A novel spin probe with long life in vivo for ESR imaging

Effect of relative configuration of TEMPO-type nitroxides on ascorbate reduction

2,2,6,6-Tetramethylpiperidin-N-oxyl (TEMPO)-type nitroxides are susceptible to bioreduction, leading to a loss of radical properties. Although it has been reported that the steric and electronic environments around the N-O moiety of nitroxides affect the reduction, how the relative configuration of nitroxide derivatives alters it is unclear. In this study, we investigated the effect of diastereomers on the radical properties of C2- and C4-disubstituted TEMPO-type nitroxides. We succeeded in isolating the diastereomers of the studied nitroxides for the first time. In addition, we compared the reactivities of nitroxide derivatives with different substituents at the C2 and C4 positions toward ascorbate reduction. We found that the bulky substituents at both C2 and C4 and the electronic effect of C4 affected the reduction of the isomers. C2- and C4-disubstituted nitroxides were administered to mice for electron spin resonance imaging to assess bioreduction in the brain. Similar to the reactivity to reduction in vitro, a difference in the bioreduction of diastereomers was observed in brain tissues. Our research strongly indicates that bioreduction can be controlled by changing the relative configuration, which can be used in the design of nitroxide derivatives for biological applications.

Inhibition of angiogenesis by antioxidant micelles

Antioxidant micelles capable of scavenging reactive oxygen species (ROS) are prepared from poly(ethylene glycol)-b-poly(dopamine) block copolymers. The micelles inhibit tube formation of human umbilical vein endothelial cells (HUVECs) by scavenging endogenous ROS. Furthermore, the micelles inhibit angiogenesis in the chicken ex ovo chorioallantoic membrane assay. The results show that antioxidant micelles containing catechol moieties may be useful in anti-angiogenic therapy to treat various diseases such as cancer.

Nitroxide radicals and nanoparticles: a partnership for nanomedicine radical delivery

This article aims to provide a research update on nitroxide radical compounds for application of anti-oxidative stress therapy. Nitroxide compounds such as 2,2,6,6-tetramethylpyperidine-1-oxyl (TEMPO) can catalytically react with reactive oxygen species (ROS) and are anticipated as new anti-oxidant therapies for several diseases. However, low-molecular-weight nitroxide compounds pose several problems such as nonspecific dispersion in normal tissues, preferential renal clearance and rapid reduction of the nitroxide radical to the corresponding hydroxylamine. Nitroxide radical compounds are also known to show dose-related antihypertensive action accompanied by reflex tachycardia, increased skin temperature, and seizures. The author has recently designed novel nanoparticles, which possess nitroxide radicals in the core for novel bioimaging and nanotherapy. Nitroxide radical-containing nanoparticles (RNP) shows high safety, long blood circulation, magnetic resonance imaging and ESR imaging sensitive character and efficient therapeutic effects to several diseases such as cerebral and renal ischemia reperfusions, ulcerative colitis and Alzheimer’s disease models. RNPs are, thus, promising as new nanotherapeutic materials.

Nitroxyl radical-containing nanoparticles for novel nanomedicine against oxidative stress injury

This article discusses the preparation and characterization of pH-sensitive nitroxyl radical-containing nanoparticles (RNPs) possessing nitroxyl radicals in the core and reactive groups on the periphery, and its biomedical application. The RNPs prepared by a self-assembling amphiphilic block copolymers composed of a hydrophilic poly(ethylene glycol) (PEG) segment and a hydrophobic poly(chloromethylstyrene) (PCMS) segment in which the chloromethyl groups were converted to 2,2,6,6-tetramethylpiperidinyloxyls (TEMPOs) via an amination of PEG-b-PCMS block copolymer with 4-amino-TEMPO are initially described. The cumulant average diameter of an RNP is approximately 40 nm, and the RNP has intense electron paramagnetic resonance signals. RNPs show a prolonged blood circulation time by the compartmentalization of nitroxyl radicals into the hydrophobic core, and disintegrate in response to a low pH environment, such as ischemic tissue, resulting in effectively scavenging reactive oxygen species due to an exposure of nitroxyl radicals from the RNP core. Thus, the RNP prepared was found to be effective for cerebral ischemia–reperfusion injury. Therefore, RNPs are promising as high-performance therapeutic nanomedicine for oxidative stress injuries.

Current status of electron spin resonance (ESR) for in vivo detection of free radicals

Much outstanding progress concerning the application of ESR spectroscopy/imaging in the biomedical field has been made in recent years. The literature in this field has already been specifically covered by several reviews. The aim of this article is to provide an overview of the most important findings, obtained in the last four years, in the detection and localization of different exogenous free radicals, as well as of endogenous free radicals in diverse experimental animal models.

Dynamic electron spin resonance (ESR) imaging of the distribution of spin labeled dextran in a mouse

The nitroxide group 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) was covalently bound to a dextran via an N-acetamido linkage to produce a novel spin probe, TEMPO-dextran (TEMPO-DX), which circulates for long time periods in an animal without metabolic degradation. TEMPO-DX was stable in mice, while small TEMPO analogs quickly disappeared after administration. Since dextran was reduced somewhat in size during synthesis, the resultant spin-labeled dextran could be excreted through the kidney. A strong L-band electron spin resonance signal was obtained shortly after intravenous administration of TEMPO-DX into the tail vein of a mouse, from which three-dimensional images of specific organs were calculated. The signal was found to persist for well over 1 h.