Detection of free radicals in living mice after inhalation of DTBN by X-band ESR

Electron paramagnetic resonance: a powerful tool to support magnetic resonance imaging research

The purpose of this paper is to describe some of the areas where electron paramagnetic resonance (EPR) has provided unique information to MRI developments. The field of application mainly encompasses the EPR characterization of MRI paramagnetic contrast agents (gadolinium and manganese chelates, nitroxides) and superparamagnetic agents (iron oxide particles). The combined use of MRI and EPR has also been used to qualify or disqualify sources of contrast in MRI. Illustrative examples are presented with attempts to qualify oxygen sensitive contrast (i.e. T1 - and T2 *-based methods), redox status or melanin content in tissues. Other areas are likely to benefit from the combined EPR/MRI approach, namely cell tracking studies. Finally, the combination of EPR and MRI studies on the same models provides invaluable data regarding tissue oxygenation, hemodynamics and energetics. Our description will be illustrative rather than exhaustive to give to the readers a flavour of 'what EPR can do for MRI'.

Heparin-polynitroxides: synthesis and preliminary evaluation as cardiovascular EPR/MR imaging probes and extracellular space-targeted antioxidants

We report here the synthesis of heparin-polynitroxide derivatives (HPNs) in which nitroxide moieties are linked either to uronic acid or glycosamine residues of the heparin macromolecule. HPNs have low anticoagulant activity, possess superoxide scavenging properties, bind to the vascular endothelium/extra-cellular matrix and can be detected by EPR and MRI techniques. As the vascular wall-targeted redox-active paramagnetic compounds, HPNs may have both diagnostic (molecular MRI) and therapeutic (ecSOD mimics) applications.

In vivo EPR: an effective new tool for studying pathophysiology, physiology and pharmacology

The development of spectrometers working at lower frequencies with improved resonators now permits the routine use of non-invasive EPR spectroscopy in vivo. The capabilities of EPR spectra to reflect environmental conditions, combined with the use of paramagnetic materials as selective non-toxic labels, has led to increasingly widespread and productive applications of the technique to complex problems involving physiology, pharmacology and pathophysiology. Some of the especially promising applications in which EPR techniques uniquely appear to provide valuable information are illustrated, including the measurement of oxygen and oxygen gradients, monitoring of the metabolism of xenobiotics, monitoring pharmacokinetics of drugs, measurement of perfusion, measurement of pH, recognition and labeling of receptors, and characterization of drug releasing systems.

In vivo detection of anthralin-derived free radicals in the skin of hairless mice by low-frequency electron paramagnetic resonance spectroscopy

Free radicals were directly detected in vivo in the skin of hairless mice by low-frequency electron paramagnetic resonance spectroscopy after topical application of anthralin under pertinent therapeutic conditions. The electron paramagnetic resonance signal intensity increased steadily, reaching a maximum after about 1 d and decreased slowly in the following days, probably because of desquamation of the skin. We conclude from the spectroscopic features (single line with a line width of 6 gauss; g = 2.0036) and from the pharmacokinetic pattern that the observed signal arises from the final products of anthralin metabolism (ether-insoluble polymeric structures--"anthralin brown"). Two potential antioxidants, vitamin E and the spin trap tert-butylphenylnitrone, decreased the amount of the anthralin-derived radical that was formed. Neither vitamin E radicals nor tert-butylphenylnitrone spin adducts were observed. We suggest that electron paramagnetic resonance is a valuable tool for the noninvasive and direct in vivo monitoring of drug-induced radical formation in the skin under therapeutic conditions.

Pharmacokinetic properties of nitroxide-labeled albumin in mice

We have conjugated bovine serum albumin (BSA) with a pyrrolidinyl nitroxide and report on the in vivo pharmacokinetic properties of this conjugate in mice. In vivo EPR measurements of nitroxide were obtained after intravenous injection of 30 mg of labeled BSA by analysis of the nitroxide signal from the tails of mice. Following in vivo nitroxide measurements, the animals were sacrificed by exsanguination and organs were removed for determination of nitroxide levels. The level of nitroxide as determined by in vivo measurements declined exponentially with time and had a half-life (t1/2) of 7 hours. Blood nitroxide levels also declined exponentially with time with an initial t1/2 of 70 minutes and a terminal t1/2 of 10 hours. Nitroxide concentration varied among different organs; no nitroxide was detected within brain whereas lung had high concentrations of nitroxide. Liver and kidney both had relatively low levels of oxidized nitroxide, though total nitroxide (reduced plus oxidized) accumulated in the kidneys with time. Nitroxide-labeled BSA was well tolerated by the mice, is relatively stable, and is mainly confined to the intravascular space. Nitroxide-labeled albumin may be useful as a contrast agent for MRI or EPR imaging.