Histochemical assessment on osteocytic osteolysis in lactating mice fed with a calcium-insufficient diet

Abstract

Objectives: This study aimed to examine if feeding lactating mice a calcium-insufficient diet while simultaneously administering alendronate (ALN) could potentially induce osteocytic osteolysis.

Methods: Lactating mice were fed calcium (Ca)-insufficient diets with or without ALN administration, and then their femurs were examined for TRAP and ALP, and observed by Kossa staining and transmission electron microscopy (TEM). Mice that had been fed a Ca-insufficient diet were then fed a ⁴⁴Ca-containing diet, and their tibial sections were examined by isotope microscopy.

Results: Mice fed a Ca-insufficient diet had a reduced number of TRAP-positive osteoclasts after ALN administration. ALN-treated, lactating mice fed a Ca-insufficient diet had enlarged lacunae in their cortical bones, and TEM imaging demonstrated expanded regions between osteocytes and lacunar walls. In ALN-treated lactating mice fed a Ca-insufficient diet, huge areas of demineralized bone matrix occurred, centered around blood vessels in the cortical bone. Isotope microscopy showed ⁴⁴Ca in the vicinity of the osteocytic lacunae, and in the broad, previously demineralized region around the blood vessels in the cortical bone of lactating mice fed a ⁴⁴Ca-sufficient diet.

Conclusions: Bone demineralization likely takes place in the periphery of the osteocytic lacunae and in the broad regions around the blood vessels of lactating mice when they are exposed to severely reduced serum Ca through a Ca-insufficient diet coupled with ALN administration.

Keywords: Isotope microscopy; Lactation; Osteocyte; Osteocytic osteolysis; Transmission electron microscopy (TEM).