Faculty Bibliography

BACKGROUND: Occupational exposure to nickel (Ni) is associated with an increased risk of lung and nasal cancers. Ni compounds exhibit weak mutagenic activity, alter the cell's epigenetic homeostasis, and activate signaling pathways. However, changes in gene expression associated with Ni exposure have only been investigated in vitro. This study was conducted in a Chinese population to determine whether occupational exposure to Ni was associated with differential gene expression profiles in the peripheral blood mononuclear cells (PBMC) of Ni-refinery workers when compared with referents. METHODS: Eight Ni-refinery workers and ten referents were selected. PBMC RNA was extracted and gene expression profiling was conducted using Affymetrix exon arrays. Differentially expressed genes (DEG) between both groups were identified in a global analysis. RESULTS: There were a total of 2,756 DEGs in the Ni-refinery workers relative to the referents [false discovery rate (FDR) adjusted P < 0.05] with 770 upregulated genes and 1,986 downregulated genes. DNA repair and epigenetic genes were significantly overrepresented (P < 0.0002) among the DEGs. Of 31 DNA repair genes, 29 were repressed in the Ni-refinery workers and 2 were overexpressed. Of the 16 epigenetic genes, 12 were repressed in the Ni-refinery workers and 4 were overexpressed. CONCLUSIONS: The results of this study indicate that occupational exposure to Ni is associated with alterations in gene expression profiles in PBMCs of subjects. Impact: Gene expression may be useful in identifying patterns of deregulation that precede clinical identification of Ni-induced cancers. Cancer Epidemiol Biomarkers Prev; 22(2); 261-9. (c)2012 AACR.

Epidemiological studies have established a positive correlation between human mortality and increased concentration of airborne particulate matters (PM). However, the mechanisms underlying PM related human diseases, as well as the molecules and pathways mediating the cellular response to PM, are not fully understood. This study aims to investigate the global gene expression changes in human cells exposed to PM(10) and to identify genes and pathways that may contribute to PM related adverse health effects. Human bronchial epithelial cells were exposed to PM(10) collected from Saudi Arabia for 1 or 4days, and whole transcript expression was profiled using the GeneChip human gene 1.0 ST array. A total of 140 and 230 genes were identified that significantly changed more than 1.5 fold after PM(10) exposure for 1 or 4days, respectively. Ingenuity Pathway Analysis revealed that different exposure durations triggered distinct pathways. Genes involved in NRF2-mediated response to oxidative stress were up-regulated after 1day exposure. In contrast, cells exposed for 4days exhibited significant changes in genes related to cholesterol and lipid synthesis pathways. These observed changes in cellular oxidative stress and lipid synthesis might contribute to PM related respiratory and cardiovascular disease.

BACKGROUND: Exposure to arsenic (As) is associated with an increased risk of several cancers as well as cardiovascular disease, and childhood neuro-developmental deficits. Arsenic compounds are weakly mutagenic, alter gene expression and posttranslational histone modifications (PTHMs) in vitro. METHODS: Water and urinary As concentrations as well as global levels of histone 3 lysine 9 di-methylation and acetylation (H3K9me2 and H3K9ac), histone 3 lysine 27 tri-methylation and acetylation (H3K27me3 and H3K27ac), histone 3 lysine 18 acetylation (H3K18ac), and histone 3 lysine 4 trimethylation (H3K4me3) were measured in peripheral blood mononuclear cells (PBMC) from a subset of participants (N = 40) of a folate clinical trial in Bangladesh (FACT study). RESULTS: Total urinary As (uAs) was positively correlated with H3K9me2 (r = 0.36, P = 0.02) and inversely with H3K9ac (r = -0.47, P = 0.002). The associations between As and other PTHMs differed in a gender-dependent manner. Water As (wAs) was positively correlated with H3K4me3 (r = 0.45, P = 0.05) and H3K27me3 (r = 0.50, P = 0.03) among females and negatively correlated among males (H3K4me3: r = -0.44, P = 0.05; H3K27me3: r = -0.34, P = 0.14). Conversely, wAs was inversely associated with H3K27ac among females (r = -0.44, P = 0.05) and positively associated among males (r = 0.29, P = 0.21). A similar pattern was observed for H3K18ac (females: r = -0.22, P = 0.36; males: r = 0.27, P = 0.24). CONCLUSION: Exposure to As is associated with alterations of global PTHMs; gender-specific patterns of association were observed between As exposure and several histone marks. Impact: These findings contribute to the growing body of evidence linking As exposure to epigenetic dysregulation, which may play a role in the pathogenesis of As toxicity. Cancer Epidemiol Biomarkers Prev; 21(12); 2252-60. (c)2012 AACR.

The complex process of carcinogenesis begins with transformation of a single cell to favor aberrant traits such as loss of contact inhibition and unregulated proliferation - features found in every cancer. Despite cancer's widespread prevalence, the early events that initiate cancer remain elusive, and without knowledge of these events cancer prevention is difficult. Here we show that exposure to As, Cr, Ni, or vanadium (V) promotes changes in gene expression that occur in conjunction with aberrant growth. We exposed immortalized human bronchial epithelial cells to one of four metals/metalloid for four to eight weeks and selected transformed clonal populations based upon anchorage independent growth of single cells in soft agar. We detected a metal-specific footprint of cancer-related gene expression that was consistent across multiple transformed clones. These gene expression changes persisted in the absence of the progenitor metal for numerous cell divisions. Our results show that even a brief exposure to a carcinogenic metal may cause many changes in gene expression in the exposed cells, and that from these many changes, the specific change(s) that each metal causes that initiate cancer likely arise.

This paper presents the first comprehensive investigation of PM2.5 and PM10 composition and sources in Saudi Arabia. We conducted a multi-week multiple sites sampling campaign in Jeddah between June and September, 2011, and analyzed samples by XRF. The overall mean mass concentration was 28.4 ± 25.4 μg/m³ for PM2.5 and 87.3 ± 47.3 μg/m³ for PM10, with significant temporal and spatial variability. The average ratio of PM2.5/PM10 was 0.33. Chemical composition data were modeled using factor analysis with varimax orthogonal rotation to determine five and four particle source categories contributing significant amount of for PM2.5 and PM10 mass, respectively. In both PM2.5 and PM10 sources were (1) heavy oil combustion characterized by high Ni and V; (2) resuspended soil characterized by high concentrations of Ca, Fe, Al, and Si; and (3) marine aerosol. The two other sources in PM2.5 were (4) Cu/Zn source; (5) traffic source identified by presence of Pb, Br, and Se; while in PM10 it was a mixed industrial source. To estimate the mass contributions of each individual source category, the CAPs mass concentration was regressed against the factor scores. Cumulatively, resuspended soil and oil combustion contributed 77 and 82% mass of PM2.5 and PM10, respectively.

The precise mechanisms by which nickel and arsenic compounds exert their carcinogenic properties are not completely understood. In recent years, alterations of epigenetic mechanisms have been implicated in the carcinogenesis of compounds of these two metals. In vitro exposure to certain nickel or arsenic compounds induces changes in both DNA methylation patterns, as well as, in the levels of posttranslational modifications of histone tails. Changes in DNA methylation patterns have been reported in human subjects exposed to arsenic. Here we review our recent reports on the alterations in global levels of posttranslational histone modifications in peripheral blood mononuclear cells (PBMCs) of subjects with occupational exposure to nickel and subjects exposed to arsenic in their drinking water. Occupational exposure to nickel was associated with an increase in H3K4me3 and decrease in H3K9me2. A global increase in H3K9me2 and decrease in H3K9ac was found in subjects exposed to arsenic. Additionally, exposure to arsenic resulted in opposite changes in a number of histone modifications in males when compared with females in the arsenic population. The results of these two studies suggest that exposure to nickel or arsenic compounds, and possibly other carcinogenic metal compounds, can induce changes in global levels of posttranslational histone modifications in peripheral blood mononuclear cells.

Background: Occupational exposure to nickel is associated with an increased risk for lung and nasal cancers. Nickel compounds exhibit weak mutagenic activity, cause gene amplification, and disrupt cellular epigenetic homeostasis. However, the nickel-induced changes in global histone modification levels have only been tested in vitro. Objective: This study was conducted in a Chinese population to determine whether occupational exposure to nickel is associated with alterations of global histone modification levels and to evaluate the inter-and intra-individual variance of global histone modification levels. Method: 45 subjects with occupational exposure to nickel and 75 referents were recruited. Urinary nickel and global H3K4 trimethylation (H3K4me3), H3K9 acetylation (H3K9ac), and H3K9 dimethylation (H3K9me2) levels were measured in peripheral blood mononuclear cells (PBMCs) of subjects. Results: H3K4me3 was elevated (0.25%+/-0.11%, 0.15%+/-0.04%, p=0.0004) and H3K9me2 was decreased (0.11%+/-0.05%, 0.15%+/-0.04%, p=0.003) in Ni-exposed subjects. H3K4me3 was positively (r=0.4, p=0.0008) and H3K9ac was negatively (r=0.1, p=0.01) associated with urinary nickel. Inter-individual variances of H3K4me3, H3K9ac, and H3K9me2 were larger relative to intra-individual variance in both groups, resulting in reliability coefficients, estimate of consistency of a set of measurements, of 0.75, 0.74, and 0.97 for H3K4me3, H3K9ac, and H3K9me2, respectively, for referent subjects. Reliability coefficients of 0.60, 0.67, and 0.79 were found for H3K4me3, H3K9ac, and H3K9me2, respectively, for Ni-exposed subjects. Conclusion: The results of this study indicate that occupational exposure to nickel is associated with alterations of global histone modification levels and that measurements of global levels of histone modifications are relatively stable over time in human PBMCs

Hexavalent chromium [Cr(VI)] is a human carcinogen that results in the generation of reactive oxygen species (ROS) and a variety of DNA lesions leading to cell death. Epigallocatechin-3-gallate (EGCG), the major polyphenol present in green tea, possesses potent antioxidative activity capable of protecting normal cells from various stimuli-induced oxidative stress and cell death. Here we demonstrated that co-treatment with EGCG protected human normal bronchial epithelial BEAS-2B cells from Cr(VI)-induced cell death in a dose-dependent manner. Cr(VI) induces apoptosis as the primary mode of cell death. Co-treatment of BEAS-2B cells with EGCG dose-dependently suppressed Cr(VI)-induced apoptosis. Fluorescence microscopic analyses and quantitative measurement revealed that EGCG significantly decreased intracellular levels of ROS induced by Cr(VI) exposure. Using a well-established K(+)/SDS precipitation assay, we further showed that EGCG was able to dose-dependently reduce DNA-protein cross-links (DPC), lesions that could be partially attributed to Cr(VI)-induced oxidative stress. Finally, analyses of Affymetrix microarray containing 28,869 well-annotated genes revealed that, among the 3412 genes changed more than 1.5-fold by Cr(VI) treatment, changes of 2404 genes (70%) were inhibited by pretreatment of EGCG. Real-time PCR confirmed the induction of 3 genes involved in cell death and apoptosis by Cr(VI), which was eliminated by EGCG. In contrast, Cr(VI) reduced the expression of 3 genes related to cellular defense, and this reduction was inhibited by EGCG. Our results indicate that EGCG protects BEAS-2B cells from Cr(VI)-induced cytotoxicity presumably by scavenging ROS and modulating a subset of genes. EGCG, therefore, might serve as a potential chemopreventive agent against Cr(VI) carcinogenesis

Mesenchymal stromal cells (MSC) have attracted the attention of scientists and clinicians due to their self-renewal, capacity for multipotent differentiation, and immunomodulatory properties. Some essential problems remain to be solved before the clinical application of MSC. Platelet lysate (PL) has recently been used as a substitute for FBS in MSC amplification in vitro to achieve clinically applicable numbers of MSC. In addition to promising trials in regenerative medicine, such as in the treatment of major bone defects and myocardial infarction, MSC have shown therapeutic effect other than direct hematopoiesis support in hematopoietic reconstruction. It has been confirmed that MSC promote hematopoietic cell engraftment and immune recovery after allogeneic hematopoietic stem cell transplantation, probably through the provision of cytokines, matrix proteins, and cell-to-cell contacts. Their suppressive effects on immune cells, including T cells, B cells, NK cells and DC cells, suggest MSCs as a novel therapy for GVHD and other autoimmune disorders. These cells thus present as promising candidates for cellular therapy in the fields of regenerative medicine, allogeneic hematopoietic stem cell transplantation, and autoimmune disorders

BACKGROUND: Hexavalent chromium [Cr(VI)] is a potent human carcinogen. Occupational exposure has been associated with increased risk of respiratory cancer. Multiple mechanisms have been shown to contribute to Cr(VI) induced carcinogenesis, including DNA damage, genomic instability, and epigenetic modulation, however, the molecular mechanism and downstream genes mediating chromium's carcinogenicity remain to be elucidated. METHODS/RESULTS: We established chromate transformed cell lines by chronic exposure of normal human bronchial epithelial BEAS-2B cells to low doses of Cr(VI) followed by anchorage-independent growth. These transformed cell lines not only exhibited consistent morphological changes but also acquired altered and distinct gene expression patterns compared with normal BEAS-2B cells and control cell lines (untreated) that arose spontaneously in soft agar. Interestingly, the gene expression profiles of six Cr(VI) transformed cell lines were remarkably similar to each other yet differed significantly from that of either control cell lines or normal BEAS-2B cells. A total of 409 differentially expressed genes were identified in Cr(VI) transformed cells compared to control cells. Genes related to cell-to-cell junction were upregulated in all Cr(VI) transformed cells, while genes associated with the interaction between cells and their extracellular matrices were down-regulated. Additionally, expression of genes involved in cell proliferation and apoptosis were also changed. CONCLUSION: This study is the first to report gene expression profiling of Cr(VI) transformed cells. The gene expression changes across individual chromate exposed clones were remarkably similar to each other but differed significantly from the gene expression found in anchorage-independent clones that arose spontaneously. Our analysis identified many novel gene expression changes that may contribute to chromate induced cell transformation, and collectively this type of information will provide a better understanding of the mechanism underlying chromate carcinogenicity