Maternal exposure to environmental DEHP exacerbated OVA-induced asthmatic responses in rat offspring

Highlights

• Maternal exposure to DEHP during pregnancy and lactation aggravates pulmonary inflammation of the rat offspring

• DEHP maternal exposure increased the OVA-induced Th2 immune response the lung of the rat offspring

• DEHP maternal exposure increased OVA-induced Th2 cytokines in lung and promoted the expression of OX40L and GATA3

• These adjuvant effects of DEHP were considered to be closely related to the enhanced TSLP expression and the JAK signals

Abstract

Di (ethylhexyl) phthalate (DEHP) is a commonly used phthalates (PAEs) compound as plasticizer and becomes a severe environmental pollutant worldwide. Studies show that DEHP, as an environmental endocrine disruptor, has potential adverse effects on human. Epidemiologic studies indicate that DEHP is positively correlated to allergic diseases. Maternal exposure to DEHP may contribute to the increasing incidence of allergic diseases in offspring. However, the role of DEHP and its detailed mechanism in allergic disease of the offspring are still unclear. The aim of our study is to investigate whether DEHP maternal exposure could aggravate the allergic responses in offspring and its mechanism. Pregnant Wistar rats were randomly divided into three groups and exposed to different doses of DEHP. Half of the offspring were challenged with OVA after birth. All the pups of each group were sacrificed at postnatal day (PND)14, PND21 and PND28. The number of inflammatory cells in bronchoalveolar lavage was counted, lung pathological changes were observed, Th2 type cytokines expressions were checked, and the expression of TSLP signaling pathway were examined. Our results showed that maternal exposure to DEHP during pregnancy and lactation aggravated the eosinophils accumulation and the pathological inflammatory changes in pups' lung after OVA challenge. And maternal exposure to DEHP during pregnancy and lactation also elevated the levels of typical Th2 cytokines in OVA-challenged rats. What's more, maternal exposure to DEHP during pregnancy and lactation increased the levels of TSLP, TSLPR and IL-7R in the offspring after OVA challenge. Our study suggested that DEHP maternal exposure could aggravate the OVA-induced asthmatic responses in offspring. And this adjuvant effect of DEHP was related with the TSLP/TSLPR/IL-7R and its downstream signal pathways.

Introduction

Di (ethylhexyl) phthalate (DEHP), as the most commonly high molecular-weight (HMW) phthalates (PAEs), is a severe environmental pollutant worldwide, added to plastics to increase the flexibility of the plastic products (Carlstedt et al., 2013, Larsson et al., 2010). Studies showed that DEHP functioned as an environmental endocrine disruptor had potential adverse effects on human. Concentrations of DEHP as great as 110 mg/L have been found in river sediments (Horn et al., 2004). Up to 2700 μg/L DEHP was found in wastewater samples collected in the United States (Jackson and Sutton, 2008). And DEHP has been widely detected in Chinese rivers and lakes, including sources of drinking water (Zhang et al., 2015). Due to polyvinyl chloride (PVC)’ widespread and growing use, there is an increasing interest and concern about these additives like DEHP have on humans and animals (Wormuth et al., 2006, Schettler, 2006). Since 1990s, a positive correlation was found between the PVC flooring and allergic diseases (Bornehag and Nanberg, 2010, Callesen et al., 2014, Larsson et al., 2010). The immune toxicity of PAEs have been studied for decades. Epidemiology studies indicated that PAEs was positively associated with allergic sensitization (Simmchen et al., 2012, Jaakkola et al., 2004, Kolarik et al., 2008). Animal experiments suggested that whether DEHP could influence the allergic responses might be associated with the exposure route (Dearman et al., 2008, Butala et al., 2004, Larsen et al., 2007, Larsen and Nielsen, 2007, Guo et al., 2012). The studies on phthalate esters' immune adjuvant or immunosuppressive mechanism more limited to in vitro studies (Fischer et al., 1998, Gourlay et al., 2003, Jepsen et al., 2004, Lee et al., 2004, Wang et al., 2012), it is difficult to clarify the mechanism of DEHP in vivo.

With the burden of children's allergic diseases, its relationship with PAEs drawn an increasing attention recently (Bornehag et al., 2004, Hsu et al., 2012, Ku et al., 2015, Lai et al., 2009). The reasons of allergic asthma in children include multiple factors, one of them is prenatal exposure. Prenatal exposure to environmental chemical contaminants might cause asthma or increase the risk of asthma symptoms throughout childhood (Smit et al., 2015, Gascon et al., 2015). Breastfeeding is also an additional means of phthalate exposure for infants. Some studies demonstrated that infants could be exposed to phthalates via breast milk (Bowman and Choudhury, 2016), indicating that exposure to DEHP during pregnancy and lactation could impact on the next generation. Various epidemiological studies of DEHP suggested a positive relation between its exposure and allergic asthma, especially in children with allergic asthma (Ait Bamai et al., 2014, Wang et al., 2014). However, the actual role of DEHP and its detailed mechanism in allergic disease of the offspring were still unclear.

The etiology of allergic asthma is the recognition of allergens or pathogenic microbial antigen by airway epithelial cells. Then a variety of cytokines were secreted, accompanied by reversible airflow obstruction, airway hyperresponsiveness (AHR), and eosinophilic and basophilic airway inflammation. And those symptoms characterized by generation of a predominant helper T cell (Th) 2-based cytokine environment (Lukacs, 2001, Lambrecht and Hammad, 2015). Th2 polarized CD4 + T cells secreting type 2 cytokines, including IL-4, IL-5 and IL-13, which stimulate the occurrence of asthma symptoms. The growing and compelling evidence indicated that airway remodeling and chronic airway epithelial injury during the first years of life facilitated the onset of asthma in childhood (Pohunek et al., 2005, Proud and Leigh, 2011). Recently, Studies had shown that the epithelial-derived cytokine thymic stromal lymphopoietin (TSLP) might play a central role in Th2 cell polarization (Gauvreau et al., 2014). TSLP, originally discovered in the supernatant of murine thymic stromal cell in 1994, was broadly defined as an epithelial-derived cytokine (Friend et al., 1994). It is overexpressed in the airways of allergic asthma patients and atopic dermatitis (AD) patients, indicating a key role in allergic inflammation (Shikotra et al., 2012, Soumelis et al., 2002). Since there is a positive correlation between DEHP and allergic diseases, whether DEHP could exacerbate allergic diseases of the next generation through maternal exposure? And how DEHP exacerbate allergic diseases of the next generation? Is this adjuvant effect of DEHP related with TSLP signal pathway?

In the present study, we investigated the changes of OVA-induced asthmatic responses in rats' offspring after DEHP exposure during pregnancy and lactation period. The regulatory effect of TSLP on OVA-induced Th2 responses was investigated. The mechanism of DEHP aggravated the offspring asthmatic responses through the TSLP pathway was studied. Our results suggested that maternal exposure to DEHP during pregnancy and lactation aggravated the OVA-induced asthmatic responses in offspring of rats. These adjuvant effects of DEHP were considered to be closely related to the enhanced TSLP expression and the changes of JAK signals.