ANTIOXIDANT ACTIONS OF OXYMETAZOLINE AND XYLOMETHAZOLINE

Anti-oxidant actions of oxymethazoline and xylomethazoline were invest igated by measuring inhibition of microsomal lipid peroxidation and hy droxyl radical scavenging activity. Oxymethazoline was shown to be a p otent inhibitor of lipid peroxidation (IC50 = 4.9 mu M at t = 15 min, IC50 = 8.1 mu M at t = 30 min), in contrast to xylomethazoline. Both c ompounds were excellent hydroxyl radical scavengers. Their rate consta nts (k(s) = 1.1 X 10(12) M(-1)s(-1) for oxymethazoline and k(s) = 4.7 X 10(10) M(-1)s(-1) for xylomethazoline) exceeded the rate constant of a known powerful scavenger cimetidine (k(s) = 1.8 X 10(10) M(-1)s(-1) ). The difference in inhibiting lipid peroxidation might be explained by the fact that only oxymethazoline has a hydroxy group which can don ate a hydrogen atom and terminate the chain reaction of lipid peroxida tion. The mechanism of hydroxyl radical scavenging activity is still u nclear. Moreover oxymethazoline seems to have a different mode of acti on in scavenging hydroxyl radicals than xylomethazoline and cimetidine which results in an extremely high rate constant. Because oxidants pl ay a role in tissue damage in inflammation, it was hypothesized that e specially oxymethazoline and to a lesser extent xylomethazoline may ha ve an additional beneficial effect, due to their anti-oxidant properti es, in the topical treatment of nasal inflammation.