Luteolin ameliorates inflammation and Th1/Th2 imbalance via regulating the TLR4/NF-κB pathway in allergic rhinitis rats

OBJECTIVE: Luteolin has an anti-allergic effect but its mechanism is not clear. This study attempted to determine the mechanisms of luteolin in rhinitis. METHODS: Allergic rhinitis rat model was established by ovalbumin (OVA) stimulation. Then, the rats were treated with normal saline, luteolin, or lipopolysaccharide (LPS) for 14 days. Nasal symptoms were scored; the histopathological changes of nasal mucosa were detected by hematoxylin-eosin staining. Serum levels of Th1 type cytokines (IFN-γ, IL-2), Th2 type cytokines (IL-4, IL-5, IL-13), and OVA-specific IgE (sIgE) were determined by ELISA. The expressions of Toll-like receptor 4 (TLR4) and p65 in nasal mucosa were detected by Western blot or immunohistochemistry. RESULTS: Luteolin decreased symptom scores, specifically, the scores in control group, model group, model + 0.1 mg/kg luteolin, model + 1 mg/kg luteolin, and model + 10 mg/kg luteolin groups were 0.63 ± 0.52, 7.88 ± 0.83, 1.38 ± 0.52, 2.75 ± 0.46, and 5.00 ± 0.53, respectively. Luteolin ameliorated nasal mucosa inflammation by promoting the down-regulated levels of Th1 type cytokines, and suppressing the up-regulated levels of Th2 type cytokines, OVE-sIgE, TLR4, and p65. LPS further increased symptom scores, aggravated nasal mucosa inflammation, improved the unbalance of Th1/Th2 type cytokines, and lowered the expressions of OVE-sIgE, TLR4, and p65. Moreover, LPS reversed the effect of luteolin on allergic rhinitis rats. CONCLUSION: Luteolin ameliorated inflammation and Th1/Th2 imbalance via regulating the TLR4/NF-κB pathway in allergic rhinitis rats. This study provided novel evidence that luteolin could be used as a candidate drug in allergic rhinitis treatment.