Dibutyl phthalate aggravated allergic asthma through endoplasmic reticulum stress in mice

Background Dibutyl phthalate (DBP) is one of the most commonly used plasticizers, and has been found to relate to allergic asthma. However, mechanisms behind the phenomenon linking DBP and allergic asthma are still not well comprehended.

Objective To investigate the role of endoplasmic reticulum stress in DBP-exacerbated allergic asthma.

Methods Thirty-two male mice were divided into four groups at random, eight mice in each group: control group, allergic asthma model group (ovalbumin, OVA), OVA+40 mg·kg⁻¹ DBP exposure group (OVA+DBP), and OVA+40 mg·kg⁻¹ DBP+50 mg·kg⁻¹ 4-phenyl butyric acid (4-PBA) group (OVA+DBP+4-PBA). The control group mice were treated with saline via intraperitoneal injection on day 21, 35, 42, and 49, and atomized saline for 30 min per day from day 54 to 60. The OVA group mice were injected with 0.3 mL OVA sensitizing solution via intraperitoneal injection on day 21, 35, 42, and 49, and atomized with 1% OVA solution from day 54 to 60. The OVA+DBP group was treated in the same way as the OVA group to build an allergic asthma model, and was orally exposed to 40 mg·kg⁻¹ DBP from day 1 to 53, plus atomized with 1% OVA solution from day 54 to 60. In order to verify the role of endoplasmic reticulum stress in DBP-exacerbated allergic asthma, 4-PBA was injected intraperitoneally every 2 d from day 1 to 53 in the OVA+DBP+4-PBA group mice. The pathological changes such as airway remodeling, inflammatory cell infiltration, and airway mucous hyperplasia in lung tissues were observed after hematoxylin-eosin (HE) and periodic acid-Schiff (PAS) staining. The contents of total immunoglobulin E (T-IgE) and ovalbumin immunoglobulin E (OVA-IgE) levels in serum, and interleukin (IL)-4, IL-5, IL-13, and IL-17A in alveolar lavage fluid (BALF) were detected by Enzyme-Linked ImmunoSorbent Assay(ELISA). The expression levels of endoplasmic reticulum stress-related proteins including inositol-requiring enzyme 1α (IRE1α), protein kinase R-like endoplasmic reticulum kinase (PERK), and activating transcription factor 6 (ATF6) were detected by immunohistochemistry.

Results Compared to the control mice, the OVA mice showed significant asthma-like symptoms, including inflammatory cell infiltration, increased inflammatory cytokines, airway remodeling, and mucous hyperplasia. Compared to the OVA group, long-term exposure to DBP aggravated airway pathological changes in the OVA+DBP mice, and increased the serum T-IgE and OVA-IgE levels (P<0.01), the Th2 (IL-4, IL-5, IL-13) and Th17 (IL-17A) cytokines in BALF (P<0.01), and the expression levels of endoplasmic reticulum stress-related proteins IRE1α, PERK and ATF-6 (P<0.01). In addition, after the 4-PBA treatment, it was found that compared with the OVA+DBP group, the expression levels of endoplasmic reticulum stress-related proteins (IRE1α, PERK and ATF-6) were down-regulated in the OVA+DBP+4-PBA group (P<0.01), the levels of cytokines (IL-4, IL-5, IL-13, and IL-17A) in BALF and T-IgE and OVA-IgE in serum were decreased (P<0.01), and airway remodeling and mucous hyperplasia were significantly alleviated.

Conclusion Long-term exposure to DBP could aggravate allergic asthma by activating the endoplasmic reticulum stress pathway. This worsening effect is accompanied by the increase of immunoglobulin IgE levels and the release of Th2 and Th17 cytokines, which in turn leads to lung histopathological changes that affect lung function.