Mechanistic and Kinetic Insights into Cellular Uptake of Biomimetic Dinitrosyl Iron Complexes and Intracellular Delivery of NO for Activation of Cytoprotective HO-1.

Dinitrosyl iron unit (DNIU), [Fe(NO) 2 ], is a natural metallocofactor for biological storage, delivery, and metabolism of nitric oxide (NO). In the attempt to gain a biomimetic insight into the natural DNIU under biological system, in this study, synthetic dinitrosyl iron complexes (DNICs) [(NO) 2 Fe(μ-SCH 2 CH 2 COOH) 2 Fe(NO) 2 ] ( DNIC-COOH ) and [(NO) 2 Fe(μ-SCH 2 CH 2 COOCH 3 ) 2 Fe(NO) 2 ] ( DNIC-COOMe ) were employed to investigate the structure-reactivity relationship of mechanism and kinetics for cellular uptake of DNICs, intracellular delivery of NO, and activation of cytoprotective heme oxygenase (HO)-1. After rapid cellular uptake of dinuclear DNIC-COOMe through a thiol-mediated pathway ( t max = 0.5 h), intracellular assembly of mononuclear DNIC [(NO) 2 Fe(SR)(S Cys )] n - /[(NO) 2 Fe(SR)(S Cys-protein )] n - occurred, followed by O 2 -induced release of free NO ( t max = 1-2 h) or direct transfer of NO to soluble guanylate cyclase, which triggered the downstream HO-1. In contrast, steady kinetics for cellular uptake of DNIC-COOH via endocytosis ( t max = 2-8 h) and for intracellular release of NO ( t max = 4-6 h) reflected on the elevated activation of cytoprotective HO-1 (∼50-150-fold change at t = 3-10 h) and on the improved survival of DNIC-COOH -primed mesenchymal stem cell (MSC)/human corneal endothelial cell (HCEC) under stressed conditions. Consequently, this study unravels the bridging thiolate ligands in dinuclear DNIC-COOH / DNIC-COOMe as a switch to control the mechanism, kinetics, and efficacy for cellular uptake of DNICs, intracellular delivery of NO, and activation of cytoprotective HO-1, which poses an implication on enhanced survival of postengrafted MSC for advancing the MSC-based regenerative medicine.