Metabolic stability of superoxide adducts derived from newly developed cyclic nitrone spin traps

Reactive oxygen species are by-products of aerobic metabolism involved in the onset and evolution of various pathological conditions. Among them, the superoxide radical is of special interest as the origin of several damaging species such as H2O2, hydroxyl radical, or peroxynitrite (ONOO-). Spin trapping coupled with ESR is a method of choice to characterize these species in chemical and biological systems and the metabolic stability of the spin adducts derived from reaction of superoxide and hydroxyl radicals with nitrones is the main limit to the in vivo application of the method. Recently, new cyclic nitrones bearing a triphenylphosphonium or permethylated β-cyclodextrin moiety have been synthesized and their spin adducts demonstrated increased stability in buffer. In this article, we studied the stability of the superoxide adducts of four new cyclic nitrones in the presence of liver subcellular fractions and biologically relevant reductants using an original setup combining a stopped-flow device and an ESR spectrometer. The kinetics of disappearance of the spin adducts were analyzed using an appropriate simulation program. Our results highlight the interest of the new spin trapping agents CD-DEPMPO and CD-DIPPMPO for specific detection of superoxide with high stability of the superoxide adducts in the presence of liver microsomes. © 2013 Elsevier Inc. All rights reserved

Optoacoustic imaging of naphthalocyanine: Potential for contrast enhancement and therapy monitoring.

We investigated in vitro and in vivo the optoacoustic responses of a silicon naphthalocyanine (SiNc), considered herein as a reporter molecule for optoacoustic imaging, elucidating its efficiency for optoacoustic (photoacoustic) signal generation and examined the in vivo performance achieved. METHODS: SiNc solutions were prepared using Cremophor E.L. in water and evaluated for light absorbing and photoacoustic contrast generating properties. Photostability and singlet oxygen generation were investigated under pulsed laser illumination and validated using photoabsorbance. HT-29 mice tumor models were used to assess the biodistribution of the compound and its performance as an optoacoustic contrast agent in vivo. RESULTS: SiNc was found to generate superior optoacoustic signals compared to the commonly used Indocyanine Green (ICG). Multispectral optoacoustic tomography (MSOT) of mouse tumors efficiently resolved the biodistribution of SiNc and the underlying perfusion parameters in vivo. In addition, we demonstrate how light-triggered SiNc reactions with molecular oxygen can be potentially sensed and discuss the relation of these measurements to the biochemical process involved in photothermal treatment. CONCLUSION: SiNc appears to be a promising family of contrast agent for optoacoustic imaging. Further development possibilities promise to expand its use in purely contrast generation settings, as well as its photodynamic therapy application

Optoacoustic imaging: An emerging modality for the gastrointestinal tract.

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Optical and opto-acoustic interventional imaging.

Many clinical interventional procedures, such as surgery or endoscopy, are today still guided by human vision and perception. Human vision however is not sensitive or accurate in detecting a large range of disease biomarkers, for example cellular or molecular processes characteristic of disease. For this reason advanced optical and opto-acoustic (photo-acoustic) methods are considered for enabling a more versatile, sensitive and accurate detection of disease biomarkers and complement human vision in clinical decision making during interventions. Herein, we outline developments in emerging fluorescence and opto-acoustic sensing and imaging techniques that can lead to practical implementations toward improving interventional vision

Optical imaging of cancer heterogeneity with multispectral optoacoustic tomography.

PURPOSE: To investigate whether multispectral optoacoustic tomography (MSOT) can reveal the heterogeneous distributions of exogenous agents of interest and vascular characteristics through tumors of several millimeters in diameter in vivo. MATERIALS AND METHODS: Procedures involving animals were approved by the government of Upper Bavaria. Imaging of subcutaneous tumors in mice was performed by using an experimental MSOT setup that produces transverse images at 10 frames per second with an in-plane resolution of approximately 150 μm. To study dynamic contrast enhancement, three mice with 4T1 tumors were imaged before and immediately, 20 minutes, 4 hours, and 24 hours after systemic injection of indocyanine green (ICG). Epifluorescence imaging was used for comparison. MSOT of a targeted fluorescent agent (6 hours after injection) and hemoglobin oxygenation was performed simultaneously (4T1 tumors: n = 3). Epifluorescence of cryosections served as validation. The accumulation owing to enhanced permeability and retention in tumors (4T1 tumors: n = 4, HT29 tumors: n = 3, A2780 tumors: n = 2) was evaluated with use of long-circulating gold nanorods (before and immediately, 1 hour, 5 hours, and 24 hours after injection). Dark-field microscopy was used for validation. RESULTS: Dynamic contrast enhancement with ICG was possible. MSOT, in contrast to epifluorescence imaging, showed a heterogeneous intratumoral agent distribution. Simultaneous imaging of a targeted fluorescent agent and oxy- and deoxyhemoglobin gave functional information about tumor vasculature in addition to the related agent uptake. The accumulation of gold nanorods in tumors seen at MSOT over time also showed heterogeneous uptake. CONCLUSION: MSOT enables live high-spatial-resolution observations through tumors, producing images of distributions of fluorochromes and nanoparticles as well as tumor vasculature

Optoacoustic imaging enabled biodistribution study of cationic polymeric biodegradable nanoparticles.

Nanosized contrast agents for molecular imaging have attracted widespread interest for diagnostic applications with high resolution in medicine. However, many solid nanoparticles exhibit a great potential to induce toxicity, hindering their use for clinical applications. On the other hand, near-infrared (NIR) dyes have also been used for extensive biological applications, but show some limitations due to their poor aqueous stability, tendency to aggregation and rapid elimination from the body. An alternative proposed in this work to overcome these limitations is the use of NIR dye-loaded nanoparticles. Here we introduce nanoparticles constructed with poly(D,L-lactide-co-glycolic acid) (PLGA), a biodegradable and biocompatible polymer widely used for biomedical applications, attached to the polycation polyethyleneimine (PEI) to obtain positively charged nanoparticles. The in vivo biodistribution of the cationic PEI-PLGA nanoparticles was investigated after administration through three different routes (intravenous, intraperitoneal and subcutaneous) using multispectral optoacoustic tomography (MSOT). The prepared nanoparticles exhibited good colloidal stability and adequate optical properties for optoacoustic imaging. The in vivo biodistribution assays indicated a strong accumulation of the particles in the liver and spleen, and retention in these organs for at least 24 h. Therefore, these nanoparticles could find promising applications in MSOT due to a sharp and characteristic optoacoustic spectrum and high optoacoustic signal generation, and become a promising building block for theranostic strategies

Dynamic imaging of PEGylated Indocyanine Green (ICG) liposomes within the tumor microenvironment using Multi-Spectral Optoacoustic Tomography (MSOT).

Multispectral optoacoustic tomography (MSOT) is a powerful modality that allows high-resolution imaging of photo-absorbers deep within tissue, beyond the classical depth and resolution limitations of conventional optical imaging. Imaging of intrinsic tissue contrast can be complemented by extrinsically administered gold nanoparticles or fluorescent molecular probes. Instead, we investigated herein generation of re-engineered clinically-used PEGylated liposomes incorporating indocyanine green (LipoICG) as a contrast strategy that combines materials already approved for clinical use, with strong photo-absorbing signal generation available today only from some metallic nanoparticles (e.g. gold nanorods). Using MSOT we confirmed LipoICG as a highly potent optoacoustic agent and resolved tissue accumulation in tumor-bearing animals over time with high-sensitivity and resolution using two tumor models of different vascularisation. We further showcase a paradigm shift in pharmacology studies and nanoparticle investigation, by enabling detailed volumetric optical imaging in vivo through the entire tumor tissue non-invasively, elucidating never before seen spatiotemporal features of optical agent distribution. These results point to LipoICG as a particle with significant advantageous characteristics over gold nanoparticles and organic dyes