title: A naphthalocyanine-based EPR probe for localized measurements of tissue oxygenation.
abstract: A new electron paramagnetic resonance (EPR) oximetry probe, based on a naphthalocyanine macrocycle, is reported to exhibit high oxygen sensitivity and favorable EPR characteristics for biological applications. The free radical probe, lithium naphthalocyanine (LiNc), is synthesized as fine microcrystalline powder with particle size less than 1 microm and high spin density. It exhibits a single sharp EPR peak, whose width varies linearly with oxygen partial pressure (pO2). The EPR spectrum is nonsaturable at typical microwave power levels (< 25 mW at X-band). These unique characteristics make this probe ideal for measuring oxygen concentration in biological tissues, in vivo. The peak-to-peak width under anoxic conditions is 0.51 G (at X-band), and it increases linearly with increase in oxygen partial pressure and reaches 26.0 G for 100% oxygen (760 mmHg), showing an oxygen sensitivity of 34 mG/mmHg. The probe responds to changes in pO2 quickly and reproducibly, thus enabling dynamic measurements of regional oxygenation in real time. The application of this probe for oximetry is demonstrated in an in vivo biological system. The changes in pO2 were monitored in the leg muscle tissue of a living mouse breathing room air and carbogen (95% oxygen + 5% CO2), alternatively. The mean pO2 measured with this probe in muscle tissues was consistent with values reported previously using other methods. Overall, the probe shows very desirable characteristics for localized measurements of tissue oxygenation.
authors.affiliation: The EPR Center, Division of Cardiology, School of Medicine, Johns Hopkins University, Baltimore, MD 21224, USA.
authors.forename: Govindasamy
authors.initials: G
authors.lastname: Ilangovan
authors.forename: Ayyakkannu
authors.initials: A
authors.lastname: Manivannan
authors.forename: Haiquan
authors.initials: H
authors.lastname: Li
authors.forename: Hisao
authors.initials: H
authors.lastname: Yanagi
authors.forename: Jay L
authors.initials: JL
authors.lastname: Zweier
authors.forename: Periannan
authors.initials: P
authors.lastname: Kuppusamy
mesh_terms: D000818:Animals; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals / Q000032:analysis; D007211:Indoles / Q000737:chemistry*; D051379:Mice; D008809:Mice, Inbred C3H; D015335:Molecular Probes; D018482:Muscle, Skeletal / Q000737:chemistry* / Q000378:metabolism; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010092:Oximetry / Q000379:methods*; D010100:Oxygen / Q000032:analysis*; D010313:Partial Pressure; D015203:Reproducibility of Results
chemical_list: D005609:Free Radicals; D007211:Indoles; D015335:Molecular Probes; D009942:Organometallic Compounds; C081756:lithium phthalocyanine; D010100:Oxygen