Anthocyanin-Rich Fraction from Kum Akha Black Rice Attenuates NLRP3 Inflammasome-Driven Lung Inflammation In Vitro and In Vivo.

BACKGROUND/OBJECTIVES: Chronic lower respiratory tract inflammation can result from exposure to bacterial particles, leading to the activation of the NLRP3 inflammasome pathway. These effects may cause irreversible respiratory damage, contributing to persistent lung injury and chronic obstructive pulmonary disease (COPD), as observed in long COVID or bacterial pneumonia in older adults' patients. Given its profound impact, the NLRP3 inflammasome has emerged as a key therapeutic target for mitigating aberrant inflammatory responses. METHODS: In this study, we investigated the anti-inflammatory effects of Kum Akha black rice, a functional food, on the attenuation of NLRP3 inflammasome pathway using lipopolysaccharide-induced A549 lung epithelial cells and a C57BL/6NJcl mouse model. The anthocyanin-rich fraction from Kum Akha black rice germ and bran extract (KA1-P1) was obtained using a solvent-partitioned extraction technique. RESULTS: KA1-P1 exhibited a high anthocyanin content (74.63 ± 1.66 mg/g extract) as determined by the pH differential method. The HPLC analysis revealed cyanidin-3-O-glucoside (C3G: 45.58 ± 0.48 mg/g extract) and peonidin-3-O-glucoside (P3G: 6.92 ± 0.29 mg/g extract) as its anthocyanin's active compounds. Additionally, KA1-P1 demonstrated strong antioxidant activity, as assessed by DPPH and ABTS assays. KA1-P1 (12.5-100 μg/mL) possessed inhibitory effects on LPS + ATP-induced A549 lung cells inflammation through the significant suppressions of NLRP3, IL-6, IL-1β, and IL-18 mRNA levels and the inhibition of cytokine secretions in a dose-dependent manner (p < 0.05). Mechanistic analysis revealed that KA1-P1 downregulated key proteins in the NLRP3 inflammasome pathway (NLRP3, ASC, pro-caspase-1, and cleaved-caspase-1). Furthermore, in vivo studies demonstrated that KA1-P1 significantly diminished LPS-induced lower respiratory inflammation in C57BL/6NJcl mice, as evidenced by the reduced bronchoalveolar lavage fluid and blood levels of inflammatory cytokines (IL-6, IL-1β, and IL-18) and diminished histopathological inflammatory lung lesions. CONCLUSIONS: Overall, our findings suggest that the anti-inflammatory properties of KA1-P1 may support its application as a functional supplement or promote the consumption of pigmented rice among the elderly to mitigate chronic lower respiratory tract inflammation mediated by the NLRP3 inflammasome pathway.