The expression of nerve growth factor in mice lung following low-level toluene exposure

ACUTE EXPOSURE TO ABUSE-LIKE CONCENTRATIONS OF TOLUENE INDUCES INFLAMMATION IN MOUSE LUNGS AND BRAIN

Toluene is an aromatic hydrocarbon commonly abused by young adolescents for its central nervous system depressant effects. While toluene's pharmacological effects at high concentrations are relatively well known, few studies have assessed toluene's effects on lung and brain tissues. The present study characterized the pathological effects of acute inhaled toluene exposure in the lungs and brains of male Swiss-Webster mice (N = 68). Using a static vapor exposure chamber, mice (PND 28) received a single 30-min toluene administration (0, 1000, 2000, or 4000 ppm). Lung and brain tissues were extracted 24 hrs post-exposure. Histology results revealed significant changes in the morphology lung tissue (e.g., irregular cellular architecture) with the 2000 and 4000 ppm exposures expressing greater signs of pathology than control 0-ppm exposure. Markers of immune system activity (F4/80 and Ly-6G) and cellular proliferation (Ki-67) in the lung revealed no significant differences. Additionally, brain tissues were analyzed for changes of astrogliosis (GFAP) and oxidative stress (GPx). GFAP showed increased astrogliosis in the striatum with 2000 ppm toluene showing significantly higher expression than control (p < 0.05), and a marginal effect in the hippocampus. No other markers showed significant changes. The increased signs of inflammation and cellular damage suggest that exposure to a single high concentration of toluene, typical of abuse, are capable of producing pathology in both lung and brain tissue.

Dietary exposure to bisphenol A affects memory function and neuroimmune biomarkers in allergic asthmatic mice

Bisphenol A (BPA) is a raw material of polycarbonate and epoxy resin. It is used for various household electrical appliances, electronic equipment, office automation equipment, medical equipment, mobile phones, paints for automobiles, internal surface coating of cans, and adhesives for civil engineering and construction. BPA is a well-known endocrine-disrupting chemical, and it was reported that BPA has an adverse effect on the nervous and immune systems. However, BPA-induced memory impairment and changes in neuroimmune biomarkers in the allergic asthmatic subject are not known yet. We aim to investigate the dietary exposure effect of BPA on brain function and biomarkers using allergic an asthmatic mouse model. Five-week-old male C3H/HeJSlc mice were fed two doses of BPA [0.901, 9.01 μg/kg/day] contained chow diet from 5 to 11 weeks old and ovalbumin (OVA) was given by intratracheal instillation every 2 weeks. Memory function was determined by a novel object recognition test. Genes related to memory and immune markers in the hippocampus were investigated with the real-time polymerase chain reaction (RT-PCR) method. In this study, impaired novel object recognition occurred in BPA-exposed mice in the presence of an allergen. Moreover, upregulation of expression level of neuroimmune biomarkers such as N-methyl-D-aspartate receptor, tumor necrosis factor-α, ionized calcium-binding adapter molecule-1, cyclooxygenase-2, and heme oxygenase-1 in the hippocampus was observed in BPA-exposed allergic asthmatic mice. These findings show that BPA exposure can induce neuroinflammation and which triggers impairment of memory function in mice with allergic asthma. Our study indicated that dietary exposure to BPA may affect higher brain functions by modulating neuroimmune biomarkers in allergic asthmatic subjects.

Memory Function, Neurological, and Immunological Biomarkers in Allergic Asthmatic Mice Intratracheally Exposed to Bisphenol A

Bisphenol A (BPA) is a major constituent of plastic products, including epoxy resin containers, mobile phones, dental sealants, as well as electronic and medical equipment. BPA is recognized as an endocrine system-disrupting chemical which has toxic effects on the brain and reproductive system. However, little is known about the effects of co-exposure of BPA with allergens on the memory function and neurological as well as immunological biomarker levels. In this study, we examined the effects of intratracheal instillation of BPA on the memory function and neuroimmune biomarker levels using a mouse model of allergic asthma. Male C3H/HeJ Jcl mice were given three doses of BPA (0.0625 pmol, 1.25 pmol, and 25 pmol BPA/animal) intratracheally once a week, and ovalbumin (OVA) intratracheally every other week from 5 to 11 weeks old. At 11 weeks of age, a novel object recognition test was conducted after the final administration of OVA, and the hippocampi and hypothalami of the animals were collected after 24 h. The expression levels of the memory function-related genes N-methyl-D-aspartate (NMDA) receptor subunits, inflammatory cytokines, microglia markers, estrogen receptor-alpha, and oxytocin receptor were examined by real-time RT-PCR (real-time reverse transcription polymerase chain reaction) and immunohistochemical methods. Impairment of the novel object recognition ability was observed in the high-dose BPA-exposed mice with allergic asthma. In addition, the allergic asthmatic mice also showed downregulation of neurological biomarkers, such as NMDA receptor subunit NR2B in the hippocampus but no significant effect on immunological biomarkers in the hypothalamus. These findings suggest that exposure to high-dose BPA triggered impairment of memory function in the allergic asthmatic mice. This is the first study to show that, in the presence of allergens, exposure to high-dose BPA may affect memory by modulating the memory function-related genes in the hippocampus.

Activation of transcription factors in a mouse lung following exposure to environmental chemical and biological agents

Environmental biological and chemical agents can modulate innate and acquired immunity in the lung via the stimulation of Toll-like receptors (TLRs). To investigate the effect of environmental chemical agents on the activation of NF-κB and activator protein (AP)-1 subunits and the role of TLR4 signaling in the lung, C3H/HeN and C3H/HeJ (TLR4-defective) mice were exposed to 0 or 50 ppm of toluene for 6 hr/day, 5 days/week for 6 weeks. Some groups of mice were also stimulated with OVA or LPS as a biological agent. The DNA-binding activities of the NF-κB subunits (p50, p52, p65 and RelB) and AP-1 family members (FosB, c-Fos, +c-Jun, JunD) were compared using TransAM ELISA kits. Exposure to toluene alone produced no significant changes in both mice. Although stimulation with OVA or LPS alone significantly increased the DNA binding activities of p50 and p52 in C3H/HeN mice, there were no interactions between biological factors and toluene. In the C3H/HeJ mice, stimulation with OVA or LPS increased p65 and p52 binding activity and the combination of exposure to toluene and OVA significantly increased the DNA binding activities of the p65 and p52 in the lung. During AP-1 activation, co-exposure to toluene and OVA increased JunD binding activity in C3H/HeJ mice, while co-exposure to toluene and LPS influenced c-Fos binding activity in C3H/HeN mice. These results indicate that TLR4 may play an important role in activation of NF-κB or AP-1 family following exposure to environmental biological and chemical agents.

Small interfering RNA targeting nerve growth factor alleviates allergic airway hyperresponsiveness

Airway hyperresponsiveness is the hallmark of allergic asthma and caused by multiple factors. Nerve growth factor (NGF), a neurotrophin, is originally known for regulation of neural circuit development and function. Recent studies indicated that NGF contributes to airway hyperresponsiveness and pathogenesis of asthma. The objective of this study is to develop a small interfering RNA against NGF to attenuate airway hyperresponsiveness and further elucidate the underlying mechanism. In a murine model of allergic asthma, the ovalbumin-sensitized mice were intratracheally delivered small interfering RNA against NGF or administered an inhibitor targeting NGF receptor, tropomyosin-related kinase A, as a positive treatment control. In this study, knockdown NGF derived from pulmonary epithelium significantly reduced airway resistance in vivo. The levels of NGF, proinflammatory cytokines and infiltrated eosinophils in airway were decreased in small interfering RNA against NGF group but not in tropomyosin-related kinase A inhibitor and mock siRNA group. Furthermore, induction of neuropeptide (substance P) and airway innervation were mediated by NGF/tropomyosin-related kinase A pathway. These findings suggested that NGF targeting treatment holds the potential therapy for antigen-induced airway hyperresponsiveness via attenuation of airway innervation and inflammation in asthma.

Expression levels of neuroimmune biomarkers in hypothalamus of allergic mice after phthalate exposure

Previously, we demonstrated that maternal exposure to phthalates enhances atopic dermatitis in male mouse offspring. However, whether phthalate exposure affects neuroimmune biomarkers in allergic mice has not yet been studied. Di-(2-ethylhexyl) phthalate (DEHP) and di-isononyl phthalate (DINP) are environmental chemicals that are commonly used as plasticizers. This study was designed to investigate the expression levels of neuroimmune biomarkers in the hypothalamus of a murine model of allergic asthma after phthalate exposure throughout juvenility until adulthood. Six-week-old C3H/HeJ Jcl male mice were treated with DEHP or DINP (0, 0.02, 0.4 or 8 nmol per body per week) and ovalbumin (OVA; 1 µg per body per 2 weeks) for 7 weeks intratracheally. On the day after the completion of the phthalate and OVA treatment, the hypothalamus from each mouse was collected, and the mRNA expression levels of neuroimmune biomarkers were examined using a real-time RT-PCR analysis. The mRNA expression levels of the proinflammatory cytokines interleukin (IL)-1β and tumor necrosis factor (TNF)-α, the chemokine CCL3, the transcription factor nuclear factor (NF)-κB, the oxidative stress marker heme-oxygenase (HO)1, a nerve growth factor, and the microglia marker Iba1 were remarkably up-regulated in the hypothalami of mice treated with 8 nmol of DEHP in the presence of the allergen. However, no significant changes were observed, except for reductions in the TNF-α and CCL2 mRNA levels, in mice exposed to DINP combined with the allergen. This study is the first report to show that high-dose DEHP exposure throughout juvenility until adulthood may induce neuroinflammation by modulating neuroimmune biomarkers in the hypothalami of allergic mice.

Dermatophagoides pteronyssinus 2 regulates nerve growth factor release to induce airway inflammation via a reactive oxygen species-dependent pathway

Group 2 allergen of Dermatophagoides pteronyssinus 2 (Der p2) induces airway inflammation without protease activity, and elevated nerve growth factor (NGF) levels are also found in this inflammation. How the allergen Der p2 regulates NGF release via reactive oxygen species (ROS) to induce inflammation remains unclear. In the present study, intratracheal administration of Der p2 to mice led to inflammatory cell infiltration, mucus gland hyperplasia, and NGF upregulation in the bronchial epithelium, as well as elevated ROS and NGF production in bronchoalveolar lavage fluids. In addition, Der p2 caused fibrocyte accumulation and mild fibrosis. p38 mitogen-activated protein kinase (MAPK) and c-Jun N-terminal kinase (JNK) inhibitors inhibited Der p2-induced NGF release in LA4 lung epithelial cells and MLg lung fibroblasts. Pretreatment with an antioxidant, tiron, reduced the Der p2-induced ROS production, NGF expression and release, p38 MAPK or JNK phosphorylation, and airway inflammation. These results suggest that Der p2 allergen-induced airway inflammation and elevated NGF release were through increasing ROS production and a MAPK-dependent pathway. The use of an antioxidant, tiron, may provide a new therapeutic modality for the treatment of allergic asthma.

Neurotrophins in lung health and disease

Neurotrophins (NTs) are a family of growth factors that are well-known in the nervous system. There is increasing recognition that NTs (nerve growth factor, brain-derived neurotrophic factor and NT3) and their receptors (high-affinity TrkA, TrkB and TrkC, and low-affinity p75NTR) are expressed in lung components including the nasal and bronchial epithelium, smooth muscle, nerves and immune cells. NT signaling may be important in normal lung development, developmental lung disease, allergy and inflammation (e.g., rhinitis, asthma), lung fibrosis and even lung cancer. In this review, we describe the current status of our understanding of NT signaling in the lung, with hopes of using aspects of the NT signaling pathway in the diagnosis and therapy of lung diseases.

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.