Immunoassay for urinary pyridinoline: the new marker of bone resorption.

Urinary pyridinoline (Pyd) and deoxypyridinoline (Dpd) are markers of bone resorption that are elevated above normal in subjects with metabolic bone disease. Total Pyd and Dpd, both free and peptide-bound forms, can be measured by HPLC after hydrolysis and cellulose chromatography. Since free Pyd is the major component of total Pyd in urine, we developed an immunoassay using free Pyd as an immunogen. This assay is much easier to perform than HPLC, requires no sample preparation, and correlates well with total Pyd measurement by HPLC (r = 0.97) and with urinary hydroxyproline (r = 0.90). The antiserum reacts most strongly with free Pyd and Dpd and minimally with glycosylated and large peptide-bound forms. The sensitivity of the Pyd immunoassay is less than 25 nM. The intraassay CV is 5-10%; the interassay CV is 10-15%. Analytic recovery studies indicated negligible sample interference. Furthermore, measurement of the Pyd in the same individuals over a 30 day time period exhibited minimal day-to-day variation. Thus, the Pyd immunoassay provides a rapid and easy method for evaluation of Pyd in urine. Pyd immunoassay may serve as a practical method of screening for metabolic bone disease and for monitoring therapeutic treatment.

Monitoring estrogen replacement therapy and identifying rapid bone losers with an immunoassay for deoxypyridinoline.

We have assessed urinary deoxypyridinoline (Dpd) levels by immunoassay in women who participated in a double-masked, placebo-controlled trial of the bone loss prevention effects of estrogen replacement therapy (ERT). Ninety-one women who had undergone recent surgical menopause were randomized to receive either placebo or 0.025, 0.05 or 0.1 mg/day transdermal 17 beta-estradiol for 2 years. Mean Dpd levels in the postmenopausal women were significantly elevated (p < 0.0001) above mean Dpd levels in a reference population of healthy, premenopausal women. Subjects in the placebo group lost 6.4% of lumbar spine bone mineral density (BMD) and 4.9% of mid-radius bone mineral content (BMC) over 2 years. Dpd levels at baseline were inversely correlated with BMD and BMC changes in the placebo group. The placebo group and subjects receiving 0.025 mg/day 17 beta-estradiol who had Dpd levels increased above the reference interval cut-off (mean + 2 standard deviations, 7.5 nmol/mmol) lost 2 times more bone mass than did those with Dpd levels below it. Dpd levels decreased significantly (p < 0.01) from baseline at 6 months following initiation of treatment with 0.05 or 0.1 mg/day 17 beta-estradiol, changes that correlated with increased lumbar spine BMD and with changes in mid-radius BMC. At 12 months, Dpd levels were lower than baseline and placebo in all three treatment groups. These data suggest utility of this Dpd immunoassay in assessing changes in bone resorption induced by surgical menopause and ERT.