3D osteocyte lacunar morphometry of human bone biopsies with high resolution microCT: from monoclonal gammopathy to newly diagnosed multiple myeloma

Abstract

Osteocytes are bone-embedded cells connected via canaliculi and they regulate the bone resorption/formation balance. Osteocyte function is altered in skeletal disorders including cancer. Multiple myeloma (MM) is a hematological malignancy, whereby plasma cells disrupt the bone homeostasis and induce excessive resorption of the mineralized extracellular matrix (ECM), as evidenced by clinical computed tomography (CT). However, morphometric analyses of the mineralized ECM and bone microporosity are not yet performed in patients with MM, nor in the precursor conditions of monoclonal gammopathy of undetermined significance (MGUS) and smoldering MM (SMM). Here, we characterize changes in 3D osteocyte lacunar morphology in bone biopsy samples obtained from patients with MGUS, SMM and newly diagnosed MM, using high resolution microCT. In the small lacunae 20-900 um3 range, we found a trend for lower lacunar density and increasing 50% cutoff of the lacunar volume cumulative distribution for diseased samples. In the larger lacunae 900-3000 um3 range, we found significantly higher lacunar density and microporosity in the MM group compared to the MGUS/SMM group. Regarding the shape distribution, the MGUS/SMM group showed a trend for flatter, more elongated and anisotropic osteocyte lacunae compared to the control group, though the differences were not statistically significant. Altogether, our findings suggest that osteocytes in human MM bone disease undergo changes in their lacunae morphology, which could be an indicator for impaired bone quality. Future studies are needed to show whether these are consistent within comparable anatomical sites and could serve as a diagnostic or prognostic marker.