Clinical, biological, and skin histopathologic effects of ionic macrocyclic and nonionic linear gadolinium chelates in a rat model of nephrogenic systemic fibrosis

Dermatological Manifestations in Patients With Chronic Kidney Disease: A Review

Chronic kidney disease (CKD) is a progressive disease and has multiple clinical manifestations; when CKD reaches the end stage, at least one cutaneous manifestation appears due to some increased toxin levels or a constant proinflammatory state. Nonspecific manifestations include pruritus, xerosis, pigmentation disorders, acquired ichthyosis, purpuric spots, and nail disorders. Some specific manifestations are bullous dermatoses, acquired perforating dermatoses (APD), eruptive xanthoma, access site infections, calcifying disorders, and nephrogenic systemic fibrosis (NSF). All these cutaneous changes negatively impact patients; early recognition and diagnosis of these dermatoses will make a difference in their quality of treatment. Exploring a patient's skin is fundamental to suspect some diseases and increased toxin levels; pruritus occurs when uremic toxins are raised, and nail disorders are associated with hypoalbuminemia. This review provides the clinician with information on the clinical manifestations that occur in CKD, including epidemiology, pathophysiology, clinical manifestations, diagnosis, histopathology, treatment, and life impact of the dermatoses in CKD.

Gadolinium-Cyclic 1,4,7,10-Tetraazacyclododecane-1,4,7,10-Tetraacetic Acid-Click-Sulfonyl Fluoride for Probing Serine Protease Activity in Magnetic Resonance Imaging

Serine protease is linked to a wide range of diseases, prompting the development of robust, selective, and sensitive protease assays and sensing methods. However, the clinical needs for serine protease activity imaging have not yet been met, and the efficient in vivo detection and imaging of serine protease remain challenging. Here, we report the development of the gadolinium-cyclic 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid-click-Sulfonyl Fluoride (Gd-DOTA-click-SF) MRI contrast agent targeting serine protease. The HR-FAB mass spectrum confirmed the successful formation of our designed chelate. The molar longitudinal relaxivity (r₁) of the Gd-DOTA-click-SF probe (r₁ = 6.82 mM^-1 s^-1) was significantly higher than that of Dotarem (r₁ = 4.63 mM^-1 s^-1), in the range of 0.01-0.64 mM at 9.4 T. The in vitro cellular study and the transmetallation kinetics study showed that the safety and stability of this probe are comparable to those of conventional Dotarem. Ex vivo abdominal aortic aneurysm (AAA) MRI revealed that this probe has a contrast-agent-to-noise ratio (CNR) that is approximately 51 ± 23 times greater than that of Dotarem. This study of superior visualization of AAA suggests that it has the potential to detect elastase in vivo and supports the feasibility of probing serine protease activity in T1-weighted MRI.

Physicochemical and Pharmacokinetic Profiles of Gadopiclenol: A New Macrocyclic Gadolinium Chelate With High T1 Relaxivity

Objectives

We aimed to evaluate gadopiclenol, a newly developed extracellular nonspecific macrocyclic gadolinium-based contrast agent (GBCA) having high relaxivity properties, which was designed to increase lesion detection and characterization by magnetic resonance imaging.

Methods

We described the molecular structure of gadopiclenol and measured the r₁ and r₂ relaxivity properties at fields of 0.47 and 1.41 T in water and human serum. Nuclear magnetic relaxation dispersion profile measurements were performed from 0.24 mT to 7 T. Protonation and complexation constants were determined using pH-metric measurements, and we investigated the acid-assisted dissociation of gadopiclenol, gadodiamide, gadobutrol, and gadoterate at 37°C and pH 1.2. Applying the relaxometry technique (37°C, 0.47 T), we investigated the risk of dechelation of gadopiclenol, gadoterate, and gadodiamide in the presence of ZnCl₂ (2.5 mM) and a phosphate buffer (335 mM). Pharmacokinetics studies of radiolabeled ¹⁵³Gd-gadopiclenol were performed in Beagle dogs, and protein binding was measured in rats, dogs, and humans plasma and red blood cells.

Results

Gadopiclenol [gadolinium chelate of 2,2′,2″-(3,6,9-triaza-1(2,6)-pyridinacyclodecaphane-3,6,9-triyl)tris(5-((2,3-dihydroxypropyl)amino)-5-oxopentanoic acid); registry number 933983-75-6] is based on a pyclen macrocyclic structure. Gadopiclenol exhibited a very high relaxivity in water (r₁ = 12.2 mM⁻¹·s⁻¹ at 1.41 T), and the r₁ value in human serum at 37°C did not markedly change with increasing field (r₁ = 12.8 mM⁻¹·s⁻¹ at 1.41 T and 11.6 mM⁻¹·s⁻¹ at 3 T). The relaxivity data in human serum did not indicate protein binding. The nuclear magnetic relaxation dispersion profile of gadopiclenol exhibited a high and stable relaxivity in a strong magnetic field. Gadopiclenol showed high kinetic inertness under acidic conditions, with a dissociation half-life of 20 ± 3 days compared with 4 ± 0.5 days for gadoterate, 18 hours for gadobutrol, and less than 5 seconds for gadodiamide and gadopentetate. The pharmacokinetic profile in dogs was typical of extracellular nonspecific GBCAs, showing distribution in the extracellular compartment and no metabolism. No protein binding was found in rats, dogs, and humans.

Conclusions

Gadopiclenol is a new extracellular and macrocyclic Gd chelate that exhibited high relaxivity, no protein binding, and high kinetic inertness. Its pharmacokinetic profile in dogs was similar to that of other extracellular nonspecific GBCAs.

Does Age Interfere With Gadolinium Toxicity and Presence in Brain and Bone Tissues?: A Comparative Gadoterate Versus Gadodiamide Study in Juvenile and Adult Rats

OBJECTIVES

The main objective of the study was to assess the effect of age on target tissue total gadolinium (Gd) retention after repeated administration of gadodiamide (linear) or gadoterate (macrocyclic) Gd-based contrast agent (GBCA) in rats. The secondary objective was to assess the potential developmental and long-term consequences of GBCA administration during neonatal and juvenile periods.

MATERIALS AND METHODS

A total of 20 equivalent human clinical doses (cumulated dose, 12 mmol Gd/kg) of either gadoterate or gadodiamide were administered concurrently by the intravenous route to healthy adult and juvenile rats. Saline was administered to juvenile rats forming the control group. In juvenile rats, the doses were administered from postnatal day 12, that is, once the blood-brain barrier is functional as in humans after birth. The tests were conducted on 5 juvenile rats per sex and per group and on 3 adult animals per sex and per group. T1-weighted magnetic resonance imaging of the cerebellum was performed at 4.7 T during both the treatment and treatment-free periods. Behavioral tests were performed in juvenile rats. Rats were euthanatized at 11 to 12 weeks (ie, approximately 3 months) after the last administration. Total Gd concentrations were measured in plasma, skin, bone, and brain by inductively coupled plasma mass spectrometry. Cerebellum samples from the juvenile rats were characterized by histopathological examination (including immunohistochemistry for glial fibrillary acidic protein or GFAP, and CD68). Lipofuscin pigments were also studied by fluorescence microscopy. All tests were performed blindly on randomized animals.

RESULTS

Transient skin lesions were observed in juvenile rats (5/5 females and 2/4 males) and not in adult rats having received gadodiamide. Persisting (up to completion of the study) T1 hyperintensity in the deep cerebellar nuclei (DCNs) was observed only in gadodiamide-treated rats. Quantitatively, a slightly higher progressive increase in the DCN/brain stem ratio was observed in adult rats compared with juvenile rats, whereas no difference was noted visually. In all tissues, total Gd concentrations were higher (10- to 30-fold higher) in the gadodiamide-treated groups than in the gadoterate groups. No age-related differences were observed except in bone marrow where total Gd concentrations in gadodiamide-treated juvenile rats were higher than those measured in adults and similar to those measured in cortical bone tissue. No significant treatment-related effects were observed in histopathological findings or in development, behavior, and biochemistry parameters. However, in the elevated plus maze test, a trend toward an anxiogenic effect was observed in the gadodiamide group compared with other groups (nonsignificant). Moreover, in the balance beam test, a high number of trials were excluded in the gadodiamide group because rats (mainly males) did not completely cross the beam, which may also reflect an anxiogenic effect.

CONCLUSIONS

No T1 hyperintensity was observed in the DCN after administration of the macrocyclic GBCA gadoterate regardless of age as opposed to administration of the linear GBCA gadodiamide. Repeated administration of gadodiamide in neonatal and juvenile rats resulted in similar total Gd retention in the skin, brain, and bone to that in adult rats with sex having no effect, whereas Gd distribution in bone marrow was influenced by age. Further studies are required to assess the form of the retained Gd and to investigate the potential risks associated with Gd retention in bone marrow in juvenile animals treated with gadodiamide. Regardless of age, total Gd concentration in the brain and bone was 10- to 30-fold higher after administration of gadodiamide compared with gadoterate.

[Gadolinium deposition-"gadolinium deposition disease"]

Gadolinium (Gd)-based contrast agents have been routinely used worldwide in diagnostic MRI since 1988. All routinely applied contrast agents for clinical use were considered extremely safe with regard to tolerance, adverse effects and diagnostic efficacy and when used at Food and Drug Administration-approved doses. With the identification of Gd-associated disorders, namely nephrogenic systemic fibrosis and adverse reactions, and in the longer term Gd-retention in the brain, this view changed and led to the withdrawal or restriction of approval of linear Gd chelates in Europe. Even though Gd deposition in different human body areas was described very early, recently published literature of intracerebral accumulation of contrast agents as well as deposition in bone have created surprising attention. Not only was the fact of Gd deposition in the body well known for many years, but there is currently no clinical evidence of patient symptoms and no resulting health issues of patients have been observed yet. The expression "gadolinium deposition disease" has been termed by active patient advocacy groups with an online presence with reports of individual members stating a broad spectrum of disorders yielding a large symptom complex after administration of Gd-based contrast agents without evidence of any pre-existing or otherwise underlying disease process which could explain the mentioned disorder.

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).

Influence of excess ligand on Nephrogenic Systemic Fibrosis associated with nonionic, linear gadolinium-based contrast agents

BACKGROUND

The molecular structure, charge, thermodynamic and kinetic stability are approximately the same for gadodiamide and gadoversetamide, the main substantive difference is that gadodiamide is manufactured with 5% free ligand to form Omniscan® and gadoversetamide with 10% free ligand to form OptiMARK®.

PURPOSE

To determine the relative risk of Nephrogenic Systemic Fibrosis (NSF) between gadodiamide (Omniscan®) and gadoversetamide (OptiMARK®) and to explore the potential contribution of the amount of excess ligand added to their commercial formulations.

MATERIALS AND METHODS

In this retrospective observational study, the number of doses and NSF cases associated with these agents were calculated based on two different approaches: the number of doses was determined based on pharmaceutical companies' information, and the number of unconfounded NSF cases was obtained from the previously published literature based on a legal database. A second analysis estimates the number of doses and NSF cases from the Food and Drug Administration (FDA) Adverse Event Reporting System (FAERS).

RESULTS

Approximately 87 million and 12 million doses of Omniscan® and OptiMARK®, respectively, have been administered worldwide since their original approval for use in the various countries throughout the world. A total of 197 and 8 unconfounded cases of NSF have been reported with Omniscan® and OptiMARK®, rendering an incidence of 2.3/million and 0.7/million for these agents, respectively. The FAERS analysis suggested reported incidences of 13.1/million and 5.0/million.

CONCLUSION

There is an approximately 3-fold greater incidence of NSF from Omniscan® than OptiMARK®. The difference in incidence might reflect the lesser quantity of added free ligand to the formulation of Omniscan®.

Safety of Gadolinium Administration in Children

The introduction of paramagnetic contrast in the late 1980s constituted a paradigm shift boosting the efficacy of magnetic resonance imaging. Due to its high magnetic moment, gadolinium-based contrast agent made its way smoothly as the flagship paramagnetic contrast. With the widespread application, reports of untoward effects started to surface. Allergic reactions, nephrogenic systemic sclerosis, and deposition in brain tissue dented the safety profile of gadolinium-based contrast agent. Better understanding of these adverse effects prompted preventive measures. This article elucidates the gadolinium-based contrast agent toxicity in the pediatric population based on the current available evidence.

Gadolinium deposition and the potential for toxicological sequelae - A literature review of issues surrounding gadolinium-based contrast agents

Every year, approximately 30 million magnetic resonance imaging scans are enhanced with gadolinium-based contrast agents (GBCAs) worldwide. Although the development of nephrogenic systemic fibrosis in patients with renal impairment is well-documented, over recent years it has become apparent that exposure to GBCAs can potentially result in gadolinium deposition within human bone and brain tissue even in the presence of normal renal function. This review will address some of the controversies surrounding the safety of GBCA administration based on evidence from in vivo experiments, animal studies and clinical studies. We additionally evaluate the potential risk of toxicity from exposure to gadolinium in light of new guidance published by the US Food and Drug Administration and the European Medicines Agency, and discuss whether gadolinium deposition disease exists as a new diagnosis.

Brain relaxometry after macrocyclic Gd-based contrast agent

PURPOSE

To assess if ratios of T1-weighted (T1w) signal intensity (SI) and quantitative T1 relaxometry (qT1) change on serial administration of macrocyclic gadobutrol.

METHODS

A total of 17 glioblastoma patients were scanned at 3.0 T magnetic resonance imaging (MRI) every 6 weeks after tumor resection with standard MRI and T1 and T2 relaxometry before and after gadobutrol administration. On co-registered images T1w SI was measured and relaxation times T1 (qT1) and quantitative T2 (qT2) were quantified in several deep grey matter nuclei as ratios relative to frontal white matter and to the pons. Ratio changes were evaluated over time with a paired t‑test and multiple regression.

RESULTS

An average of 8 (range 5-14) scans per patient were completed. Ratios of T1w SI, qT1 and qT2 remained unchanged for all target regions from the first to the last time point (p > 0.05) and did not correlate with the number of gadobutrol administrations. Multivariate regression showed no significant impact of gadobutrol on qT1 or qT2 ratios, but a significant negative effect on T1w SI ratios. Gender also had no impact on the ratios but age had a significant negative influence on the qT1 ratio.

CONCLUSION

Multiple administrations of a macrocyclic contrast agent did not change relaxation time T1 ratios in any deep grey matter structure.

Safety and Efficacy of A High Performance Graphene-Based Magnetic Resonance Imaging Contrast Agent for Renal Abnormalities

The etiology of renal insufficiency includes primary (e.g polycystic kidney disease) or secondary (e.g. contrast media, diabetes) causes. The regulatory restrictions placed on the use of contrast agents (CAs) for non-invasive imaging modalities such as X-ray computed tomography (CT) and magnetic resonance imaging (MRI) affects the clinical management of these patients. With the goal to develop a next-generation CA for unfettered use for renal MRI, here we report, in a rodent model of chronic kidney disease, the preclinical safety and efficacy of a novel nanoparticle CA comprising of manganese (Mn2+) ions intercalated graphene coated with dextran (hereafter called Mangradex). Nephrectomized rats received single or 5 times/week repeat (2 or 4 weeks) intravenous (IV) injections of Mangradex at two potential (low = 5 mg/kg, and high = 50 mg/kg) therapeutic doses. Histopathology results indicate that Mangradex does not elicit nephrogenic systemic fibrosis (NSF)-like indicators or questionable effects on vital organs of rodents. MRI at 7 Tesla magnetic field was performed on these rats immediately after IV injections of Mangradex at one potential therapeutic dose (25 mg/kg, [Mn2+] = 60 nmoles/kg) for 90 minutes. The results indicated significant (>100%) and sustained contrast enhancement in the kidney and renal artery at these low paramagnetic ion (Mn2+) concentration; 2 orders of magnitude lower than the paramagnetic ion concentration in a typical clinical dose of long circulating Gd3+-based MRI CA gadofosveset trisodium. The results open avenues for further development of Mangradex as a MRI CA to diagnose and monitor abnormalities in renal anatomy and vasculature.

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.

Gadodiamide and Dentate Nucleus T1 Hyperintensity in Patients With Meningioma Evaluated by Multiple Follow-Up Contrast-Enhanced Magnetic Resonance Examinations With No Systemic Interval Therapy

The dentate nucleus of the cerebellum may appear as hyperintense on unenhanced T1 magnetic resonance images (MRIs) of the brain. Recently, T1 signal hyperintensity has received attention owing to data on the association of this finding with the history of multiple injections of gadolinium-based contrast agents, specifically gadodiamide, in patients with multiple sclerosis and brain metastases. We conducted a retrospective study on patients with a meningioma who had routinely undergone follow-up enhanced MRI scans with gadodiamide. Across a time interval of 18 months (from January 2013 to July 2014), we identified 102 consecutive patients eligible for this study. A significant increase in T1 hyperintensity of the dentate nuclei of the cerebellum on nonenhanced scans was observed between the first and the last MRI in the group of patients with a history of at least 6 enhanced MRI scans (P < 0.01), whereas no differences were observed in the group with 1 to 5 enhanced MRI scans (P = 0.74). Further research is necessary to shed light on the mechanism of the T1 hyperintensity as well as on the histological and microstructural appearance of the dentate nucleus after multiple intravenous injections of gadodiamide. The finding raises the question of substantial dechelation of this agent in patients with normal renal function.

Linear Gadolinium-Based Contrast Agents Are Associated With Brain Gadolinium Retention in Healthy Rats

OBJECTIVES

The aim of this study was to evaluate Gd retention in the deep cerebellar nuclei (DCN) of linear gadolinium-based contrast agents (GBCAs) compared with a macrocyclic contrast agent.

MATERIALS AND METHODS

The brain tissue retention of Gd of 3 linear GBCAs (gadobenate dimeglumine, gadopentetate dimeglumine, and gadodiamide) and a macrocyclic GBCA (gadoterate meglumine) was compared in healthy rats (n = 8 per group) that received 20 intravenous injections of 0.6 mmol Gd/kg (4 injections per week for 5 weeks). An additional control group with saline was included. T1-weighted magnetic resonance imaging was performed before injection and once a week during the 5 weeks of injections and for another 4 additional weeks after contrast period. Total gadolinium concentration was measured with inductively coupled plasma mass spectrometry. Blinded qualitative and quantitative evaluations of the T1 signal intensity in DCN were performed, as well as a statistical analysis on quantitative data.

RESULTS

At completion of the injection period, all the linear contrast agents (gadobenate dimeglumine, gadopentetate dimeglumine, and gadodiamide) induced a significant increase in signal intensity in DCN, unlike the macrocyclic GBCA (gadoterate meglumine) or saline. The T1 hypersignal enhancement kinetic was fast for gadodiamide. Total Gd concentrations for the 3 linear GBCAs groups at week 10 were significantly higher in the cerebellum (1.21 ± 0.48, 1.67 ± 0.17, and 3.75 ± 0.18 nmol/g for gadobenate dimeglumine, gadopentetate dimeglumine, and gadodiamide, respectively) than with the gadoterate meglumine (0.27 ± 0.16 nmol/g, P < 0.05) and saline (0.09 ± 0.12 nmol/g, P < 0.05). No significant difference was observed between the macrocyclic agent and saline.

CONCLUSIONS

Repeated administrations of the linear GBCAs gadodiamide, gadobenate dimeglumine, and gadopentetate dimeglumine to healthy rats were associated with progressive and significant T1 signal hyperintensity in the DCN, along with Gd deposition in the cerebellum. This is in contrast with the macrocyclic GBCA gadoterate meglumine for which no effect was observed.

Gadolinium-based contrast agents: did we miss something in the last 25 years?

In the last 24 months, several clinical and experimental studies, suggested first and demonstrated later, a progressive concentration of Gadolinium in the brain of normal renal function patients, following repeated injections of some of the commercially approved Gadolinium-Based Contrast Agents. Although, till now, Gadolinium brain deposits have not been associated to any kind of neurological signs or symptoms, they oblige the radiology community to modify the actual approach in using Gadolinium contrast media in daily practice, to reduce unknown possible risks for patients.

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.

Thermodynamic stability, kinetic inertness and relaxometric properties of monoamide derivatives of lanthanide(III) DOTA complexes

A complete thermodynamic and kinetic solution study on lanthanide(III) complexes with monoacetamide (DOTAMA, L1) and monopropionamide (DOTAMAP, L2) derivatives of DOTA (DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) was undertaken with the aim to elucidate their stability and inertness in aqueous media. The stability constants of GdL1 and GdL2 are comparable, whereas a more marked difference is found in the kinetic inertness of the two complexes. The formation of the Eu(III) and Ce(III) complexes takes place via the formation of the protonated intermediates which can deprotonate and transform into the final complex through a OH(-) assisted pathway. GdL2 shows faster rates of acid catalysed decomplexation with respect to GdL1, which has a kinetic inertness comparable to GdDOTA. Nevertheless, GdL2 is one order of magnitude more inert than GdDO3A. A novel DOTAMAP-based bifunctional chelating ligand and its deoxycholic acid derivative (L5) were also synthesized. Since the coordinated water molecule in GdL2 is characterized by an exchange rate ca. two orders of magnitude greater than in GdL1, the relaxivity of the macromolecular derivatives of L5 should not be limited by the slow water exchange process. The relaxometric properties of the supramolecular adduct of GdL5 with human serum albumin (HSA) were investigated in aqueous solution by measuring the magnetic field dependence of the (1)H relaxivity which, at 20 MHz and 298 K, shows a 430% increase over that of the unbound GdL5 chelate. Thus, Gd(III) complexes with DOTAMAP macrocyclic ligands can represent good candidates for the development of stable and highly effective bioconjugate systems for molecular imaging applications.

Total gadolinium tissue deposition and skin structural findings following the administration of structurally different gadolinium chelates in healthy and ovariectomized female rats

OBJECTIVE

To assess the retention of gadolinium (Gd) in skin, liver, and bone following gadodiamide or gadoteric acid administration.

METHODS

Gd was measured in skin, liver and femur bone in female rats 10 weeks after administration of 17.5 mmol Gd/kg over 5 days of Gd agents. Rat skin microscopy, energy filtering transmission electron microscopy and elemental analysis were performed, and repeated after receiving the same dosage of gadodiamide in rats with osteoporosis induced with bilateral ovariectomy (OVX). The OVX was performed 60 days after the last injection of gadodiamide and animals sacrificed 3 weeks later.

RESULTS

Gd concentration was 180-fold higher in the skin, 25-fold higher in the femur, and 30-fold higher in the liver in rats received gadodiamide than rats received gadoteric acid. The retention of Gd in the skin with gadodiamide was associated with an increase in dermal cellularity, and Gd encrustation of collagen fibers and deposition inside the fibroblasts and other cells. No differences in Gd concentration in liver, skin, and femur were observed between rats receiving gadodiamide with or without OVX.

CONCLUSIONS

Gd tissue retention with gadodiamide was higher than gadoteric acid. Tissues Gd deposition did not alter following gadodiamide administration to ovariectomized rats.

Do ASARM peptides play a role in nephrogenic systemic fibrosis?

Nephrogenic systemic fibrosis (NSF) is a devastating condition associated with gadolinium (Gd3+)-based contrast agents (GBCAs) in patients with kidney disease. The release of toxic Gd3+ from GBCAs likely plays a major role in NSF pathophysiology. The cause and etiology of Gd3+ release from GBCAs is unknown. Increased Acidic Serine Aspartate Rich MEPE-associated peptides (ASARM peptides) induce bone mineralization abnormalities and contribute to renal phosphate-handling defects in inherited hypophosphatemic rickets and tumor-induced osteomalacia. The proteolytic cleavage of related bone matrix proteins with ASARM motifs results in release of ASARM peptide into bone and circulation. ASARM peptides are acidic, reactive, phosphorylated inhibitors of mineralization that bind Ca2+ and hydroxyapatite. Since the ionic radius of Gd3+ is close to that of Ca2+, we hypothesized that ASARM peptides increase the risk of NSF by inducing release of Gd3+ from GBCAs. Here, we show 1) ASARM peptides bind and induce release of Gd3+ from GBCAs in vitro and in vivo; 2) A bioengineered peptide (SPR4) stabilizes the Gd3+-GBCA complex by specifically binding to ASARM peptide in vitro and in vivo; and 3) SPR4 peptide infusion prevents GBCA-induced NSF-like pathology in a murine model with increased ASARM peptide (Hyp mouse). We conclude ASARM peptides may play a role in NSF and SPR4 peptide is a candidate adjuvant for preventing or reducing risk of disease.

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.

Incidence of nephrogenic systemic fibrosis in patients undergoing dialysis after contrast-enhanced magnetic resonance imaging with gadolinium-based contrast agents: the Prospective Fibrose Nephrogénique Systémique study

BACKGROUND

Nephrogenic systemic fibrosis (NSF) has been related to the use of gadolinium-based contrast agents (GBCAs) in patients undergoing dialysis. The Prospective Fibrose Nephrogénique Systémique study, a French prospective study supported by the French drug regulatory agency (Agence Nationale de Sécurité du Médicament) and the French Societies of Nephrology, Dermatology, and Radiology, aimed at determining the incidence of NSF in patients undergoing long-term dialysis.

MATERIALS AND METHODS

Adult patients undergoing long-term dialysis receiving a magnetic resonance imaging (MRI) examination prescribed between January 15, 2009 and May 31, 2011, with or without GBCA were included. The methodology was based on a patient form intended to detect any dermatological event (DE) that may occur within 4 months after the examination. Further investigations were planned with their physicians if a DE was reported.

RESULTS

A total of 571 patients were included. A total of 50.3% received GBCA. Among them, 93.4% received a macrocyclic GBCA, usually gadoteric acid (88.9%). All in all, 22 patients (3.9%) reported a DE. Dermatological diagnoses did not reveal any evidence of NSF.

CONCLUSIONS

The incidence of NSF after a single dose of a macrocyclic GBCA is null in our sample of 268 patients undergoing dialysis (hemodialysis and peritoneal dialysis). This incidence is just lower than 0.5%. When contrast-enhanced MRI can be essential, or even decisive, to the diagnosis, these results are important and reassuring if physicians need to perform contrast-enhanced MRI in patients undergoing dialysis.

A novel gadolinium-based trimetasphere metallofullerene for application as a magnetic resonance imaging contrast agent

OBJECTIVE

Macromolecular contrast agents for magnetic resonance imaging (MRI) are useful blood-pool agents because of their long systemic half-life and have found applications in monitoring tumor vasculature and angiogenesis. Macromolecular contrast agents have been able to overcome some of the disadvantages of the conventional small-molecule contrast agent Magnevist (gadolinium-diethylenetriaminepentaacetic acid), such as rapid extravasation and quick renal clearance, which limits the viable MRI time. There is an urgent need for new MRI contrast agents that increase the sensitivity of detection with a higher relaxivity, longer blood half-life, and reduced toxicity from free Gd3+ ions. Here, we report on the characterization of a novel water-soluble, derivatized, gadolinium-enclosed metallofullerene nanoparticle (Hydrochalarone-1) in development as an MRI contrast agent.

MATERIALS AND METHODS

The physicochemical properties of Hydrochalarone-1 were characterized by dynamic light scattering (hydrodynamic diameter), atomic force microscopy (particle height), ζ potential analysis (surface charge), and inductively coupled plasma-mass spectrometry (gadolinium concentration). The blood compatibility of Hydrochalarone-1 was also assessed in vitro through analysis of hemolysis, platelet aggregation, and complement activation of human blood. In vitro relaxivities, in vivo pharmacokinetics, and a pilot in vivo acute toxicity study were also performed.

RESULTS

An extensive in vitro and in vivo characterization of Hydrochalarone-1 is described here. The hydrodynamic size of Hydrochalarone-1 was 5 to 7 nm depending on the dispersing media, and it was negatively charged at physiological pH. Hydrochalarone-1 showed compatibility with blood cells in vitro, and no significant hemolysis, platelet aggregation, or complement activation was observed in vitro. In addition, Hydrochalarone-1 had significantly higher r1 and r2 in vitro relaxivities in human plasma in comparison with Magnevist and was not toxic at the doses administered in an in vivo pilot acute-dose toxicity study in mice.In vivo MRI pharmacokinetic analysis after a single intravenous injection of Hydrochalarone-1 (0.2 mmol Gd/kg) showed that the volume of distribution at steady state was approximately 100 mL/kg, suggesting prolonged systemic circulation. Hydrochalarone-1 also had a long blood half-life (88 minutes) and increased relaxivity, suggesting application as a promising blood-pool MRI contrast agent.

CONCLUSIONS

The evidence suggests that Hydrochalarone-1, with its long systemic half-life, may have significant utility as a blood-pool MRI contrast agent.

Nephrogenic systemic fibrosis is associated with hypophosphataemia: a case-control study

OBJECTIVE

Nephrogenic systemic fibrosis (NSF) is an iatrogenic fibrosing disorder that primarily affects individuals with chronic kidney disease (CKD) following exposure to gadolinium-based contrast agents (GBCAs). Derangements of calcium and phosphorus have been reported in patients with NSF. The aim of this study was to investigate potential factors in addition to GBCA exposure that may be involved in the pathogenesis of NSF. We hypothesized that patients with stage 5 CKD and NSF would manifest greater alterations in calcium, phosphorus and fibroblast growth factor 23 (FGF23) levels than those who do not have NSF.

METHODS

Levels of phosphorus, calcium, FGF23 and 25-hydroxy-vitamin D were measured in 10 patients with stage 5 CKD and biopsy-proven NSF and in 19 patients with stage 5 CKD without NSF. Statistical analyses were performed using Fisher's exact test for categorical variables and the Kruskal-Wallis test for continuous variables.

RESULTS

Patients with NSF had significantly lower phosphorus levels compared with controls (P = 0.01). There were no significant differences between NSF patients and controls in calcium, 25-hydroxy-vitamin D, intact parathyroid hormone or FGF23 levels.

CONCLUSION

Differences in phosphorus metabolism may exist between patients with stage 5 CKD and NSF compared with patients with stage 5 CKD without NSF.

Current status of nephrogenic systemic fibrosis

Nephrogenic systemic fibrosis (NSF) occurs in patients with advanced chronic kidney disease (CKD) or acute renal failure, most commonly following exposure to gadolinium-based contrast agents (GBCAs). NSF can be debilitating and associated with increased mortality. The putative association of NSF with GBCAs prompted the development of guidelines to limit the use of these contrast agents in at-risk patients. Indeed, the incidence of NSF has decreased dramatically following application of these guidelines, which appears to be the only effective means of decreasing NSF incidence. Thus, increasing clinician awareness of these updated guidelines is important. The present review introduces and compares updated guidelines for GBCA use and discusses the latest advances in the understanding of the pathogenic mechanisms and treatment of NSF.

Gadolinium contrast agent-induced CD163+ ferroportin+ osteogenic cells in nephrogenic systemic fibrosis

Gadolinium-based contrast agents are linked to nephrogenic systemic fibrosis in patients with renal insufficiency. The pathology of nephrogenic systemic fibrosis is characterized by abnormal tissue repair: fibrosis and ectopic ossification. The mechanisms by which gadolinium could induce fibrosis and ossification are not known. We examined in vitro the effect of a gadolinium-based contrast agent on human peripheral blood mononuclear cells for phenotype and function relevant to the pathology of nephrogenic systemic fibrosis using immunofluorescence, flow cytometry, real-time PCR, and osteogenic assays. We also examined tissues from patients with nephrogenic systemic fibrosis, using IHC to identify the presence of cells with phenotype induced by gadolinium. Gadolinium contrast induced differentiation of human peripheral blood mononuclear cells into a unique cellular phenotype--CD163(+) cells expressing proteins involved in fibrosis and bone formation. These cells express fibroblast growth factor (FGF)23, osteoblast transcription factors Runt-related transcription factor 2, and osterix, and show an osteogenic phenotype in in vitro assays. We show in vivo the presence of CD163(+)/procollagen-1(+)/osteocalcin(+) cells in the fibrotic and calcified tissues of nephrogenic systemic fibrosis patients. Gadolinium contrast-induced CD163(+)/ferroportin(+)/FGF23(+) cells with osteogenic potential may play a role in systemic fibrosis and ectopic ossification in nephrogenic systemic fibrosis.

A historical overview of magnetic resonance imaging, focusing on technological innovations

Magnetic resonance imaging (MRI) has now been used clinically for more than 30 years. Today, MRI serves as the primary diagnostic modality for many clinical problems. In this article, historical developments in the field of MRI will be discussed with a focus on technological innovations. Topics include the initial discoveries in nuclear magnetic resonance that allowed for the advent of MRI as well as the development of whole-body, high field strength, and open MRI systems. Dedicated imaging coils, basic pulse sequences, contrast-enhanced, and functional imaging techniques will also be discussed in a historical context. This article describes important technological innovations in the field of MRI, together with their clinical applicability today, providing critical insights into future developments.

Understanding nephrogenic systemic fibrosis

Nephrogenic systemic fibrosis (NSF) is a rare and a debilitating disease noted uncommonly in patients with impaired renal function when exposed to low-stability gadolinium-based contrast agents (Gd-CAs). According to experimental studies, cytokines released by the stimulation of effector cells such as skin macrophages and peripheral blood monocytes activate circulating fibroblasts which play a major role in the development of NSF lesions. The presence of permissive factors, presumably, provides an environment conducive to facilitate the process of fibrosis. Multiple treatment modalities have been tried with variable success rates. More research is necessary to elucidate the underlying pathophysiological mechanisms which could potentially target the initial steps of fibrosis in these patients. This paper attempts to collate the inferences from the in vivo and in vitro experiments to the clinical observations to understand the pathogenesis of NSF. Schematic representations of receptor-mediated molecular pathways of activation of macrophages and fibroblasts by gadolinium and the final pathway to fibrosis are incorporated in the discussion.

Nephrogenic systemic fibrosis

OBJECTIVE

The purpose of this article is to discuss nephrogenic systemic fibrosis (NSF) in detail regarding its history, possible pathophysiology, clinical and pathologic presentations, diagnosis, and implications for the radiology community.

CONCLUSION

NSF is a potentially lethal disorder that occurs in patients with reduced kidney function. Current evidence suggests a strong association with gadolinium-based contrast agents--mostly used in MRI--in this patient group. This has urged the radiology community to emphasize careful screening for the presence of renal dysfunction among patients for whom gadolinium-enhanced MRI is contemplated. Appropriate selection of gadolinium-based contrast agent type, avoidance of nonstandard dosage, patient education, and informed consent have been recommended by authorities.

N-acetylcysteine protects rats with chronic renal failure from gadolinium-chelate nephrotoxicity

The aim of this study was to evaluate the effect of Gd-chelate on renal function, iron parameters and oxidative stress in rats with CRF and a possible protective effect of the antioxidant N-Acetylcysteine (NAC). Male Wistar rats were submitted to 5/6 nephrectomy (Nx) to induced CRF. An ionic-cyclic Gd (Gadoterate Meglumine) was administrated (1.5 mM/KgBW, intravenously) 21 days after Nx. Clearance studies were performed in 4 groups of anesthetized animals 48 hours following Gd- chelate administration: 1--Nx (n = 7); 2--Nx+NAC (n = 6); 3--Nx+Gd (n = 7); 4--Nx+NAC+Gd (4.8 g/L in drinking water), initiated 2 days before Gd-chelate administration and maintained during 4 days (n = 6). This group was compared with a control. We measured glomerular filtration rate, GFR (inulin clearance, ml/min/kg BW), proteinuria (mg/24 hs), serum iron (µg/dL); serum ferritin (ng/mL); transferrin saturation (%), TIBC (µg/dL) and TBARS (nmles/ml). Normal rats treated with the same dose of Gd-chelate presented similar GFR and proteinuria when compared with normal controls, indicating that at this dose Gd-chelate is not nephrotoxic to normal rats. Gd-chelate administration to Nx-rats results in a decrease of GFR and increased proteinuria associated with a decrease in TIBC, elevation of ferritin serum levels, transferrin oversaturation and plasmatic TBARS compared with Nx-rats. The prophylactic treatment with NAC reversed the decrease in GFR and the increase in proteinuria and all alterations in iron parameters and TBARS induced by Gd-chelate. NAC administration to Nx rat did not modify the inulin clearance and iron kinetics, indicating that the ameliorating effect of NAC was specific to Gd-chelate. These results suggest that NAC can prevent Gd-chelate nephrotoxicity in patients with chronic renal failure.

Minimizing risk of nephrogenic systemic fibrosis in cardiovascular magnetic resonance

Nephrogenic Systemic Fibrosis is a rare condition appearing only in patients with severe renal impairment or failure and presents with dermal lesions and involvement of internal organs. Although many cases are mild, an estimated 5% have a progressive debilitating course. To date, there is no known effective treatment thus stressing the necessity of ample prevention measures. An association with the use of Gadolinium based contrast agents (GBCA) makes Nephrogenic Systemic Fibrosis a potential side effect of contrast enhanced magnetic resonance imaging and offers the opportunity for prevention by limiting use of gadolinium based contrast agents in renal failure patients. In itself toxic, Gadolinium is embedded into chelates that allow its safe use as a contrast agent. One NSF theory is that Gadolinium chelates distribute into the extracellular fluid compartment and set Gadolinium ions free, depending on multiple factors among which the duration of chelates exposure is directly related to the renal function. Major medical societies both in Europe and in North America have developed guidelines for the usage of GBCA. Since the establishment of these guidelines and the increased general awareness of this condition, the occurrence of NSF has been nearly eliminated. Giving an overview over the current knowledge of NSF pathobiochemistry, pathogenesis and treatment options this review focuses on the guidelines of the European Medicines Agency, the European Society of Urogenital Radiology, the FDA and the American College of Radiology from 2008 up to 2011 and the transfer of this knowledge into every day practice.

Hyperphosphataemia sensitizes renally impaired rats to the profibrotic effects of gadodiamide

BACKGROUND AND PURPOSE

Hyperphosphataemia is common in patients with nephrogenic systemic fibrosis (NSF). NSF has been linked to administration of gadolinium (Gd) chelates (GCs) and elevated serum phosphate levels accelerate the release of Gd from linear, non-ionic GCs but not macrocyclic GCs. Hence, we determined whether hyperphosphataemia is a cofactor or risk factor for NSF by investigating the role of hyperphosphataemia in renally impaired rats.

EXPERIMENTAL APPROACH

Firstly, the clinical, pathological and bioanalytical consequences of hyperphosphataemia were investigated in subtotal nephrectomized (SNx) Wistar rats following i.v. administration of the non-ionic, linear GC gadodiamide (5 × 2.5 mmol·kg(-1) ·day(-1) ). Secondly, the effects of several GCs were compared in these high-phosphate diet fed rats. Total Gd concentration in skin, femur and plasma was measured by inductively coupled plasma mass spectrometry (ICP-MS) and free Gd(3+) in plasma by liquid chromatography coupled to ICP-MS. Relaxometry was used to measure dissociated Gd in skin and bone.

KEY RESULTS

Four out of seven SNx rats fed a high-phosphate diet administered gadodiamide developed macroscopic and microscopic (fibrotic and inflammatory) skin lesions, whereas no skin lesions were observed in SNx rats treated with saline, the other GCs and free ligands or in the normal diet, gadodiamide-treated group. Unlike the other molecules, gadodiamide gradually increased the r(1) relaxivity value, consistent with its in vivo dissociation and release of soluble Gd.

CONCLUSIONS AND IMPLICATIONS

Hyperphosphataemia sensitizes renally impaired rats to the profibrotic effects of gadodiamide. Unlike the other GCs investigated, gadodiamide gradually dissociates in vivo. Our data confirm that hyperphosphataemia is a risk factor for NSF.