Spatial distribution of the trace elements zinc, strontium and lead in human bone tissue

TLDR

Trace elements accumulate in bone, yet high‑resolution studies of their local concentrations in bone structural units are scarce, leaving little known about Zn, Sr, and Pb distribution in cortical and trabecular bone. The study aimed to map the distribution and accumulation of Zn, Sr, and Pb in human bone tissue using synchrotron radiation‑induced micro X‑ray fluorescence and quantitative backscattered electron imaging. Fourteen femoral bone samples from osteoporotic fracture patients and healthy controls were analyzed by SR μ‑XRF and qBEI, with fluorescence maps aligned to backscattered electron images and correlated to calcium content. Zn and Pb concentrations were significantly higher in cement lines than surrounding matrix, Pb and Sr levels correlated with mineralization, Zn showed no correlation with calcium, and these patterns reveal differential accumulation mechanisms of Zn, Pb, and Sr in bone structural units.

Abstract

Trace elements are chemical elements in minute quantities, which are known to accumulate in the bone. Cortical and trabecular bones consist of bone structural units (BSUs) such as osteons and bone packets of different mineral content and are separated by cement lines. Previous studies investigating trace elements in bone lacked resolution and therefore very little is known about the local concentration of zinc (Zn), strontium (Sr) and lead (Pb) in BSUs of human bone. We used synchrotron radiation induced micro X-ray fluorescence analysis (SR μ-XRF) in combination with quantitative backscattered electron imaging (qBEI) to determine the distribution and accumulation of Zn, Sr, and Pb in human bone tissue. Fourteen human bone samples (10 femoral necks and 4 femoral heads) from individuals with osteoporotic femoral neck fractures as well as from healthy individuals were analyzed. Fluorescence intensity maps were matched with BE images and correlated with calcium (Ca) content. We found that Zn and Pb had significantly increased levels in the cement lines of all samples compared to the surrounding mineralized bone matrix. Pb and Sr levels were found to be correlated with the degree of mineralization. Interestingly, Zn intensities had no correlation with Ca levels. We have shown for the first time that there is a differential accumulation of the trace elements Zn, Pb and Sr in BSUs of human bone indicating different mechanisms of accumulation.