Oxygen-Derived Free Radical (ODFR) Action on Hyaluronan (HA), on Two HA Ester Derivatives, and on the Metabolism of Articular Chondrocytes

Oxygen-derived free radicals (ODFR) appear to be involved in the pathogenesis of arthritic disorders. In order to gain new insight on their role in the phenomenon and as a basis for a therapeutic approach, the effect of ODFR (produced by the xanthine oxidase-hypoxantine system) on hyaluronic acid, on two HA ester derivatives, and on pig articular chondrocytes was investigated. High M_r HA (1.1 × 10⁶) and low M_r HA (16 × 10⁴) were depolymerized by ODFR but the methyl and hydrocortisone esters of HA (HYAFF 2P50 and HYC13) turned out to be nearly unaffected. When articular chondrocytes were treated with ODFR, a rapid nucleoside triphosphate (NTP) depletion, a transient appearance of pyrophosphate (PP_i), and an increase of phosphomonoester and diphosphodiester concentrations have been observed. The NTP depletion and the DPDE increase are related to the concentration of free radicals. Glyceraldehyde-3-phosphate accumulation during ODFR treatment suggests that ATP depletion can occur as a consequence of the blockage of glycolysis at the level of glyceraldehyde-3-P dehydrogenase. The hypothesis is presented that PP_i can be produced from the pathway of the FAD-NAD (DPDE) biosynthesis and then either hydrolyzed by endogenous pyrophosphatases or precipitated in the form of insoluble calcium salts. Long-term treatment (16 h) with ODFR causes a loss of chondrocyte membrane integrity which can be revealed both by an increased free LDH activity and by the characteristic signal of free phospholipids in the ³¹P-NMR spectra. While high M_r HA shows a significant protective activity for chondrocytes against ODFR action, low M_r HA and ester derivatives do not. It is suggested that the therapeutic activity of HA ester derivatives can be ascribed to their in vivo hydrolysis products. Copyright 1995, 1999 Academic Press