Long‐term oral pamidronate treatment inhibits osteoclastic bone resorption and bone turnover without affecting osteoblastic function in multiple myeloma

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Abstract
This study was performed as a cross‐sectional substudy to the Danish–Swedish Pamidronate Study, a randomized placebo‐controlled multicentre trial in multiple myeloma. The purpose was to evaluate the biological effects of long‐term treatment with oral pamidronate 300 mg daily on bone metabolism by using histomorphometry and analysis of cytokines and biochemical markers of bone turnover. Sixteen patients were included after median 27.5 months of protocolized treatment; 10 patients received active treatment and 6 patients placebo. When compared with placebo, pamidronate treatment was associated with: (a) marked decreased osteoclastic resorption rate (0.86±0.59 μm/d vs. 5.7±5.0 μm/d, p=0.002), and diminished activation frequency (0.20±0.18 yr−1 vs. 0.72±0.55 yr−1, p=0.014); (b) compensatory reduced volume referent bone formation rate (0.17±0.21 yr−1 vs. 0.71±0.54 yr−1, p=0.007), but unaltered mineral appositional rate; (c) neutral (–0.66±5.6 mm) vs. negative (–2.15±2.2 μm, p=0.013) bone balance per remodelling cycle; (d) higher trabecular bone volume (21.0±6.2% vs. 13.0±3.7%, p=0.01); (e) suppressed urinary excretion and serum levels of some of the biochemical markers of bone metabolism; and (f) significant reduction of circulating soluble interleukin‐6 receptor (IL‐6sR) (25.9±4.1 ng/ml vs. 32.1±6.6 ng/ml, p=0.04), and (g) a uniform tendency of lower serum and marrow plasma levels of IL‐6, IL‐1β, and TNFα. Thus oral pamidronate was absorbed in biologically active amounts, and reduced overall bone resorption and bone turnover without impairing osteoblastic bone formation. The observation that cytokine and cytokine receptor levels were reduced extends the possible and potential beneficial actions of bisphosphonates in multiple myeloma.