Tetrahydrocurcumin, a major metabolite of curcumin, ameliorates allergic airway inflammation by attenuating Th2 response and suppressing the IL-4Rα-Jak1-STAT6 and Jagged1/Jagged2 -Notch1/Notch2 pathways in asthmatic mice

Background Curcumin (Cur), derived from Curcuma species, exhibits anti‐inflammatory, antioxidant, and anticancer effects. Although Cur has some beneficial effects on asthma, its clinical application is limited by its low bioavailability. Tetrahydrocurcumin (THC), the major active metabolite of Cur, has multiple biological functions, similarly to Cur, and importantly, it showed enhanced bioavailability in tissues and plasma. However, the effect of THC on asthma has not been reported. Objective The current study sought to investigate the efficacy of dietary THC on allergic asthma compared to that of Cur in an animal model. Methods The anti‐inflammatory effects of Cur and THC were evaluated in an ovalbumin‐induced asthmatic mouse model. The nasal symptoms, pathological alterations of the lung tissues, oxidants and antioxidants, cytokine production, T cell subsets, and Th2‐related signalling pathway activity were assessed. Results Both THC and Cur had beneficial effects on asthmatic mice with regard to nasal symptoms, pathological changes (eosinophils and mucus hyper‐production), oxidative stress (malondialdehyde), cytokine production (IL‐13), Th17 and cytotoxic T cell subsets, and Th2 signalling pathway (IL‐4Rα‐Jak1‐STAT6 and Jagged1/Jagged2‐Notch1/Notch2 axis) activity. THC was more effective than Cur in suppressing tissue eosinophilia, mucus production, and IL‐4Rα/Jak1/STAT6 pathway activity. Furthermore, only THC inhibited peripheral eosinophil levels, Th2 cytokines (IL‐4 and IL‐5), and Th2 cell subsets and enhanced an antioxidant enzyme (glutathione). Conclusion and Clinical Relevance The above results demonstrated for the first time that THC was superior to Cur in modulating allergic asthmatic phenotypes, especially attenuating the Th2 response. THC might be a potentially effective agent for asthma treatment.