Sr is likely a non-essential trace element, but in recent years, studies have shown that Sr is able to influence bone turnover [20] and has been applied in the form of strontium ranelate in therapeutic treatment of osteoporosis. Sr is chemically very similar to calcium (Ca), and can replace Ca, but still little is known about the role of Sr in normal bone metabolism as well as in bone disorders. Pb is a non-essential trace element and represents a highly toxic heavy metal. One of the main threats to human health from heavy metals is associated with exposure to Pb. Exposure to Pb is associated with chronic diseases in the nervous, this website hematopoietic, skeletal, renal and endocrine systems

[21] and [22]. Pb has been stated also as a potential risk factor for osteoporosis [23] and osteoarthritis [24]. Approximately 95% of the total body Pb burden is stored in skeleton [25] indicating that the bone tissue has a high capacity to accumulate and store Pb. In this context the bone tissue seems to have also the function to keep down the serum levels of such highly toxic elements. Human bone is essentially composed of a non-homogeneous and non-isotropic arrangement of mineralized

collagen fibrils. Cortical and trabecular bones are formed by individual osteons and bone packets (so called bone structural units — BSUs). VE821 They are produced at different moments during the (re)modeling cycle by the coordinated activity of bone cells, whereby the osteoblasts synthesize, secrete and deposit the collagenous matrix, which

then gradually mineralizes. Thus, each BSU has a certain mineral content depending on the time of deposition [26]. In general these BSUs are connected by a thin layer of mineralized non-collagenous proteins, the so called cement line/layer produced during the remodeling cycle [27]. Only very little data are available regarding the detailed spatial distribution of trace elements within such a bone tissue. Thus, the aims of this study were to map the trace elements Zn, Sr and Pb in bone tissue and to elucidate the following questions: i) is there a differential accumulation pattern of Zn, Sr and Pb ID-8 depending on Ca content of mineralized bone matrix in the bone packets, osteons, and interstitial bone? and ii) is the accumulation of Zn, Sr and Pb in cement lines different from that of mineralized bone matrix? Taking into account that the spot size of the confocal SR μ-XRF setup is about 5 times wider than the width of the cement lines the measured intensities are actually a huge underestimate of the real levels of trace elements in this region. For this purpose we analyzed trabecular and cortical bones from human femoral necks and heads using SR μ-XRF in combination with quantitative backscattered electron imaging (qBEI).