A molecular-mechanical link in shear-induced self-assembly of a functionalized biopolymeric fluid.

23Na multiple quantum filtered (MQF) rheo-NMR methods were applied to probe the molecular foundation for flow induced self-assembly in 0.5% κ-carrageenan fluid. This method is sensitive enough to utilize an endogenous sodium ion concentration of approximately 0.02%. Rheo-NMR experiments were conducted at different temperatures and shear rates to explore varying molecular dynamics of the biopolymer in the fluid under shear. The temperature in the rheo-NMR experiments was changes from 288 K to 313 K to capture transition of κ-carrageenan molecules from helices to coils. At each temperature, the fluid was also tested for flow and oscillatory shear behaviour using bulk rheometry methods. It was found that the 23Na MQF signals were observed for the 0.5% κ-carrageenan solution only under shear and when the fluid demonstrated yielding and/or shear-thinning behaviour. At temperatures of 303 K and above, no 23Na MQF signals were observed independent of the presence or absence of shear as the molecular phase transition to random coils occurs and the fluid becomes Newtonian.

Novel perspectives of sodium handling in type 2 diabetes mellitus.

INTRODUCTION: As a key regulator of body water, sodium homeostasis forms an essential component of human physiology. Type 2 Diabetes Mellitus (T2D)-associated sodium overload stems from chronic renal retention of sodium, contributing toward the development of adverse cardiovascular sequelae. AREAS COVERED: Our traditional model of sodium regulation invokes two compartments: extracellular fluid (ECF [plasma and interstitial fluid]) and intracellular fluid (ICF). Data from the Mars program reveal inconsistencies with this two-space model, including mismatches between net body sodium and water. Recent data utilizing 23Na magnetic resonance imaging (MRI) show a preponderance of bound sodium within human dermis, consistent with a third space repository and providing compelling evidence to support a three-space model in which dermal sodium binding facilitates sodium homeostasis within the ECF and ICF. This buffer is impaired in T2D, with diminishment of dermal bound sodium that may promote deleterious sequelae of sodium overload within the ECF and ICF. EXPERT OPINION: Future studies should focus on novel therapeutic opportunities for sodium regulation in T2D and other conditions of sodium dysregulation. The ratio of free:bound dermal sodium (reflecting sodium storage capacity) could be utilized as a clinical biomarker for salt and water balance, to improve diagnostic accuracy and facilitate clinical decision-making.

Matrix-Bound Growth Factors are Released upon Cartilage Compression by an Aggrecan-Dependent Sodium Flux that is Lost in Osteoarthritis.

Articular cartilage is a dense extracellular matrix-rich tissue that degrades following chronic mechanical stress, resulting in osteoarthritis (OA). The tissue has low intrinsic repair especially in aged and osteoarthritic joints. Here, we describe three pro-regenerative factors; fibroblast growth factor 2 (FGF2), connective tissue growth factor, bound to transforming growth factor-beta (CTGF-TGFß), and hepatoma-derived growth factor (HDGF), that are rapidly released from the pericellular matrix (PCM) of articular cartilage upon mechanical injury. All three growth factors bound heparan sulfate, and were displaced by exogenous NaCl. We hypothesised that sodium, sequestered within the aggrecan-rich matrix, was freed by injurious compression, thereby enhancing the bioavailability of pericellular growth factors. Indeed, growth factor release was abrogated when cartilage aggrecan was depleted by IL-1 treatment, and in severely damaged human osteoarthritic cartilage. A flux in free matrix sodium upon mechanical compression of cartilage was visualised by 23Na -MRI just below the articular surface. This corresponded to a region of reduced tissue stiffness, measured by scanning acoustic microscopy and second harmonic generation microscopy, and where Smad2/3 was phosphorylated upon cyclic compression. Our results describe a novel intrinsic repair mechanism, controlled by matrix stiffness and mediated by the free sodium concentration, in which heparan sulfate-bound growth factors are released from cartilage upon injurious load. They identify aggrecan as a depot for sequestered sodium, explaining why osteoarthritic tissue loses its ability to repair. Treatments that restore matrix sodium to allow appropriate release of growth factors upon load are predicted to enable intrinsic cartilage repair in OA. SIGNIFICANCE STATEMENT: Osteoarthritis is the most prevalent musculoskeletal disease, affecting 250 million people worldwide.1 We identify a novel intrinsic repair response in cartilage, mediated by aggrecan-dependent sodium flux, and dependent upon matrix stiffness, which results in the release of a cocktail of pro-regenerative growth factors after injury. Loss of aggrecan in late-stage osteoarthritis prevents growth factor release and likely contributes to disease progression. Treatments that restore matrix sodium in osteoarthritis may recover the intrinsic repair response to improve disease outcome.

Sodium in the dermis colocates to glycosaminoglycan scaffold, with diminishment in type 2 diabetes mellitus.

BACKGROUND: Dietary sodium intake mismatches urinary sodium excretion over prolonged periods. Our aims were to localize and quantify electrostatically bound sodium within human skin using triple-quantum-filtered (TQF) protocols for MRI and magnetic resonance spectroscopy (MRS) and to explore dermal sodium in type 2 diabetes mellitus (T2D). METHODS: We recruited adult participants with T2D (n = 9) and euglycemic participants with no history of diabetes mellitus (n = 8). All had undergone lower limb amputations or abdominal skin reduction surgery for clinical purposes. We used 20 µm in-plane resolution 1H MRI to visualize anatomical skin regions ex vivo from skin biopsies taken intraoperatively, 23Na TQF MRI/MRS to explore distribution and quantification of freely dissolved and bound sodium, and inductively coupled plasma mass spectrometry to quantify sodium in selected skin samples. RESULTS: Human dermis has a preponderance (>90%) of bound sodium that colocalizes with the glycosaminoglycan (GAG) scaffold. Bound and free sodium have similar anatomical locations. T2D associates with a severely reduced dermal bound sodium capacity. CONCLUSION: We provide the first evidence to our knowledge for high levels of bound sodium within human dermis, colocating to the GAG scaffold, consistent with a dermal "third space repository" for sodium. T2D associates with diminished dermal electrostatic binding capacity for sodium.

Imaging Sodium Dendrite Growth in All-Solid-State Sodium Batteries Using 23 Na T2 -Weighted Magnetic Resonance Imaging.

Two-dimensional, Knight-shifted, T2 -contrasted 23 Na magnetic resonance imaging (MRI) of an all-solid-state cell with a Na electrode and a ceramic electrolyte is employed to directly observe Na microstructural growth. A spalling dendritic morphology is observed and confirmed by more conventional post-mortem analysis; X-ray tomography and scanning electron microscopy. A significantly larger 23 Na T2 for the dendritic growth, compared with the bulk metal electrode, is attributed to increased sodium ion mobility in the dendrite. 23 Na T2 -contrast MRI of metallic sodium offers a clear, routine method for observing and isolating microstructural growths and can supplement the current suite of techniques utilised to analyse dendritic growth in all-solid-state cells.

Imaging Sodium Dendrite Growth in All-Solid-State Sodium Batteries Using 23Na T2-Weighted Magnetic Resonance Imaging.

Two-dimensional, Knight-shifted, T 2-contrasted 23Na magnetic resonance imaging (MRI) of an all-solid-state cell with a Na electrode and a ceramic electrolyte is employed to directly observe Na microstructural growth. A spalling dendritic morphology is observed and confirmed by more conventional post-mortem analysis; X-ray tomography and scanning electron microscopy. A significantly larger 23Na T 2 for the dendritic growth, compared with the bulk metal electrode, is attributed to increased sodium ion mobility in the dendrite. 23Na T 2-contrast MRI of metallic sodium offers a clear, routine method for observing and isolating microstructural growths and can supplement the current suite of techniques utilised to analyse dendritic growth in all-solid-state cells.

Operando visualisation of battery chemistry in a sodium-ion battery by 23Na magnetic resonance imaging.

Sodium-ion batteries are a promising battery technology for their cost and sustainability. This has led to increasing interest in the development of new sodium-ion batteries and new analytical methods to non-invasively, directly visualise battery chemistry. Here we report operando 1H and 23Na nuclear magnetic resonance spectroscopy and imaging experiments to observe the speciation and distribution of sodium in the electrode and electrolyte during sodiation and desodiation of hard carbon in a sodium metal cell and a sodium-ion full-cell configuration. The evolution of the hard carbon sodiation and subsequent formation and evolution of sodium dendrites, upon over-sodiation of the hard carbon, are observed and mapped by 23Na nuclear magnetic resonance spectroscopy and imaging, and their three-dimensional microstructure visualised by 1H magnetic resonance imaging. We also observe, for the first time, the formation of metallic sodium species on hard carbon upon first charge (formation) in a full-cell configuration.

Accelerated 19F·MRI Detection of Matrix Metalloproteinase-2/-9 through Responsive Deactivation of Paramagnetic Relaxation Enhancement.

Paramagnetic gadolinium ions (GdIII), complexed within DOTA-based chelates, have become useful tools to increase the magnetic resonance imaging (MRI) contrast in tissues of interest. Recently, "on/off" probes serving as 19F·MRI biosensors for target enzymes have emerged that utilize the increase in transverse (T 2 ∗ or T 2) relaxation times upon cleavage of the paramagnetic GdIII centre. Molecular 19F·MRI has the advantage of high specificity due to the lack of background signal but suffers from low signal intensity that leads to low spatial resolution and long recording times. In this work, an "on/off" probe concept is introduced that utilizes responsive deactivation of paramagnetic relaxation enhancement (PRE) to generate 19F longitudinal (T 1) relaxation contrast for accelerated molecular MRI. The probe concept is applied to matrix metalloproteinases (MMPs), a class of enzymes linked with many inflammatory diseases and cancer that modify bioactive extracellular substrates. The presence of these biomarkers in extracellular space makes MMPs an accessible target for responsive PRE deactivation probes. Responsive PRE deactivation in a 19F biosensor probe, selective for MMP-2 and MMP-9, is shown to enable molecular MRI contrast at significantly reduced experimental times compared to previous methods. PRE deactivation was caused by MMP through cleavage of a protease substrate that served as a linker between the fluorine-containing moiety and a paramagnetic GdIII-bound DOTA complex. Ultrashort echo time (UTE) MRI and, alternatively, short echo times in standard gradient echo (GE) MRI were employed to cope with the fast 19F transverse relaxation of the PRE active probe in its "on-state." Upon responsive PRE deactivation, the 19F·MRI signal from the "off-state" probe diminished, thereby indicating the presence of the target enzyme through the associated negative MRI contrast. Null point 1H·MRI, obtainable within a short time course, was employed to identify false-positive 19F·MRI responses caused by dilution of the contrast agent.

Probe-Specific Procedure to Estimate Sensitivity and Detection Limits for 19F Magnetic Resonance Imaging.

Due to low fluorine background signal in vivo, 19F is a good marker to study the fate of exogenous molecules by magnetic resonance imaging (MRI) using equilibrium nuclear spin polarization schemes. Since 19F MRI applications require high sensitivity, it can be important to assess experimental feasibility during the design stage already by estimating the minimum detectable fluorine concentration. Here we propose a simple method for the calibration of MRI hardware, providing sensitivity estimates for a given scanner and coil configuration. An experimental "calibration factor" to account for variations in coil configuration and hardware set-up is specified. Once it has been determined in a calibration experiment, the sensitivity of an experiment or, alternatively, the minimum number of required spins or the minimum marker concentration can be estimated without the need for a pilot experiment. The definition of this calibration factor is derived based on standard equations for the sensitivity in magnetic resonance, yet the method is not restricted by the limited validity of these equations, since additional instrument-dependent factors are implicitly included during calibration. The method is demonstrated using MR spectroscopy and imaging experiments with different 19F samples, both paramagnetically and susceptibility broadened, to approximate a range of realistic environments.

Molecular hydrogen and catalytic combustion in the production of hyperpolarized 83Kr and 129Xe MRI contrast agents.

Hyperpolarized (hp) (83)Kr is a promising MRI contrast agent for the diagnosis of pulmonary diseases affecting the surface of the respiratory zone. However, the distinct physical properties of (83)Kr that enable unique MRI contrast also complicate the production of hp (83)Kr. This work presents a previously unexplored approach in the generation of hp (83)Kr that can likewise be used for the production of hp (129)Xe. Molecular nitrogen, typically used as buffer gas in spin-exchange optical pumping (SEOP), was replaced by molecular hydrogen without penalty for the achievable hyperpolarization. In this particular study, the highest obtained nuclear spin polarizations were P =29% for(83)Kr and P= 63% for (129)Xe. The results were reproduced over many SEOP cycles despite the laser-induced on-resonance formation of rubidium hydride (RbH). Following SEOP, the H2 was reactively removed via catalytic combustion without measurable losses in hyperpolarized spin state of either (83)Kr or (129)Xe. Highly spin-polarized (83)Kr can now be purified for the first time, to our knowledge, to provide high signal intensity for the advancement of in vivo hp (83)Kr MRI. More generally, a chemical reaction appears as a viable alternative to the cryogenic separation process, the primary purification method of hp(129)Xe for the past 2 1/2 decades. The inherent simplicity of the combustion process will facilitate hp (129)Xe production and should allow for on-demand continuous flow of purified and highly spin-polarized (129)Xe.

Molecular Sensing with Hyperpolarized (129) Xe Using Switchable Chemical Exchange Relaxation Transfer.

An approach for hyperpolarized (129) Xe molecular sensors is explored using paramagnetic relaxation agents that can be deactivated upon chemical or enzymatic reaction with an analyte. Cryptophane encapsulated (129) Xe within the vicinity of the paramagnetic center experiences fast relaxation that, through chemical exchange of xenon atoms between cage and solvent pool, causes accelerated hyperpolarized (129) Xe signal decay in the dissolved phase. In this proof-of-concept work, the relaxivity of Gadolinium(III) -DOTA on (129) Xe in the solvent was increased eightfold through tethering of the paramagnetic molecule to a cryptophane cage. This potent relaxation agent can be 'turned off' specifically for (129) Xe through chemical reactions that spatially separate the Gd(III) centre from the attached cryptophane cage. Unlike (129) Xe chemical shift based sensors, the new concept does not require high spectral resolution and may lead to a new generation of responsive contrast agents for molecular MRI.

Hyperpolarized 83Kr magnetic resonance imaging of alveolar degradation in a rat model of emphysema.

Hyperpolarized (83)Kr surface quadrupolar relaxation (SQUARE) generates MRI contrast that was previously shown to correlate with surface-to-volume ratios in porous model surface systems. The underlying physics of SQUARE contrast is conceptually different from any other current MRI methodology as the method uses the nuclear electric properties of the spin I = 9/2 isotope (83)Kr. To explore the usage of this non-radioactive isotope for pulmonary pathophysiology, MRI SQUARE contrast was acquired in excised rat lungs obtained from an elastase-induced model of emphysema. A significant (83)Kr T1 relaxation time increase in the SQUARE contrast was found in the elastase-treated lungs compared with the baseline data from control lungs. The SQUARE contrast suggests a reduction in pulmonary surface-to-volume ratio in the emphysema model that was validated by histology. The finding supports usage of (83)Kr SQUARE as a new biomarker for surface-to-volume ratio changes in emphysema.

Spatial Mapping of Flow-Induced Molecular Alignment in a Noncrystalline Biopolymer Fluid Using Double Quantum Filtered (DQF) (23)Na MRI.

Flow-induced molecular alignment was observed experimentally in a non-liquid-crystalline bioplymeric fluid during developed tubular flow. The fluid was comprised of rigid rods of the polysaccharide xanthan and exhibited shear-thinning behavior. Without a requirement for optical transparency or the need for an added tracer, (23)Na magic angle (MA) double quantum filtered (DQF) magnetic resonance imaging (MRI) enabled the mapping of the anisotropic molecular arrangement under flow conditions. A regional net molecular alignment was found in areas of high shear values in the vicinity of the tube wall. Furthermore, the xanthan molecules resumed random orientations after the cessation of flow. The observed flow-induced molecular alignment was correlated with the rheological properties of the fluid. The work demonstrates the ability of (23)Na MA DQF magnetic resonance to provide a valuable molecular-mechanical link.

Pulmonary MRI contrast using Surface Quadrupolar Relaxation (SQUARE) of hyperpolarized (83)Kr.

Hyperpolarized (83)Kr has previously been demonstrated to enable MRI contrast that is sensitive to the chemical composition of the surface in a porous model system. Methodological advances have lead to a substantial increase in the (83)Kr hyperpolarization and the resulting signal intensity. Using the improved methodology for spin exchange optical pumping of isotopically enriched (83)Kr, internal anatomical details of ex vivo rodent lung were resolved with hyperpolarized (83)Kr MRI after krypton inhalation. Different (83)Kr relaxation times were found between the main bronchi and the parenchymal regions in ex vivo rat lungs. The T1 weighted hyperpolarized (83)Kr MRI provided a first demonstration of surface quadrupolar relaxation (SQUARE) pulmonary MRI contrast.

Cryogenics free production of hyperpolarized 129Xe and 83Kr for biomedical MRI applications.

As an alternative to cryogenic gas handling, hyperpolarized (hp) gas mixtures were extracted directly from the spin exchange optical pumping (SEOP) process through expansion followed by compression to ambient pressure for biomedical MRI applications. The omission of cryogenic gas separation generally requires the usage of high xenon or krypton concentrations at low SEOP gas pressures to generate hp (129)Xe or hp (83)Kr with sufficient MR signal intensity for imaging applications. Two different extraction schemes for the hp gasses were explored with focus on the preservation of the nuclear spin polarization. It was found that an extraction scheme based on an inflatable, pressure controlled balloon is sufficient for hp (129)Xe handling, while (83)Kr can efficiently be extracted through a single cycle piston pump. The extraction methods were tested for ex vivo MRI applications with excised rat lungs. Precise mixing of the hp gases with oxygen, which may be of interest for potential in vivo applications, was accomplished during the extraction process using a piston pump. The (83)Kr bulk gas phase T1 relaxation in the mixtures containing more than approximately 1% O2 was found to be slower than that of (129)Xe in corresponding mixtures. The experimental setup also facilitated (129)Xe T1 relaxation measurements as a function of O2 concentration within excised lungs.

Validating excised rodent lungs for functional hyperpolarized xenon-129 MRI.

Ex vivo rodent lung models are explored for physiological measurements of respiratory function with hyperpolarized (hp) (129)Xe MRI. It is shown that excised lung models allow for simplification of the technical challenges involved and provide valuable physiological insights that are not feasible using in vivo MRI protocols. A custom designed breathing apparatus enables MR images of gas distribution on increasing ventilation volumes of actively inhaled hp (129)Xe. Straightforward hp (129)Xe MRI protocols provide residual lung volume (RV) data and permit for spatially resolved tracking of small hp (129)Xe probe volumes during the inhalation cycle. Hp (129)Xe MRI of lung function in the excised organ demonstrates the persistence of post mortem airway responsiveness to intravenous methacholine challenges. The presented methodology enables physiology of lung function in health and disease without additional regulatory approval requirements and reduces the technical and logistical challenges with hp gas MRI experiments. The post mortem lung functional data can augment histological measurements and should be of interest for drug development studies.

Perspectives of hyperpolarized noble gas MRI beyond 3He.

Nuclear Magnetic Resonance (NMR) studies with hyperpolarized (hp) noble gases are at an exciting interface between physics, chemistry, materials science and biomedical sciences. This paper intends to provide a brief overview and outlook of magnetic resonance imaging (MRI) with hp noble gases other than hp (3)He. A particular focus are the many intriguing experiments with (129)Xe, some of which have already matured to useful MRI protocols, while others display high potential for future MRI applications. Quite naturally for MRI applications the major usage so far has been for biomedical research but perspectives for engineering and materials science studies are also provided. In addition, the prospects for surface sensitive contrast with hp (83)Kr MRI is discussed.

Combustion resistance of the 129Xe hyperpolarized nuclear spin state.

Using a methane-xenon mixture for spin exchange optical pumping, MRI of combustion was enabled. The (129)Xe hyperpolarized nuclear spin state was found to sufficiently survive the complete passage through the harsh environment of the reaction zone. A velocity profile (V(z)(z)) of a flame was recorded to demonstrate the feasibility of MRI velocimetry of transport processes in combustors.

Pathway to cryogen free production of hyperpolarized Krypton-83 and Xenon-129.

Hyperpolarized (hp) (129)Xe and hp (83)Kr for magnetic resonance imaging (MRI) are typically obtained through spin-exchange optical pumping (SEOP) in gas mixtures with dilute concentrations of the respective noble gas. The usage of dilute noble gases mixtures requires cryogenic gas separation after SEOP, a step that makes clinical and preclinical applications of hp (129)Xe MRI cumbersome. For hp (83)Kr MRI, cryogenic concentration is not practical due to depolarization that is caused by quadrupolar relaxation in the condensed phase. In this work, the concept of stopped flow SEOP with concentrated noble gas mixtures at low pressures was explored using a laser with 23.3 W of output power and 0.25 nm linewidth. For (129)Xe SEOP without cryogenic separation, the highest obtained MR signal intensity from the hp xenon-nitrogen gas mixture was equivalent to that arising from 15.5±1.9% spin polarized (129)Xe in pure xenon gas. The production rate of the hp gas mixture, measured at 298 K, was 1.8 cm(3)/min. For hp (83)Kr, the equivalent of 4.4±0.5% spin polarization in pure krypton at a production rate of 2 cm(3)/min was produced. The general dependency of spin polarization upon gas pressure obtained in stopped flow SEOP is reported for various noble gas concentrations. Aspects of SEOP specific to the two noble gas isotopes are discussed and compared with current theoretical opinions. A non-linear pressure broadening of the Rb D(1) transition was observed and taken into account for the qualitative description of the SEOP process.

Hyperpolarized (131)Xe NMR spectroscopy.

Hyperpolarized (hp) (131)Xe with up to 2.2% spin polarization (i.e., 5000-fold signal enhancement at 9.4 T) was obtained after separation from the rubidium vapor of the spin-exchange optical pumping (SEOP) process. The SEOP was applied for several minutes in a stopped-flow mode, and the fast, quadrupolar-driven T(1) relaxation of this spin I = 3/2 noble gas isotope required a rapid subsequent rubidium removal and swift transfer into the high magnetic field region for NMR detection. Because of the xenon density dependent (131)Xe quadrupolar relaxation in the gas phase, the SEOP polarization build-up exhibits an even more pronounced dependence on xenon partial pressure than that observed in (129)Xe SEOP. (131)Xe is the only stable noble gas isotope with a positive gyromagnetic ratio and shows therefore a different relative phase between hp signal and thermal signal compared to all other noble gases. The gas phase (131)Xe NMR spectrum displays a surface and magnetic field dependent quadrupolar splitting that was found to have additional gas pressure and gas composition dependence. The splitting was reduced by the presence of water vapor that presumably influences xenon-surface interactions. The hp (131)Xe spectrum shows differential line broadening, suggesting the presence of strong adsorption sites. Beyond hp (131)Xe NMR spectroscopy studies, a general equation for the high temperature, thermal spin polarization, P, for spin I ≥ 1/2 nuclei is presented.