Characterization of the depth distribution of Ca, Fe and Zn in skin samples, using synchrotron micro-x-ray fluorescence (SμXRF) to help quantify in-vivo measurements of elements in the skin

MeXpose-A Modular Imaging Pipeline for the Quantitative Assessment of Cellular Metal Bioaccumulation

MeXpose is an end-to-end image analysis pipeline designed for mechanistic studies of metal exposure, providing spatial single-cell metallomics using laser ablation-inductively coupled plasma time-of-flight mass spectrometry (LA-ICP-TOFMS). It leverages the high-resolution capabilities of low-dispersion laser ablation setups, a standardized approach to quantitative bioimaging, and the toolbox of immunohistochemistry using metal-labeled antibodies for cellular phenotyping. MeXpose uniquely unravels quantitative metal bioaccumulation (sub-fg range per cell) in phenotypically characterized tissue. Furthermore, the full scope of single-cell metallomics is offered through an extended mass range accessible by ICP-TOFMS instrumentation (covering isotopes from m/z 14-256). As a showcase, an ex vivo human skin model exposed to cobalt chloride (CoCl2) was investigated. For the first time, metal permeation was studied at single-cell resolution, showing high cobalt (Co) accumulation in the epidermis, particularly in mitotic basal cells, which correlated with DNA damage. Significant Co deposits were also observed in vascular cells, with notably lower levels in dermal fibers. MeXpose provides unprecedented insights into metal bioaccumulation with the ability to explore relationships between metal exposure and cellular responses on a single-cell level, paving the way for advanced toxicological and therapeutic studies.

Investigation of the accuracy of a portable109Cd XRF system for the measurement of iron in skin

We have previously reported the design of a portable109Cd x-ray fluorescence (XRF) system to measure iron levels in the skin of patients with either iron overload disease, such as thalassemia, or iron deficiency disease, such as anemia. In phantom studies, the system was found to have a detection limit of 1.35μg Fe per g of tissue for a dose of 1.1 mSv. However, the system must provide accurate as well as precise measurements of iron levels in the skin in order to be suitable for human studies. The accuracy of the system has been explored using several methods. First, the iron concentrations of ten pigskin samples were assessed using both the portable XRF system and ICP-MS, and the results were compared. Overall, it was found that XRF and ICP-MS reported average values for iron in skin that were comparable to within uncertainties. The mean difference between the two methodologies was not significant, 2.5 ± 4.6μg Fe per g. On this basis, the system could be considered accurate. However, ICP-MS measurements reported a wider range of values than XRF, with two individual samples having ICP-MS results that were significantly elevated (p < 0.05) compared to XRF. SynchrotronμXRF maps of iron levels in pigskin were acquired on the BioXAS beam line of the Canadian Light Source. TheμXRF maps indicated two important features in the distribution of iron in pigskin. First, there were small areas of high iron concentration in the pigskin samples, that were predominantly located in the dermis and hypodermis at depths greater than 0.5 mm. Monte Carlo modelling using the EGS 5 code determined that if these iron 'hot spots' were located towards the back of the skin at depths greater than 0.5 mm, they would not be observed by XRF, but would be measured by ICP-MS. These results support a hypothesis that iron levels in the two samples that reported significantly elevated ICP-MS results compared to XRF may have had small blood vessels at the back of the skin. Second, the synchrotronμXRF maps also showed a narrow (approximately 100μm thick) layer of elevated iron at the surface of the skin. Monte Carlo models determined that, as expected, the XRF system was most sensitive to these skin layers. However, the simulations found that the XRF system, when calibrated against homogenous water-based phantoms, was found to accurately measure average iron levels in the skin of normal pigs despite the greater sensitivity to the surface layer. The Monte Carlo results further indicated that with highly elevated skin surface iron levels, the XRF system would not provide a good estimate of average skin iron levels. The XRF estimate could, with correction factors, provide a good estimate of the iron levels in the surface layers of skin. There is limited data on iron distribution in skin, especially under conditions of disease. If iron levels are elevated at the skin surface by diseases including thalassemia and hemochromatosis, this XRF device may prove to be an accurate clinical tool. However, further data are required on skin iron distributions in healthy and iron overload disease before this system can be verified to provide accurate measurements.

Spatiotemporal distribution and speciation of silver nanoparticles in the healing wound

First observation of AgNPs dynamics in the wounds of real patients through elemental imaging and speciation.

Probing Trace Elements in Human Tissues with Synchrotron Radiation

For the past several decades, synchrotron radiation has been extensively used to measure the spatial distribution and chemical affinity of elements found in trace concentrations (<few μg/g) in animal and human tissues. Intense and highly focused (lateral size of several micrometers) X-ray beams combined with small steps of photon energy tuning (2-3 eV) of synchrotron radiation allowed X-ray fluorescence (XRF) and X-ray absorption spectroscopy (XAS) techniques to nondestructively and simultaneously detect trace elements as well as identify their chemical affinity and speciation in situ, respectively. Although limited by measurement time and radiation damage to the tissue, these techniques are commonly used to obtain two-dimensional and three-dimensional maps of several elements at synchrotron facilities around the world. The spatial distribution and chemistry of the trace elements obtained is then correlated to the targeted anatomical structures and to the biological functions (normal or pathological). For example, synchrotron-based in vitro studies of various human tissues showed significant differences between the normal and pathological distributions of metallic trace elements such as iron, zinc, copper, and lead in relation to human diseases ranging from Parkinson's disease and cancer to osteoporosis and osteoarthritis. Current research effort is aimed at not only measuring the abnormal elemental distributions associated with various diseases, but also indicate or discover possible biological mechanisms that could explain such observations. While a number of studies confirmed and strengthened previous knowledge, others revealed or suggested new possible roles of trace elements or provided a more accurate spatial distribution in relation to the underlying histology. This area of research is at the intersection of several current fundamental and applied scientific inquiries such as metabolomics, medicine, biochemistry, toxicology, food science, health physics, and environmental and public health.

Assessment of alternative methods for analyzing X-ray fluorescence spectra

When analyzing characteristic peaks in X-ray fluorescence (XRF) spectra, the peak area is the value most often used to quantify peak size. However, some studies have reported the amplitude of the peak instead of the area. When the width of the peak is allowed to vary from trial to trial in order to provide the best possible fit to the data, these two alternative methods can yield slightly different results. In the current study, these two approaches to peak analysis are compared for data obtained from bone reference materials having certified lead concentrations of 1.09 ± 0.03 μg/g, 16.1 ± 0.3 μg/g, 13.2 ± 0.3 μg/g, and 31.5 ± 0.7 μg/g. Measurements were made with an Olympus Innov-X Delta Premium portable XRF system. Using both the area and amplitude methods, lines of best fit were constructed for the lead Lα and lead Lβ signals as a function of lead concentration. Additionally, coefficients of variation were calculated for each reference material and condition of analysis. To assess possible variations over time, the procedure was performed at two points separated by about one year. The amplitude and area methods were found to produce results which were consistent and proportional. Using either method, lead XRF signal plotted as a function of known lead concentration produced adjusted r² values of ∼0.99. The amplitude method provided slightly higher adjusted r² values overall. Coefficients of variation were generally very similar between the two methods, although more pronounced differences emerged from measurements of the lowest concentration reference material.

Feasibility of the use of a handheld XRF analyzer to measure skin iron to monitor iron levels in critical organs

There exists a need for accurate, non-invasive point-of-care tests to detect body iron burden. This study investigated the use of x-ray fluorescence (XRF) measurements of skin iron as a marker for organ iron content in rats. This study also evaluated a novel application of a commercial XRF device, commonly used in mining and construction, as a rapid, portable, and non-invasive measurement tool. Rats (n = 32) were loaded with iron dextran and the iron signal of each animal's skin, liver, and kidney was measured using a conventional XRF system. A quadratic correlation was observed between liver and skin iron signal (R² = 0.92) and a linear correlation was observed between kidney and skin iron signal (R² = 0.65). As such, it is concluded that skin iron content can act as a marker for both liver and kidney iron content. The same skin samples were measured using the portable XRF device and compared to the liver and kidney samples measured in the conventional XRF system. Again, a quadratic correlation was observed between liver and skin iron signal (R² = 0.91) and a linear correlation was observed between kidney and skin iron signal (R² = 0.83). Thus, the portable XRF device can provide rapid non-invasive, skin XRF measurements. Dosimetry was performed using the portable XRF device to assess the radiological hazard associated with its use. The average skin equivalent dose from this device is 30 ± 10 mSv/min, when the device is collimated and operated at 40 kV. In conclusion, skin iron XRF measurements can act as a surrogate marker for liver iron content, and can be measured using a commercial XRF device for a portable, fast, and non-invasive measurement.

Cytocompatibility and antibacterial activity of nanostructured H2Ti5O11·H2O outlayered Zn-doped TiO2 coatings on Ti for percutaneous implants

To improve skin-integration and antibacterial activity of percutaneous implants, the coatings comprising an outer layer of H2Ti5O11·H2O (HTO) nanoarrays and an inner layer of microporous Zn-doped TiO2 were fabricated on Ti by micro-arc oxidation (MAO) followed with hydrothermal treatment (HT). During HT process, a large proportion of Zn2+ migrated out from TiO2 layer. TiO2 reacted with OH- and H2O, resulting in the nucleation of HTO. The nuclei grew to nanoplates, nanorods and nanofibres with HT process prolonged. Simultaneously, the orientation of nanoarrays changed from quasi-vertical to parallel to substrate. Compared to Ti, adhesion and proliferation of fibroblasts were enhanced on as-MAOed TiO2 and HTed coatings. The phenotype, differentiation and extracellular collagen secretion were obviously accelerated on vertical nanorods with proper interspace (e.g. 63 nm). HTed coatings showed enhanced antibacterial activity, which should be ascribed to the nano-topography of HTO.

Epidermal iron metabolism for iron salvage

BACKGROUND

The epidermis shows a reverse iron gradient from the basal layer to the stratum corneum and consequently, little epidermal intracellular iron is lost by desquamation.

OBJECTIVE

To clarify the underlying mechanism of iron salvage.

METHODS

We first used immunohistochemistry and mRNA quantification to demonstrate the distinctive expression pattern of iron metabolism molecules. The obtained results were confirmed using normal human epidermal keratinocytes (NHEKs) during in vitro differentiation. We next examined the effects of reducing ferroportin expression in vitro by ferroportin-specific siRNAs or hepcidin on the intracellular iron content of cultured NHEKs. Finally, we compared epidermal and systemic iron metabolism between Fpn^Epi-KO mice and control mice.

RESULTS

The results of both mRNA and protein expression analysis showed that most molecules participating in iron import and storage were expressed in the lower epidermis, while those involved in iron release from heme or iron transport were expressed in the upper epidermis. Consistent with their expression, keratinocyte differentiation reduced intracellular iron content. We next demonstrated that reducing ferroportin expression in vitro by ferroportin-specific siRNAs or hepcidin significantly increased the intracellular iron content. Finally, we showed that the iron content of the epidermis and squames was significantly greater in Fpn^Epi-KO mice than in control mice, and that Fpn^Epi-KO exhibited a more rapid decrease in blood hemoglobin concentration than control mice on a low iron diet.

CONCLUSION

These studies demonstrated that the epidermis is equipped with a machinery by which intracellular iron in differentiated keratinocytes is excreted to the extracellular space before reaching the stratum corneum.

Detection of lead in bone phantoms and arsenic in soft tissue phantoms using synchrotron radiation and a portable x-ray fluorescence system

The differences and commonalities between x-ray fluorescence results obtained using synchrotron radiation and a portable x-ray fluorescence device were examined using arsenic in soft tissue phantoms and lead in bone phantoms. A monochromatic beam energy of 15.8 keV was used with the synchrotron, while the portable device employed a rhodium anode x-ray tube operated at 40 kV. Bone phantoms, dosed with varying quantities of lead, were made of Plaster of Paris and placed underneath skin phantoms of either 3.1 mm or 3.9 mm thickness. These skin phantoms were constructed from polyester resin, and dosed with varying amounts of arsenic. Using an irradiation time of 120 s, arsenic Kα and Kβ, and lead Lα and Lβ characteristic x-ray peaks were analysed. This information was used to calculate calibration line slopes and minimum detection limits for each data set. As expected, minimum detection limits were much lower at the synchrotron for detecting arsenic and lead. Both approaches produced lower detection limits for arsenic in soft tissue than for lead in bone when simultaneous detection was attempted. Although arsenic Kα and lead Lα emissions share similar energies, it was possible to detect both elements in isolation by using the arsenic Kβ and lead Lβ characteristic x-rays. Greater thickness of soft tissue phantom reduced the ability to detect the underlying lead. Experiments with synchrotron radiation could help guide future efforts toward optimizing a portable x-ray fluorescence in vivo measurement device.

Elemental analysis of tissue pellets for the differentiation of epidermal lesion and normal skin by laser-induced breakdown spectroscopy

By laser induced breakdown spectroscopy (LIBS) analysis of epidermal lesion and dermis tissue pellets of hairless mouse, it is shown that Ca intensity in the epidermal lesion is higher than that in dermis, whereas Na and K intensities have an opposite tendency. It is demonstrated that epidermal lesion and normal dermis can be differentiated with high selectivity either by univariate or multivariate analysis of LIBS spectra with an intensity ratio difference by factor of 8 or classification accuracy over 0.995, respectively.

Imaging of trace elements in tissues: with a focus on laser ablation inductively coupled plasma mass spectrometry

PURPOSE OF REVIEW

Elemental imaging techniques are capable of showing the spatial distribution of elements in a sample. Their application in biomedical sciences is promising, but they are not yet widely employed. The review gives a short overview about techniques available and then focuses on the advantages of using laser ablation inductively coupled plasma mass spectrometry for elemental bioimaging. Current examples for the use of elemental imaging with medical context are given to illustrate the potential of this type of analysis for clinical applications.

RECENT FINDINGS

Recently, synchrotron-based techniques and laser ablation inductively coupled plasma mass spectrometry have been successfully applied to analyse the spatial distribution of elements in biological samples of medical relevance.

SUMMARY

Elemental bioimaging methods have a great potential for medical applications. They are complementary to molecular imaging and histological staining and are especially attractive when used in combination with stable isotope tracer experiments.