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Inhibition of IL-8 Production by Polyphenols in Human Nasal Mucosa-Derived Fibroblasts
The recruitment of leukocytes to various tissues is an essential aspect of the host’s response to inflammation and infection. Inflammation of the respiratory tract is a common condition and of considerable public health concern. Among leukocytes, neutrophils play a critical role in host defense and the inflammatory process. However, inflammation can also initiate or perpetuate a wide range of acute and chronic diseases.
Neutrophil infiltration into tissue occurs in response to chemotactic factors produced by resident cells such as fibroblasts and epithelial cells. In airway inflammation, neutrophil recruitment is primarily driven by the production of interleukin-8 (IL-8).
To investigate whether polyphenols can regulate airway inflammation by inhibiting the production of neutrophil-attracting chemokines, we analyzed IL-8 synthesis in primary cultures of human nasal mucosa-derived fibroblasts and A549 bronchial epithelial cells. These cells were pretreated with various flavanol components found in green tea at concentrations of 2, 10, and 50 μg/mL for specified time periods, followed by stimulation with the pro-inflammatory cytokine IL-1β. The secretion of IL-8 into the culture supernatant was quantitatively measured using ELISA.
Both fibroblasts and epithelial cells produced significant amounts of IL-8 upon IL-1β stimulation. Polyphenol components markedly inhibited IL-8 production. Among the tested polyphenols, epigallocatechin gallate (EGCG) and epicatechin gallate (ECG) showed strong dose-dependent inhibitory effects starting from a concentration of 10 μg/mL. Epigallocatechin (EGC) and epicatechin (EC) demonstrated moderate inhibition with longer (48-hour) pretreatment, while (-)-catechin did not exhibit effective inhibition.
In conclusion, IL-8 production induced by IL-1β in both nasal mucosa-derived fibroblasts and epithelial cells was significantly and dose-dependently suppressed by most polyphenol components. The inhibitory effect was further enhanced by extending the pretreatment duration.
These findings suggest that polyphenols can effectively regulate inflammatory responses. Furthermore, sustained polyphenol intake may offer therapeutic potential in controlling or treating pathological conditions associated with chronic inflammation.