CIRCADIAN VARIATION OF URINARY-EXCRETION OF ELASTIN AND COLLAGEN CROSS-LINKS

Urinary levels of collagen- and elastin-crosslink amino acids have bee n used as biologic markers for degradation of collagen and elastin in the body. Circadian variation of collagen-crosslink amino acids is wel l known. The current study was undertaken to determine whether there i s also circadian variation in excretion of elastin-crosslink amino aci ds. We used an isotope dilution-HPLC assay to measure the elastin-cros slink amino acids, desmosine (DES) and isodesmosine (IDES), and the co llagen-crosslink amino acids, hydroxylysyl pyridinoline (HP) and lysyl pyridinoline (LP), in urine. Sixteen apparently healthy subjects coll ected urine from 5:00 to 7:00 nM, and from 5:00 to 7:00 AM. Mean urina ry excretion of DES and IDES in women was 56% and 41% higher (P < 0.00 1), respectively, in nM versus PM specimens when normalized by the cre atinine content of the urine specimen. For men, the corresponding valu es were 11% and 13% higher (not statistically significant). Mean urina ry excretion of HP and LP in women was 61% and 71% higher (P < 0,001), respectively, in nM versus PM specimens. For men, the corresponding v alues were 11% and 19% higher (not statistically significant). Differe nces were not found in the nM versus PM rates of excretion of creatini ne in men or women. These findings demonstrate the occurrence of circa dian variation in HP, LP, DES and IDES in women but not in men. We con clude that the time of collection of urine specimens, especially from women, must be taken into consideration in using the urinary levels of these crosslink amino acids as biologic markers for collagen or elast in degradation.