The radical-scavenging activities of the flavanones hesperetin and hesperidin were investigated by differential scanning calotimeny (DSC) monitoring of the polymerization of methyl methacrylate initiated by 2,2 azobisisobutyronitrile (AIBN, an R-center dot radical) or benzoyl peroxide (BPO, a PhCOO center dot radical) at 70 degrees C under nears anaerobic conditions. Their stoichiometric factor (number of free radicals trapped by one mole of antioxidant moiety (it)) and the ratio of the rate constant of inhibition to that of propagation (k(inh)/k(p)) were determined and compared with that for trolox The n value declined in the order trolox (2.0) > hesperetin (0.8) > hespendin (0.2) in the AIBN system whereas it declined in the order hesperetin (0.9) > trolox (0.1) > hespendin (0.0) in the BPO system. The k(inh)/k(p) value declined in the order hespendin (195) > hesperetin (33) > trolox (12) in the AIBN system, whereas it declined in the order hespendin (362) > trolox (127) > hesperetin (18) in the BPO system. The n value of about 1 for hesperetin with a relatives small k(inh)/k(p) value suggests the formation of dimers, as a result of the coupling reaction of phenolic monomers. In contrast n values < < 1 for hesperidin and trolox in the BPO system resulted in very high Values for k(inh)/k(p). Hespendin was also much more able to suppress the growth of methyl methacrylate radicals, although its n value was small, suggesting that this compound may also suppress polyunsaturated fatty acid radicals. In the concentration range 250-500 mu M, hesperetin and hesperidin showed potent inhibition of LPS-induced exression of the COX-2 gene in RA W 264.7 cells, suggesting the anti-inflammatory activity of these compounds. The ability of hesperetin and hespendin to suppress COX-2 gene expression may be a consequence of their antioxidant activity.
