Allen Ray Sing Chen, M.D., M.H.S., Ph.D.

• Associate Professor of Oncology

https://www.hopkinsmedicine.org/profiles/results/directory/profile/0008071/allen-chen

The models also predicted that the untested compounds myristicin and isosafrole would be hepatocarcinogenic if studied at a dose level of 2 mmole/kg/day heart disease yoga generic procardia 30 mg visa, whereas anethole (0 heart disease symptoms procardia 30 mg purchase online. In summary coronary heart yahoo order procardia 30 mg on-line, we have developed and validated a novel machine learning approach to produce classifiers that can accurately predict carcinogenic potential of compounds cardiovascular disease facts generic procardia 30 mg with amex. This is a critical area of research because the etiology of many chronic diseases involves interactions between environmental factors and genes and proteins that modulate important physiological processes arteries clogged cheap procardia. Over 122,000 interactions between 4,000 chemicals and 13,500 genes have been curated from 270 species, and 6,800 gene-disease and 3,200 chemical-disease relationships have been captured. By integrating these data, 390,000 gene-disease relationships and 93,000 chemical-disease relationships can be inferred. Several new features were implemented to enhance data access and analyses including data download options, batch queries and the ability to compare associated data sets for chemicals, genes/proteins or diseases using a custom Venn Viewer tool. A significant amount of drugs to be withdrawn from the market and to fail during clinical trial stage of development is due to liver toxicity. In order to understand liver toxicity at the mechanistic level and develop novel tools for identifying liver toxicity issues along the various stages of drug development, there is a need to develop content-rich resources to improve our basic understanding of liver toxicity and facilitate the efficient development of novel knowledge and tools for utilization by research, industry and regulatory groups. These are (1) Liver Ontology that characterizes liver pathology and toxicity to guide data collection/curation, classification and analysis; (2) Gene Expression Data was collected from public databases and through collaboration; (3) Conduct text mining on >18 millions abstracts in PubMed with an emphasis on liver-related data; (4) Collecting hepatotoxicants and their associated mechanism Known Data through manual curation; and (5) Conducting in house omics experiment on >50 chemicals to augment and validate in silico results. Sexual dimorphism in the expression of many genes is thought to play an important role in disease susceptibility, drug metabolism, and xenobiotic response in both humans and other species. While previous research has explored sex-specific gene expression patterns in liver following various chemical challenges, we explored gene expression differences in a population of naïve mice. As expected, thousands of transcripts exhibited considerable differences in expression between females and males. Purpose: Products containing herbs and other botanicals are becoming increasingly popular as a means of promoting health. The components of such products may contain hundreds of organic moieties, many of which are poorly described or understood. In particular, many botanicals contain alkaloids ­ a diverse group of nitrogen-containing compounds with high potential for biological activity. Methods: the chemical compositions of 63 botanical species were found using multiple electronic resources, primarily "Dr. Results: 80% of the alkaloids were in the "chemical space" of 60% of the current models, including most human organ models, rodent developmental models, and carcinogenicity models. Microbe, neurotox, and reprotox simulations were insufficient to make predictions for many alkaloids. Predicting human drug metabolism is an essential part of drug discovery and the regulatory safety review of new drugs. Species-specific metabolism is a common problem encountered; drug metabolites identified in animal pharmacokinetic studies often differ from those formed in humans, leading to potential drug safety issues related to therapeutic efficacy, chronic toxicity, or drug-drug interactions. Computational prediction of human metabolites offers a rapid and inexpensive way of high-throughput screening for constructing metabolic profiles of drugs early in their development and for safety analyses. However, few computational prediction programs have been evaluated for their performance in predicting human drug metabolites. For the study reported here, 17 hepatotoxic drugs now withdrawn from the market were screened using the MetaDrug computational software program to assess the ability to predict human drug metabolites. This study found that the percentage of correct predictions for the drugs was 38% when considering all known human metabolites, while correct predictions based on major metabolites was significantly higher at 62%. In some cases the software was able to predict potential pathways for toxic metabolite formation. However, further research is needed and is under way in our applied regulatory research unit to design new strategies for prioritizing predicted metabolites to reduce over-prediction. These may include combining in vitro liver microsomes and in silico predictive data, or using multiple computational prediction paradigms to achieve consensus predictions. Molecular structure data were then linked to the dosage and exposure information for each chemical. Prediction performance was determined by adjusting the residuals of these predictions according to the degree of similarity between the test and training data set chemicals. Estimating the carcinogenic and genotoxic potentials of a pesticide product, including its active ingredient(s), its metabolites and contaminants, is an essential part of the risk assessment and risk management safety review for pesticides. The presence of carcinogenic and/or genotoxic activities of this product can limit its commercial applications and its regulatory approval. Accurate knowledge of these toxicological activities could facilitate: (1) Tiered Testing: A sequential resultsdriven approach where data from one tier of testing is used to determine the next step in testing; (2) Integrated Testing Strategies: A hypothesis-driven integration of different types of hazard and exposure information to guide prioritization and the type of testing; and (3) Lead Selection: A safer and more profitable lead selection and discovery process by the pesticide industry. Computational prediction of pesticide product activities offers a rapid and inexpensive way of screening these chemicals early in their development and performing safety analyses. However, few computational prediction programs have been evaluated for their performance in predicting pesticide activities with a comprehensive test set. The immune system included 1,030,961 reports corresponding to assorted hematological, dermatological, and immunological endpoints. The pulmonary system included 347,224 reports corresponding to breathing abnormalities, bronchospasms, laryngeal, respiratory tract, pulmonary disorders and additional endpoints. One interesting note is that experiments conducted using compounds in the Toxlite training set produced results similar to those obtained in experiments with no training set compounds. The categorized data for the these models consisted of compounds determined to be carcinogenic to a specific organ and an equal number of compounds carcinogenic to (m)any other sites except the one of interest. Since both categories for the models were populated with carcinogens, these models are different from previous carcinogenesis models that sought to determine why chemicals cause cancer. Each model was parameter optimized and validated by leave-one-out methodology to determine concordance, sensitivity, specificity, and coverage. The best concordance for each model was: clitoral gland 82; hematopoietic system 73; kidney 76; liver 77; large intestine 75; mammary gland 78; lung 80; nasal cavity 81; small intestine 88; and uterus 80%. Considering the good predictivity of the models described here for organ selective carcinogenesis, we speculate that the structural information that they contain can lead to insight for organ-selective carcinogenesis. Twenty-six immunological endpoints, and 26 pulmonary endpoints were modeled, using 1,638 modelable compounds. The Genotoxic potential in any candidate drug is carefully assessed during the discovery and development of new drugs. This is commonly done using in silico screens early on and continued with in vitro and in vivo experiments as the drug progresses closer to regulatory submission. In silico screens have several purposes, selection of compounds for experimental testing and/or to get early warning of any potential risk associated with the compound in the form of. A set of rules to aid the interpretation of the output and enhance the overall predictive performance was also derived and implemented. The validity of structural alerts was also improved by comparing the statistical significance of each alert for the different assays. Finally, all the data were combined in a weight of evidence approach to give an overall assessment of the genotoxic risk associated with each compound. This approach proved to enhance both the predictive accuracy and the breadth of chemical coverage. Over the past years there have been great efforts to develop alternative strategy, including in silico methods that would comply with regulatory constraints. Some commercial and free software tools integrate global models targeting the 2009 endpoints. For the cosmetic industry, the predictive performance of such models has to be evaluated on chemical series of interest for: Chemical prioritization; Mechanistic understanding; and, Elaboration of regulatory dossiers by providing additional information. To improve the existing models, data were categorized on the basis of the structural features generated by the Leadscope Enterprise software. Multivariate analysis was performed to identify Leadscope chemical features most relevant to skin irritation. The Dow Chemical Company has generated extensive data on the genotoxic potential of a wide variety of chemical substances using the Ames test (mutagenicity) and the in vitro chromosome aberration assay (clastogenicity). Overall the performance of the three models was comparable, showing a high specificity but rather low sensitivity. Determination of the dermal sensitization potential of a chemical is a key component of the safety assessment process for registration. The assessment of the comparative predictive accuracy of these models has not been conducted but is necessary for their effective utilization in chemical safety assessments. To address this, the predictive accuracy of these models was compared to previous in vivo evaluations on the sensitization potential of 65 industrial and agricultural chemicals. Data were further stratified to evaluate the predictive value relative to each in vivo model (guinea pig, mouse or human), and yielded similar results. The predictive performance of such models has to be assessed on a regular basis, given the chemical diversity and reactivity of new chemical entities, and regular updates in the software versions. Three major commercially available computer-assisted prediction models were evaluated with regards to bacterial mutagenicity. For each system, applicability domains and predictive performance are compared and discussed. It appears that such predictive systems provide a valuable support for the screening and categorization of chemicals in addition to further understanding of mechanistic rationale. Because our chemical space is not fully covered by these systems, there is a need for expanding their applicability domains by integrating inhouse data. In particular, computational methods have become increasingly important for profiling environmental fate and evaluating toxicity of chemical compounds, which lead to risk assessment. Many of the currently available computational methods do not consider chemical reactivity and fate either in environment and biological compartments. In this paper, we will present a chemoinformatics approach for predicting chemical reactivity in metabolism and degradation reactions. Structural alerts on chemical reactivity can be used as indicators for safety issues due to reactivity. The application of reaction rules which combine reaction types with a physicochemical evaluation of the reactions allows a more sophisticated assessment of a chemical compound. The integration of the prediction of chemical reactivity into the workflow of the hazard and risk assessment process will be demonstrated. The use of applicability domain threshold implemented in most models generally improved the external prediction accuracy but led to the decrease in chemical space coverage. We find that consensus models afford higher prediction accuracy for the external validation dataset with the highest coverage as compared to individual constituent models. Evidence suggests inflammatory mediators released by cytotoxic macrophages contribute to the pathogenic process. Resolvins are naturally occurring anti-inflammatory mediators derived from eicosapentaenoic acid. RvE2 also reduced hepatic expression of cyclooxygenase-2, which mediates the generation of proinflammatory eicosanoids. An important step in dose-response assessment is the identification of a critical effect level. The modeling focus was on machine learning methods, Random Forest, k-Nearest Neighbor, and Support Vector Machine, as well as models using Partial Least Squares. The performance of each model was assessed using a validation set not used in model development. These models show that it is very reasonable to predict critical effect values from chemical structure based on predictions of the validation set. The models can be used as an additional tool for dose-response assessment when experimental data pertaining to critical effect levels do not exist. Polaprezinc, an anti-ulcer drug developed in Japan, is a chelate compound consisting of zinc and L-carnosine. All studies were carried out in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals. The in vivo 6 hr treatment was better represented by a 6 hr treatment in vitro than a 2 hour treatment in vitro, suggesting the toxicokinetics in vivo and in vitro may be similar. The aim of this study was to explore the mechanistic role of various death proteases that activate Bid and thus initiate mitochondrial permeabilization. Diclofenac (1 mM) caused activation of caspase-8 that became apparent at 12 h and which decreased to control levels at 24 h. Pretreatment of rats with heparin reduced hepatic fibrin deposition and hypoxia and protected against liver injury induced by P. Exposure of mice to perchloroethylene (perc) is known to increase peroxisomes and cell proliferation in the liver, hepatocellular hypertrophy, and liver tumors. No significant changes in the maternal weight gain and average uterine weight between treatment groups were observed. Additionally, no significant changes in average fetal weight, crown:rump ratio or placental weight were found. Whether these changes lead to differences in post-natal lethality is currently being examined in ongoing studies. This mitochondrial depolarization caused by ethanol was associated with hepatic steatosis but little overt cell injury. The cytochrome P450 inhibitor, aminobenzotriazole (100 mg/kg), blunted mitochondrial depolarization in ~25% of hepatocytes. Taken together, the data show that acute ethanol causes widespread, reversible hepatic mitochondrial depolarization. Previously it has been shown that chronic alcohol consumption increases the sensitivity of mitochondria to undergo the permeability transition, which leads to impaired energy conservation and hepatotoxicity. Our recent study showed that ethanol ingestion causes widespread hepatic mitochondrial depolarization in vivo. This study investigated the role of ethanol metabolic pathways in this mitochondrial depolarization. Mitochondrial depolarization indicated by loss of Rh123 fluorescence occurred as early as 1 h after ethanol treatment and peaked at 6 h when ~95% hepatocytes contained depolarized mitochondria. The transcription factor Nrf2 induces numerous protective detoxification and antioxidant genes following electrophilic or oxidative stress. Nrf2 aids in liver regeneration by altering insulin signaling, however, whether Nrf2 plays a role in hepatic glucose homeostasis is unknown. Histopathology and decreased serum insulin levels confirmed reduced pancreatic islet -cells in both genotypes.

One isoform coronary heart disease icd 10 codes order line procardia, P450aromA coronary heart arteries generic procardia 30 mg otc, predominates in ovaries and controls circulating levels of estrogens that are critical to female differentiation and development cardiovascular disease statistics 2013 30 mg procardia purchase mastercard. Another isoform cardiovascular system journey of blood 30 mg procardia purchase fast delivery, P450aromB 5 cardiovascular diseases procardia 30 mg purchase overnight delivery, prevails in brains and controls local aromatization of testosterone into estrogen, controlling sex-specific reproductive behavior. In addition, differences in amino acid sequences between isoforms relate to different levels of activity. The isoforms also have different phosphorylation sites that regulate their activity, suggesting distinct sensitivity to phosphorylation. Because of these differences, we investigated whether chemicals that modulate aromatase activity affect the two isoforms differently. Global analysis of gene expression can provide significant information about the molecular basis of normal and abnormal biological function. It also provides support for the generation of hypotheses about the role of specific genes in a particular biological response. We have evaluated the effects of estrogens on gene expression in the rodent reproductive system. Exposure of rats to estrogens of varying potency produces a characteristic transcript profile that is sexand lifestage-specific. Changes in the expression of steroid metabolizing genes are consistent across sex and lifestage, but other genes. We have carried out a temporal analysis of gene expression in the juvenile rat uterus after a single dose of an estrogen. Early changes involve genes that are responsible for the cell proliferation, inhibition of apoptosis and fluid imbibition. Subsequently, there is an increase in expression of genes associated with inflammation and tissue remodeling, as well as an upregulation of apoptotic genes as the uterus returns to a pre-stimulus state. The expression of specific genes can be organized into models of coordinated gene action that can be stated as testable hypotheses. We have made progress in evaluating gene expression in a uterine adenoma cell line, for which the estrogen-driven transcript profiles appear sufficiently similar to in vivo that it appears that this system can be used to test hypotheses about the role of specific genes in the uterine response to estrogens. Gene expression analysis has utility as a predictor of mechanism of action and has the potential to be a significant adjunct to understanding the molecular control of biological responses lected by conferring growth advantage. In parallel, life, death and cell fate decisions are required for cells to avoid massive apoptotic death in response to genotoxic stress. Moreover, analysis of this data shows that over 62% of all genes induced or repressed by E2 were Sp-dependent. The covalent marking of protein arginine residues by methyl groups can promote recognition by a binding partner or a modulation in biological activity. This has helped us understand the molecular mechanisms behind the diverse biological roles of arginine methylation. Recent developments in our knowledge of how arginine methylation regulates transcription will be presented. For toxicity testing and assessment programs to address the large numbers of substances of potential concern, a paradigm shift in the assessment of chemical hazard and risk is needed that takes advantage of advances in molecular toxicology, computational sciences, and information technology. This shift represents an evolution of toxicology from an observational science, to a predictive science built upon mechanism-based, biological observations in vitro. The progress in developing robust, quantitative in vitro models of human toxicity pathways with the potential to replace the current reliance on in vivo animal data will be presented. These in vitro models identify cellular and molecular responses associated with critical biological pathways, which can result in adverse health effects when sufficiently perturbed by chemical exposure. One of the challenges to this in vitro approach is selecting appropriate cell types and endpoints that provide a sufficient battery for predicting the response of relevant toxicity pathways. The results from five laboratories and programs wherein the convergence of science, technology and regulatory need have produced initial successes in creating in vitro models of human toxicity pathways will be highlighted. Additional regulatory and sensor strategies have altered our views about mechanisms of gene regulation and disease. While the role of liganded nuclear receptors in mediating coactivator/corepressor exchange is well established, nuclear motor-dependent regulation of chromosomal organization in the three-dimensional space of the nucleus to diverse signaling events is emerging as a major parallel strategy to achieve integrated transcriptional responses revealing a key role for the modulation of nuclear architecture in orchestrating regulated gene expression programs in the mammalian nucleus, using previously unsuspected classes of sensor molecules. Thus, a network of covalent modifications and their corresponding gene fusions play important roles in many diseases of developmental and in initial steps in cancers, which is particularly well-established for leukemias, but now identified as a more general event in solid tumors. Measurement of perturbation of critical signaling pathways and cellular processes using in vitro assays provides a means to predict the potential for chemicals to cause injury in the intact animal. The assays consisted of a wide variety of technologies and endpoints and used both cell lines and primary cells. These toxicity phenotypes sometimes recapitulated the intended mechanism of action against target species for pesticide active ingredients, and other times reflected apparently unrelated activities. Initial toxicity signatures predictive of in vivo toxicity endpoints illustrate the utility of including both phenotypic cellular assays along with specific molecular targets in building predictive toxicity models. A miniaturized 3D cell-culture microarray (the Data Analysis Toxicology Assay Chip, or DataChip) has been developed for high-throughput toxicity screening of drug candidates and their cytochrome P450-generated metabolites. The DataChip consists of human cells encapsulated in 20 nL alginate gel spots arrayed on a functionalized glass slide for spatially addressable screening against multiple compounds. Similar dose responses were obtained with the DataChip and conventional 96-well plate assays, demonstrating that the near 5,000-fold miniaturization does not influence the cytotoxicity response. Drug-induced liver disease is the leading cause of pre-launch and post-market attrition of pharmaceutical compounds. Species-specific variations in liver-specific molecular pathways necessitate supplementation of animal data with in vitro assays to assess human responses to compounds. Isolated primary hepatocytes are considered to be the gold standard for evaluating drug disposition in vitro. However, hepatocytes from various species exhibit a precipitous decline in viability and phenotypic functions under conventional culture conditions. We have utilized microtechnology tools to optimize and miniaturize into a multi-well format (up to 96-well) in vitro models of the rodent and human livers. Specifically, primary hepatocytes were organized into colonies of prescribed, empirically optimized dimensions and subsequently surrounded by supportive stroma. We demonstrate utility of our platform in drug development by quantifying drug-drug interactions and susceptibility to a panel of clinical hepatotoxins. We also show that micropatterned co- are amenable to high content imaging readouts, such as those used to evaluate mechanisms of hepatotoxicity. In the future, improved in vitro models of liver tissue could eliminate problematic compounds earlier in drug discovery towards creating safer drugs for patients. Both regulations are strong incentives for seeking alternative methods in hazard/risk assessment. Although single in vitro assays are valuable in providing mechanistic insight into toxicity pathways, they cannot address the complexity of events leading to toxicity in vivo. According to the 7th amendment to the cosmetic directive, 4 in vivo endpoints will be phased out starting in March 2009: skin irritation, eye irritation, genotoxicity and acute toxicity. While there are a number of alternatives for the former 3 endpoints, clues for replacing acute toxicity remain scarce. Persistent inflammation and the formation and actions of reactive oxygen species play pivotal roles in tissue injury during disease pathogenesis and as a reaction to toxicant exposures. The associated oxidative and nitrative stresses promote diverse biological reactions including neurodegenerative disorders, cancer, atherosclerosis and stillbirth. These effects occur via sustained cell proliferation and cell death and, in some cases, via induction of a pro-angiogenic environment. Exposure to ozone, a ubiquitous urban air pollutant, leads to the generation of reactive oxygen and nitrogen species in lung macrophages inducing inflammatory genes which play a key role in subsequent tissue damage. Similarly, the developing brain is susceptible to anesthetic-induced injury; recent studies have indicated that genes along the oxidative stress pathway are altered by this anesthetic treatment. As well as a role in lung disease and neuronal injury, oxidative and nitrative stress is implicated in creating the pro-inflammatory microenvironment associated with the aggressive phenotype of inflammatory breast cancer. Targeting these pathways may help diminish the proinflammatory microenvironment that may contribute to the genetic instability and aggressive phenotype. Fundamental concepts and progresses to how one might create a rational plan of treatment, based on understanding derived from basic principles will be addressed. This session will appeal to both those with specialist knowledge in the field as well as to toxicologists looking to learn more about the role of nitrative and oxidative stress in toxicology. Evidence for participation of reactive oxygen and nitrogen species in disease states is strong, but the data largely have been developed through pharmacological, immunohistochemical, and molecular biological methods, often without sufficiently critical consideration of the limitations of each of the approaches. The selectivities of specific reactive intermediates and of the methods of analysis used to study the intermediates, as well as issues arising from subcellular and other modes of compartmentalization need to be considered in such studies. The specificities and sensitivities needed for resolution of molecular mechanisms in relevant biological models are becoming possible, largely through ongoing advances in mass spectrometry, but absolute, as distinguished from relative quantitation, identification and application of appropriate biological denominators, and distinctions of causes, effects, and unrelated responses are needed. Efforts to understand oxidation and reduction reactions in biological disease states also encounter major limitations from incomplete or even incorrect understanding of redox chemistry in the application of these principles to redox toxicology. For example, myeloperoxidase-catalyzed oxidations can be distinguished from effects of reagent hypochlorous acid, yet many studies continue to be based upon the assumption that the two modes of oxidation are identical. The challenges in studies of acute exposures are formidible and are considerably more complicated in efforts to study chronic conditions, such as the relationships of inflammatory responses with neurodegenerative disorders, cancer, atherosclerosis, stillbirth, and preterm birth. Animal models of stillbirth and premature birth can be induced by acute exposure to endotoxin, or other proinflammatory stimuli, and are associated with oxidant stress responses. The window of vulnerability to these neuronal effects of anesthetics is restricted to the period of rapid synaptogenesis, also known as the brain growth spurt. Similar dependencies on dose/duration of exposure and developmental stage are observed both in the non-human primate and in the rodent models. The duration of anesthesia to induce cell death as measured by minimal exposure requirements is similar (~6 hrs. The susceptible stage or period of development has not been completely described but begins somewhere before the last quarter of pregnancy and continues to shortly after birth in the nonhuman primate. Recent gene expression assessments indicate that genes along the oxidative stress pathway are altered by anesthetic treatment of developing animals. Together, the application of omics approaches along with traditional toxicological endpoints indicates that the susceptibility of the developing brain to anesthetics is mediated by oxidative stress. The Cox-2 enzyme is a bifunctional enzyme and produces oxygen free radicals as a byproduct of its peroxidatic function. Such an evolution should permit more focused hypothesis testing in epidemiological and clinical studies. To test this hypothesis genetically, we used a mouse strain lacking functional Ndufs4, a gene encoding a subunit required for complete assembly and function of complex I. Deletion of Ndufs4 gene abolished complex I activity in midbrain mesencephalic neurons cultured from embryonic day (E) 14 mice, but did not affect the survival of dopaminergic neurons in culture. Recent studies using several pesticides including rotenone, paraquat, and dieldrin as models to investigate signal transduction mechanisms that regulate dopaminergic neuronal death will be presented. Data is available on signal transduction pathways that promote dopaminergic neuronal survival and should be of general interest to scientists studying neurodegeneration, neurotoxicology, pesticide toxicology, signal transduction, molecular mechanisms of toxicity, and occupational and public health. Definitively pathogenic mutations are found in all of the catalytic regions and may be clustered here, although there are a few mutations in the protein-protein interaction domains. Some mutations (such as the common G2019S variant) seem to increase kinase activity directly, while others may influence regulation of the protein activity. Therefore, our current model is that many of the mutations impinge on kinase activity although they may do this in different ways. However, the cell death mechanisms underlying pesticide-induced dopaminergic neuronal degeneration have not yet been defined. A translational approach for intervention of the activation of this proapoptotic kinase will also be discussed. Exposure to these agents resulted in activation of the mitochondrial dependent apoptotic cascade, starting from cytochrome C release to caspase-3 activation, in a time- and dose-dependent manner. Because the liver plays such a key role in the metabolism and disposition of so many drugs, any disease state that results in the functional impairment of the liver has the capacity to alter the fate of most drugs within the body. Drug metabolizing enzymes and transporter proteins play a key role in the uptake, metabolism and efflux of drugs required for their elimination. In addition, the disposition and elimination of model substrates has been demonstrated in these animal models. We have recently demonstrated that the liver responds to chemical injury by regulating the expression of multiple uptake and efflux transporters. This coordinated adaptive response may allow the liver to better handle subsequent toxicant exposures. Collectively, our studies have led us to postulate that recovery from drug-induced liver injury involves differential expression of hepatobiliary transporters via signaling molecules with known hepatoprotective properties. Drug transporters play an important role in the uptake, distribution and elimination of pharmaceuticals, environmental contaminants and endogenous compounds. In the last decade, considerable interest has been centered on regulation of drug transporters and on how chemicals and disease states alter their expression. It is clearly important to understand the pharmacological and toxicological consequences of changes in drug transporter function. Both induction and repression of transporter expression have been documented with exposure to classical drug metabolizing enzyme inducers, treatment with target organ toxicants and under a variety of pathological conditions. Therefore, it is important to highlight the recent knowledge gained on how transporter expression changes during non-alcoholic steatohepatitis and druginduced hepatotoxicity, as well as regulation of blood brain barrier transporters and its implications to the management and/or treatment of central nervous system disorders. Finally, this session will address the molecular regulatory mechanisms involved and the potential functional consequences, and understanding how changes in transporter expression or function may be involved in drug-drug interactions and the implications of these effects in drug development and the clinical setting. We have focused on understanding the signals and mechanisms that modulate P-gp expression and activity in brain capillaries. Of the more than 2 million severe adverse drug reactions that occur in the United States each year, most result from inter-individual variation in the ability to metabolize and eliminate drugs from the body. Signaling is also spatially complex, involving autocrine/paracrine elements and the cytoskeletal machinery. Multiple steps in signaling are potential therapeutic targets that could be used to adjust P-gp activity in the clinic. Xenobiotic transporters influence the disposition of many xenobiotics and endogenous compounds. Consequently, alterations in expression or function of influx or efflux transporters may affect target organ concentrations, the likelihood of toxicity and increase the potential for drug interactions.

As an avian species cardiovascular quizlet procardia 30 mg order mastercard, zebra finches utilize mesotocin rather than oxytocin signaling (these nonapeptides differ by a single amino acid) cardiovascular system diseases symptoms order generic procardia line. To establish the suitability of zebra finches as an animal model to study developmental effects of oxytocin-related peptides cardiovascular knowledge test cheap procardia 30 mg on line, we have begun to characterize the receptor likely involved braunwalds heart disease 7th edition pdf order procardia with visa. Immunohistochemical experiments using an antibody raised from the mesotocin receptor specific previously cloned in our laboratory suggests that distinct mesotocin receptor expression occurs within the vocal motor brain regions and that mesotocin receptor expression varies as a function of age during vocal development coronary heart games discount procardia 30 mg with mastercard. To determine if early exposure to oxytocin could alter normal vocal development, birds were treated with either oxytocin (300 mcg/kg, 1000 mcg/kg, or 3000 mcg/kg) or vehicle for five days (days 5-9). There was no statistical difference on note stereotypy by oxytocin treated animals due to dosage and thus the animals were pooled into one group. The songs produced by the oxytocin treated animals were less wellstereotyped than those of the vehicle treated animals (p = 0. These preliminary results suggest that early post-natal oxytocin exposure may alter zebra finch vocal development. The purpose of this study was to investigate whether co-administration of L-carnitine could protect against or attenuate ketamine-induced cell death using newborn rat forebrain cultures. Neural cells collected from the newborn rat forebrain were incubated for 24 h with 1, 10 or 20 M ketamine, normal culture medium (control), or ketamine (10 M) plus 100, 500 or 1000 M L-carnitine. Prenatal stress is known to affect the development of the brain, and to exaggerate the developmental toxicity of chemicals. Comparing the incidence of these abnormalities between the in-house and supplier groups, the incidence of the cortical dysgenesis was increased slightly, and that of the abnormal pons was clearly increased in the supplier group. Children of women who were exposed to organic solvents during pregnancy have shown altered physical development, behavior (Pearson et al, 1994; Arnold et al, 1994) and visual function (Till et al, 2001; 2003; 2005). We evaluated the offspring of pregnant Long-Evans rats who were exposed to toluene vapor at concentrations of 0, 10, 100 or 1000 ppm from days 8-19 of gestation. There were no effects of toluene on maternal body weight during pregnancy or preweaning growth of offspring at any concentration, but postweaning offspring weights were significantly lower through 18 weeks in the 1000 ppm group. The rats were then trained to perform a visual signal detection task to assess learning and sustained attention. No effects of toluene exposure were observed in a lever press task, visual discrimination task or the signal detection task. These experiments have not confirmed that gestational exposure to toluene alters the visual function or behavior of offspring. We applied c-Fos immunohistochemistry to develop a method to detect abnormal brain function during the neonatal period in a chemical-induced developmental disorder model. To investigate neonatal brain function, we induced maternal deprivation, which was enough to stimulate them and induced cFos immunoreactivities in the brain areas related to the olfactory system, and stress response. To produce a chemical-induced hyperactivity rat model, we treated pregnant rats with 50 mg/kg of 5-bromo-2-deoxyuridine (BrdU) from gestation day 9 to 15. Neonatal rats at 11 days of age were perfused with a fixative following onehour maternal deprivation (neonatal rats were placed in a new empty cage for one hour). The number of c-Fos immunoreactive cells was counted in several brain areas and compared between the control and BrdU groups. The number of c-Fos immunoreactive cells in the BrdU group was decreased in the piriform cortex, the locus coeruleus and dorsal part of the septum, which plays an important role in neonatal learning and memory. In the control group, the number of c-Fos immunoreactive cells in the locus coeruleus correlated with brain areas such as the bed nucleus of the stria terminalis, piriform cortex, and the somatosensory cortex, however, these correlations disappeared in the BrdU group. Thus, c-Fos immunohistochemical observation provides a method to detect developmental neurotoxicity during the neonatal period. A time course of acetylcholinesterase inhibition on the last day of exposure was conducted to determine the peak time of inhibition following each route. In vitro studies have found that exposure to toxins that increase sodium flux into cultured neurons causes down-regulation of sodium channel subunits, which in turn affects the firing properties of the cells and synaptic activity. Here, we sought to determine whether developmental exposure to deltamethrin causes changes in sodium channel subunit expression. Pregnant mice were exposed throughout gestation and lactation to either 0 or 3 mg/kg deltamethrin every three days. Taken together, these data suggest that developmental deltamethrin exposure results in long-term alterations of isoformspecific sodium channel subunit expression which may result in region-specific alterations in neuronal activity and contribute to the behavioral deficits observed in mice developmentally exposed to deltamethrin. The study was designed to gather information on the relationship between conventional technologies and indicators for developmental (neuro)toxicity (mainly landmarks, behaviour and an extensive neuropathology survey, versus new (innovative) technologies, i. Together, the results demonstrate that modern technologies and statistical approaches may have a higher throughput and are likely to show much stronger discriminative power when it comes to demonstrations of adverse effects of developmental (neuro)toxicants. The relevance of these findings will be discussed in the context of regulatory testing of developmental (neuro)toxicity. Differences in performance between male and female rats are used to assess substances thought to affect sexual development of the brain. Most current methods for measuring sexually-differentiated behavior in rats have been limited to human observation requiring both subjective interpretation and limited quantification. Human observation is labor- intensive, restricting these techniques from being used as high-throughput screens for agents such as endocrine-active substances. Ninety-six rats were processed in a between-group design with negative- (corn oil) and positive- (50 mg/kg vinclozolin (Vz)) control groups. Quantitative assessment of play behavior showed negative-control male rats engaging in more rough-in-tumble play than females at all ages. This poster shows (1) that play behavior can be automated and computerized, producing quantified data which allows for high-throughput screening of chronic low dose exposures; and (2) that perinatal phthalate exposure can induce sexually-differentiated behavioral effects. In utero exposure to methylmercury (MeHg) induces developmental deficits in offspring, such as loss of memory function [1]. It is known that acute in vitro exposure of hippocampal brain slices to MeHg may affect the amplitude of electrically induced field potentials [2]. We investigated ex vivo the excitability of the in vitro hippocampus of juvenile (33 days) or adult rats (68 days) born from mothers which J. Developing animals are known to be more sensitive to the neurotoxic effects of the pyrethroid insecticide deltamethrin. In hippocampal brain slices, the Schaffer collaterals were stimulated with bipolar, biphasic current pulses. Short and long term plasticity were studied using paired pulse and repetitive stimuli, constructing input-output and interval curves. The results showed that 1) older rats had smaller amplitude field potentials in exposed as well as in control animals, 2) the release probability in MeHg exposed animals might be reduced in the first pulse at low intensity stimulation (10% of Imax) with small interpulse interval, and 3) unlike in the 28 day old MeHg offspring in which no changes were observed, in the 68 days MeHg group, increased population spike was observed at higher intensity (80% of Imax) and small interpulse intervals (<70 ms). These data suggest that there is more Ca2+ remaining in the presynaptic element of the 68 day MeHg group and point at life-lasting mechanistic changes in neural target tissues in the offspring after early maternal exposure as shown also by the toxicogenomics data [3]. At the microscopic level, the decrease in brain size was not observed, demonstrating the importance of accurate homology of brain sections and performance of linear morphometry for the detection of subtle differences. The peripheral sciatic nerve and its branches could be examined effectively in transverse epoxy resin sections, but for longitudinal sections paraffin embedding, presenting large nerve portions, was superior. Acrylamide and Trimethyltin are known to induce peripheral and central nervous system damage. This study was designed to identify the neurotoxic properties of Acrylamide and Trimethyltin Chloride following repeated dose gavage administration for up to twenty-eight consecutive days in the Han Wistar rat. Open-field arena assessments, motor activity assessments and grip strength tests were performed weekly, together with bodyweights and dietary intake. The brain was weighed and the brain, dorsal root ganglia, dorsal and ventral root fibres, eyes, optic nerve, sciatic nerve, tibial nerve, skeletal muscle and spinal cord for all perfused animals were processed and examined. Altered gait, lethargy, hunched posture, body tremors and respiratory pattern changes were detected following Acrylamide administration. Reduced forelimb grip strength and motor activity were detected, together with reduced bodyweight gains, dietary intake and food efficiencies. Changes in brain weights were detected and histopathological examination revealed effects in the spinal cord, ventral and root ganglia, and sciatic and tibial nerves. Altered gait, increased activity, pilo-erection, lethargy, body tremors, hunched posture and respiratory pattern changes were evident for animals treated with Trimethyltin Chloride. Lower transfer arousal and increased incidences of urination and defecation were also evident, together with increases in vocalisation. Histopathological examinations revealed changes in the spinal cord, dorsal root ganglia, dorsal and ventral roots and skeletal muscle. This study confirmed that the procedures employed are effective in identifying the neurotoxic effects of Acrylamide and Trimethyltin Chloride in the Harlan Han Wistar rat. Antipsychotics are drugs that were developed primarily to treat psychiatric illnesses including schizophrenia. Haloperidol is an antipsychotic which is frequently used during pregnancy either as an antiemetic, or antipsychotic. This experiment was designed to investigate the behavioral and neurochemical effects of prenatal haloperidol exposure on the developing rat offspring. Animals were kept in a control environment of 21 + 1 degrees C with lights on at 07:00 hr and off at 19:00 hr. It was of interest to note that there were no statistically significant changes observed in the behavioral parameters, except that male offspring showed a decrease in auditory startle response. Also, the dopamine subtype D1 receptor density was not statistically significantly different from the D2 receptor sites in the caudate nucleus. A validation study was carried out to establish a "best practice" in our laboratory environment. For instance, at 63 days, the fresh brain weight or the weight immediately after the perfusion fixation was 13 to 16% less than the weight after prolonged immersion. For macroscopic morphometry the brains were photographed from the dorsal aspect with a millimeter scale, enabling the assessment of the length of forebrain and cerebellum. Methymercury (MeHg) exposure from occupational, environmental, and contaminated foods is a significant threat to public health. MeHg readily passes the brain barrier causing severe psychological and neurological problems. The developing nervous system is particularly vulnerable to the toxin, and although MeHg poisonings have been studied for decades, the molecular components and pathways involved in the cellular pathology are largely unknown. Several studies have demonstrated that selenium can be also neurotoxic, yet protect against the MeHg-induced pathology. The molecular mechanisms involved in the selenium induced neurotoxicity and protection are ill-defined. An aim of this study is to evaluate the neurotoxic effects of MeHg and selenium on developing neurons, and to identify cytoskeletal and synaptic proteins that may contribute to the neuropathology. Hippocampal primary cell cultures from rats and mice at 14 days were exposed to either MeHg or sodium selenide (NaSe) (0-50 uM), or in combination, for 24 hours and the number of dead cells determined using propidiumiodide as a marker for cell death. A concentration-dependent increase in mortality was observed with single toxin exposures in either species, and results in dendritic fragmentation, loss of cellular integrity, and dramatic changes in a number of cytoskeletal and synaptic proteins. In contrast, co-exposure with the toxins resulted in maintenance of dendritic and synaptic integrity, that includes diffuse synaptic protein staining. Toxin-induced changes in the dendritic spines (size, volume, contact to presynaptic structures), as well as synaptic protein expression and localization are also described. Mice were assessed in open field, light-dark box and the Rota-rod apparatus at 4-5 weeks of age. Cerebella from separate mice, treated with the same MeHg exposure regimen, were dissected at 4-5 weeks of age and used for gene expression analysis using the Illumina Mouse Sentrix 6 array. Significant 2-way (treatment x strain) and 3way (treatment x sex x strain) effects were detected. The lipid metabolism category was also over represented, particularly due to steroid metabolizing genes. The implication for this project is that in addition to effects of MeHg on oxidative stress related genes; there are specific neurodevelopment effects that are the result of an interaction of a genetic predisposition and an environmental exposure. MeHg, an environmentally persistent toxicant, induces a spectrum of harmful effects on neurodevelopment. Furthermore, reduced cell number and organ size were detected at P21 in addition to behavioral effects at P35. Caspase-3 activation, a marker for apoptosis, may involve either the extrinsic pathway that depends on caspase-8 or the intrinsic pathway (involving caspase-9), which we found to underlie hippocampal neurotoxicity (Sokolowski et al. Based on the pathway definition, we used low doses of MeHg in our model of hippocampus toxicity, to define the effects of environmentally relevant exposures. Thus, capase-3, a significant endpoint protein, was detected using the most sensitive assay, immunohistochemistry, in the low-dose exposures. By using the most sensitive marker for apoptosis, caspase-3 staining, we now detect significant MeHg neurotoxicity at a 25-fold lower dose than previously defined. Future studies will characterize acute effects on hippocampal neurogenesis and later consequences on organ cell composition and cognitive functions. Disease pathology is hallmarked by senile plaques composed of Amyloid-beta (A) peptide aggregates and neurofibrillary tangles composed of hyperphosphorylated tau. This will allow us to see if alterations in the brain are reflected in the blood and thus present these proteins as potential biomarkers to screen human populations. Inflammatory activation of astrocytes is believed to be an early event in Mn neurotoxicity but glial responses to Mn in developing animals remains poorly understood. Mice were exposed to saline, 10 or 30 mg/Kg Mn by daily gavage as juveniles, adults, and juveniles + adults. It accumulates in the brain, most notably the cerebellum and hippocampus, causing irreversible damage. The neurotoxic effects and the mechanisms by which MeHg acts remain to be elucidated, especially in cases of long-term exposure. The Pb-induced changes in cholinergic and aminergic systems correspond to the cognitive and behavioral involvement of these transmitters and brain regions. Calcium co-administration to Pb-exposed rats significantly reversed the Pb-induced alterations in these transmitters and enzymes. Manganese (Mn) is an essential metal, necessary for the normal functioning of a variety of physiological processes. In humans, Mn neurotoxicity is characterized by a variety of psychiatric, cognitive and motor disturbances, the latter resembling parkinsionan symptoms. Among brain cells, astrocytes, which provide a major support for neurons, accumulate this metal at higher extent.

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The inherent ability of a stem cell to migrate may cause these cells to be aggressively metastatic cardiovascular system of a pregnant woman 30 mg procardia with amex, if transformed coronary heart operation discount procardia 30 mg free shipping. The myeloid leukemias support this view: transformed stem cells are likely to be malignant while transformed committed progenitor cells are likely to be benign cardiovascular disease death rate discount procardia online master card. Moreover cardiovascular system job generic procardia 30 mg on-line, telomerase activity (discussed in Chapter 3) cardiovascular system analogy buy procardia pills in toronto, which is necessary for tumor proliferation and progression and is present in 90% of human cancers, is present in normal stem cells and proliferative cells. Yes, the success of metastasis may be based on the number of cancer stem cells in the primary tumor; non-tumorigenic cancer cells may not have the ability to form new tumors at distant sites. It may be hypothesized that tumors arise from stem cells within a tissue or alternatively from more differentiated cells that acquire the stem cell quality of self-renewal. Alternatively, a continuum of target cells relative to different states of differentiation may exist: stem cells, progenitor cells, and terminally differentiated cells may all be targets for transformation. Further, the stage of differentiation of the target cell may affect the malignant potential and severity of the cancer. The process of differentiation is dependent upon the expression of a specific subset of genes that defines a particular type of cell. Polycomb proteins silence gene expression in stem cells and cancer the polycomb group (PcG) of proteins represses the transcription of specific sets of genes by epigenetic modifications (see Chapter 3). As p53 has been nicknamed the "guardian of the genome," the polycomb group proteins have been nicknamed the "guardians of stemness. The role of PcG proteins in stem cell maintenance and in repressing tumor suppressor genes suggests that they may have oncogenic potential. This complex contains histone methyltransferase activity and targets lysine 27 (and lysine 9) of histone H3. It is proposed that repression involves direct inhibition of the transcriptional machinery, recruitment of methyltransferases, and chromatin compaction. Although the mechanism for the de-repression is unknown, some evidence suggests that PcGs are removed from the promoter regions of their target genes and/ or a specific histone lysine demethylase is involved in reversing the epigenetic modifications initiated by the PcG proteins. PcG proteins and cancer the ability of polycomb group proteins to suppress the differentiation of stem cells implicates them in oncogenesis as abnormal regulation of differentiation can lead to cancer. In acute myeloid leukemia, most leukemic cells have a limited capacity for proliferation but are replenished by rare leukemic stem cells (see Section 8. Therefore, the ability of stem cells to self-renew is important in the maintenance of this disease. A PcG protein repressor, Bmi-1, has been demonstrated to be essential for the control of self-renewal in hematopoietic stem cells and in leukemic stem cells (Lessard and Sauvageau, 2003). In vitro, leukemic stem cells that lack Bmi-1 show growth arrest in the G1 phase of the cell cycle and begin to differentiate. In vivo, mice with a Bmi-1 gene knock-out show a progressive depletion of all blood cells indicating the essential role of Bmi-1 in hematopoietic stem cells. In addition, in mouse models using leukemic stem cells lacking Bmi-1, smaller numbers of leukemic cells are detected in the peripheral blood compared with controls, indicating that these cancer stem cells have proliferative defects. Bmi-1 normally exerts its effects partially by repressing the expression of two cdk inhibitors p16 and p14 via chromatin remodeling. The role of Bmi-1 as a human oncogene is supported by the identification of Bmi-1 gene amplification in some lymphomas. This evidence supports the theory that cells with stem cell properties drive tumor formation and progression. Role of lineage-specific transcription factors in differentiation and cancer the induction of lineage-specific gene transcription is dependent on lineage-specific transcription factors. Acute myeloid leukemia serves as an important paradigm for examining how disruption of the function of a transcription factor can interfere with differentiation and lead to cancer. The classification system of this disease is still evolving but should eventually reflect molecular features at the point of the differentiation block. Several transcription factors have been identified to be important in the development of hematopoietic lineages. Lineage-specific transcription factors activate a particular set of lineage-specific genes and/or inhibit the cell cycle for terminally differentiated cells. Many mutations that are typically found in acute myeloid leukemia affect specific transcription factors; both chromosomal translocations. The chromosomal translocation t(8;21) is identified in both hematopoietic stem cells and more differentiated cells in patients, thus providing additional evidence that the transforming mutations of acute myeloid leukemia occur in hematopoietic stem cells. Mutations in lineage-specific transcription factors are found in patients with acute myeloid leukemia subtypes that are consistent with their role in normal hematopoiesis. Thus, mutation of transcription factors involved in differentiation is an important mechanism behind oncogenesis. First, as cancer stem cells support the growth and migration of the tumor, drugs need to target this small subset of cells within the tumor. Many existing conventional drugs give hopeful initial responses that are followed by disappointing latter reoccurrences. Drugs targeted at cancer stem cells may prevent reoccurrence and actually cure metastatic cancer. The best scenario would be to find a drug that would target cancer stem cells without affecting normal stem cells of the same tissue. The efficacy of such new drugs should be determined by their effect on the cancer stem cell population and not on overall tumor regression. Drugs may be successful at killing all of the cells of a tumor except cancer stem cells, so that measuring tumor regression would not reflect the fact that the most dangerous tumor cell types remained unaffected. Differences in drug resistance between cancer stem cells and other tumor cells is a possible explanation for such a scenario. The populations of tumor cells that do not accumulate these dyes are referred to as "side-population" cells. This is a property that protects these long-living cells from foreign toxins and is not usually maintained upon differentiation. A side-population of cells with high efflux capacity has also been identified in tumor cells. This suggests that cancer stem cells have inherent drug resistance and may be an alternative mechanism to the acquired drug resistance discussed in Chapter 2. For example, the loss of breast stem cells may be acceptable for most patients as breast cancer usually strikes after child-bearing years and the breast is not a vital organ. However, destruction of skin stem cells would result in serious problems as the skin would be unable to self-renew. The rarity of cancer stem cells in tumor cell populations and the difficulty of propagating them in culture made it difficult to use highthroughput screening approaches to search for new drugs. However, the knowledge that stem-like cells can be produced by induction of the epithelial­mesenchymal transition (see Chapter 9) in epithelial cells has provided a new resource that can be used for high-throughput screening for cancer stem cell-specific drugs. Next are several examples of drug strategies that target self-renewal or differentiation pathways. The importance of the Wnt pathway in several cancers, particularly colorectal cancer, suggests that the molecular components of this pathway are good targets for new therapeutics (see Pause and Think). The observation that Tcf inhibition induces the differentiation of colorectal cancer cells into epithelial villi is evidence that supports this approach. Also, these compounds that share a core chemical structure inhibited the expression of two Tcf target genes and inhibited proliferation of colorectal cancer cells. Although in its early stages, this strategy holds promise for the development of new cancer therapeutics. As these drugs target a molecular pathway that is important in self-renewal, they have a greater chance of tumor eradication rather than just tumor regression. The first Hh pathway inhibitor, cyclopamine, a steroidal alkaloid, was isolated from wild corn lilies. Pregnant sheep that ingested high quantities of wild corn lilies gave birth to cyclopic lambs. Expression of a neuronal stem cell marker, neurofilament nestin, was decreased while expression of a marker of neuronal differentiation, Neuro D, was increased. In this case, tumor cells from the medulloblastomas were taken from the transgenic mice and transplanted subcutaneously in nude mice. Pre-clinical testing of anti-tumor activity Examine the method of investigation used in the Berman et al. Ex vivo analysis (xenografts, allografts) remove the tumor from its normal environment and cell culture lines may not truly represent the disease in humans. Later, small-molecule inhibitors were identified, some with a 100-fold increase in potency compared to cyclopamine. A small-molecule inhibitor of Smoothened, HhAntag-691, has shown promise in a transgenic mouse model (Romer et al. Treatment resulted in the reduction of expression of several genes associated with the Shh pathway, a decrease in tumor growth, and an increase in apoptosis. Genentech and collaborators are involved in the development of smallmolecule antagonists and Hedgehog-blocking antibodies as means of inhibiting the Hh pathway for new cancer treatments. Some groups are attempting to develop drugs that target Gli but, as yet, there are none in clinical trials. The mechanisms may include the induction of growth arrest and apoptosis via gene regulation. Note that treatment with retinoic acid alone causes retinoic acid syndrome in 10­15% of patients but administration with chemotherapy reduces this side-effect. Another strategy for developing a new therapy may be to inhibit homodimerization of the fusion proteins, an idea that is supported by the work of Kwok et al. Stem cells are characterized by their ability to selfrenew and to form more differentiated progeny, simultaneously. Mutations that inappropriately activate the Wnt signaling pathway promote carcinogenesis, particularly colon cancer. The degree of differentiation of the transformed founder cell may determine metastatic potential. Cancer may originate from stem cells or may involve reactivation of the self-renewal process. Drugs that target the self-renewal pathways of cancer stem cells are more likely to achieve a cure. Interference with both the Wnt and Hh signaling pathways is a recent therapeutic strategy that is being explored. Stem cells of the intestinal crypt have been identified as the cells-of-origin for cancer of the intestine (Barker et al. They used a genetically engineered inducible cre mouse in vivo system to examine Apc deletions in different cell compartments of the intestine. Chapter 9 Metastasis Introduction Most cells of the body normally remain resident within a particular tissue or organ (though hematopoietic stem cells are a notable exception). The process by which tumor cells from a primary site invade and migrate to other parts of the body is called metastasis. Metastasis is the fundamental difference between a benign and malignant growth and represents the major clinical problem of cancer. A primary tumor can be surgically removed relatively easily, whereas once hundreds or more metastases have been established throughout the body they are practically impossible to remove. The spread of cells throughout the body results in physical obstruction, competition with normal cells for nutrients and oxygen, and invasion and interference with organ function. Many of the preferences observed for the spread of specific cancers to specific metastatic locations can be explained by the directionality of blood flow. As the bloodstream is the predominant means of longdistance transport, organs in close proximity "en route" are likely to be main sites of metastasis for a particular primary tumor. However, about one-third of the locations of frequent metastases is puzzling in this regard. For example, a particular kidney cancer often metastasizes to the thyroid, a relationship that cannot be explained simply by anatomy. One explanation of this observation was described over 100 years ago in the "seed and soil" theory proposed by Stephen Paget. It described cancer cells as "seeds" requiring a match with optimal environments or "soils" to succeed. The ability of cancer cells to metastasize is dependent on the interactions of their cell surface molecules with the microenvironment, including neighboring cells and the extracellular matrix. Recent molecular evidence suggest that receptors lining the capillaries in the organs to which cancer spreads influence the destination of metastasized cells, and these findings support the "seed and soil" theory. This theory is also supported by the concept of the establishment of a pre-metastatic niche, a site of future metastasis that is altered in preparation for the arrival of tumor cells. Further studies are needed to discover the factors needed for a tumor cell to be successful in metastasis. Although cancers are largely successful in metastasizing in the long run, on the cellular level, only 1 in 10,000 metastasizing cells survives transport. An additional layer of complexity must be added to this model because a tumor cannot be viewed simply as an isolated mass of cancer cells, but instead as a tissue that recruits and receives signals from surrounding normal cells, called the tumor microenvironment or tumorassociated stroma. The interaction of tumor cells with the tumor microenvironment affects the metastatic ability of individual cancer cells: not all cells of a primary tumor contain the same ability to metastasize. The subpopulation of cancer stem cells in a primary tumor also affects metastatic potential. The interaction of the primary tumor with distant locations via signaling molecules to create a future site of metastasis has also been demonstrated (see later in the chapter). Thus, both individual tumor cells and the tumor microenvironment play a role in the process of metastasis. The interactions between cancer cells and their microenvironment are complex but they are beginning to be understood. As we examine each of the major steps take note of the contributions made by the tumor microenvironment.

References

• DeVivo DC, Haymond MW, Obert KA, et al. Defective activation of the pyruvate dehydrogenase complex in subacute necrotizing encephalomyelopathy (Leigh disease). Ann Neurol 1979;6:483.
• Weiss M, Dullenkopf A, Fischer JE, et al.; European Paediatric Endotracheal Intubation Study Group. Prospective randomized controlled multicentre trial of cuffed or uncuffed endotracheal tubes in small children. Br J Anaesth. 2009;103(6):867-873.
• Ramsey G. Studies of dreaming. Psychol Bull 1953;50:432-55.
• Bishara J, Robenshtok E, Weinberger M, et al. Infective endocarditis in renal transplant recipients. Transpl Infect Dis. 1999;1(2): 138-143.
• Lips IM, van Gils CH, van der Heide UA, et al. Health-related quality of life 3 years after high-dose intensitymodulated radiotherapy with gold fiducial marker-based position verification. BJU Int 2009;103(6):762-767.
• Giglio P, Gilbert MR. Neurologic complications of non-Hodgkin's lymphoma. Curr Hematol Malig Rep 2006; 1(4):214-219.