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Toxicological Sciences

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An adverse outcome pathway (AOP) is a conceptual framework that organizes existing knowledge concerning biologically plausible, and empirically supported, links between molecular-level perturbation of a biological system and an adverse outcome at a level of biological organization of regulatory relevance. Systematic organization of information into AOP frameworks has potential to improve regulatory decision-making through greater integration and more meaningful use of mechanistic data. However, for the scientific community to collectively develop a useful AOP knowledgebase that encompasses toxicological contexts of concern to human health and ecological risk assessment, it is critical that AOPs be developed in accordance with a consistent set of core principles. Based on the experiences and scientific discourse among a group of AOP practitioners, we propose a set of five fundamental principles that guide AOP development: (1) AOPs are not chemical specific; (2) AOPs are modular and composed of reusable components—notably key events (KEs) and key event relationships (KERs); (3) an individual AOP, composed of a single sequence of KEs and KERs, is a pragmatic unit of AOP development and evaluation; (4) networks composed of multiple AOPs that share common KEs and KERs are likely to be the functional unit of prediction for most real-world scenarios; and (5) AOPs are living documents that will evolve over time as new knowledge is generated. The goal of the present article was to introduce some strategies for AOP development and detail the rationale behind these 5 key principles. Consideration of these principles addresses many of the current uncertainties regarding the AOP framework and its application and is intended to foster greater consistency in AOP development.

Organization of existing and emerging toxicological knowledge into adverse outcome pathway (AOP) descriptions can facilitate greater application of mechanistic data, including those derived through high-throughput in vitro, high content omics and imaging, and biomarker approaches, in risk-based decision making. The previously ad hoc process of AOP development is being formalized through development of internationally harmonized guidance and principles. The goal of this article was to outline the information content desired for formal AOP description and some rules of thumb and best practices intended to facilitate reuse and connectivity of elements of an AOP description in a knowledgebase and network context. For example, key events (KEs) are measurements of change in biological state that are indicative of progression of a perturbation toward a specified adverse outcome. Best practices for KE description suggest that each KE should be defined as an independent measurement made at a particular level of biological organization. The concept of "functional equivalence" can help guide both decisions about how many KEs to include in an AOP and the specificity with which they are defined. Likewise, in describing both KEs and evidence that supports a causal linkage or statistical association between them (ie, a key event relationship; KER), best practice is to build from and contribute to existing KE or KER descriptions in the AOP knowledgebase rather than creating redundant descriptions. The best practices proposed address many of the challenges and uncertainties related to AOP development and help promote a consistent and reliable, yet flexible approach.

Cardiovascular toxicity, a prominent reason for late-stage failures in drug development, has resulted in a demand for in vitro assays that can predict this liability in early drug discovery. Current in vitro cardiovascular safety testing primarily focuses on ion channel modulation and low throughput cardiomyocyte (CM) contractility measurements. We evaluated both human induced pluripotent stem cell-derived CMs (hiPSC-CMs) and rat neonatal CMs (rat CMs) on the xCELLigence Cardio system which uses impedance technology to quantify CM beating properties in a 96-well format. Forty-nine compounds were tested in concentration-response mode to determine potency for modulation of CM beating, a surrogate biomarker for contractility. These compounds had previously been tested in vivo and in a low throughput in vitro optical-based contractility assay that measures sarcomere shortening in electrically paced dog CMs. In comparison with in vivo contractility effects, hiPSC-CM impedance had assay sensitivity, specificity, and accuracy values of 90%, 74%, and 82%, respectively. These values compared favorably to values reported for the dog CM optical assay (83%, 84%, and 82%) and were slightly better than impedance using rat CMs (77%, 74%, and 74%). The potency values from the hiPSC-CM and rat CM assays spanned four orders of magnitude and correlated with values from the dog CM optical assay (r2 = 0.76 and 0.70, respectively). The Cardio system assay has >5x higher throughput than the optical assay. Thus, hiPSC-CM impedance testing can help detect the human cardiotoxic potential of novel therapeutics early in drug discovery, and if a hazard is identified, has sufficient throughput to support the design-make-test-analyze cycle to mitigate this liability.

Susceptibility and resistance to systemic autoimmunity are genetically regulated. This is particularly true for murine mercury-induced autoimmunity (mHgIA) where DBA/2J mice are considered resistant to disease including polyclonal B cell activation, autoantibody responses, and immune complex deposits. To identify possible mechanisms for the resistance to mHgIA, we exposed mHgIA sensitive B10.S and resistant DBA/2J mice to HgCl2 and assessed inflammation and pro-inflammatory responses at the site of exposure and subsequent development of markers of systemic autoimmunity. DBA/2J mice showed little evidence of induration at the site of exposure, expression of proinflammatory cytokines, T cell activation, or autoantibody production, although they did exhibit increased levels of total serum IgG and IgG1. In contrast B10.S mice developed significant inflammation together with increased expression of inflammasome component NLRP3, proinflammatory cytokines IL-1β, TNF-α, and IFN-, hypergammaglobulinemia, splenomegaly, CD4+ T-cell activation, and production of autoantibodies. Inflammation in B10.S mice was associated with a selective increase in activity of cysteine cathepsin B but not cathepsins L or S. Increased cathepsin B activity was not dependent on cytokines required for mHgIA but treatment with CA-074, a cathepsin B inhibitor, led to transient reduction of local induration, expression of inflammatory cytokines, and subsequent attenuation of the systemic adaptive immune response. These findings demonstrate that sensitivity to mHgIA is linked to an early cathepsin B regulated inflammatory response which can be pharmacologically exploited to abrogate the subsequent adaptive autoimmune response which leads to disease.

In utero exposure of rat embryos to dimethadione (DMO), the N-demethylated teratogenic metabolite of the anticonvulsant trimethadione, induces a high incidence of cardiac heart defects including ventricular septal defects (VSDs). The same exposure regimen also leads to in utero cardiac functional deficits, including bradycardia, dysrhythmia, and a reduction in cardiac output (CO) and ejection fraction that persist until parturition (10 days after the final dose). Despite a high rate of spontaneous postnatal VSD closure, we hypothesize that functional sequelae will persist into adulthood. Pregnant Sprague Dawley rats were administered six 300 mg/kg doses of DMO, one every 12 h in mid-pregnancy beginning on the evening of gestation day 8. Postnatal cardiac function was assessed in control (CTL) and DMO-exposed offspring using radiotelemetry and ultrasound at 3 and 11 months of age, respectively. Adult rats exposed to DMO in utero had an increased incidence of arrhythmia, elevated blood pressure and CO, greater left ventricular volume and elevated locomotor activity versus CTL. The mean arterial pressure of DMO-exposed rats was more sensitive to changes in dietary salt load compared with CTL. Importantly, most treated rats had functional deficits in the absence of a persistent structural defect. It was concluded that in utero DMO exposure causes cardiovascular deficits that persist into postnatal life in the rat, despite absence of visible structural anomalies. We speculate this is not unique to DMO, suggesting possible health implications for infants with unrecognized gestational chemical exposures.

Oxidative stress is implicated in the development of non-alcoholic steatohepatitis (NASH). The Nrf2-antioxidant response element pathway protects cells from oxidative stress. Studies have shown that global Nrf2 deficiency hastens the progression of NASH. The purpose of this study was to determine whether long-term hepatocyte-specific activation of Nrf2 mitigates NASH progression. Transgenic mice expressing a constitutively active Nrf2 construct in hepatocytes (AlbCre+/caNrf2+) and littermate controls were generated. These mice were fed standard or methionine-choline-deficient (MCD) diet, a diet used to induce NASH development in rodents. After 28 days of MCD dietary feeding, mice developed significant increases in steatosis, inflammation, oxidative stress, and HSC activation compared with those mice on standard diet. AlbCre+/caNrf2+ animals had significantly decreased serum transaminases and reduced steatosis when compared with the AlbCre+/caNrf2– animals. This significant reduction in steatosis was associated with increased expression of genes involved in triglyceride export (MTTP) and β-oxidation (CPT2). However, there were no differences in the increased oxidative stress, inflammation, and HSC activation from MCD diet administration between the AlbCre+/caNrf2– and AlbCre+/caNrf2+ animals. We conclude that hepatocyte-specific activation of Nrf2-mediated gene expression decreased hepatocellular damage and steatosis in a dietary model of NASH. However, hepatocyte-specific induction of Nrf2-mediated gene expression alone is insufficient to mitigate inflammation, oxidative stress, and HSC activation in this nutritional NASH model.

1,3-Butadiene (BD), a widely used industrial chemical and a ubiquitous environmental pollutant, is a known human carcinogen. Although genotoxicity is an established mechanism of the tumorigenicity of BD, epigenetic effects have also been observed in livers of mice exposed to the chemical. To better characterize the diverse molecular mechanisms of BD tumorigenicity, we evaluated genotoxic and epigenotoxic effects of BD exposure in mouse tissues that are target (lung and liver) and non-target (kidney) for BD-induced tumors. We hypothesized that epigenetic alterations may explain, at least in part, the tissue-specific differences in BD tumorigenicity in mice. We evaluated the level of N-7-(2,3,4-trihydroxybut-1-yl)guanine adducts and 1,4-bis-(guan-7-yl)-2,3-butanediol crosslinks, DNA methylation, and histone modifications in male C57BL/6 mice exposed to filtered air or 425 ppm of BD by inhalation (6 h/day, 5 days/week) for 2 weeks. Although DNA damage was observed in all three tissues of BD-exposed mice, variation in epigenetic effects clearly existed between the kidneys, liver, and lungs. Epigenetic alterations indicative of genomic instability, including demethylation of repetitive DNA sequences and alterations in histone-lysine acetylation, were evident in the liver and lung tissues of BD-exposed mice. Changes in DNA methylation were insignificant in the kidneys of treated mice, whereas marks of condensed heterochromatin and transcriptional silencing (histone-lysine trimethylation) were increased. These modifications may represent a potential mechanistic explanation for the lack of tumorigenesis in the kidney. Our results indicate that differential tissue susceptibility to chemical-induced tumorigenesis may be attributed to tissue-specific epigenetic alterations.

Low molecular weight (LMW) respiratory sensitizers can cause occupational asthma but due to a lack of adequate test methods, prospective identification of respiratory sensitizers is currently not possible. This article presents the evaluation of structure–activity relationship (SAR) models as potential methods to prospectively conclude on the sensitization potential of LMW chemicals. The predictive performance of the SARs calculated from their training sets was compared to their performance on a dataset of newly identified respiratory sensitizers and nonsensitizers, derived from literature. The predictivity of the available SARs for new substances was markedly lower than their published predictive performance. For that reason, no single SAR model can be considered sufficiently reliable to conclude on potential LMW respiratory sensitization properties of a substance. The individual applicability domains (ADs) of the models were analyzed for adequacies and deficiencies. Based on these findings, a tiered prediction approach is subsequently proposed. This approach combines the two SARs with the highest positive and negative predictivity taking into account model specific chemical AD issues. The tiered approach provided reliable predictions for one-third of the respiratory sensitizers and nonsensitizers of the external validation set compiled by us. For these chemicals, a positive predictive value of 96% and a negative predictive value of 89% were obtained. The tiered approach was not able to predict the other two-thirds of the chemicals, meaning that additional information is required and that there is an urgent need for other test methods, e.g., in chemico or in vitro, to reach a reliable conclusion.

Demonstrating or verifying a current or past exposure to an environmental mitochondrial toxin or toxicant is extraordinarily difficult. Thus, there is a pressing need to develop a biomarker for exposure to environmental mitochondrial inhibitors. Rotenone, an environmental toxicant, is a potent inhibitor of the mitochondrial electron transfer chain. Rotenone specifically inhibits complex I throughout the body and brain, thereby producing systemic mitochondrial impairment. As such, rotenone is a prototypical clinically relevant, environmental mitochondrial toxicant that may be used as an ideal initial platform to develop accessible biomarkers of exposure. The over-arching goal of this work is to explore and validate peripheral (blood and skeletal muscle) DNA damage as a biomarker of mitochondrial toxicant exposure using the rat rotenone model. In this effort, we utilized an extremely sensitive quantitative polymerase chain reaction (QPCR)-based assay that simultaneously allows the assessment of multiple forms of mitochondrial DNA (mtDNA) and nuclear DNA (nDNA) damage. We found mtDNA damage in blood is detected after subclinical rotenone exposure and the damage persists even after complex I activity has returned to normal. With a more sustained rotenone exposure, mtDNA damage is also detected in skeletal muscle, suggesting that mtDNA damage in this tissue simply lags behind blood. Using the QPCR-based assay, we have no evidence for nDNA damage in peripheral tissues after rotenone exposure either acutely or chronically. Overall, these data support the idea that mtDNA damage in peripheral tissues in the rotenone model may provide a biomarker of past or ongoing mitochondrial toxin exposure.

Diesel exhaust (DE) exposure induces adverse cardiopulmonary effects. Cerium oxide nanoparticles added to diesel fuel (DECe) increases fuel burning efficiency but leads to altered emission characteristics and potentially altered health effects. Here, we evaluated whether DECe results in greater adverse pulmonary effects compared with DE. Male Sprague Dawley rats were exposed to filtered air, DE, or DECe for 5 h/day for 2 days. N-acetyl glucosaminidase activity was increased in bronchial alveolar lavage fluid (BALF) of rats exposed to DECe but not DE. There were also marginal but insignificant increases in several other lung injury biomarkers in both exposure groups (DECe > DE for all). To further characterize DECe toxicity, rats in a second study were exposed to filtered air or DECe for 5 h/day for 2 days or 4 weeks. Tissue analysis indicated a concentration- and time-dependent accumulation of lung and liver cerium followed by a delayed clearance. The gas-phase and high concentration of DECe increased lung inflammation at the 2-day time point, indicating that gas-phase components, in addition to particles, contribute to pulmonary toxicity. This effect was reduced at 4 weeks except for a sustained increase in BALF -glutamyl transferase activity. Histopathology and transmission electron microscopy revealed increased alveolar septa thickness due to edema and increased numbers of pigmented macrophages after DECe exposure. Collectively, these findings indicate that DECe induces more adverse pulmonary effects on a mass basis than DE. In addition, lung accumulation of cerium, systemic translocation to the liver, and delayed clearance are added concerns to existing health effects of DECe.

Accidents caused by scorpions represent a relevant public health issue in Brazil, being more recurring than incidents with snakes and spiders. The main species responsible for this situation is the yellow scorpion, Tityus serrulatus, due especially to the great frequency with which accidents occur and the potential of its venom to induce severe clinical manifestations, even death, mainly among children. Although neurotoxins are well characterized, little information is known about other components of scorpion venoms, such as peptidases, and their effect on envenomation. Previous results from our group showed that the metallopeptidases present in this venom are capable of hydrolyzing the neuropeptide dynorphin 1-13 in vitro, releasing Leu-enkephalin, which may interact with ion channels and promote indirect neurotoxicity. Thus, this study aims to get more information about the effect of toxic peptidase activity present in the venom on biologically active peptides, and to evaluate the in vitro neutralizing potential of commercial antivenoms produced by the Butantan Institute. A set of human bioactive peptides were studied as substrates for the peptidases, and the members of the neuropeptide Y family were found to be the most susceptible ones. All new substrate hydrolyses were totally inhibited by ethylenediaminetetracetic and not blocked by phenylmethanesulfonylfluoride, indicating that metallopeptidases were responsible for the peptidase activity. Also, peptidase activities were only partially inhibited by therapeutic Brazilian scorpion antivenom (SAV) and arachnid antivenom (AAV). The dose-response inhibition by both antivenoms indicates that AAV neutralizes better than SAV at the used doses. These characterizations, unpublished until now, can contribute to the improvement of our knowledge about the venom and envenomation processes by T. serrulatus.

It is widely accepted that more needs to be done to bring new, safe, and efficacious drugs to the market. Cardiovascular toxicity detected both in early drug discovery as well as in the clinic, is a major contributor to the high failure rate of new molecules. The growth of translational safety offers a promising approach to improve the probability of success for new molecules. Here we describe a cross-company initiative to determine the concordance between the conscious telemetered dog and phase I outcome for 3 cardiovascular parameters. The data indicate that, in the context of the methods applied in this analysis, the ability to detect compounds that affect the corrected QT interval (QTc) was good within the 10–30x exposure range but the predictive or detective value for heart rate and diastolic blood pressure was poor. These findings may highlight opportunities to refine both the animal and the clinical study designs, as well as refocusing the assessment of value of dog cardiovascular assessments beyond phase 1. This investigation has also highlighted key considerations for cross-company data sharing and presents a unique learning opportunity to improve future translational projects.

Acetaminophen (APAP)-induced acute liver failure (ALF) remains a major clinical problem. Although a majority of patients recovers after severe liver injury, a subpopulation of patients proceeds to ALF. Bile acids are generated in the liver and accumulate in blood during liver injury, and as such, have been proposed as biomarkers for liver injury and dysfunction. The goal of this study was to determine whether individual bile acid levels could determine outcome in patients with APAP-induced ALF (AALF). Serum bile acid levels were measured in AALF patients using mass spectrometry. Bile acid levels were elevated 5–80-fold above control values in injured patients on day 1 after the overdose and decreased over the course of hospital stay. Interestingly, glycodeoxycholic acid (GDCA) was significantly increased in non-surviving AALF patients compared with survivors. GDCA values obtained at peak alanine aminotransferase (ALT) and from day 1 of admission indicated GDCA could predict survival in these patients by receiver-operating characteristic analysis (AUC = 0.70 for day 1, AUC = 0.68 for peak ALT). Of note, AALF patients also had significantly higher levels of serum bile acids than patients with active cholestatic liver injury. These data suggest measurements of GDCA in this patient cohort modestly predicted outcome and may serve as a prognostic biomarker. Furthermore, accumulation of bile acids in serum or plasma may be a result of liver cell dysfunction and not cholestasis, suggesting elevation of circulating bile acid levels may be a consequence and not a cause of liver injury.

Organophosphate flame retardants (OPFRs) are common replacements for the phased-out polybrominated diphenyl ethers (PBDEs) and have been detected at high concentrations in environmental samples. OPFRs are structurally similar to organophosphate pesticides and may adversely affect the developing nervous system. This study evaluated the overt toxicity, uptake, and neurobehavioral effects of tris (1,3-dichloro-2-propyl) phosphate (TDCPP), tris (2-chloroethyl) phosphate (TCEP), tris (1-chloro-2-propyl) phosphate (TCPP), and tris (2,3-dibromopropyl) phosphate (TDBPP) in early life stage zebrafish. Chlorpyrifos was used as a positive control. For overt toxicity and neurobehavioral assessments, zebrafish were exposed from 0 to 5 days postfertilization (dpf). Hatching, death, or malformations were evaluated daily. Teratogenic effects were scored by visual examination on 6 dpf. To evaluate uptake and metabolism, zebrafish were exposed to 1 µM of each organophosphate (OP) flame retardant and collected on 1 and 5 dpf to monitor accumulation. Larval swimming activity was measured in 6 dpf larvae to evaluate neurobehavioral effects of exposures below the acute toxicity threshold. TDBPP elicited the greatest toxicity at >1 µM. TDCPP and chlorpyrifos were overtly toxic at concentrations ≥10 µM, TCEP, and TCPP were not overtly toxic at the doses tested. Tissue concentrations increased with increasing hydrophobicity of the parent chemical after 24 h exposures. TDCPP and TDBPP and their respective metabolites were detected in embryos on 5 dpf. For all chemicals tested, developmental exposures that were not overtly toxic significantly altered larval swimming activity. These data indicate that OPFRs adversely affect development of early life stage zebrafish.

Polychlorinated biphenyls (PCBs) are environmental chemicals which are potentially toxic to the developing brain. Their hydroxylated metabolites (OH-PCBs) are suggested to be even more toxic. Knowledge about the health effects of prenatal OH-PCB exposure is limited. We aimed to determine whether prenatal background exposure to PCBs and OH-PCBs is associated with neurological functioning in 3-month-old boys and girls. In a Dutch observational cohort study, we measured 10 PCBs and 6 OH-PCBs in maternal blood samples of 98 pregnant women. We assessed their infants neurologically with Touwen examination at 3 months and calculated an Optimality Score (OS, range 0–53, low-high optimality). We calculated correlation coefficients between compound levels and OS. Subsequently, we tested whether levels were associated with specific clusters and whether levels differed between infants with "normal" (dysfunction on ≤1 cluster) and "non-optimal" development (dysfunction on ≥2 clusters). The mean OS was 48 (range 44–52). Higher exposure to PCB-146 correlated significantly with higher OS (r = 0.209; p = 0.039). In boys, higher exposure to 4-OH-PCB-107 correlated with lower OS (r = –0.305; p = 0.030). Higher exposure to 9 PCBs and the sum of all PCBs was associated with better visuomotor and/or better sensorimotor function. Infants classified as "non-optimal" (n = 36) had significantly lower prenatal exposure to 6 PCBs and the sum of all PCBs (p < 0.05) compared with infants classified as "normal" (n = 62). In conclusion, higher prenatal exposure to Dutch background PCB levels is associated with better neurological functioning in 3-month-old infants. Prenatal exposure to 4-OH-PCB-107 is associated with less optimal neurological functioning in boys.

Tanezumab, an antibody to nerve growth factor, was administered to pregnant cynomolgus monkeys at 0, 0.5, 4, and 30 mg/kg weekly, beginning gestation day (GD) 20 through parturition (~GD165). Maternal tanezumab administration appeared to increase stillbirths and infant mortality, but no consistent pattern of gross and/or microscopic change was detected to explain the mortality. Offspring exposed in utero were evaluated at 12 months of age using light microscopy (all tissues), stereology (basal forebrain cholinergic and dorsal root ganglia neurons), and morphometry (sural nerve). Light microscopy revealed decreased number of neurons in sympathetic ganglia (superior mesenteric, cervicothoracic, and ganglia in the thoracic sympathetic trunk). Stereologic assessment indicated an overall decrease in dorsal root ganglion (thoracic) volume and number of neurons in animals exposed to tanezumab 4 mg/kg (n = 9) and 30 mg/kg (n = 1). At all tanezumab doses, the sural nerve was small due to decreases in myelinated and unmyelinated axons. Existing axons/myelin sheaths appeared normal when viewed with light and transmission electron microscopy. There was no indication of tanezumab-related, active neuron/nerve fiber degeneration/necrosis in any tissue, indicating decreased sensory/sympathetic neurons and axonal changes were due to hypoplasia or atrophy. These changes in the sensory and sympathetic portions of the peripheral nervous system suggest some degree of developmental neurotoxicity, although what effect, if any, the changes had on normal function and survival was not apparent. Overall, these changes were consistent with published data from rodent studies.

Arsenic exposure has been linked to an increased incidence of atherosclerosis. Previously, we have shown in vitro and in vivo that arsenic inhibits transcriptional activation of the liver X receptors (LXRs), key regulators of lipid homeostasis. Therefore, we evaluated the role of LXRα in arsenic-induced atherosclerosis using the apoE–/– mouse model. Indeed, deletion of LXRα protected apoE–/– mice against the proatherogenic effects of arsenic. We have previously shown that arsenic changes the plaque composition in apoE–/– mice. Arsenic decreased collagen content in the apoE–/– model, and we have observed the same diminution in LXRα–/–apoE–/– mice. However, the collagen-producing smooth muscle cells (SMCs) were decreased in apoE–/–, but increased in LXRα–/–apoE–/–. Although transcriptional activation of collagen remained the same in SMC from both genotypes, arsenic-exposed LXRα–/–apoE–/– plaques had increased matrix metalloproteinase activity compared with both control LXRα–/–apoE–/– and apoE–/–, which could be responsible for both the decrease in plaque collagen and the SMC invasion. In addition, arsenic increased plaque lipid accumulation in both genotypes. However, macrophages, the cells known to retain lipid within the plaque, were unchanged in arsenic-exposed apoE–/– mice, but decreased in LXRα–/–apoE–/–. We confirmed in vitro that these cells retained more lipid following arsenic exposure and are more sensitive to apoptosis than apoE–/–. Mice lacking LXRα are resistant to arsenic-enhanced atherosclerosis, but arsenic-exposed LXRα–/–apoE–/– mice still present a different plaque composition pattern than the arsenic-exposed apoE–/– mice.

Inorganic arsenic is a human carcinogen that likely targets the prostate. Chronic arsenic exposure malignantly transforms the RWPE-1 human prostate epithelial line to chronic arsenic exposed-prostate epithelial (CAsE-PE) cells, and a derivative normal prostate stem cell (SC) line, WPE-stem to arsenic-cancer SCs (As-CSCs). The KRAS oncogene is highly overexpressed in CAsE-PE cells and activation precedes transformation, inferring mechanistic significance. As-CSCs also highly overexpress KRAS. Thus, we hypothesize KRAS activation is key in causing and maintaining an arsenic-induced malignant phenotype, and hence, KRAS knockdown (KD) may reverse this malignant phenotype. RNA interference using shRNAmirs to obtain KRAS KD was used in CAsE-PE and As-CSC cells. Cells analyzed 2 weeks post transduction showed KRAS protein decreased to 5% of control after KD, confirming stable KD. KRAS KD decreased phosphorylated ERK, indicating inhibition of RAS/ERK signaling, a proliferation/survival pathway activated with arsenic transformation. Secreted metalloproteinase (MMP) activity was increased by arsenic-induced malignant transformation, but KRAS KD from 4 weeks on decreased secreted MMP-9 activity by 50% in As-CSCs. Colony formation, a characteristic of cancer cells, was decreased in both KRAS KD transformants. KRAS KD also decreased the invasive capacity of both cell types. KRAS KD decreased proliferation in As-CSCs, consistent with loss of rapid tumor growth. Genes predicted to impact cell proliferation (eg, Cyclin D1, p16, and p21) changed accordingly in both KD cell types. Thus, KRAS silencing impacts aspects of arsenic-induced malignant phenotype, inducing loss of many typical cancer characteristics particularly in As-CSCs.

Gold nanoparticle (AuNP) bioconjugates have been used as therapeutic and diagnostic tools; however, in vivo biocompatibility and cytotoxicity continue to be two fundamental issues. The effect of AuNPs (20 nm) conjugated with antibody [immunoglobulin G (IgG)], albumin, protein A, PEG4000, and citrate (cit) were evaluated in vitro using primary human cells of the vascular system. AuNP bioconjugates did not cause lysis of human erythrocytes, apoptosis or necrosis of human leukocytes, and endothelial cells in vitro, although AuNPs had been internalized and detected in the cytoplasm. Moreover, the influence of AuNPs on rheological parameters, blood and vessel wall characteristics was investigated in vivo by intravital microscopy assay using male Wistar rats mesentery microcirculation as model. Intravenous injection of AuNP-IgG or cit-AuNP did not cause hemorrhage, hemolysis or thrombus formation, instead suppressed the leukocyte adhesion to postcapillary vessel walls, an early stage of an inflammatory process. Furthermore, AuNP-IgG abrogated the expression of platelet-endothelial cell adhesion molecule-1, chemotaxis, and oxidative burst activation on neutrophils after leukotriene B4 stimulation, a membrane receptor-dependent stimulus, thus confirming their anti-inflammatory effects in vitro. The expression of oxidative burst activation was also suppressed after stimulating AuNP-IgG-treated neutrophils with lipid-soluble phorbol myristate acetate (PMA), confirming the direct intracellular action of AuNP-IgG on the inflammatory process in vitro. Our in vitro and in vivo experimental approaches highlighted the great potentiality of AuNP bioconjugates for therapeutic and diagnostic applications by parenteral routes.