Near-unity nuclear polarization with an open-source 129Xe hyperpolarizer for NMR and MRI

The exquisite NMR spectral sensitivity and negligible reactivity of hyperpolarized xenon-129 (HP129Xe) make it attractive for a number of magnetic resonance applications; moreover, HP129Xe embodies an alternative to rare and nonrenewable 3He. However, the ability to reliably and inexpensively produce large quantities of HP129Xe with sufficiently high 129Xe nuclear spin polarization (PXe) remains a significant challenge—particularly at high Xe densities. We present results from our “open-source” large-scale (∼1 L/h) 129Xe polarizer for clinical, preclinical, and materials NMR and MRI research. Automated and composed mostly of off-the-shelf components, this “hyperpolarizer” is designed to be readily implementable in other laboratories. The device runs with high resonant photon flux (up to 200 W at the Rb D1 line) in the xenon-rich regime (up to 1,800 torr Xe in 500 cc) in either single-batch or stopped-flow mode, negating in part the usual requirement of Xe cryocollection. Excellent agreement is observed among four independent methods used to measure spin polarization. In-cell PXe values of ∼90%, ∼57%, ∼50%, and ∼30% have been measured for Xe loadings of ∼300, ∼500, ∼760, and ∼1,570 torr, respectively. PXe values of ∼41% and ∼28% (with ∼760 and ∼1,545 torr Xe loadings) have been measured after transfer to Tedlar bags and transport to a clinical 3 T scanner for MR imaging, including demonstration of lung MRI with a healthy human subject. Long “in-bag” 129Xe polarization decay times have been measured (T1 ∼38 min and ∼5.9 h at ∼1.5 mT and 3 T, respectively)—more than sufficient for a variety of applications

Batch-Mode Clinical-Scale Optical Hyperpolarization of Xenon-129 Using an Aluminum Jacket with Rapid Temperature Ramping

We present spin-exchange optical pumping (SEOP) using a third-generation (GEN-3) automated batch-mode clinical-scale 129Xe hyperpolarizer utilizing continuous high-power (∼170 W) pump laser irradiation and a novel aluminum jacket design for rapid temperature ramping of xenon-rich gas mixtures (up to 2 atm partial pressure). The aluminum jacket design is capable of heating SEOP cells from ambient temperature (typically 25 °C) to 70 °C (temperature of the SEOP process) in 4 min, and perform cooling of the cell to the temperature at which the hyperpolarized gas mixture can be released from the hyperpolarizer (with negligible amounts of Rb metal leaving the cell) in approximately 4 min, substantially faster (by a factor of 6) than previous hyperpolarizer designs relying on air heat exchange. These reductions in temperature cycling time will likely be highly advantageous for the overall increase of production rates of batch-mode (i.e., stopped-flow) 129Xe hyperpolarizers, which is particularly beneficial for clinical applications. The additional advantage of the presented design is significantly improved thermal management of the SEOP cell. Accompanying the heating jacket design and performance, we also evaluate the repeatability of SEOP experiments conducted using this new architecture, and present typically achievable hyperpolarization levels exceeding 40% at exponential build-up rates on the order of 0.1 min–1

High Xe density, high photon flux, stopped-flow spin-exchange optical pumping: Simulations versus experiments

© 2020 Elsevier Inc. Spin-exchange optical pumping (SEOP) can enhance the NMR sensitivity of noble gases by up to five orders of magnitude at Tesla-strength magnetic fields. SEOP-generated hyperpolarised (HP) 129Xe is a promising contrast agent for lung imaging but an ongoing barrier to widespread clinical usage has been economical production of sufficient quantities with high 129Xe polarisation. Here, the ‘standard model’ of SEOP, which was previously used in the optimisation of continuous-flow 129Xe polarisers, is modified for validation against two Xe-rich stopped-flow SEOP datasets. We use this model to examine ways to increase HP Xe production efficiency in stopped-flow 129Xe polarisers and provide further insight into the underlying physics of Xe-rich stopped-flow SEOP at high laser fluxes

A 3D-printed high power nuclear spin polarizer

[Image: see text] Three-dimensional printing with high-temperature plastic is used to enable spin exchange optical pumping (SEOP) and hyperpolarization of xenon-129 gas. The use of 3D printed structures increases the simplicity of integration of the following key components with a variable temperature SEOP probe: (i) in situ NMR circuit operating at 84 kHz (Larmor frequencies of (129)Xe and (1)H nuclear spins), (ii) <0.3 nm narrowed 200 W laser source, (iii) in situ high-resolution near-IR spectroscopy, (iv) thermoelectric temperature control, (v) retroreflection optics, and (vi) optomechanical alignment system. The rapid prototyping endowed by 3D printing dramatically reduces production time and expenses while allowing reproducibility and integration of “off-the-shelf” components and enables the concept of printing on demand. The utility of this SEOP setup is demonstrated here to obtain near-unity (129)Xe polarization values in a 0.5 L optical pumping cell, including ~74 ± 7% at 1000 Torr xenon partial pressure, a record value at such high Xe density. Values for the (129)Xe polarization exponential build-up rate [(3.63 ± 0.15) × 10(−2) min(−1)] and in-cell (129)Xe spin−lattice relaxation time (T(1) = 2.19 ± 0.06 h) for 1000 Torr Xe were in excellent agreement with the ratio of the gas-phase polarizations for (129)Xe and Rb (P(Rb) ~ 96%). Hyperpolarization-enhanced (129)Xe gas imaging was demonstrated with a spherical phantom following automated gas transfer from the polarizer. Taken together, these results support the development of a wide range of chemical, biochemical, material science, and biomedical applications

XeNA: an automated ‘open-source’ 129Xe hyperpolarizer for clinical use

Here we provide a full report on the construction, components, and capabilities of our consortium’s “open-source” large-scale (~ 1 L/h) 129Xe hyperpolarizer for clinical, pre-clinical, and materials NMR/MRI (Nikolaou et al., Proc. Natl. Acad. Sci. USA, 110, 14150 (2013)). The ‘hyperpolarizer’ is automated and built mostly of off-the-shelf components; moreover, it is designed to be cost-effective and installed in both research laboratories and clinical settings with materials costing less than $125,000. The device runs in the xenon-rich regime (up to 1800 Torr Xe in 0.5 L) in either stopped-flow or single-batch mode—making cryo-collection of the hyperpolarized gas unnecessary for many applications. In-cell 129Xe nuclear spin polarization values of ~ 30%–90% have been measured for Xe loadings of ~ 300–1600 Torr. Typical 129Xe polarization build-up and T1 relaxation time constants were ~ 8.5 min and ~ 1.9 h respectively under our spin-exchange optical pumping conditions; such ratios, combined with near-unity Rb electron spin polarizations enabled by the high resonant laser power (up to ~ 200 W), permit such high PXe values to be achieved despite the high in-cell Xe densities. Importantly, most of the polarization is maintained during efficient HP gas transfer to other containers, and ultra-long 129Xe relaxation times (up to nearly 6 h) were observed in Tedlar bags following transport to a clinical 3 T scanner for MR spectroscopy and imaging as a prelude to in vivo experiments. The device has received FDA IND approval for a clinical study of chronic obstructive pulmonary disease subjects. The primary focus of this paper is on the technical/engineering development of the polarizer, with the explicit goals of facilitating the adaptation of design features and operative modes into other laboratories, and of spurring the further advancement of HP-gas MR applications in biomedicine

Direct Reprogramming of Mouse Fibroblasts into Functional Skeletal Muscle Progenitors

Summary Skeletal muscle harbors quiescent stem cells termed satellite cells and proliferative progenitors termed myoblasts, which play pivotal roles during muscle regeneration. However, current technology does not allow permanent capture of these cell populations in vitro. Here, we show that ectopic expression of the myogenic transcription factor MyoD, combined with exposure to small molecules, reprograms mouse fibroblasts into expandable induced myogenic progenitor cells (iMPCs). iMPCs express key skeletal muscle stem and progenitor cell markers including Pax7 and Myf5 and give rise to dystrophin-expressing myofibers upon transplantation in vivo. Notably, a subset of transplanted iMPCs maintain Pax7 expression and sustain serial regenerative responses. Similar to satellite cells, iMPCs originate from Pax7+ cells and require Pax7 itself for maintenance. Finally, we show that myogenic progenitor cell lines can be established from muscle tissue following small-molecule exposure alone. This study thus reports on a robust approach to derive expandable myogenic stem/progenitor-like cells from multiple cell types

Temperature-ramped 129Xe spin-exchange optical pumping

We describe temperature-ramped spin-exchange optical pumping (TR-SEOP) in an automated high-throughput batch-mode 129Xe hyperpolarizer utilizing three key temperature regimes: (i) “hot”where the 129Xe hyperpolarization rate is maximal, (ii) “warm”-where the 129Xe hyperpolarization approaches unity, and (iii) “cool” where hyperpolarized 129Xe gas is transferred into a Tedlar bag with low Rb content (<5 ng per ∼1 L dose) suitable for human imaging applications. Unlike with the conventional approach of batch-mode SEOP, here all three temperature regimes may be operated under continuous high-power (170 W) laser irradiation, and hyperpolarized 129Xe gas is delivered without the need for a cryocollection step. The variable-temperature approach increased the SEOP rate by more than 2-fold compared to the constant-temperature polarization rate (e.g., giving effective values for the exponential buildup constant γSEOP of 62.5 ± 3.7 × 10−3 min−1 vs 29.9 ± 1.2 × 10−3 min−1) while achieving nearly the same maximum %PXe value (88.0 ± 0.8% vs 90.1% ± 0.8%, for a 500 Torr (67 kPa) Xe cell loadingcorresponding to nuclear magnetic resonance/magnetic resonance imaging (NMR/MRI) enhancements of ∼3.1 × 105 and ∼2.32 × 108 at the relevant fields for clinical imaging and HP 129Xe production of 3 T and 4 mT, respectively); moreover, the intercycle “dead” time was also significantly decreased. The higher-throughput TR-SEOP approach can be implemented without sacrificing the level of 129Xe hyperpolarization or the experimental stability for automation-making this approach beneficial for improving the overall 129Xe production rate in clinical settings

Low-Load High Volume Resistance Exercise Stimulates Muscle Protein Synthesis More Than High-Load Low Volume Resistance Exercise in Young Men

BACKGROUND: We aimed to determine the effect of resistance exercise intensity (%1 repetition maximum-1RM) and volume on muscle protein synthesis, anabolic signaling, and myogenic gene expression. METHODOLOGY/PRINCIPAL FINDINGS: Fifteen men (21+/-1 years; BMI=24.1+/-0.8 kg/m2) performed 4 sets of unilateral leg extension exercise at different exercise loads and/or volumes: 90% of repetition maximum (1RM) until volitional failure (90FAIL), 30% 1RM work-matched to 90%FAIL (30WM), or 30% 1RM performed until volitional failure (30FAIL). Infusion of [ring-13C6] phenylalanine with biopsies was used to measure rates of mixed (MIX), myofibrillar (MYO), and sarcoplasmic (SARC) protein synthesis at rest, and 4 h and 24 h after exercise. Exercise at 30WM induced a significant increase above rest in MIX (121%) and MYO (87%) protein synthesis at 4 h post-exercise and but at 24 h in the MIX only. The increase in the rate of protein synthesis in MIX and MYO at 4 h post-exercise with 90FAIL and 30FAIL was greater than 30WM, with no difference between these conditions; however, MYO remained elevated (199%) above rest at 24 h only in 30FAIL. There was a significant increase in AktSer473 at 24h in all conditions (P=0.023) and mTORSer2448 phosphorylation at 4 h post-exercise (P=0.025). Phosporylation of Erk1/2Tyr202/204, p70S6KThr389, and 4E-BP1Thr37/46 increased significantly (P<0.05) only in the 30FAIL condition at 4 h post-exercise, whereas, 4E-BP1Thr37/46 phosphorylation was greater 24 h after exercise than at rest in both 90FAIL (237%) and 30FAIL (312%) conditions. Pax7 mRNA expression increased at 24 h post-exercise (P=0.02) regardless of condition. The mRNA expression of MyoD and myogenin were consistently elevated in the 30FAIL condition. CONCLUSIONS/SIGNIFICANCE: These results suggest that low-load high volume resistance exercise is more effective in inducing acute muscle anabolism than high-load low volume or work matched resistance exercise modes