Ambient BTEX exposure and mid-pregnancy inflammatory biomarkers in pregnant African American women

Risk assessment of Benzene, Toluene, Ethyl benzene, and Xylene (BTEX) in the atmospheric air around the world: A review

Volatile organic compounds, such as BTEX, have been the subject of numerous debates due to their detrimental effects on the environment and human health. Human beings have had a significant role in the emergence of this situation. Even though US EPA, WHO, and other health-related organizations have set standard limits as unhazardous levels, it has been observed that within or even below these limits, constant exposure to these toxic chemicals results in negative consequences as well. According to these facts, various studies have been carried out all over the world - 160 of which are collected within this review article, so that experts and governors may come up with effective solutions to manage and control these toxic chemicals. The outcome of this study will serve the society to evaluate and handle the risks of being exposed to BTEX. In this review article, the attempt was to collect the most accessible studies relevant to risk assessment of BTEX in the atmosphere, and for the article to contain least bias, it was reviewed and re-evaluated by all authors, who are from different institutions and backgrounds, so that the insights of the article remain unbiased. There may be some limitations to consistency or precision in some points due to the original sources, however the attempt was to minimize them as much as possible.

The Impact of Environmental Benzene, Toluene, Ethylbenzene, and Xylene Exposure on Blood-Based DNA Methylation Profiles in Pregnant African American Women from Detroit

African American women in the United States have a high risk of adverse pregnancy outcomes. DNA methylation is a potential mechanism by which exposure to BTEX (benzene, toluene, ethylbenzene, and xylenes) may cause adverse pregnancy outcomes. Data are from the Maternal Stress Study, which recruited African American women in the second trimester of pregnancy from February 2009 to June 2010. DNA methylation was measured in archived DNA from venous blood collected in the second trimester. Trimester-specific exposure to airshed BTEX was estimated using maternal self-reported addresses and geospatial models of ambient air pollution developed as part of the Geospatial Determinants of Health Outcomes Consortium. Among the 64 women with exposure and outcome data available, 46 differentially methylated regions (DMRs) were associated with BTEX exposure (FDR adjusted p-value < 0.05) using a DMR-based epigenome-wide association study approach. Overall, 89% of DMRs consistently exhibited hypomethylation with increasing BTEX exposure. Biological pathway analysis identified 11 enriched pathways, with the top 3 involving gamma-aminobutyric acid receptor signaling, oxytocin in brain signaling, and the gustation pathway. These findings highlight the potential impact of BTEX on DNA methylation in pregnant women.

Microglial NF-κB Signaling Deficiency Protects Against Metabolic Disruptions Caused by Volatile Organic Compound via Modulating the Hypothalamic Transcriptome

Prolonged exposure to benzene, a prevalent volatile organic compound (VOC), at concentrations found in smoke, triggers hyperglycemia, and inflammation in mice. Corroborating this with existing epidemiological data, we show a strong correlation between environmental benzene exposure and metabolic impairments in humans. To uncover the underlying mechanisms, we employed a controlled exposure system and continuous glucose monitoring (CGM), revealing rapid blood glucose surges and disturbances in energy homeostasis in mice. These effects were attributed to alterations in the hypothalamic transcriptome, specifically impacting insulin and immune response genes, leading to hypothalamic insulin resistance and neuroinflammation. Moreover, benzene exposure activated microglial transcription characterized by heightened expression of IKKβ/NF-κB-related genes. Remarkably, selective removal of IKKβ in immune cells or adult microglia in mice alleviated benzene-induced hypothalamic gliosis, and protected against hyperglycemia. In summary, our study uncovers a crucial pathophysiological mechanism, establishing a clear link between airborne toxicant exposure and the onset of metabolic diseases.

Effect of mir-92a-3p on hydroquinone induced changes in human lymphoblastoid cell cycle and apoptosis

Hydroquinone (HQ), one of the metabolites of benzene in humans, has significant hepatotoxic properties. Chronic exposure to HQ can lead to leukemia. In a previous study by this group, we constructed a model of malignant transformation of human lymphoblastoid cells (TK6) induced by chronic exposure to HQ with significant subcutaneous tumorigenic capacity in nude mice. miR-92a-3p is a tumor factor whose role in HQ-induced malignant transformation is not yet clear. In the present study, raw signal analysis and dual-luciferase reporter gene results suggested that miR-92a-3p could target and regulate TOB1, and the expression level of miR-92a-3p was significantly upregulated in the long-term HQ-induced TK6 malignant transformation model, while the anti-proliferative factor TOB1 was significantly downregulated. To investigate the mechanism behind this, we inhibited miR-92a-3p in a malignant transformation model and found a decrease in cell viability, a decrease in MMP-9 protein levels, a G2/M phase block in the cell cycle, and an upregulation of the expression of G2/M phase-related proteins cyclinB1 and CDK1. Inhibition of miR-92a-3p in combination with si-TOB1 restored cell viability, inhibited cyclin B1 and CDK1 protein levels, and attenuated the G2/M phase block. Taken together, miR-92a-3p reduced the cell proliferation rate of HQ19 and caused cell cycle arrest by targeting TOB1, which in turn contributed to the altered malignant phenotype of the cells. This study suggests that miR-92a-3p is likely to be a biomarker for long-term HQ-induced malignant transformation of TK6 and could be a potential therapeutic target for leukemia caused by long-term exposure to HQ.

Maternal environmental, occupational, and urinary metabolite levels of benzene compounds and their association with congenital heart diseases in offspring: a case‒control study in China

The conclusions about the association of maternal pregnancy environment, occupation, and benzene compounds with fetal CHD are not entirely consistent. Eight hundred seven CHD cases and 1008 controls were included in this study. All occupations were classified and coded against the Occupational Classification Dictionary of the People's Republic of China (2015 version). Logistic regressions were used to explore the correlation among environmental factors, occupation types, and CHDs in offspring. We found that living near public facilities and having exposure to chemical reagents and hazardous substances were significant risk factors for CHDs in offspring. We found that offspring of mothers who worked in agriculture and similar work during pregnancy suffered from CHD. The risk of all CHDs in the offspring of pregnant women working in production manufacturing and related work was significantly higher than that in unemployed pregnant women, the risk was also observed in 4 subtypes of CHDs. We compared the concentrations of the five metabolite (MA, mHA, HA, PGA, and SPMA) levels of benzene compounds in the urine of mothers in case and control groups and found no significant differences. Our study suggests that maternal exposure during pregnancy and certain environmental and occupational conditions are risk factors for CHD in offspring, but did not support an association between concentrations of metabolites of benzene compounds in the urine of pregnant women and CHDs in their offspring.

Research progress in human biological monitoring of aromatic hydrocarbon with emphasis on the analytical technology of biomarkers

Aromatic hydrocarbons are unsaturated compounds containing carbon and hydrogen that form single aromatic ring, or double, triple, or multiple fused rings. This review focuses on the research progress of aromatic hydrocarbons represented by polycyclic aromatic hydrocarbons (including halogenated polycyclic aromatic hydrocarbons), benzene and its derivatives including toluene, ethylbenzene, xylenes (o-, m- and p-), styrene, nitrobenzene, and aniline. Due to the toxicity, widespread coexistence, and persistence of aromatic hydrocarbons in the environment, accurate assessment of exposure to aromatic hydrocarbons is essential to protect human health. The effects of aromatic hydrocarbons on human health are mainly derived from three aspects: different routes of exposure, the duration and relative toxicity of aromatic hydrocarbons, and the concentration of aromatic hydrocarbons which should be below the biological exposure limit. Therefore, this review discusses the primary exposure routes, toxic effects on humans, and key populations, in particular. This review briefly summarizes the different biomarker indicators of main aromatic hydrocarbons in urine, since most aromatic hydrocarbon metabolites are excreted via urine, which is more feasible, convenient, and non-invasive. In this review, the pretreatment and analytical techniques are compiled systematically for the qualitative and quantitative assessments of aromatic hydrocarbons metabolites such as gas chromatography and high-performance liquid chromatography with multiple detectors. This review aims to identify and monitor the co-exposure of aromatic hydrocarbons that provides a basis for the formulation of corresponding health risk control measures and guide the adjustment of the exposure dose of pollutants to the population.

Prenatal benzene exposure in mice alters offspring hypothalamic development predisposing to metabolic disease in later life

Maternal exposure to environmental contaminants during pregnancy poses a significant threat to a developing fetus, as these substances can easily cross the placenta and disrupt the neurodevelopment of offspring. Specifically, the hypothalamus is essential in the regulation of metabolism, notably during critical windows of development. An abnormal hormonal and inflammatory milieu during development can trigger persistent changes in the function of hypothalamic circuits, leading to long-lasting effects on the body's energy homeostasis and metabolism. We recently demonstrated that gestational exposure to clinically relevant levels of benzene induces severe metabolic dysregulation in the offspring. Given the central role of the hypothalamus in metabolic control, we hypothesized that prenatal exposure to benzene impacts hypothalamic development, contributing to the adverse metabolic effects in the offspring. C57BL/6JB dams were exposed to benzene at 50 ppm in the inhalation chambers exclusively during pregnancy (from E0.5 to E19). Transcriptomic analysis of the exposed offspring at postnatal day 21 (P21) revealed hypothalamic changes in genes related to metabolic regulation, inflammation, and neurodevelopment exclusively in males. Moreover, the hypothalamus of prenatally benzene-exposed male offspring displayed alterations in orexigenic and anorexigenic projections, impairments in leptin signaling, and increased microgliosis. Additional exposure to benzene during lactation did not promote further microgliosis or astrogliosis in the offspring, while the high-fat diet (HFD) challenge in adulthood exacerbated glucose metabolism and hypothalamic inflammation in benzene-exposed offspring of both sexes. These findings reveal the persistent adverse effects of prenatal benzene exposure on hypothalamic circuits and neuroinflammation, predisposing the offspring to long-lasting metabolic health conditions.

Expression level and function analysis of serum miRNAs in workers with occupational exposure to benzene series

Benzene series are ubiquitous in industrial production and daily life, and can have an impact on health even at low concentrations. miRNAs have been proved to be a biomarker of a variety of diseases and carcinogens. The purpose of this study was to explore the distribution characteristics and biological function of miRNAs in subjects exposed to benzene series. In this study, serum miRNAs were measured in 247 occupationally exposed subjects and 256 controls. The relationship between cumulative exposure dose of benzene series and miRNAs was analyzed by Generalized linear model, Spearman's rank correlation, and chi-square test for trend. The function of MiRNAs target gene was analyzed by means of bioinformatics method. The results showed that the expressions of miR-181a-5p, 221-3p, 223-3p, and 342-3p were down-regulated, whilst the expression of miR-638 was up-regulated in the occupational exposure group. miR-181a-5p, 221-3p, 223-3p, 342-3p, and 638 showed dose-response relationship with benzene series, and were closely related to multiple tumor pathways. miR-181a-5p, 221-3p, 223-3p, 342-3p, and 638 may be involved in the carcinogenic process of benzene series, and can be used to evaluate the early biological effects and monitor the exposure level of benzene series. miRNAs are potential biomarkers of benzene series exposure.

Prenatal benzene exposure alters offspring hypothalamic development predisposing to metabolic disease in later life

The hypothalamus is essential in the regulation of metabolism, notably during critical windows of development. An abnormal hormonal and inflammatory milieu during development can trigger persistent changes in the function of hypothalamic circuits, leading to long-lasting effects on the body’s energy homeostasis and metabolism. We recently demonstrated that gestational exposure to benzene at smoking levels induces severe metabolic dysregulation in the offspring. Given the central role of the hypothalamus in metabolic control, we hypothesized that prenatal exposure to benzene impacts hypothalamic development, contributing to the adverse metabolic effects in the offspring. C57BL/6JB dams were exposed to benzene in the inhalation chambers exclusively during pregnancy (from E0.5 to E19). The transcriptome analysis of the offspring hypothalamus at postnatal day 21 (P21) revealed changes in genes related to metabolic regulation, inflammation, and neurodevelopment exclusively in benzene-exposed male offspring. Moreover, the hypothalamus of prenatally benzene-exposed male offspring displayed alterations in orexigenic and anorexigenic projections, impairments in leptin signaling, and increased microgliosis. Additional exposure to benzene during lactation did not promote further microgliosis or astrogliosis in the offspring, while the high-fat diet (HFD) challenge in adulthood exacerbated glucose metabolism and hypothalamic inflammation in benzene-exposed offspring of both sexes. These findings reveal the persistent impact of prenatal benzene exposure on hypothalamic circuits and neuroinflammation, predisposing the offspring to long-lasting metabolic health conditions.

Cross-sectional and longitudinal associations of styrene and ethylbenzene exposure with heart rate variability alternation among urban adult population in China

Styrene and ethylbenzene (S/EB) are the monomers of polystyrene (PS) and polyethylene (PE), respectively, and have been identified as significant hazardous air pollutants by the U.S. Environmental Protection Agency. However, the adverse effects of S/EB on human health, especially cardiovascular health, have not been well established. Urinary biomarker of S/EB exposure and heart rate variability (HRV) were measured in urban adults from the Wuhan-Zhuhai cohort and were repeated after 3-year and 6-year follow-ups. Linear mixed models were used to estimate associations of S/EB exposure biomarker with HRV and longitudinal additional annual change of HRV. The mediating role of transforming growth factor (TGF)-β1 was tested by using mediation analysis. A total of 2842 general adults were included at baseline analysis, and 4748 observations were included in the repeated measurement study. In the cross-sectional analysis, each 1% increment in urinary S/EB exposure biomarker was significantly associated with a 0.106 % (95 % CI: -0.160, -0.052), 0.109 % (-0.169, -0.049), 0.099 % (-0.145, -0.053), 0.040 % (-0.060, -0.020), and 0.031 % (-0.054, -0.007) decrement in low frequency (LF), high frequency (HF), total power (TP), standard deviation of all normal-to-normal intervals (SDNN), and square root of the mean squared difference between adjacent normal-to-normal interval, respectively. Smoking status modified the relationships of urinary S/EB exposure biomarker with TP and SDNN. TGF-β1 mediated 3.09-5.16 % of the association between urinary S/EB biomarker and lower HRV. The follow-up analyses detected a negative association between urinary S/EB exposure biomarker and the additional annual change of LF (β: -0.016; 95 % CI: -0.028, -0.004), HF (-0.014; -0.026, -0.001), and TP (-0.011; -0.021, -0.001). Our findings demonstrated that S/EB exposure was associated with HRV reduction among the general urban adults and the TGF-β pathway may play a part of the mediating role in this association.

Global preterm births attributable to BTEX (benzene, toluene, ethylbenzene, and xylene) exposure

Epidemiological studies have shown that long-term exposure to toxic volatile organic compounds, such as benzene, toluene, ethylbenzene, and xylene (BTEX), is associated with preterm births (PTB). However, global PTB attributable to long-term BTEX exposure has not been reported in the literature yet. In this study, we employed a global chemical transport model, GEOS-Chem (Goddard Earth Observing System coupled with chemistry), in conjunction with an epidemiological model, to quantify the global country-specific PTB associated with long-term BTEX exposure at the horizontal resolution of 1 km × 1 km for the year 2015. Model simulated surface annual mean BTEX concentrations in GEOS-Chem have been thoroughly evaluated against global in-situ observations, which demonstrated that model simulated BTEX concentrations fairly agreed with observations but tended to be underestimated in India. Our study found that the global annual total PTB attributable to BTEX was 2.01 million [95% confidence interval (95CI): 1.16-2.70 million] in 2015, with largest contributions from India (28.3%), followed by China (27.5%), Pakistan (6.2%), Indonesia (4.2%), Bangladesh (3.7%) and United States (2.3%). The global annual total PTB due to BTEX exposure accounted for 19.6% (95CI: 11.3-26.4%) relative to the global annual total all-cause PTB (10.24 million) in 2015. Our study has significant implications on air pollution mitigation policy associated with country-specific anthropogenic BTEX emission reductions to achieve the benefit of human health.

Evaluating Phenotypic and Transcriptomic Responses Induced by Low-Level VOCs in Zebrafish: Benzene as an Example

Urban environments are plagued by complex mixtures of anthropogenic volatile organic compounds (VOCs), such as mixtures of benzene, toluene, ethylene, and xylene (BTEX). Sources of BTEX that drive human exposure include vehicle exhaust, industrial emissions, off-gassing of building material, as well as oil spillage and leakage. Among the BTEX mixture, benzene is the most volatile compound and has been linked to numerous adverse health outcomes. However, few studies have focused on the effects of low-level benzene on exposure during early development, which is a susceptible window when hematological, immune, metabolic, and detoxification systems are immature. In this study, we used zebrafish to conduct a VOC exposure model and evaluated phenotypic and transcriptomic responses following 0.1 and 1 ppm benzene exposure during the first five days of embryogenesis (n = 740 per treatment). The benzene body burden was 2 mg/kg in 1 ppm-exposed larval zebrafish pools and under the detection limit in 0.1 ppm-exposed fish. No observable phenotypic changes were found in both larvae except for significant skeletal deformities in 0.1 ppm-exposed fish (p = 0.01) compared with unexposed fish. Based on transcriptomic responses, 1 ppm benzene dysregulated genes that were implicated with the development of hematological system, and the regulation of oxidative stress response, fatty acid metabolism, immune system, and inflammatory response, including apob, nfkbiaa, serpinf1, foxa1, cyp2k6, and cyp2n13 from the cytochrome P450 gene family. Key genes including pik3c2b, pltp, and chia.2 were differentially expressed in both 1 and 0.1 ppm exposures. However, fewer transcriptomic changes were induced by 0.1 ppm compared with 1 ppm. Future studies are needed to determine if these transcriptomic responses during embryogenesis have long-term consequences at levels equal to or lower than 1 ppm.

Prenatal Pollutant Exposures and Hypothalamic Development: Early Life Disruption of Metabolic Programming

Environmental contaminants in ambient air pollution pose a serious risk to long-term metabolic health. Strong evidence shows that prenatal exposure to pollutants can significantly increase the risk of Type II Diabetes (T2DM) in children and all ethnicities, even without the prevalence of obesity. The central nervous system (CNS) is critical in regulating whole-body metabolism. Within the CNS, the hypothalamus lies at the intersection of the neuroendocrine and autonomic systems and is primarily responsible for the regulation of energy homeostasis and satiety signals. The hypothalamus is particularly sensitive to insults during early neurodevelopmental periods and may be susceptible to alterations in the formation of neural metabolic circuitry. Although the precise molecular mechanism is not yet defined, alterations in hypothalamic developmental circuits may represent a leading cause of impaired metabolic programming. In this review, we present the current knowledge on the links between prenatal pollutant exposure and the hypothalamic programming of metabolism.