The impact of oral exposure to low‐dose tris(2‐butoxyethyl) phosphate in allergic asthmatic mice

Abstract

Tris(2-butoxyethyl) phosphate (TBEP) is a major organophosphorus flame retardant and has been widely increasing as a substitute for brominated flame retardants. TBEP may have adverse effects on human health; however, its impact on immune and allergic responses remains largely uncharacterized. In this study, the effects of low-dose TBEP comparable with the level of actual human exposure to that of human tolerable daily intake on allergic asthmatic mice were explored. Five-week-old C3H/HeJSlc male mice consumed a diet containing approximately 0.02, 0.2 or 2 μg/kg/day TBEP and were intratracheally administrated ovalbumin (OVA) (1 μg/mouse every 2 weeks from 5 to 11 weeks of age). Exposure to 2 μg/kg/day TBEP with OVA tended to enhance allergic pulmonary inflammation and significantly elevated mRNA levels of interleukin-5, eotaxin-1 and estrogen receptor alpha (ERα) compared with OVA alone. In mediastinal lymph nodes (MLNs), TBEP (0.2 or 2 μg/kg/day) with OVA significantly increased in total cell number and promoted conventional dendritic cell activation than OVA alone; MLN cell proliferation by OVA restimulation was also enhanced in these groups. In the bone marrow (BM), TBEP (0.02 or 0.2 μg/kg/day) with OVA resulted in a net decrease in total cell number and fraction of CCR2 + Gr-1 + cells; the fraction of Gr-1 + cells increased. In conclusion, oral exposure to low-dose TBEP levels equivalent to tolerable daily intake may exacerbate allergic pulmonary inflammation by promoting a skewed T-helper 2 cell response, upregulation of ERα and dysregulation of both MLN and BM microenvironments. K E Y W O R D S allergic asthma, estrogen receptor, low-dose effects, organophosphorus flame retardants, Th2 response, tris(2-butoxyethyl) phosphate 1 | INTRODUCTION Flame retardants (FRs) are used globally to meet flammability standards for building materials, textiles and appliances. Because of their toxicity, persistence in the environment and bioaccumulation, brominated FRs, including polybrominated diphenyl ethers, have been banned or voluntarily phased out in many countries. There is growing demand for less toxic alternatives (van der Veen & de Boer, 2012). In particular, the use of organophosphorus FRs (OPFRs) as FRs and plasticizers in consumer products, including plastics, textiles, paints and furniture, is gaining popularity (Marklund, Andersson, & Haglund, 2005). In Japan, approximately 100 000 tons of FR materials are used per year, of which about 27% were OPFRs (Ministry of the Environment in Japan, 2017). In the United States, the Agency for Toxic Substances and Disease Registry reports that OPFRs account for 11.5% of the total consumption of FRs (Agency for Toxic

Dietary Exposure to Flame Retardant Tris (2-Butoxyethyl) Phosphate Altered Neurobehavior and Neuroinflammatory Responses in a Mouse Model of Allergic Asthma

“…To confirm the allergic asthmatic mouse model, we measured the cellular profile of bronchoalveolar (BAL) fluid 48 h after final intratracheal instillation of OVA and serum OVA-specific immunoglobulins (Ig) in the same OVA-immunized mice and described in our previous report [ 11 ]. TBEP treatment increased eosinophils and lymphocytes in BAL fluid of OVA-immunized mice compared to vehicle-treated group.…”

“…TBEP treatment increased eosinophils and lymphocytes in BAL fluid of OVA-immunized mice compared to vehicle-treated group. Moreover, significantly increased OVA-specific IgE and IgG1 were observed in OVA-treated groups compared with the vehicle group [ 11 ]. These results indicate that OVA-treated mice show airway hyperresponsiveness and allergic asthmatic condition.…”

“…Four-week-old male C3H/HeJSlc mice were purchased from Japan SLC, Inc. (Shizuoka, Japan) and used in this study as described previously [ 11 ]. Briefly, five-week-old mice were allotted into eight groups as follows: (1) vehicle, (2) 0.02 μg/kg/day TBEP (TBEP-L), (3) 0.2 μg/kg/day TBEP (TBEP-M), (4) 2 μg/kg/day TBEP (TBEP-H), (5) ovalbumin (OVA), (6) OVA + TBEP-L, (7) OVA + TBEP-M, and (8) OVA + TBEP-H ( Figure 10 ).…”

“…In addition, TBEP exposure in early life stages showed hatchability reduction, delay time to hatching, increased the occurrence of malformations, body length reduction, slow heart rate, hypoactivity, and changes of acetylcholinesterase activity and transcriptional genes related to the nervous system in Japanese medaka [ 10 ]. Recently, our research group has reported that dietary exposure of low dose TBEP exacerbates pulmonary inflammation, estrogen receptor α expression in the lungs, and cellular responses in the mediastinal lymph nodes and bone marrow in allergic asthmatic mouse models [ 11 ]. However, the neurotoxic effects of TBEP are still limited, and mechanisms of toxicity are not well known.…”

Exposures to Organophosphate Esters and Respiratory Morbidity among School-Aged Children with Asthma

“…While several biological mechanisms may underlie these associations, the exact mechanism has not been clearly elucidated. Laboratory studies report that OPEs are involved in the development and exacerbation of asthma by eliciting increased allergic responses through immunomodulatory effects and oxidative stress, both of which are recognized risk factors in the pathophysiology of asthma. − A recent nested case-cohort study among children (ages 9–15 years) also reported significant positive associations between the OPE urinary biomarkers 2-ethylhexyl phenyl phosphate (EHPHP), bis­(2-butoxyethyl) phosphate (BBOEP), and diphenyl phosphate (DPHP) with increased levels of oxidative stress biomarkers (i.e., 8-hydroxy-2′-deoxyguanosine, hexanoyl-lysine, and 4-hydroxynonenal) …”