OXYGEN-DERIVED FREE-RADICAL (ODFR) ACTION ON HYALURONAN (HA), ON 2 HAESTER DERIVATIVES, AND ON THE METABOLISM OF ARTICULAR CHONDROCYTES

Oxygen-derived free radicals (ODFR) appear to be involved in the patho genesis 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) o n hyaluronic acid, on two HA ester derivatives, and on pig articular c hondrocytes was investigated, High M(r) HA (1.1 X 10(6)) and low M(r) HA (16 X 10(4)) were depolymerized by ODFR but the methyl and hydrocor tisone esters of HA (HYAFF 2P50 and HYC13) turned out to be nearly una ffected. When articular chondrocytes were treated with ODFR, a rapid n ucleoside triphosphate (NTP) depletion, a transient appearance of pyro phosphate (PPi), and an increase of phosphomonoester and diphosphodies ter concentrations have been observed, The NTP depletion and the DPDE increase are related to the concentration of free radicals. Glyceralde hyde-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 prese nted that PPi can be produced from the pathway of the FAD-NAD (DPDE) b iosynthesis and then either hydrolyzed by endogenous pyrophosphatases or precipitated in the form of insoluble calcium salts, Long-term trea tment (16 h) with ODFR causes a loss of chondrocyte membrane integrity which can be revealed both by an increased free LDH activity and by t he characteristic signal of free phospholipids in the P-31-NMR spectra . While high M(r) HA shows a significant protective activity for chond rocytes 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. (C) 1995 Academ ic Press, Inc.