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The biological development of hydroxypyridinone iron chelators

Gyparaki, Marilena; (1994) The biological development of hydroxypyridinone iron chelators. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

The object of this study was to screen a series of hydroxypyridinones for their potential as oral iron chelators and to determine the properties of such compounds necessary for oral efficacy. The hydroxypyridinones are water soluble neutral bidentate ligands that have high specificity for iron which they coordinate at a 3:1 ratio under physiological conditions. A protocol for screening these compounds involved in vitro studies using monolayer cultures of isolated rat hepatocytes and in vivo studies using iron-overloaded mice and non-iron-overloaded mice and rats. In the cell culture model, hepatocytes were isolated by collagenase perfusion of livers from adult male Wistar rats. After differential centrifugation, hepatocytes of greater than 90% purity were plated onto collagen-plated sterile dishes. After overnight culture at 37°C, the non-adherent cells were washed away leaving a hepatocyte monolayer of greater than 95% viability. These were pulsed for a variable time with human 59Fe-transferrin before further washes and incubation with the test chelator. Release of 59Fe was then measured over a known time period. Cell toxicity was determined at the end of the experiment by measuring the release of lactate dehydrogenase into the incubation media. In the in vivo studies with mice, the latter were iron over-loaded with iron dextran. After an equilibration period the stores were labelled with human 59Fe-lactoferrin given intravenously. Autoradiographic studies have shown that the majority of the 59Fe labelled the hepatocytes. Following a further equilibration period, the test chelators were administered either orally or intraperitoneally at variable doses. Excretion of 59Fe was measured daily in urine and faeces. Residual radioactivity in body organs and carcasses was also measured. In a second in vivo model the hepatic iron stores of adult female rats were labelled with 59Fe-ferritin. After 90 mins, by which time the 59Fe was at maximum availability, the test chelators were administered either orally or intramuscularly at a dose equivalent to the iron binding capacity of 40mg of desferrioxamine. 59Fe was measured in urine, faeces and body organs 4 hours after chelator administration, by which time chelating activity would be complete. In some experiments the bile duct of the rats was cannulated and the radioactivity of hourly fractions of bile was compared with total biliary iron excretion. The results obtained with the hepatocyte culture system paralleled in vivo data. The hydroxypyridin-4-ones that were most effective in the hepatocyte culture system were also the most active in the mouse and rat models. Their effectiveness by the oral route, in contrast to desferrioxamine, means that these compounds may have an important clinical role to play in the treatment of transfusional iron overload. The most lipophilic compounds, which were associated with the most lactate dehydrogenase release in the hepatocyte culture system, were associated with acute toxicity in mice at doses at which the most hydrophilic compounds showed no toxicity. These findings lead to the conclusion that a consideration of lipid solubility and iron binding constants is important in the overall design of iron chelators. Bidentate hydroxypyridin-4-ones with partition coefficients close to 1 represent compounds which are likely to be the most efficient in mobilising iron both at the cellular level and in vivo, as well as, being less toxic than compounds with high lipid solubility.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: The biological development of hydroxypyridinone iron chelators
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Biological sciences; Hydroxypyridinones
URI: https://discovery.ucl.ac.uk/id/eprint/10105968
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