Chlorination of pyridinium compounds -: Possible role of hypochlorite, N-chloramines, and chlorine in the oxidation of pyridinoline cross-links of articular cartilage collagen type II during acute inflammation

Reactive oxygen species produced by activated neutrophils and monocytes are thought to be involved in mediating the loss of collagen and other matrix proteins at sites of inflammation. To evaluate their potential to oxidize the pyridinoline (Pyd) cross links found in collagen types I and II, we reacted hydrogen peroxide (H2O2), hypochlorous acid/hypochlorite (HOCl/OCl-), and singlet oxygen (O-2((1)Deltag)) with the Pyd substitutes, pyridoxamine dihydrochloride and vitamin B-6, which share the same chemical structure and spectral properties of Pyd cross-links. Neither H2O2 (125-500 muM) nor O-2((1)Deltag) (10-25 muM) significantly changed the spectral properties of pyridoxamine or vitamin B-6. Reaction of HOCl/OCl- (12.5-50 muM) with pyridoxamine at pH 7.2 resulted in a concentration-dependent appearance of two new absorbance peaks and a decrease in fluorescence at 400 nm (excitation 325 nm). The new absorbance peaks correlated with the formation of an N-chloramine and the product of its subsequent reaction with pyridoxamine, In contrast, the extent to which HOCl reacted with vitamin B-6, which lacks a primary amine group, was variable at this pH. At lysosomal pH 5.5, Cl-2/HOCl/OCl- reacted with both pyridoxamine and vitamin B-6, Four of the chlorinated products of this reaction were identified by gas chromatography-mass spectrometry and included 3-chloropyridinium, an aldehyde, and several chlorinated products with disrupted rings, To evaluate the effects of Cl-2/HOCl/OCl- on Pyd cross-links in collagen, we exposed bone collagen type I and articular cartilage type II to HOCl. Treatment of either collagen type with HOCl at pH 5.0 or 7.2 resulted in the oxidation of amine groups and, for collagen type II, the specific decrease in Pyd cross-link fluorescence, suggesting that during inflammation both oxidations may be used by neutrophils and monocytes to promote the loss of matrix integrity.