Beta-thalassaemia/haemoglobin E tissue ferritins. II: A comparison of heart and pancreas ferritins with those of liver and spleen

Low-frequency low-field magnetic susceptibility of ferritin and hemosiderin

Low-frequency low-field magnetic susceptibility measurements were made on four samples of mammalian tissue iron oxide deposits. The samples comprised: (1) horse spleen ferritin; (2) dugong liver hemosiderin; (3) thalassemic human spleen ferritin; and (4) crude thalassemic human spleen hemosiderin. These samples were chosen because Mössbauer spectroscopic measurements on the samples indicated that they exemplified the variation in magnetic and mineral structure found in mammalian tissue iron oxide deposits. The AC-magnetic susceptometry yielded information on the magnetization kinetics of the four samples indicating samples 1, 2, and 3 to be superparamagnetic with values of around 10(11) s(-1) for the pre-exponential frequency factor in the Néel-Arrhenius equation and values for characteristic magnetic anisotropy energy barriers in the range 250-400 K. Sample 4 was indicated to be paramagnetic at all temperatures above 1.3 K. The AC-magnetic susceptometry data also indicated a larger magnetic anisotropy energy distribution in the dugong liver sample compared with samples 1 and 3 in agreement with previous Mössbauer spectroscopic data on these samples. At temperatures below 200 K, samples 1-3 exhibited Curie-Weiss law behavior, indicating weak particle-particle interactions tending to favor antiparallel alignment of the particle magnetic moments. These interactions were strongest for the dugong liver hemosiderin, possibly reflecting the smaller separation between mineral particles in this sample. This is the first magnetic susceptometry study of hemosiderin iron deposits and demonstrates that the AC-magnetic susceptometry technique is a fast and informative method of studying such tissue iron oxide deposits.

Hepatic molecular conversion and detoxification of ferritin iron in adult lampreys (Geotria australis), following natural and induced iron loading

Weekly intramuscular injections of 3 mg of iron as horse spleen ferritin into adult Geotria australis over 10 weeks, resulted in a progressive increase in that form of iron in the serum. However, as with control animals, the ferritin in the liver of injected lampreys consisted of one subunit type, whose M(r) (20,300) differed from those of the two subunit types of horse spleen ferritin. Thus, lampreys had converted horse spleen ferritin iron into endogenous ferritin iron, presumably in their liver. Marked rises in hepatic non-haem iron during the first 2 weeks and between weeks 8 and 10 of iron injections were accompanied by pronounced increases in superoxide dismutase (SOD) activity. This rise, which parallels the rise in SOD activity that occurs as iron increases during the very protracted upstream migration of G. australis, is consistent with the view that SOD protects against iron-mediated damage by removing the superoxide radical, which facilitates the formation of the highly toxic hydroxyl radical. A levelling off of the iron concentration between weeks 2 and 8 was accompanied by a decline in SOD activity, even though nonhaem iron levels were well above those of control animals. Enhanced SOD activity may therefore only be required when there is an elevated flux of iron in the liver through low-molecular-mass intermediates. A small amount of ferritin iron was converted into the more inert haemosiderin iron.

Iron release from ferritin and its sensitivity to superoxide ions differs among vertebrates

The influence of the superoxide-generating system, xanthine oxidase, on the release of iron from various vertebrate ferritins was determined both in the presence and absence of superoxide dismutase. The initial rate of iron release in the presence of this system was higher for ferritins from human, trout and rat liver than for those from lamprey liver and horse spleen. The proportion of this iron release that was superoxide-dependent in the case of rat, human and trout ferritins was 92, 86 and 84% respectively, whereas no such superoxide-dependent iron release occurred from the ferritins of lamprey liver and horse spleen. On the other hand, the rate of superoxide-independent iron release was of comparable magnitude for all of the species examined. The rate of superoxide-dependent iron release was related neither to the iron: protein ratios nor to the subunit size of the ferritins. However, it is significant that the ferritins with a high rate of superoxide-dependent iron release came from tissues known to be susceptible to iron damage. It is thus proposed that the resistance of lamprey liver ferritin to the mobilization of iron by superoxide ions accounts in part for the tolerance of the lamprey liver to high iron loads.

Organ-specific crystalline structures of ferritin cores in beta-thalassemia/hemoglobin E

The cores of ferritins isolated from different organs of human subjects with beta-thalassemia/hemoglobin E (beta-thal/HbE) disease have different size distributions and crystallinities depending on the source organ. These patients have not been treated by hypertransfusion regimen or iron chelation therapy. beta-Thal/HbE spleens and livers yield ferritin cores which are less crystalline than those isolated from normal spleens and livers, reflecting the more rapid deposition of iron in the diseased state. Ferritins isolated from the hearts and pancreases of beta-thal/HbE subjects were found to have larger, more crystalline cores than those from the beta-thal/HbE livers and spleens, possibly as a consequence of the role of the heart and pancreas as long-term iron deposition sites in this iron overload pathology.

Beta-thalassaemia/haemoglobin E tissue ferritins. I: Purification and partial characterization of liver and spleen ferritins

Ferritins from liver and spleen of both beta-thalassaemia/haemoglobin E (HbE) and non-thalassaemic patients were purified by heating a methanol-treated homogenate, followed by molecular exclusion chromatography. The concentrations of ferritins in the beta-thalassaemia/HbE liver and spleen were calculated as 3.8 and 2.0 mg/g wet tissue. The beta-thalassaemia/HbE ferritin iron/protein ratios were higher than those of normal ferritins. On PAGE, all ferritins gave a single major monomeric band with only very small differences in their mobility. Ferritins from thalassaemic patients also possessed bands corresponding to oligomers. On SDS/PAGE, all ferritins were resolved into two major subunits: H and L with L subunit predominating. While the isoferritin profiles of ferritins from beta-thalassaemia/HbE liver and spleen were similar to each other and to those of normal liver and spleen, some extra bands were present in the acidic region. The microstructure of these pathological ferritins appears to result, to a large degree, from the particular nature and amount of iron loading present.