Quantification of the N-terminal propeptide of human procollagen type I (PINP): comparison of ELISA and RIA with respect to different molecular forms

Insulin Resistance and Bone Metabolism Markers in Women with Polycystic Ovary Syndrome: A Cross-Sectional Study on Females from the Islamic University Medical Center

Background and Objectives: polycystic ovarian syndrome (PCOS) prevails in females in the 18-40-year-old age group and varies from 5-20% depending on the demographic and diagnostic standards. It is unknown how long passes between the onset of a specific symptom and the appearance of the disease. The three most significant characteristics of PCOS include irregular menstruation, a polycystic ovarian shape found by pelvic ultrasound, and hyperandrogenism, which could possibly delay menarche. This study's objective was to assess insulin resistance and bone bio-markers' metabolism-involved characteristics of females with PCOS. Materials and Methods: We present a cross-sectional study carried out on 100 female patients suffering from PCOS and 100 healthy female subjects as a control living in Saudi Arabia in the Al-Madinah Al-Munawara Region between May 2021 and March 2022. The age of the studied groups ranges from 20-40 years, and patients were categorized into three groups; group I (control, n = 100), group IIa (overweight or obese females with PCOS, n = 70), and group IIb (non-obese females with PCOS, n = 30). The diagnosis of PCOS was carried out as per Rotterdam criteria as recommended for adolescent and adult subjects. All the groups were subjected to physical examination, and anthropometric measures, biochemical parameters, endocrine activity, and clinical parameters were determined. The data obtained were computerized and analyzed statistically using the SPSS program for range, mean, and standard deviation. ANOVA test with post hoc Tukey test was applied to assess the pattern and variation among the test and control groups. Results: In the present study, age, waist circumstances, systolic blood pressure, and diastolic blood pressure were reported enhanced in the PCOS over the control group. Additionally, anthropometric measures were reported slightly upregulated in group IIa over group IIb (p < 0.001). Biochemical parameters including glucose, insulin incidence, and lipids were reported higher in the PCOS over the control group, where group IIa showed slightly increased values compared to group IIb (p < 0.001). On the contrary, PTH, Ca+2, and 25(OH)D levels were reported lower in the PCOS over the control group. However, in the control groups, a slight variation was reported as higher in group IIa compared to group II. In the study, PTH and 25(OH)D were found associated with bone metabolism; a lower level of PTH and 25 (OH) D is linked with a decline in bone density. Conclusions: Lower serum levels of PINP and osteocalcin along with the 25(OH)D were associated with the PCOS compared to the control group, imposing a higher risk of the syndrome. On the contrary, an elevated level of NTx in groups IIa and IIb over the control group was associated with insulin resistance and bone metabolism.

Quantitative lateral flow immunoassay for rapid detection of procollagen type I N-terminal propeptide in the monitoring of osteoporosis treatment

Appropriate follow-up after treatment initiation in patients with osteoporosis is challenging. Serum biomarkers may offer more efficient monitoring of bone mineral density (BMD) than the currently used dual X-ray absorptiometry; however, significant changes in BMD often occur over at least 12 months. During teriparatide treatment for osteoporosis, monitoring with markers such as procollagen type I propeptide (PINP), which is derived from osteoblasts, can provide clinically useful information for disease management. However, rapid and cost-effective methods for detecting serum PINP are lacking, necessitating a point-of-care test (POCT) for enhanced follow-up efficiency in osteoporosis management. For the quantitative detection of PINP, we developed a high-sensitivity lateral flow immunoassay with a stacking pad (sLFIA). We established a calibration equation based on the test line/control line ratio obtained from our PINP sLFIA results of various nonspiked serum samples to calculate the PINP concentrations in 40 serum samples and compared the result with those obtained using a fully automated electrochemiluminescence immunoassay. PINP concentrations between these two methods exhibited excellent correlation (R = 0.991). In addition, we assessed the serum PINP concentrations of patients with osteoporosis treated with teriparatide. At the 3-month follow-up, their PINP levels were nearly twice as high as those at baseline, thus implying that our method can be used for osteoporosis treatment monitoring. Our findings thus indicate that the PINP sLFIA can serve as a POCT for monitoring medication response and managing osteoporosis.

Development of a Chemiluminescence Assay for Total N-Terminal Propeptide of Type I Collagen and Its Evaluation in Lung Transplantation

Serum P1NP, one of the important biomarkers for bone turnover, is commonly used for the prediction of bone fracture and the prognosis of osteoporosis after therapy. We developed a P1NP chemiluminescence assay and evaluated changes in bone metabolism markers in lung transplant patients. The screened 2 P1NP antibodies with constructed antigens and α-1 chain antigens expressed by the Corynebacterium glutamate expression system were applied into assay development. The assay performance was evaluated to examine the reliability. A normal Q-Q plot was used to establish male reference interval. Changes of bone metabolism markers before and after lung transplantation in 19 patients were evaluated. The linear factor R of P1NP reagent was greater than 0.99. The limit of detection was 3.32 ng/ml. The precision of the three batches of P1NP reagents was lower than 8%. Method comparison with Roche P1NP reagent showed that the correlation coefficient R ² was 0.91. In the monitoring of bone mass in a short time, bone metabolism markers can better indicate the change of bone mass, while the traditional bone mineral density detection is lagging behind the bone metabolism markers. P1NP and β-CrossLap to bone mass change in patients after lung transplantation, and P1NP and β-CrossLap are very good clinical markers for bone mass monitoring.

Analytical considerations and plans to standardize or harmonize assays for the reference bone turnover markers PINP and β-CTX in blood

Procollagen type I N-propeptide (PINP) and the C-terminal telopeptide of type I collagen (β-CTX) in blood have been designated as reference bone turnover markers in osteoporosis by the International Osteoporosis Foundation (IOF) and International Federation of Clinical Chemistry and Laboratory Medicine (IFCC). The IFCC Committee on Bone Metabolism (C-BM) has examined current commercial assays and performed a multicentre study to examine the agreement between assays for PINP and β-CTX in serum and plasma. The results of these studies will inform our work towards the harmonization of PINP assays and the standardization of β-CTX assays in blood, with the development of common calibrators and reference measurement procedures in collaboration with the reagent manufacturing industry. Successful achievement of these goals will help develop universally acceptable practice guidelines for the management of osteoporosis with the inclusion of common reference intervals and treatment targets for PINP and β-CTX.

Algogenic substances and metabolic status in work-related Trapezius Myalgia: a multivariate explorative study

BACKGROUND

This study compares the levels of algesic substances between subjects with trapezius myalgia (TM) and healthy controls (CON) and explores the multivariate correlation pattern between these substances, pain, and metabolic status together with relative blood flow changes reported in our previous paper (Eur J Appl Physiol 108:657-669, 2010).

METHODS

43 female workers with (TM) and 19 females without (CON) trapezius myalgia were - using microdialysis - compared for differences in interstitial concentrations of interleukin-6 (IL-6), bradykinin (BKN), serotonin (5-HT), lactate dehydrogenas (LDH), substance P, and N-terminal propeptide of procollagen type I (PINP) in the trapezius muscle at rest and during repetitive/stressful work. These data were also used in multivariate analyses together with previously presented data (Eur J Appl Physiol 108:657-669, 2010): trapezius muscle blood flow, metabolite accumulation, oxygenation, and pain development and sensitivity.

RESULTS

Substance P was significantly elevated in TM (p=0.0068). No significant differences were found in the classical algesic substances (p: 0.432-0.926). The multivariate analysis showed that blood flow related variables, interstitial concentrations of metabolic (pyruvate), and algesic (BKN and K+) substances were important for the discrimination of the subjects to one of the two groups (R2: 0.19-0.31, p<0.05). Pain intensity was positively associated with levels of 5-HT and K+ and negatively associated with oxygenation indicators and IL-6 in TM (R2: 0.24, p<0.05). A negative correlation existed in TM between mechanical pain sensitivity of trapezius and BKN and IL-6 (R2: 0.26-0.39, p<0.05).

CONCLUSION

The present study increased understanding alterations in the myalgic muscle. When considering the system-wide aspects, increased concentrations of lactate, pyruvate and K+ and decreased oxygenation characterized TM compared to CON. There are three major possible explanations for this finding: the workers with pain had relatively low severity of myalgia, metabolic alterations preceded detectable alterations in levels of algesics, or peripheral sensitization and other muscle alterations existed in TM. Only SP of the investigated algesic substances was elevated in TM. Several of the algesics were of importance for the levels of pain intensity and mechanical pain sensitivity in TM. These results indicate peripheral contribution to maintenance of central nociceptive and pain mechanisms and may be important to consider when designing treatments.

Local administration of growth hormone stimulates tendon collagen synthesis in elderly men

Tendon collagen content and circulating growth hormone (GH) are reduced in elderly. In a placebo-controlled, double-blinded study, we examined if local injections of rhGH enhance collagen synthesis in healthy elderly men (61 ± 1 yr). Two injections of rhGH or saline (control) were injected into each of the patient's patellar tendons, respectively. Subsequently, tendon collagen fractional synthesis rate (FSR) and an indirect marker of type I collagen synthesis (PINP) were measured. Within the first 6 h after the last injections, a tendency towards a higher tendon collagen FSR was observed in 10 out of 12 subjects ( P = 0.08). Similarly, PINP was higher 3–4 h after the last GH injection ( P = 0.05). Serum IGF-I did not change from baseline, whereas peritendinous bioactive IGF-I was higher in the GH leg vs. control ( P = 0.05). In conclusion, local injections of rhGH increase tendon collagen synthesis in humans, either directly or indirectly by increasing local bioactive IGF-I.

Local administration of insulin-like growth factor-I (IGF-I) stimulates tendon collagen synthesis in humans

Collagen is the predominant structural protein in tendons and ligaments, and can be controlled by hormonal changes. In animals, injections of insulin-like growth factor I (IGF-I) has been shown to increase collagen synthesis in tendons and ligaments and to improve structural tissue healing, but the effect of local IGF-I administration on tendon collagen synthesis in human has not been studied. The purpose of this study was to study whether local injections of IGF-I would have a stimulating effect on tendon collagen synthesis. Twelve healthy nonsmoking men [age 62 ± 1 years (mean ± SEM), BMI 27 ± 1] participated. Two injections of either human recombinant IGF-I (0.1 mL Increlex©) or saline (control) into each patellar tendon were performed 24-h apart, respectively. Tendon collagen fractional synthesis rate (FSR) was measured by stable isotope technique in the hours after the second injection. Simultaneously, interstitial peritendinous (IGF-I) and [procollagen type I N-terminal propeptide (PINP)], as a marker for type I collagen synthesis, were determined by microdialysis technique. Tendon collagen FSR and PINP were significantly higher in the IGF-I leg compared with the control leg (P < 0.05). In conclusion, local IGF-I administration can directly enhance tendon collagen synthesis both within and around the human tendon tissue.

Circulating CO3-610, a degradation product of collagen III, closely reflects liver collagen and portal pressure in rats with fibrosis

Background

Hepatic fibrosis is characterized by intense tissue remodeling, mainly driven by matrix metalloproteinases. We previously identified CO3-610, a type III collagen neoepitope generated by matrix metalloproteinase (MMP)-9, and tested its performance as a fibrosis marker in rats with bile-duct ligation. In this study, we assessed whether CO3-610 could be used as a surrogate biomarker of liver fibrosis and portal hypertension in carbon tetrachloride-induced experimental fibrosis.

Results

For this study, 68 Wistar rats were used. Serum CO3-610 was measured by ELISA. Liver fibrosis was quantified by Sirius red staining. Serum hyaluronic acid (HA) was measured with a binding-protein assay. Gene expression of collagens I and III, Mmp2 and Mmp9, and tissue inhibitors of matrix metalloproteinase 1 (Timp1) and 2(Timp2) was quantified by PCR. Hemodynamic measurements were taken in a subgroup of animals. A close direct relationship was found between serum CO3-610 and hepatic collagen content (r = 0.78; P < 0.001), superior to that found for serum HA (r = 0.49; P < 0.05). CO3-610 levels in rats with severe fibrosis (43.5 ± 3.3 ng/mL, P < 0.001) and cirrhosis (60.6 ± 4.3 ng/mL, P < 0.001) were significantly higher than those in control animals (26.6 ± 1.3 ng/mL). Importantly, a highly significant relationship was found between serum CO3-610 and portal hypertension (r = 0.84; P < 0.001). Liver Mmp9 expression increased significantly in fibrotic animals but decreased to control levels in cirrhotic ones.

Conclusions

Circulating CO3-610 behaves as a reliable indicator of hepatic remodeling and portal hypertension in experimental fibrosis. This peptide could ultimately be a useful marker for the management of liver disease in patients.

Effect of administration of oral contraceptives in vivo on collagen synthesis in tendon and muscle connective tissue in young women

Women are at greater risk than men for certain kinds of diseases and injuries, which may at least partly be caused by sex hormonal differences. We aimed to test the influence of estradiol in vivo on collagen synthesis in tendon, bone, and muscle. Two groups of young, healthy women similar in age, body composition, and exercise-training status were included. The two groups were either habitual users of oral contraceptives exposed to a high concentration of synthetic estradiol and progestogens (OC, n = 11), or non-OC-users tested in the follicular phase of the menstrual cycle characterized by low concentrations of estradiol and progesterone (control, n = 12). Subjects performed 1 h of one-legged kicking exercise. The next day collagen fractional synthesis rates (FSR) in tendon and muscle connective tissue were measured after a flooding dose of [(13)C]proline followed by biopsies from the patellar tendon and vastus lateralis in both legs. Simultaneously, microdialysis catheters were inserted in vastus lateralis and in front of the patellar tendon for measurement of insulin-like growth factor I (IGF-I) and its binding proteins. Serum NH(2)-terminal propeptide of type I collagen (PINP) and urine COOH-terminal telopeptides of type-I collagen (CTX-I) were measured as markers for bone synthesis and breakdown, respectively. Tendon FSR and PINP were lower in OC compared with control. An increase in muscle collagen FSR postexercise was only observed in control (P < 0.05). Furthermore, the results indicate a lower bioavailability of IGF-I in OC. In conclusion, synthetic female sex hormones administered as OC had an inhibiting effect on collagen synthesis in tendon, bone, and muscle connective tissue, which may be related to a lower bioavailability of IGF-I.

Ethinyl oestradiol administration in women suppresses synthesis of collagen in tendon in response to exercise

Women are at greater risk than men of sustaining certain kinds of injury and diseases of collagen-rich tissues. To determine whether a high level of oestradiol has an acute influence on collagen synthesis in tendons at rest and in response to exercise, one-legged kicking exercise was performed for 60 min at 67% of maximum power by healthy, young oral contraceptive (OC) users when circulating synthetic (ethinyl) oestradiol was high (n = 11, HE-OC) and compared to similar women who had never used OCs when circulating endogenous oestrogen was low (n = 12, LE-NOC). Interstitial fluid was collected 24 h post-exercise through microdialysis catheters placed anterior to the patellar tendon in both legs and subsequently analysed for the amino-terminal propeptide of type I collagen (PINP), a marker of tendon collagen synthesis. To determine the long-term effect of OC usage, patellar tendon cross-sectional area (CSA) was measured by magnetic resonance imaging (MRI). A lower exercise-induced increase in tendon collagen synthesis was observed in HE-OC than in LE-NOC (DeltaPINP (mean +/- s.e.m.) 1.5 +/- 5.3 versus 24.2 +/- 9.4 ng ml(-1), P < 0.05). Furthermore, serum and the interstitial peritendinous tissue concentrations of insulin-like growth factor I (IGF-I) and IGF-binding proteins showed a reduced bioavailability in HE-OC compared with results in LE-NOC. No difference in patellar tendon CSA was observed between groups. In conclusion, the selective increase in tendon collagen synthesis in LE-NOC but not HE-OC 24 h post-exercise is consistent with the hypothesis that oestradiol inhibits exercise-induced collagen synthesis in human tendon. The mechanism behind this is either a direct effect of oestradiol, or an indirect effect via a reduction in levels of free IGF-I. However, the data did not indicate any long-term effect on tendon size associated with chronic OC use.

Changes of biochemical markers of bone turnover and YKL-40 following hormonal treatment for metastatic prostate cancer are related to survival

PURPOSE

Elevated serum levels of biochemical markers of bone turnover and YKL-40 in patients with metastatic prostate cancer (PC) at the time of diagnosis are associated to poor prognosis. In this study, we evaluated the value of these biomarkers in monitoring the patients during hormonal treatment.

EXPERIMENTAL DESIGN

Serum procollagen type I N-terminal propeptide (PINP), bone-specific alkaline phosphatase (BAP), CTX-I, and YKL-40 were determined by ELISA in a longitudinal study of 106 patients with metastatic PC during treatment with total androgen ablation or parenteral estrogen. Serum samples were collected with 3 months interval. Median observation time was 4.9 years (range, 3.6-6.2). A total of 78 patients died (64 within 7 months following the last blood sampling).

RESULTS

After 6 months treatment, serum PINP, BAP, and YKL-40 decreased (P < 0.0001), but not serum CTX-I compared with baseline values. Univariate Cox analysis showed that serum PINP at 6 months [log transformed and treated as a continuous variable; hazard ratio (HR), 2.2; P < 0.0001], serum BAP (HR, 1.8; P < 0.0001), and serum CTX-I (HR, 2.4; P < 0.0001), but not serum YKL-40 (HR, 1.4; P = 0.16) were associated with survival. Multivariate Cox analysis including the biomarkers 6 months after the start of treatment showed that Soloway score (HR, 3.9; P = 0.013), WHO tumor grade (HR, 3.9; P = 0.004), and serum PINP (HR, 2.2; P < 0.0001) were independent prognostic variables of survival. Scoring the biomarkers during treatment as time-dependent covariates in univariate Cox regression analysis showed that increases in serum PINP (HR, 2.0; P < 0.0001), BAP (HR, 2.1; P < 0.0001), and YKL-40 (HR, 2.1; P < 0.0001) were predictors of early death.

CONCLUSIONS

Serial monitoring of serum PINP, BAP, CTX-I, and YKL-40 in metastatic PC patients during hormonal treatment provided information of prognosis.

Increased levels of interstitial potassium but normal levels of muscle IL-6 and LDH in patients with trapezius myalgia

The mechanisms behind the development of work-related trapezius pain are suggested to involve both peripheral and central components, but the specific contribution of alterations in muscle nociceptive and other substances is not clear. Female patients with chronic trapezius myalgia (N=19; TM) and female controls (N=20; CON) were studied at rest, during 20 min repetitive low-force exercise and recovery, and had their interstitial concentrations of potassium (K(+)), lactate dehydrogenase (LDH), interleukin-6 (IL-6) and collagen turnover determined in the trapezius muscle by the microdialysis technique. K(+) levels were at all time points higher in TM than in CON (P<0.0001). Baseline levels of LDH and IL-6 were similar in both groups. In response to exercise pain intensity, rated perceived exertion, and the concentrations of K(+), LDH and IL-6 increased significantly in both groups. [K(+)] immediately decreased to baseline levels in CON but remained elevated during the first 20 min of recovery in TM (P<0.01) whereafter it returned to baseline level. In all subjects taken together mean [K(+)] correlated negatively with pressure pain threshold of trapezius (P<0.001), positively with mean pain intensity VAS (P<0.001) and mean perceived exertion (P<0.001). Rises in muscle LDH and IL-6 as well as the anabolic ratio for collagen type I was not significantly different between groups. In conclusion, patients with chronic pain in the trapezius muscle had increased levels of interstitial potassium. This finding could be causally related to myalgia or secondary to pain due to deconditioned muscle or altered muscle activity pattern.

Enhanced procollagen processing in skeletal muscle after a single bout of eccentric loading in humans

Increases in procollagen processing within skeletal muscle have previously been reported in small animal models only. While indirect measurements in humans have suggested an increase procollagen processing, no intra-skeletal muscle measurements have confirmed these findings. In this study, eight young healthy male subjects performed a single bout of unaccustomed high intensity eccentric exercise on one leg, with the contralateral leg being the control. A significant increase in the muscle interstitial concentration of the N-terminal propeptide of procollagen type I (PINP) was observed (day 0: 1.96 +/- 0.44 ng ml(-1), day 2: 1.94 +/- 0.32 ng ml(-1), day 4: 3.90 +/- 1.03 ng ml(-1), day 8: 7.23 +/- 2.34 ng ml(-1)*, *P < 0.05 vs. basal and control) with no change being noted in the control leg. By day 2 post-exercise, an increase in the histological immunoreactivity of PINP and the N-terminal propeptide of procollagen type III (PIIINP) was also shown in the exercising leg only. Further, from day 2 post-exercise, immunoreactivity for tenascin C and reactive macrophages (CD68+ cells) was seen within the perimysial and endomysial connective tissue of the exercising leg only, indicating a high mechanical load and inflammation. This study shows that following a single bout of high intensity eccentric exercise there is an increase in procollagen processing within skeletal muscle in humans.

Connective tissue responses in acute community-acquired pneumonia

Circulating connective tissue components including the aminoterminal propeptides of type III collagen (PIIINP), type I collagen (PINP) and hyaluronan were determined in patients hospitalised for pneumonia of suspected bacterial origin. Ninety patients were included, 64 of these were followed prospectively for up to 21 days after initiation of therapy. Serum PIIINP was determined by RIA, s-PINP by ELISA, and s-hyaluronan by a radiometric assay. S-PIIINP rose significantly above the zero value within 24 h in both pneumococcal pneumonia (T0: 5.3 microg/l, 95% CI: 2.7-8.1 microg/l vs. T1: 6.7 microg/l, 95% CI: 3.8-9.1, P<0.01) and in pneumonia of unknown aetiology (T0: 4.0 microg/l, 95% CI: 3.6-4.8 vs. T1: 4.5 microg/l, 95% CI: 3.8-5.1, P<0.05) followed by a gradual decline. At T1, S-PIIINP was higher in pneumococcal pneumonia compared with pneumonia of unknown aetiology (P<0.05). By contrast, s-PINP tended to decline within 24 h in both pneumococcal pneumonia (T1: 30 microg/l, 95% CI: 23-40, ns) and in pneumonia of unknown aetiology (T1: 32 microg/l, 95% CI: 22-42, ns) followed by a steady increase. The PINP antigen size distribution remained constant throughout the follow-up period. S-hyaluronan in pneumococcal pneumonia paralleled s-PIIINP reaching a peak value on day 1 (121 microg/l, 95% CI: 65-191, P=0.38). There was a positive correlation between s-PIIINP and C-reactive protein (CRP). The study demonstrates, that community-acquired pneumonia elicits a differentiated mesenchymal response, which is turned down in response to successful antibiotic therapy.

Extracellular matrix building marked by the N-terminal propeptide of procollagen type I reflect aggressiveness of recurrent breast cancer

The purpose of our study was to examine the association between extracellular matrix homeostasis and aggressive breast cancer as reflected by the synthesis of type I collagen marked by circulating concentration of the aminoterminal propeptide of type I procollagen (PINP). Pre-therapeutic serum PINP concentrations were measured in 154 healthy women and 100 patients referred with their first metastatic manifestation of breast cancer and correlated to the metastatic pattern, response to therapy, time to progression and survival with a minimal follow-up of 5 years. Fifty-four percent of the patients had serum PINP concentrations greater than the 95th percentile of the healthy controls and 38% were high PINP level patients with values clearly outside normal range (>125 ng/ml). Patients with high PINP levels were more sick (p = 0.002), had a higher tumor burden (p = 0.013) and revealed a lower responsiveness to anthracycline-based therapy (p = 0.0002) as well as an accelerated time to disease progression (p = 0.00001) and death (p = 0.0006). Median survival in the high serum PINP level group was less than half of that in the group with low PINP level (14.5 vs. 32 months). The lowest PINP levels were seen when the cancer was restricted to the lymph node and skin and increasing PINP levels were found if the cancer had spread to the lungs, the bones, the bone marrow and the liver. High PINP level at recurrence and lack of estrogen receptors (ER) independently reflected aggressive tumor behavior after recurrence with an equal great impact on time to progression and survival. Patients with a high PINP level and primarily ER-negative tumors survived a median of only 6 months with no one alive after 22 months. By contrast patients with a low PINP level and ER-positive tumors had a median survival of 37 months and 23% were still alive after 5 years. Aggressive breast cancer induces a strong fibroproliferative response with synthesis of type I collagen. Serum PINP levels may be a diagnostic and prognostic tool that indicate breast cancer activity, aggressiveness, expansion and metastasis and a predictor of outcome after anthracycline-based chemotherapy.

Clinical Utility of Biochemical Markers of Bone Remodeling

Remodeling is essential for bone health. It begins with resorption of old bone by osteoclasts, followed by the formation of new bone by osteoblasts. Remodeling is coupled (formation is linked to resorption). After middle age or perhaps beginning earlier, bone loss occurs because resorption exceeds formation. This imbalance is accentuated by estrogen deficiency as well as by many diseases and conditions. Biochemical markers that reflect remodeling and can be measured in blood or urine include resorption markers (e.g., collagen cross-links) and formation markers (e.g., alkaline phosphatase).

Bone markers exhibit substantial short-term and long-term fluctuations related to time of day, phase of the menstrual cycle, and season of the year, as well as diet, exercise, and anything else that alters bone remodeling. These biological factors, in addition to assay imprecision, produce significant intra- and interindividual variability in markers.

Bone marker measurements are noninvasive, inexpensive, and can be repeated often. Unfortunately, most of the studies that provided insight on clinical situations did not focus on markers as a primary endpoint. Bone markers have been useful in clinical practice and have been helpful in understanding the pathogenesis of osteoporosis and the mechanism of action of therapies. In clinical trials, markers aid in selecting optimal dose and in understanding the time course of onset and resolution of treatment effect. Clinical questions that might be answered by bone markers include diagnosing osteoporosis, identifying “fast bone losers” and patients at high risk of fracture, selecting the best treatment for osteoporosis, and providing an early indication of the response to treatment. Additional information is needed to define specific situations and cut points to allow marker results to be used with confidence in making decisions about individual patients.