황색 및 자색 양파 껍질의 항당뇨 및 항산화 활성 비교

Abstract

The aim of the present study was to investigate comparative anti-diabetic activities of both water and ethanol extracts derived from yellow and red onion (Allium cepa L.) peels via human recombinant protein tyrosine phosphatase 1B (PTP1B), α-glucosidase and advanced glycation end-products (AGEs) formation inhibitory assays, as well as antioxidant activities by evaluating the ability of extracts to scavenge 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), respectively. In addition, total phenolic (TP) and total flavonoid (TF) contents were measured to assess phytochemical characteristics. Higher TP and TF contents derived from both yellow and red peel ethanol extracts (YE and RE) than both yellow and red water peel extracts (YW and RW) were correlated to the corresponding higher antioxidant effects in DPPH and ABTS scavenging assays as well as anti-diabetic effects in α-glucosidase and AGEs formation assays. Between the two cultivars, yellow onion peel showed higher antioxidant activity than red onion peel. Considering the anti-diabetic potential, RE, YE, RW, and YW exhibited significant PTP1B inhibitory activities with corresponding IC50 values of 0.76 ± 0.17, 0.86 ± 0.04, 0.33 ± 0.01, and 0.30 ± 0.08 µg/mL, as compared with the positive control, ursolic acid with IC50 value of 3.40 ± 0.34 µg/mL. In particular, water extracts were found to be more effective against PTP1B inhibition than the ethanol extracts. On the other hand, yellow onion peel (YE and YW) exhibited higher α-glucosidase inhibitory activities than red onion peel (RE and RW) with the IC50 values of 3.90 ± 0.08, 5.44 ± 0.06, 5.76 ± 0.03, and 8.99 ± 0.56 µg/mL, respectively. Moreover, ethanol extracts (RE and YE) exhibited higher AGEs formation inhibitory activity than water extracts (RW and YW) with the respective IC50 values of 12.79 ± 0.22, 12.25 ± 1.35, 51.91 ± 1.53, and 25.17 ± 1.75 µg/mL. Interestingly, yellow and red onion peel extracts exhibited higher anti-diabetic activity than positive control in the respective assays. In conclusion, both yellow and red onion peel revealed significant in vitro antioxidant and anti-diabetic potential. Therefore, these results suggest that inhibitory activities of onion peel depends upon cultivar color and extraction method which could be a promising strategy to prevent diabetes and diabetic complications.