Synchrotron-Micro-XRF Imaging of human bone

Trace elements are chemical elements in minute quantities and are found naturally in the environment and human exposure derives from a variety of sources. While some trace elements are important to human health, there is a growing body of literature on the role of toxic trace elements, such as lead (Pb) in the development of numerous diseases. Pb is predominantly accumulated in the skeleton, where approximately 95 percent of the total body burden of Pb is present. Within the frame of the previous FWF project P15740 "Determination of Lead in Human Bone and Tissue" the use of Synchrotron radiation (SR) in combination with a confocal Microscopic X-ray fluorescence analysis (micro-XRF) setup proved to be an ideal instrumentation to determine the distribution of the trace elements lead (Pb), zinc (Zn), Strontium (Sr) and calcium (Ca) in normal human bone. A highly specific accumulation of Pb and Zn was discovered in the so called tidemark, the transition zone between calcified and non-calcified articular cartilage. However, very little is known about the role and exact mechanisms of Pb accumulation in the tidemark of normal articular cartilage and bone. Moreover, even less is known about a potential role of trace elements in common musculoskeletal diseases such as osteoarthritis and osteoporosis. In osteoarthritis duplication of the tidemark, has been thought of a metabolically active calcification front, are seen. A pilot study has shown a differential accumulation of trace elements in double tidemarks of osteoarthritic human samples when compared to normals. While the exposure of Pb is associated with low bone mass, to date little is known at what stage of the bone matrix mineralization process Pb is incorporated in bone, and if there are spatial differences in Pb accumulation within the bone tissue. Moreover, very little is known about the speciation of Pb in the tidemark of normal articular cartilage and bone. The aims of this project are to analyze the distribution and concentrations of lead (Pb), zinc (Zn), strontium (Sr) and calcium (Ca) in articular cartilage and bone from osteoarthritic and osteoporotic human femoral heads using SR micro-XRF from as well as laboratory based -XRF. All elemental maps will be correlated with backscattered electron images of the investigated region and data will then be compared to levels from previously analyzed bone samples from normal, healthy adults. Moreover, a speciation of Pb in the investigated calcified tissue (i.e. calcified articular cartilage, subchondral) to determine the chemical bindings of these elements will be performed using X-ray absorption near edge structure (XANES). We expect the altered bone turnover in osteoarthritis and osteoporosis to have a profound effect on the distribution of trace elements in calcified articular cartilage as well as subchondral bone. Our research may shed light on the potential role of local Pb in the development of osteoarthritis and osteoporosis. Moreover, we hope to gain further insight into the role of trace elements in bio-mineralization

During the project human tissue samples (bone and cartilage) were analysed using synchrotron-radiation induced micro X-ray fluorescence analysis (SR -XRF) with respect to the spatial distribution of the trace elements zinc (Zn), strontium (Sr) and lead (Pb) and the main element calcium (Ca). Furthermore, the chemical bonding of lead in the bone matrix has been identified by means of X-ray absorption spectroscopy (XAS). The measurements were performed at two different synchrotron radiation facilities (HASYLAB, Hamburg and ANKA, Karlsruhe, Germany). Since beam time is limited at these institutions and hard to get, a laboratory based confocal ?-XRF system with a low-power X-ray tube (50 W) was tested, to see if it can be used for prescreening the samples of future SR ?-XRF studies. The histological characteristics of the inspected bone areas were determined by quantitative backscattered electron microscopy (qBEI).Analysing tissue samples with these highly sensitive methods trace elements that may be essential to the organism, not essential or even harmful in very small amounts (g/g) can be detected. About 95% of the toxic element lead (Pb) in the human body is stored in the skeleton. Zn is a part of many enzymes and is involved in bone resorption.It could be shown that the distribution and amount of Zn, Sr, and Pb is strongly correlated with the bone structure. The cement lines (borders between bone packets) showed significant accumulations of Zn and Pb, compared to the neighbouring bone matrix. The bone packets showed a disproportionate increase of Sr and Pb with respect to the Ca content. However the altered bone metabolism in osteoporosis does not seem to influence the trace elements distribution and quantity.In the case of osteoarthritis, there is a doubling of the boundary layer between the mineralized and non- mineralized cartilage - the so-called tidemark (TM). In both, the inner and the outer TM, Pb and Zn amounts were found to be significantly increased compared to the underlying bone tissue. The amount of Pb in the outer TM was smaller than in the inner TM. This suggests that Pb is incorporated in the course of time, and Zn is an essential part of the TMs. In the case of degenerative bone and joint diseases the Pb stored in the bones and the TM might be released again long after the initial Pb exposure and damage sensitive organs such as the nervous system.Moreover, samples from patients without any known bone diseases were analysed by XAS to determine the chemical bonding state of Pb. It turned out that Pb in the TM and in the bones is bonded to carbonated calcium hydroxyapatite.The confocal ?-XRF system in the laboratory was tested with samples that were also measured at the synchrotron, and despite the not optimal measurement conditions in the laboratory, it has proven to be an easy accessible pre-screening tool for future SR ?-XRF measurements.