Gadolinium-Induced Nephrogenic Systemic Fibrosis Is Associated with Insoluble Gd Deposits in Tissues:In VivoTransmetallation Confirmed by Microanalysis

Where does the gadolinium go? A review into the excretion and retention of intravenous gadolinium

Gadolinium-based contrast agents (GBCAs) are commonly used in medical imaging. Most intravenously (IV) administered gadolinium is excreted via the kidneys, and pathological retention in renal failure leading to nephrogenic systemic fibrosis (NSF) is well described. More recently, retention of gadolinium in the body in the absence of renal disease has been identified, with unknown clinical consequences. Many patients are aware of this, either through the media or via comprehensive consent documentation. Some internet sites, without hard evidence, have suggested a constellation of possible symptoms associated with GBCA retention. Recent experience with patients ascribing symptoms to a contrast-enhanced MRI examination prompted this review of the fate of injected GBCA after MRI study, and of information available to patients online regarding gadolinium retention.

Novel Gadolinium-Free Ultrasmall Nanostructured Positive Contrast for Magnetic Resonance Angiography and Imaging

Nanostructured contrast agents are promising alternatives to Gd3+-based chelates in magnetic resonance (MR) imaging techniques. A novel ultrasmall paramagnetic nanoparticle (UPN) was strategically designed to maximize the number of exposed paramagnetic sites and r1 while minimizing r2, by decorating 3 nm titanium dioxide nanoparticles with suitable amounts of iron oxide. Its relaxometric parameters are comparable to those of gadoteric acid (GA) in agar phantoms, and the r2/r1 ratio of 1.38 at 3 T is close to the ideal unitary value. The strong and prolonged contrast enhancement of UPN before renal excretion was confirmed by T1-weighted MR images of Wistar rats after intravenous bolus injection. Those results associated with good biocompatibility indicate its high potential as an alternative blood-pool contrast agent to the GA gold standard for MR angiography, especially for patients with severe renal impairment.

Different Impact of Gadopentetate and Gadobutrol on Inflammation-Promoted Retention and Toxicity of Gadolinium Within the Mouse Brain

OBJECTIVES

Using a murine model of multiple sclerosis, we previously showed that repeated administration of gadopentetate dimeglumine led to retention of gadolinium (Gd) within cerebellar structures and that this process was enhanced with inflammation. This study aimed to compare the kinetics and retention profiles of Gd in inflamed and healthy brains after application of the macrocyclic Gd-based contrast agent (GBCA) gadobutrol or the linear GBCA gadopentetate. Moreover, potential Gd-induced neurotoxicity was investigated in living hippocampal slices ex vivo.

MATERIALS AND METHODS

Mice at peak of experimental autoimmune encephalomyelitis (EAE; n = 29) and healthy control mice (HC; n = 24) were exposed to a cumulative dose of 20 mmol/kg bodyweight of either gadopentetate dimeglumine or gadobutrol (8 injections of 2.5 mmol/kg over 10 days). Magnetic resonance imaging (7 T) was performed at baseline as well as at day 1, 10, and 40 post final injection (pfi) of GBCAs. Mice were sacrificed after magnetic resonance imaging and brain and blood Gd content was assessed by laser ablation-inductively coupled plasma (ICP)-mass spectrometry (MS) and ICP-MS, respectively. In addition, using chronic organotypic hippocampal slice cultures, Gd-induced neurotoxicity was addressed in living brain tissue ex vivo, both under control or inflammatory (tumor necrosis factor α [TNF-α] at 50 ng/μL) conditions.

RESULTS

Neuroinflammation promoted a significant decrease in T1 relaxation times after multiple injections of both GBCAs as shown by quantitative T1 mapping of EAE brains compared with HC. This corresponded to higher Gd retention within the EAE brains at 1, 10, and 40 days pfi as determined by laser ablation-ICP-MS. In inflamed cerebellum, in particular in the deep cerebellar nuclei (CN), elevated Gd retention was observed until day 40 after last gadopentetate application (CN: EAE vs HC, 55.06 ± 0.16 μM vs 30.44 ± 4.43 μM). In contrast, gadobutrol application led to a rather diffuse Gd content in the inflamed brains, which strongly diminished until day 40 (CN: EAE vs HC, 0.38 ± 0.08 μM vs 0.17 ± 0.03 μM). The analysis of cytotoxic effects of both GBCAs using living brain tissue revealed an elevated cell death rate after incubation with gadopentetate but not gadobutrol at 50 mM. The cytotoxic effect due to gadopentetate increased in the presence of the inflammatory mediator TNF-α (with vs without TNF-α, 3.15% ± 1.18% vs 2.17% ± 1.14%; P = 0.0345).

CONCLUSIONS

In the EAE model, neuroinflammation promoted increased Gd retention in the brain for both GBCAs. Whereas in the inflamed brains, efficient clearance of macrocyclic gadobutrol during the investigated time period was observed, the Gd retention after application of linear gadopentetate persisted over the entire observational period. Gadopentetate but not gadubutrol appeared to be neurotoxic in an ex vivo paradigm of neuronal inflammation.

Gadolinium and Bio-Metal Association: A Concentration Dependency Tested in a Renal Allograft and Investigated by Micro-Synchrotron XRF

Aims: This study aimed to investigate gadolinium (Gd) and bio-metals in a renal allograft of a patient who was shortly after transplantation repeatedly exposed to a Gd-based contrast agent (GBCA), with the purpose of determining whether Gd can be proven and spatially and quantitatively imaged. Further elemental associations between Gd and bio-metals were also investigated. Materials and Methods: Archival paraffin-embedded kidney tissue (eight weeks after transplantation) was investigated by microscopic synchrotron X-ray fluorescence (µSRXRF) at the DORIS III storage ring, beamline L, at HASYLAB/DESY (Hamburg, Germany). For the quantification of elements, X-ray spectra were peak-fitted, and the net peak intensities were normalized to the intensity of the incoming monochromatic beam intensity. Concentrations were calculated by fundamental parameter-based program quant and external standardization. Results: Analysis of about 15,000 µSRXRF spectra (comprising allograft tissue of four cm²) Gd distribution could be quantitatively demonstrated in a near histological resolution. Mean Gd resulted in 24 ± 55 ppm with a maximum of 2363 ppm. The standard deviation of ±55 ppm characterized the huge differences in Gd and not in detection accuracy. Gd was heterogeneously but not randomly distributed and was mostly found in areas with interstitial fibrosis and tubular atrophy. Concentrations of all other investigated elements in the allograft resembled those found in normal kidney tissue. No correlations between Gd and bio-metals such as calcium, strontium or zinc below ~40 ppm Gd existed. In areas with extremely high Gd, Gd was associated with iron and zinc. Conclusions: We could show that no dose-dependent association between Gd and bio-metals exists—least in renal tissue—at Gd concentrations below ~40 ppm Gd. This was proven compared with a GBCA-exposed end-stage renal failure in which the mean Gd was ten-fold higher. Our results could shed additional light on Gd metabolism.

Imaging of Transmetallation and Chelation Phenomena Involving Radiological Contrast Agents in Mineral-Rich Fruits

Exogenous heavy metals or non-metallic waste products, for example lanthanide or iodinated contrast media for radiological procedures, may interfere with the biochemical pools in patients and in common food sources, creating an excess buildup of exogenous compounds which may reach toxic levels. Although the mechanisms are unknown, our experiments were designed to test if this toxicity can be attributed to “transmetallation” or “chelation” reactions freeing up lanthanides or chelated transition metals in acidic fruits used as phantoms representing the biologically active and mineral-rich carbohydrate matrix. The rapid breakdown of stable contrast agents have been reported at a lower pH. The interaction of such agents with native metals was examined by direct imaging of contrast infused fresh apples and sweet potatoes using low energy X-rays (40–44 kVp) and by magnetic resonance imaging at 1.5 and 3T. The stability of the exogenous agents seemed to depend on endogenous counterions and biometals in these fruits. Proton spin echo MR intensity is sensitive to paramagnetic minerals and low energy X-ray photons are sensitively absorbed by photoelectric effects in all abundant minerals and were compared before and after the infusion of radiologic contrasts. Endogenous iron and manganese are believed to accumulate due to interactions with exogenous iodine and gadolinium in and around the infusion spots. X-ray imaging had lower sensitivity (detection limit approximately 1 part in 10⁴), while MRI sensitivity was two orders of magnitude higher (approximately 1 part in 10⁶), but only for paramagnetic minerals like Mn and Fe in our samples. MRI evidence of such a release of metal ions from the native pool implicates transmetallation and chelation reactions that were triggered by infused contrast agents. Since Fe and Mn play significant roles in the function of metalloenzymes, our results suggest that transmetallation and chelation could be a plausible mechanism for contrast induced toxicity in vivo.

Comprehensive Speciation Analysis of Residual Gadolinium in Deep Cerebellar Nuclei in Rats Repeatedly Administered With Gadoterate Meglumine or Gadodiamide

PURPOSE

Several preclinical studies have reported the presence of gadolinium (Gd) in different chemical forms in the brain, depending on the class (macrocyclic versus linear) of Gd-based contrast agent (GBCA) administered. The aim of this study was to identify, with a special focus on insoluble species, the speciation of Gd retained in the deep cerebellar nuclei (DCN) of rats administered repeatedly with gadoterate or gadodiamide 4 months after the last injection.

METHODS

Three groups (N = 6/group) of healthy female Sprague-Dawley rats (SPF/OFA rats; Charles River, L'Arbresle, France) received a cumulated dose of 50 mmol/kg (4 daily intravenous administrations of 2.5 mmol/kg, for 5 weeks, corresponding to 80-fold the usual clinical dose if adjusted for man) of gadoterate meglumine (macrocyclic) or gadodiamide (linear) or isotonic saline for the control group (4 daily intravenous administrations of 5 mL/kg, for 5 weeks). The animals were sacrificed 4 months after the last injection. Deep cerebellar nuclei were dissected and stored at -80°C before sample preparation. To provide enough tissue for sample preparation and further analysis using multiple techniques, DCN from each group of 6 rats were pooled. Gadolinium species were extracted in 2 consecutive steps with water and urea solution. The total Gd concentrations were determined by inductively coupled plasma mass spectrometry (ICP-MS). Soluble Gd species were analyzed by size-exclusion chromatography coupled to ICP-MS. The insoluble Gd species were analyzed by single-particle (SP) ICP-MS, nanoscale secondary ion mass spectroscopy (NanoSIMS), and scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy (STEM-EDX) for elemental detection.

RESULTS

The Gd concentrations in pooled DCN from animals treated with gadoterate or gadodiamide were 0.25 and 24.3 nmol/g, respectively. For gadoterate, the highest amount of Gd was found in the water-soluble fractions. It was present exclusively as low-molecular-weight compounds, most likely as the intact GBCA form. In the case of gadodiamide, the water-soluble fraction of DCN was composed of high-molecular-weight Gd species of approximately 440 kDa and contained only a tiny amount (less than 1%) of intact gadodiamide. Furthermore, the column recovery calculated for this fraction was incomplete, which suggested presence of labile complexes of dissociated Gd3+ with endogenous molecules. The highest amount of Gd was detected in the insoluble residue, which was demonstrated, by SP-ICP-MS, to be a particulate form of Gd. Two imaging techniques (NanoSIMS and STEM-EDX) allowed further characterization of these insoluble Gd species. Amorphous, spheroid structures of approximately 100-200 nm of sea urchin-like shape were detected. Furthermore, Gd was consistently colocalized with calcium, oxygen, and phosphorous, strongly suggesting the presence of structures composed of mixed Gd/Ca phosphates. No or occasional colocalization with iron and sulfur was observed.

CONCLUSION

A dedicated analytical workflow produced original data on the speciation of Gd in DCN of rats repeatedly injected with GBCAs. The addition, in comparison with previous studies of Gd speciation in brain, of SP element detection and imaging techniques allowed a comprehensive speciation analysis approach. Whereas for gadoterate the main fraction of retained Gd was present as intact GBCA form in the soluble fractions, for linear gadodiamide, less than 10% of Gd could be solubilized and characterized using size-exclusion chromatography coupled to ICP-MS. The main Gd species detected in the soluble fractions were macromolecules of 440 kDa. One of them was speculated to be a Gd complex with iron-binding protein (ferritin). However, the major fraction of residual Gd was present as insoluble particulate species, very likely composed of mixed Gd/Ca phosphates. This comprehensive Gd speciation study provided important evidence for the dechelation of linear GBCAs and offered a deeper insight into the mechanisms of Gd deposition in the brain.

Combined speciation analysis and elemental bioimaging provides new insight into gadolinium retention in kidney

This study uses a leaching approach in combination with elemental bioimaging and speciation analysis to obtain insight into the gadolinium species present in the kidney of rats that were treated with either a linear or a macrocyclic gadolinium-based contrast agent. Fresh frozen thin sections of the harvested kidneys were immersed halfway into water to wash out hydrophilic species and subsequently analyzed by laser ablation-inductively coupled plasma-mass spectrometry. The water-extracted gadolinium species were analyzed by means of hydrophilic interaction liquid chromatography-inductively coupled plasma-mass spectrometry. Information on the water-soluble species could not only be obtained from the full kidney, but also be traced back to its localization in the tissue. On longitudinal kidney sections treated with gadobutrol, it was found that water-insoluble, permanent Gd depositions were mainly located in the renal cortex, while water-soluble species were found in the medulla, which contains the intact contrast agent up to one year after injection. Moreover, kidney samples from gadodiamide-treated rats showed more water-insoluble Gd deposition in both cortex and medulla, while the concentration of intact contrast agent in the water-soluble fraction was below the limit of detection after twelve months. In conclusion, this rapid approach allowed the spatially resolved differentiation between water-soluble and insoluble gadolinium deposition and is therefore capable of generating new insight into the retention and transportation behavior of gadolinium.

Gadolinium: pharmacokinetics and toxicity in humans and laboratory animals following contrast agent administration

Gadolinium-based contrast agents (GBCAs) have transformed magnetic resonance imaging (MRI) by facilitating the use of contrast-enhanced MRI to allow vital clinical diagnosis in a plethora of disease that would otherwise remain undetected. Although over 500 million doses have been administered worldwide, scientific research has documented the retention of gadolinium in tissues, long after exposure, and the discovery of a GBCA-associated disease termed nephrogenic systemic fibrosis, found in patients with impaired renal function. An understanding of the pharmacokinetics in humans and animals alike are pivotal to the understanding of the distribution and excretion of gadolinium and GBCAs, and ultimately their potential retention. This has been well studied in humans and more so in animals, and recently there has been a particular focus on potential toxicities associated with multiple GBCA administration. The purpose of this review is to highlight what is currently known in the literature regarding the pharmacokinetics of gadolinium in humans and animals, and any toxicity associated with GBCA use.

Safety and Gadolinium Distribution of the New High-Relaxivity Gadolinium Chelate Gadopiclenol in a Rat Model of Severe Renal Failure

OBJECTIVE

The aim of this study was to investigate the toxicological profile of gadopiclenol, a new high-relaxivity macrocyclic gadolinium-based contrast agent (GBCA), in renally impaired rats, in comparison with 2 other macrocyclic GBCAs, gadoterate meglumine and gadobutrol, and 1 linear and nonionic GBCA, gadodiamide.

METHODS

Renal failure was induced by adding 0.75% wt/wt adenine to the diet for 3 weeks. During the second week of adenine-enriched diet, the animals (n = 8/group × 5 groups) received 5 consecutive intravenous injections of GBCA at 2.5 mmol/kg per injection, resulting in a cumulative dose of 12.5 mmol/kg or saline followed by a 3-week treatment-free period after the last injection. The total (elemental) gadolinium (Gd) concentration in different tissues (brain, cerebellum, femoral epiphysis, liver, skin, heart, kidney, spleen, plasma, urine, and feces) was measured by inductively coupled plasma mass spectrometry. Transmission electron microscopy (and electron energy loss spectroscopy analysis of metallic deposits) was used to investigate the presence and localization of Gd deposits in the skin. Relaxometry was used to evaluate the presence of dissociated Gd in the skin, liver, and bone. Skin histopathology was performed to investigate the presence of nephrogenic systemic fibrosis-like lesions.

RESULTS

Gadodiamide administrations were associated with high morbidity-mortality but also with macroscopic and microscopic skin lesions in renally impaired rats. No such effects were observed with gadopiclenol, gadoterate, or gadobutrol. Overall, elemental Gd concentrations were significantly higher in gadodiamide-treated rats than in rats treated with the other GBCAs for all tissues except the liver (where no significant difference was found with gadopiclenol) and the kidney and the heart (where statistically similar Gd concentrations were observed for all GBCAs). No plasma biochemical abnormalities were observed with gadopiclenol or the control GBCAs. Histopathology revealed a normal skin structure in the rats treated with gadopiclenol, gadoterate, and gadobutrol, contrary to those treated with gadodiamide. No evidence of Gd deposits on collagen fibers and inclusions in fibroblasts was found with gadopiclenol and its macrocyclic controls, unlike with gadodiamide. Animals of all test groups had Gd-positive lysosomal inclusions in the dermal macrophages. However, the textures differed for the different products (speckled texture for gadodiamide and rough-textured appearance for the 2 tested macrocyclic GBCAs).

CONCLUSIONS

No evidence of biochemical toxicity or pathological abnormalities of the skin was observed, and similar to other macrocyclic GBCAs, gadoterate and gadobutrol, tissue retention of Gd was found to be low (except in the liver) in renally impaired rats treated with the new high-relaxivity GBCA gadopiclenol.

Development of an Effective Tumor-Targeted Contrast Agent for Magnetic Resonance Imaging Based on Mn/H-Ferritin Nanocomplexes

Magnetic resonance imaging (MRI) is one of the most sophisticated diagnostic tools that is routinely used in clinical practice. Contrast agents (CAs) are commonly exploited to afford much clearer images of detectable organs and to reduce the risk of misdiagnosis caused by limited MRI sensitivity. Currently, only a few gadolinium-based CAs are approved for clinical use. Concerns about their toxicity remain, and their administration is approved only under strict controls. Here, we report the synthesis and validation of a manganese-based CA, namely, Mn@HFn-RT. Manganese is an endogenous paramagnetic metal able to produce a positive contrast like gadolinium, but it is thought to result in less toxicity for the human body. Mn ions were efficiently loaded inside the shell of a recombinant H-ferritin (HFn), which is selectively recognized by the majority of human cancer cells through their transferrin receptor 1. Mn@HFn-RT was characterized, showing excellent colloidal stability, superior relaxivity, and a good safety profile. In vitro experiments confirmed the ability of Mn@HFn-RT to efficiently and selectively target breast cancer cells. In vivo, Mn@HFn-RT allowed the direct detection of tumors by positive contrast enhancement in a breast cancer murine model, using very low metal dosages and exhibiting rapid clearance after diagnosis. Hence, Mn@HFn-RT is proposed as a promising CA candidate to be developed for MRI.

Gray Matter Nucleus Hyperintensity After Monthly Triple-Dose Gadopentetate Dimeglumine With Long-term Magnetic Resonance Imaging

OBJECTIVES

Gadolinium deposition is widely believed to occur, but questions regarding accumulation pattern and permanence remain. We conducted a retrospective study of intracranial signal changes on monthly triple-dose contrast-enhanced magnetic resonance imaging (MRI) examinations from the previously published Betaseron vs. Copaxone in Multiple Sclerosis With Triple-Dose Gadolinium and 3-Tesla MRI Endpoints Trial (N = 67) to characterize the dynamics of gadolinium deposition in several deep brain nuclei and track persistence versus washout of gadolinium deposition on long-term follow-up (LTFU) examinations (N = 28) obtained approximately 10 years after enrollment in the Betaseron vs. Copaxone in Multiple Sclerosis With Triple-Dose Gadolinium and 3-Tesla MRI Endpoints Trial.

MATERIALS AND METHODS

Using T2 and proton density images and using image analysis software (ITK-SNAP), manual regions of interest were created ascribing boundaries of the caudate nucleus, dentate nucleus, globus pallidus, pulvinar, putamen, white matter, and air. Intensity analysis was conducted on T1-weighted fat-saturated (fat-sat) images using the FSL package. A linear rigid-body transform was calculated from the fat-sat image at each target time point to the region of interest segmentation reference time point fat-sat image. Serial MRI signal was analyzed using linear mixed regression modeling with random intercept. Annual MRI signal changes including LTFU scans were assessed with t test.

RESULTS

During monthly scanning, all gray matter structures demonstrated a significant (P < 0.0001) increase in contrast-to-noise ratio. Yearly changes in deposition showed distinctive patterns for the specific nucleus: globus pallidus showed complete retention, pulvinar showed partial washout, while dentate, caudate, and putamen returned to baseline (ie, complete washout).

CONCLUSIONS

Monthly increased contrast-to-noise ratio in gray matter nuclei is consistent with gadolinium deposition over time. The study also suggests that some deep gray matter nuclei permanently retain gadolinium, whereas others demonstrate washout of soluble gadolinium.

Gadolinium distribution in kidney tissue determined and quantified by micro synchrotron X-ray fluorescence

Aims of this study were to investigate gadolinium (Gd) in kidney tissue from a female patient with severe renal failure, who had a magnetic resonance imaging (MRI) with Gd-based contrast agent (GBCA) three times prior to kidney transplantation. Secondly to assess (semi-)quantitatively the Gd concentration in renal tissue and the spatial distribution of Gd in association to suspected co-elements such as calcium (Ca) and zinc (Zn). Archival paraffin embedded kidney tissue was investigated by micro Synchrotron X-ray fluorescence (µSRXRF) at the DORIS III storage ring at beamline L, HASYLAB/DESY(Hamburg, Germany). Elementary gadolinium (Gd) could be demonstrated in a near histological resolution in areas of about 2 × 1.5 mm² of size. Mean Gd resulted in 200 ppm with a huge width of distribution (Gd-max: 2000 ppm). In kidney cortex Gd was in-homogeneously, but not randomly, distributed. Gd was verified throughout the investigated tissue. Low Gd was predominately concentrated either in areas with focally atrophic tubules or in areas with totally preserved uriniferous tubes. Moreover, strong correlations existed between Gd and calcium (Ca) or Gd and zinc (Zn) or Gd and strontium (Sr) distribution. Throughout our analysed areas copper (Cu) was nearly homogeneously distributed and Cu association to Gd could not be established, and also not for Gd to Fe. Gd in glomeruli was relatively reduced compared with mean Gd-values, while iron (Fe) distribution clearly demarks glomeruli mostly due to red blood cell iron in these capillary convolutes. Quantitative µSRXRF analysis provided an insight in element spatial distribution of Gd in the renal cortex. The strong correlation of the spatial distribution and associations between elements like Ca, Zn and Sr let us suspect that these elements are involved in the cell metabolism of GBCA. Low Gd in areas with extreme fibrosis and tubule atrophy or in areas with histologically intact tubes, let us suspect that on the one side Gd cannot be transported and deposited into these tissue areas and on the other side we assume that intact renal tubes do not reabsorb and store excreted Gd.

Chemical exposure-induced systemic fibrosing disorders: Novel insights into systemic sclerosis etiology and pathogenesis

Numerous drugs and chemical substances are capable of inducing exaggerated tissue fibrotic responses. The vast majority of these agents cause localized fibrotic tissue reactions or fibrosis confined to specific organs. Although much less frequent, chemically-induced systemic fibrotic disorders have been described, sometimes occurring as temporally confined outbreaks. These include the Toxic Oil Syndrome (TOS), the Eosinophilia-Myalgia Syndrome (EMS), and Nephrogenic Systemic Fibrosis (NSF). Although each of these disorders displays some unique characteristics, they all share crucial features with Systemic Sclerosis (SSc), the prototypic idiopathic systemic fibrotic disease, including vasculopathy, chronic inflammatory cell infiltration of affected tissues, and cutaneous and visceral tissue fibrosis. The study of the mechanisms and molecular alterations involved in the development of the chemically-induced systemic fibrotic disorders has provided valuable clues that may allow elucidation of SSc etiology and pathogenesis. Here, we review relevant aspects of the TOS, EMS, and NSF epidemic outbreaks of chemically-induced systemic fibrosing disorders that provide strong support to the hypothesis that SSc is caused by a toxic or biological agent that following its internalization by endothelial cells induces in genetically predisposed individuals a series of molecular alterations that result in the development of SSc clinical and pathological alterations.

Molecular imaging of extracellular matrix proteins with targeted probes using magnetic resonance imaging

The extracellular matrix (ECM) consists of proteins and carbohydrates that supports different biological structures and processes such as tissue development, elasticity, and preservation of organ structure. Diseases involving inflammation, fibrosis, tumor invasion, and injury are all attributed to the transition of the ECM from homeostasis to remodeling, which can significantly change the biochemical and biomechanical features of ECM components. While contrast agents have played an indispensable role in facilitating clinical diagnosis of diseases using magnetic resonance imaging (MRI), there is a strong need to develop novel biomarker-targeted imaging probes for in vivo visualization of biological processes and pathological alterations at a cellular and molecular level, for both early diagnosis and monitoring drug treatment. Herein, we will first review the pathological accumulation and characterization of ECM proteins recognized as important molecular features of diseases. Developments in MRI probes targeting ECM proteins such as collagen, fibronectin, and elastin via conjugation of existing contrast agents to targeting moieties and their applications to various diseases, are also reviewed. We have also reviewed our progress in the development of collagen-targeted protein MRI contrast agent with significant improvement in relaxivity and metal binding specificity, and their applications in early detection of fibrosis and metastatic cancer. This article is categorized under: Diagnostic Tools > in vivo Nanodiagnostics and Imaging Biology-Inspired Nanomaterials > Peptide-Based Structures Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.

Dechelation (Transmetalation): Consequences and Safety Concerns With the Linear Gadolinium-Based Contrast Agents, In View of Recent Health Care Rulings by the EMA (Europe), FDA (United States), and PMDA (Japan)

The issue of dechelation (transmetallation) in vivo after administration of the linear gadolinium-based contrast agents, and potential safety concerns, is considered on the basis of an extensive, focused literature review. Early indications of potential problems included the high level of excess ligand used in the formulation of 2 agents (indeed the 2 least stable thermodynamically) and interference with laboratory tests when blood was drawn from patients relatively soon after administration of these same agents. The advent of nephrogenic systemic fibrosis in the late 2000s raised additional major concerns.The correlation in 2014 of dentate nucleus hyperintensity on precontrast T1-weighted scans with multiple prior injections of linear gadolinium chelates, in patients with normal renal function, has driven subsequent research concerning dechelation of these agents in vivo. Unexpectedly high levels of gadolinium in the bone, skin, and liver have been found long term after administration, in animal models and in humans, although the latter data are limited. Bone may serve as a long-term reservoir, with a residual excretion phase for gadolinium after intravenous injection of the linear agents due to a subsequent slow release from bone. Many different patient populations could be vulnerable and potentially later develop clinical symptoms, although at this stage there are only limited data and small retrospective uncontrolled studies. Possible vulnerable populations include children, menopausal women, patients with osteoporosis (who are predisposed to fractures and often slow to heal or heal poorly), those receiving multiple doses, those with proinflammatory conditions, moderate renal dysfunction, or an undefined genetic predisposition. Of particular concern would be nephrogenic systemic fibrosis-like symptoms-including particularly pain and skin/joint symptoms, or disease related to the incorporation of gadolinium in hydroxyapatite in bone, in small subgroups of patients with a not yet defined propensity and/or cofactor. These concerns have led to withdrawal of the linear agents from the largest clinical market, Europe, with the exception of the hepatobiliary agents for delayed liver imaging, an indication that cannot be fulfilled by the current macrocyclic gadolinium chelates (for which these concerns do not apply).

Multimodal Imaging Study of Gadolinium Presence in Rat Cerebellum: Differences Between Gd Chelates, Presence in the Virchow-Robin Space, Association With Lipofuscin, and Hypotheses About Distribution Pathway

Purpose

The aim of this study was to investigate, based on in-depth multimodal imaging, the presence of Gd deposits, their ultrastructure, location, and co-location with endogenous elements, in the cerebellum, after repeated administrations of gadolinium-based contrast agents (GBCAs).

Methods

Rats sensitized by subtotal nephrectomy received 20 daily intravenous injections of 0.6 mmol Gd/kg for 5 weeks of commercial forms of either gadoterate, gadobenate or gadodiamide, or saline (n = 2/group). The study was randomized and blinded. Magnetic resonance imaging examination was performed weekly. One month after the last injection, electron microscopy analysis of the deep cerebellar nuclei, the granular layer of cerebellar cortex, and the choroid plexus was performed. Elemental analysis of deposits was carried out by electron energy loss spectroscopy. Secondary ion mass spectroscopy was used for complementary chemical mapping.

Results

A T1 hypersignal was evidenced in the deep cerebellar nuclei of rats treated with linear GBCAs, and Gd deposits were identified in all the studied cerebellar structures with gadobenate and gadodiamide (except in the granular layer in gadobenate-treated rats). No such effect was found with the macrocyclic GBCA gadoterate. Most of the Gd deposits revealed a characteristic spheroid “sea urchin-like” morphology, rich in phosphorus, and were localized in the basal lamina of microvessels, in the perivascular Virchow-Robin space, and in the interstitium. Gd was also identified in the glial cells, associated with lipofuscin pigments, for these same groups.

Conclusions

Transmission electron microscopy analysis of cerebellums of renally impaired rats repeatedly injected with gadobenate and gadodiamide revealed the presence of Gd. Spheroid Gd depositions consisting of a filamentous meshwork were observed in the wall of microvessels, in perivascular Virchow-Robin space, and in the interstitium. Gd was also found in choroid plexus and was associated with pigments (likely lipofuscin) in glial cells. This is consistent with the involvement of the glymphatic distribution pathway for GBCAs. No insoluble Gd deposits were detected in rats injected with the macrocyclic GBCA gadoterate and controls.

The biological fate of gadolinium-based MRI contrast agents: a call to action for bioinorganic chemists

Gadolinium-based contrast agents (GBCAs) are widely used with clinical magnetic resonance imaging (MRI), and 10 s of millions of doses of GBCAs are administered annually worldwide. GBCAs are hydrophilic, thermodynamically stable and kinetically inert gadolinium chelates. In clinical MRI, 5-10 millimoles of Gd ion is administered intravenously and the GBCA is rapidly eliminated intact primarily through the kidneys into the urine. It is now well-established that the Gd3+ ion, in some form(s), is partially retained in vivo. In patients with advanced kidney disease, there is an association of Gd retention with nephrogenic systemic fibrosis (NSF) disease. However Gd is also retained in the brain, bone, skin, and other tissues in patients with normal renal function, and the presence of Gd can persist months to years after the last administration of a GBCA. Regulatory agencies are restricting the use of specific GBCAs and inviting health care professionals to evaluate the risk/benefit ratio prior to using GBCAs. Despite the growing number of studies investigating this issue both in animals and humans, the biological distribution and the chemical speciation of the residual gadolinium are not fully understood. Is the GBCA retained in its intact form? Is the Gd3+ ion dissociated from its chelator, and if so, what is its chemical form? Here we discuss the current state of knowledge regarding the issue of Gd retention and describe the analytical and spectroscopic methods that can be used to investigate the Gd speciation. Many of the physical methods that could be brought to bear on this problem are in the domain of bioinorganic chemistry and we hope that this review will serve to inspire this community to take up this important problem.

Gadolinium as an Emerging Microcontaminant in Water Resources: Threats and Opportunities

As a result of high doses of paramagnetic gadolinium (Gd) chelates administered in magnetic resonance imaging (MRI) exams, their unmetabolized excretion, and insufficient removal in wastewater treatment plants (WWTPs), large amounts of anthropogenic Gd (Gdanth) are released into surface water. The upward trend of gadolinium-based contrast agent (Gd-CA) administrations is expected to continue growing and consequently higher and higher anthropogenic Gd concentrations are annually recorded in water resources, which can pose a great threat to aquatic organisms and human beings. In addition, the feasibility of Gd retention in patients administered with Gd-CAs repeatedly, and even potentially fatal diseases, including nephrogenic systemic fibrosis (NSF), due to trace amounts of Gd have recently arisen severe health concerns. Thus, there is a need to investigate probable adverse health effects of currently marketed Gd-CAs meticulously and to modify the actual approach in using Gd contrast media in daily practice in order to minimize unknown possible health risks. Furthermore, the employment of enhanced wastewater treatment processes that are capable of removing the stable contrast agents, and the evaluation of the ecotoxicity of Gd chelates and human exposure to these emerging contaminants through dermal and ingestion pathways deserve more attention. On the other hand, point source releases of anthropogenic Gd into the aquatic environment presents the opportunity to assess surface water—groundwater interactions and trace the fate of wastewater plume as a proxy for the potential presence of other microcontaminants associated with treated wastewater in freshwater and marine systems.

Molecular Probes for Imaging Fibrosis and Fibrogenesis

Fibrosis, or the accumulation of extracellular matrix molecules that make up scar tissue, is a common result of chronic tissue injury. Advances in the clinical management of fibrotic diseases have been hampered by the low sensitivity and specificity of noninvasive early diagnostic options, lack of surrogate end points for use in clinical trials, and a paucity of noninvasive tools to assess fibrotic disease activity longitudinally. Hence, the development of new methods to image fibrosis and fibrogenesis is a large unmet clinical need. Herein, an overview of recent and selected molecular probes for imaging of fibrosis and fibrogenesis by magnetic resonance imaging, positron emission tomography, and single photon emission computed tomography is provided.

LA-ICP-MS/MS improves limits of detection in elemental bioimaging of gadolinium deposition originating from MRI contrast agents in skin and brain tissues

A novel analytical method to detect the retention of gadolinium from contrast agents for magnetic resonance imaging (MRI) in tissue samples of patients is presented. It is based on laser ablation - inductively coupled plasma - triple quadrupole - mass spectrometry (LA-ICP-MS/MS). Both Gd and P were monitored with a mass shift of +16, corresponding to mono-oxygenated species, as well as Zn, Ca, and Fe on-mass. This method resulted in a significantly reduced background and improved limits of detection not only for phosphorus, but also for gadolinium. These improvements were essential to perform elemental bioimaging with improved resolution of 5 μm x 5 μm, allowing the detection of small Gd deposits in fibrotic skin and brain tumour tissue with diameters of approximately 50 μm. Detailed analyses of these regions revealed that most Gd was accompanied with P and Ca, indicating co-precipitation.

Urinary Gadolinium Levels After Contrast-Enhanced MRI in Individuals with Normal Renal Function: a Pilot Study

INTRODUCTION

Gadolinium-based contrast agents (GBCA) have been used to enhance magnetic resonance imaging (MRI) since 1985. Recently, the media and online groups have voiced concerns about gadolinium deposition in patients with normal renal function based on "elevated" urinary gadolinium levels. The determination of increased urinary gadolinium levels is based on reference ranges developed in individuals with normal renal function who were never exposed to GBCA. Studies suggest an elevated gadolinium urinary elimination greater than 72 h post GBCA scan. We evaluated urine gadolinium concentrations over a 30-day period in patients administered GBCA.

METHODS

In this prospective, observational pilot study, we enrolled subjects between 18 and 65 years of age with normal renal function who received GBCA for the first time. Urinary gadolinium was measured at days zero (prior to GBCA exposure), 3, 10, and 30 after GBCA exposure. We compared urinary gadolinium levels after GBCA exposure to the current reference range and calculated an estimated duration of "elevated" gadolinium urine levels in the average patient.

RESULTS

All 13 subjects had 24-h urinary gadolinium levels higher than 0.7 μg/24 h with means of 1944 (± 1432) μg/24 h on day 3, 301 (± 218) μg/24 h on day 10, and 34 (± 33) μg/24 h on day 30. Based on calculated urinary gadolinium elimination kinetics, we estimate urinary gadolinium levels will often remain above the current reference range for > 50 days.

CONCLUSION

The current reference range of 0.7 μg/24 h for 24 h urinary gadolinium is not applicable to patients for at least 30 days following GBCA exposure.

Gadolinium Retention: A Research Roadmap from the 2018 NIH/ACR/RSNA Workshop on Gadolinium Chelates

Gadolinium-based contrast agents (GBCAs) have revolutionized MRI, enabling physicians to obtain crucial life-saving medical information that often cannot be obtained with other imaging modalities. Since initial approval in 1988, over 450 million intravenous GBCA doses have been administered worldwide, with an extremely favorable pharmacologic safety profile; however, recent information has raised new concerns over the safety of GBCAs. Mounting evidence has shown there is long-term retention of gadolinium in human tissues. Further, a small subset of patients have attributed a constellation of symptoms to GBCA exposure, although the association of these symptoms with GBCA administration or gadolinium retention has not been proven by scientific investigation. Despite evidence that macrocyclic GBCAs show less gadolinium retention than linear GBCAs, the safety implications of gadolinium retention are unknown. The mechanism and chemical forms of gadolinium retention, as well as the biologic activity and clinical importance of these retained gadolinium species, remain poorly understood and underscore the need for additional research. In February 2018, an international meeting was held in Bethesda, Md, at the National Institutes of Health to discuss the current literature and knowledge gaps about gadolinium retention, to prioritize future research initiatives to better understand this phenomenon, and to foster collaborative standardized studies. The greatest priorities are to determine (a) if gadolinium retention adversely affects the function of human tissues, (b) if retention is causally associated with short- or long-term clinical manifestations of disease, and (c) if vulnerable populations, such as children, are at greater risk for experiencing clinical disease. The purpose of the research roadmap is to highlight important information that is not known and to identify and prioritize needed research. ©RSNA, 2018 Online supplemental material is available for this article .

Quantification and Assessment of the Chemical Form of Residual Gadolinium in the Brain After Repeated Administration of Gadolinium-Based Contrast Agents: Comparative Study in Rats

Supplemental digital content is available in the text.

Objective

Multiple clinical and preclinical studies have reported a signal intensity increase and the presence of gadolinium (Gd) in the brain after repeated administration of Gd-based contrast agents (GBCAs). This bioanalytical study in rat brain tissue was initiated to investigate whether the residual Gd is present as intact GBCA or in other chemical forms by using tissue fractionation and chromatography.

Materials and Methods

Rats were divided randomly in 6 groups of 10 animals each. They received 10 daily injections of 2.5 mmol/kg bodyweight of 1 of 5 different GBCAs: linear GBCAs such as gadodiamide (Omniscan; GE Healthcare), gadopentetate dimeglumine (Gd-DTPA, Magnevist; Bayer), or gadobenate dimeglumine (Multihance; Bracco) and macrocyclic GBCAs such as gadobutrol (Gadovist; Bayer) and gadoterate meglumine (Gd-DOTA, Dotarem; Guerbet) or saline. On days 3 and 24 after the last injection (p.i.), 5 randomly chosen animals of each group were killed by exsanguination, and their brains were excised and divided into cerebrum, pons, and cerebellum. The brain sections were homogenized by sonication in ice-cold buffer at pH 7.4. Soluble and insoluble fractions were separated by centrifugation, and the soluble fractions were further separated by gel permeation chromatography (GPC). The Gd concentration in all tissue fractions and in the GPC eluate was measured by inductively coupled plasma–mass spectrometry. In a recovery control experiment, all GBCAs were spiked to blank brain tissue and more than 94% recovery of Gd in the tissue fractions was demonstrated.

Results

Only traces of the administered Gd were found in the rat brain tissue on day 3 and day 24 p.i. In the animals treated with macrocyclic GBCAs, Gd was found only in the soluble brain fraction and was present solely as low molecular weight molecules, most likely the intact GBCA. In the animals treated with linear GBCAs Gd was found to a large extent in the insoluble tissue fraction. The Gd concentration in the soluble fraction was comparable to the macrocyclic agents. According to GPC, a smaller portion of the Gd in the soluble fraction of the linear GBCAs groups was bound to macromolecules larger than 250 to 300 kDa. The nature of the Gd-containing macromolecules and the insoluble species were not determined, but they appeared to be saturable with Gd. The excretion of the soluble Gd species in the linear and macrocyclic GBCA groups was still ongoing between days 3 and 24 p.i. This was also observed for the macromolecular Gd species in the linear GBCA groups, but at a slower rate.

Conclusions

The residual Gd found in the rat brain after repeated administration of all 3 linear GBCAs was present in at least 3 distinctive forms—soluble small molecules, including the intact GBCA, soluble macromolecules, and to a large extent in insoluble form. The latter 2 are most likely responsible for the prolonged signal intensity enhancement in brain structures observed in magnetic resonance imaging. No relevant differences between the 3 linear GBCAs were observed. The Gd concentrations in the brain after administration of macrocyclic GBCAs are lower, and the Gd is only present in soluble small molecules, which were slowly excreted. This underlines the crucial importance of the kinetic inertness of macrocyclic agents in the prevention of potential retention of Gd in the brain compared with the 3 linear, kinetically less restricted GBCAs.

Metaplastic Ossification of the Temporal Artery with Osteoclast-Like Giant Cells: A Mimicker of Giant Cell (Temporal) Arteritis

Purpose

To describe a patient presenting with suspected giant cell (temporal) arteritis (GCA) in whom subsequent temporal artery biopsy showed luminal narrowing by medial calcification, metaplastic ossification, and fibrointimal proliferation, consistent with calciphylaxis.

Methods

A 55-year-old man with end-stage renal disease presented with unilateral loss of vision and elevated erythrocyte sedimentation rate and was initially treated as though he had GCA; however, a subsequent temporal artery biopsy showed marked luminal narrowing by medial calcification, metaplastic ossification, and fibrointimal proliferation, consistent with calciphylaxis. In addition, the tunica media of the affected artery contained multinucleate giant cells, but these represented osteoclasts and foreign body giant cells reacting to calcium, rather than a part of GCA.

Results

This is a rare report of metaplastic ossification and the finding of non-GCA-related giant cells in the tunica media of the temporal artery, thus representing a clinical and histopathologic mimicker of GCA.

Conclusions

The clinical differential diagnosis of GCA includes other etiologies that can present similarly; however, temporal artery biopsy can discern the underlying pathology. Importantly, the identification of giant cells is not required for the diagnosis of GCA, and likewise, as our case shows, the finding of giant cells in the wall of a temporal artery does not always imply a diagnosis of GCA.

Gadolinium Deposition and Chronic Toxicity

Clinicians, radiologists, and patients should be aware of the most up-to-date data on the risks of gadolinium-based contrast agent (GBCA) administration. In this review, we discuss in vivo gadolinium retention, particularly brain tissue retention, and potential toxic effects. GBCA pharmacokinetics and biodistribution are reviewed briefly. Based on the more recent published literature and society guidelines, general safety recommendations for clinical practice are provided.

The gadolinium-based contrast agent Omniscan® promotes in vitro fibroblast survival through in situ precipitation

The current study aims to explore how the gadolinium (Gd)-based contrast agent (GBCA) Omniscan® enhanced cell viability of murine fibroblasts. The results of scanning electron microscopy showed that Omniscan® can precipitate in cell culture media and deposit on cell membranes. Energy-dispersive X-ray analysis and Fourier-transform infrared spectroscopy demonstrated the presence of Gd and phosphates in the agglomerated particles. By filtering the Omniscan®-containing medium through a 220 nm filter, it can be clearly found that the increased cell viability should be mainly attributed to the insoluble species of gadolinium rather than to chelated gadolinium. Moreover, the effects of other gadolinium-based contrast agents, Magnevist® and Dotarem®, were compared with that of Omniscan®. It is noted that the three contrast agents differed in their ability to induce cell viability, which is possibly ascribed to the different chemical stabilities of gadolinium chelates as demonstrated by the attenuation in cell growth upon the addition of excess ligands to the compounds. The results of flow cytometry analysis also showed that Omniscan® can promote cell growth via an increase in the S-phase cell population as evidenced by the elevated levels of cell cycle associated proteins cyclin D, cyclin A and the phosphorylated Rb protein. Furthermore, our results revealed that integrin-mediated signaling may play an important role in both Omniscan® and Magnevist®-enhanced focal adhesion formation since the blockade of integrins decreased the level of ERK phosphorylation induced by the two GBCAs. Taken together, these data suggested that in situ gadolinium phosphate precipitation formation mediated Omniscan®-promoted fibroblast survival, which is similar to that of gadolinium chloride. It was demonstrated that the application of GBCAs with more stable thermodynamic stability may cause less dissociation of the gadolinium ion and thus resulted in less precipitation, finally leading to lower occurrence of nephrogenic systemic fibrosis. The obtained results would also be helpful for the development of safe gadolinium-based contrast agents.

Gadolinium-Based Contrast Agent Accumulation and Toxicity: An Update

In current practice, gadolinium-based contrast agents have been considered safe when used at clinically recommended doses in patients without severe renal insufficiency. The causal relationship between gadolinium-based contrast agents and nephrogenic systemic fibrosis in patients with renal insufficiency resulted in new policies regarding the administration of these agents. After an effective screening of patients with renal disease by performing either unenhanced or reduced-dose-enhanced studies in these patients and by using the most stable contrast agents, nephrogenic systemic fibrosis has been largely eliminated since 2009. Evidence of in vivo gadolinium deposition in bone tissue in patients with normal renal function is well-established, but recent literature showing that gadolinium might also deposit in the brain in patients with intact blood-brain barriers caught many individuals in the imaging community by surprise. The purpose of this review was to summarize the literature on gadolinium-based contrast agents, tying together information on agent stability and animal and human studies, and to emphasize that low-stability agents are the ones most often associated with brain deposition.

Prospective Cohort Study of Nephrogenic Systemic Fibrosis in Patients With Stage 3-5 Chronic Kidney Disease Undergoing MRI With Injected Gadobenate Dimeglumine or Gadoteridol

OBJECTIVE

The purpose of this study was to determine the incidence of nephrogenic systemic fibrosis (NSF) in patients with chronic kidney disease (CKD) and moderate-to-severe impairment of kidney function who had not previously been exposed to gadolinium-based contrast agents (GBCAs) or referred to undergo contrast-enhanced MRI with gadobenate dimeglumine or gadoteridol.

SUBJECTS AND METHODS

Two multicenter prospective cohort studies evaluated the incidence of unconfounded NSF in patients with stage 3 CKD (estimated glomerular filtration rate [eGFR] in cohort 1, 30-59 mL/min/1.73 m(2)) or stage 4 or 5 CKD (eGFR in cohort 2, < 30 mL/min/1.73 m(2)) after injection of gadobenate dimeglumine (study A) or gadoteridol (study B). A third study (study C) determined the incidence of NSF in patients with stage 4 or 5 CKD who had not received a GBCA in the 10 years before enrollment. Monitoring for signs and symptoms suggestive of NSF was performed via telephone at 1, 3, 6, and 18 months, with clinic visits occurring at 1 and 2 years.

RESULTS

For studies A and B, the populations evaluated for NSF comprised 363 and 171 patients, respectively, with 318 and 159 patients in cohort 1 of each study, respectively, and with 45 and 12 patients in cohort 2, respectively. No signs or symptoms of NSF were reported or detected during the 2 years of patient monitoring. Likewise, no cases of NSF were reported for any of the 405 subjects enrolled in study C.

CONCLUSION

To our knowledge, and consistent with reports in the literature, no association of gadobenate dimeglumine or gadoteridol with unconfounded cases of NSF has yet been established. Study data confirm that both gadoteridol and gadobenate dimeglumine properly belong to the class of GBCAs considered to be associated with the lowest risk of NSF.

T1-Weighted Hypersignal in the Deep Cerebellar Nuclei After Repeated Administrations of Gadolinium-Based Contrast Agents in Healthy Rats: Difference Between Linear and Macrocyclic Agents

OBJECTIVES

To prospectively compare in healthy rats the effect of multiple injections of macrocyclic (gadoterate meglumine) and linear (gadodiamide) gadolinium-based contrast agents (GBCAs) on T1-weighted signal intensity in the deep cerebellar nuclei (DCN), including the dentate nucleus.

MATERIALS AND METHODS

Healthy rats (n = 7/group) received 20 intravenous injections of 0.6 mmol of gadolinium (Gd) per kilogram (4 injections per week during 5 weeks) of gadodiamide, gadoterate meglumine, or hyperosmolar saline (control group). Brain T1-weighted magnetic resonance imaging was performed before and once a week during the 5 weeks of injections and during 5 additional weeks (treatment-free period). Gadolinium concentrations were measured with inductively coupled plasma mass spectrometry in plasma and brain. Blinded qualitative and quantitative evaluations of the T1 signal intensity in DCN were performed, as well as a statistical analysis on quantitative data.

RESULTS

A significant and persistent T1 signal hyperintensity in DCN was observed only in gadodiamide-treated rats. The DCN-to-cerebellar cortex signal ratio was significantly increased from the 12th injection of gadodiamide (1.070 ± 0.024) compared to the gadoterate meglumine group (1.000 ± 0.033; P < 0.001) and control group (1.019 ± 0.022; P < 0.001) and did not significantly decrease during the treatment-free period. Total Gd concentrations in the gadodiamide group were significantly higher in the cerebellum (3.66 ± 0.91 nmol/g) compared with the gadoterate meglumine (0.26 ± 0.12 nmol/g; P < 0.05) and control (0.06 ± 0.10 nmol/g; P < 0.05) groups.

CONCLUSIONS

Repeated administrations of the linear GBCA gadodiamide to healthy rats are associated with progressive and persistent T1 signal hyperintensity in the DCN, with Gd deposition in the cerebellum in contrast with the macrocyclic GBCA gadoterate meglumine for which no effect was observed.

Risk of nephrogenic systemic fibrosis is low in patients with chronic liver disease exposed to gadolinium-based contrast agents

PURPOSE

To determine the risk of nephrogenic systemic fibrosis (NSF) in a cohort of patients with chronic liver disease.

MATERIALS AND METHODS

This retrospective, Institutional Review Board (IRB)-approved, Health Insurance Portability and Accountability Act (HIPAA)-compliant study was performed at a single tertiary liver center. The study cohort comprised 1167 patients with chronic liver disease followed in a liver clinic and exposed to gadolinium-based contrast agents (GBCAs) between February 2004 and October 2007. A retrospective review of medical records was performed. For each patient, data were collected on demographics, history of GBCA exposure, presence of purported risk factors for NSF, and histopathological evidence of NSF.

RESULTS

Of the 1167 patients with chronic liver disease, 58% (n = 678) had cirrhosis. The patients had a total of 2421 separate GBCA exposures. Fifty-five percent (n = 646) had a single exposure, 19% (n = 218) had two exposures, and 26% (n = 303) had three or more exposures. Seventy-two percent (n = 843) of patients had renal insufficiency, 25 patients (2.1%) had hepatorenal syndrome, 80 patients (6.8%) were in the perioperative liver transplant period, and 49 patients (4.2%) had one or more additional risk factors for NSF. None of the 1167 patients developed NSF.

CONCLUSION

Chronic liver disease does not appear to be a significant risk factor for NSF.

Diagnosis of nephrogenic systemic fibrosis by means of elemental bioimaging and speciation analysis

The combined use of elemental bioimaging and speciation analysis is presented as a novel means for the diagnosis of nephrogenic systemic fibrosis (NSF), a rare disease occurring after administration of gadolinium-based contrast agents (GBCA) for magnetic resonance imaging (MRI), in skin samples of patients suffering from renal insufficiency. As the pathogenesis of NSF is still largely unknown particularly with regard to the distribution and potential retention of gadolinium in the human organism, a skin biopsy sample from a suspected NSF patient was investigated. The combination of inductively coupled plasma mass spectrometry (ICP-MS), laser ablation (LA) ICP-MS for quantitative elemental bioimaging, and hydrophilic interaction liquid chromatography (HILIC) ICP-MS for speciation analysis allowed one to unambiguously diagnose the patient as a case of NSF. By means of ICP-MS, a total gadolinium concentration from 3.02 to 4.58 mg/kg was determined in the biopsy sample, indicating a considerable deposition of gadolinium in the patient's skin. LA-ICP-MS revealed a distinctly inhomogeneous distribution of gadolinium as well as concentrations of up to 400 mg/kg in individual sections of the skin biopsy. Furthermore, the correlation between the distributions of phosphorus and gadolinium suggests the presence of GdPO4 deposits in the tissue section. Speciation analysis by means of HILIC-ICP-MS showed the presence of the intact GBCA Gd-HP-DO3A eight years after the administration to the patient. The concentration of the contrast agent in the aqueous extract of the skin biopsy was found to be 1.76 nmol/L. Moreover, evidence for the presence of further highly polar gadolinium species in low concentrations was found.

Localized cutaneous argyria: two case reports and clinicopathologic review

We report 2 cases of patients who presented with blue macules clinically suspicious for blue nevi. One patient had no documented history of trauma or silver exposure, and the other reported exposure to silver over 30 years ago. Microscopic examination revealed a dermal population of brown-black globules predominantly adhering to collagen fibers. In both cases, no melanocytic proliferation was identified by immunohistochemistry. Analysis of the skin biopsies with scanning electron microscopy and energy dispersive x-ray spectroscopy demonstrated the presence of silver and selenium. These findings were diagnostic of localized cutaneous argyria. Our case reports highlight the importance of including localized cutaneous argyria in the differential diagnosis of pigmented lesions.

Design of ProCAs (protein-based Gd(3+) MRI contrast agents) with high dose efficiency and capability for molecular imaging of cancer biomarkers

Magnetic resonance imaging (MRI) is the leading imaging technique for disease diagnostics, providing high resolution, three-dimensional images noninvasively. MRI contrast agents are designed to improve the contrast and sensitivity of MRI. However, current clinically used MRI contrast agents have relaxivities far below the theoretical upper limit, which largely prevent advancing molecular imaging of biomarkers with desired sensitivity and specificity. This review describes current progress in the development of a new class of protein-based MRI contrast agents (ProCAs) with high relaxivity using protein design to optimize the parameters that govern relaxivity. Further, engineering with targeting moiety allows these contrast agents to be applicable for molecular imaging of prostate cancer biomarkers by MRI. The developed protein-based contrast agents also exhibit additional in vitro and in vivo advantages for molecular imaging of disease biomarkers, such as high metal-binding stability and selectivity, reduced toxicity, proper blood circulation time, and higher permeability in tumor tissue in addition to improved relaxivities.

Transmetallation of Gd-DTPA by Fe3+, Cu2+ and Zn2+ in water: batch experiments and coagulation-flocculation simulations

The study investigates the stability of gadolinium-DTPA complex in presence of competing metallic ions, Fe(3+), Cu(2+) and Zn(2+) using batch experiments and coagulation-flocculation simulations. High performance liquid chromatography with fluorescence detection was used for simultaneous analysis of chelate gadolinium (Gd-DTPA) and free Gd(III) ion in water. It was shown that Cu(2+) has a strong affinity for DTPA and could lead to a complete release of Gd(3+). Fe(3+) appeared also to compete strongly with Gd(3+) for DTPA binding since up to 80% of Gd-complex was dissociated under iron excess condition. Finally, zinc had a lower influence on Gd speciation: only 15% of Gd(3+) was released with addition of a 5-fold excess of Zn(2+). During coagulation-flocculation simulation, Fe(3+) was able to displace about 27% of Gd-DTPA, and no adsorption was observed onto flocs.

Fibrosis-associated single-nucleotide polymorphisms in TGFB1 and CAV1 are not associated with the development of nephrogenic systemic fibrosis

OBJECTIVE

To test the hypothesis that the subset of patients with impaired renal function who are exposed to gadolinium-containing contrast agents (GCCAs) and develop nephrogenic systemic fibrosis (NSF) have a genetic predisposition for disease.

METHODS

We examined whether an intronic single-nucleotide polymorphism (SNP) in caveolin-1 (CAV1 rs4730751) and 2 coding SNPs in transforming growth factor-beta 1 (TGFB1 rs1800471, codon 25; and rs1800470, codon 10) were associated with the NSF phenotype.

RESULTS

Forty-one patients with a history of chronic kidney disease and GCCA administration were studied, including NSF cases (n = 17) and control subjects (n = 24) without clinical or histological evidence of NSF. No significant differences in the genotype frequencies at these SNPs in TGFB1 and CAV1 were found between patients with NSF and subjects without NSF.

CONCLUSIONS

We conclude that polymorphisms in the genes encoding TGFB1 and CAV1 previously associated with the development and progression of fibrosis in several organ systems are not associated with development of NSF in this cohort of patients with renal impairment after GCCA exposure.

Gadolinium-containing magnetic resonance contrast media: investigation on the possible transchelation of Gd³⁺ to the glycosaminoglycan heparin

Retention of gadolinium (Gd) in biological tissues is considered an important cofactor in the development of nephrogenic systemic fibrosis (NSF). Research on this issue has so far focused on the stability of Gd-based contrast media (GdCM) and a possible release of Gd³⁺ from the complex. No studies have investigated competing chelators that may occur in vivo. We performed proton T(1) -relaxometry in solutions of nine approved GdCM and the macromolecular chelator heparin (250 000 IU per 10 ml) without and with addition of ZnCl₂. For the three linear, nonspecific GdCM complexes, Omniscan®, OptiMARK® and Magnevist®, 2 h of incubation in heparin at 37 °C in the presence of 2.0 mm ZnCl₂ led to an increase in T₁-relaxivity by a factor of 7.7, 5.6 and 5.1, respectively. For the three macrocyclic complexes, Gadovist®, Dotarem® and Prohance®, only a minor increase in T₁-relaxivity by a factor of 1.5, 1.6 and 1.7 was found, respectively. Without addition of ZnCl₂, no difference between the two GdCM groups was observed (factors of 1.4, 1.2, 1.1, 1.3, 1.5 and 1.4, respectively). The increase in T₁-relaxivities observed for linear GdCM complexes may be attributable to partial transchelation with formation of a macromolecular Gd-heparin complex. For comparison, mixing of GdCl₃ and heparin results in a 8.7-fold higher T₁-relaxivity compared with a solution of GdCl₃ in water. Heparin is a glycosaminoglycan (GAG) and as such occurs in the human body as a component of the extracellular matrix. GAGs generally are known to be strong chelators. Gd³⁺ released from chelates of GdCM might be complexed by GAGs in vivo, which would explain their retention in biological tissues. Plasma GAG levels are elevated in end-stage renal disease; hence, our results might contribute to the elucidation of NSF.

Extracellular matrix remodelling properties of human fibrocytes

The fibrocytes are thought to serve as a source of newly deposited collagens I and III during reparative processes and in certain fibrotic disorders, but their matrix remodelling properties are incompletely understood. We evaluated their ability to produce several extracellular matrix (ECM) components, in comparison with fibroblasts, and to participate in collagen turnover. The collagen gene expression profile of fibrocytes differed from that of fibroblasts because fibrocytes constitutively expressed relatively high levels of the mRNA encoding collagen VI and significantly lower levels of the mRNA encoding collagens I, III and V. The proteoglycan (PG) gene expression profile was also different in fibrocytes and fibroblasts because fibrocytes constitutively expressed the mRNA encoding perlecan and versican at relatively high levels and the mRNA encoding biglycan and decorin at low and very low levels, respectively. Moreover, fibrocytes expressed the mRNA for hyaluronan synthase 2 at higher level than fibroblasts. Significant differences between the two cell populations were also demonstrated by metabolic labelling and analysis of the secreted collagenous proteins, PGs and hyaluronan. Fibrocytes constitutively expressed the scavenger receptors CD163 and CD204 as well as the mannose receptors CD206 and Endo180, and internalized and degraded collagen fragments through an Endo180-mediated mechanism. The results of this study demonstrate that human fibrocytes exhibit ECM remodelling properties previously unexplored, including the ability to participate in collagen turnover. The observed differences in collagen and PG expression profile between fibrocytes and fibroblasts suggest that fibrocytes may predominantly have a matrix-stabilizing function.