Bioactive polyphenols from anacardium occidentale linn leaves and their effects on a-amylase and dipeptidyl peptidase IV activities

Abstract

Anacardium occidentale Linn. (A. occidentale L.) or cashew tree is one of the famous tropical plants among various ethnics in Malaysia. Its leaves are commonly consumed as ulam in Southeast Asia. Its leaves possess an excellent source of bioactive compounds, which are associated with numerous health benefits, including antidiabetic potency for type 2 diabetes mellitus (T2DM). The management strategies for T2DM include maintaining the postprandial blood glucose level through the inhibition of α-amylase and to prevent the hydrolysis of glucagon-like peptide-1 (GLP-1) through the inhibition of dipeptidyl peptidase IV (DPPIV). The DPPIV is a serine protease that localizes on cell surfaces and responsible for the rapid degradation of incretins such as a gastric inhibitory peptide, whilst α- amylase is served as the necessary digestive enzymes by involving in the breaking of long-chain carbohydrates into small pieces before absorption in the intestine. In this study, free, soluble ester and insoluble bound phenolic fractions from young and mature leaves of A. occidentale L. were extracted and analyzed for their phenolic compounds concentration using high-performance liquid chromatography (HPLC). Subsequently, all fractions were investigated for their inhibitory effects on α-amylase and DPPIV enzyme activities. Both free (72.45 ± 3.6%) and soluble ester (83.40 ± 4.7%) phenolic fractions in the mature leaves extracts had significantly demonstrated higher α-amylase inhibitors than the young leaves. Likewise, soluble ester (4.09 ± 0.34 µg/ml) and insoluble bound (4.87 ± 0.32 µg/ml) phenolic fractions in the mature leaves extracts were significantly more effective in inhibiting DPPIV than the young leaves. As for fractions comparison, insoluble bound derived from the young leaves extract was a more potent α-amylase inhibitor than free and soluble ester phenolic fractions (p<0.001). Soluble ester and insoluble bound phenolic fractions showed stronger inhibitors of DPPIV than the free phenolic (p<0.001), based on the maturity of the leaves. The interaction between fraction and maturity were significantly different in both young and mature leaves of A. occidentale L. according to the α- amylase, and DPPIV inhibition analyses (p<0.001). In conclusion, this study showed that A. occidentale L. leaves extracts possessed inhibition properties in α- amylase and DPPIV activities, which further may potentially be exploited in clinical study as an antidiabetic for type 2 diabetes mellitus.