Passive cutaneous anaphylaxis-inhibitory activity of flavanones from Citrus unshiu and Poncirus trifoliata

This study examined the passive cutaneous anaphylaxis-inhibitory activity of the flavanones isolated from the pericarp of Citrus unshiu (Family Rutaceae) and the fruit of Poncirus trifoliata (Family Rutaceae). Naringenin, hesperetin and ponciretin potently inhibited IgE-induced beta-hexosaminidase release from RBL-2H3 cells and the PCA reaction. Among the flavanones examined, naringenin was the most potent with an IC50 value for beta-hexosaminidase release from RBL-2H3 cells of 0.029 mM. Intraperitoneally administered naringenin (5 mg/kg) inhibited PCA by 70 +/- 1.7 %, compared with the control group. The inhibitory activity of naringenin was found to be comparable to that of azelastine, which is a commercially available antiallergic drug. However, their glycosides, hesperidin, naringin and poncirin, did not inhibit the in vitro release of beta-hexosaminidase from the RBL-2H3 cells. On the other hand, these flavanones did not improve the oxazolone-induced dermatitis in the mouse ears. When the flavanone glycosides were administered to rats, the aglycones, but not the flavanone glycosides, were excreted in urine. This suggests that the flavanone glycosides can be activated by intestinal bacteria, and may be effective toward IgE-induced atopic allergies.