Iron homeostasis: transport, metabolism, and regulation

PURPOSE OF REVIEW

Iron is essential for normal cellular function and many diseases result from disturbances in iron homeostasis. This review describes some of the recent key advances in iron transport and its regulation, how this relates to iron-related disorders, and emerging therapies for these diseases.

RECENT FINDINGS

The iron-regulatory hormone hepcidin and its target, the iron exporter ferroportin (FPN), play central roles in iron homeostasis. Recent studies have expanded our understanding of how hepcidin is regulated in response to stimulated erythropoiesis and have added some new players to the complex network of factors that influences hepcidin expression. Novel structural insights into how FPN transports iron have been an important addition to the field, as has the recognition that some zinc transporters such as ZIP14 can transport iron. Investigations into cardiac iron homeostasis have revealed a key role for FPN, and transferrin receptor 1, which is essential for cellular iron uptake, has been shown to be critical for normal immune function.

SUMMARY

The increased understanding of mechanisms of iron homeostasis that has resulted from recent research has greatly improved our ability to diagnose and manage iron-related disorders, and has offered new therapies for this important class of human diseases.

Molybdenum cofactor deficiency

Molybdenum cofactor deficiency (MoCD) is a severe autosomal recessive inborn error of metabolism first described in 1978. It is characterized by a neonatal presentation of intractable seizures, feeding difficulties, severe developmental delay, microcephaly with brain atrophy and coarse facial features. MoCD results in deficiency of the molybdenum cofactor dependent enzymes sulfite oxidase, xanthine dehydrogenase, aldehyde oxidase and mitochondrial amidoxime reducing component. The resultant accumulation of sulfite, taurine, S-sulfocysteine and thiosulfate contributes to the severe neurological impairment. Recently, initial evidence has demonstrated early treatment with cyclic PMP can turn MoCD type A from a previously neonatal lethal condition with only palliative options, to near normal neurological outcomes in affected patients. We review MoCD and focus on describing the currently published evidence of this exciting new therapeutic option for MoCD type A caused by pathogenic variants in MOCD1.

Effect of copper and diethyldithiocarbamate combination therapy on the macular mouse, an animal model of Menkes disease

Menkes disease (MD) is a neurodegenerative disorder characterized by a copper deficiency in the brain. It is caused by the defective intestinal absorption of copper resulting from a deficiency of a copper-transporting ATPase, ATP7A. This gives rise to an accumulation of copper in the intestine. The copper deficiency in the brain of MD patients cannot be improved by copper injections, because the administered copper accumulates at the blood-brain barrier and is not transported across to the neurons. To resolve this problem, we investigated the effect of a combination therapy of copper and sodium diethyldithiocarbamate (DEDTC), a lypophilic chelator, in an animal model of MD, the macular mouse. Four-week-old macular mice treated with 50 mug of CuCl2 on the 7th day after birth were used. Experimental mice were given a subcutaneous injection of CuCl2 (4 microg) and an intraperitoneal injection of DEDTC (0.2 mg/g body weight) twice a week for 4 weeks and then sacrificed. Copper concentrations and cytochrome-c oxidase activity in the brains of treated mice were higher than those of control macular mice, which received only copper or saline. The ratios of brain noradrenaline to dopamine and of adrenaline to dopamine were also increased by the treatment, suggesting that the activity of dopamine beta-hydroxylase, a copper-dependent enzyme, was improved by the treatment. Liver and renal function tests showed no abnormalities in the treated mice, although copper concentrations in the kidneys of treated mice were higher than those of control macular mice. These results suggest that DEDTC facilitates the passage of copper across the blood-brain barrier and that the combination therapy of copper and DEDTC may be an effective treatment for the neurological disturbances suffered by patients with MD.

Microelements and inherited metabolic diseases

In addition to the main groups of inherited metabolic diseases, including mitochondrial, peroxisomal and lysosomal defects, organic acidurias, porphyrias, defects of amino acids, saccharides and fatty acids metabolism, disorders of transport and utilisation of microelements have also been recognized. Recent findings concerning hereditary hemochromatosis (iron), Wilson and Menkes diseases (copper), molybdenum cofactor deficiency (molybdenum), defects of cobalamine synthesis (cobalt) and acrodermatitis enteropathica (zinc) are reviewed.

Fish-odour syndrome: dealing with offensive body odour

This article is aimed at nursing professionals who may have been, or may be confronted with, patients who complain of fish-smelling body odour. The individual may be suffering from intermittent symptoms of the fish-odour syndrome. Recent contact with sufferers of such symptoms has highlighted the need to raise awareness among nurses about this syndrome. Sufferers expressed disappointment with regard to the advice they received from primary health-care professionals with respect to their problem. In content, the advice was variable but commonly centred around methods of increasing personal hygiene. Thus, the purpose of this article is to provide factual information about the fish-odour syndrome to increase awareness among nurses who could potentially aid the management of the syndrome and relieve some of the distress of its sufferers.

Acrodermatitis enteropathica

Acrodermatitis enteropathica results from a defect in zinc metabolism inherited as an autosomal recessive trait. Zinc is chelated in the gastrointestinal tract by an oligopeptide that is normally destroyed in the bowel. Zinc deficiency results in skin and bowel lesions, as well as alterations in mental status. If the disorder is not treated, death occurs from infection and/or marasmus. Blood zinc levels confirm the diagnosis. Dramatic recovery and normal development occur when dietary zinc is supplemented.

Inborn errors of trace metal metabolism

A variety of complex systemic, hepatic and neuropsychiatric syndromes result from inborn errors of trace metal metabolism. Some of these respond to treatment and prophylactic management while for some intractable conditions prenatal diagnosis is possible. All these abnormalities provide valuable insight into the normal metabolism of these vital elements.