Plasma metabonomics investigation reveals involvement of fatty acid oxidation in hematotoxicity in Chinese benzene-exposed workers with low white blood cell count

A review of disrupted biological response associated with volatile organic compound exposure: Insight into identification of biomarkers

Volatile organic compounds (VOCs) are widespread harmful atmospheric pollutants, which have long been concerned and elucidated to be one of the risks of acute and chronic diseases for human, such as leukemia and cancer. Although numerous scientific studies have documented the potential adverse outcomes caused by VOC exposure, the mechanisms which biological response pathways of these VOC disruption remain poorly understood. Therefore, the identification of biochemical markers associated with metabolism, health effects and diseases orientation can be an effective means of screening biological targets for VOC exposure, which provide evidences to the toxicity assessment of compounds. The current review aims to understand the mechanisms underlying VOCs-elicited adverse outcomes by charactering various types of biomarkers. VOCs-related biomarkers from three aspects were summarized through in vitro, animal and epidemiological studies. i) Unmetabolized and metabolized VOC biomarkers in human samples for assessing exposure characteristics in different communities; ii) Adverse endpoint effects related biomarkers, mainly including (anti)oxidative stress, inflammation response and DNA damage; iii) Omics-based molecular biomarkers alteration in gene, protein, lipid and metabolite aspects associated with biological signaling pathway disorders response to VOC exposure. Further research, advanced machine learning and bioinformation approaches combined with experimental results are urgently needed to ascertain the selection of biomarkers and further illuminate toxic mechanisms of VOC exposure. Finally, VOCs-induced disease causes can be predicted with proven results.

Review on novel toxicological effects and personalized health hazard in workers exposed to low doses of benzene

Several recent reports indicate health hazards for workers with below occupational limit exposure to benzene (BZ). Our updated review indicates that such low exposures induced traditional as well as novel toxicity/genotoxicity, e.g., increased mitochondria copy numbers, prolongation of telomeres, impairment of DNA damage repair response (DDRR), perturbations of expression in non-coding RNAs, and epigenetic changes. These abnormalities were associated with alterations of gene expression and cellular signaling pathways which affected hematopoietic cell development, expression of apoptosis, autophagy, etc. The overarching mechanisms for induction of health risk are impaired DDRR, inhibition of tumor suppressor genes, and changes of MDM2-p53 axis activities that contribute to perturbed control for cancer pathways. Evaluation of the unusual dose-responses to BZ exposure indicates cellular over-compensation and reprogramming to overcome toxicity and to promote survival. However, these abnormal mechanisms also promote the induction of leukemia. Further investigations indicate that the current exposure limits for workers to BZ are unacceptable. Based on these studies, the new exposure limits should be less than 0.07 ppm rather than the current 1 ppm. This review also emphasizes the need to conduct appropriate bioassays, and to provide more reliable decisions on health hazards as well as on exposure limits for workers. In addition, it is important to use scientific data to provide significantly improved risk assessment, i.e., shifting from a population- to an individual-based risk assessment.

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.

LincRNA-p21 promotes p21-mediated cell cycle arrest in benzene-induced hematotoxicity by sponging miRNA-17-5p

Benzene is widely employed in manufacturing and causes hematotoxic effects and leukemia in humans. A long intergenic noncoding RNA (lincRNA)-microRNA (miRNA)-mRNA coexpression and competing endogenous RNA (ceRNA) regulatory network was constructed by bioinformatics analysis based on a benzene-induced aplastic anemia (BIAA) mouse model. In this population-based study, we observed a trend consistent with that in the BIAA mice: lincRNA-p21 and p21 were upregulated, while miRNA-17-5p expression was downregulated in benzene-exposed workers. Moreover, multiple linear regressions indicated that lincRNA-p21 was negatively associated with white blood cell (WBC) counts. Predictive thresholds of hematotoxicity were identified by ROC curve analysis with S-phenylmercapturic acid (SPMA) and lincRNA-p21 showing a better predictive ability than the other parameters and the combination of SPMA and lincRNA-p21 exhibiting the highest predictive value for hematotoxicity. LincRNA-p21 was predominantly present in the cytoplasm of bone marrow cells (BMCs) and K562 cells as assessed by fluorescence in situ hybridization (FISH). Upon exploring the underlying mechanism by which lincRNA-p21 mediates benzene-induced hematotoxicity, we observed that the negative regulation of 1,4-benzoquinone (1,4-BQ) on cell cycle arrest and inhibition of K562 cell proliferation was partially relieved by lincRNA-p21 knockdown, which can inhibit the expression of P21 and thereby suppress the toxic effects of 1,4-BQ. Finally, dual-luciferase reporter gene and RIP assay showed that, by acting as a sponge, lincRNA-p21 reduced the activity of miRNA-17-5p and consequently increased the expression of p21. In conclusion, our research suggested that benzene induces hematotoxicity via the lincRNA-p21/miRNA-17-5p/p21 signaling which might contribute to the underlying mechanism of lincRNA-p21 in benzene-induced hematotoxicity. Therefore, lincRNA-p21 can serve as a potential biomarker for the early detection of hematopoiesis inhibition in individuals with long-term exposure to low-dose benzene.

Evi1 involved in benzene-induced haematotoxicity via modulation of PI3K/mTOR pathway and negative regulation Serpinb2

Benzene is a widely used chemical and an environmental pollutant. Exposure to benzene can cause blood diseases, but the mechanisms underlying benzene haematotoxicity have not been fully clarified. Ecotropic virus integration site-1 (Evi1), a transcription factor, plays important roles in normal haematopoiesis and haematological diseases. In this study, we investigated the role and mechanism of Evi1 in benzene-induced haematotoxicity. We found that benzene exposure significantly increased Evi1 level in white blood cells (WBCs) in occupational benzene workers as well as mouse bone marrow cells. Further in vitro results demonstrated that compared with control cells exposed to same 1,4-benzoquinone (1,4-BQ, an important active metabolite of benzene) concentration, Evi1 downregulation significantly reduced cell proliferation, and disrupted cell viability, apoptosis, erythroid and megakaryotic cell differentiation and cell cycle. Additionally, down-regulation of Evi1 suppressed phosphoinositide 3-kinase (PI3K)/mTOR signalling pathway and elevated its target gene Serpinb2 following 1,4-BQ exposure. Moreover, the PI3K activator could partially relieve the inhibitory effect of down-regulation of Evi1 on cell proliferation and increase cell arrest in in G2/M phase. What's more, downregulation of Serpinb2 could partially alleviate proliferation inhibition and reverse cell cycle changes in G0/G1 phase and S phase induced by Evi1 inhibition. In conclusion, our data revealed that Evi1 downregulation aggravated the inhibition of cell proliferation and arrested cells in the G0/G1 phase when exposed to 1,4-BQ, potentially by inactivating the PI3K/mTOR pathway and upregulating downstream target gene Serpinb2. Our study provides novel insights on mechanism by which Evi1 participates in benzene-induced haematotoxicity.

Benzene Exposure Leads to Lipodystrophy and Alters Endocrine Activity In Vivo and In Vitro

Benzene is a ubiquitous pollutant and mainly accumulates in adipose tissue which has important roles in metabolic diseases. The latest studies reported that benzene exposure was associated with many metabolic disorders, while the effect of benzene exposure on adipose tissue remains unclear. We sought to investigate the effect using in vivo and in vitro experiments. Male adult C57BL/6J mice were exposed to benzene at 0, 1, 10 and 100 mg/kg body weight by intragastric gavage for 4 weeks. Mature adipocytes from 3T3-L1 cells were exposed to hydroquinone (HQ) at 0, 1, 5 and 25 μM for 24 hours. Besides the routine hematotoxicity, animal experiments also displayed significant body fat content decrease from 1 mg/kg. Interestingly, the circulating non-esterified fatty acid (NEFA) level increased from the lowest dose (p_trend < 0.05). Subsequent analysis indicated that body fat content decrease may be due to atrophy of white adipose tissue (WAT) upon benzene exposure. The average adipocyte area of WAT decreased significantly even from 1 mg/kg with no significant changes in total number of adipocytes. The percentages of small and large adipocytes in WAT began to significantly increase or decrease from 1 mg/kg (all p < 0.05), respectively. Critical genes involved in lipogenesis and lipolysis were dysregulated, which may account for the disruption of lipid homeostasis. The endocrine function of WAT was also disordered, manifested as significant decrease in adipokine levels, especially the leptin. In vitro cell experiments displayed similar findings in decreased fat content, dysregulated critical lipid metabolism genes, and disturbed endocrine function of adipocytes after HQ treatment. Pearson correlation analysis showed positive correlations between white blood cell (WBC) count with WAT fat content and plasma leptin level (r = 0.330, 0.344, both p < 0.05). This study shed light on the novel aspect that benzene exposure could induce lipodystrophy and disturb endocrine function of WAT, and the altered physiology of WAT might in turn affect benzene-induced hematotoxicity and metabolic disorders. The study provided new insight into understanding benzene-induced toxicity and the relationship between benzene and adipose tissue.

Plasma metabolomic profiling in workers with noise-induced hearing loss: a pilot study

Noise-induced hearing loss (NIHL) remains a leading occupational related disease and is a serious public health problem. Hence, the identification of potential biomarkers for NIHL prevention and diagnosis has become an urgent work. To discover potential metabolic biomarkers of NIHL, plasma metabolomics analysis in 62 NIHL patients and 62 normal hearing controls was performed using ultrahigh-performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry (UHPLC-Q-TOF MS). Orthogonal partial least square-discriminant analysis (OPLS-DA) model was applied to distinguish metabolite profile alterations in plasma samples between the two groups. The metabolites with a variable importance of projection (VIP) value > 1 and P value < 0.05 were considered to be potential metabolic biomarkers. KEGG database was performed to explore the involved pathways of potential biomarkers. Three autophagy-related genes (PI3K, AKT, and ATG5) were selected for further verification, and mRNA levels were detected using RT-qPCR analysis. Twenty plasma metabolites with VIP > 1 and P < 0.05 were significantly altered between the two groups. Totally, seven metabolic pathways involving the glycerophospholipid metabolism, glycosylphosphatidylinositol (GPI)-anchor biosynthesis, autophagy pathway, choline metabolism, the alpha-linolenic acid metabolism and linoleic acid metabolism, and retrograde endocannabinoid pathway were significantly related to NIHL. Furthermore, verification by RT-qPCR suggested that the mRNA expression levels of PI3K and AKT along with ATG5 were significantly lower in the NIHL patients compared with controls. In summary, the present study provides the first evidence that the identified aberrantly altered metabolites may be the potentially valuable biomarkers of NIHL for occupational noise-exposed workers. Autophagy signal pathway may be involved in the occurrence and development of NIHL. Moreover, this present study may be helpful to further better understand the metabolic changes in NIHL and be helpful for the understanding of pathogenic mechanism.

Metabolome-wide association study of occupational exposure to benzene

Benzene is a recognized hematotoxin and leukemogen; however, its mechanism of action in humans remain unclear. To provide insight into the processes underlying benzene hematotoxicity, we performed high-resolution metabolomic profiling of plasma collected from a cross-sectional study of 33 healthy workers exposed to benzene (median 8-h time-weighted average exposure; 20 ppma), and 25 unexposed controls in Shanghai, China. Metabolic features associated with benzene were identified using a metabolome-wide association study (MWAS) that tested for the relationship between feature intensity and benzene exposure. MWAS identified 478 mass spectral features associated with benzene exposure at false discovery rate < 20%. Comparison to a list of 13 known benzene metabolites and metabolites predicted using a multi-component biotransformation algorithm showed five metabolites were detected, which included the known metabolites phenol and benzene diolepoxide. Metabolic pathway enrichment identified 41 pathways associated with benzene exposure, with altered pathways including carnitine shuttle, fatty acid metabolism, sulfur amino acid metabolism, glycolysis, gluconeogenesis and branched chain amino acid metabolism. These results suggest disruption to fatty acid uptake, energy metabolism and increased oxidative stress, and point towards pathways related to mitochondrial dysfunction, which has previously been linked to benzene exposure in animal models and human studies. Taken together, these results suggest benzene exposure is associated with disruption of mitochondrial pathways, and provide promising, systems biology biomarkers for risk assessment of benzene-induced hematotoxicity in humans.

A Scoping Review of Technologies and Their Applicability for Exposome-Based Risk Assessment in the Oil and Gas Industry

INTRODUCTION

Oil and gas workers have been shown to be at increased risk of chronic diseases including cancer, asthma, chronic obstructive pulmonary disease, and hearing loss, among others. Technological advances may be used to assess the external (e.g. personal sensors, smartphone apps and online platforms, exposure models) and internal exposome (e.g. physiologically based kinetic modeling (PBK), biomonitoring, omics), offering numerous possibilities for chronic disease prevention strategies and risk management measures. The objective of this study was to review the literature on these technologies, by focusing on: (i) evaluating their applicability for exposome research in the oil and gas industry, and (ii) identifying key challenges that may hamper the successful application of such technologies in the oil and gas industry.

METHOD

A scoping review was conducted by identifying peer-reviewed literature with searches in MEDLINE/PubMed and SciVerse Scopus. Two assessors trained on the search strategy screened retrieved articles on title and abstract. The inclusion criteria used for this review were: application of the aforementioned technologies at a workplace in the oil and gas industry or, application of these technologies for an exposure relevant to the oil and gas industry but in another occupational sector, English language and publication period 2005-end of 2019.

RESULTS

In total, 72 articles were included in this scoping review with most articles focused on omics and bioinformatics (N = 22), followed by biomonitoring and biomarkers (N = 20), external exposure modeling (N = 11), PBK modeling (N = 10), and personal sensors (N = 9). Several studies were identified in the oil and gas industry on the application of PBK models and biomarkers, mainly focusing on workers exposed to benzene. The application of personal sensors, new types of exposure models, and omics technology are still in their infancy with respect to the oil and gas industry. Nevertheless, applications of these technologies in other occupational sectors showed the potential for application in this sector.

DISCUSSION AND CONCLUSION

New exposome technologies offer great promise for personal monitoring of workers in the oil and gas industry, but more applied research is needed in collaboration with the industry. Current challenges hindering a successful application of such technologies include (i) the technological readiness of sensors, (ii) the availability of data, (iii) the absence of standardized and validated methods, and (iv) the need for new study designs to study the development of disease during working life.

Ambient PM2.5 species and ultrafine particle exposure and their differential metabolomic signatures

BACKGROUND

The metabolomic signatures of short- and long-term exposure to PM_2.5 have been reported and linked to inflammation and oxidative stress. However, little is known about the relative contribution of the specific PM_2.5 species (hence sources) that drive these metabolomic signatures.

OBJECTIVES

We aimed to determine the relative contribution of the different species of PM_2.5 exposure to the perturbed metabolic pathways related to changes in the plasma metabolome.

METHODS

We performed mass-spectrometry based metabolomic profiling of plasma samples among men from the Normative Aging Study to identify metabolic pathways associated with PM_2.5 species. The exposure windows included short-term (one, seven-, and thirty-day moving average) and long-term (one year moving average). We used linear mixed-effect regression with subject-specific intercepts while simultaneously adjusting for PM_2.5, NO₂, O₃, temperature, relative humidity, and covariates and correcting for multiple testing. We also used independent component analysis (ICA) to examine the relative contribution of patterns of PM_2.5 species.

RESULTS

Between 2000 and 2016, 456 men provided 648 blood samples, in which 1158 metabolites were quantified. We chose 305 metabolites for the short-term and 288 metabolites for the long-term exposure in this analysis that were significantly associated (p-value < 0.01) with PM_2.5 to include in our PM_2.5 species analysis. On average, men were 75.0 years old and their body mass index was 27.7 kg/m². Only 3% were current smokers. In the adjusted models, ultrafine particles (UFPs) were the most significant species of short-term PM_2.5 exposure followed by nickel, vanadium, potassium, silicon, and aluminum. Black carbon, vanadium, zinc, nickel, iron, copper, and selenium were the significant species of long-term PM_2.5 exposure. We identified several metabolic pathways perturbed with PM_2.5 species including glycerophospholipid, sphingolipid, and glutathione. These pathways are involved in inflammation, oxidative stress, immunity, and nucleic acid damage and repair. Results were overlapped with the ICA.

CONCLUSIONS

We identified several significant perturbed plasma metabolites and metabolic pathways associated with exposure to PM_2.5 species. These species are associated with traffic, fuel oil, and wood smoke. This is the largest study to report a metabolomic signature of PM_2.5 species' exposure and the first to use ICA.

Congenital heart defects and intensity of oil and gas well site activities in early pregnancy

BACKGROUND

Preliminary studies suggest that offspring to mothers living near oil and natural gas (O&G) well sites are at higher risk of congenital heart defects (CHDs).

OBJECTIVES

Our objective was to address the limitations of previous studies in a new and more robust evaluation of the relationship between maternal proximity to O&G well site activities and births with CHDs.

METHODS

We employed a nested case-control study of 3324 infants born in Colorado between 2005 and 2011. 187, 179, 132, and 38 singleton births with an aortic artery and valve (AAVD), pulmonary artery and valve (PAVD), conotruncal (CTD), or tricuspid valve (TVD) defect, respectively, were frequency matched 1:5 to controls on sex, maternal smoking, and race and ethnicity yielding 2860 controls. We estimated monthly intensities of O&G activity at maternal residences from three months prior to conception through the second gestational month with our intensity adjusted inverse distance weighted model. We used logistic regression models adjusted for O&G facilities other than wells, intensity of air pollution sources not associated with O&G activities, maternal age and socioeconomic status index, and infant sex and parity, to evaluate associations between CHDs and O&G activity intensity groups (low, medium, and high).

RESULTS

Overall, CHDs were 1.4 (1.0, 2.0) and 1.7 (1.1, 2.6) times more likely than controls in the medium and high intensity groups, respectively, compared to the low intensity group. PAVDs were 1.7 (0.93, 3.0) and 2.5 (1.1, 5.3) times more likely in the medium and high intensity groups for mothers with an address found in the second gestational month. In rural areas, AAVDs, CTDs, and TVDs were 1.8 (0.97, 3.3) and 2.6 (1.1, 6.1); 2.1 (0.96, 4.5) and 4.0 (1.4, 12); and 3.4 (0.95, 12) and 4.6 (0.81, 26) times more likely than controls in the medium and high intensity groups.

CONCLUSIONS

This study provides further evidence of a positive association between maternal proximity to O&G well site activities and several types of CHDs, particularly in rural areas.

Application of metabolomics to characterize environmental pollutant toxicity and disease risks

The increased incidence of non-communicable human diseases may be attributed, at least partially, to exposures to toxic chemicals such as persistent organic pollutants (POPs), air pollutants and heavy metals. Given the high mortality and morbidity of pollutant exposure associated diseases, a better understanding of the related mechanisms of toxicity and impacts on the endogenous host metabolism are needed. The metabolome represents the collection of the intermediates and end products of cellular processes, and is the most proximal reporter of the body's response to environmental exposures and pathological processes. Metabolomics is a powerful tool for studying how organisms interact with their environment and how these interactions shape diseases related to pollutant exposure. This mini review discusses potential biological mechanisms that link pollutant exposure to metabolic disturbances and chronic human diseases, with a focus on recent studies that demonstrate the application of metabolomics as a tool to elucidate biochemical modes of actions of various environmental pollutants. In addition, classes of metabolites that have been shown to be modulated by multiple environmental pollutants will be discussed with an emphasis on their use as potential early biomarkers of disease risks. Taken together, metabolomics is a useful and versatile tool for characterizing the disease risks and mechanisms associated with various environmental pollutants.