Ultrasmall superparamagnetic iron oxides (USPIOs): a future alternative magnetic resonance (MR) contrast agent for patients at risk for nephrogenic systemic fibrosis (NSF)?

Abstract

Gadolinium (Gd) based contrast agents (GBCAs) in magnetic resonance imaging (MRI) are used in daily clinical practice and appear safe in most patients; however, nephrogenic systemic fibrosis (NSF) is a recently recognized severe complication associated with GBCAs. It affects primarily patients with renal disease, such as stage 4 or 5 chronic kidney disease (CKD; glomerular filtration rate <30 ml/min per 1.73 m(2)), acute kidney injury, or kidney and liver transplant recipients with kidney dysfunction. Contrast-enhanced MRI and computed tomography (CT) scans provide important clinical information and influence patient management. An alternative contrast agent is needed to obtain adequate imaging results while avoiding the risk of NSF in this vulnerable patient group. One potential alternative is ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles, which provide enhancement characteristics similar to GBCAs. We review our experience in approximately 150 patients on the potential benefits of the USPIOs ferumoxtran-10 and ferumoxytol. We focus on central nervous system (CNS) MRI but also review imaging of other vascular beds. Safety studies, including USPIO administration (ferumoxytol) as iron supplement therapy in CKD patients on and not on dialysis, suggest that decreased kidney function does not alter the safety profile. We conclude that for both CNS MR imaging and MR angiography, USPIO agents like ferumoxytol are a viable option for patients at risk for NSF.

Figures

Figure 1. Patient who presented to the Emergency Department comatose in acute renal failure with a large cerebral hemispheric mass

Axial T1-weighted MR scan without (left) and with (right) Gd 24 h post-admission when serum Cr was 6.0 mg/100 ml.

Figure 2. Schematic distribution comparing Gd versus USPIO crossing the BBB to tumor

(a) Shows Gd chelates (abbreviated Gd in the figure) crossing from the intravascular compartment through a defective BBB (arrow) to the interstitial space. GBCA, which vary in propensity to release Gd, and thereby possibly risk of NSF (see text), remains in the extracellular space at the time of imaging (minutes after infusion). Macrophages, reactive astrocytes are shown around the lesion (L) but GBCA does not enter these cells. During its short half-life (less than 1 h), Gd rapidly crosses the BBB to produce a hyperintense signal on T1-weighted sequence on MR. In CKD, Gd-chelated contrast is not cleared rapidly and can be demonstrated in tissues. (b) Ferumoxtran-10 (Fe in black) and other ultra small iron oxides are much larger particles compared to GBCAs; these particles will slowly cross the defective BBB (arrow). Due to its prolonged half-life of 25−30 h particles of ferumoxtran-10 will progressively accumulate in the interstitial space where they will be trapped by reactive astrocytes and macrophages for days (up to 7 days). The intracellular metabolism of ferumoxtran-10 will take place in the lysosome of these cells where free iron will be released to the extracelullar space. Reactive astrocytes, macrophages, and other inflammatory cell are seen in different diseases affecting the CNS, among these stroke, neoplasm, and demyelinating processes. Figure modified from Murillo et al. (reproduced with permission of Expert Reviews Ltd).

Figure 3. Nanoimaging: from bench to bedside

(a) Rat brain tumor before and after USPIO MR contrast. (b) Post-GBCA T1-weighted MRI shows a large left frontoparietal-enhancing tumor (arrows). At 24 h post–ferumoxtran, T1-weighted MRI shows intense enhancement in the left frontoparietal tumor (arrows) and a new lesion medial to the main tumor mass in the putamen (arrowhead). Cellular iron staining at the tumor–reactive brain interface shows iron uptake by the parenchymal cells with fibrillar processes (arrows) rather than by the round tumor cells (T). EM shows electron dense core of USPIO. (Reproduced from AJNR Am J Neuroradiol 2002; 23:510−519 with permission of Lippincott, Williams & Wilkins, 2008.)

Figure 4. Patient with acute disseminated encephalomyelitis (ADEM)

Axial T1-weighted MRI images without (a) and with (b) GBCA show faint, subtle enhancement in multiple brainstem lesions. At 6 days later (c) significant, more prominent, larger ferumoxtran-10 enhancement can be seen on the same site. At 3 months later (d), the lesions no longer enhance on T1-weighted images with GBCA. (Reproduced from AJNR Am J Neuroradiol 2005; 26:2290−2300 with permission of Lippincott, Williams & Wilkins, 2008).

Figure 5. Patient with Stroke

Axial T1-weighted MRI without (a) and with (b) GBCA show no significant enhancement in left insular cortex, basal ganglia, and frontoparietal lobe where DWI, T2, and FLAIR images showed high intensity (not shown) consistent with acute MCA infarction. At 10 days later, T1 images with ferumoxtran-10 (c) show significant enhancement in the same region. At 90 days later (d), axial T1-weighted image after GBCA shows no enhancement. (Reproduced from AJNR Am J Neuroradiol 2005; 26:2290−2300 with permission of Lippincott, Williams & Wilkins, 2008).

Figure 6. Ferumoxides but not ferumoxtran-10 nor ferumoxytol (even in the presence of protamine sulfate) label circulating rat mononuclear cells after intravenous infusion

Female Long Evans rats received IV ferumoxides, ferumoxtran-10, or ferumoxytol (20 mg/kg) with or without preincubation with protamine sulfate (Pro) (2 mg/kg). (a) Mononuclear cells were isolated from peripheral circulation 2 h after injection and stained with DAB-enhanced Perl's blue. Iron-labeled cells with brown stain are indicated by arrowheads. (b) Percentage of iron-positive-stained cells in total mononuclear cell population. (c) Time course of ferumoxide-Pro in vivo iron-labeled rat mononuclear cells. Data are represented as mean ± s.e.m. (Used with permission from Am J Physiol Cell Physiol 2007; 293: C1698–C1708).

Figure 7. Gd versus ferumoxytol MR pre-operatively and intra-operatively in a glioma patient using a 3 T versus a 0.15 T magnet

Glioma patient (a) T1-enhancement with GBCA. At 24 h after ferumoxytol infusion, (b) T1 enhancement, (c) T2*-weighted images. (d) Intraoperative T1-weighted 0.15 T MR 26 h after ferumoxytol injection. (Reproduced from Neurosurgery 2007; 60: 601−611; discussion 611−602, with permission of Lippincott, Williams & Wilkins, 2008).

Figure 8. Time of Flight Angiography in a patient with glioblastoma

(a) Without contrast. (b) At 15 min after GBCA, more vessels are visible. There is an early leak into the left frontal tumor. (c) At 15 min post-ferumoxytol infusion, more vessels are visible, but there is no leak into the tumor. (Reproduced from Neurosurgery 2007; 60: 601−611; discussion 611−602 with permission of Lippincott, Williams & Wilkins, 2008).

Figure 9. Perfusion MR, time-intensity curves in a patient with pineal blastoma

(a) Using GBCA, leakage of the contrast agent decreases the slope of the recovery curve in the tumor. (b) Ferumoxytol signal intensity curves show no leakage in the lesion. (Reproduced from Neurosurgery 2007; 60: 601−611; discussion 611−602 with permission of Lippincott, Williams & Wilkins, 2008).

Figure 10. Ferumoxytol susceptibility-weighted imaging at 7 T in human brain

Vasculature MRI before ferumoxytol (a) and after 4 mg/kg ferumoxytol (b).

Figure 11. MR abdominal angiograms (TR/TE: 3.5/1.3 ms) of a 60-year-old male acquired after injection of fourfold diluted ferumoxytol (4 mg/Fe/kg)

(a) First-pass image. (b) Equilibrium image. Aortic and left iliac aneurysms (large arrows) are demonstrated. The artery arising from the left iliac artery (arrowhead) supplies a transplanted kidney. The right iliac artery and vein cannot be seen due to metal artifact from right iliac aneurysm stent (small arrows). Note that in the first-pass image, the inferior vena cava is visible. Polycystic kidney disease is also demonstrated. (First-pass contrast-enhanced magnetic resonance angiography in humans using ferumoxytol, a novel ultrasmall superparamagnetic iron oxide (USPIO)-based blood pool agent. (Reproduced from J Magn Reson Imaging 2005; 21: 46−52 with permission of Wiley-Liss, Inc., a subsidiary of Wiley Inc.)