The internal structure of gadolinium and perfluorocarbon-loaded polymer nanoparticles affects ¹⁹F MRI relaxation times

19F magnetic resonance imaging (19F MRI) is an emerging technique for quantitative imaging in novel therapies, such as cellular therapies and theranostic nanocarriers. Nanocarriers loaded with liquid perfluorocarbon (PFC) typically have a (single) core-shell structure with PFC in the core due to the poor miscibility of PFC with organic and inorganic solvents. Paramagnetic relaxation enhancement acts only at a distance of a few angstroms. Thus, efficient modulation of the 19F signal is possible only with fluorophilic PFC-soluble chelates. However, these chelates cannot interact with the surrounding environment and they might result in image artifacts. Conversely, chelates bound to the nanoparticle shell typically have a minimal effect on the 19F signal and a strong impact on the aqueous environment. We show that the confinement of PFC in biodegradable polymeric nanoparticles (NPs) with a multicore structure enables the modulation of longitudinal (T1) and transverse (T2) 19F relaxation, as well as proton (1H) signals, using non-fluorophilic paramagnetic chelates. We compared multicore NPs versus a conventional single core structure, where the PFC is encapsulated in the core(s) and the chelate in the surrounding polymeric matrix. This modulated relaxation also makes multicore NPs sensitive to various acidic pH environments, while preserving their stability. This effect was not observed with single core nanocapsules (NCs). Importantly, paramagnetic chelates affected both T1 and T219F relaxation in multicore NPs, but not in single core NCs. Both relaxation times of the 19F nucleus were enhanced with an increasing concentration of the paramagnetic chelate. Moreover, as the polymeric matrix remained water permeable, proton enhancement additionally was observed in MRI.</p

The Trypanosoma brucei MISP family of invariant proteins is co-expressed with BARP as triple helical bundle structures on the surface of salivary gland forms, but is dispensable for parasite development within the tsetse vector

Trypanosoma brucei spp. develop into mammalian-infectious metacyclic trypomastigotes inside tsetse salivary glands. Besides acquiring a variant surface glycoprotein (VSG) coat, little is known about the metacyclic expression of invariant surface antigens. Proteomic analyses of saliva from T. brucei-infected flies identified, in addition to VSG and Brucei Alanine-Rich Protein (BARP) peptides, a family of GPI-anchored surface proteins herein named as Metacyclic Invariant Surface Proteins (MISP) because of its predominant expression on the surface of metacyclic trypomastigotes. The MISP family is encoded by five paralog genes with >80% protein identity, which are exclusively expressed by salivary gland stages of the parasite and peak in metacyclic stage, as shown by confocal microscopy and immuno-high resolution scanning electron microscopy. Crystallographic analysis of a MISP isoform (MISP360) and a high confidence model of BARP revealed a triple helical bundle architecture commonly found in other trypanosome surface proteins. Molecular modelling combined with live fluorescent microscopy suggests that MISP N-termini are potentially extended above the metacyclic VSG coat, and thus could be tested as a transmission-blocking vaccine target. However, vaccination with recombinant MISP360 isoform did not protect mice against a T. brucei infectious tsetse bite. Lastly, both CRISPR-Cas9-driven knock out and RNAi knock down of all MISP paralogues suggest they are not essential for parasite development in the tsetse vector. We suggest MISP may be relevant during trypanosome transmission or establishment in the vertebrate’s skin

Encapsulation of Paramagnetic Chelates in Perfluorocarbon-loaded Fractal Nanoparticles Enables Modulation of Fluorine-19 and Proton Magnetic Resonance Imaging Signal

19F magnetic resonance imaging (19F MRI) is an emerging technique for quantitative imaging of novel therapies, such as cellular therapies and theranostic nanocarriers. A modification of perfluorocarbon (PFC)-loaded, nanocarrier-based 19F MRI probes with paramagnetic chelates can enhance probe’s functionality. Liquid PFC-loaded nanocarriers typically have a core-shell structure with PFC in the core due to the poor miscibility of PFC. However, paramagnetic relaxation enhancement acts only at a distance of a few angstroms. Thus, efficient modulation of 19F signal is possible only with fluorophilic PFC-soluble chelates. Such chelates, however, cannot interact with the surroundings of nanocarriers. Conversely, chelates on the surface typically affect only the aqueous environment but not the 19F signal. We show that the confinement of PFC in biodegradable polymeric nanoparticles with fractal structure enables modulation of longitudinal and transverse 19F relaxation, as well as proton signal, using non-fluorophilic paramagnetic chelates. We compared nanoparticles with fractal multicore versus conventional core-shell structure, where the PFC is encapsulated in the core(s) and the chelate in the surrounding polymeric matrix. Importantly, paramagnetic chelates affected both longitudinal and transverse 19F relaxation in fractal multicore nanoparticles, but not in core-shell nanocapsules. Both relaxation rates of 19F nucleus increased with an increasing concentration of the paramagnetic chelate. Moreover, as the polymeric matrix remained water-permeable, proton enhancement additionally was observed in MRI. In the future, the effects of fractal confinement could be combined with more effective paramagnetic chelates to develop multifunctional imaging probes, for example, for high-sensitivity 19F MRI combined with sensing