Coherent normalization for in vivo measurements of gadolinium in bone

Doped Multiple Nanoparticles with Hydroxyapatite Coating Show Diverse Health Effects in vivo

Introduction

The lack of osteoinductive, angiogenic and antimicrobial properties of hydroxyapatite coatings (HA) on titanium surfaces severely limits their use in orthopedic and dental implants. Therefore, we doped SiO2, Gd2O3 and CeO2 nanoparticles into HA to fabricate a HASiGdCe coating with a combination of decent antibacterial, angiogenic and osteogenic properties by the plasma spraying technique.

Methods

The HASiGdCe coating was analyzed by SEM (EDS), surface roughness tests, contact angle tests, XRD, FTIR spectroscopy, tensile tests and electrochemical dynamic polarization tests. Methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa (PAO-1) were used as representative bacteria to verify the antibacterial properties of the HASiGdCe coating. We evaluated the cytocompatibility and in vitro osteoinductivity of the HASiGdCe coating by investigating its effect on the cell viability and osteogenic differentiation of MC3T3-E1 cells. We assessed the in vitro angiogenic activity of the HASiGdCe coating by migration assay, tube formation assay, and RT‒PCR analysis of angiogenic genes in HUVECs. Finally, we used infected animal femur models to investigate the biosafety, antimicrobial and osteointegration properties of the HASiGdCe coating in vivo.

Results

Through various characterization experiments, we demonstrated that the HASiGdCe coating has suitable microscopic morphology, physical phase characteristics, bonding strength and bioactivity to meet the coating criteria for orthopedic implants. The HASiGdCe coating can release Gd3+ and Ce4+, showing strong antibacterial properties against MRSA and PAO-1. The HASiGdCe coating has been shown to have superior osteogenic and angiogenic properties compared to the HA coating in in vitro cellular experiments. Animal implantation experiments have shown that the HASiGdCe coating also has excellent biosafety, antimicrobial and osteogenic properties in vivo.

Conclusion

The HASiGdCe coating confers excellent antibacterial, angiogenic and osteogenic properties on titanium implants, which can effectively enhance implant osseointegration and prevent bacterial infections, and it accordingly has promising applications in the treatment of bone defects related to orthopedic and dental sciences.

Chitosan-Based Scaffolds for Facilitated Endogenous Bone Re-Generation

Facilitated endogenous tissue engineering, as a facile and effective strategy, is emerging for use in bone tissue regeneration. However, the development of bioactive scaffolds with excellent osteo-inductivity to recruit endogenous stem cells homing and differentiation towards lesion areas remains an urgent problem. Chitosan (CS), with versatile qualities including good biocompatibility, biodegradability, and tunable physicochemical and biological properties is undergoing vigorously development in the field of bone repair. Based on this, the review focus on recent advances in chitosan-based scaffolds for facilitated endogenous bone regeneration. Initially, we introduced and compared the facilitated endogenous tissue engineering with traditional tissue engineering. Subsequently, the various CS-based bone repair scaffolds and their fabrication methods were briefly explored. Furthermore, the functional design of CS-based scaffolds in bone endogenous regeneration including biomolecular loading, inorganic nanomaterials hybridization, and physical stimulation was highlighted and discussed. Finally, the major challenges and further research directions of CS-based scaffolds were also elaborated. We hope that this review will provide valuable reference for further bone repair research in the future.

A novel calibration for L-shell x-ray fluorescence measurements of bone lead concentration using the strontium Kβ/Kαratio

Objective. Lead (Pb) is a well-known toxic element.In vivobone Pb concentration measurement is a long-term exposure metric complementary to blood Pb concentration measurement which is a metric of recent exposure.In vivohuman tibia bone Pb measurements using Pb K-shell or L-shell x-ray fluorescence (KXRF or LXRF) emissions were developed in the 1980s. KXRF bone Pb measurements using Cd-109 gamma rays and coherent-to-fluorescence ratio to account for differences between phantom andin vivomeasurements, was employed in human studies. Bone Pb LXRF method employed x-ray tubes. However, calibration procedures using ultrasound measurements of the soft tissue thickness (STT) proved inaccurate.Approach. In this study, bone and soft tissue (ST) phantoms simulatedin vivobone Pb measurements. Seven plaster-of-Paris cylindrical bone phantoms containing 1.01 mg g-1of strontium (Sr) were doped with Pb in 0, 8, 16, 29, 44, 59, and 74 μg g-1concentrations. Polyoxymethylene (POM), resin, and wax were each used to fabricate four ST phantoms in the approximate 1-4 mm thickness range. Pb LXRF measurements were performed using a previously developed optimal grazing incidence position method.Main results. Linear attenuation coefficients measurements of ST materials indicated that POM and resin mimicked well attenuation of Pb x-rays in skin and adipose tissue, respectively. POM and resin data indicated a bone Pb detection limit of 20 μg g-1for a 2 mm STT. Derived relationships between the Pb concentration, Pb LXRF and Sr Kβ/Kαratio data did not require STT knowledge. Applied to POM and resin data, the new calibration method yielded unbiased results.Significance.In vivobone Pb measurements in children were suggested following considerations of radiation dose, STT, detectability and distribution of Pb and Sr in bone. This research meets with the concerns regarding the negative effects of low levels of Pb exposure on neurodevelopment of children.

Investigating coherent normalization and dosimetry for the 241Am-La K XRF system

OBJECTIVES

Lanthanum (La) retention in bone has been shown to occur in individuals who are orally administered lanthanum carbonate (LaC), a drug to treat hyperphosphatemia. The breakdown of LaC in the gastrointestinal tract into La³⁺ and carbonate ions results in residual quantities of La being deposited in bone. We previously reported on a non-invasive x-ray fluorescence (XRF) system that was developed to quantify bone La concentrations and applied it to a series of excised cadaver tibiae. However, given interpatient variability in bone shape and size, differential signal attenuation that occurs in bone and tissue, patient movement and overlying tissue thickness at the measurement site, quantifying bone La concentrations during in vivo measurements in live subjects needs to be investigated further along with the radiation dose associated with the measurement.

APPROACH

Coherent normalization was investigated as a function of overlying tissue thickness, source-subject distance and bone radius through Monte Carlo simulation and experimental work. This was accomplished by observing the ratio of the net La K x-ray peak area to the coherently scattered peak area at 59.5 keV. In addition, the dose delivered during a 2000 s measurement was determined using radiochromic film.

MAIN RESULTS

The coherent normalization of the La x-ray signal was shown to be independent of overlying tissue thickness, source-subject movement and bone radius, which indicates that this normalization procedure can correct for these factors. The equivalent skin dose and effective dose were 18.0 mSv and 3.2 μSv, respectively for a five-year-old.

SIGNIFICANCE

While coherent normalization for the bone lead (Pb) and bone gadolinium (Gd) systems has been shown to be successful, we also report that this normalization procedure can correct for these interpatient variabilities in the in vivo ²⁴¹Am-La K XRF system.

Ex vivo quantification of lanthanum and gadolinium in post-mortem human tibiae with estimated barium and iodine concentrations using K x-ray fluorescence

OBJECTIVES

Lanthanum (La) and gadolinium (Gd) are known to deposit in bone of exposed populations, namely those who are orally administered lanthanum carbonate (LaC, La₂(CO₃)₃) or are injected with Gd-based contrast agents, respectively. In this work, bone La and Gd concentrations from the environment and diet were measured using x-ray fluorescence in ten post-mortem human tibiae. As a secondary objective, bone barium (Ba) and iodine concentrations were estimated.

APPROACH

Two calibration lines were produced for La and Gd and the minimum detection limits (MDLs) of the system were determined using a 180° irradiation-detection geometry.

MAIN RESULTS

The MDLs of the system were 0.4 µg La g^-1 bone mineral and 0.5 µg Gd g^-1 bone mineral. The mean concentrations were  -0.02  ±  0.1 µg La g^-1 bone mineral and 0.1  ±  0.2 µg Gd g^-1 bone mineral in tibiae. The average Ba and iodine concentrations estimated from the experimental La calibration line and Monte-Carlo derived sensitivity factors were determined to be 3.4  ±  0.8 µg Ba g^-1 bone mineral and  -0.5  ±  0.3 µg iodine g^-1 bone mineral. Since it was discovered that four donors previously received an iodine-based contrast agent, the mean concentrations in these donors was 27.8  ± 28.4 µg iodine g^-1 bone mineral.

SIGNIFICANCE

The XRF system has determined baseline concentrations of these four heavy metals in trace quantities from natural exposure pathways (with the exception of iodine in four donors). This indicates that the system can measure low levels in ex vivo tibiae samples and can potentially be further developed for in vivo studies involving live subjects who are directly exposed to these metals.

Gadolinium-doped mesoporous calcium silicate/chitosan scaffolds enhanced bone regeneration ability

Chitosan (CTS) and mesoporous calcium silicate (MCS) have been developed for bone defect healing; however, their bone regeneration capacity still does not satisfy the patients with bone diseases. Gadolinium (Gd) is accumulated in human bones, and plays a beneficial role in regulating cell performance and bone regeneration. We firstly constructed Gd-doped MCS/CTS (Gd-MCS/CTS) scaffolds by a lyophilization technology. The interconnected arrangement of CTS films lead to forming macropores by using ice crystals as templates during the lyophilization procedure, and the Gd-MCS nanoparticles dispersed uniformly on the macropore walls. The biocompatible chemical components and hierarchical pores facilitated the attachment and spreading of rat bone marrow-derived mesenchymal stem cells (rBMSCs). Interestingly, the Gd dopants in the scaffolds effectively activated the Wnt/β-catenin signaling pathway, resulting in excellent cell proliferation and osteogenic differentiation capacities. The osteogenic-related genes such as alkaline phosphatase (ALP), runt-related transcription factor 2 (Runx2) and collagen type1 (COL-1) were remarkably up-regulated by Gd-MCS scaffolds as compared with MCS scaffolds, and their expression levels increased in a positive correlation with Gd doping amounts. Moreover, in vivo rat cranial defect tests further confirmed that Gd-MCS/CTS scaffolds significantly stimulated collagen deposition and new bone formation. The exciting finding suggested the beneficial effects of Gd³⁺ ions on osteogenic differentiation and new bone regeneration, and Gd-MCS/CTS scaffolds can be employed as a novel platform for bone defect healing.

Measurement of gadolinium retention: current status and review from an applied radiation physics perspective

OBJECTIVE

This article briefly reviews the main measurement techniques for the non-invasive detection of residual gadolinium (Gd) in those exposed to gadolinium-based contrast agents (GBCAs). Approach and Main results: The current status of in vivo Gd measurement is discussed and is put into the context of concerns within the radiology community. The main techniques are based on applied atomic/nuclear medicine utilizing the characteristic atomic and nuclear spectroscopic signature of Gd. The main emission energies are in the 40-200 keV region and require spectroscopic detectors with good energy resolution. The two main techniques, prompt gamma neutron activation analysis and x-ray fluorescence, provide adequate detection limits for in vivo measurement, whilst delivering a low effective radiation dose on the order of a few µSv.

SIGNIFICANCE

Gadolinium is being detected in measureable quantities in people with healthy renal function who have received FDA approved GBCAs. The applied atomic/nuclear medicine techniques discussed in this review will be useful in determining the significance of this retention, and will help on advising future administration protocols.