Luis A. Jimenez

Combustion-derived nanoparticles: A review of their toxicology following inhalation exposure

This review considers the molecular toxicology of combustion-derived nanoparticles (CDNP) following inhalation exposure. CDNP originate from a number of sources and in this review we consider diesel soot, welding fume, carbon black and coal fly ash. A substantial literature demonstrates that these pose a hazard to the lungs through their potential to cause oxidative stress, inflammation and cancer; they also have the potential to redistribute to other organs following pulmonary deposition. These different CDNP show considerable heterogeneity in composition and solubility, meaning that oxidative stress may originate from different components depending on the particle under consideration. Key CDNP-associated properties of large surface area and the presence of metals and organics all have the potential to produce oxidative stress. CDNP may also exert genotoxic effects, depending on their composition. CDNP and their components also have the potential to translocate to the brain and also the blood, and thereby reach other targets such as the cardiovascular system, spleen and liver. CDNP therefore can be seen as a group of particulate toxins unified by a common mechanism of injury and properties of translocation which have the potential to mediate a range of adverse effects in the lungs and other organs and warrant further research.

Oxidative stress and calcium signaling in the adverse effects of environmental particles (PM10)

This review focuses on the potential role that oxidative stress plays in the adverse effects of PM(10). The central hypothesis is that the ability of PM(10) to cause oxidative stress underlies the association between increased exposure to PM(10) and both exacerbations of lung disease and lung cancer. Pulmonary inflammation may also underlie the cardiovascular effects seen following increased PM(10), although the mechanisms of the cardiovascular effects of PM(10) are not well understood. PM(10) is a complex mix of various particle types and several of the components of PM(10) are likely to be involved in the induction of oxidative stress. The most likely of these are transition metals, ultrafine particle surfaces, and organic compounds. In support of this hypothesis, oxidative stress arising from PM(10) has been shown to activate a number of redox-responsive signaling pathways in lung target cells. These pathways are involved in expression of genes that play a role in responses relevant to inflammation and pathological change, including MAPKs, NF-kappaB, AP-1, and histone acetylation. Oxidative stress from particles is also likely to play an important role in the carcinogenic effects associated with PM(10) and hydroxyl radicals from PM(10) cause DNA damage in vitro.

Oxidative stress and TNF-alpha induce histone acetylation and NF-kappaB/AP-1 activation in alveolar epithelial cells: potential mechanism in gene transcription in lung inflammation.

Oxidants and inflammatory mediators such as tumour necrosis factor-alpha (TNF-alpha) activate nuclear factor kappa B (NF-kappaB) and activator protein-1 (AP-1) transcription factors, and enhance the expression of both pro-inflammatory and protective antioxidant genes. Remodelling of chromatin within the nucleus, controlled by the degree of acetylation/deacetylation of histone residues on the histone core around which DNA is coiled, is important in allowing access for transcription factor DNA binding and hence gene transcription. Unwinding of DNA is important in allowing access for transcription factor DNA binding and hence gene transcription. Nuclear histone acetylation is a reversible process, and is regulated by a group of acetyltransferases (HATs) which promote acetylation, and deacetylases (HDACs) which promote deacetylation. The aim of this study was to determine whether oxidative stress and the pro-inflammatory mediator, TNF-alpha, altered histone acetylation/deacetylation and the activation of NF-kappaB and AP-1, leading to the release ofthe pro-inflammatory cytokine IL-8 in human alveolar epithelial cells (A549). Hydrogen peroxide (H2O2) (100 microM) and TNF-alpha (10 ng/ml) imposed oxidative stress in A549 cells as shown by depletion of the antioxidant reduced glutathione (GSH) concomitant with increased levels of oxidised glutathione (GSSG). Treatment of A549 cells with H2O2, TNF-alpha and the HDAC inhibitor, trichostatin A, TSA (100 ng/ml) significantly increased acetylation of histone proteins shown by immunostaining of cells and increased HAT activity, compared to the untreated cells. H2O2, and TNF-a, and TSA all increased NF-kappaB and AP-1 DNA binding to their consensus sites assessed by the electrophoretic mobility shift assay. TSA treatment potentiated the increased AP-1 and NF-KB binding, produced by H2O2 or TNF-alpha treatments in A549 cells. Both H2O2 and TNF-alpha significantly increased IL-8 release, which was further enhanced by pre-treatment of A549 cells with TSA compared to the individual treatments. This study shows that the oxidant H2O2 and the pro-inflammatory mediator, TNF-a induce histone acetylation which is associated with decreased GSH levels and increased AP-1 and NF-kappaB activation leading to enhanced proinflammatory IL-8 release in alveolar epithelial cells. This indicates a mechanism for the pro-inflammatory effects of oxidative stress.

Nanoparticle-driven DNA damage mimics irradiation-related carcinogenesis pathways

The epidemiological association between cancer and exposure to ambient air pollution particles (particles with a 50% cut-off aerodynamic diameter of 10 μm (PM10)) has been related to the ability of PM10 and its constituent nanoparticles (NPs) to cause reactive oxidative species (ROS)-driven DNA damage. However, there are no data on the molecular response to these genotoxic effects. In order to assess whether PM10, NP and ROS-driven DNA damage induce carcinogenesis pathways, A549 cells were treated with tert-butyl-hyperperoxide (Tbh), urban dust (UD), carbon black (CB), nanoparticulate CB (NPCB), benzo(a)pyrene (BaP) and NPCB coated with BaP for ≤24 h. Single- and double-strand breakage of DNA was determined by comet assay; cell cycle status was analysed using flow cytometry. Nuclear extracts or acid-extracted histones were used for Western blot analysis of p-ser15-p53 (p53 phosphorylated at ser15), p53 binding protein (53BP) 1, phospho-histone H2A.X (p-H2A.X) and phospho-BRCA1 (p-BRCA1). UD caused both single- and double-strand DNA breaks, while other tested NPs caused only single-strand DNA breaks. NPs significantly altered cell cycle kinetics. Tbh enhanced p-H2A.X after 1 and 6 h (2.1- and 2.2-fold, respectively). NP increased 53BP1 expression at 1 h (2.4–8.7-fold) and p-BRCA1 at 1–6 h. N-acetylcysteine blocked NP-driven p-ser15-p53 response. In conclusion, nanoparticles and reactive oxidative species induce DNA damage, activating p53 and proteins related to DNA repair, mimicking irradiation-related carcinogenesis pathways.

Ergothioneine inhibits oxidative stress- and TNF-α-induced NF-κB activation and interleukin-8 release in alveolar epithelial cells

Oxidants and inflammatory mediators such as tumour necrosis factor-alpha (TNF-alpha) activate transcription factors such as NF-kappa B. Interleukin-8 (IL-8) is a ubiquitous inflammatory chemokine that mediates a multitude of inflammatory events in the lung. Ergothioneine is a naturally occurring thiol compound, which possesses antioxidant property. The aim of this study was to determine whether ergothioneine can inhibit the hydrogen peroxide (H(2)O(2))- and TNF-alpha-mediated activation of NF-kappa B and the release of IL-8 in human alveolar epithelial cells (A549). Treatment of A549 cells with H(2)O(2) (100 microM) and TNF-alpha (10 ng/ml) significantly increased NF-kappa B activation using a reporter assay. Ergothioneine inhibited both H(2)O(2)- and TNF-alpha-mediated activation of NF-kappa B. Both H(2)O(2) and TNF-alpha significantly increased IL-8 release, which was inhibited by pre-treatment of A549 cells with ergothioneine compared to the control untreated cells. Ergothioneine also abolished the transcriptional activation of IL-8 in an IL-8-chloramphenicol acetyltransferase (CAT) reporter system, transfected into A549 cells. This indicates a molecular mechanism for the anti-inflammatory effects of ergothioneine.

Apocynin increases glutathione synthesis and activates AP‐1 in alveolar epithelial cells

Apocynin (4‐hydroxy‐3‐methoxy‐acetophenone) is a potent intracellular inhibitor of superoxide anion production in neutrophils. In this study, we studied the effect of apocynin on the regulation of the antioxidant glutathione (GSH) and activation of the transcription factor AP‐1 in human alveolar epithelial cells (A549). Apocynin enhanced intracellular GSH by increasing γ‐glutamylcysteine synthetase activity in A549 cells. Apocynin also increased the expression of γ‐GCS heavy subunit mRNA. This was associated with increased AP‐1 DNA binding as measured by the electrophoretic mobility shift assay. These data indicate that apocynin displays antioxidant properties, in part, by increasing glutathione synthesis through activation of AP‐1.