Editorial: Gadolinium Use in Patients with Kidney Disease: A Cause for Concern

Differential regulation of neutrophil CD18 integrin function by di- and tri-valent cations: manganese vs. gadolinium

Affinity regulation of integrin function plays an important role during both leukocyte-endothelial and leukocyte-leukocyte interactions. We compared the roles of Mn(2+) (Manganese) and Gd(3+) (Gadolinium) in regulating leukocyte CD18-integrin function. We observed that: (i) Both cations prolonged neutrophil homotypic aggregation following chemoattractant IL-8 stimulation, with Gd(3+) being effective at doses two orders of magnitude (10 microM range) lower that Mn(2+). (ii) While both Gd(3+) and Mn(2+) mediate homotypic cell aggregation via L: -selectin and CD18 integrins, their effects on the integrin subunits, LFA-1 (CD11a/CD18) and Mac-1 (CD11b/CD18), was different. Gd(3+) altered both LFA-1 and Mac-1 function, while the dominant effect of Mn(2+) was on Mac-1. This effect of Gd(3+) on LFA-1 function was confirmed in cell-free studies that measured the binding of recombinant ICAM-1 to LFA-1 immobilized on beads. (iii) Both ions augmented the binding of 327C, an antibody that recognizes active CD18 on human neutrophils, both in the presence and absence of exogenous IL-8. The effects of Mn(2+) was more pronounced since it caused 3-4-fold increase in mAb 327C binding to neutrophils compared to Gd(3+) which increased antibody binding by only approximately 80%. 327C binding was partially reduced by Ca(2+). Further, 327C binding induced by Mn(2+) did not correlate tightly with cell adhesion function. (iv) In studies that monitored intracellular Ca(2+) ([Ca(2+)](i)), the addition of Mn(2+) but not Gd(3+) to neutrophils altered [Ca(2+)](i) levels. Overall, while both Gd(3+) and Mn(2+) stabilize high affinity CD18 mediated cell adhesion, Gd(3+) affects integrin conformation while Mn(2+) may also trigger other effects.

Dialytic therapies to prevent NSF following gadolinium exposure in high-risk patients

Prolonged exposure to gadolinium-based contrast (GBC) appears to be the core pathophysiologic factor in the development of nephrogenic systemic fibrosis (NSF). As the GBC is renally excreted, this condition is predominantly seen only following exposure in patients with severe reductions in renal function. Fortunately, GBC is easily hemodialyzed with 95% of an administered dose removed after two hemodialysis sessions. Peritoneal dialysis, on the other hand, is not an efficient means of GBC removal. This has led to recommendations to hemodialyze a high-risk patient immediately following GBC administration and to repeat the treatment the following day. Although this approach seems logical and is more aggressive than the usual thrice-weekly hemodialysis schedule that most patients were receiving when they developed this devastating condition, there are no data to support the supposition that this approach will reduce the risk of NSF. Therefore, although an aggressive hemodialysis strategy postexposure is not unreasonable, it is probably best at this point to try to avoid GBC administration altogether in these high-risk patients.

Tissue deposition of gadolinium and development of NSF: a convergence of factors

Gadolinium-based contrast (GBC) exposure has recently been linked to the development of nephrogenic systemic fibrosis (NSF) in patients with underlying kidney disease and may in fact be the previously unrecognized trigger for the fibrosing process. As NSF is fairly rare in this patient population, a number of permissive factors are likely required for GBC exposure to initiate fibrosis. Advanced kidney disease is an absolute requirement whereas vascular injury and an inflammatory state, and a mix of co-factors including increased serum phosphate and calcium concentrations and iron overload further enhance risk. The combination of these events allows excess circulating gadolinium, which dissociates from its chelate to leak out of vessels and deposit in tissues. Free or bound tissue gadolinium, a rare earth metal of the lanthanoid series, promotes fibrosis via either direct binding to the collagen helix or, once the metal has been engulfed by macrophages, through the production of free oxygen radicals, cytokines, and other profibrotic factors that attract circulating fibrocytes to tissues. These fibrocytes then differentiate into fibroblast-like spindle cells that produce connective tissue matrix and other angiogenic and growth factors that further enhance tissue fibrosis. Direct gadolinium activation of transglutaminases on these tissue fibroblast-like cells may also promote fibrosis.

Technology Insight: new techniques for imaging the gut in patients with IBD

Advances in techniques for imaging the gut continue to drive the rapid development of modalities for diagnosing and assessing the activity of IBD. Abdominal ultrasound and magnetic resonance enterography have shown great potential for the diagnosis of IBD and assessment of its distribution, with the benefit of avoiding radiation exposure and serving as a safe option for pregnant patients. CT enterography or CT enteroclysis, with neutral or negative contrast, seems to be a sensitive and specific modality for detecting disease in the small bowel. The role of CT or magnetic resonance colonography in patients with IBD remains uncertain and these modalities are now best reserved for patients who decline or cannot undergo standard endoscopic evaluations. Capsule endoscopy might be the most sensitive modality for the detection of mucosal small bowel disease, but its specificity remains in question. Double-balloon endoscopy is an exciting new tool that has the distinct advantage of enabling biopsy or treatment of lesions detected during the procedure. All these techniques are at the forefront of the rapidly evolving field of imaging the gut in patients with IBD.

Ultrasound Contrast Agents in the Study of Kidney Function in Health and Disease

Ultrasound contrast agents are gas filled microbubbles that enhance the ultrasound image. They behave similarly to red blood cells and cross all capillary beds; making contrast enhanced ultrasonography (CEU) a suitable technique to study vasculature and tissue blood flow. Ultrasound contrast agents have been found to be safe after intravenous injection. CEU has been used extensively in the field of cardiology. Currently, study of renal vasculature and renal blood flow requires complicated, time consuming and expensive techniques, which are not commonly used in clinical settings. CEU potentially may serve as a relatively noninvasive and safe technique for studying renal hemodynamics in health and disease. In this article we have reviewed the literature on the use of CEU in the study of kidney disease.