Thermal Behavior of 19F Nuclear Magnetic Resonance Signal of 19F-Containing Compound in Lipid Nano-Emulsion for Potential Tumor Diagnosis

Nanotechnology as a Versatile Tool for 19F-MRI Agent's Formulation: A Glimpse into the Use of Perfluorinated and Fluorinated Compounds in Nanoparticles

Simultaneously being a non-radiative and non-invasive technique makes magnetic resonance imaging (MRI) one of the highly sought imaging techniques for the early diagnosis and treatment of diseases. Despite more than four decades of research on finding a suitable imaging agent from fluorine for clinical applications, it still lingers as a challenge to get the regulatory approval compared to its hydrogen counterpart. The pertinent hurdle is the simultaneous intrinsic hydrophobicity and lipophobicity of fluorine and its derivatives that make them insoluble in any liquids, strongly limiting their application in areas such as targeted delivery. A blossoming technique to circumvent the unfavorable physicochemical characteristics of perfluorocarbon compounds (PFCs) and guarantee a high local concentration of fluorine in the desired body part is to encapsulate them in nanosystems. In this review, we will be emphasizing different types of nanocarrier systems studied to encapsulate various PFCs and fluorinated compounds, headway to be applied as a contrast agent (CA) in fluorine-19 MRI (19F MRI). We would also scrutinize, especially from studies over the last decade, the different types of PFCs and their specific applications and limitations concerning the nanoparticle (NP) system used to encapsulate them. A critical evaluation for future opportunities would be speculated.

Effect of Dihydropyridine Enrichment in the Microstructure of the Palisade Layer on the Stability of Fat Nano-emulsions

Relationship between the stability of fat nano-emulsions and the incorporated drug at the molecular level are rarely known. Herein, fat nano-emulsions containing dihydropyridine drugs were prepared and the microstructure of their palisade layers were investigated.The prepared 1.0 mg/mL nimodipine nano-emulsion was found to contain 65.50% drug in the palisade layer. The increasing drug concentration led to a decrease-increase-decrease trend in centrifugal stability constant, particle size and proton nuclear magnetic resonance (¹H NMR) signal intensity of the lecithin trimethyl ammonium group in the nimodipine and felodipine nano-emulsions. The ¹H NMR spectra of test solutions including nano-emulsions suggest that increasing drugs penetrated into the palisade layer, resulting in the lecithin arrangement from loose to tight, and then from monolayer to bilayer. Nimodipine and felodipine nano-emulsions showed two valley values at concentrations of 0.15 and 0.75 mg/mL, and 0.30 and 0.90 mg/mL respectively, which indicated that the nano-emulsion has two more stable states corresponding to the tightly arranged mono- and bi-palisade layer. These two concentrations are positively correlated with lipophilicity of nimodipine and felodipine. Further, nimodipine liposomes were prepared to validate the effect of drugs on the arrangement of lecithin in the palisade layer. ¹H NMR characterizations of the liposomes showed a similar profile to that of nano-emulsions. These results demonstrated that the increasing drug concentration could cause a rearrangement of lecithin in the palisade layer, thus affecting emulsion stability.

Fluorinated MRI contrast agents and their versatile applications in the biomedical field

MRI has been recognized as one of the most applied medical imaging techniques in clinical practice. However, the presence of background signal coming from water protons in surrounding tissues makes sometimes the visualization of local contrast agents difficult. To remedy this, fluorine has been introduced as a reliable perspective, thanks to its magnetic properties being relatively close to those of protons. In this review, we aim to give an overall description of fluorine incorporation in contrast agents for MRI. The different kinds of fluorinated probes such as perfluorocarbons, fluorinated dendrimers, polymers and paramagnetic probes will be described, as will their imaging applications such as chemical exchange saturation transfer (CEST) imaging, physico-chemical changes detection, drug delivery, cell tracking and inflammation or tumors detection.

Protein-Engineered Nanoscale Micelles for Dynamic 19F Magnetic Resonance and Therapeutic Drug Delivery

Engineered proteins provide an interesting template for designing fluorine-19 (19F) magnetic resonance imaging (MRI) contrast agents, yet progress has been hindered by the unpredictable relaxation properties of fluorine. Herein, we present the biosynthesis of a protein block copolymer, termed "fluorinated thermoresponsive assembled protein" (F-TRAP), which assembles into a monodisperse nanoscale micelle with interesting 19F NMR properties and the ability to encapsulate and release small therapeutic molecules, imparting potential as a diagnostic and therapeutic (theranostic) agent. The assembly of the F-TRAP micelle, composed of a coiled-coil pentamer corona and a hydrophobic, thermoresponsive elastin-like polypeptide core, results in a drastic depression in spin-spin relaxation ( T2) times and unaffected spin-lattice relaxation ( T1) times. The nearly unchanging T1 relaxation rates and linearly dependent T2 relaxation rates have allowed for detection via zero echo time 19F MRI, and the in vivo MR potential has been preliminarily explored using 19F magnetic resonance spectroscopy (MRS). This fluorinated micelle has also demonstrated the ability to encapsulate the small-molecule chemotherapeutic doxorubicin and release its cargo in a thermoresponsive manner owing to its inherent stimuli-responsive properties, presenting an interesting avenue for the development of thermoresponsive 19F MRI/MRS-traceable theranostic agents.