Regulation of mammalian iron metabolism: current state and need for further knowledge

Functional ability of tendinocytes to take up Fe substances in an inflamed tendon

The fate of iron (Fe) after bleeding has been analyzed in various connective tissues, but there have been only a few inconclusive studies on Fe in the tendon. In this study, energy dispersive X-ray microanalysis and an iron staining method were used to determine the localization of Fe in cells of the equine superficial digital flexor tendon. In inflamed tendons, Fe was detected in tendinocytes as well as macrophages. In contrast, negative or weak reactions were observed in many cells in the normal tendon. Although the accepted theory states that the reticuloendothelial system (macrophages and reticuloendothelial cells) is mainly responsible for the uptake and decomposition of erythrocytes, and tendon cells under conditions of inflammation show a functional ability to take up Fe substances. It has been reported that tendinocytes have multiple functions, including synthesis and secretion of collagen, cytokines, and matrix metalloproteinases. Taking these functions into consideration, indicates that the tendinocyte is not only an active cell but also a multi-functional cell.

Antioxidants in health and disease

Free radical production occurs continuously in all cells as part of normal cellular function. However, excess free radical production originating from endogenous or exogenous sources might play a role in many diseases. Antioxidants prevent free radical induced tissue damage by preventing the formation of radicals, scavenging them, or by promoting their decomposition. This article reviews the basic chemistry of free radical formation in the body, the consequences of free radical induced tissue damage, and the function of antioxidant defence systems, with particular reference to the development of atherosclerosis.

Morphologic analysis correlates with gene expression changes in cultured F344 rat mesothelial cells

The gene expression pattern of mesothelial cells in vitro was determined after 4 or 12 h exposure to the rat mesothelial, kidney, and thyroid carcinogen and oxidative stressor potassium bromate (KBrO(3)). Gene expression changes observed using cDNA arrays indicated oxidative stress, mitotic arrest, and apoptosis in treated immortalized rat peritoneal mesothelial cells. Increases occurred in oxidative stress responsive genes HO-1, QR, HSP70, GADD45, GADD153, p21(WAF1/CIP16), GST's, GAPDH, TPX, and GPX-1(0); transcriptional regulators c-jun, c-fos, jun B, c-myc, and IkappaB; protein repair components Rdelta, RC10-II, C3, RC-7, HR6B ubiquitin-conjugating enzyme and ubiquitin; DNA repair components PCNA, msh2, and O-6 methylguanine DNA methyltransferase; lipid peroxide excision enzyme PLA2; and apoptogenic components TNFalpha, iNOS1 and FasL. Decreases occurred in bcl-2 (antiapoptotic), bax alpha, bad, and bok (proapoptotic) and cell cycle control elements (cyclins). Cyclin G and p14ink4b (which inhibit entry into cell cycle) were increased. Numerous signal transduction, cell membrane transport, membrane-associated receptor, and fatty acid biosynthesis and repair components were altered. Morphologic endpoints examined were number of mitotic figures, number of apoptotic cells, and antibody-specific localization of HO-1 (which demonstrated increased HO-1 protein expression). PCR analysis confirmed HO-1, p21(waf1/cip1), HSP70, GPX1, GADD45, QR, mdr1, PGHS, and cyclin D1 changes. A model for KBrO(3)-induced carcinogenicity in the F344 rat mesothelium is proposed, whereby KBrO(3) generates a redox signal that activates p53 and results in transcriptional activation of oxidative stress and repair genes, dysregulation of growth control, and imperfect DNA repair leading to carcinogenesis.

Human cytoplasmic aconitase (Iron regulatory protein 1) is converted into its [3Fe-4S] form by hydrogen peroxide in vitro but is not activated for iron-responsive element binding

Iron regulatory protein 1 (IRP1) regulates the synthesis of proteins involved in iron homeostasis by binding to iron-responsive elements (IREs) of messenger RNA. IRP1 is a cytoplasmic aconitase when it contains a [4Fe-4S] cluster and an RNA-binding protein after complete removal of the metal center by an unknown mechanism. Human IRP1, obtained as the pure recombinant [4Fe-4S] form, is an enzyme as efficient toward cis-aconitate as the homologous mitochondrial aconitase. The aconitase activity of IRP1 is rapidly lost by reaction with hydrogen peroxide as the [4Fe-4S] cluster is quantitatively converted into the [3Fe-4S] form with release of a single ferrous ion per molecule. The IRE binding capacity of IRP1 is not elicited with H(2)O(2). Ferrous sulfate (but not other more tightly coordinated ferrous ions, such as the complex with ethylenediamine tetraacetic acid) counteracts the inhibitory action of hydrogen peroxide on cytoplasmic aconitase, probably by replenishing iron at the active site. These results cast doubt on the ability of reactive oxygen species to directly increase IRP1 binding to IRE and support a signaling role for hydrogen peroxide in the posttranscriptional control of proteins involved in iron homeostasis in vivo.