Selective Serotonin Reuptake Inhibitors and Other Treatment Modalities for Deep Space Missions.

INTRODUCTION: As humankind ventures further into the depths of space, planning is already underway for long-duration exploration missions that will test the bounds of human performance. Deep space travel will include added risk related to stressors from the isolated, confined, and extreme environment that lies outside the boundaries of low Earth orbit. Currently, selective serotonin reuptake inhibitors (SSRIs) are considered the standard of care for many mental health diagnoses, including anxiety and depression; however, SSRIs are also associated with several undesired side effects. The utility of nonpharmacological therapies for the management of behavioral health conditions has not yet been fully explored.METHODS: A comprehensive literature search was performed using PubMed. Relevant articles pertaining to the psychological impacts of isolated, confined, and extreme environments, use of SSRIs in spaceflight, side effects associated with SSRIs, and nonpharmacological treatments for anxiety and depression were reviewed. Over 70 studies were reviewed in total.RESULTS: Reduced bone mineral density, impaired hemostatic function, significant individual variability resulting from gene polymorphisms, and drug-drug interactions are well described adverse effects of SSRIs that may complicate their operational use in the deep space environment. Four alternative therapies for the treatment of anxiety and depression may show promise for long duration missions.DISCUSSION: Although SSRIs have long been considered standard of care treatment for many behavioral health conditions, we cannot trivialize the risk that prolonged pharmacological therapy may pose. The need to mitigate these risks by exploring alternative therapies has never been more relevant.El-Khoury BB, Ray KL, Altchuler SI, Reichard JF, Dukes CH. Selective serotonin reuptake inhibitors and other treatment modalities for deep space missions. Aerosp Med Hum Perform. 2023; 94(11):843-851.

Ciprofloxacin- and azithromycin-resistant bacteria in a wastewater treatment plant.

The occurrence of antibiotic-resistant bacteria (ARB) in wastewater treatment plants (WWTPs) has become an occupational and environmental concern. WWTPs are engineered systems that treat wastewater to meet public health standards before release into the environment. The residuals, as either effluent or solids, are then discharged or beneficially recycled into the environment. Since these wastes contain a diverse array of microorganisms, some of which are resistant to commonly used antibiotics, there is a potential for these organisms to spread in the environment via residual recycling and effluent discharge. Human infections with ARB are increasing, and it is not well known how the interaction between humans and the environment plays a role in this process. WWTP workers, who are on the front lines, may come into direct contact with materials containing these microbes. This study aimed to determine the number of ARB present in both air and sewage sludges in a WWTP using nonselective media supplemented with two antibiotics (ciprofloxacin and azithromycin). The densities of total heterotrophic bacteria, ciprofloxacin-resistant bacteria, and azithromycin-resistant bacteria were 7.82 × 105 - 4.7 × 109, 7.87 × 103 - 1.05 × 108, and 2.27 × 105 - 1.16 × 109 CFU/g, respectively. The prevalence [(concentration on medium with antibiotics/concentration on medium without antibiotics) × 100] of ciprofloxacin-resistant bacteria in treated sludge was twice as low as in digested sludge and approximately three times lower than in raw sludge. For azithromycin, the prevalence of resistant bacteria in treated sludge was about the same in digested and nearly twice lower than in raw sludge. Despite a marked reduction in the mean prevalence of resistant bacteria in dewatered treated sludge for both antibiotics, these differences were not significant. The highest prevalence of antibiotic resistance was observed for azithromycin. Similarly, the prevalence of airborne azithromycin-resistant bacteria inside the belt filter press room (BFPR) was nearly seven times higher than the prevalence of airborne ciprofloxacin-resistant bacteria. These concentrations of ARB were not negligible and may represent an exposure pathway for some workers in WWTPs.

Connecting omics signatures and revealing biological mechanisms with iLINCS.

There are only a few platforms that integrate multiple omics data types, bioinformatics tools, and interfaces for integrative analyses and visualization that do not require programming skills. Here we present iLINCS ( http://ilincs.org ), an integrative web-based platform for analysis of omics data and signatures of cellular perturbations. The platform facilitates mining and re-analysis of the large collection of omics datasets (>34,000), pre-computed signatures (>200,000), and their connections, as well as the analysis of user-submitted omics signatures of diseases and cellular perturbations. iLINCS analysis workflows integrate vast omics data resources and a range of analytics and interactive visualization tools into a comprehensive platform for analysis of omics signatures. iLINCS user-friendly interfaces enable execution of sophisticated analyses of omics signatures, mechanism of action analysis, and signature-driven drug repositioning. We illustrate the utility of iLINCS with three use cases involving analysis of cancer proteogenomic signatures, COVID 19 transcriptomic signatures and mTOR signaling.

Rapid Review of Dermal Penetration and Absorption of Inorganic Lead Compounds for Occupational Risk Assessment.

Lead (Pb) exposure continues to be a significant public health issue in both occupational and non-occupational settings. The vast majority of exposure and toxicological studies have focused on effects related to inhalation and gastrointestinal exposure routes. Exposure to inorganic Pb compounds through dermal absorption has been less well studied, perhaps due to the assumption that the dermal pathway is a minor contributor to aggregate exposures to Pb compounds. The aim of this rapid review was to identify and evaluate published literature on dermal exposures to support the estimation of key percutaneous absorption parameters (Kp, flux, diffusion rate) for use in occupational risk assessment. Eleven articles were identified containing information from both in vitro and in vivo systems relevant to percutaneous absorption kinetics. These articles provided 24 individual study summaries and information for seven inorganic Pb compounds. The vast majority of study summaries evaluated (n = 22, 92%) reported detectable amounts of dermal absorption of inorganic Pb. Data were identified for four Pb compounds (Pb acetate, Pb nitrate, Pb oxide, and Pb metal) that may be sufficient to use in evaluating physiologically based pharmacokinetic models. Average calculated diffusion rates for the pool of animal and human skin data ranged from 10-7 to 10-4 mg cm-2 h-1, and Kp values ranged from 10-7 to 10-5 cm h-1. Study design and documentation were highly variable, and only one of the studies identified was conducted using standard test guideline-compliant methodologies. Two studies provided quality estimates on the impacts of dermal absorption from water-insoluble Pb compounds on blood Pb levels. These two studies reported that exposures via dermal routes could elevate blood Pb by over 6 µg dl-1. This estimation could represent over 100% of 5 µg dl-1, the blood Pb associated with adverse health effects in adults. The utility of these estimates to occupational dermal exposures is limited, because the confidence in the estimates is not high. The literature, while of limited quality, overall strongly suggests inorganic Pb has the potential for dermal uptake in meaningful amounts associated with negative health outcomes based on upper bound diffusion rate estimates. Future standard test guideline-compliant studies are needed to provide high-confidence estimates of dermal uptake. Such data are needed to allow for improved evaluation of Pb exposures in an occupational risk assessment context.

Bayesian hierarchical evaluation of dose-response for peanut allergy in clinical trial screening.

Risk-based labeling based on the minimal eliciting doses (EDs) in sensitized populations is a potential replacement for precautionary allergen labeling of food allergens. We estimated the dose-response distribution for peanut allergen using data from double-blind placebo-controlled food challenges (DBPCFCs) conducted in the US at multiple sites, testing a population believed to be similar to the general U.S. food allergic population. Our final (placebo-adjusted) dataset included 548 challenges of 481 subjects. Bayesian hierarchical analysis facilitated model fitting, and accounted for variability associated with various levels of data organization. The data are best described using a complex hierarchical structure that accounts for inter-individual variability and variability across study locations or substudies. Bayesian model averaging could simultaneously consider the fit of multiple models, but the Weibull model dominated so strongly that model averaging was not needed. The ED01 and ED05 (and 95% credible intervals) are 0.052 (0.021, 0.13) and 0.49 (0.22, 0.97) mg peanut protein, respectively. Accounting for challenges with severe reactions at the LOAEL, by using the dose prior to the LOAEL as the new LOAEL, the ED01 drops to 0.029 (0.014, 0.074) mg peanut protein. Our results could aid in establishing improved food labeling guidelines in the management of food allergies.

The Effects of Social, Personal, and Behavioral Risk Factors and PM2.5 on Cardio-Metabolic Disparities in a Cohort of Community Health Center Patients.

(1) Background: Cardio-metabolic diseases (CMD), including cardiovascular disease, stroke, and diabetes, have numerous common individual and environmental risk factors. Yet, few studies to date have considered how these multiple risk factors together affect CMD disparities between Blacks and Whites. (2) Methods: We linked daily fine particulate matter (PM2.5) measures with survey responses of participants in the Southern Community Cohort Study (SCCS). Generalized linear mixed modeling (GLMM) was used to estimate the relationship between CMD risk and social-demographic characteristics, behavioral and personal risk factors, and exposure levels of PM2.5. (3) Results: The study resulted in four key findings: (1) PM2.5 concentration level was significantly associated with reported CMD, with risk rising by 2.6% for each µg/m3 increase in PM2.5; (2) race did not predict CMD risk when clinical, lifestyle, and environmental risk factors were accounted for; (3) a significant variation of CMD risk was found among participants across states; and (4) multiple personal, clinical, and social-demographic and environmental risk factors played a role in predicting CMD occurrence. (4) Conclusions: Disparities in CMD risk among low social status populations reflect the complex interactions of exposures and cumulative risks for CMD contributed by different personal and environmental factors from natural, built, and social environments.

Estimated dermal exposure to nebulized pharmaceuticals for a simulated home healthcare worker scenario.

The duties of home healthcare workers are extensive. One important task that is frequently performed by home healthcare workers is administration of nebulized medications, which may lead to significant dermal exposure. In this simulation study conducted in an aerosol exposure chamber, we administered a surrogate of nebulizer-delivered medications (dispersed sodium chloride, NaCl) to a patient mannequin. We measured the amount of NaCl deposited on the exposed surface of the home healthcare worker mannequin, which represented the exposed skin of a home healthcare worker. Factors such as distance and position of the home healthcare worker, room airflow rate and patient's inspiratory rate were varied to determine their effects on dermal exposure. There was a 2.78% reduction in dermal deposition for every centimeter the home healthcare worker moved away from the patient. Increasing the room's air exchange rate by one air change per hour increased dermal deposition by about 2.93%, possibly due to a decrease in near field particle settling. For every 10-degrees of arc the home healthcare worker is positioned from the left side of the patient toward the right and thus moving into the ventilation airflow direction, dermal deposition increased by about 4.61%. An increase in the patient's inspiratory rate from 15-30 L/min resulted in an average of 14.06% reduction in dermal deposition for the home healthcare worker, reflecting a relative increase in the aerosol fraction inhaled by the patient. The findings of this study elucidate the interactions among factors that contribute to dermal exposure to aerosolized pharmaceuticals administered by home healthcare workers. The results presented in this paper will help develop recommendations on mitigating the health risks related to dermal exposure of home healthcare workers.

An occupational exposure limit (OEL) approach to protect home healthcare workers exposed to common nebulized drugs.

Home healthcare is a growing area of employment. Assessment of occupational health risks to home health care workers (HHCWs) is important because in many cases the unique characteristics of the home environment do not facilitate the level of exposure control afforded to caregivers in hospitals and other fixed patient care sites. This assessment is focused on health risks to HHCWs from exposure to pharmaceutical drugs used to treat asthma and other respiratory diseases, which are commonly administered to patients in aerosolized form via nebulizers. We developed risk-based exposure limits for workers in the form of occupational exposure limits (OEL) values for exposure to nebulized forms of the three most common drugs administered by this method: albuterol, ipratropium, and budesonide. The derived OEL for albuterol was 2 µg/day, for ipratropium was 30 µg/day, and for budesonide was 11 µg/day. These OELs were derived based on human effect data and adjusted for pharmacokinetic variability and areas of uncertainty relevant to the underlying data (human and non-human) available for each drug. The resulting OEL values provide an input to the occupational risk assessment process to allow for comparisons to HHCW exposure that will guide risk management and exposure control decisions.

The Library of Integrated Network-Based Cellular Signatures NIH Program: System-Level Cataloging of Human Cells Response to Perturbations.

The Library of Integrated Network-Based Cellular Signatures (LINCS) is an NIH Common Fund program that catalogs how human cells globally respond to chemical, genetic, and disease perturbations. Resources generated by LINCS include experimental and computational methods, visualization tools, molecular and imaging data, and signatures. By assembling an integrated picture of the range of responses of human cells exposed to many perturbations, the LINCS program aims to better understand human disease and to advance the development of new therapies. Perturbations under study include drugs, genetic perturbations, tissue micro-environments, antibodies, and disease-causing mutations. Responses to perturbations are measured by transcript profiling, mass spectrometry, cell imaging, and biochemical methods, among other assays. The LINCS program focuses on cellular physiology shared among tissues and cell types relevant to an array of diseases, including cancer, heart disease, and neurodegenerative disorders. This Perspective describes LINCS technologies, datasets, tools, and approaches to data accessibility and reusability.

Mode-of-action evaluation for the effect of trans fatty acids on low-density lipoprotein cholesterol.

The purpose of this work is to systematically consider the data relating to the mode of action (MOA) for the effects of industrially produced trans fatty acid (iTFA) on plasma low-density lipoprotein (LDL) levels. The hypothesized MOA is composed of two key events: increased LDL production and decreased LDL clearance. A substantial database supports this MOA, although the key events are likely to be interdependent, rather than sequential. Both key events are functions of nonlinear biological processes including rate-limited clearance, receptor-mediated transcription, and both positive and negative feedback regulation. Each key event was evaluated based on weight-of-evidence analysis and for human relevance. We conclude that the data are inadequate for a detailed dose-response analysis in the context of the evolved Bradford Hill considerations; however, the weight of evidence is strong and the overall shape of the dose-response curves for markers of the key events and the key determinants of those relationships is well understood in many cases and is nonlinear. Feedback controls are responsible for maintaining homeostasis of cholesterol and triglyceride levels and underlie both of the key events, resulting in a less-than-linear or thresholded relationship between TFA and LDL-C. The inconsistencies and gaps in the database are discussed.

Toxicokinetic and toxicodynamic considerations when deriving health-based exposure limits for pharmaceuticals.

The purpose of this paper is to describe the use of toxicokinetic (TK) and toxicodynamic (TD) data in setting acceptable daily exposure (ADE) values and occupational exposure limits (OELs). Use of TK data can provide a more robust exposure limit based on a rigorous evaluation of systemic internal dose. Bioavailability data assist in extrapolating across different routes of exposure to be protective for route-based differences of exposure. Bioaccumulation data enable extrapolation to chronic exposures when the point of departure (PoD) is from a short-term critical study. Applied in the context of chemical-specific adjustment factors (CSAFs), TK data partially replace traditional default adjustment factors for interspecies extrapolation (extrapolation from studies conducted in animals to humans) and intraspecies variability (to account for human population variability). Default adjustments of 10-fold each for interspecies and intraspecies extrapolation are recommended in several guidelines, although some organization recommend other values. Such default factors may overestimate variability for many APIs, while not being sufficiently protective for variability with other APIs. For this reason, the use of chemical specific TK and TD data are preferred. Making full use of existing TK and TD data reduces underlying uncertainties, increases transparency, and ensures that resulting ADEs reflect the best available science.

Arsenic toxicology: translating between experimental models and human pathology.

BACKGROUND: Chronic arsenic exposure is a worldwide health problem. How arsenic exposure promotes a variety of diseases is poorly understood, and specific relationships between experimental and human exposures are not established. We propose phenotypic anchoring as a means to unify experimental observations and disease outcomes. OBJECTIVES: We examined the use of phenotypic anchors to translate experimental data to human pathology and investigated research needs for which phenotypic anchors need to be developed. METHODS: During a workshop, we discussed experimental systems investigating arsenic dose/exposure and phenotypic expression relationships and human disease responses to chronic arsenic exposure and identified knowledge gaps. In a literature review, we identified areas where data exist to support phenotypic anchoring of experimental results to pathologies from specific human exposures. DISCUSSION: Disease outcome is likely dependent on cell-type-specific responses and interaction with individual genetics, other toxicants, and infectious agents. Potential phenotypic anchors include target tissue dosimetry, gene expression and epigenetic profiles, and tissue biomarkers. CONCLUSIONS: Translation to human populations requires more extensive profiling of human samples along with high-quality dosimetry. Anchoring results by gene expression and epigenetic profiling has great promise for data unification. Genetic predisposition of individuals affects disease outcome. Interactions with infectious agents, particularly viruses, may explain some species-specific differences between human pathologies and experimental animal pathologies. Invertebrate systems amenable to genetic manipulation offer potential for elaborating impacts of specific biochemical pathways. Anchoring experimental results to specific human exposures will accelerate understanding of mechanisms of arsenic-induced human disease.

Effects of arsenic exposure on DNA methylation and epigenetic gene regulation.

Arsenic is a nonmutagenic human carcinogen that induces tumors through unknown mechanisms. A growing body of evidence suggests that its carcinogenicity results from epigenetic changes, particularly in DNA methylation. Changes in gene methylation status, mediated by arsenic, have been proposed to activate oncogene expression or silence tumor suppressor genes, leading to long-term changes in the activity of genes controlling cell transformation. Mostly descriptive, and often contradictory, studies have demonstrated that arsenic exposure is associated with both hypo- and hyper-methylation at various genetic loci in vivo or in vitro. This ambiguity has made it difficult to assess whether the changes induced by arsenic are causally involved in the transformation process or are simply a reflection of the altered physiology of rapidly dividing cancer cells. Here, we discuss the evidence supporting changes in DNA methylation as a cause of arsenic carcinogenesis and highlight the strengths and limitations of these studies, as well as areas where consistencies and inconsistencies exist.

Genomewide analysis of aryl hydrocarbon receptor binding targets reveals an extensive array of gene clusters that control morphogenetic and developmental programs.

BACKGROUND: The vertebrate aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that regulates cellular responses to environmental polycyclic and halogenated compounds. The naive receptor is believed to reside in an inactive cytosolic complex that translocates to the nucleus and induces transcription of xenobiotic detoxification genes after activation by ligand. OBJECTIVES: We conducted an integrative genomewide analysis of AHR gene targets in mouse hepatoma cells and determined whether AHR regulatory functions may take place in the absence of an exogenous ligand. METHODS: The network of AHR-binding targets in the mouse genome was mapped through a multipronged approach involving chromatin immunoprecipitation/chip and global gene expression signatures. The findings were integrated into a prior functional knowledge base from Gene Ontology, interaction networks, Kyoto Encyclopedia of Genes and Genomes pathways, sequence motif analysis, and literature molecular concepts. RESULTS: We found the naive receptor in unstimulated cells bound to an extensive array of gene clusters with functions in regulation of gene expression, differentiation, and pattern specification, connecting multiple morphogenetic and developmental programs. Activation by the ligand displaced the receptor from some of these targets toward sites in the promoters of xenobiotic metabolism genes. CONCLUSIONS: The vertebrate AHR appears to possess unsuspected regulatory functions that may be potential targets of environmental injury.

BACH1 is a specific repressor of HMOX1 that is inactivated by arsenite.

Intracellular heme is a redox active molecule that can be detrimental to cells at high concentrations or under oxidizing conditions. To prevent accumulation, the inducible enzyme heme oxygenase-1 (HMOX1) catalyzes degradation of heme. In the absence of elevated intracellular heme or oxidative stress, the basic region leucine zipper transcriptional regulator BACH1 binds HMOX1 antioxidant response elements and represses transcription. Conversely, increased intracellular heme or sulfhydryl oxidation inactivate BACH1, permitting transcriptional induction of HMOX1. Here, we investigate the effect of BACH1 inactivation on the induction of HMOX1 and as a mechanism for broader gene induction. We show that BACH1 is inactivated at low micromolar arsenite concentrations and that BACH1 inactivation is necessary and sufficient for transcriptional induction of HMOX1. Because BACH1 is thought to interact with antioxidant response element motifs, we further examined the role of BACH1 as a regulator of inducible antioxidant gene expression by assessing the global profile of gene expression following BACH1 knockdown using small interfering RNA. The loss of BACH1 function in human keratinocytes results almost exclusively in HMOX1 induction, suggesting that BACH1 may function as a rheostat regulating levels of intracellular free heme.

Heme oxygenase-1 induction by NRF2 requires inactivation of the transcriptional repressor BACH1.

Oxidative stress activates the transcription factor NRF2, which in turn binds cis-acting antioxidant response element (ARE) enhancers and induces expression of protective antioxidant genes. In contrast, the transcriptional repressor BACH1 binds ARE-like enhancers in cells naïve to oxidative stress and antagonizes NRF2 binding until it becomes inactivated by pro-oxidants. Here, we describe the dynamic roles of BACH1 and NRF2 in the transcription of the heme oxygenase-1 (HMOX1) gene. HMOX1 induction, elicited by arsenite-mediated oxidative stress, follows inactivation of BACH1 and precedes activation of NRF2. BACH1 repression is dominant over NRF2-mediated HMOX1 transcription and inactivation of BACH1 is a prerequisite for HMOX1 induction. In contrast, thioredoxin reductase 1 (TXNRD1) is regulated by NRF2 but not by BACH1. By comparing the expression levels of HMOX1 with TXNRD1, we show that nuclear accumulation of NRF2 is not necessary for HMOX1 induction; rather, BACH1 inactivation permits NRF2 already present in the nucleus at low basal levels to bind the HMOX1 promoter and elicit HMOX1 induction. Thus, BACH1 confers an additional level of regulation to ARE-dependent genes that reveals a new dimension to the oxidative stress response.

Long term low-dose arsenic exposure induces loss of DNA methylation.

Arsenic ranks as the number one toxic environmental contaminant. In humans, arsenic exposure is associated with various forms of cancer, cardiovascular and skin diseases, neuropathies of the central nervous system, and genotoxic and immunotoxic effects. Although a well recognized human carcinogen, arsenic itself is not a potent mutagen and has been thought to act through epigenetic mechanisms that modify DNA methylation patterns, perhaps in conjunction with DNA-damaging agents. To develop preliminary support for a more thorough examination of this hypothesis, we have measured the effect of submicromolar and low-micromolar concentrations of arsenite on the methylation status of DNA and the biochemical reactions that regulate it. We find that arsenic causes the depletion of S-adenosylmethionine, the main cellular methyl donor, and represses the expression of the DNA methyltransferase genes DNMT1 and DNMT3A. Possibly as a consequence of these two complementary mechanisms, long-term exposure to arsenic results in DNA hypomethylation.

Involvement of phosphatidylinositol 3-kinase and extracellular-regulated kinase in hepatic stellate cell antioxidant response and myofibroblastic transdifferentiation.

Liver fibrogenesis is dependent upon transdifferentiation of hepatic stellate cells to a profibrogenic phenotype. Prooxidant stress purportedly stimulates both an antioxidant response and myofibroblastic transdifferentiation with fibrogenic gene expression; however, mechanisms by which oxidative stress mediates stellate cell activation remain unclear. To this end, stellate cells were treated with tert-butylhydroquinone (tBHQ), a known inducer of antioxidant response genes. As anticipated, tBHQ induced expression of antioxidant response element (ARE)-regulated genes via the transcription factor Nrf2. Further, tBHQ promoted transdifferentiation of quiescent stellate cells cultured on Engelbreth-Holm-Swarm extracellular matrix. Pretreatment of cultured stellate cells with a phosphatidylinositol 3-kinase (PI3K) inhibitor blocked tBHQ-mediated ARE-dependent gene induction as well as stellate cell transdifferentiation. In contrast, extracellular signal-regulated kinase, which was demonstrated to be prominently phosphorylated following tBHQ treatment, was not found to affect either induction of the antioxidant response nor stellate cell transdifferentiation. These data implicate involvement of PI3K pathways in tBHQ-mediated stellate cell activation and demonstrate a requirement for PI3K in the antioxidant response of hepatic stellate cells.

Induction of oxidative stress responses by dioxin and other ligands of the aryl hydrocarbon receptor.

TCDD and other polyhalogenated aromatic hydrocarbon ligands of the aryl hydrocarbon receptor (AHR) have been classically considered as non-genotoxic compounds because they fail to be directly mutagenic in either bacteria or most in vitro assay systems. They do so in spite of having repeatedly been linked to oxidative stress and to mutagenic and carcinogenic outcomes. Oxidative stress, on the other hand, has been used as a marker for the toxicity of dioxin and its congeners. We have focused this review on the connection between oxidative stress induction and the toxic effects of fetal and adult dioxin exposure, with emphasis on the large species difference in sensitivity to this agent. We examine the roles that the dioxin-inducible cytochromes P450s play in the cellular and toxicological consequences of dioxin exposure with emphasis on oxidative stress involvement. Many components of the health consequences resulting from dioxin exposure may be attributable to epigenetic mechanisms arising from prolonged reactive oxygen generation.

Butylhydroquinone protects cells genetically deficient in glutathione biosynthesis from arsenite-induced apoptosis without significantly changing their prooxidant status.

Arsenic, first among the top environmentally hazardous substances, is associated with skin, lung, liver, kidney, prostate, and bladder cancer. Arsenic is also a cardiovascular and a central nervous system toxicant, and it has genotoxic and immunotoxic effects. Paradoxically, arsenic trioxide is used successfully in the treatment of acute promyelocytic leukemia and multiple myeloma. Arsenic induces oxidative stress, and its toxicity is decreased by free thiols and increased by glutathione depletion. To further characterize the role of glutathione and oxidative stress in the toxicity of arsenic, we have used fetal fibroblasts from Gclm(-/-) mice, which lack the modifier subunit of glutamate-cysteine ligase, the rate-limiting enzyme in glutathione biosynthesis. Gclm(-/-) mouse embryo fibroblasts (MEFs) are eight times more sensitive to arsenite-induced apoptotic death. Because of a dramatic decrease in glutathione levels, Gclm(-/-) MEFs have a high prooxidant status that is not significantly relieved by treatment with the phenolic antioxidant tBHQ; however, tBHQ blocks arsenite-induced apoptosis in both Gclm(+/+) and Gclm(-/-) cells, although it raises a significant antioxidant response only in Gclm(+/+) cells. Global gene expression profiles indicate that tBHQ is significantly effective in reversing arsenite-induced gene deregulation in Gclm(+/+) but not in Gclm(-/-) MEFs. This effect of tBHQ is evident in the expression of metalloproteases and chaperones, and in the expression of genes involved in DNA damage and repair, protein biosynthesis, cell growth and maintenance, apoptosis, and cell cycle regulation. These results suggest that regulation of glutathione levels by GCLM determines the sensitivity to arsenic-induced apoptosis by setting the overall ability of the cells to mount an effective antioxidant response.