Chain scission of hyaluronan by carbonateand dichloride radical anions: Potential reactive species in inflammation?

The reactions of the carbonate and dichloride radical anions, CO3.- and Cl-2(.-), with the extracellular matrix glycosaminoglycan hyaluronan (HA) have been studied using the kinetic technique of pulse radiolysis and also by steady-state irradiation combined with gel permeation chromatography/multiangle laser light scattering(gpc/MALLS) to measure the rates of reaction with HA and the yield of HA chain scission, respectively. For comparison, the same measurements were made for the reactions of the free radicals (OH)-O-., Br-2(.-), and N-3(.). The carbonate and dichloride radical anions were found to react relatively quickly with HA (7.0 x 10(5) and 6.9 x 10(6) dm(3) mol(-1) s(-1), respectively) although they are much less reactive than the hydroxyl radical, (OH)-O-.. Significant yields (20 and 3 8%, respectively) of chain scission of HA by these radical anions were also determined from the gpc/MALLS experiments, providing some support for their potential participation in the depolymerization of HA in vivo. These results are compared with data obtained for the other free radicals (hydroxyl, azide radicals, and dibromide radical anions) investigated in this study in order to gain an insight into their mechanism of reaction with HA, Earlier chain scission yields of HA by hydroxyl radicals determined by the authors have also been revised using the gpc/MALLS technique employed in the current study. The yields of 52% (absence of air) and 44% (in air) are much lower than the previous values. In the current study, the effect of oxygen on the yields of HA chain breaks is discussed in terms of the reactivity of HA peroxyl radicals in the presence of superoxide radical anions. The relevance of the results of this study to mechanisms of inflammation is discussed. (c) 2006 Elsevier Inc. All rights reserved.