Investigating the Role of Sulfate Groups for the Binding of Gd3+ Ions to Glycosaminoglycans with NMR Relaxometry

Inorganic Phosphate-Induced Extracellular Vesicles from Vascular Smooth Muscle Cells Contain Elevated Levels of Hyaluronic Acid, Which Enhance Their Interaction with Very Small Superparamagnetic Iron Oxide Particles

Patients with chronic kidney disease (CKD) have a high prevalence of hyperphosphatemia, where uremic toxins like inorganic phosphate (Pi) induce a cardiovascular remodeling. Related disorders like atherosclerosis bear the risk of increased morbidity and mortality. We previously found that Pi stimulates the synthesis and sulfation of the negatively charged glycosaminoglycans (GAGs) heparan sulfate and chondroitin sulfate in vascular smooth muscle cells (VSMC). Similar GAG alterations were detected in VSMC-derived exosome-like extracellular vesicles (EV). These EV showed a strong interaction with very small superparamagnetic iron oxide particles (VSOP), which are used as imaging probes for experimental magnetic resonance imaging (MRI). Hyaluronic acid (HA) represents another negatively charged GAG which is supposed to function as binding motif for VSOP as well. We investigated the effects of Pi on the amounts of HA in cells and EV and studied the HA-dependent interaction between VSOP with cells and EV. Rat VSMC were treated with elevated concentrations of Pi. CKD in rats was induced by adenine feeding. EV were isolated from culture supernatants and rat plasma. We investigated the role of HA in binding VSOP to cells and EV via cell-binding studies, proton relaxometry, and analysis of cellular signaling, genes, proteins, and HA contents. Due to elevated HA contents, VSMC and EV showed an increased interaction with VSOP after Pi stimulation. Amongst others, Pi induced hyaluronan synthase (HAS)2 expression and activation of the Wnt pathway in VSMC. An alternative upregulation of HA by iloprost and an siRNA-mediated knockdown of HAS2 confirmed the importance of HA in cells and EV for VSOP binding. The in vitro-derived data were validated by analyses of plasma-derived EV from uremic rats. In conclusion, the inorganic uremic toxin Pi induces HA synthesis in cells and EV, which leads to an increased interaction with VSOP. HA might therefore be a potential molecular target structure for improved detection of pathologic tissue changes secondary to CKD like atherosclerosis or cardiomyopathy using EV, VSOP and MRI.

Physically Crosslinked Chondroitin Sulfate (CS)-Metal Ion (M: Fe(III), Gd(III), Zn(II), and Cu(II)) Particles for Versatile Applications and Their Biosafety

Chondroitin sulfate (CS), a well-known glycosaminoglycan, was physically crosslinked with Fe(III), Gd(III), Zn(II), and Cu(II) ions to obtain CS-Fe(III), CS-Gd(III), CS-Zn(II), and CS-Cu(II) polymeric particles for multipurpose biological applications. The CS-metal ion-containing particles in the micrometer to a few hundred nanometer size range are injectable materials for intravenous administration. The CS-metal ion-containing particles are safe biomaterials for biological applications because of their perfect blood compatibility and no significant cytotoxicity on L929 fibroblast cells up to a 10 mg/mL concentration. Furthermore, CS-Zn(II) and CS-Cu(II) particles show excellent antibacterial susceptibility, with 2.5-5.0 mg/mL minimum inhibition concentration (MIC) values against Escherichia coli and Staphylococcus aureus. Moreover, the in vitro contrast enhancement abilities of aqueous CS-metal ion particle suspensions in magnetic resonance imaging (MRI) were determined by obtaining T₁- and T₂-weighted MR images using a 0.5 Tesla MRI scanner and by calculating the water proton relaxivities. Therefore, these CS-Fe(III), CS-Gd(III), CS-Zn(II), and CS-Cu(II) particles have significant potential as antibacterial additive materials and MRI contrast enhancement agents with less toxicity.

Polyelectrolyte Chondroitin Sulfate Microgels as a Carrier Material for Rosmarinic Acid and Their Antioxidant Ability

Polyelectrolyte microgels derived from natural sources such as chondroitin sulfate (CS) possess considerable interest as therapeutic carriers because of their ionic nature and controllable degradation capability in line with the extent of the used crosslinker for long-term drug delivery applications. In this study, chemically crosslinked CS microgels were synthesized in a single step and treated with an ammonia solution to attain polyelectrolyte CS^-[NH₄]⁺ microgels via a cation exchange reaction. The spherical and non-porous CS microgels were injectable and in the size range of a few hundred nanometers to tens of micrometers. The average size distribution of the CS microgels and their polyelectrolyte forms were not significantly affected by medium pH. It was determined that the -34 ± 4 mV zeta potential of the CS microgels was changed to -23 ± 3 mV for CS^- [NH₄]⁺ microgels with pH 7 medium. No important toxicity was determined on L929 fibroblast cells, with 76 ± 1% viability in the presence of 1000 μg/mL concentration of CS^-[NH₄]⁺ microgels. Furthermore, these microgels were used as a drug carrier material for rosmarinic acid (RA) active agent. The RA-loading capacity was about 2.5-fold increased for CS^-[R]⁺ microgels with 32.4 ± 5.1 μg/mg RA loading, and 23% of the loaded RA was sustainably release for a long-term period within 150 h in comparison to CS microgels. Moreover, RA-loaded CS^-[R]⁺ microgels exhibited great antioxidant activity, with 0.45 ± 0.02 μmol/g Trolox equivalent antioxidant capacity in comparison to no antioxidant properties for bare CS particles.