China and some other countries, PFOA and PFDA concentrations in the serum of general population of Shanghai are highest. For all donors, no significant association between age and PFCs was found (p = 0.125-0.951) and no workplace significant correlation was found (p = 0.247-0.861). Since no signification is founded and PFCs exposure is prevalent, further investigation is needed to explore its source and potential health impact. These results will also provide significant background data of PFCs in Shanghai.

In situ combined chemical and biological assessment of estrogenic pollution in a water recycling system

Estrogenic pollution and its control in aquatic systems have drawn substantial attention around the world. The chemical and biological assessment approaches currently utilized in the laboratory or field cannot give an integrated assessment of the pollution when used separately. In this study, in situ chemical and biological methods were combined to detect pollution in a water recycling system. Data for the water quality index (WQI) demonstrated that the water treatment resulted in the decline of pollution from upstream to downstream. Wild male Nile tilapia, Oreochromis niloticus, was sampled in June and September. The concentrations of four common endocrine disrupting chemicals (EDCs) were determined in the tilapia liver by chromatographic analysis methods. The level of 17β-estradiol (E2) declined from upstream to downstream in both months. In contrast, the levels of bisphenol A (BPA), di-(2-ethylhcxyl) phthalate (DEHP), and perfluorooctane sulfonate (PFOS) did not display this declining tendency. The highest relative expression of vitellogenin 1 (VTG1) was observed in tilapia from upstream, then the level significantly decreased along the water system. The relative expression levels of CYP1A1 in the water system were also significantly higher than that of the control. However, no declining trend could be observed along the water system. The change of VTG1 expression corresponded well with that of E2 levels in the tilapia liver. Overall, our study assessed the pollution by endocrine disruptors using chemical and biological data with good correspondence. This study also demonstrated the effectiveness of the water recycling system in eliminating estrogen pollution in municipal sewage.