"Introduction: Musculoskeletal ailments caused by cartilage damage are common, and thanks to more modern diagnostic methods, they are more often recognized. Moreover, cartilage diseases progress with age and result from injuries, becoming a dominant problem in orthopedic surgery. The conducted research aims to produce conjugates for cartilage regeneration based on chondrogenic differentiation of mesenchymal stem cells isolated from Wharton's jelly (hUC-MSC). Composed conjugates are based on lipid carriers of kartogenin and glycosaminoglycans derivatives stabilize the whole system.
Methodology: Kartogenin (KGN) – an active substance – was encapsulated in the liposomes. The lipid carriers were covered with hydrophobically modified chondroitin sulfate (CS) or hyaluronic acid (HA). The physicochemical analysis of the obtained systems was carried out by dynamic light scattering, zeta potential, and fluorescence measurements. The thermotropic behavior of lipid membranes was studied using a Nano DSC calorimeter (TA Instruments). In addition, the interactions of polymers with liposomes (loaded or unloaded by KGN) were analyzed by microscale thermophoresis (Monolith, Nanotemper). hUC-MSC morphology imaging after incubation with the prepared formulations and metabolic toxicity test were performed. Additionally, these systems have been tested to differentiate stem cells into chondrocytes using real-time PCR (rt-PCR).
Results: CS and HA substitution by alkyl domains were confirmed by XPS spectra. KGN was successfully incorporated into the lipid bilayer. Composed formulations were stabilized by covering their surfaces with CS or HA derivatives. The changes in thermograms for an aqueous dispersion of DPPC confirmed the incorporation of polymers' hydrophobic domains into the lipid bilayer. Moreover, an increase in the liposome size and decrease in the zeta-potential values confirmed the presence of polymers on liposomes surfaces. Despite both systems: modified CS and liposomes with KGN have high negative charge, they interact because of the hydrophobic effect. According to cytotoxicity results (MTT assay), all polymers used in lipid formulations were significantly non-toxic, than pure polymers. This is explained by the fact that hydrophobic anchors are hidden in the lipid bilayer and their exposure to the cell surface is minimized. The selected genes expression was analyzed by real-time PCR. All systems have induced ACAN and SOX9 gene expression compared to untreated cells.
Conclusion: Composed hybrid lipid-polymer formulations are stable vesicles of KGN. Moreover, they can be embedded into hydrogels and provide control released of the cargo. The resulting systems are promising conjugates for the regeneration of cartilage tissue."