Effects of peanut-skin procyanidin A1 on degranulation of RBL-2H3 cells.

Peanut skin contains large amounts of polyphenols having antiallergic effects. We found that a peanut-skin extract (PSE) inhibits the degranulation induced by antigen stimulation of rat basophilic leukemia (RBL-2H3) cells. A low-molecular-weight fraction from PSE, PSEL, also had inhibitory activity against allergic degranulation. A main polyphenol in PSEL was purified by gel chromatography and fractionated by YMC-gel ODS-AQ 120S50 column. Electrospray ionization mass spectrometry (ESI-MS) analysis of the purified polyphenol gave m/z 599 [M+Na]⁺. Based on the results of ¹H-NMR, ¹³C-NMR spectra, and optical rotation analysis, the polyphenol was identified as procyanidin A1. It inhibited the degranulation caused by antigen stimulation at the IC₅₀ of 20.3 µM. Phorbol-12-myristate-13-acetate (PMA) and 2,5,-di(tert-butyl)-1,4-hydroquinone (DTBHQ)-induced processes of degranulation were also inhibited by procyanidin A1. These results indicate that peanut-skin procyanidin A1 inhibits degranulation downstream of protein kinase C activation or Ca²⁺ influx from an internal store in RBL-2H3 cells.