Differential effects of reactive oxygen species on native synovial fluid and purified human umbilical cord hyaluronate

Abstract

The ability of reactive oxygen species produced by triggered neutrophilic leukocytes, hypoxanthine/xanthine oxidase (HX/XAO), hydrogen peroxide, and hypochlorous acid/mycloperoxidase (HOC1/MPO) systems to degrade hyaluronate (HA) in human synovial fluid (SF) and purified umbilical cord HA was compared by measuring the molecular weight distribution of HA using high-performance liquid chromatography with a size-exclusion column. The exposure of noninflammatory SF to phorbol myristic acetate (PMA) -activated neutrophils or to hydrogen peroxide (H₂O₂) caused depolymerization of SF HA to the degree corresponding to that found in rheumatoid SFs. When HX/XAO was used as radical generator, the molecular weight of SF HA decreased from 3.42×10⁶ to 1.40 × 10⁴ daltons with concomitant decrease of SF viscosity to 36% from the original value. The HOC1/MPO system caused no depolymerisation of SF HA, even at very high unphysiological HOC1 concentrations that induced the precipitation of SF HA together with SF proteins. This effect was found to be comparable to conventional mucin clot formation in SF. However, purified human umbilical cord HA was easily depolymerized with HOC1/ MPO or with H₂O₂, but these effects were sensitive to the hydroxyl radical scavenger mannitol and iron chelator desferrioxamine, indicating that the formation of reactive hydroxyl radical (OH) is likely to participate in these reactions. Thus we conclude that in inflammatory SF HA is mainly depolymerized by OH produced by decomposition of H₂O₂ catalyzed by iron, free or locally bound to HA itself. In contrast to what has been reported earlier, HOC1/MPO only depolymerizes purified umbilical cord HA (in a hydroxyl radical-dependent manner) but does not depolymerize HA in SF. As a matter of fact, HOC1/MPO has a scavenging action on SF HA by consuming H₂O₂ and thus preventing the formation of reactive hydroxyl radicals.