Diselenide-bond replacement of the external disulfide bond of insulin increases its oligomerization leading to sustained activity

Seleno-relaxin analogues: effect of internal and external diselenide bonds on the foldability and a fibrosis-related factor of endometriotic stromal cells

Human relaxin-2 (H2 relaxin) is a peptide hormone of about 6 kDa, first identified as a reproductive hormone involved in vasoregulation during pregnancy. It has recently attracted strong interest because of its diverse functions, including anti-inflammatory, anti-fibrotic, and vasodilatory, and has been suggested as a potential peptide-based drug candidate for a variety of diseases. Mature H2 relaxin is constituted by the A- and B-chains stabilized by two interchain disulfide (SS) bridges and one intrachain SS linkage. In this study, seleno-relaxins, SeRlx-α and SeRlx-β, which are [C11UA,C11UB] and [C10UA,C15UA] variants of H2 relaxin, respectively, were synthesized via a one-pot oxidative chain assembly (folding) from the component A- and B-chains. The substitution of SS bonds in a protein with their analogue, diselenide (SeSe) bonds, has been shown to alter the physical, chemical, and physiological properties of the protein. The surface SeSe bond (U11A-U11B) enhanced the yield of chain assembly while the internal SeSe bond (U10A-U15A) improved the reaction rate of the folding, indicating that these bridges play a major role in controlling the thermodynamics and kinetics, respectively, of the folding mechanism. Furthermore, SeRlx-α and SeRlx-β effectively reduced the expression of a tissue fibrosis-related factor in human endometriotic stromal cells. Thus, the findings of this study indicate that the S-to-Se substitution strategy not only enhances the foldability of relaxin, but also provides new guidance for the development of novel relaxin formulations for endometriosis treatment.

Diselenide-Bridged Mesoporous Silica-Based Nanoplatform with a Triple ROS-Scavenging Effect for Intracerebral Hemorrhage Treatment

Oxidative stress (OS) is a major mediator of secondary brain injury following intracerebral hemorrhage (ICH). Thus, antioxidant therapy is emerging as an attractive strategy to combat ICH. To achieve both reactive oxygen species (ROS) scavenging ability and on-demand drug release ability, we constructed a novel polydopamine (PDA)-coated diselenide-bridged mesoporous silica nanoparticle (DSeMSN) drug delivery system (PDA-DSeMSN). Edaravone (Eda) was blocked in the pores of DSeMSN by covering the pores with PDA as a gatekeeper. The drug maintained nearly "zero release" before reaching the lesion site, while in the ROS-enriched circumstances, the PDA shell went through degradation and the doped diselenide bonds broke up, triggering the disintegration of nanoparticles and leading to Eda release. Interestingly, the ROS-degradable property of the PDA shell and diselenide bond endowed the system with enhanced ROS-eliminating capacity. The synergistic effect of ROS-responsive drug delivery and ROS-scavenging PDA-DSeMSN showed efficient antioxidative and mitochondria protective performance without apparent toxicity in vitro. Importantly, PDA-DSeMSN@Eda through intravenous administration specifically accumulated in perihematomal sites and demonstrated robust neuroprotection in an ICH mouse model through antioxidative and antiapoptotic effects with high biological safety. Thus, the PDA-DSeMSN platform holds tremendous potential as an excellent carrier for on-demand delivery of drugs and provides a new and effective strategy for the clinical treatment of ICH.

Se-Glargine: Chemical Synthesis of a Basal Insulin Analogue Stabilized by an Internal Diselenide Bridge

Insulin has long provided a model for studies of protein folding and stability, enabling enhanced treatment of diabetes mellitus via analogue design. We describe the chemical synthesis of a basal insulin analogue stabilized by substitution of an internal cystine (A6-A11) by a diselenide bridge. The studies focused on insulin glargine (formulated as Lantus® and Toujeo®; Sanofi). Prepared at pH 4 in the presence of zinc ions, glargine exhibits a shifted isoelectric point due to a basic B chain extension (ArgB31 -ArgB32 ). Subcutaneous injection leads to pH-dependent precipitation of a long-lived depot. Pairwise substitution of CysA6 and CysA11 by selenocysteine was effected by solid-phase peptide synthesis; the modified A chain also contained substitution of AsnA21 by Gly, circumventing acid-catalyzed deamidation. Although chain combination of native glargine yielded negligible product, in accordance with previous synthetic studies, the pairwise selenocysteine substitution partially rescued this reaction: substantial product was obtained through repeated combination, yielding a stabilized insulin analogue. This strategy thus exploited both (a) the unique redox properties of selenocysteine in protein folding and (b) favorable packing of an internal diselenide bridge in the native state, once achieved. Such rational optimization of protein folding and stability may be generalizable to diverse disulfide-stabilized proteins of therapeutic interest.