To investigate urinary fractions of free and peptide forms of pyridinoline cross-links in arthritis.
The free and total forms of pyridinoline (Pyr) and deoxypyridinoline (Dpyr) were measured by high-performance liquid chromatography (HPLC) in 30 pre-menopausal and 22 post-menopausal normal women, 38 women with rheumatoid arthritis (RA) and 62 women with osteoarthritis (OA). Peptide forms were calculated as total minus free. Free Dpyr and peptide form were also measured by deoxypyridinoline and carboxy-terminal telopeptide of type I collagen (CTx) immunoassays.
In normal women, all fractions of Pyr and Dpyr and immunoassays were elevated in post-menopause compared to pre-menopause. In post-menopausal normal women, the free form increased more than the peptide form. In RA, an 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 elevated in RA patients with high disease activity. Free Dpyr and CTx were significantly 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.
The menopause, RA and OA may have different effects on the urinary excretion of free and peptide-bound pyridinoline cross-links.