SUCCINATE ENHANCES ALLERGIC REACTION IN OVA-INDUCED DIARRHEAL MICE MODELS POSSIBLY VIA SUCCINATE-MAST CELL AXIS.

Background: Recently, succinic acid is reported to play an important role in many kinds of inflammation including allergic reaction in various organs through succinate receptors such as succinate receptor 1 (SUNCR1), also called as G-protein coupled receptor (GPR91), which are expressed in quite a few varieties of cells both in rodents and humans. However, the role of succinate in intestinal allergy has not been well studied yet. Our study focuses on how it works on ovalbumin (OVA) induced diarrheal mice model, using succinic disodium known as a safe food additive.
Method: We used 4-5 weeks aged female BALB/c mice for diarrheal model. Mice received intraperitoneal injection of 50μg OVA with 1mg of aluminum potassium sulfate adjuvant. After 5 days, mice received challenge tests with the same amount of OVA/ PBS mixture in gavage feeding. Mice received 2.5% disodium succinate by gavage 1h before every challenge test or 1.8 % NaCl as control. On the 5thday of challenge test, the number and features of feces were investigated. For pathological study and evaluation of mRNA expressions, each intestinal organs from stomach to ascending colon were collected. We evaluated mRNA expressions in each intestinal tissue by quantitative PCR (QT-PCR). Quantification of mast cells was investigated by toluidine blue staining. The blood sample, the feces from cecum and colon were collected, and we performed quantitative analysis of succinate, lactate, butylate, propionate and acetate using liquid chromatography-mass spectrometry analysis (LC/MS).
Results: Compared to healthy control, OVA treatment alone increased both the severity and incident rate of diarrhea, but succinate treatment alone did not. Adding succinate to OVA treatment further increased both the severity and incident rate of diarrhea compared to single treatment of OVA or succinate treatment. Pathological study showed increased accumulation of mast cells in both lamina propria and submucosa in the cecum in the OVA treated group. mRNA expressions of IL-4, IL-13 and both the intraepithelial mast cell specific protease; Mast cell protease 1 (Mcpt-1) and connective tissue mast cell specific protease; Mast cell protease 4 (Mcpt-4) were significantly increased in cecum of OVA models. Succinate treatment to OVA models increased expressions of IL-4, IL-13, Mcpt-1, and Mcpt-4 further in cecum. SUNCR1 expressions were not changed in the OVA models in cecum. Serum butyrate was significantly lower in OVA with succinate treatment group compared to OVA treatment group.
Conclusion: Succinate aggravates intestinal allergic reaction with enhancement of type2 immune responses. Increase in the mRNA expressions of Mcpt-1 and Mcpt-4 and mast cell expansion in cecum of this model suggest that succinate-mast cell axis is involved in pathophysiology.