Haemolytic anaemia in association with Escherichia coli O157 infection in two sisters

Severe iron deficiency blunts the response of the iron regulatory gene Hamp and pro-inflammatory cytokines to lipopolysaccharide

BACKGROUND

Expression of the key iron regulatory hormone hepcidin is increased by some stimuli (iron loading, inflammation) but decreased by others (increased erythropoiesis, iron deficiency). We investigated the response of hepcidin to increased erythropoiesis and iron deficiency in the presence of an acute inflammation to assess the relative strengths of these stimuli.

DESIGN AND METHODS

Sprague-Dawley rats were maintained on control or iron-deficient diets and treated with lipopolysaccharide to induce inflammation or phenylhydrazine to stimulate erythropoiesis. The levels of Hamp, IL-6 and α2m mRNA were determined by qualitative real-time polymerase chain reaction and those of serum interleukin-6 and tumor necrosis factor-α were measured by enzyme-linked immunosorbent assay. Cultured RAW264.7 and HuH7 cells were used in associated studies.

RESULTS

The increase in hepatic hepcidin levels induced by lipopolysaccharide was not affected by phenylhydrazine treatment but was blunted by iron deficiency. Lipopolysaccharide-treated iron-deficient animals also showed lower liver α2m mRNA and reduced serum interleukin-6 and tumor necrosis factor-α, suggesting a more generalized effect of iron deficiency. Similarly, RAW 264.7 cells treated with iron chelators and then stimulated with lipopolysaccharide showed lower IL-6 mRNA than cells treated with lipopolysaccharide alone. Huh7 cells treated with an iron chelator showed a blunted hepcidin response to interleukin-6, suggesting that the response of hepatic parenchymal cells to inflammatory cytokines may also be iron-dependent.

CONCLUSIONS

In any one physiological situation, net hepcidin levels are determined by the relative strengths of competing stimuli. The ability of severe iron deficiency to blunt the response to lipopolysaccharide of both hepcidin and other markers of inflammation suggests that adequate iron levels are necessary for a full acute phase response.

Enterohaemorrhagic Escherichia coli in human medicine

Enterohaemorrhagic Escherichia coli (EHEC) are the pathogenic subgroup of Shiga toxin (Stx)-producing E. coli. EHEC can cause non-bloody and bloody diarrhoea, and the haemolytic uraemic syndrome (HUS). HUS is a major cause of acute renal failure in children. E. coli O57:H7 is the predominant, but far from being the only, serotype that can cause HUS. The cascade leading from gastrointestinal infection to renal impairment is complex, with the microvascular endothelium being the major histopathological target. EHEC also produce non-Stx molecules, such as cytolethal distending toxin, which can contribute to the endothelial or vascular injury. Because there are no specific therapies for EHEC infections, efficient reservoir and human preventive strategies are important areas of ongoing investigations. This review will focus on the microbiology, epidemiology, and pathophysiology of EHEC-associated diseases, and illustrate future challenges and opportunities for their control.