COMPARISON OF 3 SERUM ASSAYS FOR BONE-COLLAGEN FORMATION DURING POSTMENOPAUSAL ESTROGEN-PROGESTIN THERAPY

Postmenopausal hormone replacement therapy (HRT) lowers the turnover r ate of the mineralized bone matrix, the predominant organic component of which is type I collagen. The effect of estrogen on bone metabolism has been monitored by measuring the circulating concentration of the carboxy-terminal propeptide of type I procollagen (PICP), which decrea ses during HRT. We have recently developed assays for the intact amino -terminal propeptide (PINP) of type I procollagen, a protein set free from the other end of the same gene product. PICP and PINP, both deriv ed from the synthesis of type I collagen, but differing in their furth er metabolism, were assessed in 47 postmenopausal women, aged 45-66 ye ars, undergoing postmenopausal HRT. Estradiol-gel applied daily was co mbined to a continuous progestin administered by three different route s. Serum samples obtained before the treatment and 6 and 12 months aft er its commencement were analyzed for PICP, PINP, PINP Col 1 (assay va riant measuring also the degradation product of PINP) and PIIINP (amin o-terminal propeptide of type III procollagen). During HRT the circula ting concentration of PICP decreased by 20%, that of PINP by 42% and t hat of PINP Col 1 by 32% in 12 months. The correlation between the two propeptides, which was 0.676 before the treatment, increased to 0.851 in 6 months and to 0.815 in 12 months. The correlations between PINP and PINP Col 1 were 0.872 before the treatment and increased to 0.925 and 0.941 after 6 and 12 months of treatment, respectively. The serum concentration of PIIINP, which reflects the turnover of the soft tissu e collagens, did not change remarkably. Our findings indicate that the intact PINP is a more dynamic marker of bone metabolism than PICP and can therefore be recommended as a marker reflecting the effect of est rogen on bone collagen formation during HRT. (C) 1997 Elsevier Science B.V.