Fluorine electron double resonance imaging for 19F MRI in low magnetic fields

Sample age effect on parameters of dynamic nuclear polarization in certain difluorobenzen isomers/MC800 asphaltene suspensions

Because of magnetic spin–spin interactivity between 19F nucleus of the solvent and delocalized electrons on the MC800 asphaltene, the Overhauser dynamic nuclear polarization (DNP) method is able to give a substantial boost in the signal acquired from studies focused on nuclear magnetic resonance (NMR). The suspensions of asphaltene in difluorobenzene isomers were studied using Overhauser effect type DNP and NMR investigations at room temperature in a small magnetic field of 1.53 mT. The used asphaltene was obtained from MC800 liquid asphalt from Heavy Iran. Each sample of the solvent medium was produced at three different concentrations of asphaltene. These samples were stored in the refrigerator for 7 years, until DNP parameters were found by new DNP tests. As a result, the influence of sample age on parameters of DNP was studied, and then the findings were analyzed.

Association of GRP78, HIF-1α and BAG3 Expression with the Severity of Chronic Lymphocytic Leukemia

INTRODUCTION

Parallel with the progression of Chronic Lymphocytic Leukemia (CLL), the levels of 78KDa Glucose-Regulated Protein (GRP78) and Hypoxia-Inducible Factor 1 alpha (HIF-1α) are increased as they may activate the induction of anti-apoptotic proteins such as BCL2 Associated Athanogene 3 (BAG3). Previous studies have indicated that there is a positive correlation among GRP78, HIF-1α and BAG3.

OBJECTIVE

This study aimed to evaluate the effect of metabolic factors involved in invasive CLL on apoptotic factors.

METHODS

A case-control study was conducted on 77 patients diagnosed with CLL along with 100 healthy individuals. Cell blood count was performed for all participants. According to Binet's classification, CLL patients were divided into different groups. B cells were isolated from the peripheral blood of CLL patients by binding to anti-CD19 beads. The expression of BAG3, GRP78 and HIF-1α genes was analyzed using the RT-PCR method. To confirm the results of RT-PCR, western blot analysis was carried out.

RESULTS

The results showed that there was a strong association among the expression of BAG3, GRP78 and HIF-1α. The stage of CLL in patients was highly correlated with the expression rate of each gene (p<0.001). Accordingly, the western blot analysis indicated that the concentrations of GRP78 and HIF-1α were significantly higher than the expression of BAG3, considering the stage of CLL.

CONCLUSION

It was shown that increased expression of GRP78 and HIF-1α could result in the elevation of BAG3, as well as the disease progression. Therefore, the role of these metabolic factors might be more pronounced compared with the anti-apoptotic agents to monitor disease progression in CLL patients.

Fluorine polymer probes for magnetic resonance imaging: quo vadis?

Over the last few years, the development and relevance of 19F magnetic resonance imaging (MRI) for use in clinical practice has emerged. MRI using fluorinated probes enables the achievement of a specific signal with high contrast in MRI images. However, to ensure sufficient sensitivity of 19F MRI, fluorine probes with a high content of chemically equivalent fluorine atoms are required. The majority of 19F MRI agents are perfluorocarbon emulsions, which have a broad range of applications in molecular imaging, although the content of fluorine atoms in these molecules is limited. In this review, we focus mainly on polymer probes that allow higher fluorine content and represent versatile platforms with properties tailorable to a plethora of biomedical in vivo applications. We discuss the chemical development, up to the first imaging applications, of these promising fluorine probes, including injectable polymers that form depots that are intended for possible use in cancer therapy.

Self-Assembled Thermoresponsive Polymeric Nanogels for 19F MR Imaging

Magnetic resonance imaging using fluorinated contrast agents (¹⁹F MRI) enables to achive highcontrast in images due to the negligible fluorine background in living tissues. In this pilot study, we developed new biocompatible, temperature-responsive, and easily synthesized polymeric nanogels containing a sufficient concentration of magnetically equivalent fluorine atoms for ¹⁹F MRI purposes. The structure of the nanogels is based on amphiphilic copolymers containing two blocks, a hydrophilic poly[ N-(2-hydroxypropyl)methacrylamide] (PHPMA) or poly(2-methyl-2-oxazoline) (PMeOx) block, and a thermoresponsive poly[ N(2,2difluoroethyl)acrylamide] (PDFEA) block. The thermoresponsive properties of the PDFEA block allow us to control the process of nanogel self-assembly upon its heating in an aqueous solution. Particle size depends on the copolymer composition, and the most promising copolymers with longer thermoresponsive blocks form nanogels of suitable size for angiogenesis imaging or the labeling of cells (approximately 120 nm). The in vitro ¹⁹F MRI experiments reveal good sensitivity of the copolymer contrast agents, while the nanogels were proven to be noncytotoxic for several cell lines.

Dynamic nuclear polarization studies on deuterated nitroxyl spin probes

Detailed dynamic nuclear polarization and electron spin resonance studies were carried out for 3-carbamoyl-2,2,5,5-tetramethyl-pyrrolidine-1-oxyl, 3-carboxy-2,2,5,5-tetramethyl-pyrrolidine-1-oxyl,3-methoxycarbonyl-2,2,5,5-tetramethy pyrolidine-1-oxyl nitroxyl radicals and their corresponding deuterated nitroxyl radicals, used in Overhauser-enhanced magnetic resonance imaging for the first time. The dynamic nuclear polarization parameters such as dynamic nuclear polarization (DNP) factor, longitudinal relaxivity, saturation parameter, leakage factor and coupling factor were estimated for deuterated nitroxyl radicals. DNP enhancement increases with agent concentration up to 3 mm and decreases above 3 mm. The proton spin-lattice relaxation time and the longitudinal relaxivity parameters were estimated. The leakage factor increases with increasing agent concentration up to 3 mm and reaches plateau in the region 3-5 mm. The coupling parameter shows the interaction between the electron and nuclear spins to be mainly dipolar in origin. DNP spectrum exhibits that the full width at half maximum values are higher for undeuterated nitroxyl radicals compared with deuterated nitroxyl radicals, which leads to the increase in DNP enhancement. The ESR parameters such as, the line width, line shape, signal intensity ratio, rotational correlation time, hyperfine coupling constant and g-factor were calculated. The narrow line width was observed for deuterated nitroxyl radicals compared with undeuterated nitroxyl radicals, which leads to the higher saturation parameter value and DNP enhancement. The novelty of the work permits clear understanding of the DNP parameters determining the higher DNP enhancement compared with the undeuterated nitroxyl radicals. Copyright © 2017 John Wiley & Sons, Ltd.

ESR line width and line shape dependence of Overhauser-enhanced magnetic resonance imaging

Electron spin resonance and Overhauser-enhanced magnetic resonance imaging studies were carried out for various concentrations of ¹⁴ N-labeled 3-carbamoyl-2,2,5,5-tetramethyl-pyrrolidine-1-oxyl in pure water. Overhauser-enhancement factor attains maxima in the range of 2.5-3 mm concentration. The leakage factor showed an asymptotic increase with increasing agent concentration. The coupling parameter showed the interaction between the electron and nuclear spins to be mainly dipolar in origin. The electron spin resonance parameters, such as the line width, line shape and g-factor, were determined. The line width analysis confirms that the line broadening is proportional to the agent concentration, and also the agent concentration is optimized in the range of 2.5-3 mm. The line shape analysis shows that the observed electron spin resonance line shape is a Voigt line shape, in which the Lorentzian component is dominant. The contribution of Lorentzian component was estimated using the winsim package. The Lorentzian component of the resonance line attains maxima in the range of 2.5-3 mm concentration. Therefore, this study reveals that the agent concentration, line width and Lorentzian component are the important factors in determining the Overhauser-enhancement factor. Hence, the agent concentration was optimized as 2.5-3 mm for in vivo/in vitro electron spin resonance imaging and Overhauser-enhanced magnetic resonance imaging phantom studies. Copyright © 2016 John Wiley & Sons, Ltd.

Fluorinated porphyrinoids as efficient platforms for new photonic materials, sensors, and therapeutics

Porphyrinoids are robust heterocyclic dyes studied extensively for their applications in medicine and as photonic materials because of their tunable photophysical properties, diverse means of modifying the periphery, and the ability to chelate most transition metals. Commercial applications include their use as phthalocyanine dyes in optical discs, porphyrins in photodynamic therapy, and as oxygen sensors. Most applications of these dyes require exocyclic moieties to improve solubility, target diseases, modulate photophysical properties, or direct the self-organization into architectures with desired photonic properties. The synthesis of the porphyrinoid depends on the desired application, but the de novo synthesis often involves several steps, is time consuming, and results in low isolated yields. Thus, the application of core porphyrinoid platforms that can be rapidly and efficiently modified to evaluate new molecular architectures allows researchers to focus on the design concepts rather than the synthesis methods, and opens porphyrinoid chemistry to a broader scientific community. We have focused on several widely available, commercially viable porphyrinoids as platforms: meso-perfluorophenylporphyrin, perfluorophthalocyanine, and meso-perfluorophenylcorrole. The perfluorophenylporphyrin is readily converted to the chlorin, bacteriochlorin, and isobacteriochlorin. Derivatives of all six of these core platforms can be efficiently and controllably made via mild nucleophilic aromatic substitution reactions using primary S, N, and O nucleophiles bearing a wide variety of functional groups. The remaining fluoro groups enhance the photo and oxidative stability of the dyes and can serve as spectroscopic signatures to characterize the compounds or in imaging applications using (19)F NMR. This review provides an overview of the chemistry of fluorinated porphyrinoids that are being used as a platform to create libraries of photo-active compounds for applications in medicine and materials.

Dynamic nuclear polarization properties of nitroxyl radical in high viscous liquid using Overhauser-enhanced Magnetic Resonance Imaging (OMRI)

The dynamic nuclear polarization (DNP) studies were carried out for (15)N labeled carbamoyl-PROXYL in pure water and pure water/glycerol mixtures of different viscosities (1.8cP, 7cP and 14cP). The dependence of DNP parameters was demonstrated over a range of agent concentration, viscosities, RF power levels and ESR irradiation time. DNP spectra were also recorded for 2mM concentration of (15)N labeled carbamoyl-PROXYL in pure water and pure water/glycerol mixtures of different viscosities. The DNP factors were measured as a function of ESR irradiation time, which increases linearly up to 2mM agent concentration in pure water and pure water/glycerol mixtures of different viscosities. The DNP factor started declining in the higher concentration region (∼3mM), which is due to the ESR line width broadening. The water proton spin-lattice relaxation time was measured at very low Zeeman field (14.529mT). The increased DNP factor (35%) was observed for solvent 2 (η=1.8cP) compared with solvent 1 (η=1cP). The increase in the DNP factor was brought about by the shortening of water proton spin-lattice relaxation time of solvent 2. The decreased DNP factors (30% and 53%) were observed for solvent 3 (η=7cP) and solvent 4 (η=14cP) compared with solvent 2, which is mainly due to the low value of coupling parameter in high viscous liquid samples. The longitudinal relaxivity, leakage factor and coupling parameter were estimated. The coupling parameter values reveal that the dipolar interaction as the major mechanism. The longitudinal relaxivity increases with the increasing viscosity of pure water/glycerol mixtures. The leakage factor showed an asymptotic increase with the increasing agent concentration. It is envisaged that the results reported here may provide guidelines for the design of new viscosity prone nitroxyl radicals, suited to the biological applications of DNP.

Dynamic nuclear polarization studies of redox-sensitive nitroxyl spin probes in liposomal solution

Overhauser-enhanced magnetic resonance imaging (OMRI) studies of a membrane-permeable nitroxyl spin probe, (2)H-enriched 3-methoxycarbonyl-2,2,5,5-tetramethyl-pyrrolidine-1-oxyl (MC-PROXYL), used in simultaneous molecular imaging is reported. Phantom imaging was performed with liposomal solutions of MC-PROXYL at varying spin probe and liposome concentrations using a field-cycle mode, custom-built OMRI scanner. Dynamic nuclear polarization (DNP) spectra of the liposomal solution of the spin probe, measured at 14.529mT using a 5mT sweep of the electron paramagnetic resonance (EPR) irradiation field showed splitting of the low and high filed hyperfine lines. Spectral measurements using D(2)O and a spin broadening agent, K(3)Fe(CN)(6) confirmed that these peaks originated from water molecules in two different environments, compartmentalized with liposomes. The nuclear Overhauser enhancement measured at different EPR irradiation times and power levels showed reduction in water nuclear magnetic resonance (NMR) signal enhancement in liposomal membrane due to the reduction in the coupling constant, rho. This study illustrates that OMRI can be used to differentiate between the intra- and extra- membrane water by loading the liposome vesicles with a lipid-permeable nitroxyl spin probe.

Electron paramagnetic resonance as a unique tool for skin and hair research

Electron paramagnetic resonance (EPR) spectroscopy and imaging (EPRI) are deeply rooted in the basic and quantum physics, but the spectrum of their applications in modern experimental and clinical dermatology and cosmetology is surprisingly wide. The main aim of this review was to show the physical foundation, technical limitations and versatility of this method in skin studies. Free radical and metal ion detection, EPR dosimetry, melanin study, spin trapping, spin labelling, oximetry and NO-metry, EPR imaging, new generation methods of EPR and EPR/NMR hybrid technology used under ex vivo and in vivo regime are portrayed in the context of clinical and experimental skin research to study problems such as oxidative and nitrosative stress generated by UV or inflammation, skin oxygenation, hydration of corneal layer of epidermis, transport and metabolism of drugs and cosmeceutics, skin carcinogenesis, skin tumors and many others. A part of the paper is devoted to hair and nail research. The review of dermatological applications of EPR is supplemented with a handful of advice concerning practical aspects of EPR experimentation and usage of EPR reagents.

Spatially resolved biologic information from in vivo EPRI, OMRI, and MRI

EPR spectroscopy can give biologically important information, such as tissue redox status, pO2, pH, and microviscosity, based on variation of EPR spectral characteristics (i.e., intensity, linewidth, hyperfine splitting, and spectral shape of free radical probes. EPR imaging (EPRI) can obtain 1D-3D spatial distribution of such spectral components using several combinations of magnetic field gradients. Overhauser enhanced MRI (OMRI) is a double-resonance technique of electron and nuclear spins. Because the Overhauser enhancement depends on transverse relaxation rate of the electron spin, OMRI can provide pO2 information indirectly, along with a high-resolution MR image. MRI can also indirectly detect paramagnetic behaviors of free radical contrast agents. Imaging techniques and applications relating to paramagnetic species (i.e., EPRI, OMRI, and MRI) have the potential to obtain maximally 5D information (i.e., 3D spatial + 1D spectral + 1D temporal dimensions, theoretically). To obtain suitable dimensionality, several factors, such as the EPR spectral information, spatial resolution, temporal resolution, will have to be taken into account. For this review, the EPRI, OMRI, and MRI applications for the study biological systems were evaluated for researchers to apply the method of choice and the mode of measurements to specific experimental systems.

Dynamic nuclear polarization properties of nitroxyl radicals used in Overhauser-enhanced MRI for simultaneous molecular imaging

DNP parameters relevant to Overhauser-enhanced magnetic resonance imaging (OMRI) are reported for a few nitroxyl radicals and their corresponding (15)N and (2)H enriched analogues, used in simultaneous imaging by OMRI. DNP enhancement was measured at 14.529 mT, using a custom-built scanner operating in a field-cycled mode, for different concentrations, ESR irradiation times and RF power levels. DNP enhancements increased with agent concentration up to 2.5 mM and decreased above 3 mM, in tune with ESR line broadening measured at X-band as a function of the agent concentration. The proton spin-lattice relaxation times (T(1)) measured at very low Zeeman field (14.529 mT) and the longitudinal relaxivity parameters were estimated. The relaxivity parameters were in good agreement with those independently computed from the linear region of the concentration dependent enhancement. The leakage factor showed an asymptotic increase with increasing agent concentration. The coupling parameters of (14)N- and (15)N-labeled carbamoyl-PROXYL showed the interaction between the electron and nuclear spins to be mainly dipolar in origin. Upon (2)H labeling, about 70% and 40% increases in enhancement for (15)N- and (14)N-labeled nitroxyl agents were observed, respectively. It is envisaged that the results reported here may enable better understanding of the factors determining DNP enhancement to design suitable 'beacons' for simultaneous molecular imaging by OMRI.

Sequential, co-registered fluorine and proton field-cycled Overhauser imaging at a detection field of 59 mT

In this work we show the feasibility of sequential, co-registered fluorine and proton field-cycled Overhauser imaging at a detection field of 59 mT. To this purpose we have built an RF coil assembly comprising an Alderman-Grant resonator for EPR irradiation at 127.7 MHz (evolution field of 4.5 mT) and a solenoidal coil for (19)F or (1)H MRI acquisition at the detection field of 59 mT. A removable tuning/matching circuit that allows the solenoid to be tuned to the (19)F frequency (2.346 MHz, FEDRI) or the (1)H frequency (2.494 MHz, PEDRI) without removing the sample was built and tested. Switching of the solenoid between the (19)F and (1)H frequency is thus achieved in less than 1 min. The co-registered FC-FEDRI and FC-PEDRI images show higher enhancement in the sample regions with higher free radical concentration. This work is the first methodological step towards the development of an MRI scanner capable of acquiring morphological ((1)H) and physiological ((19)F) images in animal models at very low fields.