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Dietary factors can reshape the gut microbiota and consequently affect disease progression. We previously reported that tetrahydrocurcumin (THC), the major active metabolite of curcumin (Cur), could ameliorate allergic inflammation in asthmatic mice. Herein, we aimed to investigate whether THC or Cur exerts anti-inflammatory effects on allergic asthma via modulating gut microbiota. Ovalbumin (OVA)-induced asthmatic mice were treated with Cur or THC, and the gut microbiota profiles were analyzed by 16S rRNA sequencing. Fecal microbiota transplantation (FMT) from Cur- or THC-fed donor mice was administered to OVA-induced asthmatic mice. Nasal symptoms and inflammation patterns of lungs and colons were evaluated in control, OVA-induced and Cur-or THC-treated mice. Both Cur and THC treatment could alter the compositions of the gut microbiota in asthmatic mice, characterized by a significant decrease in the ratio of Firmicutes to Bacteroidetes; Cur or THC supplementation also reduced the relative abundances of pro-inflammatory bacteria, e.g., Proteobacteria, Intestinimonas, Unidentified-Ruminococcaceae, and Lachnospiraceae, in OVA-induced mice. The relative abundances of Unidentified-Ruminococcaceae, Romboutsia, Intestinimonas, Akkermansia, and Mucispirillum were positively associated with the levels of Th2-related factors in asthmatic mice upon Cur or THC treatment. Moreover, THC-FMT showed better preventive effects than Cur-FMT on the development of allergic inflammation in OVA-induced mice, resulting in a reduction in symptoms and Th2-mediated inflammation in both lung and colon tissues. The results reveal that Cur- or THC-mediated alleviation of airway allergic inflammation is dependent on gut microbiota modulation. THC-induced gut microbiota may have therapeutic potential for asthma treatment.

Allergic asthma is a refractory disease that affects hundreds of millions of people worldwide. Betanin is a natural plant-derived nutrient and possesses health-promoting properties. The effects of betanin on allergic asthma remain unknown. Herein, the effects and mechanisms of betanin on allergic asthma were explored in ovalbumin (OVA)-induced BALB/c mice. Betanin in doses of 0, 20, 60, and 180 mg/kg was applied. Peripheral inflammatory cells, IgE, pulmonary pathology, T cell subsets, cytokine levels, protein expressions of the cAMP-PKA-CREB/CREM pathway, and gut microbial profile were measured. The 60 and 180 mg/kg/day betanin doses significantly downregulated IgE, eotaxin, eosinophil infiltration, mucus hyperproduction, and Th2. A 180 mg/kg/day betanin dose also significantly reduced percentages of Th17, Tc17, and Tc2 and Th2- and Th17-signature cytokines and upregulated the cAMP-PKA-CREB pathway. Additionally, 20 mg/kg/day betanin altered the gut microbial profile. In conclusion, betanin dose-dependently alleviated allergic asthma and upregulated the cAMP-PKA-CREB pathway in mice. This study provides a novel nutritional strategy to treat allergic asthma.