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FutureTox IV, a Society of Toxicology Contemporary Concepts in Toxicology workshop, was held in November 2018. Building upon FutureTox I, II, and III, this conference focused on the latest science and technology for in vitro profiling and in silico modeling as it relates to predictive developmental and reproductive toxicity (DART). Publicly available high-throughput screening data sets are now available for broad in vitro profiling of bioactivities across large inventories of chemicals. Coupling this vast amount of mechanistic data with a deeper understanding of molecular embryology and post-natal development lays the groundwork for using new approach methodologies (NAMs) to evaluate chemical toxicity, drug efficacy, and safety assessment for embryo-fetal development. NAM is a term recently adopted in reference to any technology, methodology, approach, or combination thereof that can be used to provide information on chemical hazard and risk assessment to avoid the use of intact animals (U.S. Environmental Protection Agency [EPA], Strategic plan to promote the development and implementation of alternative test methods within the tsca program, 2018, https://www.epa.gov/sites/production/files/2018-06/documents/epa_alt_strat_plan_6-20-18_clean_final.pdf). There are challenges to implementing NAMs to evaluate chemicals for developmental toxicity compared with adult toxicity. This forum article reviews the 2018 workshop activities, highlighting challenges and opportunities for applying NAMs for adverse pregnancy outcomes (eg, preterm labor, malformations, low birth weight) as well as disorders manifesting postnatally (eg, neurodevelopmental impairment, breast cancer, cardiovascular disease, fertility). DART is an important concern for different regulatory statutes and test guidelines. Leveraging advancements in such approaches and the accompanying efficiencies to detecting potential hazards to human development are the unifying concepts toward implementing NAMs in DART testing. Although use of NAMs for higher level regulatory decision making is still on the horizon, the conference highlighted novel testing platforms and computational models that cover multiple levels of biological organization, with the unique temporal dynamics of embryonic development, and novel approaches for estimating toxicokinetic parameters essential in supporting in vitro to in vivo extrapolation.

Nongenetic, environmental factors contribute to maternal morbidity and mortality through chemical exposures via air, water, soil, food, and consumer products. Pregnancy represents a particularly sensitive window of susceptibility during which physiological changes to every major organ system increase sensitivity to chemicals that can impact a woman's long-term health. Nonchemical stressors, such as low socioeconomic status, may exacerbate the effects of chemical exposures on maternal health. Racial/ethnic minorities are exposed disproportionately to both chemicals and nonchemical stressors, which likely contribute to the observed health disparities for maternal morbidities and mortality. Epidemiological studies linking exposures to adverse maternal health outcomes underscore the importance of environmental health impacts, and mechanistic studies in model systems reveal how chemicals perturb biological pathways and processes. Environmental stressors are associated with a variety of immediate maternal health impacts, including hypertensive disorders of pregnancy, fibroids, and infertility, as well as long-term maternal health impacts, such as higher risk of breast cancer and metabolic disorders. Identifying and reducing a pregnant woman's environmental exposures is not only beneficial to her offspring but also important to preserve her short- and long-term health.

Bisphenol A (BPA) is a chemical used in the production of numerous consumer products resulting in potential daily human exposure to this chemical. The FDA previously evaluated the body of BPA toxicology data and determined that BPA is safe at current exposure levels. Although consistent with the assessment of some other regulatory agencies around the world, this determination of BPA safety continues to be debated in scientific and popular publications, resulting in conflicting messages to the public. Thus, the National Toxicology Program (NTP), National Institute of Environmental Health Sciences (NIEHS), and U.S. Food and Drug Administration (FDA) developed a consortium-based research program to link more effectively a variety of hypothesis-based research investigations and guideline-compliant safety testing with BPA. This collaboration is known as the Consortium Linking Academic and Regulatory Insights on BPA Toxicity (CLARITY-BPA). This paper provides a detailed description of the conduct of the study and a midterm update on progress of the CLARITY-BPA research program.

The increasing incidence of obesity is a serious global public health challenge. Although the obesity epidemic is largely fueled by poor nutrition and lack of exercise, certain chemicals have been shown to potentially have a role in its aetiology. A substantial body of evidence suggests that a subclass of endocrine-disrupting chemicals (EDCs), which interfere with endocrine signalling, can disrupt hormonally regulated metabolic processes, especially if exposure occurs during early development. These chemicals, so-called 'obesogens' might predispose some individuals to gain weight despite their efforts to limit caloric intake and increase levels of physical activity. This Review discusses the role of EDCs in the obesity epidemic, the latest research on the obesogen concept, epidemiological and experimental findings on obesogens, and their modes of action. The research reviewed here provides knowledge that health scientists can use to inform their research and decision-making processes.

Recent data indicate that approximately 12% of children in the United States are affected by neurodevelopmental disorders, including attention deficit hyperactivity disorder, learning disorders, intellectual disabilities, and autism spectrum disorders. Accumulating evidence indicates a multifactorial etiology for these disorders, with social, physical, genetic susceptibility, nutritional factors, and chemical toxicants acting together to influence risk. Exposure to endocrine-disrupting chemicals during the early stages of life can disrupt normal patterns of development and thus alter brain function and disease susceptibility later in life. This article highlights research efforts and pinpoints approaches that could shed light on the possible associations between environmental chemicals that act on the endocrine system and compromised neurodevelopmental outcomes.

A multidisciplinary group of experts gathered in Parma Italy for a workshop hosted by the University of Parma, May 16–18, 2014 to address concerns about the potential relationship between environmental metabolic disrupting chemicals, obesity and related metabolic disorders. The objectives of the workshop were to: 1. Review findings related to the role of environmental chemicals, referred to as “metabolic disruptors”, in obesity and metabolic syndrome with special attention to recent discoveries from animal model and epidemiology studies; 2. Identify conclusions that could be drawn with confidence from existing animal and human data; 3. Develop predictions based on current data; and 4. Identify critical knowledge gaps and areas of uncertainty. The consensus statements are intended to aid in expanding understanding of the role of metabolic disruptors in the obesity and metabolic disease epidemics, to move the field forward by assessing the current state of the science and to identify research needs on the role of environmental chemical exposures in these diseases. We propose broadening the definition of obesogens to that of metabolic disruptors, to encompass chemicals that play a role in altered susceptibility to obesity, diabetes and related metabolic disorders including metabolic syndrome.

Metabolic Syndrome and Associated Diseases: From the Bench to the Clinic, a Society of Toxicology Contemporary Concepts in Toxicology (CCT) workshop was held on March 11, 2017. The meeting was convened to raise awareness of metabolic syndrome and its associated diseases and serve as a melting pot with scientists of multiple disciplines (eg, toxicologists, clinicians, regulators) so as to spur research and understanding of this condition. The criteria for metabolic syndrome include obesity, dyslipidemia (low high-density lipoprotein and/or elevated triglycerides), elevated blood pressure, and alterations in glucose metabolism. It can lead to a greater potential of type 2 diabetes, lipid disorders, cardiovascular disease, hepatic steatosis, and other circulatory disorders. Although there are no approved drugs specifically for this syndrome, many drugs target diseases associated with this syndrome thus potentially increasing the likelihood of drug-drug interactions. There is currently significant research focusing on understanding the key pathways that control metabolism, which would be likely targets of risk factors (eg, exposure to xenobiotics, genetics) and lifestyle factors (eg, microbiome, nutrition, and exercise) that contribute to metabolic syndrome. Understanding these pathways could also lead to the development of pharmaceutical interventions. As individuals with metabolic syndrome have signs similar to that of toxic responses (eg, oxidative stress and inflammation) and organ dysfunction, these alterations should be taken into account in drug development. With the increasing frequency of metabolic syndrome in the general population, the idea of a "normal" individual may need to be redefined. This paper reports on the substance and outcomes of this workshop.

Environmental exposures have a significant influence on the chronic health conditions plaguing children and adults. Although the Developmental Origins of Health and Disease (DOHaD) paradigm historically has focused on nutrition, an expanding body of research specifically communicates the effects of chemical exposures on early-life development and the propagation of non-communicable disease across the lifespan. This paper provides an overview of 20 years of research efforts aimed at identifying critical windows of susceptibility to environmental exposures and the signaling changes and epigenetic influences associated with disease progression. DOHaD grants funded by the National Institute of Environmental Health Sciences (NIEHS) in 1991, 2001 and 2011 are identified by grant-analysis software, and each portfolio is analyzed for exposures, disease endpoints, windows of exposure, study design and impact on the field based on publication data. Results show that the 1991 and 2001 portfolios comprised metals, PCBs and air pollutants; however, by 2011, the portfolio has evolved to include or expand the variety of endocrine disruptors, pesticides/persistent organic pollutants and metals. An assortment of brain-health endpoints is most targeted across the portfolios, whereas reproduction and cancer increase steadily over the same time period, and new endpoints like obesity are introduced by 2011. With mounting evidence connecting early-life exposures to later-life disease, we conclude that it is critical to expand the original DOHaD concept to include environmental chemical exposures, and to continue a research agenda that emphasizes defining sensitive windows of exposure and the mechanisms that cause disease.

Obesity and diabetes have overtaken smoking as the number 1 preventable health determinate in the United States. In its basic form, obesity is due to disruptions of the endocrine systems that control food intake, satiety, and metabolic rate. Recent studies have identified a subclass of endocrine disrupting chemicals that interfere with hormonally regulated metabolic processes, especially during early development. These chemicals, called “obesogens,” may predispose individuals to gain weight despite efforts to limit caloric intake and increase physical activity. Evidence suggests that chemical exposures early in life can predispose individuals to weight gain through programming changes, which may enhance dysfunctional eating behaviors later in life. This review examines the latest research on the obesogen hypothesis and its underpinnings in the Developmental Origins of Heath and Disease model. We provide examples of known and suspected obesogens, and evidence of their general mechanisms of action. The research reviewed here provides a solid foundation of knowledge from which health scientists may draw from and build upon to inform their research and decision-making.

In 1996, the U.S. Congress passed the Food Quality Protection Act and amended the Safe Drinking Water Act (SDWA) requiring the U.S. Environmental Protection Agency (EPA) to implement a screening program to investigate the potential of pesticide chemicals and drinking water contaminants to adversely affect endocrine pathways. Consequently, the EPA launched the Endocrine Disruptor Screening Program (EDSP) to develop and validate estrogen, androgen, and thyroid (EAT) pathway screening assays and to produce standardized and harmonized test guidelines for regulatory application. In 2009, the EPA issued the first set of test orders for EDSP screening and a total of 50 pesticide actives and 2 inert ingredients have been evaluated using the battery of EDSP Tier 1 screening assays (i.e., five in vitro assays and six in vivo assays). To provide a framework for retrospective analysis of the data generated and to collect the insight of multiple stakeholders involved in the testing, more than 240 scientists from government, industry, academia, and non-profit organizations recently participated in a workshop titled "Lessons Learned, Challenges, and Opportunities: The U.S. Endocrine Disruptor Screening Program." The workshop focused on the science and experience to date and was organized into three focal sessions: (a) Performance of the EDSP Tier 1 Screening Assays for Estrogen, Androgen, and Thyroid Pathways; (b) Practical Applications of Tier 1 Data; and (c) Indications and Opportunities for Future Endocrine Testing. A number of key learnings and recommendations related to future EDSP evaluations emanated from the collective sessions.

Recently, medical research has seen a strong push toward translational research, or "bench to bedside" collaborations, that strive to enhance the utility of laboratory science for improving medical treatment. The success of that paradigm supports the potential application of the process to other fields, such as risk assessment. Close collaboration among academic, government, and industry scientists may enhance the translation of scientific findings to regulatory decision making. The National Toxicology Program (NTP), National Institute of Environmental Health Sciences (NIEHS), and U.S. Food and Drug Administration (FDA) developed a consortium-based research program to link more effectively academic and guideline-compliant research. An initial proof-of-concept collaboration, the Consortium Linking Academic and Regulatory Insights on BPA Toxicity (CLARITY-BPA), uses bisphenol A (BPA) as a test chemical. The CLARITY-BPA program combines a core perinatal guideline-compliant 2-year chronic toxicity study with mechanistic studies/endpoints conducted by academic investigators. Twelve extramural grantees were selected by NIEHS through an RFA-based initiative to participate in the overall study design and conduct disease-relevant investigations using tissues and animals from the core study. While the study is expected to contribute to our understanding of potential effects of BPA, it also has ramifications beyond this specific focus. Through CLARITY-BPA, NIEHS has established an unprecedented level of collaboration among extramural grantees and regulatory researchers. By drawing upon the strengths of academic and regulatory expertise and research approaches, CLARITY-BPA represents a potential new model for filling knowledge gaps, enhancing quality control, informing chemical risk assessment, and identifying new methods or endpoints for regulatory hazard assessments.

Within the past few decades, the concept of endocrine-disrupting chemicals (EDCs) has risen from a position of total obscurity to become a focus of dialogue, debate, and concern among scientists, physicians, regulators, and the public. The emergence and development of this field of study has not always followed a smooth path, and researchers continue to wrestle with questions about the low-dose effects and nonmonotonic dose responses seen with EDCs, their biological mechanisms of action, the true pervasiveness of these chemicals in our environment and in our bodies, and the extent of their effects on human and wildlife health. This review chronicles the development of the unique, multidisciplinary field of endocrine disruption, highlighting what we have learned about the threat of EDCs and lessons that could be relevant to other fields. It also offers perspectives on the future of the field and opportunities to better protect human health.

Background: Bisphenol A (BPA) is a high production volume chemical used to make polycarbonate plastic and is found in many consumer products. Some studies using animal models have suggested that BPA exposures may have adverse health effects. However, research gaps have precluded a full understanding of the effects of BPA in humans and engendered controversies surrounding the chemical’s potential toxicity. Objectives: The National Institute of Environmental Health Sciences (NIEHS) and National Toxicology Program (NTP) have developed an integrated, multipronged, consortium-based approach to optimize BPA-focused research investments to more effectively address data gaps and inform decision making. Discussion: NIEHS/NTP BPA research investments made over the past 4 years include extramural research grants, establishment of a BPA Grantee Consortium, intramural research activities on BPA’s mechanisms of action, the launch of two clinical studies and an occupational study, development of a round-robin experiment to validate BPA measurements in human serum, and, in collaboration with the Food and Drug Administration (FDA), formation of a consortium to design and execute a chronic toxicity study of BPA in rats. The NIEHS’s new consortium-based approach has led to more integrated, collaborative efforts and should improve our ability to resolve controversies over the potential human health effects of exposures to low levels of endocrine-active agents.

Sponsored by the New York Academy of Sciences and Cincinnati Children's Hospital Medical Center, with support from the National Institute of Environmental Health Sciences (NIEHS), the National Institute on Drug Abuse (NIDA), and Life Technologies, "Fetal Programming and Environmental Exposures: Implications for Prenatal Care and Preterm Birth" was held on June 11-12, 2012 at the New York Academy of Sciences in New York City. The meeting, comprising individual talks and panel discussions, highlighted basic, clinical, and translational research approaches, and highlighted the need for specialized testing of drugs, consumer products, and industrial chemicals, with a view to the unique impacts these can have during gestation. Speakers went on to discuss many other factors that affect prenatal development, from genetics to parental diet, revealing the extraordinary sensitivity of the developing fetus.

Environmental chemicals have significant impacts on biological systems. Chemical exposures during early stages of development can disrupt normal patterns of development and thus dramatically alter disease susceptibility later in life. Endocrine disrupting chemicals (EDCs) interfere with the body's endocrine system and produce adverse developmental, reproductive, neurological, cardiovascular, metabolic and immune effects in humans. A wide range of substances, both natural and man-made, are thought to cause endocrine disruption, including pharmaceuticals, dioxin and dioxin-like compounds, polychlorinated biphenyls, DDT and other pesticides, and components of plastics such as bisphenol A (BPA) and phthalates. EDCs are found in many everyday products– including plastic bottles, metal food cans, detergents, flame retardants, food additives, toys, cosmetics, and pesticides. EDCs interfere with the synthesis, secretion, transport, activity, or elimination of natural hormones. This interference can block or mimic hormone action, causing a wide range of effects. This review focuses on the mechanisms and modes of action by which EDCs alter hormone signaling. It also includes brief overviews of select disease endpoints associated with endocrine disruption.

DYRK1A (the dual specificity tyrosine phosphorylation-regulated kinase 1A) plays an important role in body growth and brain physiology. Overexpression of this kinase has been associated with the development of Down syndrome in both human and animal models, whereas single copy loss-of-function of DYRK1A leads to increased apoptosis and decreased brain size. Although more than a dozen of DYRK1A targets have been identified, the molecular basis of its involvement in neuronal development remains unclear. Here we show that DYRK1A and another pro-survival member of the DYRK family, DYRK3, promote cell survival through phosphorylation and activation of SIRT1, an NAD(+)-dependent protein deacetylase that is essential in a variety of physiological processes including stress response and energy metabolism. DYRK1A and DYRK3 directly phosphorylate SIRT1 at Thr(522), promoting deacetylation of p53. A SIRT1 phosphorylation mimetic (SIRT1 T522D) displays elevated deacetylase activity, thus inhibiting cell apoptosis. Conversely, a SIRT1 dephosphorylation mimetic (SIRT1 T522V) fails to mediate DYRK-induced deacetylation of p53 and cell survival. We show that knockdown of endogenous DYRK1A and DYRK3 leads to hypophosphorylation of SIRT1, sensitizing cells to DNA damage-induced cell death. We also provide evidence that phosphorylation of Thr(522) activates SIRT1 by promoting product release, thereby increasing its enzymatic turnover. Taken together, our findings provide a novel mechanism by which two anti-apoptotic DYRK members promote cell survival through direct modification of SIRT1. These findings may have important implications in understanding the molecular mechanisms of tumorigenesis, Down syndrome, and aging.

Oxidative and hypertrophic stresses contribute to the pathogenesis of heart failure. Insulin-like growth factor-1 (IGF-1) is a peptide hormone with a complex post-transcriptional regulation, generating distinct isoforms. Locally acting IGF-1 isoform (mIGF-1) helps the heart to recover from toxic injury and from infarct. In the murine heart, moderate overexpression of the NAD(+)-dependent deacetylase SirT1 was reported to mitigate oxidative stress. SirT1 is known to promote lifespan extension and to protect from metabolic challenges. Circulating IGF-1 and SirT1 play antagonizing biological roles and share molecular targets in the heart, in turn affecting cardiomyocyte physiology. However, how different IGF-1 isoforms may impact SirT1 and affect cardiomyocyte function is unknown. Here we show that locally acting mIGF-1 increases SirT1 expression/activity, whereas circulating IGF-1 isoform does not affect it, in cultured HL-1 and neonatal cardiomyocytes. mIGF-1-induced SirT1 activity exerts protection against angiotensin II (Ang II)-triggered hypertrophy and against paraquat (PQ) and Ang II-induced oxidative stress. Conversely, circulating IGF-1 triggered itself oxidative stress and cardiomyocyte hypertrophy. Interestingly, potent cardio-protective genes (adiponectin, UCP-1 and MT-2) were increased specifically in mIGF-1-overexpressing cardiomyocytes, in a SirT1-dependent fashion. Thus, mIGF-1 protects cardiomyocytes from oxidative and hypertrophic stresses via SirT1 activity, and may represent a promising cardiac therapeutic.

Our recent study defined a new role for SIRT1 as a regulator of hepatic lipid metabolism. In the liver a major target of this sirtuin is the PPARalpha/PGC-1alpha signaling axis. Ablation of SIRT1 in the liver results in disrupted fatty acid oxidation, increased cellular stress, and elevations in proinflammatory cytokines. However, contrary to previous studies, we observed no changes in glucose production in the absence of SIRT1, despite impaired PGC-1alpha signaling. These findings point toward the involvement of other players in SIRT1-regulated hepatic metabolism. Here we discuss our findings, and comment on some of the controversy surrounding this protein in the current literature.

Hepatic metabolic derangements are key components in the development of fatty liver, insulin resistance, and atherosclerosis. SIRT1, a NAD+-dependent protein deacetylase, is an important regulator of energy homeostasis in response to nutrient availability. Here we demonstrate that hepatic SIRT1 regulates lipid homeostasis by positively regulating peroxisome proliferators-activated receptor alpha (PPARalpha), a nuclear receptor that mediates the adaptive response to fasting and starvation. Hepatocyte-specific deletion of SIRT1 impairs PPARalpha signaling and decreases fatty acid beta-oxidation, whereas overexpression of SIRT1 induces the expression of PPARalpha targets. SIRT1 interacts with PPARalpha and is required to activate PPARalpha coactivator PGC-1alpha. When challenged with a high-fat diet, liver-specific SIRT1 knockout mice develop hepatic steatosis, hepatic inflammation, and endoplasmic reticulum stress. Taken together, our data indicate that SIRT1 plays a vital role in the regulation of hepatic lipid homeostasis and that pharmacological activation of SIRT1 may be important for the prevention of obesity-associated metabolic diseases.

Retinoic acid (RA) displays potent anticarcinogenic activities that are mediated by the nuclear retinoic acid receptors (RARs). However, use of RA in oncology is limited by RA resistance acquired during carcinogenesis. Moreover, in some cancers, RA facilitates rather than inhibits growth. A clue to this paradoxical behavior was recently suggested by the findings that RA also activates PPARβ/δ, a receptor involved in mitogenic and anti-apoptotic activities. The observations that partitioning of RA between its two receptors is regulated by two intracellular lipid-binding proteins—CRABP-II, which targets RA to RAR, and FABP5, which delivers it to PPARβ/δ—further suggest that RA resistance may stem from the deregulation of the binding proteins, resulting in activation of PPARβ/δ rather than RAR. Here, we show that, in the RA-resistant mouse model of breast cancer MMTV-neu , RA indeed activates the nonclassical RA receptor PPARβ/δ. This behavior was traced to an aberrantly high intratumor FABP5/CRABP-II ratio. Decreasing this ratio in mammary tissue diverted RA from PPARβ/δ to RAR and suppressed tumor growth. The data demonstrate the existence of a mechanism that underlies RA resistance in tumors, indicate that CRABP-II functions as a tumor suppressor, and suggest that the inhibition of FABP5 may comprise a therapeutic strategy for overcoming RA resistance in some tumors.

Transcriptional activation of the nuclear receptor RAR by retinoic acid (RA) often leads to inhibition of cell growth. However, in some tissues, RA promotes cell survival and hyperplasia, activities that are unlikely to be mediated by RAR. Here, we show that, in addition to functioning through RAR, RA activates the "orphan" nuclear receptor PPARbeta/delta, which, in turn, induces the expression of prosurvival genes. Partitioning of RA between the two receptors is regulated by the intracellular lipid binding proteins CRABP-II and FABP5. These proteins specifically deliver RA from the cytosol to nuclear RAR and PPARbeta/delta, respectively, thereby selectively enhancing the transcriptional activity of their cognate receptors. Consequently, RA functions through RAR and is a proapoptotic agent in cells with high CRABP-II/FABP5 ratio, but it signals through PPARbeta/delta and promotes survival in cells that highly express FABP5. Opposing effects of RA on cell growth thus emanate from alternate activation of two different nuclear receptors.

© 2015 Heindel et al. A multidisciplinary group of experts gathered in Parma Italy for a workshop hosted by the University of Parma, May 16-18, 2014 to address concerns about the potential relationship between environmental metabolic disrupting chemicals, obesity and related metabolic disorders. The objectives of the workshop were to: 1. Review findings related to the role of environmental chemicals, referred to as "metabolic disruptors", in obesity and metabolic syndrome with special attention to recent discoveries from animal model and epidemiology studies; 2. Identify conclusions that could be drawn with confidence from existing animal and human data; 3. Develop predictions based on current data; and 4. Identify critical knowledge gaps and areas of uncertainty. The consensus statements are intended to aid in expanding understanding of the role of metabolic disruptors in the obesity and metabolic disease epidemics, to move the field forward by assessing the current state of the science and to identify research needs on the role of environmental chemical exposures in these diseases. We propose broadening the definition of obesogens to that of metabolic disruptors, to encompass chemicals that play a role in altered susceptibility to obesity, diabetes and related metabolic disorders including metabolic syndrome.

Thaddeus T. Schug * National Institute of Environmental Health Sciences, Division of Extramural Research and Training, Cellular, Organ and Systems Pathobiology Branch, Research Triangle Park, NC 27709, USA Received: February 28, 2011; Accepted: March 1, 2011; Published: March 1, 2011; Correspondence: Thaddeus T. Schug, e-mail: // //

Identifying chemicals, beyond those already implicated, to test for potential endocrine disruption is a challenge and high throughput approaches have emerged as a potential tool for this type of screening. This review focused the Environmental Protection Agency's (EPA) ToxCast(TM) high throughput in vitro screening (HTS) program. Utility for identifying compounds was assessed and reviewed by using it to run the recently expanded chemical library (from 309 compounds to 1858) through the ToxPi(TM) prioritization scheme for endocrine disruption. The analysis included metabolic and neuroendocrine targets. This investigative approach simultaneously assessed the utility of ToxCast, and helped identify novel chemicals which may have endocrine activity. Results from this exercise suggest the spectrum of environmental chemicals with potential endocrine activity is much broader than indicated, and that some aspects of endocrine disruption are not fully covered in ToxCast.

Bisphenol A (BPA) is a high production endocrine disrupting chemical found in numerous consumer products. BPA has been used commercially since 1957 to make hard polycarbonate plastics and epoxy resins used in food-can linings, cash-register receipts, and dental resins. The ubiquity of BPA in our environment results in exposure to this chemical daily in human populations. But controversy remains regarding how much BPA humans actually ingest or otherwise encounter. Many laboratory animal and human studies have linked exposures to BPA, a hormone mimicking chemical, to adverse health effects, including altered behavior and obesity in children, reproductive abnormalities, cardiovascular changes, and various cancers. However, there have been considerable inconsistencies in the outcomes from these studies with respect to the nature of the adverse health effects observed, and questions as to whether the BPA dose at which they occur are within the range of non-occupational human exposures. This chapter reviews the latest research on BPA, focusing on human exposure, discussions of biomonitoring studies and toxicokinetic models, human health effects, and research needs. We also include illustrative examples of animal models that address whether BPA-exposure is associated with changes in certain health endpoints.

The p53 tumor suppressor protein is arguably the most important guardian of the mammalian genome. p53 promotes longevity by reducing somatic mutations or the survival and proliferation of mutant cells. Under normal conditions, this proteins role is inconsequential because of the rapidity of its degradation. But stress signals of almost any form halt the degradation of p53, unleashing an active protein that triggers transient cell cycle arrest, apoptosis, or cellular senescence [1]. Both apoptosis and senescence are potent tumor suppressor mechanisms that irreversibly prevent tumorgenesis [2]. However, both processes also deplete tissues of proliferation-competent progenitor cells, which is a characteristic associated with degenerative aging. Therefore mammalian survival paradoxically lies at the mercy of p53, which oversees a tight balance between tumor suppression and long-term cell proliferation. Almost all human cancers contain impairments in the p53 signaling pathway [3]. Roughly one half of cancers have inactivating mutations of p53, while the remaining half retain function but have miscued activation, degradation or cell-cycling. Intense focus on understanding p53 regulation at the molecular level has led to interest in isolating and developing small-molecule targets of p53 activity to treat various forms of cancer. Nutlins are cis-imidazoline analogs, which inhibit the interaction between MDM2 (murine double minute 2) and p53, and were discovered by screening a chemical library done by Vassilev and colleagues [4]. MDM2 negatively regulates p53 by binding to and transporting the protein to the cytoplasm where it attaches to an E3 ubiquitin ligase and becomes subject to proteosomal degradation. Nutlins prevent p53-MDM2 interaction, and thus induce expression of p53-regulated genes, which exhibit potent anti-proliferative activities (Figure ​(Figure1A). 1A). Figure 1. The p53 signaling pathway in response to genotoxic stress in tumorogenic cells. Senescence is a complex genetic program and a cell fate decision that establishes permanent growth arrest, which is a theurapeutic goal in cancer treatment. Although there is no direct link between cellular senescence and aging, a correlation does exist, as the number of senescent cells increases in mammals as they age [5]. Activation of p53 is crucial for initiating and maintaining senescence in most cell types. However, the pro-apoptotic arm of the p53 signaling pathway in some senescent cells is dysfunctional [6,7]. In this issue of Aging, Huang et al. explore p53 transcriptional activity and apoptosis in senescent human lung fibroblasts using nutlin-3. Because nutlin-3 is not genotoxic and does not cause p53 phosphorylation or deacetylation, it effectively allows investigation of downstream p53 signaling in senescent cells. Senescent cells are characterized by highly compacted heterochromatin, termed "senescence-associated hetero-chromatin foci", or SAHF [8]. These SAHF are thought to lack sites of active gene transcription, as bulk DNA is less accessible to the loading of necessary transcription factors [9]. Huang et al. observed morphological traits typical of senescence in human fibroblast cells (WI-38), however, they also noted that basal p53 expression levels and target gene activity was normal, or even slightly higher. In an attempt to induce p53 transcription without affecting upstream signaling, the investigators exposed cells to nutlin-3. Although protein levels remain consistent in both early passage and senescent WI-38 cells, transcriptional activity of p53 was attenuated upon nutlin-3 treatment. Moreover, the combined treatment of nutlin-3, together with the DNA damaging compound doxorubicin, boosted p53 levels and restored normal transcriptional activity. Huang et al. conclude that the decline in p53 functionality in senescent cells is due to changes in upstream signaling that ultimately leads to destabilization of p53 and abrogated signaling. They point to the possibility that the pro-apoptotic functions of p53 may be redundant in senescent cells, which have already lost their ability to proliferate and become cancerous. These findings add to a recent publication by this group revealing that nutlin-3 can induce a senescence-like state in several epithelial cancer cell lines [10], but it is reversible and cells resume proliferation upon drug removal and normalization of p53 signaling. Perhaps in senescent cells p53 is at a balance, coordinating between DNA damage signaling and apoptosis. Further studies will be important to help identify and optimize therapeutic targets used to treat tumor suppression without the downsides associated with continual drug treatment or accelerating aging. The study by Huang and coworkers highlights several important issues in cancer therapy development. In addition to p53-mediated apoptosis, nutlins may induce and maintain a permanent dormancy in cancer cells. The ability for nutlin-3 to activate p53 without the genotoxic stresses incurred by most chemotherapeutic agents is of tremendous clinical importance. It may be of value to note that acetylation of p53 also inhibits p53-MDM2 interactions [11,12]. Several recent reports have identified the longevity gene, SIRT1, as key regulator of p53 acetylation [13-15]. Use of small molecule inhibitors of SIRT1, such as Tenovin 6, in tandem with nutlins, may provide a double hit on the p53 pathway and push the balance toward acetylated and activated p53 protein levels sufficient enough to induce apoptosis in cancer cells (Figure ​(Figure1B)1B) [16].

Both the National Institute of Environmental Health Sciences (NIEHS) and the U.S. Food and Drug Administration (FDA) work to promote and protect public health. The NIEHS achieves this mission by conducting research, including toxicological studies, on agents of public health concern through its intramural laboratories, the National Toxicology Program (NTP), grants and contracts to research labs across the country, and interagency agreements. The FDA, in turn, reviews and uses information from these and other studies and, where needed, performs studies of its own to develop standards to ensure that the products it regulates meet its requirements, maximizing product benefits while protecting the public from unacceptable risks. The FDA and NIEHS have a long history of working together to generate and evaluate toxicological data necessary both for setting standards and for informing important regulatory decisions. For example, collaborative research projects between the NTP (itself a collaboration involving the National Institutes of Health, FDA, and Centers for Disease Control and Prevention) and the FDA National Center for Toxicological Research (NCTR) have contributed to safety determinations and regulation of a number of ingredients in dietary supplements, animal feed, and cosmetics and have been important for assessing potential risks of both human and veterinary pharmaceuticals (NTP 2013). For several years, the NIEHS and FDA have been working collaboratively to address potential health concerns about bisphenol A (BPA), a chemical used in manufacturing the packaging of some foods and beverages, in some medical devices, and in some thermal papers. In September 2008, the NTP completed a review of available research on BPA and concluded that there was “some concern for effects on the brain, behavior, and prostate gland in fetuses, infants, and children at current human exposures.” The NTP report also recognized the existence of substantial uncertainties, stating that “Overall, the current literature cannot yet be fully interpreted for biological or experimental consistency or for relevance to human health” [NTP-Center for the Evaluation of Risks to Human Reproduction (CERHR) 2008]. In 2008, the FDA, which has regulatory authority over many consumer and medical products containing BPA, issued a draft assessment of BPA (FDA 2008). In 2009, the FDA provided additional updates to the assessment and expressed its agreement with the the NTP’s perspective (FDA 2013). The FDA, like the NTP, also identified substantial uncertainties both in reported BPA research findings and in their implications for human health. Both agencies called for further research focused on key questions about BPA to help address and reduce these uncertainties. Since that time, the FDA and NIEHS have worked both independently and collaboratively to address areas of concern and to reduce uncertainties, including collaboration to enhance the relevance and usefulness of planned research in assessing potential risks to human health. These collaborative efforts have resulted in a number of important advances in our understanding of BPA. Both the focus and careful planning of the research, as well as the research findings themselves, are highly relevant for approaching other similar issues. Important accomplishments include technological and methodological advances in critical assays [e.g., determining levels of the active form of BPA in blood (Patterson et al. 2013)] and assuring strong study design, performance, and analysis, including carefully addressing considerations such as control groups and statistical analysis (Delclos 2013). The FDA/NCTR and the NIEHS Clinical Research Unit have incorporated these advances and perspectives in planning and carrying out a comprehensive investigation of BPA pharmacokinetics in human volunteers. The FDA/NIEHS collaboration has also more generally supported approaches to the design and conduct of studies that enhance study utility and reliability for supporting sound decision making. We have worked together to support both large-scale regulatory studies that examine multiple biological end points of concern, and new and unprecedented collaborations between academic and regulatory scientists that enable smaller-scale exploratory studies of mechanistic and other end points not traditionally evaluated in regulatory toxicological studies. The results of our collaborations to date have been especially important in improving the understanding of how BPA is metabolized and handled once in the body. This has greatly reduced key uncertainties concerning potential levels of internal exposure in humans. For example, we have learned that newborn and young rodents have significant age-dependent differences in metabolic capabilities, resulting in their not being able to metabolize BPA as well as adult rodents do and thus being exposed to higher levels internally; this is not the case for nonhuman primates (Doerge et al. 2010). Multiple pharmacokinetic studies in monkeys (supported by preliminary results in humans) have now demonstrated that newborn and young primates metabolize BPA at or very near the level of adult metabolism (Fisher et al. 2011; Patterson et al. 2013). Additional collaborative studies in pregnant primates have also shown both that potential fetal exposure is significantly reduced by the mother’s metabolic capabilities and that the fetus can effectively metabolize BPA (Doerge et al. 2010; Patterson et al. 2013). Through the combined and collaborative efforts of the NIEHS and FDA, many important questions surrounding BPA and risks to human health have been or will be addressed in the near future. The promise of this collaborative approach between FDA regulatory researchers and NIEHS academic researchers extends well beyond BPA. It represents a new model for filling knowledge gaps and enhancing the value of investments in research, developing and promoting best methods and practices, informing chemical risk assessment, and identifying new methods or end points with the potential to improve regulatory hazard assessments and enhance protection of humans. The goal of all our efforts is to support and perform the best science we can to inform the best possible decision making. Strong science is the common ground that can help us—particularly in situations of controversy where emotions and beliefs may become strong and positions polarized—to work together to accomplish what we all want to accomplish, keeping the public safe. Everyone involved in collaborative research has a role to play in building our understanding of the potential biological and/or health effects of substances and advancing technologies and methodologies, with the shared goal of protecting the public health.

Obesity rates have risen steadily in the United States and around the world over the past century, with a marked escalation within the past two decades. Conventional wisdom within the medical community is that the burgeoning obesity epidemic is the product of poor nutrition and lack of exercise, but increasingly researchers are questioning whether those factors are wholly responsible. Emerging research about alternative factors is setting the stage for today's "Perfect Storm" for obesity.

Two articles in this issue of Environmental Health Perspectives—Xia et al. (2013) and Bonner et al. (2013)—report results of a unique collaborative approach to environmental health research. The consortium behind these studies (the Nano GO Consortium), which is developing standardized methods for assessing the health and safety implications of engineered nanomaterials (ENMs), represents a new model of shared science that may offer lessons for other emerging and fast-evolving areas of research. ENMs (man-made particles with any external dimension between 1 and 100 nm) have enabled considerable advances in electronics, drugs and medical devices, environmental remediation, and many other areas (Kessler 2011). They are fast becoming ubiquitous in products such as sunscreens, cosmetics, clothing, and building materials. Global demand for nanomaterials and nanoenabled devices is expected to approach $3.1 trillion by 2015 (Marquis et al. 2009). As the production and use of ENMs grows, there are increased opportunities for ENMs to interact with biological systems. The physical, chemical, and biological characteristics of ENMs that make them useful for so many applications also make them potentially hazardous for living systems. The unique properties stemming from their small dimensions, such as high reactivity, large surface area, and the tunable nature of their optical, electrical, and magnetic properties, differentiate them from other materials in fundamental ways. The vast and expanding array of ENMs entering the environment could present health risks to researchers, workers, and consumers. Although researchers have made progress in understanding biological responses to nanomaterials, the risks of exposure are not sufficiently understood to allow development of science-based risk assessment guidelines to support regulatory decision making (Maynard et al. 2006). There is a need to examine nanomaterial exposure, absorption, distribution, metabolism, and excretion and to relate ENM properties to biological responses at the cellular, tissue, and whole-organism level. Determining the health effects of ENMs presents some unique challenges. The thousands of ENMs in use today are made from an enormous range of substances, vary considerably in size, and take a diversity of shapes, including spheres, cubes, cones, tubes, and other forms. They are also produced in different laboratories across the world using a variety of methods. In the scientific literature, findings on the properties and toxicity of these materials are mixed and often difficult to compare across studies. To improve the reliability and reproducibility of data in this area, there is a need for uniform research protocols and methods, handling guidelines, procurement systems, and models. Because ENMs behave as particles, their size, shape, agglomeration state, surface chemistry, reactivity, and surface area, along with the number of particles, are all important parameters of ENM dose and are therefore factors in determining the ENM dose–response relationship. As a result, full and accurate characterization of the physical and chemical properties of ENMs is critical in assessing the biological effects of these materials. However, most of the published research does not provide detailed physical and chemical characterization of the nanomaterials or identify which characteristics are instrumental in their biological effects. New risk assessment models are needed that incorporate detailed characterization of ENMs with mechanistic and systems-level effects. Although there is still much to learn about the toxicity of ENMs, we are fortunate to start with a clean slate: There are as yet no documented incidences of human disease due to ENM exposure (Xia et al. 2009). Because ENMs are manmade rather than natural substances, we have an opportunity to design, manufacture, and use these materials in ways that allow us to reap the maximum benefits—and minimal risk—to humans. With $13 million from the American Recovery and Reinvestment Act (2009), the National Institute of Environmental Health Sciences (NIEHS) awarded 13 2-year grants to advance research on the health impacts of ENMs (NIEHS 2013). Ten grants were awarded through the National Institutes of Health (NIH) Grand Opportunities program and three were funded through the NIH Challenge Grants program. One goal of this investment was to develop reliable, reproducible methods to assess exposure and biological response to nanomaterials. To advance their shared goal, the grantees were brought together to form the Engineered Nanomaterials Grand Opportunity (Nano GO) consortium. Within the framework of the consortium, grantees designed and conducted a series of “round-robin” experiments in which similar or identical methods were used to perform in vitro and in vivo tests on the toxicity of selected nanomaterials concurrently at 13 different laboratories. The consortium quickly became an active hub of communication. Four in-person meetings, combined with conference calls held at least bimonthly, allowed consortium members to work closely together to share experiences and results, identify problems, and refine methods and protocols as the tests proceeded. These experiments and their results are described by Xia et al. (2013) and Bonner et al. (2013). The findings of the round-robin studies elucidate some important biological interactions of ENMs and can help inform the development of predictive models needed to establish regulatory guidelines for ENM production and use. Beyond the specific outcomes related to the toxicity of the tested nanomaterials, however, several broader lessons can be drawn from the structure of the Nano GO Consortium and the research process itself. First, the process of working together to design and conduct concurrent round-robin experiments was crucial to the participants’ ability to develop reliable, reproducible research methods and protocols for studying the health effects of ENMs. Frequent communication among principal investigators and laboratory technicians allowed consortium members to continuously compare, troubleshoot, and refine protocols, ultimately significantly improving the harmonization of results. In addition, centralized characterization of the selected ENMs proved critical to researchers’ ability to standardize approaches and interpret results across laboratories. The NIEHS Centers for Nanotechnology Health Implications Research consortium, launched in 2011, will continue to build upon these protocols. Second, the consortium structure motivated participants to communicate much more openly than is typical in most areas of research. In a discussion session held during the consortium’s final meeting, several participants noted that the shared goal of harmonization of methods and results across laboratories encouraged participants to fully engage with the planning process and to scrupulously follow the protocols to avoid being an outlier. In addition, repeating the same experiments in different laboratories proved scientifically valuable because researchers were able to have more confidence in the results. Finally, several participants identified interdisciplinary collaboration as a key benefit of the consortium. Drawing upon participants’ diverse collective knowledge allowed the group to effectively tackle complex problems that would have been much more difficult for a single laboratory or researcher to resolve alone. In addition, some participants reflected that interdisciplinary exchanges helped them achieve unexpected advances that will be valuable in moving the field forward. Conducting experiments in a round-robin format within a consortium structure is an unfamiliar approach for most researchers. Although some researchers acknowledged that working collaboratively with such a large and diverse group at times stretched the limits of their comfort zones, the consortium ultimately proved to be “greater than the sum of its parts,” resulting in reliable, standardized protocols that would have been difficult for researchers to achieve by working independently. Indeed, many participants reflected that participating in the consortium not only benefitted their shared goals but also enhanced their individual research efforts. The round-robin approach and the overall consortium structure may be valuable models for other emerging areas of science.

Fetal and early postnatal development constitutes the most vulnerable time period of human life in regard to adverse effects of environmental hazards. Subtle effects during development can lead to functional deficits and increased disease risk later in life. The hypothesis stating that environmental exposures leads to altered programming and, thereby, to increased susceptibility to disease or dysfunction later in life has garnered much support from both experimental and epidemiological studies. Similar observations have been made on the long-term impact of nutritional unbalance during early development. In an effort to bridge the fields of nutritional and environmental developmental toxicity, the Society of Toxicology sponsored this work. This report summarizes novel findings in developmental toxicity as reported by select invited experts and meeting attendees. Recommendations for the application and improvement of current and future research efforts are also presented.

Sirtuins are a family of protein deacetylases, deacylases, and ADP-ribosyltransferases that regulate life span, control the onset of numerous age-associated diseases, and mediate metabolic homeostasis. We have uncovered a novel role for the mitochondrial sirtuin SIRT4 in the regulation of hepatic lipid metabolism during changes in nutrient availability. We show that SIRT4 levels decrease in the liver during fasting and that SIRT4 null mice display increased expression of hepatic peroxisome proliferator-activated receptor α (PPARα) target genes associated with fatty acid catabolism. Accordingly, primary hepatocytes from SIRT4 knockout (KO) mice exhibit higher rates of fatty acid oxidation than wild-type hepatocytes, and SIRT4 overexpression decreases fatty acid oxidation rates. The enhanced fatty acid oxidation observed in SIRT4 KO hepatocytes requires functional SIRT1, demonstrating a clear cross talk between mitochondrial and nuclear sirtuins. Thus, SIRT4 is a new component of mitochondrial signaling in the liver and functions as an important regulator of lipid metabolism.

A central goal of green chemistry is to avoid hazard in the design of new chemicals. This objective is best achieved when information about a chemical’s potential hazardous effects is obtained as early in the design process as feasible. Endocrine disruption is a type of hazard that to date has been inadequately addressed by both industrial and regulatory science. To aid chemists in avoiding this hazard, we propose an endocrine disruption testing protocol for use by chemists in the design of new chemicals. The Tiered Protocol for Endocrine Disruption (TiPED) has been created under the oversight of a scientific advisory committee composed of leading representatives from both green chemistry and the environmental health sciences. TiPED is conceived as a tool for new chemical design, thus it starts with a chemist theoretically at “the drawing board.” It consists of five testing tiers ranging from broad in silico evaluation up through specific cell- and whole organism-based assays. To be effective at detecting endocrine disruption, a testing protocol must be able to measure potential hormone-like or hormone-inhibiting effects of chemicals, as well as the many possible interactions and signaling sequellae such chemicals may have with cell-based receptors. Accordingly, we have designed this protocol to broadly interrogate the endocrine system. The proposed protocol will not detect all possible mechanisms of endocrine disruption, because scientific understanding of these phenomena is advancing rapidly. To ensure that the protocol remains current, we have established a plan for incorporating new assays into the protocol as the science advances. In this paper we present the principles that should guide the science of testing new chemicals for endocrine disruption, as well as principles by which to evaluate individual assays for applicability, and laboratories for reliability. In a ‘proof-of-principle’ test, we ran 6 endocrine disrupting chemicals (EDCs) that act via different endocrinological mechanisms through the protocol using published literature. Each was identified as endocrine active by one or more tiers. We believe that this voluntary testing protocol will be a dynamic tool to facilitate efficient and early identification of potentially problematic chemicals, while ultimately reducing the risks to public health.

Background: The past decade has seen tremendous expansion in the production and application of engineered nanomaterials (ENMs). The unique properties that make ENMs useful in the marketplace also make their interactions with biological systems difficult to anticipate and critically important to explore. Currently, little is known about the health effects of human exposure to these materials. Objectives: As part of its role in supporting the National Nanotechnology Initiative, the National Institute of Environmental Health Sciences (NIEHS) has developed an integrated, strategic research program—“ONE Nano”—to increase our fundamental understanding of how ENMs interact with living systems, to develop predictive models for quantifying ENM exposure and assessing ENM health impacts, and to guide the design of second-generation ENMs to minimize adverse health effects. Discussion: The NIEHS’s research investments in ENM health and safety include extramural grants and grantee consortia, intramural research activities, and toxicological studies being conducted by the National Toxicology Program (NTP). These efforts have enhanced collaboration within the nanotechnology research community and produced toxicological profiles for selected ENMs, as well as improved methods and protocols for conducting in vitro and in vivo studies to assess ENM health effects. Conclusion: By drawing upon the strengths of the NIEHS’s intramural, extramural, and NTP programs and establishing productive partnerships with other institutes and agencies across the federal government, the NIEHS’s strategic ONE Nano program is working toward new advances to improve our understanding of the health impacts of engineered nanomaterials and support the goals of the National Nanotechnology Initiative.

The prevalence of obesity and diabetes has risen dramatically in the United States and in other regions of the world over the past two decades. Perhaps even more important is that these metabolic diseases are rising dramatically in our children. There is considerable evidence that the risk factors for obesity and diabetes may begin early in life, during pregnancy, and in early childhood. Evidence shows that rapid weight gain in the first few months of life is associated with obesity later in life. Obesity and diabetes, like other complex diseases, are caused by a series of interactions between genetic, behavioral, and environmental factors. While there are certainly important genetic and lifestyle components contributing to obesity and diabetes, evidence also points to a contributing role of environmental influences, particularly exposure to endocrine disrupting chemicals during periods of development. Here we review current epidemiological and experimental relationships between these chemicals, their mechanisms of action, and the role of environmental exposures in the obesity and diabetes epidemic.

Sirtuin 1 (SIRT1), the mammalian ortholog of yeast Sir2, is a highly conserved NAD(+)-dependent protein deacetylase that has emerged as a key metabolic sensor that directly links environmental nutrient signals to animal metabolic homeostasis. SIRT1 is known to be involved in gluconeogenesis in the liver, fat mobilization in white adipose tissue, and insulin secretion in the pancreas. Recent studies have shown SIRT1 to regulate fatty acid oxidation in the liver, sense nutrient availability in the hypothalamus, influence obesity-induced inflammation in macrophages, and modulate the activity of the circadian clock in metabolic tissues. The activity of SIRT1 also appears to be under the control of AMPK and adiponectin. This review focuses on the involvement of SIRT1 in regulating metabolic diseases associated with obesity. It includes brief overviews of sirtuin signaling, with emphasis on SIRT1's role in the liver, macrophage, brain, and adipose tissue as it relates to obesity.

Macrophage activation and infiltration into resident tissues is known to mediate local inflammation and is a hallmark feature of metabolic syndrome. Members of the sirtuin family of proteins regulate numerous physiological processes, including those involved in nutrient regulation and the promotion of longevity. However, the important role that SIRT1, the leading sirtuin family member, plays in immune response remains unclear. In this study, we demonstrate that SIRT1 modulates the acetylation status of the RelA/p65 subunit of NF-κB and thus plays a pivotal role in regulating the inflammatory, immune, and apoptotic responses in mammals. Using a myeloid cell-specific SIRT1 knockout (Mac-SIRT1 KO) mouse model, we show that ablation of SIRT1 in macrophages renders NF-κB hyperacetylated, resulting in increased transcriptional activation of proinflammatory target genes. Consistent with increased proinflammatory gene expression, Mac-SIRT1 KO mice challenged with a high-fat diet display high levels of activated macrophages in liver and adipose tissue, predisposing the animals to development of systemic insulin resistance and metabolic derangement. In summary, we report that SIRT1, in macrophages, functions to inhibit NF-κB-mediated transcription, implying that myeloid cell-specific modulation of this sirtuin may be beneficial in the treatment of inflammation and its associated diseases.

Chronic inflammation is increasingly recognized as an underlying factor in the development of several pathological disorders including obesity-associated metabolic disease, heart disease, atherosclerosis and rheumatoid arthritis. Macrophages, which are key sentinels of the innate immune system, play

Obesity rates have risen steadily in the United States and around the world over the past century, with a marked escalation within the past two decades. Conventional wisdom within the medical community is that the burgeoning obesity epidemic is the product of poor nutrition and lack of exercise, but increasingly researchers are questioning whether those factors are wholly responsible. Emerging research about alternative factors is setting the stage for today’s “Perfect Storm” for obesity.

SIRT1 (sirtuin 1), the mammalian orthologue of yeast Sir2, is a highly conserved NAD+-dependant deacetylase that is emerging as an important regulator of aging and metabolic disease. SIRT1 and its family members promote longevity in different model organisms, including yeast, worms, flies and mice.

The p53 tumor suppressor protein controls cell fate by inducing apoptosis or cell cycle arrest in response to cell stress [1]. Cell cycle arrest can be temporary (quiescent) or permanent (senescent) depending on p53 regulation [2, 3]. Under normal conditions, p53 binds to MDM2, which transports the protein to the cytoplasm where it undergoes rapid proteosomal degradation. A class of chemotherapeutic molecules called Nutlins inhibit p53-MDM2 interaction, and can therefore be used to control p53 activity in cancer cells [4]. In this issue of Aging, Korotchkina et al make use of nutlin-3a to dissect the mechanism by which p53 induces cellular senescence and quiescence [5]. The group demonstrates that p53-mediated senescence is irreversible in cells that maintain mTOR (mammalian target of rapamycn) signaling. However, when mTOR signaling is inhibited, activation of p53 leads to quiescence (Figure ​(Figure1).1). These findings may have broad implications because the mTOR pathway is dysregulated in many forms of cancer [6]. Figure 1. p53-induced senescence or quiescence. Establishing the mechanisms involved in cell cycle arrest and cell dormancy is critical for understanding cancer cell proliferation. Demidenko et al. have previously demonstrated that despite its ability to induce cell cycle arrest, in some cell types p53 is a suppressor, not an inducer of cellular senescence [7]. They have also shown that cells (HT-p21-9) induced into senescence using an ITPG-inducible p21 expression construct, were converted to quiescence in the presence of p53. In the same cells, nutlin-3a-induction of p53 caused reversible cell cycle arrest, and cells resumed proliferation after removal of nutlin-3a. The same group has also demonstrated that when the cell cycle is blocked, activation of mTOR is required for induction of senescence. Addition of the TOR inhibitor rapamycin converted p21-induced senescent cells back to quiescence [7]. These findings suggest that activa-tion of p53 sets in motion cell cycle arrest, after which its ability to exercise senescence is dependent on its interaction with the mTOR pathway. Senescence is achieved if p53 is incapable of disabling mTOR. Therefore, activating both mTOR and p53 in order to achieve a permanent state of cell dormancy, may prove to be a promising therapeutic strategy for treating cancer. In their current study, Korotchkina et al further explore the role of mTOR as a senescence-inducing factor. They show that nutlin-3a-induced senescent cells converted to a quiescent state when mTOR was inactivated with rapamycin (Figure ​(Figure1).1). Furthermore, the authors show that in p53-mediated quiescent cells, depletion of TSC2, a negative regulator of mTOR, results in conversion to senescence. This body of work may also offer explanations as to the role that p53 plays in aging. Others have shown that p53 function declines with age [8, 9], and mild activation of p53 may increase the lifespan of mice [10]. It will be interesting to further determine the interactions between p53 and mTOR in both models of cancer and aging.

Phthalates are a group of chemicals used to make plastics softer and more flexible. They are used in hundreds of products, such as vinyl flooring, adhesives, detergents, lubricating oils, automotive plastics, plastic clothes (raincoats) and personal-care products (soaps, shampoos, hair sprays and nail polishes). People are exposed to phthalates by eating and drinking foods that have been in contact with containers and products containing phthalates. To a lesser extent, exposure can occur from breathing in air that contains vapors or dust contaminated with phthalate particles. Once phthalates enter a person's body, they are converted into breakdown products that pass out quickly in urine. However, biomonitoring studies that measure urine metabolites in humans show widespread exposure to phthalates. Phthalates have been labeled as potential endocrine disrupting chemicals (EDCs) because studies have demonstrated that they interfere with hormones of the reproductive system. Recently, we reported for the first...