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Gadolinium Retention, Brain T1 Hyperintensity,
and Endogenous Metals
A Comparative Study of Macrocyclic Versus Linear Gadolinium
Chelates in Renally Sensitized Rats
Marlène Rasschaert, MS,*†‡§||¶ Andréa Emerit, MS,* Nathalie Fretellier, PhD,* Cécile Factor, PhD,*
Philippe Robert, PhD,* Jean-Marc Idée, PharmD, MS,* and Claire Corot, PharmD, PhD*
Objectives: This preclinical study was designed to compare gadolinium (Gd)
brain uptake after repeated injections of a macrocyclic Gd-based contrast agent
(GBCA) (gadoterate meglumine) or 2 linear GBCAs (L-GBCAs) (gadobenate
dimeglumine or gadodiamide) on a translational model of moderate renal impair-
ment in rats.
Methods: The study was carried out in subtotally nephrectomized rats. Animals
received 4 intravenous injections per week of GBCA (gadoterate meglumine,
gadobenate dimeglumine, or gadodiamide) for 5 weeks, resulting in a cumulative
dose of 12 mmol/kg, followed by a 1-month injection-free period. T1 hyper-
intensity in the deep cerebellar nuclei (DCNs) was investigated, and brain struc-
tures were carefully dissected to determine elemental Gd, iron (Fe), copper (Cu),
and zinc (Zn) distribution by mass spectrometry. Urinary excretion of endoge-
nous metals was also investigated soon after GBCA administration and several
days later in order to assess a potential transmetalation phenomenon.
Results: Unlike gadoterate, repeated injections of L-GBCAs gadobenate and
gadodiamide both induced T1 hyperintensity in the DCNs. Fine dissection of ce-
rebral and cerebellar structures demonstrated very low levels or absenceof Gd af-
ter repeated injections of gadoterate, in contrast to the two L-GBCAs, for which
the highest total Gd concentration was demonstrated in the DCNs (Gd concentra-
tion in DCNs after 4.5 weeks of injection-free period: 27.1 ± 6.5 nmol/g for
gadodiamide [P< 0.01 vs saline and P< 0.05 vs gadoterate]; 12.0 ± 2.6 nmol/
g for gadobenate [P< 0.09 vs saline]; compared with 1.4 ± 0.2 nmol/g for
gadoterate [ns vs saline]). The distribution of Gd concentration among the various
brain structures dissected was also well correlated with the Fe distribution in these
structures. No difference in endogenous metal levels in brain structures was ob-
served. However, injection of gadobenate or gadodiamide resulted in an increase
in urinary Zn excretion (urinary Zn concentrations: 57.9 ± 20.5 nmol/mL with
gadobenate [P< 0.01 vs gadoterate and saline] and 221.6 ± 83.3 nmol/L with
gadodiamide [P< 0.0001 vs all other treatments] vs 8.1 ± 2.3 nmol/L with saline
and 10.6 ± 4.8 nmol/L with gadoterate]).
Conclusions: In a model of renally impaired rats, only traces of gadoterate
meglumine were detected in the brain with no T1 hyperintensity of the DCNs,
whereas marked Gd retention was observed in almost all brain areas after injec-
tions of the L-GBCAs, gadobenate dimeglumine and gadodiamide. Brain struc-
tures with higher Gd uptake corresponded to those structures containing more
Fe. Urinary Zn excretion was significantly increased after a single injection
of L-GBCAs.
Key Words: cerebellum, endogenous metals, gadobenate dimeglumine,
gadodiamide, gadolinium uptake, gadoterate meglumine,
magnetic resonance imaging, renal impairment
(Invest Radiol 2018;00: 00–00)
The recent findings of gadolinium (Gd) accumulation in the brain
following repeated injections of Gd-based contrast agents (GBCAs)
have raised considerable interest in the scientific community, and this
accumulation could potentially represent a major concern for patients.
Health authorities, especially the US Food and Drug Administration
and the European Medicines Agency, have urged marketing authoriza-
tion holders to elucidate this phenomenon, which may require reevalu-
ation of the safety of GBCAs in everyday use.
It is generally accepted that Gd accumulation in tissues is much
higher with linear GBCAs (L-GBCAs) than macrocyclic agents and
is inversely proportional to their thermodynamic conditional stability
constant log Kcond, calculated for pH 7.4 and kinetic stabilities for
L-GBCAs and driven by the high kinetic stabilities (ie, very low disso-
ciation kinetics) of macrocyclic GBCAs (M-GBCAs),
1
as demonstrated
in nonclinical models
2,3
and in humans.
4–10
Gadolinium accumulation
in the central nervous system depends on the cumulative dose,
7
with
heterogeneous cerebral Gd distribution.
11,12
The detection of at-risk populations is of critical clinical impor-
tance, and recent clinical studies have focused on potentially sensitized
populations such as pediatric patients,
13–15
newborns after potential ex-
posure by injection to the mother during pregnancy,
16–18
or renally
impaired subjects.
19,20
Almost all preclinical studies are performed in rodent species,
which constitute a relevant translational model,
21,22
reproducing the
T1 effect and Gd accumulation in the deep cerebellar nuclei (DCNs).
A previous study demonstrated that moderate renal impairment
induced by subtotal nephrectomy constituted a sensitive model to study
brain Gd uptake in the rat. Indeed, it amplified the brain Gd retention
and T1 hyperintensity for an identical injected dose of gadodiamide
compared with animals with normal renal function.
23
Gadolinium up-
take was positively correlated with the severity of renal impairment.
24
We therefore decided to compare the behavior of different molecular
categories of GBCAs in this same model.
This model seems to be translationally and clinically relevant, as
the estimated prevalence of chronic kidney disease (CKD) in patients
70 years or older in the United States (estimated with the CKD-EPI
equation) is 46.8%,
24
and the vast majority of these patients present
stage 3 CKD, that is, moderate renal failure (glomerular filtration rate
between 30 and 59 mL/min per 1.73 m
2
).
24,25
Older people represent a population of major concern, in which
contrast-enhanced magnetic resonance imaging (MRI) examinations are
commonly performed. This population of patients may be repeatedly
Received for publication November 22, 2017; and accepted for publication, after revi-
sion, December 5, 2017.
From the *Guerbet Research and Innovation Department, Aulnay-sous-Bois; and
†INSERM, U1196; ‡Institut Curie, PSL Research University; §Université Paris
Sud; ||Université Paris-Saclay; and }CNRS, UMR 9187, Orsay, France.
Correspondence to: Marlène Rasschaert, MS, Guerbet Research and Innovation
Department, Guerbet, BP57400, 95943 Roissy CDG Cedex, France. E-mail:
marlene.rasschaert@guerbet-group.com.
Copyright© 2018 The Author(s). Published by Wolters Kluwer Health, Inc. This is an
open-access article distributed under the terms of the Creative Commons
Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND),
where it is permissible to download and share the work provided it is properly
cited. The work cannot be changed in any way or used commercially without per-
mission from the journal.
ISSN: 0020-99 96/18/0000–0000
DOI: 10.1097/RLI.0000000000000447
ORIGINAL ARTICLE
Investigative Radiology •Volume 00, Number 00, Month 2018 www.investigativeradiology.com 1
exposed to linear Gd chelates, which are not contraindicated for pa-
tients with stage 3 CKD.
26,27
The purpose of this study was therefore to compare all categories
of GBCAs, that is, a linear ionic GBCA (gadobenate), a linear nonionic
GBCA (gadodiamide), and an M-GBCA (gadoterate), in a rat model of
moderate renal failure mimicking a substantial population of patients
exposed to GBCAs.
MATERIALS AND METHODS
All experimental procedures and animal care were carried out ac-
cording to French regulations and in compliance with European Direc-
tive 2010/63/EU on the protection of animals used for scientific
purposes. All experiments (administrations, imaging, image analyses,
and total Gd concentration measurements) were carried out blindly.
Animal Model and Administration Protocol
The study was carried out on 5/6th subtotally nephrectomized fe-
male Sprague-Dawley rats (SPF/OFA rats; Charles River, L'Arbresle,
France) aged 10 weeks and weighing 246 ± 15 g at the beginning of
the study. Subtotal nephrectomy was performed at Charles River Labo-
ratories: a first surgical procedure was performed when the rats were
6 weeks old to excise 1 kidney, and a second procedure was performed
1 week later to remove the 2 poles of the remaining kidney. After
2 weeks of recovery and acclimatization, the animals were randomized
(n = 10/group, except for the saline group, which included 9 rats). The
rats were housed 2 per cage, at an ambient temperature of 22°C ± 2°C,
hygrometry of 45% ± 10%, in a room with 12:12-hour light-dark cy-
cles. Rats had access to water and food ad libitum.
The animals received 20 injections of 0.6 mmol Gd/kg per in-
jection (1.2 mL/kg) of meglumine gadoterate (macrocyclic ionic
GBCA, Dotarem 500 mmol Gd/L [Guerbet, France], batches
14GD107A and 16GD091A), dimeglumine gadobenate (linear ionic
GBCA, MultiHance 500 mmol Gd/L [Bracco, Italy], batch SP6251H),
or gadodiamide (linear nonionic GBCA, Omniscan 500 mmol Gd/L
[GE Healthcare, Chalfont St Giles, United Kingdom], batch
12965458), and the control group received 0.9% saline solution
(CDM Lavoisier, Paris, France) (1.2 mL/kg). Intravenous injections
were performed in the tail once a day, 4 days a week for 5 weeks, un-
der isoflurane anesthesia (IsoFlo; Axience, Pantin, France). The 0.6-
mmol Gd/kg dose corresponds to the clinical dose (0.1 mmol Gd/kg)
adjusted to the body surface area of the rat according to the US Food
and Drug Administration guidelines.
28
A 4.5-week injection-free
period was observed after the last injection. The study protocol is
showninFigure1.
Creatinine Clearance
Endogenous creatinine clearance (CrCl) was determined from
plasma and 24-hour urine collected atthe beginning (ie, the week before
the first administration) of the study, after the administration period (the
week after the last administration), and at completion of the study (ie,
4 weeks after the last administration). Plasma and urine creatinine con-
centrations were assayed by an enzymatic technique on an Abbott Ar-
chitect ci8200 automated analyzer (Abbott, Rungis, France).
Magnetic Resonance Imaging Protocol
Magnetic resonance imaging procedures were performed once a
week, using a dedicated phased-array quadrature head coil in a gradient/
shims insert B-GA 12S HP (660 mT/m intensity and 4570 T/m/s max-
imum slew rate) on a 4.7 T preclinical magnet (Biospec 47/40; Bruker,
Ettlingen, Germany). The first MRI was performed before the first in-
jection, and subsequent MRI examinations were performed once a week
(just before the f irst injection of the week, ie, 72 hours after the last
injection of the previous week). An MRI examination consisted of a
T1-weighted 2-dimensional FLASH (fast low-angle shot) sequence
(repetition time/echo time, 50/1.78 milliseconds; 48 averages; in-
plane resolution, 164 164 μm
2
; slice thickness, 700 μm; acquisition
time 6 minutes 36 seconds), targeted exclusively on the cerebellum
(11 slices), and T1 mapping on the slice displaying the DCNs, using
a FAIR (flow-sensitive alternating inversion recovery)–RARE (rapid
acquisition with relaxation enhancement) sequence with 8 inversion
times (0, 100, 200, 400, 600, 800, 1200, 2000 milliseconds; repetition
time/effective echo time, 36.9/2079.9 milliseconds; 4 averages; in-
plane resolution 164 164 μm
2
; slice thickness, 700 μm; and acqui-
sition time, 11 minutes 5 seconds).
FIGURE 1. Study protocol. Subtotally nephrectomized rats received 20 injections of 0.6 mmol/kg over 5 weeks (cumulative dose of 12 mmol Gd/kg).
Rasschaert et al Investigative Radiology •Volume 00, Number 00, Month 2018
2www.investigativeradiology.com © 2018 Wolters Kluwer Health, Inc. All rights reserved.
Blood and Tissue Collection
On days 16, 30 (before the daily injection), 37, and 45 (before
the weekly MRI examination), rats were anesthetized with isoflurane,
and a 600-μL sublingual blood sample was drawn. Plasma was har-
vested after centrifugation and frozen at −20°C for subsequent determi-
nation of Gd concentrations. At completion of the study, on week 10
(day 66), the animals were anesthetized with 5% isoflurane in oxygen.
Sublingual venous blood was collected in heparinized tubes, and the
rats were subsequently killed by exsanguination via the abdominal
aorta. Venous plasma was collected after centrifugation and frozen at
−20°C. For 4 to 6 rats per group (Fig. 1) (the other rats were used for
other experiments), the forebrain was carefully harvested, and the fol-
lowing structures: cortical forebrain, amygdala, olfactory bulbs, mid-
brain, hippocampus, hypothalamus, thalamus, and striatum, were
dissected.
29,30
The frozen cerebellum was sliced using a Brain Slicer
Matrix (Stoelting Co, Wood Dale, Ill), and the DCNs, cerebellum ex-
cept the DCNs (called “cerebellum*”), and brain stem were carefully
dissected. The DCNs was clearly distinguishable on 1-mm slices of
fresh tissue as shown in Figure 2. Tissues were then frozen at −20°C
for determination of total Gd concentrations.
Image Analysis
All image analyses were performed under blinded (for both test
groups and all time points) and randomized conditions. Both qualita-
tive and quantitative evaluations of the DCN T1 signal intensity
were performed.
Qualitative Analysis of MRI Scans
Qualitative evaluation of T1 signal enhancement in the DCNs
was performed under blinded conditions for the rat, group, and time
point. A 3-point scoring scale for the DCNs relative to adjacent areas
was applied: a score of 0 was attributed for no enhancement in the
DCNs, 1 for doubtful enhancement, and 2 for definite enhancement.
Quantitative Analysis of MRI Scans
Blinded quantitative analysis of signal intensity on randomized
images was performed by positioning regions of interest in the various
cerebellar structures: cerebellar parenchyma, brain stem, and left and
right DCNs. Signal intensity was calculated as the ratio of the DCNs with
the highest signal to the brain stem signal (DCN
max
-to-brain stem ratio).
R1 Mapping and Determination
R1 mapping was calculated from the FAIR-RARE acquisition on a
pixel-by-pixel basis using in-house software written in MATLAB (The
Mathworks Inc, Natick, Mass). The same regions of interest as those used
for the FLASH sequence were positioned, and the R1 value was extracted.
Determination of Tissue Total Gd, Iron, Copper, and
Zinc Concentrations
Total Gd concentrations in the various tissues collected were
determined by inductively coupled plasma mass spectrometry (ICP-
MS) (7700x; Agilent Technologies, Santa Clara, Calif ) after sample
mineralization in 65% nitric acid for 8 hours at a temperature of
80°C. The lower limits of quantification (LLOQs) of Gd were
0.02 nmol/mL in plasma, 0.14 nmol/g in DCNs, 0.03 nmol/g in hypo-
thalamus, and 0.02 nmol/g in other brain matrices. The LLOQs in
urine were 0.07 nmol/mL for Gd, 8 nmol/mL for iron (Fe), and
7 nmol/mL for copper (Cu) and zinc (Zn).
For calculation of means, SDs, and for statistical tests, values less
than the LLOQ were arbitrarily replaced by LLOQ, and values less than
the limit of detection were arbitrarily replaced by 0.
Urinary Excretion of Gd and Endogenous Metals
In addition to the 24-hour urine collection performed for deter-
mination of CrCl (before any injection [day 3], 4 days [day 36], and
1 month [day 64] after the last injection), rats were also placed in a me-
tabolism cage for 4 hours, starting 1 hour after the daily GBCA injec-
tion, at weeks 2 and 4 (days 11 and 25), in order to determine the
urinary excretion of endogenous metals (Fe, Zn, Cu) and total Gd fol-
lowing a GBCA injection.
Statistical Analysis
Values are shown as individual data, or mean ± SD. Dixon exclu-
sion test was used to exclude aberrant values at a 5% risk. Normality
was verified by the Shapiro-Wilk test.
31
A 2-way analysis of variance
with repeated measures was performed for CrCl and plasma Gd concen-
trations. When 1 or several parameters (time or group) were significant,
Tukey post hoc tests were applied to compare values for these parame-
ters. Two-way analysis of variance and Tukey post hoc tests were also
applied for quantification of T1 signal enhancement in DCNs, R1 map-
ping, and urinary excretion of metals. Kruskal-Wallis test and Dunn
post hoc test, when required, were used for simple comparison of total
Gd concentrations in the various brain tissues between groups. Pearson
correlation coefficient was calculated for correlations between metals.
Graphs present the values for all rats, but repeated-measure statistics
were performed only on values from rats that completed the study. A
significance level of 5% was adopted.
RESULTS
During the second MRI examination, 1 rat in the saline group died
of anesthesia, and 3 rats in the gadobenate group and 1 rat in the
gadodiamide group died during the study (2 rats in the gadobenate group
lost between 17% and 19% of body weight and were killed for ethical rea-
sons on days 21 and 52; the others were found dead, 1 in the gadodiamide
group on day 51 with a body weight loss of 23% and 1 in the gadobenate
group on day 57 with a body weight loss of 12%). Consequently, on com-
pletion of the study, the numbers of rats per group were 10 for gadoterate,
9 for gadodiamide, 8 for saline, and 7 for gadobenate.
Creatinine Clearance
Subtotal nephrectomy resulted in moderate renal impairment
(CrCl of tested rats was 0.21 ± 0.05 mL/min per 100 g prior to adminis-
tration of the test compounds). A transient improvement in renal function
was observed after the injection period (CrCl of 0.31 ± 0.09 mL/min per
100 g), independently of the group (P< 0.0001 for all groups). After the
injection-free period, CrCl decreased (P< 0.0001 for all groups vs post-
injection), reaching an intermediate value (CrCl of 0.25 ± 0.05 mL/min
FIGURE 2. Fresh cerebellar slices of 1 mm, starting (left) from the caudal extremity, obtained with the Brain Slicer Matrix. Coronal plane. Deep cerebellar
nuclei (red arrows) appear in light pink, surrounded by white matter.
Investigative Radiology •Volume 00, Number 00, Month 2018 Comparative CNS Gd Uptake in Renally Impaired Rats
© 2018 Wolters Kluwer Health, Inc. All rights reserved. www.investigativeradiology.com 3
per 100 g) between the first 2 CrCl measurements. The rats in the
gadobenate and gadodiamide groups that died during the study had se-
verely impaired renal function: 0.09, 0.10, and 0.14 mL/min per 100 g
for the rats in the gadobenate group and 0.13 mL/min per 100 g for the
rat in the gadodiamide group at the last CrCl estimation.
Qualitative Evaluation of T1 Enhancement of DCNs on
T1-Weighted MRI Examinations
Typical images at week 10 are shown in Figure 3A. A progres-
sive and lasting increase in T1 enhancement of the DCNs compared
with surrounding areas was found in both the gadobenate and
gadodiamide groups from week 4, whereas no T1 enhancement was ob-
served with gadoterate or for the control group (score <0.5). The T1 en-
hancement effect was higher in the gadodiamide group than in the
gadobenate group (Fig. 3B).
Quantitative Evaluation of T1 Enhancement in the DCNs
Quantitatively, significant T1 enhancement was confirmed in the
gadodiamide group, from the third week of injections (P< 0.05) until
the end of the injection-free period (P< 0.01 vs the control group),
compared with the saline and gadoterate groups. The T1 enhancement
in the gadobenate group seemed to be intermediate (on completion of
the injection-free period, P= 0.074 compared with saline) (Fig. 4).
R1 Mapping
A trend toward an increase in R1 relaxation rate was observed af-
ter injections for gadobenate (P= 0.107 vs the control group), and a sig-
nificant increase in R1 relaxation rate was observed for gadodiamide
(P< 0.0001) compared with the control and gadoterate groups, whereas
the R1 relaxation rate in DCNs in the gadoterate group remained similar
to that of the saline group, regardless of the time point. R1 enhancement
was maintained after the injection-free period in the gadodiamide group
(P< 0.01 vs saline, P< 0.001 vs gadoterate) (Fig. 5).
Total Gd Concentrations Determined by ICP-MS in the
Dissected Brain Areas
The highest total Gd concentrations were observed with
gadodiamide in the DCNs, olfactory bulbs, striatum, thalamus, and cer-
ebellar parenchyma (Fig. 6).
Some of the dissected brain areas presented a high total Gd
concentration ratio for gadodiamide versus gadoterate (>7) and
FIGURE 3. A, Typical T1-weighted MR images (4.7 T) of all treated groups, at study completion (week 10). B, Qualitative scoring of T1 enhancement in
DCNs on weekly T1-weighted sequences (blinded). The DCN scores were attributed as follows: 0 = no T1 enhancement, 1 = doubtful T1 enhancement,
2 = definite T1 enhancement. All values are expressed as mean + SD.
FIGURE 4. Quantitative follow-up of T1 enhancement in the DCNs on
weekly T1-weighted sequences. T1 enhancement is described by the
DCN–to–brain stem ratio of T1 signal intensity. First MRI after the injection
period is MRI 6. Gadodiamide versus saline and gadodiamide versus
gadoterate: P< 0.05 from the fourth MRI examination. All values are
expressed as mean + SD.
Rasschaert et al Investigative Radiology •Volume 00, Number 00, Month 2018
4www.investigativeradiology.com © 2018 Wolters Kluwer Health, Inc. All rights reserved.
for gadodiamide versus gadobenate (>3.5), whereas this ratio was
close to 2 for the other structures. Statistical analyses comparing
the test groups for the structures more prone to store Gd are shown
in Figure 7.
No significant difference in terms of endogenous metal concen-
trations was observed between the test groups (data not shown). How-
ever, a good correlation was observed between tissue total Gd and
total Fe concentrations for the gadodiamide and gadobenate groups:
higher Fe concentrations in brain structures were correlated with higher
total Gd concentrations (Fig. 8, A and B). No correlation was observed
between Fe and total Gd concentrations in the gadoterate group
(Fig. 8C). Furthermore, total Gd concentration did not correlate with
tissue copper or Zn concentrations (Cu-Gd correlation: r= 0.6,
r=0.35,r= 0.53; and Zn-Gd correlation: r=0.15,r= 0.41, and
r=−0.23, for gadodiamide, gadobenate, and gadoterate, respectively).
Plasma Total Gd Concentrations
After the injection period, plasma total Gd concentrations pro-
gressively decreased, but still remained above the lower limit of quanti-
fication on day 66, that is, 1 month after the last injection. Overall,
FIGURE 5. Relaxation rate R1 (s
−1
) determined in the DCNs from T1 mapping sequences performed at the beginning of the study, after 5 weeks of
injections, and at completion of the study (4 weeks after the last injection). Circles: values for rats that did not complete the study. Individual values are
given, as well as mean ± SD. According to the Dixon exclusion test at a 5% risk, 1 value in gadobenate and gadodiamide groups at week 1 was excluded,
as well as 1 value in saline, gadobenate, and gadodiamide groups at week 10.
FIGURE 6. Total Gd concentrations determined by ICP-MS in the various dissected brain areas (cerebellum*: except for DCNs) 4½weeks after the last
injection (20*0.6 mmol Gd/kg body weight). Individual values are given, as well as mean ± SD.
Investigative Radiology •Volume 00, Number 00, Month 2018 Comparative CNS Gd Uptake in Renally Impaired Rats
© 2018 Wolters Kluwer Health, Inc. All rights reserved. www.investigativeradiology.com 5
plasma Gd curves were similar between gadoterate and gadodiamide.
However, plasma total Gd concentrations in the gadobenate group were
significantly lower (P< 0.01 until day 30 compared with gadodiamide
and P< 0.05 until day 37 compared with gadoterate) (Fig. 9).
Urinary Excretion of Gd and Endogenous Metals
Immediately after injection ofGBCAs at days 11 and 25 (Fig. 1),
the urinary excretion of Gd was significantly increased (P<0.0001for
all vs saline) (Fig. 10). However, the Gd excretion was reduced by a fac-
tor of 3 to 4 in the case of gadobenate compared with the other GBCA-
treated groups (P< 0.0001). A nonsignificant increase in endogenous
urinary Fe excretion was observed on day 25 in the gadodiamide group
compared with the other 3 groups, whereas no difference in endogenous
urinary copper excretion was observed between the groups (group ef-
fect: P= 0.66) (Fig. 10).
At both days 11 and 25, a substantial increase in endogenous
urinary Zn excretion was observed after injection of gadobenate
(7-fold increase, P< 0.01 vs saline and gadoterate), and an even
greater increase was observed after injection of gadodiamide (27-
fold increase, P< 0.0001 vs other groups), whereas urinary Zn ex-
cretion after gadoterate was increased only 1.3-fold compared with
saline (not statistically significant).
DISCUSSION
Moderate renal impairment has been shown to represent a trans-
lational model of potentiation of brain Gd uptake, which isproportional
to baseline renal function.
23
Baseline CrCl measured at the beginning of
the study was 0.21 ± 0.05 mL/min per 100 g, comparable to the value
reported by Rasschaert et al
23
(0.19 ± 0.06 mL/min per 100 g), corre-
sponding to stage 3 CKD. The use of a nonclinical model of moderate
renal impairment would seem to be clinically relevant, because stage 3
CKD is very common in the elderly population, more prone to undergo
MRI examinations.
24,25
Three rats treated with gadobenate and 1 rat treated with
gadodiamide that were killed for ethicalreasons or that were found dead
presented the lowest CrCl values in their respective groups (CrCl values
between 0.09 and 0.15 mL/min per 100 g), suggesting that poor base-
line renal function compromises the safety of these L-GBCAs.
Qualitative and Quantitative Assessment of T1
Enhancement in the DCNs
T1 signal enhancement in the DCNs was monitored weekly by
T1-weighted MRI sequences on a 4.7 T nonclinical magnet. T1 signal
intensity in the DCNs was quantified with respect to brain stem signal
intensity, as classically assessed in both clinical and nonclinical studies,
although this area also accumulates Gd (total Gd concentrations of
1.4 ± 0.5 nmol/g for gadobenate, 3.6 ± 0.8 nmol/g for gadodiamide,
and 0.7 ± 0.09 nmol/g for gadoterate) and may consequently underesti-
mate T1 signal enhancement in the DCNs. Images were scored qualita-
tively under blinded conditions. Scoring of T1 signal intensity, starting
after 3 weeks of injections (ie, a cumulative dose of 7.2 mmol Gd/kg
body weight), revealed doubtful T1 signal enhancement in the DCNs
after gadobenate administrations and definite T1 signal enhancement
after gadodiamide administrations, whereas no effect was observed in
the gadoterate group. Analysis of the DCN–to–brain stem ratio clearly
distinguished between the group treated with gadodiamide for 3 weeks
and the saline and gadoterate groups, and this ratio continued to
slightly increase, even during the injection-free period. Regarding
the gadobenate-treated group, intermediate T1 signal enhancement
was observed in the DCNs (mean, 55% ± 16% increase of the signal ra-
tio compared with the signal ratio observed with gadodiamide). No
FIGURE 7. Total Gd concentration in the main brain structures that accumulate Gd (cerebellum*: all parenchyma except for the DCNs). Individual values
are given, as well as mean ± SD. According to the Dixon exclusion test at a 5% risk, 1 saline-treated rat was excluded for DCNs, 1 saline and 1
gadoterate-treated rats for olfactory bulbs, and 1 gadoterate-treated rat for the cerebellum*(*P<0.05;**P<0.01;***P< 0.001).
Rasschaert et al Investigative Radiology •Volume 00, Number 00, Month 2018
6www.investigativeradiology.com © 2018 Wolters Kluwer Health, Inc. All rights reserved.
effects on the T1 signal of the DCNs were demonstrated in the gadoterate
group, regardless of the time point.
R1 mapping confirmed T1 signal enhancement in the DCNs
with gadobenate and gadodiamide, even after the administration-free
period for gadodiamide (ie, at week 10).
Persistence of T1 signal enhancement throughout the study, de-
spite reports that Gd is partially cleared from the tissues,
11,32
suggests
a change in the form of Gd stored in brain tissues. The total Gd
concentration would be expected to be lower on day 66 than on day
45, but the T1 signal ratio actually increased or remained relatively sta-
ble, suggesting that residual Gd is transformed into a storage form that
enhances the T1 effect, or that Gd is cleared more rapidly from the brain
stem than from the DCNs. It can be hypothesized that Gd dissociated
from L-GBCAs progressively binds to (yet unidentified) macromole-
cules, as recently shown.
33
Gianolio et al
34
suggested that this form of
Gd could be responsible for the majority of the T1 signal enhancement.
Total Gd Concentrations in Brain Structures
The highest Gd concentration in the DCNs was observed
with the 2 L-GBCAs: 27.1 ± 6.5 nmol/g for gadodiamide and
12.0 ± 2.6 nmol/g for gadobenate, that is, 20- and 9-fold higher than
the total Gd concentration measured in the DCNs with gadoterate, re-
spectively. Furthermore, high Gd accumulation in the olfactory bulbs
was observed after administration of L-GBCAs (consistent with the re-
sults observed in mice),
11
and interestingly, the olfactory bulbs are also
the major area of storage of manganese after exposure reported in both
rodents (oral exposure)
35
and humans (respiratory exposure).
36
While total Gd concentration ratios for many brain structures
(amygdala, cortical forebrain, hippocampus, hypothalamus, brain stem,
midbrain) were equal to approximately 2 between gadodiamide and
gadobenate and between gadobenate and gadoterate, some structures
seemed to store higher proportions of Gd after gadodiamide injections
compared with gadobenate injections: olfactory bulb (ratio of 4.8 be-
tween gadodiamide and gadobenate), cerebellar cortex (ratio of 4.0),
and striatum (ratio of 3.4). As gadodiamide is the GBCA more prone
to dissociate in vivo and release free Gd
3+
,
33
we can speculate that these
structures are more likely to accumulate Gd in a dissociated form than
the other structures.
Total Gd concentrations observed in brain areas in our study were
1.5-2-fold higher than those reported by Kartamihardja et al,
11
but with
generally the same order of distribution between brain structures. These
authors studied the distribution and washout of gadodiamide and
gadoterate in renally impaired mice. These discrepancies in total Gd
concentration could be explained by differences in the species studied
(rat vs mouse), the renal impairment model (subtotal nephrectomy vs
electrocoagulation), the washout time in the present study, and the cu-
mulative dose (100 mmol Gd/kg in mice, which would be equivalent
to 50 mmol/kg for rats, after adjustment for body surface area, versus
12 mmol Gd/kg in our study).
28
Total Gd concentrations observed in the various brain structures
after administration of L-GBCAs were correlated with Fe concentra-
tion, but not with Zn and Cu concentrations. These results support the
possibility of Gd versus Fe transmetalation for L-GBCAs. The thermo-
dynamic constants are much higher for Fe
3+
(eg, for Fe-BOPTA:
FIGURE 8. Correlations between mean brain tissue total Gd and
Fe concentrations measured in brain areas for the various GBCAs
(cerebellum*: all cerebellar parenchyma except for the DCNs). A, Tissue
Fe versus total Gd concentrations in gadodiamide-treated rats. B, Tissue
Fe versus total Gd concentrations in gadobenate-treated rats. C, Tissue
Fe versus total Gd concentrations in gadoterate-treated rats.
FIGURE 9. Time course of plasma total Gd concentration over the
entire study. During the injection period (days 16 and 30), plasma was
collected just before the second injection of the week (24 hours after
the 9th injection and 24 hours after the 17th injection).
Investigative Radiology •Volume 00, Number 00, Month 2018 Comparative CNS Gd Uptake in Renally Impaired Rats
© 2018 Wolters Kluwer Health, Inc. All rights reserved. www.investigativeradiology.com 7
log K
cond
= 23.4) than for Cu
2+
or Zn
2+
(log K
cond
of Cu-BOPTA = 17.3
and log K
cond
of Zn-BOPTA = 13.9),
1
and Fe concentrations are higher.
However, it should be noted that only the labile fraction of the Fe pool
(mainly in the Fe
2+
form) is susceptible to transmetalation. No differ-
ence in total endogenous metal concentrations in brain structures was
observed between the various groups, which can be explained by the
fact that ICP-MS is an elemental technique that does not take into ac-
count the labile fraction of the metals. Another possible explanation
for the Gd-Fe correlation could be that Gd and Fe access brain areas
such as the DCNs, olfactory bulb, or striatum via the same pathways.
Interestingly, it has been reported that the brain areas associated
with T1 signal enhancement after more than 35 administrations of
L-GBCAs to patients were the posterior thalamus, substantia nigra,
red nucleus, cerebellar peduncle, colliculi, dentate nucleus, and globus
pallidus,
37
that is, the brain structures associated with the highest
Fe concentrations.
38
Plasma Gd Concentration
A classic pharmacokinetic profile was observed for plasma total
Gd concentrations during the study. However, plasma Gd was still de-
tected 1 month after the last injection. Plasma total Gd concentrations
were lower following administration of gadobenate at all time points
compared with the other GBCA groups, which could be attributed to
specific biliary excretion of this GBCA related to its aromatic moiety,
especially in the context of renal impairment and in the rat species.
39–41
This excretion pattern has been previously described in renally impaired
rats.
42
In the case of gadobenate, the rat model may underestimate the
Gd concentrations, because of a different pharmacokinetics profile
and excretion pathway in this species compared with the human spe-
cies. Indeed, only 3% to 5% of gadobenate is taken up by the hepato-
cytes in humans, while this phenomenon accounts for approximately
50% of the molecule in the rat with normal renal function.
39
Urinary Excretion of Gd and Endogenous Metals
Urinary excretion of Gd and endogenous metals (Fe, Zn, Cu)
was determined immediately after GBCA injection, at days 11 and 25
and on days 36 and 64, in a context of tissue Gd retention. As found
in the plasma Gd concentrations, Gd urinary excretion was reduced in
gadobenate in comparison with gadoterate and gadodiamide, because
of the specific hepatic excretion of this molecule. The Gd urinary excre-
tion is reduced by a factor of 3 to 4. In this model, the hepatic excretion
would then represent approximately 70% of gadobenate excretion. Re-
garding endogenous metals, a substantial increase in urinary Zn con-
centrations was observed immediately after injections of gadodiamide
and gadobenate. Urinary Zn excretion occurring immediately after
GBCA injection has been described in patients receiving a single ad-
ministration of the L-GBCA gadodiamide and, to a lesser extent,
gadopentetate, but not with gadoterate.
43
In the case of gadodiamide,
the excess free ligand caldiamide (5% wt/vol) can chelate endogenous
metals, and by extrapolating from data in humans, a significant propor-
tion of plasma total and labile Zn could be available for chelation com-
pared with plasma Fe or copper.
43–46
The affinity constant (log K
therm
) for Zn-DTPA-BMA is 12.04 ver-
sus 7.17 for Ca-DTPA-BMA.
37
However, although the pharmaceutical
FIGURE 10. Urinary excretion of endogenous Zn, Fe, and Cu (measured by ICP-MS) at various time points (day −3: before injection period; day 36:
after the injection period; day 64: after injection-free period), and 1 to 5 hours after injection of GBCAs (at day 11 and day 25). Individual values
are given, as well as mean.
Rasschaert et al Investigative Radiology •Volume 00, Number 00, Month 2018
8www.investigativeradiology.com © 2018 Wolters Kluwer Health, Inc. All rights reserved.
solution of gadobenate does not contain any added free ligand in the
pharmaceutical solution,
47
it induced a significant increase in urinary
excretion of endogenous Zn. Therefore, the most plausible explana-
tion for this phenomenon is a transmetalation phenomenon occurring
between Gd
3+
and Zn
2+
, possibly facilitated by the presence of ele-
ments capable of binding Gd
3+
, such as proteins and PO
4
3−
, displacing
the equilibrium.
48–51
Gadolinium versus Zn transmetalation may
therefore also be responsible for part of the Zn excretion observed
with gadodiamide.
Overall, clinical and nonclinical studies published over recent
years have clearly demonstrated that less thermodynamically and kinet-
ically stable GBCAs are associated with higher Gd accumulation in
brain and body tissues, with a tropism for certain structures, such as
the DCNs. Although all GBCAs enter cerebrospinal fluid and brain tis-
sue via the choroid plexus, M-GBCAs remain chelated and return to the
circulation to be subsequently eliminated in urine, whereas less stable
L-GBCAs rapidly dissociate in the tissues, and Gd is therefore trapped
in the brain. Gianolio et al
34
recently showed that, after 22 injections of
0.6 mmol/kg of gadodiamide in the rat, the tissues studied only 3 days
after the last injection mostly contained dissociated Gd (<20% of che-
lated Gd in the cerebellum and 4% in the cerebrum). In contrast, only
very low levels of the M-GBCA, gadoteridol, were observed and en-
tirely in its original chelated form. Frenzel et al
33
reported fairly similar
results, with a decreasing proportion of chelated Gd over time (3-day
injection-free period vs 24-day injection-free period).
According to one hypothesis of dechelation, chelated Gd could
form a ternary complex with PO
4
3−
, which would then allow dechelation
of an intermediate state Gd
3+
(PO
4
3−
) from the ligand.
51–53
Once
dechelated, Gd either remains in this precipitated form or is immedi-
ately bound to macromolecules (thereby leading to T1 hyperintensity),
either peptides or proteins.
33,54
The coexistence or predominance of
these various forms would putatively lead to different levels and forms
of toxicity.
In conclusion, in a sensitive translational model of a common at-
risk population, only traces of Gd were observed in the brain following
injections of gadoterate, in contrast to the linear Gd chelates gadobenate
and gadodiamide. Gadolinium brain uptake from L-GBCAs is associ-
ated with T1 hyperintensity in the DCNs, which could be due to binding
of dissociated and soluble Gd derived from L-GBCAs to macromole-
cules. Furthermore, the global distribution of Gd after administration
of L-GBCAs (but not the macrocyclic gadoterate) in brain areas was
correlated with the local tissue distribution of Fe, which supports the
possibility of Gd versus Fe transmetalation or is a hint for the same
pathway to access the brain. The precise localization of Gd tissue stor-
age and identification of the Gd-binding macromolecules have yet to be
documented, as well as long-term putative neurotoxic effects associated
with repeated administration of L-GBCAs.
ACKNOWLEDGMENTS
The authors thank Evangeline M'Boumba, MS, for the Gd deter-
mination in tissues, and Anthony Saul, PhD, and Hélène Poenaru, for
reviewing the English language. The authors also thank Jean-Luc
Guerquin-Kern, PhD; Sergio Marco, PhD; and Jean-Pierre Laissy,
MD, PhD, for helpful discussions.
REFERENCES
1. Port M, Idée JM, Medina C, et al. Efficiency, thermodynamic and kinetic stability
of marketed gadolinium chelates and their possible clinical consequences: a critical
review. Biometals. 2008;21:469–490.
2. Robert P, Violas X, Grand S, et al. Linear gadolinium-based contrast agents are as-
sociated with brain gadolinium retention in healthy rats. Invest Radiol.2016;51:
73–82.
3. Jost G, Lenhard DC, Sieber MA, et al. Signal increase on unenhanced T1-weighted
images in the rat brain after repeated, extended doses of gadolinium-based con-
trast agents: comparison of linear and macrocyclic agents. Invest Radiol. 2016;
51:83–89.
4. White GW, Gibby WA, Tweedle MF. Comparison of Gd(DTPA-BMA) (Omniscan)
versus Gd(HP-DO3A) (ProHance) relative to gadolinium retention in human
bone tissue by inductively coupled plasma mass spectroscopy. Invest Radiol.
2006;41:272–278.
5. Errante Y, Cirimele V, Mallio CA, et al. Progressive increase of T1 signalintensity
of the dentate nucleus on unenhanced magnetic resonance images is associated
with cumulative dosesof intravenously administered gadodiamide in patientswith
normal ren al function, suggesting dechelation. Invest Radiol. 2014;49:6 85–690.
6. Weberling LD, Kieslich PJ, Kickingereder P, et al. Increased signal intensity in the
dentate nucleus on unenhanced T1-weighted images after gadobenate dimeglumine
administration. Invest Radiol. 2015;50:743–748.
7. McDonald RJ, McDonald JS, Kallmes DF, et al. Intracranial gadolinium deposi-
tion after contrast-enhanced MR imaging. Radiology. 2015;275:772–782.
8. Radbruch A, Weberling LD, KieslichPJ, et al. Gadolinium retention in the dentate
nucleus andglobus pallidus is dependent on the class of contrast agent.Radiology.
2015;275:783–791.
9. Kanda T, Ishii K, Kawaguchi H, et al. High signal intensity in the dentate nucleus
and globuspallidus on unenhanced T1-weighted MRimages: relationship with in-
creasing cumulative dose of a gadolinium-based contrast material. Radiology.
2014;270:834–841.
10. Radbruch A, Weberling LD, Kieslich PJ, et al. Intraindividual analysis of signal
intensity changes in the dentate nucleus afterconsecutive serial applications of lin-
ear and macrocyclic gadolinium-based contrast agents. Invest Radiol. 2016;51:
683–690.
11. Kartamihardja AA, Nakajima T, Kameo S, et al. Distribution and clearance of
retained gadolinium inthe brain: differences between linear and macrocyclic gad-
olinium based contrast agents in a mouse model. Br J Radiol. 2016;89:20160509.
12. Lohrke J, Frisk AL, Frenzel T, et al. Histology and gadolinium distribution in the
rodent brain after the administration of cumulative high doses of linear and mac-
rocyclic gadolinium-based contrast agents. Invest Radiol. 2017;52:324–333.
13. Scala M, Koob M, de Buttet S, et al. A Pharmacokinetics, efficacy, and safety
study of gadoterate meglumine in pediatric subjects aged younger than 2 years.
Invest Radiol. 2018;53:70–79.
14. Roberts DR, Chatterjee AR, Yazdani M, et al. Pediatric patients demonstrate pro-
gressive T1-weighted hyperintensity in the dentate nucleus following multiple
doses of g adoliniu m-based c ontrast a gent. AJNR Am J Neuroradiol.2016;37:
2340–2347.
15. Renz DM, Kümpel S, Böttcher J, et al. Comparison of unenhanced T1-weighted
signal intensities within the dentate nucleus and theglobus pallidus after serial ap-
plications of gadopentetate dimeglumine versus gadobutrol in a pediatric popula-
tion. Invest Radiol. 2018;53 :119–127.
16. Prola-Netto J, Woods M, Roberts VHJ, et al. Gadolinium chelate safety in preg-
nancy: barely detectable gadolinium levels in the juvenile nonhuman primate
after in utero exposure [published online ahead of print September 4, 2017].
Radiology. 2017.
17. Erdene K, Nakajima T, Kameo S, et al. Organ retention of gadolinium in mother
and pup mice: effect of pregnancy and type of gadolinium-based contrast agents.
Jpn J Radiol. 2017;35 :568–573.
18. Khairinisa MA, Takatsuru Y, Amano I, et al. The effect of perinatal gadolinium-
based contrast agents on adult mice behavior. Invest Radiol. 2018;53:1 10–118.
19. Barbieri S, Schroeder C, Froehlich JM, et al. High signal intensity in dentate nu-
cleus and globus pallidus on unenhanced T1-weighted MR images in three pa-
tients with impaired renal function and vascular calcification. Contrast Media
Mol Imaging. 2016;11:2 45–250.
20. Cao Y, Zhang Y, Shih G, et al. Effect of renal function on gadolinium-related sig-
nal increases on unenhanced T1-weighted brain magnetic resonance imaging. In-
vest Radiol. 2016;51 :677–682.
21. Cenci MA, Whishaw IQ, Schallert T. Animal models of neurological deficits: how
relevant is the rat? Nat Rev Neurosci. 2002;3:574–579.
22. Shah A, Garzon-Muvdi T, Mahajan R, et al. Animal models of neurological dis-
ease. Adv Exp Med Biol. 2010;671:23–40.
23. Rasschaert M, Idée JM, Robert P, et al. Moderate renal failure accentuates T1 sig-
nal enhancement in the deep cerebellar nuclei of gadodiamide-treated rats. Invest
Radiol. 2017;52:255–264.
24. Stevens LA, Viswanathan G, Weiner DE. Chronic kidney disease and end-stage
renal disease in the elderly population: current prevalence, future projections,
and clinical significanc e. Adv Chronic Kidney Dis. 2010;17:293–301.
25. Duru OK, Vargas RB, Kermah D, et al. Highprevalence of stage 3 chronic kidney
disease in older adults despite normal serum creatinine. J Gen Intern Med.2009;
24:86–92.
26. European Medicine Agency. Assessment report for gadolinium-containing con-
trast agents. Procedure No. EMEA/H/A-31/1097. July 1, 2010. Available at:
http://www.ema.europa.eu/docs/en_GB/document_library/Referrals_document/
gadolinium_31/WC500099538.pdf. Accessed 14 July, 2017.
Investigative Radiology •Volume 00, Number 00, Month 2018 Comparative CNS Gd Uptake in Renally Impaired Rats
© 2018 Wolters Kluwer Health, Inc. All rights reserved. www.investigativeradiology.com 9
27. Food and DrugAdministration.FDA Drug Safety Communication:new warnings
for using gadolinium based contrast agents in patients with kidney dysfunction.
October 9, 2010. Available at: http://www.fda.gov/Drugs/DrugSafety/
ucm223966.htm. Accessed 14 July, 2017.
28. Food and Drug Administration. US Department of Health and Human Services.
Center for Drug Evaluation and Research. Guidance for Industry. Estimating the
maximum safestarting dose in initialclinical trials for therapeuticsin adult healthy
volunteers. July 6, 2005. Available at: http://www.fda.gov/downloads/Drugs/…/
Guidances/UCM078932.pdf. Accessed June 15, 2017.
29. Tissue prep and protein assay 2012. Available at: https://fr.scribd.com/document/
317128344/Tissue-Prep-and-Protein-Assay-2012. Accessed 5 December, 2017.
30. Spijker S. Dissection of rodent brain regions. In: Li KW, ed. Neuroproteomics
(Neuromethods, Volume 57). New York, NY: Humana Press; 2011:13–26.
31. Shapiro SS, Wilk MB. An analysis of variance test for normality (complete sam-
ples). Biometrika. 1965;52:591–611.
32. Smith AP, Marino M, Roberts J, et al. Clearance of gadolinium fromthe brain with
no pathologic effect after repeated administration of gadodiamide in healthy rats:
an analytical and histologic study. Radiology. 2017;282:743–751.
33. Frenzel T, Apte C, Jost G, et al. 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. Invest Radiol.
2017;52:396–404.
34. Gianolio E, Bardini P, Arena F, et al. Gadolinium retention in the rat brain: assess-
ment of the amounts of insoluble gadolinium-containing species and intact gado-
linium complexes after repeated administration of gadolinium-based contrast
agents. Radiology. 2017;285:83 9–849.
35. O'Neal SL, Hong L, Fu X, et al. Manganese accumulation in bone following
chronic exposure in rats: steady-state concentration and half-life in bone. Toxicol
Lett. 2014;229:93–100.
36. Sen S, FlynnMR, Du G, et al. Manganeseaccumulation in theolfactory bulbs and
other brain regions of “asymptomatic”welders. Toxicol Sci. 2011;121:160–167.
37. Zhang Y, Cao Y, Shih GL, et al. Extent of signal hyperintensity on unenhanced
T1-weighted brain MR images after more than 35 administrations of linear
gadolinium-based contrast agents. Radiology. 2017;282:516–525.
38. Hallgren B, Sourander P. The effect of age on the non-haemin iron in the human
brain. JNeurochem. 1 958;3:41–51.
39. Lorusso V, Arbughi T, Tirone P, et al. Pharmacokinetics and tissue distribution
in animals of gadobenate ion, the magnetic resonance imaging contrast en-
hancing component of gadobenate dimeglumine 0.5 M solution for injection
(MultiHance). J Comput Assist Tomogr. 1999;23 suppl 1:S181–S194.
40. Kirchin MA, Lorusso V, Pirovano G. Compensatory biliary and urinary excretion
of gadobenate ion after administration of gadobenate dimeglumine (MultiHance
(®)) in cases of impaired hepatic or renal function: a mechanism that may aid in
the prevention of nephrogenic systemic fibrosis? Br J Radiol. 2015;88 :20140526.
41. Ersoy H, Rybicki FJ. Biochemical safetyprofiles of gadolinium-based extracellu-
lar contrast agents and nephrogenic systemic fibrosis. J Magn Reson Imaging.
2007;26:1190–1197.
42. Fretellier N, Idée J, Bruneval P, et al. Hyperphosphataemia sensitizes renally im-
paired rats to the profibrotic effects of gadodiamide. Br J Pharmacol. 2012;165:
1151–1162.
43. Kimura J,Ishiguchi T, Matsuda J, et al. Human comparative study of zinc and cop-
per excretion via urine after administration of magnetic resonance imaging con-
trast agents. Radiat Med. 2005;23:322–326.
44. Zalewski P, Truong-Tran A, Lincoln S, et al. Use of a zinc fluorophore to measure
labile pools of zinc in body fluids and cell-conditioned media. Biotechniques.
2006;40:509–520.
45. Mills E, Dong XP, Wang F, et al. Mechanisms of brain iron transport: insight
into neurodegeneration and CNS disorders [review]. Future Med Chem. 2010;
2:51–64.
46. Cabantchik ZI. Labile iron in cells and body fluids: physiology, pathology, and
pharmacology [review]. Front P ha rm ac ol. 2014;5: 45.
47. Idée JM, Port M, Robic C, et al. Role of thermodynamic and kinetic parameters in
gadolinium chelate stability. J Magn Reson Imaging. 2009;30:124 9–1258.
48. Tweedle MF, Hagan JJ, Kumar K, et al. Reaction of gadolinium chelates with en-
dogenously available ions. Magn Reson Imaging. 1991;9:409–415.
49. Taupitz M, Stolzenburg N, Ebert M, et al. Gadolinium-containing magnetic reso-
nance contrast media: investigation on the possible transchelation of Gd
3+
to the
glycosaminoglycan heparin. Contrast Media Mol Imaging. 2013;8:108–116.
50. Laurent S, Elst LV, Copoix F, et al. Stabilityof MRI paramagnetic contrast media:
a proton relaxometric protocol for transmetallation assessment. Invest Radiol.
2001;36:115–122.
51. Idée JM, Fretellier N, Robic C, et al. The role of gadolinium chelatesin the mech-
anism of nephrogenic systemic fibrosis: a critical update. Crit Rev Toxicol.2014;
44:895–913.
52. Baranyai Z, Pálinkás Z, Uggeri F, et al. Dissociation kinetics of open-chain and
macrocyclic gadolinium(III)-aminopolycarboxylate complexes related to mag-
netic resonance imaging: catalytic effect of endogenous ligands. Chemistry.
2012;18:16426–16435.
53. Robic C, CatoenS, de Goltstein MC, et al.The role of phosphateon Omniscan(®)
dechelation: an in vitro relaxivity study at pH 7. Biometals. 2011;24:759–768.
54. Knoepp F, Bettmer J, Fronius M. Gadolinium released by the linear gadolinium-
based contrast-agent Gd-DTPA decreases the activity of human epithelial Na
+
channels (ENaCs). Biochim Biophys Acta. 2017;1859:1040–1048.
Rasschaert et al Investigative Radiology •Volume 00, Number 00, Month 2018
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