Comparison of Total Phenolic Contents, Antioxidant and Anti-Inflammation Activity in Sweetpotato Leaves Obtained from 24 Different Cultivars

Abstract

Abstract Objectives Sweetpotato is one of the most important crops in the world. However, most of the sweetpotato leaves (SPLs) are discarded despite their high nutritional values. To evaluate the potential utility of SPLs as a functional food, the objectives were to measure the total phenolic contents and their antioxidant activities and to determine the anti-inflammatory effects of SPL phenolic extracts from 24 different cultivars in Arkansas. Methods Sweetpotato leaves were analyzed for total phenolics (TP) and antioxidant activities using Folin-Ciocalteu's assay and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, respectively. To assess cell viability and nitric oxide (NO) inhibition activities, RAW 264.7 cells were pretreated with SPL phenolic extracts at the concentrations of 50–500 μg/mL for 1 h and stimulated with lipopolysaccharide (LPS, 100 ng/mL). Cell viability and NO production were measured using the Cell Proliferation assay and Griess reaction system, respectively. All statistical analyses were performed using the ANOVA procedure (SAS 9.4) with significance at P < 0.05 level. Results Among 24 SPL extracts, SPL#1, 3, 9, 38, and 11 exhibited the strong DPPH scavenging activity with 247, 137, 117, 111 and 106 mM Trolox equivalent/g, respectively. Extracts of SPL#1, 9, 3, 7, and 10 showed a high content of phenolics with containing 17.6, 14.8, 14.7, 14.3 and 14.2 mg gallic acid equivalent/g. When the RAW 264.7 cells were treated with 50–500 μg/mL of SPLs for 24 h, SPL extracts up to 250 μg/mL did not cause any significant cytotoxicity. After inducing inflammation with LPS, 50–100 μg/mL of 24 SPL treatments lowered NO levels (11–44%) in a dose-dependent manner compared to the positive control (P < 0.05). Also, SPL#1, 3, 9, 38, and 11, indicating the highest DPPH radical scavenging activity, showed significant NO reduction (15–49%) at the concentrations of 50–200 μg/mL (P < 0.05). Conclusions The findings showed that sweetpotato leaves are a good source of phenolics to exert significant antioxidant activity and NO inhibitory effects in a cellular system, suggesting that sweetpotato leaves may be used as a functional food for improving immune response. Funding Sources The work was supported by USDA-NIFA.