Sweetpotato Leaves Inhibit Lipopolysaccharide-Induced Inflammation in RAW 264.7 Macrophages via Suppression of NF-κB Signaling Pathway

Abstract

Limited information is available regarding the health-promoting activities of sweetpotato leaves (SPL). The present study investigated antioxidant and anti-inflammatory effects, and phenolic contents in 29 SPL cultivars harvested in 2018 and 2019. Extracts showed total phenolic contents 9.4–23.1 mg gallic acid equivalent/g, and DPPH radical scavenging activity indicated 36.6–247.3 mM of Trolox equivalent/g. SPL extracts were identified to contain bioactive components such as, chlorogenic acid (11.7–22.1 μg/mg), 3,4-dicaffeoylquinic acid (16.3–59.9 μg/mg), 3,5-dicaffeoylquinic acid (50.9–72.7 μg/mg), chlorophyll B (6.1–12.3 μg/mg), lutein (1.9–4.9 μg/mg), chlorophyll A (2.7–4.3 μg/mg) and β-carotene (0.1 ≤ μg/mg). RAW 264.7 murine macrophage cells were pretreated with 100–200 μg/mL of SPL extracts and 20 μM of dexamethasone, and inflammation was stimulated by lipopolysaccharide (LPS, 100 ng/mL) treatment for 24 h. In LPS-treated cells, prostaglandin E2 production and COX-2 expression were not downregulated by pretreatment of SPL extracts. However, SPL pretreated cells showed significant suppression of nitric oxide (NO), TNF-α, and IL-1β levels under the LPS-induced inflammatory condition. In addition, SPL extracts induced an anti-inflammatory effect in LPS-stimulated RAW 264.7 cells through suppression of NF-κB nuclear translocation, IKK-α and IκB-α phosphorylation, and iNOS expression. These results indicate that SPL extract can be utilized as a functional food ingredient.

Keywords

• anti-inflammation
• NF-κB signaling pathway
• phenolic compounds
• sweetpotato leaves