Mutagenicity assessment of two potential impurities in preparations of 5-amino-2,4,6 triiodoisophthalic acid, a key intermediate in the synthesis of the iodinated contrast agent iopamidol.

5-Aminoisophthalic acid and 5-nitroisophthalic acid (5-NIPA) are potential impurities in preparations of 5-amino-2,4,6-triiodoisophthalic acid, which is a key intermediate in the synthesis of the iodinated contrast agent iopamidol. We have studied their mutagenicity in silico (quantitative structure-activity relationships, QSAR) and by the bacterial reverse mutation assay (Ames test). First, the compounds were screened with the tools Derek Nexus™ and Leadscope®. Both compounds were flagged as potentially mutagenic (class 3 under ICH M7). However, contrary to the in silico prediction, neither chemical was mutagenic in the Ames test (plate incorporation method) with or without S9 metabolic activation.

Evaluation of gadolinium-based contrast agents in juvenile CD-1 mice including behavioral evaluations.

INTRODUCTION: Seven gadolinium-based contrast agents (GBCAs), four linear and three macrocyclic, were evaluated for potential effects on development, including behavior of juvenile CD-1 mice. METHODS: The GBCAs were administered via intravenous injection once daily on postnatal day (PND) 9, 12, 15, 18, and 21 (PND 1 was the day of delivery) at doses up to twice the human equivalent clinical dose (i.e., 0.63 mmol Gd/kg for gadoxetate disodium and 2.5 mmol Gd/kg for the other GBCAs). Mice were bled for evaluation of exposure (plasma) to gadolinium (Gd) on PND 9, 12, and 70. At scheduled euthanasia, the liver, spleen, brain, skin (dorsal surface), bone (left femur), and kidneys were excised from up to six mice/sex/group on PND 10, 22, or 70 for the determination of Gd levels and histopathological analysis. All mice were monitored for toxicity, growth and survival, sexual maturation, and behavior. CONCLUSION: Gd was quantifiable in the brain tissues with levels declining over time. There was no long-term effect on the growth and development for mice exposed to any of the GBCAs. There was no impact on neurodevelopment as assessed by brain histology and validated neurobehavioral tests, including a functional observational battery, motor activity, and learning and memory as evaluated in the Morris water maze. For all GBCAs, the highest dose tested represented the no-observable-adverse-effect level in juvenile mice.

Evaluation of gadolinium-based contrast agents in pregnant CD-1 mice and subsequent in utero exposure of the developing offspring, including behavioral evaluations.

INTRODUCTION: The offspring of CD-1 mice exposed during pregnancy to one of seven gadolinium-based contrast agents (GBCAs) were evaluated for potential effects on postnatal development and behavior. The GBCAs, comprising four linear (gadopentetate dimeglumine, gadodiamide, gadobenate dimeglumine, and gadoxetate disodium) and three macrocyclic (gadoterate meglumine, gadoteridol, and gadobutrol), were administered via intravenous injection once daily from Gestation Day 6 through 17 following confirmed mating (Day 0) at doses of at least twice the human equivalent recommended clinical dose (i.e., 0.63 mmol Gd/kg for gadoxetate disodium and 2.5 mmol Gd/kg for the other GBCAs). All dams were allowed to deliver naturally. F0 generation females were monitored for maternal toxicity and gadolinium (Gd) levels in blood and brain. Offspring were evaluated for Gd levels in blood and brain at birth and on Day 70 postpartum. F1 generation mice were evaluated for survival and growth preweaning. Selected pups/litter were evaluated postweaning for sexual maturation, growth, and behavior. Gd was quantifiable in the brain of the F1 offspring on PND 1, with levels declining over time. There was no long-term effect of any GBCA on the growth and development of any offspring. There was no impact on neurodevelopment, as assessed by brain histology and validated neurobehavioral tests, including a battery of functional observational tests, motor activity, and learning and memory as evaluated in the Morris water maze. CONCLUSION: At the end of the postweaning period, the highest dose tested was considered the no-observable-adverse-effect level (NOAEL) in the F0 and F1 offspring for all tested GBCAs.

Fluorescence-based absolute quantification of near-infrared probes in tissue extracts for biodistribution analyses.

In recent years, significant progress has been made in the development of fluorescent contrast agents for clinical applications. For the development of a fluorescent probe, it is crucial to evaluate its safety profile, including biodistribution. Specific methods need to be developed for the absolute quantification of fluorescent probes in tissue specimens from animals administered with test compounds in the framework of biodistribution/efficacy/toxicity studies. Here, we describe a new method for the absolute quantification of fluorescent probes in tissue specimens from animals administered with compounds that have absorption and emission wavelength in the Near-Infrared region (600-800 nm). The protocol is based on the standard addition approach in order to minimize the interference of the matrix on the analyte signal causing inaccuracy in the absolute determination of the concentration. The measurement of the fluorescence intensity is done via a microplate reader. The method has been fully validated and applied for the quantification of a fluorescence-guided surgery targeted contrast agent in a Good Laboratory Practice (GLP) biodistribution study. Results clearly demonstrate that this procedure is fully applicable in a preclinical setting and that it overcomes common issues associated with fluorescence signal quantification in tissue extracts.

Gadolinium retention in a rat model of subtotal renal failure: are there differences among macrocyclic GBCAs?

BACKGROUND: Gd levels are higher in tissues of animals with compromised renal function, but studies to compare levels after exposure to different macrocyclic gadolinium-based contrast agents (GBCAs) are lacking. We compared Gd levels in tissues of subtotally nephrectomised (SN) rats after repeated exposure to macrocyclic GBCAs. METHODS: Sprague-Dawley SN male rats (19 per group) received 16 injections of gadoteridol, gadobutrol, or gadoterate meglumine at 0.6 mmol Gd/kg 4 times/weeks over 4 weeks. A control group of healthy male rats (n = 10) received gadoteridol at the same dosage. Plasma urea and creatinine levels were monitored. Blood, cerebrum, cerebellum, liver, femur, kidney(s), skin and peripheral nerves were harvested for Gd determination by inductively coupled plasma-mass spectrometry at 28 and 56 days after the end of treatment. RESULTS: Plasma urea and creatinine levels were roughly twofold higher in SN rats than in healthy rats at all timepoints. At day 28, Gd levels in the peripheral nerves of gadobutrol- or gadoterate-treated SN animals were 5.4 or 7.2 times higher than in gadoteridol-treated animals (p < 0.001). Higher Gd levels after administration of gadobutrol or gadoterate versus gadoteridol were also determined in kidneys (p ≤ 0.002), cerebrum (p ≤ 0.001), cerebellum (p ≤ 0.003), skin (p ≥ 0.244), liver (p ≥ 0.053), and femur (p ≥ 0.271). At day 56, lower Gd levels were determined both in SN and healthy rats for all GBCAs and tissues, except the femur. CONCLUSIONS: Gd tissue levels were lower following gadoteridol exposure than following gadobutrol or gadoterate exposure.

Gadolinium Clearance in the First 5 Weeks After Repeated Intravenous Administration of Gadoteridol, Gadoterate Meglumine, and Gadobutrol to rats.

BACKGROUND: Studies of gadolinium (Gd) clearance from animals in the first weeks after administration of gadolinium-based contrast agents (GBCAs) have previously looked at solitary timepoints only. However, this does not give information on differences between GBCAs and between organs in terms of Gd elimination kinetics. PURPOSE: To compare Gd levels in rat cerebellum, cerebrum, skin, and blood at 1, 2, 3, and 5 weeks after repeated administration of macrocyclic GBCAs. STUDY TYPE: Prospective. ANIMAL MODEL: One hundred eighty male Sprague-Dawley rats randomized to three groups (n = 60/group), received intravenous administrations of gadoteridol, gadoterate meglumine, or gadobutrol (0.6 mmol/kg for each) four times/week for 5 consecutive weeks. Rats were sacrificed after washout periods of 1, 2, 3, or 5 weeks. FIELD STRENGTH/SEQUENCE: Not applicable. ASSESSMENT: Cerebellum, cerebrum, skin, and blood were harvested for Gd determination by inductively coupled plasma-mass spectrometry (15 animals/group/all timepoints). STATISTICAL TESTS: Anova and Dunnett's test (data with homogeneous variances and normal distribution). Kruskal-Wallis and Wilcoxon's rank sum tests (data showing nonhomogeneous variances or a non-normal distribution, significance levels: P < 0.05, P < 0.01, and P < 0.001). RESULTS: Gd levels in cerebellum, cerebrum, and skin were significantly lower after gadoteridol than after gadoterate and gadobutrol at all timepoints. Mean cerebellum Gd concentrations after gadoteridol, gadoterate, and gadobutrol decreased from 0.693, 0.878, and 1.011 nmol Gd/g at 1 week to 0.144, 0.282, and 0.297 nmol Gd/g at 5 weeks after injection. Similar findings were noted for cerebrum and skin. Conversely, significantly higher Gd levels were noted in blood after gadoteridol compared to gadobutrol at 1, 2, and 3 weeks and compared to gadoterate at all timepoints. DATA CONCLUSION: Gadoteridol is eliminated more rapidly from rat cerebellum, cerebrum, and skin compared to gadoterate and gadobutrol in the first 5 weeks after administration, resulting in lower levels of retained Gd in these tissues. EVIDENCE LEVEL: 1 TECHNICAL EFFICACY: Stage 5.

Macrocyclic MR contrast agents: evaluation of multiple-organ gadolinium retention in healthy rats.

OBJECTIVES: The purpose of this study was to compare Gd levels in rat tissues after cumulative exposure to four commercially available macrocyclic gadolinium-based contrast agents (GBCAs). METHODS: Sixty-five male Sprague-Dawley rats were randomized to four exposure groups (n = 15 per group) and one control group (n = 5). Animals in each exposure group received 20 GBCA administrations (four per week of ProHance®, Dotarem®, Clariscan™, or Gadovist® for 5 consecutive weeks) at a dose of 0.6 mmol/kg bodyweight. After 28-days' recovery, animals were sacrificed and tissues harvested for Gd determination by inductively coupled plasma-mass spectroscopy (ICP-MS). Histologic assessment of the kidney tissue was performed for all animals. RESULTS: Significantly (p ≤ 0.005; all evaluations) lower Gd levels were noted with ProHance® than with Dotarem®, Clariscan™, or Gadovist® in all soft tissue organs: 0.144 ± 0.015 nmol/g vs. 0.342 ± 0.045, 0.377 ± 0.042, and 0.292 ± 0.047 nmol/g, respectively, for cerebrum; 0.151 ± 0.039 nmol/g vs. 0.315 ± 0.04, 0.345 ± 0.053, and 0.316 ± 0.040 nmol/g, respectively, for cerebellum; 0.361 ± 0.106 nmol/g vs. 0.685 ± 0.330, 0.823 ± 0.495, and 1.224 ± 0.664 nmol/g, respectively, for liver; 38.6 ± 25.0 nmol/g vs. 172 ± 134, 212 ± 121, and 294 ± 127 nmol/g, respectively, for kidney; and 0.400 ± 0.112 nmol/g vs. 0.660 ± 0.202, 0.688 ± 0.215, and 0.999 ± 0.442 nmol/g, respectively, for skin. No GBCA-induced macroscopic or microscopic findings were noted in the kidneys. CONCLUSIONS: Less Gd is retained in the brain and body tissues of rats 28 days after the last exposure to ProHance® compared to other macrocyclic GBCAs, likely due to unique physico-chemical features that facilitate more rapid and efficient clearance.

Pharmaceutical Development and Safety Evaluation of a GMP-Grade Fucoidan for Molecular Diagnosis of Cardiovascular Diseases.

The adhesion molecule P-selectin is present on the cell surface of both activated endothelium and activated platelets. The present study describes the pharmaceutical development, safety evaluation, and preclinical efficacy of a micro-dosed radiotracer. The macromolecular nanoscale assembly consisted of a natural compound made of a sulfated fucose-rich polysaccharides (fucoidan) and a radionuclide (technetium-99m) for the detection of P-selectin expression in cardiovascular diseases. After extraction and fractionation from brown seaweeds, the good manufacturing practice (GMP) production of a low molecular weight (LMW) fucoidan of 7 kDa was achieved and full physicochemical characterization was performed. The regulatory toxicology study in rats of the GMP batch of LMW fucoidan revealed no adverse effects up to 400 µg/kg (×500 higher than the expected human dose) and pseudoallergy was not seen as well. In a myocardial ischemia-reperfusion model in rats, the GMP-grade LMW fucoidan labeled with technetium-99m detected P-selectin upregulation in vivo. The present study supports the potential of using 99mTc-fucoidan as an imaging agent to detect activated endothelium in humans.

Differences in gadolinium retention after repeated injections of macrocyclic MR contrast agents to rats.

PURPOSE: To compare the levels of gadolinium in the blood, cerebrum, cerebellum, liver, femur, kidneys, and skin after multiple exposure of rats to the macrocyclic gadolinium-based contrast agents (GBCAs) gadoterate, gadobutrol, and gadoteridol. MATERIALS AND METHODS: Fifty male Wistar Han rats were randomized to three exposure groups (n = 15 per group) and one control group (n = 5). Animals in the exposure groups received a total of 20 GBCA administrations (four administrations per week for 5 consecutive weeks) at a dose of 0.6 mmol/kg bodyweight. After a 28-day recovery period animals were sacrificed and the blood and tissues harvested for determination of gadolinium (Gd) levels. Gd determination was performed by inductively coupled plasma mass spectrometry (ICP-MS). RESULTS: After 28 days' recovery no Gd was found in the blood, liver, or skin of any animal in any group. Significantly lower levels of Gd were noted with gadoteridol compared to gadoterate and gadobutrol in the cerebellum (0.150 ± 0.022 vs. 0.292 ± 0.057 and 0.287 ± 0.056 nmol/g, respectively; P < 0.001), cerebrum (0.116 ± 0.036 vs. 0.250 ± 0.032 and 0.263 ± 0.045 nmol/g, respectively; P < 0.001), and kidneys (25 ± 13 vs. 139 ± 88 [P < 0.01] and 204 ± 109 [P < 0.001], respectively). Higher levels of Gd were noted in the femur (7.48 ± 1.37 vs. 5.69 ± 1.75 and 8.60 ± 2.04 nmol/g, respectively) with significantly less Gd determined for gadoterate than for gadobutrol (P < 0.001) and gadoteridol (P < 0.05). CONCLUSION: Differences exist between macrocyclic agents in terms of their propensity to accumulate in tissues. The observed differences in Gd concentration point to differences in GBCA washout rates in this setting and in this experimental model, with gadoteridol being the GBCA that is most efficiently removed from both cerebral and renal tissues. LEVEL OF EVIDENCE: 2 Technical Efficacy: Stage 5 J. Magn. Reson. Imaging 2018;47:746-752.

Non-clinical assessment of safety and gadolinium deposition after cumulative administration of gadobenate dimeglumine (MultiHance®) to neonatal and juvenile rats.

To determine the impact of single and cumulative doses of MultiHance on toxicity, pharmacokinetics, tissue gadolinium presence, behavior and neurological function in juvenile rats. Juvenile male and female rats received either physiological saline or MultiHance at 0.6, 1.25 or 2.5 mmol/kg bodyweight. Animals received either single or six consecutive MultiHance administrations and were sacrificed the day after the last administration or after a 60-day treatment-free period. Animals were assessed for behavior, cognitive function, grip strength, gait, pupillary reflex, and auditory reflex, as well as for physical development, sexual maturation and histopathology. Gadolinium presence in brain, femur, kidneys, liver and skin was determined using inductively coupled plasma-mass spectrometry (ICP-MS). No effects of MultiHance on behavior, cognitive function or any other parameter were noted, even for the highest administered cumulative dose (15 mmol/kg). Gadolinium presence was variable across tissues and decreased during the 60-day treatment-free period. The highest levels were noted in the femur and the lowest levels in the brain. Gadolinium presence in juvenile rat brain following single or repeated MultiHance administrations was minimal and non-impactful.

Steady-State Serum T3 Concentrations for 48 Hours Following the Oral Administration of a Single Dose of 3,5,3'-Triiodothyronine Sulfate (T3S).

OBJECTIVE: Sulfate conjugation of thyroid hormones is an alternate metabolic pathway that facilitates the biliary and urinary excretion of iodothyronines and enhances their deiodination rate, leading to the generation of inactive metabolites. A desulfating pathway reverses this process, and thyromimetic effects have been observed following the parenteral administration of 3,5,3'-triiodothyronine (T3) sulfate (T3S) in rats. The present study investigated whether T3S is absorbed after oral administration in humans and if it represents a source of T3. METHODS: Twenty-eight hypothyroid patients (7 men and 21 women; mean age, 44 ± 11 years) who had a thyroidectomy for thyroid carcinoma were enrolled. Replacement thyroid hormone therapy was withdrawn (42 days for thyroxine, 14 days for T3) prior to 131I remnant ablation. A single oral dose of 20, 40, 80 (4 patients/group), or 160 µg (16 patients/group) of T3S was administered 3 days before the planned administration of 131I. Blood samples for serum T3S and total T3 (TT3) concentrations were obtained at various times up to 48 hours after T3S administration. RESULTS: At all T3S doses, serum T3S concentrations increased, reaching a peak at 2 to 4 hours and progressively returning to basal levels within 8 to 24 hours. The T3S maximum concentration (Cmax) and area under the 0- to 48-hour concentration-time curve (AUC0-48h) were directly and significantly related to the administered dose. An increase in serum TT3 concentration was observed (significant after 1 hour), and the concentration increased further at 2 and 4 hours and then remained steady up to 48 hours after T3S administration. There was a significant direct correlation between the TT3 AUC0-48h and the administered dose of T3S. No changes in serum free thyroxine (T4) concentrations during the entire study period were observed, whereas serum thyroid-stimulating hormone levels increased slightly at 48 hours, but this was not related to the dose of T3S. No adverse events were reported. CONCLUSION: (1) T3S is absorbed following oral administration in hypothyroid humans; (2) after a single oral dose, T3S is converted to T3 in a dose-dependent manner, resulting in steady-state serum T3 concentrations for 48 hours; (3) T3S may represent a new agent in combination with T4 in the therapy of hypothyroidism, if similar conversion of T3S to T3 can be demonstrated in euthyroid patients who are already taking T4.

Toxicological assessment of gadolinium release from contrast media.

In vivo gadolinium release was evaluated for MultiHance, Omniscan and Gadovist estimating gadolinium content in liver, kidneys, spleen, femur and brain after single or repeated intravenous administrations to rats at 1 mmol/kg. Gadolinium acetate (GdAc) at a daily dose of 0.03 mmol/kg and physiological saline were used as positive and negative controls, respectively. No changes in blood chemistry, haematology nor histopathology were seen with any of the tested contrast media, whereas an increase in white blood cell count and in serum cholesterol were found after GdAc at 0.18 mmol/kg cumulative dose. Analogously, gadolinium content in target organs (as % of injected dose) after any of contrast media was 100-200 times lower than after GdAc, either after single or repeated administrations. Under these experimental conditions, the rank of residual gadolinium found in these organs was GdAcOmniscan >Gadovist >MultiHance. Depopulation of lymphocytes in periarteriolar lymphatic sheaths (PALS) areas of the spleen was noted in rats treated with a single dose of GdAc sacrificed 24h post-dosing, but not in repeated dose rats sacrificed 48 h after last dosing. It was, therefore, concluded that this was a transient phenomenon and that PALS are rapidly repopulated with lymphocytes. With all contrast media, gadolinium content after a 2-day washout following a 3-week repeated administration period was lower than the amount found 24h after a single administration. Accordingly, the observed gadolinium content in organs should actually be in a complexed form (possibly the injected complex) which is subjected to elimination.

Margins of safety of intravascular contrast media: body weight, surface area or toxicokinetic approach?

The margin of safety of a drug is defined as the ratio between toxicity in animals and safety in humans. For intravascular contrast media, the margin of safety is traditionally the ratio between LD50 and diagnostic dose, both doses being based on bodyweight. The shift to surface area dramatically reduces this margin to unacceptable values. Toxicokinetics, which relates systemic exposure associated with early toxic signs in animals to plasma level in man, seems the most accurate and predictive criterion.