Inhibitory evaluation of oligonol on α-glucosidase, protein tyrosine phosphatase 1B, cholinesterase, and β-secretase 1 related to diabetes and Alzheimer's disease

Oligonol is a low-molecular-weight form of polyphenol that is derived from lychee fruit extract and contains catechin-type monomers and oligomers of proanthocyanidins. This study investigates the anti-diabetic activities of oligonol via alpha-glucosidase and human recombinant protein tyrosine phosphatase 1B (PTP1B) assays, as well as its anti-Alzheimer activities by evaluating the ability of this compound to inhibit acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and beta-site amyloid precursor protein cleaving enzyme 1 (BACE1). Oligonol exhibited potent concentration-dependent anti-diabetic activities by inhibiting alpha-glucosidase and PTP1B with IC50 values of 23.14 A mu g/mL and 1.02 A mu g/mL, respectively. Moreover, a kinetics study revealed that oligonol inhibited alpha-glucosidase (K (i) = 22.36) and PTP1B (K (i) = 8.51) with characteristics typical of a mixed inhibitor. Oligonol also displayed potent concentration-dependent inhibitory activity against AChE and BChE with IC50 values of 4.34 A mu g/mL and 2.07 A mu g/mL, respectively. However, oligonol exhibited only marginal concentration-dependent BACE1 inhibitory activity with an IC50 value of 130.45 A mu g/mL. A kinetics study revealed mixed-type inhibition against AChE (K (i) = 4.65) and BACE1 (K (i) = 58.80), and noncompetitive-type inhibition against BChE (K (i) = 9.80). Furthermore, oligonol exhibited dose-dependent inhibitory activity against peroxynitrite (ONOO-)-mediated protein tyrosine nitration. These results indicate that oligonol has strong preventative potential in diabetes mellitus and in Alzheimer's disease.