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

Spectroscopic methods for assessing the molecular origins of macroscopic solution properties of highly concentrated liquid protein solutions

In cases of subcutaneous injection of therapeutic monoclonal antibodies, high protein concentrations (>50 mg/ml) are often required. During the development of these high concentration liquid formulations (HCLF), challenges such as aggregation, gelation, opalescence, phase separation, and high solution viscosities are more prone compared to low concentrated protein formulations. These properties can impair manufacturing processes, as well as protein stability and shelf life. To avoid such unfavourable solution properties, a detailed understanding about the nature of these properties and their driving forces are required. However, the fundamental mechanisms that lead to macroscopic solution properties, as above mentioned, are complex and not fully understood, yet. Established analytical methods for assessing the colloidal stability, i.e. the ability of a native protein to remain dispersed in solution, are restricted to dilute conditions and provide parameters such as the second osmotic virial coefficient, B₂₂, and the diffusion interaction coefficient, k_D. These parameters are routinely applied for qualitative estimations and identifications of proteins with challenging solution behaviours, such as high viscosities and aggregation, although the assays are prepared for low protein concentration conditions, typically between 0.1 and 20 mg/ml ("ideal" solution conditions). Quantitative analysis of samples of high protein concentration is difficult and it is hard to obtain information about the driving forces of such solution properties and corresponding protein-protein self-interactions. An advantage of using specific spectroscopic methods is the potential of directly analysing highly concentrated protein solutions at different solution conditions. This allows for collecting/gaining valuable information about the fundamental mechanisms of solution properties of the high protein concentration regime. In addition, the derived parameters might be more predictive as compared to the parameters originating from assays which are optimized for the low protein concentration range. The provided information includes structural data, molecular dynamics at various timescales and protein-solvent interactions, which can be obtained at molecular resolution. Herein, we provide an overview about spectroscopic techniques for analysing the origins of macroscopic solution behaviours in general, with a specific focus on pharmaceutically relevant high protein concentration and formulation conditions.

In Vivo and In Situ Detection of Macromolecular Free Radicals Using Immuno-Spin Trapping and Molecular Magnetic Resonance Imaging

SIGNIFICANCE

In vivo free radical imaging in preclinical models of disease has become a reality. Free radicals have traditionally been characterized by electron spin resonance (ESR) or electron paramagnetic resonance (EPR) spectroscopy coupled with spin trapping. The disadvantage of the ESR/EPR approach is that spin adducts are short-lived due to biological reductive and/or oxidative processes. Immuno-spin trapping (IST) involves the use of an antibody that recognizes macromolecular 5,5-dimethyl-pyrroline-N-oxide (DMPO) spin adducts (anti-DMPO antibody), regardless of the oxidative/reductive state of trapped radical adducts. Recent Advances: The IST approach has been extended to an in vivo application that combines IST with molecular magnetic resonance imaging (mMRI). This combined IST-mMRI approach involves the use of a spin-trapping agent, DMPO, to trap free radicals in disease models, and administration of an mMRI probe, an anti-DMPO probe, which combines an antibody against DMPO-radical adducts and an MRI contrast agent, resulting in targeted free radical adduct detection.

CRITICAL ISSUES

The combined IST-mMRI approach has been used in several rodent disease models, including diabetes, amyotrophic lateral sclerosis (ALS), gliomas, and septic encephalopathy. The advantage of this approach is that heterogeneous levels of trapped free radicals can be detected directly in vivo and in situ to pin point where free radicals are formed in different tissues.

FUTURE DIRECTIONS

The approach can also be used to assess therapeutic agents that are either free radical scavengers or generate free radicals. Smaller probe constructs and radical identification approaches are being considered. The focus of this review is on the different applications that have been studied, advantages and limitations, and future directions. Antioxid. Redox Signal. 28, 1404-1415.

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.

Concentration dependence of nitroxyl spin probes in liposomal solution: electron spin resonance and overhauser-enhanced magnetic resonance studies

In this work, the detailed studies of electron spin resonance (ESR) and overhauser-enhanced magnetic resonance imaging (OMRI) were carried out for permeable nitroxyl spin probe, MC-PROXYL as a function of agent concentration in liposomal solution. In order to compare the impermeable nature of nitroxyl radical, the study was also carried out only at 2 mM concentration of carboxy-PROXYL. The ESR parameters were estimated using L-band and 300 MHz ESR spectrometers. The line width broadening was measured as a function of agent concentration in liposomal solution. The estimated rotational correlation time is proportional to the agent concentration, which indicates that less mobile nature of nitroxyl spin probe in liposomal solution. The partition parameter and permeability values indicate that the diffusion of nitroxyl spin probe distribution into the lipid phase is maximum at 2 mM concentration of MC-PROXYL. The dynamic nuclear polarization (DNP) parameters such as DNP factor, longitudinal relaxivity, saturation parameter, leakage factor and coupling factor were estimated for 2 mM MC-PROXYL in 400 mM liposomal dispersion. The spin lattice relaxation time was shortened in liposomal solution, which leads to the high relaxivity. Reduction in coupling factor is due to less interaction between the electron and nuclear spins, which causes the reduction in enhancement. The leakage factor increases with increasing agent concentration. The increase in DNP enhancement was significant up to 2 mM in liposomal solution. These results paves the way for choosing optimum agent concentration and OMRI scan parameters used in intra and extra membrane water by loading the liposome vesicles with a lipid permeable nitroxyl spin probes in OMRI experiments.

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.

Overhauser Geomagnetic Sensor Based on the Dynamic Nuclear Polarization Effect for Magnetic Prospecting

Based on the dynamic nuclear polarization (DNP) effect, an alternative design of an Overhauser geomagnetic sensor is presented that enhances the proton polarization and increases the amplitude of the free induction decay (FID) signal. The short-pulse method is adopted to rotate the enhanced proton magnetization into the plane of precession to create an FID signal. To reduce the negative effect of the powerful electromagnetic interference, the design of the anti-interference of the pick-up coil is studied. Furthermore, the radio frequency polarization method based on the capacitive-loaded coaxial cavity is proposed to improve the quality factor of the resonant circuit. In addition, a special test instrument is designed that enables the simultaneous testing of the classical proton precession and the Overhauser sensor. Overall, comparison experiments with and without the free radical of the Overhauser sensors show that the DNP effect does effectively improve the amplitude and quality of the FID signal, and the magnetic sensitivity, resolution and range reach to 10 pT/Hz 1 / 2 @1 Hz, 0.0023 nT and 20-100 μ T, respectively.