Quantification of local zinc and tungsten deposits in bone with LA-ICP-MS using novel hydroxyapatite-collagen calibration standards.

Tungsten has recently emerged as a potential toxicant and is known to heterogeneously deposit in bone as reactive polytungstates. Zinc, which accumulates in regions of bone remodeling, also has a heterogenous distribution in bone. Determining the local concentrations of these metals will provide valuable information about their mechanisms of uptake and action. A series of bone (BN), 7:3 hydroxyapatite:collagen (HC), and hydroxyapatite (HA) standards were spiked with tungsten and zinc and used as calibration standards for laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis of bone tissue. The analytical performance of these standards was studied and validated at different step sizes using NIST SRM 1486 Bone Meal. The effect of matrix-matched calibration was assessed by comparing the calibration with BN and HC standards, which incorporate both inorganic and organic components of bone, to that of HA standards. HC standards were found to be more homogenous (RSD < 10%) and provide a linear calibration with better accuracy (R2 > 0.994) compared to other standards. The limits of detection for HC at a 15 µm step size were determined to be 0.24 and 0.012 µg g-1 for zinc and tungsten, respectively. Using this approach, we quantitatively measured zinc and tungsten deposits in the femoral bone of a mouse exposed to 15 µg mL-1 tungsten for four weeks. Localized concentrations of zinc (942 µg g-1) and tungsten (15.7 µg g-1) at selected regions of enrichment were substantially higher than indicated by bulk measurements of these metals.

Addressing K/L-edge overlap in elemental analysis from micro-X-ray fluorescence: bioimaging of tungsten and zinc in bone tissue using synchrotron radiation and laser ablation inductively coupled plasma mass spectrometry.

Synchrotron radiation micro-X-ray fluorescence (SR-µXRF) is a powerful elemental mapping technique that has been used to map tungsten and zinc distribution in bone tissue. However, the heterogeneity of the bone samples along with overlap of the tungsten L-edge with the zinc K-edge signals complicates SR-µXRF data analysis, introduces minor artefacts into the resulting element maps, and decreases image sensitivity and resolution. To confirm and more carefully delineate these SR-µXRF results, we have employed laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to untangle the problem created by the K/L-edge overlap of the tungsten/zinc pair. While the overall elemental distribution results are consistent between the two techniques, LA-ICP-MS provides significantly higher sensitivity and image resolution compared with SR-µXRF measurements in bone. These improvements reveal tissue-specific distribution patterns of tungsten and zinc in bone, not observed using SR-µXRF. We conclude that probing elemental distribution in bone is best achieved using LA-ICP-MS, though SR-µXRF retains the advantage of being a non-destructive method with the capability of being paired with X-ray techniques, which determine speciation in situ. Since tungsten is an emerging contaminant recently found to accumulate in bone, accurately determining its distribution and speciation in situ is essential for directing toxicological studies and informing treatment regimes. Graphical abstract Tungsten and zinc localization and uptake in mouse femurs were imaged by synchrotron radiation, left, and by laser ablation ICP-MS, right. The increased resolution of the LA-ICP-MS technique resolves the problem of the overlap in tungsten's L-edge and zinc's K-edge.

Investigating water interactions with collagen using 2H multiple quantum filtered NMR spectroscopy to provide insights into the source of double quantum filtered signal in tissue.

In an effort to provide insight into the molecular origins of the (2)H double quantum filtered (DQF) NMR signal observed in connective tissue, specifically spinal disc tissue, (2)H multiple quantum filtered (MQF) NMR spectroscopy is used to study the structure and dynamics of D2O in collagen as a function of hydration. Residual quadrupolar coupling constants are measured and decrease from 3500 to 20 Hz while T2 relaxation times increase from 0.65 to 20 ms as hydration increases. Analysis of the data indicates that the quadrupolar coupling and T2 relaxation arises when water molecules spend time in restricted environments. The residual quadrupolar coupling is influenced almost exclusively by the most restricted water sites, the clefts of the triple helices not exposed on the surface of the fibrils, while the T2 relaxation has secondary contributions from less restricted water environments. The magnitudes of the measured values are consistent with results from DQF NMR studies of spinal disc tissue, supporting the assertion that water binding to collagen is a major contributor to the DQF NMR signal observed in spinal disc tissue.