E. R. Huehns

In vivo Evaluation of Hydroxypyridone Iron Chelators in a Mouse Model

The 59Fe excretion caused by a range of bidentate N-substituted [R group = methyl (CP20), ethyl (CP21), propyl (CP22), isopropyl (CP23), butyl (CP24) or hexyl (CP25)] 3-hydroxypyrid-4-one chelators in iron-overloaded mice is presented. All the compounds cause significant iron excretion when given intraperitoneally, but that the most hydrophobic compounds, CP24 and CP25, were toxic except at low doses. The excretion caused by CP21, CP22 and CP23 were significantly greater than that caused by CP20 and slightly larger than that caused by an equivalent dose of desferrioxamine. These compounds (CP20 through CP24) also caused significant excretion of 59Fe when administered orally. Compounds CP21, CP22 and CP24 were significantly more active than compounds CP20 and CP23. It is concluded that the N-ethyl or N-propyl 3-hydroxypyrid-4-ones are the most promising compounds for clinical application. Preliminary experiments using a hexadentate pyrid-2-one, CP130, show that this causes significant 59Fe excretion both when given intraperitoneally or orally.

Facilitated uptake of zinc into human erythrocytes: Relevance to the treatment of sickle-cell anaemia

The ability of a number of heterocyclic metal chelators to deliver zinc into red cells, to release the liganded zinc to haemoglobin and thereby cause a left shift in the oxygen dissociation curve of intact red cells has been investigated. Incubation of neutrally charged zinc-pyrone and zinc-pyridin-2-one complexes with red cells led to the rapid accumulation of zinc within cells, whereas unliganded zinc in the form of zinc acetate, zinc chloride or zinc sulphate accumulated only slowly. The rate at which zinc was delivered to red cells by pyrone and pyridin-2-one ligands increased with increasing lipid solubility of the ligands. The uptake of zinc into both normal adult and sickle red cells was associated with a dose-dependent increase in the oxygen affinity of haemoglobin. The degree of left shift in the oxygen dissociation curve following the incubation of red cells with zinc-pyrone and -pyridin-2-one complexes suggests that these complexes may find application as agents to increase the oxygen affinity of haemoglobin in sickle cell disease and thereby decrease the probability of intravascular sickling at low tissue oxygen tensions. Ethylmaltol appears to be a particularly useful agent due to its known low toxicity.

Selection of Hydroxypyridin-4-Ones for the Treatment of Iron Overload Using In Vitro and In Vivo Models

The hydroxypyridin-4-one group of iron chelators show promise as potential compounds for the treatment of iron overload by the oral route. In the search for the compounds best suited for long term clinical use, a balance has to be struck between the desire to mobilise the maximum amount of iron and the wish to minimise the potential toxicity of such compounds. In this article we review the approach we have used to evaluate which of the hydroxypyridinones have the properties best suited for further development prior to clinical trials in man. The diversity of a number of closely related compounds substituted on the ring nitrogen have allowed us to study the properties of chelators responsible for cellular mobilisation of iron(III), as well as those which may contribute to their toxicity. The primary hepatocyte culture model has facilitated the investigation of the contribution of their iron binding constant, as well as the critical importance of their relative lipid solubility to both cellular iron mobilisation and toxicity. Similarly studies in mice have confirmed that the factors affecting cellular iron release also control iron excretion in whole animals. Further we have demonstrated that the acute toxicity of this group of compounds is closely linked to the size of the available iron pool.(ABSTRACT TRUNCATED AT 250 WORDS)

Hb Sun Prairie: diagnostic pitfalls in thalassemic hemoglobinopathies.

We report an Asian Indian family in which two daughters have Hb Sun Prairie, a known unstable alpha 2-globin variant [codon 130, GCT-->CCT; alpha 2 130(H13)Ala-->Pro beta 2]. While the homozygous probands have chronic hemolysis-the same phenotype as previously reported, the heterozygous parents are asymptomatic with a thalassemia carrier phenotype, distinct from the chronic hemolytic state previously described in a heterozygote. Unlike the earlier cases in which family studies were not available, this family clearly exhibits autosomal recessive inheritance, unusual amongst variants within the same region of helix H. Globin chain biosynthesis ratios initially suggested a beta-thalassemic hemoglobinopathy-this was excluded by normal sequence analysis of both beta-globin genes. This case report further illustrates the complexity of phenotypes in the thalassemic hemoglobinopathies. It also demonstrates inversion of the alpha/beta-globin chain biosynthesis ratio, a phenomenon which had been noted in other alpha-globin variants and can be a confounding factor in the investigation of thalassemic hemoglobinopathies.