Total and free deoxypyridinoline after acute osteoclast activity inhibition.
BACKGROUND
Deoxypyridinoline (Dpd) is one of the two pyridinium cross-links that provide structural rigidity to type I collagen in bone. During osteoclastic resorption, Dpd is released into circulation and is excreted in the urine in free and peptide-bound forms. Free and total Dpd are highly correlated, but whether the free-to-total cross-link ratio is constant in both normal and high bone turnover states remains controversial. To compare free and total Dpd performance in a physiological condition, urinary free and total Dpd were measured after a short-term inhibition of osteoclast activity such as that induced by an oral calcium load.


METHODS
Total and free Dpd were measured by HPLC and by immunosorbent assay, respectively, in two groups of subjects, one (calcium-treated; n = 16) taking calcium and the other not (control; n = 9).


RESULTS
The urinary excretion of total Dpd at 2 and 4 h after oral calcium loading was decreased compared with controls. By contrast, changes in free Dpd were similar in the calcium-treated and control groups, reflecting only circadian rhythm.


CONCLUSIONS
Total and free Dpd do not show comparable sensitivity in detecting short-term inhibition of osteoclast activity. The degradation process of peptide-bound to free Dpd could render free Dpd insensitive to acute changes of osteoclast activity.
Rubinacci
A
A
Bone Metabolic Unit, Scientific Institute H San Raffaele, Via Olgettina 60, 20132 Milan, Italy. a.rubinacci@hsr.it
Melzi
R
R
Zampino
M
M
Soldarini
A
A
Villa
I
I
D000328:Adult; D000368:Aged; D000596:Amino Acids / Q000378:metabolism / Q000652:urine*; D015415:Biomarkers / Q000652:urine; D001862:Bone Resorption / Q000652:urine; D002118:Calcium; D002851:Chromatography, High Pressure Liquid; D005260:Female; D006801:Humans; D007118:Immunoassay; D008297:Male; D008875:Middle Aged; D010010:Osteoclasts / Q000378:metabolism*; D010455:Peptides / Q000378:metabolism; D011485:Protein Binding; D012680:Sensitivity and Specificity
D000596:Amino Acids; D015415:Biomarkers; D010455:Peptides; C036020:deoxypyridinoline; D002118:Calcium