Chemical constituents from acid hydrolyzates of Panax quinquefolius total saponins and their inhibition activity to α-glycosidase and protein tyrosine phosphatase 1B

OBJECTIVE: To investigate the hypoglycemic components from the acid hydrolyzates of Panax quinquefolius total saponins, and screen the active compounds by in vitro inhibitory activities to α-glycosidase enzymes and protein tyrosine phosphatase-1B (PTP1B). METHODS: The hydrolyzates were chromatographed repeatedly over silica gel column, and the structures of the compounds were determined by means of NMR. The in vitro bioassay was performed through the inhibitory effects on α-glucosidase or/and PTP1B. RESULTS: Eight compounds were isolated, which identified as 20(S)-panaxadiol (1), (20S,24R)-dammarane-20,24-epoxy-3β,6α,12β,25-tetraol (2), 20(R)-dammarane-3β,12β,20,25-tetraol (3), 20(S)-dammarane-3β,6α,12β,20,25-pentol (4), 20(R)-dammarane-3β,12β,20,25-tetrahydroxy-3β-O-β-d-glucopyranoside (5), β-sitosterol (6), oleanolic acid (7) and 20(S)-protopanaxadiol (8). Compound 5 was ginseng triterpenoid isolated from the acid hydrolysates of total saponins from P. quinquefolius for the first time. In this paper, the possible in vitro inhibitory activities were investigated. Compound 5 exhibited significantly inhibitory activity against α-glucosidase, and the IC(50) value [(0.22 ± 0.21) µmol/L] was about 43-fold lower than positive control. For the PTP1B inhibition assay, compound 5 indicated the strongest inhibitory effect with IC(50) of (5.91 ± 0.38) µmol/L, followed by compound 4 with IC(50) of (6.21 ± 0.21) µmol/L, which were all showed competitive inhibitory pattern by using a Lineweaver-Burk plot. CONCLUSION: These results supported the potential application of dammaranes from acid hydrolyzates of P. quinquefolius total saponins can be used as ingredients of ancillary anti-diabetic agent or functional factor.