Comparison of biochemical markers of bone resorption in patients with metabolic and malignant bone diseases

Instability and variability of urinary telopeptides and free crosslinks

BACKGROUND

The use of the urinary bone degradation markers, NTx and free Dpd, in the diagnosis and monitoring of pathological bone resorption has been studied intensely. Urinary NTx and Dpd are normalized by creatinine to account for differences in diuresis.

METHODS

We investigated the effects of storage (-20 degrees C for 119 days) on concentrations of NTx, Dpd and creatinine in the urine of 40 subjects. Precipitates (visible upon thawing) were resuspended, but specimens were not recentrifuged (in contrast to previous experiments).

RESULTS

After storage at -20 degrees C, the NTx and creatinine concentrations in urine specimens were significantly decreased by about 18% and 22% (p < 0.01 and p < 0.0001), respectively. Thus, the quotient of NTx/creatinine was slightly increased after storage (p < 0.05). Free Dpd and free Dpd/creatinine were both significantly increased after storage (p < 0.0001)--by about 20% and 60%, respectively.

CONCLUSIONS

We suggest that storage at -20 degrees C frees Dpd and denatures the epitope used in NTx quantification, and that these changes are usually masked by the removal of free Dpd via recentrifugation and by the decrease in creatinine in NTx/creatinine. Additionally, we suggest that the quotient Dpd/NTx should be evaluated as an alternative to normalizing via creatinine excretion.

Pamidronate increases markers of bone formation in patients with multiple myeloma in plateau phase under interferon-alpha treatment

Bisphosphonates are potent inhibitors of osteoclastic activity and reduce the disease-related skeletal complications when they are used in combination with chemotherapy in patients with multiple myeloma (MM). Pamidronate also inhibits apoptosis of primary osteoblastic cells and probably induces apoptosis on human MM cells and osteoclasts. It has been reported that interferon-alpha (IFN-alpha) decreases bone resorption and that low doses of IFN-alpha result in a significant increase in serum osteocalcin (OSC). The aim of this study was to determine the effects of pamidronate treatment on biochemical markers of bone resorption [cross-linked N-telopeptides of type I collagen (NTx)], bone formation [bone alkaline phosphatase (BAP) and OSC], disease activity [beta2-microglobulin, CRP, paraprotein], and interleukin-6 (IL-6) in patients with MM in plateau phase under IFN-alpha maintenance. The above parameters were evaluated in 28 patients (13 M, 15 F, median age 70 years) during maintenance treatment, before the addition of pamidronate and after 1, 3, 6, 9, 12, and 14 months of the combined therapy. The addition of pamidronate to maintenance treatment resulted in a significant reduction of NTx, IL-6, beta2-microglobulin, CRP from the 3rd month and paraprotein from the 6th month of treatment, whereas BAP and OSC were significantly increased from the 6th month. These changes continued during the 14-month follow-up of the combined treatment. Multivariate analysis showed a significant negative correlation between changes of BAP and OSC and the patients' age. The greater increase of the bone formation markers was observed in younger patients. These results suggest that, in addition to the inhibition of osteoclastic activity, pamidronate in combination with IFN-alpha was shown to induce bone formation in patients with MM in the plateau phase.

Biochemical markers and skeletal metastases

BACKGROUND

Skeletal metastases are common occurrences in patients with malignancies such as breast and prostate carcinoma, but they are difficult to diagnose nonradiologically, and treatment is difficult to follow clinically. Recent developments suggest that biochemical markers of bone remodeling, such as the bone collagen breakdown product N-telopeptide and the bone formation marker known as bone specific alkaline phosphatase, hold great promise as clinical tools for the management of patients with metastatic bone disease.

METHODS

Serum levels of the bone formation marker known as bone specific alkaline phosphatase (BAP), along with serum levels of the bone collagen breakdown product carboxyterminal telopeptide of Type I collagen (ICTP) and urine levels of pyridinoline (PYD), deoxypridinoline (DPD), and N-telopeptide (NTx), were measured in a large cohort of patients with newly diagnosed or progressive cancer of the breast, prostate, lung, and other sites. Bone marker levels were correlated with the presence or absence of bone scan-documented metastases; metastatic disease extension in terms of the number of skeletal sites involved; and the type of lesion, whether blastic or lytic. Sites examined included the pelvis, spine, skull, ribs, and long bones.

RESULTS

All of the bone markers examined, including BAP and NTx, were abnormally elevated in a high proportion of patients with confirmed metastases to bone. Urine NTx levels and bone specific alkaline phosphatase were significantly correlated with the number of skeletal sites involved, and a significant correlation between marker level and extent of skeletal involvement was also observed. In addition, both markers were higher in patients with a blastic disease presentation than in patients with osteolytic lesions.

CONCLUSIONS

Biochemical markers of bone resorption and bone formation are abnormally raised in the blood and urine of patients with metastatic bone disease. Markers of bone collagen breakdown, such as N-telopeptide, as well as markers of osteoblast function, such as bone specific alkaline phosphatase, appear to be of use in assessing and managing patients with malignancies that metastasize to bone. In this study, both NTx and BAP showed a significant correlation with both the presence of bone metastases and the extent of skeletal involvement. Biochemical markers of bone remodeling can also be used to guide decision making regarding the treatment of metastatic bone disease and to determine the effectiveness of therapy for patients with cancer to bone whose broad-based symptoms make it difficult to discern true response to therapy.