The role of in vitro gene expression profiling in particulate matter health research

Effects of Particulate Matter Inhalation during Exercise on Oxidative Stress and Mitochondrial Function in Mouse Skeletal Muscle

Particulate matter (PM) has deleterious consequences not only on the respiratory system but also on essential human organs, such as the heart, blood vessels, kidneys, and liver. However, the effects of PM inhalation on skeletal muscles have yet to be sufficiently elucidated. Female C57BL/6 or mt-Keima transgenic mice were randomly assigned to one of the following four groups: control (CON), PM exposure alone (PM), treadmill exercise (EX), or PM exposure and exercise (PME). Mice in the three-treatment group were subjected to treadmill running (20 m/min, 90 min/day for 1 week) and/or exposure to PM (100 μg/m3). The PM was found to exacerbate oxidative stress and inflammation, both at rest and during exercise, as assessed by the levels of proinflammatory cytokines, manganese-superoxide dismutase activity, and the glutathione/oxidized glutathione ratio. Furthermore, we detected significant increases in the levels of in vivo mitophagy, particularly in the PM group. Compared with the EX group, a significant reduction in the level of mitochondrial DNA was recorded in the PME group. Moreover, PM resulted in a reduction in cytochrome c oxidase activity and an increase in hydrogen peroxide generation. However, exposure to PM had no significant effect on mitochondrial respiration. Collectively, our findings in this study indicate that PM has adverse effects concerning both oxidative stress and inflammatory responses in skeletal muscle and mitochondria, both at rest and during exercise.

Temporal, compositional, and functional differences in the microbiome of Bangkok subway air environment

With the growing numbers of the urban population, an increasing number of commuters have relied on subway systems for rapid transportation in daily life. Analyzing the temporal distribution of air microbiomes in subway environments is crucial for the assessment and monitoring of air quality in the subway system, especially with regard to public health. This study employed culture-independent metabarcode sequencing to analyze bacterial diversity and variations in bacterial compositions associated with bioaerosols collected from a subway station in Bangkok over a four-month period. The bacteria obtained were found to consist primarily of Proteobacteria, Firmicutes, and Actinobacteria, with variations at the family, genus, and species levels among samples obtained in different months. The vast majority of these bacteria are most likely derived from outside environments and human body sources. Many of the bacteria found in Bangkok subway station were also identified as "core microorganisms" of subway environments around the world, as suggested by the MetaSUB Consortium. The diversity of bacterial communities was shown to be influenced by several air quality variables, especially ambient temperature and the quantity of particulate matters, which showed positive correlations with several bacterial species such as Acinetobacter lwoffii, Staphylococcus spp., and Moraxella osloensis. In addition, metabolic profiles inferred from metabarcode-derived bacterial diversity showed significant variations across different sampling times and sites and can be used as a starting point to further explore the functional roles of specific groups of bacteria in the subway environment. This study thus introduced the information required for surveillance of microbiological impacts and their contributions to the well-being of subway commuters in Bangkok.

Effect modification by sex for associations of fine particulate matter (PM2.5) with cardiovascular mortality, hospitalization, and emergency room visits: systematic review and meta-analysis

Particulate matter with aerodynamic diameter no larger than 2.5 μm (PM2.5) has been linked to cardiovascular diseases (CVDs) but evidence for vulnerability by sex remains unclear. We performed systematic review and meta-analysis to synthesize the state of scientific evidence on whether cardiovascular risks from PM2.5 differ for men compared to women. The databases Pubmed, Scopus, Embase, and GreenFILE were searched for studies published Jan. 1995 to Feb. 2020. Observational studies conducting subgroup analysis by sex for impacts of short-term or long-term exposure to PM2.5 on target CVDs were included. Data were independently extracted in duplicate and pooled with random-effects meta-regression. Risk ratios (RRs) for long-term exposure and percent changes in outcomes for short-term exposure were calculated per 10 μg/m3 PM2.5 increase. Quality of evidence of risk differences by sex was rated following Grading of Recommendations Assessment, Development and Evaluation (GRADE). A total of 12,502 articles were screened, with 61 meeting inclusion criteria. An additional 32 studies were added from citation chaining. RRs of all CVD mortality for long-term PM2.5 for men and women were the same (1.14; 95% CI: 1.09, 1.22) indicating no statistically different risks. Men and women did not have statistically different risks of daily CVD mortality, hospitalizations from all CVD, ischemic heart disease, cardiac arrest, acute myocardial infarction, and heart failure from short-term PM2.5 exposure (difference in % change in risk per 10 μg/m3 PM2.5: 0.04 (95% CI, -0.42 to 0.51); -0.05 (-0.47 to 0.38); 0.17 (-0.90, 1.24); 1.42 (-1.06, 3.97); 1.33 (-0.05, 2.73); and -0.48 (-1.94, 1.01), respectively). Analysis using GRADE found low or very low quality of evidence for sex differences for PM2.5-CVD risks. In conclusion, this meta-analysis and quality of evidence assessment of current observational studies found very limited evidence of the effect modification by sex for effects of PM2.5 on CVD outcomes in adults, which can inform clinical approaches and policies.

Mechanisms of cardiovascular toxicity induced by PM2.5: a review

An increasing number of studies have shown that exposure to particulate matter with a diameter ≤ 2.5 μm (PM_2.5) could affect the onset and development of cardiovascular diseases. To explore the underlying mechanisms, the studies conducted in vitro investigations using different cell lines. In this review, we examined recently published reports cited by PubMed or Web of Science on the topic of cardiovascular toxicity induced by PM_2.5 that carried the term in vitro. Here, we summarized the suggested mechanisms of PM_2.5 leading to adverse effects and cardiovascular toxicity including oxidative stress; the increase of vascular endothelial permeability; the injury of vasomotor function and vascular reparative capacity in vascular endothelial cell lines; macrophage polarization and apoptosis in macrophage cell lines; and hypermethylation and apoptosis in the AC16 cell line and the related signaling pathways, which provided a new research direction of cardiovascular toxicity of PM_2.5.

Upregulation of epithelial metallothioneins by metal-rich ultrafine particulate matter from an underground railway

Airborne particulate matter (PM) is a leading cause of mortality and morbidity. However, understanding of the range and mechanisms of effects of PM components is poor. PM generated in underground railways is rich in metals, especially iron. In the ultrafine (UFPM; <0.1 μm diameter) fraction, the combination of small size and metal enrichment poses an unknown health risk. This study aimed to analyse transcriptomic responses to underground UFPM in primary bronchial epithelial cells (PBECs), a key site of PM deposition. The oxidation state of iron in UFPM from an underground station was determined by X-ray absorption near edge structure (XANES) spectroscopy. Antioxidant response was assayed using a reporter cell line transfected with an antioxidant response element (ARE)-luciferase construct. Differentiated PBECs were exposed to UFPM for 6 h or 24 h for RNA-Seq and RT-qPCR analysis. XANES showed predominance of redox-active Fe3O4, with ROS generation confirmed by induction of ARE-luciferase expression. 6 h exposure of PBECs to UFPM identified 52 differentially expressed genes (DEGs), especially associated with epithelial maintenance, whereas 24 h exposure yielded 23 DEGs, particularly involved with redox homeostasis and metal binding. At both timepoints, there was upregulation of members of the metallothionein family, low molecular weight proteins with antioxidant activity whose main function is binding and homeostasis of zinc and copper ions, but not iron ions. This upregulation was partially inhibited by metal chelation or ROS scavenging. These data suggest differential regulation of responses to metal-rich UFPM depending on exposure period, and highlight novel pathways and markers of PM exposure, with the role of metallothioneins warranting further investigation.

MicroRNA biomarkers for chemical hazard screening identified by RNA deep sequencing analysis in mouse embryonic stem cells

We investigated the responses of microRNAs (miRNAs) using mouse embryonic stem cells (mESCs) exposed to nine chemicals (bis(2-ethylhexyl)phthalate, p-cresol, p-dichlorobenzene, phenol, pyrocatecol, chloroform, tri-n-butyl phosphate, trichloroethylene, and benzene), which are listed as "Class I Designated Chemical Substances" from the Japan Pollutant Release and Transfer Register. Using deep sequencing analysis (RNA-seq), several miRNAs were identified that show a substantial response to general chemical toxicity (i.e., to these nine chemicals considered as a group) and several miRNA biomarkers that show a substantial and specific response to benzene. The functions of the identified miRNAs were investigated in accordance with Gene Ontology terms of their predicted target genes, indicating regulation of cellular processes. We compared the results with those for the long non-coding RNAs (ncRNAs) and mRNAs reported in our previous studies in addition to previously identified miRNAs that are either up- or down-regulated in response to the benzene as stimuli. We also observed that the changes in expression of miRNAs were smaller than those for long ncRNAs and mRNAs. Taken together the current and previous results revealed that toxic chemical stimuli regulate the expression of miRNAs. We believe that the use of miRNAs, including the thus identified miRNAs, as biomarkers contribute to predicting the potential toxicity of particular chemicals or identifying human individuals that have been exposed to chemical hazards.

PM2.5-induced ADRB2 hypermethylation contributed to cardiac dysfunction through cardiomyocytes apoptosis via PI3K/Akt pathway

BACKGROUND

Long-term exposure to fine particulate matter (PM_2.5) can causally contribute to progression of atherosclerosis, risk of ischemic heart disease and death, but the underlying mechanism is little known. Since DNA methylation impacts the process of heart disease, it might be useful in exploring potential mechanistic pathways linking PM_2.5 exposure and heart disease.

OBJECTIVES

Here, we investigated the PM_2.5-induced ADRB2 hypermethylation and the involving epigenetic mechanism of PM_2.5-induced cardiomyocytes apoptosis and cardiac dysfunction.

METHODS AND RESULTS

In vitro, PM_2.5 markedly augmented cardiotoxicity including oxidative damage and apoptosis in cardiomyocytes AC16 as well as epigenetic alteration. DNA methylation profiling revealed a significant gene-ADRB2 was involved in the cardiac relative GO and KEGG pathways. Methylation chip and Bisulfite Sequencing PCR (BSP) both identified the hypermethylation status of ADRB2 which encodes β2-Adrenergic receptor (β2AR). Mechanistic study showed ADRB2 hypermethylation-induced down-regulation of β2AR inhibited PI3K/Akt and then activated Bcl-2/BAX and p53 pathway in AC16. The transgenic cell lines showed over-expression of ADRB2 weakened the PM_2.5-induced cardiomyocytes apoptosis in opposite way, but was augmented by PI3K inhibitor (LY294002). In vivo, echocardiography showed the heart contractile function was decreased after SD rats intratracheal instillation of PM_2.5 for 30 days. The myocardial interstitial edema, myocardial gap expansion and myofibril disorder in PM_2.5 treated group were observed in rats heart tissue. What's more, basal expression of β2AR and VEGFR2 decreased in heart tissue as the dosage of PM_2.5 increasing, meanwhile PM_2.5 markedly attenuated PI3K/Akt pathway followed by augmented Bcl-2/BAX and p53 pathway, thus caused a greater number of TUNEL positive cardiomyocytes resulted in cardiac dysfunction in vivo.

CONCLUSIONS

PM_2.5 exposure could cause the myocardial ADRB2 hypermethylation and activate the β2AR/PI3K/Akt pathway, resulted in PM_2.5-induced cardiomyocytes apoptosis and cardiac dysfunction. Our study suggested that the ADRB2 demethylation or ADRB2/β2AR activation may serve as a potential pathway to prevent cardiac dysfunction induced by PM_2.5 exposure.

384-Channel electrochemical sensor array chips based on hybridization-triggered switching for simultaneous oligonucleotide detection

We investigated the feasibility of simultaneous detection of multiple environmentally- and biomedically-relevant RNA biomarker target sequences on a single newly fabricated 384-ch sensor array chip aiming at practical application. The individual sensor is composed of a photolithographically-fabricated Au/Cr-based electrode modified with peptide nucleic acid (PNA) probes. The sensor array chips showed sequence-specific responses upon hybridization of the probes with target sequences complementary to the probes in contrast to mismatch versions. The target oligonucleotides have 15-22 mer sequences from messenger RNAs for estrogen-responsive genes and microRNAs for lung cancer biomarkers. The dependence on target concentrations of sensor responses was observed by using a single chip on which experiments for detection of several target concentrations proceeded simultaneously, with the detection limit of 7.33 × 10^-8 M. As more realistic samples, oligonucleotide samples amplified by PCR from a synthesized template sequence were applied to the chip. They showed sequence-specific responses, revealing the potential for fabricated sensor array chips to be utilized to analyze PCR samples. Unlike complicated and expensive chips that require nanofabrication, our sensor array chips based on glass coated with gold thin films are simple and can be fabricated from inexpensive and readily available materials.

DNA methylation: A critical epigenetic mechanism underlying the detrimental effects of airborne particulate matter

Exposure to airborne particulate matter (PM) does great harm to the health of human beings. To date, PM exposure has been closely associated with respiratory and cardiovascular diseases, as well as some types of cancer. As the associations of PM with the adverse health effects are well documented in literatures, the underlying mechanisms have not been completely clarified. With the field of epigenetics rising in recent years, PM-associated epigenetic alterations have gradually turned into the hot research topic. DNA methylation is one of the earliest-discovered and best-studied epigenetic mechanisms, of which the alteration can influence the transcription initiation of genes. A number of studies have been published to demonstrate that PM exposure is linked with DNA methylation patterns in the human genome. DNA methylation is the potential regulator of the biological effects of PM exposure. In the present review, DNA methylation related to PM exposure was elaborated on genome-wide and gene-specific methylation. In particular, genome-wide DNA methylation was composed of the alterations in global methylation content and genome-wide methylation profile; gene-specific methylation included the methylation changes in mechanism-related and disease-specific genes. Representative epidemiological and experimental studies were cited to elucidate the viewpoints, focusing on both PM-related methylation changes and the mediating effects of DNA methylation between PM and the health impacts. This review will provide advantageous clues for subsequent studies on the DNA methylation in relation to PM exposure.

Variation in doses and duration of particulate matter exposure in bronchial epithelial cells results in upregulation of different genes associated with airway disorders

Exposure to particulate matter < 2.5 μm (PM2.5) is associated with a variety of airway diseases. Although studies have demonstrated that high doses of PM2.5 cause cytotoxicity and changes to gene expression in bronchial epithelial cells, the effect of lower doses and repeated exposure to PM2.5 are less well studied. Here, we treated BEAS-2B cells with varying doses of PM2.5 for 1-7 days and examined the expression of a variety of genes implicated in airway disorders. At high doses, PM2.5 increased the expression of IL6, TNF, TSLP, CSF2, PTGS2, IL4R, and SPINK5. Other genes such as ADAM33, ORMDL3, DPP10 and CYP1A1, however, were increased by PM2.5 at much lower doses (≤1 μg/cm2). Repeated exposure to PM2.5 at 1 or 5 μg/cm2 every day for 7 days increased the sensitivity and magnitude of change for all of the aforementioned genes. Genes such as IL13 and TGFB1, increased only when cells were repeatedly exposed to PM2.5. Treatment with an antioxidant, or inhibitors to aryl hydrocarbon receptor or NF-κB attenuated the effect of PM2.5. These data demonstrate that PM2.5 exerts pleiotropic actions that differ by dose and duration that affect a variety of genes important to the development of airway disease.

Transcriptional profiling of human bronchial epithelial cell BEAS-2B exposed to diesel and biomass ultrafine particles

BACKGROUND

Emissions from diesel vehicles and biomass burning are the principal sources of primary ultrafine particles (UFP). The exposure to UFP has been associated to cardiovascular and pulmonary diseases, including lung cancer. Although many aspects of the toxicology of ambient particulate matter (PM) have been unraveled, the molecular mechanisms activated in human cells by the exposure to UFP are still poorly understood. Here, we present an RNA-seq time-course experiment (five time point after single dose exposure) used to investigate the differential and temporal changes induced in the gene expression of human bronchial epithelial cells (BEAS-2B) by the exposure to UFP generated from diesel and biomass combustion. A combination of different bioinformatics tools (EdgeR, next-maSigPro and reactome FI app-Cytoscape and prioritization strategies) facilitated the analyses the temporal transcriptional pattern, functional gene set enrichment and gene networks related to cellular response to UFP particles.

RESULTS

The bioinformatics analysis of transcriptional data reveals that the two different UFP induce, since the earliest time points, different transcriptional dynamics resulting in the activation of specific genes. The functional enrichment of differentially expressed genes indicates that the exposure to diesel UFP induces the activation of genes involved in TNFα signaling via NF-kB and inflammatory response, and hypoxia. Conversely, the exposure to ultrafine particles from biomass determines less distinct modifications of the gene expression profiles. Diesel UFP exposure induces the secretion of biomarkers associated to inflammation (CCXL2, EPGN, GREM1, IL1A, IL1B, IL6, IL24, EREG, VEGF) and transcription factors (as NFE2L2, MAFF, HES1, FOSL1, TGIF1) relevant for cardiovascular and lung disease. By means of network reconstruction, four genes (STAT3, HIF1a, NFKB1, KRAS) have emerged as major regulators of transcriptional response of bronchial epithelial cells exposed to diesel exhaust.

CONCLUSIONS

Overall, this work highlights modifications of the transcriptional landscape in human bronchial cells exposed to UFP and sheds new lights on possible mechanisms by means of which UFP acts as a carcinogen and harmful factor for human health.

Regulation of TLR4 in silica-induced inflammation: An underlying mechanism of silicosis

Silicosis is an incurable lung disease affecting millions of workers in hazardous occupations. It is caused by chronic exposure to the dust that contains free crystalline silica. Silica-induced lung damage occurs by several main mechanisms including cell death by apoptosis, fibrosis and production of cytokines. However, the signal pathways involved in these mechanisms are not fully characterized. In this study, the toll-like receptor 4 (TLR4)-related signal pathway was examined in silica-treated U937-differentiated macrophages. The expression level of TLR4 was measured by both quantitative PCR and Western blot. Confirmation of the involvement of MyD88/TIRAP and NFκB p65 cascade was performed by Western blot. The secretion of cytokines IL-1β, IL-6, IL-10 and TNFα was measured by enzyme-linked immunosorbent assay. Our results showed that TLR4 and related MyD88/TIRAP pathway was associated with silica-exposure in U937-differentiated macrophages. Protein expression of TLR4, MyD88 and TIRAP was upregulated when the U937-differentiated macrophages were exposed to silica. However, the upregulation was attenuated when TLR4 inhibitor, TAK-242 was present. At different incubation times of silica exposure, it was found that NFκB p65 cascade was activated at 10-60 minutes. Release of cytokines IL-1β, IL-6, IL-10 and TNFα was induced by silica exposure and the induction of IL-1β, IL-6 and TNFα was suppressed by the addition of TAK-242. In conclusion, our study demonstrated that TLR4 and related MyD88/TIRAP pathway was involved in silica-induced inflammation in U937-differentiated macrophages. Downstream NFκB p65 cascade was activated within 1 hour when the U937-differentiated macrophages were exposed to silica. The better understanding of early stage of silica-induced inflammatory process may help to develop earlier diagnosis of silicosis.

Identification of RNA biomarkers for chemical safety screening in mouse embryonic stem cells using RNA deep sequencing analysis

Although it is not yet possible to replace in vivo animal testing completely, the need for a more efficient method for toxicity testing, such as an in vitro cell-based assay, has been widely acknowledged. Previous studies have focused on mRNAs as biomarkers; however, recent studies have revealed that non-coding RNAs (ncRNAs) are also efficient novel biomarkers for toxicity testing. Here, we used deep sequencing analysis (RNA-seq) to identify novel RNA biomarkers, including ncRNAs, that exhibited a substantial response to general chemical toxicity from nine chemicals, and to benzene toxicity specifically. The nine chemicals are listed in the Japan Pollutant Release and Transfer Register as class I designated chemical substances. We used undifferentiated mouse embryonic stem cells (mESCs) as a simplified cell-based toxicity assay. RNA-seq revealed that many mRNAs and ncRNAs responded substantially to the chemical compounds in mESCs. This finding indicates that ncRNAs can be used as novel RNA biomarkers for chemical safety screening.

Pulmonary toxicity and global gene expression changes in response to sub-chronic inhalation exposure to crystalline silica in rats

Exposure to crystalline silica results in serious adverse health effects, most notably, silicosis. An understanding of the mechanism(s) underlying silica-induced pulmonary toxicity is critical for the intervention and/or prevention of its adverse health effects. Rats were exposed by inhalation to crystalline silica at a concentration of 15 mg/m³, 6 hr/day, 5 days/week for 3, 6 or 12 weeks. Pulmonary toxicity and global gene expression profiles were determined in lungs at the end of each exposure period. Crystalline silica was visible in lungs of rats especially in the 12-week group. Pulmonary toxicity, as evidenced by an increase in lactate dehydrogenase (LDH) activity and albumin content and accumulation of macrophages and neutrophils in the bronchoalveolar lavage (BAL), was seen in animals depending upon silica exposure duration. The most severe histological changes, noted in the 12-week exposure group, consisted of chronic active inflammation, type II pneumocyte hyperplasia, and fibrosis. Microarray analysis of lung gene expression profiles detected significant differential expression of 38, 77, and 99 genes in rats exposed to silica for 3-, 6-, or 12-weeks, respectively, compared to time-matched controls. Among the significantly differentially expressed genes (SDEG), 32 genes were common in all exposure groups. Bioinformatics analysis of the SDEG identified enrichment of functions, networks and canonical pathways related to inflammation, cancer, oxidative stress, fibrosis, and tissue remodeling in response to silica exposure. Collectively, these results provided insights into the molecular mechanisms underlying pulmonary toxicity following sub-chronic inhalation exposure to crystalline silica in rats.

Exposure to airborne PM2.5 suppresses microRNA expression and deregulates target oncogenes that cause neoplastic transformation in NIH3T3 cells

Long-term exposure to airborne PM_2.5 is associated with increased lung cancer risk but the underlying mechanism remains unclear. We characterized global microRNA and mRNA expression in human bronchial epithelial cells exposed to PM_2.5 organic extract and integrally analyzed microRNA-mRNA interactions. Foci formation and xenograft tumorigenesis in mice with NIH3T3 cells expressing genes targeted by microRNAs were performed to explore the oncogenic potential of these genes. We also detected plasma levels of candidate microRNAs in subjects exposed to different levels of air PM_2.5 and examined the aberrant expression of genes targeted by these microRNAs in human lung cancer. Under our experimental conditions, treatment of cells with PM_2.5 extract resulted in downregulation of 138 microRNAs and aberrant expression of 13 mRNAs (11 upregulation and 2 downregulation). In silico and biochemical analyses suggested SLC30A1, SERPINB2 and AKR1C1, among the upregulated genes, as target for miR-182 and miR-185, respectively. Ectopic expression of each of these genes significantly enhanced foci formation in NIH3T3 cells. Following subcutaneous injection of these cells into nude mice, fibrosarcoma were formed from SLC30A1- or SERPINB2-expressing cells. Reduced plasma levels of miR-182 were detected in subjects exposed to high level of PM_2.5 than in those exposed to low level of PM_2.5 (P = 0.043). Similar results were seen for miR-185 although the difference was not statistically significant (P = 0.328). Increased expressions of SLC30A1, SERPINB2 and AKR1C1 were detected in human lung cancer. These results suggest that modulation of miR-182 and miR-185 and their target genes may contribute to lung carcinogenesis attributable to PM_2.5 exposure.

Integrative transcriptomic and protein analysis of human bronchial BEAS-2B exposed to seasonal urban particulate matter

BACKGROUND

Exposure to particulate matter (PM) is associated with various health effects. Physico-chemical properties influence the toxicological impact of PM, nonetheless the mechanisms underlying PM-induced effects are not completely understood.

OBJECTIVES

Human bronchial epithelial cells were used to analyse the pathways activated after exposure to summer and winter urban PM and to identify possible markers of exposure.

METHODS

BEAS-2B cells were exposed for 24 h to 10 μg/cm(2) of winter PM2.5 (wPM) and summer PM10 (sPM) sampled in Milan. A microarray technology was used to profile the cells gene expression. Genes and microRNAs were analyzed by bioinformatics technique to identify pathways involved in cellular responses. Selected genes and pathways were validated at protein level (western blot, membrane protein arrays and ELISA).

RESULTS

The molecular networks activated by the two PM evidenced a correlation among oxidative stress, inflammation and DNA damage responses. sPM induced the release of pro-inflammatory mediators, although miR-146a and genes related to inflammation resulted up-regulated by both PM. Moreover both PM affected a set of genes, proteins and miRNAs related to antioxidant responses, cancer development, extracellular matrix remodeling and cytoskeleton organization, while miR-29c, implicated in epigenetic modification, resulted up-regulated only by wPM. sPM effects may be related to biological and inorganic components, while wPM apparently related to the high content of organic compounds.

CONCLUSIONS

These results may be helpful for the individuation of biomarkers for PM exposure, linked to the specific PM physico-chemical properties.

Mechanism-Based Classification of PAH Mixtures to Predict Carcinogenic Potential

We have previously shown that relative potency factors and DNA adduct measurements are inadequate for predicting carcinogenicity of certain polycyclic aromatic hydrocarbons (PAHs) and PAH mixtures, particularly those that function through alternate pathways or exhibit greater promotional activity compared to benzo[a]pyrene (BaP). Therefore, we developed a pathway-based approach for classification of tumor outcome after dermal exposure to PAH/mixtures. FVB/N mice were exposed to dibenzo[def,p]chrysene (DBC), BaP, or environmental PAH mixtures (Mix 1-3) following a 2-stage initiation/promotion skin tumor protocol. Resulting tumor incidence could be categorized by carcinogenic potency as DBC >> BaP = Mix2 = Mix3 > Mix1 = Control, based on statistical significance. Gene expression profiles measured in skin of mice collected 12 h post-initiation were compared with tumor outcome for identification of short-term bioactivity profiles. A Bayesian integration model was utilized to identify biological pathways predictive of PAH carcinogenic potential during initiation. Integration of probability matrices from four enriched pathways (P < .05) for DNA damage, apoptosis, response to chemical stimulus, and interferon gamma signaling resulted in the highest classification accuracy with leave-one-out cross validation. This pathway-driven approach was successfully utilized to distinguish early regulatory events during initiation prognostic for tumor outcome and provides proof-of-concept for using short-term initiation studies to classify carcinogenic potential of environmental PAH mixtures. These data further provide a 'source-to-outcome' model that could be used to predict PAH interactions during tumorigenesis and provide an example of how mode-of-action-based risk assessment could be employed for environmental PAH mixtures.

In Vivo Exposures to Particulate Matter Collected from Saudi Arabia or Nickel Chloride Display Similar Dysregulation of Metabolic Syndrome Genes

Particulate matter (PM) exposures have been linked to mortality, low birth weights, hospital admissions, and diseases associated with metabolic syndrome, including diabetes mellitus, cardiovascular disease, and obesity. In a previous in vitro and in vivo study, data demonstrated that PM(10μm) collected from Jeddah, Saudi Arabia (PMSA), altered expression of genes involved in lipid and cholesterol metabolism, as well as many other genes associated with metabolic disorders. PMSA contains a relatively high concentration of nickel (Ni), known to be linked to several metabolic disorders. In order to evaluate whether Ni and PM exposures induce similar gene expression profiles, mice were exposed to 100 μg/50 μl PM(SA) (PM-100), 50 μg/50 μl nickel chloride (Ni-50), or 100 μg/50 μl nickel chloride (Ni-100) twice per week for 4 wk and hepatic gene expression changes were determined. Ultimately, 55 of the same genes were altered in all 3 exposures. However, where the two Ni groups differed markedly was in the regulation (up or down) of these genes. Ni-100 and PM-100 groups displayed similar regulations, whereby 104 of the 107 genes were similarly modulated. Many of the 107 genes are involved in metabolic syndrome and include ALDH4A1, BCO2, CYP1A, CYP2U, TOP2A. In addition, the top affected pathways, such as fatty acid α-oxidation, and lipid and carbohydrate metabolism, are involved in metabolic diseases. Most notably, the top diseased outcome affected by these changes in gene expression was cardiovascular disease. Given these data, it appears that Ni and PM(SA) exposures display similar gene expression profiles, modulating the expression of genes involved in metabolic disorders.

Gene expression changes consistent with neuroAIDS and impaired working memory in HIV-1 transgenic rats

BACKGROUND

A thorough investigation of the neurobiology of HIV-induced neuronal dysfunction and its evolving phenotype in the setting of viral suppression has been limited by the lack of validated small animal models to probe the effects of concomitant low level expression of multiple HIV-1 products in disease-relevant cells in the CNS.

RESULTS

We report the results of gene expression profiling of the hippocampus of HIV-1 Tg rats, a rodent model of HIV infection in which multiple HIV-1 proteins are expressed under the control of the viral LTR promoter in disease-relevant cells including microglia and astrocytes. The Gene Set Enrichment Analysis (GSEA) algorithm was used for pathway analysis. Gene expression changes observed are consistent with astrogliosis and microgliosis and include evidence of inflammation and cell proliferation. Among the genes with increased expression in HIV-1 Tg rats was the interferon stimulated gene 15 (ISG-15), which was previously shown to be increased in the cerebrospinal fluid (CSF) of HIV patients and to correlate with neuropsychological impairment and neuropathology, and prostaglandin D2 (PGD2) synthase (Ptgds), which has been associated with immune activation and the induction of astrogliosis and microgliosis. GSEA-based pathway analysis highlighted a broad dysregulation of genes involved in neuronal trophism and neurodegenerative disorders. Among the latter are genesets associated with Huntington's disease, Parkinson's disease, mitochondrial, peroxisome function, and synaptic trophism and plasticity, such as IGF, ErbB and netrin signaling and the PI3K signal transduction pathway, a mediator of neural plasticity and of a vast array of trophic signals. Additionally, gene expression analyses also show altered lipid metabolism and peroxisomes dysfunction. Supporting the functional significance of these gene expression alterations, HIV-1 Tg rats showed working memory impairments in spontaneous alternation behavior in the T-Maze, a paradigm sensitive to prefrontal cortex and hippocampal function.

CONCLUSIONS

Altogether, differentially regulated genes and pathway analysis identify specific pathways that can be targeted therapeutically to increase trophic support, e.g. IGF, ErbB and netrin signaling, and reduce neuroinflammation, e.g. PGD2 synthesis, which may be beneficial in the treatment of chronic forms of HIV-associated neurocognitive disorders in the setting of viral suppression.

Interactions between polycyclic aromatic hydrocarbons in complex mixtures and implications for cancer risk assessment

In this review we discuss the effects of exposure to complex PAH mixtures in vitro and in vivo on mechanisms related to carcinogenesis. Of particular concern regarding exposure to complex PAH mixtures is how interactions between different constituents can affect the carcinogenic response and how these might be included in risk assessment. Overall the findings suggest that the responses resulting from exposure to complex PAH mixtures is varied and complicated. More- and less-than additive effects on bioactivation and DNA damage formation have been observed depending on the various mixtures studied, and equally dependent on the different test systems that are used. Furthermore, the findings show that the commonly used biological end-point of DNA damage formation is insufficient for studying mixture effects. At present the assessment of the risk of exposure to complex PAH mixtures involves comparison to individual compounds using either a surrogate or a component-based potency approach. We discuss how future risk assessment strategies for complex PAH mixtures should be based around whole mixture assessment in order to account for interaction effects. Inherent to this is the need to incorporate different experimental approaches using robust and sensitive biological endpoints. Furthermore, the emphasis on future research should be placed on studying real life mixtures that better represent the complex PAH mixtures that humans are exposed to.