Lysosomal proteases play a crucial role in maintaining cell homeostasis. Human cathepsin D manages protein turnover degrading misfolded and aggregated proteins and favors apoptosis in the case of proteostasis disruption. However, when cathepsin D regulation is affected, it can contribute to numerous disorders. The down-regulation of human cathepsin D is associated with neurodegenerative disorders, such as neuronal ceroid lipofuscinosis. On the other hand, its excessive levels outside lysosomes and the cell membrane lead to tumor growth, migration, invasion and angiogenesis. Therefore, targeting cathepsin D could provide significant diagnostic benefits and new avenues of therapy. Herein, we provide a brief overview of cathepsin D structure, regulation, function, and its role in the progression of many diseases and the therapeutic potentialities of natural and synthetic inhibitors and activators of this protease.

Current developments in bioequivalent technology have led to the creation of excellent models that mimic the structure and function of human organs. These models are based on the original tissues and organs of the human body, but they lack the complex interaction with the extensive network of vasculature, and this is a major challenge for these models. A functional vasculature is essential for oxygen, nutrient, and waste exchange. It is also responsible for inductive biochemical exchange, and provides a structural pattern for organ growth. In vitro systems, containing no perfusable vessels, suffer from the quick formation of a necrotic core of organoids, and further development does not occur due to increased metabolic demands. Another key limitation of 3D-based techniques is the absence of accurate architectural structures and large-scale tissue sizes. Recently, new 3D bioprinting methods have been developed for organoids and spheroids as living building blocks. These methods aim to address some of the challenges associated with 3D technologies. In this review, we discuss recent strategies for vascularization via organoids and spheroids, which are used as structural units in bioprinting to recreate natural organs and tissues with ever-increasing accuracy in structure and function.

One of the leading trends in the modern tissue engineering is the development of new effective methods of decellularization aimed at the removal of cellular components from a donor tissue, reducing its immunogenicity and the risk of rejection. Supercritical CO₂ (scCO₂)-assisted processing has been proposed to improve the outcome of decellularization, reduce contamination and time costs. The resulting products can serve as personalized tools for tissue-engineering therapy of various somatic pathologies. However, the decellularization of heterogeneous 3D structures, such as the aortic root, requires optimization of the parameters, including preconditioning medium composition, the type of co-solvent, values of pressure and temperature inside the scCO₂ reactor, etc. In our work, using an ovine aortic root model, we performed a comparative analysis of the effectiveness of decellularization approaches based on various combinations of these parameters. The protocols were based on the combinations of treatments in alkaline, ethanol or detergent solutions with scCO₂-assisted processing at different modes. Histological analysis demonstrated favorable effects of the preconditioning in a detergent solution. Following processing in scCO₂ medium provided a high decellularization degree, reduced cytotoxicity, and increased ultimate tensile strength and Young’s modulus of the aortic valve leaflets, while the integrity of the extracellular matrix was preserved.

The influence of chitosan (CS) and amphiphilic polymers (AP: pluronic F108 and polyvinylpyrrolidone (PVP)) on the photocatalytic activity of rose bengal (RB) in a model reaction of tryptophan photo-oxidation in phosphate-buffered saline (PBS) was studied. It was shown that in the presence of CS, the effective rate constant k_eff of tryptophan photo-oxidation catalyzed by RB in PBS solution decreases by a factor of two. This is due to the ionic interaction of the RB with the chitosan. Rose bengal in a slightly acidic environment (pH 4.5) passes into a neutral lactone form, which sharply reduces the photosensitizing properties of the dye. It was demonstrated that the introduction of AP into a solution containing RB and CS prevents direct interaction between RB and CS. This is evidenced by the presence of photocatalytic activity of the dye in the RB-AP-CS systems, as well as bathochromic shifts of the main absorption bands of the dye, and an increase in the optical density and luminescence intensity of the RB when AP is introduced into a buffer solution containing RB and chitosan. The presence of RB-CS and RB-AP interaction in aqueous and PBS media is confirmed by the increase in the degree of fluorescence anisotropy (r) of these binary systems. In an aqueous solution, the value of r for the RB-F108-CS system decreases by a factor of 3.5 (compared to the value of r for the RB-CS system), which is associated with the localization of the dye in pluronic micelles. In PBS, the fluorescence anisotropy is practically the same for all systems, which is related to the stability of the dye structure in this medium. The presence of interaction between RB and AP in aqueous solutions was confirmed by the proton NMR method. In addition, the formation of RB-F108 macromolecular complexes, which form associates during solution concentration (in particular, during evaporation), was shown by AFM. Such RB-AP-CS systems may be promising for practical application in the treatment of local foci of infections by aPDT.

A hydrophobic derivative of ciprofloxacin, hexanoylated ciprofloxacin (CPF-hex), has been used as a photoinitiator (PI) for two-photon polymerization (2PP) for the first time. We present, here, the synthesis of CPF-hex and its application for 2PP of methacrylate-terminated star-shaped poly (D,L-lactide), as well a systematic study on the optical, physicochemical and mechanical properties of the photocurable resin and prepared three-dimensional scaffolds. CPF-hex exhibited good solubility in the photocurable resin, high absorption at the two-photon wavelength and a low fluorescence quantum yield = 0.079. Structuring tests showed a relatively broad processing window and revealed the efficiency of CPF-hex as a 2PP PI. The prepared three-dimensional scaffolds showed good thermal stability; thermal decomposition was observed only at 314 °C. In addition, they demonstrated an increase in Young’s modulus after the UV post-curing (from 336 ± 79 MPa to 564 ± 183 MPa, which is close to those of a cancellous (trabecular) bone). Moreover, using CPF-hex as a 2PP PI did not compromise the scaffolds’ low cytotoxicity, thus they are suitable for potential application in bone tissue regeneration.