Haem binding to human serum albumin (HSA) endows the protein with peculiar spectroscopic properties. Here, the effect of ibuprofen and warfarin on the spectroscopic properties of ferric haem–human serum albumin (ferric HSA–haem) and of ferrous nitrosylated haem–human serum albumin (ferrous HSA–haem‐NO) is reported. Ferric HSA–haem is hexa‐coordinated, the haem‐iron atom being bonded to His105 and Tyr148. Upon drug binding to the warfarin primary site, the displacement of water molecules − buried in close proximity to the haem binding pocket − induces perturbation of the electronic absorbance properties of the chromophore without affecting the coordination number or the spin state of the haem‐iron, and the quenching of the 1H‐NMR relaxivity. Values of Kd for ibuprofen and warfarin binding to the warfarin primary site of ferric HSA–haem, corresponding to the ibuprofen secondary cleft, are 5.4 ± 1.1 × 10−4 m and 2.1 ± 0.4 × 10−5 m, respectively. The affinity of ibuprofen and warfarin for the warfarin primary cleft of ferric HSA–haem is lower than that reported for drug binding to haem‐free HSA. Accordingly, the Kd value for haem binding to HSA increases from 1.3 ± 0.2 × 10−8 m in the absence of drugs to 1.5 ± 0.2 × 10−7 m in the presence of ibuprofen and warfarin. Ferrous HSA–haem‐NO is a five‐coordinated haem‐iron system. Drug binding to the warfarin primary site of ferrous HSA–haem‐NO induces the transition towards the six‐coordinated haem‐iron species, the haem‐iron atom being bonded to His105. Remarkably, the ibuprofen primary cleft appears to be functionally and spectroscopically uncoupled from the haem site of HSA. Present results represent a clear‐cut evidence for the drug‐induced shift of allosteric equilibrium(a) of HSA.

It was established through in vivo T1 measurements at low magnetic fields that tumour cells display proton T1 values that are markedly longer than those shown by healthy tissue. Moreover, it has been found that the elongation of T1 parallels the aggressiveness of the investigated tumour. The T1 lengthening is associated with an enhanced water exchange rate across the transcytolemmal membrane through an overexpression/upregulation of GLUT1 and Na+/K+ ATPase transporters. It follows that the intracellular water lifetime represents a hallmark of tumour cells that can be easily monitored by measuring T1 at different magnetic field strengths ranging from 0.2 to 200 mT.

Fast-field cycling magnetic resonance imaging FFC-MRI Earth-field MRI Pre-polarised MRI Free-radical imaging Magnetisation-transfer contrast Mots-clés : IRM en champ cyclé FFC-IRM IRM en champ magnétique terrestre IRM prépolarisée Imagerie par radicaux libres Contraste par transfert de magnetisationMagnetic resonance imaging (MRI) and fast field-cycling (FFC) NMR are both welldeveloped methods. The combination of these techniques, namely fast field-cycling magnetic resonance imaging (FFC-MRI) is much less well-known. Nevertheless, FFC-MRI has a number of significant applications and advantages over conventional techniques, and is being pursued in a number of laboratories. This article reviews the progress in FFC-MRI over the last two decades, particularly in the areas of Earth's field and prepolarised MRI, as well as free radical imaging using field-cycling Overhauser MRI. Different approaches to magnet design for FFC-MRI are also described. The paper then goes on to discuss recent techniques and applications of FFC-MRI, including protein measurement via quadrupolar cross-relaxation, contrast agent studies, localised relaxometry and FFC-MRI with magnetisation-transfer contrast. r é s u m é L'imagerie par Résonance Magnétique (IRM, ou MRI en anglais) et la RMN avec cyclage de champ rapide (« fast field cycling », FFC) sont toutes deux des méthodes bien développées. La combinaison de ces techniques, c'est-à-dire l'imagerie par résonance magnétique avec cyclage de champ rapide (FFC-MRI en anglais) est beaucoup moins bien connue. Cependant, la FFC-MRI a un nombre d'applications et d'avantages significatifs par rapport aux techniques conventionnelles, et son étude est poursuivie dans un certain nombre de laboratoires. Cet article passe en revue les progrès de la FFC-MRI au cours des deux dernières décennies, en particulier dans les domaines de l'imagerie en champ terrestre avec pré-polarisation, de même que l'imagerie des radicaux libres en utilisant la FFC-MRI avec effet Overhauser. Diverses approches à la conception des aimants pour FFC-MRI sont également décrites. L'article continue en discutant des techniques et applications récentes de la FFC-MRI, telles que la mesure des protéines par relaxation croisée quadrupolaire, les études d'agents de contraste, la relaxométrie localisée et la FFC-MRI avec contraste par transfert d'aimantation.

Hemalbumin [i.e., Fe(III)-protoporphyrin IX-human serum albumin; Fe(III)heme-HSA] is an important intermediate in the recovery of heme iron following hemolysis. Relaxometric data are consistent with the occurrence of a hexacoordinated high-spin Fe(III) center with no water in the inner coordination sphere. The relatively high relaxation enhancement observed for an aqueous solution of Fe(III)heme-HSA (r1p=4.8 mM(-1)s(-1) at 20 MHz, pH 7, and 25 C) is ascribed to the occurrence of a strong contribution from water molecules in the second coordination sphere. Structural analysis of the putative binding region has been performed by a Monte Carlo simulated annealing procedure, which allowed us to identify His105 and Tyr148 as axial ligands. The role of a tyrosinate as the sixth Fe(III)heme ligand is supported by the pH-dependent analysis. Interestingly, when Fe(III) is replaced by Mn(III), the occurrence of a fast exchanging water molecule at pH values close to neutrality is detected. As the pH is increased, the Mn(III) containing system behaves analogously to Fe(III)heme-HSA. At higher pH, the phenolate ligand is eventually displaced by OH- from both Fe(III) and Mn(III) centers. Support for the proposed bonding scheme has been gained also from competitive binding assays for the sixth coordination site by fluoride, azide, and imidazole ligands.

Melanin granules (MGs) have been extracted from human Chinese black hairs by either acid hydrolysis (CH-typeand a soluble but still pigmented fraction called melanin free acid (MFA). MFA can be isolated by precipitation at acidic pH. The 13 C-CPMAS NMR and EPR spectra of these derivatives indicated that ROM has a structure very similar to that of parent MGs, whereas MFA shows a decrease of the protein content with respect to the melanin and a decreased amount of bound iron. Thus, the oxidative degradation of CP-type MGs is a process not involving the bulk of MGs, but rather it proceeds from the solvent-exposed outer parts to the interior.

Fluorine MRI ((19) F MRI) is receiving an increasing attention as a viable alternative to proton-based MRI ((1) H MRI) for dedicated application in molecular imaging. The (19) F nucleus has a high gyromagnetic ratio, a 100% natural abundance and is furthermore hardly present in human tissues allowing for hot spot MR imaging. The applicability of (19) F MRI as a molecular and cellular imaging technique has been exploited, ranging from cell tracking to detection and imaging of tumors in preclinical studies. In addition to applications, developing new contrast materials with improved relaxation properties has also been a core research topic in the field, since the inherently low longitudinal relaxation rates of perfluorocarbon compounds result in relatively low imaging efficiency. Borrowed from (1) H MRI, the incorporation of lanthanides, specifically Gd(III) complexes, as signal modulating ingredients in the nanoparticle formulation has emerged as a promising approach to improvement of the fluorine signal. Three different perfluorocarbon emulsions were investigated at five different magnetic field strengths. Perfluoro-15-crown-5-ether was used as the core material and Gd(III)DOTA-DSPE, Gd(III)DOTA-C6-DSPE and Gd(III)DTPA-BSA as the relaxation altering components. While Gd(III)DOTA-DSPE and Gd(III)DOTA-C6-DSPE were favorable constructs for (1) H NMR, Gd(III)DTPA-BSA showed the strongest increase in (19F) R(1). These results show the potential of the use of paramagnetic lipids to increase (19F) R(1) at clinical field strengths (1.5-3 T). At higher field strengths (6.3-14 T), gadolinium does not lead to an increase in (19F) R(1) compared with emulsions without gadolinium, but leads to an significant increase in (19F) R(2). Our data therefore suggest that the most favorable situation for fluorine measurements is at high magnetic fields without the inclusion of gadolinium constructs.

A novel Gd(III) complex with a modified DO3A-like chelating cage has been synthesized and characterized as a candidate contrast agent responsive to the concentration of free thiols in tissues (essentially represented by reduced glutathione, GSH). The novel compound (called Gd-DO3AS-Act) bears a flexible linker ending with a 2-pyridyl-dithio group, that can promptly react with free thiols (XSH) to form mixed disulfides of the form Gd-DO3AS-SX. Compound Gd-DO3AS-Act is characterized by a millimolar relaxivity as high as 8.1 mM(-1) s(-1) (at 20 MHz, 25 degrees C and pH 7.4). Upon reaction with GSH, the Gd-DO3AS-SG covalent adduct is formed and the millimolar relaxivity drops to 4.1 mM(-1) s(-1). Such a decrease in relaxivity is explained on the basis of the formation of an intramolecular coordinative bond between one of the glutathionyl carboxyl groups and the Gd(III) centre, lowering the hydration state of the paramagnetic centre. (1)H-NMR dispersion profiles together with (17)O-NMR transverse relaxation time versus temperature profiles confirm that the hydration of the Gd(III) centre is strongly reduced ongoing from Gd-DO3AS-Act to the Gd-DO3AS-SG adduct. The relaxivity difference brought about by the reaction of Gd-DO3AS-Act with GSH can be enhanced up to 60% in the presence of poly-beta-cyclodextrin.

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