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Relaxation-Based In Vivo Discrimination of Oxidized and Reduced States of a Redox-Switchable 19F MRI Probe

Zoltán Garda1,2, Frédéric Szeremeta1, Csilla Noémi Tóth1

  • 1Centre de Biophysique Moléculaire, CNRS UPR 4301, Université d'Orléans, rue Charles Sadron, 45071 Orléans, France.

Journal of the American Chemical Society
|May 14, 2025
PubMed

Insights

This study introduces a novel fluorinated iron chelate (FeL1) as a redox-responsive MRI probe. It enables sensitive detection and discrimination of different redox states in biological tissues, advancing diagnostic capabilities.

Area of Science:

  • Biomedical Imaging
  • Chemical Biology
  • Magnetic Resonance Imaging (MRI)

Background:

  • Assessing tissue redox state via MRI is crucial for understanding pathologies.
  • Redox-responsive imaging probes offer enhanced reliability through distinct signals in reduced and oxidized forms.
  • Existing probes may lack specificity or sensitivity for biological redox sensing.

Purpose of the Study:

  • To develop and characterize a novel, small, fluorinated, redox-active iron chelate (FeL1) as a prototype MRI contrast agent.
  • To evaluate the FeL1 probe's ability to generate distinct and quantifiable signals in its reduced (Fe(II)L1) and oxidized (Fe(III)L1) states.
  • To demonstrate the probe's utility for in vivo redox state monitoring using MRI.

Main Methods:

  • Synthesis and characterization of the FeL1 chelate, forming stable complexes with Fe(II) and Fe(III).
  • Measurement of redox potential, proton relaxivity, and 19F relaxation times (T1, T2) for both Fe(II)L1 and Fe(III)L1.
  • Application of specific MRI pulse sequences (RARE, UTE) for detecting and discriminating redox states in phantom and in vivo mouse models.

Main Results:

  • FeL1 exhibits a redox potential suitable for biological sensing (+240 mV vs NHE) and undergoes redox switching with biological reductants/oxidants (H2O2, cysteine, glutathione, ascorbate).
  • Significant differences in proton relaxivity and 19F relaxation times were observed between Fe(II)L1 and Fe(III)L1, enabling distinct signal generation.
  • Both redox states were successfully detected and discriminated in 19F MR phantom images and in vivo in mice with high sensitivity and signal-to-noise ratios.

Conclusions:

  • The FeL1 chelate serves as an effective prototype redox-responsive MRI probe, capable of generating discrete and quantifiable signals.
  • The probe's distinct relaxation properties allow unambiguous visualization and discrimination of its redox states in biological systems.
  • FeL1 holds promise for advancing MRI-based diagnostics by enabling direct monitoring of tissue redox status.

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