Hidekazu Fujimaki

Nanoparticles and neurotoxicity.

Humans are exposed to nanoparticles (NPs; diameter < 100 nm) from ambient air and certain workplaces. There are two main types of NPs; combustion-derived NPs (e.g., particulate matters, diesel exhaust particles, welding fumes) and manufactured or engineered NPs (e.g., titanium dioxide, carbon black, carbon nanotubes, silver, zinc oxide, copper oxide). Recently, there have been increasing reports indicating that inhaled NPs can reach the brain and may be associated with neurodegeneration. It is necessary to evaluate the potential toxic effects of NPs on brain because most of the neurobehavioral disorders may be of environmental origin. This review highlights studies on both combustion-derived NP- and manufactured or engineered NP-induced neuroinflammation, oxidative stress, and gene expression, as well as the possible mechanism of these effects in animal models and in humans.

Inhalation of diesel exhaust enhances antigen-specific IgE antibody production in mice

To examine the effects of diesel exhaust (DE) inhalation on IgE antibody production, BALB/c mice were exposed to 0 (control), 3.0 and 6.0 mg/m3 DE inhalation for 3 weeks. Intranasal sensitization with ovalbumin (OA) three times at intervals of 3 weeks was conducted immediately before, immediately after and 3 weeks after DE inhalation. Body weight and thymus weight for the DE-exposed and control mice were essentially the same but spleen weight in mice exposed to 6 mg/m3 significantly increased. Anti-OA IgE antibody titers in the sera of mice exposed to 6 mg/m3 was significantly higher than the control. Total IgE and anti-OA IgG in sera for DE-exposed and control mice remained basically the same. To investigate cytokine production in mice exposed to 6 mg/m3, spleen cells from DE-exposed and control mice were stimulated with OA in vitro and cytokine production in the culture supernatants was measured by ELISA. In vitro antigen-stimulated interleukin-4 (IL-4) and -10 (IL-10) production in spleen cells of exposed mice significantly increased compared to the control. In vitro interferon (IFN)-gamma production in spleen cells of exposed mice markedly decreased. DE inhalation is thus shown to have adverse effect on antigen-specific IgE antibody production in mice through alteration of the cytokine network.

IL-4 production in mediastinal lymph node cells in mice intratracheally instilled with diesel exhaust particulates and antigen

To clarify the relationship between air pollutants and IgE antibody production, interleukin 4 (IL-4) production was investigated in BALB/c mice intratracheally injected with diesel exhaust particulates (DEP) mixed with antigen (Ovalbumin (OA) or Japanese Cedar Pollen (JCP)). BALB/c mice were injected with DEP plus OA or OA alone three times with a 3-week interval. After the last instillation, proliferative response and lymphokine-producing activity of mediastinal lymph node cells (LNC) were examined in vitro. Proliferative response to OA in mediastinal LNC from mice injected with DEP plus OA was enhanced 4-17 times of that from control mice. IL-4-producing activity by OA stimulation also enhanced in mediastinal LNC from mice injected with DEP plus OA. A significantly larger amount of anti-OA IgE antibody was detected in sera from DEP- and OA-injected mice compared with those from control mice. The levels of IL-4, estimated by JCP antigen in mediastinal LNC, from mice injected with DEP plus JCP were two-fold higher than those from mice injected with JCP alone. These results suggest that intratracheal instillation of DEP affects antigen-specific IgE antibody responses via local T-cell activation, especially enhanced IL-4 production.

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on T cell-derived cytokine production in ovalbumin (OVA)-immunized C57Bl/6 mice.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is known to suppress both cellular and humoral immunity. Effector T cell-derived type-2 cytokines, including IL-4 and IL-5, play pivotal roles in humoral immunity. Herein, we studied whether TCDD affects type-2 cytokine productions during the immune response. C57Bl/6 mice were intraperitoneally immunized with ovalbumin (OVA) and orally administered 5 or 20 microg TCDD/kg on Day 0, and then challenged with OVA on Day 21. Seven days later (Day 28), antigen-specific antibodies in plasma, and T cell-derived cytokines produced by splenocytes and proliferation of splenocytes upon ex vivo re-stimulation with OVA were investigated. The quantities of IgM class and IgG1 class OVA-specific antibodies in plasma were reduced by 5 or 20 microg TCDD/kg and by 20 microg TCDD/kg, respectively. While thymus weight and cellularity were reduced by 20 microg TCDD/kg, spleen weight and cellularity were not changed by either 5 or 20 microg TCDD/kg. The proportions of B and T cells in the spleen were not affected by TCDD exposure. On the other hand, splenocytes from mice treated with 5 or 20 microg TCDD/kg were shown to produce less IL-4 or IL-5 upon ex vivo re-stimulation with OVA. Production of the T cell growth factor IL-2 was also decreased in splenocytes from TCDD-treated mice. In contrast, the type-1 cytokine IFN-gamma was increased by TCDD. Twenty micrograms of TCDD/kg suppressed OVA- or T cell mitogen (Con A)-stimulated proliferation of splenocytes, but did not affect B cell mitogen (LPS)-stimulated proliferation. These results suggested compromised T cell activation and suppressed type-2 cytokine production by T cells to be involved in the impaired humoral immunity associated with TCDD exposure.

Intranasal Instillation of Diesel Exhaust Particulates and Antigen in Mice Modulated Cytokine Productions in Cervical Lymph Node Cells

To investigate cytokine production stimulated by diesel exhaust particulates (DEP) and antigen through the intranasal route, mice were administered with DEP mixed with ovalbumin (OA) 3 times at an interval of 3 weeks. After the last instillation, cervical lymph node cells (LNC) were cultured in vitro with OA and antigen-presenting cells. The proliferative response to OA in cervical LNC from mice instilled with DEP and OA was noted to have increased significantly compared to mice instilled with OA alone. Interleukin 4 (IL-4) and interferon (IFN)-gamma in culture supernatants were measured with ELISA. OA-stimulated IL-4 production in cervical LNC from mice instilled with DEP and OA markedly increased beyond that in the control mice. In contrast, OA-stimulated IFN-gamma production in cervical LNC from mice instilled with OA was 3 times that for DEP and OA-instilled mice. OA-specific IgE antibody in sera showed a trend to be increased in mice intranasally instilled with DEP and OA. These results suggest that intranasal instillation of DEP and antigen in mice may modulate in vitro antigen-stimulated cytokine production from cervical LNC with a consequent increase in IgE antibody production.

Induction of apoptosis in mouse thymocytes by cadmium

In the thymus apoptosis is an important process in T cell maturation and differentiation. Cadmium (Cd) is an ubiquitous toxic metal that is capable of modulating immune responses. To investigate the induction of apoptosis and immunomodulation by environmental chemicals, we cultured mouse thymocytes with Cd and/or dexamethasone (DEX). DNA fragmentation was analyzed by gel electrophoresis, ELISA and flow cytometry. Treatment with either Cd or DEX induced DNA fragmentation in the thymocytes. Exposure to 10 microM Cd killed thymocytes by apoptosis rather than necrosis. However, no synergistic or additive effect was observed in the induction of apoptosis when DEX was added to the Cd. These results suggest that Cd may modulate the function of the thymus by the induction of apoptosis through mechanisms that differ from those used by DEX.

Spatial learning and memory function-related gene expression in the hippocampus of mouse exposed to nanoparticle-rich diesel exhaust.

Diesel exhaust particles are a major constituent of ambient particulate matter, and most particles emitted directly from diesel exhaust are smaller than 1microm in diameter. Recently, the toxicity of diesel engine-derived nanoparticles has come to be recognized as an emerging social issue. In the present study, we investigated spatial learning ability and memory function-related gene expressions in mouse hippocampus after the exposure of animals to nanoparticle-rich diesel exhaust (NRDE) with or without a bacterial cell wall component. Lipoteichoic acid (LTA), a cell wall component derived from Staphylococcus aureus, was used to induce systemic inflammation. Male BALB/c mice were exposed to clean air (particle concentration, 4.58microg/m(3)) or NRDE (148.86microg/m(3)) for 5h per day on 5 days of the week for 4 weeks in an exposure chamber, with or without the weekly intraperitoneal injection of LTA. On the day after the final day of exposure, we used a Morris water maze apparatus to examine the ability of the animals to perform a spatial learning task. After the completion of the test, the animals were sacrificed and the hippocampus was collected from each mouse; the expressions of NMDA receptor subunits (NR1, NR2A and NR2B), proinflammatory cytokines (IL-1beta and TNF-alpha) and the oxidative stress marker heme oxygenase 1 were then investigated using real-time RT-PCR. In the Morris water maze task, NRDE/LTA (+) group took a longer time to reach the hidden platform than clear air/LTA (-) group. However, NRDE exposure alone did not affect it. The relative mRNA levels of the NMDA receptor subunits and proinflammatory cytokines were higher in hippocampus of NRDE/LTA (+) group compared to clear air/LTA (-) group. These results indicate that co-exposure of NRDE and LTA could affect spatial learning and memory function-related gene expressions in mouse hippocampus.

Effect of environmental pollutants on the production of pro-inflammatory cytokines by normal human dermal keratinocytes.

The effect of the environmental pollutants, diesel exhaust particles (DEP) and formaldehyde (FA), on the production of pro-inflammatory cytokines (interleukin (IL)-1alpha, IL-1beta, tumor necrosis factor (TNF)-alpha and IL-8) by normal human dermal keratinocytes (hKCs) was investigated. Normal hKCs were incubated with various concentrations of DEP (0.4, 0.8, 4, or 20 microg/ml) or FA (0.25, 0.5, 1, or 5 microg/ml), and cytokine production was then determined by enzyme-linked immunosorbent assay (ELISA). DEP (20 microg/ml) induced IL-1beta production without altering cell growth. The increased production of IL-1beta induced by this concentration of DEP was further enhanced by the presence of phorbol 12-myristate 13-acetate (PMA), although PMA alone did not affect the levels of IL-1beta. IL-8 production was also increased by DEP (0.4 and 0.8 microg/ml), which is consistent with the results that these concentrations of DEP increased the number of cells significantly after 72 h incubation. Although FA alone did not stimulate the production of IL-1beta or IL-8 by keratinocytes, FA (0.5 microg/ml and 5 microg/ml) significantly increased IL-8 and IL-1beta production, respectively, in cells stimulated with PMA. IL-1alpha production was not modulated by FA or DEP even in the presence of PMA. TNF-alpha was produced by unstimulated keratinocytes at barely detectable levels after 48 h incubation. Although basal levels of TNF-alpha in the culture supernatants were increased after stimulation with PMA, neither pollutant alone nor combination with PMA affected the levels of TNF-alpha. These in vitro findings suggest that environmental pollutants may act as modulating factors of cutaneous inflammation by affecting the ability of keratinocytes to release pro-inflammatory cytokines.

Effect of prolonged exposure to low concentrations of formaldehyde on the corticotropin releasing hormone neurons in the hypothalamus and adrenocorticotropic hormone cells in the pituitary gland in female mice.

We examine the effect on the hypothalamus-pituitary-adrenal gland (HPA) axis of prolonged exposure to low levels of formaldehyde in female C3H/He mice, using immunocytochemical and RT-PCR methods. Two groups of female mice were exposed to differing concentrations (0, 80, 400, 2000 ppb) of formaldehyde inhalation for 16 h/day, 5 days/week, for 12 weeks. The corticotropin releasing hormone (CRH)-immunoreactive (ir) neurons in the hypothalamus were then examined, together with the adrenocorticotropin hormone (ACTH)-ir cells and ACTH mRNA in the pituitary. One group comprised sham control mice. The other group was made allergic by injection of ovalbumin (OVA) and alum prior to exposure to formaldehyde, since most sick building syndrome (SBS) sufferers are women with allergic disease. These animals were further exposed to aerosolized OVA as a booster four times during the exposure period. Our results showed a dose-dependent increase in the number of CRH-ir neurons in the non-allergy (NAG) group. A similar pattern was found in ACTH-ir cells and ACTH mRNA. The allergy (AG) model group showed an increase in basal levels of all markers of HPA activity. Moreover, the AG mice appeared to respond to the lowest concentration of formaldehyde, and all indices of HPA activity were reduced at the highest concentrations of formaldehyde. These results relate to an important clinical issue and also have implications in the broader area of HPA regulation. We conclude that our experimental system may be a suitable animal model for SBS and/or multiple chemical sensitivity (MCS).

Neurotoxicity of toluene.

Chemical susceptibility is triggered by a large range of chemicals present both indoors and outdoors including pesticides, cleaning products, perfumes, scented products and cigarette smoke. Health risk after chemical exposure depends on age, sex, genetic factors, socioeconomic status, nutritional status, and environmental factors. Toluene is one of volatile organic chemicals that causes different sensitivity in individuals. Although neurotoxic and immunotoxic effects of toluene have been studied extensively, the underlying mechanism remains obscure. This review highlights the possible neuroimmune factors influencing toluene sensitivity and neurotoxicity in a mouse model.