Iatrogenic Iron Overload in Dialysis Patients at the Beginning of the 21st Century

Target-based Anemia Management with Erythropoiesis Stimulating Agents (Risks and Benefits Relearned) and Iron (Still More to Learn)

The FDA first licensed erythropoiesis stimulating agents (ESA) for use in patients with ESRD in 1989. Hemoglobin targets for treatment with ESAs were established at the outset on the basis of descriptive pre-ESA literature and Phase I-III data in patients with ESRD. Postrelease literature in ESA-treated patients accumulating over time initially supported improvement in indices of both cardiovascular and other organ function as well as quality of life with therapy. Recommended treatment targets for hemoglobin would evolve further in the United States from four iterations of evidence- and opinion-based practice guidelines appearing between 1997 and 2007. Several randomized, controlled trials published from 1998 to 2009 examined normalization and near-normalization of hemoglobin in patients with both ESRD and CKD; they raised fundamental questions as to the safety of robust correction of anemia. These findings, taken together with subsequent actions of the FDA in ESA labeling and CMS's quality expectations for hemoglobin in payment for dialysis treatments, would result in a comprehensive reassessment of the hemoglobin targets in ESA therapy. A marked decrease in both national ESA utilization and hemoglobin attainment has ensued as a result. This discussion addresses the history of the striking changes in enthusiasm for hemoglobin-targeted anemia therapy from 1989 to the present, and similarly examines the evolution of ferritin-targeted iron administration, which has followed different-and markedly slower-historical development.

Signal-intensity-ratio MRI accurately estimates hepatic iron load in hemodialysis patients

Background

Iron overload, diagnosed by means of magnetic resonance imaging (MRI), is an increasingly recognized disorder in hemodialysis patients. Specific MRI protocols have been shown to provide a reliable estimation of tissue iron content in non-renal patient populations but have not been validated in dialysis patients. Such validation studies require liver biopsy for histological comparison, but this invasive and risky procedure raises ethical concerns, especially regarding frail patients with end-stage renal disease.

Materials and methods

We compared in a pilot study Scheuer’s histological classification and Deugnier and Turlin’s histological classification of iron overload (Perls staining) with signal-intensity-ratio MRI values obtained with the Rennes University algorithm in 11 hemodialysis patients in whom liver biopsy was formally indicated for their medical follow-up.

Results

For Scheuer’s histological classification, the Wilcoxon non-parametric matched-pairs test showed no significant difference in the ranking of iron overload by the two methods eg histology and MRI (sum of ranks = 1.5; p = 1). The MRI and Scheuer’s histological classifications were tightly correlated (rho = 0.866, p = 0.0035, Spearman’s coefficient), as were the absolute liver iron concentrations (LIC) at MRI (rho = 0.860, p = 0.0013, Spearman’s coefficient). The absolute liver iron concentrations at MRI were also highly correlated with Deugnier and Turlin’s histological scoring (rho = 0.841, p = 0.0033, Spearman’s coefficient).

Conclusions

This pilot study shows that liver iron determination based on signal-intensity-ratio MRI (Rennes University algorithm) very accurately identifies iron load in hemodialysis patients, by comparison with liver histology.

Citrate and albumin facilitate transferrin iron loading in the presence of phosphate

Labile plasma iron (LPI) is redox active, exchangeable iron that catalyzes the formation of reactive oxygen species. Serum transferrin binds iron in a non-exchangeable form and delivers iron to cells. In several inflammatory diseases serum LPI increases but the reason LPI forms is unknown. This work evaluates possible pathways leading to LPI and examines potential mediators of apo transferrin iron loading to prevent LPI. Previously phosphate was shown to inhibit iron loading into apo transferrin by competitively binding free Fe³⁺. The reaction of Fe³⁺ with phosphate produced a soluble ferric phosphate complex. In this study we evaluate iron loading into transferrin under physiologically relevant phosphate conditions to evaluate the roles of citrate and albumin in mediating iron delivery into apo transferrin. We report that preformed Fe³⁺-citrate was loaded into apo transferrin and was not inhibited by phosphate. A competition study evaluated reactions when Fe³⁺ was added to a solution with citrate, phosphate and apo transferrin. The results showed citrate marginally improved the delivery of Fe³⁺ to apo transferrin. Studies adding Fe³⁺ to a solution with phosphate, albumin and apo transferrin showed that albumin improved Fe³⁺ loading into apo transferrin. The most efficient Fe³⁺ loading into apo transferrin in a phosphate solution occurred when both citrate and albumin were present at physiological concentrations. Citrate and albumin overcame phosphate inhibition and loaded apo transferrin equal to the control of Fe³⁺ added to apo transferrin. Our results suggest a physiologically important role for albumin and citrate for apo transferrin iron loading.

Iron mediated toxicity and programmed cell death: A review and a re-examination of existing paradigms

Iron is an essential micronutrient that is problematic for biological systems since it is toxic as it generates free radicals by interconverting between ferrous (Fe²⁺) and ferric (Fe³⁺) forms. Additionally, even though iron is abundant, it is largely insoluble so cells must treat biologically available iron as a valuable commodity. Thus elaborate mechanisms have evolved to absorb, re-cycle and store iron while minimizing toxicity. Focusing on rarely encountered situations, most of the existing literature suggests that iron toxicity is common. A more nuanced examination clearly demonstrates that existing regulatory processes are more than adequate to limit the toxicity of iron even in response to iron overload. Only under pathological or artificially harsh situations of exposure to excess iron does it become problematic. Here we review iron metabolism and its toxicity as well as the literature demonstrating that intracellular iron is not toxic but a stress responsive programmed cell death-inducing second messenger.