Novel DFO-functionalized mesoporous silica for iron sensing. Part 2. Experimental detection of free iron concentration (pFe) in urine samples

Successful in vivo chelation treatment of iron(III) overload pathologies requires that a significant fraction of
the administered drug actually chelates the toxic metal. Increased mobilization of the iron(III) in experiments
on animals or humans, most often evaluated from urinary output, is usually used as an assessment tool for
chelation therapy. Alternatively, the efficiency of a drug is estimated by calculating the complexing ability of
a chelating agent towards Fe(III). The latter is calculated by the pFe value, defined as the negative logarithm
of the concentration of the free metal ion in a solution containing 10 mMtotal ligand and 1 mMtotal metal at a
physiological pH of 7.4. In theory, pFe has to be calculated taking into account all the complexation
equilibria involving the metal and the possible ligands. Nevertheless, complexation reactions in complex
systems such as serum and urine may hardly be accurately modelled by computer software. The
experimental determination of the bioavailable fraction of iron(III) in biological fluids would therefore be
of the utmost relevance in the clinical practice. The efficiency of the therapy could be more easily
estimated as well as the course of overload pathologies. In this context, the aim of the present work was
the development of a sensor to assess the free iron directly in biological fluids (urine) of patients under
treatment with chelating agents. In the proposed device (DFO-MS), the strong iron chelator
deferoxamine (DFO) is immobilized on the MCM-41 mesoporous silica. The characterization of the
iron(III) sorption on DFO-MS was undertaken, firstly in 0.1 M KNO3, then directly in urine samples, in
order to identify the sorption mechanism. The stoichiometry of the reaction in the solid phase was found
to be: Fe + DFO + H => Fe(HDFO) with an exchange constant (average value) of log bex=40(1).
The application of DFO-MS to assess pFe in SPU (Simulating Pathology Urine) samples was also
considered. The results obtained were very promising for a future validation and subsequent application
of the sensor in samples of patients undergoing chelation therapy.