Design of liposome-based pH sensitive nanoSPIN probes: nano-sized particles with incorporated nitroxides

Abstract

Liposome-based nanoSized Particles with Incorporated Nitroxides, or nanoSPINs, were designed for EPR applications as pH probes in biological systems. Phospholipid membrane of the liposomes with incorporated gramicidin A showed selective permeability to a small analyte, H + , while protecting entrapped sensing nitroxide from biological reductants. An application of the pH-sensitive nanoSPIN in an ischemia model in rat heart homogenate allows for monitoring ischemia-induced acidosis while protecting encapsulated nitroxide against bioreduction.

In vivo Spectroscopy and Imaging of Nitroxide Probes

“…The imidazoline nitroxide spin pH probes allowed for EPR spectroscopy and imaging of tissue pH. NanoSized Particles with Incorporated Nitroxides, or nanoSPINs, may serve as a future platform for stabilized nitroxide-based biosensors (Woldman et al, 2009). In particular, encapsulation of NO-sensitive nitronyl nitroxides may protect the sensing probe from biological reductants while retaining sensitivity to a small analyte, molecule of nitric oxide.…”

“…The bulky ethyl substitutes at positions 2 and 5 around the NO fragment of the RSG are introduced to enhance its stability towards bioreduction (Kirilyuk et al, 2004). The binding of the radical to hydrophilic tripeptide, GSH, prevents probe diffusion across the plasma membrane, and therefore, enforces probe localization to extracellular aqueous volumes (Woldman et al, 2009). Recently the RSG probe has been used to monitor tissue pHe in mice bearing breast cancer tumors for assessment of therapeutic effectiveness of various treatments (Bobko et al, 2012).…”

Development and Application of Spin Traps, Spin Probes, and Spin Labels

“…Another approach to increase stability of nitroxides is their encapsulation in different molecular "containers" such as liposomes, cyclodextrins, cucurbituriles, and calixarenes (Kirilyuk et al, 2010;Mezzina et al, 2015;Woldman et al, 2009). In some cases, e.g., in liposomes, the lifetime of nitroxides increases by several orders of magnitude; yet liposomes cannot be used in vivo.…”

Ionizable Nitroxides for Studying Local Electrostatic Properties of Lipid Bilayers and Protein Systems by EPR

“…Thus, the titration should be carried out in a way to ensure uniform pH in the sample. The latter could be achieved by either incorporating a gramicidine A channel into lipid bilayers to provide for proton permeability (53) or by subjecting the lipid preparation to a few freeze-thaw cycles such as employed by Voinov et al . (42) The former approach is imperative for titration of unilamellar vesicles.…”