Serum Levels of Type I and III Procollagen Fragments in Paget's Disease of Bone*

Patients with Paget's disease of bone were found to have elevated serum levels of type I procollagen carboxy-terminal peptide (pColl-I-C) which correlated with other measurements of disease activity. The elevated levels of pColl-I-C decreased within hours after the injection of salmon calcitonin and within weeks after oral dichloromethylene diphosphonate treatment. The decrease in serum pColl-I-C after a single injection of salmon calcitonin was associated with a decrease in urinary hydroxyproline excretion, both of which rose toward pretreatment values within 7 h. The pColl-I-C levels remained normal for months after dichloromethylene diphosphonate therapy was discontinued. Using a RIA for the type III procollagen amino-terminal peptide (pColl-III-N), it was found that serum levels were also elevated in patients with Paget's disease. The levels of pColl-III-N alsodecreased after the injection of salmon calcitonin, but not to the same extent as those of pColl-I-C. After chronic therapy with dichloromethylene diphosphonate, serum levels of pColl-III-N decreased, but not into the normal range. We postulate that whereas pColl-I-C is derived from synthesis of mineralized bone collagen, pColl-III-N is derived from the loose fibrous stroma replacing marrow in areas closely associated with active Pagetic bone disease.