In Vitro Chondrogenesis Induction by Short Peptides of the Carboxy-Terminal Domain of Transforming Growth Factor β1

Τransforming growth factor β1 (TGF-β1) comprises a key regulator protein in many cellular processes, including in vivo chondrogenesis. The treatment of human dental pulp stem cells, separately, with Leu83-Ser112 (C-terminal domain of TGF-β1), as well as two very short peptides, namely, 90-YYVGRKPK-97 (peptide 8) and 91-YVGRKP-96 (peptide 6) remarkably enhanced the chondrogenic differentiation capacity in comparison to their full-length mature TGF-β1 counterpart either in monolayer cultures or 3D scaffolds. In 3D scaffolds, the reduction of the elastic modulus and viscous modulus verified the production of different amounts and types of ECM components. Molecular dynamics simulations suggested a mode of the peptides' binding to the receptor complex TβRII-ALK5 and provided a possible structural explanation for their role in inducing chondrogenesis, along with endogenous TGF-β1. Further experiments clearly verified the aforementioned hypothesis, indicating the signal transduction pathway and the involvement of TβRII-ALK5 receptor complex. Real-time PCR experiments and Western blot analysis showed that peptides favor the ERK1/2 and Smad2 pathways, leading to an articular, extracellular matrix formation, while TGF-β1 also favors the Smad1/5/8 pathway which leads to the expression of the metalloproteinases ADAMTS-5 and MMP13 and, therefore, to a hypertrophic chondrocyte phenotype. Taken together, the two short peptides, and, mainly, peptide 8, could be delivered with a scaffold to induce in vivo chondrogenesis in damaged articular cartilage, constituting, thus, an alternative therapeutic approach for osteoarthritis.

Strong Binding of C-Glycosylic1,2-Thiodisaccharides to Galectin-3─Enthalpy-Driven Affinity Enhancement by Water-Mediated Hydrogen Bonds

Galectin-3 is involved in multiple pathways of many diseases, including cancer, fibrosis, and diabetes, and it is a validated pharmaceutical target for the development of novel therapeutic agents to address unmet medical needs. Novel 1,2-thiodisaccharides with a C-glycosylic functionality were synthesized by the photoinitiated thiol-ene click reaction of O-peracylated 1-C-substituted glycals and 1-thio-glycopyranoses. Subsequent global deprotection yielded test compounds, which were studied for their binding to human galectin-3 by fluorescence polarization and isothermal titration calorimetry to show low micromolar Kd values. The best inhibitor displayed a Kd value of 8.0 μM. An analysis of the thermodynamic binding parameters revealed that the binding Gibbs free energy (ΔG) of the new inhibitors was dominated by enthalpy (ΔH). The binding mode of the four most efficient 1,2-thiodisaccharides was also studied by X-ray crystallography that uncovered the unique role of water-mediated hydrogen bonds in conferring enthalpy-driven affinity enhancement for the new inhibitors. This 1,2-thiodisaccharide-type scaffold represents a new lead for galectin-3 inhibitor discovery and offers several possibilities for further development.

Affinity Crystallography Reveals Binding of Pomegranate Juice Anthocyanins at the Inhibitor Site of Glycogen Phosphorylase: The Contribution of a Sugar Moiety to Potency and Its Implications to the Binding Mode

Anthocyanins (ACNs) are dietary phytochemicals with an acknowledged therapeutic significance. Pomegranate juice (PJ) is a rich source of ACNs with potential applications in nutraceutical development. Glycogen phosphorylase (GP) catalyzes the first step of glycogenolysis and is a molecular target for the development of antihyperglycemics. The inhibitory potential of the ACN fraction of PJ is assessed through a combination of in vitro assays, ex vivo investigation in hepatic cells, and X-ray crystallography studies. The ACN extract potently inhibits muscle and liver isoforms of GP. Affinity crystallography reveals the structural basis of inhibition through the binding of pelargonidin-3-O-glucoside at the GP inhibitor site. The glucopyranose moiety is revealed as a major determinant of potency as it promotes a structural binding mode different from that observed for other flavonoids. This inhibitory effect of the ACN scaffold and its binding mode at the GP inhibitor binding site may have significant implications for future structure-based drug design endeavors.