Effects of Cations on HPTS Fluorescence and Quantification of Free Gadolinium Ions in Solution; Assessment of Intracellular Release of Gd3+ from Gd-Based MRI Contrast Agents.

8-Hydroxypyrene-1,3,6-trisulfonate (HPTS) is a small, hydrophilic fluorescent molecule. Since the pKa of the hydroxyl group is close to neutrality and quickly responds to pH changes, it is widely used as a pH-reporter in cell biology for measurements of intracellular pH. HPTS fluorescence (both excitation and emission spectra) at variable pH was measured in pure water in the presence of NaCl solution or in the presence of different buffers (PBS or hepes in the presence or not of NaCl) and in a solution containing BSA. pKa values have been obtained from the sigmoidal curves. Herein, we investigated the effect of mono-, di-, and trivalent cations (Na+, Ca2+, La3+, Gd3+) on fluorescence changes and proposed its use for the quantification of trivalent cations (e.g., gadolinium ions) present in solution as acqua-ions. Starting from the linear regression, the LoD value of 6.32 µM for the Gd3+ detection was calculated. The effects on the emission were also analyzed in the presence of a combination of Gd3+ at two different concentrations and the previously indicated mono and di-valent ions. The study demonstrated the feasibility of a qualitative method to investigate the intracellular Gd3+ release upon the administration of Gd-based contrast agents in murine macrophages.

Photoacoustic ratiometric assessment of mitoxantrone release from theranostic ICG-conjugated mesoporous silica nanoparticles.

A theranostic nanosystem based on indocyanine green (ICG) covalently conjugated to mesoporous silica nanoparticles (MSNs) loaded with the anticancer drug mitoxantrone (MTX) is proposed as an innovative photoacoustic probe. Taking advantage of the characteristic PA signal displayed by both ICG and MTX, a PA-ratiometric approach was applied to assess the drug release profile from the MSNs. After complete in vitro characterization of the nanoprobe, a proof-of-concept study has been carried out in tumour-bearing mice to evaluate in vivo its effectiveness for cancer imaging and chemotherapeutic agent delivery.

Gadolinium Retention in the Rat Brain: Assessment of the Amounts of Insoluble Gadolinium-containing Species and Intact Gadolinium Complexes after Repeated Administration of Gadolinium-based Contrast Agents.

Purpose To evaluate the speciation of gadolinium-containing species after multiple administrations of the gadolinium-based contrast agents (GBCAs) gadodiamide and gadoteridol and to quantify the amount of intact gadolinium complexes and insoluble gadolinium-containing species. Materials and Methods A total dose of 13.2 mmol per kilogram of body weight of each GBCA was administered in healthy Wistar rats over a period of 8 weeks. Three days after the final administration, rats were sacrificed, and the brains were excised and divided into three portions. Each portion of brain homogenate was divided into two parts, one for determination of the total gadolinium concentration with inductively coupled plasma mass spectrometry and one for determination of the amount of intact GBCA and gadolinium-containing insoluble species. Relaxometric measurements of gadodiamide and gadolinium trichloride in the presence of polysialic acid were also performed. Results The mean total gadolinium concentrations for gadodiamide and gadoteridol, respectively, were 0.317 µg/g ± 0.060 (standard deviation) and 0.048 µg/g ± 0.004 in the cortex, 0.418 µg/g ± 0.078 and 0.051 µg/g ± 0.009 in the subcortical brain, and 0.781 µg/g ± 0.079 and 0.061 µg/g ± 0.012 in the cerebellum. Gadoteridol comprised 100% of the gadolinium species found in rats treated with gadoteridol. In rats treated with gadodiamide, the largest part of gadolinium retained in brain tissue was insoluble species. In the cerebellum, the amount of intact gadodiamide accounts for 18.2% ± 10.6 of the total gadolinium found therein. The mass balance found for gadolinium implies the occurrence of other soluble gadolinium-containing species (approximately 30%). The relaxivity of the gadolinium polysialic acid species formed in vitro was 97.8 mM/sec at 1.5 T and 298 K. Conclusion Gadoteridol was far less retained, and the entire detected gadolinium was intact soluble GBCA, while gadodiamide yielded both soluble and insoluble gadolinium-containing species, with insoluble species dominating. © RSNA, 2017 Online supplemental material is available for this article.

Enzyme-Responsive LipoCEST Agents: Assessment of MMP-2 Activity by Measuring the Intra-liposomal Water 1 H†NMR Shift.

Mobile proton-containing solutes can be detected by MRI by the chemical exchange saturation transfer (CEST) method. CEST sensitivity is dramatically enhanced by using, as exchanging protons, the water molecules confined inside liposomes, shifted by a paramagnetic shift reagent. The chemical shift of the intraliposomal water resonance (δIL ) is affected by the overall shape of the supramolecular system. δIL of a spherical LipoCEST acts as a sensitive reporter of the distribution of streptavidin proteins anchored at the liposome surface by biotinylated phospholipids. This finding prompted the design of a MMP-2 responsive LipoCEST agent as the streptavidin moieties can be released from the liposome surfaces when a properly tailored enzyme-cleavable peptide is inserted on the phospholipids before the terminal biotin residues. δIL reports on the overall changes in the supramolecular architecture associated to the cleavage carried out by MMP-2.

Gd-loaded-RBCs for the assessment of tumor vascular volume by contrast-enhanced-MRI.

The assessment of the fractional vascular volume (vV) in the tumor area is of great interest in the characterization of tumor and it can be useful to monitor the outcome of anti-angiogenetic therapies. The high spatial and temporal resolution of Magnetic Resonance Imaging makes it the election imaging modality to monitor in vivo the vascular volume changes. Commonly used MRI methods to obtain this information rely on the administration of contrast agents that modify the bulk water relaxation times but, unfortunately, they can provide only an estimate of vV since they are not fully retained in the vascular space. Herein, Gd-loaded Red Blood Cells (Gd-RBCs) are proposed as a contrast agent able to provide quantitative information on tumor vascularization. Being Gd-RBCs fully retained in the vascular space, the proposed method does not suffer for the limitations associated to the use of extracellular Gd-agents that quickly extravasate in the leaky tumor vasculature. Furthermore, the long half-life and biocompatibility of Gd-RBCs allows repeating the measurement many times upon their administration; this ensures the possibility to in vivo evaluate the change of vascular volume during tumor growth. For these reasons, Gd-RBCs may represent a highly biocompatible imaging reporter of vasculature, able to quantitatively assess changes in the vascular volume in the ROI.