Induction of activator protein-1 through reactive oxygen species by crystalline silica in JB6 cells

Mitochondrial respiratory complex III sustains IL-10 production in activated macrophages and promotes tumor-mediated immune evasion

The cytokine interleukin-10 (IL-10) limits the immune response and promotes resolution of acute inflammation. Because of its immunosuppressive effects, IL-10 up-regulation is a common feature of tumor progression and metastasis. Recently, IL-10 regulation has been shown to depend on mitochondria and redox-sensitive signals. We have found that Suppressor of site IIIQo Electron Leak 1.2 (S3QEL 1.2), a specific inhibitor of reactive oxygen species (ROS) production from mitochondrial complex III, and myxothiazol, a complex III inhibitor, decrease IL-10 in lipopolysaccharide (LPS)-activated macrophages. IL-10 down-regulation is likely to be mediated by suppression of c-Fos, which is a subunit of activator protein 1 (AP1), a transcription factor required for IL-10 gene expression. S3QEL 1.2 impairs IL-10 production in vivo after LPS challenge and promotes the survival of mice bearing B16F10 melanoma by lowering tumor growth. Our data identify a link between complex III-dependent ROS generation and IL-10 production in macrophages, the targeting of which could have potential in boosting antitumor immunity.

Release of Crystalline Silica Nanoparticles during Engineered Stone Fabrication

Inhalation exposure to respirable crystalline silica (RCS) during the fabrication of engineered stone-based kitchen countertops has been on the rise in recent years and has become a significant occupational health problem in the United States and globally. Little is known about the presence of nanocrystalline silica (NCS), i.e., particles below 100 nm. We present a methodology to quantify the crystalline silica content in the sub-100 nm size fraction of the aerosol released during engineered stone fabrication using X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. Aerosol was generated in a test chamber designed per EN 1093-3 and sampled using cascade impactors. XRD and FTIR analysis showed the presence of both α-quartz (15-60%) and cristobalite (10-50%) polymorphs in all size fractions. With increasing particle size, the cristobalite content increased. Seventy percent of the total aerosol mass in the sub-100 nm fraction was found to be crystalline silica, qualitatively confirmed by electron diffraction and electron energy loss spectroscopy. The presence of other minerals was detected in all size fractions; no polymeric resin binder was detected in the sub-100 nm fraction. Although the sub-100 nm fraction was about 1% of the aerosol mass, it accounted for 4-24% of the aerosol surface area based on the total lung deposition. If the surface area is a more relevant exposure metric, the assessment of the efficacy of current engineering control systems using mass as an exposure metric may not provide adequate protection.

Silica Nanoparticles Shed Light on Intriguing Cellular Pathways in Human Tracheal Smooth Muscle Cells: Revealing COX-2/PGE2 Production through the EGFR/Pyk2 Signaling Axis

The use of manufactured silica nanoparticles (SiNPs) has become widespread in everyday life, household products, and various industrial applications. While the harmful effects of crystalline silica on the lungs, known as silicosis or chronic pulmonary diseases, are well understood, the impact of SiNPs on the airway is not fully explored. This study aimed to investigate the potential effects of SiNPs on human tracheal smooth muscle cells (HTSMCs). Our findings revealed that SiNPs induced the expression of cyclooxygenase-2 (COX-2) mRNA/protein and the production of prostaglandin E2 (PGE2) without causing cytotoxicity. This induction was transcription-dependent, as confirmed by cell viability assays and COX-2 luciferase reporter assays. Further analysis, including Western blot with pharmacological inhibitors and siRNA interference, showed the involvement of receptor tyrosine kinase (RTK) EGF receptor (EGFR), non-RTK Pyk2, protein kinase Cα (PKCα), and p42/p44 MAPK in the induction process. Notably, EGFR activation initiated cellular signaling that led to NF-κB p65 phosphorylation and translocation into the cell nucleus, where it bound and stimulated COX-2 gene transcription. The resulting COX-2 protein triggered PGE2 production and secretion into the extracellular space. Our study demonstrated that SiNPs mediate COX-2 up-regulation and PGE2 secretion in HTSMCs through the sequential activation of the EGFR/Pyk2/PKCα/p42/p44MAPKs-dependent NF-κB signaling pathway. Since PGE2 can have both physiological bronchodilatory and anti-inflammatory effects, as well as pathological pro-inflammatory effects, the increased PGE2 production in the airway might act as a protective compensatory mechanism and/or a contributing factor during airway exposure to SiNPs.

Positive effects of low-dose photodynamic therapy with aminolevulinic acid or its methyl ester in skin rejuvenation and wound healing: An update

In dermatology, photodynamic therapy (PDT) is widely used in skin tumors, infections, etc., because of the killing effect triggered by toxic reactive oxygen species (ROS). However, the ROS concentration is determined by various photosensitizer concentrations and formulations, as well as various irradiation parameters. Low-dose PDT leads to sufficiently low ROS level, which results in biological effects that are the exact opposite of the killing potency. Therefore, in recent years, low-dose PDT has been exploited in improving aging and wound. Low-dose ALA/MAL PDT might improve aging through promoting the proliferation of fibroblasts, blocking DNA damage, counteracting oxidative stress, inhibiting melanogenesis, and remodeling lymphatic vessels in aged skin. Promoting fibroblasts and epidermal stem cells proliferation and migration, promoting granulation tissue formation and angiogenesis and regulating the inflammatory process might be the mechanisms of low-dose ALA/MAL PDT in wound healing. Nevertheless, the positive effects of low-dose PDT have not been thoroughly investigated in dermatology, and high-quality studies are still needed to fill the relevant vacancy.

Cerium oxide nanozymes confer a cytoprotective and bio-friendly surface micro-environment to methacrylate based oro-facial prostheses

Poly-(methyl methacrylate) (PMMA) is the preferred biomaterial for orofacial prostheses used for the rehabilitation of naso-palatal defects. However, conventional PMMA has limitations determined by the complexity of the local microbiota and the friability of oral mucosa adjacent to these defects. Our purpose was to develop a new type of PMMA, i-PMMA, with good biocompatibility and better biological effects such as higher resistance to microbial adhesion of multiple species and enhanced antioxidant effect. The addition of cerium oxide nanoparticles to PMMA using a mesoporous nano-silica carrier and polybetaine conditioning, resulted in an increased release of cerium ions and enzyme mimetic activity, without tangible loss of mechanical properties. Ex vivo experiments confirmed these observations. In stressed human gingival fibroblasts, i-PMMA reduced the levels of reactive oxygen species and increased the expression of homeostasis-related proteins (PPARg, ATG5, LCI/III). Furthermore, i-PMMA increased the levels of expression of superoxide dismutase and mitogen-activated protein kinases (ERK and Akt), and cellular migration. Lastly, we demonstrated the biosafety of i-PMMA using two in vivo models: skin sensitization assay and oral mucosa irritation test, respectively. Therefore, i-PMMA offers a cytoprotective interface that prevents microbial adhesion and attenuates oxidative stress, thus supporting physiological recovery of the oral mucosa.

Methamphetamine signals transcription of IL1β and TNFα in a reactive oxygen species-dependent manner and interacts with HIV-1 Tat to decrease antioxidant defense mechanisms

Methamphetamine (Meth) abuse is a common HIV co-morbidity that is linked to aggravated Central Nervous System (CNS) inflammation, which accentuates HIV- associated neurological disorders, triggered both directly or indirectly by the drug. We used the well-established human innate immune macrophage cell line system (THP1) to demonstrate that Reactive Oxygen Species (ROS) immediately induced by Meth play a role in the increased transcription of inflammatory genes, in interaction with HIV-1 Tat peptide. Meth and Tat, alone and together, affect early events of transcriptional activity, as indicated by changes in RNA polymerase (RNAPol) recruitment patterns throughout the genome, via ROS-dependent and -independent mechanisms. IL1β (IL1β) and TNF α (TNFα), two genes with defining roles in the inflammatory response, were both activated in a ROS-dependent manner. We found that this effect occurred via the activation of the activator protein 1 (AP-1) comprising cFOS and cJUN transcription factors and regulated by the SRC kinase. HIV-1 Tat, which was also able to induce the production of ROS, did not further impact the effects of ROS in the context of Meth, but promoted gene activity independently from ROS, via additional transcription factors. For instance, HIV-1 Tat increased NFkB activation and activated gene clusters regulated by Tata box binding peptide, ING4 and IRF2. Importantly, HIV-1 Tat decreased the expression of anti-oxidant genes, where its suppression of the detoxifying machinery may contribute to the aggravation of oxidative stress induced by ROS in the context of Meth. Our results provide evidence of effects of Meth via ROS and interactions with HIV Tat that promote the transcription of inflammatory genes such as IL1β and TNFα.

Nicotine stimulates CYP1A1 expression in human hepatocellular carcinoma cells via AP-1, NF-κB, and AhR

Cytochrome P450 1A1 (CYP1A1) is a member of a subfamily of enzymes involved in the metabolism of both endogenous and exogenous substrates and the chemical activation of xenobiotics to carcinogenic derivatives. Here, the effects of nicotine, a major psychoactive compound present in cigarette smoke, on CYP1A1 expression and human hepatocellular carcinoma (HepG2) cell proliferation were investigated. Nicotine stimulated CYP1A1 expression via the transcription factors, activator protein 1, nuclear factor-kappa B, and the aryl hydrocarbon receptor (AhR) signaling pathway. Pharmacological inhibition and mutagenesis studies indicated that p38 mitogen-activated protein kinase, as well as RelA (or p65), mediated the upregulation of CYP1A1 of nicotine in HepG2 cells. The antioxidant compound, N-acetyl-cysteine, abrogated nicotine-activated production of reactive oxygen species and inhibited CYP1A1 expression by nicotine. Furthermore, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity was inhibited by diphenyleneiodonium (an NADPH oxidase inhibitor). Thus, these results demonstrated that AhR played an important role in nicotine-induced CYP1A1 expression. Additionally, liver hepatocellular carcinoma HepG2 cells treated with nicotine exhibited markedly enhanced proliferation via CYP1A1 expression and Akt activation.

Scutellarin Suppresses Patient-Derived Xenograft Tumor Growth by Directly Targeting AKT in Esophageal Squamous Cell Carcinoma

Scutellarin is a flavonoid compound that is found in Scutellaria barbata It has been reported to exhibit anticancer and anti-inflammation activities. However, the anticancer properties of scutellarin and its molecular targets have not been investigated in esophageal squamous cell carcinoma (ESCC). In the current study, we report that scutellarin is a potential AKT inhibitor that suppresses patient-derived xenograft ESCC tumor growth. To identify possible molecular targets of scutellarin, potential candidate proteins were screened by an in vitro kinase assay and Western blotting. We found that scutellarin directly binds to the AKT1/2 proteins and inhibits activities of AKT1/2 in vitro The AKT protein is activated in ESCC tissues and knockdown of AKT significantly suppresses growth of ESCC cells. Scutellarin significantly inhibits anchorage-dependent and independent cell growth and induces G₂ phase cell-cycle arrest in ESCC cells. The inhibition of cell growth by scutellarin is dependent on the expression of the AKT protein. Notably, scutellarin strongly suppresses patient-derived xenograft ESCC tumor growth in an in vivo mouse model. Taken together, our data suggest that scutellarin is a novel AKT inhibitor that may prevent progression of ESCC.

Purpurogallin is a novel mitogen-activated protein kinase kinase 1/2 inhibitor that suppresses esophageal squamous cell carcinoma growth in vitro and in vivo

Purpurogallin is a natural compound that is extracted from nutgalls and oak bark and it possesses antioxidant, anticancer, and anti-inflammatory properties. However, the anticancer capacity of purpurogallin and its molecular target have not been investigated in esophageal squamous cell carcinoma (ESCC). Herein, we report that purpurogallin suppresses ESCC cell growth by directly targeting the mitogen-activated protein kinase kinase 1/2 (MEK1/2) signaling pathway. We found that purpurogallin inhibits anchorage-dependent and -independent ESCC growth. The results of in vitro kinase assays and cell-based assays indicated that purpurogallin also strongly attenuates the extracellular signal-regulated kinase 1/2 (ERK1/2) signaling pathway and also directly binds to and inhibits MEK1 and MEK2 activity. Furthermore, purpurogallin contributed to S and G2 phase cell cycle arrest by reducing cyclin A2 and cyclin B1 expression and also induced apoptosis by activating poly (ADP ribose) polymerase (PARP). Notably, purpurogallin suppressed patient-derived ESCC tumor growth in an in vivo mouse model. These findings indicated that purpurogallin is a novel MEK1/2 inhibitor that could be useful for treating ESCC.

The Role of NADPH Oxidases and Oxidative Stress in Neurodegenerative Disorders

For a number of years, nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOX) was synonymous with NOX2/gp91^phox and was considered to be a peculiarity of professional phagocytic cells. Over the last decade, several more homologs have been identified and based on current research, the NOX family consists of NOX1, NOX2, NOX3, NOX4, NOX5, DUOX1 and DUOX2 enzymes. NOXs are electron transporting membrane proteins that are responsible for reactive oxygen species (ROS) generation-primarily superoxide anion (O₂^●-), although hydrogen peroxide (H₂O₂) can also be generated. Elevated ROS leads to oxidative stress (OS), which has been associated with a myriad of inflammatory and degenerative pathologies. Interestingly, OS is also the commonality in the pathophysiology of neurodegenerative disorders, such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS) and multiple sclerosis (MS). NOX enzymes are expressed in neurons, glial cells and cerebrovascular endothelial cells. NOX-mediated OS is identified as one of the main causes of cerebrovascular damage in neurodegenerative diseases. In this review, we will discuss recent developments in our understanding of the mechanisms linking NOX activity, OS and neurodegenerative diseases, with particular focus on the neurovascular component of these conditions. We conclude highlighting current challenges and future opportunities to combat age-related neurodegenerative disorders by targeting NOXs.

Remodeling of dermal collagen in photoaged skin using low-dose 5-aminolevulinic acid photodynamic therapy occurs via the transforming growth factor-β pathway

5-Aminolevulinic acid photodynamic therapy (ALA-PDT) is known to be effective in the treatment of photoaged skin. However, the molecular mechanisms still remain elusive. Protoporphyrin IX (PpIX) fluorescence is primarily located in the epidermis while ALA-PDT affects the dermal collagen, presumably by an indirect mechanism. This study aimed to investigate the molecular communication in low-dose ALA-PDT occurring between epidermal keratinocytes and dermal fibroblasts. Western blotting and enzyme-linked immunosorbent assays were performed to evaluate collagen expression and transforming growth factor-β (TGF-β) signaling in human keratinocytes and dermal fibroblasts. The impact on fibroblast proliferation was assessed by morphology and proliferating cell nuclear antigen immunofluorescence. Skin biopsies from mice were used to analyze the histological changes in dermal collagen and PpIX distribution. When fibroblasts were cocultured with keratinocytes treated with low-dose ALA-PDT, collagen synthesis and fibroblast proliferation were enhanced. Low-dose ALA-PDT stimulated TGF-β1 expression in keratinocytes. Fibroblasts cocultured with low-dose ALA-PDT-treated keratinocytes also showed activation of the TGF-β pathway. In vivo, PpIX fluorescence was densely distributed in photoaged mouse epidermis while collagen in the mouse dermis underwent remodeling. This study suggests that low-dose ALA-PDT can stimulate keratinocytes to release TGF-β1, activating the TGF-β pathway in dermal fibroblasts to remodel collagen in the dermis.

Pulmonary Toxicity of Expancel® Microspheres in the Rat

Expancel® microspheres are thermoplastic microspheres enclosing hydrocarbon. These microspheres expand when heated, producing many applications. Because they have unknown biological persistence and toxicity, we investigated the toxicity of two unexpanded (11.1 and 15.4 μm mean diameter) and two expanded (3.1 and 5.5 μm mass median aerodynamic diameter) Expancel® microspheres in intratracheally-instilled, male, Sprague–Dawley rats. Pulmonary histopathology was evaluated at 28 days postexposure. Bronchoalveolar lavage fluid was evaluated at days 1, 7, 14, and 28 days postexposure. Crystalline silica was the positive control. By histopathology, both unexpanded and expanded microspheres caused granulomatous bronchopneumonia characterized by macrophages and giants cells, suggesting a persistent foreign body response. Expanded, but not unexpanded microspheres, also caused eosinophilic bronchitis and bronchiolitis, mucous metaplasia of airways and organized granulomatous inflammation with associated fibrosis and frequent airway obstruction. In contrast, alveolar macrophage activation, polymorphonuclear leukocytes, LDH and albumin in bronchoalveolar laveage fluid were initially elevated but returned to near control levels at 28 days, and did not reflect the persistent granulomatous bronchopneumonia caused by Expancel® microspheres. These findings emphasize the importance of histopathology for evaluating pulmonary toxicity, suggest that Expancel® microspheres are a potential occupational hazard, and indicate a need for additional studies on their potential pulmonary toxicity.

[Supplementary materials are available for this article. Go to the publisher’s online edition of Toxicology Pathology for the following free supplemental resources: motion within unexpected microspheres in H&E-stained lung (supplementary Figure 1 ); broncholar epithelium 28 days following exposure to 551 DE 20 microspheres (supplementary Figure 2 ); membrane ruffling and some instances of phagocytosis within the microspheres (supplementary Figure 3 )]

Diabetes-Induced Reactive Oxygen Species: Mechanism of Their Generation and Role in Renal Injury

Diabetes induces the onset and progression of renal injury through causing hemodynamic dysregulation along with abnormal morphological and functional nephron changes. The most important event that precedes renal injury is an increase in permeability of plasma proteins such as albumin through a damaged glomerular filtration barrier resulting in excessive urinary albumin excretion (UAE). Moreover, once enhanced UAE begins, it may advance renal injury from progression of abnormal renal hemodynamics, increased glomerular basement membrane (GBM) thickness, mesangial expansion, extracellular matrix accumulation, and glomerulosclerosis to eventual end-stage renal damage. Interestingly, all these pathological changes are predominantly driven by diabetes-induced reactive oxygen species (ROS) and abnormal downstream signaling molecules. In diabetic kidney, NADPH oxidase (enzymatic) and mitochondrial electron transport chain (nonenzymatic) are the prominent sources of ROS, which are believed to cause the onset of albuminuria followed by progression to renal damage through podocyte depletion. Chronic hyperglycemia and consequent ROS production can trigger abnormal signaling pathways involving diverse signaling mediators such as transcription factors, inflammatory cytokines, chemokines, and vasoactive substances. Persistently, increased expression and activation of these signaling molecules contribute to the irreversible functional and structural changes in the kidney resulting in critically decreased glomerular filtration rate leading to eventual renal failure.

HOI-02 induces apoptosis and G2-M arrest in esophageal cancer mediated by ROS

Reactive oxygen species (ROS) are chemically reactive molecules that perform essential functions in living organisms. Accumulating evidence suggests that many types of cancer cells exhibit elevated levels of ROS. Conversely, generation of ROS has become an effective method to kill cancer cells. (E)-3-hydroxy-3-(4-(4-nitrophenyl)-2-oxobut-3-en-1-yl) indolin-2-one, which is an NO2 group-containing compound designated herein as HOI-02, generated ROS and, in a dose-dependent manner, decreased esophageal cancer cell viability and inhibited anchorage-independent growth, followed by apoptosis and G2-M arrest. Moreover, results of an in vivo study using a patient-derived xenograft mouse model showed that HOI-02 treatment suppressed the growth of esophageal tumors, without affecting the body weight of mice. The expression of Ki-67 was significantly decreased with HOI-02 treatment. In addition, the phosphorylation of c-Jun, and expression of p21, cleaved caspase 3, and DCFH-DA were increased in the HOI-02-treated group compared with the untreated control group. In contrast, treatment of cells with (E)-3-(4-(4-aminophenyl)-2-oxobut-3-en-1-yl)-3-hydroxyindolin-2-one, which is an NH2 group-containing compound designated herein as HOI-11, had no effect. Overall, we identified HOI-02 as an effective NO2 group-containing compound that was an effective therapeutic or preventive agent against esophageal cancer cell growth.

Activation of Proinflammatory Responses in Cells of the Airway Mucosa by Particulate Matter: Oxidant- and Non-Oxidant-Mediated Triggering Mechanisms

Inflammation is considered to play a central role in a diverse range of disease outcomes associated with exposure to various types of inhalable particulates. The initial mechanisms through which particles trigger cellular responses leading to activation of inflammatory responses are crucial to clarify in order to understand what physico-chemical characteristics govern the inflammogenic activity of particulate matter and why some particles are more harmful than others. Recent research suggests that molecular triggering mechanisms involved in activation of proinflammatory genes and onset of inflammatory reactions by particles or soluble particle components can be categorized into direct formation of reactive oxygen species (ROS) with subsequent oxidative stress, interaction with the lipid layer of cellular membranes, activation of cell surface receptors, and direct interactions with intracellular molecular targets. The present review focuses on the immediate effects and responses in cells exposed to particles and central down-stream signaling mechanisms involved in regulation of proinflammatory genes, with special emphasis on the role of oxidant and non-oxidant triggering mechanisms. Importantly, ROS act as a central second-messenger in a variety of signaling pathways. Even non-oxidant mediated triggering mechanisms are therefore also likely to activate downstream redox-regulated events.

Mechanisms of nanoparticle-induced oxidative stress and toxicity

The rapidly emerging field of nanotechnology has offered innovative discoveries in the medical, industrial, and consumer sectors. The unique physicochemical and electrical properties of engineered nanoparticles (NP) make them highly desirable in a variety of applications. However, these novel properties of NP are fraught with concerns for environmental and occupational exposure. Changes in structural and physicochemical properties of NP can lead to changes in biological activities including ROS generation, one of the most frequently reported NP-associated toxicities. Oxidative stress induced by engineered NP is due to acellular factors such as particle surface, size, composition, and presence of metals, while cellular responses such as mitochondrial respiration, NP-cell interaction, and immune cell activation are responsible for ROS-mediated damage. NP-induced oxidative stress responses are torch bearers for further pathophysiological effects including genotoxicity, inflammation, and fibrosis as demonstrated by activation of associated cell signaling pathways. Since oxidative stress is a key determinant of NP-induced injury, it is necessary to characterize the ROS response resulting from NP. Through physicochemical characterization and understanding of the multiple signaling cascades activated by NP-induced ROS, a systemic toxicity screen with oxidative stress as a predictive model for NP-induced injury can be developed.

Bioreactivity of the crystalline silica polymorphs, quartz and cristobalite, and implications for occupational exposure limits (OELs)

Silica or silicon dioxides (SiO₂) are naturally occurring substances that comprise the vast majority of the earth's crust. Because of their prevalence and commercial applications, they have been widely studied for their potential to induce pulmonary fibrosis and other disorders. Historically, the focus in the workplace has been on the development of inflammation and fibrotic lung disease, the basis for promulgating workplace standards to protect workers. Crystalline silica (CS) polymorphs, predominantly quartz and cristobalite, are used in industry but are different in their mineralogy, chemistry, surface features, size dimensions and association with other elements naturally and during industrial applications. Epidemiologic, clinical and experimental studies in the literature historically have predominantly focused on quartz polymorphs. Thus, in this review, we summarize past scientific evaluations and recent peer-reviewed literature with an emphasis on cristobalite, in an attempt to determine whether quartz and cristobalite polymorphs differ in their health effects, toxicity and other properties that may dictate the need for various standards of protection in the workplace. In addition to current epidemiological and clinical reports, we review in vivo studies in rodents as well as cell culture studies that shed light on mechanisms intrinsic to the toxicity, altered cell responses and protective or defense mechanisms in response to these minerals. The medical and scientific literature indicates that the mechanisms of injury and potential causation of inflammation and fibrotic lung disease are similar for quartz and cristobalite. Our analysis of these data suggests similar occupational exposure limits (OELs) for these minerals in the workplace.

Mechanisms of crystalline silica-induced pulmonary toxicity revealed by global gene expression profiling

A proper understanding of the mechanisms underlying crystalline silica-induced pulmonary toxicity has implications in the management and potential prevention of the adverse health effects associated with silica exposure including silicosis, cancer and several auto-immune diseases. Human lung type II epithelial cells and rat lungs exposed to crystalline silica were employed as experimental models to determine global gene expression changes in order to understand the molecular mechanisms underlying silica-induced pulmonary toxicity. The differential gene expression profile induced by silica correlated with its toxicity in the A549 cells. The biological processes perturbed by silica exposure in the A549 cells and rat lungs, as identified by the bioinformatics analysis of the differentially expressed genes, demonstrated significant similarity. Functional categorization of the differentially expressed genes identified cancer, cellular movement, cellular growth and proliferation, cell death, inflammatory response, cell cycle, cellular development, and genetic disorder as top ranking biological functions perturbed by silica exposure in A549 cells and rat lungs. Results of our study, in addition to confirming several previously identified molecular targets and mechanisms involved in silica toxicity, identified novel molecular targets and mechanisms potentially involved in silica-induced pulmonary toxicity. Further investigations, including those focused on the novel molecular targets and mechanisms identified in the current study may result in better management and, possibly, reduction and/or prevention of the potential adverse health effects associated with crystalline silica exposure.

The role of p53 in silica-induced cellular and molecular responses associated with carcinogenesis

Crystalline silica (silica), a suspected human carcinogen, produces an increase in reactive oxygen species (ROS) when fractured using mechanical tools used in several occupations. Although ROS has been linked to apoptosis, DNA damage, and carcinogenesis, the role of enhanced ROS production by silica in silica-induced carcinogenesis is not completely understood. The goal of this study was to compare freshly fractured and aged silica-induced molecular alterations in human immortalized/transformed bronchial epithelial cells (BEAS-IIB) and lung cancer cells with altered (H460) or deficient (H1299) p53 expression. Exposure to freshly fractured or aged silica produced divergent cellular responses in certain downstream cellular events, including ROS production, apoptosis, cell cycle and chromosomal changes, and gene expression. ROS production increased significantly following exposure to freshly fractured silica compared to aged silica in BEAS-IIB and H460 cells. Apoptosis showed a comparable enhanced level of induction with freshly fractured or aged silica in both cancer lines with p53 functional changes. p53 protein was present in the BEAS-IIB and was absent in cancer cell lines after silica exposure. Exposure to freshly fractured silica also resulted in a rise in aneuploidy in cancer cells with a significantly greater increase in p53-deficient cells. Cytogenetic analysis demonstrated increased metaphase spreads, chromosome breakage, rearrangements, and endoreduplication in both cancer cells. These results suggest that altered and deficient p53 affects the cellular response to freshly fractured silica exposure, and thereby enhances susceptibility and augments cell proliferation and lung cancer development.

Raw single-wall carbon nanotubes induce oxidative stress and activate MAPKs, AP-1, NF-kappaB, and Akt in normal and malignant human mesothelial cells

BACKGROUND

Single-wall carbon nanotubes (SWCNTs), with their unique physicochemical and mechanical properties, have many potential new applications in medicine and industry. There has been great concern subsequent to preliminary investigations of the toxicity, biopersistence, pathogenicity, and ability of SWCNTs to translocate to subpleural areas. These results compel studies of potential interactions of SWCNTs with mesothelial cells.

OBJECTIVE

Exposure to asbestos is the primary cause of malignant mesothelioma in 80-90% of individuals who develop the disease. Because the mesothelial cells are the primary target cells of asbestos-induced molecular changes mediated through an oxidant-linked mechanism, we used normal mesothelial and malignant mesothelial cells to investigate alterations in molecular signaling in response to a commercially manufactured SWCNT.

METHODS

In the present study, we exposed mesothelial cells to SWCNTs and investigated reactive oxygen species (ROS) generation, cell viability, DNA damage, histone H2AX phosphorylation, activation of poly(ADP-ribose) polymerase 1 (PARP-1), stimulation of extracellular signal-regulated kinase (ERKs), Jun N-terminal kinases (JNKs), protein p38, and activation of activator protein-1 (AP-1), nuclear factor kappaB (NF-kappaB), and protein serine-threonine kinase (Akt).

RESULTS

Exposure to SWCNTs induced ROS generation, increased cell death, enhanced DNA damage and H2AX phosphorylation, and activated PARP, AP-1, NF-kappaB, p38, and Akt in a dose-dependent manner. These events recapitulate some of the key molecular events involved in mesothelioma development associated with asbestos exposure.

CONCLUSIONS

The cellular and molecular findings reported here do suggest that SWCNTs can cause potentially adverse cellular responses in mesothelial cells through activation of molecular signaling associated with oxidative stress, which is of sufficient significance to warrant in vivo animal exposure studies.

Inflammation and lung cancer: roles of reactive oxygen/nitrogen species

The lung is a highly specialized organ that facilitates uptake of oxygen and release of carbon dioxide. Due to its unique structure providing enormous surface area to outside ambient air, it is vulnerable to numerous pathogens, pollutants, oxidants, gases, and toxicants that are inhaled continuously from air, which makes the lung susceptible to varying degrees of oxidative injury. To combat these unrelenting physical, chemical, and biological insults, the respiratory epithelium is covered with a thin layer of lining fluid containing several antioxidants and surfactants. Inhaled toxic agents stimulate the generation of reactive oxygen/nitrogen species (ROS/RNS), which in turn provoke inflammatory responses resulting in the release of proinflammatory cytokines and chemokines. These subsequently stimulate the influx of polymorphonuclear leukocytes (PMNs) and monocytes into the lung so as to combat the invading pathogens or toxic agents. In addition to the beneficial effects, persistent inhalation of the invading pathogens or toxic agents may result in overwhelming production of ROS/RNS, producing chronic inflammation and lung injury. During inflammation, enhanced ROS/RNS production may induce recurring DNA damage, inhibition of apoptosis, and activation of proto-oncogenes by initiating signal transduction pathways. Therefore, it is conceivable that chronic inflammation-induced production of ROS/RNS in the lung may predispose individuals to lung cancer. This review describes the complex relationship between lung inflammation and carcinogenesis, and highlights the role of ROS/RNS in cancer development.

D-Psicose inhibits the expression of MCP-1 induced by high-glucose stimulation in HUVECs

Monocyte chemoattractant protein-1 (MCP-1) is a 76-amino-acid chemokine thought to be the major chemotactic factor for monocytes. MCP-1 is found in macrophage-rich areas of atherosclerotic lesions. Recent report indicates that MCP-1 is induced by glucose-stimulation, raising the important link between diabetes mellitus and atherosclerosis. One of the rare sugars, d-psicose (d-ribo-2-hexulose) is present in small quantities in commercial carbohydrate complexes, however the physiological functions of d-psicose have not been evaluated. In this study, we examined the effects of d-psicose on MCP-1 expression in human umbilical vein endothelial cells (HUVECs). Results showed that MCP-1 mRNA and protein were stimulated following exposure to 22.4 mM glucose. Transcriptional activity of MCP-1 promoter paralleled endogenous expression of the gene and this activity was dependent on the dose of d-glucose. d-Psicose inhibited these effects. Next we used inhibitors of selected signal transduction pathways to show that high-glucose (HG) stimulated MCP-1 promoter activity was sensitive to p38-Mitogen-Activated Protein Kinase (p38-MAPK) pathway inhibitor. As expected, a dominant-negative p38-MAPK abolished the stimulatory effect of HG on the promoter activity. To incubate the cells with HG and d-psicose reduced the activation of p38-MAPK. Together, these results indicate that the d-psicose suppression of HG induced MCP-1 expression is mediated in part by inhibition of the p38-MAPK pathway and raise the possibility that d-psicose may be of therapeutic value in the treatment of diseases such as atherosclerosis.

Comparative cytotoxicity of cadmium and mercury in a human bronchial epithelial cell line (BEAS-2B) and its role in oxidative stress and induction of heat shock protein 70

A number of toxic heavy metals, such as cadmium (Cd) and mercury (Hg), are widely used in occupational settings, and exposure to these metals is associated with the development of pulmonary diseases. Cytotoxicity, apoptosis, and reactive oxygen species (ROS) generation were tested to compare the biological reactivity of these two heavy metals using a human bronchial epithelial cell line, BEAS-2B. Further, heat-shock protein 70 (Hsp70) expression was observed as a sensitive indicator of cellular stress. Exposure to metals (0-50 microM) for 72 h showed more significant cytotoxicity in Cd-treated than Hg-treated cells. Apoptosis was significantly increased in the cells exposed to 50 microM of Cd (3.5-fold) and Hg (3.6-fold). Cd and Hg produced an induction of Hsp70 protein as assayed by Western blotting and enzyme-linked immunosorbent assay (ELISA). Induction of Hsp70 protein by these metals was inhibited by addition of N-acetylcysteine. However, addition of catalase blocked the synthesis of Hsp70 only in Hg-treated cells. Hsp70B and Hsp70C mRNA expression was induced by both metals, while Hsp70A mRNA expression showed no change. Electron spin resonance (ESR) tests showed that hydroxyl radical generation was greater in the reaction of cells with Hg compared to Cd. Intracellular generation of ROS was detected in the cells exposed to both Cd and Hg. These results suggest that both cytotoxicity and apoptosis were significantly elevated with all metals tested; however, Cd was relatively more toxic. Hsp70 protein and mRNA were sensitive to exposure to these metals. Depletion of sulfhydryl groups of cellular proteins and generation of ROS may be involved in metal-induced lung cell damage.

Comparative in vitro toxicity of grape- and citrus-farm dusts

Agricultural workers are exposed to a variety of airborne dusts, including crystalline silica and other inorganic minerals. This study was designed to characterize the organic and inorganic components of agricultural dusts in California grape- and citrus-farm fields and to compare their cytotoxicity using in vitro toxicity bioassays as predictors of pathogenicity. Aerosolized dusts collected from farm fields were characterized by scanning-electron-microscopic energy-dispersive x-ray analysis, x-ray diffraction, trace metal analysis by plasma emission spectroscopy, and surface area measurements. As indicators of cytotoxicity, cell viability, release of alveolar enzymes activities (lactate dehydrogenase, N-acetyl glucosaminidase), production of reactive oxygen species (ROS), such as H2O2 and hydroxyl radical (OH), and lipid peroxidation were monitored after exposure of cells to grape- and citrus-farm dusts or inorganic components of these dusts. In addition, activation of nuclear factor kappa B and activator protein-1 were evaluated at the peak time for response of 36 h postexposure. All toxicity studies were done in comparison with crystalline silica of similar particle size and diameter using the same mass concentrations as farm dusts. The results showed that inorganic minerals in the aerosolized farm dust fractions were mostly composed of aluminum silicates, crystalline silica, and free iron. Crystalline silica used in these studies was more cytotoxic than grape- and citrus-farm dusts. However, in general, citrus farm dust exhibited the greatest ability to generate ROS and induce lipid peroxidation. These results support human epidemiologic studies, reporting an increased incidence of pulmonary fibrosis in farm workers, by documenting the potential of farm dusts to induce oxidative stress and initiate disease development.

Expression of heme oxygenase-1 in the lungs of rats exposed to crystalline silica

Oxidative stress is thought to be the pathogenesis of pulmonary fibrosis induced by particles, and heme oxygenase-1 (HO-1) protects lung tissue against oxidative stress. We hypothesized that HO-1 is also associated with oxidative lung injury caused by exposure to particles. The present study was conducted to investigate the time course of HO-1 expression of lungs exposed to crystalline silica in vivo. Male Wistar rats were administered 1 mg or 2 mg of crystalline silica suspended in saline by a single intratracheal instillation and were sacrificed at 3 d, 1 wk, 1 month, 3 months and 6 months of recovery time. The expression of HO-1 was observed by western blot analysis and immunostaining. Protein levels of HO-1 were increased compared to the controls at 3 d, and from 1 month to 6 months following intratracheal instillation of 2 mg of crystalline silica. The levels of HO-1 were increased compared to the controls from 1 month to 6 months following intratracheal instillation of 1 mg of crystalline silica. Many HO-1 positive cells were found particularly in the alveolar macrophages during immunostaining. These findings suggest that HO-1 is related to lung injury arising from exposure to crystalline silica.

Heparin affin regulatory peptide/pleiotrophin mediates fibroblast growth factor 2 stimulatory effects on human prostate cancer cells

Fibroblast growth factor 2 (FGF2) is a pleiotropic growth factor that has been implicated in prostate cancer formation and progression. In the present study we found that exogenous FGF2 significantly increased human prostate cancer LNCaP cell proliferation and migration. Heparin affin regulatory peptide (HARP) or pleiotrophin seems to be an important mediator of FGF2 stimulatory effects, since the latter had no effect on stably transfected LNCaP cells that did not express HARP. Moreover, FGF2, through FGF receptors (FGFRs), significantly induced HARP expression and secretion by LNCaP cells and increased luciferase activity of a reporter gene vector carrying the full-length promoter of HARP gene. Using a combination of Western blot analyses, as well as genetic and pharmacological inhibitors, we found that activation of FGFR by FGF2 in LNCaP cells leads to NAD(P)H oxidase-dependent hydrogen peroxide production, phosphorylation of ERK1/2 and p38, activation of AP-1, increased expression and secretion of HARP, and, finally, increased cell proliferation and migration. These results establish the role and the mode of activity of FGF2 in LNCaP cells and support an interventional role of HARP in FGF2 effects, providing new insights on the interplay among growth factor pathways within prostate cancer cells.

Mechanisms of silica-induced IL-8 release from A549 cells: initial kinase-activation does not require EGFR activation or particle uptake

Understanding how mineral particles trigger cellular responses is crucial in order to elucidate what characteristics determine their harmful effects. It is not clear whether cellular effects are triggered through the cell membrane or require particle uptake. However, studies with asbestos suggest that activation of the epidermal growth factor receptor (EGFR) may be important. We have previously reported that crystalline silica-induced interleukin (IL)-8 release from human lung epithelial cells (A549) was regulated through Src family kinases (SFKs) and the mitogen-activated protein kinases (MAPKs) p38 and extracellular signal-regulated kinase (ERK)-1 and -2. The present study shows that SFK and p38 phosphorylation increased almost immediately upon crystalline silica exposure, whereas ERK1/2 phosphorylation increased after 10 min of exposure. The p38 inhibitor SB202190 increased the silica-induced ERK1/2 phosphorylation suggesting that p38 activity may attenuate activation of ERK1/2. Scanning electron microscopy showed that some silica particles were phagocytosed between 1 and 4h of exposure, but that the majority remained bound by microvilli on the cell surface. The EGFR inhibitor AG1478 attenuated both silica-induced IL-8 release and phosphorylation of SFKs and ERK1/2. However, AG1478 also inhibited the respective background levels, and the EGFR was not phosphorylated at the onset of silica exposure. The results suggest that crystalline silica triggers p38 and SFK-ERK1/2 signaling through interactions with membrane components as both pathways were rapidly activated prior to particle internalization. However, the silica-induced up-regulation of IL-8 release through the SFK-ERK1/2 pathway does not appear to be initiated through activation of the EGFR, although basal EGFR activity may affect the magnitude of the responses.

Essential role of ROS-mediated NFAT activation in TNF-alpha induction by crystalline silica exposure

Occupational exposure to crystalline silica has been associated with progressive pulmonary silicosis and lung cancer, but the underlying molecular mechanisms are not well understood. Previous studies have shown that crystalline silica exposure can generate reactive oxygen species (ROS) and induce the expression of the inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) in cells. TNF-alpha is believed to be critical in the development of silica-related diseases. Thus it will be of significance to understand the mechanisms of TNF-alpha induction by silica exposure. Given the fact that the transcription factor nuclear factor of activated T cells (NFAT) plays an important role in the regulation of TNF-alpha and can also be activated by ROS, in this study we investigated the potential role of ROS in silica-induced NFAT activity as well as TNF-alpha expression in Cl41 cells. The results showed that exposure of cells to silica led to NFAT transactivation and TNF-alpha induction, where superoxide anion radical (O(2)(-).), but not H(2)O(2), was involved. The knockdown of NFAT3 by its specific small interfering RNA significantly attenuated the silica-induced TNF-alpha transcription. This study demonstrated that silica was able to activate NFAT in an O(2)(-).-dependent manner, which was required for TNF-alpha induction.

Respiratory burst: role in signal transduction in alveolar macrophages

Alveolar macrophages play an important role in defense against airborne pathogens and particles. These macrophages respond through both the adaptive and acquired immune responses, and through the activation of a multitude of signaling pathways. One major macrophage defense mechanism is respiratory burst, the production of reactive oxygen species (ROS). While the ROS produced may act directly in pathogen killing, they may also be involved as secondary signaling messengers. This review focuses on the activation of four main signaling pathways following the production of reactive oxygen species. These pathways include the nuclear factor kappa beta (NFkB), activating protein-1 (AP-1), mitogen-activating protein kinase (MAPK), and phosphotidyl inositol-3 kinase (PI3K) pathways. This review also briefly examines the role of ROS in DNA damage, in particular looking at the base excision repair pathway (BER), the main pathway involved in repair of oxidative DNA damage. This review highlights many of the studies in the field of ROS, signal transduction, and DNA damage; however, work still remains to further elucidate the role of ROS in disease.

Heat shock protein 70 as an indicator of early lung injury caused by exposure to arsenic

Heat shock proteins (HSPs) are a family of highly conserved proteins that are induced by a number of stresses including toxic metals. Heat shock proteins expression has been reported to be an early and sensitive biomarker of cell stress. Arsenic is a naturally occurring metal that exists widely in the environment and is used in several industries. Exposure to arsenic is associated with the development of pulmonary cancers. We monitored changes in Hsp70 and markers of oxidative injury induced by arsenic in human pulmonary epithelial cells (BEAS-2B). Hsp70 protein, mRNA and reactive oxygen species (ROS) generation were measured after exposing cells to arsenic as markers of injury. Hsp70 protein expression showed significant 7.9-fold and 31.5-fold increase using Western blotting and ELISA assay, respectively, at a 50 microM As(III) with a 12 h exposure and an 12 h recovery time. Hsp70A and Hsp70B mRNA expression showed a two-fold increase and Hsp70C mRNA expression showed a six-fold increase. As(III)-induced Hsp70 protein expression was inhibited significantly by catalase and NAC, indicating mediation of ROS in Hsp70 expression. Intracellular glutathione (GSH) was significantly depleted by As(III) exposure. Lipid peroxidation by-product, 8-isoprostane, was increased six-fold at 24 h exposure to 20 microM As(III). Electron spin resonance and confocal microscope studies also showed As(III)-stimulated ROS generation. These results suggest that cellular injury by arsenic is mediated through ROS generation resulting in the expression of Hsp70. It is possible that Hsp70 may prove to be a sensitive biomarker for arsenic exposure with other markers of oxidative stress in human serum.

Differential modulation of MAP kinases by zinc deficiency in IMR-32 cells: role of H(2)O(2)

The influence of zinc deficiency on the modulation of the mitogen-activated protein kinases (MAPKs) extracellular signal-regulated kinase (ERK1/2), p38, and c-Jun N-terminal kinase (JNK) was studied. Using human IMR-32 cells as a model of neuronal cells, the role of oxidants on MAPKs and activator protein-1 (AP-1) activation in zinc deficiency was investigated, characterizing the participation of these events in the triggering of apoptosis. Relative to controls, cells incubated in media with low zinc concentrations showed increased cell oxidants and hydrogen peroxide (H(2)O(2)) release, increased JNK and p38 activation, high nuclear AP-1-DNA binding activity, and AP-1-dependent gene expression. Catalase addition to the media prevented the increase of cellular oxidants and inhibited JNK, p38, and AP-1 activation. Low levels of ERK1/2 phosphorylation were observed in the zinc-deficient cells in association with a reduction in cell proliferation. Catalase treatment did not prevent the above events nor the increased rate of apoptosis in the zinc-deficient cells. It is first demonstrated that a decrease in cellular zinc triggers H(2)O(2)-independent, as well as H(2)O(2)-dependent effects on MAPKs. Zinc deficiency-induced increases in cellular H(2)O(2) can trigger the activation of JNK and p38, leading to AP-1 activation, events that are not involved in zinc deficiency-induced apoptosis.

Involvement of protein kinase C in crystalline silica-induced activation of the MAP kinase and AP-1 pathway

Crystalline silica has long been well established as a fibrogenic agent, and recent evidence has implicated it as a potential human carcinogen. However, the mechanisms of silica-induced disease development and progression are not well understood. Our previous studies demonstrated that crystalline silica is able to activate activator protein-1 (AP-1) through mitogen-activated protein kinase (MAPK) pathways. The present study investigates the possible involvement of protein kinase C (PKC) in silica-induced activation of the MAPK/AP-1 signal transduction pathway. Treatment of mouse epidermal cells (JB6 cell line) with freshly fractured silica stimulated translocation of PKCalpha and PKCepsilon from the cytosol to the membrane and activated AP-1 transcription activity. Pretreatment of cells with PKC inhibitors, including RO-32-0432, calphostin C, and bisindolylmaleimide I, inhibited silica-induced AP-1 activation and phosphorylation of ERKs and p38 kinase. These inhibitory effects by PKC inhibitors were dose dependent. Furthermore, overexpression of dominant negative mutant (DNM) of PKCalpha or PKCepsilon markedly blocked AP-1 activation as well as phosphorylation of ERKs and p38 kinase induced by freshly fractured silica. These results demonstrate that PKCalpha and PKCepsilon are essential in silica-induced AP-1 activation through the MAP kinase (ERKs and p38 kinases) pathway.

Curcumin Derivatives Inhibit the Formation of Jun-Fos-DNA Complex Independently of their Conserved Cysteine Residues

Curcumin, a major active component of turmeric, has been identified as an inhibitor of the transcriptional activity of activator protein-1 (AP-1). Recently, it was also found that curcumin and synthetic curcumin derivatives can inhibit the binding of Jun-Fos, which are the members of the AP-1 family, to DNA. However, the mechanism of this inhibition by curcumin and its derivatives was not disclosed. Since the binding of Jun-Fos dimer to DNA can be modulated by redox control involving conserved cysteine residues, we studied whether curcumin and its derivatives inhibit Jun-Fos DNA binding activity via these residues. However, the inhibitory mechanism of curcumin and its derivatives, unlike that of other Jun-Fos inhibitors, was found to be independent of these conserved cysteine residues. In addition, we investigated whether curcumin derivatives can inhibit AP-1 transcriptional activity in vivo using a luciferase assay. We found that, among the curcumin derivatives examined, only inhibitors shown to inhibit the binding of Jun-Fos to DNA by Electrophoretic Mobility Shift Assay (EMSA) inhibited AP-1 transcriptional activity in vivo. Moreover, RT-PCR revealed that curcumin derivatives, like curcumin, downregulated c-jun mRNA in JB6 cells. These results suggest that the suppression of the formation of DNA-Jun-Fos complex is the main cause of reduced AP-1 transcriptional activity by curcuminoids, and that EMSA is a suitable tool for identifying inhibitors of transcriptional activation.

Blackberry extracts inhibit activating protein 1 activation and cell transformation by perturbing the mitogenic signaling pathway

Blackberries are natural rich sources of bioflavonoids and phenolic compounds that are commonly known as potential chemopreventive agents. Here, we investigated the effects of fresh blackberry extracts on proliferation of cancer cells and neoplastic transformation induced by 12-O-tetradecanoylphorbol-13-acetate (TPA), as well as the underlying mechanisms of signal transduction pathways. Using electron spin resonance, we found that blackberry extract is an effective scavenger of free radicals, including hydroxyl and superoxide radicals. Blackberry extract inhibited the proliferation of a human lung cancer cell line, A549. Pretreatment of A549 cells with blackberry extract resulted in an inhibition of 8-hydroxy-2'-deoxyguanosine (8-OHdG) formation induced by ultraviolet B (UVB) irradiation. Blackberry extract decreased TPA-induced neoplastic transformation of JB6 P+ cells. Pretreatment of JB6 cells with blackberry extract resulted in the inhibition of both UVB- and TPA-induced AP-1 transactivation. Furthermore, blackberry extract also blocked UVB- or TPA-induced phosphorylation of ERKs and JNKs, but not p38 kinase. Overall, these results indicated that an extract from fresh blackberry may inhibit tumor promoter-induced carcinogenesis and associated cell signaling, and suggest that the chemopreventive effects of fresh blackberry may be through its antioxidant properties by blocking reactive oxygen species-mediated AP-1 and mitogen-activated protein kinase activation.

Essential role of p53 in silica-induced apoptosis

Occupational exposure to mineral dusts, such as silica, has been associated with progressive pulmonary inflammation, lung cancer, and fibrosis. However, the mechanisms involved in this process are poorly understood. Because p53 is a key transcription factor regulating many important apoptosis-related genes, we hypothesized that p53 may play a key role in silica-induced apoptosis and that abnormal regulation of p53 by silica may contribute to development of lung cancer as well as silicosis. We used both in vitro and in vivo studies to test this hypothesis. Treatment of JB6 cells carrying a p53-luciferase reporter plasmid with silica caused dose-dependent p53 transactivation. Western blot indicates that silica not only stimulated p53 protein expression but also caused p53 phosphorylation at Ser392. TUNEL and DNA fragmentation analysis show that silica caused apoptosis in both JB6 cells and wild-type p53 (p53+/+) fibroblasts but not in p53-deficient (p53-/-) fibroblasts. Similar results were obtained by in vivo studies. Intratracheal instillation of mice with silica induced apoptosis in the lung of p53+/+ mice, whereas this induction was significantly inhibited in p53-/- mice. Confocal image analysis indicates that most apoptotic cells induced by silica were alveolar macrophages. These results demonstrate for the first time that silica induces p53 transactivation via induction of p53 protein expression and phosphorylation of p53 protein and that p53 plays a crucial role in the signal transduction pathways of silica-induced apoptosis. This finding may provide an important link in understanding the molecular mechanisms of silica-induced carcinogenesis and pathogenesis in the lung.

Signaling pathways controlling the production of inflammatory mediators in response to crystalline silica exposure: role of reactive oxygen/nitrogen species

Occupational exposure to crystalline silica has been linked to pulmonary fibrosis and lung cancer. Surface properties of crystalline silica are critical to the production of oxidant species, chemokines, inflammatory cytokines, and proliferative factors involved in the initiation and progression of silica-induced damage, inflammation, alveolar type II cell hyperplasia, fibroblast activation, and disease. The transcription factors nuclear factor kappaB (NF-kappaB) and activator protein 1 (AP-1) have been shown to play key roles in gene promotion for inflammatory mediators, oncogenes, and growth factors. This review summarizes evidence that in vitro and in vivo exposure to crystalline silica results in activation of NF-kappaB and AP-1. Signaling pathways for activation of these transcription factors are described. In addition, the role of silica-induced reactive oxygen species and nitric oxide in the activation of these signaling events is presented. Last, the generalizability of mechanisms regulating silica-induced pulmonary responses to pulmonary reactions to other occupational particles is discussed.

Inhibition of AP-1 and Neoplastic Transformation by Fresh Apple Peel Extract

Consumption of fruits and vegetables has been associated with a low incidence of cancers and other chronic diseases. Previous studies suggested that fresh apples inhibit tumor cell proliferation. Here we report that oral administration of apple peel extracts decreased the number of nonmalignant and malignant skin tumors per mouse induced by 12-O-tetradecanolyphorbol-13-acetate (TPA) in 7,12-dimethylbenz(a)anthracene-initiated mouse skin. ESR analysis indicated that apple extract strongly scavenged hydroxyl (OH) and superoxide (O(2)(-)) radicals. Mechanistic studies showed that pretreatment with apple peel extract inhibited AP-1 transactivation induced by ultraviolet B irradiation or TPA in JB6 cells and AP-1-luciferase reporter transgenic mice. This inhibitory effect appears to be mediated by the inhibition of ERKs and JNK activity. The results provide the first evidence that an extract from fresh apple peel extract may inhibit tumor promoter-induced carcinogenesis and associated cell signaling, and suggest that the chemopreventive effects of fresh apple may be through its antioxidant properties by blocking reactive oxygen species-mediated AP-1-MAPK activation.

Response of alveolar macrophages from inducible nitric oxide synthase knockout or wild-type mice to an in vitro lipopolysaccharide or silica exposure

The role of nitric oxide (NO) in pulmonary disease has been controversial with both antiinflammatory (scavenging radicals and inhibiting NF-êB activation) and proinflammatory (forming highly reactive peroxynitrite and augmenting NF-êB activation by inflammatory agents) actions reported. Therefore, a study has been initiated to determine whether deletion of the inducible nitric oxide synthase (iNOS) gene in the C57BL/6J mouse alters the pulmonary macrophage response to lipopolysaccharide (LPS) or silica. The objective of the initial phase of this study was to determine the difference in responsiveness of alveolar macrophages (AMs), harvested from naive wild-type (WT) or iNOS knockout (iNOS KO) mice, to an in vitro LPS or silica exposure. Primary AMs were obtained by bronchoalveolar lavage (BAL) from age- and weight-matched iNOS KO and WT mice. The cells were treated with interferon-gamma (IFN-ã) (50 U/ml), IFN-ã (50 U/ml) + LPS (1 microg/ml), LPS (0.01-100 microg/ml), or silica (25-250 microg/ml). The following parameters were measured: nitrate and nitrite (NOx), tumor necrosis factor-á (TNF-á), macrophage inflammatory protein-2 (MIP-2), intracellular generation of the reactive oxygen species (ROS) hydrogen peroxide (H(2)O(2) and superoxide (O(*-2)), and basal (unstimulated) total antioxidant capacity. Data show a significant increase in NOx production upon exposure to IFN-ã +/- LPS in the WT but not iNOS KO AMs. NOx production by iNOS KO or WT AMs was not altered by in vitro exposure to LPS or silica alone. LPS, but not silica, induced TNF-á and MIP-2 production in both iNOS KO and WT AMs. Statistical analysis of concentration response curves found a significant tendency for greater mediator production in the iNOS KO versus WT AMs. Basal intracellular production of H(2)O(2) and O(*- 2) was significantly greater in the iNOS KO compared to WT AMs. In contrast, LPS- (10 microg/ml) or silica- (100 microg/ml) stimulated intracellular oxidant production was lower in iNOS KO AMs, but overall (basal + stimulated) inflammatory capacity was similar between the cell types. The basal total antioxidant production of the iNOS KO AMs was approximately twofold higher than the WT AMs. In conclusion, certain compensatory changes appear to occur in AMs from iNOS KO mice. In response to the inability to induce NO production, iNOS KO AMs exhibit significantly higher basal generation of H(2)O(2) and (O(*- 2)) as well as higher total antioxidant levels. In addition, LPS induced TNF-á and MIP-2 production tend to be higher in AMs from iNOS KO mice. Such compensatory changes in the AM response may affect the response of iNOS KO mice to inflammatory exposures.

Phosphoinositide 3-kinase activity leads to silica-induced NF-kappaB activation through interacting with tyrosine-phosphorylated I(kappa)B-alpha and contributing to tyrosine phosphorylation of p65 NF-kappaB

The role of the subunits of phosphoinositide (PI) 3-kinase in NF-kappaB activation in silica-stimulated RAW 264.7 cells was investigated. Results indicate that PI3-kinase activity was increased in response to silica. The p85alpha subunit of PI3-kinase interacted with tyrosine-phosphorylated I(kappa)B-alpha in silica-stimulated cells. PI3-kinase specific inhibitors, such as wortmannin and LY294003, substantially blocked both silica-induced PI3-kinase and NF-kappaB activation. The inhibition of NF-KB activation by PI3-kinase inhibitors was also observed in pervanadate-stimulated but not in LPS-stimulated cells. Furthermore, tyrosine phosphorylation of NF-kappaB p65 was enhanced in cells stimulated with silica, pervanadate or LPS, and wortmannin substantially inhibited the phosphorylation event induced by the first two stimulants but not LPS. Antioxidants, such as superoxide dismutase (SOD), N-acetylcysteine (NAC) and pyrrolidine dithiocarbamate (PDTC), blocked silica-induced PI3-kinase activation, suggesting that reactive oxygen species may be important regulatory molecules in NF-kappaB activation by mediating PI3-kinase activation. Our data suggest that p85 and p110 subunits of PI3-kinase play a role in NF-kappaB activation through interaction with tyrosine-phosphorylated I(kappa)B-alpha and contributing to tyrosine phosphorylation of p65 NF-kappaB.

High glucose accelerates MCP-1 production via p38 MAPK in vascular endothelial cells

In diabetes mellitus (DM), hyperglycemia causes cardiovascular lesions through endothelial dysfunction. Monocyte chemoattractant protein-1 (MCP-1) is implicated in the pathogenesis of cardiovascular lesions. By using human umbilical vein endothelial cells, we investigated the effect of hyperglycemia on MCP-1 production and its signaling pathways. Chronic incubation with high glucose increased mRNA expression and production rate of MCP-1 in a time (1-7 days)- and concentration (10-35 mM)-dependent manner. Chronic exposure to high glucose resulted in enhancement of generation of reactive oxygen species (ROS), as determined by increasing level of 2,7-dichlorofluorescein (DCF), and subsequent activation of p38 mitogen-activated protein kinase (MAPK). Neither c-Jun NH(2)-terminal kinase nor extracellular signal-regulated kinase1/2 was affected. SB203580 or FR167653, p38 MAPK specific inhibitors, completely suppressed MCP-1 expression. Catalase suppressed p38 MAPK phosphorylation and MCP-1 expression. These results indicate that hyperglycemia can accelerate MCP-1 production through the mechanism involving p38 MAPK, ROS-sensitive signaling pathway, in vascular endothelial cells.

Role of reactive oxygen species and MAPKs in vanadate-induced G(2)/M phase arrest

Cell growth arrest is an important mechanism in maintaining genomic stability and integrity in response to environmental stress. Using the human lung alveolar epithelial cancer cell line A549, we investigated the role of reactive oxygen species (ROS), extracellular signal-regulated protein kinase (ERK), and p38 protein kinase in vanadate-induced cell growth arrest. Exposure of cells to vanadate led to cell growth arrest at the G(2)/M phase and caused upregulation of p21 and phospho-cdc2 and degradation of cdc25C in a time- and dose-dependent manner. Vanadate stimulated mitogen-activated protein kinases (MAPKs) family members, as determined by the phosphorylation of ERK and p38. PD98059, an inhibitor of ERK, and SB202190, an inhibitor of p38, inhibited vanadate-induced cell growth arrest, upregulation of p21 and cdc2, and degradation of cdc25C. In addition to hydroxyl radical ((*)OH) formation, cellular reduction of vanadate generated superoxide radical (O(2)(*)(-)) and hydrogen peroxide (H(2)O(2)), as determined by confocal microscopy using specific dyes. Generation of O(2)(*)(-) and H(2)O(2) was inhibited by specific antioxidant enzymes, superoxide dismutase (SOD) and catalase, respectively. ROS activate ERK and p38, which in turn upregulate p21 and cdc2 and cause degradation of cdc25C, leading to cell growth arrest at the G(2)/M phase. Specific ROS affect different MAPK family members and cell growth regulatory proteins with different potencies.

p38 Signaling-mediated hypoxia-inducible factor 1alpha and vascular endothelial growth factor induction by Cr(VI) in DU145 human prostate carcinoma cells

Chromium(VI) (Cr(VI)) is widely used in industry and is a potent inducer of tumors in animals. The present study demonstrates that Cr(VI) induces hypoxia-inducible factor 1 (HIF-1) activity through the specific expression of HIF-1alpha but not HIF-1beta subunit and increases the level of vascular endothelial growth factor (VEGF) expression in DU145 human prostate carcinoma cells. To dissect the signaling pathways involved in Cr(VI)-induced HIF-1 expression, we found that p38 mitogen-activated protein kinase signaling was required for HIF-1alpha expression induced by Cr(VI). Neither phosphatidylinositol 3-kinase nor extracellular signal-regulated kinase activity was required for Cr(VI)-induced HIF-1 expression. Cr(VI) induced expression of HIF-1 and VEGF through the production of reactive oxygen species in DU145 cells. The major species of reactive oxygen species responsible for the induction of HIF-1 and VEGF expression is H(2)O(2). These results suggest that the expression of HIF-1 and VEGF induced by Cr(VI) may be an important signaling pathway in the Cr(VI)-induced carcinogenesis.

Comparison of low doses of aged and freshly fractured silica on pulmonary inflammation and damage in the rat

Most previous studies of silica toxicity have used relatively high exposure doses of silica. In this study, male rats received by intratracheal instillation either vehicle, aged or freshly fractured silica at a dose of either 5 microg/rat once a week for 12 weeks (total dose=60 microg) or 20 microg/rat once a week for 12 weeks (total dose=240 microg). One week after the last exposure, bronchoalveolar lavage (BAL) was conducted and markers of pulmonary inflammation, alveolar macrophage (AM) activation and pulmonary damage were examined. For rats exposed to a total of 60 microg silica, both aged and freshly fractured silica increased polymorphonuclear leukocytes (PMN) yield and AM activation above control to a similar degree, but no evidence of pulmonary damage, as measured by BAL fluid lactate dehydrogenase activity or albumin concentration, was detected. For rats exposed to 240 microg silica, aged or freshly fractured silica increased PMN yield and AM activation above control. However, zymosan-stimulated and L-NAME sensitive AM chemiluminescence was greater for rats exposed to freshly fractured silica compared to aged silica. Exposure to 240 microg aged or freshly fractured silica also resulted in pulmonary damage, but the extent of this damage did not differ between the two types of silica. The results suggest that exposure of rats to silica levels far lower than those previously examined can cause pulmonary inflammation. In addition, exposure to freshly fractured silica causes greater generation of reactive oxygen species from AM, measured as AM chemiluminescence, in comparison to aged silica, but there is an apparent threshold below which this difference does not occur.

Diseases caused by silica: mechanisms of injury and disease development

While silica particles are considered to be fibrogenic and carcinogenic agents, the mechanisms responsible are not well understood. This article summarizes literature on silica-induced accelerated silicosis, chronic silicosis, silico-tuberculosis, bronchogenic carcinoma, and immune-mediated diseases. This article also discusses the generation of reactive oxygen species (ROS) that occurs directly from the interaction of silica with aqueous medium and from silica-stimulated cells, the molecular mechanisms of silica-induced lung injuries with focus on silica-induced NF-kappaB activation, including its mechanisms, possible attenuation and relationship to silica-induced generation of cyclooxygenase II and TNF-alpha. Silica-induced AP-1 activation, protooncogene expression, and the role of ROS in these processes are also briefly discussed.