Effects of organic chemicals derived from ambient particulate matter on lung inflammation related to lipopolysaccharide

Biological Response-Enhancing Activity with Antigens in A549 Cells Exposed to Representative Polycyclic Aromatic Hydrocarbons

The question of what kinds of airborne particles, including diesel exhaust particles and their adherent chemical constituents, exacerbate the activity of allergic and inflammatory respiratory diseases has not been elucidated in detail. Therefore, chemicals that have amplifying actions on Dermatophagoides farinae (Df) body extract-induced IL-8, the inflammatory cytokines of the innate immune system, were comprehensively examined using commonly used human alveolar epithelial cells, A549, as simple screening for 17 polycyclic aromatic hydrocarbons (PAHs), which are representative organic constituents in atmospheric samples. The significant amplifying actions of two PAHs, dibenzo[a,l]pyrene (DB[a,l]P) at 50 nM and dibenzo[a,i]pyrene (DB[a,i]P) at 2 μM for 48 h, for IL-8 protein release induced by mite antigens in epithelial cells were observed for the first time. In contrast, the enhancement of IL-8 was not observed in protein levels for these PAHs without the antigens. Meanwhile, the significant synergistic amplifying effect of DB[a,l]P at 50 nM on proinflammatory actions was measured in gene expression (i.e., IL-8, IL-6, ICAM-1, and TNF-α) levels in the experimental setting; for the results, the induction of TNF-α may have been the essential factor that enhanced the amplifying activity of DB[a,l]P for IL-8 gene expression and protein release. Examining the exacerbating effect on allergic pathophysiological states for DB[a,l]P is planned for further study.

Modeling the Effect of TNF-α upon Drug-Induced Toxicity in Human, Tissue-Engineered Myobundles

A number of significant muscle diseases, such as cachexia, sarcopenia, systemic chronic inflammation, along with inflammatory myopathies share TNF-α-dominated inflammation in their pathogenesis. In addition, inflammatory episodes may increase susceptibility to drug toxicity. To assess the effect of TNF-α-induced inflammation on drug responses, we engineered 3D, human skeletal myobundles, chronically exposed them to TNF-α during maturation, and measured the combined response of TNF-α and the chemotherapeutic doxorubicin on muscle function. First, the myobundle inflammatory environment was characterized by assessing the effects of TNF-α on 2D human skeletal muscle cultures and 3D human myobundles. High doses of TNF-α inhibited maturation in human 2D cultures and maturation and function in 3D myobundles. Then, a tetanus force dose-response curve was constructed to characterize doxorubicin's effects on function alone. The combination of TNF-α and 10 nM doxorubicin exhibited a synergistic effect on both twitch and tetanus force production. Overall, the results demonstrated that inflammation of a 3D, human skeletal muscle inflammatory system alters the response to doxorubicin.

Beyond infection - Maternal immune activation by environmental factors, microglial development, and relevance for autism spectrum disorders

Immune molecules such as cytokines and chemokines and the cells that produce them within the brain, notably microglia, are critical for normal brain development. This recognition has in recent years led to the working hypothesis that inflammatory events during pregnancy, e.g. in response to infection, may disrupt the normal expression of immune molecules during critical stages of neural development and thereby contribute to the risk for neurodevelopmental disorders such as autism spectrum disorder (ASD). This hypothesis has in large part been shepherded by the work of Dr. Paul Patterson and colleagues, which has elegantly demonstrated that a single viral infection or injection of a viral mimetic to pregnant mice significantly and persistently impacts offspring immune and nervous system function, changes that underlie ASD-like behavioral dysfunction including social and communication deficits. Subsequent studies by many labs - in humans and in non-human animal models - have supported the hypothesis that ongoing disrupted immune molecule expression and/or neuroinflammation contributes to at least a significant subset of ASD. The heterogeneous clinical and biological phenotypes observed in ASD strongly suggest that in genetically susceptible individuals, environmental risk factors combine or synergize to create a tipping or threshold point for dysfunction. Importantly, animal studies showing a link between maternal immune activation (MIA) and ASD-like outcomes in offspring involve different species and diverse environmental factors associated with ASD in humans, beyond infection, including toxin exposures, maternal stress, and maternal obesity, all of which impact inflammatory or immune pathways. The goal of this review is to highlight the broader implications of Dr. Patterson's work for the field of autism, with a focus on the impact that MIA by diverse environmental factors has on fetal brain development, immune system development, and the pathophysiology of ASD.

Gestational Exposure to Air Pollution Alters Cortical Volume, Microglial Morphology, and Microglia-Neuron Interactions in a Sex-Specific Manner

Microglia are the resident immune cells of the brain, important for normal neural development in addition to host defense in response to inflammatory stimuli. Air pollution is one of the most pervasive and harmful environmental toxicants in the modern world, and several large scale epidemiological studies have recently linked prenatal air pollution exposure with an increased risk of neurodevelopmental disorders such as autism spectrum disorder (ASD). Diesel exhaust particles (DEP) are a primary toxic component of air pollution, and markedly activate microglia in vitro and in vivo in adult rodents. We have demonstrated that prenatal exposure to DEP in mice, i.e., to the pregnant dams throughout gestation, results in a persistent vulnerability to behavioral deficits in adult offspring, especially in males, which is intriguing given the greater incidence of ASD in males to females (∼4:1). Moreover, there is a striking upregulation of toll-like receptor (TLR) 4 gene expression within the brains of the same mice, and this expression is primarily in microglia. Here we explored the impact of gestational exposure to DEP or vehicle on microglial morphology in the developing brains of male and female mice. DEP exposure increased inflammatory cytokine protein and altered the morphology of microglia, consistent with activation or a delay in maturation, only within the embryonic brains of male mice; and these effects were dependent on TLR4. DEP exposure also increased cortical volume at embryonic day (E)18, which switched to decreased volume by post-natal day (P)30 in males, suggesting an impact on the developing neural stem cell niche. Consistent with this hypothesis, we found increased microglial-neuronal interactions in male offspring that received DEP compared to all other groups. Taken together, these data suggest a mechanism by which prenatal exposure to environmental toxins may affect microglial development and long-term function, and thereby contribute to the risk of neurodevelopmental disorders.

Toll like receptor-3 priming alters diesel exhaust particle-induced cytokine responses in human bronchial epithelial cells

Inflammation is considered central in the pathology of health effects from airborne particulate matter (PM). Preexisting inflammatory disorders, such as asthma, but also pulmonary infections, appear to be a risk factor of adverse health effects from PM exposure. Thus, to assess whether and how preexisting inflammation may sensitize lung cells toward additional proinflammatory effects of PM, human bronchial epithelial cells (BEAS-2B) were primed with the highly proinflammatory Toll-like receptor 3 (TLR3) ligand, Poly I:C, prior to exposure with diesel exhaust particles (DEP). DEP-exposure alone induced increased gene-expression of interleukin-6 (IL-6) and CXCL8 (IL-8) but did not affect expression of CCL5 (RANTES), while TLR3-priming alone induced expression of IL-6, CXCL8 and CCL5. DEP-exposure exacerbated IL-6 and CXCL8 responses in TLR3-primed cells, while TLR3-induced CCL5 was suppressed by DEP. TLR3-priming and DEP-exposure resulted in possible additive effects on p38 phosphorylation and IκB-degradation, while DEP rather suppressed ERK and JNK-activation. However, TLR3-priming elicited a considerable increase in p65-phosphorylation at serine 536 which is known to enhance the transcriptional activity of NF-κB. DEP-exposure was unable to induce p65-phosphorylation. Thus TLR3-priming may affect susceptibility toward DEP by activating both shared and complementing pathways required for optimal expression of proinflammatory genes such as IL-6 and CXCL8. The study underscores that primed "sick" cells may be more susceptible toward effects of particle-exposure and respond both stronger and differently compared to unprimed "healthy" cells.

Mechanisms of chemokine responses by polycyclic aromatic hydrocarbons in bronchial epithelial cells: sensitization through toll-like receptor-3 priming

We have previously observed that 1-nitropyrene (1-NP) and its amine metabolite 1-aminopyrene (1-AP) induce differential chemokine responses in human bronchial epithelial cells (BEAS-2B) characterized by maximum responses for CXCL8 (IL-8) and CCL5 (RANTES), respectively. In the present study, we further explored the effects of 1-NP and 1-AP on chemokine responses. The results suggest that the differential effect of 1-NP and 1-AP on CXCL8 and CCL5 in BEAS-2B cells was mainly related to effects at higher concentrations, which in the case of 1-NP seemed to be linked to ROS-formation and/or metabolic activation by CYP-enzymes. However, at a low concentration (1 μM) where neither 1-NP, 1-AP nor unsubstituted pyrene had any effect on chemokine responses, we found that all three PAHs potentiated CXCL8 and CCL5 responses induced by the TLR3 ligand polyinosinic:polycytidylic acid (Poly I:C) in BEAS-2B cells. As neither benzo[a]pyrene nor β-naphthoflavone induced a similar effect in Poly I:C-primed cells, the response seemed independent of aryl hydrocarbon receptor-mediated mechanisms. The results show that priming cells with an inflammogenic stimuli like Poly I:C sensitizes the cells toward additional pro-inflammatory effects of certain PAHs. The study underscores that testing on healthy cells or animals may not be sufficient to fully evaluate chemokine responses and the pro-inflammatory potential of organic chemicals.

A lifespan approach to neuroinflammatory and cognitive disorders: a critical role for glia

Cognitive decline is a common problem of aging. Whereas multiple neural and glial mechanisms may account for these declines, microglial sensitization and/or dystrophy has emerged as a leading culprit in brain aging and dysfunction. However, glial activation is consistently observed in normal brain aging as well, independent of frank neuroinflammation or functional impairment. Such variability suggests the existence of additional vulnerability factors that can impact neuronal-glial interactions and thus overall brain and cognitive health. The goal of this review is to elucidate our working hypothesis that an individual's risk or resilience to neuroinflammatory disorders and poor cognitive aging may critically depend on their early life experience, which can change immune reactivity within the brain for the remainder of the lifespan. For instance, early-life infection in rats can profoundly disrupt memory function in young adulthood, as well as accelerate age-related cognitive decline, both of which are linked to enduring changes in glial function that occur in response to the initial infection. We discuss these findings within the context of the growing literature on the role of immune molecules and neuroimmune crosstalk in normal brain development. We highlight the intrinsic factors (e.g., chemokines, hormones) that regulate microglial development and their colonization of the embryonic and postnatal brain, and the capacity for disruption or "re-programming" of this crucial process by external events (e.g., stress, infection). An impact on glia, which in turn alters neural development, has the capacity to profoundly impact cognitive and mental health function at all stages of life.

Meteo-climatic conditions influence the contribution of endotoxins to PM10 in an urban polluted environment

A decrease in inhalable particulate matter (PM10) pollution is a top priority in urban areas of northern Italy. The sources of PM10 are both anthropogenic and natural. The former have been broadly investigated while the latter are less well known. Endotoxins are natural compounds of PM10 and are potentially toxic. Endotoxins are part of the outer membrane of Gram-negative bacteria. Their health effects are linked to environmental exposure. The effects mainly consist of respiratory symptoms, including pulmonary function decline. The occurrence of endotoxins has been proven in several occupational environments where organic materials supply an optimal substrate for bacteria growth. Knowledge about the presence of these contaminants in the environment is limited. The aim of this work is to evaluate the endotoxin levels of PM10 in the urban air of Turin, and to investigate the influence of seasonal and meteo-climatic factors. The sampling was conducted from January to December 2007. Endotoxin determination was performed by an LAL assay after extraction optimization. The PM10 levels ranged from 11.90 to 104.74 microg/m(3) (48.28 +/- 23.09) while the endotoxin levels ranged between 0.09 and 0.94 EU/m(3) (0.42 +/- 0.23). The seasonal trends of PM10 and endotoxin are inversely proportional. There is a statistically significant correlation between endotoxin and temperature (r = 0.532 p < 0.01), as well as between endotoxin and relative humidity (r = -0.457 p < 0.01). However, temperature has a predominant role. We observed that urban endotoxin concentrations are narrow in range and that the contribution of endotoxins to the total PM10 is only two millionths.

Effects of pulmonary exposure to carbon nanotubes on lung and systemic inflammation with coagulatory disturbance induced by lipopolysaccharide in mice

Despite intensive research as to the pathogenesis of lipopolysaccharide (LPS)-related inflammation with coagulatory disturbance, their exacerbating factors have not been well explored. This study examined the effects of pulmonary exposure to two types of nano-sized materials (carbon nano-tubes: CNT [single-wall: SWCNT, and multi-wall: MWCNT]) on lung inflammation and consequent systemic inflammation with coagulatory disturbance induced by pulmonary exposure to LPS in mice and their cellular mechanisms in vitro. ICR male mice were divided into 6 experimental groups that intra-tracheally received the vehicle, two types of CNT (4 mg/kg), LPS (33 mu g/kg), or LPS plus either type of CNT. Twenty-four hours after treatment, both types of CNT alone induced lung inflammation with enhanced lung expression of proinflammatory cytokines, but did not synergistically exacerbate lung inflammation elicited by LPS. SWCNT significantly induced/ enhanced pulmonary permeability and hyperfibrinogenemia and reduced activated protein C in the absence or presence of LPS, whereas MWCNT did moderately. Both CNT moderately, but not significantly, elevated circulatory levels of proinflammatory cytokines and chemokines. In the presence of LPS, CNT tended to elevate the levels of the mediators with an overall trend, which was more prominent with SWCNT than with MWCNT. In vitro study showed that both CNT amplified LPS-induced cytokine production from peripheral blood monocytes. These results suggest that CNT can facilitate systemic inflammation with coagulatory disturbance, at least in part, via the activation of mononuclear cells, which is accompanied by moderate enhancement of acute lung inflammation related to LPS.

Particulate matter, oxidative stress and neurotoxicity

Particulate matter (PM), a component of air pollution has been epidemiologically associated with sudden deaths, cardiovascular and respiratory illnesses. The effects are more pronounced in patients with pre-existing conditions such as asthma, diabetes or obstructive pulmonary disorders. Clinical and experimental studies have historically focused on the cardiopulmonary effects of PM. However, since PM particles carry numerous biocontaminants that are capable of triggering free radical production and cytokine release, the possibility that PM may affect organs systems sensitive to oxidative stress must be considered. Four independent studies that summarize the neurochemical and neuropathological changes found in the brains of PM exposed animals are described here. These were recently presented at two 2007 symposia sponsored by the Society of Toxicology (Charlotte, NC) and the International Neurotoxicology Association (Monterey, CA).