Electron paramagnetic resonance spectroscopy in radiation research: Current status and perspectives

Naringenin loaded solid lipid nanoparticles alleviate oxidative stress and enhance oral bioavailability of naringenin

Naringenin (Nrg) is the most abundant natural dietary flavonoid with promising anti-inflammatory potential. However, its therapeutic application is limited due to poor absorption, low bioavailability, and inability to cross physiological barriers. Herein, we designed biocompatible solid lipid nanoparticles (SLNs) to overcome these challenges and to enhance the oral bioavailability and therapeutic potential of Nrg. Nrg-loaded solid lipid nanoparticles (Nrg-SLNs) were fabricated from natural fatty acids, stearic (Nrg-SANPs), or a combination of stearic and lauric acid as binary nanoparticles (Nrg-SLNPs) by the hot melt encapsulation technique. The optimized Nrg-loaded nanoparticles exhibited a hydrodynamic diameter of 74 nm for SANPs and 91 nm for SLNPs, a zeta potential of -25 mV to -37 mV, and entrapment efficiency ranging from 79 % to 85 %. Electron paramagnetic resonance (EPR) spectroscopy indicated an in vitro radical protection factor (RPF) of 215 ± 2 × 1014 radicals/mg for Nrg-SLNPs, which was significantly higher than free Nrg and Nrg-SANPs. Almost 87 % reduction in oxidative stress was recorded with Nrg-SLNPs in a stress-induced lymphocyte model. In vivo studies using the Wistar rat model exhibited around 9-12-fold higher oral bioavailability of Nrg after nanoencapsulation in SLNs, as determined by high-performance liquid chromatography (HPLC). Whereas, hematological and histopathological analysis did not show any damage to the vital organs in vivo. This study presents Nrg-SLNPs as an efficient and biocompatible carrier to enhance the oral bioavailability and therapeutic activity of the natural flavonoids and warrants their further exploration in humans.

Application of magnetic particle imaging to evaluate nanoparticle fate in rodent joints

Nanoparticles are a promising approach for improving intra-articular drug delivery and tissue targeting. However, techniques to non-invasively track and quantify their concentration in vivo are limited, resulting in an inadequate understanding of their retention, clearance, and biodistribution in the joint. Currently, fluorescence imaging is often used to track nanoparticle fate in animal models; however, this approach has limitations that impede long-term quantitative assessment of nanoparticles over time. The goal of this work was to evaluate an emerging imaging modality, magnetic particle imaging (MPI), for intra-articular tracking of nanoparticles. MPI provides 3D visualization and depth-independent quantification of superparamagnetic iron oxide nanoparticle (SPION) tracers. Here, we developed and characterized a polymer-based magnetic nanoparticle system incorporated with SPION tracers and cartilage targeting properties. MPI was then used to longitudinally assess nanoparticle fate after intra-articular injection. Magnetic nanoparticles were injected into the joints of healthy mice, and evaluated for nanoparticle retention, biodistribution, and clearance over 6 weeks using MPI. In parallel, the fate of fluorescently tagged nanoparticles was tracked using in vivo fluorescence imaging. The study was concluded at day 42, and MPI and fluorescence imaging demonstrated different profiles in nanoparticle retention and clearance from the joint. MPI signal was persistent over the study duration, suggesting NP retention of at least 42 days, much longer than the 14 days observed based on fluorescence signal. These data suggest that the type of tracer - SPIONs or fluorophores - and modality of imaging can affect interpretation of nanoparticle fate in the joint. Given that understanding particle fate over time is paramount for attaining insights about therapeutic profiles in vivo, our data suggest MPI may yield a quantitative and robust method to non-invasively track nanoparticles following intra-articular injection on an extended timeline.

Breath biomarkers of total body irradiation in non-human primates

BACKGROUND

Radiation exposure causes oxidative stress, eliciting production of metabolites that are exhaled in the breath as volatile organic compounds (VOCs). We evaluated breath VOCs as potential biomarkers for use in radiation biodosimetry.

METHODS

Five anesthetized non-human primates receive total body irradiation (TBI) of three daily fractions of 120 cGy per day for three days, resulting in a cumulative dose of 10.8 Gy. Breath samples were collected prior to irradiation and after each radiation fraction, and analyzed with gas chromatography mass spectrometry.

RESULTS

TBI elicited a prompt and statistically significant increase in the abundance of several hundred VOCs in the breath, including some that were increased more than five-fold, with100% sensitivity and 100% specificity for radiation exposure. The most significant breath VOC biomarkers of radiation mainly comprised straight-chain n-alkanes (e.g. hexane), as well as methylated alkanes (e.g. 3-methyl-pentane) and alkane derivatives (e.g. 2-butyl-1-octanol), consistent with metabolic products of oxidative stress. An unidentified breath VOC biomarker increased more than ten-fold following TBI, and rose linearly with the total cumulative dose of radiation (R2=0.92).

CONCLUSIONS

TBI of non-human primates elicited increased production of breath VOCs consistent with increased oxidative stress. These findings provide a rational basis for further evaluation of breath VOC biomarkers in human radiation biodosimetry.

Heterogeneity of radiation response in mesenchymal subtype glioblastoma: molecular profiling and reactive oxygen species generation

BACKGROUND

Radiotherapy-induced tumor death remains critical in the successful first-line management of glioblastoma, whereas resistance to radiation serves as a major factor in disease progression. Mesenchymal shift has been identified as a driver in GBM recurrence, with gene expression associated with enhanced repair of macromolecular damage caused by radiation.

METHODS

Using distinct mesenchymal subtype GBM cells lines, radiation response was assessed by clonogenic assay and orthotopic mouse tumor model. RNA-sequencing was performed in the setting of increasing radiation dosing while real-time assessment of ROS generation was achieved by the measurement of hydroxyl spin trap adducts via electron paramagnetic resonance.

RESULTS

Radiation-induced cell death determined by clonogenic assay was significantly different at low dose (4-8 Gy) between the resistant U3035 cells and the sensitive U3020 cells. Similar trends were present in the in vivo NSG mouse model following radiation dosing on post-implantation day 7-10, with the rate of reduction in tumor bioluminescence reversing between the U3020 and U3035 cells after the third dose of radiation. Changes in gene expression following radiation determined by RNA-sequencing indicate both U3035 and U3020 cells demonstrate a shift toward more mesenchymal profiles, with concurrent shift away from pro-neural subtype gene expression in the U3020 cells that appeared to develop resistance to radiation in vivo. Persistence of ROS generated following radiation was greater in U3020 cells shown to be more sensitive to radiation.

CONCLUSIONS

Despite the same molecular classification, distinct GBM cell lines can demonstrate differential response to radiation and potential for mesenchymal shift associated with radiation resistance.

The Use of Fluorescent Probes to Detect ROS in Photodynamic Therapy

Photodynamic therapy employs nontoxic dyes called photosensitizers (PS) that are excited by visible light of the correct wavelength to produce a variety of reactive oxygen species (ROS) by an interaction between the long-lived PS triplet states with ambient oxygen. The most important type of ROS in photodynamic therapy (PDT) is singlet oxygen, which is produced by a Type II energy transfer process. On the other hand, superoxide, hydrogen peroxide, and hydroxyl radicals can be produced by a Type I electron transfer process. This chapter describes a set of fluorescent probes that can be used to tease apart these different ROS produced when various PS are illuminated in solution. Singlet oxygen sensor green (SOSG) is used for singlet oxygen, 4-hydroxyphenyl-fluorescein (HPF) for hydroxyl radicals, Amplex Red for hydrogen peroxide, and nitroblue-tetrazolium or XTT for superoxide.

Use of fluorescent probes for ROS to tease apart Type I and Type II photochemical pathways in photodynamic therapy

Photodynamic therapy involves the excitation of a non-toxic dye by harmless visible light to produce a long-lived triplet state that can interact with molecular oxygen to produce reactive oxygen species (ROS), which can damage biomolecules and kill cells. ROS produced by electron transfer (Type 1) include superoxide, hydrogen peroxide and hydroxyl radical (HO), while singlet oxygen (1O2) is produced by energy transfer. Diverse methods exist to distinguish between these two pathways, some of which are more specific or more sensitive than others. In this review we cover the use of two fluorescence probes: singlet oxygen sensor green (SOSG) detects 1O2; and 4-hydroxyphenyl-fluorescein (HPF) that detects HO. Interesting data was collected concerning the photochemical pathways of functionalized fullerenes compared to tetrapyrroles, stable synthetic bacteriochlorins with and without central metals, phenothiazinium dyes interacting with inorganic salts such as azide.

Peroxidase-like activity of Fe3O4@carbon nanoparticles enhances ascorbic acid-induced oxidative stress and selective damage to PC-3 prostate cancer cells

Ascorbic acid (AA) is capable of inhibiting cancer cell growth by perturbing the normal redox state of cells and causing toxic effects through the generation of abundant reactive-oxygen species (ROS). However, the clinical utility of AA at a tolerable dosage is plagued by a relatively low in vivo efficacy. This study describes the development of a peroxidase-like composite nanoparticle for use in an AA-mediated therapeutic strategy. On the basis of a high-throughput, one-pot solvothermal approach, Fe3O4@C nanoparticles (NPs) were synthesized and then modified with folic acid (FA) on the surface. Particular focus is concentrated on the assessment of peroxidase-like catalytic activity by a chromogenic reaction in the presence of H2O2. The carbon shell of Fe3O4@C NPs contains partially graphitized carbon and thus facilitates electron transfer in the catalytic decomposition of H2O2, leading to the production of highly reactive hydroxyl radicals. Along with magnetic responsiveness and receptor-binding specificity, the intrinsic peroxidase-like catalytic activity of Fe3O4@C-FA NPs pronouncedly promotes AA-induced oxidative stress in cancer cells and optimizes the ROS-mediated antineoplastic efficacy of exogenous AA. In vitro experiments using human prostate cancer PC-3 cells demonstrate that Fe3O4@C-FA NPs serve as a peroxidase mimic to create hydroxyl radicals from endogenous H2O2 that is yielded in response to exogenous AA via an oxidative stress process. The usage of a dual agent leads to the enhanced cytotoxicity of PC-3 cells, and, because of the synergistic effect of NPs, the administrated dosage of AA is reduced markedly. However, because normal cells (HEK 293T cells) appear to have a higher capacity to cope with additionally generated ROS than cancer cells, the NP-AA combination shows little damage in this case, proving that selective killing of cancer cells could be achieved owing to preferential accumulation of ROS in cancer cells. A possible ROS-mediated mechanism is discussed to elucidate the pharmaceutical profile of the NP-AA agent. In general, this foundational study reveals that the peroxidase-like nanomaterials are applicable for modulating oxidative stress for the selective treatment of cancer cells by generating a high level of endogenous ROS.

Understanding the antibacterial mechanism of CuO nanoparticles: revealing the route of induced oxidative stress

To date, there is still a lack of definite knowledge regarding the interaction of CuO nanoparticles with bacteria and the possible permeation of the nanoparticles into bacterial cells. This study was aimed at shedding light on the size-dependent (from the microscale down to the small nanoscale) antibacterial activity of CuO. The potent antibacterial activity of CuO nanoparticles was found to be due to ROS-generation by the nanoparticles attached to the bacterial cells, which in turn provoked an enhancement of the intracellular oxidative stress. This paradigm was confirmed by several assays such as lipid peroxidation and reporter strains of oxidative stress. Furthermore, electron microscopy indicated that the small nanoparticles of CuO penetrated the cells. Collectively, the results reported herein may reconcile conflicting concepts in the literature concerning the antibacterial mechanism of CuO nanoparticles, as well as highlight the potential for developing sustainable CuO nanoparticles-based devices for inhibiting bacterial infections.

Radiation-induced biomarkers for the detection and assessment of absorbed radiation doses

Radiation incident involving living organisms is an uncommon but a very serious situation. The first step in medical management including triage is high-throughput assessment of the radiation dose received. Radiation exposure levels can be assessed from viability of cells, cellular organelles such as chromosome and different intermediate metabolites. Oxidative damages by ionizing radiation result in carcinogenesis, lowering of the immune response and, ultimately, damage to the hematopoietic system, gastrointestinal system and central nervous system. Biodosimetry is based on the measurement of the radiation-induced changes, which can correlate them with the absorbed dose. Radiation biomarkers such as chromosome aberration are most widely used. Serum enzymes such as serum amylase and diamine oxidase are the most promising biodosimeters. The level of gene expression and protein are also good biomarkers of radiation.