Glycosaminoglycans are fragmented by hydroxyl, carbonate, and nitrogen dioxide radicals in a site-selective manner: implications for peroxynitrite-mediated damage at sites of inflammation

Martin

et al. 2013

Hypochlorous acid (HOCl), produced in inflammatory conditions by the enzyme myeloperoxidase, and its anion, perchlorite ( OCl -) exist in vivo at almost equal concentrations. Their reactions with hyluronan and heparin (as a model for sulphated glycosaminoglycans in the extracellular matrix), have been studied as a function of pH. The major product in these reactions is the chloramide derivative of the glycosaminoglycans. Spectral, chloramide yield and kinetic measurements show sharply contrasting behaviour of heparin and hyaluronan and the data allow the calculation of second-order rate constants for the reactions of both HOCl and OCl -for all reaction pathways leading to the formation of chloramides and also oxidation products . By comparison with hyaluronan, it can be demonstrated that both N-sulphate and O-sulphate groups in heparin influence the proportions of these pathways in this glycosaminoglycan. Evidence is also given for further oxidation pathways involving a reaction of HOCl with the chloramide product of hyaluronan but not with heparin. The significance of these results for mechanisms of inflammation, particularly for fragmentation of extracellular matrix glycosaminoglycans is discussed.

Section: Introductionsupporting

confidence: 65%

Chlorination and oxidation of heparin and hyaluronan by hypochlorous acid and hypochlorite anions: effect of sulfate groups on reaction pathways and kinetics

Akeel

Martin

et al. 2013

“…The fragmentation of HA and other glycosaminoglycans has also been investigated intensively by Davies and co-workers using both electron paramagnetic resonance (EPR) spectroscopy and sensitive PAGE techniques to show peroxynitrous acid, carbonate and hydroxyl radicals react largely in a sitespecific process to produce an array of HA fragments, in a "ladder-type display" each separated from the neighbour by the molecular mass of the repeating disaccharide unit in HA [17,18]. Similar site-selective fragmentation was also observed when glycosaminoglycan chloramides (formed through reaction with hypochlorite) were reduced by copper (I) ions and superoxide anion radicals [19,20].…”

Section: Introductionmentioning

confidence: 99%

One-electron oxidation and reduction of glycosaminoglycan chloramides: A kinetic study

Parsons

Houée-Levin⊥

et al. 2013

Hypochlorous acid and its acid-base counterpart, hypochlorite ions, produced in inflammatory conditions, may produce chloramides of glycosaminoglycans, the latter being significant components of the extracellular matrix (ECM). This may occur through the binding of myeloperoxidase directly to the glycosaminoglycans.The N-Cl group in the chloramides is a potential selective target for both reducing and oxidising radicals, leading possibly to more efficient and damaging fragmentation of these biopolymers relative to the parent glycosaminoglycans. In this study,the fast reaction techniques of pulse radiolysis and nanosecond laser flash photolysis have been used to generate both oxidizing and reducing radicals to react with the chloramides of hyaluronan (HACl) and heparin (HepCl).The strong reducing formate radicals and hydrated electrons were found to react rapidly with both HACl and HepCl with rate constants of (1-1.7) x 10 8 M -1 s -1 and (0.7-1.2) x 10 8 M -1 s -1 for formate radicals and 2.2 x 10 9 M -1 s and 7.2 x 10 8 M -1 s -1 for hydrated electrons, respectively. The spectral characteristics of the products of these reactions were identical and were consistent with initial attack at the N-Cl groups, followed by elimination of chloride ions to produce nitrogencentred radicals, which re-arrange subsequently and rapidly to produce C-2 radicals on the glucosamine moiety supporting an earlier EPR study by Rees et 3 This is the first study therefore to conclusively demonstrate that reducing radicals react rapidly with glycosaminoglycan chloramides in a site-specific attack at the N-Cl groups, probably to produce a 100 % efficient biopolymer fragmentation process. Although less reactive, carbonate radicals, which may be produced in vivo via reactions of peroxynitrite with serum levels of carbon dioxide ,also appear to react in a highly site-specific manner at the N-Cl group. It is not yet known if such site-specific attacks by this important in vivo species lead to a more efficient fragmentation of the biopolymers than would be expected for attack by the stronger oxidising species, the hydroxyl radical. It is clear however that the N-Cl group formed in inflammatory conditions in the extracellular matrix does present a more likely target for both reactive oxygen species and for reducing species than the N-H groups in the parent glycosaminoglycans. Graphical abstract4

“…The use of the latter technique showed the novel and potentially biologically significant result that peroxynitrous acid, carbonate and hydroxyl radicals react largely in a site-specific process to produce an array of HA fragments, in a "ladder-type display" each separated from the neighbour by the molecular mass of the repeating disaccharide unit in HA, thus mimicking to a significant extent the action of the enzyme, hyaluronidase [17,18]. Similar site-selective fragmentation was also observed when glycosaminoglycan chloramides (formed through reaction with hypochlorite) were reduced by copper (I) ions and superoxide anion radicals [19,20].…”

Section: Introductionmentioning

confidence: 99%

Reaction of superoxide radicals with glycosaminoglycan chloramides: a kinetic study

Parsons

Heyes

et al. 2013

Hypochlorous acid and its acid-base counterpart, hypochlorite ions, produced in inflammatory conditions, may produce chloramides of glycosaminoglycans, perhaps through the binding of myeloperoxidase directly to the glycosaminoglycans. The N-Cl group in the chloramides is a potential target for reducing species such as Cu(I) and superoxide radicals. Laser flash photolysis has been used here to obtain, for the first time, the rate constants for the direct reaction of superoxide radicals with the chloramides of hyaluronan and heparin. The rate constants were in the range 2.2 -2.7 x 10 3 M -1 s -1 . The rate constant for the reaction with the amino acid, taurine, was found to be much lower at 3.5 -4.0 x 10 2 M -1 s -1 . This demonstration that superoxide anion radicals react directly with hyaluronan and heparin chloramides may support the mechanism first proposed by Rees et al, Biochem. J. 381: 175-184; for an efficient fragmentation of these glycosaminoglycans in the extracellular matrix under inflammatory conditions. 3