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. 2026 Mar 17;148(12):12990–12997. doi: 10.1021/jacs.5c21753

Kupffer Cell Capture-Evading Modifiable Sub-20 nm Lipid Nanodisc-Based 19F Magnetic Resonance Imaging Probes

Kodai Fukushima †, Tomoya Yamamoto †,‡,§, Kazuya Kikuchi †,§,*
PMCID: PMC13047669  PMID: 41840854

Abstract

19F magnetic resonance imaging (MRI) is an innovative imaging method that enables sensitive visualization of 19F-containing probes and has been applied to biomedical imaging. A key strategy in probe design is incorporation of a large number of highly mobile 19F nuclei that can enhance the MRI signal intensity. However, conventional emulsion-based probes are difficult to reduce to below 80 nm in diameter, making them prone to uptake by Kupffer cells and resulting in poor delivery efficiency to target tissues. Moreover, smaller probes based on nanocrystals or polymers suffer from low 19F mobility, leading to weak signal intensity. In this study, we utilized lipid nanodiscs to confine highly mobile 19F-labeled lipids, developing sub-20 nm 19F MRI probes with diameters of approximately 10 nm. The resulting probes exhibited a unique behavior in vivo, distinct from that of conventional probes: they avoided Kupffer cell uptake and were excreted via kidneys. MR signals remained detectable after surface modification. PEGylated nanodiscs exhibited a slower accumulation in the bladder compared with unmodified counterparts, likely due to their prolonged circulation time induced by PEG modification. With the potential to reach tissues previously inaccessible and be modified with various functional moieties, our nanodisc-based platform offers broad opportunities for biomedical applications, including visualization of diverse organs and monitoring of biochemical reactions in vivo.

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Introduction

19F magnetic resonance (19F MRI) has recently been attracting attention as a method to monitor the location of probes containing 19F nuclei administered in vivo. − Due to its second highest gyromagnetic ratio after 1H, the 19F nuclei yield strong magnetic resonance signals with negligible background in biological systems. These advantageous characteristics allow the localization of 19F-based probes with high imaging contrast. As a result, 19F MRI has been widely employed in various biomedical imaging applications, including targeted probe delivery and in vivo cell tracking. − Furthermore, 19F MRI probes have been developed that can be switched on by specific enzymatic or biomarker-triggered cleavage of paramagnetic metals in vivo, − enabling estimation of the enzyme or biomarker concentrations and their spatiotemporal activities.

In the design of 19F MRI probes, it is desirable to incorporate a high number of 19F nuclei into particles to increase the local concentration of the nuclei, while ensuring that these nuclei retain high mobility to provide long T 2 relaxation times. To meet these requirements, several types of probes have been developed, including nanoemulsion-based probes, ,, silica nanoparticle probes, − ,, and polymer-coated probes (Figure a). In these probes, liquid perfluorocarbons are encapsulated, allowing the 19F nuclei to retain high mobility. Moreover, these nanoparticle-based probes can be readily functionalized with targeting ligands or enzyme-responsive moieties. This enables control over the relaxation times of the abundant 19F nuclei at the introduced sites as well as their delivery efficiency. On the other hand, these probes typically have diameters of at least 80 nm, which promotes Kupffer cell uptake and hinders efficient delivery to targeted tissues. , Nanocrystal- − and fluorinated polymer-based , probes have been explored to overcome the size issue (Figure b). While they can be as small as approximately 10 nm, they suffer from weak signals due to low-fluorine mobility and offer limited flexibility for surface modification. Previous studies have also reported that nanoparticles stabilized with rigid materials such as silica tend to be sequestered in the liver and accumulate over a long period of time. ,, Therefore, an ideal 19F MRI probe would be composed of soft materials that allow the formation of small particles (10–20 nm in diameter) while maintaining high mobility of the internal 19F nuclei.

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Schematic illustration of (a) 19F MRI probes with encapsulated perfluorocarbon. (b) 19F MRI probes with smaller size. (c) Nanodisc-based 19F MRI probes developed in the current work.

In this study, we designed and developed a novel sub-20 nm 19F MRI probe based on lipid nanodiscs that satisfy the above requirements for small size and high 19F nuclear mobility (Figure c). Lipid nanodiscs are nanoparticles with 10–20 nm in diameter where phospholipid bilayers are solubilized into a discoidal structure by amphiphilic polymers or proteins. − In addition to their use in structural studies of membrane proteins, they have recently been applied to in vivo imaging and drug delivery. − An important feature of lipid nanodiscs is that, similar to intrinsic dynamic properties of phospholipid bilayers, phospholipids exhibit lateral diffusion, thereby maintaining high molecular mobility. , Thus, the use of 19F-labeled phospholipids to construct nanodiscs allows the fabrication of nanoparticles with diameters of 10–20 nm that maintain high internal 19F nuclear mobility. Such nanostructures represent a novel class of sub-20 nm, soft-material-based 19F MRI probe. Intravenous administration of this nanodisc-based probe into mice resulted in renal excretion, thereby confirming the development of a nanoparticle-based 19F MRI probe that circulates in the bloodstream while avoiding significant Kupffer cell uptake. Furthermore, by incorporating PEG-modified phospholipids as modified components, we demonstrated that these nanodiscs can be surface-functionalized readily.

Results and Discussion

The Design and Preparation of 19F-Labeled Nanodiscs

To develop a sub-20 nm 19F MRI probe, we conceived the use of lipid nanodiscs as the phospholipid can undergo lateral diffusion and thus maintain high mobility of the lipid content. For this purpose, we designed C13–F6PC as the fluorinated phospholipid to be incorporated into the nanodiscs. In this design, we selected C13:0 fatty acid because they are similar in length to 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC; C14:0), the most commonly used lipid in nanodiscs that exhibit high mobility and high stability at physiological temperature. To increase the number of 19F nuclei with equivalent chemical shift, a CF3 group was incorporated at the terminal position of the fatty acid chain. The synthesis of C13–F6PC was accomplished in three steps, starting from a commercially available alkenyl alcohol to obtain the fluorinated fatty acid, which was then condensed with glycero-3-phosphocholine to yield target phospholipid (Scheme ). For the amphiphilic polymer for nanodisc formation, we selected styrene-maleic acid (SMA) copolymer which is widely utilized for solubilizing phospholipid bilayer into disc-shaped nanodiscs. ,

1. Synthetic Route to the Fluorinated Phospholipid C13–F6PC .

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The preparation of 19F-labeled nanodiscs was achieved through a two-step process: formation of 19F-labeled liposomes followed by nanodisc assembly. Hydration of lipid membranes composed of 19F-labeled phospholipids yielded stable liposomes, which were spontaneously converted into 19F-labeled nanodiscs upon mixing with SMA copolymer and stirring at 37 °C for 1 h. SMA copolymer, consisting of hydrophobic styrene and hydrophilic maleic acid residues, effectively solubilizes lipid bilayers by embedding its styrene groups into the hydrophobic acyl chains and exposing its maleic acid groups to the aqueous phase (Figure a). This amphiphilic interaction stabilizes the bilayer fragments, thereby enabling the formation of nanodiscs. The 19F-labeled nanodiscs were purified by gel permeation chromatography (GPC), which effectively removed residual polymers (Figure S1). Quantification of the incorporated phospholipids revealed that approximately 80% of the 19F-labeled phospholipids were successfully assembled into nanodiscs (Table S1).

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Preparation and characterization of nanodisc-based 19F MRI probes. (a) Schematic illustration of the preparation process. (b) Transmission electron microscopy image, (c) dynamic light scattering profile, and (d) 19F NMR spectrum of the 19F-labeled nanodiscs. Nanodiscs were prepared at a lipid/SMA polymer ratio of 1:2.5.

Physical Property Evaluation of 19F-Labeled Nanodiscs

The purified lipid nanodiscs were characterized in terms of their size by transmission electron microscopy (TEM; Figure b), dynamic light scattering (DLS; Figure c), and atomic force microscopy (AFM; Figure S2). DLS analysis revealed a particle diameter of 9.1 ± 2.5 nm, indicating the formation of monodisperse and sub-20 nm nanodiscs. Similarly, TEM observation revealed disc-shaped particles of approximately 10 nm in diameter. This indicated that the complex of 19F-labeled phospholipids and SMA copolymer formed sub-20 nm discoidal structures as intended. Notably, the particle size obtained here was significantly smaller than that of conventional nanoparticle-based 19F MRI probes (>80 nm), highlighting the potential of the nanodisc approach in minimizing Kupffer cell uptake. The nanodiscs exhibited a slightly negative zeta potential (−1.3 mV), consistent with previously reported SMA-based polymer nanodiscs (Figure S3a).

Next, we observed that 19F NMR measurement of the 19F-labeled nanodiscs yielded a single peak derived from the 19F-labeled phospholipid, suggesting that these nanodiscs are capable of providing detectable MR signals as probes (Figure d). The T 2 relaxation time of these signals was measured to be 321 ms at 37 °C, which is sufficiently long (>100 ms) for use in 19F MRI. Since the T 2 relaxation time increases with higher mobility of 19F nuclei, these results indicated that the 19F-labeled lipids retain sufficient mobility within the nanodiscs for detection by MRI. Interestingly, the T 2 relaxation time was found to depend on both temperature and the lipid/polymer ratio (Table ). The observed temperature dependence can be attributed to the characteristic gel-to-liquid crystalline phase transition inherent to phospholipid bilayers. For example, within a lipid/polymer ratio of 1:1 to 1:3.33, the T 2 relaxation time increased markedly above a threshold temperature of approximately 30–37 °C that may be the phase-transition temperature of C13–F6PC. This interpretation is further supported by differential scanning calorimetry analysis of the nanodisc samples, which revealed a phase transition at around 30 °C (Figure S4). The dependence of T 2 relaxation on the polymer/lipid ratio at 30–37 °C, where lipid bilayer within nanodiscs is assumed to be in liquid–crystalline phase, is likely attributable to the extent of bilayer solubilization and reduced mobility of phospholipids that are in direct contact with the polymer. For example, at lower polymer ratio, such as lipid/polymer ratios of 1:1 to 1:3.33, there is a tendency for the T 2 relaxation time to become shortened at 30 and 37 °C. This is likely due to incomplete solubilization of the lipid bilayer by the polymer molecules that leads to increase in the nanodisc particle size, as observed by DLS at different lipid/polymer ratio (Figure S5). The larger particle size reduces rotational tumbling, leading to an increased rotational correlation time and thereby shortening the T 2 relaxation time of the 19F nuclei. This trend was not observed at 25 °C, presumably because the lipid bilayer is not in the liquid crystalline phase. At higher polymer ratios such as a lipid/polymer ratio of 1:10, the T 2 relaxation time is also shortened. This is likely because the increased number of polymer molecules per lipid molecule reduces the overall nanodisc diameter as observed in the DLS (Figure S5d) and increases the fraction of lipids in contact with the rigid polymer, thereby lowering their mobility and shortening the T 2 relaxation times. Taken together, these findings suggest that conditions with lipid/polymer ratios of 1:2.5 to 1:3.33 preserve the characteristic bilayer structure within the nanodiscs. Under these conditions, the lateral diffusion of lipids is retained and hence enhances the mobility of the 19F nuclei, making the nanodiscs suitable as 19F MRI probes.

1. Effects of Temperature and Lipid/Polymer Ratio on the T 2 Relaxation Time of the 19F-Labeled Nanodiscs.

lipid/polymer ratio (w/w) T 2 relaxation time (ms)
  25 °C 30 °C 37 °C
1:10 15.5 19.1 26.5
1:5 80.8 96.7 39.8
1:3.33 74.5 70.2 261.7
1:2.5 78.4 184.5 321.7
1:1 86.4 77.4 169.3
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Application of 19F-Labeled Nanodiscs to 19F MRI

The developed 19F-labeled nanodiscs were subjected to 19F MRI measurement to assess their utility as probes (Figure a). As an initial evaluation, phantom MRI experiments were conducted, which confirmed that the positions of the samples could be distinctly visualized by 19F MRI. This result demonstrates that the 19F-labeled nanodiscs generate sufficiently intense signals to serve as detectable MRI probes. Since the signal intensity is proportional to the probe concentration, this probe allows reliable quantitative imaging of local probe concentration (Figure b). The 19F MRI detection limit, defined as the 19F concentration giving an S/N of 3 was 6.54 mM. For comparison, we prepared a PFCE-based nanoemulsion based on the previous report and evaluated its detection limit using optimized T E and T R values while keeping the total acquisition time identical (Figure S6). Under these conditions, the detection limit of our nanodisc formulation was lower than that of the PFCE nanoemulsion (detection limit for [19F]: 17.0 mM), indicating higher 19F MRI sensitivity (Table S2).

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(a) MRI images of 19F-labeled nanodiscs dispersed in pH 8.0 sodium phosphate buffer within a phantom setup. 19F concentration: 50 mM, 25 mM, 10 mM and 5 mM. Samples were connected to a thermostated line set to 38 °C. MRI images were acquired using the rapid acquisition with refocused echoes (RARE) method. For 1H MRI, T R = 2500 ms, T E = 30 ms, number of averages = 4, RARE factor = 8, acquisition time = 2 m 40 s. For 19F MRI, T R = 1000.0 ms, T E = 27.18 ms, number of acquisition = 512, RARE factor = 16, acquisition time = 17 m 4 s. (b) Correlation between the concentration of the 19F-labeled nanodisc and the corresponding normalized 19F MRI signal intensity obtained from (a). (c) 1H, 19F, and merged MRI data of 19F-labeled nanodisc-containing aqueous solution injected intravenously into a live mouse. Injected 19F concentration: 50 mM (200 μL). 1H and 19F MRI images were acquired using the RARE method. For 1H MRI, T R = 2500 ms, T E = 16.7 ms, number of averages = 4, RARE factor = 8, acquisition time = 2 m 40 s. For 19F MRI, T R = 2000.0 ms, T E = 27.18 ms, number of acquisition = 512, RARE factor = 16, acquisition time = 35 m 20 s.

Additionally, in another phantom measurement, one of the samples was connected to a thermostated line set to 38 °C. The sample maintained at 38 °C exhibited a slightly stronger MRI signal intensity, which can be attributed to the increased temperature dependent T 2 relaxation time at higher temperature as described above (Figure S7). These findings suggest that the nanodiscs have the potential to function as temperature-sensitive MRI probes, enabling their application as molecular thermometers in vivo.

We next investigated the in vivo applicability of the 19F-labeled nanodiscs, which were administered to mice by tail vein injection (Figure c). In contrast to conventional 19F MRI probes, the developed nanodiscs produced no detectable signal in the liver but showed clear 19F MRI signals in the bladder. These results indicate that the nanodisc-based 19F MRI probe is excreted renally while avoiding Kupffer cell uptake. For comparison, a PFCE-based nanoemulsion was coadministered with the nanodiscs, and the 19F MRI images were acquired separately for nanodiscs and PFCE based nanoemulsions by exploiting distinct 19F chemical shifts at 1 and 18 h postinjection (Figure S8). While the nanodisc-derived signal was no longer detectable at 18 h, the PFCE nanoemulsion signal remained observable near the liver region indicating prolonged retention, consistent with previous reports. , This outcome aligns with previous observations that sub-20 nm and soft nanoparticles tend to evade Kupffer cell uptake more effectively than larger or rigid counterparts, and be rapidly excreted via kidneys. − ,, Thus, the use of sub-20 nm nanodiscs for 19F MRI design holds potential to target tissues that could not be visualized by previous approaches.

Given that the nanodiscs were largely cleared via the renal route within 24 h, the long-term persistence of the formulation in vivo is expected to be minimal. In contrast to metabolically inert perfluorocarbons such as PFCE, the fluorinated lipids used in this study are less likely to persist in vivo over extended periods. , We also assessed the cytotoxicity of the nanodiscs and confirmed the absence of apparent cytotoxicity (Figure S9). In addition, no apparent adverse effects or mortality were observed in mice following administration of the nanodiscs. Although the long-term effects of the fluorinated phospholipids and this nanodisc formulation warrant further investigation, previous studies have reported low long-term toxicity and immunogenicity of SMA-based polymers, supporting the biocompatibility of this platform.

Under the current probe and acquisition conditions, obtaining sufficiently strong in vivo signals requires ∼ 35 min, which limits the temporal resolution. However, this limitation could be mitigated by increasing the number of magnetically equivalent 19F nuclei per phospholipid and introducing paramagnetic metal chelates to optimize T 1/T 2 relaxation times. In addition, further optimization of pulse sequences and implementation of nonuniform sampling strategies − could improve sensitivity and temporal resolution in 19F MRI.

Surface Modifiability of Nanodisc-Based MRI Probes

In the context of 19F MRI probe design, incorporation of surface modification enables introduction of chemical responsiveness or tissue-specific targeting ligands that broadens the utility of the probe. Therefore, it is critical to evaluate whether the newly developed probes remain functional in 19F MRI with such surface modifications. Previous studies on nanodisc-based imaging and drug delivery have demonstrated that modification of the phospholipids with bulky headgroups enables control of the delivery destinations of the nanodiscs. However, for application as MRI probes, modification of the 19F-labeled lipids may affect the mobility of the 19F labels and potentially reduce the MRI signal. To address this concern, we investigated whether the incorporation of polymer-conjugated lipids into our nanodiscs for surface modification would alter the 19F MRI signal intensity.

In this experiment, nanodiscs were prepared by mixing C13–F6PC with 20 mol % DSPE-PEG2000 (1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino­(polyethylene glycol)-2000]), following the same preparation protocol for the unmodified nanodiscs (Figure a). PEGylation of such nanoparticles is an important strategy, as it suppresses nanoparticle-induced formation of protein aggregate called protein corona and prolongs blood circulation and enhances tissue-specific delivery of the nanodiscs. The nanodiscs obtained with PEGylated lipids had a diameter of 11.9 nm ± 3.7 nm as determined by DLS, which was approximately 2.8 nm larger than that of unmodified nanodiscs (Figure b). In addition, they showed shorter retention times upon GPC purification, suggesting increased particle size (Figure c). The zeta potential of the PEG-modified nanodiscs was slightly negative (−4.9 mV), comparable to that of the nonfunctionalized nanodiscs (Figure S4b). Furthermore, 1H NMR analysis confirmed the incorporation of PEGylated lipids into the nanodiscs, and the actual molar ratio of C13–F6PC to DSPE-PEG2000 in the nanodiscs was determined to be 81:19 (Figure S10). 19F NMR measurements of the developed nanodiscs showed a peak derived from the 19F-labeled phospholipid similar to that observed in the unmodified nanodiscs (Figure d). The T 2 relaxation time was 129.2 ms, shorter than that of the unmodified nanodiscs, but remained above 100 ms, which is sufficient for its application in 19F MRI measurements (Table S3).

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Preparation and characterization of nanodisc-based 19F MRI probes modified with PEG. (a) Schematic illustration of the preparation process. (b) The DLS profile. (c) The GPC profile in comparison with unmodified 19F nanodisc. (d) The 19F NMR spectrum. Nanodiscs were prepared at a lipid/SMA polymer ratio of 1:2.5.

Importantly, when the 19F NMR relaxation times were measured in the presence of 20% fetal bovine serum (FBS), the T 2 relaxation time of the unmodified 19F-labeled nanodiscs markedly decreased, whereas the PEG-modified nanodiscs exhibited only a minimal reduction (Table S4). The observed decrease in relaxation time for the nonfunctionalized nanodiscs is likely attributed to protein absorption onto the nanodiscs, which may reduce their rotational and diffusional mobility and/or restrict the motion of the 19F-labeled lipids within the nanodiscs. These results indicate that PEGylation effectively suppresses protein absorption onto the nanodiscs, which is expected to improve their blood circulation time and enhance the overall stability of the nanodiscs in biological environments.

We examined the PEG-modified nanodisc probe by 19F MRI. Phantom MRI experiments confirmed that the PEG-modified nanodiscs generated a clear 19F signal, with an intensity that was proportional to their concentration (Figure a,b). Under in vivo 19F MRI conditions, a strong signal was also detected from the bladder after intravenous administration of the probes in mice (Figure c). Furthermore, we compared the time-course changes in the in vivo 19F MRI signal after intravenous administration of unmodified nanodiscs and PEG-modified ones in mice. For both probes, an increase in 19F MRI signal intensity in the bladder region was observed between 15 min and 2 h postinjection (Figure d). When the 19F MRI signal-to-noise ratio (SNR) was normalized to the value at 2 h postinjection for comparison, the PEG-modified probes exhibited a slightly delayed accumulation in the bladder compared with the unmodified nanodiscs (Figure S11). This result suggests the PEGylation prolongs blood circulation time, likely due to an increase in probe size and/or reduced protein absorption.

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(a) MRI images of 19F-labeled nanodiscs modified with PEG dispersed in pH 8.0 sodium phosphate buffer within a phantom setup. 19F concentration: 50 mM, 25 mM, 10 mM and 5 mM. Samples were connected to a thermostated line set to 38 °C. MRI images were acquired using the RARE method. For 1H MRI, T R = 2500 ms, T E = 30 ms, number of averages = 4, RARE factor = 8, acquisition time = 2 m 40 s. For 19F MRI, T R = 1000.0 ms, T E = 27.18 ms, number of acquisition = 512, RARE factor = 16, acquisition time = 17 m 4 s. (b) Correlation between the concentration of the 19F-labeled nanodisc and the corresponding normalized 19F MRI signal intensity obtained from (a). (c) 1H, 19F, and merged MRI data from a living mouse injected intravenously with 19F-labeled nanodiscs aqueous solution. Injected 19F: 50 mM (200 μL). 1H/19F MRI RARE method. For 1H MRI, T R = 2500 ms, T E = 16.7 ms, number of averages = 4, RARE factor = 8, acquisition time = 2 m 40 s. For 19F MRI, T R = 2000.0 ms, T E = 27.18 ms, number of acquisition = 512, RARE factor = 16, acquisition time = 35 m 20 s. (d) Time-course changes of 19F MRI images for unmodified nanodisc and PEG-modified nanodisc probes. Signal intensities were normalized by the noise level.

To examine whether 19F MR signals from circulating nanodiscs could be detected in the bloodstream, additional 19F MRI experiments were conducted using FLASH-based sequences in order to enhance signals originating from probes flowing in the bloodstream (Figure S12). However, no detectable 19F MR signals were observed in the vascular region under our experimental conditions. Further optimization of imaging sequences and probe design to increase the detectable 19F signal in the bloodstream will be an important subject for future studies.

Finally, to investigate the structural integrity of nanodiscs during renal clearance, we analyzed urine samples collected from mice administered unmodified nanodiscs by 19F NMR. The 19F NMR spectrum of the urine samples showed a signal in the chemical shift region assigned to the fluorinated lipids. The peak exhibited slightly longer T 2 relaxation times than that of nanodiscs before administration, suggesting morphological alteration during renal clearance, potentially involving partial disassembly and interaction with other biomolecules resulting in partial solubilization of lipids (Table S5).

The size of nanodiscs is slightly above the reported size cut off of glomerular filtration (∼5.5 nm for quantum dots and 8.8 nm for tungsten nanodots). Additionally, reports showing that rod-shaped carbon nanotubes and plate-shaped carbon nanosheet , can undergo glomerular filtration suggest that nanoparticle aspect ratio is also an important factor in renal filtration, which may also be applicable to nanodiscs. Furthermore, the soft and deformable nature of nanodiscs may also facilitate their passage through the glomerular filtration barrier as suggested in a recent review. Overall, nanodisc-based probes appear to undergo relatively slow renal clearance. Nonetheless, they may still pass through the glomerular filtration barrier, a process that may involve substantial time and mechanical stress and could lead to partial disassembly. The delayed accumulation of the larger PEGylated nanodiscs in the bladder is also likely attributable to this effect.

Taken together, these findings suggest that our nanodisc-based 19F MRI probes are capable of incorporating approximately 20 mol % of headgroup-modified lipids and their PEGylation improves the performance as nanodisc-based 19F MRI probes. These results suggest that diverse functionalities can be introduced into the nanodiscs simply by mixing modified lipids during their preparation. As indicated above, PEGylation shortened T 2 relaxation time likely due to an increase in nanodisc size resulting in the increased rotational correlation time and decreased signal intensity; however, PEGylation can suppress protein absorption and prolong circulation, thereby potentially enhancing the in vivo signal by increasing the effective probe availability during imaging. For future applications, this design flexibility could enable selective probe delivery to and visualization of tumor tissues through incorporation of tumor-targeting ligands. Similarly, those nanodisc probes could allow detection of enzymatic activities by introducing cleavable sites for paramagnetic metal complexes. Combined, these features can expand the application of the 19F MRI probes for visualization of biological information in tissues and organs that remained previously inaccessible with conventional probes.

Conclusions

In this study, we demonstrated that incorporation of 19F-labeled phospholipids into lipid nanodiscs enabled their application as 19F MRI probes. By employing lipid nanodiscs as a “cage” to encapsulate highly mobile 19F-labeled molecules, we successfully developed 19F MRI probes that are much smaller than conventional counterparts. This design enables clear detection of 19F MRI signals from the nanodiscs in both phantom measurements and in vivo imaging in mice. Importantly, our nanodiscs exhibit in vivo biodistribution distinct from that of conventional 19F MRI probes, characterized by renal clearance without Kupffer cell uptake. Moreover, the observation of clear 19F MRI signals even after PEG-based surface modification suggests that these nanodiscs can accommodate additional functional features such as chemical responsiveness or ability to incorporate various ligands. These probes have the potential to reach tissues that were previously inaccessible and can accommodate diverse functionalization, making it a promising new platform for 19F MRI probes.

Supplementary Material

ja5c21753_si_001.pdf (2.1MB, pdf)

Acknowledgments

We thank Dr. Shigeyoshi Saito (Department of Medical Physics and Engineering, Division of Health Sciences, Graduate School of Medicine, The University of Osaka) for the instructions on animal experiments and 1H/19F MRI measurements. We also thank Yuko Wakabayashi (Immunology Frontier Research Center, The University of Osaka) for the management of animal welfare and the maintenance of laboratory for MRI experiments. We also thank Prof. Takashi Hayashi, Dr. Koji Oohora and Hiroki Uchida (Department of Engineering, The University of Osaka) for the instructions on AFM measurements. The DSC measurements were performed at Analytical Instrument Facility, Graduate School of Science, The University of Osaka. This work was supported by a Grant-in-Aid for Transformative Research Areas (A) “Latent Chemical Space” [JP23H04880 and JP23H04881 (K.K.)] from the Ministry of Education, Culture, Sports, Science and Technology, Japan. This research was also supported by JSPS KAKENHI (grant numbers: JP21H04706, JP23KK0106, and JP24H00494 to K.K.; JP25K18127 to T.Y.); the JSPS CORE-to-CORE Program “Asian Chemical Biology Initiative”. This research was financially supported by the 31st Magnetic Research Grant from the Watanabe Foundation (T.Y.).

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/jacs.5c21753.

  • Includes materials, instruments, synthesis of compounds, experimental procedures, and supplementary figures and tables (PDF)

∥.

K.F. and T.Y. contributed equally.

The authors declare no competing financial interest.

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