Dysregulated iron metabolism in patients on hemodialysis

The two main causes of death in patients on maintenance hemodialysis (MHD) are cardiovascular disease and infection. In the current report, we discuss the association of the iron-catalyzed Fenton reaction and iron sequestration with complications in MHD patients. In particular, we have studied the deregulation of several iron transport systems of polymorphonuclear leukocytes (PMNLs) and the effects of TNF-α on human umbilical vein endothelial cells or PMNLs obtained from MHD patients and controls, and the following results were obtained. (1) Iron was sequestered in MHD-PMNLs, in which the protein governing iron transport was dysregulated. (2) TNF-α accelerated iron accumulation and oxidative stress in human umbilical vein endothelial cells in a manner similar to that in MHD-PMNLs. (3) An endosomal iron transport protein, or natural resistance-associated macrophage protein 1, was decreased in PMNLs from MHD patients, and TNF-α caused a decline in this protein's expression in control PMNLs. (4) The mitochondrial iron chaperone protein frataxin was decreased in MHD-PMNLs, which was linked to the acceleration of oxidative stress and hypercytokinemia. (5) The index of arterial stiffness was aggravated in MHD patients and was associated with serum hepcidin and TNF-α levels, which could inhibit iron exit from cells. With regard to bacterial infections, iron availability to these intracellular pathogens is critical for their growth. In particular, iron accumulation in cells and endosomes may accelerate the spread of infection. Cardiovascular disease has been shown to be linked to oxidative stress caused by iron sequestration in vascular cells and macrophages as well as by the alteration of iron metabolism in mitochondria, and the observed increase in hepcidin and TNF-α may accelerate these crucial steps of oxidative stress in vascular disease. Thus, because surplus iron in the body may escalate the dysregulation of iron metabolism, as observed in MHD patients, iron supplementation for renal anemia treatment should be prudent.