Mucosal iron-binding proteins in mice with X-linked anaemia

Studies of the ferroxidase activity of native and chemically modified xanthine oxidoreductase

The O2-utilizing (type O, oxidase) form of xanthine oxidoreductase is primarily responsible for its ferroxidase activity. This form of xanthine oxidoreductase has 1000 times the ferroxidase activity of the serum ferroxidase caeruloplasmin. It has the ability to catalyse the oxidative incorporation of iron into transferrin at very low Fe2+ and O2 concentrations. Furthermore, the pH optimum of the ferroxidase activity of the enzyme is compatible with the conditions of pH that normally exist in the intestinal mucosa, where it has been proposed that xanthine oxidoreductase may facilitate the absorption of ionic iron. Modification of the molybdenum (Mb) centres of the enzyme in vitro by treatment with cyanide, methanol or allopurinol completely abolishes its ferroxidase activity. The feeding of dietary tungsten to rats, which prevents the incorporation of molybdenum into newly synthesized intestinal xanthine oxidoreductase, results in the progressive loss of the ferroxidase activity of intestinal-mucosa homogenates. Removal of the flavin centres from the enzyme also results in the complete loss of ferroxidase activity; however, the ferroxidase activity of the flavin-free form of the enzyme can be restored with artificial electron acceptors that interact with the molybdenum or non-haem iron centres. The presence of superoxide dismutase or catalase in the assay system results in little inhibition of the ferroxidase activity of xanthine oxidoreductase.

The bioavailability of iron, lead and cadmium via gastrointestinal absorption: a review

The primary route of entry of essential metals and most pollutant metals into the body is by gastrointestinal absorption. Although intraluminal factors influence the bioavailability of metals, the major control level of absorption probably resides in the intestinal mucosal cell. Interrelationships between various metals may effect their bioavailability at both the luminal and mucosal levels. It has also been shown that the nutritional status may have a profound influence on the absorption of some metals; iron, calcium, and protein deficiency may enhance the absorption of several pollutant metals, although this is apparently not simply an increased gut permeability to all heavy metals. Valid speculations regarding the absorption of pollutant metals is difficult since, even after several decades of intensive study, the precise mechanisms of controlling the absorption of iron and other trace metals are unknown.

Inherited metabolic disease in laboratory animals: a review

Research on the screening for and study of animal models of inherited metabolic disease is reviewed. It is emphasized that an animal model, to be of value, must be an inherited deficiency of the same enzyme as the one deficient in the human syndrome. If this criterion is adhered to there is a remarkable identity in aetiology between animal and man. Specific examples of inherited metabolic disease in laboratory animals are described for: amino acid metabolism; lysosomal storage diseases, carbohydrate metabolism, transport disorders and trace element metabolism; the mutants found in mice being the easiest to manipulate biochemically and genetically. There is still a lack of adequate screening programmes for animal homologues of the more serious human inborn errors (such as lysosomal storage diseases) where laboratory studies could provide significant advances in therapy.

Mucosal uptake, mucosal transfer and retention of iron, measured by whole-body counting

A method is described which enables simple and accurate measurement of the separate steps of iron absorption. A double isotope technique was used with 59Fe as a tracer and 51Cr (as CrCl3) as an inert, not absorbable indicator. With a whole-body counter it was possible not only to measure initial mucosal uptake and retention but also to calculate mucosal transfer of iron. Thus faeces collection for determination of mucosal uptake of iron was no longer necessary. Absorption of a physiological dose of inorganic iron was studied in 25 normal subjects (15 males and 10 females), in 21 patients with uncomplicated iron deficiency and in 8 patients with idiopathic haemosiderosis. A significant difference was demonstrated between normals and patients with iron deficiency and in idiopathic haemosiderosis with respect to the various steps of iron absorption. The method provides a simple tool for the study of the regulation of iron absorption at the luminal and intracellular site of the intestinal mucosal cell.