Comparison of free and peptide-bound pyridinoline cross-links excretion inrheumatoid arthritis and osteoarthritis

Objective. To investigate urinary fractions of free and peptide forms of py ridinoline crosslinks in arthritis. Patients and methods. The free and total forms of pyridinoline (Pyr) and de oxypyridinoline (Dpyr) were measured by high-performance liquid chromatogra phy (HPLC) in 30 premenopausal and 22 post-menopausal normal women, 38 wome n with rheumatoid arthritis (RA) and 62 women with osteoarthritis (OA). Pep tide forms were calculated as total minus free. Free Dpyr and peptide form were also measured by deoxypyridinoline and carboxyterminal telopeptide of type I collagen (CTx) immunoassays. Results. In normal women, all fractions of Pyr and Dpyr and immunoassays we re elevated in post-menopause compared to pre-menopause. In post-menopausal normal women, the free form increased more than the peptide form. In RA, a n increase in the fractions of Pyr was greater than Dpyr. Peptide and total cross-links correlated with the disease activity of RA and they were eleva ted in RA patients with high disease activity. Free Dpyr and CTx were signi ficantly lower in OA than in normal women. Peptide and total Pyr and Dpyr, and immunoassayed Dpyr were significantly higher in the radiographic later stage of OA than in the early stage of OA. Conclusions. The menopause, RA and OA may have different effects on the uri nary excretion of free and peptide-bound pyridinoline cross-links.