Social barriers to safe sanitation access among housed populations in the United States: A systematic review.

BACKGROUND: Nearly six million people residing in the United States do not have access to safely managed sanitation. Housed populations may lack access to centralized wastewater treatment systems or functioning onsite wastewater treatment systems, which subsequently places them at higher risk for adverse health outcomes associated with unsafe sanitation. OBJECTIVES: We sought to understand the various social barriers that impact access to safe sanitation in the United States. METHODS: We included peer-reviewed studies published between January 2000 and March 2023. The publication search was conducted using Scopus, ProQuest Social Science Database, and HeinOnline. We extracted data on social barriers and physical factors associated with access to sanitation. RESULTS: Twenty publications met the inclusion criteria, and data relating to 11 social barriers and two physical factors were extracted. The social barriers to safe sanitation access mentioned most frequently were found to be socioeconomic status and race-based discrimination. Studies discussed sanitation in communities in five states. DISCUSSION: Barriers pertained to lack of access to centralized wastewater treatment system, inadequate repair or replacement of septic systems, and lack of safely managed onsite sanitation systems. We discuss the intersectionality of the barriers, the underlying policy and history that leads to them, and make recommendations to address inequitable access to safe sanitation. Legislation and policy must be critically reviewed at national, state, and local levels to limit or eliminate ability for utilities to be extended on the basis of a community's income and property values or racial makeup. Policy recommendations also include additional community engagement, onsite sanitation system monitoring, and knowledge dissemination and education of septic system users. More geographically diverse research and research on sanitation in specific communities such as those of migrant farmworkers, undocumented persons, and tenants are recommended.

Presence of Perfluoroalkyl Substances in Landfill Adjacent Surface Waters in North Carolina.

Landfills pose an important public health risk, especially in historically disenfranchised communities that are disproportionately sited for landfills and in rural areas where private wells may be impacted. Landfills are major sources of perfluoroalkyl substances (PFAS) that migrate into the surrounding environment. This study characterized PFAS in surface waters adjacent to two landfills, one in Sampson County (SC) and one in Orange County (OC) in North Carolina. In addition to municipal solid waste and construction and demolition waste, the landfill in SC accepts industrial sludge from a chemical plant that produces proprietary PFAS. Over four months, 35 surface water samples were collected at upstream, landfill-adjacent, and downstream/downgradient sites. Thirty-four PFAS were analyzed using liquid chromatography with tandem mass spectroscopy. Of those, six novel and six legacy PFAS were detected. Legacy PFAS were detected in surface water near both landfills, with the highest concentrations adjacent to the landfill. Novel PFAS were only detected in surface water near the SC landfill and showed the highest concentrations adjacent to the landfill, indicating offsite migration of PFAS. These findings support the need for more comprehensive and frequent monitoring of groundwater and surface water wells near landfills and stricter regulation regarding the landfilling of industrial materials.

Photovoice Reveals Residents' Concerns for Air and Water Quality in Industry-Impacted Rural Community.

Rural communities of color in the southeastern U.S. experience a high burden of environmental hazards from concentrated industry placement. Community-engaged research and qualitative methods can improve our understanding of meaning-making in a community impacted by polluting facilities. This study applies the photovoice method to assess how a predominantly African American community in rural North Carolina, impacted by a landfill and confined animal feeding operations (CAFOs), perceives their health-related quality of life (HRQoL). Two research questions were developed with community-based partners: (a) How do environmental health concerns in this community influence residents' perceptions of their HRQoL? and (b) How do community and county factors facilitate or inhibit community organizing around these concerns? Three photo assignment sessions were held to engage participants in discussions related to the research questions. Researchers analyzed discussion audio recordings and identified themes related to concerns about the following issues: health and quality of life, the landfill industry's influence on community cohesion and self-determination, and actions to address environmental injustice in Sampson County. Photovoice benefits community-engaged researchers by providing a process for assessing the research interests of a community. Photovoice also serves community organizers by providing residents with a structured way to discuss their lived experiences and strategize ways to reduce hazard exposure.

Sulfur dioxide reduction at coal-fired power plants in North Carolina and associations with preterm birth among surrounding residents.

Coal-fired power plants (CFPP) are major contributors of air pollution, including the majority of anthropogenic sulfur dioxide (SO2) emissions, which have been associated with preterm birth (PTB). To address a 2002 North Carolina (NC) policy, 14 of the largest NC CFPPs either installed desulfurization equipment (scrubbers) or retired coal units, resulting in substantial reductions of SO2 air emissions. We investigated whether SO2 air emission reduction strategies at CFPPs in NC were associated with changes in prevalence of PTB in nearby communities. Methods: We used US EPA Air Markets Program Data to track SO2 emissions and determine the implementation dates of intervention at CFPPs and geocoded 2003-2015 NC singleton live births. We conducted a difference-in-difference analysis to estimate change in PTB associated with change in SO2 reduction strategies for populations living 0-<4 and 4-<10 miles from CFPPs pre- and postintervention, with a comparison of those living 10-<15 miles from CFPPs. Results: With the spatial-temporal exposure restrictions applied, 42,231 and 41,218 births were within 15 miles of CFPP-scrubbers and CFPP-retired groups, respectively. For residents within 4-<10 miles from a CFPP, we estimated that the absolute prevalence of PTB decreased by -1.5% [95% confidence interval (CI): -2.6, -0.4] associated with scrubber installation and -0.5% (95% CI: -1.6, 0.6) associated with the retirement of coal units at CFPPs. Our findings were imprecise and generally null-to-positive among those living within 0-<4 miles regardless of the intervention type. Conclusions: Results suggest a reduction of PTB among residents 4-<10 miles of the CFPPs that installed scrubbers.

North Carolina's Changing Energy Generation Profile and Reductions in Key Air Pollutants, 2000-2019.

BACKGROUND Coal combustion releases a number of airborne toxins. The North Carolina Clean Smokestacks Act (CSA) of 2002 required North Carolina coal-fired power plants (CFPP) to reduce nitrogen oxides (NOX) emissions by 2009 and sulfur dioxide (SO2) emissions to 2 benchmarks by 2009 and 2013.METHODS We utilized publicly available databases from the Energy Information Administration and the Environmental Protection Agency to characterize North Carolina's electricity generation profile from 2000 until 2019 and evaluate corresponding NOx and SO2 emissions by sector over the same time period.RESULTS Between 2000 and 2008 in North Carolina, approximately 60% of electric power was generated by CFPPs. Since then, North Carolina's electric power generation has transformed from predominant dependence on coal to approximately equal dependence on natural gas and nuclear power (each at ~ 30%), with coal close behind (~ 25%). Renewables have increased, although marginally relative to the rapid increase in natural gas. Despite the stark drop in reliance on CFPPs for energy in North Carolina and subsequent drop in emissions, CFPPs still contribute ~ 60% of SO2 air pollution as of 2017.LIMITATIONS This analysis relies upon electricity generation and emissions data self-reported by utilities and publicly available from federal agenciesCONCLUSION North Carolina's electric utilities met the 2009 and 2013 regulatory benchmarks set by the CSA, which resulted in substantial reductions in SO2 emissions from the fuel combustion electric generation sector. Still, CFPPs remain the primary utility-related and overall anthropogenic contributor of SO2 air pollution in North Carolina.

Identifying qualitative differences in PPARα signaling networks in human and rat hepatocytes and their significance for next generation chemical risk assessment methods.

In this paper, we evaluate the PPARα signaling network in rats, examining transcriptional responses in primary hepatocytes exposed to a PPARα specific ligand, GW7647. These transcriptomic studies were complemented with ChIP-seq studies of PPARα binding and transcription binding motif identification for PPARα responsive genes. We also conducted a limited study of GW7647 dosing the in intact rat to examine differences in transcriptional responses for primary hepatocytes in vitro and in the intact liver. The rat network has a much larger number of down-regulated genes and pathways than we had found in the human and the PPARα binding motifs in rat differed for upregulated and down regulated genes. Based on these results and comparison with our previous work with the human PPARα signaling network, we identified qualitative differences in the transcriptional networks controlled by PPARα activation in the two species that provide an explanation of the interspecies differences in the responses of humans and rodents to GW7647 and likely to other PPARα agonists. These studies also allow some observations on the manner in which in vitro, fit-for-purpose assays in human hepatocytes could form the basis for risk assessment without recourse to in-life studies in rodents or other test species.

Connecting Environmental Justice and Community Health: Effects of Hog Production in North Carolina.

Environmental justice means equal access to a healthful environment for all. In North Carolina, many sources of pollution disproportionately affect low-income communities and communities of color. Clinicians who recognize effects of environmental injustices can improve patient care and community health. As an example, we present the effects of industrial-scale hog operations in North Carolina.

A map of the PPARα transcription regulatory network for primary human hepatocytes.

Nuclear receptor activation in liver leads to coordinated alteration of the expression of multiple gene products with attendant phenotypic changes of hepatocytes. Peroxisome proliferators including endogenous fatty acids, environmental chemicals, and drugs induce a multi-enzyme metabolic response that affects lipid and fatty acid processing. We studied the signaling network for the peroxisome proliferator-associated receptor alpha (PPARα) in primary human hepatocytes using the selective PPARα ligand, GW7647. We measured gene expression over multiple concentrations and times and conducted ChIP-seq studies at 2 and 24h to assess genomic binding of PPARα. Over all treatments there were 192 genes differentially expressed. Of these only 51% showed evidence of PPARα binding-either directly at PPARα response elements or via alternative mechanisms. Almost half of regulated genes had no PPARα binding. We then developed two novel bioinformatics methods to visualize the dose-dependent activation of both the transcription factor circuitry for PPARα and the downstream metabolic network in relation to functional annotation categories. Available databases identified several key transcription factors involved with the non-genomic targets after GW7647 treatment, including SP1, STAT1, ETS1, ERα, and HNF4α. The linkage from PPARα binding through gene expression likely requires intermediate protein kinases to activate these transcription factors. We found enrichment of functional annotation categories for organic acid metabolism and cell lipid metabolism among the differentially expressed genes. Lipid transport processes showed enrichment at the highest concentration of GW7647 (10 µM). While our strategy for mapping transcriptional networks is evolving, these approaches are necessary in moving from toxicogenomic methods that derive signatures of activity to methods that establish pathway structure, showing the coordination of the activated nuclear receptor with other signaling pathways.

Divergent effects of sulforaphane on basal and glucose-stimulated insulin secretion in ß-cells: role of reactive oxygen species and induction of endogenous antioxidants.

PURPOSE: Oxidative stress is implicated in pancreatic ß-cell dysfunction, yet clinical outcomes of antioxidant therapies on diabetes are inconclusive. Since reactive oxygen species (ROS) can function as signaling intermediates for glucose-stimulated insulin secretion (GSIS), we hypothesize that exogenously boosting cellular antioxidant capacity dampens signaling ROS and GSIS. METHODS: To test the hypothesis, we formulated a mathematical model of redox homeostatic control circuit comprising known feedback and feedforward loops and validated model predictions with plant-derived antioxidant sulforaphane (SFN). RESULTS: SFN acutely (30-min treatment) stimulated basal insulin secretion in INS-1(832/13) cells and cultured mouse islets, which could be attributed to SFN-elicited ROS as N-acetylcysteine or glutathione ethyl ester suppressed SFN-stimulated insulin secretion. The mathematical model predicted an adapted redox state characteristic of strong induction of endogenous antioxidants but marginally increased ROS under prolonged SFN exposure, a state that attenuates rather than facilitates glucose-stimulated ROS and GSIS. We validated the prediction by demonstrating that although 24-h treatment of INS-1(832/13) cells with low, non-cytotoxic concentrations of SFN (2-10 µM) protected the cells from cytotoxicity by oxidative insult, it markedly suppressed insulin secretion stimulated by 20 mM glucose. CONCLUSIONS: Our study indicates that adaptive induction of endogenous antioxidants by exogenous antioxidants, albeit cytoprotective, inhibits GSIS in ß-cells.

Association between arsenic suppression of adipogenesis and induction of CHOP10 via the endoplasmic reticulum stress response.

BACKGROUND: There is growing evidence that chronic exposure to inorganic arsenic (iAs) is associated with an increased prevalence of type 2 diabetes (T2D). However, the mechanisms for the diabetogenic effect of iAs are still largely unknown. White adipose tissue (WAT) actively stores and releases energy and maintains lipid and glucose homeostasis. OBJECTIVE: We sought to determine the mechanisms of arsenic suppression of adipogenesis. METHODS: The effects and associated mechanisms of iAs and its major metabolites on adipogenesis were determined in 3T3-L1 preadipocytes, mouse adipose-derived stromal-vascular fraction cells (ADSVFCs), and human adipose tissue-derived stem cells (ADSCs). RESULTS: Exposure of 3T3-L1 preadipocytes to noncytotoxic levels of arsenic, including inorganic arsenite (iAs3+, ≤ 5 µM), inorganic arsenate (≤ 20 µM), trivalent monomethylated arsenic (MMA3+, ≤ 1 µM), and trivalent dimethylated arsenic (DMA3+, ≤ 2 µM) decreased adipogenic hormone-induced adipogenesis in a concentration-dependent manner. In addition, iAs3+, MMA3+, and DMA3+ exhibited a strong inhibitory effect on adipogenesis in primary cultured mouse ADSVFCs and human ADSCs. Time-course studies in 3T3-L1 cells revealed that inhibition of adipogenesis by arsenic occurred in the early stage of terminal adipogenic differentiation and was highly correlated with the induction of C/EBP homologous protein (CHOP10), an endoplasmic reticulum (ER) stress response protein. Induction of CHOP10 by arsenic is associated with reduced DNA-binding activity of CCAAT/enhancer-binding protein ß (C/EBPß), which regulates the transcription of peroxisome proliferator-activated receptor γ and C/EBPα. CONCLUSIONS: Low-level iAs and MMA3+ trigger the ER stress response and up-regulate CHOP10, which inhibits C/EBPß transcriptional activity, thus suppressing adipogenesis. Arsenic-induced dysfunctional adipogenesis may be associated with a reduced capacity of WAT to store lipids and with insulin resistance.

Adipose deficiency of Nrf2 in ob/ob mice results in severe metabolic syndrome.

Nuclear factor E2-related factor 2 (Nrf2) is a transcription factor that functions as a master regulator of the cellular adaptive response to oxidative stress. Our previous studies showed that Nrf2 plays a critical role in adipogenesis by regulating expression of CCAAT/enhancer-binding protein ß and peroxisome proliferator-activated receptor γ. To determine the role of Nrf2 in the development of obesity and associated metabolic disorders, the incidence of metabolic syndrome was assessed in whole-body or adipocyte-specific Nrf2-knockout mice on a leptin-deficient ob/ob background, a model with an extremely positive energy balance. On the ob/ob background, ablation of Nrf2, globally or specifically in adipocytes, led to reduced white adipose tissue (WAT) mass, but resulted in an even more severe metabolic syndrome with aggravated insulin resistance, hyperglycemia, and hypertriglyceridemia. Compared with wild-type mice, WAT of ob/ob mice expressed substantially higher levels of many genes related to antioxidant response, inflammation, adipogenesis, lipogenesis, glucose uptake, and lipid transport. Absence of Nrf2 in WAT resulted in reduced expression of most of these factors at mRNA or protein levels. Our findings support a novel role for Nrf2 in regulating adipose development and function, by which Nrf2 controls the capacity of WAT expansion and insulin sensitivity and maintains glucose and lipid homeostasis.

Modeling drug- and chemical-induced hepatotoxicity with systems biology approaches.

We provide an overview of computational systems biology approaches as applied to the study of chemical- and drug-induced toxicity. The concept of "toxicity pathways" is described in the context of the 2007 US National Academies of Science report, "Toxicity testing in the 21st Century: A Vision and A Strategy." Pathway mapping and modeling based on network biology concepts are a key component of the vision laid out in this report for a more biologically based analysis of dose-response behavior and the safety of chemicals and drugs. We focus on toxicity of the liver (hepatotoxicity) - a complex phenotypic response with contributions from a number of different cell types and biological processes. We describe three case studies of complementary multi-scale computational modeling approaches to understand perturbation of toxicity pathways in the human liver as a result of exposure to environmental contaminants and specific drugs. One approach involves development of a spatial, multicellular "virtual tissue" model of the liver lobule that combines molecular circuits in individual hepatocytes with cell-cell interactions and blood-mediated transport of toxicants through hepatic sinusoids, to enable quantitative, mechanistic prediction of hepatic dose-response for activation of the aryl hydrocarbon receptor toxicity pathway. Simultaneously, methods are being developing to extract quantitative maps of intracellular signaling and transcriptional regulatory networks perturbed by environmental contaminants, using a combination of gene expression and genome-wide protein-DNA interaction data. A predictive physiological model (DILIsym™) to understand drug-induced liver injury (DILI), the most common adverse event leading to termination of clinical development programs and regulatory actions on drugs, is also described. The model initially focuses on reactive metabolite-induced DILI in response to administration of acetaminophen, and spans multiple biological scales.

Deficiency in the nuclear factor E2-related factor 2 renders pancreatic ß-cells vulnerable to arsenic-induced cell damage.

Chronic human exposure to inorganic arsenic (iAs), a potent environmental oxidative stressor, is associated with increased prevalence of type 2 diabetes, where impairment of pancreatic ß-cell function is a key pathogenic factor. Nuclear factor E2-related factor 2 (Nrf2) is a central transcription factor regulating cellular adaptive response to oxidative stress. However, persistent activation of Nrf2 in response to chronic oxidative stress, including inorganic arsenite (iAs³âº) exposure, blunts glucose-triggered reactive oxygen species (ROS) signaling and impairs glucose-stimulated insulin secretion (GSIS). In the current study, we found that MIN6 pancreatic ß-cells with stable knockdown of Nrf2 (Nrf2-KD) by lentiviral shRNA and pancreatic islets isolated from Nrf2-knockout (Nrf2⁻/⁻) mice exhibited reduced expression of several antioxidant and detoxification enzymes in response to acute iAs³âº exposure. As a result, Nrf2-KD MIN6 cells and Nrf2⁻/⁻ islets were more susceptible to iAs³âº and monomethylarsonous acid (MMA³âº)-induced cell damage, as measured by decreased cell viability, augmented apoptosis and morphological change. Pretreatment of MIN6 cells with Nrf2 activator tert-butylhydroquinone protected the cells from iAs³âº-induced cell damage in an Nrf2-dependent fashion. In contrast, antioxidant N-acetyl cysteine protected Nrf2-KD MIN6 cells against acute cytotoxicity of iAs³âº. The present study demonstrates that Nrf2-mediated antioxidant response is critical in the pancreatic ß-cell defense mechanism against acute cytotoxicity by arsenic. The findings here, combined with our previous results on the inhibitory effect of antioxidants on ROS signaling and GSIS, suggest that Nrf2 plays paradoxical roles in pancreatic ß-cell dysfunction induced by environmental arsenic exposure.

Regulatory role of KEAP1 and NRF2 in PPARγ expression and chemoresistance in human non-small-cell lung carcinoma cells.

The nuclear factor-E2-related factor 2 (NRF2) serves as a master regulator in cellular defense against oxidative stress and chemical detoxification. However, persistent activation of NRF2 resulting from mutations in NRF2 and/or downregulation of or mutations in its suppressor, Kelch-like ECH-associated protein 1 (KEAP1), is associated with tumorigenicity and chemoresistance of non-small-cell lung carcinomas (NSCLCs). Thus, inhibiting the NRF2-mediated adaptive antioxidant response is widely considered a promising strategy to prevent tumor growth and reverse chemoresistance in NSCLCs. Unexpectedly, stable knockdown of KEAP1 by lentiviral shRNA sensitized three independent NSCLC cell lines (A549, HTB-178, and HTB-182) to multiple chemotherapeutic agents, including arsenic trioxide (As(2)O(3)), etoposide, and doxorubicin, despite moderately increased NRF2 levels. In lung adenocarcinoma epithelial A549 cells, silencing of KEAP1 augmented the expression of peroxisome proliferator-activated receptor γ (PPARγ) and genes associated with cell differentiation, including E-cadherin and gelsolin. In addition, KEAP1-knockdown A549 cells displayed attenuated expression of the proto-oncogene cyclin D1 and markers for cancer stem cells (CSCs) and reduced nonadherent sphere formation. Moreover, deficiency of KEAP1 led to elevated induction of PPARγ in response to As(2)O(3). Pretreatment of A549 cells with PPARγ agonists activated PPARγ and augmented the cytotoxicity of As(2)O(3). A mathematical model was formulated to advance a hypothesis that differential regulation of PPARγ and detoxification enzymes by KEAP1 and NRF2 may underpin the observed landscape changes in chemosensitivity. Collectively, suppression of KEAP1 expression in human NSCLC cells resulted in sensitization to chemotherapeutic agents, which may be attributed to activation of PPARγ and subsequent alterations in cell differentiation and CSC abundance.

Cross-regulations among NRFs and KEAP1 and effects of their silencing on arsenic-induced antioxidant response and cytotoxicity in human keratinocytes.

BACKGROUND: Nuclear factor E2-related factors (NRFs), including NRF2 and NRF1, play critical roles in mediating the cellular adaptive response to oxidative stress. Human exposure to inorganic arsenic, a potent oxidative stressor, causes various dermal disorders, including hyperkeratosis and skin cancer. OBJECTIVE: We investigated the cross-regulations among NRF2, NRF1, and KEAP1, a cullin-3-adapter protein that allows NRF2 to be ubiquinated and degraded by the proteasome complex, in arsenic-induced antioxidant responses. RESULTS: In human keratinocyte HaCaT cells, selective knockdown (KD) of NRF2 by lentiviral short hairpin RNAs (shRNAs) significantly reduced the expression of many antioxidant enzymes and sensitized the cells to acute cytotoxicity of inorganic arsenite (iAs(3+)). In contrast, silencing KEAP1 led to a dramatic resistance to iAs(3+)-induced apoptosis. Pretreatment of HaCaT cells with NRF2 activators, such as tert-butylhydroquinone, protects the cells against acute iAs(3+) toxicity in an NRF2-dependent fashion. Consistent with the negative regulatory role of KEAP1 in NRF2 activation, KEAP1-KD cells exhibited enhanced transcriptional activity of NRF2 under nonstressed conditions. However, deficiency in KEAP1 did not facilitate induction of NRF2-target genes by iAs(3+). In addition, NRF2 silencing reduced the expression of KEAP1 at transcription and protein levels but increased the protein expression of NRF1 under the iAs(3+)-exposed condition. In contrast, silencing KEAP1 augmented protein accumulation of NRF2 under basal and iAs3+-exposed conditions, whereas the iAs(3+)-induced protein accumulation of NRF1 was attenuated in KEAP1-KD cells. CONCLUSIONS: Our studies suggest that NRF2, KEAP1, and NRF1 are coordinately involved in the regulation of the cellular adaptive response to iAs(3+)-induced oxidative stress.

Nuclear factor erythroid-derived factor 2-related factor 2 regulates transcription of CCAAT/enhancer-binding protein ß during adipogenesis.

Nuclear factor erythroid-derived factor 2-related factor 2 (Nrf2) is a cap-n-collar basic leucine zipper transcription factor that is involved in the cellular adaptive response to oxidative stress. Our previous study reported that targeted disruption of the Nrf2 gene in mice decreases adipose tissue mass and protects against obesity induced by a high-fat diet. Deficiency of Nrf2 in preadipocytes and mouse embryonic fibroblasts led to impaired adipogenesis. Consistent with these findings, the current study found that lack of Nrf2 in primary cultured mouse preadipocytes and 3T3-L1 cells hampered adipogenic differentiation induced by hormonal cocktails. Stable knockdown of Nrf2 in 3T3-L1 cells blocked the enhanced adipogenesis caused by deficiency of kelch-like ECH-associated protein 1 (Keap1), a Cul3-adapter protein that allows for Nrf2 to be ubiquinated and degraded by the 26S protesome complex. In addition, increased production of reactive oxygen species (ROS) and activation of Nrf2 occurred at the very early stage upon adipogenic hormonal challenge in 3T3-L1 cells, followed by an immediate induction of CCAAT/enhancer-binding protein ß (C/EBPß). Knockdown of Nrf2 led to reduced expression of C/EBPß induced by adipogenic hormonal cocktails, chemical Nrf2 activators or Keap1 silencing. Cebpß promoter-driven reporter assays and chromatin immunoprecipitation suggested that Nrf2 associates with a consensus antioxidant response element (ARE) binding site in the promoter of the Cebpß gene during adipogenesis and upregulates its expression. These findings demonstrate a novel role of Nrf2 beyond xenobiotic detoxification and antioxidant response, and suggest that Nrf2 is one of the transcription factors that control the early events of adipogenesis by regulating expression of Cebpß.

Prolonged inorganic arsenite exposure suppresses insulin-stimulated AKT S473 phosphorylation and glucose uptake in 3T3-L1 adipocytes: involvement of the adaptive antioxidant response.

There is growing evidence that chronic exposure of humans to inorganic arsenic, a potent environmental oxidative stressor, is associated with the incidence of type 2 diabetes (T2D). One critical feature of T2D is insulin resistance in peripheral tissues, especially in mature adipocytes, the hallmark of which is decreased insulin-stimulated glucose uptake (ISGU). Despite the deleterious effects of reactive oxygen species (ROS), they have been recognized as a second messenger serving an intracellular signaling role for insulin action. Nuclear factor erythroid 2-related factor 2 (NRF2) is a central transcription factor regulating cellular adaptive response to oxidative stress. This study proposes that in response to arsenic exposure, the NRF2-mediated adaptive induction of endogenous antioxidant enzymes blunts insulin-stimulated ROS signaling and thus impairs ISGU. Exposure of differentiated 3T3-L1 cells to low-level (up to 2 µM) inorganic arsenite (iAs³(+)) led to decreased ISGU in a dose- and time-dependent manner. Concomitant to the impairment of ISGU, iAs³(+) exposure significantly attenuated insulin-stimulated intracellular ROS accumulation and AKT S473 phosphorylation, which could be attributed to the activation of NRF2 and induction of a battery of endogenous antioxidant enzymes. In addition, prolonged iAs³(+) exposure of 3T3-L1 adipocytes resulted in significant induction of inflammatory response genes and decreased expression of adipogenic genes and glucose transporter type 4 (GLUT4), suggesting chronic inflammation and reduction in GLUT4 expression may also be involved in arsenic-induced insulin resistance in adipocytes. Taken together our studies suggest that prolonged low-level iAs³(+) exposure activates the cellular adaptive oxidative stress response, which impairs insulin-stimulated ROS signaling that is involved in ISGU, and thus causes insulin resistance in adipocytes.

Long isoforms of NRF1 contribute to arsenic-induced antioxidant response in human keratinocytes.

BACKGROUND: Human exposure to inorganic arsenic (iAs), a potent oxidative stressor, causes various dermal disorders, including hyperkeratosis and skin cancer. Nuclear factor-erythroid 2-related factor 1 (NRF1, also called NFE2L1) plays a critical role in regulating the expression of many antioxidant response element (ARE)-dependent genes. OBJECTIVES: We investigated the role of NRF1 in arsenic-induced antioxidant response and cytotoxicity in human keratinocytes. RESULTS: In cultured human keratinocyte HaCaT cells, inorganic arsenite (iAs3+) enhanced the protein accumulation of long isoforms (120-140 kDa) of NRF1 in a dose- and time-dependent fashion. These isoforms accumulated mainly in the nuclei of HaCaT cells. Selective deficiency of NRF1 by lentiviral short-hairpin RNAs in HaCaT cells [NRF1-knockdown (KD)] led to decreased expression of γ-glutamate cysteine ligase catalytic subunit (GCLC) and regulatory subunit (GCLM) and a reduced level of intracellular glutathione. In response to acute iAs3+ exposure, induction of some ARE-dependent genes, including NAD(P)H:quinone oxidoreductase 1 (NQO1), GCLC, and GCLM, was significantly attenuated in NRF1-KD cells. However, the iAs3-induced expression of heme oxygenase 1 (HMOX-1) was unaltered by silencing NRF1, suggesting that HMOX-1 is not regulated by NRF1. In addition, the lack of NRF1 in HaCaT cells did not disturb iAs3+-induced NRF2 accumulation but noticeably decreased Kelch-like ECH-associated protein 1 (KEAP1) levels under basal and iAs3+-exposed conditions, suggesting a potential interaction between NRF1 and KEAP1. Consistent with the critical role of NRF1 in the transcriptional regulation of some ARE-bearing genes, knockdown of NRF1 significantly increased iAs3+-induced cytotoxicity and apoptosis. CONCLUSIONS: Here, we demonstrate for the first time that long isoforms of NRF1 contribute to arsenic-induced antioxidant response in human keratinocytes and protect the cells from acute arsenic cytotoxicity.

Low-level arsenic impairs glucose-stimulated insulin secretion in pancreatic beta cells: involvement of cellular adaptive response to oxidative stress.

BACKGROUND: Chronic exposure of humans to inorganic arsenic, a potent environmental oxidative stressor, is associated with incidence of type 2 diabetes (T2D). A key driver in the pathogenesis of T2D is impairment of pancreatic beta-cell function, with the hallmark of beta-cell function being glucose-stimulated insulin secretion (GSIS). Reactive oxygen species (ROS) derived from glucose metabolism serve as one of the metabolic signals for GSIS. Nuclear factor-erythroid 2-related factor 2 (Nrf2) is a central transcription factor regulating cellular adaptive response to oxidative stress. OBJECTIVES: We tested the hypothesis that activation of Nrf2 and induction of antioxidant enzymes in response to arsenic exposure impedes glucose-triggered ROS signaling and thus GSIS. METHODS AND RESULTS: Exposure of INS-1(832/13) cells to low levels of arsenite led to decreased GSIS in a dose- and time-dependent fashion. Consistent with our hypothesis, a significantly enhanced Nrf2 activity, determined by its nuclear accumulation and induction of its target genes, was observed in arsenite-exposed cells. In keeping with the activation of Nrf2-mediated antioxidant response, intracellular glutathione and intracellular hydrogen peroxide-scavenging activity was dose dependently increased by arsenite exposure. Although the basal cellular peroxide level was significantly enhanced, the net percentage increase in glucose-stimulated intracellular peroxide production was markedly inhibited in arsenite-exposed cells. In contrast, insulin synthesis and the consensus GSIS pathway, including glucose transport and metabolism, were not significantly reduced by arsenite exposure. CONCLUSIONS: Our studies suggest that low levels of arsenic provoke a cellular adaptive oxidative stress response that increases antioxidant levels, dampens ROS signaling involved in GSIS, and thus disturbs beta-cell function.