Günter Weiss

Translational regulation via iron-responsive elements by the nitric oxide/NO-synthase pathway.

Nitric oxide (NO) produced from L‐arginine by NO synthases (NOS) is a transmitter known to be involved in diverse biological processes, including immunomodulation, neurotransmission and blood vessel dilatation. We describe a novel role of NO as a signaling molecule in post‐transcriptional gene regulation. We demonstrate that induction of NOS in macrophage and non‐macrophage cell lines activates RNA binding by iron regulatory factor (IRFs), the central trans regulator of mRNAs involved in cellular iron metabolism. NO‐induced binding of IRF to iron‐responsive elements (IRE) specifically represses the translation of transfected IRE‐containing indicator mRNAs as well as the biosynthesis of the cellular iron storage protein ferritin. These findings define a new biological function of NO and identify a regulatory connection between the NO/NOS pathway and cellular iron metabolism.

Circulating Methylated SEPT9 DNA in Plasma Is a Biomarker for Colorectal Cancer

BACKGROUND The presence of aberrantly methylated SEPT9 DNA in plasma is highly correlated with the occurrence of colorectal cancer. We report the development of a new SEPT9 biomarker assay and its validation in case-control studies. The development of such a minimally invasive blood-based test may help to reduce the current gap in screening coverage. METHODS A new SEPT9 DNA methylation assay was developed for plasma. The assay comprised plasma DNA extraction, bisulfite conversion of DNA, purification of bisulfite-converted DNA, quantification of converted DNA by real-time PCR, and measurement of SEPT9 methylation by real-time PCR. Performance of the SEPT9 assay was established in a study of 97 cases with verified colorectal cancer and 172 healthy controls as verified by colonoscopy. Performance based on predetermined algorithms was validated in an independent blinded study with 90 cases and 155 controls. RESULTS The SEPT9 assay workflow yielded 1.9 microg/L (CI 1.3-3.0) circulating plasma DNA following bisulfite conversion, a recovery of 45%-50% of genomic DNA, similar to yields in previous studies. The SEPT9 assay successfully identified 72% of cancers at a specificity of 93% in the training study and 68% of cancers at a specificity of 89% in the testing study. CONCLUSIONS Circulating methylated SEPT9 DNA, as measured in the new (m)SEPT9 assay, is a valuable biomarker for minimally invasive detection of colorectal cancer. The new assay is amenable to automation and standardized use in the clinical laboratory.

KDIGO Clinical Practice Guideline for Anemia in Chronic Kidney Disease

To the Editor: We have read the letter to the editor by Jerzy Przedlacki1 and the response from the authors2 of the Kidney Disease-Improving Global Outcomes (KDIGO) clinical practice guidelines for bisphosphonate (BP) treatment in chronic kidney disease (CKD), and would like to share our concerns regarding the use of BP treatment of CKD. The kidney is the organ that excretes many drugs, and any change in renal function will affect the pharmacology of these drugs. Existing or residual renal function of the patient will have to be taken into account while prescribing drugs. This is just as important for the patient with CKD 4 or 5, including those with CKD 5 already on peritoneal dialysis or hemodialysis, who may still have residual renal function. Nephrotoxic drugs including nonsteroidal anti-inflammatory drugs can very readily destroy whatever residual renal function patients may still have. Residual renal function is important to preserve as it contributes to less patient morbidity and mortality3 in the dialysis patient. Recently, there have been adverse reports of a certain BP that works by inhibiting osteoclast-mediated bone resorption, thereby slowing the breakdown of bone to reduce the risk of fractures. As of 14 August 2009, there have been 139 post-marketing reports of renal impairment following its use as an infusion worldwide. Many of these occur in patients with pre-existing medical conditions or risk factors (elderly, renal impairment, and/or concurrent dehydration), or in those on nonsteroidal anti-inflammatory drugs or other concurrent exposure to other nephrotoxic agents. There have also been cases requiring dialysis, and occasional fatal outcomes have been reported in patients with pre-existing renal impairment and concomitant risk factors.4, 5, 6, 7

Iron, anaemia, and inflammatory bowel diseases

Iron deficiency anaemia is one of the most common disorders in the world. Also, one third of inflammatory bowel disease (IBD) patients suffer from recurrent anaemia. Anaemia has significant impact on the quality of life of affected patients. Chronic fatigue, a frequent IBD symptom itself, is commonly caused by anaemia and may debilitate patients as much as abdominal pain or diarrhoea. Common therapeutic targets are the mechanisms behind anaemia of chronic disease and iron deficiency. It is our experience that virtually all patients with IBD associated anaemia can be successfully treated with a combination of iron sucrose and erythropoietin, which then may positively affect the misled immune response in IBD.

The Role of Neopterin as a Monitor of Cellular Immune Activation in Transplantation, Inflammatory, Infectious, and Malignant Diseases

The accumulated knowledge about the organization and function of the human immune system contributes to a better understanding of the pathogenesis of most diverse disorders and is opening new avenues for therapeutic regimens. To gain further insight into the complex interactions within the components of the immune system, it has become increasingly necessary to develop rapid and simple methods to monitor the status of the immune system in patients. The determination of neopterin concentrations in human body fluids allows to investigate sensitively the cell-mediated immune status to be investigated with considerable sensitivity. In recent years it was shown that production and release of neopterin is inducible in human monocytes/macrophages by interferon gamma. Increased neopterin levels indicate endogenous formation of gamma interferon, and monitoring of neopterin levels therefore permits the activation status of the cell-mediated immune system to be examined. Neopterin concentrations in serum and in urine increase in parallel to the clinical course of infections with viruses, intracellular bacteria, and parasites. In patients with human immunodeficiency virus infection neopterin concentration in serum and urine is a significant predictor of disease progression, the statistical power being similar to CD4+ T-cell numbers. In patients with autoimmune disorders, neopterin levels correlate with the extent and the activity of the disease. Neopterin concentrations are also sensitive indicators of immunological complications in allograft recipients. In certain malignant diseases neopterin concentrations correlate with the stage of the disease and bear prognostic information. Results of neopterin measurements agree with the important role that the cellular immune system plays in these disorders.

Iron and immunity: a double-edged sword

Iron is a crucial element for many central metabolic pathways of the body. Lack of iron leads to growth arrest and anaemia while increased accumulation of this metal, as it occurs in highly frequent inherited diseases such as hereditary haemochromatosis and thalassaemia, is associated with toxic radical formation and progressive tissue damage. As shown by several groups, iron also modulates immune effector mechanisms, such as cytokine activities (IFN‐γ effector pathways towards macrophages), nitric oxide (NO) formation or immune cell proliferation, and thus host immune surveillance. Therefore, gaining control over iron homeostasis is one of the central battlefields in deciding the fate of an infection with intracellular pathogens or a malignant disease. Thus, the reticulo‐endothelial system has evoked sophisticated strategies to control iron metabolism in general and especially the handling of the metal within immune cells.

Iron metabolism in the anemia of chronic disease.

BACKGROUND The most frequent clinical condition exemplifying the interplay between iron and immune function is the anemia of chronic disease (ACD). METHODS Based on a review of the current literature this article provides an overview of our current knowledge of iron homeostasis during inflammation, how this contributes to ACD, but also emphasizes pitfalls in diagnosing iron availability and correcting iron deficiency in this setting. RESULTS A diversion of iron from the circulation into the reticuloendothelial system and the resutling iron limitation for erythropoiesis are central for the development of ACD. Acute-phase proteins, such as hepcidin, as well as pro- and anti-inflammatory cytokines affect iron acquisition and release pathways of monocytes and macrophages thereby leading to iron restriction within the RES and systemic hypoferremia. These metabolic effects are in part exerted via cytokine-mediated modulation of transcriptional/translational expression of iron metabolism genes or by inducing labile radical formation, which then regulate the posttranscriptional regulation of cellular iron homeostasis. In addition, inflammatory processes affect macrophage iron acquisition via erythrophagocytosis while hepcidin inhibits macrophage iron release via direct interaction with the central iron export protein ferroportin. GENERAL SIGNIFICANCE Being aware of the effects of iron on cell mediated immune effector function and the central importance of the metal as a nutrient of invading pathogens, iron restriction within the RES harbors potential benefits for the host and may serve as a defense strategy of the body. Therapeutic manipulation of iron balance and transport under inflammatory conditions is thus a major challenge harboring both, putative beneficial and detrimental effects.

The struggle for iron – a metal at the host–pathogen interface

Iron holds a central position at the host–pathogen interface because mammalian and microbial cells have an essential demand for the metal, which is required for many metabolic processes. In addition, cross‐regulatory interactions between iron homeostasis and immune function are evident. While iron affects the secretion of cytokines and the activity of transcription factors orchestrating immune responses, immune cell‐derived mediators and acute‐phase proteins control both systemic and cellular iron homeostasis. Additionally, immune‐mediated strategies aim at restricting the supply of the essential nutrient iron to pathogens, which represents an effective strategy of host defence. On the other hand, microbes have evoked multiple strategies to utilize iron because a sufficient supply of this metal is linked to pathogen proliferation, virulence and persistence. The control over iron homeostasis is a central battlefield in host–pathogen interplay influencing the course of an infectious disease in favour of either the mammalian host or the pathogenic invader. This review summarizes our current knowledge on the combat of host cells and pathogens for the essential nutrient iron focusing on the immune‐regulatory roles of iron on cell‐mediated immunity necessary to control intracellular microbes, the hosts mechanisms of iron restriction and on the counter‐acting iron‐acquisition strategies employed by intracellular microbes.

Neopterin, Biochemistry and Clinical Use as a Marker for Cellular Immune Reactions

Large amounts of neopterin are produced and released from human macrophages on stimulation with interferon-gamma. Neopterin is biologically stable, and it can be easily quantified in human body fluids. Neopterin measurements are useful to monitor allograft recipients to detect immunological complications. In autoimmune diseases, neopterin concentrations reflect the extent and activity of the disease. In infectious syndromes and in patients with cancer, neopterin concentrations provide prognostic information. In addition to providing clinically useful information, neopterin monitoring allows insight into the immunopathogenesis of a variety of diseases.

Nitric oxide and oxidative stress (H2O2) control mammalian iron metabolism by different pathways.

Several cellular mRNAs are regulated posttranscriptionally by iron-responsive elements (IREs) and the cytosolic IRE-binding proteins IRP-1 and IRP-2. Three different signals are known to elicit IRP-1 activity and thus regulate IRE-containing mRNAs: iron deficiency, nitric oxide (NO), and the reactive oxygen intermediate hydrogen peroxide (H2O2). In this report, we characterize the pathways for IRP-1 regulation by NO and H2O2 and examine their effects on IRP-2. We show that the responses of IRP-1 and IRP-2 to NO remarkably resemble those elicited by iron deficiency: IRP-1 induction by NO and by iron deficiency is slow and posttranslational, while IRP-2 induction by these inductive signals is slow and requires de novo protein synthesis. In contrast, H2O2 induces a rapid posttranslational activation which is limited to IRP-1. Removal of the inductive signal H2O2 after < or = 15 min of treatment (induction phase) permits a complete IRP-1 activation within 60 min (execution phase) which is sustained for several hours. This contrasts with the IRP-1 activation pathway by NO and iron depletion, in which NO-releasing drugs or iron chelators need to be present during the entire activation phase. Finally, we demonstrate that biologically synthesized NO regulates the expression of IRE-containing mRNAs in target cells by passive diffusion and that oxidative stress endogenously generated by pharmacological modulation of the mitochondrial respiratory chain activates IRP-1, underscoring the physiological significance of NO and reactive oxygen intermediates as regulators of cellular iron metabolism. We discuss models to explain the activation pathways of IRP-1 and IRP-2. In particular, we suggest the possibility that NO affects iron availability rather than the iron-sulfur cluster of IRP-1.